Allen CSAR Executive Summary

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
Executive Summary —Allen Steam Station
On August 20, 2014, the North Carolina General Assembly passed Session Law 2014-122, the
Coal Ash Management Act of 2014 (CAMA). Section § 130A-309.211 of the bill requires the
owner of a coal combustion residuals surface impoundment to submit a Groundwater
Assessment 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 on December 30, 2014 for characterization of the Allen Steam Station
(Allen) ash basin and assessment of soil and groundwater potentially impacted by the ash basin
system. The Work Plan was subsequently conditionally approved by the NCDENR in
correspondence dated February 24, 2015. This CSA report was prepared to comply with 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 no later than 90 days
after submittal of this CSA unless an extension is requested and granted.
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 statutes,
regulations and documents:
Groundwater Classification and Standards, Title 15A NCAC Subchapter 2L
Coal Ash Management Act of 2014, N.C. Gen. Stat. §§130A-309.200 et seq.;
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 24, 2015; and
Subsequent meetings and correspondence between Duke Energy and NCDENR.
For this CSA, the source area is defined as the ash basin, which consists of the active ash basin
and the inactive ash basin. Source characterization was performed to identify physical and
chemical properties of ash, ash basin surface water, ash porewater, and ash basin seeps. The
ash, ash basin surface water, ash porewater, and seep analytical results were compared to 2L
Groundwater Standards, IMACs, and other regulatory screening levels for the purpose of
identifying constituents of interest (COls). These COls are considered to be associated with
potential impacts to soil and groundwater from the ash basin.
This CSA also identifies constituents that exceeded North Carolina Groundwater Quality
Standards, as specified in 15A NCAC 2L.0202 (2L Standards), or Interim Maximum Allowable
Concentration (IMAC) established by NCDENR pursuant to 15A NCAC 2L.0202(c) from
groundwater sample locations outside the ash basin boundary. For the purposes of this report,
these constituents were also identified as COls. Some COls are present in background and

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Allen Steam Station Ash Basin FN
EXECUTIVE SUMMARY
upgradient monitoring wells and thus require careful examination to determine whether their
presence downgradient of the ash basin is naturally occurring or a result of ash handling and
storage. The IMACs were issued in 2010, 2011 and 2012; however, NCDENR has not
established a 2L Standard for these constituents as described in 15A NCAC 2L.0202(c). For this
reason, the IMACs noted in this report are for reference only.
In addition to evaluating the distribution of constituents across the Allen site, significant factors
affecting constituent transport, and the geological and hydrogeological features influencing the
movement and chemical and physical character of the COls were also evaluated.
The assessment consisted of the following activities:
• Completion of soil and rock borings and installation of groundwater monitoring wells to
facilitate collection and analysis of chemical, physical, and hydrogeological parameters
of subsurface materials and groundwater encountered within and beyond the ash basin
waste and compliance boundaries.
• Collection and analysis of solid phase (e.g., soil, rock and ash) and liquid phase (e.g.,
groundwater, ash basin porewater, ash basin surface water, and seep) samples;
• 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 soil or groundwater impacts at the site.
• 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 ash basin are also naturally occurring or might be influenced by
migration of constituents from the ash basin. Naturally occuring metals and consituents
reported in background groundwater samples at concentrations greater than 2L
Standards or IMACs include antimony, barium, chromium, cobalt, iron, manganese, total
dissolved solids (TDS), and vanadium.
• Groundwater in the shallow, deep, and bedrock flow layers beneath the ash basin flows
horizontally to the east toward the Catawba River, with the north portion of the inactive
ash basin flowing to the northeast and north toward Duke Energy property and the
discharge canal. This flow direction is away from the direction of the nearest public or
private water supply wells. The Catawba River and discharge canal serve as hydrologic
boundaries for groundwater within the shallow layer at the site. There are no water
supply wells located between the ash basin and the Catawba River or between the ash
basin and the discharge canal.
• The geological and hydrogeological features influencing the migration, chemical, and
physical characteristics of contaminants are related to the Piedmont hydrogeologic
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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system present at the site. The CSA found that the direction of the migration of coal ash
related contaminants is toward the Catawba River. The rate of groundwater movement
varies with the hydraulic conductivity and porosity of the site soil, TZ, and bedrock
materials, which ranged from 8.7 ft/yr to 78.9 ft/yr in soils, 7.3 x 104 ft/yr to 4.9 x 107 ft/yr
in the TZ (PWR), and 1.0 x 105 ft/yr to 5.3 x 105 ft/yr in bedrock.
• The USEPA has identified constituents for groundwater detection monitoring programs
at coal combustion residuals (CCR) ash basins and landfills. These consituents were
selected as leading indicators of groundwater contamination from CCR units, which may
be evaluated for statistically significant increases over background with time. Boron and
sulfate are among these detection monitoring constituents, are expected to be highly
mobile in the groundwater environment, and therefore can be used to represent the
general extent of groundwater impacted by the ash basin at the site. The horizontal and
vertical migration of boron best represents the groundwater flow and potential transport
system at the site. Sulfate is generally a good indicator, but can naturally occur above its
applicable standards and should be carefully considered for use as an indicator.
• Boron exceedances are present in shallow groundwater immediately downgradient and
east of the active ash basin and the inactive ash basin, with higher concentrations east
of the inactive ash basin in the direction of groundwater flow toward the Catawba River.
The boron exceedances in deep groundwater are present beneath the east portion of
the active ash basin and immediately downgradient of the active ash basin. Boron
exceedances in bedrock are limited to the area downgradient and east of the inactive
ash basin. Vertical migration of boron is generally limited by the underlying bedrock.
• Sulfate exceedances at the site are limited to shallow groundwater beneath the northern
extent of the inactive ash basin and immediately north and downgradient of the inactive
ash basin. The highest concentration of sulfate was reported in monitoring well GWA-6S.
Several other COls exhibited their highest concentrations at the site in GWA-6S, and
were not detected at elevated concentrations where boron exceedances are present
along the east boundary of the ash basin. It appears that groundwater impacts at GWA-
6S may not be fully attributable to the ash basin and may be influenced by another
industrial activity at the site.
• Figure ES -1 depicts the horizontal extent of 2L Standard exceedances for boron and
sulfate in the shallow, deep, and bedrock groundwater flow layers at the site.
• Based on data obtained during this CSA, the groundwater flow direction, and the extent
of exceedances of boron and sulfate, it appears that groundwater impacted by the ash
basin is contained within the Duke Energy property boundary.
• Exceedances of 2L Standards and IMACs were observed in monitoring wells at the
outermost extent of the monitoring well system, including upgradient and background
wells. A preliminary review found that the upgradient and background exceedances at
the outermost extent of the monitoring system are related to background water quality,
naturally occurring conditions, and/or sampling conditions. A second round of sampling
will be performed at all locations sampled during the CSA. The results from the CSA
sampling, the second round of sampling, and the site-specific background
concentrations will be used to confirm that these observed exceedances do not
ES -3

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
represent groundwater impacts attributable to the ash basin. The results of this
evaluation will be presented in the CSA supplement.
• The horizontal extent of soil contamination is limited to the area beneath the inactive ash
basin and the active ash basin. Where soil impacts were identified, the vertical extent of
contamination beneath the ash/soil interface is generally limited to the uppermost soil
sample collected beneath the ash basin.
• Seep samples collected from NCDENR and CSA -identified seeps located east of the
ash basin indicate boron was present and reported above its 2L Standard. This is
consistent with groundwater impacts identified east and downgradient of the ash basin.
• Ongoing in -stream monitoring for NPDES surface water quality data of samples within
the Catawba River collected upstream and downstream of the ash basin do not indicate
that the ash storage onsite has resulted in increased constituent concentrations above
the North Carolina Surface Water Quality Standards (213 Standards) downstream of the
Allen Steam Station for select constituents.
ESA Source Information
Duke Energy owns and operates Allen, which is located near the town of Belmont, in Gaston
County, North Carolina. Allen began operation in 1957 as a coal-fired generating station and
currently operates five coal-fired units. The coal ash residue from Allen's coal combustion
process has historically been disposed in the ash basin system located to the south of the
station and adjacent to the Catawba River. Discharge from the ash basin system is permitted by
the NCDENR Division of Water Resources (DWR) under the NPDES Permit NC0004979.
The ash basin system at Allen consists of an active ash basin and an inactive ash basin. In
general, the ash basin is located south of the power complex in historical drainage features
formed from tributaries that flowed toward the Catawba River. There is one earthen
embankment dam and one earthen dike impounding the active ash basin: the East Dam,
located along the west bank of the Catawba River, and the North Dike, separating the active
and inactive ash basins. The original ash basin at the Allen site (the inactive ash basin) began
operation in 1957 and was formed by constructing an underlying portion of the earthen North
Dike and the northern portion of the main East Dam where tributaries flowed toward the
Catawba River. As the original ash basin capacity diminished over time, the active ash basin
was formed in 1973 by constructing the southern portion of the East Dam and raising the North
Dike. Ash has been sluiced to the active ash basin since 1973.
Two unlined dry ash storage areas, two unlined structural fill units, and a double -lined dry ash
landfill are located within the footprint of the inactive ash basin. The ash landfill was constructed
in 2009. Construction of the structural fill units began in 2003 and was completed in 2009. The
dry ash storage areas were constructed in 1996.
The ash basin is operated as an integral part of the station's wastewater treatment system,
which receives permitted and variable discharges from the ash removal system, coal pile runoff,
landfill leachate, flue gas desulfurization (FGD) wastewater, the station yard drain sump, and
site stormwater.
ES -4

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN
Steam Station Ash Basin
EXECUTIVE SUMMARY
The CSA found that soil and groundwater beneath and downgradient of the ash basin (within
the property boundary) have been impacted by ash handling and storage at the Allen site as
described in Section ES.4.2. Ash basin COls in soil, groundwater, and seeps are likely the
results of leaching from coal ash contained in the ash basin. However, exceedances of
antimony, barium, chromium, cobalt, iron, manganese, TDS, and vanadium may be due in part
or in whole to naturally occurring conditions based on review of background soil and
groundwater quality data.
ES.2 Initial Abatement and Emergency Response
No imminent hazard to human health or the environment has been identified; therefore, initial
abatement and emergency response actions have not been required.
ES.3 Receptor Information
Properties located within a 0.5 -mile radius of the Allen ash basin compliance boundary generally
consist of Allen Steam Station to the north with residential properties beyond, residential
properties and some undeveloped land in Gaston County to the west and south, and residential
properties and some undeveloped land in Mecklenburg County to the east and southeast across
the Catawba River.
Duke Energy submitted a receptor survey to NCDENR (HDR 2014a) in September 2014, and
subsequently submitted to NCDENR a supplement to the receptor survey (HDR 2014b) 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 human
health risk assessment. 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 Allen ash basin compliance boundary requesting information on the presence of
water supply wells and well usage.
The CSA receptor 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 Allen
ash basin compliance boundary:
• NCDENR DWR 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;
• Mecklenburg County Groundwater and Wastewater Services Well Information System
online database;
• Gaston County Health and Human Services Department, Environmental Health
Services;
0 Charlotte -Mecklenburg Utilities Department;

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• Belmont Water and Sewer Department; and
• USGS National Hydrography Dataset.
During the week of October 8, 2014, HDR mailed 402 water supply well survey questionnaires
to property owners within a 0.5 -mile radius of the Allen ash basin compliance boundary
requesting information on the presence of water supply wells and well usage for the properties.
The review of these records identified four public water supply wells and 219 private water
supply wells within the 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.
Several surface water bodies that flow east from the topographic divide along South Point Road
toward the Catawba River were identified within a 0.5 -mile radius of the ash basin.
NCDENR conducted a well testing program to assess private water supply wells near the Allen
site. The results of the NCDENR sampling were evaluated as part of the screening level risk
assessment and are summarized in Section ES.4.9.
ESA Sampling / Investigation Results
ES.4.1 Background Findings
As part of the CSA, Duke Energy installed seven additional background monitoring wells (BG -
1 S/D, BG-2S/D/BR, and BG-3S/D) at the site. The background locations were selected to
maximize physical separation from the ash basin in areas believed not to be impacted by the
ash basin based on existing knowledge of the site to provide sufficient background water quality
in the future. Based on data obtained in this CSA, the newly installed BG wells are not located
hydraulically downgradient of the ash basin, and are considered representative of background
groundwater quality conditions at the site.
Existing ash basin compliance monitoring well AB -1 R has been considered by Duke Energy to
represent background water quality at the site since being installed in 2010. AB -1 R is located to
the northwest of the inactive ash basin at the compliance boundary and has not previously
exhibited 2L exceedances. However, recent increasing trends of detection monitoring
constituents in samples collected from AB -1 R indicate groundwater in the vicinity of AB -1 R may
be influenced by the northwest portion of the inactive ash basin.
Analyses of groundwater samples collected from the new background monitoring wells indicated
that the following naturally occurring metals exceeded 2L Standards or IMACs in background
locations: antimony, barium, chromium, cobalt, iron, manganese, TDS, and vanadium. The
results for all other constituents were reported below 2L Standards or IMACs.
The range of concentrations reported in the new background wells is presented below

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
Constituent of Interest
Groundwater 21L Standard
or IMACs* (pg/L
Background Well
Range of Results N /L
Aluminum
NE
130 to 3,800
Antimony
1.
<0.5 to 4.8
Arsenic
10
<0.5 to 2.3
Barium
700
19 to 1,400
Boron
700
<50
Cobalt
1 *
0.63 to 2.4
Copper
1,000
1.4 to 12.7
Iron
300
71 to 3,700
Lead
15
<0.1 to 0.85
Manganese
50
<5 to 620
pH
6.5 -8.5 SU
5.89 to 12.66
Selenium
20
<0.5 to 1.2
Sulfate
250,000
1,100 to 30,300
Thallium
0.2*
<0.1 to 0.14
TDS
500,000
33,000 to 2,040,000
Vanadium
0.3*
2.7 to 22.5
ES.4.2 Nature and Extent of Contamination
Soil and groundwater beneath and downgradient of the ash basin (within the property boundary)
have been impacted by ash handling and storage at the Allen site as described below. The
extent of the contamination is noted below.
ES.4.2.1 Soil
The horizontal extent of soil contamination is limited to the area beneath the inactive ash basin
and the active ash basin. Where soil impacts were identified, the vertical extent of contamination
beneath the ash/soil interface is generally limited to the uppermost soil sample collected
beneath the ash basin. Reported concentrations of soil samples were compared to background
concentrations in addition to the North Carolina Industrial Health and Protection of Groundwater
PSRGs to delineate the extent of contamination. The following COls exceeded North Carolina
PSRGs beneath the active ash basin: arsenic, barium, and cobalt. The only COI that exceeded
North Carolina PSRGs beneath the inactive ash basin was arsenic, which was limited to one
uppermost soil sample.
ES.4.2.2 Groundwater
Details of the nature and extent of contamination for each COI identified in the source
characterization (listed in Section 7.5.5) is described below.
• Aluminum was reported above background concentrations at one location, but there is
no 2L Standard or IMAC established for aluminum.
• Antimony concentrations that exceeded the IMAC are mainly limited to the deep and
bedrock flow layers. One exceedance was reported in the shallow bedrock well BG -3S.
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN
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EXECUTIVE SUMMARY
In the deep flow layer, IMAC exceedances were reported beneath the north portion of
the active ash basin (AB -24D), immediately downgradient of the eastern portion of the
active ash basin (AB -26D), immediately downgradient and east of the inactive ash basin
(AB -31 D), and upgradient and offsite to the west (GWA-14D). In the bedrock flow layer,
exceedances were reported beneath the west portion of the active ash basin (AB-
23BRU) and in bedrock background monitoring well BG-2BR.
• Arsenic concentrations that exceeded the 2L Standard are limited to the shallow flow
layer near the westernmost extent of the inactive ash basin (AB -36S) and immediately
downgradient and north of the inactive ash basin (GWA-6S). No arsenic exceedances
were reported in the deep and bedrock wells.
• Barium concentrations that exceeded the 2L Standard are limited to shallow well AB -36S
located in the western portion of the inactive ash basin and the background bedrock well
BG-2BR. No other barium exceedances were reported in shallow, deep, and bedrock
wells.
• Boron concentrations that exceeded the 2L Standard are present in the shallow, deep,
and bedrock flow layers. In the shallow flow layer, boron exceedances were reported
immediately downgradient and east of the active ash basin dam (AB -26S) and the
inactive ash basin dam (AB -31 S), and to the east toward the Catawba River (GWA-4S).
In the deep flow layer, exceedances were reported beneath the northeast portion of the
active ash basin (AB -27D) and immediately downgradient of the southeast portion of the
active ash basin (AB -22D). In the bedrock flow layer, one boron exceedance was
reported downgradient and east of the inactive ash basin (GWA-5BR). No other boron
exceedances were reported in shallow, deep, and bedrock wells.
• Cobalt concentrations that exceeded the IMAC in the shallow and deep flow layers are
generally widespred across the site. In the shallow layer, exceedances are concentrated
downgradient and east of the ash basin from GWA-1 S (furthest south) to the north
toward GWA-7S, west of the ash basin at monitoring wells AB -2, AB -13S and GWA-14S,
and one isolated exceedance at GWA-9S. The highest concentration of cobalt was
reported in shallow well GWA-6S. In the deep flow layer, cobalt concentrations that
exceeded the IMAC are also widespread in the same general areas of the site. Cobalt
was reported above the IMAC in shallow background well BG -3S and deep background
well BG -21D. No cobalt exceedances were reported in bedrock wells.
• Copper concentrations did not exceed its 2L Standard in any of the groundwater
samples at the site.
• Iron concentrations that exceeded the 2L Standard vary in the shallow and deep wells
and are widespread across the site. In the bedrock wells, iron exceedances were only
reported in monitoring wells GWA-1 BR and GWA-6BR.
• Lead concentrations did not exceed its 2L Standard in any of the groundwater samples
at the site.
• Manganese concentrations that exceeded the 2L Standard vary in the shallow and deep
wells and are widespread across the site. In the bedrock wells, only one exceedance of
manganese was reported in monitoring well GWA-613R.

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN
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EXECUTIVE SUMMARY
• Selenium concentrations that exceeded the 2L Standard are limited to one shallow
monitoring well, GWA-6S. No other selenium exceedances were reported in shallow,
deep, and bedrock wells.
• Sulfate concentrations that exceeded the 2L Standard are limited to the shallow flow
layer at the north boundary of the inactive ash basin (AB -33S) and immediately north
and downgradient of the inactive ash basin (GWA-6S). No other sulfate exceedances
were reported in deep and bedrock wells.
• Thallium concentrations that exceeded the IMAC are limited to one shallow monitoring
well, GWA-6S. No other thallium exceedances were reported in shallow, deep, and
bedrock wells.
• TDS concentrations that exceeded the 2L Standard are present in the shallow, deep and
bedrock flow layers. In the shallow flow layer, exceedances are limited to the north
boundary of the inactive ash basin (AB -33S) and immediately north and downgradient of
the inactive ash basin (GWA-6S). In the deep flow layer, exceedances are limited to
beneath the north portion of the active ash basin (AB -24D) and upgradient and offsite to
the west of the inactive ash basin (GWA-14D). In the bedrock flow layer, exceedances
are limited to beneath the west portion of the active ash basin (AB-23BRU) and the
background bedrock monitoring well located approximately 1,700 feet west of the
inactive ash basin (BG-2BR). The 2L exceedances of TDS at GWA-14D and BG-2BR
are not likely attributable to the ash basin.
• Vanadium concentrations that exceeded the IMAC vary in the shallow, deep, and
bedrock wells and are widespread across the site. The concentrations of vanadium are
generally higher in the deep and bedrock wells than in the shallow wells.
Beryllium, cadmium, chromium, nickel, and zinc are not included in the list of COls included in
Section 7.5.5 due to the lack of exceedances of regulatory criteria for the source
characterization media samples. However, these constituents are considered COls based on 2L
Standard or IMAC exceedances in groundwater samples collected as part of this CSA. Details
of the nature and extent of contamination for each of these additional COls is described below.
Beryllium concentrations that exceeded the IMAC are limited to one shallow monitoring
well, GWA-6S. No other beryllium exceedances were reported in shallow, deep, and
bedrock wells.
• Cadmium concentrations that exceeded the 2L Standard are limited to one shallow
monitoring well, GWA-6S. No other cadmium exceedances were reported in shallow,
deep, and bedrock wells.
• Chromium concentrations that exceeded the 2L Standard are present in the shallow,
deep and bedrock flow layers. In the shallow flow layer, exceedances are limited to
voluntary monitoring wells located south of the ash basin (AB -5) and downgradient to the
east of the active ash basin (AB -6R). In the deep flow layer, exceedances are limited to
beneath the central portion of the active basin (AB -21 D and AB -24D), immediately
downgradient and east of the active ash basin (AB -26D), upgradient and west of the
inactive ash basin (GWA-14D), and the background well BG -1 D. In the bedrock flow
layer, exceedances are limited to beneath the south-central portion of the active ash
basin (AB -21 BR and AB-23BRU) and the background monitoring well BG-2BR.

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EXECUTIVE SUMMARY
• Nickel concentrations that exceeded the 2L Standard are limited to one shallow
monitoring well, GWA-6S. No other nickel exceedances were reported in shallow, deep,
and bedrock wells.
• Zinc concentrations that exceeded the 2L Standard are limited to one shallow monitoring
well, GWA-6S. No other zinc exceedances were reported in shallow, deep, and bedrock
wells.
ES.4.3 Maximum Contaminant Concentrations
Maximum COI concentrations in ash porewater samples are located throughout the ash basin.
The higher concentrations of constituents were mainly located in the southwest portion of the
active ash basin and the south portion of the inactive ash basin
Maximum COI concentrations in shallow groundwater are generally located downgradient to the
north of the ash basin in the vicinity of monitoring well GWA-6S and to the east of the ash basin
in the vicinity of AB -33S. Maximum COI concentrations in deep groundwater are generally
located downgradient to the east of the active ash basin (AB -26D) and the inactive ash basin
(AB -31 D).
COls with maximum concentrations detected at GWA-6S include aluminum, arsenic, cobalt,
copper, manganese, selenium, sulfate, thallium, and TDS. The maximum concentration of boron
was detected in shallow groundwater immediately downgradient of the inactive ash basin (AB -
31S).
The maximum contaminant concentrations for source characterization COls reported in
groundwater, ash porewater, ash basin surface water, and seep water samples collected during
the CSA are listed below.

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Allen Steam Station Ash Basin
EXECUTIVE SUMMARY
Notes:
1. NS indicates not sampled.
2. J indicates an estimated concentration.
3. J+ indicates an estimated concentration, biased high.
ES4.4 Source Characterization
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 to
identify physical and chemical properties of ash, ash basin surface water, ash porewater, and
ash basin seeps. The physical and chemical properties evaluated as part of the characterization
have been used to better understand impacts to soil and groundwater from the source area and
will also be utilized as part of groundwater model development in the CAP.
Review of laboratory analytical results of ash samples collected from the active and inactive ash
basin identified eight Cols, which include arsenic, barium, boron, cobalt, iron, manganese,
selenium and vanadium. COls identified in ash porewater samples include antimony, arsenic,
boron, cobalt, iron, manganese, pH, sulfate, thallium, TDS and vanadium. Cols identified in ash
basin surface water samples include aluminum, copper, and lead.
ES -11
Maximum Constituent of Interest (COI) Concentrations
COI
Groundwater
Ash Porewater
Ash Basin
Seep Water
(lag/L)
(Ng/L)
Surface Water
(Ng/L)
N /L
Aluminum
101,000
5,190
470
200
GWA-6S
AB-29SL
SW -4
S-4
Antimony
6
10.3
0.49
0.31 J
AB -31 D
AB-29SL
SW -4
ANWW-004
Arsenic
193
1,370
4
9
GWA-6S
AB -20S
SW -1
ANSW-015
Barium
210
990
85
150
GWA-14D)
AB -36S
SW -2)
ANSW-015
Boron
1,800
7,400
1,900
1,900
AB -31 S
AB -21 SL
SW -2
ANWW-002
Cobalt
4,160
42.3
2.2
1.2
GWA-6S
AB -28S
SW -4
S-3
Copper
337
1.4
4.6
11.3
GWA-5BR
AB -38S
SW -4
ANWW-001
Iron
95,900
60,700
820
2,200
AB -34S
AB -39S
SW -4
S-3
Lead
5.8 J+
0.43
1
0.2
AB -26D
AB -21 S
SW -4
S-3
Manganese
207,000
11,100
150
890
GWA-6S
AB -35S
SW -4
S-4
pH
3.68-11.84
5.9-10.32
7.29-8.03
7.71 -7.94
GWA-6S / AB -24D)
(AB38S / AB-29SL
SW -1 / SW -3)
(S-4/S-3
Selenium
73.5
18.7
2
0.94
GWA-6S
AB-29SL
SW -4
ANWW-002
Sulfate
1,830,000
390,000
77,300
76,800
GWA-6S
AB -20S
SW -1
ANWW-002
Thallium
1.3
0.75
0.2
0.11
GWA-6S
AB -25S
SW -4
ANWW-002
TDS
3,920,000
1,120,000
418,000
58,200
GWA-6S
AB -20S
SW -2
ANWW-002
Vanadium
93.2
70.8
8.2
1.3
AB -26D
AB-29SL
SW -4
(S-3, ANWW-004
Notes:
1. NS indicates not sampled.
2. J indicates an estimated concentration.
3. J+ indicates an estimated concentration, biased high.
ES4.4 Source Characterization
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 to
identify physical and chemical properties of ash, ash basin surface water, ash porewater, and
ash basin seeps. The physical and chemical properties evaluated as part of the characterization
have been used to better understand impacts to soil and groundwater from the source area and
will also be utilized as part of groundwater model development in the CAP.
Review of laboratory analytical results of ash samples collected from the active and inactive ash
basin identified eight Cols, which include arsenic, barium, boron, cobalt, iron, manganese,
selenium and vanadium. COls identified in ash porewater samples include antimony, arsenic,
boron, cobalt, iron, manganese, pH, sulfate, thallium, TDS and vanadium. Cols identified in ash
basin surface water samples include aluminum, copper, and lead.
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EXECUTIVE SUMMARY
SPLP (Synthetic Precipitation Leaching Procedure) testing was conducted to evaluate the
leaching potential of Cols from ash. Although SPLP analytical results are being compared to
the 2L Standards and IMACs, these leaching results do not represent groundwater samples.
The results of SPLP analyses indicated that the following COls exceeded their 2L Standards:
antimony, arsenic, chromium, cobalt, iron, lead, manganese, selenium, thallium, and vanadium.
However, many factors influence the transport of these COls and any potential impacts to
groundwater over time will be investigated through modeling as part of the CAP.
Two seeps associated with the ash basin at Allen (S-3 and S-4) and five NCDENR sample
locations (seeps and stormwater outfalls) (ANSW015, ANWW001, ANWW002, ANWW003,
ANWW004) were sampled during this CSA. The NCDENR samples had reported exceedances
of the 2L Standard or IMAC for boron, manganese, TDS, and vanadium. Seeps S-3 and S-4
were reported above their respective 2L standards for boron, cobalt, iron, manganese, and
vanadium. Other seeps planned to be sampled (7 seep locations and 9 NCDENR sample
locations were dry during multiple sampling attempts.
ES4.5 Regional Geology and Hydrogeology
The Allen site is within the Charlotte terrane, one of a number of tectonostratigraphic terranes
that have been defined in the southern and central Appalachians and is in the western portion of
the larger Carolina superterrane (Figure 5-1; Horton et al. 1989; Hibbard et al. 2002; Hatcher et
al. 2007). On the northwest side, the Charlotte terrane is in contact with the Inner Piedmont
zone along the Central Piedmont suture along its northwest boundary and is distinguished from
the Carolina terrane to the southeast by its higher metamorphic grade and portions of the
boundary may be tectonic (Secor et al. 1998; Dennis et al. 2000).
The Charlotte terrane is dominated by complex sequence of plutonic rocks that intrude a suite of
meta -igneous rocks (amphibolite metamorphic grade) including mafic gneisses, amphibolites,
meta-gabbros, and metavolcanic rocks with lesser amounts of granitic gneiss and ultramafic
rocks with minor metasedimentary rocks including phyllite, mica schist, biotite gneiss, with
quartzite and marble along its western portion (Butler and Secor 1991; Hibbard et al. 2002). The
general structure of the belt is primarily a function of plutonic contacts.
The groundwater system in the Piedmont region is described as being comprised of two
interconnected layers, or two -medium system: 1) residual soil/saprolite and weathered fractured
rock (regolith) overlying 2) fractured crystalline bedrock. 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, saprolite, and weathered/fractured rock is a hydrogeologic unit that covers and
crosses various types of rock (LeGrand 1988). This regolith layer serves as the uppermost zone
of the unconfined groundwater system and provides an intergranular medium through which the
recharge and discharge of water to and from the underlying fractured rock occurs. A transition
zone (TZ) of higher hydraulic conductivity at the base of the regolith is present in many areas of
the Piedmont (Schaeffer 2014a).
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Typically, the residual soil/saprolite is partially saturated and the water table fluctuates within it.
Water movement is generally preferential through the overlying soil and saprolite and
weathered/fractured bedrock of the TZ. The character of such layers 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.
ES4.6 Site Geology and Hydrogeology
The Allen Steam Station and its associated ash basin system are located in the Charlotte
terrane. The Charlotte terrane consists of an igneous complex of Neoproterozoic to Paleozoic
ages (Hibbard et al, 2002) that range from intermediate to mafic in composition (Butler and
Secor 1999). The Charlotte terrane is bordered on the east and southeast by the Carolina
terrane and to the west and northwest by the Inner Piedmont (Cat Square and Tugaloo
terranes) and the Kings Mountain terrane. The structural contact of the Inner Piedmont and
Charlotte terrane is the Central Piedmont Shear Zone.
The Charlotte terrane is a meta -igneous terrane consisting of volcanic and plutonic rocks that
have been subjected to deformation and high grade metamorphism due to tectonic stress during
and after intrusion of the igneous units. Foliation is noted in many of the boring logs but is not
intense and is not dominant with respect to structure of the rock mass.
Bedrock at the site consists of meta -quartz diorite and meta -diabase. The meta -quartz diorite is
very light gray to dark gray, fine to coarse grained, non -foliated and massive to foliated,
composed dominantly of plagioclase, quartz, biotite, and hornblende..Epidote was not noted in
the cores. The meta -diabase is greenish black to very dark greenish gray, is mostly non -foliated
and is noted as aphanitic to fine grained although it is described as fine to coarse grained in
some logs. Meta -quartz diorite is the primary rock type underlying the site with the meta -diabase
occurring as dikes within the meta -quartz diorite during a late syn -plutonic stage.
Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at Allen is consistent with the Piedmont regolith -fractured rock
system and is an unconfined, connected system of flow layers. In general, groundwater within
the shallow and deep layers (S and D wells) and bedrock layer (BR wells) flows from west and
southwest to the east toward the Catawba River (Lake Wylie) and to the north toward Duke
Energy property and the discharge canal.
ES4.7 Existing Groundwater Monitoring Data
Duke Energy implemented voluntary groundwater monitoring around the Allen ash basin from
May 2004 until November 2010. During this period, the voluntary groundwater monitoring wells
were sampled two times per year and the analytical results were submitted to NCDENR DWR.
Groundwater monitoring as required by the Allen NPDES Permit NC0004979 began in March
2011. 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.
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One or more 2L Standards or IMACs have been exceeded in groundwater samples collected at
monitoring wells AB -1 R, AB -4S, AB -4D, AB -9S, AB -9D, AB -10S, AB -10D, AB -11 D, AB -12S,
AB -12D, AB -13S, AB -13D, and AB -14D. Exceedances have historically occurred for boron, iron,
manganese, pH, and nickel.
Compliance groundwater monitoring wells were sampled as part of this CSA to supplement the
expanded groundwater assessment, assess background groundwater quality and calculate
statistical analyses of background groundwater chemical concentrations.
ES4.8 Screening Level Risk Assessments
The prescribed goal of the human health and ecological screening level risk assessments is to
evaluate the analytical results from the COI sampling and analysis effort and using the various
criteria taken from applicable guidance, determine which of the COls may present an
unacceptable risk, in what media, and therefore, should be carried through for further evaluation
in a baseline human health or ecological risk assessment or other analysis, if required.
Contaminants of Potential Concern (COPCs) are those COls that have been identified as
having possible adverse effects on human or ecological receptors that may have exposure to
the COPCs at or near the site. The COPCs serve as the foundation for further evaluation of
potential risks to human and ecological receptors.
To support the CSA effort and inform corrective action decisions, a screening level evaluation of
potential risks to human health and the environment to identify preliminary, media -specific
COPCs has been 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). The criteria for identifying COPCs
vary by the type of receptor (human or ecological) and media.
COls 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
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.
The screening level risk assessment evaluated NCDENR water well testing results from private
water supply wells located near Allen. According to NCDENR's August 18, 2015 online
summary of well testing near coal ash ponds, approximately 118 water supply wells have been
sampled and analyzed as part of the NCDENR well testing program, as described in Section
12.1.5. In summary, NCDENR recommended that the majority of wells sampled should not be
utilized for drinking water due to the presence of one or more constituents, primarily due to
concentrations of vanadium, hexavalent chromium, and iron; and in far fewer instances, due to
detected concentrations of antimony, cobalt, lead, sulfate, and thallium.
ES4.9 Development of Site Conceptual Model
In the initial site conceptual hydrogeologic model presented in the Work Plan dated December
30, 2014, the geological and hydrogeological features influencing the movement, chemical, and
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report FN
Steam Station Ash Basin
EXECUTIVE SUMMARY
physical characteristics of contaminants were related to the Piedmont hydrogeologic system
present at the site.
A hydrogeological site conceptual model was developed from data generated during previous
assessments, existing groundwater monitoring data, and CSA activities. The ash basin
discharges porewater to the subsurface beneath the basin and via seeps through the
embankments. Groundwater flows to the east and north from ash basin toward the Catawba
River and the discharge canal, respectively. There are no surface water features located at the
site between the ash basin and the Catawba River to the east or between the ash basin and the
discharge canal to the north.
Horizontal migration of groundwater at the site is controlled by the Catawba River to the east
and the discharge canal to the north. The conceptual site model will continue to be refined
following evaluation of the completed groundwater model in the CAP.
ES4.10 Identification of Data Gaps
Through completion of the CSA activities and evaluation of data collected, data gaps have been
identified that should be evaluated further 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.
ES 4.10.1 Data Gaps Resulting from Temporal Constraints
These data gaps are generally present due to insufficient time to collect, analyze, or evaluate
data collected during the CSA activities. It is expected that these data gaps will be remedied in
the CSA supplement to be submitted to NCDENR following completion of the second
comprehensive groundwater sampling event.
• Mineralogical characterization of soil: A total of 23 soil samples were submitted to a
third -party mineralogical testing laboratory for analysis of soil composition. As of the date
of this report, Duke Energy has not received results of this testing; however, results
should be available for inclusion in the CSA supplemental.
• Speciation of Select Inorganics: In order to meet requirements of the NORR,
groundwater samples were collected from monitoring wells located along inferred
groundwater flow transects for speciation of arsenic, chromium, iron, manganese, and
selenium. Adjustments to speciation sampling, described in Section 15.0, will be
incorporated in to the CSA supplement sampling event and results will be included in the
CSA supplement. Additional speciation samples are not currently needed for CAP
development or further risk assessment.
ES4.10.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities
• Sampling data since March 2014 for existing background monitoring well A13-1 R and the
groundwater flow direction determined from the CSA activities indicate this well may be
influenced by the ash basin. In order to evaluate the continued use of AB -1 R as the site
background monitoring well, additional assessment is recommended to further evaluate

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
groundwater quality and flow characteristics from the northwest portion of the inactive
ash basin and in the vicinity of AB -1 R.
• The highest concentrations of COls in groundwater at the site are present in the shallow
flow layer near monitoring well GWA-6S, located immediately north of the inactive ash
basin. Several of the Cols reported in GWA-6S were not reported above their 2L
Standard or IMAC in any other groundwater monitoring wells onsite, including beryllium,
cadmium, nickel, selenium, thallium, and zinc. Selenium and thallium were identified in
the source characterization. However, the other COls beryllium, cadmium, nickel, and
zinc, were not identified in the source characterization as COls. In addition, sulfate and
TDS were reported at their highest concentrations at GWA-6S. Boron was not reported
above the laboratory reporting limit for totals concentrations (reporting limit elevated due
to dilution), but the estimated value (1,400J pg/L) reported for the dissolved
concentration of boron in the GWA-6S sample exceeded the 2L Standard. Although
boron and sulfate (leading indicators of groundwater contamination from CCR units) are
present in shallow groundwater at GWA-6S, the elevated concentrations of other COls
not identified in the source characterization indicate that groundwater impacts at GWA-
6S are likely influenced by another industrial activity at the site and not fully attributable
to the ash basin. Further assessment should be performed separately from the ongoing
ash basin groundwater assessment being conducted in accordance with CAMA.
• The deep montioring well (GWA-6D) installed at the GWA-6S/D/BR well nest contained
grout contamination following installation and was therefore not sampled during the CSA
activities. COls in groundwater collected from the bedrock well at this location (GWA-
6BR) only include iron, manganese, and vanadium, which is likely attributable to
background. Although the results from GWA-6BR indicate that the potential ash basin
impacts detected in GWA-6S do not extend into bedrock, GWA-61D should be reinstalled
and groundwater samples should be collected to better understand the vertical extent of
COls in groundwater in the vicinity of monitoring wells GWA-6S/D/BR.
• Background monitoring wells BG-2S/D/BR are located approximately 1,700 linear feet
west of the northwest extent of the ash basin across South Point Road. South Point
Road is a topographic high and based on the slope -aquifer system in the Piedmont, this
road is likely located along a groundwater divide. Therefore, groundwater in the vicinity
of BG-2S/D/BR is not likely affected by the ash basin. Monitoring well BG-2BR serves as
the only background bedrock well for the site. Installation of one additional bedrock well,
deep well, and shallow well located north of the discharge canal should be considered to
improve the understanding of background groundwater quality near the Allen site.
• No surface waters are present downgradient of the ash basin in the direction of
groundwater flow toward the Catawba River and the discharge canal. However, a
surface water drainage feature with intermittent flows was observed along the west
boundary of the southwest portion of the ash basin. This surface water feature is located
between GWA-9S/D and the westernmost extent of the active ash basin. When
available, surface water samples should be collected and analyzed from this drainage
feature to evaluate potential migration from ash in the westernmost extent of this area of
the ash basin.
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
TDS was reported at a concentration of 750,000 pg/L in monitoring well GWA-14D,
which exceeds the 2L Standard of 500,000 pg/L. The TDS concentration reported in
GWA-14S (43,000 pg/L) is significantly less. Reported TDS concentrations in
compliance well AB -14D and voluntary wells AB -2 and AB -2D are considerably lower
than the concentration in GWA-14D. These compliance and voluntary wells are
generally located between GWA-14S/D and the west boundary of the ash basin. Note
that boron was not reported above the laboratory reporting limit for the samples collected
from GWA-14S/D. Based on no detections of boron at GWA-14S/D, the differences in
cations and anions from ash porewater and downgradient groundwater, the lack of
elevated TDS concentrations in the compliance and voluntary wells listed above, and the
estimated direction of groundwater flow, the reported TDS concentration in GWA-14D
was not likely caused by the ash basin. However, additional assessment is
recommended offsite and west of the ash basin to further evaluate groundwater quality
and groundwater flow west of the ash basin.
ES.5 Conclusions
The CSA identified the horizontal and vertical extent of groundwater contamination at the Allen
site and found it is limited to within the Duke Energy property boundary. The source and cause
of impacts for certain parameters in some areas of the site, as shown on Figure ES -1, is the
coal ash contained in the ash basin. The cause of contamination shown on this figure 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.
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 site is required to
address soil and groundwater contamination. Proposed corrective action will be outlined in the
Corrective Action Plan to be submitted in accordance with CAMA.
The horizontal extent of soil contamination is limited to the area beneath the inactive ash basin
and the active ash basin. Where soil impacts were identified, the vertical extent of contamination
beneath the ash/soil interface is generally limited to the uppermost soil sample collected
beneath the ash basin. Reported concentrations of soil samples were compared to background
concentrations in addition to the North Carolina Industrial Health and Protection of Groundwater
PSRGs to delineate the extent of contamination. The CSA found that impacted soil beneath the
active ash basin includes arsenic, barium, and cobalt. The only COI that exceeded North
Carolina PSRGs beneath the inactive ash basin was arsenic, which was limited to one
uppermost soil sample.
The CSA found that groundwater COls at the site include antimony, arsenic, barium, beryllium,
boron, cadmium, chromium, cobalt, iron, manganese, nickel, selenium, sulfate, thallium, TDS,
vanadium, and zinc, although many of these constituents are found above 2L Standards due to
naturally occurring concentrations. The approximate horizontal extent of groundwater impacts is
limited to beneath the ash basin and immediately downgradient of the ash basin to the east and
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Allen Steam Station Ash Basin FN
EXECUTIVE SUMMARY
north, within the Duke Energy property boundary. The approximate vertical extent of
groundwater impacts is generally limited to the shallow and deep flow layers, and vertical
migration of COls is limited by the underlying bedrock.
Significant factors affecting contaminant transport are those factors that determine how the
contaminant reacts with the soil/rock matrix, resulting in retention by the soil/rock matrix and
removal of the contaminant from groundwater. The interaction between the contaminant and the
retention by soils are affected by the chemical and physical characteristics of the soil, the
geochemical conditions present in the matrix (if present), the matrix materials, and the chemical
characteristics of the contaminant. Migration 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 respective soil/rock matrix. The data indicates that geologic
conditions present beneath the ash basin impedes the vertical migration of contaminants. The
CSA found that the direction of mobile contaminant transport is radially to the east and north
toward the Catawba River and the discharge canal, and not towards off-site receptors.
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.
In accordance with CAMA, Duke Energy is required to implement closure and remediation of the
Allen ash basin no later than August 1, 2029 (or sooner if classified as intermediate or high risk).
Closure for the Allen ash basin was not defined in CAMA.
Based on the findings of this CSA report, soil and groundwater contamination is present
beneath and downgradient of the ash basin. Duke Energy will pursue corrective action under
15A NCAC 02L .0106. The approaches to corrective action under rule .0106(k) or (1) 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.
ES -18