NC0024406_01_BCSS_CAP Update 2019_Text_20191231

I IP
synTerra
CORRECTIVE ACTION PLAN
UPDATE
Site Name and Location:
Belews Creek Steam Station
3195 Pine Hall Road
Belews Creek, NC 27009
Groundwater Incident No.:
88227
NCO024406
NPDES Permit No.:
NCDEQ CCR Impoundment Ranking
Low -Risk
Date of Report:
December 31, 2019
Permittee and Current
Duke Energy Carolinas, LLC
Property Owner:
526 South Church Street
Charlotte, NC 28202-1803
[phone]
Consultant Information:
SynTerra Corporation
148 River Street, Suite 220
Greenville, South Carolina 29601-2567
[phone]
Latitude and Longitude of Facility:
N 36.2819444/W-80.0�P,7,;W2'e

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
Note to the Reader from Duke Energy
Duke Energy Carolinas, LLC (Duke Energy) is pleased to submit this groundwater
Corrective Action Plan (CAP) for the Belews Creek Steam Station (BCSS) located in
Stokes 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 BCSS coal ash basin. Activities 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 basin at the BCSS as low -risk pursuant
to CAMA.
Thousands of multi -media samples have been collected at the BCSS yielding over
175,000 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 area 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 ash basin decanting to
remove the hydraulic head, thereby mitigating the risk of potential COI migration into
groundwater; and (h) complete ash basin closure. In addition, we intend to implement a
robust groundwater remediation program that includes actively addressing COI in
groundwater above applicable standards at or beyond the compliance boundary using a
combination of groundwater extraction, clean water infiltration, and treatment. These
corrective action measures will most effectively achieve remediation of the
groundwater through the use of extraction wells to the north and northwest of the ash
basin and clean water infiltration wells to the north and northwest of the basin.
Significantly, groundwater modeling simulations indicate these measures will control
COI discharge at the compliance boundary and meet the remedial objectives for COI
beyond the 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

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
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 the BCSS 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 the BCSS. 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 the BCSS
using USEPA guidance demonstrate that risks to potential human health and
ecological receptors associated with the coal ash basin 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 170 monitoring wells over 30 separate monitoring events, and
performing over 140 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
compliance boundary with water filtration systems under a program approved by the
NCDEQ. These alternate water supplies provide additional peace of mind for our
neighbors. Importantly, ongoing multi -media sampling of the nearby surface water
aquatic systems, including the Dan River and Belews 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
Belews Creek Steam Station 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 Carolinas, LLC (Duke Energy). The plan pertains to the Belews Creek
Steam Station (BCSS, Belews Creek, Station or Site) coal combustion residuals (CCR) ash
basin. The Site is located in Stokes County, North Carolina (Figure ES-1). The closed
Pine Hall Road (PHR) Landfill located within the ash basin drainage system and ash
basin compliance boundary is considered a component of this CAP Update.
This CAP Update addresses the requirements of Section 130A-309.211 (b) of the North
Carolina General Statutes (G.S.), as amended by the Coal Ash Management Act
(CAMA) of 2014. The 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 adjusted on
September 10, 2019 (Appendix A).
This CAP Update evaluates remedies for constituents of interest (COIs) in groundwater
associated with the BCSS ash basin and the PHR Landfill.
Specifically, this CAP Update focuses on constituents detected at concentrations 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] at or beyond the
compliance boundary. The COIs were detected in the following areas:
• North of the ash basin
• Northwest of the ash basin
In accordance with G.S. requirements, a CAP pertaining to Belews Creek was
previously submitted to the NCDEQ in two parts, as follows:
• Corrective Action Plan Part 1— Belews Creek Steam Station Ash Basin (HDR 2015b)
• Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) — Belews
Creek Steam Station Ash Basin (HDR 2016b)
This CAP Update considers data collected through April 2019.
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Ash basin closure is detailed in separate documents prepared by AECOM. Closure
scenarios include a closure -in -place (hybrid) scenario and a closure -by -excavation
scenario. The groundwater remediation alternatives evaluated and recommended in
this CAP Update consider both closure scenarios. Groundwater modeling simulations
consistently indicate the different closure scenarios have a similar effect on COI
concentrations in groundwater.
Summary of CAP Approach
As stated above, this CAP Update meets the corrective action requirements under G.S.
130A-309.211 (b) and Subchapter 02L .0106. The preferred groundwater remediation
approach assumes source control through either basin closure -in -place or closure -by -
excavation. The groundwater remediation approach presented in this CAP Update can
be implemented under either closure scenario to achieve 02L .0202 groundwater quality
standards at the 500 foot compliance boundary within approximately 13 years after
system start up and operation, based on groundwater modeling simulations. The focus
of groundwater corrective action at the BCSS is reducing COIs to concentrations less
than applicable criteria at or beyond the compliance boundary consistent with
Subchapter 02L .0106(e)(4) and to address Subchapter 02L .01060). 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
criteria. If a COI does not have an 02L standard or IMAC, then the background value
defines the COI criteria.
Duke Energy has implemented, or plans to implement the following multi -component
Corrective Action Plan:
Source Control Measures
• Completion of ash basin decanting, currently underway, will reduce the
hydraulic head in the dam area, thereby significantly reducing the hydraulic
driving force for potential COI migration in groundwater to the north and
northwest. As of December 1, 2019, approximately 469,400,000 gallons water
have been removed from the ash basin and the water elevation has decreased
by 10.6 feet. Completion of decanting is projected to occur during or before
September 2020. Groundwater modeling indicates that the average linear
velocity of groundwater will decrease from 5.0 feet per day (ft/d) to 10.0 ft/d
prior to decanting to 0.1 ft/day to 5.0 ft/day after decanting.
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• Operation of the toe -drain water collection system at the base of the BCSS
dam will lower groundwater levels and redirect water collected from the
unnamed tributary, thereby improving surface water and groundwater
quality in the area north of the ash basin.
• Ash basin closure is detailed in a separate document prepared by AECOM.
Closure scenarios include a closure -in -place (hybrid) and closure -by -
excavation.
Groundwater Remediation Measures
A robust groundwater remediation approach planned for the Site includes actively
addressing COIs with concentrations greater than applicable standards at or beyond
the compliance boundary using a combination of groundwater extraction combined
with clean water infiltration and treatment. Site data and groundwater models were
used to evaluate and optimize an effective remedial approach to reduce COI
concentrations north and northwest of the ash basin. The following is a summary of
components of the preferred remediation system that would be installed in areas
north and northwest of the ash basin:
• 10 existing vertical extraction wells northwest of the ash basin
• 113 new vertical extraction wells north and northwest of the ash basin
• 47 vertical clean water infiltration wells north and northwest of the ash basin
• One horizontal clean water infiltration well northwest of the ash basin
Effectiveness Monitoring Plan (EMP)
• Duke Energy has prepared an effectiveness monitoring plan (EMP)
summarized in Section 6.8 and provided in Appendix P of this CAP Update.
The EMP includes an optimized groundwater monitoring network for the ash
basin based on Site -specific COI mobility and distribution. The EMP is also
designed to be adaptable and to address areas where changes to groundwater
conditions are likely to occur due to additional corrective action
implementation or basin closure activities. The 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 basin closure activities.
Details and rationale for CAP activities are provided within this report and summarized
in the following sections.
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ES.2 Background
Plant Operations
Electrical power -generation operations began at Belews Creek in 1974 with the use of
two coal-fired steam units. CCR materials, composed primarily of fly ash and bottom
ash, were initially deposited in the ash basin by hydraulic sluicing operations. In 1984,
fly ash sluicing was replaced with a dry fly ash handling system. In 2018, a dry bottom
ash collection system was installed. All bottom ash and fly ash is currently handled dry.
Placement of ash in the Site ash basin ceased by the end of 2018; all ash is either used for
beneficial reuse or placed in the onsite Craig Road Landfill. The Site ash basin has
operated under a National Pollution Discharge Elimination System (NPDES) Permit
issued by the NCDEQ Division of Water Resources (DWR) since initial 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 impoundment at the Site
as low -risk (Appendix A). The letter cited that Duke Energy has "established
permanent water supplies as required by G.S. Section 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 G.S. Section 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 Area
The Belews Creek coal ash basin is the primary source area evaluated in this CAP.
The ash basin, constructed from 1970 to 1972, is located approximately 3,200 feet
northwest of the steam station powerhouse. The ash basin consists of a single cell
impounded by the main earthen dam located on the north end of the ash basin and an
embankment dam (Pine Hall Road dam) located in the northeast portion of the basin
along Pine Hall Road. The area contained within the ash basin waste boundary is
approximately 283 acres.
CCR materials, composed primarily of fly ash and bottom ash, were initially deposited
in the unlined ash basin via sluice lines beginning in 1974. CCR material (both bottom
ash and fly ash) was converted to dry handling in 2018. Deposition of all waste streams
into the ash basin discontinued on March 27, 2019 in preparation for ash basin closure.
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Decanting of the ash basin pond was initiated on March 27, 2019. The former operating
elevation of the ash basin pond was 750 feet. As of December 1, 2019 approximately
469,400,000 gallons of water had been pumped from the ash basin with a corresponding
reduction in hydraulic head of 10.6 feet in elevation. Completion of ash basin
decanting, as part of the ash basin closure process, is scheduled to occur on or before
September 30, 2020.
Additional Source Area
The closed PHR Landfill, which occupies approximately 67.2 acres, is located in the
southern portion of the original ash basin footprint. The PHR Landfill received an initial
permit (Permit No. 8503 - INDUS) to operate from NCDENR Division of Waste
Management (DWM) in December 1984. The landfill was permitted to receive fly ash.
The capacity of the landfill is approximately 3,616,800 tons. The landfill is unlined, and
designed with a 1-foot-thick soil cap on the side slopes and 2-foot-thick soil cap on
flatter areas. A subsequent expansion (Phase I Expansion), permitted in 2003, was also
unlined but was permitted with a synthetic cap system to be applied at closure. After
groundwater concentrations greater than 02L standards were detected near the landfill
and adjacent to the ash basin, the placement of additional ash in the Phase I Expansion
was halted and the closure design was changed to use an engineered cover system for
the above -grade portion of the landfill. The PHR Landfill was closed per the approved
capping -and -closure plan, which included a synthetic cover system consisting of 40-
millimeter linear low -density polyethylene (LLDPE) with a geonet installed over all
previously active landfill areas. It further included a minimum 2-foot soil -only cover on
the area north of the landfill covering the historical ash basin and stormwater features.
The construction of the engineered cover system, including the additional soil cover,
was completed in December 2008. The cover system is a source control measure
implemented for the landfill.
The PHR Landfill is within the ash basin drainage system (i.e. watershed). Groundwater
monitoring data indicate constituents similar to COIs (e.g. boron and chloride),
identified from groundwater monitoring of the ash basin, and are present in
groundwater beneath and within a limited horizontal extent of the landfill footprint.
The ash basin compliance boundary and landfill compliance boundary overlap, with
the exception of an area of the landfill compliance boundary that is south of the ash
basin compliance boundary. All groundwater COI migration from the landfill is
confined within the landfill compliance boundary, with the exception of some COI
migration north of the landfill and within the ash basin compliance boundary. COI
migration north of the landfill has a commingled plume with the ash basin plume.
Groundwater model simulations predict that groundwater COI migration from the
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landfill will not migrate beyond the landfill compliance boundary in the future.
Groundwater from the closed landfill and the ash basin flows primarily north, where
corrective action is planned; therefore, the PHR Landfill is included in the groundwater
CAP.
Pre -Basin Closure Activities
To accommodate closure of the ash basin, decanting (removal) of free water from the
basin began on March 27, 2019 as required by a Special Order by Consent (SOC) issued
through North Carolina Environmental Management Commission (EMC) on July 12,
2018 (EMC SOC WQ S18-004; Appendix B of Appendix K). The SOC requires
completion of decanting by September 30, 2020. Decanting of ponded water from the
ash basin before closure will reduce or eliminate seepage from constructed or non -
constructed seeps. Constructed seeps are seeps on or within the dam structure that
convey wastewater via a pipe or constructed channel to an NPDES-regulated receiving
water. Seeps that do not meet the constructed seep definition are considered non -
constructed seeps. Decanting is considered an important component of the corrective
action strategy because it will significantly reduce the hydraulic head and gradients,
thereby reducing the groundwater flow velocity and COI migration potential associated
with the ash basin. As of December 1, 2019, approximately 469,400,000 gallons water
have been removed from the ash basin and the water elevation has decreased by 10.6
feet.
Basis for CAP Development
A substantial amount of data related to the ash basin, PHR Landfill and the general
Belews Creek site has been collected to date. A summary of the BCSS assessment
documentation used to prepare this CAP is presented in Table ES-1.
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TABLE ES-1
SUMMARY OF BCSS ASSESSMENT DOCUMENTATION
Comprehensive Site Assessment Report - Belews Creek Steam Station Ash Basin [HDR
Engineering, Inc. of the Carolinas (HDR 2015a)].
Corrective Action Plan Part 1 - Belews Creek Steam Station Ash Basin (HDR 2015b).
Ash Basin Closure Plan Report, 100% Draft Closure Plan for CCR Posting - Belews Creek
Steam Station (AECOM 2016).
Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) - Belews Creek
Steam Station Ash Basin (HDR 2016b).
Comprehensive Site Assessment Supplement 2 - Belews Creek Steam Station Ash Basin
(HDR 2016a).
Basis of Design Report (100% Submittal) - Belews Creek Steam Station (SynTerra
2017a).
Comprehensive Site Assessment Update - Belews Creek Steam Station Ash Basin
(SynTerra 2017b).
Preliminary Updated Groundwater Flow and Transport Modeling Report - Belews Creek
Steam Station (Falta Environmental 2018).
Human Health and Ecological Risk Assessment Summary Update - Belews Creek Steam
Station (SynTerra 2018).
Community Impact Analysis of Ash Basin Closure Options at the Belews Creek Steam
Station (Exponent 2018).
Belews Creek Steam Station HB 630 Provision of Permanent Water Supply Completion
Documentation (Duke Energy 2018)
Closure Options Analysis (AECOM 2018)
Ash Basin Pumping Test Report - Belews Creek Steam Station (SynTerra 2019a).
Surface Water Evaluation to Assess 15A NCAC 02B - Belews Creek Steam Station
(SynTerra 2019b).
2018 Annual Groundwater Monitoring Report (SynTerra 2019c).
Updated Background Threshold Values for Soil and Groundwater (SynTerra, 2019d).
Prepared by: ALA Checked by: CDE
NCDEQ reviewed the October 31, 2017 CSA Update report, and in an April 26, 2018,
letter to Duke Energy, NCDEQ stated that sufficient information was provided to allow
the preparation of this CAP Update (Appendix A).
The assessment work referenced in the documents listed in Table ES-1 has resulted in a
significantly large dataset that has informed the development of this CAP Update. As of
June 2019, the following data collection and analyses activities have been completed:
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TABLE ES-2
SUMMARY OF BCSS ASSESSMENT ACTIVITIES
Tasks
Total
Total Monitoring Wells Installed [CAMA and CCR Wells around basin(s)]
173
Groundwater Monitoring Events
30
Groundwater Samples Collected
2,985
Individual Analyte Results
175,726
Off -Site Water Supply Well Sampling (Total inorganic analysis) - Number
of Analyses
4,753
Ash Pore Water - Number of Analyses (Total and dissolved)
8,497
Ash Pore Water Sampling Events
15
Surface Water Monitoring Events
15
Surface Water Sample Locations
25
Area of Wetness Sample Events
21
Ash Samples (Within ash basin analyzed for SPLP)
7
Soil Samples Collected
134
Soil Sample Locations
45
Sediment Sample Locations
33
Geotechnical Soil Sample Locations
74
Geochemical Ash, Soil, Partially Weathered Rock, Whole Rock Samples
80
Hydraulic Conductivity Tests (Slug Tests, Pumping Tests, Packer Tests,
FLASH Analysis of Bedrock HPF Data)
79
Groundwater Flow & Transport Simulations
85
PHREEQC Geochemical Simulations
62
Prepared by: ALA Checked by: DAA
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
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A COI management process was developed by Duke Energy at the request of NCDEQ
to gain an understanding of the COI behavior and distribution in groundwater and to
aid in the selection of the appropriate remedial approach. The COI 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 Site -related COIs in groundwater based on
Site hydrogeology and geochemical conditions.
3. Determine the COI distribution at the Belews Creek ash basin and PHR Landfill
under current or predicted future conditions.
This COI management process is supported by multiple lines of technical evidence
including empirical data collected at the Site, geochemical modeling, and groundwater
flow and transport modeling. This approach has been used to understand and predict
constituent behavior in the subsurface related to the ash basin and the PHR Landfill, or
to identify constituents that are naturally occurring. COIs that have migrated at or
beyond the compliance boundary at concentrations greater than 02L, IMAC and
background values that are related to an ash basin would be subject to corrective action.
Constituents that are naturally occurring at concentrations greater than the 02L
standard do not warrant corrective action. Details of the COI management approach are
presented in Section 6.0 and Appendix H.
Groundwater
In conformance with requirements of G.S. Section 130A-309.211, groundwater corrective
action is the main focus of this CAP Update. Groundwater constituents to be addressed
with corrective action are those detected in groundwater at or beyond the compliance
boundary at concentrations greater than the 02L standard, IMAC, or background
concentrations, whichever is greater.
Soil
Data indicate that unsaturated soil constituent concentrations are generally consistent
with background concentrations or are less than regulatory screening values. In the few
instances where unsaturated soil constituent concentrations are greater than the
Preliminary Soil Remediation Goal (PSRG) Protection of Groundwater (POG) standards
or background values, constituent concentrations are within range of background
dataset concentrations or there are no mechanisms by which the constituent could have
been transported from the ash basin or PHR Landfill to the unsaturated soils. Therefore,
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this CAP Update focuses on remediation of groundwater associated with ash basin and
additional source area (closed PHR Landfill).
Risk Assessment
The human health and ecological risk assessments, prepared based on state and federal
guidance, demonstrated no measurable difference in modeled risks to potential human
or ecological receptors compared with background concentrations. The updated risk
assessments for the Belews Creek ash basin and PHR Landfill are presented in Section
5.4 and Appendix E of this CAP Update. Data from water supply wells, Belews
Reservoir and the Dan River indicate no evidence of increased risk posed by
groundwater migration associated with the ash basin and PHR Landfill based on
evaluation of concentrations of CCR constituents in environmental media and potential
receptors.
Risk Ranking
In accordance with G.S. Section 130A-309.211(cl) of House Bill 630 (2016) Duke Energy
installed 36 water filtration systems at surrounding properties within a 0.5-mile radius
of the ash basin compliance boundary. Installation of filtration systems, along with
certain improvements to the Belews Creek dam completed by Duke Energy, resulted in
the ash basin 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 constituent interactions specific to the Site and is critical
to understanding the subsurface conditions related to the ash basin and PHR Landfill.
The updated CSM developed for the BCSS included in this CAP is based on a U.S.
Environmental Protection Agency (USEPA) document titled "Environmental Cleanup
Best Management Practices: Effective Use of the Project Life Cycle Conceptual Site
Model" (EPA, 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 Site
characterization and remediation as the Site progresses through the project life cycle
and new data become available. The current BCSS CSM is consistent with Stage 4
"Design CSM", Stage 4 allows for iterative improvement of the site CSM during design
of the remedy while also supporting the development of the basis for the remedy
design (USEPA, 2011).
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Multiple lines of evidence have been used to develop the CSM based on the large BCSS
data set generated. 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 for the BCSS ash basin, PHR
Landfill and the surrounding area which forms the basis of this CAP Update.
Supporting details for the CSM are presented in Section 5.0.
Key conclusions of the CSM include the following:
• No material increases in risk to human health related to the ash basin and PHR
Landfill have been identified. The Site -specific risk assessment conducted for
the ash basin and PHR Landfill indicates 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 risk to residential receptors near the ash basin and the PHR Landfill (no
completed exposure pathways).
• The ash basin and PHR Landfill 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, and killdeer bird) that
might access surface water and sediments downgradient of the ash basin and
PHR Landfill.
• Based on groundwater flow patterns, the location of water supply wells in the
area, and an evaluation of groundwater analytical data, groundwater from the
source area does not flow toward water supply wells. Groundwater data
collected from water supply wells and on -Site monitoring wells, groundwater
elevation measurements from 30 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 program implemented by Duke Energy
provides water filtration systems to private and public surrounding properties
with water supply wells within a 0.5-mile radius of the ash basin compliance
boundary. The hydrogeologic data collected at Belews Creek confirms that Site -
related COIs have not affected off -Site water supply users. Groundwater
modeling predicts that Site -related COIs will not affect off -Site water supply
users. However, Duke Energy installed 36 water filtration systems at
surrounding properties in accordance with G.S. Section 130A-309.211(cl).
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• The hydrogeologic setting of the BCSS ash basin and PHR Landfill 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 simulations indicate that ash basin
decanting will affect groundwater flow patterns within the basin by lowering
hydraulic heads in and around the ash basin dam, which will reduce the rate of
COI transport. As of December 1, 2019, approximately 469,400,000 gallons of
water have been removed from the ash basin and the water elevation has
decreased by 10.6 feet.
• The physical setting and hydraulic processes control the COI flow pattern
within the ash basin, underlying groundwater system, and downgradient
areas. The ash basin is predominantly a horizontal water flow -through system.
Groundwater enters the upgradient side of the ash basin; it is supplemented by
rainfall infiltration and flows laterally through the middle of the ash basin under
a low horizontal gradient, and then flows downward near the dam. This flow
system results in limited downward migration of COIs into the underlying
saprolite upgradient from the dam. Near the dam, COIs in water either
discharge through the NPDES permitted outfall or flow downward out of the
basin and under the dam. Beyond the dam, groundwater flows upward toward
the unnamed tributary discharge zone, limiting downward migration of COIs to
the area proximate to the dam. The exception is near the northwest corner of the
basin, where the hydraulic head from the operating water level of the basin
caused COI migration west of the dam. Bedrock wells installed at various depths
within the basin footprint and downgradient of the dam structure support the
flow characteristics. However, ash basin decanting will re-establish a hydraulic
divide along the topographic ridge to the northwest, preventing groundwater
flow and additional COI migration.
• Horizontal distribution of COIs in groundwater at or beyond the ash basin
compliance boundary is limited to areas north and northwest of the ash basin.
The physical extent of constituent migration north and northwest of the ash basin
is controlled by hydrologic divides, dilution from unaffected groundwater and
the groundwater -to -surface water discharge zones. All groundwater COI
migration from the PHR Landfill occurs within with the landfill compliance
boundary, with the exception of some COI migration north of the landfill, but
within the ash basin compliance boundary.
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• 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), a response to changing geochemical
parameters (i.e., pH and Eh) and the sorption capacity of the soil and/or rock.
Based on geochemical modeling:
o Non -conservative, reactive COIs (i.e., arsenic and beryllium) will remain
in mineral phase assemblages that are stable under variable Site
conditions north and northwest of the basin, demonstrating sorption as an
effective attenuation mechanism.
o Variably reactive COIs (e.g., cobalt and manganese) can exhibit mobility
depending on pore water geochemical conditions and availability of
sorption sites.
o Conservative, non -reactive COIs (e.g., boron, chloride, and total dissolved
solids) 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 into less permeable zones. 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 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 scenarios,
currently under appeal, and account for potential mobilization of COIs.
• COIs in groundwater are contained within Duke Energy's property, with the
exception of Parcel A, an unoccupied 2.67-acre property located northwest of
the ash basin. The plume associated with the ash basin has been characterized
and is stable with exceptions to the north and northwest of the ash basin. A 10-
well groundwater extraction system was installed upgradient of Parcel A as an
accelerated interim remedial action to hydraulically reduce COI transport from
the ash basin toward Parcel A. The system became operational in March 2018.
Flow and transport groundwater model predictions indicate the decanting of the
water in the ash basin will lower the hydraulic head within the ash basin and
reduce or eliminate additional COI migration northwest of the ash basin.
• Groundwater -to -surface water interaction has not caused, and is not predicted
to cause, concentrations of COIs greater than NCAC, Title 15A Subchapter 02B,
Page ES-13

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
Surface Water and Wetland Standards (02B). Analytical results for surface water
samples collected from the Dan River and Belews Reservoir indicate that these
water bodies meet 02B standards under current conditions. Evaluation of future
surface water quality conditions of basin -related jurisdictional streams was
conducted using a surface water mixing model with closure option model
simulation inputs. The evaluation indicates that no future groundwater COI
migration would result in constituent concentrations greater than applicable 02B
surface water criteria.
The aquatic systems (Dan River and Belews Reservoir) surrounding the BCSS
ash basin are healthy, based on multiple lines of evidence including robust
fish populations, species variety, and other indicators based on years of
sampling data. Multiple water quality and biological assessments conducted by
Duke Energy as part of the NDPES monitoring program, combined with the
results of the ecological risk assessment, indicate that there are no adverse
ecological effects to the main surface water systems proximate to the ash basin or
PHR Landfill area.
• Most of the COIs identified in the CSA Update occur naturally in
groundwater, some at concentrations greater than the 02L standard or IMAC.
Groundwater at BCSS naturally contains cadmium, cobalt, iron, and vanadium at
concentrations greater than 02L standard or IMAC. The occurrence of inorganic
constituents in groundwater of the Piedmont Physiographic Province is well
documented in the literature. For example, iron has natural background
concentrations in the shallow flow zone at the Site greater than 02L and
vanadium has natural background concentrations in all flow zones at the Site
greater than its IMAC. For the BCSS CAP Update, vanadium is evaluated based
on its Site -specific statistically derived background value and on additional lines
of evidence to determine whether constituent concentrations represent migration
from the ash basin or are naturally occurring.
These CSM aspects, combined with the updated human health and ecological risk
assessments, provide the basis for the corrective action plan developed for the ash basin
and the closed Pine Hall Road Landfill.
ES.4 Corrective Action Approach
Corrective Action Objectives and Zones Requiring Corrective Action
Migration of COIs related to the ash basin in groundwater at or beyond the compliance
boundary occurs in localized areas to the north and northwest of the ash basin.
Groundwater corrective action was also evaluated for the PHR Landfill. It was
Page ES-14

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
determined that groundwater flow from the landfill is primarily to the north and that
no migration of COIs related to the PHR Landfill has occurred at or beyond the portion
of the landfill compliance boundary that is not included in the ash basin compliance
boundary. Because the PHR Landfill is within the drainage network of the ash basin,
and groundwater flow from the landfill and the ash basin is northward, groundwater
from the landfill will be captured through the planned groundwater remediation
system, north of the ash basin. To satisfy G.S. and maintain compliance with 02L, the
corrective action approach planned for the ash basin focuses on restoring ash basin -
affected groundwater at or beyond the compliance boundary. The following remedial
objectives address the regulatory requirements of NCAC Title 15A Subchapter 02L for
the BCSS CAP Update:
• Restore groundwater quality at or beyond the compliance boundary by returning
COIs to the 02L/IMAC groundwater quality standards, or applicable background
concentrations (whichever are greater), or as close thereto as is economically and
technologically feasible consistent with Subchapter 02L .0106(a).
• Use a phased CAP approach that includes initial active remediation with
effectiveness monitoring of remedy implementation followed by monitored
natural attenuation (MNA) as provided in Subchapters 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 values after satisfying the
requirements set out in Subchapter 02L .0106(k).
The compliance boundary for the ash basin is shown in Figure ES-1. Groundwater
concentrations greater than 02L/IMAC/applicable background concentration values
occur locally at or beyond the ash basin compliance boundary north and northwest of
the ash basin. COI concentrations are less than 02L groundwater standards typically
within 500 and 750 feet of the waste boundary, north and northwest of the ash basin.
The area proposed for corrective action is shown in Figure ES-2.
Summary of Source Control and Corrective Measures
It is critical to take into account the various activities Duke Energy has/will perform to
improve subsurface conditions related to the ash basin and PHR Landfill at the BCSS.
The remedial program incorporates source control by basin decanting and closure,
active groundwater remediation and effectiveness monitoring. Table ES-3 summarizes
the discrete components of the planned corrective action for COI -affected groundwater.
Page ES-15

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION, AND
MONITORING
Groundwater Remedy
Rationale
Component
Source Control Activities
Ash Basin Decanting
Active source remediation by removing ponded water in
the ash basin. Decanting will lower the hydraulic head
within the basin and reduce hydraulic gradients, reducing
groundwater seepage velocities and COI transport
potential. Decanting will return the groundwater flow
system to its approximate natural condition, flowing
toward the axis of the perennial steam valley, then
northward.
Decanting was initiated on March 27, 2019. As of
December 1, 2019, approximately 469,400,000 gallons of
water have been pumped from the ash basin with a
corresponding reduction in hydraulic head of 10.6 feet in
elevation. Decanting is scheduled to be completed on or
before September 30, 2020.
In addition, ash basin decanting will be effective in
reducing or eliminating seeps identified under the SOC.
Ash Basin Closure
The ash basin closure -in -place option and closure- by -
excavation options are considered source control
activities. Extensive groundwater modeling indicates that
either method results in similar effects with respect to
groundwater remediation.
Toe -Drain Water Collection
A toe -drain water collection system that consists of a 16-
System
inch diameter by 18 foot deep wet well has been installed
below the ash basin dam adjacent to the unnamed
tributary. The wet well storage capacity is approximately
2,000 cubic feet. The wet well and pump station storage
capacity is approximately 2,000 cubic feet. The system
construction and testing is complete and will begin
operation in January 2020. Once in operation, the toe -
drain system will collect water from the toe of the ash
basin dam and route it to the Dan River through new
discharge piping to a permitted NPDES outfall.
Page ES-16

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION, AND
MONITORING
Groundwater Remedy
Rationale
Component
Active Groundwater Remediation Activities
Interim Action Plan
A 10-well groundwater extraction system was installed
Accelerated Remediation
adjacent to Parcel A in the area northwest of the ash
Groundwater Extraction
basin. The system was activated on March 14, 2018. The
System
system currently operates at approximately 12 gallons
per minute (gpm) extraction flow rate. As of November
2019, approximately 9,900,000 gallons of water have
been extracted by the system. Post -decanting, the 10
interim action extraction wells are expected to have
reduced extraction rates as a result of the reduced
hydraulic head of the ash basin. The system is predicted
to remove a total of 2.5 gpm. Continued operation of the
system is included in the remedial alternatives evaluated.
Active Groundwater
Groundwater remediation focused on meeting the stated
Remediation
remedial objectives at and beyond the compliance
boundary is planned. These efforts will focus on the area
north and northwest of the ash basin, where COIs are
detected at concentrations greater than applicable
criteria.
To meet the above -referenced CAP objectives, 10 existing
extraction wells with the addition of 113 extraction wells,
47 clean water infiltration wells, and one horizontal clean
water infiltration well are planned to be placed in areas to
reduce COI concentrations based on actual Site data and
groundwater modeling simulations.
Institutional Controls and Monitoring
Maintain Ownership and
ICs in the form of a Declaration of Perpetual Land Use
Institutional Controls (ICs)
Restrictions might be requested in the future based on
Consisting of a Land Use
the results of groundwater remediation activities
Restriction
Permanent Water Solution for
Groundwater data from the Site indicate that surrounding
Water Supply Well Users
water supply wells have not been affected by Site -related
within a 0.5-mile radius of the
COIs. However, the installation of water filtration
Coal Ash Basin Compliance
systems by Duke Energy for 36 surrounding properties
Boundary and Associated
has been completed and approved by NCDEQ to address
Water Filtration System
current and future stakeholder concerns. Duke Energy
Maintenance
maintains these systems on behalf of the property
owners.
Page ES-17

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE ES-3
COMPONENTS OF SOURCE CONTROL, ACTIVE REMEDIATION, AND
MONITORING
Groundwater Remedy
Component
Rationale
Effectiveness Groundwater
Duke Energy plans to monitor groundwater to confirm the
Monitoring
corrective action objectives are met and maintained over
time. This monitoring program includes provisions for
monitoring COIs within the compliance boundary as
required under NCAC Title 15A. 0107(k)(2). Flow and
transport plus geochemical modeling have been
conducted to predict future groundwater conditions after
closure. Effectiveness monitoring will provide data to
validate modeling or provide input for model refinement
in the future, if needed. The CAP Update includes a
comprehensive review of groundwater data collected
through April 2019 and a plan to optimize the monitoring
program. Within thirty (30) days of CAP approval, Duke
Energy would implement the effectiveness monitoring
program.
Provision for Adaptive The BCSS ash basin and surrounding area is a complex
Management of Groundwater site; therefore, Duke Energy believes it is important to
Remedies allow for an adaptive approach during implementation of
this CAP. This approach is consistent with the Interstate
Technology and Regulatory Council (ITRC) document
titled Remediation Management of Complex Sites (ITRC,
2017). This approach might 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 MCDEQ's authority
under 15A NCAC 02L .0106(k).
Prepared by: ALA Checked by: CDE
Notes:
COI - Constituents of Interest
NCDEQ - North Carolina Department of Environmental Quality
ICs - Institutional Controls
CAP - Corrective Action Plan
Corrective Action at Remediation Zones
The area proposed for groundwater remediation in accordance with 02L requirements
is to the north and northwest of the ash basin at or beyond the compliance boundary
(Figure ES-2). Multiple potential groundwater remedial technologies were initially
screened as part of this CAP Update to identify the most applicable remedial methods
based on Site specific hydrogeologic conditions and COI distribution in groundwater.
After the initial screening, the following remedial alternatives were further evaluated in
detail:
Page ES-18

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
• Remedial Alternative 1: Monitored Natural Attenuation
• Remedial Alternative 2: Groundwater extraction and treatment
• Remedial Alternative 3: Groundwater extraction combined with clean water
infiltration and treatment
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
• 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 Alternative 3: groundwater extraction combined with clean water
infiltration and treatment would most effectively achieve the remedial objectives
presented above. The well layout for Alternative 3 is depicted in Figure ES-3. This
alternative consists of:
• 10 existing vertical extraction wells to the northwest of the ash basin
• 113 new vertical extraction wells to the north and northwest of the ash basin
• 47 vertical clean water infiltration wells north and northwest of the ash basin
• One horizontal clean water infiltration well northwest of the ash basin
Page ES-19

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
It is anticipated that the new clean water infiltration and extraction wells will be
screened within the saprolite, transition, and bedrock flow zones, with depths ranging
from approximately 30 feet below ground surface (bgs) to 180 feet bgs.
The flow and transport model predicts the groundwater remediation system will have a
total infiltration flow rate of approximately 165 gpm and a total groundwater extraction
flow rate of approximately 90 gpm. The extracted water is planned to be treated and
then discharged through an existing permitted NPDES outfall location. Details on this
approach are presented in Section 6.0. Remedial performance monitoring will be
performed to evaluate remedy effectiveness as described in Section 6.8 of this CAP
Update.
It is recommended that prior to implementation, pilot testing of the proposed
alternative will be conducted at the areas north and northwest of the dam. Pilot testing
and treatment tests to be conducted include: 1) groundwater extraction and clean water
infiltration, 2) 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
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-20

^� DAN RIVER���
1 f c
C�r� `PARCELA ��y I '`.��•� T �4 ���
ASH BASIN COMPLI�CE •�■ J
BOUNDARY �- LINED RETENTION]
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ASH BASIN -ram
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�_J j (CLOSED) STRUCTURAL FILL
(CLOSED)
LUG l�
FGD LANDFILL
■
! CRAIG ROAD }
r �� - • - LANDFILL
SOURCE: ' L
2016 USGS TOPOGRAPHIC MAP, BELEWS LAKE
QUADRANGLE, OBTAINED FROM THE USGS STORE AT
https://store.usgs.gov/map-locator.
DUKE COUNTY
ENERGY®
CAROLINAS G c `s vnNsroN=sa
w
r
FIGURE ES-1
USGS LOCATION MAP
CORRECTIVE ACTION PLAN UPDATE
BELEWS CREEK STEAM STATION
BELEWS CREEK, NORTH CAROLINA
DRAWN BY: B.YOUNG DATE: 05/15/2019 1 GRAPH ICSCALE
REVISEDBY: B.YOUNG DATE: 07/08/2019 1,000 0 1,000 2,000
CHECKED BY: A. ALBERT DATE: 07/08/2019
APPROVED BY: A. ALBERT DATE: 07/08/2019 (IN FEET)
PROJECT MANAGER: A. ALBERT

NOTES:
/
1. THE BOUNDARY OF THE AREA PROPOSED FOR GROUNDWATER REMEDIATION REPRESENTSTHE
MAXIMUMAREAOF COI CONCENTRATION IN GROUNDWATER GREATER THAN CRITERIAEALTA
♦,
ENVIRONMENTAL, 2019).
2. NATURAL RESOURCES TECHNICAL REPORT (NRTR) WAS PREPARED BYAMEC FOSTER WHEELER
INC., JULV 2, 2015.
3.ALLBOUNDARIES ARE APPROXIMATE.
p �
PROPERTY BOUNDARY PROVIDED BY DUKE ENERGY CAROLINAS.
♦ ��• ,.F
♦
~, 0
2
` O /
5. AERIAL PHOTOGRAPHY OBTAINED FROM GOGGLE EARTH PRO ON JUNE 11, 2019. AERIAL WAS
COLLECTED ON FEBRUARY 3, 2019.
SS. DRAWG HAS BEEN SET WITH APROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE
YSTEM FIINPS3200 INAD8312011 ).
I
,
L
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ti
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I OPO
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•4
LEGEND
AREA PROPOSED FOR
GROUNDWATER REMEDIATION
ASH BASIN WASTE BOUNADRY
ASH BASIN COMPLIANCE
BOUNDARY
PINE HALL ROAD LANDFILL
(CLOSED)
STRUCTURAL FILL (CLOSED)
LANDFILL COMPLIANCE BOUNDARY
LINED RETENTION BASIN
_ DUKE ENERGY CAROLINAS
PROPERTY LINE
STREAM (AMEC NRTR 2015)
7-7 WETLANDS (AM EC NRTR 2015)
GRAPHIC SCALE
DUKE 600 0 600 1,200 FIGURE ES-2
ENERGY® (IN FEET) AREA PROPOSED FOR
CAROLINAS CORRECTIVE ACTION
DRAWN BY: J. KIRTZ DATE: 05/16/2019 CORRECTIVE ACTION PLAN UPDATE
141p REVISED BY: C. WYATT DATE: 12/16/2019
CHECKED BY: C. EADY DATE: 12/16/2019 BELEWS CREEK STEAM STATION
APPROVED BY: C. EADY DATE: 12/16/2019
synTerra PROJECT MANAGER: A.ALBERT BELEWS CREEK, NORTH CAROLINA
www.synterracorp.com

I
0°
a's
PROPOSED
/
/ a
/
yo a o o-
� o s
° o �48"MANHOLE /
° ° WITH AIR VENT I I
a\
P I
• p - / 48"MANHOLE? _----- ---
wlrHAIR vENr = =NOT FOR CONSTRUCTION
•�/ ,�(�� �� r — � � FLOW � — ---
PARCEL
(2.67ACRES) D LEGEND
EXISTING EXTRACTION SYSTEM WELLS EX-1 THRU EX-10
P Q PROPOSED EXTRACTION WELL IN SAPROLITE
i
PROPOSED ® PROPOSED CLEAN WATER INFILTRATION WELL IN SAPROLITE
CLEAN PHYSICAL -CHEMICAL — WATER TREATMENT SYSTEM _ • PROPOSED EXTRACTION WELL IN TRANSITION ZONE
• \ — -
• INFILTRATION o — ® PROPOSED CLEAN WATER INFILTRATION WELL IN TRANSITION ZONE
• HORIZONTAL WELL PROPOSED EXTRACTION WELL IN BEDROCK
�
® PROPOSED CLEAN WATER INFILTRATION WELL IN BEDROCK
PROPOSED EXTRACTION PROPOSED CLEAN WATER INFILTRATION HORIZONTAL WELL (SAPROLITE)
• EX-4? COLLECTION AND PUMP STATION PROPOSED CLEAN WATER INFILTRATION PIPING
4 ° PROPOSED CLEAN WATER INFILTRATION PIPING FLOW DIRECTION
PROPOSED EXTRACTION PIPING
I / PROPOSED EXTRACTION PIPING FLOW DIRECTION
•,' EX 6— — — — — — — DECANT PIPING
FLOW� DECANT PIPING FLOW DIRECTION
• EX-7 DUKE ENERGY CAROLINAS PROPERTY LINE
r ASH BASIN — — — — ASH BASIN COMPLIANCE BOUNDARY
• EX-8 WASTE BOUNDARY
EXISTING EXTRACTION ® ASH BASIN PONDED WATER
SYSTEM (EX-1 THRU EX-10) NOTES
/ .) ALL BOUNDARIES ARE APPROXIMATE.
2.)
.)DUKEENERGYADNS.PROPERTY LINES ARE REPRESENTED SAMPLE LOCATIONS WERE DERIVED FROM VARIOUS SOURCES AND AREA MIX OF SURVEYED AND
I APPROXIMATE LOCATIONS. THEREFORE LOCATIONS ARE DEEMED TO BEAPPROXIMATE.
3JTHE TOPOGRAPHY IS SHOWN FOR REFERENCE PURPOSES ONLY AND SHOULD NOT BE USED FOR DESIGN OR ENGINEERING PURPOSES THE TOPOGRAPHY BASED
EX- ON A COMBINATION OF SOURCES.
LIDAR DATA OBTAINED FROM NC FLOODPLAIN MAPPING PROGRAM -SPATIAL DATA DOWNLOAD AT htt Sdd.nc. o DaWD°wni° xN d.as Ps// B / p
DATA WAS SOURCED FROM THEIR PHASE 3-2015 Q L2 LIDAR
DROPOSED CLEAN WATER 4.) THE WATERS OF THE US DELINEATION HAS NOT BEEN APPROVED BY THE U.S. ARMY CORPS OF ENGINEERS AT THE TIME OF THE MAP CREATION. THIS MAP IS
PRELIMINARY JURISDICTIONAL DETERMINATION ONLY. THE PRELIMINARY WETLANDS AND STREAM BOUNDARIES WETLANDS AND STREAMS BOUNDARIES WERE
=1 LTRATIO N STO RAG E TAN K OBTAINED FROM AMEC FOSTER WHEELER ENVIRONMENTAL AND INFRASTRUCTURE INC. NATURAL RESOURCE TECHNICAL REPORT (NRTR) FOR BELEWS CREEK
Q ° STATION", DATED TUNE 2015.
5.) SITE FEATURES INCLUDING UTILITIES ARE BASED ON SEVERAL SOURCES. ANY UTILITIES SHOWN ARE FOR REFERENCE PURPOSES ONLY AND HAVE NOT BEEN
'ER TREATMENTSYSTEM APPROXIMATELY WITH
RLOCATEDEGARDS TO THEIR HORIZONTAL OR VERTICAL LOCATIONS IN THE FIELD. ALL FEATURES INCLUDING UTILITIES ARE DEEMED TO BE
2017 AERIAL PHOTOGRAPHS OBTAINED FROM NC ONE MAP AT
https://n nemap.maps.arcgis,com/apps/web,ppviewer/,,de.hlm171d=2c8a9b366c4841f1be2b464347dO4a2b
2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSP FLOWN ON APRIL 17, 2014.
O 6.) DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM FIP 3200 (NAD83 AND NAVD 88.
o GRAPHIC SCALE
f DUKE 200 0 100 200
ENERGY IN FEET FIGURE ES-3
CAROLINAS DRAWN BY: J. CHASTAIN DATE:12/15/2019 PROPOSED CORRECTIVE ACTION APPROACH
REVISED BY: DATE:- CORRECTIVE ACTION PLAN UPDATE
APPROVED BY, J. CL MMER DATE:12/15/2019 BELEWS CREEK STEAM STATION
PROJECT MANAGER: A. ALBERT BELEWS CREEK, NORTH CAROLINA
synTerra www.synterracorp.com

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE OF CONTENTS
SECTION
PAGE
EXECUTIVE SUMMARY.................................................................................................... ES-1
ES.1 Introduction..................................................................................................................
1
ES.2 Background...................................................................................................................
4
ES.3 CSM Overview...........................................................................................................10
ESA Corrective Action Approach....................................................................................
14
1.0 INTRODUCTION.........................................................................................................1-1
1.1 Background................................................................................................................1-2
1.2 Purpose and Scope....................................................................................................1-3
1.3 Regulatory Basis for Closure and Corrective Action...........................................1-4
1.4 List of Considerations by the Secretary for Evaluation of Corrective Action
Plans............................................................................................................................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 Basin ....................1-9
1.5.3 Overview of Existing Permits and Special Orders by Consent....................1-10
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 DEQ 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..................................................................................
5-3
Page

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
5.1.2.1 Groundwater Flow Direction..................................................................... 5-4
5.1.2.2 Groundwater Seepage Velocities............................................................... 5-7
5.1.2.3 Hydraulic Gradients.................................................................................. 5-10
5.1.2.4 Particle Tracking Results........................................................................... 5-11
5.1.2.5 Subsurface Heterogeneities.......................................................................5-11
5.1.2.6 Bedrock Matrix Diffusion and Flow ........................................................ 5-12
5.1.2.7 Onsite and Offsite Pumping Influences .................................................. 5-14
5.1.2.8 Groundwater Balance................................................................................ 5-15
5.1.2.9 Effects of Naturally Occurring Constituents .......................................... 5-18
5.2 Source Area Location.............................................................................................. 5-19
5.3 Summary of Potential Receptors.......................................................................... 5-19
5.3.1 Surface Water.......................................................................................................5-20
5.3.1.1 Environmental Assessment of Belews Reservoir and the Dan River.
5-21
5.3.2 Availability of Public Water Supply................................................................ 5-21
5.3.3 Water Supply Wells............................................................................................ 5-21
5.3.4 Future Groundwater Use Area......................................................................... 5-22
5.4 Human Health and Ecological Risk Assessment Results .................................. 5-22
5.5 CSM Summary........................................................................................................ 5-25
6.0 CORRECTIVE ACTION APPROACH FOR SOURCE AREA 1 (ASH BASIN
AND CLOSED PHR LANDFILL)............................................................................. 6-1
6.1 Extent of Constituent Distribution......................................................................... 6-2
6.1.1 Source Material within the Waste Boundary....................................................6-2
6.1.1.1 Description of Waste Material and History of Placement ...................... 6-2
6.1.1.2 Specific Waste Characteristics of Source Material ................................... 6-3
6.1.1.3 Volume and Physical Horizontal and Vertical Extent of Source
Material.......................................................................................................... 6-5
6.1.1.4 Volume and Physical Horizontal and Vertical Extent of Anticipated
Saturated Source Material........................................................................... 6-6
6.1.1.5 Saturated Ash and Groundwater...............................................................6-6
6.1.1.6 Chemistry within Waste Boundary........................................................... 6-8
6.1.1.7 Other Potential Source Material — Pine Hall Road Landfill ................. 6-14
6.1.1.8 Interim Response Actions......................................................................... 6-14
Page ii

Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.1.2 Extent of Constituent Migration beyond the Compliance Boundary .........
6-18
6.1.2.1 Piper Diagrams...........................................................................................
6-26
6.1.3 Constituents of Interest......................................................................................
6-28
6.1.4 Horizontal and Vertical Extent of COIs...........................................................6-38
6.1.4.1 COIs in Unsaturated Soil...........................................................................
6-40
6.1.4.2 Horizontal and Vertical Extent of Groundwater in Need of
Restoration...................................................................................................
6-42
6.1.5 COI Distribution in Groundwater....................................................................
6-46
6.1.5.1 Conservative Constituents........................................................................
6-46
6.1.5.2 Non -Conservative Constituents...............................................................
6-50
6.1.5.3 Variably Conservative Constituents........................................................6-51
6.2 Potential Receptors Associated with Source Area .............................................
6-52
6.2.1 Surface Waters - Downgradient within a 0.5-Mile Radius of the Waste
Boundary..............................................................................................................
6-52
6.2.2 Water Supply Wells............................................................................................
6-55
6.2.2.1 Provision of Alternative Water Supply ...................................................
6-55
6.2.2.2 Findings of Drinking Water Supply Well Surveys ................................
6-57
6.2.3 Future Groundwater Use Areas........................................................................
6-62
6.3 Human and Ecological Risks.................................................................................
6-62
6.4 Description of Remediation Technologies..........................................................
6-63
6.4.1 Monitored Natural Attenuation........................................................................
6-63
6.4.2 In -Situ Technologies...........................................................................................
6-65
6.4.3 Groundwater Extraction....................................................................................
6-70
6.4.4 Groundwater Treatment....................................................................................
6-76
6.4.5 Groundwater Management...............................................................................
6-80
6.4.6 Technology Evaluation Summary....................................................................
6-85
6.5 Evaluation of Remedial Alternatives...................................................................
6-85
6.5.1 Remedial Alternative 1- Monitored Natural Attenuation ...........................
6-86
6.5.1.1 Problem Statement and Remediation Goals ...........................................
6-86
6.5.1.2 Conceptual Model......................................................................................
6-86
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.5.1.3 Predictive Modeling...................................................................................6-88
6.5.2 Remedial Alternative 2 - Groundwater Extraction and Treatment ............
6-89
6.5.2.1 Problem Statement and Remediation Goals ...........................................
6-89
6.5.2.2 Conceptual Model......................................................................................
6-90
6.5.2.3 Predictive Modeling...................................................................................6-91
6.5.3 Remedial Alternative 3 - Groundwater Extraction Combined with Clean
Water Infiltration and Treatment......................................................................
6-92
6.5.3.1 Problem Statement and Remediation Goals ...........................................
6-93
6.5.3.2 Conceptual Model......................................................................................
6-93
6.5.3.3 Predictive Modeling...................................................................................6-95
6.6 Remedial Alternatives Screening Criteria...........................................................
6-96
6.7 Remedial Alternatives Criteria Evaluation.......................................................
6-102
6.7.1 Remedial Alternative 1 - Monitored Natural Attenuation .........................
6-102
6.7.2 Remedial Alternative 2 - Groundwater Extraction and Treatment ..........
6-107
6.7.3 Remedial Alternative 3 - Groundwater Extraction Combined with Clean
Water Infiltration and Treatment....................................................................
6-111
6.8 Proposed Remedial Alternative Selected for Source Area ..............................
6-116
6.8.1 Description of Proposed Remedial Alternative and Rationale for
Selection..............................................................................................................
6-117
6.8.2 Design Details....................................................................................................
6-122
6.8.2.1 Process Flow Diagrams for Major Components of Proposed
Remedy......................................................................................................
6-123
6.8.2.2 Engineering Designs with Assumptions, Calculations, and
Specifications.............................................................................................
6-132
6.8.2.3 Permits for Remedy and Schedule.........................................................
6-136
6.8.2.4 Schedule and Cost of Implementation..................................................
6-137
6.8.2.5 Measure to Ensure Health and Safety ...................................................
6-138
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................................................................................................
6-138
6.8.3 Requirements for 02L .0106(1) - MNA............................................................
6-138
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Corrective Action Plan Update December 2019
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TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
6.8.4 Requirements for 02L .0106(k) — Alternate Standards ................................. 6-138
6.8.5 Sampling and Reporting.................................................................................. 6-139
6.8.6 Sampling and Reporting Plan after Termination of Active
Remediation....................................................................................................... 6-147
6.8.7 Proposed Interim Activities Prior to Implementation.................................6-148
6.8.8 Contingency Plan.............................................................................................. 6-148
6.8.8.1 Description of Contingency Plan........................................................... 6-148
6.8.8.2 Decision Metrics for Contingency Plan Areas ...................................... 6-149
6.9 Summary and Conclusions.................................................................................. 6-152
7.0 PROFESSIONAL CERTIFICATIONS...................................................................... 7-1
8.0 REFERENCES................................................................................................................ 8-1
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Corrective Action Plan Update December 2019
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LIST OF FIGURES
Executive Summary
Figure ES-1 USGS Location Map
Figure ES-2 Area Proposed for Corrective Action
Figure ES-3 Proposed Corrective Action Approach
1. Introduction
Figure 1-1 USGS Location Map
Figure 1-2 Site Layout Map
Figure 1-3 1966 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 - Shallow Flow Zone (April 8, 2019)
Figure 5-4b
Water Level Map - Transition Flow Zone (April 8, 2019)
Figure 5-4c
Water Level Map - Bedrock Flow Zone (April 8, 2019)
Figure 5-5a
Velocity Vector Map for Pre -Decanting Conditions
Figure 5-5b
Velocity Vector Map for Closure -in -Place (Hybrid) Conditions
Figure 5-5c
Velocity Vector Map for Closure -by -Excavation Conditions
Figure 5-6
Map of Surface Waters
Figure 5-7a
Water Supply Well Sample Locations
Figure 5-7b
HB 630 Provision of Permanent Water Supply Completion Map
6.0 Source Area Evaluation - Ash Basin
Figure 6-1 Fly Ash and Bottom Ash Interbedded Depiction
Figure 6-2 General Cross Section A -A' - Ash Basin
Figure 6-3 General Cross Section B-B' - Ash Basin
Figure 6-4 Saturated Ash Thickness Map for Pre -Decanting and Post -Closure
Conditions
Figure 6-5 Unsaturated Soil Sample Locations and Exceedances
Figure 6-6a General Cross Section A -A' - Ash Basin - Conservative Group -
Mean of Boron, Chloride, Lithium, and Total Dissolved Solids
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Corrective Action Plan Update December 2019
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LIST OF FIGURES (CONTINUED)
6.0 Source Area Evaluation - Ash Basin (Continued)
Figure 6-6b
General Cross Section A -A' - Ash Basin - Non -Conservative Group -
Mean of Arsenic, Beryllium, Strontium, and Thallium
Figure 6-6c
General Cross Section A -A' - Ash Basin - Variable Group - Mean of
Cobalt, Iron, and Manganese
Figure 6-7
Geochemical Water Quality Plots
Figure 6-8
Ash Pore Water and Groundwater Piper Diagrams
Figure 6-9
Site Layout - Decanting Monitoring Network
Figure 6-10a
Hydrographs - Ash Basin and South, East, and West of Ash Basin
Figure 6-10b
Hydrographs - Within Ash Basin and North of Ash Basin
Figure 6-10c
Hydrographs - Northwest of Ash Basin
Figure 6-11a
Isoconcentration Map Arsenic in Deep Flow Zone
Figure 6-11b
Isoconcentration Map Arsenic in Bedrock Flow Zone
Figure 6-12a
Isoconcentration Map Beryllium in Shallow Flow Zone
Figure 6-12b
Isoconcentration Map Beryllium in Deep Flow Zone
Figure 6-13a
Isoconcentration Map Boron in Shallow Flow Zone
Figure 6-13b
Isoconcentration Map Boron in Deep Flow Zone
Figure 6-13c
Isoconcentration Map Boron in Bedrock Flow Zone
Figure 6-14a
Isoconcentration Map Chloride in Shallow Flow Zone
Figure 6-14b
Isoconcentration Map Chloride in Deep Flow Zone
Figure 6-14c
Isoconcentration Map Chloride in Bedrock Flow Zone
Figure 6-15a
Isoconcentration Map Cobalt in Shallow Flow Zone
Figure 6-15b
Isoconcentration Map Cobalt in Deep Flow Zone
Figure 6-16
Isoconcentration Map Iron in Deep Flow Zone
Figure 6-17a
Isoconcentration Map Lithium in Shallow Flow Zone
Figure 6-17b
Isoconcentration Map Lithium in Deep Flow Zone
Figure 6-18a
Isoconcentration Map Manganese in Shallow Flow Zone
Figure 6-18b
Isoconcentration Map Manganese in Deep Flow Zone
Figure 6-18c
Isoconcentration Map Manganese in Bedrock Flow Zone
Figure 6-19a
Isoconcentration Map Strontium in Shallow Flow Zone
Figure 6-19b
Isoconcentration Map Strontium in Deep Flow Zone
Figure 6-19c
Isoconcentration Map Strontium in Bedrock Flow Zone
Figure 6-20a
Isoconcentration Map Total Dissolved Solids in Shallow Flow Zone
Figure 6-20b
Isoconcentration Map Total Dissolved Solids in Deep Flow Zone
Figure 6-20c
Isoconcentration Map Total Dissolved Solids in Bedrock Flow Zone
Figure 6-21a
Isoconcentration Map Thallium in Shallow Flow Zone
Figure 6-21b
Isoconcentration Map Thallium in Deep Flow Zone
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
LIST OF FIGURES (CONTINUED)
6.0 Source Area Evaluation - Ash Basin (Continued)
Figure 6-22a General Cross Section B-B' - Ash Basin - Conservative Group -
Mean of Boron, Chloride, Lithium, and Total Dissolved Solids
Figure 6-22b
General Cross Section B-B' - Ash Basin - Non -Conservative Group -
Mean of Arsenic, Beryllium, Strontium and Thallium
Figure 6-22c
General Cross Section B-B' - Ash Basin - Variable Group - Mean of
Cobalt, Iron and Manganese
Figure 6-23
Seep and Surface Water Piper Diagrams
Figure 6-24
Pourbaix Diagram for Iron -Water System
Figure 6-25a
Remedial Alternative 3 - Well System Layout- Groundwater
Remediation by Extraction combined with Clean Water Infiltration
and Treatment
Figure 6-25b
Remedial Alternative 3 - Conceptual Vertical Clean Water
Infiltration Well Schematic - Groundwater Remediation by
Extraction combined with Clean Water Infiltration and Treatment
Figure 6-25c
Remedial Alternative 3 - Conceptual Horizontal Well -
Groundwater Remediation by Extraction combined with Clean
Water Infiltration and Treatment
Figure 6-25d
Remedial Alternative 3 - Conceptual Extraction Well Schematic -
Groundwater Remediation by Extraction combined with Clean
Water Infiltration and Treatment
Figure 6-25e
Remedial Alternative 3 - Conceptual Trench Detail - Groundwater
Remediation by Extraction combined with Clean Water Infiltration
and Treatment
Figure 6-25f
Remedial Alternative 3 - Dan River Water Intake Schematic -
Groundwater Remediation by Extraction combined with Clean
Water Infiltration and Treatment
Figure 6-25g
Remedial Alternative 3 - Groundwater Remediation by Clean
Water Infiltration and Extraction Term - Simulated Boron
Concentrations in All Flow Zones
Figure 6-26
Conceptual Process Flow Diagram Groundwater Clean Water
Infiltration System
Figure 6-27
Conceptual Process Flow Diagram Groundwater Extraction System
Figure 6-28
Conceptual Process Flow Diagram Groundwater Treatment System
Figure 6-29
CAP Implementation Gantt Chart
Figure 6-30
Effectiveness Monitoring Well Network and Flow Paths
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
LIST OF FIGURES (CONTINUED)
6.0 Source Area Evaluation - Ash Basin (Continued)
Figure 6-31 Effectiveness Monitoring Plan Work Flow and Optimization Flow
Diagram
Figure 6-32 Termination of Groundwater Remediation Flow Diagram
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Corrective Action Plan Update December 2019
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LIST OF TABLES
Executive Summary
Table ES-1 Summary of BCSS Assessment Documentation
Table ES-2 Summary of BCSS Assessment Activities
Table ES-3 Components of Source Control, Active Remediation, and Monitoring
3.0 Summary of Background Determinations
Table 3-1 Summary of Onsite Facilities
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 Groundwater Balance Summary
Table 5-3 Surface Water Classification
6.0 Source Area Evaluation - Ash Basin
Table 6-1
Boron Concentrations in Groundwater Below Source Area
Table 6-2
Soil PSRG POG Standard Equation Parameters and Values
Table 6-3
Summary of Unsaturated Soil Analytical Results
Table 6-4
Source Area Interim Actions
Table 6-5
Means of Groundwater COIs - January 2018 to April 2019
Table 6-6
COI Management Matrix
Table 6-7
Summary Trend Analysis Results for Monitoring Wells
Table 6-8
Seep Corrective Action Strategy
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
Table 6-12
Remedial Technology Screening Summary
Table 6-13
Alternative 3 Groundwater Extraction and Clean Water Infiltration Well
Summary
Table 6-14 Environmental Sustainability Comparisons for Remediation Alternatives
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
LIST OF TABLES (CONTINUED)
6.0 Source Area Evaluation - Ash Basin (Continued)
Table 6-15 Modeled Clean Water Infiltration Well Details
Table 6-16 Modeled Groundwater Extraction Well Details
Table 6-17 Effectiveness Monitoring Plan Elements
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
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
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 Plan Approach
Appendix I
Monitored Natural Attenuation Report
Appendix J
Interim Remediation Action Construction Drawings
Interim Action Plan Accelerated Remediation Groundwater
Extraction System 2018 Startup and Effectiveness Monitoring Report
Interim Action Plan 2019 Effectiveness Monitoring Report
Appendix K
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 L
Remedial Alternative Cost Estimate Details
Appendix M
Sustainability Calculations
Appendix N
Remediation Alternatives Summary
Appendix O
Proposed Remedial Alternative Design Calculations
Appendix P
Groundwater Effectiveness Monitoring Plan
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Corrective Action Plan Update December 2019
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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
BCSS
Belews Creek Steam Station
BGS
Below Ground Surface
BOD
Basis of Design
BR
Bedrock
BTV
Background Threshold Value
CAMA
Coal Ash Management Act
CAP
Corrective Action Plan
CCR
Coal Combustion Residuals
CFR
Code of Federal Register
COI
Constituent of Interest
CSA
Comprehensive Site Assessment
CSM
Conceptual Site Model
CWTS
Constructed Wetlands Treatment System
cy
cubic yards
Duke Energy
Duke Energy Carolinas, LLC
DWM
Division of Waste Management
Eh
Oxidation Reduction Potential
FLASH
Flow -Log Analysis of Single Holes
EMP
Effectiveness Monitoring Program
EPRI
Electric Power Research Institute
FGD
Flue Gas Desulfurization
GPM
Gallons per minute
G.S.
North Carolina General Statute
GTB
Geotechnical Borings
HAO
Hydrous Aluminum Oxide
HB
Highway Business District
HDPE
High -Density Polyethylene
HFO
Hydrous Ferric Oxide
HPF
Heat Pulse Flow Meter
IAP
Interim Action Plan
IMAC
Interim Maximum Allowable Concentration
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Corrective Action Plan Update December 2019
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LIST OF ACRONYMS (CONTINUED)
IMP
Interim Monitoring Plan
ISV
In -situ Vitrification
Kd
Partition Coefficient
LEAF
Leaching Environmental Assessment Framework
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
NORR
Notice of Regulatory Requirements
NPDES
National Pollutant Discharge Elimination System
NRTR
National Resource Technical Report
ORP
Oxidation Reduction Potential
OSWER
Office of Solid Waste and Emergency Response
PRB
Permeable Reactive Barrier
PHR
Pine Hall Road
Plant/Site
Belews Creek Steam Station
POG
Protection of Groundwater
PSRG
Preliminary Soil Remediation Goal
S.0
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
UMC
United Methodist Church
USEPA
United States Environmental Protection Agency
USGS
United States Geological Survey
Work Plan
Groundwater Assessment Work Plan
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
1.0 INTRODUCTION
(CAP Content Section 1)
SynTerra prepared this groundwater corrective action plan (CAP) Update on behalf of
Duke Energy Carolinas, LLC (Duke Energy). The plan pertains to the Belews Creek
Steam Station (BCSS or Site) coal combustion residual (CCR) ash basin. Duke Energy
owns and operates BCSS, located in Belews Creek, Stokes County, North Carolina
(Figure 1-1).
In accordance with Section 130A-309.211 (b) of the of the North Carolina General
Statutes (G.S.), as amended by Coal Ash Management Act (CAMA), Duke Energy is
submitting this groundwater CAP Update to prescribe methods and materials to restore
groundwater quality associated with CAMA-regulated units. The CAP 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.
In accordance with G.S. requirements, a CAP for BCSS was previously submitted to the
North Carolina Department of Environmental Quality (NCDEQ) in two parts:
• Corrective Action Plan Part 1— Belews Creek Steam Station Ash Basin (HDR 2015b)
• Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) — Belews
Creek Steam Station Ash Basin (HDR 2016b)
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 Belews Creek stating that
sources hydrologically connected to the ash basin are to be assessed and included in an
updated CAP. The Pine Hall Road (PHR) Landfill is included as an additional source
hydrologically connected to the ash basin.
In addition to the CAP Update, Duke Energy will be submitting CCR Surface
Impoundment Closure Plans (Closure Plan) to NCDEQ on/before December 31, 2019
under separate cover. This CAP has been developed to be effective with the various
closure scenarios developed for the Site.
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Corrective Action Plan Update December 2019
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The CAP content and submittal schedule is 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.
1.1 Background
(CAP Content Section 1.A)
A substantial amount of assessment data has been collected for the BCSS ash basin and
the closed PHR Landfill to support this CAP Update. Site assessment was performed
and the BCSS Comprehensive Site Assessment (CSA) Update Report, dated October 31,
2017 (SynTerra, 2017b) was prepared and submitted in accordance with requirements in
Subchapter 02L .0106 (g). The CSA:
• Identified the source(s) and causes of constituent of interest (COIs) in
groundwater.
• Found no imminent hazards to public health and safety.
• Identified receptors and potential exposure pathways.
• Sufficiently determined the horizontal and vertical extent of COIs in soil and
groundwater.
• Determined the geological and hydrogeological features influencing the
movement, chemical makeup, and physical characteristics of COIs.
NCDEQ provided review of the CSA Update to Duke Energy in a letter dated April 26,
2018 and stated that the information provided sufficiently warranted preparation of this
CAP Update (Appendix A). This CAP Update builds on previous documents to provide
a CAP for addressing the requirements in Subchapter 02L .0106 for corrective action
and the restoration of groundwater quality.
Detailed descriptions of Site operational history, the conceptual Site 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 — Belews Creek Steam Station Ash Basin (HDR
Engineering, Inc. of the Carolinas (HDR 2015a).
• Corrective Action Plan Part 1— Belews Creek Steam Station Ash Basin (HDR 2015b).
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
• Corrective Action Plan Part 2 (included CSA Supplement 1 as Appendix A) —
Belews Creek Steam Station Ash Basin (SynTerra 2016a).
• Comprehensive Site Assessment Supplement 2 — Belews Creek Steam Station Ash Basin
(HDR 2016a).
• Basis of Design Report (100% Submittal) — Belews Creek Steam Station (SynTerra
2017a).
• Comprehensive Site Assessment Update — Belews Creek Steam Station Ash Basin
(SynTerra 2017b).
• Ash Basin Pumping Test Report — Belews Creek Steam Station (SynTerra, 2019a)
• Surface Water Evaluation to Assess 15A NCAC 02B.0200 Compliance for
Implementation of Corrective Action Under 15A NCAC 02L .0106 (k) and (l) — Belews
Creek Steam Station (SynTerra, 2019b)
• 2018 CAMA Annual Interim Monitoring Report (SynTerra, 2019c)
1.2 Purpose and Scope
(CAP Content Section LB)
The purposes of this corrective action approach are the following:
Restore groundwater affected by the ash basin and PHR Landfill at or beyond
the compliance boundary to the applicable groundwater standards, or as close to
the standards as is economically and technically feasible, consistent with
Subchapter 02L .0106(a).
• 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 might potentially affect a water supply well.
• Meet the requirements for corrective action plans specified in G.S. Section 130A-
309.211 (b).
The scope of the CAP and this CAP Update is defined by G.S. Section 130A-309.211,
amended by CAMA. The legislation required, among other items, assessment of
groundwater at coal combustion residual impoundments and corrective action in
conformance with the requirements of Subchapter 02L. The corrective action 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 0.5 mile downgradient from the established
compliance boundary.
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
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 constituents associated with the ash basin at or beyond the compliance
boundary, north and northwest of the ash basin. Design information and steps
necessary for implementation are included in the CAP Update. Once the CAP is
approved by NCDEQ, implementation is planned to begin within 30 days as required
by the G.S.
1.3 Regulatory Basis for Closure and 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), indicate the coal ash basin and the related contiguous unit — the closed
PHR Landfill — have demonstrated that constituent concentrations in groundwater
greater than applicable regulatory standards are and will remain contained within the
ash basin compliance boundary with the exception of the areas immediately north and
northwest of ash basin. In these areas, constituent concentrations return to below
standards within 500 to 750 feet north and northwest of the waste boundary.
The regulatory requirements for corrective action at coal combustion residuals surface
impoundments under CAMA are 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 groundwater
restoration in conformance with the requirements of Subchapter L of Chapter 2 of Title
15A of the North Carolina Administrative Code (15A NCAC Subchapter 02L). In
accordance with G.S. Section 130A-309.211(b)(1), the groundwater CAP 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
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
• 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 Subchapter 02L
.0106 (e), (h) and (i).
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 presents an evaluation of the options available for corrective action
under Subchapter 02L .0106(j), (k), and (1).
• Under paragraph (j), 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 Update has been prepared in general accordance the NCDEQ guidance
document titled 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).
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
In the interim of CAP development and implementation, a Settlement Agreement
between NCDEQ and Duke Energy signed on September 29, 2015, required that
accelerated remediation be implemented at sites that demonstrate off -site affected
groundwater migration, including BCSS. Historical and ongoing assessment
information indicates the potential for off -Site affected groundwater migration
northwest of the BCSS ash basin in the area of Parcel A. After correspondence with
NCDEQ and conditional approval of an Interim Action Plan (IAP), Duke Energy began
interim action activities to target Parcel A in 2016 with a pilot test for a groundwater
extraction system along the northwest corner of the ash basin. The primary objective of
the groundwater extraction system is to reduce groundwater migration of source area
constituents from the ash basin toward the area northwest of the ash basin and to
achieve a hydraulic boundary proximal to the extraction well network. A Basis of
Design (BOD) report was submitted to the NCDEQ Division of Water Resources (DWR)
on September 1, 2017. In a letter with comments dated October 31, 2017, NCDEQ
granted permission for Duke Energy to proceed with installation of the extraction well
network. Duke Energy provided responses to NCDEQ comments along with report
and figure revisions on December 14, 2017. Operation of the extraction system began in
March 2018 and continues, with weekly system monitoring and annual effectiveness
monitoring reporting, through present day.
In addition to the IAP and groundwater CAP, the Belews Creek ash basin is subject to
closure requirements under CAMA. Basin closure activities will provide source control
within the ash basin and are considered a component of the overall corrective action for
the site. It is important to note that the Belews Creek ash basin meets the low -risk
classification criteria set forth in CAMA for CCR surface impoundments. On October
12, 2018, NCDEQ confirmed that Duke Energy satisfactorily completed the alternate
water provision under CAMA, G.S. Section 130A-309.211(cl). On November 13, 2018,
the NCDEQ confirmed that Duke Energy rectified certain dam safety deficiencies,
reclassifying the ash basins from their prior draft ranking of "intermediate" to "low -
risk". Under CAMA, a low -risk coal combustion residuals surface impoundment may
be closed by excavation, closure -in -place, or a hybrid approach.
On April 1, 2019, NCDEQ issued a determination that the Belews Creek coal ash basin
is to be closed using the excavation approach (Appendix A). This decision was
subsequently appealed by Duke Energy. The CAP approach described herein can be
implemented under either closure scenario, closure -by -excavation or closure -in -place
(hybrid).
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1.4 List of Considerations by the Secretary for Evaluation of
Corrective Action Plans
(CAP Content Section 1.D.a through g)
Potential active remedial alternatives were developed using the criteria included in the
NCDEQ's CAP Guidance (NCDEQ, 2019). 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 effects on the environment and local
community
• Technical and logistical feasibility
• Time required to initiate
• Predicted time required to meet remediation goals
• 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 effects 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 6.7 for use in evaluating remedial alternatives in Section 6.8.
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In addition, institutional controls [(provided by the restricted designation (RS)] may be
proposed by Duke Energy to limit access to groundwater use (Subchapter 02L .0104).
The RS designation may be requested for areas outside of an established compliance
boundary when groundwater may not be suitable for use as drinking water supply
without treatment. RS designation is a temporary designation and 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 LE)
1.5.1 Location and History of Land Use
(CAP Content Section LE.a)
The BCSS is situated in the Piedmont physiographic province of north -central
North Carolina. Duke Energy owns approximately 600 acres around the BCSS.
The station is located on the northwest side of Belews Reservoir on Pine Hall
Road in Belews Creek, Stokes County, North Carolina (Figure 1-1). BCSS is a
two -unit coal-fired electricity generating plant with a combined capacity of 2,240
megawatts (MW). The station began commercial operations in 1974 with Unit 1
(1,120 MW) followed by Unit 2 (1,120 MW) in 1975. Cooling water for BCSS is
provided by Belews Reservoir, which was created to serve this purpose.
The area surrounding the ash basin generally consists of residential properties,
farm land, undeveloped land, the Dan River and Belews Reservoir (Figure 1-2).
Natural topography associated with the ash basin ranges from an approximate
high elevation of 878 feet North American Vertical Datum of 1988 (NAVD 88)
southeast of the ash basin near the intersection of Pine Hall Road and Middleton
Loop to an approximate low elevation of 646 feet at the base of the ash basin dam
located at the north end of the ash basin. An unnamed tributary, situated
beginning approximately 300 feet from the base of the ash basin dam, extends
4,300 feet from southeast to northwest where it enters the Dan River. The
elevation at the discharge point to the Dan River is approximately 578 feet. The
elevation of Belews Reservoir is approximately 725 feet.
Based on a review of available historical aerial photography, the area historically
consisted of a combination of agricultural land, rural residential, and woodlands
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prior to the impoundment of Belews Creek for the formation of Belews Reservoir
and construction of the station. Figure 1-3 presents an aerial photograph from
1966 prior to development of the station and construction of Belews Reservoir.
1.5.2 Operations and Waste Streams Coincident with the Ash
Basin
(CAP Content Section LE W
Coal -Related Operations and Waste Streams Coincident with
the Ash Basin
Coal is a highly combustible sedimentary or metamorphic rock typically dark in
coloration and present in rock strata known as coal beds or seams. Coal is
predominantly made up of carbon and other elements such as hydrogen, oxygen,
nitrogen, and sulfur as well as trace metals. The composition of coal makes it
useful as a fossil fuel for combustion processes. Coal results from the conversion
of dead vegetative matter into peat and lignite. The exact composition of coal
varies depending on the environmental and temporal factors associated with its
formation.
Coal has arrived at BCSS through rail transportation since operations began.
Coal storage has historically occurred at the Site's coal pile located immediately
northwest of the powerhouse. The coal pile is located within a groundwater
drainage area separate from and southeast of the ash basin (Figure 1-2). The coal
pile is not within the scope of this CAP Update (see Section 3.0). The coal is
stored on the pile then conveyed via transfer belts to the station where it is
pulverized before being utilized in the boilers. Coal ash and other CCRs are
produced from coal combustion. The smaller ash particles (fly ash) are carried
upward in the flue gas and are captured by an air pollution control device, such
as an electrostatic precipitator. The larger ash particles (bottom ash) fall to the
bottom of the boiler.
Approximately 70 percent to 80 percent of ash produced during coal combustion
is fly ash (EPRI 1995). Typically, 65 percent to 90 percent of fly ash has particle
sizes that are less than 0.010 millimeter (mm). In general, fly ash has a grain size
distribution similar to that of silt. The remaining 20 percent to 30 percent of ash
produced is considered bottom ash. Bottom ash consists of angular particles with
a porous surface and is normally gray to black in color. Bottom ash particle
diameters can vary from approximately 38 mm to 0.05 mm. In general, bottom
ash has a grain size distribution similar to that of fine gravel to medium sand
(EPRI 1995).
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Non -Coal -Related Operations and Waste Streams Coincident
with the Ash Basin
Environmental incidents at the BCSS site have occurred only in the vicinity of the
Plant area. Incidents that initiated notifications to NCDEQ and subsequent
remediation under NCDEQ's DWM mainly consisted of motor/lubrication or
transformer oil. These incidents had no effect on the ash basin constituent
distribution in groundwater because the Plant area is separated from the ash
basin by a hydrogeologic divide (Figure 1-2) and is not considered a component
of this CAP. No non -coal or environmental incidents (i.e., releases that initiated
notification to NCDEQ) are known to have occur in the vicinity of, or coincident
to, the ash basin. Therefore, no environmental incidents at the BCSS are relevant
to this CAP Update.
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 BCSS ash basin to
the Dan River (Outfall 006) in accordance with NPDES Permit NC0024406. The
sources of wastewater managed under the NPDES permit include non -contact
cooling water, ash basin discharge, sanitary waste, cleansing and polishing
water, low volume wastes, groundwater and stormwater from process areas. The
facility operates the following outfalls:
• Outfall 001: Once -through cooling water, includes screen backwash,
recirculating cooling water, station equipment cooling water, and once -through
cooling water. This outfall discharges to Belews Reservoir.
• Internal Outfall 002: FGD wastewater (discharging to ash pond)
Internal Outfall 006A: Ash basin discharge consisting of waste streams from
the powerhouse and yard holding sumps, ash sluice lines, chemical holding pond,
coal yard sumps, stormwater, coal pile collection basins (collecting contact
stormwater from coal piles), remediated groundwater, emergency release of
anhydrous ammonia, seepage from coal ash basin, emergency overflow from the
retention basin, emergency overflows from the existing designated effluent
channel, and treated flue gas desulfurization (FGD) wastewater from internal
outfall 002. The wastewater from Outfall 006A discharges to the Dan River.
Ash basin discharges are to be conveyed through a toe -drain water
collection system at the base of BCSS dam, which will redirect water from
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the unnamed tributary. Once in operation, the toe -drain water collection
system at the base of the BCSS dam will lower groundwater levels and
redirect water collected from the unnamed tributary, thereby improving
surface water and groundwater quality in the area north of the ash basin.
Outfall 006: Waste streams that previously flowed to the ash basin have been
rerouted to the new lined retention basin (LRB). The LRB accepts wastes from the
holding basin, various sumps, coal pile runoff, stormwater runoff, cooling tower
blowdown, FGD wastewater, groundwater and various low volume wastes.
Discharge from the new LRB flows to Outfall 006. Outfall 006 flows to the Dan
River.
• Outfall 005: Formerly stormwater outfall SW002, this outfall consists of once -
through non -contact chiller water and storm water. This outfall discharges to
Belews Reservoir.
• Outfall 007. This is an emergency spillway for the South Coal Basin. This outfall
discharges to Belews Reservoir. The spillway is designed for a flood greater than a
100-year event. Sampling of this spillway is waived due to unsafe conditions
associated with sampling during overflow event.
• Internal Outfall 009: Domestic wastewater plant. The wastewater from this
outfall discharges to the Dan River via Outfall 006.
• Toe Drain Outfall 111: Ash basin discharge through toe drains at the base of
the ash basin dam. This outfall discharges to the unnamed tributary to Dan River.
Toe drain outfall 111 will be rerouted to outfall 006A by March 31, 2020.
Special Order by Consent
A Special Order by Consent (SOC) was issued to Duke Energy on July 19, 2018
(Appendix B of Appendix K), to address the elimination of seeps from Duke
Energy's coal ash basins during the separate and independent process of ash
basin closure. 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, now under way, is expected to substantially
reduce or eliminate discharge from 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, are to be characterized. After post -decanting seep
characterization, an amendment to the CAP and/or Closure Plan, may be
required to address remaining seeps. The SOC terminates 180 days after
decanting or 30 days after approval of the amended CAP. Basin decanting at
BCSS began on March 27, 2019. As of December 1, 2019, approximately
469,400,000 gallons water have been removed from the ash basin and the water
elevation has decreased by 10.6 feet. The SOC requires completion of decanting
by September 30, 2020.
Permitted Solid Waste Facilities
There are four solid waste facilities associated with BCSS:
1. Craig Road Landfill (NCDEQ Permit No. 8504-INDUS)
2. FGD Residue Landfill (NCDEQ Permit No. 8505-INDUS)
3. Closed Structural Fill (NCDEQ Permit No. CCB0070)
4. Closed Pine Hall Road Landfill (NCDEQ Permit No. 8503-INDUS)
The Craig Road Landfill and the FGD Residue Landfill are located south of the
ash basin on the south side of Belews Reservoir (Figure 1-1). The closed
structural fill, constructed by using fly ash generated from BCSS, is located south
of the ash basin on the south side of Pine Hall Road. The closed PHR Landfill is
located south of the ash basin and north of Pine Hall Road. Only the PHR
Landfill is located within the ash basin compliance boundary and is addressed as
part of this CAP Update.
Additional Permits
In addition to NPDES wastewater discharge permit NC0024406, the facility also
holds NPDES stormwater discharge permit NC000573, air permit #01983 (for two
coal/No. 2 fuel oil -fired electric utility boilers), a hazardous wastes permit
NCD000856591 as a RCRA small quantity generator, and industrial landfill
permits 85-03, 85-04, and 85-05.
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 Site, including environmental related projects, such
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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.
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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. In a letter from
NCDEQ to Duke Energy dated April 26, 2018, NCDEQ stated that sufficient
information had been provided in the 2017 CSA Update to allow preparation for the
CAP Update. The letter also provided a number of CSA-related comments and items
required to be addressed prior to or as part of the CAP Update submittal (Appendix A).
On May 23, 2018, NCDEQ Winston Salem Regional Office (WSRO) submitted an email
with the subject: Duke Coal: Belews Creek Full Draft Comments for Discussion Friday (19
pages in total) and to the report titled 'Draft Comments about the CSA Update Report, October
31, 2017, Belews Creek Steam Station' to Duke Energy (Appendix A). The email outlines
additional draft comments to the 2017 CSA Update.
2.2 Duke Energy's Response to DEQ Letter
(CAP Content Section 2.B and 2.B.a)
Responses to all NCDEQ comments within the April, 2018 letter are summarized in
Appendix B. Responses to the May 23, 2018 emailed additional draft comments are
provided in Appendix B. Responses provide references to sections and elements of the
CAP Update where the specific comments are addressed and/or provides additional
supporting information to address the comments. Additional content related to
NCDEQ's comments are either included within sections of this CAP Update or as
standalone appendices to this CAP Update, such as the groundwater modeling report
and surface water evaluation reports.
Activities that directly addressed NCDEQ comments include:
• An additional monitoring well was installed within the shallow flow zone
beneath the ash basin to address the pre-existing data gap. Discussion of data
acquired from the groundwater monitoring wells beneath the ash basin is
presented in Section 6.1.
• Groundwater samples continued to be collected on a quarterly basis as part of
the Belews Creek Interim Monitoring Plan (IMP). Additional sampling results
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augmented the groundwater quality database. Comprehensive groundwater
analytical data are included in Appendix C, Table 1.
• An additional groundwater monitoring well cluster was installed northwest,
downgradient of the ash basin to evaluate horizontal and vertical delineation of
the northwest groundwater plume. Discussion of groundwater constituent extent
in included in Section 6.1.
• Characterization of fractured bedrock based on additional evaluation of
lineaments, the bedrock fracture system, and the bedrock matrix. A report
summarizing the evaluation and implications for bedrock groundwater flow and
transport is included in Appendix F.
• Additional assessment of the Dan River and Belews Reservoir surface water and
sediment was performed in February 2018. There were no constituent
concentrations greater than 02B surface water standards attributable to the
groundwater plume(s). A report summarizing the sampling, results, evaluation,
and conclusions of the surface water evaluation was submitted to NCDEQ in
March 2019 and is included in Appendix K.
• An evaluation of potential affected groundwater migration to surface water
under future conditions was conducted and the results of the evaluation are
presented in Appendix K. There were no constituent concentrations predicted to
be greater than 02B surface water standards attributable to the groundwater
plume(s).
• Background soil dataset and BTVs were updated. Information about background
determinations is presented in Section 4.0. Updated soil BTVs are listed on
Table 4-2.
• Background groundwater dataset and BTVs was updated to include data
through December 2018. Information about background determinations is
presented in Section 4.0. Updated groundwater BTVs are listed on Table 4-3.
• The Belews Creek 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.
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• The Belews Creek Conceptual Site Model (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.
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3.0 OVERVIEW OF SOURCE AREAS BEING PROPOSED FOR
CORRECTIVE ACTION
(CAP Content Section 3)
The ash basin is the only CAMA-regulated unit at the Site. The only additional source
located within or adjacent to the ash basin and is addressed under this CAP Update is
the closed PHR Landfill. Figure 1-2 shows the location of the ash basin waste boundary
and compliance boundary, and the PHR Landfill waste boundary (CAP Content Section
3.A and 3.A.a).
Other facilities at the Site are not part of the source area addressed herein. A consensus
reached with the NCDEQ DWR regarding sources not considered for corrective action
as part of this CAP Update and was provided in a letter from NCDEQ to Duke Energy
dated April 5, 2019 (Appendix A). Brief descriptions of these facilities, their status of
inclusion or exclusion as part of the source area, and the rationale for inclusion or
exclusion is provided in Table 3-1 (CAP Content Section 3.B).
The Belews Creek ash basin and closed PHR Landfill are the two sources carried
forward as part of this CAP Update. Three onsite facilities, including the PHR Landfill,
Chemical Pond, and Constructed Wetlands Treatment System (CWTS), are identified as
hydrologically connected within the drainage systems (i.e. watershed) of the ash basin,
two of which were formerly part of the ash basin waste water treatment system:
Chemical Pond and CWTS. There is no evidence that source material associated with
the Chemical Pond and CWTS have contributed to any constituent migration in
groundwater, and therefore these facilities are not carried forward for corrective action
as part of this CAP Update.
The closed PHR Landfill is under NCDEQ DWM regulatory oversight and is monitored
on a semiannual basis. Groundwater sampling data indicate constituents similar to
COIs identified from groundwater monitoring of the ash basin [e.g. boron, total
dissolved solids (TDS)] are present in groundwater beneath and within a limited
horizontal extent of the landfill footprint. The ash basin compliance boundary and
landfill compliance boundary overlap, with the exception of an area of the landfill south
of the ash basin compliance boundary (Figure 1-2). All groundwater constituent
migration from the landfill occurs within with the landfill compliance boundary, with
the exception of some constituent migration north of the landfill, within the ash basin
compliance boundary. Constituent migration north of the landfill has a comingled
plume with the ash basin plume. Groundwater constituent migration from the landfill
is predicted to not migrate beyond the landfill compliance boundary in the future.
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Groundwater from the closed landfill and the ash basin primarily flows north, where
corrective action is planned. Corrective action approach for the ash basin and PHR
Landfill is discussed in detail in Section 6.0.
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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 in the Piedmont physiographic province of north -central North
Carolina. 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 constituents from a source
area. If the assessment data concentrations are less than background, it is likely
constituent migration from the source area 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 through the use and
interpretation of 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 area
• Consideration of other constituents present at concentrations greater than
background values
The BCSS and nine other Duke Energy facilities (Allen Steam Station, Buck Steam
Station, Cape Fear Steam Electric Plant, Cliffside Steam Station, Dan River Steam
Station, Marshall Steam Station, Mayo Steam Electric Plant, Riverbend Steam Station,
and Roxboro Steam Electric Plant) are situated in the Piedmont physiographic province
of north -central North Carolina. The nine Duke Energy facilities are located within a
120-mile radius from Belews Creek. 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 BTVs 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 coal ash basin or additional source areas. A map
showing the background locations for all media including groundwater, surface water,
soil, and sediments are shown in Figure 4-1 (CAP Content Section 4.A). Tables referenced
in this section present background datasets for each media, statistically calculated
background threshold values (BTVs) for soil and groundwater, and background dataset
ranges for surface water and sediment.
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
migration to surface water (Appendix K) 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 are included in Appendix C, Table 4 (CAP
Content Section 4.B). Background soils samples were collected from multiple
unsaturated depth intervals (Table 4-1). All samples were collected from depth
intervals greater than one foot above the seasonal high water table. The BCSS
background soil boring locations, unsaturated soil depth interval and number of
discrete samples collected from the unsaturated soil depth interval are presented in
Table 4-1.
The suitability of each of these locations for evaluating background conditions was
addressed in a technical memorandum (May 26, 2017). In a response letter 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 and SynTerra, 2017).
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Duke Energy previously submitted soil provisional background threshold values
(PBTVs) — Proposed Background Threshold Values for Naturally Occurring Concentrations in
Groundwater and Soil (SynTerra, 2017) and subsequent updated soil BTVs to NCDEQ —
Updated Background Threshold Values for Soil Technical Memorandum (SynTerra, 2017).
NCDEQ provided comments on PBTVs in a response letter dated September 1, 2017;
and NCDEQ provided approval of updated BTVs in a response letter dated May 14,
2018. Responses letters are provided in Appendix A. Soil background values for Belews
Creek were updated in 2019 and are provided, along with the original soil BTVs for
comparison and North Carolina Piedmont soil BTV ranges for comparison, in Table 4-2
(CAP Content Section 4.B).
The updated BTVs were calculated using data from background unsaturated soil
samples collected June 2015 to April 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 titled, "Background
Threshold Value Statistical Outlier Evaluation —Allen, Belews Creek, Cliftside, Marshall, Mayo,
and Roxboro Sites,", which was provided as an attachment to the Updated Background
Threshold Values for Constituent Concentrations in Groundwater (SynTerra, 2019). 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 and SynTerra, 2017).
4.2 Background Concentrations for Groundwater
The groundwater system beneath to the Site is divided into the following three flow
zones to distinguish the interconnected groundwater system: the shallow flow layer,
deep (transition zone) flow layer, and the bedrock flow layer. The BCSS flow zones and
background groundwater monitoring wells installed within each flow zone include:
0 Shallow flow zone: BG-1S, BG-2S, BG-3S, MW-202S, and MW-3
• Deep flow zone: BG-1D, BG-2D, BG-3D, and MW-202D
• Bedrock flow zone: BG-2BRA and MW-202BR
The locations of the background monitoring wells are shown on Figure 4-1. The
groundwater background dataset with the appropriate 02L standards, IMAC, and BTVs
is included in Appendix C, Table 4 (CAP Content Section 4.C). The suitability of each of
these locations for background purposes was evaluated in the Updated Background
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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 (NCDEQ, 2017)
provided in Appendix A.
Duke Energy previously submitted groundwater PBTVs — Proposed Background
Threshold Values for Naturally Occurring Concentrations in Groundwater and Soil (SynTerra,
2017) and subsequent updated groundwater BTVs to NCDEQ — Updated Background
Threshold Values for Groundwater Technical Memorandum (SynTerra, 2017). NCDEQ
provided comments, on the initial PBTVs in a response letter dated September 1, 2017;
and approval of updated BTVs in a response letter dated May 14, 2018. Responses
letters are provided in Appendix A. Groundwater background values for each
groundwater flow zone at BCSS were updated in 2019 and are provided, along with the
original groundwater BTVs and North Carolina Piedmont groundwater BTV ranges for
comparison, in Table 4-3 (CAP Content Section 4.C).
The updated background dataset was calculated using concentration data from
background groundwater samples collected from 2011 to 2018. Background values were
calculated in accordance with the Revised Statistical Methods for Developing Reference
Background Concentrations for Groundwater and Soil at Coal Ash Facilities (HDR and
SynTerra, 2017). The updated background datasets for each flow system used to
statistically assess naturally occurring concentrations of inorganic constituents in
groundwater are presented in the report Updated Background Threshold Values for
Constituent Concentrations in Groundwater (SynTerra, 2019d) provided to NCDEQ on
June 13, 2019. The updated background dataset for each hydrogeologic flow zone
consists of an aggregate of total (non -filtered) concentration data pooled across
background monitoring wells installed within that flow layer. The use of updated
groundwater BTVs is currently under appeal.
4.3 Background Concentrations for Surface Water
Background surface water sample locations in the Dan River and Belews Reservoir are
located upstream, or outside potential affected groundwater migration from the 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.
Background surface water sample locations include three locations from the Dan River
and four locations from Belews Reservoir. Surface water sample locations are shown on
Figure 4-1. Locations are summarized below with the surface water body and spatial
distribution relative to the source area:
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• Dan River sample locations upstream of potential groundwater migration to
surface water from the ash basin area: SW-DR-BG, SW-DR-BG2, and SW-DR-TFC
• Belews Reservoir sample location downstream, northeast of potential
groundwater migration to surface water from the ash basin: SW-BL-D
• Belews Reservoir sample location on the southern (opposite) side of the reservoir
from the source area: SW-BL-BG
• Belews Reservoir sample locations on the southern (opposite) side of the
reservoir from the source area, downgradient of the lined Craig Road Landfill:
SW-BL-U2 and SW-BL-U3
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. Background surface water analytical
dataset ranges compared to 02B and USEPA criteria are included in Table 4-4 (CAP
Content Section 4.D). The surface water background dataset with the appropriate 02B
standards is included in Appendix C, Table 2 (CAP Content Section 4.D).
Background data sets from each location include data from five or more samples.
Surface water samples from background locations have been collected in accordance
with NCDEQ guidance as part of periodic sampling events, which include the
comprehensive sampling event in February 2018 used to assess surface water
compliance for implementation of corrective action under Subchapter 02L .0106 (k) and
(1). Analytical results from background surface water sample locations indicate all
constituent concentrations are less than 02B standards with the exception of turbidity in
the Dan River.
4.4 Background Concentrations for Sediment
All background sediment sample locations are co -located with background surface
water sample locations in the Dan River and Belews Reservoir. Background sediment
sample locations are located upstream, or outside potential groundwater migration
from the source area to sediment. Sediment background sample locations remain
outside of future migration areas as determined by groundwater predictive modeling.
Background sediment sample locations (Figure 4-1) include:
• Dan River: SD-DR-BG, SD-DR-BG2, and SD-DR-TFC
• Belews Reservoir: SD-BL-BG, SD-BL-D, SD-BL-U2, and SD-BL-U3
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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). The sediment background dataset is
included in Appendix C, Table 5 (CAP Content Section 4.E).
Background data sets include one sample collected from each location. Sediment
samples were collected concurrently with a background surface water sample.
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5.0 CONCEPTUAL SITE MODEL
(CAP Content Section 5)
The Conceptual Site Model (CSM) is a descriptive and illustrative representation of the
hydrogeologic conditions and constituent interactions specific to the Site. The purpose
of the CSM pertaining to the Belews Creek ash basin and PHR Landfill is to provide a
current understanding of the distribution of constituents with regard to the Site -specific
geology/hydrogeology and geochemical processes that control the transport and
potential presence of constituents in various media. This information is also considered
with respect to exposure pathways to potential human and ecological receptors.
The CSM presented in this section is based on an 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 BCSS 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.
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 at the ash basin and PHR Landfill is divided into the
following three flow zones to distinguish the interconnected groundwater
system: the shallow flow zone, deep (transition zone) flow zone, and the bedrock
flow zone. The following is a summary of the natural hydrostratigraphic unit
assessment observations:
Shallow flow zone (S): Shallow flow zone includes fill, regolith, and
saprolite. Fill material was used in the construction of the ash basin dam
and generally consisted of reworked silts, clays, and sands. The range of
fill thickness observed at four locations on the ash basin main dam was 23
feet to 69 feet. The regolith is in -place soil that develops by weathering.
The soil consists primarily of silt with sand, clayey sand, sandy clay, clay
with gravel, and clayey silts. The range of regolith thickness observed was
5 feet to 68 feet. Saprolite is soil developed by in -place weathering of rock
that retains remnant bedrock structure (such as a planar fabric associated
with relict foliation). Saprolite consists primarily of medium dense to very
dense silty sand, sandy silt, sand, sand with gravel, sand with clay, clay
with sand, and clay. Sand particle size ranges from fine- to coarse -grained.
The range of saprolite/weathered rock observed was less than 1 foot to 49
feet. The shallow flow zone might or might not be saturated depending
on the topographic area of the Site.
Deep flow zone (D): The deep flow zone (transition zone) consists of a
relatively transmissive zone of partially weathered bedrock encountered
below the shallow zone. Observations of core recovered from this zone
included rock fragments, unconsolidated material, and highly oxidized
bedrock material. The transition zone thickness ranges from 0 feet to 30
feet.
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• 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. The main
rock type in the immediate vicinity of the ash basin is mica schist. Rock
core samples have been identified as metamorphic rock with a foliated
fabric (i.e., the elongated minerals are oriented parallel to each other or
form some bands). The principal minerals are biotite, quartz, muscovite,
and plagioclase (Appendix F, Attachment D). 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). The majority of water -producing fracture
zones were found within the top 50 feet of competent rock. Belews Creek
bedrock fracture orientation and flow profile characterization data sets
support overall fracturing and fracture aperture decreases with increasing
depth, and a general decline in hydraulic conductivity with increasing
depth below the top of bedrock (Appendix F). Groundwater flow in
bedrock fractures is anisotropic and difficult to predict, and velocities
change as groundwater moves between factures of varying orientations,
gradients, pressure, and size. A detailed evaluation of bedrock conditions
is located in Appendix F.
5.1.2 Site Hydrogeologic Setting
(CAP Content Section 5.A.a)
The groundwater system in the natural materials (saprolite/transition
zonelbedrock) is consistent with the regolith-fractured rock system and is
characterized as an unconfined, interconnected groundwater system typical of
the Piedmont Physiographic Province.
A conceptual model of groundwater flow in the Piedmont, which applies to the
BCSS site, was developed by LeGrand (1988, 1989) and Daniel and Harned
(2017a) (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
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current conditions. Groundwater is
recharged by 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).
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.
FIGURE 5-2
LEGRAND SLOPE
AQUIFER SYSTEM
51—A-6.B.-4.Y—ITouw L. 11m3c
T?iarhar-R.—darp
�rue¢dwatwr Fbw Dmxao.
Compartmented groundwater flow,
applicable to the Belews Creek ash basin and PHR Landfill, is described in detail
in A Master Conceptual Model for Hydrogeological Site Characterization in the
Piedmont and Mountain Region of North Carolina (LeGrand, 2004).
5.1.2.1 Groundwater Flow Direction
(CAP Content Section 5.A.a.i)
A groundwater divide is located east of the ash basin and PHR Landfill
represented by a topographical ridge approximated by Pine Hall Road and
a topographical ridge west of the ash basin and PHR Landfill along
Middleton Loop. Another groundwater divide exists north of the ash basin
along a ridgeline that extends from the east of the basin dam toward the
northeast. An exception is a localized area near the northwest corner of the
ash basin, where the hydraulic head created by the operational water level
in the ash basin causes groundwater from the ash basin to flow beyond a
thin pre -basin topographical divide along Middleton Loop.
With the exception of the northwest corner of the ash basin, groundwater
on the basin side of each ridge flows toward the basin while groundwater
on the opposite side of the ridge flows away from the basin. The hydraulic
divides provide natural hydraulic control of ash basin constituent migration
within the stream valley system, with the predominant direction of
groundwater flow being to the north. Groundwater model simulations
indicate that lowering the hydraulic head in the ash basin by decanting and
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subsequent closure will re-establish the groundwater divide along
Middleton Loop Road to the northwest of the ash basin (Appendix G).
The ash basin and PHR Landfill were constructed within a former perennial
stream valley. The ash basins physical setting is a horizontal flow -through
water system with groundwater movement into the upgradient end,
flowing generally north through the middle regions and downward near
the dam (Figure 5-3). Near the dam, vertical hydraulic gradients, imposed
by hydraulic pressure of basin free water, promote downward vertical
gradients into the groundwater system. The hydraulic pressure and
downward vertical gradient of the ponded water in the basin near the dam
is the most important factor contributing to constituent migration in
groundwater. Beyond the dam, groundwater flows upward. Generally, the
physical setting of the ash basin within a 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 remains in the ash basin and PHR Landfill's stream valley
system. Therefore, areas upgradient and side -gradient of the ash basin and
PHR Landfill have groundwater divides that limit groundwater flow in
these directions.
FIGURE 5-3
GENERAL PROFILE OF ASH BASIN PRE -DECANTING FLOW
CONDITIONS IN THE PIEDMONT
SS-••• PRECIPITATION
RUNOFF
EARTHEN
ASH DAM
-' ---- - -- -- --
FLOW
HEAD
CHANGE
GROUNDWATER FLOW
ENTERING BASIN _ -
(FORMER STREAM CHANNEL)
FLOW/SEEPAGE BENEATH DAM -
Note:
Drawing is not to scale
Water -level maps for each groundwater flow zone were constructed from
pre -decanting groundwater elevations, obtained in April 2019 (Figures 5-4a,
5-4b and 5-4c). April 2019 water level measurements and elevations are
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presented in Table 5-1. General groundwater flow directions can be
inferred from the water -level contours. The groundwater flow direction for
each flow zone associated with the basin is generally from south to north.
Groundwater flow directions developed from water -level elevations
measured in the shallow, deep, and bedrock wells indicate groundwater
flow from the ash basin is generally to the north and northwest toward the
Dan River.
Predictive flow and transport model simulations indicate that the cessation
of sluicing and subsequent decanting in the ash basin will reduce the
potential for constituent transport prior to complete closure of the basin.
Model simulations predict downward migration of groundwater below the
dam north of the ash basin will be limited without the presence of ponded
water in the basin.
The following are conclusions pertaining to groundwater flow beneath the
Site:
• 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
dam.
• Upward vertical gradients occur beyond or downstream of the dam,
which is the main groundwater discharge zone.
Empirical Site data from over 30 monitoring events over multiple seasonal
variations and groundwater flow and transport modeling simulations
support groundwater flow is away from water supply wells and that there
are no exposure pathways between the ash basin and the pumping wells
used for water supply in the vicinity of the Site. Domestic and public water
supply wells now connected to a filtration system are outside, or upgradient
of the groundwater flow system containing the ash basin and the PHR
Landfill.
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5.1.2.2 Groundwater Seepage Velocities
(CAP Content Section 5.A.a.i)
Groundwater seepage velocities were calculated for current conditions
using horizontal hydraulic gradients determined from measurements
collected in April 2019 (Table 5-1). Hydraulic conductivity 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 (K) for each zone and model
flow layer. Conductivity values ranged from 0.05 to 4.0 feet per day
(feet/day) for the shallow flow zone, from 0.01 to 7.0 feet/day for the deep
flow zone, and from 0.0002 to 0.7 feet/day for the bedrock flow zone.
Hydraulic conductivity values used in calculating seepage velocity were
selected based on area's location within or proximity to subdivided
hydraulic conductivity zones. The flow and transport model provided an
effective porosity of 30 percent for the shallow and deep flow zone, and 1
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
79S n(
e d l
Using the April 2019 groundwater elevation data, the average horizontal
groundwater flow velocity in the vicinity of the ash basin is:
• 0.19 feet/day (approximately 70 ft/yr) in the shallow flow zone
• 0.41 feet/day (approximately 149 ft/yr) in the deep flow zone
• 0.25 feet/day (approximately 92 ft/yr) in the bedrock flow zone
Groundwater modeling predicts groundwater elevation changes associated
with closure activities will change flow velocities and result in a more
pronounced groundwater divide upgradient, east and west of the Belews
Creek ash basin and PHR Landfill. As of December 1, 2019, approximately
469,400,000 gallons water have been removed from the ash basin. The water
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elevation in the ash basin has decreased by 10.6 feet in response to
decanting, indicating significant water level changes in the ash basin have
already occurred. For visualization, velocity vector maps of groundwater
under pre -decanting and future conditions were developed. The pre -
decanting conditions map was created from comprehensive Site data
incorporated into the calibrated flow and transport model. The future
condition maps were created using predicted flow fields for the excavation
closure scenario. Saturated conditions in the deep flow zone are relatively
constant across the Site; therefore, the deep flow zone was selected for the
velocity vector maps.
• Velocity vector map for groundwater in the deep flow zone under
pre -decanting conditions - Figure 5-5a
• Velocity vector map for groundwater in the deep flow zone under
Closure -In -Place conditions - Figure 5-5b
• Velocity vector map for groundwater in the deep flow zone under
Closure -By -Excavation conditions - Figure 5-5c
These depictions illustrate potential future changes in groundwater flow
compared to pre -decanting groundwater flow throughout the Site. Key
conclusions from the predictive model simulation of future ash basin
closure conditions include:
Differences between the closure -in -place and closure -by -excavation
closure scenarios velocity vecotors are minimal north of the ash
basin, and nearly no differences are observed northwest of the ash
basin (Figure 5-5b and Figure 5-5c).
North of the ash basin, velocity vectors under pre -decanting
conditions indicate groundwater velocity is greatest (5.0 to 10.0
feet/day) beneath and immediately downstream of the ash basin dam
and flows predominantly north (Figure 5-5a). Post ash basin closure,
the velocity vector directions turn inward, simulating the natural
funneling system of the historical stream valley, and the flow
velocities are reduced to 0.1 to 5.0 feet/day (Figure 5-5b and
Figure 5-5c). Under both pre -decanting and post -closure site
conditions, in the area immediately north of the current dam
location, the velocity vectors turn sharply toward the perennial
stream, where groundwater discharges. This flow pattern has limited
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the northward movement of groundwater plumes, and will continue
to do so after ash basin closure.
• Northwest of the basin, velocity vectors under pre -decanting
conditions, which include the interim action groundwater extraction
system, indicate groundwater flow from the ash basin toward the
northwest with a flow velocity that ranges from 0.1 to 1.0 feet/day
(Figure 5-5a). Post ash basin closure, a hydraulic divide is predicted
northwest of the ash basin boundary, where the velocity vector
directions diverge and the velocity decreases several orders of
magnitude from 0.001 to 0.01 feet/day (Figure 5-5b and Figure 5-5c).
The groundwater flow from the ash basin to the northwest area is
reversed, indicating that post -closure conditions will limit any
movement of constituents farther northwest from the current ash
basin location.
East of the basin, velocity vectors under pre -decanting conditions
indicate a groundwater flow direction is divided along a topographic
ridge with a relatively low velocity of 0.01 to 0.1 feet/day (Figure 5-
5a). Post ash basin closure, limited change from pre -decanting Site
conditions is observed ((Figure 5-5b and Figure 5-5c).
South and southwest of the ash basin and PHR Landfill, velocity
vectors under pre -decanting conditions demonstrate groundwater
flow within the basin does not cross the hydraulic divide represented
by the topographic ridge along Pine Hall Road (Figure 5-5a) Post ash
basin closure, the hydraulic divide remains and is enhanced (Figure
5-5b and Figure 5-5c). In both cases, groundwater flow within the
basin and PHR Landfill remains to the north-northwest toward the
perennial stream with no flow toward Belews Reservoir.
• Velocity vectors depictions for pre-deanting and post -closure site
conditions support that groundwater flow from the ash basin and
PHR Landfill does not, and will not, flow in the direction of
residential areas and water supply wells to the southwest and to the
east-northeast.
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5.1.2.3 Hydraulic Gradients
(CAP Content Section 5.A.a.i)
Hydraulic gradients are nearly flat across large areas of the ash basin due to
the influence of standing water. The average horizontal hydraulic gradients
(measured in feet/foot) for each flow zone is: 0.065 ft/ft (shallow flow zone),
0.069 ft/ft (deep flow zone), and 0.056 ft/ft (bedrock flow zone) based on
hydraulic gradient calculations using April 2019 groundwater elevation
data and are consistent with gradients calculated from other monitoring
events, including data presented in the 2018 CAMA Annual Interim
Monitoring Report (SynTerra, 2019c).
Vertical hydraulic gradients were calculated at clustered wells from the
water level data and the midpoint elevations of the well screens. Within the
ash basin, an upward vertical gradient was observed between the ash pore
water and the deep flow zone at well cluster AB-7S/-7D (-0.707 ft/ft). Farther
to the north in the ash delta, a small downward, near neutral, vertical
gradient occurred between the ash pore water and shallow flow zone at
well cluster AB-4SL/-4SAP (0.001 ft/ft). At the ash basin dam, an upward
gradient occurred at the well pair AB-1D/-1BR between the deep and
bedrock flow zones (-0.007 ft/ft). A downward vertical gradient is indicated
in the shallow, deep, and bedrock flow zones on the upstream side of the
ash basin dam based on the groundwater flow and transport modeling
results, which are supported by over 170 monitoring wells monitored at the
Belews Creek ash basin and PHR Landfill.
Beyond the ash basin dam, an upward gradient is observed at groundwater
monitoring well cluster MW-200 S/D/BR. Between the shallow flow zone
(MW-200S) and the bedrock flow zone the upward vertical gradient is
calculated to be approximately -0.3 ft/ft. Bedrock well MW-200BR is a free
flowing artesian well. Well cluster MW-200S/D/BR is positioned at the ash
basin compliance boundary. The upward component of groundwater flow
to the groundwater discharge zone minimizes the horizontal extent of
constituent migration downgradient of the ash basin compliance boundary.
The vertical gradient shifts to a downward direction further downstream of
the ash basin dam in the stream valley north of the ash basin dam due to
upland recharge from the topographic ridge along Middleton Loop. This is
downward vertical gradient is observed at well cluster GWA-24S/D/BR,
where the upward vertical gradient is calculated to be 0.2 ft/ft between the
deep and bedrock flow zones.
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Northwest of the ash basin, a downward vertical gradient is observed at
well pair GWA-11S/D (0.588 ft/ft). Further downgradient, smaller
downward vertical gradients are observed at well pairs GWA-27S/D (0.086
ft/ft) and GWA-21S/D (0.088 ft/ft). The vertical gradient shifts to an upward
direction farther to the north between the shallow and deep flow zones.
This is observed at well pairs GWA-30S/D (-0.013 ft/ft) and GWA-31S/D (-
0.179 ft/ft) located upgradient or adjacent to streams northwest of the ash
basin.
5.1.2.4 Particle Tracking Results
(CAP Content Section 5.A.a.ii)
Particle tracking is not available for Belews Creek.
5.1.2.5 Subsurface Heterogeneities
(CAP Content Section 5.A.a.iii)
The nature of groundwater flow across the Site is based on the character
and configuration of the ash basin 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
flow zone, deep flow zone, and the bedrock flow zone. The shallow flow
zone is composed of residual soil/saprolite. Typically, the residual
soil/saprolite is partially saturated and the water table fluctuates within it.
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 saprolite, transition
zone and in fractures and joints of the underlying bedrock. The shallow
water table and bedrock water -bearing zones are interconnected. 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 Belews Creek,
horizontal groundwater flow within the bedrock should occur
approximately parallel to the hydraulic gradient, with no preferential flow
direction (Appendix F). Consistent with this interpretation, the current
groundwater flow model for BCSS does not simulate plan -view anisotropy.
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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.
Identification of piping near and around the ash basins was conducted by
Stantec in 2014 and 2015, and utilities at the Site were also included on a
2015 topographic map by WSP USA, Inc. (CSA Update, 2017). Based on
groundwater flow direction at the Site and identified subsurface
underground utilities present at the site, 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
unaffected 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 therefore 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 within the matrix occurs on a much larger
surface area than would be the case if the solute mass remained entirely
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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 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 at the Site and calculated
fracture apertures decrease 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 Snow 1968),
and indicates that the overall volumetric rate of groundwater flow in the
bedrock decreases with depth (Appendix F).
The available data do not indicate any predominant bedrock fracture sets at
BCSS. Overall, a wide range of open fracture dip angles and dip directions
is observed. Based on the orientations of lineaments and open bedrock
fractures, horizontal groundwater flow within the bedrock should occur
approximately parallel to the hydraulic gradient, with no preferential flow
direction (i.e., no expected, significant anisotropy) (Appendix F). Consistent
with this interpretation, the current groundwater flow model for BCSS does
not simulate plan -view anisotropy.
Rock core samples from bedrock locations which represent areas of affected
groundwater migration, north and northwest of the ash basin and are
interpreted to coincide with zones of preferential groundwater flow were
analyzed for porosity, bulk density and thin section petrography.
The reported matrix porosity values ranged from 0.50 percent to 0.73
percent with an average of 0.62 percent. Bulk density ranged from 2.80
grams per cubic centimeter (g/cm3) to 2.84 g/cm3 with an average of 2.82
g/cm3 (Appendix F). Petrographic evaluation classified both samples as
mica schist with a foliated fabric (i.e., the elongated minerals are oriented
parallel to each other or form some bands). The principal minerals are
biotite, quartz, muscovite, and plagioclase (Appendix F).
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The bedrock beneath the BCSS site is crystalline, and consists of and granite,
diorite, gneiss and schist. Solid samples of unfractured metamorphic rock
and plutonic igneous rock have low porosities - rarely larger than 2%. In
general, crystallite rock porosity is much lower than that of sedimentary
rocks. The reported matrix porosity values are within the range of those
reported for crystalline rocks in the literature (Freeze and Cherry, 1979;
L6fgren, 2004; Zhou and others, 2008; Ademeso and others, 2012). The
presence of measurable matrix porosity suggests that matrix diffusion
contributes to plume retardation at the site (Lipson and others, 2005). 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 model.
5.1.2.7 Onsite and Offsite Pumping Influences
(CAP Content Section 5.A.a.v)
Current onsite pumping within the groundwater flow system containing
the ash basin include interim actions ash basin decanting the accelerated
remediation groundwater extraction system. Decanting was initiated on
March 27, 2019. As of December 1, 2019, approximately 469,400,000 gallons
water have been removed from the ash basin and the water elevation has
decreased by 10.6 feet. The accelerated remediation groundwater extraction
system currently operates at approximately 12 gpm extraction flow rate. As
of November 2019, approximately 9,900,000 gallons of water have been
extracted by the system. Post -decanting, the 10 interim action extraction
wells are expected to have reduced extraction rates as a result of the
reduced hydraulic head of the ash basin. Effects of interim actions on the
groundwater system are discussed more in Section 6.1.
Because much of the area surrounding the ash basin is either residential
properties, farm land, or undeveloped land, potential offsite pumping
influences would be limited to domestic and public water supply wells.
Water supply wells are outside, or upgradient of the groundwater flow
system containing the ash basin. Flow and transport modeling indicated
private water wells within the model area remove only a small amount of
water from the overall hydrologic system (Appendix G).
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5.1.2.8 Groundwater Balance
(CAP Content Section 5.A.a.vi)
The ash basin and PHR Landfill are located within a single watershed and
groundwater flow system. The location of the groundwater divides
defining the edge of the watershed change due to decanting and closure
activities because of changing hydraulic conditions. The flow and transport
model was used to evaluate the ash basin hydraulic conditions prior to
decanting, post decanting and post closure (both closure -in -place and
closure -by -excavation). Each scenario water balance was developed for
using the results from flow and transport model current and predicted
groundwater simulations (Appendix G). The approximate groundwater
flow budget in the ash basin watershed under each simulated scenario is
summarized in the Table 5-2.
Pre -Decanting Conditions Groundwater Balance
Under pre -decanting conditions, the watershed area contributing flow
toward the basin is estimated to be approximately 620 acres. Removing the
areas that do not contribute recharge to the groundwater system, including
the closed PHR Landfill, former constructed wetlands area, and the free
water surface of the ash basin pond, the remaining area is approximately
270 acres.
• Groundwater recharge from the ash basin pond is estimated to be
200 gallons per minute (gpm), and is the primary water balance
component for groundwater recharge under pre -decanting
conditions.
• Groundwater recharge from the 270 acres of uncapped watershed is
estimated to be 120 gpm.
• Groundwater recharge from limited downward vertical flow from
the southern, upgradient portion of the ash basin is estimated to be
20 gpm.
• Drains in the simulation, primarily located upgradient of the ash
basin pond, receive an estimated groundwater discharge of
approximately 70 gpm.
• Groundwater that flows through and immediately under the dam
within the saprolite, transition zone and shallow bedrock, and then
discharges to surface water downstream of the dam, is estimated to
be 150 gpm.
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The remaining 120 gpm of groundwater discharge, not accounted for in the
directly related ash basin categories in the table above, is assumed to be
divided between water that flows through the ridge to the northwest and
flow through the deep bedrock under the dam to the north.
Post -Decanting Conditions Groundwater Balance
The flow and transport model was used to evaluate the ash basin and PHR
Landfill 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 (Table 5-2). The groundwater
simulation during post -decanting includes the interim extraction system
wells northwest of the ash basin that remove groundwater from the system.
Groundwater divide depths and widths are expected to change due to
decanting and closure activities. The extent of the ash basin and PHR
Landfill watershed under pre -decanting conditions does not include the
interim extraction system, however under post -decanting conditions the
watershed extent expands to include the interim extraction system. Under
simulated post -decanting conditions, the watershed area contributing flow
towards the basin is estimated at approximately 650 acres. Removing the
areas that do not contribute recharge to the groundwater system, including
the closed PHR Landfill, and former constructed wetlands area, and the free
water surface of the ash basin pond through decanting, the remaining area
is approximately 570 acres.
• Groundwater recharge from the 570 acres of uncapped watershed is
estimated to be 100 gpm.
• Groundwater recharge occurring in the footprint of the former ash
basin is estimated to be 119 gpm.
• Drains in the simulation receive an estimated groundwater discharge
of approximately 174 gpm.
• Groundwater that flows through and immediately under the dam
within the saprolite, transition zone and shallow bedrock, and then
discharges to surface water downstream of the dam, is estimated to
be 45 gpm.
• Existing interim action groundwater extraction wells discharge 2
gpm.
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The estimated discharge to streams downgradient of the ash basin dam is
reduced from approximately 150 gpm during pre -decanting conditions to
45 gpm after decanting. All other groundwater flow that is assumed to
contribute to groundwater flowing through the ridge to the northwest and
flow through the deep bedrock under the dam to the north is reduced from
120 gpm during pre -decanting conditions to almost indiscernible flow (-2
gpm). The reestablished groundwater divide northwest of the ash basin is
expected to significantly reduce or eliminate groundwater flow to the
northwest. The remaining groundwater flows north. Decanting the ash
basin has the greatest impact on the water balance, reducing the total
groundwater flow budget by more than 120 gpm from pre -decanting
conditions.
Post -Closure Conditions Groundwater Balances
The flow and transport model was used to evaluate the ash basin and PHR
Landfill hydraulic conditions that would occur after two ash basin closure
scenarios. A water balance was developed for the simulated groundwater
system under post -closure conditions (Table 5-2). The groundwater
simulation during post- closure includes the interim extraction system wells
northwest of the ash basin that remove groundwater from the system.
The extent of the ash basin watershed under post -closure conditions is
expected to remain the same as post -decanting conditions. The largest
hydraulic differences between post -decanting and post -closure Site
conditions is the area of capped surfaces and lowering or removal of the ash
basin dam. Removing the areas that do not contribute recharge to the
groundwater system, including the closed PHR Landfill, and former
constructed wetlands area, and the closure option resulting landfill, the
remaining area is approximately 430 acres for closure -in -place and 510 acres
for closure -by -excavation.
• Groundwater recharge from the acres of uncapped watershed is
estimated to be either 92 or 120 gpm, depending on the selected
closure option.
• Groundwater recharge occurring in the footprint of the former ash
basin is estimated to be either 56 or 119 gpm, depending on the
selected closure option.
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• Drains in the simulation receive an estimated groundwater discharge
of approximately 157 or 195 gpm, depending on the selected closure
option.
Because it is expected the dam will be significantly lowered or
removed during the ash basin closure process, there is no estimated
groundwater flow through and immediately under the dam under
post -closure conditions.
Existing interim action groundwater extraction wells discharge 2
gpm. These scenarios do not include additional groundwater
remediation.
5.1.2.9 Effects of Naturally Occurring Constituents
(CAP Content Section 5.A.a.vii)
Metals and inorganic constituents, typically associated with CCR material,
are naturally occurring and present in the Piedmont physiographic
province of north -central North Carolina. The metals and inorganic
constituents occur in soil, bedrock, groundwater, surface water, and
sediment. During the Belews Creek 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 Belews Creek
contain naturally occurring constituents that are also typically related to
CCR material and likely effect the chemistry of groundwater at the Site.
Arsenic, total chromium, cobalt, iron, manganese, selenium and thallium
were present in background soil and rock samples at concentrations greater
than the preliminary soil remediation goals (PSRGs) for protection of
groundwater (POG) values (Table 4-2).
These results suggest that arsenic, total chromium, cobalt, iron, manganese,
selenium and thallium might occur naturally in groundwater at the Site.
Analytical results for groundwater at background locations indicate that
hexavalent chromium, total chromium, cobalt, iron, lithium, manganese,
molybdenum, strontium, and vanadium are present at concentrations
greater than 02L/IMAC standards in one or more flow zones (Table 4-3).
Therefore, downgradient concentrations of these constituents are compared
to background values for corresponding flow zone. Generally,
downgradient concentrations of hexavalent chromium, total chromium,
molybdenum, and vanadium concentrations are within background
concentration ranges.
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The horizontal flow -through water system related to the ash basin
described in the CSM has resulted in limited transport of constituents from
the ash basin into underlying groundwater. Near the dam, affected
groundwater flows under the dam and either discharges to the ash basin toe
drain systems or flows downward to the underlying groundwater system.
Beyond the dam, groundwater flows upward toward the unnamed
tributary, limiting downward migration of constituents to the area in close
proximity north of the dam. There is a component of groundwater flow
northwest of the ash basin where the hydraulic head created by the
operational water level in the ash basin causes groundwater from the ash
basin to flow beyond a thin pre -basin topographical divide along Middleton
Loop. The constituent management process, and a detailed discussion of
constituent migration and distribution is presented in Section 6.0.
5.2 Source Area Location
(CAP Content Section 5.A.b)
The ash basin, located across Pine Hall Road to the northwest of the station, is generally
bounded by an earthen dam and a natural ridge to the northeast, Middleton Loop to the
west, and Pine Hall Road to the south and east (Figure 1-2). Middleton Loop and Pine
Hall Road, located along topographic ridges, represent hydrogeologic divides that
affect groundwater flow within an area approximately 0.5 miles northeast, east, south,
and west of the ash basin. Topography to the west of Middleton Loop generally slopes
downward toward the Dan River to the north. Topography to the south and east of Pine
Hall Road generally slopes downward toward Belews Reservoir to the south and
southeast.
5.3 Summary of Potential Receptors
(CAP Content Section 5.A.c)
G.S. Section 130A-309.201(13) 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.
The site -specific risk assessment conducted for the ash basin and PHR Landfill indicates
no measurable difference between evaluated Site -related risks and risks imposed by
background concentrations (Appendix E). It is determined that there is no identified
material increases in risks to human health related to the ash basin and PHR Landfill.
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Additionally, multiple lines of evidence support that groundwater from the ash basin
area has not and does not flow towards any water supply wells based on groundwater
flow patterns and the location of water supply wells in the area. However, Duke
Energy has implemented a permanent water solution which provides owners of
surrounding properties with water supply wells within a 0.5-mile radius of the ash
compliance boundary with water filtration systems.
The site -specific risk assessment conducted for the ash basin also indicates that there is
no increase in risks to ecological receptors. The Dan River and Belews Reservoir aquatic
systems surrounding the BCSS are healthy based on multiple lines of evidence
including robust fish populations, species variety and other indicators based on years of
sampling data.
5.3.1 Surface Water
The Site is located in the Roanoke River watershed. The ash basin and PHR
Landfill are located between Belews Reservoir to the south and east and the Dan
River to the north. Associated North Carolina surface water classifications for
Belews Reservoir and the Dan River are summarized in Table 5-3.
Surface water intakes associated with BCSS plant operations include:
• An intake from Belews Reservoir used to pump water for BCSS plant
operations
• An intake from Belews Reservoir used to pump water for landfill
operations at the Craig Road Landfill
• A backup intake from the Dan River to pump water from the Dan River
for Belews Reservoir makeup water, if needed (for example, under
drought conditions)
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 boundary is provided in Figure 5-6. The surface water
information is provided from the Natural Resources Technical Report (NRTR)
prepared by AMEC Foster Wheeler (July, 2015). In addition, permitted outfalls
under the NPDES and the SOC locations are shown on Figure 5-6. Non -
constructed and dispositioned seep sample locations between the ash basin and
the Dan River and Belews Reservoir are managed by the SOC and are subject to
the monitoring and evaluation requirements contained in the SOC.
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5.3.1.1 Environmental Assessment of Belews Reservoir
and the Dan River
The NPDES permit for Belews Creek Steam Station requires Duke Energy to
conduct monthly outfall and instream water quality monitoring at 10
locations including within the Dan River. Trace elements (arsenic, selenium)
monitoring in fish muscle tissue is also conducted annually in accordance
with a study plan approved by the NCDEQ.
Belews Reservoir and the Dan River have been monitored by Duke Energy
since 1969.Over the years, specific assessments have been conducted for
water quality and chemistry as well as abundance and species composition
of phytoplankton, zooplankton, macroinvertebrates, aquatic macrophytes,
fish, and aquatic wildlife. These assessments have all demonstrated that
Belews Reservoir and the Dan River have been environmentally healthy
and functioning ecosystems, and ongoing sampling programs have been
established to ensure the health of these systems will continue.
Furthermore, these data indicate that there have been no significant effects
to the local aquatic systems related to coal ash constituents over the last 30
years. More information related environmental health assessments
conducted for the Dan River and Belews Reservoir, including sampling
programs, water quality and fish community assessments, and fish tissue
analysis, can be found in Appendix E.
5.3.2 Availability of Public Water Supply
No municipal water supply lines are available to residents within a 0.5-mile
radius of the ash basin compliance boundary.
The BCSS plant is supplied with municipal water from the City of Winston-
Salem; however, the water supply line enters the Duke property from the south
along Craig Road. The water supply line does not extend beyond that location.
The nearest available municipal water supply line, provided by the Town of
Walnut Cove, is located at the intersection of Martin Luther King Jr. Road and
Crestview Drive, approximately 4.5 miles to the west of the Duke Power Steam
Plant Road entrance to the Station.
5.3.3 Water Supply Wells
No public or private drinking water wells or wellhead protection areas were
found to be located downgradient of the ash basin. A total of 50 private water
supply wells and one public supply well were identified within the 0.5-mile
radius of the ash basin compliance boundary (Figure 5-7a). Most of these water
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supply wells are located northeast of the ash basin along Pine Hall Road and
Middleton Loop, and west and southwest of the ash basin along Middleton
Loop, Old Plantation Road, Pine Hall Road, and Martin Luther King Jr. Road.
Discussion, with supporting material and data, of alternative water supply
provisions (water filtration systems) provided by Duke Energy for surrounding
occupied residences and findings of the drinking water supply well survey are
included in Section 6.2.
5.3.4 Future Groundwater Use Area
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of the Belews Creek ash basin and PHR Landfill at and beyond the
predicted area of potential affected groundwater, with the exception of a 2.67
parcel northwest of the ash basin. Therefore, no future groundwater use areas
are anticipated downgradient of the basin and PHR Landfill.
Under G.S. Section 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 boundary. Duke Energy also voluntarily provided permanent water
solutions to business, schools, and churches within a 0.5-mile radius not
connected to a public water supply. It is anticipated that public and private
properties within a 0.5-mile of the ash basin compliance boundary 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 installed water treatment
systems to include replenishing expendables (salt for brine tank 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)
A human health and ecological risk assessment pertaining to Belews Creek was
prepared and is included in Appendix E. The risk assessment focuses on the potential
effects of CCR constituents from the Belews Creek ash basin 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
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risks to on -Site or off -Site human receptors potentially exposed to CCR constituents that
might have migrated from the ash basin; and 2) there is no evidence of risks to
ecological receptors potentially exposed to CCR constituents that might have migrated
from the ash basin. This risk assessment uses analytical results from groundwater,
surface water, and sediment samples collected March 2015 through June 2019.
Evaluation of risks associated with AOW locations and soil beneath the ash basin are
not subject to this assessment and will be evaluated independent from the CAP.
Consistent with the iterative risk assessment process and guidance, updates to the risk
assessment have been made to the original 2016 risk assessment (HDR, 2016b) 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 (HDR, 2016b)
2. Comprehensive Site Assessment (CSA) Update (SynTerra, 2017b)
3. Human Health and Ecological Risk Assessment Summary Update for Belews Creek
Steam Station, Appendix B of Community Impact Analysis of Ash Basin Closure
Options at the Belews Creek Steam Station (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 (HDR, 2016b), and
is based on NCDENR, 2003; NCDEQ, 2017; and USEPA risk assessment guidance
(USEPA, 1989; 1991a; 1998).
Human health and ecological CSM 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 basin was 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
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(COPCs) are different than COIs in that COPOC are those elements in which the
maximum detected concentrations exceeded human health or ecological screening
values. COPCs are carried forward for further evaluation in the deterministic risk
assessment. Constituents remaining as a result of the screening were carried forward in
the baseline 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 associated with the construction
worker exposure scenario.
• On- and off -Site surface water and sediment pose no unacceptable risks for
recreational receptors (swimmer, wader, boater, and recreational fisher).
• Consumption of fish in the Dan River by a subsistence fisher resulted in Hazard
Quotients (HQs) greater than 1 for cobalt and zinc. However, the exposure
model used assumed rates for bioconcentration and fish consumption, which
resulted in overestimated risks for the subsistence fisher.
• Consumption of fish by a subsistence fisher resulted in an estimated Excess
Lifetime Cancer Risk (ELCR) that is within the risk range of IX 10-4 to 1 x 10-6 for
hexavalent chromium for the Dan River and Belews Reservior; however, the EPC
used in the risk model was comparable to upgradient hexavalent chromium
concentrations.
Findings of the baseline ecological risk assessment include the following:
Ecological Exposure Area 1:
• No HQs based on NOAELS or LOAELs were greater than unity for wildlife
receptors (mallard duck, great blue heron, river otter) exposed to surface
water and sediments.
• Modeled risk estimates resulted in aluminum HQs greater than 1 based on
the NOAEL and LOAEL for the killdeer and based on NOAELs for the
muskrat. The modeled risk is considered negligible given the natural
occurrence of aluminum in surface water, sediment, and soil in the region.
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Ecological Exposure Area 3:
• No HQs based on NOAELS or LOAELs were greater than unity for wildlife
receptors (mallard duck, great blue heron, river otter) exposed to surface
water and sediments.
• Modeled risk estimates resulted in aluminum HQs greater than 1 based on
the NOAEL and LOAEL for the killdeer and based on NOAELs for the
muskrat. The modeled risk is considered negligible given the natural
occurrence of aluminum in surface water, sediment, and soil in the region.
In summary, there is no evidence of unacceptable risks to human and ecological
receptors exposed to environmental media potentially affected by CCR constituents at
Belews Creek. 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 Belews Creek CSM presented herein describes and illustrates geologic and
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 effects of constituents in various media and potential exposure
pathways to human and ecological receptors.
In summary, the ash basin and PHR Landfill were constructed within a former
perennial stream valley 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 dam. The upward flow of water into
the basin minimizes downward vertical constituent migration to groundwater
immediately underlying saturated ash in the upgradient ends of the basin. Due to the
prevailing horizontal flow within the ash basin, there is limited vertical flow of ash
basin pore water into the underlying groundwater. The elevated constituent
concentrations found in groundwater near the dam is due to the operating hydraulic
head in the basin. The ponded water in the basin is the most important factor
contributing to constituent migration in groundwater.
Based on empirical Site data from over 30 monitoring events over multiple seasonal
variations and groundwater flow and transport modeling simulations support
groundwater flow is away from water supply wells and that there are no exposure
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pathways between the ash basin and the pumping wells used for water supply in the
vicinity of the Site.
Through ash basin decanting and closure, the hydraulic head and the rate of constituent
migration from the ash basin to the groundwater system will be reduced based on basin
hydrogeology described above. Either closure option 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 basin is expected to be further contained within the stream valley
and continue flowing north of the ash basin footprint, and therefore will not flow
towards any water supply wells.
Multiple lines of evidence have been used to develop this CSM based on the large data
set generated for Belews Creek. This CSM provides the basis for this CAP Update
developed for the Belews Creek ash basin to comply with G.S. Section 130A-309.211,
amended by CAMA.
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6.0 CORRECTIVE ACTION APPROACH FOR SOURCE AREA 1
(ASH BASIN AND CLOSED PHR LANDFILL)
(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 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 area. Constituents of interest (COI) are those constituents identified from the
"constituent management process" described below and are specific to the source area,
not the Site. This evaluation assists in identifying constituents and areas that warrant
corrective action under G.S. Section 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 COIs that warrant corrective action. 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,
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• Maximum mean constituent concentrations,
• 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 constituents that have migrated from the
Belews Creek ash basin and PHR Landfill and warrant corrective action. The results of
the constituent management process (described in detail in Section 6.1.3) identify 11
groundwater COIs for the Belews Creek ash basin and PHR Landfill: arsenic, beryllium,
boron, chloride, cobalt, lithium, iron, manganese, strontium, TDS, and thallium.
Data indicate unsaturated soil constituent concentrations are generally consistent with
background concentrations or are less than regulatory screening values. In the few
instances where unsaturated soil constituent concentrations are greater than
Preliminary Soil Remediation Goal (PSRG) Protection of Groundwater (POG) standards
or background values, constituent concentrations are within range of background
dataset concentrations or there are no mechanisms by which the constituent could have
been transported from the ash basin or PHR Landfill to the unsaturated soils, therefore,
no soil constituents were identified for the Belews Creek ash basin and PHR Landfill.
6.1 Extent of Constituent Distribution
This section provides an in-depth review of constituent characteristics associated with
source area 1 and the mobility, distribution and extent of constituent migration within,
at, and beyond the point of compliance.
6.1.1 Source Material within the Waste Boundary
(CAP Content Section 6.A.a)
The ash basin and the PHR Landfill waste boundaries are shown on Figure 1-2.
An overview of the material within the ash basin and PHR Landfill is presented
in the following subsections.
6.1.1.1 Description of Waste Material and History of
Placement
(CAP Content Section 6.A.a.i)
The ash basin consists of a single cell impounded by the main earthen dam
located on the north end of the ash basin and an embankment dam (Pine
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Hall Road dam) located in the northeast portion of the basin along Pine Hall
Road (Figure 1-2). The main dam is approximately 2,000 feet long with a
maximum height of approximately 140 feet. The top of the dam is at an
elevation of 770 feet, and the crest is 20 feet wide. The ash basin, constructed
from 1970 to 1972, is located approximately 3,200 feet northwest of the BCSS
powerhouse. The area contained within the ash basin waste boundary is
approximately 283 acres. The normal operating elevation of the BCSS ash
basin pond is 750 feet, while full pond elevation is approximately 768.2 feet.
The full pond capacity of the ash basin is estimated to be 17,656,000 cubic
yards (cy) or approximately 10,940 acre feet.
CCR materials, composed primarily of fly ash and bottom ash, were initially
deposited in the unlined ash basin via sluice lines beginning in 1974. In
1984, BCSS converted from a wet fly ash handling system to a dry fly ash
handling system. After 1984, fly ash was handled dry and was only sluiced
to the ash basin during maintenance or abnormal conditions. Bottom ash
continued to be sluiced to the ash basin until May 2018 when the facility
converted to a dry bottom ash handling system. Deposition of all waste
streams into the ash basin ceased on March 27, 2019 in preparation for ash
basin closure.
6.1.1.2 Specific Waste Characteristics of Source Material
(CAP Content Section 6.A.a.ii)
Source characterization was performed through the completion of soil
borings, installation of monitoring wells, and collection and analysis of
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.
Seventeen (17) borings (AB-4S/SL/D/BR, AB-5S/D/GTB1, AB-6S/SL/D/GTB,
AB-7S/D/GTB, and AB-8S/SL/D) were advanced within the ash basin waste
boundary to obtain ash samples for chemical analyses (Figure 1-2). Borings
at the AB-1, AB-2, and AB-3 locations were advanced through the main
earthen dam without encountering ash, and three borings at the AB-9
1 Geotechnical boring
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Belews Creek Steam Station SynTerra
location drilled through the chemical pond dike (one of which was
advanced into bedrock) did not encounter ash. Ash was encountered in
borings AB-4, AB-5, AB-6, AB-7, and AB-8 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 materials. Ash was generally
described as gray to dark gray, non -plastic, loose to medium density, dry to
wet, fine- to coarse -grained sandy silt texture. Physical properties analyses
(grain size, specific gravity, and moisture content) were performed on seven
ash samples from the ash basin and measured using American Society for
Testing and Materials (ASTM) methods. Ash is generally characterized as a
non -plastic silty (medium to fine) sand or silt. Ash exhibits a lower specific
gravity, compared to soil, with two values reported from 1.7 (AB-6GTB) to
2.2 (AB-7SL). Moisture content of the ash samples ranges from 11.2 percent
to 65.4 percent.
Within an ash basin, ash typically contains interbedded layers of fly ash and
bottom ash as a result of the varying rates and pathways of bottom ash and
fly ash settlement. 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 6-1). 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 6-1
FLY ASH AND BOTTOM ASH INTERBEDDED DEPICTION
Particle Size Distribution Report
RAJ
,w r5_
xGra,ml
xsaneI
xF:,e.
0.0
OD
0.0
00
0.0
Coame
Fiy
Coarse
MpAlym
Fi1a
Sllr
co
9.6
16.2
32.7
27.8
13.3
0.4
D_D49-7
0.0
0.010.4
44.8
44.6
0.0
0.0
20.4
772
l.4
0.0
0.022.6
45.9
22.3
SOIL DATA
snam lE
4Eo�rr
-
O
B—Z
ABMW_3
3 "9
wry. s Iy 6 — SAND (SG = 2 674)
O
wag
AB -3
4O-Od2 O
Bmwa & 8rn fi _'I' CI AY (SO - 2 654)
tl
Boxing
MW-12
5.0-d.2
Reddish brown fi. sandy SILT (SG - 2.714)
O
B-9
MW-12
50.0-5235
Ligbr grey s. —dy SILT (SG - 2.694)
0
Boons
MW-13
2.3.475
GM & brows FL sandy SMT (50- 2.654)
6.1.1.3 Volume and Physical Horizontal and Vertical
Extent of Source Material
(CAP Content Section 6.A.a.iii)
The full pond capacity of the ash basin is estimated to be 17,656,000 cy.
Based on CCR inventory data through July 312019, topographic and
bathymetric surveys, the ash basin is estimated to contain approximately
9,975,800 cy of ash (AECOM, 2018). The horizontal limits of the source
material is depicted by the waste boundaries as shown on Figure 1-2. Based
on borings located within the ash basin, the maximum depth of CCR within
the ash basin is estimated to be approximately 80 feet. Volume and physical
horizontal and vertical extent of ash material within the basin as a cross-
section transect (A -A') along the centerline, from south to north, is
presented in Figure 6-2. Volume and physical vertical extent of ash material
at the basin northern portion as across -section transect (B-B') along the
ridgeline, from west to east, is presented in Figure 6-3.
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6.1.1.4 Volume and Physical Horizontal and Vertical
Extent of 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 6-4. Water levels of ash pore water wells under pre -
decanting conditions range from 3 feet to 7 feet below grade surface. Ash
basin decanting was initiated in March 2019. As of December 1, 2019,
469,400,000 million gallons of water has been decanted and the
corresponding pond water elevation has decreased by 10.6 significantly
reducing areas of saturated ash. The range of saturated ash thickness is
between a few feet to 80 feet, with greatest volume of saturated ash in the
central portion of the ash basin and a lesser volume of saturated ash in other
areas of the basin, including a majority of the portion of the basin covered
by ponded water (Figure 6-4). Using modeled potentiometric levels of the
saturated ash surface compared to pre -ash basin historical topographic
contours, the volume of saturated ash within the basin under pre -decanting
conditions was approximately 9,180,000 cy (AECOM, 2018).
Under ash basin closure by closure -in -place part of the ash is excavated and
moved to the southern part of the ash basin where it is capped with a final
cover system. The anticipated range of saturated ash thickness after closure
by closure -in -place is between a few feet to 50 feet, with the greatest volume
of anticipated saturated ash in the south central portion of the ash basin and
a lesser volume of anticipated saturated ash in the southern ash basin
fingers (Figure 6-4). The estimate is based on the approximated bottom of
ash from the flow and transport model simulation (Appendix G) and
simulated hydraulic heads. Closure -in -place simulated saturated ash
thickness is based on closure model results with an underdrain system
installed.
Under the closure -by -excavation option, it is anticipated all of the ash in the
ash basin would be excavated, and therefore no saturated ash would remain
in the ash basin footprint.
6.1.1.5 Saturated Ash and Groundwater
(CAP Content Section 6.A.a.v)
Based on the trend analysis results, the thickness of saturated ash remaining
in place following closure (closure -in -place only) will have limited to no
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
adverse effect on future groundwater quality. Layered ash within the basin
has resulted in relatively low vertical hydraulic conductivity, further
reducing the potential for downward flow of pore water into underlying
residual material. The horizontal flow -through ash basin system results in
low to non -detectable constituent concentrations in groundwater
underlying saturated ash within the basin except in the vicinity of the dam
where downward vertical hydraulic gradients are observed. The horizontal
flow -through system is consistent with Site -specific data, as observed with
boron concentration data from groundwater below the source area
(Table 6-1).
In summary, the data from five well cluster locations within the ash basin
demonstrate low (less than 260 µg/L and below the 02L groundwater
standard) to non -detectable boron concentrations consistent with the flow -
through system and suggests there is no correlation between the thickness
of saturated ash and the underlying groundwater quality (Table 6-1).
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 Belews Creek.
The 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. This is due to the downward
vertical hydraulic gradient in these areas, which enhances migration of
constituents.
Under pre -decanting conditions, the analysis demonstrates saturated ash
and ash pore water are not significantly contributing constituent
concentrations to underlying groundwater except near dikes and dams,
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
where downward vertical gradients exist. Pre -decanting conditions
represent the greatest opportunity for constituent 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
dam. Under post -decanting, the hydraulic head of the ash basin will be
reduced, therefore reducing the downward vertical gradient occurring near
the dam and the rate of constituent migration from the ash basin to the
groundwater system. Decanting the basin to reduce the vertical hydraulic
gradient 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)
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 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)
Ash Solid Phase and Synthetic Precipitation Leaching
Po ten tial
(CAP Content Section 6.A.a.vi.1.1 and 6.A.a.vi.1.2)
Ash samples collected inside the ash basin waste boundary were analyzed
for total extractable inorganics using EPA Methods 6010/6020. For
information purposes, ash samples were compared to soil background
values and preliminary soil remediation goals (PSRGs) for protection of
groundwater (POG). The ash analytical data do not represent soil conditions
outside of or beneath the ash basin. Concentrations of arsenic, boron,
chromium, cobalt, iron, manganese, selenium, and vanadium in ash
samples were greater than concentrations of the same constituents in soil
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background samples. The concentrations of these constituents in ash
samples also were greater than PSRG for POG (Appendix C, Table 4).
In addition, seven ash samples collected from borings completed within the
ash basin were analyzed for leachable inorganics using synthetic
precipitation leaching procedures EPA Method 1312 (Appendix C, Table 6).
The purpose of the SPLP testing is to evaluate the potential for leaching of
constituents that might result in concentrations greater than the 02L
standards or IMACs. SPLP analytical results are compared with the 02L or
IMAC comparative values to evaluate potential source contribution; the
data do not represent groundwater conditions. The results of the SPLP
analyses indicated that concentrations of antimony, arsenic, chromium,
cobalt, iron, manganese, selenium, thallium, 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 Belews Creek ash basin were conducted using two
LEAF tests, USEPA LEAF 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 constituents, such as boron, the leachable concentration of
boron present in ash from Belews Creek is considerably lower than the total
boron concentration (Appendix H, Attachment C). Belews Creek data
indicate that there is a process by which the constituents might become
stable within the ash and would make the constituent unavailable for
leaching. The exact mechanisms of this process are unknown, however,
literature suggests that incorporating constituents, such as boron, into the
silicate mineral phases is a potential mechanism (Boyd, 2002). The leaching
behavior of several constituents as a function of pH, examined using
USEPA LEAF method 1313, demonstrated that for anionic constituents, the
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
leaching increased with increasing pH and the cationic constituents showed
the opposite trend (Appendix H, Attachment C).
Soil beneath Ash
(CAP Content Section 6.A.a.vi 1.4 and 6.A.a.vi 1.5)
Soil samples within the ash basin waste boundary include samples collected
from beneath the ash basin and samples collected from the fill material
within the ash basin dam and chemical pond dike. Soil samples beneath the
ash basin were saturated. Saturated soil samples collected within the waste
boundary are from borings associated with AB-2D/GTB, AB-31), AB-41),
AB-5D, AB-6D/GTB, AB-7D, AB-8D, AB-9S/D and SB-3. Temporary
geotechnical borings (GTB) were used for soil sample collection purposes
(i.e., no monitoring wells were installed at these locations).
Constituents considered for soil evaluation were limited to constituents
identified as COIs from the Belews Creek CSA Update (SynTerra, 2017),
since soil impacts would be related to ash pore water interaction to the
underlying soils within the basin and groundwater migration beyond the
ash basin. The range of constituent concentrations in saturated soils within
the waste boundary, along with a comparison with soil background values
and North Carolina PSRG POG standards (NCDEQ, May 2019), whichever
is greater, is provided in Appendix C, Table 4. For constituents lacking an
established target concentration for soil remediation (i.e. chloride and
sulfate), the following equation was used in general accordance with the
references in Subchapter 02L .0202 to calculate a POG value.
CSoi1= Cg. [Kd + (9w + 6aH')IPb]df
Where necessary, the PSRG POG values were calculated using laboratory
testing and physical soil data for effective porosity (0.3) and dry bulk
density (1.6 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, 2012). Soil PSRG POG standard equation
parameters and values used in the equation above are outlined on
Table 6-2. Resulting PSRG POG calculated values for chloride and sulfate
were 938 mg/kg and 1,438 mg/kg, respectively (Appendix C, Table 4).
Saturated soil and rock is considered a component of the groundwater flow
system and can serve as a source for constituents in groundwater at the Site.
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Corrective Action Plan Update December 2019
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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 constituent
concentrations over time in the saprolite, transition zone, and bedrock
materials throughout the models. Historical transport models simulate the
migration of constituents through the soil and rock from the ash basin, and
these results are used as the starting concentrations for the predictive
simulations.
Unsaturated soil and rock is considered a potential secondary source to
groundwater. Constituents present in unsaturated soil or 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. Unsaturated fill (i.e. dam construction material) samples were
collected from borings associated with AB-1 and AB-3S (Figure 6-5).
Analytical results for unsaturated soil data within the waste boundary can
be found on Table 6-3.Only unsaturated fill material sample AB-01S [20-
21.5 feet below ground surface (bgs)], collected from the ash basin dam,
have concentrations of arsenic (61.1 mg/kg) and iron (40,600 mg/kg) greater
than the PSRG for POG or background values, whichever is greater. Arsenic
and iron concentrations are within range of background soil concentrations
(Table 6-3). Additionally, source control and ash basin closure activities will
lower water elevation in this area, reducing the potential for leaching
constituents into the groundwater system. No other unsaturated soil
samples within the waste boundary had concentrations greater than PSRG
POG or background values.
No saturated soils beneath the ash basin have been analyzed for leachable
inorganics using SPLP procedures EPA Method 1312.
Ash Pore Water
(CAP Content Section 6.A.a.vi.1.6 and 6.A.a.vi.3)
The ash basin is a permitted waste water treatment system. Water within
the ash basin is not groundwater; therefore, ash pore water isoconcentration
maps are not prepared. Ash pore water data is provided for general
information purposes only in Appendix C, Table 1. Figures 6-6a, 6-6b, and
6-6c represent ash pore water constituent distribution in cross section (A -A')
from south to north. This cross-section represents the greatest horizontal
and vertical extent and volume of source material in relation to a hydrologic
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
divide (GWA-8S/D) and in ash pore water and in groundwater below the
ash basin (AB-4S/SL/SAP/D/BR/BRD). For further discussion of geochemical
trends within the ash pore water, see Appendix H, Section 2. All ash pore
water sample locations are shown on Figure 1-2, and analytical results are
provided in Appendix C, Table 1.
One ash pore water monitoring well and three groundwater monitoring
wells located in areas that could be sensitive to changing Site conditions
from ash basin closure activities, including decanting, were selected for
monitoring water elevation and geochemical parameters. Water elevations
are monitored with pressure transducers and geochemical parameters,
including pH, oxidation reduction potential (ORP) and specific conductivity
(two locations only), are monitored using multi parameter (or geochemical)
sondes. Locations monitored with multi parameter sondes are depicted on
Figure 6-7, and include:
• AB-4 LOWER ASH: ash pore water well located central to the ash
basin delta
• AB-4SAP: shallow flow zone monitoring well located within the
footprint of the ash basin, below ash pore water well AB-4 LOWER
ASH
• AB-2D: deep flow zone well located downgradient of the ash basin,
below the ash basin dam
• GWA-20D: deep flow zone well located downgradient and
northwest of the ash basin
Hydrographs and geochemical water quality parameter time series plots for
each location are included on Figure 6-7.Observations of water elevation
and multi parameter records from monitored locations include:
• Ash pore water and shallow flow zone monitoring locations within
the waste boundary show a response to ash basin decanting by
reduced groundwater elevation levels (Figure 6-7).
Deep flow zone monitoring locations less than 500 feet downgradient
of the ash basin show a response to ash basin decanting by reduced
groundwater elevation levels (Figure 6-7).
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
• Geochemical parameters pH and ORP do not show significant shifts
or variability in records since ash basin decanting commenced
(Figure 6-7). This suggests geochemical conditions have remained
stable under changing Site conditions at locations within the waste
boundary and downgradient of the source area.
Geochemical parameter specific conductivity is monitored at the two
deep flow zone monitoring locations (AB-2D and GWA-20D)
downgradient of the ash basin. Specific conductivity has increased at
each location, however the increasing trend appears to be consistent
with the trends prior to reduction of water levels, therefore, is
unlikely related to ash basin decanting and could reflect natural
variability.
In general, ash pore water and groundwater geochemical parameters
appear stable under changing site conditions. Ash pore water pH and ORP
do not appear to be significantly affected by lowering the ash basin pond's
water level, and therefore represent stable conditions in which an increase
in constituent dissolution and mobility is unlikely to occur. Additionally,
groundwater pH and ORP, monitored beneath and downgradient of the ash
basin, are unaffected by even larger reductions in water levels, indicating
stable geochemical conditions in which constituent dissolution and mobility
are unlikely to occur.
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 and Schwartz 1998). Piper diagrams of ash pore water
monitoring data (Figure 6-8) are used to assess 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. 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 6-8.
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
6.1.1.7 Other Potential Source Material — Pine Hall Road
Landfill
(CAP Content Section 6.A.a.vii)
The NCDENR DWM issued an initial permit (No. 8503 — INDUS) to operate
the now -closed PHR Landfill (Figure 1-2) in December 1984. The landfill
was permitted to receive fly ash. The landfill is unlined and designed with a
1-foot thick soil cap on the side slopes and 2 feet thick on flatter areas. A
subsequent expansion (Phase I Expansion), permitted in 2003, was also
unlined but was permitted with a synthetic cap system to be applied at
closure. The landfill was permitted to receive fly ash. The capacity of the
landfill is approximately 3,616,800 tons. After groundwater monitoring
indicated CCR constituent concentrations greater than 02L standards near
the landfill and adjacent to the ash basin, the placement of additional ash in
the Phase I Expansion was discontinued and the closure design was
changed to include an engineered cover system for the above -grade portion
of the landfill. The engineered cover system consists of a 40-mil linear low -
density polyethylene geomembrane, a geonet composite, 18 inches of
compacted soil, and 6 inches of vegetative soil cover. The total footprint of
the landfill is approximately 67.2 acres. A total of approximately 8,500,000
cy of ash was placed within the PHR Landfill from December 1984 to March
2008. The construction of the engineered cover system for the Phase I
Expansion, including the additional soil cover on the 14.5-acre section, was
completed in December 2008. The cover system is a source control measure
implemented for the landfill.
6.1.1.8 Interim Response Actions
(CAP Content Section 6.A.a.viii)
Interim response actions to date include ash basin decanting, the installation
of an interim action accelerated remediation groundwater extraction
system, source area stabilization, and operation of a toe -drain water
collection system at the base of the Belews Creek ash basin dam. A
summary of each interim action and the intended remedy are described in
Table 6-4.
Ash Basin Decanting
(CAP Content Section 6.A.a.viii.1)
Ash basin decanting commenced on March 27, 2019, and is scheduled to be
completed by September 2020. Decanting is a form of active source
remediation by removing ponded water in the ash basin, which is
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
considered a critical component of reducing constituent migration from the
ash basin. Reduction of constituent migration occurs through decanting by
significantly reducing the hydraulic head and gradients, thereby reducing
the groundwater seepage velocity and constituent transport potential.
Prior to ash basin closure, the operating level of the ash basin was
maintained at 750 feet. From predictive flow and transport modeling, a
hydraulic divide is expected to reform, along the topographic ridge
represented by Middleton Loop, as a result of lowering and removing the
ash basin hydraulic head. Water elevation of the ash basin was reduced by
approximately four feet between the commencement of decanting in March
2019 and April 2019. Water level data from April 8, 2019 depicts early stages
of the hydraulic divide reforming (Figures 5-4a through 5-4c).
Four ponded water points from the ash basin fingers, one ash pore water
point, one shallow groundwater point located beneath the ash basin, and 19
groundwater monitoring wells located north, east, south, and west of the
ash basin were selected for monitoring water elevations using pressure
transducers to record changing site conditions from ash basin decanting
(Figure 6-9). Ash basin finger ponded water, ash pore water, and
groundwater decanting network hydrographs, using water elevations
recorded between January or February 2019 (May 2019 for ash basin fingers
only) through November 2019 are depicted on Figures 6-10a through 6-10c.
Observations from hydrographs include:
By December 1, 2019, water level in the ash basin pond has decreased
by 10.6 feet since decanting started (Figure 6-10a). Note that water
elevations displayed on Figures 6-10a through 6-10c are not current
to December 1, 2019.
• Ash basin finger water levels on average have decreased by
approximately one foot (Figure 6-10a). The minimal drawdown of
water levels observed in the ash basin fingers suggests the fingers are
only weakly connected to the pond.
• All groundwater monitoring locations show a response to ash basin
decanting by reduced groundwater elevation levels (Figures 6-10a
through 6-10c).
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
Groundwater monitoring wells northwest of the ash basin (i.e. CCR-
2S/D, GWA-20SA/D, GWA-21, and GWA-27D) and north of the ash
basin (i.e., AB-1BR and AB-21)) show the largest degree of response
from decanting by greatest reduction in water levels relative to wells
south, east and west of the ash basin (Figures 6-10a through 6-10c).
• Water elevation records from groundwater monitoring wells CCR-
2S. CCR-11S and GWA-20SA indicate water levels decreased below
the transducer elevation in July 2019 (Figures 6-10a through 6-10c).
Transducers were installed at elevations approximately in the middle
of the monitoring well's 10-foot screened interval. Water levels
recorded below transducer elevations suggests the monitoring well is
nearly dry (i.e., insufficient water available for monitoring purposes).
Interim Action Accelerated Remediation Groundwater
Extraction System
(CAP Content Section, 6.A.a.viii.1)
A Settlement Agreement between NCDEQ and Duke Energy signed on
September 29, 2015, requires accelerated remediation to be implemented at
sites that demonstrate off -site affected groundwater migration. BCSS is
included in that agreement. Historical and ongoing assessment indicates
the potential for off -Site groundwater flow northwest of the BCSS ash basin
in the area of Parcel A. After correspondence with NCDEQ and conditional
approval of an Interim Action Plan (IAP), Duke Energy began interim
action activities to target Parcel A in 2016. Interim action activities
associated with Parcel A consisted of pilot testing a groundwater extraction
system along the northwest corner of the ash basin.
The primary objective of the groundwater extraction system is to reduce
migration of constituents in groundwater from the ash basin toward the
area northwest of the ash basin and to achieve a hydraulic boundary
proximal to the extraction well network. As required by NCDEQ, Duke
Energy submitted draft basis of design (BOD) reports for review and
comments in 2016 and 2017. A 100 percent BOD report was submitted to
NCDEQ DWR on September 1, 2017. In a letter with comments dated
October 31, 2017, NCDEQ granted permission for Duke Energy to proceed
with installation of the extraction well network. Operation of the extraction
system began in March 2018. As of April 30, 2019, the system has pumped
over 6,900,000 gallons of groundwater and approximately 500 pounds of
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Corrective Action Plan Update December 2019
Belews Creek Steam Station SynTerra
boron based on the data collected (Appendix J). As of November 25, 2019,
the system has pumped over 9,800,000 gallons of groundwater.
Based on pumping test information and groundwater modeling scenarios,
10 extraction wells (EX-1 through EX-10) were installed between the ash
basin and Parcel A. The groundwater extraction well system, which started
operating in March 2018, is currently pumping at a combined rate of
approximately 12 gpm.
Post -decanting, the 10 interim action extraction wells are predicted to have
a combined pumping rate of approximately 2.5 gpm, due to the reduction in
groundwater elevation in the area.
Water -level monitoring of the extraction system is conducted using data
logging pressure transducers on a continual basis with water -level
monitoring on an hourly basis at select monitoring wells near the
groundwater extraction system. The Interim Action Plan Accelerated
Remediation Groundwater Extraction System 2018 Startup and Effectiveness
Monitoring Report and the Interim Action Plan 2019 Effectiveness Monitoring
Report can be found in Appendix J.
Source Area Stabilization
(CAP Content Section, 6.A.a.viii.2)
In an April 2, 2015 correspondence, NCDEQ provided a notice of
deficiencies related to the ash basin dam including excessive seepage,
bare/sparse vegetation, outlet pipe abandonment, slope improvements and
weighted filter overlay. In response, Duke Energy undertook activities in
2016 to correct the deficiencies (see letter dated August 5, 2016, Appendix
A). The activities included:
• Installation of an aggregate seepage collection and filter overlay
system and earth fill buttress (weighted filer overlay) graded to
match previous embankment slopes
• Removal of stumps of felled trees and woody vegetation
• Installation of 8-inch solid and perforated pipes to transport seepage
captured within existing horizontal and new filter aggregate
• Installation of two trapezoidal flumes for measure/monitor seepage
flows conveyed by the weighted filter overlay
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• Installation of a new riprap lined outlet channel, stormwater culverts,
riprap lined ditches, seepage collection berm and concrete ditch
• Permanent grouting of outlet pipe from former discharge structure,
and
• Restoration of bare/sparse vegetated areas.
Pursuant to G.S. Section 130A-309.213(d)(1) and based upon determinations
in a letter dated November 13, 2018, NCDEQ has classified the CCR surface
impoundment at BCSS as low -risk (Appendix A). 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.
Toe -Drain Water Collection System
(CAP Content Section, 6.A.a.viii.1)
A toe -drain water collection system that consists of a wet well and pump
station has been installed below the ash basin dam adjacent to the unnamed
tributary. The wet well details consist of a 16 inch diameter by 18 feet deep
well has been installed below the ash basin dam adjacent to the unnamed
tributary. The toe -drain collect system is designed to hydraulically control
and maintain groundwater levels at the base of the dam between
approximately 624 and 629 feet NAVD 88. This is approximately 15 feet
below current groundwater elevations (Figures 5-4a through 5-4c) based on
April 2019 water elevation data. The wet well and pump station storage
capacity is approximately 2,000 cubic feet. The system construction and
testing is complete and will begin operation in January 2020. Once in
operation, the toe -drain system will collect water from the toe of the ash
basin dam and route it to the Dan River through new discharge piping to a
permitted NPDES outfall. Therefore, water from the ash basin will no
longer discharge to the unnamed tributary, which will improve surface
water and groundwater quality.
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 at or beyond the point of
compliance. The point of compliance at Belews Creek is the ash basin compliance
boundary. The compliance boundary for groundwater quality at the Site is
defined in accordance with Title Subchapter 02L .0107(a) as being established at
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either 500 feet from the waste boundary or at the property boundary, whichever
is closer to the waste. The PHR Landfill also has a waste boundary and a
compliance boundary approximately 250 feet from the landfill waste boundary.
The ash basin compliance boundary and landfill compliance boundary overlap,
with the exception of an area of the landfill compliance boundary that is south of
the ash basin compliance boundary (Figure 1-2). All groundwater constituent
migration from the landfill occurs within with the landfill compliance boundary,
with the exception of some constituent migration north of the landfill, within the
ash basin compliance boundary. Based on predictive modeling, groundwater
constituent migration from the landfill will not migrate beyond the landfill
compliance boundary, outside of the ash basin compliance boundary.
Analytical sampling results associated with the source area: ash basin and PHR
Landfill for each media are included in the following tables and appendix tables:
• Soil: Appendix C, Table 4 and Table 6-3 (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 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
compliance boundary are generally consistent with background concentrations
or are less than regulatory screening values (Table 6-3). Horizontal and vertical
extent of constituent concentrations in soil is discussed further in Section 6.1.4.
Groundwater Constituent Extent
(CAP Content Section 6.A.b.ii.2)
The ash basin compliance boundary extends 500 feet beyond the ash basin waste
boundary, or to the property boundary, whichever is closer. Groundwater
concentrations greater than 02L/IMAC/ background values occur locally at or
beyond the compliance boundary in two areas:
1. Northwest of the ash basin
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2. North of the basin dam
The maximum extent of affected groundwater migration for all flow zones is
represented by boron concentration greater than the 02L standard. Boron has
migrated from the ash basin to areas north and northwest, at or beyond the
compliance boundary. The boron plume is approximately 750 feet beyond the
northwest portion of the ash waste boundary, and approximately 500 feet
beyond the northern portion of the ash basin waste boundary. The PHR Landfill
boron plume is within the landfill compliance boundary south, east and west of
the source area, but has migrated approximately 100 feet north of the landfill's
compliance boundary; this portion of the boron plume is within the ash basin
waste boundary and compliance boundary. Boron has not migrated at or beyond
the point of compliance in any other areas. This is because groundwater divides
in areas upgradient and side -gradient of the basin limit constituent transport to
primary flow paths consistent with the site CSM. Additionally, stream valleys
and streams downgradient of the basin (tributaries to the Dan River north and
northwest of the ash basin) are groundwater discharge zones that limit the
horizontal transport of constituents downgradient of the basin. Also, due to the
limited presence and mobility of most constituents in the groundwater system,
constituent concentrations in groundwater have not caused, and will not cause,
current surface water quality standards to be exceeded (Appendix K).
Chloride, lithium, and TDS have concentrations that are greater than their
respective groundwater regulatory standards, or background values (lithium), at
or beyond the compliance boundary. The distributions of chloride, lithium, and
TDS occur as continuous plumes and are confined within the extent of the 02L
boron plume and also have a smaller footprint than boron, and occur in an area
that is more localized to the ash basin's north and northwest waste boundary.
Other constituents, including arsenic, beryllium, chromium (VI), cobalt, iron,
manganese, molybdenum, strontium, and thallium, have concentrations greater
than their respective groundwater regulatory standards at or beyond the
compliance boundary north and northwest of the ash basin. Generally, non -
conservative and variable constituents exhibit little migration from the ash basin
north and northwest of the ash basin. Some constituents, such as arsenic,
beryllium, iron, and thallium do not have concentrations greater than applicable
criteria with distributions that represent a continuous discernable plume in all
flow zones. The extent and maximum concentrations of non -conservative and
variable constituents which have a discernable plume correlate to the migration
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of boron at concentrations greater than the 02L standard. The distribution of non -
conservative and variable constituents are generally confined within the extent of
the 02L boron plume with distributions in highly localized footprints relative to
the ash basin's north and northwest waste boundary.
There are few exceptions where non -conservative and variable constituents occur
in areas where boron is non -detect or less than the 02L standards at or beyond
the compliance. One exception is arsenic and iron concentrations at an isolated
location northeast of the ash basin dam. Location is adjacent to a wetland, where
reducing conditions might enhance arsenic and iron solubility. The constituent
concentrations of arsenic and iron at this location do not exhibit a discernable
plume with other occurrences of arsenic and iron greater than 02L standards.
Other exceptions include one, or up to four (molybdenum in bedrock), isolated
detections of chromium (VI) and molybdenum concentrations that do not exhibit
a discernable plume within the flow zone.
Section 6.1.3 includes a constituent management process for determining which
groundwater constituents warrant corrective action, and Section 6.1.4 provides
isoconcentration maps and cross -sections depicting groundwater flow and
constituent distribution and extent in groundwater (CAP Content Section 6.A.b.i).
Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Seeps at Belews 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 the following seeps:
• Non -constructed seeps to be monitored — S-2, S-6, S-8, S-9, and S-10
Non -constructed seeps dispositioned — S-1, S-3, S-4, S-5, S-7, S-12, S-13, S-
14, S-15, and S-16
• Constructed seep to be monitored per terms of the NPDES Permit - S-11
[non -constructed seep S-18 flow to a portion of the NPDES wastewater
treatment system (i.e., seep S-11) and is monitored per terms of the NPDES
Permit]
The SOC defines dispositioned:
1. The seep is dry for at least three consecutive quarters;
2. The seep does not flow to waters of the State;
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3. The coal ash basin no longer impacts the seep for all constituents over four
consecutive sampling events;
4. An engineering solution has eliminated the seep.
Non-dispositioned seeps, where monitoring conducted has indicated the
presence of CCR affects, include: S-2, S-6, S-8, S-9, S-10, S-11, and S-18
(Figure 5-6). Table 6-8 provides a summary of seep general location and
approximate flow rate. Analytical results for these seep samples are included in
Appendix C, Table 3. Seeps at Belews Creek are contained within well-defined
channels. Therefore, potential constituent migration related to seep flow are
constrained in localized areas along the channel. Surface water sampling
conducted downstream of non-dispositioned seeps S-2 and S-6, near the point
where the channels confluence with the Dan River and Belews Reservoir,
demonstrate that flow from seeps has not caused constituent concentrations
greater than 02B standards in the river or reservoir. Surface water samples that
were collected at or near the confluence of seeps S-2 and S-6 with the Dan River
and Belews Reservoir are shown on Figure 5-6. Applicable Dan River surface
water samples, collected at or near the confluence of seep S-2 with the river
include SW-DR-1 and S-2-D. The applicable Belews Reservoir surface water
sample collected at or near the confluence of the seep S-6 with the reservoir
includes SW-BL-S-06. Analytical results for these surface water samples are
included in Appendix C, Table 2.
Seeps S-8 and S-9 confluence with Belews Reservoir have limited accessibility.
Seeps S-10, S-11, S-15, and S-18 are comingled and all flow into the unnamed
tributary. Prior to 2019, the unnamed tributary was the designated effluent
channel for the ash basin. For these reasons these channels were not included in
conducted surface water sampling at the time.
Surface Water Constituent Extent
(CAP Content Section 6.A.b.ii.4)
Surface water samples have been collected from NCDEQ approved locations
over multiple events from the Dan River and Belews Reservoir to confirm
groundwater downgradient of the ash basin has not resulted in surface water
concentrations greater than 02B water quality standards. Groundwater
monitoring data consistently indicate the ash basin constituent plume does not
extend to either the Dan River or the Belews Reservoir and that there are no
surface water quality exceedances related to the BCSS ash basin. Surface water
samples were collected to evaluate acute and chronic water quality values.
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Surface water samples were also collected at background locations (upgradient
of potential migration areas) within the Dan River, and Belews Reservoir.
Analytical results were evaluated with respect to 02B water quality standards
and background data. Surface water conditions is further discussed in
Section 6.2.1 and the full report for BCSS surface water current conditions can be
found in Appendix K.
Additionally, environmental assessments of the Dan River and Belews Reservoir
have all demonstrated that Belews Reservoir and the Dan River have been
environmentally healthy and functioning ecosystems, and ongoing sampling
programs have been established to ensure the health of these systems will
continue. Furthermore, these data indicate that there have been no significant
effects to the local aquatic systems related to coal ash constituents over the last 30
years. More information related environmental health assessments conducted for
the Dan River and Belews 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.b.ii.5)
All sediment sample locations are co -located with surface water or tributary
stream seep 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 water quality. Because no regulatory standards are established for
seidment inorganic constituents, both background sediment constituent
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 constituents in sediment from surface waters, including the Dan
River, Belews Reservoir, and seeps, was conducted through a comparison
evaluation between sediment sample constituent analytical results, from one-
time grab samples, and constituent concentration ranges from background
sediment datasets. Samples collected from Belews Reservoir and the Dan River
were compared with background dataset ranges from the respective surface
water body. No background sediment locations from either Belews Reservoir or
Dan River tributary stream channels are sampled at Belews Creek, therefore
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ranges of constituent concentrations from both Belews Reservoir and the Dan
River background sediment results are used to compare sediment sample results
collected from tributary stream channels.
Sediments Collected from the Dan River and Belews Reservoir
The risk assessment concludes that on- and off -Site sediment, collected from the
Dan River and Belews Reservoir, pose no unacceptable risks for recreational
receptors (i.e., swimmer, wader, boater, and recreational fisher; Appendix E)
Eight sediment samples have been collected from the Dan River and Belews
Reservoir. Downstream sediment sample locations (Figure 1-2) per water body
included:
• Four locations downstream of seeps, along the bank of the Dan River
include sediment samples: SD-DR-01, SD-DR-02, SD-DR-03, SD-DR-04
Four locations downstream of seeps, along the banks of Belews Reservoir
include sediment samples: SD-BL-GWA-04D/S, SD-BL-S-06, SD-BL-S-07,
SD-BL-S-13/14
Of the eight sediment samples, co -located with surface water sample locations in
the Dan River or Belews Reservoir, four samples have constituent concentrations
greater than the maximum detected concentrations in background sediment.
Constituent concentrations from Dan River or Belews Reservoir sediment
samples detected greater than background concentrations include arsenic,
beryllium, chloride, cobalt, iron, strontium, and thallium.
Of the four sediment samples collected along the bank of the Dan River, one
sample, SD-DR-02, has results of constituent concentrations greater than the
maximum detected constituent concentrations in background sediment.
Sediment sample SD-DR-02 is located at the confluence of seep S-2 stream and
the Dan River (Figure 1-2). Sediment sample SD-DR-02 has constituent
concentrations greater than background concentrations of arsenic, beryllium,
cobalt, iron, strontium, and thallium. Sediment sample results collected further
downstream of SD-DR-02 along the bank of the Dan River are within the
background concentration ranges, suggesting the constituent concentrations
greater than background ranges at SD-DR-02 are localized affects. Surface water
sample results co -located with SD-DR-02 sediment sample are less than 02B
surface water standards and generally within surface water background
constituent concentration ranges (Appendix K).
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Of the four sediment samples collected in association with the Belews Reservoir,
three samples SD-BL-GWA-04D/S, SD-BL-S-07 and SD-BL-S-13/14, located east of
the ash basin (Figure 1-2), have concentrations of chloride greater than the
maximum detected concentration of chloride in Belews Reservoir background
sediment results. Sediment sample SD-BL-S-07 has a concentration of arsenic
greater than the maximum background concentration of arsenic. Surface water
samples co -located with samples SD-BL-GWA-04D/S, SD-BL-S-07 and SD-BL-S-
13/14 sediment samples are less than 02B surface water standards and generally
within surface water background constituent concentration ranges
(Appendix K).
Sediment Collected from Seeps
There are 11 sediment samples (S-1 through S-11), co -located with seep sample
locations around the ash basin (Figure 1-2). Several seeps have been
dispositioned per the SOC; of the seeps not dispositioned and are regulated per
the SOC, only four have sediment samples with constituents detected greater
than background concentrations. Constituents detected in sediment with
concentrations greater than background include arsenic, cobalt, iron, and
strontium.
• Sediment sample S-2 has a concentration of arsenic detected greater than
background concentrations. Decanting has been effective in reducing flow
at seep S-2. Further decanting, and groundwater corrective action
proposed in this CAP Update might cause seep to become dry.
• Sediment sample S-6 has a concentration of strontium detected greater
than background concentrations. Decanting has been effective in reducing
flow at seep S-6. Further decanting, and ash basin closure might cause
seep to become dry.
• Sediment sample S-10 has a concentration of arsenic detected greater than
background concentrations. Decanting has been effective in reducing flow
at seep S-10. Further decanting, and groundwater corrective action
proposed in this CAP Update might cause seep to become dry.
• Sediment sample S-11 has arsenic, cobalt, iron, and strontium detected
greater than background concentrations. Since sediment was collected at
S-11 location, seep S-11 has been modified by a toe -drain collection
system. Water discharging from the ash basin will be collected by the toe -
drain collection system, therefore water from the ash basin no longer
discharges to seep S-11 and then downstream unnamed tributary, which
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will improve surface water quality at this location. The toe -drain
collection system is part of the Belews Creek NPDES ash basin wastewater
treatment system.
After completion of decanting, all seeps, constructed and non -constructed and if
not dispositioned in accordance with the SOC, are to be characterized post -
decanting for determination of seep disposition by the decanting process. If a
seep is dispositioned, no corrective action for the location would be proposed.
After seep characterization, an amendment to this CAP Update and submitted
based on the schedule outlined in the SOC, may be required to address non-
dispositioned seeps. Corrective action strategies for seeps, including seeps S-2, S-
6, and S-10, are discussed in Section 6.8. Seep corrective action measures target
reducing flow and the saturated zone at seeps and therefore reduces the
potential for additional leaching and sorption of constituents to occur with
sediment.
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 shallow, deep and
bedrock background locations and downgradient of the ash basin locations
are included on Figure 6-8. Data used for the piper diagrams include
groundwater data between January 2018 and April 2019 with a charge
balance between -10 and 10%.
• 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.
Shallow groundwater monitoring wells GWA-01S, GWA-17S, GWA-
27S, and MW-200S plot near ash pore water points indicating water
quality proportions of major anions and cations are more similar to
ash pore water than background groundwater (Figure 6-8). Boron
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concentrations from each of these shallow monitoring wells, with the
exception of GWA-17S, are greater than the 02L standard, which
supports that groundwater in these areas is affected by the source
area (Appendix C, Table 1).
Deep groundwater monitoring wells GWA-01D, GWA-11D, GWA-
20D, GWA-21D, and MW-200D plot near ash pore water points
indicating water quality more similar to ash pore water than
background groundwater (Figure 6-8). Boron is detected at each of
these deep monitoring well locations with the exception of GWA-
01D. The concentration of boron at GWA-20D is greater than the 02L
standard (Appendix C, Table 1).
• Bedrock groundwater monitoring well MW-200BR plots in the region
of between the ash pore water and background results. This area is
identified as "potential mixing" on Figure 6-8. This bedrock
monitoring location is below the ash basin dam, north of the basin,
and exhibits artesian conditions. Boron detected at MW-200BR is
below the 02L standard (geometric mean of 155 µg/L), however the
well exhibits the greatest concentration of boron in bedrock at or
beyond the compliance boundary (Appendix C, Table 1).
Seep and Surface Water Piper Diagrams
Piper diagrams of seep, Dan River and Belews Reservoir surface water data
are included on Figure 6-23. 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%. From ash pore water and
groundwater piper diagrams (Figure 6-23), areas identified where ash pore
water tends to plot is noted as "affected"; areas that show potential mixing
with affected water is noted as "potential mixing", and areas that are similar
to background (or native) water quality are noted as "generally unaffected".
• Seeps S-2, S-4, S-6, S-9, and S-10 plot within the area where ash pore
water tends to plot (Figure 6-23). Each of these seeps, with the
exception of S-4, are covered by the SOC. No surface water samples
from the Dan River or Belews Reservoir plot within the area of ash
pore water quality (Figure 6-23).
Surface water samples S-02D and SW-BL-S-07 plot within the region
of between the affected and generally unaffected water quality. This
area is identified as "potential mixing" on Figure 6-23. Surface water
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sample S-02D is collected from the Dan River at the point of
confluence between the stream where SOC seep S-02 is located and
the Dan River. Sample results from S-02D are less than 02B standards
(Appendix C, Table 2). Surface water sample SW-BL-S-07 is collected
from the Belews Reservoir downstream of seep S-07. Sample results
from SW-BL-S-07 are less than 02B standards (Appendix C, Table 2).
• Remaining seep and surface water samples plot with water quality in
the region of generally unaffected (Figure 6-23). Surface water
sample results are less than 02B standards with the exception of
turbidity for some Dan River samples (Appendix C, Table 2).
6.1.3 Constituents of Interest
(CAP Content Section 6.A.c)
This CAP Update evaluates the extent of, and remedies for constituents
associated with the BCSS ash basin and PHR Landfill that warrant corrective
action, which are those that are at or beyond the compliance boundary to the
north and northwest of the source area 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. The distribution of constituents in relation to the
source area, co -occurrence with CCR indicator constituents, such as boron, and
migration directions based on groundwater flow direction are considered in
determination of COIs.
The following list of COIs was developed as part of the CSA Update for Belews
Creek (SynTerra, 2017):
• Antimony
• Arsenic
• Barium
• Beryllium
• Boron
• Cadmium
• Chloride
• Iron
• Manganese
• Chromium (Total) • Molybdenum
• Chromium
(Hexavalent)
• Cobalt
• pH
• Selenium
• Strontium
• Sulfate
• Total Dissolved Solids
• Thallium
• Vanadium
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son
(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
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 basin, since soil impacts
would be related to ash pore water interaction to the underlying soils within the
basin and groundwater migration at or beyond the ash basin.
Belews Creek samples of background soil and rock media indicate that some
naturally occurring constituents that are also typically related to CCR material
and likely effect the chemistry of groundwater at the Site, are present at
concentrations greater than the PSRGs POG values (Table 4-2). Constituents with
background values greater than PSRGs POG values include arsenic, total
chromium, cobalt, iron, manganese, selenium and thallium.
Data indicate unsaturated soil constituent concentrations are generally consistent
with background concentrations or are less than regulatory screening values
(Table 6-3). In the few instances where unsaturated soil constituent
concentrations are greater than Preliminary Soil Remediation Goal (PSRG)
Protection of Groundwater (POG) standards or background values, constituent
concentrations are within range of background dataset concentrations or there
are no mechanisms by which the constituent could have been transported from
the ash basin to the unsaturated soils. Horizontal and vertical extent of
constituent 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 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 at or beyond the compliance boundary. A measure 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
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representation of the concentrations observed over several months to years of
groundwater monitoring. Evaluating COI plume geometries with central
tendency data minimizes the potential for incorporating occasions where COIs
are reported at concentrations outside of the typical concentration range, and
potentially greater, or substantially less than enforceable groundwater standards.
Previous Site assessments 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.
NCDEQ (October 24, 2019; Appendix A) recommended use of a lower
confidence limit (LCL95) rather than the central tendency value. LCL95
concentration were calculated for each COI. The LCL95 concentration for the
sample with the highest COI LCL95 concentration is provided for comparison to
the COI mean concentration in Table 1 of the technical memorandum titled COI
Management Plan Approach — Belews Creek Steam Station (Arcadis, 2019b) included
within Appendix H. The mean is typically higher than the LCL95 value, and
therefore, is a more conservative approach for evaluation and comparison to
applicable criteria.
The mean of up to six quarters of valid data was calculated for each identified
COI to analyze groundwater conditions and define the extent of COI migration
at or beyond the 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, non -detect 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.
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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
mean or mean value is less than or equal to the dataset's mode, the value
was reported as "<RL" (e.g. the reporting limit for boron is 50 µg/L; for
wells with geometric mean or mean analysis concentrations less than 50
µg/L the mean analysis result would be shown as "<50").
Sample results were excluded from calculations for the following conditions:
• 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.0 might be related to grout from well construction.
• 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.
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
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dataset. Data from Table 6-5 are used in evaluating COI plume geometry in the
vicinity of the ash basin.
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.
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
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.
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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,
2017) and 2019 IMP submitted by Duke Energy, March 20, 2019, and
approved by NCDEQ April 4, 2019 (Appendix A). 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 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.
NCDEQ (October 24, 2019 letter; Appendix A) recommended use of a
lower confidence limit (LCL95) concentration rather than the central
tendency value. 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
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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
• 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
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are used for planning appropriate corrective action, 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. 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
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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 COI: antimony, boron, chloride,
lithium, and total dissolved solids. Geochemical model simulations
support that these constituents would transport conservatively (Ka
values <1 liter per kilogram [L/kg]) as soluble species under most
conditions, and that the mobility of these COIs will not change
significantly due to current geochemical conditions or potential
geochemical changes related to remedial actions.
• Non -Conservative, Reactive COI: arsenic, barium, beryllium,
cadmium, total chromium, strontium, and vanadium. 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 COIs is unlikely to be
geochemically affected by current geochemical conditions or
potential geochemical changes related to remedial actions.
• Variably Reactive COI: hexavalent chromium, cobalt, iron,
manganese, molybdenum, selenium, sulfate, and thallium.
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 COIs to the groundwater pH and
Eh indicates 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, 2017) and the 2018 CAMA
Annual Interim Monitoring Report (SynTerra, 2019), 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.
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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 19 inorganic
groundwater COIs (not including pH) identified in the CSA Update (CSA
Update, 2017), 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 plume characteristics (e.g. molybdenum in bedrock
flow zone). These nine constituents include:
• Antimony • Molybdenum
• Barium • Selenium
• Cadmium • Sulfate
• Chromium • Vanadium
• Chromium (IV)
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
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remain at stable concentrations, typically less than background values,
02L standard, or IMAC (Appendix H).
The remaining 10 inorganic groundwater COIs exhibit mean
concentrations greater than background values, 02L standard, or IMAC
downgradient of the ash basin at or beyond the compliance boundary.
These constituents are as follows:
• Arsenic
• Beryllium
• Boron
• Chloride
• Cobalt
• Iron
• Manganese
• Strontium
• Total Dissolved Solids
• Thallium
Lithium has been added to the constituent list at the Belews Creek ash
basin. Lithium was not previously analyzed for in collected groundwater
samples until the second quarterly sampling event in 2018 (April 2018).
This was after the submission of the CSA (CSA Update, 2017) and
therefore lithium was not evaluated in that submittal.
As discussed in the CSA Update (SynTerra, 2017), not all constituents with
results greater than background values can be attributed to the 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 or vertical distribution of affected groundwater migration from
the source area.
6.1.4 Horizontal and Vertical Extent of COIs
(CAP Content Section 6.A.d)
The COIs at the BCSS have been delineated horizontally and vertically in
groundwater based on sampling and analysis data collected from 173 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. The presence of COIs
downgradient of the ash basin waste boundary is limited to between 500 and 750
feet. Furthermore, an evaluation of site data indicates that COI presence in
groundwater decreases with depth. Supporting information for these findings
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are presented in the COI management evaluation presented in Section 6.1.3 and
in Appendix H.
Boron, a conservative (non -reactive) constituent, is the main COI that is present
in site groundwater in a discernable plume, although boron concentrations
decline below its 02L standard within 500 to 750 feet beyond the ash basin waste
boundary BCSS. Boron typically has greater concentrations in CCR than in native
soil and is relatively soluble and mobile in groundwater (Chu, 2017). Chloride,
lithium, and TDS are also conservative constituents and have a similar geometry,
but smaller in extent, plume footprint as boron. Additional constituent
concentrations 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. Non -conservative and variable constituents have
smaller, and generally isolated, plume geometries relative to boron because of
their high Ka values and reactivity, which reduce their mobility. 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; Figures 6-13a through 6-13c) 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. Geometric 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 6-11a through 6-21b). Non -
conservative constituents, boron, chloride and TDS, are mapped with empirical
Site data and supplemented with flow and transport model simulated plume
depictions where no data is available.
The flow and transport model calibration targets are boron concentrations
measured in 157 monitoring wells in the second quarter of 2019. All sampled
wells are included in the calibration. Data that has been collected since that
timeframe were not included in the updated model calibration process. Fall 2019
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data from relatively newly installed wells suggest the model predictions are
accurate, or conservative; the model over -predicts the actual groundwater
concentrations in some areas.
Vertical extent of the COI plume is depicted on two generalized cross -sectional
depictions of the Site. Cross-section A -A' is oriented south to north and displays
the general basin footprint topography and depth of saturated ash in the basin's
delta and free water near the dam (Figures 6-6a through 6-6c). Cross section B-B'
is orientated west to east and displays the areas evaluated for corrective actions,
the areas northwest of the basin and near the dam (Figures 6-22a through 6-22c).
At or beyond the compliance boundary, the maximum extent of COI -
groundwater affected by the ash basin occurs north and northwest of the ash
basin.
6.1.4.1 COIs in Unsaturated Soil
(CAP Content Section 6.A.d.i)
Unsaturated soil at or near the compliance boundary is considered a
potential secondary source to groundwater. Constituents present in
unsaturated soil or 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. Therefore, constituents
considered for unsaturated soil evaluation as related to the ash basin and
PHR Landfill were the same constituents identified as COIs in groundwater
for the ash basin and PHR Landfill.
Belews Creek samples of background soil and rock media indicate that
some naturally occurring constituents that are also typically related to CCR
material and likely effect the chemistry of groundwater at the Site, are
present at concentrations greater than the PSRGs POG values (Table 4-2).
Constituents with background values greater than PSRGs POG values
include arsenic, total chromium, cobalt, iron, manganese, selenium and
thallium.
Unsaturated soils samples at or near the compliance boundary were
collected from borings during well installation activities upgradient of the
ash basin from wells GWA-05S, GWA-07S, GWA-08D, GWA-09GTB, and
MW-202BR; and downgradient of the ash basin from wells GWA-01S,
GWA-10D, and MW-200BR (Figure 6-5). An evaluation of the potential
nature and extent of COIs in unsaturated soil at or beyond the waste
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boundary was conducted by comparing unsaturated soil concentraitons
with background values or PSRG POG standards, whichever is greater
[(Table 6-3) (CAP Content Section 6.A.d.i)]. PSRG POG standards were
calculated for chloride (938 mg/kg) and sulfate (1,438 mg/kg) (Table 6-2).
Constituents detected at concentrations greater than either background
values or the PSRG POG standard, whichever is greater, in unsaturated soil
samples (depth), upgradient or downgradient of the ash basin, at or beyond
compliance boundary include:
• pH: GWA-05S (25-26.5), MW-202BR (60-61.5)
• Arsenic: GWA-01S (20-21.5), GWA-10D (2-3), MW-200BR (0-1.5)
• Barium: GWA-09GTB (40-41.5)
• Chromium: GWA-09GTB (40-41.5)
• Selenium: GWA-07S (30-31.5)
No necessary corrective action for soils is identified at the Site 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:
Background soil and rock indicate that arsenic, chromium, and
selenium occur at natural concentrations greater than the PSRGs
POG values. Although greater than background values or PSRG
POG, arsenic, chromioum, and selenium detections at or beyond the
compliance boundary are within the range of concentrations detected
in soil samples from background locations as shown in Table 6-3.
• Additionally, all unsaturated soil samples with values reported
greater than the PSRG POG standard or background values,
including barium detected at GWA-09GTB (40-41.5), are vertically
delineated by groundwater constituent concentrations in the
corresponding flow layer of the soil sample depth (Table 6-3).
In the two locations upgradient of the ash basin, where unsaturated
soil COI concentrations are greater than the PSRG POG standards or
background values [i.e. GWA-07S (30-31.5) and GWA-09GTB (40-
41.5), Table 6-3], there are no mechanisms by which the COI could
have been transported from the ash basin to the unsaturated soils,
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since groundwater from the ash basin primarily flows north and the
ash basin is bound by hydraulic divides south, east, and west, as
depicted by the pre -decanting vector velocity map (Figure 5-5a).
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 northwest of the ash basin.
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 northwest of the BCSS
ash basin. Additional detail for these two areas is provided below.
Northern Extent of COI -Affected Groundwater
Boron, chloride, lithium, and TDS mean concentrations near the compliance
boundary support the following observations regarding the northern extent
COI -affected by the ash basin groundwater:
• The shallow and deep flow zone groundwater COIs north of the ash
basin are within the compliance boundary and have relatively similar
geometries (Figures 6-13a and Figure 6-13b). This supports the
interpretation that these two zones are hydraulically connected.
Differences between the groundwater COIs are related to hydraulic
conditions; the shallow flow zone has limited saturated thickness in
the area near the center of the dam (i.e., AB-2S) and directly
downgradient of the dam (i.e., CCR-6S is a dry well).
• Based on Site empirical data, COI -affected groundwater in shallow
and deep bedrock at concentrations greater than 02L standards is
horizontally limited to the area beneath the western portion of the
ash basin dam, within the compliance boundary, however,
groundwater flow and transport modeling indicates the bedrock 02L
plume extends northwest of the ash basin beyond the compliance
boundary (Figure 6-13c). The vertical extent of 02L bedrock
groundwater plume is generally limited to the top 50 feet of bedrock
(Figure 6-6a).
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• North of the ash basin, COI -affected groundwater is vertically and
horizontally delineated downgradient, beyond the compliance
boundary. Delineation is demonstrated by groundwater COIs that
are not detected or are detected at concentrations less than regulatory
standard at monitoring wells GWA-24D/BR (Figures 6-11b and
6-21b).
The north groundwater COI plume shape relates to hydraulic conditions
associated with the flow -through system described in the CSM
(Section 5.0). Upward and neutral gradients limit COI migration from the
ash pore water to groundwater below ash and below the basin, except near
the dam where a downward vertical hydraulic gradient promotes
downward COI migration in groundwater.
Downgradient of the dam, groundwater flows upward toward the
unnamed tributary channel discharge zone, 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:
• Below the ash basin dam and near the compliance boundary, a
strong upward gradient is observed between the bedrock and the
upper flow zones at well pair MW-200S/BR (4295 ft/ft). Bedrock
well MW-200BR is a flowing artesian well.
At the compliance boundary, mean concentrations of boron, chloride,
and TDS, at groundwater monitoring wells MW-200S/D/BR, are
greater than background values, but less than the 02L standards
(Figures 6-13a-c, 6-14a-b, and 6-20a-b). Lithium is only slightly
greater than background in bedrock monitoring well MW-200BR
(Appendix C, Table 1).
At or beyond the compliance boundary, mean concentrations of boron,
chloride, and TDS, from groundwater monitoring wells GWA-24S/D/BR,
are less than background values, except for TDS (value) at GWA-24D
(Figures 6-20a and 6-20b); all of these analytes are less than the 02L
standards at this well cluster. Additionally, water discharging from the ash
basin will be collected by a toe -drain collection system, therefore water from
the ash basin will no longer discharge to the unnamed tributary, which will
improve surface water quality; and a groundwater -to -surface water
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evaluation concludes that groundwater migration from the ash basin source
area has not resulted in exceedances of 02B surface water quality standards
in the Dan River.
Northwestern Extent of COI -Affected Groundwater
Boron, chloride, lithium, and TDS mean concentrations at or beyond the
compliance boundary support the following observations regarding the
northwest extent of COI -affected by the ash basin groundwater:
• Shallow and deep flow zones have similar COI plume geometries
northwest of the ash basin. This supports the interpretation that these
flow zones are hydraulically connected (Figures 6-13a-b, 6-14a-b,
6-17a-b, and 6-20a-b).
• Empirical data from the Site indicates no groundwater with boron
concentrations greater than 02L standards extends in the bedrock
northwest of the ash basin. However, flow and transport modeling
suggests that the 02L boron plume has migrated to shallow bedrock
(Figure 6-13c). Other conservative constituents, chloride and TDS,
have also migrated to the bedrock flow zone at concentrations
greater than 02L (Figure 6-14c and Figure 6-20c). Bedrock plumes
tend to be smaller than shallow and deep flow zone plumes, which is
consistent with the overall lower hydraulic conductivity of the
bedrock compared to the shallow and deep zones (Figures 6-6a and
Figure 6-22a).
Groundwater affected by COIs from the ash basin is vertically and
horizontally delineated downgradient of the compliance boundary
based on COI concentrations less than regulatory standard or below
detection from groundwater monitoring wells CCR-13S/D/BR, GWA-
2S/D, GWA-30S/D, and GWA-31S/D (Figures 6-13a-c, Figures
6-14a-b, Figure 6-17a-b, and Figures 6-20a-b).
The northwest groundwater COI plume shape relates to hydraulic
conditions associated with a partial hydraulic divide along Middleton Loop,
convergence of groundwater flow toward natural stream valleys, and
vertical hydraulic gradients. The extent of COI -affected groundwater
migration related to hydraulic conditions is supported by the following
observations:
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Groundwater monitoring wells GWA-20SA/D and GWA-27S/D are
centrally located within the groundwater COI plume. GWA-20SA/D
is located at the compliance boundary, and GWA-27S/D is located
downgradient of the reduced (approximately 250 foot) compliance
boundary. These wells are located in relatively permeable zones of
higher conductance (2.0 feet/day in saprolite and 0.3 feet/day in the
transition zone from calibrated conductivities), compared to the
mean hydraulic conductivity values identified at the Site
(Appendix G).
• Mean concentrations of boron, chloride, lithium, and TDS, from
groundwater monitoring wells GWA-20SA/D and GWA-27S/D, are
generally greater than the regulatory standards or background
values (lithium does not have a regulatory standard). GWA-20SA/D
boron, chloride, lithium, and TDS concentrations provide the greatest
extent relative to other groundwater monitoring results from wells at
or beyond the compliance boundary (Figures 6-13a-b, 6-14a-b,
6-17a-b, and 6-20a-b). Downgradient of GWA-20SA/D,
concentrations of boron, chloride, lithium, and TDS at GWA-27S/D
are generally less, but still greater than those at other groundwater
monitoring wells at or beyond the compliance boundary (Figures
6-13a-b, 6-14a-b, 6-17a-b, and 6-20a-b).
Groundwater monitoring wells GWA-11S/D and GWA-21S/D are
near or at the perimeter of the groundwater COI plume beyond the
compliance boundary (200 feet). These wells are located
downgradient of the compliance boundary in low permeability zones
of lower conductance (0.5 feet/day in saprolite and 0.1 feet/day in the
transition zone from calibrated conductivities) that are adjacent to
zones of higher conductance identified at the Site (Appendix G).
• Mean concentrations of boron, chloride, lithium, and TDS, at
groundwater monitoring wells GWA-11S/D and GWA-21S/D, are
less than the 02L standards or background values, with the exception
of GWA-11S (boron and lithium), GWA-1113 and GWA-21S (lithium)
( Figures 6-13a-b, 6-14a-b, 6-17a-b, and 6-20a-b).
Shallow and deep groundwater monitoring wells CCR-13S/D, GWA-
30S/D, and GWA-31S/D delineate the downgradient extent of boron,
chloride, and TDS COI -affected groundwater northwest of the ash
basin (Figures 6-13a-b, 6-14a-b, and 6-20a-b).
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6.1.5 COI Distribution in Groundwater
(CAP Content Section 6.A.e)
Constituents distribution in groundwater is discussed based on constituent
groupings, determined by alike geochemical behavior and mobility. Constituent
groupings and COIs that are subject to corrective action, and discussed in this
section, are as follows:
• Conservative, non -reactive constituents: boron, chloride, lithium, and
TDS
• Non -conservative, reactive constituents: arsenic, beryllium, thallium, and
strontium
• Variably reactive constituents: cobalt, iron, and manganese
COIs identified in the CSA that are not mapped in this CAP Update generally
not only have limited spatial occurrences within the compliance boundary, but
are further spatially limited to isolated areas within the compliance boundary
that do not have a discernable plume geometry.
6.1.5.1 Conservative Constituents
(CAP Content Section 6.A.e.i)
Boron, chloride, lithium, and TDS mean isoconcentration maps and cross
sections support the following observations regarding the extent of COI -
affected groundwater represented by these conservative constituents:
• Shallow and deep flow zone groundwater COI plumes northeast of
the ash basin are within the compliance boundary.
• Shallow and deep flow zone groundwater COI plumes north and
northwest of the ash basin extend beyond the compliance boundary,
but concentrations decline to below applicable standards within 500
to 750 feet of the waste boundary.
• The shallow and deep flow zone groundwater COI plumes have
relatively similar COI plume geometries (Figures 6-13a-b, 6-14a-b, 6-
17a-b, and 6-20a-b). This supports a connected, unconfined flow
system between the shallow and deep flow zones.
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• Empirical data from the Site indicates no groundwater with boron
concentrations greater than 02L standards extends in the bedrock
northwest of the ash basin. However, flow and transport modeling
suggests that the 02L boron plume has migrated to shallow bedrock
(Figure 6-13c). Other conservative constituents, chloride and TDS,
have also migrated to the bedrock flow zone at concentrations
greater than 02L (Figure 6-14c and Figure 6-20c). Bedrock plumes
tend to be smaller than shallow and deep flow zone plumes, which is
consistent with the overall lower hydraulic conductivity of the
bedrock compared to the shallow and deep zones (Figures 6-6a and
Figure 6-22a).
COI -affected groundwater migration is vertically and horizontally
bounded downgradient of the basin, beyond the compliance
boundary. COI -affected groundwater delineation is demonstrated by
detected constituent concentrations that are less than regulatory
standard or -are not detected at non -detect from groundwater
monitoring wells CCR-13S/D/BR, GWA-2S/D, GWA-24S/D/BR,
GWA-30S/D, and GWA-31S/D (Figures 6-13a-c, 6-14a-b, 6-17a-b, and
6-20a-b).
The maximum extent of COI -affected groundwater migration for all flow
zones is represented by boron. Chloride, lithium, and TDS concentrations
identified as being greater than their respective groundwater regulatory
standards are associated with COI -affected groundwater migration from the
ash basin but are generally confined within the extent of the 02L boron
plume and have a more localized footprint to the ash basins north and
northwest waste boundary (Figures 6-13a through 6-14c).
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). Trend analysis and results are prepared by Arcadis U.S. Inc.
and included in a technical memorandum titled Plume Stability Evaluation —
Belews Creek Steam Station (Arcadis, 2019). The technical memorandum is
included as in Appendix I as Attachment A.
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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. Statistically significant, decreasing concentration trend (D)
2. Statistically 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)
Ash pore water and groundwater wells within the waste boundary
generally have no trends or stable trends, suggesting limited changing
conditions and the plume is stable. Ash pore water and groundwater within
the waste boundary Mann -Kendall results indicate:
• Over 50% of ash pore water trend results indicate no trends for
boron, chloride, lithium and TDS and approximately 25% of trend
results indicate stable trends for conservative constituents (i.e. boron,
chloride, lithium and TDS) (Table 6-7).
• Only one constituent at one well has an increasing trend, lithium at
AB-4S (Table 6-7).
• Over 50% trend results for groundwater within the waste boundary,
indicate stable trends for conservative constituents (Table 6-7).
• No boron trends are increasing from groundwater wells within the
waste boundary. Boron trends are decreasing in two of three deep
flow wells below the as basin dam (Table 6-7). This is consistent with
information presented in the CSM in Section 5.0
Groundwater monitoring wells north of the ash basin, between the waste
boundary and compliance boundary, include CCR-4S/D, CCR-5S/D, CCR-
6S/D, CCR-7S/D, CCR-8S/D/AD, and GWA-2S/D; and groundwater
monitoring wells northwest of the ash basin, between the waste boundary
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and compliance boundary, include wells CCR-1S/D, CCR-2S/D, and GWA-
18S/D. Mann -Kendall results for groundwater wells between the waste
boundary and compliance boundary indicate:
• Approximately 36% of trend results for groundwater wells between
the waste boundary and compliance boundary have stable trends for
conservative constituents (Table 6-7).
• Only 18% of groundwater wells between the waste boundary and
compliance boundary have increasing trends of boron
concentrations. Wells with increasing trends are CCR-21), CCR-4S/D,
and CCR-7S/D, and are located downgradient north and northwest
of the ash basin (Table 6-7).
• For wells between the waste boundary and compliance, located east
and west of the ash basin, boron results are non -detect (e.g. CCR-
1S/D, CCR-11S/D, CCR-12S/DA, GWA-2S/D, GWA-181)) (Table 6-7).
Groundwater monitoring wells north of the ash basin and at or beyond the
compliance boundary include GWA-1S/D/BR, GWA-24S/D/BR, GWA-
32S/D, and MW-200S/D/BR. Groundwater monitoring wells northwest of
the ash basin and at or beyond the compliance boundary include GWA-
10S/DA, GWA-11S/D, GWA-19SA/D/BR, GWA-20SA/D/BR, GWA-21S/D,
GWA-27S/D/BR, GWA-30S/D, GWA-31S/D. Corrective action
implementation will address areas where the these wells are located. Mann -
Kendall results for groundwater wells downgradient, at or beyond the
compliance boundary indicate:
Only 17% of trend results for groundwater wells at or beyond the
compliance boundary have increasing trends for conservative
constituents (Table 6-7). Majority of increasing trends occur in wells
northwest of the ash basin.
Approximately 38% of trends results for groundwater wells at or
beyond the compliance boundary have stable trends. Majority of
stable trends occur in deep flow zone wells for constituents lithium
and TDS (Table 6-7).
• Majority (75%) of increasing trends occur for constituents boron and
chloride. Of the majority, 72% of increasing trends occur in wells
along primary groundwater flow paths from the ash basin (i.e.
shallow and deep wells GWA-1S/D, GWA-10S/D, GWA-11S/D,
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GWA-20SA/D, GWA-21S/D, GWA-27S/D) (Table 6-7). This is
consistent with information presented in the CSM in Section 5.0
• Bedrock well MW-200BR is the only bedrock well with increasing
trends (boron and chloride), where groundwater has an upward
vertical gradient in bedrock below the dam from the pressure head of
the ash basin pond water elevation (Table 6-7). This is consistent
with information presented in the CSM in Section 5.0.
The north and northwest groundwater plume appear unstable, with several
conservative constituents indicating increasing concentrations trends that
suggest the plume is still expanding. Some locations with increasing trends
have concentrations greater than comparative criteria.
6.1.5.2 Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
Arsenic, beryllium, thallium, and strontium isoconcentration maps and
cross -sections support the following observations regarding the extent of
COI -affected groundwater represented by these non -conservative
constituents:
Arsenic within the deep flow zone occurs at a single isolated
location, GWA-19D, within the extent of the 02L boron plume.
Shallow and bedrock groundwater arsenic occurrences are single
isolated locations, GWA-32S and GWA-20BR, and are outside the
extent of the 02L boron plume. GWA-32S is located downgradient of
a wetland; where reducing conditions might enhance arsenic
solubility (Figures 6-11a through 6-11b).
Beryllium exhibits a localized plume -like distribution in shallow
groundwater in the northwest corner of ash basin. Isolated single
detection of beryllium greater than IMAC in deep groundwater in
the northwest corner of ash basin. Beryllium within the deep flow
zone occurs at a single isolated location, GWA-21D, within the extent
of the 02L boron plume. Beryllium is not detected greater than IMAC
in bedrock groundwater (Figures 6-12a through 6-12b).
• Thallium in shallow groundwater exhibits a localized plume -like
distribution north and northwest of the ash basin. Thallium within
the deep flow zone occurs at two locations, GWA-21D and GWA-
27D, within the extent of the 02L boron plume. There are no
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detections of thallium in bedrock groundwater above IMAC (Figures
6-21a through 6-21b).
• Localized plume -like distributions of strontium greater than
background concentrations occur in shallow and deep groundwater
north and northwest of the ash basin. Occurrences of strontium in
shallow and deep groundwater occur primarily within the extent of
the 02L boron plume. The only three occurrences of strontium
greater than background in bedrock do not exhibit a plume -like
pattern; none of the three locations are concurrent with boron greater
than the 02L standard (Figures 6-19a through 6-19c).
6.1.5.3 Variably Conservative Constituents
Cobalt, iron, and manganese isoconcentration maps and cross -sections
support the following observations regarding the extent of COI -affected
groundwater represented by these variable constituents:
Localized plume -like distributions of cobalt greater than the IMAC
standard occur in shallow and deep groundwater north and
northwest of the ash basin. Occurrences of cobalt in shallow and
deep groundwater occur primarily within the extent of the 02L boron
plume. There are no detections of cobalt in bedrock groundwater
greater than IMAC (Figures 6-15a through 6-15b).
Iron in deep groundwater occurs at four isolated locations northwest
and north of the ash basin. With the exception of on location (GWA-
321)), the remaining locations are within the extent of the 02L boron
plume. Shallow groundwater has a single (GWA-32S), isolated
occurrence or iron greater than the background value (Figure 6-16).
Monitoring wells GWA-32S/D are downgradient of a wetlands area
to the northeast and both have iron concentrations greater than
comparative criteria but boron significantly less than the 02L
standard. Reducing conditions of the upstream wetland area might
enhance iron solubility in a localized area.
Localized plume -like distributions of manganese concentrations
occur in shallow and deep groundwater north and northwest of the
ash basin. Occurrences of manganese in shallow and deep
groundwater occur primarily within the extent of the 02L boron
plume. Bedrock groundwater has a single (MW-200BR), isolated
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occurrence of manganese greater than the 02L standard (Figures
6-18a through 6-18c).
6.2 Potential Receptors Associated with Source Area
(CAP Content Section 6.B)
CSA and ongoing monitoring data confirm that affected groundwater is limited to
between 500 and 750 feet immediately downgradient of the ash basin Groundwater
migration from the ash basin and PHR Landfill is limited to Duke Energy property
except for an unoccupied 2.67 parcel located northwest of the ash basin. Groundwater
migration from the ash basin and PHR Landfill does not reach any water supply wells,
and modeling indicates this will remain the case in the future. Therefore, potential
receptors are limited to nearby surface water bodies, including the Dan River, Belews
Reservoir, and their tributary streams, including the unnamed tributary.
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 ash
basin compliance boundary, along with permitted outfalls under the NPDES and
the SOC locations are shown on Figure 5-6 (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 Figure 5-6, is greater than the required 0.5 mile
radius of the waste boundary. The ash basin and PHR Landfill are located
between Belews Reservoir to the south and east and the Dan River to the north.
Associated North Carolina surface water classifications for Belews Reservoir and
the Dan River are summarized in Section 5.3.1 and Table 5-3 (CAP Content
Section 6.B.a.iii).
For groundwater corrective action to be implemented under Subchapter .02L
.0106(k), groundwater discharge to surface water cannot result in exceedances of
standards for surface waters contained in 15A NCAC 02B .0200 (02B). Surface
water constituents with 02B standards include: arsenic, barium, beryllium,
cadmium, chloride, chromium (hexavalent and trivalent), copper, fluoride, lead,
mercury, nickel, nitrate and nitrite, selenium, silver, sulfate, total dissolved
solids, thallium, total hardness, and zinc.
Surface water samples were collected from the Dan River and Belews Reservoir
to confirm groundwater downgradient of the ash basin has not resulted in
surface water concentrations greater than 02B water quality standards.
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Groundwater monitoring data consistently indicate the ash basin constituent
plume does not extend to either the Dan River or the Belews Reservoir. A map
of surface water sample locations for groundwater discharge to surface water
evaluation is included in Appendix K (CAP Content Section 6.B.a.iv). Surface
water samples were collected, using division approved protocols, to evaluate
acute and chronic water quality values. Surface water samples were also
collected at background locations (upgradient of potential migration areas)
within the Dan River, and Belews Reservoir. Analytical results were evaluated
with respect to 02B water quality standards and background data.
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
surface water samples from the Belews Reservoir and Dan River. 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 02B criteria are alkalinity, aluminum, antimony, iron and
manganese. 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 alkalinity in Dan River downstream samples and aluminum in
two Belews Reservoir upstream samples. Dan River downstream samples have
alkalinity concentrations greater than USEPA criteria and greater than
background Dan River concentrations. Two Belews Reservoir upstream samples,
SW-BL-U2 and SW-BL-U3, have greater concentrations of aluminum greater than
USEPA criteria and greater than other Belews Reservoir upstream and
downstream samples.
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. The full report for BCSS
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 23, 2019. Surface water data has been reevaluated as a result of surface
water quality standards updated by NCDEQ on June 6, 2019. The revised report
is provided in Appendix K.
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General findings of the evaluation of current surface water quality conditions at
BCSS include:
• Groundwater migration from the ash basin source area has not resulted in
exceedances of the 02B surface water quality standards at the Dan River or
Belews Reservoir.
• Previously identified seeps are deemed covered by Special Order by
Consent EMC SOC WQ S18-004 (SOC).
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 north and northwest of the ash basin
(specifically jurisdictional streams associated with seeps S-3, S-4, S-5, S-11, S-15,
and S-18) could potentially 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 BCSS groundwater discharge to surface water under future
conditions can be found in Appendix K.
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 Subchapter 02L
.0106 (k) or (1)
• Modeling scenarios illustrate the maximum extent of COI -affected
groundwater occurs during years 2032 through 2100. The predicted
extent of COI -affected groundwater migration is anticipated to encompass
an area outside the ash basin footprint that reaches jurisdictional streams,
as identified in the NRTR (AMEC Foster Wheeler, 2015), associated with
non -disposition seeps S-3, S-4, S-5, S-11, S-15, and S-18.
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• The predicted extent of COI -affected groundwater migration from the ash
basin would not reach the Dan River or migrate toward Belews Reservoir
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)
A total of 50 private water supply wells and one public supply well were
identified within the 0.5-mile radius of the ash basin compliance boundary
(Figure 5-7a and Figure 5-7b). The 0.5-mile radius from the ash basin
compliance boundary, for which data is evaluated and depicted on figures, is
greater than the required 0.5-mile radius from the waste boundary and is
consistent with the drinking water well and receptor surveys.
Most of these water supply wells are located northeast of the ash basin along
Pine Hall Road and Middleton Loop, and west and southwest of the ash basin
along Middleton Loop, Old Plantation Road, Pine Hall Road, and Martin Luther
King Jr. Road. No public or private drinking water wells or wellhead protection
areas were found to be located downgradient of the ash basin as discussed in
Section 5.3. This finding has been supported by field observations, a review of
public records, an evaluation of historical groundwater flow direction data and
results of groundwater flow and transport modeling (Appendix G). The location
and information pertaining to water supply wells located upgradient or side -
gradient of the facility, within 0.5 miles of the ash basin compliance boundary,
were included in drinking water supply well survey reports.
6.2.2.1 Provision of Alternative Water Supply
(CAP Content Section 6.B.b.i)
Although results from local water supply well testing do not indicate effects
from the source area, private and public water supply wells identified
within the 0.5-mile radius from ash basin compliance boundary have been
offered a water treatment system, per G.S. Section 130A-309.211(cl)
requirements.
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Duke Energy identified a total of 45 private resident properties eligible for
connections for a water treatment system near BCSS. A property eligibility
was contingent that the property did not include:
• A business
• A church
• A school
• Connection to the public water supplier
• An empty lot
Of the 45 eligible connections, 11 either opted out of the option to connect to
a water treatment system or did not respond to the offer. Duke Energy also
voluntarily provided permanent water solutions to business, schools, and
churches within a 0.5-mile radius not connected to a public water supply
that were otherwise not eligible per G.S. Section 130A-309.211(cl). At
Belews Creek, this included providing water treatment systems to one
business, LCW Associates LLC, and one church, Withers Chapel United
Methodist Church (UMC). Duke Energy installed 36 water filtration
systems at surrounding properties in accordance with G.S. Section 130A-
309.211(c1).
On August 31, 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. Section
130A-3099.211(cl) at BCSS. Both documents are provided in Appendix D.
Figure 5-7a and Figure 5-7b (CAP Content Section 6.B.b.i) shows the private
and public water supply well locations with reference to water treatment
systems installed along with vacant parcels and residential properties
whose owners have either decided to opt out of the water treatment system
program 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) and all water
supply wells are outside of the area of groundwater affected by the ash
basin and PHR Landfill.
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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 ash basin
compliance boundary, 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 ash basin compliance
boundary, have been reported to NCDEQ:
• Drinking Water Well and Receptor Survey — Belews Creek Steam Station
(HDR 2014a)
• Supplement to Drinking Water Well and Receptor Survey — Belews Creek
Steam Station (HDR 2014b)
• Comprehensive Site Assessment Report — Belews Creek Steam Station Ash
Basin (HDR 2015a)
• Comprehensive Site Assessment Update Report — Belews Creek Steam
Station Ash Basin (SynTerra 2017)
The survey identified two public supply wells within a 0.5-mile radius of
the ash basin compliance boundary. The LCW Associates LLC public water
supply well is located approximately 1,700 feet (0.3 miles) southwest and
upgradient of the ash basin. The Withers Chapel UMC public water supply
well is located approximately 1,750 feet (0.3 miles) northeast and upgradient
of the ash basin.
As documented in the 2017 CSA Update, NCDEQ arranged for independent
analytical laboratories to collect and analyze water samples in the first part
of 2015 from private wells identified during the well survey, if the owner
agreed to have their well sampled. NCDEQ collected and analyzed
groundwater samples from seven private water supply wells within a 0.5
mile radius of the BCSS ash basin compliance boundary. NCDEQ
continued to collect and analyze samples from water supply wells within a
0.5 mile radius of the BCSS ash basin compliance boundary during the latter
part 2015 and early 2016. A total of 36 samples from 36 private water
supply wells were collected by NCDEQ. Duke Energy collected samples
from private water supply wells in 2016 and 2017 after the NCDEQ
sampling effort. For many of the wells sampled in this program, as with
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standard practice, samples were split for analysis by Duke Energy's
certified (North Carolina Laboratory Certification #248) laboratory.
Table 6-9 (CAP Content Section 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.
Although some of the water supply wells may be installed in the bedrock
flow zone. Groundwater concentrations of boron, which is a constituent that
conservatively indicates influence from the Belews Creek ash basin or
closed PHR Landfill, is not detected in the vicinity of the water supply wells
and is only detected in bedrock monitoring wells at locations within the
compliance boundary, approximately over 3,000 feet from the closest water
supply well.
The major findings from the water supply well evaluation include:
All water supply wells west of the ash basin and PHR Landfill are in
a separate drainage system separated by a hydrologic divide
represented by Middleton Loop. Vector velocities depict
groundwater flowing away, on either side of the hydraulic divide
represented by Middleton Loop (Figure 5-5a).
All water supply wells to the southwest are upgradient of the ash
basin, not within the direction of groundwater flow from the ash
basin and PHR Landfill (Figure 5-4c).
All water supply wells to the north and northeast are upgradient of
the ash basin, not within the direction of groundwater flow from the
ash basin and PHR Landfill (Figure 5-4c).
Groundwater modeling simulation indicated as source control (i.e.
decanting and ash basin closure) continues, a hydraulic divide is
expected to be reestablished northwest of the ash basin, along the
topographic ridge represented by Middleton Loop (Figure 5-5b and
Figure 5-5c).
• All water supply wells are outside of the conservative constituent
02L groundwater plumes from the ash basin and PHR Landfill.
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Isoconcentration contour maps for boron, chloride, and TDS of all
flow zones support water supply wells are not within the footprint of
conservative concentration groundwater plumes (Figures 6-13a-c,
6-14a-b, 6-17a-b, and 6-20a-b).
Ten of the 20 COIs identified in the CSA Update (SynTerra, 2017)
were present greater than 02L standards or bedrock background
values including: antimony, arsenic, hexavalent chromium, total
chromium, cobalt, iron, manganese, molybdenum, strontium and
vanadium. With the exception of antimony, these metals are
characterized as non -conservative or variably conservative
geochemical behavior and generally migrate within a short distance
of the ash basin waste boundary. Of these metals, only cobalt, iron,
manganese and strontium are detected at concentrations greater than
comparative criteria downgradient of the ash basin, at or beyond the
compliance boundary in a plume configuration; however, these
constituents are not associated with the ash basin based on the local
hydrogeology as described above. The other constituents (antimony,
arsenic, hexavalent chromium, total chromium, molybdenum, and
vanadium) are not detected at or beyond the compliance boundary at
concentrations greater than comparative criteria downgradient of the
ash basin.
The conservative, highly mobile constituents, boron, chloride and
TDS were not present greater than 02L standards or background
values in any water supply well, which is consistent with the local
hydrogeology as described above.
• Concentrations of antimony greater than IMAC values were
observed in two water supply wells west of the ash basin. No
discernable plume associated with the ash basin and PHR Landfill
was identified. This finding has been confirmed by 30 consecutive
onsite groundwater monitoring events.
• Arsenic is only present in groundwater in the shallow and deep flow
zones greater than the 02L standard north of the ash basin at isolated
locations (Figure 6-11a and 6-11b). Concentrations of arsenic greater
than 02L standards were observed in nine water supply wells, to the
west and southwest of the ash basin, approximately 4,000 feet from
the nearest location with arsenic greater than the 02L standard,
downgradient of the source area. No discernable plume associated
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with the ash basin and PHR Landfill is identified in water supply
wells with arsenic concentrations greater than 02L. This finding has
been confirmed by 30 consecutive onsite groundwater monitoring
events.
Concentrations of chromium greater than background values were
observed in one water supply wells west of the ash basin. No
discernable plume associated with the ash basin and PHR Landfill
was identified. This finding has been confirmed by 30 consecutive
onsite groundwater monitoring events.
• Concentrations of cobalt greater than IMAC values were observed in
two wells. Both wells were located to the northeast of the ash basin.
No discernable plume associated with the ash basin and PHR
Landfill was identified. This finding has been confirmed by 30
consecutive onsite groundwater monitoring events.
Hexavalent chromium is only present in groundwater in one bedrock
monitoring well, within the compliance boundary, greater than the
02L standard north of the ash basin. Concentrations of hexavalent
chromium greater than background values were observed in nine
water supply wells, to the northeast and southwest of the ash basin.
No discernable plume associated with the ash basin and PHR
Landfill was identified in water supply wells with hexavalent
chromium concentrations greater than background. This finding has
been confirmed by 30 consecutive onsite groundwater monitoring
events.
• Iron is only present in groundwater in the deep flow zone greater
than the 02L standard north of the ash basin at isolated locations
(Figure 6-16). Concentrations of iron greater than background values
were observed in seven water supply wells. The wells are located to
the north, northeast and west of the ash basin, approximately 1,100
feet from the nearest location with iron greater than the 02L
standard, downgradient of the source area. No discernable plume
associated with the ash basin and PHR Landfill was identified in
water supply wells with iron concentrations greater than 02L. This
finding has been confirmed by 30 consecutive onsite groundwater
monitoring events.
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Manganese is present in groundwater shallow, deep, and bedrock
flow zones downgradient, north and northwest of the source area, at
concentrations greater than comparative criteria (Figure 6-18 a
through c). Concentrations of manganese greater than background
values were observed in seven water supply wells. The wells are
located to the northeast and southwest of the ash basin,
approximately 3,300 feet from the nearest location with manganese
greater than the 02L standard, downgradient of the source area. No
discernable plume associated with the ash basin and PHR Landfill
was identified in water supply wells with manganese concentrations
greater than background. This finding has been confirmed by 30
consecutive onsite groundwater monitoring events.
• Molybdenum is found greater than background values north and
northwest of the ash basin at isolated locations that do no exhibit a
plume configuration. Concentrations of molybdenum greater than
background values were observed in five water supply wells west
and southwest of the ash basin. No discernable plume associated
with the ash basin and PHR Landfill was identified in water supply
wells with molybdenum concentrations greater than background.
This finding has been confirmed by 30 consecutive onsite
groundwater monitoring events.
Strontium is present in groundwater shallow, deep, and bedrock
flow zones downgradient, north and northwest of the source area, at
concentrations significantly greater than background (Figure 6-19a
though c). Concentrations of strontium greater than background
values were observed in nine water supply wells, approximately
3,000 feet from the nearest location with strontium greater than the
background, downgradient of the source area. No discernable plume
associated with the ash basin and PHR Landfill is identified in water
supply wells with strontium concentrations greater than background.
This finding has been confirmed by 30 consecutive onsite
groundwater monitoring events.
Concentrations of vanadium greater than background values were
observed in two water supply wells. The wells are located to the west
of the ash basin. No discernable plume associated with the ash basin
and PHR Landfill was identified. This finding has been confirmed by
30 consecutive onsite groundwater monitoring events.
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6.2.3 Future Groundwater Use Areas
(CAP Content Section 6.B.c)
Duke Energy owns the land and controls the use of groundwater on the land
downgradient of the ash basin and PHR Landfill within and beyond the
predicted area of potential groundwater COI influence. Therefore, no future
groundwater use areas are anticipated downgradient of the ash basin or PHR
Landfill.
It is anticipated that private and public properties within a 0.5-mile radius of the
ash basin 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 5-7a and 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 ash basin is expected to be further
contained within the stream valley and continue flowing north of the ash basin
footprint, and therefore will not flow towards any water supply wells
[(Appendix G) (CAP Content Section 6.B.c.ii)].
6.3 Human and Ecological Risks
(CAP Content Section 6.0
Updated human health and ecological risk assessments were prepared for the BCSS
consistent with the CAP content guidance. The updated risk assessments incorporate
results from surface water, sediments, and groundwater samples collected March 2015
through June 2019. Primary conclusions from the risk assessment update include: (1)
the ash basin does not cause an increase in risks to potential human receptors located
on -Site or off -Site; and (2) the ash basin does not cause an increase in risks to ecological
receptors. These conclusions are further supported by multiple water quality and
biological assessments conducted by Duke Energy as part of the NDPES monitoring
program. A more detailed discussion regarding human health and ecological risk
associated with the ash basin can be found in Section 5.4. An update to the BCSS
human health and ecological risk assessment is included in Appendix E.
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6.4 Description of Remediation Technologies
(Supplemental Information for CAP Content Section 6.D.a.iv)
This section provides supplemental information beyond the CAP content guidance to
introduce groundwater remediation technologies and considers a range of individual
groundwater remediation technologies that may be used to formulate comprehensive
groundwater remediation alternatives for consideration at Belews Creek. 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 6.7.
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).
MNA processes potentially applicable to inorganic constituents include:
• Dispersion • Sorption • Biological stabilization
• Dilution • Radioactive decay • Chemical stabilization
• Transformation • Phytoremediation
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.
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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).
The NCDEQ and USEPA have guidance documents that prescribe the
investigative and analytical processes required for an MNA demonstration
(NCDEQ, 2017). 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 at Belews Creek, 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
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implemented that eliminate or mitigate the source of CCR constituents in
groundwater. The MNA evaluation for the technical applicability at Belews
Creek 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
When used for the purpose of groundwater remediation, low permeability
barriers (LPBs) are structures constructed in -situ to redirect groundwater flow.
Materials used to construct LPBs are either impermeable (e.g., steel sheet pile) or
have a permeability that is two orders of magnitude or lower than 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.
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 reactive 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 Belews Creek
would involve installation by means of drilling because bedrock is
approximately 50 feet (or greater) below ground surface downgradient of the ash
basin.
Construction of a LPB at Belews Creek 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 at the BCSS. 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.
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Groundwater Infiltration and Flushing
Groundwater flushing by infiltration can be accomplished by many methods
including vertical wells, horizontal wells, and infiltration galleries.
In -situ groundwater flushing involves the infiltration or injection of clean water
into groundwater to accelerate flushing of targeted 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. 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 or the clean water source and pre -design collection of data is important
for most sites where this technology might be considered.
Flushing of relatively mobile and unreactive constituents like boron can be
accomplished using clean water.
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 a clean water into groundwater enhances physical 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).
Groundwater flushing is a technology that has possible application at Belews
Creek to enhance the capture of mobile constituents. Groundwater flushing by
infiltration will be retained for further consideration.
Encapsulation
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).
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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
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.
Microencapsulation and ISV would not be feasible for the areas north and
northwest of the ash basin that would need to be encapsulated, due to the size
and depths of the areas requiring groundwater remediation.
Encapsulation technologies 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.
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Permeable Reactive Barrier
The USEPA defines a permeable reactive barrier (PRB) 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 (USEPA, 1997).
Construction of PRBs involves emplacement of reactive media below the ground
surface for the purpose of 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 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
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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 adsorber
(Wright, 2003).
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.
The ability to maintain adequate reactive reagent concentrations at depth over an
extended period of time is a significant operational and performance
consideration. This technology was considered during the evaluation process for
the interim action system northwest of the basin. However, upon evaluation, it
was not chosen as the most effective remedial approach for the area. Permeable
reactive barriers are not carried forward for further evaluation for the same
reasons this technology was not chosen for the interim action system. Reasons
include:
• Detected concentrations of aluminum, iron, and manganese dissolved in
groundwater could react with, and clog, treatment areas, diminishing the
hydraulic conductivity through the PRB.
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• 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.
6.4.3 Groundwater Extraction
Groundwater extraction is often used when remediating mobile constituents in
groundwater. Groundwater extraction can be used to withdraw effected
groundwater from the subsurface for the purpose of reducing the mass of one or
more target constituent(s) in an aquifer. Groundwater extraction can be used to
hydraulically contain effected groundwater and mitigate groundwater
constituent migration. Groundwater extraction can be conducted using a variety
of methods that are discussed in the following sub -sections.
Groundwater extraction is currently being used at BCSS to capture COI -affected
groundwater downgradient, northwest of the ash basin. A more comprehensive
system of groundwater extraction wells could be added to the existing system to
capture COI -affected groundwater near or beyond the ash basin compliance
boundary (e.g., to the north of the ash basin main dam).
Vertical Extraction Wells
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 technology, 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 aquifers can be problematic for vertical extraction wells. Relatively
close spacing of vertical wells might be necessary to capture a constituent plume
if the aquifer 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
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where the groundwater level and desired pumping level is relatively shallow
(less than 25 to 30 feet below the ground surface). Submersible pumps (deep well
single- or multi -stage centrifugal pumps) can be used to extract groundwater
from larger diameter wells with deeper groundwater levels. Also, deep well jet
pumps can be used, and they have the advantage of mechanical equipment
above grade; therefore, 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.
Groundwater modeling conducted for Belews Creek indicates that vertical
groundwater extraction wells can produce sufficient yield for effective
constituent mass removal. The use of vertical groundwater extraction wells is
retained for further consideration.
Additionally, shallow groundwater extraction wells installed near seep locations
can be an effective surface water protection supplement to a groundwater
management system. If applied at Belews Creek, shallow groundwater extraction
effectiveness would be best applied as corrective action to address seep(s)
located north of the ash basin dam, if not dispositioned after completion of
decanting.
Horizontal/Angular Well Extraction Wells
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, and similar shallow or near subsurface
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 is
precisely monitored to avoid subsurface obstructions and to install the well as
designed. Tracking accuracy generally decreases with increasing depth of
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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 might 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 the 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.
Groundwater modeling conducted for Belews Creek indicates that groundwater
vertical extraction wells can produce sufficient yield for purposes of hydraulic
containment and/or constituent mass removal. Vertical extraction wells are
deemed more cost effective than horizontal wells and therefore use of horizontal
or angular groundwater extraction wells is not retained for further consideration.
Extraction Trenches
Shallow horizontal groundwater extraction (collection or intercept) trenches can
be installed in areas near surface waters where groundwater might discharge.
Trenches can be utilized to prevent groundwater from discharging into surface
waters and can be effective in lowering or managing the water table.
Trenches might be used as temporary installations to intercept and monitor
subsurface flow or can be retained as a permanent installation. Trenches must be
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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
(< 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.
Although this technology is not capable of achieving depths necessary to
remediate groundwater, shallow groundwater extraction trenches are easy to
install and can be an effective surface water protection supplement to a
groundwater management system. If applied at Belews Creek, trench technology
effectiveness would be best applied as corrective action to address seep(s)
located north of the ash basin dam, if not dispositioned after completion of
decanting. The use of shallow groundwater extraction trenches is retained for
further consideration.
Hydraulic Fracturing
The effectiveness of groundwater extraction systems can sometimes be improved
in low permeability formations, including bedrock, with the use of 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.
Hydraulic fracturing generally involves the application of high pressures to
propagate existing fractures or to create fractures following fracture nucleation.
When hydraulic fracturing 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, oa
thick gel at high pressure into the borehole to propagates the fracture. The
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residual gel biodegrades and the resultant fracture is a permeable sand -filled lens
that might be as large as 60 feet in diameter (USEPA, 1995).
The presence of COIs in the bedrock groundwater at Belews Creek is limited
compared to the distribution and concentrations of COIs in saprolite and
transition zone groundwater. The use of hydraulic fracturing to enhance
remediation of bedrock groundwater is not considered further because the extent
of COIs in bedrock groundwater is limited.
Phytoremediation
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 tree well 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
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target depth. The boring is backfilled with soil that might include reactive
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.
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
(US EPA, 1982).
Ground cover plants stabilize soil/sediment and control hydraulics. In addition,
densely rooted groundcover plants and grasses can also be used to remediate
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 tree wells 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 wetland plants with robust root systems and 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
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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).
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 would be an effective surface water protection
supplement to a groundwater management system. If applied at Belews Creek,
phytoremediation technology effectiveness would be best applied as corrective
action to address low flowing seeps north of the ash basin dam and in remote
locations of the Site, if not dispositioned after completion of decanting.
Therefore, the use of phytoremediation is retained for further consideration for
shallow groundwater extraction as a corrective action strategy for seeps.
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 NPDES permitted outfalls at Belews Creek
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 Belews Creek.
The pH adjustment of extracted groundwater is not expected but is retained due
to the average value for pH in shallow (saprolite) groundwater at the Belews
Creek Site is 5.3 S.0 which is below the permit limit. However, extracted
groundwater would consist of mixed shallow, deep, and bedrock groundwater.
The average pH of groundwater downgradient of the ash basin from all flow
zones is approximately 6.8 S.U, which is within the current permit requirement,
however, this treatment technology will be retained for further consideration.
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Precipitation
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 and metal complexes is commonly
illustrated in Pourbaix diagrams
FIGURE 6-24
POURBAIX DIAGRAM FOR
IRON -WATER SYSTEM
Simplified Pourbaix diagram
for iron -water system at 77°F (25°C)
E,i' ._
2.0
FcO4' (aq)
Fe°+ (aq)
i.�
u.x e d
FezOi h
q,q Fe4 (aq) c
a h `
Fe W
0 2 a 6 N 10 12 14 PH
(pH vs Eh). https:Hrsteyn.wordpress.com/pourbaix-diagrams
As illustrated in the Pourbaix diagram (Figure 6-24), iron is soluble (aqueous or
aq) at a pH of approximately 3.5 S.U. or less under aerobic conditions (Eh > 0 V).
If the pH is increased, ferric (Fe+3) iron will react to form insoluble (solid or s)
complexes and precipitate out of solution, provided that the redox potential
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).
Precipitation technology might be warranted as a means to treat, or pretreat,
extracted groundwater to satisfy NPDES permitted discharge limits.
Precipitation technologies are retained for further consideration. Dissolved
constituent precipitation technology equipment is readily available.
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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. 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 can become 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 SO 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
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proper disposal. The slow rinse is followed by a fast "raw" water rinse to verify
water quality requirements are being met.
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.
Membrane Filtration
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.
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 at Belews Creek 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.
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6.4.5 Groundwater Management
Extracted groundwater must be managed of 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
The BCSS has an NPDES permit that authorizes the discharge of specific waste
streams to the Dan River via NPDES Outfall 006. The ash basin is closed (i.e. does
not receive waste inputs); however, discharge, via Outfall 006A, from the ash
basin remains active, as basin closure activities remain in progress (i.e., ash basin
decanting and dewatering). The wastewater from Outfall 006A discharges
Outfall 006, which then discharge to the Dan River.
Active waste streams that previously discharged to the ash basin have been re-
routed to the new lined retention basin (LRB). Outfall 006 is constructed for the
LRB and replaces Outfall 003A. Outfall 006 discharges to the Dan River and is the
ultimate disposal of extracted groundwater.
Anticipated groundwater remediation parameter levels are within NPDES
permit limits for Outfall 006A/006 as summarized on Table 6-10. Therefore,
disposal of extracted groundwater utilizing the NPDES discharge system will be
retained for further consideration.
Publicly Owned Treatment Works (POTW)
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 Town of Madison wastewater treatment plant (WWTP) is located at 403
Lindsey Bridge Rd, Madison, NC 27025, or about 9.5 miles northeast of Belews
Creek near the shoreline of the Dan River. The Madison WWTP uses a process in
treating and purifying water for the Town of Madison and Rockingham County.
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The treatment process consists of five steps, including coagulation, flocculation,
sedimentation, filtration and disinfection. The Town of Madison WWTP limits
their influent a daily flow rate of 1.5 million gallons per day (MGD).
Discharge of extracted groundwater to the Town of Madison WWTP is not
retained for further consideration at this time because of the extensive distance
required to pipe extracted groundwater from the Belews Creek site to the
WWTP. Disposal of extracted groundwater via NPDES Internal Outfall 006A
and Outfall 006 is considered the most viable option.
Non -Discharge Permit/Infiltration Gallery
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 extracted water by
way of an infiltration gallery must not result in concentrations greater than 02L
groundwater standards or affect the model predictions. Consequently,
groundwater treatment must reliably produce an effluent waste stream that does
not result in groundwater concentrations greater than the 02L standard.
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 over a half of the native soil is FpC2 (Fairview -Poplar Forest complex), RpE
(Rhodhiss, Fairview, and Stott Knob), and others similar in properties, and
consist of a sandy clay loam to fine sandy loam (USDA, 2019). The capacity of
the most limiting layer of this soil type to transmit water is described as ranging
from moderately high to high (0.57 to 1.98 inches/hour) capacity.
Before extracted water could be recycled for infiltration gallery use, inorganic
constituents, including boron, chloride, cobalt, manganese among others, would
have to be treated. Treatment would have to be sufficient so wastewater recycled
to the groundwater system would not result in constituent concentrations greater
than 02L groundwater standards. Treatment of conservative and variably
conservative constituents could result in a complicated systems with significant
operation and maintenance efforts. Therefore, the use of infiltration galleries to
dispose of treated groundwater is not retained for further consideration.
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Non -Discharge Permit/Land Application
Land application of groundwater involves the distribution of extracted
groundwater onto land to irrigate 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 in soil must
be continuously delivered to growing tissues through roots and vascular tissues
to maintain cell wall biosynthesis and optimal plant development (Takano, June
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, November 2002). If extracted groundwater is
land applied, boron would be made available for plant uptake.
Extracted groundwater could be used to irrigate more than 300 acres of planted
vegetative cover following the 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 would either infiltrate into the soil or migrate downslope to
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 effective up to 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 groundwater 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 who 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, groundwater, or
wetlands.
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 is not retained as an alternative means for
disposal of extracted wastewater.
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Beneficial Reuse
Beneficial reuse of extracted groundwater involves the evaluation of existing
Station water demand and the repurposing of extracted groundwater to satisfy a
need for water. Beneficial reuse of extracted groundwater can do the following:
• 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.
A NCDEQ 2018 Annual Water Use Report for the BCSS indicated that water was
withdrawn from Belews Reservoir every day in 2018. The average daily
withdrawal in a given month ranged from 588.7 MGD to 1459.0 MGD. The
average daily discharge in a given month ranged from 585.7 to 1455.0 MGD
(NCDEQ, 2018). Beneficial reuse of extracted groundwater will not be retained
for further consideration at Belews Creek, but this might be reconsidered in the
future.
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. This
beneficial reuse option is a potential application for Belews Creek, but only
as a system improvement and supplemental source of water for fire
protection. It will be determined at a later date whether the extracted water
is appropriate for beneficial reuse based on actual extraction rates of
operational system.
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. However, certain groundwater constituents including the
constituents that comprise alkalinity would be diluted by non -contact
cooling water obtained from Belews Reservoir. This beneficial reuse option
is a potential application for Belews Creek, but only as a system
improvement and supplemental source of water for non -contact cooling
water. It will be determined at a later date whether the extracted water is
appropriate for beneficial reuse based on actual extraction rates of
operational system.
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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 basin 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 expense to substitute extracted
groundwater for dust suppression and truck wash water obtained from the
plant water intake on Belews Reservoir. 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 several groundwater
extraction technologies including vertical extraction wells, horizontal extraction
wells, extraction trenches, and phytoremediation. Groundwater treatment
technologies retained include pH adjustment and precipitation. These
technologies were retained to meet NPDES permit discharge limits which was
the only technology retained for disposal of extracted groundwater. No
beneficial reuse technology is retained at this time.
6.5 Evaluation of Remedial Alternatives
(CAP Content Section 6.D)
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 6.7. Technologies evaluated and retained for consideration as discussed in
Section 6.5 were used to formulate the following three groundwater remedial
alternatives to remediate Site groundwater:
• Remedial Alternative 1: Monitored Natural Attenuation
• Remedial Alternative 2: Groundwater extraction and treatment
• Remedial Alternative 3: Groundwater extraction combined with clean water
infiltration and treatment
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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 ash basin compliance
boundary. Under this alternative the groundwater plume could continue to
migrate beyond the current compliance boundary north and northwest of the ash
basin for more than 100 years; compliance is predicted to be achieved in
approximately 700 years after ash basin closure completed (Appendix G). A
detailed 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 the
Belews Creek ash basin and PHR Landfill occur at or beyond the
compliance boundary to the north and northwest of the ash basin 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
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 the BCSS (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: arsenic, beryllium,
boron, chloride, cobalt, iron, lithium, manganese, strontium, thallium, and
TDS (CAP Content Section 6.D.a.i.1). These are the COIs that indicate a
discernable plume associated with the source area.
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 are hydraulically controlled within
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the topographic drainage basin downgradient of the ash basin, with the
exception of the area to the northwest of the dam.
Source control is a primary component of MNA as a remedial strategy. Ash
basin decanting commenced on March 27, 2019, and is scheduled to be
completed by September 2020. As of December 1, 2019, approximately
469,400,000 gallons water have been removed from the ash basin and the
water elevation has decreased by 10.6 feet. Decanting is a form of active
source control by removing ponded water in the ash basin, which is
considered a critical component of reducing constituent migration from the
ash basin. After decanting and basin closure, the groundwater divides that
control the migration of COI will become more pronounced (along Pine
Hall Road) or will be re-established (along Middleton Loop). The decanting
will reduce the potentiometric head responsible for the downward vertical
gradient upstream of the ash basin dam. A lower downward gradient
would reduce downward COI migration. As a result, constituent
concentration reductions through natural attenuation processes are
anticipated following decanting.
The following five physical natural attenuation mechanisms are an effective
corrective action approach north and northwest of the Site 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
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The following three chemical natural attenuation mechanisms are also an
effective corrective action approach north and northwest of the Site because
they aid in stabilizing control of reactive and variable reactive COI's arsenic,
beryllium, cobalt, iron, manganese, strontium, and thallium in groundwater
by the following processes:
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
More information on one or more effective natural attenuation mechanism
for reducing the concentration of the COI 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 this alternative include groundwater monitoring wells within the
former source area and near the former waste boundary, along
downgradient flow transects, at the point of compliance, in sentinel areas
prior to receptors, and near the maximum predicted extent of migration.
There are 175 monitoring wells installed associated with the ash basin. 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
(primarily relying on natural attenuation by dilution). The simulation
suggests that the groundwater plume could continue to migrate beyond the
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current compliance boundary north and northwest of the ash basin for more
than 100 years; compliance is predicted to be achieved in approximately 700
years after ash basin closure completed with an MNA approach to
corrective action. The time to achieve compliance is likely conservative
because the area of remediation northwest of the compliance boundary has
been calibrated in the flow and transport model with a low hydraulic
conductivity zone in order to simulate boron transport in the bedrock flow
zone that matches empirical Site data.
The flow and transport modeling report that provides the predictions for
boron is presented in Appendix G. The simulated boron concentrations for
the years 2050, 2100, 2150, and 2200 for each closure scenario with MNA are
depicted in Appendix G, Figures 6-7a through 6-7d and Figures 6-14a
through 6-14d. 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 and
Treatment
(CAP Content Section 6.D.a)
Alternative 2 consists of groundwater extraction and treatment as a remedial
alternative for the areas north and northwest of the ash basin at or beyond the
compliance boundary. This alternative provides technology for groundwater
capture (i.e. extraction) to address Site specific COIs. Under this alternative,
compliance will be achieved in an excess of 300 years after system startup and
operation.
6.5.2.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
CCR constituents in groundwater associated with the Belews Creek ash
basin and PHR Landfill occur at or beyond the compliance boundary to the
north and northwest of the ash basin 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 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
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documented lack of human health or ecological risk at the BCSS (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: arsenic, beryllium,
boron, chloride, cobalt, iron, lithium, manganese, strontium, thallium, and
TDS (CAP Content Section 6.D.a.i.1). These are the COIs that indicate a
discernable plume associated with the source area.
The conceptual model and predictive modeling discussions summarize the
foundations for development of the groundwater extraction combined with
clean water infiltration and treatment 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 Alternative 2 include:
• 10 existing extraction wells, which are part of the current interim
action system
• Approximately 103 new extraction wells to the north and northwest
of the ash basin
• Pumps, associated piping, and control systems
• Discharge piping and structure
• pH adjustment or other treatment systems
The flow and transport model predicts each extraction well to have a flow
rate of approximately 0.1 gpm, for a total groundwater extraction system
flow rate of approximately 10 gpm. Post -decanting, the 10 interim action
extraction wells are predicted to remove a total of about 2.5 gpm. The
number of extraction wells is estimated based on multiple groundwater
extraction simulations of flow and transport modeling results. Results
generally provide a similar conclusion for flow rate, number of wells, and
time to meet compliance.
Based on the CSM (Section 5.0) and flow and transport modeling results
(Appendix G), the groundwater COIs are hydraulically controlled within
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the topographic drainage basin downgradient of the ash basin, with the
exception of the area to the northwest of the dam, which will be remedied
by the planned remediation system.
The distribution of conservative COIs (boron, chloride and TDS) represents
the area of maximum COI distribution at or beyond the compliance
boundary and is the focus of corrective action. 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. With
some exceptions, other COIs have generally not migrated horizontally or
vertically in the shallow, deep, and bedrock flow zones appreciably from
the source area, and are not expected to do so due to constituent
geochemical characteristics and Site geochemical and hydrogeologic
conditions as detailed in Appendix G and H.
It is expected that extracted water would be treated and discharge through
the existing NPDES Internal Outfall 006A and Outfall 006 locations based
on currently available groundwater data and the current permit. Initially,
the groundwater would be treated by pH adjustment and flocculation in the
system used to treat the water from decanting and dewatering the ash
basin. Post -decanting and dewatering of the ash basin provides an
intervening period, where modifications to the decanting/dewatering
treatment system or alternatives, including beneficial reuse, will be
considered. If necessary a modified treatment method will be selected based
on the quantity and quality of the extracted groundwater.
A preliminary summary of groundwater data and current discharge permit
limits is presented in the table NPDES Permit Limits and Anticipated
Groundwater Remediation Parameter Levels in Section 6.5.
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. A groundwater extraction
system would result in localized groundwater extraction and removal of
COI mass. The low permeability of 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 0.1 gpm. The flow and transport report (Appendix G) and
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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 at any point in time will be approximately 1,500 feet beyond the
compliance boundary. Simulations indicate that boron concentrations in
groundwater would meet the 02L boron standard of 700 µg/L at the
compliance boundary in excess of 300 years after system startup and
operation. The time to achieve compliance is likely conservative because the
area of remediation northwest of the compliance boundary has been
calibrated in the flow and transport model with a low hydraulic
conductivity zone in order to simulate boron transport in the bedrock flow
zone that matches empirical Site data.
6.5.3 Remedial Alternative 3 - Groundwater Extraction
Combined with Clean Water Infiltration and Treatment
(CAP Content Section 6.D.a)
Alternative 3 consists of groundwater extraction combined with clean water
infiltration for remediation of the groundwater north and northwest of the ash
basin at or beyond the compliance boundary. This alternative provides an
effective combination of technology for groundwater remediation at or beyond
the compliance boundary.
Under this alternative, flow and transport modeling indicates compliance with
02L can be achieved in approximately 13 years after system startup and
operation along the majority of the compliance boundary.
Near the northwest perimeter of the ash basin waste boundary, the 500 foot
compliance boundary is reduced by approximately 250 feet. The reduced
compliance boundary follows a 500 foot section of the Duke Energy property
boundary. The reduced compliance boundary results in a longer timeframe to
achieve compliance in the small area. The predicted timeframe to achieve
compliance for the small area is approximately 36 years after system startup and
operation.
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6.5.3.1 Problem Statement and Remediation Goals
(CAP Content Section 6.D.a.i)
CCR constituents in groundwater associated with the Belews Creek ash
basin and PHR Landfill occur at or beyond the compliance boundary to the
north and northwest of the ash basin 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 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 the BCSS (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: arsenic, beryllium,
boron, chloride, cobalt, iron, lithium, manganese, strontium, thallium, and
TDS (CAP Content Section 6.D.a.i.1). These are the COIs that indicate a
discernable plume associated with the source area.
The conceptual model and predictive modeling discussions summarize the
foundations for development of the groundwater extraction combined with
clean water infiltration and treatment 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.
6.5.3.2 Conceptual Model
(CAP Content Section 6.D.a.ii)
The applicable technologies that comprise this alternative include:
• 10 existing extraction wells, which are part of the current interim
action system
• 113 new extraction wells to the north and northwest of the ash basin
• 47 clean water infiltration wells north and northwest of the ash basin
• One 900 foot horizontal clean water infiltration well
• Pumps, associated piping, and control systems
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• An infiltration water intake structure and distribution piping
• Infiltration and discharge piping and structure
• pH adjustment or other treatment systems, if necessary
The proposed design and well locations are shown on Figure 6-25a. The
flow and transport model predicts a total groundwater infiltration system
flow rate of approximately 165 gpm will be required and a total
groundwater extraction system flow rate of approximately 90 gpm. Post -
decanting, the 10 interim action extraction wells are predicted to remove a
total of about 2.5 gpm. The number of extraction and clean water infiltration
wells is estimated based on flow and transport modeling results
(Appendix G). A general summary of the systems anticipated number of
groundwater extraction wells and clean water infiltration wells per flow
zone with corresponding depth ranges, and system flow rate and operation
assumptions is included in Table 6-13.
The system's design includes a large number of extraction wells to be
completed into the shallow bedrock to allow full drawdown within the
transition zone. Depths of shallow bedrock extraction wells are dependent
on the transition zone and bedrock contact depth and ranges from 60 feet
bgs to 120 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 downgradient of the ash basin, with the
exception of the area to the northwest of the dam.
The distribution of conservative COIs (boron, chloride and TDS) represents
the area of maximum COI distribution at or beyond the compliance
boundary and is the focus of corrective action. 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. With
some exceptions, other COIs have generally not migrated horizontally or
vertically in the shallow, deep, and bedrock flow zones appreciably from
the source area, and are not expected to do so due to constituent
geochemical characteristics and Site geochemical and hydrogeologic
conditions as detailed in Appendix G and H.
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It is expected that infiltration water would be treated for pH and suspended
solids using pH adjustment technology and flocculation technology. It is
expected that extracted water would be treated and discharge through the
existing NPDES Internal Outfall 006A and Outfall 006 locations based on
currently available groundwater data and the current permit. Initially, the
groundwater would be treated by pH adjustment and flocculation in the
system used to treat the water from decanting and dewatering the ash
basin. Post -decanting and dewatering of the ash basin provides an
intervening period, where modifications to the decanting/dewatering
treatment system or alternatives, including beneficial reuse, will be
considered. If necessary a modified treatment method will be selected based
on the quantity and quality of the extracted groundwater.
A preliminary summary of groundwater data and current discharge permit
limits is presented in the table NPDES Permit Limits and Anticipated
Groundwater Remediation Parameter Levels in Section 6.4.
6.5.3.3 Predictive Modeling
(CAP Content Section 6.D.a.iii)
A clean water infiltration and extraction 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 clean water infiltration will increase the
effectiveness of the system flushing the system with clean infiltration water
and reducing COI concentrations. Groundwater flow and transport
simulated groundwater extraction flow rates, with an assumed 50 percent
well efficiency, are approximately 0.8 gpm. Groundwater flow and
transport simulated groundwater infiltration flow rates, with an assumed
25 percent well efficiency, are approximately 0.8 gpm. The flow and
transport report (Appendix G) and geochemical modeling report
(Appendix H) provide detailed predictions, descriptions, and explanations
of the effects of clean water infiltration and extraction.
The flow and transport model predicts the maximum extent of the boron
plume at any point in time will be approximately 1,500 feet beyond the
compliance boundary. Simulations indicate that boron concentrations in
groundwater can meet the 02L boron standard of 700 µg/L at a majority of
the compliance boundary in approximately 13 years after system startup
and operation. The area where the compliance boundary is reduced has a
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longer timeframe, approximately 36 years after system startup and
operation, to achieve compliance (Appendix G). The time to achieve
compliance is likely conservative because the area of remediation northwest
of the compliance boundary has been calibrated in the flow and transport
model with a low hydraulic conductivity zone in order to simulate boron
transport in the bedrock flow zone that matches empirical Site data.
6.6 Remedial Alternatives Screening Criteria
(Supplemental Information for CAP Content Section 6.D.a.iv)
This section provides supplemental information beyond the CAP content criteria used
to evaluate groundwater remediation alternatives at BCSS. 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 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
Additional considerations for remedial alternative evaluations include:
• Adaptive site management and remediation considerations
• Sustainability
Protection of Human Health and the Environment
The Updated Human and Ecological Risk Assessments report (Appendix E) has
determined that there are no imminent hazards to public health and safety or the
environment associated with coal ash basin or coal ash constituents in Site soil and
groundwater. The updated risk assessment indicates acceptable risk and no exposure
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to residential receptors at or near the ash basin (no completed exposure pathways). The
assessment did not result in an increase of risks to ecological receptors (mallard duck,
great blue heron, muskrat, river otter) 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)
• CCR (40 CFR § 257.96)
• Well construction and maintenance standards (NCAC Title 15A Subchapter 02C)
• NPDES (40 CFR Part 122)
• Sediment erosion and control (NCAC Title 15A Chapter 04)
Appendix I includes a detailed evaluation of the applicability of Alternative 1: MNA as
a remedial alternative for the Site.
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
• 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
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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
• Time until protection is achieved
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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 Site Conceptual Model 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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Sustainabi/ity
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 environmental benefit of cleanup
activities through reductions of the environmental 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 environmental 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 environmental footprint.
SiteWiseTM estimates collateral environmental 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 publicly owned treatment works (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. These two elements were set aside as less -relevant to
remedy selection for the purposes of this CAP Update than the other quantifiable data
points available. 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 Remedial Alternatives Criteria Evaluation
(CAP Content Section 6.D.a.iv)
Groundwater remediation Alternatives 1, 2 and 3 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 6.6. The groundwater
remediation alternatives formulated in Section 6.5 will undergo detailed comparative
analysis in the following subsections. A summary of the remediation alternatives
detailed analysis is also included in Appendix N.
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 the ash basin 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. Surface water quality standards
downgradient of the COI -affected plume 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
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mechanisms will reduce COI concentrations, and model predictions indicate that
no existing water supply wells would be impacted. After decanting, the
hydraulic divide along Middleton Loop will be re-established and additional
COI migration from the source area toward the area northwest of the ash basin
will be reduced or eliminated.
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:
(1) 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
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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 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 unlikely that the concentrations would 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 36 water filtration
systems within a half -mile of the ash basin compliance boundary in accordance
with G.S. Section 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
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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 the lack of
unacceptable current risk to human and ecological receptors indicates current
conditions are protective. Therefore, the technology is effective in the short-term.
There are 175 monitoring wells installed associated with the ash basin. Although
some within the immediate area of the basin will have to be abandoned as part of
closure, 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)
There are 175 monitoring wells installed associated with the ash basin. 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 and immediately. Other than the abandonment of select
wells within the ash basin 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.
Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
The flow and transport model predicts that the groundwater plume could
continue to migrate beyond the current compliance boundary north and
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northwest of the ash basin for more than 100 years; compliance is predicted to be
achieved in approximately 700 years after ash basin closure completed. 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 Belews Creek ash basin and PHR Landfill have extensive groundwater
monitoring well networks in place. MNA performance monitoring would utilize
a subset of existing wells on Site with approximately 10 additional wells installed
within the ash basin footprint, post -closure. 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 700 years) indicates
that life cycle costs could be significant. A detailed cost estimate for this
Alternative is provided in Appendix L.
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 affected, with the
exception of Parcel A, where active remediation is ongoing. The remaining
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
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program is an essential part of any future remedial strategy. An MNA
effectiveness monitoring program would provide information about changing
Site conditions during and after source control measures.
Sustainability
Sustainability analysis was completed as described in Section 6.6. The footprint
was quantified based on energy use and associated emissions, during the
construction phase (e.g., well installations) and groundwater monitoring
activities (e.g., transportation). The results of the footprint calculations for MNA
are summarized in Table 6-14. A summary of sustainability calculations for
Alternative 1 can be found in Appendix M.
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 during construction and
throughout the cleanup timeframe when compared to the other alternatives.
6.7.2 Remedial Alternative 2 — Groundwater Extraction and
Treatment
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 ash basin 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. 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 the source area. However, modeling results for this alternative,
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for both the north and northwest areas, predict that the extraction flow rate per
well would be approximately 0.1 gpm after basin decanting and after
implementation of source control measures. Modeling results indicate that the
02L standard for boron could be achieved in excess of 300 years following full-
scale implementation. Thus, groundwater remediation under this alternative
would be slow compared with that of Alternative 3.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
Groundwater extraction only and treatment 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. If the water supply for clean
water infiltration wells is from a surface water source, 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 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 after basin decanting and
source control measures have been implemented. 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
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groundwater would be discharged through the NPDES permitted outfalls
006A/006. 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 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.
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, depending on the discharge permit timeframe.
Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
Time to achieve the remediation goal of reducing the concentration of boron
beyond the compliance boundary to levels less than the 02L standard was
estimated by predictive flow and transport modeling. The flow and transport
model predicts that boron concentrations in groundwater would meet the 02L
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boron standard of 700 µg/L at the compliance boundary in excess of 300 years
after system startup and operation.
Cost
(CAP Content Section 6.D.a.iv.9)
The estimated costs for this alternative have not been developed. However, 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 system
operating indicates that the life cycle costs would likely be the largest of the three
alternatives. A detailed cost estimate for this Alternative is provided in
Appendix L.
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 only and treatment system. No
landowner is anticipated to be affected, with the exception of Parcel A, where
interim action remediation is ongoing. The remaining 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 Dan River and
that the discharge would be treated as necessary to meet permit limits. An
expanded groundwater extraction system which addresses potential COI plume
expansion across the entire north and northwest perimeter of the basin might
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 and treatment 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 even if modeling predicts
essentially the same effects between MNA and groundwater extraction.
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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
Sustainability analysis was completed as described in Section 6.6. The
environmental 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
treatment) and groundwater monitoring activities (e.g., transportation). The
results of the environmental footprint calculations for Alternative 2 are
summarized in Table 6-14. A summary of sustainability calculations for
Alternative 2 can be found in Appendix M.
The environmental footprint of Alternative 2 is the most emission -intensive
remedial alternative being considered. Alternative 1 (MNA) requires
significantly less materials and energy than Alternative 2 and is therefore
characterized by a dramatically smaller footprint. Alternative 2 presents
dramatically higher energy -consumption metrics when measured against
Alternative 3. Alternative 2 utilizes a similar number of extraction wells as
Alternative 3 with no clean -water infiltration -wells or, which will generate a
lower material -related environmental footprint for the construction phase.
However, the extended timeframe of remediation system operation for
Alternative 2 (at least 300 years) when compared to Alternative 3 (13 years)
requires energy usage and produces air emissions far exceeding the levels of
Alternative 3. The quantitative analysis of the environmental footprints of the
remedial alternatives under consideration for this CAP indicates Alternative 2 to
be the least sustainable option.
6.7.3 Remedial Alternative 3 — Groundwater Extraction
Combined with Clean Water Infiltration and Treatment
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
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to human health related to the ash basin 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. 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. 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.
Compliance with Applicable Regulations
(CAP Content Section 6.D.a.iv.2)
Clean water infiltration, extraction and treatment would comply with applicable
regulations. Those regulations would include: CAMA, groundwater standards,
clean water infiltration 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. If the
water supply for clean water infiltration wells is from a surface water source,
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)
Clean water infiltration and extraction will contribute to effective and permanent
achievement of groundwater standards by facilitating movement of impacted
groundwater such that the COI plume is hydraulically controlled and COI mass
is more effectively removed as predicted by modeling results.
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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)
Although the COIs are inorganic and cannot be destroyed, a groundwater
extraction combined with clean water infiltration would help reduce COI
concentrations and, therefore, toxicity, mobility, and volume of COI -affected
groundwater. 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 outfalls
006A/006. 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 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. Groundwater remediation that implements
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 clean water infiltration and 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
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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.
The 900-foot long horizontal clean water infiltration well in the right-of-way of
Middleton Loop would require the approval of the NC DOT.
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, depending on the discharge permit timeframe.
Time Required to Meet Remediation Goals
(CAP Content Section 6.D.a.iv.8)
Time to achieve the remediation goal of reducing the concentration of boron
beyond the compliance boundary to levels less than the 02L standard was
estimated by predictive flow and transport modeling. The flow and transport
model predicts that boron concentrations in groundwater can meet the 02L boron
standard of 700 µg/L at a majority of the compliance boundary in approximately
13 years after system startup and operation. The area where the compliance
boundary is reduced has a longer timeframe, approximately 36 years after
system startup and operation, to achieve compliance.
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. Relative to Alternative 2,
additional material and equipment would be required for clean water
infiltration, therefore the capital and also 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. A detailed cost estimate for this Alternative is provided in
Appendix L.
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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 clean water infiltration and extraction system. No
landowner is anticipated to be affected, with the exception of Parcel A, where
interim action remediation is ongoing. The remaining 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 Dan River and
that the discharge would be treated as necessary to meet permit limits. An
expanded groundwater extraction system which addresses potential COI plume
expansion across the entire north and northwest perimeter of the basin 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 and treatment under 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
and would likely be perceived as more robust than MNA.
Adaptive Site Management and Remediation Considerations
Clean water infiltration and 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 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 of the system
discharge can be modified to address changes in COI concentrations or permit
limits.
Sustainabi/ity
Sustainability analysis was completed as described in Section 6.6. The
environmental 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
treatment) and groundwater monitoring activities (e.g., transportation). The
results of the environmental footprint calculations for Alternative 3 are
summarized in Table 6-14. A summary of sustainability calculations for
Alternative 3 can be found in Appendix M.
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The footprint of Alternative 3 is the second -most, emission -intensive remedial
alternative 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 utilizes the same number of
extraction wells as Alternative 2, but also utilizes one 900 foot horizontal and 47
vertical clean -water infiltration wells, which Alternative 2 does not employ. The
additional remediation system components required by Alternative 3 will
generate higher material -related footprint emissions for the construction phase
than Alternative 2. 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 (13 to 36 years) when compared to Alternative 2 (at least 300 years)
produces air emissions less than half of 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.
6.8 Proposed Remedial Alternative Selected for Source Area
(CAP Content Section 6.E)
Based on the alternatives detailed analysis using criteria presented in Section 6.7, the
favored remedy for groundwater remediation is Alternative 3, Groundwater Extraction
Combined with Clean Water Infiltration and Treatment.
To comply with 15A NCAC 02L .0106(h), corrective action plans must contain the
following items, which are included in the following subsection:
• A description of the proposed targeted 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 COI plume.
Each of these corrective action plan components are included in the following
subsections.
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6.8.1 Description of Proposed Remedial Alternative and
Rationale for Selection
(CAP Content Section 6.E.a)
The preferred 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 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 in the expeditious timeframe through groundwater extraction
combined with flushing effect of clean water infiltration. Although there are no
significant risks to human or ecological receptors, the alternative will meet the
regulatory requirements most effectively and provide further protection for
downgradient surface water.
The groundwater remediation system includes 10 existing extraction wells, 113
vertical extraction wells, 47 vertical clean water infiltration wells, and one 900
foot horizontal clean water infiltration well. It also includes all associated piping
and controls, and, as necessary, pH adjustment and other treatment facilities for
both infiltration and extraction water. Figure 6-25a provides a conceptual layout
of the proposed groundwater extraction combined with clean water infiltration
remediation system. Model results predict the 02L standard of 700 µg/L for
boron can be achieved at a majority of the BCSS ash basin compliance boundary
in approximately 13 years after system startup and operation. The area where the
compliance boundary is reduced has a longer timeframe, approximately 36 years
after system startup and operation, to achieve compliance (Figure 6-25g).
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 and treatment
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 Belews Creek, 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
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tiered analysis did not meet evaluation criteria for selecting the groundwater
remedial alternative, including:
• Predicted timeframe to achieve applicable criteria at the compliance
boundary is 700 years, which does not meet the criteria of achieving the
standards at a timeframe similar to more active remedies.
• Historical and ongoing assessment indicates the potential for off -Site
groundwater flow northwest of the BCSS ash basin.
• The maximum extent of the 02L bedrock groundwater plumes has
migrated at or beyond the compliance boundary, and is predicted, based
on the groundwater model, to continue expanding in the bedrock flow
zone in the future, at or beyond the compliance boundary northwest of
the ash basin.
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.
Alternative 2 and Alternative 3, remediation systems represent an adaptable
approach. The system could be modified relatively easily if conditions change.
The addition of wells or adjusting well pumping schemes can be readily
accomplished. Although groundwater extraction from Alternative 2 and
Alternative 3 involves a verified remedial technology for groundwater capture
and provides a long-term and permanent approach, Alternative 3 is a more
robust system.
The flow rate predicted for Alternative 2 is insufficient to restore ash basin -
affected groundwater at or beyond the compliance boundary within a reasonable
(i.e. approximately 30 years) timeframe, and therefore does not meet the Duke
Energy's corrective action goals. The additional volume of groundwater created
by infiltration from clean water infiltration has the ability to increase the flushing
capacity of the system with clean water and reducing COI concentrations,
significantly increasing the effectiveness of the remediation system. Alternative
3, groundwater extraction and clean water infiltration, is projected to satisfy
remedial action objectives in a shorter timeframe (approximately 13 years)
relative to Alternative 2 (greater than 300 years). Alternative 3 includes clean
water infiltration wells, with groundwater infiltration rates of 1.2 gpm for
vertical wells and 110 gpm for the one horizontal well, for a total system
infiltration rate of approximately 165 gpm. The extraction rate per well for
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Alternative 3 is approximately 0.8 gpm, for a total system extraction rate of
approximately 90 gpm. Comparatively, Alternative 2 relies on technology where
extraction rates are limited to the groundwater formation's natural flow rates,
without the additional volume of water from clean water infiltration wells to
increase flushing capacity. The extraction rate per well for Alternative 2 is
approximately 0.1 gpm, for a total system extraction rate of approximately 10
gpm. By supplementing the natural groundwater system with clean water
infiltration, extraction rates increase by approximately eight -fold, and therefore,
increases the effectiveness of the remediation system and reduce the timeframe
to meet compliance by more than 250 years.
Additionally, Alternative 2 does not restore ash basin -affected groundwater at or
beyond the compliance boundary by returning COI concentrations to the
groundwater quality standards, or applicable background concentrations
(whichever are greater), or as closely thereto as is economically and
technologically feasible consistent with 15A NCAC 02L .0106(a). An extraction
only and treatment system would have to maintain operation for a longer period
of time, relative to Alternative 3, which adds a substantial operation and
maintenance (O&M) cost and lessens the economically feasibility.
Although the clean water infiltration and extraction and the groundwater
extraction system generate a larger environmental footprint in the sustainability
analysis than MNA, the footprint of a groundwater remediation system is still
small in comparison to other elements of the ash basin closure process. During
design phases of the groundwater remediation project, opportunities for energy
efficiency and reduction of the project environmental footprint can be evaluated.
Potential duplication of intensive construction efforts should be considered.
Relative to Alternative 2, Alternative 3 would accelerate removal of COI mass
from the groundwater system, reducing the groundwater plume footprint to
within a 500 foot compliance boundary, and achieve compliance within a shorter
timeframe as is economically and technologically feasible. Therefore Alternative
3 is the favored remedial alternative for implementation at Belews Creek.
This alternative is readily implementable, although it is the most costly
alternative due to the addition of the clean water infiltration wells. The long-term
effectiveness would be documented through an effectiveness monitoring
program detailed in Section 6.8.5. The system would be adaptable based on
effectiveness monitoring field data results.
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Seep Corrective Action
As stated in the SOC, decanting of the ash basin is expected to substantially
reduce or eliminate the seeps. After completion of decanting, remaining seeps,
(constructed and non -constructed), would to be characterized post -decanting for
determination of disposition. After seep characterization, an amendment to the
CAP and/or Closure Plan, may be required to address remaining seeps. Duke
Energy has already taken steps to address non-dispositioned seep(s) directly
downstream the ash basin dam. Duke Energy is aware of other currently non-
dispositioned seeps around the Belews Creek ash basin, PHR Landfill and other
facilities onsite that might not be dispositioned by source control measures.
Non-dispositioned seeps, where monitoring conducted has indicated the
presence of CCR affects (S-2, S-6, S-8, S-9, S-10, S-11, and S-18), 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, effects of decanting on seep thus far,
approximate average flow rate, and predicted change in water elevations after
decanting is complete from flow and transport model simulations. Corrective
action strategies for seep locations are included in Table 6-8 and discussed
herein.
Decanting has been effective in reducing flow at seep S-2, located in a channel
northwest of ash basin that flow to the Dan River, and seep S-6, located east of
ash basin downstream of the former ash basin permitted outfall to Belews
Reservoir. In August 2019, flow at seep S-2 was insufficient for measuring and
flow at seep S-6 was recorded as 0.005 cubic feet per second (cfs), approximately
half of the average flow rate. To date, water elevation of the ash basin has
decreased by 9.5 feet, and is expected to continue decreasing until decanting is
completed in September 2020. Groundwater corrective action via groundwater
extraction and ash basin decanting are anticipated corrective action strategies for
seep S-2. Ash basin closure will address the former ash basin outfall channel,
west of Pine Hall road and upstream of seep S-6, by excavating and regrading
the channel to slope away from Belews Reservoir and towards the interior of ash
basin footprint. Decanting and ash basin closure are anticipated corrective action
strategies for seep S-6.
Source control measures (i.e. decanting and ash basin closure) associated with the
ash basin are not anticipated to reduce flow seep location S-8, because it is not
within the ash basin and PHR Landfill drainage system. Because of the seeps
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relatively remote location and low flowing conditions, corrective action using
phytoremediation technology would be considered. Phytoremediation would
capture and extract shallow groundwater to reduce or eliminate flow at the seep
location.
Seep S-9 is associated with the Structural Fill, therefore corrective action for this
location will be addressed in the corrective action plan for the Structural Fill.
Source control measures associated with the ash basin are not anticipated to
reduce flow at this location because it is not within the ash basin and PHR
Landfill drainage system.
No corrective action is necessary for seep S-11 because this seep is a permitted
NPDES outfall (Toe Drain Outfall 111). Duke Energy has constructed a toe -drain
collection system to collect ash basin discharge at this location. Flow from this
location will be collected by the toe -drain collection system and discharged via
permitted Outfalls 006A/006. Non -constructed seep S-18 flows to S-11 and is
monitored per terms of the NPDES Permit
As of August 2019, decanting has been effective in reducing flow at seep S-10,
such that flow is reported as 0.02 cfs, approximately 0.1 cfs less than average
flow. Decanting and groundwater corrective action via groundwater extraction
are anticipated corrective action strategies for seep S-10. If seep S-10 continues
have low flow conditions, and is not disposition after decanting is complete,
phytoremediation technology could be implemented to capture and extract
shallow groundwater to reduce or eliminate flow at the seep location. If seep S-10
sustains nears its average flow rate after ash basin decanting is complete, seep S-
10 is proximate to the area requiring groundwater corrective action, which
provides the flexibility to integrate seep corrective action into an adaptable
groundwater remedy system. Under these circumstances, potential corrective
action remedies include, but not limited to, a shallow groundwater extraction
trench or shallow groundwater extraction well(s). An extraction trench or well(s)
would capture shallow groundwater flow to reduce or eliminate flow at the seep
location. Seep S-18 flows to the S-11; if S-18 is not dispositioned after decanting is
complete, seep S-18 could be managed as part of the remedy for seep S-10. It is
expected that water collected from shallow groundwater extraction would be
managed as part of the proposed groundwater remedy system.
In summary, decanting, ash basin closure, and groundwater extraction are the
anticipated corrective action strategies to address seeps S-2, S-6, S-10 and S-18.
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An engineering solution has been applied to seep S-11. No corrective action is
necessary for this location, because the location is part of the ash basin waste
water treatment system (Toe Drain Outfall 111) and under the NPDES permit.
Should additional corrective action measures be needed to address flow at seeps
S-10 and S-18, applicable technologies include, but not limited to,
phytoremediation and/or shallow groundwater extraction with either trench or
extraction well technology. Seeps S-8 and S-9 are anticipated to potentially
require additional corrective action measures. Seep S-9 will be addressed in the
corrective action plan for the Structural Fill. Based on available data and
information, the best fit technology for corrective action of seep S-8 is
phytoremediation technology. Description and screening of specific remedial
technologies, including phytoremediation and extraction trenches and wells, is
included in Section 6.4.
Final corrective action plans for seeps that are not dispositioned after completion
of decanting will be proposed in an amendment to this CAP Update and
submitted based on the schedule outlined in the SOC.
6.8.2 Design Details
(CAP Content Section 6.E.b)
Design of the proposed clean water infiltration and 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 models will likely 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.
The intent of the remedial alternative design is be to maximize pore volume
exchange (i.e. groundwater flushing) and establish groundwater flow control and
capture in areas downgradient of the ash basin. Basic installation components of
the recommended remedial alternative include:
10 existing extraction wells, which are part of the current interim action
system
• 113 new extraction wells and appurtenances
• 47 clean water infiltration wells and appurtenances
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• One 900 foot horizontal clean water infiltration well 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
• Upgrades to the existing physical -chemical wastewater treatment system,
if needed
• Clean water infiltration water treatment system
• Piping to transfer water from the Dan River to the clean water infiltration
water treatment system
• Clean water infiltration water distribution system
• Electric power supply
• Groundwater remediation telemetry system
6.8.2.1 Process Flow Diagrams for Major Components of
Proposed Remedy
(CAP Content Section 6.E.b.i)
Conceptual process flow diagrams for clean water infiltration, extraction,
and treatment systems are provided on Figure 6-26 through Figure 6-28.
The detailed design elements presented below may be adjusted based on a
final technical review.
Below is 10-step process for remedy design considerations and
implementation of major components, including design assumptions,
calculations, and specifications where applicable at the conceptual design
stage.
Site Preparation (Step I — Create Access)
Installation of the proposed clean water infiltration and 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.
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Safe access roads for mobile construction equipment (e.g., drill rigs), as well
as long-term operation and maintenance needs, will likely require extensive
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 somewhat extensive tree and
brushy vegetation removal and grubbing, will require erosion and
sedimentation control (ESC) to be implemented and likely reviewed and
approved by a regulatory agency. Adaptable ESC should be planned to
limit project delays by avoiding formal modifications of plans.
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. Design elements would be adapted from
the existing 10-well pumping system including any lessons learned from its
operation. Clean water infiltration tests would be conducted to determine
the 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 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 predictive flow and transport modeling, if needed
• Confirm groundwater extraction well capture zones in the saprolite
and transition zone flow zones beyond available data
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• 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 test results will be used to:
• Determine site -specific well infiltration rates
• Validate predictive flow and transport modeling
• Refine calibration predictive flow and transport modeling, if needed
• If warranted, make adjustments to the clean water infiltration system
design
• If warranted, make design adjustments to conveyances for recharge
groundwater
• If warranted, make design adjustments to the clean water infiltration
treatment system
The extraction and clean water infiltration wells used for testing would be
included in the final groundwater remediation system design.
Clean Water Infiltration and 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 47 vertical clean water infiltration wells, one 900 foot
horizontal well, and 113 extraction wells (Figure 6-25a). The new clean
water infiltration and extraction wells would be installed to the north and
northwest of the ash basin. 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).
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Clean water infiltration and extraction wells would be completed in the
saprolite, transition zone and bedrock at depths ranging from <30 feet bgs to
180 feet bgs. The number and depth of clean water infiltration and
extraction wells is estimated based on flow and transport modeling results
(Appendix G). Modeled clean water infiltration well details are provided
on Table 6-15; and modeled extraction well details are provided on
Table 6-16.
All groundwater clean water 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). The clean water infiltration and extraction wells might be drilled
using hollow stem auger, air percussion/hammer, sonic drilling
technologies, 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 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 vertical clean water infiltration, horizontal clean water
infiltration wells, and extraction wells are included as Figure 6-25b, Figure
6-25c, and Figure 6-25d.
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
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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 6-25e).
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 4A)
(CAP Content Section 6.E.b.i)
An HDPE distribution header would convey clean water from the
infiltration water treatment system to each clean water infiltration well
(Figure 6-28). A seal at the top of the well through which the infiltration
pipe and wiring would enter the well, would be designed to be leak free.
The hydraulic head at each clean water infiltration well would be controlled
by a pressure control valve. Ten -feet of water (4.34 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 based on the hydraulic conductivity of the strata
receiving the clean water.
The amount of water flowing into the clean water infiltration well 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 clean water infiltration well would monitor well head pressures
(Figure 6-25b).
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.
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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.
A double -ended horizontal injection well would be installed along
Middleton Loop by certified North Carolina well driller as shown
conceptually on Figure 6-25c. A typical horizontal environmental well is
installed at an angle approximately minus 12 degrees from horizontal
(Ellington-DTD, 2004). The equipment would set up at a distance such that
the boring at an angle that is predetermined and would reach the point of
beginning of the screen at the target depth of the screen. A directional pilot
bore smaller than the diameter of the well would be installed using a
navigational system, such as a wireline navigation system. Drilling fluid
would be used for cutting the borehole and stabilizing the borehole wall
until the well materials are installed. Surface seals would be installed in the
annulus at both ends, and the well would be developed. One end of the
well would be capped with a water -tight seal. The well head would be
completed in a manner similar to the vertical injection wells. (Ellington-
DTD, 2019).
Extraction Wells (Step 4B)
(CAP Content Section 6.E.b.i)
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 submersible pump would be measured using a flow rate and flow
totalizer meter before being conveyed to groundwater discharge piping for
treatment and disposal (Figure 6-27). 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,
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• and a flow control valve such as a stainless steel globe or gate valve
(Figure 6-25d)
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 Clean Water Infiltration Water Treatment
(Step 5 — Build Infiltration Treatment)
(CAP Content Section 6.E.b.i)
Based on water quality and implementation access and feasibility, water
used for clean water infiltration will be obtained from the Dan River rather
than Belews Reservoir. Water supplied to the clean water infiltration wells
is non -potable water that is suitable for infiltration as part of the
remediation process and not for consumption.
The raw water intake would be located along the southeast bank of the Dan
River which is located on the north side of the Duke property. A general
water intake station and pump schematic is depicted in Figure 6-25f. The
raw water intake would consist of a wet well connected to the river. Raw
water would travel through screens before entering the wet well. Duplex
pumps would be used for redundancy and for operation and
maintenance. Once in the wet well, vertical turbine pumps would pump
the raw water from an elevation of approximately 577 feet NAVD 88 to
equalization tanks followed by a modular treatment system (Figure 6-28).
The equalization tanks and the modular treatment systems would be
located on the northwest side of Middleton Loop at an elevation of
approximately 757 feet NAVD 88. The treatment system would condition
the water prior to storage and distribution to the clean water infiltration
wells.
The Dan River is a dynamic source of water and would provide water of
varying quality. Prior to infiltration, treatment of the water would address
suspended particulates and TDS and biological growth (e.g., algae and
bacteria) that would be present in raw river water. The 02L standard for
TDS is 500 mg/L.
A modular flocculation, settling, and filtration treatment process might be
used to reduce TDS to concentrations less than 500 mg/L and to disinfect the
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river water. A polymer and a disinfectant (e.g., sodium hypochlorite) would
be added to raw river water in a rapid mix tank. The polymer would
flocculate with TDS and the disinfectant would kill waterborne bacteria and
algae. Treated water and flocculant would flow from the rapid mix tank to
a modular sedimentation tank where the flocculant and particulates would
settle. Sedimentation tank effluent would undergo filtration to remove
suspended flocculant and particulates. The filtered water would be
pumped to a holding tank where infiltration water would be stored prior to
distribution to the clean water infiltration wells. Water leaving the holding
tank would undergo dechlorination (e.g., sulfur dioxide or sodium
metabisulfite) as it enters the clean water infiltration water distribution
system (Figure 6-28).
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
physical -chemical treatment plant on the southeast side of Middleton
Loop. The equalization tanks, treatment system, transfer pumps, and
holding tank would be housed in an enclosed structure to prevent exposure
to prevailing weather conditions.
Groundwater Extraction Water Treatment
(Step 6 - Address Groundwater Treatment)
(CAP Content Section 6.E.b.i)
Extracted groundwater would be treated using the treatment system that is
currently being used to treat decanted water from the ash pond. This
treatment system uses a flocculation process called CoMag® provided by
Evoqua Water Technologies (Figure 6-28). With the CoMag® system, the
traditional process of flocculation, coagulation and clarification remain the
same. However, more rapid settling of the floc is attained by the addition of
magnetite, a rock mineral made up of oxides of iron, as ballast.
A flocculent, such as alum, ferric chloride or poly -aluminum chloride is
currently being added to the influent. The resultant chemical floc is infused
with magnetite, which increases solids density. The floc then travels to a
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conventional clarifier that separates the treated water from the sludge. The
treated water would discharged through the permitted outfall. Extracted
groundwater would undergo this same treatment process to satisfy
applicable NPDES discharge requirements.
Clean Water Infiltration Well Distribution System
(Step 7 — Conceptual Clean Water Infiltration System
Considerations)
The purpose of the groundwater clean water infiltration distribution system
is to convey water from the Dan River to the clean water infiltration water
treatment system and to convey water from the clean water 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 sediment that
may collect in the pipes.
Infiltration water would be transferred from the Dan River to a treatment
and storage plant located at an elevation higher than the clean water
infiltration wells. The positive hydraulic head of the infiltration water
treatment system relative to the clean water infiltration wells would enable
distribution of infiltration water to the clean water infiltration well network
via gravity drain and maintain positive pressures for the clean water
infiltration wells. Pressure regulating valves would be installed at each
clean water infiltration well to control groundwater infiltration rate.
Groundwater infiltration might create the potential for matrix saturation
near the ground surface, with the potential for surface discharges. Based on
pilot tests, final well placement, modeling, and observations, lysimeters,
piezometers or other moisture detection devices are anticipated to be part of
routine monitoring. The details associated with the monitoring in and
around the clean water infiltration wells will be provided with the system
design package.
The 900-foot long horizontal infiltration well in the right-of-way of
Middleton Loop would require the approval of the NC DOT.
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Groundwater Extraction Well Discharge Piping
(Step 8 — Conceptual Extraction System Considerations)
The proposed groundwater extraction system would consist of 113 new
groundwater extraction wells. Based upon predictive groundwater flow
and transport modeling, the groundwater extraction wells would generate
on average 1.8 gpm of extracted groundwater per well or approximately 90
gpm of extracted groundwater collectively. One hundred nine (109) of the
new wells would be in the area northwest of the ash pond (Figure 6-25a),
four would be in the area near toe drains of the ash pond dam (Figure 6-
25a); and there are 10 existing extraction wells on the ash basin side of
Middleton Loop.
Each of the groundwater extraction wells northwest of the ash pond would
discharge into one of a series of headers. Extracted groundwater in these
headers then would flow by gravity to a pump station with a wet well.
From the wet well, collected groundwater would be pumped to the
decanted ash water physical -chemical treatment system located on the
southeast side of Middleton Loop. This would require that the
groundwater discharge piping cross Middleton Loop below grade.
The pumps in four extraction wells near the toe drains of the ash pond dam
would discharge to a small pump station with a wet well. From the wet
well, the extracted groundwater would be pumped to the to the decanted
ash water treatment system.
6.8.2.2 Engineering Designs with Assumptions,
Calculations, and Specifications
(CAP Content Section 6.E.b.ii)
Pipelines (Step 9 — Pipeline Specifics)
(CAP Content Section 6.E.b.ii)
HDPE piping will be used for water conveyance in most case where buried
piping will be installed. Polyvinyl Chloride (PVC) and/or Ductile Iron Pipe
(DIP) may be used for gravity sewer and where unusual circumstance
occur. Water conveyance will include:
• Groundwater pumped from extraction wells and conveyed to the
physical -chemical wastewater treatment system
• Surface water pumped from the Dan River and conveyed to a clean
water infiltration water treatment system
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• Clean water 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 @
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.
The locations of the HDPE piping systems for extraction and clean water
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
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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 165 gpm for the clean water infiltration system and
90 gpm for the groundwater extraction system. Infiltration water
distribution lines would connect to each well part of the groundwater clean
water infiltration system. Likewise, each groundwater extraction well will
be connected to a header that ultimately conveys extracted groundwater to
the physical -chemical water treatment on the southeast side of Middleton
Loop. Preliminary calculations pertaining to the piping design (e.g., pipe
sizing, pressures, flow, friction losses, etc.) are provided in Appendix O.
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 10 — 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
graphically represented conceptual network layouts are found in
Appendix O.
The extraction network consists of 10 existing extraction wells and 113 new
extraction wells with trunk lines for conveyance and branching pipes
providing connections to the wells. The network largely operates in gravity
flow, collecting the majority of the flow from the extraction wells and
conveying under pressure from a common collection point to the treatment
system. 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
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system was verified, pipe diameters and required pump head outputs were
calculated. The calculation outputs took into account the interacting flows
in the system, pipe cleanouts for periodic jetting, 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 47 vertical clean water
infiltration wells and one 900 foot horizontal clean water infiltration well.
Clean water infiltration wells flow via gravity from an elevated infiltration
tank at the natural high point of the site's topography. The clean water
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 over a hundred additional submersible pumps, two vertical
turbine pumps, and the clean water infiltration water treatment system, 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
infiltration and 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
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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.
6.8.2.3 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 might be needed for the proposed remedy include:
• Erosion and Sediment Control permit
• In Situ Groundwater Remediation Injection Well permit
• NPDES Stormwater permit
• Right -of -Way (ROW) encroachment agreement with North Carolina
Department of Transportation
• Water Withdrawal and Transfer registration
• Wetlands permit
The schedule for obtaining permits is based off the project implementation
schedule included in Section 6.8.2.
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6.8.2.4 Schedule and Cost of Implementation
(CAP Content Section 6.E.b.iv)
A Gantt chart (Figure 6-29) 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
Duke Energy progress reports would be submitted to NCDEQ monthly.
A detailed cost estimate for this Alternative is provided in Appendix L.
The cost estimate is based on capital costs for design and implementation,
and the operations, maintenance (O&M) 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, and
routine and non -routine maintenance costs.
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6.8.2.5 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 the ash basin 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. 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.
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 basin and the additional source area
hydrologically connected to the ash basin, the PHR Landfill, 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.
6.8.3 Requirements for 02L .0106(I) - MNA
(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 Belews Creek 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
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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
• Proposed corrective action plan would be consistent with all other environmental
laws
Because historical and ongoing assessment indicates the potential for off -Site
groundwater flow northwest of the ash basin, Belews Creek does not meet
requirements for implementing corrective action under 02L .0106(k) at this time.
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
consistent with 02L .0106(h)(4). The EMP is designed to monitor groundwater
conditions at the BCSS 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.
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Duke Energy implemented an Interim Monitoring Plan (IMP) after the plan was
that was submitted to NCDEQ on October 23, 2018. Additional modifications to
the plan were approved by NCDEQ on April 4, 2019 (Appendix A). 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 P, is designed to be adaptable and target key
areas where changes to groundwater conditions are most likely to occur due to
corrective action and ash basin closure activities. The EMP will be used to
evaluate progress towards remediation. EMP key areas for monitoring are based
on the following considerations:
• Include background locations
• Include designated flow paths with area of groundwater remediation
• Within areas of observed or anticipated changing Site conditions, and/or
have increasing constituent concentration trends
• Will effectively monitor COIs plume stability and model simulation
verification
EMP elements including well systems, locations, frequency, parameters,
schedule and reporting evaluation are summarized below and outlined on
Table 6-17. Effectiveness monitoring well locations are illustrated on Figure 6-30.
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
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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 6-31.
Optimization of the plan to help determine the remedy's performance,
appropriate number of sample locations, sampling frequency, and laboratory
analytes, and statistical analysis to evaluate the plume stability conditions would
be conducted during EMP review periods. The optimization process would be
conducted using software designed to improve long-term groundwater
monitoring programs such as Monitoring and Remediation Optimization System
(MAROS).
Progress Reports and Schedule
(CAP Content Section 6.E.e.i)
After groundwater remediation implementation, evaluation of Site conditions,
groundwater transport rates, and 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:
• 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 would 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,
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• 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 adjustments and optimization 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 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.
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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. This monitoring would be
implemented north and northwest of the ash basin (Figure 6-30). EMP
groundwater well monitoring network objectives are outlined below:
• Compliance with 02L
• Measure and track the effectiveness of the proposed clean water
infiltration and extraction system
• Monitor plume status at or beyond the compliance boundary
(horizontally and vertically)
• Verify predictive model simulations
• Verify no unacceptable impact to downgradient receptors
• Verify attainment of 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 59 groundwater monitoring wells (Table 6-17).
Several of the existing monitoring wells at the site might be abandoned
from ash basin and landfill 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 network 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),
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• Transport rates, and
• Plume stability
Horizontal and vertical coverage would be provided by using
groundwater monitoring wells located along three primary groundwater
flow paths within the groundwater remediation 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 6-30 and described below:
1. At waste boundary
2. 250 feet downgradient from waste boundary. If the waste boundary
and compliance boundary are located sufficiently close to evaluate
COI trends over time, this interval location would not be
monitored.
3. 500 feet downgradient of waste boundary (CAMA compliance
boundary)
4. 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 would be installed in 31 wells along the three
primary flow paths in the remedy area (Figure 6-30). 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, monitored using pH and Eh, would 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 from groundwater remediation,
and during and after ash basin closure. Having groundwater quality and
water level data 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 might be conducted using Mann -Kendall trend
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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 would be conducted using data from EMP geochemically
non -reactive, conservative constituents (Table 6-17). These constituents
include boron, chloride, 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 6-30) 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 59 monitoring wells to be included in the 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 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 6-17 is proposed
for newly installed wells.
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
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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 P. Samples would be analyzed by a
North Carolina certified laboratory for the parameters listed in Table 6-17
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, 11 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:
o Arsenic
o
Lithium
o Beryllium
o
Manganese
o Boron
o
Strontium
o Chloride
o
Total Dissolved Solids
o Cobalt
o
Thallium
o Iron
o
Geochemically conservative, non -reactive constituents boron,
chloride, 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, 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.
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• 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 6-17 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 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 6-32 (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
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.
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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 will begin within 30 days of
NCDEQ approval of the CAP Update.
Prior to pilot testing, the 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
• Submittal of permit and registration applications to NCDEQ.
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 comprehensive clean water infiltration and
extraction 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:
• Operations (including clean water infiltration and extraction wells,
pumping, piping, electrical, and controls)
• Groundwater quality
• Groundwater levels
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• Groundwater treatment
• Comparison to predicted concentrations and water levels
A health and safety plan and an operations manual will be prepared. 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 clean water infiltration and extraction well water
levels and flow rates. The control system will have remote monitoring
capability 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 will help ensure effective
operations:
Processes to ensure effective operation of each clean water
infiltration and extraction well is maintained. Maintaining target
flow rates and water levels for each well is important to minimize the
potential for loss of groundwater flow control. Each well will 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
the prescribed range. In addition to automated systems, each element
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of the system will be physically inspected and maintained as part of a
routine operations and maintenance program.
If the system detects a leak related to pumping, piping and/or wells,
the respective element of the system will 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.
If pH adjustment or other water treatment technology is employed,
continuous monitoring of key parameters will ensure proper
operation of the system. Variances between prescribed ranges will
alert the operator and other key personnel and may result in
automatic system shut down.
• The operator inspection schedule, completion, and notes for key
systems will be documented.
• A system maintenance schedule will be established to ensure
effective operation. System elements will be maintained in
accordance with manufacturer's recommendations, which will be
contained in a system Operation and Maintenance (O&M) Manual.
Corrective measures, performed by appropriately skilled personnel,
will be taken if mechanical issues are identified during routine
maintenance monitoring.
A foreseeable potential interruption in system operations will be an
intervening period between startup of the groundwater extraction and clean
water infiltration system and the end of ash basin decanting/dewatering.
Initially, the extracted groundwater will be treated in the system that is
currently operating to treat the water from dewatering of the ash basin.
This is a CoMag® system provided by Evoqua Water Technologies and the
treatment system is designed for 850 gpm. Prior to this intervening period,
an assessment of the requirement to treat the extracted groundwater will be
performed. Modifications to the decanting/dewatering treatment system or
alternatives, including beneficial reuse, will be considered. The assessment
and modifications will be based on the quality and quantity of extracted
groundwater and the anticipated discharge limitations.
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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 clean water infiltration or
extraction wells, or changing flow rates or target water levels.
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 clean water infiltration and extraction 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.
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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
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, 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 Summary and Conclusions
This CAP Update meets the corrective action requirements 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 BCSS coal ash basin that are
beyond the Site's compliance boundary to the north and northwest of the ash basin.
Remedial Alternative 3, groundwater extraction combined with clean water infiltration
and treatment, is selected as the preferred groundwater corrective action option for
Belews Creek. This alternative meets the correction action objectives described in
Section 1.0 of this CAP in the expeditious timeframe through groundwater extraction
combined with flushing effect of clean water infiltration. Although there are no
significant risks to human or ecological receptors, the alternative will meet the
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regulatory requirements most effectively and provide further protection for
downgradient surface water. This alternative is readily implementable, although it is
the most costly alternative due to the addition of the clean water infiltration wells. The
system would be adaptable based on effectiveness monitoring field data results.
In addition to the selection and description of the preferred corrective action
groundwater remedy, this CAP Update also provides:
• A groundwater remediation approach that can be implemented under either
closure scenario (closure -in -place or closure -by -excavation).
• A screening process of multiple potential groundwater corrective action
alternatives that would address areas requiring corrective action.
• 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 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)
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7.0 PROFESSIONAL CERTIFICATIONS
(CAP Content Section 7)
Certification for the Submittal of a Corrective Action Plan
Responsible Party and/or Permittee: Duke Energy Carolinas, LLC
Contact Person: Paul Draovitch
Address: 525 South Church Street
City: Charlotte State: NC Zip Code: 28202-1803
Site Name: Belews Creek Steam Station.
Address: 3195 Pine Hall Road
City: Belews Creek State: NC Zip Code: 27009
Groundwater Incident Number (applicable): 88227
We, Ashley L. Albert Professional Geologist and James E. Clemmer, a Professional Engineer
(circle one) for SynTerra Corporation (firm or company of employment) do hereby certify that the
information herein as part of the required Corrective Action Plan (CAP) and that to the best of our
knowledge the data, assessments, conclusions, recommendations and other associated materials are
correct, complete and accurate.
Sworn to and subscribed
before.me this
�. z0-.
DARNELL B. DELLINGER
` Notary Pubk,1510of South Cx*a
My CommInIon Expkas 1212212025
(Affix Seal and Signature)
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CA ' •
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8.0 REFERENCES
(CAP Content Section 8)
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.
AECOM. 2016. "Ash Basin Closure Plan Report, 100% Draft Closure Plan for CCR
Posting- Belews Creek Steam Station." Belews Creek, NC.
AECOM. 2018. 'Belews Creek Steam Station Closure Options Analysis - Summary
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