NC0004774_1_FINAL_CSA Supplement 2_Buck_Report_20160802

Comprehensive Site Assessment
Supplement 2
Buck Steam Station Ash Basin
Site Name and Location
Buck Steam Station
1555 Dukeville Road
Salisbury, NC 28146
Groundwater Incident No.
Not Assigned
NPDES Permit No.
NC0004774
Date of Report
August 2, 2016
Permittee and Current Property Owner
Duke Energy Carolinas, LLC
526 South Church St
Charlotte, NC 28202-1803
704.382.3853
Consultant Information
HDR Engineering, Inc. of the Carolinas
440 South Church St, Suite 900
Charlotte, NC 28202
704.338.6700
Latitude and Longitude of Facility
35042' 49" N, 800 22' 35" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
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Malcolm F. Schaeffer, L.G.
Senior Geologist

Table of Contents
Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
TABLE OF CONTENTS
Paqe
ExecutiveSummary................................................................................................................... 1
Section1 — Background.............................................................................................................
3
1.1 Purpose of CSA Supplement 2....................................................................................
3
1.2 Site Description............................................................................................................
4
1.3 History of Site Groundwater Monitoring........................................................................
5
1.3.1 NPDES Sampling.................................................................................................
5
1.3.2 CSA Sampling......................................................................................................
6
1.3.3 Post-CSA Sampling..............................................................................................
7
1.3.4 NCDEQ Water Supply Well Sampling...................................................................
7
Section 2 — CSA Review Comments..........................................................................................
9
2.1 NCDEQ General Comments and Responses...............................................................
9
2.2 NCDEQ Site -Specific Comments and Responses.......................................................
9
2.3 Errata...........................................................................................................................9
Section 3 — Additional Assessment...........................................................................................10
3.1 Additional Assessment Activities................................................................................10
3.1.1 Well Installation....................................................................................................10
3.1.2 Well Gauging and Sampling.................................................................................12
3.2 Additional Assessment Results...................................................................................12
3.2.1 Groundwater Flow Direction.................................................................................12
3.2.2 Sampling Results.................................................................................................12
Section 4 — Background Concentrations...................................................................................16
4.1 Methodology...............................................................................................................16
4.2 Observation for Background Wells..............................................................................18
Section 5 — Anticipated Additional Assessment Activities..........................................................19
5.1 Proposed Additional Assessment Monitoring Wells.....................................................19
5.2 Implementation of the Effectiveness Monitoring Plan..................................................19
Section 6 — Conclusions and Recommendations......................................................................20

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
TABLE OF CONTENTS
FIGURES
1-1 Site Location Map
1-2 Sample Location Map
1-3 NCDEQ Water Supply Well Sampling
3-1 Potentiometric Surface - Shallow Flow Layer
3-2 Potentiometric Surface - Deep Flow Layer
3-3 Potentiometric Surface - Bedrock Flow Layer
3-4.1 Antimony Isoconcentration Contour Map - Shallow Wells (S)
3-4.2 Antimony Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.3 Antimony Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.4 Arsenic Isoconcentration Contour Map - Shallow Wells (S)
3-4.5 Arsenic Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.6 Arsenic Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.7 Barium Isoconcentration Contour Map - Shallow Wells (S)
3-4.8 Barium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.9 Barium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.10 Boron Isoconcentration Contour Map - Shallow Wells (S)
3-4.11 Boron Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.12 Boron Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.13 Cadmium Isoconcentration Contour Map - Shallow Wells (S)
3-4.14 Cadmium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.15 Cadmium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.16 Hexavalent Chromium Isoconcentration Contour Map - Shallow Wells (S)
3-4.17 Hexavalent Chromium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.18 Hexavalent Chromium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.19 Chromium (Total) Isoconcentration Contour Map - Shallow Wells (S)
3-4.20 Chromium (Total) Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.21 Chromium (Total) Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.22 Cobalt Isoconcentration Contour Map - Shallow Wells (S)
3-4.23 Cobalt Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.24 Cobalt Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.25 Iron Isoconcentration Contour Map - Shallow Wells (S)
3-4.26 Iron Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.27 Iron Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.28 Manganese Isoconcentration Contour Map - Shallow Wells (S)
3-4.29 Manganese Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.30 Manganese Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.31 Selenium Isoconcentration Contour Map - Shallow Wells (S)
3-4.32 Selenium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.33 Selenium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.34 Sulfate Isoconcentration Contour Map - Shallow Wells (S)
3-4.35 Sulfate Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.36 Sulfate Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.37 Total Dissolved Solids Isoconcentration Contour Map - Shallow Wells (S)
3-4.38 Total Dissolved Solids Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.39 Total Dissolved Solids Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.40 Thallium Isoconcentration Contour Map - Shallow Wells (S)
3-4.41 Thallium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.42 Thallium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.43 Vanadium Isoconcentration Contour Map - Shallow Wells (S)

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin FN
TABLE OF CONTENTS
3-4.44 Vanadium Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.45 Vanadium Isoconcentration Contour Map — Bedrock Wells (BR)
3-5.1 Site Cross Section Locations
3-5.2 Cross Section A -A' (1 of 2)
3-5.3 Cross Section A -A' (2 of 2)
3-5.4 Cross Section B-B' (1 of 2)
3-5.5 Cross Section B-B' (2 of 2)
3-5.6 Cross Section C-C' (1 of 2)
3-5.7 Cross Section C-C' (2 of 2)
3-6.1 Piper Diagram — Background Groundwater, Porewater, Areas of Wetness, and Surface
Water
3-6.2 Piper Diagram — Shallow Groundwater, Porewater, Areas of Wetness, and Surface
Water
3-6.3 Piper Diagram — Deep Groundwater, Porewater, Areas of Wetness, and Surface Water
3-6.4 Piper Diagram — Bedrock Groundwater, Porewater, Areas of Wetness, and Surface
Water
TABLES
1-1 Well Construction Information
1-2 NPDES Historical Data
1-3 Range of 2L Groundwater Standard Exceedances from NPDES Sampling
2-1 Responses to General NCDEQ Comments
2-2 Total and Effective Porosity and Specific Storage by Flow Layer
3-1 Round 5 Analytical Results of Groundwater Monitoring
3-2 Round 5 Analytical Results of Porewater Monitoring
3-3 Round 5 Analytical Results of Ash Basin Surface Water Locations
3-4 Round 5 Analytical Results of Areas of Wetness
3-5 Summary of Groundwater Elevations
3-6 Summary of Cation -Anion Balance Differences
APPENDICES
A Monitoring Well Logs and Core Photos
B Field Sampling Forms and Slug Test Reports
C Laboratory Report and Chain -of -Custody Forms

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
EXECUTIVE SUMMARY
Executive Summary
Duke Energy Carolinas, LLC (Duke Energy) owns and formerly operated the Buck Steam
Station (Buck), located in Salisbury, Rowan County, North Carolina (Figure 1-1). Buck began
operation as a coal-fired generating station in 1926 and was taken offline in April 2013. The
Buck Combined Cycle Station (BCCS) natural gas generating facility was constructed at the site
and began operations in late 2011. Coal combustion residuals (CCR) and other liquid
discharges from Buck's coal combustion process were historically disposed into the site ash
basin system. Discharge from the ash basin is permitted by the North Carolina Department of
Environmental Quality (NCDEQ)' Division of Water Resources (DWR) under the National
Pollutant Discharge Elimination System (NPDES) Permit NC0004774.
This Comprehensive Site Assessment (CSA) Supplement 2 report addresses the following:
Y Summary of groundwater, porewater, ash basin surface water, and area of wetness
(AOW) monitoring data through April 2016;
Y Responses to NCDEQ review comments pertaining to the CSA;
Y Findings from assessment activities conducted since the submittal of the CSA report,
including additional assessments previously identified in the CSA;
Y Update on the development of provisional background groundwater concentrations; and
Y Description of planned additional source area assessment activities.
Boron, the primary site -derived constituent in groundwater, was detected at concentrations
greater than the 15A NCAC (North Carolina Administrative Code) 02L.0202 Groundwater
Quality Standards (21L Standards or 2L) beneath and downgradient (north-northeast) of the ash
basin. Boron has not been detected in groundwater beyond the compliance boundary. The
hydrogeologic nature of the ash basin setting is the primary control mechanism on groundwater
flow and constituent transport.
Groundwater monitoring results from Round 5 of CSA well sampling and NPDES groundwater
monitoring data are presented herein. Updated summary tables, isoconcentration maps, cross
sections, and graphical representations of the data are included.
Presentation of site -specific proposed provisional background concentrations (PPBCs) was
included in the Corrective Action Plan (CAP) Part 1 report and should be refined as more data
becomes available and pending input from NCDEQ. With refinement of the PPBCs, the
evaluation of whether the presence of constituents of interest (COls) downgradient of the source
areas is naturally occurring or potentially attributed to the source areas can be advanced in
more detail.
The following conclusions and recommendations are offered:
Prior to September 18, 2015, the NCDEQ was referred to as the North Carolina Department of Environment and
Natural Resources (NCDENR). Both naming conventions are used in this report, as appropriate.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin FN
EXECUTIVE SUMMARY
Y Groundwater monitoring results from Round 5 of sampling, including data from additional
assessment groundwater monitoring wells, indicate consistency with previous sampling
results, specifically the extent of impact to groundwater from ash basin -related
constituents (e.g., boron).
Y Additional monitoring wells (GWA-2S, GWA-15S/D and GWA-17S) within the vicinity of
GWA-2BR/BRU were installed to refine understanding of constituent concentrations
between Cell 2 and Cell 3. Analytical results from these wells are generally consistent
with data obtained from GWA-2BR; however, iron and manganese concentrations in the
new wells were approximately one to several orders of magnitude higher than in well
GWA-2BRU during the Round 5 sampling event.
Y The horizontal extent of ash -related impacts is adequately defined at the Buck site.
However, the vertical extent of ash -related impacts is not defined at the Cell 1 dam,
within Cell 2, and north of Cell 3.
Y Refinement of PPBCs should be conducted once the minimum number of viable
observations per background well are available.
Y Additional monitoring wells should be installed at the Cell 1 dam, within Cell 2, and north
of Cell 3 to refine vertical delineation of groundwater impacts in these areas.
Y Duke Energy will implement the effectiveness monitoring plan in accordance with
recommendations provided in the CAP Part 2 report as well as subsequent discussions
with NCDEQ.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
Section 1 — Background
Duke Energy Carolinas, LLC (Duke Energy) owns and formerly operated the Buck Steam
Station (Buck), located in Salisbury, Rowan County, North Carolina (Figure 1-1). Buck began
operation as a coal-fired generating station in 1926 and was taken offline in April 2013. The
Buck Combined Cycle Station (BCCS) natural gas generating facility was constructed at the site
and began operations in late 2011. Coal combustion residuals (CCR) and other liquid
discharges from Buck's coal combustion process were historically disposed into the site ash
basin system. Discharge from the ash basin is permitted by the North Carolina Department of
Environmental Quality (NCDEQ) Division of Water Resources (DWR) under the National
Pollutant Discharge Elimination System (NPDES) Permit NC0004774.
The Comprehensive Site Assessment (CSA) report for Buck was submitted to NCDEQ on
August 23, 2015. Given the compressed timeframe for submittal, certain information was not
included in the CSA report because the data was not yet available. Thus, Duke Energy
committed to providing this information after submittal of the CSA report. In addition, NCDEQ's
review of the CSA report led to requests for additional information. As such, CSA Supplement 1,
submitted to NCDEQ on February 18, 2016, as an appendix to the Corrective Action Plan (CAP)
Part 2 provided information to address the temporal constraints, information requested by
NCDEQ subsequent to submittal of the CSA report, additional data validation reporting, and a
response to site -specific NCDEQ comments obtained during in -person meetings.
1.1 Purpose of CSA Supplement 2
The purpose of this CSA Supplement 2 is to provide data obtained during additional well
installation and sampling conducted between January and April 2016. These activities were
conducted to refine the understanding of subsurface geologic/hydrogeologic conditions and the
extent of impacts from historical production and storage of coal ash. This CSA Supplement 2
was prepared in coordination with Duke Energy and NCDEQ as a result of requests for
additional information and areas identified for additional assessment. It includes the following
information:
Y A brief summary and update of groundwater sampling data from the NPDES, CSA, and
post-CSA monitoring well sampling events;
Y A brief summary of results of NCDEQ water supply well sampling activities;
Y A summary of NCDEQ comments on the CSA report and responses to those comments;
Y A description of additional assessment activities conducted since submittal of the CSA
report and the findings of those assessment activities;
Y An updated approach for the refinement of proposed provisional background
concentrations (PPBCs) for groundwater at the Buck site; and
Y A description of additional planned assessment activities.
As a complement to the CSA report and the CSA Supplement 1, this CSA Supplement 2
provides an updated evaluation of the extent of impacts from the ash basin and related ash
storage facilities based on existing CSA groundwater monitoring wells and monitoring wells
installed subsequent to submittal of the CSA report (herein referred to as additional assessment

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
wells). Additional assessment groundwater monitoring wells are shown on Figure 1-2 with
green text labels.
1.2 Site Description
The Buck site is located on the south bank of the Yadkin River near Salisbury, in Rowan
County, North Carolina. The Buck site occupies approximately 640 acres and is owned by Duke
Energy. Buck was a six -unit coal-fired electricity generating facility, but has been offline since
April 2013. Construction of the 620 MW BCCS began in 2008 and commercial operations began
in late 2011. Buildings and other structures associated with power production are generally
located in the northwestern portion of the site and the eastern portion of the site is generally
wooded with the exception of the ponded areas of the ash basin.
The ash basin system at Buck consists of three cells, associated earthen dikes, discharge
structures, and two canals. The cells are designated as Cell 1 Active Ash Basin Primary Cell
(Cell 1), Cell 2 Active Ash Basin Old Primary Cell (Cell 2), and Cell 3 Active Ash Basin
Secondary Cell (Cell 3). The ash basin system is located to the south (Cell 1) and east (Cells 2
and 3) of the retired Buck units and BCCS. The ash basin system discharges to the Yadkin
River, located on the northeast side of the Buck site via NPDES permitted Outfall 002. An
approximately 14-acre unlined dry ash storage area (herein referred to as the `ash storage
area') is located on the eastern side of Cell 1 and contains dewatered ash that was excavated
from Cell 1 in 2009 to provide additional volume in Cell 1 for sluiced ash. The ash storage area
is located within the footprint and drainage area of Cell 1 and has a vegetated soil cover.
Topography at the Buck site ranges from an approximate high elevation of 734 feet at the
communications cell tower near the southwest edge of the property to an approximate low
elevation of 620 feet at the Yadkin River on the northern margin of the site, with a total elevation
change of approximately 114 feet over an approximate distance of 0.9 mile. Surface water
drainage flow generally follows site topography from south to north across the site except where
natural drainage patterns have been modified by the ash basin or other construction features. A
site layout map is included as Figure 1-2.
The groundwater system in the natural materials (alluvium, soil, soil/saprolite, and bedrock) at
the Buck site is consistent with the Piedmont regolith-fractured rock system and is an
unconfined, connected system of flow layers. In general, groundwater within the shallow and
deep layers (S and D wells) and bedrock layer (BR wells) flows from west and southwest to the
east toward the unnamed tributary and to the north toward the Yadkin River.
The source area is defined as the ash basin, which consists of Cell 1, Cell 2, and Cell 3, as well
as the ash storage area. Source characterization was performed to identify physical and
chemical properties of ash, ash basin surface water, porewater, and ash basin areas of wetness
(AOW).
The compliance boundary for groundwater quality at the Buck site is defined in accordance with
Title 15A NCAC 02L .0107(a) as being established at either 500 feet from the waste boundary
or at the property boundary, whichever is closer to the waste boundary. As described in the
CSA report, analytical results for groundwater samples were compared to the North Carolina
Groundwater Quality Standards, as specified in 15A NCAC 2L.0202 (21L Standards or 2L) or

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
Interim Maximum Allowable Concentration (IMAC) established by NCDEQ pursuant to 15A
NCAC 2L.0202(c), or North Carolina Department of Health and Human Services (DHHS) Health
Screening Level (HSL) (hexavalent chromium only) for the purpose of identifying constituents of
interest (COls). The IMACs were issued for certain constituents in 2010, 2011, and 2012;
however, NCDEQ has not established a 2L Standard for those constituents as described in 15A
NCAC 2L.0202(c). For this reason, the IMACs noted in this document are for reference
purposes only.
Areas of 2L Standard or IMAC exceedances of antimony, boron, chromium, sulfate, and total
dissolved solids (TDS) are within and beneath or immediately adjacent to the source areas. The
limited downgradient extent of impacts indicates that physical and geochemical processes (i.e.,
dispersion and sorption) beneath the Buck site reduce the lateral migration of COIs. In
accordance with LeGrand's slope -aquifer system characteristic of the Piedmont, whereby
groundwater from shallow, deep, and bedrock flow layers discharges into surficial waterbodies,
groundwater at the Buck site discharges into the Yadkin River and creeks along the eastern and
western boundaries of the site that flow into the Yadkin River.
1.3 History of Site Groundwater Monitoring
Monitoring wells were installed by Duke Energy in 2006 as part of the voluntary monitoring
system for groundwater near the ash basin. The voluntary groundwater monitoring wells were
sampled twice each year by Duke Energy and the analytical results were submitted to NCDEQ
DWR. A review of voluntary monitoring well sampling results obtained between 2006 and 2010
indicates the following:
Y Boron exceeded the 2L Standard in wells MW-3S and MW-3D during each of the
voluntary sampling events. This well pair is located downgradient of Cell 3.
Y Chromium exceeded the 2L Standard in voluntary well MW-2D during consecutive
sampling events in 2006 and 2007; however, turbidity was measured at 887
nephelometric turbidity units (NTU) and 105 NTU, respectively, during these events.
Chromium did not exceed the 2L Standard in this well during subsequent sampling
events in late 2007 and 2008, and has not been sampled since 2008. Well MW-2D is
located just beyond the waste boundary northwest of Cell 1.
Y Iron and manganese have intermittently exceeded the 2L Standards in voluntary
monitoring wells screened in the shallow and deep flow layers. However, these
exceedances may be attributable to naturally occurring conditions and require additional
evaluation as site -specific PPBCs are refined.
Construction details for voluntary monitoring wells are provided in Table 1-1. The location of the
ash basin voluntary monitoring wells, the approximate ash basin waste boundary, and the
compliance boundary are shown on Figure 1-2.
1.3.1 NPDES Sampling
NPDES compliance monitoring wells (compliance wells) were installed in December 2010.
Compliance groundwater monitoring, as required by the NPDES permit, began in March 2011.
From March 2011 through July 2016, compliance groundwater monitoring wells at the Buck site

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
have been sampled three times each year, resulting in 17 total monitoring events during that
time. A review of NPDES compliance well sampling results indicates the following:
Y Chromium has sporadically exceeded the 2L Standard in two compliance wells (MW-7S
and MW-9S) screened within the shallow flow layer along the southern and western
waste boundary of Cell 1, and one compliance well (MW-12S) in the southern waste
boundary of Cell 3.
Y Boron exceeded the 2L Standard in compliance well MW-11 D, screened in the deep flow
layer and located downgradient of Cell 3, during each of the NPDES sampling events.
Y Iron and manganese have intermittently exceeded the 2L Standards in compliance wells
screened in the shallow and deep flow layers located across the site during the NPDES
sampling period. However, these exceedances may be attributable to naturally occurring
conditions and require additional evaluation as site -specific PPBCs are refined.
Historical analytical results and a summary of the range of exceedances within the NPDES
groundwater monitoring program are provided in Tables 1-2 and 1-3, respectively.
1.3.2 CSA Sampling
The CSA for the Buck site began in February 2015 and was completed in August 2015. Sixty-
four groundwater monitoring wells and 44 soil borings were installed/advanced as part of this
assessment to characterize the ash, soil, rock, and groundwater at the Buck site. One
comprehensive round of sampling and analysis was included in the CSA report and included
sampling of soil, groundwater, ash basin surface water, and porewater (Figure 1-2). In addition,
hydrogeological evaluation testing was performed on newly installed wells.
The following constituents were reported as COls in the CSA report:
Y Soil: arsenic, barium, boron, cobalt, iron, manganese, selenium, and vanadium.
Y Groundwater: antimony, arsenic, barium, boron, chromium, cobalt, hexavalent chromium,
iron, manganese, nickel, pH, selenium, sulfate, thallium, TDS, and vanadium.
Y Surface water: samples from tributaries were not collected as the locations were either
dry or not accessible.
Y Porewater: aluminum, antimony, arsenic, cadmium, chromium, cobalt, copper, iron, lead,
manganese, thallium, vanadium, and zinc.
Horizontal and vertical delineation of source -related soil impacts was presented in the CSA
report. Where soil impacts were identified beneath the ash basin (beneath the ash/soil
interface), the vertical extent of contamination was generally limited to the soil samples collected
just beneath the ash.
Groundwater impacts at the site attributable to ash handling and storage were delineated during
the CSA activities with the following areas requiring refinement:
Y Horizontal and vertical extent northeast and southeast of GWA-2BRU/BR between Cell 2
and Cell 3.
Y Speciation of arsenic, chromium, iron, manganese, and selenium in select wells in
groundwater along inferred flow transects.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
Y Surface water and AOW sampling needed due to inaccessible or dry sample locations in
Round 1 sampling.
1.3.3 Post-CSA Sampling
Four additional rounds of groundwater sampling of the CSA wells have occurred since submittal
of the CSA report. Round 2 of groundwater monitoring occurred in September 2015 and was
reported in the Corrective Action Plan (CAP) Part 1 (submitted on November 20, 2015). Rounds
3 and 4 of groundwater monitoring occurred in November and December 2015 and results were
reported in the CSA Supplement 1 as part of the CAP Part 2 report (submitted on February 19,
2016). Round 5 of groundwater monitoring was conducted in March 2016 and is the focus of the
data evaluation presented in Section 3 of this CSA Supplement 2.
1.3.4 NCDEQ Water Supply Well Sampling
Section § 130A-309.209 (c) of CAMA indicates that NCDEQ requires sampling of water supply
wells to evaluate whether the wells may be adversely impacted by releases from CCR
impoundments. NCDEQ required sampling of all drinking water receptors within 0.5 mile of the
Buck compliance boundary in all directions, since the direction of groundwater flow had not
been determined at Buck at the time of sampling. Between February and August 2015, NCDEQ
arranged for independent analytical laboratories to collect and analyze water samples obtained
from wells identified during the Drinking Water Well Survey2, 3 if the owner agreed to have their
well sampled. The NCDEQ-directed water supply well sampling consisted of collection and
analysis of the following:
Y A total of 89 private drinking water supply wells within 0.5 mile of the Buck compliance
boundary; and
Y A total of 7 reference or background water supply wells in the vicinity of Buck.
In addition, Duke Energy collected samples from 17 background water supply wells located
within a 2- to 10-mile radius of the Buck site. The locations of the private water supply wells
identified within 0.5 mile of the Buck compliance boundary, including NCDEQ-directed sampling
locations with updated analytical results provided to Duke Energy, are shown on Figure 1-3.
The results of water supply well testing conducted by the NCDEQ in the vicinity of the Buck
facility indicated that boron was detected in 8 of the 89 NCDEQ-sampled water supply wells;
boron was detected in 1 of the 7 NCDEQ background wells and in 1 of the 17 Duke Energy
background wells. pH was below the drinking water standard range in 42 of the 89 NCDEQ-
sampled water supply wells. This result is not unexpected, based on a study published by the
United States Geological Survey4 and additional North Carolina -specific studies5 showing that
groundwater pH in the state is commonly below the Maximum Contaminant Level (MCL) range
2 HDR. 2014a. Buck Combined Cycle Station Ash Basin Drinking Water Supply Well and Receptor Survey. NPDES
Permit NC0004774September 30, 2014.
3 HDR. 2014b. Buck Combined Cycle Station Ash Basin. Supplement to Drinking Water Supply Well and Receptor
Survey. NPDES Permit NC0004774. November 6, 2014.
4 Chapman, M.J.,Cravotta III, C.A., Szabo, Z. and Linsay, B.D. 2013 Naturally occurring contaminants in the
Piedmont and Blue Ridge crystalline -rock aquifers and Piedmont Early Mesozoic basin siliciclastic-rock aquifers,
eastern United States, 1994-2008 (Scientific Investigations Report No. 2013-5072). U.S. Geological Survey.
5 Briel, L.I. 1997. Water quality in the Appalachian Valley and Ridge, the Blue Ridge, and the Piedmont physiographic
provinces, eastern United States (Professional Paper No. 1422-D). U.S. Geological Survey.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 1 - BACKGROUND
of 6.5 to 8.5 Standard Units. Lead was above the drinking water standard in 1 of the 89
NCDEQ-sampled water supply wells. None of the NCDEQ-sampled water supply well results
were above Federal primary drinking water standards (MCLs), with the exception of the pH
results and lead result noted above.
"Do Not Drink" letters were issued by the DHHS for 79 water supply wells at Buck, with
hexavalent chromium and vanadium being the primary constituents listed in the letters. After
review of studies on how the federal government and other states manage these elements in
drinking water, state health officials withdrew the "Do Not Drink" warnings for these two
constituents. Letters were issued for other constituents as follows: iron (14 wells), zinc (3 wells),
chromium (2 wells), lead (1 well), manganese (1 well), and cobalt (1 well).
Based on data obtained during the NCDEQ water supply well sampling, Duke Energy used a
multiple -lines -of -evidence approach to evaluate whether the presence of constituents in water
supply wells near Buck are the result of migration of CCR-impacted groundwater. This approach
consisted of a detailed evaluation of groundwater flow and groundwater chemical signatures.
The results of the groundwater flow evaluation confirmed that groundwater flow is predominantly
to the north toward the Yadkin River from the topographic divides southwest, south, and
southeast of the ash basin system with localized flow to the west of Cell 1 and in an area east of
the source that requires further evaluation. Thus, groundwater flow from areas associated with
the ash basin and the ash storage area is away from the water supply wells. A review of
topographic and monitoring well groundwater elevation data at Buck found no evidence of
mounding associated with the ash basin.
The results of the groundwater chemical signature evaluation indicate that constituent
concentrations in the water supply wells are generally consistent with background levels,
including boron. Further, the different constituent clustering patterns from the porewater wells
and the water supply wells indicate that the source water for the water supply wells is not
CCR-impacted groundwater. The conclusion from the groundwater chemical signature
evaluation is that water supply wells in the vicinity of the Buck facility are not impacted by CCR
releases from the ash basin.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 2 — CSA REVIEW COMMENTS
Section 2 — CSA Review Comments
Representatives of NCDEQ's Central Office and Mooresville Regional Office (MRO) met with
Duke Energy and HDR on October 15, 2015 to present their review comments to the CSA
report. Comments were organized in two categories: general comments applicable to all Duke
Energy Carolinas CSA reports regardless of site and site -specific comments applicable to Buck.
2.1 NCDEQ General Comments and Responses
General comments applicable to the CSA reports, and responses to the comments, are
presented in Table 2-1.
2.2 NCDEQ Site -Specific Comments and Responses
Site -specific comments and responses were included in the CSA Supplement 1, which was
submitted to NCDEQ on February 19, 2016 as part of the CAP Part 2 report.
2.3 Errata
Editorial comments and corrections to the CSA report were included in the CSA Supplement 1,
which was submitted to NCDEQ on February 19, 2016 as part of the CAP Part 2 report. Since
the issuance of the CAP Part 2 report, additional evaluation of site data has occurred, resulting
in refinement by flow layer of total porosity, secondary (effective) porosity, and specific storage
for the lower hydrostratigraphic units (deep transition zone) and bedrock), as provided in Table
2-2.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
Section 3 — Additional Assessment
Additional assessment activities identified in the CSA report were addressed and the findings
are discussed in the following sections.
Additional Assessment Activities
Additional assessment activities included monitoring well installation and sampling, as
discussed below.
3.1.1 Well Installation
The following areas at the Buck site required additional assessment to refine the extent of
groundwater impacts attributable to the ash basin:
Y Horizontal extent in the shallow flow layer at the GWA-2BR/BRU well nest; and
Y Horizontal extent in the shallow and deep flow layers northwest and southwest of GWA-
2BR/BRU.
The purpose of these wells was to provide information regarding constituent concentrations
between Cell 2 and Cell 3. Subsequent discussions with Duke Energy and NCDEQ resulted in
the installation of additional monitoring wells beyond those described above. A summary of
those additional assessment wells and installation dates, as well as the purpose for installation,
is provided in the table below.
Boring [Well
Installation
Purpose for Installation
Results
Identification
Date
GWA-1-SB
2/3/2016
Soil samples located outside of the
Soil samples collected
ash basin for synthetic precipitation
leaching procedure (SPLP) analysis to
GWA-6-SB
1/14/2016
compare results against SPLP
analysis of ash
GWA-2S
1/19/2016
Well Installed to further assess
Water level measured and
groundwater flow south of Cells 2 and
used for contouring of
3
shallow flow layer
GWA-13SR
1/20/2016
Installed in vicinity of MW-13D and
Water level measured and
BG-3S/D to further refine assessment
used for contouring of
of groundwater flow in area around
Cell 2
shallow flow layer
Water level measured and
GWA-13D
2/1/2016
used for contouring of
deep flow layer
GWA-14S
3/4/2016
Installed to further refine assessment
Water level measured and
of groundwater flow in area around
used for contouring of
Cell 2
shallow flow layer
GWA-14D
3/4/2016
Water level measured and
used for contouring of
deep flow layer
GWA-14BR
2/18/2016
Well dry after installation
attempted two times
GWA-15S
3/10/2016
Installed to further refine assessment
Water level measured and
of groundwater flow in area around
used for contouring of
Cell 2
shallow flow layer
mi

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Boring /Well
Installation
Purpose for Installation
Results
Identification
Date
GWA-15D
3/10/2016
Water level measured and
used for contouring of
deep flow layer
3/2/2016
Water level measured and
GWA-17S
Installed in vicinity of MW-5S/D and
GWA-3S/BRU/BR to further refine
used for contouring of
assessment of groundwater flow in
shallow flow layer
area to the east of plant operations
Installed to refine assessment of
GWA-18S
1/30/2016
Cobalt concentration
concentrations downgradient of Cell 2
exceeded [MAC
GWA-18D
1/29/2016
Concentrations of arsenic,
hexavalent chromium,
TDS, and vanadium
exceeded applicable
criteria
GWA-19S
2/13/2016
Installed to refine assessment of
Concentrations of
concentrations downgradient of Cell 1
chromium, hexavalent
chromium, cobalt, iron,
manganese, and
vanadium exceeded
applicable criteria
GWA-19D
2/19/2016
Concentrations of
chromium, hexavalent
chromium, cobalt, iron,
manganese, and
vanadium exceeded
applicable criteria
GWA-20S
2/12/2016
Wells needed west of Dukeville Road
Concentrations of
and west of GWA-10S/D and GWA-
hexavalent chromium,
11 S/D to define extent of
cobalt, manganese, and
exceedances in this location
vanadium exceeded
applicable criteria
Concentrations of cobalt,
GWA-20D
2/20/2016
manganese, and
vanadium exceeded
applicable criteria
MW-6BR
2/10/2016
Well installed south of ash basin to
Concentrations of iron and
further evaluate groundwater quality
vanadium exceeded
upgradient of the ash basin
applicable criteria
Monitoring well logs and core photos, field sampling and slug test records, and analytical
laboratory reports are included in Appendices A, B, and C, respectively.
Additional assessment wells that were planned for installation but were not completed included
the following:
Y GWA-16S/D — Not installed due to off -site access issues.
Y GWA-17D —Groundwater was not encountered on top of bedrock.
Y MW-813R — Drilling location is currently inaccessible due to access issues as a result
of poor vicinity drainage.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Note that concentrations of select constituents exceeded their applicable 2L/IMAC/DHHS HSL
criteria in additional assessment wells GWA-18S/D, GWA-19S/D, GWA-20S/D, and MW-6BR.
These wells will continue to be evaluated for validity as down -gradient delineation wells as
additional sampling events are conducted and PPBCs are revised for the Buck site.
3.1.2 Well Gauging and Sampling
Round 5 of groundwater, ash basin surface water, AOW, and ash basin water sampling
activities was completed between February 17 and April 27, 2016. Groundwater analytical
parameters and methods for Round 5 were consistent with those used during previous sampling
events, as presented in previous reports. A total of 89 groundwater and porewater monitoring
wells were sampled during the Round 5 event. Sample locations are depicted on Figure 1-2.
3.2 Additional Assessment Results
Findings and results from Round 5 of sampling and analysis and additional assessment
activities are presented below. Note that the Round 3 and 4 monitoring events focused on
sampling of background wells only. Therefore, groundwater elevation and analysis results are
compared to data previously obtained during Round 1 and 2 monitoring events. A summary of
the analytical results is presented in Tables 3-1 through 3-4 for groundwater, porewater, ash
basin surface water, and AOWs, respectively. A summary of groundwater elevations measured
during the Round 1 through 5 gauging events is presented in Table 3-5.
3.2.1 Groundwater Flow Direction
On June 17, 2016, monitoring wells were manually gauged from the top of the PVC casing
using an electronic water level indicator accurate to 0.01 foot. Groundwater elevations were
generally higher than those measured during Rounds 1 and 2, which is likely attributable to
seasonal variation of the water table. Groundwater flow direction was consistent with flow
directions identified in Rounds 1 and 2, and generally flows from the southern portion of the site
to the north, toward the Yadkin River, and slightly northeast and northwest to unnamed
tributaries of the Yadkin River. Groundwater elevations and inferred contours for the shallow,
deep, and bedrock flow layers are depicted on Figures 3-1, 3-2, and 3-3, respectively. These
groundwater flow directions are consistent with interpretations made in the CSA report.
3.2.2 Sampling Results
3.2.2.1 SUMMARY OF ROUND 1 AND 2 GROUNDWATER SAMPLING RESULTS
As previously mentioned in Section 1.3.2, the following COls were identified in groundwater as
a result of sampling conducted during the CSA: antimony, arsenic, barium, boron, chromium,
cobalt, hexavalent chromium, iron, manganese, nickel, pH, selenium, sulfate, thallium, TDS, and
vanadium. Boron, sulfate, and TDS exceeded their 2L Standards and PPBCs either beneath or
downgradient of the ash basin and dry ash storage area, and are considered to be detection
monitoring constituents in Code of Federal Regulations Title 40 (40 CFR) Section 257 Appendix
III of the U.S. Environmental Protection Agency's (USEPA) Hazardous and Solid Waste
Management System; Disposal of Coal Combustion Residuals from Electric Utilities CCR Rule.
The USEPA detection monitoring constituents are potential indicators of groundwater
contamination from CCR as these constituents are associated with CCR and move with
12

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 3 - ADDITIONAL ASSESSMENT
groundwater flow, unlike other constituents whose movement is impeded by chemical or
physical interactions with soil and weathered rock.
3.2.2.2 ROUND 5 POREWATER SAMPLING RESULTS
A total of 10 porewater samples were collected from monitoring wells (AB-2S/SL, AB-3S, AB-
4S/SL, AB-5S/SL, AB-7S/SL, and AB-8S) screened within ash in Cells 1, 2, and 3.
Concentrations of antimony, arsenic, barium, boron, cobalt, iron, manganese, TDS, thallium,
and vanadium that exceed the applicable 2L Standard or IMAC were detected in porewater
samples collected during the Round 5 sampling event. The range and number of exceedances
of each COI in porewater is listed below.
Y Antimony: 1.7J pg/L to 18.6 pg/L; 5 exceedances/10 samples
Y Arsenic: 33.3 pg/L to 998 pg/L; 10/10
Y Barium: 883 pg/L; 1/10
Y Boron: 1,320 pg/L to 8,460 pg/L; 6/10
Y Cobalt: 6.5 pg/L to 17.6 pg/L; 4/10
Y Iron: 321 pg/L to 19,200 pg/L; 5/10
Y Manganese: 52.1 pg/L to 3,770 pg/L
Y TDS: 635,000 pg/L; 1/10
Y Thallium: 0.32J pg/L; 1/10
Y Vanadium: 0.44 pg/L to 150 pg/L
3.2.2.3 ROUND 5 GROUNDWATER SAMPLING RESULTS
In general, the COls identified during Round 5 groundwater sampling are consistent with the
results obtained during Rounds 1 and 2. A summary of Round 5 sampling results per COI
identified during the CSA is as follows:
Y Antimony exceeded the IMAC in one well (GWA-20S) screened within the shallow flow
layer west of Cell 1, and in the deep and bedrock flow layers within and downgradient of
Cell 1, downgradient of Cell 3, and upgradient of Cells 2 and 3. In general, dissolved -
phase concentrations were consistent with total concentrations, with the exception of
results obtained from well AB-9D, indicating that elevated antimony concentrations are
not likely caused by turbiditiy. However, antimony was detected above the IMAC in
background well BG-3D, indicating that antimony may be present as a naturally occuring
constituent.
Y Arsenic exceeded the 2L Standard in well GWA-18D, located downgradient of the ash
basin system. Arsenic was not detected above the 2L Standard in other wells sampled
during Round 5. Total and dissolved concentrations were similar in samples collected
from GWA-18D.
Y Barium did not exceed the 2L Standard in wells screened within the shallow, deep, or
bedrock flow layers during the Round 5 sampling event.
Y Boron excceded the 2L Standard in the shallow flow layer in wells located within the ash
storage area and downgradient of the Cell 3 dam; and in the deep flow layer in wells
located within Cell 1 and Cell 3. Boron did not exceed the 2L Standard in the bedrock
13

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
flow layer. In general, total and dissolved concentrations were consistent in each
sample.
Y Chromium exceeded the 2L Standard in the shallow flow layer in wells located within
and downgradient of Cell 1 and upgradient of Cells 1 and 2. Chromium exceeded the 2L
Standard in the deep flow layer in wells located within Cells 1 and 3; however, dissolved
phase concentrations were significantly lower than total concentrations, indicating that
these exceedances may be turbidity -derived. Chromium did not exceed the 2L Standard
in the bedrock flow layer with the exception of one exceedance in a dissolved -phase
sample (well AB-913R).
Y Cobalt exceeded the IMAC in the shallow flow layer in wells across the Buck site.
Concentrations were generally the highest beneath the ash storage area and
downgradient of Cell 1. Total and dissolved concentrations were consistent within each
sample. Cobalt exceedances in the deep flow layer were less frequent and at lower
concentrations than were observed in the shallow flow layer. Again, total and dissolved
concentrations were consistent within each sample. Cobalt was not detected above the
IMAC in wells installed within the bedrock flow layer.
Y Hexavalent chromium exceeded the DHHS HSL in the shallow flow layer in wells located
downgradient of the ash basin system, sidegradient of Cells 1 and 3, and upgradient of
Cells 1, 2, and 3. Hexavalent chromium also exceeded the DHHS HSL in the deep flow
layer with higher frequency and concentrations than were observed in the shallow flow
layer. Exceedances in the bedrock flow layer were less frequent and generally restricted
to wells within and downgradient of Cells 1 and 3, with the exception of well GWA-2BR
located between Cells 2 and 3. Note that dissolved phase analyses for hexavalent
chromium were not performed on groundwater samples.
Y Iron exceeded the 2L Standard in the shallow flow layer in wells downgradient of the ash
basin system and upgradient of Cells 1 and 2. Except in a few instances, dissolved
concentrations were typically an order of magnitude less than total concentrations.
Exceedances in the deep flow layer were less frequent and restricted to areas beneath
and downgradient of the ash basin system. Total and dissolved concentrations in deep
flow layer wells were consistent within each sample. Exceedances in the bedrock flow
layer were limited to two wells: GWA-6BR located downgradient of Cells 2 and 3, and
MW-6BR located upgradient of Cell 1.
Y Manganese exceeded the 2L Standard in the shallow and deep flow layers in wells
across the Buck site. Manganese exceeded the 2L Standard in the bedrock flow layer in
one well (GWA-6BR) located downgradient of the ash basin system. In general, total and
dissolved concentrations were consistent within each sample collected from shallow and
deep flow layer wells.
Y Nickel was not detected above the 2L Standard in any wells during the Round 5
sampling event.
Y pH was measured outside of the range specified in 2L (6.5-8.5 Standard Units) in the
shallow, deep, and bedrock flow layers across the Buck site. However, as discussed in
Section 1.3.4, this can be expected in the Piedmont Province of North Carolina.
14

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Y Selenium exceeded the 2L Standard in one well (AS-1 S) screened within the shallow
flow layer and in one well (AB-4BR) screened within the bedrock flow layer. Both wells
are located within the waste boundary of the ash basin system.
Y Sulfate exceeded the 2L Standard in two wells (AS-1 S and GWA-12S) screened within
the shallow flow layer, one well (GWA-6BRU) within the deep flow layer, and one well
(GWA-6BR) within the bedrock flow layer. These wells are located within or
downgradient of the ash basin waste boundary.
Y Thallium did not exceed the IMAC in the shallow, deep, or bedrock flow layers with one
exception: the dissolved (and laboratory estimated [J-flagged]) concentration reported in
well GWA-19D.
Y TDS exceeded the 2L Standard in one well (AS-1 S) screened within the shallow flow
layer, three wells (GWA-6BRU, GWA-14D, and GWA-18D) within the deep flow layer,
and two wells (AB-9BR and GWA-6BR) within the bedrock flow layer. With the exception
of GWA-14D, these wells are located within or downgradient of the ash basin waste
boundary.
Y Vanadium exceeded the IMAC in the shallow and deep flow layers in wells across the
Buck site, including background wells. Less frequent exceedances were detected in the
bedrock flow layer in wells located within and downgradient of the ash basin waste
boundary.
Note that although cadmium was not previously identified as a COI, it did exceed the 2L
Standard in well AB-6BRU during the Round 5 sampling event.
The horizontal extent of exceedances is presented in the form of isoconcentration figures
(Figures 3-4.1 through 3-4.45). The vertical extent of boron is presented on applicable cross
sections (Figures 3-5.1 through 3-5.7). In addition, cross sections show hydrostratigraphic
layers, rock lithology, rock core recovery (REC) and rock quality designation (RQD; a measure
of rock mass discontinuities/fracturing) in response to comments received from NCDEQ.
3.2.2.4 COMPARISON OF POREWATER AND GROUNDWATER RESULTS
Based upon review of data collected during Round 5 sampling, constituent concentrations in the
porewater were one or more orders of magnitude higher than groundwater concentrations in
wells screened within the shallow flow layer. Considering that porewater wells are located within
the waste boundary and screened within ash, it is expected that concentrations in these wells
are higher than in wells beyond the waste boundary.
Possible exceptions were manganese, sulfate, and TDS. Concentrations of these constituents
in porewater and groundwater were generally within the same order of magnitude.
Piper diagrams presented in the CSA report provided evidence of mixing ash basin porewater
and groundwater, and Round 5 analytical results are consistent with previous presentations. In
general, the ionic composition of groundwater and ash basin surface water at the Buck site is
predominantly rich in calcium and magnesium. Piper diagrams with cation -anion balance
differences < 10% are presented in Figures 3-6.1 through 3-6.4. In addition, overall cation -
anion balance differences are summarized in Table 3-6.
15

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 4 — BACKGROUND CONCENTRATIONS
Section 4 — Background Concentrations
Presentation of site -specific PPBCs was included in the CAP Part 1 report and is pending
refinement as the required minimum number of additional sampling results become available.
Regulations providing North Carolina groundwater quality standards are provided in T15A
NCAC 02L .0202. Section (b)(3) of the regulation provides that:
Where naturally occurring substances exceed the established standard, the standard shall
be the naturally occurring concentration as determined by the Director.
The reference background concentrations determined by the methodology described below will
be submitted to the NCDEQ DWR as the proposed naturally occurring site background
concentrations for the specific constituents. A site -specific report documenting the procedures,
evaluations, and calculation will be prepared and submitted to NCDEQ.
4.1 Methodology
As stated in the USEPA Unified Guidance (USEPA 2009) (Unified Guidance):
The Unified Guidance recommends that a minimum of at least 8 to 10
independent background observations be collected before running most
statistical tests. Although still a small sample size by statistical standards, these
levels allow for minimally acceptable estimates of variability and evaluation of
trend and goodness -of fit. However, this recommendation should be considered
a temporary minimum until additional background sampling can be conducted
and the background sample size enlarged.s
Once the required minimum number of samples is available, HDR will calculate PPBCs utilizing
the appropriate methods in the Unified Guidance, the USEPA ProUCL software, and guidance
found in the North Carolina Division of Water Quality (NCDWQ) technical assistance document
Evaluating Metals in Groundwater at DWQ Permitted Facilities.
This process will also follow HDR's proposed method to establish reference background
concentrations for constituents according to the Environmental Protection Agency's Hazardous
and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric
Utilities; Final Rule (EPA CCR).' The proposed method will be developed in consultation with
Synterra, Duke Energy's groundwater assessment consultant for Duke Energy Progress sites,
to ensure consistency in approach.
6 U.S. Environmental Protection Agency (USEPA) Unified Guidance (USEPA 2009), 5.2.1 Selecting Monitoring
Constituents and Adequate Sample Sizes
HDR modified its earlier methods to establish reference background concentration so that both state and federal
regulations are comparable. Having similar processes to address the two sets of regulations will minimize confusion.
16

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 4 — BACKGROUND CONCENTRATIONS
As recommended by the USEPA Unified Guidance, HDR will calculate the 95 percent upper
prediction limits (UPL95) as the proposed reference background concentration value for each
constituent at the Buck site.$
HDR will calculate UPL95 values for each of the constituents using their respective
concentrations observed in the samples taken from the set of site -specific background wells
once a minimum of eight observations per constituent are available. Samples will not be used to
develop reference background concentrations whenever turbidity is 10 NTU or greater. Only
non -filtered results will be utilized. HDR will review and evaluate the corresponding filtered
results; however, they will not be used for compliance purposes at this time.
The data across the background wells will be pooled prior to estimating the reference
background concentration using the UPL95 approach.
When implementing this approach, HDR will consider that the background wells are screened in
different hydrostratigraphic units (shallow, transition zone, or bedrock). While there are
differences as described, the fundamental assumption will be that the constituent concentrations
sampled at these background wells, when pooled, will serve as an estimate of overall well field
conditions for a given constituent. HDR will test this assumption using statistical methods and if
distinct sub -groups exist, separate background concentrations for each distinct sub -group of
wells by hydrostratigraphic unit (shallow, transition zone, and bedrock) will be calculated.
The methodology used to calculate upper prediction limits (UPLs) for the constituents will be
generally completed in three parts as follows:
1. Analyze Preliminary Data
2. Determine Differences Across Sub -Groups
3. Develop Background Threshold Values (UPLs)
Part 1 of the process includes the preliminary data analyses used to assess and transform the
data where necessary such that the data can be used to calculate UPLs. Statistical methods will
be used to evaluate outliers, serial correlation, seasonality, spatial variability, trends, and
appropriateness of the period of record (sampling period).
Part 2 of the process includes describing the approach to test for sub -group differences. Types
of sub -groups to test include seasonal sub -groups (winter, spring, summer, and fall) and well
class sub -groups (bedrock, shallow, or deep). If the groups are statistically different after testing,
the same steps described in Part 1 can be applied to the partitioned data to better understand
the distribution of the samples within a sub -group for each constituent. The reference
8 There are different methods that can be used to estimate the reference background concentrations such as the UPL
and the upper tolerance limit (UTL). HDR selected the UPL as it is the statistic recommended by the USEPA Unified
Guidance (page 2-15). The Unified Guidance recommends the UPL over the UTL for the following reasons, (1). The
ability to estimate a UTL which can control for Type I error rates when simultaneously testing an exact number of
multiple future or independent observations is not as precise as when estimating the appropriate UPL. (2) The
mathematical underpinnings of UPLs under re -testing strategies are well established, while those for re -testing with
tolerance limits are not. Re -testing strategies are now encouraged and sometimes required under assessment
monitoring situations. (3) Statistically, the two limits are similar, especially under normal assumptions; to avoid
confusion, the UPL is generally chosen over the UTL.
17

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 4 — BACKGROUND CONCENTRATIONS
background concentration values using the UPL95 for a constituent will be produced for each
sub -group of samples, provided the sub -groups represent distinct populations.
Part 3 of the process involves describing the statistical analyses and presenting the resulting
background threshold values (UPLs) for each constituent.
4.2 Observation for Background Wells
Currently, the Buck site has the following number of usable observations at background wells
for implementation of the background concentration methodology described in Section 4.1:
Y MW-6S (Voluntary Monitoring Well) — 17 observations
Y MW-61D (Voluntary Monitoring Well) — 17 observations
Y MW-6BR (Additional Assessment Monitoring Well) — 0 observations
Y BG-1 BR (CSA Monitoring Well)
— 0 observations
Y BG-1S (CSA Monitoring Well) —
3 observations
Y BG-1 D (CSA Monitoring Well) —
5 observations
Y BG-21D (CSA Monitoring Well) —
4 observations
Y BG-2S (CSA Monitoring Well) —
4 observations
Y BG-3D (CSA Monitoring Well) — 5 observations
Y BG-3S (CSA Monitoring Well) — 5 observations
It is expected that with interim monitoring implementation, the Buck site will have the
appropriate number of data points to perform the calculation of UPL95s. HDR is considering
alternatives that will provide the required number of sample events and will provide an update
on that evaluation at a later date.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 5 — ANTICIPATED ADDITIONAL ASSESSMENT ACTIVITIES
Section 5 — Anticipated Additional Assessment
Activities
Anticipated additional assessment activities are summarized below.
Proposed Additional Assessment Monitoring Wells
Based on review of site information and analytical data available at this time, there are several
locations at the site where additional groundwater assessment is warranted to refine delineation
of the vertical extent of groundwater impacts associated with potential coal ash -related
constituents. The following wells are currently planned for installation during Fall of 2016:
Proposed Additional
Monitoring Wells
AB-4BRL
AB-10BR
MW-11 BR
Location
Within Cell 2
On Cell 1 (additional
primary pond) dam
North of Cell 3
Purpose
Evaluate possible vertical
extent of vanadium (114
pg/L) in AB-4BR during
Round 5 sampling.
Evaluate possible vertical
extent of boron (1,880
pg/L), hexavalent chromium
(5.5 pg/L), and vanadium
(3.5 pg/L) detected in AB-
10D during Round 5
sampling.
Evaluate possible vertical
extent of boron (1,160 pg/L)
in MW-11 D during NPDES
samDlina in March 2016.
Approximate
Monitoring Well
Depth(s) (ft)
170
160
100
The information obtained from the borings will be reviewed against the existing conceptual site
model to evaluate if modifications or refinement are required.
Implementation of the Effectiveness Monitoring Plan
The effectiveness monitoring plan proposed in CAP Part 2 provided detailed information
regarding field activities to be performed during collection of groundwater, ash basin surface
water, and AOW samples associated with the ash basin, which consists of Cell 1, Cell 2, and
Cell 3, as well as the ash storage area at the Buck site. The monitoring plan is intended to
evaluate the effectiveness of proposed corrective actions and address the need to evaluate
baseline conditions and seasonal variation in groundwater, ash basin surface water, and AOWs.
Duke Energy will implement the effectiveness monitoring plan in accordance with
recommendations provided in the CAP Part 2 report as well as subsequent discussions with
NCDEQ.

Duke Energy Carolinas, LLC I CSA Supplement 2
Buck Steam Station Ash Basin 01
SECTION 6 — CONCLUSIONS AND RECOMMENDATIONS
Section 6 — Conclusions and Recommendations
The following conclusions have been developed from the information presented in this CSA
Supplement 2 report:
Y Groundwater monitoring results from Round 5 of sampling, including data from additional
assessment groundwater monitoring wells, indicate consistency with previous sampling
results, specifically the extent of impact to groundwater from ash basin -related
constituents (e.g., boron).
Y Additional monitoring wells (GWA-2S, GWA-15S/D, and GWA-17S) within the vicinity of
GWA-2BR/BRU were installed to refine understanding of constituent concentrations
between Cell 2 and Cell 3. Analytical results from these wells are generally consistent
with data obtained from GWA-2BR; however, iron and manganese concentrations in the
new wells were approximately one to several orders of magnitude higher than in well
GWA-2BRU during the Round 5 sampling event. Multiple attempts at well development
at GWA-15S (4 total attempts before sampling) and GWA-17S (4 total attempts before
sampling), in particular, may be an indicator of these differences.
Y Concentrations of select constituents exceeded their applicable 2L/IMAC/DHHS HSL
criteria in additional assessment wells GWA-18S/D, GWA-19S/D, GWA-20S/D, and MW-
6BR.
Y The vertical extent of ash -related impacts is not defined at the Cell 1 dam, within Cell 2,
and north of Cell 3.
Based on the conclusions presented above, the following recommendations are offered:
Y Refinement of PPBCs should be conducted once the minimum number of viable
observations per background well are available.
Y Evaluation of groundwater quality in the vicinity of wells GWA-18S/D, GWA-19S/D,
GWA-20S/D, and MW-6BR should be continued to refine their use as delineation wells
upgradient and downgradient of the ash basin system.
Y Additional monitoring wells should be installed at the Cell 1 dam, within Cell 2, and north
of Cell 3 to refine vertical delineation of groundwater impacts in these areas.
Y Duke Energy will implement the effectiveness monitoring plan in accordance with
recommendations provided in the CAP Part 2 report as well as subsequent discussions
with NCDEQ.
20

Figures

Tables

Appendix A
Boring Logs
Core Photos
F-j

Appendix B
Field Sampling Forms
Slug Test Report
F-j

V
Appendix C
Laboratory Reports and
Chain -of -Custody Forms
F-j