NC0005088_1_FINAL_CSA Supplement 2_Report_20160808

Comprehensive Site Assessment
Supplement 2
Cliffside Steam Station Ash Basin
Site Name and Location
Groundwater Incident No.
NPDES Permit No.
Date of Report
Permittee and Current Property Owner
Consultant Information
Latitude and Longitude of Facility
Cliffside Steam Station
573 Duke Power Road
Mooresboro, NC 28114
Not Assigned
NC0005088
August 8, 2016
Duke Energy Carolinas, LLC
526 South Church St
Charlotte, NC 28202-1803
704.382.3853
HDR Engineering, Inc. of the Carolinas
440 South Church St, Suite 900
Charlotte, NC 28202
704.338.6700
350 13'25" N, 810 45'22" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
�•.••'�� CARO1� •�,
z� E N91N Y
FLAE Al ,
CS j
Malcolm F. Schaeffer, L.G.
Senior Geologist

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin
TABLE OF CONTENTS
Table of Contents
Paqe
ExecutiveSummary ...................................................................................................................
1
Section1 — Background.............................................................................................................
4
1.1 Purpose of CSA Supplement 2....................................................................................
4
1.2 Site Description............................................................................................................
5
1.3 History of Site Groundwater Monitoring........................................................................
7
1.3.1 NPDES Sampling.................................................................................................
8
1.3.2 CSA Sampling......................................................................................................
8
1.3.3 Post -CSA Sampling..............................................................................................
9
1.3.4 NCDEQ Water Supply Well Sampling...................................................................
9
Section 2 — CSA Review Comments.........................................................................................12
2.1 NCDEQ General Comments and Responses..............................................................12
2.2 NCDEQ Site -Specific Comments and Responses......................................................12
2.3 Errata..........................................................................................................................12
Section 3 — Additional Assessment...........................................................................................13
3.1 Additional Assessment Activities................................................................................13
3.1.1 Well Installation....................................................................................................13
3.1.2 Well Gauging and Sampling.................................................................................16
3.2 Additional Assessment Results...................................................................................16
3.2.1 Groundwater Flow Direction.................................................................................16
3.2.2 Sampling Results.................................................................................................17
Section 4 — Background Concentrations...................................................................................23
4.1 Methodology...............................................................................................................23
4.2 Observation for Background Wells..............................................................................25
Section 5 — Anticipated Additional Assessment Activities..........................................................26
5.1 Proposed Additional Assessment Monitoring Wells.....................................................26
5.2 Implementation of the Effectiveness Monitoring Plan..................................................27
Section 6 — Conclusions and Recommendations......................................................................28

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
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 Beryllium Isoconcentration Contour Map - Shallow Wells (S)
3-4.11 Beryllium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.12 Beryllium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.13 Boron Isoconcentration Contour Map - Shallow Wells (S)
3-4.14 Boron Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.15 Boron 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 Mercury Isoconcentration Contour Map - Shallow Wells (S)
3-4.32 Mercury Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.33 Mercury Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.34 Selenium Isoconcentration Contour Map - Shallow Wells (S)
3-4.35 Selenium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.36 Selenium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.37 Sulfate Isoconcentration Contour Map - Shallow Wells (S)
3-4.38 Sulfate Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.39 Sulfate Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.40 Total Dissolved Solids Isoconcentration Contour Map - Shallow Wells (S)
3-4.41 Total Dissolved Solids Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.42 Total Dissolved Solids Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.43 Thallium Isoconcentration Contour Map - Shallow Wells (S)

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin
TABLE OF CONTENTS
3-4.44 Thallium Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.45 Thallium Isoconcentration Contour Map — Bedrock Wells (BR)
3-4.46 Vanadium Isoconcentration Contour Map — Shallow Wells (S)
3-4.47 Vanadium Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.48 Vanadium Isoconcentration Contour Map — Bedrock Wells (BR)
3-5.1 Site Cross Section Locations
3-5.2 Cross Section A -A'
3-5.3 Cross Section B -B' (Sheet 1 of 2)
3-5.4 Cross Section B -B' (Sheet 2 of 2)
3-5.5 Cross Section C -C'
3-5.6 Cross Section D -D'
3-5.7 Cross Section E -E'
3-5.8 Cross Section F -F'
3-5.9 Cross Section G -G'
3-5.10 Cross Section H -H'
3-5.11 Cross Section I -I'
3-5.12 Cross Section J -J'
3-5.13 Cross Section K -K'
3-5.14 Cross Section L -L'
3-5.15 Cross Section M -M'
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 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 Well Boring 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
Cliffside Steam Station Ash Basin FN
EXECUTIVE SUMMARY
Executive Summary
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Cliffside Steam Station
(CSS), located in Mooresboro, in Rutherford and Cleveland Counties, North Carolina (Figure 1-
1). CSS began operations in 1940 with Units 1 through 4. Unit 5 began operations in 1972,
followed by Unit 6 in 2012. Units 1 through 4 were retired from service in 2011 as part of Duke
Energy's decommissioning and demolition program, and were imploded in October 2015.
Currently only Units 5 and 6 are in operation. Coal combustion residuals (CCR) and other liquid
discharges from CSS's coal combustion process have been historically disposed into the
station's ash basin system. The ash basin system consists of the active ash basin, the Units 1-4
inactive ash basin, and the Unit 5 inactive ash basin. Discharge from the active 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 NC0005088.
This Comprehensive Site Assessment (CSA) Supplement 2 report provides the following:
• Summary of groundwater, porewater, surface water, and area of wetness (AOW)
monitoring data through April 2016;
• Responses to NCDEQ review comments pertaining to the CSA;
• Findings from assessment activities conducted since submittal of the CSA report,
including additional assessment previously identified in the CSA;
• Update on the development of provisional background groundwater concentrations; and
• 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 (south-southeast) of the ash
basin. Boron has not been detected in groundwater beyond the compliance boundary. The
hydrogeologic nature of the ash basin 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 during implementation of effectiveness monitoring by Duke Energy 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.
1 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 Executive Summary, as appropriate.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
EXECUTIVE SUMMARY
The following conclusions and recommendations are offered:
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).
• Monitoring well GWA-34S was installed to determine the horizontal extent of
exceedances reported at MW -34S and to better define groundwater flow direction.
Exceedances of the North Carolina Groundwater Quality Standards, as specified in 15A
NCAC 2L.0202 (2L Standards or 2L) or Interim Maximum Allowable Concentration
(IMAC) established by NCDEQ pursuant to 15A NCAC 2L.0202(c), of cobalt and
manganese were observed at this location during the Round 5 sampling. The
groundwater elevation measured in GWA-34S supports the previously interpreted
groundwater flow direction toward the Broad River.
• Additional assessment wells were installed to refine understanding of the horizontal
extent of exceedances.
o Monitoring wells GWA-35S and GWA-35D were installed along the U5-1, U5-2,
1_15-3 transect. Exceedances of the 2L Standard or IMAC for cobalt, iron,
manganese, and vanadium were detected during the Round 5 sampling.
o Monitoring wells GWA-36S, GWA-36D, GWA-37S, and GWA-37D were installed
to refine understanding of exceedances reported at GWA-4S/D. Exceedances of
the 2L Standard, IMAC, or North Carolina Department of Health and Human
Services (NCDHHS) Health Screening Level (HSL) for cobalt, manganese,
sulfate, and vanadium in GWA-36D, and hexavalent chromium, sulfate, and total
dissolved solids (TDS) in GWA-37D, were detected in one or more of these wells
during the Round 5 sampling.
o Monitoring wells GWA-38S and GWA-38D were installed to refine understanding
of exceedances reported at GWA-14S/D. Exceedances of the 2L Standard,
IMAC, or DHHS HSL for hexavalent chromium, cobalt, iron, manganese,
vanadium, antimony, arsenic, and chromium were detected in one or more of
these wells during the Round 5 sampling.
• Additional assessment wells GWA-39S, GWA-40S, GWA-41 S, GWA-42S, GWA-44S,
GWA-44D, GWA-44BR, GWA-48BR, GWA-24BR, AB-5BR, and AB-3BR were installed
to better refine groundwater flow direction. Groundwater elevations indicate that
groundwater in the central portion of the site flows toward Suck Creek.
• Monitoring wells GWA-43S and GWA-43D were installed to refine understanding of the
horizontal extent of exceedances reported at MW-23D/BR and GWA-33S/D/BR and to
better define groundwater flow direction. Exceedances of the 2L Standard, IMAC, or
DHHS HSL of cobalt, vanadium, hexavalent chromium, and manganese in GWA-43S
and iron in GWA-43D were observed at this location during the Round 5 sampling. The
groundwater elevations measured in these wells indicates groundwater flows toward the
Broad River.
• Monitoring wells GWA-45S and GWA-45D were installed to determine the horizontal
extent of exceedances reported at MW -42S and MW -42D and to better define

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
EXECUTIVE SUMMARY
groundwater flow direction. Exceedances of the 2L Standard, IMAC, or DHHS HSL of
hexavalent chromium, selenium, cobalt, manganese, and mercury in GWA-45S and
antimony, arsenic, and vanadium in GWA-45D were observed at this location during the
Round 5 sampling. The groundwater elevations measured for wells GWA-45S/D support
the previously interpreted groundwater flow direction toward the Broad River.
• Refinement of PPBCs should be conducted once the minimum number of viable
observations per background well are available.
• Additional monitoring wells should be installed to refine the vertical and horizontal
delineation of groundwater exceedances north, east, and downgradient of Unit 5 inactive
ash basin and dam, west of Units 1-4 inactive ash basin, northwest and west of the ash
storage area, and west and southwest of the active ash basin.
• 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
Cliffside Steam Station Ash Basin FN
SECTION 1 — BACKGROUND
Section 1 — Background
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the Cliffside Steam Station
(CSS), located in Mooresboro, in Rutherford and Cleveland Counties, North Carolina (Figure 1-
1). CSS began operations in 1940 with Units 1 through 4. Unit 5 began operations in 1972,
followed by Unit 6 in 2012. Units 1 through 4 were retired from service in 2011 as part of Duke
Energy's decommissioning and demolition program, and were imploded in October 2015.
Currently only Units 5 and 6 are in operation. Coal ash residue and other liquid discharges from
CSS's coal combustion process have been disposed in the station's ash basin system since its
construction. The ash basin system consists of the active ash basin, the Units 1-4 inactive ash
basin, and the Unit 5 inactive ash basin. Discharge from the active ash basin is permitted by the
North Carolina Department of Environmental Quality (NCDEQ)2 Division of Water Resources
(DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit
NC0005088.
The Comprehensive Site Assessment (CSA) report for CSS was submitted to NCDENR on
August 18, 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 12, 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 February and May 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:
• A brief summary and update of groundwater sampling data from the NPDES, CSA, and
post -CSA monitoring well sampling events;
• A brief summary of results of NCDEQ water supply well sampling events;
• A summary of NCDEQ comments on the CSA report and responses to those comments;
• A description of additional assessment activities conducted since submittal of the CSA
report and the findings of those assessment activities;
• An updated approach for the refinement of proposed provisional background
concentrations (PPBCs) for groundwater at the CSS site; and
• A description of additional planned assessment activities.
2 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 document, as appropriate.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 — BACKGROUND
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 basins 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
wells). Additional assessment groundwater monitoring wells are shown on Figure 1-2 with
green text labels.
1.2 Site Description
The CSS site is located in Mooresboro, in Rutherford and Cleveland Counties, North Carolina.
The CSS site occupies approximately 1,000 acres and is owned by Duke Energy. CSS is a
coal-fired electricity generating facility with a current capacity of 1,381 megawatts (MW). The
station began commercial operations in July 1940 with Units 1-4 (198 MW total). Unit 5 (556
MW) began operations in 1972, increasing the total plant capacity to 754 MW. Construction of
Unit 6, an 825 MW clean -coal unit, 3 began in 2008 and the unit began commercial operations in
2012. Units 1-4 were retired from service in October 2011, and Units 5 and 6 continue to
operate and use the active ash basin. Unit 5 operates with wet bottom ash and wet fly ash
handling. Unit 6 operates with dry bottom ash and dry fly ash handling. The CSS ash basin
system is located both west and east-southeast from the station and adjacent to the Broad
River, and consists of an active ash basin, the Units 1-4 inactive ash basin, and the Unit 5
inactive ash basin. An ash storage area is located within the ash basin system waste boundary.
The Units 1-4 inactive ash basin is located immediately east of the retired Units 1-4. It was
constructed in 1957 and began operations the same year. The Units 1-4 ash basin was retired
in 1977 once it reached capacity, although five small settling cells still exist on the western
portion of the footprint, and the limited stormwater that drains to these cells is pumped to the
active ash basin (located southeast of the Units 1-4 inactive ash basin).
The Unit 5 inactive ash basin is located on the western portion of the site, west and southwest
of Units 5 and 6, and is currently used as a laydown yard for the station. This ash basin was
constructed in 1970 (in advance of Unit 5 operations) and received sluiced ash from Unit 5
starting in 1972 until it was retired in 1980 when it reached full capacity. The basin currently
receives stormwater from a localized drainage area, which is then routed into the active ash
basin.
The active ash basin is located on the eastern portion of the site, east and southeast of Units 5
and 6. Construction of the active ash basin occurred in 1975 and it began receiving sluiced ash
from Unit 5. The active ash basin was later expanded in 1980 to its current footprint and
continues to receive sluiced bottom ash and fly ash from Unit 5 in addition to other waste
streams identified below.
An unlined dry ash storage area, which is split into an eastern and western portion, is also
located within the northwestern portion of the active ash basin waste boundary. This ash
storage area was likely created when ash was removed from the active ash basin in the 1980s
to provide additional capacity for sluiced ash. The CSA investigation results were not conclusive
3 Clean -coal units include technologies designed to remove or reduce air pollutant emissions to the atmosphere.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 - BACKGROUND
in identifying the boundaries of the ash in the ash storage area and additional field work to
resolve this area was recommended in the CSA report and additional assessment is being
implemented. The eastern portion of the ash storage area may be a spoils area remnant from
embankment dam construction, but no data were collected to confirm this during the CSA.
The active ash basin is an integral part of the station's wastewater treatment system and
historically received inflows from the ash removal system, station yard drain sump, stormwater
flows, station wastewater, and other permitted discharges. Currently, the Unit 5 ash removal
system and the station yard drainage system are routed through high density polyethylene pipe
sluice lines into the active ash basin. Inflows to the active ash basin are variable based on Unit
5 and Unit 6 operations.
Duke Energy also operates the Coal Combustion Products (CCP) Landfill in accordance with
the NCDEQ Industrial Solid Waste Permit No. 81-06. The landfill was constructed with an
engineered liner and leachate collection system and is permitted to receive fly ash, bottom ash,
boiler slag, mill rejects, flue gas desulfurization sludge, gypsum, leachate basin sludge, non-
hazardous sandblast material, limestone, ball mill rejects, coal, carbon, sulfur pellets, cation and
anion resins, sediment from sumps, cooling tower sludge, and filter bags. The landfill is located
approximately 1,800 feet southwest of the Unit 5 inactive ash basin, northeast of the intersection
of Old U.S. Highway 221A and Ballenger Road.
Topography at the CSS site generally slopes from south to north with an elevation difference of
approximately 190 feet over an approximate linear distance of 4,000 feet. Site elevations are
highest southwest of the active ash basin and southwest of the Unit 5 inactive ash basin and
lowest at the interface with the Broad River along the northern extent of the site. Surface water
drainage generally follows site topography and flows from the south to the north across the site
except where natural drainage patterns have been modified by the ash basin or other
construction. Unnamed drainage features are located near the western and eastern extents of
the site and generally flow north to the Broad River. Suck Creek transects the site from south to
north, discharging to the Broad River. The approximate pond elevation for the active ash basin
is 762 feet. The elevation of the Broad River adjacent to the site is approximately 656 feet. 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 CSS 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 south to north toward the
Broad River. Groundwater in the shallow and deep wells located west of the active ash basin
and east of Unit 6 flows toward Suck Creek and on to the Broad River based on monitoring of
groundwater elevations.
The source areas are defined as the Unit 5 inactive ash basin, the Units 1-4 inactive ash basin,
the ash storage area, and the active ash basin. As described in the CSA, source
characterization was performed to identify physical and chemical properties of ash, ash basin
surface water, ash porewater, and ash basin areas of wetness (AOW).

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 - BACKGROUND
The compliance boundary for groundwater quality at the CSS 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 (2L Standards or 2L) or
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, IMAC, or NCDHHS HSL exceedances are beneath and downgradient of
the source areas. The extent of impacts indicates that physical and geochemical processes
beneath the site inhibit the lateral migration of COIs. Vertical migration of COls was observed in
select well clusters (shallow, deep, and bedrock) and is likely influenced by infiltration of
precipitation and/or ash basin water, where applicable, through the shallow and deep flow layers
into underlying fractured bedrock. In accordance with LeGrand's slope -aquifer system
characteristic of the Piedmont, whereby groundwater from shallow, deep, and bedrock flow
layers into surficial waterbodies, groundwater at the CSS site discharges into the Broad River.
1.3 History of Site Groundwater Monitoring
Monitoring wells were installed by Duke Energy in 1995/1996, 2005, and 2007 as part of the
voluntary monitoring system for groundwater near the active ash basin. In addition, MW -2D -A
was installed in 2011 to replace MW -2D. Duke Energy implemented an enhanced voluntary
groundwater monitoring around the CSS active ash basin from August 2008 until August 2010.
During this period, the voluntary groundwater monitoring wells were sampled two times per year
and the analytical results were submitted to NCDENR DWR. A review of voluntary monitoring
well sampling results obtained between 2008 and 2011 indicates the following:
• Boron exceeded the 2L Standard in voluntary monitoring well CLMW-1 during the
August 2008, February 2009, and August 2009 sampling events. This monitoring well is
located north of the active ash basin in the southern end of the western portion of the
ash storage area.
• Chromium exceeded the 2L Standard in voluntary monitoring well MW -2D during the
August 2009, February 2010, and August 2010 sampling events. Monitoring well MW -
2D -A was installed to replace MW -21D in 2011. Voluntary monitoring well MW -2D -A was
sampled in April 2011 and an exceedance of chromium was not reported.
• Iron and manganese exceeded the 2L Standards between 2008 and 2011 in several
voluntary monitoring wells screened in the shallow and deep flow layers. These
exceedances may be attributable to naturally occurring conditions and require additional
evaluation as site-specific PPBCs are refined.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 — BACKGROUND
Construction details for voluntary monitoring wells are provided in Table 1-1. The location of the
ash basin voluntary and compliance monitoring wells, the approximate ash basin waste
boundaries, and the compliance boundaries are shown on Figure 1-2.
1.3.1 NPDES Sampling
NPDES compliance monitoring wells (compliance wells) were installed in 2010 and 2011.
Compliance groundwater monitoring, as required by the NPDES permit, began in April 2011.
From April 2011 through July 2016, compliance groundwater monitoring wells at the CSS site
have been sampled three times per year, resulting in 16 total sampling events during that time.
A review of the NPDES compliance well sampling results indicates the following:
• Antimony exceeded the IMAC once in compliance wells MW-20DR, MW -23D, MW -24D,
and MW-24DR over the period of monitoring.
• Chromium exceeded the 2L Standard once in compliance wells MW-20DR, MW -23D,
and MW-25DR over the period of monitoring. However, the turbidity in monitoring well
MW -25D during the chromium exceedance reported in April 2011 was reported at 683
nephelometric turbidity units (NTI I), which may have affected the chromium result.
• 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.
• Sulfate exceeded the 2L Standard in 15 out of 16 sampling events in monitoring well
MW -23D.
• Total dissolved solids (TDS) exceeded the 2L Standard in monitoring well MW-20DR
once over the period of monitoring and in monitoring well MW -23D during all 16
sampling events.
• Thallium exceeded the IMAC in monitoring well MW-20DR during the April 2015
sampling event.
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 CSS site began in January 2015 and was completed in August 2015. As part of
this assessment, 131 soil/ash and rock borings (for groundwater monitoring wells) were installed
to characterize the ash, soil, rock and groundwater at the CSS site.. One comprehensive round
of sampling was summarized in the CSA report and included sampling of soil, groundwater,
porewater, and surface water (see Figure 1-2 for sampling locations). In addition,
hydrogeological evaluation testing was performed on newly installed wells.
The following constituents were reported as COls in the CSA report:
• Soil: arsenic, cobalt, iron, manganese, selenium, thallium, and vanadium

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 — BACKGROUND
Groundwater: antimony, arsenic, barium, beryllium, boron, hexavalent chromium,
chromium,4 cobalt, iron, lead, manganese, mercury, nickel, pH, sulfate, TDS, and
vanadium
• Surface water: aluminum
Horizontal and vertical delineation of source -related soil impacts was presented in the CSA
report. Where soil impacts were identified beneath the ash basins (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 for additional assessment:
• Horizontal and vertical extent west of the active ash basin in the vicinity of monitoring
wells MW -23D and GWA-14D.
• Horizontal and vertical extent east of the Unit 5 inactive ash basin to the east of
monitoring wells MW -42D and GWA-4D.
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 report (submitted on November 16, 2015).
Rounds 3 and 4 of background well groundwater monitoring occurred in November and
December 2015 and were reported in the CSA Supplement 1 as part of the CAP Part 2 report
(submitted on February 12, 2016). Round 5 of groundwater monitoring was conducted between
February and April 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
CSS compliance boundary in all directions, since the direction of groundwater flow had not been
determined at CSS at the time of the 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 Surveys, 6 if the owner agreed to have their
well sampled. The NCDEQ-directed water supply well sampling consisted of collection and
analysis of the following:
A total of 22 samples collected from 22 private drinking water supply wells within 0.5
mile of the CSS compliance boundary; and
4 Unless otherwise noted, references to chromium in this document should be assumed to indicate total chromium.
5 HDR. 2014a. Cliffside Steam Station Ash Basin Drinking Water Supply Well and Receptor Survey. NPDES Permit
NC0005088 September 30, 2014.
6 HDR. 2014b. Cliffside Steam Station Ash Basin. Supplement to Drinking Water Supply Well and Receptor Survey.
NPDES Permit NC0005088. November 6, 2014

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin
SECTION 1 — BACKGROUND
• A total of 8 reference or background water supply wells in the vicinity of CSS.
In addition, Duke Energy collected samples from 9 background water supply wells located within
a 2- to 10 -mile radius of the CSS site. The locations of the private water supply wells identified
within 0.5 mile of the CSS 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 CSS
facility indicated that boron was detected in 11 of the 22 NCDEQ-sampled water supply wells
within 0.5 mile of the compliance boundary and in none of the background well samples
collected by NCDEQ and Duke Energy. pH was below the drinking water standard range in 5 of
the 22 NCDEQ-sampled water supply wells and in NCDEQ- and Duke Energy -sampled
background wells. This result is not unexpected, based on a study published by the United
States Geological Survey' and additional North Carolina -specific studies$ showing that
groundwater pH in the state is commonly below the Maximum Contaminant Level (MCL) range
of 6.5 to 8.5 Standard Units. None of the NCDEQ-sampled water supply well results were above
Federal primary drinking water standards (MCLs), with the exception of the pH and lead results
noted above.
Boron is a naturally occurring compound, usually found in various inorganic forms in sediments
and sedimentary rocks. Boron presents in water, soil, and air originates from both natural and
anthropogenic sources.
Natural weathering of boron -containing rocks is thought to be the primary source of boron
compounds in water and soil. Releases to air from oceans, volcanos, and geothermal steam are
other natural sources of boron in the environment.
Human causes of boron contamination include releases to air from power plants, chemical
plants, and manufacturing facilities. Fertilizers, herbicides, and industrial wastes are among the
sources of soil contamination. Contamination of water can come directly from industrial
wastewater and municipal sewage, as well as indirectly from air deposition and soil runoff.
Borates in detergents, soaps, and personal care products can also contribute to the presence of
boron in water. Boric acid and its sodium salts are registered for use as pesticides9.
"Do Not Drink" letters were issued by the DHHS for 18 water supply wells at CSS, with
hexavalent chromium and iron being the primary constituents listed in the letters and vanadium
being identified in three 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 hexavalent chromium, iron, and vanadium. Letters were issued for other
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.
8 Briel, L.I. 1997. Water quality in the Appalachian Valley and Ridge, the Blue Ridge, and the Piedmont physiographic
�rovinces, eastern United States (Professional Paper No. 1422-D). U.S. Geological Survey.
USEPA Office of Water. January 2008. Health Effects Support Document for Boron. Document Number EPA -822-
R-08-002.
IN

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 1 - BACKGROUND
constituents as follows: iron (9 wells), cobalt (4 wells), chromium (1 well), manganese (2 wells),
and sodium (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 CSS 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 from the
higher topography located south of the Cliffside property to the north toward the Broad River.
Groundwater also flows west of the active ash basin and east of Unit 6 toward Suck Creek and
on to the Broad River. Thus, groundwater flow from areas associated with the ash basin, ash
landfills, and the ash storage area is away from the water supply wells. A review of topographic
and monitoring well groundwater elevation data at CSS 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 and sulfate. The conclusion from the groundwater chemical signature evaluation
is that water supply wells in the vicinity of the CSS facility are not impacted by CCR releases
from the ash basin.
Is

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 2 — CSA REVIEW COMMENTS
Section 2 — CSA Review Comments
Representatives of NCDEQ's Central Office and Asheville Regional Office (ARO) met with Duke
Energy and HDR on October 20, 2015 to present NCDEQ's 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 CSS.
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 12, 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 12, 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.
12

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside 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 section.
Additional Assessment Activities
Additional assessment activities included monitoring well installation and sampling, as
discussed below.
3.1.1 Well Installation
Additional wells were installed to refine understanding of groundwater flow direction and extent
of exceedances at CSS. Refinement of exceedances focused primarily on the extent and nature
of TDS exceedances of the 2L Standard in the deep wells MW -23D and GWA-14D and
additional refinement of the extent and nature of exceedances in the area east of the Unit 5
inactive ash basin to the east of MW -42D and GWA-4D. To address the TDS exceedances in
MW -23D and GWA-14D, monitoring wells GWA-38S/D were installed. To address the extent of
exceedances at MW -42D, monitoring wells GWA-45S/D were installed. To address the extent of
exceedances at GWA-4D, monitoring wells GWA-36S/D and GWA-37S/D were installed.
Subsequent discussions with Duke Energy and NCDEQ resulted in the installation of additional
monitoring wells beyond those described above. A summary of additional assessment wells and
installation dates, as well as the purpose for installation, is provided in the table below.
Boring /Well Installation
Identification I Date
U5 -3S -A
U5-2BR
U5 -2S -SL -A
U5-8BR
2/26/2016
2/26/2016
Purpose for Installation
This is a replacement well for U5 -
3S, which was dry
NCDEQ requested a bedrock well at
this well cluster location
2/26/2016 ' NCDEQ requested this replacement
well for U5 -2S -SL, which had an
obstruction
6/8/2016
GWA-31BR-A 1 3/21/2016
NCDEQ requested a bedrock well at
this cluster location
NCDEQ requested this replacement
well for GWA-31 BR, which was dry
GWA-34S i 3/29/2016 NCDEQ requested this well be
installed to refine horizontal extent of
exceedances reported at MW -34S
and to better define groundwater
flow direction
Results
Concentrations of hexavalent
chromium, cobalt, iron,
manganese, vanadium
exceeded applicable criteria
Concentrations of arsenic,
cobalt, iron, manganese,
thallium, and vanadium
exceeded applicable criteria
Concentrations of antimony,
arsenic, chromium, cobalt, iron,
lead, manganese, thallium, and
vanadium exceeded applicable
criteria
Not installed in time for
sampling inclusion during the
Round 5 sampling event
Concentrations of antimony,
chromium, iron, and vanadium
exceeded applicable criteria
Water level measured and used
for contouring of shallow flow
layer. Concentrations of cobalt
and manganese exceeded
applicable criteria.
13

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
Boring /Well
Installation
Purpose for Installation
Results
Identification
Date
GWA-35S
4/7/2016
NCDEQ requested additional wells
along the U5-1, U5-2, U5-3 transect
Concentrations of cobalt, iron,
manganese, and vanadium
GWA-35D
4/5/2016
to refine horizontal extent of
exceeded applicable criteria
exceedances
GWA-36S
2/17/2016
Monitoring wells needed for
Concentrations of cobalt and
refinement of the delineation of
manganese exceeded
exceedances reported at GWA-4S/D
applicable criteria
GWA-36D
2/16/2016
Concentrations of cobalt,
manganese, sulfate, and
vanadium exceeded applicable
3/8/2016
Monitoring wells needed for
criteria
GWA-37S
Concentrations of cobalt, iron,
refinement of the delineation of
and manganese exceeded
exceedances reported at GWA-4S/D
applicable criteria
Concentrations of hexavalent
GWA-37D
3/8/2016
chromium, cobalt, manganese,
sulfate, TDS exceeded
applicable criteria
GWA-38S
2/16/2016
Monitoring wells needed for
Inadvertently not sampled
refinement of the delineation of
during the Round 5 sampling
exceedances reported at GWA-
14S/D
event
GWA-38D
2/16/2016
Concentrations of antimony,
arsenic, chromium, hexavalent
chromium, cobalt, iron,
manganese, and vanadium
exceeded applicable criteria
GWA-39S
4/8/2016
NCDEQ requested these wells for
Water level measured and used
refinement of groundwater flow
for contouring of shallow flow
direction
layer
Water level measured and used
GWA-40S
4/8/2016
for contouring of shallow flow
layer
GWA-41S
4/8/2016
Well was abandoned
(Later
Abandoned
Water level measured and used
GWA-42S
4/1/2016
for contouring of shallow flow
layer
GWA-43S
3/30/2016
Wells requested by NCDEQ to refine
Water level measured and used
extent of exceedances reported at
for contouring of shallow flow
MW-23D/BR and GWA-33S/D/BR,
layer. Concentrations of
and to better define groundwater
hexavalent chromium, cobalt,
flow direction in this location
manganese, and vanadium
exceeded applicable criteria
GWA-43D
3/29/2016
Water level measured and used
for contouring of deep flow
layer. Concentrations of cobalt,
iron, and vanadium exceeded
applicable criteria.
14

Boring /Well I Installation
Identification
Date
GWA-44S
2/11/2016
GWA-44D
2/12/2016
2/11/2016
GWA-44BR
GWA-45S
GWA-45D
GWA-46 D
2/11/2016
2/12/2016
3/1/2016
GWA-47D 3/8/2016
GWA-48BR 3/11/2016
GWA-24BR 3/10/2016
AB-5BR I 3/1/2016
AB-3BR 5/31/2016
MW -23S 1 3/1/2016
Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
Purpose for Installation
NCDEQ requested additional wells
west of MW-23D/DR to better define
groundwater flow and vertical
gradients in this location
NCDEQ requested additional wells
east of MW-42S/D to delineate
horizontal extent of exceedances
and better define groundwater flow
in this location
NCDEQ requested additional wells
near GWA-27D-A to delineate
horizontal extent of exceedances
and better define groundwater flow
in this location
NCDEQ requested additional wells
near GWA-26S/D, between the wells
and Suck Creek, to delineate
horizontal extent of exceedances
and better define groundwater flow
in this location
NCDEQ requested additional
bedrock wells in these areas to
better define groundwater flow
direction in the bedrock flow layer
NCDEQ requested a shallow
monitoring well be installed at the
MW-23D/DR compliance well cluster
Results
Water level measured and used
for contouring of shallow flow
Water level measured and used
for contouring of deep flow
Water level measured and used
for contouring of bedrock flow
Water level measured and used
for contouring of shallow flow
layer. Concentrations of
hexavalent chromium, cobalt,
manganese, mercury, and
selenium exceeded applicable
criteria.
Water level measured and used
for contouring of deep flow
layer. Concentrations of
antimony, arsenic, hexavalent
chromium, selenium, and
vanadium exceeded applicable
criteria.
Water level measured and used
for contouring of deep flow
layer. Inadvertently not sampled
during the Round 5 sampling
event
Water level measured and used
for contouring of deep flow
layer. Concentrations of cobalt,
iron, manganese, thallium, and
vanadium exceeded applicable
criteria
Water level measured and used
for contouring of bedrock flow
layer
Water level was inadvertently
not measured during the
6/17/2016 depth to water
measurement event
Concentrations of hexavalent
chromium, cobalt, and
manganese exceeded
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.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin
SECTION 3 - ADDITIONAL ASSESSMENT
Additional assessment wells that were planned for installation but were not completed included
the following:
• GWA-41 S
— Abandoned due to not encountering water on top of bedrock.
• GWA-46S
— Abandoned due to not encountering water on top of bedrock.
• GWA-47S
— Abandoned due to not encountering water on top of bedrock.
In addition, monitoring wells GWA-46D and GWA-47D were installed to refine the horizontal
extent of exceedances; however, analytical results were not available at the time of this report.
Several additional assessment wells exhibit pH results of 9 or above, which is indicative of
cement leakage beyond the borehole seal. In addition, several monitoring wells were sampled
with turbidity greater than 10 NTU. The evaluation of groundwater quality data obtained from
these wells during Round 5 sampling must be qualified and further evaluated. The additional
assessment wells were installed by North Carolina -licensed drillers according to construction
standards described in 15A NCAC 2C.0107.
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 24 and April 21, 2016. Groundwater analytical
parameters and methods for Round 5 were consistent with those used during previous sampling
events, as presented in previous reports. The analytical results of radionuclide sampling were
not available for inclusion within this report. A total of 166 groundwater and ash 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 sampling 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 sampling 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 16, 2015, 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 Broad River, with groundwater in the central portion of the site flowing
toward Suck Creek and then north to the Broad River. Groundwater elevations and inferred
potentiometric contours for the shallow, deep, and bedrock flow layers are depicted on Figures
16

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
3-1, 3-2, and 3-3, respectively. These groundwater flow results 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, beryllium, boron,
chromium, cobalt, hexavalent chromium, iron, lead, manganese, mercury, nickel, pH, sulfate,
thallium, TDS, and vanadium. Boron, sulfate, and TDS exceeded their 2L Standards and
PPBCs either beneath or downgradient of the ash basins and 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 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 13 porewater samples were collected from monitoring wells (AB -1 S, AB -2S, AB-
3S/SL, AB-4S/SL, AB -5S, AB -6S, IB -1S, IB -3S, U5 -S -SL -A, U5-7S/SL) screened within ash in
the Units 1-5 inactive ash basin, Units 1-4 inactive ash basin, and the active ash basin.
Concentrations of antimony, arsenic, boron, chromium, cobalt, hexavalent chromium, iron, lead,
manganese, pH, sulfate, thallium, TDS, and vanadium that exceed the applicable 2L Standard,
IMAC, or DHHS HSL were detected in porewater samples collected during the Round 5
sampling event (see Table 3-2). The range and number of exceedances of each COI in
porewater is listed below.
• Antimony: 2.1 J pg/L to 7.5 pg/L; 4 exceedances/13 samples
• Arsenic: 103 pg/L to 2,030 pg/L; 9/13
• Boron: 895 pg/L to 3,550 pg/L; 6/13
• Chromium: 36.6 pg/L; 1/13
• Cobalt: 2.1 pg/L to 122 pg/L; 6/13
• Hexavalent Chromium: 0.088 pg/L; 1/13
• Iron: 406 pg/L to 64,200 pg/L; 10/13
• Lead: 15.5 pg/L; 1/13
• Manganese: 86.1 pg/L to 22,600 pg/L; 11/13
• pH: 5.8 to 6.4 SU (low end) and 9.1 to 9.5 SU (high end); 7/13
• Sulfate: 267,000 pg/L to 1,060,000 pg/L; 3/13
• Thallium: 0.24J pg/L to 2.4 pg/L; 7/13
• TDS: 864,000 pg/L; 1/13
• Vanadium: 0.31 pg/L to 93.3 pg/L; 9/13
17

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
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 (see Table 3-1). A summary of Round 5 sampling
results per COI identified during the CSA is as follows:
• Antimony exceeded the IMAC in one well (GWA-28S) screened within the shallow flow
layer west of the active ash basin downstream dam and east of the eastern portion of
the ash storage area. Antimony exceedances were reported in the deep flow layer
upgradient, cross -gradient and beneath the Unit 5 inactive ash basin, upgradient of the
Units 1-4 inactive ash basin, and downgradient and beneath the active ash basin.
Antimony exceedances in the bedrock flow layer were reported beneath the Unit 5
inactive ash basin, beneath the eastern and western portions of the ash storage area,
and northwest of the Units 1-4 inactive ash basin near the Broad River. In general,
dissolved -phase concentrations were consistent with total concentrations in samples
with exceedances, indicating that elevated antimony concentrations are not likely caused
by turbidity.
• Arsenic exceeded the 2L Standard in the shallow flow layer monitoring well U5 -8S,
located at the south end of the Unit 5 inactive ash basin and in AS -7S located in the
western portion of the ash storage area. Arsenic exceedances in the deep flow layer
were reported in monitoring well U5 -21D in the western portion of the Unit 5 inactive ash
basin and in two monitoring wells east of the Unit 5 inactive ash basin, between the
basin and Suck Creek. An arsenic exceedance was reported in the bedrock flow layer at
U5-2BR located beneath the western portion of the Unit 5 inactive ash basin. Total and
dissolved arsenic concentrations were similar in samples with exceedances reported.
• Barium did not exceeded the 2L Standard in any of the samples collected from the
monitoring wells in the shallow or deep flow layers. Barium exceeded the 2L Standard in
the bedrock flow layer monitoring well AS-7BR located in the western portion of the ash
storage area and monitoring well GWA-29BR located downgradient of the Units 1-4
inactive ash basin. Total and dissolved barium concentrations were similar in samples
with exceedances reported.
• Beryllium exceeded the 2L Standard in the shallow flow layer monitoring well AS -1 SB
located in the western portion of the ash storage area and in bedrock monitoring well
GWA-29BR located downgradient of the Units 1-4 inactive ash basin. Total and
dissolved beryllium concentrations were similar in sample AS -1 SB.
• Boron exceeded the 2L Standard in the shallow flow layer in wells located within and
downgradient of the western portion of the ash storage area and downgradient of the
active ash basin downstream dam. A boron exceedance was reported in the deep flow
layer in monitoring well GWA-27D-A located downgradient of the active ash basin,
between the basin and Suck Creek. Boron did not exceed the 2L Standard in the
bedrock flow layer. In general, total and dissolved concentrations were consistent in
each sample with a reported exceedance.
• Chromium exceeded the 2L Standard in the shallow flow layer in monitoring well AS -6S
located within the eastern portion of the ash storage area; however, the dissolved phase
concentration was significantly lower than the total concentration, indicating that this

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin
SECTION 3 — ADDITIONAL ASSESSMENT
exceedance may be turbidity -derived. Chromium exceeded the 2L Standard in the deep
flow layer in monitoring well GWA-38D located upgradient of the Units 1-4 inactive ash
basin, beneath (AB-3BRU) and east and upgradient of the active ash basin (GWA-23D),
and beneath the eastern portion of the ash storage area (AS-513RU). Dissolved phase
concentrations at AS-513RU and GWA-23D were significantly lower than total
concentrations, indicating that these exceedances may be turbidity -derived. Chromium
exceedances in the bedrock flow layer were reported in monitoring well GWA-31 BR
located beneath the Units 5 inactive ash basin, A13 -513R located beneath the
southeastern portion of the active ash basin, east and upgradient of the active ash basin
(GWA-23D), and beneath the eastern portion of the ash storage area (AS-513RU).
However, dissolved phase concentrations were significantly lower than total
concentrations, indicating that these exceedances may be turbidity -derived.
Cobalt exceeded the IMAC in the shallow flow layer in wells across the CSS site.
Concentrations were generally the highest beneath the western portion of the ash
storage area and downgradient of the Unit 5 inactive ash basin. Cobalt exceedances
were also reported in background monitoring wells BG -1 S and MW -32S, indicating that
cobalt may be present as a naturally occurring constituent. Total and dissolved
concentrations were generally consistent for each sample with an exceedance. Cobalt
exceedances in the deep flow layer were less frequent and at generally lower
concentrations than were observed in the shallow flow layer. Cobalt exceeded the IMAC
in monitoring well U5-2BR beneath the western portion of the Unit 5 inactive ash basin,
at GWA-44BR west of the active ash basin and Suck Creek, and at GWA-21 BR located
downgradient of the active ash basin downstream dam. Total and dissolved
concentrations were generally consistent within each sample with a reported
exceedance in the deep and bedrock flow layers.
Hexavalent chromium exceeded the DHHS HSL in the shallow flow layer in wells located
downgradient of the Unit 5 inactive ash basin, upgradient and downgradient of the Units
1-4 inactive ash basin, downgradient of the ash storage area, and upgradient and
downgradient of the active ash basin. Hexavalent chromium exceeded the DHHS HSL in
background wells MW -30S and MW -32S, indicating that hexavalent chromium may be
present as a naturally occurring constituent. 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. Hexavalent chromium exceeded the DHHS HSL in
background wells BG -2D, MW -30D and MW -32D, indicating that hexavalent chromium
may be present as a naturally occurring constituent. Exceedances in the bedrock flow
layer were less frequent and generally restricted to wells within and downgradient of the
Unit 5 inactive ash basin and the ash storage area, with the exception of monitoring well
MW-22BR located upgradient of the active ash basin. Hexavalent chromium exceeded
the DHHS HSL in background well BG -1 BR. Note that dissolved phase analyses for
hexavalent chromium were not performed on groundwater samples.
Iron exceeded the 2L Standard in the shallow flow layer across the CSS site in wells
downgradient within and downgradient of the Unit 5 inactive ash basin and the active
ash basin and ash storage area. Iron exceedances were also reported upgradient of the
Units 1-4 inactive ash basin on the west side of Suck Creek. Total and dissolved
19

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
concentrations varied with regards to how similar the reported concentrations were, with
some concentrations almost equal while others reported total concentrations an order of
magnitude greater than the dissolved concentrations, indicating that elevated iron
concentrations are not likely caused by turbidity. Iron exceeded the 2L Standard in
background well MW-3OS, indicating that iron may be present as a naturally occurring
constituent. Exceedances in the deep flow layer were reported in areas on the eastern
and western portions of the site, and beneath and downgradient of the Unit 5 inactive
ash basin, the Units 1-4 inactive ash basin, and the active ash basin. Total and dissolved
concentrations in deep flow layer wells were generally consistent within each sample
with a reported exceedance. Iron exceeded the 2L Standard in background monitoring
wells BG -2D and MW-24DR. Iron exceedances in the bedrock flow layer were reported
beneath the Unit 5 inactive ash basin, upgradient of the Units 1-4 inactive ash basin
west of Suck Creek, beneath the southern end of the active ash basin, and
downgradient of the active ash basin and ash storage area. Iron exceeded the 2L
Standard in background monitoring well MW -3213R.
• Manganese exceeded the 2L Standard in the shallow and deep flow layers in wells
across the CSS site. In general, total and dissolved concentrations were consistent
within each sample collected from shallow and deep flow layer wells. Manganese
exceeded the 2L Standard in background wells BG -1 S and BG -1 D in the shallow and
deep flow layers, respectively, indicating that manganese may be present as a naturally
occurring constituent. Manganese exceeded the 2L Standard in the bedrock flow layer
beneath and upgradient of the Unit 5 inactive ash basin, upgradient of the Units 1-4
inactive ash basin west of Suck Creek, at the southern end of the active ash basin, and
downgradient of the active ash basin. In general, total and dissolved concentrations
were consistent within each sample with exceedances collected from bedrock flow layer.
• Mercury exceeded the 2L Standard in monitoring well GWA-45S in the shallow flow
layer. The dissolved concentration was less than the laboratory reporting limit, indicating
that the elevated mercury concentration is likely caused by turbidity. Mercury exceeded
the 2L Standard in monitoring well AB -4D in the deep flow layer. The dissolved
concentration was approximately an order of magnitude less than the total
concentration, indicating that the elevated mercury concentration is likely caused by
turbidity. Mercury exceedances were not reported in any monitoring wells in the bedrock
flow layer during the Round 5 sampling event.
• 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 CSS site. However, as discussed in
Section 1.3.4, this can be expected in the Piedmont Province of North Carolina.
• Selenium exceeded the 2L Standard in monitoring wells downgradient of the Units 1-4
inactive ash basin, beneath and downgradient of the ash storage area, and side -gradient
of the Unit 5 inactive ash basin. In general, total and dissolved concentrations were
consistent within each sample with exceedances collected from the shallow flow layer. A
selenium exceedance was reported in the deep flow layer at monitoring well GWA-45D,
side -gradient of the Unit 5 inactive ash basin. In general, the total and dissolved
concentrations in GWA-45D were consistent. Selenium exceedances were not reported
in any monitoring wells in the bedrock flow layer during the Round 5 sampling event.
20

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
• Sulfate exceeded the 2L Standard in the shallow flow layer in monitoring well GWA-44S
located upgradient of the Units 1-4 inactive ash basin on the west side of Suck Creek,
and within and downgradient of the western portion of the ash storage area. Sulfate
exceedances in the deep flow layer were reported in monitoring well GWA-44D located
upgradient of the Units 1-4 inactive ash basin on the west side of Suck Creek, and within
and downgradient of the eastern portion of the Unit 5 inactive ash basin including
monitoring well GWA-37D located outside of the Unit 5 inactive ash basin provisional
compliance boundary. Sulfate exceedances in the bedrock flow layer were reported in
monitoring well GWA-44BR located upgradient of the Units 1-4 inactive ash basin on the
west side of Suck Creek.
Thallium exceeded the IMAC in the shallow flow layer side -gradient and downgradient of
the Unit 5 inactive ash basin, within the active ash basin, and within and downgradient of
the western portion of the ash storage area. In general, total and dissolved
concentrations were consistent within each sample with exceedances collected from
shallow flow layer. Thallium exceedances in the deep flow were reported beneath the
Unit 5 inactive ash basin saddle dam, downgradient of the active ash basin upstream
dam, beneath the western portion of the ash storage area, and side -gradient of the
active ash basin. In general, total and dissolved concentrations were consistent within
each sample with exceedances collected from shallow flow layer. A thallium exceedance
was reported in the bedrock flow layer in monitoring well U5-2BR located beneath the
western portion of the Unit 5 inactive ash basin. Total and dissolved concentrations were
consistent for this sample.
TDS exceeded the 2L Standard in the shallow flow layer in monitoring well GWA-44S
located upgradient of the Units 1-4 inactive ash basin on the west side of Suck Creek,
and in monitoring well AS -1 SB located within the western portion of the ash storage
area. TDS exceedances in the deep flow layer were reported in monitoring well GWA-
42D located east of and cross -gradient of the Units 5 inactive ash basin, and within and
downgradient of the eastern portion of the Unit 5 inactive ash basin including monitoring
well GWA-37D located outside of the Unit 5 inactive ash basin provisional compliance
boundary. TDS exceedances in the bedrock flow layer were reported in monitoring well
U5-4BR located beneath the Unit 5 inactive ash basin main dam, GWA-44BR located
upgradient of the Units 1-4 inactive ash basin on the west side of Suck Creek, GWA-
29BR located downgradient of the Units 1-4 inactive ash basin, and AS-7BR located
beneath the western portion of the ash storage area.
Vanadium exceeded the IMAC in the shallow and deep flow layers in wells across the
CSS site. Less frequent exceedances were detected in the bedrock flow layer.
Vanadium exceedances were reported in some of the background wells in each of the
shallow, deep, and bedrock flow layers. In general, total and dissolved concentrations
were consistent within each sample with exceedances collected from three flow layers.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
The horizontal extent of exceedances is presented in the form of isoconcentration figures
(Figures 3-4.1 through 3-4.48). The vertical extent of boron is presented on applicable cross
sections (Figures 3-5.1 through 3-5.15). In addition, cross sections show hydrostratigraphic
layers, rock Iithology, 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 barium, beryllium, chromium, cobalt, hexavalent chromium,
manganese, mercury, selenium, sulfate, thallium, 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 surface water at the CSS 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.
22

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
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 T1 5A
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 referenced 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.'o
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.
10 U.S. Environmental Protection Agency (USEPA) Unified Guidance (USEPA 2009), 5.2.1 Selecting Monitoring
Constituents and Adequate Sample Sizes
11 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.
23

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
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 CSS site. 12
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.
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, 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
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
'Z 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.
24

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FYZ
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 CSS site has the following number of usable observations at background wells for
implementation of the background concentration methodology described in Section 4.1:
• MW -24D (Compliance Monitoring Well) — 16 observations
• MW-24DR (Compliance Monitoring Well) — 17 observations
• CCPMW-1 S (CCP Landfill Monitoring Well) — 3 observations
• CCPMW-1 D (CCP Landfill Monitoring Well) — 3 observations
• BG -1 S (CSA Monitoring Well) — 6 observations
• BG -1 D (CSA Monitoring Well) — 6 observations
• BG -1 BR (CSA Monitoring Well) — 6 observations
• BG -2D (CSA Monitoring Well) — 1 observation
• MW -30S (CSA Monitoring Well) —
4 observations
• MW -30D (CSA Monitoring Well) —
5 observations
• MW -32S (CSA Monitoring Well) —
6 observations
• MW -32D (CSA Monitoring Well) —
5 observations
• MW-32BR (CSA Monitoring Well)
— 5 observations
It is expected that with interim monitoring implementation, the CSS 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
Cliffside Steam Station Ash Basin FN
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 Location Purpose
Monitoring Wells I
GWA-2BR Downgradient of Unit
Evaluate downgradient extent of
5 inactive ash basin
exceedances in deep and bedrock
wells U5-4BR (TDS, sulfate, Cr[IV],
Cr, Sb) and U5 -51D (TDS, sulfate,
Mn) located on the Unit 5 inactive
ash basin dam.
_
U5-5BR On Unit 5 inactive
_
Evaluate vertical extent of
ash basin dam
exceedances reported in U5 -51D
(TDS, sulfate, Mn).
MW-38BR North of Unit 5
_
I Evaluate vertical extent of
INACTIVE ash Basin,
exceedances reported in MW -38D
adjacent to BroadI
(TDS, sulfate, Mn).
River
GWA-48S East of Unit 5
inactive ash basin
GWA-14BR
AS-2BR
AS-7BRL
GWA-20BR
West of Units 1-4
inactive ash basin
Evaluate horizontal extent of
exceedances reported in GWA-5S
(TDS, sulfate, Co, Mn). _
Evaluate vertical extent of
exceedances reported in GWA-
14D (TDS, sulfate).
Northwest of ash Evaluate vertical extent of
storage area located exceedances reported in AS -21D
adjacent to active (TDS, sulfate).
ash basin
On western ash Evaluate vertical extent of
storage area located exceedances reported in AS-7BR
adjacent to active(TDS, sulfate, Cr).
I
ash basin
West of active ash
basin and secondary
dam
GWA-27BRI Southwest of active
ash basin
Evaluate extent of exceedances
reported in AB -21D (Fe, Mn) and
GWA-20D (Co, Mn).
Evaluate vertical extent of
exceedances reported in GWA
27D (Boron).
Approximate
Monitoring Well
Depth(s) (ft.)
90
120
125
30
105
130
190
110
The information obtained from the borings will be reviewed against the existing conceptual site
model to evaluate if modifications or refinement are required.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 5 — ANTICIPATED ADDITIONAL ASSESSMENT ACTIVITIES
5.2 Implementation of the Effectiveness Monitoring Plan
The effectiveness monitoring plan as part of the 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 Units 1-4 inactive ash basin, the Unit 5 inactive
ash basin, the active ash basin, and ash storage area at CSS. 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.
27

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 6 — CONCLUSIONS AND RECOMMENDATIONS
Section 6 — Conclusions and Recommendations
The following findings and conclusions have been developed from the information presented in
this CSA Supplement 2 report:
• 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 -sourced
constituents (e.g., boron).
• NCDEQ requested installation of additional monitoring wells 1_15-2BR, U5 -2S -SL -A, U5-
8BR, GWA-31 BR -A, and MW -23S, which was completed.
• Monitoring well GWA-34S was installed to determine the horizontal extent of
exceedances reported at MW -34S and to better define groundwater flow direction.
Exceedances of the 2L Standard or IMAC of cobalt and manganese were observed at
this location during the Round 5 sampling. The groundwater elevation measured in
GWA-34S supports the previously interpreted groundwater flow direction toward the
Broad River.
• Additional assessment wells were installed to refine understanding of the horizontal
extent of exceedances.
o Monitoring wells GWA-35S and GWA-35D were installed along the U5-1, 1_15-2,
U5-3 transect. Exceedances of the 2L Standard or IMAC for cobalt, iron,
manganese, and vanadium were detected during the Round 5 sampling.
o Monitoring wells GWA-36S, GWA-36D, GWA-37S, and GWA-37D were installed
to refine understanding of exceedances reported at GWA-4S/D. Exceedances of
the 2L Standard, IMAC, or DHHS HSL for cobalt, manganese, sulfate, and
vanadium in GWA-36D, and hexavalent chromium, sulfate, and TDS in GWA-
37D were detected in one or more of these wells during the Round 5 sampling.
o Monitoring wells GWA-38S and GWA-38D were installed to refine understanding
of exceedances reported at GWA-14S/D. Exceedances of the 2L Standard,
IMAC, or DHHS HSL for hexavalent chromium, cobalt, iron, manganese,
vanadium, antimony, arsenic, and chromium were reported in one or more of
these wells during the Round 5 sampling.
• Additional assessment wells GWA-39S, GWA-40S, GWA-41 S, GWA-42S, GWA-44S,
GWA-44D, GWA-44BR, GWA-48BR, GWA-24BR, AB -SBR, and AB-3BR were installed
to better refine groundwater flow direction. Groundwater elevations indicate that
groundwater in the central portion of the site flows toward Suck Creek.
• Monitoring wells GWA-43S and GWA-43D were installed to refine understanding of the
horizontal extent of exceedances reported at MW-23D/BR and GWA-33S/D/BR and to
better define groundwater flow direction. Exceedances of the 2L Standard, IMAC, or
DHHS HSL of cobalt, vanadium, hexavalent chromium, and manganese in GWA-43S
and iron in GWA-43D were observed at this location during the Round 5 sampling. The
groundwater elevations measured in these wells indicates groundwater flows toward the
Broad River.

Duke Energy Carolinas, LLC I CSA Supplement 2
Cliffside Steam Station Ash Basin FN
SECTION 6 — CONCLUSIONS AND RECOMMENDATIONS
• Monitoring wells GWA-45S and GWA-45D were installed to determine the horizontal
extent of exceedances reported at MW -42S and MW -42D and to better define
groundwater flow direction. Exceedances of the 2L Standard, IMAC, or DHHS HSL of
hexavalent chromium, selenium, cobalt, manganese, and mercury in GWA-45S and
antimony, arsenic, and vanadium in GWA-45D were observed at this location during the
Round 5 sampling. The groundwater elevations measured for wells GWA-45S/D support
the previously interpreted groundwater flow direction toward the Broad River.
Based on the conclusions presented above, the following recommendations are offered:
• Refinement of PPBCs should be conducted once the minimum number of viable
observations per background well are available.
• Evaluation of PPBCs along with pH and turbidity results for further understanding of
naturally occurring exceedances.
• Additional monitoring wells should be installed to refine the vertical and horizontal
delineation of groundwater exceedances in north, east, and downgradient of Unit 5
inactive ash basin and dam, west of Units 1-4 inactive ash basin, northwest and west of
the ash storage area, and west and southwest of the active ash basin.
• 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.

Figures

Tables

Appendix A
Monitoring Well Logs
Core Photos
F -j

Appendix 6
Field Sampling Forms
Slug Test Reports
F -j

Appendix C
Laboratory Report and
Chain -of -Custody Forms
F -j