NC0001422_01_CAP Update 2020_Text_20200814

1610
synTerra
CORRECTIVE ACTION PLAN
UPDATE
Site Name and Location:
L.V. Sutton Energy Complex
801 Sutton Steam Plant Road
Wilmington, NC 28401
Groundwater Incident No.:
Not Assigned
NPDES Permit No.:
NC0001422
NCDEQ CCR Impoundment Ranking:
High Priority
Date of Report:
August 3, 2020
Permittee and Current
Duke Energy Progress, LLC
Property Owner:
410 South Wilmington Street
Raleigh, North Carolina 27601
[phone]
Consultant Information:
SynTerra Corporation
148 River Street
Greenville, South Carolina 29601
[phone]
Latitude and Longitude of Facility:
N 34.283296 ��,A4,nW,7,;985860
P.
NC PG 2602
ect Manager
1867f5
Lqg '� �C PE 18675
oject Engineer

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
EXECUTIVE SUMMARY
This groundwater Corrective Action Plan (CAP) Update is for the L.V. Sutton Energy
Complex (Sutton, Site) located in Wilmington, North Carolina. This CAP addresses
constituents of interest (COIs) in groundwater related to coal ash from two ash basins
and three additional source areas. These areas and their current status are summarized
as follows:
• 1971 ash basin — excavation complete in 2019
• 1984 ash basin — excavation complete in 2019
• Former process area (FPA) — excavation complete in 2020
• Former ash disposal area (FADA) — excavation complete in 2020
• Former coal pile area (FCPA) — coal remaining after the coal-fired units were
decommissioned was removed by 2015
This CAP Update, which incorporates data collected through March 2020, examines and
presents the selected groundwater corrective action approaches to address COIs in
groundwater at concentrations greater than North Carolina Administrative Code
(NCAC), Title 15A, Subchapter 02L, Groundwater Classification and Standards (02L) /
Interim Maximum Allowable Concentrations (IMACs) or background threshold values
(BTV). The FPA, FADA, and FCPA at Sutton are not regulated by Coal Ash
Management Act of 2014 (CAMA). However, due to its small size and close proximity
to the 1971 ash basin, the FPA is evaluated along with the CAMA units for practical
purposes. For the purpose of evaluating corrective action options, the Site's source areas
are grouped into two multi -unit areas:
• Source Area 1-1971 ash basin, 1984 ash basin, and FPA
• Source Area 2 — FADA and FCPA
COI concentrations are evaluated against the applicable COI criterion, which is defined
as the 02L Standard, IMAC, or BTV, whichever is greater. COIs have been detected at
concentrations greater than COI criteria along the western compliance boundary, in
limited areas just beyond the northwest corner of the 1984 basin, southeast of the 1971
ash basin and FPA, and south and southwest of the FADA and FCPA. Additionally,
some COI concentrations in groundwater are slightly greater than COI criteria in a
localized off -Site area east of the property boundary.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
Significant corrective action has already occurred, including closure of the coal-fired
generation plant, source control by excavation, and groundwater extraction from nine
wells along the eastern property boundary. In addition to those corrective action
measures, the following remedial actions are proposed:
• Monitored natural attenuation (MNA) and confirmation monitoring along with a
restricted groundwater use designation for an area that includes the FCPA and a
part of the cooling pond
• Continued operation of the existing groundwater extraction and treatment
system
• Implementation of a post -excavation Effectiveness Monitoring Plan (EMP) with a
five-year review period to monitor the effectiveness of the corrective action
ES.1 Introduction
SynTerra prepared this CAP Update on behalf of Duke Energy Progress, LLC (Duke
Energy) for Sutton - located in New Hanover County, North Carolina (Figure ES-1).
This CAP Update evaluates the extent of, and remedies for, COIs that occur in
groundwater beyond the compliance boundary of the ash basins. The COIs evaluated
are associated with the Site's source areas (former ash basins, FADA, FPA, and FCPA).
Specifically, this CAP Update focuses on constituents detected at concentrations greater
than applicable COI criteria at or beyond the ash basin compliance boundary. COI
concentrations greater than COI criteria occur in groundwater to a limited extent
beyond the compliance boundary in the following areas:
• Southeast of the 1971 ash basin and FPA
• Northwest and west of the 1984 ash basin
• Southwest and south of the FADA and former coal pile
• A localized area beyond the Site's eastern property boundary
This CAP Update considers data collected through March 2020.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
In accordance with requirements of CAMA, a CAP pertaining to Sutton was previously
submitted to the North Carolina Department of Environmental Quality (NCDEQ) in
two parts, as follows:
• Corrective Action Plan Part 1— L.V. Sutton Energy Complex (SynTerra, 2015b)
• Corrective Action Plan Part 2 — L.V. Sutton Energy Complex (SynTerra, 2016a)
Summary of CAP Approach
This CAP Update meets the corrective action requirements under North Carolina
General Statutes (G.S.) 130A-309.211 (b) and Subchapter 02L .0106. This CAP Update is
consistent with the revised CAP guidance approved by NCDEQ in a letter titled
Updated Corrective Action Plan and Comprehensive Site Assessment Content — Duke Energy
Coal Ash Facilities, to Duke Energy, dated June 26, 2020 (Appendix A).
The corrective action approach for the Site includes source control and groundwater
remediation with a combination of groundwater extraction, MNA, and effectiveness
monitoring. Source control by excavation was completed in June 2020. The source
control measures that have been completed are significant steps toward groundwater
remediation. Post-dewatering and excavation groundwater flow and quality data were
evaluated. Key findings from this evaluation include:
• Improvements in groundwater quality are occurring as a result of closure
activities.
• 91% of COI datasets have either stable to declining concentration trends.
• Groundwater elevations have decreased locally through ash basin dewatering
and closure activities resulting in flow reversals away from the eastern property
boundary towards the ash basins resulting in a hydraulic divide being
reestablished east of the eastern property boundary.
• Groundwater reduction -oxidation (redox) conditions have become more oxic in
both the upper and lower surficial flow zones based on increasing groundwater
dissolved oxygen (DO) concentrations and redox potential (ORP) trends. These
observed shifts toward more positive groundwater redox conditions support
natural attenuation of redox-sensitive constituents including iron, manganese,
and arsenic.
The focus of groundwater corrective action at Sutton is to reduce COI concentrations to
less than applicable comparison criteria at or beyond the compliance boundary,
consistent with 15A NCAC 02L .0106(e)(4), and to address 15A NCAC 02L .01060).
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
Applicable criteria in this case are defined as the 02L groundwater standard/IMAC or
BTV, whichever is greater. If a COI does not have an 02L standard or IMAC, then the
background value is the COI criterion. Soil COIs are those detected in unsaturated soil
that might leach to groundwater at concentrations greater than the applicable standard.
The COIs in unsaturated soil are also evaluated for potential corrective action.
Duke Energy has implemented, or plans to implement, the following multi -component
CAP at the Site:
Source Control Measures
• Excavation of ash from the 1971 and 1984 ash basins in accordance with
CAMA was completed by July 2019.
• Excavation of ash from the FADA was completed by June 2020.
• Removal of coal from the former coal pile (now FCPA) was completed by
2015.
• Excavation of the FPA was completed by April 2020.
• Groundwater extraction and treatment along the eastern Site boundary began
in 2017 and is ongoing.
• In accordance with the terms of National Pollutant Discharge Elimination
System (NPDES) permit NC001422 (effective July 1, 2020), combine water in
the excavated 1971 ash basin and FADA with water from the Site's cooling
water effluent canal. The water can then be discharged to NPDES permitted
Outfall 001.
Proposed Corrective Action
• Continued operation of the nine -well groundwater extraction system along
the eastern Site boundary installed in 2017 to reduce COI concentrations in
groundwater off -Site. Although the COI concentrations have substantially
decreased in the area, continued operation is planned because the specific
decommissioning conditions defined in the Basis of Design (BOD) report
have not been met (CAP approval and implementation, and four consecutive
monitoring events with all COIs at concentrations less than applicable
criteria) (Geosyntec, 2017). With ash pore water removal and basin
excavation, the groundwater flow direction has returned to natural
conditions (with the exception of the area influenced by the groundwater
extraction system). The natural groundwater flow direction from the source
areas is toward the southwest. The former eastward groundwater flow, and
Page ES-4

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
the resulting COI migration to the east, is no longer occurring (with the
exception of the area influenced by the extraction wells). The reversal in
groundwater flow direction near the source areas and the operation of the
extraction system have effectively reduced COI concentrations along the
eastern property line. Decommissioning conditions are expected to be met
within five years. At that time, termination of the groundwater extraction
system is anticipated under Subchapter 02L .0106(m).
• Implement MNA and confirmation/effectiveness monitoring along with a
restricted groundwater use designation (RS). This approach is supported by
an evaluation of groundwater data before and after source area excavation,
which confirms generally stable plume conditions with a limited COI
presence beyond the compliance boundary. These findings are supported by
groundwater flow and transport modeling results. This is the most viable
option for remediating groundwater to standards at the compliance
boundary.
• The RS is proposed for the small areas beyond the compliance boundary
where COI concentrations in groundwater could persist for a period of time.
The current and future anticipated use of the property is industrial with an
active combined -cycle power -generating facility. The RS area would be
within the Duke Energy Site boundary and therefore can be maintained.
• The proposed EMP includes a five-year review period after which time the
effectiveness of source control, operation of the extraction system, removal of
water in the former 1971 basin and FADA, and MNA can be evaluated using
additional post -excavation data.
ES.2 Background
Site operations, which started in 1954, included use of coal-fired boilers that burned
bituminous coal as fuel to produce steam for generation of electrical power. Coal ash
was sluiced to the FADA, FPA, 1971 ash basin, and 1984 ash basin, collectively referred
to as the ash management area, as described below. Coal was stored in an area to the
south of the FADA. The FPA, located adjacent to the 1971 basin, was used for
wastewater treatment for a brief period of time in the 1970s when the Site temporarily
burned fuel oil. For the purpose of remedial option selection, the multiunit source area
is subdivided into two areas; Source Area 1 (1971 ash basin/1984 ash basin/FPA) and
Source Area 2 (FADA/FCPA).
Coal -burning operations ceased in 2013 when the facility converted to natural gas; ash
has not been generated at the Site since that time.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
The ash basins and the cooling pond (Lake Sutton) are operated under updated NPDES
Permit NC001422 issued by the NCDEQ Division of Water Resources (DWR) effective
July 1, 2020.
Source Areas
Source Area 1 (Figure ES-1) includes three CCR treatment units on the north side of the
cooling pond effluent canal:
• An unlined 1971 ash basin (Figure ES-2) is one of the units. A portion of the 1971
basin was constructed by excavation below the water table for borrow material to
construct the earthen dikes. The 1971 ash basin was operated until 2013. The dam
elevation was approximately 28 feet North American vertical datum of 1988
(NAVD 88) and the ash pore water elevation was approximately 12 feet NAVD
88 prior to excavation, compared with the surrounding ground elevation of
approximately 9.5 feet NAVD 88 and a cooling pond normal water level of
approximately 8 feet NAVD 88. The 1984 ash basin (Figure ES-2) was
constructed with a 12-inch-thick clay liner above the water table. Located
adjacent to north side of the 1971 basin, the 1984 ash basin was operated until
2013 with a similar dam height. The 1984 basin had an operating water level of
18 feet NAVD 88.
• The 1971 ash basin had an outfall to the cooling pond that operated from 1971 to
1984 when the new 1984 basin was put into operation. Discharge from the 1971
ash basin to the cooling pond ceased at that time however, an emergency outfall
remained for periods of heavy rain. The emergency outfall was rarely used.
• The two basins (1971 and 1984) were hydraulically connected. The sluice lines
discharged into either the 1971 basin or the 1984 basin. The NPDES Outfall from
the system was located south of the basins on the Cape Fear River near the intake
canal. An ash stack for drying ash for potential beneficial reuse was located on
the south side of the 1971 basin.
• The 1984 ash basin had an outfall to the cooling pond that was in operation from
1984 to 2001. In 2001, an underground line was installed from the 1984 ash basin
outfall to the outfall at the Cape Fear River. This line could not fully
accommodate all of the 1984 ash basin discharge. There was still a portion of
discharge from the 1984 ash basin to the cooling pond between 2001 and 2015
when the cooling pond was reclassified as waters of the state.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
• The FPA (Figure ES-2), adjacent to the southeast corner of the 1971 basin, was a
small settling basin that was used when the Site was co -firing fuel oil for a few
years during the 1970s. At that time, sluice waters were directed to the settling
basin before being directed to the 1971 basin. The FPA settling basin was
subsequently filled with solids, including CCRs. The FPA is not regulated by
CAMA; however, due to its small size relative to the ash basins and location,
groundwater downgradient of the FPA cannot be distinguished from
groundwater downgradient of the 1971 ash basin. For this reason, the FPA
assessment data is evaluated with Source Area 1 in the CAP Update.
Source Area 2 (Figure ES-1) includes two former operational areas located on the south
side of the cooling pond effluent canal:
• The FADA (Figure ES-2), also known as the lay of land area (LOLA), is located
south of the ash basins, on the south side of the cooling pond effluent canal. It is
believed that ash might have been sluiced to this area from approximately 1954
to 1972.
• The FCPA (Figure ES-2) is located south of the FADA, west of the power plant
near the Cape Fear River. Coal was stockpiled in this area prior to use on -Site.
Coal removal was conducted from 2013 to 2015.
Hydrogeo/ogica/ Mode/
The Site is located within the North Carolina Coastal Plain. The Coastal Plain comprises
a wedge-shaped sequence of stratified marine and non -marine sedimentary
unconsolidated deposits on crystalline basement. Bedrock was not encountered during
Site assessment activities at Sutton. The groundwater system at Sutton can be divided
into two hydrostratigraphic layers (flow zones), the surficial zone and the Peedee zone:
• Surficial zone — The surficial zone, which extends to approximately 50 feet
below ground surface (bgs) and consists of clean, medium- to coarse -grained
sand, is subdivided into an upper surficial flow zone and a lower surficial flow
zone. The surficial zone becomes coarser -grained with depth, with the lower
surficial zone consisting primarily of poorly sorted sands with discontinuous
layers of coarse sand and fine gravel. The water table at the Site averages about
10 feet below the groundwater surface, with a relatively flat horizontal gradient
of approximately 0.001 foot per foot (ft/ft). The natural groundwater flow
direction is toward the southwest toward the cooling pond and the Cape Fear
River. The Cape Fear River flows south along the western side of the cooling
pond.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
• Peedee zone — The Peedee Formation extends to the deepest horizon explored
(150 feet bgs) during assessments at the Site. The Peedee is also subdivided into
an upper flow zone and a lower flow zone. The Peedee becomes finer -grained
with depth and typically occurs as a clayey silt with low plasticity. The 2018 CSA
Update included a successful demonstration that the COIs observed in the
Peedee flow zones are naturally occurring due to salt water intrusion. The
NCDEQ concurred with that conclusion, and therefore, the Peedee is not
evaluated as part of this CAP Update (Appendix A).
Basis for CAP Development
Duke Energy prepared and submitted a Comprehensive Site Assessment (CSA) Update
in January 2018. NCDEQ reviewed the CSA Update, and in a June 11, 2018, letter to
Duke Energy, NCDEQ stated that sufficient information was provided to allow the
preparation of this CAP Update (Appendix A).
A COI management process was developed by Duke Energy at the request of NCDEQ
to gain understanding of the COI behavior and distribution in groundwater and to aid
in 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 02L.
2. Understand the potential mobility of Site -related COIs in groundwater based on
Site hydrogeology and geochemical conditions.
3. Determine the COI distribution in groundwater associated with the ash basins
and additional source areas under current and predicted future conditions.
ES.3 CSM Overview
The Conceptual Site Model (CSM) is a summary of the hydrogeological and
geochemical conditions that control the COI distribution in groundwater. The CSM is
based on a comprehensive groundwater dataset collected over multiple years. The
following provides an overview of the updated CSM of the Site ash basins and
additional source areas. The updated CSM forms the basis of this CAP Update.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
Key conclusions of the CSM include the following:
• The COI plume in the surficial flow zones at Sutton is not expanding and has
receded in some areas, particularly along the eastern property boundary near
the extraction system. Migration of COIs is controlled by a combination of
factors, including:
1. A hydrologic divide to the east of the Sutton property
2. Effects of the groundwater extraction system at the eastern property
boundary
3. Dilution from unaffected groundwater
4. The groundwater -to -surface water discharge zones (i.e., the cooling pond
and the Cape Fear River) immediately adjacent to the downgradient, west
side of the source areas
COIs occur in groundwater at concentrations greater than 02L
standards/IMACs or BTVs in limited areas beyond the ash basins' compliance
boundary. Boron concentrations greater than the 02L standard are predicted to
occur approximately 375 feet or less west beyond the ash basins' compliance
boundary. Selenium concentrations greater than the 02L standard occur to a
limited extent (approximately 375 feet) northwest of the 1984 ash basin waste
boundary, near the cooling pond. Selenium is no longer present above 02L
standard in wells north of (beyond) the compliance boundary. Molybdenum and
strontium are detected at concentrations greater than BTVs approximately 100
feet southeast of the 1971 ash basin compliance boundary. Arsenic and boron are
detected at concentrations greater than 02L or BTV downgradient (southwest) of
the FADA and FCPA, beyond the compliance boundary.
• The hydrogeological setting of the ash basins and hydraulic processes during
ash basin operations controlled migration of COIs from the ash basins to the
underlying groundwater system and to downgradient areas. During ash basin
operations, groundwater flow from the 1971 basin was radial due to the
mounding effect of the water in the unlined basin and relatively flat topographic
setting. The mounding created a component of groundwater flow and COI
migration to the east prior to basin closure. Since closure, the groundwater flow
direction has returned to natural conditions with flow predominantly to the
southwest, toward the cooling pond and the Cape Fear River. Therefore, ash
pore water removal and basin excavation have stopped the migration of COIs
toward the east (with the exception of the area influenced by the extraction
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
system). Groundwater discharge to the cooling pond limits the extent of COI
migration to the west from the ash basin. Groundwater discharge to the Cape
Fear River limits the extent of COI migration to the southwest of the FADA and
coal pile.
• Recent basin closure/ash excavation and coal removal are predicted reduce
future COI migration. Basin closure activities have caused constituent
concentrations to decrease, including constituent concentrations in areas east of
the property boundary, due to elimination of the elevated hydraulic head in the
1971 ash basin and the return of the natural groundwater flow direction toward
the southwest. Completion of basin closure, ash removal from the FADA,
excavation of the FPA, and removal of coal from the FCPA as source control
measures would further reduce or eliminate constituent loading to soil and
groundwater, and, through natural hydrologic flushing and geochemical
conditions favorable for natural attenuation, constituent concentrations are
predicted to decline.
• The horizontal distribution of COIs in groundwater is contained mostly
within Duke Energy's property, with the exception of an isolated area east of
the Site where off -Site migration of COIs previously occurred due to the radial
flow from the 1971 basin. Currently, the extent of COIs is mostly within the
compliance boundary with the exception of isolated areas southeast of the 1971
ash basin, northwest and west of the 1984 basin, and southwest of the FADA and
FCPA. COI concentrations in groundwater east of the Site are steadily
decreasing. At the time of CAP Update preparation, off -Site monitoring well
SMW-1C contained boron concentrations slightly greater than 02L. Confirmation
monitoring is proposed for this area as part of the EMP. Concentrations are
expected to continue to decrease due to source removal and the ongoing
groundwater extraction at the eastern property line.
• Vertical distribution of COIs in groundwater at Sutton is limited to the upper
and lower surficial flow zones. Downward vertical migration of COIs is limited
by contact with the less permeable Peedee Formation below the surficial flow
zones. Based on evaluation of assessment results, it was determined that
groundwater in the Peedee Formation is affected by natural saltwater intrusion
unrelated to Site operations.
• Geochemical processes stabilize and limit migration of certain constituents.
The geochemical conditions that have the greatest effect on COI mobility are pH,
ferrihydrite concentrations [and thus sorption capacity via formation of hydrous
ferric oxide (HFO) sorption sites], ion exchange capacity, and hydraulic
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
conditions. The effects of pH values and HFO concentrations are correlated
chemical controls while changes in groundwater flow and dilution would result
from physical controls. The increasing reduction/oxidation potential (Ex) values
measured for several wells over the past year indicate that ferrihydrite
precipitation might increase, which would increase the sorption capacity of all
COIs. Furthermore, infiltrating rainwaters are expected to be strongly oxidizing
(e.g., high Ex) due to saturation of dissolved oxygen and lead to increased
ferrihydrite precipitation. These are examples of the positive geochemical
conditions that should stabilize and limit migration of COIs with time.
• Remedial goals normally achievable through active remediation might already
be occurring at the Site. Groundwater sampling results over the past year
demonstrate that while the pH is remaining relatively stable within each flow
zone, there is a notable increase in the Ex of groundwater indicating that the
groundwater is returning to an oxidizing state, which will enhance sorption. This
increase in Ex might lead to the oxidation of Fe(II) to Fe(III) and potentially the
precipitation of ferrihydrite, which would provide additional sorption sites for
COI attenuation. It appears the system is naturally approaching elevated Ex
values. Though not confirmed, the increased Ex might be due to the large flux of
infiltrating rainwater after excavation. These observations can be confirmed with
the proposed five-year post -excavation EMP (Section 5.11).
• COIs identified at the Site occur naturally in groundwater, some at
concentrations greater than the 02L and IMAC standards. The natural
occurrence of inorganic constituents in groundwater of the Coastal Plain
Physiographic Province is documented in various studies, including peer -
reviewed published technical literature. Groundwater at Sutton, particularly
within the Peedee flow zones, naturally contains boron, chloride, iron,
manganese, sulfate, total dissolved solids (TDS), and vanadium at concentrations
greater than or similar to applicable 02L standards or IMACs. For example,
vanadium has natural background concentrations in all flow zones at the Site
greater than the IMAC value. For this Sutton CAP Update, vanadium and other
COIs are evaluated based on the Site -specific statistically derived background
values and additional lines of evidence to determine whether constituent
concentrations represent migration from the Sutton source areas or are naturally
occurring.
• Groundwater/surface water interaction has not caused, and is not predicted to
cause, COI concentrations greater than surface water quality criteria. Analytical
results for surface water samples collected from the cooling pond (a permitted
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
wastewater treatment unit) and the Cape Fear River indicate that these water
bodies meet water quality criteria under current conditions. An evaluation of
future surface water quality conditions in the cooling pond was conducted using
a surface water mixing model with model simulation inputs. The evaluation
indicates that future groundwater COI migration is not predicted to result in
constituent concentrations greater than applicable surface water criteria.
ES.4 Corrective Action Approach
As detailed in this CAP Update, source control by excavation was recently completed at
the Site, including complete excavation of the 1971 and 1984 ash basins in 2019 and
excavation of the FPA and FADA in 2020.
The COI concentrations downgradient of the source areas are generally stable or
decreasing. Evidence of conditions favorable for natural attenuation is beginning to
emerge with recent data. The hydrologic and geochemical conditions are anticipated to
stabilize with time after recent completion of the closure activities. The reduction in
head and mass contribution from the former source areas is anticipated to be sufficient
for natural attenuation processes to reduce COI concentrations beyond the compliance
boundary. Post -excavation effectiveness monitoring is proposed to confirm the
preliminary stable or decreasing COI concentration trends.
The nine -well groundwater extraction system along the eastern property boundary has
been in operation since August 2017. The extraction system operation, along with the
reversal of the natural groundwater flow direction after closure of the 1971 basin, has
significantly reduced COI concentrations in groundwater near the eastern property
boundary and in off -Site wells. Operation of the system until the BOD decommissioning
goals are met is planned.
The water remaining in the excavated 1971 ash basin and FADA contains arsenic
concentrations greater than North Carolina Administrative Code, Title 15A Subchapter
02B — Surface Water and Wetlands Standards (02B). Prior to discharge at Outfall 001,
water in these areas is anticipated to be mixed with cooling water from the effluent
canal to meet the monthly average total arsenic limit of 44.8 µg/L at Outfall 001 in
accordance with the terms of NPDES permit NC0001422 (effective July 1, 2020). MNA is
proposed for use in the areas with limited COI migration beyond the compliance
boundary. The use of MNA is proposed based on generally stable or decreasing COI
concentration trends. A groundwater restricted use designation (RS) can be used to
prevent installation of water supply wells in the cooling pond and FCPA.
Page ES-12

•
♦.
BUTTON PLANT /
PARCEL LINE ♦
r•
r
I ♦
♦
I ♦
♦ COMPLIANCE I BOUNDARY ` FORMER ASH BASIN �♦� � LANDFILL WASTE
• WASTE BOUNDARY • ♦ BOUNDARY
•
Lake Sutton
•
• FORMER 1984 44
• ASH BASIN •
I •
EXCAVATED1971
•
♦♦ 'r r �. � � ASH BASIN �s � FORMER PROCESS AREA
♦r ♦, FORMER ASH DISPOSAL
\ • /AREA WASTE BOUNDARY
l••
SOURCE:
2019 USGS TOPOGRAPHIC MAP, CASTLE HAYNE AND
LELAND QUADRANGLES, OBTAINED FROM THE USGS STORE AT
https://store.usgs.gov/map-locator.
FORMER COAL PILE AREA
WASTE BOUNDARY
� L
EFFLUENT DISCHARGE CANAL
I I POWER PLANT
L__J
DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH
CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200 (NAD83/2011).
%� DUKE
ENERGY
w(NsroN-saLEror
FIGURE ES-1
SITE LOCATION MAP
CORRECTIVE ACTION PLAN UPDATE
PROGRESSCHARLOTTE
rNEW
L.V. SUTTON ENERGY COMPLEX
WILMINGTON, NORTH CAROLINA
DRAWN BY:J.NIRTz DATE:11/18/201scRAPHIcscALE
REVISED BY: C. CURRIER DATE: 07/22/2020
000 0 000 000
CHECKED BYT DATE: 07/22/2020
synTerra
B.
APPROVED BY: B. WYLIE DATE: 07/22/2020
WYLIEN
PROJECT MANAGER: B. WYLIE
(IN FEET)
www.svnterracorD.com

A: ``s •
k
AREA 1 B
•
j
1984 ASH
BASIN
(LIN
1071
AREA 2
1983
r crrcuc�nu ..
I Gr_GAIn
NPDES OUTFALL LOCATION
EXTRACTION WELL
• SUPPLY WELLS
GROUNDWATER FLOW DIRECTION
SURFACE WATER FLOW DIRECTION
EFFLUENT DISCHARGE CANAL
- ASH BASIN COMPLIANCE BOUNDARY
ANTICIPATED EFFLUENT CANAL
EXTENSION
ASH BASIN WASTE BOUNDARY
ONSITE LANDFILL BOUNDARY
FORMER ASH DISPOSAL AREA WASTE
BOUNDARY
ONSITE LANDFILL COMPLIANCE
BOUNDARY
FORMER PROCESS AREA BOUNDARY
FORMER COAL PILE AREA BOUNDARY
_ DUKE ENERGY PROGRESS PROPERTY
LINE
AREAS 1A/1 B/4 - CONFIRMATION
GROUNDWATER MONITORING
AREAS 2/3A- ONGOING CLOSURE
ACTIVITIES
AREA 3B - MNA REMEDY
NOTES:
1. THE OUTLINE OF AREAS 1 THROUGH 4 REPRESENT THE
AREAS WHERE THE MAXIMUM EXTENT OF COIS ARE
GREATER THAN COMPARISON CRITERIA IN GROUNDWATER
ASSOCIATED WITH THE SUTTON SOURCE AREAS.
2. PROPERTY BOUNDARY PROVIDED BY DUKE ENERGY
PROGRESS.
3. ALL BOUNDARIES ARE APPROXIMATE.
4. AERIAL PHOTOGRAPHY OBTAINED FROM TERRA SERVER
ON JUNE 17, 2019. IMAGE COLLECTED APRIL 4, 2019.
5. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH
CAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200
(NAD83/2011).
(' DUKE
ENERGY
PROGRESS
1
AREA 1A � 0
AREA 3B
GRAPHIC SCALE
500 0 500 1,000
(IN FEET)
DRAWN BY: C. WYATT DATE: 10/07/2019
REVISED BY: C. CURRIER DATE: 07/30/2020
CHECKED BY: T. HARTMAN DATE: 07/30/2020
APPROVED BY: B. WYLIE DATE: 07/30/2020
PROJECT MANAGER: B. WYLIE
•
FIGURE ES-2
•
•
7
AREAS PROPOSED FOR CORRECTIVE ACTION
CORRECTIVE ACTION PLAN UPDATE
L.V. SUTTON ENERGY COMPLEX
WILMINGTON, NORTH CAROLINA

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
TABLE OF CONTENTS
SECTION
PAGE
EXECUTIVE SUMMARY.................................................................................................... ES-1
ES.1 Introduction.......................................................................................................... ES-2
ES.2 Background........................................................................................................... ES-5
ES.3 CSM Overview..................................................................................................... ES-8
ESA Corrective Action Approach............................................................................ ES-12
1.0 INTRODUCTION.........................................................................................................1-1
1.1 Background..............................................................................................................1-2
1.2 Purpose and Scope..................................................................................................1-3
1.3 Regulatory Basis for Corrective Action...............................................................1-4
1.4 Facility Description.................................................................................................1-8
1.4.1 Location and History of Land Use.............................................................1-8
1.4.2 Operations and Waste Streams Coincident with the Ash Basin .......... 1-12
1.4.3 Overview of Existing Permits and Special Orders by Consent ...........1-14
2.0 OVERVIEW OF SOURCE AREAS BEING PROPOSED FOR
CORRECTIVEACTION..............................................................................................2-1
3.0 SUMMARY OF BACKGROUND DETERMINATIONS......................................3-1
3.1 Background Concentrations for Soil....................................................................3-2
3.2 Background Concentrations for Groundwater...................................................3-3
3.3 Background Concentrations for Surface Water..................................................3-5
3.4 Background Concentrations for Sediment.......................................................... 3-6
4.0 CONCEPTUAL SITE MODEL................................................................................... 4-1
4.1 Site Geologic and Hydrogeologic Setting .........................................
4.1.1 Groundwater Flow Direction and Gradients ........................
4.1.2 Subsurface Heterogeneities......................................................
4.1.3 Bedrock Matrix Diffusion and Flow .......................................
4.1.4 Effects of Naturally Occurring Constituents .........................
4.2 Location of Source Areas within Hydrogeologic Setting ...............
4.3 Summary of Potential Receptors.......................................................
4.3.1 Surface Water.............................................................................
............... 4-11
............... 4-12
............... 4-12
................ 4-13
Page i

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
4.3.1.1 Environmental Assessment of Lake Sutton ....................................
4-14
4.3.2 Availability of Public Water Supply........................................................4-15
4.3.3 Water Supply Wells....................................................................................4-16
4.3.4 Future Groundwater Use Area.................................................................4-17
4.4
Summary of Human Health and Ecological Risk Assessment Results.........
4-18
4.5
CSM Summary......................................................................................................
4-18
3.0 CORRECTIVE ACTION APPROACH FOR SOURCE AREAS ...........................
5-1
SOURCE AREA 1 - 1971/1984 ASH BASINS AND FPA..................................................
5-9
5.1
Source Area 1 Extent of Constituent Distribution ..............................................
5-9
5.1.1 Source Material within the Waste Boundary .........................................
5-10
5.1.1.1 Description of Waste Material and History of Placement ............5-11
5.1.1.2 Specific Waste Characteristics of Source Material .........................5-11
5.1.1.3 Interim Response Actions..................................................................
5-13
5.1.2 Extent of Constituent Migration Beyond the Compliance
Boundary.....................................................................................................
5-16
5.1.2.1 Soil Constituent Extent.......................................................................5-17
5.1.2.2 Groundwater Constituent Extent .....................................................
5-19
5.1.2.3 Seep Constituent Extent.....................................................................
5-22
5.1.2.4 Surface Water Constituent Extent....................................................5-22
5.1.2.5 Sediment Constituent Extent.............................................................
5-22
5.1.2.6 Piper Diagrams....................................................................................5-25
5.1.3 Horizontal and Vertical Extent of Groundwater in Need of
Restoration..................................................................................................
5-27
5.1.4 COI Distribution in Groundwater...........................................................
5-32
5.1.4.1 Plume Stability....................................................................................
5-32
5.1.4.2 Site Geochemical Conditions Affecting COI Behavior ..................
5-34
5.2
Summary of Human and Ecological Risks ........................................................
5-38
5.3
Source Area 1 Evaluation of Remedial Alternatives ........................................
5-39
5.3.1 Remedial Alternative 1..............................................................................
5-41
Page ii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
5.3.1.1 Problem Statement and Remedial Goals .........................................
5-43
5.3.1.2 Effects of Source Control and Corrective Action ...........................
5-43
5.3.1.3 Screening Criteria Evaluation...........................................................
5-44
5.3.2 Remedial Alternative 2..............................................................................
5-45
5.3.2.1 Problem Statement and Remedial Goals .........................................
5-45
5.3.2.2 Effects of Source Control and Corrective Action ...........................5-45
5.3.2.3 Screening Criteria Evaluation...........................................................
5-46
5.4 Source Area 1 Proposed Remedial Alternative Selected .................................
547
5.4.1 Description of Proposed Remedial Alternative and Rationale for
Selection.......................................................................................................
5-47
5.4.2 Design Details.............................................................................................
5-49
5.4.2.1 Process Flow Diagrams for All Major Components of
ProposedRemedy...............................................................................
5-49
5.4.2.2 Engineering Designs with Assumptions, Calculations, and
Specifications.......................................................................................
5-49
5.4.2.3 Permits Needed for Remedy and Approximate Schedule............
5-49
5.4.2.4 Schedule and Approximate Cost of Implementation ....................
5-49
5.4.2.5 Health and Safety Measures..............................................................
5-50
5.4.3 Requirements for 02L .0106(1) - MNA.....................................................
5-50
5.4.4 Requirements for 02L .0106(k) - Alternate Remediation Goals...........
5-52
5.5 Source Area 1 Summary and Conclusions........................................................
5-52
SOURCE AREA 2 (SA2) - FADA AND FCPA..................................................................5-53
5.6 SA2 Extent of Constituent Distribution.............................................................
5-53
5.6.1 Source Material within the Waste Boundary .........................................
5-56
5.6.1.1 Description of Waste Material and History of Placement ............5-57
5.6.1.2 Specific Waste Characteristics of Source Material .........................5-57
5.6.1.3 Interim Response Actions..................................................................
5-58
5.6.2 Extent of Constituent Migration Beyond the Compliance
Boundary.....................................................................................................
5-59
Page iii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
5.6.2.1 Soil Constituent Extent.......................................................................5-60
5.6.2.2 Groundwater Constituent Extent .....................................................
5-61
5.6.2.3 Seep Constituent Extent.....................................................................
5-62
5.6.2.4 Surface Water Constituent Extent....................................................5-63
5.6.2.5 Sediment Constituent Extent.............................................................
5-63
5.6.2.6 Piper Diagrams....................................................................................
5-63
5.6.3 Horizontal and Vertical Extent of Groundwater in Need of
Restoration..................................................................................................
5-64
5.6.4 COI Distribution in Groundwater...........................................................
5-66
5.6.4.1 Plume Stability....................................................................................
5-66
5.6.4.2 Site Geochemical Conditions Affecting COI Behavior ..................
5-68
5.7 Summary of Human and Ecological Risks........................................................5-70
5.8 Source Area 2 Evaluation of Remedial Alternatives........................................5-71
5.8.1 Remedial Alternative 1..............................................................................
5-72
5.8.1.1 Problem Statement and Remedial Goals .........................................
5-73
5.8.1.2 Effects of Source Control and Corrective Action ...........................5-74
5.8.1.3 Screening Criteria Evaluation...........................................................
5-74
5.8.2 Remedial Alternative 2..............................................................................
5-75
5.8.2.1 Problem Statement and Remedial Goals .........................................
5-75
5.8.2.2 Effects of Source Control and Corrective Action ...........................5-76
5.8.2.3 Screening Criteria Evaluation...........................................................
5-77
5.9 Source Area 2 Proposed Remedial Alternative Selected .................................
5-77
5.9.1 Description of Proposed Remedial Alternative and Rationale for
Selection.......................................................................................................
5-77
5.9.2 Design Details.............................................................................................
5-79
5.9.2.1 Process Flow Diagrams for All Major Components of
ProposedRemedy...............................................................................5-79
5.9.2.2 Engineering Designs with Assumptions, Calculations, and
Specifications.......................................................................................
5-79
Page iv

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
TABLE OF CONTENTS (CONTINUED)
SECTION
PAGE
5.9.2.3 Permits Needed for Remedy and Approximate Schedule ............
5-79
5.9.2.4 Schedule and Approximate Cost of Implementation ....................
5-79
5.9.2.5 Measures to Ensure Health and Safety ............................................
5-80
5.9.3 Requirements for 02L .0106(1) - MNA.....................................................5-80
5.9.4 Requirements for 02L .0106(k) - Alternate Remediation Goals...........
5-81
5.10 Source Area 2 Summary and Conclusions........................................................
5-83
5.11 Effectivness Monitoring Plan(EMP)..................................................................5-83
5.11.1 Progress Reports and Schedule................................................................
5-84
5.11.2 Sampling and Reporting Plan During Active Remediation .................5-85
5.11.3 Sampling and Reporting Plan after Termination of Active
Remediation................................................................................................
5-89
5.12 Proposed Interim Activities Prior to Implementation.....................................5-89
5.13 Contingency Plan..................................................................................................
5-89
5.13.1 Description of Contingency Plan.............................................................5-89
5.13.2 Decision Metrics for Implementing Contingency Plan .........................5-90
6.0 PROFESSIONAL CERTIFICATION.........................................................................6-1
7.0 REFERENCES................................................................................................................
7-1
Page v

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF FIGURES
Executive Summary
Figure ES-1 Site Location Map
Figure ES-2 Areas Proposed for Corrective Action
Section 1.0 Introduction
Figure 1-1 Site Location Map
Figure 1-2 Historical USGS Topographic Map
Figure 1-3 Site Layout with Monitoring Well Locations
Figure 1-4 Simplified Site Layout Map
Section 2.0 Overview of Source Areas Being Proposed for Corrective Action
Figure 2-1 Map of CCR and Former Coal Pile Management Areas
Figure 2-2 General Cross Section A -A' - Source Area 1- Ash Basins West to East
Figure 2-3 General Cross Section B-B' - Source Area 1- Ash Basins and FPA North to
South
Figure 2-4 General Cross Section C-C' - Source Area 2 - FADA and Former Coal Pile
Area North to South
Figure 2-5 General Cross Section D-D' - Source Area 2 - FADA and Former Coal Pile
Area West to East
Section 3.0 Summary of Background Determinations
Figure 3-1 Background Sample Location Map
Section 4.0 Conceptual Site Model
Figure 4-1 Water Level Map - Surficial Flow Zone - February 26 & 27, 2020
Figure 4-2a Hydrographs - Eastern Property Line
Figure 4-2b Historical Hydrographs -1971 Ash Basin and FPA
Figure 4-2c Historical Hydrographs -1984 Ash Basin
Figure 4-2d Hydrographs - Former Ash Disposal Area (FADA) and Former Coal Pile
Area (FCPA)
Figure 4-3a Simulated Groundwater Flow Direction - Upper Surficial Flow Zone -
Current Conditions
Figure 4-3b Simulated Groundwater Flow Direction - Lower Surficial Flow Zone -
Current Conditions
Figure 4-4 Potential Surface Water Receptors
Figure 4-5 HB 630 Compliance
Page vi

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF FIGURES (CONTINUED)
Section 5.0 Corrective Action Approach for Source Area 1 (71/84/FPA) and Source
Area 2 (FADA/FCPA)
Source Area 1 (1971 Ash Basin/1984 Ash Basin/FPA)
Figure 5-1a Arsenic in Unsaturated Soil - Source Areas 1 & 2 -1971 Ash Basin, Former
Process Area, Coal Pile, and Former Ash Disposal Area
Figure 5-1b Cobalt in Unsaturated Soil - Source Area 1 & 2 -1971 Ash Basin, Former
Process Area, Coal Pile, and Former Ash Disposal Area
Figure 5-1c Selenium in Unsaturated Soil - Source Area 1 & 2 -1971 Ash Basin,
Former Process Area, Coal Pile, and Former Ash Disposal Area
Figure 5-1d Vanadium in Unsaturated Soil - Source Area 1 & 2 -1971 Ash Basin,
Former Process Area, Coal Pile, and Former Ash Disposal Area
Figure 5-2a Arsenic in Unsaturated Soil - Source Area 1-1984 Ash Basin
Figure 5-2b Selenium in Unsaturated Soil - Source Area 1-1984 Ash Basin
Figure 5-3a 1984 Ash Basin Arsenic SPLP Model Simulations
Figure 5-3b 1984 Ash Basin Arsenic Boron SPLP Model Simulations
Figure 5-3c 1984 Ash Basin Arsenic Selenium SPLP Model Simulations
Figure 5-4 Ash Basin Groundwater Quality Piper Diagrams
Figure 5-5 Supply Well Groundwater Quality Piper Diagrams
Figure 5-6 Surface Water Quality Piper Diagrams
Figure 5-7a Isoconcentration Map - Source Area 1- Arsenic in Upper Surficial Flow
Zone
Figure 5-7b Isoconcentration Map - Source Area 1- Arsenic in Lower Surficial Flow
Zone
Figure 5-8a
Isoconcentration Map -
Source Area 1
- Boron in Upper Surficial Flow
Zone
Figure 5-8b
Isoconcentration Map -
Source Area 1-
Boron in Lower Surficial Flow
Zone
Figure 5-9a
Isoconcentration Map -
Source Area 1-
Molybdenum in Upper Surficial
Flow Zone
Figure 5-9b
Isoconcentration Map -
Source Area 1-
Molybdenum in Lower Surficial
Flow Zone
Figure 5-10
Isoconcentration Map -
Source Area 1- Selenium in Lower Surficial Flow
Zone
Figure 5-11a
Isoconcentration Map -
Source Area 1-
Strontium in Upper Surficial Flow
Zone
Page vii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF FIGURES (CONTINUED)
Figure 5-11b Isoconcentration Map - Source Area 1- Strontium in Lower Surficial Flow
Zone
Figure 5-12a General Cross Section A -A' - Source Area 1 Ash Basins West to East -
Conservative Group
Figure 5-12b General Cross Section B-B' - Source Area 1 Ash Basins and FPA North to
South - Conservative Group
Figure 5-13a General Cross Section A -A' - Source Area 1 Ash Basins West to East -
Non -Conservative Group
Figure 5-13b General Cross Section B-B' - Source Area 1 Ash Basins and FPA North to
South - Non -Conservative Group
Figure 5-14a General Cross Section A -A' - Source Area 1 Ash Basins West to East -
Variable Group
Figure 5-14b General Cross Section B-B' - Source Area 1 Ash Basins and FPA North to
South - Variable Group
Figure 5-15a Concentration Plots - Arsenic versus Ex
Figure 5-15b Time versus Concentration - Arsenic and Ex Upgradient of Source Area 1
Figure 5-15c Time versus Concentration - Arsenic and Ex Downgradient of Source
Area 1
Figure 5-16 Interim Action System Layout
Figure 5-17 Proposed Restricted Groundwater Use
Figure 5-18 Conceptual Confirmation Monitoring Well Network - Alternatives 1 & 2 -
1971/1984 Ash Basin and FPA
Figure 5-19 Remedial Alternative 2 - Confirmation Monitoring with RS Designation -
Source Area 1
Figure 5-20 Simulated Boron Concentrations - Source Areas 1 & 2 - Alternatives 1 & 2
Figure 5-21 Simulated Selenium Concentrations - Source Areas 1 & 2 -
Alternatives 1 & 2
Figure 5-22 Implementation Gantt Chart - Source Area 1
Source Area 2 (FADA/FCPA)
Figure 5-23 FADA and Former Coal Pile Groundwater Piper Diagrams
Figure 5-24a Isoconcentration Map - Source Area 2 - Arsenic in Upper Surficial Flow
Zone
Figure 5-24b Isoconcentration Map - Source Area 2 - Arsenic in Lower Surficial Flow
Zone
Figure 5-25a Isoconcentration Map - Source Area 2 - Boron in Upper Surficial Flow
Zone
Page viii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF FIGURES (CONTINUED)
Figure 5-25b Isoconcentration Map - Source Area 2 - Boron in Lower Surficial Flow
Zone
Figure 5-26a
General Cross Section C-C' -
Source Area 2 FADA and FCPA North to
South - Conservative Group
Figure 5-26b
General Cross Section D-D' -
Source Area 2 FADA and FCPA West to
East - Conservative Group
Figure 5-27a
General Cross Section C-C' -
Source Area 2 FADA and FCPA North to
South - Non -Conservative Group
Figure 5-27b
General Cross Section D-D' -
Source Area 2 FADA and FCPA West to
East - Non -Conservative Group
Figure 5-28 Time versus Concentration - Arsenic and EH near Source Area 2
Figure 5-29 Conceptual MNA Well Network - Alternatives 1 & 2 - FADA and FCPA
Figure 5-30 Remedial Alternative 2 - MNA with RS Designation - Source Area 2
Figure 5-31 Implementation Gantt Chart - Source Area 2
Figure 5-32 Effectiveness Monitoring Program Systems and Flow Paths -
Alternatives 1 & 2 - Source Areas 1 & 2
Figure 5-33 Federal Regulatory Groundwater Monitoring - Source Areas 1 & 2
Figure 5-34 Effectiveness Monitoring Plan Work Flow and Optimization Flow
Diagram
Figure 5-35 Termination of Groundwater Remediation Flow Diagram
Page ix

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF TABLES
Section 1.0 Introduction
Table 1-1 Summary of Historical On -Site Environmental Incidents
Section 2.0 Overview of Source Areas Being Proposed for Corrective Action
Table 2-1 Summary of On -Site Facilities
Section 3.0
Summary of Background Determinations
Table 3-1
Background Threshold Values for Soil
Table 3-2
Background Threshold Values for Groundwater
Table 3-3
Background Dataset Ranges for Surface Water
Table 3-4
Background Dataset Ranges for Sediment
Section 4.0 Conceptual Site Model
Table 4-1 February 2020 Groundwater Level Elevations
Table 4-2 Horizontal Hydraulic Gradients and Flow Velocities
Table 4-3 Vertical Hydraulic Gradients
Table 4-4 Water Supply Well Analytical Results Summary
Table 4-5 House Bill 630 Implementation Summary
Section 5.0 Corrective Action Approach for Source Area 1(71/84/FPA) and Source
Area 2 (FADA/FCPA)
Source Area 1-1971 Ash Basin/1984 Ash Basin/FPA
Table 5-1 Constituents of Interest Evaluation - Source Area 11971 Ash Basin, 1984
Ash Basin, Former Process Area
Table 5-2 Summary of Interim Actions - Source Area 1
Table 5-3a Summary of Unsaturated Soil Analytical Results - Source Area 1
Table 5-3b Summary of Unsaturated Soil SPLP - Source Area 1
Table 5-4 Summary of Central Tendency and Lower Confidence Limit Analysis
Results - SA1
Table 5-5 Sediment Concentrations of COIs - SA1 and SA2
Table 5-6 Remedial Technology Screening Summary - SA1 and SA2
Table 5-7 Extraction Well Groundwater Analytical Results
Table 5-8 Summary Trend Analysis Results for Groundwater Monitoring Wells -
SA1
Page x

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF TABLES (CONTINUED)
Source Area 2 — FADA/FCPA
Table 5-9 Constituents of Interest Evaluation — Source Area 2 Former Ash Disposal
Area and Former Coal Pile Area
Table 5-10 Summary of Interim Actions — Source Area 2
Table 5-11a Summary of Unsaturated Soil Analytical Results — Source Area 2
Table 5-11b Summary of Unsaturated Soil SPLP Results — Source Area 2
Table 5-12 Summary of Central Tendency and Lower Confidence Limit Analysis
Results — SA2
Table 5-13 Summary Trend Analysis Results for Groundwater Monitoring Wells —
SA2
Table 5-14 Post -Excavation Effectiveness Monitoring Plan Elements — Source
Areas 1 & 2
Page xi

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex 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
Updated Groundwater Flow and Transport Modeling Report
Appendix G
Geochemical Model Report
Appendix H
Compliance Value Calculation Approach
Appendix I
Monitored Natural Attenuation Report
Appendix J
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 Plume Stability Analysis
Post -Excavation Conditions Analysis
Appendix M Former Ash Disposal Area and Former Coal Pile Area Assessment
Report
Appendix N Remedial Alternative Cost Estimate Details
Appendix O Remediation Alternatives Summary
Appendix P Post -Excavation Groundwater and Surface Water Effectiveness
Monitoring Plan
Page xii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF ACRONYMS AND ABBREVIATIONS
02B
NCAC Title 15A, Subchapter 02B. Surface Water and Wetland
Standards
02L
NCAC Title 15A, Subchapter 02L. Groundwater Classification and
Standards
ASTM
American Society for Testing and Materials
BGS
below ground surface
BOD
Basis of Design
BTV
background threshold value
CAMA
Coal Ash Management Act of 2014
CAP
Corrective Action Plan
CCP
coal combustion products
CCR
coal combustion residuals
CFPUA
Cape Fear Public Utility Authority
COI
constituent of interest
CSA
Comprehensive Site Assessment
CSM
Conceptual Site Model
D
decreasing concentration trend
CTV/mean
central tendency value
dh/dl
hydraulic gradient
Duke Energy
Duke Energy Progress, LLC
DMW
Division of Waste Management
DWR
Division of Water Resources
EH
reduction/oxidation potential
ELCR
excess lifetime cancer risk
EMP
Effectiveness Monitoring Program
E&SC
erosion and sediment control
ER
exceedance ratio
FADA
former ash disposal area
FCPA
former coal pile area
FPA
former process area
ft/day
feet per day
ft/ft
foot per foot
ft/year
feet per year
gpm
gallons per minute
G.S.
North Carolina General Statutes
GWPS
groundwater protection standards
HDPE
high -density polyethylene liner
Page xiii

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF ACRONYMS AND ABBREVIATIONS (CONTINUED)
HFO
hydrous ferric oxide
HQ
non -carcinogenic risk estimate
I
increasing concentration trend
IAP
Interim Action Plan
IMAC
Interim Maximum Allowable Concentration
IMP
Interim Monitoring Plan
K
hydraulic conductivity
Kd
partition coefficient
L/kg
liter per kilogram
LCL95
lower confidence limit
LOLA
Lay of Land Area
MCL
maximum contaminant level
µg/L
micrograms per liter
mg/kg
milligrams per kilogram
mg/L
milligrams per Liter
MNA
Monitored Natural Attenuation
NAVD 88
North American Vertical Datum of 1988
NC
not calculated
NCAC
North Carolina Administrative Code
NCDENR
North Carolina Department of Environment and Natural Resources
NCDEQ
North Carolina Department of Environmental Quality
ND
non -detect concentrations
NE
number of samples to evaluate trend
ne
effective porosity
NORR
Notice of Regulatory Requirements
NPDES
National Pollutant Discharge Elimination System
NRP
Notice of Residual Petroleum
NT
no significant trend
O&M
Operation and Maintenance
PTO
permit to operate
POG
protection of groundwater
PSRG
preliminary soil remediation goal
RS
Restricted Use Designation
S
stable, no significant trend
Sutton/Site
L.V. Sutton Energy Complex (entire property)
SA1
Source Area 1
SA2
Source Area 2
Page xiv

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
LIST OF ACRONYMS AND ABBREVIATIONS (CONTINUED)
SAP
Sampling analysis protocol
SARP
Site Analysis and Removal Plan
SOC
Special Order by Consent
SPLP
Synthetic Precipitation Leaching Procedure
TDS
total dissolved solids
USEPA
U.S. Environmental Protection Agency
Us
groundwater seepage flow velocity
WQMP
Water Quality Monitoring Plan
Page xv

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
1.0 INTRODUCTION
SynTerra prepared this groundwater Corrective Action Plan (CAP) Update on behalf of
Duke Energy Progress, LLC (Duke Energy). The plan pertains to the L.V. Sutton Energy
Complex (Sutton, Site) in New Hanover County, North Carolina (Figure 1-1). This CAP
Update evaluates the effects of coal combustion residuals (CCRs) and on -Site source
areas related to coal-fired electricity -generating operations that occurred at Sutton from
1954 through 2013. This CAP Update also examines the remedial approach for
addressing those effects. Comprehensive groundwater assessment activities indicate
that the source areas [1971 ash basin, 1984 ash basin, the former process area (FPA), the
former ash disposal area (FADA), and the former coal pile area (FCPA)] have
contributed to constituent concentrations in groundwater being greater than applicable
regulatory standards beyond the ash basins' compliance boundary.
Duke Energy is submitting this groundwater CAP Update to prescribe methods and
materials for restoring groundwater quality associated with CAMA-regulated units and
additional source areas. This CAP Update considers instances of constituents detected
at concentrations greater than applicable North Carolina groundwater standards [North
Carolina Administrative Code (NCAC), Title 15A, Subchapter 02L, Groundwater
Classification and Standards (02L) / Interim Maximum Allowable Concentrations
(IMACs) or background values, whichever is greater], at or beyond the compliance
boundary.
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 of 2014
(CAMA). In accordance with G.S. requirements, a CAP for Sutton was previously
submitted to the North Carolina Department of Environmental Quality (NCDEQ) in
two parts:
• Corrective Action Plan Part 1— L.V. Sutton Energy Complex (SynTerra, 2015b)
• Corrective Action Plan Part 2 —L.V. Sutton Energy Complex (SynTerra, 2016a)
This CAP Update is being submitted to the North Carolina Department of
Environmental Quality (NCDEQ) as originally requested in a June 11, 2018, letter from
NCDEQ to Duke Energy. NCDEQ approved a revised CAP submittal date of August 3,
2020 in a letter dated February 26, 2020. This CAP Update is consistent with NCAC Title
Page 1-1

Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
15A, Subchapter 02L .0106 corrective action requirements, and with the following CAP
guidance correspondences between the NCDEQ and Duke Energy:
• A letter titled Corrective Action Plan Content for Duke Energy Coal Ash Facilities, to
Duke Energy, dated April 27, 2018
• A letter titled Duke Energy Interpretation of Corrective Action Plan Content Guidance
Provided by the North Carolina Department of Environmental Quality, dated January
23, 2019
• A letter titled Duke Energy Interpretation of Corrective Action Plan Content Guidance
(January 23, 2019) — NCDEQ Response and Conditional Approval, dated September
10, 2019
• A letter titled RE: North Carolina Department of Environmental Quality Letter Dated
January 31, 2020, Issues Related to Implementation of Closure Plans and Groundwater
Corrective Action Plan (CAPS), dated March 4, 2020.
• A letter titled Updated Corrective Action Plan and Comprehensive Site Assessment
Content Duke Energy Coal Ash Facilities, dated June 26, 2020.
The letters listed above are included in Appendix A.
To facilitate the review process, this CAP Update includes section references to the
document titled Corrective Action Plan Content for Duke Energy Coal Ash Facilities
(Appendix A). The section references are included throughout this CAP Update as
italicized brackets [i.e., "(CAP Content Section... )"] beneath report section headings and
within text that reference the applicable CAP content section reference from the 2019
NCDEQ guidance document and March 2020 guidance submitted by Duke Energy.
1.1 Background
(CAP Content Section 1.A)
A substantial amount of data related to the Site's CCR source areas and the FCPA has
been collected to support this CAP Update. Site assessment was performed, and the
Sutton Comprehensive Site Assessment (CSA) Update Report (SynTerra, 2018) was
prepared and submitted in accordance with requirements in Subchapter 02L. 0106(g).
The CSA:
• Identified the source(s) and causes of constituents of interest (COls) in
groundwater.
• Found no imminent hazards to public health and safety.
• Identified receptors and potential exposure pathways.
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• Sufficiently determined the horizontal extent and vertical extent of COIs in soil
and groundwater within and downgradient of the source areas.
• Determined the geological and hydrogeological features influencing the
movement, chemical makeup, and physical characteristics of COIs.
In the letter dated June 11, 2018, NCDEQ (Appendix A) indicated that assessment
activities have been sufficient to proceed with preparation of a CAP Update but
requested additional investigation (i.e., characterization of additional areas) in
conjunction with preparation of the CAP Update. Additional detail and responses to
comments provided in the June 11, 2018 NCDEQ letter are included as Appendix B.
Assessment activities associated with additional source areas were performed, as
described in Appendix M. This CAP Update builds on previous documents and
information from recent assessment activities to provide a CAP for addressing the
requirements in 15A NCAC 02L .0106 for corrective action and the restoration of
groundwater quality at the Site.
Detailed descriptions of Site operational history, the Conceptual Site Model (CSM),
physical setting and features, geology/hydrogeology, and findings of the CSA and other
CAMA-related work are documented in the following Site assessment reports:
1. Comprehensive Site Assessment — L.V. Sutton Energy Complex (SynTerra, 2015a)
2. Comprehensive Site Assessment Supplement 1— L.V. Sutton Energy Complex
(SynTerra, 2016b)
3. Comprehensive Site Assessment Supplement 2 — L.V. Sutton Energy Complex
(SynTerra, 2016c)
4. Comprehensive Site Assessment Update — L.V. Sutton Energy Complex (SynTerra,
2018)
1.2 Purpose and Scope
(CAP Content Section 1.B)
The purposes of the corrective action evaluated in this CAP are to:
• Restore groundwater quality at or beyond the ash basins' compliance boundary
downgradient of the Sutton CAMA-regulated source areas (ash basins and
coincident FPA) to the applicable groundwater standards or as close to the
standards as is economically and technically feasible, consistent with 15A NCAC
02L .0106(a).
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• Restore groundwater quality at or beyond the compliance boundary near the
FADA and FCPA by reducing COI concentrations to the calculated remediation
goals, or as close as is economically and technologically feasible, consistent with
15A NCAC 02L .0106(a) and as allowed by G.S. 130A-310.65-310.77 (amended by
Session Law 2015-286).
• Address response requirements contained within 15A NCAC 02L .0107(k) for
COI concentrations greater than standards (1) in adjoining classified
groundwater and/or (2) presenting an imminent hazard to public health and
safety.
• Meet the requirements for corrective action plans found in G.S. Section 130A-
309.211(b).
The scope of this CAP Update is defined by G.S. Section 130A-309.211, amended by
CAMA. The legislation requires, among other activities, assessment of groundwater at
CCR impoundments and corrective action in conformance with the requirements of
02L. These corrective actions for restoration of groundwater quality requirements were
codified into G.S. Section 130A-309.211, which was further amended by House Bill 630
to require a provision for alternate water supply for receptors within 0.5 of a mile from
the established compliance boundary. On October 12, 2018, the NCDEQ confirmed that
Duke Energy satisfactorily completed the alternate water provision under CAMA, G.S.
Section 130A-309.211(cl) (Appendix A).
Based on current Site conditions and the results from the Site investigations, this CAP
Update develops and compares alternative methods for corrective action and presents
the recommended plan. This CAP Update presents a holistic, multi -component
corrective action approach for groundwater COIs associated with the ash basins, FPA,
FADA, and FCPA at or beyond the compliance boundary northwest, west, and
southeast of the ash basins, in an isolated off -Site area east of the property line, and
southwest of the FADA and FCPA. 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 Corrective Action
(CAP Content Section 1.C)
Comprehensive groundwater assessment activities were 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). Constituent concentrations in groundwater greater than
applicable regulatory standards are contained within the compliance boundary with the
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exception of small areas west of the ash basins, southeast of the 1971 basin, off -Site east
of the ash basins, and southwest of the FADA and FCPA.
The regulatory requirements for corrective action at CCR surface impoundments under
CAMA are in G.S. Section 130A-309.211(b), (c), and (c1). G.S. Section 130A-309.211(b)
requires that the CAP shall provide recommendations for groundwater restoration in
conformance with the requirements of 02L. In accordance with 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
• A monitoring plan for evaluating the effectiveness of the proposed corrective action and
detecting movement of any constituent plumes
• Any other information related to groundwater assessment required by NCDEQ
In addition to CAMA, requirements for CAPs are also contained in 15A NCAC 02L
.0106(e), (h), and (i).
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
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In a letter dated December 18, 2009, NCDEQ informed Duke Energy that the North
Carolina Attorney General's Office clarified how corrective action requirements apply
to facilities permitted prior to December 30, 1983. The Attorney General determined
that facilities with related constituent concentrations greater than groundwater
standards, permitted under G.S. 143-215.1, and permitted prior to December 30, 1983,
fall under 15A NCAC 02L .0106(c). The letter then stated that this clarification gives
Duke Energy the option to seek approval of a CAP that does not require remediation to
groundwater standards [15A NCAC 02L .0106(k)] or may allow natural attenuation by
natural processes [15A NCAC 02L .0106(1)].
This CAP Update presents an evaluation of the options available for corrective action
under 15A NCAC 02L .0106(j), (k), and (1).
• Under paragraph 0), corrective action would be implemented using remedial
technology for restoration of groundwater quality to 02L standards.
Under paragraph (k), a request for approval of a corrective action plan may be
submitted without requiring groundwater remediation to 02L standards 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 is prepared in general accordance with 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 April 27, 2018, adjusted on September 10, 2019, and again on March 4, 2020,
provided in Appendix A (CAP Content Section 1.C.c).
In addition to this CAP Update, the Sutton ash basins are subject to closure
requirements under CAMA. Ash removal from non-CAMA units (including the FADA
and FPA), basin closure activities, and removal of coal from the coal pile provide source
control and are considered significant components of the overall corrective action for
the Site.
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 demonstrated off -site affected
groundwater migration, including Sutton. Historical and ongoing assessment
information indicates COIs have migrated off -Site to the east in the past. After
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correspondence with NCDEQ and conditional approval of an Interim Action Plan
(IAP), Duke Energy began interim action (groundwater extraction) to remediate COIs in
groundwater along the eastern property line. The primary objective of the groundwater
extraction system is to prevent migration of constituents in groundwater from the 1971
ash basin off -Site beyond the eastern property boundary. A Basis of Design (BOD)
report was submitted to the NCDEQ Division of Water Resources (DWR) in January
2017 (Geosyntec, 2017). After DWR approval of the BOD report, Duke Energy
proceeded with installation of the nine -well extraction network along the eastern
property line. Operation of the system began in August 2017 with system monitoring
and annual effectiveness monitoring reporting, through present day.
Ash Basin Closure Requirements
G.S. 130A-309.214 requires submittal of a plan for the closure of ash basins throughout
the state of North Carolina. In general, closure of ash basins might be through
installation of an engineered cover system or by excavation of the ash for beneficial
reuse or disposal off -site or on -site. In accordance with G.S. 130A-309.214(a), closure of
each ash basin must be completed no later than:
• December 31, 2019, for high -risk impoundments
• December 31, 2024, for intermediate -risk impoundments
• December 31, 2029, for low -risk impoundments
The deadlines mentioned above would not apply if a variance is granted, nor if a site
has been identified for implementation of an ash beneficiation project described in G.S.
E[Ci17�C�IZ�•�C'�
Sutton was deemed a "high -priority" site under CAMA, and complete closure of the
ash basins by August 1, 2019, was specifically required. From May 2015 to June 2019,
Duke Energy excavated ash from the ash basins. In accordance with CAMA
requirements, ash removed from the basins was placed in an off -Site structural fill or
on -Site lined landfill. Excavation of ash from the ash basins at Sutton was completed in
July 2019. Approximately 6,320,000 tons of ash were removed from the ash basins. Duke
Energy submitted a report to NCDEQ on April 18, 2019, documenting the fulfillment of
Sutton ash removal requirements from the 1971 basin, and a similar report pertaining to
the 1984 basin was submitted to NCDEQ on August 27, 2019. NCDEQ provided
confirmation of ash removal and fulfillment of excavation requirements for Sutton in
correspondence dated July 25, 2019 (1971 basin), and December 13, 2019 (1984 basin).
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Removal of ash, ash pore water, and coal for source control is a significant component
of corrective action at Sutton. This CAP Update has been developed with consideration
of these recent source control measures.
1.4 Facility Description
(CAP Content Section 1.E)
1.4.1 Location and History of Land Use
(CAP Content Section LE.a)
The Site is owned and operated by Duke Energy. The property occupies
approximately 3,300 acres along the Cape Fear River near the City of Wilmington
in New Hanover County, North Carolina (Figure 1-1).
Historical topographic maps and aerial photographs indicate the property was
undeveloped rural land prior to startup of Site operations (CSA Update,
SynTerra 2018) in 1954. Site operations started in 1954 as a two -unit coal-fired
electricity -generating facility. A third unit was added in 1972 increasing the
maximum capacity to 575 MW. The three coal-fired units were retired in
November 2013, and they were replaced with a 625 MW combined cycle plant
operating on natural gas. A historical United States Geographical Survey (USGS)
topographic map is included as Figure 1-2.
A natural gas -fired electricity -generating facility has been in operation at the Site
since 2013. Facility structures associated with current power production are
located primarily in the south central portion of the Site. The northern and
southern portions of the Site are primarily undeveloped areas containing small
sand hills, pine woods, and brush (Figure 1-3). A simplified Site layout figure is
provided as Figure 1-4.
The Site's 1,100-acre cooling pond, also known as Lake Sutton, is located east of
the Cape Fear River, between the river and source areas (1971 basin, 1984 basin,
FPA, FADA, and FCPA). The cooling pond is both a National Pollutant
Discharge Elimination System (NPDES) permitted wastewater treatment unit
and waters of the State. The cooling pond was only a wastewater treatment unit
from initial operations until early 2015 when the NPDES permit was modified to
classify the unit as both a wastewater treatment unit and waters of the state. This
CAP Update would refer to this Site feature as the cooling pond.
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Surrounding Land Use
Land use within the 0.5-mile radius of the ash basin compliance boundary
generally consists of the Cape Fear River to the west, undeveloped land to the
north and south, and a sand quarry and light industrial use properties to the east
(Figure 1-4). An interstate roadway crosses the Site in the southern portion.
The Site and all surrounding properties are zoned industrial (I-2). Properties
north and south of the Site are comprised primarily of wooded land. Properties
east of the Site contain wooded land, a sand quarry, an asphalt plant, a
commercial refueling station, and various light industrial offices and
warehouses. No residential properties are located adjacent to the Site. No
significant change in land use surrounding the Site is anticipated.
Former Coal -Burning Operations and Ash Management
Site operations, which started in 1954, included use of coal-fired boilers to burn
bituminous coal as fuel and produce steam for generation of electrical power.
Coal was primarily received by rail during the entire operation of the coal-fired
power plant. During a short period from 2006 to 2008, coal was also transported
by barge, offloaded from vessels on the Cape Fear River, and then transported by
conveyor to the FCPA. Coal was historically stored at the Site's former coal pile,
an unlined area located west of the old power plant between the Cape Fear River
and the coal -burning power plant. The FCPA consists of approximately 14 acres
bounded to the north by the FADA, to the east by vacant land that formerly
contained the steam power plant buildings (now razed) and parking areas, and
to the south and west by the cooling pond and intake canal from the cooling
pond.
Coal ash was sluiced to four areas, collectively referred to as the ash
management area. The former ash management area is located adjacent to the
cooling pond, north of the plant, as shown on Figure 1-1. The former ash
management area consists of:
• The FADA, also known as the lay of land area (LOLA), is located south of
the ash basins, on the south side of the cooling pond effluent canal. It is
suspected that ash might have been placed in this area from
approximately 1954 to 1972. The FADA did not have a dam around the
area. Therefore, ash placement in the area would not have produced a
significant hydraulic head. The permitted Outfall (001) to the Cape Fear
River was located southwest of the FADA, as shown on Figure 1-1.
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
• The 1971 ash basin (old ash basin) was an unlined ash basin built in about
1971. A portion of the 1971 basin was constructed by excavation below the
water table for borrow material used for construction of the 1971 ash basin
earthen dikes. Ash pore water stored within the basin was approximately
12 feet North American vertical datum of 1988 (NAVD 88) in elevation
compared with the surrounding ground level elevation of approximately
9.5 feet NAVD 88. The hydraulic head in the basin created a radial
component of groundwater flow away from the basin. Prior to
construction of the 1984 ash basin, the 1971 ash basin used a historical
outfall to discharge to the cooling pond.
• The 1984 ash basin (new ash basin) was constructed with a 12-inch-thick
clay liner wholly above the water table. It was located near the northern
portion of the former ash management area and was operational from
1984 to 2013. The dam surrounding the basin was approximately 28 feet
NAVD 88 in elevation compared with the surrounding ground level of
approximately 9.5 feet NAVD 88, with a separator dike separating it from
the 1971 basin. The 1984 basin was hydraulically connected to the 1971
basin. Outfall 004 was located on the west side of the basin that
discharged to the cooling pond (or via underground pipe to Outfall 001)
as managed by Site personnel.
An area known as the FPA is adjacent to the southeast corner of the 1971
basin. The FPA was a small settling basin used for a short time period
when the Site was co -firing fuel oil. At that time, sluice waters were
directed to the settling basin before being directed to the 1971 basin. The
settling basin was approximately 250 feet by 150 feet with concrete -lined
side walls. The settling basin was subsequently filled with CCRs and
solids. Excavation the FPA was completed in April 2020.
Coal -burning operations ceased in 2013 when the facility was converted to
natural gas; ash has not been generated at the Site since that time.
Source Area Closure Activities
Excavation of ash from the 1971 and 1984 ash basins began on May 21, 2015. Ash
basin closure at Sutton followed plans outlined in a Site Analysis and Removal Plan
(SARP) prepared by Geosyntec Consultants of NC (Geosyntec, 2016). This
activity entailed removal of CCR with excavators from the 1984 basin, removal of
CCR from the 1971 ash basin to the maximum extent practicable with excavators
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followed by excavation beneath the water table via dredging, and transferring
the removed CCR to an off -Site structural fill or on -Site lined landfill.
During 2015 and 2016, ash was removed from the Site, initially by truck and then
by train, for use as structural fill at the Brickhaven facility. An on -Site lined ash
landfill was subsequently constructed east of the ash management area in 2016
and 2017 (Figure 1-4). Starting in July 2017, CCR from the ash basins were placed
in the newly constructed on -Site coal combustion products (CCP) landfill.
Excavation of ash from the 1971 and 1984 basins was completed in July 2019.
As noted during installation of ash pore water monitoring well ABMW-01, ash in
the 1971 basin was as deep as 40 feet below the water table. Geotechnical borings
to identify the bottom surface of ash in the 1971 basin confirmed this observation.
CCR material below the water table was removed by dredging. After CCR
removal, water remained in the 1971 basin; currently, the water in the 1971 basin
is separated from the cooling pond by sheet piling and an earthen dike.
No monitoring wells were installed within the footprint of the 1984 ash basin due
to the presence of the clay liner. The water table is not present above the clay
liner. Monitoring wells were not installed beneath the liner due to concern of
introducing additional COIs to groundwater beneath the basin. Ponded water
not representative of the groundwater table was present in the northern portion
of the basin at an average elevation of 18 feet NAVD 88. That ponded water was
removed during the decanting stage of basin closure. Ash was removed by
excavator and was placed in either an off -Site structural fill or on -Site landfill.
The basin was regraded after excavation and is now an open, vegetated field.
The three areas of CCR or coal storage not governed by CAMA are the FPA,
FADA, and FCPA. All three areas are located coincident with the ash basins and
are evaluated in this CAP Update. Coal has not been brought on -Site and stored
at the FCPA since the coal fired units were decommissioned in 2013. Coal
removal at this area was completed in 2015. This action was not court ordered.
Duke Energy excavated fuel waste and CCR from the FPA and FADA, an action
not required under CAMA, in an effort to remove CCR to the maximum extent
practicable.
Excavation of the fuel waste and CCRs in the FPA is complete as of April 2020.
Removal of ash from the FADA began in July 2019. Ash in the FADA was as
deep as 17 feet below the water table. CCR material below the water table was
primarily removed by excavators. Dredging was used to remove ash in isolated
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areas the excavators could not access. Ash was removed and placed in the on -
Site CCP Landfill. Removal of ash from the FADA was completed in June 2020.
Currently, a portion of the FADA is filled with water; this water is separated
from the cooling pond by sheet piling and an earthen dike.
Initial Abatement Activities
In 2017, a groundwater extraction system consisting of nine recovery wells
screened in the surficial flow zone was installed to reduce CCR constituent
migration in groundwater off -Site to the east. The recovery wells are located
along the eastern property line, east of the 1971 and 1984 ash basins. A
wastewater treatment system was constructed north of the 1984 ash basin to treat
ash pore water from the basins during closure, effluent from the groundwater
extraction system, and leachate from the on -Site CCP Landfill. The groundwater
extraction system has been operational since August 2017.
1.4.2 Operations and Waste Streams Coincident with the Ash
Basin
(CAP Content Section LE.b)
Coal -Related Operational Storage and Waste Streams
Coincident with the Ash Basins
Coal is a highly combustible sedimentary rock typically dark in color 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. The exact composition of coal varies depending on the
environmental and temporal factors associated with its formation.
Coal was historically stored at the Site's former coal pile, an unlined area located
west of the power plant between the Cape Fear River and the plant (Figure 1-1).
Based on review of historical aerial photographs during the CSA, the
approximate location of the former coal pile remained generally consistent
throughout coal -burning operations at the Site, with minor changes to the
footprint depending on the volume of coal stockpiled on -Site. During operations,
coal stored on the pile was conveyed via transfer belts to the facility, where it
was pulverized before being used in the boilers for combustion.
The FCPA is not regulated under CAMA; however, assessment and
characterization have been conducted. Results of FCPA assessment and
characterization are incorporated into this CAP Update (Appendix M).
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Non -Coal -Related Operational Storage and Waste Streams
Coincident with the Ash Basins
Historical environmental incidents at the Site have been resolved with the
appropriate regulatory authorities and are not considered components of this
CAP Update.
In addition to the historical incidents discussed below and in Table 1-1, there
were four historical releases of CCR material at the Site. These releases were
caused by periods of heavy rain.
On September 20, 2010 a minor breach occurred in the 1984 ash basin
dam. An incident report was provided to NCDEQ and is included in
Appendix A.
• On September 15, 2018 the on -Site landfill was damaged by Hurricane
Florence. Ash was released from the landfill in the area between the 1984
ash basin and landfill. Ash contact water made it into cooling pond near
the existing boat ramp area, along the perimeter of the landfill, and into
the north and south stormwater retention ponds. Released ash was
removed and documented into reports submitted to NCDEQ.
On June 2, 20219, a large rain event caused significant erosion of the west
side of on -Site landfill cells 3 and 4. Ash was released to the west, north,
and minor areas of the east perimeter stormwater ditches. NCDEQ was
notified and the released material was removed.
• On September 6, 2019, Hurricane Dorian caused minor erosion on the east
side of on -Site Landfill cells 6 and 7. Ash was released to the east
perimeter ditch but did not reach the stormwater retention ponds.
Released material was removed promptly and NCDEQ was notified of the
release.
Environmental incidents (i.e., releases) at the Site have occurred only in the
vicinity of the facility infrastructure (Table 1-1). Incidents that initiated
notifications to NCDEQ consisted of releases of fuel oil, diesel fuel, and kerosene
(including by unknown parties). In late 2017, stained soil was observed during
demolition activities associated with the combustion turbines and tank farm area
at the Sutton facility, located adjacent to the FADA and FCPA. Initial soil
samples indicated the presence of historical diesel fuel organics greater than the
threshold limits. Upon receipt of analytical results, NCDEQ was notified on
December 5, 2017, and per subsequent NCDEQ directives, Duke completed soil
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L.V. Sutton Energy Complex SynTerra
and groundwater assessment activities in accordance with 15A NCAC 2L .0500.
The agency ranked the Site "Low Risk" and approved conditional closure of the
incident (Incident 94367) via the Notice of Residual Petroleum (NRP) deed
restriction process. In a letter dated April 16, 2020 NCDEQ confirmed that the
incident has been resolved with no further action required. A restricted use area
was conservatively established in the area of petroleum release. There is no
evidence that this incident affected groundwater beneath and downgradient of
Source Area 2. Duke Energy submitted the following reports and documentation
as part of this investigation:
1. Notice of Residual Petroleum for Duke Energy L.V. Sutton Demolition Area,
2020. New Hanover County, NC Register of Deeds Book 6293 Pages 882-888 and
Book 67 Page 333. Duke Energy Progress Site No. 104541. March 6, 2020.
2. Geosyntec, 2019a. Supplemental Risk Based Assessment Sampling Event, Duke
Energy L.V. Sutton Demolition Area, NCDEQ Incident Number 94367. July 15,
2019.
3. Geosyntec, 2019b. Initial Site Assessment Report Addendum, Duke Energy L.V.
Sutton Demolition Area, NCDEQ Incident Number 94367. March 29, 2019.
4. Geosyntec, 2018. Initial Site Assessment Report, Duke Energy L.V. Sutton
Demolition Area, NCDEQ Incident Number 94367. March 5, 2018.
1.4.3 Overview of Existing Permits and Special Orders by
Consent
(CAP Content Section 1.E.0
NPDES Permit / Special Order by Consent
Duke Energy was authorized to discharge wastewater from the Sutton ash basins
to the Cape Fear River via Outfall 001 in accordance with National Pollutant
Discharge Elimination System (NPDES) Permit NC0001422. The NPDES permit
was revised on June 12, 2020 and became effective July 1, 2020. The sources of
wastewater inflows permitted for discharge into the Site ash basins historically
included fly ash, bottom ash, stormwater runoff (including runoff from the
former coal pile), cooling pond blowdown, recirculated cooling water, non -
contact cooling water, and treated wastewater.
The NPDES permit authorizes discharge of the following: cooling water, low
volume wastes, stormwater, and treated wastewater to the effluent canal (Outfall
008); wastewater (Outfalls 002, 004, and 008); and treated wastewater, ash pond
discharge, stormwater, landfill leachate, and groundwater from the extraction
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system (Outfall 001). The Outfall locations are indicated on Figure 1-3. The
treated groundwater effluent is tested monthly by Evoqua Rockford for metals,
pH, and turbidity.
The saturated portion of the ash, below the water table and within the 1971 ash
basin, was removed by dredging. Some of the wastewater from the dredging
operations was piped to the water treatment system for treatment prior to
discharge at Outfall 001 under the Site NPDES permit. In addition, the leachate
from the on -Site CCP Landfill is also treated on -Site prior to release at Outfall 001
under the Site NPDES permit.
Special Order by Consent
No seeps have been identified at the Site; therefore, no Special Order by Consent
(SOC) was issued.
Permitted Solid Waste Facilities
Since July 2017, CCRs from the Site ash basins have been placed in the newly
constructed on -Site solid waste landfill [NCDEQ Division of Waste Management
(DWM); Permit No. 6512-Indus-2016]. Permits to operate (PTO) individual cells
of the on -Site CCP Landfill were issued by NCDEQ DWM on the following
dates:
• Cell 3 - July 6, 2017
• Cell 4 - August 25, 2017
• Cell 5 - December 7, 2017
• Cell 6 - February 7, 2018
• Cells 7 and 8 - May 16, 2018
The landfill is located east of the former ash management area (Figure 1-1). The
landfill was constructed with a double high -density polyethylene liner (HDPE)
with leak detection, groundwater monitoring, and leachate collection systems.
Duke Energy conducts routine solid waste landfill compliance monitoring in
accordance with the NCDEQ DWM Permit. The landfill Water Quality
Monitoring Plan (WQMP) lists the groundwater wells, parameters, and
frequency of monitoring required.
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Additional Permits
Erosion and sediment control (E&SC) permits are required for activities related
to construction and excavation. Those activities include general construction
projects, environmental assessment, and remediation projects if the area of
disturbance is greater than 1 acre. Multiple E&SC permits have been obtained for
various projects implemented at the Site, including environmental related
projects, such as well installation and access road construction. Most of the E&SC
permits are closed as the related projects are completed. E&SC permits would
continue to be obtained before implementation of additional construction
projects, as appropriate.
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2.0 OVERVIEW OF SOURCE AREAS BEING PROPOSED FOR
CORRECTIVE ACTION
(CAP Content Section 3)
For the purposes of remedial options, the Site's source areas are grouped into two
multiunit areas:
• Source Area 1 (SA1) —1971 ash basin, 1984 ash basin, and FPA
• Source Area 2 (SA2) — FADA and FCPA
The former 1971 ash basin and former 1984 ash basin are the CAMA-regulated units at
the Site. The FPA, an additional source area located coincident with the 1971 ash basin,
is considered in this CAP. The FADA, also a source area not regulated by CAMA, is
located downgradient of the ash basins. The FCPA, which is an additional source area
located coincident of the FADA portion of the ash management area, is also considered
in this CAP (Figure 2-1) (CAP Content Section 3.A and 3.A.a). A summary of on -Site
facilities is included as Table 2-1. With excavation of ash and removal of coal, the
remaining unsaturated soil in areas with COI concentrations greater than screening
values for protection of groundwater (POG) preliminary soil remediation goals (PSRGs)
are also evaluated as part of the corrective action planning process. The North Carolina
POG PSRGs are risk -based screening levels that are based on the USEPA regional
screening levels (RSLs) for residential and industrial soil (USEPA, 2019).
Consensus was reached with NCDEQ DWR and Duke Energy regarding additional
sources considered for corrective action as part of this CAP Update. The additional
sources at the Site include the FPA, FADA, and FCPA. The consensus was provided in a
letter from NCDEQ to Duke Energy dated April 5, 2019 (Appendix A) (CAP Content
Section 3.B). There are no other source areas considered in this CAP Update.
Brief descriptions of facilities, their status of inclusion or exclusion as part of the source
area, and the rationale for inclusion or exclusion is provided in the Table 2-1 (CAP
Content Section 3.B). The corrective action approach for the former ash basins, FADA,
FPA, and FCPA is discussed in detail in Section 5.0.
CAMA applies to CCR surface impoundments, which are defined as topographic
depressions, excavations, or diked areas constructed primarily of earthen materials,
without a base liner, and that meet other criteria related to design, usage, and
ownership (G.S. Section 130A-309.201).
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At Sutton, CAMA-regulated corrective action is required to remediate the former ash
basin system (the combined 1971 ash basin and 1984 ash basin). The FPA, FADA and
FCPA are not CAMA-regulated source areas. However, due to its small size and close
proximity to the 1971 ash basin, the FPA is evaluated with the CAMA units in this CAP
Update. The data collected as part of the FPA assessment is presented and evaluated as
part of the Source Area 1 discussion (Section 5.1). The data collected as part of the
FADA and FCPA assessment are presented and evaluated both in the Source Area 2
discussion (Section 5.6) and in Appendix M. General cross sections are provided as a
visual tool to aid in discussion of source material occurrence and groundwater
distribution at the Site (Figures 2-2 through 2-5). General cross section A -A' is oriented
parallel to groundwater flow within Source Area 1 (Figure 2-2). General cross section B-
B' is oriented perpendicular to groundwater flow within Source Area 1 (Figure 2-3).
General cross section C-C' is oriented perpendicular to groundwater flow within Source
Area 2 (Figure 2-4). General cross section D-D' is oriented parallel to groundwater flow
within Source Area 2 (Figure 2-5).
For source areas not regulated by CAMA, G.S. 130A-310.65 through 130A-310.77 (as
amended by Session Law 2015-286) allows risk -based remediation as a cleanup option
at sites where the use of remedial actions and land use controls can ensure properties
are safe for intended uses. Therefore, under state regulation and guidance, groundwater
cleanup values can be derived using a risk -based approach and applied as remediation
goals at industrial sites. Because the measures are risk -based, the cleanup values are
protective of human health. The additional source areas are evaluated using this risk -
based approach. An exception to this law is North Carolina's CAMA, which requires
Duke Energy to remediate effects from permitted coal ash impoundments to the 02L
standard.
As required by CAMA, the corrective action objective is to remediate groundwater
beyond the compliance boundary of the 1971 ash basin,1984 ash basin, and FPA to the
02L standards. Corrective action objectives based on risk -based groundwater
remediation goals is a technically justified approach for the FADA and FCPA at Sutton,
which are not regulated by CAMA.
Sections 5.1 through 5.5 describe the environmental conditions near the ash basins and
FPA and provide recommendations for corrective action for Source Area 1.
Sections 5.6 through 5.10 describe the environmental conditions near the FADA and
FCPA and provide recommendations for corrective action for Source Area 2.
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3.0 SUMMARY OF BACKGROUND DETERMINATIONS
(CAP Content Section 4)
Metals and inorganic constituents, typically associated with CCR material, are naturally
occurring and present in the Coastal Plain physiographic province of eastern North
Carolina. Those metals and inorganic constituents can occur in soil, groundwater,
surface water, and sediment. Background analytical results are used to compare
detected constituent concentration ranges from the source area relative to native
conditions.
The statistically derived background values for the Site are used for screening of
assessment data collected in areas of potential migration of COIs from a source area. If
data show that constituent concentrations are less than background values, COI
migration probably has not occurred in the area. If data show that constituent
concentrations are greater than background values, additional lines of evidence are
used to determine whether the concentrations represent migration from a source area.
Those lines of evidence include (but might not be limited to):
• Evaluation of whether the concentration is within the range of background
concentrations detected at the Site, or within the background range for the region
• Evaluation of whether there is a migration mechanism through the use and
interpretation of hydrologic mapping (across multiple flow zones), flow and
transport modeling, and the CSM
• Determination of whether concentration patterns represent a discernable plume
or migration pattern
• Consideration of natural variations in Site geology or geochemical conditions
between background locations and locations downgradient to source areas
• Determination of whether other COIs are present at concentrations greater than
those observed at background locations
As more background data become available, background values might be updated to
continue to refine the understanding of background conditions. However, these
multiple lines of evidence, and additional steps in the evaluation process, would
continue to be important tools for distinguishing 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 Sutton source areas (i.e., ash basins, FPA, FADA, and FCPA).
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A map showing the background locations for all media — including groundwater,
surface water, soil, and sediments — is shown in Figure 3-1 (CAP Content Section 4.A).
Tables referenced in this section present the 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, along with the
statistically derived BTVs, are discussed in Sections 3.1 and 3.2. The BTVs were not
calculated for surface water and sediment; however, background locations for surface
water and sediment were approved by NCDEQ as part of the evaluation of potential
groundwater -to -surface water effects (Appendix K). Background locations for surface
water are further discussed in Section 3.3, and background locations for sediment are
further discussed in Section 3.4. The background surface water and sediment samples
were collected at locations upstream of the source areas and associated permitted
Outfalls. Background values from those locations were used for comparison with
results from downgradient locations.
3.1 Background Concentrations for Soil
Background soil boring locations are shown on Figure 3-1. The soil background dataset
with the appropriate POG PSRGs and BTVs are included in Appendix C, Table 4 (CAP
Content Section 4.B). Background soil samples were collected from multiple unsaturated
depth intervals.
During 2016 and 2017, Duke Energy and NCDEQ exchanged communications to
determine background soil sample locations and to develop provisional BTVs for soil
(Appendix A). The exchange is summarized as follows:
• December 15, 2016 - Duke Energy submitted the soil dataset recommended for
calculating background values for soil.
• April 28, 2017 - NCDEQ provided direction for site assessment and corrective
action.
• May 26, 2017 - Duke Energy submitted a revised background soil dataset
recommended for calculating background values for soil.
• July 7, 2017 - NCDEQ required the collection of additional samples based on the
review of the revised background soil dataset for developing soil BTVs.
• October 11, 2017 - Duke Energy submitted updated background values after
additional samples were collected in August 2017 to satisfy the requirement for
additional sampling.
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Duke Energy recalculated background soil values using an updated background soil
dataset provided in the 2018 CSA Update (SynTerra, 2018). NCDEQ provided approval
of soil BTVs in a letter to Duke Energy dated May 14, 2018 (Appendix A).
NCDEQ recognized that as new data are gathered, refinement of the BTVs might be
necessary. Thus, a periodic review of the soil dataset and recalculation of the soil BTVs
might occur.
Duke Energy presented an updated dataset for BTVs pertaining to constituents in soil
with the report Updated Background Threshold Values for Constituent Concentrations in Soil
(SynTerra, 2020a) in February 2020. Updated soil BTVs were calculated using data from
background unsaturated soil samples collected from January 2015 through August 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).
Approval of updated soil BTVs is pending (Appendix A). The 2020 updated
background datasets and BTVs are used throughout this report.
The 2018 approved soil BTVs pertaining to Sutton are provided in Table 3-1. The 2020
updated soil BTVs submitted to NCDEQ in February 2020 are also included.
Additional background soil samples have not been collected since August 2017;
therefore, the background soil dataset is current. The background soil dataset with the
appropriate POG PSRGs and BTVs for COIs is included in Appendix C, Table 4 (CAP
Content Section 4.B).
3.2 Background Concentrations for Groundwater
The groundwater system at Sutton can be divided into two hydrostratigraphic layers
(flow zones) to distinguish the interconnected groundwater system — the surficial zone
and the Peedee zone.
• Surficial zone — The surficial zone, which extends to approximately 50 feet
below ground surface (bgs), is subdivided into an upper surficial flow zone and
a lower surficial flow zone.
• Peedee zone — The Peedee flow zone extends to the deepest extent explored (150
feet bgs) during assessments at the Site. The Peedee is also subdivided into an
upper flow zone and a lower flow zone. The Peedee becomes finer -grained with
depth and often is a low -plasticity, clayey silt.
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Currently, the approved background groundwater monitoring wells within each of the
flow zones at Sutton include:
• Upper surficial zone: MW-5B, MW-8B, MW-37B, MW-41B
• Lower surficial zone: MW-5C, MW-8, MW-37C, MW-41C
• Upper Peedee zone: MW-5CD, MW-5D, MW-8D, MW-37CD, MW-37D, MW-41D
• Lower Peedee zone: MW-5RE, MW-8E, MW-37E, MW-41E
Wells MW-4, MW-4A, MW-4B, MW-5A, and MW-5E were formerly used as
background monitoring wells at the Site. Wells MW-4, MW-4A, and MW-4B were
replaced in the monitoring program by wells MW-37B and MW-37C in 2015, and well
MW-5E was replaced by well MW-5RE in 2016. MW-5A was removed from the
sampling plan during the Interim Monitoring Plan (IMP) optimization process because
sufficient background upper surficial data were available. The locations of the
background groundwater monitoring wells are shown in Figure 3-1.
During 2016 and 2017, Duke Energy and NCDEQ exchanged communications to
determine background groundwater sample locations and to develop BTVs pertaining
to groundwater (Appendix A). The exchange is summarized as follows:
• December 15, 2016 - Duke Energy submitted the dataset recommended for
calculating background values pertaining to groundwater.
• April 28, 2017 - NCDEQ provided direction for site assessment and corrective
action.
• May 26, 2017 - Duke Energy submitted a revised background groundwater
dataset recommended for use in calculating background values pertaining to
groundwater.
• July 7, 2017 - NCDEQ approved the revised background groundwater datasets
for developing groundwater BTVs pertaining to constituent concentrations in the
upper and lower surficial flow zones, with the exception of hexavalent
chromium for the lower surficial zone, pending collection of additional samples.
The revised background groundwater datasets pertaining to the upper and lower
Peedee flow zones were not approved due to insufficient number of samples.
• September 5, 2017 - Duke Energy submitted a summary of the revised
background groundwater dataset and the statistically determined background
values.
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• October 11, 2017 — NCDEQ approved a portion of groundwater BTVs pertaining
to Sutton. NCDEQ also required additional data collection for several
constituents, primarily in the upper and lower Peedee flow zones.
Duke Energy recalculated background groundwater values using an updated
background groundwater dataset provided in the 2018 CSA Update (SynTerra, 2018).
NCDEQ provided partial approval of groundwater BTVs in a letter to Duke Energy
dated May 14, 2018 (Appendix A). NCDEQ approved all upper and lower surficial flow
zone BTVs with the exception of cobalt in the upper surficial due to a transcription error
in the dataset. Methane and nitrate+nitrite BTVs for the upper and lower Peedee flow
zones and chromium(VI), total radium, and total uranium BTVs in the lower Peedee
flow zone were not approved due to an insufficient number of samples.
DWR recognized that as new data are gathered, refinement of the BTVs might be
necessary. Thus, a periodic review of the groundwater dataset and recalculation of the
groundwater BTVs might occur.
The updated background datasets for each flow zone were presented in the report
Updated Background Threshold Values for Constituent Concentrations in Groundwater
(SynTerra, 2020a). Duke Energy provided the report to NCDEQ on February 14, 2020.
The updated groundwater BTVs are calculated for data collected through September
2019, and were calculated in accordance with the guidance and statistical evaluation
methodologies agreed upon by Duke Energy and NCDEQ. NCDEQ DWR approval is
pending (Appendix A). The updated BTVs are referenced in text, tables, and figures
within this CAP Update.
The 2018 approved groundwater BTVs for COIs in each groundwater flow zone at
Sutton are provided in Table 3-2. The BTVs that were not approved by NCDEQ are
indicated in the table notes. The 2020 updated groundwater BTVs submitted to NCDEQ
in February 2020 are also included in Table 3-2. 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 zone. The background datasets for all COIs contained more than the required
minimum of 10 valid sample results within the surficial and Peedee flow zones at the
Site (Appendix C, Table 1) (CAP Content Section 4.0 and 5.A.a.vii).
3.3 Background Concentrations for Surface Water
Background surface water sample locations collected from the Cape Fear River are
located upstream or outside potential groundwater flow from the source areas to
surface water. Surface water background sample locations are outside of future
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groundwater -to -surface water migration pathways, as determined by groundwater
predictive modeling results (Appendix K).
Background surface water sample locations include three locations (SW-CFUP, SW-14,
and SW-15) in the Cape Fear River upstream of the Site (Figure 3-1). No true
background location is available in the cooling pond due to the manner in which Site
process water is circulated within the cooling pond. The background surface water
dataset is comprised of background samples from the Cape Fear River only.
Background surface water sample locations are located upgradient of potential
groundwater influence from the ash basins and potential source areas, such as NPDES
Outfall 001. Background surface water sample locations are shown on Figure 3-1.
Background surface water data are used for general comparative purposes. The
analytical results provide a comparative range of naturally occurring constituent
concentrations present at background locations. Background surface water analytical
dataset ranges are compared with North Carolina Administrative Code, Title 15A
Subchapter 02B — Surface Water and Wetlands Standards (02B) and U.S. Environmental
Protection Agency (USEPA) criteria in Table 3-3 (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 datasets from each location include data from four or more sampling
events. 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 March 2018 used to assess surface water
compliance for implementation of corrective action under 15A NCAC 02L .0106(k) and
(1). Analytical results from background surface water sample locations in the Cape Fear
River indicate COI concentrations are less than 02B standards.
3.4 Background Concentrations for Sediment
Background sediment sample locations are co -located with background surface water
sample locations in the Cape Fear River. Background sediment sample locations are
located upstream or outside potential groundwater migration from the source area.
Background sediment sample locations remain outside of future migration areas, as
determined by groundwater predictive modeling.
Background sediment sample locations include SW-CFUP, SW-14, and SW-15.
Background sediment sample locations are shown on Figure 3-1.
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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 3-4 (CAP Content Section 4.E). The sediment background dataset
with comparative POG PSRGs is included in Appendix C, Table 5 (CAP Content Section
4.E).
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4.0 CONCEPTUAL SITE MODEL
The Conceptual Site Model (CSM) is a summary of the hydrogeological conditions and
COI interactions specific to the Site. The purpose of the CSM that pertains to the Sutton
ash basins, FPA, FADA and FCPA is to provide a current understanding of constituents
with regard to the Site -specific geology/hydrogeology and geochemical processes that
control the potential presence and migration of COIs 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 a document titled "Environmental Cleanup
Best Management Practices: Effective Use of the Project Life Cycle Conceptual Site Model"
(USEPA, 2011). That document, which describes six CSM stages for an environmental
project life cycle, 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 Sutton CSM is consistent with Stage 4 "Characterization CSM," which
allows for iterative improvement of the site CSM during design of the remedy while
supporting development of remedy design basis (USEPA, 2011).
Changes to Site conditions, such as changes after basin closure (completed in 2019) and
excavation of the FADA and FPA (completed in 2020), have been incorporated into the
CSM. Predicted and observed effects would be compared on an ongoing basis to refine
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the understanding of groundwater flow and constituent transport relative to potential
receptors.
This information was used to augment the development of the corrective action
strategy, long-term Site monitoring, and periodic evaluation of remediation
performance metrics.
4.1 Site Geologic and Hydrogeologic Setting
(CAP Content Section 5.A.a)
Site Geologic Setting
(CAP Content Section 5.A.a)
The groundwater system at the Site is divided into the following three zones to
distinguish the interconnected aquifer system: the upper surficial flow layer, the lower
surficial flow layer, and the Peedee flow layer. The following is a summary of the
natural hydrostratigraphic unit assessment observations with the corresponding well
notation:
• Upper surficial zone (A, B): The upper surficial zone consists of well -sorted,
light-colored, and loose to moderately dense sand with little shell or organics.
The upper surficial zone grades gradually into the lower surficial zone generally
between 20 feet bgs and 30 feet bgs.
• Lower surficial zone (C): The lower surficial zone consists primarily of poorly
sorted sands with discontinuous layers of coarse sand and small gravel. Thin
laminae of silts and clays also occur in the lower portion of this zone. Wood
remnants were encountered in places near the contact with the upper Peedee
Formation, which is generally encountered at approximately 50 feet bgs.
• Peedee zone (CD, D, E): The Peedee Formation extends to the deepest extent
explored (150 feet bgs) during assessments at the Site. The upper portion of the
Peedee consists of dark gray or medium to dark green fine-grained sands, and
silt with clay lenses and laminae. At depths below 75 feet, thin layers of
sandstone are present at a few locations. The Peedee becomes finer -grained with
increasing depth and typically occurs as low -plasticity, clayey silt.
Site Hydrogeologk Setting
(CAP Content Section 5.A.a)
The Site is located in the Coastal Plain physiographic province of North Carolina. The
Coastal Plain comprises a wedge-shaped sequence of stratified marine and non -marine
unconsolidated sedimentary deposits on crystalline basement. The sedimentary
sequences range in age from recent to lower Cretaceous (Narkunas, 1980).
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The surficial sands are underlain by the Peedee Formation in the Site area. The Peedee
Formation contains fine- to medium -grained sand interbedded with gray to black
marine clay and silt. Sand beds are commonly gray or greenish gray and contain
varying amounts of glauconite. Thin beds of consolidated calcareous sandstone and
impure limestone are interlayered with the sands in some places. The Peedee Formation
contains a confining unit at the top in areas south of the Site. In the Wilmington area,
the Peedee confining unit has an average thickness of 10 feet. However, the Peedee
confining unit was not encountered at the Site.
In the eastern part of the North Carolina Coastal Plain, groundwater is obtained from
the surficial, Castle Hayne, and Peedee aquifers. The Coastal Plain groundwater system
consists of aquifers comprised of permeable sands, gravels, and limestone separated by
confining units of less permeable material.
According to Winner Jr. and Coble (1989), the surficial aquifer consists primarily of fine
sands, clays, shells, peat beds, and scattered deposits of coarse -grained material in the
form of relic beach ridges and floodplain alluvium. The areal extent of the surficial
aquifer in the Coastal Plain is approximately 25,000 square miles, with an average
thickness of 35 feet. The average estimated hydraulic conductivity is 29 feet per day
(Winner Jr. and Coble, 1989).
4.1.1 Groundwater Flow Direction and Gradients
(CAP Content Section 5.A.a.i)
Groundwater Flow Direction
Groundwater from the source areas currently flows northeast to southwest
under a low gradient to the discharge zone within the cooling pond or Cape Fear
River. A water level map of the surficial flow zones was constructed from
groundwater elevations obtained in February 2020 (Figure 4-1). The map shows
the post -basin excavation groundwater flow direction. February 2020 water level
elevations are presented in Table 4-1. There is a groundwater divide in the area
of the sand quarry/asphalt production plant east of the Site; groundwater beyond
that divide flows east toward the Northeast Cape Fear River. Depth to
groundwater at the Site is generally 5 feet bgs to 15 feet bgs. Prior to Site
alterations (ash pore water removal and construction of the on -Site CCP
Landfill), flow from the ash basins was radial, and the groundwater divide east
of the Site was located within the current on -Site CCP Landfill footprint. Those
prior Site conditions influenced COI distribution.
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Groundwater flow has been affected by source and ash pore water removal,
operation of the groundwater extraction system, water supply wells (both on -Site
and off -Site to the east), and changing conditions at the adjacent sand quarry to
the east. The Site is located approximately 12 miles west of the Atlantic Ocean. It
has been determined that the Peedee Formation is affected by saltwater intrusion
(SynTerra, 2018).
A cooling pond of approximately 1,100 acres is used at the Site. The cooling pond
is located between the ash basins and the Cape Fear River. Water is circulated
around the cooling pond by way of plant processes. Water enters the power
station through the intake from the cooling pond and exits through the effluent
canal, and then flows counter -clockwise within the cooling pond before
returning to the plant for reuse. Make-up water is pumped from the Cape Fear
River on the northwest side of the cooling pond.
Basin closure resulted in the return of groundwater flow to the natural
conditions of east to west. Empirical Site data from more than 40 monitoring
events over multiple seasonal variations and groundwater flow and transport
modeling simulations support that groundwater flow is currently away from
water supply wells located east of the source areas (Appendix F).
Eastern Site Boundary
Based on groundwater elevation measurements, the eastern portion of the Site is
currently upgradient of the former ash basins, with the exception of the area
within the localized eastward flow induced by the groundwater extraction
system. However, during the CSA, before basin closure and the installation of
the groundwater extraction system, groundwater elevation measurements
indicated radial flow from the 1971 ash basin, which resulted in COI migration
eastward. Previous data also indicated that a local groundwater divide was
present in the northern portion of the current on -Site CCP Landfill. Depth -to -
water along the eastern Site boundary ranges from 10 feet bgs to 15 feet bgs,
which is deeper than in other areas due to topography.
The groundwater extraction system, installed in 2017, was designed to restore
groundwater quality along the eastern property boundary. Groundwater
elevation data indicate the local groundwater divide is now present east of the
Site, in the area of the sand quarry. Due to the high permeability of the surficial
aquifer, observed drawdown in wells near the groundwater extraction system is
limited. Hydrographs of select wells near the eastern property line and extraction
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system showing the limited drawdown in the area are included as Figure 4-2a.
Since basin closure and construction of the on -Site CCP Landfill, data indicate
that groundwater flow is consistently northeast to southwest across the Site.
Four Site production wells are in operation in the eastern portion of the Site
along Sutton Steam Plant Road. These wells are located south of the
groundwater extraction system and are screened in the surficial flow zones. The
wells, operated intermittently, appear to create a more southerly (rather than
southwesterly) flow component to groundwater in that area. COI migration does
not appear to be affected by these wells.
The 1971 BasinlFPA and 1984 Ash Basin
Closure of the 1971 and 1984 ash basins was completed in July 2019. The 1971 ash
basin was constructed by excavating (dredging) below the water table to a depth
of approximately 40 feet below grade in some areas. Therefore, with the elevated
hydraulic head in the 1971 ash basin, there might have been approximately 45 to
50 feet of saturated ash present before excavation.
The 1971 ash basin is bound by the 1984 ash basin to the north and east, by the
effluent canal to the south, and by the cooling pond to the west. The effluent
canal and the cooling pond affect the groundwater elevation in the surficial
aquifer west and south of the 1971 ash basin. Prior to closure, the ash basin pore
water seeped into the porous sands of the surficial aquifer underneath the
unlined 1971 ash basin and into the perimeter dam. The contrast of
permeabilities across the surficial/Peedee formational contact reduces downward
vertical groundwater flow. Therefore, the preferential flow path for COIs from
the ash basins is horizontal within the lower surficial flow zone. Hydrographs of
select wells near the southeast corner of the 1971 ash basin are included as
Figure 4-2b. As shown on the hydrographs, water levels in wells near the 1971
ash basin are higher than those in downgradient wells. Prior to excavation, the
dam elevation was approximately 28 feet NAVD 88, and the ash pore water
elevation was approximately 12 feet NAVD 88. For comparison purposes, the
surrounding ground elevation is approximately 9.5 feet NAVD 88, and the
cooling pond normal water level is approximately 8 feet NAVD 88.
The 1971 ash basin has been excavated and dredged and is currently submerged;
water within the former ash basin is separated by sheet piling from the effluent
canal and the cooling pond.
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The 1984 ash basin, constructed at approximately original ground surface,
contained a clay liner. Ponded water with an estimated elevation of 18 feet
NAVD 88 was generally present in the northern portion of the basin, prior to
basin closure, compared with the cooling pond elevation of 8 feet NAVD 88. The
1984 ash basin had Outfall 004 to the cooling pond that was in operation from
1984 to 2001. The basin rarely had a discharge through Outfall 004 to the cooling
pond. Normally, water was piped to NPDES Outfall 001. In 2001, an
underground line was installed from the 1984 ash basin outfall to the outfall at
the Cape Fear River. This line could not fully accommodate all of the 1984 ash
basin discharge. There was still a portion of discharge from the 1984 ash basin to
the cooling pond between 2001 and 2015 when the cooling pond was reclassified
as waters of the state.
Groundwater flow from the 1984 ash basin prior to closure was radial, under the
dam to the west, north, east, and south. Current data indicate groundwater flow
is westward toward the cooling pond. Depth to groundwater in this area is
generally 5 feet bgs to 10 feet bgs. Hydrographs of select wells near the northern
waste boundary of the 1984 ash basin are included as Figure 4-2c. The
hydrographs show a weaker horizontal gradient near the 1984 basin compared
with the historical gradients near the 1971 basin (Figure 4-2b). This indicates the
1984 basin created less localized mounding than the 1971 basin.
The FPA, adjacent to the southeast corner of the 1971 basin, was a small settling
basin that was used when the Site was co -firing fuel oil for a few years during
the 1970s. At that time, sluice waters were directed to the settling basin located in
the FPA before being directed to the 1971 basin. The FPA was subsequently filled
with solids, including CCR. The FPA has been determined to be an additional
source of COIs, primarily arsenic and vanadium, to groundwater southeast of the
area.
The FADA and FCPA
Topography across the FADA is nearly flat, decreasing slightly to the south.
Groundwater is approximately three feet bgs in the FADA. Groundwater flow
direction in the FADA is west to southwest toward the cooling pond and the
intake canal. As part of closure, a portion of the area would become part of the
Plant's effluent canal.
The FCPA, located adjacent to the FADA to the south, is approximately 14 acres.
The area around the FCPA is topographically bowl -shaped with groundwater
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approximately three feet bgs. Groundwater flow in the FCPA is to the southwest,
toward the intake canal and Cape Fear River. The footprint of the FCPA has been
regraded and it now collects stormwater from the former coal -burning facility. A
collection sump is located in the southwest corner of the FCPA. Water from this
sump is periodically pumped into the effluent canal as a permitted NPDES
Outfall. The groundwater gradient in the FADA and FCPA is greater than in
other areas of the Site, dropping almost 3 feet from MW-16 in the northeast
corner to MW-43 in the southwest corner (Figure 4-1). Pumping of collected
stormwater from the FCPA might be affecting the groundwater level in the
adjacent MW-43 well cluster and creating the steeper groundwater gradient in
this area. Hydrographs of select wells near the FADA and FCPA illustrate this
hydraulic gradient and are included as Figure 4-2d.
Groundwater Seepage Velocities
(CAP Content Section 5.A.a.ii)
Groundwater seepage velocities were calculated using horizontal hydraulic
gradients (Table 4-2) determined from water level measurements collected in
February 2020 (or the most recent data available for abandoned wells). Hydraulic
conductivity (K) and effective porosity (ne) values were taken from the updated
flow and transport model (Appendix F). Calibrated hydraulic conductivity and
porosity values for each flow zone were used to align velocity calculations with
model predictions.
The horizontal hydraulic conductivities (K) used are:
• 60 feet per day (ft/day) in the upper surficial flow zone
• 125 ft/day in the lower surficial flow zone
The effective porosities used are 30 percent in the upper and lower surficial flow
zones.
The horizontal groundwater seepage flow velocity (vs) can be estimated using a
modified form of the Darcy Equation:
where dl is the gradient.
K dh
19S = n(dl) e
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Using the February 2020 groundwater elevation data, the average horizontal
groundwater flow velocity at the Site is:
• 34 feet per year (ft/yr) in the upper surficial flow zone
• 82 ft/yr in the lower surficial flow zone
Near the 1971 and 1984 ash basins, the calculated horizontal groundwater
seepage velocity is approximately:
• 38 ft/yr in the upper surficial flow zone
• 156 ft/yr in the lower surficial flow zone
In the FADA and FCPA, the calculated horizontal groundwater seepage velocity
was approximately:
• 120 ft/yr in the upper surficial flow zone
• 246 ft/yr in the lower surficial flow zone
COI plume patterns, particularly those of boron, total dissolved solids (TDS), and
strontium, indicate groundwater flow was once radial from the basins.
Hydraulic Gradients
(CAP Content Section 5.A.a.i)
Hydraulic gradients were calculated from water levels collected from various
well clusters located near the ash basins, along the eastern property line, and off -
Site to the east. The water level elevations collected in February 2020 are
summarized in Table 4-1.
Horizontal hydraulic gradients across the Site are low, generally less than 0.0006
foot per foot (ft/ft). This is relatively consistent across the Site. However, as
previously stated, the horizontal gradient in the FADA and FCPA is generally
0.0026 ft/ft, but might increase due to the periodic operation of a sump pump.
Based on hydraulic gradient calculations using February 2020 groundwater
elevation data, the average horizontal hydraulic gradients for each flow zone are:
0.0006 ft/ft (upper surficial flow zone), 0.001 ft/ft (lower surficial flow zone), and
0.0007 ft/ft (upper Peedee flow zone) (Table 4-2). The calculated horizontal
hydraulic gradients generally align with simulated groundwater flow directions
(Figures 4-3a and 4-3b).
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Vertical hydraulic gradients were calculated at clustered wells throughout the
Site from the water level data and the midpoint elevations of the well screens
(Table 4-3). Vertical gradients vary throughout the Site; however, in general,
vertical gradients are slight (from 0.001 to 0.002 ft/ft). Historically, downward
gradients, between the surficial and Peedee flow zones, have been observed at
MW-23, near the ash basins. Upward gradients have been observed east of the
Site, in off -Site well cluster SMW-6B/C/D. Changes in vertical gradients have
been observed along the eastern Site boundary in the area of the groundwater
extraction wells, where gradients change from upward to downward at AW-2
and MW-12R/AW-6RD. This change could be due to the operation of the
extraction wells. Upward vertical gradients are also observed in wells near the
cooling pond, indicating groundwater from the upper and lower surficial flow
zones is discharging to the cooling pond.
Eastern Site Boundary
Based on recent water levels in wells installed along the eastern Site boundary
(well clusters AW-2, AW-5, and MW-12R/AW-6RD), vertical gradients are
generally flat between the lower surficial and upper Peedee flow zones. Vertical
migration of COIs is limited by the low relative permeability of the upper Peedee
zone. Monitoring well cluster gradients potentially influenced by the extraction
wells, identified as wells that presently have upward gradients but had
downward gradients under pre -pumping conditions, include AW-5C/D and
MW-12R/AW-6RD (Figure 4-2a). Upward gradients are also noted at background
locations MW-37C/D, MW-38C/D, and MW-40C/D, and at off -Site wells SMW-
6C/D (Table 4-3).
The greatest change in vertical gradient along the recovery well line, compared
with pre -pumping conditions, is observed at MW-12R/AW-6RD (Figure 4-2a).
Prior to the startup of the extraction system, this well cluster exhibited a
downward vertical gradient; however, as stated in the 2019 IAP report, a slight
upward vertical gradient in this area is observed (SynTerra, 2020). The
groundwater extraction system appears to be inducing an upward vertical
gradient in some areas; thus, the groundwater chemistry could be affected by the
saltwater intrusion occurring in the Peedee flow zone (SynTerra, 2018). No
obvious indications of this influence has yet been observed in groundwater COI
concentrations.
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1971 and 1984 Ash Basins
At compliance well cluster MW-23, located at the compliance boundary east of
the 1971 basin, no vertical gradient is observed. At well cluster MW-40, located
adjacent to the northwest portion of the 1984 basin, a slight upward gradient is
observed between the lower surficial and upper Peedee flow zones. This upward
gradient has been noted consistently since well installation in 2018; also, this
upward gradient indicates groundwater -to -surface water discharge to the nearby
cooling pond.
FADAIFCPA
At well cluster MW-16, located in the northeast corner of the FADA, no vertical
gradient was observed. At well cluster MW-44, located at the southwestern
downgradient edge of the FCPA, a slight downward gradient was observed
between the upper surficial and lower surficial flow zones. This downward
gradient indicates groundwater migration beneath the intake canal toward the
Cape Fear River.
4.1.2 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 basins and other source areas relative to specific Site
features such as manmade and natural drainage features, engineered drains,
streams, 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 upper
surficial flow zone, the lower surficial flow zone, and the Peedee flow zone. The
upper and lower surficial flow zones consist of silty sands with more coarse
material (gravel, coarse sands) present in the lower surficial flow zone.
Groundwater flow through this zone is typical of flow through a porous media
under relatively high hydraulic conductivities. The underlying Peedee flow zone
consists of tight silts and clays with significantly lower hydraulic conductivities.
Preferential groundwater flow at the contact between the lower surficial and the
Peedee flow zones is expected to be lateral.
An anthropogenic subsurface heterogeneity previously existed at the 1971 basin.
The surficial zone was excavated to a depth of approximately 40 feet bgs to
construct the 1971 basin. Sluicing of ash to the basin created a mounding effect
and radial groundwater flow from the basin. A preferential flow path existed
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vertically within the basin and then laterally within the lower surficial flow zone
along the Peedee flow zone contact.
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. (SynTerra, 2018a).
A higher than normal horizontal hydraulic gradient exists in Source Area 2,
potentially attributable to the operation of the stormwater collection sump in the
southwest corner of the FCPA. Water from this sump is periodically pumped
into the effluent canal in accordance with the terms of NPDES permit
NC0001422. This appears to cause a horizontal groundwater gradient in Source
Area 2 that is greater than those in other areas of the Site, as water levels
decrease almost 3 feet from MW-16 in the northeast corner of the FADA to MW-
43 in the southwest corner of the FCPA (Figure 4-1). The effects of pumping from
the stormwater collection sump are observed in the adjacent MW-43 well cluster
(Figure 4-2d).
4.1.3 Bedrock Matrix Diffusion and Flow
(CAP Content Section 5.A.a.iv)
No bedrock has been encountered at the Site; therefore, bedrock matrix diffusion
and flow is not applicable to Sutton.
4.1.4 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 Coastal Plain physiographic province of
North Carolina. The metals and inorganic constituents occur in soil,
groundwater, surface water, and sediment. During the Sutton CSA efforts, soil
samples were collected during drilling activities and analyzed for metals and
inorganic constituents. Results indicate that soil at Sutton contains naturally
occurring constituents that are also typically related to CCR material and likely
affect the chemistry of groundwater at the Site. Iron is commonly present in
background soil samples at concentrations up to 10 times the POG PSRG value
[150 milligrams per kilogram (mg/kg)] (Appendix C, Table 4). Analytical results
for groundwater at background locations indicate that arsenic, cobalt, iron,
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manganese, and vanadium are present at concentrations greater than 02L
standards/IMACs (Appendix C, Table 1).
These results suggest that arsenic, cobalt, iron, manganese, and vanadium occur
naturally in soil and groundwater at the Site. Therefore, when applicable,
concentrations of these constituents at the Site are compared with background
values.
4.2 Location of Source Areas within Hydrogeologic Setting
(CAP Content Section S.A.b)
The ash basins, located northwest of the plant, were bounded by earthen dams on all
sides (Figure 1-1). The FADA, located adjacent to the former coal -burning plant to the
west, was bounded by the cooling pond to the west, the former coal pile to the south,
the plant to the southeast, and the effluent canal to the north. The former coal pile was
bounded by the FADA to the north, the intake canal to the south and west, and the
former coal -burning plant property to the east.
4.3 Summary of Potential Receptors
(CAP Content Section 5.A.c)
G.S. 130A-309.201(13) defines a 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 NORR CSA guidance dated August 13,
2014, receptors cited in this section refer to public and private water supply wells and
surface water features.
The former potential receptors included on -Site and off -Site water supply wells to the
east of the source areas. These potential receptors have been mitigated through the
change in the groundwater flow direction, the operation of the extraction well system,
and installation of water lines and filtration systems.
The current potential surface water receptors, the cooling pond and the Cape Fear
River, have been evaluated.
The Site -specific risk assessment conducted for the ash basins and adjacent source areas
indicates no measurable difference between evaluated Site -related risks and risks
imposed by background concentrations. It is determined that there is no identified
material increases in risks to human health or ecological receptors related to the ash
basins and additional source areas.
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4.3.1 Surface Water
The Site is located in the Cape Fear River watershed. The source areas are
separated from the Cape Fear River to the west by the cooling pond. The Site's
cooling pond is a closed -circulation system. An intake on the Cape Fear River
supplies recharge water for the cooling pond.
Surface water bodies that bound the Sutton facility and corresponding surface
water classifications are listed in the following table (CAP Content Section
6.B.a.iii).
Adjacent Surface
Water Body
Surface Water Classification
(15A NCAC 02B .0300)
Cape Fear River
C, Sw
Cooling Pond (Lake Sutton)
C, Sw
Notes:
1) Class C waters are protected for secondary recreation, fishing, wildlife, and aquatic life,
including propagation and survival.
Figure 4-4 provides 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 [from the Natural Resources
Technical Report (NRTR) prepared by AMEC Foster Wheeler (June 2015)] (CAP
Content Section 6.B.a). In addition, the final permitted Outfall location under the
NPDES permit is also shown on Figure 4-4 (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
concentrations greater than surface water criteria contained in 15A NCAC 02B
.0200. 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, TDS,
thallium, total hardness, and zinc.
Surface water samples were collected from the cooling pond and the Cape Fear
River to confirm groundwater downgradient of Source Area 1 has not resulted in
surface water concentrations greater than 02B water quality criteria. 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 Cape Fear River. Because the cooling pond is closed circular system,
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no appropriate background location exists. Samples collected up -river of the
cooling pond in the Cape Fear River are appropriate for use as background.
Analytical results were evaluated with respect to 02B surface water quality
criteria 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 cooling pond and Cape Fear 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 less than laboratory detection
limits or concentrations were generally comparable to background
concentrations.
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 Sutton groundwater
discharge to surface water and the evaluation of surface waters to evaluate
compliance with 15A NCAC 02B .0200 was submitted to NCDEQ in January 2020
and is included in Appendix K. This report does not include the Cape Fear River
sample near the intake canal (SW-17). That location was added to support the
future conditions evaluation (Appendix K). NCDEQ approved the current
conditions surface water evaluation and requested that sediment results be
discussed in this CAP Update. Sediment results are discussed in Section 5.1.2.5.
The evaluation of current surface water quality conditions at Sutton confirmed
groundwater migration from the source areas has not resulted in constituent
concentrations greater than 02B surface water quality criteria at the cooling pond
or Cape Fear River.
4.3.1.1 Environmental Assessment of Lake Sutton
The following discussion is a summary of historical and recent
environmental assessment of the NPDES permitted cooling pond.
Additional detail is included as Attachment 11 to the Updated Risk
Assessment (Appendix E).
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Lake Sutton was constructed in 1972 as part of a wastewater treatment
system to provide cooling water for the coal-fired L.V. Sutton Steam Electric
Plant and to receive ash pond effluent, both activities authorized by NPDES
permit NC0001422. The lake and facility continued to operate as permitted
until December of 2013, when the coal plant was permanently shut down
and was replaced by the combined -cycle natural gas -fired L.V. Sutton
Energy Complex. During the period of coal-fired operations, Lake Sutton
was not designated waters of the State; therefore the lake was neither
subject to compliance with water quality standards nor were there any
NPDES permit monitoring requirements of Lake Sutton itself. Nevertheless,
Duke Energy conducted a robust monitoring program on the lake from the
1970s to present.
Lake Sutton has been monitored by Duke Energy since 1972. 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. Trace element (arsenic, copper, selenium) monitoring of sediment
is conducted annually in accordance with a study plan approved by
NCDEQ. These assessments have demonstrated that Lake Sutton has been
an environmentally healthy and functioning ecosystem, and ongoing
sampling programs have been established in an effort to support the
continued health of these systems. Furthermore, these data indicate that
there have been no significant effects to the local aquatic systems related to
coal ash constituents over the past 50 years. More information related to
environmental health assessments of the cooling pond — including
sampling programs, water quality, fish community assessments, and fish
tissue analysis — can be found in Appendix E.
4.3.2 Availability of Public Water Supply
Public water is available at the Site in the form of a Cape Fear Public Utility
Authority (CFPUA) water line servicing Site personnel trailers. Public water is
also available to properties along US Highway 421 and on Fredrickson Road. The
CFPUA provides water service to those areas. Properties within a 0.5-mile radius
of the Site's compliance boundary are either supplied public water by CFPUA or
have a supply well. Duke Energy has provided water filtration systems to
properties with supply wells where the option was accepted.
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4.3.3 Water Supply Wells
(CAP Content Section 6.B.b)
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 basins compliance boundaries, have been
reported to NCDEQ:
• Drinking Water Well and Receptor Survey Report (SynTerra, September 2014)
• Supplement to Drinking Water Well and Receptor Survey (SynTerra,
November 2014)
• Update to Drinking Water Well and Receptor Survey (SynTerra, September
2016)
A total of 30 supply wells were identified within the 0.5-mile radius of the ash
basin compliance boundary and were offered either a connection to municipal
water or a filtration system. Of the 30 property owners, 17 either opted out of the
option to connect to a water treatment system or did not respond to the offer
(Table 4-5). These properties are located east of the ash basins (Figure 4-5). The
0.5-mile radius from the ash basin compliance boundary, for which data are
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 (Figure 4-5). COIs historically migrated off -Site to the east
eventually toward properties with supply wells. Supply wells were sampled to
determine the extent of COI migration (Table 4-4). Boron was not detected at
concentrations greater than 02L; however, concentrations were greater than
background.
As discussed in Section 4.1.1, due to flow reversal, nearby supply wells and
wellhead protection areas are no longer located downgradient of the source
areas. 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.
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Provision of Alternative Water Supply
(CAP Content Section 6.B.b.i)
Duke Energy identified 30 supply wells within the survey radius. None of the
properties are residential. Property eligibility for provision of an alternate water
supply under HB 630 was contingent that the property did not include:
• A business
• A church
• A school
• Connection to the public water supplier
• An empty lot
All the properties in the area are either business related, are an empty lot, or have
a connection to public water available. However, Duke Energy voluntarily
connected four properties to the CFPUA municipal water supply system and
installed water filtration systems on eight water supply wells located at
surrounding properties (Figure 4-5). One additional property located on U.S.
Highway 421 North is planned to be connected to the CFPUA municipal water
supply system in 2020 (Table 4-5).
On October 12, 2018, the NCDEQ confirmed that Duke Energy satisfactorily
completed the alternate water provision under CAMA, G.S. Section 130A-
309.211(c1) (Appendix D) due to the lack of eligible properties in the area.
4.3.4 Future Groundwater Use Area
Water supply wells were identified within a 0.5-mile radius of the Site ash basin
compliance boundary. Two CFPUA wells identified within this radius were
abandoned. The CFPUA supplies water to some properties within this area with
a direct line. Due to the reversal of groundwater flow previously referenced in
this report, water supply wells within a 0.5-mile radius of the Site compliance
boundary are no longer downgradient, and therefore, no future groundwater use
areas are anticipated downgradient of the source areas.
Water supply well locations with reference to properties connected to the public
water supply, along with vacant parcels and properties whose owners have
either decided to opt -out of the water treatment system program or did not
respond to the offer are listed on Table 4-5. Those water supply wells are now
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located upgradient of the source areas and are outside of the area of
groundwater affected by source areas.
Duke Energy has a performance monitoring plan in place, with details of the
plan outlined in the Permanent Water Supply — Water Treatment Systems,
Performance Monitoring Plan (Duke Energy, 2017). Duke Energy provides
quarterly maintenance of the water treatment systems, which includes
replenishing expendables (salt for brine tank and neutralizer media) and
providing system checks and needed adjustments. Laboratory samples of pre-
treated and treated water are collected annually to coincide with system
installation, unless there is evidence the system is not performing properly, in
which case samples would be collected more frequently.
4.4 Summary of Human Health and Ecological Risk Assessment
Results
(CAP Content Section 5.A.d)
The 2018 CSA Update report concluded there was no evidence of unacceptable risks to
humans and wildlife at the Site attributed to CCR constituent migration in groundwater
from the ash basins and FADA. The 2016 risk assessment concluded there was no
evidence of unacceptable risks to humans and wildlife exposed to CCR constituents.
The 2020 risk assessment update (Appendix E) concluded there is no evidence of
unacceptable risks to human and ecological receptors exposed to environmental media
potentially affected by the source areas at Sutton. This conclusion is further supported
by multiple water quality and biological assessments conducted by Duke Energy as part
of the NPDES monitoring program.
The update to the human health and ecological risk assessment would support a Risk
Classification of "Low" for groundwater -related considerations.
4.5 CSM Summary
The Sutton CSM presented herein summarizes the 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 geologic/hydrogeologic and
geochemical processes that control the migration and potential effects of constituents in
various media and potential exposure pathways to human and ecological receptors.
In summary, ash was initially sluiced onto open ground for lay of land deposition at the
FADA. The ash basins were later constructed of earthen berms. The 1971 basin was
unlined and extended approximately 40 feet below grade, into the surficial flow zone.
The 1984 basin was constructed with earthen berms and a clay liner approximately at
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Site grade. The ash basin dams were constructed at an elevation of approximately 28
feet NAVD 88 and the operating head was approximately 12 feet NAVD 88. The coal
pile was located in an unlined area at Site grade.
During operation of the ash basins, groundwater flow was radial from the basins and to
the southwest toward the Cape Fear River from the FADA and FCPA. The eastward
flow was enhanced by the operation of off -Site industrial water supply wells. The low
hydraulic conductivity of the zone below the surficial flow zone also created
preferential flow laterally along the surficial/Peedee contact.
Site changes — including removal of ash pore water, basin excavation, and construction
of the on -Site CCP Landfill — have resulted in an apparent shift of groundwater flow to
naturally occurring conditions (east to west). Water supply wells located east of the Site
are now located upgradient of the source areas.
Risk assessment results conclude that there are no identified material increases in risks
to human health or ecological receptors related to the ash basins, FPA, FADA and/or
FCPA.
Analytical results obtained from surface water samples collected from the cooling pond
and the Cape Fear River during low flow conditions indicate that the groundwater that
migrates from the ash basins, FPA, FADA, or FCPA is not resulting in COI
concentrations greater than 02B surface water criteria. Comparisons with the USEPA
criteria confirm that the interception of the Site's groundwater by the surface waters
does not result in adversely affected surface waters.
Through ash basin closure, the hydraulic head and the rate of constituent migration
from the ash basins, FPA, FADA, and FCPA to the groundwater system have been
reduced as described above. Future predicted flow patterns show that groundwater
flow, under post -ash basin excavation conditions, is expected to continue west toward
the Cape Fear River, away from water supply wells.
Multiple lines of evidence, based on the large dataset generated for Sutton, have been
used to develop this CSM. In compliance with G.S. Section 130A-309.211 (amended by
CAMA), the CSM supports development of this CAP Update pertaining to the Sutton
ash basins, FPA, FADA, and FCPA.
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5.0 CORRECTIVE ACTION APPROACH FOR SOURCE AREAS
(CAP Content Section 6)
Groundwater contains varying concentrations of naturally occurring inorganic
constituents. Constituents sporadically detected in groundwater at concentrations
slightly greater than the applicable standard do not necessarily demonstrate horizontal
or vertical distribution of COI -affected groundwater migration from source areas (ash
basins and adjacent sources). COI concentrations were evaluated against the applicable
COI criterion, which is defined as the 02L Standard, IMAC, or BTV, whichever is
greater. Constituents with concentrations greater than COI criteria were evaluated to
determine whether the level of concentration is present due to source areas. COIs are
those constituents identified from the "constituent management process" described
below. This evaluation assisted in identifying whether a unit is subject to corrective
action under G.S. Section 130A-309.211 and 15A NCAC 02L .0106.
A COI Management Plan was developed at the request of NCDEQ to evaluate and
summarize COI concentrations in groundwater at the Site. Results of this COI
Management Plan are used to identify areas that might require corrective action and to
determine appropriate Site -specific mapping of COI concentrations on figures based on
the actual distribution of each COI in Site groundwater. Table 5-1 presents the COI
management matrix for determining COIs subject to corrective action downgradient of
Source Area 1. Table 5-9 presents the COI management matrix for determining COIs
subject to corrective action downgradient of Source Area 2.
• Groundwater COIs to be addressed with corrective action are those which
exhibit concentrations in groundwater greater than COI criteria at or beyond the
compliance boundary.
• 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 COIs that do not exhibit a
discernable plume or COIs that have no correlation with other soluble
constituents associated with coal ash or another primary source (e.g., boron or
sulfate).
Numerous Site assessment activities have been completed to date and support the CSM.
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 used within the COI Management Plan include the hydrogeologic setting,
groundwater hydraulics, constituent concentrations, groundwater flow and transport
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modeling results, geochemical modeling results, and groundwater geochemical
conditions.
A three -step process was used in the COI Management Plan approach:
Step 1. Regulatory Review: Evaluate the applicable regulatory context
Step 2. COI Mobility: Evaluate of the mobility of target constituents
Step 3. COI Distribution: Determine the distribution of constituents within Site
groundwater
The primary goal of the COI Management Plan is to use science -based evidence to
determine the realistic distribution and behavior of coal and coal ash -related
constituents in groundwater. The COI Management Plan presents multiple lines of
evidence to understand the actual presence of COIs in the subsurface at the Site, uses
the results from the COI Management Plan approach to identify Site -specific COIs for
inclusion in corrective action planning, and presents the COI mapping approach for the
CAP. The COI Management Plan approach is summarized below.
Step 1; Regulatory Review
Step 1 of the COI Management Plan process starts with the current COI list identified in
the CSA Update (SynTerra, 2018a) and 2019 IMP submitted by Duke Energy on March
20, 2019, and approved by NCDEQ on April 4, 2019 (Appendix A).
NCDEQ recommended use of a lower confidence limit (LCL95) concentration rather
than the central tendency value (CTV) for calculating a statistical dataset (compliance
values) to evaluate Site COIs for corrective action (Appendix A). Duke Energy
proposed the calculation of CTVs when insufficient data were available to calculate an
LCL95 (Appendix A). NCDEQ agreed with Duke Energy's statistical approach in an
email dated May 5, 2020. LCL95 or CTV concentrations for each COI were calculated.
A statistical approach was used to calculate compliance values — either the LCL95 or
CTV — for Site groundwater COIs. A summary of COI compliance value calculation
results is presented in Table 5-4. The methodology for calculating COI compliance
values is presented in the technical memorandum, COI Compliance Value Calculation
(Appendix H).
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The compliance value calculations conducted using groundwater data collected from
January 1, 2015 through March 2020 produced three possible outputs: LCL95, CTV, or
not calculated (NC). The output for a COI at an individual groundwater monitoring
well depends on the following:
• The most recent sample collection date that yielded valid groundwater data
• The number of valid groundwater data
• The percentage of non -detections (constituent concentration less than the
laboratory reporting limit) in the COI dataset
The compliance value calculations will produce an LCL95 if each of the following
conditions exist:
• There are four or more valid data pertaining to a COI from an individual well.
• Less than 50 percent of the valid data are non -detects.
The compliance value calculations will produce a CTV if:
• The date when valid groundwater samples were collected was in 2019 or 2020,
and one of the following occurred:
o There are fewer than four valid data pertaining to a COI from an
individual well.
o The percentage of non -detects in the valid dataset is 50 percent or greater.
o A non -parametric distribution is selected, but there is insufficient data
coverage (typically when n = 4) to calculate an LCL95 with statistical
confidence.
The compliance value calculations will produce an NC if the criteria above is not
satisfied because one of the following situations exists:
• An LCL cannot be calculated and the most recent valid data pertaining to a COI
was collected before 2019.
• Analysis pertaining to the COI was not conducted on any groundwater samples
collected from an individual monitoring well.
COI compliance value concentrations were screened against their respective COI
criterion defined as the 02L standard/IMAC or BTV (whichever is greater), or if
applicable, against the calculated remediation goals. In addition, COI concentrations
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were compared with their respective COI criterion for groundwater monitoring
locations at or beyond the compliance boundary.
Step 2: COI Mobility
Step 2 of the COI Management Plan process evaluates COI mobility to identify
hydrogeologic and geochemical conditions and relative COI mobility based on:
• Review of regulatory agency and peer -reviewed literature to identify general
geochemical characteristics of COIs
• Analysis of empirical data and results from geochemical and flow and transport
modeling conducted for the Site
• Identification of COI -specific mobility as conservative (non -reactive), non -
conservative (reactive), or variably reactive based on results from geochemical
modeling (Appendix G)
Step 3: COI Distribution
Step 3 of the COI Management Plan process evaluates the relative presence of COIs in
Site groundwater. Descriptions of the horizontal and vertical distribution of COIs with
LCL95/CTV concentrations greater than COI criteria, or if applicable, greater than
calculated remediation goals, at or beyond the compliance boundary are summarized in
Section 5.1.3 (Source Area 1) and Section 5.6.3 (Source Area 2). The COI Management
Plan approach considers the distribution of COIs on a Site -wide basis. These
distributions are used for planning appropriate corrective action as well as determining
which COIs to map on figures.
Primary descriptions of COI distributions include plume -like distributions for relatively
mobile COIs such as boron and isolated location(s) for COIs that do not exhibit plume -
like distributions. Boron is the COI with the most plume -like distribution. Some COIs
with isolated concentrations greater than applicable criteria are not associated with the
boron plume; those isolated COI concentrations are presented in more detail in
Table 5-1 (Source Area 1) and Table 5-9 (Source Area 2) within the context of the Site
CSM.
The rationale for inclusion of COIs in mapping on figures in the 2020 CAP Update is
based on the horizontal and vertical distribution of COIs with concentrations greater
than respective COI criterion. Wells that have COI concentration(s) greater than the COI
criterion are listed in COI management tables [Table 5-1 (Source Area 1) and Table 5-9
(Source Area 2)].
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Outcome of COI Management Plan Process
Constituents with concentrations greater than the COI criterion beyond the compliance
boundary were grouped by geochemical behavior and mobility. A comprehensive
evaluation of available data was used to demonstrate constituent distribution and
correlation with other soluble constituents associated with coal or coal ash and to
evaluate the spatial occurrence with a discernable COI 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 areas in
the direction of groundwater flow at concentrations greater than the COI criterion with
a discernable plume that correlates with other soluble constituents.
COIs were assigned to mobility categories based on geochemical modeling results and
information derived from peer -reviewed literature. COI mobility categories are based
on the concept of conservative versus non -conservative COIs introduced by NCDEQ in
the September 10, 2019, CAP Content Guidance document. The use of three mobility
categories for COIs was first introduced during in -person COI Management meetings
held with NCDEQ in September 2019 pertaining to other Duke Energy facilities. Based
on geochemical modeling results, COI mobility categories were expanded from
conservative versus non -conservative to include the following:
• Conservative, Non -Reactive COIs: Boron, calcium, chloride, fluoride, lithium,
magnesium, potassium, sodium, and TDS. Site -specific geochemical model
simulations support that these constituents would migrate conservatively [Ka
values less than 1 liter per kilogram (L/kg)] as soluble species under most
conditions, and that the mobility of these COIs would not change significantly
due to current geochemical conditions or potential geochemical changes related
to remedial actions.
• Non -Conservative, Reactive COIs: Arsenic, selenium, and vanadium. Site -
specific geochemical model simulations support that these constituents are
subject to significant attenuation in most cases and have high partition coefficient
(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 COIs: Cobalt, hexavalent chromium, iron, manganese,
molybdenum, strontium, and sulfate. Site -specific geochemical model
simulations, and resulting Ka values, indicate these constituents might react
conservatively or non -conservatively in relation to geochemical changes and are
dependent on the pH and reduction/oxidation potential (Ex) of the system. The
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sensitivity of these COIs to the groundwater pH and Ex indicates that these
constituents could respond to natural changes, such as water level fluctuations
imposed by seasonality, or dredging and source control activities that have the
potential to change the groundwater pH or Ex.
As discussed in the CSA Update (SynTerra, 2018a) and the 2018 CAMA Annual Interim
Monitoring Report (SynTerra, 2019c), not all constituents with concentrations greater
than background values can be attributed to the source area(s). Constituents
sporadically detected in groundwater at concentrations slightly greater than the
applicable standard do not necessarily demonstrate horizontal or vertical distribution of
COI -affected groundwater migration from source areas (ash basins and adjacent
sources).
COI Management Plan Summary
A three -step process was used for the COI Management Plan approach considering the
regulatory context, the mobility of constituents, and the distribution of constituents
within Site groundwater. A comprehensive approach was followed utilizing extensive
Site data. The COI Management Plan approach incorporated numerous components of
the Site CSM in a holistic manner.
For the regulatory review portion of the COI Management Plan, mean COI
concentrations were compared COI criteria, or if applicable, calculated remediation
goals to identify concentrations that were greater than those applicable criteria.
Exceedance ratio (ER) values indicate COI concentrations that are greater than COI
criteria, or if applicable, calculated remediation goals are typically within one order of
magnitude (ER less than 10) to two orders of magnitude (ER less than 100) greater than
applicable criteria.
Results of the COI Management Plan evaluation were also used to identify areas that
require groundwater corrective action as described in Section 5.1.3 and 5.6.3 based on
the historical distribution of each COI in Site groundwater.
Constituents of Interest (COIs)
(CAP Content Section 6.A.c)
Site -specific COIs were developed by evaluating groundwater sampling results with
respect to concentrations greater than regulatory criteria or background values,
whichever is greater, and additional regulatory input/requirements. The distribution of
constituents in relation to the source areas, co -occurrence with a CCR indicator
constituent such as boron, and migration directions based on groundwater flow
direction are considered in determination of COIs.
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The following list of COIs was developed as part of the CSA Update for Sutton
(SynTerra, 2018a):
• Alkalinity • Molybdenum
• Arsenic • pH
• Boron • Potassium
• Calcium • Selenium
• Chromium (Hexavalent) • Sodium
• Chloride • Strontium
• Cobalt • Sulfate
• Iron • TDS
• Manganese • Vanadium
• Magnesium
Subsequent sampling and analysis for USEPA CCR Rule compliance indicated fluoride
and lithium are additional COIs at Sutton.
Soil
(CAP Content Section 6.A.c.i.1)
Unsaturated soil within waste boundaries is considered a potential secondary source to
groundwater. Constituents, if present in unsaturated soil, have the potential to leach
into the groundwater system if exposed to favorable geochemical conditions for
chemical dissolution to occur. Constituents considered for unsaturated soil evaluation
were the same constituents identified as COIs for the ash basins and additional source
areas, since effects on soil, if present, would be related to ash pore water interaction to
the underlying unsaturated soils within the waste boundaries. The horizontal extent
and vertical extent of COI concentrations in unsaturated soil, and reasons why no
necessary corrective action for soils is identified at the Site, is discussed further in
Sections 5.1.2.1(SA1) and 5.6.2.1(SA2).
Groundwater
(CAP Content Section 6.A.c.i.2)
A statistical analysis (LCL95/CTV analysis) of groundwater constituent data (January
2015 to March 2020) was conducted to calculate compliance values. Those values were
sought to support the analysis of groundwater conditions and to provide a basis for
defining the extent of the COI migration beyond the compliance boundary. The
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statistical analysis was used to calculate representative values of the full dataset of
constituent concentrations, which may vary over orders of magnitude. A single sample
result might not be an accurate representation of the concentrations observed over
several months to years of groundwater monitoring. Evaluating constituent plume
geometries with LCL95/CTV data minimizes the potential for incorporating occasions
when COIs are reported at concentrations outside of the typical concentration range,
and potentially greater, or substantially less than enforceable groundwater standards.
Previous Site assessment mapping based on single COI concentrations for each well
might have overrepresented or underrepresented areas affected by the ash basins by
posting a single dataset on maps and cross -sections that might have included isolated
data anomalies.
Tables 5-4 and 5-14 present the compliance value analysis results of the COI data for
each source area using groundwater monitoring results from January 2015 to March
2020. Data from Table 5-4 are used in evaluating COI plume geometry in the vicinity of
Source Area 1 and data from Table 5-12 are used in evaluating COI plume geometry in
the vicinity of Source Area 2. A detailed description of the COI management process
and results are presented in Section 5.1 for Source Area 1 and Section 5.6 for Source
Area 2.
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SOURCE AREA 1 — 1971/1984 ASH BASINS AND FPA
5.1 Source Area 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.
Source Area 1 is considered the outermost boundary of the combined extent of the 1971
and 1984 ash basins, and the FPA (Figure 2-1). Due to the Site hydrogeology as
described in the CSM (Section 4.1), potential effects from the 1971 ash basin, 1984 ash
basin, and FPA to groundwater would be addressed by the groundwater remedies
proposed herein.
Constituent Management Approach
As discussed in the beginning of Section 5, a COI management process was developed
by Duke Energy at the request of NCDEQ to gain understanding of the COI behavior
and distribution in groundwater distribution and to select the appropriate remedial
approach. The management process uses a matrix evaluation [Table 5-1 (CAP Content
Section 6.A.c.i.2)]
Using the COI management process, 14 of 20 inorganic groundwater constituents (not
including pH) identified in the CSA (CSA Update, 2018a) exhibit concentrations that are
currently less than COI criteria at or beyond the compliance boundary, or have few
concentrations greater than comparison criteria but with no discernable COI plume
characteristics. These fourteen constituents include:
• Alkalinity
• Lithium
• Calcium
• Magnesium
• Chloride
• Manganese
• Chromium (VI)
• Potassium
• Cobalt
• Sodium
• Fluoride
• Sulfate
• Iron • TDS
These constituents are not expected to migrate distances at or beyond the compliance
boundary or migrate distances that would present risk to potential receptors, and are
predicted, based on geochemical modeling, to remain at stable concentrations, typically
less than COI criteria. Cobalt, lithium and TDS are only detected at concentrations
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greater than standards near the waste boundary and not at locations beyond the
compliance boundary. Several COIs including alkalinity, calcium, magnesium,
potassium, and sodium are major ions commonly detected in Coastal Plain aquifer
groundwater at similar concentrations (Appendix L).
As shown in Table 5-1, concentrations of arsenic, boron, molybdenum, selenium,
strontium, and vanadium occur at or beyond the compliance boundary greater than
comparative criteria in one or more groundwater monitoring wells. Vanadium is not
considered a COI subject to corrective action due to the following rationale:
• Vanadium, at concentrations greater than comparative criteria at or beyond the
compliance boundary is present in only three wells (CCR-114C, FPA-2B, and
MW-39C). MW-39C is north of the 1984 ash basin and 500 feet north of the
compliance boundary. Vanadium concentrations greater than the BTV are only
detected in wells within the compliance boundary near the FPA (FPA-2B) and
northern 1984 ash basin waste boundary (CCR-114C). Lower surficial wells
located between CCR-114C and MW-39C do not have vanadium concentrations
greater than comparative criteria. Therefore, there is no discernable plume of
vanadium extending to MW-39C.
The remaining five COIs exhibit concentrations greater than COI criteria with plume
characteristics associated with Source Area 1 at or beyond the compliance boundary.
These five constituents are as follows:
• Arsenic • Selenium
• Boron • Strontium
• Molybdenum
5.1.1 Source Material within the Waste Boundary
(CAP Content Section 6.A.a)
An overview of material formerly within the waste boundary of the ash basins
and FPA is presented in the following subsections. A description of material
formerly within the FPA is included in Section 5.1.1.1.
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Recent groundwater monitoring data from within the waste boundary of the ash
basins are limited because of well abandonments associated with ash excavation.
Data limitations include:
• Within the 1971 ash basin waste boundary, available data are from April
2015 until September 2015; wells within the 1971 ash basin waste
boundary were abandoned as part of basin excavation.
• No wells were installed within the lined 1984 ash basin waste boundary.
5.1.1.1 Description of Waste Material and History of
Placement
(CAP Content Section 6.A.a.i)
Coal ash and other CCRs were historically sluiced to the 1971 ash basin,
1984 ash basin and FPA, collectively referred to as Source Area 1. Source
Area 1 is located adjacent to the cooling pond, north of the plant, as shown
on Figure 1-3. The waste material has been excavated. The history of
placement is as follows:
• The 1971 ash basin was built around 1971 and operated until 2013.
• The 1984 ash basin was in operation from 1984 to 2013.
The FPA was used when the Site was co -firing fuel oil for a few years
during the 1970s.
5.1.1.2 Specific Waste Characteristics of Source Material
(CAP Content Section 6.A.a.ii)
The waste has been excavated from Source Area 1. Prior to excavation,
source characterization was performed during the CSA (SynTerra, 2018).
Characterization activities included:
• Installing soil borings
• Installing monitoring wells
• Collecting and analyzing associated solid matrix and aqueous
samples
• Determining physical properties of ash
• Identifying constituents present in ash
• Measuring constituent concentrations in ash pore water
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• Performing laboratory analyses to estimate constituent
concentrations from leaching of ash
Two ash samples from AB-1 were collected during the CAMA investigation
from the 1971 ash basin for physical and chemical testing (Figure 1-3). The
ash data from the 1971 ash basin is similar to the ash in the 1984 basin and
the FPA due to the interconnected nature of the basins and the common
origin of the ash.
SPLP analysis was conducted on seventy-two (72) samples collected during
ash excavation of the 1971 and 1984 ash basins as required by Superior
Court Civil Action No. 13-CVS-11032 order by Superior Court Judge Paul
Ridgeway on June 1, 2016 in settlement between NCDEQ Sierra Club,
Waterkeeper Alliance, Cape Fear River Watch, Inc., and Duke Energy (13-
CVS-11032, 2016). Leachate from the SPLP analysis were analyzed for 33
constituents. Four (4) constituents (antimony, chromium, cobalt, and iron)
were detected in the SPLP leachate at concentrations greater than the 02L or
IMAC in 1 to 13 of the ash samples. Arsenic, selenium, and vanadium were
detected in the SPLP leachate at concentrations greater than the 02L or
IMAC in 67 or more of the ash samples (Appendix C, Table 7).
Physical Properties of Ash
The hydraulically sluiced deposits of ash consisted of interbedded fine- to
coarse -grained fly ash and bottom ash materials. Ash was generally
described in boring logs as gray to dark bluish gray with a silty to sandy
texture, consistent with fly ash and bottom ash. Physical properties analyses
(e.g., grain size, specific gravity, and moisture content) were performed
using American Society for Testing and Materials (ASTM) International
methods. As a result of these analyses, the ash is generally characterized as
a non -plastic sandy silt. The ash samples collected from the 1971 ash basin
exhibited a lower specific gravity, compared with soil, with ash sample
values reported from 2.2 to 2.3 (dimensionless) compared with soil sample
values reported at 2.7. Moisture content of the ash samples ranged from 28.2
percent to 74.1 percent.
Within the ash basins, interbedded layers of fly ash and bottom ash
typically result from varying rates and pathways of bottom ash and fly ash
settlement. The illustration that follows provides a depiction of the typical
interbedded nature of fly ash and bottom ash within an ash basin, as seen
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L.V. Sutton Energy Complex SynTerra
from an ash boring photograph. 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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5.1.1.3 Interim Response Actions
(CAP Content Section 6.A.a.viii)
Interim response actions to date in the area of Source Area 1 include
excavation of ash and installation of an interim action accelerated
remediation groundwater extraction system along the eastern property
boundary. A summary of each interim action and the intended remedy is
presented in Table 5-2. Ash excavation activities and changing Site
conditions are discussed in the following subsections and have been
previously discussed in Section 4.5.
Ash Basin Excavation
Sutton was deemed a "high -priority" site under CAMA and was specifically
required to complete excavation of the ash basins by August 1, 2019.
Excavation of the unsaturated ash was followed by dredging the saturated
ash from the 1971 ash basin. The dredged ash was transferred to the 1984
ash basin, which was used as a temporary settling basin for the separation
of ash from liquid. After separation from the ash, the liquid (wastewater)
was transferred to the on -Site Evoqua treatment system or back to the 1971
ash basin. CCR from the ash basins was transferred to a structural fill or
lined landfill, in accordance with CAMA requirements. Ash basin
excavation was completed by July 2019. Soil samples were collected from
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unsaturated areas beneath the ash basins to assess COI concentrations in
unsaturated soil post -excavation (Figures 5-1a through 5-2b). The majority
of area exposed during 1971 basin excavation is submerged; thus, very few
unsaturated soil samples could be collected from the excavated basin.
The 1971 ash basin is currently filled with water that is separated from the
cooling pond by sheet piling and an earthen dike. In accordance with the
terms of National Pollutant Discharge Elimination System (NPDES) permit
NC001422 (effective July 1, 2020), planned additional closure activities
consist of combining water in the excavated 1971 ash basin and with water
from the Site's cooling water effluent canal. The water can then be
discharged to NPDES permitted Outfall 001. Duke Energy has completed
final grading within the former 1984 ash basin footprint.
Removal of fuel waste and CCR from the FPA began in early 2020 and was
completed in April 2020. As part of excavation of the FPA, soil samples
were collected from beneath the FPA as demonstration of closure
(Figures 5-1a through 5-1d).
Results of Ash Excavation
Excavation of ash has affected groundwater flow patterns post -closure, due
to elimination of water table mounding within saturated ash in the unlined
1971 ash basin. Groundwater flow conditions have returned to those of the
natural groundwater flow regime with flow predominantly to the west,
toward the cooling pond and Cape Fear River under a low hydraulic
gradient.
West of the ash basins, boron and arsenic concentrations have historically
been greater than COI criteria in the upper and lower surficial flow zones.
Since excavation of ash from the ash basins, concentrations of boron and
arsenic in the area are decreasing or remained stable, but have not increased
which indicates closure activities have been successful in reducing COI
concentrations as well as the potential for plume expansion, as discussed in
the plume stability report (Appendix L).
North of the 1984 ash basin, boron concentrations have historically been less
than the 02L standard. Selenium concentrations have historically been
greater than the 02L standard. Concentrations of selenium in the area north
of the 1984 ash basin were decreasing prior to and during ash excavation.
Selenium continues to be detected at concentrations greater than the 02L
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standard in the area but those concentrations continue to decrease
(Appendix L).
Southeast of the 1971 ash basin, boron and arsenic concentrations have
historically been greater than 02L standards in the lower surficial flow zone.
Since excavation of ash from the ash basins, concentrations of boron and
arsenic in the area have decreased or remained stable, but have not
increased, which indicates closure activities have been successful in
reducing COI concentrations and the potential for plume expansion.
Potential or apparent increasing concentrations of COIs observed at Sutton
are anticipated to be temporary in nature; decreasing COI concentrations
are anticipated in the future due to removal of ash source material.
Completion of ash excavation activities from the ash basins provides an
important component of the corrective action strategy because the vast
majority of the source of groundwater COIs were removed. The remaining
potential for groundwater plume migration is confined to conditions
already present in the groundwater flow system.
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 demonstrated off -Site effects of groundwater migration. Sutton is
included in that agreement.
As an interim remedial action, Duke Energy installed a system of nine
groundwater extraction wells along the eastern property boundary as
previously described in Section 1.4.1. The primary objective of the
groundwater extraction system was to prevent migration of constituents in
groundwater from the 1971 ash basin off -Site beyond the eastern property
boundary. The extraction system wells are screened in the surficial aquifer.
The system became operational in August 2017. The nine -well extraction
system operates at a combined total average flow rate of approximately 500
gallons per minute (gpm). The extracted groundwater is treated in an on -
Site treatment facility for NPDES parameters and discharged to the Cape
Fear River at Outfall 001 under the NPDES permit.
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Effectiveness monitoring is being performed as specified in the BOD report
(Geosyntec, January 2017). IAP monitoring includes sampling 26
monitoring wells on a semiannual basis for CAMA parameters.
An annual performance monitoring report has been prepared and
submitted to the NCDEQ each year since system startup. During the period
of the 2019 report (April 2019 through March 2020), the extraction system
removed 217,915,013 gallons of groundwater (SynTerra, 2020). As stated in
the most recent IAP annual report, the extraction system continues to be
effective in reducing off -Site COI migration, which is indicated by the
steady decrease of COI concentrations in wells along the property line. The
Interim Action Plan 2019 Performance Monitoring Report is included in
Appendix J.
The BOD report includes conditions for system decommissioning:
A final groundwater corrective action plan is developed and
implemented.
Four consecutive events of of groundwater performance monitoring
analytical results must indicate that off -Site migration of COIs have
been reduced to less than COI criteria.
The BOD decommissioning conditions are anticipated to be met within five
years of this CAP Update submittal. The extraction wells were sampled as
part of the CAP Update preparation. Results (Table 5-7) indicate COI
concentrations greater than applicable criteria continue to be captured by
the system. As of the preparation of this CAP Update, no off -Site
concentrations detected in the most recent IAP sampling event were greater
than COI criteria. However, the following COIs do not have an 02L
standard or IMAC and are detected at concentrations greater than BTVs in
off -Site wells: molybdenum and strontium. For this reason, continued
operation of the extraction well system is recommended.
5.1.2 Extent of Constituent Migration Beyond the Compliance
Boundary
(CAP Content Section 6.A.b)
This section is an overview of constituent occurrences beyond the compliance
boundary pertaining to Source Area 1. The compliance boundary for
groundwater quality at the Site is defined in accordance with 15A NCAC 02L
.0107(a) as being established at either 500 feet from the waste boundary or at the
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property boundary, whichever is closer to the CCR unit. An exception to this rule
occurs at the Site. The Site's cooling pond, an NPDES-permitted waste unit,
defines the western compliance boundary. The cooling pond was only a
wastewater treatment unit from initial operations until early 2015 when the
NPDES permit was modified to classify the unit as waters of the state. While the
cooling pond is considered waters of the State it also remains a permitted
wastewater treatment unit.
Analytical sampling results associated with the ash basins and FPA source areas
for each media are included in the following tables and appendices:
• Soil: Appendix C, Table 4 and Tables 5-3a through 5-3b (CAP Content
Section 6.A.b.ii.1)
• Groundwater: Appendix C, Table 1 and Table 5-4 (CAP Content Section
6.A.b.ii.2)
• Seeps: Not applicable
• Surface water: Appendix C, Table 2 and Appendix J (CAP Content Section
6.A.b.ii.4)
• Sediment: Appendix C, Table 5 (CAP Content Section 6.A.b.ii.5)
5.1.2.1 Soil Constituent Extent
(CAP Content Section 6.A.b.ii.1)
Unsaturated soils were collected as part of closure of the 1971 and 1984 ash
basins (Table 5-3a). Unsaturated soils were collected in the vicinity of the
FPA during monitoring well installation (Table 5-3a). Additional soil
samples were collected beneath the excavated FPA as part of closure
(Table 5-3a). The potential for COI concentrations in unsaturated soil to
contribute to observed COI concentrations in groundwater is discussed in
the following sections.
1971 Ash Basin Unsaturated Soils
The 1971 ash basin contained approximately 40 feet of saturated ash below
the water table. That material was removed by dredging. Basin water is
now present in the footprint of the excavated 1971 ash basin and contained
via earthen dikes and steel sheet piling. Unsaturated soil samples as part of
closure activities could not be collected in most areas of the 1971 ash basin.
A small number of soil samples were collected in the southeast area of the
1971 basin where ash was not placed below the water table.
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With the exception of iron, unsaturated soils collected from the 1971 basin
after the closure of the basin do not contain concentrations greater than
POG PSRGs (Table 5-3a and Figures 5-1a through 5-1d). The iron
concentrations detected are greater than the POG PSRG (150 mg/kg);
however, all concentrations are less than the soil BTV (2,553 mg/kg).
Synthetic Precipitation Leaching Procedure (SPLP) results also indicate no
concentrations are present greater than 02L standard in the unsaturated
area of the 1971 ash basin (Table 5-3b). These results indicate unsaturated
soil located in the southeast corner of the 1971 ash basin do not represent an
additional source of COIs requiring corrective action.
1984 Ash Basin Unsaturated Soils
Unsaturated soils collected from the 1984 ash basin after excavation of the
basin contain concentrations greater than the POG PSRG (5.8 mg/kg) for
arsenic in the southern and western portions of the 1984 ash basin
(Table 5-3a). Arsenic concentrations greater than the POG PSRG were
detected in the shallow 0-to-6-inch soil sample interval, and in some areas
extended to 30 inches bgs. SPLP results also indicate arsenic concentrations
greater than the 02L standard where soil concentrations are greater than the
POG PSRG (Table 5-3b). Other COIs detected at concentrations greater than
POG PSRGs include molybdenum and selenium. Boron, arsenic,
molybdenum, selenium, and strontium are the primary CAP groundwater
COIs associated with the 1984 ash basin.
Unsaturated soil sample locations displaying arsenic and selenium
concentrations greater than POG PSRG values are included as Figures 5-2a
and 5-2b. Boron, arsenic, and selenium SPLP analytical results from
unsaturated soils were used in the flow and transport model to predict
groundwater concentrations beneath the 1984 ash basin as a result of COIs
leaching from soil (Figures 5-3a through 5-3c). The model simulates
predicted groundwater concentrations in years 2025, 2030, 2040, and 2050.
While arsenic concentrations persist in time due to a greater Ka value, the
migration to downgradient areas is also limited. According to model
results, arsenic is not predicted to migrate beyond the immediate area
around the soil sample location. Model results for boron, arsenic, and
selenium indicate the mass of constituents released from unsaturated soil,
by itself, would not result in constituent concentrations greater than 02L
standards at the compliance boundary. This analysis shows that the
potential removal of additional unsaturated soil from the 1984 ash basin
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would not significantly affect future groundwater quality. Since the soil
samples were collected, the area has been regraded, making the potential
removal of additional unsaturated soil impractical and of little benefit.
Therefore, unsaturated soils within the 1984 ash basin do not represent a
source of COIs requiring further corrective action. A technical memo
describing the rationale, methods, and results of the unsaturated soil model
evaluation are included in Appendix F.
Former Process Area Soils
Unsaturated soils were collected as part of the FPA assessment drilling in
July 2019 and as part of closure sampling in February 2020. Unsaturated
soils collected from the FPA after excavation contain concentrations greater
than the POG PSRG for arsenic, calcium, cobalt, iron, magnesium,
manganese, potassium, selenium, and sodium (Table 5-3a and Figures 5-1a
through 5-1d). Several COIs occur naturally in coastal plain soils, including
calcium, magnesium, potassium, and sodium. SPLP results indicate none of
these naturally occurring COIs have the potential to leach to groundwater at
concentrations greater than applicable criteria in the lower surficial flow
zone (Figure 5-3b).
SPLP results also indicate arsenic, cobalt, iron, manganese, and vanadium
concentrations greater than 02L (Table 5-3b). However, iron, cobalt, and
manganese SPLP results do not indicate the potential for concentrations
greater than the lower surficial BTVs. Arsenic and vanadium SPLP results
indicate the potential for COIs to leach to groundwater at concentrations
greater than applicable criteria. However, groundwater results indicate
limited horizontal and vertical migration of arsenic and vanadium in
groundwater associated with the FPA. These results indicate unsaturated
soil located near and beneath the excavated FPA do not represent an
additional source of COIs requiring corrective action.
See Section 5.1.3 for discussion of the horizontal and vertical distribution of
COIs in groundwater associated with Source Area 1.
5.1.2.2 Groundwater Constituent Extent
(CAP Content Section 6.A.b.ii.2)
The ash basin compliance boundary extends 500 feet beyond the ash basins
waste boundary, cooling pond edge, or to the property boundary,
whichever is closer. While the cooling pond is considered waters of the
State, it is also a permitted wastewater treatment unit. Groundwater
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concentrations greater than COI criteria occur locally at or beyond the
compliance boundary in four areas:
1. An isolated area northwest of the 1984 ash basin waste boundary
2. West of the 1984 ash basin with discharge to the cooling pond
approximately 375 feet beyond the compliance boundary; which is
the shore -line rather than 500 feet from the waste boundary, based
on flow and transport model results
3. East of the ash basins in isolated areas along the eastern property line
approximately 800 feet beyond the compliance boundary
4. Southeast of the 1971 ash basin and FPA approximately 100 feet
beyond the compliance boundary
The cooling pond borders the ash basins to the west and COI concentrations
(primarily boron and arsenic) are currently greater than 02L standards in
wells installed at the western 1984 ash basin waste boundary. Due to the
close proximity of the cooling pond, additional downgradient wells are not
available to verify the extent of migration in groundwater under the cooling
pond. The cooling pond is a groundwater discharge zone that limits the
horizontal transport of constituents downgradient of the ash basin. The flow
and transport model predictions indicate the maximum extent of migration
of boron under the cooling pond is approximately 375 feet.
Due to the limited presence and mobility of COIs in the groundwater, the
groundwater discharge to the cooling pond has not caused, and is not
predicted to cause, constituent concentrations in the cooling pond water to
be greater than 02B surface water quality criteria (Appendix K).
The maximum extent of CCR-affected groundwater migration for all flow
zones is generally represented by a boron concentration greater than the
02L standard [700 micrograms per liter (µg/L)]. At the time of CAP Update
preparation, NCDEQ is currently reviewing a proposal to revise the 02L
boron standard to 4,000 µg/L. No groundwater samples collected from
Source Area 1 wells screened in the upper and lower surficial flow zones
contain boron at concentrations greater than 4,000 µg/L. Boron historically
migrated with groundwater to the east and off -Site. The most recent March
2020 sampling results indicate boron concentrations are now less than 02L
in all off -Site monitoring wells. Boron concentrations are also less than 02L
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in wells between the compliance boundary and the eastern property line.
The boron plume associated with Source Area 1 has decreased in size and is
now contained mostly within the compliance boundary.
The LCL95 analysis indicates one off -Site well (SMW-1C) with boron
concentrations greater than the 02L standard. This well is located near the
hydraulic divide east of the Site and boron concentrations there have
steadily decreased since the first quarter of 2018 (Appendix L). Flow and
transport model simulations indicate groundwater moves very slowly in
this isolated area near the hydraulic divide and is probably not significantly
affected by the extraction system (Appendix F). Concentrations are
expected to continue to decrease.
Generally, non -conservative and variably reactive constituents exhibit little
migration from the ash basins. The extent and maximum concentrations of
non -conservative and variable constituents that have a discernable plume
correlate with the migration of boron at concentrations greater than the 02L
standard.
There are few exceptions where non -conservative and variably reactive
constituents occur in areas where boron is non -detected or less than 02L at
or beyond the compliance boundary. These exceptions are molybdenum
and strontium concentrations east of the ash basins. Molybdenum and
strontium are detected at concentrations greater than background
concentrations for the surficial flow zone in wells near the nine -well
extraction system. Upward vertical gradients are observed at lower surficial
and upper Peedee well pairs near the extraction system (Table 4-3). The
continuous operation of the extraction system in the surficial flow zone is
probably creating this vertical gradient, potentially allowing molybdenum
and strontium, which naturally occur at greater concentrations in the
underlying upper Peedee flow zone, to migrate upward into the lower
surficial flow zone.
A detailed matrix evaluation and rationale of groundwater constituents
requiring corrective action is presented in Section 5.1. Section 5.1.3
provides isoconcentration maps and cross sections depicting groundwater
flow and constituent distribution (CAP Content Section 6.A.b.i).
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5.1.2.3 Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Does not apply to Sutton, no seeps have been identified at the Site.
5.1.2.4 Surface Water Constituent Extent
(CAP Content Section 6.A.b.11.4)
The extent of constituent migration within surface water related to both
Source Area 1 and Source Area 2 is discussed in this section.
Surface water samples were collected from the cooling pond and the Cape
Fear River to confirm groundwater downgradient of the source areas has
not resulted in surface water concentrations greater than 02B water quality
criteria. A map of all surface water sample locations for the groundwater
discharge to surface water evaluation is included in Figure 4-4. Surface
water samples were collected to evaluate acute and chronic water quality
values. Due to the limited presence and mobility of most constituents in the
groundwater system, COI concentrations in groundwater have not caused,
and are not predicted to cause, concentrations greater than current surface
water quality criteria (Appendix K). Analytical results were evaluated with
respect to 02B water quality criteria and background data. Surface water
conditions are further discussed in Section 4.3.1; the full reports for the
Sutton surface water current and future conditions can be found in
Appendix K.
Additionally, environmental assessments of the cooling pond have all
demonstrated that the cooling pond has been an environmentally healthy
and functioning ecosystem; ongoing sampling programs have been
established to protect the health of those systems. Furthermore, the data
indicate that there have been no significant effects to the local aquatic
systems related to coal ash constituents over the past 50 years. More
information related to the environmental health assessments pertaining to
the cooling pond - including sampling programs, water quality and fish
community assessments, and fish tissue analysis, - can be found in
Appendix E.
5.1.2.5 Sediment Constituent Extent
(CAP Content Section 6.A.b.ii.5)
The extent of constituent migration within sediments related to both Source
Area 1 and Source Area 2 is discussed in this section.
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Sediment sample locations are co -located with surface water sample
locations (Figure 4-4). 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 sediment
inorganic constituents, both background sediment constituent concentration
ranges and co -located surface water sample results are considered in this
sediment evaluation. Table 3-4 presents constituent ranges of background
sediment datasets. Analytical results for all sediment samples are provided
in Appendix C, Table 5.
Assessment of COIs in sediment from the cooling pond and Cape Fear
River was conducted through a comparison of analytical results from
potential groundwater discharge zones and background sediment
concentration ranges. The background sediment samples were collected
from the Cape Fear River upstream of the cooling pond and the Site NPDES
Outfalls.
Sediment sample locations (Figure 4-4) included:
• Upstream/background Cape Fear River (two locations) — SW-14,
SW-15
• Downstream Cape Fear River (one location) — SW-17
• Cooling Pond — eastern shore in groundwater to surface water
discharge zone (seven locations) — SW-1 through SW-7
• Cooling Pond — beyond the predicted groundwater to surface water
discharge zone (three locations) — SW-11, SW-12 and SW-13
• Cooling Pond/intake canal — western edge of the FADA and FCPA
(four locations) — SW-8 through SW-10 and SW-16
Of the sediment samples collected in the cooling pond, eight samples had at
least one constituent concentration greater than the maximum detected
concentration in background sediment. Constituents from the cooling pond
sediment samples with concentrations greater than background
concentrations include arsenic, boron, calcium, cobalt, magnesium,
manganese, molybdenum, potassium, selenium, strontium, sulfate, and
vanadium (Table 5-5). Surface water samples co -located with the sediment
samples collected from the cooling pond have COI concentrations less than
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02B surface water criteria and are generally within background
concentration ranges (Table 3-3). A summary of the results is provided
below:
Sediment samples SW-4 and SW-6, located at the cooling pond shore
next to Source Area 1, had arsenic concentrations greater than at
background locations. Nearby sediment samples collected from the
cooling pond shore near Source Area 1 had arsenic concentrations
less than those detected at background locations indicating the
arsenic is localized. Sediment sample SW-6 also had molybdenum at
a concentration greater than those detected at background locations.
No other nearby sediment samples contained molybdenum
concentrations greater than background, indicating localized
molybdenum concentrations in sediment.
• Sediment samples SW-8, SW-9, and SW-10, located at the cooling
pond shore next to Source Area 2, had calcium and strontium
concentrations greater than those detected at background locations.
Calcium is a common element in the coastal plain. While strontium is
detected at concentrations greater than the sediment background
range and the Site -specific soil BTV, the concentrations are less than
the POG PSRG pertaining to strontium.
• Three sediment samples (SW-11, SW-12, and SW-13) were collected
from areas beyond the extent of potential groundwater discharge in
the cooling pond from Source Area 1. One or more locations had
concentrations of arsenic, boron, calcium, cobalt, magnesium,
manganese, molybdenum, potassium, selenium, strontium, sulfate,
and vanadium greater than concentrations detected at background
locations. Several constituents including boron, calcium, cobalt,
magnesium, manganese, potassium are detected at concentrations
only slightly greater than concentrations detected at background
locations indicating they may be naturally occurring. The remaining
constituents (arsenic, molybdenum, selenium, strontium, and sulfate)
with concentrations greater than screening values are considered in
the risk assessment of the cooling pond, a permitted wastewater
treatment unit.
One sediment sample, SW-17, was collected from the Cape Fear
River downgradient of Source Area 2 (Figure 4-4). No COIs were
detected at concentrations greater than those detected background
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locations in the SW-17 sediment sample. This indicates COIs in
Source Area 2 groundwater are not migrating to nearby Cape Fear
River sediment.
As evaluated in the risk assessment (Appendix E), there is no evidence that
sediments in the cooling pond or Cape Fear River adjacent to the Site pose
an increased risk to on -Site or off -Site human receptors or ecological
receptors. Additionally, Duke Energy has monitored the cooling pond since
1972. Assessments such as water quality, chemistry, and general species
composition have demonstrated that the cooling pond is an
environmentally healthy and functioning ecosystem. These assessments
indicated that there have been no significant effects on the cooling pond
related to Site operations over the past 50 years. Therefore, no corrective
action for sediment in the cooling pond or Cape Fear River is planned at
this time.
5.1.2.6 Piper Diagrams
(CAP Content Section 6.A.b.iii)
Piper diagrams can be used to differentiate water sources 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 upper and lower
surficial flow zones are included on Figure 5-4. Monitoring locations
included on Figure 5-4 include upgradient/background locations, locations
within the waste boundary, and locations downgradient of Source Area 1.
Data used for the Piper diagrams include groundwater data from June 2019
to March 2020 with a charge balance between -10 and 10 percent. Evaluation
of the Piper diagrams for groundwater associated with Source Area 1
(Figure 5-4) include:
Surficial wells now located in upgradient areas do not plot with
background or ash pore water wells. This is evidence of
concentrations returning to natural conditions. Upgradient surficial
wells located east of the ash basins are expected to plot closer to
background locations as the Site continues to stabilize after source
removal.
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Wells located on the western, downgradient edge of the ash basins
plot closely together and are generally separated from wells on the
eastern, upgradient side of the ash basins. This is additional evidence
of decreasing COI concentrations in upgradient groundwater.
Supply Well Groundwater Piper Diagrams
Piper diagrams of water supply, background, and ash pore water data are
included on Figure 5-5. Data used for the piper diagrams include most
recent available water supply data (Appendix C, Table 2) with a charge
balance between -10 and 10 percent. Evaluation of the Piper diagrams for
water supply groundwater associated with Source Area 1 (Figure 5-5)
include:
• The majority of supply wells plot closely with background
groundwater locations. Exceptions occur for supply well samples
collected prior to January 2018. This supports the conclusion that
the extraction system has effectively stopped off -Site migration of
COIs.
Surface Water Piper Diagrams
Piper diagrams of cooling pond and Cape Fear River surface water data are
included on Figure 5-6. Data used for the Piper diagrams include most
recent available surface water data (Appendix C, Table 2) with a charge
balance between -10 and 10 percent. Evaluation of the Piper diagrams for
surface water associated with both source areas (Figure 5-6) include:
Background surface water samples plot closely with downgradient
surface water samples. This is evidence that the surface waters
evaluated at the Site are not affected by migration of COIs in
groundwater.
• Almost all downgradient surface water samples have nearly identical
proportions of calcium, chloride, magnesium, carbonate, and sulfate.
This is evidence of uniform characteristics and concentrations in
downgradient surface water locations at the Site.
• No samples are magnesium -chloride type water, a signature typical
of ash pore water (Figure 5-4). This indicates no evidence of impacts
from mixing groundwater with surface water at the Site.
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5.1.3 Horizontal and Vertical Extent of Groundwater in Need
of Restoration
(CAP Content Section 6.A.d.ii)
COIs in groundwater associated with Source Area 1 (1971 ash basin, 1984 ash
basin, and FPA) that occur at concentrations greater than COI criteria are
proposed for corrective action in the following areas:
• Isolated area northwest of the 1984 ash basin waste boundary
• 375 feet west of the 1971/1984 ash basin compliance boundary
• 100 feet southeast of the 1971 ash basins compliance boundary
• Within the footprint of the 1971 ash basin
• Isolated areas east of the ash basins along the property line and an isolated
area off -Site
Northwestern Extent of COI -Affected Groundwater
Selenium concentrations near the compliance boundary support the following
observations regarding the northwestern extent of COIs in groundwater affected
by the 1984 ash basin:
• Selenium is present in the lower surficial zone north of the 1984 ash basin
near the compliance boundary at concentrations that have historically
been greater than the 20 µg/L 02L standard (Figure 5-10). MW-38C,
located 500 feet north of the compliance boundary, historically contained
selenium at concentrations greater than 02L. Selenium concentrations at
MW-38C have been less than 02L since early 2017; the statistically
representative value is 7.7 µg/L. Statistical analysis of samples collected
from CCR-115C and MW-40C, located south of MW-38C between the 1984
waste and compliance boundaries, indicates selenium concentrations
continue to be greater than 02L.
Selenium concentrations in this area between the waste and compliance
boundaries are decreasing, with recent concentrations near the 02L
standard (20 µg/L). Selenium concentrations greater than 02L are limited
to this area of the Site and are present only in the lower surficial flow
zone.
Groundwater concentrations in this area are within compliance since
selenium concentrations greater than 02L are no longer present in
monitoring wells beyond the compliance boundary. Groundwater
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concentrations in this area have reached compliance under natural
attenuation as a result of Site changes due to basin closure. As part of the
EMP (Section 5.11), confirmation groundwater sampling is proposed to
confirm the recent changes in selenium concentrations.
Western Extent of COI -Affected Groundwater
Arsenic, boron, molybdenum, selenium, and strontium concentrations near the
compliance boundary support the following observations regarding the western
extent of groundwater affected by COIs attributed to the 1971 and 1984 ash
basins:
Arsenic, boron, molybdenum, and strontium concentrations in the upper
and lower surficial zones are greater than COI criteria west of the 1971
and 1984 ash basins and near the compliance boundary (Figures 5-7a
through 5-11b). Selenium concentrations in the lower surficial flow zone
are greater than the 02L standard in wells between the waste boundary
and compliance boundary (Figure 5-10). The waste and compliance
boundaries are co -located in this area due to the close proximity of the
cooling pond.
• Arsenic and boron concentrations in the upper and lower surficial zones
in this area are stable. Molybdenum, selenium, and strontium
concentrations in the upper and lower surficial zones in this area are
generally decreasing or stable (Appendix L).
• The horizontal extent of COIs is limited in this area due to the presence of
the cooling pond. No wells are available downgradient of the waste
boundary due to the proximity of the cooling pond. The cooling pond is a
groundwater discharge zone that limits the horizontal migration of
constituents downgradient of the basin (Appendix F).
Flow and transport model simulations indicate boron might have
migrated a short distance (375 feet) from the compliance boundary
beneath the cooling pond. Groundwater then discharges to the cooling
pond (Figure 5-20). The model indicates selenium might have migrated a
short distance (500 feet) from the compliance boundary in the lower
surficial zone in an isolated area at the northwestern edge of the 1984 ash
basin (Figure 5-21).
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• Due to the limited presence and mobility of most constituents in the
groundwater system, COI concentrations in groundwater have not
caused, and are not predicted to cause, concentrations in the cooling pond
to be greater than current surface water quality criteria (Appendix K).
Southeastern Extent of COI -Affected Groundwater
Arsenic, molybdenum, and strontium concentrations near the compliance
boundary support the following observations regarding the southeastern extent
of groundwater affected by COIs attributed to the 1971 ash basin and FPA
groundwater:
• Boron and arsenic concentrations in the lower surficial zone have
historically been greater than the 02L standard southeast of the 1971 ash
basin and FPA, beyond the compliance boundary. However, boron and
arsenic concentrations in this area have decreased to concentrations less
than 02L standards since completion of source removal.
Statistical analysis of the dataset also indicates decreasing concentrations
at the compliance boundary, with no values greater than 02L standards
for arsenic and boron beyond the compliance boundary (Figures 5-7a
through 5-8b; Appendix L).
Molybdenum and strontium concentrations in the lower surficial flow
zone are greater than BTVs southeast of the 1971 ash basin and FPA
approximately 75 feet beyond the compliance boundary (Figures 5-9b and
5-11b). Molybdenum and strontium concentrations in this area are less
than BTVs in the upper surficial flow zone.
Statistical analysis of the dataset indicates stable or decreasing
molybdenum and strontium concentrations with only one well (FPA-4C)
with increasing concentrations. FPA-4C is located between the waste
boundary and compliance boundary.
Q12020 groundwater levels and predictive modeling both indicate
groundwater is no longer flowing southeast but has reverted to natural
conditions with groundwater primarily flowing southwest toward the
effluent canal (Figures 4-1, 4-3a, and 4-3b). COI concentrations are not
expected to increase or migrate to the southeast beyond the compliance
boundary.
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• Groundwater concentrations in this area are very close to compliance
since arsenic concentrations greater than 02L are no longer present in
monitoring wells at or beyond the compliance boundary. With the
exception of molybdenum and strontium concentrations (COIs that do not
have a 02L standard or IMAC value), groundwater concentrations in this
area have reached compliance under natural attenuation as a result of Site
changes due to basin closure. As part of the EMP (Section 5.11),
confirmation groundwater sampling is proposed to confirm both the
recent changes in arsenic concentrations and the expectation that
molybdenum and strontium concentrations should continue to decrease.
Extent of COI -Affected Groundwater within Excavated Area of
1971 Ash Basin
The excavation of coal ash at the 1971 ash basin has resulted in the formation of a
water feature containing approximately 320 million gallons of water. The water
in the former 1971 ash basin contains arsenic at a concentration of about 75 µg/L,
which is greater than the 02B criterion and federal maximum contaminant level
(MCL) drinking water criteria (10 µg/L) and the groundwater BTV value (14
µg/L). Arsenic concentrations in wells surrounding the 1971 ash basin support
the following observations regarding the extent of COIs in groundwater affected
by the 1971 ash basin water:
Arsenic concentrations are greater than the 02L standard in the upper and
lower surficial flow zones in the area surrounding the water in the 1971
ash basin (Figures 5-7a and 5-7b).
• The former 1971 ash basin excavated area is separated from the cooling
pond by a sheet pile wall. The arsenic concentration in the cooling pond is
much lower — approximately 2 µg/L. As part of closure, water in the
excavated 1971 ash basin is planned to be pumped out and replaced at an
equal rate with water from the effluent canal.
Statistical analysis of the arsenic data in the area indicates increasing
concentrations in the upper surficial zone (CCR-109B and FPA-9B) and
decreasing concentrations in the lower surficial zone (CCR-109C and FPA-
9C; Appendix L). This observation is evidence of unstable geochemical
conditions. Concentrations in the lower surficial are beginning to decrease
as expected after source removal. However, increasing concentrations in
the upper surficial indicate instability with arsenic concentrations in the
1971 excavated area water, which probably affects concentrations in
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surrounding groundwater. The arsenic concentration at the downgradient
side (CCR-109B — 39 µg/L) of the 1971 basin is greater than the
upgradient side (FPA-9B — 4.2 µg/L), indicating concentrations should
decrease in downgradient areas now that source removal is complete.
Eastern Extent of COI -Affected Groundwater
Boron, molybdenum, and strontium concentrations beyond the compliance
boundary support the following observations regarding the eastern extent of
groundwater affected by COIs attributed to Source Area 1:
• There are no wells beyond the eastern compliance boundary in the upper
surficial flow zone with boron concentrations greater than the 02L
standard (700 µg/L) (Figure 5-8a). Boron concentrations in the lower
surficial zone east of the compliance boundary have historically been
greater than the 02L standard. Boron concentrations are now less than 02L
in all wells beyond the eastern compliance boundary (Figure 5-8b). Boron
concentrations in SMW-1C until recently have been greater than the 02L
standard but have steadily decreased since 2017 and are now less than 02L
(Appendix L).
• Boron concentrations along the property boundary are less than the 02L
standard and continue to decrease as a result of operation of the extraction
system (Appendix L).
• Molybdenum concentrations are greater than the BTV (1 µg/L) in a small
area about 75 feet beyond the eastern compliance boundary (MW-23B and
MW-23C). The molybdenum concentrations in MW-23B and MW-23C are
decreasing (Appendix L). Isolated molybdenum concentrations greater
than the BTV are present in wells near the groundwater extraction system
(Figures 5-9a and 5-9b). The isolated concentrations near the extraction
system are potential evidence of upwelling of upper Peedee flow zone
groundwater due to the operation of the extraction wells. The BTV for
molybdenum in the upper Peedee zone (26 µg/L) is greater than the
surficial flow zone BTV (1 µg/L). Naturally occurring molybdenum is
probably mixing with upper and lower surficial groundwater causing the
isolated occurrences of molybdenum concentrations greater than the BTV.
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Strontium concentrations are not greater than the BTV in upper surficial
wells east of the compliance boundary (Figure 5-11a). Isolated
concentrations greater than the BTV are observed in two lower surficial
wells (AW-4C and SMW-1C) east of the compliance boundary (Figure 5-
11b). Strontium concentrations at AW-4C are variable (Appendix L) and
probably are present due to upwelling of upper Peedee flow zone
groundwater containing naturally occurring strontium near the extraction
system. Strontium concentrations at SMW-1C are stable and located
beyond the hydrologic divide.
5.1.4 COI Distribution in Groundwater
Constituent distribution in groundwater is discussed based on constituent
groupings, determined by similar geochemical behavior and mobility.
Constituent groupings and COIs subject to corrective action are as follows:
• Conservative, non -reactive constituents: boron
• Non -conservative, reactive constituents: arsenic and selenium
• Variably reactive constituents: molybdenum and strontium
COIs identified in the CSA that are not mapped in this CAP Update have limited
spatial occurrences within the compliance boundary and are spatially limited to
isolated areas within the compliance boundary without a discernable plume
geometry (Table 5-1).
5.1.4.1 Plume Stability
(CAP Content Section 6.A.e.i.1)
Mann -Kendall trend analysis was performed using constituent datasets for
groundwater wells within the waste boundary, between the waste
boundary and compliance boundary, and downgradient of the source area,
at or beyond the compliance boundary (Table 5-8). Trend analysis and
results were prepared by Arcadis U.S. Inc. and are included as
Attachment A in Appendix L.
The analysis was performed using analytical results for samples collected
from 2019 through Q12020. The analysis targeted COIs identified in the
2018 CSA Update (Table 5-1). Trend analysis results are presented where at
least four samples were available and frequency of detection was greater
than 50 percent. Statistically significant trends are reported at the 95 percent
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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 percent 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)
For both source areas, 2,415 datasets were evaluated for trends. Excluding
the NE trends described above, 88 percent of the remaining datasets had
statistically significant decreasing trends, stable trends, no trends, or greater
than 50 percent non -detect concentrations. Only 12 percent of the trends
were statistically increasing. Excluding both NE and ND trends described
above, 85 percent of the remaining datasets had statistically significant
decreasing trends, stable trends, or no trends. (Appendix L).
Trend analyses of groundwater monitoring wells north, west, south, and
east of Source Area 1 near or beyond the compliance boundary indicate the
following:
Approximately 88 percent of trend results for groundwater wells at
or beyond the compliance boundary indicate stable trends, no trends,
non -detect, or decreasing trends for conservative constituents
(Table 5-8).
Only 12 percent of trend results for groundwater wells at or beyond
the compliance boundary have increasing trends for one or more
2018 CSA Update COIs (Table 5-8).
These results demonstrate a generally decreasing to stable plume. Wells
with increasing COI concentration trends are generally located east and
west of the source areas, along the waste boundary of the ash basins.
Total statistically increasing trends account for 247 of the 2,128 datasets (12
percent excluding NE results). Major ions identified as Site COIs (alkalinity,
calcium, magnesium, potassium, and sodium) account for 47 percent of 247
total increasing concentration trends. These major ion constituents are
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commonly detected in Coastal Plain aquifer groundwater at the
concentrations detected in Site groundwater (Appendix L). It should also be
noted that very little groundwater data is available after ash excavation
from Source Area 1. No data is available after excavation of the FPA. It is
anticipated that post -excavation concentrations will decrease due to natural
attenuation.
5.1.4.2 Site Geochemical Conditions Affecting COI
Behavior
The plume stability analysis was conducted to determine if COI
concentrations are decreasing, remaining steady, or increasing with time
(Appendix L). Following excavation of the ash, downgradient COI
concentrations are expected to decrease over time as the COIs are diluted by
upgradient groundwater and infiltrating rainwater. Analysis of the trends
presented in Appendix L revealed the following conclusions:
The plume is generally stable to decreasing for COIs in Site
groundwater.
Most major ions (sodium, potassium, calcium, magnesium, chloride,
and sulfate) as well as boron had decreasing concentrations
indicative of a stable to decreasing plume with time (i.e., dilution and
dispersion of the residual COIs following excavation).
There were statistically significant increasing concentration trends in
a limited number of wells for arsenic, molybdenum, cobalt, selenium,
and sulfate either at or beyond the compliance boundary or between
the waste boundary and compliance boundary (Appendix L). Each of
these COIs exhibits some attenuation by sorption, ion exchange, or
(co)precipitation and thus may be more slowly removed from the
system by dilution from upgradient groundwater and infiltrating
rainwater and dispersion.
As discussed in further detail in the geochemical report (Appendix G), the
groundwater system is expected to approach a new local equilibrium or
steady state condition. This is particularly important with respect to
changes in pH and Ex which may alter COI mobility. As the excavation was
completed relatively recently[fuly 2019 (ash basins) and April 2020 (FPA)]
and changes in Ex are being currently observed (Appendix G), collection of
additional data in the future is needed to determine if the current trends in
geochemical conditions and COI concentrations will continue.
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Conservative Constituents
(CAP Content Section 6.A.e.i)
Conservative cross sections and geochemical modeling support the
following observations regarding the geochemical conditions affecting the
extent of COI -affected groundwater represented by boron, a conservative
(non -reactive) COI downgradient of Source Area 1 (Figures 5-12a and
5-12b; Appendix G):
• Most of the soluble boron behaves as a conservative tracer with little
chemical attenuation.
The variability in boron Ka values is primarily due to variability in
the ferrihydrite (HFO sorption site) concentrations for each well
along the transect. However, all predicted Ka values are low,
resulting in conservative migration of boron and the prediction of
attenuation by physical means.
• As B(III) is the only stable oxidation state of boron in water, changes
in Ex would not change the redox speciation of boron and thus is
unlikely to directly influence attenuation.
• Changes in groundwater flow conditions would cause boron to wash
out of the downgradient wells and cause a persistent concentration
of boron similar to background concentrations.
• Given the generally non -reactive, conservative behavior of boron,
closure activities emphasizing hydraulic control is the most beneficial
method for attenuating boron.
Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
Non -conservative COI cross sections and geochemical modeling support
the following observations regarding the geochemical conditions affecting
the extent of COI -affected groundwater represented by arsenic and
selenium, non -conservative (reactive) COIs downgradient of Source Area 1
(Figures 5-13a and 5-13b; Appendix G):
• A notable Site characteristic regarding arsenic accumulation is that
the Site was formerly a wetland prior to installation of the ash basins.
The high concentrations of organic matter, iron, and other nutrients
within a wetland have been observed to lead to accumulation of
arsenic and heavy metals (Appendix G). Thus, the observed
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concentrations of arsenic might be due to accumulation within
residual wetland soils after basin installation.
• In the 1984 and 1971 basins, the simulated concentrations of arsenic
remain less than the comparative criteria for the upper surficial flow
zone but are initially greater than the comparative criteria in the
lower surficial flow zone within Source Area 1. Flow and transport
modeling indicates the major input of groundwater into the 1971
basin is through the lower surficial flow zone (Appendix F). Thus,
the observation of greater arsenic concentrations in the lower
surficial flow zone indicates this zone was the main input of arsenic
into the 1971 basin prior to excavation.
• In the presence of high concentrations of ferrihydrite, arsenic
sorption is very strong and will drastically reduce pore water arsenic
concentrations. However, even with ferrihydrite present, other
oxoanions like sulfate (SO4 Z) and phosphate (PO4 3) will compete
with arsenate (As04 3) for ferrihydrite sorption sites and limit arsenic
sorption.
• Based on these results, greater concentrations of arsenic in pore
water might be expected if both of the following situations occur:
1. Elevated levels of sulfate and phosphate are present
2. pH and EH conditions are decreased which will result in the
dissolution of ferrihydrite and loss of sorption sites
• Changes in pH and competition with anions (e.g., chloride and
sulfate) will have a major effect on selenium groundwater
concentrations. The selenium concentrations observed in wells in the
northern region of the Site are influenced by competition with sulfate
and chloride; it is expected that the concentrations would gradually
decrease as all three anions are washed out of the system
downgradient to the west. The time for this to occur depends on the
groundwater flow rate and changes in concentration of all three ions
over time. As sulfate and chloride have lower Ka values, those anions
are expected to wash out of the system first, followed by selenium.
Given the increasing trends in groundwater dissolved oxygen
concentrations and oxidation-reduction potential and decreasing
trends in iron and manganese concentrations identified in the post -
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excavation groundwater conditions evaluation (Appendix L), arsenic
concentrations are expected to attenuate naturally in the future as
groundwater becomes more oxic and iron and manganese in
groundwater precipitate as oxide minerals, providing sorption sites
for arsenic.
Variably Reactive Constituents
(CAP Content Section 6.A.e.iii)
Variably reactive COI cross sections and geochemical modeling support the
following observations regarding the geochemical conditions affecting the
extent of COI -affected groundwater represented by molybdenum and
strontium, variably reactive COIs downgradient of Source Area 1
(Figures 5-14a and 5-14b; Appendix G):
The greatest geochemical control of molybdenum and strontium
mobility is pH. Any activities that cause an increase in pH may lead
to increased mobility of variably reactive constituents. Changes in EH
would only indirectly influence mobility by changing the
concentration of HFO sorption sites. Therefore, like many other
COIs, a critical concern is maintaining Site conditions that allow
ferrihydrite to persist.
o The pH and EH ranges observed at Sutton and predicted in the
geochemical model indicate that ferrihydrite would persist if
the current geochemical conditions continue after excavation.
The simulated, relatively persistent concentrations of molybdenum
in the geochemical model are reasonably consistent with
groundwater measurements in the CCR-110 through CCR-114 well
clusters since 2016. Concentrations in the lower flow zone appear to
be decreasing slightly while those in the upper flow zone appear to
remain relatively stable or are decreasing.
• Post -excavation groundwater monitoring for molybdenum can
confirm whether the accumulation of molybdenum from sorption
and input from upgradient wells would sustain the observed
concentrations.
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5.2 Summary of Human and Ecological Risks
The human health risk assessment evaluated current and future exposure scenarios to
assess potential human health risks. The following conclusions were made:
• Exposure to CCR constituents by current and future residences is considered an
incomplete pathway. There are no residences located adjacent to the Site. Current
and future residents are not at risk under current Site conditions.
• On -Site groundwater and soil pose no carcinogenic or non -carcinogenic risk for
the trespasser, commercial industrial worker, and construction worker under
exposure scenarios.
• No evidence of carcinogenic or non -carcinogenic risks associated with the
recreational swimmer, wader, or boater exposure scenarios was identified.
• No evidence of carcinogenic or non -carcinogenic risks associated with the
recreational fisher exposure scenario was identified.
• There is no increase in estimated risks for the subsistence fisher exposure
scenario attributable to the source areas. Vanadium in upstream surface water
samples also resulted in a non -carcinogenic risk estimate (HQ) greater than 1.0.
Hexavalent chromium concentrations in upstream surface water samples also
resulted in estimated values within USEPA's range for excess lifetime cancer
risk (ELCR). This indicates the modeled concentration of vanadium and
hexavalent chromium in fish tissue is likely overestimated.
The ecological risk assessment evaluated current and future exposure scenarios to
assess potential ecological risks. The following conclusions were made:
Ecological Exposure Area 1 (Cooling Pond)
• No risks were identified for the great blue heron and river otter exposed to
surface water and sediments in the cooling pond.
• The mallard, killdeer, and muskrat populations had modeled risk results for
aluminum. Aluminum occurs naturally in soil, sediment, and surface water in
this area. The modeled risk estimates for exposure of aluminum to the killdeer,
mallard, and muskrat are considered negligible.
Copper, selenium and vanadium sediment concentrations resulted in potential
ecological risk for killdeer, mallard, and muskrat populations. Substituting
background concentrations of vanadium and selenium in the model also results
in risk for those species. A conservative sediment fraction intake rate is factored
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into the ecological exposure model and likely overestimates risk for this endpoint
and constituents.
Ecological Exposure Area 2 (Cape Fear River)
• No risks were identified for the mallard duck, great blue heron, and river otter
exposed to surface water and sediments in the Cape Fear River.
• The mallard and killdeer populations had modeled risk results for aluminum.
Aluminum occurs naturally in soil, sediment, and surface water in this area. The
modeled risk estimates for exposure of aluminum to the killdeer and mallard are
considered negligible based on natural and background conditions.
Ecological Exposure Area 3 (Former Ash Basins)
Surface Soil:
• No risks were identified for the terrestrial species red-tailed hawk exposed to
surface soil in the former ash basins.
• The American robin, meadow vole, and red fox had modeled risk for
aluminum in surface soil. The model likely overstates risk as aluminum
occurs naturally in soil, sediment, and surface water in this area.
Subsurface Soil:
• The meadow vole and red fox had modeled risk in subsurface soil for
aluminum. The modeled risk estimates are considered negligible based on the
natural conditions of aluminum in soil.
In summary, there is no evidence of unacceptable risks to human and ecological
receptors exposed to environmental media potentially affected by CCR constituents at
Sutton. This conclusion is further supported by multiple water quality and biological
assessments conducted by Duke Energy as part of the NPDES monitoring program. The
risk assessment for Sutton is included as Appendix E.
5.3 Source Area 1 Evaluation of Remedial Alternatives
(CAP Content Section 6.D.a)
Technologies were screened (Table 5-6) and used to formulate the following three
groundwater remedial alternatives in the area of the 1971 and 1984 ash basins and FPA:
Remedial Alternative 1
1. Source control by excavation
2. Continued groundwater extraction at the eastern property line
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3. Confirmation monitoring
Remedial Alternative 2
1. Source control by excavation
2. Continued groundwater extraction at the eastern property line
3. Confirmation monitoring with a restricted groundwater use designation of
the limited area beneath the cooling pond where COI concentrations are
predicted to be greater than applicable groundwater standards
4. Five-year effectiveness monitoring plan (EMP) review
The flow and transport evaluation included a modeled pump and treat system used to
simulate a potential active corrective action system that could be used to achieve COI
Criteria within thirty years (Appendix F). This simulation includes 40 extraction wells
and 20 clean -water infiltration wells operating for thirty years and targets the former
1984 ash basin, 1971 ash basin, and FPA. Due to closure activities and groundwater flow
direction reversal, limited land surface is available downgradient of Source Area 1
suitable for extraction and injection wells. The simulated system utilized as much
downgradient land surface as possible. The simulation modeled 40 extraction wells
pumping approximately 2.9 million gallons per day (MGD) and 20 infiltration wells
pumping approximately 1.4 MGD (Appendix F).
Thirty years after the operation of the pump and treat system (2050), simulated
concentrations of boron and selenium are present beyond the compliance boundary at
concentrations greater than applicable criteria within the upper and lower surficial flow
zones (Appendix F). The pump and treat system simulation indicates that even with a
robust system (3.6 MGD extraction and 2.4 MGD infiltration), COI concentrations
greater than applicable criteria will remain beyond the compliance boundary after 30
years. Additionally, simulations indicate selenium concentrations greater than 02L
would be present beyond the compliance boundary under the pump and treat system
scenario for a longer period of time than under the MNA scenario (Appendix F). For
these reasons, a pump and treat system was determined to not be technically or
financially justifiable and was not selected as a remedial alternative (Appendix O).
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 5.4 and Section 5.5.
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5.3.1 Remedial Alternative 1
Alternative 1 is the use of source control, continued operation of interim
remedial measures, and confirmation monitoring of natural attenuation as a
remedial alternative to address groundwater COI concentrations greater than
regulatory standards.
Source Area 1 has undergone source control and interim remedial measures.
Source Area 1 has also undergone the extensive hydrogeologic characterization
necessary to evaluate natural attenuation processes and rates. Excavation of the
ash at Source Area 1 began on May 21, 2015, and was completed in July 2019.
Excavation of CCR in the FPA began in early 2020 and was completed in April
2020. The excavated ash was transported to an off -Site structural fill or placed in
the on -Site landfill.
The ash and ash pore water removal has changed the flow direction so that post -
excavation groundwater flow from the former basins is no longer toward the east
but is toward the cooling pond and Cape Fear River. The 9-well extraction
system captures groundwater in the small area to the west beneath the on -Site
landfill. Water that remains in the former 1971 basin, which is isolated from the
cooling pond by sheet piling and earthen dams, is planned to be mixed with
effluent water until the water meets NPDES discharge limits at Outfall 008 so
that the former 1971 basin can become part of effluent canal.
Since August 2017, nine extraction wells have been in operation to address
groundwater at the eastern property boundary (Figure 5-16). The extraction
wells have pumped more than 500 million gallons of groundwater for treatment
and discharge (SynTerra, 2020). The March 2020 sampling results of the
extraction wells show limited COIs greater than the 02L standard; the March
2020 sampling also indicates that boron concentrations in all of the extraction
wells are less than the 02L standard (Table 5-7). COI concentrations at off -Site
wells are decreasing. The extraction system BOD specifies four consecutive
monitoring events with no off -Site concentrations greater than COI criteria prior
to discontinuing system operations. Alternative 1 proposes continued operation
and annual reporting under the IAP program.
Site -specific groundwater data, including saturated material from the surficial
flow zones, has been collected at Sutton for MNA evaluation. A comprehensive
analysis of MNA is provided in Appendix I.
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The MNA evaluation included a review of the conceptual site model (CSM),
geological data, historical groundwater analytical results, groundwater -to -
surface water interactions, flow and transport modeling, and geochemical
modeling to determine whether MNA is an appropriate remedial alternative for
Sutton. MNA encompasses a strategy and set of procedures for using
physiochemical and biological processes in aquifers to reduce constituent
concentrations to values less than regulatory criteria (Appendix I).
The MNA evaluation concludes that COI concentrations downgradient of Source
Area 1 are variable but are generally stable or decreasing. Evidence of conditions
favorable for natural attenuation is beginning to emerge with recent data. The
hydrologic and geochemical conditions are anticipated to stabilize with time
after completion of the closure activities. A five-year post -excavation EMP is
proposed to confirm that natural attenuation is occurring as predicted or more
rapidly (Appendix I). The MNA evaluation includes a detailed discussion of
natural attenuation mechanisms that are occurring at the Site. Dominant
attenuation mechanisms identified and evaluated at the Site include:
• A Conservative COI — boron — is naturally attenuated by physical
processes such as dilution and dispersion but generally is not strongly
attenuated by reactions with aquifer solids.
Variably reactive COIs —molybdenum and strontium— are attenuated by
dilution and dispersion and have the potential to be attenuated by one or
more other mechanisms (sorption, precipitation, or ion exchange),
dependent on the pH and EH of the system.
• Non -conservative COIs — arsenic and selenium — are attenuated by
dilution and dispersion, sorption, and other reactions with aquifer solids.
Additional discussion and demonstration of natural attenuation of Source Area 1
COIs are included in Appendix I.
On the western side of the 1984 ash basin, some COIs are present in groundwater
at concentrations greater than the 02L standard. The flow and transport
modeling indicates the maximum extent of migration is approximately 375 feet
under the cooling pond, the groundwater discharge zone. The surface water
evaluation indicates 02B water quality criteria are met; therefore, attenuation
within the permitted wastewater treatment unit is protective of human health
and the environment.
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5.3.1.1 Problem Statement and Remedial Goals
CCR constituents in groundwater associated with the ash basins and the
FPA, at or beyond the compliance boundary at concentrations greater than
COI criteria are the focus of the CAP. The goal of corrective action is to
restore groundwater quality at or beyond the compliance boundary by
returning COIs to applicable COI criterion concentrations, or as closely
thereto as is economically and technologically feasible consistent with 15A
NCAC 02L. 0106(a).
The following groundwater COIs are addressed by corrective action
(Table 5-1):
• Arsenic • Selenium
• Boron • Strontium
• Molybdenum
The CSM and predictive modeling discussions summarize the foundations
for development of the alternative. More extensive discussion of the CSM
can be found in Section 4, discussion of flow and transport modeling can be
found in Appendix F, and discussion of geochemical modeling can be
found in Appendix G.
5.3.1.2 Effects of Source Control and Corrective Action
The CSM was updated to consider conditions after the completion of ash
excavation (Section 4). The source of ongoing COI migration from the ash
basins into groundwater was substantially reduced with the excavation of
the ash. Interim remedial measures have been initiated to eliminate COI
migration east of the 1971 ash basin. The groundwater flow direction is now
west, toward the cooling pond. The only known remaining source of COIs
is the water contained within the excavated areas and COIs sorbed to the
unsaturated or saturated material beneath the excavated source areas. COI
concentration reductions through natural attenuation processes in the
subsurface are anticipated. Confirmation monitoring of natural attenuation
would address COIs in the area near the ash basin compliance boundary
downgradient of Source Area 1.
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5.3.1.3 Screening Criteria Evaluation
Each alternative was screened using the following criteria:
1. Protection of human health and the environment
2. Compliance with applicable federal, state, and local regulations
3. Long-term effectiveness and permanence
4. Reduction of toxicity, mobility, and volume
5. Short-term effectiveness at minimizing effects on the environment
and local community
6. Technical and logistical feasibility
7. Time required to initiate
8. Predicted time required to meet remediation goals
9. Cost
10. Community acceptance
The results of the screening are included as Appendix O. Because the
groundwater downgradient of Source Area 1 is not used for drinking water
and would not be used for drinking water in the foreseeable future, there is
no risk to human health. Analytical results obtained from surface water
samples collected from the cooling pond and the Cape Fear River during
low -flow conditions indicate that the groundwater that migrates from the
ash basins is not resulting in COI concentrations greater than 02B surface
water criteria.
Existing data and the results from the flow and transport model and the
geochemical model suggest that natural attenuation mechanisms are
potentially applicable for all COIs, as described in Appendix H. The flow
and transport and geochemical modeling reports in Appendices F and G
provide detailed predictions, descriptions, and explanations of the effects of
MNA after excavation of the ash basins and FPA. The models are built and
calibrated using observed data representative of existing conditions. Recent
groundwater data from under the ash basins is not available due to ash
excavation activities. There is limited ground surface available in the
unsaturated portion of the former 1971 basin. Additional wells could be
installed but are not proposed due to the close proximity of waste boundary
wells. The conceptual MNA well network for Source Area 1 is presented on
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Figure 5-18. Collection of additional monitoring data to further assess the
effectiveness of source control is proposed for five years after approval of
this CAP. The EMP is further described in Section 5.11.
5.3.2 Remedial Alternative 2
Similar to Alternative 1, Alternative 2 uses source control, continued operation of
interim remedial measures, and confirmation monitoring of natural attenuation.
Additionally, in order to restrict the unlikely use of groundwater in this area, this
alternative proposes a restricted groundwater use designation (RS) (15A NCAC
02L .0104) for the small area beneath the cooling pond where COI concentrations
are predicted to be greater than COI criteria. The area proposed for RS
designation is shown on Figure 5-17. Alternative 2 also provides a five-year EMP
review.
5.3.2.1 Problem Statement and Remedial Goals
As described in Section 5.3.1.1, CCR constituents in groundwater associated
with Source Area 1 occur at or beyond the compliance boundary at
concentrations greater than applicable COI criteria. The goal of corrective
action is to restore groundwater quality at or beyond the compliance
boundary by returning COIs to concentrations less than COI criteria or as
closely thereto as is economically and technologically feasible consistent
with 15A NCAC 02L. 0106(a).
This alternative goes further than Alternative 1 by applying institutional
controls intended to prevent the unlikely use of groundwater downgradient
of the 1971 and 1984 ash basins under the cooling pond.
5.3.2.2 Effects of Source Control and Corrective Action
As discussed in Section 5.3.1.2, recent source control is a substantial
component of corrective action and has allowed the return to the natural
groundwater flow direction to the west except for the groundwater that is
influenced by the interim corrective action system. A restricted
groundwater use designation for the small area beneath the cooling pond
where predicted COI concentrations are greater than COI criteria would
prevent any unlikely use of groundwater and provide additional protection
to human health. The effectiveness of source control would be assessed
through routine monitoring for five years (Section 5.11).
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Measurements at Sutton over the past year demonstrate that while the pH is
remaining relatively stable within each flow zone, there is a notable increase
in the Ex of groundwater (Figure 5-15a) indicating that the groundwater is
returning to an oxidizing state, which will enhance sorption.
As the excavation of the 1971 and 1984 ash basins was completed relatively
recently (July 2019), it is expected that the system will continue to change
until new local equilibrium or a steady state condition is reestablished. This
is particularly important with respect to changes in pH and Ex which would
alter COI mobility. Collection of additional data in the future is needed to
determine if the current trends in geochemical conditions and COI
concentrations will continue as predicted or at a more rapid rate. It appears
the system is naturally approaching increased EH values (Figures 5-15b and
5-15c. Though not confirmed, the increased EH might be due to the large
flux of infiltrating rainwater after excavation.
This mechanism is further indicated to be occurring in Site groundwater
based on results from a post -excavation groundwater conditions evaluation
conducted by Arcadis, U.S. (Appendix L). Statistically significant increasing
trends in groundwater dissolved oxygen concentrations and oxidation-
reduction potential were demonstrated for the upper and lower surficial
flow zones. Generally decreasing to stable groundwater concentrations of
iron and manganese was also demonstrated.
These observations can be confirmed with the proposed five-year post -
excavation EMP (Section 5.11).
5.3.2.3 Screening Criteria Evaluation
The screening of Alternative 1 (Section 5.2.1.3) is also applicable for
Alternative 2 with the exception of the use of a Restricted Designation,
which would provide additional protection of human health through
institutional controls (Appendix O).
Because the groundwater downgradient of Source Area 1 is not used for
drinking water and would not be used for drinking water in the foreseeable
future, there is no risk to human health. This alternative further guards
against the use of groundwater as drinking water. Analytical results
obtained from surface water samples collected from the cooling pond and
the Cape Fear River during low flow conditions indicate that the
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groundwater migration from the ash basins is not resulting in COI
concentrations greater than 02B surface water criteria.
Effectiveness monitoring can be used to assess whether aquifer conditions
stabilize to oxic conditions favorable for COI concentration reductions. If
this does not occur, an active remedy could be developed to target areas
that require additional oxidation of COIs to achieve compliance. The active
remedy would be evaluated as part of the contingency option
(Section 5.12).
5.4 Source Area 1 Proposed Remedial Alternative Selected
Based on the alternatives analysis presented in Section 5.3 and summarized in
Appendix O, the selected remedy for groundwater remediation is Alternative 2. The
conceptual MNA network for Source Area 1 including the proposed Restricted
Groundwater Use area is presented on Figure 5-19.
5.4.1 Description of Proposed Remedial Alternative and
Rationale for Selection
The selected remedy for groundwater remediation, Alternative 2, is intended to
provide the remedial technology that has demonstrated the ability to provide the
most effective means for restoration of groundwater quality for Source Area 1.
Alternative 2 is proposed to restore groundwater quality at or beyond the
compliance boundary by returning COIs to acceptable concentrations (COI
criteria), or as closely thereto as is economically and technologically feasible. This
alternative is consistent with 15A NCAC 02L. 0106(a), and to address 15A NCAC
02L .0106(j) (CAP Content Section 6.E.a.i). Additionally, this alternative was
selected because it demonstrated the scalability to address COIs in groundwater
as needed after a five-year effectiveness monitoring period with institutional
controls on groundwater use.
Groundwater sampling results at Sutton over the past year demonstrate that
while the pH is remaining relatively stable within each flow zone, there is a
notable increase in the Ex of groundwater. This increase in Ex may lead to the
oxidation of Fe(II) to Fe(III) and potentially the precipitation of ferrihydrite,
which would provide additional sorption sites for COI attenuation. It appears
the system is naturally approaching elevated Ex values. Though not confirmed,
the increased Ex may be due to the large flux of infiltrating rainwater following
excavation. These observations can be confirmed with the proposed five-year
post -excavation EMP (Section 5.11).
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This alternative meets the corrective action objectives described in Section 1.0 of
this CAP Update in a reasonable timeframe. Although there are no significant
risks to human or ecological receptors, Alternative 2 would meet the regulatory
requirements most effectively.
All groundwater remedial alternatives evaluated contribute to continued
protection of human health and the environment; however, the approach of
Alternative 2 is the most practical solution given the scalability for compliance
and costs. The rationale for selections follows, and is based on multiple lines of
evidence, including empirical data collected at Sutton, geochemical modeling,
and groundwater flow and transport modeling.
The alternatives rely on natural attenuation processes, and while there is
evidence to suggest that natural attenuation is occurring, the effects of source
removal and interim actions are still being evaluated. The effectiveness of the
source control measures would be assessed for approximately five years to
evaluate the effects of interim measures and to confirm natural attenuation is
occurring as predicted.
Alternative 2 is readily implementable. The long-term effectiveness would be
documented through an effectiveness monitoring program detailed in
Section 5.11. The system would be adaptable based on effectiveness monitoring
field data results.
To comply with 15A NCAC 02L .0106(h), corrective action plans must contain
the following items, which are discussed in the following subsections:
• 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
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5.4.2 Design Details
The selected alternative does not require additional design details. The extraction
system is operating as designed and no changes are proposed to the design
details outlined in the BOD report (Geosyntec, 2017). Basic installation
components of the recommended alternative include:
• Restricted designation of groundwater under the cooling pond
approximately 375 feet west of the ash basins until achievement of COI
criteria
5.4.2.1 Process Flow Diagrams for All Major Components
of Proposed Remedy
The anticipated steps for construction and implementation of the alternative
do not warrant process flow diagrams. Alternative 2 is readily
implementable and does not require additional construction.
5.4.2.2 Engineering Designs with Assumptions,
Calculations, and Specifications
The anticipated steps for construction and implementation of the alternative
do not warrant additional assumptions, calculations, and specifications.
Alternative 2 is readily implementable.
5.4.2.3 Permits Needed for Remedy and Approximate
Schedule
No additional permits are needed for the selected alternative. The project
implementation schedule is included in Section 5.4.2.4.
5.4.2.4 Schedule and Approximate Cost of
Implementation
Since implementation of corrective action might be affected by factors that
are not yet well defined, the implementation schedule would be refined as
necessary as the project proceeds.
An implementation schedule for the proposed corrective action is provided
as Figure 5-22. The exact timeline of the schedule milestones is dependent
on various factors, including NCDEQ review and approval, weather, and
field conditions.
Duke Energy would provide reports to document progress; Duke Energy
would assume full responsibility for operation of the groundwater
remediation system.
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Reporting would 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 installation 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 on mutually
agreed upon intervals.
A detailed cost estimate for Alternative 2 is provided in Appendix N. The
cost estimate is based on capital costs for design and implementation, and
the operations and maintenance (O&M) and monitoring costs 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 five-year reporting, and routine and non -routine
maintenance costs.
5.4.2.5 Health and Safety Measures
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in
risks to human health related to Source Area 1 have been identified. The
groundwater corrective action is being planned to address regulatory
requirements. The risk assessment identified no current human health or
ecological risk associated with groundwater downgradient of the ash basins
and FPA. Water supply wells are located upgradient.
5.4.3 Requirements for 02L .0106(I) — MNA
(CAP Content Section 6.E.c)
The requirements for implementing corrective action by MNA, under
02L .0106(l), are provided here and in Appendix I. MNA would comply with
applicable regulations assuming the conditions provided in 02L can be achieved.
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State and federal groundwater regulations allow for MNA as an acceptable
remediation program if regulatory requirements are met. The following are the
applicable 02L regulations:
(l) Any person required to implement an approved corrective action plan for a
non -permitted site pursuant to this Rule may request that the Director approve
such a plan based upon natural processes of degradation and attenuation of
contaminants. A request submitted to the Director under this Paragraph shall
include a description of site specific conditions, including written documentation
of projected groundwater use in the contaminated area based on current state or
local government planning efforts, the technical basis for the request, and any
other information requested by the Director to thoroughly evaluate the request. In
addition, the person making the request must demonstrate to the satisfaction of
the Director: (1) that all sources of contamination and free product have been
removed or controlled pursuant to Paragraph (f) of this Rule, (2) that the
contaminant has the capacity to degrade or attenuate under the site -specific
conditions, (3) that the time and direction of contaminant travel can be predicted
with reasonable certainty; (4) that contaminant migration will not result in any
violation of applicable groundwater standards at any existing or foreseeable
receptor; (5) that contaminants have not and will not migrate onto adjacent
properties, or that: (A) such properties are served by an existing public water
supply system dependent on surface waters or hydraulically isolated
groundwater, or (B) the owners of such properties have consented in writing to
the request; (6) that, if the contaminant plume is expected to intercept surface
waters, the groundwater discharge will not possess contaminant concentrations
that would result in violations of standards for surface waters contained in 15A
NCAC 2B .0200, (7) that the person making the request will put in place a
groundwater monitoring program sufficient to track the degradation and
attenuation of contaminants and contaminant by-products within and down
gradient of the plume and to detect contaminants and contaminant by-products
prior to their reaching any existing or foreseeable receptor at least one year's time
of travel upgradient of the receptor and no greater than the distance the
groundwater at the contaminated site is predicted to travel in five years; (8) that
all necessary access agreements needed to monitor groundwater quality pursuant
to Subparagraph (7) of this Paragraph have 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.
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Appendix I includes a detailed checklist for MNA requirements at Sutton
(Section 8.0). Sutton meets all requirements for MNA with the exception of a
demonstration of natural attenuation with distance on the western edge of both
source areas using monitoring well data. Due to reversal of groundwater flow
direction at the Site, there is insufficient land surface downgradient of the source
areas to monitor attenuation with distance. The downgradient wells are located
at or near the waste boundary. A five-year post -excavation monitoring period is
proposed to allow sufficient time to collect post -excavation groundwater data
and confirm predicted natural attenuation of COIs downgradient of the source
areas.
5.4.4 Requirements for 02L .0106(k) —Alternate Remediation
Goals
(CAP Content Section 6.E.d)
Source Area 1 is governed by CAMA and thus does not meet the requirements
under .0106(k).
5.5 Source Area 1 Summary and Conclusions
This CAP Update meets the corrective action requirements for Source Area 1 under G.S.
Section 130A-309.211 and 15A NCAC 02L .0106 and also addresses
15A NCAC 02L .01060). This CAP Update proposes a remedy for COIs in groundwater
associated with Source Area 1 that are beyond the compliance boundary. This CAP
Update provides:
• A groundwater remediation approach that can be implemented
• A screening and ranking process of multiple potential groundwater corrective
action alternatives that address areas requiring corrective action
• A selection and description of the favored corrective action groundwater
remedy: Alternative 2 — source control by excavation, continued operation of the
groundwater extraction system, confirmation monitoring with an RS designation
of a small portion of the cooling pond, and a five-year EMP review period
• A schedule for the implementation and operation of the corrective action
strategy
• A monitoring plan for evaluating the effectiveness of corrective action on the
restoration of groundwater quality
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SOURCE AREA 2 (SA2) — FADA AND FCPA
5.6 SA2 Extent of Constituent Distribution
This section provides an in-depth review of constituent characteristics associated with
Source Area 2 and the mobility, distribution, and extent of constituent migration within,
at, and beyond the point of compliance. The ash basin compliance boundary extends
into a portion of the FADA. Source Area 2 does not have a compliance boundary. The
discussion in the following sections references the compliance boundary of the ash
basins, which extends to the northern area of the FADA, as the point of compliance for
Source Area 2 (Figure 1-1). The majority of Source Area 2 is beyond, and downgradient
of, the compliance boundary.
Source Area 2 is considered the outermost boundary of the combined extent of the
FADA and FCPA (Figure 2-1). Potential effects of the FADA and FCPA on groundwater
would be addressed by the groundwater remedies proposed herein.
As outlined in Section 5.0, a COI Management Plan was developed at the request of
NCDEQ to evaluate and summarize COI concentrations in groundwater at the Site.
Results of this COI Management Plan are used to identify areas that might require
corrective action and to determine appropriate Site -specific mapping of COI
concentrations on figures based on the actual distribution of each COI in Site
groundwater. Table 5-9 presents the COI management matrix for determining COIs
subject to corrective action in groundwater beneath and downgradient of the FADA
and FCPA.
Constituent Management Approach
As outlined in Section 2, remediation goals are calculated in this CAP Update for the
non-CAMA Source Area 2 (the FADA and FCPA) using the North Carolina Risk
Calculator. In the case of this Source Area, risk -based remediation goals are appropriate
for determining corrective action objectives. For source areas not regulated by CAMA,
G.S. 130A-310.65 through 130A-310.77 (as amended by Session Law 2015- 286) allows
risk -based remediation as a cleanup option at sites where the use of remedial actions
and land use controls can bolster the safety of properties for intended uses. Therefore,
under state regulation and guidance, groundwater cleanup values can be derived using
a risk -based approach and applied as remediation goals at industrial sites. Because the
measures are risk -based, the remediation goals are protective of human health. Source
Area 2 was evaluated using this approach.
As detailed in Appendix E and summarized in the table below, concentrations of boron,
chromium (VI), molybdenum, selenium, strontium, sulfate, and vanadium at wells near
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the FADA and FCPA are less than the applicable risk -based concentrations calculated
for the Source Area 2 (86 µg/L for beryllium; 53 µg/L for cadmium; 2,608 µg/L for
nickel, 83,115 µg/L for strontium, 1 µg/L for thallium, 437 µg/L for vanadium, and
41,819 µg/L for zinc). Risk -based concentrations were not calculated for sulfate and TDS
because the NCDEQ risk calculator does not include those COIs. Concentrations of
arsenic, cobalt, iron, lithium, and manganese are greater than the applicable risk -based
concentrations calculated for the Source Area 2.
2018 CSA Update
Constituents of
Interest
02L
Standard/
IMAC
Maximum
Site -specific
BTV
Calculated Risk-
Based
Remediation Goal
Maximum
Concentration
Near Source Area 2
Alkalinity
20 mg/L
165 mg/L
NC
272 mg/L
Arsenic
10 lag/L
14 lag/L
8.3 lag/L
141 Ng/L
Boron
7001ag/L
501ag/L
5,5411ag/L
1,2901ag/L
Calcium
NE
68 mg/L
NC
218 mg/L
Chloride
250 mg/L
30 mg/L
NC
78 mg/L
Cobalt
1 lag/L
7 lag/L
8.0 lag/L
9.0 Ng/L
Chromium (VI)
10 lag/L
0.1 lag/L
37 lag/L
0.13 lag/L
Fluoride
2 mg/L
0.5 mg/L
NC
0.67 mg/L
Iron
300 lag/L
28,300 lag/L
19,394 lag/L
33,050 Ng/L
Lithium
NE
5 fag/L
55 lag/L
102 Ng/L
Magnesium
NE
3 mg/L
NC
26.2 mg/L
Manganese
50 lag/L
744 lag/L
484 lag/L
1,148 Ng/L
Molybdenum
NE
1 pg/L
139 pg/L
79 lag/L
Potassium
NE
5 fag/L
NC
11.6 mg/L
Selenium
20 pg/L
1 pg/L
139 pg/L
1.29 lag/L
Sodium
NE
13 mg/L
NC
67.1 mg/L
Strontium
NE
167 lag/L
16,623 fag/L
2,200 lag/L
Sulfate
250 mg/L
22 mg/L
NC
404 mg/L
Total Dissolved
Solids
500 mg/L
880 mg/L
NC
723 mg/L
Vanadium
0.31ag/L
2lag/L
871ag/L
741ag/L
Notes:
Calculated risk -based remediation goals are taken from Appendix E
Maximum concentrations are the maximum LCL95/CTV for Source Area 2 (Table 5-12)
Grey highlighted, bold cells indicate maximum constituent concentrations that are greater than the calculated
risk -based cleanup value. See Table 5-9 for additional evaluation details.
NE - not established
mg/L - milligrams per Liter
pg/L - micrograms per Liter
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Assessment of the coal pile was completed in July 2019. Methods, data, results, and
conclusions of that assessment are included as Appendix M. Risk -based remediation
goals are not included in the assessment evaluation. Alternative remedial goals are used
in the following discussion to identify COIs associated with the FADA and FCPA that
require corrective action.
As discussed in the beginning of Section 5, a 'COI management process' was developed
by Duke Energy at the request of NCDEQ to gain understanding of the COI behavior
and distribution in groundwater distribution and to select the appropriate remedial
approach. In general, the COI management process consists of three steps:
Step 1. Regulatory Review: Evaluate the applicable regulatory context
Step 2. COI Mobility: Evaluate of the mobility of target constituents
Step 3. COI Distribution: Determine the distribution of constituents within Site
groundwater
The management process uses a matrix evaluation [Table 5-9 (CAP Content Section
6.A.c.i.2)].
This COI management process for Source Area 2 is supported by multiple lines of
evidence, including empirical data collected at the Site, geochemical modeling,
groundwater flow and transport modeling, and the human health and ecological risk
assessment. This approach has been used to understand and predict COI behavior in
the subsurface related to Source Area 2 or COIs that are naturally occurring. COIs in
groundwater at concentrations greater than COI criteria that are related to Source Area
2 would be subject to corrective action evaluation. Remediation goals have been
calculated. COIs that are naturally occurring at concentrations greater than remediation
goals and COI criteria do not require corrective action.
Using the COI management process, 19 of 20 inorganic groundwater COIs exhibit mean
concentrations that are currently less than remediation goals and COI criteria at or
beyond compliance boundary, or have few concentrations greater than comparison
criteria but with no discernable COI plume. These constituents are not mapped on
figures in this 2020 CAP Update. These 19 constituents include:
• Boron
• Molybdenum
• Alkalinity • Calcium
• Chloride • Selenium
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• Chromium (VI)
• Strontium
• Cobalt
• Sulfate
• Fluoride
• Manganese
• Iron
• TDS
• Lithium
• Vanadium
• Magnesium
• Sodium
• Potassium
Those constituents are not expected to migrate distances at or beyond the compliance
boundary for Source Area 2 or migrate distances that would present risk to potential
receptors. Based on geochemical modeling, constituents from Source Area 2 are
predicted to remain at stable concentrations, typically less than remediation goals and
COI criteria.
As shown in Table 5-9, the only remaining COI, arsenic, exhibits concentrations greater
than the BTV and 02L standard in groundwater downgradient of Source Area 2 at or
beyond the compliance boundary. The groundwater BTV for arsenic in the lower
surficial (14 µg/L) is greater than both the 02L standard (10 µg/L) and the calculated
remediation goal (8 µg/L). Therefore, the BTV is the appropriate remediation goal.
Results of the COI Management Plan evaluation were used to identify COIs for
mapping on figures in the CAP Update. COIs to be mapped include arsenic and boron.
Boron concentrations downgradient of Source Area 2 are not greater than the
remediation goal (5,541 µg/L). The maximum extent of CCR and coal -affected
groundwater migration for all flow zones is generally represented by boron
concentrations greater than the 02L standard (700 µg/L). Boron concentrations
downgradient of Source Area 2 are mapped in the CAP Update to illustrate the
horizontal and vertical extent of COI migration.
Results of the COI Management Plan evaluation were also used to identify areas that
require groundwater corrective action as described in Section 5.6.3 based on the actual
distribution of each COI in Site groundwater.
5.6.1 Source Material within the Waste Boundary
(CAP Content Section 6.A.a)
An overview of the source material formerly present within the FADA and
FCPA is presented in the following subsections.
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Recent monitoring data from within the waste boundary of the FADA is limited
because of well abandonments associated with ash excavation.
Available data are from April 2015 until June 2019; wells within the FADA waste
boundary were abandoned as part of excavation.
No wells were installed within the actual footprint of the FCPA because the
surface depression left after coal removal collects stormwater and is saturated
near the ground surface or has standing water. Therefore, the monitoring wells
were installed upgradient and downgradient of the FCPA.
5.6.1.1 Description of Waste Material and History of
Placement
Ash generated from coal combustion was originally sluiced to the FADA,
also known as the "lay of land area" (Figure 2-1). The FADA is located
south of the ash basins, on the south side of the cooling water effluent canal
and near the former coal pile area (Figure 1-4). It is believed that ash might
have been sluiced to this area from approximately 1954 to 1972. The FADA
contained approximately 840,000 tons of ash, which varied in thickness
from a few feet to 17 feet. The ash in the FADA extended to the
groundwater table in most areas. The excavation of the ash was completed
in June 2020. The water is separated from the effluent canal by sheet piling
and earthen dams.
Coal was historically stored at the Site's coal pile (now the FCPA) an
unlined area located south of the FADA between the power plant and the
Cape Fear River. The FCPA consists of approximately 14 acres bounded to
the north by the FADA, to the east by vacant land formerly containing plant
buildings (now razed) and parking areas, and to the south and west by the
cooling pond and intake canal. Coal was primarily received by rail during
the entire operation of the coal-fired power plant. During a short period
from 2006 to 2008, coal was also transported by barge, offloaded from
vessels on the Cape Fear River, and then transported by conveyor to the
FCPA. The coal that was remaining after decommissioning of the coal units
in 2013 was removed from 2013 to 2015. A bowl -shaped depression remains
as the footprint of the FCPA.
5.6.1.2 Specific Waste Characteristics of Source Material
Source characterization of coal ash is described in Section 5.1.1.2.One ash
sample from AB-2 was collected during the CAMA investigation from the
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FADA for physical and chemical testing (Figure 1-3). The physical and
chemical properties discussed in Section 5.1.1.2 are similar to those of the
FADA with the exception that it is likely that the FADA contained less fly
ash than the basins since the ash placed there was generated prior to use of
air pollution control systems.
At the time of CAP preparation, ten (10) samples have been collected during
ash excavation of the FADA as required by Superior Court Civil Action No.
13-CVS-11032 order by Superior Court Judge Paul Ridgeway on June 1,
2016 in settlement between NCDEQ, Sierra Club, Waterkeeper Alliance,
Cape Fear River Watch, Inc., and Duke Energy (13-CVS-11032, 2016). SPLP
results are not available for ash samples collected from the FADA. For
informational purposes, total metal analytical results are included in
Appendix C, Table 5.
Coal ash is produced from the combustion of coal. The coal is dried,
pulverized, and conveyed to the burner area of a boiler. The Site started
operations in 1954 and eventually consisted of three coal-fired boilers that
primarily used bituminous coal as fuel to produce steam. Bituminous coal
ash typically yields slightly acidic to alkaline solutions (pH 5 to 10) on
contact with water. Additional discussion of characteristics of coal stored at
the FCPA is included in Appendix M.
5.6.1.3 Interim Response Actions
Interim response actions to date in the area of the FADA and FCPA include
excavation of ash previously contained within the FADA and removal of
coal from the Site (Table 5-10). The coal was removed from 2013 to 2015
after the Site's coal-fired units were decommissioned. Ash excavation
activities at the FADA and changing Site conditions that pertain to the
excavation of the ash are discussed in the following subsections:
FADA Excavation and Coal Removal
Excavation of the FADA began in July 2019 and was completed in June
2020. The FADA is currently filled with water that is separated from the
cooling pond by sheet piling and an earthen dike. In accordance with the
terms of National Pollutant Discharge Elimination System (NPDES) permit
NC001422 (effective July 1, 2020), planned additional closure activities
consist of combining water in the excavated FADA and with water from the
Site's cooling water effluent canal. The water can then be discharged to
NPDES permitted Outfall 001.
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Coal has not been stored on -Site since 2015. The FCPA was assessed during
the summer of 2019. Results of that assessment are included as
Appendix M.
Results of Source Removal
No significant changes to water levels in the area of the FADA and FCPA
were observed during ash excavation activities. Due to excavation and
dredging of ash below the water table, the excavated FADA contains water,
which is separated from the effluent canal with steel sheet piling and
earthen dams. The inundated portion of the FADA is a localized
groundwater recharge zone.
At the time of CAP Update preparation, no post -excavation data pertaining
to wells downgradient of the FADA are available. Coal has not been stored
on -Site since 2015 but all FCPA wells are also downgradient of the FADA.
Source removal activities at the FADA have caused geochemical instability
in the FADA and downgradient areas causing COI concentrations to
increase in some areas. The horizontal extent and vertical extent of COIs
downgradient of Source Area 2 are discussed in Section 5.6.3.
5.6.2 Extent of Constituent Migration Beyond the Compliance
Boundary
(CAP Content Section 6.A.b)
Since the FADA and FCPA do not have a compliance boundary, this section is an
overview of constituent occurrences in areas extending downgradient of the ash
and coal storage areas to groundwater discharge zones. The extent of potential
groundwater migration from Source Area 2 are the following groundwater -to -
surface water discharge zones downgradient of the area: the cooling pond, the
intake canal, and the Cape Fear River.
Analytical sampling results associated with the FADA and FCPA source areas
for each media are included in the following tables and appendices:
Soil: Appendix C, Table 4 and Tables 5-11a and 5-11b (CAP Content
Section 6.A.b.ii.1)
• Groundwater: Appendix C, Table 1 and Table 5-12 (CAP Content Section
6.A.b.ii.2)
• Seeps: Not applicable
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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)
5.6.2.1 Soil Constituent Extent
(CAP Content Section 6.A.b.ii.1)
Due to the presence of ash and shallow water table, only a limited number
of unsaturated soils were collected from within the FADA (Tables 5-11a
and 5-11b). Unsaturated soils were collected in the vicinity of the FCPA
during monitoring well installation (Tables 5-11a and 5-11b). The potential
for COI concentrations in unsaturated soil to contribute to observed COI
concentrations in groundwater is discussed in the following sections.
FADA Unsaturated Soils
Due to shallow groundwater within the FADA, unsaturated soil samples
could only be collected downgradient of the FADA during installation of
monitoring wells MW-15RB and MW-15RC (Figures 5-1a through 5-1d).
With the exception of calcium and magnesium, unsaturated soils collected
downgradient of the FADA do not contain constituent concentrations
greater than POG PSRGs (Figures 5-1a through 5-1d; Table 5-11a). Calcium
and magnesium concentrations are less than POG PSRGs in the deeper
sample collected at MW-15SB. This indicates COI concentrations decrease
with depth in soil and are less than POG PSRGs in soils located above the
water table. With the exception of arsenic, cobalt, iron, and vanadium, SPLP
results indicate no concentrations greater than COI criteria as a result of
unsaturated soils leaching COIs to groundwater (Table 5-11b). As noted in
the soil total metals results, SPLP constituent concentrations also decrease
significantly with depth. These results indicate unsaturated soil located
downgradient of the FADA do not represent an additional source of COIs
requiring corrective action.
FCPA Unsaturated Soils
Unsaturated soils were collected during monitoring well installation as part
of the FCPA assessment completed in July 2019 (Figures 5-1a through 5-1d;
Tables 5-11a and 5-11b). Results of that assessment are included as
Appendix M.
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Arsenic, iron, and vanadium were detected at concentrations greater than
the POG PSRG or BTV at only one location, MW-43SB, at a depth of 1 to 2
feet bgs. (Figures 5-1a through 5-1d; Table 5-11a). Arsenic and vanadium
are not detected at concentrations greater than POG PSRGs in the deeper
sample (2 to 4 feet bgs) collected at MW-43SB. The iron concentration in the
2- to 4-foot depth interval at MW-43SB (2,700 mg/kg) is less than half the
concentration of overlying soil and is similar to the Site BTV for iron (2,533
mg/kg). SPLP results indicate unsaturated soils near the FCPA have the
potential to leach concentrations of cobalt, iron, and vanadium at
concentrations greater than COI criteria. However, no SPLP results indicate
the potential to leach COIs to groundwater at concentrations greater than
the calculated remediation goals. These results indicate unsaturated soils
located near the FCPA do not represent an additional source of COIs
requiring corrective action.
5.6.2.2 Groundwater Constituent Extent
(CAP Content Section 6.A.b.ii.2)
The FADA and FCPA were not NPDES-permitted units and thus there is no
compliance boundary. The compliance boundary from the ash basin
extends to within the FADA. The maximum extent of constituent migration
in groundwater would be bound by the downgradient groundwater -to -
surface water discharge zones: the cooling pond, the intake canal, and the
Cape Fear River.
Boron is an effective indicator for evaluating CCR constituent migration in
groundwater due to low background concentrations and a low Ka value.
Boron is detected at concentrations greater than the 02L standard in
groundwater approximately 400 feet or less beyond the waste boundary of
the FADA west of the intake canal near the Cape Fear River. At the time of
CAP Update preparation, NCDEQ is currently reviewing a proposal to
revise the 02L boron standard to 4,000 µg/L. No groundwater samples
collected from Source Area 2 wells screened in the upper and lower surficial
flow zones contain boron at concentrations greater than 4,000 µg/L. Boron
concentrations associated with Source Area 2 are not greater than the
remediation goal (5,541 µg/L). The maximum compliance value for
groundwater in the area is 1,290 µg/L.
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Arsenic is the only COI requiring corrective action as a result of the COI
management process (Table 5-9). Arsenic in groundwater at concentrations
greater than the BTV is predicted to be approximately 600 feet or less
beyond the FADA waste boundary west of the FCPA and approximately
100 feet or less south of the FADA waste boundary. Arsenic concentrations,
in combination with boron concentrations, downgradient of Source Area 2
are mapped in the CAP Update to illustrate horizontal and vertical extent of
COI migration.
The cooling pond borders the FADA to the west. Arsenic was previously
detected in abandoned wells along the western FADA waste boundary at
concentrations greater than 02L in the upper surficial and greater than the
BTV in the lower surficial. The cooling pond is a groundwater discharge
zone that limits the horizontal extent of migration to the west of Source
Area 2. However, groundwater migration and discharge have not caused,
and are not predicted to cause, constituent concentrations to be greater than
current 02B surface water quality criteria in the cooling pond (Appendix K).
Generally, non -conservative and variably reactive constituents exhibit little
migration from the source area.
There are few exceptions where non -conservative and variably reactive
constituents occur in areas where boron is non -detect or less than the 02L
standards. Those exceptions are iron and vanadium concentrations in
monitoring well MW-43B. Iron and vanadium concentrations have
fluctuated more than other COIs on -Site, likely due to fluctuation in the
water table, which can cause precipitation and dissolution of COIs, and
concentration fluctuations (Appendix L). Geochemical (Appendix G) and
flow and transport (Appendix F) groundwater modeling results, predict
decreasing COI concentrations associated with Source Area 2.
A detailed matrix evaluation and rationale of groundwater constituents
requiring corrective action is presented in Table 5-9. Section 5.6.3 provides
isoconcentration maps and cross -sections depicting groundwater flow and
constituent distribution and extent in groundwater (CAP Content Section
6.A.b.i).
5.6.2.3 Seep Constituent Extent
(CAP Content Section 6.A.b.ii.3)
Does not apply to Sutton; no seeps have been identified at the Site.
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5.6.2.4 Surface Water Constituent Extent
(CAP Content Section 6.A.b.ii.4)
The extent of constituents in surface water related to both Source Area 1 and
Source Area 2 are discussed in Section 5.1.2.4.
5.6.2.5 Sediment Constituent Extent
(CAP Content Section 6.A.b.ii.5)
The extent of constituents in sediment related to both Source Area 1 and
Source Area 2 are discussed in Section 5.1.2.5.
5.6.2.6 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 upper and lower
surficial flow zone background locations and downgradient of Source Area
2 are included on Figure 5-23. Data used for the Piper diagrams include
groundwater data from June 2019 through March 2020 with a charge
balance between -10 and 10 percent. Evaluation of the Piper diagrams for
groundwater associated Source Area 2 (Figure 5-23) include:
Surficial wells located both upgradient and downgradient of the
FADA generally plot together. This supports the conclusion that
some COIs might be migrating from Source Area 1 beneath the
effluent canal.
Surficial wells located upgradient and downgradient of the FCPA
generally plot together. This supports the conclusion that the
primary source of COIs in Source Area 2 is the FADA. Groundwater
flows from the FADA through the FCPA.
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5.6.3 Horizontal and Vertical Extent of Groundwater in Need
of Restoration
(CAP Content Section 6.A.d.ii)
COIs in groundwater associated with Source Area 2 occur at concentrations
greater than remediation goals and COI criteria in the following areas within the
surficial flow zones:
• Within the footprint of the excavated FADA
• Southwest of the FADA, including the FCPA, to the Cape Fear River
Extent of COI -Affected Groundwater within Excavated Area of
FADA
The excavation of coal ash at the FADA has resulted in the formation of a water
feature with characteristics similar to the water within the 1971 ash basin
excavated area. The water in the excavated FADA contains arsenic at a
concentration of about 12 µg/L, which is greater than the 02L standard and
federal maximum contaminant levels (MCL) drinking water criteria (10 µg/L)
and the BTV value (14 µg/L). Data from wells surrounding the FADA support
the following observations regarding the extent of COIs in groundwater affected
by the FADA water:
Arsenic concentrations are greater than the 02L standard in the upper and
lower surficial flow zones in wells downgradient of the FADA
(Figures 5-24a and 5-24b).
• The excavated FADA is separated from the cooling pond by earthen
dams. The arsenic concentration in the cooling pond is much lower;
approximately 2 µg/L. As part of closure activities, water in the excavated
FADA be pumped out and replaced at an equal rate with water from the
cooling water effluent canal.
• Statistical analysis of the arsenic data in the area indicates increasing
concentrations in downgradient lower surficial flow zone wells (MW-
15RB, MW-15RC, MW-20D, MW-43C, MW-45B, and MW-45C;
Appendix L). Only two upper surficial wells exhibit increasing
concentrations for arsenic (MW-15RB and MW-43B).
Arsenic concentrations downgradient of the FADA are greater than
arsenic concentrations upgradient, indicating concentrations should
decrease in downgradient areas after source removal.
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Southwestern Extent of COI -Affected Groundwater
The southwestern extent of COI -affected groundwater by the FADA and FCPA
groundwater is defined by arsenic concentrations:
Arsenic was detected at concentrations greater than the 02L standard in
upper surficial zone wells MW-43B and MW-44B. Those wells are located
on the southern and western perimeter of the FCPA. The 02L value for
arsenic (10 µg/L) is the applicable comparative standard for arsenic in the
upper surficial.
• Arsenic was detected at concentrations greater than the BTV in lower
surficial zone well MW-44C. MW-44C is located on the downgradient,
western perimeter of the FCPA. The BTV for arsenic (14 µg/L) is the
appropriate comparative standard for arsenic in the lower surficial.
• Arsenic and boron was detected at concentrations greater than applicable
criteria in lower surficial monitoring well MW-45C (Figures 5-24a through
5-25b). MW-45C is located west of the intake canal; downgradient of the
FADA and FCPA. Concentrations are less than applicable criteria in the
upper surficial flow zone well at the same location (MW-45B). This
indicates COIs are migrating beneath the intake canal toward the Cape
Fear River in the lower surficial flow zone only. COIs in upper surficial
groundwater are likely discharging directly to the intake canal.
The 2019 calibrated flow and transport model aids in understanding
groundwater flow near Source Area 2 (Appendix F). Simulated
groundwater flow direction in the upper and lower surficial zones is
shown on Figures 4-3a and 4-3b. A portion of the groundwater migrating
from the 1971 ash basin area is flowing beneath the effluent canal into the
excavated FADA. The presence of the intake canal and Cape Fear River
causes groundwater to flow to the southwest upgradient of the FCPA. The
majority of groundwater upgradient of the FCPA is sourced from the area
southeast of the 1971 ash basin and FPA. Only a small fraction of the
northwestern portion of the former coal pile is affected by discharge from
the 1971 ash basin.
• In addition to the simulated groundwater flow maps, further evidence is
found in values of arsenic and boron in the wells north of the FADA but
on the south side of the intake canal (MW-13R, MW-13RD, MW-49B, MW-
49C, MW-47B, MW-47C, MW-16, and MW-16D). The wells closest to the
western side of the FADA (MW-13R, MW-13RD, MW-49B, and MW-49C)
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have concentrations of arsenic and boron greater than applicable criteria,
while the wells closes to the eastern side of the FADA (MW-47B, MW-47C,
MW-16, and MW-16D) contain much lower concentrations (Table 5-12).
There are six wells located on the south side of the FADA but upgradient
of the FCPA (MW-20, MW-20D, MW-46B, MW-46C, MW-15RB, and MW-
15RC). Evaluation of the arsenic data in these wells indicates one average
value greater than the 02L standard for arsenic at 15RB. The remaining
five average values for arsenic are below applicable criteria. These
findings also show that the FADA is not a significant source of COIs for
the FCPA.
Water quality data from wells constructed near the FADA and FCPA
show no evidence of plumes for the remaining COIs. Concentrations are
sporadic and more indicative of localized conditions rather than a defined
plume.
5.6.4 COI Distribution in Groundwater
COI distribution in groundwater is discussed based on constituent groupings,
determined by similar geochemical behavior and mobility. Based on the above
evaluation, arsenic (considered a non -conservative, reactive constituent) is the
only constituent with concentrations greater than applicable criteria in areas
beyond the compliance boundary.
Other COIs identified in the CSA but not mapped in this CAP Update occur
sporadically without a discernable plume within and downgradient of Source
Area 2.
5.6.4.1 Plume Stability
Mann -Kendall trend analysis was performed using constituent datasets for
groundwater wells within the waste boundary, between the waste
boundary and compliance boundary, and downgradient of Source Area 2,
at or beyond the compliance boundary (Table 5-13). Trend analysis and
results were prepared by Arcadis U.S. Inc. and are included as
Attachment A in Appendix L.
The analysis was performed using analytical results for samples collected
from 2019 through quarter 1 of 2020 pertaining to COIs identified in the
2018 CSA Update (Table 5-9). Trend analysis results are presented where at
least four samples were available and frequency of detection was greater
than 50 percent. Statistically significant trends are reported at the 95 percent
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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 percent 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)
For both source areas, a total of 2,415 datasets were evaluated for trends.
Excluding the NE trends described above, 88 percent of the remaining
datasets had statistically significant decreasing trends, stable trends, no
trends, or greater than 50 percent non -detect concentrations. Only 12
percent of the trends were statistically increasing. Excluding both NE and
ND trends described above, 85 percent of the remaining datasets had
statistically significant decreasing trends, stable trends, or no trends.
(Appendix L).
Trend analyses of groundwater monitoring wells downgradient of Source
Area 2 near or beyond the compliance boundary indicate the following:
In general, wells downgradient of the FADA show steady increases
and recent decreases for COIs with maximum detected values
greater than applicable criteria (Table 5-13). This indicates recent
instability in the system during source removal.
Wells downgradient of the FCPA show steady increases for COIs
with maximum detected values greater than applicable criteria
(Table 5-13). This observation shows further instability in the system
during FADA source removal. Wells downgradient of the FCPA
should be exhibiting stable or deceasing concentrations because
source material was removed prior to 2015.
Total statistically increasing trends account for 247 of the 2,128 datasets (12
percent excluding NE results). Major ions identified as Site COIs (alkalinity,
calcium, magnesium, potassium, and sodium) account for 47 percent of 247
total increasing concentration trends. These major ion constituents are
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commonly detected in Coastal Plain aquifer groundwater at the
concentrations detected in Site groundwater (Appendix L). It should also be
noted that no groundwater data is available at the time of CAP Update
preparation following ash excavation from Source Area 2. It is anticipated
that post -excavation concentrations will decrease due to natural
attenuation.
5.6.4.2 Site Geochemical Conditions Affecting COI
Behavior
The plume stability analysis was conducted to determine if COI
concentrations are decreasing, remaining steady, or increasing with time
(Appendix L). Following excavation of the ash, downgradient COI
concentrations are expected to decrease over time as the COIs are diluted by
upgradient groundwater and infiltrating rainwater. Analysis of the trends
presented in Appendix L revealed the following conclusions:
The plume is generally stable to decreasing for COIs in Site
groundwater.
Most major ions (sodium, potassium, calcium, magnesium, chloride,
and sulfate) as well as boron had decreasing concentrations
indicative of a stable to decreasing plume with time (i.e., dilution of
the residual COIs following excavation.
There were statistically significant increasing concentration trends in
a limited number of wells for arsenic, molybdenum and sulfate at or
beyond the compliance boundary (Appendix L). Each of these COIs
exhibits some attenuation by sorption, ion exchange, or
(co)precipitation and thus may be more slowly removed from the
system by dilution from upgradient groundwater and infiltrating
rainwater.
As discussed in further detail in the geochemical report (Appendix G), the
groundwater system is expected to approach a new local equilibrium or
steady state condition. This is particularly important with respect to
changes in pH and Ex which would alter COI mobility. As the excavation
was completed recently (June 2020) and changes in Ex are being currently
observed (Appendix G), collection of additional data in the future is needed
to determine if the current trends in geochemical conditions and COI
concentrations will continue.
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Conservative Constituents
(CAP Content Section 6.A.e.i)
Not applicable; no conservative (non -reactive) COIs have been identified for
corrective action downgradient of Source Area 2.
Conservative COI cross sections with boron concentrations in groundwater
are provided for comparison purposes as Figures 5-26a and 5-26b.
Non -Conservative Constituents
(CAP Content Section 6.A.e.ii)
Non -conservative COI cross sections and geochemical modeling support
the following observations regarding the geochemical conditions affecting
the extent of COI -affected groundwater represented by arsenic, the non -
conservative (reactive) COI downgradient of Source Area 2 (Figures 5-27a
and 5-27b; Appendix G):
• As stated in Section 5.1.4.2, a notable Site characteristic regarding
arsenic accumulation is that the Site was formerly a wetland prior to
installation of the FADA and FCPA. The FCPA currently exhibits
wetland characteristics (saturated soil, cattails and bull rush
vegetation, etc.). The high concentrations of organic matter, iron, and
other nutrients within a wetland have been observed to lead to
accumulation of arsenic and heavy metals (Appendix G). Thus, the
observed concentrations of arsenic might be due to accumulation
within residual wetland soils after basin installation.
In the presence of high concentrations of ferrihydrite, arsenic
sorption is very strong and would drastically reduce pore water
arsenic concentrations. However, even with ferrihydrite present,
other oxoanions like sulfate (SO4 2) and phosphate (PO4 3) would
compete with arsenate (AS04 3) for ferrihydrite sorption sites and
limit arsenic sorption.
Based on these results, greater concentrations of arsenic in
groundwater downgradient of Source Area 2 might be expected if
each of the following occurs:
1. Elevated levels of sulfate and phosphate are present and
2. pH and EH conditions are decreased which would result in
the dissolution of ferrihydrite and loss of sorption sites.
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• Given the increasing trends in groundwater dissolved oxygen
concentrations and oxidation-reduction potential and decreasing
trends in iron and manganese concentrations identified in the post -
excavation groundwater conditions evaluation (Appendix L), arsenic
concentrations are expected to attenuate naturally in the future as
groundwater becomes more oxic and iron and manganese in
groundwater precipitate as oxide minerals, providing sorption sites
for arsenic.
Variably Conservative Constituents
(CAP Content Section 6.A.e.iii)
Not applicable; no variably reactive COIs have been identified for corrective
action downgradient of Source Area 2.
5.7 Summary of Human and Ecological Risks
The human health risk assessment evaluated current and future exposure scenarios to
assess potential human health risks. The following conclusions were made:
• With the exception of arsenic, all calculated risk -based remediation goals for the
non-CAMA units based on a conservative HQ of 0.2 are greater than the 02L and
IMAC values
• Exposure to Source Area 2 constituents by current and future residences is
considered an incomplete pathway. There are no residences adjacent to the
property. Current and future residents are not at risk under current Site
conditions.
• On -Site groundwater and soil pose no carcinogenic or non -carcinogenic risk for
the trespasser, commercial industrial worker, and construction worker under
exposure scenarios.
• No evidence of carcinogenic or non -carcinogenic risks associated with the
recreational swimmer, wader, or boater exposure scenarios was identified.
• No evidence of carcinogenic or non -carcinogenic risks associated with the
recreational fisher exposure scenario was identified.
• There is no increase in estimated risks for the subsistence fisher exposure
scenario attributable to the source areas. Vanadium in upstream surface water
samples also resulted in a non -carcinogenic risk estimate (HQ) greater than 1.0.
Hexavalent chromium concentrations in upstream surface water samples also
resulted in estimated values within USEPA's range for ELCR. This indicates the
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modeled concentration of vanadium and hexavalent chromium in fish tissue is
likely overestimated.
Ecological Exposure Area 1 (Cooling Pond)
• Refer to Section 5.2.
Ecological Exposure Area 2 (Cape Fear River)
• Refer to Section 5.2.
Ecological Exposure Area 4 (FCPA, FADA)
• No HQs based on NOAELs or LOAELs were greater than unity for the
terrestrial species red fox exposed to subsurface soil
• The meadow vole had limited (NOAEL-based) modeled risk results greater
than unity for exposure to aluminum and vanadium in subsurface soil.
In summary, there is no evidence of unacceptable risks to human and ecological
receptors exposed to environmental media potentially affected by Source Area 2
constituents at Sutton. This conclusion is further supported by multiple water quality
and biological assessments conducted by Duke Energy as part of the NPDES
monitoring program.
5.8 Source Area 2 Evaluation of Remedial Alternatives
(CAP Content Section 6.D.a)
The following two remedial alternatives pertaining to the groundwater associated with
Source Area 2 are evaluated (Appendix O):
Remedial Alternative 1
1. Source control by excavation
2. Monitored Natural Attenuation (MNA)
Remedial Alternative 2
1. Source control by excavation
2. MNA with a restricted use designation of groundwater beneath and
downgradient of Source Area 2
3. Five-year EMP review
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The flow and transport evaluation included a modeled pump and treat system used to
simulate a potential active corrective action system that would be used to achieve COI
criteria within thirty years (Appendix F). This simulation includes a total of 11
extraction wells and 13 clean -water infiltration wells operating for thirty years and
targets the FADA and FCPA. Due to closure activities and groundwater flow direction
reversal, limited land surface is available downgradient of both source areas suitable for
extraction and injection wells. The system was simulated to utilize as much
downgradient land surface as possible. The simulation includes 11 extraction wells
pumping approximately 0.8 MGD and 13 infiltration wells pumping approximately 0.9
MGD (Appendix F).
Thirty years after the operation of the pump and treat system (2050), simulated
concentrations of boron and selenium are present beyond the compliance boundary at
concentrations greater than applicable criteria within the upper and lower surficial flow
zones (Appendix F). The pump and treat system simulation indicates that even with a
robust system (0.8 MGD extraction and 0.9 MGD infiltration), COI concentrations
greater than applicable criteria will remain beyond the compliance boundary after 30
years. For these reasons, a pump and treat system was determined to not be technically
or financially justifiable and was not selected as a remedial alternative (Appendix O).
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 5.9 and Section 5.10.
5.8.1 Remedial Alternative 1
Alternative 1 is the use of source control, natural attenuation and effectiveness
monitoring to address groundwater concentrations greater than regulatory
standards.
Excavation of the ash at Source Area 2 began in July 2019 and was completed in
June 2020. Excavated ash was placed in the on -Site CCP Landfill.
Source Area 2 has undergone source control by excavation. Source Area 2 has
also undergone the hydrogeologic characterization necessary to evaluate natural
attenuation processes and rates.
Water that remains in the FADA, which is isolated from the cooling pond by
sheet piling and earthen dams, is planned to be mixed with effluent water until
the water meets NPDES discharge limits at Outfall 008 so that the FADA can
become part of effluent canal.
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Site -specific groundwater data have been collected from the surficial flow zones
at Source Area 2 for MNA evaluation. A comprehensive analysis of MNA is
provided in Appendix I.
The MNA evaluation concludes that COI concentrations downgradient of Source
Area 2 are variable but are generally stable or decreasing. Evidence of conditions
favorable for natural attenuation is beginning to emerge with recent data. The
hydrologic and geochemical conditions are anticipated to stabilize with time
after completion of the closure activities. A five-year post -excavation EMP to
confirm natural attenuation is proposed (Appendix P). The MNA evaluation
includes a detailed discussion of natural attenuation mechanisms that are
occurring at the Site. Dominant attenuation mechanisms identified and evaluated
at the Site include (Appendix I):
A non -conservative COIs — arsenic — would be attenuated by dilution
and dispersion, sorption, and other reactions with aquifer solids.
Additional discussion and demonstration of natural attenuation of Source Area 2
COIs is included in Appendix I.
Southwest of Source Area 2, COIs are present in groundwater at concentrations
greater than the 02L standard. The flow and transport modeling indicates the
maximum extent of migration is the Cape Fear River, the primary groundwater
discharge zone. The surface water evaluation indicates 02B water quality criteria
are met; therefore, natural attenuation would be protective of human health and
the environment with a groundwater use restriction in the area.
5.8.1.1 Problem Statement and Remedial Goals
COIs in groundwater associated with the FADA and FCPA were detected at
concentrations greater than applicable 02L standards/IMACs, calculated
remediation goals, or BTVs, whichever is greater. Remediation goals are to
restore groundwater quality by returning COIs to acceptable concentrations
COI criteria), or as closely there to as is economically and technologically
feasible consistent with 15A NCAC 02L. 0106(a).
The only groundwater COI to be addressed by corrective action in Source
Area 2 is arsenic, because other COI concentrations are less than applicable
criteria or don't exhibit a discernable plume as identified on Table 5-9 and
discussed in Section 5.1. The remedial goal for arsenic in groundwater is
the BTV, which is currently 14 µg/L.
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5.8.1.2 Effects of Source Control and Corrective Action
The vast majority of the source of COI migration from Source Area 2 into
groundwater was recently eliminated (June 2020) with the removal of ash.
The coal has been removed since 2015. COI concentration reductions
through natural attenuation processes in the are anticipated. The NPDES
permit allows for a maximum arsenic concentration monthly average of 44.8
µg/L to be discharged at Outfall 001. Recent data indicate a maximum
arsenic concentration of 12.8 µg/L in water contained within the excavated
FADA. Natural attenuation and under Alternative 1 would address COIs
downgradient of Source Area 2. Alternative 1 would be additionally
effective through the use of restricted groundwater use designations to
address COIs in groundwater southwest of Source Area 2.
Currently, COIs in groundwater do not pose an unacceptable risk to human
health or the environment under conservative exposure scenarios. If
implemented, effectiveness monitoring, combined with active remediation
of FADA water, would not pose an unacceptable risk to human health or
the environment (Appendix E). The application of a restricted use
designation of groundwater beneath and downgradient of Source Area 2
would provide additional protections to human health.
5.8.1.3 Screening Criteria Evaluation
Alternative 1 was screened using the following criteria:
1. Protection of human health and the environment
2. Compliance with applicable federal, state, and local regulations
3. Long-term effectiveness and permanence
4. Reduction of toxicity, mobility, and volume
5. Short-term effectiveness at minimizing effects on the environment
and local community
6. Technical and logistical feasibility
7. Time required to initiate
8. Predicted time required to meet remediation goals
9. Cost
10. Community acceptance
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The results of the screening are included as Appendix O. Because the
groundwater downgradient of Source Area 2 is not used for drinking water
and would not be used for drinking water in the foreseeable future, there is
no risk to human health.
Existing data and the results from the flow and transport model and the
geochemical model suggest that natural attenuation mechanisms are
potentially applicable for the COIs associated with Source Area 2, as
described in Appendix I. Time after excavation is needed to completely
confirm post -excavation trends observed in preliminary data (Appendix L).
No additional wells are proposed for the Source Area 2 conceptual MNA
well network (Figure 5-29). Collection of additional monitoring data, source
control effectiveness monitoring, to further evaluate natural attenuation
process following ash excavation is proposed for five years following
approval of the CAP in accordance with the EMP Section 5.11 and
Appendix P.
The flow and transport and geochemical modeling reports in Appendices F
and G provide detailed predictions, descriptions, and explanations of the
effects of MNA after excavation of the FADA and coal removal from the
FCPA. The models are built and calibrated using observed data
representative of existing conditions.
5.8.2 Remedial Alternative 2
Similar to Alternative 1, Alternative 2 uses source control, a restricted use
designation of groundwater beneath and downgradient Source Area 2, and
effectiveness monitoring for natural attenuation as a remedial alternative to
address COI concentrations greater than regulatory standards in groundwater
relative to regulatory standards. Alternative 2 also includes a five year
effectiveness monitoring period.
Additionally, to prevent the unlikely use of groundwater in this area as drinking
water unless the groundwater meets applicable standards, this alternative
proposes a restricted groundwater use designation (RS) [15A NCAC 02L .0104].
The conceptual MNA well network for Source Area 2 and area proposed for RS
designation are shown on Figure 5-30.
5.8.2.1 Problem Statement and Remedial Goals
As described in Section 5.8.1.1, COIs in groundwater associated with
Source Area 2 occur downgradient of the FCPA at concentrations greater
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than applicable COI criteria. The goal of corrective action is to restore
groundwater quality downgradient of the FCPA by returning COIs to
acceptable concentrations (COI criteria), or as closely thereto as is
economically and technologically feasible consistent with 15A NCAC 02L.
0106(a).
As with Alternative 1, the only groundwater COI to be addressed by
corrective action in Source Area 2 is arsenic, because other COI
concentrations are less than applicable criteria or don't exhibit a discernable
plume. The remedial goal for arsenic in groundwater is the BTV, which is
currently 14 µg/L.
5.8.2.2 Effects of Source Control and Corrective Action
The flow and transport model predicts reductions in COI concentrations
through natural attenuation processes in the subsurface. Natural
attenuation is predicted to address COIs downgradient of Source Area 2
after source control.
Measurements at Sutton over the past year demonstrate that while the pH is
relatively stable within each flow zone, there is a notable increase in the Ex
of groundwater (Figure 5-28) indicating that the groundwater is returning
to an oxidizing state, which will enhance sorption. As the excavation of
Source Area 2 was completed relatively recently (June 2020), it is expected
that the system will continue to change until new local equilibrium or a
steady state condition is re-established (Appendix G). Collection of
additional data in the future is needed to determine if the current trends in
geochemical conditions and COI concentrations will continue. It appears the
system is naturally approaching elevated Ex values. Though not confirmed,
the increased Ex may be due to the large flux of infiltrating rainwater after
excavation.
This mechanism is further indicated to be occurring in Site groundwater
based on results from a post -excavation groundwater conditions evaluation
conducted by Arcadis, U.S. (Appendix L). Statistically significant increasing
trends in groundwater dissolved oxygen concentrations and oxidation-
reduction potential were demonstrated for the upper and lower surficial
flow zones. Generally decreasing to stable groundwater concentrations of
iron and manganese was also demonstrated.
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These observations can be confirmed with the proposed five-year post -
excavation EMP (Section 5.11).
5.8.2.3 Screening Criteria Evaluation
The screening of Alternative 1 is also applicable to the screening criteria for
Alternative 2, Table 5-6. Because the groundwater downgradient of Source
Area 2 is not used for drinking water and would not be used for drinking
water in the foreseeable future, there is no risk to human health. This
alternative prevents the use of groundwater as drinking water.
Groundwater effectiveness monitoring as outlined in Section 5.11 and
Appendix P is designed to evaluate post -excavation conditions.
Collection of additional monitoring data to further evaluate natural
attenuation is proposed for 5 years.
5.9 Source Area 2 Proposed Remedial Alternative Selected
Based on the alternatives analysis presented in Section 5.8 and summarized in
Appendix O, the selected remedy for groundwater remediation of Source Area 2 is
Alternative 2. The conceptual MNA network for Source Area 2, including the proposed
Restricted Groundwater Use area, is presented on Figure 5-30.
5.9.1 Description of Proposed Remedial Alternative and
Rationale for Selection
The selected remedy for groundwater remediation, Alternative 2, is intended to
provide the remedial technology that has demonstrated the ability to provide the
most effective means for restoration of groundwater quality for Source Area 2.
Alternative 2 is proposed to restore groundwater quality downgradient of the
FCPA by returning COIs to acceptable concentrations (COI criteria), or as closely
thereto as is economically and technologically feasible. Alternative 2 is consistent
with 15A NCAC 02L. 0106(a), and to address 15A NCAC 02L .0106(j) (CAP
Content Section 6.E.a.i). Additionally, Alternative 2 was selected because it
demonstrated the scalability to address COIs in groundwater as needed after a
five-year effectiveness monitoring period with institutional controls on
groundwater use.
Alternative 2 meets the corrective action objectives described in Section 1.0 of
this CAP Update in a reasonable timeframe. Although there are no significant
risks to human or ecological receptors, Alternative 2 would meet the regulatory
requirements most effectively.
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Groundwater sampling results at Sutton over the past year demonstrate that
while the pH is relatively stable within each flow zone, there is a notable increase
in the Ex of groundwater indicating that the groundwater is returning to an
oxidizing state which will enhance sorption (Figure 5-28). This increase in Ex is
expected to lead to the oxidation of Fe(II) to Fe(III) and the precipitation of
ferrihydrite, which would provide additional sorption sites for COI attenuation.
It appears the system is naturally approaching elevated Ex values. Though not
confirmed, the increased Ex may be due to the large flux of infiltrating rainwater
following excavation. These observations can be confirmed with the proposed
five-year post -excavation EMP (Section 5.11).
The approach of Alternative 2 is the most practical solution given the scalability
for compliance and costs. The rationale for selection of Alternative 2 follows, and
is based on multiple lines of evidence, including empirical data collected at
Sutton, geochemical modeling, and groundwater flow and transport modeling.
Each alternative relies on natural attenuation processes, and, while there is
evidence to suggest that natural attenuation is occurring, the effects of source
removal are not yet documented. Those effects would be further evaluated
during the five-year effectiveness monitoring period.
Alternative 2 is readily implementable. The long-term effectiveness would be
documented through an effectiveness monitoring program detailed in
Section 5.11. The system would be adaptable based on effectiveness monitoring
field data results. Potential duplication of intensive construction efforts should be
considered.
To comply with 15A NCAC 02L .0106(h), corrective action plans must contain
the following items, which are discussed in the following subsections:
• 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
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5.9.2 Design Details
The selected alternative does not require additional design details. Basic
installation components of the recommended alternative include:
Restricted use designation of groundwater beneath and downgradient of
Source Area 2
5.9.2.1 Process Flow Diagrams for All Major Components
of Proposed Remedy
The anticipated steps for construction and implementation of the alternative
do not warrant process flow diagrams. Alternative 2 is readily
implementable and does not require additional construction.
5.9.2.2 Engineering Designs with Assumptions,
Calculations, and Specifications
The anticipated steps for construction and implementation of the alternative
do not warrant assumptions, calculations, and specifications. Alternative 2
is readily implementable.
5.9.2.3 Permits Needed for Remedy and Approximate
Schedule
No additional permits are needed for the selected alternative.
The schedule for project implementation schedule is included in
Section 5.9.2.4.
5.9.2.4 Schedule and Approximate Cost of
Implementation
An implementation schedule for the proposed corrective action is provided
as Figure 5-31. The exact timeline of the schedule milestones is dependent
on various factors, including NCDEQ review and approval, permitting,
weather, and field conditions. Since implementation of corrective action
might be affected by factors that are not yet well defined, the
implementation schedule would be refined as necessary as the project
proceeds.
Duke Energy would provide reports to document progress.
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Reporting would 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 installation 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 on mutually
agreed intervals.
A detailed cost estimate for Alternative 2 is provided in Appendix L. The
cost estimate is based on capital costs for design and implementation, and
on the operations and maintenance (O&M) and monitoring costs, on an
annual basis. The design costs include work plans, design documents, and
reports necessary for implementation of Alternative 2. 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 five-year reporting, and routine and non -routine
maintenance costs.
5.9.2.5 Measures to Ensure Health and Safety
There is no measurable difference between evaluated Site risks and risks
indicated by background concentrations; therefore, no material increases in
risks to human health related to Source Area 2 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 FADA
and FCPA. Water supply wells are located upgradient.
5.9.3 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 5.8.1 and Appendix I.
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5.9.4 Requirements for 02L .0106(k) -Alternate Remediation
Goals
(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 cleanup option where the use of remedial actions and land use
controls can manage properties safely for intended use. Risk -based corrective
action is where constituent concentrations are remediated to an alternative
remedial goal based on the actual posed risks instead of applicable BTVs 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
Proposed corrective action plan would be consistent with all other
environmental laws
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The FADA and FCPA are not CAMA-regulated source areas. In accordance with
North Carolina Session Law 2015-286, corrective action using risk -based
groundwater cleanup values as target cleanup levels is recommended based on
several conditions:
• The FADA and FCPA are eligible for corrective action using a risk -based
approach per Session Law 2015-286.
• Coal from the FCPA has been removed.
• No risk to potential receptors have been identified.
• No concentrations greater than 02B surface water standards have been
observed in the cooling pond or Cape Fear River.
• The groundwater plume is now confined to Duke Energy property and is
expected to remain on -Site.
• No water supply wells exist on -Site or within a 0.5-mile radius of Source
Area 2.
• The groundwater plume is generally stable, with the exception of some
trends of increasing COI concentrations that are anticipated to be
temporary in nature and that are beginning to demonstrate stability (e.g.,
concentrations at MW-44C and MW-45C).
• Natural attenuation processes are active at the Site and are expected to
persist.
• Ongoing future environmental monitoring is anticipated to confirm that
the above -mentioned conditions continue.
• The Site is owned and controlled by Duke Energy and is expected to
remain in use as an industrial site with an electrical generating natural gas
plant and maintenance facility.
• Land use controls would be applied to the Site and would be maintained
by Duke Energy.
There is some uncertainty regarding the distance arsenic has migrated beyond
the downgradient property line due to the conservative assumptions of the
predictive models (Appendices F and G). A five-year post -excavation
monitoring plan is proposed to collect sufficient post -excavation data to confirm
model predictions.
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5.10 Source Area 2 Summary and Conclusions
This CAP Update meets the corrective action requirements for Source Area 2 under G.S.
Section 130A-309.211 and 15A NCAC 02L .0106 and also addresses 15A NCAC 02L
.01060). This CAP Update proposes a remedy for COIs in groundwater associated with
Source Area 2 that are beyond the compliance boundary and to reduce constituent
concentrations in FADA water. This CAP Update provides:
• A groundwater remediation approach that can be implemented
• A screening and ranking process of multiple potential groundwater corrective
action alternatives that address areas requiring corrective action
• A selection and description of the favored corrective action groundwater
remedy: Alternative 2 — source control by excavation, MNA with an RS
designation of the area beneath and downgradient of Source Area 2, and a five-
year EMP review period
• A schedule for the implementation and operation of the corrective action
strategy
• A monitoring plan for evaluating the effectiveness of corrective action on the
restoration of groundwater quality (Section 5.11)
• Planned activities prior to full-scale implementation
5.11 Effectivness Monitoring Plan (EMP)
The following effectiveness monitoring plan (EMP) is designed to be applied to both
Source Area 1 and Source Area 2 to document progress towards remedial objectives
over time. The plan is designed to be adaptive and can be modified as groundwater
conditions change with time.
Duke Energy implemented an IMP that was submitted to NCDEQ on February 2, 2017.
Modifications to the plan were submitted on June 12, 2017, December 20, 2017, March 3,
2019, and April 4, 2019. An additional IMP revision is planned for Q3 2020 and would
align with the proposed EMP. The IMP includes the locations of groundwater wells
sampled quarterly and semiannually.
An EMP is required by G.S. Section 130A-309.211 (b)(1)(e). The IMP would be replaced
by the EMP upon NCDEQ approval of the CAP Update. The EMP would begin within
30 days of CAP approval in accordance with G.S. Section 130A-309.211(b)(3). The EMP
is designed to be adaptable and would target key areas where changes to groundwater
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conditions are most likely to occur due to corrective action and ash basin closure
activities. EMP key areas for monitoring include the following:
• Background locations
• Designated flow paths
• Areas of observed or anticipated changing Site conditions and/or where
increasing constituent concentration trends have been observed
• Perimeter areas to monitor plume stability and verify model simulations
• Areas monitored under separate state or federal requirements
EMP elements include the groundwater monitoring well system, surface water
monitoring locations, sampling protocol, frequency, parameters, and reporting
(Table 5-14). Effectiveness monitoring well locations are depicted on Figure 5-32. An
EMP work -flow and optimization process is outlined on a flow chart on Figure 5-34.
5.11.1 Progress Reports and Schedule
(CAP Content Section 6.E.e.i)
Schedule and reporting of EMP include:
• Annual Reporting Evaluation: The EMP would 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, model predictions and
regulatory standards. A flow diagram outlining the EMP work -flow and
optimization process is presented on Figure 5-34.
• Results of the evaluation would be reported in annual monitoring reports.
The reports would include the following:
o Laboratory reports on electronic media
o Tables summarizing the past year's monitoring events
o Historical data tables
o Figures showing the historical data versus time for the designated
monitoring locations and parameters
o Figures showing sample locations
o Statistical analysis (Mann -Kendall test) of data to determine
whether trends are present
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o Identification of constituent concentrations greater than
comparative values
o Groundwater elevation contour maps in plan view and COI
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)
o Any notable observations related to water level fluctuations or
constituent concentration trends attributable to extraction system
performance or water table drawdown
o Evaluation of the Contingency Plan decision metrics to determine
whether a contingency option is needed
o Recommendations regarding modifications to the plan
Five-year Review: Evaluation of statistical concentration trends, analytical
result comparison and model verification will be conducted. Flow and
transport models may be updated as part of the five-year review process
to refine future predictions and the associated routine data needed to
confirm the predictions.
The EMP can be re-evaluated and modified as part of each review period as
additional corrective actions are implemented or water quality observations
warrant modification of the plan. Optimization of the system could be evaluated
if the remedy is determined to be effective or when conditions re -stabilize after
the recently completed excavation activities. Optimization of the system could
include a lesser monitoring frequency and/or parameter list.
5.11.2 Sampling and Reporting Plan During Active Remediation
The EMP is a comprehensive effectiveness monitoring plan pertaining to key
areas of the Site (Figure 5-32 and Table 5-14). The following sections provide an
overview of the proposed post -excavation EMP. Additional detail is provided as
Appendix P.
Groundwater and Surface Water Monitoring Systems
The EMP monitoring would be conducted in coordination with required federal
regulatory groundwater and surface water monitoring to provide an integrated
and 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 with regard to
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potential receptors, and (3) confirm 02B/02L, flow and transport, and
geochemical model predictions. EMP systems and objectives are outlined below:
1. Groundwater remedy effectiveness monitoring would be implemented
(Figure 5-32). Monitoring objectives include:
• Compliance with 02L
• Compliance with 02B
• Measure and track the effectiveness of the existing extraction
system Monitor plume status (horizontally and vertically)
• Verify predictive model simulations
• Verify no unacceptable risks to downgradient receptors
• Verify attainment of active remedy objectives
• Identify new potential releases of constituents into groundwater
from changing site conditions
2. Federal regulatory groundwater monitoring has been implemented along
the waste boundary of the ash basins (Figure 5-33). Monitoring objectives
include:
• Compliance with applicable federal regulations and groundwater
protection standards (GWPS)
• Semiannual CCR groundwater monitoring. Required federal
regulatory monitoring may be discontinued after three consecutive
events of GWPS compliance for all wells in the system is achieved.
• CCR groundwater monitoring would provide horizontal and
vertical monitoring of plume status and changing Site conditions
along the former basin waste boundary and background locations.
The EMP would include 77 existing monitoring wells and 12 surface water
locations for performance and effectiveness monitoring (Table 5-14).
Groundwater Monitoring Flow Paths — Trend Analysis
The monitoring program would provide adequate horizontal and vertical
coverage to monitor:
Changes in groundwater quality as Site conditions change (e.g., the
aquifer returns to equilibrium conditions following excavation)
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• Transport rates
• COI plume stability
Horizontal and vertical coverage would be provided by using groundwater
monitoring wells located along primary groundwater flow paths downgradient
of the source areas. To monitor the effectiveness of the corrective action
approach, groundwater monitoring wells are proposed at specific intervals from
the source area toward a receptor as depicted in Figure 5-32 and described
below:
1. Within source area
2. At waste boundary
3. 250 feet downgradient from waste boundary (if accessible)
4. 500 feet downgradient of waste boundary (compliance boundary)
5. No less than one year of travel time upgradient of receptor or potential
receptor and no greater than the distance groundwater is expected to
travel in five years
Plume stability evaluation would be based primarily on results of trend analyses.
Trend analyses would be conducted using Mann -Kendall trend test. The Mann -
Kendall trend test is a non -parametric test that calculates trends based on ranked
data and has the flexibility to accommodate any data distribution and is
insensitive to outliers and non -detects. The test is best used when large variations
in the magnitude of concentrations may be present and may otherwise influence
a time -series trend analysis.
Trend analysis of designated groundwater monitoring flow path wells would be
part of the decision metrics for evaluating whether natural attenuation processes
would achieve remedial goals or whether the contingency plan for either source
area may be needed.
Sampling Frequency
Quarterly sampling for one year followed by semiannual monitoring after
implementation of corrective action is recommended for the 75 existing wells to
be included in the EMP. At the time of this CAP Update preparation, a limited
dataset of post -excavation IMP events (June 2019, September 2019, December
2019, and February 2020) is available for existing wells, which would be used to
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supplement trend analysis and to establish a baseline to evaluate corrective
action performance.
Due to the recently completed source control activities, existing wells would be
monitored quarterly for one year to build the dataset. Sampling frequency would
switch to semiannual following the first year of quarterly sampling. Quarterly
and semiannual monitoring of parameters outlined on Table 5-14 is proposed.
Quantitative evaluations would also determine additional data needs (i.e.,
increased sampling frequency) for refining statistical and empirical model
development.
Sampling and Analysis Protocol
(CAP Content Section 6.E.e.ii)
EMP sampling and analysis protocol would be similar to the existing IMP with
some tailoring to the anticipated changing Site conditions. Groundwater samples
would be collected using low -flow sampling techniques in accordance with the
Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment
Program, North Carolina, June 10, 2015 as revised March 2020. Surface water
samples would be collected in accordance with the Surface Water Evaluation Plan
to Assess 15A NCAC 2B Compliance — L.V. Sutton Energy Complex and the NCDEQ
comment letter to that evaluation plan (Appendix P). Samples would be
collected and managed in accordance with a quality assurance and control
protocol established in the sampling analysis protocol (SAP). Samples would be
analyzed by a North Carolina certified laboratory for the parameters listed in
Table 5-14. Laboratory detection limits for each constituent are targeted to be at
or less than applicable regulatory values (i.e., 02L, IMAC, or 02B).
The following seven field parameters would 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, redox potential, and oxidation reduction potential.
Major cations and anions would be analyzed to evaluate monitoring data quality
(electrochemical charge balance). Those include alkalinity, bicarbonate alkalinity,
aluminum, calcium, iron, magnesium, manganese, nitrate + nitrite, potassium,
and sodium. Ferrous iron, and sulfate analyses are also proposed as monitoring
parameters. Ferrous iron and sulfate analysis would be used to monitor potential
dissolution of iron oxides and sulfide precipitates as an indicator of changing
conditions. Those parameters are indicated on Table 5-14 as water quality
parameters.
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5.11.3 Sampling and Reporting Plan after Termination of Active
Remediation
Termination of the groundwater extraction system operation would be consistent
with the BOD for the system and implemented in accordance with 15A NCAC
02L .0106(m). Groundwater remediation effectiveness monitoring would
transition to the compliance monitoring in the area when NCDEQ determines
that the remediation monitoring phase is complete. Decision metrics for
termination of groundwater remediation are presented as a flow diagram on
Figure 5-35.
5.12 Proposed Interim Activities Prior to Implementation
(CAP Content Section 6.E. )
In accordance with requirements of G.S. Section 130A-309.211(b)(3), implementation of
the proposed corrective action would begin within 30 days of NCDEQ approval of the
CAP Update.
Additional interim activities to be conducted prior to implementation of the corrective
action remedy include:
• Continued IMP monitoring
• Implementation of the EMP within 30 days of CAP Update approval following
the existing IMP calendar schedule
5.13 Contingency Plan
(CAP Content Section 6.E.g)
5.13.1 Description of Contingency Plan
(CAP Content Section 6.E.g.i)
Conservative assumptions are used in the predictive modeling prepared as part
of this CAP Update. Greater than normal mobility constants were used for non -
conservative constituents such as arsenic and selenium. This causes the models
to predict longer timeframes for natural attenuation and increased mobility of
COIs. A five-year post -excavation EMP is proposed to confirm natural
attenuation of COIs is already happening and is progressing quicker than
indicated by predictive modeling. If, at the end of the five-year review period,
natural attenuation has not occurred at a satisfactory rate, a contingency plan
consisting of the following options can be implemented:
• Update the geochemical model with additional data to evaluate
effectiveness of natural attenuation
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• Update the flow and transport model with additional data to evaluate
effectiveness of natural attenuation
Review of applicable remedial technologies currently available to
determine the most appropriate and cost-effective solution for the COI
concentrations observed beyond the compliance boundary
If an active remedy contingency system is determined to be necessary, a design
plan for the operation of the system would be defined in greater detail, including
final design elements of the system not presented in this CAP Update. The
design plan would address the following areas:
• Operation of the system
• Groundwater quality over the previous five years
• Predicted groundwater COI concentrations after implementation of the
contingency option
A health -and -safety plan and an operations manual would be prepared as part of
the design documents. The health -and -safety plan would deal with the
management of spills and other unplanned releases, the operations manual
would address operational training, including backup personnel, emergency
response training, and reporting to appropriate authorities.
5.13.2 Decision Metrics for Implementing Contingency Plan
(CAP Content Section 6.E.g.ii)
The purpose of the EMP is to monitor groundwater and surface water conditions
relative to remedial action objectives. The EMP annual and five-year reviews can
be used to assess data trends to determine whether an active remedy a
contingency option is needed to achieve objectives in a reasonable timeframe.
This section outlines decision metrics and possible contingency actions.
Comparison to Predicted Concentrations
Many aspects of the proposed remediation approach are based on modeling and
predicted groundwater conditions. At the time of the five-year EMP review,
extensive post -excavation groundwater data would be available and can be used
to assess changes over time compared with model predictions. As discussed in
Section 5.11.1, flow and transport and geochemical models may be updated as
part of the five-year EMP review process to refine future predictions. If updated,
the models would be used both to confirm natural attenuation of COIs is
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occurring under a reasonable timeframe and to refine the contingency option
system design.
Groundwater Quality
The EMP includes a primary network of wells that would provide focused
monitoring in critical areas (Section 5.11). As outlined in Section 5.11.1, an
annual progress report is proposed to evaluate the effectiveness of corrective
action.
After each sampling event, data would be entered into a comprehensive data
base system. The proposed EMP annual progress report includes an annual
statistical analysis (Mann -Kendall test) of data to determine whether trends are
present and evaluate COI plume changes. To assess the effectiveness of changes
or to determine whether the unexpected data trends are temporary, increased
monitoring frequency or additional monitoring locations may be conducted.
If, at the end of the five-year EMP period, results continue to show non-
conformance with predicted natural attenuation, the need for the contingency
option would be re-evaluated. A technology would be selected if the following
conditions are not met at the end of the five-year EMP review:
• COI concentrations have decreased in EMP wells downgradient of the
source areas
• Surface water and sediment samples collected from 02B/02L EMP
locations have not resulted in violations of 02B surface water criteria
• No groundwater receptors are present downgradient of the source areas
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6.0 PROFESSIONAL CERTIFICATION
(CAP Content Section 7)
Certification for the Submittal of a Corrective Action Plan
Responsible Party and/or Permittee: Duke Energy Progress, LLC
Contact Person: Paul Draovitch
Address: 410 South Wilmington Street
City: Raleigh State: NC Zip Code: 27601
Site Name: L.V. Sutton Energy Complex
Address: 801 Sutton Steam Plant Road
City: Wilmington State: NC Zip Code: 28401
Groundwater Incident Number: Not Assigned
We, William Wylie Professional Geologist and James Clemmer, a Professional Engineer
for SynTgrra Corporation (firm or company of employment) do hereby certify that the
information indicated herein is as part of the required Corrective Action Plan (CAP) and that
to the best of our knowledge of the data, assessments, conclusions, recommendations and
other associated materials are correct, complete and accurate. ►,►��►►►�►►�+���.,,
CA
1; 2 ,C._ ? • •' .f ILL`
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William J Wylie, NC LG 2602
00"a 0CA 161"'p, roject Manager
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7.0 REFERENCES
(CAP Content Section 8)
Duke Energy. (2017). Permanent Water Supply — Water Treatment Systems, Performance
Monitoring Plan.
Geosyntec. (2016). Site Analysis and Removal Plan
Geosyntec. (2017). Interim Action Plan Implementation Basis of Design Report, L.V. Sutton
Energy Complex. January, 2017.
Geosyntec. (2018). Initial Site Assessment Report, Duke Energy L.V. Sutton Demolition Area,
NCDEQ Incident Number 94367. March 5, 2018.
Geosyntec. (2019a). Supplemental Risk Based Assessment Sampling Event, Duke Energy L.V.
Sutton Demolition Area, NCDEQ Incident Number 94367. July 15, 2019.
Geosyntec. (2019b). Initial Site Assessment Report Addendum, Duke Energy L.V. Sutton
Demolition Area, NCDEQ Incident Number 94367. March 29, 2019.
HDR and SynTerra. (2017). Statistical Methods for Developing Reference Background
Concentrations for Groundwater and Soil at Coal Ash Facilities. HDR Engineering,
Inc. and SynTerra Corporation.
Narkunas, James, 1980. Groundwater evaluation in the central Coastal Plain of North
Carolina: Raleigh, N.C., North Carolina Department of Natural Resources and
Community Development, 119 p.
NCDEQ. (2016) North Carolina Administrative Code Title 15A, Subchapter 02L, Section
.0100, Groundwater Classification and Standards. Retrieved from
http://reports.oah.state.nc.us/ncac/title2015a20-20environmental20
quality/chapter200220-20environmental20management/subchapter20l/
subchapter20120rules.pdf
NCDEQ. (2017). Internal Technical Guidance: Evaluating Impacts to Surface Water from
Discharging Groundwater Plumes. October 31, 2017
SynTerra. (2014a). Drinking Water Well and Receptor Survey Report. September 2014
SynTerra. (2014b). Supplement to Drinking Water Well and Receptor Survey. November
2014
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Corrective Action Plan Update August 2020
L.V. Sutton Energy Complex SynTerra
SynTerra. (2015a). Comprehensive Site Assessment, L. V. Sutton Energy Complex.
SynTerra. (2015b). Corrective Action Plan Part 1, L. V. Sutton Energy Complex.
SynTerra. (2016a). Corrective Action Plan Part 2, L. V. Sutton Energy Complex.
SynTerra. (2016b). Comprehensive Site Assessment Supplement 1, L. V. Sutton Energy
Complex.
SynTerra. (2016c). Comprehensive Site Assessment Supplement 2, L. V. Sutton Energy
Complex.
SynTerra. (2016d). Update to Drinking Water Well and Receptor Survey. September 2016
SynTerra. (2018). Comprehensive Site Assessment Update, L. V. Sutton Energy Complex.
SynTerra. (2020). Updated Background Threshold Values for Constituent Concentrations in
Soil.
USEPA. (2015). National Recommended Water Quality Criteria — Human Health Criteria
Table.
USEPA. (2018a). National Recommended Water Quality Criteria — Aquatic Life Criteria Table.
USEPA. (2018b). Final Aquatic Life Ambient Water Quality Criteria for Aluminum.
United States Environmental Protection Agency (USEPA). (2019). USEPA Regional
Screening Levels. November 2019 Update. Available at:
https://www.epa.gov/risk/regional-screening-levels-rsls
Winner, M.D., Jr., and Coble, R.W., 1989. Hydrogeologic framework of the North Carolina
Coastal Plain aquifer system: U.S. Geological Survey Open -File Report 87-690, 155
p-
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