NC0003468_DRSS CSA Rpt_20150814

Comprehensive Site Assessment Report
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.
Date of Report
NC0003468
August 14, 2015
Permittee and Current Property Owner Duke Energy Carolinas, LLC
526 South Church St
Charlotte, NC 28202
800.559.3853
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 48' 70" N, 790 71' 80" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
Mark Filardi, L.G.
Senior Geologist
Senior Geologist
�>DUKE I=
ENERGY )�

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-1

Executive Summary
On August 20, 2014, the North Carolina General Assembly passed Senate Bill 729, the Coal
Ash Management Act of 2014 (CAMA). Section § 130A-309.209 of the bill requires the owner of
a coal combustion residuals surface impoundment to submit a Groundwater Assessment Work
Plan (Work Plan) to the North Carolina Department of Environment and Natural Resources
(NCDENR) no later December 31, 2014 and a Groundwater Assessment Report (herein
referred to as a Comprehensive Site Assessment [CSA]) no later than 180 days following
approval of the Work Plan. Duke Energy Carolinas, LLC (Duke Energy) submitted a Work Plan
to NCDENR for assessment and characterization of the Dan River Steam Station (DRSS) ash
basin and ash storage areas on December 29, 2014. The Work Plan was subsequently
conditionally approved by the NCDENR in correspondence dated February 16, 2015. This CSA
report was prepared to comply with the CAMA and is submitted to NCDENR within the allotted
180 day timeframe. Data generated during the CSA will be used in development of the
Corrective Action Plan (CAP), due 90 days after submittal of this CSA.
The purpose of this CSA is to characterize the extent of contamination resulting from historical
production and storage of coal ash, evaluate the chemical and physical characteristics of the
contaminants, investigate the geology and hydrogeology of the site including factors relating to
contaminant transport, and examine risk to potential receptors and exposure pathways. This
CSA was prepared in general accordance with requirements outlined in the following regulations
and documents:
 Classifications and Water Quality Standards Applicable to the Groundwaters of North
Carolina in Title 15A NCAC 02L .0106(g);
 Coal Ash Management Act in G.S. 130A-309.209(a);
 Notice of Regulatory Requirements (NORR) issued by NCDENR on August 13, 2014;
 Conditional Approval of Revised Groundwater Assessment Work Plan issued by
NCDENR on February 16, 2015; and
 Subsequent meetings and correspondence between Duke Energy and NCDENR.
The assessment addresses the horizontal and vertical extent of contamination in soil,
groundwater, and surface water. If a constituent1 concentration exceeded the North Carolina
Groundwater Quality Standards, as specified in T15A NCAC .0202L (2L Standards) or Interim
Maximum Allowable Concentration (IMAC)2, it has been designated as a “Constituent of
Interest” (COI). Some COIs (e.g., iron and manganese) are also present in background
monitoring wells and thus require careful examination to determine whether their presence
downgradient of the ash basin or ash storage areas is naturally occurring or a result of ash

1 Constituents are elements, chemicals, or compounds that were identified in the approved Work Plan for sampling
and analysis, and include antimony, arsenic, boron, chromium, cobalt, iron, manganese, selenium, thallium,
vanadium, sulfate, and total dissolved solids (TDS).
2 Appendix #1 of 15A NCAC Subchapter 02L Classifications and Water Quality Standards Applicable to The
Groundwaters of North Carolina, lists Interim Maximum Allowable Concentrations (IMACs). The IMACs were issued
in 2010 and 2011; however, NCDENR has not established a 2L Standard for these constituents as described in 15A
NCAC 02L.0202(c). For this reason, IMACs noted in this report are for reference only.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-2

handling and storage. In addition to evaluating the distribution of constituents across the DRSS
site, significant factors affecting constituent transport, and the geological and hydrogeological
features influencing the movement and chemical and physical character of the COIs were also
evaluated.
The assessment consisted of the following activities:
 Completion of soil borings and installation of groundwater monitoring wells to faciliatate
collection and analysis of chemical, physical, and hydrogeological parameters of
subsurface materials encountered within and beyond the waste and compliance
boundaries;
 Evaluation of testing data to supplement the Site Conceptual Model (SCM);
 Revision to the Receptor Survey previously completed in 2014; and
 Completion of a Screening-level Risk Assessment.

Based on scientific evaluation of historical and new data obtained during completion of the
above-referenced activities, the following conclusions can be drawn:
 No imminent hazard to human health or the environment has been identified as a result
of groundwater migration from the ash basin or ash storage areas. Recent groundwater
assessment results are consistent with previous results from historical and routine
compliance boundary monitoring well data.
 Upgradient, background monitoring wells contain naturally occurring metals and other
constituents at concentrations that exceeded their respective 2L Standards or IMACs.
This information is used to evaluate whether concentrations in groundwater
downgradient of the basin and ash storage areas are also naturally occurring or might be
influenced by migration of constituents from the ash basin and ash storage areas.
Examples of naturally occuring metals and consituents include cobalt, iron, manganese,
thallium, total dissolved solids (TDS), and vanadium. These metals and constituents
were detected in background groundwater samples at concentrations greater than 2L
Standards or IMACs.
 Groundwater in the shallow aquifer under the DRSS ash basin and under the ash
storage areas flows horizontally to the southeast and discharges to the Dan River. This
flow direction is away from the direction of the nearest public or private water supply
wells. The Dan River serves as a lower hydrologic boundary for groundwater within the
shallow aquifer, and serves as a discharge feature for shallow groundwater flow from the
ash basin. Regional groundwater flow in the vicinity of the DRSS is south/southeast
toward the Dan River.There are no water supply wells located between the ash basin
and the Dan River.
 Groundwater data identified a local groundwater divide north of Ash Storage 1 where
groundwater in the shallow aquifer intially flows north prior to intersecting an unnamed
tributary to the Dan River which then flows in a southeasterly direction towards the Dan
River.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-3

 There are no indications of exceedances of 2L Standards or IMACs north of the DRSS
site attributable to the ash storage areas. Residences located north of the ash storage
areas are serviced by municipal water.
 Surface water quality data for samples collected within the Dan River during this CSA
indicate that the water quality in the river has not been imapcted by ash above the North
Carolina Surface Water Quality Standards (2B Standards).
 There are no known exceedances of 2L Standards for arsenic and boron beyond the
DRSS property boundary. Arsenic and boron are the primary constituents detected in
shallow aquifer in the three-dimensional area beneath the ash basin with measured
concentrations exceeding background concentrations and 2L Standards.
 The horizontal migration of boron in the shallow aquifer best represents the dominant
flow and transport system. Vertical migration of constituents is genearlly limited by
underlying bedrock.Boron is highly soluble and was identified by the USEPA as one of
the leading indicators for releases of contaminants from ash. Because of these
characteristics, boron can be used to represent the general extent of the shallow aquifer
impacted by the ash basin and ash storage areas
 TDS and sulfate exceeded the 2L Standards in an isolated area east of the DRSS
historical site property boundary. Based on the relatively low concentrations of other
ash-related constituents in these wells, the presence of TDS and sulfate may not be
attributed to groundwater migration from the ash basin.
 Aluminum, arsenic, chromium, cobalt, copper, lead, thallium, and zinc exceeded the 2B
Standards in the surface water sample (SW-3) collected from the unnamed tributary to
the Dan River located east of the Secondary Cell. It should be noted that boron was not
detected in levels that exceeded 2B Standards at this location. However, analyses of
surface water sample SW-6, collected from the Dan River near the confluence with the
tributary stream, indicate that the Dan River has not been adversely affected by the
water quality at sample location SW-3.
Note that as required to by CAMA, Duke Energy has agreed to remove the ash in the ash basin
and ash storage areas via excavation. Approximately 1.2 million tons of ash will be transported
to a lined landfill. It is anticipated that the remainder of ash will be placed into a lined landfill to
be constructed in the vicinity of Ash Storage 1. The initial phase of ash removal is scheduled to
commence 60 days after all necessary permits and approvals are obtained. Closure of the ash
impoundments is anticipated to occur by August 2019.
ES.1 Source Information
Duke Energy owns and formerly operated the Dan River Steam Station, located on the Dan
River in Rockingham County near Eden, North Carolina. 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 the ash basin system located northeast of the station and adjacent to the Dan
River. Discharge from the ash basin system is currently permitted by the NCDENR’s Division of
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-4

Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES)
Permit NC0003468.
The ash basin system at the plant was used to retain and settle ash generated from coal
combustion at DRSS. The ash basin system is located adjacent to the Dan River and consists
of a Primary Cell, a Secondary Cell, and associated embankments and outlet works. The ash
basin cells are unlined and are not currently closed. Two ash storage areas also exist to the
north and upgradient of the Primary and Secondary Cells and consist of ash dredged from the
Primary Cell. The ash storage areas are unlined and have a vegetative soil cap.
The ash basin was operated as an integral part of the site’s wastewater treatment system.
During operation of the coal-fired units, the ash basin received variable inflows of fly ash, bottom
ash, pyrites, stormwater runoff (including runoff from the coal pile), cooling water, powerhouse
floor drains, sanitary waste effluent, station yard drainage sump, and boiler chemical cleaning
wastes. The coal ash was historically sluiced to the southwest corner of the Primary Cell on a
variable basis (i.e., dependent on DRSS operations) via sluice pipes.
The CSA found that exceedances of ash-related constituents in soil, groundwater, and surface
water are likely the result of leaching from the coal ash contained in the ash basin and ash
storage areas. However, exceedances of iron, manganese, and vanadium may be due in part to
naturally occurring conditions based on a review of background groundwater quality data.
ES.2 Initial Abatement and Emergency Response
On February 2, 2014, a portion of the 36-inch corrugated metal stormwater pipe, which was
located under the Primary Cell of the ash basin, failed and released up to 39,000 tons of coal
ash into the Dan River. Immediate action was taken to stop the release and begin assessment
of the environmental impact. Ash deposits were removed from the immediate vicinity of the pipe
failure and other downstream locations. Duke Energy has worked extensively with various
federal, state, and local agencies to address the coal ash release to the Dan River including
removal of an estimated 4,000 cubic yards of coal ash and extensive environmental quality
monitoring.
According to a January 27, 2015 U.S. Environmental Protection Agency (USEPA) Information
Update related to the release, “Following extensive surface water and sediment sampling, no
further ash removal is planned. There have been no exceedances of human health screening
thresholds, or any recent exceedances of ecological screening thresholds, for contaminants
associated with ash. Further, removal of ash [in] some places could be more detrimental to the
ecosystem than leaving it in place.” Long-term ash deposition monitoring through July 2015 was
also directed by an Administrative Order of Consent between the USEPA and Duke Energy.
The USEPA has overseen ash deposition sampling to date and will determine whether
additional ash deposition sampling is required beyond July 2015.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-5

ES.3 Receptor Survey
Properties located within a 0.5-mile radius of the DRSS ash basin compliance boundary are
located in and southeast of Eden, Rockingham County, North Carolina. The majority of the land
is undeveloped property. Residential properties are located north and northwest of the ash
basin compliance boundary within the 0.5-mile radius. One residence is located south of DRSS
across the Dan River within the 0.5-mile radius. Two industrial properties are located northeast
of DRSS; one of these properties has a wastewater treatment plant discharging into the Dan
River. Farm land is located southeast of the station across the Dan River.
Duke Energy submitted a receptor survey to the NCDENR (HDR 2014a) in September 2014,
and subsequently submitted to NCDENR a supplement to the receptor survey (HDR 2014b) in
November 2014. The update included contacting and/or reviewing the agencies/records to
identify public and private water supply sources identified and reviewing questionnaires that
were received after the submittal of the November 2014 supplement to the September 2014
receptor survey (i.e. questionnaires received af ter October 31, 2014).
The purpose of the receptor survey was to identify the exposure locations that are critical to be
considered in the groundwater transport modeling and human health risk assessment.
The updated survey activities included contacting the following agencies and/or reviewing the
following records to identify public and private water supply sources, confirm the location of
wells, identify surface water features, and/or identify any wellhead protection areas located
within a 0.5-mile radius of the DRSS ash basin compliance boundary:
 NCDENR Department of Environmental Health (DEH) Public Water Supply Section’s
(PWSS) most current Public Water Supply Water Sources GIS point data set;
 NCDENR DWR Source Water Assessment Program (SWAP) online database for public
water supply sources;
 Environmental Data Resources (EDR) local/regional water agency records review;
 Rockingham County Environmental Health Department;
 City of Eden Director of Environmental Services;
 Dan River Water Inc., a private water utility company; and
 United States Geological Survey (USGS) National Hydrography Dataset (NHD)

The review of these records identified three private water supply wells and one private water
supply spring, not currently in use, and several tributaries to the Dan River within a 0.5-mile
radius of the ash basin compliance boundary. All three water supply wells are located more than
2,000 feet away from the Dan River ash basin compliance boundary and are either upgradient
or across the Dan River from the ash basin system. No public water supply wells or wellhead
protection areas were identified within a 0.5-mile radius of the ash basin compliance boundary.
No water supply wells (including irrigation wells and unused or abandoned wells) were identified
within the ash basin potential area of interest. Several unnamed tributaries were identified
adjacent to or downgradient of the DRSS site. No information gathered as part of this
assessment suggests that water supply wells or springs located within the 0.5-mile radius of the
compliance boundary are impacted by the Dan River ash basin system.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-6

ES.4 Sampling / Investigation Results
ES.4.1 Background Findings
As part of the CSA, Duke Energy installed four additional background monitoring wells (one
shallow, two deep, and one bedrock monitoring well) and three soil borings to provide
background soil and groundwater quality data. The background locations selected were away
from areas that may have potentially been impacted by site activities and would not be impacted
by groundwater flow from areas potentially impacted by ash. Analyses of groundwater samples
collected from these additional and existing background wells indicated that the following
naturally occurring constituents exceeded 2L Standards or IMACs in background locations:
cobalt, iron, manganese, pH, thallium, TDS, and vanadium. The results for all other constituents
were reported below 2L Standards or IMACs.
Constituent of Interest Groundwater 2L Standard
or IMACs (µg/L) Range of Exceedances
Antimony 1 <0.5 µg/L (BG-5S) to 1.21 µg/L (MW-23BR)
Arsenic 10 <0.5 µg/L (BG-5D) to 6.36 µg/L (MW-23BR)
Beryllium 4 0.087 µg/L (MW -23BR) to <0.2 µg/L (BG-5S)
Chromium 10 0.22 µg/L (MW -23BR) to 1.2 µg/L (BG-5D)
Cobalt 1 1 µg/L (MW -23BR) to 2.1 µg/L (BG-5D)
Iron 300 110 µg/L (MW -23BR) to 890 µg/L (BG-5S)
Lead 15 0.057 µg/L (MW -23D) to 0.078 µg/L (BG-5D)
Manganese 50 110 µg/L (BG-5S) to 910 µg/L (BG-5D)
pH 6.5-8.5 6.89 µg/L (MW-23D) to 7.45 µg/L (MW -23D)
Selenium 20 <1.0U µg/L (MW-23BR) to <0.5 µg/L (BG-5S)
Sulfate 250,000 29,800 µg/L (BG-5D) to 41,300 µg/L (MW -23D)
Thallium 0.2 < 0.1 µg/L (MW-23D) to 0.019 µg/L (BG-5S)
TDS 500,00 175,000 µg/L (BG-5S) to 252,000 µg/L (MW -23D)
Vanadium 0.3 <1.0 µg/L (BG-5D) to 2.6 µg/L (MW-23D)
ES.4.2 Nature and Extent of Contamination
Soil and groundwater beneath the ash basin and ash storage areas (within the compliance
boundary) have been impacted by ash handling and storage at the DRSS site as described
below. Concentrations of selected constituents exceeded their respective 2L Standards or
IMACs in groundwater beyond the compliance boundary. The extent of the contamination is
noted below:
ES.4.2.1 Groundwater – Shallow Aquifer
Arsenic and boron were the primary constituents detected in groundwater at concentrations that
exceeded the background concentrations and 2L Standards. Both constituents were detected
above the 2L Standards in a three-dimensional area beneath the ash basin and ash storage
areas in the shallow aquifer. Boron is highly soluble and was identified by the USEPA as one of
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-7

the leading indicators for releases of contaminants from ash. There are no known exceedances
of 2L Standards for arsenic or boron beyond the DRSS property boundary.
TDS and sulfate exceeded the 2L Standards in an isolated area east of the DRSS historical site
property boundary. Based on the relatively low concentrations of other ash-related constituents
in these wells, the presence of TDS and sulfate may not be attributable to groundwater
migration from the ash basin.
Within the shallow aquifer, three COIs were identified boron, sulfate, and TDS. Boron, sulfate,
and TDS rarely exceeded their respective 2L Standards in shallow groundwater samples but are
mobile and were noted at higher concentrations within and in the immediate vicinity of the ash
basin and ash storage areas than in background wells and other areas of the site likely not
influenced by the ash basin or ash storage areas. Four other COIs identified in the shallow
aquifer were isolated in specific locations and do not appear to be transported across the site:
antimony, chromium, selenium, and thallium.
Because of these characteristics, boron can be used to represent the general extent of the
shallow aquifer impacted by the ash basin and ash storage areas.
Boron, TDS and sulfate concentrations in shallow aquifer are shown on Figure ES-1. Vertical
migration of constituents is generally limited by the underlying bedrock.
ES.4.2.2 Groundwater - Bedrock Aquifer
Three of the constituents with concentrations in excess of 2L Standards and IMAC in the
bedrock aquifer (iron, manganese, and vanadium) were found to be naturally occurring metals
in the background wells. Nine other constituents were found in the bedrock aquifer in
concentrations greater than their 2L Standards or IMAC: antimony, arsenic, boron, chromium,
cobalt, selenium, sulfate, TDS, and thallium. These were detected in isolated locations and
existing evidence indicates that they have not migrated extensively across the site or beyond
the compliance boundary.
ES.4.2.3 Groundwater - East of the Ash Basin
The unnamed tributary stream located to the east of the Secondary Cell is likely a discharge
location for groundwater flowing east from the Secondary Cell. Analytical results from surface
water sample location SW -3 exceeded the 2B Standards for aluminum, arsenic, chromium,
cobalt, copper, lead, and zinc. The results of analyses from surface water sample location SW -
6, collected from the Dan River near the confluence with the tributary stream, indicate that the
Dan River has not been adversely affected by the water quality in the stream containing sample
location SW -3. A review of constituent data from adjacent well MW -21S is inconclusive as to the
correlation of the groundwater chemistry, background well data, and the SW -3 results.
ES.4.2.4 Seep Samples
Seep sampling results at the DRSS site have identified four COIs as primary constituents in the
seep water: cobalt, iron, manganese, and vanadium.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-8

Comparing COI concentrations in the seep water to the maximum COI concentrations
encountered in groundwater sampled from the background wells indicates four seep locations
(CCSW001, CCSW002, DRRC001, and S-1) where at least one seep COI concentration
exceeded the maximum groundwater COI concentration. Four COIs were identified in the seep
water are cobalt, iron, manganese, and vanadium. One or more of the identified COIs
exceeded applicable standards for all seep samples collected.
ES.4.2.5 Soil, Rock, and Sediment Samples
Soil samples were obtained from 38 separate locations during CSA drilling activities within the
DRSS site (including locations beneath the ash basin and ash storage areas). Seven COIs
were identified in soil samples obtained from these locations: arsenic (21 locations), boron (4
locations), cobalt (37 locations), iron (38 locations), manganese (37 locations), selenium (16
locations), and vanadium (38 locations). With the exception of boron and selenium, all of these
COIs appear in one or more of the background soil boring locations at concentrations exceeding
the applicable soil standard. The COI concentrations observed in the soil from the various
locations within the DRSS site generally bracket the concentrations observed in soil samples
from the background locations or within reasonable proximity of the bracketed background
concentrations.
Rock samples (including partially weathered rock [PWR] samples) were obtained from 15
separate locations during CSA drilling activities within the DRSS site, including locations
beneath the ash basin and ash storage areas. Seven COIs were identified in rock samples
obtained from these locations: arsenic (9 locations), barium (1 location), cobalt (14 locations),
iron (15 locations), manganese (14 locations), selenium (5 locations), and vanadium (14
locations). With the exception of barium, all of these COIs appear within the background
locations where rock was obtained (BG-5D and MW-23BR) at concentrations exceeding the
applicable soil standards.
Sediment samples were obtained from 3 seep and 6 surface water locations at the DRSS site.
Five COIs were identified in the sediment samples: arsenic (3 locations), cobalt (8 locations),
iron (9 locations), manganese (9 locations), and vanadium (9 locations). With the exception of
arsenic, all of these COIs appear within the background locations where sediment was obtained
(SW -5 and SW -8) at concentrations exceeding the applicable soil standards.
ES.4.3 Maximum Contaminant Concentrations
The maximum contaminant concentrations reported in groundwater, ash porewater, seep water,
and ash basin surface water samples collected during the CSA are listed below.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-9

Constituent of
Interest
Maximum Constituent of Interest Concentrations
Groundwater
(µg/L)
Ash Porewater
(µg/L)
Seep Water
(µg/L)
Ash Basin Surface Water
(µg/L)
Aluminum 6,940 13,200 3,410 613
Antimony 2.9 9.8 N/A 1.21
Arsenic 809 422 1.68 51.1
Barium 380 810 74 99
Beryllium 3.7 12.1 N/A N/A
Boron 1,310 630 130J+ 364
Cadmium 1.8 1.3 N/A N/A
Chromium 30.1 50 3.86 N/A
Cobalt 29.2 34.1 4.88 N/A
Copper 10.9 197 6.15J+ 5.11J+
Iron 36,400 25,100 5,720 323
Lead 9.42 77.4 3.97 N/A
Manganese 3,700 1,500 2,200 154
Nickel 46.9 70.1 3.3 2.5
Selenium 35.3 12.2 N/A 2.87
Sulfate 416,000 125,000 38,400 90,000
TDS 873,000 358,000 211,000 270,000
Thallium 0.55 3.4 0.036J N/A
Vanadium 15.3 254 8.06 6.65
Zinc 390 51 11J+ 212
Notes:
1. N/A indicates that a constituent was not detected above the reporting detected limit.
2. J indicates an estimated concentration.
3. J+ indicates an estimated concentration, biased high.
ES.4.4 Source Characterization
Source characterization was performed through the completion of borings and installation of
groundwater monitoring wells within the footprint of the ash basin cells and ash storage areas,
and associated solid matrix (ash) and aqueous sample (ash porewater) collection and analysis.
Ash samples were collected for analysis of physical characteristics (e.g., grain size, porosity) to
provide data for evaluation of retention/transport properties within and beneath the ash basin
and ash storage areas. Ash samples were collected for analysis of chemical characteristics
(e.g., total inorganics, leaching potential). The results of the characterization will be used to
refine the SCM and provide data for use in the CAP.
Review of laboratory analytical results of ash samples collected from the ash basin and ash
storage areas identified eight COIs: arsenic, barium, boron, cobalt, iron, manganese, selenium,
and vanadium. COIs identified in porewater in the ash basin included antimony, arsenic, barium,
beryllium, chromium, cobalt, iron, lead, manganese, thallium, and vanadium. COIs identified in
porewater in the ash storage areas included arsenic, boron, chromium, cobalt, iron, manganese,
pH, and vanadium. COIs identified in surface water within the basin included aluminum, arsenic,
copper, and zinc.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-10

SPLP (Synthetic Precipitation Leaching Procedure (SPLP) testing was conducted to evaluate
the leaching potential of constituents from ash. Results of the SPLP analyses indicated that the
following COIs exceeded their 2L Standards: antimony, arsenic, barium, beryllium, chromium,
cobalt, iron, lead, manganese, selenium, thallium, and vanadium. However, many factors
influence the transport of these COIs and potential impacts to groundwater over time will be
investigated through modeling as part of the CAP.
Four seeps (S-1 through S-4) associated with the DRSS ash basin and four NCDENR-identified
seeps (INFSW009, CSSW001, CCSW002OUT, and DRRC001) were planned to be sampled
during this CSA. Seeps S-2, S-3, S-4 and INFSW009 were dry at the time of sampling. Several
attempts were made to obtain these samples, but were unsuccessful. Constituents that
exceeded the 2L Standards in seep samples were cobalt, iron, manganese, and vanadium.
ES.4.5 Regional Geology and Hydrogeology
The DRSS site is located in the Dan River Triassic Basin within the Piedmont Physiographic
province. The Dan River Triassic Basin is in the western belt of rift basins and is bounded on the
southeast by the Milton terrane. The basin is one of several exposed rift basins that form two
parallel belts that strike northeasterly within the Piedmont province. The basins are aligned
subparallel to the Appalachian terranes (Figure 5-1). The Appalachian terranes formed along
pre-existing zones of faulting and then subsided during a period of crustal stretching (Olsen et
al. 1991).
The contact between the Triassic rocks of the basin and the crystalline rocks of the Milton belt
along the southeast basin margin is an unconformity, but several minor, northwest dipping
normal faults are present locally (Thayer 1970). Minor, interbasin normal faults are present. The
sedimentary rocks of the basin consist of interbedded conglomerate, sandstone, mudstone,
siltsone, shale, and thin coal beds (Olsen et al. 1991; Thayer and Robbins 1992). The rocks dip
moderately to steeply northwest toward the Chatham fault zone (Thayer 1970).
The hydrogeologic regime in the Dan River Basin is characterized by fractured, bedded
sedimentary sequences underlying soil and saprolite. Groundwater may occur under both
unconfined, water table conditions (similar to most Piedmont crystalline sites) and confined
conditions. Controls of groundwater flow are a combination of the interaction of factors including
topography, stratigraphic sequence and lithology, distribution and intensity of fractures,
presence of diabase intrusions (both dikes and sills), basalt flows, and weathering processes of
the bedrock (Venkatakrishnan and Gheorghiu 2003).
ES.4.6 Site Geology and Hydrogeology
Geology at the DRSS site is comprised of two interconnected layers, or mediums: 1) residual
soil/saprolite and weathered fractured rock (regolith) overlying 2) fractured bedrock (Figure 5-3).
The regolith layer is a thoroughly weathered and structureless residual soil that occurs near the
ground surface with the degree of weathering decreasing with depth. The residual soil grades
into saprolite, a coarser grained material that retains the structure of the parent bedrock.
Beneath the saprolite, partially weathered/fractured bedrock occurs with depth until sound
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-11

bedrock is encountered. The site is underlain by rocks of the Pine Hall (Tph) and Cow Branch
(Tcb) Formations (Figure 6-1). Alluvial and terrace deposits consisting of unconsolidated sand,
silt, and clay with occasional sub-rounded to well-rounded pebbles occur along the Dan River
and major tributaries. A transition zone (TZ) at the base of the regolith has been interpreted to
be present in many areas of the Piedmont and, based on this investigation, is present in the
Dan River Basin. Harned and Daniel (1989) characterize the TZ zone as consisting of partially
weathered/fractured bedrock and lesser amounts of saprolite that grade into bedrock, describing
the TZ zone as “being the most permeable part of the system, even slightly more permeable
than the soil zone”. Harned and Daniel (1989) suggest the zone may serve as a conduit of rapid
flow and transmission of water.
In general, groundwater within the shallow aquifer (S wells), TZ (D wells), and fractured bedrock
(BR wells) flows from the northern extent of the property boundary south and southeast toward
the Dan River. However, in the area north of Ash Storage 1, groundwater elevation data
suggest the presence of a groundwater divide extending from MW -12 to GWA-1 where
groundwater within the shallow aquifer and TZ flows north, away from the DRSS site. Shallow
groundwater flow direction is shown on Figure 6-5. Groundwater flow within the TZ is shown on
Figure 6-6. Groundwater flow within fractured bedrock is shown on Figure 6-7.
ES4.7 Existing Groundwater Monitoring Data
Groundwater monitoring prior to 2015 consisted of nine voluntary and seven compliance wells
installed within the DRSS property boundary. Duke Energy implemented NPDES compliance
groundwater monitoring around the DRSS ash basin in 1993, with three wells installed in 1993
and an additional well installed in 1995. During this period, the compliance wells were generally
sampled two times per year. Four additional wells were added to an expanded voluntary
monitoring program in 2008. Beginning in 2008, the complete network of eight compliance and
voluntary groundwater monitoring wells were sampled two times per year, and the analytical
results were submitted to NCDENR. In 2010, additional compliance groundwater monitoring
wells were installed at the site. Groundwater monitoring as required by the DRSS NPDES
Permit NC0003468 began in March 2011 utilizing the compliance monitoring wells. NPDES
Permit Condition A (11), Version 1.1, dated June 15, 2011, lists the groundwater monitoring
wells to be sampled, the parameters and constituents to be measured and analyzed, and the
requirements for sampling frequency and reporting results.
Elevated concentrations of boron, iron, and manganese have been detected in one or more of
the following groundwater monitoring wells: MW -20S, MW -21S/D, MW-22S/D, and MW-23D.
The distribution and magnitude of iron and manganese exceedances is indicative of background
conditions.
Historical analytical results from compliance and voluntary groundwater monitoring wells were
utilized to assess background groundwater quality and calculate statistical analyses of
groundwater results. Compliance groundwater monitoring wells were sampled as part of this
CSA to supplement the expanded groundwater assessment.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-12

ES.4.8 Screening-Level Risk Assessments
The human health and ecological screening-level risk assessments were performed as part of
this CSA and identified media-specific Contaminants of Potential Concern (COPCs) that may
adversely impact human and/or ecological receptors under site-specific exposure scenarios.
COPCs were determined by comparing maximum concentrations or Reporting Limits (RLs) of
COIs in on- and off-site sampling locations to risk-based screening level criteria for soil,
groundwater, surface water, and sediment.
Those COPCs identified during the human health screening-level risk assessment are noted
below:
 In groundwater, antimony, arsenic, barium, beryllium, boron, cadmium, chromium,
cobalt, iron, manganese, mercury, molybdenum, nickel, selenium, strontium, thallium,
and vanadium exceeded their respective screening values.
 In soil, arsenic, cobalt, iron, manganese, sodium, and thallium exceeded their respective
screening values.
 In surface water, aluminum, arsenic, cobalt and thallium maximum concentrations
exceeded their respective screening values. Beryllium, boron, total chromium, copper,
iron, lead, manganese, mercury, sodium, vanadium and zinc were also retained as
COPCs by default, based on a lack of criteria for comparison.
 In sediment, aluminum, antimony, arsenic, cobalt, iron, manganese, thallium, and
vanadium exceeded their respective screening values.
COPCs identified during the ecological screening-level risk assessment are noted below:
In soil, all COIs except cadmium, sodium, and strontium exceeded their respective
screening levels. Cadmium is the only COI that was excluded as a COPC in soil, as the
other two have no ecological criteria and were thereby retained as COPCs by default.
See Table 12-6 for detailed information, including the maximum concentrations detected.
The exceedances were typically within the same order of magnitude as the screening
levels, with the exceptions of aluminum, boron, total chromium, iron, manganese,
molybdenum, selenium, and vanadium, which were relatively higher.
 In surface water (freshwater), beryllium, cadmium, and copper exceeded their
respective screening values. Barium, cobalt, manganese, molybdenum, strontium, and
vanadium were retained based on a lack of criteria for comparison. See Table 12-7 for
detailed information on the screening performed and contaminant category for each
COPC.
 In sediment, COPCs included antimony, arsenic, cadmium and copper. In addition,
aluminum, barium, beryllium, boron, cobalt, iron, manganese, molybdenum, strontium
and vanadium were retained due to issues related to their RL exceeding the screening
value or based on a lack of criteria for comparison. Details on the COPC screening and
contaminant category are provided in Table 12-8.
COIs were not screened out as COPCs based on a comparison to background concentrations,
as the NCDENR Division of Waste Management’s Screening Level Environmental Risk
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-13

Assessment guidance (2003) does not allow for screening based on background. Site-specific
background concentrations will be considered in the uncertainty section of the baseline
ecological risk assessment, if determined to be necessary.
This initial screening does not specifically identify that health or environmental risks are present;
however, the results indicate constituents in environmental media could be of concern and
further investigation by a site-specific risk assessment may be warranted.
ES.4.9 Development of Site Conceptual Model
The human health and ecological risk assessment conceptual site models, illustrating potential
pathways of exposure from source to receptors are provided in this report.
In the initial site conceptual hydrogeologic model presented in the Work Plan, the geological and
hydrogeological features influencing the movement, chemical, and physical characteristics of
contaminants were related to the Piedmont hydrogeologic system at the site.
A hydrogeological site conceptual model was developed from data generated during previous
assessments, existing groundwater monitoring data, and 2015 groundwater assessment
activities. The CSA found that the direction of the movement of the contaminants is generally to
the south/southeast towards the Dan River with a northerly component of groundwater flow
north of Ash Storage 1 towards an unnamed tributary to the Dan River that exists north of the
DRSS site.
ES.4.10 Identification of Data Gaps
Data gaps were identified that will require further evaluation to refine the SCM through
completion of additional groundwater assessment field activities and evaluation of data collected
during those activities. The data gaps have been organized into two groups: 1) data gaps
resulting from temporal constraints and 2) data gaps resulting from evaluation of data collected
during the CSA.
ES.4.10.1 Data Gaps Resulting from Temporal Constraints
Data gaps identified in this category are generally present due to insufficient time to collect,
analyze, or evaluate data collected during the CSA activities. It is expected that the majority of
these data gaps will be remedied in a CSA supplement to be submitted to NCDENR following
completion of the second comprehensive groundwater sampling event.
Temporal data gaps include refinement of speciation sampling in groundwater monitoring wells.
The CSA speciation sampling effort was based upon anticipated groundwater flow paths and
constituents whose valence state may affect toxicity or mobility.
 Mineralogical Characterization of Soil and Rock – a total of 16 soil, three TZ, and 9
bedrock samples were submitted to three third-party mineralogical testing laboratories
for analysis of soil and rock composition. As of the date of this report, Duke Energy has
not received all of the results of this testing; however, results will be provided in the CSA
supplement.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-14

 Additional Speciation of Monitoring Wells – in order to meet the requirements of the
NORR, Duke Energy conducted speciation of groundwater samples for arsenic,
chromium, iron, manganese, and selenium from selected wells along inferred
groundwater flow transects. Speciation sampling will be performed at the following
locations during the second comprehensive sampling event: along flow transects, at ash
basin surface water sample locations, and at wells with exceedances of 2L Standards for
speciation constituents. Adjustments to the speciation sampling are proposed in Section
15.0, the results of which will be reported in the CSA supplement.
ES.4.10.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities
Data gaps resulting from evaluation of data collected include:
 Evaluation of the need for additional monitoring wells north and east of Ash Storage 1
 Evaluation of additional bedrock background groundwater monitoring wells (and
continued sampling attempts at previously dry wells such as BG-1D)
 Evaluation of impacts to surface water at SW -3 (located in the tributary stream along the
eastern property boundary), collection of seep samples (S-2 through S-4) to assess
potential groundwater discharge to surface water, and
 Additional review of information regarding areas of non-ash contamination to evaluate
potential interference with remedial efforts, if applicable.

ES.5 Conclusions
The CSA identified the horizontal and vertical extent of groundwater contamination at the DRSS
site, and found that the source of the contamination within that boundary is the coal ash
contained in the ash basin and ash storage areas. The cause of contamination is leaching of
constituents from the coal ash into the underlying soil and groundwater.
Background monitoring wells contained naturally occurring metals and other constituents at
concentrations that exceeded their respective 2L Standards or IMACs. These included cobalt,
iron, manganese, thallium, TDS, and vanadium..
The CSA identified arsenic, boron, cobalt, iron, manganese, selenium, and vanadium as soil
COIs. Groundwater COIs were identified as antimony, arsenic, boron, chromium, cobalt, iron,
manganese, selenium, sulfate, thallium, TDS, and vanadium. Cobalt, iron, manganese, and
vanadium occur naturally in regional groundwater. The CSA identified the horizontal and vertical
extent of soil contamination, with the exception of off-site areas east and north of Ash Storage 1
(as described in Section 14.1.1). Duke Energy has notified NCDENR of the need for refinement
of COI delineation north and east of Ash Storage 1, and is coordinating additional fieldwork with
NCDENR.
Movement of each contaminant is related to the groundwater flow direction, the groundwater
flow velocity, and the rate at which a particular contaminant reacts with materials in the aquifer.
The data indicates that geologic conditions present beneath the ash basins impedes the vertical
migration of contaminants. The CSA found that the direction of mobile contaminant transport is
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
EXECUTIVE SUMMARY

ES-15

generally in a southeasterly direction towards the Dan River, as anticipated, and not towards
other off-site receptors. North of Ash Storage 1 there is evidence of a northerly flow of
groundwater into an unnamed tributary which flows southeasterly towards the Dan River. No
information gathered as part of this CSA suggests that water supply wells or springs within the
0.5-mile radius of the compliance boundary are impacted by the DRSS ash basin system.
The human health and ecological screening-level risk assessments did not specifically identify
the presence of health or environmental risks; however, the results indicate that constituents in
environmental media could be of concern and further investigation by a site-specific risk
assessment may be warranted. No imminent hazards to human health and the environment
were identified during the screening-level risk assessments.
Duke Energy is required by CAMA to remove the ash in the DRSS ash basin and ash storage
areas. Based on the results of soil and groundwater samples collected beneath the ash basin
and the ash storage areas, some residual contamination will remain after excavation; however,
the degree of contamination and the persistence of this contamination over time cannot be
determined at this time. Duke Energy will pursue corrective action under 15A NCAC 02L .0106.
The approaches to corrective action under rule .0106(k) or (l) will be evaluated along with other
remedies depending on the results of groundwater modeling and evaluation of the site’s
suitability to use Monitored Natural Attenuation or other industry-accepted methodologies.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

i

Table of Contents
Section Page No.
1.0 Introduction ..................................................................................................................... 1
1.1 Purpose of Comprehensive Site Assessment .............................................................. 1
1.2 Regulatory Background ............................................................................................... 2
1.2.1 NCDENR Requirements ....................................................................................... 2
1.2.2 Notice of Regulatory Requirements ...................................................................... 3
1.2.3 Coal Ash Management Act Requirements ............................................................ 3
1.3 NCDENR-Duke Energy Correspondence ..................................................................... 4
1.4 Approach to Comprehensive Site Assessment ............................................................ 5
1.4.1 NORR Guidance ................................................................................................... 5
1.4.2 USEPA Monitored Natural Attenuation Approach ................................................. 5
1.4.3 ASTM Site Conceptual Model Guidance ............................................................... 5
1.5 Limitations and Assumptions ....................................................................................... 6
2.0 Site History and Description ............................................................................................ 8
2.1 Site Location, Acreage, and Ownership ....................................................................... 8
2.2 Site Description ............................................................................................................ 8
2.3 Adjacent Property, Zoning, and Surrounding Land Uses .............................................. 8
2.4 Adjacent Surface Water Bodies and Classifications ..................................................... 9
2.5 Meteorological Setting ................................................................................................. 9
2.6 Hydrologic Setting ........................................................................................................ 9
2.7 Permitted Activities and Permitted Waste ...................................................................10
2.8 NPDES and Surface Water Monitoring .......................................................................10
2.9 NPDES Flow Diagram ................................................................................................10
2.10 History of Site Groundwater Monitoring .......................................................................11
2.10.1 Voluntary Groundwater Monitoring Wells .............................................................12
2.10.2 Compliance Groundwater Monitoring Wells .........................................................12
2.11 Assessment Activities or Previous Site Investigations .................................................13
2.12 Decommissioning Status.............................................................................................14
3.0 Source Characteristics ...................................................................................................16
3.1 Coal Combustion and Ash Handling System ...............................................................16
3.2 Description of Ash Basin and Other Ash Storage Areas ..............................................16
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

ii

3.2.1 Primary and Secondary Ash Basin Cells ..............................................................16
3.2.2 Ash Storage 1 ......................................................................................................17
3.2.3 Ash Storage 2 ......................................................................................................17
3.2.4 Dredge Dikes .......................................................................................................18
3.3 Physical Properties of Ash ..........................................................................................18
3.4 Chemical Properties of Ash .........................................................................................19
4.0 Receptor Information ......................................................................................................21
4.1 Summary of Previous Receptor Survey Activities .......................................................21
4.2 Summary of CSA Receptor Survey Activities and Findings .........................................22
4.3 NCDENR Well Water Testing Program .......................................................................23
5.0 Regional Geology and Hydrogeology .............................................................................24
5.1 Regional Geology .......................................................................................................24
5.2 Regional Hydrogeology ...............................................................................................25
6.0 Site Geology and Hydrogeology .....................................................................................29
6.1 Site Geology ...............................................................................................................29
6.1.1 Soil Classification .................................................................................................29
6.1.2 Rock Lithology .....................................................................................................30
6.1.3 Structural Geology ...............................................................................................31
6.1.4 Fracture Trace Study ...........................................................................................31
6.1.5 Effects of Structure on Groundwater Flow ............................................................33
6.1.6 Soil and Rock Mineralogy and Chemistry .............................................................33
6.2 Site Hydrogeology.......................................................................................................34
6.2.1 Groundwater Flow Direction .................................................................................34
6.2.2 Hydraulic Gradient ...............................................................................................34
6.2.3 Effects of Geologic/Hydrogeologic Characteristics on Contaminants ...................35
6.2.4 Site Hydrogeologic Conceptual Model .................................................................35
7.0 Source Characterization .................................................................................................36
7.1 Ash Basin ...................................................................................................................36
7.1.1 Ash (Sampling and Chemical Characteristics) .....................................................36
7.1.2 Ash Basin Surface Water (Sampling and Chemical Characteristics) ....................36
7.1.3 Ash Porewater (Sampling and Chemical Characteristics) ....................................36
7.1.4 Ash Porewater Speciation ....................................................................................37
7.1.5 Radiological Laboratory Testing ...........................................................................37
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

iii

7.2 Ash Storage Areas ......................................................................................................37
7.2.1 Ash (Sampling and Chemical Characteristics) .....................................................37
7.2.2 Ash Porewater (Sampling and Chemical Characteristics) ....................................38
7.3 Leaching Potential of Ash ...........................................................................................38
7.4 Seeps .........................................................................................................................38
7.4.1 Review of NCDENR March 2014 Sampling Results .............................................38
7.4.2 Ash Basin and NCDENR Seep Sampling Results – CSA Activities ......................39
7.5 COIs Exceeding Applicable Standards........................................................................39
7.5.1 COIs in Ash .........................................................................................................39
7.5.2 COIs in Surface Water .........................................................................................40
7.5.3 COIs in Ash Porewater ........................................................................................40
7.5.4 COIs in Seeps and Stormwater ............................................................................40
8.0 Soil and Rock Characterization ......................................................................................41
8.1 Background Sample Locations ...................................................................................41
8.2 Analytical Methods and Results ..................................................................................41
8.3 Comparison of Soil Results to Applicable Levels ........................................................41
8.4 Comparison of Soil Results to Background .................................................................42
8.4.1 Background Soil, PWR, and Rock ........................................................................42
8.4.2 Soil, PWR, and Rock Beneath the Ash Basin ......................................................42
8.4.3 Soil, PWR, and Rock Beneath the Ash Storage Areas .........................................42
8.4.4 Soil, PWR and Rock Outside the Waste Boundary ..............................................42
9.0 Surface Water and Sediment Characterization ...............................................................44
9.1 Surface Water .............................................................................................................44
9.1.1 Comparison of Exceedances to 2B Standards .....................................................44
9.1.2 Comparison of Exceedances to Background........................................................44
9.1.3 Discussion of Results for Constituents without 2B Standards ..............................45
9.2 Surface Water Speciation ...........................................................................................46
9.3 Sediments ...................................................................................................................47
10.0 Groundwater Characterization ........................................................................................48
10.1 Regional Groundwater Data for Constituents of Interest .............................................48
10.1.1 Antimony ..............................................................................................................48
10.1.2 Arsenic.................................................................................................................49
10.1.3 Barium .................................................................................................................49
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

iv

10.1.4 Beryllium ..............................................................................................................50
10.1.5 Boron ...................................................................................................................51
10.1.6 Chromium ............................................................................................................51
10.1.7 Cobalt ..................................................................................................................51
10.1.8 Iron ......................................................................................................................51
10.1.9 Lead ....................................................................................................................52
10.1.10 Manganese ......................................................................................................52
10.1.11 Selenium ..........................................................................................................53
10.1.12 Sulfate ..............................................................................................................54
10.1.13 Thallium ...........................................................................................................54
10.1.14 Vanadium .........................................................................................................55
10.1.15 pH ....................................................................................................................55
10.2 Background Wells .......................................................................................................56
10.3 Discussion of Redox Conditions ..................................................................................57
10.4 Groundwater Analytical Results ..................................................................................57
10.4.1 Ash Basin: Primary and Secondary Cells .............................................................58
10.4.2 Ash Storage Areas ...............................................................................................58
10.4.3 Beyond the Waste Boundary ...............................................................................58
10.4.4 Off-Site ................................................................................................................58
10.5 Comparison of Results to 2L Standards ......................................................................59
10.6 Comparison of Results to Background ........................................................................59
10.6.1 Background .........................................................................................................59
10.6.2 Ash Basin: Primary and Secondary Cells .............................................................60
10.6.3 Ash Storage Areas ...............................................................................................60
10.6.4 Beyond the Waste Boundary ...............................................................................60
10.6.5 Off-Site ................................................................................................................60
10.7 Groundwater Geochemistry ........................................................................................61
10.8 Groundwater Speciation .............................................................................................61
10.9 Radiological Laboratory Testing ..................................................................................62
10.10 CCR Rule Groundwater Detection and Assessment Monitoring Parameters ...........62
11.0 Hydrogeological Investigation .........................................................................................64
11.1 Hydrostratigraphic Layer Development .......................................................................64
11.2 Hydrostratigraphic Layer Properties ............................................................................65
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

v

11.2.1 Borehole In-Situ Tests .........................................................................................65
11.2.2 Monitoring Well and Observation Well Slug Tests ................................................66
11.2.3 Laboratory Permeability Tests .............................................................................67
11.2.4 Hydrostratigraphic Layer Parameters ...................................................................67
11.3 Vertical Hydraulic Gradients ........................................................................................67
11.4 Groundwater Velocity ..................................................................................................67
11.5 Contaminant Velocity ..................................................................................................68
11.6 Plume's Physical and Chemical Characterization ........................................................68
11.6.1 Shallow Aquifer ....................................................................................................69
11.6.2 Bedrock Aquifer ...................................................................................................70
11.7 Groundwater / Surface Water Interaction ....................................................................70
11.8 Estimated Seasonal High and Seasonal Low Groundwater Elevations – Compliance
and Voluntary Wells ...............................................................................................................70
12.0 Screening Level Risk Assessment ..................................................................................71
12.1 Human Health Screening ............................................................................................71
12.1.1 Introduction ..........................................................................................................71
12.1.2 Site Conceptual Model .........................................................................................71
12.1.3 Human Health Risk-Based Screening Levels .......................................................74
12.1.4 Site-Specific Risk Based Remediation Standards ................................................75
12.1.5 NCDENR Receptor Well Investigation .................................................................75
12.1.6 Human Health Screening Summary .....................................................................75
12.2 Ecological Screening ..................................................................................................76
12.2.1 Introduction ..........................................................................................................76
12.2.2 Ecological Setting ................................................................................................76
12.2.3 Fate and Transport Mechanisms ..........................................................................81
12.2.4 Comparison to Ecological Screening Levels ........................................................81
12.2.5 Uncertainty and Data Gaps ..................................................................................82
12.2.6 Scientific/Management Decision Point .................................................................83
12.2.7 Ecological Risk Screening Summary ...................................................................83
13.1 Fate and Transport Groundwater Modeling .................................................................84
13.2 Batch Geochemical Modeling .....................................................................................85
13.3 Geochemical Site Conceptual Model ..........................................................................85
14.0 Data Gaps – Site Conceptual Model Uncertainties .........................................................88
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
TABLE OF CONTENTS

vi

14.1 Data Gaps ..................................................................................................................88
14.1.1 Data Gaps Resulting from Temporal Constraints .................................................88
14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities .........89
14.2 Site Heterogeneities ....................................................................................................89
14.3 Impact of Data Gaps and Site Heterogeneities ...........................................................89
15.0 Planned Sampling for CSA Supplement .........................................................................90
15.1 Sampling Plan for Inorganic Constituents ...................................................................90
15.2 Sampling Plan for Speciation Constituents .................................................................90
16.0 Interim Groundwater Monitoring Plan .............................................................................91
16.1 Sampling Frequency ...................................................................................................91
16.2 Constituent and Parameter List ...................................................................................91
16.3 Proposed Sampling Locations ....................................................................................91
16.4 Proposed Background Wells .......................................................................................91
17.0 Discussion ......................................................................................................................92
17.1 Summary of Completed and Ongoing Work ................................................................92
17.2 Nature and Extent of Contamination ...........................................................................93
17.2.1 Groundwater – Surficial Aquifer ...........................................................................93
17.2.2 Groundwater - Bedrock Aquifer ............................................................................93
17.2.3 Groundwater - East of the Ash Basin ...................................................................94
17.3 Maximum Contaminant Concentrations ......................................................................94
17.4 Contaminant Migration and Potentially Affected Receptors .........................................95
18.0 Conclusions ....................................................................................................................96
18.1 Source and Cause of Contamination ..........................................................................96
18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate them in
Accordance to 15A NCAC 02L .0106(f) .................................................................................96
18.3 Receptors and Significant Exposure Pathways ...........................................................96
18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination and Significant
Factors Affecting Contaminant Transport ..............................................................................96
18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and
Physical Character of the Contaminants ................................................................................98
18.6 Proposed Continued Monitoring ..................................................................................99
18.7 Preliminary Evaluation of Corrective Action Alternatives .............................................99
19.0 References ................................................................................................................... 100

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

vii

List of Figures (organized by CSA report section)
Executive Summary
 ES-1: Site Conceptual Model – Plan View Map

1.0 Introduction
<No Figures>

2.0 Site History and Description
 Figure 2-1: Site Location Map
 Figure 2-2: Site Layout Map
 Figure 2-3: Pre-Ash Basin USGS Map
 Figure 2-4: Site Features Map
 Figure 2-5: Site Vicinity Map
 Figure 2-6: Dan River Steam Station Water Schematic Flow Diagram
 Figure 2-7: Compliance and Voluntary Monitoring Wells

3.0 Source Characteristics
 Figure 3-1: Photo of Fly Ash and Bottom Ash
 Figure 3-2: Elemental Composition for Bottom Ash, Fly Ash, Shale, and Volcanic
Ash
 Figure 3-3: Coal Ash TCLP Leachate Concentration vs. Regulatory Limits
 Figure 3-4: Trace Elements in Fly Ash vs Soil
 Figure 3-5: Trace Elements in Bottom Ash vs Soil

4.0 Receptor Information
 Figure 4-1: Receptor Map – USGS Base
 Figure 4-2: Receptor Map – Aerial Base
 Figure 4-3: Ash Basin Underground Features Map
 Figure 4-4: Ash Storage Area Underground Features Map
 Figure 4-5: Surface Water Bodies s
 Figure 4-6: Contiguous Property Owners to the Ash Basin Waste Boundary

5.0 Regional Geology and Hydrogeology
 Figure 5-1: Tectonostratigraphic Map of the Southern and Central Appalachians
 Figure 5-2: Regional Geologic Map
 Figure 5-3: Interconnected, Two-Medium Piedmont Groundwater System
 Figure 5-4: Conceptual Variations of the Transition Zone due to Rock Type /
Structure
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

viii

 Figure 5-5: Piedmont Slope-Aquifer System

6.0 Site Geology and Hydrogeology
 Figure 6-1: Site Geologic Map
 Figure 6-2: Monitoring Well and Sample Location with Transects Map
 Figure 6-3: Topographic Lineaments and Rose Diagram
 Figure 6-4: Aerial Photography Lineaments and Rose Diagram
 Figure 6-5: Water Table Surface Map – S Wells
 Figure 6-6: Potentiometric Surface Map – D Wells
 Figure 6-7: Potentiometric Surface Map – BR Wells

7.0 Source Characterization
 Figure 7-1: Source Characterization Sample Location Map

8.0 Soil and Rock Characterization
 Figure 8-1: Soil Analytical Results – Plan View (PSRG Exceedances)
 Figure 8-2: Cross Section A-A’ Solid Matrix Analytical Results
 Figure 8-3: Cross Section B-B’ Solid Matrix Analytical Results
 Figure 8-4: Cross Section C-C’ Solid Matrix Analytical Results
 Figure 8-5: Cross Section D-D’ Solid Matrix Analytical Results

9.0 Surface Water and Sediment Characterization
 Figure 9-1: Seep and Surface Water Sample Locations
 Figure 9-2: NCDENR March 2014 Sample Locations

10.0 Groundwater Characterization
 Figure 10-1: Mean Arsenic Groundwater Concentrations by County
 Figure 10-2: Mean Iron Groundwater Concentrations by County
 Figure 10-3: Manganese Concentrations in Well Water Compared to Soil Systems
 Figure 10-4: Regional Groundwater Quality – Manganese
 Figure 10-5: Regional Groundwater Quality - pH
 Figure 10-6: Thallium Distribution in Soil
 Figure 10-7: Regional Groundwater Quality - Vanadium
 Figure 10-8: Monitoring Well and Sample Location Map
 Figure 10-9: Typical Well Construction Details
 Figure 10-10: Time Series Plot: Compliance Well MW -20S Antimony vs. Turbidity
 Figure 10-11: Time Series Plot: Compliance Well MW -21S Antimony vs. Turbidity
 Figure 10-12: Time Series Plot: Compliance Well MW -22D Antimony vs. Turbidity
 Figure 10-13: Time Series Plot: Compliance Well MW -21S Arsenic vs. Turbidity
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

ix

 Figure 10-14: Time Series Plot: Compliance Well MW-20S Iron vs. Turbidity
 Figure 10-15: Time Series Plot: Compliance Well MW -22S Iron vs. Turbidity
 Figure 10-16: Time Series Plot: Compliance Well MW -22D Iron vs. Turbidity
 Figure 10-17: Time Series Plot: Compliance Well MW -23D Iron vs. Turbidity
 Figure 10-18: Time Series Plot: Compliance Well MW -20S Manganese vs. Turbidity
 Figure 10-19: Time Series Plot: Compliance Well MW -20D Manganese vs. Turbidity
 Figure 10-20: Time Series Plot: Compliance Well MW -21S Manganese vs. Turbidity
 Figure 10-21: Time Series Plot: Compliance Well MW -21D Manganese vs. Turbidity
 Figure 10-22: Time Series Plot: Compliance Well MW -22S Manganese vs. Turbidity
 Figure 10-23: Time Series Plot: Compliance Well MW -22D Manganese vs. Turbidity
 Figure 10-24: Time Series Plot: Compliance Well MW-23D Manganese vs. Turbidity
 Figure 10-25: Time Series Plot: Compliance Well MW -20S pH vs. Turbidity
 Figure 10-26: Time Series Plot: Compliance Well MW -21S pH vs. Turbidity
 Figure 10-27: Time Series Plot: Compliance Well MW -23D pH vs. Turbidity
 Figure 10-28: Time Series Plot: Compliance Well MW -21D Sulfate vs. Turbidity
 Figure 10-29: Time Series Plot: Compliance Well MW -21D Total Dissolved Solids
(TDS) vs. Turbidity
 Figure 10-30: Time Series Plot: Shallow Compliance Monitoring Wells - Antimony
 Figure 10-31: Time Series Plot: Deep Compliance Monitoring Wells - Antimony
 Figure 10-32: Time Series Plot: Shallow Compliance Monitoring Wells – Arsenic
 Figure 10-33: Time Series Plot: Deep Compliance Monitoring Wells – Arsenic
 Figure 10-34: Time Series Plot: Shallow Compliance Monitoring Wells – Boron
 Figure 10-35: Time Series Plot: Deep Compliance Monitoring Wells – Boron
 Figure 10-36: Time Series Plot: Shallow Compliance Monitoring Wells – Iron
 Figure 10-37: Time Series Plot: Deep Compliance Monitoring W ells – Iron
 Figure 10-38: Time Series Plot: Shallow Compliance Monitoring Wells – Manganese
 Figure 10-39: Time Series Plot: Deep Compliance Monitoring Wells – Manganese
 Figure 10-40: Time Series Plot: Shallow Compliance Monitoring Wells – pH
 Figure 10-41: Time Series Plot: Deep Compliance Monitoring Wells – pH
 Figure 10-42: Time Series Plot: Shallow Compliance Monitoring Wells – Sulfate
 Figure 10-43: Time Series Plot: Deep Compliance Monitoring Wells – Sulfate
 Figure 10-44: Time Series Plot: MW -20S vs MW -23D(BG) – Manganese (Total)
 Figure 10-45: Time Series Plot: MW -20D vs MW -23D(BG) – Manganese (Total)
 Figure 10-46: Time Series Plot: MW -21S vs MW-23D(BG) – Manganese (Total)
 Figure 10-47: Time Series Plot: MW -21D vs MW -23D(BG) – Manganese (Total)
 Figure 10-48: Time Series Plot: MW -22S vs MW-23D(BG) – Manganese (Total)
 Figure 10-49: Time Series Plot: MW -22D vs MW -23D(BG) – Manganese (Total)
 Figure 10-50: Time Series Plot: MW -20S vs MW-23D(BG) – Iron (Total)
 Figure 10-51: Time Series Plot: MW -22S vs MW-23D(BG) – Iron (Total)
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

x

 Figure 10-52: Time Series Plot: MW -22D vs MW -23D(BG) – Iron (Total)
 Figure 10-53: Time Series Plot: MW -20S vs MW-23D(BG) – pH (Field)
 Figure 10-54: Time Series Plot: MW -21S vs MW-23D(BG) – pH (Field)
 Figure 10-55: Stacked Time Series Plot: Manganese Exceedances for Compliance
Wells
 Figure 10-56: Stacked Time Series Plot: Iron Exceedances for Compliance Wells
 Figure 10-57: MW-20S vs MW -23D (BG) Ratio of Concentrations
 Figure 10-58: MW-20D vs MW-23D (BG) Ratio of Concentrations
 Figure 10-59: MW-21S vs MW -23D (BG) Ratio of Concentrations
 Figure 10-60: MW-21D vs MW-23D (BG) Ratio of Concentrations
 Figure 10-61: MW-22S vs MW -23D (BG) Ratio of Concentrations
 Figure 10-62: MW-22D vs MW-23D (BG) Ratio of Concentrations
 Figure 10-63: Groundwater Analytical Results – Plan View (2L Exceedances)
 Figure 10-64: Antimony Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-65: Antimony Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-66: Figure 10-3: Antimony Isoconcentration Contour Map – Shallow
Aquifer (BR Wells)
 Figure 10-67: Arsenic Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-68: Arsenic Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-69: Arsenic Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-70: Beryllium Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-71: Beryllium Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-72: Beryllium Isoconcentration Contour Map – Shallow Aquifer (BR Wells)
 Figure 10-73: Boron Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-74: Boron Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-75: Boron Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-76: Chromium Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-77: Chromium Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-78: Chromium Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-79: Cobalt Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-80: Cobalt Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-81: Cobalt Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-82: Iron Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-83: Iron Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-84: Iron Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-85: Manganese Isoconcentration Contour Map – Shallow Aquifer (S
Wells)
 Figure 10-86: Manganese Isoconcentration Contour Map – Shallow Aquifer (D
Wells)
 Figure 10-87: Manganese Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-88: Selenium Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-89: Selenium Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-90: Selenium Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-91: Sulfate Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-92: Sulfate Isoconcentration Contour Map – Shallow Aquifer (D Wells)
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

xi

 Figure 10-93: Sulfate Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-94: TDS Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-95: TDS Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-96: TDS Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-97: Thallium Isoconcentration Contour Map – Shallow Aquifer (S Wells)
 Figure 10-98: Thallium Isoconcentration Contour Map – Shallow Aquifer (D Wells)
 Figure 10-99: Thallium Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-100: Vanadium Isoconcentration Contour Map – Shallow Aquifer (S
Wells)
 Figure 10-101: Vanadium Isoconcentration Contour Map – Shallow Aquifer (D
Wells)
 Figure 10-102: Vanadium Isoconcentration Contour Map – Deep Aquifer (BR Wells)
 Figure 10-103: Cross Section A-A’ with Groundwater Analytical Results
 Figure 10-104: Cross Section B-B’ with Groundwater Analytical Results
 Figure 10-105: Cross Section C-C’ with Groundwater Analytical Results
 Figure 10-106: Cross Section D-D’ with Groundwater Analytical Results
 Figure 10-107: Cation/Anion Concentrations in Ash Basin Porewater Samples
 Figure 10-108: Cation/Anion Concentrations in Surface Water and Ash Basin Water
 Figure 10-109: Cation/Anion Concentrations in Seeps
 Figure 10-110: Cation/Anion Concentrations in Background Wells
 Figure 10-111.1: Cation/Anion Concentrations in Shallow Wells (S Wells)
 Figure 10-111.2: Cation/Anion Concentrations in Shallow Wells (S Wells)
 Figure 10-112.1: Cation/Anion Concentrations in Deep Wells (D Wells)
 Figure 10-112.2: Cation/Anion Concentrations in Deep Wells (D Wells)
 Figure 10-112.3: Cation/Anion Concentrations in Deep Wells (D Wells)
 Figure 10-113.1: Cation/Anion Concentrations in Bedrock Wells (BR Wells)
 Figure 10-113.2: Cation/Anion Concentrations in Bedrock Wells (BR Wells)
 Figure 10-114: Sulfate/Chloride Ratio in Ash Basin Porewater Samples
 Figure 10-115: Sulfate/Chloride Ratio in Surface Water and Ash Basin Samples
 Figure 10-116: Sulfate/Chloride Ratio in Seep Samples
 Figure 10-117: Sulfate/Chloride Ratio in Background Monitoring Wells
 Figure 10-118.1: Sulfate/Chloride Ratio in Shallow Wells
 Figure 10-118.2: Sulfate/Chloride Ratio in Shallow Wells
 Figure 10-119.1: Sulfate/Chloride Ratio in Deep Wells
 Figure 10-119.2: Sulfate/Chloride Ratio in Deep Wells
 Figure 10-120: Sulfate/Chloride Ratio in Bedrock Wells
 Figure 10-121: Piper Diagram: Seeps and Surface Water
 Figure 10-122: Piper Diagram: Ash Basin Water, Porewater, Seeps, and
Background Wells
 Figure 10-123: Piper Diagram: Ash Basin Water, Porewater, and Backgrounds
Monitoring Wells
 Figure 10-124: Piper Diagram: Ash Basin Porewater, Surface Water and
Downgradient Monitoring Wells
 Figure 10-125: Detection Monitoring Constituents Detected in Shallow Wells
 Figure 10-126: Detection Monitoring Constituents Detected in Deep Wells
 Figure 10-127: Detection Monitoring Constituents Detected in Bedrock Wells
 Figure 10-128: Assessment Monitoring Constituents Detected in Shallow Wells
 Figure 10-129: Assessment Monitoring Constituents Detected in Deep Wells
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF FIGURES

xii

 Figure 10-130: Assessment Monitoring Constituents Detected in Bedrock Wells
Hydrogeological Investigation
 Figure 11-1: Major Transects
 Figure 11-2: Hydrostratigraphic Cross Section A-A’
 Figure 11-3: Hydrostratigraphic Cross Section B-B’
 Figure 11-4: Hydrostratigraphic Cross Section C-C’
 Figure 11-5: Hydrostratigraphic Cross Section D-D’
 Figures 11-6: Comparison of Groundwater and Surface Water – Plan View (2L
Exceedances)
 Figure 11-7: Groundwater Velocities – S Wells
 Figure 11-8: Groundwater Velocities – D Wells
 Figure 11-9: Groundwater Velocities – BR Wells
Screening Level Risk Assessment
 Figure 12-1 Human Health Screening Conceptual Site Model
 Figure 12-2: Ecological Screening Conceptual Site Model
Groundwater Modeling
<No Figures>
Data Gaps – Conceptual Site Model Uncertainties
<No Figures>
Planned Sampling for CSA Supplement
<No Figures>
Interim Groundwater Monitoring Plan
<No Figures>
Discussion
<No Figures>
Conclusions and Recommendations
<No Figures>
References
<No Figures>
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF TABLES

xiii

List of Tables (organized by CSA report section)
Executive Summary
<No Tables>

1.0 Introduction
 Table 1-1: Comparison of Sampling Data to Federal and State Regulatory
Standards

2.0 Site History and Description
 Table 2-1: NPDES Groundwater Monitoring Requirements
 Table 2-2: Exceedances of 2L Standards at Compliance Wells (January 2011 – May
2015)
 Table 2-3: Summary of Onsite Environmental Incidents

3.0 Source Characteristics
 Table 3-1: Range (10th percentile – 90th percentile) in Bulk Composition of Fly Ash,
Bottom Ash, Rock, and Soil

4.0 Receptor Information
 Table 4-1: Public and Private Water Supply Wells within 0.5-mile Radius of Ash
Basin Compliance Boundary
 Table 4-2: Property Owner Addresses Contiguous to the Ash Basin Waste
Boundary

5.0 Regional Geology and Hydrogeology
<No Tables>

6.0 Site Geology and Hydrogeology
 Table 6-1: Soil Mineralogy Results
 Table 6-2: Soil Chemistry Results – Oxides
 Table 6-3: Soil Chemistry Results – Elemental
 Table 6-4: Transition Zone Mineralogy Results
 Table 6-5: Transition Zone Mineralogy Results – Oxides
 Table 6-6: Whole Rock Chemistry – Oxides
 Table 6-7: Whole Rock Chemistry – Elemental
 Table 6-8: Summary of Horizontal Hydraulic Gradient Calculations

7.0 Source Characterization
 Table 7-1: Solid Matrix Parameters and Analytical Methods
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF TABLES

xiv

 Table 7-2.1: Ash Sample Results - Ash Basin
 Table 7-2.2: Ash Sample Results – Ash Storage Area
 Table 7-3: Aqueous Matrix Parameters and Analytical Methods
 Table 7-4: Ash Basin Surface Water Sample Results
 Table 7-5: Ash Basin Porewater Sample Results
 Table 7-6: Porewater Speciation Results
 Table 7-7: Porewater Radiological Testing Results
 Table 7-8: Ash Sample SPLP Results
 Table 7-9: NCDENR March 2014 Sampling Results
 Table 7-10: Seep Sample Results
 Table 7-11: Seep Speciation Results

8.0 Soil and Rock Characterization
 Table 8-1: Solid Matrix Sampling Plan
 Table 8-2: Soil, Ash, and Rock Parameters and Constituent Analysis – Analytical
Methods
 Table 8-3: Total Inorganic Results – Background Soil
 Table 8-4: Total Inorganic Results – Background PWR and Bedrock
 Table 8-5: Total Inorganic Results – Soil
 Table 8-6: Totals Inorganic Results – PWR and Bedrock
 Table 8-7: Frequency and Concentration Ranges for COI Exceedances of North
Carolina PSRGs
 Table 8-8: Range of Constituent Concentrations and Comparison to Range of
Background Soil, PWR, and Bedrock Concentrations – Beneath Ash Basin
 Table 8-9: Range of Constituent Concentrations and Comparison to Range of
Background Soil, PWR, and Bedrock Concentrations – Beneath the Ash Storage
Areas
 Table 8-10: Range of Constituent Concentrations and Comparison to Range of
Background Soil, PWR, and Bedrock Concentrations – Outside Waste Boundary

9.0 Surface Water and Sediment Characterization
 Table 9-1: Surface Water Sample Results – Totals and Dissolved
 Table 9-2: Frequency and Concentration Ranges for COI Exceedances of North
Carolina 2B Standards
 Table 9-3: Range of Constituent Concentrations and Comparison to Range of
Background Surface Water Concentrations – Ash Basin Surface Water
 Table 9-4: Range of Constituent Concentrations and Comparison to Range of
Background Surface Water Concentrations – Dan River Surface Water
 Table 9-5: Range of Constituent Concentrations and Comparison to Range of
Background Surface Water Concentrations – Tributary Stream Surface Water
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF TABLES

xv

 Table 9-6: Range of Constituent Concentrations Without 2B Standards and
Comparison to Range of Background Surface Water Concentrations – Ash Basin
Surface Water
 Table 9-7: Range of Constituent Concentrations Without 2B Standards and
Comparison to Range of Background Surface Water Concentrations – Dan River
Surface Water
 Table 9-8: Range of Constituent Concentrations Without 2B Standards and
Comparison to Range of Background Surface Water Concentrations – Tributary
Stream Surface Water
 Table 9-9: Surface Water Speciation Results
 Table 9-10: Sediment Sample Results – Totals

10.0 Groundwater Characterization
 Table 10-1: COIs Near DRSS with Associated State and Federal Drinking Water
Standards
 Table 10-2: Regional Average Concentrations of Iron in Groundwater
 Table 10-3: Regional Average Concentrations of Manganese in Groundwater
 Table 10-4: Concentration of Manganese in 20-Mile Radius Surrounding DRSS
 Table 10-5: Concentration of Vanadium in 20-Mile Radius Surrounding DRSS
 Table 10-6: Monitoring Well Construction Information
 Table 10-7: Compliance and Voluntary Well Construction Information
 Table 10-8: Redox Potential
 Table 10-9: Background Groundwater Sample Results
 Table 10-10: Ash Basin Groundwater Sample Results
 Table 10-11: Groundwater Sample Results
 Table 10-12: Groundwater Sample Results Compared to North Carolina 2L
Standards
 Table 10-13: Range of Constituent Concentrations and Comparison to Range of
Background Groundwater Concentrations – Beneath Ash Basin
 Table 10-14: Range of Constituent Concentrations and Comparison to Range of
Background Groundwater Concentrations – Beneath Ash Storage Area
 Table 10-15: Range of Constituent Concentrations and Comparison to Range of
Background Groundwater Concentrations – Beyond Waste Boundary
 Table 10-16: Range of Constituent Concentrations and Comparison to Range of
Background Groundwater Concentrations – Off-Site
 Table 10-17: Groundwater Speciation Results
 Table 10-18: Groundwater Radiological Testing Results

11.0 Hydrogeological Investigation
 Table 11-1: Soil/Material Properties for Ash, Fill, Alluvium, Soil/Saprolite
 Table 11-2: Field Permeability Test Results
 Table 11-3: Slug Test Permeability Results
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF TABLES

xvi

 Table 11-4: Historic Slug Test Permeability Results
 Table 11-5: Laboratory Permeability Test Results
 Table 11-6: Hydrostratigraphic Layer Properties – Horizontal Hydraulic Conductivity
 Table 11-7: Hydrostratigraphic Layer Properties – Vertical Hydraulic Conductivity
 Table 11-8: Total Porosity for Upper Hydrostratigraphic Units (A, F, S, M1, and M2)
 Table 11-9: Estimated Effective Porosity/Specific Yield and Specific Storage for
Upper Hydrostratigraphic Units (A, F, S, M1, and M2)
 Table 11-10: Total Porosity, Secondary (Effective) Porosity/Specific Yield, and
Specific Storage for Lower Hydrostratigraphic Units (TZ and BR)
 Table 11-11: Hydraulic Gradients –Vertical
 Table 11-12: Groundwater Velocities

12.0 Screening Level Risk Assessment

 Table 12-1: Selection of Human Health COPCs – Groundwater
 Table 12-2: Selection of Human Health COPCs – Soil
 Table 12-3: Selection of Human Health COPCs – Surface Water
 Table 12-4: Selection of Human Health COPCs – Sediment
 Table 12-5: Contaminants of Potential Human Health Concern
 Table 12-6: Selection of Ecological COPCs – Soil
 Table 12-7: Selection of Ecological COPCs – Freshwater
 Table 12-8: Selection of Ecological COPCs – Sediment
 Table 12-9: Contaminants of Potential Ecological Concern
 Table 12-10: Threatened and Endangered Species in Rockingham County

13.0 Groundwater Modeling
<No Tables>

14.0 Data Gaps – Conceptual Site Model Uncertainties
<No Tables>

15.0 Planned Sampling for CSA Supplement
 Table 15-1: Wells with 2L Standard Exceedances – Constituents to be Speciated

16.0 Interim Groundwater Monitoring Plan
 Table 16-1: Recommended Parameters and Constituents
 Table 16-2: Sample Locations in Interim Groundwater Monitoring Plan

17.0 Discussion
 Table 17-1: Maximum Contaminant Concentrations
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF TABLES

xvii

18.0 Conclusions and Recommendations
<No Tables>

19.0 References
<No Tables>
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF APPENDICES

xviii

List of Appendices (provided electronically)

Appendix A: Introduction
 NORR Letter
 Summary of Work Plan Submittals and NCDENR-Duke Energy Correspondence
 Revised Groundwater Assessment Work Plan

Appendix B: Receptor Information
 Updated Receptor Survey Report

Appendix C: Source Characterization
 Drilling Procedures
 Drilling and Installation Variances

Appendix D: Soil and Rock Characterization
 Sampling Procedures
 Sampling Variances

Appendix E: Field, Sampling, and Data Analysis Quality Assurance / Quality
Control
 Field and Sampling Quality Assurance / Quality Control Procedures
 Data Analysis Quality Assurance / Quality Control Procedures

Appendix F: Surface Water and Sediment Characterization
 Sampling Procedures
 Sampling Variances

Appendix G: Groundwater Characterization
 Well Development Procedure
 Well Development Forms
 Sampling Procedures
 Sampling Forms
 Sampling Variances
 Evaluation of Turbidity in Existing Voluntary and Compliance Wells
 Evaluation of Need for Off-site Monitoring Wells
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF APPENDICES

xix

Statistical Analysis of Groundwater Results

Appendix H: Hydrogeological Investigation
 Boring Logs
 Well Construction Records
 Historical Boring Logs and Well Construction Records
 Soil Physical Lab Reports
 Mineralogy Lab Reports
 Slug Test Reports
 Field Permeability Data
 Historic Permeability Data
 Fetter-Bear Diagrams – Porosity
 Estimated Seasonal High and Low Groundwater Elevations Calculation

Appendix I: Screening Level Risk Assessment Supporting Data
 Trustee Letters and Responses
 Checklist for Ecological Assessments/Sampling

Appendix J: Historical Analytical Results Table

Appendix K: Laboratory Reports

Appendix L: Soil Sample and Rock Core Photographs

Appendix M: Certification Form for CSA

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF ACRONYMS AND ABBREVIATIONS

xx

List of Acronyms and Abbreviations
µg/L micrograms per liter
2L Standards 15A NCAC 02L .0202 Groundwater Quality Standards
AMEC AMEC Environment & Infrastructure
APS NCDENR DWR Aquifer Protection Section
AST Aboveground Storage Tank
ASTM American Society for Testing and Materials
BG Background
bgs Below ground surface
BR Bedrock
CAMA Coal Ash Management Act
CAP Corrective Action Plan
CCR Coal Combustion Residuals
COI Constituent of Interest
COPC Contaminant of Potential Concern
CSA Comprehensive Site Assessment
CSM Conceptual Site Model
DEH NCDENR Department of Environmental Health
DO Dissolved oxygen
DRCCS Dan River Combined Cycle Station
DRSS Dan River Steam Station
DTW Depth to Water
Duke Energy Duke Energy Carolinas, LLC
DWR NCDENR Division of Water Resources
EDR Environmental Data Resources
EPD Georgia Environmental Protection Division
EPRI Electric Power Research Institute
ESH Estimated Seasonal High
ESL Estimated Seasonal Low
GSCM Geochemical Site conceptual model
GIS Geographic Information Systems
HFO Hydrous ferric oxide
HQ Hazard Quotient
IMAC Interim Maximum Allowable Concentration
Kd Sorption Coefficient
mD millidarcies
MDL Method detection limit
mg/kg Milligrams per kilogram
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF ACRONYMS AND ABBREVIATIONS

xxi

mm milligrams
MNA Monitored Natural Attenuation
MRL Method reporting limit
MW Megawatt
N Standard Penetration Testing Values
NRCS Natural Resources Conservation Service
NCAC North Carolina Administrative Code
NCDENR North Carolina Department of Environment and Natural Resources
NCDHHS North Carolina Department of Health and Human Services
NCNHP North Carolina Natural Heritage Program
NCWRC North Carolina Wildlife Resources Commission
ng/L Nanograms per liter
NHD USGS National Hydrography Dataset
NORR Notice of Regulatory Requirements
NPDES National Pollutant Discharge Elimination System
NTU Nephelometric Turbidity Unit
NURE National Uranium Resource Evaluation
PL Prediction Limit
PMCL Primary Maximum Contaminant Level
ppb parts per billion
ppm parts per million
PSRG Preliminary Soil Remediation Goal
PWR Partially Weathered Rock
PWSS NCDENR Department of Environmental Health Public Water Supply Section
RCRA Resource Conservation and Recovery Act
REC Recovery
RL Reporting Limit
RQD Rock Quality Designation
RSL USEPA Regional Screening Level
SCM Site Conceptual Model
SCS U.S. Department of Agriculture Soil Conservation Service
SLERA Screening Level Ecological Risk Assessment
SMCL Secondary Maximum Contaminant Level
SMDP Scientific/Management Decision Point
SPLP Synthetic Precipitation Leaching Procedure
SQL Sample Quantitation Limit
SWAP NCDENR DWR Source Water Assessment Program
TCLP Toxicity Characteristic Leaching Procedure
TDS Total Dissolved Solids
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
LIST OF ACRONYMS AND ABBREVIATIONS

xxii

TZ Transition Zone
UNC University of North Carolina
UNCC University of North Carolina at Charlotte
USCS Unified Soil Classification System
USDA U.S. Department of Agriculture
USEPA U.S. Environmental Protection Agency
USGS U.S. Geological Survey
UST Underground Storage Tank

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

1

1.0 Introduction
Duke Energy Carolinas, LLC (Duke Energy) owns and operated the Dan River Steam Station
(DRSS), located on the Dan River in Rockingham County near Eden, North Carolina. 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 two ash basins located northeast of the
station and adjacent to the Dan River. Discharge from the ash basins is currently permitted by
the North Carolina Department of Environment and Natural Resources (NCDENR) Division of
Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES)
Permit NC0003468.
Duke Energy has implemented voluntary and NPDES permit-required compliance groundwater
monitoring at DRSS. Compliance groundwater monitoring as required by the NPDES permit
began in 1993and included MW -9, MW -10, MW -11, and MW-12. In 2007, additional monitoring
wells, MW -9D, MW -10D, MW -11D, and MW-12D, were installed as part of Duke Energy’s
voluntary monitoring program. From 1993 to 2010, biannual voluntary groundwater monitoring
was performed around the DRSS ash basin with analytical results submitted to NCDENR DWR.
In October 2010, new compliance monitoring wells, MW -20S/D, MW-21S/D, MW -22S/D, and
MW -23D, were installed and the monitoring wells previously installed became part of the
voluntary monitoring program. Additional groundwater monitoring was required beginning in
March 2011 with the frequency of sampling and the parameters to be analyzed outlined in the
NPDES permit. From January 2011 through May 2015, the compliance groundwater monitoring
wells at the DRSS site have been sampled a total of 14 times as part of triannual sampling
required in the NPDES permit. NPDES Permit Condition A (11), Version 1.1, dated June 15,
2011, lists the groundwater monitoring wells to be sampled, the parameters and constituents to
be measured and analyzed, and the requirements for sampling frequency and reporting results.
Recent monitoring events have indicated exceedances of 15A NCAC 02L .0200 Groundwater
Quality Standards (2L Standards; refer to North Carolina Administrative Code Title 15A
Department of Environmental and Natural Resources Division of Water Quality Subchapter 2L
Section .0100, .0200, .0300 Classifications and Water Quality Standards Applicable to the
Groundwaters of North Carolina) at DRSS, prompting NCDENR’s requirement for Duke Energy
to perform a groundwater assessment at the site and prepare a Comprehensive Site
Assessment (CSA) report. The Coal Ash Management Act of 2014 (CAMA) also directed
owners of coal combustion residuals (CCR) surface impoundments to conduct groundwater
monitoring and assessment and submit a Groundwater Assessment Report. This CSA is
submitted to meet the requirements of both NCDENR and the CAMA.
1.1 Purpose of Comprehensive Site Assessment
The purpose of this Comprehensive Site Assessment (CSA) is to characterize the extent of
contamination resulting from historical production and storage of coal ash, evaluate the
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

2

chemical and physical characteristics of the contaminants, investigate the geology and
hydrogeology of the site including factors relating to contaminant transport, and examine risk to
potential receptors and exposure pathways. This CSA was prepared in general accordance with
requirements outlined in the following regulations and documents:
 Classifications and Water Quality Standards Applicable to the Groundwaters of North
Carolina in Title 15A NCAC 02L .0106(g);
 Coal Ash Management Act in G.S. 130A-309.209(a);
 Notice of Regulatory Requirements (NORR) issued by NCDENR on August 13, 2014;
 Conditional Approval of Revised Groundwater Assessment Work Plan issued by
NCDENR on February 16, 2015; and
 Subsequent meetings and correspondence between Duke Energy and NCDENR.
This assessment includes evaluation of possible impacts from the ash basins and related ash
storage facilities, and consisted of the following activities:
 Completion of soil borings and installation of groundwater monitoring wells to faciliatate
collection and analysis of chemical, physical, and hydrogeological parameters of
subsurface materials encountered within and beyond the waste and compliance
boundaries;
 Evaluation of testing data to supplement the site conceptual model (SCM);
 Update of the receptor survey previously completed in 2014; and
 Completion of a screening-level risk assessment.
In this report, constituents are those chemicals or compounds that were identified in the
approved W ork Plan for sampling and analysis. For DRSS, these include antimony, arsenic,
boron, chromium, cobalt, iron, manganese, selenium, thallium, vanadium, sulf ate, and total
dissolved solids (TDS). If a constituent exceeded its respective regulatory standard or screening
level in the medium in which it was found, the constituent was then termed a Constituent of
Interest (COI) and evaluated in the human health and ecological screening-level risk
assessment (Section 12.0).
1.2 Regulatory Background
1.2.1 NCDENR Requirements
NCDENR DWR regulates wastewater discharges from coal ash ponds to state waters, streams,
and lakes, and requires groundwater monitoring and stormwater management at these facilities.
Duke Energy’s coal-fired power facilities are regulated through federal NPDES wastewater
permits. As part of these permits, the facilities must also comply with the state water quality
standards and U.S. Environmental Protection Agency (USEPA) water quality criteria.
Groundwater monitoring is performed at Duke Energy facilities in accordance with approved
monitoring plans and NPDES permits for each site. Included in these monitoring evaluations is a
determination if site-specific background concentrations (i.e., naturally occurring constituents in
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

3

the soil profile and groundwater) for various constituents (e.g., iron and manganese) are
contributing to reported concentrations. For each facility, if it is determined that activities on the
property are causing noncompliance with NCDENR DWR regulatory requirements, the agency
will require the permittee to perform an assessment and to develop and implement a Corrective
Action Plan (CAP) in accordance with state regulations.
1.2.2 Notice of Regulatory Requirements
Chapter 143, North Carolina General Statutes, authorizes and directs the Environmental
Management Commission of the Department of Environment and Natural Resources to protect
and preserve the water and air resources of the State. NCDENR DWR has the delegated
authority to enforce adopted pollution control rules. NCDENR DWR Rule 15A NCAC 02L
.0103(d) states that “no person shall conduct or cause to be conducted any activity which
causes the concentration of any substance to exceed that specified in” 15A NCAC 02L .0202,
Groundwater Quality Standards.
On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter
notifying Duke Energy that exceedances of the groundwater quality standards 15A NCAC 02L
.0200 Classifications and Water Quality Standards Applicable to the Groundwaters of North
Carolina were reported at 14 coal ash facilities owned and operated by Duke Energy, including
DRSS. The NORR stipulated that for each coal ash facility, Duke Energy shall conduct a CSA
following submittal of a Groundwater Assessment Work Plan (Work Plan) and receptor survey.
In accordance with the NORR requirements, a Work Plan was developed, a receptor survey
was performed to identify all receptors within a 0.5-mile radius (2,640 feet) of the ash basin
compliance boundary, and a CSA was conducted for each coal ash facility. The NORR letter is
included in Appendix A.
1.2.3 Coal Ash Management Act Requirements
The Coal Ash Management Act (CAMA) of 2014 – General Assembly of North Carolina Senate
Bill 729 Ratified Bill (Session 2013) identifies the Dan River site as one of four high priority coal
combustion impoundments that are to be closed no later than August 1, 2019. CAMA requires
that the CCR in the high priority impoundments be removed and disposed in a landfill, used in a
structural fill, or for beneficial reuse.
As a component of implementing this objective, CAMA provides instructions for owners of CCR
surface impoundments to perform various groundwater monitoring and assessment activities.
Section §130A-309.209 of the CAMA ruling specifies groundwater assessment and corrective
actions, drinking water supply well surveys and provisions of alternate water supply, and
reporting requirements as follows:
(a) Groundwater Assessment of Coal Combustion Residuals Surface Impoundments.
– The owner of a coal combustion residuals surface impoundment shall conduct
groundwater monitoring and assessment as provided in this subsection. The
requirements for groundwater monitoring and assessment set out in this
subsection are in addition to any other groundwater monitoring and assessment
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

4

requirements applicable to the owners of coal combustion residuals surface
impoundments.
(1) No later than December 31, 2014, the owner of a coal combustion residuals
surface impoundment shall submit a proposed Groundwater Assessment
Plan for the impoundment to the Department for its review and approval. The
Groundwater Assessment Plan shall, at a minimum, provide for all of the
following:
a. A description of all receptors and significant exposure pathways.
b. An assessment of the horizontal and vertical extent of soil and
groundwater contamination for all contaminants confirmed to be present
in groundwater in exceedance of groundwater quality standards.
c. A description of all significant factors affecting movement and transport
of contaminants.
d. A description of the geological and hydrogeological features influencing
the chemical and physical character of the contaminants.
2) The Department shall approve the Groundwater Assessment Plan if it
determines that the Plan complies with the requirements of this subsection
and will be sufficient to protect public health, safety, and welfare; the
environment; and natural resources.
(3) No later than 10 days from approval of the Groundwater Assessment Plan,
the owner shall begin implementation of the Plan.
(4) No later than 180 days from approval of the Groundwater Assessment Plan,
the owner shall submit a Groundwater Assessment Report to the Department.
The Report shall describe all exceedances of groundwater quality standards
associated with the impoundment.
1.3 NCDENR-Duke Energy Correspondence
In response to both the NORR letter and CAMA requirements, Duke Energy submitted a Work
Plan to NCDENR DWR on September 25, 2014 establishing proposed site assessment
activities and schedules for the implementation, completion, and submission of a CSA report in
accordance with 15A NCAC 02L .0106(g). NCDENR DWR reviewed the Work Plan and
provided Duke Energy with initial comments on November 4, 2014. A revised Work Plan was
subsequently submitted to the NCDENR DWR on December 30, 2014, and NCDENR DWR
provided final comments and conditional approval of the revised Work Plan on February 19,
2015. In addition, Duke Energy submitted proposed adjustments to the CSA guideline and
requested clarifications regarding groundwater sampling and speciation of selected constituents
to NCDENR on May 14 and May 22, 2015. NCDENR provided responses to these proposed
revisions and clarifications in June 2015. Copies of relevant correspondence including Work
Plan submittals are included in Appendix A.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

5

1.4 Approach to Comprehensive Site Assessment
The CSA approach was developed based on the NORR guidelines and CAMA requirements.
Development of the SCM is based on several documents including but not limited to USEPA’s
Monitored Natural Attenuation tiered approach, ASTM 1689-95 (2014) Standard Guide for
Developing Site Conceptual Models for Contaminated Sites, and comments received by
NCDENR.
1.4.1 NORR Guidance
The NORR letter (Appendix A) outlines general guidelines for the CSA report, including
guidance from 15A NCAC 02L .0106(g) as described in Section 1.1. The NORR letter also
includes Guidelines for Comprehensive Site Assessment for those involved in the investigation
of contaminated soil and/or groundwater. The components included in the NORR guidelines
were used in developing the site Work Plan and this CSA report.
1.4.2 USEPA Monitored Natural Attenuation Approach
In accordance with NCDENR requirements and the February 16, 2015 Conditional Approval
letter (Appendix A), the elements of the USEPA’s Monitored Natural Attenuation (MNA) tiered
approach has been utilized as part of the investigation associated with the CSA. MNA may be
used as a component to meet corrective action requirements if site conditions meet the
requirements associated with use of MNA. The approach involves a detailed analysis of site
characteristics controlling and sustaining attenuation to support evaluation and selection of MNA
as part of a cleanup action for inorganic contaminant plumes in groundwater (USEPA 2007).
The site characterization is conducted in a step-wise manner to facilitate collection of data
necessary to progressively evaluate the effectiveness of natural attenuation processes within
the site aquifer(s). Four general elements are included in the tiered site analysis approach:
 Demonstration of active contaminant removal from groundwater and dissolved plume
stability;
 Determination of the mechanism and rate of attenuation;
 Determination of the long-term capacity for attenuation and stability of immobilized
contaminants, before, during, and after any proposed remedial activities; and
 Design of performance monitoring program, including defining triggers for assessing the
remedial action strategy failure, and establishing a contingency plan.
Duke Energy will evaluate the USEPA MNA approach further during preparation of the CAP.
1.4.3 ASTM Site Conceptual Model Guidance
American Society of Testing and Materials (ASTM) standard guidance document E1689-95
Developing Conceptual Site Models for Contaminated Sites (ASTM 2014) was used as a
general component of this CSA. The guidance document provides direction in developing
conceptual site models used for the integration of technical information from multiple sources,
selection of sampling locations to establish background concentrations of substances,
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

6

identification of data needs and guidance of data collection activities, and evaluation of risks to
human and environmental health posed by a contaminated site. According to ASTM E1689-95,
six basic activities are associated with developing a conceptual site model:
 Identification of potential contaminants;
 Identification and characterization of the source(s) of contaminants;
 Delineation of potential migration pathways through environmental media, such as
groundwater, surface water, soils, sediment, biota, and air;
 Establishment of background areas of contaminants for each contaminated medium;
 Identification and characterization of potential environmental receptors (human and
ecological); and
 Determination of the limits of the study area or system boundaries.

Development of a conceptual site model is typically iterative and the complexity of the model
should be consistent with the complexity of the site and available data. Information gained
through site investigation activities is used to characterize existing physical, biological, and
chemical systems at a site. The SCM describes and integrates processes that determine
contaminant releases, contaminant migration, and environmental receptor exposure to
contaminants. Development of the model is essential to determine potential exposure routes
and identify possible impacts to human health and the environment (ASTM 2014).
The conceptual site model is used to integrate site information, identify data gaps, and
determine whether additional information is needed at the site. The model is also used to
facilitate selection of remedial alternatives and determine effectiveness of remedial actions in
reducing the exposure of environmental receptors to contaminants (ASTM 2014).
This CSA was conducted in accordance with the conditionally approved Work Plan to meet the
NCDENR, NORR, and CAMA regulatory requirements described in Section 1.2, and using the
NORR, USEPA, and ASTM approaches described above. This assessment information will be
used to develop a CAP, to be submitted separately, for the DRSS site that will provide a
demonstration of these criteria in support of the recommended site remedy.
Data obtained from sampling during this CSA are compared to federal and state regulatory
standards shown in Table 1-1. Beginning in Section 7.0, laboratory results are compared to the
above-referenced regulatory standards and discussed as either “exceeding” or “not exceeding”
those standards. The evaluation of exceedances of these standards forms the basis for
determining the need for additional work later in this document.
1.5 Limitations and Assumptions
Development of this CSA is based on information provided to HDR by both public and private
entities including universities, federal, state and local governments, and information and
analytical reports generated by Duke Energy. HDR assumes the information in these
documents to be accurate and reliable. This information was used to estimate exposure routes
and migration pathways in the subsurface. This CSA was developed using a standard of care
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
1.0 INTRODUCTION

7

ordinarily used by engineering practice under the same or similar circumstances, but may
include assumptions based on the accuracy and reliability of data from various entities. CAMA
Section §130A-309.209 requires that “No later than 180 days from approval of the Groundwater
Assessment Plan, the owner shall submit a Groundwater Assessment Report to the
Department”. The schedule dictated by CAMA is compressed relative to the normal schedule
required for CSA reports; therefore, data interpretation is limited and subject to change upon
receipt of additional data in subsequent rounds of sampling and additional data collected to
resolve data gaps identified in Section 14.0. The additional data will be used to inform the
corrective actions identified in the CAP.
This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

8

2.0 Site History and Description
This section provides a description of the DRSS site based on relevant historical data and
representative information. The purpose of this characterization is to familiarize readers with the
DRSS site.
2.1 Site Location, Acreage, and Ownership
The DRSS site is located on the north bank of the Dan River in Eden, Rockingham County,
North Carolina (Figure 2-1). The entire DRSS and DRCCS site (Dan River site) occupies
approximately 380 acres of land (Figure 2-2). Construction began at the DRSS in 1948 and
commercial operation began in 1949. In December 2009, construction commenced on the
DRCCS. The DRCCS began commercial operation in 2012 and generates at a capacity of 620
megawatts (MW). Based on the NORR Guideline heading, Provide a history of property
ownership and use under the Site History and Source Characterization, this CSA report includes
a history of Duke Energy ownership. As of the date of this report, multiple inquiries have not
revealed site history information prior to Duke Energy ownership.
2.2 Site Description
DRSS is a former coal-fired electricity generating facility along the Dan River. The three-unit
station began commercial operation in 1949 with operation of a single coal-fired unit (Unit 1)
with a second unit (Unit 2) being added in 1950. A third unit was added by 1955 and resulted in
a total installed capacity of 276 MW . A 1953 United States Geological Survey (USGS)
topographic map depicting the site prior to construction of the ash basin features is shown on
Figure 2-3. All three coal-fired units, along with three 28 MW oil-fired combustion turbine units,
were retired in 2012. The DRCCS, a 620 MW combined cycle natural gas facility, began
commercial operations on December 10, 2012.
The natural topography at the DRSS site generally slopes from northwest to southeast and
ranges 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 elevation varies about 124 feet over an approximate distance of 0.7
miles. Surface water drainage generally follows site topography and flows from the northwest to
the southeast across the site except where drainage patterns have been modified by the ash
basins or other construction (refer to Section 3.2). A site features map is shown on Figure 2-4.
2.3 Adjacent Property, Zoning, and Surrounding Land Uses
Properties located within a 0.5-mile radius of the DRSS ash basin compliance boundary are
located in and southeast of Eden, in Rockingham County, North Carolina. The majority of the
land is undeveloped property and land use is found to be typical of rural property. Residential
properties are located north and northwest of the ash basin compliance boundary within the 0.5-
mile radius. One residence is located south of DRSS across the Dan River within the 0.5-mile
radius. Two industrial properties are located northeast of DRSS; one of these properties has a
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

9

wastewater treatment plant discharging into the Dan River downstream of the site. Farm land is
located southeast of the station across the Dan River. Figure 2-5 depicts these properties
surrounding the Dan River site.
2.4 Adjacent Surface Water Bodies and Classifications
The DRSS site is situated within the Upper Dan River watershed in the Roanoke River Basin.
The ash basin location is adjacent to the Dan River. Two unnamed tributaries are located along
the eastern and western boundaries of the DRCCS property (Figure 4-5). Two other unnamed
tributaries are located south of the DRSS site and across the Dan River. No other surface water
bodies exist within 0.5 mile of the compliance boundary. Surface water classification for Dan
River is Class C, as defined in 15A NCAC 02B.0101(c-1). Class C waters are protected for
secondary recreation, fishing, wildlife, consumption of fish, aquatic life including propagation,
maintenance and survival of biological integrity, and agriculture. Surface water features located
at the site are shown on Figure 2-2 and Figure 4-5.
2.5 Meteorological Setting
According to the U.S. Department of Agriculture Soil Conservation Service (USDA-SCS) soil
survey (1994), the average summer temperature in Rockingham County is 74°F and the
average daily maximum temperature is 85°F. During winter, the average temperature is 38°F
and the average daily minimum temperature is 28°F. The total annual precipitation in
Rockingham County is 42 inches, with over half of this rainfall (22 inches) occurring from April
through September. Thunderstorms occur approximately 45 days each year (USDA-SCS 1994).
The average relative humidity in midafternoon is approximately 55 percent, with humidity
reaching higher levels at night. The prevailing wind is from the southwest; average wind speed
is approximately nine miles per hour (USDA-SCS 1994).
2.6 Hydrologic Setting
Two unnamed tributaries of the Dan River are located along the eastern and western sides of
the DRSS site. Edgewood Road generally runs north to south and is located along a surface
water divide. Contours for the groundwater surface generally mimic the site surface topography,
such that east of Edgewood Road groundwater generally flows toward the unnamed tributary
located on the east side of the property and toward the ash basins, ultimately discharging into
the Dan River. Similarly, groundwater on the western side of Edgewood Road generally flows
toward the unnamed tributary located on the west side of the property or towards the Dan River.
Groundwater flow is discussed in further detail in Section 6.0.
Water levels within the Primary Cell of the ash basin have historically fluctuated approximately
11 feet from October 1984 until April 2013. The water elevation in the Primary Cell has ranged
from approximately 526 to 537 feet. Water levels within the Secondary Cell of the ash basin
have historically fluctuated approximately 12 feet from October 1984 until April 2013. The water
elevation in the Secondary Cell has ranged from approximately 518 to 526 feet.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

10

The ash basin affects the local groundwater elevations that underlie the basin. Water level
measurements recorded downgradient of the Secondary Cell indicate localized groundwater
mounding due to the presence of the basin The hydrologic setting is described in further detail
in Section 5.0.
2.7 Permitted Activities and Permitted Waste
Duke Energy is authorized to discharge wastewater to the surface waters of North Carolina or to
a separate storm sewer system that has been adequately treated and managed in accordance
with NPDES Permit NC0003468, which was renewed on March 1, 2013 and expires on April 30,
2017. Any other point source discharge to surface waters of the state is prohibited unless it is an
allowable non-stormwater discharge or is covered by another permit, authorization, or approval.
The NPDES permit authorizes discharges in accordance with effluent limitations, monitoring
requirements, and other conditions set forth in the permit.
An inactive (closed) asbestos and land clearing and inert debris landfill, Permit 79B-LCID, is
located on the west side of Edgewood Road.
2.8 NPDES and Surface Water Monitoring
The NPDES program regulates wastewater discharges to surface waters to ensure that surface
water quality standards are maintained. The NPDES permitting program requires that permits
be renewed every five years.
The current NPDES permit requires surface water monitoring as part of the permit conditions.
Surface water samples are required to be collected at Outfall 001 and Outfall 002 (see Section
2.9). The sample locations, parameters, and constituents to be measured and analyzed, and the
requirements for sampling frequency and reporting results are specified in the permit.
2.9 NPDES Flow Diagram
As stated in the NPDES Permit NC0003468, the NPDES permit allows continued discharge into
the Dan River from the following:
 Once-through cooling water and cooling tower blowdown from the combined cycle unit,
intake screen backwash, plant collection sumps (low volume wastes), and treated
domestic wastewater from Outfall 001;
 Wastes from the filtered water plant including miscellaneous wash down water and
laboratory wastes (low volume waste sources) from internal Outfall 001A;
 An ash basin discharge consisting of low volume wastes, boiler cleaning wastewater,
ash disposal, stormwater, boiler blowdown, and metal washing wastewater from Outfall
002; and
 A yard sump overflow consisting of stormwater runoff, miscellaneous sumps, and coal
yard runoff from Outfall 002A.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

11

The NPDES flow diagram for DRSS is provided on Figure 2-6. This figure shows the sources of
inflows into the basin. Outfalls 004 and 006, shown on Figure 2-6, are not included in the current
NPDES permit. Located at the south end of the Service Water Settling Pond, they are believed
to be stormwater outfalls.
2.10 History of Site Groundwater Monitoring
Duke Energy has implemented voluntary and NPDES permit-required compliance groundwater
monitoring at DRSS. Compliance groundwater monitoring as required by the NPDES permit
began in 1993 which included sampling of the following monitoring wells: MW -9, MW -10, MW-
11, and MW -12. In 2007, additional monitoring wells, MW -9D, MW -10D, MW-11D, and MW -
12D, were installed as part of Duke Energy’s voluntary monitoring program. From 1993 to 2010,
biannual voluntary groundwater monitoring was performed around the DRSS ash basin with
analytical results submitted to NCDENR DWR. In October 2010, new compliance monitoring
wells, MW -20S/D, MW -21S/D, MW -22S/D, and MW-23D, were installed and the monitoring
wells previously installed became part of the voluntary monitoring program. Additional
groundwater monitoring was required beginning in March 2011 with the frequency of sampling
and the parameters to be analyzed outlined in the NPDES permit. From January 2011 through
May 2015, the compliance groundwater monitoring wells at the DRSS site have been sampled a
total of 14 times as part of triannual sampling required in the NPDES permit. NPDES Permit
Condition A (11), Version 1.1, dated June 15, 2011, lists the groundwater monitoring wells to be
sampled, the parameters and constituents to be measured and analyzed, and the requirements
for sampling frequency and reporting results The location of the ash basin voluntary and
compliance monitoring wells, the approximate ash basin waste boundary, and the compliance
boundary are shown on Figure 2-7. The compliance boundary for groundwater quality at the
DRSS ash basin 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.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

12

2.10.1 Voluntary Groundwater Monitoring Wells
Groundwater monitoring prior to 2015 consisted of eight voluntary and seven compliance wells
installed within the DRSS site boundary. Duke Energy implemented voluntary groundwater
monitoring around the DRSS ash basin in 2007 and continued until 2010... During this period,
the voluntary groundwater monitoring wells were sampled two times per year and the analytical
results were submitted to NCDENR.
2.10.2 Compliance Groundwater Monitoring Wells
In 2010, compliance groundwater monitoring wells were installed at the DRSS site.
Groundwater monitoring as required by the DRSS NPDES Permit NC0003468 began in March
2011 utilizing the compliance monitoring wells. NPDES Permit Condition A (11), Version 1.1,
dated June 15, 2011, lists the groundwater monitoring wells to be sampled, the parameters and
constituents to be measured and analyzed, and the requirements for sampling frequency and
reporting results (provided in Table 2-1).
Compliance groundwater monitoring wells were installed in December 2010. Locations for the
compliance groundwater monitoring wells were approved by the NCDENR DWR Aquifer
Protection Section (APS). All compliance monitoring wells listed in Table 2-1 are sampled three
times per year (January, May, and September). Analytical results are submitted to NCDENR
DWR before the last day of the month following the month of sampling for all compliance
monitoring wells. The compliance groundwater monitoring is performed in addition to the current
NPDES monitoring of the discharge flows from the ash basin.
From January 2011 through May 2015, the compliance groundwater monitoring wells at the
DRSS site have been sampled a total of 14 times. During this period, these monitoring wells
were sampled in:
 January, May, and September 2011
 January, May, and September 2012
 January, May, and September 2013
 January, May, and September 2014
 January and May 2015
The results of each sampling event are submitted to NCDENR as required by the permit. The
compliance groundwater monitoring system for the DRSS ash basin system consists of the
following monitoring wells: MW -20S, MW -20D, MW-21S, MW -21D, MW-22S, MW -22D, and
MW -23D. Monitoring well MW -23D serves as the background well for compliance groundwater
monitoring.
As documented in NCDENR’s NORR letter dated August 13, 2014, one or more 2L Standards
have been exceeded in groundwater samples collected from each of the compliance monitoring
wells, including the background well. Exceedances have occurred in one or more wells during
one or more sampling events for arsenic, boron, iron, manganese, pH, antimony, sulfate, and
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

13

TDS. Table 2-2 presents exceedances measured at each of these groundwater monitoring wells
from January 2011 through May 2015.
Monitoring wells MW -20S and MW-20D are located north of the ash storage areas. Monitoring
wells MW -21S and MW -21D are located east of and adjacent to the Secondary Cell. Monitoring
wells MW -20S and MW -21S were installed via rotary drilling methods using hollow stem augers,
with the well screen installed above auger refusal to monitor the shallow aquifer within the
saprolite layer. These wells were installed with screen lengths of 15 feet and 5 feet,
respectively. The wells were installed with the screened interval for MW -20S from 4 feet to 19
feet below ground surface (bgs) and the screened interval for MW -21S from 3.5 feet to 8.5 feet
bgs.
Monitoring wells MW -20D and MW -21D were installed via rotary drilling methods using hollow
stem augers and by rock coring techniques (HQ-diameter barrel) with the well screen installed
in the uppermost region of the fractured rock transition zone (TZ). These wells were installed
with 5-foot-long screens. The wells were installed with the screened interval for MW-20D from
36.5 feet to 41.5 feet bgs and the screened interval for MW-21D from 13.6 feet to 18.6 feet bgs.
Monitoring wells MW -22S and MW-22D are located south of the Primary Cell. Monitoring wells
MW -22S and MW -22D are located at the toe of the earthen dam impounding the Primary Cell,
where large-diameter cobbles/boulders prevented installation by the drilling techniques used for
wells MW -20S, MW -20D, MW-21S, and MW-21D. Wells MW -22S and MW-22D were installed
using an air-powered ODEX drilling system. Well MW -22S was installed to monitor the surficial
aquifer with a 10-foot-long screen from 12.35 feet to 22.35 feet bgs. MW -22D was installed to
monitor the fractured rock TZ with a 5-foot-long screen from 31.95 feet to 36.95 feet bgs.
Monitoring well MW -23D, the background well, is located approximately 3,100 feet northwest of
the Primary Cell. Well MW -23D was installed to evaluate background water quality at the site.
Well, MW -23D was installed by rotary drilling methods using hollow stem augers and by rock
coring techniques (HQ-diameter barrel) with the well screen installed in the uppermost region of
the fractured rock TZ. This well was installed with a 10-foot-long screen from 6.7 feet to 16.7
feet bgs.
2.11 Assessment Activities or Previous Site Investigations
Between 1990 and 2013, several historical onsite investigations have been conducted in
response to fuel oil releases linked to the piping and aboveground storage tanks (ASTs)
associated with the former combustion turbine system and leaks from former gasoline
underground storage tanks (USTs). A summary of the historical environmental incidents on-site
is provided in Table 2-3.
In September 2013, assessment activities in support of the conceptual closure design of the
DRSS ash basin. The work performed as part of this study included the installation and
sampling of 27 observation wells between June and July 2013. Results from this assessment
have been used to supplement data obtained from the current groundwater assessment. Select
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

14

existing monitoring wells installed as part of the ash basin conceptual closure assessment were
resampled to supplement the current groundwater assessment.
On February 2, 2014, a portion of a 36-inch corrugated metal storm water pipe, located under
the Primary Cell of the ash basin, failed and released up to 39,000 tons of coal ash into the Dan
River. Immediate action was taken to stop the release and begin assessment of the
environmental impact. Ash deposits were removed from the property and other downstream
locations. Duke Energy has worked extensively with various federal, state and local agencies to
address the coal ash release to the Dan River, including removal of an estimated 4,000 cubic
yards of coal ash and extensive environmental quality monitoring. According to a January 27,
2015 USEPA Information Update related to the release, “Following extensive surface water and
sediment sampling, no further ash removal is planned. There have been no exceedances of
human health screening thresholds, or any recent exceedances of ecological screening
thresholds, for contaminants associated with ash. Further, removal of ash [in] some places
could be more detrimental to the ecosystem than leaving it in place.” Long-term monitoring
through July 2015 was also directed by an Administrative Order of Consent between the
USEPA and Duke Energy. The USEPA has overseen sampling to date and will determine
whether additional sampling is required beyond July 2015.
2.12 Decommissioning Status
The multi-year DRSS decommissioning process is being accomplished using a phased
approach that involves cleaning and removing equipment, demolishing the powerhouse and
auxiliary buildings, and restoring the site. Phase 1 began in the fall of 2013 and included
removal of a small portion of the exterior brick on the power plant near the river to allow for
modifications to the new natural gas plant's water-intake system. Auxiliary buildings and the
decommissioned combustion turbine units and fuel oil tank were then demolished. Phase 2 of
the decommissioning process is scheduled to begin in 2015 and will include demolition of the
power plant. Between these two decommissioning phases, electrical equipment that is critical to
Duke Energy’s power transmission system has been relocated.
In conjunction with decommissioning activities and in accordance with CAMA requirements,
Duke Energy shall permanently close the DRSS ash basin by August 1, 2019. Closure of the
DRSS ash basin was defined in CAMA as excavation of ash from the site, and beneficial reuse
of the material or relocation to a lined structural fill or landfill. As part of the DRSS closure
process, Duke Energy submitted a coal ash excavation plan to state regulators in November
2014. The excavation plan details a multiphase approach for removing coal ash from the site
with an emphasis on the first 12 to 18 months of activities.
During Phase I of the excavation, an estimated 1.2 million tons of material will be excavated
from the Primary and Secondary cells or dry ash stacks (described further in Section 3.2). This
material is planned to be taken to the Maplewood (Amelia) Landfill in Jetersville, Virginia. An
alternate landfill, Atlantic Landfill in Waverly, Virginia, was identified to accept material
excavated in the event of any issues at the Maplewood Landfill. Ash will be transported by rail
car to the landfill and installation of a rail loading system to accommodate this transport of ash is
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
2.0 SITE HISTORY AND DESCRIPTION

15

currently in progress. Should the situation arise that rail car transportation is disrupted, truck
transportation will be utilized. Subsequent phase(s) will remove the remaining ash at the site.
Duke Energy is in the permitting process for an on-site landfill that will be located approximately
where Ash Storage 1 is located. The landfill will be lined and construction is projected to be
completed by June 2017. The permit-to-construct application is scheduled to be submitted to
the NCDENR Division of Waste Management in the third quarter of 2015. The construction
schedule will depend upon receipt of the required permits.
Duke Energy will begin moving coal ash within 60 days after receiving necessary permits and
approvals. Dewatering of the ash basins will begin along with project planning for later phases
to identify storage options for the remaining ash on the plant property. Ash impoundments will
be closed by August 1, 2019.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
3.0 SOURCE CHARACTERISTICS

16

3.0 Source Characteristics
This section provides a general description of the DRSS coal combustion and ash handling
system, a description of the ash basin and other ash storage areas, and a discussion of the
general physical and chemical properties of ash.
3.1 Coal Combustion and Ash Handling System
Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and conveyed
to the burner area of a boiler. The smaller particles produced by coal combustion, referred to as
fly ash, are carried upward in the flue gas and are captured by an air pollution control device,
such as an electrostatic precipitator. The larger particles of ash that fall to the bottom of the
boiler are referred to as bottom ash.
Coal ash residue from the coal combustion process was disposed in the DRSS ash basin from
approximately 1956 until the last coal-fired generating units were retired in 2012. Fly ash from
the electrostatic precipitators was collected in hoppers. Bottom ash and boiler slag was
collected in the bottom of the boilers. After collection, both fly ash and bottom ash/boiler slag
were sluiced to the ash basin using conveyance water withdrawn from the Dan River. The sluice
lines conveyed the water/ash slurry and other flows to the southwest corner of the Primary Cell.
Refer to Figure 2-2 for a depiction of these features.
DRSS historically produced approximately 50,000 tons of ash per year. Note that this quantity is
an estimate and actual quantities fluctuated based on burn rates, coal types, and outages.
During operation of the coal-fired units, the ash basin received variable inflows from the ash
removal system and discharge of cooling water. The ash basin no longer receives sluiced ash
but currently receives variable inflows from the station yard drain sump and stormwater flows.
Duke Energy is in the process of evaluating alternatives for removing these flows from the ash
basin to allow total decommissioning of the ash basin.
3.2 Description of Ash Basin and Other Ash Storage Areas
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 shown on Figure 2-2. The
ash basin is impounded by earthen dams and an earthen/ash divider dam separates the
Primary Cell from the Secondary Cell. The dry ash storage areas are located topographically
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 removed from the
ash basin.
3.2.1 Primary and Secondary Ash Basin Cells
The current ash basin was constructed over three phases beginning in 1956 and ending in
1976. Based on a review of historical construction drawings, it appears that the dams were
constructed of earthen materials borrowed from within the ash basin footprint.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
3.0 SOURCE CHARACTERISTICS

17

The original ash basin was constructed in 1956 with a footprint that lies within the current
Primary Cell. The dam was constructed as a homogenous sandy silt embankment with an
approximate crest elevation of 525 feet. In 1968 and 1969, the footprint of the ash basin was
expanded to the footprint of the current Primary and Secondary Cells by constructing an earthen
dam with a crest elevation of 530 feet. At this period, the ash basin was a single impoundment.
In 1976, the single basin was divided into the current Primary and Secondary Cells by
construction of an interior dike on top of existing ash. This divider dike was constructed as an
earthen embankment at elevation 540 feet. The embankment for what is now the Primary Cell
was raised to 540 feet.
The area contained within the waste boundary for the Primary and Secondary Cells currently
extends over an area of approximately 53 acres. The Primary Cell extent is approximately 28.1
acres and contains approximately 1 million tons of ash material. The Primary Cell has a crest
elevation of approximately 540 feet and has an impoundment surface area of approximately
21.8 acres. The Secondary Cell extent is approximately 15.3 acres and contains approximately
200,000 tons of ash material. The Secondary Cell has a crest elevation of approximately 530
feet and has a current impoundment surface area of approximately 12.2 acres. The elevation of
the Dan River adjacent to the ash basin is approximately 482 feet.
During operation of the coal-fired units, the ash basin received variable inflows of fly ash, bottom
ash, pyrites, stormwater runoff (including runoff from the coal pile), cooling water, powerhouse
floor drains, sanitary waste effluent, station yard drainage sump, and boiler chemical cleaning
wastes. Flow was historically routed from the Primary Cell to the Secondary Cell through a
concrete discharge tower. Since the February 2, 2014 release within the Primary Cell, all inflows
into the ash basin are now routed directly to the Secondary Cell. Effluent from the Secondary
Cell is routed to the Dan River via a concrete discharge tower located in the Secondary Cell.
The water surface in both the Primary and Secondary Cells is controlled by the use of stop logs.
3.2.2 Ash Storage 1
The ash storage area identified as Ash Storage 1 is located north of the Primary and Secondary
Cells on an upland area of the site. The unit is bounded by a topographic rise to the north, filling
former drainages of the rise to the south (Figure 2-2). The surface area within the waste
boundary for Ash Storage 1 encompasses approximately 20.1 acres. The CCR and soil material
stored in the Ash Storage 1 footprint was placed during several projects between 1994 and
2010 and totals approximately 1.1 million tons.
Ash was previously dredged to the southernmost portion of Ash Storage 1, and free liquids were
allowed to gravity drain to the topographically lower dredge pond located between the dry ash
storage areas. Once dewatered, ash was hauled and placed dry in Ash Storage 1 and Ash
Storage 2 and a vegetated soil cap covers the storage area footprint (Figure 2-2).
3.2.3 Ash Storage 2
The ash storage area identified as Ash Storage 2 is located southwest of Ash Storage 1 and on
the southwest slope of a former ridge on the site. The cell is bounded by a topographic rise to
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
3.0 SOURCE CHARACTERISTICS

18

the north, filling a former drainage at the southwest base of the former ridge (Figure 2-2). The
area contained within the waste boundary for Ash Storage 2 encompasses approximately 13.4
acres. The CCR and soil material in Ash Storage 2 was placed in 1994 and during 1997-1998
and totals approximately 372,000 tons.
Ash Storage 2 was created in a similar manner as Ash Storage 1, using ash removed from the
ash basin. A vegetated soil cap covers the surface of Ash Storage 2, and the footprint this
capped surface is currently used as a laydown area when needed for various projects at the
site.
3.2.4 Dredge Dikes
In 1980, newer dikes, referred to as the dredge dikes, were constructed north of the Primary
and Secondary Cells using on-site earthen fill material to create a dredge pond between the ash
basin and two dry storage areas referred to as Ash Storage 1 and 2 (discussed above). The
crest of these dikes was constructed at an elevation of 560 feet. Ash that was removed from the
ash basin was placed upgradient of these dikes and allowed to drain into the topographically
lower dredge pond. The drained ash was then removed from the dredge pond and compacted in
the ash storage areas. The discharge tower for the dredge pond discharges to the Secondary
Cell of the ash basin.
3.3 Physical Properties of Ash
Ash in the DRSS ash basin consists of fly ash and bottom ash produced from the combustion of
coal. The physical and chemical properties of coal ash result from reactions that occur during
the combustion of the coal and subsequent cooling of the flue gas. In general, coal is dried,
pulverized, and conveyed to the burner area of a boiler for combustion. As described in Section
3.1, material that forms larger particles of ash and falls to the bottom of the boiler is referred to
as bottom ash. Smaller particles of ash, known as fly ash, are carried upward in the flue gas and
are captured by an air pollution control device.
Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash (EPRI
1993). Typically 65 to 90 percent of fly ash has particle sizes that are less than 0.010 millimeter
(mm). In general, fly ash has a grain size distribution similar to that of silt. The remaining 20 to
30 percent of ash produced is considered to be bottom ash. Bottom ash consists of angular
particles with a porous surface and is normally gray to black in color. Bottom ash particle
diameters can vary from approximately 0.05 to 38 mm. In general, bottom ash has grain size
distribution similar to that of fine to very coarse sand (EPRI 1995).
Based on published literature not specific to the DRSS site, the specific gravity of fly ash
typically ranges from 2.1 to 2.9 and the specific gravity of bottom ash typically ranges from 2.3
to 3.0. The permeability of fly ash and bottom ash vary based on material density, but would be
within the range of a sand-gravel with a similar gradation, grain size distribution and density
(EPRI 1995). Permeability and other physical properties of the ash found in the DRSS ash basin
are presented in later sections of this report.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
3.0 SOURCE CHARACTERISTICS

19

3.4 Chemical Properties of Ash
In general, the specific mineralogy of coal ash varies based on many factors including the
chemical composition of the coal, which is directly related to the geographic region where the
coal was mined, the type of boiler where the combustion occurs (i.e., thermodynamics of the
boiler), and air pollution control technologies employed.
The overall chemical composition of coal ash resembles that of siliceous rocks from which it
was derived, particularly shale. Oxides of silicon, aluminum, iron, and calcium make up more
than 90 percent of most siliceous rocks, soils, fly ash, and bottom ash. Other major and minor
elements (sulfur, sodium, potassium, magnesium, titanium) make up an additional 8 percent,
while trace constituents account for less than 1 percent. The following constituents are
considered to be trace elements: arsenic, barium, cadmium, chromium, lead, mercury,
selenium, copper, manganese, nickel, lead, vanadium, and zinc (EPRI 2010).
According to Duke Energy, the coal sources generally used for combustion at DRSS were low
sulfur coal from Central Appalachia, comprised of Eastern Kentucky, Southern West Virginia,
and Southwestern Virginia.
The majority of fly ash particles are glassy spheres mainly composed of amorphous or glassy
aluminosilicates, crystalline matter, and carbon. Figure 3-1 presents a photograph of ash
collected from the ash basin at Duke Energy’s Cliffside Steam Station showing a mix of fly ash
and bottom ash at 10 µm and 20 µm magnifications. The glassy spheres can be observed in the
photograph. The glassy spheres are generally resistant to dissolution. During the later stages of
the combustion process and as the combustion gases are cooling after exiting the boiler,
molecules from the combustion process condense on the surface of the glassy spheres. These
surface condensates consist of soluble salts (e.g., calcium (Ca2+)); sulfate (SO42-); metals (e.g.,
copper (Cu), zinc (Zn)); and other minor elements (e.g., boron (B), selenium (Se), and arsenic
(As)) (EPRI 1994).
The major elemental composition of fly ash (approximately 95 percent by weight) is composed
of mineral oxides of silicon, aluminum, iron, calcium. Oxides of magnesium, potassium, titanium
and sulfur comprise approximately 4 percent by weight (EPRI 1995). Trace elemental
composition typically is approximately 1 percent by weight and may include arsenic, antimony,
barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium,
silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental
composition of fly ash and bottom ash compared with typical values for shale and volcanic ash.
Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values
for soil and rock. In addition to these constituents, fly ash may contain unburned carbon.
Bituminous coal ash typically yields slightly acidic to alkaline solutions with pH levels ranging
from approximately 5 to 10 on contact with water.
The geochemical factors controlling the reactions associated with leaching of ash are complex.
Factors such as the chemical speciation of the constituent, solution pH, solution-to-solid ratio,
and other factors control the chemical concentration of the resultant solution. Constituents that
are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
3.0 SOURCE CHARACTERISTICS

20

leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium,
and iron represent the larger fractions of fly ash and bottom ash by weight. The presence of
calcium may limit the release of arsenic by forming calcium-arsenic precipitates. Formation of
iron hydroxide compounds may also sequester arsenic and retard or prevent release of arsenic
to the environment. Similar processes and reactions may affect other constituents of concern;
however, certain constituents such as boron and sulfate will likely remain highly mobile.
In addition to the variability that might be seen in the mineralogical composition of the ash,
which is based on different coal types, different age of ash in the basin, and other factors, it is
anticipated that the chemical environment of the DRSS ash basin varies over time, distance,
and depth.
EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash,
and flue gas desulfurization residue) from 50 different power plants were subjected to USEPA
Method 1311 Toxicity Characteristic Leaching Procedure (TCLP) (USEPA 2008) leaching and
no TCLP result exceeded the TCLP hazardous waste limit. Figure 3-3 provides the results of
that testing. The report also presents the trace element concentrations for fly ash and bottom
ash compared to USEPA Residential Soil Screening Levels (RSLs) for ingestion and dermal
exposure. Figure 3-4 shows the 10th to 90th percentile range for trace element concentrations
(milligrams per kilogram [mg/kg]) in fly ash and the associated USEPA RSLs. The trace element
concentrations for arsenic were greater than the RSLs for arsenic. The RSLs of the remaining
constituents were greater than or within the 10th to 90th percentile range for their trace element
concentrations.
Figure 3-5 shows similar data for bottom ash. As with fly ash, the trace element concentrations
for arsenic in bottom ash were greater than the RSLs for arsenic. The RSLs for chromium were
within the 10th to 90th percentile range of concentrations for chromium in bottom ash. The 10th to
90th percentile range for the remaining constituents were below their respective RSLs.
Site-specific ash data is discussed further in Section 7.0 of this report.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
4.0 RECEPTOR INFORMATION

21

4.0 Receptor Information
Section §130A-309.201(13) of the CAMA defines receptor as “any human, plant, animal, or
structure which is, or has the potential to be, affected by the release or migration of
contaminants. Any well constructed for the purpose of monitoring groundwater and contaminant
concentrations shall not be considered a receptor.” In accordance with the NORR CSA
Guidelines, receptors cited in this section refer to public and private water supply wells
(including irrigation wells and unused wells) and surface water features. Refer to Section 12.0
for a discussion of non-water supply wells and other receptors that were evaluated as part of
this CSA effort.
Note that one of the receptor survey requirements in the NORR CSA Guidelines is that
subsurface utilities are to be mapped within 1,500 feet of the known extent of contamination in
order to evaluate the potential for preferential pathways. For the DRSS, the subsurface utilities
are not viewed as potential preferential pathways for contaminant migration through
underground utility corridors because the Dan River serves as the lower hydraulic boundary for
groundwater flow from potentially impacted areas. For this reason, subsurface utilities within
1,500 feet down-gradient of the ash basin were not mapped. However, pertinent structures
(e.g., stormwater drainage pipes) located proximal to ash management features were identified
and are presented on Figure 4-3.
4.1 Summary of Previous Receptor Survey Activities
Duke Energy submitted a receptor survey to NCDENR (HDR 2014a) in September 2014,
followed by a supplement to the receptor survey (HDR 2014b) submitted to NCDENR in
November 2014. The purpose of the receptor survey was to identify the potential exposure
locations that are critical to be considered in the groundwater transport modeling and screening-
level risk assessment activities. The supplementary information was obtained from responses to
water supply well survey questionnaires mailed to property owners within a 0.5-mile (2,640-foot)
radius of the DRSS ash basin compliance boundary requesting information on the presence of
water supply wells and well usage.
The survey activities included contacting and/or reviewing the following agencies/records to
identify public and private water supply sources, confirm the location of wells, and/or identify any
wellhead protection areas located within a 0.5-mile radius of the DRSS ash basin compliance
boundary:
 NCDENR Department of Environmental Health (DEH) Public Water Supply Section’s
(PWSS) most current Public Water Supply Water Sources GIS point data set;
 NCDENR DWR Source Water Assessment Program (SWAP) online database for public
water supply sources;
 Environmental Data Resources (EDR) local/regional water agency records review;
 Rockingham County Environmental Health Department;
 City of Eden’s Director of Environmental Services;
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
4.0 RECEPTOR INFORMATION

22

 Dan River Water Inc., a private water utility company; and
 United States Geological Survey (USGS) National Hydrography Dataset (NHD).
In addition, a field reconnaissance was performed on June 18, 2014 and July 9, 2014, to identify
public and private water supply wells (including irrigation wells and unused or abandoned wells)
and surface water features located within a 0.5-mile radius of the DRSS ash basin compliance
boundary. A windshield survey was conducted from public roadways to identify water meters,
fire hydrants, valves, and any potential well heads/well houses, and Duke Energy site personnel
identified water supply wells located on Duke Energy property.
During the week of October 8, 2014, 252 water supply well survey questionnaires were mailed
to property owners requesting information on the presence of water supply wells and well usage
information for each property. The mailing list was compiled from a query of the parcel
addresses included in the Rockingham County GIS database utilizing the 0.5-mile offset.
Between July 16 and July 22, 2015, the agencies/records listed above were contacted to
provide additional information. Updated information is provided in Appendix B.
4.2 Summary of CSA Receptor Survey Activities and Findings
As part of this CSA report, Duke Energy updated the previously completed receptor survey
activities based on the CSA Guidelines provided in the NORR issued by NCDENR. The update
included contacting and/or reviewing the agencies/records to identify public and private water
supply sources identified in Section 4.1 and reviewing questionnaires that were received after
submittal of the November 2014 supplement to the September 2014 receptor survey (i.e.,
questionnaires received after October 31, 2014).
A summary of the receptor survey findings is provided below. The identified water supply wells
are shown in the USGS receptor map on Figure 4-1. Available property and well information for
the identified wells is provided in Tables 4-1. Table 4-2 provides a summary of surrounding
property owner’s names and addresses. Figures 4-2 through 4-6 present an aerial receptor
map, ash basin underground features map, ash storage area underground features map, aerial
map of surface water bodies, and surrounding property owners map, respectively.
 Three reported private water supply wells were identified within a 0.5-mile radius of the
ash basin compliance boundary.
 One private water supply spring, reportedly not currently in use, was identified within a
0.5-mile radius of the ash basin compliance boundary.
 No public water supply wells were identified within a 0.5-mile radius of the ash basin
compliance boundary.
 Several unnamed tributaries of the Dan River were identified within a 0.5-mile radius of
the ash basin compliance boundary.
 No water supply wells (including irrigation wells and unused or abandoned wells) were
identified within a 0.5-mile radius of the ash basin compliance boundary.
 No wellhead protection areas were identified within a 0.5-mile radius of the ash basin
compliance boundary.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
4.0 RECEPTOR INFORMATION

23

Based on the returned water supply well questionnaires since October 31, 2014, no additional
receptors were identified. Further details of HDR’s receptor survey activities and findings are
presented in Appendix B.
4.3 NCDENR Well Water Testing Program
Section § 130A-309.209 (c) of the CAMA requires the owner of a CCR surface impoundment to
conduct a Drinking Water Supply Well Survey that identifies all drinking water supply wells
within one-half mile down-gradient from the established compliance boundary of the
impoundment and submit the Survey to the Department. Since the direction of groundwater flow
had not been fully established at the sites, NCDENR required the sampling to include all
potential drinking water receptors within 1,500 feet of the compliance boundary in all directions.
Between February and July 2015, NCDENR arranged for independent analytical laboratories to
collect and analyze water samples obtained from private wells identified during the Drinking
Water Supply Well Survey, if the owner agreed to have their well sampled. At the DRSS site, no
private wells within 1,500 feet of the compliance boundary were sampled per the directive of
NCDENR. It is important to note that all three water supply wells are located more than 2,000
feet away from the DRSS ash basin compliance boundary and are either upgradient or across
the Dan River from the ash basin system. No information gathered as part of this CSA suggests
that water supply wells or springs within the 0.5-mile radius of the compliance boundary are impacted
by the DRSS ash basin system.
This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY

24

5.0 Regional Geology and Hydrogeology
5.1 Regional Geology
North Carolina is divided into three physiographic provinces: the Atlantic Coastal Plain,
Piedmont, and Blue Ridge (Fenneman 1938). DRSS is located in the Dan River Triassic Basin
within the Piedmont province. The Piedmont province is bounded to the east and southeast by
the Atlantic Coastal Plain and to the west by the escarpment of the Blue Ridge Mountains, with
a width ranging from 150 miles to 225 miles in the Carolinas (LeGrand 2004).
The topography of the Piedmont region is characterized by low, rounded hills and long, rolling,
northeast- to southwest-trending ridges (Heath 1984). Stream valley to ridge relief in most areas
ranges from 75 feet to 200 feet. Along the Coastal Plain boundary, the Piedmont region rises
from an elevation of 300 feet, to the base of the Blue Ridge Mountains at an elevation of up to
1,500 feet (LeGrand 2004). Rocks within the Dan River Basin consist of relatively hard and
brittle sedimentary rocks that result in linear strike ridges, narrow valleys, and high relief (Olsen
et al. 1991) in contrast to the low hills and subdued ridges of the Piedmont province proper.
The Dan River Triassic Basin (Danville Basin in Virginia) is one of several exposed rift basins
that form two parallel belts that strike northeasterly within the Piedmont province. The basins
are aligned subparallel to the Appalachian terranes (Figure 5-1) and formed along pre-existing
zones of faulting and then subsided during a period of crustal stretching (Olsen et al. 1991). The
Dan River Basin is located in the western belt of rift basins and is bounded on the southeast by
the Milton terrane, one of a number of tectonostratigraphic terranes that have been defined in
the southern and central Appalachians, and on the northwest by the Sauratown Mountains
Anticlinorium and the Smith River allochthon (Figure 5-1; Horton et al. 1989; Hibbard et al.
2002; Hatcher et al. 2007). The Milton belt is characterized by strongly foliated gneisses and
schists, commonly with distinct compositional layering and felsic composition; quartzite, calc-
silicate gneiss, and marble are minor units (Carpenter 1982; Butler and Secor 1991). The
majority of the rocks in the belt are metamorphosed to the sillimanite and kyanite grade of
amphibolite metamorphism (Butler and Secor 1991). The Sauratown Mountains anticlinorium
consists of four stacked thrust sheets and subsequent erosion has exposed a complex,
multitiered window or exposure of these thrust sheets (Horton and McConnell 1991). A complex
sequence of interlayered and faulted calc-silicate gneiss, biotite-augen gneiss, quartz-feldspar
gneiss, epidosite, and amphibolite characterize the anticlinorium (Horton and McConnell 1991).
The Smith River allochthon consists predominately of biotite gneiss in North Carolina (Horton
and McConnell 1991).
In terms of structural position of the Dan River Basin, it is bounded on the northwest by the
Chatham fault zone, a southeast dipping normal fault system. The fault zone strikes N30E to
N40E and dips at approximately 45 degrees to the southeast (Thayer and Robbins 1992).
Movement along the fault zone occurred during and after basin filling with a total displacement
along the zone of as much as 4,500 meters (Thayer 1970). The contact between the Triassic
rocks of the basin and the crystalline rocks of the Milton belt along the southeast basin margin is
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY

25

an unconformity, but several minor, northwest dipping normal faults are present locally (Thayer
1970). Minor, interbasin normal faults are present. The sedimentary rocks of the basin consist of
interbedded conglomerate, sandstone, mudstone, siltsone, shale, and thin coal beds (Olsen et
al. 1991; Thayer and Robbins 1992). The rocks dip moderately to steeply northwest toward the
Chatham fault zone (Thayer 1970).
Thayer (1970) divided the rocks of the basin into three stratigraphic formations (oldest to
youngest): 1) Pine Hall Formation, 2) Cow Branch Formation, and 3) Stoneville Formation. The
Pine Hall Formation is along the southeast margin of the basin and consists of gray to red,
medium- to coarse-grained conglomerate, pebbly sandstone grading upward into massive,
bioturbated red siltstone and mudstone. This sequence defines an upward fining sequence
suggesting braided river deposits (Thayer 1970; Thayer and Robbins 1992). The Cow Branch
Formation conformably overlies and interfingers with the Pine Hall Formation and consists of
black and gray bedded, carbonaceous shales and mudstones, sandstones, and thin coal beds
deposited in a lacustrine environment (Thayer 1970; Thayer and Robbins 1992). Overlying and
interfingering with the Cow Branch Formation is the Stoneville Formation that consists of red,
gray, and brown, poorly-sorted conglomerates, arkosic sandstones, and mudstones deposited
in alluvial fans and braided streams that developed adjacent to the northwest border fault zone
(Thayer 1970; Thayer and Robbins 1992). Alluvial and terrace deposits consisting of
unconsolidated sand, silt, and clay with occasional sub-rounded to well-rounded pebbles occur
along the Dan River and major tributaries. A geologic map of the region is shown on Figure 5-2.
5.2 Regional Hydrogeology
The hydrogeologic regime in the Dan River Basin is characterized by fractured, bedded
sedimentary sequences underlying soil and saprolite. Groundwater may occur under both
unconfined, water table conditions (similar to most Piedmont crystalline sites) and confined
conditions. Controls of groundwater flow are a combination of the interaction of factors including
topography, stratigraphic sequence and lithology, distribution and intensity of fractures,
presence of diabase intrusions (both dams and sills), basalt flows, and weathering processes of
the bedrock (Venkatakrishnan and Gheorghiu 2003).
Groundwater flow has both local and regional components with shallow groundwater
discharging locally to nearby streams (and some movement downward into the deeper flow
system) and deeper groundwater flow toward points of regional discharge, that are generally
higher order stream courses (Venkatakrishnan and Gheorghiu 2003). Both shallow and deep
groundwater systems generally flow in a direction similar to the topographic gradient.
Although the DRSS site is not underlain by metamorphic and/or igneous rocks, the conceptual
groundwater system for fractured crystalline rocks developed by Heath (1980), Harned and
Daniel (1992), and LeGrand (1988, 1989, 2004) is applicable based on review of the available
data from previous studies and investigations and the data collected during the CSA field
investigation.

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY

26

The groundwater system is comprised of two interconnected layers, or mediums: 1) residual
soil/saprolite and weathered fractured rock (regolith) overlying 2) fractured bedrock (Heath
1980; Harned and Daniel 1992; Figure 5-3). The regolith layer is a thoroughly weathered and
structureless residual soil that occurs near the ground surface with the degree of weathering
decreasing with depth. The residual soil grades into saprolite, a coarser grained material that
retains the structure of the parent bedrock. Beneath the saprolite, partially weathered/fractured
bedrock occurs with depth until sound bedrock is encountered. This mantle of residual
soil/regolith, saprolite, and weathered/fractured rock is a hydrogeologic unit that covers and
crosses various types of rock (LeGrand 1988). This soil/regolith layer serves as the shallow
unconfined groundwater system and provides an intergranular medium through which the
recharge and discharge of water from the underlying fractured rock occurs. Within the fractured
sedimentary bedrock, the fractures control both the hydraulic conductivity and storage capacity
of the rock mass. A TZ at the base of the regolith has been interpreted to be present in many
areas of the Piedmont and based on this investigation is present in the Dan River Basin. Harned
and Daniel (1989) describe the TZ as consisting of partially weathered/fractured bedrock and
lesser amounts of saprolite that grade into bedrock. They also describe the TZ as “being the
most permeable part of the system, even slightly more permeable than the soil zone” (Harned
and Daniel 1992). Harned and Daniel (1992) suggested the zone may serve as a conduit of
rapid flow and transmission of water.
Until recently, most of the information supporting the existence of the TZ was qualitative based
on observations made during the drilling of boreholes and water-wells, although some
quantitative data is available for the Piedmont region (Stewart 1964; Stewart et al. 1964; Nutter
and Otton 1969; Harned and Daniel 1992). Using a database of 669 horizontal hydraulic
conductivity measurements in boreholes at six locations in the Carolina Piedmont, Schaeffer
(2009; 2014a) statistically showed that a TZ of higher hydraulic conductivity exists in the
Piedmont groundwater system when considered within Harned and Daniel’s (1989) two types of
bedrock conceptual framework.
The TZ is comprised of partially weathered rock (PWR), open, steeply dipping fractures, and low
angle stress relief fractures, either singly or in various combinations below drilling refusal
(auger, roller cone, or casing advancer; Schaeffer 2011; 2014b). The TZ has less advanced
weathering relative to the regolith and generally the weathering has not progressed to the
development of clay minerals that would decrease the permeability of secondary porosity
developed during weathering (i.e., the new fractures developed during the weathering process,
and/or the enhancement of existing fracture systems). The characteristics of the TZ can vary
widely based on the interaction of rock type, degree of weathering, degree of systematic
fracturing, presence of stress-relief fracturing, and the general characteristics of the bedrock
(foliated/layered, massive, or in between). The TZ is not a continuous layer between the regolith
and bedrock; it thins and thickens within short distances and is absent in places (Schaeffer
2011; 2014b). The absence, thinning, and thickening of the TZ are related to the characteristics
of the underlying bedrock (Schaeffer 2014b).
As previously described, the TZ may vary due to different rock types and associated rock
structure. Harned and Daniel (1992) divided bedrock into two conceptual models: 1)
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY

27

foliated/layered structures (metasedimentary and metavolcanic sequences; in the case of the
DRSS site, sedimentary bedding) and 2) massive/plutonic structures (plutonic and metaplutonic
complexes) (Figure 5-4). Strongly foliated/layered (sedimentary) rocks are thought to have a
well-developed TZ due to the breakup and weathering along the foliation planes or layering,
resulting in numerous rock fragments (Harned and Daniel 1992). More massive/plutonic rocks
are thought to develop an indistinct TZ because they do not contain foliation/layering and tend
to weather along relatively widely spaced fractures (Harned and Daniel 1992). Schaeffer
(2014a) proved the Harned and Daniel (1989) hypothesis that foliated/layered bedrock would
have a better developed TZ than massive/plutonic bedrock. The foliated/layered bedrock TZ has
a statistically significant higher hydraulic conductivity than the massive/plutonic bedrock TZ
(Schaeffer 2014a).
LeGrand’s (1988, 1989) conceptual model of the groundwater setting in the Piedmont,
applicable to the DRSS site, incorporates the Daniel and Harned (1992) two-medium
regolith//bedrock with TZ system into an entity that is useful for the description of groundwater
conditions. That entity is the surface drainage basin that contains a perennial stream (LeGrand
1988). Each basin is similar to adjacent basins and the conditions are generally repetitive from
basin to basin. Within a basin, movement of groundwater is generally restricted to the area
extending from the drainage divides to a perennial stream (Slope-Aquifer System; Figure 5-5;
LeGrand 1988, 1989, 2004). Rarely does groundwater move beneath a perennial stream to
another more distant stream or across drainage divides (LeGrand 1989). The crests of the water
table underneath topographic drainage divides represent natural groundwater divides within the
slope-aquifer system and may limit the area of influence of wells or contaminant plumes located
within their boundaries. The concave topographic areas between the topographic divides may
be considered as flow compartments that are open-ended down slope.
Therefore, the groundwater system is a two-medium system generally restricted to the local
drainage basin. The groundwater occurs in a system composed of two interconnected layers:
residual soil/saprolite and weathered rock (TZ) overlying fractured sedimentary rock. The
systems are separated by the TZ portion of the residual soil, saprolite, and weathered rock.
Typically, the residual soil/saprolite is partially saturated and the water table fluctuates within it.
Water movement is generally preferential through the weathered/fractured and fractured
bedrock of the TZ (i.e., enhanced permeability zone). The character of such aquifers results
from the combined effects of the rock type, fracture system, topography, and weathering.
Topography exerts an influence on both weathering and the opening of fractures, while the
weathering of the crystalline rock modifies both transmissive and storage characteristics.
The sedimentary rocks in the Dan River Basin are hard with tight grain packing (Thayer and
Robbins 1992). The primary porosity and permeability of the conglomerates and sandstones are
very low. Thayer and Robbins (1992) found that the average primary porosity of eight
sandstones from the basin is 3.8% with a low mean permeability of 0.05 millidarcies (mD), both
due to the tight grain packing and high percentage of allogenic clay matrix. The fine-grained
shales and mudstones have lower primary porosity and permeability than the sandstones.
Groundwater flow paths in this geologic environment are almost invariably restricted to the zone
underlying the topographic slope extending from a topographic divide to an adjacent stream.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY

28

Under natural conditions, the general direction of groundwater flow can be approximated from
the surface topography (LeGrand 2004).
Groundwater recharge in the region is derived entirely from infiltration of local precipitation.
Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater
discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains
(LeGrand 2004). Average annual precipitation contributing to recharge in the Piedmont ranges
from 42 to 46 inches. Mean annual recharge in the Piedmont ranges from 4.0 to 9.7 inches per
year (Daniel 2001).

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

29

6.0 Site Geology and Hydrogeology
6.1 Site Geology
DRSS and its associated ash basin system are located in the Dan River Triassic Basin, one of
several northeast-trending Triassic basins that occur within the Piedmont Province. Thayer
(1970) divided the rocks of the basin into three stratigraphic formations (oldest to youngest): 1)
Pine Hall Formation, 2) Cow Branch Formation, and 3) Stoneville Formation. The Pine Hall
Formation is along the southeast margin of the basin and consists of gray to red, medium- to
coarse-grained conglomerate, pebbly sandstone grading upward into massive, bioturbated red
siltstone and mudstone. This sequence defines an upward fining sequence suggesting braided
river deposits (Thayer 1970; Thayer and Robbins 1992). The Cow Branch Formation
conformably overlies and interfingers with the Pine Hall Formation and consists of black and
gray bedded, carbonaceous shales and mudstones, sandstones (arkosic), and thin coal beds
deposited in a lacustrine environment (Thayer 1970; Thayer and Robbins 1992). The site is
underlain by rocks of the Pine Hall (Tph) and Cow Branch (Tcb) Formations (Figure 6-1).
Alluvial and terrace deposits consisting of unconsolidated sand, silt, and clay with occasional
sub-rounded to well-rounded pebbles occur along the Dan River and major tributaries.
A site geologic map, based on Carpenter (1982), field reconnaissance, and the first rock type
encountered in boreholes installed for this CSA, is presented on Figure 6-1. Diabase boulders
were found on the DRSS site north of the DRCCS (Figure 6-1) near the inferred diabase dike of
Carpenter (1992) confirming its existence at that location and suggesting that it continues to the
southeast as shown on the regional and site geologic maps. None of the boreholes encountered
the dike. The alluvial contact, with a location different than that shown on Figure 5-2, along the
Dan River south of the ash basin system, is based on borehole data and field reconnaissance.
The installed well and sample locations are shown on Figure 6-2.
6.1.1 Soil Classification
A total of 67 borings were installed as part of this assessment. The following soils/materials
were encountered in the boreholes:
 Ash – Ash was encountered in borings advanced within the ash basin and ash storage
areas, as well as in some borings advanced through the basin perimeter and
intermediate dams. Ash several inches thick was encountered in one location within the
ash dredge area located between Ash Storage 1 and Ash Storage 2. Ash was generally
described as gray to dark bluish gray with a silty to sandy texture, consistent with fly ash
and bottom ash.
 Fill – Fill material generally consisted of re-worked silts and clays that were borrowed
from one area of the site and re-distributed to other areas. Fill was used in the
construction of dams and as cover for ash storage areas.
 Alluvium – Alluvium is unconsolidated soil and sediment that has been eroded and
redeposited by streams and rivers. Alluvium may consist of a variety of materials ranging
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

30

from silts and clays to sands and gravels. During site construction and plant operation,
alluvial deposits have been removed or covered. Alluvium was encountered in borings
along the Dan River during the project subsurface exploration activities. Designations
between alluvium and fill are approximate and were challenging to distinguish due to the
similarities in material.
 Residuum (Residual soils) – Residuum is the in-place weathered soil that consists of
red, brown, yellow, and gray clayey silt to silty clay. This unit was encountered in various
thicknesses across the site. It is believed that substantial thicknesses of residuum were
removed to practical excavation depths and used for fill. Designations between residuum
and fill are approximate and were challenging to distinguish due to the similarities in
material.
 Saprolite – Saprolite is soil developed by in-place weathering of rock similar to the
bedrock that consists of red, brown, yellow, and gray clayey silt to silty clay with traces of
sand and rock fragments. The primary distinction from residuum is that saprolite typically
retains some structure (e.g., mineral banding) from the parent rock. This unit was found
across the site as a generally thin (e.g., less than 5 feet thick) stratigraphic unit. It is
assumed that historical earthwork on-site may have been carried vertically downward
through the residuum to or near the PWR, thus removing much of the saprolite.

Undisturbed and split-spoon samples collected during the field investigation were tested for
various geotechnical parameters including natural moisture content, Atterberg Limits
(undisturbed samples only), grain size with hydrometer, total porosity (undisturbed samples
only), and vertical hydraulic conductivity (undisturbed samples only), and were classified using
the Unified Soil Classification System (USCS). Geotechnical index property testing was
completed for disturbed and undisturbed samples in accordance with ASTM standards. Twenty-
eight undisturbed (“Shelby Tube”) samples received a full suite of geotechnical index testing.
The index property testing program for undisturbed samples comprised USCS classification
(ASTM D 2487), natural moisture content (ASTM D 2216), Atterberg Limits (ASTM D 4318),
grain size distribution, including sieve analysis and hydrometer (ASTM D 422), total porosity
calculated from Specific Gravity (ASTM D 854), and hydraulic conductivity (ASTM D 5084). Five
undisturbed samples were unable to receive the complete index property testing program due to
low recovery, wax and gravel mixed in the tube, loose material, or damaged tubes. Twenty-two
disturbed (“Split Spoon” or “Jar”) samples received grain size distribution with hydrometer
(ASTM D 422), and natural moisture content (ASTM D 2216). The results are presented in
Section 11.0.
6.1.2 Rock Lithology
Major rock types at the DRSS site are sandstones, siltstones, mudstones, shales, and
conglomerates. The sandstones are gray to red, fine-grained, poorly sorted, mineralogically
immature, and exhibit tight grain packing. Coarser, detrital micas (biotite and muscovite) are
oriented parallel to bedding. The finer-grained matrix consists of angular quartz and feldspar
mixed with detrital sericite, illite, and chlorite. The siltstones are gray to red, very fine-grained
and are similar to the sandstone units in mineralogy and structure. Layers of interlayered
sandstone and siltstone (layers up to 1 inch thick) are present in the core and exhibit fining
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

31

upwards sequences. The mudstones are red to black, non-fissile, very fine-grained, poorly
sorted with larger grains of quartz, minor plagioclase, and muscovite. They exhibit tight grain
packing. Well-developed laminations with larger mica flakes and calcite stringers are present
parallel to the laminations. The matrix consists of angular quartz and feldspar mixed with detrital
sericite, illite, and chlorite and is calcareous. The darker mudstones are carbonaceous. The
shale, generally black, is fissile and is similar to the mudstones in mineralogy and texture. The
conglomerates occur in thin layers within sandstone beds and both matrix-supported and clasts-
supported conglomerates were noted in the rock core. The conglomerates consist of angular to
subrounded quartz and alkali and plagioclase feldspars grains with the finer portions of the
conglomerates having mineralogy and texture as the sandstones.
6.1.3 Structural Geology
Bedding planes are the major structural feature at the DRSS site. The bedding is oriented N30°-
45°E with dips of 20° to 45° NW with sandstone bedding varying from thinly (0.03 to 0.3 foot) to
thickly bedded (1 to 3 feet), mudstone bedding from thinly (0.03 to 0.3 foot) to medium (0.3 to 1
foot) bedded, and minor shale interlayers are thinly laminated (<0.03 foot). Two major joint sets
were noted in the rock core: one parallel to the strike of bedding (N30°-45°E) with steep dips
and one perpendicular to bedding (N45°-60°W) with steep dips. Other minor fracture
orientations were noted. Minor faulted areas were noted in the rock core and were generally
parallel to the strike of bedding with dips from 60° to near vertical and are related to movement
along the Chatham fault zone during deposition.
The map pattern of the Pine Hall and Cow Branch Formations (Figures 5-2 and 6-1) suggests
that gentle folding has occurred along northeast axes parallel to the basin boundaries. The map
pattern can also result from the intertongue relationship between the two formations or
unrecognized intrabasinal faults (Thayer and Robbins 1992).
6.1.4 Fracture Trace Study
6.1.4.1 Introduction
Fracture trace analysis is a remote sensing technique used to identify lineaments on
topographic maps and aerial photography that may correlate to locations of bedrock fractures
exposed at the earth’s surface. Fracture trace analysis is a useful tool for identifying potential
fracture locations, and hence potential preferential pathways for infiltration and flow of
groundwater near a site; however, results are not definitive. Lineaments identified as part of
fracture trace analysis may or may not correspond to actual locations of fractures exposed at
the surface, and if fractures are present, it cannot be determined from fracture trace analysis
whether these are open, healed, or potential groundwater flow paths.
The effectiveness of fracture trace analysis in the Piedmont region is hampered by dense
vegetative cover and abundant alteration of the surface by present and past human activity
(e.g., agriculture, residential development, commercial/industrial activity). The ability to identify
small-scale lineaments on aerial photography that might otherwise be apparent is thereby
hindered.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

32

6.1.4.2 Methods
Available geologic maps for the area were consulted prior to performance of aerial photography
and topographic map interpretation to identify lithologies and structures in the area, and likely
fracture orientations. Both low-altitude aerial photography provided by Duke Energy (from WSP
Global, Inc.) covering approximately 4 square miles, and USGS 1:24000 scale topographic
maps covering an area of approximately 84 square miles were examined.
Maps examined included portions of the Eden Northeast, North Carolina and Eden Southeast,
North Carolina USGS 7.5’ (1:24,000 Scale) topographic quadrangles. Digital copies of the
quadrangles were obtained and viewed on a monitor at up to 7x magnification. Lineaments
identified were plotted directly on the digital images.
Photography provided for review included 1”=600’ scale, 9 x 9 inch black-and-white (grayscale)
contact prints dated April 17, 2014. Stereo coverage was complete across the area shown on
Figure 6-4. The photography was examined using a Lietz Sokkia MS-27 mirror stereoscope with
magnifying binocular eyepiece. Lineaments identified on the photographs were marked on hard
copies of scanned images (600 dpi resolution), and subsequently compiled onto a photomosaic
base.
Rose diagrams were prepared for lineament trends identified from both aerial photography and
topographic map interpretation, and are included as inserts on the respective figures (Figures 6-
3 and 6-4).
6.1.4.3 Results
Lineaments identified from topographic mapping are shown and lineament trends indicated by a
rose diagram are included on Figure 6-3. More lineaments were found in the polydeformed and
metamorphosed Paleozoic rocks south of Dan River.
Three marked lineament trends are apparent in the topography: 1) generally east to east-
northeast-trending lineaments subparallel to the structural fabric in the Paleozoic sequence; 2)
northeast-trending lineaments in both the Paleozoic and Mesozoic sequences, subparallel to the
normal fault north of Eden and possibly related to opening and infilling of the Dan River Basin;
and 3) north- to northwest-trending lineaments of the type generally associated with Triassic
extensional tectonics and emplacement of diabase dikes in the Piedmont.
A cluster of north to northwest-trending lineaments in Paleozoic rocks south and southwest of
DRSS may be associated with two large diabase dikes inferred from aeromagnetic data
(Carpenter 1982). A long, northward-trending linear segment of Town Creek south-southeast of
DRSS suggests the presence of a major structure, possibly a diabase dike that was not inferred
by Carpenter 1982. If related to a dike, the dike has a northerly trend and does not pass
beneath DRSS.
Lineaments identified from aerial photography are shown and lineament trends indicated by a
rose diagram are included on Figure 6-4. A total of 15 lineaments were identified from aerial-
photography interpretation, all within the Paleozoic sequence south of the Dan River. Most are
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

33

characterized by a northwest trend. North-trending lineaments located along the lower
(northern) reaches of Town Creek potentially indicate the presence of a diabase dike as
discussed above. A number of northeast- to east-trending lineaments also occur across the
area south of the Dan River.
6.1.5 Effects of Structure on Groundwater Flow
The significant geologic structures with respect to groundwater movement in the bedrock of the
regolith-fractured rock aquifer system at the site are the bedding planes, joints, and minor faults
and a diabase dike that cuts across the other rock units. Differential weathering of the
sedimentary rocks related to rock type could result in northeast-trending depressions along the
top of the bedrock surface below the regolith and could direct groundwater flow along it as well
as result in highly variable thickness of the TZ. The joints are generally discontinuous and
confined to sedimentary layers within the bedrock and will not impart significant directionality to
overall groundwater flow paths. The extent of the minor northeast-trending faulting noted in the
rock core is not known, but would add additional directionality in the northeast direction. The
north- to northwest-trending diabase dike could either form a barrier to flow, a flow path, or have
no effect on groundwater flow depending on its degree of fracturing and weathering. A non-
fractured diabase dike would be a flow barrier and would direct groundwater flow along its
contact. A highly fractured, weathered dike could act as a flow channel.
6.1.6 Soil and Rock Mineralogy and Chemistry
Soil and rock mineralogy and chemistry analyses are incomplete as of the date of this report.
Soil mineralogy and chemistry results through July 31, 2015 are shown in Table 6-1
(mineralogy), Table 6-2 (chemistry, % oxides), and Table 6-3 (chemistry, elemental
composition). The mineralogy and chemical composition of TZ materials are presented in Table
6-4 (mineralogy) and Table 6-5 (chemistry). Whole rock chemistry results (% oxides and
elemental composition) are shown in Tables 6-6 and 6-7, respectively. Petrographic analysis of
rock (thin-sections) and the remaining soil mineralogy and chemistry analyses will be included in
the CSA supplement.
The dominant mineral constitutes in the soils are quartz, feldspar (both alkali and plagioclase
feldspars), and muscovite/illite, Soils exhibiting a higher degree of weathering show an increase
in kaolinite with higher percentage amorphous phase (lacking distinct crystalline structure).
Other minerals identified include chlorite, biotite, calcite, dolomite, hornblende/amphibole, pyrite,
ilmenite, goethite, gypsum and smectiite/chlotite. The major oxides in the soils are SiO2 (41.59%
- 75.49%), Al2O3 (13.12% - 34.56%), and Fe2O3 (2.61% - 11.02%). Major TZ minerals are
quartz, feldspar, muscovite/vermiculite/illite, kaolinite, chlorite, and smectite. The major oxides
are SiO2 (50.4% - 67.9%), Al2O3 (16.2% - 25.5%), and Fe2O3 (8.5% - 15.1%).

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

34

6.2 Site Hydrogeology
6.2.1 Groundwater Flow Direction
Accessible voluntary, compliance, closure, and ash basin assessment monitoring wells were
gauged for depth to water and total well depth during a comprehensive groundwater elevation
reading event on June 28 and 29, 2015. Depth to water measurements were subtracted from
surveyed top of well casing elevations to produce groundwater elevations in shallow, deep, and
bedrock monitoring wells. Groundwater flow direction was estimated by contouring these
groundwater elevations.
The shallow aquifer includes the shallow and deep groundwater monitoring wells (S and D
wells) and the deep aquifer only includes the fractured bedrock wells (BR wells). In general,
groundwater within the shallow aquifer/TZ (S/D wells), and fractured bedrock (BR wells) flows
from the northern extent of the DRSS property boundary south and southeast toward the Dan
River. However, in the area north of Ash Storage 1, groundwater elevation data suggest the
presence of a groundwater divide extending from MW -12 east to GWA-1. To the north of this
divide, localized groundwater within the shallow aquifer/ TZ flows north, away from the DRSS
site and toward an unnamed tributary that flows to the Dan River. Data gathered as part of this
CSA support the understanding that groundwater flow beneath the ash storage areas is to the
south and southeast toward the Dan River rather than to the north. Shallow groundwater flow
direction is shown on Figure 6-5. Groundwater flow within the TZ is shown on Figure 6-6.
Groundwater flow within fractured bedrock is shown on Figure 6-7.
6.2.2 Hydraulic Gradient
Horizontal hydraulic gradients were derived for the shallow aquifer, TZ, and fractured bedrock
by calculating the difference in hydraulic heads over the length of the flow path between two
wells with similar well construction (e.g., both wells having 15-foot screens within the same
water–bearing unit). The following equation was used to calculate horizontal hydraulic gradient:
i = dh / dl
where i is the hydraulic gradient; dh is the difference between two
hydraulic heads (measured in feet); and dl is the flow path length
between the two wells (measured in feet).
Applying this equation to wells installed during the CSA yields the following average horizontal
hydraulic gradients (measured in feet/foot):
 S wells: 0.030
 D wells: 0.029
 BR wells: 0.037
A summary of hydraulic gradient calculations is presented in Table 6-6. Note that vertical
hydraulic gradients are discussed in Section 11.3.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
6.0 SITE GEOLOGY AND HYDROGEOLOGY

35

6.2.3 Effects of Geologic/Hydrogeologic Characteristics on Contaminants
Migration, retardation, and attenuation of COIs in the subsurface is a factor of both physical and
chemical properties of the media in which the groundwater passes. Soil samples were collected
and analyzed for grain size, total porosity, soil sorption (Kd), and anions/cations to provide data
necessary for completion of the three-dimensional groundwater model discussed in Section
13.0. As agreed upon with NCDENR (Appendix A), results of the groundwater model will be
presented in the CAP.
6.2.4 Site Hydrogeologic Conceptual Model
The site hydrogeologic conceptual model (referred to as the site conceptual model, or SCM) is a
conceptual interpretation of the processes and characteristics of a site with respect to the
groundwater flow and other hydrologic processes at the site. The May 31, 2007 NCDENR
document, Hydrogeologic Investigation and Reporting Policy Memorandum was used as
general guidance to developing the model. General components of the SCM consist of
developing and describing the following aspects of the site: geologic/soil framework, hydrologic
framework, and the hydraulic properties of site materials. More specifically, the SCM describes
how these site-specific aspects affect groundwater flow at the site. In addition to these site-
specific aspects, the SCM:
 Describes the site and regional geology,
 Presents longitudinal and transverse cross-sections showing the hydrostratigraphic
layers,
 Develops the hydrostratigraphic layer properties required for the groundwater model,
 Presents a groundwater contour map showing the potentiometric surface of the shallow
aquifer, and
 Presents information on horizontal and vertical groundwater gradients.
The SCM serves as the basis for developing and understanding the hydrogeologic
characteristics of the site and for developing a groundwater flow and transport model. Historic
site groundwater elevations and ash basin water elevations were used to develop a historic
estimated seasonal high groundwater contour map for the site. A fracture trace analysis
(described previously in Section 6.1.4) was also performed for the DRSS site, as well as on-
site/near-site geologic mapping, to better understand site geology and to confirm and support
the SCM.
An updated SCM, based on data obtained during the CSA activities and refined through
completion of groundwater modeling, will be presented in the CAP.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
7.0 SOURCE CHARACTERIZATION

36

7.0 Source Characterization
At the DRSS site, source characterization was performed through the completion of soil borings,
installation of monitoring wells, and collection and analysis of associated solid matrix and
aqueous samples. Ash samples were collected for analysis of physical characteristics (e.g.,
grain size, porosity) to provide data for evaluation of retention/transport properties within and
beneath the ash basin and ash storage areas. Ash samples were collected for analysis of
chemical characteristics (e.g., total inorganics, leaching potential) to provide data for evaluation
of constituent concentrations and distribution. Samples were collected in general accordance
with the W ork Plan. Drilling and installation variances are documented in Appendix C. For the
purpose of this CSA report and for use throughout this section, the term COI is used to refer to
any constituent or parameter that exceeded its applicable regulatory standard.
Ash, ash basin surface water, porewater, and seep sample locations used for source
characterization are shown on Figure 7-1. COIs and laboratory methods used for analysis of
solid matrix samples are presented in Table 7-1. Laboratory results of total inorganic and
anion/cation analyses of ash samples are presented in Table 7-2. Laboratory results of aqueous
matrix (groundwater, surface water, ash porewater and seeps) parameters and analytical
methods are presented in Table 7-3. Laboratory results of ash basin surface water samples are
presented in Table 7-4. Ash basin porewater sample results are presented in Table 7-5.
7.1 Ash Basin
7.1.1 Ash (Sampling and Chemical Characteristics)
Nine borings (AB-5D, AB-10D, AB-15D, AB-20S, AB-25BR, AB-35BR, MW-308BR, MW-311BR,
and MW -314BR) were advanced within the ash basin waste boundary to obtain ash samples for
chemical analyses.
Eight COIs (arsenic, , boron, cobalt, iron, manganese, selenium, and vanadium) were reported
above the North Carolina Preliminary Soil Remediation Goals (PSRGs) for Industrial Health
and/or Protection of Groundwater Standards in one or more ash samples (see Table 7-2).
7.1.2 Ash Basin Surface Water (Sampling and Chemical Characteristics)
Two surface water samples (SW -1 and SW-9) were collected from within the ash basin. Sample
SW -9 was collected from the Primary Cell and SW -1 was collected from surface water within the
Secondary Cell (see Figure 7-1).
Four COIs (aluminum, arsenic, copper, and zinc) were reported above 2B Standards for both
SW -1 and SW -9 (see Table 7-4).
7.1.3 Ash Porewater (Sampling and Chemical Characteristics)
Ash porewater refers to water samples collected from wells installed within the ash basin and
screened in ash. HDR does not consider these results to be representative of groundwater.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
7.0 SOURCE CHARACTERIZATION

37

Four ash porewater monitoring wells (AB-5S, AB-10S, AB-10SL, and AB-25S) were installed
within the waste boundary of the ash basin and were screened within ash. In addition, one
temporary monitoring well (AB-15S) was installed within the Primary Cell of the ash basin to
facilitate collection of an ash porewater sample. Note that a permanent well could not be
installed in this location due to concerns with stability of ash within the basin, as documented on
the variance table in Appendix C.
Six COIs (antimony, arsenic,, cobalt, iron, manganese, and vanadium) were reported above 2L
Standards or IMACS in porewater samples collected from wells in the ash storage areas and
ash basin (see Table 7-5). Arsenic and vanadium concentrations generally increased in the
direction of groundwater flow (e.g., from well MW -5S to well MW-10S). In general, cobalt, iron,
and manganese concentrations decreased in the direction of groundwater flow. Several other
COIs exceeded 2L Standards or IMACs, but appeared to be isolated instances and not
influenced by groundwater flow. Ash porewater sample locations and exceedances of 2L
Standards or IMACs are shown on Figure 7-1.
7.1.4 Ash Porewater Speciation
Speciation is the analysis of the composition of a particular analyte in a system. Speciation is
important for understanding the fate and transport of COIs. Three locations, AB-10S, AB-10SL,
and AB-25S, were sampled for chemical speciation analyses of arsenic (III), arsenic (V),
chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV), and selenium
(VI). Results for chemical speciation of porewater samples are presented in Table 7-6. Further
evaluation of chemical speciation results will be included in the CAP.
7.1.5 Radiological Laboratory Testing
Dissolved radionuclides from naturally occurring sources (e.g. soil or rock) may exist in water.
The USEPA regulates various radionuclides in drinking water. For purposes of this assessment,
radium-226, radium-228, natural uranium, uranium-233, uranium-234, and uranium-236 were
analyzed. Three locations, AB10S/SL and AB-25S, were sampled for the analytes listed above.
Results for radiological laboratory testing of porewater samples are presented in Table 7-7.
Further evaluation of radiological laboratory testing results will be included in the CAP.
7.2 Ash Storage Areas
7.2.1 Ash (Sampling and Chemical Characteristics)
Eight borings (AS-4D, AS-8D/BR, MW -301BR, MW-303BR, MW-306BR, MW -315BR, and MW-
318D) were advanced within the ash storage waste boundary to obtain ash samples for
chemical analyses.
Eight COIs (arsenic, barium, boron, cobalt, iron, manganese, selenium, and vanadium) were
reported to have exceeded either the North Carolina Industrial Health or Protection of
Groundwater PSRGs (see Table 7-2).
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
7.0 SOURCE CHARACTERIZATION

38

7.2.2 Ash Porewater (Sampling and Chemical Characteristics)
As part of this CSA, monitoring wells installed within the ash storage areas were constructed
with screened intervals set below ash. Prior to this CSA effort, between June and July 2013,
AMEC Environment & Infrastructure (AMEC) installed monitoring wells within the ash storage
area with well screens set in ash that serve to monitor ash porewater. The following monitoring
wells were used to monitor porewater: OW-305S, OW-315D, and OW-320D.
A review of data collected by AMEC indicates that arsenic, boron, chromium, cobalt, iron,
manganese, and vanadium exceeded the 2L Standards or IMACs in groundwater samples
collected from one or more of the above-referenced wells.
7.3 Leaching Potential of Ash
In addition to total inorganic testing of ash samples, 16 ash samples collected from borings
completed within the ash basin and ash storage areas were analyzed for leachable inorganics
using Synthetic Potential Leaching Procedure (SPLP) analysis (see Table 7-8). The purpose of
the SPLP testing is to evaluate the mobility, or leaching potential of COIs to impact groundwater
above the 2L Standards or IMACs. The results of SPLP analyses indicated that the following
COIs exceeded their 2L Standards or IMACs: antimony, arsenic, barium, beryllium, chromium,
cobalt, iron, lead, manganese, selenium, thallium, and vanadium. However, it is unclear to what
severity these COIs would impact groundwater if infiltration continues over time. Based on this
analysis, development of site-specific leaching values would be beneficial as a more realistic
screening value to protect groundwater.
7.4 Seeps
7.4.1 Review of NCDENR March 2014 Sampling Results
In March 2014, NCDENR sampled the following seeps at DRSS (see Figure 7-1 and Table 7-9):
 NPDES Outfall 002
 INFSW009
 SW009 #2165
 NPDES 001, SW021, old NPDES 005 (OUT001)
 NPDES004 and SW2
 Old NPDES006
 CCSW002OUT
 CCSW001
 DRRC001 (also CCSW002OUT48)

Based on review of the March 2014 sampling results and measured field parameters, the
following COIs exceed 2B Standards at one or more locations: dissolved oxygen (DO),
aluminum, nickel, and zinc.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
7.0 SOURCE CHARACTERIZATION

39

March 2014 sampling results and measured field parameters were also compared to 2L
Standards. Iron, manganese, zinc, and pH exceeded their respective 2L Standards.
7.4.2 Ash Basin and NCDENR Seep Sampling Results – CSA Activities
7.4.2.1 Ash Basin Seeps
Four seeps (S-1 through S-4) are associated with the DRSS ash basin. Seeps S-1 through S-3
are located near an unnamed tributary along the eastern property boundary and downgradient
of the Secondary Cell. Seep S-4 is located at the southwestern toe of the Primary Cell dam,
adjacent to the boat ramp and river near the southern property boundary. Seep locations are
shown on Figure 7-1.
Several attempts were made to sample seeps S-2 through S-4, but these seeps were dry during
each attempt and, therefore, were not sampled. Seep S-1 was successfully sampled and
analytical results are provided in Table 7-10. Three COIs exceeded 2L Standards or IMACs at
Seep S-1: cobalt, manganese, and vanadium.
7.4.2.2 NCDENR Seeps
Four NCDENR-identified seeps (INFSW009, CSSW001, CCSW002OUT, and DRRC001) were
planned to be sampled during this groundwater assessment. Seep INFSW009 was dry at the
time of sampling; however, samples were collected from CSSW001, CCSW002OUT, and
DRRC001. Samples collected from one or more of these seep locations exceeded 2L Standards
or IMACs for the following COIs: cobalt, iron, manganese, and vanadium (see Table 7-10).
7.4.2.3 Seep Speciation
Speciation is the analysis of the composition of a particular analyte in a system. Speciation is
important for understanding the fate and transport of COIs. Four locations, CCSW001,
CCSW002, DRRC001, and S-1, were sampled for chemical speciation analyses of arsenic (III),
arsenic (V), chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV),
and selenium (VI). Results for chemical speciation of surface water are presented in Table 7-11.
Further evaluation of chemical speciation results will be included in the CAP.
7.5 COIs Exceeding Applicable Standards
Based on evaluation of the ash, ash basin surface water, and seep sampling data, the following
COIs exceeding applicable standards were identified:
7.5.1 COIs in Ash (based on total inorganics analysis, as shown in Table 7-2)
 Arsenic
 Barium
 Boron
 Cobalt
 Iron
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
7.0 SOURCE CHARACTERIZATION

40

 Manganese
 Selenium
 Vanadium
7.5.2 COIs in Surface Water (based on water quality analysis, as shown in Table 7-4)
 Aluminum
 Arsenic
 Copper
 Zinc
7.5.3 COIs in Ash Porewater (based on water quality analysis, as shown in Table 7-5
and data reviewed from 2013 assessment activities in support of conceptual
closure design of DRSS ash basin)
 Antimony
 Arsenic
 Boron
 Chromium
 Cobalt
 Iron
 Lead
 Manganese
 pH
 Vanadium
7.5.4 COIs in Seeps and Stormwater (based on water quality analysis, as shown in
Table 7-10)
 Cobalt
 Iron
 Managanese
 Vanadium
This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
8.0 SOIL AND ROCK CHARACTERIZATION

41

8.0 Soil and Rock Characterization
The purpose of soil and rock characterization is to evaluate the physical and geochemical
properties in the subsurface with regard to COI presence, retardation, and migration. Soil and
rock sampling was performed in general accordance with the procedures described in the Work
Plan. Refer to Appendix D for a detailed description of these methods and Appendix E for field
and sampling quality control / quality assurance protocols.
Soil, PWR, and bedrock samples were collected from background locations, beneath the ash
basin and ash storage areas, and beyond the waste boundaries. Table 8-1 summarizes the soil
and rock sampling plan utilized for groundwater assessment activities. Variances from the
proposed sampling plans are presented in Appendix D. The boring locations are shown on
Figure 8-1.
The petrographic analysis of rock (thin-sections), rock chemistry (laboratory) and soil
mineralogy and chemistry will be included in the CSA Supplement.
8.1 Background Sample Locations
Background (BG) boring locations were identified based on the SCM at the time the Work Plan
was submitted. The BG locations were selected in areas assumed to not be impacted by and
topographically upgradient of the DRSS ash basin and ash storage areas. Based on the
groundwater contours shown on Figures 6-5 through 6-7 and the updated SCM, the BG
locations are considered to be hydraulically upgradient of the ash basin and ash storage areas.
The BG boring locations (BG-5S/D, BG-1D, MW -23BR, and SB-1 through SB-3) are considered
to be representative of background soil conditions at the site.
8.2 Analytical Methods and Results
Table 8-2 summarizes analyses and analytical methods for soil, PWR, and bedrock samples
collected. Total inorganic results for background soil samples are presented in Table 8-3. Total
inorganic results for background PWR and bedrock samples are presented in Table 8-4. Total
inorganic results for soil samples are presented in Table 8-5. Total inorganic results for PWR
and bedrock samples are presented in Table 8-6. Figure 8-1 depicts the total inorganic results
for soil, PW R, and bedrock analysis. Cross-section transects are presented on Figure 6-2.
Cross-sections presenting the vertical distribution of COIs along the transect are depicted on
Figures 8-2 through 8-5.
8.3 Comparison of Soil Results to Applicable Levels
Soil, PWR, and bedrock analytical results are compared to the North Carolina PSRGs for
Industrial Health and Protection of Groundwater Standards and are included in Tables 8-3
through 8-6. Frequency and concentration ranges for COI exceedances of North Carolina
PSRGs are listed in Table 8-7.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
8.0 SOIL AND ROCK CHARACTERIZATION

42

8.4 Comparison of Soil Results to Background
In addition to comparing results to regulatory criteria, soil sample results have also been
compared to background concentrations as discussed below. Refer to Figure 8-1 for soil boring
locations.
8.4.1 Background Soil, PWR, and Rock
Background soil locations are identified as SB-1, SB-2, SB-3, BG-1D, BG-5D, and MW -23BR.
The range of concentrations of COIs in background soil samples are provided below and a
summary of results is provided in Table 8-3.
 Arsenic – 3.9 mg/kg to 20 mg/kg
 Cobalt – 5.6 mg/kg to 42.6 mg/kg
 Iron – 16,500 mg/kg to 95,900 mg/kg
 Manganese – 82.7 mg/kg to 2,840 mg/kg
 Selenium – Not detected above the MDL (<5.4 mg/kg to <7.2 mg/kg)
 Vanadium – 16.0 mg/kg to 54.4 mg/kg
8.4.2 Soil, PWR, and Rock Beneath the Ash Basin
Soil, PWR, and rock samples beneath the ash basin were obtained from AB-5D, AB-10D, AB-
15D, AB-25BR, AB-30D, AB-35BR, MW -308BR, MW -310BR, MW-311BR, and MW-314BR. The
range of constituent concentrations along with a comparison to the range of reported
background soil concentrations is provided in Table 8-8.
Constituent concentrations of soils beneath the ash basin tend to be higher for arsenic,
selenium, and vanadium compared to background soil concentrations. Concentrations for
cobalt, iron, and manganese are similar to or lower than background soil concentrations.
8.4.3 Soil, PWR, and Rock Beneath the Ash Storage Areas
Soil, PWR, and rock samples beneath the ash storage areas were obtained from AS-2D, AS-
4D, AS-6D, AS-8D, AS-10D, MW -303BR, MW-315BR, and MW -318D.
The range of constituent concentrations along with a comparison to the range of reported
background soil concentrations is provided in Table 8-9.
Constituent concentrations of soils beneath the ash storage areas tend to be higher for arsenic,
cobalt, and selenium compared to background soil concentrations. Concentrations for iron,
manganese and vanadium are similar to or lower than background soil concentrations.
8.4.4 Soil, PWR and Rock Outside the Waste Boundary
Soil, PWR, and rock samples outside the waste boundary were obtained from GWA-1D, GWA-
2D, GWA-3D, GWA-4D, GWA-6S, GWA-7S, GWA-8D, GWA-9D, GWA-10D, GWA-11D, GWA-
12S, GWA-12D, GWA-14S, GWA-15D, MW-301BR, MW-317BR, BG-1D, BG-5D, SB-1, SB-2,
and SB-3.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
8.0 SOIL AND ROCK CHARACTERIZATION

43

The range of constituent concentrations along with a comparison to the range of reported
background soil concentrations is provided in Table 8-10.
Constituent concentrations of soils outside the waste boundary tend to be higher for arsenic,
iron, and selenium compared to background soil concentrations. Concentrations for cobalt,
manganese, and vanadium are similar to or lower than background soil concentrations.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
9.0 SURFACE WATER AND SEDIMENT CHARACTERIZATION

44

9.0 Surface Water and Sediment
Characterization
The purpose of surface water and sediment characterization is to evaluate whether storage of
CCR has migrated to surface waters in the vicinity of the ash basin and ash storage areas.
Sampling was performed in general accordance with the procedures described in the Work
Plan. Sampling methodology and variances to that methodology are described in Appendix F.
Surface water and sediment sample locations are shown on Figure 9-1. NCDENR’s March 2014
sample locations are shown on Figure 9-2.
9.1 Surface Water
Surface water samples were obtained from locations along the Dan River and two tributary
streams that flow north to south along the eastern and western property boundaries. Surface
water parameters and laboratory methods used for analysis of aqueous matrix samples are
presented in Table 7-1. Surface water sample results for total and dissolved fractions are
presented in Table 9-1.
9.1.1 Comparison of Exceedances to 2B Standards
Surface water analytical results are compared to the 2B Standards. Concentration ranges for
exceedances of COIs are listed in Table 9-2. Note that antimony, cadmium, and sulfide were not
detected in surface water.
9.1.2 Comparison of Exceedances to Background
9.1.2.1 Background Surface Water
Background surface water locations are identified as SW-5 and SW-8. Note that sample SW -8
was collected from the Dan River upstream of the DRSS site. Background concentrations for
COIs at these two locations are provided below:
 Aluminum – <5.0 micrograms per liter (µg/L) to 90 µg/L
 Arsenic – <1.0 µg/L to 0.22J3 µg/L
 Chromium – <1.0 µg/L to 0.59 µg/L
 Cobalt – <1.0 µg/L to 0.32J µg/L
 Copper – 1.3 µg/L to 4.62J+ µg/L
 Lead – <1.0 µg/L to 0.64 µg/L
 Thallium – <0.1 µg/L to <0.2 µg/L
 Zinc – <0.005 µg/L to <0.01 µg/L

3 J = Detected, estimated concentration
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
9.0 SURFACE WATER AND SEDIMENT CHARACTERIZATION

45

9.1.2.2 Ash Basin Surface Water
Ash basin surface water was obtained at locations SW -1 and SW -9.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-3.
Constituent concentrations of surface water within the ash basin tend to be higher for aluminum,
arsenic, copper, and zinc compared to background surface water concentrations.
Concentrations for chromium, cobalt, lead, and thallium are similar to or lower than background
surface water concentrations.
9.1.2.3 Dan River Surface Water
Dan River surface water locations are identified as SW -6 and SW -7.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-4.
Constituent concentrations of surface water from the Dan River tend to be higher for arsenic,
chromium, cobalt, lead and zinc compared to background surface water concentrations.
Concentrations for aluminum, copper, and thallium are similar to or lower than background
surface water concentrations.
9.1.2.4 Tributary Stream Surface Water
Tributary surface water locations are identified as SW -3 and SW -4.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-5.
Constituent concentrations of surface water from the tributary tend to be higher for aluminum,
arsenic, chromium, copper, lead, thallium and zinc compared to background surface water
concentrations.
9.1.3 Discussion of Results for Constituents without 2B Standards
In addition to the COIs discussed above, surface water samples were also analyzed for the
following constituents that do not have 2B Standards: boron, iron, manganese, mercury,
selenium, and vanadium. In lieu of 2B Standards, concentrations of COIs have been compared
to background concentrations in the sections below.
9.1.3.1 Background Surface Water
Background surface water locations are identified as SW -5 and SW-8.
 Boron – 0.057 mg/L to 0.18 mg/L
 Iron – 0.412 mg/L
 Manganese – 0.055 mg/L to 0.29 mg/L
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
9.0 SURFACE WATER AND SEDIMENT CHARACTERIZATION

46

 Mercury – 1.2J+ nanograms per liter (ng/L) to 2.96J+ ng/L
 Selenium – <0.5 µg/L to <1 µg/L
 Vanadium – 0.42 µg/L to 2.5 µg/L
9.1.3.2 Ash Basin Surface Water
Ash basin surface water was obtained at locations SW -1 and SW -9.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-6.
Constituent concentrations of surface water within the ash basin tend to be higher for selenium
and vanadium compared to background surface water concentrations. Concentrations for boron,
iron, manganese, and mercury are similar to or lower than background surface water
concentrations.
9.1.3.3 Dan River Surface Water
Dan River surface water locations are identified as SW -6 and SW -7.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-7.
Constituent concentrations of surface water from the Dan River tend to be higher for mercury
and vanadium compared to background surface water concentrations. Concentrations for boron,
manganese, and selenium are similar to or lower than background surface water
concentrations.
9.1.3.4 Tributary Stream Surface Water
Tributary surface water locations are identified as SW -3 and SW -4.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 9-8.
Constituent concentrations of surface water from the tributary tend to be higher for iron
manganese and vanadium compared to background surface water concentrations.
Concentrations for boron, mercury, and selenium are similar to or lower than background
surface water concentrations.
9.2 Surface Water Speciation
Speciation is the analysis of the composition of a particular analyte in a system. Speciation is
important for understanding the fate and transport of COIs. Three locations, SW-3, SW-4, and
SW -5, were sampled for chemical speciation analyses of arsenic (III), arsenic (V), chromium
(VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV), and selenium (VI).
Results for chemical speciation of surface water are presented in Table 9-9. Further evaluation
of chemical speciation results will be included in the CAP.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
9.0 SURFACE WATER AND SEDIMENT CHARACTERIZATION

47

9.3 Sediments
Sediment samples were collected coincidentally with each of the surface water samples (SW -3
through SW -8), with the exception of ash basin surface water sample locations, and at S-1 (S-1
was dry at the time samples were collected). Sediment samples were analyzed for COIs in
accordance with the constituent and parameter list used for soil and rock characterization (see
Table 8-1). In the absence of NCDENR sediment criteria, the sediment sample results were
compared to North Carolina PSRGs, and ranges of exceedances are presented in Table 9-2.
Sediment sample locations are shown on Figure 9-1. Exceedances of soil PSRGs are
summarized in Table 9-10.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

48

10.0 Groundwater Characterization
The purpose of groundwater characterization is to characterize the groundwater on the site for
comparison to 2L Standards or IMACs, and to inform the corrective actions identified in the
CAP. Groundwater sampling methods and the rationale for sampling locations were in general
accordance with the procedures described in the Work Plan. Refer to Appendix G for a detailed
description of these methods. Variances from the proposed well installation locations, methods,
quantities, and well designations are presented in Appendix G.
10.1 Regional Groundwater Data for Constituents of Interest
Individual sampling events serve to characterize the hydrogeologic and chemical conditions at a
particular monitoring location, at a particular time. When interpreting the results from a sampling
event, a number of factors that affect the sample results should be taken into consideration.
Among these are the geologic and hydrogeologic setting, the location of the sample points in
the regional groundwater flow system, potential interactions between suspected contaminants,
and the geological and biological constituents present in the formation (Barcelona 1985).
As a result of these factors, it may be possible that the analytical results of a given constituent
are influenced by naturally occurring conditions as opposed to conditions caused by releases
from the ash basin. This section presents an overview of the regional and statewide
groundwater conditions for COIs found at the DRSS ash basin system that have promulgated
state or federal standards.
The 2L Standards recognize that the concentrations of naturally occurring substances in
groundwater may exceed the standard established in .0202(g). Rule .0202(b)(3) states that
when this occurs, the Director of the DWR will determine the standard.
COIs at the DRSS site, along with the associated state and federal drinking water standards,
are listed in Table 10-1. North Carolina 2L Standards are established by NCDENR, whereas
Primary and Secondary Maximum Contaminant Levels (PMCLs and SMCLs) are established by
the USEPA. PMCLs are legally enforceable standards set to protect human health. SMCLs are
non-enforceable guidelines set to account for aesthetic considerations, such as taste, color, and
odor (USEPA 2014c).
Regional background information on COIs at the DRSS site are provided (in alphabetical order)
in Sections 10.1.1 through 10.1.14. In addition, regional background information on pH is
provided in Section 10.1.15, as pH levels can affect the leachability of metal ions in
groundwater.
10.1.1 Antimony
Antimony is a silvery-white, brittle metal. In nature, antimony combines with other elements to
form antimony compounds. Small amounts of antimony are naturally present in rocks, soils,
water, and underwater sediments.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

49

Only a few ores of antimony have been encountered in North Carolina. Antimony has been
found in combination with other metals, and is found most commonly in Cabarrus County and
other areas of the Carolina Slate Belt (Chapman et al. 2013).
In a USGS study of naturally occurring trace minerals in North Carolina, 57 private water supply
wells were sampled to obtain trace mineral data. Of the wells sampled, no wells contained
antimony above the USEPA PMCL (Chapman et al. 2013). Antimony is compared to IMAC
since no 2L Standard has been established for this constituent by NCDENR.
10.1.2 Arsenic
Natural arsenic occurs commonly and comes mainly from the soil. The USEPA estimates that
the amount of natural arsenic released into the air as dust from the soil is approximately equal
to the amount of arsenic released by all human activities (EPRI 2008).
DRSS is located in Rockingham County, North Carolina. Data collected from 577 private wells
across Rockingham County from 1998 to 2010 indicated that 0.69% of samples had arsenic
concentrations exceeding the PMCL. The average arsenic concentration was reported as 1.8
µg/L (NCDHHS 2010b).
Sanders et al. (2011) found strong geological patterns in groundwater arsenic concentrations
across the state of North Carolina (see Figure 10-1).The DRSS site is located in an area where
the average concentrations of naturally occurring arsenic in groundwater is between 2.6 and 5.0
µg/L.
10.1.3 Barium
Two forms of barium, barium sulfate and barium carbonate, are often found in nature as
underground ore deposits. Barium is sometimes found naturally in drinking water and food.
However, since certain barium compounds (barium sulfate and barium carbonate) do not mix
well with water, the amount of barium found in drinking water is typically small.
Barium compounds such as barium acetate, barium chloride, barium hydroxide, barium nitrate,
and barium sulfide dissolve more easily in water than barium sulfate and barium carbonate, but
because they are not commonly found in nature, they do not usually occur in drinking water
unless the water is contaminated by barium compounds that are released from waste sites
(EPRI 2008).
Barium is naturally released into the air by soils as they erode in wind and rain, and is released
into the soil and water by eroding rocks. Barium released into the air by human activities comes
mainly from barium mines, metal production facilities, and industrial boilers that burn coal and
oil. Anthropogenic sources of barium in soil and water include copper smelters and oil-drilling
waste disposal sites. Industries reporting to the USEPA released 119,646 tons of barium and
barium compounds into the environment in 2005 (EPRI 2008).
Regional metamorphic grade greenschist to upper amphibolite in the Piedmont’s King’s
Mountain Belt contains deposits of barium sulfate (barite). Barium is especially common as
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

50

concretions and vein fillings in limestone and dolostone, which are not common geologic facies
in North Carolina; however, at various times in the past century and a half, the Carolinas have
been major producers of barite (USEPA 2014c).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at the University of North Carolina (UNC) analyzed 245 private well water samples in
Rockingham County. The samples were tested by the North Carolina State Laboratory of Public
Health from 1998 to 2012. The study found an average barium concentration of 50 µg/L. No
samples exceeded the 2,000 µg/L PMCL for barium (NCDHHS 2010b).
10.1.4 Beryllium
Beryllium is a hard, gray metal that is very lightweight. In nature, it combines with other
elements to form beryllium compounds. Small amounts of these compounds are naturally
present in soils, rocks, and water. Emeralds and aquamarines are gem-quality examples of a
mineral (beryl) that is a beryllium compound.
Beryllium combines with other metals to form mixtures called alloys. Beryllium and its alloys are
used to construct lightweight aircraft, missile, and satellite components. Beryllium is also used in
nuclear reactors and weapons, X-ray transmission windows, heat shields for spacecraft, rocket
fuel, aircraft brakes, bicycle frames, precision mirrors, ceramics, and electrical switches (EPRI
2008).
Most of the beryl occurring in North Carolina is along the south and southwest sides of the Blue
Ridge Mountains. The most notable mines include the Biggerstafff, Branchand, and Poteat
mines in Mitchell County; the Old Black mine in Avery County; and the Ray mine in Yancey
County. The beryl forms golden or pale-green well-formed prismatic crystals ranging in size
from a fraction of an inch to about 3 inches in diameter. It is generally found near the cores of
bodies of pegmatites of moderate size that contain considerable amounts of perthitic microcline.
Production has been negligible, and no regular production appears possible. Green beryl
(aquamarine and emerald) was mined commercially many years ago at the Grassy Creek
emerald mine and the Grindstaff emerald mine on Crabtree Mountain in Mitchell County. The
Ray mine in Yancey County has also produced some golden beryl and aquamarine (Brobst
1962).
Beryllium-containing minerals are also common in granites and pegmatites throughout the
Piedmont region; however, to a much lesser degree than the Blue Ridge Mountains Province
(Brobst 1962).
Beryllium is concentrated in silicate minerals relative to sulfides and in feldspar minerals relative
to ferromagnesium minerals. The greatest known naturally occurring concentrations of beryllium
are found in certain pegmatite bodies. Beryllium is not likely to be found in natural water above
trace levels due to the insolubility of oxides and hydroxides at the normal pH range (Brobst
1962).
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

51

10.1.5 Boron
While boron is relatively abundant on the earth’s surface, boron and boron compounds are
relatively rare in all geological provinces of North Carolina. Natural sources of boron in the
environment include volatilization from seawater, geothermal vents, and weathering of clay-rich
sedimentary rocks. Total contributions from anthropogenic sources are less than contributions
from natural sources. Anthropogenic sources of boron include agriculture, refuse, coal and oil
burning power plants, by-products of glass manufacturing, and sewage and sludge disposal
(EPRI 2005).
Boron is usually present in water at low concentrations. Surface waters typically have
concentrations of 0.001 to 5 mg/L, with an average concentration of about 0.1 mg/L.
Background boron concentrations in groundwater near power plants were compiled from data
presented in EPRI technical reports, and ranged from <0.01 to 0.59 mg/L with a median
concentration of 0.07 mg/L (EPRI 2005).
10.1.6 Chromium
Chromium is a blue-white metal found naturally only in combination with other substances. It
occurs in rocks, soil, plants, and volcanic dust and gases (EPRI 2008). Background
concentrations of chromium in groundwater generally follow the media in which they occur. Most
chromium concentrations in groundwater are low, averaging less than 1.0 µg/L worldwide.
Chromium tends to occur in higher concentrations in felsic igneous rocks (such as granite and
metagranite) and ultramafic igneous rocks; however, it is not a major component of the igneous
or metamorphic rocks found in the North Carolina Piedmont or the Blue Ridge (Chapman 2013).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 245 private well water samples in Rockingham County. The samples
were tested by the North Carolina State Laboratory of Public Health from 1998 to 2012. The
study found an average chromium concentration of 5.2 µg/L (range: 0.5 to 40 µg/L). No samples
exceeded the 100 µg/L PMCL for chromium (NCDHHS 2010b).
10.1.7 Cobalt
The concentration of cobalt in surface and groundwater in the United States is generally low—
between 1 and 10 parts of cobalt in 1 billion parts of water (ppb) in populated areas. The
concentration may be hundreds or thousands of times higher in areas that are rich in cobalt-
containing minerals or in areas near mining or smelting operations. In most drinking water,
cobalt levels are less than 1 to 2 ppb (USGS 1973).
10.1.8 Iron
Iron is a naturally occurring element that may be present in groundwater from the erosion of
natural deposits (NCDHHS 2010a). Iron commonly exceeds state and federal regulatory
standards in North Carolina groundwater. According to Harden 2009, iron exceedances
occurred in over half of the state’s 10 geozones. The average concentration of iron detected in
North Carolina private well water from sampling conducted in 2010 (NCDHHS 2010a) is shown
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

52

on Figure 10-2. A study by the Superfund Research program at UNC found that only 15 of the
100 counties in North Carolina had average concentrations below the SMCL of 300 µg/L. The
DRSS site is in an area where the average naturally occurring iron concentrations in
groundwater range from 300 to 500 µg/L.
A 2015 study by NCDENR (Summary of North Carolina Surface Water Quality Standards 2007-
2014) found that while concentrations vary regionally, “iron occurs naturally at significant
concentrations in the groundwaters of NC,” with a statewide average concentration of 1320 µg/L
(Table 10-2).
10.1.9 Lead
Lead is a heavy, bluish-gray metal that occurs naturally in the earth’s crust. It is rarely found as
a pure metal, but is instead typically found with other elements to form lead compounds. Lead is
soft and malleable. It combines with other metals to form mixtures called alloys and is
commonly found in pipes, weights, firearm ammunition, sheets used to shield humans from
radiation, pigments in paint and dye, ceramic glazes, and caulk. The largest use for lead is in
vehicle storage batteries (EPRI 2008).
Lead is the 34th most abundant element in the earth’s crust, averaging 15 parts per million
(ppm). In igneous rocks its concentration ranges from approximately 5 ppm in gabbro to 20 ppm
in granite. Typical concentrations in sedimentary rocks range from an average of 7 ppm in
sandstone, 9 ppm in carbonates, 20 ppm in shale, to as much as 80 ppm in deep-sea clays
(USGS 1973).
A variety of lead-bearing igneous, metamorphic, and sedimentary rock units are distributed
throughout North Carolina. The Kings Mountain belt once hosted a lead mine, with minerals
such as galena, chalcopyrite, and pyrite present in vein quartz throughout the host rock (Horton
1991).
A statistical summary of groundwater quality in North Carolina was conducted by the Superfund
Research Program at UNC. The study found that four North Carolina counties had average lead
concentrations which exceeded the PMCL of 15 µg/L. The North Carolina State Laboratory of
Public Health tested 584 private well water samples from Rockingham County from 1998 to
2012. The county was found to have an average groundwater lead concentration of 3.6 µg/L.
The PMCL of 15 µg/L was exceeded in 14 samples.
10.1.10 Manganese
Manganese is a naturally occurring silvery-gray transition metal that resembles iron, but is more
brittle and is not magnetic. It is found in combination with iron, oxygen, sulfur, or chlorine to form
manganese compounds. Manganese occurs naturally in soils, saprolite, and bedrock and is
thus a natural component of groundwater (EPRI 2008).
Manganese concentrations tend to cluster by soil system and geozone throughout North
Carolina, as shown on Figure 10-3. The Carolina Slate and Milton geozones have the highest
proportions of manganese-exceedances, although six other geozones exceeded the state
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

53

standard as well (Gillespie 2013). Geozones with magmatic-arc rocks and low-grade
metamorphic rocks, seen on Figure 10-3 tend to include abundant manganese-bearing mafic
minerals and are likely to contribute manganese for subsurface water cycling (Gillespie 2013).
These rock types are distributed throughout North Carolina and contribute to spatial variations
of manganese concentrations throughout the state. High manganese concentrations are
associated with silty soils and sedimentary, unconsolidated, or weathered lithologic units. Low
concentrations are associated with non-weathered igneous bedrock and soils with high
hydraulic conductivity (Gillespie 2013; Polizzoto 2014).
Manganese is most readily released to the groundwater through the weathering of mafic or
siliceous rocks (Gillespie 2013). When manganese-bearing minerals in saprolite, such as biotite,
are exposed to acidic weathering, the metal can be liberated from the host-mineral and released
to groundwater. It can then migrate through pre-existing fractures during the movement of
groundwater through bedrock. If this aqueous-phase of manganese is exposed to higher pH in
the groundwater system, it will precipitate out of solution. This results in preferential pathways
becoming “coated” in manganese oxides and introduces a concentrated source of manganese
into groundwater (Gillespie 2013).
Manganese(II) in suspension with silt or clay is commonly oxidized by microorganisms present
in soil, leading to the precipitation of manganese minerals (USDHHS-ATSDR 2012).
Roughly 40-50% of North Carolina’s wells have manganese concentrations higher than the
state drinking water standard (Gillespie 2013). Concentrations are spatially variable throughout
the state, ranging from less than 0.01 mg/L to more than 2 mg/L. This range of values reflects
naturally derived concentrations of the constituent and is largely dependent on the bedrock’s
mineralogy and extent of weathering (Gillespie 2013).
In a 2015 study by NCDENR (Summary of North Carolina Surface Water Quality Standards
2007-2014) it was found that manganese concentrations vary regionally; however, “manganese
occurs naturally at significant concentrations in the groundwater of NC,” with a statewide
average concentration of 102 µg/L. The study found the regional variations summarized in Table
10-3.
Using the USGS National Uranium Resource Evaluation (NURE) database, all manganese
groundwater test results from water supply wells within a 20-mile radius of the DRSS site are
shown on Figure 10-4 and also provided in Table 10-4. These results generally represent
concentrations found in deeper aquifers below the uppermost surficial aquifer.
10.1.11 Selenium
Selenium is a semi-metallic gray metal that commonly occurs naturally combined with rocks and
soil. It is common to find trace amounts of selenium in food, drinking water, and air-borne dust.
Over geologic time, selenium has been introduced to the earth’s surface and atmosphere
through volcanic emissions and igneous extrusions. Weathering and transport partition the
element into residual soils, where it is available for plant uptake, or to the aqueous environment,
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

54

where it may remain dissolved, enter the aquatic food chain, or redeposit within a sedimentary
rock such as shale (EPRI 2008).
Groundwater containing selenium is typically the result of either natural processes or industrial
operations. Naturally, selenium’s presence in groundwater is from leaching out of selenium-
bearing rocks. It is most common in shale ranging from 0.6 to 103 milligrams per kilogram
(mg/kg). Anthropogenically, selenium is released as a function of the discharge from petroleum
and metal refineries and from ore mining and processing facilities. Ore mining may enhance the
natural erosive process by loosening soil, creating concentrations in erodible tailings piles, and
exposing selenium containing rock to runoff (Martens 2002; USEPA 2014).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 245 private well water samples in Rockingham County. The samples
were tested by the North Carolina State Laboratory of Public Health from 1998 to 2012. The
study found an average selenium concentration of 2.7 µg/L (range: 2.5 to 26 µg/L). No samples
exceeded the 50 µg/L PMCL for selenium (NCDHHS 2010b).
10.1.12 Sulfate
Sulfate is a naturally occurring substance found in minerals, soil, and rocks. It is present in
ambient air, groundwater, plants, and food. The principal commercial use of sulfate is in the
chemical industry. Sulfate is discharged into water in industrial wastes and through atmospheric
deposition (USEPA 2003).
While sulfate has an SMCL, and no enforceable maximum concentration set by the USEPA,
ingestion of water with high concentrations of sulfate may be associated with diarrhea,
particularly in susceptible populations, such as infants and transients (USEPA 2012).
In the Piedmont and Blue Ridge Aquifers chapter of the USGS Ground Water Atlas of the
United States, the groundwater of this region as a whole is described as “generally suitable for
drinking… but iron, manganese, and sulfate locally occur in objectionable concentrations”
(USGS 1997). The Dan River-Danville, Virginia area (located approximately 22 miles
downstream from DRSS) is an early Mesozoic basin, and the Atlas describes aquifers in this
area as having average sulfate concentrations of 29 mg/L. However, sulfate concentrations up
to 1200 mg/L have been reported from water in deep wells (USGS 1997).
10.1.13 Thallium
Pure thallium is a soft, bluish white metal that is widely distributed in trace amounts in the
earth's crust. In its pure form, it is odorless and tasteless. It can be found in pure form or mixed
with other metals in the form of alloys. It can also be found combined with other substances
such as bromine, chlorine, fluorine, and iodine to form salts (EPRI 2008).
Traces of thallium naturally exist in rock and soil. As rock and soil erode, small amounts of
thallium can occur in groundwater. In a USGS study of trace metals in soils, the variation in
thallium concentrations in A (i.e., surface) and C (i.e., substratum) soil horizons was estimated
across the United States. The overall thallium concentrations ranged from <0.1 mg/kg to 8.8
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

55

mg/kg. North Carolina concentrations from this study are depicted on Figure 10-6. Thallium is
compared to IMAC since no 2L Standard was established for this constituent by NCDENR.
In a study by the Georgia Environmental Protection Division (EPD) of the Blue Ridge Mountain
and Piedmont aquifers, 120 testing sites were sampled for various constituents. Thallium was
not detected at any of these sites (MRL = 1 µg/L) (Donahue and Kibler 2007).
10.1.14 Vanadium
Vanadium is widely distributed in the earth’s crust at an average concentration of 100 ppm
(approximately 100 mg/kg), similar to that of zinc and nickel. Vanadium is the 22nd most
abundant element in the earth’s crust (EPRI 2008). Occurrence of vanadium in groundwater is
known to be limited to its soluble oxidation state, V(V). Vanadium presence is mostly limited to
groundwater with relatively high DO concentrations and a basic pH (i.e., pH > 7) (Wright and
Belitz 2010; Canadian Council of Ministers of the Environment 1999).
In a study by the Georgia EPD, 120 sites in the Blue Ridge and Piedmont physiographic regions
(regions shared with North Carolina) were sampled and detectible traces of vanadium were
found in six samples (with a reporting limit of 10 µg/L). Only two of these samples were in basic
pH groundwater while the rest were sampled in more acidic waters.
Using the USGS NURE database, all vanadium groundwater test results from water supply
wells within a 20-mile radius of DRSS are shown on Figure 10-7 and provided in Table 10-5.
Concentrations near DRSS range from 0.10 to 1.20 µg/L. These results generally represent
concentrations found in deeper aquifers below the uppermost surficial aquifer.
10.1.15 pH
The pH scale is used to measure acidity or alkalinity. A pH value of 7 indicates neutral water. A
value lower than the USEPA-established SMCL range (<6.5 Standard Units) is associated with
bitter, metallic tasting water and corrosion. A value higher than the SMCL range (>8.5 Standard
Units) is associated with a slippery feel, soda taste, and deposits in the water (USEPA 2013).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 577 private well water samples for pH in Rockingham County. The
samples were analyzed by the North Carolina State Laboratory of Public Health from 1998 to
2012. The study found an average pH of 7, with values ranging from 4.6 to 9.2. A total of 100
samples (17.3% of all samples) fell outside the USEPA’s PMCL range of 6.5-8.5 for pH
(NCDHHS 2010a).
Using the USGS NURE database, all pH groundwater test results from water supply wells within
a 20-mile radius of DRSS are shown on Figure 10-5. These results generally represent
concentrations found in deeper aquifers below the uppermost surficial aquifer.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

56

10.2 Background Wells
BG boring locations were identified based on the SCM at the time the Work Plan was submitted.
The BG locations were chosen in areas assumed not to be impacted by and topographically
upgradient of the ash basin and ash storage areas. Based on the developed groundwater
elevation contours (Figures 6-5 through 6-7) and the updated SCM, the BG locations are
considered to be hydraulically upgradient of the ash basin and ash storage areas. The BG
boring locations are considered to be representative of background groundwater quality
conditions at the site.
Background monitoring wells include one existing groundwater monitoring well (MW -23D) and
four newly installed groundwater monitoring wells (MW -23BR, BG-1D, and BG-5S/D) located
near the western property boundary. Background groundwater monitoring wells are depicted on
Figure 10-8. Well construction details are summarized in Tables 10-6 and 10-7. A generalized
well construction diagram for newly installed wells is shown on Figure 10-9. Well installation
procedures are documented in Appendix G, along with variances from the Work Plan. Boring
logs are provided in Appendix H.
Background monitoring well MW -23D was previously installed in 2010 as a compliance
monitoring well to evaluate background water quality at the site. MW -23D was installed to a
depth of 20.11 feet bgs and screened from 10.11 to 20.11 feet bgs. Groundwater flow in the
vicinity of MW -23D is to the west-southwest toward an unnamed tributary that flows south into
the service water settling pond and ultimately to the Dan River. Historical groundwater data for
MW -23D dates back to January 2011. The compliance monitoring wells are sampled three
times per year (January, May, and September) and 15 sampling events have been conducted to
date. This is considered sufficient data to adequately perform statistical analysis of background
concentrations in well MW-23D (Appendix G). Duke Energy recognizes that the NCDENR DWR
Director is responsible for establishing site-specific background levels for groundwater as stated
in 15A NCAC 02L .0202(a)(3). The concentrations in the statistical report are provided as
information to aid in this determination, and for comparative purposes for groundwater at the
site.
Newly installed background monitoring well MW -23BR was installed to evaluate background
water quality within the bedrock in close proximity to MW -23D. Well MW -23BR was installed to
61.0 feet bgs and screened from 56.0 to 61.0 feet bgs. Groundwater flow in the vicinity of MW -
23BR is similar to well MW-23D, as described above. Currently, insufficient data are available to
statistically evaluate background concentrations in well MW -23BR. As data become available
through periodic monitoring, statistical analysis will be performed.
Background monitoring wells BG-1D, BG-5D, and BG-5S were installed to evaluate background
water quality in the TZ and regolith. BG-1D was installed to 14.0 feet bgs and screened from 9.0
to 14.0 feet bgs, BG-5D was installed to 33.0 feet bgs and screened from 28.0 to 33.0 feet bgs,
and BG-5S was installed to 20.5 feet bgs and screened from 10.5 to 20.5 feet bgs. A shallow
groundwater monitoring well could not be installed at the proposed BG-1S location because
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

57

shallow bedrock was encountered at approximately 7 feet bgs and no groundwater was
encountered in the boring.
Based on review of available information, additional bedrock background wells are
recommended to enhance understanding of background conditions in bedrock beneath the site.
The number of shallow and deep background wells located within the property boundary of the
site is adequate for monitoring background groundwater quality. The background wells are
located hydraulically upgradient and were strategically placed to maximize physical separation
from the ash basin and ash storage areas.
Time series plots, time history plots, and stacked time series plots are depicted on Figure 10-10
through Figure 10-57.
10.3 Discussion of Redox Conditions
Determination of the reduction/oxidation (redox) condition of groundwater is an important
component of groundwater assessments, and helps to understand the mobility, degradation,
and solubility of contaminants. By applying the framework of the Excel Workbook for Identifying
Redox Processes in Ground Water (Jurgens, McMahon, Chapelle, and Eberts 2009) to the
analytical results in the following sections, the predominant redox process, or category, to
samples collected during the groundwater assessment was assigned. Categories include oxic,
suboxic, anoxic, and mixed. Assignment of redox category was based upon concentrations of
DO, nitrate as nitrogen, manganese (II), iron (II), sulfate, and sulfide as inputs. Constituent
criteria appropriate for inputs to the Excel Workbook, as well as an explanation of the redox
assignments, can be found in Tables 1 and 2, respectively, of the USGS Open File Report
2009-1004 (Jurgens, McMahon, Chapelle, and Eberts 2009). Redox assignment results are
presented in Table 10-8.
10.4 Groundwater Analytical Results
A total of 61 groundwater monitoring wells were installed at DRSS between March and June
2015 as part of the groundwater assessment program. Groundwater monitoring well locations
are shown on Figure 10-8. Monitoring well information is provided in Table 10-6 and 10-7.
Monitoring wells were installed in general accordance with procedures described in the Work
Plan and a detailed description is provided in Appendix H. Boring logs are also provided in
Appendix H.
Groundwater monitoring wells were developed prior to sampling activities in general accordance
with well development procedures detailed in Appendix G. Also included in Appendix G are the
groundwater sampling procedures and variances from the Work Plan. Groundwater sample
results are compared to 2L Standards or IMACs. Background groundwater sample field
parameters and laboratory results for totals and dissolved constituents are summarized in Table
10-9. Ash basin groundwater results are provided in Table 10-10. Groundwater sample
laboratory results for totals and dissolved constituents are summarized in Table 10-11.
Groundwater sampling results relative to 2L Standards and IMACs are depicted on Figure 10-
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

58

63. Field and sampling quality control / quality assurance protocols are provided in Appendix E.
Variances from the proposed sampling plans are presented in Appendix H.
10.4.1 Ash Basin: Primary and Secondary Cells
A total of 17 groundwater monitoring wells (five shallow, four deep and eight bedrock) were
installed within the footprint of the Primary and Secondary Cells and associated dams. These
borings include the following: AB-5S/D, AB-10S/SL/D, AB-25S/D/BR, AB-30S/D/BR, AB-35BR,
MW -308BR, MW -310BR, MW -311BR, MW -314BR and MW-22BR. These groundwater
monitoring wells were installed to evaluate groundwater quality within and beneath the active
ash basin.
Ten existing groundwater monitoring wells located within the ash basin system and associated
dams were sampled to supplement groundwater quality data for this groundwater assessment.
These wells include the following: MW -9, MW -9D, MW-10, MW -10D, MW -11, MW-11D, MW-
22S/D, OW -308D, and OW-310D.
10.4.2 Ash Storage Areas
A total of 12 groundwater monitoring wells (one shallow, six deep and five bedrock) were
installed within the footprint of Ash Storage 1 and 2 waste boundaries. These monitoring wells
include the following: AS-2D, AS-4D, AS-6D, AS-8D/BR, AS-10D, AS-12S, MW -301BR, MW-
303BR, MW -306BR, MW-315BR, and MW -318BR. The groundwater monitoring wells
associated with the ash storage areas were installed to evaluate the potential impact of the ash
storage areas on groundwater quality. Due to difficulties during drilling activities, the proposed
AS-12D was not installed; however, a shallow groundwater monitoring well AS-12S was
installed at this location as detailed in the variance table included in Appendix G.
10.4.3 Beyond the Waste Boundary
A total of 24 groundwater monitoring wells (eleven shallow, eleven deep, and two bedrock) were
installed outside the waste boundary of the ash basin and ash storage areas. These monitoring
wells include the following: GWA-1S/D, GWA-2S/D, GWA-3S/D, GWA-4S/D, GWA-5BR, GWA-
6S/D, GWA-7S/D, GWA-8S/D, GWA-9S/D, GWA-10S/D, GWA-11S/D, GWA-12S/D, and MW-
317BR. The groundwater monitoring wells located outside the waste boundaries were installed
to evaluate the potential impact of the ash basin and ash storage areas on groundwater quality.
GWA-10S was dry at the time of sampling, and was unable to be sampled.
A total of four existing groundwater monitoring wells are being sampled to supplement
groundwater quality data for this groundwater assessment. These wells include the following:
MW -20S/D and MW -21S/D.
10.4.4 Off-Site
A total of three groundwater monitoring wells (one shallow and two deep) were installed off-site
immediately adjacent to the eastern property boundary of the site. The groundwater monitoring
wells located off-site were installed to assess potential impact from site activities on
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

59

groundwater quality on the adjacent property downgradient of the ash basin and ash storage
areas. These wells include the following: GWA-14S/D and GWA-15D. A shallow groundwater
monitoring well as unable to be installed at GWA-15S because groundwater was not
encountered above shallow bedrock. GWA-14S was dry at time of sampling, and was unable to
be sampled.
10.5 Comparison of Results to 2L Standards
Groundwater results were compared to 2L Standards or IMACs and exceedances are
summarized below. Table 10-12 presents groundwater results with exceedances of 2L
Standards and Figure 10-63 depicts groundwater sample exceedances of 2L Standards or
IMACs.
10.6 Comparison of Results to Background
10.6.1 Background
With the exception of cobalt, iron, lead, manganese, thallium, TDS, and vanadium, the results
for all other COIs were reported to be less than their respective 2L Standards or IMACs. The
background concentration range for constituents that are considered COIs at the DRSS site are
provided below:
 Antimony – <0.5 µg/L to 1.21 µg/L
 Arsenic – <0.5 µg/L to 6.36 µg/L
 Beryllium – 0.087 µg/L to <0.2 µg/L
 Boron – <50.0 µg/L
 Chromium – 0.22 µg/L to 1.2 µg/L
 Cobalt – 1 µg/L to 2.1 µg/L
 Iron – 110 µg/L to 890 µg/L
 Lead – 0.057 µg/L to 0.078 µg/L
 Manganese – 110 µg/L to 910 µg/L
 pH – 6.2 µg/L to 7.45 µg/L
 Selenium – <0.5 µg/L
 Sulfate – 29,800 µg/L to 41,300 µg/L
 Thallium – < 0.1 µg/L to 0.019 µg/L
 TDS – 175,000 µg/L to 252,000 µg/L
 Vanadium – <1.0 µg/L to 2.6 µg/L
Please refer to Section 10.1 for a comparison of the above-referenced site-specific constituent
concentrations to regional groundwater constituent concentrations.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

60

10.6.2 Ash Basin: Primary and Secondary Cells
With the exception of antimony, arsenic, boron, chromium, cobalt, iron, lead, manganese, pH,
thallium, TDS, and vanadium, the results for all other COIs were reported less than the 2L or
IMAC Standards.
The range of constituent concentrations along with a comparison to the range of reported
background groundwater concentrations is provided in Table 10-13.
Constituent concentrations of groundwater beneath the ash basin tend to be higher for
antimony, arsenic, boron, chromium, cobalt, iron, lead, manganese, thallium, TDS and
vanadium compared to background groundwater concentrations.
10.6.3 Ash Storage Areas
With the exception of antimony, arsenic, boron, chromium, cobalt, iron, lead, manganese, pH,
thallium, TDS, and vanadium, the results for all other COIs were reported less than the 2L
Standards or IMACs.
The range of constituent concentrations along with a comparison to the range of reported
background groundwater concentrations is provided in Table 10-14.
Constituent concentrations of groundwater beneath the ash storage areas tend to be higher for
antimony, boron, chromium, cobalt, iron, manganese, selenium, TDS and vanadium compared
to background groundwater concentrations.
10.6.4 Beyond the Waste Boundary
With the exception of antimony, beryllium, chromium, cobalt, iron, manganese, pH, sulfate,
thallium, TDS, and vanadium the results for all other COIs were reported less than the 2L
Standards or IMACs.
The range of constituent concentrations along with a comparison to the range of reported
background surface water concentrations is provided in Table 10-15.
Constituent concentrations of groundwater beyond the waste boundary tend to be higher for
antimony, beryllium, chromium, cobalt, sulfate, and vanadium compared to background surface
water concentrations. Concentrations for iron, manganese, thallium, and TDS are similar to or
lower than background groundwater concentrations.
10.6.5 Off-Site
With the exception of iron, manganese, sulfate, TDS, and vanadium, the results for all other
COIs were reported less than the 2L Standards or IMACs.
The range of constituent concentrations along with a comparison to the range of reported
background groundwater concentrations is provided in Table 10-16.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

61

Constituent concentrations of groundwater off-site tend to be higher for sulfate and TDS
compared to background groundwater concentrations. Concentrations for iron, manganese, and
vanadium are similar to or lower than background surface water concentrations.
Groundwater isoconcentration contours with respect to each COI are depicted on Figures 10-64
through 10-102. Cross-sections are presented on Figure 6-2. Cross-sections presenting
horizontal and vertical distribution of COIs along the transect are depicted on Figures 10-103
through 10-106. COIs with exceedances of 2L Standards or IMACs will be modeled in the CAP.
The USEPA recommends that when possible, especially when sampling for constituents that
may be biased by the presence of turbidity, the turbidity values in the stabilized well should be
less than 10 Nephelometric Turbidity Units (NTUs) (USEPA 2002).
10.7 Groundwater Geochemistry
There are two types of ions: cations (positively charged ions) and anions (negatively charged
ions). Cations and anions are used in hydrogeological investigations to assess naturally
occurring ions in groundwater. There are eight ions commonly used to evaluate groundwater:
four cations (calcium, magnesium, sodium, and potassium) and four anions (chloride, sulfate,
carbonate, and bicarbonate). The geochemical composition of groundwater aids in aquifer
characterization, and piper diagrams are used to graphically depict geochemistry of
groundwater samples collected at a particular site.
Cation and anion concentrations at the DRSS site from upgradient groundwater monitoring
wells and ash basin groundwater monitoring wells are compared on Figures 10-107 through 10-
113. In general, calcium, chloride, magnesium, sodium, and sulfate are elevated, but calcium
and sulfate are three to four orders of magnitude higher in ash basin groundwater monitoring
wells compared to the upgradient monitoring wells. Sulfate/chloride ratio in ash basin, seep,
and background monitoring wells, as well as shallow, deep, and bedrock wells, are provided in
Figures 10-114 through 120.
Piper diagrams were generated for the DRSS site to compare the geochemistry between ash
basin porewater, surface water, seeps, upgradient and downgradient groundwater monitoring
wells and background groundwater monitoring wells. 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 are
included as Figures 10-121 through 10-124.
10.8 Groundwater Speciation
Speciation is the analysis of the composition of a particular analyte in a system. Speciation is
important for understanding the fate and transport of COIs. Fourteen locations, AB-10D, AB-
25D, AB-30S/D, AB-35BR, AS-4D, AS-8D, OW-308D, OW310D, GWA-10D, MW -21S/D, MW-
22S, and MW -23D, were sampled for chemical speciation analyses of arsenic (III), arsenic (V),
chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV), and selenium
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

62

(VI). Results for chemical speciation of surface water are presented in Table 10-17. Further
evaluation of chemical speciation results will be included in the CAP.
10.9 Radiological Laboratory Testing
Radionuclides may exist dissolved in water from natural sources (e.g. soil or rock). The USEPA
regulates various radionuclides in drinking water. For purposes of this assessment, radium-226,
radium-228, natural uranium, uranium-233, uranium-234, and uranium-236 were analyzed.
Three locations, AB-10D, AB-25D/BR, MW-11, MW-11D, and BG-5S/D, were sampled for the
analytes listed above. Results for radiological laboratory testing are presented in Table 10-18.
Further evaluation of radiological laboratory testing results will be included in the CAP.
10.10 CCR Rule Groundwater Detection and Assessment
Monitoring Parameters
Appendix III to Part 257 Constituents for Detection Monitoring and Appendix IV to Part
257 Constituents for Assessment Monitoring
On April 17, 2015, the USEPA published its final rule “Disposal of Coal Combustion Residuals
from Electric Utilities” (Final Rule) to regulate the disposal of CCR as solid waste under subtitle
D of the Resource Conservation and Recovery Act (RCRA). Among other requirements, the
Final Rule establishes requirements for a groundwater monitoring program consisting of
detection monitoring and, if necessary, assessment monitoring and corrective action.

USEPA selected constituents to be used in the groundwater detection monitoring program as
indicators of groundwater contamination from CCR. USEPA selected constituents for detection
monitoring that are present in CCR, would be expected to migrate rapidly, and that would
provide early detection as to whether contaminants were migrating from the disposal unit (80 FR
74: 21397).
As stated in the FR (80 FR 74: 21342):

These detection monitoring constituents or inorganic indicator parameters are:
boron, calcium, chloride, fluoride, pH, sulfate and total dissolved solids (TDS).
These inorganic indicator parameters are known to be leading indicators of
releases of contaminants associated with CCR and the Agency strongly
recommends that State Directors add these constituents to the list of indicator
parameters to be monitored during detection monitoring of groundwater if and
when a MSWLF decides to accept CCR. (Emphasis added)

NCDENR requested that figures be included in the CSA report that depict groundwater
analytical results for the constituents in 40 CFR 257, Appendix III detection monitoring and 40
CFR 257, Appendix IV assessment monitoring.
Constituents for detection monitoring listed in 40 CFR 257 Appendix III are:
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
10.0 GROUNDWATER CHARACTERIZATION

63

 Boron
 Calcium
 Chloride
 Fluoride (this constituent was not analyzed for in the CSA)
 pH
 Sulfate
 TDS
The analytical results for the detection monitoring constituents are found on Figures 10-125
through 10-127.

Constituents for assessment monitoring listed in 40 CFR 257 Appendix IV include:

 Antimony
 Arsenic
 Barium
 Beryllium
 Cadmium
 Chromium
 Cobalt
 Fluoride (not analyzed for the CSA)
 Lead
 Lithium (not analyzed for the CSA)
 Mercury
 Molybdenum
 Selenium
 Thallium
 Radium 226 and 228 combined
The analytical results for the assessment monitoring constituents are found on Figures 10-128
through 10-130.
Aluminum, copper, iron, manganese, and sulfide were included in the Appendix IV constituents
in the draft rule; USEPA removed these constituents in the Final Rule. Therefore, these
constituents are not included on the above-referenced figures. In addition, NCDENR requested
that vanadium be included on these figures. Exceedances of the relevant regulatory standards
of the constituents listed above including vanadium are presented in Figure 10-63.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

64

11.0 Hydrogeological Investigation
The purpose of the hydrogeological investigation is to characterize site hydrogeological
conditions including groundwater flow direction, hydraulic gradient and conductivity,
groundwater and contaminant velocity, and slug and aquifer test results. The hydrogeological
investigation was performed in general accordance with the procedures described in the Work
Plan. Refer to Appendix H for a description of these methods.
11.1 Hydrostratigraphic Layer Development
The following materials were encountered during the site exploration and are consistent with
material descriptions from previous site exploration studies:
 Ash – Ash was encountered in borings advanced within the ash basin and ash storage
areas, as well as in some borings advanced through the pond perimeter and
intermediate dam. Ash several inches thick was encountered in one location within the
ash dredge area located between Ash Storage 1 and Ash Storage 2. Ash was generally
described as gray to dark bluish gray with a silty to sandy texture, consistent with fly ash
and bottom ash.
 Fill – Fill material generally consisted of re-worked materials from the DRSS site. The
base of filled areas was difficult to distinguish from in-place soil/saprolite.
 Alluvium – Alluvium is unconsolidated soil and sediment that has been eroded and
redeposited by streams and rivers.
 Residuum (Residual Soils) – Residuum is the in-place soil that develops by weathering.
 Saprolite/Weathered Rock – Saprolite is soil developed by in-place weathering of rock.
 Partially Weathered/Fractured Rock – Partially weathered (slight to moderate) and/or
highly fractured rock was encountered below refusal (auger, casing advancer, etc.).
 Bedrock – Sound rock in boreholes, generally slightly weathered to fresh and relatively
unfractured.

Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at DRSS is consistent with the regolith-fractured rock system and is
an unconfined, connected aquifer system without confining layers as discussed in Section 5.2.
The Dan River groundwater system is divided into two layers referred to in this report as the
shallow aquifer and bedrock aquifer to distinguish flow layers within t he connected aquifer
system.

The classification system of Schaeffer (2014a) was used to show that the TZ is present in the
Piedmont groundwater system (discussed in Section 5.2), and was modified to define the
hydrostratigraphic layers of the natural groundwater system. The classification system is based
on Standard Penetration Testing values (N) and the Recovery (REC) and Rock Quality
Designation (RQD) collected during the drilling and logging of the boreholes (Borehole/Well logs
in Appendix H). The ash, fill, and alluvial layers are as encountered at the site. The natural
system (except alluvium) includes the following layers:
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

65

 M1 – Soil/Saprolite: N<50
 M2 – Saprolite/Weathered Rock: N>50 or REC<50%
 TZ – Transition Zone: REC>50% and RQD<50%
 BR – Bedrock: REC>85% and RQD>50%.

Rock core runs that fell between the values for TZ and BR (REC<85% and RQD>50% or
REC>85% and RQD<50%) were assigned a hydrostratigraphic layer based on a review of the
borehole logs, rock core photographs, and geologic judgment. The same review was performed
in making the final determination of the thickness of the TZ as it could extend into a run that
meets the BR criterion because of the potential 15% core loss in that run.
The above layer designations (M1, M2, TZ, and BR) are used on the geologic cross-sections
shown on Figure 11-1 and presented Figures 11-2 to 11-5 and in the data tables and
hydrostratigraphic layer parameter tables presented in this section. The ash, fill and alluvial
layers are represented by A, F, and S, respectively, on the cross-sections and tables.
Groundwater analytical results are presented on Figure 11-6.
11.2 Hydrostratigraphic Layer Properties
The material properties required for the groundwater flow and transport model (total porosity,
effective porosity, specific yield and specific storage) for ash, fill, alluvium, and soil/saprolite
were developed from laboratory testing. Table 11-1 presents the laboratory test data (test
reports in Appendix H) and published data (Domenico and Mifflin 1965). Table 11-1 has a
column labeled ‘Estimated Specific Yield/Effective Porosity’ estimated from the laboratory soil
data (grain size analysis) utilizing Fetter-Bear diagrams (worksheets in Appendix H), as
described by Johnson (1967). This technique provides a simple method to estimate specific
yield; however, there are limitations to the method that may not provide an accurate
determination of the specific yield of a single sample (Robson 1993). Specific yield/effective
porosity were determined for a number of samples of the A, F, S, M1, and M2 layers to provide
an average and range of expected values.
Hydraulic conductivity (horizontal and vertical) of all layers except TZ and BR were developed
utilizing the data collected during this investigation and historic data. The hydraulic conductivity
of the hydrostratigraphic layers were determined by in-situ permeability testing (falling head,
constant head, and packer testing where appropriate); slug tests in completed monitoring wells;
and laboratory testing of undisturbed samples (ash, fill, soil/saprolite; test results in Appendix
H). The effective porosity (primarily fracture porosity) and specific storage of the TZ and bedrock
were estimated from published data (Sanders 1998; Domenico and Mifflin 1965).
11.2.1 Borehole In-Situ Tests
In-situ horizontal (open hole) and vertical (flush bottom) permeability tests, either falling or
constant head as appropriate for field conditions, were performed in each of the
hydrostratigraphic units above refusal, ash, fill, alluvium, and soil/saprolite. In-situ borehole
horizontal permeability tests, either falling or constant head tests as appropriate for field
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

66

conditions, were performed just below refusal in the first 5 feet of a rock cored borehole (TZ if
present).
The flush bottom test involves advancing the borehole through the overburden with a casing
advancer until the test interval is reached. The cutting tool is removed from the casing and the
casing is filled with water to the top and the drop of the water level in the casing is measured
over a period of 60 minutes. In the open hole test, after the top of the test interval is reached,
the cutting tool (but not the casing) is advanced an additional number of feet (5 feet in the
majority of tests) and drop of the water level in the casing is measured over a period of 60
minutes. The constant head test is similar except the water level is kept at a constant level in
the casing and the water flow-in is measured over a period of 60 minutes. The constant head
test was only used when the water level in the borehole was dropping too quickly back to the
static water level such that the time interval was insufficient to calculate the hydraulic
conductivity. The results from the field permeability testing are summarized in Table 11-2 and
the worksheets provided in Appendix H.
Packer tests (shut-in and pressure tests) were conducted in a minimum of five boreholes. The
shut-in test is performed by isolating the zone between the packers (in effect, a piezometer) and
measuring the resulting water level over time until the water level is stable. The shut-in test
provides an estimate of the vertical gradient during the test interval. The pressure test involves
forcing water under pressure into rock through the walls of the borehole providing a means of
determining the apparent horizontal hydraulic conductivity of the bedrock. Each interval is tested
at three pressures with three steps of 20 minutes up and two steps of 5 minutes back down. The
pressure test results are summarized in Table 11-2 and the shut-in and packer tests worksheets
are provided in Appendix H.
Where possible, tests were conducted at borehole locations specified in the Work Plan and at
test intervals based on site-specific conditions at the time of the groundwater assessment work.
The U.S. Bureau of Reclamation (1995) test method and calculation procedures, as described
in Chapter 10 of their Ground Water Manual (2nd Edition), were used for the field permeability
and packer tests.
11.2.2 Monitoring Well and Observation Well Slug Tests
Hydraulic conductivity (slug) tests were completed in monitoring wells and observation wells
under the direction of the Lead Geologist/Engineer. Slug tests were performed to meet the
requirements of the May 31, 2007 NCDENR Memorandum titled, Performance and Analysis of
Aquifer Slug Tests and Pumping Tests Policy. Water level change during the slug tests was
recorded by a data logger. The slug test was performed for no less than 10 minutes, or until
such time as the water level in the test well recovered 95 percent of its original pre-test level,
whichever occurred first. Slug tests were terminated after 60 minutes, even if the 95 percent
pre-test level was not achieved. Slug test field data was analyzed using the Aqtesolv (or similar)
software and the Bouwer and Rice method.
The slug test results are presented in Table 11-3 and the Slug Test Report is provided in
Appendix H. Historic slug test data is presented in Table 11-4.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

67

11.2.3 Laboratory Permeability Tests
Laboratory permeability tests were conducted on undisturbed samples (Shelby Tubes) of ash,
fill, soil, and saprolite collected during the field investigation. The tests were performed in
accordance with ASTM D 5084 (ASTM 2010). The results of the laboratory permeability tests
are presented in Table 11-5.
11.2.4 Hydrostratigraphic Layer Parameters
The soil material parameters for the A (ash), F (fill), S (alluvium), M1 (soil/saprolite), and M2
(saprolite/weathered rock) were developed by grouping the data into their respective
hydrostratigraphic units and calculating the mean, median, and standard deviation of the
different parameters. Values for specific storage are based on published data (Domenico and
Mifflin 1965). The values are presented in Tables 11-6 and 11-7.
The hydraulic conductivity parameters were developed by grouping the data into their respective
hydrostratigraphic units and calculating the geometric mean, median, and standard deviation of
the different parameters. Vertical hydraulic conductivity values are not available for the TZ and
BR units, but are unlikely to be equal. As an initial assumption, vertical hydraulic conductivity
can be considered to be equal to the horizontal hydraulic conductivity and adjusted as
necessary during flow modeling. Horizontal and vertical hydraulic conductivity parameters are
presented Tables 11-8 and 11-9, respectively. The values of secondary (effective) porosity and
specific retention for the TZ and BR units are based on published values (Sanders 1998;
Domenico and Mifflin 1965). The values are presented in Table 11-10.
Further development of the above parameters and others required for the flow and contaminant
transport model will be provided in the CAP.
11.3 Vertical Hydraulic Gradients
Horizontal hydraulic gradient is calculated by taking the difference in hydraulic head over the
distance between two wells with similar well construction. Section 6.2.2 provides additional
details for horizontal hydraulic gradients calculated for the site.
Vertical hydraulic gradient was calculated by taking the difference in groundwater elevation in a
deep and shallow well pair over the difference in total well depth of the deep and shallow well
pair. A positive output indicates upward flow and a negative output indicates downward flow.
Sixteen well pair locations, each consisting of a shallow and deep groundwater monitoring well,
were used to calculate vertical hydraulic gradient across the site. Based on review of the results,
vertical gradient of groundwater is generally downward across the site. Vertical gradient
calculations are summarized in Table 11-11.
11.4 Groundwater Velocity
Average groundwater velocity was calculated using Darcy’s Law. Darcy’s Law is a derived
equation that describes the flow of fluid through a porous media. The following equation was
used to calculate groundwater velocities through each hydrostratigraphic unit present at the site:
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

68

v = Ki
n
where v is velocity; K is horizontal hydraulic conductivity; i is
horizontal hydraulic gradient; and n is the effective porosity
Average groundwater velocities were calculated using horizontal hydraulic gradients established
in Section 6.2.2, horizontal hydraulic conductivity values for each hydrostratigraphic unit
established in Table 11-8, and effective porosity values established in Tables 11-9 and 11-10.
Hydrostratigraphic layers are defined in Section 11.1. Average groundwater velocity results are
summarized in Table 11-12. Figures 11-7 and 11-8 show groundwater velocity ranges for
hydrostratigraphic units typically present at the site in the shallow aquifer. Figure 11-9 shows
groundwater velocity ranges in bedrock at the site in the deep aquifer.
11.5 Contaminant Velocity
Contaminant velocity will be provided in the CAP.
11.6 Plume's Physical and Chemical Characterization
Plume physical and chemical characterization is detailed below for each COI detected in
groundwater samples collected at the DRSS site based on review of isoconcentration maps
(Figures 10-64 through 10-102) and cross sections (Figures 10-103 through 10-106). Total
results were utilized in evaluation of plume physical and chemical characteristics and are based
on one round of comprehensive groundwater sampling of the newly installed groundwater
monitoring wells installed as part of this assessment, in which some constituents may be
potentially influenced by turbidity. For the purposes of this discussion, the shallow aquifer
includes the analytical results reported in the shallow (S) and deep (D) wells, and the deep
aquifer includes the analytical results reported in the bedrock (BR) wells.
 Antimony – Antimony was not dected in the shallow aquifer above the laboratory RL.
Exceedances in D wells were restricted to areas north of Ash Storage 1 and along the
downgradient extent of the ash basin. Antominy was detected above the IMAC Standard
in background bedrock wells MW -23BR, MW -317BR, and AB-25BR.
 Arsenic – In general, concentrations of arsenic in the shallow aquifer were localized in
the ash storage areas and ash basin, and the concentration varied within those areas.
The only concentration of arsenic detected above 2L Standards in the deep aquifer was
isolated to AB-35BR, located within the Secondary Cell of the ash basin.
 Boron – Concentrations of boron in the shallow aquif er were highest in Ash Storage 2
and decreased with groundwater flow toward the downgradient side of the Primary Cell
of the ash basin. Concentrations of boron above 2L Standards in the deep aquifer were
isolated to MW -306BR in Ash Storage 1 and decreased with groundwater flow direction.
 Chromium – Concentrations of chromium above 2L Standards in the shallow aquifer
were detected around the perimeter of Ash Storage 1. Concentrations of chromium in
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

69

the deep aquifer were localized in Ash Storage 2 and increased with groundwater flow
toward the downgradient side of the Primary Cell of the ash basin.
 Cobalt – Concentrations of cobalt above 2L Standards varied in the shallow aquifer and
were widespread across the site. Concentrations of cobalt above IMAC Standards in the
deep aquifer were isolated to the MW -315BR in Ash Storage 2.
 Iron – Concentrations of iron above 2L Standards varied in both the shallow and deep
aquifer, and were widespread across the site.
 Manganese – Concentrations of manganese above 2L Standards varied in both the
shallow and deep aquifer, and were widespread across the site.
 Selenium – Concentrations of selenium above 2L Standards were isolated in the shallow
aquifer at AS-10D.
 pH – values of pH outside the 2L standards range vary in both the shallow and deep
aquifer and are wide spread across the site.
 Sulfate – Concentrations of sulfate above 2L standards in the shallow aquifer were
isolated to GWA-8D and MW -21D, located immediately downgradient of the Secondary
Cell of the ash basin. The concentrations above 2L Standards of sulfate in the deep
aquifer were isolated to MW-308R and GWA-5BR, located within the Secondary Cell of
the ash basin and immediately downgradient.
 TDS – Concentrations of TDS above 2L Standards followed the same pattern as sulfate
concentrations for the shallow aquifer. In the deep aquifer, concentrations of TDS were
localized within Ash Storage 1 and the Secondary Cell of the ash basin. TDS
concentrations increased in the direction of groundwater flow.
 Thallium – Concentrations of thallium above IMAC Standards in the shallow aquifer were
localized in Ash Storage 2 and decreased with groundwater flow direction. An isolated
concentration was detected at GWA-6D, located immediately downgradient of the
Primary Cell in the ash basin. Thallium concentrations above IMAC Standards in the
deep aquifer were isolated to background well MW -23BR, located near the western-most
property boundary.
 Vanadium – Concentrations of vanadium varied in both the shallow and deep aquifer,
and were widespread across the site.
11.6.1 Shallow Aquifer
Arsenic and boron were the primary constituents detected in groundwater at concentrations that
exceeded background concentrations and 2L Standards. Both constituents were detected
above 2L Standards in a three-dimensional area beneath the ash basin and ash storage areas
in the surficial aquifer. There are no known exceedances of 2L Standards for arsenic or boron
beyond the DRSS property boundary.
TDS and sulfate exceeded the 2L Standards in an isolated area east of the DRSS historical site
property boundary. Based on the relatively low concentrations of other ash-related constituents
in these wells, the presence of TDS and sulfate may not be attributable to groundwater
migration from the ash basin.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
11.0 HYDROGEOLOGICAL INVESTIGATION

70

The horizontal migration of boron in the surficial aquifer best represents the dominant flow and
transport system at the DRSS site. Vertical migration of constituents is generally limited by
underlying bedrock.
11.6.2 Bedrock Aquifer
Within the bedrock aquifer, three COIs were identified as primary constituents in the
groundwater: iron, manganese, and vanadium. These constituents were identified as naturally
occurring metals in the background wells. Nine other COIs were identified in the bedrock
aquifer: antimony, arsenic, boron, chromium, cobalt, selenium, sulfate, TDS, and thallium.
These constituents were detected in isolated locations and do not appear to have migrated
extensively across the DRSS site or beyond the compliance boundary.
11.7 Groundwater / Surface Water Interaction
As discussed in Section 5.2, shallow and deep groundwater flow typically follows the
topographic gradient and shallow groundwater generally discharges to nearby surface water
bodies (i.e., streams). Groundwater/surface water interaction is evident at the DRSS site based
on review of COIs present in groundwater and surface water samples. Monitoring well MW -21S
exceeded the 2L Standard for arsenic and SW-3, located downgradient of MW -21S, also
exceeded the 2B Standard for arsenic. Both MW -21S and SW-3 are located downgradient of
the Secondary Cell. This suggests groundwater/surface water interaction at the DRSS site,
which indicates migration of COIs from the ash basin to groundwater and ultimately to surface
water at the site.
11.8 Estimated Seasonal High and Seasonal Low Groundwater
Elevations – Compliance and Voluntary Wells
Estimated Seasonal High (ESH) and Estimated Seasonal Low (ESL) groundwater elevations
were calculated using historical groundwater elevations for select compliance and voluntary
wells at the site. The calculated ESH and ESH depth to water (DTW) was performed statistically
by multiplying the standard deviation of the historical DTW measurements by a factor of 1.2 and
then adding to the mean DTW measurement. To obtain the site modification factors for ESL and
ESH conditions, the calculated ESH and ESL DTW in the historical site wells were compared to
the current groundwater levels on site and the difference was calculated. The difference
between ESH and ESL DTW and current conditions was then averaged for the representative
site wells to create a modification factor to add to current DTW . MW -20S and MW -21S were
selected as the most representative shallow wells for natural seasonal fluctuations at the DRSS
site, as they are located outside of the ash basin embankments and are, therefore, less likely to
be influenced by the water level in the ash basin. Appendix H summarizes calculated ESH and
ESL groundwater elevations for newly installed groundwater monitoring wells.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

71

12.0 Screening Level Risk Assessment
A screening-level evaluation of potential risks to human health and the environment to identify
preliminary, media-specific Contaminants of Potential Concern (COPCs) that may adversely
impact human and/or ecological receptors under site-specific exposure scenarios was
performed in accordance with applicable federal and state guidance, including the Guidelines
for Performing Screening Level Ecological Risk Assessments within the North Carolina Division
of Waste Management (NCDENR 2003). These serve as the foundation for evaluating potential
risks to human and ecological receptors.
In this assessment, the maximum concentrations detected for all COIs (or other appropriate
data point, such as the analytical reporting limit [RL]) in the 2015 sampling and analyses for coal
ash detection and assessment monitoring analytes were compared against established and
conservative human health and ecological screening toxicity reference values, likely to be
protective for even the most sensitive types of receptors.
These comparisons were used to determine which COIs present a potentially unacceptable risk
to human and/or ecological receptors and may warrant further evaluation. Those COIs
determined to pose a potential for adverse impacts were identified as preliminary COPCs.
Other factors that were considered qualitatively in the evaluation of final COPCs to be
incorporated into a baseline risk assessment included frequency of detection and a comparison
to background. Site- and media-specific risk-based remediation standards were calculated,
pending additional sample collection, if and where additional sampling and site-specific
standards were deemed necessary.
12.1 Human Health Screening
12.1.1 Introduction
This screening-level human health risk assessment was prepared in accordance with applicable
NCDENR and USEPA guidance and the approved Work Plan.
12.1.2 Site Conceptual Model
The Conceptual Site Model (CSM) is a dynamic tool for understanding site conditions and
potential exposure scenarios for human receptors that may be exposed to site-related
contamination. The CSM provides graphical representation of the following:
 A source and mechanism of chemical release,
 A retention or transport medium for COPCs,
 A point of contact between the human receptor and the medium, and
 A route of exposure to constituents for the potential human receptor at the contact point.
An exposure pathway is considered complete only if all four “source to receptor” components
are present. A CSM has been prepared illustrating potential exposure pathways from the source
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

72

area to possible receptors (see Figure 12-1). Information in the CSM was used in conjunction
with the analytical data collected as part of the CSA to determine COPCs for the site.
Potential receptors are defined as human populations that may be subject to contaminant
exposure. Both current and future land and water use conditions were considered when
determining exposure scenarios. Current and future land use of the DRSS site including the ash
basin system is expected to remain predominantly industrial while decommissioning of the coal-
fired generating station is in progress (Duke Energy 2014b). The DRCCS natural gas generating
facility will remain in active use for the foreseeable future. Lands surrounding the site include
residential, agricultural and undeveloped areas, as well as the Dan River, which supplies
drinking water to various municipalities (USEPA 2014a).
The following potential receptors are identified in the CSM:
 Current/future on-site construction worker with potential exposure to groundwater in
trenches, surface and subsurface soil and surface water;
 Current/future on-site outdoor worker with potential exposure to surface soil and surface
water;
 Current/future adult and child off-site resident with potential exposure to surface soil and
groundwater; and
 Current/future on-site trespasser with potential exposure to surface soil, surface water,
and sediment.
Other exposure pathways for all potential receptors were evaluated and it was determined that
they would not have a significant impact on the risk assessment (e.g., outdoor worker inhalation
of inorganics in surface water in open air). Other exposure scenarios will also serve as
surrogates that will provide information about the magnitude of these potential risks.
The following sections describe each receptor and potentially complete exposure pathway.
12.1.2.1 Current/Future Construction Worker
It is assumed that construction activities during decommissioning and restoration of DRSS could
take place on-site and that construction workers could potentially be exposed to COPCs in
various media during this timeframe. The potentially complete exposure pathways include
incidental ingestion, dermal contact, and particulate inhalation exposure to surface and
subsurface soil. For example, construction workers in a trench could come in contact with
groundwater COPCs with inhalation toxicity criteria and incidentally ingest or have dermal
contact with (over limited parts of the body) groundwater. Dermal contact and incidental
ingestion exposure to surface water could also be considered a potentially complete exposure
pathway for this receptor.
12.1.2.2 Current/Future Outdoor Worker
Outdoor workers are assumed to be involved with non-intrusive activities (e.g., landscapers that
will maintain the site). This receptor reflects a longer timeframe and different exposure pathway
than that of construction workers. Outdoor workers are assumed to have incidental ingestion,
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

73

dermal contact, and particulate inhalation exposure to surface soil as well as dermal contact and
incidental ingestion exposure to surface water.
Exposure to COPCs in groundwater was not identified in the CSM because outdoor workers are
assumed not to ingest untreated water. Also, any COPC aerosols or fumes are assumed to
dissipate in open air, with limited opportunity for dermal contact. Construction worker exposure
scenarios are considered a conservative surrogate to estimate the potential risk from
groundwater to outdoor workers.
12.1.2.3 Current/Future Off-Site Resident (Adult/Child)
The potential for off-site residents to be exposed to COPCs in untreated groundwater was
included in the CSM, as three private water supply wells and one private water supply spring
reportedly not currently in use are located within a 0.5-mile radius of the ash basin compliance
boundary surrounding DRSS (reference Section 4.0, HDR 2014a, HDR 2014b, and Figure 4-1).
These exposures considered all on and off-site monitoring well data, excluding the receptor
survey data, which was performed separately. It is important to note, however, that all three
water supply wells are located greater than 2,000 feet away from the Dan River ash basin
compliance boundary and are either upgradient or across the Dan River from the ash basin
system. No information gathered as part of this assessment suggests that any water supply well
or spring is impacted by the Dan River ash basin system. Exposure routes include ingestion of
groundwater (not incidental, but potable use) as well as dermal contact during
bathing/showering and inhalation during bathing/showering for those metals in groundwater with
available inhalation-based toxicity criteria.
Residents are assumed to be exposed to contaminants in surface soil during non-intrusive
outdoor activities (e.g., gardening); the potential exposure pathways include ingestion, dermal
and inhalation of soil particulates.
The Dan River is a public drinking water supply with the nearest intake at Danville, Virginia (23
miles downstream) that is treated before consumption (USEPA 2014a). Therefore, residential
exposure of untreated surface water was not evaluated.
12.1.2.4 Current/Future Trespasser (Adolescent/Adult)
Trespassers may come into direct contact with or incidentally ingest surface water and sediment
while on-site and near the Dan River during what is assumed to be predominantly recreational
activity. This will occur at different rates depending on the specific activity and setting. The
exposure parameters for this scenario were determined and incorporated on- and off-site data
for these media.
Exposure routes include incidental ingestion, dermal contact and particulate inhalation of
surface soil, as well as incidental ingestion and dermal contact with surface water and sediment.
This receptor reflects greater exposure to surface water, sediment and soil COPCs compared to
potential exposures of similar potential receptors (e.g., off-site recreator).
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

74

12.1.3 Human Health Risk-Based Screening Levels
A comparison of contaminant concentrations in various media to corresponding risk-based
screening levels has been made and is presented in Tables 12-1 through 12-5. These include:
 Soil: USEPA industrial soil Regional Screening Levels (RSLs) at a target cancer risk of
1E-06 and noncancer Hazard Quotient of 0.1 Groundwater: USEPA tap water RSLs and
NCDENR 2L Standards; and
 Surface Water: USEPA National Recommended Water Quality Criteria and NCDENR 15
NCAC.02B surface water standards, considering the surface water classification for local
water bodies Sediment: USEPA residential soil RSLs.
Tables 12-1 through 12-5 present a summary of the COIs that were detected at concentrations
exceeding their relevant human health or other applicable criteria on a media-specific basis, in
ground and surface water, sediment, and soil. Those COIs exceeding relevant screening criteria
are identified as COPCs for purposes of this human health risk assessment.
 In groundwater, aluminum, copper, lead, titanium, thallium, and zinc were eliminated as
COPCs. With the exception of sodium, which was retained as a result of having no
screening value for comparison, all other COIs exceeded their respective screening
value. See Table 12-1 for maximum concentrations detected, the detailed screening
results, identification of COPCs and contaminant categories.
 In soil, arsenic, cobalt, iron, manganese, sodium, and thallium were detected at
concentrations exceeding the industrial soil screening levels are determined to be
COPCs. See Table 12-2 for the soil COI maximum concentrations, COPC and
contaminant category data.
 Aluminum, arsenic, cobalt and thallium maximum concentrations exceed their respective
screening values and have been determined to be COPCs in surface water, as shown in
Table 12-3. Beryllium, boron, total chromium, copper, iron, lead, manganese, mercury,
sodium, vanadium and zinc are also retained as COPCs based on a lack of criteria for
comparison.
 Sediment COPCs and contaminant categories are presented in Table 12-4, which shows
that aluminum, antimony, arsenic, cobalt, iron, manganese, thallium, and vanadium are
determined to be COPCs based on exceedances of screening values.
COIs were not screened out as COPCs based on a comparison to background concentrations,
as USEPA recommends all COIs exceeding risk-based screening levels be considered in a
baseline risk assessment (USEPA 2002). Statistical background concentrations have been
developed as Prediction Limits (PLs), calculated for each COI using groundwater data in site
background wells. PLs are a calculation of the upper limit of possible future values based on the
Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities Unified Guidance
(USEPA 2009). If concentrations of COI detected exceed the PL, then the groundwater
concentrations are assumed to have increased above background levels. Site-specific
background concentrations will be considered in the uncertainty section of the baseline risk
assessment, if determined to be required.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

75

NCDENR guidance requires a determination of COPC contaminant categories as a result of the
data comparison to screening levels. These categories are presented in the ecological COPC
tables (Tables 12-6 through 12-9) and include:
 Category 1 – Contaminants whose maximum detection exceeds the media specific
ecological screening value included in the COPC tables.
 Category 2 – Contaminants that generated a laboratory sample quantitation limit (SQL)
that exceeds the USEPA Region IV media-specific ecological screening value for that
contaminant.
 Category 3 – Contaminants that have no USEPA Region IV ecological screening value,
but were detected above the laboratory SQLs.
 Category 4 – Contaminants that were not detected above the laboratory SQLs and have
no USEPA Region IV ecological screening value.
 Category 5 – Contaminants whose SQL or maximum detection exceeds the North
Carolina Surface Water Quality Standards.
12.1.4 Site-Specific Risk Based Remediation Standards
Based on results of the comparison to risk-based screening levels, media-specific remediation
standards were calculated in accordance with the Eligibility Requirements and Procedures for
Risk-Based Remediation of Industrial Sites Pursuant to North Carolina General Statute 130A-
310.65 to 310.77, should additional sample collection and site-specific standards be deemed
necessary.
12.1.5 NCDENR Receptor Well Investigation
Although three off-site private water supply wells and one water supply spring not currently in
use were identified within 0.5-mile radius of the ash basin compliance boundary, none of these
were sampled and analyzed for COIs as part of NCDENR’s well testing program, as described
in Section 4.0. No information on sampling results or recommendations from NCDENR on well
water consumption for the DRSS site, or communities surrounding the DRSS site, is available at
this time. All three water supply wells are located greater than 2,000 feet away from the Dan
River ash basin compliance boundary and are either upgradient or across the Dan River from
the ash basin system. No information gathered as part of this assessment suggests that water
supply wells or springs located within the compliance boundary are impacted by the DRSS ash
basin system.
12.1.6 Human Health Screening Summary
A CSM was developed to identify potential pathways of exposure from COPC source to receptor
populations, including several possible exposure scenarios. Maximum concentrations of COIs
were compared to media-specific screening levels, COIs exceeding screening levels, and those
having no screening levels or issues with RLs were retained as COPCs, in accordance with
guidance. As a result of the screening, the majority of COIs were determined to be COPCs in
groundwater and soil. Only four COIs exceeded their surface water screening values; most are
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

76

retained as COPCs by default due to a lack of criteria being available for comparison. Eight
COIs were determined to be COPCs based on exceedances of their screening values.
12.2 Ecological Screening
12.2.1 Introduction
This screening-level ecological risk assessment (SLERA) has been prepared in accordance with
the Guidelines for Conducting a Screening Level Ecological Risk Assessments within the North
Carolina Division of Waste Management (NCDENR 2003).
12.2.2 Ecological Setting
12.2.2.1 Site Summary
Refer to Section 2.0 for a description of the DRSS site.
12.2.2.2 Regional Ecological Setting
The DRSS site is located in the Triassic Basins eco-region of North Carolina adjacent to the
Dan River; this relatively small eco-region is surrounded by the Northern Inner Piedmont eco-
region (Griffith et al. 2002).
12.2.2.3 Description of the Eco-Region and Expected Habitats
This eco-region consists of irregular plains with low rounded hills and ridges and low to
moderate gradient streams with wider valleys. It has generally lower elevations than the Inner
Piedmont. The common rock types include unmetamorphosed shales, sandstones, mudstones
and siltstones covered by red sandy loam to silty clay. Land cover includes mixed white oak
forests, croplands and pastures; bottomland hardwood forests once existed in the wider
floodplains; these have since then been covered by water supply reservoirs (Griffith et al. 2002).
12.2.2.4 Watershed in which the Site is Located
The DRSS site is located in the Roanoke River Basin watershed. The North Carolina portion of
the river basin encompasses approximately 3,500 square miles in all or in part of 19 counties.
12.2.2.5 Average Rainfall
The average annual precipitation for Eden, North Carolina is 45.02 inches over the past 30
years. The average for the State of North Carolina is 48.87 inches (Weather DB 2015).
12.2.2.6 Average Temperature
The average temperature for Eden, North Carolina is 59.85°F. The average winter temperature
is 47.4°F. The average spring temperature is 55°F. The average summer temperature is 75.3°F
and average fall temperature is 61.6°F (Weather DB 2015).
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

77

12.2.2.7 Length of Growing Season
According to the North Carolina State University Cooperative Extension, the average growing
season for Rockingham County is 203 days, with a standard deviation of 15 days.
12.2.2.8 Threatened and Endangered Species that use Habitats in the Eco-Region
A list of federal and state threatened and endangered species for Rockingham County is
provided in Table 12-10.
12.2.2.9 Site-Specific Ecological Setting
An ecological checklist has been completed for this site and is provided in Appendix I.
The DRSS site is located on the Dan River in Rockingham County near the town of Eden, North
Carolina. The June 2015 AMEC Natural Resources Technical Report identified 13 potential
jurisdictional wetland areas on the site, measuring a total of approximately 2.53 acres. One
potentially jurisdictional pond was identified. There were 16 potential jurisdictional drainage
features within the study are: eight intermittent and eight perennial streams.
An area next to the Dan River and Stream 3 is within the 100-year flood zone. The western
boundary of the site, including Streams 9 and 14 and Wetland L, are within the 100-year flood
zone (AMEC 2015).
Requests for information were submitted to several federal and state agencies, in accordance
with the North Carolina Guidelines for Performing Screening Level Ecological Risk Assessments
(NCDENR 2003). A copy of the requests and responses are provided in Appendix I and a
summary of the information is provided below.
North Carolina Department of Cultural Resources
In a letter dated June 18, 2015, the North Carolina Department of Cultural Resources indicated
that there are no recorded archaeological sites located on-site and four archaeological sites
within one-half mile of the DRSS site. These include:
 31RK1(Lower Sauratown), a Native American village site containing intact subsurface features.
It is located in the floodplain on the south side of the Dan River. This site is currently
listed in the National Register of Historic Places.
 31RK5 (Power Plant Site), a Native American village site containing intact subsurface
features. It is located in the floodplain on the south side of the Dan River.
 31RK33 (Sauratown Plantation), a late 18th to early 19th century domestic structure with
an archaeological component. It is located on a hilltop south of the Dan River. The
standing structure is currently listed in the National Register of Historic Places.
 31RK61 is a Native American site located within the floodplain on the south side of the
Dan River. This site is likely similar to sites 31RK1 and 31RK5.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

78

North Carolina Natural Heritage Program
In a letter dated June 9, 2015, the North Carolina Natural Heritage Program (NCNHP) provided
information obtained from their database, both for the DRSS site and within a one-mile radius.
According to the NCNHP database, the ROA/Dan River Aquatic Habitat, a Natural Area, is
located within the DRSS site. There are no other Natural Areas or Managed Areas within a one-
mile radius.
North Carolina Wildlife Resources Commission
In a letter dated June 19, 2015, the North Carolina Wildlife Resources Commission (NCWRC)
reported the following:
 The DRSS site drains to the Dan River in the Roanoke River basin.
 There are records for the federal and state endangered Roanoke logperch (Percina rex)
being present in the Dan River watershed.
 There are records for the federal species of concern and state endangered green floater
(Lasmigona subviridis), the federal species of concern and state significantly rare
Roanoke bass (Ambloplites cavifrons), the state threatened bigeye jumprock
(Moxostoma ariommum), and the state significantly rare Roanoke hogsucker
(Hypentelium roanokense) and quillback (Carpoides cyprinus) in the Dan River
watershed. In addition, there are historical records for the state threatened Jacob’s
ladder (Polemonium reptans var. reptans), the state significantly rare coppery emerald
(Somatochlora georgiana), and the state significantly rare glade wild quinine
(Parthenium auriculatum) near the site.
 There is recreational fishing in the Dan River. Recreational aquatic species include
largemouth bass, catfish, and sunfish. It is likely the site is too industrialized to support
any ecologically, recreationally or commercially important terrestrial wildlife species.
However, raccoon, opossum, skunk, white-tailed deer, coyotes, and other species
commonly found throughout the Northern Piedmont region may be found on the site.
Recreationally important wildlife species in the vicinity of the site include, but are not
limited to bear, white-tailed deer, beaver, mink, muskrat, nutria, otter, skunk, weasel,
bobcat, opossum, raccoon, fox, rabbit, squirrel, various species of wild ducks and geese,
quail, and wild turkey.
United States Department of Agriculture Forest Service, National Forests in North Carolina
In an email dated May 28, 2015, the United States Department of Agriculture Forest Service
reported that there are no Designated and Proposed Federal Wilderness and Natural Areas,
National Preserves and Forests, or Federal Land Designated for the Protection of Natural
Ecosystems with a half-mile of the DRSS site.
United States Department of the Interior, National Park Service
In an email dated June 3, 2015, the United States Department of the Interior, National Park
Service indicated that “the NPS has not identified any resource concerns at this time”.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

79

12.2.2.10 On-Site and Off-Site Land Use
On-site land use is approximately 40% heavy industrial, 20% light industrial, 30% undisturbed,
and 10% water bodies, and cleared areas. Land use within a one-mile radius of the site is 30%
undisturbed, 20% residential, 15% recreational, 10% light industrial, 10% urban, 10%
agricultural, and 5% waterbodies (including the Dan River). There are several areas designated
for recreational use (i.e., a boat launch, golf course, and park) in the local area as well.
12.2.2.11 Habitats within the Site Boundary
Based on the findings of a July 7, 2015 site visit, the following habitats are present on site:
 82 acres of Mixed Hardwoods
 18 acres of Pine Plantation
 15 acres of Bottomland Hardwoods
 17 acres of Shrub/Scrub
 77 acres of Open Fields
 Aquatic features including ash basins, streams, and wetlands
For a detailed description of habitats, refer to the Checklist for Ecological Assessments provided
in Appendix I.
12.2.2.12 Description of Man-made Units that may Act as Habitat
A 34-acre ash basin (Primary and Secondary Cell) is present on the site.
12.2.2.13 Site Layout and Topography
The natural topography at the DRSS site ranges from an approximately 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. Topography generally slopes from northwest to
southeast with an elevation loss of approximately 125 feet over an approximate distance of 0.7
miles. Surface water drainage generally follows site topography and flows from the northwest to
the southeast across the site except where natural drainage patterns have been modified by the
ash basin or other construction (HDR 2014b).
12.2.2.14 Surface Water Runoff Pathways
Swales and drainage ditches were observed during the July 7, 2015 site visit.
12.2.2.15 Soil Types
Based on lithological data obtained from soil borings completed by AMEC during ash basin
closure assessment activities, subsurface stratigraphy consists of the following material types:
fill, ash, residuum, saprolite, alluvium, PWR, and bedrock. In general, fill, residuum, saprolite,
and PWR were encountered on most areas of the site. Ash was encountered within ash ponds
and storage areas, while alluvium was encountered within and adjacent to historical drainage
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

80

features and the Dan River. Bedrock was not encountered during AMEC’s activities but is
known to underlie the PWR at depth (HDR 2014c).
AMEC’s review of the National Resource Conservation Service (NRCS) Soil Survey indicated
the presence of four soil map units within the study area; Ayersville gravelly loam, 15 to 45
percent slopes (AyF); Clover sandy loam, 2 to 8 percent slopes (CmB); Clover sandy loam, 8 to
15 percent slopes (CmD); Dan River loam, 0 to 2 percent slopes, frequently flooded (DaA); and
Udorthents, loamy (Ud). Open water areas (W) are also mapped within the study area. The Dan
River loam, 0 to 2 percent slopes, is frequently flooded (DaA) and considered to be a hydric soil
by the NRCS (AMEC 2015).
12.2.2.16 Species Normally Expected to Use Site under Relatively Unaffected Conditions
Terrestrial communities occur in both natural and disturbed habitats in the study area; these
may support a diversity of wildlife species. Information on the species that would normally be
expected to use this and similar sites in the Piedmont eco-region under relatively unaffected
conditions was obtained from relevant literature, mainly the Biodiversity of the Southeastern
United States, Upland Terrestrial Communities (Wiley and Sons 1993) and Biodiversity of the
Southeastern United States, Aquatic Communities (Wiley and Sons 1993).
Mammal species that may be present include eastern cottontail (Sylvilagus floridanus), gray
squirrel (Sciurus carolinensis), various vole, rat and mice species, red (Vulpes vulpes) and gray
fox (Urocyon cinereoargenteus), raccoon (Procyon lotor), Virginia opossum (Didelphis
virginiana), and white-tailed deer (Odocoileus virginiana).
Avian species are the most diverse. Canopy dwellers include the great crested flycatcher
(Myiarchus crinitus), Carolina chickadee (Parus carolinensis), tufted titmouse (P. bicolor), white-
breasted nuthatch (Sitta carolinensis), blue-gray gnatcatcher (Polioptila caerulea), red-eyed
vireo (Vireo olivaceus), yellow-throated vireo (V. flavifrons), various warblers and tanagers,
American redstart (Setophaga ruticilla),
Subcanopy species include a variety of woodpeckers, eastern pewee (Contopus virens),
Acadian flycatcher (Empidonax virescens), American crow (Corvus brachyrhynchos), blue jay
(Cyanocitta cristata) and Carolina wren (Thryothorus ludovicianus).
Catbirds (Dumetella carolinensis), brown thrashers (Toxostoma rufum), and mockingbirds
(Mimus polyglottos) are found along adjacent brushy edges, fields and thickets.
Understory species include wood thrush (Hylocichla mustelina), American robin (Turdus
migratorius), white-eyed vireo (Virea griseus), Kentucky warbler (Oporornis formosus), common
yellow-throat (Geothlypis trichas), and yellow breasted chat (Icteria virens). Predatory birds
include several hawk and owl species and the turkey vulture (Cathartes aura),
Amphibians and reptiles that tend to be associated with the terrestrial-aquatic interface in
streams, rivers, and open waters may include certain turtles, e.g., the Striped Mud and Gulf
Coast Spiny Softshell turtles; and frogs, snakes and amphibians such as the Three‐lined
salamander. For a more detailed description, see Appendix I.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

81

Streams of the southeastern piedmont support a range of aquatic benthic macroinvertebrate
groups including mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera),
water beetles (Coleoptera), dragonflies and damselflies (Odonata), dobsonflies and alderflies
(Megaloptera), true flies (Diptera), worms (Oligochaeta), crayfish (Crustacea), and clams and
snails (Mollusca).
Streams, rivers, ponds, and reservoirs support populations of game fish that may include
redbreast sunfish (Lepomis auritus), bluegill (Lepomis macrochirus), warmouth (Lepomis
gulosus), and largemouth bass (Micropterus salmoides). The most widespread non-game fish
species are American eel (Anguilla rostrata), eastern silvery minnow (Hybognathus regius),
bluehead chub (Nocomis leptocephalus), golden shiner (Notemigonus crysoleucas), spottail
shiner (Notropis hudsonius), whitefin shiner (N. niveus), swallowtail shiner (N. procne), creek
chub (Semotilus atromaculatus), creek chubsucker (Erimyzon oblongus), silver redhourse
(Moxostoma anisurum), yellow bullhead (Ictalurus natalis), flat bullhead (I. platycephalus),
margined madtom (Noturus insignis), and tessellated darter (Etheostoma olmstedi).
12.2.2.17 Species of Special Concern
For a detailed list of species of special concern that may be present, see Table 12-10.
12.2.2.18 Nearby Critical and/or Sensitive Habitats
For a detailed description, see Section III.D of the Ecological Checklist provided in Appendix I.
12.2.3 Fate and Transport Mechanisms
Potential fate and transport mechanisms at or near the DRSS site include erosion, seeps,
stormwater runoff and flow of surface water bodies. An ecological CSM (Figure 12-2) has been
prepared illustrating potential exposure pathways from the source area to possible ecological
receptors. Information in the ecological CSM was used in conjunction with analytical data
collected as part of the CSA to develop an understanding of the sources, pathways and media
of exposure, as well as the receptors potentially impacted by site-related COPCs.
12.2.4 Comparison to Ecological Screening Levels
The sampling and analysis program completed as part of the CSA is described earlier in this
report. Media of primary concern for ecological receptors, (i.e., surface water, sediment, and
soil) have been sampled extensively, in accordance with the NCDENR-approved Work Plan.
The results of the comparison of COI concentrations in various media to risk-based screening
levels is presented in Tables 12-6 through 12-9 and include:
 USEPA Region IV Recommended Ecological Screening Values for soil, surface water
and sediment, and
 USEPA National Recommended Water Quality Criteria and North Carolina Freshwater
Aquatic Life Standards.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

82

The potential for ecological risk was also estimated by calculating screening hazard quotients
(HQ) using the appropriate screening value of each contaminant and comparing that value to
the USEPA Region IV Ecological Screening Values. COIs having a HQ greater than or equal to
1 were identified as COPCs.
A determination of which category the COPCs fall into as a result of the data comparison to
screening levels is presented in the media-specific ecological COPC tables (Tables 12-6
through 12-8). These include the categories described in Section 12.1.3.
Table 12-9 presents a summary of the COIs that were detected at concentrations exceeding
their relevant ecological screening media-specific criteria. Those COIs exceeding the relevant
criteria are identified as ecological COPCs for purposes of the SLERA. Note that NCDENR
SLERA guidance does not allow for exclusion of COIs as COPCs based on a comparison to
background concentrations.
In soil, all COIs except cadmium, sodium, and strontium were detected at concentrations
exceeding the ecological soil screening levels. Cadmium is the sole COI that was excluded as a
COPC in soil, as the other two have no ecological criteria and are thereby retained as COPCs
by default. Reference Table 12-6 for detailed information, including the maximum
concentrations detected. The exceedances were typically within the same order of magnitude
as the screening levels, with the exceptions of aluminum, boron, total chromium, iron,
manganese, molybdenum, selenium and vanadium, which were relatively higher.
Based on the comparison of maximum detected concentrations to screening criteria, beryllium,
cadmium, and copper were identified as ecological COPCs in surface water (freshwater).
Barium, cobalt, manganese, molybdenum, strontium, and vanadium were retained by default
due to the fact that there are no ecological criteria available or a comparison to RLs. Further
information on the screening performed and characterization as to the contaminant category for
each COPC is provided in Table 12-7.
COPCs identified in sediment based on a comparison of maximum detected concentrations to
available criteria include antimony, arsenic, cadmium and copper. Aluminum, barium, beryllium,
boron, cobalt, iron, manganese, molybdenum, strontium and vanadium were retained due to
issues related to their RL exceeding the screening value or there being no screening value
available. Details of the COPC screening and contaminant category are provided in Table 12-8.
COIs were not screened out as COPCs based on a comparison to background concentrations,
as NCDENR SLERA guidance does not allow for screening based on background. Site-specific
background concentrations, discussed above in Section 12.1.3, were considered in the
uncertainty section of the baseline ecological risk assessment, if determined to be necessary.
12.2.5 Uncertainty and Data Gaps
Uncertainties are inherent in any environmental investigation and risk evaluation involving
natural heterogeneity of media, nature, and extent of constituents in the environment, due to
their individual fate and transport characteristics and varied, site-specific conditions. These
uncertainties are considered in developing the sampling and analysis plan, data quality
assurance processes, and understanding of the site.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
12.0 SCREENING-LEVEL RISK ASSESSMENT

83

Screening-level assessments performed as part of the CSA were designed to be very
conservative in identifying potential COPCs that would be carried forward into a baseline human
health and/or ecological risk assessment. They included all on- and off-site analytical data, and
used the maximum concentration detected as the comparison point to applicable screening
criteria. Also, no COIs were eliminated as COPCs based on background levels; this will be
evaluated in the baseline risk assessment, if they are required to be performed. These are
highly unlikely to be the actual exposure concentrations, given the natural attenuation, dilution,
and distances to potential receptors.
There is a high level of confidence that any constituent with potential to impact human health or
ecological receptors has been identified as a result of these assessments.
12.2.6 Scientific/Management Decision Point
If, through the HQ analysis, it is determined that COIs were detected at maximum
concentrations exceeding applicable screening criteria, it is an indication that additional
assessment of potential risks is warranted. This does not mean that impacts are, in fact,
occurring; only that further data collection or evaluation should be considered.
This determination is known as the Scientific/Management Decision Point (SMDP) and the
conclusion reached must be one of the following:
 There is adequate information to conclude that the ecological risks are neglibible; or
 Site has inadequate data to complete the risk characterization. Data gaps need to be
filled prior to completion of the screening process; or
 The information indicates a potential for adverse ecological effects and a more thorough
assessment is warranted.
Given that several COPCs have been identified as having an HQ of greater than 1 in soil,
surface water, and sediment, there is adequate information indicating a potential for adverse
effects to occur and a baseline ecological risk assessment may be warranted. The need for a
separate baseline ecological risk assessment should be considered in light of the other ongoing
or planned environmental impact studies for this site.
12.2.7 Ecological Risk Screening Summary
The SLERA identified the potential for adverse ecological impacts to exist due to exposure to
COPCs in soil, surface water and/or sediment. Cadmium is the only COI that was excluded as a
COPC in soil and several COPCs exceeded their respective screening criteria by one or two
orders of magnitude. Notably fewer COPCs were identified in surface water and sediment, and
several of those were retained by default for having no criteria or due to RL issues, and not due
to maximum concentrations actually exceeding screening criteria. Impacts from limited
ecological receptor groundwater exposure are minimal and have not been evaluated. For
DRSS, identification of potential data gaps and overall coordination of further ecological risk
assessment efforts, specifically for surface water and sediment impacts, should consider other
activities that are ongoing related to ash basin closure activities to avoid duplication of effort.
This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
13.0 GROUNDWATER MODELING

84

13.0 Groundwater Modeling
Groundwater modeling will be performed and submitted in the CAP in accordance with
NCDENR’s Conditional Approval letter for the Work Plan. The groundwater modeling will consist
of groundwater flow and fate and transport modeling, performed with MODLFOW and MT3DMS,
and batch geochemical modeling, performed with PHREEQC. The following section presents an
overview of the fate and transport modeling, the batch geochemical modeling, and the site
geochemical conceptual model. The CAP will also include a discussion of the geochemical
properties of the COIs and how these properties relate to the retention and mobility of these
constituents.
13.1 Fate and Transport Groundwater Modeling
A three-dimensional groundwater flow and contaminant fate and transport model
(MODFLOW/MT3DMS Model) will be developed for the DRSS ash basin. The objective of the
modeling will be to predict the following in support of the CAP:
 Predict concentrations of the COIs at the compliance boundary or other locations of
interest over time,
 Estimate the groundwater flow and constituent loading to surface water discharge areas,
and
 Predict approximate groundwater elevations in the ash for the proposed corrective
action.
The model and model report will be developed in general accordance with the guidelines found
in the memorandum Groundwater Modeling Policy, NCDENR DWQ, May 31, 2007 (NCDENR
modeling guidelines).
The groundwater model will be developed from the hydrogeologic conceptual model presented
in the CSA, from existing wells and boring information provided by Duke Energy, and from
information developed during the groundwater site investigation. The model will also be
supplemented with additional information developed by HDR from other Piedmont sites, as
applicable. The CSM is a conceptual interpretation of the processes and characteristics of a site
with respect to the groundwater flow, boundary conditions, and other hydrologic processes at
the site.
Although the site is anticipated to conform generally to the LeGrand conceptual groundwater
model, due to the configuration of the ash basin, the additional possible sources (dry ash
storage area, cinder storage area), and the boundary conditions present at the site, a three-
dimensional groundwater model is warranted.
Groundwater modeling will be performed under the direction of Dr. William Langley, P.E.,
Department of Civil and Environmental Engineering, University of North Carolina at Charlotte
(UNCC). Groundwater flow and constituent fate and transport will be modeled using Visual
MODFLOW 2011.1 (flow engine USGS MODFLOW 2005) and MT3DMS.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
13.0 GROUNDWATER MODELING

85

The modeling process, the development of the model, the development of the hydrostratigraphic
layers, the model extent (or domain), and the proposed model boundary conditions were
described in Section 7.0 of the Work Plan. To date, no changes to the proposed model
development are warranted based on data collected during the site investigation.
The MT3DMS model will use site specific Kd values developed from samples collected along
the major flow transects. The testing to develop the Kd terms is underway, but is not complete
at this time; therefore, the results of that testing will be presented in the CAP. The methods used
to develop the Kd terms were presented in Section 7.7.2 of the W ork Plan.
13.2 Batch Geochemical Modeling
As described in the W ork Plan, batch geochemical simulations using PHREEQC will be used to
estimate sensitivity of the proposed sorption constants used with MT3DMS and to assist in
understanding the mechanisms involved in attenuation of selected constituents. Geochemical
modeling using PHREEQC can be used to indicate the extent to which a COI is subject to
solubility constraints, a variable Kd, or other processes. PHREEQC can also identify postulated
solid phases calculation of their respective saturation indices. The specific locations where the
batch geochemical modeling will be performed will be determined after development of the Kd
terms and a review of site analytical data.
13.3 Geochemical Site Conceptual Model
SCMs are developed to be a representation of what is known or suspected about a site with
respect to contamination sources, release mechanisms, transport, and fate of those
contaminants.4 SCMs can be a written and/or graphic presentation of site conditions to reflect
the current understanding of the site, identify data gaps, and be updated as new information is
collected throughout the project. SCMs can be utilized to develop understanding of the different
aspects of site conditions, such as a hydrogeologic site conceptual model, to help understand
the site hydrogeologic condition affecting groundwater. SCMs can also be used in a risk
assessment to understand contaminant migration and pathways to receptors.
On June 25, 2015, NCDENR made the following request in their Clarification of Attachment 1
Groundwater Assessment Plan Conditional Letters of Approval Items Related to Speciation –
May 22, 2015 e-mail:
Since speciation of groundwater and surface water samples is a critical
component of both the site assessments and corrective action, the Division
expects a geochemical site site conceptual model (SCM) developed as a
subsection in the Comprehensive Site Assessment (CSA) Reports. The
geochemical SCM should provide a summary of the geochemical interactions
between the solution and solid phases along the groundwater flowpath that
impact the mobility of metal constituents. At a minimum, the geochemical SCM
will describe the adsorption/desorption and mineral precipitation/dissolution

4 EPA MNA Volume 1
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
13.0 GROUNDWATER MODELING

86

processes that are believed to impact dissolved concentrations along the aquifer
flowpaths away from the ash basin sources. The model descriptions should
include the data upon which the conceptual model is based and any calculations
(such as mineral saturation indices) that are made to develop the site-specific
model.
Metal speciation analyses cover a broad aspect of metals’ geochemistry,
including solution complexation with other dissolved species and specific
association with aquifer solids, such as a metal adsorbed onto HFO or
precipitated as a sulfate mineral. A comprehensive speciation analysis that
requires a relatively complete groundwater analysis is expected that includes use
of an ion speciation computer code (such as PHREEQC) capable of calculating
solution complexes, surface complexation onto HFO, and mineral saturation
indices. This type of speciation calculation is necessary for the development of a
geochemical SCM and understanding metal mobility in an aquifer.
In previous correspondence, NCDENR agreed that the proposed geochemical modeling
described in the Work Plan, to be performed using PHREEQC, will be included in the CAP.
Specifically, the model descriptions and calculations, such as mineral saturation indices, will be
provided in the CAP. This approach will allow completion of the testing to develop the site-
specific Kd terms and site mineralogy, and will allow the geochemical modeling to be
coordinated with the groundwater flow and transport model.
Elements of the geochemical site conceptual model (GSCM) described below will be
incorporated into the fate and transport and the geochemical modeling performed for the CAP.
The GSCM will be updated as additional data and information associated with contaminants,
site conditions, or processes such as migration of contaminants is developed. The GSCM will
be useful in understanding the transport and attenuation factors that affect the mobility of
contaminants at the site and the long-term capacity of the site for attenuation and stability of
immobilized contaminants.
The GSCM will describe the geochemical aspects of the site sources that influence contaminant
transport. Site sources at Dan River consist of the dry ash storage areas (Ash Storage 1 and
Ash Storage 2) and the Primary and Secondary Cells; these source areas are subject to
different processes that generate leachate migrating into the underlying soil layers and into the
groundwater. For example, the dry ash storage areas would generate leachate as a result of
infiltration of precipitation, while the ash basin would generate leachate based on the pond
elevation in the basin. General factors affecting the geochemistry of the site are as follows:
Factors Affecting Ash Formation (Primary Source):
 Chemical and mineralogical composition of coal
 Thermodynamics of coal combustion process
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
13.0 GROUNDWATER MODELING

87

Factors Affecting Leaching in Ash Basin (Primary Source Release Mechanism):
 Chemical composition of ash
 Mineral phase of ash
 Physical characteristics of ash
 Inflow of water into/out of basin
 Period of time ash has been in basin
 Geochemical conditions in ash basin
 Precipitation-dissolution reactions
 Sorptive properties of materials in ash
Factors Affecting Leaching in Dry Ash Storage Area (Primary Source Release
Mechanism):
 Chemical composition of ash in storage area
 Mineral phase of ash in storage area
 Physical characteristics of ash in storage area
 Inflow of precipitation in to ash storage area
 Period of time ash has been in storage
 Geochemical conditions in ash storage area
 Precipitation-dissolution reactions
 Sorptive properties of materials in ash
Factors Affecting Sorption and Precipitation of Constituents onto Soil/Aquifer Materials
Beneath Ash (Secondary Source Release Mechanism):
 Chemical composition of soil
 Physical composition of soil
 Rate of infiltration/percolation of porewater
 Chemical composition of leachate infiltrating into soil
 Sorption capacity of soil
 Geochemistry of groundwater flowing beneath unit
Factors Affecting Desorption and Dissolution of Constituents From Soil/Aquifer Materials
Beneath Ash (Secondary Source Release Mechanism):
 Chemical composition of soil
 Physical composition of soil
 Rate of infiltration/percolation of porewater
 Attenuation capacity of soil
 Chemical composition of leachate or precipitation infiltrating into soil
 Geochemistry of groundwater flowing beneath unit
The results of the Kd testing, site mineralogy testing, and geochemical modeling developed in
the CAP will be used to refine the GSCM.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
14.0 DATA GAPS – CONCEPTUAL SITE MODEL UNCERTAINTIES

88

14.0 Data Gaps – Site Conceptual Model
Uncertainties
14.1 Data Gaps
Through completion of groundwater assessment field activities and evaluation of data collected
during those activities, Duke Energy has identified data gaps that will require further evaluation
to refine the SCM. The data gaps have been separated into two groups: 1) data gaps resulting
from temporal constraints and 2) data gaps resulting from evaluation of data collected during the
CSA.
14.1.1 Data Gaps Resulting from Temporal Constraints
Data gaps identified in this category are generally present due to insufficient time to collect,
analyze, or evaluate data collected during the CSA activities. It is expected that the majority of
these data gaps will be remedied in a CSA Supplement to be submitted in consultation with
NCDENR.
 Mineralogical Characterization of Soil and Rock: A total of 15 soil, six TZ, and eight
bedrock samples were submitted to three third-party mineralogical testing laboratories
for analysis of soil and rock composition. As of the date of this report, Duke Energy ha s
not received results of this testing; however, results should be available for inclusion in
the CSA Supplement.
 Horizontal Delineation of Groundwater Contamination: As part of W ork Plan
development prior to field mobilization, Duke Energy reviewed existing groundwater
quality data from compliance monitoring wells to evaluate the potential for off-site
migration of COIs and the potential need for installation of off-site wells. This evaluation
prompted the need to install groundwater monitoring wells GWA-14S/D and GWA-15D
on the adjacent Duke Energy-owned property east/northeast of the Secondary Cell.
Review of newly obtained groundwater quality data from wells installed east and north of
Ash Storage 1 indicates a need to refine the understanding of horizontal distribution of
constituents in these two areas. This evaluation will conclude prior to submittal of the
CSA Supplement.
 Additional Speciation of Monitoring Wells: In order to meet the NORR requirements,
Duke Energy conducted speciation of groundwater samples for arsenic, chromium, iron,
manganese, and selenium from selected wells along inferred groundwater flow
transects. Additional speciation sampling may be performed at the following potential
locations: along flow transects, at ash basin surface water sample locations, and at wells
with exceedances of 2L Standards for speciation constituents in consultation with
NCDENR. Adjustments to the speciation sampling from that presented herein are
proposed in Section 15.0, the results of which will be presented in the CSA Supplement.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
14.0 DATA GAPS – CONCEPTUAL SITE MODEL UNCERTAINTIES

89

14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities
 Bedrock Background Wells: Review of laboratory data indicates that well MW -23BR
serves as the only background monitoring well screened within bedrock. The need for
additional background bedrock monitoring wells will be evaulated and discussed with
NCDENR.
 Background Surface Water Data: Background surface water samples were collected
from one location within a tributary water body (SW -5) and one location in the Dan River
(SW -8) during one sampling event. Additional sampling locations within upstream
reaches of the two tributary streams, as well as additional sampling events within the
Dan River will be considered to refine the background surface water constituent
concentrations.
 Surface Water Impacts at SW-3: Results of analyses of surface water and sediment
samples at the SW -3 location in the tributary stream along the eastern property
boundary indicate potential impact by ash. Duke Energy re-sampled the SW-3 location
on August 11, 2015. The results of this sampling event will be discussed in the CSA
Supplement.
 Seep Samples: Seep sample locations S-2, S-3, and S-4 were dry during several
attempted sampling events. Collection of water from these seeps is essential to
determine whether groundwater is discharging to surface water.
 Review of Non-Ash Contamination Information: Review of information regarding areas of
non-ash contamination (i.e., petroleum-contaminated areas) to evaluate potential
interference with remedial methods is needed, if applicable.
14.2 Site Heterogeneities
Site heterogeneities regarding groundwater flow were not identified during completion of the
CSA. In general, groundwater within the surficial aquifer, TZ material, and fractured bedrock
flows south/southeast toward the Dan River, with the exception of the area north of Ash Storage
1. In this area, groundwater elevation data suggest the presence of a groundwater divide
extending from MW -12 east to GWA-1 where localized groundwater within the surficial aquifer
and TZ north of Ash Storage 1 flows north, away from the DRSS site.
Site heterogeneities regarding COI concentrations were not identified during completion of this
CSA. However, heterogeneities may be identified following completion of the groundwater
model for the DRSS site.
14.3 Impact of Data Gaps and Site Heterogeneities
Certain data gaps may be addressed with additional groundwater sampling at existing wells. As
discussed in Section 15.0, a second comprehensive groundwater sampling event is currently
under discussion in consultation with NCDENR. A plan for interim groundwater sampling
between submittal of the CSA and implementation of the anticipated CAP is proposed in Section
16.0 and will further supplement the existing data.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
15.0 PLANNED SAMPLING FOR CSA SUPPLEMENT

90

15.0 Planned Sampling for CSA Supplement
In accordance with CAMA, a second comprehensive groundwater sampling event at the DRSS
site is currently under discussion in consultation with NCDENR and Duke Energy. The second
sampling event will be conducted to:
 Supplement data obtained during the initial sampling event;
 Evaluate seasonal variation in groundwater results; and
 Collect additional samples for chemical speciation of arsenic, chromium, iron,
manganese, and selenium.
15.1 Sampling Plan for Inorganic Constituents
The second sampling event for inorganic constituents will consist of sampling all locations
(monitoring wells, seeps, surface water, and sediment) that were sampled during the initial
sampling event. Locations that were previously dry will be re-evaluated and sampled if sufficient
water is present. All samples collected will be analyzed for total inorganic compounds. Samples
with exceedances of 2L Standards during the initial sampling event will also be analyzed for
dissolved-fraction inorganics.
In addition, surface water samples will be collected upstream and downstream of location SW-3
to refine surface water/groundwater interaction within the tributary stream east of the ash basin.
15.2 Sampling Plan for Speciation Constituents
Speciation sampling will be performed at the following potential locations: along flow transects,
at ash basin surface water sample locations, and at wells with exceedances of 2L Standards for
speciation constituents.
A summary of the proposed sampling program for the second comprehensive sampling event is
included on Table 15-1 and potential sampling locations are shown on Figure 6-2.

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
16.0 INTERIM GROUNDWATER MONITORING PLAN

91

16.0 Interim Groundwater Monitoring Plan
CAMA requires a schedule for continued / interim groundwater monitoring. Given that Duke
Energy has committed to excavating the existing ash basin and ash storage areas to a lined
landfill, certain groundwater monitoring wells in these areas will be abandoned. As such, Duke
Energy plans to conduct interim groundwater monitoring of select wells, as identified in Section
16.3, to bridge the gap between completion of CSA activities and implementation of the
proposed CAP.
16.1 Sampling Frequency
One additional interim groundwater sampling will occur during 2015 and the results will be
submitted in coordination with NCDENR. Interim groundwater sampling on a quarterly basis is
proposed until the CAP is approved by NCDENR. This sampling frequency will allow for
evaluation of seasonal fluctuations in COI concentrations, as well as provide additional data for
statistical analysis of site-specific background concentrations.
16.2 Constituent and Parameter List
The proposed constituents and parameters for analysis are presented in Table 16-1.
16.3 Proposed Sampling Locations
The proposed sampling locations are presented in Table 16-2 and shown on Figure 6-2.
16.4 Proposed Background Wells
The proposed background wells are GWA-1S/D, GWA-9S/D, MW-23D, MW-23BR, and BG-
5S/D. Note that outside of this Interim Groundwater Monitoring Plan, background wells are
planned to be sampled during the interim groundwater sampling event in 2015 (assuming timing
will be such that the samples are not auto-correlated).

This page is intentionally left blank.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
17.0 DISCUSSION

92

17.0 Discussion
17.1 Summary of Completed and Ongoing Work
To date, the following activities have been completed in support of this CSA:
 Installation of 61 groundwater monitoring wells within the ash basin and ash storage
areas, beyond the waste boundary, in background locations, and on an adjacent off-site
property;
 Completion of 2 temporary groundwater monitoring wells within the Primary Cell of the
ash basin;
 Completion of 3 soil borings in background areas of the site;
 Completion of topographic and well/boring location surveys;
 Collection of ash samples from borings completed within the waste boundary and
analysis for total inorganics, TOC, anions/cations, SPLP, and physical properties;
 Collection of soil samples from borings completed within the waste boundary, beyond
the waste boundary, off-site, and background locations and analysis for total inorganics,
TOC, anions/cations, and physical properties;
 Collection of PWR and bedrock samples from borings completed within the waste
boundary, beyond the waste boundary, and background locations and analysis for total
inorganics, TOC, and anions/cations;
 Collection of soil samples for analysis of chemistry and mineralogy;
 Collection of rock samples for chemical analysis;
 Collection of rock samples for petrographic analysis (thin-sections);
 Performance of in-situ horizontal (open hole) and vertical (flush bottom) permeability
tests;
 Completion of packer tests in 11 bedrock borings;
 Completion of rising- and falling-head slug tests in 57 newly installed monitoring wells;
 Collection of groundwater samples from 74 newly installed, compliance, voluntary, and
previously installed monitoring wells, and analysis of samples for total and dissolved
inorganics and anions/cations;
 Speciation of groundwater samples for arsenic, chromium, iron, manganese, and
selenium in groundwater samples collected from 18 monitoring wells installed along
anticipated groundwater flow transects;
 Collection of 8 surface water samples, 4 groundwater seep samples, and 9 sediment
samples, and analysis for total inorganics and anions/cations;
 Speciation of 7 surface water and groundwater seep samples for arsenic, chromium,
iron, manganese, and selenium;
 Evaluation of solid and aqueous matrix laboratory data;
 Completion of an updated Receptor Survey;
 Completion of fracture trace analysis; and
 Preparation of this CSA report.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
17.0 DISCUSSION

93

The following activities are ongoing (as described in Section 14.1.1) and will be provided in the
CSA Supplement:
 Analysis of soil samples for chemistry and mineralogy and rock samples for chemistry
and petrography;
 Evaluation of the need for additional groundwater monitoring wells to better define the
horizontal delineation of groundwater beyond Duke Energy property boundaries; and
 Additional speciation of constituents found to be in excess of their respective 2L
Standards.
17.2 Nature and Extent of Contamination
Soil and groundwater beneath the ash basin and ash storage areas (within the compliance
boundary) have been impacted by ash handling and storage at the DRSS site as described
below. Concentrations of several constituents exceed their respective 2L Standards or IMACs in
groundwater beyond the Compliance Boundary. However, the presence and magnitude of
exceedances for certain constituents may be attributed to naturally occurring conditions and not
necessarily attributed to ash handling at the DRSS site. The extent of the contamination is noted
in the following sections.
17.2.1 Groundwater – Surficial Aquifer
Arsenic and boron were the primary constituents detected in groundwater at concentrations that
exceeded the background concentrations and 2L Standards. Both constituents were detected
above the 2L Standards in a three-dimensional area beneath the ash basin and ash storage
areas in the surficial aquifer. There are no known exceedances of 2L Standards for arsenic or
boron beyond the DRSS property boundary.
TDS and sulfate exceeded the 2L Standards in an isolated area east of the DRSS historical site
property boundary. Based on the relatively low concentrations of other ash-related constituents
in these wells, the presence of TDS and sulfate may not be attributable to groundwater
migration from the ash basin.
The horizontal migration of boron in the surficial aquifer best represents the dominant flow and
transport system. Vertical migration of constituents is generally limited by underlying bedrock.
17.2.2 Groundwater - Bedrock Aquifer
Within the bedrock aquifer, three COIs were identified as primary constituents in groundwater:
iron, manganese, and vanadium. These COIs were identified as naturally occurring metals in
the background wells. Nine other COIs were identified in the bedrock aquifer: antimony, arsenic,
boron, chromium, cobalt, selenium, sulfate, TDS, and thallium. These COIs appear in isolated
locations and do not appear to have migrated extensively across the site or beyond the
compliance boundary.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
17.0 DISCUSSION

94

17.2.3 Groundwater - East of the Ash Basin
Based on review of laboratory data obtained from surface water sample SW -3, collected from
the unnamed tributary located east of the Secondary Cell, it appears that impacted groundwater
has migrated beyond the compliance boundary to the tributary stream east of the ash basin.
Aluminum, arsenic, chromium, cobalt, copper, lead, and zinc exceeded 2B Standards in the
surface water sample (SW-3). However, the results of analyses of sample SW -6, collected from
the Dan River near the confluence with the tributary stream, indicate that the Dan River has not
been adversely affected by the water quality at sample location SW -3. A review of constituent
data from adjacent well MW -21S is inconclusive as to the correlation of the groundwater
chemistry, background well data and the SW -3 results.
Within the shallow aquifer, three COIs were identified as primary indicator COIs in shallow
groundwater: boron, sulfate, and TDS. Boron, sulfate, and TDS rarely exceeded their respective
2L Standards, but are highly mobile constituents and were observed at higher concentrations
within and in the vicinity of the ash basin and ash storage areas than in background and other
areas of the site likely not influenced by the ash basin or ash storage areas.
Five COPCs were identified as primary risk assessment COPCs due to their widespread
presence above associated 2L Standards or IMACs: arsenic, cobalt, iron, manganese, and
vanadium. Arsenic rarely exceeded its 2L Standard and did indicate significant migration, but it
was found at significantly higher concentrations within certain portions of the ash basin and ash
storage areas. Although exceedances of associated 2L Standards or IMACs for cobalt, iron,
manganese, and vanadium were detected across the site, concentrations of these parameters
were generally similar between areas likely to be impacted and background or other areas of
the site likely not influenced by the ash basin or ash storage areas. Four other COIs identified in
the shallow aquifer were isolated in specific locations and do not appear to be transported
across the site: antimony, chromium, selenium, and thallium.
Within the bedrock aquifer, three COPCs were identified as primary risk assessment COPCs
due to their widespread presence above associated 2L Standards or IMACs: iron, manganese,
and vanadium. Although exceedances of associated 2L Standards or IMACs for iron,
manganese, and vanadium were detected across the site, concentrations of these parameters
were generally similar between areas likely to be impacted and background or other areas of
the site likely not influenced by the ash basin or ash storage areas. Nine other COPCs identified
in the deep aquifer were isolated in specific locations and do not appear to be transported
across the site: antimony, arsenic, boron, chromium, cobalt, selenium, sulfate, TDS, and
thallium.
17.3 Maximum Contaminant Concentrations
Maximum contaminant concentrations were determined for ash, soil, groundwater, and surface
water based on the results of sample analyses for each medium. These concentrations were
used to perform screening-level ecological risk assessments based on the North Carolina
Division of Waste Management guidelines (NCDENR 2003).
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
17.0 DISCUSSION

95

COIs evaluated for maximum contaminant concentrations for groundwater included antimony,
arsenic, boron, chromium, cobalt, iron, manganese, selenium, sulfate, thallium, TDS, and
vanadium. COIs evaluated for maximum contaminant concentrations for porewater included
antimony, arsenic, barium, boron, chromium, cobalt, iron, lead, manganese, thallium, TDS, and
vanadium. Maximum constituent concentrations are shown on Figure 10-61 and Table10-11.
For the COIs identified on the basis of ash basin porewater concentrations, boron is the most
prevalent in groundwater with the highest concentration being detected in the surficial aquifer
between the ash storage areas at the AS-12S well location. While boron is prevalent at the site,
it is limited in area and depth (reference Figures 10-73 through 10-75 and Table10-11).
Groundwater affected by boron discharges to the Dan River via groundwater flow and via the
unnamed tributary at the SW -3 location. The maximum concentration of boron in soil was
detected in a sample collected 34-35.5 feet below Ash Storage 2.

The highest concentration of arsenic in groundwater occurs beneath the Ash Storage 1
(reference Figures 10-67 through 10-69 and Table 10-11). The CSA data indicate that arsenic
has not migrated in the direction of public or private water supply wells.

The highest concentration of cobalt in groundwater was detected in a shallow well (MW -11)
within the downgradient dam of the Secondary Cell. Cobalt was also detected in samples from
multiple background well locations (reference Figures 10-79 through 10-81 and Table 10-11).
17.4 Contaminant Migration and Potentially Affected Receptors
In general, groundwater flows from north to south toward the Dan River. Surface water and
sediment sample results from samples collected within the Dan River stream channel did not
identify COIs in excess of applicable regulatory criteria. However, laboratory results for surface
water and sediment samples collected at the SW -3 location in the unnamed tributary east of and
adjacent to the Secondary Cell identified the following COIs above applicable regulatory criteria:
arsenic, chromium, cobalt, copper, lead, manganese, thallium, vanadium, and zinc. The
presence and magnitude of these COIs indicate potential impact from ash.
The human health and ecological SCMs, provided on Figures 12-1 and 12-2, illustrate
potentially affected receptors; these receptors will be reviewed and revised as necessary based
on the information indicated above.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
18.0 CONCLUSIONS

96

18.0 Conclusions
18.1 Source and Cause of Contamination
The CSA found that the source and cause of the contamination for certain parameters in some
areas of the DRSS site is the coal ash contained in the ash basin and ash storage areas. The
cause of this contamination is leaching of constituents from the coal ash into the underlying soil
and groundwater. However, some groundwater, surface water, and soil standards were also
exceeded due to naturally occurring elements found in the subsurface.
18.2 Imminent Hazards to Public Health and Safety and Actions
Taken to Mitigate them in Accordance to 15A NCAC 02L
.0106(f)
15A NCAC 02L .0106(g)(2) requires the site assessment to identify any imminent hazards to
public health and safety and the actions taken to mitigate them in accordance with Paragraph (f)
of .0106(g). The CSA found no imminent hazards to public health and safety; therefore, no
actions to mitigate imminent hazards are required. However, corrective action at the DRSS site
is required to address soil and groundwater contamination.
18.3 Receptors and Significant Exposure Pathways
The NORR and CAMA requirements concerning receptors were completed and results are
provided in Section 4.0. A screening-level human health risk assessment and screening level
ecological risk assessment was performed with the results provided in Section 12.0. The
identified receptors and significant exposure pathways are identified in the human health and
ecological SCMs (Figures 12-1 and 12-2).
18.4 Horizontal and Vertical Extent of Soil and Groundwater
Contamination and Significant Factors Affecting
Contaminant Transport
The CSA identified the horizontal and vertical extent of groundwater contamination within the
compliance boundary, and found that the source and cause of the groundwater exceedances
within that boundary is the coal ash contained in the ash basin and ash storage areas. The
cause of contamination is leaching of constituents from the coal ash into the underlying soil and
groundwater.
The approximate horizontal and vertical extent of soil contamination is shown on Figures 8-1
through 8-5. Soil contamination is considered to be present where soil analytical results were in
excess of the site soil background concentrations or in excess of the soil screening levels
protective of groundwater. The assessment found the soil contaminants are composed of iron,
manganese, arsenic, chromium, and selenium. The CSA identified the horizontal and vertical
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
18.0 CONCLUSIONS

97

extent of soil contamination, with the exception of off-site areas east and north of Ash Storage 1
(as described in Section 14.1.1).

Background monitoring wells contain naturally occurring metals and other constituents at
concentrations that exceeded their respective 2L Standards or IMACs. Examples of naturally
occurring metals and constituents include cobalt, iron, lead, manganese, thallium, TDS, and
vanadium. These naturally occurring metals and constituents were detected in background
groundwater samples at concentrations greater than 2L Standards or IMACs.

The horizontal and vertical extent of groundwater contamination is shown, with the exception of
areas associated with data gaps identified in Section 14.1.1, on Figures 10-64 through 10-102.
Groundwater contamination is considered to be present where the analytical results were in
excess of the site background concentrations and in excess of the 2L Standards or IMACs. The
approximate extent of groundwater contamination is shown on these figures and is limited to an
area within the compliance boundary, between the ash storage areas and the Dan River, with
the exception of areas associated with the data gaps identified in Section 14.1.1. The CSA
found the groundwater COIs to be antimony, arsenic, boron, chromium, cobalt, iron,
manganese, sulfate, thallium, TDS, and vanadium. Iron and manganese are constituents that
may be naturally occurring in regional groundwater as previously discussed in Sections 10.1.8
and 10.1.10, respectively.

No imminent hazards to human health or the environment were identified as a result of the CSA.

The significant factors affecting contaminant transport are those factors that determine how the
contaminant reacts with the soil or aquifer material, resulting in retention to the soil or aquifer
material and removal of the contaminant from groundwater. The interaction between the
contaminant and the soil or aquifer material are affected by the chemical and physical
characteristics of the soil, the geochemical conditions present in the aquifer (if present), the
aquifer materials, and the chemical characteristics of the contaminant. Movement of each
contaminant is related to the groundwater flow direction, the groundwater flow velocity, and the
rate at which a particular contaminant reacts with materials in the aquifer. The data indicates
that geologic conditions present beneath the ash basins impedes the vertical migration of
contaminants. The CSA found that the direction of mobile contaminant transport is generally in a
southeasterly direction towards the Dan River, as anticipated, and not towards other off-site
receptors. North of Ash Storage 1 there is evidence of a northerly flow of groundwater into an
unnamed tributary of the Dan River. No information gathered as part of this CSA suggests that
water supply wells or springs within the 0.5-mile radius of the compliance boundary are
impacted by the DRSS ash basin system.
The two primary mechanisms that immobilize metals (iron and manganese) and semi-metals
(arsenic, boron, and selenium) and prevent their movement in groundwater are sorption and
precipitation (NCDENR 2007a). The major attenuation mechanism for sulfate, a non-metal, is
sorption (EPRI 2004). In these processes, the contaminant is in effect removed from
groundwater and partitions onto the surface of the soil or aquifer matrix (adsorption) or
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
18.0 CONCLUSIONS

98

precipitates into a solid phase, in both cases, removing the contaminant from groundwater.
Many factors specific to the constituent and to site conditions are involved in determining which
of these mechanisms occur and how much of the contaminant partitions out of the groundwater.

Sections 7.0, 8.0, 9.0, and 10.0 present the results of testing performed to determine the
chemical, physical, and mineralogical characteristics of the soil and aquifer materials and the
site groundwater. As described above, determination of the mechanism and the amount of
contaminant removed from the groundwater depends on several site-specific factors. The
adsorptive capacity of the site soils and aquifer materials to the specific groundwater
contaminants by development of site-specific partition coefficient Kd terms, as described in
Section 13.0. The Kd testing will provide site-specific values for the ability and capacity of site
soils to remove contaminants from groundwater and will assist in understanding the
mechanisms affecting contaminant transport at the site. The Kd tests and the associated
groundwater modeling will also allow for evaluation of the long-term contaminant loading and
the capacity of the site soil and aquifer material to attenuate this loading. The results of this
testing, the groundwater modeling, and the evaluation of the long term groundwater conditions
at the site will be presented in the CAP.
18.5 Geological and Hydrogeological Features influencing the
Movement, Chemical, and Physical Character of the
Contaminants
As anticipated in the initial site conceptual hydrogeologic model presented in the Work Plan,
geological and hydrogeological features influencing the movement, chemical, and physical
characteristics of contaminants are related to the Piedmont hydrogeologic system present at the
DRSS site. Movement of the contaminants is related to the groundwater flow direction, the
groundwater flow velocity, and the rate at which a particular contaminant reacts with materials in
the aquifer. The CSA found that the direction of the contaminants’ movement is towards the Dan
River, as anticipated. The rate of groundwater movement varies with the hydraulic conductivity
and porosity of the site soil ranges from approximately 2.5 (saprolite) feet/year to 137.9 (fill)
feet/year. These ranges for rock material are from 7.28 X 104 feet/year to 1.02 X 105 feet/year.
The geological and hydrogeological features of the site influence the movement of the
contaminants by removal of constituents through sorption or precipitation of contaminants. The
degree and rate at which these processes occur depend on many factors associated with the
solution containing the contaminant and the potentially sorbing soil or aquifer material.
These factors include redox conditions, concentration of the solution, chemical composition of
the solution and the contaminant, and mineralogy of the soil or rock matrix. The influence of
these factors as determined by the chemical, physical, hydrologic, and mineralogical
characterization of the ash, ash basin porewater, groundwater, and site soil and rock will be
incorporated into the groundwater modeling discussed in Section 13.0. Geological and
hydrogeological features at the site do not influence the physical character of the constituents
other than through the process of sorption and precipitation. The Kd term development and
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
18.0 CONCLUSIONS

99

leaching tests results, which will be presented in the CAP, will be key to understanding the
influences of the site soils and rock on the constituents.
The groundwater model will provide information useful to evaluating the capacity of the site soil
and aquifer material to attenuate the loading imposed by the conditions modeled for the
proposed corrective action.
18.6 Proposed Continued Monitoring
A plan for continued monitoring of select monitoring wells and parameters/constituents is
presented in Section 16.0 and will be implemented following approval of this CSA report.
18.7 Preliminary Evaluation of Corrective Action Alternatives
Duke Energy previously committed to removing the ash in the ash basin and ash storage areas
via excavation. Approximately 1.2 million tons of ash will be transported to a lined landfill, as
described in Section 2.12. It is anticipated he remainder of ash will be placed into a lined landfill
to be constructed in the vicinity of Ash Storage 1. The initial phase of ash removal is scheduled
to commence 60 days after all necessary permits and approvals are obtained. Closure of the
ash impoundment is anticipated to be completed by August 2019. The soil dams will be
removed and the unimpacted material will be used in site re-grading. The depression left in the
ash basin after ash removal will be filled with on-site and imported fill material, re-graded, and
appropriate vegetation planted to establish a long-term stable, erosion resistant site condition.
Based on the results of soil samples and groundwater samples collected beneath the ash basin
and the ash storage areas, residual contamination will remain after excavation; however, the
degree and persistence of this contamination over time cannot yet be determined. In the
subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L .0106 (k) or
(l) depending on results of the groundwater modeling and evaluation of the site’s suitability to
use MNA. This would potentially require evaluation of MNA using the approach found in
Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volumes 1 and 2
(USEPA 2007) and the potential modeling of groundwater surface water interaction. If these
approaches are found to be unsatisfactory, additional measures such as active remediation by
hydraulic capture and treatment, among others, will be evaluated. When properly applied,
alternatives such as these can provide effective long-term management of sites requiring
corrective action.

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

100

19.0 References
AMEC. 2015. Natural Resources Technical Report, Dan River Steam Station, Rockingham
County, North Carolina. June 24.
American Society of Testing and Materials. 2014. E1689-95, “Developing Site conceptual
models for Contaminated Sites,” ASTM International, West Conshohocken, PA, DOI:
10.1520/E1689.
American Society of Testing and Materials. 2010a. D2216, "Standard Test Methods for
Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass," ASTM
International, West Conshohocken, PA, DOI: 10.1520/ D2216-10.
American Society of Testing and Materials. 2010b. D4318, "Standard Test Methods for Liquid
Limit, Plastic Limit, and Plasticity Index of Soils," ASTM International, West
Conshohocken, PA, DOI: 10.1520/D4318-10.
American Society of Testing and Materials. 2010c. D854, "Standard Test Methods for Specific
Gravity of Soil Solids by Water Pycnometer," ASTM International, West Conshohocken,
PA, DOI: 10.1520/D0854-1.
American Society of Testing and Materials. 2010d. D5084, "Standard Test Methods for
Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible
Wall Permeameter," ASTM International, West Conshohocken, PA, DOI:
10.1520/D5084-1.
American Society of Testing and Materials. 2007. D422, "Standard Test Method for Particle-
Size Analysis of Soils," ASTM International, West Conshohocken, PA, DOI:
10.1520/D0422-63R07.
American Society of Testing and Materials. 2001. D2487, “Standard Practice for Classification
of Soils for Engineering Purposes (Unified Soil Classification System),” ASTM
International, West Conshohocken, PA, DOI: 10.1520/D2487-11.
Barcelona, M. J., Gibb, J. P., et al. 1985. Practical Guide for Ground-water Sampling. Illinois
State Water Survey. Department of Energy and Natural Resources. Champaign, Illinois.
Brobst, D. A. 1962. Geology of the Spruce Pine District Avery, Mitchell and Yancey Counties
North Carolina: USGS Geological Survey Bulletin 1122-A.
Butler, J. R. and Secor, D. T., Jr. 1991. The Central Piedmont, in, Horton, J. W., Jr. and Zullo, V.
A., eds., The Geology of the Carolinas: The University of Tennessee Press, Knoxville, p.
59-78.
Canadian Council of Ministers of the Environment. 1999. Canadian soil quality guidelines for the
protection of environmental and human health: Vanadium (1997). In: Canadian
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

101

environmental quality guidelines, 1999, Canadian Council of Ministers of the
Environment, Winnipeg.
Carpenter, P. A., III. 1982. Geologic map of Region G, North Carolina: North Carolina
Department of Natural Resources and Community Development, Geological Survey
Section, Regional Geology Series 2, Scale 1:125,000.
Chapman, M. J., Cravotta, C. A., III, Szabo, Z., and Lindsey, B. D. 2013. Naturally occurring
contaminants in the Piedmont and Blue Ridge crystalline-rock aquifers and Piedmont
Early Mesozoic basin siliciclastic-rock aquifers, eastern United States, 1994–2008: U.S.
Geological Survey Scientific Investigations Report 2013–5072.
Charlotte-Mecklenburg Storm Water Services. Undated. Catawba River Basin. [Online] URL:
http://charmeck.org/stormwater/whatsmywatershed/Documents/CatawbaWatershed.pdf
Cunningham, W. L. and Daniels, C. C, III. 2001. Investigation of ground-water availability and
quality in Orange County, North Carolina: U. S. Geological Survey, Water-Resources
Investigations Report 00-4286, 59 p.
Daniel, C. C., III, Smith, D. G., and Elmers, J. L. 1989. Hydrogeology and simulation of ground-
water flow in the thick regolith-fractured crystalline rock aquifer system of Indian Creek
Basin, North Carolina: United States Geological Survey Water-Supply Paper 2341-C, p.
C1 – C137.
Daniel, C. C., III, and Sharpless, N. B. 1983. Ground-water supply potential and procedures for
well-site selection upper Cape Fear basin, Cape Fear basin study, 1981-1983: North
Carolina Department of Natural Resources and Community Development and U.S.
Water Resources Council in cooperation with the U.S. Geological Survey, 73 p.
Daniels, J. L. and Das, G. P. 2014. Practical Leachability and Sorption Considerations for Ash
Management, Geo-Congress 2014 Technical Papers: Geocharacterization and Modeling
for Sustainability. Wentworth Institute of Technology, Boston, MA.
DeBruyn, J. 2012. "Duke University Study Shows That Coal Ash Toxins Reaching Lakes and
Rivers." Catawba Riverkeeper Foundation, 15 Oct. 2012.
Deer, W. A., R. A. Howie, and J. Zussman. 1966. An Introduction to the Rock-Forming Minerals:
John Wiley & Sons Inc., New York, N. Y., 528p.
Domenico, P. A. and Mifflin, M. D. 1965. Water from Low-Permeability Sediments and Land
Subsidence. Water Resources Research, Vol. 1, No. 4, p. 563-576.
Donahue, J. and Kibler, S. 2007. Georgia Department of Natural Resources. Environmental
Protection Division. Groundwater Quality in the Piedmont/Blue Ridge Unconfined Aquifer
System of Georgia. Atlanta: 2007.
Duke Energy. 2014a. Coal Ash Excavation and Removal – Dan River Steam Station [Online]
URL: https://www.duke-energy.com/pdfs/am-Dan River-excavation-fact-sheet.pdf
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

102

Duke Energy. 2014b. 2014 News Release [Online] URL: https://www.duke-
energy.com/news/releases/2014111301.asp
Duke Energy. 2014c. Technical Memorandum, “Cliffside Seepage Sample Metallurgy File
#5153 Revision 1”.
Duke Energy Corporation. 2013a. Mountain Island Lake. [Online] URL: http://www.duke-
energy.com/lakes/facts-and-maps/mountain-island.asp
Duke Energy. 2013b. Dan River Decommissioning Project. [Online] URL: https://www.duke-
energy.com/pdfs/am-Dan River-decommissioning-project.pdf
Electric Power Research Institute. 2010. Comparison of Coal Combustion Products to Other
Common Materials, 1020556, Final Report September 2010.
Electric Power Research Institute. 2008. Toxics Release Inventory. Chemical Profile: Arsenic.
Palo Alto, CA.

Electric Power Research Institute. 2005. Chemical Constituents in Coal Combustion Product
Leachate: Boron, EPRI, Palo Alto, CA: 2005. Technical Report 1005258.
Electric Power Research Institute. 2004. Electric Power Research Institute, “Chemical
Attenuation Coefficients for Arsenic Species Using Soil Samples Collected from
Selected Power Plant Sites: Laboratory Studies”, Product ID: 1005505, December 2004.
Electric Power Research Institute. 1995. Coal Ash Disposal Manual: Third Edition, EPRI TR-
104137, January 1995.
Electric Power Research Institute. 1994. “A Field and Laboratory Study of Solute Release from
Sluices Fly Ash”, EPRI TR-104585, December 1994.
Electric Power Research Institute. 1993. Electric Power Research Institute, Physical and
Hydraulic Properties of Fly Ash and Other By-Products from Coal Combustion, EPRI TR-
101999. February 1993.
Fenneman, N. M. 1938. Physiography of eastern United States. McGraw-Hill.
Find Average Temperature for US Cities. 2015. [Online] URL:
http://temperature.weatherdb.com/
FMC Corporation. 2015. "Selenium at the Gay Mine." [Online] URL: http://fmc-idaho.com/the-
gay-mine/selenium/
Freeze, R. A. and Cherry, J. A. 1979. Ground Water, Englewood Cliffs, NJ, Prentice-Hall.
Gillespie, E. 2013. Characterizing the Sources and Variability of Manganese in Well Water of
the North Carolina Piedmont. International Conference on the Biogeochemistry of Trace
Elements.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

103

Gillispie, E. C., Austin, R., Abraham, J., Wang, S., Bolich, R., Bradley, P., Amoozegar, A.,
Duckworth, O., Hesterberg, D., and Polizzotto, M. L. 2014. Sources and variability of
manganese in well water of the North Carolina Piedmont. Water Resources Research
Institute of the University of North Carolina System Annual 2014 Conference, Raleigh,
NC, March 2014. Poster Presentation.
Goldsmith, R., Milton, D. J., and Horton, J. W., Jr. 1988. Geologic map of the Charlotte 1o x 2o
quadrangle, North Carolina and South Carolina: United States Geological Survey,
Miscellaneous Investigations Series, Map I-1251-E, scale 1:250,000.
Griffith, G. E., Omernik, J. M., Comstock, J. A., Shafale, M. P., McNab, W. H., Lenat, D. R.,
Glover, J. B., and Shelburne, V. B. 2002. Ecoregions of North Carolina and South
Carolina, (color poster with map, descriptive text, summary tables, and photographs):
Reston, Virginia, U.S. Geological Survey (map scale 1:1,500,000).
Harden, S. L., Chapman, M. J., and Harned, D. A. 2009. Characterization of groundwater quality
based on regional geologic setting in the Piedmont and Blue Ridge Physiographic
Provinces, North Carolina: U.S. Geological Survey Scientific Investigations Report 2009–
5149.
Harned, D. A. and Daniel, C. C., III. 1992. The transition zone between bedrock and regolith:
Conduit for contamination?, p. 336-348, in Daniel, C. C., III, White, R. K., and Stone, P.
A., eds., Groundwater in the Piedmont: Proceedings of a Conference on Ground Water
in the Piedmont of the Eastern United States, October 16-18, 1989, Clemson University,
693p.
Hatcher, R. D. Jr., Bream, B. R., and Merschat, A. J. 2007. Tectonic map of the southern and
central Appalachians: A tale of three orogens and a complete Wilson cycle, in Hatcher,
R. D., Jr, Carlson, M. P., McBride, J. H., and Martinez Catalan, J. R., eds., 4-D
Framework of Continental Crust: Geological Society of America Memoir 200, p. 595-632.
HDR. 2014a. Dan River Steam Station – Ash Basin Drinking Water Supply Well and Receptor
Survey. [Online] URL: http://portal.ncdenr.org/web/wq/drinking-water-receptor-surveys
HDR. 2014b. Dan River Steam Station – Ash Basin Supplement to Drinking Water Supply Well
and Receptor Survey. [Online] URL: http://portal.ncdenr.org/web/wq/drinking-water-
receptor-surveys
HDR. 2014c. Dan River Steam Station – Ash Basin. Proposed Groundwater Assessment Work
Plan (Rev. 1), NPDES Permit NC0003468.
Heath, R. C. 1984. “Ground-water regions of the United States.” U.S. Geological Survey Water-
Supply Paper 2242, 78 p.
Heath, R. C. 1980. Basic elements of groundwater hydrology with reference to conditions in
North Carolina: U.S. Geo-logical Survey Open-File Report 80–44, 86 p.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

104

Hibbard, J. P., Stoddard, E. F., Secor, D. T., and Dennis, A. J. 2002. The Carolina Zone:
overview of Neoproterozoic to Early Paleozoic peri-Gondwanan terranes along the
eastern flank of the southern Appalachians: Earth-Science Reviews 57, p. 299-339.
Horton, J. W., Jr., Drake, A. A., Jr., and Rankin, D. W. 1989. Tectonostratigraphic terranes and
their Paleozoic boundaries in the central and southern Appalachians, in, Dallmeyer, R;
D., ed., Terranes in the circum-Atlantic Paleozoic orogens: Geological Society of
America Special Paper 230, p. 213-245.
Horton, J. W., Jr. and McConnell, K. I., 1991, The Western Piedmont, p. 36-58, in, Horton, J.
W., Jr., and Zullo, V. A., eds., The Geology of the Carolinas: The University of
Tennessee Press, Knoxville, Tennessee, 406p.
Johnson, A. I. 1967. Specific Yield - Compilation of Specific Yields for Various Materials. United
States Geological Survey Water Supply Paper 1662-D, p. D1-D74.
Jurgens, B. C., McMahon, P. B., Chapelle, F. H., and Eberts, S. M. 2009. An Excel® Workbook
for Identifying Redox Processes in Ground Water. U.S. Geological Survey National
Water-Quality Assessment Program, Open File Report 2009-1004,
Krauskopf, K. B. 1972. Geochemistry of micronutrients: in Micronutrients in Agriculture, J.J.
Mortvedt, F.R. Cox, L.M. Shuman, and R.M. Walsh, eds., Soil Science Society of
America, Madison, Wisconsin, p. 7-36.
LeGrand, H. E. 2004. A Master Conceptual Model for Hydrogeological Site Characterization in
the Piedmont and Mountain Region of North Carolina, A Guidance Manual, North
Carolina Department of Environment and Natural Resources Division of Water Quality,
Groundwater Section.
LeGrand, H. E. 1989. A conceptual model of ground water settings in the Piedmont region. In
Ground Water in the Piedmont , ed. C.C. Daniel III, R.K. White, and P.A. Stone, 693.
Proceedings of a Conference on Ground Water in the Piedmont of the Eastern United
States, Clemson University, Clemson, South Carolina. Charlotte, NC: U.S. Geological
Survey.
LeGrand, H. E. 1988. Region 21, Piedmont and Blue Ridge. In Hydrogeology, The Geology of
North America, vol. O-2, ed. W.B. Back, J.S. Rosenshein, and P.R. Seaber, 201–207.
Geological Society of America. Boulder CO: Geological Society of America.
Martens, D. A. 2002. "Selenium." Encyclopedia of Soil Science. New York: Marcel Dekker, 840-
42.

National Drinking Water Database [Online] URL: http://www.ewg.org/tap-
water/whatsinyourwater/1085/NC/NorthCarolina/Thallium-total/
North Carolina Department of Environment and Natural Resources. 2015. NPDES Permit for
Dan River Steam Station. [Online] URL:
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

105

http://portal.ncdenr.org/c/document_library/get_file?uuid=38c490a7-5b93-4540-a593-
d8ae3014d724&groupId=38364
North Carolina Department of Environment and Natural Resources. 2013a. 15A NCAC 2B
.0200s. Classifications and Water Quality Standards Applicable to the Surface Waters
and Wetlands of North Carolina. NC and EPA Combined Surface Water Quality
Standards and Criteria Table. May 15. [Online] URL:
http://portal.ncdenr.org/web/wq/ps/csu/swstandards
North Carolina Department of Environment and Natural Resources. 2013b. 15A NCAC 02L.
Groundwater Rules. Groundwater Standards Table. April 1. [Online] URL:
http://portal.ncdenr.org/web/wq/ps/csu/gwstandards#4
North Carolina Department of Environment and Natural Resources. 2013c. 15A NCAC 02L.
Groundwater Rules. Interim Maximum Allowable Concentrations (IMACs) Table. April 1.
[Online] URL: http://portal.ncdenr.org/web/wq/ps/csu/gwstandards#4
North Carolina Department of Environment and Natural Resources. 2007a. “Hydrogeologic
Investigation and Reporting Policy Memorandum”, dated May 31, 2007.
North Carolina Department of Environment and Natural Resources. 2007b. “Performance and
Analysis of Aquifer Slug Tests and Pumping Tests Policy,” May 31, 2007.
North Carolina Department of Environment and Natural Resources. 2004. A Master Conceptual
Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region
of North Carolina, A Guidance Manual. Division of Water Quality, Groundwater Section.
Prepared for the Groundwater Section by Harry E. LeGrand Sr., Independent
Hydorgeologist. 2004.
North Carolina Department of Environment and Natural Resources. 2003. Guidelines for
Performing Screening Level Ecological Risk Assessments with the North Carolina
Division of Waste Management. North Carolina Department of Environment and Natural
Resources, Division of Waste Management. October 2003. [Online] URL:
http://portal.ncdenr.org/web/wm/guidelines-for-performing-screening-level-ecological-
risk-assessments
North Carolina Department of Environment and Natural Resources – Division of Water
Resources. 2015. NC Surface Water Classifications, NC Classifications Website [Online]
URL: http://ncdenr.maps.arcgis.com/apps/webappviewer/
index.html?id=6e125ad7628f494694e259c80dd64265
North Carolina Department of Environment and Natural Resources - Division of Water Quality.
2013. Classification and Water Quality Standards Applicable to the Groundwaters of
North Carolina, NCDENR, Raleigh, NC.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

106

North Carolina Department of Environment and Natural Resources – Division of Water Quality.
2012. Evaluating Metals in Groundwater at DWQ Permitted Facilities: A Technical
Assistance Document for DWQ Staff.
North Carolina Department of Environment and Natural Resources – Division of Water Quality.
2007. North Carolina Water Supply Watersheds, Division of Water Quality. [Online]
URL:http://portal.ncdenr.org/c/document_library/get_file?uuid=df30416f-cd0e-46bd-
9ce4-fcc470aa324d&groupId=38364
North Carolina Department of Health and Human Services, Department of Public Health. 2010a.
“Concentration of Iron Detected in NC Private Well Water, Average 1998-2010 and
Average 2010.” Well Water & Health. University of North Carolina Superfund Research
Program.

North Carolina Department of Health and Human Services. 2010b. Occupational &
Environmental Epidemiology, Well Water and Health [Online] URL:
http://epi.publichealth.nc.gov/oee/wellwater/

North Carolina Department of Public Health. 2015. Fish Consumption Advisories. Division of
Public Health. March 27. [Online] URL:
http://epi.publichealth.nc.gov/oee/fish/advisories.html
North Carolina Geological Survey. 1985. Geologic map of North Carolina: North Carolina
Geological Survey, General Geologic Map, scale 1:500000.

North Carolina State University, A&T State University, NC Cooperative Extension Resources.
1996. Table 1. Average length of growing season for selected North Carolina Counties
(1951-1980) [Online] URL:http://content.ces.ncsu.edu/average-growing-season-for-
selected-north-carolina-locations/

North Carolina Wildlife Resources Commission. Undated. Riverine Aquatic
Communities. Piedmont Ecoregion. [Online] URL:
http://www.ncwildlife.org/Portals/0/Conserving/documents/Piedmont/P_Riverine_
aquatic_communities.pdf.

Nutter, L. J. and Otton, E. G. 1969. Groundwater occurrence in the Maryland Piedmont:
Maryland Geological Survey Report of Investigations, No. 10, 42p.
Olsen, P. E., Froelich, A. J., Daniels, D. L., Smoot, J. P., and Gore, P. J. W. 1991. Rift basins of
early Mesozoic age, p.142-170, in Horton, J. W., Jr., and Zullo, V. A., eds., The Geology
of the Carolinas: The University of Tennessee Press, Knoxville, Tennessee, 406p.
Parkhurst, D. L. and Appelo, C. A. J. 2013. Description of input and examples for PHREEQC
version 3—A computer program for speciation, batch-reaction, onedimensional
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

107

transport, and inverse geochemical calculations: U.S. Geological Survey Techniques
and Methods, book 6, chap. A43, 497 p.
Pippin, C. G., Chapman, M. J., Huffman, B. A., Heller, M. J., and Schelgel, M. E. 2008.
Hydrogeologic setting, ground-water flow, and ground-water quality at the Lantree
Peninsula research station, Iredell County, North Carolina, 2000–2005: U.S. Geological
Survey Scientific Investigations Report 2008–5055, 89 p. [Online] URL:
http://pubs.water.usgs.gov/sir2008–5055.
Polizzotto, M. 2014. Surface and Subsurface Properties Regulating Manganese Contamination
of Groundwater in the North Carolina Piedmont. Progress Report to the Water
Resources Research Institute of The University of North Carolina. WRRI Project 13-05-
W.
Robson, S. G. 1993. Techniques for estimating specific yield and specific retention from grain-
size data and geophysical logs from clastic bedrock aquifers: United States Geological
Survey, Water-Resources Investigations Report 93-4198, 19p.
Ruhl, L., Vengosh, A., Dwyer, G. S., Hsu-Kim, H., Schwartz, G., Romanski A., and Smith, S. D.
2012. “The impact of coal combustion residue effluent on water resources: a North
Carolina example.” Environ Sci Technol. 2012 Nov 6;46(21):12226-33. doi:
10.1021/es303263x. Epub 2012 Oct 15.
Sanders, L. L. 1998. A Manual of Field Hydrogeology. Prentice Hall, 381p.
Sanders, A. P, Messier, K. P., Shehee, M., Rudo, K., Serre, M. L., and Fry, R. C. 2011. Arsenic
in North Carolina: Public Health Implications, Environment International, Vol. 38 pp. 10-
16.
Schaeffer, M. F. 2014a. Piedmont groundwater system, Part 1 – The transition zone between
regolith and bedrock: Existence: Geological Society of America, Abstracts with Program,
April 2014, v. 46, no. 3, p. 26-27.
Schaeffer, M. F. 2014b. Piedmont groundwater system, Part 2 – The transition zone between
regolith and bedrock: Characteristics: Geological Society of America, Abstracts with
Program, April 2014. v. 46, no. 3, p. 27.
Schaeffer, M. F. 2011. Carolina Piedmont groundwater system: What does the transition zone
look like?: 19th Annual David S. Snipes/Clemson Hydrogeology Symposium, April 7,
2011, p. 43-44.
Schaeffer, M. F. 2009. Hydraulic conductivity of Carolina Piedmont soil and bedrock: Is a
transition zone present between the regolith and bedrock?: 17th Annual David S.
Snipes/Clemson Hydrogeology Symposium, April 2, 2009, p. 32-36.
Seal, B., Verplanck, P., Van Gosen, B., and Grosz, A. 2012. "Geologic and Environmental
Characteristics of Rare Earth Element Deposit Types Found in the United States."
Lecture. Apr 4, 2012.
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

108

Stewart, J. W. 1964. Infiltration and permeability of weathered crystalline rocks, Georgia Nuclear
Laboratory, Dawson County, Georgia: United States Geological Survey, Bulletin 1133-D,
p. D1-D57.
Stewart, J. W., Callahan, J. T., Carter, R. F, et al. 1964. Geologic and hydrologic investigation at
the site of the Georgia Nuclear Laboratory, Dawson County, Georgia: United States
Geological Survey Bulletin 1133-F, p. F1-F90.
Tang, G., Mayes, M. A., Parker, J. C., and Jardine, P. M. 2010. CXTFIT/Excel–A modular
adaptable code for parameter estimation, sensitivity analysis and uncertainty analysis for
laboratory or field tracer experiments. Computers & Geosciences, 36(9), 1200-1209.
Thayer, P. A. 1970. Stratigraphy and geology of the Dan River Triassic Basin, North Carolina:
Southeastern Geology, v. 12, p.1-31.
Thayer, P. A. and Robbins, E. I. 1992. Sedimentology of Triassic Dan River Group, North
Carolina and Virginia, p.189-200, in Dennison, J. M. and Stewart, K. G., eds., Geologic
field guides to North Carolina and vicinity: Southeastern section, Geological Society of
America Field Trip Guides, Department of Geology, University of North Carolina at
Chapel Hill, Chapel Hill, North Carolina, Geologic Guidebook No. 1, 233p.
U.S. Department of Agriculture – Soil Conservation Service. 1994. Soil Survey of Rockingham
County, North Carolina.
U.S. Department of Health and Human Services – Public Health Service, Agency for Toxic
Substances and Disease Registry. 2012. Potential for Human Exposure. In Toxicological
Profile for Manganese.
U.S. Department of Health and Human Services – Public Health Service, Agency for Toxic
Substances and Disease Registry. 2004. Potential for Human Exposure. In Toxicological
Profile for Cobalt.
U.S. Environmental Protection Agency. Undated. RCRA Corrective Action Workshop on
Results-Based Project Management.
U.S. Environmental Protection Agency. 2015. Regional Screening Levels Generic Tables.
January. [Online] URL: http://www.epa.gov/reg3hwmd/risk/human/rb-
concentration_table/Generic_Tables/index.htm
U.S. Environmental Protection Agency. 2014a. Administrative Settlement Agreement and Order
on Consent for Removal Action. Eden Ash Spill, (a/k/a/ Duke Coal Ash Spill). Duke
Energy Carolinas, LLC. May. [Online] URL: https://www.duke-
energy.com/news/releases/2014052202.asp
U.S. Environmental Protection Agency. 2014b. "Basic Information about Selenium in Drinking
Water." Water: Basic Information about Regulated Drinking Water Contaminants.

Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

109

U.S. Environmental Protection Agency. 2014c. National Primary Drinking Water Regulations
U.S. Environmental Protection Agency. 2014d. National Recommended Water Quality Criteria.
Aquatic and Human Health Criteria Tables. December 3. [Online] URL:
http://water.epa.gov/scitech/swguidance/standards/criteria/current/index.cfm
U.S. Environmental Protection Agency. 2013. Guidance on the Management of Contaminated
Land and Groundwater at EPA Licensed Sites.
U.S. Environmental Protection Agency. 2012. Sulfate in Drinking Water. Accessed on 7/30/15
http://water.epa.gov/drink/contaminants/unregulated/sulfate.cfm
U.S. Environmental Protection Agency. 2009. Statistical Analysis of Groundwater Monitoring
Data at RCRA Facilities Unified Guidance.
U.S. Environmental Protection Agency. 2007. Monitored Natural Attenuation of Inorganic
Contaminants in Ground Water. Volume 1, Technical Basis for Assessment.
U.S. Environmental Protection Agency. 2003. EPA 822-R-03-007, Drinking Water Advisory:
Consumer Acceptability Advice and Health Effects Analysis on Sulfate
U.S. Environmental Protection Agency Region 4. 2001. Ecological Risk Assessment Bulletins--
Supplement to RAGS. Tables 1 - 4. November 30. [Online] URL:
http://www.epa.gov/region4/superfund/programs/riskassess/ecolbul.html#tbl1
U.S. Environmental Protection Agency. 1998. Guidelines for Ecological Risk Assessment. April.
[Online] URL http://www2.epa.gov/sites/production/files/2014-
11/documents/eco_risk_assessment1998.pdf
U.S. Environmental Protection Agency. 1997. Ecological Risk Assessment Guidance for
Superfund: Process for Designing and Conducting Ecological Risk Assessments, Interim
Final. June. [Online] URL: http://www.epa.gov/oswer/riskassessment/ecorisk/ecorisk.htm
U.S. Environmental Protection Agency. 1992. Batch-type procedures for estimating soil
adsorption of chemicals. TechnicalResource Document 530/SW -87/006-F.
U.S. Fish and Wildlife Service. 2015. Endangered and Threatened Species and Species of
Concern by County for North Carolina. [Online] URL:
http://www.fws.gov/raleigh/species/cntylist/nc_counties.html
U.S. Fish and Wildlife Service. Undated. USFWS Responds to Coal Ash Release to the Dan
River in North Carolina and Virginia. [Online] URL:
https://www.fws.gov/contaminants/Documents/DanRiverCoalAshReleaseFacts.pdf
U.S. Geological Survey. 1997. Ground Water Atlas of the United States. HA 730-L.
U.S. Geological Survey. Undated. Mineral Resources Database:
http://mrdata.usgs.gov/soilgeochemistry/#/detail/element/81
Duke Energy Carolinas, LLC | Comprehensive Site Assessment Report
Dan River Steam Station Ash Basin
19.0 REFERENCS

110

U.S. Geological Survey. 1973. United States Mineral Resources. United States Government
Printing Office.
Venkatakrishnan, R. and Gheorghiu, F. 2003. Conceptual groundwater flow models identified in
Triassic Basins, eastern United States: EGS-AGU-EUG Joint Assembly, Abstract from
Meeting, Held in Nice, France, 6-11 April 2003, Abstract #8569.
Weather DB. 2015. Eden, North Carolina Average Rainfall. [Online] URL:
http://rainfall.weatherdb.com/
Wiley and Sons. 1993. Biodiversity of the Southeastern United States, Upland Terrestrial
Communities.
World Health Organization. 1996. Iron in Drinking-water. Guidelines for Drinking-water.
Wright, M. T., and K. Belitz. 2010. "Factors Controlling the Regional Distribution of Vanadium in
Groundwater." Ground Water 48.4 (2010): 515-25. Web.)
This page is intentionally left blank.

Figures

This page is intentionally left blank.

Tables