Buck CSAR Executive Summary

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Buck Steam Station Ash Basin FN
EXECUTIVE SUMMARY
Executive Summary - Buck Steam Station
On August 20, 2014, the North Carolina General Assembly passed Session Law 2014-122, the
Coal Ash Management Act of 2014 (CAMA). N.C. Gen. Stat. § 130A-309.211 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 submitted a Work Plan to NCDENR 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) for the Buck Steam Station (Buck).
NCDENR reviewed the Work Plan and provided Duke Energy with initial comments on
November 4, 2014. A revised Work Plan was subsequently submitted to NCDENR on
December 30, 2014 and NCDENR provided final comments and conditional approval of the
revised Work Plan on February 24, 2015. This CSA 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 statutes, regulations and documents:
• Groundwater Classification and Standards, Title 15A North Carolina Administrative Code
(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
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 2L Standards or IMACs from groundwater
sample locations outside the ash basin boundary. For the purposes of this report, these
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
constituents were also identified as COls. Some COls (e.g., iron and manganese) are present in
background and 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. Descriptions of COls outside the ash basin boundary are identified in
Section 10 (Groundwater Characterization) and Section 11 (Hydrogeological Investigation) of
this CSA. This inclusive approach to identification of COls will be refined during development of
the CAP to focus on those constituents that are attributable to the ash basin. COls were also
evaluated in the human health and ecological screening level risk assessment in Section 12.0.
In addition to evaluating the distribution of constituents across the Buck 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.
Some Cols (e.g., antimony, cobalt, chromium, iron, manganese and vanadium) 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 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 Buck site, significant factors
affecting constituent transport, the geological and hydrogeological features influencing the
movement and the chemical -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
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.
• 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 generally consistent with previous results
from historical and routine compliance boundary monitoring well data although some
new COls were identified due to a more robust sampling program.
• 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
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
downgradient of the basin and ash storage area are also naturally occurring, originate
from upgradient sources or might be influenced by migration of constituents from the ash
basin and ash storage area. Examples of naturally occuring metals and consituents
include antimony, chromium, cobalt, iron, manganese, and vanadium, which were all
detected in background groundwater samples at concentrations greater than 2L
Standards or IMACs.
Groundwater flow is predominately in the north direction toward the Yadkin River and is
downgradient from and not towards off-site receptors. However, there also is a
component of groundwater flow to the west of Cell 1 and there is localized flow in an
area east of the source that requires further evaluation (between Cells 2 and 3).
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 source, aside
from the single permitted well owned by Duke Energy.
The U.S. Environmental Protection Agency (USEPA) has identified constituents for
groundwater detection monitoring programs that can be used as indicators of
groundwater contamination from coal combustion residuals which may be evaluated for
statistically significant increases over background with time. Specifically, boron and
sulfate would be expected to migrate rapidly and would provide early detection as to
whether contaminants were migrating from the ash basin system. The horizontal and
vertical migration of boron best represents the groundwater flow and potential transport
system at the site. Sulfate, while generally a good indicator, can occasionally occur
naturally above its applicable standards and should be used as an indicator with more
caution. Sulfate exceedances at well locations outside the waste boundary appear to be
unrelated to the ash basin, and may be related to the bedrock geology. This is indicated
by the unique geochemistry and lack of boron observed at certain wells exhibiting
exceedances of sulfate, as well as the general lack of sulfate exceedances in ash basin
porewater. Figure ES -1 indicates the estimated horizontal extent of 2L Standard
exceedances for boron in the shallow, deep, and bedrock monitoring layers at the site.
The horizontal migration of boron in the flow layers best represent the dominant flow and
transport system in the vicinity of the ash basin and ash storage area. Vertical migration
of constituents is impeded but not eliminated 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, deep, and bedrock flow layers impacted by
the ash basin and ash storage area.
The approximate extent of groundwater impacted with COI exceedances attributable to
CCRs, such as boron, is limited to the shallow, deep, and bedrock flow layers beneath
the ash basin and ash storage area, and areas immediately downgradient of the ash
basin and ash storage area located to the north. Based on available data, it appears
groundwater impacted by the ash basin and ash storage area is contained within the
Duke Energy property boundary.
• There are no indications of boron exceedances of the 2L Standards or IMACs
upgradient from the Buck site.
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
• The assessment identified potential soil and groundwater impacts. The approximate
extent of measured constituents is primarily limited to an area within the ash basin
compliance boundary and the area north of the compliance boundary to the Yadkin
River. There also appears to be a smaller component of groundwater flow west of ash
basin Cell 1 (and within the property boundary) resulting in potential movement of
constituents beyond the western compliance boundary between Cell 1 and the unnamed
tributary to the Yadkin River near the western extent of the Buck site.
• NCDENR identified seeps and CSA -identified seeps that contained water were sampled
during the CSA field program. The one NCDENR seep that could be sampled
(BSWW002 S001) did not exhibit USEPA ash indicator exceedances of the 2L
Standards.Samples obtained from CSA -identified seeps S-9 and TERRACOTTA PIPE
#1, both located near the base of the Cell 1 dam, were reported above the 2L Standard
for boron.
• Sediment was sampled at 14 active and dry seep locations. The only USEPA ash
related COI that exhibited an exceedance of the North Carolina Industrial Health and
Protection of Groundwater Preliminary Soil Remediation Goal (PSRG) was boron which
occurred at location TERRACOTTO PIPE #1.
• The data included in this CSA are to be used in the development of a Corrective Action
Plan, due 90 days after submittal of this CSA. This will include groundwater modeling to
evaluate the site's suitability to use monitored natural attenuation (MNA). If not
applicable, additional measures such as active remediation by hydraulic capture and
treatment, among others, would be evaluated. When properly applied, alternatives such
as these can provide effective long term management of sites requiring corrective action.
Brief summaries of essential portions of the CSA are presented in the following sections.
ESA Source Information
Duke Energy owns and formerly operated the Buck station, located on the Yadkin River in
Rowan County near the town of Salisbury, North Carolina. Buck began operation in 1926 as a
coal-fired generating station. The Buck Combined Cycle Station (BCCS) natural gas facility was
constructed at the site and began operating in late 2011. Subsequently, Buck was
decommissioned and taken offline in April 2013. The coal ash residue from Buck's coal
combustion process was historically disposed of in the station's ash basin system located
adjacent to the station and the Yadkin River. The discharge from the ash basin system is
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 NC0004774.
Since 2006, Duke Energy has implemented voluntary and NPDES permit -required groundwater
monitoring at Buck. Twice per year voluntary groundwater monitoring around the Buck ash
basin was performed from November 2006 until May 2010, with analytical results submitted to
the NCDENR DWR. Compliance groundwater monitoring as required by the NPDES permit
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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began in March 2011. From March 2011 through July 2015, the compliance groundwater
monitoring wells at Buck have been sampled three times per year for a total of 14 times.
The Buck ash basin system is located near the Yadkin River and comprises three cells
designated as Cell 1, Cell 2, and Cell 3, and associated embankments and outlet works. The
ash basin is located to the south (Cell 1) and southeast (Cells 2 and 3) of the retired Buck Units
through 6 and the BCCS. An area between Cell 1 and Cell 2 has also been utilized for storage
of dredged ash from Cell 1 and is referred to as the ash storage area. This unlined storage area
is located topographically upgradient and adjacent to the east side of Cell 1. The dry ash
storage area was constructed in 2009 by excavating ash within the eastern half of Cell 1 in
order to provide additional capacity for sluiced ash and covers approximately 14 acres.
All coal ash from Buck was disposed of in the ash basin from approximately 1957 until 2013. Fly
ash precipitated from flue gas and bottom ash collected in the bottom of the boilers were sluiced
to the ash basin using conveyance water withdrawn from the Yadkin River.
The ash basin system 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, the station yard drain sump, and site stormwater.
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 are not required.
ES.3 Receptor Information
Properties located within a 0.5 -mile radius of the Buck ash basin compliance boundary generally
consist of residential, agricultural, and undeveloped properties located in Rowan County to the
west, south, and east of the ash basin. The Yadkin River flows east along the northern
boundary. Hunting and game lands are located north of the ash basin system across the Yadkin
River in Davidson County.
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 based on the CSA Guidelines. 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 after 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 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
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EXECUTIVE SUMMARY
wells, and/or identify any wellhead protection areas located within a 0.5 -mile radius of the Buck
ash basin compliance boundary:
• NCDENR Division of Water Resources (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;
• Rowan County Health Department Environmental Health Division;
• Davidson County Health Department;
• Salisbury -Rowan Utilities Department; and
• USGS National Hydrography Dataset.
The review of these records identified a total of 166 private water supply wells within a 0.5 -mile
radius of the Buck ash basin compliance boundary. The Rowan County Health Department had
records for 28 of the 166 identified private water supply wells. Ten additional private water
supply wells are assumed to exist since well houses could not be visually observed at these
residences located within a 0.5 -mile radius of the Buck ash basin compliance boundary. Two
public water supply wells were identified within a 0.5 -mile radius of the Buck ash basin
compliance boundary. One water supply well was identified within the Duke Energy property
boundary that supplies drinking water to the site.. Several unnamed tributaries of the Yadkin
River were identified within a 0.5 -mile radius of the ash basin, and several surface water
features that flow toward the Yadkin River were identified within a 0.5 -mile radius of the Buck
ash basin.
ESA Sampling / Investigation Results
ES.4.1 Background Findings
As part of the CSA, Duke Energy installed seven additional nested wells (three shallow, two
deep, one upper bedrock, and one bedrock monitoring well) in selected areas of the site
upgradient from the ash basin and ash storage area to supplement the existing nested shallow
and deep monitoring wells (installed in 2006) by providing additional background soil and
groundwater quality data. The COI concentration range in background groundwater samples
which exceeded the 2L Standard are provided below.

Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Buck Steam Station Ash Basin FN
EXECUTIVE SUMMARY
Constituent of Interest
Groundwater 2L Standard
or IMACs (Ng/L)
Range of Exceedances
Antimony
1
3.8 pg/L to 5.8 Ng/L
Chromium
10
0.22J pg/L to 10.3 pg/L
Cobalt
1
4 Ng/L to 7.2 pg/L
Iron
300
306J Ng/L to 1,900 pg/L
Manganese
50
54 pg/L to 850 Ng/L
Vanadium
0.3
0.86J pg/L to 26.6 pg/L
These COls were found to be present within groundwater monitoring wells at several locations
across the site. Their presence within the background wells at concentrations exceeding the 2L
or IMAC Standards requires analysis to determine whether downgradient exceedances are due
to natural condition or impacts from the ash basin and ash storage area.
ES.4.2 Nature and Extent of Contamination
Soil and groundwater beneath the ash basin and ash storage area has been impacted by ash
handling and storage at the Buck site. Concentrations of several COls appear to exceed their
respective 2L Standards or IMACs in groundwater beyond the compliance boundary toward the
Yadkin River, although some of these COls also exceed 2L in the background wells. These
exceedances appear contained on Duke Energy Property. Samples obtained from on-site
seeps also exhibit concentrations of COls exceeding their respective 2L Standards or IMACs.
ES.4.2.1 Groundwater - Shallow Flow Layer
Within the shallow flow layer (including beneath the ash storage area), there are five Cols
identified as in the groundwater in multiple groundwater samples: cobalt, chromium, iron,
manganese, and vanadium. All of these COls also appear within one or more of the background
well locations at concentrations exceeding the applicable groundwater standard. Almost all of
the iron exceedances within the shallow aquifer (12 of 13) occurred within unfiltered samples
indicating the source of the iron within the shallow groundwater samples is primarily suspended
solids. Six other COls identified in the shallow flow layer are antimony, boron, nickel, selenium,
sulfate, and Total Dissolved Solids, but they are in isolated locations.
ES.4.2.2 Groundwater - Deep Flow Layer
Within the deep flow layer (including beneath the ash basin and ash storage area), there are
seven COls identified in the groundwater (D wells): antimony, boron, chromium, cobalt, iron,
manganese, and vanadium. Vanadium also appears within three of the deep flow layer
background well locations at concentrations exceeding the applicable 2L Standard or IMAC.
Almost all of the iron exceedances within the deep flow layer (10 of 12) occurred within
unfiltered samples indicating the source of the iron within the deep flow layer groundwater
samples is primarily suspended solids. Two other COls identified in the deep flow layer are
sulfate and TDS, but they are in isolated locations.
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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ES.4.2.3 Groundwater — Bedrock Flow Layer
Within the bedrock flow layer (including beneath the ash basin), there are four COls identified in
the groundwater (BR and BRU wells): antimony, chromium, iron, manganese, and vanadium.
None of these COls appear within the bedrock background well location (BG-3BRU) at a
concentration exceeding the applicable groundwater standard. All eight of the iron exceedances
within the bedrock flow layer occurred within unfiltered samples indicating the source of the iron
within the bedrock groundwater samples is primarily suspended solids. Six other COls identified
in the bedrock flow layer are barium, boron, cobalt, selenium, sulfate and TDS, but they are in
isolated locations.
ES.4.2.4 Seep Samples
Seep sampling results at the Buck site have identified nine Cols in the seep water: antimony,
arsenic, boron, chromium, cobalt, iron, manganese, thallium, and vanadium. Comparing COI
concentrations in the seep water to the maximum COI concentrations encountered in
groundwater sampled from the background wells indicates nine seep locations (BSWW002
S001, Terracotta Pipe #1, Culvert Discharge, S-1, S-2, S-3, S-5, S-8, and S-9) where at least
one seep COI concentration exceeded the maximum background groundwater COI
concentration (arsenic, boron, chromium, cobalt, iron, manganese, thallium, and vanadium) .
ES.4.2.5 Soil, Rock and Sediment Concentrations
Soil samples were obtained from 29 separate locations during CSA drilling activities within the
Buck site (including locations beneath the ash basin and ash storage area). Eight Cols were
identified in soil samples obtained from these locations: arsenic (5 locations), barium (1
location), boron (4 locations), cobalt (29 locations), iron (29 locations), manganese (29
locations), selenium (5 locations), and vanadium (29 locations). With the exception of barium, all
of these COls appear in one or more of the background well locations at concentrations
exceeding the most restrictive PSRG standard. The COI concentrations observed in the soil
from the various locations within the Buck 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 ten
separate locations during CSA drilling activities within the Buck site, including locations beneath
the ash basin and ash storage area. Five COls were identified in rock samples obtained from
these locations: arsenic (1 location), cobalt (8 locations), iron (10 locations), manganese (9
locations), and vanadium (8 locations). With the exception of arsenic, all of these COls appear
within the background location where rock was obtained (BG -2) at concentrations exceeding the
most restrictive PSRG standard.
Sediment samples were obtained from 14 seep locations at the Buck site. Seven COls were
identified in the sediment samples: arsenic (4 locations), boron (1 location), cobalt (all
locations), iron (all locations), manganese (13 locations), selenium (1 location) and vanadium
(all locations). A background sediment location (SW -2) was not obtained due to dry conditions
at the time of sampling; therefore a comparison of these results with background conditions is
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Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
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EXECUTIVE SUMMARY
not possible at this time. Such a comparison may be possible after completion of the second
comprehensive sampling event and will be included in the CSA supplement.
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.
J = Estimated Concentration
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, ash storage area,
associated solid matrix (ash), and aqueous sample (ash porewater),and the collection and
analysis of samples. Ash samples were collected for analysis of physical characteristics (e.g.,
grain size, porosity, etc.) to provide data for evaluation of retention/transport properties within
and beneath the ash basin and ash storage area. Ash samples were collected for analysis of
chemical characteristics (e.g., total inorganics, leaching potential, etc.). The results of the
characterization will be used to refine the CSM and to provide data for use in the CAP.
Review of laboratory analytical results of ash samples collected from the ash basin and ash
storage area identified eight COls including arsenic, cobalt, barium, boron, cobalt, iron,
manganese, selenium, and vanadium. COls identified in ash basin porewater include antimony,
arsenic, barium, boron, cobalt, iron, manganese, thallium, and vanadium. COls identified in ash
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Maximum Constituent of Interest (COI) Concentrations
COI
Background
wells
Groundwater
(Ng/L)
Ash Porewater
(N9/L)
Seep Water
(N9/L)
Ash Basin Surface
Water
(Ng/L)
Aluminum
160
n/a
n/a
n/a
13,000
Antimony
5.8
19.3
24.4
1.8
n/a
Arsenic
11
14.9
1,350
38.6
71.3
Barium
86
830
720
n/a
n/a
Boron
49J
3,000
6,500
820
n/a
Cadmium
0.025J
n/a
n/a
n/a
0.37
Chromium
10.3
65.4
n/a
32.7
n/a
Cobalt
6.8
356
44.7
41.1
23.9
Copper
45.8
n/a
n/a
n/a
32.4
Iron
1,900
27,900
44,700
34,900
n/a
Lead
0.24
n/a
n/a
n/a
12.7
Manganese
850
4,100
3,900
3,900
n/a
Nickel
10.9
107
n/a
n/a
n/a
Selenium
0.39J
30.3
n/a
n/a
n/a
Sulfate
22,700
703,000
n/a
n/a
n/a
TDS
175,000
1,046,000
565,000
n/a
n/a
Thallium
0.032J
0.24
0.67
n/a
0.45
Vanadium
26.6
67.9
347
132
n/a
Zinc
77
n/a
n/a
n/a
50
J = Estimated Concentration
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, ash storage area,
associated solid matrix (ash), and aqueous sample (ash porewater),and the collection and
analysis of samples. Ash samples were collected for analysis of physical characteristics (e.g.,
grain size, porosity, etc.) to provide data for evaluation of retention/transport properties within
and beneath the ash basin and ash storage area. Ash samples were collected for analysis of
chemical characteristics (e.g., total inorganics, leaching potential, etc.). The results of the
characterization will be used to refine the CSM and to provide data for use in the CAP.
Review of laboratory analytical results of ash samples collected from the ash basin and ash
storage area identified eight COls including arsenic, cobalt, barium, boron, cobalt, iron,
manganese, selenium, and vanadium. COls identified in ash basin porewater include antimony,
arsenic, barium, boron, cobalt, iron, manganese, thallium, and vanadium. COls identified in ash
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basin surface water include aluminum, antimony, arsenic, cadmium, cobalt, copper, lead,
thallium, and zinc.
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 samples do not represent groundwater samples. The
results of SPLP analyses indicated that the following COls exceeded their 2L Standards:
antimony, arsenic, chromium, cobalt, iron, 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.
There are 14 seeps (S-1 through S-10, Culvert Discharge, Wet Area Near Pump House,
Terracotta Pipe #1, and Terracotta Pipe #2) located within the Duke Energy property boundary
and three seeps (S-1 A, S-1 B, and S-1 C) located outside of the Duke Energy property boundary
associated with the ash basin at the Buck site, excluding the "NCDENR seeps." Duke Energy
was not able to obtain permission from the property owner to obtain off-site seep samples S-1 A,
S-1 B, and S-1 C; therefore these seeps were not sampled. Twelve of the 14 on-site seeps were
sampled as the remaining seeps (Wet Area Near Pump House and Terracotta Pipe #2) were
dry on the day of sampling. Of the seep locations sampled in time for this report, seven COls
were reported exceeding the 2L Standards: boron, chromium, cobalt, iron, manganese, thallium,
and vanadium.
There are six NCDENR seep locations identified at Buck for sampling. Only one seep,
BSWWO02 S001, was active on the day of sampling and the rest were dry. Samples collected
from BSWWO02 S001 exceeded the 2L or IMAC Standards for the following COls: antimony,
arsenic, iron, manganese, and vanadium.
ES.4.5 Regional Geology and Hydrogeology
The Buck 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 (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 in origin (Secor et al. 1998; Dennis et al. 2000).
The Charlotte terrane is dominated by a 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
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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).
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.
ES.4.6 Site Geology and Hydrogeology
The Buck site and its associated ash basin and ash storage areas 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 felsic 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 Buck site is underlain by interbedded felsic, intermediate, and mafic metavolcanic rocks.
The felsic metavolcanic rocks are fine- to medium -grained, locally coarse-grained or
agglomeritic, rhyolitic to dacitic metatuffs. The intermediate and mafic metavolcanic rocks are
fine- to medium -grained, locally coarse-grained or agglomeritic rocks of basaltic, andesitic, and
dacitic compositions. They are primarily tuffs and flows and with minor hypabyssal intrusives
present. The rocks are metamorphosed to the upper amphibolite grade of metamorphism.
Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at Buck is consistent with the Piedmont regolith -fractured rock
system and is an unconfined, connected system of three flow layers. In general, groundwater
within the shallow, deep (TZ), and bedrock layers flows radially from the ash basins and
nouthward toward the Yadkin River.
ES.4.7 Existing Groundwater Monitoring Data
Twelve monitoring wells were installed by Duke Energy in 2006 as part of a voluntary
groundwater monitoring system near the ash basin. Voluntary monitoring wells MW -2S and
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MW -2D were abandoned during construction of the Buck Combined Cycle Station. With the
exception of MW -6S, MW -6D, MW -3S, and MW -3D, no samples are currently being collected
from the voluntary wells, and as a result, they are not included in this CSA.
Compliance groundwater monitoring as required by the Buck NPDES Permit NC0004774 began
in March 2011 and includes 14 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). Locations for the compliance groundwater monitoring wells were
approved by the NCDENR DWR or it predecessor.
One or more groundwater quality standards (2L Standards) have been exceeded in
groundwater samples collected from each of the compliance monitoring wells. Exceedances
have occurred for boron, chromium, iron, manganese, pH, sulfate, and total dissolved solids
(TDS).
ES.4.8 Screening -Level Risk Assessment
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.
Constituents of Probable 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, as shown in the comparison of
contaminant concentrations in various media to corresponding risk-based screening levels
presented in Tables 12-1 through 12-9.
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.
This initial screening, does not specifically identify that health or environmental risks are
present, rather the results indicate constituents in the environmental media for further
investigation by a site-specific risk assessment. It should be noted that the observed levels of
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certain COls in the naturally occurring background at Buck would also warrant consideration of
a BERA.
ES.4.9 Development of Conceptual Site 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. Groundwater flow is predominately in the north direction toward the Yadkin River and
is downgradient from and not towards off-site receptors. However, there also is a component of
groundwater flow to the west of Cell 1 and there is localized flow in an area east of the source
that requires further evaluation (between Cells 2 and 3).
ES.4.10 Identification of 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 CSM. The data gaps have been separated into three groups: 1) data gaps resulting
from temporal constraints, 2) data gaps resulting from evaluation of data collected during the
CSA, and 3) data gaps resulting from other sources.
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.
• 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.
• 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. Adjustments to the speciation sampling are proposed in
Section 15.0, the results of which will be reported in the CSA supplement.
• Dry Sampling Locations — Due to dry conditions at the time of the initial sampling event,
several proposed surface water and seep sampling locations were dry and could not be
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comprehensive groundwater sampling event. If successful, the results will be provided in
the CSA supplement. These locations include:
o Surface water locations SW -1 and SW -2 located along an unnamed tributary to the
Yadkin River on the east side of the Buck site.
o On-site seeps:. Seeps identified as Wet Area Near Pump House and Terracotta
Pipe #2 were dry and could not be sampled.
o NCDENR seep locations BS SWO01 AA S001, BS SWO03AA S001, BSSWO01 S001,
BSSW074SO01, and BSSW074SO01.
ES.4.10.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities
• A shallow groundwater monitoring well in the nest of GWA-2BRU and GWA-2BR would
assist with the groundwater flow direction determination in this location. Additional
monitoring well nests nortwest and southwest of GWA-2BRU/BR would assist in refining
groundwater flow direction in this area and provide information regarding constituent
concentrations between the Cell 2 Primary Pond and the southern pond associated with
the Cell 3 Secondary Pond.
• The bedrock background monitoring well BG -1 BR could not be sampled due to
insufficient water in the well during the sampling event. A replacement bedrock
background well in this location may be warranted if BG -1 BR is not a viable well. Also, a
bedrock well installed at the BG-3S/D would provide additional data regarding
background bedrock concentrations at the site.
• Groundwater samples were not collected from all of the onsite voluntary wells or existing
monitoring wells that were installed during the site closure investigation. During
subsequent sampling events, groundwater elevations will be measured and groundwater
samples will be collected from these wells in conjunction with the newly installed
assessment monitoring wells.
• The vanadium method reporting limit provided by the analytical laboratory was 1.0 ug/L.
The IMAC for vandium is 0.3 ug/L. The vanadium results reported at concentrations less
than the laboratory method reporting limit are estimated. During subsequent monitoring
events, a laboratory method reporting equal to or less than the IMAC should be utilized.
• 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.
• Obtain soil samples located outside of the ash basin for SPLP analysis to compare
results against SPLP analysis of ash.
• Perform mineralogy analysis of soil and rock samples in wells where COls are present
above 2L or IMAC Standards to determine if constituents occur naturally
ES.4.10.3 Data Gaps Resulting from Other Sources
• Sampling of Off -Site Seeps — the Work Plan included obtaining a surface water sample
(S -1A) and samples at two seep locations (S-1 B and S-1 C) associated with an off-site
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pond located near the eastern extent of Duke Energy's property boundary. Duke Energy
was not able to obtain permission from the property owner to collect these samples.
ES.5 Conclusions
The CSA found that the source and cause of impacts (as shown on figure ES -1) for certain
parameters in some areas of the site is the coal ash contained in the ash basin and ash storage
area. The cause of this contamination, shown on the referenced figure, is leaching of
constituents from the coal ash into the underlying soil and groundwater and subsequent
transport of the groundwater downgradient from the ash basin. 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 actions at the Buck site are
required to address soil and groundwater contamination shown on Figure ES -1. These will be
addressed as part of the CAP.
The CSA identified the horizontal and vertical extent of groundwater contamination within the
compliance boundary (as shown in figure ES -1), and found that the source and cause of the
groundwater exceedances within that boundary is a result of both natural conditions and the
coal ash contained in the ash basin and ash storage area. In general, COls exceeding 2L
Standards or IMACs on the northern side of the waste boundary are judged to be highly
influenced by the source. Some of these exceedances were measured outside the compliance
boundary, although within the Duke Energy property boundary.
Background monitoring wells contain naturally occurring metals and other constituents at
concentrations that exceeded their respective 2L Standards or IMACs. Examples of naturally
occurring constituents include antimony, cobalt, iron, manganese, and vanadium. Some of these
naturally occurring constituents were also detected in newly installed background monitoring
well groundwater samples at concentrations greater than 2L Standards or IMACs.
The horizontal and vertical extent of groundwater impacts above 2L Standards or IMACs is
shown, with exception of the areas associated with the data gaps identified in Section 14.1 on
Figures 10-10 through 10-51. Groundwater contamination is considered to be present where the
analytical results were greater than the site background concentrations and in excess of the 2L
Standards or IMACs. The assessment found COI groundwater concentrations above
background concentrations for antimony, arsenic, barium, boron, chromium, cobalt, iron,
manganese, nickel, selenium, thallium, vanadium, sulfate, and TDS. The approximate extent of
groundwater contamination is shown on these figures and is generally limited to an area within
the ash basin compliance boundary and the area north of the compliance boundary near the
Yadkin River (within the Duke Energy property boundary). Exceedances measured south, east,
and west of the waste boundary are judged to be predominately related to natural conditions,
although some source related exceedances were identified. All source related exceedances are
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judged to be within the compliance boundary in these areas; however, some data gaps were
identified as discussed in Section 17.
The CSA found that the primary direction of flow and mobile contaminant transport is
predominately to the north toward the Yadkin River (within the Duke Energy property
boundaries) and not towards other off-site receptors. 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 source.
This CSA also identified the horizontal and vertical extent of soil contamination as shown on
Figures 8-1 through 8-4. Soil contamination is considered to be present where analytical results
for COls were in excess of the maximum site soil background concentrations and in excess of
the most restrictive PSRG for each COI. The approximate contaminated soil extent is shown on
these figures. The assessment found the soil contaminants in excess of the maximum
background soil COI concentrations are arsenic, barium, boron, and iron.
Groundwater flow is predominately in the north direction toward the Yadkin River. However,
there also is a component of groundwater flow to the west of Cell 1 and there is localized flow in
an area east of the source that requires further evaluation (between Cells 2 and 3).
Exceedances of COls have been observed in monitoring wells in these areas and near the ash
basin west compliance boundary. The exceedances, however, do not include COls identified by
the USEPA as indicators of CCR related contamination. Further, the constituents identified with
exceedances to the south, east and west of the source have also been identified in the
background wells.
In accordance with CAMA, Duke Energy is required to implement closure and remediation of the
Buck ash basin no later than August 1, 2029. Closure for the Buck ash basin was not defined in
CAMA. However, CAMA does require Duke Energy to submit a proposed CAP such that
NCDENR can prioritize site closure based on risk classifications.
No later than December 31, 2015, NCDENR is to develop proposed classifications for all coal
combustion residuals surface impoundments, including active and retired sites, for the purpose
of closure and remediation. At which time a schedule for closure and required remediation that
is based on the degree of risk to public health, safety and welfare, the environment, and natural
resources posed by the impoundments and that gives priority to the closure and required
remediation of impoundments that pose the greatest risk (CAMA 2014).
The classification for the Buck ash basin will be based upon this CSA and the corrective action
plan (CAP) which is to be submitted within 90 days of submittal of the CSA. The risk
classifications as described in CAMA include:
(1) High-risk impoundments shall be closed as soon as practicable, but no later than
December 31, 2019. A proposed closure plan for such impoundments must be submitted
as soon as practicable, but no later than December 31, 2016.
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(2) Intermediate -risk impoundments shall be closed as soon as practicable, but no later
than December 31, 2024. A proposed closure plan for such impoundments must be
submitted as soon as practicable, but no later than December 31, 2017.
(3) Low-risk impoundments shall be closed as soon as practicable, but no later than
December 31, 2029. A proposed closure plan for such impoundments must be submitted
as soon as practicable, but no later than December 31, 2018.
Following NCDENR's risk classification determination, a Closure Plan for the ash basin is to be
submitted for NCDENR's approval (CAMA 2014).
Based on the findings of this CSA report, the future CAP, NCDENR's risk classification, and the
approved Closure Plan, appropriate action will be taken for ash basin closure.
In the subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L .0106
(k) or (1) depending on the results of the groundwater modeling and the 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 (EPA Reference) and the potential modeling of groundwater surface water interaction. If
these approaches are found to not be satisfactory, additional measures such as active
remediation by hydraulic capture and treatment, among others, would be evaluated. When
properly applied, alternatives such as these can provide effective long term management of
sites requiring corrective action.
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