NC0002468_FINAL_CSA Sup 2_Report_20160901

Comprehensive Site Assessment
Supplement 2
Dan River Steam Station Ash Basin
Site Name and Location Dan River Steam Station
900 South Edgewood Road
Eden, NC 27288
Groundwater Incident No. Not Assigned
NPDES Permit No. NC0003468
Date of Report September 1, 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 360 29' 28" N, 790 43' 16" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
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Malcolm F. Schaeffer, L.G.
Senior Geologist

Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

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Table of Contents
Page
Executive Summary ................................................................................................................... 1
Section 1 – Background ............................................................................................................. 3
1.1 Purpose of CSA Supplement ....................................................................................... 3
1.2 Site Description ............................................................................................................ 4
1.3 History of Site Groundwater Monitoring ........................................................................ 5
1.3.1 NPDES Sampling ................................................................................................. 6
1.3.2 CSA Sampling ...................................................................................................... 7
1.3.3 Post-CSA Sampling .............................................................................................. 7
1.3.4 NCDEQ Water Supply Well Sampling ................................................................... 8
Section 2 – CSA Review Comments .......................................................................................... 9
2.1 NCDEQ General Comments and Responses ............................................................... 9
2.2 NCDEQ Site-Specific Comments and Responses ....................................................... 9
2.3 Errata ........................................................................................................................... 9
Section 3 – Additional Assessment ...........................................................................................10
3.1 Additional Assessment Activities ................................................................................10
3.1.1 Well Installation ....................................................................................................10
3.1.2 Well Gauging and Sampling .................................................................................11
3.2 Additional Assessment Results ...................................................................................11
3.2.1 Groundwater Flow Direction .................................................................................12
3.2.2 Sampling Results .................................................................................................12
Section 4 – Background Concentrations ...................................................................................16
4.1 Methodology ...............................................................................................................16
4.2 Proposed Provisional Background Concentrations......................................................18
Section 5 – Anticipated Additional Assessment Activities ..........................................................19
5.1 Proposed Additional Assessment Monitoring Well ......................................................19
5.2 Implementation of the Effectiveness Monitoring Plan ..................................................19
Section 6 – Recommendations and Conclusions ......................................................................20

Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

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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 Beryllium Isoconcentration Contour Map – Shallow Wells (S)
3-4.8 Beryllium Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.9 Beryllium Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.10 Boron Isoconcentration Contour Map – Shallow Wells (S)
3-4.11 Boron Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.12 Boron Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.13 Hexavalent Chromium Isoconcentration Contour Map – Shallow Wells (S)
3-4.14 Hexavalent Chromium Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.15 Hexavalent Chromium Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.16 Chromium (Total) Isoconcentration Contour Map – Shallow Wells (S)
3-4.17 Chromium (Total) Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.18 Chromium (Total) Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.19 Cobalt Isoconcentration Contour Map – Shallow Wells (S)
3-4.20 Cobalt Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.21 Cobalt Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.22 Iron Isoconcentration Contour Map – Shallow Wells (S)
3-4.23 Iron Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.24 Iron Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.25 Manganese Isoconcentration Contour Map – Shallow Wells (S)
3-4.26 Manganese Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.27 Manganese Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.28 Sulfate Isoconcentration Contour Map – Shallow Wells (S)
3-4.29 Sulfate Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.30 Sulfate Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.31 Total Dissolved Solids Isoconcentration Contour Map – Shallow Wells (S)
3-4.32 Total Dissolved Solids Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.33 Total Dissolved Solids Isoconcentration Contour Map – Bedrock Wells (BR)
3-4.34 Vanadium Isoconcentration Contour Map – Shallow Wells (S)
3-4.35 Vanadium Isoconcentration Contour Map – Deep Wells (D and BRU)
3-4.36 Vanadium Isoconcentration Contour Map – Bedrock Wells (BR)
3-5.1 Site Cross Section Locations
3-5.2 Cross Section A-A’ (1 of 1)
3-5.3 Cross Section B-B’ (1 of 1)
3-5.4 Cross Section C-C’ (1 of 1)
3-5.5 Cross Section D-D’ (1 of 1)
3-6.1 Piper Diagram – Background Groundwater, Porewater, Areas of Wetness, and Surface
Water
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

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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 Summary of Groundwater Elevations
3-5 Summary of Cation-Anion Balance Differences

APPENDICES
A Monitoring Well Logs and Core Photos
B Field Sampling Forms and Slug Test Report
C Laboratory Report, Chain-of-Custody Forms, and Validation Report

Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

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Executive Summary
Duke Energy Carolinas, LLC (Duke Energy) owns and formerly operated the Dan River Steam
Station (DRSS), located on the Dan River in Rockingham County near Eden, North Carolina
(Figure 1-1). DRSS began operation as a coal-fired generating station in 1949 and was retired
from service in 2012. The Dan River Combined Cycle Station (DRCCS) natural gas generating
facility was constructed at the site and began operations in 2012. Historically, coal ash residue
from DRSS’s coal combustion process was disposed of in an ash basin located northeast of the
station and adjacent to the Dan River. Discharge from the ash basin is currently permitted by
the North Carolina Department of Environmental Quality (NCDEQ)1 Division of Water
Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit
NC0003468.
This Comprehensive Site Assessment (CSA) Supplement 2 report addresses the following:
• Summary of groundwater, porewater, ash basin surface water, 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 the submittal of the CSA report,
including additional assessments 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 (2L Standards or 2L) beneath the ash basin as well as within the ash storage
area. Boron has not been detected in porewater or in groundwater beyond the compliance
boundary downgradient of the ash basin dam.
Groundwater monitoring results from Round 5 of CSA well sampling (completed between March
and April 2016) and NPDES groundwater monitoring data are presented herein. Updated
summary tables, isoconcentration maps, cross sections, and other figures are included. In
general, groundwater data reported from previous rounds of monitoring are consistent with
recent groundwater data, specifically the extent of impact to groundwater from ash basin-related
constituents (e.g., boron and sulfate).
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 (COIs) downgradient of the source
areas is naturally occurring or potentially attributed to the source areas can be advanced in
more detail when additional sampling data is available.
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.
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Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

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The following conclusions and recommendations are offered:
• Based on their locations either upgradient or across the Dan River from the ash basin
and being hydraulically isolated, the water supply wells in the vicinity of the DRSS facility
are not impacted by Coal Combustion Residuals (CCR) releases from the ash basin.
• 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 and sulfate).
• Groundwater monitoring results from Round 6 of sampling should be evaluated in the
additional assessment wells, as several were not installed for inclusion within the Round
5 sampling event. In addition, surface water sampling results should be evaluated along
with the additional assessment well results.
• Refinement of PPBCs should be conducted once the minimum number of viable
observations (e.g., eight) per background well is available.
• An additional monitoring well (GWA-8BR) should be installed downgradient of Ash
Storage 2 to refine the vertical delineation of groundwater impacts in these areas.
• 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 | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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Section 1 – Background
Duke Energy Carolinas, LLC (Duke Energy) owns and formerly operated the Dan River Steam
Station (DRSS), located on the Dan River in Rockingham County near Eden, North Carolina
(Figure 1-1). DRSS began operation as a coal-fired generating station in 1949 and was retired
from service in 2012. The Dan River Combined Cycle Station (DRCCS) natural gas generating
facility was constructed at the site and began operations in 2012. Historically, coal ash residue
from DRSS’s coal combustion process was disposed of in an ash basin located northeast of the
station and adjacent to the Dan River. Discharge from the ash basin is currently 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
NC0003468.
The Comprehensive Site Assessment (CSA) for the DRSS was submitted to NCDEQ on August
14, 2015. Given the compressed timeframe for submittal, certain information was not included in
the CSA report because the data was not yet available. 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, which was
submitted to NCDEQ on February 10, 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.
1.1 Purpose of CSA Supplement
The purpose of this CSA Supplement 2 is to provide data obtained during additional well
installation and sampling conducted between March and July 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 activities;
• 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 DRSS 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 report, as appropriate.
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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As a complement to the CSA report and the CSA Supplement 1, this CSA Supplement 2
provides an updated evaluation of the extent of impacts from the ash basin and related ash
storage facilities based on existing CSA groundwater monitoring wells and monitoring wells
installed subsequent to submittal of the CSA report (herein referred to as additional assessment
wells). Additional groundwater monitoring wells are shown on Figure 1-2 with green text labels.
1.2 Site Description
DRSS is a former coal-fired electricity generating facility along the Dan River approximately 4.5
miles from the city of Eden, North Carolina. Construction of DRSS commenced in 1948 and the
station began commercial operation in 1949 with a single coal-fired unit. A second unit was
added in 1950 and a third unit was added by 1955, resulting in a total installed capacity of 276
megawatts (MW). All three coal-fired units, along with three 28 MW oil-fired combustion turbine
units, were retired in 2012. Construction of the DRCCS, a 620 MW combined cycle natural gas
facility, commenced in December 2009 and commercial operations began on December 10,
2012.
The DRSS ash basin is located adjacent to the Dan River and consists of a Primary Cell, a
Secondary Cell, and associated embankments and outlet works, as further described in the
CSA report (HDR 2015). The ash basin is impounded by earthen dams and an earthen/ash
divider dam separates the Primary Cell from the Secondary Cell. Water levels within the Primary
Cell have historically fluctuated approximately 11 feet from October 1984 until April 2013,
ranging from approximately 526 to 537 feet. Since the DRSS facility was retired, processed
water and stormwater inflow to the ash basin system have been rerouted from the Primary Cell
to the Secondary Cell, resulting in decreased water levels in the Primary Cell. Water levels
within the Secondary Cell have historically fluctuated approximately 8 feet from October 1984
until April 2013, ranging from approximately 518 to 526 feet. The ash storage areas are located
upgradient of the ash basin and consist of Ash Storage 1, Ash Storage 2, a former dredge pond,
and associated dredge dikes. The ash storage areas contain ash that was previously removed
from the ash basin.
Topography at the DRSS site generally slopes from northwest to southeast, ranging from an
approximate high elevation of 606 feet near the northern property boundary just west of
Edgewood Road to an approximate low elevation of 482 feet at the interface with the Dan River.
Ground surface relief varies by approximately 124 feet over an approximate distance of 0.7
miles. Surface water drainage generally follows site topography and flows from northwest to
southeast across the site except where drainage patterns have been modified by the ash basin
or other construction.
The groundwater system in the natural materials (alluvium, soil, soil/saprolite, and bedrock) at
DRSS is consistent with the Piedmont regolith-fractured rock system and consists of an
unconfined, connected system without confining layers. The groundwater system at DRSS is a
two-layer system: shallow (regolith) and deep (bedrock). In general, groundwater at the site
flows from the northern extent of the DRSS property boundary to the south/southeast toward the
Dan River.
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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The primary source areas at DRSS are defined as the ash basin (Primary and Secondary cells)
and the ash storage areas (Ash Storage 1 and Ash Storage 2). Source characterization was
performed to identify physical and chemical properties of ash, ash basin surface water,
porewater, and areas of wetness (AOW).
The compliance boundary for groundwater quality at the DRSS 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 (COIs). 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 DHHS HSL exceedances are limited to within or directly
adjacent to the sources. The limited downgradient extent of impacts indicates that physical and
geochemical processes (i.e., dispersion and sorption) beneath the DRSS site reduce the lateral
migration of COIs.
1.3 History of Site Groundwater Monitoring
Duke Energy has implemented voluntary and NPDES permit-required compliance groundwater
monitoring at the DRSS site since 1993, in accordance with NPDES Permit NC0003468. From
1993 to 2010, voluntary groundwater monitoring was performed twice annually around the
DRSS ash basin with analytical results submitted to NCDENR DWR. In October 2010, new
compliance monitoring wells were installed and the existing monitoring wells became part of the
voluntary monitoring program. Additional groundwater monitoring was required beginning in
March 2011 with the frequency of sampling and parameters to be analyzed outlined in the
NPDES permit.
A review of voluntary monitoring well sampling results obtained between 1993 and 2011
indicates the following:
• Boron exceeded the 2L Standard in the deep flow layer in MW -9D in all sampling events
from April 2008 to September 2011.
• Chromium 3 exceeded the 2L Standard in the shallow flow layer in well MW -12 during the
April 2004 and October 2006 voluntary sampling events. Chromium exceeded the 2L
Standard in the deep flow layer in well MW -11D during the April and October sampling
events in 2008 and the April 2009 sampling event.
• Iron and manganese have intermittently exceeded the 2L Standards in voluntary wells
screened in the shallow and deep flow layers located across the site. However, these
3 Unless otherwise noted, references to chromium in this document indicate total chromium.
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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exceedances may be attributable to naturally occurring conditions and require additional
evaluation as site-specific PPBCs are refined.
• Lead exceeded the 2L Standard in the shallow flow layer in well MW -12 during the April
1998 and April 2000 voluntary sampling events. Lead exceeded the 2L standard in the
deep flow layer in well MW-11D during the April 2008 sampling event.
Construction details for voluntary monitoring wells are provided in Table 1-1. The location of the
ash basin voluntary monitoring wells, the approximate ash basin waste boundary, and the
compliance boundary are shown on Figure 1-2.
As described in Section 1.2, the compliance boundaries for groundwater quality at the DRSS
site are defined in accordance with Title 15A NCAC 02L .0107(a) as being established at either
500 feet from the waste boundaries or at the property boundary, whichever is closer to the
waste boundary. After additional review, Duke Energy became aware that the compliance
boundaries currently depicted should be revised to accurately reflect Duke Energy property
ownership. The current property depiction was obtained from county GIS records and shows
specific areas consisting of rights-of-way not under ownership of Duke Energy. Duke Energy is
in the process of revising these areas and will submit revised compliance boundary figures to
NCDEQ for approval.
1.3.1 NPDES Sampling
NPDES compliance monitoring wells (compliance wells) were installed in December 2010.
Compliance groundwater monitoring, as required by the NPDES permit, began in December
2011. From January 2011 through May 2016, compliance groundwater monitoring wells at the
DRSS site have been sampled three times each year, resulting in 17 monitoring events during
that time.
One or more groundwater quality criteria (2L Standard and IMAC) has been exceeded in
groundwater samples collected from the compliance monitoring wells. Exceedances have
occurred in one or more wells during one or more sampling events for antimony, arsenic, boron,
iron, manganese, sulfate, total dissolved solids (TDS), and thallium. A review of NPDES
compliance well sampling results indicates the following:
• Antimony exceeded the IMAC in the shallow flow layer in MW -20S in May 2012; in MW -
21S in January 2011, May 2011, September 2011, May 2012, and September 2015; and
in MW -22S in January 2016. Antimony exceeded the IMAC in the deep flow layer in
MW -20D in September 2015 and January 2016; in MW -21D in September 2015; in MW -
22D in January 2012, May 2012, January 2013, May 2013, May 2015, September 2015,
and January 2016; in MW-23D in September 2015 and January 2016.
• Arsenic exceeded the 2L Standard in the shallow flow layer in MW -21S in all sampling
events from January 2011 through May 2016.
• Boron exceeded the 2L Standard in the shallow flow layer in MW -22S in May 2013,
September 2014, and May 2016. Boron exceeded the 2L Standard in the deep flow layer
in MW -22D in all sampling events from January 2012 through May 2016 with the
exception of September 2012 and May 2013.
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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• 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 the deep flow layer in MW -21D in all sampling
events from January 2011 through May 2016 with the exception of September 2014.
• TDS exceeded the 2L Standard in the deep flow layer in MW -21D in all sampling events
from January 2011 through May 2016.
• Thallium exceeded the IMAC in the deep flow layer in MW -20D in September 2015.
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 DRSS site began in February 2015 and was completed in August 2015. Sixty-
three groundwater monitoring wells and three soil borings were installed/advanced as part of
this assessment to characterize the ash, soil, rock, and groundwater at the DRSS site. One
comprehensive round of sampling and analysis was included in the CSA report and included
sampling of groundwater, ash, ash basin surface water, Dan River surface water, tributary
surface water, porewater, and AOW (Figure 1-2). In addition, a hydrogeological evaluation was
performed on newly installed wells.
The following constituents were reported as COIs in the CSA report:
• Soil: iron, manganese, arsenic, chromium, and selenium
• Groundwater: antimony, arsenic, boron, chromium, cobalt, iron, manganese, sulfate,
thallium, TDS, and vanadium
• Surface Water: aluminum, arsenic, copper, lead, and vanadium
Horizontal and vertical delineation of source-related soil impacts was presented in the CSA
report. Where soil impacts were identified beneath the ash basin (beneath the ash/soil
interface), the vertical extent of contamination was generally limited to the soil samples collected
just beneath the ash.
Groundwater impacts at the site attributable to ash handling and storage were delineated during
the CSA activities with the following areas requiring refinement:
• Vertical extent in the vicinity of Ash Storage 1
• Horizontal and vertical extent north of Ash Storage 1
1.3.3 Post-CSA Sampling
Four additional rounds of groundwater sampling of the CSA wells have occurred since submittal
of the CSA report. Round 2 of groundwater monitoring occurred in September 2015 and was
reported in the Corrective Action Plan (CAP) Part 1 (submitted on November 12, 2015). Rounds
3 and 4 of background groundwater monitoring occurred in November and December 2015, and
results were reported in the CSA Supplement 1 as part of the CAP Part 2 report (submitted on
Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 1 – BACKGROUND

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February 10, 2016). Round 5 of groundwater monitoring was conducted in March 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
DRSS compliance boundary in all directions, since the direction of groundwater flow had not
been determined at DRSS at the time of sampling. However, no private wells within a 0.5-mile
radius of the compliance boundary were sampled at the DRSS sites, nor were “Do Not Drink”
letters issued by the DHHS.
Two reported private water supply wells are located at residences north of the DRSS within a
0.5-mile radius of the ash basin compliance boundary. Two additional reported private water
supply wells are located at residences south of the DRSS within a 0.5-mile radius of the ash
basin compliance boundary; they are located on the southern side of Dan River in Rockingham
County (Wells 1 and 4 shown on Figure 1-3). Information evaluated as part of the CSA
indicated that the identified water supply wells would not be impacted as they are either
hydraulically upgradient or across the Dan River from the ash basin. Additional assessment
wells GWA-20S and GWA-20D have been installed on the south side of the Dan River
downgradient of the two private water supply wells (Wells 1 and 4). These two wells are not
within the Dan River Triassic Basin, but are installed within alluvium and metamorphic rocks of
the Milton terrane. Furthermore, Well 4 is upstream and upgradient of the Dan River ash basin.
As such, the water supply wells in the vicinity of the DRSS facility are not impacted by CCR
releases from the ash basin.

Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 2 – CSA REVIEW COMMENTS

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Section 2 – CSA Review Comments
Representatives of NCDEQ’s Central Office and Winston-Salem Regional Office (WSRO) met
with Duke Energy and HDR on September 23, 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
DRSS.
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 10, 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 10, 2016 as part of the CAP Part 2 report. Since
the issuance of the CAP Part 2 report, additional evaluation of site data has occurred, resulting
in refinement by flow layer of total porosity, secondary (effective) porosity, and specific storage
for the lower hydrostratigraphic units (deep transition zone and bedrock), as provided in Table
2-2.

Duke Energy Carolinas, LLC | CSA Supplement 2
Dan River Steam Station Ash Basin
SECTION 3 – ADDITIONAL ASSESSMENT

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Section 3 – Additional Assessment
Additional assessment activities identified in the CSA report were addressed and the findings
are discussed in the following sections.
3.1 Additional Assessment Activities
Additional assessment activities included monitoring well installation and sampling, as
discussed below.
3.1.1 Well Installation
Additional monitoring wells were installed to refine understanding of groundwater flow direction
and extent of exceedances at DRSS. Refinement of exceedances focused primarily on the
extent of groundwater impacts in the vicinity of Ash Storage 1. To address the extent of
exceedances near Ash Storage 1, monitoring well GWA-18D was installed.
Subsequent discussions with Duke Energy and NCDEQ resulted in the installation of additional
monitoring wells beyond described above. A summary of those additional assessment wells and
installation dates, as well as the purpose for installation, is provided in the table below.
Boring/Well
Identification
Installation
Date
Purpose for Installation Result
GWA-5BRD 7/7/2016 Well requested by NCDEQ to
further evaluate vertical extent of
exceedances observed at GWA-
5BR
Not installed in time for sampling
inclusion during the Round 5
sampling event
GWA-16S 6/14/2016 Wells requested by NCDEQ to
further evaluate horizontal extent of
exceedances observed at GWA-
14S/D and GWA-15S/D
Not installed in time for sampling
inclusion during the Round 5
sampling event
GWA-16D 6/15/2016 Not installed in time for sampling
inclusion during the Round 5
sampling event
GWA-18D 6/9/2016 Wells requested by NCDEQ to
further evaluate horizontal extent of
exceedances north of Ash Storage
1
Not installed in time for sampling
inclusion during the Round 5
sampling event
GWA-20S 6/21/2016 Wells requested by NCDEQ to
evaluate water quality across the
Dan River
Not installed in time for sampling
inclusion during the Round 5
sampling event
GWA-20D 6/23/2016 Not installed in time for sampling
inclusion during the Round 5
sampling event
MW-317BRL 7/12/2016 Wells requested by NCDEQ to
further evaluate the vertical extent
of exceedances observed between
AS-8D/BR and MW -317BR
Not installed in time for sampling
inclusion during the Round 5
sampling event
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Boring/Well
Identification
Installation
Date
Purpose for Installation Result
BG-10S 6/10/2016 To provide additional background
groundwater quality for
determination of PPBCs at the site
Not installed in time for sampling
inclusion during the Round 5
sampling event
BG-10D 6/13/2016 Not installed in time for sampling
inclusion during the Round 5
sampling event
BG-10BR 6/22/2016 Not installed in time for sampling
inclusion during the Round 5
sampling event

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
because groundwater was not encountered above refusal depth:
• GWA-17S/D – This well nest had been requested by NCDEQ to further evaluate
horizontal extent of exceedances observed at GWA-14S/D and GWA-15S/D.
• GWA-18S – This well had been requested by NCDEQ to further evaluate horizontal
extent of exceedances north of Ash Storage 1.
In addition, AOWs were not sampled during the Round 5 event due to dry and/or non-flowing
conditions.
Several monitoring wells exhibit pH levels of 9 or above, which may be indicative of cement
leakage beyond the borehole seal. In addition, several monitoring wells had a turbidity value of
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, porewater, ash basin surface water, surface water, and ash basin
water sampling activities was completed between March 28 and April 26, 2016. Groundwater
analytical parameters and methods for Round 5 were consistent with those used during
previous sampling events, as presented in previous reports. A total of 60 groundwater and
porewater monitoring wells were sampled during the Round 5 event. Sample locations are
depicted on Figure 1-2.
3.2 Additional Assessment Results
Findings and results from Round 5 of sampling and analysis and additional assessment
activities are presented below. Note that the Round 3 and 4 monitoring events focused on
sampling of background wells only; therefore, groundwater elevation and analysis results are
compared to data previously obtained during Round 1 and 2 monitoring events. A summary of
the analytical results is presented in Tables 3-1 through 3-3 for groundwater, porewater, and
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ash basin surface water, respectively. A summary of groundwater elevations measured during
the Round 1 through 5 gauging events is presented in Table 3-4.
3.2.1 Groundwater Flow Direction
On June 12, 2016, monitoring wells were manually gauged from the top of the PVC casing
using an electronic water level indicator accurate to 0.01 foot. Groundwater elevations were
generally higher than those measured during Rounds 1 and 2, which is likely attributable to
seasonal variation of the water table. Groundwater flow direction was consistent with flow
directions identified in Rounds 1 and 2, and generally flows to the northern extent of the DRSS
property boundary to the south/southeast toward the Dan River. The groundwater flow direction
is away from the direction of the nearest public or private water supply wells. Groundwater
elevations and inferred contours for the shallow, deep, and bedrock flow layers are depicted on
Figures 3-1, 3-2, and 3-3, respectively and show an upward gradient in the deep and bedrock
flow layers at the Dan River, These groundwater flow directions are consistent with
interpretations made in the CSA report.
3.2.2 Sampling Results
3.2.2.1 SUMMARY OF ROUND 1 AND 2 GROUNDWATER SAMPLING RESULTS
As previously mentioned in Section 1.3.2, the following COIs were identified in groundwater as
a result of sampling conducted during the CSA: antimony, arsenic, boron, chromium, cobalt,
iron, manganese, sulfate, thallium, TDS, and vanadium. In addition, beryllium, hexavalent
chromium, and pH exceeded applicable criteria during the Round 5 sampling event and may be
considered additional COIs.
3.2.2.2 ROUND 5 POREWATER SAMPLING RESULTS
A total of four porewater samples were collected from monitoring wells (AB-10S, AB-10SL, AB-
25S, and AB-5S) screened within the ash basin Primary and Secondary cells. Concentrations of
antimony, arsenic, hexavalent chromium, cobalt, iron, manganese, selenium, thallium,
vanadium, and pH that exceed the applicable 2L Standard, IMAC, or DHHS HSL were detected
in porewater samples collected during the Round 5 sampling event. The range and number of
exceedances of each COI in porewater is listed below.
• Antimony: 4.3 µg/L; 1 exceedances/4 samples
• Arsenic: 172 µg/L to 249 µg/L; 3/4
• Beryllium: no exceedances in porewater
• Boron: no exceedances in porewater
• Chromium: no exceedances in porewater
• Hexavalent Chromium: 0.54 µg/L; 1/4
• Cobalt: 13.5 µg/L to 31.2 µg/L; 2/4
• Iron: 13,200 µg/L to 37,500 µg/L; 2/4
• Manganese: 371 µg/L to 1400 µg/L; 2/4
• Selenium: 21.6 µg/L; 1/4
• Sulfate: no exceedances in porewater
• Thallium: 0.3 µg/L to 0.66 µg/L; 2/4
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• TDS: no exceedances in porewater
• Vanadium: 0.71 µg/L to 55.9 µg/L; 4/4
• pH: 6.3; 1/4
3.2.2.3 ROUND 5 GROUNDWATER SAMPLING RESULTS
A total of 57 groundwater monitoring wells were sampled during March and April 2016 as part of
the Round 5 sampling event. In addition, a total of three Field Duplicate (FD) samples were
collected from the groundwater wells. The analytical results for the groundwater monitoring well
samples are presented on Table 3-1. In general, the COIs identified during Round 5
groundwater sampling are consistent with the results obtained during Rounds 1 and 2. A
summary of Round 5 sampling results per COI identified during the CSA is as follows:
• Antimony: 1.1 µg/L to 2.3 µg/L; 5 exceedances/57 samples (5/57)
o Antimony exceeded the IMAC in the deep flow layer in wells located within the
ash basin and north of Ash Storage 1. Antimony exceedances in the bedrock
flow layer were detected at concentrations that were similar to concentrations
measured in the deep flow layer. Antimony was detected above the IMAC in
background well BG-1D, indicating that antimony may be present as a naturally
occurring constituent. In general, total and dissolved concentrations were
consistent in each sample. There were no exceedances for antimony in wells
screened within the shallow flow layer.
• Arsenic: 11.3 µg/L to 319 µg/L; 2/57
o Arsenic exceeded the 2L Standard in the deep flow layer in one well (OW -308D)
located within the Secondary Cell of the ash basin and one well (AB-35BR) in the
bedrock flow layer. The measured exceedance in the deep flow layer was
significantly higher than the exceedance measured in the bedrock flow layer.
There were no exceedances for arsenic in wells screened within the shallow flow
layer.
• Beryllium: 7.7 µg/L; 1/57
o Beryllium exceeded the 2L Standard in one well (GWA-7S) screened within the
shallow flow layer. There were no exceedances for beryllium in wells screened
within the deep and bedrock flow layers.
• Boron: 735 µg/L to 1640 µg/L; 6/57
o Boron exceeded the 2L Standard in one well (AS-12S) screened within the
shallow flow layer. Boron was detected above the 2L Standard in four wells (MW -
318D, MW -9D, AB-25D, and AS-2D) in the deep flow layer within the ash basin
and ash storage areas, and MW -311BR in the bedrock flow layer within the ash
basin.
• Chromium: 10.4 µg/L to 160 µg/L; 1/57
o Chromium exceeded the 2L Standard in the bedrock flow layer in one well (MW -
317BR). There were no exceedances for chromium in wells screened within the
shallow and deep flow layers.
• Hexavalent Chromium: 0.072J µg/L to 12.6 µg/L; 18/57
o Hexavalent chromium exceeded the DHHS HSL in the shallow flow layer in wells
located across the DRSS site. Hexavalent chromium also exceeded the DHHS
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HSL in the deep flow layer with similar frequency as the shallow flow layer within
and upgradient of the ash basin. Exceedances of hexavalent chromium in the
bedrock flow layer wells occurred at two locations (MW-317BR and AB-25BR).
Concentrations in six background wells (BG-5S, GWA-9S, GWA-12S, BG-1D,
BG-5D, and MW-23D) also exceeded the DHSS HSL. Note that dissolved phase
analyses were not performed on groundwater samples for hexavalent chromium.
• Cobalt: 1.3 µg/L to 34.1 µg/L; 14/57
o Cobalt exceeded the IMAC in seven shallow flow layer wells. Cobalt
exceedances in the deep flow layer occurred at six locations and in one FD, and
were measured at similar concentrations as observed in the shallow flow layer.
Cobalt exceedances in the bedrock flow layer were exhibited in one bedrock well
(MW -308BR), which is located within the Secondary Cell of the ash basin. Total
and dissolved concentrations were generally consistent across the sample set.
• Iron: 322 µg/L to 31,400 µg/L; 21/57
o Iron exceeded the 2L Standard in the shallow flow layer in wells in multiple areas
of the DRSS site. Exceedances of iron in the deep flow layer were more frequent
throughout the site than in the shallow flow layer. Exceedances of iron in the
bedrock flow layer exceeded the 2L Standard in four wells. Two FD wells, one in
the deep flow layer and one in the bedrock flow layer, also indicated
exceedances of the 2L Standard. Total and dissolved concentrations were
generally inconsistent across the sample set.
• Manganese: 76.3 µg/L to 7460 µg/L; 41/57
o Manganese exceeded the 2L Standard in the shallow, deep, and bedrock flow
layers in wells located across the DRSS site. Total and dissolved concentrations
were generally consistent across the sample set.
• Selenium: No exceedances in groundwater
• Sulfate: 388,000 µg/L to 811,000 µg/L; 3/57
o Sulfate exceeded the 2L Standard in one well within the deep flow layer (GWA-
8D) and two wells within the bedrock flow layer (MW -308BR and GWA-5BR).
These wells are located upgradient from and within the ash basin. There were no
exceedances for sulfate in wells screened within the shallow flow layer.
• Thallium: No exceedances in groundwater
• TDS: 522,000 µg/L to 1,400,000 µg/L; 5/57
o TDS exceeded the 2L Standard in three wells screened within the deep flow
layer (GWA-1D, GWA-8D, and AS-2D) and two wells within the bedrock flow
layer (MW -308BR and GWA-5BR). The bedrock flow layer wells with TDS
exceedances are located within the ash basin at wells MW -308BR and GWA-
5BR. There were no exceedances for TDS in wells screened within the shallow
flow layer.
• Vanadium: 0.32 µg/L to 20.1 µg/L; 18/57
o Vanadium exceeded the IMAC in the shallow, deep, and bedrock flow layers in
wells across the DRSS site, including one background well. Total and dissolved
concentrations were generally consistent across the sample set.
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• pH: 4.8 to 12.2; 23/57
o PH exceeded the 2L Standard in the shallow, deep, and bedrock flow layers in
wells across the DRSS site including three background wells (BG-5S, GWA-12S,
and MW -23D).
The horizontal extent of exceedances is presented in the form of isoconcentration figures
(Figures 3-4.1 through 3-4.36). The vertical extent of boron and sulfate is presented on
applicable cross sections (Figures 3-5.1 through 3-5.5). In addition, cross sections show
hydrostratigraphic layers, rock lithology, rock core recovery (REC) and rock quality designation
(RQD; a measure of rock mass discontinuities/fracturing) in response to comments received
from NCDEQ.
3.2.2.4 COMPARISON OF POREWATER AND GROUNDWATER RESULTS
Based upon review of data collected during Round 5 sampling, the concentrations of COIs
identified in porewater were generally consistent with groundwater concentrations with the
possible exceptions of beryllium, boron, selenium, and thallium within the shallow flow layer.
Exceedances of beryllium and boron were exhibited in shallow groundwater wells, but not in
porewater wells. Exceedances of selenium and thallium were exhibited in porewater wells, but
not in groundwater wells.
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, geochemistry of groundwater and surface water at the DRSS site is predominantly rich
in calcium, magnesium, and bicarbonate with the exception of downgradient groundwater
monitoring wells, which trend closer to a calcium-, magnesium- and sulfate-rich geochemical
composition. 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 3-5.

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SECTION 4 – BACKGROUND CONCENTRATIONS

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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 calculations will be prepared and submitted to the 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.4
Once the required minimum number of samples is available, HDR will calculate PPBCs using
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).5 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.
4 U.S. Environmental Protection Agency (USEPA) Unified Guidance (USEPA 2009), 5.2.1 Selecting Monitoring
Constituents and Adequate Sample Sizes 5 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.

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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 DRSS site.6
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 is 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 collected from 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 is that the constituent concentrations
sampled at these background wells, when pooled, will serve as an estimate of overall 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 (deep), 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 (shallow, transition zone (deep), and bedrock). 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
6 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.
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reference 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 Proposed Provisional Background Concentrations
Currently, the DRSS site has the following number of usable observations at background wells
for implementation of the background concentration methodology described in Section 4.1:
• BG-1D (CSA Monitoring Well) – 3 observations
• BG-5S (CSA Monitoring Well) – 6 observations
• BG-5D (CSA Monitoring Well) – 6 observations
• BG-10S (Additional Assessment Monitoring Well) – 0 observations
• BG-10D (Additional Assessment Monitoring Well) – 0 observations
• BG-10BR (Additional Assessment Monitoring Well) – 0 observations
• GWA-9S (CSA Monitoring Well) – 5 observations
• GWA-9D (CSA Monitoring Well) – 5 observations
• GWA-12S (CSA Monitoring Well) – 2 observations
• GWA-12D (CSA Monitoring Well) – 6 observations
• MW -23D (Compliance Monitoring Well) – 3 observations
• MW -23BR (CSA Monitoring Well) – 5 observations

It is expected that with interim monitoring implementation, the DRSS 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 | CSA Supplement 2
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SECTION 5 – ANTICIPATED ADDITIONAL ASSESSMENT ACTIVITIES

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Section 5 – Anticipated Additional Assessment
Activities
Anticipated additional assessment activities are summarized below.
5.1 Proposed Additional Assessment Monitoring Well
Based on review of site information and analytical data available at this time, there is one
location 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 well is currently planned for installation during Fall of 2016:
Proposed
Additional
Monitoring Wells
Location Purpose Approximate
Monitoring Well
Depth(s) (ft)
GWA-8BR Downgradient
(southwest) of Ash
Storage 2
Evaluate vertical extent of
exceedances reported in GWA-
8D (TDS and sulfate).
70

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, porewater, ash basin
surface water, surface water, and AOW samples associated with the ash basin (Primary and
Secondary cells) and the ash storage areas (Ash Storage 1 and Ash Storage 2) at the DRSS
site. The monitoring plan is intended to evaluate the effectiveness of proposed corrective
actions and address the need to evaluate baseline conditions and seasonal variation in
groundwater, ash basin surface water, and AOWs.
Duke Energy will implement the effectiveness monitoring plan in accordance with
recommendations provided in the CAP Part 2 report as well as subsequent discussions with
NCDEQ.

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Dan River Steam Station Ash Basin
SECTION 6 – RECOMMENDATIONS AND CONCLUSIONS

20
Section 6 – Recommendations and Conclusions
The following conclusions have been developed from the information presented in this CSA
Supplement 2 report:
• Based on their locations either upgradient or across the Dan River from the ash basin
and being hydraulically isolated, the water supply wells in the vicinity of the DRSS facility
are not impacted by CCR releases from the ash basin.
• 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 and sulfate).
Based on the conclusions presented above, the following recommendations are offered:
• Groundwater monitoring results from Round 6 of sampling should be evaluated in the
additional assessment wells as several were not installed for inclusion within the Round
5 sampling event. In addition, surface water sampling results should be evaluated along
with the additional assessment well results.
• Refinement of PPBCs should be conducted once the minimum number of viable
observations (e.g., eight) per background well is available.
• An additional monitoring well (GWA-8BR) should be installed downgradient of Ash
Storage 2 to refine the vertical delineation of groundwater impacts in these areas.
• 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

A
Appendix A
Monitoring Well Boring Logs
Core Photos

B
Appendix B
Field Sampling Forms
Slug Test Report

C
Appendix C
Laboratory Report and
Chain-of-Custody Forms
Validation Report