NC0003425_01_Rox_CAP Update 2019_Text_20191231

synTerra
CORRECTIVE ACTION PLAN
UPDATE
Site Name and Location:
Roxboro Steam Electric Plant
1700 Dunnaway Road
Semora, North Carolina 27343
Groundwater Incident No.:
Not Assigned
NPDES Permit No.:
NC0003425
NCDEQ CCR Impoundment Ranking
Low -Risk
Date of Report:
December 31, 2019
Permittee and Current
Duke Energy Progress, LLC
Property Owner:
410 South Wilmington Street
Raleigh, NC 27601
[phone]
Consultant Information:
SynTerra Corporation
148 River Street, Suite 220
Greenville, SC 29601
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Latitude and Longitude of Facility:
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Note to the Reader from Duke Energy
Duke Energy Progress, LLC (Duke Energy) is pleased to submit this groundwater
Corrective Action Plan (CAP) for the Roxboro Steam Electric Plant (Roxboro) located in
Person County, North Carolina. Since 2010, Duke Energy has been engaged in extensive site
investigation activities to comprehensively characterize environmental conditions in soil,
groundwater, surface water, and sediments associated with the presence of coal combustion
residuals (CCR) in and around the Roxboro coal ash basins, the East Ash Basin and the
West Ash Basin. Since 2016, Duke Energy has also assessed additional areas including the
Gypsum Storage Area (GSA) and the Dry Fly Ash (DFA) silos, transport, and handling area
(DFAHA). Activities, as applicable, have been performed in compliance with the North
Carolina Coal Ash Management Act of 2014, as amended (CAMA), as well as the United
States Environmental Protection Agency's (USEPA) CCR Rule. In 2018, the North Carolina
Department of Environmental Quality (NCDEQ) ranked the ash basins at Roxboro as low -
risk pursuant to CAMA.
Thousands of multi -media samples have been collected at Roxboro yielding over 130,000
individual analyte results. All of this work has been coordinated with the NCDEQ, which
has provided review, comments, and approvals of plans and reports related to these
activities. This CAP provides the results of these extensive assessment activities, and
presents a robust corrective action program to address groundwater conditions where
concentrations of constituents of interest (COI) are above applicable regulatory criteria.
Closure plan(s) to address the ash basin source areas are submitted separately.
As detailed in this CAP, we have begun to implement, and will continue implementing,
source control measures at the site, including (i) complete decanting of the East Ash Basin
and West Ash Basin to lower the hydraulic head within the basins and decrease hydraulic
gradients, reducing groundwater seepage velocities and COI transport potential; and (ii)
complete closure of the East Ash Basin and West Ash Basin. In addition, we intend to
implement a robust groundwater remediation program that includes extraction and
treatment at the East Ash Basin, and a combination of groundwater extraction and clean
water infiltration at the GSA and the DFAHA. These corrective action measures will most
effectively achieve remediation of the groundwater through the installation of (i) extraction
wells in the area of the unnamed pond north of the East Ash Basin; (ii) extraction wells on
the northeast side of the East Ash Basin; (iii) extraction wells in the comingling zone near
the near the DFAHA; and (iv) extraction wells and clean water infiltration wells in the area
adjacent to the Intake Canal. Significantly, groundwater modeling simulations indicate (i)
these measures will address COI at or beyond the East Ash Basin compliance boundary;
and (ii) at such time the site -specific considerations detailed within this CAP have been
satisfied, including, but not limited to, securing all required state approvals, installing the

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
necessary equipment, and commencing full-scale system operation, COI at or beyond the
East Ash Basin compliance boundary will meet the remedial objectives in nine years.
Critically, as discussed above, the model indicates that COI concentrations currently meet
the 02L Standards at and beyond the West Ash Basin compliance boundary.
This CAP contains over 2,500 pages of technical information that we believe represents one
of the most detailed and well supported corrective action plans ever submitted to the
NCDEQ and forms the basis of the robust groundwater remediation approach described
above. Thousands of labor hours by PhD -level scientists, engineers, and geologists have
been performed to obtain and evaluate the large amount of data generated at Roxboro and
inform this CAP. This combined effort has enabled a comprehensive understanding of site
conditions, creation of a highly detailed three-dimensional groundwater flow and solute
transport model used to simulate remediation scenarios, and evaluation and selection of a
site -specific corrective action program for Roxboro. Duke Energy believes it is also
important to provide a science -based perspective on these extensive studies, which include
the following key findings:
• The human health and ecological risk assessments performed for Roxboro using
USEPA guidance demonstrate that risks to potential human health and ecological
receptors associated with the coal ash basins and downgradient additional source
areas are not measurably greater than risks posed by naturally occurring
background conditions.
Ash basin -related constituents have not affected, nor are they predicted to affect,
off -site water supply wells. This has been confirmed by analytical results from
groundwater samples and water level measurements collected from over 172
monitoring wells over 36 separate monitoring events, and performing over 249
groundwater and geochemical modeling simulations.
In addition, even though no off -site wells were impacted, Duke Energy has already
provided owners of surrounding properties within 0.5-mile radius of the ash basin
compliance boundaries with water filtration systems under a program approved by the
NCDEQ that provides additional peace of mind for our neighbors. Importantly, ongoing
multi -media sampling of the nearby surface water aquatic systems, including the Hyco
Reservoir, confirm that these surface water systems are healthy with robust fish
populations.
Duke Energy looks forward to proactively implementing this CAP.

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
EXECUTIVE SUMMARY
(CAP Content Section Executive Summary)
ES.1 Introduction
SynTerra prepared this groundwater corrective action plan (CAP) update on behalf of
Duke Energy Progress, LLC (Duke Energy). This CAP Update pertains to the Roxboro
Steam Electric Plant's (Roxboro, Plant, or Site) two coal combustion residuals (CCR)
surface impoundments (ash basins): the East Ash Pond/Basin (EAB) and the West Ash
Basin (WAB) located in Person County, North Carolina (Figure ES-1).
This CAP Update addresses the requirements of Section 130A-309.211(b) of the North
Carolina General Statutes (G.S.), as amended by Coal Ash Management Act (CAMA).
This CAP Update is consistent with North Carolina Administrative Code (NCAC), Title
15A, Subchapter 02L .0106 corrective action requirements, and with the CAP guidance
provided by the North Carolina Department of Environmental Quality (NCDEQ) in a
letter to Duke Energy, dated April 27, 2018 and supplemented on September 10, 2019
(Appendix A).
Specifically, this CAP Update focuses on constituent concentrations detected greater
than applicable North Carolina groundwater standards [NCAC Title 15A, Subchapter
02L, Groundwater Classification and Standards (02L); Interim Maximum Allowable
Concentrations (IMAC); or background values, whichever is greater)].
The extent of, and remedies for, constituent affected groundwater beyond the
compliance boundary of the EAB to the north and northeast, as well as, north of
downgradient additional source areas, gypsum storage area (GSA) and Dry Fly Ash
(DFA) silos, transport, and handling area (hereafter referred to as the DFAHA), are
sources areas evaluated in this CAP Update. Constituent concentrations in groundwater
associated with the WAB are less than applicable regulatory standards at and beyond
the compliance boundary. Therefore, groundwater corrective action under 02L is not
required for the WAB.
In accordance with G.S. requirements, a CAP pertaining to Roxboro was previously
submitted to NCDEQ in two parts, as follows:
• Corrective Action Plan Part 1— Roxboro Steam Electric Plant (SynTerra, 2015b);
• Corrective Action Plan Part 2 — Roxboro Steam Electric Plant (SynTerra, 2016a).
This CAP Update considers data collected through June 2019.
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Ash basin closure for the EAB and WAB is detailed in separate documents prepared by
Wood Environment & Infrastructure Solutions, Inc. (Wood). Closure options evaluated
in this CAP include a hybrid closure -in -place scenario and closure -by -excavation
scenario for the EAB and closure -in -place and closure -by -excavation scenario for the
WAB. Therefore, the groundwater remediation alternatives evaluated and
recommended in this CAP Update consider the closure -in -place and closure -by -
excavation scenarios for the EAB. Groundwater modeling simulations consistently
indicate the closure -in -place and closure -by -excavation scenarios have a similar effect
on the concentrations of unit -specific constituents of interest (COI) in groundwater.
Summary of CAP Approach
This CAP Update meets the corrective action requirements under G.S. and Subchapter
02L .0106. For the EAB, the preferred groundwater remediation approach assumes
source control by reducing and/or eliminating further releases of COIs to groundwater,
under the closure -in -place or closure -by -excavation scenarios. Both closure scenarios
provide similar source control by reducing and/or eliminating further releases of COIs
to groundwater. The focus of groundwater corrective action related to the EAB is
reducing COIs below their applicable criteria at and beyond the ash basin compliance
boundary consistent with Subchapter 02L .0106(e)(4) and to address Subchapter 02L
.01060). Groundwater remediation associated with downgradient sources, the GSA and
DFAHA, is to reduce COIs below applicable 15A NCAC 02L .0202 criteria. Applicable
criteria in this case is defined as the 02L groundwater standard, interim maximum
allowable concentration (IMAC), or background, whichever is greatest, defined as the
COI criterion. If a COI does not have a 02L standard or IMAC, the background value
defines the COI criteria.
Groundwater quality data confirms, based on one year of monitoring results, that COIs
identified for the WAB do not exceed applicable 15A NCAC 02L .0202 groundwater
quality standards at or beyond the WAB compliance boundary; therefore, groundwater
corrective action under 15A NCAC 02L.0106 is not required at this time for the WAB.
The Plant's industrial and LCID landfills are positioned on top of a portion of the EAB,
unable to be evaluated for potential groundwater impacts independent of the EAB;
therefore, the landfills are considered EAB additional sources in this CAP Update. The
EAB additional sources are included in the evaluation of current and potential future
groundwater impacts from and remedial alternatives for the EAB. The GSA and
DFAHA are additional sources located downgradient of the EAB (downgradient
additional sources) and are able to be evaluated for potential groundwater influences
independently of the EAB. Due to proximity of those downgradient additional sources
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and CCR related plume extent downgradient of the EAB, the GSA and DFAHA are
evaluated for corrective action, separate from the EAB, as a component of this CAP
Update (Figure ES-1).
Additional sources independent of the EAB and WAB referenced in this report, but not
evaluated for remedial action include a decommissioned sluice line area (north of the
WAB) and eastern discharge canal historical deposition area (northeast of the GSA in
the historical realignment area of the discharge canal) (Figure ES-1).
This CAP Update includes evaluation of three general source areas as described above.
• Source Area 1: EAB and additional source areas which include the industrial
landfill and the LCID landfill
• Source Area 2: WAB
• Source Area 3: Downgradient additional source areas which include the GSA
and DFAHA
Duke Energy has implemented, or plans to implement the following multi -component
corrective action plan:
Source Control Measures
• Completion of ash basin decanting from the WAB to reduce the hydraulic
head in the dam area thereby reducing the hydraulic driving force for
potential COI migration in groundwater.
• Decanting of the EAB ponded areas, if needed, for completion of ash basin
closure.
Groundwater Remediation Measures (Source Area 1 (EAB) and Source Area 3 (GSA
and DFAHM
A robust groundwater remediation approach is planned for the EAB that includes
actively addressing COIs in groundwater greater than applicable standards at or
beyond the EAB compliance boundary using groundwater extraction in addition to
the area downgradient of the downgradient additional sources, the GSA and
DFAHA, adjacent to the Intake Canal, using groundwater extraction and clean water
infiltration.
Groundwater models were used to evaluate and optimize an effective remedial
approach. The following is a summary of components of the preferred remedial
system:
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Source Area 1
• 5 extraction wells in the area of the unnamed pond north of the EAB
compliance boundary,
• 15 extraction wells on the northeast side of the EAB compliance boundary,
• 12 extraction wells near the north of the EAB compliance boundary adjacent
to the DFAHA, and
Source Area 3
• 18 extraction wells and 27 clean water infiltration wells adjacent to the Intake
Canal.
Effectiveness Monitoring Plan (EMP)
(Source Area 1 (EAB) and Source Area 3 (GSA and DFAHA))
• Duke Energy has prepared an Effectiveness Monitoring Plan (EMP) as
discussed in Section 6.8.5 and provided in Appendix O of this CAP Update.
This EMP includes an optimized groundwater monitoring network for the
EAB, GSA, and DFAHA sources based on site -specific COI mobility and
distribution. The EMP is designed to be adaptable and targets key areas
where changes to groundwater conditions are most likely to occur during
corrective action implementation and basin closure activities. The monitoring
plan includes provisions for a post -closure monitoring program in accordance
with G.S. Section 130A-309.214(a)(4)k.2 upon completion of EAB closure
activities.
Confirmatory Monitoring Plan (CMP)
(Source Area 2 (WAB))
• Duke Energy has prepared a Confirmation Monitoring Plan (CMP) as
discussed in Section 6.15.5 and provided in Appendix P of this CAP Update.
This CMP includes an optimized groundwater monitoring network for the
WAB based on site -specific COI mobility and distribution. The monitoring
plan includes provisions for a post -closure monitoring program in accordance
with G.S. Section 130A-309.214(a)(4)k.2 upon completion of WAB closure
activities.
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ES.2 Background
Plant Operations
Operations began at Roxboro in the 1960s and capacity was added through the 1980s.
Four coal-fired units are in operation at the Plant. CCR materials, composed primarily
of fly ash and bottom ash, were historically managed by depositing ash within the two
ash basins. Those ash basins are referenced using each basin's relative location on the
Site. The EAB was constructed in 1966 and the WAB was constructed in 1973. CCRs
were deposited in the basins predominately by hydraulic sluicing operations until the
Plant was modified for dry fly ash handling and the on -site industrial landfill for CCR
disposal was placed in service in the late 1980s. After DFA conversion in 1986, all
sluicing operations to the EAB were discontinued. Wet sluicing of bottom ash and
intermittent fly ash continued to the WAB until final system upgrades for dry ash
handling system were completed in December 2018. All bottom ash and fly ash is
currently handled dry and disposed within the on -site industrial landfill or transported
offsite for beneficial use. The EAB and WAB have operated under a National Pollution
Discharge Elimination System (NPDES) Permit issued by the NCDEQ Division of Water
Resources (DWR) since their operations began.
Pursuant to G.S. Section 130A-309.213(d)(1), a November 13, 2018 letter from NCDEQ to
Duke Energy documented the classification of the CCR surface impoundments (EAB
and WAB) at Roxboro as low -risk (Appendix A). The letter cited that Duke Energy has
"established permanent water supplies as required by NCGS 130A-309.211(cl)" and has
"rectified any deficiencies identified by, and otherwise complied with the requirements
of, any dam safety order issued by the Environmental Management
Commission... pursuant to NCGS 143-215.32." The relevant closure requirements for
low -risk impoundments are in G.S. Section 130A-309.214(a)(3), which states low -risk
impoundments shall be closed as soon as practicable, but no later than December 31,
2029.
Source Areas
The EAB and the WAB are the main sources areas evaluated in this CAP Update.
General information is provided below for the additional source areas.
Industrial Landfill (Source Area 1)
The industrial landfill is a Solid Waste facility permitted in the late 1980s (NCDEQ
Permit No. 7302-INDUS). The industrial landfill, positioned above and mostly within
the EAB waste boundary, began operation in 1988. The initial industrial landfill
footprint was permitted and constructed without an engineered base liner system. In
2004, the industrial landfill began operating in areas constructed with an engineered
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base liner system (Phases 1- 6), located inside the waste boundary of the initial
industrial landfill footprint. The area between the initial, unlined, industrial landfill
footprint and the engineered base liner system for Phases 1 - 6 is commonly referred to
as the halo area. Dry fly ash placed in the unlined portion of the industrial landfill,
including the halo area, is unsaturated. The halo area is partially closed with an
engineered cap system on a portion of the western side. The remaining halo area is
covered with soil, which allows infiltration of precipitation into the underlying CCR
material. Infiltration occurring in the soil covered areas of the halo area are likely
contributing to COI exceedances beyond the EAB compliance boundary. Since
Phases 1- 6 of the industrial landfill are designed and constructed with an engineered
base liner system, the additional source area referred to as the industrial landfill only
focuses on the halo area. The industrial landfill currently operates in Phases 1- 6.
Leachate from Phases 1- 6 of the industrial landfill was deposited by gravity flow into
the EAB until the spring of 2019. The industrial landfill leachate is now captured in a
header system, which is routed to surge tanks that allow a steady flow of leachate to
enter the Plant wastewater system for treatment.
Since the industrial landfill is located on top of and adjacent to the EAB and contains
CCR similar to the EAB, it is an additional source area that cannot be evaluated
independently of the EAB.
Land Clearing and Inert Debris Landfill (Source Area 1)
The land clearing and inert debris (LCID) landfill is a Solid Waste facility permitted to
operate in 2002 (NCDEQ DWM Permit No. 73-D). The LCID landfill is located entirely
within the compliance boundary and adjacent to and partially over the western lobe of
the EAB, abutting the Dunnaway Road entrance to the Plant. General construction
debris and inert material, including asbestos containing material, was disposed in the
approximate 4.5 acre LCID landfill. The LCID landfill has not been used in many years
but maintains a Permit to Operate. The landfill has an interim cover of soil and
vegetation.
Since the LCID landfill is located on top of and adjacent to the EAB, it is an additional
source area that cannot be evaluated independently of the EAB.
Gypsum Storage Area (GSA) (Source Area 3)
Gypsum, a by-product of flue gas desulfurization (FGD), is staged in the GSA, located
north of the EAB, prior to transport off -Site for beneficial re -use. The GSA is an
approximate 12.5-acre area constructed in April 2006 with approximately 131,319 cubic
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yards of DFA used as structural fill in topographical low-lying areas. The use of DFA as
structural fill was in accordance with notification requirements of Section .1700 of the
Solid Waste Management 15A NCAC 13B Rules as approved by NCDENR DWM in
December 2005. A geosynthetic clay liner (GCL) with a plastic laminated geomembrane
was installed following final grading. The GCL was placed laminate side up directly
over a six-inch layer of DFA followed by a six-inch layer of DFA, 12-inches of fill soil
and a six-inch layer of top soil. Groundwater data downgradient of the GSA indicates
COIs greater than groundwater regulatory standards.
Since the GSA is located downgradient of the EAB and monitoring wells provide water
quality data between the EAB and GSA, this additional source area can be evaluated
independently of the EAB.
DFA Silos, Transport, and Handling Area (DFAHA) (Source Area 3)
The DFA silos, transport, and handling operational area is located adjacent to the
western side of the GSA and is used for processing of DFA for beneficial use, storage
and management of DFA prior to disposal, and transport of DFA to the industrial
landfill. DFA is delivered to the silo area by aboveground pipes via a pressure dry
blower method. Five silos (Silos #1 through #5), each with a capacity of 5,000 cubic
yards, are used in the storage process. The silo area was initially developed in 1986
with Silos #1 through #4. Storm water and dust suppression water is collected through
drains and curbing and routed via in -ground steel pipes to a sump located southeast
and adjacent to Silo #4. Wastewater from the sump was historically deposited in the
EAB for treatment. Flows from the sump are now routed to the Plant wastewater
treatment system for processing. Fugitive DFA material from storage, management,
and transportation operations is present on and within separations of the concrete
roadway and non -paved areas. Rainfall infiltration and surface water runoff from dust
suppression are mechanisms for COI infiltration in the area. Groundwater monitoring
data indicate constituent concentrations greater than groundwater regulatory standards
are present in the area.
Since the DFAHA is located downgradient of the EAB and monitoring wells provide
water quality data between the EAB and DFAHA, this additional source area can be
evaluated independently of the EAB.
Pre -Basin Closure Activities
To prepare for closure of the ash basins, passive decanting (removal) of free water from
the WAB began in December 2018 through the cessation of sluicing. Active decanting,
as required by a Special Order by Consent (SOC) issued through the North Carolina
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Environmental Management Commission (EMC) on August 15, 2018 (EMC SOC WQ
S18-005, Appendix B of Appendix J), is pending approval of the revised NPDES permit.
The SOC requires completion of decanting by June 30, 2020. Decanting of free, ponded
water from the WAB before closure will reduce or eliminate seepage from constructed
and non -constructed seeps. Decanting is considered a critical component of the
corrective action strategy for the WAB because it will significantly reduce the hydraulic
head and vertical gradients near the dam and dikes, thereby reducing the groundwater
flow velocity and constituent migration associated with the WAB. The EAB is not
subject to decanting as a requirement of the SOC. However, ponded areas of the EAB
will be decanted, if needed, to complete closure of the EAB.
Initial ash basin closure efforts included ceasing all wastewater flows to the ash basins.
A wastewater conveyance system was installed to divert DFAHA sump wastewater
flows from the EAB to the Plant wastewater treatment system for processing. The
conveyance system was placed into operation in June 2019. The industrial landfill
leachate collection system was modified to divert the seven leachate gravity flow
discharge locations from EAB to the Plant wastewater treatment system for processing.
The leachate collection system modifications included piping, sumps, a lift station, and
equalization tanks, which route the landfill leachate to the recently installed plant
consolidated sump where the leachate comingles with other wastewater flows. The
leachate collection system was placed into service in May 2019.
The industrial landfill Closure Plan was revised in 2018 to limit infiltration of
precipitation into the halo area of the industrial landfill. In July 2019, a portion of the
halo area encompassing approximately 4.38 acres was certified closed with an
engineered cover system containing a geosynthetic liner.
Basis for CAP Development
A substantial amount of data related to the EAB, WAB, downgradient additional source
areas, and general Roxboro site has been collected to date. A summary of Roxboro
assessment documentation used to prepare this CAP Update is presented in Table ES-1.
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TABLE ES-1
SUMMARY OF ROXBORO ASSESSMENT DOCUMENTATION
Comprehensive Site Assessment Report - Roxboro Steam Electric Plant (SynTerra, 2015a).
Corrective Action Plan Part 1 - Roxboro Steam Electric Plant (SynTerra, 2015b).
Corrective Action Plan Part 2 - Roxboro Steam Electric Plant (SynTerra, 2016a).
Comprehensive Site Assessment, Supplement 1 - Roxboro Steam Electric Plant (SynTerra
2016b)
Update to Drinking Water Well Receptor Survey - Roxboro Steam Electric Plant (SynTerra,
2016c)
Ash Basin Extension Impoundments and Discharge Canals Assessment Report - Roxboro
Steam Electric Plant (SynTerra, 2017a)
Gypsum Storage Area Structural Fill (CCB 003) Assessment Report - Roxboro Steam
Electric Plant (SynTerra, 2017b).
Comprehensive Site Assessment Update - Roxboro Steam Electric Plant (SynTerra, 2017d).
Human Health and Ecological Risk Assessment Summary Update - Roxboro Steam Electric
Plant (SynTerra, 2018).
Community Impact Analysis of Ash Basin Closure Options at the Roxboro Steam Electric
Plant (Exponent, 2018).
Roxboro Steam Station HB630 Provision of Permanent Water Supply Completion
Documentation (August 2018, Appendix D).
Ash Basin Pumping Test Report - Roxboro Steam Electric Plant (SynTerra, 2019a).
Surface Water Evaluation to Assess 15A NCAC 2B - Roxboro Steam Electric Plant (SynTerra,
2019b).
2018 Annual Groundwater Monitoring Report (SynTerra, 2019c)
Updated Background Threshold Values for Constituent Concentrations in Groundwater
(SynTerra, 2019d)
Prepared by: KTL Checked by: CDE
The NCDEQ provided review comments of the 2017 CSA Update report to Duke
Energy in a May 7, 2018 letter. The letter stated that sufficient information was provided
to allow preparation of this CAP Update (Appendix A).
The assessment work referenced in the documents listed in Table ES-1 have resulted in
a very large dataset that has informed the development of this CAP Update. The
Roxboro data collection and analyses activities as of June 2019 are summarized in Table
ES-2.
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TABLE ES-2
SUMMARY OF ROXBORO ASSESSMENT ACTIVITIES
Tasks
Total
Monitoring Wells Evaluated in this CAP
172
Groundwater Monitoring Events
36
Groundwater Samples Collected
2,215
Individual Analyte Results
130,265
Off -Site Water Supply Well Sampling (Total inorganic analysis) - Number
of Analyses
2,019
Ash Pore Water - Number of Analyses (Total and dissolved)
6,772
Ash Pore Water Sampling Events
17
Surface Water Monitoring Events
5
Surface Water Sample Locations
10
Area of Wetness Sample Events
13
Ash Samples (Within ash basin analyzed for SPLP)
5
Soil Samples Collected
199
Soil Sample Locations
108
Sediment Sample Locations
43
Geotechnical Soil Sample Locations
14
Geochemical Ash, Soil, Partially Weathered Rock, Whole Rock Samples
70
Hydraulic Conductivity Tests (Slug Tests, Pumping Tests, Packer Tests,
FLASH Analysis of Bedrock HPF Data)
280
Groundwater Flow & Transport Simulations
56
PHREEQC Geochemical Simulations
193
Prepared by: KTL Checked by: CDE
Notes:
Data available to SynTerra as of June 2019
FLASH - Flow -Log Analysis of Single Holes
HPF - Heat Pulse Flow
SPLP - Synthetic Precipitation Leaching Procedure
PHREEQC - pH Redox Equilibrium in computer code C
A constituent management process was developed by Duke Energy at the request of
NCDEQ to gain a thorough understanding of the constituent behavior and distribution
in groundwater and to aid in identification of COIs related to the ash basins that may
require corrective action. The constituent management process consists of three steps:
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1. Performing a detailed review of the applicable regulatory requirements under
NCAC, Title 15A, Subchapter 02L,
2. Understanding the potential mobility of site -related constituents in groundwater
based on site hydrogeology and geochemical conditions, and
3. Determining the constituent distribution related to the ash basins and
downgradient source areas under current or predicted future conditions.
Multiple lines of evidence including empirical data, geochemical modeling, and
groundwater flow and transport modeling support this constituent management
process. This approach has been used to understand and predict constituent behavior
in the subsurface related to the ash basins and downgradient sources, or constituents
that are naturally occurring. Constituents that have migrated beyond the compliance
boundary at concentrations greater than 02L, IMAC and background that are related to
the ash basins and downgradient source areas are subject to corrective action.
Constituents that are naturally occurring at concentrations greater than the 02L
standard do not require corrective action. Details on the constituent management
approach are presented in Section 6.0.
Groundwater
In conformance with requirements of G.S. Section 130A-309.211, groundwater corrective
action is the focus of this CAP Update. Groundwater COIs to be addressed with
corrective action are those that exhibit concentrations in groundwater at or beyond the
compliance boundary greater than the 02L standard, IMAC, or background
concentrations, whichever is greatest.
Soil
Data indicate unsaturated soil COI concentrations are generally consistent with
background concentrations or are less than regulatory screening values. In the few
instances where unsaturated soil COI concentrations are greater than Preliminary Soil
Remediation Goal (PSRG) Protection of Groundwater (POG) standards and background
values, there are no mechanisms by which the COI could have been transported from
the ash basins or the downgradient additional source areas to the unsaturated soils.
Therefore, no COIs are identified and corrective action for soil is not required.
Risk Assessment
The human health and ecological risk assessments were prepared using standard
USEPA methods and demonstrated no measurable difference in modeled risks to
potential human nor ecological receptors compared with background concentrations.
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Data from water supply wells and Hyco Reservoir indicated no evidence of
unacceptable risk posed by groundwater migration associated with the ash basins or
the downgradient additional source areas based on evaluation of concentrations of CCR
constituents in environmental media and potential receptors. The risk assessments
related to the ash basins and downgradient source areas are presented in Section 5.4
and Appendix E of this CAP Update.
Risk Ranking
In accordance with G.S. 130A-309.211(cl), Duke Energy installed 80 water filtration
systems at surrounding properties within a 0.5-mile radius of the ash basin compliance
boundaries. Installation of water filtration systems, along with certain improvements to
the ash basin dams completed by Duke Energy, resulted in the ash basins being ranked
as low risk.
ES.3 CSM Overview
The Conceptual Site Model (CSM) is a written and graphical representation of the
hydrogeologic conditions and COI interactions specific to the Site. It is critical to
understanding the subsurface conditions related to the ash basins and the
downgradient additional source areas. The updated CSM developed for Roxboro
included in this CAP Update is based on a United States Environmental Protection
Agency (USEPA) document titled "Environmental Cleanup Best Management Practices:
Effective Use of the Project Life Cycle Conceptual Site Model" (USEPA, 2011). This
document describes six CSM stages for a project life cycle. The CSM is an iterative tool
designed to assist in the decision -making process for characterization and remediation
as the Site progresses through the project life cycle and new data becomes available. The
current Roxboro CSM is consistent with Stage 4 "Design CSM", which allows for
iterative improvement of the Site CSM during design of the remedy while supporting
development of remedy design basis (USEPA, 2011).
Multiple lines of evidence have been used to develop the CSM based on the large data
set generated for Roxboro. The remedial action evaluation to meet the effectiveness
criteria in the CAP guidance provided by NCDEQ is also based on the updated CSM
(NCDEQ, 2019).
The following provides an overview of the updated CSM pertaining to the Roxboro ash
basins and downgradient additional source areas. The updated CSM forms the basis of
this CAP Update. Supporting details for the CSM are presented in Section 5.
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Key conclusions of the CSM include the following:
No risks to human health related to the EAB, WAB, and downgradient
additional sources have been identified. The site -specific risk assessment
conducted for the Roxboro site indicates that there is no measurable difference
between evaluated Site -related risks and risks imposed by background
concentrations. Site -specific risk assessments indicate incomplete potential
exposure pathways and no unacceptable risk to residential receptors near the ash
basins and downgradient additional sources (no completed exposure pathways).
The EAB, WAB, and downgradient additional source areas do not increase
risks to ecological receptors. The assessment did not indicate an increase of
risks to ecological receptors (mallard duck, great blue heron, muskrat, river otter,
bald eagle, American robin, meadow vole, red-tailed hawk, red fox and killdeer
bird) exposed to surface water and sediments associated with the ash basins and
downgradient additional source areas.
Groundwater from the EAB, WAB, and downgradient additional source areas
has not and does not flow towards water supply wells based on groundwater
flow patterns, the location of water supply wells, and evaluation of
groundwater analytical data. Groundwater data collected from water supply
wells and on -Site monitoring wells, groundwater elevation measurements from
over 25 monitoring events, and groundwater flow and transport modeling
results all indicate that Site COIs are not affecting, and have not affected, water
supply wells.
• The permanent water solution implemented by Duke Energy provides owners
of surrounding properties with water supply wells within a 0.5-mile of the
EAB and WAB compliance boundaries with water filtration systems. The
hydrogeologic data collected at Roxboro confirms that Site -related COIs are not
affecting off -Site water supply users. Predictive groundwater modeling
simulations indicate that Site -related COIs will not affect off -Site water supply
users. Nevertheless, Duke Energy installed 80 water filtration systems at
surrounding water supply users in accordance with NCGS 130A-309.211(cl).
• The hydrogeologic setting of the ash basins and the downgradient additional
source areas limits COI transport. The Site, located in the Piedmont
Physiographic Province, conforms to the general hydrogeologic framework for
sites in the Blue Ridge/Piedmont area, which are characterized by groundwater
flow in a slope -aquifer system within a local drainage basin with a perennial
stream (LeGrand 2004). Predictive groundwater flow and transport model
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
simulations indicate passive decanting from cessation of sluicing and active
decanting to the WAB will affect groundwater flow patterns within the basin by
lowering hydraulic heads in and around the WAB dam, which will reduce the
rate of COI transport, and provide source control prior to completion of basin
closure. Lower hydraulic heads and the cessation of ash placement into the WAB
combine to cause the maximum extent of the boron plume to remain within the
compliance boundary for modeled closure scenarios. With a few exceptions, the
groundwater data indicate the partial closure of the industrial landfill with lined
portions for continued DFA disposal has resulted in stable or decreasing COI
concentrations in groundwater associated with the EAB.
The physical setting and hydraulic processes control the COI flow pattern
within the ash basins, underlying groundwater system, and downgradient
areas. The ash basins are primarily horizontal water flow -through systems.
Groundwater entering into the upgradient side of the ash basins is supplemented
by rainfall infiltration and flows laterally through the middle of the ash basins
under a low horizontal gradient, and then flows vertically downward near the
dams. This flow system results in limited downward migration of COIs into the
thin, underlying regolith upgradient from each dam. Near the dams, COIs flow
downward under the dams. Beyond the dams, COIs in groundwater flow
upward toward NPDES-permitted wastewater ponds, limiting downward
migration of COIs to the area proximate to the dam. The exceptions to this occur
to the northeast and south of the EAB and unlined portion of the industrial
landfill. The flow -through system associated with open water basins does not
apply to the lined industrial landfill associated with the EAB. At the WAB, the
dam to the north of the basin and the dikes along the western perimeter (western
discharge canal) caused vertical COI migration due to the operating hydraulic
head. Passive and active decanting is anticipated to re-establish a hydraulic low
within the WAB along the former impounded stream valley.
Groundwater flow associated with the GSA and DFAHA is north toward the
Intake Canal. Bedrock data at various depths around the ash basin perimeters
and downgradient areas support the flow characteristics and limited COI
distribution.
• Horizontal distribution of COIs in groundwater proximate to the basins is
limited spatially to the north. The physical extent of constituent migration is
controlled by hydrologic divides to the west, south and east of the ash basins;
dilution from unaffected groundwater; and the discharge of groundwater to
surface water. The groundwater discharges to NPDES-permitted wastewater
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
ponds. Groundwater from the WAB discharges to the heated water discharge
pond, and groundwater from the EAB discharges to the Unit 3 heated water
discharge pond and the Unit 3 cooling tower pond. Groundwater downgradient
(north) of the EAB is also affected by the DFAHA, which discharges to the Intake
Canal.
• Geochemical processes stabilize and limit certain constituent migration along
the flow path. Each COI exhibits a unique geochemical behavior related to the
specific constituent partition coefficient (Ka), response to changing geochemical
parameters (i.e., pH and Eh), and sorption capacity of the soil and/or rock. Based
on geochemical modeling:
o Non -conservative, reactive COIs (i.e., uranium and vanadium) will remain
in mineral phase assemblages that are stable under variable Site
conditions, demonstrating sorption as an effective attenuation mechanism.
o Variably reactive COIs [i.e., chromium (total), chromium (hexavalent),
cobalt, iron, manganese, molybdenum, selenium, and strontium) can
exhibit mobility depending on pore water geochemical conditions and
availability of sorption sites.
o Conservative, non -reactive COIs (i.e., antimony, boron, and sulfate)
migrate in groundwater as soluble species and are not strongly attenuated
by reactions with solids but are reduced in concentration with distance
primarily by physical processes such as mechanical mixing (dispersion),
dilution, and diffusion. Sorption of boron to clay particles might occur,
especially for groundwater with slightly alkaline to alkaline pH values.
Maximum boron sorption occurs at pH values between about 7.5 standard
units (S.U.) and 10 S.U., then decreases at pH values greater than 10 S.U.
(EPRI 2005, ATSDR 2010).
The groundwater corrective action strategies evaluated herein consider the
potential for dynamic geochemical conditions under basin closure options,
currently under appeal, and account for potential mobilization of COIs.
• COIs in groundwater are contained within Duke Energy's property. COI
distribution extends from the ash basins toward NPDES-permitted wastewater
ponds and, in the case of the EAB, toward downgradient additional source areas.
The plumes associated with the ash basins has been characterized and are stable.
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Groundwater/surface water interaction has not caused, and is not predicted to
cause, COIs at concentrations greater than NCAC, Title 15A, Subchapter 02B,
Surface Water and Wetland Standards (02B). Analytical results for surface water
samples collected from the Intake Canal (north of the EAB and the downgradient
additional source areas) and jurisdictional intermittent Stream 11A (southwest of
the EAB) indicate that these water bodies meet 02B standards under current
conditions. An evaluation of future surface water quality conditions of the Intake
Canal and basin -related jurisdictional streams was conducted using a surface
water mixing model with closure scenario model simulation inputs. The
evaluation indicates that no future groundwater COI migration would result in
constituent concentrations greater than applicable 02B surface water criteria to
the Intake Canal and Stream 11A.
• The aquatic systems of the Hyco Reservoir, including the Intake Canal, are
healthy based on multiple lines of evidence including robust fish populations,
species variety and other indicators based on years of sampling data. This
finding combined with the results of the ecological risk assessment indicate that
there are no significant ecological effects to the main surface water systems
proximate to the ash basins or the downgradient additional source areas.
Most of the Roxboro COIs identified in the CSA Update occur naturally in
groundwater, and some naturally occur at concentrations greater than the 02L
standard or IMAC. Groundwater at Roxboro naturally contains cobalt,
chromium (total), cobalt, iron, manganese, molybdenum, strontium, sulfate, total
dissolved solids (TDS), uranium (total), and vanadium. The occurrence of
inorganic constituents in groundwater of the Piedmont Physiographic Province
is well documented in the literature. COIs such as iron, manganese and
vanadium, have natural background threshold values in all flow zones at the site
greater than their 02L standard or IMAC value. For the Roxboro CAP Update,
these COIs are evaluated based upon their site -specific statistically derived
background values, and additional lines of evidence to determine if the
constituent concentrations detected represent migration from the ash basins,
additional source areas, or are naturally occurring.
These CSM aspects, combined with the human health and ecological risk assessments,
provide the basis for this CAP Update developed for the WAB and EAB, including
downgradient additional source areas.
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
ES.4 Corrective Action Approach
Corrective Action Objectives and Areas Requiring Corrective Action
East Ash Basin (Source Area 1)
Migration of COIs in groundwater related to the EAB extend beyond the compliance
boundary to the north and northeast. The EAB compliance boundary extends 500 feet
beyond the waste boundary. To satisfy NC G.S. Section 130A-309.211(b) and maintain
compliance with 02L, the corrective action approach planned for the EAB focuses on
restoring affected groundwater at or beyond the compliance boundary. The following
remedial objectives address the regulatory requirements of NCAC Title 15A Subchapter
02L pertaining to the EAB in this Roxboro CAP Update:
• Restore EAB affected groundwater quality at or beyond the compliance
boundary by returning COIs to the 02L/IMAC/applicable background
concentration (whichever are greater), or as closely thereto as is economically
and technologically feasible consistent with 15A NCAC 02L .0106(a).
• Use a phased CAP approach that includes initial active remediation with
effectiveness monitoring of remedy implementation as provided in 15A NCAC
02L .0106(j) and (1).
• If appropriate, given future site conditions, Duke Energy may seek approval of
an alternate plan that does not require meeting groundwater
02L/IMAC/applicable background concentration (whichever are greater) after
satisfying the requirements set out in 15A NCAC 02L .0106(k).
The EAB areas of proposed corrective action are shown on Figures ES-2.
Downgradient Additional Source Areas (Source Area 3)
The presence and distribution of COI -affected groundwater in the DFAHA is attributed
to contact water runoff from, and seepage through separations, of the paved areas in
addition to precipitation infiltration through DFA deposited on local gravel and
vegetated areas. The Flow and Transport Model indicates the southern portion of the
DFAHA COI affected groundwater is comingled with COI -affected groundwater from
the upgradient EAB. For the GSA, COI -affected groundwater is attributed to comingled
plumes associated mostly with historical operations of gypsum handling, infiltration of
surface water runoff from the gypsum storage area and wastewater ponds and the
structural fill. The northeastern portion of the GSA has COI -affected groundwater due
to infiltration of the historical eastern discharge canal deposition area. Groundwater
flow from these areas discharges to the adjacent Intake Canal to the north. There are no
Page ES-17

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
waste or compliance boundaries associated with the GSA and DFAHA. Surface water
adjacent to the GSA and DFAHA was evaluated as a part of this CAP Update. No COI
concentrations exceeding 02B surface water standards were present in the Intake Canal
nor are predicted to exceed 02B surface water standards in the future. There are no
waste or compliance boundaries associated with the GSA and DFAHA. Surface water
adjacent to the GSA and DFAHA was evaluated as a part of this CAP Update. No COI
concentrations exceeding 02B surface water standards were present in the Intake Canal
nor are predicted to exceed 02B surface water standards in the future. To satisfy
regulatory requirements of NCAC Title 15A Subchapter 02L, the corrective action
approach planned for the GSA and DFAHA — affected groundwater near the Intake
Canal, focuses on mitigation of groundwater to reduce or prevent potential future
impact to surface water. The following remedial objectives address the regulatory
requirements of NCAC Title 15A Subchapter 02L for the additional source areas in this
CAP Update:
• Reduce or prevent potential future COI related groundwater impacts to surface
water adjacent to the GSA and DFAHA as economically and technologically
feasible consistent with 15A NCAC 02L .0106(a).
• Use a phased CAP approach that includes initial active remediation with
effectiveness monitoring of remedy implementation as provided in 15A NCAC
02L .0106(j) and (1).
• If appropriate, given future site conditions, Duke Energy may seek approval of
an alternate plan that does not require meeting groundwater
02L/IMAC/applicable background concentration (whichever are greater) after
satisfying the requirements set out in 15A NCAC 02L .0106(k).
The areas of proposed corrective action for the GSA/DFAHA is shown on Figure ES-2.
West Ash Basin (Source Area 2)
This CAP Update is prepared to meet the requirements under CAMA Section 309.211(b)
and includes documentation that supports groundwater quality does not exceed
applicable 02L groundwater quality standards at or beyond the ash basin compliance
boundary; therefore, groundwater corrective action under 15A NCAC 02L .0106 is not
required at this time for the WAB.
Summary of Source Control and Corrective Measures
It is critical to take into account all of the various activities Duke Energy has and will
perform to improve subsurface conditions at Roxboro related to the WAB, EAB, and the
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
downgradient additional source areas. The remedial program incorporates source
control by current and potential future basin decanting, closure of the WAB and EAB,
and active groundwater remediation for the EAB and downgradient additional source
areas. Effectiveness monitoring of the EAB and downgradient additional source areas
and compliance monitoring for the WAB are planned. Table ES-3 summarizes the
discrete components of source control efforts ahead of EAB and WAB closure in
addition to planned monitoring and corrective action for COI -affected groundwater
beyond the EAB compliance boundary and between the downgradient additional
source areas and Intake Canal.
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION,
AND MONITORING
Groundwater Remedy
Rationale
Component
Source Control Activities
EAB and WAB
Active source control by removing ponded water in the
Ash Basin Decanting
WAB. Passive decanting through the cessation of ash
sluicing to the WAB began in December 2018. Passive
decanting of the WAB has lowered the hydraulic head
within the ash basin and reduced hydraulic gradients,
reducing groundwater seepage velocities and COI
transport potential. Passive decanting is ongoing, active
decanting will be implemented upon receipt of the
NPDES permit, if needed, at the WAB. Decanting for the
WAB is expected return the groundwater flow system to
its approximate natural condition, flowing toward the
axis of the former perennial steam valley, then
northward.
EAB and WAB
The ash basin closure scenarios, either closure -in -place
Ash Basin Closure
or closure -by -excavation (submitted independent of
this CAP Update), are considered source control
activities. Extensive groundwater modeling of EAB and
WAB indicate that either closure scenario provides
similar source control by reducing and/or eliminating
further releases of COIs to groundwater.
Page ES-19

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION,
AND MONITORING
Groundwater Remedy
Rationale
Component
Active Groundwater Remediation Activities
Source Area 1
Groundwater remediation focused on meeting the
EAB Active Groundwater
stated remedial objectives at and beyond the EAB
Remediation
compliance boundary. These efforts focus on areas
downgradient of the EAB to the north and northeast of
the compliance boundary where COIs are present at
concentrations greater than applicable criteria.
To meet the above -referenced CAP objectives, 20
extraction wells are planned to be placed in areas to the
north and northeast of the EAB and 12 extraction wells
north of the EAB and the comingling area near the
DFAHA. The proposed strategy is to reduce COI
concentrations based on groundwater modeling
simulations.
Source Area 3
Groundwater remediation focused on groundwater
Downgradient Additional
quality downgradient of the GSA and DFAHA to mitigate
Source Areas Active
potential future impact to surface water. To meet the
Groundwater Remediation
above referenced CAP objective, 18 extraction wells
(GSA and DFAHA)
with 27 clean water infiltration wells are proposed north
of the downgradient additional source areas. The
proposed strategy is to provide hydraulic control of COI
migration and remove COI mass based on groundwater
modeling simulations.
Institutional Controls and Monitoring
EAB and WAB
Groundwater data at the Site indicates that surrounding
Permanent Water Solution
water supply wells are not and have not been affected
for Water Supply Well
by Site -related COIs. Nevertheless, installation and
Users within a 0.5-mile
maintenance by Duke Energy of water filtration systems
radius of the Coal Ash
for 80 domestic and public water supply well users has
Basin Compliance
been completed and approved by the NCDEQ to
Boundary and Associated
address current and future stakeholder concerns. Duke
Water Filtration System
Energy maintains these systems on behalf of the
Maintenance
property owners.
Page ES-20

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION,
AND MONITORING
Groundwater Remedy
Rationale
Component
EAB, WAB, and
Duke Energy owns the land downgradient of the ash
Downgradient Additional
basins and the GSA/DFAHA and controls its use. Duke
Energy ownership of property mitigates potential future
Source Areas
Maintain Ownership and
risk by controlling or eliminating potential exposure
Institutional Controls (ICs)
pathways associated with Site -related COIs. ICs in the
Consisting of a Land Use
form of a Declaration of Perpetual Land Use Restrictions
Restriction
may be requested in the future based on the results of
the groundwater remediation activities.
Source Area 1 and Source
Duke Energy plans to monitor groundwater to confirm
the corrective action objectives are met and maintained
Area 3
Effectiveness Groundwater
over time. This monitoring program includes provisions
Monitoring (EAB and
for monitoring EAB COIs within the compliance
Downgradient Additional
boundary as required under NCAC Title 15A. 0107(k)(2)
Source Areas)
and downgradient of the EAB compliance boundary and
the additional source areas. Flow and transport plus
geochemical modeling have been conducted to predict
future groundwater conditions after closure.
Effectiveness monitoring will provide data to validate
modeling in the future. This CAP Update includes a
comprehensive review of groundwater data collected
through June 2019 and a plan to optimize the
monitoring program. Within thirty (30) days of CAP
approval, Duke Energy would implement the
effectiveness monitoring program (EMP).
Source Area 2 (WAB)
Duke Energy will monitor WAB groundwater to confirm
Confirmation Monitoring
that concentrations at the compliance boundary remain
Plan
in compliance with 02L. Flow and transport plus
geochemical modeling have been conducted to predict
future groundwater conditions after closure.
Confirmation monitoring will provide data to validate
modeling in the future. Within thirty (30) days of CAP
approval, Duke Energy would implement the
Confirmation Monitoring Plan (CMP).
Page ES-21

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION,
AND MONITORING
Groundwater Remedy
Rationale
Component
EAB and Downgradient
The Roxboro EAB, GSA, DFAHA, and surrounding areas
are complex; therefore, Duke Energy believes it is
important to allow for an adaptive approach during
Additional Source Areas
Provision for Adaptive
Management of
implementation of groundwater remediation through
Groundwater Remedies
ash basin closure. This approach is consistent with the
Interstate Technology and Regulatory Council (ITRC)
document titled Remediation Management of Complex
Sites (ITRC, 2017). This approach may include (i)
adjustments to the groundwater remedy, if necessary,
based on new data, or if conditions change; or (ii) an
alternate groundwater standard for boron of 4,000 pg/L
(USEPA tap water regional screening level) pursuant to
NCDEQ's authority under 15A NCAC 02L .0106(k).
Prepared by: KTL Checked by: CDE
Corrective Action at Remediation Zones (Source Area 1 and Source
Area 3)
The areas proposed for groundwater remediation in accordance with 02L requirements
are to the north and northeast of the EAB at or beyond the compliance boundary and
north of the GSA and DFAHA adjacent to the Intake Canal (Figure ES-2). Multiple
potential groundwater remedial technologies were initially screened as part of the CAP
Update to identify the most applicable remedial methods based upon site specific
hydrogeologic conditions and COI distribution in groundwater. After the initial
screening, the following remedial alternatives were screened in detail:
• Remedial Alternative 1: Monitored natural attenuation
0 Remedial Alternative 2: Groundwater extraction
• Remedial Alternative 3: Groundwater extraction combined with clean water
infiltration
These remedial alternatives were further screened against the following criteria
outlined in Section 6.D.iv. (1-10) of the CAP guidance (NCDEQ, 2019):
• Protection of human health and the environment
• Compliance with applicable federal, state, and local regulations
• Long-term effectiveness and permanence
Page ES-22

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
• Reduction of COI toxicity and mobility, and volume of COI -affected
groundwater
• Short-term effectiveness at minimizing effects on the environment and local
community
• Technical and logistical feasibility
• Time required to initiate
• Predicted time required to meet remediation goals
• Cost
• Sustainability
• Community acceptance
Groundwater modeling simulations were performed to evaluate the effectiveness of the
alternatives and to develop the most effective approach. The results of the analysis
indicate that groundwater extraction will best achieve the remedial objectives for the
EAB (Source Area 1) and groundwater extraction with clean water infiltration will best
achieve the remedial objectives for the GSA and DFAHA (Source Area 3). The
corrective action system layout is depicted on Figure ES-3.
The most effective remedial approach consists of:
Source Area 1
• 5 extraction wells in the area of the unnamed pond north of the EAB;
• 15 extraction wells on the northeast side of the EAB;
• 12 extraction wells north of the EAB in the comingling zone near the DFAHA;
and
Source Area 3
• 18 extraction wells and 27 clean water infiltration wells adjacent to the Intake
Canal.
It is recommended that prior to implementation; pilot testing of the proposed
alternative will be conducted for areas slated for corrective action. Pilot testing and
treatment tests to be conducted include: 1) groundwater extraction, 2) clean water
infiltration, and 3) treatment testing of extraction and clean water infiltration water.
Pilot study results will inform the design of the full-scale system. Planned activities
prior to full-scale implementation, where either submittal of the remedial performance
Page ES-23

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
monitoring plan (i.e., effectiveness monitoring plan), or the pilot test work plan and
permit applications (as applicable) will be submitted to NCDEQ within 30 days of CAP
approval to fulfill G.S. Section 130A-309.211(b)(3).
Page ES-24

10
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ENERGY WINSTON-SALEM CORRECTIVE ACTION PLAN UPDATE
PROGRESS �RALEIGH ROXBORO STEAM ELECTRIC PLANT
SEMORA, NORTH CAROLINA
CHARLOTTE
DRAWN BY. J. KI RTZ DATE: 06/11/2019 GRAPHIC SCALE
REVISED BY: C. WYATT DATE: 12/19/2019 0 500 1,000 2,000 3,000
WnTerra CHECKED BY: K. LAWING DATE: 12/19/2019
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DATE: 06/05/2019
DATE: 12/18/2019
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DATE: 12/18/2019
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DATE: 12/18/2019
PROJECT MANAGER: C. EADY
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AREAS PROPOSED FOR ACTIVE GROUNDWATER
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ASH BASIN WASTE BOUNDARY
ASH BASIN COMPLIANCE BOUNDARY
SOLID WASTE LANDFILL BOUNDARY
SOLID WASTE LANDFILL COMPLIANCE BOUNDARY
DUKE ENERGY PROGRESS PROPERTY LINE
EFFLUENT DISCHARGE CANAL
> STREAMS (AMEC NRTR)
WETLANDS (AM EC NRTR)
NOTES:
1. THE OUTLINE OF AREA 1 BEYOND THE ASH BASIN COMPLIANCE BOUNDARY REPRESENTS
THE MAXIMUM FUTURE EXTENT OF BORON PLUME (MAX-B)ABOVE 02L STANDARD
PREDICTED FOR ALL FLOW LAYERS AND ALL YEARS, BASED ON FLOW AND TRANSPORT
MODELING.
2. ALL BOUNDARIES ARE APPROXIMATE
3. DUKE ENERGY PROPERTY LINES ARE REPRESENTED BASED ON DUKE ENERGY'S
INTERPRETATION OF HISTORICAL DOCUMENTED PROPERTY BOUNDARIES AND CURRENT
PERSON COUNTY GIS.
4. THE WATERS OF THE US DELINEATION HAS NOT BEEN APPROVED BY THE USARMY CORPS
OF ENGINEERSAT THE TIME OF THE MAP CREATION. THIS MAP IS A PRELIMINARY
JURISDICTIONAL DETERMINATION ONLY. THE PRELIMINARY WETLANDSAND STREAMS
BOUNDARIES WERE OBTAINED FROMAMEC FOSTER WHEELER ENVIRONMENTAL &
INFRASTRUCTURE, INC. NATURAL RESOURCE TECHNICAL REPORT (NRTR) FOR ROXBORO
STEAM ELECTRIC PLANT DATED JUNE 2015.
5.AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON OCTOBER 11, 2017.
AERIAL WAS COLLECTED ON JUNE 13, 2016.
6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINASTATE PLANE
COORDINATE SYSTEM FIPS 3200 (NAD83).
FIGURE ES-2
AREAS PROPOSED FOR CORRECTIVE ACTION
EAST ASH BASIN
CORRECTIVE ACTION PLAN UPDATE
ROXBORO STEAM ELECTRIC PLANT
SEMORA, NORTH CAROLINA

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Figure ES-3
Proposed Corrective Action Approach
Provided in separate electronic figure file as a
large sheet size

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
TABLE OF CONTENTS
SECTION
PAGE
EXECUTIVE SUMMARY.................................................................................................... ES-1
ES.1 Introduction.......................................................................................................... ES-1
ES.2
Background...........................................................................................................
ES-5
ES.3
CSM Overview...................................................................................................
ES-12
ESA
Corrective Action Approach............................................................................
ES-17
1.0
INTRODUCTION........................................................................................................1-1
1.1
Background..............................................................................................................1-2
1.2
Purpose and Scope..................................................................................................1-4
1.3
Regulatory Basis for Corrective Action...............................................................1-5
1.4
List of Considerations by the Secretary for Evaluation of Corrective
ActionPlans.............................................................................................................1-7
1.5
Facility Description.................................................................................................1-8
1.5.1 Location and History of Land Use.................................................................1-8
1.5.2 Operations and Waste Streams Coincident with the Ash Basins ............1-10
1.5.3 Overview of Existing Permits and Special Orders by Consent................1-14
2.0
RESPONSE TO CSA UPDATE COMMENTS IN SUPPORT OF CAP
DEVELOPMENT.......................................................................................................... 2-1
2.1
Facility -Specific Comprehensive Site Assessment (CSA) Comment Letter and
DraftComments......................................................................................................2-1
2.2
Duke Energy's Response to NCDEQ CSA Comment Letter ............................
2-1
3.0
OVERVIEW OF SOURCE AREAS BEING PROPOSED FOR
CORRECTIVE ACTION.............................................................................................3-1
4.0
SUMMARY OF BACKGROUND DETERMINATIONS.....................................4-1
4.1
Background Concentrations for Soil....................................................................4-2
4.2
Background Concentrations for Groundwater...................................................4-3
4.3
Background Concentrations for Surface Water..................................................4-4
4.4
Background Concentrations for Sediment..........................................................
4-5
5.0
CONCEPTUAL SITE MODEL.................................................................................. 5-1
5.1
Site Geologic and Hydrogeologic Setting............................................................5-2
5.1.1 Site Geologic Setting.........................................................................................
5-2
5.1.2 Site Hydrogeologic Setting..............................................................................
5-4
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Roxboro Steam Electric Plant SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
5.1.2.1
Groundwater Flow Direction.................................................................... 5-4
5.1.2.2
Groundwater Seepage Velocities..............................................................5-8
5.1.2.3
Hydraulic Gradients.................................................................................
5-10
5.1.2.4
Particle Tracking Results..........................................................................5-11
5.1.2.5
Subsurface Heterogeneities.....................................................................
5-12
5.1.2.6
Bedrock Matrix Diffusion and Flow.......................................................5-13
5.1.2.7
Onsite and Offsite Pumping Influences.................................................5-16
5.1.2.8
Ash Basin Groundwater Balance............................................................
5-16
5.1.2.9
Effects of Naturally Occurring Constituents.........................................5-22
5.2
Source Area Locations..........................................................................................5-22
5.3
Summary of Potential Receptors........................................................................
5-24
5.3.1 Public and Private Water Supply Wells......................................................5-24
5.3.2 Availability of Public Water Supply............................................................5-24
5.3.3 Surface Water...................................................................................................5-25
5.3.4 Environmental Assessment of Hyco Reservoir ..........................................
5-25
5.3.5 Future Groundwater Use Area.....................................................................
5-26
5.4
Human Health and Ecological Risk Assessment Results ................................
5-26
5.5
CSM Summary......................................................................................................5-29
6.0
CORRECTIVE ACTION APPROACH FOR SOURCE AREAS ..........................
6-1
SOURCE
AREA 1 (SA1) — EAST ASH BASIN, INDUSTRIAL LANDFILL,
AND LCID LANDFILL...............................................................................................6-3
6.1
SA1 Extent of Constituent Distribution...............................................................
6-3
6.1.1 Source Material Within the Waste Boundary ...............................................
6-3
6.1.1.1 Description of Waste Material and History of Placement ....................
6-3
6.1.1.2 Specific Waste Characteristics of Source Material.................................6-4
6.1.1.3 Volume of Physical Horizontal and Vertical Extent of
SourceMaterial...........................................................................................
6-6
6.1.1.4 Volume and Physical Horizontal and Vertical Extent and
Anticipated Saturated Source Material ...................................................
6-7
6.1.1.5 Saturated Ash and Groundwater.............................................................
6-8
6.1.1.6 Chemistry Within Waste Boundary.......................................................
6-10
6.1.1.7 Other Potential Source Material..............................................................
6-14
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TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.1.1.8 Interim Response Actions........................................................................ 6-14
6.1.2 Extent of Constituent Migration Beyond the Compliance Boundary ..... 6-15
6.1.2.1 Piper Diagrams..........................................................................................6-21
6.1.3 Constituents of Interest (COIs)..................................................................... 6-23
6.1.4 Horizontal and Vertical Extent of COIs.......................................................6-32
6.1.4.1 COIs in Unsaturated Soil......................................................................... 6-34
6.1.4.2 Horizontal and Vertical Extent of Groundwater in
Needof Restoration................................................................................. 6-35
6.1.5 COI Distribution in Groundwater................................................................ 6-38
6.1.5.1 Conservative Constituents....................................................................... 6-39
6.1.5.2 Non -Conservative Constituents............................................................. 6-43
6.1.5.3 Variably Conservative Constituents...................................................... 6-43
6.2 SA1 Potential Receptors Associated with Source Area 1................................ 6-43
6.2.1 Surface Waters — Downgradient Within a 0.5-Mile Radius
of the Waste Boundary................................................................................... 6-44
6.2.2 Water Supply Wells........................................................................................ 6-46
6.2.2.1 Provision of Alternative Water Supply ................................................. 6-46
6.2.2.2 Findings of Drinking Water Supply Well Surveys .............................. 6-47
6.2.3 Future Groundwater Use Areas Associated With Source Area 1............ 6-48
6.3 SA1 Human and Ecological Risks...................................................................... 6-48
6.4 SA1 Description of Remediation Technologies ................................................ 6-49
6.4.1 Monitored Natural Attenuation................................................................... 6-49
6.4.2 In -Situ Technologies....................................................................................... 6-51
6.4.3 Groundwater Extraction................................................................................ 6-56
6.4.4 Groundwater Treatment................................................................................ 6-62
6.4.5 Groundwater Management........................................................................... 6-65
6.4.6 Technology Evaluation Summary................................................................ 6-71
6.5 SA1 Evaluation of Remedial Alternatives......................................................... 6-71
6.5.1 Remedial Alternative 1— Monitored Natural Attenuation ....................... 6-71
6.5.1.1 Problem Statement and Remediation Goals ......................................... 6-72
Page iii

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TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.5.1.2 Conceptual Model..................................................................................... 6-72
6.5.1.3 Predictive Modeling.................................................................................
6-74
6.5.2 Remedial Alternative 2 - Groundwater Extraction ...................................
6-74
6.5.2.1 Problem Statement and Remediation Goals .........................................
6-74
6.5.2.2 Conceptual Model.....................................................................................
6-75
6.5.2.3 Predictive Modeling.................................................................................
6-76
6.6 SA1 Remedial Alternatives Screening Criteria.................................................6-77
6.7 SA1 Remedial Alternatives Criteria Evaluation...............................................6-83
6.7.1 Remedial Alternative 1: Monitored Natural Attenuation .........................
6-83
6.7.2 Remedial Alternative 2 - Groundwater Extraction ...................................
6-88
6.8 SA1 Proposed Remedial Alternative Selected For Source Area 1..................
6-91
6.8.1 Description of Proposed Remedial Alternative and Rationale
forSelection......................................................................................................
6-92
6.8.2 Design Details..................................................................................................6-93
6.8.2.1 Process Flow Diagrams for All Major Components of
ProposedRemedy....................................................................................
6-94
6.8.2.2 Engineering Designs with Assumptions, Calculations and
Specifications............................................................................................
6-99
6.8.2.3 Permits for Remedy and Schedule.......................................................
6-102
6.8.2.4 Schedule and Cost of Implementation.................................................
6-102
6.8.2.5 Measures to Ensure Health and Safety ................................................
6-103
6.8.2.6 Description of All Other Activities and Notifications Being
Conducted to Ensure Compliance with 02L, CAMA, and Other
Relevant Laws and Regulations...........................................................
6-103
6.8.3 Requirements for 02L .0106(1) - MNA Rule ..............................................
6-104
6.8.4 Requirements for 02L .0106(k) -Alternate Standards .............................
6-104
6.8.5 Sampling and Reporting..............................................................................
6-105
6.8.5.1 Progress Reports and Schedule.............................................................
6-106
6.8.5.2 Sampling and Reporting Plan During Active Remediation .............
6-108
6.8.6 Sampling and Reporting Plan after Termination of
Active Remediation......................................................................................
6-112
6.8.7 Proposed Interim Activities Prior to Implementation .............................
6-113
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TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.8.8 Contingency Plan..........................................................................................
6-113
6.8.8.1 Description of Contingency Plan..........................................................
6-113
6.8.8.2 Decision Metrics for Contingency Plan Areas ....................................
6-114
6.9 SA1 Summary and Conclusions.......................................................................
6-117
SOURCE AREA 2 (SA2) — WEST ASH BASIN..............................................................
6-119
6.10 SA2 Extent of Constituent Distribution...........................................................
6-119
6.10.1 Source Material Within the Waste Boundary ...........................................
6-119
6.10.1.1 Description of Waste Material and History of Placement ................
6-119
6.10.1.2 Specific Waste Characteristics of Source Material .............................
6-121
6.10.1.3 Volume of Physical Horizontal and Vertical Extent
ofSource Material..................................................................................
6-121
6.10.1.4 Volume and Physical Horizontal and Vertical Extent
and Anticipated Saturated Source Material .......................................
6-122
6.10.1.5 Saturated Ash and Groundwater.........................................................
6-122
6.10.1.6 Chemistry Within Waste Boundary .....................................................
6-123
6.10.1.7 Other Potential Source Material............................................................
6-127
6.10.1.8 Interim Response Actions......................................................................
6-127
6.10.2 Extent of Constituent Migration Beyond the
Compliance Boundary..................................................................................
6-128
6.10.2.1 Piper Diagrams........................................................................................
6-130
6.10.3 Constituents of Interest (COIs)...................................................................
6-131
6.10.4 Horizontal and Vertical Extent of COIs.....................................................6-132
6.10.4.1 COIs in Unsaturated Soil.......................................................................
6-133
6.10.4.2 Horizontal and Vertical Extent of Groundwater in
Need of Restoration...............................................................................
6-135
6.10.5 COI Distribution in Groundwater..............................................................
6-137
6.10.5.1 Conservative Constituents.....................................................................
6-137
6.10.5.2 Non -Conservative Constituents...........................................................
6-139
6.10.5.3 Variably Conservative Constituents....................................................
6-139
6.11 SA2 Potential Receptors Associated with Source Area 2 ..............................
6-140
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TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.11.1 Surface Waters - Downgradient within 0.5 Mile of Waste Boundary.. 6-140
6.11.2 Water Supply Wells...................................................................................... 6-140
6.11.2.1 Provision of Alternative Water Supply ............................................... 6-140
6.11.2.2 Findings of Drinking Water Supply Well Surveys ............................ 6-141
6.11.3 Future Groundwater Use Areas Associated With Source Area 2.......... 6-141
6.12 SA2 Human and Ecological Risks.................................................................... 6-142
6.13 SA2 Description of Remediation Technologies .............................................. 6-142
6.14 SA2 Remedial of Remedial Alternatives......................................................... 6-142
6.15 SA2 Proposed Remedial Alternative Selected For Source Area 1................ 6-143
6.15.1 Description of Proposed Remedial Alternative and
Rationale for Selection..................................................................................6-143
6.15.2 Design Details................................................................................................6-143
6.15.3 Requirements for 02L .0106(1) - MNA Rule .............................................. 6-143
6.15.4 Requirements for 02L .0106(k) - Alternate Standards ............................. 6-143
6.15.5 Sampling and Reporting.............................................................................. 6-143
6.15.5.1 Progress Reports and Schedule............................................................. 6-143
6.15.5.2 Sampling and Reporting Plan During Active Remediation ............. 6-144
6.15.5.3 Confirmation Monitoring Plan............................................................. 6-144
6.15.6 Sampling and Reporting Plan After Termination of
ActiveRemediation...................................................................................... 6-149
6.15.7 Proposed Interim Activities Prior to Implementation ............................. 6-149
6.15.8 Contingency Plan in Case of Insufficient Remediation Performance ... 6-149
6.15.8.1 Description of Contingency Plan.......................................................... 6-149
6.15.8.2 Decision Metrics for Contingency Plan Areas .................................... 6-149
6.16 SA2 Summary and Conclusions....................................................................... 6-150
SOURCE AREA 3 (SA3) - GYPSUM STORAGE AREA AND DFA SILOS,
TRANSPORT, AND HANDLING AREAS........................................................6-152
6.17 SA3 Extent of Constituent Distribution........................................................... 6-152
6.17.1 Source Material Within the Waste Boundary ........................................... 6-152
6.17.1.1 Description of Waste Material and History of Placement ................ 6-152
6.17.1.2 Specific Waste Characteristics of Source Material ............................. 6-153
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TABLE OF CONTENTS (CONTINUED)
SECTION
6.17.1.3 Volume of Physical Horizontal and Vertical Extent
PAGE
ofSource Material..................................................................................
6-154
6.17.1.4 Volume and Physical Horizontal and Vertical Extent and
Anticipated Saturated Source Material ...............................................
6-154
6.17.1.5 Saturated Ash and Groundwater.........................................................
6-155
6.17.1.6 Chemistry Within Waste Boundary .....................................................
6-156
6.17.1.7 Other Potential Source Material............................................................
6-156
6.17.1.8 Interim Response Actions......................................................................
6-156
6.17.2 Extent of Constituent Migration beyond the Compliance Boundary ... 6-156
6.17.2.1 Piper Diagrams........................................................................................
6-159
6.17.3 Constituents of Interest (COIs)...................................................................
6-160
6.17.4 Horizontal and Vertical Extent of COIs.....................................................6-161
6.17.4.1 COIs in Unsaturated Soil.......................................................................
6-162
6.17.4.2 Horizontal and Vertical Extent of Groundwater in
Needof Restoration...............................................................................
6-162
6.17.5 COI Distribution in Groundwater..............................................................
6-163
6.17.5.1 Conservative Constituents.....................................................................
6-163
6.17.5.2 Non -Conservative Constituents...........................................................
6-164
6.17.5.3 Variably Conservative Constituents....................................................
6-164
6.18 SA3 Potential Receptors Associated with Source Area 3 ..............................
6-165
6.18.1 Surface Waters — Downgradient Within a 0.5-Mile Radius
of the Waste Boundary.................................................................................6-165
6.18.2 Water Supply Wells......................................................................................
6-168
6.18.2.1 Provision of Alternative Water Supply ...............................................
6-168
6.18.2.2 Findings of Drinking Water Supply Well Surveys ............................
6-169
6.18.3 Future Groundwater Use Areas Associated With Source Area 1..........
6-169
6.19 SA3 Human and Ecological Risks....................................................................
6-169
6.20 SA3 Description of Remediation Technologies ..............................................
6-169
6.21 SA3 Evaluation of Remedial Alternatives.......................................................
6-169
6.21.1 Remedial Alternative 1— Monitored Natural Attenuation .....................
6-170
6.21.1.1 Problem Statement and Remediation Goals .......................................
6-170
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TABLE OF CONTENTS (CONTINUED)
SECTION PAGE
6.21.1.2 Conceptual Model................................................................................... 6-171
6.21.1.3 Predictive Modeling............................................................................... 6-171
6.21.2 Remedial Alternative 2 — Groundwater Extraction ................................. 6-172
6.21.2.1 Problem Statement and Remediation Goals ....................................... 6-172
6.21.2.2 Conceptual Model................................................................................... 6-172
6.21.2.3 Predictive Modeling............................................................................... 6-173
6.21.3 Remedial Alternative 3 — Groundwater Extraction with Clean Water
Infiltration...................................................................................................... 6-174
6.21.3.1 Problem Statement and Remediation Goals ....................................... 6-174
6.21.3.2 Conceptual Model................................................................................... 6-174
6.21.3.3 Predictive Modeling............................................................................... 6-176
6.22 SA3 Remedial Alternatives Screening Criteria...............................................6-176
6.23 SA3 Remedial Alternatives Criteria Evaluation ............................................. 6-176
6.23.1 Remedial Alternative 1: Monitored Natural Attenuation Protection of
Human Health and the Environment........................................................ 6-177
6.23.2 Remedial Alternative 2 — Groundwater Extraction ................................. 6-180
6.23.3 Remedial Alternative 3 —Groundwater Extraction and Clean Water
Infiltration...................................................................................................... 6-184
6.24 SA3 Proposed Remedial Alternative Selected For Source Area 3................ 6-188
6.24.1 Description of Proposed Remedial Alternative and
Rationale for Selection..................................................................................6-188
6.24.2 Design Details................................................................................................6-190
6.24.2.1 Process Flow Diagrams for All Major Components of Proposed
Remedy.................................................................................................... 6-191
6.24.2.2 Engineering Designs with Assumptions, Calculations and
Specifications.......................................................................................... 6-199
6.24.2.3 Permits for Remedy and Schedule....................................................... 6-202
6.24.2.4 Schedule and Cost of Implementation................................................. 6-203
6.24.2.5 Measure to Ensure Health and Safety .................................................. 6-203
6.24.2.6 Description of All Other Activities and Notifications Being
Conducted to Ensure Compliance with 02L, CAMA, and Other
Relevant Laws and Regulations........................................................... 6-203
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Corrective Action Plan Update December 2019
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TABLE OF CONTENTS (CONTINUED)
SECTION
6.24.3 Requirements for 02L .0106(1) - MNA Rule ....................................
6.24.4 Requirements for 02L .0106(k) - Alternate Standards ...................
6.24.5 Sampling and Reporting....................................................................
6.24.5.1 Progress Reports and Schedule ...................................................
6.24.5.2 Sampling and Reporting Plan During Active Remediation ...
6.24.6 Sampling and Reporting Plan after Termination of
Active Remediation............................................................................
6.24.7 Proposed Interim Activities Prior to Implementation ...................
6.24.8 Contingency Plan................................................................................
PAGE
...... 6-204
...... 6-204
...... 6-204
...... 6-204
...... 6-204
...... 6-204
...... 6-205
...... 6-205
6.25 SA3 Summary and Conclusions....................................................................... 6-205
7.0 PROFESSIONAL CERTIFICATION........................................................................7-1
8.0 REFERENCES............................................................................................................... 8-1
Page ix

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
LIST OF FIGURES
Executive Summary
Figure ES-1 USGS Location Map
Figure ES-2 Areas Proposed for Corrective Action - East Ash Basin
Figure ES-3 Proposed Corrective Action Approach
1.0 Introduction
Figure 1-1
USGS Location Map
Figure 1-2
Site Layout Map - East Ash Basin
Figure 1-3
Site Layout Map - West Ash Basin
Figure 1-4
1964 Aerial Photograph
4.0 Summary of Background Determinations
Figure 4-1 Background Sample Location Map
5.0 Conceptual Site Model
Figure 5-1
Conceptual Site Model - Pre -Decanting Conditions
Figure 5-2
LeGrand Slope Aquifer System
Figure 5-3
General Profile of Ash Basin Pre -Decanting Flow Conditions in the
Piedmont
Figure 5-4a
Water Level Map - East Ash Basin - Transition/Bedrock Flow Zone
Figure 5-4b
Water Level Map - West Ash Basin - Transition/Bedrock Flow Zone
Figure 5-5a
Velocity Vector Map for Pre -Decanting Conditions - Transition Flow
Zone (Layer 13)
Figure 5-5b
Velocity Vector Map for Closure -in -Place Conditions - Transition Flow
Zone (Layer 13)
Figure 5-5c
Velocity Vector Map for Closure by Excavation Conditions - Transition
Flow Zone (Layer 13)
Figure 5-6a
Velocity Vector Map for Pre -Decanting Conditions - Bedrock Flow
Zone (Layer 15)
Figure 5-6b
Velocity Vector Map for Closure -in -Place Conditions - Bedrock Flow
Zone (Layer 15)
Figure 5-6c
Velocity Vector Map for Closure by Excavation Conditions - Bedrock
Flow Zone (Layer 15)
Figure 5-7a
Water Supply Well Sample Locations
Figure 5-7b
HB 630 Permanent Water Supply Completion Map
Figure 5-8
Map of Surface Waters
Page x

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
LIST OF FIGURES (CONTINUED)
6.0 Corrective Action Approach for Source Areas
Figure 6-1 Map of Source Areas
Figure 6-2 Fly Ash and Bottom Ash Interbedded Depiction
Figure 6-3 General Cross Section A -A' - East Ash Basin
Figure 6-4 General Cross Section B-B' - East Ash Basin
Figure 6-5 Saturated Ash Thickness Map - Pre -Decanting and Closure -in -Place
Conditions - East Ash Basin
Figure 6-6a
General Cross Section A -A' - East Ash Basin - Conservative Group -
Mean of Boron, Sulfate, and TDS
Figure 6-6b
General Cross Section A -A' - East Ash Basin - Variable Group- Mean
of Selenium and Strontium
Figure 6-7a
General Cross Section B-B' - East Ash Basin - Conservative Group -
Mean of Boron, Sulfate, and TDS
Figure 6-7b
General Cross Section B-B' - East Ash Basin - Variable Group- Mean of
Selenium and Strontium
Figure 6-8
Ash Pore Water and Groundwater Piper Diagrams - East Ash Basin
Figure 6-9
Seep and Surface Water Quality Piper Diagrams - East Ash Basin
Figure 6-10a
Isoconcentration Map Boron in Transition Flow Zone - East Ash Basin
Figure 6-10b
Isoconcentration Map Boron in Bedrock Flow Zone - East Ash Basin
Figure 6-11a
Isoconcentration Map Sulfate in Transition Flow Zone - East Ash Basin
Figure 6-11b
Isoconcentration Map Sulfate in Bedrock Flow Zone - East Ash Basin
Figure 6-12a
Isoconcentration Map TDS in Transition Flow Zone - East Ash Basin
Figure 6-12b
Isoconcentration Map TDS in Bedrock Flow Zone - East Ash Basin
Figure 6-13a
Isoconcentration Map Selenium in Transition Flow Zone - East Ash
Basin
Figure 6-13b
Isoconcentration Map Selenium in Bedrock Flow Zone - East Ash Basin
Figure 6-14a
Isoconcentration Map Strontium in Transition Flow Zone - East Ash
Basin
Figure 6-14b
Isoconcentration Map Strontium in Bedrock Flow Zone - East Ash
Basin
Figure 6-15
Unsaturated Soil Sample Locations and Exceedances - East Ash Basin
Figure 6-16
Pourbaix Diagram for Iron -Water System
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
LIST OF FIGURES (CONTINUED)
Figure 6-17a
Remedial Alternative 3 - Well System Layout - Groundwater
Remediation by Extraction combined with Clean Water Infiltration and
Treatment
Figure 6-17b
Remedial Alternative 3 - Conceptual Vertical Clean Water Infiltration
Well Schematic - Groundwater Remediation by Extraction combined
with Clean Water Infiltration and Treatment
Figure 6-17c
Remedial Alternative 3 - Conceptual Vertical Extraction Well
Schematic - Groundwater Remediation by Extraction combined with
Clean Water Infiltration and Treatment
Figure 6-17d
Remedial Alternative 3 - Conceptual Trench Detail - Groundwater
Remediation by Extraction combined with Clean Water Infiltration and
Treatment
Figure 6-17e
Remedial Alternative 3 - Groundwater Remediation by Extraction
combined with Clean Water Infiltration and Treatment - Simulated
Boron Concentrations in All Flow Zones
Figure 6-18a
Conceptual Process Flow Diagram - Clean Water Infiltration System
Figure 6-18b
Conceptual Process Flow Diagram - Groundwater Extraction System
Figure 6-19
CAP Implementation Gantt Chart
Figure 6-20
Effectiveness Monitoring Plan Systems and Flow Paths - East Ash
Basin
Figure 6-21a
Effectiveness Monitoring Plan Work Flow and Optimization Flow
Diagram
Figure 6-21b
Termination of Groundwater Remediation Flow Diagram
Figure 6-22
General Cross Section C-C' - West Ash Basin
Figure 6-23
General Cross Section D-D' - West Ash Basin
Figure 6-24
Saturated Ash Thickness Map Pre -Decanting and Closure -In -Place
Conditions - West Ash Basin
Figure 6-25
General Cross Section C-C' - West Ash Basin - Conservative Group
Mean of Boron
Figure 6-26
General Cross Section D-D' - West Ash Basin - Conservative Group
Mean of Boron
Figure 6-27
Geochemical Water Quality Plots - West Ash Basin
Figure 6-28
Ash Pore Water and Groundwater Piper Diagrams - West Ash Basin
Figure 6-29
Decanting Monitoring Network - West Ash Basin
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
LIST OF FIGURES (CONTINUED)
Figure 6-30a
Hydrographs - West Ash Basin
Figure 6-30b
Hydrographs — West Ash Basin
Figure 6-31a
Isoconcentration Map Boron in Saprolite/Transition Flow Zone - West
Ash Basin
Figure 6-31b
Isoconcentration Map Boron in Bedrock Flow Zone - West Ash Basin
Figure 6-32
Unsaturated Soil Sample Locations and Exceedances - West Ash Basin
Figure 6-33
Confirmation Monitoring Plan Network - West Ash Basin
Figure 6-34
Confirmation Monitoring Plan Work Flow Diagram
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Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
LIST OF TABLES
Executive Summary
Table ES-1 Summary of Roxboro Assessment Documentation
Table ES-2 Summary of Roxboro Assessment Activities
Table ES-3 Components of Source Control, Active Remediation, and Monitoring
3.0 Overview of Source Areas Being Proposed for Corrective Action
Table 3-1 Corrective Action Evaluation Summary of Roxboro Ash Basins and
Hydraulically Connected Additional Source Areas
4.0 Summary of Background Determinations
Table 4-1 Background Soil Sample Summary
Table 4-2 Background Values for Soil
Table 4-3 Background Values for Groundwater
Table 4-4 Background Dataset Ranges for Surface Water
Table 4-5 Background Dataset Ranges for Sediment
5.0 Conceptual Site Model
Table 5-1 April 2019 Water Level Measurements and Elevations
Table 5-2 Watershed Groundwater Balance Summary - West Ash Basin
Table 5-3 Watershed Groundwater Balance Summary - East Ash Basin
Table 5-4 Surface Water Classifications
6.0 Corrective Action Approach for Source Areas
Table 6-1 Boron Concentrations in Groundwater Below Source Area 1 — East Ash
Basin
Table 6-2 Source Area Interim Actions — East Ash Basin
Table 6-3 Soil PSRG POG Standard Equation Parameters and Values
Table 6-4 Summary of Unsaturated Soil Sample Analytical Results — East Ash Basin
Table 6-5 Means of Groundwater COIs - January 2018 to April 2019 — East Ash Basin
Table 6-6 COI Management Matrix — East Ash Basin
Table 6-7 Summary of Trend Analysis Results for Groundwater Monitoring Wells —
East Ash Basin
Table 6-8 Seeps Corrective Action Strategy — East Ash Basin
Table 6-9 Water Supply Well Analytical Results Summary
Table 6-10 NPDES Permit Limits and Anticipated Groundwater Remediation
Parameter Levels
Table 6-11 Feature Irrigation System Setback
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LIST OF TABLES (CONTINUED)
Table 6-12 Remedial Technology Screening Summary
Table 6-13 Alternative 2 Extraction Well Summary - Source Area 1
Table 6-14 Environmental Sustainability Comparisons for Remediation Alternatives -
Source Area 1
Table 6-15 Modeled Groundwater Extraction Well Details - Source Area 1 and Source
Area 3
Table 6-16 Groundwater Effectiveness Monitoring Plan Elements
Table 6-17 Boron Concentrations in Groundwater Below Source Area 3 - West Ash
Basin
Table 6-18 Source Area Interim Actions - West Ash Basin
Table 6-19 Summary of Unsaturated Soil Sample Analytical Results - West Ash Basin
Table 6-20 Means of Groundwater COIs - January 2018 to April 2019 - West Ash
Basin
Table 6-21 COI Management Matrix - West Ash Basin
Table 6-22 Summary of Trend Analysis Results for Groundwater Monitoring Wells -
West Ash Basin
Table 6-23 Groundwater Confirmation Monitoring Plan Elements
Table 6-24 Alternative 3 Extraction and Clean Water Infiltration Well Summary -
Source Area 3
Table 6-25 Environmental Sustainability Comparisons for Remediation Alternatives -
Source Area 3
Table 6-26 Modeled Clean Water Infiltration Well Details - Source Area 3
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LIST OF APPENDICES
Appendix A Regulatory Correspondence
Appendix B Comprehensive Site Assessment Update Report Review Comments
and Responses
Appendix C Updated Comprehensive Analytical Data Tables (electronic)
Appendix D HB 630 Provision of Water Supply Completion Documentation
Appendix E Human Health and Ecological Risk Assessment
Appendix F Fractured Bedrock Evaluation
Appendix G Updated Groundwater Flow and Transport Modeling Report
Appendix H Geochemical Model Report
COI Management Technical Memorandum
Appendix I Monitored Natural Attenuation Report
Appendix J Surface Water Evaluation to Assess 15A NCAC 02B .0200 Compliance
for Implementation of Corrective Action under 15A NCAC 02L .0106
(k) and (1) Report
Surface Water Future Conditions Evaluation to Assess 15A NCAC
02B .0200 Compliance for Implementation and Termination of
Corrective Action under 15A NCAC 02L .0106 (k), (1), and (m) Report
Appendix K Remedial Alternative Cost Estimate Details
Appendix L Sustainability Calculations
Appendix M Remediation Alternative Summary
Appendix N Proposed Remedial Alternative Design Calculations
Appendix O Effectiveness Monitoring Plan
Appendix P Confirmation Monitoring Plan
Appendix Q Boring and Well Construction Logs
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LIST OF ACRONYMS
02B
NCDEQ Title 15A, Subchapter 02B. Surface Water and Wetland
Standards
02L
NCDEQ Title 15A, Subchapter 02L. Groundwater Classification and
Standards
AOW
Area of Wetness
ASTM
American Society for Testing and Materials
BGS
Below Ground Surface
BR
Bedrock
BTV
Background Threshold Value
CAMA
Coal Ash Management Act
CAP
Corrective Action Plan
CCR
Coal Combustion Residuals
CFR
Code of Federal Register
CMP
Confirmation Monitoring Plan
COI
Constituent of Interest
CSA
Comprehensive Site Assessment
CSM
Conceptual Site Model
Cy
cubic yards
DFA
Dry Fly Ash
DFAHA
Dry Fly Ash silos, transport, and handling area
Duke Energy
Duke Energy Progress, LLC
DWM
Division of Waste Management
EAB
East Ash Basin/Pond
EMP
Effectiveness Monitoring Program
EPD
Environmental Protection Division
EPRI
Electric Power Research Institute
FGD
Flue Gas Desulfurization
G.S.
North Carolina General Statutes
GSA
Gypsum Storage Area
GTB
Geotechnical Boring
HAO
Hydrous Aluminum Oxide
HB
Highway Business District
HDPE
High -Density Polyethylene
HFO
Hydrous Ferric Oxide
HSZ
Hyco Shear Zone
IMAC
Interim Maximum Allowable Concentration
IMP
Interim Monitoring Plan
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LIST OF ACRONYMS (CONTINUED)
ISV
In -situ Vitrification
Ka
Partition Coefficient
LCID
Land Clearing Inert Debris
LRB
Lined Retention Basin
MAROS
Monitoring and Remediation Optimization System
Mg/L
Milligrams per liter
Mil
Thousandths of Inch
Mm
Millimeter
MNA
Monitored Natural Attenuation
NAVD 88
North American Vertical Datum of 1988
NCAC
North Carolina Administrative Code
NCDENR
North Carolina Department of Environment and Natural Resources
NCDEQ
North Carolina Department of Environmental Quality
NCGS
North Carolina General Statute
NORR
Notice of Regulatory Requirements
NPDES
National Pollutant Discharge Elimination System
NRTR
National Resource Technical Report
OSWER
Office of Solid Waste and Emergency Response
PRB
Permeable Reactive Barrier
PBTV
Provisional Background Threshold Value
Plant/Site
Roxboro Steam Electric Plant
POG
Protection of Groundwater
PSRG
Preliminary Soil Remediation Goal
PWR
Partially Weathered Rock
RQD
Rock Quality Designation
S.U.
Standard Units
SOC
Special Order by Consent
SPLP
Synthetic Precipitation Leaching Procedure
SW
Surface Water
TCLP
Toxicity Characteristic Leaching Procedure
TDS
Total Dissolved Solids
TOC
Total Organic Carbon
TZ
Transition Zone
USEPA
United States Environmental Protection Agency
USCS
Unified Soil Classification System
USGS
United States Geological Survey
WAB
West Ash Basin
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1.0 INTRODUCTION
(CAP Content Section 1)
SynTerra prepared this groundwater corrective action plan (CAP) Update on behalf of
Duke Energy Progress, LLC (Duke Energy). The plan pertains to the Roxboro Steam
Electric Plant's (Roxboro, Plant, or Site) two coal combustion residuals (CCR)
impoundments (ash basins): the East Ash Basin/Pond (EAB) and the West Ash Basin
(WAB). The plans considered the industrial and Land Clearing Inert Debris (LCID)
landfills, positioned on top of a portion of the EAB, and additional source areas
downgradient of the EAB: the Gypsum Storage Area (GSA) and the Dry Fly Ash (DFA)
silos, transport, and handling area (referred to hereafter as the DFAHA). Duke Energy
owns and operates the Plant, located in Semora, Person County, North Carolina (Figure
1-1).
In accordance with North Carolina General Statutes (G.S.) Section 130A-309.211 (b), as
amended by the 2014 North Carolina Coal Ash Management Act (CAMA), Duke
Energy is submitting this CAP Update to prescribe the methods and materials for the
restoration of groundwater quality associated with the EAB and downgradient
additional source areas. This CAP Update considers constituent concentrations detected
greater than applicable North Carolina groundwater standards [NC Administrative
Code, Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L);
Interim Maximum Allowable Concentrations (IMAC); or background values],
whichever is greater, at or beyond the compliance boundary. Constituents with
concentrations above corresponding standards were evaluated to determine if the level
of concentration is present due to the source unit. Constituents of interest (COI) are
those constituents identified from the constituent management process described in
Section 6.1 and are specific to individual source unit(s), not the Site. This evaluation
assisted in identifying if a unit is subject to corrective action under G.S. 130A-309.211
and 15A NCAC 02L .0106.
Groundwater quality data confirms that COIs associated with the WAB do not exceed
applicable 15A NCAC 02L .0202 groundwater quality standards at or beyond the ash
basin compliance boundary; therefore, groundwater corrective action under 15A NCAC
02L .0106 is not required at this time for the WAB.
In accordance with G.S. Section 130A-309.211, a CAP pertaining to Roxboro was
previously submitted to the North Carolina Department of Environmental Quality
(NCDEQ) in two parts:
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• Corrective Action Plan Part 1— Roxboro Steam Electric Plant (SynTerra, 2015b)
• Corrective Action Plan Part 2 — Roxboro Steam Electric Plant (SynTerra, 2016a)
This CAP Update is being submitted to NCDEQ, as originally requested in a June 2,
2017, letter from NCDEQ to Duke Energy. In an April 5, 2019, letter to Duke Energy,
NCDEQ issued revised CAP deliverable schedules and requested assessment of
additional potential sources of constituents to groundwater at Roxboro stating that
sources hydrologically connected to the ash basins are to be assessed and included in an
updated CAP. For potential source areas not related to the ash basins, including the
coal pile storage area, would require the submittal of a Comprehensive Site Assessment
(CSA).
Timeframes are in accordance with subsequent correspondence between NCDEQ and
Duke Energy, including CAP content guidance issued by NCDEQ on April 27, 2018 and
adjusted on September 10, 2019. This CAP Update includes section references to the
document, Corrective Action Plan Content for Duke Energy Coal Ash Facilities (provided in
Appendix A), beneath report section headings and within text in parentheses to
facilitate the review process.
In addition to the CAP Update, Duke Energy is required to submit a CCR Surface
Impoundment Closure Plan (Closure Plan) for the EAB and WAB to NCDEQ on/before
December 31, 2019. Duke Energy is required to submit final closure plans consistent
with the detailed requirements of G.S. Section 130A-309.211, which is provided under
separate cover. This CAP Update has been developed to be effective with the closure -in -
place and closure -by -excavation scenarios developed for Roxboro.
1.1 Background
(CAP Content Section LA)
A substantial amount of assessment data has been collected for Roxboro to support this
CAP Update. Site assessment was completed and the CSA Update Report (SynTerra,
2017d) was performed in accordance with requirements in 15A NCAC 02L .0106(g). The
CSA:
• Identified the source(s) and cause of COIs in groundwater.
• Found no imminent hazards to public health and safety.
• Identified receptors and significant exposure pathways.
• Sufficiently determined the horizontal and vertical extent of COIs in soil and
groundwater.
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• Determined the geological and hydrogeological features that affect the
movement, chemical makeup, and physical characteristics of COIs.
NCDEQ provided review of the CSA Update to Duke Energy in a letter dated May 7,
2018 and stated that sufficient information was provided to allow preparation of this
CAP Update (Appendix A). This CAP Update builds on previous documents to
provide a CAP for addressing the requirements in 15A NCAC 02L .0106 for corrective
action and the restoration of groundwater quality, as applicable.
Detailed descriptions of Site operational history, the Site conceptual model, physical
setting and features, geology/hydrogeology, and findings of the CSA and other CAMA-
related work are documented in the following reports:
• Comprehensive Site Assessment Report — Roxboro Steam Electric Plant (SynTerra,
2015a).
• Corrective Action Plan Part 1 — Roxboro Steam Electric Plant (SynTerra, 2015b).
• Corrective Action Plan Part 2 — Roxboro Steam Electric Plant (SynTerra, 2016a).
• Comprehensive Site Assessment Supplement 1— Roxboro Steam Electric Plant
(SynTerra, 2016b).
• Ash Basin Extension Impoundments and Discharge Canals Assessment Report —
Roxboro Steam Electric Plant (SynTerra, 2017a)
• Gypsum Storage Area Structural Fill (CCB 003) Assessment Report — Roxboro Steam
Electric Plant (SynTerra, 2017b)
• Comprehensive Site Assessment Update — Roxboro Steam Electric Plant (SynTerra,
2017d).
• Ash Basin Pumping Test Report — Roxboro Steam Electric Plant (SynTerra, 2019a)
• Surface Water Evaluation to Assess 15A NCAC 02B.0200 Compliance for
Implementation of Corrective Action Under 15A NCAC 02L.0106 W and (l)
(SynTerra, 2019b)
• 2018 CAMA Annual Interim Monitoring Report — Roxboro Steam Electric Plant
(SynTerra, 2019c).
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1.2 Purpose and Scope
(CAP Content Section 1.B)
The purposes of this CAP Update is to:
• Restore groundwater beyond the EAB compliance boundary affected by the ash
basin to the standards or as close to the standards as is economically and
technically feasible in accordance with 15A NCAC 02L .0106.
• Reduce or prevent potential future COI related groundwater impacts to surface
water adjacent to the GSA and DFAHA.
• Address response requirements contained within 15A NCAC 02L .0107(k) for
exceedances of standards (1) in adjoining classified groundwater, (2) presenting
an imminent hazard to public health and safety, and/or (3) in bedrock
groundwater that may potentially affect a water supply well.
• Meet the requirements for corrective action plans specified in G.S. Section 130A-
309.211(b).
• Provide supporting evidence that groundwater quality does not exceed
applicable 15A NCAC 02L .0202 groundwater quality standards at or beyond the
WAB compliance boundary.
The scope of the CAP and this CAP Update is defined by G.S. Section 130A-309.211,
amended by CAMA. The CAMA legislation required, among other items, assessment of
groundwater at coal combustion residual impoundments and corrective action in
conformance with the requirements of 15A NCAC 02L. These corrective actions for
restoration of groundwater quality requirements were codified into G.S. Section 130A-
309.211, which was further amended by House Bill 630 to require a provision for
alternate water supply for receptors within a 0.5-mile radius downgradient from the
established compliance boundary.
Based on conditions and results from the Site investigations, this CAP Update develops
and compares alternative methods for corrective action and presents the recommended
plan. This CAP Update presents a holistic, multi -component corrective action approach
for groundwater COIs associated with the EAB and downgradient additional source
areas. Design information and steps necessary for corrective action implementation are
included in this CAP Update. For the WAB, migration of ash basin -sourced
constituents in groundwater does not extend past the compliance boundary. Therefore,
the CAP Update for the WAB focuses on constituent concentrations detected greater
than applicable regulatory criteria [02L; IMAC; or background threshold values,
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Roxboro Steam Electric Plant SynTerra
whichever is greater], and verifying decreasing groundwater concentrations during
decanting and subsequent closure of the WAB.
Upon NCDEQ approval of this CAP Update, implementation will begin within 30 days
as required in G.S. Section 309.211(b)(3).
1.3 Regulatory Basis for Corrective Action
(CAP Content Section 1.0
Comprehensive groundwater assessment activities, conducted in accordance with a
Notice of Regulatory Requirements (NORR) issued to Duke Energy on August 13, 2014
by the North Carolina Department of Environment and Natural Resources (NCDENR)
(Appendix A) (CAP Content Section 1.C.b), indicate the EAB (including the industrial
and LCID landfills) with contribution from downgradient additional source areas, the
GSA and the DFAHA, have contributed to COI concentrations in groundwater greater
than applicable 15A NCAC 02L .0202 groundwater quality standards.
The regulatory requirements for corrective action at CCR surface impoundments are
found in G.S. Section 130A-309.211(b), (c), and (c1). Section (b) of G.S. Section 130A-
309.211 requires that the CAP shall provide for the restoration of groundwater in
conformance with the requirements of Subchapter L of Chapter 2 of Title 15A of the
North Carolina Administrative Code (15A NCAC 02L). In accordance with G.S. Section
130A-309.211(b)(1), the groundwater corrective action plan shall include, at a minimum,
the following (CAP Content Section 1.C.a):
• A description of all exceedances of the groundwater quality standards, including
any exceedances that the owner asserts are the result of natural background
conditions
• A description of the methods for restoring groundwater in conformance with the
requirements of Subchapter L of Chapter 2 of Title 15A of the NCAC and a
detailed explanation of the reasons for selecting these methods
• Specific plans, including engineering details, for restoring groundwater quality
• A schedule for implementation of the groundwater corrective action plan
• A monitoring plan for evaluating the effectiveness of the proposed corrective
action and detecting movement of any constituent plumes
• Any other information related to groundwater assessment required by NCDEQ
In addition to CAMA, requirements for CAPs are also contained in 15A NCAC 02L
.0106(e), (h) and (i).
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Section 02L .0106(e)(4) requires implementation of an approved CAP for restoration of
groundwater quality at or beyond the compliance boundary in accordance with a
schedule established by the Secretary.
To comply with 02L .0106(h), CAPs must include (CAP Content Section 1.C.b):
• A description of the proposed corrective action and reasons for its selection
• Specific plans, including engineering details where applicable, for restoring
groundwater quality
• A schedule for the implementation and operation of the proposed plan
• A monitoring plan for evaluating the effectiveness of the proposed corrective
action and the movement of the constituent plume
This CAP Update will present an evaluation of the options available for corrective
action under 15A NCAC 02L .0106(j), (k), and (1) for the EAB and downgradient
additional source areas and, in the event corrective action is required under future
conditions, for the WAB.
• Under paragraph 0), corrective action would be implemented using remedial
technology for restoration of groundwater quality to the standards (02L)
• Under paragraph (k), a request for approval of a corrective action plan may be
submitted without requiring groundwater remediation to the standards (02L) if,
the requirements in (k) are met
• Under paragraph (1), a request for approval of a corrective action plan may be
submitted based on natural processes of degradation and attenuation if the
requirements in (1) are met
This CAP has been prepared in general accordance with the NCDEQ guidance
document Corrective Action Plan Content for Duke Energy Coal Ash Facilities, which
provides an outline of the technical content and format, presented in the NCDEQ's
letter dated September 10, 2019, provided in Appendix A. (CAP Content Section 1.C.c)
In addition to this groundwater CAP Update, the Roxboro ash basins are subject to
closure requirements under CAMA. Basin closure activities will provide source control
within the ash basins and are considered a component of the overall corrective action
for the site. The Roxboro ash basins meet the low -risk classification criteria set forth in
CAMA for CCR surface impoundments. On November 14, 2018, NCDEQ confirmed
that Duke Energy had established permanent water supplies for surrounding properties
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by August 31, 2018, and rectified prior dam safety deficiencies, reclassifying the ash
basins from its prior draft ranking of "intermediate" to "low -risk". Under G.S. Section
130A-309.214, a low -risk CCR surface impoundment may be closed by excavation,
closure -in -place, or a hybrid approach.
On April 1, 2019, NCDEQ issued a determination that the Roxboro CCR surface
impoundments to be closed by "movement of coal ash to an existing or new CCR,
industrial or municipal solid waste landfill located on -site or off -site" (Appendix A).
Closure for each ash basin is detailed in separate documents; therefore, this CAP
Update considers multiple ash basin closure scenarios: closure -in -place or closure -by -
excavation. Each closure scenario will be effective in addressing the ash basin source
area, which is an important part of the overall corrective action strategy. Groundwater
modeling simulations consistently indicate the closure -in -place and closure -by -
excavation scenarios have a similar effect on the concentrations of unit -specific
constituents of interest (COI) in groundwater.
1.4 List of Considerations by the Secretary for Evaluation of
Corrective Action Plans
(CAP Content Section 1.D.a through g)
Potential targeted active remedial alternatives for the EAB were developed using the
criteria included in the NCDEQ's CAP Guidance (NCDEQ, 2018). Although the GSA
and the DFAHA are non-CAMA sources, potential remedial alternatives were
developed using the same CAP guidance criteria. Groundwater quality data confirms
that constituents identified at the WAB do not exceed applicable 15A NCAC 02L .0202
groundwater quality standards at or beyond the ash basin compliance boundary;
therefore, groundwater corrective action under 15A NCAC 02L .0106 is not required for
the WAB at this time.
An evaluation of remedial alternatives was performed based on the following criteria:
• Protection of human health and the environment
• Compliance with applicable federal, state, and local regulations
• Long-term effectiveness and permanence
• Reduction of toxicity, mobility, and volume
• Short-term effectiveness at minimizing impact on the environment and local
community
• Technical and logistical feasibility
• Time required to initiate
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• Predicted time required to meet remediation goals
• Estimated Cost
• Community acceptance
In the evaluation of CAPS as specified in 02L .0106(i), the criteria includes:
• A consideration of the extent of any violations
• The extent of any threat to human health or safety
• The extent of damage or potential adverse impact to the environment
• Technology available to accomplish restoration
• The potential for degradation of the constituents in the environment
• The time and costs estimated to achieve groundwater quality restoration
• The public and economic benefits to be derived from groundwater quality
restoration
These 02L .0106(i) criteria form the basis for defining the screening criteria outlined in
Section 6.6 for use in evaluating remedial alternatives in Section 6.7.
In addition, institutional controls [provided by the restricted designation (RS)] may be
proposed by Duke Energy to limit access to groundwater use (15A NCAC 02L .0104).
Duke Energy owns and maintains property downgradient of the ash basins. The RS
designation may be requested for areas outside of an established compliance boundary
when groundwater might not be suitable for use as drinking water supply without
treatment. The RS designation is a temporary designation and is removed by the
NCDEQ Director upon a determination that the quality of the groundwater has been
restored to the applicable standards or when the groundwater has been reclassified by
the NCDEQ. NCDEQ is authorized to designate existing or potential drinking water
(Class GA groundwater) as RS where the Director has approved a CAP, or the
termination of corrective action, that will not result in the immediate restoration of such
groundwater to the standards established in 02L.
1.5 Facility Description
(CAP Content Section 1.E)
1.5.1 Location and History of Land Use
(CAP Content Section 1.E.a)
Roxboro is located on the southeast side of Hyco Reservoir in Semora, Person
County, North Carolina (Figure 1-1). The Plant began operations in 1966 as a
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Roxboro Steam Electric Plant SynTerra
coal-fired electrical generating station with additional generating units added in
1968, 1973, and 1980. Cooling water for Roxboro is provided by Hyco Reservoir
via the Intake Canal, which was created to serve this purpose. CCR materials,
composed primarily of fly ash and bottom ash, were historically managed by
depositing ash within the two ash basins: the EAB and the WAB. The EAB was
constructed in 1966 and the WAB was constructed in 1973. CCRs were deposited
in the basins predominately by hydraulic sluicing operations until the Plant was
modified for dry fly ash handling and the on -site industrial landfill for CCR
disposal was placed in service in the late 1980s. After DFA conversion in 1986, all
sluicing operations to the EAB were discontinued. Wet sluicing of bottom ash
and intermittent fly ash continued to the WAB until final system upgrades for
dry ash handling system were completed in December 2018. All bottom ash and
fly ash is currently handled dry and disposed within the industrial landfill or
transported offsite for beneficial use.
The Site is surrounded by commercial, rural residential, agricultural, and
wooded land (Figure 1-2 and Figure 1-3). Hyco Reservoir is the dominant feature
on the northern and western portion of the Site. Hyco Reservoir was formed
when Hyco River and its three main tributaries; North Hyco Creek, South Hyco
Creek, and Cobbs Creek were dammed in the early 1960s. The 3,750-acre Hyco
Reservoir has approximately 120 miles of shoreline with a normal water
elevation of approximately 410 feet (NAVD 88).
The Roxboro generating station and supporting facilities lie within an
approximately 6,095-acre parcel (including Hyco Reservoir) owned by Duke
Energy. Based on a review of available historical and aerial photography, the Site
consisted of a combination of agricultural land, rural residential, and woodlands
before to the formation of Hyco Reservoir. Figure 1-4 presents an aerial
photograph from 1951 prior to development of the Site and construction of Hyco
Reservoir (CAP Content Section 1.E.a).
Land use within a 0.5-mile radius of the EAB and WAB compliance boundaries
include an industrial facility (building materials manufacturing), agricultural
land (pasture), rural residential parcels, wooded land, a school (Woodland
Elementary School) and Hyco Reservoir. According to the Person County
Geographic Information System Department, part of the Duke Energy property,
including the Plant and the WAB, and the industrial facility property are zoned
General Industrial. The remaining portions of the Duke Energy property,
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including the EAB and all surrounding properties are zoned Residential (CAP
Content Section 1.E.a).
The EAB and WAB are the dominant features on the portion of the property west
of McGhees Mill Road and north of Semora Road. The ash basins are bound by
McGhees Mill Road to the east; Concord-Ceffo Road to the south, Semora Road
to the southwest and Hyco Reservoir to the west and north (CAP Content Section
5.b) (Figure 1-2 and Figure 1-3). Ridges east, south and west of the ash basins,
including a ridge positioned between the basins (represented by Dunnaway
Road), coincide with groundwater divides that provide control of groundwater
migration to within the former stream valleys.
1.5.2 Operations and Waste Streams Coincident with the Ash
Basins
(CAP Content Section 1.E.b)
Coal -Related Operational Storage and Waste Streams
Coincident to the Ash Basins
Industrial Landfill
The industrial landfill is a Solid Waste facility permitted in the late 1980s
(NCDEQ Permit No. 7302-INDUS). The industrial landfill, positioned above and
mostly within the EAB waste boundary, began operation in 1988. The Roxboro
landfill is permitted to receive CCRs and incidental amounts of other wastes
generated at the Roxboro Plant and other Duke Energy Corporation fossil
facilities. Over 90 percent of the waste managed at the landfill consists of fly ash,
bottom ash, and off -spec flue gas desulfurization (FGD) residue (gypsum). Other
wastes are defined in the landfill Operations Plan. In 2004, the industrial landfill
began operating in areas constructed with an engineered base liner system
(Phases 1— 6), located inside the waste boundary of the initial industrial landfill
footprint. Phases 1-5 of the Roxboro industrial landfill were constructed with an
engineered single flexible membrane liner system encompassing approximately
70.4 acres (Figure 1-2). Phase 6 was constructed with a double -engineered
flexible membrane liner system encompassing approximately 23.4 acres. Phase 1
initial waste placement began in 2004. Waste placement is currently occurring in
Phase 6.
Portions of the unlined industrial landfill extend beyond the waste boundary of
Phases 1 - 6 to the north, northeast and south; those areas are commonly referred
to as the halo area. Dry fly ash placed in the unlined portion of the industrial
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landfill, including the halo area, is unsaturated. The halo area is partially closed
with an engineered cap system on a portion of the western side. The remaining
halo area is covered with soil, which allows infiltration of precipitation into the
underlying CCR material.
Leachate from Phases 1— 6 of the industrial landfill was deposited by gravity
flow into the EAB until the spring of 2019. Leachate historically discharged in six
locations (LP-1 through LP-6) routed to the ash basin for treatment. As a
component to facilitate ash basin closure, the six leachate discharge points have
been consolidated to a single flow captured in a header system. The leachate
flow is routed to surge tanks that allow a steady flow of leachate to enter the
Plant wastewater system for treatment. Beginning in April 2019, a single
composite leachate sample (LP -A) is collected from a dedicated sampling port
upstream of the leachate holdings tanks.
Groundwater monitoring at the landfill consists of six groundwater monitoring
wells (GMW-6, GMW-7, GMW-8R, GMW-9, GMW-10 and GMW-11) installed
around the perimeter of the landfill. Monitoring well GMW-9 is identified as the
upgradient background well for the groundwater monitoring system.
Installation of monitoring wells GMW-6, GMW-9, and GMW-10 occurred in
March and October 2002, with piezometers, PZ-12 installed in May 2003 and PZ-
14 installed December 2009. Replacement wells installed have included GMW-7
in 2010, GMW-11 in 2011, and GMW-8R in 2018. Groundwater sampling related
to the landfill is performed on a semi-annual basis as described in the Water
Quality Monitoring Plan (WQMP) (revision dated June 19, 2019 pending
approval; submitted to the Division for approval on June 26, 2019) in accordance
with NCDEQ DWM Solid Waste Section Permit No. 7302-INDUS associated with
the lined landfill. The monitoring includes the six landfill monitoring wells.
Dry Fly Ash silos, transport, and handling area (DFAHA)
The DFA silos, transport, and handling operational area is located adjacent to the
western side of the GSA (Figure 1-2) and is used for processing of DFA for
beneficial use, storage and management of DFA prior to disposal, and transport
of DFA to the industrial landfill. DFA is delivered to the silo area by above-
ground pipes via a pressure dry blower method. Five silos (Silos #1 through #5);
80 feet in height and 50 feet in diameter each with a capacity of 5,000 cubic yards
are used in the storage process. The silo area was developed in 1986 with Silos
#1 thorough #4 and associated concrete pavement loading areas and concrete
paved roadways with curbing developed from 1986 through 1990. Silos #1
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through #4 were brought into service from 1986 to 1990 with Silo #5 available for
service in 2016. The paved areas were designed to capture storm water and dust
suppression water in curbing and surface area catch basins, which route the
water via in -ground steel pipes to a sump located southeast and adjacent to Silo
#4. Wastewater from the sump was historically deposited in the EAB for
treatment. Flows from the sump are now routed to the Plant wastewater
treatment system for processing. Prior to initial development, the area was
vacant land. Additional development to the southwest includes an Operations
and Maintenance (O&M) building and the electrical substation to power the Unit
3 cooling towers and associated booster pumps. According to available historical
construction plans and site personnel, structural fill (including DFA) was not
used during site development for this area. Fugitive DFA material from storage,
management, and transportation operations is present on and within separations
of the concrete roadway and non -paved areas.
Gypsum Storage Area (GSA)
The Gypsum Storage Area is located adjacent to the DFAHA and north of the
EAB (Figure 1-2). FGD technology was installed at the Plant in 2008 to reduce
SO2 emissions for all the steam units. A by-product of the FGD process is the
production of calcium sulfate (gypsum) which can be utilized to produce
gypsum wallboard. To accommodate storage of gypsum intended for beneficial
reuse, the 12.5-acre GSA constructed to accommodate up to 300,000 tons of
gypsum. Prior to construction, a portion of the future GSA was occupied by a
concrete batch plant (removed in the spring of 2007). The remaining areas were
vacant land.
To accommodate GSA development, approximately 131,319 cubic yards of DFA
were used as structural fill in topographical low lying areas. Notification for
construction using coal ash as structural fill was accepted in a letter, dated
December 16, 2005, from NCDENR DWM to Progress Energy Service Company,
LLC (Appendix A). The use of DFA as structural fill was in accordance with
notification requirements with Section .1700 of the Solid Waste Management 15A
NCAC 13B Rules. A stipulation that DFA would not be placed within 50 feet of a
water body, within 50 feet of any remaining wetlands that remain unfilled, and
within 2 feet of the seasonal high groundwater table was documented. A
geosynthetic clay liner (GCL) with a plastic laminated geomembrane was
installed following final grading. The GCL was placed laminate side up directly
over a six-inch layer of DFA followed by a six-inch layer of DFA, 12-inches of fill
soil and a six-inch layer of top soil. Notification of construction completion was
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submitted to NCDENR DWM on March 27, 2007 with deed recordation provided
on August 24, 2007, revised November 27, 2007 (Appendix A).
DFA as structural fill was placed in the western and central portions of the GSA
to fill in former topographical low-lying areas. Using preconstruction
topographic maps and final grade drawings (Progress Energy, August, 2006) and
geotechnical boring information obtained during construction, up to
approximately 30 feet of DFA was placed in the western portion and up to 17 feet
of DFA was placed in the central portion of the unit. According to the
Notification of Recordation of Structural Fill filed with the Person County
Register of Deeds on October 27, 2007 (Appendix A), the volume of DFA used as
structural fill is approximately 131,319 cubic yards.
Details regarding assessment activities associated with the GSA are provided in
the Gypsum Storage Area Structural Fill (CCB 003) Assessment Report — Roxboro
Steam Electric Plant (SynTerra, 2017a).
Non -Coal -Related Operations and Waste Streams Coincident to
the Ash Basins
LCID Landfill
The LCID landfill is a Solid Waste facility permitted to operate in 2002 (NCDEQ
DWM Permit No. 73-D). The LCID landfill is located entirely within the
compliance boundary and adjacent to and partially over the western lobe of the
EAB, abutting the Dunnaway Road entrance to the Plant (Figure 1.2). General
construction debris and inert material, including asbestos containing material,
was disposed in the approximate 4.5 acre LCID landfill. The LCID landfill has
not been used in many years but maintains a Permit to Operate. The landfill has
an interim cover of soil and vegetation. Based on recent geophysical data
evaluations (September 2019), approximately 1.8 acres of LCID materials is
underlain by suspected CCR materials which follows areas of historic
topographic lows.
Non -Coal -Related Waste Incidents
Non -coal related operations or environmental incidents were not identified to
have occurred in the vicinity of the EAB or WAB. Incidents at Roxboro that
initiated notifications to NCDEQ consisted of releases of petroleum related
constituents occurring only in the vicinity of the power plant or related to off -site
petroleum releases. The power plant is located in an area separated from the ash
basins by NPDES-permitted wastewater ponds (Figure 1-2 and Figure 1-3).
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1.5.3 Overview of Existing Permits and Special Orders by
Consent
(CAP Content Section 1.E.0
NPDES Permit
Duke Energy is authorized to discharge wastewater from the Roxboro ash basins
to Hyco Reservoir (Outfall 003) in accordance with NPDES Permit NC0003425,
which is currently under renewal. The facility has two permitted outfalls in the
current NPDES discharge permit. The sources of wastewater for these outfalls
include non -contact cooling water, ash basin discharge, sanitary waste, cleansing
and polishing water, low volume wastes, and storm water from process areas.
The facility operates the following outfalls (except where subsequently noted,
descriptions below are excerpted directly from the existing NPDES permit):
Internal Outfall 002: Ash Pond Treatment System. Discharged directly to the
heated water discharge pond and ultimately to Hyco Reservoir through Outfall
003. The ash basin receives ash transport water, low volume wastewater, runoff,
cooling tower blowdown from unit number 4, and domestic sewage treatment
plant effluent.
• Outfall 003: Heated Water Discharge Canal System. Discharged directly to
Hyco Reservoir. Discharge from once -through cooling water, stormwater, seepage
from ash pond dam, anhydrous ammonia testing waters and effluent from the ash
pond (Outfall 002).
Internal Outfall 005: Cooling Tower Blowdown System. Discharged directly to
the heated water discharge pond and ultimately to Hyco Reservoir through
Outfall 003. Discharge from cooling tower blowdown from unit number 4 into
the ash transport system, and ultimately into the ash pond (Outfall 002), and low
volume waste treatment system.
Outfall 006: Coal Pile Runoff Treatment System. Discharged directly to Hyco
Reservoir. Discharge from runoff from the coal pile and other handling areas,
runoff from the limestone and emergency gypsum stack, raw water tank drainage,
incidental leakage from absorbent seals, and the truck wheel wash water. These
waters are routed to a retention pond for treatment by neutralization,
sedimentation, and equalization prior to being discharged directly to Hyco
Reservoir.
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• Internal Outfall 008: Domestic Wastewater Treatment System. Discharge of
effluent from the domestic treatment system into the ash pond or the low volume
waste treatment system (Outfall 012) upon completion of construction.
• Internal Outfall 009: Chemical Metal Cleaning Treatment System. Discharge
from chemical metal cleaning wastes into the ash pond or the low volume waste
treatment system (Outfall 012) upon completion of construction.
• Internal Outfall 010: Flue Gas Desulfurization Treatment System. Discharges
to the western discharge canal. Discharge from FGD wet scrubber treatment
system consisting of a settling pond and a bioreactor.
• Internal Outfall 011: Flue Gas Desulfurization Treatment System. Upon
completion of construction operate a FGD system discharging to the low volume
waste treatment system (Outfall 012) or the discharge canal.
• Internal Outfall 012A: Low Volume Wastes Treatment System. Upon
completion of construction of a waste treatment system discharge landfill
leachate, silo wash water, contact and non -contact storm water runoff in the
discharge canal.
• Outfall 012B: Low Volume Wastes Treatment System. Upon completion of
construction of a low volume waste treatment system discharge low volume
waste, metal cleaning wastes, ash silo wash water, cooling water from unit 4,
anhydrous ammonia testing waters and emergency flows, domestic sewage
treatment plant effluent, cooling tower blowdown and storm water runoff in the
discharge canal.
The Roxboro Plant is also authorized to discharge stormwater to Hyco Reservoir
in accordance with NPDES Permit NCS000581.
Special Order by Consent
A Special Order by Consent (SOC) was issued to Duke Energy on August 15,
2018 (Appendix A), to address seeps from the ash basins during the separate and
independent process of EAB and WAB closures. The locations included in the
SOC are subject to the monitoring and evaluation requirements contained in the
SOC. The SOC provided definition for constructed seeps (seeps that [1] are on or
within the dam structures and [2] convey wastewater via a pipe or constructed
channel directly to a receiving water] or non -constructed seeps (seeps that do not
meet the "constructed seep" definition). Ash basin decanting and dewatering is
expected to substantially reduce or eliminate the seeps.
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The SOC requires Duke Energy to accelerate ash basin decanting. After
completion of decanting, remaining seeps, if not dispositioned in accordance
with the SOC, will be characterized. After post -decanting seep characterization,
an amendment to the CAP and/or Closure Plan, to address remaining seeps
might be required. The SOC terminates 180 days after decanting or 30 days after
approval of the amended CAP. No free or ponded water is present in the EAB;
therefore, decanting is not anticipated for the EAB. Passive decanting through
the cessation of sluicing at the WAB began in December 2018. Active decanting
of the WAB cannot commence until approval of the revised NPDES permit
currently under review by NCDEQ. The SOC requires completion of decanting
by June 30, 2020.
Solid Waste Permits
There are two landfills permitted by the NCDEQ Division of Waste Management
(DWM), Solid Waste Section (SWS) associated with Roxboro:
1. The industrial landfill (NCDEQ Permit No. 7302-INDUS) is located on top,
adjacent, and mostly within the footprint of the EAB waste boundary.
2. The land clearing and inert debris (LCID) landfill (NCDEQ Permit No. 73-
D) is located along the western margin of the western lobe of the EAB.
Erosion and Sediment Control Permits
Erosion and Sediment Control (E&SC) permits are required for construction and
excavation related activities including general construction projects and
environmental assessment and remediation projects if the area of disturbance is
greater than one acre. Multiple E&SC permits have been obtained for various
projects implemented at the Roxboro, including environmental related projects,
such as well installation and access road construction. Most of the E&SC permits
are closed as the related projects are completed. E&SC permits will continue to
be obtained prior to implementation of additional construction projects, as
appropriate.
Air Quality/Hazardous Waste Permits
The Roxboro Plant holds a Title V air quality operating permit (#001001T56) and
a hazardous waste permit (NCD000830653) as a RCRA small quantity generator.
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2.0 RESPONSE TO CSA UPDATE COMMENTS IN SUPPORT OF CAP
DEVELOPMENT
(CAP Content Section 2)
2.1 Facility -Specific Comprehensive Site Assessment (CSA)
Comment Letter and Draft Comments
(CAP Content Section 2.A)
On October 31, 2017, Duke Energy submitted a CSA Update to NCDEQ (SynTerra,
2017d). In a letter from NCDEQ to Duke Energy dated May 7, 2018, NCDEQ stated that
sufficient information had been provided in the CSA Update to allow preparation of a
CAP Update. The letter also provided CSA-related comments and items required to be
addressed prior to or as part of the CAP Update submittal (Appendix A).
On June 7, 2018, NCDEQ Raleigh Regional Office (RRO) submitted an email with the
subject: Draft comprehensive review comments for Mayo and Roxboro and attached the
report titled 'Roxboro CSA Update Draft review (3-16-2018)' to Duke Energy (Appendix
A). The email outlines additional draft comments to the 2017 CSA Update.
2.2 Duke Energy's Response to NCDEQ CSA Comment Letter
(CAP Content Section 2.B and 2.B.a.)
Responses to each of the NCDEQ comments within the May 7, 2018 letter and the draft
March 16, 2018 document are summarized in Appendix B. Additional content related to
NCDEQ's comments are either included within sections of this CAP Update or in
appendices to this CAP Update, such as the groundwater modeling reports (Appendix
G and Appendix H) and surface water evaluation reports (Appendix J).
Activities that directly addressed NCDEQ comments concerning the Roxboro CSA
Update include:
• Groundwater samples continued to be collected on a quarterly basis as part of
the Interim Monitoring Plan (IMP) after CSA Update submittal. Additional
sampling results augmented the groundwater quality database. Comprehensive
groundwater analytical data are included in Appendix C, Table 1.
• Additional soil assessment, including assessment of soil at NCDEQ approved
locations surrounding the ash basins and associated impoundment perimeters,
was performed. Discussion of soil assessment results are presented in Sections
6.1 and 6.10.
• Additional assessment of surface water and sediment from the Intake Canal and
a jurisdictional stream (Stream 11A) southwest of the EAB was performed during
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in April/May 2018 and May 2019. There were no constituent concentrations
greater than 02B surface water standards attributable to the groundwater plume.
A report summarizing the sampling, results, evaluation, and conclusions of the
surface water evaluation related to the Intake Canal was submitted to NCDEQ
on March 21, 2019 and revised December 2019 for results related to Stream 11A is
included in Appendix J.
• An evaluation of potential groundwater migration and associated impacts to
surface water under future conditions was conducted for the Intake Canal and
Stream 11A with the results of the evaluation presented in Appendix J. There
were no constituent concentrations predicted to be greater than 02B surface
water standards attributable to the groundwater plume.
• Background groundwater and soil datasets and background threshold values
(BTVs) were updated to include data through December 2018. Information about
background determinations is presented in Section 4. Updated soil BTVs are
listed on Table 4-2 and updated groundwater BTVs are listed on Table 4-3.
• The Roxboro flow and transport model and geochemical model were updated to
incorporate additional assessment data and information. The models were used
to evaluate current and predicted future Site conditions. The flow and transport
model report is provided as Appendix G. The geochemical model report is
provided as Appendix H.
• The Roxboro CSM was updated to reflect the most recent understanding of Site
conditions based upon updated Site data, assessment results, and model
predictions. The updated CSM is presented in Section 5.0.
• A bedrock groundwater monitoring, HWMW-1BR, was install adjacent to MW-1,
located downgradient and northeast of the WAB main dam to assess bedrock
groundwater quality (Figure 1-3). The well borehole was installed in December
2018 using air hammer drilling techniques. The shallow bedrock monitoring
well was installed to the first measureable water bearing fracture (> 1 gpm) in the
bedrock, similar to the previous investigations conducted at the site. The general
lithology consisted of saprolitic micaceous clayey silts to a depth 14 feet bgs with
saturated conditions encountered at approximately 7.5 feet bgs. A transition
zone of interlayered partially weathered granitic schist was determined from 14
feet bgs to a depth of 44 feet bgs. The bedrock interface was intercepted at 44 feet
bgs and characterized as a fine-grained, foliated black and white mica schist with
potassium feldspar and epidote. A 6-inch diameter Schedule 40 PVC surface
casing was installed to a depth of 49 feet bgs, approximately 5 feet into bedrock.
The boring was subsequently drilled to a depth of 102 feet bgs to capture a water
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bearing fracture zone determined at 95 - 97 feet bgs. A 2-inch diameter 10-foot
length pre -packed well screen was set from 91 to 101 feet bgs. Following well
installation, the well was developed for a minimum of two hours. Well
construction information, along with boring and well construction logs, is
summarized in the well construction table provided in Appendix Q.
Groundwater analytical results for HWMW-1BR are provided in Appendix C,
Table 1. In summary, no boron was detected above the laboratory reporting
limit with remaining constituents detected at concentrations below approved
bedrock background levels.
• Groundwater monitoring well clusters, MW-38 and MW-39, were installed in the
two lobes south of the WAB extension impoundment to access groundwater
quality in these areas. A Technical Memorandum, Roxboro Steam Electric Plant
West Ash Basin (WAB) Southern Extension Impoundment (SEI) — Additional Wells
(dated February 4, 2019), was submitted to NCDEQ Raleigh Regional Office
(RRO) on February 6, 2019 to provide the rationale and location for two
proposed well clusters, MW-38 and MW-39, in the southern portions of the WAB
SEI. Owing to access limitations to the MW-38 location and NCDEQ RRO
concurrence for the MW-39 location, a revised Technical Memorandum (Revision
1), dated February 15, 2019, was submitted to NCDEQ RRO on February 18,
2019. In submittal of the revised Technical Memorandum, approval for
proposed monitoring well cluster location MW-39 was requested. At the time of
issuance, a feasible access route had not been established to monitoring well
cluster MW-38. Duke Energy requested to seek approval at a later date from the
NCDEQ RRO for the proposed MW-38 location, once a viable access route was
established. The NCDEQ RRO approved the revised February 15, 2019 Technical
Memorandum in email correspondence dated March 7, 2019. A second revised
Technical Memorandum, dated May 16, 2019, provided an alternate location for
the MW-38 well cluster owing to access challenges. The NCDEQ RRO approved
the alternate location of MW-38 in an email correspondence dated June 10, 2019.
The locations of the MW-38 and MW-39 well clusters are shown in Figure 1-3,
CAP Update.
The MW-39 well cluster was installed in April 2019 using air hammer drilling
techniques. During drilling, unsaturated conditions were observed in the
saprolite zone, leading to the installation of transition zone (D) and bedrock (BR)
wells without the accompaniment of a saprolite (S) well. The shallow bedrock
monitoring well was installed to the first measureable water bearing fracture (> 1
gpm) in the bedrock, similar to the previous investigations conducted at the site.
The general lithology consisted of saprolitic micaceous silty sands and
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alternating sequences of partially weather rock to a depth 48 feet bgs with
saturated conditions encountered at approximately 27.5 feet bgs. The bedrock
interface was intercepted at 48 feet bgs and characterized as a fine-grained,
granitic gneiss with potassium feldspar and quartzite. For the bedrock well
(MW-39BR), a 6-inch diameter Schedule 40 PVC surface casing was installed to a
depth of 55 feet bgs, approximately 6 feet into bedrock. The boring was
subsequently drilled to a depth of 250 feet bgs to capture a water bearing fracture
zone determined at 203 feet bgs. A 2-inch diameter 15-foot length pre -packed
well screen was set from 195-210 feet bgs. The remainder of the borehole was
backfilled with hydrated bentonite pellets to approximately 7 feet below the
bottom of the screen. The transition zone well, MW-39D was installed to a depth
of 49 feet bgs using a 2-inch 10-foot length pre -packed well screen set from 39-49
feet bgs. Following well installation, the wells were developed for a minimum of
two hours. Well construction information, along with boring and well
construction logs, is summarized in the well construction table provided in
Appendix Q.
The MW-38 well cluster was installed in September - November 2019 using air
hammer drilling techniques. As with the MW-39 cluster, no saturated conditions
were observed in the saprolite zone, leading to the installation of transition zone
(D) and bedrock (BR) wells without the accompaniment of a saprolite (S) well.
The shallow bedrock monitoring well was installed to the first measureable
water bearing fracture (> 1 gpm) in the bedrock, similar to the previous
investigations conducted at the site. The general lithology consisted of saprolitic
micaceous silty sands and alternating sequences of partially weather rock to a
depth 54 feet bgs with saturated conditions encountered at approximately 29 feet
bgs. The bedrock interface was intercepted at 54 feet bgs and characterized as a
fine-grained, granite / granitic schist with potassium feldspar and quartzite. For
the bedrock well (MW-39BR), a 6-inch diameter Schedule 40 PVC surface casing
was installed to a depth of 55 feet bgs. The boring was subsequently drilled to a
depth of 600 feet bgs to intercept potential water bearing fractures. During
boring installation, no water bearing fractures were observed to the bottom of the
well. Subsequently, packer testing was conducted to confirm visual
observations; however, packer testing did not reveal water bearing fractures with
the exception of a potential fracture zone between 95-105 feet bgs. To further
support field observations and packer testing results, geophysical logging of the
MW-38BR boring was conducted between October 3-4, 2019 by GEL Solutions,
Inc. (GEL). The GEL geophysical logging report is provide in Appendix F. No
water bearing factures were determined based on the geophysical logging with
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the exception of a fracture zone observed between 95-105 bgs. Based on the field
and geophysical logging information, a 2-inch diameter 15-foot length pre -
packed well screen was set from 95-110 feet bgs. The bottom of the boring was
backfilled with a bentonite cement grout from 600 feet bgs to 145 feet bgs
followed by hydrated bentonite pellets from 145 feet to 125 bgs. The transition
zone well, MW-38D was installed to a depth of 54 feet bgs using a 2-inch 5-foot
length pre -packed well screen set from 49 feet to 54 feet bgs. Following well
installation, the wells were developed for a minimum of two hours. Well
construction information, along with boring and well construction logs, is
summarized in the well construction table provided in Appendix Q.
Groundwater analytical results for MW-39 well cluster are provided in the
Updated Comprehensive Analytical Data Tables as provided in Appendix C of
the CAP Update report. In summary, no boron was detected above the
laboratory reporting limit with remaining constituents detected at concentrations
below approved transition zone and bedrock background levels.
Groundwater analytical data is not available for the MW-38 cluster; however,
analytical results for MW-39 well cluster are provided in Appendix C, Table 1.
For the MW-39 cluster, no boron was detected above the laboratory reporting
limit with remaining constituents detected at concentrations below approved
transition zone and bedrock background levels.
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3.0 OVERVIEW OF SOURCE AREAS BEING PROPOSED FOR
CORRECTIVE ACTION
(CAP Content Section 3)
The EAB and WAB are the only CCR-regulated surface impoundments at Roxboro. The
industrial and the LCID landfills, which are regulated by NCDEQ DWM SWS, are
considered in the CAP Update. While not regulated by CAMA, the DFAHA and the
GSA units are located downgradient to the EAB and are considered in this CAP Update.
Figure 1-2 and Figure 1-3 shows the location of the ash basin waste boundaries and
compliance boundaries, including the industrial landfill waste and compliance
boundary (Figure 1-2) (CAP Content Section 3.A and 3.A.a). Other facilities at the Site
that are not coincident with the EAB or WAB are addressed herein. A consensus was
reached with the NCDEQ DWR regarding potential sources not considered for
corrective action as part of this CAP Update was provided in a letter from NCDEQ to
Duke Energy dated April 5, 2019 (Appendix A; CAP Content Section 3.B). A brief
description of these facilities, their status for consideration as part of the source areas to
be evaluated as part of this CAP Update, and the rationale is provided in Table 3-1.
Potential Source Areas Not Evaluated for Corrective Action
Two potential additional source areas, independent of the EAB and WAB, are
referenced in this CAP Update. The areas are associated with now abandoned, or no
longer active, historical operational features of the Plant. The potential source areas
have verified residual CCR present, which is planned for removal in the future.
Decommissioned Sluice Line Corridor Area
Residual CCR material identified in an area of the abandoned sluice line corridor will
be removed as a part of the sluice line decommissioning project. An area of the now
abandoned and mostly removed fly ash and bottom ash sluice lines, located just north
of the WAB, has residual ash present on the ground surface (Figure 1-3). The sluice lines
were permanently taken out of service in December 2018. Elevated COIs present in
groundwater monitoring well MW-5D, located north of the WAB compliance boundary,
downgradient of the WAB, resulted in a field investigation, which revealed the
presence of residual ash likely due to maintenance of the historic sluice lines. To
facilitate future ash basin closure, wastewater flows were redirected from the ash basins
to newly installed Plant wastewater treatment facilities. Decommissioning of the now
abandoned sluice line piping is currently in progress. Upon completion of piping and
support removal, the area north of the WAB, near MW-5D, will be remediated such that
visible CCR is removed.
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Historical Eastern Discharge Canal Deposition Area
CCR material identified in an area of the eastern discharge canal will be removed.
Elevated COIs present in groundwater monitoring well MW-03BR, located just beyond
the northeast corner of the GSA (Figure 1-2), resulted in review of historical documents
and field investigation. Review of historical figures revealed that the eastern discharge
canal outlet alignment was modified in the late 1980's resulting in an area likely used as
a wastewater polishing pond, to have been abandoned with CCR residual remaining in
place. Roxboro General Site Arrangement drawing (D-4503) (revision 4 referenced "As -
Built"), dated November 15, 1990, identifies the likely historical polishing pond area in
Grid 12-A noted as "area drained and ash covered with earth". Drawing D-4503 was
included as Exhibit 5 in the October 31, 2017 letter from Duke Energy to NCDEQ, titled
Response to August 25 Letter, regarding compliance boundaries. Field investigation of the
area confirmed the presence of coal ash residuals. Duke Energy is in the process of
developing a plan to remove visible ash in the localized area of the historic polishing
pond.
Sources Not Connected to the Ash Basin/To Be Addressed In
Subsequent CSAs
(CAP Content Section 3.B)
Coal Pile Storage Area
The coal pile storage area occupies approximately 20 acres and is located in the north -
central portion of the Plant (Figure 1-2). Surface water runoff from the area currently
discharges directly to Hyco Reservoir through NPDES Outfall 006; however, the
construction of a coal pile retention basin to capture runoff is planned for 2020 in the
adjacent, undeveloped area to the northwest of the coal pile storage area. The coal pile
storage area is bounded to the north by the coal rail line followed by Hyco Reservoir
and to the east by the Intake Canal. The coal pile storage area is bounded to the south
by the powerhouse of the Roxboro Plant with ancillary structures and to the west by the
limestone storage area. The coal pile storage area is located separate from and not
considered coincident to the Roxboro ash basins.
Pursuant to technical direction provided in a NCDEQ September 8, 2017 letter, "Duke
Energy must ultimately address soil and groundwater contamination resulting from all
primary and secondary sources at the coal ash facilities, not just the CCR surface
impoundments. Other primary sources include CCR storage areas, raw coal piles and
structural fills." Additional clarification was provided in correspondence from the
NCDEQ dated April 5, 2019 (Appendix A), which required submittal of a CSA of
sources not associated with the ash basins including the coal pile storage area. A Coal
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Pile Groundwater Assessment workplan, dated May 2, 2019, was submitted by Duke
Energy to the NCDEQ on May 7, 2019. Approval of the workplan was provided by
NCDEQ on May 21, 2019 with the caveat that the assessment activities and results be
provided in the CAP Update report with results provided in the geochemical and flow
and transport modeling evaluation. In a follow-up correspondence from NCDEQ,
dated June 14, 2019, the NCDEQ stated the coal pile assessment could be included in a
separate CSA with submittal required by March 31, 2020.
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4.0 SUMMARY OF BACKGROUND DETERMINATIONS
(CAP Content Section 4)
Metals and inorganic constituents, typically associated with CCR material, are naturally
occurring and present at background locations not affected by the ash basin operations.
The metals and inorganic constituents occur in soil, groundwater, surface water, and
sediment. Background analytical results are used to compare detected constituent
concentration ranges from the source area relative to native conditions.
The statistically derived background values for the site are used for screening of
assessment data collected in areas of potential migration of COIs from a source area. If
the assessment data concentrations are less than background, it is likely COI migration
has not occurred in the area. If the assessment data concentrations are greater than
background, additional lines of evidence are used to determine whether the
concentrations represent migration from a source area. Additional lines of evidence
include, but may not be limited to:
• Evaluation of whether the concentration is within the range concentrations
detected at the Site, or within the range for the region
• Evaluation of whether there is a migration mechanism such as through hydraulic
mapping (across multiple flow zones), flow and transport modeling, and
understanding of the CSM
• Evaluation of concentration patterns (i.e., do the patterns represent a discernable
plume or migration pattern?)
• Consideration of natural variations in Site geology or geochemical conditions
between upgradient (background locations) and downgradient areas
• Consideration of other constituents present at concentrations greater than
background values.
Roxboro and nine other Duke Energy facilities (Allen Steam Station, Belews Creek
Steam Station, Buck Steam Station, Cape Fear Steam Electric Plant, Cliffside Steam
Station, Dan River Steam Station, Marshall Steam Station, Mayo Steam Electric Plant,
and Riverbend Steam Station) are situated in the Piedmont physiographic province of
north -central North Carolina. The nine Duke Energy facilities are located within a 180-
mile radius from Roxboro. Statistically derived background values from these facilities
provide a geographic regional background range for comparison. Generally,
background values derived from the Piedmont facilities are similar, with some
exceptions.
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As more background data become available, the background values may be updated to
continue to refine the understanding of background conditions. However, these
multiple lines of evidence, and additional steps in the evaluation process, will continue
to be important tools to distinguish between background conditions and areas affected
by constituent migration.
Background sample locations were selected to be in areas that represent native
conditions not affected by the Site's coal ash basins or additional source areas (Figure 4-
1) (CAP Content Section 4.A). Background soil and groundwater locations approved by
NCDEQ, as well as statistically derived BTVs, are detailed in Sections 4.1 and 4.2. BTVs
were not calculated for surface water and sediment; however, background locations for
surface water and sediment were approved by NCDEQ as part of the evaluation of
potential groundwater to surface water impacts (Appendix J) and are detailed in
Sections 4.3 and 4.4.
4.1 Background Concentrations for Soil
The locations of the background soil borings are shown on Figure 4-1. The soil
background dataset with the appropriate protection of groundwater (POG) preliminary
soil remediation goals (PSRGs) and BTVs is included in Appendix C, Table 4 (CAP
Content Section 4.B). The background soil dataset includes samples collected from
multiple depth intervals. The background soil boring locations, unsaturated depth
interval, and number of discrete samples collected from the unsaturated soil depth
interval included in the Table 4-1. All samples were collected from depth intervals
greater than 0.5 feet below the ground surface and greater than 1 foot above the
seasonal high water table.
The suitability of each of these locations for evaluating background conditions was
addressed in a technical memorandum to NCDEQ dated May 26, 2017. In a response
dated July 7, 2017, NCDEQ approved use of the soil data for determination of BTVs
(NCDEQ, 2017). BTVs were calculated using data from background unsaturated soil
samples collected June 2015 to April 2017 and in accordance with the Revised Statistical
Methods for Developing Reference Background Concentrations for Groundwater and Soil at
Coal Ash Facilities (HDR Engineering, Inc. and SynTerra, 2017). Calculated soil BTVs
were submitted to NCDEQ in an Updated Background Threshold Values for Soil Technical
Memorandum, dated August 28, 2017. NCDEQ provided comments and conditional
approval of BTVs in a response letter dated September 1, 2017 with final approval on
May 23, 2018 (Appendix A).
Soil BTVs at Roxboro were updated in 2019 and are provided, along with the original
soil BTVs from 2017 for comparison, in Table 4-2 (CAP Content Section 4.B). The
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updated BTVs were calculated using data from background unsaturated soil samples
collected February 2015 to July 2017 but the 2019 dataset retained extreme outlier
concentrations when data validation and geochemical analysis of background
groundwater concentrations indicated that those outlying concentrations did not result
from sampling error or laboratory analytical error. The approach used to evaluate
whether extreme outlier concentrations should be retained in background soil datasets
is presented the technical memorandum prepared by Arcadis U.S., Inc. (Arcadis), titled,
"Background Threshold Value Statistical Outlier Evaluation —Allen, Belews Creek, Cliffside,
Marshall, Mayo, and Roxboro Sites,". which was provided as an attachment to the Updated
Background Threshold Values for Constituent Concentrations in Groundwater (SynTerra,
2019e). The updated BTVs were calculated in accordance with the Revised Statistical
Methods for Developing Reference Background Concentrations for Groundwater and Soil at
Coal Ash Facilities (HDR Engineering, Inc. and SynTerra, 2017).
4.2 Background Concentrations for Groundwater
The groundwater background dataset with the appropriate 02L standards, IMAC, and
BTVs is included in Appendix C, Table 1 (CAP Content Section 4.C). The groundwater
system related to the ash basins is divided into the following three flow zones to
distinguish the interconnected groundwater system: the shallow (surficial) flow zone,
deep (transition) flow zone, and the bedrock flow zone. However, the shallow flow
zone is almost entirely unsaturated for most portions of the site with saturated
conditions primarily observed in monitoring wells situated near surface water features,
such as the Plant NPDES-permitted wastewater ponds and the Intake Canal. The flow
zones and background groundwater monitoring wells installed within the viable flow
zone include:
• Deep flow zone: BG-1, MW-15D, and MW-18D
• Bedrock flow zone: BG-1BR, MW-10BR, MW-14BR, MW-15BR, MW-18BR, and
MW-19BRL.
The locations of the background monitoring wells are shown on Figure 4-1. The
suitability of each of these locations for background purposes was evaluated in the
Background Threshold Values for Groundwater technical memorandum (May 26, 2017).
Identified groundwater data appropriate for inclusion in the statistical analysis to
determine BTVs was approved by NCDEQ in a response letter dated July 7, 2017
(Appendix A). Calculated groundwater BTVs were submitted to NCDEQ in an Updated
Background Threshold Values for Groundwater Technical Memorandum, dated August 16,
2017. NCDEQ provided comments and approval of BTVs in a response letter dated
September 1, 2017 (Appendix A).
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Groundwater BTVs in each groundwater flow zone at Roxboro were updated in 2019
with the inclusion of five additional background groundwater monitoring wells.
Background wells BG-2BR, MW-26BR, MW-29BR, MW-30BR, and CCR-112BR-BG are
screened in the bedrock flow zone. The updated BTVs were calculated using
concentration data from background groundwater samples collected November 2010 to
December 2018. BTVs were calculated in accordance with the Revised Statistical Methods
for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash
Facilities (HDR Engineering, Inc. and SynTerra, 2017).
The updated background datasets for each flow system were presented in the report
Updated Background Threshold Values for Constituent Concentrations in Groundwater
(SynTerra, 2019) provided to NCDEQ on June 13, 2019. The updated background data
set for each hydrogeologic flow zone consists of an aggregate of total (non -filtered)
concentration data pooled across the background monitoring wells installed within that
flow layer. The 2017 and 2019 groundwater background values in each groundwater
flow zone at Roxboro, including a range of background values for the Piedmont, are
provided in Table 4-3 (CAP Content Section 4.C). The use of groundwater BTVs is
currently under appeal.
4.3 Background Concentrations for Surface Water
Background surface water sample locations are located upgradient from, or outside of,
potential groundwater migration from a source area to surface water. Surface water
background sample locations are outside of future groundwater to surface water
migration pathways as determined by groundwater predictive modeling results
(Appendix G).
Background surface water sample locations include three locations (SW-1, SW-2 and
SW-3) in Hyco Reservoir, located west of a topographic ridge (groundwater divide)
separate from the WAB. A background surface water sample (RSW-6) was also
collected from the Intake Canal of Hyco Reservoir, which is located approximately 1,500
feet northeast of the EAB eastern discharge canal discharge point and outside of
potential groundwater impacts based on empirical data from the groundwater
monitoring network. Surface water sample locations are shown on Figure 4-1.
Background surface water data are used for general comparative purposes. The
analytical results provide a comparative range of naturally occurring constituent
concentrations present at background locations. Surface water samples from the RSW-6
background location have been collected in accordance with NCDEQ guidance as part
of the comprehensive sampling event in April/May 2018 used to assess surface water
compliance for implementation of corrective action under 15A NCAC 02L .0106(k) and
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(1). Analytical results from each background surface water sample location indicate
detected constituent concentrations are less than 02B standards. Background surface
water analytical dataset ranges compared to 02B and United States Environmental
Protection Agency (USEPA) criteria are included in Table 4-4 (CAP Content Section 4.D).
Background surface water analytical results compared with 02B criteria are included in
Appendix C, Table 2 (CAP Content Section 4.D).
4.4 Background Concentrations for Sediment
Background sediment sample locations are co -located with background surface water
sample locations in the Hyco Reservoir (SW-1, SW-2 and SW-3) and the Intake Canal
(RSW-6). Background sediment sample locations are located upgradient, or outside
potential groundwater migration from the source areas to sediment. Groundwater
predictive modeling shows that sediment background sample locations remain outside
future areas of impact from the source area.
The background sediment sample locations are shown on Figure 4-1. Background
sediment data are used for general comparative purposes. The analytical results
provide a comparative range of naturally occurring constituent concentrations present
at background locations. Background sediment analytical dataset ranges are presented
in Table 4-5 (CAP Content Section 4.E). Background sediment analytical results are
presented in Appendix C, Table 5 (CAP Content Section 4.E).
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5.0 CONCEPTUAL SITE MODEL
(CAP Content Section 5)
The conceptual site model is a descriptive and illustrative representation of the
hydrogeologic conditions and COI interactions specific to the Site. The purpose of the
CSM pertaining to the ash basins and the downgradient additional source area is to
provide an understanding of the distribution of constituents with regard to the Site -
specific geological/hydrogeological and geochemical processes controlling the transport
and potential impacts of COIs in various media. This information is also considered
with respect to potential exposure pathways to human and ecological receptors.
The CSM presented in this section is based on the United States Environmental
Protection Agency (USEPA) document titled, Environmental Cleanup Best Management
Practices: Effective Use of the Project Life Cycle Conceptual Site Model (USEPA, 2011). That
document describes six CSM stages for an environmental project life cycle and is an
iterative tool to assist in the decision process for characterization and remediation
during the life cycle of a project as new data become available. The six CSM stages for
an environmental project life cycle are described below:
1. Preliminary CSM Stage - Site representation based on existing data; conducted
prior to systematic planning efforts.
2. Baseline CSM Stage - Site representation used to gain stakeholder consensus or
disagreement, identifies data gaps and uncertainties; conducted as part of the
systematic planning process.
3. Characterization CSM Stage - Continual updating of the CSM as new data or
information is received during investigations; supports remedy decision making.
4. Design CSM Stage - Targeted updating of the CSM to support remedy design.
5. Remediation/Mitigation CSM Stage - Continual updating of the CSM during
remedy implementation; and providing the basis for demonstrating the
attainment of cleanup objectives.
6. Post Remedy CSM Stage - The CSM at this stage is used to support reuse
planning and placement of institutional controls if warranted.
The current Roxboro CSM is consistent with Stage 4 "Design CSM", which allows for
iterative improvement of the site CSM during design of the remedy while supporting
development of remedy design basis (USEPA, 2011). A three-dimensional depiction of
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the CSM under conditions prior to decanting and basin closure is presented as Figure 5-
1.
Anticipated changes to Site conditions, such as with decanting and basin closure, have
been incorporated into the CSM based on groundwater modeling simulations.
Predicted and observed effects will be compared on an ongoing basis to further refine
the CSM. Long-term Site monitoring and periodic evaluation of Site conditions will be
incorporated into the CSM to support documentation and future Site planning needs.
5.1 Site Geologic and Hydrogeologic Setting
(CAP Content Section 5.A.a)
5.1.1 Site Geologic Setting
(CAP Content Section 5.A.a)
The groundwater system associated with the EAB and WAB is divided into the
following three distinct hydrostratigraphic zones to distinguish the
interconnected groundwater system: the shallow (surficial) flow zone, deep
(transition) flow zone, and the bedrock flow zone. The following is a summary of
the natural hydrostratigraphic zone assessment observations:
• Shallow (surficial) flow zone (S) - Surficial flow zone includes residual
soils, fill and reworked soils, alluvium, regolith, and saprolite. Each type
of shallow soil was not encountered at every boring location. Surficial
soils consisting of silty sands or clays were usually encountered in the
upper 20 feet, which generally grade to saprolite. Saprolite is soil
developed by in -place weathering of rock that retains remnant bedrock
structure. Saprolite consists primarily of medium dense to very dense silty
sand, sandy silt, sand, sand with gravel, sand with clay, and clay with
sand, and clay. Sand particle sizes range from fine- to coarse -grained.
Saprolite is mostly thin (ranging from nonexistent to about 48 feet deep)
and almost entirely unsaturated for most portions of the Site. This
generalization is not consistent for the northern portions of the Site closest
to the Intake Canal and the NPDES-permitted wastewater ponds, where a
thick, saturated saprolite zone is present (e.g., GPMW-1 well cluster).
Alluvium was encountered at a few locations, such as ABMW-5 on the
north side of the EAB, but was not common across the Site. Shallow zone
wells are labeled with an "S".
• Deep (transition) flow zone (D) - The deep flow zone consists of a
relatively transmissive zone of partially weathered rock encountered
below the shallow zone and is generally continuous throughout the
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Roxboro Plant area. The transition zone is mostly comprised of partially
weathered rock that is gradational between saprolite and underlying
competent bedrock. The change from partially weathered rock to
competent bedrock is subjective and at Roxboro is defined by subtle
changes in weathering, secondary staining and mineralization, core
recovery, and the degree of fracturing in the rock. The range of transition
zone thickness observed was less than 1 foot to 45 feet. Both saturated
and unsaturated conditions occur in the transition zone at Roxboro.
Transition zone wells are labeled with a "D".
Bedrock flow zone (BR) — Bedrock is defined as lithified solid rock, based
on sample recovery and/or drilling resistance, that is generally slightly
weathered to unweathered and fractured to varying degrees. Bedrock in
the area includes volcanic and sedimentary rocks that have been
metamorphosed, intruded by coarse -grained granitic rocks, and subjected
to regional structural deformation. The dominant rock type consists of
biotite gneiss, felsic gneiss or granitic gneiss. Field observations
determined that biotite gneiss is more common in the north/northwest
portion of the Site, felsic gneiss in the central portion and granitic gneiss
or granite in the south southeastern portion of the Site.
In general, groundwater movement in the bedrock flow zone occurs in
secondary porosity represented by fractures. Water -bearing fractures
encountered are only mildly productive (providing water to wells).
Bedrock fractures encountered approximate to the ash basins tend to be
isolated with low interconnectivity. However, fracture occurrence in
bedrock approximate to the ash basins is influenced by their position
relative to the Hyco Shear Zone (HSZ). The basins are situated close to the
contact between the main zone and upper zone of the hanging wall of the
HSZ near the northward bend of the HSZ. Given the proximity of the site
to the contact between the two zones of the hanging wall, fracture
occurrence is expected to be high as a result of shearing forces within the
HSZ (Hibbard et al., 1998). This occurrence creates the potential for
preferential fracture flow and constituent transport at depth. The majority
of water producing fracture zones are found within the top 50 feet of
competent rock; however, mildly productive fractures are observed to
depths to 450 feet bgs at the northern areas of both ash basins consistent
with the HSZ. Groundwater flow in bedrock fractures is anisotropic and
difficult to predict, and velocities change as groundwater moves between
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factures of varying orientations, gradients, pressure, and size. Bedrock
zone wells are labeled with a 'BR," 'BRL," "BRLL" and "BRLLL"
designation depending of bedrock fracture depth interval. A detailed
evaluation of bedrock conditions is further provided in Appendix F (CAP
Content Section S.A.a.iv).
5.1.2 Site Hydrogeologic
Setting
(CAP Content Section 5.A.a)
The groundwater system in the natural
materials (shallow/transition/bedrock
flow zones) is consistent with the
regolith-fractured rock system and is
characterized as an unconfined,
interconnected groundwater flow system
indicative of the Piedmont
Physiographic Province.
A conceptual model of groundwater
flow in the Piedmont, which is
applicable to Roxboro, was developed by
LeGrand (1988, 1989) and Daniel and
FIGURE 5-2
LEGRAND SLOPE
GROUNDWATER SYSTEM
Harned (1992) (Figure 5-2). The model
assumes a regolith and bedrock drainage basin with a perennial stream. The
model describes conditions before ash -basin construction, but the general
groundwater flow directions are still relevant under current conditions.
Groundwater is recharged by drainage and rainfall infiltration in the upland
areas followed by discharge to the perennial stream. Flow in the regolith follows
porous media principals, while flow in bedrock occurs in fractures. Rarely does
groundwater move beneath a perennial stream to another more distant stream or
across drainage divides (LeGrand, 1989).
5.1.2.1 Groundwater Flow Direction
(CAP Content Section 5.A.a.i)
Topographic drainage divides represent natural groundwater divides
within the slope -aquifer system. The areas between the topographic divides
are flow compartments that are open-ended down slope. Compartmented
groundwater flow, applicable to the ash basins, is described in detail in A
Master Conceptual Model for Hydrogeological Site Characterization in the
Piedmont and Mountain Region of North Carolina (LeGrand, 2004). The
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topography surrounding Roxboro is a critical component of this CSM
because the groundwater elevation contours tend to mirror topography.
Groundwater flow divides are also proximate to topographic surface water
flow divides. A groundwater divide is located to the east of the EAB
approximately along McGhees Mill Road and to the south and west along
Dunnaway Road. The same groundwater divide that coincides with
Dunnaway Road is located to the east of the WAB. Other approximate
groundwater divides for the WAB include Semora Road (NC HWY 57) to
the south and a topographic ridge west of the WAB. Groundwater on the
basin side of each ridge flows toward the middle of the basin while
groundwater on the opposite side of the ridge flows away from the basin.
The topographically controlled flow direction provides natural hydraulic
control of ash basin constituent migration within the stream valley system,
with the predominant direction of groundwater flow being to the north-
northwest.
The EAB and WAB are each constructed within a former perennial stream
valley. The former stream valleys are bound by natural ridges that generally
slope southeast to northwest with an elevation change of approximately 150
feet. Higher elevations of approximately 560 feet (NAVD 88) are south and
southeast of the ash basins near McGhees Mill Road and Semora Road with
the lowest elevations north of the main dams at NPDES permitted
wastewater ponds and the Intake Canal, where pool elevation is
approximately 410 feet. This steep hydraulic gradient to the northwest
controls the direction of groundwater flow to the north-northwest.
The EAB and WAB physical settings are flow -through water systems with
groundwater migration into the upgradient end, flowing laterally through
the middle regions and migrating downward near the dams (Figure 5-3).
Generally, the physical setting of an ash basin within a former perennial
stream valley limits the horizontal and vertical migration of constituents to
areas near and directly downgradient of the basin's dam. The primary flow
path of the groundwater (the area of potential constituent migration in
groundwater from the basin) remains in the basin's historic stream valley
system. Areas upgradient and side -gradient of the basin reflect
groundwater divides that limit constituent migration to the primary flow
path. The downgradient NPDES permitted wastewater ponds are
groundwater discharge zones that limit the horizontal migration of
constituents downgradient of the basins.
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FIGURE 5-3
GENERAL PROFILE OF ASH BASIN PRE -DECANTING FLOW
CONDITIONS IN THE PIEDMONT
PRECIPITATION
Note:
Drawing is not to scale
Water -level maps combining the transition and bedrock groundwater flow
zones for each basin were constructed from groundwater measurements
collected in April 2019 (Figures 5-4a (EAB) and 5-4b (WAB)). April 2019
water level measurements and elevations are presented in Table 5-1.
General groundwater flow directions can be inferred from the groundwater
elevation contours. The groundwater flow direction for the
transition/bedrock flow zone associated with each ash basin is generally
from south to north-northwest toward the NPDES-permitted wastewater
ponds.
The following are conclusions pertaining to groundwater flow beneath the
EAB:
• Horizontal groundwater flow velocities in areas with saturated ash
within the EAB are less than those seen upgradient of the EAB and
below the EAB main dam.
• Horizontal groundwater flow is toward NPDES-permitted
wastewater ponds and the GSA/DFAHA. Farther downgradient
flow from GSA and DFAHA is toward the Intake Canal.
• Downward vertical gradients occur just upstream of the EAB main
dam and to a lesser extent upstream of the EAB separator dike.
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Groundwater recharge through rainfall precipitation within the halo
area, which is outside of the lined portion of the industrial landfill,
creates a downward groundwater flow as observed in areas to the
north and south of the EAB.
Upward vertical gradients occur beyond or downstream of the EAB
main dam, separator dike and the eastern discharge canal, which are
groundwater discharge zones.
The following are conclusions pertaining to groundwater flow beneath the
WAB:
Horizontal groundwater flow velocities in areas with free ponded
water within the ash basin are less than those seen upgradient of the
ash basin and below the ash basin dam.
Downward vertical gradients occur just upstream of the ash basin
main dam and upstream of the western discharge canal dikes.
Upward vertical gradients occur beyond or downstream of the main
dam and western discharge canal, which are groundwater discharge
zones.
For the WAB, predictive flow and transport model simulations indicate that
decanting of the WAB will reduce the hydraulic head at the dam and filter
dike. The groundwater flow system associated with the WAB will remain
constrained within the groundwater discharge zones: the western discharge
canal to the west and the NPDES permitted heated water discharge pond to
the north.
Using empirical Site groundwater elevation data, groundwater flow and
transport modeling simulations support groundwater flow is away from
water supply wells. Model simulations predict no exposure pathways
between the ash basins and downgradient additional source areas and the
pumping wells used for water supply. Domestic and public water supply
wells are upgradient or outside of the groundwater flow system containing
the ash basins. Domestic and public water supply wells are not affected by
constituents released from the ash basins or by the different closure
scenarios according to groundwater flow and transport model simulations
(Appendix G).
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5.1.2.2 Groundwater Seepage Velocities
(CAP Content Section 5.A.a.i)
Groundwater seepage velocities were calculated using horizontal hydraulic
gradients determined from water level measurements collected in April
2019 (Table 5-1). Hydraulic conductivity (K) and effective porosity (ne)
values were taken from the updated flow and transport model (Appendix
G). Calibrated conductivity and porosity values for each flow zone were
used in an effort to align velocity calculations with model predictions.
The flow and transport model provided subdivided hydraulic conductivity
zones and a calibrated hydraulic conductivity for each zone and model flow
layer. Simulated hydraulic conductivity value for the deep flow zone is 1
ft/day, and 0.3 ft/day for the bedrock flow zone. Hydraulic conductivity
values used in calculating seepage velocities were selected based on area's
location within or proximity to subdivided hydraulic conductivity zones.
The flow and transport model uses an estimated effective porosity of 20
percent for the deep flow zone and 5 percent for the bedrock flow zone
(Appendix G).
The horizontal groundwater seepage flow velocity (v,) can be estimated
using a modified form of the Darcy Equation:
K dh
VS _ne (dl
Using the April 2019 groundwater elevation data, the calculated horizontal
groundwater flow velocity in the vicinity of the EAB is:
• 0.10 ft/day (35.8 ft/yr) in the transition zone
• 0.12 ft/day (42.9 ft/yr) in the bedrock zone
The calculated horizontal groundwater flow velocity in the vicinity of the
WAB is:
• 0.10 ft/day (35.2 ft/yr) in the transition zone
• 0.12 ft/day (42.2 ft/yr) in the bedrock zone
Groundwater modeling predicts groundwater elevation changes associated
with closure activities will alter flow velocities and result in a more
pronounced historical stream valley system within each ash basin footprint.
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For visualization, velocity vector maps of groundwater under pre -decanting
and closure conditions were developed. The pre -decanting conditions map
for the WAB was created from comprehensive Site data incorporated into
the calibrated flow and transport model. Decanting of the EAB is currently
not planned since ponded water is not present in the EAB. The closure
condition maps were created using predicted flow fields for the closure -by -
excavation and closure -in -place scenarios. Plan view velocity vector maps
for groundwater in transition and bedrock flow zones under pre -decanting
and closure conditions include:
• Velocity vector map for groundwater in the transition zone under
pre -decanting conditions - Figure 5-5a
• Velocity vector map for groundwater in the transition zone under
closure -in -place conditions - Figure 5-5b
• Velocity vector map for groundwater in the transition zone under
closure -by -excavation conditions - Figure 5-5c
• Velocity vector map for groundwater in the bedrock zone under pre -
decanting conditions - Figure 5-6a
• Velocity vector map for groundwater in the bedrock zone under
closure -in -place conditions - Figure 5-6b
• Velocity vector map for groundwater in the bedrock zone under
closure -by -excavation conditions - Figure 5-6c
Key conclusions from the predictive model simulation of pre -decanting and
post -closure groundwater flow conditions include:
East Ash Basin
Under future conditions, the velocity vector directions and flow velocities
within the transition and bedrock flow zones near the EAB main dam
remain relatively unchanged from current conditions. Minor exceptions
include reduced flow velocities (1.0 to 0.2 ft/day) in the bedrock flow zones
beneath the EAB main dam following closure (Figure 5-6b through Figure
5-6c).
East of the EAB, the velocity vector directions and flow velocities remain
relatively consistent with current conditions; with the exception of
increased flow velocities (1.0 to 5.0 ft/day) in the transition flow zone
beneath the separator dike following closure -by -excavation (Figure 5-5a
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through Figure 5-50. In contrast, reduced flow velocities (0.5 to 0.01 ft/day)
are depicted in the bedrock flow zone beneath the separator dike following
closure -in -place (Figure 5-6a through Figure 5-6c).
South and west of the EAB, velocity vectors and flow velocities in the
transition and bedrock flow zones remain relatively unchanged between
pre -decanting and the closure -in -place scenario. Under closure -by -
excavation scenario, flow velocities decrease (0.5 to 0.01 ft/day) within the
transition and bedrock flow zones in the vicinity of the western lobe of the
ash basin (Figure 5-5a through Figure 5-6c).
West Ash Basin
Groundwater flow patterns experience noticeable changes within the
interior of the ash basin. Exceptions include the southern portion of the
WAB where free water will remain following closure.
Under future conditions, the transition and bedrock velocity vectors turn
inwards and flow velocities significantly increase (0.01 to >5.0 ft/day). This
simulates the natural funneling system of the historical perennial stream
(Figure 5-5a through Figure 5-60.
At the northern extent of the WAB near the main dam, flow velocity vectors
decrease (1.0 to 0.2 ft/day) following the closure -in -place scenario. For the
closure -by -excavation scenario, velocity vector directions turn inward and
the flow velocities reduce to 0.001 ft/day (Figure 5-5a and Figure 5-6c).
5.1.2.3 Hydraulic Gradients
(CAP Content Section 5.A.a.i)
Hydraulic gradient calculations using April 2019 groundwater elevation
data are consistent with gradients calculated from other monitoring events,
including data presented in the 2018 CAMA Annual Interim Monitoring
Report (SynTerra, 2019c). The average horizontal hydraulic gradients
(measured in feet/foot (ft/ft)) for each flow zone across the site was:
• EAB - 0.02 ft/ft (transition zone), and 0.02 ft/ft (bedrock) and;
• WAB - 0.02 ft/ft (transition zone), and 0.02 ft/ft (bedrock)
No gradients were calculated in the shallow zone due to its limited extent.
Hydraulic gradients are primarily neutral (flat or nearly flat) across large
areas of the ash basins due to the influence of standing water in the WAB
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and the overlying lined industrial landfill in the eastern lobe of the EAB.
Groundwater flow is minimal in these areas due to low hydraulic gradients,
and as a result, there is little to no downward flow of pore water into the
residual material underlying the ash basins.
Vertical hydraulic gradients were calculated at clustered wells from the
water level data and the midpoint elevations of the well screens. Positive
vertical gradients indicate downward flow and negative hydraulic
gradients indicate upward flow. Within the WAB, the average vertical
gradient is neutral (flat). With sluicing operations to the EAB discontinued
in 1980's and the industrial landfill constructed on top of and adjacent to the
EAB, a different hydraulic system than an operating basin with free-
standing water (i.e., WAB) is created. However, within the EAB, the vertical
gradient between the ash and the bedrock is slightly upward (-0.01 ft/ft).
The vertical gradient in the bedrock (GMW-8R/MW-21BRLR) at the
southern end of the EAB is downward (0.04 ft/ft) toward a jurisdictional
intermittent stream, Stream 11A, that discharges to the western lobe of the
EAB.
Downgradient of the EAB and WAB main dams, groundwater in general
flows upward toward the NPDES-permitted wastewater ponds, limiting
downward migration of COIs to the area in close proximity to the dams.
The average vertical gradient north of the WAB main dam is upward
(average -0.07 ft/ft). Although an average vertical gradient north of the EAB
dam is slightly downward (0.03 ft/ft (GMW-1A/CCR-102BR and GMW-
2/CCR-103BR)), the adjacent Unit 3 hot water pond likely has an influence
to groundwater levels in this area. Farther to the northeast of the EAB main
dam, upward vertical gradients are noted (MW-22D/MW-22BR: -0.01 ft/ft).
5.1.2.4 Particle Tracking Results
(CAP Content Section 5.A.a.ii)
As discussed in CSA Update (SynTerra, 2017d), a numerical capture zone
analysis related to the EAB and WAB was conducted to evaluate potential
impact of upgradient water supply pumping wells. The analysis employed
MODPATH to interface with the MODFLOW flow model. MODPATH is a
"particle tracking" model that traces groundwater flow lines from a starting
position. MODPATH was used to trace groundwater flow lines around
pumping wells to indicate where the water being pumped from the well
originates (i.e., well capture zone analysis). The analysis for Roxboro
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indicates that well capture zones from wells located to the southeast, south
and southwest of the Roxboro Plant are limited to the immediate vicinity of
the well head and do not extend toward the ash basins. None of the particle
tracks originating in the ash basins moved into the well capture zones.
5.1.2.5 Subsurface Heterogeneities
(CAP Content Section S.A.a.iii)
The nature of groundwater flow across the Site is based on the character
and configuration of the ash basins relative to specific Site features such as
manmade and natural drainage features, engineered drains, streams, and
lakes; hydraulic boundary conditions; and subsurface media properties.
Natural subsurface heterogeneities at the Site are represented by three flow
zones that distinguish the interconnected groundwater system: the shallow
(surficial) flow zone, deep (transition) flow zone, and the bedrock flow
zone, as discussed in Section 5.1.1. The shallow flow zone is composed of
residual soil/saprolite. Typically, the residual soil/saprolite is partially
saturated and the water table fluctuates. Water movement is generally
preferential through the weathered/fractured and fractured bedrock of the
transition zone where permeability and seepage velocity is enhanced.
Groundwater within the Site area exists under unconfined, or water table,
conditions within the surficial zone, transition zone and in fractures and
joints of the underlying bedrock. The saprolite, where saturated thickness is
sufficient, acts as a reservoir for supplying groundwater to the fractures and
joints in the bedrock. Based on the orientations of lineaments and open
bedrock fractures at Roxboro, horizontal groundwater flow within the
bedrock primarily occurs approximately parallel to the hydraulic gradient,
with no preferential flow direction (Appendix F). Consistent with this
interpretation, the current groundwater flow model for Roxboro does not
simulate plan -view anisotropy.
NORR CSA guidance requires a "site map showing location of subsurface
structures (e.g., sewers, utility lines, conduits, basements, septic tanks, drain
fields, etc.) within a minimum of 1,500 feet of the known extent of
contamination" in order to evaluate the potential for preferential pathways.
Locations of historic subsurface utilities in the Plant area to 1,500 feet
beyond the basin are difficult to completely map with certainty. However,
identification of piping near and around the ash basins was conducted by
Stantec in 2014 and utilities around the Site were included on a 2014
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topographic map prepared by WSP Global, Inc. (CSA Update, 2017b).
Based on groundwater flow direction at the Site, depth to groundwater and
identified subsurface underground utilities, including recent wastewater
redirect conveyance system to the Plant wastewater system, there are no
potential preferential pathways for contaminant migration through
underground utility corridors.
5.1.2.6 Bedrock Matrix Diffusion and Flow
(CAP Content Section 5.A.a.iv)
Matrix Diffusion Principles
When solute plumes migrate through fractures, a solute concentration
gradient occurs between the plume within the fracture versus the initially
clean groundwater in the unfractured bedrock matrix next to the fracture. If
the matrix has pore spaces connected to the fracture, a portion of the solute
mass will move by molecular diffusion from the fracture into the matrix.
This mass is removed, at least temporarily, from the flow regime in the
open fracture. This effect is known as matrix diffusion (Freeze and Cherry
1979). When the plume concentrations later decline in the fractures (e.g.,
during plume attenuation and/or remediation), the concentration gradient
reverses and solute mass that has diffused into the matrix begins to diffuse
back out into the fractures. This effect is sometimes referred to as reverse
diffusion.
Matrix diffusion causes the bulk mass of the advancing solute plume in the
fracture to advance slower than would occur in the absence of mass transfer
into the matrix. This effect retards the advance of any solute, including
relatively non -reactive solutes like chloride and boron. The magnitude of
plume retardation increases with increasing plume length, because longer
plumes have more contact for diffusion to transfer solute mass from the
fracture to the matrix (Lipson et al 2006). The magnitude of plume
retardation also increases with increasing matrix porosity.
If the solute sorbs to solids, the retarding effect increases. Sorption of solutes
that have diffused into the matrix occurs on a much larger surface area than
would be the case if the solute mass remained entirely within the fracture.
The combined effect of adsorption on the fracture surface and adsorption in
the matrix further enhances plume retardation relative to the advance that
would occur in the absence of adsorption. If sorption is reversible, when
reverse diffusion occurs, the sorbed mass can desorb and transfer back into
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the aqueous phase and diffuse back to the fractures. Solute mass that has
been converted into stable mineral species would not undergo desorption.
Site -Specific Data Pertaining to Matrix Diffusion
Overall, the bedrock hydraulic conductivity in bedrock near the EAB and
WAB decreases with increasing depth below the top of rock (Appendix F).
The observed decline in bedrock hydraulic conductivity and hydraulic
aperture with increasing depth is consistent with expectations based on the
literature (Gale, 1982 and Neretnieks, 1985), and indicates that the overall
volumetric rate of groundwater flow in the bedrock decreases with depth
(Appendix F).
The Site is located within the Hyco Shear Zone (HSZ), a regional bedrock
structure that is oriented east-northeast (ENE) by west-southwest (WSW),
with a general foliation dip direction toward the south-southeast (SSE).
Where bedrock fractures at the site show preferential orientations, they
generally align with the structural fabric within the HSZ.
Based on the predominant orientations of lineaments and bedrock fractures
near the ash basins, general interpretations can be made regarding the
potential for preferential flow directions. Horizontal groundwater flow
within the bedrock in the vicinity of the EAB would not be expected to
show any preferential orientation, because fractures in that area do not
indicate a significant preferential orientation. Thus, groundwater near the
EAB is expected to flow in the direction of the hydraulic gradient. Near the
WAB, horizontal groundwater flow may occur preferentially in a general
direction of ENE -WSW, parallel to the predominant strike of bedrock
fractures and consistent with the HSZ structure. Horizontal flow rates in the
perpendicular map directions (NNW -SSE) near the WAB are expected to be
comparatively less. The difference in hydraulic conductivity and flow as a
function of map direction is referred to as anisotropy.
The observed decline in bedrock hydraulic conductivity and hydraulic
aperture with increasing depth is consistent with expectations based on the
literature and indicates that the overall volumetric rate of groundwater flow
in the bedrock decreases with depth. Nevertheless, the detection of boron at
concentrations greater than 02L standards at depths of approximately 400
feet bgs (monitoring well MW-108BRLL (EAB) and monitoring wells MW-
205BRLLL and MW-208BRLLL (WAB)) indicates the possible presence of
steep preferential flow zones extending to similar depths near these
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monitoring wells. As noted above, several lineaments have been identified
in the vicinity of the ash basins at the Site. The possibility of preferential
flow zones in bedrock will be considered during groundwater model
calibration based on the deep bedrock investigation results.
For the WAB, the hydraulic conductivity and hydraulic aperture values in
approximately the upper 60 feet of the MW-38BR borehole, which is located
south of the WAB impoundment (Figure 1-3), are smaller than those in the
upper portion of the bedrock at the other deep bedrock boreholes installed
at locations generally north of the ash basins. As observed during drilling,
packer testing, and geophysical logging, the bottom 500 feet (bgs) of the
MW-38BR borehole exhibits no measurable transmissivity. These results
suggest that the overall bedrock permeability at this location - near the
southern end of the WAB - is less than that in the investigated areas further
north at the site (Appendix F).
Rock core samples were selected from three locations of the EAB (ABMW-
7BR, MW-1BR and MW-22BR) and one location from the WAB (CCR-
207BR). Two additional rock core samples were selected from areas
representing background conditions, which include rock core samples from
MW-13BR for the EAB and BG-2BR for the WAB. Rock core samples were
analyzed for porosity, bulk density, and thin section petrography.
The reported matrix porosity values ranged from 0.10 percent to 4.83
percent with an average of 2.04 percent. Bulk density ranged from 2.60
grams per cubic centimeter (g/cm3) to 2.80 g/cm3 with an average of 2.70
g/cm3 (Appendix F). Petrographic evaluation classified all 10 samples as
igneous rocks. Specifically, five samples were classified as quartz diorite,
four samples were classified as tonalite, and one sample as vein/fracture fill.
The principal minerals were plagioclase, quartz, biotite, and amphibole.
Accessory minerals consist of epidote, pyrite, potassium -feldspar, zircon,
apatitie, magnetite, and sphene. Three samples showed extensive
weathering, as indicated by the alteration of plagioclase into sericite/illitic
clays (ABMW-7, 88 feet bgs; ABMW-7, 126 feet bgs; and MW-1BR, 36 feet
bgs). In the remaining seven samples, plagioclase crystals are locally altered
into sericite. Biotite and amphibole are altered into chlorite. Fe -calcite and
Fe -dolomite are rare to minor.
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The reported matrix porosity values are within the range of those reported
for crystalline rocks in the literature (Freeze and Cherry, 1979; LBfgren,
2004; Zhou et al., 2008; Ademeso et al., 2012). The presence of measurable
matrix porosity suggests that matrix diffusion contributes to plume
retardation at the Site (Lipson et al., 2005). In addition, the identification of
sericite (a mixture of muscovite, illite, or paragonite produced by
hydrothermal alteration of feldspars) in all the thin section samples
indicates the bedrock has the capacity to sorb constituents such boron and
other elements associated with coal ash. The influences of matrix diffusion
and sorption are implicitly included in the groundwater fate and transport
model as a component of the constituent partition coefficient (Ka) term used
for the bedrock layers.
5.1.2.7 Onsite and Offsite Pumping Influences
(CAP Content Section 5.A.a.v)
Currently, onsite pumping within the groundwater flow system is not
conducted. Pumping of ponded water (decanting) within the WAB and
EAB, if needed for ash basin closure, will commence upon approval of the
NPDES permit. In the interim, sluicing was ceased to the WAB in mid -
December 2018. Sluicing ceased to the EAB in the mid-1980s. Uptake of
Plant cooling and process water occurs through the Intake Canal and intake
bay, extensions of Hyco Reservoir. Based on the Roxboro 2018 annual water
use report, average daily withdrawal was approximately 592.12 million
gallons per day.
Because much of the area surrounding the Roxboro is either residential,
farm, or undeveloped land, potential offsite pumping influences would be
limited to domestic and public water supply wells. Existing water supply
wells are outside or upgradient in the groundwater flow system containing
the ash basins. Flow and transport modeling indicate private water supply
wells within the model area remove only a small amount of water from the
overall hydrologic system (Appendix G).
5.1.2.8 Ash Basin Groundwater Balance
(CAP Content Section 5.A.a.vi)
EAB and WAB Groundwater Balances
(CAP Content Section 5.A.a.vi)
The EAB and WAB are each located within a single watershed and
groundwater flow system. The location of the groundwater divides
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defining the edge of the watersheds will change due to decanting of ponded
water from the WAB and closure activities for both basins due to changing
hydraulic conditions. The flow and transport model was used to evaluate
the hydraulic conditions for the WAB prior to decanting, post decanting
and post closure (both closure in place and closure -by -excavation) for both
ash basins (Appendix G). Each scenario water balance was developed using
the results from flow and transport model for pre -decanting and predicated
future groundwater simulations.
WAB Groundwater Balance
The approximate groundwater flow budget in WAB watershed under each
simulated scenario is summarized in Table 5-2.
WAB Pre -Decanting Conditions Groundwater Balance
(CAP Content Section 5.A.a.vi)
Under pre -decanting conditions, the watershed area contributing flow
toward the basin is estimated at approximately 352 acres.
• Groundwater recharge from the watershed recharge area of 352 acres
is estimated to be 103 gpm. This includes 65 gpm from the 169 acres
outside of the ash basin and 38 gpm from the 183 acres of the ash
basin.
• Water discharge from the groundwater system by ponded water is
approximately 35 gpm.
• Water discharge from the groundwater system by streams outside
the ash basin is approximately 18 gpm.
• Groundwater that flows through and under the main dam is
estimated to be 14 gpm.
• Groundwater that flows through and under the filter dam is
estimated to be 8 gpm.
WAB Post -Decanting Groundwater Balance
(CAP Content Section 5.A.a.vi)
The flow and transport model was used to evaluate the WAB hydraulic
conditions that would occur after decanting of the ash basin. A water
balance was developed for the simulated groundwater system under post -
decanting conditions.
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The extent of the WAB watershed during decanting is expected to be larger
than that under current conditions. Under simulated post -decanting
conditions, the watershed area contributing flow toward the basin is
estimated at approximately 363 acres.
• Groundwater recharge from the watershed recharge area of 363 acres
is estimated to be 129 gpm. This includes 73 gpm from the 180 acres
outside of the ash basin and 56 gpm from the 183 acres of the ash
basin.
• The drainages inside the ash basin represent the decanting system to
remove ponded water in the ash basin. Water discharge by decanting
drain is approximately 82 gpm.
• Water discharge from the groundwater system by streams outside
the ash basin is approximately 17 gpm.
• Groundwater that flows through and under the main dam is
estimated to be 13 gpm.
• Groundwater that flows through and under the filter dam is
estimated to be 1.5 gpm.
Decanting the ash basin has a significant impact on flow through and under
the filter dam to the south. The estimated flows are reduced from 8 gpm
prior to decanting to 1.5 gpm after decanting of the ponded water in the ash
basin.
WAB Post -Closure Groundwater Balances
(CAP Content Section 5.A.a.vi)
The flow and transport model was used to evaluate the ash basin hydraulic
conditions that would occur after the two ash basin closure scenarios:
closure -in -place and closure -by -excavation. A water balance was developed
for the simulated groundwater system under each post -closure condition.
The extent of the watershed under post closure conditions is expected to be
larger than that under the post -decanting conditions. The approximate
watershed area is expected to at 365 acres under closure -in -place conditions,
and at 465 acres under closure -by -excavation scenario.
• Groundwater recharge from areas outside of the ash basin footprint
is estimated to be 69 gpm for closure -in -place and 115 gpm for
closure -by -excavation.
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• Groundwater recharge from the area within the ash basin footprint is
affected differently by the closure options. Closure -in -place reduces
groundwater recharge from within the ash basin footprint from 56
gpm post -decanting to 2 gpm post -closure because of the
impermeable final cover system. Groundwater recharge within the
ash basin footprint under closure -by -excavation conditions is similar
to that under post -decanting conditions.
• Under closure -in -place conditions, drains inside the ash basin
represent the drain system under the final cover system to control the
groundwater elevation. Estimated groundwater discharge to the
drain system is approximately 40 gpm.
• Under closure -by -excavation conditions, drains inside the ash basin
represent the streams that form within the excavated ash basin
footprint after closure. Estimated groundwater discharge to the
streams is approximately 146 gpm.
• Water discharge from the groundwater system by streams outside
the ash basin is approximately 17-20 gpm, depending on the selected
closure option.
• Under closure -in -place conditions, groundwater that flows through
and under the main dam is estimated to be 6 gpm; groundwater that
flows through under the filter dam is estimated to be 3 gpm.
• Under closure -by -excavation conditions, both the main dam and the
filter dam are breached to allow water from the heated water
discharge pond to impound the excavated area. Groundwater that
flows through and under the main dam is estimated to be 0.2 gpm.
Flow direction at the filter dam is reversed from the post -decanting
condition. Under closure -by -excavation conditions, 78 gpm of
groundwater is recharged through and under the filter dam to the
watershed.
EAB Groundwater Balance
The approximate groundwater flow budget in EAB watershed under each
simulated scenario is summarized in Table 5-3.
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EAB Pre -Decanting Conditions Groundwater Balances
(CAP Content Section 5.A.a.vi)
Under pre -decanting conditions, the watershed area contributing flow
toward the basin is estimated at approximately 313 acres.
• Groundwater recharge from the watershed recharge area of 313 acres
is estimated to be 88 gpm. This includes 61 gpm from the 190 acres
outside of the ash basin and 27 gpm from the 123 acres of the ash
basin.
• Water discharge from the groundwater system by a wetland area
upgradient of the main dam and minor ponded water inside the ash
basin is approximately 26 gpm.
• Water discharge from the groundwater system by streams and seeps
inside the ash basin is approximately 10 gpm.
• Water discharge from the groundwater system by streams outside
the ash basin is approximately 32 gpm.
• Groundwater that flows through and under the main dam is
estimated to be 20 gpm.
• Groundwater that flows through and under the separator dike is
estimated to be 5 gpm.
EAB Post -Decanting Groundwater Balances
(CAP Content Section 5.A.a.vi)
Potential decanting activity may be carried out to lower the water level in
areas of the EAB. Simulation of these activities did not change the extent of
the watershed compared to that under the current conditions. Water
balance analysis results for post -decanting conditions are similar to the
results under current conditions. The major change is that flow discharge to
"pond and wetland area in the ash basin" is incorporated in the flow
discharged to "drainage inside the ash basin" under post -decanting
condition. This is because pond and wetland areas were represented as
general head boundaries under current condition and as drains under post -
decanting conditions.
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EAB Post -Closure Groundwater Balances
(CAP Content Section 5.A.a.vi)
The flow and transport model was used to evaluate the ash basin hydraulic
conditions that would occur after two ash basin closure options: closure -in -
place and closure -by -excavation. A water balance was developed for the
simulated groundwater system under each post -closure scenario. The extent
of watershed is expected to be 324 acres under closure -in -place conditions,
and 311 acres under closure -by -excavation conditions.
Groundwater recharge from areas outside of the ash basin footprint
is estimated to be 57 gpm for closure -in -place and 21 gpm for
closure -by -excavation. The significant decrease in recharge under
closure -by -excavation scenario is caused by the installation of a
proposed landfill with an impermeable capping system.
• Groundwater recharge from the area within the ash basin footprint is
affected by the closure option. Closure -in -place reduces
groundwater recharge from within the ash basin footprint from 26
gpm post -decanting to approximately 1 gpm post -closure due to the
installation of the impermeable capping system. Closure -by -
excavation decreases groundwater recharge within the ash basin
footprint from 26 gpm post -decanting to 14 gpm post -closure
because of the expansion of the existing landfill and the installation
of a capping system.
• Under the closure -in -place scenario, drains inside the ash basin
represent the drain system under the final cover system to control the
groundwater elevation. Estimated groundwater discharge to the
drain system is approximately 13 gpm.
• Under the closure -by -excavation scenario, drains inside the ash basin
represent the streams that form within the excavated ash basin
footprint after closure, as well as under -liner drain below the landfill.
Estimated groundwater discharge to the streams is approximately 10
gpm.
• The closure -by -excavation scenario includes a proposed unlined
stormwater basin upgradient of the main dam inside the ash basin.
Estimated groundwater discharge to this stormwater basin is
approximately 4 gpm.
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Water discharge from the groundwater system by streams outside
the ash basin remains approximately 32 gpm under closure -in -place
scenario. Under the closure -by -excavation scenario, water discharge
to streams outside the ash basin decreases to approximately 9 gpm
due to the installation of a landfill with an impermeable capping
system.
• Groundwater that flows through and under the main dam is
estimated to be approximately 13-15 gpm depending on the selected
closure scenario.
• Groundwater that flows through and under the separator dike is
estimated to be approximately 3 gpm under both closure options.
5.1.2.9 Effects of Naturally Occurring Constituents
(CAP Content Section 5.A.a.vi)
Metals and inorganic constituents, typically associated with CCR material,
are naturally occurring and present in the Piedmont physiographic
province of north -central North Carolina (Chapman, 2013). The metals and
inorganic constituents occur in soil, bedrock, groundwater, surface water,
and sediment. During the Roxboro CSA assessment, samples of soil and
rock were collected during drilling activities and analyzed for metals and
inorganic constituents. Results indicate that soil and rock at Roxboro
contain naturally occurring constituents that are also typically related to
CCR material and likely affect the chemistry of groundwater at the Site.
Chromium, cobalt, iron, and manganese were present in background soil
and rock samples at concentrations greater than the PSRG POG values
(Table 4-2, Section 4).
Analytical results for groundwater at background locations indicate that
chromium, cobalt, iron, manganese, TDS and vanadium are present at
concentrations greater than 02L/IMAC standards, which are consistent with
the range of concentrations determined for groundwater in the Piedmont
(Table 4-3, Section 4). Therefore, the downgradient concentrations of these
constituents are within background concentration ranges.
5.2 Source Area Locations
(CAP Content Section 5.A.b)
Roxboro has two ash basins and downgradient additional source areas considered in
the CSM and modeling scenarios for evaluation of corrective action.
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East Ash Basin, Industrial Landfill, and LCID landfill (Source Area 1)
Source Area 1 consists of the EAB/industrial landfill/LCID landfill and is generally
located east and north of Dunnaway Road, west of McGhees Mill Road, and is bound to
the north by the Unit 3 cooling tower pond and the Unit 3 hot water pond (Figure 1-2).
Dunnaway Road and McGhees Mill Road, located along topographically high ridges,
coincide with hydrogeologic divides that affect groundwater flow within an area west,
south, and east of Source Area 1. Topography to the northeast of Dunnaway Road
generally slopes downward toward the EAB. Similarly, topography west of McGhees
Mill Road generally slopes downward toward the EAB. The EAB is bound to the north
by the main dam adjoining the NPDES-permitted Unit 3 hot water pond.
West Ash Basin (Source Area 2)
Source Area 2 consists of the WAB. The WAB is generally located west of Dunnaway
Road, north of Semora Road, and bound to the north by the main dam followed by the
NPDES-permitted heated water discharge pond. The westernmost extent of the WAB is
largely defined by the western discharge canal (Figure 1-3). Dunnaway Road and
Semora Road, located along topographically high ridges, coincide with hydrogeologic
divides that affect groundwater flow within an area east and south of the WAB.
Topography to the west of Dunnaway Road generally slopes downward toward the
WAB. Topography to the north of Semora Road generally slopes downward towards
the WAB. Similarly, west of the western discharge canal, a north -south trending
topographically high ridge affects groundwater flow within an area west of the WAB.
Topography east of the unnamed ridge generally slopes downward toward the western
discharge canal and WAB. Topography west of the unnamed ridge generally slopes
downward toward the Hyco Reservoir.
GSA/DFAHA (Source Area 3)
The GSA and the DFAHA are located adjacent to each other and are both positioned
north and downgradient of the EAB (Figure 1-2). North of both units include
GSA/DFAHA unlined wastewater ponds followed by railroad lines use for coal
transport to the coal pile storage area, and the Intake Canal. To the east of the GSA is
the eastern discharge canal. Located to the west of the DFAHA are the NPDES
permitted wastewater ponds: Unit 3 cooling tower pond and the Unit 3 heated water
discharge pond. The topography across the GSA/DFAHA area is relatively flat to
accommodate unit operations with an overall slope to the north toward the unlined
wastewater ponds.
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5.3 Summary of Potential Receptors
(CAP Content Section 5.A.c)
G.S. Section 130A-309.201(13), amended by CAMA, defines receptor as "any human,
plant, animal, or structure which is, or has the potential to be, affected by the release or
migration of contaminants. Any well constructed for the purpose of monitoring groundwater
and contaminant concentrations shall not be considered a receptor." In accordance with the
NORR CSA guidance, receptors cited in this section refer to public and private water
supply wells and surface water features.
5.3.1 Public and Private Water Supply Wells
Groundwater from beneath the ash basins has not and will not flow towards any
water supply wells based on the CSM, groundwater flow patterns prior to and
post ash basin closure (either scenario), the location of water supply wells in the
area, and evaluation of groundwater analytical data. Assessment activities
including groundwater data from water supply wells and on -Site monitoring
wells, groundwater elevation measurements, and groundwater flow and
transport modeling results all indicate that ash basin related constituents are not
affecting, and will not affect, water supply wells.
No public or private drinking water wells or wellhead protection areas were
found to be located downgradient of the EAB, WAB and the GSA/DFAHA. A
total of 87 private water supply wells were identified within the 0.5-mile radius
of the EAB and WAB compliance boundaries (Figure 5-7a). Most of these wells
are associated with residences located to the east and upgradient of the EAB,
along McGhees Mill Road and The Johnson Lane; and residences to the south
and upgradient of the WAB, on Dunnaway Road and Semora Road. Discussion
with supporting material and data, of alternative water supply provisions (water
filtration systems) provided by Duke Energy for surrounding occupied
residences (Figure 5-7b) and findings of the drinking water supply well survey
are presented included in Section 6.2.2.
5.3.2 Availability of Public Water Supply
No municipal water supply lines are available within a 0.5-mile radius of the
EAB and WAB compliance boundaries. The nearest municipal water supply line,
provided by the City of Roxboro, is located at the intersection of Country Club
Lane and Chub Lake Road, approximately 4.5 miles to the east of the Dunnaway
Road entrance to the Plant.
Roxboro operates a Non -Transient Non -Community Water System that pulls
surface water from the intake bay for potable water production. Potable water
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production is a batch process, in which potable water is processed a few times
per week depending on need. On average, the potable water system produces
approximately 50,000 gallons per week.
5.3.3 Surface Water
The Site is located in the Roanoke River Basin on the southeast side of Hyco
Reservoir. The ash basins are located in proximity to Hyco Reservoir. Hyco
Reservoir is impounded by an earthen dam with a concrete spillway overflow at
an elevation of approximately 410 feet (NAVD 88). An after bay to Hyco
Reservoir is located immediately downstream of the reservoir dam and is used to
maintain downstream river flow for the Hyco River, which flows northeastward.
Surface water bodies within 0.5 mile of the ash basins, and the associated North
Carolina surface water classifications, are indicated on Figure 5-8 and
summarized in Table 5-4.
The only surface water intake located in the vicinity of the Plant is the intake bay
associated with the Intake Canal used to supply water from Hyco Reservoir for
Roxboro Plant operations (Figure 1-2).
A depiction of surface water features — including wetlands, ponds, unnamed
tributaries, seeps, streams, lakes, and rivers — within a 0.5-mile radius of the ash
basin compliance boundaries is provided in Figure 5-8. Surface water
information is provided from the Natural Resources Technical Report (NRTR)
prepared by AMEC Foster Wheeler (January, 2014). In addition, NPDES-
permitted outfalls and locations covered by the SOC are shown on Figure 5-8
(CAP Content Section 5.B).
5.3.4 Environmental Assessment of Hyco Reservoir
The Roxboro NPDES permit (NPDES No. NC00003425) requires Duke Energy to
conduct an environmental monitoring program on Hyco Reservoir under a study
plan approved by the NCDEQ. The program includes reservoir surface water
sampling, fish and sediment sampling for select trace elements, and fish
community assessment. Hyco Reservoir has been monitored by Duke Energy
since the late 1970s. It has been documented that historical impacts to the aquatic
during the 1970s and 1980s occurred from selenium in the plant discharges.
However, after the discovery of the cause and reduction of selenium in the
discharges in 1989, the effects were gradually eliminated and Hyco Reservoir
recovered and has maintained overall good health since the early 2000s. The
assessments carried out by Duke Energy have demonstrated that Hyco Reservoir
has been an environmentally healthy and functioning ecosystem for almost 20
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years. Data from these assessments indicate that the systems installed at the
Roxboro Plant for the protection of the water quality, the aquatic community,
and human health have been effective. The program data is reported to NCDEQ
in environmental monitoring reports to support the NPDES permit requirement.
More information related to the environmental health assessments conducted for
Hyco Reservoir, including sampling programs, water quality and fish
community assessments, and fish tissue analysis, can be found in Appendix E.
5.3.5 Future Groundwater Use Area
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of the ash basins within and beyond the predicted area of
potential groundwater COI influence from the ash basins and downgradient
source areas. Therefore, no future groundwater use areas are anticipated
downgradient of the ash basins and downgradient additional source areas.
Under G.S. 130A-309.211(cl), Duke Energy provided permanent water solutions
to all eligible households within a 0.5-mile radius of the ash basin compliance
boundaries. It is anticipated that residences within the 0.5-mile radius will
continue to rely on groundwater resources for water supply for the foreseeable
future. Duke Energy has a performance monitoring plan in place, with details of
the plan outlined in the Permanent Water Supply — Water Treatment Systems
document. Duke Energy will provide quarterly maintenance of the water
treatment systems to include replenishing expendables (salt for brine tank(s) and
neutralizer media) and providing system checks and needed
adjustments. Laboratory samples of pre-treated and treated water will be
collected annually to coincide with system installation, unless there is evidence
the system is not performing properly, in which case samples will be collected
more frequently.
5.4 Human Health and Ecological Risk Assessment Results
(CAP Content Section 5.A.d)
The human health and ecological risk assessment indicated there is no evidence of
unacceptable risks to on -Site or off -Site human receptors potentially exposed to CCR
constituents that may have migrated from the ash basins and downgradient additional
source areas, and there is no evidence of unacceptable risks to ecological receptors
potentially exposed to CCR constituents that may have migrated from the ash basins
and downgradient additional source areas.
A human health and ecological risk assessment pertaining to the Roxboro was prepared
and is included in Appendix E. The risk assessment focuses on the potential impacts of
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CCR constituents from the Roxboro ash basins, including the downgradient additional
source areas, on groundwater, surface water, and sediment. Groundwater flow
information was used to focus the risk assessment on areas where exposure of humans
and wildlife to CCR constituents could occur. Primary conclusions of the risk
assessment include: 1) there is no evidence of unacceptable risks to on -Site or off -Site
human receptors potentially exposed to CCR constituents that may have migrated from
the ash basins; and 2) there is no evidence of unacceptable risks to ecological receptors
potentially exposed to CCR constituents that may have migrated from the ash basins.
This risk assessment uses analytical results from groundwater, surface water, and
sediment samples collected March 2015 through June 2019.
Hyco Reservoir is not affected by groundwater flow from the ash basins and
downgradient additional source areas; therefore, there is no exposure of CCR
constituents to humans and wildlife using Hyco Reservoir. Evaluation of risks
associated with seep locations and soil beneath the ash basins are not subject to this
assessment and will be evaluated independent from the CAP Update.
Consistent with the iterative risk assessment process and guidance, updates to the risk
assessment have been made to the original 2016 risk assessment (SynTerra, 2016a) in
order to incorporate new site data and refine conceptual site models. The original risk
assessment was prepared in accordance with a work plan for risk assessment of CCR-
affected media at Duke Energy sites (Haley & Aldrich, 2015).
The following risk assessment reports have been prepared:
1. Baseline Human Health and Ecological Risk Assessment, Appendix F of the CAP Part
2 (SynTerra, 2016a)
2. Comprehensive Site Assessment (CSA) Update (SynTerra, 2017d)
3. Human Health and Ecological Risk Assessment Summary Update for Roxboro Steam
Electric Plant, Appendix B of Community Impact Analysis of Ash Basin Closure
Options at the Roxboro Steam Electric Plant (Exponent, 2018)
To help evaluate options for groundwater corrective action, this risk assessment
characterized potential effects on human health and the environment related to
naturally occurring elements, associated with coal ash, present in environmental media.
This risk assessment follows the methods of the 2016 risk assessment (SynTerra, 2016a)
and is based on NCDENR, 2003; NCDEQ, 2017; and USEPA risk assessment guidance
(USEPA, 1989; 1991a; 1998).
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Human health and ecological conceptual site models were developed and further
refined to guide identification of exposure pathways, exposure routes, and potential
receptors for evaluation. Additional information regarding groundwater flow and the
treatment of source areas other than the ash basins (GSA and DFAHA) were
incorporated into the refinement of CSMs presented in Appendix E.
Environmental data evaluated in the risk assessment were compared to human health
and ecological screening values. Risk assessment constituents of potential concern
(COPCs) are different than COIs in that COPC are those elements in which the
maximum detected concentration exceeded human health or ecological screening
values. COPCs are carried forward for further evaluation in the deterministic risk
assessment. Appendix E contains the results of the screening assessment.
No unacceptable risks from exposure to environmental media were identified. Results
of the human health risk assessment indicate the following:
• On -site groundwater poses no unacceptable risk for the construction worker
under these exposure scenarios.
• On -site surface water and sediment pose no unacceptable risk for the trespasser
under these exposure scenarios.
• Exposure to CCR constituents by current and future commercial/industrial
worker, residences and recreational receptors is incomplete.
Findings of the baseline ecological risk assessment include the following:
• No HQs based on no observed adverse effects levels (NOAELs) or lowest
observed adverse effects levels (LOAELs) were greater than unity for the mallard
duck, great blue heron, river otter, and bald eagle exposed to surface water and
sediments in the Water Intake Basin (WIB) (i.e., Intake Canal) exposure area.
• Two endpoints, muskrat and killdeer bird, had limited modeled risk results
greater than unity for aluminum and copper. The modeled risk is primarily
NOAEL based and driven by concentrations in sediment.
• With the exception of aluminum, no HQs based on NOEALS or LOAELs were
greater than unity for the muskrat in the WIB Exposure Area.
• With the exception of aluminum, no HQs based on LOAELs were greater than
unity for the killdeer bird in the WIB Exposure Area. Exposure of the killdeer
bird to aluminum and copper resulted in NOAEL based HQs greater than 1.0.
LOAEL based HQs for copper were less than unity.
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• Multiple lines of evidence indicate the modeled risk to aluminum and copper are
overestimated.
The modeled risks are considered negligible based on natural and background
conditions. The exposure models likely overstate risks to aluminum and copper. In
summary, there is no evidence of unacceptable risks to human and ecological receptors
exposed to environmental media potentially affected by CCR constituents at Roxboro.
This conclusion is further supported by multiple water quality and biological
assessments conducted by Duke Energy as part of the NDPES monitoring program.
5.5 CSM Summary
The Roxboro CSM presented in herein describes and illustrates hydrogeologic
conditions and constituent interactions specific to the Site. The CSM presents an
understanding of the distribution of constituents with regard to the Site -specific
geological/hydrogeological and geochemical processes that control the transport and
potential impacts of constituents in various media and potential exposure pathways to
human and ecological receptors.
In summary, the ash basins were constructed within former perennial stream valleys in
the Piedmont of North Carolina, and exhibit limited horizontal and vertical constituent
migration, with the predominant area of migration occurring near and downgradient of
the ash basin dams and dikes. Downgradient surface water bodies, the NPDES
permitted wastewater ponds are groundwater discharge zones that limit the horizontal
migration of constituents downgradient of the basins. The upward flow of water into
the basins minimizes downward vertical constituent migration to groundwater
immediately underlying saturated ash in the upgradient ends of the basins. Due to the
prevailing horizontal flow within the ash basins, there is limited vertical flow of ash
basin pore water into the underlying groundwater. The elevated constituent
concentrations found in groundwater near the WAB dam is due to the operating
hydraulic head in the basin. The ponded water in the WAB is the most important factor
contributing to constituent migration in groundwater.
Groundwater flow is away from water supply wells and there are no exposure
pathways between the ash basins including the downgradient additional source areas
and the pumping wells used for water supply in the vicinity of the Roxboro site, based
on empirical site data. Risk assessment results conclude that there is no identified
material increases in risks to human health and ecological receptors related to the ash
basins and the downgradient additional source areas.
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Through decanting of the WAB and EAB (as needed) and closure for both basins, the
rate of constituent migration from the ash basins to the groundwater system will be
reduced based on basin hydrogeology described above. Either closure scenario
considered by Duke Energy will significantly reduce infiltration to the remaining ash,
reducing the rate of constituent migration. Based on future predicted groundwater flow
patterns, under post ash basin closure conditions, and the location of water supply
wells in the area, groundwater flow direction from the ash basins is expected to be
further contained within the stream valleys and continue flowing north of the ash basin
footprints, and therefore will not flow towards any water supply wells.
Multiple lines of evidence have been used to develop the CSM based on the large data
set generated for Roxboro. The CSM provides the basis for this CAP Update developed
for the Roxboro ash basins and downgradient additional non-CAMA source areas to
comply with G.S. 130A-309.211.
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6.0 CORRECTIVE ACTION APPROACH FOR SOURCE AREAS
(CAP Content Section 6)
Groundwater contains varying concentrations of naturally occurring inorganic
constituents. Constituents in groundwater with sporadic and low concentrations greater
than the corresponding standard (02L/IMAC/background value, as applicable) do not
necessarily demonstrate horizontal or vertical distribution of COI -affected groundwater
migration from the source unit. Constituents with concentrations above corresponding
standards were evaluated to determine if the level of concentration is present due to the
source unit. COIs are those constituents identified from the constituent management
process described below and are specific to individual source unit(s), not the Site. This
evaluation assisted in identifying if a unit is subject to corrective action under G.S.
130A-309.211 and 15A NCAC 02L .0106.
A constituent management process was developed by Duke Energy at the request and
acceptance of NCDEQ (NCDEQ letter dated October 24, 2019, Appendix A), to gain a
thorough understanding of constituent behavior and distribution in site groundwater
and to aid in identifying unit -specific COIs. The constituent management process
consists of three steps:
1. Perform a detailed review of the applicable regulatory requirements under
NCAC, Title 15A, Subchapter 02L
2. Understand the potential mobility of unit -related constituents in groundwater
based on Site hydrogeology and geochemical conditions
3. Determine the constituent distribution at the unit under current and predicted
future conditions.
This constituent management process is supported by multiple lines of evidence
including empirical data collected at the site, geochemical modeling, and groundwater
flow and transport modeling. The management process uses a matrix evaluation to
identify those constituents that have migrated downgradient of the source unit, in the
direction of groundwater flow at concentrations greater than 02L/IMAC/background
value with a discernable plume. The matrix evaluation considers the following per
constituent:
• Regulatory criteria,
• Site and Piedmont background values,
• Maximum mean constituent concentrations,
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• Exceedance ratios,
• Number and distribution of wells at or beyond the compliance boundary with
constituent concentrations greater than criterion,
• Constituent presence in ash pore water at concentrations greater than criterion,
and
• Constituent geochemical mobility
This approach has been used to identify unit -specific COIs that have migrated from the
ash basins and downgradient additional sources and may require corrective action. The
results of the constituent management process (described in detail in Section 6.1.3)
identified unit -specific groundwater COIs for each of the ash basins and the
downgradient additional source areas. No constituents in unsaturated soil were present
in concentrations greater than the corresponding standard (PSRG POG or background
value); therefore, no soil COIs were identified for the EAB and WAB.
COIs identified in groundwater for the EAB (Source Area 1, Figure 6-1), that have
migrated beyond the compliance boundary, and for the GSA/DFAHA (Source Area 3,
Figure 6-1), that have migrated to the Intake Canal, at concentrations greater than
02L/IMAC/background values are subject to corrective action.
Over the last four consecutive monitoring events (January 2018 to April 2019), COI
concentrations for the WAB (Source Area 2, Figure 6-1) have been less than applicable
02L standards in groundwater samples collected from monitoring wells at or beyond
the compliance boundary. Therefore, the WAB is in compliance with 02L requirements
and corrective action under 02L is not required.
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SOURCE AREA 1 (SA1) — EAST ASH BASIN, INDUSTRIAL LANDFILL,
AND LCID LANDFILL
This section provides the corrective action approach and information to support the
approach for Source Area 1 (EAB/industrial landfill/LCID landfill) as shown in Figure
6-1. As stated in Section 3.0, the Plant's industrial and LCID landfills are positioned on
top of a portion of the EAB and sit mostly, or entirely, within the EAB compliance
boundary, unable to be evaluated for potential groundwater impacts independent of
the EAB; therefore, are considered EAB additional sources in this CAP Update. The
EAB additional sources are included in the evaluation of current and potential future
groundwater impacts from and remedial alternatives for the EAB. Reference to
evaluation, sources, and remediation in this CAP Update, associated with the EAB;
include the industrial and LCID landfills even if not implicitly stated.
6.1 SA1 Extent of Constituent Distribution
6.1.1 Source Material Within the Waste Boundary
(CAP Content Section 6.A.a)
For purpose of evaluation and reporting, the waste boundary of Source Area 1 is
considered the outermost boundary of the combined extent of the EAB,
industrial landfill, and LCID landfill (Figure 6-1).
6.1.1.1 Description of Waste Material and History of
Placement
(CAP Content Section 6.A.a.i)
East Ash Basin
The EAB consists of a single unlined unit impounded by a main earthen
dam located on the north end of the EAB (main dam) (Figure 1-2). The EAB
main dam was constructed between 1964 and 1965, with an earth -fill
embankment having a maximum height of approximately 50 feet. In 1973,
the dam was raised 20 feet to its present configuration by placement of rock
fill over a filter blanket on the original downstream slope. The EAB main
dam is approximately 1,330 feet in length, design crest width of 15 feet, and
crest level at elevation 470 feet.
The industrial landfill is located on top and partially within the EAB waste
boundary. The construction of the industrial landfill included the creation
of an earthen separator dike in the eastern portion of the EAB for landfill
foundation, resulting in the EAB extension impoundment. The area
contained within the EAB waste boundary is approximately 71.3 acres
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(including the 12.7 acres for the extension impoundment). The industrial
landfill is discussed further in Section 1.5.2.
The EAB accepted waste streams in accordance with the Roxboro NPDES
permit. EAB waste streams historically, and mostly, included bottom ash
and fly ash with ash transport water used to convey ash via sluicing.
Additional waste streams included but were not limited to landfill leachate,
coal pile runoff, stormwater, cooling tower blowdown, and low volume
wastewater (boiler blowdown, oily waste treatment, waste backwash from
treatment processes, plant area wash water, equipment heat exchanger
water, and treated domestic waste). Upon construction of the industrial
landfill and conversion from a wet to dry ash handling system, sluicing to
the EAB ceased in the late 1980's. To begin closure of the EAB,
modifications were completed in June 2019 to re -direct remaining waste
stream flows to new plant wastewater treatment units. As of June 30, 2019,
the EAB ceased receipt of all wastewater flows.
Industrial Landfill Halo Area
The industrial landfill is discussed further in Section 1.5.2. The initial
unlined area of the industrial landfill was permitted to construct and
operate on November 21, 1988 and accepted solid waste material in
accordance with the Roxboro Solid Waste permit until Phase 1, the initial
landfill area with an engineered base liner system, was constructed and
permitted to operate in 2004. Solid waste in the initial area of the industrial
landfill consisted mostly of fly ash with incidental amounts of bottom ash
and other waste materials produced in the generating process.
Land Clearing and Inert Debris Landfill
The LCID landfill is located to the west of the EAB abutting the Dunnaway
Road entrance to the Plant and encompasses approximately 8.5 acres. The
landfill was permitted to operate in 2002 (NCDEQ DWM Permit No. 73-D)
and was used to dispose general construction debris and inert material
including asbestos. Based on recent geophysical data evaluations
(September 2019), approximately 1.8 acres of LCID materials is underlain by
suspected CCR materials which follows areas of historic topographic lows.
6.1.1.2 Specific Waste Characteristics of Source Material
(CAP Content Section 6.A.a.ii)
Source Area 1 characterization was performed through the completion of
soil borings, installation of monitoring wells, and collection and analysis of
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associated solid matrix and aqueous samples. Source characterization was
performed to identify the physical and chemical properties of the ash in the
source areas. The source characterization involved determining physical
properties of ash, identifying the constituents present in ash, measuring
concentrations of constituents in the ash pore water, and performing
laboratory analyses to estimate constituent concentrations from leaching of
ash.
East Ash Basin
Four borings (AB-04 through AB-07) were advanced within the EAB waste
boundary to obtain ash samples for chemical analyses (Figure 1-2). Ash was
encountered in borings AB-04, AB-05, AB-06, and AB-07 at varying
intervals. Ash was not observed in borings outside the ash basin perimeter.
The hydraulically sluiced deposits of ash consisted of interbedded fine -to
coarse -grained fly ash and bottom ash material. Ash was generally
described in field observations as gray to dark gray, non -plastic, loose to
medium density, dry to wet, fine- to course -grained sandy silt texture.
Physical properties analyses (grain size, specific gravity, and moisture
content) were performed on four ash samples from the ash basin and
measured using ASTM methods. Fly ash is generally characterized as a
moderately dense silty fine sand or silt. Bottom ash is generally
characterized as a loose, poorly graded (fine- to coarse -grained) sand.
Compared with soil, ash exhibited a slightly lower specific gravity, with
four values reported ranging from 2.154 (AB-04 - 28' to 30' bgs) to 2.685
(AB-04 - 51' to 53' bgs). Moisture content of the ash samples ranges from
13.4 (AB-05 - 45' to 46' bgs) percent to 65.2 percent (AB-04 - 28' to 30' bgs).
A depiction of the typical interbedded nature of fly ash and bottom ash
within an ash basin, as seen from an ash boring photograph can be found
below (Figure 6-2). Layers of bottom ash are typically more permeable than
layers of fly ash due to the coarser grain size of bottom ash.
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Corrective Action Plan Update December 2019
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FIGURE 6-2
FLY ASH AND BOTTOM ASH INTERBEDDED DEPICTION
Report
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SOIL DATA
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Cney & W - S. seedy SILT (SG - 3.654)
Industrial Landfill Halo Area
As described in Section 1.5.2, the unlined portion of the industrial landfill
accepted solid waste in accordance with the Roxboro Solid Waste permit.
Solid waste mostly included fly ash with incidental amounts of bottom ash
as similar to described above related to the EAB source material.
Land Clearing and Inert Debris Landfill
The LCID landfill historically accepted land clearing waste, yard trash,
untreated and unpainted wood, uncontaminated soil, inert debris such as
unpainted rock, brick, concrete, concrete block, asphalt, and asbestos waste
from the plant. Approximately 1.8 acres of LCID materials is underlain by
suspected CCR materials which follows areas of historic topographic lows.
6.1.1.3 Volume of Physical Horizontal and Vertical Extent
of Source Material
(CAP Content Section 6.A.a.iii)
East Ash Basin
Based on topographic and bathymetric surveys, the EAB impoundment
area is estimated to contain approximately 3.24 million cubic yards (3.89
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million tons) of ash (Wood, 2019) as shown in Figure 6-1 (Source Area 1).
Based on borings located within the EAB, the maximum depth of CCR is
approximately 80 feet. Volume and physical vertical extent of ash material
within the basin as cross-section transect (A -A') from north to south, is
presented in Figure 6-3. Volume and physical vertical extent of ash
material within the basin as cross-section (B-B') along the center line of the
eastern lobe, from northwest to southeast, is presented in Figure 6-4.
Industrial Landfill Halo Area
The industrial landfill halo area is the unlined portion of the industrial
landfill that extends beyond the phases constructed with an engineered
base liner system (Figure 6-1). A portion of the halo area encompassing
approximately 4.38 acres was certified closed with an engineered cover
system in July 2019 (Section 1.5.2).
Land Clearing and Inert Debris Landfill
The LCID landfill is located to the west of the EAB abutting the Dunnaway
Road entrance to the Plant and encompasses approximately 8.5 acres
(Figure 6-1). Based on recent geophysical data evaluations (September
2019), approximately 1.8 acres of LCID materials is underlain by suspected
CCR materials which follows areas of historic topographic lows.
6.1.1.4 Volume and Physical Horizontal and Vertical
Extent and Anticipated Saturated Source Material
(CAP Content Section 6.A.a.iv)
East Ash Basin
Volume and physical horizontal and vertical extent of saturated ash
material within the EAB in plan -view is presented in Figure 6-5. The range
of ash thickness measured during the 2015 CSA activities was 55 feet to 80
feet near the north side of the basin where the ash is sufficiently stable for
drill rig access. Ash is thickest in areas that coincide with the former stream
valley of the eastern lobe of the EAB. A lesser amount of ash is present in
the western lobe of the EAB. A determination of ash thickness and
saturated conditions could not be made underlying the industrial landfill.
Ash within the EAB is saturated to depths of approximately 10 feet below
grade surface at monitoring wells locations, yielding approximately 70 feet
of saturated ash in the thickest ash location monitored.
Using modeled potentiometric levels of the saturated ash surface compared
to pre -ash basin historical topographic contours, the volume of saturated
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ash within the EAB is approximately 3,240,000 cubic yards (Wood, 2019).
The anticipated saturated thickness of ash will decrease as the closure
process progresses. In either closure scenario, residual ash in the EAB
extension impoundment will be excavated.
Industrial Landfill Halo Area
Dry fly ash placed in the unlined portion of the industrial landfill, including
the halo area, is unsaturated.
Land Clearing and Inert Debris Landfill
Using modeled potentiometric levels of the saturated ash surface compared
to pre -ash basin historical topographic contours, the thickness of saturated
ash within the topographic low of the LCID ranges from less than 5 feet to
10 feet bgs (Figure 6-5). Due to the unknown actual extent of saturated ash
with the LCID, a volume estimate cannot be made.
6.1.1.5 Saturated Ash and Groundwater
(CAP Content Section 6.A.a.v)
The thickness of saturated ash remaining in place following the closure -in -
place scenario will have limited to no adverse effect on future groundwater
quality. Layered ash within the EAB has resulted in relatively low vertical
hydraulic conductivity, further reducing the potential for downward flow
of pore water into underlying residual material. The CSM indicates that the
flow -through ash basin system should result in low to non -detectable COI
concentrations in groundwater underlying saturated ash within the EAB
except in the vicinity of the main dam/separator dike and the industrial
landfill halo area where downward vertical hydraulic gradients are
observed. Boron is the CCR constituent most indicative of groundwater
migration from the source area with a discernable COI plume pattern.
Using boron data, the generalized flow -through system is consistent with
Site -specific data as summarized in Table 6-1.
In summary, the analytical data from three of the monitoring wells
(ABMW-04BR, ABMW-06BR, and ABMW-07BRL) located within the EAB
exhibit low (less than 250 µg/L and below the 02L groundwater standard) to
non -detectable boron concentrations consistent with the flow -through
system conceptual site model. The monitoring well cluster, ABMW-5/5D,
located to the south and adjacent to the EAB main dam, exhibit boron
concentrations ranging from 13,100 µg/L to 28,800 µg/L in ABMW-5 to 2,200
µg/L to 2,980 µg/L in ABMW-5D. The data from these two well locations is
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also consistent with the CSM for ash basin systems with downward flow in
close proximity to the dams and dikes. The data suggests there is no
correlation between the thickness of saturated ash and the underlying
groundwater quality.
As shown in the preceding table, and discussed in Section 6.1.1, exceptions
to the CSM are near earthen dikes and associated with EAB additional
sources (the halo area). Groundwater recharge through rainfall
precipitation within the halo area, which is outside of the lined portion of
the industrial landfill, creates a downward groundwater flow as observed
in areas to the north and south of the EAB. Downward vertical hydraulic
gradients as observed in bedrock well clusters CCR-108BRL/MW-
108BRL/MW-108BRLL and GMW-8R/MW-21BRLR. Elevated COIs in
groundwater within the halo zone are likely related to remnant fly ash with
incidental bottom ash within the halo area that migrates downward
following the flow direction. The EAB earthen separator dike is anticipated
to have a similar effect on hydraulic heads as the dam, forcing flow
downward rather than flowing laterally within the basin. Downstream from
the separator dike, affected groundwater discharges to the eastern extension
impoundment area.
A technical memorandum, titled Saturated Ash Thickness and Underlying
Groundwater Boron Concentrations — Allen, Belews Creek, Cliffside, Marshall,
Mayo, and Roxboro Sites, (Arcadis, 2019) conducted linear regression analyses
to evaluate the relationships between saturated ash thickness and
concentrations of boron in ash pore water and underlying groundwater.
The linear regression analysis was conducted using analytical data from
Piedmont ash basins, including data from Roxboro.
A statistical evaluation was performed using a dataset, which included 89
monitoring wells completed in shallow, transition, and bedrock
groundwater zones directly beneath ash basins and 54 ash pore water
monitoring wells completed in saturated ash. Linear regression results
indicated that 87% of the groundwater monitoring locations below
saturated ash locations have less than 02L concentrations of boron in
groundwater. Exceptions to this relationship occur for select groundwater
wells located near ash basin dikes and dams and the EAB halo zone. This is
due to the downward vertical hydraulic gradient in these areas, which
enhances migration of COIs.
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Under pre -decanting conditions, the analysis demonstrates saturated ash
and ash pore water are not significantly contributing COI concentrations to
underlying groundwater except near dikes and dams, where downward
vertical gradients exist. Pre -decanting conditions represent the greatest
opportunity for COI migration to occur, not because of the volume of
saturated ash, but because of the existing ash basin hydraulic head and the
downward vertical hydraulic gradient near the dams and dikes. Although
decanting is not directly occurring within the EAB, conveyances linking the
EAB and WAB is anticipated to allow for a reduction in ash pore water
within the EAB. Under post -decanting, the hydraulic head of the ash basin
will be reduced, therefore reducing the downward vertical gradient
occurring near the dams and dikes and the rate of constituent migration
from the ash basin to the groundwater system. Decanting the WAB to
reduce the vertical hydraulic gradient, and to a lesser extent to the EAB if
decanting is needed, is the most important factor to limit further constituent
migration in groundwater.
6.1.1.6 Chemistry Within Waste Boundary
(CAP Content Section 6.A.a.vi)
East Ash Basin
Analytical sampling results associated with material from within the ash
basin waste boundary, including the EAB halo area, are included in the
following appendix tables or appendices:
• Ash solid phase: Appendix C, Table 4 (CAP Content Section
6.A.a.vi.1.1)
• Ash and soil synthetic precipitation leaching procedures (SPLP):
Appendix C, Table 6 (CAP Content Section 6.A.a.vi.1.2)
• Ash Leaching Environmental Assessment Framework: Appendix H,
Attachment C (CAP Content Section 6.A.a.vi.1.3)
• Soil: Appendix C, Table 4 (CAP Content Section 6.A.a.vi 1.4)
• Ash pore water: Appendix C, Table 1 (CAP Content Section
6.A.a.vi.1.6)
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Ash Solid Phase and Synthetic Precipitation Leaching
Potential
(CAP Content Section 6.A.a.vi.1.1 and 6.A.a.vi.1.2)
Ash samples collected inside the EAB waste boundary were analyzed for
total extractable inorganics using EPA Methods 6010/6020. Concentrations
of arsenic, boron, chromium (total), cobalt, iron, manganese, molybdenum,
selenium and vanadium were greater than concentrations of the same
constituents in soil background samples. The concentrations of these
constituents, except vanadium, in ash samples also were greater than
PSRGs for POG (Appendix C, Table 4). In addition, two ash samples
collected from borings completed within the ash basin (AB-05 (48-50') and
AB-07 (76-78') were analyzed for leachable inorganics using synthetic
precipitation leaching procedures (SPLP) and Method 1312 (Appendix C,
Table 6). The purpose of the SPLP testing is to evaluate the potential for
leaching of constituents to result in concentrations greater than the 02L
standards or IMACs. SPLP analytical results are compared with the 02L
comparative values to evaluate potential source contribution; the data do
not represent groundwater conditions. Analyses indicated that
concentrations of antimony, arsenic, chromium (total), iron, manganese,
nitrate, selenium, and vanadium were greater than the 02L or IMAC
comparative value.
Ash Leaching Environmental Assessment Framework
(CAP Content Section 6.A.a.vi.1.3)
Ash samples were analyzed for extractable metals analysis, including HFO
(hydrous ferric oxide)/HAO (hydrous aluminum oxide), using the Citrate-
Bicarbonate-Dithionite (CBD) method. Leaching environmental assessment
framework (LEAF) is a leaching evaluation framework for estimating
constituent release from solid materials. Leaching studies of consolidated
ash samples from the EAB were conducted using two LEAF tests, EPA
methods 1313 and 1316 (USEPA, 2012a, b). The data are presented and
discussed in the Geochemical Modeling Report in Appendix H, Attachment
C.
Leaching test results, using USEPA LEAF method 1316, indicate that, even
for conservative COIs such as boron, the leachable concentration of boron
present in ash from the Roxboro basins is considerably less (at least one
order of magnitude) than the total boron concentration (Appendix H,
Attachment C). The Roxboro data indicate that there is a process by which
the COIs might become stable within the ash and would make the COI
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unavailable for leaching. The exact mechanisms of this process are
unknown, however, literature suggests that incorporating COIs, such as
boron, into the silicate mineral phases is a potential mechanism (Boyd,
2002). The leaching behavior of several COIs as a function of pH, examined
using USEPA LEAF method 1313, demonstrated that for anionic COIs, the
leaching increased with increasing pH and the cationic COIs showed the
opposite trend (Appendix H, Attachment C).
Soil Beneath Ash
(CAP Content Section 6.A.a.vi 1.4 and 1.5)
Soil was collected from borings beneath the EAB within the waste boundary
at locations AB-5, AB-6, and AB-7 (Figure 1-2). All soil samples collected
from within the EAB waste boundary taken from beneath the ash were
saturated. Saturated soil and rock is considered a component of the
groundwater flow system and can serve as a source for groundwater COIs
at the Site. The potential leaching and sorption of constituents in the
saturated zone is included in the flow and transport and geochemical model
evaluations (Appendix G and H) by continuously tracking the COI
concentrations over time in the saprolite, transition zone, and bedrock
materials throughout the models. Historical transport models simulate the
migration of COIs through the soil and rock from the ash basins, and these
results are used as the starting concentrations for the predictive simulations.
Saturated soil samples with values reported greater than the PSRG POG or
background values are vertically delienated by groundwater constituent
concentrations in the corresponding flow zone of the soil sample depth.
Saturated soils beneath the ash basins have been analyzed for leachable
inorganics using SPLP procedures EPA Method 1312. SPLP was used to
determine the ability of simulated rainwater to leach site -specific
constituents out of the soil to groundwater. The 02L/IMAC values are used
for reference only of SPLP data; SPLP test results do not represent
groundwater; therefore, comparison to 2L/IMAC is for information only.
The SPLP analysis revealed several constituents including: antimony,
arsenic, barium, chromium, cobalt, iron, lead, manganese, nickel, nitrate,
thallium, and vanadium were present at concentrations greater than the 02L
or IMAC in the leachate from soil underlying the ash basins; however, only
for chromium and vanadium did the leachate concentrations exceed the
groundwater background values. Cobalt, iron, manganese, and vanadium
appear to be ubiquitous across the Roxboro Site in soils regardless of
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location (e.g., beneath ash, upgradient, downgradient) and tend to leach in
concentrations that are often greater than the 02L/IMAC in the leachate
even for soils not beneath the ash basins.
Ash Pore Water
(CAP Content Section 6.A.a.vi.1.6 and 6.A.a.vi.3)
The EAB is a NPDES-permitted wastewater treatment unit. Water within
the ash basin is not groundwater; therefore, isoconcentration maps were not
prepared for ash pore water and comparison to 02L/IMAC/background
values is not appropriate. All ash pore water sample locations are shown on
Figure 1-2 and analytical results are provided in Appendix C, Table 1.
Figures 6-6a and 6-6b represent ash pore water distribution in cross section
(A -A') from south to north. Figures 6-7a and 6-7b represent ash pore water
distribution in cross section (B-B') from southeast to northwest. Cross
section B-B' captures the greatest vertical extent of source material
(approximately 80 feet) upstream from the EAB main dam at well cluster
ABMW-7. Ash pore water concentrations are provided for general purposes
only and are not compared to 02L/IMAC and background values since it is
not groundwater. For further discussion of geochemical trends within the
ash pore water, see Appendix H, Section 2.
Ash Pore Water Piper Diagrams
(CAP Content Section 6.A.a.vi.2)
Piper diagrams can be used to differentiate water sources in hydrogeology
(Domenico & Schwartz, 1998). Piper diagrams of ash pore water monitoring
data are used to assess the relative abundance of major cations (e.g.,
calcium, magnesium, potassium, and sodium) and major anions (e.g.,
chloride, sulfate, bicarbonate, and carbonate) in water (Figure 6-8). Data
used for the piper diagrams include ash pore water data collected between
January 2018 and April 2019 with a charge balance between -10 and 10
percent.
Ash pore water results tend to plot with higher proportions of sulfate,
chloride, calcium, and magnesium, which is generally characteristic of ash
pore water (EPRI, 2006). The area where ash pore water tends to plot on the
piper diagram is identified as "affected" on Figure 6-8. The ash pore water
for the EAB follows this trend with most wells plotting in the high
sulfate/chloride and calcium/magnesium zone of the piper diagram.
However, ABMW-6 tends to plot in the more neutral zone of the piper
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diagram identified as "generally unaffected" similar to Site background
monitoring wells.
6.1.1.7 Other Potential Source Material
(CAP Content Section 6.A.a.v11)
As stated in Section 3.0 and discussed in detail in Section 1.5.2, the Plant's
industrial landfill halo area and LCID landfill are positioned on top of a
portion of the EAB and sit mostly, or entirely, within the EAB compliance
boundary, unable to be evaluated for potential groundwater impacts
independent of the EAB; therefore, the landfills are considered EAB
additional sources in this CAP Update.
6.1.1.8 Interim Response Actions
(CAP Content Section 6.A.a.viii)
Interim response actions conducted to date or planned are summarized in
Table 6-2. Details describing each action are presented below.
Cessation of EAB Wastewater Flows
As an initial phase of ash basin closure, a wastewater conveyance system
was installed to divert DFAHA wastewater flows from the EAB to the
recently installed plant wastewater treatment system. DFAHA wastewater
flows have been rerouted, now flowing to the recently installed plant
consolidated sump and ultimately to the Lined Retention Basin (LRB) for
treatment. The system was placed into operation on June 30, 2019.
Cessation of Industrial Landfill Leachate Flows
As an initial phase of ash basin closure, a leachate collection system was
installed to capture the seven landfill leachate gravity flow discharge
locations that flowed to the EAB. The leachate collection system includes
piping, sumps, a lift station, and equalization tanks, which route the landfill
leachate to the recently installed plant consolidated sump where the
leachate comingles with other wastewater flows. The leachate collection
system was placed into service in May 2019.
Source Area Stabilization
In a correspondence dated August 22, 2016, NCDEQ provided a notice of
deficiencies related to the Roxboro East Ash Pond (PERSO-033) and the
Roxboro West Ash Pond South Rock Filter (PERSO-039). For the EAB, the
need for pipe removal was indicated. In response, Duke Energy undertook
activities to correct the deficiencies; in general accordance with design
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drawings, pursuant to the Dam Safety Certificate of Approval, dated June 3,
2016. The activities included:
• Disconnect existing ash sluice lines.
• Remove existing lines within the concrete trench box.
• Remove existing pipe on dike slopes and install blind flanges at the
nearest joint beyond the toe of slope.
• Excavate and dispose off -site the existing trench box and all
associated bedding material.
• Backfill the excavation using compacted material to 98% Standard
Proctor in 6-inch lifts
• Replace asphalt roadway with new pavement of equivalent
thickness, including base material.
In a letter dated February 2, 2017, the dam repairs were approved by
NCDEQ (Appendix A).
Source Control
The industrial landfill Closure Plan was revised in 2018 to limit infiltration
of precipitation into the unlined portion of the industrial landfill that
extends beyond the phases constructed with an engineered base liner
system (halo area). A revised landfill Closure Plan was submitted to the
NCDEQ DWM on January 8, 2018 and subsequently approved on March 5,
2018. The revised landfill Closure Plan modified the previously approved
halo area soil final cover to an engineered cover system, containing a
geosynthetic liner, for closure. Approximately 4.38 acres on a portion of the
western side of the initial halo area was certified closed with an engineered
cover system in July 2019.
6.1.2 Extent of Constituent Migration Beyond the Compliance
Boundary
(CAP Content Section 6.A.b)
This section is an overview of constituent occurrences beyond the point of
compliance. The point of compliance for the Source Area 1 is the combined EAB
and industrial landfill compliance boundary. The compliance boundary for
groundwater quality at EAB is defined in accordance with Title Subchapter 02L
.0107(a) as being established at either 500 feet from the waste boundary or at the
property boundary, whichever is closer to the waste. The industrial landfill
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compliance boundary is defined by 15A NCAC 13B .0201 as 250 feet from the
waste. The ash basin compliance boundary and the industrial landfill compliance
boundary overlap in areas to the southeast and north. (Figure 1-2) and are
referred to in this report as the EAB compliance boundary.
Analytical sampling results associated with the EAB for each media are included
in the following tables and appendix tables:
• Soil: Appendix C, Table 4 and Table 6-4 (CAP Content Section 6.A.b.ii.1)
• Groundwater: Appendix C, Table 1 and Table 6-5 (CAP Content Section
6.A.b.11'.2)
• Seeps: Appendix C, Table 3 (CAP Content Section 6.A.b.ii.3)
• Surface water: Appendix C, Table 2 and Appendix K (CAP Content Section
6.A.b.ii.4)
• Sediment: Appendix C, Table 5 (CAP Content Section 6.A.b.ii.5)
Soil Constituent Extent
(CAP Content Section 6.A.b.ii.1)
Data indicate unsaturated soil constituent concentrations at or beyond the EAB
compliance boundary are generally consistent with background concentrations
or are less than regulatory screening values. Unsaturated soil at or beyond the
waste boundary is considered a potential seconday source to groundwater.
Constituents present in unsaturated soil or paritally saturated soil (vadose zone)
have the potential to leach into the groundwater system if exposed to favorable
geochemical conditions for chemical dissolution. Possible effects from the ash
basin to soils would be a result of ash pore water interaction with underlying
soils within the basin and groundwater migration beyond the basin. Therefore,
constituents considered for soil evaluation were limited to the constituents
identified as groundwater COIs in the CSA Update (SynTerra, 2017d) for
Roxboro ash basin (antimony, boron, chromium, chromium (VI), cobalt, iron,
manganese, molybdenum, selenium, strontium, sulfate, TDS, uranium and
vanadium).
For constituents lacking an established target concentration for soil remediation
(e.g., sulfate), the following equation was used in general accordance with the
reference in 15A NCAC 02L .0202 to calculate a POG value using Site -specific
data.
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Csoil = Cgw Lkd + (Ow + 6aH')IPb]df
Of the consituents evaluated, sulfate was the only constituent that required the
calculation of a Site -specific PSRG POG value. The PSRG POG value was
calculated using laboratory testing and physical soil data for effective porosity
(0.3) and dry bulk density (1.6 kilograms per liter [kg/L]) prepared in part for
flow and transport modeling for the Site. Soil water partition coefficients (Ka)
were obtained from the Groundwater Quality Signatures for Assessing Potential
Impacts from Coal Combustion Product Leachate (EPRI, 2010). The resulting PSRG
POG calculated value for sulfate was 1,938 mg/kg (Table 6-3). A summary of the
parameters and values used to calculated the PSRG POG for sulfate is provided
in Table 6-3. The range of constituent concentrations in unsaturated soils, along
with a comparison with soil background values and North Carolina PSRG POG
standards (NCDEQ February 2018), whichever is greater, is provided in Table 6-
4.
Constituents detected at concentrations greater than either the background value
and the PSRG POG in unsaturated soil samples (depth in feet) near or beyond
the waste boundary include (Table 6-4):
• Chromium: MW-2BR (2-2.5), GMW-8BR (6-7), MW-34D (2-4')
• Molybdenum: GMW-8BR (6-7)
• Sulfate: MW-3BR (0-2)
GMW-8BR is located south and adjacent to the industrial landfill with potential
exposure to ash landfill operations. MW-34D is located in the DFAHA with
potential exposure to DFA influences from ash transportation to the industrial
landfill and dust suppression operations. MW-3BR is located in the northeast
corner of the GSA with potential influence from the gypsum storage operations.
MW-2BR is located along Dunnaway Road, east of the LCID landfill, and in
between the EAB and WAB with potential exposure to historic landfill
operations.
Data indicate unsaturated soil constituent concentrations at or beyond the
compliance boundary are consistent with background concentrations or are less
than regulatory screening values (Table 6-4). Therefore, there are no constituents
in soil related to the EAB.
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Groundwater Constituent Extent
(CAP Content Section 6.A.a.ii.2)
The maximum extent of ash basin -affected groundwater migration for all flow
zones is represented by boron concentrations greater than the 02L standard.
Groundwater concentrations greater than 02L/IMAC/applicable background
concentration values occur locally at or beyond the compliance boundary,
associated with the EAB, in three areas:
1. Northeast of EAB (CW-1/MW-1BR/1BRL)
2. North of EAB (MW-22D/BR)
3. Northwest of EAB (MW-37S/D/BR)
Sulfate and TDS have concentrations that are greater than their respective
groundwater regulatory standards at or beyond the compliance boundary. The
distribution of sulfate and TDS is generally confined within the extent of the 02L
boron plume.
Constituents including selenium, strontium, and vanadium have concentrations
greater than their respective groundwater regulatory standards at or beyond the
EAB compliance boundary. The distribution of these constituents are confined
within the extent of the 02L boron plume. One exception includes strontium
concentrations at isolated locations southeast of the EAB in upgradient areas as
discussed in the strontium assessment technical memo provided in Appendix H.
Another exception includes locations where additional sources associated with
the GSA and the DFAHA that positioned downgradient and beyond the EAB
compliance boundary have contributed to affected groundwater as discussed in
Section 6-17.
The indication of iron, manganese, cobalt and chromium at concentrations
greater than 02L/IMAC values in background wells MW-18D/BR is provided in
the geochemical model report proved in Appendix H, Section 3. The
groundwater observed in MW-18D and MW-18BR generally has a neutral pH (7
to 8) and reducing conditions. As discussed in the geochemical report (Appendix
H: Section 3 and Attachments B, D, and E) reducing conditions will favor the
formation of more soluble Fe(II) and Mn(II) species, thus increasing the aqueous
concentrations as observed in MW-18D and MW-18BR. There are also some
observations of chromium and cobalt greater than 02L/IMAC values. The co -
association of cobalt and other transition metals (including chromium) with
manganese oxide minerals is discussed in the Geochemical Report (Appendix H,
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Section 3.8). The known co -associations of Mn with other transition metals along
with the lack of measurements of generally mobile COIs such as boron or sulfate,
indicate that the observations of Fe, Mn, Co, and Cr above 02L/IMAC levels in
MW-18D and MW-18BR are due to background influences and are not
attributable to the ash basin.
Section 6.1.3 includes a detailed matrix evaluation and rationale of groundwater
constituents requiring corrective action, and Section 6.1.4 provides
isoconcentration maps and cross sections depicting groundwater flow and
constituent distribution in groundwater at or beyond the compliance boundary
(CAP Content Section 6.A.b.i).
Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Seeps at Roxboro are subject to the monitoring and evaluation requirements
contained in the SOC. The SOC states that the effects from non -constructed seeps
should be monitored. For the EAB (per Attachment A to the SOC), the non -seep
location S-13 is an in -stream sample point to be monitored in accordance with the
NPDES Permit. S-13 consists of constructed seep S-09 and non -constructed seep
5-21, which flow to the unnamed tributary (eastern discharge canal) and
discharge to the Intake Canal.
Non-dispositioned seeps, where monitoring conducted has indicated the
presence of CCR affects, are evaluated for whether corrective action would be
anticipated for the seep location, and if so, potential corrective action
technologies that would be feasible for the location. The evaluation considers
seep location, approximate average flow rate, and predicted change in water
elevations from flow and transport model simulations. Potential correction action
strategies for seep locations are included in Table 6-8 and discussed herein.
S-21 is a well-defined channel, approximately 3 feet wide and 40 feet in length
that is positioned approximately 150 feet northeast of an existing sedimentation
basin on the northeast side of the EAB. The seep has typically been dry or
insufficient to sample since initial sampling conducted in May 2017. No
corrective action is intended for this location, however, monitoring will continue
in accordance with the NPDES permit.
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Surface Water Constituent Extent
(CAP Content Section 6.A.b.ii.4)
Surface water samples have been collected NCDEQ-approved locations over
multiple events from the Intake Canal and Stream 11A, to confirm groundwater
downgradient of the EAB and the downgradient non-CAMA source areas has
not resulted in surface water concentrations greater than 02B water quality
standards. Groundwater monitoring data consistently indicate a comingled
constituent plume associated with the EAB and the DFAHA along with the GSA
does extent to the Intake Canal. Surface water samples were collected to
evaluate acute and chronic water quality values. Surface water samples were
also collected at a background location in the Intake Canal consistent with an
upgradient groundwater monitoring well cluster, MW-14, and MW-28BR
(upgradient of potential migration areas). Analytical results were evaluated with
respect to 02B water quality standards and background data. All of this data
confirms that there are no surface water quality exceedances related to the EAB
and the downgradient non-CAMA sources. Surface water conditions is further
discussed in Section 6.2.1 and the full report for the Roxboro surface water
current conditions can be found in Appendix J.
Additionally, an environmental assessment of Hyco Reservoir, as discussed in
Section 5.3.4, have demonstrated that Hyco Reservoir has been an
environmentally healthy and functioning ecosystem for almost 20 years. Data
from these assessments indicate that the systems installed at the Roxboro Plant
for the protection of the water quality, the aquatic community, and human health
have been effective. More information related to the environmental health
assessments conducted for Hyco Reservoir, including sampling programs, water
quality and fish community assessments, and fish tissue analysis, can be found in
Appendix E.
Sediment Constituent Extent
(CAP Content Section 6.A.a.ii.5)
Sediment sample locations are generally co -located with surface water sample
locations (Figure 1-2). Similar to saturated soils and groundwater, sediment is
considered a component of the surface water system, and the potential leaching
and sorption of constituents in the saturated zone is related to surface water
quality. Because no regulatory standards are established for sediment inorganic
constituents, both background sediment COI concentration ranges and co -
located surface water sample results are considered in the sediment evaluation.
Table 4-5 presents constituent ranges of background sediment datasets per water
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body. Analytical results for all sediment samples are provided in Appendix C,
Table 5.
Assessment of COIs in sediment from surface waters, including the Hyco
Reservoir and the Intake Canal, was conducted through a comparison evaluation
between sediment sample COI analytical results, from one-time grab samples,
and COI concentration ranges from background sediment datasets. No sediment
samples were collected from the non -seep location S-13, since the location is an
in -stream sample point that discharges from two 36-inch RCP culverts to the
Intake Canal. Samples collected from the Intake Canal and Stream 11A were
comparable with background dataset range from the Intake Canal background
sample, RSW-6.
6.1.2.1 Piper Diagrams
(CAP Content Section 6.A.b.iii)
Piper diagrams can be used to differentiate water sources in hydrogeology
by assessing the relative abundance of major cations (i.e., calcium,
magnesium, potassium, and sodium) and major anions (i.e., chloride,
sulfate, bicarbonate, and carbonate) in water.
Groundwater Piper Diagrams
Piper diagrams of groundwater monitoring data from surficial zone,
transition zone, and bedrock zone background locations and downgradient
of the ash basin (Figure 6-8) are used to assess the relative abundance of
major cations (e.g., calcium, magnesium, potassium, and sodium) and major
anions (e.g., chloride, sulfate, bicarbonate, and carbonate) in groundwater.
Data used for the piper diagrams include groundwater data results from
sampling between January 2018 and April 2019 with a charge balance
between -10 and 10 percent.
• Background groundwater from each flow zone tends to plot central
to the diagram indicating water quality is more balanced between
major anions and cations. The area where background groundwater
(or native groundwater) tends to plot on the piper diagram is
identified as "generally unaffected" on Figure 6-8.
• Transition flow zone monitoring wells GPMW-1D, GPMW-2D,
GPMW-3D, MW-36D, MW-34D, MW-22D, and GMW-2 plot near ash
pore water points indicating water quality more similar to ash pore
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water than background groundwater (Figure 6-8). This is likely due
to these wells being near the GSA and the DFAHA.
• Bedrock groundwater monitoring wells GPMW-1BR, GPMW-2BR,
GPMW-3BR, and MW-3BR also fall into the "affected" zone of the
piper diagram. These wells are also located downgradient of the GSA
and the DFAHA.
The distribution of results on the piper diagrams in Figure 6-8 indicate no
conclusion can be made regarding impact to groundwater from the ash
basin based on relative abundance of major cations and anions.
Seep and Surface Water Piper Diagrams
Piper diagrams of EAB seeps (S-13, S-14, and S-21), the Intake Canal (RSW-1
through RSW-5), Stream 11A (RSW-9) and background locations for the
Intake Canal (RSW-6) and Hyco Reservoir (SW-1 through SW-3) surface
water data are included on Figure 6-9. Data used for the piper diagrams
include most recent available seep and surface water data (Appendix C,
Table 2) with a charge balance between -10 and 10%. As discussed in
Section 6.1.1, ash pore water from the EAB does not plot on piper diagrams
in an area that is distinguishable from background groundwater. Therefore,
the data shown on Figure 6-9 cannot be used to make inferences regarding
potential effects to surface water from the EAB. General observations from
the seep and surface water piper diagrams include:
Seep S-21 plot within the area where ash pore water tends to plot. S-
21 is typically dry or insufficient to sample since initial sampling
conducted in May 2017. This seep will continue to be monitored in
accordance with the NPDES permit.
Seeps S-13 and S-14 and surface water samples collected from the
Intake Canal, including the background location, RSW-6, plot within
the region of between the affected and generally unaffected water
quality. This area is identified as "potential mixing". Sample results
from the Intake Canal are less than 02B standards (Appendix C,
Table 2). The non -seep location S-13 is an in -stream sample point to
be monitored in accordance with the NPDES Permit. S-13 consists of
constructed seep S-09 and non -constructed seep S-21, which flow to
the unnamed tributary (eastern discharge canal) and discharge to the
Intake Canal. S-14 is at the discharge point of an underground 36-
inch diameter reinforced concrete pipe that flows from the unnamed
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pond north of the EAB (and its compliance boundary) to the
wastewater detention basin positioned northwest of the GSA.
• The remaining surface water samples from Hyco Reservoir and the
Stream 11A plot with water quality in the region of generally
unaffected.
6.1.3 Constituents of Interest (COIs)
(CAP Content Section 6.A.a.c)
This CAP Update evaluates the extent of and remedies for COIs associated with
the EAB that are at or beyond the compliance boundary to the north and
northeast detected at concentrations greater than regulatory criteria or
background values, whichever is greater.
Site -specific COIs were developed by evaluating groundwater sampling results
with respect at concentrations greater than regulatory criteria or background
values, whichever is greater and additional regulatory input/requirements. The
distribution of constituents in relation to the ash management areas, co -
occurrence with CCR indicator constituents such as boron and sulfate, and
migration directions based on groundwater flow direction are considered in
determination of groundwater COIs.
The following list of COIs was developed as part of the CSA Update for Roxboro
(SynTerra, 2017d):
• Antimony
• Boron
• Chromium (Hexavalent)
• Chromium (Total)
• Cobalt
• Iron
• Manganese
• Molybdenum
• pH
• Selenium
• Strontium
• Sulfate
• Total Dissolved Solids (TDS)
• Uranium
• Vanadium
Soil
(CAP Content Section 6.A.c.i.1)
Unsaturated soil at or near the compliance boundary is considered a potential
secondary source to groundwater. Constituents, if present in unsaturated soil or
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partially saturated soil (vadose zone), have the potential to leach into the
groundwater system if exposed to favorable geochemical conditions for chemical
dissolution to occur. Constituents considered for unsaturated soil evaluation
were the same constituents identified as COIs for the ash basins, since soil
impacts, if present, would be related to ash pore water interaction to the
underlying soils within the basin, groundwater migration at or beyond the ash
basin. Piedmont soils, including those at the Site are naturally rich in aluminum,
iron, and manganese and other metals and metalloids including those that are
considered COIs at the Site.
Data indicate unsaturated soil COI concentrations, if present, are generally
consistent with background concentrations or are less than regulatory screening
values (Table 6-4). In the few instances where unsaturated soil COI
concentrations are greater than PSRG POG standards or background values, COI
concentrations are within range of background dataset concentrations or there
are no mechanisms by which the COI could have been transported from the ash
basin to the unsaturated soils.
Horizontal and vertical extent of COI concentrations in soil, and reasons why no
necessary corrective action for soils is identified at the Site, is discussed further in
Section 6.1.4.
Groundwater
(CAP Content Section 6.A.c.i.2)
A measures of central tendency analysis of groundwater constituent data
(January 2018 to April 2019) was conducted and means were calculated to
support the analysis of groundwater conditions to provide a basis for defining
the extent of the constituent migration at or beyond the compliance boundary of
the EAB. A measures of central tendency analysis was completed to capture the
appropriate measure of central tendency (arithmetic mean, geometric mean, or
median) for each dataset of constituent concentrations. Constituent
concentrations in a single well might vary over orders of magnitude; therefore, a
single sample result might not be an accurate representation of the
concentrations observed over several months to years of groundwater
monitoring. Evaluating constituent plume geometries with central tendency data
minimizes the potential for incorporating occasions where constituents are
reported at concentrations outside of the typical concentration range, and
potentially greater, or substantially less than enforceable groundwater standards.
Previous Site assessment mapping based on single constituent concentrations for
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each well might have overrepresented areas affected by the ash basin by posting
a single data set on maps and cross -sections that might have included isolated
data anomalies.
The mean of up to six quarters of valid data was calculated for each identified
constituent to analyze groundwater conditions and define the extent of
constituent migration at or beyond the EAB compliance boundary. At a
minimum, four quarters of valid data were used for calculating means; however,
if fewer than four quarters of valid data were available, the most recent valid
sample result was reported. Less than four quarters of valid data were not
available either because the well was recently installed or sample results from
one or more quarters were excluded. For use in calculating means, nondetect
values were assigned the laboratory reporting limit and estimated (J-flag) values
were treated as the reported value. Procedures for excluding data from
calculating means are based on USEPA's National Functional Guidelines
(USEPA, 2017a, 2017b), published research about leaching of elements from coal
combustion fly ash (Izquierdo, and others 2012), and professional judgement.
The following steps outline the approach followed in calculating central
tendency values for constituent concentrations in groundwater:
1. If the maximum analytical value divided by the minimum value for each
constituent was greater than or equal to 10 (i.e. the data set ranges over an
order of magnitude), the geometric mean of the analytical values was
used.
2. If the maximum analytical value divided by the minimum value for each
constituent was less than 10 (i.e. the data set range is within an order of
magnitude), the arithmetic mean was used.
3. The median of the data was used for records that contain zeros or negative
values (e.g., total radium). Negative values were set to zero prior to
calculating the median concentration.
4. If the dataset mode (most common) is equal to the RL, and the geometric
or mean value is less than or equal to the dataset's mode, the value is
reported as "<RL" (e.g. the reporting limit for boron is 50 µg/L; for wells
with geometric mean or mean analysis concentration less than 50 µg/L,
the mean analysis result would be shown as "<50").
Sample results were excluded from calculations for the following conditions:
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• Duplicate sampling events for a given location and date. The parent
(CAMA) sample was retained.
• Turbidity was greater than 10 Nephelometric Turbidity Units (NTUs)
• Records where pH was greater than 10 standard units (S.U.). Data with
pH greater than 10 S.U. might suggest well grout impacts.
• Data flagged as unusable (RO qualified)
• Data reported as non -detect with a reporting limit (RL) greater than the
normal laboratory reporting limit
• Negative values for total radium were set equal to 0.
For each constituent at Roxboro, the arithmetic mean was determined to be the
most appropriate measure of central tendency. Table 6-5 (CAP Content Section
6.A.b.ii.2) presents the mean analysis results of the constituent data using
groundwater monitoring sampling results from January 2018 to April 2019.
Where means could not be calculated, the most recent valid sample was
evaluated to determine whether the sample result is an appropriate
representation of the historical dataset. Data from Table 6-5 are used in
evaluating constituent plume geometry in the vicinity of the EAB.
Constituent Management Approach
A COI Management Plan was developed at the request of NCDEQ to evaluate
and summarize constituent concentrations in groundwater at the Site (Appendix
H). Results of this COI Management Plan are used to identify areas that may
require corrective action and to determine appropriate Site -specific mapping of
constituent concentrations on figures based on the actual distribution of each
constituent in Site groundwater.
• Groundwater COIs to be addressed with corrective action are those which
exhibit concentrations in groundwater at or beyond the compliance
boundary greater than the 02L standard, IMAC, or BTV, whichever is
highest. Table 6-6 presents the constituent management matrix for
determining COIs subject to corrective action at Roxboro.
The COI Management Plan is also used to discern constituents at naturally
occurring concentrations greater than 02L that would not be subject to
corrective action. Examples include naturally occurring constituents that
do not exhibit a discernable plume or constituents that have no correlation
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with other soluble constituents associated with coal ash or another
primary source (e.g., boron).
A three -step process was utilized in the COI Management Plan approach:
1. An evaluation of the applicable regulatory context
2. An evaluation of the mobility of target constituents
3. A determination of the distribution of constituents within Site
groundwater
The primary goal of the COI Management Plan is to utilize science -based
evidence to determine the realistic distribution and behavior of coal ash -related
constituents in groundwater. The COI Management Plan presents multiple lines
of evidence used to understand the actual constituent presence in the subsurface
at the Site, uses results from the COI Management Plan approach to identify Site -
specific COIs for inclusion for corrective action planning, and presents the COI
mapping approach for the CAP. The COI Management Plan approach is
described in detail in Appendix H and summarized below.
Numerous Site -assessment activities have been completed to date and support
the CSM, described in Section 5 as shown in Table ES-2. Data generated from
these Site assessment activities have been considered within the COI
Management Plan approach. Components of the Site assessment activities and
data evaluations utilized within the COI Management Plan include the
hydrogeologic setting, groundwater hydraulics, constituent concentrations,
groundwater flow and transport modeling results, geochemical modeling results,
and groundwater geochemical conditions.
Step 1: Regulatory Review
Step 1 of the COI Management Plan process considers the relevant
regulatory references listed in Appendix H. The regulatory analysis starts
with the current constituent list identified in the CSA Update (SynTerra,
2017d) and the 2019 IMP submitted by Duke Energy, March 20, 2019, and
approved by NCDEQ April 4, 2019. Constituent concentrations were
screened against their respective constituent criterion defined as the
maximum of the 02L groundwater quality standard, IMAC, and
background. COI concentrations were screened against their respective
constituent criterion for groundwater monitoring locations at or beyond
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the compliance boundary. Groundwater constituent concentrations used
in the screening are based on a calculated central tendency value (mean)
including data from 2018 through the 2nd quarter of 2019.
In October 24, 2019 correspondence, NCDEQ recommended use of a lower
confidence limit (LCL95) concentration rather than the central tendency
value (Appendix A). LCL95 concentrations were calculated for each
constituent and the LCL95 concentration for the sample with the highest
COI LCL95 concentration is provided in Table 1 of the COI Management
Plan in Appendix H. for comparison to the maximum constituent mean
concentration. Table 2 of the COI Management Plan in Appendix H
provides a comparison of the maximum constituent central tendency
concentrations compared with the maximum constituent LCL95
concentrations for wells located at or beyond the compliance boundary for
the Allen Steam Station, Belews Creek Stream Station, Cliffside Steam
Station, Marshall Steam Station, Mayo Steam Electric Plant, and Roxboro
Steam Electric Plant Sites. The constituent LCL95 concentrations were
typically lower than the constituent central tendency value with very few
exceptions. The number of wells exceeding constituent criteria using the
constituent LCL95 concentration was typically equal to or less than the
number of wells exceeding constituent criteria using the constituent
central tendency concentration. There were no increases in the number of
wells exceeding constituent criteria for the Site when comparing the
LCL95 to the constituent criterion and the number of exceedances was
typically less for LCL95. Use of the constituent central tendency
concentrations in the COI Management Plan process provides a
conservative estimate of the extent of constituents in Site groundwater.
Step 2: COI Mobility
Step 2 of the COI Management Plan process evaluates the constituent
mobility to identify hydrogeologic and geochemical conditions and
relative constituent mobility based on:
• Review of regulatory agency and peer -reviewed literature to
identify general geochemical characteristics of constituents,
• Analysis of empirical data and results from geochemical and flow
and transport modeling conducted for the Site, and
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• Identification of constituent -specific mobility as conservative (non -
reactive), non -conservative (reactive), or variably reactive based on
results from geochemical modeling (Appendix H).
Site -specific groundwater geochemical conditions that may affect
constituent transport and distribution are described in Table 1 of the COI
Management Plan in Appendix H.
Step 3: COI Distribution
Step 3 of the COI Management Plan process evaluates the relative
presence of constituents in Site groundwater. Descriptions of the
horizontal and vertical distribution of constituents with mean
concentrations above their respective COI criterion at and beyond the
compliance boundary are summarized in Table 1 of the COI Management
Plan in Appendix H and provided in more detail in Table 6-6 (CAP
Content Section 6.A.c.i.2). The COI Management Plan approach considers
the distribution of constituents on a Site -wide basis. These distributions
are used for planning appropriate corrective action, if necessary, as well as
determining which constituents to map on figures.
Primary descriptions of constituent distributions include plume -like
distributions for relatively mobile constituents such as boron and isolated
location(s) for constituents that do not exhibit plume -like distributions.
Boron is the constituent with the most plume -like distribution. Some
constituents with isolated exceedances of constituent criteria are not
associated with the boron plume and these exceedances are described in
more detail in Table 6-6 to place these exceedances within the context of
the Site CSM.
Rationale for inclusion or exclusion of constituents from mapping on
figures in the 2019 CAP Update is based on the horizontal and vertical
distribution of constituents with concentrations greater than their
respective constituent criterion. All wells that have constituent mean
concentration(s) greater than the constituent criterion are listed in Table 6-
6.
Outcome of COI Management Plan Process
Constituents with concentrations greater than the constituent criterion beyond
the compliance boundary were grouped by geochemical behavior and mobility.
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A comprehensive evaluation (i.e., means and groupings) of available data was
used to demonstrate constituent distribution and correlation with other soluble
constituents associated with coal ash, and to evaluate the spatial occurrence with
a discernable constituent plume in the direction of groundwater flow
downgradient of the source area. This evaluation emphasizes the depiction of
those constituents that have migrated downgradient of the source area, in the
direction of groundwater flow at concentrations greater than the constituent
criterion with a discernable plume that correlates with other soluble constituents.
Constituents were assigned to mobility categories based on geochemical
modeling results and information derived from peer -reviewed literature.
Constituent mobility categories are based on the concept of conservative versus
non -conservative constituents introduced by NCDEQ in the January 23, 2019
CAP content guidance document. The use of three mobility categories for
constituents was first introduced during in -person COI Management meetings
held with NCDEQ in September 2019 for the Allen, Marshall, Mayo, and
Roxboro Sites. Based on geochemical modeling results, constituent mobility
categories were expanded from conservative versus non -conservative to include
the following:
• Conservative, Non -Reactive constituents: [boron and TDS] Geochemical
model simulations support that these constituents would transport
conservatively (Kd values <1 liter per kilogram [L/kg]) as soluble species
under most conditions, and that the mobility of these constituents will not
change significantly due to current geochemical conditions or potential
geochemical changes related to remedial actions.
• Non -Conservative, Reactive constituents: [arsenic and chromium]
Geochemical model simulations support that these constituents are subject
to significant attenuation in most cases and have high Ka values indicating
the mobility of these constituents is unlikely to be geochemically affected
by current geochemical conditions or potential geochemical changes
related to remedial actions.
Variably Reactive constituents: [barium, hexavalent chromium, cobalt,
iron, manganese, molybdenum, strontium, sulfate, and vanadium]
Geochemical model simulations, and resulting Ka values, support these
constituents may be non -reactive or reactive in relation to geochemical
changes and are dependent on the pH and Eh of the system. The
sensitivity of these constituents to the groundwater pH and Eh indicates
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that these constituents could respond to natural changes, such as water
level fluctuations imposed by seasonality, or decanting and source control
activities that have the potential to change the groundwater pH or Eh.
As discussed in the CSA Update (SynTerra, 2017d) and the 2018 CAMA Annual
Interim Monitoring Report (SynTerra, 2019c), not all constituents with results
greater than background values can be attributed to the ash basin or another
source area. Naturally occurring groundwater contains varying concentrations of
inorganic constituents. Sporadic and low -concentration occurrences of these
constituents in the groundwater data do not necessarily demonstrate horizontal
and vertical distribution of COI -affected groundwater migration from the ash
basin.
Summary
A three -step process was utilized for the COI Management Plan approach
considering the regulatory context, the mobility of constituents, and the
distribution of constituents within Site groundwater. A comprehensive, multiple
lines of evidence approach was followed utilizing extensive Site data. The COI
Management Plan approach incorporated numerous components of the Site CSM
in a holistic manner. Clear rationale was provided for every step of the COI
Management process.
For the regulatory review portion of the COI Management Plan, mean
constituent concentrations were compared with constituent criteria to identify
constituents that exceeded their respective constituent criterion. Use of the
constituent central tendency concentrations in the COI Management Plan process
was shown to provide a conservative estimate of the extent of constituents in Site
groundwater. Exceedance ratio values indicate constituent concentrations that
exceed constituent criteria are typically within one order of magnitude (ER <10)
above the constituent criterion.
Using the constituent management process, nine of 14 inorganic groundwater
constituents (not including pH) identified in the CSA Update (CSA Update,
2017d), exhibit mean concentrations that are currently less than background
values, 02L standard, or IMAC at or beyond the compliance boundary, or have
few concentrations greater than comparison criteria but with no discernable COI
plume characteristics (e.g. vanadium in the bedrock flow zone). These nine
constituents include:
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• Antimony
• Chromium
• Chromium (VI)
• Cobalt
• Iron
• Manganese
• Molybdenum
• Total Uranium
• Vanadium
These constituents are not expected to migrate distances at or beyond the
compliance boundary or migrate distances that would present risk to potential
receptors, and are predicted, based on geochemical modeling, to remain at stable
concentrations, typically less than background values, 02L standard, or IMAC
(Appendix H).
The remaining five constituents exhibit mean concentrations greater than
background values, 02L standard, or IMAC with plume characteristics
downgradient of the EAB at or beyond the compliance boundary. These
constituents are as follows:
• Boron • Strontium
• Selenium • Total Dissolved Solids (TDS)
• Sulfate
As discussed in the CSA Update (SynTerra, 2017d), not all constituents with
results greater than background values can be attributed to the EAB. Naturally
occurring groundwater contains varying concentrations of inorganic
constituents. Sporadic and low -concentration occurrences of these constituents
in the groundwater data do not necessarily demonstrate horizontal or vertical
distribution of COI -affected groundwater migration from the EAB.
6.1.4 Horizontal and Vertical Extent of COIs
(CAP Content Section 6.A.d)
The COIs at the EAB have been delineated horizontally and vertically in
groundwater based on sampling and analysis data collected from 172 monitoring
wells present at the site. The majority of COIs are either present below their
applicable standards, do not exhibit discernable plumes, or have migrated a
limited distance from the ash basin in groundwater to the north and northeast. .
Supporting information for these findings are presented in the COI management
evaluation presented in Section 6.1.3 and in Appendix H.
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Boron, a conservative (nonreactive) constituent is the main COI that is present in
site groundwater in a discernable plume, although boron concentrations decline
below its 2L standard range between 300 to 400 feet beyond the EAB waste
boundary with the exception of the comingled plumes associated with the
DFAHA. Boron typically has greater concentrations in CCR than in native soil
and is relatively soluble and mobile in groundwater (Chu, 2017). Sulfate and TDS
are also conservative constituents and represent similar discernable COI plume
geometries as boron. Additional constituent concentrations, selenium and
strontium, identified as being greater than their respective groundwater
regulatory standards or background values, and are associated with COI -affected
groundwater migration from the ash basin, are confined within the extent of the
02L boron plume at the Site due to the relatively higher Ka values and
geochemical properties. Therefore, the maximum extent of the 02L boron plume
(700 µg/L) was used to determine the maximum extent of COI -affected
groundwater migration.
Since naturally occurring COIs might be present at concentrations greater than
background values, isoconcentration maps of the primary CCR indicator COI (i.e.
boron) is the most representative of the groundwater COI plume extent in three-
dimensional space.
Isoconcentration maps and cross -sections use groundwater analytical data to
spatially and visually define areas where groundwater COI concentrations are
greater than background values and/or 02L/IMAC. Means of groundwater COI
monitoring sampling results from January 2018 to April 2019 provide an
understanding of groundwater flow dynamics and direction to define the
horizontal and vertical extent of the COI plume.
Horizontal extent of the COI plume is depicted on isoconcentration maps
(Figures 6-10a through 6-14b). Vertical extent of the COI plume is depicted on
two generalized cross -sectional depictions of the Site. Cross-section A -A' is
oriented north to south and displays the general EAB layout including: industrial
landfill profile with underlying saturated ash, areas evaluated for corrective
action, and downgradient GSA and subsequent Intake Canal (Figures 6-6a and 6-
6b). Cross section B-B' is orientated northwest to southeast and displays the EAB
extension impoundment, industrial landfill profile with underlying saturated
ash, and NPDES permitted surface water bodies downgradient of the main dam
(Figures 6-7a and 6-7b).
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At or beyond the compliance boundary, the maximum extent of COI -
groundwater affected by the EAB occurs northeast and north of Source Area 1.
6.1.4.1 COIs in Unsaturated Soil
(CAP Content Section 6.A.d.i)
Unsaturated soil samples at or beyond the waste boundary were collected
from soil borings and during well installation activities (Figure 6-15). In
response to the CSA Update (SynTerra, 2017), NCDEQ requested additional
evaluation of unsaturated soil surrounding, especially along the margins, of
the ash basin to determine the degree of possible impact from historical
CCR management at Roxboro. Additional unsaturated soil samples along
the perimeter of the EAB waste boundary have been collected as various
field efforts between June 2018 and June 2019. An evaluation of the
potential nature and extent of COIs in unsaturated soil at or beyond the
waste boundary was conducted by comparing unsaturated soil
concentrations with background values or PSRG POG standards, whichever
is greater (Table 6-4) (CAP Content Section 6.A.d.i).
Constituents detected at concentrations greater than either the background
value or the PSRG POG in unsaturated soil samples (depth in feet) near or
beyond the waste boundary include:
• Chromium: MW-2BR (2-2.5), GMW-8R (6-7), MW-34D (2-4)
• Iron: MW-34D (8-9), PSB-37 (1.5-2), PSB-38 (1.5-2), PSB-45 (1.5-2),
PSB-47 (1.5-2)
• Manganese: PSB-44 (1.5-2), PSB-45 (1.5-2)
• Molybdenum: GMW-8R (6-7)
• Sulfate: MW-3BR (0-2)
No necessary corrective action for soils is identified at the EAB because
there is no potential secondary source to groundwater from leaching of
unsaturated soil constituent concentrations that are greater than either
background values or the PSRG POG standard, for the following reasons:
• Concentrations of chromium greater than the PSRG POG and
background were reported upgradient from the EAB at MW-2BR (2-
2.5), where there are no mechanism by which the COI could have
been transported from the ash basin to the unsaturated soils. MW-
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2BR is positioned on a hydraulic divide, where groundwater flows
north and east on the east side of the divide and north and west on
the west side of the divide based on pre -decanting conditions (Figure
6-15). The remaining unsaturated soil samples where chromium is
greater than the PSRG POG and background are vertically delineated
by deeper soil samples (Table 6-4).
• Concentrations in unsaturated soil were lesser than background
values or PSRG POG beyond the EAB compliance boundary, with
the exception of sulfate at MW-3BR (0-2') (Table 6-4). Concentrations
of sulfate greater than the PSRG POG at MW-3BR within shallow
soils are likely attributed to bulk gypsum storage with the area. Soil
sample MW-3BR (21-23') provides vertical delineation at this
location, where sulfate concentrations are reported lesser than
background values.
Although greater than background values or PSRG POG, iron and
manganese detections at or beyond the waste boundary are within
the range of concentrations detected in soil samples from
background locations as shown in Table 6-4.
• Detections greater than the PSRG POG for molybdenum in
unsaturated soil at GMW-8R (6-7) are vertically delineated by GMW-
8R (10.5-11.5). Furthermore, concentrations of molybdenum in
groundwater at GMW-8R are less than background values and 02L
(Appendix C, Table 1).
6.1.4.2 Horizontal and Vertical Extent of Groundwater in
Need of Restoration
(CAP Content Section 6.A.d.ii)
This section discusses the horizontal and vertical extent of groundwater in
need of restoration in areas north and northeast of the EAB. Groundwater
is not in need of restoration adjacent to the ash basin to the south, east, and
west due to the lack of COIs above applicable standards in these areas. A
limited number of COIs in groundwater are present at or beyond the
compliance boundary to the north and northeast of the EAB. Additional
detail for these two areas is provided below.
Northeast Extent of COI -Affected Groundwater
Northeast and downgradient of Source Area 1, the COI -affected
groundwater at or near the compliance boundary is defined by boron at
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concentrations greater than 02L. The extent of affected groundwater
transport related to hydraulic conditions is supported by the following
observations:
• The shallow and transition flow zones are unsaturated in the vicinity
of the industrial landfill waste boundary and EAB compliance
boundary.
The bedrock flow zone groundwater boron extent northeast of the
EAB is beyond the compliance boundary (Figure 6-10b). This is
supported by the groundwater flow and transport model and
bedrock well cluster CW-1, MW-1BR, and MW-1BRL.
Bedrock well cluster CW-1, MW-1BR, and MW-1BRL, positioned
along the EAB compliance boundary, defines the northeastern extent
of the COI -affected groundwater. This well cluster provides a vertical
profile of the bedrock flow zone where total well depths extend to
approximately 40 feet bgs (CW-1), 76 feet bgs (MW-1BR), and 216
feet bgs (MW-1BR). A strong downward hydraulic gradient occurs
between CW-1 to MW-1BR (0.195 ft/ft) and between MW-1BR to
MW-1BRL (0.214 ft/ft). These wells are located in relatively
permeable zones of lesser conductance (0.01 to 0.1 ft/day in upper
bedrock from calibrated conductivities), compared to the geomean
hydraulic conductivity values identified at the Site.
Mean analysis of boron from these wells indicates concentrations are
greater than 02L in MW-1BR and below background in CW-1 and
MW-1BRL.
• Bedrock COI —affected groundwater at concentrations greater than
02L standard is horizontally delineated using bedrock groundwater
monitoring wells (MW-29BR and MW-30BR) east of the eastern
discharge canal. The eastern discharge canal, a groundwater to
surface water discharge area, appears to limit the groundwater COI -
affected groundwater distribution.
The northeastern groundwater COI -affected groundwater extent
relates to hydraulic conditions associated with industrial landfill halo
area, an exception to the flow -through system described in the flow
and transport model report (Appendix G). Downward vertical
hydraulic gradients observed in bedrock promote downward COI
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migration in groundwater along the industrial landfill waste
boundary.
• Northeast and downgradient of the EAB, groundwater flows
upward toward the eastern discharge canal; limiting downward
migration of COIs. The extent of COI -affected groundwater northeast
of EAB is limited by hydraulic conditions in that area.
North Extent of COI -Affected Groundwater
North and downgradient of the EAB in the vicinity of the unnamed pond
(Figure 1-2), the COI -affected groundwater extent at or near the compliance
boundary is defined by boron, selenium, sulfate, and TDS at concentrations
greater than 02L or background. The extent of affected groundwater
transport related to hydraulic conditions is supported by the following
observations:
The northern groundwater COI extent relates to hydraulic conditions
associated with unlined portion of the industrial landfill (halo area),
an exception to the flow -through system described in the flow and
transport model report (Appendix G). The COI -affected
groundwater from the EAB comingles downgradient with similar
COI -affected groundwater contributed by downgradient additional
sources detailed as Source Area 3. These downgradient additional
sources roughly begin along the northernmost ash basin compliance
boundary and extend north towards the Intake Canal.
The shallow and transition flow zones north of the EAB are generally
unsaturated between the industrial landfill waste boundary and the
ash basin compliance boundary.
The transition flow zone groundwater COI extent north of the EAB is
beyond the compliance boundary. Mean concentrations of sulfate
and selenium, at groundwater monitoring well MW-22D, is greater
than the 02L or background, whichever is greater (Figures 6-10a and
6-13a).
Bedrock COI -affected groundwater at concentrations greater than
02L standard and background extends north beyond the EAB
compliance boundary. Mean concentrations of boron, sulfate, and
TDS, at MW-22BR, is greater than 02L or background, whichever is
greater (Figures 6-10b, 6-11b, and 6-12b).
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North -Northwest Extent of COI -Affected Groundwater
North-northwest and downgradient of the EAB and adjacent to the
DFAHA, the COI -affected groundwater extent at or near the compliance
boundary is defined by boron, selenium, sulfate, and TDS at concentrations
greater that 02L or background. The extent of affected groundwater
transport related to hydraulic conditions is supported by the following
observations:
The groundwater COI extent relates to hydraulic conditions
associated with the EAB comingling with similar COI -affected
groundwater from addition source areas, predominately the
DFAHA.
Deep and upper bedrock flow zones have similar COI -affected
groundwater geometries northwest of the ash basin. This supports
the interpretation that these flow zones are hydraulically connected
(Figures 6-10a through 6-14b).
• In this area, NPDES permitted wastewater ponds adjoin the ash
basin downstream of the main dam within the ash basin compliance
boundary. These wastewater ponds act as groundwater to surface
water discharge areas and limit horizontal delineation of COI -
affected groundwater at concentrations greater than 02L standards or
background. The simulated COI -affected groundwater plume in this
area exceeds beyond the compliance boundary to the north-
northwest (Figures 6-10a through 6-14b).
• Downgradient of the EAB dam, groundwater flows upward toward
the NPDES permitted wastewater ponds, limiting downward
migration of COIs to the area just upstream from the dam. The
extent of COI -affected groundwater north of the dam is limited by
hydraulic conditions in that area.
6.1.5 COI Distribution in Groundwater
(CAP Content Section 6.A.e)
As part step two of the constituent management process and the geochemical
modeling evaluation (Appendix H), constituents identified in the CSA Update
(SynTerra, 2017d) as COIs were grouped by geochemical behavior and mobility.
An evaluation (i.e. mean analysis and mobility groupings) of available data was
used to demonstrate constituent distribution in groundwater to evaluate the
spatial occurrence with a discernable plume in the direction of groundwater flow
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direction downgradient of the ash basin. The evaluation grouped constituents
into three mobility groups: conservative (non -reactive), non -conservative
(reactive), and variably reactive.
6.1.5.1 Conservative Constituents
Boron, sulfate, and TDS geomean isoconcentration maps and cross sections
support the following observations regarding the extent of COI -affected
groundwater represented by these conservative constituents:
• Bedrock flow zone COI -affected groundwater extends northeast,
north, and north-northwest of the EAB beyond the compliance
boundary.
• Transition and bedrock flow zone COI -affected groundwater to the
west of the EAB are within the compliance boundary.
• The deep and bedrock flow zone COI -affected groundwater have
relatively similar COI geometries (Figures 6-10a through 6-
12b). This supports a connected, unconfined flow system between
the deep flow zone and upper bedrock.
• Beyond the compliance boundary, COI -affected groundwater in the
transition zone and bedrock flow zones appears to be horizontally
limited to the east by the eastern discharge canal (Figure 6-10a and
Figure 6-10b). Vertical COI -affected groundwater extends into
deeper bedrock flow zone in limited areas to the east of the EAB
(Figures 6-10b). The bedrock flow zone at Roxboro is unconfined and
largely connected the upper flow zones, supported by similar COI
geometries when flow zones are saturated.
COI -affected groundwater migration is horizontally bounded
downstream of the EAB main dam by NPDES-permitted wastewater
ponds within the compliance boundary. North of the EAB, COI -
affected groundwater mixes with additional source areas
downgradient of the EAB (Figures 6-10a and 6-10b).
The maximum extent of COI -affected groundwater migration for all flow
zones is represented by boron. Sulfate and TDS concentrations identified as
being greater than their respective groundwater regulatory standards are
associated with COI -affected groundwater migration from the EAB but are
generally confined within the extent of the 02L boron plume (Figures 6-10a
through 6-12b).
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Plume Behavior and Stability
(CAP Content Section 6.A.e.i.1)
Mann -Kendall trend analysis was performed using conservative constituent
datasets for ash pore water and groundwater wells within the waste
boundary, between the waste boundary and compliance boundary, and
downgradient the source area, at or beyond the compliance boundary
(Table 6-7). A plume stability analysis conducted by Arcadis (2019), using
the Mann -Kendall trend approach, is described in detail in Appendix I and
summarized below. The analysis was performed using analytical results for
samples collected from 2011 through 2019. Trend analysis results are
presented where at least four samples were available and frequency of
detection was greater than 50%. Statistically significant trends are reported
at the 95% confidence level. The analysis of constituent concentrations
through time produced six possible results:
1. Statically significant, decreasing concentration trend (D)
2. Statically significant, increasing concentration trend (I)
3. Greater than 50% of concentrations were non -detect (ND).
4. Insufficient number of samples to evaluate trend (n <4) (NE)
5. No significant trend, and variability is high (NT)
6. Stable. No significant trend, and variability is low (S)
Groundwater wells within the waste boundary generally have no trends,
stable trends, or increasing trends. Increasing trends within the waste
boundary are associated with wells upstream and adjacent to the EAB main
dam. This is consistent with information presented in the CSM in Section
5.0. Groundwater within the waste boundary Mann Kendall results
indicate:
• Excluding ND and NE trends, approximately 50% of calculated
trends for wells within the waste boundary generally have no trends,
stable trends, or decreasing trends for boron, sulfate, and TDS (Table
6-7).
• Conservative constituents sulfate and TDS with increasing trends
remain below the comparison criteria (Appendix C, Table 1).
• Increasing trends of boron within ABMW-7BR are vertically
delineated by lower bedrock well ABMW-7BRL, where conservative
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constituents (i.e., boron, sulfate, and TDS) exhibit a stable trend or no
trend. Within the subsequent lower bedrock well, ABMW-7BRLL, an
insufficient number of samples were available for trend evaluation;
however, conservative constituents are reported below background
and 02L standards.
Groundwater monitoring wells northwest of the EAB, between the waste
boundary and compliance boundary, include CCR-110D/BR, CCR-101D/BR,
CCR-102BR, GMW-1A, and MW-11D/BR. Mann Kendall results for
groundwater wells between the waste boundary and compliance boundary
indicate:
• Sulfate concentrations within MW-11D and MW-11BR were
identified as having increasing trends (Table 6-7). Sulfate
concentrations within the MW-11D/BR well pair are consistent with
background concentrations and reported less than the 02L standard
(Appendix C, Table 1).
• TDS concentrations with increasing trends within CCR-101BR
remain less than background and the 02L standard (Appendix C,
Table 1).
• Excluding ND results, the remaining concentration trends for
conservative constituents northwest of the EAB are either decreasing,
stable, or no significant trend was identified (Table 6-7).
Groundwater monitoring wells north and northeast of the EAB, between
the waste boundary and compliance boundary include CCR-103BR, CCR-
104BR, CCR-105BR, CCR-106BR, CCR-107BR, GMW-2, GMW-6, GMW-10,
GMW-11, MW-35S/D/BR, and MW-37S/D/BR. Mann Kendall results for
groundwater wells between the waste boundary and compliance boundary
indicate:
• An insufficient number of samples were available from recently
installed groundwater monitoring well clusters MW-35S/D/BR, and
MW-37S/D/BR (Table 6-7).
Over 50% of the remaining trend results for conservative constituents
within groundwater wells between the waste boundary and
compliance boundary are either decreasing, stable, or no significant
trend was identified (Table 6-7).
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Approximately 46% of groundwater wells between the waste
boundary and compliance boundary have increasing trends of
conservative constituents. Downgradient transition zone wells with
increasing trends are GMW-2 and GMW-6. Downgradient bedrock
wells with increasing trends are CCR-106BR, CCR-107BR, GMW-10,
and GMW-11. (Table 6-7).
• Increasing concentration trends of boron and sulfate were identified
within GMW-10; however, reported concentrations in 2019 indicate
concentrations less than comparison criteria (Appendix C, Table 1).
• Monitoring wells northeast of the EAB with increasing trends in
conservative constituents are positioned hydraulically upgradient
from areas proposed for corrective action.
Groundwater monitoring wells north and northeast of the EAB,
downgradient near or beyond the compliance boundary, are largely
associated with Source Area 3 and discussed in Section 6.17.5.1. Mann
Kendall results for groundwater wells MW-1BR, MW-1BRL, MW-27BR,
MW-28BR, and MW-29BR, between the waste boundary and compliance
boundary indicate:
• Over 50% of trend results for conservative constituents within
groundwater wells near or beyond the compliance boundary are
either decreasing, stable, or no significant trend was identified (Table
6-7).
Increasing concentration trends of sulfate and TDS were identified
within MW-27BR and MW-28BR, where greater than 50% of boron
concentration trends were identified as non -detect (Table 6-7).
• Increasing boron, sulfate, and TDS concentration trends were
identified for bedrock well MW-1BR (Table 6-7).
The groundwater plume northwest of the EAB appears stable, with detected
concentrations of conservative constituents reported less than background
or the 02L standard. The groundwater plume north and northeast of the
EAB appears unstable in areas, with several conservative constituents
indicating increasing concertation trends that suggest the plume is still
expanding. Some locations with increasing trends have concentrations
greater than comparative criteria.
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6.1.5.2 Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
Through the utilization of the matrix evaluation (Table 6-6) derived from
the constituent management process, non -conservative constituents are not
brought forth for corrective action related to the EAB. For monitoring wells
at or beyond the compliance boundary, means for non -conservative
constituents are either within Site -specific background values (vanadium)
or do not exhibit a discernable plume at the Site [uranium (total)].
6.1.5.3 Variably Conservative Constituents
Selenium and strontium isoconcentration maps and cross sections support
the following observations regarding the extent of COI -affected
groundwater represented by these variable constituents:
• A plume -like distribution of selenium greater than the 02L
standard occurs in the transition flow zone north of the EAB
(Figure 6-13a). Five monitoring wells, one in the shallow flow zone
(MW-35S) and four in the transition zone (GMW-6, MW-34D, MW-
35D, and MW-22D) are within the plume -like distribution of the
transition flow zone (Figures 6-13a). This plume -like distribution is
somewhat similar within the bedrock flow zone. Two monitoring
wells (GMW-11 and MW-37BR) are greater than the 02L standard
north and northwest of the EAB. (Figure 6-13b).
• Numerous concentrations of strontium are greater than
background within the transition and bedrock flow zones (Figure
6-14a and 6-14b). Concentrations are distributed within the north,
northwest, and northeast depicting a somewhat plume -like
distribution. A discussion regarding the strontium distribution in
groundwater for the EAB is provided as a technical memo in the
Appendix H.
6.2 SA1 Potential Receptors Associated with Source Area 1
(CAP Content Section 6.B)
Assessment findings and ongoing monitoring data confirm that affected groundwater
from Source Area 1 do not reach any water supply wells, and modeling indicates this
will remain the case in the future. CSA results and ongoing monitoring data indicate
Source Area 1 has affected groundwater quality immediately downgradient of the EAB;
however, groundwater discharge from the EAB is to the north to the NPDES-permitted
wastewater units and the comingled zone with the DFAHA. Groundwater effects are
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limited to between 300 and 400 feet from the EAB compliance boundary with the
exception of the comingled zone with the DFAHA and are within the Duke Energy
property. Duke Energy owns the land and controls the use of groundwater on the land
downgradient of the EAB within and beyond the predicted area of potential
groundwater COI influence from the EAB.
6.2.1 Surface Waters — Downgradient Within a 0.5-Mile
Radius of the Waste Boundary
(CAP Content Section 6.B.a)
A depiction of surface water features — including wetlands, ponds, unnamed
tributaries, seeps, streams, lakes, and rivers — within a 0.5-mile radius of the
Source Area 1 compliance boundary, along with permitted outfalls under the
NPDES and the SOC locations, are shown on Figure 5-8 (CAP Content Section
6.B.a.i and 6.B.a.ii). The 0.5-mile radius from the ash basin compliance boundary,
for which data is evaluated and depicted on figures, includes and is greater than
the required 0.5-mile radius from the waste boundary and is consistent with the
drinking water well and receptor surveys.
The EAB is located south of the downgradient additional source areas (Source
Area 3), which are located between Source Area 1 and the Intake Canal.
Associated North Carolina surface water classifications for the Intake Canal, a
component of Hyco Reservoir, are summarized in Section 5.3.2 and Table 5-4
(CAP Content Section 6.B.a.iii). For groundwater corrective action to be
implemented under 15A North Carolina Administrative Code (NCAC) .02L
.0106(k), groundwater discharge to surface water cannot result in exceedances of
standards for surface waters contained in 15A NCAC 02B .0200. Groundwater
downgradient of the EAB discharges to NPDES-permitted wastewater ponds.
However, a component of groundwater to the south of the EAB does discharge
to the unnamed jurisdictional stream (Stream #11A) (Figure 5-8). Surface water
samples were collected from Stream 11A to confirm groundwater downgradient
of the EAB have not resulted in surface water concentrations greater than NCAC
02B water quality standards. Groundwater monitoring data at the proximate
location, positioned upgradient, has indicated the EAB constituent plumes
extend to the compliance boundary in the direction of Stream #11A. Surface
water samples were collected to evaluate acute and chronic water quality values.
Analytical results were evaluated with respect to NCAC 02B water quality
standards and background data. The surface water samples were collected in
accordance with NCDEQ DWR Internal Technical Guidance: Evaluating Impacts
to Surface Water from Discharging Groundwater Plumes - October 31, 2017.
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Analytical results indicate constituent concentrations less than applicable 2B
criteria for samples collected by Stream 11A. Comparisons of surface water data
with the applicable USEPA National Recommended Water Quality Criteria for
Protection of Aquatic Life, Human Health and/or Water Supply (USEPA, 2015;
2018a; 2018b) was conducted on the surface water samples. As stated by the
USEPA, these criteria are not a regulation, nor do they impose a legally -binding
requirement. Therefore, comparisons with these criteria are only for situational
context. The constituents that have corresponding USEPA criteria but do not
have NCDEQ 02B criteria are alkalinity, aluminum, antimony, iron and
manganese. All concentrations of alkalinity, aluminum, antimony, iron and
manganese in downstream samples were either non -detect (i.e. antimony) or
concentrations were generally comparable to background concentrations.
The full report for Roxboro groundwater discharge to surface water and the
evaluation of surface waters to evaluate compliance with 15A NCAC 02B .0200
was submitted to NCDEQ on March 21, 2019. Surface water data has been
reevaluated as a result of surface water quality standards updated by NCDEQ on
June 6, 2019. A revision to the report was made to include the assessment of
Stream 11A. A copy of the revised report is provided in Appendix J.
Surface Water - Future Conditions Evaluation
An evaluation of potential future groundwater migration to surface water was
conducted to identify areas where further evaluation might be warranted. For
areas of potential future groundwater migration to surface water, a mixing
model approach was used for the evaluation of future surface water quality
conditions. Flow and transport modeling results were used to determine where
groundwater migration from the ash basin might intersect surface water in the
future. Predictive groundwater modeling using boron as a proxy for COI plume
migration demonstrated the area to the south of the EAB (specifically
jurisdictional Stream 11A) is not anticipated to be influenced by future
groundwater migration. A groundwater to surface water mixing model approach
was used to determine the potential surface water quality in the future
groundwater discharge zones. The full report for Roxboro groundwater
discharge to surface water under future conditions can be found in Appendix J.
General findings of the evaluation of future surface water conditions in potential
groundwater discharge areas include:
• The surface water mixing model evaluation confirms that predicted
resultant constituent concentrations in applicable surface waters are less
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than 02B surface water standards. Therefore, the criteria for compliance
with 02B is met, allowing potential corrective action under 15A NCAC
02L .0106 (k), (1), or (m).
The predicted extent of COI -affected groundwater migration from the ash
basin would not reach Stream 11A post ash basin closure, based on
predicted future hydraulic head elevations and groundwater flow
direction.
Seeps currently governed by the SOC that remain and are not
dispositioned 90 days after completion of decanting would be
characterized for determination of corrective action applicability. Where
applicable, and accounting for seep jurisdictional status, corrective action
planning at that time would occur.
6.2.2 Water Supply Wells
(CAP Content Section 6.B.b)
No public or private drinking water wells or wellhead protection areas were
found to be located downgradient of Source Area 1 as discussed in Section 5.3.2.
A total of 87 private water supply wells were identified within the 0.5-mile
radius of the EAB and WAB compliance boundary. Most of these wells are
associated with residences located to the east and upgradient of the Site, along
McGhees Mill Road and The Johnson Lane; and residences located south and
upgradient of the Site, on Dunnaway Road and Semora Road.
Table 6-9 (CAP Content 6.B.b.ii) provides tabulated results for the NCDENR and
Duke Energy sampling results as well as identified exceedances of 02L standards,
IMACs, and bedrock background values. A well -by -well summary of COI
exceedances and characterization is presented in Table 6-9. The exceedance
evaluation compares bedrock background values since it is assumed area water
supply wells are installed within the bedrock, which is typical for water supply
wells in the Piedmont.
6.2.2.1 Provision of Alternative Water Supply
Although results from local water supply well testing do not indicate effects
from the source area, water supply wells identified within the 0.5-mile
radius from the EAB and WAB compliance boundaries have been offered a
water treatment system in accordance with G.S. 130A-309.211(cl).
Duke Energy identified a total of 87 eligible connections for a water
treatment system within the 0.5-mile radius of the ash basin compliance
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boundaries. A property eligibility was contingent that the property did not
include a business; a church; a school; connection to the public water
supplier; and an empty lot.
Of the 87 eligible connections, three opted out of the option to connect to a
water treatment system and three did not respond to the offer. One
household will receive a water filtration system in the future due to an
inoperable well pump. Duke Energy installed 80 water filtration systems at
surrounding occupied residences. Additionally, Duke Energy voluntarily
connected a water filtration system to the Woodland Elementary School that
was not eligible per G.S. Section 130A-309.211(cl).
On August 30, 2018, Duke Energy provided completion documentation to
NCDEQ to fulfill the requirements of House Bill 630. NCDEQ provided
correspondence, dated October 12, 2018, to confirm that Duke Energy
satisfactorily completed the alternate water provisions under G.S. 130A-
309.211(c1) at Roxboro. Both documents are provided in Appendix D.
Figure 5-7a and Figure 5-7b (CAP Content Section 5.A.a,b,c) shows the
private and public water supply well locations with reference to water
treatment systems installed, vacant parcels, and residential properties that
opted out or did not respond to the offer. As discussed in Section 5.0, all of
the private water supply wells are located either upgradient or side -
gradient of the ash basin (in separate drainage systems).
6.2.2.2 Findings of Drinking Water Supply Well Surveys
(CAP Content Section 6.B.b.ii)
The location and information pertaining to water supply wells located
upgradient or side -gradient of the facility, within 0.5 miles of the EAB and
WAB compliance boundaries, were included in drinking water supply well
survey reports. Results from surveys conducted to identify potential
receptors for groundwater, including public and private water supply wells
and surface water features within a 0.5-mile radius of the EAB and WAB
compliance boundaries, have been reported to NCDEQ:
The major findings from the water supply well evaluation include:
All water supply wells are outside the COI plumes for Source Area 1
as shown in the isoconcentration figures for all flow zones (Figures 6-
10a through 6-14b).
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• All water supply are upgradient of the ash basin (Figure 5-7a).
Boron, a primary indicator COI that exhibits a discernable plume
related to the ash basin, was not detected above the laboratory
reporting limit in any of the water supply wells sampled (Table 6-9).
The analytical data indicates no CCR related exceedances of
regulatory and background concentrations in water supply wells
sampled in the receptor survey program.
This evaluation and the detailed evaluation results presented in the CSA
Update (SynTerra, 2017) indicate no impact to water supply wells from the
Roxboro ash basins (or Source Area 1). These findings has been confirmed
by 36 consecutive groundwater monitoring events. Furthermore, based on
flow and transport modeling, no future impact to water supply wells is
predicted.
6.2.3 Future Groundwater Use Areas Associated With Source
Area 1
(CAP Content Section 6.B.c)
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of Source Area 1. Therefore, no future groundwater use areas are
anticipated between Source Area 1 and the Intake Canal.
It is anticipated that private and public properties within a 0.5-mile radius of the
EAB compliance boundary will continue to rely on groundwater resources for
water supply for the foreseeable future; therefore, Duke Energy will provide
periodic maintenance of the provided water treatment systems for each property
that accepted the alternative water supply [(Figure 5-7b) (CAP Content Section
6.B.c.i)].
Based on future predicted groundwater flow patterns, under post ash basin
closure conditions, and the location of water supply wells in the area,
groundwater flow direction from the EAB is expected to be further contained
within the former stream valley and therefore will not flow towards any water
supply wells [(Appendix G) (CAP Content Section 6.B.c.ii)].
6.3 SA1 Human and Ecological Risks
(CAP Content Section 6.0
Updated human health and ecological risk assessments were prepared for Roxboro
consistent with the CAP content guidance. Primary conclusions from the human health
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and ecological risk assessment risk assessment are that there is no evidence of
unacceptable risks to on -Site or off -Site human receptors potentially exposed to CCR
constituents that may have migrated from the ash basins and the DFAHA/GSA. There
is no evidence of unacceptable risks to ecological receptors potentially exposed to CCR
constituents that may have migrated from the ash basins and the DFAHA/GSA. A more
detailed discussion regarding human health and ecological risk associated with Source
Area 1 can be found in Section 5.4. An update to the Roxboro human health and
ecological risk assessment is included in Appendix E
6.4 SA1 Description of Remediation Technologies
This section provides supplemental information beyond the CAP content guidance to
introduce groundwater remediation technologies and considers a range of individual
technologies that might be used to formulate comprehensive groundwater remediation
alternatives for consideration for Source Area 1. The most feasible remedial options
identified will form the basis, in whole or in part, for the remedial alternatives
evaluated in Section 6.6. Groundwater remediation technologies will be evaluated
based upon two primary criterion:
• Can a technology be effective when addressing one or more site -specific COIs?
• Can a technology be feasibly implemented under site -specific conditions and be
effective?
The remedial alternative screening includes the criteria in the NCDEQ CAP Guidance
(April 27, 2018). Technologies that are clearly not workable under Site conditions will
not be carried forward. Technologies that have potential application will be retained for
further consideration. Technologies retained for further consideration might be used to
formulate comprehensive groundwater remedial alternatives in Section 6.5.
6.4.1 Monitored Natural Attenuation
Monitored natural attenuation (MNA) is a groundwater remedy that relies on
natural processes to reduce constituent concentrations in groundwater over time.
The primary objective of an MNA strategy is to identify and quantify natural
attenuation processes specific to a site and demonstrate that those processes will
reduce constituent concentrations in groundwater to levels less than regulatory
standards (USEPA, 1999, NCDEQ, 2017).
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MNA processes potentially applicable to inorganic constituents include:
• Dispersion • Sorption • Biological stabilization
• Dilution • Radioactive decay • Chemical stabilization
• Transformation • Phyto-attenuation
Dilution from recharge to groundwater, mineral precipitation, and COI
adsorption will occur over time and distance from the source area, thereby,
reducing COI concentrations through attenuation. MNA can be used in
combination with other remediation technologies such as source control.
Routine monitoring of select locations for COI concentrations is used to confirm
the effectiveness of the approach.
The USEPA does not consider MNA to be a "no action" option. Source control
and long-term monitoring are fundamental components of any MNA remedy.
Furthermore, MNA is an alternative means of achieving remediation objectives
that might be appropriate for specific, well -documented site circumstances
where its use will satisfy applicable statutory and regulatory requirements
(USEPA, 1999).
The USEPA, as shown below, considers MNA to be in -situ (USEPA, 1999):
"The term "monitored natural attenuation". as used in this Directive, refers to the
reliance on natural attenuation processes (within the context of a carefully controlled
and monitored site cleanup approach) to achieve site -specific remediation objectives
within a time frame that is reasonable compared to that offered by other more active
methods. The "natural attenuation processes" that are at work in such a remediation
approach include a variety of physical, chemical, or biological processes that, under
favorable conditions, act without human intervention to reduce the mass, toxicity,
mobility, volume, or concentration of contaminants in soil or groundwater. These in -
situ processes include biodegradation, dispersion; dilution, sorption; volatilization... "
MNA is compared to other viable remediation methods during the remedy
selection process. MNA should be selected only if it will meet site remediation
objectives within a timeframe that is reasonable compared to that offered by
other methods (USEPA, 1999). A contingency remedy should be proposed at the
time MNA is selected to be a site remedy (NCDWM, 2000).
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The NCDEQ and USEPA have guidance documents that prescribe the
investigative and analytical processes required for an MNA demonstration
(NCDEQ, 2017c). NCAC 02L provides additional requirements for MNA
implementation. USEPA developed a tiered approach to support evaluation and,
if appropriate, selection of MNA as a remedial technique (USEPA, 2007). Three
decision tiers require progressively greater site information and data to assess
the potential effectiveness of MNA as a remedy for inorganic constituents in
groundwater.
MNA will be retained for further consideration for Source Area 1, as
groundwater COIs do not pose an unacceptable risk to human health or the
environment under conservative exposure scenarios and a source control
measure will be implemented that eliminate or mitigate the source of CCR
constituents in groundwater. The MNA evaluation for the technical applicability
at Source Area 1 is provided in Appendix I.
6.4.2 In -Situ Technologies
Groundwater remediation technologies that are implemented in -situ, or in place,
are discussed here.
Low Permeability Barriers
Construction of a low permeability barrier (LPB) for Source Area 1 would
involve drilling to competent bedrock and injecting bentonite or grout into
fractured bedrock, the transition zone, and possibly into saprolite flow zones.
Keying the LPB into a natural barrier to groundwater flow such as a competent
confining unit (e.g., aquitard) or bedrock cannot be achieved with certainty due
to the complex Piedmont geology present with Source Area 1. Installation of an
effective low permeability barrier to depths approaching 50 feet would be
technically challenging and costly; therefore, LPB technology will not be retained
for further consideration.
When used for the purpose of groundwater remediation, LPBs are structures
constructed in -situ to redirect or contain groundwater flow. Materials used to
construct LPBs are either impermeable (e.g., steel sheet pile) or have a
permeability that is at least two orders of magnitude lower than the permeability
of the saturated media that comprises a targeted groundwater flow path. For
this reason, LPBs are typically keyed into a natural barrier to groundwater flow
such as a competent confining unit (e.g., aquitard) or bedrock to prevent
groundwater from flowing under the LPB.
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LPBs can be used to redirect groundwater away from a potential receptor,
redirect groundwater away from a source area, or redirect COI laden
groundwater towards a groundwater extraction system or in -situ groundwater
treatment system (e.g., permeable reactor barrier). The design and technique
used to construct a LPB typically depends upon the length of the LPB, the depth
to a competent confining layer or bedrock, and cost considerations. Sheet piling,
trenching, and vertical drilling are the most common means to construct a LPB.
Sheet piling and trenching are typically limited to depths of approximately 50
feet whereas installation of a LPB using drilling techniques can achieve depths
greater than 50 feet. For this reason, construction of a LPB at Source Area 1
would involve installation by means of drilling because bedrock is
approximately 50 feet (or greater) below ground surface downgradient of the ash
basin.
At the EAB, a hydraulic barrier would have to be sealed throughout the
transition zone and at the surface of the fractured bedrock. The transition zone is
a highly fractured weathered rock formation that is a primary conduit for
groundwater flow. In the areas where remediation is required, the transition
zone is present from approximately 6 feet bgs to 43 feet bgs with a variable
thickness, ranging from approximately 5 feet to 38 feet. The average thickness of
the transition zone is approximately 18 feet. In cases where the altered
groundwater flow pattern might include flow beneath the barrier into fractured
rock, use of barriers becomes more difficult because a seal is needed to prevent
underfloor. The heterogeneity and fractured bedrock geologic proposes
challenges for constructing an effective barrier.
Groundwater Infiltration and Flushing
Groundwater flushing by infiltration can be accomplished by many methods
including vertical wells, horizontal wells, and infiltration galleries. Groundwater
flushing is a technology that has possible application for Source Area 1 and
Source Area 3 to enhance the capture of mobile constituents. Groundwater
flushing by infiltration will be retained for further consideration.
In -situ groundwater flushing involves the infiltration or injection of clean water
into groundwater to accelerate flushing of target constituents. Constituents
mobilized by flushing would be captured by an extraction well. Flushing can
enhance natural constituent transport mechanisms such as advection, dispersion,
and molecular diffusion. This technology is potentially applicable to a broad
range of constituents. Flushing of relatively mobile and unreactive constituents
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like boron can be accomplished using clean water. Furthermore, in -situ flushing
has potential applicability at almost any depth. However, successful
implementation is site -specific. Factors affecting the effectiveness include the
degree of subsurface heterogeneity, the variability of hydraulic conductivity, and
the organic content of soil. Suitability testing of the clean water source and pre -
design collection of data is important for most sites where this technology might
be considered.
In -situ infiltration can also be used to enhance conventional pump and treat
technology at locations with limited natural recharge or low permeability. The
introduction of clean water into groundwater enhances groundwater flow by
increasing the hydraulic gradient between the point of infiltration and the point
of extraction or discharge. Addition of clean water can mobilize COIs, such as
boron, and enhance the hydraulic gradient to improve hydraulic capture of COIs
(USEPA, 1996).
Encapsulation
Encapsulation technologies for Source Area 1 are not carried forward for further
evaluation for the following reasons:
• The area and depth requiring groundwater remediation is greater than
feasible for this technology, which is best implemented in areas of limited
size or extent.
• The varied geological conditions pose the unlikelihood that the
performance of an implemented technology will be uniform.
Encapsulation technologies act to prevent waste materials and constituents from
coming into contact with potential leaching agents such as water. Materials used
to encapsulate a waste must be both chemically compatible with the waste and
inert to common environmental conditions such as rain infiltration, groundwater
flow, and freeze/thaw cycles (USEPA, 2002). Waste materials can generally be
encapsulated in three ways: microencapsulation, macroencapsulation or in -situ
vitrification (ISV).
Microencapsulation involves mixing the waste together with the encasing
material before solidification occurs. Macroencapsulation involves pouring the
encasing material over and around a larger mass of waste, thereby enclosing it in
a solidified block. Grout, sulfur polymer stabilization/solidification, chemically
bonded phosphate ceramic encapsulation, and polyethylene encapsulation are
examples of the techniques that have used to improve the long-term stability of
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waste materials (USEPA, 2002). ISV involves the use of electrical power to heat
and melt constituent laden soil and buried wastes (e.g., ash). ISV uses an array of
electrodes inserted into the ground. Electrical power is applied to the electrodes,
which establishes an electric current through the soil. The electric current
generates sufficient heat (>2500 °F) to melt subsurface soil and waste materials.
The molten material cools to form a hard monolithic, chemically inert crystalline
glass -like product with low leaching characteristics (USEPA, 1994). Two
additional considerations associated with this technology are permanence of the
reaction product insolubility and the ability to distribute reactants sufficiently to
ensure adequate contact with the COIs.
Contact between the encasing material and affected media could propose a
challenge in the transition zone and fractured rock formations. It is difficult to
ensure that encasing material are uniformly distributed in transition zone and
fractured bedrock to assure adequate encapsulation of affected media.
Permeable Reactive Barrier
The ability to maintain adequate reactive reagent concentrations at depth over an
extended period of time is a significant operational and performance
consideration. Permeable reactive barriers (PRBs) are not carried forward for
further evaluation for the following reasons:
• Detected concentrations of aluminum, iron and manganese dissolved in
groundwater could react with, and clog, treatment areas, diminishing the
hydraulic conductivity through the PRB.
• There is recent favorable data suggesting that the technology might be
effective in reducing some coal ash -related constituents; however, PRB
technology is not well suited to treat boron.
The USEPA defines a permeable reactive barrier as being:
An emplacement of reactive media in the subsurface designed to intercept a
contaminant plume, provide a flow path through the reactive media, and transform
the contaminant(s) into environmentally acceptable forms to attain remediation
concentration goals down -gradient of the barrier.
Construction of PRBs involves emplacement of reactive media below the ground
surface for treating groundwater containing dissolved COIs. The PRB media is
designed to be more hydraulically conductive than the saturated media
surrounding the PRB so that groundwater will flow through the PRB media with
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little resistance. The depth and breadth of PRBs are oriented perpendicular to
groundwater flow direction so that the PRB will intercept groundwater targeted
for treatment. Design of the PRB thickness takes into account groundwater
velocity and the need to provide sufficient groundwater residence and contact
time for constituents to react with PRB media. PRBs can be installed as
permanent or semi -permanent treatment units. The PRB reactive media in a
permanent treatment unit is designed to remain in over the needed timeframe
whereas the reactive media in a semi -permanent treatment unit is designed to be
replaced periodically once it is spent.
Two of the most common PRB designs are the continuous wall and the "funnel
and gate". The continuous wall design involves the installation of a trench
downgradient of a constituent plume that is oriented perpendicular to
groundwater flow. The funnel and gate configuration involves construction of
two LPBs that redirect groundwater flow towards the PRB. This allows for a
smaller PRB design and treatment of a greater volume of groundwater. A design
factor for both designs is the ability for the PRB be keyed in a low permeability -
confining layer or in bedrock to minimize the potential for groundwater
underflow beneath the PRB.
Media commonly used in PRBs for the treatment of inorganic COIs includes
zero -valence iron (ZVI), apatite, zeolites, and materials used to affect
groundwater pH. The mechanisms that take inorganic constituents out of
solution includes adsorption, ion exchange, oxidation-reduction, or precipitation.
ZVI (FeO) is an effective reducing agent; donates an electron (FeO --* Fe+2 + 2e-).
ZVI particles can remove divalent metallic cations through reductive
precipitation, surface adsorption, complexation, or co -precipitation with iron
oxyhydroxides. ZVI has been used to treat cationic metals such mercury (Hg+2),
nickel (Ni+2), cadmium (Cd+2), and lead (Pb+2) (USEPA, 2009).
Apatite is a media used in PRBs to treat groundwater for the removal of certain
metals in solution including lead, cadmium, and zinc. Apatite refers to a group
of crystalline phosphate minerals; namely, hydroxylapatite, fluorapatite and
chlorapatite. Apatite IITM is an amorphous form of a carbonated hydroxy-apatite
that has random nanocrystals of apatite embedded in it. The apatite nanocrystals
are capable of precipitating various phosphate phases of metals and
radionuclides. Apatite II is also an efficient non-specific surface absorber
(Wright, 2003).
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Zeolite is any of a large group of minerals consisting of hydrated
aluminosilicates of sodium, potassium, calcium, and barium. Zeolites have large
internal surface areas capable of treating inorganics by both adsorption and
cation exchange.
Limestone and materials containing limestone such as recycled cement can be
used as a PRB media for raising the pH of acidic groundwater like that are found
in mine runoff (Indraratna, 2010).
Sulfate reduction facilitated by naturally occurring bacteria has been shown to
effectively treat acidic to net alkaline groundwater containing dissolved heavy
metals, including aluminum, in a variety of situations. The chemical reactions are
facilitated by the bacteria desulfovibrio. This is a well -proven technology often
used to treat acidic runoff from historic mining operations.
6.4.3 Groundwater Extraction
Groundwater extraction is often used when remediating mobile constituents in
groundwater. Groundwater extraction can be used to withdraw affected
groundwater from the subsurface for the purpose of reducing the mass of one or
more target constituent(s) in a groundwater system. Groundwater extraction can
be used to hydraulically contain affected groundwater and mitigate groundwater
constituent migration (USEPA, 1996). Groundwater extraction can be conducted
using a variety of methods that are discussed in the following sub -sections.
Vertical Extraction Wells
Groundwater modeling conducted for Source Area 1 and Source Area 3 indicates
that vertical groundwater extraction wells can produce sufficient yield for
effective constituent mass removal without supplemental measures. The use of
vertical groundwater extraction wells is retained for further consideration.
A vertical well is the most common design for groundwater extraction. Drilling
techniques used to install vertical groundwater extraction wells range from
GeoProbe® direct push, to hollow stem auger, mud rotary, air rotary, and sonic
drill rigs, and other methods. Groundwater extraction wells can be designed and
screened in unconsolidated saturated media such as sand, saprolite, alluvium,
transition zone, fractured bedrock, silts, and clays. Alternatively, groundwater
extraction wells installed in bedrock can be completed as open -hole borings.
Low yielding groundwater systems can be problematic for vertical extraction
wells. Relatively close spacing of vertical wells may be necessary to capture a
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constituent plume if the yield is low. Enhanced yield can be accomplished
through injection or infiltration of water upgradient of the wells to increase the
availability of water and hydraulic head. Alternatively, low yielding wells can
be effective through intermittent pumping to remove sorbed constituents with
each pump cycle.
Pump options include submersible pumps and centrifugal pumps depending
upon the anticipated yield, depth to water and well diameter. Shallow
centrifugal pumps (shallow well jet pumps) can be used in small diameter wells
where the groundwater level and desired pumping level is relatively shallow
(less than 25 to 30 feet below the ground surface). Submersible pumps (single- or
multi -stage centrifugal pumps) can be used to extract groundwater from larger
diameter wells with deeper groundwater levels. Deep well jet pumps have the
advantage of mechanical equipment above grade and power only needs to be
provided to a few pump stations rather than to every well as with submersible
pump systems. All require routine maintenance of the pumps, vaults, piping
and well screens to sustain desired performance.
Horizontal/Angular Well Extraction Wells
Horizontal/angular wells are generally more expensive and, therefore, used for
special circumstances. Vertical extraction wells are deemed more cost effective
than horizontal/angular wells. The use of horizontal or angular groundwater
extraction wells is not retained for further consideration.
Horizontal groundwater extraction wells offer advantages over vertical
groundwater extraction wells when access is difficult or to reduce the number of
system elements requiring maintenance. For example, horizontal wells can be
installed below buried utilities, buildings, coal piles, and similar surface or near
surface features. Also, horizontal wells can be more efficient and effective when
remediating constituent plumes distributed over a large area within a relatively
thin flow zone. Fewer horizontal wells would be required under this scenario
compared with the number of vertical wells that might be required to achieve
similar remediation goals. Furthermore, recovery efficiency might be increased
relative to vertical wells due to the ability of a single horizontal well to contact a
larger horizontal area, particularly where the horizontal groundwater
transmissivity is greater than the vertical transmissivity.
Installation of a directionally drilled well involves the use of an auger bit that can
be steered in three dimensions. The progress of direction boring installations are
precisely monitored to avoid subsurface obstructions and to install the well as
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designed. Tracking accuracy generally decreases with increasing depth of
installation. Site hydrogeologic and geologic conditions can also affect tracking
accuracy.
Directionally drilled horizontal wells can be completed as blind holes (single -end
completion) or surface-to-surface holes (double -end completion). Single -end
holes involve one drill opening, with drilling and well installation taking place
through this single opening. Borehole collapse may be more likely in single -
ended drilling since the hole is left unprotected between drilling and reaming
and between reaming and casing installation. An additional complication
associated with single -ended completion involves the precise steering of reaming
tools required to match the original borehole path. In contrast, double -end holes
are typically easier to install since reaming tools and well casing can be pulled
backward from the opposite opening, and the hole does not have to be left open.
Materials used for horizontal wells are typically the same or similar as those used
for vertical wells. Factors to consider in the choice of well screen and casing
materials to be used with horizontal wells include axial strength, tensile strength,
and flexibility (Miller, 1996).
Angle drilled wells are constructed in the same way as a vertical well with the
exception that the drill rig mast is positioned at an angle that is purposely not
plumb. The drilling mast angle and the targeted drilling depth will determine
horizontal offset of the well screen and submersible pump from the location
where drilling was initiated. Otherwise, angled wells function in the same
manner as vertical wells.
Extraction Trenches
Shallow trenches are easy to install and can be an effective surface water
protection supplement to a groundwater management system. If applied at
Roxboro, trench technology effectiveness would be limited to the area north of
Source Area 1. Implementation in this area would be difficult due to the
infrastructure in the area. Therefore, the use of horizontal extraction trenches is
not retained for further consideration.
Shallow horizontal groundwater extraction (collection or intercept) trenches can
be installed in areas near surface waters where groundwater might discharge.
These trenches can be utilized to prevent groundwater from discharging into
surface waters and can be effective in lowering or managing the water table.
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Trenches might be used as temporary installations to intercept and monitor
subsurface flow or can be retained as a permanent installation. Trenches must be
deep enough to tap and provide an outlet for ground water that is in shallow,
permeable strata or in water -bearing sand. The spacing of trenches varies with
soil permeability and drainage requirements.
Extraction trenches function similar to horizontal wells but are installed with
excavation techniques. They can be cost-effective to construct at shallow depths
(less than or equal to 35 feet below ground surface) using conventional
equipment. Trenches can be installed to depths of approximately 50 feet below
ground surface using specialty equipment. Horizontal collection trenches are
usually not cost-effective for deeper installations or bedrock applications.
Horizontal collection trenches do have the advantage of generally having lower
operations and maintenance costs compared with the costs of multiple vertical
wells.
Hydraulic Fracturing
Hydraulic fracturing generally involves the application of high pressures to
propagate existing fractures or to create fractures following fracture nucleation.
A limitation is that unintended fracture patterns negatively affecting the COI
plume control might occur. This approach is not optimal due to the possibility of
unintended fracture pattern formation. Hydraulic fracturing is not retained for
further evaluation.
The effectiveness of groundwater extraction systems can sometimes be improved
in low permeability formations, including bedrock, with the use of hydraulic
fracturing techniques.
Pneumatic fracturing involves injection of highly pressurized air into
consolidated sediments to extend existing fractures and create a secondary
network of fissures and channels. Similarly, hydraulic fracturing involves the
use of high pressure water to extend existing fractures and create a secondary
network of fissures and channels.
When hydraulic is applied to unconsolidated materials, a disk shaped notch that
serves as the starting point for the fracture is created using high pressure water
to cut into the formation. Pumping of a slurry of water, sand, or a thick gel at
high pressure into the borehole propagates the fracture. The residual gel
biodegrades and the resultant fracture is a permeable sand -filled lens that may
be as large as 60 feet in diameter (USEPA, 1995).
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Phytoremediation
Phytoremediation technology can be used to extract groundwater; however,
phytoremediation is not capable of achieving extraction rates necessary to
achieve groundwater remediation within reasonable timeframes. Although,
phytoremediation is not retained for consideration for groundwater corrective
action, phytoremediation could be an effective surface water protection
supplement to a groundwater management system.
Phytoremediation involves the use of plants and trees as a means to extract
groundwater. Water uptake by trees is used for plant growth and
metabolism. Water uptake by plants and trees is ultimately released into the
atmosphere via the pore -like structures on the leaves called stoma. Water on the
leaves evaporates into the atmosphere. The loss of water by plants and trees is
called transpiration. The amount of water transpired by plants, and therefore
water uptake by plants is a function of:
• Plant type: Plants that are native to and regions must conserve water and
therefore transpire less than plants that are native to wet regions.
• Temperature: Transpiration rates increase with increasing temperature
and decrease with decreasing temperatures.
• Relative humidity: Transpired water on plant leaves evaporate at a faster
rate when the relative humidity is low and that results in a
correspondingly higher transpiration rate. The opposite is true when the
relative humidity is high.
• Wind and air movement: Increased movement of air around a plant will
increase the rate of transpiration by plants
• Availability of soil moisture: Plants can sense when soil moisture is
lacking and will reduce their transpiration rate.
The growth rate of selected plant species and the growing season can be limiting
factors for the effectiveness of this technique. Maintenance can be long term and
require, in most cases, fertilizing, regular monitoring, and harvesting.
Phytoremediation using TreeWell® technology involves the installation of a 3 to 5
foot diameter boring to a target depth, typically a flow zone containing COIs. A
Root SleeveTM liner and aeration tubing are installed from ground surface to
target depth. The boring is backfilled with soil that might include reactive
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media. If filled with reactive media, the tree well would serve as a PRB as well as
a means to promote phytoremediation.
A tree is planted within the tree well followed by placement of plastic cover over
the soil surrounding the tree. The plastic cover minimizes infiltration of
precipitation into the tree well. The tree well design forces the tree to draw
water from the targeted depth via the Root SleeveTM liner. Groundwater is also
drawn through reactive media, if present. Consequently, the tree and the tree
well are capable of uptake of some COIs and serve as a means of groundwater
treatment and enhanced natural attenuation.
Ground cover plants stabilize soil/sediment and control hydraulics. In addition,
densely rooted groundcover plants and grasses can also be used to
phytoremediate constituents. Phytoremediation groundcovers are one of the
more widely used applications and have been applied at various bench- to full-
scale remediation projects. Furthermore, in the context of this document,
phytoremediation groundcovers are vegetated systems typically applied to
surface soils as opposed to TreeWells° which are targeted to deep soil and/or
groundwater. The typical range of effectiveness for phytoremediation
groundcovers is 1-2 feet below ground surface; however, depths down to 5 feet
have been reported as within the range of influence under some situations (ITRC,
2009)
Constructed treatment wetlands are manmade wetlands built to remove various
types of pollutants that may be present in water that flows through them. They
are constructed to recreate, to the extent possible, the structure and function of
natural wetlands, which is to act as filters. Wetlands are ideally suited to this
role. They possess a rich microbial community in the sediment to effect the
biochemical transformation of pollutants, they are biologically productive, and
most importantly, they are self-sustaining.
Metals are removed in constructed wetlands by a variety of mechanisms
including the following. Settling and sedimentation achieve efficient removal of
particulate matter and suspended solids. The chemical process that results in
short-term retention or long-term immobilization of constituents is sorption.
Sorption includes the combined processes of adsorption and absorption.
Chemical precipitation involves the conversion of metals in the influent stream to
an insoluble solid form that settles out. (ITRC, 2003)
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Phytoremediation technology can be also be used as a means to treat extracted
groundwater. Aquaculture treatment technologies have been applied to the
treatment of water. Those using aquatic plants have been demonstrated capable
treatment of metals and other non-metal elements including boron and arsenic
(USEPA, 1982).
Phytoremediation might not be a viable option for areas with groundwater levels
greater than 30 feet deep. Since remediation via plants is seasonal, the
technology is most applicable where there is minimal risk to receptors and the
length of time to achieve remedial goals is not a limiting factor.
6.4.4 Groundwater Treatment
Several technologies exist for treatment of extracted groundwater to remove or
immobilize constituents ex -situ, or above ground. The following technologies are
used for treatment of extracted groundwater. These groundwater treatment
technologies are scalable for small to large flow rates.
pH Adjustment
Adjustment of the pH of extracted groundwater, if required prior to discharge, is
a proven technology. Permitted discharges will impose specific limits on the pH
of discharged wastewater. The existing NPDES permitted outfalls at Roxboro
are required to maintain a pH between 6.0 and 9.0 S.U. Facilities and equipment
to adjust the pH of wastewater to satisfy NPDES discharge requirements are
currently in -place at Roxboro.
The average pH of groundwater associated with Source Area 1 is 6.38 S.U. in the
shallow flow zone, 6.64 S.U. in the transition flow zone, and 6.90 S.U. in the
bedrock flow zone. Therefore, pH adjustment of extracted groundwater is not
expected but is retained as a contingency if conditions change after closure of the
EAB. The average value for pH of groundwater from all flow zones is
approximately 6.64 S.U., which is within the NPDES permit requirement.
Precipitation
Precipitation technology might be warranted to treat, or pretreat, extracted
groundwater to satisfy NPDES permitted discharge limits; however, the
indication is that extracted groundwater will not cause violations of the NPDES
permit when discharged. Therefore, precipitation technologies are not retained
for further consideration.
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Precipitation of metals and other inorganic constituents has been used
extensively to treat extracted groundwater.
The process involves the conversion of
soluble (dissolved) constituents to insoluble
particulates that will precipitate. The
insoluble particles are subsequently
removed by physical methods such as
clarification or filtration. The process
might involve adjustment of the
wastewater pH and/or reduction -oxidation
(redox) potential or Eh (volts). The
stability of soluble and insoluble metals
FIGURE 6-16
POURBAIX DIAGRAM FOR
IRON -WATER SYSTEM
Simplified Pourbaix diagram
for iron -water system at 77°F (25°C)
E,r
2.0
1.6
1.2
0.8
and metal complexes is illustrated in 0.4
Pourbaix diagrams (pH vs Eh). 0.0
-0.4
As illustrated in the Pourbaix diagram -0.8
(Figure 6-16), iron is soluble (aqueous or -1.2
an) at a pH of approximately 3 5 S U or
k m
t FC042- (ag)
Fe'+ (aq)
e d
FeKb h
Fe'+(aq) c
a h c
Fe [s} 3
less under aerobic conditions (Eh > 0 V). If - 0 . 2 4 6 s 10 12 14 PH
the pH is increased, ferric (Fe+3) iron will https://rsteyn.wordpress.com/pourbaix-diagrams
react to form insoluble (solid or s) complexes and precipitate out of solution,
provided that the redox potential (Eh) remains between 0.75 and 1.5 V.
Adjustment of groundwater pH and Eh can be used to remove other metals
including cadmium, chromium, copper, nickel, and zinc.
Flocculation is another method that can be used to remove inorganics from an
aqueous waste stream. This technology involves adding a flocculent to extracted
water and then removing (through sedimentation or filtration) formed
particulates to reduce concentrations, such as total suspended solid (TSS).
Ion Exchange
Ion exchange processes are reversible chemical reactions that can be used for the
removal of dissolved ions from solution and replacing them with other similarly
charged ions. A limitation of this technology is that there must be a feasible and
economical method to dispose of the regeneration effluent. An additional
challenge could be groundwater influent streams that might have geochemical
characteristics that result in interference in the ion exchange process. Because of
these challenges, ion exchange is not retained for further consideration.
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The ion exchange medium might consist of a naturally occurring material such as
zeolites or a synthetic resin with a mobile ion attached to an immobile functional
acid or base group. Mobile ions held by the ion exchange resin are exchanged
with solute or target ions in the waste stream having a stronger affinity to the
functional group.
Ion exchange resins can be cation resins or anion resins of varying strength. Ion
exchange resins are generally classified as being:
• Strong acid cation (SAC) resins.
• Weak acid cation (WAC) resins.
• Strong base anion (SBA) resins.
• Weak base anion (WBA) resins.
Over time, a resin becomes saturated with the targeted or competing ions.
Breakthrough might occur when a resin becomes saturated. The possibility of
breakthrough is evident when effluent concentrations of the targeted metal ion
steadily increases over time and approach influent concentrations. Ion resins
should be replaced or regenerated before breakthrough occurs. Ion selective
born resins are available and do not have the same competition considerations.
However, capacity and regeneration are still potential limitations and key design
parameters.
Regeneration is laborious and requires safe handling of concentrated chemical
reagents and waste. The first step in the co -flow regeneration process (regenerant
is introduced via ion exchange bed influent) is to backwash the system with
water. The regenerant solution is introduced to drive off ions and restores the
resin capacity to about 60 to 80 percent of the total resin ion exchange capacity.
Sodium hydroxide is a commonly used regenerant for WBA resins; weaker
alkalis such as ammonia (NH3) and sodium carbonate (Na2CO3) can also be used
(SAMCO, 2019).
When sufficient contact time has passed, a slow water rinse is applied to the
resin bed to push the regenerant solution throughout the resin and subsequently
remove the regenerant from the system. The regenerant should be retained for
proper disposal. The slow rinse is followed by a fast "raw" water rinse to verify
water quality requirements are being met.
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Membrane Filtration
Permeable membrane filtration technologies can filter one or more target
constituents simultaneously and can achieve low effluent concentrations.
However, permeable membrane filtration technologies are also susceptible to
fouling and often require a pretreatment step. They can also generate a high
concentration reject effluent which might require additional treatment prior to
disposal. These technologies typically have high capital costs. Membrane
filtration is not carried forward for further evaluation for the following reasons:
Extracted groundwater is not expected to be greater than permit discharge
limits.
Pretreatment and a high volume of reject effluent that requires additional
treatment prior to disposal make this technology costly and high
maintenance.
There are a number of permeable membrane filtration technologies that can be
utilized to remove metals and other constituents from extracted groundwater.
The most common is reverse osmosis. Microfiltration, ultrafiltration, and
nanofiltration are also permeable membrane filtration technologies that are used
less frequently.
All four technologies use pressure to force influent water through a permeable
membrane. Permeable membrane filtration technologies are selected and
designed so that influent water can pass through the membrane while target
constituents are filtered (retained) by the membrane. The permeable membrane
filtration technologies discussed differ in the size of the molecules filtered and
the pressures needed to allow permeate to pass through the membranes.
6.4.5 Groundwater Management
Extracted groundwater must be managed or used as supplemental process water
prior to discharge. The disposition of extracted groundwater is discussed in the
following sections.
National Pollutant Discharge Elimination System (NPDES)
Permitted Discharge
Based on existing groundwater quality data, the extracted groundwater from
Source Area 1 can be discharged under the existing NPDES permit, subject to
pending approval, and will be retained for further consideration.
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The NPDES permit contains three outfalls to Hyco Reservoir (Outfalls 001, 003,
and 006) and multiple internal outfalls for streams entering the discharge canal
(Section 1.5.3). The composition of extracted groundwater was estimated using
modeled flow rates for the proposed extraction wells and mean concentrations of
COIs in monitoring wells near the EAB and downgradient additional source
areas.
Based on the estimated concentrations, discharging the extracted groundwater at
Outfall 003 should not affect compliance. Anticipated groundwater remediation
parameter levels and the available NPDES permit limits are summarized on
Table 6-10. The extracted groundwater would be conveyed to the sump at the
DFA silo area from which it is pumped to the main sump and on to the LRB.
Effluent from the LRB is treated and discharged to the heated water discharge
pond. Effluent from the heated water discharge pond discharges to the Hyco
Reservoir through Outfall 003.
Publicly Owned Treatment Works (POTW)
The City of Roxboro wastewater treatment plant (WWTP) is located at 902 Cavel
Chub Lake Rd, Roxboro, NC, approximately 8 miles southeast of the Roxboro
Plant. The City of Roxboro Public Works Department is responsible for sewer
distribution lines to the Roxboro WWTP. The installation of this length of sewer
line between the Roxboro Plant and the Roxboro WWTP would likely be cost
prohibitive. Discharge of extracted groundwater to the City of Roxboro WWTP is
not retained for further consideration at this time. Disposal of extracted
groundwater through the lined retention basin and NPDES Outfall 003 is
considered the most viable option.
This groundwater disposal option involves the discharge of extracted
groundwater to a sewer that discharges to the local POTW. The feasibility of this
disposal option depends on a number of factors including:
• The proximity of the nearest sewer line relative to the groundwater
extraction system.
• The available capacity of a POTW to accept a new waste stream.
• The suitability of a groundwater waste stream on POTW operations.
• Capital costs, pretreatment requirements, and disposal fees.
The City of Roxboro WWTP is operated under NPDES permit # NCO021024 and
has the following limits on their influent:
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• Daily flow rate: 5 million gallons per day (MGD).
• pH: minimum 6.00 S.U./maximum 9.00 S.U.
The maximum monthly influent flow rate was 3.08 MGD during December 2018.
Consequently, it appears that the City of Roxboro WWTP has approximately 1.92
MGD of available treatment capacity.
Non -Discharge Permit/Infiltration Gallery
The use of infiltration galleries to dispose of treated groundwater is not retained
for further consideration due to the significant treatment that would be required
to achieve an acceptable water quality for returning the extracted groundwater to
the groundwater system.
Disposition of treated groundwater by way of infiltration into underlying
groundwater involves the construction of an infiltration gallery to receive and
distribute the treatment effluent or wastewater. Discharge of wastewater by way
of an infiltration gallery cannot result in a violation of 02L groundwater
standards. Consequently, groundwater treatment must reliably produce an
effluent waste stream that will not result in a 02L groundwater violation.
The construction and use of infiltration galleries are permitted under 15A NCAC
02T .0700. The effectiveness of an infiltration system will depend in large part on
the type of soils or classification of soils receiving the wastewater. Annual
hydraulic loading rates shall be based on in -situ measurement of saturated
hydraulic conductivity in the most restrictive horizon for each soil mapping unit.
United States Department of Agriculture (USDA) soil map of the Site indicates
that the predominant soil types in the northeast portion of the site that might be
used for an infiltration gallery are Siloam loams (SmB, SmD and SmF). These soil
types are described as moderately slow permeability (USDA, 1995).
Non -Discharge Permit/Land Application
Land application of extracted groundwater could be used as a means to maintain
the vegetative cover that would be established following implementation of
source control measures. However, the designated area would have to be able to
take continuous flow during both dry and wet seasons, which would not be
practical. Additionally, unless the vegetation is harvested, boron uptake will be
returned to the soil and aquifer upon death and decomposition of the plant
matter. Therefore, land application will not be retained as an alternative means
for disposal of extracted wastewater.
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Land application of groundwater involves the distribution of extracted
groundwater onto land for the purposes of irrigating the vegetative cover and
supplying the vegetative cover with nutrients beneficial for growth. The
vegetative cover can include grasses, tree wells, wetland species, native species
of trees and shrubs, and ornamental trees and shrubbery.
The primary focus of groundwater remediation efforts is to reduce boron
concentrations beyond the anticipated compliance boundary to acceptable levels.
Consequently, extracted groundwater would be expected to contain boron.
Boron is essential for plant growth. More specifically, boron has to be
continuously delivered to growing tissues from soil through roots and vascular
tissues to maintain cell wall biosynthesis and optimal plant development
(Takano, 2006). Boron is also essential for plant nitrogen assimilation, for the
development of root nodules in nitrogen -fixing plants, and for the formation of
polysaccharide linkages in plant cell walls (Park, 2002). If extracted groundwater
is land applied, boron would be made available for plant uptake.
Extracted groundwater could be used to irrigate over 83 acres of vegetative cover
planted following implementation of source control measures. Land application
of extracted groundwater would occur within the compliance boundary. A large
scale irrigation system could be used to apply thousands of gallons of water onto
the vegetative cover daily. Of the water applied, much of it would be lost to
evaporation, particularly during sunny dry periods. Likewise, water taken up by
vegetation would be lost by way of plant transpiration. All remaining water
either would infiltrate into the soil or would migrate downslope to streams or
wetland areas via surface water runoff.
Land application of extracted groundwater must comply with 15A NCAC 02T —
Waste Not Discharged To Surface Waters. Duke Energy would submit an
application for a non -discharge permit in accordance with 15A NCAC 02T .0105 -
.0109. General permits can be made effective for a term not to exceed eight years.
General permits issued pursuant to 15A NCAC 02T shall be considered
individual permits for purposes of compliance boundaries established under 15A
NCAC 02L .0107. Permitted facilities shall designate an Operator in Responsible
Charge and a back-up operator as required by the Water Pollution Control
System Operators Certification Commission.
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Application of wastewater to the ground surface or surface irrigation of
wastewater is governed by 15A NCAC 02L .0500 - Wastewater Irrigation Systems.
Requirements under this subsection include:
• A soil scientist must prepare a soil report that evaluates receiving soil
conditions and makes recommendations for loading rates of liquids and
wastewater constituents.
• A hydrogeologic report must be prepared by a licensed Geologist, soil
scientist, or professional engineer for industrial waste treatment systems
with a design flow of over 25,000 gallons per day.
• The applicant must prepare a Residuals Management Plan.
• Each facility shall provide flow equalization with a capacity of 25 percent
of the daily system design flow unless the facility uses lagoon treatment.
• Disposal areas shall be designed to maintain one -foot vertical separation
between the seasonal high water table and the ground surface.
• Automatically activated irrigation systems shall be connected to a rain or
moisture sensor to prevent irrigation during precipitation events or wet
conditions that would cause runoff.
Setback requirements for irrigation sites (15A NCAC 02T .056) are summarized
in Table 6-11.
The DWR might require monitoring and reporting to characterize the waste
(extracted groundwater) and its effect upon surface water, ground water, or
wetlands.
Beneficial Use
The NCDEQ 2018 Annual Water Use Report for the Roxboro indicated that water
was withdrawn from Intake Canal of Hyco Reservoir every day in 2018. The
average daily withdrawal in a given month ranged from 170.3 million gallons
per day (MGD) to 977.6 MGD with an annual daily average of 592.12 MGD. The
average daily discharge in a given month ranged from 170.4 MGD to 972 MGD
with an annual daily average of 595.6 MGD (NCDEQ, 2018). Beneficial reuse of
extracted groundwater will not be retained for further consideration, but this
might be reconsidered in the future.
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Beneficial reuse of extracted groundwater involves the evaluation of existing
Station water demand and repurposing extracted groundwater to satisfy a need
for water. Beneficial reuse of extracted groundwater can:
• Provide an alternative to groundwater treatment.
• Reduce reliance on sources of non -potable water required for plant
operations.
• Reduce the need and capacity for wastewater treatment.
Operational uses of the water might include cooling tower makeup water, non -
contact cooling water, dust suppression, and fire protection. Beneficial use can
be less expensive because operation and maintenance needs are less than those of
potential treatment and NPDES discharge or discharge to the city of Roxboro
POTW.
Beneficial Reuse: Fire Protection
A limited amount of extracted groundwater might be used to supplement or
supply water stored for fire suppression within Station operations. However, the
need for fire suppression water is limited; storage is problematic and would not
justify the effort and expense to substitute extracted groundwater for fire
suppression water obtained from the Intake Canal.
Beneficial Reuse: Non -Contact Cooling Water
Extracted groundwater might be used to supplement or supply makeup water
used for non -contact cooling within Station operations. The alkalinity of
groundwater could pose potential scaling problems for some applications. In
addition, it is possible that operation of the groundwater remediation system
could extend beyond plant decommissioning. Use of extracted groundwater for
non -contact cooling water is not retained, but might be reconsidered in the
future.
Beneficial Reuse: Dust Suppression and Truck Wash
A limited amount of extracted groundwater can possibly be used for dust
suppression during implementation of source control measures. Similarly,
extracted groundwater can possibly be used for washing the tires of haul trucks
leaving the ash basins during implementation of source control measures. The
use of extracted groundwater for dust suppression and truck washing would be
confined within ash basin limit of ash disposal. However, the need for dust
suppression and truck wash water is limited and would not justify the effort and
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expense to substitute extracted groundwater for dust suppression and truck
wash water obtained from the Intake Canal. Therefore, beneficial use of the
water is not retained for further consideration.
6.4.6 Technology Evaluation Summary
A summary of the remedial technologies presented above and the rationale for
either retaining or rejecting a specific technology is presented in Table 6-12.
In conclusion, remedial technologies retained for further consideration include,
MNA, in -situ technology groundwater flushing, and groundwater extraction
technologies including vertical extraction wells. Disposal of extracted
groundwater through the NPDES permitted wastewater system was retained
since technologies are already in place to meet NPDES permit discharge limits.
No beneficial reuse technology is retained at this time.
6.5 SA1 Evaluation of Remedial Alternatives
(CAP Content Section 6.D)
Technologies evaluated and retained for consideration as discussed in Section 6.4 were
used to formulate the following two groundwater remedial alternatives to remediate
groundwater associated with Source Area 1:
• Remedial Alternative 1: Monitored Natural Attenuation
• Remedial Alternative 2: Groundwater extraction
A third alternative involving groundwater extraction and clean water infiltration, as
discussed in the Section 6.22 for Source Area 3, is not considered for Source Area 1
since flow and transport modeling simulations (Appendix G) demonstrate that the
inclusion of clean water infiltration did not provide any distinct advantages over
groundwater extraction alone in achievement for compliance of COI migration beyond
the EAB compliance boundary. These groundwater remedial alternatives are presented
and described in the following subsections. Information to address CAP Content Section
6.D.a.iv is provided in Section 6.6 and Section 6.7.
6.5.1 Remedial Alternative 1 — Monitored Natural Attenuation
(CAP Content Section 6.D.a)
Alternative 1 is the use of MNA as a remedial alternative to address
groundwater COI concentrations at or beyond the EAB compliance boundary.
Under this alternative and based on flow and transport model simulations, the
COI -affected groundwater plumes would naturally attenuate to less than the 02L
standard in approximately 200 years after basin closure regardless of which
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closure scenario is implemented. A comprehensive analysis of MNA is provided
in Appendix I.
6.5.1.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
A limited number of CCR constituents in groundwater associated with
Source Area 1 occur at or beyond the compliance boundary to the northeast
and north of the EAB at concentrations detected greater than applicable 02L
standards, IMAC, or background values, whichever is greater. Remediation
goals are to restore groundwater quality at and beyond the compliance
boundary by returning COIs to acceptable concentrations (02L/IMAC or
background, whichever is greater), or as closely thereto as is economically
and technologically feasible consistent with 15A NCAC 02L. 0106(a) (CAP
Content Section 6.D.a.i.2). In the future, alternative standards may be
proposed as allowed under 02L .0106(k). This approach is considered
reasonable given the documented lack of human health or ecological risk at
Roxboro (CAP Content Section 6.D.a.i.2).
The following groundwater COIs to be addressed by corrective action are
identified (Table 6-6) and discussed in Section 6.1: boron, sulfate and TDS.
These are the COIs that indicate a discernable plume associated with Source
Area 1.
More extensive discussion of the CSM can be found in Section 5.0,
discussion of flow and transport modeling in Appendix G, and discussion
of geochemical modeling in Appendix H.
6.5.1.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
Based on the CSM (Section 5.0) and flow and transport modeling results
(Appendix G), the groundwater COIs associated with Source Area 1 are
hydraulically controlled within the topographic drainage basin of the EAB,
with the exception of the landfill halo area.
The following three chemical natural attenuation mechanisms are an
effective corrective action approach for Source Area 1 because they aid in
stabilizing control some of the reactive ash basin -associated COIs in
groundwater by the following processes:
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• Sorption: Chemical attachment of electrochemically charged ions to
charged receptors in the subsurface media
• Precipitation: Removal of a COI from a dissolved state in
groundwater by incorporation into the matrix of a solid such as a
mineral or an amorphous mass
Ion Exchange: Incorporation of an ion into the crystal structure of a
matrix mineral or amorphous solid
The following five physical natural attenuation mechanisms are also an
effective corrective action approach north and northeast of Source Area 1
because they control the migration and distribution of all or some COIs,
particularly boron, chloride, lithium, and TDS, in groundwater by the
following processes:
• Dilution: Reduce COI concentrations through mixing with
unaffected groundwater
• Dispersion: Reduce COI concentrations through variability of the
flow velocity and concentration gradients
• Transfer to surface water: Reduce COI concentrations through
mixing and flushing with surface water without exceeding 02B
standards
• Groundwater flow control within the stream valley system: Control
COI migration within hydraulic divide boundaries south, east and
west of the ash basin
• Phyto-attenuation: Uptake of the COI by plants or organisms
More information on one or more of the effective natural attenuation
mechanisms for reducing the concentration of the COIs in groundwater can
be found in Appendix I, Table ES-1.
Currently, COIs in groundwater do not pose an unacceptable risk to human
health or the environment under conservative exposure scenarios and, if
implemented alone, MNA would not pose an unacceptable risk to human
health or the environment in the future. Source control and groundwater
monitoring would verify protection of human health and the environment
and to confirm model predictions. The applicable technologies that would
support Alternative 1 include groundwater monitoring wells within the
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former source area and near the former waste boundary, along
downgradient flow transects at a potential future compliance boundary, in
sentinel areas prior to receptors, and near the maximum predicted extent of
migration. There are 172 monitoring wells installed associated with the ash
basins and additional non-CAMA sources. A majority of the wells have
dedicated sampling equipment and an approved interim monitoring plan is
in place. A subset of these monitoring wells could be immediately used for
monitoring the effectiveness of Alternative 1.
6.5.1.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
Predictive modeling has been conducted to estimate when boron
concentrations would be reduced to 02L standards using MNA alone. The
simulations indicate boron concentrations would naturally attenuate to less
than the 02L standard in more than 200 years after basin closure. The flow
and transport modeling report that provides the predictions for boron,
sulfate and TDS is presented in Appendix G. Similarly, a geochemical
modeling report is presented in Appendix H. It describes the natural
attenuation of the constituents that have multiple natural attenuation
mechanisms, in addition to dilution.
6.5.2 Remedial Alternative 2 — Groundwater Extraction
(CAP Content Section 6.D.a)
Alternative 2 consists of groundwater extraction for remediation of the
groundwater north and northeast of Source Area 1, outside of the compliance
boundary and north associated with the comingling zone of Source Areas 1 and
3. Under this alternative, flow and transport modeling indicates compliance with
02L would be achieved in 9 years after system startup and operation along the
basin compliance boundary.
6.5.2.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
CCR constituents in groundwater associated with the EAB occur at or
beyond the compliance boundary to the northeast and north of the EAB at
concentrations detected greater than applicable 02L standards, IMAC, or
background values, whichever is greater. Remediation goals are to restore
groundwater quality at or beyond the compliance boundary by returning
COIs to acceptable concentrations (02L/IMAC or background, whichever is
greater), or as closely thereto as is economically and technologically feasible
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consistent with 15A NCAC 02L. 0106(a). In the future, alternative standards
may be proposed as allowed under 02L .0106(k). This approach is
considered reasonable given the documented lack of human health or
ecological risk at Roxboro (CAP Content Section 6.D.a.i.2).
The following groundwater COIs to be addressed by corrective action are
identified (Table 6-6) and discussed in Section 6.1: boron, sulfate and TDS.
The conceptual model and predictive modeling discussions summarize the
foundations for development of the groundwater extraction alternative.
More extensive discussion of the CSM can be found in Section 5.0,
discussion of flow and transport modeling in Appendix G, and discussion
of geochemical modeling in Appendix H.
6.5.2.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
The applicable technologies that comprise this alternative include:
• 20 extraction wells to the north and northeast of the EAB:
5 extraction wells in the area of the unnamed pond north of the
EAB, and
■ 15 extraction wells are in the area northeast of the EAB.
• 12 extraction wells in the comingling zone near the DFAHA.
• Pumps, associated piping, and control systems
• Discharge piping and structure
The proposed design and well locations are shown on Figure 6-17a. The
wells are screened through the transition and bedrock flow zones with an
average screen length of 146 feet to an average depth of 226 feet bgs. The
flow and transport model predicts a total groundwater extraction flow rate
of approximately 23 gpm. The number of extraction wells is estimated
based on flow and transport modeling results (Appendix G). Table 6-13
summarizes the extraction well system information.
The system's design includes a large number of extraction wells to be
completed into bedrock to allow full drawdown within the transition (if
saturated) and upper bedrock flow zones. Depths of bedrock extraction
wells are dependent on the current vertical distribution of COIs within
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bedrock in these areas and ranges from 120 feet bgs to 180 feet bgs in the
design.
Based on the CSM (Section 5.0) and flow and transport modeling results
(Appendix G), the groundwater COIs are hydraulically controlled within
the topographic drainage basin of the EAB, with the exception of the landfill
halo area and downgradient additional source areas, which will be
remedied by the planned remediation system.
The distribution of conservation COIs (boron, sulfate, and TDS) represents
the area of maximum COI distribution at or beyond the EAB compliance
boundary. Focusing remedial action selection on addressing the mobile
COIs will also address the reactive COIs as they will follow the same flow
path but with greater attenuation. This alternative addresses all the Site
specific COIs through groundwater extraction. Because this alternative
provides hydraulic control and capture of boron, the most mobile COI, it
addresses all of the targeted COIs.
It is expected that extracted water would be discharged through the LRB by
way of the in -ground sump at the DFA silos area. The LRB discharges to
the wastewater discharge canal system through internal outfall 012B. The
discharge canal goes to the heated water discharge pond with discharge to
Hyco Reservoir through NPDES Outfall 003. Based on currently available
groundwater data, the current NPDES permit, and the draft permit issued
for renewal in 2018, the extracted discharge would not cause violations. A
preliminary summary of groundwater data and discharge permit limits is
presented in the table NPDES Permit Limits and Anticipated Groundwater
Remediation Parameter Levels in Section 6.4.5.
Analysis of predicted specific COI concentrations and mass in extracted
groundwater during conceptual design of the extraction system may be
completed to further assess compliance with discharge regulatory
requirements. Treatment technologies, if necessary, for extracted
groundwater will be evaluated after NCDEQ approval of the CAP Update
and after pilot testing for the proposed extraction system is complete.
6.5.2.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
A groundwater extraction system would hydraulically control and remove
COI mass at or beyond the compliance boundary. The low permeability of
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the formations might limit extraction flow rates. Groundwater flow and
transport simulated groundwater extraction flow rates, with an assumed 50
percent well efficiency, are approximately 0.7 gpm. The flow and transport
report (Appendix G) and geochemical modeling report (Appendix H)
provide detailed predictions, descriptions, and explanations of the effects of
groundwater extraction.
The flow and transport model predicts the maximum extent of the COI
plume, sourced from the EAB, at any point in time will be approximately
300 feet beyond the compliance boundary (Figure 6-17e). Simulations
indicate that boron concentrations in groundwater would meet the 02L
boron standard of 700 µg/L at the compliance boundary in approximately 9
years after system startup and operation.
6.6 SA1 Remedial Alternatives Screening Criteria
(Supplemental Information for CAP Content Section 6.D.a.iv)
This section provides supplemental information beyond the CAP content guidance to
describe the screening criteria used to evaluate groundwater remediation alternatives at
Cliffside.
The screening criteria used to evaluate technologies and alternatives for groundwater
corrective action associated with Source Area 1 per are described below. These
screening criteria are based on the criteria outlined in 15A NCAC 02L .0106(i) and 40
CFR 300.430. The source of the screening criteria descriptions is provided in 40 CFR
300.430. These screening criteria will be used in evaluating remedial alternatives
identified in Section 6.5.
• Protection of human health and the environment
• Compliance with applicable regulations
• Technical and logistical feasibility
• Time required to initiate and implement corrective action alternative
• Short-term effectiveness
• Long-term effectiveness and permanence
• Reduction of toxicity, mobility, and volume
• Time required to achieve remediation goals
• Cost
• Community acceptance
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Additional considerations for remedial alternative evaluations include:
• Adaptive site management and remediation considerations
• Sustainability
Protection of Human Health and the Environment
The Human and Ecological Risk Assessments report (Appendix E) has determined that
there are no unacceptable risks to public health and safety or the environment
associated with coal ash basin or coal ash constituents in Site soil and
groundwater. The risk assessment indicates acceptable risk and no exposure to
residential receptors at or near the ash basin (no completed exposure pathways). The
assessment did not indicate an increase of risks to ecological receptors (mallard duck,
great blue heron, muskrat, river otter, bald eagle, American robin, meadow vole, red-
tailed hawk, red fox and killdeer bird) exposed to surface water and sediments
associated with the ash basin. Regardless, potential corrective measures are being
evaluated for regulatory compliance.
Technologies and remedial alternatives are evaluated to determine whether they can
achieve regulatory compliance within a reasonable timeframe, without detriment to
human health and the environment.
Compliance with Applicable Regulations
Technologies and alternatives are herein evaluated to assess compliance with applicable
federal and state environmental laws and regulations. These include:
• CAMA (NC SB 729, Subpart 2)
• Groundwater Standards (NCAC, Title 15A, Subchapter 02L)
• Well construction and maintenance standards (NCAC Title 15A Subchapter 02C)
• NPDES (40 CFR Part 122)
• Sediment erosion and control (NCAC Title 15A Chapter 04)
Technical and Logistical Feasibility
The ease or difficulty of implementing technologies and alternatives are assessed by
considering the following types of factors as appropriate:
• Technical feasibility, including technical difficulties and unknowns associated
with the construction and operation of a technology, the reliability of the
technology, ease of undertaking additional remedial actions, and the ability to
monitor the effectiveness of the remedy
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• Administrative feasibility, including activities needed to coordinate with
agencies, and the ability and time required to obtain any necessary approvals
and permits
• Availability of services and materials, including the availability of adequate off -
Site treatment, storage capacity, and disposal capacity and services; as well as the
availability of necessary equipment and specialists, and provisions to ensure any
necessary additional resources
Time Required to Initiate and Implement Corrective Action
Alternative
The time required to initiate and fully implement a groundwater remedial action takes
into consideration the following activities, if applicable:
• Source control measures
• Bench -scale testing, if needed
• Treatability testing
• Pilot testing
• Hydraulic conductivity testing
• Groundwater remedial alternative system design
• Permitting
• Procurement
• System installation
• System startup
These activities may be requisite to finalizing the system design, attaining regulatory
approval, or initiating construction. Therefore, these activities may dictate the time
needed to initiate and fully implement a groundwater remedial alternative.
Short-term Effectiveness
The short-term effects of alternatives are assessed considering the following:
• Short-term risks that might be posed to the community during implementation
• Potential impacts on workers during implementation and the effectiveness of
mitigation
• Potential environmental effects during implementation and the effectiveness of
mitigation
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• Time until protection is achieved
Long-term Effectiveness and Permanence
Technologies and alternatives are assessed for long-term effectiveness in reducing COI
concentrations and permanence in maintaining those reduced concentrations in
groundwater, along with the degree of certainty that technologies will be successful.
Factors considered, as appropriate, include the following:
• Magnitude of residual risk remaining from untreated material remaining at the
conclusion of remedial activities. The characteristics of the residuals should be
considered to the degree that they could affect long-term achievement of
remediation goals, considering their volume, toxicity, and mobility. Since there
is no current risk, the potential for a remedial technology to increase potential
risk to a receptor is considered in the evaluation process.
• Adequacy and reliability of controls as a means of evaluating alternatives in
addition to managing residual risk.
Reduction of Toxicity, Mobility, and Volume
The degree to which technologies employ recycling or treatment that reduces toxicity,
mobility, or volume will be assessed, including how treatment is used to address the
principal risks posed at the Site. Factors considered, as appropriate, include the
following:
• The treatment or recycling processes the technologies employ and constituents
that will be treated
• The mass of COIs that will be destroyed, treated, or recycled
• The degree of expected reduction in toxicity, mobility, or volume
• The degree to which the treatment is irreversible
• The type and quantity of residuals that will remain after treatment, considering
the persistence, toxicity, and mobility of such substances and their constituents
• The degree to which treatment reduces the inherent hazards posed by risks at the
Site
Time Required to Achieve Remediation Goals
This criterion includes the estimated time necessary to achieve remedial action
objectives. This includes time required for permitting, pilot scale testing, design
completion and approval, and implementation of approved remedies.
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Cost
The costs of construction and long-term costs to operate and maintain the technologies
and alternatives are considered. Costs that are grossly excessive compared to overall
effectiveness may be considered as one of several factors used to eliminate alternatives.
Alternatives that provide effectiveness and implementability similar to that of another
alternative by employing a similar method of treatment or engineering control, but at
greater cost, may be eliminated.
Community Acceptance
This assessment considers likely support, concerns, or opposition from community
stakeholders about the alternatives. This assessment might not be fully informed until
comments on the proposed plan are received. However, some general assumptions of
how an alternative would be accepted by the community can be made.
Adaptive Site Management and Remediation Considerations
Remediation alternatives are evaluated to determine whether an adaptive site
management process would address challenges associated with meeting remedial
objectives. Adaptive site management is the process of iteratively reviewing site
information, remedial system performance, and current data to determine whether
adjustments or changes in the remediation system are appropriate. The adaptive site
management approach may be adjusted over the site's life cycle as new site information
and technologies become available. This approach is particularly useful at complex sites
where remediation is difficult and may require a long time, or where NCDEQ approves
alternate groundwater standards for COIs, such as 4,000 µg/L for boron, pursuant to its
authority under 15A NCAC 02L .0106(k). Duke Energy might request alternate
standards for ash basin -related constituents, including boron as allowed under 15A
NCAC 02L .0106(k). Alternate standards are appropriate at the BCSS given the lack of
human health and ecological risks at the Site. Factors included in this evaluation
include:
• Potential to hinder use of alternative or contingency technologies later
• Suitability to later modifications or synergistic with other technologies
• Information that could be gained from technology implementation to improve
the CSM and better inform future remediation decision -making
• Ability to adjust and optimize the technology based on performance data
• Suitability for implementation in a sequential remedial action strategy
• Flexibility to implement optimization without significant system modifications
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Sustainability
In accordance with sustainability corporate governance documents integral to Duke
Energy and guidance provided by the USEPA, analysis of the sustainability of the
remedial alternatives proposed in this CAP Update was identified as an important
element to be completed as part of remedy selection process described herein.
Sustainable site remediation projects maximize the benefit of cleanup activities through
reductions of the footprint of selected remedies, while preserving the effectiveness of
the cleanup measures.
The USEPA, along with ASTM International, developed the Standard Guide to Greener
Cleanups - ASTM E2893, which was utilized during the evaluation process as part of
the remedial alternative selection effort. ASTM E2893 describes a process to evaluate
and implement cleanup activities in order to reduce the footprint of remediation
projects. Two primary approaches are described in the document: a qualitative Best
Management Practices (BMP) process and quantitative evaluation. Quantitative
evaluation was utilized for remedy selection in this CAP Update.
As stated in the ASTM standard, during the remedial selection process, "... the user
considers how various remedial options may contribute to the environmental footprint.
Conducting a quantitative evaluation at this phase of the remedial alternative selection
process provides stakeholders with information to help identify environmental
footprint reduction opportunities for all alternatives that are protective of human health
and the environment, comply with applicable environmental regulations and guidance,
and meet project objectives (ASTM, 2016)."
Each remedial alternative has been assessed using SiteWiseTM, a public domain tool for
evaluating remediation projects based on the overall footprint. SiteWiseTM estimates
collateral impacts through several quantitative sustainability metrics. The output data
from SiteWiseTM that can be utilized for remedial alternative comparison includes
greenhouse gases, energy usage, and criteria air pollutants (including sulfur oxides,
oxides of nitrogen, and particulate matter), water use, and resource consumption. The
assessment quantified impacts associated with activities expected to occur during the
remedial alternative construction phase, system operations where applicable and long-
term monitoring.
Two core elements of the USEPA's Greener Cleanup principles were not quantified
through the use of the SiteWiseTM tool, as part of the alternatives evaluation: water
consumption and waste generation. The analysis tool is set up to quantify the footprint
of municipal water use and the accompanying discharge of wastewater for treatment to
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a POTW. The remediation activities proposed in the CAP Update do not use municipal
water or discharge to a POTW, thereby making that input inapplicable for the
calculation. Due to the difficulty of estimating reliable quantities of waste generated
during construction the input was considered too uncertain to use as a criteria. For the
quantitative evaluation of alternatives discussed here, the primary assessments for
consideration during sustainability screening are CO2, NOx, SOx, PM10 and energy
usage.
Results of these sustainability evaluations are presented and discussed in the detailed
analysis sections of the specific alternatives (Section 6.7).
6.7 SA1 Remedial Alternatives Criteria Evaluation
(CAP Content Section 6.D.a.iv)
Groundwater remediation Alternatives 1 and 2 were formulated in Section 6.5 using
groundwater remediation technologies evaluated and retained for consideration
in Section 6.4. The criterion for conducting detailed analysis of each groundwater
remedial alternative are presented and explained in Section 6.7. The groundwater
remediation alternatives formulated in Section 6.5 will undergo detailed comparative
analysis in the following subsections. A summary of the remediation alternative
detailed analysis is also included in Appendix M.
6.7.1 Remedial Alternative 1: Monitored Natural Attenuation
Protection of Human Health and the Environment
(CAP Content Section 6.D.a.iv.1)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in risks
to human health related to Source Area 1 have been identified. The groundwater
corrective action is being planned to address regulatory requirements. The risk
assessment identified no current human health or ecological risk associated with
groundwater downgradient of the ash basin. Water supply wells are located
upgradient of the ash basin and water supply filtration systems have been
provided to those who selected this option. There are no surface water quality
concerns downgradient of the COI -affected plume since the groundwater
discharges to the NPDES-permitted wastewater ponds.
Based on the absence of receptors, it is anticipated that MNA would continue to
be protective of human health and the environment because modeling results
indicate COI concentrations will diminish with time. Natural attenuation
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mechanisms will reduce COI concentrations, and model predictions indicate that
no existing water supply wells would be impacted.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
MNA would comply with applicable regulations assuming the conditions
provided in 02L can be achieved. State and federal groundwater regulations
allow for MNA as an acceptable remediation program if regulatory requirements
are met. The following are the applicable 02L regulations:
(l) Any person required to implement an approved corrective action plan for a non -
permitted site pursuant to this Rule may request that the Director approve such a
plan based upon natural processes of degradation and attenuation of contaminants. A
request submitted to the Director under this Paragraph shall include a description of
site specific conditions, including written documentation of projected groundwater
use in the contaminated area based on current state or local government planning
efforts; the technical basis for the request; and any other information requested by the
Director to thoroughly evaluate the request. In addition, the person making the
request must demonstrate to the satisfaction of the Director: (1) that all sources of
contamination and free product have been removed or controlled pursuant to
Paragraph (f) of this Rule; (2) that the contaminant has the capacity to degrade or
attenuate under the site -specific conditions; (3) that the time and direction of
contaminant travel can be predicted with reasonable certainty; (4) that contaminant
migration will not result in any violation of applicable groundwater standards at any
existing or foreseeable receptor; (5) that contaminants have not and will not migrate
onto adjacent properties, or that: (A) such properties are served by an existing public
water supply system dependent on surface waters or hydraulically isolated
groundwater, or (B) the owners of such properties have consented in writing to the
request; (6) that, if the contaminant plume is expected to intercept surface waters, the
groundwater discharge will not possess contaminant concentrations that would
result in violations of standards for surface waters contained in 15A NCAC 2B
.0200, (7) that the person making the request will put in place a groundwater
monitoring program sufficient to track the degradation and attenuation of
contaminants and contaminant by-products within and down gradient of the plume
and to detect contaminants and contaminant by-products prior to their reaching any
existing or foreseeable receptor at least one year's time of travel upgradient of the
receptor and no greater than the distance the groundwater at the contaminated site is
predicted to travel in five years; (8) that all necessary access agreements needed to
monitor groundwater quality pursuant to Subparagraph (7) of this Paragraph have
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been or can be obtained, (9) that public notice of the request has been provided in
accordance with Rule .0114(b) of this Section; and (10) that the proposed corrective
action plan would be consistent with all other environmental laws.
Appendix I includes a detailed evaluation of the applicability of Alternative 1:
MNA as a remedial alternative for the Site.
Long -Term Effectiveness and Permanence
(CAP Content Section 6.D.a.iv.3)
MNA would be an effective long-term technology, assuming source control and
institutional controls (such as an RS designation) for the affected area. Natural
attenuation mechanisms are understood and have been documented
(Appendix I). Once equilibrium conditions of COI concentrations less than 02L
standards are achieved, it is predicted the concentrations would not increase.
Implementation of MNA will not result in increased residual risk as current
conditions and predicted conditions do not indicate unacceptable risk to human
health or environment. Additionally, Duke Energy installed 80 water filtration
systems within a half -mile of the ash basin compliance boundaries in accordance
with G.S. 130A-309.211(cl). Furthermore, institutional controls (provided by the
restricted designation) to limit access to groundwater use are proposed.
The adequacy and reliability of this approach would be documented with the
implementation and maintenance of an effectiveness monitoring program to
identify variations from the expected conditions. If factors that are not known at
this time were to affect the attenuation process in the future, alternative
measures could be taken. Monitoring will be in place to evaluate progress and
allow sufficient time to implement changes.
Reduction of Toxicity, Mobility, and Volume
(CAP Content Section 6.D.a.iv.4)
While the COIs are inorganic and cannot be destroyed, they exist in the aquifer
as molecules that interact with the natural components of the matrices to prevent
mobility and toxicity to receptors. MNA can reduce aqueous concentrations
while increasing solid phase concentrations and can therefore, under certain
geochemical conditions, reduce COI plume concentrations, volume, and mass.
There are no treatment or recycling processes involved with MNA as well as no
residuals.
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Short-term Effectiveness
(CAP Content Section 6.D.a.iv.5)
The stability and limited areal extent of the COI plume, along with no
unacceptable risks to human and ecological receptors, indicate current conditions
are protective. Therefore, the technology is effective in the short-term.
There are 172 monitoring wells installed at the Roxboro site including wells
associated with the EAB and the GSA/DFAHA. Although some wells within the
immediate area of the EAB will have to be abandoned as part of the closure
process, monitoring wells along the waste boundary and at select downgradient
areas will remain to monitor natural attenuation in the short-term.
Technical and Logistical Feasibility
(CAP Content Section 6.D.a.iv.6)
A majority of the 172 monitoring wells have dedicated sampling equipment and
an approved interim monitoring plan is in place. A subset of these monitoring
wells could be immediately used for MNA purposes. Therefore, the technology
could be implemented easily and immediately. Other than the abandonment of
select wells within the EAB from closure and potential installation of additional
monitoring wells, no construction is required to implement this option.
Implementation of an MNA program is a well-defined process, with established
requirements for sampling, laboratory analysis, reporting, performance review,
and communication of findings to stakeholders.
Time Required to Initiate and Implement Corrective Action
Technologies and Alternatives
(CAP Content Section 6.D.a.iv.7)
The time required for implementation of an MNA program could be as
immediate as approval of the approach since an extensive monitoring well
network already exists. Procedures for collection, analysis, and communication
of results are also established and currently in place.
Predicted Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that concentrations of COIs would meet
02L standards at the compliance boundary for more than 200 years after ash
basin closure. This estimate is based on boron reaching a concentration of 700
µg/L at the existing compliance boundary.
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Cost
(CAP Content Section 6.D.a.iv.9)
Roxboro has an extensive groundwater monitoring well networks in place. MNA
performance monitoring for Source Area 1 would utilize a subset of existing
wells. Procedures for collection, analysis, and communication of results are also
established and currently in place. Because there would be less required
materials and therefore a smaller capital cost and annual cost, the costs of
Alternative 1 would be comparatively less, when compared to Alternative 2.
Despite this, the significantly longer lifetime of the Alternative 1 system
operating (for more than 200 years) indicates that life cycle costs could be
significant.
Community Acceptance
(CAP Content Section 6.D.a.iv.10)
It is expected that there will be positive and negative sentiment about
implementation of an MNA program. No landowner is anticipated to be affected.
The property is owned by Duke Energy, which is anticipated to have
institutional controls. However, until the final corrective action is developed and
comments are received and reviewed, assessment of community acceptance will
not be fully informed.
MNA as a remedial alternative would be protective of human health and the
environment. Consistent with the USEPA Office of Solid Waste and Emergency
Response (OSWER) Directive 9200.4-17P (April 21, 1999) the use of MNA "does
not imply that EPA or the responsible parties are 'walking away' from cleanup or
financial responsibility at a site."
Adaptive Site Management and Remediation Considerations
MNA is an adaptable process and can be an effective tool in identifying the need
for alternative approaches if unexpected changes in Site conditions occur. An
MNA program would not hinder or preempt the use of other remedial
approaches in the future if conditions change. In fact, an effectiveness monitoring
program is an essential part of any future remedial strategy. An MNA
effectiveness monitoring program for Source Area 1 would provide information
about changing Site conditions during and after source control measures.
Sustainabi/ity
The footprint of Alternative 1 was quantified based on energy use and associated
emissions, during groundwater monitoring activities (e.g., transportation). The
results of the footprint calculations for MNA are summarized in Table 6-14. A
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summary of sustainability calculations for Alternative 1 can be found in
Appendix L.
The footprint of the MNA alternative is the least energy -intensive of the remedial
alternatives being considered, providing reduced, comparative footprint metrics
in overall energy use and across all air emission parameters. The MNA
alternative utilizes significantly fewer resources throughout the cleanup
timeframe when compared to the other alternatives.
6.7.2 Remedial Alternative 2 — Groundwater Extraction
Protection of Human Health and the Environment
(CAP Content Section 6.D.a.iv.1)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in risks
to human health related to Source Area 1 have been identified. The groundwater
corrective action is being planned to address regulatory requirements. The risk
assessment identified no current human health or ecological risk associated with
groundwater downgradient of Source Area 1. Water supply wells are located
upgradient of the EAB and water supply filtration systems have been provided
to those who selected this option. There are no surface water quality concerns
downgradient of the COI -affected plume since the groundwater discharges to
the NPDES-permitted wastewater ponds.
Based on the absence of receptors, it is anticipated that groundwater extraction
would create conditions that continue to be protective of human health and the
environment because the COI concentrations will diminish with time. By
extracting COI mass within the existing COI plumes, which are not affecting
receptors, active groundwater extraction would further protect human health
and the environment. Therefore, water supply wells would remain unaffected by
COIs related to the source area.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
Groundwater extraction would comply with applicable regulations. Those
regulations would include: CAMA, groundwater standards, and extraction well
installation and permitting. Discharge of extracted water would be in compliance
with appropriate discharge requirements, such as pH or other COI limitations in
the NPDES permit, and proper operation and maintenance of an effectiveness
monitoring system. Activities will also be in compliance with applicable
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regulations with proper operation and maintenance of an effectiveness
monitoring system.
Long-term Effectiveness and Permanence
(CAP Content Section 6.D.a.iv.3)
Groundwater extraction may contribute to effective and permanent achievement
of groundwater standards. Although, as indicated by the modeling results for
this alternative, extraction flow rates would be low. However, it still can provide
a benefit through hydraulic capture, which is a significant factor in achieving
remedial objectives. If factors that are not known at this time were to affect the
remediation process in the future, alternative measures could be taken to modify
the remedial approach.
Reduction of Toxicity, Mobility, and Volume
(CAP Content Section 6.D.a.iv.4)
Although the COIs are inorganic and cannot be destroyed, a groundwater
extraction system would help reduce COI concentrations and, therefore, toxicity,
mobility, and volume of COI -affected groundwater. Groundwater extraction
would remove constituent mass from the area of regulatory concern. The
extracted groundwater would be appropriately treated and discharged according
to applicable regulatory requirements. It is anticipated that extracted
groundwater would be discharged to Hyco Reservoir through the NPDES
permitted Outfall 003. Analysis of predicted specific COI concentrations and
mass in extracted groundwater during conceptual design of the remediation
system may be completed to further assess compliance with discharge regulatory
requirements. Treatment technologies for extracted groundwater would be
further evaluated after NCDEQ approves the CAP Update and after pilot testing
for the proposed extraction system is complete.
Short-term Effectiveness
(CAP Content Section 6.D.a.iv.5)
The stability and limited extent of the COI plume, along with the absence of
completed exposure pathways, indicates there are no short-term effects on the
environment, workers or the local community. While there are areas with COI
concentrations greater than 02L concentrations, the areas are not presenting
unacceptable short-term risks. Hydraulic capture of groundwater would occur as
soon as the groundwater extraction system is placed into service.
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Technical and Logistical Feasibility
(CAP Content Section 6.D.a.iv.6)
Installation of the proposed a groundwater extraction system would require
significant efforts in planning, designing, and execution of site preparation. The
extensive layout of groundwater remediation system wells, piping, and
treatment system components, as well as site topography and other access
constraint, such as power block infrastructure that would pose significant
challenges to constructability. However, with early awareness of the
aforementioned complexities and effective communications between the design,
implementation and project management teams, successful construction of the
system would be anticipated.
Time Required to Initiate and Implement Corrective Action
Technologies and Alternatives
(CAP Content Section 6.D.a.iv.7)
Design and installation of the system could be completed in approximately two
to three years after CAP approval.
Predicted Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that concentrations of COIs would meet
02L standards at the compliance boundary in approximately 9 years after ash
basin closure. This estimate is based on boron reaching a concentration of 700
µg/L at the existing compliance boundary.
Cost
(CAP Content Section 6.D.a.iv.9)
The increase in materials and equipment required, the capital cost and annual
cost would be significantly more than Alternative 1. Despite this, the
significantly less lifetime of the Alternative 2 system operating indicates that the
life cycle costs would be much less compared to Alternative 1. A detailed cost
estimate for Alternative 2 is provided in Appendix K.
Community Acceptance
(CAP Content Section 6.D.a.iv.10)
It is expected that there will be positive and negative sentiment about
implementation of a groundwater extraction system. No landowner is
anticipated to be affected. It is anticipated that the extracted groundwater would
be discharged through a NPDES permitted outfall that flows to Hyco Reservoir
and that the discharge would meet all permit limits. A groundwater extraction
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system which addresses potential COI plume expansion across the entire north
and northeast perimeter of the EAB may improve public perception.
It is anticipated that groundwater extraction would generally receive more
positive community acceptance than MNA under Alternative 1 since it involves
more active measures to attempt physical extraction of COI mass from
groundwater. This alternative would likely be perceived as more robust than
MNA in addressing groundwater impacts. Until the final Site remedy is
developed and comments are received and reviewed, assessment of community
acceptance will not be fully known.
Adaptive Site Management and Remediation Considerations
Groundwater extraction using conventional well technology is an adaptable
process. It can be easily modified to address changes to COI plume configuration
or COI concentrations. Individual well pumping rates can be adjusted or
eliminated or additional wells can be installed to address COI plume changes.
Also, while it is not expected, treatment of the system discharge can be modified
to address changes in COI concentrations or permit limits.
Sustainabi/ity
The footprint for Alternative 2 was quantified based on energy use and
associated emissions, during the construction phase (e.g., material quantities and
transportation), active remediation activities (e.g., groundwater pumping and
treatment) and groundwater monitoring activities (e.g., transportation). The
results of the footprint calculations for Alternative 2 are summarized in Table 6-
14. A summary of sustainability calculations for Alternative 2 can be found in
Appendix L.
The emission -intensive Alternative 2 requires significantly more materials and
energy than Alternative 1; however, the reduced timeframe of remediation
system operation for Alternative 2 (9 years) is significantly less that Alternative 1
(greater than 200 years) and therefore presents a dramatically smaller
environmental footprint.
6.8 SA1 Proposed Remedial Alternative Selected
For Source Area 1
(CAP Content Section 6.E)
Based on the alternatives detailed analysis presented in Section 6.7 and summarized in
Appendix L, the selected remedy for groundwater remediation is Alternative 2,
Groundwater Extraction.
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6.8.1 Description of Proposed Remedial Alternative and
Rationale for Selection
(CAP Content Section 6.E.a)
The selected remedy for groundwater remediation, Alternative 2, is intended to
provide the remedial technology that has demonstrated to provide the most
effective means for restoration of groundwater quality at or beyond the
compliance boundary by returning COIs to acceptable concentrations (02L/IMAC
or background, whichever is greater), or as closely thereto as is economically and
technologically feasible, consistent with 15A NCAC 02L. 0106(a), and to address
15A NCAC 02L .0106(j) (CAP Content Section 6.E.a.i).
This alternative meets the correction action objectives described in Section 1.0 of
this CAP Update in the expeditious timeframe through groundwater extraction.
Although there are no significant risks to human or ecological receptors, the
alternative will meet the regulatory requirements most effectively.
The groundwater remediation system includes 32 vertical extraction wells. It also
includes all associated piping and controls in order to discharge the extracted
water to the LRB. Figure 6-17a provides a conceptual layout of the proposed
groundwater extraction system. Model results predict the 02L standard of 700
µg/L for boron will be achieved at the EAB compliance boundary in
approximately 9 years after remedial alternative implementation (Figure 6-17e).
Both groundwater remedial alternatives evaluated contribute to continued
protection of human health and the environment, however, a the approach of
groundwater extraction to be the most practical solution given the predicted time
frames for 02L compliance and costs. Rationale for selections follows, and is
based off multiple lines of evidence, including empirical data collected at
Roxboro, geochemical modeling, and groundwater flow and transport modeling.
Alternative 1 relies on natural attenuation processes and, while there is evidence
to suggest that natural attenuation is occurring, one or more levels of the MNA
tiered analysis did not meet evaluation criteria for selecting groundwater
remedial alternative, including:
• Predicted timeframe to achieve applicable criteria at the compliance
boundary is greater than 200 years, which does not meet the criteria of
achieving the standards at a timeframe similar to more active remedies.
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• Boron concentrations greater than the 02L standard occur in bedrock, at or
beyond the compliance in areas north and northeast of the EAB, based on
empirical data supported by groundwater model simulations.
More detail on the results from the MNA tiered analysis and why MNA alone is
not an appropriate corrective action solution at this time can be found in
Appendix I. MNA may be an appropriate polishing remedy in the future.
Under Alternative 2, groundwater extraction is predicted to satisfy remedial
action objectives in a quicker timeframe (approximately 9 years) and at a reduced
cost and environmental footprint as compared to MNA (greater than 200 years).
Groundwater extraction generates a larger footprint in the sustainability
analysis. During design phases of the groundwater remediation project,
opportunities for energy efficiency and reduction of the project footprint can be
evaluated. The adaptability considerations that affect the cost analysis also
should be considered in sustainability considerations. Potential duplication of
intensive construction efforts should be considered.
This alternative is readily implementable, although it is the most costly
alternative due to the addition of the extraction wells. The long-term
effectiveness would be documented through an effectiveness monitoring
program detailed in Section 6.8.6. The system would be adaptable based on
effectiveness monitoring field data results.
6.8.2 Design Details
(CAP Content Section 6.E.b)
Design of the proposed groundwater extraction system would require a pilot test
(i.e., installation of a portion of the system) to facilitate refinement of the final
system design. A pilot test work plan will be prepared to facilitate
implementation of the system. As part of this process, the groundwater flow and
transport model may be refined, if necessary, to determine the final number and
locations of system wells. As the pilot testing and design process evolves,
refinements to the systems and timeframe, including a potential reduction in the
time needed to achieve compliance may occur compared to the model
predictions presented in this CAP Update.
The intent of the design would be to maximize pore volume exchange and
establish groundwater flow control and capture in areas adjacent to the EAB
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compliance boundary requiring corrective action. Basic installation components
of the recommended alternative include:
• 32 extraction wells and appurtenances
• Well vault and wellhead piping, fittings, and instrumentation
• A system to control water level within each groundwater extraction well
• Groundwater extraction system discharge piping
• Electric power supply
• Groundwater remediation telemetry system
• pH adjustment or other treatment systems, if necessary
Conceptual process flow diagrams for the groundwater extraction system is
provided on Figures 6-18b. The detailed design elements presented below may
be adjusted based on a final technical review.
6.8.2.1 Process Flow Diagrams for All Major Components
of Proposed Remedy
(CAP Content Section 6.E.b.i)
Below is a multi -step process for remedy design considerations and
implementation of major components, including design assumptions,
calculations, and specifications where applicable at the conceptual design
stage. Conceptual process flow diagrams for extraction and treatment
systems are provided on Figure 6-18b.
Site Preparation (STEP 1 — Create Access)
Installation of the proposed groundwater extraction system would require
significant efforts in planning, designing, and execution of site preparation.
The extensive layout of groundwater remediation system wells, piping, and
treatment system components pose challenges to constructability. However,
with early awareness of the aforementioned complexities and effective
communications between the design, implementation and project
management teams, successful construction of the system would be
anticipated.
Safe access roads for mobile construction equipment (e.g., drill rigs), as well
as long-term operation and maintenance needs, will likely require clearing,
grubbing, grading and access improvement.
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A certain level of flexibility regarding well placement is expected to be
required due to site conditions encountered during construction. Prior to
construction and following the pump tests, an assessment of the precise
locations of wells would be made in collaboration with the modeler, if
needed. If the model predictions are not affected, relocation from the
predetermined location due to terrain or other site -specific constraints
would expedite construction.
Land disturbance, anticipated to include some vegetation removal and
grubbing, will require erosion and sedimentation control to be implemented
and likely reviewed and approved by a regulatory agency. Adaptable E&SC
should be planned to limit project delays by avoiding formal modifications
of plans.
Additionally, arrangements will be required in order to maintain an
acceptable minimum working distance from the railroad tracks for safety.
Pilot Tests (STEP 2 — To Finalize Design)
A pilot test would involve installation of a portion of the planned system to
evaluate how the system performs and to make initial progress towards
remediation at the same time. The results of the pilot test would be used to
refine and scale up the final design thereby maximizing the likelihood of
successful operation in the field.
Extraction pilot test wells will be screened within or across a flow zone
similar to model simulations to the extent feasible.
Pilot test results will be used to:
• Determine site -specific well yields for each flow zone
• Validate predictive flow and transport modeling
• Refine calibration of the predictive flow and transport modeling, as
needed
• Confirm groundwater extraction well capture zones in the transition
and bedrock flow zones beyond the available data
• If warranted, make adjustments to the groundwater extraction
system design
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• If warranted, make design adjustments to conveyances for extracted
groundwater
• If warranted, make design adjustments to the groundwater treatment
system
The extraction wells used for pilot testing would be included in the final
groundwater remediation system design.
Extraction Well Design (STEP 3 - Install Wells)
(CAP Content Section 6.E.b.i)
The preliminary design for the groundwater remediation system includes
installation of 32 extraction wells (Figures 6-17a). The extraction wells
would be installed north and northeast of the EAB. The locations are based
on predicted COI plume configuration, with the intent of capturing
groundwater for COI mass removal and reduced migration of potenitally
mobile COIs. The predicted effects of the wells are defined in detail in flow
and transport modeling results (Appendix G).
The groundwater extraction wells would be completed in the transition and
bedrock flow zones with an average screen length of 146 feet to an average
depth of 226 feet bgs based on modeling simulations. Groundwater
extraction wells would be installed by a North Carolina licensed well driller
in accordance with NCAC 15A, Subchapter 2C - Well Construction
Standards, Rule 108 Standards of Construction: Wells Other Than Water
Supply (15A NCAC 02C .0108). Modeled extraction well details are
provided on Table 6-15. Typical well construction schematics for extraction
wells are included as Figure 6-17c.
The groundwater extraction wells might be drilled using hollow stem
auger, air percussion/hammer, sonic methods, or a combination thereof. The
drilling method would depend on Site conditions. All materials and
installations would be in accordance with 15A NCAC 02C. Completed
wells would be at least 6 inches in diameter to facilitate the installation of
pumps and instrumentation (e.g., level control) in groundwater extraction
wells. The top of the sand pack would extend to approximately 2 feet above
the top of well screens. A bentonite well seal at least 2 feet thick would be
installed on top of the sand pack. Neat cement grout with 5 percent
bentonite would be placed on top of the bentonite well seal and would fill
the remaining well annulus to within 3 feet of the ground surface. The
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groundwater extraction wells would be constructed with threaded casings.
Materials of construction and screen lengths and slot sizes will be based on
pilot testing. Wound wedge wire screens might be used to enhance
hydraulic efficiency and facilitate rehabilitation. Typical well construction
schematics for extraction wells are included as Figure 6-17c.
Well Head Configuration (STEP 4 — Construct Well Heads)
The proposed extraction well vaults would be precast concrete with
aluminum access doors that include a drainage channel. The concrete
enclosures would be finished below grade and the piping and fittings in the
enclosures would be Type 304 stainless steel to reduce risk of damage
during O&M. Due to the location of plant infrastructure and utilities, a few
of the extraction wells will be located in internal plant roads. Plant
personnel have indicated that the vehicular traffic on these roads are
passenger cars and light trucks travelling at speeds of 30 miles per hour or
less. Well heads that cannot be protected by bollards must have enclosures
meeting the appropriate H2O loading.
Any above ground piping would be insulated and heat traced. The piping
would transition from the Type 304 stainless steel to high density
polyethylene (HDPE) at a flange near the opening where the HDPE pipe
leaves the enclosure. The buried sections of pipe would be fusion -welded
HDPE (Figure 6-17d).
The enclosures would have a 2-inch drain with a compression cap for
controlled release of rainwater or condensate. A water level sensor would
be mounted on the wall of the enclosure approximately 6-inches above the
floor. Should water accumulate to that level, the extraction pump would be
stopped and an alarm sent to the operator, who can ascertain the cause of
the high water level.
Extraction Wells (STEP 5)
A pump would be installed in each groundwater extraction well. Selection
of pump type (e.g., electric submersible or pneumatic) would be determined
in the final design. If the water level in the well is above the top water level
switch, the pump would run to pump the water to lower water level switch,
which would cause the pump shut off. The flow of extracted groundwater
from the pump would be measured using a flow rate and flow totalizer
meter before being conveyed to groundwater discharge piping for disposal
(Figure 6-18b). Other appurtenances in the piping system would include:
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• a check valve to prevent back flow into the well,
• a sampling port, a pressure gauge to indicate the pressure generated
by the pump,
• ball valves to isolate piping for maintenance,
• flow control valve such as a stainless steel globe or gate valve (Figure
6-170
Operational parameters, such as flow and water level, and critical
malfunctions, such as accumulation of water in the well vault, would be
transmitted via telemetry system to inform the system operator of the status
in the well and enclosure.
Groundwater Extraction Water Treatment (STEP 6 —
Address Groundwater Treatment)
Extracted groundwater would be treated by conveyance to the LRB at the
site through the DFA silo sump. The water would discharged through the
permitted outfalls. Extracted groundwater would undergo any treatment
processes applicable to the LRB to satisfy applicable NPDES discharge
requirements.
Groundwater Extraction Well Discharge Piping (STEP 7 —
Conceptua/ Extraction System Considerations)
The proposed groundwater extraction system would consist of 32 new
groundwater extraction wells. Based upon predictive groundwater flow
and transport modeling, the groundwater extraction wells would generate
on average 0.7 gpm of extracted groundwater per well or about 23 gpm of
extracted groundwater collectively.
Each of the groundwater extraction wells would discharge into one of a
series of headers. Extracted groundwater in these headers then would flow
by gravity to one of several tanks. The collected groundwater in these tanks
would be pumped to a conveyance line ultimately discharging into the DFA
silo sump.
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6.8.2.2 Engineering Designs with Assumptions,
Calculations and Specifications
(CAP Content Section 6.E.b.ii)
Pipelines (STEP 8 — Pipeline Specifics)
High density polyethylene (HDPE) piping will be used for water
conveyance in all areas where buried piping will be installed. Water
conveyance will include groundwater pumped from extraction wells and
conveyed to the LRB.
HDPE piping will conform to standard HDPE pipe specifications such as
the following:
• ASTM F714, "Standard Specification for Polyethylene (PE) Plastic
Pipe (DR -PR) Based on Outside Diameter,"
• ASTM D3035,"Standard Specification for Polyethylene (PE) Plastic
Pipe (DR -PR) Based on Controlled Outside Diameter."
• ANSI/AWWA C906, 'Polyethylene (PE) Pressure Pipe and Fittings,
4" to 63", for Water Distribution and Transmission."
• Cell Classification PE445574C per ASTM D3350
• Plastics Pipe Institute (PPI) TR-4 Listing as PE4710 / PE3408
• Hydrostatic Design Basis 1,600 psi @ 73°F (23°C) and 1,000 psi @
140°F (60°C) per ASTM D2837
Fittings will be molded from HDPE compound having cell classification
equal to or exceeding the compound used in the pipe manufacture to ensure
compatibility of polyethylene resins. Substitution may be allowed for
approved material with use of flanged joint sections.
Heat fusion welding of the piping and fittings would be in accordance with
Duke Procedure Number: CCP-ENGSTD-NA-QA-004, "Quality Assurance
and Quality Control of HDPE Pipe Butt Fusion Joints Revision 3," July 8,
2019. Only qualified operators trained in Duke Energy's HDPE fusion
standards would be allowed to perform fusion welding.
Flanged connections would be in accordance with Duke Procedure
Number: CCP-ENGSTD-NA-QA-005, "Requirements for Installation of
Polyethylene Flanged Joints Revision Number 0," August 5, 2019.
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The locations of the HDPE piping systems for extraction are generally in
low traffic areas. The HDPE piping will be typically installed below grade
in 3-foot deep excavated trenches constructed with compacted granular
bedding material. The trenches will be backfilled with a minimum of 2-feet
of excavated native soil and compacted. Pipe in areas with regular traffic of
more than two axles will be installed in trenches designed to comply with
AWWA M-55, "PE Pipe — Design and Installation" or an approved
alternative design.
The design flow is 23 gpm for the groundwater extraction system. Each
groundwater extraction well will be connected to a header that ultimately
conveys extracted groundwater to the DFA silo sump. Preliminary
calculations pertaining to the piping design (e.g., pipe sizing, pressures,
flow, friction losses, etc.) are provided in Appendix N.
Localized collection tanks and pumps or pump stations might be integrated
into the piping system to allow for independent operation of various
segments of the system.
Hydrostatic leak testing in accordance with the most current edition of
Handbook of Polyethylene Pipe, or an approved alternate method, will be
performed and passed prior to the piping being placed into operation.
Pipe Network Calculations (STEP 9 — Pipeline Headloss
Calculations)
The groundwater extraction network was designed using Pipe Flow°
Expert. Pipe Flow° Expert is a software used to determine volumetric flow
rates, pressure in pipes, friction losses, pump head, and other information.
The calculated outputs and graphically represented conceptual network
layouts are found in Appendix N.
The extraction network consists of 32 extraction wells with trunk lines for
conveyance and branching pipes providing connections to the wells. The
network ultimately operates in gravity flow. The network was evaluated by
generating a model with well elevations and depths, pipe lengths, etc. Once
these values were incorporated, the calculations were performed using the
model to determine the nature of flow in the network and to ensure that the
desired movement in the pipe system was occurring. After the flow through
the system was verified, pipe diameters and required pump head outputs
were calculated. The calculation outputs took into account the interacting
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flows in the system and frictional losses from fittings and pipes to provide
evidence of the efficacy of the proposed pipe network layout design.
Telemetry System Design
The groundwater remediation system would be managed using telemetry
system that would enable remote monitoring and operational capabilities.
The telemetry system would be designed to meet the system owner O&M
requirements.
Electrical Design
It is unlikely that existing electrical capacity in the vicinity of the proposed
groundwater remediation system would be sufficient to provide electrical
power to the pumps, the small transfer pump in the collection well, and
other power requirements. Additional electrical capacity is anticipated to
meet groundwater remediation system power requirements.
System Operation and Maintenance Issues
The effectiveness of the system will be dependent on maintaining adequate
extraction flow rates through the wells, and stable water levels, for an
extended period of time. This will necessitate effective operation and
maintenance of the wells. As described in this section and in the
Contingency Plan (Section 6.8.8), each well will be equipped with a control
and monitoring system and monitored continuously by the control system,
and an alert sent if the water level falls outside the prescribed range.
Adjustments to pumping operations can be made if the root cause of the
alert is determined to be system performance.
Another factor in maintaining the effectiveness of the wells will be
monitoring and maintaining the well screens to prevent a loss of efficiency
due to mineral and/or biological fouling. If well performance monitoring
indicates a decrease in flow rate, the well will be inspected for fouling and
the screens will be cleaned as appropriate. Additionally, cleanouts will be
installed on pipes to facilitate periodic maintenance, preventing mineral
scaling or biological fouling on the conveyance pipe network.
In addition to well performance monitoring and maintenance, other system
elements, such as pumps controls, will receive routine maintenance in
accordance with the manufacturer's recommendations.
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6.8.2.3 Permits for Remedy and Schedule
(CAP Content Section 6.E.b.iii)
The design documents would provide the necessary plans and
specifications for procurement and construction purposes. This would
include Site layout drawings, plans and profiles, well enclosure details,
trench and discharge piping outlet details, well construction schematics,
piping and instrumentation diagrams/drawings and complete equipment,
materials and construction specifications.
Permit applications that may be needed for the proposed remedy include:
• Erosion and Sediment Control permit
• NPDES Stormwater permit
The schedule for obtaining permits is based on the project implementation
schedule discussed in Section 6.8.2.4 and presented on Figure 6-19.
6.8.2.4 Schedule and Cost of Implementation
(CAP Content Section 6.E.b.iv)
A Gantt chart (Figure 6-19) is provided for outlining a general timeline of
implementation tasks following CAP Update submittal. The exact timeline
of the schedule milestones is dependent on various factors, including
NCDEQ review and approval, permitting, weather, and field conditions.
Duke Energy will provide construction reports monthly from the beginning
of construction until construction is complete and Duke Energy assumes
full responsibility for operation of the groundwater remediation system.
Reporting will include:
• Health and Safety/Man Hours
• Tasks completed the prior month
• Problems affecting schedule (e.g., inclement weather)
• Measures taken to achieve construction milestones (e.g., increase
number of drilling crews)
• Contingency actions employed, if any
• Tasks to be completed by next reporting period
• Provide updated schedule/Gantt chart
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Duke Energy progress reports would be submitted to NCDEQ on a monthly
basis or as mutually agreed.
A detailed cost estimate for Alternative 2 is provided in Appendix K. The
cost estimate is based on capital costs for design and implementation, the
O&M cost, and monitoring costs, including well redevelopment and
replacement on an annual basis. The design costs include work plans,
design documents and reports necessary for implementation of the
alternative. Implementation costs include procurement and construction.
O&M costs are based on annual routine labor, materials and equipment to
effectively conduct monitoring, routine annual and 5-year reporting, as
applicable, and routine and non -routine maintenance costs.
6.8.2.5 Measures to Ensure Health and Safety
(CAP Content Section 6.E.b.v)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in
risks to human health related to Source Area 1 have been identified. The
groundwater corrective action is being planned to address regulatory
requirements. The risk assessment identified no current human health or
ecological risk associated with groundwater downgradient of the ash basin.
Water supply wells are located upgradient of the EAB and water supply
filtration systems have been provided to those who selected this option.
There are no surface water quality concerns downgradient of the COI -
affected plume since the groundwater discharges to the NPDES-permitted
wastewater ponds. Based on the absence of receptors, it is anticipated that
groundwater extraction would create conditions that continue to be
protective of human health and the environment because the COI
concentrations will diminish with time.
6.8.2.6 Description of All Other Activities and
Notifications Being Conducted to Ensure
Compliance with 02L, CAMA, and Other Relevant
Laws and Regulations
(CAP Content Section 6.E.b.vi)
This CAP Update is for the ash basins and the downgradient additional
sources as identified in NCDEQs April 5, 2019 letter (Appendix A). The
CAP Update addresses the requirements of G.S. Section 130A-309.211(b),
complies with NCAC 15A Subchapter 02L. 0106 corrective action
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requirements, and follows the CAP guidance provided by NCDEQ in a
letter to Duke Energy.
6.8.3 Requirements for 02L .0106(I) — MNA Rule.
(CAP Content Section 6.E.c)
The requirements for implementing corrective action by MNA, under 02L
.0106(1), are provided in Section 6.7.1 and Appendix I. MNA is not applicable at
this time for the EAB as described in Section 6.8.1.
6.8.4 Requirements for 02L .0106(k) — Alternate Standards
(CAP Content Section 6.E.d)
Regulation 02L .0106(k), states that a request may be made for approval of a
corrective action plan that uses standards other than the 02L groundwater
quality standards. G.S. Section 130A, Article 9, Part 8 allows risk -based
remediation as a clean-up option where the use of remedial actions and land use
controls can manage properties safely for intended use. Risk -based corrective
action is where constituent concentrations are remediated to an alternative
standard based on the actual posed risks rather than applicable background -
levels or regulatory standards. The requirements for implementing corrective
action by remediating to alternate standards, under 02L .0106(k), are as follows:
• Sources are removed or controlled;
• Time and direction of contaminant travel can be predicted with reasonable
certainty;
• COIs have and will not migrate onto adjacent properties unless specific
conditions are met (i.e., alternative water sources, written property owner
approval, etc.);
• Standards specified in Rule .0202 of this Subchapter will be met at a location no
closer than one year time of travel upgradient of an existing or foreseeable
receptor, based on travel time and the natural attenuation capacity of subsurface
materials or on a physical barrier to groundwater migration that exists or will be
installed by the person making the request,
• If contaminant plume is expected to intercept surface waters, the groundwater
discharge will not possess contaminant concentrations that would result in
violations of standards for surface waters contained in 15A NCAC 02B .0200;
• Public notice of the request has been provided in accordance with Rule .0114(b) of
this Section; and
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• Proposed corrective action plan would be consistent with all other environmental
laws
The alternative groundwater clean-up values may be used to aid in risk
management decisions at Roxboro This approach is particularly useful at
complex sites where changes in site conditions may require an extended period
of time or where NCDEQ approves alternate groundwater standards for COIs,
such as 4,000 µg/l for boron, pursuant to its authority under G.S. Section 15A
NCAC 02L .0106(k).
6.8.5 Sampling and Reporting
(CAP Content Section 6.E.e)
An effectiveness monitoring plan (EMP) has been developed as part of this CAP
Update consistent with 02L. 0106(h)(4). The EMP is designed to monitor
groundwater conditions at Roxboro and document progress towards the
remedial objectives over time. This plan is designed to be adaptive over the
project life cycle and can be modified as the groundwater remediation system
design is prepared, completed, or evaluated for termination.
Duke Energy implemented an Interim Monitoring Plan (IMP) that was submitted
to NCDEQ on December 21, 2018 and subsequent additional modifications were
agreed upon between Duke Energy and NCDEQ. The IMP includes the locations
of groundwater wells sampled quarterly and semiannually.
The EMP is required by G.S. Section 130A-309.211(b)(1)(e). The IMP will be
replaced by the EMP upon NCDEQ approval of the CAP Update. Either
submittal of the EMP, or the pilot test work plan and permit applications (as
applicable), will fulfill G.S. Section 130A-309.209(b)(3).
The EMP, presented in Appendix O, is designed to be adaptable and would
target key areas where changes to groundwater conditions are most likely to
occur due to corrective action and ash basin closure activities. EMP key areas for
monitoring are based on the following considerations:
• Include background locations
• Include designated flow paths
• Within areas of observed or anticipated changing Site conditions, and/or
have increasing constituent concentration trends
• Will effectively monitor COI plume stability and model simulation
verification
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• The EMP will be used to evaluate progress towards remediation
EMP elements including well systems, locations, frequency, parameters,
schedule and reporting evaluation are summarized below and outlined on Table
6-16. Effectiveness monitoring well locations are illustrated on Figure 6-20. The
EMP will be implemented 30 days after CAP approval, and will continue until
there is a total of three years of data confirming COIs are below applicable
standards at or beyond the compliance boundary, at which time a request for
completion of active remediation will be filed with NCDEQ. If applicable
standards are not met, the EMP will continue and transition to post -closure
monitoring, if necessary.
After ash basin closure and following ash basin closure certification, a post -
closure groundwater monitoring plan (PCMP) will be implemented at the Site
for a minimum of 30 years in accordance with G.S. Section 130A-309.214(a)(4)k.2.
If groundwater monitoring results are below applicable standards at the
compliance boundary for three years, Duke Energy may request completion of
corrective action in accordance with G.S. Section 130A-309.214(a)(3)b. If
groundwater monitoring results are above applicable standards, the PCMP will
continue. An EMP work flow and optimization process is outlined on a flow
chart on Figure 6-21a.
Optimization of the plan to help determine the remedy's performance,
appropriate number of sample locations, sampling frequency, laboratory
analytes, and statistical analysis to evaluate the plume stability conditions will be
conducted during EMP review periods. Optimization evaluation would be
conducted using software designed to improve long-term groundwater
monitoring programs such as Monitoring and Remediation Optimization System
(MAROS).
6.8.5.1 Progress Reports and Schedule
(CAP Content Section 6.E.e.i)
After groundwater remediation implementation, evaluation of Site
conditions, groundwater transport rates, and COI plume stability would be
based on quantitative rationale using statistical, mathematical, modeling, or
empirical evidence. Existing data from historical monitoring and pilot
testing would be used to provide baseline information prior to groundwater
remediation implementation. Schedule and reporting of system quantitative
evaluations, review and optimization would include:
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• Annual Reporting Evaluation: The EMP will be evaluated annually
for optimization and adaption for effective long-term observations,
using a data -need rationale for each location. The annual evaluation
would include a comparison of observed concentrations compared to
model predictions and an evaluation of statistical concentration trends,
such as the Mann -Kendall test.
Results of the evaluation would be reported in annual monitoring
reports and are proposed to be submitted to NCDEQ annually. The
reports will include the following:
■ Laboratory reports on electronic media,
■ Tables summarizing the past year's monitoring events,
■ Historical data tables,
■ Figures showing the historical data versus time for the
designated monitoring locations and parameters,
■ Figures showing sample locations,
■ Statistical analysis (Mann -Kendall test) of data to determine if
trends are present, if performed,
■ Identification of exceedances of comparative values,
■ Groundwater elevation contour maps in plan view and
isoconcentration contour maps in plan view for one or more of
the prior year's sampling events (as mutually agreed upon by
Duke Energy and NCDEQ),
■ Any notable observations related to water level fluctuations or
constituent concentration trends attributable to extraction system
performance or water table drawdown, and
■ Recommendations regarding modifications to the Plan
• 5-Year Review: Similar to annual evaluation and reporting, the EMP
would be re-evaluated and modified as part of each 5-year review
period as adaptive or, if necessary, additional corrective actions are
implemented or water quality observations warrant adjustments of the
plan. The annual evaluation would include elements of the annual
evaluation, plus updated background analysis, confirmation of risk
assessment, evaluation of statistical concentration trends, analytical
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result comparison and model verification. If needed, flow and
transport models could be updated as part of the 5-year review process
to refine future predictions and the associated routine data needed to
confirm the predictions.
Optimization of the monitoring network could be evaluated if the
remedy is determined to be effective or when conditions re -stabilize
after the implementation of closure or, if necessary, additional
corrective action implementation. Optimization of the monitoring
network could include a lesser monitoring frequency and/or parameter
list. Flow and transport model predictions indicate very slow changes
in conservative (boron) concentrations will occur over time.
Geochemical model predictions indicate very little or much slower
changes in the remaining COI distributions will occur. Therefore, a
monitoring frequency consistent with these predictions would be
proposed following confirmation of the models through site data.
If necessary, modifications to the corrective action approach would be
proposed to achieve compliance within the target timeframe.
A flow diagram for effectiveness monitoring plan work and optimization is
depicted on Figure 6-21a.
6.8.5.2 Sampling and Reporting Plan During Active
Remediation
(CAP Content Section 6.E.e.ii)
Groundwater Monitoring Network
EMP monitoring will provide a comprehensive monitoring strategy that (1)
monitors the performance and effectiveness of the selected remedial
alternative, (2) can provide adequate areal (horizontal) and vertical
coverage to monitor plume status at or beyond the compliance boundary
and with regard to potential receptors, and (3) confirm flow and transport
and geochemical model predictions. Active groundwater remedy
performance monitoring would be implemented north, north-northwest
and northeast of the EAB (Figure 6-20). EMP systems and objectives are
outlined below:
• Compliance with 02L
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• Measure and track the effectiveness of the proposed extraction
system
• Monitor plume status (horizontally and vertically)
• Verify predictive model simulations
• Verify no unacceptable impact to downgradient receptors
• Verify attainment of active remedy objectives through validated
model simulations
• Identify new potential releases of constituents into groundwater
from changing site conditions
• Monitor approved background locations
The EMP would include 42 existing monitoring wells for performance and
effectiveness monitoring (Table 6-16). Several of the existing monitoring
wells at the site might be abandoned from ash basin closure and related
construction activities. In the event that closure activities extend to the
proposed EMP well locations, the layout of wells would be modified, if
necessary.
Groundwater Monitoring Flow Paths - Trend Analysis
The monitoring program will provide adequate horizontal and vertical
coverage in the area of groundwater remediation to monitor:
Changes in groundwater quality as Site conditions change (e.g.,
groundwater remediation effects, ash basin closure commences),
• Transport rates, and
• Plume stability
Horizontal and vertical coverage would be provided by using groundwater
monitoring wells located downgradient of the source areas within the
corrective action area. To monitor performance, groundwater monitoring
wells are located within the area of corrective action at specific intervals or
as close as possible from the source area to a receptor as illustrated in
Figure 6-20.
Multi parameters sondes would be installed in wells along the primary flow
paths in the active remedy area (Figure 6-20). Table 6-16 provides a detailed
list of monitoring wells to be included in the EMP, along with wells
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proposed to have multi parameter sondes installed. Daily monitoring of
changes in groundwater quality on a real-time basis using multi -parameter
sondes and telemetry technology would allow continuous monitoring and
evaluation of geochemical conditions. Geochemical conditions (pH, Eh, and
dissolved oxygen) will be compared to geochemical modeling results to
evaluate changes that could potentially affect the mobility (Ka) of reactive
and variably reactive COIs. Water levels would also be monitored by the
multi -parameter sondes to verify simulated changes to groundwater flow
during and after basin closure. Having groundwater quality and water level
data in readily available will increase the response time to implement
contingencies if field parameters significantly deviate from predicted
responses. Contingency plans are included in Section 6.8.8.
Plume stability evaluation would be based primarily on results of trend
analyses. Trend analyses may be conducted using Mann -Kendall trend test.
The Mann -Kendall trend test is a non -parametric test that calculates trends
based on ranked data and has the flexibility to accommodate any data
distribution and is insensitive to outliers and non -detects. The test is best
used when large variations in the magnitude of concentrations may be
present and may otherwise influence a time -series trend analysis.
Trend analysis will be conducted using data from EMP geochemically
nonreactive, conservative constituents (Table 6-7). These constituents
include boron, sulfate, and TDS, and best depict the areal extent of the
plume and plume stability and physical attenuation, either from active
remedy or natural dilution and dispersion.
Trend analysis of designated groundwater monitoring flow path wells
(Figure 6-20) would be part of the decision metrics for determining
termination of the active remedy.
Sampling Frequency
Multiple years of quarterly and semiannual monitoring data are available
for use in trend analysis and to establish a baseline to evaluate corrective
action performance. The monitoring plan sampling frequency is based on
semi-annual sampling events to be consistent with other groundwater
monitoring performed at the Site.
Semi-annual monitoring following implementation of corrective action is
recommended for the 42 existing monitoring wells to be included in the
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EMP. Over four years of quarterly monitoring data are available for existing
wells, which will be used to supplement trend analysis and to establish a
baseline to evaluate corrective action performance.
Newly installed wells to be added to the EMP, if needed, would be
monitored by quarterly sampling events. Quarterly sampling would target
locations of proposed newly installed wells with fewer than four quarters of
data. Quarterly monitoring of parameters outlined on Table 6-16 is
proposed for newly installed wells (if applicable).
Quantitative evaluations would also determine additional data needs (i.e.,
increased sampling frequency) for refining statistical and empirical model
development. Additional monitoring described in the contingency plan
would be implemented if significant geochemical condition changes are
identified that could result in mobilization of reactive or variably -reactive
COIs.
Sampling and Analysis Protocols
EMP sampling and analysis protocol will be similar to the existing IMP with
some adjustment for anticipated changing site conditions. Detailed
protocols are presented in Appendix O. Samples would be analyzed by a
North Carolina certified laboratory for the parameters listed in Table 6-16
as summarized below. Laboratory detection limits for each constituent are
targeted to be at or less than applicable regulatory values (i.e., 02L or
IMAC).
• Groundwater Quality Parameters: Based on the constituent
management approach, 5 constituents warrant corrective action at
the Site, and are included as groundwater quality parameters to be
monitored as part of the EMP. These constituents are as follows:
• Boron • Sulfate
• Selenium • Total Dissolved Solids (TDS)
• Strontium
Geochemically conservative, non -reactive constituents boron, sulfate,
and TDS best depict the areal extent of the groundwater plume.
Analyses of these constituents will be used to monitor plume stability
and physical attenuation from groundwater flushing and extraction,
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by comparing monitoring results with flow and transport model
simulations.
Changing geochemical conditions that could cause sorption or
precipitation/co-precipitation mechanisms that might affect mobility of
non -conservative and variable constituents would be evaluated using
multi parameter sonde data.
Groundwater Field Parameters: The following six field parameters
will be monitored to confirm that monitoring well conditions have
stabilized prior to sample collection and to evaluate data quality: water
level, pH, specific conductance, temperature, dissolved oxygen, and
oxidation reduction potential. For remedy performance monitoring,
these parameters will be measured daily by a multi -parameter sondes
installed in each flow path monitoring well and used to evaluate
geochemical conditions from remedy effectiveness.
Major cations and anions would be analyzed to evaluate monitoring data
quality (electrochemical charge balance). These include alkalinity,
bicarbonate alkalinity, aluminum, calcium, iron, magnesium, manganese,
nitrate + nitrite, potassium and sodium. Total organic carbon (TOC), ferrous
iron, and sulfate analyses are also proposed as monitoring parameters.
TOC is recommended to help determine if an organic compound is
contributing to TDS, and ferrous iron and sulfate to monitor potential
dissolution of iron oxides and sulfide precipitates as an indicator of
changing conditions related to corrective action. These parameters are
indicated on Table 6-16 as water quality parameters.
6.8.6 Sampling and Reporting Plan after Termination of
Active Remediation
(CAP Content Section 6.E.e.iii)
Termination of the proposed remedial alternative for Source Area 1 will be
consistent with and implemented in accordance with NCDEQ Subchapter 02L
.0106(m). A flow chart of the decision metrics, request, and review timeline for
termination is outlined on Figure 6-21b (CAP Content Section 6.E.e.iii.1). This
process will provide stakeholders an opportunity to evaluate terminating the
system, as appropriate, in the vicinity of the well or wells where groundwater
restoration completion is being evaluated.
Trend analysis described in Section 6.8.5 would be part of the decision metrics
for determining termination of the active remedy (CAP Content Section
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6.E.e.iii.1.A and B). Groundwater remediation effectiveness monitoring will
transition to the attainment monitoring phase when NCDEQ determines that the
remediation monitoring phase is complete at a particular well or area.
6.8.7 Proposed Interim Activities Prior to Implementation
(CAP Content Section 6.E.f)
In accordance with requirements of G.S. Section 130A-309.211(b)(3),
implementation of the proposed corrective action for Source Area 1 will begin
within 30 days of NCDEQ approval of the CAP Update.
During pilot testing, extracted groundwater will be collected and analyzed for
geochemical parameters consistent with the NPDES permit.
Additional interim activities to be conducted prior to implementation of the
corrective action remedy include:
• Implementation of the EMP within 30 days of CAP approval
Submittal of permit and registration applications to NCDEQ, as
applicable.
6.8.8 Contingency Plan
(CAP Content Section 6.E.g)
The purpose of the contingency plan is to monitor changes in conditions and
operations to effectively reach the remedial action objectives. The contingency
plan addresses operations, groundwater conditions and performance.
The contingency plan will be defined in greater detail as design elements of the
system are finalized. A groundwater monitoring program to measure and track
the effectiveness of the proposed groundwater remediation system is described
in Section 6.8.5. This plan is designed to be adaptive and can be modified as the
groundwater remediation system design is prepared, completed, or evaluated for
termination.
6.8.8.1 Description of Contingency Plan
(CAP Content Section 6.E.g.i)
The contingency plan addresses the following areas and is applicable to
Source Area 1 and Source Area 3:
• Operations (including extraction and infiltration wells, pumping,
piping, electrical, and controls)
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• Groundwater quality
• Groundwater levels
• Groundwater treatment
• Comparison to predicted concentrations and water levels
A health and safety plan and an operations manual will be prepared as part
of the design documents. The health and safety plan will deal with
management of spills and other unplanned releases and the operation
manual will address operational training including backup personnel,
emergency response training, and reporting to appropriate authorities.
6.8.8.2 Decision Metrics for Contingency Plan Areas
(CAP Content Section 6.E.g.ii)
This section outlines decision metrics and possible contingency actions in
support of a resilient groundwater corrective action strategy.
Operations
A computer control telemetry system will be installed with the system to
provide timely information to the Site Operator regarding key operational
features, particularly extraction and infiltration well water levels and flow
rates. The control system will be tied into a remote monitoring station to
alert key personnel as to the nature and urgency of the issue. The system
will be programmed with expected values for measured parameters. Alerts
will be sent when actual values are outside the programmed range. Based
on the alerts, the functional problem will be evaluated and repairs or
replacement of faulty equipment will be completed. The expected duration
of operations will exceed the life expectancy of most of the mechanical
equipment that will comprise the system so ongoing replacement of
equipment will be part of the operations and maintenance program.
Several aspects of the monitoring system would be used to optimize system
operations, including:
• Processes to ensure effective operation of each extraction and clean
water infiltration well is maintained. Maintaining target flow rates
and water levels for each well is important to minimize the potential
for loss of extracted groundwater flow control. Each well would be
monitored continuously by the control system, with all data being
recorded, and an alert sent if the flow rate or water level is outside
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the prescribed range. In addition to automated systems, each element
of the system will be physically inspected and maintained as part of a
routine operations and maintenance program.
• Leak detection systems could detect possible leaks related to
pumping, piping and/or wells, and the respective element of the
system could be shut down and a message will be immediately sent
to the operator and to backup personnel. The potential leak will be
inspected and repaired prior to restarting the system element.
• Continuous monitoring of key parameters would help maintain
proper operation of the system, if pH adjustment or other water
treatment technology is employed. Variances between prescribed
ranges will alert the operator and other key personnel and may result
in automatic system shut down.
• Routine documented inspections of key components of the system
would be done by the operator to track system status and system
performance.
• System maintenance schedules would be established to track system
performance. System elements will be maintained in accordance with
manufacturer's recommendations, which will be contained in a
system O&M Manual. Corrective measures, performed by
appropriately skilled personnel, will be taken if mechanical issues are
identified during routine maintenance monitoring.
Groundwater Quality
The EMP includes a primary network of wells that will provide focused
monitoring in critical areas following corrective action implementation.
After each sampling event, data will be entered into a comprehensive data
base system. Trend analyses will be conducted, spatially and temporally, to
evaluate COI plume changes. If groundwater quality field parameters or
constituent concentrations significantly deviate from predicted responses, a
focused investigation will be conducted to determine if the variation is due
to system performance or other factors. Based on this analysis, possible
responses could include adding or deleting extraction and infiltration wells,
or changing flow rates or target water levels.
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To assess the effectiveness of changes, or to determine if the unexpected
data trends are temporary, increased monitoring frequency or additional
monitoring locations may be conducted.
If subsequent results continue to show non-conformance, a more
comprehensive assessment and corrective action plan for the specific non-
conformance may be completed and implemented.
Groundwater Levels
Water levels in selected EMP monitoring wells will be monitored using
downhole instrumentation until Site conditions have stabilized. Water level
data will be evaluated as part of the ongoing monitoring. Technical
evaluations will include spatial and temporal trend analyses, drawdown
calculations, and flow and transport model refinement to reflect current
conditions, as needed. If results conclude that water levels are not similar to
predicted patterns a focused investigation will be conducted that could
include adjusting system pumping rates, refining the flow and transport
model for extraction and infiltration rates, adding monitoring wells to the
EMP monitoring network for greater resolution, installation of monitoring
wells in key areas, and/or other activities.
If subsequent results from ongoing investigation continue to show non-
conformance, a corrective action response with suggested approaches to
determine possible reasons for the non-conformance would be implemented
until resolution is achieved.
Groundwater Treatment
If extracted groundwater treatment is required prior to discharge through a
permitted outfall, evaluation of that system will be part of the routine
monitoring program.
If a treatment system is not meeting performance standards or if trends
suggest performance is not optimal, an analysis of the trends and an
assessment of the system will be completed and corrective measures
implemented. Changes could be the result of changing influent
characteristics.
Comparison to Predicted Concentrations and Water Levels
Many aspects of the proposed remediation approach are based on modeling
and predicted groundwater conditions. As remedial efforts begin, hydraulic
conditions change, and additional groundwater data are collected, the
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models will be updated. However, as conditions change, especially at the
beginning of the process there maybe deviations from existing data trends
and model predictions. The models will be updated to reflect changing
conditions, as necessary, and changes in predicted results will be analyzed
to determine if the remedial approach needs to be modified to effectively
address the changes.
Given that groundwater infiltration is an element of the system for Source
Area 3, there is a potential that soil might become saturated near the ground
surface, with the potential to create surface discharges. If this occurs,
reducing infiltration rates by adjusting water -level controllers at wells near
the area or increasing the extraction system would be used to control
surficial saturation.
6.9 SA1 Summary and Conclusions
This CAP Update meets the corrective action requirements for Source Area 1 under G.S.
and Subchapter 02L .0106 and to addresses Subchapter 02L .0106(j). This CAP Update
proposes a remedy for COIs in groundwater associated with the Source Area 1
(including the EAB, industrial landfill, and LCID landfill) that are beyond the
compliance boundary to the north and northeast of the EAB and to control migration of
COI -affected groundwater. This CAP Update provides:
• A groundwater remediation approach that can be implemented under either
closure scenario (closure -in -place or closure -by -excavation).
• A screening and ranking process of multiple potential groundwater corrective
action alternatives that would address areas requiring corrective action.
• A selection and description of the favored corrective action groundwater
remedy: Alternative 2, Groundwater Extraction.
• Specific plans, including engineering design details, for restoring groundwater
quality.
• A schedule for the implementation and operation of the corrective action
strategy.
• A monitoring plan for evaluating the performance and effectiveness of corrective
action groundwater remedy, and its effect on the restoration of groundwater
quality.
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Planned activities prior to full-scale implementation, where either submittal of the EMP,
or the pilot testing work plan and permit applications (as applicable) will be submitted
to NCDEQ within 30 days of CAP approval to fulfill G.S. Section 130A-309.211(b)(3).
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SOURCE AREA 2 (SA2) — WEST ASH BASIN
6.10 SA2 Extent of Constituent Distribution
This section provides an in-depth review of constituent characteristics associated with
the WAB and the mobility, distribution and extent of constituent migration within, at,
and beyond the point of compliance.
6.10.1 Source Material Within the Waste Boundary
(CAP Content Section 6.A.a)
For purpose of evaluation and reporting, the waste boundary of Source Area 2 is
considered the outermost boundary of the WAB (Figure 6-1). An overview of
the material within the WAB is presented in the following subsections.
6.10.1.1 Description of Waste Material and History of
Placement
(CAP Content Section 6.A.a.i)
The WAB consists of a single unit impounded by the main earthen dam
located on the north end of the ash basin (Figure 1-3). The main dam is an
earth fill embankment with a central low permeability earth core
constructed between two cofferdams over a prepared rock foundation with
a central core keyway excavated 10 feet into rock. The main dam is
approximately 1,360 feet long with a maximum height of approximately 70
feet. The top of the dam is at an elevation of 470 feet, and the crest is
approximately 20 feet wide.
A row of engineered toe drains are located at the base of the main dam
which discharges to the heated water discharge pond. In 1987, the main
dam was raised 13 feet and a series of dikes (Dikes #1 through #4) were
installed within the pre 1987 ash basin to increase the storage capacity. The
western side of the pre-1987 ash basin circulation was modified to increase
settling time. The modification resulted in the current configuration of the
western discharge canal. The rock filter dike (Dike #1), constructed of rock
fill (from the construction of the western discharge canal) with a sand filter
blanket, was installed near the southern end of the WAB (area within the
WAB often referred to as the southern extension impoundment) to filter
solids prior to wastewater entering the western discharge canal. The
modifications to the WAB were authorized by NCDEQ in a Permit to
Construct issued March 26, 1986 completed in 1987. In 2016, alterations
were made to the discharge structures on the filter dike with the origina148-
inch diameter riser structures abandoned (grouted) in place and installation
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of a new primary discharge structure and new emergency spillway
structures. The area contained within the WAB waste boundary is
approximately 183 acres.
The WAB accepted waste streams in accordance with the Roxboro NPDES
permit. The WAB waste streams historically included bottom ash and fly
ash with ash transport water used to convey ash via sluicing. Additional
waste streams included but were not limited to EAB effluent, coal pile
runoff, stormwater runoff, cooling tower blowdown, and low volume
wastewater (boiler blowdown, oily waste treatment, waste backwash from
treatment processes, plant area wash water, equipment heat exchanger
water, and treated domestic waste). With the construction of the industrial
landfill at the EAB in the late 1980's to accommodate transition to a dry ash
system, sluicing of DFA to the WAB ceased with the exception of brief
periods of system shut down or plant start up. Wet sluicing of bottom ash
continued to the WAB until final system upgrades were completed in
December 2018. All Roxboro CCR has been handled dry since December
2018 with no sluicing to the WAB since that time. During 2019,
modifications were completed to re -direct plant stormwater, wastewater
and process flows. All wastewater flows to the WAB ceased on June 30,
2019 except interbasin discharge from the EAB. Stormwater outflow from
part of the EAB currently discharges into the WAB through existing culvert
pipes located under Dunnaway Road.
Flue gas desulfurization technology was installed at the Plant in 2008 to
reduce SO2 emissions for all the steam units. Three FGD ponds were
constructed entirely within the WAB waste boundary footprint to support
treatment of the scrubber wastewater. The three FGD ponds are located on
the western side of the WAB and are formed by dams that share abutment
features. The three ponds are the West FGD Settling Pond, East FGD
Settling Pond, and FGD Forward Flush Pond. The two FGD settling ponds
receive FGD blowdown. The FGD Forward Flush Pond receives inflow
from the back -flush of the facility bioreactor.
The FGD West Settling Pond and portions of the FGD Forward Flush Pond
containment dikes are constructed of compacted dry fly ash material, with
portions of the FGD Flush Pond dikes constructed of compacted soil. The
FGD East Settling Pond containment dike was constructed on the east side
of the FGD West Settling Pond and the north side of the FGD Flush Pond
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dikes. The north and east containment dikes of the FGD East Settling Pond
were constructed of compacted soil. The outer perimeter of the FGD Pond
dikes have topsoil and grass vegetation for erosion protection on the
exterior slopes. A liner system on the interior slopes and bottom of each
pond area consists of an 18-inch GCL and a surface liner of 60-mil-thick,
linear low -density polyethylene with a heavy nonwoven geotextile
membrane. The FGD wastewater is treated in the adjacent bioreactor with
discharge to the NPDES permitted heated water discharge pond via the
western discharge canal.
6.10.1.2 Specific Waste Characteristics of Source Material
(CAP Content Section 6.A.a.ii)
Source Area 2 characterization was performed through the completion of
soil borings, installation of monitoring wells, and collection and analysis of
associated solid matrix and aqueous samples as discussed in Section 6.1.1.2.
Three borings (AB-01 through AB-03) were advanced within the WAB
waste boundary to obtain ash samples for chemical analyses (Figure 1-3).
Ash was encountered in borings AB-01, AB-02, and AB-03 to depth ranging
from 7 feet bgs (AB-03) to 79 feet bgs (AB-01). Ash was not observed
outside the ash basin waste boundary in any other borings completed for
this assessment.
The waste material in the WAB is derived from the same sources as the
EAB, and like the EAB, coal ash within the WAB is composed of
interbedded fine-grained fly ash to coarse -grained bottom ash materials.
Ash was generally described in field observations as gray to dark gray, non -
plastic, loose to medium density, dry to wet, fine- to course -grained sandy
silt texture. Physical properties analyses such as grain size and moisture
content were performed on seven ash samples from the ash basin and
measured using ASTM methods. Although no samples were collected for
specific gravity, the moisture content of the ash samples ranges from 13.2
(AB-03 - 3' to 5' bgs) percent to 45.3 percent (AB-01- 40' to 41' bgs).
6.10.1.3 Volume of Physical Horizontal and Vertical Extent
of Source Material
(CAP Content Section 6.A.a.iii)
Based on topographic and bathymetric surveys, the WAB impoundment
area, which includes the FGD ponds, is estimated to contain approximately
10,811,166 cy (12,973,400 tons) of ash (Wood, 2019) as shown in Figure 6-1
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(Source Area 2). Volume and physical vertical extent of ash material within
the basin as cross-section transect (C-C') from southwest to northeast, is
presented in Figure 6-22. Volume and physical vertical extent of ash
material within the basin as cross-section (D-D') along the centerline of the
WAB from south to north, is presented in Figure 6-23.
6.10.1.4 Volume and Physical Horizontal and Vertical
Extent and Anticipated Saturated Source Material
(CAP Content Section 6.A.a.iv)
Volume and physical horizontal and vertical extent of saturated ash
material under pre -decanting conditions, within the basin in plan -view is
presented in Figure 6-24. The ash thickness measured was 79 feet where the
ash is sufficiently stable for drill rig access. Ash is thickest in areas that
coincide with the former stream valley in the central portion of the basin.
Thinner areas of ash extend out to the boundaries (fingers) of the basin. A
lesser amount of ash is present in other areas of the basin currently covered
by ponded water (Figure 6-24). Ash within the basin, prior to passive
decanting (Section 1.5.3), was saturated at depths of 3 to 6 feet below grade
surface at monitoring wells locations, yielding approximately 76 feet of
saturated ash in the thickest ash location monitored.
Using modeled potentiometric levels of the saturated ash surface compared
to pre -ash basin historical topographic contours, the volume of saturated
ash within the WAB and extension impoundment under pre -decanting
conditions was approximately 8,288,843 cy (Wood, 2019). The saturated
thickness of ash will decrease as the decanting and closure process
progresses.
6.10.1.5 Saturated Ash and Groundwater
(CAP Content Section 6.A.a.v)
The thickness of saturated ash remaining in place following the closure -in -
place scenario will have limited to no adverse effect on future groundwater
quality. Layered ash within the WAB has resulted in relatively low vertical
hydraulic conductivity, further reducing the potential for downward flow
of pore water into underlying residual material. The CSM indicates that the
flow -through ash basin system should result in low to non -detectable COI
concentrations in groundwater underlying saturated ash within the basin
except in the vicinity of the dam and dikes where downward vertical
hydraulic gradients are observed. Boron is the CCR constituent most
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indicative of groundwater migration from the source area with a
discernable COI plume pattern. Using boron data, the generalized flow -
through system is consistent with Site -specific data as summarized in the
Table 6-17.
In summary, three of the monitoring wells (ABMW-01BR, ABMW-02BR,
and ABMW-03BRL) located within the WAB exhibit low (less than 622 µg/L
and below the 02L groundwater standard) to non -detectable boron
concentrations consistent with the flow -through system CSM. The
remaining monitoring well (ABMW-03BR), which is located in close
proximity to WAB main dam, exhibits boron concentrations ranging from
2,770 µg/L to 4,650 µg/L. The data from this well location is consistent with
the CSM for ash basin systems with downward flow in close proximity to
the dams. The data suggests there is no correlation between the thickness of
saturated ash and the underlying groundwater quality. See Section 6.1.1.5
regarding a discussion of the linear regression analyses to evaluate the
relationships between saturated ash thickness and concentrations of boron
in ash pore water and underlying groundwater.
6.10.1.6 Chemistry Within Waste Boundary
(CAP Content Section 6.A.a.vi)
Analytical sampling results associated with material from within the ash
basin waste boundary are included in the following appendix tables or
appendices:
• Ash solid phase: Appendix C, Table 4 (CAP Content Section
6.A.a.vi.1.1)
• Ash and soil SPLP: Appendix C, Table 6 (CAP Content Section
6.A.a.vi.1.2)
• Ash Leaching Environmental Assessment Framework: Appendix H,
Attachment C (CAP Content Section 6.A.a.vi.1.3)
• Soil: Appendix C, Table 4 (CAP Content Section 6.A.a.vi 1.4)
• Ash pore water: Appendix C, Table 1 (CAP Content Section
6.A.a.vi.1.6)
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Ash Solid Phase and Synthetic Precipitation Leaching
Potential
(CAP Content Section 6.A.a.vi.1.1 and 6.A.a.vi.1.2)
Ash samples collected inside the WAB waste boundary were analyzed for
total extractable inorganics using EPA Methods 6010/6020. Concentrations
of arsenic, boron, chromium (total), cobalt, iron, manganese, molybdenum,
selenium and vanadium were greater than concentrations of the same
constituents in soil background samples. The concentrations of these
constituents in ash samples also were greater than background
concentrations and PSRG POGs with the exception of vanadium (Appendix
C, Table 4).
In addition, three ash samples collected from borings completed within the
WAB were analyzed for leachable inorganics using SPLP and Method 1312
(Appendix C, Table 6). SPLP analytical results are compared with the 02L
comparative values to evaluate potential source contribution; the data do
not represent groundwater conditions. SPLP results indicated that
concentrations of antimony, arsenic, boron, cadmium, cobalt, manganese,
nickel, nitrate, selenium, thallium, vanadium and zine were greater than the
02L or IMAC comparative value. Tables of analytical results, subdivided for
ash solid phase and ash SPLP, can be found in Appendix C, Table 6.
Ash Leaching Environmental Assessment Framework
(CAP Content Section 6.A.a.vi.1.3)
Ash samples were analyzed for extractable metals analysis, including
HFO/HAO, using the CBD method. Leaching studies of consolidated ash
samples from the WAB were conducted using two LEAF tests, EPA
methods 1313 and 1316 (USEPA, 2012a, b). The data are presented and
discussed in the Geochemical Modeling Report in Appendix H, Attachment
C. Further discussion that includes the WAB is provided in Section 6.1.1.6.
Soil Beneath Ash
(CAP Content Section 6.A.a.vi 1.4)
All soil samples collected from within the WAB waste boundary from
beneath the ash basin were saturated, including those obtained from
borings associated with AB-MW-01BR, AB-02, and AB-03 (Figure 1-3). All
saturated soil samples with values reported greater than the PSRG POGs or
background values are vertically delineated by groundwater constituent
concentrations in the corresponding flow layer of the soil sample depth.
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No unsaturated soil conditions were observed in samples collected beneath
the ash basin. The range of constituent concentrations in soils within the
WAB waste boundary with a comparison to soil background values and
PSRG POGs, whichever is greater, is provided in Appendix C, Table 4. For
constituents lacking an established target concentration for soil remediation
(i.e. sulfate), the PSRG POG values were calculated and provided in Section
6.1.2. Soil SPLP constituent concentrations within the waste boundary along
with a comparison to 02L/IMAC is provided in Appendix C, Table 6 (CAP
Content Section 6.A.a.vi.1.4). Further discussion regarding the SPLP analysis
of saturated soil is provided in Section 6.1.1.6.
Ash Pore Water
(CAP Content Section 6.A.a.vi.1.6 and 6.A.a.vi.3)
The WAB is a NPDES-permitted wastewater treatment unit. Water within
the ash basin is not groundwater; therefore, isoconcentration maps were not
prepared for ash pore water and comparison to 02L/IMAC/background
values is not appropriate. All ash pore water sample locations are shown
on Figure 1-3 and analytical results are provided in Appendix C, Table 1.
Figure 6-22 represents ash pore water distribution in cross section (C-C')
from southwest to northeast and Figure 6-23 represents ash pore water
distribution in cross-section (D-U) from south to north. Figure 6-23
represents the greatest physical horizontal and vertical extent of volume of
source material within the ash basin (ABMW-1/BR and ABMW-2/BR). For
further discussion of geochemical trends within the ash pore water, see
Appendix H, Section 2.
Two groundwater monitoring wells located in areas that could be sensitive
to changing Site conditions from ash basin closure activities, including
decanting (passive and active), were selected for monitoring geochemical
parameters and water elevation. Geochemical parameters (pH, oxidation
reduction potential (ORP), and specific conductivity) are monitored using
multi -parameter (or geochemical) sondes. The multi -parameter sondes are
equipped with pressure transducers to monitor water elevations. Locations
monitored with multi -parameter sondes are depicted on Figure 6-27 and
include:
• CCR-208S: shallow zone monitoring well located between the
western discharge canal and the FGD ponds
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CW-4: transition zone monitoring well located along the western
discharge canal below the confluence with the WAB extension
impoundment and the filter dike.
In addition, multiple monitoring wells including interior ash basin wells
(ABMW-1/BR/OWAU 30'/OWAM 30'; ABMW-2/BR; and ABMW-3/BR) and
perimeter ash basin wells (MW-2, CCR-206S, CCR-208BR, and CCR217BR)
are equipped with pressure transducers to monitoring water elevations
during decanting. Passive decanting from the WAB began in December
2018 with the cessation of ash sluicing to the ash basin. Hydrographs and
geochemical water quality parameter time series plots for each location
from April 2019 through September 2019 are included on Figure 6-30a and
6-30b. Observations of water elevation and multi -parameter records from
monitored locations include:
• By September 2019, the water level in the ash basin pond decreased
by up to 14 feet based on pond water measurements provided by the
Plant.
• The ash pore water monitoring locations within the ash basin waste
boundary shows a response to passive decanting by reduced
groundwater elevation levels of up to 2-3 feet (Figure 6-30a).
• Similar responses are noted in the shallow zone wells along the
western discharge canal and downgradient of the ash basin dam
(MW-2) (Figure 6-30b).
• The geochemical parameter pH does not show significant shifts or
variability in records since ash basin passive decanting commenced;
however, a decreasing trend in ORP is observed in CCR-208S. An
initial increasing trend was observed in CW-4; however, the trend as
stabilized since June 2019 (Figure 6-27). This suggests geochemical
conditions have remained relatively stable under changing basin
conditions; however, additional data will need to be collected for
trend analysis.
In general, water level within the ash basin show responses to passive
decanting of the basin. Groundwater pH and ORP, monitored adjacent to
the WAB, are relatively stable; however, a decreasing trend is noticed with
ORP measurement in a few wells. With decreasing ORP trends, constituent
mobility will begin to stabilize and attenuate through the formation of
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sulfide minerals. Additional data will need to be collected during the
decanting process for trend analysis.
Ash Pore Water Piper Diagrams
(CAP Content Section 6.A.a.vi.2)
As discussed in Section 6.1.1.6, Piper diagrams can be used to differentiate
water sources in hydrogeology (Domenico & Schwartz, 1998). Data used for
the piper diagrams include ash pore water data between January 2018 and
April 2019 with a charge balance between -10 and 10.
Ash pore water results tend to plot with higher proportions of sulfate,
chloride, calcium, and magnesium, which is generally characteristic of ash
pore water (EPRI, 2006). The area where ash pore water tends to plot on the
piper diagram is identified as "affected" on Figure 6-28. However, ABMW-
2 tends to plot in the more neutral zone of the piper diagram identified as
"generally unaffected" similar to Site background monitoring wells.
6.10.1.7 Other Potential Source Material
(CAP Content Section 6.A.a.vii)
No other potential source material is related to the WAB.
6.10.1.8 Interim Response Actions
(CAP Content Section 6.A.a.viii.1-2)
Interim response actions conducted to date or planned are summarized in
Table 6-18. Details describing each action are presented below.
Ash Basin Decanting
Passive decanting through the cessation of sluicing at the WAB began in
December 2018. Active decanting of the WAB will commence upon
approval of the revised NPDES permit currently under review by NCDEQ
or approval from NCDEQ. The SOC requires completion of decanting by
June 30, 2020.
Sixteen groundwater monitoring wells positioned within and at perimeter
locations of the WAB were selected for monitoring water elevations using
pressure transducers to record changing site conditions from ash basin
decanting (Figure 6-29). The monitoring wells include interior ash basin
wells: ABMW-1/BR/OWAU 30'/OWAM 30'; ABMW-2/BR; and ABMW-3/BR
and perimeter ash basin wells: MW-2, CCR-206S, CCR-208BR, and
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CCR-217BR. Observations from the groundwater decanting network
hydrographs are discussed in Section 6.10.1.6.
Source Area Stabilization
In a correspondence dated August 22, 2016, NCDEQ provided a notice of
deficiencies related to the Roxboro East Ash Pond (PERSO-033) and the
Roxboro West Ash Pond South Rock Filter (PERSO-039). For the WAB
South Rock Filter, the deficiency included spillway repair and the need for
installation of a new spillway to assure the pond areas can effectively
contain and safely pass the inflow design flood storm event. In response,
Duke Energy undertook activities to correct the deficiencies; in general
accordance with design drawings, pursuant to the Dam Safety Certificate of
Approval, dated June 3, 2016. The activities included:
• Raising the crest level of select dam crest areas
• Stormwater management improvements at the pipe bridge
• Construction of a new primary discharge structure and new
emergency spillway structures, and
• In -place abandonment of the existing riser/outlet structures within
the West Ash Pond.
In a letter dated February 2, 2017, the dam repairs were approved by
NCDEQ (Appendix A).
6.10.2 Extent of Constituent Migration Beyond the Compliance
Boundary
(CAP Content Section 6.A.b)
There are no constituent concentrations in soil, groundwater, or surface water
associated with the WAB greater than applicable regulatory criteria at or beyond
the compliance boundary based on monitoring results from January 2018 to
April 2019. The compliance boundary for groundwater quality at the WAB is
defined in accordance with Title Subchapter 02L .0107(a) as being established at
either 500 feet from the waste boundary or at the property boundary, whichever
is closer to the waste.
Analytical sampling results associated with the WAB for each media are
included in the following tables and appendix tables:
Soil: Appendix C, Table 4 and Table 6-19 (CAP Content Section 6.A.b.ii.1)
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• Groundwater: Appendix C, Table 1 and Table 6-20 (CAP Content Section
6.A.b.ii.2)
• Seeps: Appendix C, Table 3 (CAP Content Section 6.A.b.ii.3)
• Surface water: Appendix C, Table 2 (CAP Content Section 6.A.b.ii.4)
• Sediment: Appendix C, Table 5 (CAP Content Section 6.A.b.ii.5)
Soil Constituent Extent
(CAP Content Section 6.A.b.ii.1)
Data indicate unsaturated soil COI concentrations at or beyond the compliance
boundary are generally consistent with background concentrations or are less
than regulatory screening values (Table 6-19). Horizontal and vertical extent of
COI concentrations in soil is discussed further in Section 6.10.4.
Groundwater Constituent Extent
Groundwater concentrations greater than 02L/IMAC/applicable background
concentration values occur within the WAB compliance boundary.
As discussed in Section 3.0, elevated COIs present in groundwater monitoring
well MW-51), located near the WAB compliance boundary, downgradient of the
WAB, are a result of residual ash present in the sluice line corridor area likely
due to maintenance of the historic sluice lines. Decommissioning of the now
abandoned sluice line piping is currently in progress. Upon completion of
piping and support removal, the area north of the WAB, near MW-5D, will be
remediated such that visible CCR is removed.
Section 6.1.3 includes a detailed matrix evaluation and Section 6.10.4 provides
isoconcentration maps and cross sections depicting groundwater flow and
constituent distribution in groundwater within the compliance boundary (CAP
Content Section 6.A.b.i).
Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Seeps at Roxboro are subject to the monitoring and evaluation requirements
contained in the SOC. The SOC states that the effects from non -constructed seeps
should be monitored. Attachment A to the SOC identifies S-08 as a non -
constructed seep associated with the WAB. S-08 is located approximately 30 feet
west of chimney toe drain S-07 and discharges to the NPDES-permitted heated
water discharge pond.
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Dispositioned seeps associated with the WAB include the chimney toe drains S-
01 through S-07. Seep discharge from the chimney toe drains flow to the
NPDES-permitted heated water discharge pond.
As stated in the SOC, decanting of the ash basin is expected to substantially
reduce or eliminate the seeps. Seeps currently governed by the SOC that remain
and are not dispositioned 90 days after completion of decanting would be
characterized for determination of corrective action applicability. Where
applicable, and accounting for seep jurisdictional status, corrective action
planning at that time would occur.
Surface Water Constituent Extent
(CAP Content Section 6.A.b.ii.4)
Water in the heated water discharge pond, which also receives surface water
from toe drains of the WAB main dam, the western discharge canal and the
extension impoundment, is subject to NPDES discharge permit requirements via
Outfall #003 and is not considered waters of the state. As a result, no surface
water samples were collected from the heated water discharge pond, the western
discharge canal and the extension impoundment for an evaluation of
groundwater discharge to surface water and an evaluation of compliance with
15A NCAC 02B .0200.
Sediment Constituent Extent
(CAP Content Section 6.A.b.ii.5)
As stated above, water in the heated water discharge pond, which also receives
surface water from toe drains of the WAB main dam, the western discharge canal
and the extension impoundment, is subject to NPDES discharge permit
requirements via Outfall #003 and is not considered Waters of the State. As a
result, no sediments samples were collected from the heated water discharge
pond or the western discharge canal for evaluation of groundwater discharge to
surface water and an evaluation of compliance with 15A NCAC 02B .0200.
6.10.2.1 Piper Diagrams
(CAP Content Section 6.A.b.iii)
Piper diagrams can be used to differentiate water sources in hydrogeology
by assessing the relative abundance of major cations (i.e., calcium,
magnesium, potassium, and sodium) and major anions (i.e., chloride,
sulfate, bicarbonate, and carbonate) in water.
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Groundwater Piper Diagrams
Piper diagrams (Figure 6-28), and a discussion of the evaluation, for
groundwater monitoring data from shallow, deep and bedrock background
locations and downgradient of the ash basin locations is included in Section
6.1.2.1.
Bedrock groundwater monitoring wells CCR-204BR, CCR-205BR, CCR-
206BR, CCR-207BR, and CCR-208BR all plot in the "affected" zone of the
piper diagram. These bedrock monitoring locations are the western edge of
the ash basin adjacent to the western discharge canal.
The distribution of results on the piper diagrams in Figure 6-28 indicate no
conclusion can be made regarding effects on groundwater from the ash
basin based on relative abundance of major cations and anions.
Seep and Surface Water Piper Diagrams
Dispositioned seeps associated with the WAB include the chimney toe
drains S-01 through S-07. Seep discharge from the chimney toe drains flow
to the NPDES-permitted heated water discharge pond. S-08 is located
approximately 30 feet west of chimney toe drain 5-07 and discharges to the
NPDES-permitted heated water discharge pond. No data was used from
the WAB seeps since the seep analytical data reflects discharge directly from
the WAB toe drains. Water in the heated water discharge pond, which also
receives surface water from toe drains of the WAB main dam, the western
discharge canal and the extension impoundment, is subject to NPDES
discharge permit requirements via Outfall #003 and is not considered
waters of the state. Additional discussion regarding surface water related to
the Hyco Reservoir is provided in Section 6.1.2.1.
6.10.3 Constituents of Interest (COIs)
(CAP Content Section 6.A.c)
This CAP Update evaluates the extent of COIs in groundwater associated with
the WAB. The list of ash -basin related constituents developed for the Roxboro
ash basins and development of COIs associated with the ash basins through the
constituent management process is provided in Section 6.1.3.
Soil
(CAP Content Section 6.A.c.i.1)
Data indicate unsaturated soil COI concentrations are generally consistent with
background concentrations or are less than regulatory screening values
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(Table 6-19.) In the few instances where unsaturated soil COI concentrations are
greater than PSRG POG standards or background values, COI concentrations are
within range of background dataset concentrations or there are no mechanisms
by which the COI could have been transported from the ash basin to the
unsaturated soils. Horizontal and vertical extent of COI concentrations in soil,
and reasons why no necessary corrective action for soils is identified related to
the WAB is discussed further in Section 6.10.4.
Groundwater
(CAP Content Section 6.A.c.i.2)
A measures of central tendency analysis of the COI data (January 2018 to April
2019) was conducted and means were calculated to support the analysis of
groundwater conditions to provide a basis for defining the extent of the COI
migration beyond the compliance boundary of the WAB. Further discussion of
the measure of central tendency analysis is provided in Section 6.1.3.
Table 6-20 presents the mean analysis results of the COI data using groundwater
monitoring sampling results from January 2018 to April 2019. Where means
could not be calculated, the most recent valid sample was evaluated to determine
whether the sample result is an appropriate representation of the historical
dataset.
Using the constituent management process detailed in Section 6.1.3, data from
Table 6-21 are used in evaluating COI plume geometry in the vicinity of the
WAB. Of 14 inorganic groundwater COIs identified in the CSA (CSA Update,
2017), boron is remaining COI that exhibits a plume like distribution within the
WAB compliance boundary.
The mean concentrations of boron, sulfate and TDS greater than their 02L
standards in monitoring wells CW-5 and MW-5D/BR, which are positioned north
of the WAB compliance boundary, are associated with the sluice line corridor
and not groundwater migration from the WAB. In addition, a decreasing trend
is observed with boron, sulfate and TDS over the last four sampling events since
April 2018. CCR material associated with the sluice line corridor will be
remediated separately outside the scope of this CAP Update.
6.10.4 Horizontal and Vertical Extent of COIs
(CAP Content Section 6.A.d)
The maximum extent of affected groundwater migration from the ash basin is
north of the WAB dam toward the NPDES-permitted heated water discharge
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pond and west of the WAB dikes toward the western discharge canal. The
plume geometry is largely shaped by hydraulic conditions associated with the
basin, basin dam, free water within the basin, and the western discharge canal as
detailed in Section 5.0.
Boron, a conservative (non -reactive) constituent, continues to be a key indicator
of ash basin -affected groundwater migration and plume characteristics
associated with the ash basin. The maximum extent of the 02L boron plume (700
µg/L) represents the maximum extent of ash basin -affected groundwater
migration.
6.10.4.1 COIs in Unsaturated Soil
CAP Content Section 6.A.d.i)
Based on the unsaturated soil evaulation, there are no constituents in soil
associated with the WAB that require corrective action at Roxboro.
Although greater than background values or PSRG POG, unsaturated soil
samples are within the range of concentrations detected in soil samples
from Site -specific or Piedmont background locations as shown in Table 4-2.
Unsaturated soil samples at or beyond the waste boundary were collected
from soil borings and during well installation activities (Figure 6-32). In
response to the CSA Update (SynTerra, 2017), NCDEQ requested additional
evaluation of unsaturated soil surrounding, especially along the margins, of
the ash basin to determine the degree of possible impact from historical
CCR management at Roxboro. Additional unsaturated soil samples along
the perimeter of the WAB waste boundary have been collected at various
field efforts between June 2018 and June 2019. An evaluation of the
potential nature and extent of COIs in unsaturated soil at or beyond the
waste boundary was conducted by comparing unsaturated soil
concentrations with background values or PSRG POG standards, whichever
is greater (Table 6-19) (CAP Content Section 6.A.d.i).
Constituents detected at concentrations greater than either the background
value or the PSRG POG standard, whichever is greater, in unsaturated soil
samples (depth), beyond the waste boundary include:
Chromium: PSB-6 (1.5-2), PSB-7 (1.5-2), PSB-8 (1.5-2), PSB-9 (1.5-2),
PSB-13 (1.5-2), PSB-16 (1.5-2), PSB-22 (1.5-2), PSB-23 (1.5-2), PSB-29
(1.5-2), PSB-32 (1.5-2), MW-4 (23-25), and MW-15 (0-2)
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• Cobalt: PSB-6 (1.5-2), PSB-7 (1.5-2), PSB-8 (1.5-2), PSB-9 (1.5-2), PSB-
13 (1.5-2), PSB-22 (1.5-2), PSB-23 (1.5-2), PSB-25 (1.5-2), PSB-32 (1.5-2),
and SB-31 (0.5-1)
• Iron: PSB-7 (1.5-2), PSB-8 (1.5-2), PSB-9 (1.5-2), PSB-13 (1.5-2), PSB-22
(1.5-2), PSB-23 (1.5-2), PSB-25(1.5-2), PSB-27 (1.5-2), PSB-29 (1.5-2),
PSB-30 (1.5-2), PSB-31 (1.5-2), PSB-32 (1.5-2), PSB-33 (1.5-2), PSB-34
(1.5-2), MW-208BRL (4-5), MW-7 (0-2), MW-10BR (0-2), and MW-15
(0-2).
• Manganese: PSB-6 (1.5-2), PSB-7 (1.5-2), PSB-8 (1.5-2), PSB-9 (1.5-2),
PSB-13 (1.5-2), PSB-15 (0-2), PSB-22 (1.5-2), PSB-23 (1.5-2), PSB-25
(1.5-2), PSB-32 (1.5-2), SB-31 (0-2), and MW-6BR (0-2).
• Selenium: PSB-21 (1.5-2)
Unsaturated soil constituent concentrations that are greater than either
background values or the PSRG POG standard, for the following reasons:
Concentrations of chromium, cobalt, iron and manganese greater
than the PSRG POG and background were reported at several
locations collected along the WAB waste boundary. Locations were
field located approximately five to 10 feet outside the visible extent of
ash or high water marked observed at the time of sample collection.
Unsaturated soil samples were collected from 1.5 to 2 feet bgs. The
Roxboro background data set does not consider near surface samples
less than two feet bgs, where similar concentrations have been
reported [e.g., MW-15 (0-2) and SB-31 (0.5-1)]. Although greater than
background values or PSRG POG, chromium detections are generally
within the range of concentrations detected in soil samples from
Piedmont Sites Table 4-2. No necessary corrective action for soils is
identified at the WAB because samples collected near the soil/ash
interface along the ash basin waste boundary indicated exceedances
marginally above Site -specific and within the range of Piedmont
background.
Concentrations of chromium, cobalt, iron, and manganese greater
than the PSRG POG and background were reported upgradient from
the WAB within the ash basin compliance boundary or outside the
ash basin compliance boundary (Table 6-19) where there are no
mechanism by which the COI could have been transported from the
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ash basin to the unsaturated soils. Futhermore, locations are
vertically delineated by deeper soil samples (Table 6-19) or
concentrations within grounter reported less than comparative
crieria (Appendix C, Table 4).
MW-4BR (23-25) and background locations MW-15 (0-2) and SB-31
(0.5-1), where there are no mechanism by which the COI could have
been transported from the ash basin to the unsaturated soils.
Futhermore, locations are vertically delineated by deeper soil
samples (Table 6-19) or concentrations within grounter reported less
than comparative crieria (Appendix C, Table 4).
6.10.4.2 Horizontal and Vertical Extent of Groundwater in
Need of Restoration
(CAP Content Section 6.A.d.ii)
Based on groundwater sampling data from January 2018 to April 2019,
there are no COI concentrations greater than 02L standards associated with
constituent migration from the ash basin at or beyond the compliance
boundary, groundwater corrective action associated with the ash basin is
not required. The most recent boron concentrations through April 2019 and
the historical maximum boron concentration for wells near and beyond the
compliance are presented in Appendix C, Table 1. This section will focus on
the horizontal and vertical extent of boron, the primary COI migration
indicator parameter for shallow, transition zone, and bedrock groundwater
for CAP evaluation.
The horizontal extent of affected groundwater migration in each flow layer
is depicted on the boron plume maps (Figures 6-31a and 6-31b). The 02L
boron plume and background boron plume represent a maximum extent of
ash basin -affected groundwater migration in each flow layer. The 02L boron
plume and background boron plume depicted on Figure 6-31 and Figure 6-
31b were generated from the flow and transport model and informed by
boron mean concentration data. The model predictions are conservative and
may over -predict the extent of boron distribution in groundwater. The
vertical extent of the boron -affected groundwater migration is shown on
generalized cross-section C-C' and D-D' (Figures 6-25 and 6-26). As
indicated on Figure 6-25, Figure 6-26, Figure 6-31a, and Figure 6-31b, the
maximum extent of ash basin -affected groundwater occurs northwest of the
ash basin but does not extend beyond the compliance boundary.
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Boron plume maps and cross -sections support the following observations
regarding the extent of affected groundwater:
• Mean concentrations of boron from ash pore water monitoring wells
ABMW-1 and ABMW-2 are greater than the 02L standard (Table 6-
20).
Mean concentrations of boron in shallow and transition groundwater
monitoring wells (CCR-202D, CCR-203D, CCR-206S, CCR-207S,
CCR-208S, CCR-209S, CCR-210S, CCR-211S, and MW-2) at the
northwest portion of the WAB are greater than the 02L standard
(Table 6-20).
• Mean concentrations of boron in bedrock groundwater monitoring
wells (ABMW-1BR, ABMW-2BR, ABMW-3BR) within the WAB
boundary vary in concentration based on proximity to the main dam
and dikes. ABMW-3BR, adjacent and downstream of the WAB main
dam, mean concentrations are greater than the 02L standard. Further
south, mean concentrations of boron within ABMW-1BR are greater
than background but less than the 02L standard. Furthest south,
mean concentration of boron within ABMW-2BR is less than
background (non -detect), supporting the flow -through with limited
downward migration CSM discussed in Section 5.0 (Table 6-20).
Boron concentrations at the ABMW-3 well cluster are vertically
delineated by lower bedrock well ABMW-3BRL, where mean boron
concentrations are less than background (non -detect).
• Mean concentrations of boron in bedrock groundwater monitoring
wells near or beyond the ash basin waste boundary (CCR-202BR,
CCR-203BR, CCR-204BR, CCR-205BR, CCR-206BR, CCR-207BR,
CCR-208BR, CCR-209BR, CCR-210BR, CCR-211BR, MW-205BRL,
MW-205BRLL, MW-205BRLLL, MW-208BRLL, MW-208BRLLL) at
the northwest portion of the WAB are greater than the 02L standard
(Table 6-25).
Wells located in areas of downward (positive) vertical hydraulic
gradients are due to the effect of the ash basin ponded water
upgradient of the WAB main dam and western discharge canal dikes
as discussed in the CSM (Section 5.0).
• Maximum boron concentrations in groundwater are within wells at
the northwest portion of the WAB located on the east bank of the
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western discharge canal. To the west of the western discharge canal,
mean concentrations of boron with bedrock groundwater monitoring
wells (MW-8BR, MW-9BR, MW-12BR, MW-31BR, MW-32BR, and
MW-33BR) are less than background, which supports that the
groundwater flow system associated with the WAB will remain
constrained within the groundwater discharge zones discussed in
Section 5.0 (Table 6-20).
• The maximum extent of affected groundwater migration from the
ash basin is north of the WAB dam toward the NPDES-permitted
heated water discharge pond and west of the WAB dikes toward the
western discharge canal. The plume geometry is largely shaped by
hydraulic conditions associated with the basin, basin dam, free water
within the basin, and the western discharge canal as detailed in
Section 5.0.
The shallow/transition zone and bedrock flow zone boron plumes are
within the compliance boundary and have relatively similar
geometries (Figures 6-31a and 6-31b). This supports the
interpretation that these two zones are hydraulically connected.
• The mean concentration of boron at the compliance boundary (MW-
31BR, MW-32BR, MW-33BR, MW-8BR, MW-9BR, CW-2, CW-2D) are
less than background and the 02L standard (Table 6-20).
• Concentrations of boron greater than background within transition
zone and bedrock groundwater monitoring wells CW-5, MW-5D,
and MW-5BR are associated with the decommissioned sluice line
corridor, an additional source area not related to the WAB. Boron
concentrations within the CW-5/MW-5BR/D well cluster remain less
than the 02L standard.
6.10.5 COI Distribution in Groundwater
(CAP Content Section 6.A.e)
As discussed in Section 6.1.5, COIs were grouped by geochemical behavior and
mobility with discussions for each provided below.
6.10.5.1 Conservative Constituents
Boron geomean isoconcentration maps and cross sections support the
following observations regarding the extent of COI -affected groundwater
represented by these conservative constituents:
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• Deep and bedrock flow zone groundwater COI plumes east and west
(sidegradient) of the WAB are within the compliance boundary.
• Deep and bedrock flow zone groundwater COI plumes north,
northeast, and northwest (downgradient) of the WAB are within the
compliance boundary.
• Deep and bedrock flow zone groundwater COI plumes south
(upgradient) of the WAB are within the compliance boundary.
• The deep and bedrock flow zone groundwater COI plumes have
relatively similar COI plume geometries (Figures 6-31a and 6-31b).
This supports a connected, unconfined flow system between the
deep flow zone and upper bedrock.
• The maximum extent of COI -affected groundwater migration for all
flow zones is represented by boron. Sulfate and TDS concentrations
identified as being greater than their respective groundwater
regulatory standards are associated with COI -affected groundwater
migration from the WAB but are generally confined within the extent
of the 02L boron plume.
Plume Behavior and Stability
(CAP Content Section 6.A.e.i.1)
A discussion regarding the Mann -Kendall trend analysis for plume
behavior and stability is provided in Section 6.1.5.1.
Groundwater wells within the waste boundary generally have stable or
decreasing trends. One increasing trend was observed associated with
boron concentrations at ABMW-1BR. Groundwater within the waste
boundary Mann Kendall results indicate:
• Over 90% of trends for conservative constituents in groundwater
within the waste boundary generally indicate no trends, stable
trends, decreasing trends, or non -detect for boron, sulfate, and TDS.
(Table 6-22).
• The increasing trend for conservative constituent boron within
ABMW-1BR was reported below the 02L standard during the April
2019 sampling event (Appendix C, Table 1).
Groundwater monitoring wells north and west of the WAB, between the
waste boundary and compliance boundary, generally indicate no trends,
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stable trends, decreasing trends, or non -detect for boron, sulfate, and TDS.
(Table 6-22). Mann Kendall results for groundwater wells to the north and
west indicate:
Excluding NE results, approximately 32% of trends indicate
increasing concentration trends predominately in wells to north and
northwest of the WAB, in the direction of NPDES-permitted
wastewater features. This is consistent with information presented in
the CSM in Section 5.0. Wells to the north and northwest include
CCR-201BR, CCR-202BR/D, CCR-203BR/D/S, CCR-204BR, CCR-
205BR, CCR-206BR, and MW-2 (Table 6-22).
Groundwater monitoring wells at or beyond the compliance boundary
general indicate no trends, stable trends, decreasing trends, or non -detect
for boron, sulfate, and TDS (Table 6-22). Mann Kendall results for
groundwater wells to the north and west indicate:
• Well cluster CW-5 and MW-5BR/D is associated with the
decommissioned sluice line area, where the majority of concentration
trends for conservative constituents are decreasing (Table 6-22).
Concentrations trends within boron for WAB wells near or beyond
the compliance boundary were unable to be determined as a result of
non -detect concentrations, with the exception of MW-32BR, where
concentrations are below the laboratory reporting limit (Appendix C,
Table 1).
The groundwater plume west of the WAB generally appears stable. North
of the WAB, the majority of increasing trends within conservative
constituents are observed, where COI affected groundwater migration is in
the direction of the NPDES-permitted heated water discharge pond.
6.10.5.2 Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
There are no non -conservative COIs associated with the WAB; therefore,
this section is not applicable.
6.10.5.3 Variably Conservative Constituents
(CAP Content Section 6.A.e.i)
There are no variably reactive COIs associated with the WAB; therefore, this
section is not applicable.
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6.11 SA2 Potential Receptors Associated with Source Area 2
(CAP Content Section 6.B)
Assessment findings and ongoing monitoring data confirm that affected groundwater
from Source Area 2 do not reach any water supply wells, and modeling indicates this
will remain the case in the future. CSA results indicate Source Area 2 has affected
groundwater quality immediately downgradient of the WAB; however, groundwater
discharges to the NPDES-permitted heated water discharge pond as described in
Section 5.0. COI -affected groundwater is limited to Duke Energy property within the
WAB compliance boundary. Ash basin -affected groundwater does not reach any water
supply wells and modeling indicates this will remain the case in the future.
6.11.1 Surface Waters — Downgradient within 0.5 Mile of
Waste Boundary
(CAP Content Section 6.B.a)
A depiction of surface water features — including wetlands, ponds, unnamed
tributaries, seeps, streams, lakes, and rivers — within a 0.5-mile radius of the
Source Area 2 waste boundary, along with permitted outfalls under the NPDES
and the SOC locations are shown on Figure 5-8 (CAP Content Section 6.B.a.i
and6.B.a.ii). Water in the western discharge canal is subject to NPDES discharge
permit requirements associated with Internal Outfall 002.
Water in the heated water discharge pond, which also receives surface water
from toe drains of the WAB main dam, the western discharge canal and the
WAB, is subject to NPDES discharge permit requirements via Outfall #003 and is
not considered Waters of the State. As a result, no surface water samples were
collected from the heated water discharge pond, the western discharge canal and
the extension impoundment for an evaluation of groundwater discharge to
surface water and an evaluation of compliance with 15A NCAC 02B .0200.
6.11.2 Water Supply Wells
(CAP Content Section 6.B.b)
No public or private drinking water wells or wellhead protection areas were
found to be located downgradient of the Source Area 2 as discussed in Section
5.3.2. A discussion regarding the water supply wells and tabulated results (Table
6-9 (CAP Content 6.B.b.ii)) for the NCDENR and Duke Energy sampling events is
provided in Section 6.2.2.
6.11.2.1 Provision of Alternative Water Supply
Information regarding the provision of alternative water supply for Source
Area 2 is the same as discussed in Section 6.2.2.1.
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6.11.2.2 Findings of Drinking Water Supply Well Surveys
(CAP Content Section 6.B.b.ii)
The major findings from the water supply well evaluation related to the
WAB include:
• All water supply wells are outside the boron plume for the WAB as
defined on the boron plume maps for all flow zones (Figures 6-31a
through 6-31b).
• All water supply wells to the southwest, south, and southeast are
upgradient of the ash basin (Figures 5-7a).
• Boron, the primary constituent exhibiting a discernable plume
related to the ash basin, was not detected above the laboratory
reporting limit in any of the water supply wells sampled (Table 6-9).
• TDS was detected in one well at concentrations greater than
background values but is located south and upgradient of the WAB
(Figure 5-7a). Additionally, no discernable manganese plume
associated with the WAB was identified. Therefore, TDS in this well
is not attributed to the WAB.
Vanadium was detected in one well at a concentration greater than
background values but is located south and upgradient of the WAB
(Figure 5-7a). Additionally, no discernable vanadium plume
associated with the WAB was identified. Vanadium in this well is not
attributed to the WAB.
This evaluation and the detailed evaluation results presented in the CSA
Update (SynTerra, 2017) indicate no impact to water supply wells from the
Roxboro ash basins (or Source Area 2). Furthermore, based on flow and
transport modeling, no future impact to water supply wells is predicted.
6.11.3 Future Groundwater Use Areas Associated With Source
Area 2
(CAP Content Section 6.B.c)
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of Source Area 2. Therefore, no future groundwater use areas are
anticipated downgradient of the Source Area 2.
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6.12 SA2 Human and Ecological Risks
(CAP Content Section 6.0
Primary conclusions from the human health and ecological risk assessment risk
assessment are that there is no evidence of unacceptable risks to on -Site or off -Site
human receptors potentially exposed to CCR constituents that may have migrated from
the ash basins and the DFAHA/GSA. There is no evidence of unacceptable risks to
ecological receptors potentially exposed to CCR constituents that may have migrated
from the ash basins and the DFAHA/GSA. A more detailed discussion regarding
human health and ecological risk associated with Source Area 2 can be found in Section
5.4. An update to the Roxboro human health and ecological risk assessment is included
in Appendix E
6.13 SA2 Description of Remediation Technologies
This section is not applicable for the WAB. Analytical data obtained over one year of
monitoring indicate the WAB is currently in compliance with 02L groundwater quality
standards; therefore, groundwater corrective action under 15A NCAC 02L .0106 is not
required at this time for the WAB.
6.14 SA2 Remedial of Remedial Alternatives
(CAP Content Section 6.E)
This section is not applicable for the WAB. Analytical data obtained over one year of
monitoring indicate the WAB is currently in compliance with 02L groundwater quality
standards; therefore, groundwater corrective action under 15A NCAC 02L .0106 is not
required at this time for the WAB.
Adaptive site management allows iterative review of site information and data to
determine whether changing site conditions warrant adjustments to site management
and monitoring approaches. Adaptive site management approaches may be adjusted
over the site's life cycle as new information and technologies become available. This
approach is particularly useful at complex sites where changes in site conditions may
require an extended period of time or where NCDEQ approves alternate groundwater
standards for COIs, such as 4,000 µg/l for boron, pursuant to its authority under G.S.
Section 15A NCAC 02L .0106(k). Although groundwater concentrations do not exceed
the 02L standard of 700 µg/l for boron at or beyond the ash basin compliance boundary,
Roxboro could be approved for alternate standards given the lack of human health and
ecological risks at the Site.
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6.15 SA2 Proposed Remedial Alternative Selected
For Source Area 2
(CAP Content Section 6.E)
This section is not applicable for the WAB. Analytical data obtained over one year of
monitoring indicate the WAB is currently in compliance with 02L groundwater quality
standards; therefore, groundwater corrective action under 15A NCAC 02L .0106 is not
required at this time for the WAB.
6.15.1 Description of Proposed Remedial Alternative and
Rationale for Selection
(CAP Content Section 6.E.a)
This section is not applicable for the WAB.
6.15.2 Design Details
(CAP Content Section 6.E.b)
This section is not applicable for the WAB.
6.15.3 Requirements for 02L .O1O6(I) — MNA Rule
(CAP Content Section 6.E.c)
This section is not applicable for the WAB.
6.15.4 Requirements for O2L .O1O6(k) — Alternate Standards
(CAP Content Section 6.E.d)
This section is not applicable for the WAB.
6.15.5 Sampling and Reporting
(CAP Content Section 6.E.e)
Sampling and analysis locations and frequency is conducted for the WAB in
accordance with the established IMP. As defined in NCDEQ correspondence,
Facility Interim Monitoring Plans Networks and Sampling Requirements (December
21, 2016) (Appendix A), the IMP was implemented to collect data to facilitate
completion of the CSA and CAP. Implementation of the IMP commenced in the
second quarter of 2017. Additional modifications to the plan were approved by
NCDEQ on June 7, 2019 (Appendix A). Analytical results of IMP sampling are
submitted to NCDEQ quarterly.
6.15.5.1 Progress Reports and Schedule
(CAP Content Section 6.E.e.i)
This section is not applicable for Source Area 2. Since no remediation
system will be installed, no progress reports or schedule for remediation
alternatives is required.
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6.15.5.2 Sampling and Reporting Plan During Active
Remediation
(CAP Content Section 6.E.e.ii)
This section is not applicable for Source Area 2. Since corrective action is
not proposed, an EMP is not required.
6.15.5.3 Confirmation Monitoring Plan
(CAP Content Section 6.E.e)
An EMP is required by G.S. Section 130A-309.211(b)(1)(e) for evaluating the
effectiveness of proposed corrective action. Analytical data obtained over
one year of monitoring indicate the WAB is currently in compliance with
02L groundwater quality standards; therefore, groundwater corrective
action under 15A NCAC 02L .0106 is not required at this time for the WAB.
Because corrective action is not required, an EMP is not required.
The WAB is in compliance with 02L at this time; therefore, Duke Energy
requests that the IMP be replaced by a Confirmation Monitoring Plan
(CMP). The CMP, presented in Appendix P, is designed to be adaptable and
target key areas where changes to groundwater conditions are most likely
to occur throughout the ash basin closure process. CMP key areas for
monitoring are based on the following considerations:
• Include background locations
• Include designated flow paths
• Within areas of observed or anticipated changing Site conditions,
and/or have increasing constituent concentration trends
• Monitor constituent plume stability and verify model simulation
CMP elements including well systems, locations, frequency, parameters,
schedule, and reporting are summarized below and outlined on Table 6-23.
Confirmation monitoring well locations are illustrated on Figure 6-33. The
CMP will be implemented within 30 days of CAP approval and will
continue until there is a total of three years of data confirming that COIs are
below applicable standards at or beyond the compliance boundary, at
which time a request for completion of corrective action will be filed with
NCDEQ. If applicable standards are not met, the CMP will continue and
transition to post -closure monitoring if necessary.
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After ash basin closure and following ash basin closure certification, the
PCMP will be developed and implemented for a minimum of 30 years in
accordance with G.S. Section 130A-309.212(a)(4)k.2. If groundwater
monitoring results are below applicable standards for three consecutive
years, Duke Energy may request termination of the PCMP in accordance
with G.S. Section 130A-309.214(a)(3)b.
A conceptual flow diagram for CMP and PCMP elements is depicted on
Figure 6-34.
Reporting and Schedule
(CAP Content Section 6.E.e.i)
Groundwater corrective action is not required for the WAB; therefore,
"effectiveness" progress reports and schedule and a sampling and analysis
plan during remediation are not applicable.
During basin closure, evaluation of Site conditions and constituent plume
stability would be based on quantitative rationale using statistical,
mathematical, modeling, or empirical evidence. Existing data from
historical monitoring would be used to provide baseline information.
Schedule and reporting of confirmation monitoring data, including plan
review and optimization, while the CMP is active, would include:
Annual Reporting Evaluation: The data collected as part of the CMP will
be evaluated annually. The evaluation will include a summary of annual
groundwater monitoring results, evaluation of statistical concentration
trends, comparison of observed concentrations to model predictions,
evaluation of 02L compliance, and recommendation for plan adjustments, if
applicable.
Results of the evaluation would be reported in annual monitoring reports
submitted to NCDEQ. The reports will include:
• Laboratory reports on electronic media,
• Tables summarizing the past year's monitoring events,
• Historical data tables,
• Figures showing sample locations,
• Figures showing the historical data versus time for the designated
monitoring locations and parameters with emphasis on those
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constituents identified as part of the constituent management process
(Section 6.1.3),
• Statistical analysis (Mann -Kendall test) of data to determine if trends
are present,
• Identification of exceedances of comparative values,
• Groundwater elevation contour maps in plan view and
isoconcentration contour maps in plan view for one or more of the
prior year's sampling events (as mutually agreed upon by Duke
Energy and NCDEQ),
• Any notable observations related to water level fluctuations or
constituent concentration trends attributable to changing Site
conditions, and
• Recommendations regarding adjustments to the CMP, if needed
Sampling and Evaluation
(CAP Content Section 6.E.e.ii)
The CMP is a comprehensive monitoring plan that integrates multiple
monitoring systems designed for key areas of the Site with unique
characteristics or monitoring requirements.
Groundwater Monitoring Network
The Roxboro CMP monitoring network will (1) monitor Site conditions, (2)
provide adequate areal (horizontal) and vertical coverage to monitor plume
status with regard to potential receptors, and (3) confirm flow and transport
and geochemical model predictions. The CMP would include 48 existing
monitoring wells for confirmation monitoring (Figure 6-33).
Groundwater Monitoring Flow Paths - Trend Analysis
The CMP will provide adequate horizontal and vertical coverage to
monitor:
Changes in groundwater quality as Site conditions change (e.g., ash
basin closure commences and groundwater flow and transport
conditions respond)
• Transport rates
• Constituent plume stability
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The monitoring network includes wells along primary groundwater flow
paths. Groundwater monitoring wells are located as indicated in Figure 6-
33 and described below:
1. Background locations
2. 500 feet downgradient of waste boundary or compliance boundary,
as applicable
3. No less than one year travel time upgradient of receptor or potential
receptor and no greater than the distance groundwater is expected to
travel in five years
Multi -parameters sondes will be installed in 8 wells along the primary
groundwater flow paths (Figure 6-33). Monitoring of changes in
groundwater quality on a real-time basis using multi -parameter sondes and
telemetry technology will allow continuous monitoring and evaluation of
geochemical conditions. Geochemical conditions, monitored using pH and
Eh, will be compared, as needed, to geochemical modeling results to
evaluate changes that could potentially affect the mobility (Ka) of reactive
and variably reactive COIs. The multi -parameter sondes also monitor water
levels which will be used to verify simulated changes to groundwater flow.
Groundwater quality and water level data will increase the response time to
implement contingencies if field parameters significantly deviate from
predicted responses. A contingency plan is included in Section 6.15.8.
Plume stability evaluation will be based primarily on results of trend
analyses. Trend analyses will be conducted using Mann -Kendall trend test.
Mann -Kendall trend tests will be conducted using data from CMP
(geochemically nonreactive, conservative constituents). For the WAB, boron
best depicts the areal extent of the plume and plume stability and physical
attenuation.
Sampling Frequency
Sampling for the CMP will be semi-annually. Multiple years of quarterly
and semi-annual monitoring data are available for use in trend analysis and
to establish a baseline to evaluate corrective action performance. Therefore,
semi-annual sampling at locations defined in the CMP will provide
adequate analytical data to monitor plume stability. Quantitative
evaluations will determine if additional data is necessary (i.e., increased
sampling frequency) for refining statistical and empirical model
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development. Additional monitoring described in the contingency plan will
be implemented if significant geochemical condition changes are identified
that could result in mobilization of reactive or variably -reactive COIs.
Sampling and Analysis Protocols
(CAP Content Section 6.E.e.ii)
CMP sampling and analysis protocol will be similar to the existing IMP and
could be adjusted in the future based on further analysis. Detailed protocols
are presented in the CMP document (Appendix P). Samples will be
analyzed by a North Carolina -certified laboratory for the parameters listed
in Table 6-23 as summarized below. Laboratory detection limits for each
constituent are targeted to be at or less than applicable regulatory values
(i.e., 02L, IMAC, background).
Groundwater quality confirmation monitoring parameters:
Conservative constituent analyses of boron will be conducted to
monitor groundwater conditions using designated wells along the
groundwater flow paths. Boron was selected because it is non -
reactive to changing geochemical conditions and encompasses the
areal extent of the plume. Physical attenuation mechanisms of
dilution and dispersion will be evaluated by comparing monitoring
results with flow and transport model simulations. Changing
geochemical conditions that could cause sorption or precipitation/co-
precipitation mechanisms would be evaluated using multi -parameter
sondes.
• Groundwater field parameters: Six field parameters will be
monitored to confirm that monitoring well conditions have stabilized
prior to sample collection and to evaluate data quality: water level,
pH, specific conductance, temperature, dissolved oxygen, and
oxidation reduction potential.
Additional geochemical parameters: Cations and anions will be
analyzed to evaluate monitoring data quality (electrochemical charge
balance). These include alkalinity, bicarbonate alkalinity, aluminum,
calcium, iron, magnesium, manganese, nitrate + nitrite, potassium
and sodium. Total organic carbon (TOC), ferrous iron, and sulfate
analyses are also proposed as monitoring parameters. TOC is
recommended to help determine if an organic compound is
contributing to TDS, and ferrous iron and sulfate to monitor potential
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dissolution of iron oxides and sulfide precipitates as an indicator of
changing conditions.
6.15.6 Sampling and Reporting Plan After Termination of
Active Remediation
(CAP Content Section 6.E.e.iii)
As previously described, Source Area 2 groundwater is in compliance with 02L
standards, corrective action is not required.
6.15.7 Proposed Interim Activities Prior to Implementation
(CAP Content Section 6.E. f)
This section is not applicable for Source Area 2.
6.15.8 Contingency Plan in Case of Insufficient Remediation
Performance
(CAP Content Section 6.E.g)
This section is not applicable for the WAB. Because no remediation system will
be installed; there is no remediation system that could have insufficient
performance. However, Duke Energy has developed the contingency plan
described below that identifies conditions that trigger further evaluation
6.15.8.1 Description of Contingency Plan
(CAP Content Section 6.E.g.i)
Analytical data will obtained and evaluated in accordance with the CMP or
PCMP to identify if a more active approach to groundwater corrective
action is potentially warranted. The evaluation will be conducted to
determine if additional data is needed to validate conditions (more frequent
sampling, additional parameters, additional monitoring location, etc.) and
determine if the WAB CAP should be updated to evaluate corrective action
approaches and technologies.
6.15.8.2 Decision Metrics for Contingency Plan Areas
(CAP Content Section 6.E.g.ii)
Potential corrective approach evaluation is warranted if:
• Changing groundwater quality conditions downgradient of the ash
basin represented by an increase of a COI concentration over four
consecutive monitoring events.
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• Changing surface water quality conditions downgradient of the ash
basin represented by an increase of a COI concentration over four
consecutive monitoring events.
Site conditions measurably different than predictive model
simulations, including geochemical condition changes, which could
result in mobilization of reactive and variably reactive, COIs.
Potential remedial alternatives considered would be screened against the
following criteria outlined in 15A NCAC 02L .0106(i).
• Protection of human health and the environment
• Compliance with applicable federal, state, and local regulations
• Long-term effectiveness and permanence
• Reduction of toxicity, mobility, and volume
• Short-term effectiveness at minimizing effects on the environment
and local community
• Technical and logistical feasibility
• Time required to initiate
• Predicted time required to meet remediation goals
• Cost
• Sustainability
• Community acceptance
6.16 SA2 Summary and Conclusions
Groundwater corrective action is not required by 02L for the WAB because there are no
exceedances of basin -derived COIs in groundwater beyond the compliance boundary.
Multiple lines of evidence provided in this CAP indicate that the groundwater plume
originating from the WAB, represented by boron, does not currently, nor is it predicted
to, extend beyond the compliance boundary.
Although active groundwater corrective action is not required, a CMP is proposed. The
CMP is designed to be protective of human health and the environment by providing
systematic evaluation of groundwater conditions at and beyond the compliance
boundary in the event of changing conditions that warrant attention occur. The CMP
will begin within 30 days of CAP Update approval.
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Duke Energy's preferred groundwater remediation approach assumes source control
through either basin closure -in -place or closure -by -excavation. Source control measures
are separate from the CAP Update and do not affect the preferred groundwater
remediation approach.
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SOURCE AREA 3 (SA3) — GYPSUM STORAGE AREA AND DFA SILOS,
TRANSPORT, AND HANDLING AREAS
This section provides the corrective action approach and information to support the
approach for Source Area 3, the Gypsum Storage Area and the DFA silos, transport, and
handling areas (Figure 6-1). The GSA and DFAHA are additional sources located
downgradient of the EAB (downgradient additional sources) and are able to be
evaluated for potential groundwater influences independently of the EAB. Due to
proximity of those additional sources and CCR related plume extent downgradient of
the EAB, the GSA and DFAHA are evaluated for corrective action, separate from the
EAB, as a component of this CAP Update.
6.17 SA3 Extent of Constituent Distribution
6.17.1 Source Material Within the Waste Boundary
(CAP Content Section 6.A.a)
The GSA and the DFAHA have no waste boundaries demarcated for either of the
units (Figure 6-1); however, an overview of material associated with each of the
units is presented in the following subsections.
6.17.1.1 Description of Waste Material and History of
Placement
(CAP Content Section 6.A.a.i)
Gypsum Storage Area
A description of the GSA is provided in Section 1.5.2. The 12.5-acre GSA
was designed and constructed to accommodate storage of gypsum intended
for beneficial reuse. To accommodate GSA development, approximately
131,319 cubic yards of DFA was used as structural fill in topographical low
lying areas. The use of DFA as structural fill was in accordance with
notification requirements of Section .1700 of the Solid Waste Management
15A NCAC 13B Rules. Stipulation regarding use of DFA for structural fill
are that DFA would not be placed within 50 feet of a water body, within 50
feet of any remaining wetlands that remain unfilled and within 2 feet of the
seasonal high groundwater table. A geosynthetic clay liner with a plastic
laminated geomembrane was installed following final grading. The GCL
was placed laminate side up directly over a six-inch layer of DFA followed
by a six-inch layer of DFA, 12-inches of fill soil and a six-inch layer of top
soil.
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DFA silos, transport, and handling areas
A description of the DFAHA is provided in Section 1.5.2. The DFAHA is
located adjacent to and west of the GSA and is used for storage and
management of DFA prior to disposal in the industrial landfill or for
beneficial reuse. Fugitive DFA material from storage, management and
transportation operations is present on and within separations of the
concrete roadway and non -paved areas. The concrete surface areas
described above have visible stress cracks in addition to insufficient curbing
in some areas, apparent by DFA deposition on surrounding gravel and
vegetated surfaces. Additionally, curbing along the haul road has
separated from the road surface allowing precipitation and water used for
dust suppression to leave the intended area of containment. Rainfall
infiltration and surface water runoff from dust suppression are mechanisms
for COI infiltration in the area.
6.17.1.2 Specific Waste Characteristics of Source Material
(CAP Content Section 6.A.a.ii)
Gypsum Storage Area
Three monitoring well clusters, GPMW-1, GPMW-2 and GPMW-3, were
installed along the northern extent of the GSA adjacent to and upgradient of
the Intake Canal. The well clusters were installed at the northwest, central
and northeast corners of the gypsum storage area as shown on Figure 1-2.
The monitoring well clusters were installed in March 2017. No soil samples
were collected during boring installation for each monitoring well. No
indications of structural fill were observed in the saprolite zone from soil
cuttings during drilling of GPMW-1 and GPMW-2 well clusters. However,
saprolitic silty clay with observations of gravel and fill was observed to a
depth of 18.5 feet bgs at the GPMW-3 well cluster. Details regarding the
well installation activities can be found in the Gypsum Storage Area Structural
Fill (CCB 003) Assessment Report — Roxboro Steam Electric Plant (SynTerra,
2017a).
As part of the 2015 CSA activities, MW-3BR, located at the northeast corner
of the GSA (Figure 1-2) was installed. MW-3BR is an upper bedrock
monitoring well with a screened interval from 57 to 67 feet bgs with
competent bedrock intercepted at 48 feet bgs. No indications of structural
fill were observed in the saprolite zone from soil cuttings taken during
drilling of MW-3BR. An exception is approximately one foot of ash
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observed from 1.5 to 2.5 feet bgs likely used as a fill during the construction
of the GSA.
DFA silos, transport, and handling areas
Four monitoring well clusters, MW-34 through MW-37, were installed in
the DFAHA area (Figure 1-2) in March/April 2019. Clayey sand fill was
observed from a depth of 2-4 feet bgs at each of the boring locations;
however, no indications of structural fill (as DFA) were observed in the
saprolite zone from soil samples and cuttings taken during drilling of the
well clusters. Lithological information and well construction details are
provided in the boring and well construction logs provided in Appendix Q.
6.17.1.3 Volume of Physical Horizontal and Vertical Extent
of Source Material
(CAP Content Section 6.A.a.iii)
Gypsum Storage Area
DFA as structural fill was placed in the western and central portions of the
GSA to fill in former topographical low-lying areas. Using preconstruction
topographic maps and final grade drawings (Progress Energy, 2006) and
geotechnical boring information obtained during construction, up to
approximately 30 feet of DFA was placed in the western portion and up to
17 feet of DFA was placed in the central portion. According to the deed
recordation provided in the March 27, 2007 Notification of Recordation of
Structural Fill (Appendix A), the volume of DFA used as structural fill is
approximately 131,319 cubic yards.
DFA silos, transport, and handling areas
According to available historical construction plans and site personnel,
structural fill (including DFA) was not used during site development for the
DFAHA. No records or estimates are available to determine the volume of
historical or current fugitive DFA material related to the DFAHA.
6.17.1.4 Volume and Physical Horizontal and Vertical
Extent and Anticipated Saturated Source Material
(CAP Content Section 6.A.a.iv)
Gypsum Storage Area
Cross-section A -A' (Figure 6-3), oriented north to south, displays the
general EAB layout including the industrial landfill profile with underlying
saturated ash and the downgradient GSA and subsequent Intake Canal.
The geological cross-section across the GSA incorporated lithological
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information obtained from the GSA assessment activities and MACTEC
geotechnical borings obtained during the construction of the gypsum
storage pad with groundwater elevations posted from April 2019.
Based on the April 2019 water level data, the DFA structural fill for the GSA
appears to be situated at or above the water table with the presence of a
liner positioned on top of the fill material.
DFA silos, transport, and handling areas
According to available historical construction plans and site personnel and
supported by soil boring installation, structural fill (including DFA) was not
used during site development for the DFAHA.
6.17.1.5 Saturated Ash and Groundwater
(CAP Content Section 6.A.a.v)
Gypsum Storage Area
The DFA structural fill appears to be situated at or above the water table
with the presence of a liner positioned on top of the fill material. A review
of analytical data indicates the DFA structural fill has not impacted shallow
groundwater in the western and the central portion of the GSA where the
majority of the DFA structural fill was placed. This observation is based on
the lack of the CCR constituents in GPMW-2D, which is positioned
downgradient of the DFA structural fill, and that the fill appears to be
situated above the water table. The presence of boron in the transition zone
along the eastern portion, as indicated by GPMW-3D/BR, may be attributed
to preferential groundwater flow along the eastern discharge canal
including the historical eastern discharge canal deposition area (Section
3.0). In addition, the detection of elevated selenium, sulfate and TDS
concentrations in this area can be attributed to infiltration of surface water
runoff from the gypsum storage unlined storm water ponds north of the
unit. The presence of boron in GPMW-1 well cluster and GPMW-2BR is
likely related to comingled plumes associated with the DFAHA and
downgradient COI -affected groundwater from the EAB, as supported by
the flow and transport model (Appendix G).
DFA silos, transport, and handling areas
This section is not applicable since saturated ash is not present associated
with the DFAHA.
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6.17.1.6 Chemistry Within Waste Boundary
(CAP Content Section 6.A.a.vi)
The GSA and the DFAHA have no waste boundaries demarcated for either
of the units; therefore, this section is not applicable.
6.17.1.7 Other Potential Source Material
(CAP Content Section 6.A.a.vii)
No other potential source materials are related to the GSA and the DFAHA.
A description of the historical eastern discharge canal deposition area to the
east of the GSA is provided in Section 3.0.
6.17.1.8 Interim Response Actions
(CAP Content Section 6.A.a.viii.)
No interim response actions have been conducted related to the GSA and
the DFAHA.
6.17.2 Extent of Constituent Migration beyond the Compliance
Boundary
(CAP Content Section 6.A.b)
The GSA and the DFAHA have no waste boundaries and related compliance
boundaries associated with the units. However, analytical sampling results
associated with the GSA and the DFAHA for each media are included, as
applicable, in the following tables and appendix tables:
• Soil: Appendix C, Table 4 and Table 6-4 (CAP Content Section 6.A.b.ii.1)
• Groundwater: Appendix C, Table 1 and Table 6-5 (CAP Content Section
6.A.b.ii.2)
• Seeps: Appendix C, Table 3 (CAP Content Section 6.A.b.ii.3)
• Surface water: Appendix C, Table 2 and Appendix J (CAP Content Section
6.A.b.ii.4)
• Sediment: Appendix C, Table 5 (CAP Content Section 6.A.b.ii.5)
Soil Constituent Extent
(CAP Content Section 6.A.a.ii.1)
Analytical data of unsaturated soil associated with the GSA (MW-3BR ((0-2 feet
bgs) and (21-23 feet bgs)) indicate chromium (total), cobalt, iron and manganese
were detected at concentrations greater than the PSRG POG. However, the
detected concentration are generally consistent with background concentrations
(Table 6-4). For the DFAHA, similar concentrations of chromium (total), cobalt,
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iron and manganese were detected in the shallow soil samples ((2-4 feet bgs) and
(6-10 feet bgs) collected from the MW-34 through MW-37 well clusters; however,
detected concentrations are, as well, generally consistent with background
concentrations. Horizontal and vertical extent of COI concentrations in soil is
discussed further in Section 6.17.4.
Groundwater Constituent Extent
(CAP Content Section 6.A.a.ii.2)
Groundwater concentrations greater than 02L/IMAC/applicable background
concentration values occur within the DFAHA and upgradient and
downgradient locations associated with the GSA.
Boron, sulfate and TDS concentrations greater than their respective groundwater
regulatory standards were observed in each of the DFAHA bedrock wells (MW-
34BR through MW-37BR); two of the transition zone wells (MW-35D and MW-
36D) and the shallow well, MW-35S. The shallow well, MW-375, demonstrated
sulfate and TDS concentrations greater than their respective groundwater
standard. Other constituents including selenium, strontium, and vanadium have
concentrations greater than their respective groundwater regulatory standards
associated with the DFAHA. Of these constituents, all concentrations greater
than regulatory standards are at locations where boron concentrations are
greater than 02L standards. The distribution of these constituents are confined
within the extent of the 02L boron plume. The presence and distribution of the
constituents in the DFAHA is attributed to infiltration of DFA from contact water
runoff from precipitation and dust suppression operations and COI -affected
groundwater from the upgradient EAB.
For the GSA, a similar pattern of boron, sulfate and TDS greater than their
respective groundwater regulatory standards is observed in the GPMW-1 cluster
and GPMW-2BR, which is likely related to comingled plumes associated with the
DFAHA and downgradient COI -affected groundwater from the EAB. The
presence of boron in the GPMW-1 well cluster and GPMW-2BR is supported by
the flow and transport model (Appendix G). For GPMW-2D and the GPMW-3
cluster, the distribution of boron, sulfate and TDS greater than their respective
groundwater regulatory standards is attributable to either groundwater flow
along the eastern discharge canal including the historical eastern discharge canal
deposition area and infiltration of surface water runoff from gypsum storage as
discussed in Section 6.18.1.
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Section 6.1.3 includes a detailed matrix evaluation and rationale of groundwater
constituents requiring corrective action, and Section 6.1.4 provides
isoconcentration maps and cross sections depicting groundwater flow and
constituent distribution in groundwater for the GSA/DFAHA in reference to the
EAB compliance boundary (CAP Content Section 6.A.b.i).
Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Seeps at Roxboro are subject to the monitoring and evaluation requirements
contained in the SOC. The SOC states that the effects from non -constructed seeps
should be monitored. For the GSA/DFAHA, the non-dispositioned seep location
5-14 is at the discharge point of an underground 36-inch diameter reinforced
concrete pipe that flows from the unnamed pond north of the EAB (and its
compliance boundary) to the wastewater detention basin positioned northwest of
the GSA. Flow is likely to remain at the conduit from the EAB unnamed pond.
It is anticipated proposed groundwater remediation activities will reduce flows
to the EAB unnamed pond thereby reducing flows via 5-14. Table 6-8 provides a
summary of seep general location and approximate flow rate.
Surface Water Constituent Extent
(CAP Content Section 6.A.b.ii.4)
Surface water samples have been collected from the Intake Canal to confirm
groundwater downgradient of the downgradient GSA/DFAHA has not resulted
in surface water concentrations greater than 02B water quality standards.
Groundwater monitoring data consistently indicate a comingled constituent
plume associated with the EAB and the DFAHA along with the GSA does extent
to the Intake Canal. Surface water samples were collected to evaluate acute and
chronic water quality values. Surface water samples were also collected at a
background location in the Intake Canal consistent with an upgradient
groundwater monitoring well cluster, MW-14, and MW-28BR (upgradient of
potential migration areas). Analytical results were evaluated with respect to 02B
water quality standards and background data. Surface water conditions is
further discussed in Section 6.18.1 and the full report for the Roxboro surface
water current conditions can be found in Appendix J.
Sediment Constituent Extent
(CAP Content Section 6.A.a.ii.5)
Sediment sample locations are generally co -located with surface water sample
locations (Figure 1-2). Similar to saturated soils and groundwater, sediment is
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considered a component of the surface water system, and the potential leaching
and sorption of constituents in the saturated zone is related to water quality.
Because no regulatory standards are established for sediment inorganic
constituents, both background sediment COI concentration ranges and co -
located surface water sample results are considered in this sediment evaluation.
Table 4-5 presents constituent ranges of background sediment datasets per water
body. Analytical results for all sediment samples are provided in Appendix C,
Table 5.
Assessment of COIs in sediment from surface waters, including the Hyco
Reservoir and the Intake Canal, and seeps, was conducted through a comparison
evaluation between sediment sample COI analytical results, from one-time grab
samples, and COI concentration ranges from background sediment datasets.
Samples collected from the Intake Canal are comparable with background
dataset range from the Intake Canal background sample, RSW-6.
Sediments Collected from Seeps
No sediments samples were collected from seep 5-14 associated with the GSA.
6.17.2.1 Piper Diagrams
(CAP Content Section 6.A.b.iii)
Piper diagrams can be used to differentiate water sources in hydrogeology
by assessing the relative abundance of major cations (i.e., calcium,
magnesium, potassium, and sodium) and major anions (i.e., chloride,
sulfate, bicarbonate, and carbonate) in water.
Groundwater Piper Diagrams
Piper diagrams (Figure 6-8), and a discussion of the evaluation, for
groundwater monitoring data from shallow, deep and bedrock background
locations and downgradient of the EAB including the GSA/DFAHA
locations is provided in Section 6.1.2.1.
Seep and Surface Water Piper Diagrams
Piper diagrams for seep S-14 and surface water samples collected from the
Intake Canal are included on Figure 6-9. A discussion regarding the Piper
diagram evaluation associated with the seep and surface water is provided
in Section 6.1.2.1.
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6.17.3 Constituents of Interest (COIs)
(CAP Content Section 6.A.a.c)
This CAP Update evaluates the extent of, and remedies for COIs in groundwater
associated with the DFAHA and the GSA, including the comingled plume area
to the northwest of the EAB compliance boundary, detected at concentrations
greater than 02L, IMAC, or background values, whichever is greater.
Soil
(CAP Content Section 6.A.c.i.1)
Horizontal and vertical extent of COI concentrations in soil, and reasons why no
necessary corrective action for soils is identified at the Site, is discussed further in
Section 6.1.4.
Constituents considered for unsaturated soil evaluation were the same
constituents identified as COIs for the EAB, since soil impacts would be related
to rainwater infiltration to the underlying soils and groundwater migration at or
beyond the ash basin or structural fill associated with the GSA.
Data indicate unsaturated soil COI concentrations are generally consistent with
background concentrations or are less than regulatory screening values (Table 6-
4). In the few instances where unsaturated soil COI concentrations are greater
than PSRG POG standards or background values, COI concentrations are within
range of background dataset concentrations.
Groundwater
(CAP Content Section 6.A.c.i.2)
A measure of central tendency analysis of groundwater COI data (January 2018
to April 2019) was conducted and means were calculated to support the analysis
of groundwater conditions to provide a basis for defining the extent of the COI
migration associated with the comingled plume in the DFAHA area and from the
GSA. Further discussion regarding a central tendency analysis is provided in
Section 6.1.3.
Table 6-5 presents the mean analysis results of the COI data using groundwater
monitoring sampling results from January 2018 to April 2019. Where means
could not be calculated, the most recent valid sample was evaluated to determine
whether the sample result is an appropriate representation of the historical
dataset.
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Using the constituent management process detailed in Section 6.1.3, data from
Table 6-5 are used in evaluating COI plume geometry in the vicinity of the
DFAHA and GSA. Five COIs exhibit mean concentrations greater than
background values, 02L standard, or IMAC with plume characteristics
downgradient of the DFAHA and GSA. These constituents are as follows:
• Boron • Strontium
• Selenium • Total Dissolved Solids (TDS)
• Sulfate
As discussed in the CSA Update (SynTerra, 2017d), not all constituents with
results greater than background values can be attributed to the DFAHA and
GSA. Naturally occurring groundwater contains varying concentrations of
inorganic constituents. Sporadic and low -concentration occurrences of these
constituents in the groundwater data do not necessarily demonstrate horizontal
or vertical distribution of COI -affected groundwater migration from the
downgradient additional sources.
6.17.4 Horizontal and Vertical Extent of COIs
(CAP Content Section 6.A.d)
Isoconcentration maps and cross -sections use groundwater analytical data to
spatially and visually define areas where groundwater COI concentrations are
greater than background values and/or 02L/IMAC. Means of groundwater COI
monitoring sampling results from January 2018 to April 2019 provide an
understanding of groundwater flow dynamics and direction to define the
horizontal and vertical extent of the COI plume. Horizontal extent of the COI
plume is depicted on isoconcentration maps (Figures 6-10a through 6-14b).
Vertical extent of the COI plume is depicted on two generalized cross -sectional
depictions of the Site. Cross-section A -A' is oriented north to south and displays
the general EAB layout including: industrial landfill profile with underlying
saturated ash, areas evaluated for corrective action, and downgradient GSA and
subsequent Intake Canal (Figures 6-6a and 6-6b). Cross section B-B' is orientated
northwest to southeast and displays the eastern extension impoundment,
industrial landfill profile with underlying saturated ash, and NPDES permitted
surface water bodies downgradient of the main dam (Figures 6-7a and 6-7b).
The maximum extent of COI -groundwater affected by the comingled
EAB/DFAHA and the GSA occurs to the north to the Intake Canal.
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6.17.4.1 COIs in Unsaturated Soil
(CAP Content Section 6.A.d.i)
As discussed in Section 6.1.4.1, unsaturated soil samples at or beyond the
EAB waste boundary and within the DFAHA/GSA area were collected from
soil borings and during well installation activities (Figure 6-15). In response
to the CSA Update (SynTerra, 2017d), NCDEQ requested additional
evaluation of unsaturated soil surrounding, especially along the margins, of
the ash basin to determine the degree of possible impact from historical
CCR management at Roxboro. Additional unsaturated soil samples
surrounding the EAB waste boundary have been collected as various field
efforts between June 2018 and June 2019. An evaluation of the potential
nature and extent of COIs in unsaturated soil beyond the waste boundary
was conducted by comparing unsaturated soil concentrations with
background values or PSRG POG standards, whichever is greater (Table 6-
4) (CAP Content Section 6.A.d.i). An evaluation of unstaturated soil
associated with the DFAHA and GSA is included in Section 6.1.4.1.
6.17.4.2 Horizontal and Vertical Extent of Groundwater in
Need of Restoration
(CAP Content Section 6.A.d.ii)
This section discusses the horizontal and vertical extent of groundwater in
need of restoration in areas north of Source Area 3.
Northern Extent of COI Affected Groundwater
The northern extent of the COI plume associated with the comingled
EAB/DFAHA area and the GSA is defined by boron, sulfate, and TDS at
concentrations greater than 02L or background. The extent of affected
groundwater transport related to hydraulic conditions is supported by the
following observations:
The COI -affected groundwater from the EAB comingles
downgradient with similar COI -affected groundwater contributed by
the GSA and DFAHA. These downgradient additional sources
roughly begin along the northernmost EAB compliance boundary
and extend north towards the Intake Canal.
• Mean concentrations of boron, sulfate and TDS increase and continue
to exceed the 02L standards in groundwater monitoring wells
GPMW-1S/D/BR, GPMW-2D/BR, and GPMW-3D/BR. Similarly, the
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mean concentrations of strontium and TDS at these well clusters is
greater that the BTV (Figures 6-10a through 6-14b).
6.17.5 COI Distribution in Groundwater
(CAP Content Section 6.A.e)
6.17.5.1 Conservative Constituents
Boron, sulfate, and TDS mean isoconcentration maps and cross sections
support the following observations regarding the extent of COI -affected
groundwater represented by these conservative constituents:
• The GSA and DFAHA contribute to the boron, sulfate, and TDS COI -
affected groundwater plumes downgradient of the ash basin
compliance boundary (Figures 6-10a through 6-12b).
• The vertical extent of the COI -affected groundwater for conservative
constituent migration is shown on generalized cross-section A -A'
(Figure 6-6a).
• The deep and bedrock flow zone COI -affected groundwater plumes
have relatively similar geometries (Figures 6-10a through 6-12b).
This supports a connected, unconfined flow system between the
deep flow zone and upper bedrock.
• The COI -affected groundwater plumes depicted on Figure 6-10a
through Figure 6-12b were generated from the flow and transport
model and informed by empirical data. The model predictions are
conservative and may over -predict the extent of conservative
constituent distribution in groundwater. This is generally observed
in the areas of bedrock monitoring wells associated with the GSA
(GPMW-2BR and GPMW-3BR), where mean concentrations indicate
concentrations less than the USEPA drinking water equivalent level
(4,000 µg/L).
• COI -affected groundwater plumes for conservative constituents
extend into the intake canal, a groundwater to surface water
discharge area evaluated within Appendix J.
The maximum extent of COI -affected groundwater migration for all flow
zones is represented by boron. Sulfate and TDS concentrations identified as
being greater than their respective groundwater regulatory standards are
associated with COI -affected groundwater migration from the GSA and
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DFAHA but are generally confined within the extent of the 02L boron
plume (Figures 6-10a through 6-12b).
Plume Behavior and Stability
(CAP Content Section 6.A.e.i.1)
Mann -Kendall trend analysis was performed on a select set of wells
associated with the DFAHA and the GSA using the same methodology as
presented in Section 6.1.5.1. The analysis was performed using analytical
results for samples collected from 2015 through 2019, for unit specific COIs.
Within the vicinity of the DFAHA and GSA, groundwater Mann Kendall
results indicate:
• Excluding NE results, approximately 60% of trends for conservative
constituents in groundwater indicate no trend, stable trend,
decreasing trend, or non -detect for boron, sulfate, and TDS. (Table 6-
7).
• An insufficient number of samples were available from recently
installed groundwater monitoring well clusters MW-34D/BR, and
MW-36D/BR (Table 6-7).
Concentration trends for wells within the vicinity of the DFAHA and GSA
generally have stable or increasing trends (Table 6-7).
6.17.5.2 Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
Through the utilization of the matrix evaluation (Table 6-6) derived from
the constituent management process, non -conservative constituents are not
brought forth for corrective action for Source Area 3. The means for non -
conservative constituents are either within Site -specific background values
(vanadium) or do not exhibit a discernable plume at the Site [uranium
(total)].
6.17.5.3 Variably Conservative Constituents
Selenium and strontium isoconcentration maps and cross sections support
the following observation regarding the extent of COI -affected groundwater
represented by these variable constituents. A plume -like distribution of
selenium greater than the 02L standard occurs in the transition flow zone
north of the EAB (Figure 6-13a). Five monitoring wells, one in the shallow
flow zone (MW-35S) and four in the transition zone (GMW-6, MW-34D,
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MW-35D, and MW-22D) are within the plume -like distribution of the deep
flow zone (Figures 6-13a). This plume -like distribution is somewhat similar
within the bedrock flow zone. Two monitoring wells (GMW-11 and MW-
37BR) are greater than the 02L standard north and northwest of the EAB in
the comingled area with the DFAHA (Figure 6-13b).
6.18 SA3 Potential Receptors Associated with Source Area 3
(CAP Content Section 6.B)
Assessment findings and ongoing monitoring data indicate Source Area 3 has affected
groundwater quality immediately downgradient of DFAHA and the GSA to the
adjacent Intake Canal. Groundwater effects are limited to within the Duke Energy
property. COI -affected groundwater from Source Area 3 does not reach any water
supply wells, and modeling indicates this will remain the case in the future. Duke
Energy owns the land and controls the use of groundwater on the land downgradient of
Source Area 3. Therefore, potential receptors are limited to the Intake Canal.
6.18.1 Surface Waters — Downgradient Within a 0.5-Mile
Radius of the Waste Boundary
(CAP Content Section 6.B.a)
There are no waste boundaries associated with Source Area 3; however, a
depiction of surface water features — including wetlands, ponds, unnamed
tributaries, seeps, streams, lakes, and rivers — within a 0.5-mile radius of the
combined Source Area 1 waste boundary, along with permitted outfalls under
the NPDES and the SOC locations are shown on Figure 5-8 (CAP Content Section
6.B.a.i and 6.B.a.ii). Associated North Carolina surface water classifications for the
Intake Canal, an extension of Hyco Reservoir are summarized in Section 5.3.1
and Table 5-4 (CAP Content Section 6.B.a.iii).
For groundwater corrective action to be implemented under 15A North Carolina
Administrative Code (NCAC) .02L .0106(k), groundwater discharge to surface
water cannot result in exceedances of standards for surface waters contained in
15A NCAC 02B .0200. Groundwater downgradient of Source Area 3 discharges
to the Intake Canal. Sample locations within the Intake Canal include RSW-01
through RSW-05. The samples were collected to confirm groundwater
downgradient of Source Area 3 have not resulted in surface water concentrations
greater than NCAC 02B water quality standards. Surface water samples were
collected to evaluate acute and chronic water quality values. Analytical results
were evaluated with respect to NCAC 02B water quality standards and
background data. The surface water samples were collected in accordance with
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NCDEQ DWR Internal Technical Guidance: Evaluating Impacts to Surface Water
from Discharging Groundwater Plumes - October 31, 2017.
Analytical results indicate constituent concentrations less than applicable 2B
criteria with the exception of total barium and total hardness present in the RSW-
03 sample collected on May 3, 2018 and dissolved copper relative to the chronic
criteria at the RSW-04 location.
The indication of total barium and total hardness from the RSW-03 location on
May 3, 2018 is considered an anomaly associated with wind-blown fugitive
materials (gypsum and DFA) present at the adjacent gypsum conveyor system
base located approximately 120 feet to the east of the RSW-03 location.
Supporting evidence of this anomaly includes:
• Plant station meteorological data indicate wind gusts greater than 25 miles
per hour (mph) coming from the east during the May 3, 2018 sampling
event.
• Several other constituents including boron, strontium, aluminum,
manganese, potassium, sodium and zinc are present above background in
RSW-03 for that particular sample set (Appendix C, Table 4-2); the
dissolved constituent concentrations do not show similar increases.
Total hardness is influenced by aluminum, barium, iron, manganese,
strontium, and zinc if present in large enough concentrations (Hardness in
Drinking -Water, its Sources, its Effects on Humans and its Household
Treatment. S. Akram and F. Rehman, J. Chemistry and Applications, June
2018). Therefore the detection of atypically high concentrations of these
constituents from RSW-03 during this sampling event likely resulted in an
increase in total hardness.
The indication of dissolved copper at the RSW-04 sample location is considered
an anomaly. On the April 30, 2018 event, a dissolved copper concentration was
measured at 4.88 µg/L but was not confirmed by the total copper concentration of
1.26 µg/L. On May 1, 2018, two samples were collected one hour apart as part of
the acute evaluation. The first acute sample had a dissolved copper
concentration of 1.26 µg/L and a total concentration of 1.64 Jig/L. The second
acute sample had a dissolved copper concentration of 5.23 µg/L but was not
confirmed by the total concentration of 1.64 µg/L. The remaining dissolved
copper concentrations from RSW-04 are 1.19 µg/L (May 2, 2018) and 1.16 µg/L
(May 3, 2018). Dissolved copper concentrations greater than the total copper
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values are considered anomalous. These anomalous dissolved copper
concentrations resulted in a mean value of 2.834 µg/L, which is slightly higher
than the chronic mean value of 2.7 µg/L.
SynTerra has observed that filters used in the sample collection process can be
the source of dissolved copper in samples. Therefore, it is possible that the
dissolved copper detected in samples as described above is a result of filter
contamination of the samples. However, dissolved copper was not detected in
associated filter blank quality assurance/quality control samples. Copper is not a
constituent associated with groundwater migration from the ash basins.
Therefore, the dissolved copper concentrations in these samples do not indicate
influence of groundwater migration from the Site to surface water.
Comparisons of surface water data with the applicable USEPA National
Recommended Water Quality Criteria for Protection of Aquatic Life, Human
Health and/or Water Supply (USEPA, 2015; 2018a; 2018b) was conducted on the
surface water samples. As stated by the USEPA, these criteria are not a
regulation, nor do they impose a legally -binding requirement. Therefore,
comparisons with these criteria are only for situational context. The constituents
that have corresponding USEPA criteria but do not have NCDEQ 02B criteria are
alkalinity, aluminum, antimony, iron and manganese. All concentrations of
alkalinity, aluminum, antimony, iron and manganese in downstream samples
were either non -detect (i.e. antimony) or concentrations were generally
comparable to background concentrations, with the exception of aluminum, iron
and manganese results from Intake Canal downstream sample RSW-3. Surface
water sample collected on May 3, 2018 from RSW-3 location had anomalously
high aluminum, iron, and manganese concentrations greater than surface water
sample results collected earlier that week at the same location, background, and
USEPA criteria. The anomalously high concentrations of aluminum, iron, and
manganese are likely attributable to anomalous high wind weather conditions
during the sampling event.
The full report for Roxboro groundwater discharge to surface water and the
evaluation of surface waters to evaluate compliance with 15A NCAC 02B .0200
was submitted to NCDEQ on March 21, 2019. A revision to the report was made
to include the assessment of Stream 11A associated with Source Area 1. A copy
of the revised report is provided in Appendix J.
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Surface Water - Future Conditions Evaluation
An evaluation of potential future groundwater migration to surface water was
conducted to identify areas where further evaluation might be warranted. For
areas of potential future groundwater migration to surface water, a mixing
model approach was used for the evaluation of future surface water quality
conditions. Flow and transport modeling results were used to determine where
groundwater migration from the ash basin might intersect surface water in the
future. Predictive groundwater modeling using boron as a proxy for COI plume
migration demonstrated the Intake Canal is not anticipated to be influenced by
future groundwater migration. A groundwater to surface water mixing model
approach was used to determine the potential surface water quality in the future
groundwater discharge zones. The full report for Roxboro groundwater
discharge to surface water under future conditions can be found in Appendix J.
General findings of the evaluation of future surface water conditions in potential
groundwater discharge areas include:
• The surface water mixing model evaluation confirms that predicted
resultant constituent concentrations in applicable surface waters are less
than 02B surface water standards. Therefore, the criteria for compliance
with 02B is met, allowing potential corrective action under 15A NCAC
02L .0106 (k) or (1).
• The predicted extent of COI -affected groundwater migration from Source
Area 3 would not reach the Intake Canal, based on predicted future
hydraulic head elevations and groundwater flow direction.
6.18.2 Water Supply Wells
(CAP Content Section 6.B.b)
No public or private drinking water wells or wellhead protection areas were
found to be located downgradient of Source Area 3 as discussed in Section 5.3.2.
Additional discussion regarding Source Area 3 is similar to Source Area 1
components as provided in Section 6.2.2.
6.18.2.1 Provision of Alternative Water Supply
A discussion regarding the provision of alternate water supply is provided
in Section 6.2.2.1.
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6.18.2.2 Findings of Drinking Water Supply Well Surveys
(CAP Content Section 6.B.b.ii)
A discussion regarding the finding from the drinking water supply well
survey is provided in Section 6.2.2.2.
6.18.3 Future Groundwater Use Areas Associated With Source
Area 3
(CAP Content Section 6.B.c)
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of Source Area 3. Therefore, no future groundwater use areas are
anticipated between Source Area 3 and the Intake Canal. Additional information
is provided in Section 6.2.3.
6.19 SA3 Human and Ecological Risks
(CAP Content Section 6.0
Primary conclusions from the human health and ecological risk assessment risk
assessment are that there is no evidence of unacceptable risks to on -Site or off -Site
human receptors potentially exposed to CCR constituents that may have migrated from
the ash basins and the DFAHA/GSA. There is no evidence of unacceptable risks to
ecological receptors potentially exposed to CCR constituents that may have migrated
from the ash basins and the DFAHA/GSA. A more detailed discussion regarding
human health and ecological risk associated with Source Area 3 can be found in Section
5.4. An update to the Roxboro human health and ecological risk assessment is included
in Appendix E.
6.20 SA3 Description of Remediation Technologies
The various remedial technologies that may be used to formulate comprehensive
groundwater remediation alternatives for consideration related to Source Area 3 is
similar to the technologies provided for Source Area 1 in Section 6.4. Technologies
retained for further consideration are used to formulate comprehensive groundwater
remedial alternatives in Section 6.23. A summary of the remedial technologies
presented in Section 6.4 and the rationale for either retaining or rejecting a specific
technology is similar to Source Area 1 as presented in Table 6-12.
6.21 SA3 Evaluation of Remedial Alternatives
(CAP Content Section 6.D)
Technologies evaluated and retained for consideration as discussed in Section 6.4 were
used to formulate the following three groundwater remedial alternatives to remediate
groundwater associated with Source Area 3:
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• Remedial Alternative 1: Monitored Natural Attenuation
• Remedial Alternative 2: Groundwater extraction
• Remedial Alternative 3: Groundwater extraction and clean water infiltration
These groundwater remedial alternatives are presented and described in the
following subsections. Information to address CAP Content Section 6.D.a.iv is
provided in Section 6.22 and Section 6.23.
6.21.1 Remedial Alternative 1 — Monitored Natural Attenuation
(CAP Content Section 6.D.a)
Alternative 1 is the use of MNA as a remedial alternative to address
groundwater COI concentrations associated with Source Area 3. Under this
alternative, compliance is predicted to be achieved in greater than 200 years after
the EAB closure is completed. A comprehensive analysis of MNA is provided in
Appendix I.
6.21.1.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
A limited number of CCR constituents in groundwater associated with
Source Area 3 occur to the north adjacent to the Intake Canal at
concentrations detected greater than applicable 02L standards, IMAC, or
background values, whichever is greater. Remediation goals are to restore
groundwater quality at Intake Canal boundary by returning COIs to
acceptable concentrations (02L/IMAC or background, whichever is greater),
or as closely thereto as is economically and technologically feasible
consistent with 15A NCAC 02L. 0106(a) (CAP Content Section 6.D.a.i.2).
The following groundwater COIs to be addressed by corrective action are
identified (Table 6-6) and discussed in Section 6.18: boron, sulfate, and
TDS.
The conceptual model and predictive modeling discussions summarize the
foundations for development of the MNA alternative. More extensive
discussion of the CSM can be found in Section 5.0, discussion of flow and
transport modeling in Appendix G, and discussion of geochemical
modeling in Appendix H.
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6.21.1.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
Based on the CSM (Section 5.0) and flow and transport modeling results
(Appendix G), the groundwater COIs associated with Source Area 3 are
hydraulically controlled by the Intake Canal to the north, by the eastern
discharge canal to the east and by the NPDES-permitted wastewater ponds
to the west.
No source control measures are planned for the DFAHA area; however,
Duke Energy is investigating the DFAHA/GSA to determine if operational
changes or engineering controls, outside of active remediation, are
warranted.
Currently, COIs in groundwater do not pose an unacceptable risk to human
health or the environment under conservative exposure scenarios and, if
implemented alone, MNA would not pose an unacceptable risk to human
health or the environment in the future. Source control and groundwater
monitoring would verify protection of human health and the environment
and to confirm model predictions. The applicable technologies that would
support Alternative 1 include groundwater monitoring wells within the
source area and near the unit boundaries. The MNA monitoring network
consists the existing monitoring wells near the DFAHA and GSA area for
monitoring the effectiveness of Alternative 1. These monitoring wells,
which are part of the current IMP, would continue to be sampled on a
semiannual basis to provide data to evaluate the performance of the
remediation.
6.21.1.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
Predictive modeling has been conducted to estimate when boron
concentrations would be reduced to 02L standards using MNA alone. The
simulations indicate boron concentrations would naturally attenuate to less
than the 02L standard in approximately 200 years after basin closure. The
flow and transport modeling report that provides the predictions for boron
is presented in Appendix G. Similarly, a geochemical modeling report is
presented in Appendix H.
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6.21.2 Remedial Alternative 2 - Groundwater Extraction
(CAP Content Section 6.D.a)
Alternative 2 consists of groundwater extraction for remediation of the
groundwater north of Source Area 3 including north of the area associated with
the comingling zone of Source Areas 1 and 3. Under this alternative, flow and
transport modeling indicates compliance with 02L would be achieved in
approximately 180 years after system startup and operation along the Intake
Canal.
6.21.2.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
A limited number of CCR constituents in groundwater associated with the
Source Area 3 occur north at concentrations detected greater than applicable
02L standards, IMAC, or background values, whichever is greater.
Remediation goals are to restore groundwater quality at or beyond the
Intake Canal boundary by returning COIs to acceptable concentrations
(02L/IMAC or background, whichever is greater), or as closely thereto as is
economically and technologically feasible consistent with 15A NCAC 02L.
0106(a) (CAP Content Section 6.D.a.i.2).
The conceptual model and predictive modeling discussions summarize the
foundations for development of the groundwater extraction alternative.
More extensive discussion of the CSM can be found in Section 5.0,
discussion of flow and transport modeling in Appendix G, and discussion
of geochemical modeling in Appendix H.
6.21.2.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
The applicable technologies that comprise this alternative include:
• 22 extraction wells along the intake canal by the GSA/DFAHA.
• Pumps, associated piping, and control systems
• Discharge piping and structure
The flow and transport model predicts a total groundwater extraction flow
rate of approximately 44 gpm. The number of extraction wells is estimated
based on flow and transport modeling results (Appendix G).
The system's design includes a large number of extraction wells to be
completed into bedrock to allow full drawdown within the transition (if
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saturated) and upper bedrock flow zones. Depths of bedrock extraction
wells are dependent on the current vertical distribution of COIs within
bedrock in these areas and ranges from 120 feet bgs to 180 feet bgs in the
design.
The distribution of conservation COIs (boron, sulfate, and TDS) represents
the area of maximum COI distribution at or beyond the DFAHA/GSA.
Focusing remedial action selection on addressing the mobile COIs will also
address the reactive COIs as they will follow the same flow path but with
greater attenuation. This alternative addresses all the Site specific COIs
through groundwater extraction. Because this alternative provides
hydraulic control and capture of boron, the most mobile COI, it addresses
all of the targeted COIs.
It is expected that extracted water would be discharged through the LRB by
way of the in -ground sump at the DFA silos area. The LRB discharges to
the wastewater discharge canal system through internal outfall 012B. The
discharge canal goes to the heated water discharge pond with discharge to
Hyco Reservoir through NPDES Outfall 003. Based on currently available
groundwater data, the current NPDES permit, and the draft permit issued
in 2018, the extracted discharge would not cause violations. A preliminary
summary of groundwater data and discharge permit limits is presented in
the table NPDES Permit Limits and Anticipated Groundwater Remediation
Parameter Levels as discussed in Section 6.4.5.
6.21.2.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
A groundwater extraction system would result in localized groundwater
flow control and removal of COI mass. The flow and transport report
(Appendix G) and geochemical modeling report (Appendix H) provide
detailed predictions, descriptions, and explanations of the effects of
groundwater extraction.
The flow and transport model predicts the maximum extent of the boron
plume, sourced from the DFAHA/GSA, at any point in time will be
approximately 400 feet to the Intake Canal (Appendix G). Simulations
indicate that boron concentrations in groundwater would meet the 02L
boron standard of 700 µg/L at the Intake Canal in approximately 180 years
after implementation.
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6.21.3 Remedial Alternative 3 — Groundwater Extraction with
Clean Water Infiltration
(CAP Content Section 6.D.a)
Alternative 3 consists of groundwater extraction with clean water infiltration for
remediation of the groundwater north of Source Area 3 including north of the
area associated with the comingling zone of Source Areas 1 and 3. This
alternative provides an effective combination of technologies for groundwater
remediation associated with Source Area 3. Under this alternative, flow and
transport modeling indicates compliance with 02L would be achieved in
approximately 9 years after system startup and operation along the Intake Canal
boundary.
6.21.3.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
A limited number of CCR constituents in groundwater associated with the
Source Area 3 occur north at concentrations detected greater than applicable
02L standards, IMAC, or background values, whichever is greater.
Remediation goals are to restore groundwater quality at the Intake Canal
boundary by returning COIs to acceptable concentrations (02L/IMAC or
background, whichever is greater), or as closely thereto as is economically
and technologically feasible consistent with 15A NCAC 02L. 0106(a).
The following groundwater COIs to be addressed by corrective action are
identified (Table 6-6) and discussed in Section 6.1: boron, sulfate, and TDS.
The conceptual model and predictive modeling discussions summarize the
foundations for development of the groundwater extraction and clean water
infiltration alternative. More extensive discussion of the CSM can be found
in Section 5.0, discussion of flow and transport modeling in Appendix G,
and discussion of geochemical modeling in Appendix H.
6.21.3.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
The applicable technologies that comprise this alternative include:
• 18 extraction wells along the Intake Canal north of the GSA/DFAHA.
27 infiltration wells along the Intake Canal north of the
GSA/DFAHA.
• Pumps, associated piping, and control systems
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• Discharge piping and structure
The flow and transport model predicts a total groundwater infiltration
system flow rate of approximately 76 gpm will be required and a total
groundwater extraction system flow rate of approximately 48 gpm. The
proposed design and well locations are shown on Figure 6-17a. The number
of extraction and infiltration wells is estimated based on flow and transport
modeling results (Appendix G). Table 6-24 summarizes the systems
extraction well and infiltration well information.
The system design includes a large number of extraction wells to be
completed to the shallow bedrock to allow full drawdown within the deep
(transition zone) and bedrock flow zones. Depths of extraction wells are
dependent on the contacts between the deep and bedrock flow zones and
fractures within the bedrock. As a result, extraction well depths would be
installed to a depth of 180 feet bgs in the design.
The system design also includes a large number of clean water infiltration
wells to be completed into the deep (transition zone) and bedrock flow
zones. Depths of infiltration wells are dependent on the contacts between
deep and bedrock flow zones and fractures within the bedrock. As a result,
infiltration well depths of 180 feet bgs in the design.
The distribution of conservation COIs (boron, sulfate, and TDS) represents
the area of maximum COI distribution at or beyond the GSA/DFAHA.
Focusing remedial action selection on addressing the mobile COIs will also
address the reactive COIs as they will follow the same flow path but with
greater attenuation. This alternative addresses all the Site specific COIs
through groundwater extraction and clean water infiltration. Because this
alternative provides hydraulic control and capture of boron, the most
mobile COI, it addresses all of the targeted COIs.
It is expected that extracted water would be discharged through the LRB by
way of the in -ground sump at the DFA silos area. The LRB discharges to
the discharge canal through internal outfall 012B. The discharge canal goes
to the heated water discharge pond with discharge to Hyco Reservoir
through NPDES Outfall 003. Based on currently available groundwater
data, the current NPDES permit, and the draft permit issued in 2018, the
extracted discharge would not cause violations. A preliminary summary of
groundwater data and discharge permit limits is presented in the table
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NPDES Permit Limits and Anticipated Groundwater Remediation Parameter
Levels in Section 6.4.4.
6.21.3.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
A groundwater extraction and clean water infiltration system would result
in localized groundwater flow control and increase the rate of mass
removal. While the low permeability of the formations will still limit flow,
the additional volume of groundwater created by infiltration will increase
the effectiveness of the system by flushing the system with clean water and
reducing COI concentrations. The flow and transport report (Appendix G)
and geochemical modeling report (Appendix H) provide detailed
predictions, descriptions, and explanations of the effects of groundwater
extraction and infiltration.
The flow and transport model predicts the maximum extent of the boron
plume at any point in time will be approximately 400 feet to the unit
boundary with the Intake. Predictive model simulations indicate that boron
concentrations in groundwater would meet the 02L boron standard of 700
µg/L at the Intake Canal boundary within approximately 9 years after
implementation.
6.22 SA3 Remedial Alternatives Screening Criteria
(CAP Content Section 6.D.a.iv)
The screening criteria used to evaluate technologies and alternatives for groundwater
corrective action associated with Source Area 3 are similar to Source Area 1 as
presented in Section 6.6. These screening criteria were used in evaluating the remedial
alternatives identified in Section 6.21.
6.23 SA3 Remedial Alternatives Criteria Evaluation
(CAP Content Section 6.D.a.iv)
Groundwater remediation Alternatives 1, 2, and 3 were formulated in Section 6.21
using groundwater remediation technologies evaluated and retained for consideration
in Section 6.22. The groundwater remediation alternatives formulated in Section
6.21 will undergo detailed comparative analysis in the following subsections. A
summary of the remediation alternative detailed analysis is also included in Appendix
M.
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6.23.1 Remedial Alternative 1: Monitored Natural Attenuation
Protection of Human Health and the Environment
(CAP Content Section 6.D.a.iv.1)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in risks
to human health related to Source Area 3 have been identified. The groundwater
corrective action is being planned to address regulatory requirements. The risk
assessment identified no unacceptable current human health or ecological risk
associated with groundwater downgradient of the ash basin. Water supply wells
are located upgradient of the Source Area 3 and water supply filtration systems
have been provided to those who selected this option. Surface water quality
standards downgradient of the COI -affected plume from Source Area 3 are also
met.
Based on the absence of receptors, it is anticipated that MNA would continue to
be protective of human health and the environment because modeling results
indicate COI concentrations will diminish with time. Natural attenuation
mechanisms will reduce COI concentrations, and model predictions indicate that
no existing water supply wells would be impacted.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
MNA would comply with applicable regulations assuming the conditions
provided in 02L can be achieved. State and federal groundwater regulations
allow for MNA as an acceptable remediation program if regulatory requirements
are met. Appendix I includes a detailed evaluation of the applicability of
Alternative 1: MNA as a remedial alternative for the Site.
Long -Term Effectiveness and Permanence
(CAP Content Section 6.D.a.iv.3)
MNA would be an effective long-term technology, assuming source control and
institutional controls (such as an RS designation) for the affected area. Natural
attenuation mechanisms are understood and have been documented
(Appendix I). Once equilibrium conditions of COI concentrations less than 02L
standards are achieved, it is predicted the concentrations would not increase.
Implementation of MNA will not result in increased residual risk as current
conditions and predicted conditions do not indicate unacceptable risk to human
health or environment. The adequacy and reliability of this approach would be
documented with the implementation and maintenance of an effectiveness
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monitoring program to identify variations from the expected conditions. If
factors that are not known at this time were to affect the attenuation process in
the future, alternative measures could be taken. Monitoring will be in place to
evaluate progress and allow sufficient time to implement changes.
Reduction of Toxicity, Mobility, and Volume
(CAP Content Section 6.D.a.iv.4)
MNA can reduce aqueous concentrations while increasing solid phase
concentrations and can therefore, under certain geochemical conditions, reduce
COI plume concentrations, volume, and mass. There are no treatment or
recycling processes involved with MNA as well as no residuals.
Short-term Effectiveness
(CAP Content Section 6.D.a.iv.5)
The stability and limited areal extent of the COI plume, along with no
unacceptable risks to human and ecological receptors, indicate current conditions
are protective. Therefore, the technology is effective in the short-term.
There are 172 monitoring wells installed at the Roxboro site including wells
associated with the EAB and the GSA/DFAHA. Although some wells within the
immediate area of the EAB will have to be abandoned as part of the closure
process, monitoring wells along and within the GSA/DFAHA unit boundaries
will remain to monitor natural attenuation in the short-term.
Technical and Logistical Feasibility
(CAP Content Section 6.D.a.iv.6)
There are 172 monitoring wells installed at the Roxboro site including wells
associated with the EAB and the GSA/DFAHA. A majority of the wells have
dedicated sampling equipment and an approved interim monitoring plan is in
place. A subset of these monitoring wells could be immediately used for MNA
purposes. Therefore, the technology could be implemented easily.
Time Required to Initiate and Implement Corrective Action
Technologies and Alternatives
(CAP Content Section 6.D.a.iv.7)
The time required for implementation of an MNA program could be as
immediate as approval of the approach since an extensive monitoring well
network already exists. Procedures for collection, analysis, and communication
of results are also established and currently in place.
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Predicted Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that concentrations of COIs would meet
02L standards at the Intake Canal boundary in approximately 200 years after ash
basin closure (Appendix G). This estimate is based on boron reaching a
concentration of 700 µg/L at the unit boundary with the Intake Canal.
Cost
(CAP Content Section 6.D.a.iv.9)
Roxboro has an extensive groundwater monitoring well networks in place. MNA
performance monitoring for Source Area 3 would utilize a subset of existing
wells on Site. Procedures for collection, analysis, and communication of results
are also established and currently in place. Because there would be less required
materials and therefore a smaller capital cost and annual cost, the costs of
Alternative 1 would be comparatively less, when compared to Alternatives 2 and
3. Despite this, the significantly longer lifetime of the Alternative 1 system
operating (approximately 200 years) indicates that life cycle costs could be
significant.
Community Acceptance
(CAP Content Section 6.D.a.iv.10)
It is expected that there will be positive and negative sentiment about
implementation of an MNA program. No landowner is anticipated to be affected.
The property is owned by Duke Energy which is anticipated to have institutional
controls. However, until the final corrective action is developed and comments
are received and reviewed, assessment of community acceptance will not be fully
informed.
Adaptive Site Management and Remediation Considerations
MNA is an adaptable process and can be an effective tool in identifying the need
for alternative approaches if unexpected changes in Site conditions occur. An
MNA program would not hinder or preempt the use of other remedial
approaches in the future if conditions change. In fact, an effectiveness monitoring
program is an essential part of any future remedial strategy. An MNA
effectiveness monitoring program for Source Area 3 would provide information
about changing Site conditions during and after source control measures.
Sustainability
The footprint of Alternative 1 was quantified based on energy use and associated
emissions, during groundwater monitoring activities (e.g., transportation). The
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results of the footprint calculations for MNA are summarized in Table 6-25. A
summary of sustainability calculations for Alternative 1 can be found in
Appendix L.
The footprint of the MNA alternative is the least energy -intensive of the remedial
alternatives being considered, providing reduced, comparative footprint metrics
in overall energy use and across all air emission parameters. The MNA
alternative utilizes significantly fewer resources throughout the cleanup
timeframe when compared to the other alternatives.
6.23.2 Remedial Alternative 2 - Groundwater Extraction
Protection of Human Health and the Environment
(CAP Content Section 6.D.a.iv.1)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in risks
to human health related to the Source Area 3 have been identified. The
groundwater corrective action is being planned to address regulatory
requirements. The risk assessment identified no unacceptable current human
health or ecological risk associated with groundwater downgradient of Source
Area 3. Water supply wells are located upgradient of Source Area 3 and water
supply filtration systems have been provided to those who selected this option.
Surface water quality standards downgradient of the COI -affected plume are
also met. Based on the absence of receptors, it is anticipated that groundwater
extraction would create conditions that continue to be protective of human
health and the environment because the COI concentrations will diminish with
time.
By extracting COI mass within the existing COI plumes, which are not affecting
receptors, active groundwater extraction would further protect human health
and the environment. Therefore, water supply wells would remain unaffected by
COIs related to Source Area 3.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
Groundwater extraction would comply with applicable regulations. Those
regulations would include: CAMA, groundwater standards, and extraction well
installation and permitting. Discharge of extracted water would be in compliance
with appropriate discharge requirements, such as pH or other COI limitations in
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the NPDES permit and proper operation and maintenance of an effectiveness
monitoring system.
Activities will also be in compliance with applicable regulations with proper
operation and maintenance of an effectiveness monitoring system
Long-term Effectiveness and Permanence
(CAP Content Section 6.D.a.iv.3)
Groundwater extraction may contribute to effective and permanent achievement
of groundwater standards. Although, as indicated by the modeling results for
this alternative, extraction flow rates would be low. Predictive modeling results
indicate that the 02L standard for boron could be achieved in approximately 180
years following full-scale implementation. However, it still can provide a benefit
through hydraulic capture, which is a significant factor in achieving remedial
objectives. If factors that are not known at this time were to affect the
remediation process in the future, alternative measures could be taken to modify
the remedial approach.
Reduction of Toxicity, Mobility, and Volume
(CAP Content Section 6.D.a.iv.4)
Groundwater extraction would remove constituent mass from the area of
regulatory concern. The extracted groundwater would be appropriately treated
and discharged according to applicable regulatory requirements. It is anticipated
that extracted groundwater would be discharged to Hyco Reservoir through the
NPDES permitted Outfall 003. Analysis of predicted specific COI concentrations
and mass in extracted groundwater during conceptual design of the remediation
system may be completed to further assess compliance with discharge regulatory
requirements. Treatment technologies for extracted groundwater will be
evaluated after NCDEQ approves the CAP Update and after pilot testing for the
proposed extraction system is complete.
Short-term Effectiveness
(CAP Content Section 60.a.iv.5)
The stability and limited extent of the COI plume, along with the absence of
completed exposure pathways, indicates there are no short-term effects on the
environment, workers or the local community. While there are areas with COI
concentrations greater than 02L concentrations, the areas are not presenting
unacceptable short-term risks. Hydraulic capture of groundwater would occur as
soon as the groundwater extraction system is placed into service.
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Technical and Logistical Feasibility
(CAP Content Section 6.D.a.iv.6)
Installation of the proposed a groundwater extraction system would require
significant efforts in planning, designing, and execution of site preparation. The
extensive layout of groundwater remediation system wells, piping, and
treatment system components, as well as site topography and access constraints
pose significant challenges to constructability. However, with early awareness of
the aforementioned complexities and effective communications between the
design, implementation and project management teams, successful construction
of the system would be anticipated.
Time Required to Initiate and Implement Corrective Action
Technologies and Alternatives
(CAP Content Section 6.D.a.iv.7)
Design and installation of the system could be completed in approximately two
to three years after CAP approval.
Predicted Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that concentrations of COIs would meet
02L standards at the unit boundary with the Intake Canal in approximately 180
years.
Cost
(CAP Content Section 6.D.a.iv.9)
The cost estimate for Alternative 2 is based on capital costs for design and
implementation, the O&M costs and monitoring costs, including well
redevelopment and replacement on an annual basis. The design costs include
work plans, design documents and reports necessary for implementation of the
alternative. Implementation costs include procurement and construction. O&M
costs are based on annual routine labor, materials and equipment to effectively
conduct monitoring, routine annual and 5-year reporting, as applicable, and
routine and non -routine maintenance costs.
Due to the increase in materials and equipment required, the capital cost and
annual cost would be more than Alternative 1 and less than Alternative 3.
Because Alternative 3 requires the additional material and equipment for clean
water infiltration, the capital and operating cost would be greater than
Alternative 2. Despite this, the significantly longer lifetime of the Alternative 2
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system operating indicates that the life cycle costs would likely be the largest of
the three alternatives.
Community Acceptance
(CAP Content Section 6.D.a.iv.10)
It is expected that there will be positive and negative sentiment about
implementation of a groundwater extraction system. No landowner is
anticipated to be affected. It is anticipated that the extracted groundwater would
be discharged through a NPDES permitted outfall that flows to Hyco Reservoir
and that the discharge would meet all permit limits. A groundwater extraction
system which addresses potential COI plume expansion north of the
GSA/DFAHA to the Intake Canal may improve public perception. Until the final
Site remedy is developed and comments are received and reviewed, assessment
of community acceptance will not be fully known.
It is anticipated that groundwater extraction would generally receive more
positive community acceptance than MNA under Alternative 1 since it involves
more active measures to attempt physical extraction of COI mass from
groundwater. This alternative would likely be perceived as more robust than
MNA in addressing groundwater impacts.
Adaptive Site Management and Remediation Considerations
Groundwater extraction using conventional well technology is an adaptable
process. It can be easily modified to address changes to COI plume configuration
or COI concentrations. Individual well pumping rates can be adjusted or
eliminated or additional wells can be installed to address COI plume changes.
Also, while it is not expected, treatment of the system discharge can be modified
to address changes in COI concentrations or permit limits.
Sustainability
The footprint was quantified based on energy use and associated emissions,
during the construction phase (e.g., material quantities and transportation),
active remediation activities (e.g., groundwater pumping) and groundwater
monitoring activities (e.g., transportation). The results of the footprint
calculations for Alternative 2 are summarized in Table 6-25. A summary of
sustainability calculations for Alternative 2 can be found in Appendix L.
The footprint of Alternative 2 is the most emission -intensive remedial alternative
being considered. Alternative 1 requires significantly less materials and energy
than Alternative 2 and is therefore characterized by a dramatically smaller
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footprint. Alternative 2 presents lower, but generally comparable, energy
consumption metrics when measured against Alternative 3. Although
Alternative 2 uses extraction wells, no clean -water infiltration wells are used
generating a lower material -related environmental footprint for the construction
phase. However, the extended timeframe of remediation system operation for
Alternative 2 (approximately 180 years) when compared to Alternative 3
(approximately 9 years) requires energy usage and produces air emissions
exceeding the levels of Alternative 3. The quantitative analysis of the footprints
of the remedial alternatives under consideration for this CAP indicates
Alternative 2 to be the least sustainable option.
6.23.3 Remedial Alternative 3 —Groundwater Extraction and
Clean Water Infiltration
Protection of Human Health and the Environment
(CAP Content Section 6.D.a.iv.1)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in risks
to human health related to Source Area 3 have been identified. The groundwater
corrective action is being planned to address regulatory requirements. The risk
assessment identified no unacceptable human health or ecological risk associated
with groundwater downgradient of Source Area 3. Water supply wells are
located upgradient of Source Area 3 and water supply filtration systems have
been provided to those who selected this option. Surface water quality standards
downgradient of the COI -affected plume are also met. Based on the absence of
receptors, it is anticipated that groundwater extraction and clean water
infiltration would create conditions that continue to be protective of human
health and the environment because the COI concentrations will diminish with
time.
By extracting COI mass within the existing COI plumes, which are not affecting
receptors, active groundwater extraction and clean water infiltration would
further protect human health and the environment. While the low permeability
of the formations will still limit flow, the additional volume of infiltration water
created will increase the effectiveness of the system in enhancing COI mass
movement for extraction. Therefore, water supply wells would remain
unaffected by COIs related to the source area.
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Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
Groundwater extraction and clean water infiltration would comply with
applicable regulations. Those regulations would include: CAMA, groundwater
standards, infiltration and extraction well installation and permitting. Discharge
of extracted water would be in compliance with appropriate discharge
requirements, such as pH or other constituent limitations in the NPDES permit
and proper operation and maintenance of an effectiveness monitoring system.
The water supply for clean water infiltration wells will be from an unaffected
groundwater source; therefore, additional permitting may be required.
Activities will also be in compliance with applicable regulations with proper
operation and maintenance of an effectiveness monitoring system.
Long-term Effectiveness and Permanence
(CAP Content Section 6.D.a.iv.3)
Groundwater extraction combined with clean water infiltration will contribute to
effective and permanent achievement of groundwater standards by facilitating
movement of affected groundwater such that the COI plume is hydraulically
controlled and COI mass is more effectively removed as predicted by modeling
results.
The adequacy and reliability of this approach would be documented with the
implementation of an effectiveness monitoring program that would identify
variations from the expected outcome. If factors that are not known at this time
were to affect the remediation process in the future, alternative measures could
be taken to modify the remedial approach.
Reduction of Toxicity, Mobility, and Volume
(CAP Content Section 6.D.a.iv.4)
Groundwater extraction combined with clean water infiltration would remove
constituent mass from the area of regulatory concern. The extracted groundwater
would be appropriately treated and discharged according to applicable
regulatory requirements. It is anticipated that extracted groundwater would be
discharged through the NPDES permitted Outfall 003. Analysis of predicted
specific COI concentrations and mass in extracted groundwater during
conceptual design of the remediation system may be completed to further assess
compliance with discharge regulatory requirements. Treatment technologies for
clean water infiltration and extracted groundwater will be evaluated after
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NCDEQ approves the CAP Update and after pilot testing for the proposed
extraction and infiltration system is complete.
Short-term Effectiveness
(CAP Content Section 6.D.a.iv.5)
The stability and limited extent of the COI plume, along with the absence of
completed exposure pathways, indicates there are no short-term effects on the
environment, workers or the local community. While there are areas with COI
concentrations greater than 02L concentrations, the areas are not presenting
unacceptable short-term risks. Hydraulic control and capture of groundwater
would occur as soon as the groundwater extraction and clean water infiltration
system is placed into service.
Technical and Logistical Feasibility
(CAP Content Section 6.D.a.iv.6)
Installation of the proposed groundwater extraction and clean water infiltration
system would require significant efforts in planning, designing, and execution of
site preparation. The extensive layout of groundwater remediation system wells,
piping, and treatment system components, as well as site topography and access
constraints pose significant challenges to constructability. However, with early
awareness of the aforementioned complexities and effective communications
between the design, implementation and project management teams, successful
construction of the system would be anticipated.
Time Required to Initiate and Implement Corrective Action
Technologies and Alternatives
(CAP Content Section 6.D.a.iv.7)
Design and installation of the system could be completed in approximately two
to three years after CAP approval.
Predicted Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that concentrations of COIs would meet
02L standards at the unit boundary with the Intake Canal in approximately 9
years after implementation.
Cost
(CAP Content Section 60.a.iv.9)
The cost estimate for Alternative 3 is based on capital costs for design and
implementation, the O&M costs and monitoring costs, including well
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redevelopment and replacement on an annual basis. The design costs include
work plans, design documents and reports necessary for implementation of the
alternative. Implementation costs include procurement and construction. O&M
costs are based on annual routine labor, materials and equipment to effectively
conduct monitoring, routine annual and 5-year reporting as applicable, and
routine and non -routine maintenance costs. The estimated costs for this
alternative are presented in Appendix K.
The increase in materials and equipment required, the capital cost and annual
cost would be significantly more than Alternative 1. Relative to Alternative 2,
additional material and equipment would be required for clean water
infiltration; therefore, the capital and the operating cost would be greater than
Alternative 2. Despite this, the significantly less lifetime of the Alternative 3
system operating indicates that the life cycle costs would be the least of the three
alternatives.
Community Acceptance
(CAP Content Section 6.D.a.iv.10)
It is expected that there will be positive and negative sentiment about
implementation of a groundwater extraction and clean water infiltration system.
No landowner is anticipated to be affected as the affected property is owned by
Duke Energy. It is anticipated that the extracted groundwater would be
discharged through a NPDES permitted outfall that flows to the Hyco Reservoir.
A groundwater extraction and clean water infiltration system which addresses
potential COI plume expansion north of the GSA/DFAHA may improve public
perception. Until the final Site remedy is developed and comments are received
and reviewed, assessment of community acceptance will not be fully known.
It is anticipated that groundwater extraction combined with clean water
infiltration would receive more positive community acceptance than Alternative
1 or Alternate 2 since it involves more active measures and results in a
significantly shorter timeframe to meet applicable groundwater standards.
Adaptive Site Management and Remediation Considerations
Groundwater extraction and clean water infiltration using conventional well
technology is an adaptable process. It can be easily modified to address changes
to COI plume configuration or COI concentrations. Individual well infiltration
and pumping rates can be adjusted or eliminated or additional wells can be
installed to address COI plume changes. Also, while it is not expected, treatment
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of the system discharge can be modified to address changes in COI
concentrations or permit limits.
Sustainability
The footprint of Alternative 3 was quantified based on energy use and associated
emissions, during the construction phase (e.g., material quantities and
transportation), active remediation activities (e.g., groundwater pumping and
treatment) and groundwater monitoring activities (e.g., transportation). The
results of the footprint calculations for Alternative 3 are summarized in Table 6-
25. A summary of sustainability calculations for Alternative 3 can be found in
Appendix L.
The footprint of Alternative 3 is the second most emission -intensive of the
remedial alternatives being considered. Alternative 1 (MNA) requires
significantly less materials and energy than Alternative 3 and is therefore
characterized by a dramatically smaller footprint. Alternative 3 presents higher,
but generally comparable, footprint metrics when measured against Alternative
2. Alternative 3 utilizes clean -water infiltration wells as compared to Alternative
2, generating a higher material -related footprint for the construction phase. The
analysis indicates operating the infiltration well network to be more energy -
intensive in Alternative 3 than Alternative 2, as well. However, the reduced
timeframe of remediation system operation for Alternative 3 (approximately 9
years) when compared to Alternative 2 (approximately 180 years) produces air
emissions approaching the levels of Alternative 3. Opportunities for system
optimization and energy savings could be pursued throughout the remediation
timeframe, as conditions change and component technologies possibly evolve.
6.24 SA3 Proposed Remedial Alternative Selected For Source Area 3
(CAP Content Section 6.E)
Based on the alternatives detailed analysis presented in Section 6.23 and summarized in
Appendix L, the selected remedy for groundwater remediation is Alternative 3,
Groundwater Extraction and Clean Water Infiltration.
6.24.1 Description of Proposed Remedial Alternative and
Rationale for Selection
(CAP Content Section 6.E.a)
The selected remedy for groundwater remediation, Alternative 3, is intended to
provide the remedial technology that has demonstrated to provide the most
effective means for restoration of groundwater quality downgradient of Source
Area 3 by returning COIs to acceptable concentrations (02LAMAC or
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background, whichever is greater), or as closely thereto as is economically and
technologically feasible, consistent with 15A NCAC 02L. 0106(a), and to address
15A NCAC 02L .0106(j) (CAP Content Section 6.E.a.i).
This alternative meets the correction action objectives described in Section 1.0 of
this CAP Update in the expeditious timeframe through groundwater extraction
and clean water infiltration. Although there are no unacceptable risks to human
or ecological receptors, the alternative will meet the regulatory requirements
most effectively.
The groundwater remediation system includes 18 vertical extraction wells and 27
vertical clean water infiltration wells. It also includes all associated piping and
controls in order to discharge the extracted water to the LRB. Figure 6-17a
provides a conceptual layout of the proposed groundwater extraction and clean
water infiltration system. Model results predict the 02L standard of 700 µg/L for
boron will be achieved at the Intake Canal boundary approximately 9 years after
remedial alternative implementation (Figure 6-17e).
All three groundwater remedial alternatives evaluated contribute to continued
protection of human health and the environment, however, the approach of
groundwater extraction combined with clean water infiltration appears to be the
most practical solution given the predicted time frames for 02L compliance.
Rationale for selections follows, and is based off multiple lines of evidence,
including empirical data collected at Roxboro, geochemical modeling, and
groundwater flow and transport modeling.
Alternative 1 relies on natural attenuation processes and, while there is evidence
to suggest that natural attenuation is occurring, one or more levels of the MNA
tiered analysis did not meet evaluation criteria since the predicted timeframe to
achieve applicable criteria at the Intake Canal boundary is approximately 200
years. More detail on the results from the MNA tiered analysis and why MNA
alone is not an appropriate corrective action solution at this time can be found in
Appendix I. MNA may be an appropriate polishing remedy in the future.
Alternative 2, groundwater extraction is projected to satisfy remedial action
objectives in a quicker timeframe (approximately 180 years) as compared to
MNA (approximately 200 years). Alternative 3, groundwater extraction and
infiltration is projected to satisfy remedial action objectives in a shorter
timeframe (approximately 9 years).
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Although groundwater extraction from Alternative 2 and groundwater
extraction and clean water infiltration from Alternative 3 involve verified
remedial technologies and provide a long-term and permanent approach,
Alternative 3 is a more robust system that uses clean water infiltration to flush
COIs from the area. Relative to Alternative 2, Alternative 3 would accelerate
removal of COI mass from the groundwater system achieving compliance within
a shorter timeframe. The long-term effectiveness would be documented through
an effectiveness monitoring program as provided in Appendix O.
For both Alternative 2 (groundwater extraction) and Alternative 3 (groundwater
extraction and clean water infiltration) for the GSA/DFAHA are adaptable
approaches. Either system could be modified relatively easily if conditions
change. The addition of wells or adjusting well pumping schemes can be readily
accomplished.
Of the three alternatives evaluated in the CAP Update, Alternative 3 has the
highest estimated cost. While cost is a factor in selection, it should be weighed
against the other criteria in meeting remediation goals especially time to achieve
compliance. The fact that groundwater extraction and infiltration is adaptable
and could be modified to address changing conditions should also be considered
in the cost evaluation.
Groundwater extraction or groundwater extraction with clean water infiltration
generate larger footprints in the sustainability analysis than MNA. However,
during design phases of the groundwater remediation project, opportunities for
energy efficiency and reduction of the project footprint can be evaluated. The
adaptability considerations that affect the cost analysis also should be considered
in sustainability considerations. Potential duplication of intensive construction
efforts should be considered.
This alternative is readily implementable, although it is the most costly
alternative due to the addition of the extraction wells. The long-term
effectiveness would be documented through an effectiveness monitoring
program detailed in Section 6.8.6. The system would be adaptable based on
effectiveness monitoring field data results.
6.24.2 Design Details
(CAP Content Section 6.E.b)
Design of the proposed clean water infiltration and groundwater extraction
system would require a pilot test (i.e., installation of a portion of the system) to
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facilitate refinement of the final system design. A pilot test work plan will be
prepared to facilitate implementation of the system. As part of this process, the
groundwater flow and transport model may be refined to determine the final
number and locations of system wells. As the pilot testing and design process
evolves, refinements to the systems and timeframe, including a potential
reduction in the time needed to achieve compliance may occur compared to the
model predictions presented in this CAP Update.
The intent of the design would be to maximize pore volume exchange (i.e.
groundwater flushing) and establish groundwater flow control and capture in
areas downgradient of Source Area 3. Basic installation components of the
recommended alternative include:
• 18 extraction wells and appurtenances
• 27 clean water infiltration wells and appurtenances
• Well vault and wellhead piping, fittings, and instrumentation
• A system to control water level within each groundwater extraction well
• Groundwater extraction system discharge piping
• Clean water infiltration pre-treatment system
• Piping to transfer water from the clean water infiltration water supply
wells to the infiltration water treatment system
• Clean water Infiltration water distribution system
• Electric power supply
• Groundwater remediation telemetry system
• pH adjustment or other treatment systems, if necessary
Conceptual process flow diagrams for infiltration and extraction, and treatment
systems are provided on Figures 6-18a and 6-18b. The detailed design elements
presented below may be adjusted based on a final technical review.
6.24.2.1 Process Flow Diagrams for All Major Components
of Proposed Remedy
(CAP Content Section 6.E.b.i)
Below is a multi -step process for remedy design considerations and
implementation of major components, including design assumptions,
calculations, and specifications where applicable at the conceptual design
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stage. Conceptual process flow diagrams for extraction and treatment
systems are provided on Figure 6-18b.
Site Preparation (STEP 1 — Create Access)
Installation of the proposed groundwater extraction and clean water
infiltration system would require significant efforts in planning, designing,
and execution of site preparation. The extensive layout of groundwater
remediation system wells, piping, and treatment system components, as
well as railroad access constraints pose significant challenges to
constructability. However, with early awareness of the aforementioned
complexities and effective communications between the design,
implementation and project management teams, successful construction of
the system would be anticipated.
Safe access roads for mobile construction equipment (e.g., drill rigs), as well
as long-term operation and maintenance needs, will likely require clearing,
grubbing, grading and access improvement.
A certain level of flexibility regarding well placement is expected to be
required due to site conditions encountered during construction. Prior to
construction and following the pump tests, an assessment of the precise
locations of wells would be made in collaboration with the modeler. If the
model predictions are not affected, relocation from the predetermined
location due to terrain or other site -specific constraints would expedite
construction.
Land disturbance, anticipated to include some vegetation removal and
grubbing, will require erosion and sedimentation control to be implemented
and likely reviewed and approved by a regulatory agency. Adaptable E&SC
should be planned to limit project delays by avoiding formal modifications
of plans.
Additionally, arrangements will be required in order to maintain an
acceptable minimum working distance from the railroad tracks for safety.
Pilot Tests (STEP 2 — To Finalize Design)
A pilot test would involve installation of a portion of the planned system to
evaluate how the system performs and to make initial progress towards
remediation at the same time. The results of the pilot test would be used to
refine and scale up the final design thereby maximizing the likelihood of
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successful operation in the field. Clean water infiltration tests would be
conducted to determine the infiltration rates of clean water infiltration wells
screened within or across saprolite, transition zone, and bedrock flow
zones.
Extraction pilot test wells will be screened within or across a flow zones, as
similar to model simulations to the feasible. Extraction pilot test results will
be used to:
• Determine site -specific well yields for each flow zone
• Validate predictive flow and transport modeling
• Refine calibration predictive flow and transport modeling as needed
• Confirm groundwater extraction well capture zones in the saprolite,
transition and bedrock flow zones beyond available data
• If warranted, make adjustments to the groundwater extraction
system design
• If warranted, make design adjustments to conveyances for extracted
groundwater
• If warranted, make design adjustments to the groundwater treatment
system
Clean water infiltration test wells will be screened within or across flow
zones, similar to model simulations to the extent feasible. Groundwater
infiltration pilot test results will be used to:
• Determine site -specific well infiltration rates
• Validate predictive flow and transport modeling
• If warranted, make adjustments to the clean water infiltration system
design
• If warranted, make design adjustments to conveyances for clean
water infiltration
• If warranted, make design adjustments to the clean water infiltration
treatment system
The extraction and clean water infiltration wells used for pilot testing would
be included in the final groundwater remediation system design.
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Extraction and Clean Water Infiltration Well Design (STEP 3
- Install Wells)
(CAP Content Section 6.E.b.i)
The preliminary design for the groundwater remediation system includes
installation of 27 clean water infiltration wells and 18 extraction wells
(Figures 6-17a). The extraction and clean water infiltration wells would be
installed north of the DFAHA/GSA adjacent to the Intake Canal. The
locations are based on predicted COI plume configuration, with the intent
of capturing groundwater to create groundwater flow control, COI mass
removal, and reduced migration of potentially mobile COIs. The predicted
effects of the wells are defined in detail in flow and transport modeling
results (Appendix G).
Groundwater extraction and clean water infiltration wells would be
completed in the saprolite, transition zone and bedrock to anticipated
depths of 180 feet bgs. Groundwater infiltration and extraction wells would
be installed by a North Carolina licensed well driller in accordance with
NCAC 15A, Subchapter 2C - Well Construction Standards, Rule 108
Standards of Construction: Wells Other Than Water Supply (15A NCAC
02C .0108). Modeled extraction well details are provided on Table 6-15.
The groundwater extraction and clean water infiltration wells might be
drilled using hollow stem auger, air percussion/hammer, sonic drilling
methods, or a combination thereof. The drilling method would depend on
Site conditions. Completed wells would be at least 6 inches in diameter to
facilitate the installation of pumps and instrumentation (e.g., level control)
in groundwater extraction and infiltration wells. The top of the sand pack
would extend to approximately 2 feet above the top of well screens. A
bentonite well seal at least 2 feet thick would be installed on top of the sand
pack. Neat cement grout with 5 percent bentonite would be placed on top of
the bentonite well seal and would fill the remaining well annulus to within
3 feet of the ground surface. The groundwater clean water infiltration wells
and extraction wells would be constructed with threaded casings. Materials
of construction and screen lengths and slot sizes will be based on pilot
testing. Wound wedge wire screens might be used to enhance hydraulic
efficiency and facilitate rehabilitation. All materials and installations would
be in accordance with 15A NCAC 02C. Typical well construction
schematics for infiltration and extraction wells are included as Figure 6-18b
and Figure 6-18c.
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Well Head Configuration (STEP 4 — Construct Well Heads)
(CAP Content Section 6.E.b.i)
The proposed extraction and clean water infiltration well vaults would be
precast concrete with aluminum access doors that include a drainage
channel. The concrete enclosures would be finished below grade and the
piping and fittings in the enclosures would be Type 304 stainless steel to
reduce risk of damage during O&M.
Any above ground piping would be insulated and heat traced. The piping
would transition from the Type 304 stainless steel to high density
polyethylene (HDPE) at a flange near the opening where the HDPE pipe
leaves the enclosure. The buried sections of pipe would be fusion -welded
HDPE (Figure 6-18d).
The enclosures would have a 2-inch drain with a compression cap for
controlled release of rainwater or condensate. A water level sensor would
be mounted on the wall of the enclosure approximately 6-inches above the
floor. Should water accumulate to that level, the extraction pump or
infiltration water would be stopped and an alarm sent to the operator, who
can ascertain the cause of the high water level.
Clean Water Infiltration Wells (STEP 5)
(CAP Content Section 6.E.b.i)
A suitable water source for infiltration is required. As presented in the
comprehensive analytical data table (Appendix Q Table 2), the quality of
the water in the Intake Canal with an average concentration of 650 µg/L
boron, which is the most convenient source of clean water, excludes the
water from the Intake Canal as a viable source for infiltration. The quality
of water in the background bedrock monitoring well, MW-28BR, appears
suitable for infiltration water with treatment for iron, manganese and
vanadium, if necessary (Appendix Q Table 1). Additional water quality
testing on MW-28BR and drawdown pilot tests will be conducted to further
assess the ability of this area to produce 76 gpm of water of acceptable
quality. Based on data from MW-28BR, the groundwater may require
treatment for background levels of iron, manganese, and vanadium which
will be further evaluated during the design phase.
The water for infiltration would be stored in a tank near the well system
and an HDPE distribution header would convey the infiltration water from
the infiltration water treatment system to each clean water infiltration well
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(Figure 6-17b). A seal at the top of the well through which the infiltration
pipe and wiring would enter the well and would be designed to be leak
free.
The hydraulic head at each clean water infiltration well would be controlled
by a pressure control valve. Twenty -feet of water (8.68 pounds per square
in. gauge) is the infiltration pressure used in the predictive groundwater
flow and transport model, but the pressure could be increased or decreased
to achieve performance objectives. Operation of the clean water infiltration
wells would comply with 15A NCAC 02C.0225. Infiltration pressures and
rates would be determined in pilot testing based on the hydraulic
conductivity of the strata receiving the clean water.
The amount of water flowing into the clean water infiltration wells would
be measured by a flow rate and flow totalizing meter. At startup, a ball
valve at the top of the well would be opened to allow water to displace the
air in the well and system piping. Also, pressure transducers installed at
the top of each infiltration well would monitor well head pressures (Figure
6-17b).
Other appurtenances in the piping system would include a pressure gauge,
ball valves to isolate piping for maintenance, and a solenoid valve that
would close to stop the flow of infiltration water in the event high water
level in the vault.
Operational parameters, such as infiltration flow rate, totalized infiltration
flow, and well head pressure, as well as critical malfunctions such as
accumulation of water in the well vault would be transmitted to the
groundwater remediation system owner via telemetry system.
Extraction Wells (STEP 6)
(CAP Content Section 6.E.b.i)
The purpose of the proposed collection system is to convey extracted
groundwater to the sump near the existing DFA silos for conveyance to the
existing LRB.
A pump would be installed in each groundwater extraction well. Selection
of pump type (e.g., electric submersible or pneumatic) would be determined
in the final design. If the water level in the well is above the top water level
switch, the pump would run to pump the water to lower water level switch,
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which would cause the pump shut off. The flow of extracted groundwater
from the pump would be measured using a flow rate and flow totalizer
meter before being conveyed to groundwater discharge piping for disposal
(Figure 6-18b). Other appurtenances in the piping system would include:
• a check valve to prevent back flow into the well,
• a sampling port, a pressure gauge to indicate the pressure generated
by the pump,
• ball valves to isolate piping for maintenance, and
• a flow control valve such as a stainless steel globe or gate valve
(Figure 6-17c).
Operational parameters, such as flow and water level, and critical
malfunctions, such as accumulation of water in the well vault, would be
transmitted via telemetry system to inform the system operator of the status
in the well and enclosure.
Clean Water Infiltration Water Treatment (STEP 7 — Build
Infiltration Treatment)
Water used for clean water infiltration will be obtained from a water supply
well in an area of the Site with unaffected groundwater. Once collected
from the well, pumps would pump the raw water to equalization tanks. If
the water quality is not suitable for infiltration, the groundwater would be
treated in a modular treatment system (Figure 6-18a). The equalization
tanks and the modular treatment systems would be located in the proximity
of the infiltration system near the production well(s). The treatment system
would condition the water, as necessary, prior to storage and distribution to
the infiltration wells.
Parallel treatment processes would facilitate infiltration system operation
and maintenance and should achieve optimal runtime and
performance. Individual system components (e.g., vertical turbine pumps,
equalization tanks, modular treatment system or transfer pumps) could be
operated singularly or in parallel and achieve 100 percent groundwater
infiltration capacity. Liquid waste materials generated as a result of
maintenance (e.g., filter backwash or wash water) would be directed to the
LRB through the DFA silo sump. The equalization tanks, treatment system,
transfer pumps, and holding tank would be housed in an enclosed structure
to prevent exposure to prevailing weather conditions.
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Groundwater Extraction Water Treatment (STEP 8 —
Address Groundwater Treatment)
(CAP Content Section 6.E.b.i)
Extracted groundwater would be treated by conveyance to the LRB at the
site through the DFA silo sump. The water would discharged through the
permitted outfalls. Extracted groundwater would undergo any treatment
processes applicable to the LRB to satisfy applicable NPDES discharge
requirements.
Clean Water Infiltration Well Distribution System (STEP 9 —
Conceptual Clean Water Infiltration System Considerations)
The purpose of the clean water infiltration distribution system is to convey
water from water supply wells to the infiltration water treatment system
and to convey water from the infiltration water treatment system to the
clean water infiltration wells. The distribution system design would have
features similar to a drinking water distribution system. For example,
distribution lines would be constructed with blowoffs so that the system
may be flushed to remove buildup on piping walls.
Infiltration water would be transferred from the water supply well to a
treatment and storage plant. A booster pump will convey water from the
storage tanks and to provide the hydraulic head to the infiltration well
network to maintain positive pressures for infiltration. Pressure regulating
valves would be installed at each infiltration well to control clean water
infiltration rate.
Groundwater Extraction Well Discharge Piping (STEP 10 —
Conceptual Extraction System Considerations)
The proposed groundwater extraction system would consist of 18 new
groundwater extraction wells. Based upon predictive groundwater flow
and transport modeling, the groundwater extraction wells would generate
on average 2.7 gpm of extracted groundwater per well or about 48 gpm of
extracted groundwater collectively.
Each of the groundwater extraction wells would discharge into one of a
series of headers. Extracted groundwater in these headers then would flow
by gravity to one of several tanks. The collected groundwater in these tanks
would be pumped to a conveyance line ultimately discharging into the DFA
silo sump.
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6.24.2.2 Engineering Designs with Assumptions,
Calculations and Specifications
(CAP Content Section 6.E.b.ii)
Pipelines (STEP 11— Pipeline Specifics)
(CAP Content Section 6.E.b.ii)
High density polyethylene (HDPE) piping will be used for water
conveyance in all areas where buried piping will be installed. Water
conveyance will include:
• Groundwater pumped from extraction wells and conveyed to the
LRB
Groundwater pumped from the infiltration water supply wells and
conveyed to a infiltration water treatment system
Infiltration water treatment system effluent to clean water infiltration
wells
HDPE piping will conform to standard HDPE pipe specifications such as
the following:
• ASTM F714, "Standard Specification for Polyethylene (PE) Plastic
Pipe (DR -PR) Based on Outside Diameter,"
• ASTM D3035,"Standard Specification for Polyethylene (PE) Plastic
Pipe (DR -PR) Based on Controlled Outside Diameter."
• ANSI/AWWA C906, "Polyethylene (PE) Pressure Pipe and Fittings,
4" to 63", for Water Distribution and Transmission."
• Cell Classification PE445574C per ASTM D3350
• Plastics Pipe Institute (PPI) TR-4 Listing as PE4710 / PE3408
• Hydrostatic Design Basis 1,600 psi @ 73°F (23°C) and 1,000 psi @
1407 (60°C) per ASTM D2837
Fittings will be molded from HDPE compound having cell classification
equal to or exceeding the compound used in the pipe manufacture to ensure
compatibility of polyethylene resins. Substitution may be allowed for
approved material with use of flanged joint sections.
Heat fusion welding of the piping and fittings would be in accordance with
Duke Procedure Number: CCP-ENGSTD-NA-QA-004, "Quality Assurance
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and Quality Control of HDPE Pipe Butt Fusion Joints Revision 3," July 8,
2019. Only qualified operators trained in Duke Energy's HDPE fusion
standards would be allowed to perform fusion welding.
Flanged connections would be in accordance with Duke Procedure
Number: CCP-ENGSTD-NA-QA-005, "Requirements for Installation of
Polyethylene Flanged Joints Revision Number 0," August 5, 2019.
The locations of the HDPE piping systems for extraction and infiltration are
generally in low traffic areas. The HDPE piping will be typically installed
below grade in 3-foot deep excavated trenches constructed with compacted
granular bedding material. The trenches will be backfilled with a minimum
of 2-feet of excavated native soil and compacted. Pipe in areas with regular
traffic of more than two axles will be installed in trenches designed to
comply with AWWA M-55, "PE Pipe — Design and Installation" or an
approved alternative design.
The design flow rate is 76 gpm for the clean water infiltration system and 48
gpm for the groundwater extraction system. Infiltration water distribution
lines would connect to each well of the clean water infiltration system.
Likewise, each groundwater extraction well will be connected to a header
that ultimately conveys extracted groundwater to DFA silo sump.
Preliminary calculations pertaining to the piping design (e.g., pipe sizing,
pressures, flow, friction losses, etc.) are provided in Appendix N.
Localized collection tanks and pumps or pump stations might be integrated
into the piping system to allow for independent operation of various
segments of the system.
Hydrostatic leak testing in accordance with the most current edition of
Handbook of Polyethylene Pipe, or an approved alternate method, will be
performed and passed prior to the piping being placed into operation.
Pipe Network Calculations (STEP 12 — Pipeline Headloss
Calculations)
(CAP Content Section 6.E.b.ii)
The extraction and clean water infiltration networks for the proposed
alternative were designed using Pipe Flow® Expert. Pipe Flow° Expert is a
software used to determine volumetric flow rates, pressure in pipes, friction
losses, pump head, and other information. The calculated outputs and
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graphically represented conceptual network layouts are found in Appendix
N.
The extraction network consists of 18 extraction wells with trunk lines for
conveyance and branching pipes providing connections to the wells. The
network ultimately operates in gravity flow. The network was evaluated by
generating a model with well elevations and depths, pipe lengths, etc. Once
these values were incorporated, the calculations were performed using the
model to determine the nature of flow in the network and to ensure that the
desired movement in the pipe system was occurring. After the flow through
the system was verified, pipe diameters and required pump head outputs
were calculated. The calculation outputs took into account the interacting
flows in the system and frictional losses from fittings and pipes to provide
evidence of the efficacy of the proposed pipe network layout design.
The clean water infiltration network consists of 27 clean water infiltration
wells. Clean water infiltration wells flow via gravity from an elevated
infiltration tank at the natural high point of the site's topography. The
infiltration network was evaluated similarly to the extraction network;
however, due to the operation under gravity flow from an elevated tank,
the network was designed to be operated without conveyance or infiltration
pumps. Accordingly, the calculations performed using the model were to
determine the pipe diameters and the required elevation of the infiltration
water tank.
Telemetry System Design
The groundwater remediation system would be managed using telemetry
system that would enable remote monitoring and operational capabilities.
The telemetry system would be designed to meet the system owner O&M
requirements.
Electrical Design
It is unlikely that existing electrical capacity in the vicinity of the proposed
groundwater remediation system would be sufficient to provide electrical
power to pumps, the clean water infiltration water treatment system, and
other power requirements. Additional electrical capacity is anticipated to
meet groundwater remediation system power requirements.
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System Operation and Maintenance Issues
The effectiveness of the system will be dependent on maintaining adequate
clean water infiltration and groundwater extraction flow rates through the
wells, and stable water levels, for an extended period of time. This will
necessitate effective operation and maintenance of the wells. As described
in this section and in the Contingency Plan (Section 6.8.8), each well will be
equipped with a control and monitoring system and monitored
continuously by the control system, and an alert sent if the water level falls
outside the prescribed range. Adjustments to pumping operations can be
made if the root cause of the alert is determined to be system performance.
Another factor in maintaining the effectiveness of the wells will be
monitoring and maintaining the well screens to prevent a loss of efficiency
due to mineral and/or biological fouling. If well performance monitoring
indicates a decrease in flow rate, the well will be inspected for fouling and
the screens will be cleaned as appropriate. Additionally, cleanouts will be
installed on pipes to facilitate periodic maintenance, preventing mineral
scaling or biological fouling on the conveyance pipe network.
In addition to well performance monitoring and maintenance, other system
elements, such as pumps controls, will receive routine maintenance in
accordance with the manufacturer's recommendations.
6.24.2.3 Permits for Remedy and Schedule
(CAP Content Section 6.E.b.iii)
The design documents would provide the necessary plans and
specifications for procurement and construction purposes. This would
include Site layout drawings, plans and profiles, well enclosure details,
trench and discharge piping outlet details, well construction schematics,
piping and instrumentation diagrams/drawings and complete equipment,
materials and construction specifications.
Permit applications that may be needed for the proposed remedy include:
• Erosion and Sediment Control permit
In Situ Groundwater Remediation Injection Well permit
• NPDES Stormwater permit
The schedule for obtaining permits is based on the project implementation
schedule included in Section 6.8.6.
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6.24.2.4 Schedule and Cost of Implementation
(CAP Content Section 6.E.b.iv)
A Gantt chart (Figure 6-19) is provided for outlining a general timeline of
implementation tasks following CAP Update submittal. The exact timeline
of the schedule milestones is dependent on various factors, including
NCDEQ review and approval, permitting, weather, and field conditions.
See Section 6.8.2.4 for additional discussion.
6.24.2.5 Measure to Ensure Health and Safety
(CAP Content Section 6.E.b.v)
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in
risks to human health related to Source Area 3 have been identified. The
groundwater corrective action is being planned to address regulatory
requirements. The risk assessment identified no current human health or
ecological risk associated with groundwater downgradient of the ash basin.
Water supply wells are located upgradient of Source Area 3 and water
supply filtration systems have been provided to those who selected this
option. Surface water quality standards downgradient of the COI -affected
plume are also met. Based on the absence of receptors, it is anticipated that
groundwater extraction and clean water infiltration would create conditions
that continue to be protective of human health and the environment
because the COI concentrations will diminish with time.
6.24.2.6 Description of All Other Activities and
Notifications Being Conducted to Ensure
Compliance with 02L, CAMA, and Other Relevant
Laws and Regulations
(CAP Content Section 6.E.b.vi)
This CAP Update is for the ash basins and the downgradient additional
sources as identified in NCDEQs April 5, 2019 letter (Appendix A). The
CAP Update addresses the requirements of G.S. Section 130A-309.211(b),
complies with NCAC 15A Subchapter 02L. 0106 corrective action
requirements, and follows the CAP guidance provided by NCDEQ in a
letter to Duke Energy.
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6.24.3 Requirements for 02L .0106(I) — MNA Rule.
(CAP Content Section 6.E.c)
The requirements for implementing corrective action by MNA, under 02L
.0106(l), are provided in Section 6.7.1 and Appendix I. MNA is not applicable at
this time for the GSA/DFAHA as described in Section 6.24.1.
6.24.4 Requirements for 02L .0106(k) —Alternate Standards
(CAP Content Section 6.E.d)
The requirements for implementing corrective action under alternate standards
per Regulation 02L .0106(k) is discussed in Section 6.8.4.
6.24.5 Sampling and Reporting
(CAP Content Section 6.E.e)
An EMP has been developed as part of this CAP Update consistent with 02L.
0106(h)(4). The EMP is designed to monitor groundwater conditions at Roxboro
and document progress towards the remedial objectives over time. This plan is
designed to be adaptive over the project life cycle and can be modified as the
groundwater remediation system design is prepared, completed, or evaluated for
termination. See Section 6.8.5 regarding sampling and reporting associated with
Source Area 3 that is consistent with Source Area 1.
6.24.5.1 Progress Reports and Schedule
(CAP Content Section 6.E.e.i)
The effectiveness monitoring plan for Source Area 3 will be consistent with
the EMP presented in Section 6.8.5.1 and provided in Appendix O.
6.24.5.2 Sampling and Reporting Plan During Active
Remediation
(CAP Content Section 6.E.e.ii)
See Section 6.8.5.2 regarding sampling and reporting during active
remediation for Source Area 3.
6.24.6 Sampling and Reporting Plan after Termination of
Active Remediation
(CAP Content Section 6.E.e.iii)
Termination of the proposed remedial alternative for Source Area 3 will be
consistent with and implemented in accordance with NCDEQ Subchapter 02L
.0106(m). The termination process for Source Area 3 will be accordance with the
decision metrics, request, and review timeline for termination is outlined in
Section 6.8.7 (CAP Content Section 6.E.e.iii.1).
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6.24.7 Proposed Interim Activities Prior to Implementation
(CAP Content Section 6.E. f)
In accordance with requirements of G.S. Section 130A-309.211(b)(3),
implementation of the proposed corrective action for Source Area 1 will begin
within 30 days of NCDEQ approval of the CAP Update.
Prior to pilot testing, the clean infiltration water will be sampled for geochemical
and physical parameters for baseline conditions to evaluate the potential for
biofouling and plugging of the clean water infiltration well screens. During pilot
testing, extracted groundwater will be collected and analyzed for geochemical
parameters consistent with the NPDES permit.
Additional interim activities to be conducted prior to implementation of the
corrective action remedy include:
• Implementation of the EMP within 30 days of CAP approval
• Submittal of permit and registration applications to NCDEQ, as
applicable.
6.24.8 Contingency Plan
(CAP Content Section 6.E.g)
The purpose of the Contingency Plan is to monitor changes in conditions and
operations to effectively reach the remedial action objectives. The contingency
plan addresses operations, groundwater conditions and performance.
The Contingency Plan will be defined in greater detail as design elements of the
system are finalized. A groundwater monitoring program to measure and track
the effectiveness of the proposed extraction and infiltration system for Source
Area 3 is consistent with Source Area 1 and is described in Appendix O. This
plan is designed to be adaptive and can be modified as the groundwater
remediation system design is prepared, completed, or evaluated for termination.
The contingency plan for Source Area 3 will be similar to the contingency plan
proposed for Source Area 1 as described in Section 6.8.8.
6.25 SA3 Summary and Conclusions
This CAP Update meets the corrective action requirements for Source Area 3 under G.S.
and Subchapter 02L.0106 and to addresses Subchapter 02L.01060). This CAP Update
proposes a remedy to control migration of COI -affected groundwater associated with
the Source Area 3: the GSA and the DFAHA.
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This CAP Update provides:
• A screening and ranking process of multiple potential groundwater corrective
action alternatives that would address areas requiring corrective action.
• A selection and description of the favored corrective action groundwater
remedy: Alternative 3, Groundwater Extraction and Clean Water Infiltration.
• Specific plans, including engineering design details, for restoring groundwater
quality.
• A schedule for the implementation and operation of the corrective action
strategy.
• A monitoring plan for evaluating the performance and effectiveness of corrective
action groundwater remedy, and its effect on the restoration of groundwater
quality.
Planned activities prior to full-scale implementation, where either submittal of the EMP,
or the pilot testing work plan and permit applications (as applicable) will be submitted
to NCDEQ within 30 days of CAP approval to fulfill G.S. Section 130A-309.211(b)(3).
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7.0 PROFESSIONAL CERTIFICATION
Certification for the Submittal of a Corrective Action Plan
Responsible Party and/or Permittee: Duke Energy Progress, LLC
Contact Person: Paul Draovitch
Address: 52.5 South Church Street
City: Charlotte State: NC Zip Code: 28202
Site Name: Roxboro Steam Electric Plant
Address: 1700 Dunnaway Road
City: Semora State: NC Zip Code: 28401
Groundwater Incident Number (applicable): NA/Coal Ash Management Act CAP
I, Craig D. Eadx, a Professional Geologist and James E. Clemmer, a Professional Engineer for
SynTerra Corporation (firm or company of employment) do hereby certify that the information
indicated below is enclosed as part of the required Corrective Action Plan (CAP) and that to the best of
my knowledge the data, assessments, conclusions, recommendations and other associated materials
are correct, complete and accurate. I I I I
Sworn to and subscribed
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8.0 REFERENCES
Ademeso, O.A., J.A. Adekoya and B.M. Olaleye. (2012). The Inter -relationship of Bulk
Density and Porosity of Some Crystalline Basement Complex Rocks: A Case
Study of Some Rock Types In Southwestern Nigeria. Journal of Engineering, Vol. 2,
No. 4, pp. 555-562.
Arcadis. (2019). Saturated Ash Thickness and Underlying Groundwater Boron
Concentrations — Allen, Belews Creek, Cliffside, Marshall, Mayo, and Roxboro
Sites. March 2019.
ASTM. (2014). E1689-95: Standard Guide for Developing Conceptual Site Models for
Contaminated Sites. ASTM International, West Conshohocken, PA, 2014.
ASTM. (2016). E2893-16e1: Standard Guide for Greener Cleanups, ASTM International,
West Conshohocken, PA, 2016.
ATSDR. (2010). Toxicolical Profile for Boron. Agency for Toxic Substances and Disease
Registry.
Butler, J., & Secor, D. (1991). The Central Piedmont, in the Geology of the Carolinas. In J.
W. Horton, & V. A. Zullo (Eds.), The geology of the Carolinas: Carolina Geological
Society fiftieth anniversary volume (1 ed.). Knoxville, TN: Univ. of Tennessee Press.
Chapman, M. J., Cravotta, III, C. A., Szabo, Z., & Lindsey, B. D. (2013). Naturally
occurring contaminants in the Piedmont and Blue Ridge crystalline -rock aquifers and
Piedmont Early Mesozoic basin siliciclastic-rock aquifers, eastern United States, 1994-
2008. United States Geological Survey, Water Resources Investigations Report 00-
4286.
Chu, Jacob, Paula Panzino, and Lisa JN Bradley. (2017). An Approach to Using
Geochemical Analysis to Evaluate the Potential Presence of Coal Ash
Constituents in Drinking Water." 2017 World of Coal Ash (WOCA). Lexington, KY.
Daniel, C. C., & Dahlen, P. R. (2002). Preliminary hydrogeologic assessment and study plan
for a regional ground -water resource investigation of the Blue Ridge and Piedmont
provinces of North Carolina. Raleigh, North Carolina: U.S. GEOLOGICAL SURVEY
Water -Resources Investigations Report 02-4105.
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Domenico, P. A., and F. W. Schwartz. (1998). Physical and chemical hydrogeology. Vol.
44. New York: Wylie.
Duke Energy, (2015). Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin
Groundwater Assessment Program, North Carolina.
Duke Energy. (2017). Retrieved October 20, 2017, from Duke Energy:
https://www.duke-energy.com/ /media/pdfs/our-company/ash-
management/duke-energy-ash-metrics.pdf?la=en
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