NC0004979_1_FINAL_CSA Supplement 2_Allen_Report_20160802

Comprehensive Site Assessment
Supplement 2
Allen Steam Station Ash Basin
Site Name and Location
Allen Steam Station
253 Plant Allen Road
Belmont, NC 28012
Groundwater Incident No.
Not Assigned
NPDES Permit No.
NC0004979
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
350 11' 25" N, 81 ° 00' 32" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
�•o��Y► ARO(,',•�
/�E AL
%.._RAItCIS...• .
Malcolm F. Schaeffer, L.G.
Senior Geologist

Table of Contents
Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 Compliance Monitoring............................................................................
5
1.3.2 CSA Sampling......................................................................................................
6
1.3.3 Post-CSA Sampling..............................................................................................
6
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 Surface Water......................................................................................................12
3.1.3 Well Gauging and Sampling.................................................................................12
3.2 Additional Assessment Results...................................................................................12
3.2.1 Groundwater Flow Direction.................................................................................12
3.2.2 Sampling Results.................................................................................................13
Section 4 — Background Concentrations...................................................................................18
4.1 Methodology...............................................................................................................18
4.2 Observation for Background Wells..............................................................................20
Section 5 — Anticipated Additional Assessment Activities..........................................................21
5.1 Proposed Monitoring Wells — Refine Site Conceptual Model.......................................21
5.2 Implementation of the Effectiveness Monitoring Plan..................................................22
Section 6 — Conclusions and Recommendations......................................................................23

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 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 Cadmium Isoconcentration Contour Map - Shallow Wells (S)
3-4.17 Cadmium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.18 Cadmium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.19 Hexavalent Chromium Isoconcentration Contour Map - Shallow Wells (S)
3-4.10 Hexavalent Chromium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.21 Hexavalent Chromium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.22 Chromium (Total) Isoconcentration Contour Map - Shallow Wells (S)
3-4.23 Chromium (Total) Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.24 Chromium (Total) Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.25 Cobalt Isoconcentration Contour Map - Shallow Wells (S)
3-4.26 Cobalt Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.27 Cobalt Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.28 Iron Isoconcentration Contour Map - Shallow Wells (S)
3-4.29 Iron Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.30 Iron Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.31 Manganese Isoconcentration Contour Map - Shallow Wells (S)
3-4.32 Manganese Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.33 Manganese Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.34 Nickel Isoconcentration Contour Map - Shallow Wells (S)
3-4.35 Nickel Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.36 Nickel Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.37 Selenium Isoconcentration Contour Map - Shallow Wells (S)
3-4.38 Selenium Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.39 Selenium Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.40 Sulfate Isoconcentration Contour Map - Shallow Wells (S)
3-4.41 Sulfate Isoconcentration Contour Map - Deep Wells (D and BRU)
3-4.42 Sulfate Isoconcentration Contour Map - Bedrock Wells (BR)
3-4.43 Total Dissolved Solids Isoconcentration Contour Map - Shallow Wells (S)
3-4.44 Total Dissolved Solids Isoconcentration Contour Map - Deep Wells (D and BRU)

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
TABLE OF CONTENTS
3-4.45 Total Dissolved Solids Isoconcentration Contour Map — Bedrock Wells (BR)
3-4.46 Thallium Isoconcentration Contour Map — Shallow Wells (S)
3-4.47 Thallium Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.48 Thallium Isoconcentration Contour Map — Bedrock Wells (BR)
3-4.49 Vanadium Isoconcentration Contour Map — Shallow Wells (S)
3-4.50 Vanadium Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.51 Vanadium Isoconcentration Contour Map — Bedrock Wells (BR)
3-4.52 Zinc Isoconcentration Contour Map — Shallow Wells (S)
3-4.53 Zinc Isoconcentration Contour Map — Deep Wells (D and BRU)
3-4.54 Zinc Isoconcentration Contour Map — Bedrock Wells (BR)
3-5.1 Site Cross Section Locations
3-5.2 Cross Section A -A' (1 of 3)
3-5.3 Cross Section A -A' (2 of 3)
3-5.4 Cross Section A -A' (3 of 3)
3-5.5 Cross Section B-B' (1 of 3)
3-5.6 Cross Section B-B' (2 of 3)
3-5.7 Cross Section B-B' (3 of 3)
3-5.8 Cross Section C-C' (1 of 2)
3-5.9 Cross Section C-C' (2 of 2)
3-5.10 Cross Section D-D' (1 of 2)
3-5.11 Cross Section D-D' (2 of 2)
3-5.12 Cross Section E-E' (1 of 2)
3-5.13 Cross Section E-E' (2 of 2)
3-5.14 Cross Section F-F' (1 of 2)
3-5.15 Cross Section F-F' (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 Comment
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 Ash Basin Surface Water Locations
3-5 Round 5 Analytical Results of Areas of Wetness
3-6 Summary of Groundwater Elevations
3-7 Summary of Cation -Anion Balance Differences

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
TABLE OF CONTENTS
APPENDICES
A Monitoring Well Logs and Core Photos
B Field Sampling Forms and Slug Test Reports
C Laboratory Report and Chain -of -Custody Forms
iv

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
EXECUTIVE SUMMARY
Executive Summary
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the coal-fired Allen Steam
Station (Allen), located in Belmont, Gaston County, North Carolina (Figure 1-1). Allen began
operations in 1957 with Units 1 and 2. Unit 3 began operations in 1959, followed by Unit 4 in
1960 and Unit 5 in 1961. The coal combustion residuals (CCR) and other liquid discharges from
Allen's coal combustion process have been disposed in the station's ash basins (including the
active and inactive ash basins, Retired Ash Basin [RAB] Ash Landfill area, ash storage areas,
and structural fill areas). 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 NC0004979.
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 March 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, sulfate, and arsenic, the primary site -derived constituent in groundwater, were detected
at concentrations greater than the 15A NCAC (North Carolina Administrative Code) 02L.0202
Groundwater Quality Standards (2L Standards or 2L) beneath and downgradient (east and
north-northeast) of the ash basin system. These constituents have 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. The
stream valley in which the ash basin was constructed is a distinct slope -aquifer system in which
flow of groundwater into the ash basin and out of the ash basin is restricted to the local flow
regime.
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:
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 report, as appropriate.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 (i.e., arsenic, boron, sulfate).
Y Groundwater flow direction in the shallow, deep and bedrock regimes are consistent with
groundwater flow directions depicted in the CSA and CAP reports.
Y The horizontal extent of ash -related groundwater impacts have been defined at the Allen
site. However, the vertical extent of ash -related groundwater impacts is not fully
delineated beneath the ash basin, downgradient of the ash basin and upgradient and
southwest of the active ash basin.
Y Calculation of PPBCs using additional analytical results should be conducted to inform
decisions regarding the future sampling network.
Y Additional bedrock monitoring wells will be installed to refine the vertical extent of
potential ash -related groundwater impacts at the site.
Y Groundwater monitoring as proposed in the CAP Part 2 should continue.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
Section 1 — Background
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the coal-fired Allen Steam
Station (Allen), located in Belmont, Gaston County, North Carolina (Figure 1-1). Allen began
operations in 1957 with Units 1 and 2. Unit 3 began operations in 1959, followed by Unit 4 in
1960 and Unit 5 in 1961. The coal combustion residuals (CCR) and other liquid discharges from
Allen's coal combustion process have been disposed in the station's ash basins (including the
active and inactive ash basins, Retired Ash Basin [RAB] Ash Landfill area, ash storage areas,
and structural fill areas). 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 NC0004979.
The Comprehensive Site Assessment (CSA) report for the Allen Steam Station was submitted
to NCDEQ on August 23, 2015. Given the compressed timeframe for submittal requirements,
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 19, 2016, 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 monitoring
well installation and sampling conducted at the site between January 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 identified additional assessment. It includes the following
information:
Y A brief summary and update of groundwater monitoring data from the NPDES, CSA, and
post-CSA 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 Allen 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 resulting from the ash basins and
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 report, as appropriate.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
related ash storage facilities based on existing (CSA) and additional (post-CSA) assessment
results. Additional assessment groundwater monitoring wells are shown on Figure 1-2.
1.2 Site Description
The Allen site is located on the west bank of the Catawba River on Lake Wylie in Belmont,
Gaston County, North Carolina. The entire Allen site is approximately 1,009 acres in area and is
owned by Duke Energy. Duke Energy also owns property along the Station Discharge Canal to
the east and west of South Point Road (NC 273). In addition to the power plant property, Duke
Energy owns and operates the Catawba-Wateree Project (Federal Energy Regulatory
Commission [FERCj Project No. 2232). Lake Wylie reservoir is part of the Catawba-Wateree
Project and is used for hydroelectric generation, municipal water supply, and recreation. The
Allen site is bounded by the west bank of the Catawba River to the east, Reese Wilson Road
and Nutall Oak Lane to the south, South Point Road to the west, and a local topographic divide
to the north of the Station Discharge Canal. The Station Discharge Canal is located northwest of
the ash basin and Plant Allen Road. South Point Road runs north to south and is generally
located along a local topographic divide. Reese Wilson Road and Nutall Oak Lane run from
west to east and are generally located along a local topographic divide.
Topography at the Allen site ranges from an approximate high elevation of 650 feet to 680 feet
near the west and southwest boundaries of the site to an approximate low elevation of 570 feet
at the shoreline of the Catawba River.
As described in the CSA, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at the Allen 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 Catawba River and to the north toward the Station
Discharge Canal.
The source area in the CSA was defined as the ash basin, which consists of the active ash
basin and the inactive ash basin, which includes the Retired Ash Basin [RABj Ash Landfill, ash
storage areas, and structural fills. Source characterization was performed during the CSA to
identify physical and chemical properties of ash, ash basin surface water, ash basin porewater,
and ash basin areas of wetness (AOW).
The compliance boundary for groundwater quality at the Allen 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 (21- 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

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
NCAC 2L.0202(c). For this reason, the IMACs noted in this document are for reference
purposes only.
Source -related groundwater exceedances at the site are limited to beneath or adjacent to the
sources and indicate that physical and geochemical processes beneath the Allen site inhibit
lateral migration of the COIs. The groundwater system at Allen is characterized as an
unconfined, connected aquifer system and is divided into three layers referred to as the shallow,
deep (transition zone), and bedrock flow layers. In general, groundwater flows from the western
and southwestern property boundary to the east and northeast where it discharges to the
Catawba River. Vertical migration of COls was observed in select well clusters and is likely
influenced by infiltration from precipitation events and/or ash basin water, through the shallow
and deep flow layers into underlying fractured bedrock.
1.3 History of Site Groundwater Monitoring
Groundwater monitoring was initiated in 2004 when Duke Energy installed voluntary monitoring
wells to monitor groundwater near the ash basin and ash storage areas. The voluntary
groundwater monitoring wells were sampled twice each year and analytical results were
submitted to NCDENR DWR through 2010. Compliance groundwater monitoring, as required by
the ash basin NPDES permit, began in March 2011.
As required by CAMA, additional monitoring wells were installed and sampled in 2015 and
2016. Construction details for existing voluntary, compliance, and CAMA monitoring wells are
provided in Table 1-1. The location of existing voluntary, compliance, and CAMA monitoring
wells; the approximate ash basin waste boundary; and the compliance boundary are shown on
Figure 1-2.
1.3.1 NPDES Compliance Monitoring
Compliance groundwater monitoring has been performed in accordance with the conditions of
NPDES Permit NC0004979 since March 2011. The compliance boundary for groundwater
quality at the Allen 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. The compliance groundwater monitoring system for the Allen ash
basin consists of the following monitoring wells: AB-1 R, AB-4S, AB-4D, AB-9S, AB-9D, AB-1 OS,
A13-1 OD, AB-11 D, AB-12S, AB-12D, A13-13S, A13-13D, and AB-14D. All the compliance
monitoring wells were installed in 2010. From March 2011 through July 2016, compliance
groundwater monitoring wells at the Allen site have been sampled three times each year (in
March, July, and November), resulting in 17 total monitoring events. Review of NPDES
compliance well sampling results indicates the following:
Y Exceedances have occurred at least once for antimony, boron, iron, manganese, nickel,
and pH in one or more compliance wells across the site.
Y The only compliance well with exceedances of boron has been AB-9S, which is
screened in the shallow flow layer and is located immediately downgradient and east of
the ash basin.
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.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 — BACKGROUND
1.3.2 CSA Sampling
The CSA for the Allen site began in February 2015 and was completed in August 2015. Eighty
groundwater monitoring wells and nine additional soil borings were installed/advanced as part of
the assessment to characterize ash, soil, rock, and groundwater at the Allen site. One
comprehensive round of groundwater sampling and analysis was included in the CSA report.
Sampling and analysis of soil, AOWs, sediment, ash basin surface water, and ash basin
porewater were also included in the CSA report. In addition, hydrogeological evaluation testing
was performed when installing the CSA wells. Monitoring well and sample locations are
depicted on Figure 1-2.
Constituents in groundwater were compared to the North Carolina Groundwater Quality
Standards, as specified in 15A NCAC 2L.0202 (2L Standards) 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 (NCDHHS) Health Screening Level (HSL)
(hexavalent chromium only) for the purpose of identifying constituents of interest (COls). The
IMACs were issued in 2010, 2011 and 2012; however, NCDEQ has not established a 2L
Standard for these constituents as described in 15A NCAC 2L.0202(c). For this reason, the
IMACs noted in this document are for reference purposes only. The following constituents were
reported as COls in the CSA Report:
Y Soil: arsenic, barium, and cobalt
Y Groundwater and ash basin porewater: antimony, arsenic, barium, beryllium, boron,
cadmium, chromium, cobalt, iron, manganese, nickel, selenium, sulfate, thallium, total
dissolved solids (TDS), vanadium, and zinc
Y Ash basin surface water: aluminum, copper, and lead
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:
Y Horizontal and vertical extent north and east of the inactive ash basin.
Y Horizontal extent west of the active ash basin beyond the waste boundary.
1.3.3 Post-CSA Sampling
Four additional rounds of groundwater monitoring 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, which consisted of background monitoring
only, 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, which consisted of site -wide sampling, was conducted in March 2016
and is the primary focus of the data evaluation presented in Section 3 of this CSA Supplement
2.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 - BACKGROUND
An additional site -wide sampling event was performed in May/June 2016. Results from the
May/June 2016 sampling event are not included in 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 wells may be adversely impacted by releases from CCR
impoundments. NCDEQ required sampling of all drinking water receptors within 0.5 mile of the
Allen compliance boundary in all directions, since the direction of groundwater flow had not
been determined at Allen 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 Survey3, 4 if the owner agreed to have their
well sampled, as follows:
Y A total of 124 samples were collected within a 0.5-mile radius of the Allen ash basin
compliance boundary; and
Y A total of 23 samples were collected in the vicinity of the Allen site, and by Duke Energy
from background water supply wells located within a 2- to 10-mile radius of the Allen site
boundary.
The locations of the water supply wells identified within 0.5 mile of the Allen compliance
boundary, including NCDEQ-directed sampling locations with updated analytical results
provided to Duke Energy, are shown on Figure 1-3.
The concentration of boron and other potential coal ash indicators were low and/or not above
screening levels in the water supply wells sampled by NCDEQ. Boron was detected in 27 of 124
samples in the NCDEQ-sampled water supply wells, and in 4 of 23 samples in the background
water supply wells. Of the 124 wells sampled, there were exceedances of the 2L Standard for
the following constituents:
Y Antimony — 1 exceedance
Y Cobalt — 2 exceedances
Y Copper — 4 exceedances
Y Iron — 15 exceedances
Y Lead — 1 exceedance
Y Manganese — 1 exceedance
Y Thallium — 1 exceedance
Y Zinc — 2 exceedances
"Do Not Drink" letters were initially issued by DHHS for 141 water supply wells at Allen, 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
3 HDR. 2014a. Allen Combined Cycle Station Ash Basin Drinking Water Supply Well and Receptor Survey. NPDES
Permit NC0004979 September 30, 2014.
4 HDR. 2014b. Allen Combined Cycle Station Ash Basin. Supplement to Drinking Water Supply Well and Receptor
Survey. NPDES Permit NC0004979. November 6, 2014.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 1 - BACKGROUND
constituents. Letters were issued for other constituents as follows: iron (13 wells), cobalt (1
well), lead (2 wells), sodium (1 well), strontium (1 well), sulfate (1 well), and thallium (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 Allen 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
horizontal with flow to the east toward the Lake Wylie, and the north portion of the inactive ash
basin flowing to the northeast and north toward Duke Energy property and the Station
Discharge Canal. Thus, groundwater flow from areas associated with the ash basins and the
ash storage area is away from the water supply wells.
A review of groundwater elevations measured in monitoring wells at Allen found evidence of
mounding in the active ash basin. The net effect of the localized gradients resulting from
mounding is reflected in the current data set. The mounding appears to be caused by the
variable discharge of water to the northern and western portions of the active ash basin.
Mounding in this area of the active ash basin is more apparent in the September 2015
groundwater elevation data compared to May 2016 data. A review of historical groundwater
analytical results for boron and sulfate from NPDES compliance wells adjacent to the area
where mounding is occurring (AB-4S/D, AB-11 D, AB-12S/D and AB-13S/D) does not indicate
evidence of impacts from coal ash indicator constituents, which suggests that overall
groundwater flow is away from the water supply wells. Although this data suggests that
groundwater between the area of mounding and the off -site water supply wells is not impacted
by coal ash, Duke Energy is installing additional assessment monitoring wells west of the ash
basin in the vicinity of the off -site water supply wells to further evaluate groundwater quality and
to better define the dominant groundwater flow direction west of the ash basin. Furthermore,
Duke Energy is planning to perform additional studies to further evaluate the effects of
mounding in 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
concentrations, including boron and sulfate. The conclusion from the evaluation is that there is
no connection between the CCR-impacted groundwater and the water quality exceedances
found in the local water supply wells.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 Allen.
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 (transition zone and bedrock), as provided in Table 2-2.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 Allen site required additional assessment to refine the extent of
groundwater impacts attributable to the ash basin:
Y Horizontal and vertical extent north and east of the inactive ash basin. Horizontal extent
west of the active ash basin beyond the waste boundary.
Additional surface water samples to be collected from the Catawba River to augment previously
collected samples were proposed, and are described below in Section 3.1.2.
Based on NCDEQ comments on the CSA report and subsequent discussions with NCDEQ,
installation of 26 additional monitoring wells was initiated in December 2015 and completed in
March 2016 (with the exception of GWA-21 BR, which was installed in June 2016). The
additional monitoring wells serve to refine the horizontal and vertical extent of potential
groundwater impacts, the understanding of groundwater flow directions, and/or geochemical
and groundwater modeling predictions. The additional assessment wells installed (post-CSA)
include the following:
Boring /Well
Installation
Purpose for Installation
Results
Identification
Date
12/22/2015
1/9/2016
1/8/2016
I Wells installed north of the Station
Discharge Canal to improve the
understanding of background
Sample results included in
analytical results table and
isoconcentration maps. Water
BG-4S
BG-4D
BG-4BR
groundwater quality at the Allen
levels measured and used for
site.
contouring of shallow, deep,
I
bedrock flow lavers.
AB-4BR
12/22/2015 Well installed west of the ash basin Sample results included in
to further evaluate groundwater analytical results table and
quality and groundwater flow west isoconcentration maps. Water
of the ash basin. level measured and used for
_j contouring of bedrock flow layer.
2/10/2016 I Well installed west of the ash basin Sample results included in
AB-14BR
to further evaluate groundwater analytical results table and
quality and groundwater flow west isoconcentration maps. Water
of the ash basin. i level measured and used for
contouring of bedrock flow laver.
mi

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin FN
SECTION 3 — ADDITIONAL ASSESSMENT
Boring /Well Installation I Purpose for Installation
Identification I Date
GWA-6DA
GWA-17S
GWA-17D
GWA-18S
GWA-18D
GWA-19S
GWA-19D
GWA-21 S
GWA-21 D
GWA-21 BR
GWA-22S
GWA-22D
GWA-23S
GWA-23D
GWA-24S
GWA-24D
GWA-24BR
GWA-26S
GWA-26D
1/12/2016 Due to grout contamination in
GWA-6D, a replacement well was
installed to better understand the
vertical extent of COls in
aroundwater at this location.
1 /5/2016
1 /6/2016
1 /9/2016
1 /8/2016
3/24/2016
3/23/2016
2/9/2016
2/16/2016
6/6/2016
1 /20/2016
1/19/2016
1/19/2016
1/21/2016
3/1/2016
2/29/2016
3/14/2016
1 /27/2016
1 /27/2016
Wells installed to assess offsite
groundwater quality and refine
groundwater flow direction.
Wells installed to assess
groundwater quality and flow
northwest of the ash basin in the
vicinity of AB-1 R.
Wells installed offsite and west of
the ash basin to assess
groundwater quality and flow west
of the ash basin.
Wells installed offsite and west of
the ash basin to assess
groundwater quality and flow west
of the ash basin. Note that GWA-
21 BR was installed to evaluate
bedrock west of the site.
Wells installed offsite and west of
the ash basin to assess
groundwater quality and flow west
of the ash basin.
Results
Sample results included in
analytical results table and
isoconcentration maps.
Sample results included in
analytical results table and
isoconcentration maps. Water
levels measured and used for
contouring of shallow and deep
flow layers.
Sample results included in
analytical results table and
isoconcentration maps. Water
levels measured and used for
contouring of shallow and deep
flow lavers.
Sample results included in
analytical results table and
isoconcentration maps. Water
levels measured and used for
contouring of shallow and deep
flow layers.
Sample results included in
analytical results table and
isoconcentration maps. Water
levels measured and used for
contouring of shallow, deep, and
bedrock flow layers.
Sample results included in
analytical results table and
isoconcentration maps. Water
level measured in GWA-22S and
-22D and used for contouring of
shallow and deep flow layers.
Wells installed offsite and west of I Sample results included in
the ash basin to assess analytical results table and
groundwater quality and flow west isoconcentration maps. Water
of the ash basin. levels measured and used for
contouring of shallow and deep
flow layers.
Wells installed offsite and west of
the ash basin to assess
groundwater quality and flow west
of the ash basin. Note that GWA-
24BR was installed to evaluate
bedrock west of the site.
Sample results included in
analytical results table and
isoconcentration maps. Water
levels measured and used for
contouring of shallow, deep, and
bedrock flow layers.
Wells installed to assess I Sample results included in
groundwater quality and flow to the analytical results table and
southwest of the ash basin. isoconcentration maps. Water
levels measured and used for
contouring of shallow and deep
flow layers.
111

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
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.
The following wells that were proposed as additional assessment wells were not installed due to
off -site access agreement and utility interference issues:
Y GWA-20S/D/BR — GWA-21 BR was added to supplement bedrock characterization
data west of the ash basin in place of GWA-2013R.
Y GWA-25S/D — Not installed due to off -site access agreement and utility interference
issues. No alternate location has been proven accessible to date.
3.1.2 Surface Water
Additional surface water samples were proposed to be taken from the Catawba River mid-
stream to augment existing SW-6 and SW-7 samples. This data would be used to refine surface
water interaction modeling described in Section 4 of CAP 2 and evaluate potential 213 Standard
impacts to surface waters. SW-6 and SW-7 were sampled during the Round 5 monitoring event;
however, sampling from mid -stream is still pending due to safety and access issues.
3.1.3 Well Gauging and Sampling
Round 5 of groundwater, porewater, surface water, AOW, site surface water, and ash basin
water sampling activities were completed between March 16 and 22, 2016. Groundwater
analytical parameters and methods for Round 5 were consistent with those employed for
sampling results presented in previous reports. However, the analytical results of radionuclide
sampling were not available for inclusion within this report. A total of 119 groundwater and ash
porewater monitoring wells were sampled during the Round 5 event. Monitoring well 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 are presented in Tables 3-1, 3-2, 3-3, 3-4, and 3-5 for groundwater,
porewater, site surface water, 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 3-6.
3.2.1 Groundwater Flow Direction
On May 23, 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 elevation contours were
developed for the shallow, deep, and bedrock flow layers using these measurements, and are
depicted on Figures 3-4, 3-5, and 3-6, respectively. Groundwater elevations were generally
consistent with those measured during Rounds 1 and 2. Therefore, groundwater flow directions
were consistent with those identified in the CSA and CAP Part 2, indicating stable groundwater
flow conditions at the site since the CSA. Groundwater generally flows from the western portion
12

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
of the site to the east, toward the Catawba River, and to the north toward the Station Discharge
Canal north of the inactive ash basin.
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 and evaluated in the CAP Reports: antimony,
arsenic, barium, boron, cobalt, iron, manganese, selenium, sulfate, thallium, TDS, and
vanadium in addition to isolated exceedances of beryllium, cadmium, chromium, nickel and zinc.
Areas of 2L Standard or IMAC exceedances were limited to groundwater beneath or
immediately downgradient of the ash basin. Boron exceedances were present in shallow
groundwater immediately downgradient and east of the active ash basin and the inactive ash
basin, with higher concentrations east of the inactive ash basin. Boron exceedances in deep
groundwater were present beneath the east portion of the active ash basin and immediately
downgradient of the active ash basin. Boron exceedances in bedrock were limited to the area
downgradient and east of the inactive ash basin. Sulfate exceedances at the site were limited to
shallow groundwater beneath the northern extent of the inactive ash basin and immediately
north and downgradient of the inactive ash basin. The sulfate exceedances in this area of the
site may be influenced by another industrial activity at the site. Boron and sulfate are among
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 as they are expected to be highly mobile in the groundwater environment, and therefore
can be used to represent the general extent of groundwater impacted by the ash basin at the
site.
Concentrations of other COls were similar in the Round 1 and 2 sampling events.
3.2.2.2 ROUND 5 POREWATER SAMPLING RESULTS
Porewater samples were collected from 10 monitoring wells screened within the active ash
basin (AB-20S, AB-21 S/SL, AB-23S, AB-24S/SL, AB-25S/SL, AB-27S, and AB-28S) and 7
monitoring wells screened within the inactive ash basin (AB-29S, AB-29SL, AB-30S, AB-35S,
AB-37S, AB-38S, and AB-39S). Concentrations of antimony, arsenic, boron, cobalt, hexavalent
chromium, iron, manganese, selenium, sulfate, TDS, thallium, and/or vanadium exceeded their
applicable 2L Standard, IMAC, or DHHS HSL in one or more porewater sample collected during
the Round 5 sampling event. The range and number of exceedances of each COI in porewater
is listed below.
Y Antimony: 5.9 pg/L to 7.3 lag/L (3 exceedances of 17 samples)
Y Arsenic: 37.9 pg/L to 1,380 pg/L (15 of 17)
Y Boron: 823 pg/L to 6,740 pg/L (10 of 17)
Y Cobalt: 1.4 pg/L to 28.9 pg/L (9 of 17)
Y Hexavalent chromium: 0.076 pg/L to 0.38 pg/L (2 of 17)
Y Iron: 305 pg/L to 56,600 pg/L (10 of 17)
13

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Y Manganese: 53.5 pg/L to 13,100 pg/L (13 of 17)
Y Selenium: 194 pg/L (1 of 17)
Y Sulfate: 420,000 pg/L (1 of 17)
Y TDS: 305,000 pg/L to 594,000 pg/L (4 of 17)
Y Thallium: 0.22J pg/L to 1 AJ pg/L (2 of 17)
Y Vanadium: 0.95 J+ pg/L to 56.4 pg/L (14 of 17)
The list of COls and concentrations of COls have remained stable in porewater through
sampling Rounds 1, 2, and 5.
3.2.2.3 ROUND 5 GROUNDWATER SAMPLING RESULTS
In general, Round 5 groundwater sampling results were similar to Round 1 and 2 results in each
groundwater flow layer upgradient, beneath the ash basin, and downgradient of the ash basin.
Concentrations of antimony, arsenic, barium, beryllium, boron, cadmium, chromium, cobalt,
hexavalent chromium, iron, manganese, nickel, selenium, sulfate, TDS, thallium, vanadium,
and/or zinc exceeded their applicable 2L Standard, IMAC, or DHHS HSL in one or more
groundwater sample collected during the Round 5 sampling event. A summary of Round 5
groundwater sampling results for each COI identified during the CSA is provided below.
Y Antimony concentrations that exceeded the IMAC were mainly limited to the deep and
bedrock flow layers. In the deep flow layer, exceedances were reported beneath the
south-central (AB-21 D) and west (AB-23BRU and AB-24D) portions of the active ash
basin, beneath the structural fill and inactive ash basin (AB-35D), immediately
downgradient of the eastern portion of the active ash basin (AB-26D), immediately
downgradient and east of the inactive ash basin (AB-31 D), beneath the south-central
portion of the active ash basin (AB-21 D), and beneath the structural fill and inactive ash
basin (AB-35D). In the bedrock flow layer, exceedances were reported downgradient of
the east portion of the active ash basin (GWA-3BR), downgradient of the northeast
portion of the inactive ash basin(GWA-5BR), and in background well BG-2BR. No
antimony exceedances beneath or downgradient of the ash basin exceeded the
concentration reported in BG-2BR.
Y Arsenic concentrations that exceeded the 2L Standard were limited to the shallow flow
layer beneath the westernmost extent of the inactive ash basin (AB-36S) and
immediately downgradient and north of the inactive ash basin (GWA-6S). No arsenic
exceedances were reported in the deep and bedrock wells.
Y Barium concentrations that exceeded the IMAC were limited to the shallow flow layer
beneath the westernmost extent of the inactive ash basin (AB-36S) and background
bedrock well BG-2BR. No other samples from monitoring wells located beneath or
downgradient of the ash basin exhibited exceedances.
Y Beryllium concentrations that exceeded the IMAC were limited to one shallow monitoring
well (GWA-6S) located immediately north and downgradient of the inactive ash basin.
No other beryllium exceedances were reported in shallow, deep, and bedrock wells.
Y Boron concentrations that exceeded the 2L Standard are present in the shallow, deep,
and bedrock flow layers. In the shallow flow layer, boron exceedances were reported
beneath the east portions of the inactive ash basin and to the east toward the Catawba
14

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
River, as well as beneath the east portion of the active ash basin dam. In the deep flow
layer, exceedances were reported beneath the northeast portion of the active ash basin
(AB-27D) and immediately downgradient of the southeast portion of the active ash basin
(AB-22D). In the bedrock flow layer, one boron exceedance was reported downgradient
and east of the inactive ash basin (GWA-5BR). No other boron exceedances were
reported in shallow, deep, and bedrock wells.
Y Cadmium concentrations that exceeded the 2L Standard were limited to the shallow flow
layer immediately north of the inactive ash basin (AB-33S and GWA-6S). No other
cadmium exceedances were reported in shallow, deep, and bedrock wells.
Y Chromium (total) concentrations that exceeded the 2L Standard were present in the
shallow, deep and bedrock flow layers including background samples. In the shallow
flow layer, exceedances were limited to downgradient and east of the active ash basin
(AB-6R). In the deep flow layer, exceedances were limited to beneath the central portion
of the active basin (AB-21 D and AB-23BRU), immediately downgradient and east of the
active ash basin (GWA-3D), and upgradient and west of the inactive ash basin (GWA-
14D and GWA-15D). In the bedrock flow layer, exceedances were limited to beneath the
central portion of the active ash basin (AB-21 BR and AB-25BR) and the background
monitoring well BG-213R.
Y Cobalt concentrations that exceeded the IMAC in the shallow and deep flow layers were
generally across the site, including in background samples. In the shallow layer,
exceedances were concentrated downgradient and east of the ash basin and west and
upgradient of the ash basin. In the deep flow layer, cobalt concentrations that exceeded
the IMAC were beenath portions of the inactive ash basin and west of the active ash
basin. Cobalt was reported above the IMAC in one bedrock well (AB-413R) located
immediately northwest of the active ash basin.
Y Hexavalent chromium that exceeded the DHHS HSL varied in the shallow, deep and
bedrock flow layers, and were generally across the site, including background wells.
Note that only two exceedances were reported out of the 17 porewater samples
collected from ash basin porewater wells.
Y Iron concentrations that exceeded the 2L Standard varied in the shallow and deep wells
and were generally across the site, including background wells.
Y Manganese concentrations that exceeded the 2L Standard varied in the shallow, deep,
and bedrock flow wells and were generally across the site, including background wells.
Y Nickel concentrations that exceeded the 2L Standard were limited to one shallow
monitoring well (GWA-6S) located immediately north and downgradient of the inactive
ash basin. No other nickel exceedances were reported in shallow, deep, and bedrock
wells.
Y Selenium concentrations that exceeded the 2L Standard were limited to one shallow
monitoring well (GWA-6S) located immediately north and downgradient of the inactive
ash basin. No other selenium exceedances were reported in shallow, deep, and bedrock
wells.
Y Sulfate concentrations that exceeded the 2L Standard were limited to the shallow flow
layer immediately north of the inactive ash basin (AB-33S and GWA-6S). No other
sulfate exceedances were reported in deep and bedrock wells.
15

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Y TDS concentrations that exceeded the 2L Standard were limited to the shallow flow layer
immediately north of the inactive ash basin (AB-33S and GWA-6S), the deep flow layer
west and upgradient of the inactive ash basin (GWA-14D), and in background bedrock
well BG-2BR. The 2L exceedances of TDS at GWA-14D and BG-2BR are not likely
attributable to the ash basin.
Y Thallium concentrations that exceeded the IMAC were limited to the shallow flow layer
immediately north of the inactive ash basin (AB-33S and GWA-6S). No other thallium
exceedances were reported in shallow, deep, and bedrock wells.
Y Vanadium concentrations that exceeded the IMAC varied in the shallow, deep, and
bedrock flow wells and are generally across the site, including background wells.
Vanadium concentrations were generally reported higher in the deep and bedrock wells
than in shallow wells.
Y Zinc concentrations that exceeded the 2L Standard were limited to one shallow
monitoring well (GWA-6S) located immediately north and downgradient of the inactive
ash basin. No other zinc exceedances were reported in shallow, deep, and bedrock
wells.
The list of COls and concentrations have remained stable at the site through sampling Rounds
1,2and 5.
Concentrations of COls and the horizontal extent of exceedances are depicted on
isoconcentration maps, included as Figures 3-4.1 through 3-4.54. The vertical extents of boron
and sulfate are presented on cross sections (Figures 3-5.1 through 3-5.15; the location of the
cross sections are shown on Figure 3-5.1). 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) details in response to NCDEQ comments.
3.2.2.4 COMPARISON OF POREWATER AND GROUNDWATER RESULTS
Considering that porewater wells are located within the waste boundary and screened within
ash, it can be expected that concentrations of COls are higher in porewater than in wells
beyond the waste boundary. Based upon review of data collected during Round 5 sampling,
constituent concentrations in porewater were generally one or more orders of magnitude higher
than shallow groundwater concentrations for the following COIs: arsenic, barium, boron, and
iron.
As noted below, concentrations of some COls were either generally similar (within one order of
magnitude) in shallow groundwater and porewater, isolated occurrences, or lower in porewater
than in shallow groundwater.
Y Concentrations of antimony, cobalt, manganese, and thallium were generally similar in
shallow groundwater and porewater.
Y Concentrations of beryllium, cadmium, chromium (total), nickel, selenium, sulfate, TDS,
and zinc were generally similar in shallow groundwater and porewater except for the
isolated location immediately north and downgradient of the inactive ash basin.
16

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 3 — ADDITIONAL ASSESSMENT
Y Concentrations of hexavalent chromium were generally lower in porewater when
compared to shallow gorundwater.
Piper diagrams presented in the CSA report provided evidence of mixing ash basin porewater
and groundwater. In general, the ionic composition of groundwater and surface water at the
Allen site is predominantly rich in calcium and magnesium. Piper diagrams area presented in
Figures 3-6.1 through 3-6.4. Sample results with cation -anion balance differences > 10% are
were excluded.
3.2.2.5 ROUND 5 SURFACE WATER RESULTS
Surface water sampling results from Round 5 were similar to Round 2 results. Note that surface
water samples were not collected from outside the ash basin during Round 1. SW-5 was
collected along the southwest portion of the property outside of the waste boundary, while SW-6
and SW-7 were collected from the western bank of the Catawba River. Surface water sample
locations are shown on Figure 1-2.
Review of Round 5 surface water sampling results indicates the following:
Y Aluminum exceeded its 2B Standard at sample locations SW-5, SW-6, and SW-7.
Y Boron was reported at a concentration of 10,900 ug/L at location SW-5.
Y Chloride, cobalt, copper, and TDS exceeded their 2B Standards at location SW-5.
Y Copper and lead concentrations at locations SW-5 and SW-7 exceeded their 2B
Standards.
17

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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.5
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).6 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.
5 U.S. Environmental Protection Agency (USEPA) Unified Guidance (USEPA 2009), 5.2.1 Selecting Monitoring
Constituents and Adequate Sample Sizes
6 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.

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 Allen 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
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.
19

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin FN
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 Allen site has the following number of usable observations at background wells
for implementation of the background concentration methodology described in Section 4.1:
Y BG-1 S (CSA Monitoring Well) — 5 observations
Y BG-1 D (CSA Monitoring Well) —
4 observations
Y BG-2S (CSA Monitoring Well) —
3 observations
Y BG-2D (CSA Monitoring Well) —
4 observations
Y BG-2BR (CSA Monitoring Well)
— 4 observations
Y BG-3S (CSA Monitoring Well) —
2 observations
Y BG-3D (CSA Monitoring Well) — 4 observations
Y BG-4S (Additional Assessment Monitoring Well) — 1 observation
Y BG-4D (Additional Assessment Monitoring Well) — 1 observation
Y BG-4BR (Additional Assessment Monitoring Well) — 0 observations
It is expected that with interim monitoring implementation, the Allen 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.
20

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen 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 Monitoring Wells — Refine Site Conceptual Model
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-21 BRL
/_1-IP4044 V
AB-24BR
AB-27BR
AB-38BR
GWA-4BR
GWA-9BR
Location
Within active ash
basin
On south end of
East Dike
Within primary
pond area of active
ash basin
North of primary
pond 3, on the
North Dike
Northwest portion
of inactive ash
basin
East of inactive ash
basin
West of active ash
basin
Purpose
Evaluate possible extent of
exceedances in bedrock at
AB-21.
Evaluate possible extent of
exceedances in bedrock at
AB-22. This will also provide
additional BR data at
southeast end of active ash
basin.
Evaluate possible extent of
exceedances in bedrock
beneath the active ash
basin.
Evaluate possible extent of
exceedances in bedrock at
AB-27.
Evaluate possible extent of
exceedances in bedrock at
AB-38. This will also provide
additional BR data beneath
the northwest extent of the
inactive ash basin.
Evaluate possible extent of
exceedances in bedrock at
GWA-4.
Evaluate possible extent of
exceedances in bedrock at
west end of active ash basin.
This will also provide
additional BR data between
the western extent of the
active ash basin and offsite
private water supply wells.
Approximate
Monitoring Well
Depth(s) (ft)
225
225
175
175
125
150
175
21

Duke Energy Carolinas, LLC I CSA Supplement 2
Allen Steam Station Ash Basin 01
SECTION 5 — ANTICIPATED ADDITIONAL ASSESSMENT ACTIVITIES
The information obtained from the borings will be reviewed against the existing conceptual site
model to evaluate if modifications or refinement are required.
5.2 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, surface water, and
AOW samples associated with the ash basin, which consists of the active ash basin and the
inactive ash basin, which includes the RAB Ash Landfill, ash storage areas, and structural fill at
the Allen 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, 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
Allen 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 (i.e., arsenic, boron, sulfate).
Y Groundwater flow direction in the shallow, deep and bedrock regimes are consistent with
groundwater flow directions depicted in the CSA and CAP reports.
Y The horizontal extent of ash -related groundwater impacts have been defined at the Allen
site. However, the vertical extent of ash -related groundwater impacts is not fully
delineated beneath the ash basin, downgradient of the ash basin and upgradient and
southwest of the active ash basin.
Based on the conclusions presented above, the following recommendations are offered:
Y Calculation of PPBCs using additional analytical results should be conducted to inform
decisions regarding the future sampling network.
Y Additional bedrock monitoring wells will be installed to refine the vertical extent of
potential ash -related groundwater impacts at the site, as described in Section 5.1.
Y Groundwater monitoring as proposed in the CAP Part 2 should continue.
23

Figures

Tables

Appendix A
Monitoring Well Logs
Core Photos
F-j

Appendix B
Field Sampling Forms
Slug Test Reports
F-j

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