HomeMy WebLinkAboutNC0004987_Marshall CSA Report_NCDENR Submittal_20150908Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin
Site Name and Location
Groundwater Incident No.
NPDES Permit No.
Date of Report
Permittee and Current Property Owner
Consultant Information
Latitude and Longitude of Facility
Marshall Steam Station
8320 NC Highway 150 E
Terrell, NC 28682
Not Assigned
NC0004987
September 8, 2015
Duke Energy Carolinas, LLC
526 South Church St
Charlotte, NC 28202-1803
704.382.3853
HDR Engineering, Inc. of the Carolinas
440 South Church St, Suite 900
Charlotte, NC 28202
704.338.6700
' 350 35' 52" N, 800 57' 54" W
This document has been reviewed for accuracy and quality
commensurate with the intended application.
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DUKE
ENERGY
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Malcolm Schaeffer, L.G.
Senior Geologist
FEZ
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin FN
EXECUTIVE SUMMARY
Executive Summary — Marshall 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 act requires the
owner of a coal combustion residuals surface impoundment to submit a Groundwater
Assessment Work Plan (Work Plan) to the North Carolina Department of Environment and
Natural Resources (NCDENR) no later than 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 Marshall
Steam Station (MSS) ash basin, dry ash landfill (Phases I and II), and Photovoltaic (PV)
structural fill and assessment of potential impacts to soil, groundwater, and surface water. The
Work Plan was subsequently conditionally approved by the NCDENR in correspondence dated
March 12, 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 to
develop the Corrective Action Plan (CAP), due no later than 90 days after submittal of this CSA
unless an extension is requested and granted by NCDENR.
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 risks 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 March 12, 2015; and
• Subsequent meetings and correspondence between Duke Energy and NCDENR.
For this CSA, the source area is defined as the ash basin, dry ash landfill (Phases I and II), and
PV structural fill. Source characterization was performed to identify physical and chemical
properties of ash, ash basin surface water, ash porewater, and ash basin seeps. The analytical
results for source characterization samples were compared to North Carolina Groundwater
Quality Standards, as specified in 15A NCAC 2L.0202 (21- Standards), or Interim Maximum
Allowable Concentrations (IMACs), and other regulatory screening levels for the purpose of
identifying constituents of interest (COls) that may be associated with potential impacts to soil,
groundwater, and surface water from the source area. 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.
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EXECUTIVE SUMMARY
Some COls are present in background and upgradient monitoring wells and may be naturally
occurring, and thus require careful examination to determine whether their presence
downgradient of the source area is naturally occurring or a result of ash handling and storage.
In addition to evaluating the distribution of constituents across the MSS site, significant factors
affecting constituent transport and the geological and hydrogeological features influencing the
movement and chemical and physical character of the COls were 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, seep, and surface water)
samples;
• Evaluation of testing data to supplement the initial site conceptual model presented in
the Work Plan;
• 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, groundwater, or surface water impacts at the site.
Upgradient, background monitoring wells contain naturally occurring metals and other
constituents at concentrations that exceed their respective 2L Standards or IMACs. This
information is used to evaluate whether concentrations in groundwater downgradient of
the source area are naturally occurring or potentially influenced by migration of
constituents from the source area. Naturally occuring metals and constituents reported in
background groundwater samples at concentrations greater than 2L Standards or
IMACs include barium, chromium, cobalt, iron, lead, manganese, thallium, and
vanadium.
• Groundwater in the shallow, deep, and bedrock flow layers beneath the ash basin flows
to the southeast toward Lake Norman and slightly east toward an unnamed tributary on
Duke Energy property that flows to Lake Norman. This flow direction is away from the
direction of the nearest public or private water supply wells. Lake Norman serves as a
hydrologic boundary for groundwater within the shallow layer at the site. There are no
water supply wells located between the source area and Lake Norman.
• The geological and hydrogeological features influencing the migration, chemical, and
physical characteristics of contaminants are related to the Piedmont hydrogeologic
system present at the site. The CSA found that the migration of coal ash -related
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EXECUTIVE SUMMARY
contaminants is toward Lake Norman and an unnamed tributary that flows to Lake
Norman, and appears to be contained within the ash basin compliance boundary.
• The U.S. Environmental Protection Agency (USEPA) has identified select constituents
as leading indicators for detecting groundwater contamination from coal combustion
residuals (CCR) units, which may be evaluated for statistically significant increases over
background concentrations with time. Boron and sulfate are leading indicators 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
MSS 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 at the site are primarily present in the shallow and deep flow layers
beneath the dry ash landfill (Phase II), east and downgradient of the ash basin and dry
ash landfill (Phase 1), and southeast and downgradient of the ash basin. There are also
boron exceedances present in the deep flow layer beneath the central portion of the ash
basin and beneath the western portion of the ash basin. Boron exceedances in bedrock
are limited to the area beneath the ash landfill. The boron concentrations are generally
higher in the shallow and deep layers beneath the dry ash landfill (Phase II) and in the
deep layer beneath the western portion of the ash basin. Bedrock is impeding vertical
migration of groundwater and limiting the vertical extent of boron impacts.
• Based on data obtained during this CSA, groundwater flow direction, and the extent of
exceedances of boron, it appears that groundwater impacted by the source area is
contained within Duke Energy property and the ash basin compliance boundary. Figure
ES-1 depicts the horizontal extent of 2L Standard exceedances for boron in the shallow,
deep, and bedrock groundwater flow layers at the site.
• 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 constituent
exceedances of barium, chromium, cobalt, iron, lead, manganese, thallium, and
vanadium at the outermost extent of the monitoring system to the west, north, and
northwest are related to background water quality, naturally occurring conditions, and/or
sampling conditions.
• The horizontal extent of soil contamination is limited to the area beneath the 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
ash.
ES.1 Source Information
Duke Energy owns and operates MSS, which is located on Lake Norman in Catawba County
near the town of Terrell, North Carolina. MSS began operation in 1965 as a coal-fired
generating station and currently operates four coal-fired units. The CCR from MSS's coal
combustion process has historically been stored in the station's ash basin located to the north of
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EXECUTIVE SUMMARY
the station and adjacent to Lake Norman. The ash basin system at MSS consists of a single cell
impounded by an earthen dike located on the southeast end of the ash basin. The ash basin
system was constructed in 1965 and is located north of the power plant. Inflows from the station
to the ash basin are discharged into the southwest portion of the ash basin.
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.
During operations of the coal-fired units, the sluice lines discharge the water/slurry and other
permitted flows to the southwest portion of the ash basin. Inflows to the ash basin are highly
variable due to station operations and weather.
The dry ash landfill consists of two units; which are located adjacent to the east (Phase 1) and
northeast (Phase II) portions of the ash basin. Phase I was constructed in September 1984 and
the unit was closed in March 1986. Placement of ash in the Phase II unit began around March
1986 and was completed in 1999. The dry ash landfill units were constructed prior to the
requirement for lining industrial landfills and were closed with a soil and vegetative cover
system.
The PV structural fill was constructed of fly ash under the structural fill rules found in 15A NCAC
13B .1700 et seq. and is located adjacent to and partially on top of the northwest portion of the
ash basin. Placement of dry ash in the PV structural fill area began in October 2000 and the unit
was closed with a soil and vegetative cover system in February 2013.
The industrial landfill No. 1, which is located over portions of the northernmost extent of the ash
basin, was constructed with a leachate collection and removal system and a three -component
liner system. The subgrade for portions of the industrial landfill were constructed of fly ash under
the structural fill rules found in 15A NCAC 13B .1700 et seq.
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 Survey
Properties located within a 0.5-mile radius of the MSS ash basin compliance boundary generally
consist of undeveloped land and Lake Norman to the east, undeveloped land and residential
properties located to the north and west, portions of the MSS site (outside the compliance
boundary), undeveloped land and residences to the south, and commercial properties to the
southeast along North Carolina Highway 150.
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 CSA receptor survey activities included contacting and/or reviewing state and
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EXECUTIVE SUMMARY
local 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
MSS ash basin compliance boundary. 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 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 MSS ash basin compliance boundary requesting information
on the presence of water supply wells and well usage for the properties.
The receptor survey activities identified four public water supply wells and 83 private water
supply wells in use, along with six assumed private water supply wells, located 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 from the topographic divide along Sherrills Ford Road toward Lake Norman were
identified within a 0.5-mile radius of the ash basin compliance boundary. No water supply wells
(including irrigation wells and unused or abandoned wells) were identified between the source
area and Lake Norman.
ESA Sampling / Investigation Results
ES.4.1 Background Findings
As part of the CSA, Duke Energy installed six additional background monitoring wells (three
shallow, two deep, and one bedrock). Based on existing knowledge of the site, the background
locations were selected to maximize physical separation from the ash basin, dry ash landfill
units, and PV structural fill in areas believed not to be impacted by ash to provide sufficient
background soil and groundwater quality data. Analyses of groundwater samples collected from
the six newly installed background wells and two existing ash basin compliance background
wells indicated that the following naturally occurring constituents exceed 2L Standards or IMACs
in background locations: barium, chromium, cobalt, iron, lead, manganese, thallium, 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.
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EXECUTIVE SUMMARY
Table ES-1. Concentrations Reported in New Background Wells
Constituent of Interest
NC 2L Standard or IMAC
(jig/L)Range
Background Well
of Concentrations /L
Antimony
1 *
0.33J to <2.5
Arsenic
10
0.17J to 7.5
Barium
700
28 to 760
Beryllium
4*
<0.2 to <1
Boron
700
26J+ to <50
Chloride
250,000
1,200 to 4,800
Chromium
10
1.2J+ to 80.4
Cobalt
1 *
0.38J to 11.9
Iron
300
77 to 18,200
Lead
15
0.078J to 17.5
Manganese
50
4.1 J to 380
Selenium
20
0.37J to <2.5
Sulfate
250,000
<1000 to 16,000
TDS
500,000
42,000J+ to 369,000
Thallium
0.2*
0.018J to <0.5
Vanadium
0.3*
2.2J to 100
Notes:
1. pg/L indicates micrograms per liter.
2. J indicates an estimated concentration.
3. J+ indicates an estimated concentration, biased high.
4. * denotes an IMAC
ES.4.2 Source Characterization
Source characterization was performed through the completion of soil and rock 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 be utilized as part of groundwater model development in the CAP.
Review of laboratory analytical results of ash samples collected from the ash basin, dry ash
landfill (Phase II), and PV structural fill identified nine COls: antimony, arsenic, barium, boron,
cobalt, iron, manganese, selenium, and vanadium.
COls identified in ash porewater samples include antimony, arsenic, barium, beryllium, boron,
cadmium, chloride, chromium, cobalt, iron, lead, manganese, nickel, selenium, sulfate, thallium,
TDS, and vanadium.
COls identified in ash basin surface water samples include arsenic, beryllium, boron, cadmium,
chloride, cobalt, copper, lead, manganese, nickel, selenium, sulfate, thallium, TDS, vanadium,
and zinc.
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EXECUTIVE SUMMARY
Synthetic Precipitation Leaching Procedure (SPLP) testing was conducted to evaluate the
leaching potential of constituents from ash. Although SPLP analytical results are being
compared to 2L Standards and IMACs, these leaching results do not represent groundwater
samples. The results of SPLP analyses indicate that the following constituents exceeded their
2L Standards: antimony, arsenic, barium, boron, chromium, cobalt, iron, lead, manganese,
nickel, selenium, thallium, and vanadium. However, many factors influence the transport of
these constituents and any potential impacts to groundwater over time will be investigated
through modeling as part of the CAP.
One seep sample associated with the ash basin (S-2), one NCDENR seep re -sample location
(MSSW001 S001), and one NCDENR surface water re -sample location (MSSW002 S001) were
sampled during this CSA. Seep sample S-2 contained reported concentrations above 2L
Standards or IMACs for arsenic, barium, boron, beryllium, chromium, cobalt, lead, manganese,
selenium, thallium, TDS, and vanadium. Note that the reported concentrations in sample S-2
are likely affected by turbidity/suspended solids. The NCDENR re -samples had reported
exceedances of 2L Standards or IMACs, or 2B Standards', for arsenic, boron, cobalt,
manganese, thallium, TDS, and vanadium.
ES.4.3 Nature and Extent of Contamination
The CSA found that soil and groundwater beneath the ash basin and dry ash landfill (Phase 11),
soil and groundwater to the east and downgradient of the ash basin and dry ash landfill (Phase
1), and groundwater to the southeast and downgradient of the ash basin (within the compliance
boundary) have been impacted by ash handling and storage at the MSS site.
Ash basin COls in soil and groundwater in these areas are likely the result of leaching from coal
ash contained in the ash basin and dry ash landfill units. However, exceedances of some COls
(i.e., barium, chromium, cobalt, iron, lead, manganese, thallium, 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.4.3.1 Soil
The horizontal extent of soil impacts is limited to the area beneath the ash basin and one
location east and downgradient of the dry ash landfill (Phase 1). Where soil impacts were
identified beneath the ash basin, the vertical extent of contamination beneath the ash/soil
interface is generally limited to the uppermost soil sample collected beneath ash. Reported
concentrations of soil samples were compared to background concentrations in addition to the
North Carolina Industrial Health (Industrial) and Protection of Groundwater (POG) Preliminary
Soil Remediation Goals (PSRGs) to delineate the extent of contamination. Arsenic was the only
COI with exceedances of background concentrations and North Carolina PSRGs beneath the
ash basin and at the one location east of the dry ash landfill (Phase 1). In general, constituent
concentrations of barium, cobalt, iron, manganese, and vanadium were higher in soil compared
to ash, and are considered to represent naturally occurring background conditions.
' Surface water classifications in North Carolina are promulgated in Title15A NCAC Subchapter 2B (2B Standards).
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ES.4.3.2 Groundwater
The approximate horizontal extent of groundwater impacts is limited to beneath the ash basin
and dry ash landfill (Phase II), east and downgradient of the ash basin and dry ash landfill
(Phase 1), and southeast and downgradient of the ash basin, within the ash basin compliance
boundary. The approximate vertical extent of groundwater impacts is generally limited to the
shallow and deep flow layers, and vertical migration of Cols is impeded by the underlying
bedrock.
Constituents with concentrations that exceeded 2L Standards or IMACs at the site that are likely
due to naturally occurring concentrations include antimony, barium, chromium, cobalt, iron, lead,
manganese, thallium, and vanadium.
Concentrations of several COls exceeded their respective 2L Standards or IMACs in
groundwater at the site and appear to be caused by the source area, including arsenic,
beryllium, boron, chloride, selenium, sulfate, and TDS. The nature and extent of contamination
for each source -related COI identified in groundwater are described below.
• Arsenic concentrations that exceeded the 2L Standard are limited to the shallow flow
layer immediately downgradient of the ash basin dam.
• Beryllium concentrations that exceeded the IMAC are limited to the shallow flow layer at
one location east and downgradient of the ash basin and dry ash landfill (Phase 1).
• Boron concentrations that exceeded the 2L Standard are present in the shallow, deep,
and bedrock flow layers. In the shallow flow layer, boron exceedances were reported
beneath the dry ash landfill (Phase II), east and downgradient of the ash basin and dry
ash landfill (Phase 1), and southeast and downgradient of the ash basin. In the deep flow
layer, exceedances were reported beneath the dry ash landfill (Phase 11), beneath the
central portion of the ash basin, beneath the western portion of the ash basin, and east
and downgradient of the ash basin and dry ash landfill (Phase 1). In the bedrock flow
layer, one boron exceedance was reported beneath the dry ash landfill (Phase II).
• Chloride concentrations that exceeded the 2L Standard are limited to the shallow flow
layer downgradient of the ash basin and dry ash landfill (Phase 1) and the deep flow
layer beneath the central portion of the ash basin.
• Selenium concentrations that exceeded the 2L Standard are limited to the shallow and
bedrock layers beneath the dry ash landfill (Phase II).
• Sulfate concentrations that exceeded the 2L Standard are limited to the shallow and
deep flow layers beneath the dry ash landfill (Phase II).
• TDS concentrations that exceeded the 2L Standard are present in the shallow and deep
flow layers. In the shallow flow layer, TDS exceedances were reported beneath the dry
ash landfill (Phase II), to the east and downgradient of the ash basin and dry ash landfill
(Phase 1), and southeast and downgradient of the ash basin. In the deep flow layer,
exceedances were reported beneath the dry ash landfill (Phase II), beneath the central
portion of the ash basin, southeast and downgradient of the ash basin, and to the south
and upgradient of the ash basin at GWA-21D.
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ESAA 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 central portion of the ash
basin, in the dry ash landfill (Phase 11), and the PV structural fill porewater.
The maximum concentrations of COls in groundwater were mainly detected in shallow
groundwater beneath the dry ash landfill (Phase 11), east and downgradient of the ash basin and
dry ash landfill (Phase 1), and southeast and downgradient of the ash basin. The maximum
concentration of boron was detected in deep groundwater beneath the dry ash landfill (Phase
11).
The maximum contaminant concentrations for COls reported in groundwater, ash porewater,
seep water, and ash basin surface water samples collected during the CSA are listed below.
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EXECUTIVE SUMMARY
Table ES-2. Maximum Constituent of Interest Concentrations
Maximum Constituent of Interest (COI) Concentrations (Ng/L)
COI
Ash Basin
Background
Groundwater
Ash Porewater
Seep Water
Surface Water
Groundwater
Antimony
11.4
26.6
0.86
0.32
<2.5
GWA-6D
AB-20S
S-2
SW-1
BG-2BR
Arsenic
10.5
6,380
87.1
24.4
7.5
MW-7S
AB-12SL
S-2
SW-3
BG-2BR
Barium
960
780
990
77
760
AL-2S
AB-12SL
S-2
SW-2
BG-3D
Beryllium
9.9
23.5
15.2
14.4
<1
AL-1 S
AB-5S
S-2
SW-3
MW-4
Boron
15,200
73,400
6,800
7,000
<50
AL-41D
AL-3S
MSSW002
SW-1
all BG wells
Cadmium
0.7
6.3
6,800
1.8
<0.08
AL-1 S
AL-3S
S-2
SW-3
several BG wells
Chloride
464,000
3,650,000
218,000
231,000
4,800
AB-12D
AB-12S
MSSW001
SW-1
BG-1 D
Chromium
189
71.6
85.7
7
80.4
GWA-2D
AB-20S
S-2
SW-5
BG-2BR
Cobalt
57.6
423
333
291
11.9
MW-7S
AB-20S
S-2
SW-3
BG-2BR
Copper
21.5
245
112
17.7
137
GWA-7S
AB-5S
S-2
SW-5
BG-2BR
Iron
54,000
2,300,000
242
1,370
18,200
AL-2S
AB-5S
MSWW002
SW-3
BG-2BR
Lead
10.2
28.7
227
2.6
17.5
AB-11S
AB-20S
(S-2)
(SW-5)
(BG-2BR
Manganese
9,690
19,400
11,600
42,100
380
AB-1 S
AB-5S
S-2
SW-3
BG-2BR
Nickel
66
333
51
115
49.6
MW-14S
AB-5S
S-2
SW-3
BG-3S
Selenium
108
454
25.1
33.2
<2.5
AL-2S
AB-20S
S-2
SW-3
MW-4
Sulfate
979,000
8,850,000
140,000
1,210,000
16,000
AL-2S
AB-5S
MSSW001)
SW-4
BG-3D
TDS
1,610,000
11,600,000
989,000
1,710,000
369,000
AL-2S
AB-12S
MSSW001 S001
SW-5
BG-2BR
Thallium
0.37
14.8
8.6
2.3
0.23J
MW-7S
(AB-20S)
(S-2
(SW-5)
(BG-2BR
Vanadium
57.5
163
566
1.8
100
AB-7D
AL-3S
S-2
SW-2
BG-2BR
Zinc
170
890
240
160
68
AL-2S
AB-5S
S-2
SW-5
BG-2BR
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ES.4.5 Regional Geology and Hydrogeology
The MSS site is underlain by the Charlotte and Kings Mountain terranes (Horton et al. 1989;
Hibbard et al. 2002; Hatcher et al. 2007). On the northwest side, the Charlotte/Kings Mountain
terranes are in contact with the Inner Piedmont zone along the Central Piedmont suture along
its northwest boundary, The Kings Mountain terrane is distinguished by its abundance of
metasedimentary and metavolcanic rocks at lower metamorphic grade than the metaigneous
rocks of higher metamorphic grade in the Charlotte terrane (Butler 1991; Butler and Secor 1991;
Hatcher et al. 2007). The Charlotte terrane is dominated by a complex sequence of plutonic
rocks that intrude a suite of metaigneous rocks (amphibolite metamorphic grade) including mafic
gneisses, amphibolites, metagabbros, and metavolcanic rocks with lesser amounts of granitic
gneiss and ultramafic rocks with minor metasedimentary rocks. Units mapped by Goldsmith et
al. (1988) underlying the eastern portion of the MSS site are alaskitic granite described as a
fine-grained light colored muscovite-biotite granite and a fine-grained biotite gneiss of
granodioritic composition of probable volcanic origin.
The groundwater system in the Piedmont province, in most cases, is comprised of two
interconnected layers, or mediums: 1) residual soil/saprolite and weathered fractured rock
(regolith) overlying 2) fractured crystalline bedrock (Heath 1980; Harned and Daniel 1992;
Figure 5-3). The regolith layer is a thoroughly weathered and structureless residual soil that
occurs near the ground surface with the degree of weathering decreasing with depth. The
residual soil grades into saprolite, a coarser grained material that retains the structure of the
parent bedrock. Beneath the saprolite, partially weathered/fractured bedrock occurs with depth
until sound bedrock is encountered. The regolith layer serves as the principal storage reservoir
and provides an intergranular medium through which the recharge and discharge of water from
the underlying fractured rock occurs. Within the fractured crystalline bedrock layer, the fractures
control both the hydraulic conductivity and storage capacity of the rock mass. A transition zone
(TZ) at the base of the regolith has been interpreted to be present in many areas of the
Piedmont. Harned and Daniel (1992) described the zone as consisting of partially
weathered/fractured bedrock and lesser amounts of saprolite that grades into bedrock and they
described the zone as "being the most permeable part of the system, even slightly more
permeable than the soil zone". Harned and Daniel (1992) suggested the zone may serve as a
conduit of rapid flow and transmission of contaminated water.
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.
ES.4.6 Site Geology and Hydrogeology
The Geologic Map of the Charlotte Quadrangle, North Carolina and South Carolina shows four
map/rock units underlying MSS: a biotite gneiss, quartz-sericite schist, the High Shoals Granite,
and alaskitic (light-colored) granite. The primary rock types encountered in the boreholes during
the CSA included medium- to coarse -grained biotite gneiss with some schistose texture, biotite
schist, a fine- to medium -grained biotite gneiss, granite, meta -quartz diorite, and quartz-sericite
schist. The medium- to coarse -grained biotite gneiss and granite are part of the High Shoals
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EXECUTIVE SUMMARY
Granite and are present in the western portion of the site. In the area mapped as alaskitic
granite, the primary rock encountered in the boreholes is a meta -quartz diorite and it underlies
the eastern portion of the ash basin. The fine- to medium -grained biotite gneiss (metavolcanic)
and the quartz-sericite schist (metasedimentary) are between the High Shoals Granite and the
meta -quartz diorite and underlie the middle portion of the ash basin. The rocks have been
subject to multiple deformations due to tectonic stress before and during the intrusion of the
meta -quartz diorite and High Shoals Granite. The biotite gneiss (metavolcanic) and quartz-
sericite schist (metasedimentary) have undergone polyphase folding resulting in two subparallel,
axial planar foliations that are pervasive. Most of the rock encountered in the boreholes exhibits
some degree of foliation/schistosity related to these fold events and is the dominant structure
with respect to the bedrock underlying MSS.
Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at MSS is consistent with the regolith-fractured rock system and is
an unconfined, connected system of flow layers. The MSS groundwater system is divided into
three layers referred to in this report as the shallow, deep (TZ), and bedrock flow layers to
distinguish the flow layers within the connected aquifer system. In general, groundwater within
the shallow and deep layers (S and D wells) and bedrock layer (BR wells) flows from northwest
and north to the southeast toward Lake Norman.
ES4.7 Existing Groundwater Monitoring Data
Duke Energy implemented voluntary groundwater monitoring around the MSS ash basin from
November 2007 until October 2011. During this period, the voluntary groundwater monitoring
wells were sampled a total of nine times, and the analytical results were submitted to NCDENR
DWR. Groundwater monitoring as required by the MSS NPDES Permit NC0004987 began in
February 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.
Compliance and voluntary 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.
Concentrations of several COls were reported above 2L Standards or IMACs in groundwater
samples collected from compliance and voluntary monitoring wells located downgradient of the
source area, including arsenic, boron, cobalt, manganese, selenium, thallium, and TDS. Sample
results from upgradient and background compliance wells are consistent with previous results.
ES.4.8 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 further evaluated in a baseline
human health or ecological risk assessment or other analysis, if required. Contaminants of
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EXECUTIVE SUMMARY
Potential Concern (COPCs) are those Cols 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 was performed in accordance with applicable federal and state guidance, including the
Guidelines for Performing Screening Level Ecological Risk Assessments within the North
Carolina Division of Waste Management (NCDENR 2003). The criteria for identifying COPCs
vary by the type of receptor (human or ecological) and media in which they occur.
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 included a review of NCDENR water well testing results
from private water supply wells located near MSS. According to NCDENR's August 20, 2015
online summary of well testing near coal ash ponds, approximately 38 water supply wells have
been sampled and analyzed as part of the NCDENR well testing program. In summary, the
North Carolina Department of Health and Human Services (NCDHHS) recommended that 35
wells sampled should not be utilized for drinking water due to the presence of one or more
constituents above screening levels defined by DHHS, including chromium, iron, lead,
manganese, and vanadium. These constituents are naturally occurring in groundwater in the
region surrounding the MSS site.
ES.4.9 Development of Site Conceptual Model
In the initial hydrogeologic site conceptual 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 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 southeast toward Lake Norman and an unnamed
tributary that flows to Lake Norman. Horizontal migration of groundwater at the site is controlled
by topographic highs along the west and north property boundaries and Lake Norman to the
southeast. The site conceptual hydrogeologic model will continue to be refined following
evaluation of the completed groundwater model in the CAP.
ES.4.10 Identification of Data Gaps
Through completion of the CSA activities and evaluation of data collected, data gaps have been
identified that will be evaluated further to refine the site conceptual model. The data gaps have
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EXECUTIVE SUMMARY
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. Temporal data gaps consist of
evaluation of petrographic analysis of rock data and refinement of speciation sampling in
groundwater monitoring wells. Data gaps resulting from evaluation of the data collected during
the CSA activities consist of evaluation of additional background groundwater monitoring wells,
collection of background surface water samples (located in unnamed tributaries northwest of the
ash basin and PV structural fill), and additional assessment to fully delineate the horizontal
extent of boron concentrations in groundwater east and downgradient of the ash basin and dry
ash landfill (Phase 1).
ES.5 Conclusions
The CSA identified the horizontal and vertical extent of groundwater contamination resulting
from the ash basin, dry ash landfill (Phases I and 11), and the PV structural fill at the MSS site,
and found it is limited to within the ash basin compliance boundary. The source and cause of
impacts from boron, as shown on Figure ES-1, is the CCR contained in the ash basin. The
cause of contamination shown on this figure is leaching of constituents from CCR into the
underlying soil and groundwater at the site. However, some groundwater, surface water, and
soil standards were also exceeded due to naturally occurring elements found in the subsurface,
including antimony, barium, chromium, cobalt, iron, lead, manganese, thallium, and vanadium.
The CSA found no imminent hazards to public health and the environment; therefore, no actions
to mitigate imminent hazards are required. However, corrective action at the site is required to
address soil and groundwater contamination present at the site. Proposed corrective action will
be outlined in the CAP to be submitted in accordance with CAMA.
The horizontal extent of soil impacts is limited to the area beneath the ash basin and one
location east and downgradient of the dry ash landfill (Phase 1). Where soil impacts were
identified beneath the ash basin, the vertical extent of contamination beneath the ash/soil
interface is generally limited to the uppermost soil sample collected beneath ash. Arsenic was
the only COI with exceedances of background concentrations and North Carolina PSRGs
beneath the ash basin. In general, constituent concentrations of barium, cobalt, iron,
manganese, and vanadium were higher in soil compared to ash, and are considered to
represent naturally occurring background conditions.
The CSA found that groundwater COls at the site include antimony, arsenic, barium, beryllium,
boron, chloride, chromium, chromium, cobalt, iron, manganese, selenium, sulfate, thallium,
TDS, and vanadium, 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 dry ash landfill (Phase II), east and downgradient of the
ash basin and dry ash landfill (Phase 1), and southeast and downgradient of the ash basin,
within the ash basin compliance boundary. The approximate vertical extent of groundwater
impacts is generally limited to the shallow and deep flow layers. Bedrock is impeding vertical
migration of groundwater and limiting the vertical extent of groundwater impacts.
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EXECUTIVE SUMMARY
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,
geochemical conditions present in the matrix (if present), matrix materials, and 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 impede the vertical migration of contaminants. The
CSA found that the direction of mobile contaminant transport is to the southeast toward Lake
Norman and an unnamed tributary that flows to Lake Norman, 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
MSS ash basin no later than August 1, 2029 (or sooner if classified as intermediate or high risk).
Closure for the MSS ash basin was not defined in CAMA.
Based on the findings of this CSA report, soil and groundwater impacts are present beneath and
downgradient of the ash basin, and remain within Duke Energy property and the ash basin
compliance boundary. 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.
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TABLE OF CONTENTS
Table of Contents
Section Page No.
1.0 Introduction........................................................................................................................1
1.1 Purpose of Comprehensive Site Assessment................................................................1
1.2 Regulatory Background..................................................................................................2
1.2.1 NCDENR Requirements..........................................................................................2
1.2.2 Notice of Regulatory Requirements........................................................................3
1.2.3 Coal Ash Management Act Requirements..............................................................3
1.3 NCDENR-Duke Energy Correspondence.......................................................................4
1.4 Approach to Comprehensive Site Assessment..............................................................4
1.4.1 NORR Guidance.....................................................................................................5
1.4.2 USEPA Monitored Natural Attenuation Approach...................................................5
1.4.3 ASTM Conceptual Site Model Guidance.................................................................5
1.5 Limitations and Assumptions..........................................................................................6
2.0 Site History and Description...............................................................................................8
2.1 Site Location, Acreage, and Ownership.........................................................................8
2.2 Site Description..............................................................................................................8
2.3 Adjacent Property, Zoning, and Surrounding Land Uses...............................................9
2.4 Adjacent Surface Water Bodies and Classifications.......................................................9
2.5 Meteorological Setting....................................................................................................9
2.6 Hydrologic Setting........................................................................................................10
2.7 Permitted Activities and Permitted Waste....................................................................10
2.8 NPDES and Surface Water Monitoring........................................................................11
2.9 NPDES Flow Diagram..................................................................................................11
2.10 History of Site Groundwater Monitoring........................................................................12
2.10.1 Voluntary Groundwater Monitoring Wells..............................................................12
2.10.2 Compliance Groundwater Monitoring Wells..........................................................12
2.11 Assessment Activities or Previous Site Investigations..................................................13
2.12 Decommissioning Status..............................................................................................14
3.0 Source Characteristics.....................................................................................................15
3.1 Coal Combustion and Ash Handling System................................................................15
3.2 Description of Ash Basin and Other Ash Storage Areas..............................................15
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3.2.1 Ash Basin..............................................................................................................15
3.2.2 Dry Ash Landfill.....................................................................................................16
3.2.3 FGD Landfill..........................................................................................................16
3.2.4 Industrial Landfill No. 1..........................................................................................17
3.2.5 Demolition Landfill.................................................................................................17
3.2.6 Asbestos Landfill...................................................................................................17
3.2.7 Photovoltaic Farm Structural Fill...........................................................................17
3.3 Physical Properties of Ash............................................................................................17
3.4 Chemical Properties of Ash..........................................................................................18
4.0 Receptor Information........................................................................................................20
4.1 Summary of Previous Receptor Survey Activities........................................................20
4.2 Summary of CSA Receptor Survey Activities and Findings.........................................21
4.3 NCDENR Well Water Testing Program........................................................................22
5.0 Regional Geology and Hydrogeology..............................................................................23
5.1 Regional Geology.........................................................................................................23
5.2 Regional Hydrogeology................................................................................................24
6.0 Site Geology and Hydrogeology......................................................................................27
6.1 Site Geology.................................................................................................................27
6.1.1 Soil Classification..................................................................................................27
6.1.2 Rock Lithology.......................................................................................................28
6.1.3 Structural Geology.................................................................................................29
6.1.4 Geologic Mapping.................................................................................................29
6.1.5 Fracture Trace Analysis........................................................................................30
6.1.6 Effects of Structure on Groundwater Flow............................................................32
6.1.7 Soil and Rock Mineralogy and Chemistry.............................................................32
6.2 Site Hydrogeology........................................................................................................32
6.2.1 Groundwater Flow Direction..................................................................................32
6.2.2 Hydraulic Gradient.................................................................................................33
6.2.3 Effects of Geological/Hydrogeological Characteristics on Contaminants..............33
6.2.4 Site Hydrogeologic Conceptual Model..................................................................34
7.0 Source Characterization...................................................................................................35
7.1 Ash Basin.....................................................................................................................36
7.1.1 Ash (Sampling and Chemical Characteristics)......................................................36
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7.1.2 Ash Porewater (Sampling and Chemical Characteristics).....................................37
7.1.3 Ash Basin Surface Water (Sampling, and Chemical Characteristics) ...................38
7.2 Dry Ash Landfill............................................................................................................39
7.2.1 Ash (Sampling and Chemical Characteristics)......................................................39
7.2.2 Porewater (Sampling and Chemical Characteristics)............................................39
7.3 PV Structural Fill...........................................................................................................39
7.3.1 Ash (Sampling and Chemical Characteristics)......................................................39
7.3.2 Porewater (Sampling and Chemical Characteristics)............................................40
7.4 Leaching Potential of Ash.............................................................................................40
7.4.1 Leaching Characteristics.......................................................................................40
7.4.2 Sampling and Chemical Characteristics................................................................41
7.5 Seeps...........................................................................................................................41
7.5.1 Review of NCDENR March 2014 Sampling Results.............................................41
7.5.2 Ash Basin and NCDENR Resampling Results — CSA Activities ...........................42
7.6 COls.............................................................................................................................43
7.6.1 COls in Ash (based on total inorganics analysis, as shown in Table 7-2).............43
7.6.2 COls in Ash Porewater (based on water quality analysis, as shown in Table 7-5)43
7.6.3 COls in Ash Basin Surface Water (based on water quality analysis, as shown in
Table7-6)............................................................................................................................44
7.6.4 COls in Seeps and NCDENR Resamples (based on water quality analysis, as
shownin Table 7-8).............................................................................................................44
7.6.5 Summary of COls from Source Characterization..................................................44
8.0 Soil and Rock Characterization........................................................................................46
8.1 Background Sample Locations.....................................................................................46
8.2 Analytical Methods and Results...................................................................................46
8.3 Comparison of Soil and Rock Results to Applicable Levels.........................................47
8.4 Comparison of Soil Results to Background..................................................................47
8.4.1 Background Soil, PWR, and Rock.........................................................................47
8.4.2 Soil, PWR, and Rock Beneath the Ash Basin.......................................................48
8.4.3 Soil Beneath the PV Structural Fill........................................................................48
8.4.4 Soil, PWR, and Rock Beneath the Dry Ash Landfill (Phase II)..............................48
8.4.5 Soil Outside the Waste Boundaries.......................................................................48
9.0 Surface Water and Sediment Characterization................................................................49
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9.1 Surface Water...............................................................................................................49
9.2 Sediment......................................................................................................................49
10.0 Groundwater Characterization.........................................................................................50
10.1 Regional Groundwater Data for Constituents of Interest..............................................50
10.1.1 Antimony...............................................................................................................50
10.1.2 Arsenic..................................................................................................................51
10.1.3 Barium...................................................................................................................51
10.1.4 Beryllium................................................................................................................52
10.1.5 Boron.....................................................................................................................
53
10.1.6 Chloride.................................................................................................................53
10.1.7 Chromium..............................................................................................................54
10.1.8 Cobalt....................................................................................................................
54
10.1.9 Iron........................................................................................................................54
10.1.10 Lead...................................................................................................................
55
10.1.11 Manganese........................................................................................................
55
10.1.12 Selenium............................................................................................................56
10.1.13 Sulfate................................................................................................................57
10.1.14 TDS....................................................................................................................57
10.1.15 Thallium.............................................................................................................58
10.1.16 Vanadium...........................................................................................................58
10.1.17 pH......................................................................................................................59
10.2 Background Wells.........................................................................................................59
10.3 Discussion of Redox Conditions...................................................................................61
10.4 Groundwater Analytical Results...................................................................................61
10.4.1 Upgradient of the Ash Basin, Dry Ash Landfill (Phases I and 11), and PV Structural
Fill 62
10.4.2 Beneath the Ash Basin..........................................................................................63
10.4.3 Beneath the Dry Ash Landfill (Phase II)................................................................63
10.4.4 Downgradient of the Ash Basin and Dry Ash Landfill (Phase 1) ............................63
10.5 Comparison of Results to 2L Standards.......................................................................63
10.6 Comparison of Results to Background.........................................................................64
10.6.1 Existing Background Wells MW-4 and MW-4D.....................................................64
10.6.2 Newly Installed Background Wells........................................................................64
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10.6.3 Upgradient of the Ash Basin, Dry Ash Landfill (Phases I and II), and PV Structural
Fill 65
10.6.4 Beneath the Ash Basin..........................................................................................66
10.6.5 Beneath the Dry Ash Landfill (Phase II)................................................................67
10.6.6 Downgradient of the Ash Basin and Dry Ash Landfill (Phase 1) ............................68
10.6.7 Compliance and Voluntary Wells..........................................................................69
10.7 Cation and Anion Water Quality Data...........................................................................70
10.8 Groundwater Speciation...............................................................................................70
10.9 Radiological Laboratory Testing...................................................................................70
10.10 CCR Rule Groundwater Detection and Assessment Monitoring Parameters...............71
11.0 Hydrogeological Investigation..........................................................................................73
11.1 Hydrostratigraphic Layer Development........................................................................73
11.2 Hydrostratigraphic Layer Properties.............................................................................74
11.2.1 Borehole In -Situ Tests...........................................................................................74
11.2.2 Monitoring Well and Observation Well Slug Tests................................................75
11.2.3 Laboratory Permeability Tests...............................................................................76
11.2.4 Hydrostratigraphic Layer Parameters....................................................................76
11.3 Hydraulic Gradient........................................................................................................76
11.4 Groundwater Velocity...................................................................................................77
11.5 Contaminant Velocity....................................................................................................77
11.6 Plume's Physical and Chemical Characterization........................................................77
11.7 Groundwater / Surface Water Interaction.....................................................................80
11.8 Estimated Seasonal High and Seasonal Low Groundwater Elevations — Compliance
andVoluntary Wells................................................................................................................81
12.0 Screening -Level Risk Assessment...................................................................................82
12.1 Human Health Screening.............................................................................................82
12.1.1 Introduction............................................................................................................
82
12.1.2 Conceptual Site Model..........................................................................................83
12.1.3 Human Health Risk -Based Screening Levels.......................................................85
12.1.4 Site -Specific Risk Based Remediation Standards.................................................86
12.1.5 NCDENR Receptor Well Investigation..................................................................86
12.1.6 Human Health Risk Screening Summary ..............................................................87
12.2 Ecological Screening....................................................................................................87
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12.2.1 Introduction............................................................................................................
87
12.2.2 Ecological Setting..................................................................................................87
12.2.3 Fate and Transport Mechanisms...........................................................................92
12.2.4 Comparison to Ecological Screening Levels.........................................................93
12.2.5 Uncertainty and Data Gaps...................................................................................94
12.2.6 Scientific/Management Decision Point..................................................................
95
12.2.7 Ecological Risk Screening Summary....................................................................95
13.0 Groundwater Modeling.....................................................................................................96
13.1 Fate and Transport Groundwater Modeling..................................................................96
13.2 Batch Geochemical Modeling.......................................................................................97
13.3 Geochemical Site Conceptual Model...........................................................................97
14.0 Data Gaps — Conceptual Site Model Uncertainties........................................................100
14.1 Data Gaps..................................................................................................................100
14.1.1 Data Gaps Resulting from Temporal Constraints................................................100
14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities .......
100
14.2 Site Heterogeneities...................................................................................................101
14.3 Impact of Data Gaps and Site Heterogeneities..........................................................101
15.0 Planned Sampling for CSA Supplement........................................................................102
15.1 Sampling Plan for Inorganic Constituents..................................................................102
15.2 Sampling Plan for Speciation Constituents................................................................102
16.0 Interim Groundwater Monitoring Plan............................................................................103
16.1 Sampling Frequency...................................................................................................103
16.2 Constituent and Parameter List..................................................................................103
16.3 Proposed Sampling Locations....................................................................................103
16.4 Proposed Background Wells......................................................................................103
17.0 Discussion......................................................................................................................104
17.1 Summary of Completed and Ongoing Work...............................................................104
17.2 Nature and Extent of Contamination..........................................................................105
17.3 Maximum Contaminant Concentrations.....................................................................106
17.4 Contaminant Migration and Potentially Affected Receptors.......................................107
18.0 Conclusions....................................................................................................................108
18.1 Source and Cause of Contamination..........................................................................108
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18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate them in
Accordance to 15A NCAC 02L.0106(f).................................................................................108
18.3 Receptors and Significant Exposure Pathways..........................................................108
18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination and Significant
Factors Affecting Contaminant Transport..............................................................................108
18.5 Geological and Hydrogeological Features influencing the Movement, Chemical, and
Physical Character of the Contaminants...............................................................................109
18.6 Proposed Continued Monitoring.................................................................................110
18.7 Preliminary Evaluation of Corrective Action Alternatives............................................110
19.0 References.....................................................................................................................111
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LIST OF FIGURES
List of Figures (organized by CSA report section)
Executive Summary
• Figure ES-1: Site Conceptual Model: Plan View Map — Area of Boron Exceedances
of 2L Standards
1.0 Introduction
<No Figures>
2.0 Site History and Description
• Figure 2-1: Site Location Map
• Figure 2-2: Site Layout Map
• Figure 2-3: Pre -Ash Basin USGS Map
• Figure 2-4: Site Features Map
• Figure 2-5: Site Vicinity Map
• Figure 2-6: Marshall Steam Station Flow Schematic Diagram
• Figure 2-7: Compliance and Voluntary Monitoring Wells
3.0 Source Characteristics
• Figure 3-1: Photo of Fly Ash and Bottom Ash
• Figure 3-2: Elemental Composition for Bottom Ash, Fly Ash, Shale, and Volcanic
Ash
• Figure 3-3: Coal Ash TCLP Leachate Concentration vs. Regulatory Limits
• Figure 3-4: Trace Elements in Fly Ash vs Soil Screening Levels
• Figure 3-5: Trace Elements in Bottom Ash vs Soil Screening Levels
4.0 Receptor Information
• Figure 4-1: Receptor Map — USGS Base
• Figure 4-2: Receptor Map — Aerial Base
• Figure 4-3: Ash Basin Underground Features Map
• Figure 4-4: Surface Water Bodies
• Figure 4-5: Properties Contiguous to the Ash Basin Waste Boundary
5.0 Regional Geology and Hydrogeology
• Figure 5-1: Tectonostratigraphic Map of the Southern and Central Appalachians
• Figure 5-2: Regional Geologic Map
• Figure 5-3: Interconnected Two -Medium Piedmont Groundwater System
• Figure 5-4: Conceptual Variations of the Transition Zone due to Rock Type /
Structure
• Figure 5-5: Piedmont Slope -Aquifer System
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LIST OF FIGURES
6.0 Site Geology and Hydrogeology
• Figure 6-1: Site Geologic Map
• Figure 6-2: Monitoring Well and Sample Locations
• Figure 6-3: Topographic Lineaments and Rose Diagram
• Figure 6-4: Aerial Photography Lineaments and Rose Diagram
• Figure 6-5: Water Table Surface Map — S wells
• Figure 6-6: Potentiometric Surface Map — D wells
• Figure 6-7: Potentiometric Surface Map — BR wells
7.0 Source Characterization
• Figure 7-1: Source Characterization Sample Location Map
8.0 Soil and Rock Characterization
•
Figure 8-1: Soil Analytical Results — Plan View (PSRG Standard Exceedances)
•
Figure 8-2: Cross Section Location Map
•
Figure 8-3.1: Cross Section A -A' with Solid Matrix Analytical Results —
Sheet 1
•
Figure 8-3.2: Cross Section A -A' with Solid Matrix Analytical Results —
Sheet 2
•
Figure 8-3.3: Cross Section A -A' with Solid Matrix Analytical Results —
Sheet 3
•
Figure 8-3.4: Cross Section A -A' with Solid Matrix Analytical Results —
Sheet 4
•
Figure 8-4.1: Cross Section B-B' with Solid Matrix Analytical Results —
Sheet 1
•
Figure 8-4.2: Cross Section B-B' with Solid Matrix Analytical Results —
Sheet 2
•
Figure 8-5.1: Cross Section C-C' with Solid Matrix Analytical Results
— Sheet 1
•
Figure 8-5.2: Cross Section C-C' with Solid Matrix Analytical Results
— Sheet 2
•
Figure 8-5.3: Cross Section C-C' with Solid Matrix Analytical Results
— Sheet 3
9.0 Sediment Characterization
• Figure 9-1: Seep and Surface Water Sample Location
10.0 Groundwater Characterization
• Figure 10-1: Statewide Arsenic Concentrations in Groundwater
• Figure 10-2: Regional Chloride Concentrations in Groundwater
• Figure 10-3: Statewide Iron Concentrations in Groundwater
• Figure 10-4: Statewide Manganese Concentrations in Groundwater
• Figure 10-5: Regional Manganese Concentrations in Groundwater
• Figure 10-6: National Thallium Concentrations in Soil
• Figure 10-7: Regional Vanadium Concentrations in Groundwater
• Figure 10-8: Regional pH in Groundwater
• Figure 10-9: Monitoring Well and Sample Locations
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF FIGURES
• Figure 10-10: Typical Well Construction Details
• Figure 10-11: Stacked Time Series Plot: Boron Concentration in Shallow Wells
Compared to Background Well — MW-4
• Figure 10-12: Stacked Time Series Plot: Iron Concentration in Shallow Wells
Compared to Background Well — MW-4
• Figure 10-13: Stacked Time Series Plot: Manganese Concentration in Shallow
Wells Compared to Background Well — MW-4
• Figure 10-14: Stacked Time Series Plot: Sulfate Concentration in Shallow Wells
Compared to Background Well — MW-4
• Figure 10-15: Stacked Time Series Plot: TDS Concentration in Shallow Wells
Compared to Background Well — MW-4
• Figure 10-16: Stacked Time Series Plot: pH Concentration in Shallow Wells
Compared to Background Well — MW-4
• Figure 10-17: Stacked Time Series Plot: Boron Concentration in Deep Wells
Compared to Background Well — MW-4D
• Figure 10-18: Stacked Time Series Plot: Iron Concentration in Deep Wells
Compared to Background Well — MW-4D
• Figure 10-19: Stacked Time Series Plot: Manganese Concentration in Deep Wells
Compared to Background Well — MW-4D
• Figure 10-20: Stacked Time Series Plot: Sulfate Concentration in Deep Wells
Compared to Background Well — MW-4D
• Figure 10-21: Stacked Time Series Plot: TDS Concentration in Deep Wells
Compared to Background Well — MW-4D
• Figure 10-22: Stacked Time Series Plot: pH Concentration in Deep Wells Compared
to Background Well — MW-4D
• Figure 10-23: Stacked Time Series Plot: MW-14D — Boron and Turbidity
• Figure 10-24: Stacked Time Series Plot: MW-14S — Boron and Turbidity
• Figure 10-25: Stacked Time Series Plot: MW -4
— Iron and Turbidity
• Figure 10-26: Stacked Time Series Plot: MW -4D — Iron and Turbidity
• Figure 10-27.1: Stacked Time Series Plot: MW -10D
— Iron and Turbidity
• Figure 10-27.2: Stacked Time Series Plot: MW -10S
— Iron and Turbidity
• Figure 10-28.1: Stacked Time Series Plot: MW -11 D—
Iron and Turbidity
• Figure 10-28.2: Stacked Time Series Plot: MW -11
S
— Iron and Turbidity
• Figure 10-29.1: Stacked Time Series Plot: MW -12D
— Iron and Turbidity
• Figure 10-29.2: Stacked Time Series Plot: MW -12S
— Iron and Turbidity
• Figure 10-30.1: Stacked Time Series Plot: MW -13D—
Iron and Turbidity
• Figure 10-30.2: Stacked Time Series Plot: MW -13S
— Iron and Turbidity
• Figure 10-31.1: Stacked Time Series Plot: MW -14D
— Iron and Turbidity
• Figure 10-31.2: Stacked Time Series Plot: MW -14S — Iron and Turbidity
• Figure 10-32: Stacked Time Series Plot: MW -4 — Manganese and Turbidity
• Figure 10-33: Stacked Time Series Plot: MW -4D — Manganese and Turbidity
• Figure 10-34.1: Stacked Time Series Plot: MW -10D — Manganese and Turbidity
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF FIGURES
• Figure 10-34.2: Stacked Time Series Plot: MW -10S — Manganese and Turbidity
• Figure 10-35.1: Stacked Time Series Plot: MW -11 D — Manganese and Turbidity
• Figure 10-35.2: Stacked Time Series Plot: MW -11 S — Manganese and Turbidity
• Figure 10-36.1: Stacked Time Series Plot: MW -12D — Manganese and Turbidity
• Figure 10-36.2: Stacked Time Series Plot: MW -12S — Manganese and Turbidity
• Figure 10-37.1: Stacked Time Series Plot: MW -13D — Manganese and Turbidity
• Figure 10-37.2: Stacked Time Series Plot: MW -13S — Manganese and Turbidity
• Figure 10-38.1: Stacked Time Series Plot: MW -14D — Manganese and Turbidity
• Figure 10-38.2: Stacked Time Series Plot: MW -14S — Manganese and Turbidity
• Figure 10-39: Stacked Time Series Plot: MW -4 — pH and Turbidity
• Figure 10-40: Stacked Time Series Plot: MW -41D — pH and Turbidity
• Figure 10-41.2: Stacked Time Series Plot: MW -10S — pH and Turbidity
• Figure 10-41.2: Stacked Time Series Plot: MW -10D — pH and Turbidity
• Figure 10-42.1: Stacked Time Series Plot: MW -11 S — pH and Turbidity
• Figure 10-42.2: Stacked Time Series Plot: MW -11 D — pH and Turbidity
• Figure 10-43: Stacked Time Series Plot: MW -12S — pH and Turbidity
• Figure 10-44: Stacked Time Series Plot: MW -12D — pH and Turbidity
• Figure 10-45: Stacked Time Series Plot: MW -13S — pH and Turbidity
• Figure 10-46: Stacked Time Series Plot: MW -13D — pH and Turbidity
• Figure 10-47: Stacked Time Series Plot: MW -14S — pH and Turbidity
• Figure 10-48: Stacked Time Series Plot: MW -14D — pH and Turbidity
• Figure 10-49: Stacked Time Series Plot: MW -14S — TDS and Turbidity
• Figure 10-50: Stacked Time Series Plot: MW -14D — TDS and Turbidity
• Figure 10-51: Correlation Plot: AB-4S vs. AB-1 R Ratio (BG) of Boron
• Figure 10-52: Correlation Plot: AB-9S vs. AB-1 R (BG) Ratio of Iron
• Figure 10-53: Correlation Plot: AB-9D vs. AB-1 R (BG) Ratio of Manganese
• Figure 10-54: Correlation Plot: AB-1 OS vs. AB-1 R (BG) Ratio of pH
• Figure 10-55: Correlation Plot: AB-1 OD vs. AB-1 R (BG) Ratio of Sulfate
• Figure 10-56: Correlation Plot: AB-11 D vs. AB-1 R (BG) Ratio of Total Dissolved
Solids
• Figure 10-57: Stacked Time Series Plot: Antimony in Compliance Wells
• Figure 10-58: Stacked Time Series Plot: Arsenic in Compliance Wells
• Figure 10-59: Stacked Time Series Plot: Barium in Compliance Wells
• Figure 10-60: Stacked Time Series Plot: Boron in Compliance Wells
• Figure 10-61: Stacked Time Series Plot: Cadmium in Compliance Wells
• Figure 10-62: Stacked Time Series Plot: Chromium in Compliance Wells
• Figure 10-63: Stacked Time Series Plot: Iron in Compliance Wells
• Figure 10-64: Stacked Time Series Plot: Lead in Compliance Wells
• Figure 10-65: Stacked Time Series Plot: Manganese in Compliance Wells
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF FIGURES
• Figure 10-66: Stacked Time Series Plot: Mercury in Compliance Wells
• Figure 10-67: Stacked Time Series Plot: Nickel in Compliance Wells
• Figure 10-68: Stacked Time Series Plot: Nitrate in Compliance Wells
• Figure 10-69: Stacked Time Series Plot: pH
• Figure 10-70: Stacked Time Series Plot: Selenium in Compliance Wells
• Figure 10-71: Stacked Time Series Plot: Sulfate in Compliance Wells
• Figure 10-72: Stacked Time Series Plot: TDS in Compliance Wells
• Figure 10-73: Stacked Time Series Plot: Groundwater Elevation in Compliance
Wells
• Figure 10-74: Groundwater Analytical Results — Plan View (21- or IMAC
Exceedances)
• Figure 10-75: Antimony Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-76: Antimony Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-77: Antimony Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-78: Arsenic Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-79: Arsenic Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-80: Arsenic Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-81: Barium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-82: Barium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-83: Barium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-84: Beryllium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-85: Beryllium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-86: Beryllium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-87: Boron Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-88: Boron Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-89: Boron Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-90: Chloride Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-91: Chloride Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-92: Chloride Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-93: Chromium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-94: Chromium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-95: Chromium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-96: Cobalt Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-97: Cobalt Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-98: Cobalt Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-99: Iron Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-100: Iron Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-101: Iron Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-102: Lead Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-103: Lead Isoconcentration Contour Map — Deep Wells (D)
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin
���
LIST OF FIGURES
• Figure 10-104:
Lead Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-105:
Manganese Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-106:
Manganese Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-107:
Manganese Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-108:
Selenium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-109:
Selenium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-110:
Selenium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-111: Sulfate Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-112: Sulfate Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-113: Sulfate Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-114: Thallium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-115: Thallium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-116: Thallium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-117: TDS Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-118: TDS Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-119: TDS Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-120: Vanadium Isoconcentration Contour Map — Shallow Wells (S)
• Figure 10-121: Vanadium Isoconcentration Contour Map — Deep Wells (D)
• Figure 10-122: Vanadium Isoconcentration Contour Map — Bedrock Wells (BR)
• Figure 10-123.1: Cross Section A -A' with Groundwater Analytical Results — Sheet 1
• Figure 10-123.2: Cross Section A -A' with Groundwater Analytical Results — Sheet 2
• Figure 10-123.3: Cross Section A -A' with Groundwater Analytical Results — Sheet 3
• Figure 10-123.4: Cross Section A -A' with Groundwater Analytical Results — Sheet 4
• Figure 10-124.1: Cross Section B-B' with Groundwater Analytical Results — Sheet 1
• Figure 10-124.2: Cross Section B-B' with Groundwater Analytical Results — Sheet 2
• Figure 10-125.1: Cross Section C-C' with Groundwater Analytical Results — Sheet 1
• Figure 10-125.2: Cross Section C-C' with Groundwater Analytical Results — Sheet 2
• Figure 10-125.3: Cross Section C-C' with Groundwater Analytical Results — Sheet 3
• Figure 10-126: Cation and Anion Concentration in Ash Basin Porewater Samples
• Figure 10-127.1: Cation and Anion Concentrations in Ash Basin Surface Water
Samples
• Figure 10-127.2: Cation and Anion Concentrations in Surface Water Samples
Collected Outside of the Waste Boundary
• Figure 10-128: Cation and Anion Concentration in Ash Basin Seeps
• Figure 10-129: Cation and Anion Concentration in Ash Basin Groundwater
Background Wells
• Figure 10-130: Cation and Anion Concentration in Ash Basin Groundwater
Downgradient Shallow Wells
• Figure 10-131: Cation and Anion Concentration in Ash Basin Groundwater
Downgradient Deep Wells
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF FIGURES
• Figure 10-132: Cation and Anion Concentration in Ash Basin Groundwater
Downgradient Bedrock Wells
• Figure 10-133: Cation and Anion Concentration in Ash Basin Groundwater
Upgradient Shallow Wells
• Figure 10-134: Cation and Anion Concentration in Ash Basin Groundwater
Upgradient Deep Wells
• Figure 10-135: Cation and Anion Concentration in Ash Basin Groundwater
Upgradient Bedrock Wells
• Figure 10-136: Cation and Anion Concentration in Ash Basin Groundwater All
Shallow Wells — Sheet 1
• Figure 10-137: Cation and Anion Concentration in Ash Basin Groundwater All
Shallow Wells — Sheet 2
• Figure 10-138: Cation and Anion Concentration in Ash Basin Groundwater All Deep
Wells — Sheet 1
• Figure 10-139: Cation and Anion Concentration in Ash Basin Groundwater All Deep
Wells — Sheet 2
• Figure 10-140: Cation and Anion Concentration in Ash Basin Groundwater All
Bedrock Wells
• Figure 10-141: Sulfate:Chloride Ratio in Porewater
• Figure 10-142.1: Sulfate: Chloride Ratio in Ash Basin Surface Water Samples
• Figure 10-142.2: Sulfate: Chloride Ratio in Upgradient Bedrock Monitoring Wells
• Figure 10-143: Sulfate:Chloride Ratio in Seeps
• Figure 10-144: Sulfate: Chloride Ratio in Groundwater Background Wells
• Figure 10-145: Sulfate:Chloride Ratio in Groundwater Downgradient Shallow Wells
• Figure 10-146: Sulfate:Chloride Ratio in Groundwater Downgradient Deep Wells
• Figure 10-147: Sulfate:Chloride Ratio in Groundwater Downgradient Bedrock Wells
• Figure 10-148: Sulfate:Chloride Ratio in Groundwater Upgradient Shallow Wells
• Figure 10-149: Sulfate:Chloride Ratio in Groundwater Upgradient Deep Wells
• Figure 10-150: Sulfate:Chloride Ratio in Groundwater Upgradient Bedrock Wells
• Figure 10-151: Sulfate: Chloride Ratio in Groundwater All Shallow Wells — Sheet 1
• Figure 10-152: Sulfate: Chloride Ratio in Groundwater All Shallow Wells — Sheet 2
• Figure 10-153: Sulfate: Chloride Ratio in Groundwater All Deep Wells — Sheet 1
• Figure 10-154: Sulfate: Chloride Ratio in Groundwater All Deep Wells — Sheet 2
• Figure 10-155: Sulfate:Chloride Ratio in Groundwater All Bedrock Wells
• Figure 10-156: Piper Diagram — Ash Basin Porewater, Water and Background
Monitoring Wells
• Figure 10-157: Piper Diagram — Ash Basin Porewater, Water and Seeps
• Figure 10-158: Piper Diagram — Ash Basin Porewater, Water and All Surface Water
• Figure 10-159: Piper Diagram — Ash Basin Porewater, Water and Downgradient
Shallow Wells
• Figure 10-160: Piper Diagram —Ash Basin Porewater, Water and Downgradient
Deep Wells
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF FIGURES
• Figure 10-161: Piper Diagram —Ash Basin Porewater, Water and Downgradient
Bedrock Wells
• Figure 10-162: Piper Diagram —Ash Basin Porewater, Water and Upgradient
Shallow Wells
• Figure 10-163: Piper Diagram — Ash Basin Porewater, Water and Upgradient Deep
Wells
• Figure 10-164:
Piper Diagram —Ash Basin Porewater, Water and Upgradient
Bedrock Wells
• Figure 10-165:
Piper Diagram — Ash Basin Porewater, Water and All Shallow
• Figure 10-166:
Piper Diagram — Ash Basin Porewater, Water and All Deep
• Figure 10-167:
Piper Diagram — Ash Basin Porewater, Water and All Bedrock Wells
• Figure 10-168:
Detection Monitoring Constituents Detected in Shallow Wells
• Figure 10-169:
Detection Monitoring Constituents Detected in Deep Wells
• Figure 10-170:
Detection Monitoring Constituents Detected in Bedrock Wells
• Figure 10-171:
Assessment Monitoring Constituents Detected in Shallow
• Figure 10-172:
Assessment Monitoring Constituents Detected in Deep Wells
• Figure 10-173:
Assessment Monitoring Constituents Detected in Bedrock Wells
11.0 HydrogeologicalInvestigation
<No Figures>
12.0 Screening -Level Risk Assessment
• Figure 12-1: Human Health Screening Conceptual Site Model
• Figure 12-2: Ecological Screening Conceptual Site Model
13.0 Groundwater Modeling
<No Figures>
14.0 Data Gaps — Conceptual Site Model Uncertainties
<No Figures>
15.0 Planned Sampling for CSA Supplement
<No Figures>
16.0 Interim Groundwater Monitoring Plan
<No Figures>
17.0 Discussion
<No Figures>
18.0 Conclusions
<No Figures>
19.0 References
<No Figures>
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin FN
LIST OF FIGURES
XVI
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin FN
LIST OF TABLES
List Of Tables (organized by CSA report section)
Executive Summary
• Table ES-1: Concentrations Reported in New Background Wells
• Table ES-2. Maximum Constituent of Interest Concentrations
1.0 Introduction
• Table 1-1: Comparison of Sampling Data to Federal and State Regulatory
Standards
2.0 Site History and Description
• Table 2-1: Groundwater Monitoring Requirements
• Table 2-2: Exceedances of 2L Standards or IMACs at Compliance Wells (February
2011-June 2015)
• Table 2-3: Summary of Onsite Environmental Incidents
3.0 Source Characteristics
• Table 3-1: Range (10th percentile — 901h percentile) in Bulk Composition of Fly Ash,
Bottom Ash, Rock, and Soil (Source: EPRI 2009a)
4.0 Receptor Information
• Table 4-1: Public and Private Water Supply Wells within 0.5-mile Radius of Ash
Basin Compliance Boundary
• Table 4-2: Surrounding Property Addresses
5.0 Regional Geology and Hydrogeology
<No Tables>
6.0 Site Geology and Hydrogeology
• Table 6-1: Soil Mineralogy Results
• Table 6-2: Soil Chemistry Results, % Oxides
• Table 6-3: Soil Chemistry Results, Elemental Composition
• Table 6-4: Transition Zone Mineralogy Results
• Table 6-5: Transition Zone Chemistry Results, % Oxides
• Table 6-6: Transition Zone Results, Elemental Composition
• Table 6-7: Whole Rock Chemistry Results, % Oxides
• Table 6-8: Whole Rock Chemistry Results, Elemental Composition
• Table 6-9: Summary of Hydraulic Gradient Calculations
Xvii
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF TABLES
7.0 Source Characterization
• Table 7-1: Soil and Ash Parameters and Analytical Methods
• Table 7-2: Cation/Anion Sample Results
• Table 7-3: Ash Basin Surface Water, Porewater and Seep Parameters and
Analytical Methods
• Table 7-4: Ash Porewater Field Parameters
• Table 7-5 :Ash Basin Porewater Sample Results
• Table 7-6: Ash Basin Surface Water Results
• Table 7-7: Ash Sample SPLP Results
• Table 7-8: Seep Sample Results
• Table 7-9: Ash Porewater Sample Results - Speciation
• Table 7-10: Ash Basin Surface Water and Seep Sample Results - Speciation
• Table 7-11: NCDENR March 2014 Sampling Results
8.0 Soil and Rock Characterization
• Table 8-1: Soil, Ash, and Rock Parameters and Constituent Analysis — Analytical
Methods
• Table 8-2: Total Inorganic Results — Background Soil
• Table 8-3: Total Inorganic Results — Background Rock and PWR
• Table 8-4: Total Inorganic Results —Soil
• Table 8-5: Totals Inorganic Results — Rock
• Table 8-6: Background Soil Sample SPLP Results
• Table 8-7: Soil Sample SPLP Results Below Ash Basin
• Table 8-8: Range of Constituent Concentrations in Soil Samples Beneath the Ash
Basin Compared to Reported Background Concentrations
• Table 8-9: Range of Constituent Concentrations in Soil Samples Beneath the PV
Structural Fill Compared to Reported Background Concentrations
• Table 8-10: Range of Constituent Concentrations in Soil/Rock Samples Beneath the
Dry Ash (Phase II) Landfill Compared to Reported Background Concentrations
• Table 8-11: Range of Constituent Concentrations in Soil Samples Outside the
Waste Boundary Compared to Reported Background Concentrations
9.0 Sediment Characterization
• Table 9-1: Surface Water Sample Results — Totals and Dissolved
• Table 9-2: Sediment Sample Results — Totals
10.0 Groundwater Characterization
• Table 10-1: COls near Marshall Steam Station with their Associated State and
Federal Drinking Water Standards
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin FN
LIST OF TABLES
• Table 10-2: Constituents in Private Wells
• Table 10-3: Iron and Manganese Concentrations
• Table 10-4: Redox Conditions — General Redox Category
• Table 10-5: New Monitoring Well Construction Information
• Table 10-6: Existing Compliance and Voluntary Monitoring Well Construction
Information
• Table 10-7: Groundwater Sample Results — Background — Totals and Dissolved
• Table 10-8: Groundwater Sample Results — Totals and Dissolved
• Table 10-9: Groundwater Results Beneath Dry Ash Landfill (Phase II)
• Table 10-10: Groundwater Field Parameters
• Table 10-11: COI Concentrations Upgradient of the Ash Basin, Dry Ash Landfill
(Phases I and II), and PV Structural Fill
• Table 10-12: COI Concentrations Beneath Ash Basin
• Table 10-13: COI Concentrations Beneath the Dry Ash Landfill (Phase II)
• Table 10-14: COI Concentrations in Downgradient of the Ash Basin
• Table 10-15: COI Concentrations in Voluntary and Compliance Wells
• Table 10-16: Groundwater Sample Results — Speciation
• Table 10-17: Groundwater Sample Results — Radiological
11.0 Hydrogeological Investigation
• Table 11-1: Soil/Material Properties for Ash, Fill, Alluvium, Soil/Saprolite
• Table 11-2: Field Permeability Test Results
• Table 11-3: Slug Test Permeability Results
• Table 11-4: Historic Slug Test Permeability Results
• Table 11-5: Laboratory Permeability Test Results
• Table 11-6: Historic Laboratory Permeability Test Results
• Table 11-7: Total Porosity for Upper Hydrostratigraphic Units (A, F, S, M1, and M2)
• Table 11-8: Estimated Effective Porosity/Specific Yield and Specific Storage for
Upper Hydrostratigraphic Units (A, F, S, M1, and M2)
• Table 11-9: Hydrostratigraphic Layer Properties —Horizontal Hydraulic Conductivity
• Table 11-10: Hydrostratigraphic Layer Properties —Vertical Hydraulic Conductivity
• Table 11-11: Total Porosity, Secondary (Effective) Porosity/Specific Yield, and
Specific Storage for Lower Hydrostratigraphic Units (TZ and BR)
• Table 11-12: Groundwater Velocities
• Table 11-13: Hydraulic Gradients —Vertical
12.0 Screening -Level Risk Assessment
• Table 12-1: Selection of Human Health COPCs — Groundwater
• Table 12-2: Selection of Human Health COPCs — Soil
• Table 12-3: Selection of Human Health COPCs — Surface Water
XiX
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin FN
LIST OF TABLES
• Table 12-4: Selection of Human Health COPCs — Sediment
• Table 12-5: Contaminants of Potential Human Health Concern
• Table 12-6: Selection of Ecological COPCs — Soil
• Table 12-7: Selection of Ecological COPCs — Freshwater
• Table 12-8: Selection of Ecological COPCs — Sediment
• Table 12-9: Contaminants of Potential Ecological Concern
• Table 12-10: Threatened and Endangered Species in Catawba County
13.0 Groundwater Modeling
<No Tables>
14.0 Data Gaps — Conceptual Site Model Uncertainties
<No Tables>
15.0 Planned Sampling for CSA Supplement
• Table 15-1: CSA Supplemental Sampling Plan
16.0 Interim Groundwater Montoring Plan
<No Tables>
17.0 Discussion
<No Tables>
18.0 Conclusions
<No Tables>
19.0 References
<No Tables>
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin
LIST OF APPENDICES
List of Appendices (provided electronically)
Appendix A: Introduction
• NORR Letter
• Summary of Work Plan Submittals and NCDENR-Duke Energy Correspondence
• Revised Groundwater Assessment Work Plan
Appendix B: Receptor Information
• Updated Receptor Survey Report
• NCDENR Well Water Sampling Results
• NCDENR Water Supply Well Tracking Spreadsheet
• Background Water Supply Well Analytical Results
Appendix C: Source Characterization
• Drilling Procedures
• Drilling and Installation Variances
• Soil Mineralogy / Rock Chemistry Methods
Appendix D: Soil and Rock Characterization
• Sampling Procedures
• Sampling Variances
Appendix E: Field and Sampling Quality Assurance / Quality Control
Appendix F: Surface Water and Sediment Characterization
• Sampling Procedures
• Sampling Variances
Appendix G: Groundwater Characterization
• Well Development Procedure
• Well Development Forms
• Well Abandonment Forms
• Sampling Procedure
• Sampling Variances
• Evaluation of Turbidity in Existing Voluntary and Compliance Wells
• Evaluation of Need for Off -site Monitoring Wells
• Statistical Analysis of Groundwater Results
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin
LIST OF APPENDICES
Appendix H: Hydrogeological Investigation
• Boring Logs
• Well Construction Records
• Historical Boring Logs and Well Construction Records
• Soil Physical Lab Reports
• Mineralogy Lab Reports
• Slug Test Reports
• Field Permeability Data
• Fetter -Bear Diagrams — Porosity
• Estimated Seasonal High Groundwater Elevations Calculation
Appendix I: Screening -Level Risk Assessment
• Trustee Letters and Responses
• Checklist for Ecological Assessments / Sampling
Appendix J: Historical Analytical Results Table
Appendix K: Laboratory Reports
Appendix L: Soil Sample and Rock Core Photographs
Appendix M: Certification Form for CSA
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report ���
Marshall Steam Station Ash Basin
LIST OF ACRONYMS AND ABBREVIATIONS
List of Acronyms and Abbreviations
pg/L micrograms per liter
2L Standards 15A NCAC 02L .0202 Groundwater Quality Standards
AMEC
AMEC Environment & Infrastructure
APS
NCDENR DWR Aquifer Protection Section
ASTM
American Society for Testing and Materials
BG
Background
bgs
Below ground surface
BR
Bedrock
CAMA
Coal Ash Management Act
CAP
Corrective Action Plan
CCP
Coal Combustion Products
CCR
Coal Combustion Residuals
COI
Constituent of Interest
COPC
Contaminant of Potential Concern
CSA
Comprehensive Site Assessment
CSM
Conceptual Site Model
DTW
Depth to Water
Duke Energy
Duke Energy Carolinas, LLC
DWM
NCDENR Division of Waste Management
DWR
NCDENR Division of Water Resources
EDR
Environmental Data Resources
EPD
Georgia Environmental Protection Division
EPRI
Electric Power Research Institute
ESH
Estimated Seasonal High
ESL
Estimated Seasonal Low
GSCM
Geochemical Site Conceptual Model
GIS
Geographic Information Systems
HFO
Hydrous ferric oxide
HQ
Hazard Quotient
IMAC
Interim Maximum Allowable Concentration
Kd
Sorption Coefficient
mD
millidarcies
mg/kg
Milligrams per kilogram
MNA
Monitored Natural Attenuation
MSS
Marshall Steam Station
MW
Megawatt
N
Standard Penetration Testing Values
Duke Energy Carolinas, LLC I Comprehensive Site Assessment Report
Marshall Steam Station Ash Basin
���
LIST OF ACRONYMS AND ABBREVIATIONS
NRCS
Natural Resources Conservation Service
NCAC
North Carolina Administrative Code
NCDENR
North Carolina Department of Environment and Natural Resources
NCDHHS
North Carolina Department of Health and Human Services
NCNHP
North Carolina Natural Heritage Program
NORR
Notice of Regulatory Requirements
NPDES
National Pollutant Discharge Elimination System
NTU
Nephelometric Turbidity Unit
NURE
National Uranium Resource Evaluation
PL
Prediction Limit
PMCL
Primary Maximum Contaminant Level
ppb
parts per billion
ppm
parts per million
PSRG
Preliminary Soil Remediation Goal
PWR
Partially Weathered Rock
PWSS
NCDENR DWR Public Water Supply Section
RCRA
Resource Conservation and Recovery Act
REC
Recovery
RL
Reporting Limit
RQD
Rock Quality Designation
RSL
USEPA Regional Screening Level
SCM
Site Conceptual Model
SCS
U.S. Department of Agriculture Soil Conservation Service
SLERA
Screening Level Ecological Risk Assessment
SMCL
Secondary Maximum Contaminant Level
SPLP
Synthetic Precipitation Leaching Procedure
SQL
Sample Quantitation Limit
TCLP
Toxicity Characteristic Leaching Procedure
TDS
Total Dissolved Solids
TZ
Transition Zone
UNC
University of North Carolina
UNCC
University of North Carolina at Charlotte
USDA
U.S. Department of Agriculture
USEPA
U.S. Environmental Protection Agency
USGS
U.S. Geological Survey
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Marshall Steam Station Ash Basin
1.0 INTRODUCTION
1.0 Introduction
Duke Energy Carolinas, LLC (Duke Energy) owns and operates Marshall Steam Station (MSS),
which is located on Lake Norman in Catawba County near the town of Terrell, North Carolina.
MSS began operations in 1965 as a coal-fired generating station and currently operates four
coal-fired units. The coal combustion residual (CCR) material from MSS has historically been
stored in the station's ash basin located to the north of the station and adjacent to Lake Norman.
Discharge from the ash basin is currently permitted by the North Carolina Department of
Environment and Natural Resources (NCDENR) Division of Water Resources (DWR) under the
National Pollutant Discharge Elimination System (NPDES) Permit NC0004987.
Duke Energy has implemented voluntary and NPDES permit -required compliance groundwater
monitoring at MSS. Voluntary groundwater monitoring around the MSS ash basin was
performed from November 2007 until October 2011 (a total of nine sampling events), with
analytical results submitted to NCDENR DWR. Compliance groundwater monitoring required by
the NPDES permit began in February 2011. From February 2011 through June 2015, the
compliance groundwater monitoring wells at MSS have been sampled three times per year for a
total of 14 times as part NPDES permit -required sampling, with results submitted to NCDENR
DWR.
Recent monitoring events have indicated exceedances of 15A NCAC 02L.0202 Groundwater
Quality Standards (2L Standards) at MSS, prompting NCDENR's requirement for Duke Energy
to perform a groundwater assessment at the site and prepare this Comprehensive Site
Assessment (CSA) report. The Coal Ash Management Act of 2014 (CAMA), NC Session Law
2014-122, also directed owners of CCR surface impoundments to conduct groundwater
monitoring and assessment and submit a Groundwater Assessment Report. This CSA is
submitted to meet the requirements of both NCDENR and CAMA.
1.1 Purpose of Comprehensive Site Assessment
The purpose of this CSA is to characterize the extent of contamination resulting from historical
production and storage of coal ash, evaluate the chemical and physical characteristics of the
contaminants, investigate the geology and hydrogeology of the site including factors relating to
contaminant transport, and examine risk to potential receptors and exposure pathways. This
CSA was prepared in general accordance with requirements outlined in the following regulations
and documents:
• Groundwater Classification and Standards, Title 15A NCAC Subchapter 2L;
• Coal Ash Management Act of 2014, N.C. Gen. Stat. §§ 1 30A-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 March 12, 2015; and
• Subsequent meetings and correspondence between Duke Energy and NCDENR.
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1.0 INTRODUCTION
This assessment includes evaluation of possible impacts from the ash basin and related ash
storage facilities, and 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 media encountered within and beyond the ash basin, dry ash landfill
(Phases I and 11), and structural fill waste and compliance boundaries;
• Collection and evaluation of data to supplement the site conceptual model (SCM);
• Update of the receptor survey previously completed in 2014; and
• Completion of a screening -level risk assessment.
Constituents in groundwater were compared to the North Carolina Groundwater Quality
Standards, as specified in 15A NCAC 2L.0202 (2L Standards) or Interim Maximum Allowable
Concentrations (IMACs) established by NCDENR pursuant to 15A NCAC 2L.0202(c). 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.
For this CSA, the source area is defined as the ash basin, dry ash landfill (Phases I and II), and
photovoltaic (PV) structural fill. Source characterization was performed to identify physical and
chemical properties of ash, ash basin surface water, ash porewater, and ash basin seeps. The
analytical results for source characterization samples were compared to 2L Standards or
IMACs, and other regulatory screening levels for the purpose of identifying constituents of
interest (COls) that may be associated with potential impacts to soil, groundwater, and surface
water from the source area. Some COls are present in background and upgradient monitoring
wells and may be naturally occurring, and thus require careful examination to determine
whether their presence downgradient of the source area is naturally occurring or a result of ash
handling and storage.
In addition to evaluating the distribution of constituents across the MSS 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.
1.2 Regulatory Background
1.2.1 NCDENR Requirements
NCDENR DWR regulates wastewater discharges from coal ash ponds to state waters, streams,
and lakes, and requires groundwater monitoring and stormwater management at these facilities
Duke Energy's coal-fired power facilities are regulated through federal NPDES wastewater
permits. These permits require that the facilities must also comply with the state water quality
standards and U.S. Environmental Protection Agency (USEPA) water quality criteria.
Groundwater monitoring is performed at Duke Energy's facilities in accordance with approved
monitoring plans and NPDES permits for each site. Included in these monitoring evaluations is a
determination if site -specific background concentrations (i.e., naturally occurring constituents in
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1.0 INTRODUCTION
the soil profile and groundwater) for various constituents (e.g., iron and manganese) contribute
to reported concentrations. For each facility, if it is determined that activities on the property are
causing noncompliance with NCDENR regulatory requirements, the agency will require the
permittee to perform an assessment and develop and implement a Corrective Action Plan
(CAP) in accordance with state regulations.
1.2.2 Notice of Regulatory Requirements
On August 13, 2014, NCDENR issued a NORR letter notifying Duke Energy that exceedances
of the 2L Standards were reported at 14 coal ash facilities owned and operated by Duke
Energy, including MSS. The NORR stipulated that for each coal ash facility, Duke Energy shall
conduct a CSA following submittal of a Groundwater Assessment Work Plan (Work Plan) and
receptor survey. In accordance with the NORR requirements, a Work Plan was developed, a
receptor survey was performed to identify all receptors within a 0.5-mile radius (2,640 feet) of
the ash basin compliance boundary, and a CSA was conducted for each coal ash facility. The
NORR letter is included in Appendix A.
1.2.3 Coal Ash Management Act Requirements
CAMA requires that ash from Duke Energy coal plant sites located in the State either (1) be
excavated and relocated to fully lined storage facilities or (2) go through a classification process
to determine closure options and schedule. Closure options can include a combination of
excavating and relocating ash to a fully lined structural fill, excavating and relocating the ash to
a lined landfill (on -site or off -site), and/or capping the ash with an engineered synthetic barrier
system, either in place or after being consolidated to a smaller area on -site.
As a component of implementing this objective, CAMA provides instructions for owners of coal
combustion residuals surface impoundments to perform various groundwater monitoring and
assessment activities. Section §1 30A-309.21 1 of CAMA ruling specifies groundwater
assessment and corrective actions, drinking water supply well surveys and provisions of
alternate water supply, and reporting requirements. Section 130A-309.21 1 (a) states:
(a) Groundwater Assessment of Coal Combustion Residuals Surface Impoundments.
— The owner of a coal combustion residuals surface impoundment shall conduct
groundwater monitoring and assessment as provided in this subsection. The
requirements for groundwater monitoring and assessment set out in this
subsection are in addition to any other groundwater monitoring and assessment
requirements applicable to the owners of coal combustion residuals surface
impoundments.
(1) No later than December 31, 2014, the owner of a coal combustion residuals
surface impoundment shall submit a proposed Groundwater Assessment
Plan for the impoundment to the Department for its review and approval. The
Groundwater Assessment Plan shall, at a minimum, provide for all of the
following:
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1.0 INTRODUCTION
a. A description of all receptors and significant exposure pathways.
b. An assessment of the horizontal and vertical extent of soil and
groundwater contamination for all contaminants confirmed to be present
in groundwater in exceedance of groundwater quality standards.
c. A description of all significant factors affecting movement and transport
of contaminants.
d. A description of the geological and hydrogeological features influencing
the chemical and physical character of the contaminants.
e. A schedule for conitnued groundwater monitoring.
f. Any other information related to groundwater assessment required by the
Department.
(2) The Department shall approve the Groundwater Assessment Plan if it
determines that the Plan complies with the requirements of this subsection
and will be sufficient to protect public health, safety, and welfare; the
environment; and natural resources.
(3) No later than 10 days from approval of the Groundwater Assessment Plan,
the owner shall begin implementation of the Plan.
(4) No later than 180 days from approval of the Groundwater Assessment Plan,
the owner shall submit a Groundwater Assessment Report to the Department.
The Report shall describe all exceedances of groundwater quality standards
associated with the impoundment.
1.3 NCDENR-Duke Energy Correspondence
In response to both the NORR letter and CAMA requirements, Duke Energy submitted a Work
Plan to NCDENR on September 25, 2014 establishing proposed site assessment activities and
schedules for the implementation, completion, and submission of a CSA report in accordance
with 15A NCAC 02L.0106(g). NCDENR 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 March 12, 2015. In addition, Duke Energy submitted
proposed adjustments to the CSA guidelines and requested clarifications regarding groundwater
sampling and speciation of selected constituents to NCDENR on May 14 and May 22, 2015.
NCDENR provided responses to these proposed revisions and clarifications in June 2015.
Copies of relevant correspondence including Work Plan submittals are included in Appendix A.
1.4 Approach to Comprehensive Site Assessment
The CSA approach was developed based on the NORR guidelines and CAMA requirements.
Development of the SCM is based on several documents including but not limited to USEPA's
Monitored Natural Attenuation (MNA) of Inorganic Constituents in Groundwater (Vols. 1 and 2)
(USEPA 2007a, 2007b), American Society for Testing and Materials (ASTM) 1689-95 (2014)
Standard Guide for Developing Site Conceptual Models for Contaminated Sites, and comments
received by NCDENR.
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1.0 INTRODUCTION
1.4.1 NORR Guidance
The NORR letter (Appendix A) outlines general guidelines for the CSA report, including
guidance from 15A NCAC 02L .0106(g) as described in Section 1.1. The NORR letter also
includes Guidelines for Comprehensive Site Assessment for those involved in the investigation
of contaminated soil and/or groundwater. The components included in the NORR guidelines
were used in developing the site Work Plan and this CSA report.
1.4.2 USEPA Monitored Natural Attenuation Approach
In accordance with NCDENR requirements and the March 12, 2015 Conditional Approval letter
(Appendix A), elements of the USEPA's MNA approach have been utilized as part of the
investigation associated with the CSA. The MNA approach is described in the USEPA's
guidance document entitled Monitored Natural Attenuation of Inorganic Contaminants in
Groundwater (Vols. 1 and 2) (USEPA 2007a, 2007b). MNA may be used as a component to
meet corrective action requirements if site conditions meet the requirements associated with
use of MNA. The approach involves a detailed analysis of site characteristics controlling and
sustaining attenuation to support evaluation and selection of MNA as part of a cleanup action for
inorganic contaminant plumes in groundwater (USEPA 2007a, 2007b). The site characterization
is conducted in a step -wise manner to facilitate collection of data necessary to progressively
evaluate the effectiveness of natural attenuation processes within the site aquifer(s). Four
general elements are included in the tiered site analysis approach:
• Demonstration of active contaminant removal from groundwater and dissolved plume
stability;
• Determination of the mechanism and rate of attenuation;
• Determination of the long-term capacity for attenuation and stability of immobilized
contaminants, before, during, and after any proposed remedial activities; and
• Design of a performance monitoring program, including defining triggers for assessing
the remedial action strategy failure, and establishing a contingency plan.
Duke Energy will evaluate the USEPA MNA approach further during preparation of the CAP.
1.4.3 ASTM Conceptual Site Model Guidance
ASTM standard guidance document E1689-95 Standard Guide for Developing Conceptual Site
Models for Contaminated Sites (ASTM 2014) was used as a general component of this CSA.
The guidance document provides direction in developing conceptual site models used for the
integration of technical information from multiple sources, selection of sampling locations to
establish background concentrations of substances, identification of data needs and guidance of
data collection activities, and evaluation of risks to human and environmental health posed by a
contaminated site. According to ASTM Ell 689-95, six basic activities are associated with
developing a conceptual site model:
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1.0 INTRODUCTION
• Identification of potential contaminants;
• Identification and characterization of the source(s) of contaminants;
• Delineation of potential migration pathways through environmental media, such as
groundwater, surface water, soils, sediment, biota, and air;
• Establishment of background areas of contaminants for each contaminated medium;
• Identification and characterization of potential environmental receptors (human and
ecological); and
• Determination of the limits of the study area or system boundaries.
Development of a conceptual site model is typically iterative and the complexity of the model
should be consistent with the complexity of the site and available data. Information gained
through site investigation activities is used to characterize existing physical, biological, and
chemical systems at a site. The conceptual site model describes and integrates processes that
determine contaminant releases, contaminant migration, and environmental receptor exposure
to contaminants. Development of the model is essential to determine potential exposure routes
and identify possible impacts to human health and the environment (ASTM 2014).
The conceptual site model is used to integrate site information, identify data gaps, and
determine whether additional information is needed at the site. The model is also used to
facilitate selection of remedial alternatives and effectiveness of remedial actions in reducing the
exposure of environmental receptors to contaminants (ASTM 2014).
This CSA was conducted in accordance with the conditionally approved Work Plan to meet the
NCDENR, NORR, and CAMA regulatory requirements described in Section 1.2, and using the
NORR, USEPA, and ASTM approaches described above. This assessment information will be
used to develop a CAP, to be submitted separately, for the MSS site that will provide a
demonstration of these criteria in support of the recommended site remedy.
Data obtained from sampling during this CSA are compared to federal and state regulatory
standards shown in Table 1-1. Beginning in Section 7.0, laboratory results are compared to the
above -referenced regulatory standards and discussed as either "exceeding" or "not exceeding"
those standards. The evaluation of exceedances of these standards forms the basis for
determining the need for additional work described later in this document.
1.5 Limitations and Assumptions
Development of this CSA is based on information provided to HDR by both public and private
entities including universities, federal, state and local governments, and information and
analytical reports generated by Duke Energy. HDR assumes the information in these
documents to be accurate and reliable. This information was used to estimate exposure routes
and migration pathways in the subsurface. This CSA was developed using a standard of care
ordinarily used by engineering practice under the same or similar circumstances, but may
include assumptions based on the accuracy and reliability of data from various entities. CAMA
Section §1 30A-309.21 1 (a)(4) requires that "No later than 180 days from approval of the
Groundwater Assessment Plan, the owner shall submit a Groundwater Assessment Report to
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1.0 INTRODUCTION
the Department." The schedule dictated by CAMA is compressed; therefore, data interpretation
is limited and subject to change upon receipt of additional data in subsequent rounds of
sampling and additional data collected to resolve data gaps identified in Section 14.0. The
additional data will be used to inform the corrective actions identified in the CAP.
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2.0 SITE HISTORY AND DESCRIPTION
2.0 Site History and Description
This section provides a description of the MSS site based on relevant historical data and
representative information. The purpose of this characterization is to familiarize readers with the
MSS site.
2.1 Site Location, Acreage, and Ownership
The MSS site is located on the west bank of Lake Norman near the town of Terrell, Catawba
County, North Carolina (Figure 2-1). The entire MSS site is approximately 1,446 acres in area
and is owned by Duke Energy. Based on the NORR Guideline heading, Provide a history of
property ownership and use under the Site History and Source Characterization, this CSA report
includes a history of Duke Energy ownership and site usage. As of the date of this report,
multiple inquiries have not revealed site history information prior to Duke Energy ownership.
In addition to the power plant property, Duke Energy owns and operates the Catawba-Wateree
Hydroelectric Project (Federal Energy Regulatory Commission [FERC] Project No. 2232). Lake
Norman reservoir is part of the Catawba-Wateree project and is used for hydroelectric
generation, a source of cooling water for MSS and Duke Energy's McGuire Nuclear Station,
municipal water supply, and recreation. Duke Energy performed a review of property ownership
within the FERC project boundary property surrounding the ash basin compliance boundary.2
The review indicated that Duke Energy owns all of the property within the ash basin compliance
boundary that is also located within the FERC project boundary. The Duke Energy property
boundary and ash basin compliance boundary are shown on Figure 2-2.
2.2 Site Description
MSS is a four -unit, coal-fired electric generating plant. The first two units (Units 1 and 2) began
operation in 1965 and 1966, generating 350 MW each. The remaining units (Units 3 and 4)
began operation in 1969 and 1970, generating 648 MW each. Improvements to the plant since
1970 have increased the electric generating capacity to 2,090 MW.
The MSS ash basin is situated between MSS to the south, and topographic divides located
along Sherrills Ford Road to the west, along Island Point Road to the north, and Duke Energy
property to the east. Natural topography at the site generally slopes downward from these
divides to the ash basin and toward Lake Norman (Figure 2-2). The ash basin system is
described further in Section 3.2. A 1954 USGS topographic map depicting the site prior to
construction of the ash basin is shown on Figure 2-3.
The air pollution control system for the coal-fired units at MSS includes a flue gas
desulfurization (FGD) system that was placed into operation in 2007. Coal is delivered to the
station by a railroad line. Other areas of the site are occupied by facilities supporting the
production or transmission of power (one switchyard and associated transmission lines), the
2 The ash basin compliance boundary is defined in accordance with Title15A NCAC 02L .0107(a) as
being established at either 500 feet from the waste boundary or at the property boundary, whichever is
closer to the waste.
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2.0 SITE HISTORY AND DESCRIPTION
FGD wastewater treatment system, and the gypsum handling station (associated with the FGD
system). A site features map is included as Figure 2-4.
2.3 Adjacent Property, Zoning, and Surrounding Land Uses
The area surrounding MSS generally consists of residential properties, undeveloped land, and
Lake Norman. Properties located within a 0.5-mile radius of the MSS ash basin compliance
boundary generally consist of undeveloped land and Lake Norman to the east, undeveloped
land and residential properties located to the north and west, portions of the MSS site (outside
the compliance boundary), undeveloped land, and residences to the south, and commercial
properties to the southeast along North Carolina Highway 150. Figure 2-5 depicts properties
surrounding the MSS site.
2.4 Adjacent Surface Water Bodies and Classifications
Surface water features located on the site are shown on Figure 2-2. The site is located along
the shores of Lake Norman which is part of the Catawba River watershed. The ash basin is
adjacent to Lake Norman. Surface water classifications in North Carolina are promulgated in
Title15A NCAC Subchapter 2B. The surface water classification for the Catawba River is Class
WS-IV; B and CA waters. Class WS-IV waters are protected as water supplies which are
generally in moderately to highly developed watersheds. Point source discharges of treated
wastewater are permitted pursuant to Rules .0104 and .0211 of this Subchapter. Local
programs to control nonpoint sources and stormwater discharges of pollution are required
suitable for all Class C uses (i.e., freshwaters protected for secondary recreation, fishing,
aquatic life including propagation and survival, and wildlife). Class B waters are protected for all
Class C uses in addition to primary recreation. Primary recreational activities include swimming,
skin diving, water skiing, and similar uses involving human body contact with water where such
activities take place in an organized manner or on a frequent basis. A Critical Area is described
as being within 0.5 miles of Class B waters that drains to water supplies as measured from the
normal pool elevation of the reservoir.
2.5 Meteorological Setting
According to the U.S. Department of Agriculture Soil Conservation Service (USDA-SCS) soil
survey (1975) the average summer temperature in Catawba County is 78°F and the average
daily maximum temperature is 88°F. During winter, the average temperature is 420F and the
average daily minimum temperature is 31 OF. Precipitation is well distributed throughout the
county and throughout the year, and averages approximately 49.2 inches per year. Much of the
rainfall during the growing season (April to November) comes from thunderstorms. The average
relative humidity in midafternoon is approximately 67 percent, with humidity reaching higher
levels at night. The prevailing wind is from the northwest, and average wind velocity is
approximately 8 miles per hour (USDA-SCS 1974).
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2.0 SITE HISTORY AND DESCRIPTION
2.6 Hydrologic Setting
The MSS site is bounded by Lake Norman to the southeast, Sherrills Ford Road to the west,
and Island Point Road to the north. The plant's discharge canal is located southeast of the ash
basin dam and north of North Carolina Highway 150. Topography at the MSS site ranges from
approximately 880 to 900 feet elevation near the west and north boundaries of the site to an
approximate low elevation of 760 feet at the shoreline of Lake Norman. Topography generally
slopes from a northwest to southeast direction with an elevation change of approximately 120 to
140 feet over an approximate distance of 1.5 miles. Based on the slope -aquifer system,
groundwater at the site is expected to flow from topographic divides along Sherrills Ford Road
(west) and Island Point Road (north) towards the ash basin and into Lake Norman. Site
topography prior to construction of the ash basin (Figure 2-3) indicates that surface water
historically flowed from the northern and western boundaries of the site toward Lake Norman to
the southeast.
One unnamed tributary that flows into Lake Norman is located approximately 400 linear feet
east of the dry ash landfill (Phase 1) (described in Section 3.2.2). The dry ash landfill (Phase 1) is
located on a topographic high adjacent to, and east of, the ash basin. Groundwater
potentiometric surface contours generally mimic surface topography in this area of the site and
indicate groundwater flows toward the unnamed tributary and Lake Norman. A more detailed
discussion of groundwater flow at the MSS site is provided in Section 6.0.
Overall, surface water drainage in the vicinity of the ash basin generally follows site topography
and flows from the northwest to the southeast except where natural drainage patterns have
been modified by the ash basin or other construction. The full operating pond elevation for the
active ash basin is approximately 790 feet. The normal water elevation of Lake Norman is
approximately 760 feet.
Water levels within the ash basin have fluctuated 1.34 feet from 2000 until 2015, ranging from
788.26 to 789.60 feet since 2000.
2.7 Permitted Activities and Permitted Waste
Duke Energy is authorized to discharge wastewater from MSS to receiving waters designated
as the Catawba River in accordance with NPDES Permit NC0004987 dated January 18, 2011.
The NPDES permit authorizes the following discharges in accordance with effluent limitations,
monitoring requirements, and other conditions set forth in the permit:
• Once -through cooling water and intake screen backwash through Outfall 001;
• Treated wastewater (consisting of metal cleaning wastes, coal pile runoff, ash transport
water, domestic wastewater, low volume wastes, and FGD wet scrubber wastewater
through internal Outfall 004 (upstream of the ash settling basin);
• Yard sump overflows through Outfalls 002A and 00213;
• Non -contact cooling water from the induced draft (ID) fan control house through Outfall
003; and
Im
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2.0 SITE HISTORY AND DESCRIPTION
• Discharge from the treatment works through the ash settling basin into the Catawba
River (i.e., Lake Norman at this point along the Catawba River Basin) via Outfall 002.
Discharge locations to Lake Norman (NPDES Outfalls 001 and 002) are shown on Figure 2-4
Two active permitted landfills (the FGD Residue Landfill and Industrial Landfill No. 1), one
closed dry ash landfill consisting of two units (dry ash landfill Phases I and II), one closed
demolition and construction debris landfill, one closed asbestos landfill, and one fly ash
structural fill unit (PV structural fill) are located partially or wholly outside the ash basin footprint
Further details regarding these waste management units are included in Section 3.2.
Duke Energy is permitted to discharge stormwater to the Catawba River in accordance with
NPDES Draft Permit NCS000548 dated May 15, 2015. Any other point source discharge to
surface waters of the state is prohibited unless it is an allowable non-stormwater discharge or is
covered by another permit, authorization, or approval.
2.8 NPDES and Surface Water Monitoring
The NPDES program regulates wastewater discharges to surface waters to ensure that surface
water quality standards are maintained. The NPDES permitting program requires that permits
be renewed every five years. The most recent NPDES permit (described above) for MSS
became effective January 18, 2011. A draft permit was issued by NCDENR dated May 5, 2015.
The current NPDES permit requires surface water sampling and discharge monitoring reporting
as part of the permit conditions (see section 2.9). The sample locations, parameters, and
constituents to be measured and analyzed, and the requirements for sampling frequency and
reporting results are outlined in the permit.
NPDES Flow Diagram
The NPDES flow diagram from the submitted NPDES permit application for MSS is provided on
Figure 2-6. The current NPDES permit allows discharges of once -through cooling water (Outfall
001), ash settling pond water (Outfall 002), and ID fan control house cooling water (Outfall 003)
Once -through cooling water (Outfall 001) and ash settling pond water (Outfall 002) discharge
directly to the Catawba River (Lake Norman). Wastewater inputs to the ash settling pond from
MSS consists of ash sluice water, miscellaneous equipment cooling wastewater, boiler and
turbine sumps, sanitary wastes, and other low volume wastes.
Low volume waste sources include, but are not limited to: wastewater from wet scrubber air
pollution control systems, ion exchange water treatment system, water treatment evaporator
blowdown, laboratory and sampling stream, boiler blowdown, floor drains, and recirculating
service water systems. Wastewater from the wet scrubber air pollution control system is treated
using a physical/chemical treatment followed by a bioreactor (internal Outfall 004). The
remaining waste streams receive some treatment such as neutralization, oil separation, as
necessary, and discharge to the ash basin and subsequently to Lake Norman.
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2.0 SITE HISTORY AND DESCRIPTION
The ash settling pond accommodates flows from two yard drain sumps, an ash removal system,
FGD Waste Water treatment system, low volume wastes and non -point source storm water.
Total average influent from these sources is approximately 8.3 MGD; however, at times, due to
unit loads, rainfall, evaporation and seepage of ash basin ponds, the amount of effluent may be
different than influent volumes.
2.10 History of Site Groundwater Monitoring
The location of the ash basin voluntary and compliance monitoring wells, the ash basin waste
boundary, and the compliance boundary are shown on Figure 2-7. The compliance boundary for
groundwater quality at the MSS ash basin site is defined in accordance with Title 15A NCAC
02L .0107(a) as being established at either 500 feet from the waste boundary or at the property
boundary, whichever is closer to the waste.
2.10.1 Voluntary Groundwater Monitoring Wells
Monitoring wells MW-6S, MW-6D, MW-7S, MW-7D, MW-8S, MW-8D, MW-9S, and MW-9D
were installed by Duke Energy in 2006 as part of a voluntary monitoring system. Duke Energy
implemented voluntary groundwater monitoring around the MSS ash basin from November
2007 until October 2011. During this period, the voluntary groundwater monitoring wells were
sampled a total of nine times and the analytical results were submitted to NCDENR DWR.
2.10.2 Compliance Groundwater Monitoring Wells
Groundwater monitoring as required by the MSS NPDES Permit NC0004987 began in February
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 (provided in Table 2-1).
Locations for the compliance groundwater monitoring wells were approved by the former
NCDENR DWR Aquifer Protection Section (APS).
The compliance groundwater monitoring system for the MSS ash basin consists of the following
wells: MW-4, MW-4D, MW-10S, MW-1 OD, MW-11 S, MW-11 D, MW-12S, MW-12D, MW-13S,
MW-13D, MW-14S, and MW-14D. All compliance monitoring wells listed in Table 2-1 are
sampled three times per year (February, June, and October). Analytical results are submitted to
the NCDENR DWR before the last day of the month following the month of sampling for all
compliance monitoring wells. The compliance groundwater monitoring is performed in addition
to the normal NPDES monitoring of the discharge flows from the ash basin.
From February 2011 through June 2015, the compliance groundwater monitoring wells at MSS
have been sampled a total of 14 times. During this period, these monitoring wells were sampled
in:
• February, June, and October 2011
• February, June, and October 2012
• February, June, and October 2013
• February, June, and October 2014
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2.0 SITE HISTORY AND DESCRIPTION
• February, June 2015
One or more 2L Standards have been exceeded in groundwater samples collected from each of
the compliance monitoring wells. Exceedances have occurred for boron, iron, manganese, pH,
sulfate, thallium, and/or total dissolved solids (TDS). Table 2-2 presents exceedances measured
from February 2011 through June 2015.
With the exception of monitoring wells MW-4 and MW-4D, all the compliance monitoring wells
were installed in 2010. Monitoring well MW-4 was installed by Duke Energy in 1989 as part of
the Marshall Dry Ash Landfill (Permit No. 1804) groundwater monitoring network. Monitoring
well MW-4D was installed by Duke Energy in 2006 as part of a voluntary monitoring system.
Based on the locations of monitoring wells MW-4 and MW-4D relative to the ash basin, they
were incorporated into the ash basin compliance monitoring network.
Monitoring wells MW-4, MW-10S, MW-11 S, MW-12S, MW-13S, and MW-14S were installed
with 10-foot to 15-foot well screens placed above auger refusal to monitor the shallow flow layer
within the saprolite.
Monitoring wells MW-4D3, MW-1 OD, MW-11 D, MW-12D, MW-13D, and MW-14D were installed
with 5-foot well screens placed in the uppermost region of the fractured rock transition zone (TZ
— deep flow layer).
All compliance monitoring wells were installed at or near the compliance boundary. MW-10S
and MW-1 OD are located southeast of the ash basin near the shore of Lake Norman. MW-14S
and MW-14D are located east of the ash basin and the dry ash landfill. Monitoring wells MW-
11 S, MW-11 D, MW-12S, MW-12D, MW-13S, and MW-13D are located along the western
compliance and property boundary upgradient of the ash basin.
2.11 Assessment Activities or Previous Site Investigations
Between 1988 and 2015, several environmental incidents (i.e., releases) occurred at the site
that have initiated notifications to NCDENR or required a subsurface investigation. The historical
incidents have generally consisted of releases that had potential to impact soil and groundwater
at the site, waters of the U.S., or occurred within a containment structure. A summary of the
historical on -site environmental incidents is provided in Table 2-3.
Duke Energy was notified in a letter dated November 9, 2011 from NCDENR Division of Waste
Management (DWM) that exceedances of 2L Standards were reported in samples collected
from compliance groundwater monitoring wells at the dry ash landfill (Phases I and 11) and the
FGD landfill. Descriptions of the dry ash landfill and FGD landfill are summarized in Sections
3.2.2 and 3.2.3, respectively. NCDENR requested that Duke Energy submit groundwater
assessment work plans for each of these landfills to the DWM Solid Waste Section. The
requested work plans were submitted by Duke Energy on February 9, 2012 and approved by
DWM on February 20, 2012 (FGD landfill) and March 23, 2012 (dry ash landfill). The
3 S&ME, Inc., Ash Basin Monitoring Well Installation, Duke Power -Marshall Steam Station, S&ME Project
No. 1356-06-834, December 4, 2006.
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2.0 SITE HISTORY AND DESCRIPTION
assessment of groundwater exceedances associated with the FGD landfill was submitted to
NCDENR on July 12, 2012. The assessment associated with the dry ash landfill was submitted
to NCDENR on December 21, 2012.
In a letter dated March 16, 2012, the former NCDENR DWR APS requested Duke Energy begin
additional assessment activities at stations where measured and modeled concentrations of
groundwater constituents exceeded the 2L Standards at the compliance boundary. Duke
Energy submitted Proposed Groundwater Assessment Work Plan, Duke Energy Carolinas, LLC,
Marshall Steam Station Ash Basin, NPDES Permit NC 0004987 (dated March 15, 2013) to
address this request by NCDENR for MSS.
2.12 Decommissioning Status
In accordance with CAMA, Duke Energy is required to implement closure and remediation of the
MSS ash basin by no later than December 31, 2029. Closure for the MSS ash basin was not
defined in CAMA. However, CAMA does require Duke Energy to submit a proposed closure
plan such that NCDENR can prioritize site closure based on risk classifications.
No later than December 31, 2015, NCDENR is to develop proposed risk -ranking classifications
for all CCR surface impoundments, including active and retired sites, for the purpose of closure
and remediation. A schedule for closure and required remediation will then be made based on
the degree of risk to public health, safety and welfare, the environment, and natural resources
posed by the impoundments. The schedule will prioritize closure and required remediation of
impoundments that pose the greatest risk.
The risk -ranking classification for the MSS ash basin will be based upon this CSA and the CAP,
along with nine other considerations detailed in CAMA Section 130A-309.213(a), such as
structural condition and hazard potential of the impoundment. The risk classification outcomes
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.
(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. Unrelated, but similar to CAMA requirements, the USEPA
CCR Rule requires Closure Plans to be developed and placed on a public website for most
North Carolina coal ash sites, including MSS, by October 2016.
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3.0 SOURCE CHARACTERISTICS
3.0 Source Characteristics
This section provides a general description of the MSS coal combustion and ash handling
system, the general physical and chemical properties of ash, and the MSS ash basin to
characterize primary sources of contamination on the site.
3.1 Coal Combustion and Ash Handling System
Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and conveyed
to the burner area of a boiler. The smaller particles produced by coal combustion, referred to as
fly ash, are carried upward in the flue gas and are captured by an air pollution control device,
such as an electrostatic precipitator or FGD system. The larger particles of ash that fall to the
bottom of the boiler are referred to as bottom ash.
Coal ash residue from the coal combustion process has historically been disposed in the MSS
ash basin. Fly ash from the electrostatic precipitators was collected in hoppers. Bottom ash and
boiler slag was collected in the bottom of the boilers. After collection, both fly ash and bottom
ash/boiler slag were sluiced to the ash basin using conveyance water withdrawn from Lake
Norman. Refer to Figure 2-4 for a depiction of these features.
During operations of the coal-fired units, the sluice lines discharged the water/slurry and other
flows to the southwest portion of the ash basin. Inflows to the ash basin are highly variable due
to variability in station operations and weather.
3.2 Description of Ash Basin and Other Ash Storage Areas
The ash basin system at MSS consists of a single cell impounded by an earthen dike located on
the southeast end of the ash basin. The ash basin system is located north of the power plant.
Inflows from the station to the ash basin are discharged into the southwest portion of the ash
basin.
Discharge from the ash basin is through a concrete discharge tower located in the eastern
portion of the ash basin. The concrete discharge tower drains through a 30-inch-diameter
slip -lined corrugated metal pipe which discharges into Lake Norman. The ash basin pond
elevation is controlled by the use of concrete stoplogs in the discharge tower.
The following sections provide additional details of the MSS ash basin system, ash storage
areas, and other waste management units.
3.2.1 Ash Basin
The initial MSS ash basin was constructed in 1965 by building an earthen dike at the confluence
where Holdsclaw Creek historically entered the Catawba River. The earthen dike was
constructed to impound water and ash was sluiced to the basin. In general, the ash basin is
located in a historical depression formed from Holdsclaw Creek and small tributaries that fed the
creek. The basin has a dendritic shape consisting of coves of deposited ash, dikes which
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3.0 SOURCE CHARACTERISTICS
impound ash in portions of the basin, and four main areas of ponded water. The area contained
within the ash basin waste boundary is approximately 394 acres.
All coal ash from MSS was disposed of in the ash basin from approximately 1965 until 1984. 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 Lake Norman. Since 1984, fly ash has
mainly been disposed of in the on -site dry ash landfills (described below) and bottom ash has
continued to be sluiced to the ash basin.
While FGD residue is not placed in the ash basin, contact stormwater and leachate from the
FGD landfill, along with FGD wastewater treatment system effluent, are routed to the ash basin.
The FGD residue produced by the air treatment system at MSS is primarily gypsum
(CaSO4•H20) and is sold for re -use or disposed of in one of the onsite landfills. Bottom ash is
sluiced to concrete pits where the water is allowed to decant and then flow to the ash basin via
a discharge canal. Bottom ash is then excavated from the pit and discharge canal that flows to
the ash basin, and sold for off -site beneficial reuse or used for roads at the ash basin facility.
During operations, the sluice water/ash slurry (and other flows) is discharged into the southwest
portion of the ash basin.
3.2.2 Dry Ash Landfill
Two unlined ash landfill units, referred to as the Marshall dry ash landfill (NCDENR Division of
Solid Waste Permit No. 1804-INDUS), are located adjacent to the east (Phase 1) and northeast
(Phase II) portions of the ash basin. Phase I contains approximately 280,000 tons of fly ash,
which was placed from September 1984 through March 1986. Placement of ash in the Phase II
areas began around March 1986 and was completed in 1999. Phase 11 contains approximately
2,515,000 tons of fly ash. The approximate boundaries of Phase I and II units are shown on
Figures 2-2 and 2-7. The landfill units were constructed prior to the requirement for lining
industrial landfills and were closed with a soil cover system.
3.2.3 FGD Landfill
The FGD landfill (NCDENR Division of Solid Waste Permit No. 1809-INDUS) is located to the
west of the ash basin. In general, the topography of this landfill site slopes from the west-
northwest to the east-southeast towards the MSS ash basin. The landfill is currently in
operation, but is planned to cease operation on October 18, 2015. The landfill is permitted to
receive the following types of waste generated at Duke Energy Corporation facilities: FGD
residue (gypsum), clarifier sludge, fly ash, bottom ash, construction and demolition waste,
asbestos waste, mill rejects (pyrites), waste limestone material, land clearing and inert debris,
boiler slag, ball mill rejects, sand blast material, and coal waste. The landfill is constructed with
an engineered liner system. Contact stormwater and leachate are collected and piped or
discharged to the ash basin.
As a condition of the permit to operate the FGD landfill, leachate sampling is performed twice
per year in March and September. Since 2012, the FGD landfill leachate has been sampled six
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3.0 SOURCE CHARACTERISTICS
times. Leachate sample results are provided in Appendix J. Note that the FGD landfill leachate
was sampled only once in 2013.
3.2.4 Industrial Landfill No. 1
The Industrial Landfill No. 1 (NCDENR Permit No. 1812-INDUS) is located adjacent to the north
portion of the ash basin. The landfill was constructed with a Ieachate collection and removal
system and a three -component liner system where the components consist of a primary
geomembrane, secondary geomembrane (with a leak detection system between them), and soil
liner. The landfill is permitted to receive the following types of waste generated at Duke Energy
Corporation facilities: fly ash, bottom ash, FGD residue, FGD clarifier sludge, asbestos material,
land clearing and inert debris, coal mill rejects, waste limestone material, boiler slag,
construction and demolition waste, sand blast material, ball mill rejects, coal waste, and pyrites.
The landfill was constructed over portions of residual material and over portions of the ash
basin. The subgrade for portions of this landfill were constructed of fly ash under the structural
fill rules found in 15A NCAC 13B .1700 et seq. Contact stormwater and Ieachate are collected
and piped to the ash basin.
3.2.5 Demolition Landfill
The demolition landfill (NCDENR Permit No. 1804-INDUS) is located adjacent to the north
portion of the ash basin directly north of the dry ash landfill (Phase II). The landfill received
construction and demolition waste from MSS starting in September 1984. The landfill was
closed with a soil cap in 2008.
3.2.6 Asbestos Landfill
The asbestos landfill (NCDENR Permit No. 1804-INDUS) is located adjacent to the north portion
of the ash basin and adjacent to the demolition landfill. The landfill received asbestos waste
from MSS and other Duke Energy facilities starting in December 1987. The landfill was closed
with a soil cap in 2008.
3.2.7 Photovoltaic Farm Structural Fill
The photovoltaic farm structural fill (PV structural fill) was constructed of fly ash under the
structural fill rules found in 15A NCAC 13B .1700 et seq and is located adjacent to and partially
on top of the northwest portion of the ash basin. The PV structural fill is used for renewable
energy production and contains a solar panel field on the south portion of the structural fill unit.
Placement of dry ash in the structural fill began in October 2000. The structural fill was
completed and closed in February 2013.
3.3 Physical Properties of Ash
Ash in the MSS ash basin consists of fly ash and bottom ash produced from the combustion of
coal. The physical and chemical properties of coal ash result from reactions that occur during
the combustion of the coal and subsequent cooling of the flue gas. In general, coal is dried,
pulverized, and conveyed to the burner area of a boiler for combustion. As described in Section
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3.1, material that forms larger particles of ash and falls to the bottom of the boiler is referred to
as bottom ash. Smaller particles of ash, known as fly ash, are carried upward in the flue gas and
are captured by an air pollution control device.
Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash (EPRI
1993). Typically 65 to 90 percent of fly ash has particle sizes that are less than 0.010 millimeter
(mm). In general, fly ash has a grain size distribution similar to that of silt. The remaining 20 to
30 percent of ash produced is considered to be bottom ash. Bottom ash consists of angular
particles with a porous surface and is normally gray to black in color. Bottom ash particle
diameters can vary from approximately 0.05 to 38 millimeters. In general, bottom ash has a
grain size distribution similar to that of fine gravel to medium sand (EPRI 1995).
Based on published literature not specific to this site, the specific gravity of fly ash typically
ranges from 2.1 to 2.9 and the specific gravity of bottom ash typically ranges from 2.3 to 3.0.
The permeability of fly ash and bottom ash vary based on material density, but would be within
the range of a silt -sand -gravel with a similar gradation, grain size distribution, and density (EPRI
1995). Permeability and other physical properties of the ash found in the MSS ash basin are
presented in later sections of this report.
3.4 Chemical Properties of Ash
The specific mineralogy of coal ash varies based on many factors including the chemical
composition of the coal, which is directly related to the geographic region where the coal was
mined, the type of boiler where the combustion occurs (i.e., thermodynamics of the boiler), and
air pollution control technologies employed.
The overall chemical composition of coal ash resembles that of siliceous rocks from which it
was derived, particularly shale. Oxides of silicon, aluminum, iron, and calcium make up more
than 90 percent of most siliceous rocks, soils, fly ash, and bottom ash. Other major and minor
elements (sulfur, sodium, potassium, magnesium, titanium) make up an additional 8 percent,
while trace constituents account for less than 1 percent. The following constituents are
considered to be trace elements: arsenic, barium, cadmium, chromium, lead, mercury,
selenium, copper, manganese, nickel, lead, vanadium, and zinc (EPRI 2010).
According to Duke Energy, the MSS plant has typically burned bituminous coal from Central
Appalachia, Northern Appalachia, and Illinois Basin sources.
The majority of fly ash particles are glassy spheres mainly composed of amorphous or glassy
aluminosilicates, crystalline matter, and carbon. Figure 3-1 presents a photograph of ash
collected from the ash basin at Duke Energy's Cliffside Steam Station showing a mix of fly ash
and bottom ash at 10 pm and 20 pm magnifications. The coal source generally used at Cliffside
Steam Station is similar to the sources used at MSS. The glassy spheres can be observed in
the photograph. The glassy spheres are generally resistant to dissolution. During the later
stages of the combustion process and as the combustion gases are cooling after exiting the
boiler, molecules from the combustion process condense on the surface of the glassy spheres.
These surface condensates consist of soluble salts (e.g. calcium (Ca2+), sulfate (S042-), metals
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3.0 SOURCE CHARACTERISTICS
(copper (Cu), zinc (Zn), and other minor elements (e.g., boron (B), selenium (Se), and arsenic
(As)) (EPRI 1994).
The major elemental composition of fly ash (approximately 95 percent by weight) is composed
of mineral oxides of silicon, aluminum, iron, calcium. Oxides of magnesium, potassium, titanium
and sulfur comprise approximately 4 percent by weight (EPRI 1995). Trace elemental
composition typically is approximately 1 percent by weight and may include arsenic, antimony,
barium, boron, cadmium, chromium, copper, manganese, mercury, nickel, lead, selenium,
silver, thallium, zinc, and other elements. For comparison, Figure 3-2 shows the elemental
composition of fly ash and bottom ash compared with typical values for shale and volcanic ash.
Table 3-1 shows the bulk composition of fly ash and bottom ash compared with typical values
for soil and rock. In addition to these constituents, fly ash may contain unburned carbon.
Bituminous coal ash typically yields slightly acidic to alkaline solutions with pH levels ranging
from approximately 5 to 10 on contact with water.
The geochemical factors controlling the reactions associated with leaching of ash are complex.
Factors such as the chemical speciation of the constituent, solution pH, solution -to -solid ratio,
and other factors control the chemical concentration of the resultant solution. Constituents that
are held on the glassy surfaces of fly ash such as boron, arsenic, and selenium may initially
leach more readily than other constituents. As noted in Table 3-1, aluminum, silicon, calcium,
and iron represent the larger fractions of fly ash and bottom ash by weight. The presence of
calcium may limit the release of arsenic by forming calcium -arsenic precipitates. Formation of
iron hydroxide compounds may also sequester arsenic and retard or prevent release of arsenic
to the environment. Similar processes and reactions may affect other constituents of concern;
however, certain constituents such as boron and sulfate will likely remain highly mobile.
In addition to the variability that might be seen in the mineralogical composition of the ash,
which is based on different coal types, different age of ash in the basin, and other factors, it is
anticipated that the chemical environment of the MSS ash basin varies over time, distance, and
depth.
EPRI (2010) reports that 64 samples of coal combustion products (including fly ash, bottom ash,
and FGD residue) from 50 different power plants were subjected to USEPA Method 1311
Toxicity Characteristic Leaching Procedure (TCLP) leaching and no TCLP result exceeded the
TCLP hazardous waste limit. Figure 3-3 provides the results of that testing. The report also
presents the trace element concentrations for fly ash and bottom ash compared to USEPA
Residential Soil Screening Levels (RSLs) for ingestion and dermal exposure. Figure 3-4 shows
the 10th to 90th percentile range for trace element concentrations (milligrams per kilogram
[mg/kg]) in fly ash and the associated USEPA RSLs. The trace element concentrations for
arsenic were greater than the RSL for arsenic. The RSLs of the remaining constituents were
greater than or within the 10th to 90th percentile range for their trace element concentrations.
Figure 3-5 shows similar data for bottom ash. As with fly ash, the trace element concentrations
for arsenic in bottom ash were greater than the RSL for arsenic. The RSL for chromium was
within the 10t" and 901" percentile range of concentrations for chromium in bottom ash. The 10tn
to 90t, percentile range for the remaining constituents were below their respective RSLs.
Site -specific ash data is discussed in Section 7.0 of this report.
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4.0 RECEPTOR INFORMATION
4.0 Receptor Information
Section §130A-309.201(13) of the CAMA defines receptor as "any human, plant, animal, or
structure which is, or has the potential to be, affected by the release or migration of
contaminants. Any well constructed for the purpose of monitoring groundwater and contaminant
concentrations shall not be considered a receptor." In accordance with the NORR CSA
guidance, receptors cited in this section refer to public and private water supply wells (including
irrigation wells and unused wells) and surface water features. Refer to Section 12.0 for a
discussion of receptors that were evaluated as part of this CSA effort.
Note that one of the NORR CSA guidance requirements for the receptor survey is that
subsurface utilities are to be mapped within 1,500 feet of the known extent of contamination in
order to evaluate the potential for preferential pathways. For MSS, the subsurface utilities are
not viewed as potential preferential pathways for contaminant migration through underground
utility corridors because Lake Norman serves as the lower hydraulic boundary for groundwater
flow from potentially impacted areas. For this reason, subsurface utilities within 1,500 feet
downgradient of the ash basin were not mapped. However, pertinent structures (e.g.,
stormwater drainage pipes) located proximal to ash management features were identified and
are presented on Figure 4-3.
4.1 Summary of Previous Receptor Survey Activities
Duke Energy submitted a receptor survey to NCDENR (HDR 2014a) in September 2014,
followed by a supplement to the receptor survey (HDR 2014b) that was submitted to NCDENR
in November 2014. The purpose of the receptor survey was to identify the potential exposure
locations that are critical to be considered in the groundwater transport modeling and screening -
level risk assessment activities. The supplementary information was obtained from responses to
water supply well survey questionnaires mailed to property owners within a 0.5-mile (2,640-foot)
radius of the MSS ash basin compliance boundary requesting information on the presence of
water supply wells and well usage.
The survey activities included contacting and/or reviewing the following agencies/records to
identify public and private water supply sources, confirm the location of wells, and/or identify any
wellhead protection areas located within a 0.5-mile radius of the MSS ash basin compliance
boundary:
• NCDENR Public Water Supply Section's (PWSS) most current Public Water Supply
Water Sources Geographic Information Systems (GIS) point data set;
• NCDENR DWR Source Water Assessment Program online database for public water
supply sources;
• Environmental Data Resources (EDR) local/regional water agency records review;
• Catawba County Environmental Health Department;
• City of Hickory Public Utilities Department; and
• United Stated Geological Survey (USGS) National Hydrography Dataset.
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In addition, a field reconnaissance was performed on March 31, 2014 to identify public and
private water supply wells (including irrigation wells and unused or wells) and surface water
features located within a 0.5-mile radius of the MSS ash basin compliance boundary. A
windshield survey was conducted from public roadways to identify water meters, fire hydrants,
valves, and any potential well heads/well houses, and Duke Energy site personnel identified
water supply wells located on Duke Energy property.
During the week of October 8, 2014, 262 water supply well survey questionnaires were mailed
to property owners within a 0.5-mile radius of the MSS ash basin compliance boundary
requesting information on the presence of water supply wells and well usage for the properties.
The mailing list was compiled from a query of the parcel addresses included in the Catawba
County GIS database utilizing the 0.5-mile offset.
Between July 23 and July 28, 2015, the agencies/records listed above were contracted to
provide additional update information. Updated information is provided in Appendix B.
4.2 Summary of CSA Receptor Survey Activities and Findings
As part of this CSA report, Duke Energy updated the previously completed receptor survey
activities based on the CSA Guidelines provided in the NORR issued by NCDENR. The update
included contacting and/or reviewing the agencies/records to identify public and private water
supply sources identified in Section 4.1 and reviewing any questionnaires that were received
after submittal of the November 2014 supplement to the September 2014 receptor survey (i.e.
questionnaires received after October 31, 2014).
A summary of the receptor survey findings as of August 2015 is provided below. The identified
water supply wells are shown on the USGS receptor map on Figure 4-1. Available property and
well information for the identified water supply wells is provided in Table 4-1. Table 4-2 provides
a summary of surrounding property owner's information. Figures 4-2 through 4-5 present an
aerial -based receptor map, ash basin underground features map, aerial map of surface water
bodies, and map of surrounding properties, respectively.
• A total of 83 private water supply wells were identified within a 0.5-mile radius of the ash
basin compliance boundary. The Catawba County Environmental Health Department
had records for 4 of the 83 identified private water supply wells.
• Six private water supply wells are assumed at residences located within a 0.5-mile
radius of the ash basin compliance boundary based on the lack of public water supply in
the area and proximity to other residences that have private wells.
• Four public water supply wells were identified within a 0.5-mile radius of the ash basin
compliance boundary; however, one of those wells (PWS: NC0118497) is not currently
in use. The Catawba County Environmental Health Department had records for one
public water supply well (PWS ID: 0118676), owned by Duke Energy.
• Several surface water bodies that flow from the topographic divide along Sherrills Ford
Road toward Lake Norman were identified within a 0.5-mile radius of the ash basin.
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• No water supply wells (including irrigation wells and unused or abandoned wells) were
identified between the source area and Lake Norman.
• No wellhead protection areas were identified within a 0.5-mile radius of the ash basin
compliance boundary.
Further details of HDR's receptor survey activities and findings are presented in Appendix B
NCDENR Well Water Testing Program
Section §130A-309.211(c) of the CAMA requires the owner of a coal combustion residuals
surface impoundment to conduct a Drinking Water Supply Well Survey that identifies all drinking
water supply wells within 0.5 mile down -gradient from the established compliance boundary of
the impoundment and submit the Well Survey to NCDENR. Since the direction of groundwater
flow was not fully established at the site, NCDENR required the sampling to include all potential
drinking water receptors within 1,500 feet of the compliance boundary in all directions. Between
February and July 2015, NCDENR arranged for independent analytical laboratories to collect
and analyze water samples obtained from private wells identified during the Well Survey, if the
owner agreed to have their well sampled.
Appendix B provides tabulated sampling results provided by Duke Energy from NCDENR, a
water supply well tracking spreadsheet provided by NCDENR, and well sample results provided
by NCDENR for wells outside of the 1,500-foot radius that would be considered to represent
background results. For many of the wells sampled in this program, as with standard practice,
samples were split for analysis by Duke Energy's certified (North Carolina Laboratory
Certification #248) laboratory. The results were judged by Duke Energy to be substantially
similar to the NCDENR results. Therefore, only the NCDENR results are provided in Appendix
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5.0 REGIONAL GEOLOGY AND HYDROGEOLOGY
5.0 Regional Geology and Hydrogeology
5.1 Regional Geology
North Carolina is divided into three physiographic provinces: the Atlantic Coastal Plain,
Piedmont, and Blue Ridge (Fenneman 1938). The MSS site is located in in the Piedmont
province. The Piedmont province is bounded to the east and southeast by the Atlantic Coastal
Plain and to the west by the escarpment of the Blue Ridge Mountains, with a width of 150 miles
to 225 miles in the Carolinas (LeGrand 2004).
The topography of the Piedmont region is characterized by low, rounded hills and long, rolling,
northeast -southwest trending ridges (Heath 1984). Stream valley to ridge relief in most areas
ranges from 75 feet to 200 feet. Along the Coastal Plain boundary, the Piedmont region rises
from an elevation of 300 feet above mean sea level, to the base of the Blue Ridge Mountains at
an elevation of 1,500 feet (LeGrand 2004).
The MSS site is underlain by the Charlotte and Kings Mountain terranes, two of a number of
tectonostratigraphic terranes that have been defined in the southern and central Appalachians,
and located within 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/Kings
Mountain terranes are in contact with the Inner Piedmont zone along the Central Piedmont
suture along its northwest boundary, The Kings Mountain terrane is distinguished by its
abundance of metasedimentary and metavolcanic rocks at lower metamorphic grade than the
metaigneous rocks of higher metamorphic grade in the Charlotte terrane (Butler 1991; Butler
and Secor 1991; Hatcher et al. 2007). The Charlotte terrane 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 MSS site is located at the northern extent of
the Kings Mountain terrane (Figure 5-1) and underlies the western portion of the site while the
eastern portion of the site is underlain by rocks of the Charlotte terrane.
The Charlotte terrane is dominated by a complex sequence of plutonic rocks that intrude a suite
of metaigneous rocks (amphibolite metamorphic grade) including mafic gneisses, amphibolites,
metagabbros, and metavolcanic rocks with lesser amounts of granitic gneiss and ultramafic
rocks with minor metasedimentary rocks. The general structure of the terrane is primarily a
function of plutonic contacts. Units mapped by Goldsmith et al. (1988) underlying the eastern
portion of the MSS site are alaskitic granite described as a fine-grained light colored muscovite-
biotite granite (DOga) and a fine-grained biotite gneiss of granodioritic composition of probable
volcanic origin (bgf).
The Kings Mountain terrane has a distinctive metasedimentary sequence with interlayered
quartzite, metaconglomerate, marble, and schists derived from both sedimentary and volcanic
protoliths (Keith and Sterrett 1931; Kesler 1944; King 1955; Horton and Butler 1977). Rocks of
the terrane are intensely deformed with a tectonic style distinct from the adjacent terranes
(Horton and Butler 1991; Schaeffer 1981). Metamorphic grade in the Kings Mountain terrane is
primarily middle greenschist to lower amphibolite grade with the northern portion of the terrane
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up to upper amphibolite grade (sillimanite grade) near MSS (Butler 1991). At the northern
boundary of the terrane near MSS, the primary rock units underlying the western portion of the
MSS site are the Battleground Formation (Zbs) and the High Shoals Granite (IPhs). A regional
geologic map of the area around MSS is shown on Figure 5-2.
The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The
regolith includes residual soil and saprolite zones and, where present, alluvial deposits.
Saprolite, the product of chemical weathering of the underlying bedrock, is typically composed
of clay and coarser granular material and reflects the texture and structure of the rock from
which it was formed. The weathering products of granitic rocks are quartz -rich and sandy
textured. Rocks poor in quartz and rich in feldspar and ferro-magnesium minerals form a more
clayey saprolite.
5.2 Regional Hydrogeology
The groundwater system in the Piedmont province, in most cases, is comprised of two
interconnected layers, or mediums: 1) residual soil/saprolite and weathered fractured rock
(regolith) overlying 2) fractured crystalline bedrock (Heath 1980; Harned and Daniel 1992;
Figure 5-3). The regolith layer is a thoroughly weathered and structureless residual soil that
occurs near the ground surface with the degree of weathering decreasing with depth. The
residual soil grades into saprolite, a coarser grained material that retains the structure of the
parent bedrock. Beneath the saprolite, partially weathered/fractured bedrock occurs with depth
until sound bedrock is encountered. This mantle of residual soil, saprolite, and
weathered/fractured rock is a hydrogeologic unit that covers and crosses various types of rock
(LeGrand 1988). This layer serves as the principal storage reservoir and provides an
intergranular medium through which the recharge and discharge of water from the underlying
fractured rock occurs. Within the fractured crystalline bedrock layer, the fractures control both
the hydraulic conductivity and storage capacity of the rock mass. A TZ at the base of the
regolith has been interpreted to be present in many areas of the Piedmont. Harned and Daniel
(1992) described the zone as consisting of partially weathered/fractured bedrock and lesser
amounts of saprolite that grades into bedrock and they described the zone as "being the most
permeable part of the system, even slightly more permeable than the soil zone". Harned and
Daniel (1992) suggested the zone may serve as a conduit of rapid flow and transmission of
contaminated water.
Most of the information supporting the existence of the TZ until recently was qualitative based
on observations made during the drilling of boreholes and water -wells, although some
quantitative data is available for the Piedmont region (Stewart 1964; Stewart et al. 1964; Nutter
and Otton 1969; Harned and Daniel 1992). Schaeffer (2009, 2014a) using a database of 669
horizontal conductivity measurements in boreholes at six locations in the Carolina Piedmont
statistically showed that a TZ of higher hydraulic conductivity exists in the Piedmont
groundwater system when considered within Harned and Daniel's (1992) two types of bedrock
conceptual framework.
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The TZ is comprised of partially weathered rock, open, steeply dipping fractures, and low angle
stress relief fractures, either singly or in various combinations below refusal (auger, roller cone,
or casing advancer; Schaeffer 2011; 2014b). It has less advanced weathering relative to the
regolith and generally the weathering has not progressed to the development of clay minerals
that would decrease the permeability of secondary porosity developed during weathering, new
fractures develop during the weathering process, and /or existing fractures are opened. The
characteristics of the TZ can vary widely based on the interaction of rock type, degree of
weathering, degree of systematic fracturing, presence of stress -relief fracturing, and the general
characteristics of the bedrock (foliated/layered, massive, or in between). The TZ is not a
continuous layer between the regolith and bedrock; it thins and thickens within short distances
and is absent in places (Schaeffer 2011; 2014b). The absence, thinning, and thickening of the
TZ are related to the characteristics of the underlying bedrock (Schaeffer 2014b).
The TZ may vary due to different rock types and associated rock structure. Harned and Daniel
(1992) further divided the bedrock into two conceptual models: 1) foliated/layered
(metasedimentary and metavolcanic sequences) and 2) massive/plutonic (plutonic and
metaplutonic complexes) structures (Figure 5-4). Strongly foliated/layered rocks are thought to
have a well -developed TZ due to the breakup and weathering along the foliation planes or
layering, resulting in numerous rock fragments (Harned and Daniel 1992). More massive rocks
are thought to develop an indistinct TZ because they do not contain foliation/layering and tend
to weather along relatively widely spaced fractures (Harned and Daniel 1992). Schaeffer
(2014a) proved Harned and Daniel's (1992) hypothesis that foliated/layered bedrock would have
a better developed TZ than plutonic/massive bedrock. The foliated/layered bedrock TZ has a
statistically significant higher hydraulic conductivity than the massive/plutonic bedrock TZ
(Schaeffer 2014a).
LeGrand's (1988, 1989) conceptual model of the groundwater setting in the Piedmont
incorporates Daniel and Harned's (1989) above two -medium system into an entity that is useful
for the description of groundwater conditions. That entity is the surface drainage basin that
contains a perennial stream (LeGrand 1988). Each basin is similar to adjacent basins and the
conditions are generally repetitive from basin to basin. Within a basin, movement of
groundwater is generally restricted to the area extending from the drainage divides to a
perennial stream (Slope -Aquifer System; Figure 5-5; LeGrand 1988; 1989; 2004). Rarely does
groundwater move beneath a perennial stream to another more distant stream or across
drainage divides (LeGrand 1989). The crests of the water table underneath topographic
drainage divides represent natural groundwater divides within the slope -aquifer system and may
limit the area of influence of wells or contaminant plumes located within their boundaries. The
concave topographic areas between the topographic divides may be considered as flow
compartments that are open-ended down slope.
Therefore, in most cases in the Piedmont, the groundwater system is a two -medium system
restricted to the local drainage basin. The groundwater occurs in a system composed of two
interconnected layers: residual soil/saprolite and weathered rock overlying fractured crystalline
rock separated by the TZ. Typically, the residual soil/saprolite is partially saturated and the
water table fluctuates within it. Water movement is generally through the weathered/fractured
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and fractured bedrock. The near -surface fractured crystalline rocks can form extensive aquifers
The character of such aquifers results from the combined effects of the rock type, fracture
system, topography, and weathering. Topography exerts an influence on both weathering and
the opening of fractures, while the weathering of the crystalline rock modifies both transmissive
and storage characteristics.
The igneous and metamorphic bedrock in the Piedmont consist of interlocking crystals and
primary porosity is very low, generally less than 3 percent. Secondary porosity of crystalline
bedrock due to weathering and fractures ranges from 1 to 10 percent (Freeze and Cherry 1979);
but, porosity values of 1 to 3 percent are more typical (Daniel and Sharpless 1983). Daniel
(1990) reported that the porosity of the regolith ranges from 35 to 55 percent near land surface
but decreases with depth as the degree of weathering decreases.
In natural areas, groundwater flow paths in the Piedmont are almost invariably restricted to the
zone underlying the topographic slope extending from a topographic divide to an adjacent
stream. Under natural conditions, the general direction of groundwater flow can be
approximated from the surface topography (LeGrand 2004).
Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation.
Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater
discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains
(LeGrand 2004). Mean annual recharge in the Piedmont ranges from 4.0 to 9.7 inches per year
(Cunningham and Daniel 2001).
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6.0 Site Geology and Hydrogeology
6.1 Site Geology
The MSS site and its associated ash basin system is underlain by the Charlotte and Kings
Mountain terranes, two of a number of tectonostratigraphic terranes that have been defined in
the southern and central Appalachians and is located within the western portion of the larger
Carolina superterrane (Figure 5-1; Horton et al. 1989; Hibbard et al. 2002; Hatcher et al. 2007).
The Charlotte terrane is dominated by a complex sequence of plutonic rocks that intrude a suite
of metaigneous rocks (amphibolite metamorphic grade) including mafic gneisses, amphibolites,
metagabbros, and metavolcanic rocks with lesser amounts of granitic gneiss and ultramafic
rocks with minor metasedimentary rocks. The Kings Mountain terrane has a distinctive
metasedimentary sequence with interlayered quartzite, metaconglomerate, marble, and schists
derived from both sedimentary and volcanic protoliths (Keith and Sterrett 1931; Kesler 1944;
King 1955; Horton and Butler 1977). The site geologic map is presented on Figure 6-1.
6.1.1 Soil Classification
A total of 96 borings were installed as part of this assessment. The following soils/materials
were encountered in the boreholes:
• Ash — Ash was encountered in borings advanced within the ash basin, dry ash landfill
(unit 2), and structural fill, as well as in some borings advanced through the ash basin
perimeter and dikes. Ash was generally described as dark yellow brown to very dark
gray, non -plastic, loose to very loose, and dry to wet.
• Fill — Fill material generally consisted of re -worked sandy silts, clays, and sands that
were borrowed from areas of the site and re -distributed to other areas. Fill was
classified in the boring logs as silty sand, gravel with clay and sand, sand with silt and
gravel, and silt. Fill is primarily used in the construction of dikes, as cover for ash
storage areas, and as bottom liner for ash storage areas.
• Alluvium — Alluvium encountered in borings AB-91D, AB-11 D, GWA-3D and AB-20D
was classified as sand, sand with silt and gravel with sand, wet, medium dense.
• Residuum (Residual soils) — Residuum is the in -place weathered soil that consists
primarily of silt, sand with silt, clay with sand, sandy silt with gravel, clay, sandy clay,
and sandy clay with gravel at the MSS site. Residuum varied in thickness and was
relatively thin compared to the thickness of saprolite.
• Saprolite — Saprolite is soil developed by in -place weathering of rock that retains
remnant bedrock structure. Saprolite at the MSS site is classified primarily as sand
with silt, silty sand, sand with silt and gravel, sand, clayey sand, clayey sand with
gravel, and sand with gravel. Saprolite is primarily tens of feet thick but in some cases
over 80 feet thick.
Geotechnical index property testing of the above soil/materials was performed for disturbed and
undisturbed samples in accordance with ASTM standards. Sixteen ('Shelby Tube') samples
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were submitted for geotechnical index testing. Index property testing for undisturbed samples
comprised Unified Soil Classification System classification (ASTM D 2487), natural moisture
content (ASTM D 2216), Atterberg Limits (ASTM D 4318), grain size distribution, including sieve
analysis and hydrometer (ASTM D 422), total porosity calculated from specific gravity (ASTM D
854), and hydraulic conductivity (ASTM D 5084). Three undisturbed samples were unable to
receive the full suite of index property tests due to low recovery, wax and gravel mixed in the
tube, loose material, or damaged tubes. Twenty-eight disturbed ('Split Spoon,' or'Jar') samples
received grain size distribution with hydrometer (ASTM D 422), and natural moisture content
(ASTM D 2216). The results of the testing are presented in Section 11.0.
6.1.2 Rock Lithology
The Geologic Map of the Charlotte 1 ° x 2° Quadrangle, North Carolina and South Carolina
(Goldsmith et al. 1988) describes four map units underlying the MSS site as biotite gneiss (bgf),
quartz sericite schist (Battleground Formation - Zbs), the High Shoals Granite (IPhs), and a
quartz -alkali feldspar rich granite (alaskitic (light-colored) granite (DOga).
Descriptions of lithology of rock core collected during the CSA and previous site investigations
include:
• Biotite gneiss with some schistose texture, medium- to coarse -grained
• Meta -granite
• Granite
• Meta -quartz diorite
• Biotite gneiss, fine- to medium -grained
• Biotite schist
• Quartz-sericite schist
The High Shoals Granite is primarily logged as biotite gneiss, medium- to coarse -grained,
schistose in places, and generally with well -developed banding in places consistent with the
description of the unit by Goldsmith et al. (1988) as being a "very light gray, coarse -grained,
porphyritic, gneissoid biotite granite or granitic gneiss". Meta -granite and granite were also
logged in the area underlain by the High Shoals Granite.
Alaskitic granite (DOga; as mapped by Goldsmith et al. 1988) does not underlie the MSS site.
The primary rock identified from rock core in the Goldsmith et al. mapped unit is meta -quartz
diorite. The mapped alaskitic granite is changed to a meta -quartz diorite unit (mqd; widespread
in the Charlotte terrane) and the contacts of the unit have been reinterpreted based on the
borehole data.
The northern portion of the Battleground Formation (Zbs; Figure 5-2) is underlain by fine- to
medium -grained biotite gneiss and biotite schist; not quartz-sericite schist as mapped by
Goldsmith et al. (1988). They are similar to the biotite gneiss encountered in the area identified
by Goldsmith et al. (1988) as biotite gneiss with a volcanic protolith (bgf; Figure 5-2). Quartz-
sericite schist was encountered in previous boreholes at MSS with one of the boreholes in the
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Battleground Formation (Zbs; Figure 5-2), but encountered in the biotite gneiss unit at other
locations on the MSS site.
The primary lithology encountered in the CSA boreholes and previous boreholes is shown on
the site geologic map (Figure 6-1) and the contacts have been reinterpreted to reflect the
lithologies encountered during the CSA and previous investigations, and the implied/interpreted
structural relationships.
6.1.3 Structural Geology
The Charlotte and Kings Mountain terranes have been subject to multiple deformations due to
tectonic stress before and during the intrusion of the meta -quartz diorite and High Shoals
Granite (Horton 1981; Schaeffer 1981; Butler and Secor 1991). The Kings Mountain terrane has
undergone polyphase folding; the two earliest folding events were isoclinal to tight, resulting in
two subparallel, axial planar foliations (Schaeffer 1981). Most of the rock encountered in the
boreholes exhibits some degree of foliation/schistosity related to these fold events and is the
dominant structure with respect to the bedrock underlying MSS.
The revised geologic map discussed in the following sections suggests that the contact between
the Zbs and bgf units is folded with a north-northeast trending fold axis parallel to the contact of
the High Shoals Granite with these units. The meta -quartz diorite (mqd) was likely intruded
during the late stages of the second fold event near the peak of regional metamorphism, a
relationship that has been documented to the south in the Kings Mountain terrane (Horton 1981;
Schaeffer 1981).
Data from the rock core shows a number of joint dip angles that cannot be properly defined as
joint sets since there is no orientation information. For the purpose of this discussion, the joints
are assessed based on dip angle alone. The most prevalent dip angles are sets that range from
30 to 40 degrees and from 0 to 10 degrees. These two sets are predominant based on the
number of joints noted on the boring logs. Less predominant joint sets dipping 15 to 25 degrees
and 60 to 65 degrees are also noted on the boring logs. A steeply dipping set ranging from 80 to
90 degrees is not noted as frequently but since a vertical boring is less likely to intercept sub -
vertical joints it is probable that the 80 to 90-degree dipping set is at least as prevalent as the
aforementioned sets. Iron and manganese staining is noted on all of the sets so it is reasonable
to assess that the joint sets are pathways for groundwater flow. The degree of openness of any
of the joints is difficult to assess from rock core since the core is often broken at a joint and no
longer retains its actual openness. However, some of the logs describe some joints as tight to
open.
6.1.4 Geologic Mapping
Geologic mapping was conducted in June of 2015 to map any available outcrops at the site and
within a 2-mile radius of the site using a Brunton compass to attempt to characterize rock types,
the orientation (strike and dip) of structure such as foliation, joint sets, folds, and shears/shear
zones. Due to limited outcrop locations, geologic mapping was not successful in thoroughly
characterizing structure of the rock. Only three outcrops were located that presented the
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opportunity to map rock structure. These measurements do provide evidence of the overall
orientation of foliation in the vicinity of the MSS site. The measurements of foliation from these
outcrops were: N50°E; 76°SE, N60°E; 50°SE, and N65°E; WSE.
The site location and well locations (Figure 6-2) were overlaid on the Geologic Map of the
Charlotte 1 ° x 20 Quadrangle, North Carolina and South Carolina (Goldsmith et al.1988). Field
mapping and the use of the borehole data, as discussed in Section 6.1.2, resulted in changes in
geologic units (alaskitic granite [DOga] change to meta -quartz diorite [mqd]), locations of
contacts, and their contact relationships. The contact between the Zbs and bgf unit was moved
south and the contact relationship interpreted to be due to tight folding and tight folding of the
Zbs and bgf units are located northeast of the mqd unit based on the borehole data. The contact
of the meta -quartz diorite into the surrounding rocks has been interpreted based on the
borehole data. Figure 6-1 presents the revised geologic map of the MSS site.
6.1.5 Fracture Trace Analysis
6.1.5.1 Introduction
Fracture trace analysis is a remote sensing technique used to identify lineaments on
topographic maps and aerial photography that may correlate to locations of bedrock fractures
exposed at the earth's surface. Although fracture trace analysis is a useful tool to identify
potential fracture locations, and hence potential preferential pathways for infiltration and flow of
groundwater near a site, results are not definitive. Lineaments identified as part of fracture trace
analysis may or may not correspond to actual locations of fractures exposed at the surface, and
if fractures are present, it cannot be determined from fracture trace analysis whether these are
open or healed. Healed fractures intruded by diabase are common in the vicinity of the site.
Strongly linear features at the earth's surface are commonly formed by weathering along steeply
dipping to vertical fractures in bedrock. Morphological features such as narrow, sharp -crested
ridges, narrow linear valleys, linear escarpments, and linear segments of streams otherwise
characterized by dendritic patterns are examples. Linear variations in vegetative cover are also
sometimes indicative of the presence of exposed fractures, though in many cases these result
from unrelated human activity or other geological considerations (e.g., change in lithology).
Straight (as opposed to curvilinear) features are commonly associated with the presence of
steeply dipping fractures. Curvilinear features in some cases are associated with exposed
moderately -dipping fractures, but these also can be a result of preferential weathering along
lithologic contacts, or along foliation planes or other geologic structure. As part of this study,
only strongly linear features were considered, as these are far more commonly indicative of
steeply dipping or vertical fractures.
The effectiveness of fracture trace analysis in the eastern United States, including in the
Piedmont, is commonly hampered by the presence of dense vegetative cover, and oftentimes
extensive land -surface modification owing to present and past human activity. Aerial
photography interpretation is most affected, as identification of small-scale features can be
rendered difficult or impossible in developed areas.
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6.1.5.2 Methods
Available geologic maps for the area were consulted prior to performance of aerial photography
and topographic map interpretation to identify lithologies and geologic structure in the area that
can control fracture occurrence and orientation. Topographic -map interpretation was performed
over an area of approximately 60 square miles, and aerial -photography interpretation was
performed over an area of approximately 20 square miles.
Topographic -map interpretation involved examination of the Lake Norman North, N.C.,
Troutman, N.C., Denver, N.C. and Catawba, N.C. 1:24,000-scale USGS 7.5-minute topographic
quadrangles. Digital copies of the quadrangles were obtained and viewed on a monitor at up to
7x magnification. Lineaments identified were plotted directly on the digital images.
Photography provided for review included 1 "=600' scale, 9 x 9 inch black -and -white (grayscale)
contact prints dated April 17, 2014. Stereo coverage was complete across the review area. The
photography was examined using a Lietz Sokkia MS-27 mirror stereoscope with magnifying
binocular eyepiece. Lineaments identified on the photographs were marked on hard copies of
scanned images (600dpi resolution), and subsequently compiled onto a photomosaic base.
6.1.5.3 Results
Lineaments identified from topographic maps are shown and lineament trends indicated by a
rose diagram are included on Figure 6-3. A total of 55 topographic lineaments were identified
across the study area, mainly north, east and southeast of the site in areas underlain by fine-
grained biotite gneiss. Lineaments are less well developed in areas underlain by the High
Shoals Granite in the northwest part of the study area, and by biotite meta-granodiorite in the
southwest corner of the study area. The lineaments trend primarily toward the northeast and
north-northeast, subparallel to the strike of foliation and fold axes in rocks near the site as
shown by Goldsmith et al. (1988). The north-northeast trending lineaments have a strong
preferred orientation at approximately N50E due to a well -developed axial planar
cleavage/foliation in the Kings Mountain terrane rocks near the site. Northwest trending
lineaments are also relatively common. These likely reflect trends of regional joint sets that
commonly overprint earlier structures in the Piedmont, and in some areas are associated with
Triassic diabase dike intrusion.
Lineaments identified from aerial photography are shown and lineament trends indicated by a
rose diagram is included on Figure 6-4. A total of 36 lineaments were identified, primarily in the
form of linear morphological lows (linear stream valleys, ravines and gullies), linear
morphological features in upland areas, and light colored linear outcrops that appear to be
quartzo-feldspathic material intruded into the igneous units (or possibly the quartz-sericite schist
of the Battleground Formation [Zbs]). Lineaments were identified mainly south of the site, in
areas underlain by the biotite gneiss unit. Few lineaments were discernable in areas north of the
site, in part due to the presence of dense vegetative cover.
Lineament trends identified from examination of aerial photography are generally consistent with
those identified from topographic -map interpretation. Prevalent orientations are toward the
north-northeast and northeast in conformance with bedrock structure as discussed for the
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topographic map lineaments. The well defined N50E orientation for north-northeast trending
lineaments identified on topographic maps was also apparent for smaller -scale features
identified on aerial photography.
6.1.6 Effects of Structure on Groundwater Flow
The most important effects of structural geology on groundwater flow in the western and
northern portion of the site is the well -developed foliation in the IPhs, Zbs, and bgf units and the
likely interconnected joint sets discussed in Sections 6.1.3. The meta -quartz diorite is less
foliated than the other units and it is not know if mafic dikes are present within the unit at the site
as has been noted in the unit in other areas of the Charlotte terrane (Gilbert et al. 1982). The
unit is jointed and these joints will likely have the greatest impact on groundwater flow. Since it
is difficult to define joint sets based on dip angle alone, it is also difficult to define which joints
are most relevant with respect to groundwater flow.
6.1.7 Soil and Rock Mineralogy and Chemistry
Soil mineralogy and chemistry analyses are complete and the results are shown in Table 6-1
(mineralogy), Table 6-2 (chemistry, % oxides), and Table 6-3 (chemistry, elemental
composition). Completed laboratory analyses of the mineralogy and chemical composition of TZ
materials are presented in Tables 6-4 (mineralogy), 6-5 (chemistry, % oxides), and 6-6
(chemistry, elemental). Completed rock chemistry results are presented in Table 6-7 (chemistry,
% oxides) and Table 6-8 (chemistry, elemental). The petrographic analysis of six rock samples
(thin -sections) is incomplete as of the date of this report and will be included in the CSA
supplement.
The dominant minerals in the soils are quartz, feldspar (both alkali and plagioclase feldspars),
kaolinite, muscovite/illite, and biotite. Three samples (MS-02, MS-06, and AB-6BR) reported
tremolite from 15.3 to 32.2 (wt %). Other minerals identified include vermiculite, hydroxyapatite,
hematite, ilmenite, magnetite, mullite, and amorphous materials (that contain smectites,
amorphous, mica, and/or amorphous iron oxide/hydroxide). The major oxides in the soils are
Si02 (51.15% - 68.78), A1203 (11.49% - 25.51 %), and Fe203 (2,67% - 10.04%). MnO ranges
from 0.02% to 0.11 %. The dominant minerals in the TZ are quartz, feldspar (both alkali and
plagioclase feldspars), biotite, and amphibolite. The major oxides in the TZ are Si02 (52.92% -
57.81 %), AI203 (16.53%-19.15%), and Fe203 (6.51 % - 10.51 %). MnO ranges from 0.09% to
0.15%. The major oxides in the rock samples are Si02 (50.83% - 62.09%), A1203 (10.93% -
20.79%), and Fe203 (4.36% - 8.63 %). MnO ranges from 0.06% to 0.11 % in the rock samples.
6.2 Site Hydrogeology
6.2.1 Groundwater Flow Direction
Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at MSS is consistent with the regolith-fractured rock system and is
an unconfined, connected aquifer system without confining layers as discussed in Section 5.2.
The MSS groundwater system is divided into three layers referred to in this report as the
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shallow, deep (TZ), and bedrock flow layers to distinguish the flow layers within the connected
aquifer system.
Accessible voluntary, compliance, and ash basin assessment monitoring wells were gauged for
depth to water and total well depth during a comprehensive gauging event on July 22, 23, and
24, 2015. Depth to water measurements were subtracted from surveyed top of well casing
elevations to produce groundwater elevations in shallow, deep, and bedrock monitoring wells.
Groundwater flow direction was estimated by contouring these groundwater elevations.
In general, groundwater within the shallow, deep, and bedrock flow layers at the site flows from
the northwest and north to the southeast toward Lake Norman. Shallow groundwater flow
direction is shown on Figure 6-5. Groundwater flow direction within the deep layer is shown on
Figure 6-6. Groundwater flow direction within the bedrock layer is shown on Figure 6-7.
6.2.2 Hydraulic Gradient
Horizontal hydraulic gradient was derived for the shallow aquifer, TZ, and fractured bedrock by
calculating the difference in hydraulic head over the length of the flow path between two wells
with similar well construction (e.g., both wells having 15-foot screens within the same water -
bearing unit). The following equation was used to calculate horizontal hydraulic gradient:
1= dh / dl
where 1 is the hydraulic gradient; dh is the difference between two
hydraulic heads; and dl is the flow path length between the two
wells
Applying this equation to wells installed during the CSA activities yields the following average
horizontal hydraulic gradients (measured in foot/feet):
• S wells: 0.018
• Dwells: 0.017
• BR wells: 0.010
A summary of hydraulic gradient calculations is presented in Table 6-9. Note that vertical
hydraulic gradients are discussed in Section 11.3.
6.2.3 Effects of Geological/Hydrogeological Characteristics on Contaminants
Migration, retardation, and attenuation of contaminants in the subsurface are a factor of both
physical and chemical properties of the media in which the groundwater passes. Soil samples
were collected and analyzed for grain size, total porosity, soil sorption (Kd), and anions/cations
to provide data necessary for development of the three-dimensional groundwater model
discussed in Section 13.0. As previously agreed upon with NCDENR, the results of the
groundwater model will be presented in the CAP.
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6.2.4 Site Hydrogeologic Conceptual Model
The site hydrogeologic conceptual model (SCM) is a conceptual interpretation of the processes
and characteristics of a site with respect to the groundwater flow and other hydrologic
processes at the site. The NCDENR document, "Hydrogeologic Investigation and Reporting
Policy Memorandum," dated May 31, 2007, was used as general guidance to developing the
model. General components of the SCM consist of developing and describing the following
aspects of the site: geologic/soil framework, hydrologic framework, and the hydraulic properties
of site materials. More specifically, the SCM describes how these aspects of the site affect the
groundwater flow at the site. In addition to these site aspects, the SCM:
• Describes the site and regional geology and hydrogeology (Sections 5.0, 5.1, 6.1 and
6.2);
• Presents longitudinal and transverse cross -sections showing the hydrostratigraphic
layers, (Section 11.1);
• Develops the hydrostratigraphic layer properties required for the groundwater model,
(Section 11.2);
• Presents a groundwater contour map showing the potentiometric surface of the shallow
aquifer, (Section 6.2.1); and
• Presents information on horizontal (Section 6.2.2) and vertical groundwater gradients
(Section 11.3).
The SCM serves as the basis for understanding the hydrogeologic characteristics of the site and
for developing a groundwater flow and transport model. Historic site groundwater elevations
were used to develop historic estimated seasonal high groundwater elevations for the site. A
summary of the estimated seasonal high groundwater elevations for existing site monitoring
wells is included in Appendix H. Seasonal high groundwater elevations for newly installed
monitoring wells will be determined upon reporting of an appropriate number of sampling
events. A fracture trace analysis was also performed for the site (Section 6.1.5) as well as
onsite/near-site geologic mapping (Section 6.1.4), to better understand site geology and to
confirm and support the SCM.
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7.0 Source Characterization
For this CSA, the source area is defined as the ash basin, the dry ash landfill (Permit No. 1804),
and the PV structural fill (see Figure 7-1). For convenience purposes in this report, the dry ash
landfill (Permit No. 1804), which consists of two units, is referred to as "Phase I" (the smaller,
southeastern unit) and "Phase II" (the larger, northern unit). 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. These activities identified
physical and chemical properties of ash, ash porewater, ash basin surface water, and ash basin
seeps. The source characterization involved the following:
• Reviewing selected physical properties of ash;
• Identifying constituents found in ash, ash porewater, and ash basin surface water;
• Evaluating the leaching potential of constituents from ash; and
• Identifying constituents from potential ash basin seeps.
The physical and chemical properties evaluated as part of this characterization will be used to
better understand impacts to soil and groundwater from the source area. The properties will also
be utilized as part of groundwater model development in the CAP.
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 the ash basin and ash
storage areas. Ash samples were also collected for analysis of chemical characteristics (e.g.,
total inorganics, leaching potential, etc.) to provide data for evaluation of constituent
concentrations and distribution. Samples were collected in general accordance with the Work
Plan. Sampling variances are documented in Section 8.0.
For the purpose of identifying COls associated with the source area in this CSA report, the ash,
ash porewater, ash basin surface water, and seep sample results were compared to the
following regulatory standards or criteria:
• Ash — North Carolina Industrial Health (Industrial) and/or Protection of Groundwater
(POG) PSRGs4
• Ash porewater — 2L Standards or IMACs5
• Ash basin surface water — 2B Standards6
• Seeps — 2L Standards or IMACs
These comparisons are useful in understanding potential impacts to soil, groundwater, and
surface water and provide further insight regarding the nature of the COI. However, the
4 NCDENR Division of Waste Management Inactive Hazardous Sites Branch Preliminary Soil Remediation Goals
March 2015.
5 Appendix #1 of Classifications and Water Quality Standards Applicable to The Groundwaters of North Carolina, lists
IMACs. 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 02L.0202(c). For this reason, IMACs noted in this report are for
reference only.
6 North Carolina Surface Water Quality Standards, 15A NCAC Subchapter 2B (26 Standards).
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7.0 SOURCE CHARACTERIZATION
exceedances of standards or criteria identified in this comparison do not necessarily indicate
that exceedances of groundwater, surface water, or soil standards are present outside the ash
basin. For example, comparison of analytical results for ash samples to cleanup standards for
soil can provide insight to the types of constituents and the concentrations present in ash
relative to the levels of the same constituents in soils; however, an exceedance of a PSRG
value in an ash sample does not necessarily indicate that exceedances are present in the
underlying soil.
Ash, ash porewater, ash basin surface water, and seep sample locations used for source
characterization are shown on Figure 7-1. Constituents and laboratory methods used for
analysis of solid matrix samples are presented in Table 7-1. Laboratory results of total inorganic
and anion/cation analyses of ash samples are presented in Table 7-2. Aqueous matrix (ash
basin surface water, ash porewater and seeps) parameters and analytical methods are
presented in Table 7-3. Ash porewater samples with exceedances of 2L Standards or IMACs
are provided on Figure 7-2. Field parameters recorded at the time of ash porewater sample
collection are included in Table 7-4. Ash basin porewater sample results are presented in Table
7-5. Laboratory results of ash basin surface water samples are presented in Table 7-6.
Synthetic Precipitation Leaching Procedure (SPLP) analyses of ash samples are presented in
Table 7-7. Seep sample results are presented in Table 7-8. Appendix C contains source
characterization methods and variances.
As described in the approved Work Plan, both unfiltered and filtered (0.45 pm filter) ash
porewater and ash basin surface water samples were collected for analyses of inorganics
constituents. Unless otherwise noted, concentration results discussed are for the unfiltered
samples and represent total concentrations.
In addition, speciation samples were collected from select monitoring well locations along
estimated hydraulic flow transects, from ash basin surface water sample locations, and from
seeps. Speciation is the analysis of the composition of a particular analyte in a system and can
be valuable in understanding the fate and transport of constituents. The chemical speciation
analyses included arsenic (III and V), chromium (III and VI), iron (II and III), manganese (II and
IV), and selenium (IV and VI).
Speciation results for ash porewater samples are presented in Table 7-9. Speciation results for
ash basin surface water samples are provided in Table 7-10.
7.1 Ash Basin
7.1.1 Ash (Sampling and Chemical Characteristics)
Ash samples were collected for chemical analyses from the following borings advanced within
the ash basin boundary: AB-31D, A13-41D, AB-51D, AB-6D/BR, AB-71D, AMID, AB-10D, AB-12D,
AB-13D, AB-14D, AB-15D, AB-17D, AB-18D, AB-20D, AB-21 S, SB-2, SB-3, SIB-7, SB-10, SB-
11, SB-13, and SB-14.
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Antimony, arsenic, barium, boron, cobalt, iron, manganese, selenium, and vanadium were
reported above their respective Industrial or POG PSRGs in one or more of the ash basin ash
samples (see Table 7-2). Below is a summary of each constituent exceedance for ash samples
collected in the ash basin.
• Antimony exceeded the POG PSRG in one sample from SB-13, but did not exceed the
Industrial PSRG.
• Arsenic exceeded its Industrial and POG PSRGs in all of the ash basin ash samples
except for two samples from AB-51D and one sample from AB-12D.
• Barium exceeded its POG PSRG in one sample from AB-10D, but did not exceed its
Industrial PSRG.
• Boron exceeded its POG PSRG in samples from AB-20D, SB-13, and SB-7, but did not
exceed the Industrial PSRG.
• Cobalt exceeded its POG PSRG in the majority of ash basin ash samples, but did not
exceed the Industrial PSRG in any of the samples.
• Iron exceeded its POG PSRGs in all of the ash basin ash samples, but did not exceed
its Industrial PSRGs in any of the samples.
• Manganese exceeded its POG PSRG in approximately half of the ash basin ash
samples, but did not exceed its Industrial PSRG in any of the samples.
• Selenium exceeded its POG PSRG in the majority of ash basin ash samples, but did not
exceed the Industrial PSRG in any of the samples.
• Vanadium exceeded its POG PSRG in all of the ash basin ash samples except for one
sample from AB-41D and one sample form AB-51D.
7.1.2 Ash Porewater (Sampling and Chemical Characteristics)
Ash porewater refers to water samples collected from wells installed within the ash basin and
screened within ash. Eighteen porewater monitoring wells (AB-3S, AB-4S, AB-4SL, AB-5S, AB-
6S, AB-7S, AB-8S, AB-1 OS, AB-10SL, AB-12S, AB-12SL, AB-13S, AB-14S, AB-15S, AB-15SL,
AB-17S, AB-18S, and AB-21 S) were installed within the ash basin and screened within the ash
layer. While it is helpful to understand constituent concentrations in ash porewater relative to 2L
Standards, it is important to note that ash porewater is within the waste boundary of the ash
basin and is not considered to be representative of groundwater.
Antimony, arsenic, barium, beryllium, boron, cadmium, chloride, chromium, cobalt, iron,
manganese, nickel, sulfate, thallium, TDS, and vanadium were reported above their 2L
Standards or IMACs in one or more of the ash basin porewater samples (see Table 7-5). See
Section 17.3 for maximum contaminant concentrations for ash porewater. Below is a summary
of each COI exceedance for porewater samples collected in the ash basin.
• Antimony exceeded its IMAC in two ash porewater samples (AB-10SL and AB-13S)
collected within the ash basin.
• Arsenic exceeded its 2L Standard in each ash porewater samples collected in the
southern portion of the ash basin except samples collected from AB-3S, AB-4S, and AB-
5S.
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• Barium exceeded its 2L Standard in one ash porewater sample collected in the central
portion of the ash basin (AB-12SL).
• Beryllium, cadmium, chromium, and nickel exceeded their respective IMAC (beryllium)
or 2L Standard (cadmium, chromium, and nickel) in one ash porewater sample collected
within the ash basin (AB-5S).
• Boron exceeded its 2L Standard in all but two ash porewater samples collected within
the ash basin.
• Chloride exceeded its 2L Standard in only one ash porewater sample (AB-12S) collected
within the ash basin.
• Cobalt exceeded its IMAC in nine ash porewater samples collected within the ash basin.
• Iron and manganese exceeded their respective 2L Standards in all but two (AB-4S and
AB-4SL) ash porewater samples collected within the ash basin.
• Sulfate exceeded its 2L Standard in nine ash porewater samples collected within the ash
basin, mainly in the central and southwest portions of the ash basin.
• Thallium exceeded its IMAC in eight ash porewater samples collected within the ash
basin.
• TDS exceeded its 2L Standard in eleven ash porewater samples collected within the ash
basin.
• Vanadium exceeded its IMAC in all but one ash porewater sample (AB-21 S) collected
within the ash basin.
Chemical speciation samples were also collected from five ash porewater monitoring wells (AB-
12S, AB-12SL, AB-15SL, AB-4S, and AB-4SL) within the ash basin. The speciation results are
provided in Table 7-9.
7.1.3 Ash Basin Surface Water (Sampling, and Chemical Characteristics)
Five surface water samples (SW-1, SW-2, SW-3, SW-4, and SW-5) were collected from open
water within the ash basin.
Arsenic, beryllium, cadmium, cobalt, copper, lead, nickel, thallium, zinc, chloride, and sulfate
were reported above 2B Standards in one or more of the ash basin surface water samples.
Arsenic, beryllium, boron, cobalt, manganese, nickel, selenium, sulfate, thallium, TDS, and
vanadium were reported above their respective 2L Standards or IMACs in one or more of the
ash basin surface water samples (see Table 7-6).
Chemical speciation samples were collected at two of the five ash basin surface water sample
locations and the speciation results are provided in Table 7-10.
While it is helpful to understand constituent concentrations in ash basin surface water relative to
2B and 2L Standards, it is important to note that ash surface water is collected from within the
ash basin waste boundary and is not considered to be representative of groundwater or surface
water of the state.
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7.0 SOURCE CHARACTERIZATION
7.2 Dry Ash Landfill
7.2.1 Ash (Sampling and Chemical Characteristics)
Six ash samples were collected for chemical analyses from three borings (AL-21D, AL-31D, and
AL-41D) advanced within the dry ash landfill boundary (Phase 11). No soil borings were advanced
within the footprint of the dry ash landfill (Phase 1) for this CSA.
Arsenic, boron, cobalt, iron, manganese, selenium, and vanadium were reported above their
respective Industrial or POG PSRGs in one or more of the ash samples (see Table 7-2). Below
is a summary of each constituent exceedance for ash samples collected within the dry ash
landfill.
• Arsenic exceeded its Industrial and POG PSRGs in each of the samples collected within
the dry ash landfill.
• Boron and manganese exceeded their respective POG PSRG in three of the dry ash
landfill ash samples, but did not exceed their respective Industrial PSRGs in any of the
samples.
• Cobalt, iron, selenium, and vanadium exceeded their respective POG PSRGs in each
dry ash landfill ash sample, but did not exceed their respective Industrial PSRGs in any
of the samples.
7.2.2 Porewater (Sampling and Chemical Characteristics)
One porewater monitoring well (AL-3S) was installed within the dry ash landfill (Phase II) and
screened within ash. As discussed in Section 7.1.2, AL-3S is not considered to be
representative of groundwater.
Antimony, arsenic, boron, cadmium, cobalt, iron, manganese, selenium, thallium, vanadium,
sulfate, and TDS were reported above their respective 2L Standards or IMACs in the ash
porewater sample collected from AL-3S (see Table 7-5).
PV Structural Fill
7.3.1 Ash (Sampling and Chemical Characteristics)
Thirteen ash samples were collected for chemical analyses from eight borings (AB-20D, SB-2,
SB-3, SB-4, SB-5, SB-7, SB-8, and SB-9) advanced within the PV structural fill boundary.
Arsenic, boron, cobalt, iron, manganese, selenium, and vanadium were reported above their
respective Industrial and/or POG PSRGs in one or more of the ash samples (see Table 7-2).
Below is a summary of each constituent exceedance for ash samples collected within the PV
structural fill.
• Arsenic exceeded its Industrial and POG PSRGs in each of the ash samples collected
within the PV structural fill.
0 Boron exceeded its POG PSRG in six ash samples collected within PV structural fill.
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• Cobalt, iron, and vanadium exceeded their respective POG PSRGs in each of the ash
samples collected within the PV structural fill, but did not exceed their respective
Industrial PSRGs in any of the samples.
• Manganese exceeded its POG PSRG in four ash samples collected within the PV
structural fill, but did not exceed its respective Industrial PSRGs in any of the samples.
• Selenium exceeded its POG PSRG in each of the ash samples collected within the PV
structural fill, with the exception of one ash sample from boring S13-7. Selenium was not
detected above its Industrial PSRG in any of the ash samples collected within the PV
structural fill.
Note that a portion of the PV structural fill is situated on top of the ash basin. Thus, shallow ash
samples (3 to 5 feet below ground surface [ft bgs] interval) collected from borings AB-20D and
SB-3 represent ash within the PV structural fill. Ash samples collected from deeper intervals
(greater than 3 to 5 ft bgs) represent ash within the ash basin. All ash samples collected from
borings SB-2 and SIB-7 represent ash within the PV structural fill. Note that ash samples
collected from boring SIB-9 were not analyzed for total inorganics due to a laboratory error.
7.3.2 Porewater (Sampling and Chemical Characteristics)
One porewater monitoring well (AB-20S) was installed within the PV structural fill and screened
within ash. As discussed in Section 7.1.2, AB-20S is not considered to be representative of
groundwater.
Antimony, arsenic, beryllium, boron, cadmium, chromium, cobalt, iron, lead, manganese, nickel,
selenium, thallium, vanadium, sulfate, and TDS were reported above their respective 2L
Standards or IMACs in the sample collected from AB-20S (see Table 7-5).
7.4 Leaching Potential of Ash
7.4.1 Leaching Characteristics
Differences in the constituents leached and concentrations of leached constituents will likely
occur across the differing environments in which ash is stored at the MSS site. For example,
ash stored in the dry ash landfill and PV structural fill units would likely experience differences in
the time of exposure to the leaching solution, the liquid to solid ratio, and the chemical
properties of leaching liquid as compared to the partially saturated ash in the ash basin.
In general, the infiltration for the dry ash landfill units and PV structural fill is variable and
intermittent, as infiltration is precipitation induced. The infiltration rate is dependent on a number
of factors with the primary factors being climate, vegetation, and soil properties. The
precipitation and air temperature are the two aspects of climate that most directly affect
groundwater infiltration. Vegetation affects the infiltration rate through interception and by
means of transpiration. The primary soil properties that affect infiltration are represented by the
hydraulic conductivity of the material.
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For areas where saturated conditions exist, the infiltration and subsequent groundwater
recharge would be represented by Darcy's law. However, in the case of an ash basin, the
recharge flow rate calculation is complicated by flow/seepage through the earthen dike, and
through the material underlying the ash basin (soil/saprolite, transition zone, and bedrock). An
area where the surface is saturated or where water is present in the ash basin will receive
constant infiltration with the rate being controlled by the factors described above.
The potential migration of contaminants from the ash basin, dry ash landfill (Phases I and 11),
and PV structural fill will occur by the movement of ash leachate into the underlying soil layers
and groundwater through infiltration. The infiltration of precipitation for the dry ash landfill
(Phases I and II), the PV structural fill, and the infiltration of the ash basin water into the
underlying soil material will be modeled in the groundwater model being prepared for the CAP.
Boron was identified by the USEPA (2015) as one of the leading indicators for releases of
contaminants associated with CCR, which may be evaluated for statistically significant
increases over background concentrations with time. Boron is mobile when released to
groundwater; it does not readily precipitate, and has a relatively low affinity for sorption.
Because of these characteristics, boron can be used to represent the general extent of
groundwater impacted by CCR.
7.4.2 Sampling and Chemical Characteristics
In addition to total inorganic testing of ash samples, 13 ash samples collected from borings
within the ash basin, dry ash landfill (Phase II), and the PV structural fill were analyzed for
leachable inorganics using SPLP. The purpose of the SPLP testing is to evaluate the leaching
potential of constituents that may result in impacts to groundwater above 2L Standards or
IMACs.
The ash samples collected from the ash basin (seven samples), the dry ash landfill (Phase II)
(two samples), and the PV structural fill (four samples) for SPLP testing were collected from the
deeper ash sample in the boring (i.e., approximately 2 to 3 feet above the ash/soil interface
where field conditions allowed).
The results of SPLP analyses indicated that the following constituents exceeded their 2L
Standards or IMACs in one or more of the samples: antimony, arsenic, barium, boron,
chromium, cobalt, iron, lead, manganese, nickel, selenium, thallium, and vanadium. Analytical
testing results are included in Table 7-7. Although SPLP analytical results are being compared
to the 2L Standards or IMACs, the levels of constituents in these samples do not represent
groundwater conditions at the site.
7.5 Seeps
7.5.1 Review of NCDENR March 2014 Sampling Results
NCDENR performed a surface water sampling event at the MSS site in March 2014. The
locations and analytical results of this sampling event were provided by NCDENR to Duke
Energy and are assumed to be accurate. Based on the information provided, it appears the
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March 2014 sampling event included a potential seep and the NPDES permitted outfall.
NCDENR analyzed samples for total inorganic metals only; dissolved analyses were not
performed. The location of these samples is presented on Figure 7-1. The results from the
NCDENR March 2014 sampling event are provided in Table 7-11.
Sample identifiers for the NCDENR March 2014 samples include:
• MSSWO01 S001 (potential seep)
• MSWWO02 S001 (permitted NPDES outfall 002)
The NCDENR sample results were reviewed prior to site assessment activities and were
identified to be re -sampled as part of the CSA activities. A discussion of the re -sampling results
is provided in Section 7.5.2.
7.5.2 Ash Basin and NCDENR Resampling Results — CSA Activities
7.5.2.1 Ash Basin Seeps
One seep (S-2) potentially associated with the MSS ash basin was identified prior to and during
the CSA activities. Seep S-2 is located downgradient of the ash basin between the toe of the
ash basin dam and Lake Norman, and is at roughly the same location as MSSWO01 S001
sampled by NCDENR in March 2014. The location of seep S-2 is shown on Figure 7-1.
Arsenic, barium, beryllium, boron, chromium, cobalt, lead, manganese, selenium, thallium,
vanadium, and TDS were reported above their respective 2L Standards or IMACs for the
sample collected from seep S-2 (see Table 7-8). Note that the dissolved concentrations of
beryllium, chromium, selenium, thallium, and vanadium were all below laboratory reporting limits
for seep sample S-2, suggesting that laboratory analytical results for total concentrations of
these samples may be affected by turbidity or suspended solids.
7.5.2.2 NCDENR Resample Locations
The two NCDENR March 2014 sample locations appeared to be a seep (MSSWO01 S001) and
a surface water discharge sample at the permitted NPDES outfall 002 (MSWWO02 S001), which
are both potentially influenced by the ash basin and therefore re -sampled during the CSA
activities. Analytical results for re -sample MSSWO01 S001 were compared to the 2L Standards
or IMACs based on the location representing a seep. Results for re -sample MSWWO02 S001
were compared to 2B Standards based on the sample location being representative of a
discharge to surface water (i.e., Lake Norman). The analytical results for the NCDENR re -
samples are provided in Table 7-8.
Boron, cobalt, manganese, thallium, and TDS were reported above their respective 2L
Standards or IMACs in NCDENR re -sample MSSWO01 S001. Arsenic and TDS were reported
above their respective 2B Standards in NCDENR re -sample MSWWO02 S001. Note that the
dissolved concentrations of arsenic were below the 2L or 2B Standards for both NCDENR re -
samples.
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In addition, chemical speciation samples were collected from the two NCDENR re -sample
locations for the same speciation analyses as the ash basin surface water and ash basin
porewater samples, and results are provided in Table 7-10.
cols
Based on evaluation of the ash, ash porewater, ash basin surface water, and seep sampling
data, the following COls exceeding applicable standards were identified:
7.6.1 COls in Ash (based on total inorganics analysis, as shown in Table 7-2)
• Antimony
• Arsenic
• Barium
• Boron
• Cobalt
• Iron
• Manganese
• Selenium
• Vanadium
7.6.2 COls in Ash Porewater (based on water quality analysis, as shown in Table 7-5)
• Antimony
• Arsenic
• Barium
• Beryllium
• Boron
• Cadmium
• Chloride
• Chromium
• Cobalt
• Iron
• Lead
• Manganese
• Nickel
• Selenium
• Sulfate
• Thallium
• TDS
• Vanadium
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7.6.3 COls in Ash Basin Surface Water (based on water quality analysis, as shown in
Table 7-6)
• Arsenic
• Beryllium
• Boron (21- Standards only)
• Cadmium (2B Standards only)
• Chloride (2B Standards only)
• Cobalt
• Copper (2B Standards only)
• Lead (2B Standards only)
• Manganese (21- Standards only)
• Nickel
• Selenium (21- Standards only)
• Sulfate
• Thallium
• TDS (21- Standards only)
• Vanadium (21- Standards only)
• Zinc (2B Standards only)
7.6.4 COls in Seeps and NCDENR Resamples (based on water quality analysis, as
shown in Table 7-8)
• Arsenic
• Barium
• Beryllium
• Boron
• Chromium
• Cobalt
• Lead
• Manganese
• Selenium
• Thallium
• TDS
• Vanadium
7.6.5 Summary of COls from Source Characterization
• Antimony
• Arsenic
• Barium
• Beryllium
• Boron
• Cadmium
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• Chloride
• Chromium
• Cobalt
• Copper (ash basin surface water only)
• Iron
• Lead
• Manganese
• Nickel
• Selenium
• Sulfate
• Thallium
• TDS
• Vanadium
• Zinc (ash basin surface water only)
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8.0 Soil and Rock Characterization
The purpose of soil and rock characterization is to evaluate the physical and geochemical
properties in the subsurface with regard to COI presence, retardation, and migration. Soil and
rock sampling was performed in general accordance with the procedures described in the Work
Plan. Refer to Appendix D for a description of these methods and variances, and Appendix E for
field sampling and data quality control / quality assurance protocols.
Soil, PWR, and bedrock samples were collected from background locations, beneath the ash
basin, beneath the dry ash landfill (Phase II), beneath the PV structural fill, and beyond the ash
basin waste boundary. Included in Appendix D are the soil and rock sampling plan utilized for
groundwater assessment activities as well as variances from the proposed sampling plan. The
boring locations are shown on Figure 6-2.
8.1 Background Sample Locations
Background (BG) boring locations were identified based on the SCM at the time the Work Plan
was submitted. The background locations were selected in areas believed not to be impacted
based upon existing knowledge of the site and topographically upgradient of the MSS ash
basin. Based on the groundwater contours shown on Figures 6-5 through 6-7 and the updated
SCM, the BG boring locations are considered to be hydraulically upgradient of the ash basin.
The BG boring locations (BG-1 S/D, BG-2S/BR, and BG-3S/D) are considered to be
representative of background soil conditions at the site.
8.2 Analytical Methods and Results
Table 8-1 summarizes analyses and analytical methods for soil, PWR, and bedrock samples
collected. Total inorganic results for background soil samples are presented in Table 8-2. Total
inorganic results for background PWR and bedrock samples are presented in Table 8-3. Total
inorganic results for soil samples other than background are presented in Table 8-4. Total
inorganic results for PWR and bedrock samples other than background are presented in Table
8-5.
Figure 8-1 depicts the total inorganic results for soil, PWR, and bedrock sample exceedances in
plan view. Cross-section transects are presented in plan view on Figure 8-2. Cross -sections
presenting the vertical distribution of COls along each transect are depicted on Figures 8-3.1
through 8-5.3.
SPLP results for background soil samples are presented in Table 8-6. SPLP results for soil
samples beneath the ash basin are presented in Table 8-7. Although SPLP analytical results
are being compared to 2L Standards and IMACs, the levels of constituents in these samples are
not directly representative of groundwater conditions.
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8.3 Comparison of Soil and Rock Results to Applicable Levels
Soil analytical results are compared to the North Carolina Industrial and POG PSRGs included
in Tables 8-2 (background) and 8-4 (soil other than background). Analytical results for the PWR
and bedrock samples are compared to the same PSRGs and are included in Tables 8-3
(background) and 8-5 (rock other than background). Frequency and concentration ranges for
COls with PSRG exceedances in soil are presented in Table 8-8 (soil beneath ash basin), Table
8-9 (soil beneath PV structural fill), Table 8-10 (soil beneath dry ash landfill, Phase II), and
Table 8-11 (soil outside waste boundary). The sections below provide a summary of COls with
PSRG exceedances in at least one of the samples analyzed. Parameters not listed below were
not reported at concentrations exceeding their respective North Carolina PSRGs in the collected
soil samples.
8.4 Comparison of Soil Results to Background
In addition to comparing results to regulatory criteria, soil sample results have also been
compared to background concentrations as discussed below. Refer to Figure 8-2 for soil boring
locations.
8.4.1 Background Soil, PWR, and Rock
Background soil locations are identified as BG-1 S, BG-1 D, BG-2BR, and BG-3D. Boron was not
detected above its laboratory minimum reporting limit in any of the background soil samples. All
other constituents were detected at least once in the 14 samples that were obtained from the
four background borings. Background soil concentrations are provided below for COls that were
identified in ash (see Section 7.5). Arsenic was reported above its Industrial PSRG in seven of
the 14 background soil samples. Antimony, barium, cobalt, iron, manganese, selenium, and
vanadium exceeded North Carolina POG PSRGs at least once in background soils.
The concentrations of COls (identified in ash) in background soils are provided below and a
summary of results is provided in Table 8-2. Of note, concentrations of arsenic and selenium
were higher in background rock samples than in background soil samples.
• Antimony 4AJ to <7.2 mg/kg (one exceedance)
• Arsenic 3AJ to 39.9 mg/kg (seven of 14 exceedances)
• Barium
45.7 to 1,670 mg/kg (five of 14 exceedances)
• Boron
13.1 to 68.6 mg/kg (no exceedances)
• Cobalt
5.6J to 41.8 mg/kg (13 of 14 exceedances)
• Iron
4,960J to 45,400 mg/kg (all samples exceeded)
• Manganese
63.9 to 799 mg/kg (13 of 14 exceedances)
• Selenium
3.7J to 40.1 mg/kg (four of 14 exceedances)
• Vanadium
24.0 to 83.3 mg/kg (all samples exceeded)
Notes:
mg/kg = milligrams per kilogram
J = Estimated concentration
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8.0 SOIL AND ROCK CHARACTERIZATION
8.4.2 Soil, PWR, and Rock Beneath the Ash Basin
Soil, PWR, and rock samples beneath the ash basin were obtained from borings AB-3D, AB-4D,
AB-4SL, A13-5D, A13-513R, AB-6D, A13-613R, AB-6EB, AB-7D, AB-8D, A13-10D, A13-12D, A13-13D,
AB-14D, AB-15D, AB-1513R, AB-17D, AB-18D, AB-20D, AB-21 D, AL-3D, SB-2, SB-3, SB-7, SB-
10, SB-11, S13-13, S13-14, and SB-15. The range of constituent concentrations along with a
comparison to the range of reported background soil concentrations is provided in Table 8-8.
Constituent concentrations of soils beneath the ash basin are generally higher for arsenic in the
uppermost soil sample compared to background soil concentrations. Concentrations for
antimony, barium, boron, cobalt, iron, manganese, selenium, and vanadium are similar to or
lower than background soil concentrations.
8.4.3 Soil Beneath the PV Structural Fill
Soil samples beneath the PV structural fill were obtained from borings SB-4, SB-5, S13-8, and
S13-9. PWR or rock samples were not collected from borings below the structural fill. The range
of constituent concentrations along with a comparison to the range of reported background soil
concentrations is provided in Table 8-9.
Constituent concentrations of soil beneath the PV structural fill are generally similar to, or lower
than, background concentrations for antimony, arsenic, barium, boron, cobalt, iron, manganese,
selenium, and vanadium. Arsenic and selenium were reported above background
concentrations in the uppermost soil sample in soil boring SB-8.
8.4.4 Soil, PWR, and Rock Beneath the Dry Ash Landfill (Phase II)
Soil, PWR, and rock samples beneath the dry ash landfill (Phase II) were obtained from borings
AL-2D, AL-213R, and AL-4D. The range of constituent concentrations along with a comparison to
the range of reported background soil concentrations is provided in Table 8-10.
Constituent concentrations of soils beneath the dry ash landfill (Phase II) are generally similar
to, or lower than, background concentrations for antimony, arsenic, barium, boron, cobalt, iron,
manganese, selenium, and vanadium.
8.4.5 Soil Outside the Waste Boundaries
Soil samples outside the waste boundary were obtained from borings AL-1 D, GWA-2D, GWA-
4D, GWA-5D, GWA-6D, GWA-7S, and GWA-913R. PWR or rock samples were not collected
from borings outside the waste boundary. The range of constituent concentrations along with a
comparison to the range of reported background soil concentrations is provided in Table 8-11.
Constituent concentrations of soils outside the waste boundary are generally similar to, or lower
than, background concentrations for antimony, arsenic, barium, boron, cobalt, iron, manganese,
selenium, and vanadium. One soil sample collected from boring AL-1 D contained a reported
concentration of arsenic that exceeded background concentrations and the North Carolina
Industrial and POG PSRGs. AL-1 D was located immediately east and downgradient of the dry
ash landfill (Phase 1).
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9.0 Surface Water and Sediment
Characterization
The purpose of surface water and sediment characterization is to evaluate whether COls from
the source area have migrated to surface waters outside and in the vicinity of the ash basin
waste boundary. The surface water and sediment characterization sampling was performed in
general accordance with the procedures described in the Work Plan with exceptions noted.
Sampling methodology and variances to that methodology are described in Appendix F. Surface
water and sediment sample locations are shown on Figure 9-1.
As described in the approved Work Plan, both unfiltered and filtered (0.45 pm filter) samples
were collected for analyses of constituents whose results may be biased by the presence of
turbidity.' Unless otherwise noted, concentration results discussed are for the unfiltered samples
and represent total concentrations.
9.1 Surface Water
One surface water sample (SW-6) was obtained from an unnamed tributary that flows to Lake
Norman. The location of the surface water sample SW-6 was identified to be downgradient of
the dry ash landfill (Phase 1) and the ash basin. Surface water parameters and laboratory
methods used for analysis of aqueous matrix samples are presented in Table 7-3. Surface
water sample results for total and dissolved fractions are presented in Table 9-1.
Surface water analytical results are compared to the 213 Standards. Cobalt was reported at
concentrations above its 213 Standards. Note that boron, manganese, and vanadium do not
have established 213 Standards; however, concentrations were reported above their respective
2L Standard or IMAC.
9.2 Sediment
One sediment sample was collected coincidentally with surface water sample SW-6. The
sediment sample was collected and analyzed for constituents and parameters included in the
list used for soil and rock characterization (see Table 8-1). In the absence of NCDENR sediment
criteria, the sediment sample results were compared to North Carolina PSRGs, and results of
the sediment sample laboratory analyses are presented in Table 9-2.
Concentrations of cobalt, iron, manganese, selenium, and vanadium were reported above their
respective North Carolina POG PSRGs, but below their Industrial PSRGs, in sediment sample
SW-6.
The USEPA (EPA 2002) recommends that when possible, especially when sampling for contaminants that may be
biased by the presence of turbidity, the turbidity reading is desired to stabilize at a value below 10 Nephelometric
Turbidity Units (NTUs).
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10.0 Groundwater Characterization
The purpose of groundwater characterization is to compare groundwater at the site to 2L
Standards or IMACs, and to inform the corrective actions identified in the CAP. Groundwater
sampling methods and the rationale for sampling locations were in general accordance with the
procedures described in the Work Plan. Refer to Appendix G for a description of these methods.
Variances from the proposed well installation locations, methods, quantities, and well
designations are presented in Appendix G.
10.1 Regional Groundwater Data for Constituents of Interest
Individual sampling events serve to characterize the hydrogeologic and chemical conditions at a
particular monitoring location, at a particular time. When interpreting the results from a sample
event, a number of factors that affect the sample results should be considered. Among these
are the geologic and hydrogeologic setting, the location of the sample point in the regional
groundwater flow system, and potential interactions between suspected contaminants and the
geological and biological constituents present in the formation (Barcelona et al. 1985).
As a result of these factors, it may be possible that the analytical results of a given constituent
are influenced by naturally occurring conditions as opposed to conditions caused by releases
from the ash basin. This section presents an overview of the regional and statewide
groundwater conditions for COls found at the MSS site and for COls in groundwater that have
exceeded state standards.
The 2L Standards recognize that the concentrations of naturally occurring substances in
groundwater may exceed the standards established in 15A NCAC 2L.0202(g). Rule .0202(b)(3)
states that when this occurs, the Director of the DWR will determine the standard.
North Carolina 2L Standards and IMACs are established by NCDENR, whereas primary and
secondary Maximum Contaminant Levels (MCLs and SMCLs) are established by the USEPA.
Primary MCLs are legally enforceable standards for public water supply systems set to protect
human health in drinking water. Secondary MCLs are non -enforceable guidelines set to account
for aesthetic considerations, such as taste, color, and odor (USEPA 2014).
Table 10-1 lists COls that exceeded 2L Standards or IMACs in groundwater samples collected
at the site. Regional background information for COls that exceed 2L Standards or IMACs in
groundwater at the MSS site are provided (in alphabetical order) in Sections 10.1.1 through
10.1.16. In addition, regional background information on pH is provided in Section 10.1.17, as
pH levels can affect the leachability of metal ions in groundwater.
10.1.1 Antimony
Antimony is a silvery -white, brittle metal. In nature, antimony combines with other elements to
form antimony compounds. Small amounts of antimony are naturally present in rocks, soils,
water, and underwater sediments.
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Only a few ores of antimony have been encountered in North Carolina. Antimony has been
found in combination with other metals, and is found most commonly in Cabarrus County and
other areas of the Carolina Slate Belt (Chapman et al. 2013).
In a USGS study of naturally occurring trace minerals in North Carolina, 57 private water supply
wells were sampled to obtain trace mineral data. Of the wells sampled, no wells contained
antimony above the USEPA primary MCL (Chapman et al. 2013). Antimony is compared to
IMAC since no 2L Standard has been established for this constituent by NCDENR.
10.1.2 Arsenic
Natural arsenic occurs commonly and comes mainly from the soil. The USEPA estimates that
the amount of natural arsenic released into the air as dust from the soil is about equal to the
amount of arsenic released by all human activities (EPRI 2008b).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at the University of North Carolina (UNC) analyzed private well water samples tested
by the North Carolina State Laboratory of Public Health from 1998-2010. The MSS site is
located in Catawba County, North Carolina. Since it is near the border of Iredell County,
statistics for both counties are included here. Data collected from 1,479 private wells across
Catawba and Iredell counties from 1998-2010 indicated that 10 samples had arsenic
concentrations exceeding the primary MCL of 10 tag/L, which is the same as the North Carolina
2L Standard for arsenic. Summary statistics for both counties are provided in Table 10-2.
In a state-wide investigation into arsenic concentrations in private wells, Sanders et al. (2011)
found strong geological patterns in arsenic concentrations in groundwater across the state of
North Carolina (Figure 10-1). The MSS site is located in an area where the average
concentration of naturally occurring arsenic in groundwater varies between 1.1 and 2.5 pg/L.
10.1.3 Barium
Two forms of barium, barium sulfate and barium carbonate, are often found in nature as
underground ore deposits. Barium is sometimes found naturally in drinking water and food.
However, since certain barium compounds (barium sulfate and barium carbonate) do not mix
well with water, the amount of barium found in drinking water is typically small.
Barium compounds such as barium acetate, barium chloride, barium hydroxide, barium nitrate,
and barium sulfide dissolve more easily in water than barium sulfate and barium carbonate, but
because they are not commonly found in nature, they do not usually occur in drinking water
unless the water is contaminated by barium compounds that are released from waste sites
(EPRI 2008c).
Barium is naturally released into the air by soils as they erode in wind and rain, and is released
into the soil and water by eroding rocks. Barium released into the air by human activities comes
mainly from barium mines, metal production facilities, and industrial boilers that burn coal and
oil. Anthropogenic sources of barium in soil and water include copper smelters and oil drilling
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waste disposal sites. Industries reporting to the USEPA released 119,646 tons of barium and
barium compounds into the environment in 2005 (EPRI 2008c).
Regional metamorphic greenschist to upper amphibolite facies rocks in the Piedmont's Kings
Mountain Belt contains deposits of barium sulfate (barite). Barium is especially common as
concretions and vein fillings in limestone and dolostone, which are not common geologic rocks
in North Carolina; however, at various times in the past century and a half, the Carolinas have
been major producers of barite (USEPA 2014).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed private well water samples tested by the North Carolina State
Laboratory of Public Health from 1998-2010. Data collected from 422 private wells across
Catawba and Iredell counties from 1998-2010 indicate that all barium concentrations were
below a laboratory detection level of 50 pg/L, with no exceedances of the federal primary MCL
of 2,000 pg/L. Summary statistics for both counties are provided in Table 10-2.
10.1.4 Beryllium
Beryllium is a hard, gray metal that is very lightweight. In nature, it combines with other
elements to form beryllium compounds. Small amounts of these compounds are naturally
present in soils, rocks, and water. Emeralds and aquamarines are gem -quality examples of a
mineral (beryl) that is a beryllium compound.
Beryllium combines with other metals to form mixtures called alloys. Beryllium and its alloys are
used to construct lightweight aircraft, missiles, and satellite components. Beryllium is also used
in nuclear reactors and weapons, X-ray transmission windows, heat shields for spacecraft,
rocket fuel, aircraft brakes, bicycle frames, precision mirrors, ceramics, and electrical switches
(EPRI 2008d).
Most of the beryllium occurring in North Carolina is along the south and southwest sides of the
Blue Ridge Mountains. The most notable mines include the Biggerstafff, Branchand, and Poteat
mines in Mitchell County; the Old Black mine in Avery County; and the Ray mine in Yancey
County. The beryllium forms golden or pale -green well -formed prismatic crystals ranging in size
from a fraction of an inch to about 3 inches in diameter. It is generally found near the cores of
bodies of pegmatites of moderate size that contain considerable amounts of perthitic microcline.
Production has been negligible, and no regular production appears possible. Green beryllium
(aquamarine and emerald) was mined commercially many years ago at the Grassy Creek
emerald mine and the Grindstaff emerald mine on Crabtree Mountain in Mitchell County. The
Ray mine in Yancey County has also produced some golden beryllium and aquamarine (Brobst
1962). Beryllium -containing minerals are also common in granites and pegmatites throughout
the Piedmont; however, to a much lesser degree than the Blue Ridge Mountains Province
(Brobst 1962).
Beryllium is concentrated in silicate minerals relative to sulfides and in feldspar minerals relative
to ferromagnesium minerals. The greatest known naturally occurring concentrations of beryllium
are found in certain pegmatite bodies. Beryllium is not likely to be found in natural water above
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trace levels due to the insolubility of oxides and hydroxides at the normal pH range (Brobst
1962). In groundwater, beryllium concentrations are compared to IMAC since no 2L Standard
has been established for this constituent by NCDENR.
10.1.5 Boron
While boron is relatively abundant on the earth's surface, boron and boron compounds are
relatively rare in all geological provinces of North Carolina. Natural sources of boron in the
environment include volatilization from seawater, geothermal vents, and weathering of clay -rich
sedimentary rocks. Total contributions from anthropogenic sources are less than contributions
from natural sources. Anthropogenic sources of boron include agriculture, refuse, coal and oil
burning power plants, by-products of glass manufacturing, and sewage and sludge disposal
(EPRI 2005).
Boron is usually present in water at low concentrations. Surface waters typically have
concentrations of 0.001 to 5 mg/L, with an average concentration of about 0.1 mg/L.
Background boron concentrations in groundwater near power plants were compiled from data
presented in EPRI technical reports, and ranged from <0.01 to 0.59 mg/L with a median
concentration of 0.07 mg/L (EPRI 2005).
10.1.6 Chloride
Chloride is a major ion, and occurs widely in nature as a salt of sodium (NaCI), potassium (KCI),
and calcium (CaC12). Oceans typically contain about 19,000 mg/L of chloride (Feth 1981).
Elevated levels of chloride may occur in groundwater as a result of sea water intrusion, or
erosion halite (USGS 2009).
The USEPA has not established an MCL for chloride because it is not known to have adverse
effects on human health. An SMCL of 250 mg/L has been established for chloride because of
taste and corrosive considerations. The taste threshold for chloride depends on the associated
cation. A study by Lockhart (1955) found that people detected a salty taste in water at 210, 310,
and 222 mg/L from the respective sodium, potassium, and calcium salts. The taste of coffee is
affected when brewed with water containing chloride concentrations ranging from 400 to 530
mg/L, depending on chlorides corresponding cation (Lockhart, Tucker, and Merritt 1955).
Chloride concentrations above 250 mg/L in drinking water may cause corrosion in water
distribution systems (McConnell and Lewis 1972).
Using the USGS National Uranium Resource Evaluation (NURE) database, all chloride
groundwater test results within a 20-mile radius of the MSS site are shown on Figure 10-2.
These samples were taken at depths ranging from 20 to 500 ft bgs, and the chloride
concentrations range from below detection limits to 38.4 pg/L.
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10.1.7 Chromium
Chromium is a blue -white metal found naturally only in combination with other substances. It
occurs in rocks, soil, plants, and volcanic dust and gases (EPRI 2008a). Background
concentrations of chromium in groundwater generally follow the media in which they occur. Most
chromium concentrations in groundwater are low, averaging less than 1.0 lag/L worldwide.
Chromium tends to occur in higher concentrations in felsic igneous rocks (such as granite and
metagranite) and ultramafic igneous rocks; however, it is not a major component of the igneous
or metamorphic rocks found in the North Carolina Piedmont or the Blue Ridge (Chapman et al.
2013).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 423 private well water samples in Catawba and Iredell counties. The
samples were tested by the North Carolina State Laboratory of Public Health from 1998-2010.
Statistics for both counties are included in Table 10-2. This study found average chromium
concentrations were 713.6 lag/L and 5.3 lag/L in Catawba and Iredell counties, respectively
(NCDHHS 2010).
10.1.8 Cobalt
The concentration of cobalt in surface and groundwater in the United States is generally low —
between 1 and 10 parts of cobalt in 1 billion parts of water (ppb) in populated areas. The
concentration may be hundreds or thousands of times higher in areas that are rich in cobalt -
containing minerals or in areas near mining or smelting operations. In most drinking water,
cobalt levels are less than 1 to 2 ppb (USGS 1973). Cobalt is compared to IMAC since no 2L
Standard has been established for this constituent by NCDENR.
10.1.9 Iron
Iron is a naturally occurring element that may be present in groundwater from the erosion of
natural deposits (NCDHHS 2010). Iron commonly exceeds state and federal regulatory
standards in North Carolina groundwater. According to Harden 2009, iron exceedances
occurred in over half of the state's 10 geozones. The average concentration of iron detected in
North Carolina private well water from sampling conducted in 2010 is shown on Figure 10-3
(NCDHHS 2010). A study by the Superfund Research program at UNC found that only 15 of the
100 counties in North Carolina had average concentrations below the SMCL of 300 lag/L.
Average concentrations for Catawba and Iredell counties were 1,606 lag/L and 412 lag/L,
respectively. Summary statistics are reported in Table 10-2.
A 2015 study by NCDENR (Summary of North Carolina Surface Water Quality Standards 2007-
2014) found that while concentrations vary regionally, "iron occurs naturally at significant
concentrations in the groundwaters of NC," with a statewide average concentration of 1,320
lag/L. Regional variations from this study are summarized in Table 10-3.
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10.1.10 Lead
Lead is a heavy, bluish -gray metal that occurs naturally in the earth's crust. It is rarely found as
a pure metal, but is instead typically found with other elements to form lead compounds. Lead is
soft and malleable. It combines with other metals to form mixtures called alloys and is
commonly found in pipes, weights, firearm ammunition, sheets used to shield humans from
radiation, pigments in paint and dye, ceramic glazes, and caulk. The largest use for lead is in
vehicle storage batteries (EPRI 2008e).
Lead is the 34`h most abundant element in the earth's crust, averaging 15 parts per million
(ppm). In igneous rocks its concentration ranges from approximately 5 ppm in gabbro to 20 ppm
in granite. Typical concentrations in sedimentary rocks range from an average of 7 ppm in
sandstone, 9 ppm in carbonates, 20 ppm in shale, to as much as 80 ppm in deep-sea clays
(USGS 1973).
A variety of lead -bearing igneous, metamorphic, and sedimentary rock units are distributed
throughout North Carolina. The Kings Mountain belt once hosted a lead mine, with minerals
such as galena, chalcopyrite, and pyrite present in vein quartz throughout the host rock (Horton
1981).
A statistical summary of groundwater quality in North Carolina was conducted by the Superfund
Research Program at UNC. The study found that four North Carolina counties had average lead
concentrations which exceeded the primary MCL of 15 tag/L. The North Carolina State
Laboratory of Public Health tested 1,525 private well water samples from Catawba and Iredell
counties from 1998-2010. The counties were found to have average groundwater lead
concentrations of 7.7 tag/L and 4.3 tag/L respectively. The primary MCL was exceeded in 30
samples (NCDHHS 2010).
10.1.11 Manganese
Manganese is a naturally occurring silvery -gray transition metal that resembles iron, but is more
brittle and is not magnetic. It is found in combination with iron, oxygen, sulfur, or chlorine to form
manganese compounds. Manganese occurs naturally in soils, saprolite, and bedrock and is
thus a natural component of groundwater (EPRI 2008f).
Manganese concentrations tend to cluster by soil system and geozone throughout North
Carolina, as shown on Figure 10-4. The Carolina Slate and Milton geozones have the highest
proportions of manganese-exceedances, although six other geozones exceeded the state
standard as well (Gillespie 2013). Geozones with magmatic -arc rocks and low-grade
metamorphic rocks, seen on Figure 10-4, tend to include abundant manganese -bearing mafic
minerals likely to contribute manganese for subsurface water cycling (Gillespie 2013). These
rock types are distributed throughout North Carolina and contribute to spatial variations of
manganese concentrations throughout the state. High manganese concentrations are
associated with silty soils, and sedimentary, unconsolidated, or weathered lithologic units. Low
concentrations are associated with non -weathered igneous bedrock and soils with high
hydraulic conductivity (Polizzotto 2014; Gillespie 2013).
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Manganese is most readily released to the groundwater through the weathering of mafic or
siliceous rocks (Gillespie 2013). When manganese -bearing minerals in saprolite, such as biotite,
are exposed to acidic weathering, the metal can be liberated from the host -mineral and released
to groundwater. It can then migrate through pre-existing fractures during the movement of
groundwater through bedrock. If this aqueous -phase manganese is exposed to higher pH in the
groundwater system, it will precipitate out of solution. This results in preferential pathways
becoming "coated" in manganese oxides and introduces a concentrated source of manganese
into groundwater (Gillespie 2013).
Manganese(II) in suspension of silt or clay is commonly oxidized by microorganisms present in
soil, leading to the precipitation of manganese minerals (Agency for Toxic Substances and
Disease Registry 2012).
Roughly 40-50% of North Carolina wells have manganese concentrations higher than the state
drinking water standard (Gillespie 2013). Concentrations are spatially variable throughout the
state, ranging from less than 0.01 mg/L to more than 2 mg/L. This range of values reflects
naturally derived concentrations of the constituent and is largely dependent on the bedrock's
mineralogy and extent of weathering (Gillespie 2013).
In a 2015 study by DENR (Summary of North Carolina Surface Water Quality Standards 2007-
2014) it was found that concentrations vary regionally, however "manganese occurs naturally at
significant concentrations in the groundwater of NC," with a statewide average concentration of
102 pg/L. The study found the regional variations summarized in Table 10-3.
Using the USGS NURE database, all manganese groundwater test results within a 20-mile
radius of the MSS site are shown on Figure 10-5. These samples were taken at depths ranging
from 20 to 500 ft bgs, and the manganese concentrations range from below detection limits to
271.6 pg/L. Manganese concentrations in the four locations nearest to MSS are less than the
SMCL and 2L Standards of 50 pg/L.
10.1.12 Selenium
Selenium is a semi -metallic gray metal that commonly occurs naturally in rocks and soil. It is
common to find trace amounts of selenium in food, drinking water, and air -borne dust. Over
geologic time, selenium has been introduced to the earth's surface and atmosphere through
volcanic emissions and igneous extrusions. Weathering and transport partition the element into
residual soils, where it is available for plant uptake, or to the aqueous environment, where it
may remain dissolved, enter the aquatic food chain, or redeposit within a sedimentary rock such
as shale (EPRI 2008g).
Groundwater containing selenium is typically the result of either natural processes or industrial
operations. Naturally, selenium's presence in groundwater is from leaching out of selenium -
bearing rocks. It is most common in shale ranging from 0.6 to 103 mg/kg. Anthropogenically,
selenium is released as a function of the discharge from petroleum and metal refineries and
from ore mining and processing facilities. Ore mining may enhance the natural erosive process
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by loosening soil, creating concentrations in erodible tailings piles, and exposing selenium
containing rock to runoff (Martens 2002; USEPA 2014).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 420 private well water samples in Catawba and Iredell counties.
These samples were tested by the North Carolina State Laboratory of Public Health from 1998-
2010. The concentrations ranged from 2.5 to 19.5 pg/L and no samples exceeded the 50 pg/L
primary MCL for selenium (NCDHHS 2010). Selenium summary statistics are reported in Table
10-2.
10.1.13 Sulfate
Sulfate is a naturally occurring substance found in minerals, soil, and rocks. It is present in
ambient air, groundwater, plants, and food. The principal commercial use of sulfate is in the
chemical industry. Sulfate is discharged into water in industrial wastes and through atmospheric
deposition (USEPA 2003).
While sulfate has an SMCL and no enforceable maximum concentration set by the USEPA,
ingestion of water with high concentrations of sulfate may be associated with diarrhea,
particularly in susceptible populations, such as infants and transients (USEPA 2012).
In the Piedmont and Blue Ridge Aquifers chapter of the USGS Ground Water Atlas of the
United States, the groundwater of this region as a whole is described as "generally suitable for
drinking... but iron, manganese, and sulfate locally occur in objectionable concentrations"
(USGS 1997).
10.1.14 TDS
Groundwater contains a wide variety of dissolved inorganic constituents as a result of chemical
and biochemical interactions between the groundwater and the elements in the soil and rock
through which it passes. TDS mainly consist of cation and anion particles (e.g., calcium,
chlorides, nitrate, phosphorus, iron, sulfur, and others) that can pass through a 2-micron filter
(USEPA 1997). TDS is therefore a measure of the total amount of dissolved ions in the water,
but does not identify specific constituents, or explain the nature of ion relationships (Water
Research Center 2004).
TDS concentrations in groundwater can vary over many orders of magnitude and generally
range from 0 — 1,000,000 pg/L. The ions listed below are referred to as the major ions as they
make up more than 90 percent of the TDS in groundwater. TDS concentrations resulting from
these constituents are commonly greater than 5,000 pg/L (Freeze and Cherry 1979).
• Sodium (Na')
• Magnesium (Mg2+)
• Calcium (Ca2+)
• Chloride (CI-)
• Bicarbonate (HCO3")
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• Sulfate (S042-)
Minor ions in groundwater include boron, nitrate, carbonate, potassium, fluoride, strontium, and
iron. TDS concentrations resulting from minor ions typically range between 10 to 1,000 pg/L
(Freeze and Cherry 1979). Trace constituents make up an even smaller portion of TDS in
groundwater and include aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium,
cobalt, lead, manganese, nickel, selenium, thallium, vanadium, and zinc among others. TDS
concentrations resulting from trace constituents are typically less than 100 pg/L (Freeze and
Cherry 1979). In some cases, contributions from anthropogenic sources can increase some of
the elements contained within TDS to occur at concentration levels that are orders of magnitude
above the normal ranges indicated above.
Because TDS is not considered a hazard to human health, it has no USEPA-defined MCL. The
USEPA has established an SMCL for TDS because elevated levels are associated with
negative aesthetic effects, such as taste and odor of drinking water. Water containing more than
2,000,000 — 3,000,000 pg/L TDS is generally too salty to drink (the TDS of seawater is
approximately 35,000,000 tag/L) (Freeze and Cherry 1979).
In the April 2015 CCR Rule, the USEPA listed TDS as an indicator constituent (along with
boron, calcium, chloride, fluoride, pH, and sulfate). USEPA defines indicator constituents as
those that are present in CCRs and would rapidly move through the surface layer relative to
other constituents, and thus provide an early detection of whether contaminants are migrating
from the CCR unit (USEPA 2015a).
10.1.15 Thallium
Pure thallium is a soft, bluish white metal that is widely distributed in trace amounts in the
earth's crust. In its pure form, it is odorless and tasteless. It can be found in pure form or mixed
with other metals in the form of alloys. It can also be found combined with other substances
such as bromine, chlorine, fluorine, and iodine to form salts (EPRI 2008h).
Traces of thallium naturally exist in rock and soil. As rock and soil erode, small amounts of
thallium can occur in groundwater. In a USGS study of trace metals in soils, the variation in
thallium concentrations in A (i.e., surface) and C (i.e., substratum) soil horizons was estimated
across the United States. The overall thallium concentrations ranged from <0.1 mg/kg to 8.8
mg/kg. North Carolina concentrations from this study are shown on Figure 10-6. Thallium is
compared to IMAC since no 2L Standard was established for this constituent by NCDENR.
In a study by the Georgia Environmental Protection Division (EPD) of the Blue Ridge Mountain
and Piedmont aquifers, 120 sites were sampled for various constituents. Thallium was not
detected at any of these sites (method reporting limit = 1 pg/L) (Donahue and Kibler 2007).
10.1.16 Vanadium
Vanadium is widely distributed in the earth's crust at an average concentration of 100 ppm
(approximately 100 mg/kg), similar to that of zinc and nickel. Vanadium is the 22nd most
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abundant element in the earth's crust (EPRI 2008i). Occurrence of vanadium in groundwater is
known to be limited to its soluble oxidation state, V(V). Vanadium presence is mostly limited to
groundwater with relatively high dissolved oxygen concentrations and a basic pH (i.e., pH > 7)
(Wright and Belitz 2010; Canadian Council of Ministers of the Environment 1999). Vanadium is
compared to IMAC since no 2L Standard has been established for this constituent by NCDENR.
In a study by the Georgia EPD, 120 sites in the Blue Ridge and Piedmont physiographic regions
(regions shared with North Carolina) were sampled and detectible traces of vanadium were
found in six samples (with a reporting limit of 10 pg/L).
Using the USGS NURE database, all vanadium groundwater test results within a 20-mile radius
of the MSS site are shown on Figure 10-7. These samples were taken at depths ranging from
20 to 500 ft bgs, and the vanadium concentrations range from below detect to 19.2 pg/L. In the
four locations nearest to MSS, three concentrations are below the North Carolina IMAC of 0.3
pg/L, and one concentration is substantially greater. There is no federal MCL or SMCL for
vanadium.
10.1.17 pH
The pH scale is used to measure acidity or alkalinity. A pH value of 7 indicates neutral water. A
value lower than the USEPA-established SMCL range (<6.5 Standard Units) is associated with
an increased likelihood of experiencing bitter, metallic tasting water, and corrosion. A value
higher than the SMCL range (>8.5 Standard Units) is associated with a slippery feel, soda taste,
and deposits in the water (USEPA 2013).
In a statistical summary of groundwater quality in North Carolina, the Superfund Research
Program at UNC analyzed 1,480 private well water samples for pH in Catawba and Iredell
counties. The samples were analyzed by the North Carolina State Laboratory of Public Health
from 1998-2010. This study found that 22.22% of wells in Catawba County and 13.44% of wells
in Iredell County had a pH result outside of the USEPA's SMCL range (Table 10-2).
Using the USGS NURE database, all pH test results within a 20-mile radius of the MSS site are
shown on Figure 10-8.
10.2 Background Wells
Background (BG) monitoring well locations were identified based on the SCM at the time the
Work Plan was submitted. The background locations were strategically placed to maximize
physical separation from the ash basin, dry ash landfill, and PV structural fill in locations
believed not to be impacted based on existing knowledge of these areas, to provide sufficient
background water quality in the future.
Six background groundwater monitoring wells BG-1 S/D, BG-2S/BR, and BG-3S/D were
installed during the CSA activities to evaluate background water quality in the shallow (S wells),
deep (D wells), and bedrock (BR well) flow layers. The background monitoring wells were
installed northeast of the MSS ash basin and are separated from the source area by a series of
topographic divides. Background monitoring wells are depicted on Figure 10-9. A generalized
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well construction diagram for newly installed wells is shown on Figure 10-10. Well installation
procedures are documented in Appendix G, along with variances from the work plan. Boring
logs are provided in Appendix H. Predictive Limit Standards are also depicted in Appendix G.
Based on the developed groundwater elevation contours shown on Figures 6-5 through 6-7 and
the updated SCM, the newly installed background wells are not located hydraulically
downgradient of the ash basin, dry ash landfill, and PV structural fill areas, and are
representative of background groundwater quality conditions at the site. Currently, insufficient
data are available to statistically evaluate background concentrations in the newly installed
background monitoring wells. As data becomes available through periodic monitoring, statistical
analysis will be performed.
The background monitoring wells are located between 1,800 feet (BG-2S/BR) and 3,800 feet
(BG-1 S/D) northeast of the nearest extents of the ash basin waste boundary. Several
topographic divides separate the background wells from the ash basin and based on the slope
aquifer system in the Piedmont, and these topographic features likely represent groundwater
divides. Therefore, it is highly unlikely that groundwater in the vicinity of the background wells is
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 and one deep well located south of Lake Norman and east of the
MSS plant will be considered to provide sufficient background water quality in the future for the
site.
Existing ash basin compliance wells MW-4 and MW-4D have been considered by Duke Energy
to represent background water quality at the site since they were installed in 1989 and 2006,
respectively. MW-4 and MW-4D are located outside and upgradient (north) of the ash basin
waste boundary. MW-4 was installed to a total depth of 47.5 feet bgs with a 10-foot well screen
to monitor groundwater in the shallow layer. MW-4D was installed to a total depth of
approximately 60 feet bgs with a 5-foot screen to monitor groundwater in the top 15 feet of
fractured rock (similar to the newly installed groundwater assessment D wells). Historical
groundwater data for these monitoring wells dates back to November 2007, including a total of
20 sampling events. The wells have been sampled three times per year (February, June, and
November) since February 2011. This is considered sufficient data to adequately perform
statistical analysis of background concentrations in MW-4 and MW-4D (included in Appendix G).
Duke Energy recognizes that the NCDENR DWR Director is responsible for establishing site -
specific background levels for groundwater as stated in 15A NCAC 02L.0202(b)(3). The
concentrations in the statistical report are provided as information to aid in this determination,
and for comparative purposes for groundwater at the site. Prediction Limit Standards, developed
in accordance with Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities -
Unified Guidance (USEPA 2009), are provided in Appendix G for MW-4 And MW-4D.
Several compliance monitoring wells have previously exhibited concentrations in groundwater
exceeding 2L Standards or IMACs, including boron (MW-14S and MW-14D), iron (several
wells), manganese (several wells), sulfate (MW-14S and MW-14D), pH (several wells), TDS
(several wells), and thallium (MW-14S). MW-4 and MW-4D have historically been considered
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background wells at the site because they have not previously exhibited 2L exceedances or
detectable concentrations of any monitored constituents except for three instances of iron and
pH exceedances. Water table surface contours (Figure 6-5) indicate groundwater flow in the
vicinity of MW-4 is to the south toward the ash basin. Therefore, MW-4 and MW-4D were
utilized as site background monitoring wells for stacked time series plots for monitoring wells
depicted in Figures 10-11 through 10-72. The stacked time series plots compare turbidity to
constituent concentrations in all compliance wells. In addition, a trend plot showing groundwater
elevations in compliance monitoring wells over time is provided as Figure 10-73. Select
compliance (and voluntary) monitoring wells were sampled as part of this CSA and the results
are discussed in Section 10.6.7.
10.3 Discussion of Redox Conditions
Determination of the reduction/oxidation (redox) condition of groundwater is desirable as part of
groundwater assessments to help understand the mobility, degradation, and solubility of
contaminants. By applying the framework of the Excel Workbook for Identifying Redox
Processes in Ground Water (Jurgens, McMahon, Chapelle, and Eberts 2009) to the analytical
results, the predominant redox process, or category, was assigned to samples collected during
the groundwater assessment. Categories include oxic, suboxic, anoxic, and mixed. Assignment
of redox category was based upon concentrations of dissolved oxygen, nitrate as nitrogen,
manganese (II), iron (II), sulfate, and sulfide as inputs. Constituent criteria appropriate for inputs
to the Excel Workbook, as well as an explanation of the redox assignments, can be found in
Tables 1 and 2, respectively, of the USGS Open File Report 2009-1004 (Jurgens, McMahon,
Chapelle, and Eberts 2009). Redox assignment results are presented in Table 10-4.
10.4 Groundwater Analytical Results
A total of 83 groundwater monitoring wells were installed at MSS between March and July 2015
as part of the CSA. Eighteen of the newly installed wells are screened within ash basin
porewater, one well is screened within PV structural fill porewater, and one is screened within
dry ash landfill (Phase II) porewater (see Section 7). The remaining 63 newly installed wells
located outside or beneath the ash basin boundary, dry ash landfill (Phases I and II), and PV
structural fill represent groundwater. These monitoring wells were installed in general
accordance with procedures described in the Work Plan and a description is provided in
Appendix C. All site groundwater monitoring well locations are shown on Figure 10-9. New
monitoring well construction information is provided in Table 10-5. Boring logs are also provided
in Appendix H. Existing compliance and voluntary monitoring well information is provided in
Table 10-6.
Installed groundwater monitoring wells were developed prior to sampling activities in general
accordance with well development procedures detailed in Appendix G. Well development forms
are also included in Appendix G. Groundwater samples were subsequently collected and
analyzed in general accordance with the procedures and methods described in the Work Plan
and in Duke Energy's Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater
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Assessment Program, dated May 22, 2015. Any variances from the proposed development and
groundwater sampling plans are included in Appendix G.
As described in the approved Work Plan, both unfiltered and filtered (0.45 pm filter) samples
were collected for analyses of constituents.8 Unless otherwise noted, concentration results
discussed are for the unfiltered samples and represent total concentrations
Groundwater samples were collected from background locations (described above), locations
upgradient of the ash basin, beneath the ash basin, beneath the dry ash landfill (Phase 11), and
downgradient of the ash basin and dry ash landfill (Phase 1). Groundwater samples were also
collected from existing voluntary and compliance monitoring wells.
Parameters and constituent analytical methods for the groundwater samples collected are
provided in Table 7-3. Laboratory results for groundwater samples were compared to 2L
Standards and IMACs (Appendix K). Background groundwater results are presented in Table
10-7. Groundwater sample results (for total and dissolved constituents and other parameters)
for monitoring wells located upgradient of the ash basin (not considered background), beneath
the ash basin, and downgradient of the ash basin are presented in Table 10-8. Groundwater
sample results for monitoring wells located beneath the dry ash landfill are presented in Table
10-9. Field parameters collected at the time of sampling are provided in Table 10-10
Groundwater analytical results for constituents that exceeded the 2L Standards or IMACs are
depicted on Figure 10-74. Field and sampling quality control / quality assurance protocols are
provided in Appendix E.
10.4.1 Upgradient of the Ash Basin, Dry Ash Landfill (Phases I and II), and PV Structural
Fill
Seventeen groundwater monitoring wells (8 shallow, 8 deep, and 1 bedrock) were installed in
locations anticipated to be upgradient (separate from background) of the ash basin, dry ash
landfill, and PV structural fill: GWA-2S/D, GWA-3S/D, GWA-4S/D, GWA-5S/D, GWA-6S/D,
GWA-7S/D, GWA-8S/D, GWA-9BR, and AB-11 S/D. These groundwater monitoring wells were
installed to evaluate groundwater quality upgradient of the ash basin and to confirm
groundwater flow direction.
Groundwater flow direction as shown on the water table surface and deep and bedrock well
potentiometric surface maps (Figure 6-5 through 6-7) indicate that these monitoring wells are
located upgradient of the ash basin, the dry ash landfill (Phases I and 11), and the PV structural
fill.
Monitoring wells GWA-8S/D were installed to the north of the ash basin across Island Point
Road. Island Point Road is a topographic divide to the north of the ash basin and based on the
slope -aquifer system in the Piedmont, this road is located along a groundwater divide.
8 The USEPA (EPA 2002) recommends that when possible, especially when sampling for contaminants
that may be biased by the presence of turbidity, the turbidity reading is desired to stabilize at a value
below 10 Nephelometric Turbidity Units (NTUs)
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10.4.2 Beneath the Ash Basin
A total of 20 groundwater monitoring wells (1 shallow, 16 deep and 3 bedrock) were installed
beneath the footprint of the ash basin: AB-3D, AB-4D, AB-5D/BR, AB-6D/BR, AB-7D, AB-8D,
AB-10D, AB-12D, AB-13D, AB-14D, AB-15D/BR, AB-16S/D, AB-17D, AB-18D, AB-20D, and
AB-21 D. These groundwater monitoring wells were installed to evaluate groundwater quality
within the shallow, TZ, and bedrock zones beneath the ash basin. Note that ash was only
encountered in AB-21 D from approximately 17 to 30 ft bgs.
10.4.3 Beneath the Dry Ash Landfill (Phase 11)
Five monitoring wells (1 shallow, 3 deep, and 1 bedrock) were installed beneath the footprint of
the dry ash landfill (Phase II) and outside the ash basin waste boundary: AL-2S/D/BR, AL-3D,
and AL-41D. These groundwater monitoring wells were installed to evaluate groundwater quality
within the shallow, TZ, and bedrock zones beneath the dry ash landfill (Phase II).
10.4.4 Downgradient of the Ash Basin and Dry Ash Landfill (Phase 1)
A total of 15 groundwater monitoring wells (6 shallow, 5 deep, and 4 bedrock) were installed
downgradient of the ash basin and the dry ash landfill (Phase 1). The downgradient monitoring
wells are: AB-1 S/D/BR, AB-2S/D, AB-9S/D/BR, AL-1 S/D, GWA-1 S/D/BR, MW-14BR, and OB-1
(WLO). These groundwater monitoring wells were installed to evaluate groundwater quality
within the shallow, TZ, and bedrock zones downgradient of the ash basin and dry ash landfill
(Phase 1).
Monitoring wells AB-1 S/D/BR, AB-2S/D, and GWA-1 S/D/BR were installed within the footprint of
the Marshall Active Ash Basin Dam (CATAW-054) between the ash basin and Lake Norman.
Monitoring wells AB-9S/D/BR were installed just outside the ash basin northeast of the
constructed wetland wastewater treatment area and are considered downgradient of the
northwest portion of the ash basin. Monitoring well OB-1 (WLO) was installed between two outer
portions of the western extent of the ash basin and was originally proposed for the collection of
water levels only. However, groundwater samples were collected for laboratory analysis from
OB-1 (WLO) as part of this CSA.
Monitoring wells AL-1S/D and MW-14BR were installed east of the dry ash landfill (Phase 1)
between the ash basin and dry ash landfill (Phase 1), and an unnamed tributary that flows to
Lake Norman. The water table surface and deep potentiometric surface maps indicate
groundwater flows from the ash basin and dry ash landfill (Phase 1) in the direction of these
monitoring wells toward the unnamed tributary that flows to Lake Norman.
10.5 Comparison of Results to 2L Standards
Groundwater results were compared to 2L Standards and IMACs, and exceedances are
summarized below. Groundwater sample exceedances of 2L Standards and IMACs are shown
on Figure 10-74 and also provided in Table 10-8. See Section 17.3 for maximum contaminant
concentrations for groundwater.
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COls found in groundwater at the site include antimony, arsenic, barium, beryllium, boron,
chloride, chromium, cobalt, iron, lead, manganese, selenium, sulfate, thallium, TDS, and
vanadium, although many of these constituents reported above 2L Standards or IMACs are
likely due to naturally occurring concentrations, as discussed in Section 10.6.
Several Cols identified from source characterization sampling did not exceed their 2L
Standards or IMACs, including cadmium, copper, nickel, and zinc.
10.6 Comparison of Results to Background
10.6.1 Existing Background Wells MW-4 and MW-41D
Existing compliance monitoring wells MW-4 and MW-41D have historically been designated as
background wells at the site based on available data and non-exceedances of 2L Standards or
IMACs. With the exception of iron and pH, the results for all other monitored constituents have
been reported less than the 2L Standards or IMACs. Ranges of groundwater concentrations
reported in MW-4 and MW-4D for COls that exceeded 2L Standards or IMACs in groundwater
at the site, and that have been monitored at MW-4 and MW-41D since November 2007, are listed
below. Note that cobalt and vanadium were not previously included in the compliance
monitoring program at the site, but were added to the program in March 2015.
• Antimony <1 pg/L
• Arsenic <1 to <2 pg/L
• Barium
39.5 to 59 pg/L
• Beryllium
<1 pg/L
• Boron
<50 to <100 pg/L
• Chloride
1,300 to 2,100 pg/L
• Chromium
1.3 to <5 pg/L
• Cobalt
<1 pg/L
• Iron
16 to 1,380 pg/L
• Lead
<1 to <2 pg/L
• Manganese
<5 to 48 pg/L
• Selenium
<1 to <2 pg/L
• Sulfate
100 to 1,400 pg/L
• Thallium
<0.2 pg/L
• TDS
10,000 to 95,000 pg/L
• Vanadium
NA
Notes:
pg/L = micrograms per liter
NA = No analytical results through June 2015
10.6.2 Newly Installed Background Wells
Sampling results from the newly installed background wells (BG-1 S/D, BG-2S/BR, and BG-
3S/D) indicate that the following constituents exceeded 2L Standards or IMACs in one or more
of the newly installed background wells: barium, chromium, cobalt, iron, lead, manganese,
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thallium, and vanadium. Ranges of groundwater concentrations in newly installed background
wells for COls that exceeded 2L Standards or IMACs in groundwater at the site are listed below.
• Antimony
0.33J to <2.5 pg/L
• Arsenic
0.17J to 7.5 pg/L
• Barium
28 to 760 pg/L
• Beryllium
<0.2 to 0.76J pg/L
• Boron
26J+ to <50 pg/L
• Chloride
2,700 to 4,800 pg/L
• Chromium
3.1 to 80.4 pg/L
• Cobalt
0.38J to 11.9 pg/L
• Iron
140 to 18,200 pg/L
• Lead
0.19 to 17.5 pg/L
• Manganese
20 to 380 pg/L
• Selenium
0.37J to 1.6J pg/L
• Sulfate
1,100 to 16,000 pg/L
• Thallium
0.018J to 0.23J pg/L
• TDS
114,000 to 369,000 pg/L
• Vanadium
3.5 to 100 pg/L
Notes:
pg/L = micrograms per liter
J = Estimated concentration
J+ = Estimated concentration, biased high
The concentration ranges for antimony, arsenic, beryllium, boron, iron, lead, selenium, and
thallium in newly installed background wells (except for BG-2BR) from this first sampling event
are generally similar to concentration ranges in MW-4 and MW-4D. Concentrations of
constituents reported in the BG-2BR sample tend to be the maximum concentration for each
constituent in all background wells. The concentration ranges for barium, chromium, cobalt,
manganese, sulfate, and TDS are much broader in newly installed wells in this first sampling
event than in MW-4 and MW-41D.
Refer to Section 10.1 for a comparison of the above -referenced site -specific constituent
concentrations to regional groundwater constituent concentrations.
10.6.3 Upgradient of the Ash Basin, Dry Ash Landfill (Phases I and II), and PV Structural
Fill
With the exception of antimony, chromium, cobalt, iron, manganese, TDS, and vanadium, the
results for all other constituents were reported less than the 2L Standards or IMACs in
upgradient groundwater assessment monitoring wells GWA-2S/D, GWA-3S/D, GWA-5S/D,
GWA-5S/D, GWA-6S/D, GWA-7S/D, GWA-8S/D, GWA-9BR, and AB-11 S/D. The groundwater
sample results were also compared to the background and regional groundwater concentration
ranges. Ranges of groundwater concentrations for Cols that exceeded 2L Standards or IMACs
in groundwater upgradient of the ash basin, dry ash landfill (Phases I and II), and PV structural
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fill, along with the site background and regional groundwater concentration ranges, are provided
in Table 10-11.
Concentrations of COls in groundwater upgradient of the ash basin are similar to MW-4 and
MW-41D background concentrations and concentrations measured in newly installed background
wells.
10.6.4 Beneath the Ash Basin
With the exception of antimony, boron, chloride, cobalt, iron, manganese, TDS, and vanadium,
the results for all other constituents were reported less than the 2L Standards or IMACs in
groundwater assessment monitoring wells beneath the ash basin (AB-31D, AB-41D, AB-5D/BR,
AB-6D/BR, AB-71D, AB-81D, AB-10D, AB-12D, AB-13D, AB-14D, AB-15D/BR, AB-16S/D, AB-
17D, AB-18D, AB-20D, and AB-21 D). Ranges of groundwater concentrations for COls that
exceeded 2L Standards or IMACs in groundwater beneath the ash basin, along with the site
background and regional groundwater concentration ranges are provided in Table 10-12.
Concentrations of several COls reported in groundwater beneath the ash basin are higher than
MW-4 and MW-41D background concentration ranges and new background well concentrations
including boron, chloride, cobalt, manganese, sulfate, and TDS. A summary of these
groundwater sample results is provided below.
• Boron was reported at concentrations that exceeded background concentrations and the
2L Standard of 700 pg/L in deep monitoring wells AB-10D (1,200 pg/L), AB-12D (3,500
pg/L), and AB-61D (5,500 pg/L). AB-1 OD and AB-12D are located in the central portion of
the ash basin south of the dry ash landfill (Phase II). AB-6D is located in the west portion
of the ash basin. Bedrock well AB-6BR contained a boron concentration of 90 pg/L.
Several other deep monitoring wells spread throughout the ash basin (AB-31D, AB-41D,
and AB-14D) contained concentrations of boron that were higher than background, but
were below the 2L Standard.
• Chloride was reported at concentrations that exceeded background concentrations and
the 2L Standard of 250,000 pg/L in deep montioring well AB-12D (464,000 pg/L). AB-
12D is located in the central portion of the ash basin. Several other monitoring wells
spread throughout the ash basin (AB-41D, AB-5BR, AB-6BR, AB-71D, AB-10D, and AB-
16D) contained concentrations of chloride that were higher than background, but were
below the 2L Standard.
• Cobalt was reported at a concentration of 22.6 pg/L in the shallow well AB-16S, which is
higher than background concentrations and the IMAC of 1 pg/L. Several other
monitoring wells spread throughout the ash basin contained concentrations that
exceeded the IMAC, but were similar to or below background.
• Manganese was reported at concentrations that exceeded background concentrations
and the 2L Standard of 50 pg/L in shallow monitoring well AB-16S and deep montioring
wells AB-51D, AB-5BR, AB-61D, AB-81D, AB-1 OD, and AB-21 D.
• Sulfate was reported at concentrations that exceeded background concentrations in
monitoring wells AB-31D, AB-5D/BR, AB-6BR, AB-7D, AB-12D, AB-13D, AB-14D, AB-
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15D/BR, AB-16D, and AB-20D, but were all below the 2L Standard of 250,000 pg/L. The
highest concentration was reported in AB-12D (219,000 pg/L).
TDS was reported at a concentration of 1,530,000 pg/L in deep monitoring well AB-12D,
which is higher than background and the 2L Standard of 500,000 pg/L.
10.6.5 Beneath the Dry Ash Landfill (Phase II)
With the exception of barium, boron, chromium, cobalt, iron, manganese, selenium, sulfate,
TDS, and vanadium, the results for all other constituents were reported less than the 2L
Standards or IMACs in groundwater assessment monitoring wells beneath the dry ash landfill
(Phase II) (AL-2S/D/BR, AL-31D, and AL-41D). Ranges of groundwater concentrations for COls
that exceeded 2L Standards or IMACs in groundwater beneath the dry ash landfill (Phase II),
along with the site background and regional groundwater concentration ranges are provided in
Table 10-13.
Concentrations of several COls reported in groundwater beneath the dry ash landfill (Phase II)
are higher than MW-4 and MW-41D background concentration ranges and new background well
concentrations including barium, boron, cobalt, iron, manganese, selenium, sulfate, and TDS. A
summary of these groundwater sample results is provided below.
• Barium was reported at a concentration of 960 pg/L in the shallow well AL-2S, which is
higher than background concentrations and the 2L Standard of 700 pg/L.
• Boron was reported at concentrations that exceeded background concentrations and the
2L Standard of 700 pg/L in shallow monitoring well AL-2S (6,500 pg/L) and deep
monitoring wells AL-21D (6,500 pg/L), AL-31D (4,000 pg/L), and AL-4D (15,200 pg/L).
• Cobalt was reported at a concentration of 15.8 pg/L in the deep well AL-21D, which is
higher than background concentrations and the IMAC of 1 pg/L. Monitoring wells AL-2S,
AL-31D, and AL-4D contained concentrations that exceeded the IMAC but were similar to
or below background.
• Iron was reported at a concentration of 54,000 pg/L in the shallow well AL-2S, which is
higher than background concentrations and the 2L Standard of 300 pg/L. Monitoring
wells AL-2D, AL-31D, and AL-4D contained concentrations that exceeded the 2L
Standard, but were similar to or below background. The iron concentrations generally
exhibited a significant difference between unfiltered and filtered results, indicating that
suspended solids may have contributed to higher concentrations in unfiltered samples.
• Manganese was reported at concentrations that exceeded background concentrations
and the 2L Standard of 50 pg/L in shallow monitoring well AL-2S and deep montioring
wells AL-2D, AL-31D, and AL-41D.
• Selenium was reported at concentrations that exceeded background concentrations and
the 2L Standard of 20 pg/L in shallow monitoring well AL-2S and bedrock monitoring well
AL-213R. Monitoring wells AL-2D, AL-3D, and AL-41D contained concentrations that
exceeded background concentrations but were below the 2L Standard.
• Sulfate was reported at concentrations that exceeded background concentrations and
the 2L Standard of 250,000 pg/L in shallow monitoring well AL-2S and deep montioring
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wells AL-2D, AL-3D, and AL-4D. The sulfate concentration in bedrock well AL-2BR was
higher than background but did not exceed the 2L Standard.
• TDS was reported at concentrations that exceeded background concentrations and the
2L Standard of 500,000 pg/L in shallow monitoring well AL-2S and deep monitoring wells
AL-2D, AL-3D, and AL-4D. The sulfate concentration in bedrock well AL-2BR was higher
than background but did not exceed the 2L Standard.
10.6.6 Downgradient of the Ash Basin and Dry Ash Landfill (Phase 1)
With the exception of boron, beryllium, chloride, chromium, cobalt, iron, manganese, selenium,
thallium, TDS, and vanadium, the results for all other constituents were reported less than the
2L Standards or IMACs in downgradient groundwater assessment monitoring wells GWA-
1 S/D/BR, AB-1 S/D/BR, AB-2S/D, AB-9S/D/BR, AL-1 S/D, GWA-1 S/D/BR, MW-14BR, and OB-1
(WLO). Ranges of groundwater concentrations for COls that exceeded 2L Standards or IMACs
in downgradient monitoring wells, along with the site background and regional groundwater
concentration ranges are provided in Table 10-14.
Concentrations of several COls reported in groundwater downgradient of the ash basin and dry
ash landfill (Phase 1) are higher than MW-4 and MW-4D background concentration ranges and
new background well concentrations including beryllium, boron, chloride, cobalt, manganese,
selenium, sulfate, thallium, and TDS. A summary of these groundwater sample results is
provided below.
• Beryllium was reported at a concentration of 9.9 pg/L in the shallow well AL-1 S, which is
higher than background and the IMAC of 4 pg/L.
• Boron was reported at concentrations that exceeded background concentrations and the
2L Standard of 700 pg/L in shallow monitoring wells AB-1 S (5,200 pg/L) and AL-1 S
(4,200 pg/L), and deep monitoring well AL-1 D (1,300 pg/L). Deep monitoring wells AB-
1 D and AB-2D, and bedrock well AB-1 BR contained concentrations that exceeded
background concentrations but were below the 2L Standard.
• Chloride was reported at a concentration that exceeded background concentrations and
the 2L Standard of 250,000 pg/L in shallow monitoring well AL-1 S. Shallow wells AB-1 S
and AB-2S, deep wells AB-1 D and AL-1 D, and bedrock well AB-1 BR contained
concentrations that exceeded background concentrations but were below the 2L
Standard.
• Cobalt was reported at concentrations of 27.1 pg/L in the shallow well AB-1 S and 28.1
pg/L in the deep well AB-9D, which are higher than background concentrations and the
IMAC of 1 pg/L. Monitoring wells AB-1 D, AB-2S, AB-9S, AL-1 S, AL-1 D, GWA-1 BR, and
GWA-1 S contained concentrations that exceeded the IMAC but were similar to or below
background.
• Manganese was reported at concentrations that exceeded background concentrations
and the 2L Standard of 50 pg/L in shallow monitoring wells AB-1 S, AL-1 S, and GWA-1 S,
and deep montioring well AL-2D.
• Selenium was reported at a concentration of 6.1 pg/L in shallow well AB-1 S, which is
higher than background but below the 2L Standard of 20 pg/L.
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• Sulfate was reported at concentrations that exceeded background concentrations, but
were below the 2L Standard of 250,000 pg/L in several wells including AB-1 BR, AB-1 D,
AB-1 S, AB-21D, AB-2S, AL-1 D, AL-1 S, AB-9BR, GWA-1 BR, and GWA-1 D.
• Thallium was reported at concentrations that exceeded background concentrations and
its IMAC of 0.2 pg/L in shallow monitoring wells AB-1S and AL-1S.
• TDS was reported at concentrations that exceeded background concentrations and the
2L Standard of 500,000 pg/L in shallow monitoring well AB-1 S and AL-1 S, and deep
monitoring wells AB-1 D and AL-1 D. The sulfate concentration in deep well GWA-1 D was
higher than background, but did not exceed the 2L Standard.
10.6.7 Compliance and Voluntary Wells
The following compliance and voluntary monitoring wells were sampled to supplement
groundwater data for this CSA: MW-4, MW-41D, MW-7S, MW-10S, MW-1 OD, MW-11 S, MW-
11 D, MW-12S, MW-12D, MW-13S, MW-13D, MW-14S, and MW-14D. Ranges of groundwater
concentrations for the COls that exceeded 2L Standards or IMACs in compliance and voluntary
groundwater monitoring wells at the site are included in Table 10-15. The following COls were
reported above background concentrations and 2L Standards or IMACs in voluntary monitoring
well MW-7S: arsenic, boron, cobalt, manganese, selenium, thallium, and TDS. Beryllium,
chloride, and sulfate were reported in MW-7S above background concentrations but were below
their respective 2L Standards or IMACs. Boron was reported above background concentrations
and the 2L Standard in compliance monitoring wells MW-14S and MW-14D. TDS was reported
above background and the 2L Standard in MW-14S, and was reported above background but
below the 2L Standard in MW-14D. Chloride, selenium, and sulfate were reported above
background in MW-14S and MW-14D, but below the 2L Standard. All other compliance and
voluntary wells had reported concentrations similar to or below background concentrations.
Sample results from upgradient compliance wells are consistent with previous results from
historical and routine compliance monitoring well data for the site. With the exception of cobalt,
iron, manganese, and vanadium, the results for all other constituents were reported less than
the 2L Standards or IMACs and were generally similar to or less than background
concentrations.
The USEPA recommends that when possible, especially when sampling for constituents that
may be biased by the presence of turbidity, that turbidity values in the stabilized well should be
less than 10 Nephelometric Turbidity Units (NTUs) (USEPA 2002). Compliance monitoring wells
with analytical results exceeding the 2L Standards for iron and/or manganese have been
individually plotted with the associated turbidity values (Figures 10-25 through 10-38.2).
Maximum contaminant concentrations for groundwater can be found in Section 17.3.
Groundwater isoconcentration contours for each COI that exceeded 2L Standards or IMACs in
groundwater at the site are depicted in Figures 10-75 through 10-122. Cross -sections
presenting horizontal and vertical distribution of COls along the transects are depicted on
Figures 10-123.1 through 10-125.3. COls with exceedances of 2L Standards or IMACs will be
modeled in the CAP.
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10.7 Cation and Anion Water Quality Data
Cation and anion concentrations can be used to describe the chemical composition of
groundwater in an aquifer. In natural waters, the cations calcium, magnesium, sodium and
potassium and the anions, chloride, sulfate, carbonate, and bicarbonate will make up 95% to
100% of the ions in solution.
Cation and anion concentrations at the MSS site from ash basin porewater, ash basin surface
water, background groundwater monitoring wells, upgradient groundwater monitoring wells,
downgradient groundwater monitoring wells, seeps, and surface water sample SW-6 are shown
on Figures 10-126 through 10-140. In addition, Figures 10-141 through 10-155 depict ratios of
sulfate and chloride in monitoring wells across the site. In general, calcium, magnesium, and
sulfate are elevated in ash basin porewater wells compared to upgradient and background
wells.
The relative concentrations and distribution of the cations and anions can be used to compare
the relative ionic composition of different water quality samples through the use of Piper
diagrams. Piper diagrams were generated for the MSS site to compare geochemistry between
ash basin porewater and ash basin surface water to background monitoring wells, upgradient
monitoring wells, downgradient monitoring wells, seeps, surface water sample SW-6, and all
wells at the site. In general, geochemistry of groundwater at the site is less chloride and sulfate
rich than ash basin porewater, ash basin surface water, and downgradient groundwater which
were observed to be trending closer to calcium, chloride, magnesium, and sulfate rich. Piper
diagrams are included as Figures 10-156 through 10-167.
10.8 Groundwater Speciation
Twenty-two monitoring wells, including groundwater assessment wells located along anticipated
flow transects, existing and new background wells, and compliance monitoring wells that were
sampled as part of this CSA were sampled for chemical speciation analyses of arsenic (III),
arsenic (V), chromium (VI), iron (II), iron (III), manganese (II), manganese (IV), selenium (IV),
and selenium (VI). Groundwater speciation results for monitoring wells sampled as part of this
CSA are provided in Table 10-16. Further evaluation of chemical speciation results will be
included in the CAP.
10.9 Radiological Laboratory Testing
Radionuclides may exist dissolved in water from natural sources (e.g., soil or rock). The USEPA
regulates various radionuclides in drinking water. For purposes of this assessment, radium-226,
radium-228, natural uranium-238, uranium-233, uranium-234, and uranium-236 were analyzed.
Five wells (BG-1 S/D, MW-7S, MW-14S, and MW-14D) were sampled for the analytes listed
above. Results for radiological laboratory testing are presented in Table 10-17. Further
evaluation of radiological laboratory testing results will be included in the CAP.
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10.10 CCR Rule Groundwater Detection and Assessment
Monitoring Parameters
Appendix III to Part 257 Constituents for Detection Monitoring and Appendix IV to Part
257 Constituents for Assessment Monitoring
On April 17, 2015, USEPA published its final rule "Disposal of Coal Combustion Residuals from
Electric Utilities" (Final Rule), amending 40 CFR Parts 257 & 261, to regulate the disposal of
CCR as solid waste under subtitle D of the Resource Conservation and Recovery Act (RCRA).
Among other requirements, the Final Rule establishes requirements for a groundwater
monitoring program consisting of detection monitoring and, if necessary, assessment monitoring
and corrective action.
The USEPA defined a phased approach to groundwater monitoring. The first phase is detection
monitoring where indicators would be monitored to determine whether groundwater was
potentially being contaminated. The parameters USEPA considers to be indicators of
groundwater contamination are boron, calcium, chloride, fluoride, pH, sulfate, and TDS. In
selecting the constituents for detection monitoring, USEPA chose constituents that are present
in CCR and would rapidly move through the surface layer, relative to other constituents, and
thus provide an early detection of whether contaminants are migrating from the CCR unit. When
a statistically significant increase over background levels is detected for any of these
constituents, the Final Rule requires the facility to begin an assessment monitoring program to
determine if releases of CCR constituents have occurred. The parameters selected for
assessment monitoring are antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt,
fluoride, lead, lithium, mercury, molybdenum, radium 226 and 228, selenium, and thallium
(USEPA 2015a).
USEPA selected constituents for detection monitoring that are present in CCR, would be
expected to migrate rapidly, and that would provide early detection as to whether contaminants
were migrating from the disposal unit. (80 Fed. Reg. 21302, 21397).
As stated in the FR (80 FR 21302, 21342):
These detection monitoring constituents or inorganic indicator parameters are:
boron, calcium, chloride, fluoride, pH, sulfate and total dissolved solids (TDS).
These inorganic indicator parameters are known to be leading indicators of
releases of contaminants associated with CCR and the Agency strongly
recommends that State Directors add these constituents to the list of indicator
parameters to be monitored during detection monitoring of groundwater if and
when a MSWLF decides to accept CCR. (Emphasis added)
NCDENR requested that figures be included in the CSA report that depict groundwater
analytical results for the constituents in 40 CFR 257, Appendix III detection monitoring and 40
CFR 257, Appendix IV assessment monitoring.
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Constituents for detection monitoring listed in 40 CFR 257 Appendix III are:
• Boron
• Calcium
• Chloride
• Fluoride (this constituent was not analyzed for in the CSA)
• pH
• Sulfate
• Total dissolved solids (TDS)
Results for detection monitoring constituents are found on Figures 10-168 through 10-170.
Constituents for assessment monitoring listed in 40 CFR 257 Appendix IV include:
• Antimony
• Arsenic
• Barium
• Beryllium
• Cadmium
• Chromium
• Cobalt
• Fluoride (not analyzed for in the CSA)
• Lead
• Lithium (not analyzed for in the CSA)
• Mercury
• Molybdenum
• Selenium
• Thallium
• Radium 226 and 228 combined
Results for assessment monitoring constituents are found on Figures 10-171 through 10-173.
Aluminum, copper, iron, manganese, and sulfide were included in the Appendix IV constituents
in the draft rule; USEPA removed these constituents in the final rule. Therefore, these
constituents are not included on the above -referenced figures. In addition, NCDENR requested
that vanadium be included on these figures. Vanadium concentrations are included on the
isoconcentration maps included as Figures 10-120 through 10-122 and on Figure 10-74 where
vanadium exceeded the IMAC.
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11.0 Hydrogeological Investigation
The purpose of the hydrogeological investigation is to characterize site hydrogeological
conditions including groundwater flow direction, hydraulic gradient and conductivity,
groundwater and contaminant velocity, and slug and aquifer test results. The hydrogeological
investigation was performed in general accordance with procedures described in the Work Plan.
Refer to Appendix H for a description of these methods.
11.1 Hydrostratigraphic Layer Development
The following materials were encountered during the site exploration and are consistent with
material descriptions from previous site exploration studies:
• Ash — Ash was encountered in borings advanced within the ash basin, dry ash landfill,
and PV structural fill, as well as in some borings advanced through basin dikes. Ash was
generally described as dark yellow -brown to very dark gray, non -plastic, loose to very
loose, and dry to wet.
• Fill — Fill is primarily used in the construction of dikes and as cover for landfills and the
structural fill. Fill material at the MSS site generally consisted of re -worked sandy silts,
clays, and sands that were borrowed from one area of the site and re -distributed to other
areas. Fill was classified in the boring logs as silty sand, gravel with clay and sand, sand
with silt and gravel, and silt.
• Alluvium —Alluvium encountered in borings AB-91D, AB-11 D, GWA-31D and AB-20D was
classified as sand, sand with silt and gravel with sand, wet, and medium dense.
• Residuum (Residual soils) — Residuum is the in -place weathered soil that consists
primarily of silt, sand with silt, clay with sand, sandy silt with gravel, clay, sandy clay, and
sandy clay with gravel at the MSS site. Residuum varied in thickness and was relatively
thin compared to the thickness of saprolite.
• Saprolite — Saprolite is soil developed by in -place weathering of rock that retains
remnant bedrock structure. Saprolite at the MSS site was classified primarily as sand
with silt, silty sand, sand with silt and gravel, sand, clayey sand, clayey sand with gravel,
and sand with gravel. Saprolite was primarily tens of feet thick at the MSS site, but in
some cases was over 80 feet thick.
• Partially Weathered/Fractured Rock — Partially weathered (slight to moderate) and/or
highly fractured rock was encountered below auger refusal.
• Bedrock — Sound rock in boreholes was generally slightly weathered to fresh and
relatively unfractured.
Based on the CSA site investigation, the groundwater system is consistent with the regolith-
fractured bedrock system discussed in Section 5.2. To define the hydrostratigraphic units, the
classification system described by Schaeffer (2014a), used to show that the TZ is present in the
Piedmont groundwater system (discussed in Section 5-2), was modified to define the
hydrostratigraphic layers of the natural groundwater system. The classification system is based
on Standard Penetration Testing values (N) and the Recovery (REC) and Rock Quality
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Designation (RQD) collected during the drilling and logging of the boreholes (refer to
borehole/well logs in Appendix H). The ash, fill, and alluvial layers are as encountered at the
site. The natural system (except alluvium) includes the following layers:
• M1 — Soil/Saprolite: N<50
• M2 — Saprolite/Weathered Rock: N>50 or REC<50%
• TZ — Transition Zone: REC>50% and RQD<50%
• BR — Bedrock: REC>85% and RQD>50%
Rock core runs that fell between the values for TZ and BR (REC<85% and RQD>50% or
REC>85% and RQD<50%) were assigned a hydrostratigraphic layer based on a review of the
borehole logs, rock core photographs, and geologic judgment. The same review was performed
in making the final determination of the thickness of the TZ as it could extend into the next core
run that meets the BR criterion because of potential core loss or fractured/jointed rock with
indications of water movement (iron/manganese staining).
The above layer designations (M1, M2, TZ, and BR) are used on the geologic cross -sections
with transect locations shown on Figure 8-2. The ash, fill, and alluvial layers are represented by
A, F, and S, respectively, on the cross -sections and applicable tables referenced in this section.
11.2 Hydrostratigraphic Layer Properties
The material properties required for the groundwater flow and transport model, total porosity,
effective porosity, specific yield and specific storage for ash, fill, alluvium, and soil/saprolite were
developed from CSA laboratory testing (Table 11-1; test data in Appendix H), historic laboratory
testing (Table 1-1 in Appendix H), and published data (Domenico and Mifflin 1965). Table 11-1
has a column titled 'Estimated Specific Yield/Effective Porosity' and the values are estimated
from the laboratory soil data (grain size analysis) utilizing Fetter -Bear diagrams (worksheets in
Appendix H), as described by Johnson (1967) and published data. This technique provides a
simple method to estimate specific yield; however, there are limitations to the method that may
not provide an accurate determination of the specific yield of a single sample (Robson 1993).
Specific yield/effective porosity were determined for a number of samples of the A, F, S, M1,
and M2 layers to provide an average and range of expected values. The effective porosity
(primarily fracture porosity) and specific storage of the TZ and bedrock were estimated from
published data (Sanders 1998; Domenico and Mifflin 1965).
Hydraulic conductivity (horizontal and vertical) of all layers, except vertical hydraulic conductivity
for the TZ and bedrock (BR), was developed utilizing site historic permeability data, in -situ
permeability testing (falling head, constant head, and packer testing where appropriate), slug
tests in completed monitoring wells, and laboratory testing of undisturbed samples (ash, fill,
soil/saprolite test results in Appendix H) during this investigations
11.2.1 Borehole In -Situ Tests
In -situ horizontal (open hole) and vertical (flush bottom) permeability tests, either falling or
constant head as appropriate for field conditions, were performed in each of the
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hydrostratigraphic units above refusal, ash, fill, alluvium, and soil/saprolite. In -situ borehole
horizontal permeability tests, either falling or constant head tests as appropriate for field
conditions, were performed just below refusal in the first 5 feet of a rock cored borehole (TZ, if
present).
The flush bottom test involves advancing the borehole through the overburden with a casing
advancer until the test interval is reached. The cutting tool is removed from the casing and the
casing is filled with water to the top and the drop of the water level in the casing is measured
over a period of 60 minutes. In the open hole test, after the top of the test interval is reached,
the cutting tool but not the casing, is advanced an additional number of feet (5 feet in the
majority of tests) and drop of the water level in the casing is measured over a period of 60
minutes. The constant head test is similar except the water level is kept at a constant level in
the casing and the water flow -in is measured over a period of 60 minutes. The constant head
test was only used when the water level in the borehole was dropping too quickly back to the
static water level such that the time interval was insufficient to calculate the hydraulic
conductivity. The results of the field permeability testing are summarized in Table 11-2 and the
worksheets are provided in Appendix H.
Packer tests (shut-in and pressure tests) were conducted in a minimum of five boreholes. The
shut-in test is performed by isolating the zone between the packers (in effect, a piezometer) and
measuring the resulting water level over time until the water level is stable. The shut-in test
provides an estimate of the vertical gradient during the test interval. The pressure test involves
forcing water under pressure into rock through the walls of the borehole providing a means of
determining the apparent horizontal hydraulic conductivity of the bedrock. Each interval is tested
at three pressures with three steps of 20 minutes up and two steps of 5 minutes back down. The
pressure test results are summarized in Table 11-2 and the shut-in and packer tests worksheets
are provided in Appendix H.
Where possible, tests were conducted at borehole locations specified in the Work Plan and at
test intervals based on site -specific conditions at the time of the groundwater assessment work.
The U.S. Bureau of Reclamation (1995) test method and calculation procedures, as described
in Chapter 10 of their Ground Water Manual (2nd Edition), were used for the field permeability
and packer tests.
11.2.2 Monitoring Well and Observation Well Slug Tests
Hydraulic conductivity (slug) tests were completed in monitoring wells and observation wells
under the direction of the Lead Geologist/Engineer. Slug tests were performed to meet the
requirements of the May 31, 2007 NCDENR memorandum titled, Performance and Analysis of
Aquifer Slug Tests and Pumping Tests Policy. Water level change during the slug tests was
recorded by a data logger. The slug test was performed for no less than 10 minutes, or until
such time as the water level in the test well recovered 95 percent of its original pre-tests level,
whichever occurred first. Slug tests were terminated after 60 minutes even if the 95 percent pre-
test level was not achieved. Slug test field data was analyzed using the Aqtesolv (or similar)
software and the Bouwer and Rice method.
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Slug test results are presented in Table 11-3 and the slug test report is provided in Appendix H
Historic slug test data is presented in Table 11-4.
11.2.3 Laboratory Permeability Tests
Laboratory permeability tests were conducted on undisturbed samples (Shelby tubes) of ash,
fill, soil, and saprolite collected during the field investigation. The tests were performed in
accordance with ASTM D 5084 (ASTM 2010d). Results of the laboratory permeability tests are
presented in Table 11-5 and historic laboratory permeability tests are presented in Table 11-6.
11.2.4 Hydrostratigraphic Layer Parameters
The soil material parameters for the A (ash), F (fill), S (alluvium), M1 (soil/saprolite), and M2
(saprolite/weathered rock) were developed by grouping the data into their respective
hydrostratigraphic unit and calculating the mean, median, and standard deviation of the different
parameters. Estimated values for total porosities for the hydrostratigraphic layers A, F, S, M1,
and M2 are presented in Table 11-7. Values for estimated effective porosity/specific yield are
presented in Table 11-8. The values for specific storage presented in Table 11-8 are based on
published data (Domenico and Mifflin 1965). The hydraulic conductivity parameters were
developed by grouping the data into their respective hydrostratigraphic units and calculating the
geometric mean, median, and standard deviation of the different parameters. Vertical hydraulic
conductivity values are not available for the TZ and BR units, but are unlikely to be equal. As an
initial assumption, vertical hydraulic conductivity for these units can be considered equal to the
horizontal hydraulic conductivity and adjusted as necessary during flow model calibration.
Horizontal and vertical hydraulic conductivity parameters are presented Tables 11-9 and 11-10,
respectively. The values of secondary (effective) porosity and specific storage for the TZ and
BR units are based on published values (Sanders 1998; Domenico and Mifflin 1965), and are
presented in Table 11-11. Further development of the above parameters and others required for
the flow and contaminant transport model will be provided in the CAP.
11.3 Hydraulic Gradient
Horizontal hydraulic gradient is calculated by taking the difference in hydraulic head over the
distance between two wells with similar well construction. Section 6.2.2 provides additional
details for horizontal hydraulic gradients calculated for the site.
Vertical hydraulic gradient was calculated by taking the difference in groundwater elevation in a
deep and shallow well pair over the difference in total well depth of the deep and shallow well
pair. A positive output indicates upward flow and a negative output indicates downward flow.
Sixteen well pair locations, each consisting of a shallow and deep groundwater monitoring well,
were used to calculate vertical hydraulic gradient across the site. Based on review of the results,
vertical gradient of groundwater is generally downward across the site. Vertical gradient
calculations are summarized in Table 11-13.
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11.4 Groundwater Velocity
Darcy's Law is an equation that describes the flow rate or flux of fluid through a porous media.
To calculate the velocity that water moves through a porous media, the specific discharge, or
Darcy flux, is divided by the effective porosity, n, The result is the average linear velocity or
seepage velocity of groundwater between two points.
The following equation was used to calculate groundwater velocities through each
hydrostratigraphic unit present at the site:
v = Ki
n
where vis velocity; Kis horizontal hydraulic conductivity; i is
horizontal hydraulic gradient; and n is the effective porosity
Seepage velocities for groundwater were calculated using horizontal hydraulic gradients
established in Section 6.2.2, horizontal hydraulic conductivity values for each hydrostratigraphic
unit established in Table 11-10, and effective porosity values established in Tables 11-9 and 11
12. Hydrostratigraphic layers are defined in Section 11.1. Average groundwater seepage
velocity results are summarized in Table 11-12.
The rate of groundwater migration varies with the hydraulic conductivity and porosity of the site
soil, TZ, and bedrock materials; and ranged from 6.5 ft/yr to 88.6 ft/yr in soils, 3.0 x 104 ft/yr to
3.2 x 107 ft/yr in the TZ (PWR), and 2.7 x 105 ft/yr to 6.9 x 105 ft/yr in bedrock.
11.5 Contaminant Velocity
Contaminant velocity depends on factors such as the rate of groundwater flow, the effective
porosity of the aquifer material, and the soil -water partition coefficient, or Kd term. Site -specific
Kd terms will be developed using samples collected during the site investigation. Testing to
develop the Kd terms is still underway and the results will be presented in the CAP. The
groundwater modeling to be performed in the CAP will identify groundwater velocities for the
modeled contaminants.
11.6 Plume's Physical and Chemical Characterization
The physical and chemical characterization of groundwater impacts at the site is detailed below
for each COI that exceeded its respective 2L Standard or IMAC in groundwater samples at the
site.
Isoconcentration maps showing the horizontal extent of all COls detected in groundwater above
2L Standards and IMACs in shallow, deep, and bedrock wells are included as Figures 10-75
through 10-122. Note that the horizontal extents of constituents depicted in these figures are
based on a single groundwater sampling event.
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• Antimony concentrations that exceeded the IMAC are mainly limited to the deep flow
layer at three locations upgradient of the ash basin (GWA-2D, GWA-31D, and GWA-6D).
Antimony was reported at a concentration slightly above the IMAC in bedrock well AB-
6BR, which is located beneath the west portion of the ash basin.
• Arsenic concentrations that exceeded the 2L Standard are limited to the shallow flow
layer immediately downgradient of the ash basin dam in voluntary monitoring well MW-
7S (10.4 fag/L). No arsenic exceedances were reported in the deep and bedrock wells.
• Barium concentrations that exceeded the 2L Standard are limited to shallow well AL-2S
(960 pg/L) located beneath the dry ash landfill (Phase II). No other groundwater samples
exceeded background barium concentrations in shallow, deep, and bedrock wells.
Barium was reported at a concentration of 760 pg/L in the deep background well BG-31D.
• Beryllium concentrations that exceeded the IMAC are limited to the shallow flow layer
downgradient of the ash basin and dry ash landfill (Phase 1) in monitoring well AL-1S
(9.9 pg/L). No other beryllium 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
beneath the dry ash landfill (Phase 11) (AL-2S; 6,500 pg/L), to the east and downgradient
of the ash basin and dry ash landfill (Phase 1) (MW-14S; 2,700 pg/L and AL-1 S; 4,600
fag/L), and to the southeast and downgradient of the ash basin (AB-1 S; 5,200 pg/L and
MW-7S; 5,300 pg/L). In the deep flow layer, exceedances were reported beneath the dry
ash landfill (Phase 11) (AL-2D; 6,500 pg/L, AL-31D; 4,000 pg/L and AL-41D; 15,200 pg/L),
beneath the central portion of the ash basin (AB-1 OD; 1,200 pg/L and AB-12D; 3,500
pg/L), beneath the western portion of the ash basin (AB-6D; 5,500 pg/L), and east and
downgradient of the ash basin and dry ash landfill (Phase 1) (MW-14D; 2,600 pg/L and
AL-1 D; 1,300 pg/L). In the bedrock flow layer, one boron exceedance was reported
beneath the dry ash landfill (Phase 11) (AL-2BR; 2,100 pg/L).
• Chloride concentrations that exceeded the 2L Standard are limited to the shallow flow
layer downgradient of the ash basin and dry ash landfill (Phase 1) in monitoring well AL-
1 S (260,000 pg/L) and the deep flow layer beneath the central portion of the ash basin
(AB-12D; 464,000 pg/L). No other chloride 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, including background samples. In the shallow flow layer,
chromium exceedances were reported beneath the dry ash landfill (Phase 11) (AL-2S;
15.5 pg/L), to the east and downgradient of the ash basin and dry ash landfill (Phase 1)
(AL-1 S; 30.9 pg/L), upgradient of the ash basin (GWA-7S; 22.1 pg/L), and in background
well BG-3S (73.7 fag/L), which exhibited the highest chromium concentration in the
shallow layer. The chromium exceedances in shallow groundwater generally exhibited a
significant difference between unfiltered and filtered results, indicating that suspended
solids may have contributed to higher concentrations in unfiltered samples. In the deep
flow layer, exceedances are limited to three locations upgradient of the ash basin (GWA-
2D, GWA-31D, and GWA-61D). The highest concentration was reported in GWA-21D (182
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pg/L). In the bedrock flow layer, chromium exceedances were reported beneath the dry
ash landfill (Phase II) (AL-2BR; 17.5 pg/L) and in background well BG-2BR (80.4 pg/L).
• Cobalt concentrations that exceeded the IMAC are present across the site in the
shallow, deep, and bedrock flow layers, including in background samples. In the shallow
layer, concentrations that exceeded the IMAC and background are located downgradient
and southeast of the ash basin at monitoring wells AB-1 S (27.1 pg/L) and MW-7S (57.6
pg/L), and beneath the north portion of the ash basin at monitoring well AB-16S (22.6
pg/L). In the deep flow layer, cobalt concentrations that exceeded the IMAC and
background are located beneath the dry ash landfill (Phase II) (AL-2D; 15.8 pg/L) and
adjacent to and downgradient of the central portion of the ash basin (AB-9D; 28.1 pg/L).
The maximum background concentration of cobalt was reported in the bedrock
monitoring well BG-2BR (11.9 pg/L). Two other bedrock wells contained cobalt
concentrations (AB-5BR; 7.9 pg/L and GWA-1 BR; 1.7 pg/L) that exceeded the IMAC,
but were below background concentrations.
• Iron concentrations that exceeded the 2L Standard are present in the shallow, deep, and
bedrock wells and are generally across the site, including background wells. The highest
iron concentrations were reported in background bedrock well BG-2BR (18,200 pg/L)
and beneath the dry ash landfill (Phase II) in shallow well AL-2S (54,000 pg/L). The iron
concentrations generally exhibited a significant difference between unfiltered and filtered
results, indicating that suspended solids may have contributed to higher concentrations
in unfiltered samples.
• Lead concentrations did not exceed the 2L Standard in any of the groundwater samples
at the site except for the bedrock background well BG-2BR (17.5 pg/L).
• Manganese concentrations that exceeded the 2L Standard are present in the shallow,
deep, and bedrock wells and are generally reported across the site, including
background wells. The highest concentrations reported in the shallow wells are
southeast and downgradient of the ash basin (AB-1 S; 8,000 pg/L and MW-7S; 6000
pg/L), east and downgradient of the dry ash landfill (Phase 1) (AL-1 S; 3,600 pg/L), and
beneath and adjacent to the dry ash landfill (Phase II) (AL-2S; 1,200 pg/L and AB-16S;
1,400 pg/L). The highest concentrations were reported in the deep wells are beneath the
dry ash landfill (Phase II) (AL-2D; 8,400 pg/L) and beneath the southwest portion of the
ash basin (AB-5D; 1,800 pg/L). Bedrock concentrations vary and are within the
background range for manganese except for the reported concentration at AB-5BR (650
pg/L).
• Selenium concentrations that exceeded the 2L Standard are limited to the shallow and
bedrock layers beneath the dry ash landfill (Phase II). The concentration reported in
shallow well AL-2S (108 pg/L) was significantly higher than the concentration reported in
the bedrock well at this location (AL-2BR; 24 pg/L). No other selenium exceedances
were reported in shallow, deep, and bedrock wells.
• Sulfate concentrations that exceeded the 2L Standard are limited to the shallow and
deep flow layers beneath the dry ash landfill (Phase II). The highest concentration of
sulfate was reported in shallow well AL-2S (979,000 pg/L). Concentrations were
considerably lower in the deep wells beneath the dry ash landfill (Phase II) (AL-2D;
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386,000 pg/L, AL-31D; 402,000 pg/L, and AL-41D; 308,000 pg/L). No other sulfate
exceedances were reported in deep and bedrock wells.
Thallium concentrations that exceeded the IMAC are present in the shallow flow layer
east of the ash basin and dry ash landfill (Phase 1) (AL-1 S; 0.33 pg/L), and southeast
and downgradient of the ash basin (AB-1 S; 0.28 pg/L and MW-7S; 0.37 pg/L). Thallium
was reported at an estimated concentration of 0.23J pg/L in the background bedrock
well BG-213R. No other thallium exceedances were reported in shallow, deep, and
bedrock wells.
• TDS concentrations that exceeded the 2L Standard are present in the shallow and deep
flow layers. In the shallow flow layer, TDS exceedances were reported beneath the dry
ash landfill (Phase 11) (AL-2S; 1,610,000 pg/L), to the east and downgradient of the ash
basin and dry ash landfill (Phase 1) (MW-14S; 552,000 pg/L and AL-1 S; 831,000 pg/L),
and to the southeast and downgradient of the ash basin (AB-1 S; 781,000 pg/L and MW-
7S; 800,000 pg/L). In the deep flow layer, exceedances were reported beneath the dry
ash landfill (Phase II) (AL-2D; 761,000 pg/L, AL-31D; 692,000 pg/L and AL-41D; 582,000
pg/L), beneath the central portion of the ash basin (AB-12D; 1,530,000 pg/L), southeast
and downgradient of the ash basin (AB-1 D; 541,000 pg/L), and to the south and
upgradient of the ash basin at GWA-21D (650,000 pg/L).
• Vanadium concentrations that exceeded the IMAC vary in the shallow, deep, and
bedrock wells and are generally reported across the site, including background wells.
The highest reported concentration of vanadium was in background bedrock well BG-
213R (100 pg/L).
11.7 Groundwater / Surface Water Interaction
As discussed in Section 5.2, shallow and deep groundwater flow typically follows the
topographic gradient and groundwater generally discharges to nearby surface water bodies (i.e.,
Lake Norman and the unnamed tributary east of the ash basin and dry ash landfill [Phase 1]).
Groundwater/surface water interaction is evident at the site based on review of groundwater
flow direction and parameters present in groundwater. Piper diagrams were generated for the
site to compare geochemistry between ash basin porewater, upgradient groundwater monitoring
wells, downgradient groundwater monitoring wells, seeps, and surface water sample SW-6 (see
Figures 10-156 through 10-167).
In general, geochemistry of groundwater at the site is less calcium and chloride rich than ash
basin porewater, ash basin surface water, and downgradient groundwater, which were observed
to be trending closer to calcium, magnesium, and sulfate rich. Seep data and surface water data
(SW-6) indicate similar geochemistry to ash basin porewater and downgradient monitoring
wells, with the exception of trending less sulfate rich.
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11.8 Estimated Seasonal High and Seasonal Low Groundwater
Elevations — Compliance and Voluntary Wells
Estimated Seasonal Low (ESL) and Estimated Seasonal High (ESH) groundwater elevations
were calculated using historical groundwater elevations for select compliance and voluntary
wells at the site. The calculated ESL and ESH depth to water (DTW) was performed statistically
by multiplying the standard deviation of the historical DTW measurements by a factor of 1.2 and
then adding to the mean DTW measurement. To obtain the site modification factors for ESL and
ESH conditions, the calculated ESL and ESH DTW in the historical site wells were compared to
the current groundwater levels on site and the difference was calculated. This difference
between ESH and ESL DTW and current conditions was then averaged for the representative
site wells to create a modification factor to add to current DTW.
Existing monitoring wells MW-1, MW-2, MW-3, MW-4, MW-5 MW-6, MW-7, MW-8S, MW-9S,
MW-10S, MW-11 S, MW-12S, MW-13S, MS-8, MS-9, MS-11, MS-12, MS-14, MS-15, MS-16
and 013-1 were selected as the most representative shallow wells for natural seasonal
fluctuations at the site, as they are located outside of the ash basin embankments and are,
therefore, less likely to be influenced by the water level in the ash basins. Appendix H
summarizes calculated ESH and ESL groundwater elevations for compliance and voluntary
groundwater monitoring wells.
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12.0 Screening -Level Risk Assessment
The prescribed goal of the human health and ecological screening -level risk assessments is to
evaluate 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. 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 was performed in accordance with applicable federal and state guidance, including the
Guidelines for Performing Screening Level Ecological Risk Assessments within the North
Carolina Division of Waste Management (NCDENR 2003). 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.
In the human health and ecological screening -level risk assessments, the maximum
concentrations detected for all COls or other appropriate data point (i.e., the analytical reporting
limit [RL]) in the 2015 sampling and analyses for coal ash detection and assessment monitoring
analytes were compared against established and conservative human health and ecological
screening toxicity reference values, likely to be protective for even the most sensitive types of
receptors.
These comparisons are used to determine which COls present a potentially unacceptable risk to
human and/or ecological receptors and may warrant further evaluation. Those COls determined
to pose a potential for adverse impacts are identified as preliminary COPCs.
Other factors that will be considered qualitatively in the evaluation of final COPCs that would be
incorporated into a baseline risk assessment include frequency of detection and a comparison
to background. Site- and media -specific risk -based remediation standards may be calculated,
pending additional sample collection, if and where additional sampling and site -specific
standards are deemed necessary.
12.1 Human Health Screening
12.1.1 Introduction
This screening -level human health risk assessment has been prepared in accordance with
applicable NCDENR and USEPA guidance and the approved Work Plan.
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12.1.2 Conceptual Site Model
The Conceptual Site Model (CSM) is a dynamic tool for understanding site conditions and
potential exposure scenarios for human receptors that may be exposed to site -related
contamination. The CSM provides graphical representation of the following:
• A source and mechanism of chemical release;
• A retention or transport medium for COPCs;
• A point of contact between the human receptor and the medium; and
• A route of exposure to constituents for the potential human receptor at the contact point.
An exposure pathway is considered complete only if all four "source to receptor" components
are present. A CSM has been prepared illustrating potential exposure pathways from the source
area to possible receptors (see Figure 12-1). The information in the CSM has been used in
conjunction with the analytical data collected as part of the CSA to determine COPCs for the
site.
Potential receptors are defined as human populations that may be subject to contaminant
exposure. Both current and future land and water use conditions were considered when
determining exposure scenarios. Current and future land use of the MSS site and associated
ash basin, dry ash landfill, and PV structural fill is expected to remain predominantly industrial
as all four units of the coal-fired generating station are in operation (HDR 2014a). Lands
surrounding the site include residential and undeveloped lands, as well as the Catawba River —
specifically Lake Norman, which supplies water to various municipalities (HDR 2014c).
The following potential receptors are identified in the CSM:
• Current/future on -site construction worker with potential exposure to groundwater in
trenches, surface and subsurface soil and surface water;
• Current/future on -site outdoor worker with potential exposure to surface soil and surface
water;
• Current/future adult and child off -site resident with potential exposure to surface soil and
groundwater; and
• Current/future on -site trespasser with potential exposure to surface soil, surface water
and sediment.
Other exposure pathways for all potential receptors were evaluated and it was determined that
they would not have a significant impact on the risk assessment (e.g., outdoor worker inhalation
of inorganics in surface water in open air). Other exposure scenarios will also serve as
surrogates that will provide information about the magnitude of these potential risks.
The following sections describe each receptor and potentially complete exposure pathway.
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12.1.2.1 Current/Future Construction Workers
It was assumed that construction activities during ash basin closure activities at MSS could take
place on -site and that construction workers would potentially be exposed to COPCs in various
media during this timeframe. The potentially complete exposure pathways include incidental
ingestion, dermal contact, and particulate inhalation exposure to surface and subsurface soil.
Construction workers in a trench with contact to groundwater are expected to have inhalation of
metal COPCs with inhalation toxicity criteria and incidental ingestion of and dermal contact (over
limited parts of the body) with groundwater. Given the presence of ash basins, dermal contact
and incidental ingestion exposure to surface water would also be considered a potentially
complete exposure pathway for this receptor.
12.1.2.2 Current/Future Outdoor Worker
Outdoor workers are assumed to be involved with non -intrusive activities (e.g., landscapers that
will maintain the site). This receptor reflects a longer timeframe and different exposure pathways
than that of construction workers. Outdoor workers are assumed to have incidental ingestion,
dermal contact, and particulate inhalation exposure to surface soil as well as dermal contact and
incidental ingestion exposure to surface water (e.g., ash basins).
Exposure to COPCs in groundwater is not identified in the CSM because outdoor workers are
assumed not to ingest untreated water; any COPCs aerosols or fumes will dissipate in open air,
and there is limited opportunity for dermal contact. Construction worker exposure scenarios are
considered a conservative surrogate to estimate the potential risk from groundwater to outdoor
workers.
12.1.2.3 Current/Future Off -Site Resident (Adult/Child)
The potential for off -site residents to be exposed to COPCs in untreated groundwater is
included in the CSM as approximately 80 private water supply wells, which were identified within
a 0.5-mile radius of the MSS ash basin compliance boundary, as described in Section 4.0 and
the 2014 Drinking Water Supply Well and Receptor Survey and its supplement (HDR 2014a,
2014b) (Figure 4-1). These exposures will consider all on and off -site monitoring well data,
excluding the receptor survey data, which is being handled independent of the risk analysis.
Exposure routes are to include ingestion of groundwater (not incidental, but potable use) as well
as dermal contact during bathing/showering and inhalation during bathing/showering for those
metals in groundwater with available inhalation -based toxicity criteria.
Residents are assumed to be exposed to contaminants in surface soil during non -intrusive
outdoor activities (e.g., gardening); the potential exposure pathways include ingestion, dermal
contact, and inhalation of soil particulates.
Lake Norman is a public drinking water supply that is treated before consumption; therefore,
residential exposure to COPCs in (untreated) surface water is not evaluated.
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12.1.2.4 Current/Future Trespasser (Adolescent/Adult)
Trespassers may come into direct contact with or incidentally ingest surface water and sediment
while on -site and near Lake Norman during what is assumed to be predominantly recreational
activity. This will occur at different rates depending on the specific activity and setting. The
exposure parameters for this scenario will be determined and will incorporate all on- and off -site
data for these media.
Exposure routes are to include incidental ingestion, dermal contact, and particulate inhalation of
surface soil, as well as incidental ingestion and dermal contact with surface water and sediment.
This receptor reflects greater exposure to surface water, sediment and soil COPCs compared to
potential exposures of similar potential receptors (e.g., off -site recreator).
12.1.3 Human Health Risk -Based Screening Levels
A comparison of contaminant concentrations in various media to corresponding risk -based
screening levels has been made and is presented in Tables 12-1 through 12-5. These include:
• Soil: USEPA Industrial Soil Regional Screening Levels (RSLs) at a target cancer risk of
1 E-06 and noncancer Hazard Quotient (HQ) of 0.1
• Groundwater: USEPA Tap Water RSLs and NCDENR 2L Groundwater Standards
• Surface water: USEPA National Recommended Water Quality Criteria and NCDENR 213
Standards, considering the surface water classification for local water bodies
• Sediment: USEPA Residential Soil RSLs
Table 12-1 presents the Comparison of Groundwater Sample Concentrations to USEPA
Tapwater Regional Screening Levels and NCDENR 2L Standards; Table 12-2, the Comparison
of Soil Sample Concentrations to USEPA Industrial Soil RSLs; Table 12-3, the Comparison of
Surface Water Sample Concentrations to USEPA National Recommended Water Quality
Criteria and NCDENR213 Standards; and Table 12-4, the Comparison of Sediment Sample
Concentrations to USEPA Residential Soil RSLs.
Table 12-5 presents a summary of the Cols that were detected at concentrations exceeding
their relevant human health or other applicable criteria on a media -specific basis, in
groundwater and surface water, sediment, and soil.
Those COls exceeding relevant screening criteria are identified as COPCs for purposes of this
human health risk assessment.
In groundwater, copper, lead and zinc were eliminated as COPCs. With the exception of sodium
and titanium, which were retained as a result of having no screening value for comparison and
cadmium, whose RL exceeded the screening value, all other COls exceeded their respective
screening value. See Table 12-1 for maximum concentrations detected, the detailed screening
results, identification of COPCs and contaminant categories.
In soil, arsenic, cobalt, iron and thallium were detected at concentrations exceeding the
industrial soil screening levels and are determined to be COPCs. Sodium is retained by default,
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as it does not have a screening value. See Table 12-2 for the soil COI maximum concentrations,
COPCs, and contaminant category data.
Cobalt's maximum concentration exceeded its screening value and has been determined to be
a COPC in surface water, as shown in Table 12-3. Beryllium, boron, cadmium, total chromium,
lead, manganese, mercury, selenium, sodium, vanadium and zinc are also retained as COPCs
based on a lack of criteria for comparison.
Sediment COPCs and contaminant categories are presented in Table 12-4, which shows that
aluminum, antimony, arsenic, cobalt, iron, thallium, and vanadium are determined to be COPCs
based on exceedances of screening values. Sodium is also retained as a COPC based on lack
of criteria for comparison.
COls were not screened out as COPCs based on a comparison to background concentrations,
as USEPA recommends all COls exceeding risk -based screening levels be considered in a
baseline risk assessment (USEPA 2002). Statistical background concentrations have been
developed as Prediction Limits (PLs), calculated for each COI using groundwater data in site
background wells. PLs are a calculation of the upper limit of possible future values based on the
Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities Unified Guidance
(USEPA 2009). If concentrations of COls detected exceed the PL, then the groundwater
concentrations are assumed to have increased above background levels. Site -specific
background concentrations will be considered in the uncertainty section of the baseline risk
assessment, if determined to be required.
12.1.4 Site -Specific Risk Based Remediation Standards
Based on the results of the comparison to risk -based screening levels, media -specific
remediation standards will be calculated in accordance with the Eligibility Requirements and
Procedures for Risk -Based Remediation of Industrial Sites pursuant to N.C. Gen. Stat. § 130A-
310.65 to 310.77, should additional sample collection and site -specific standards be deemed
necessary.
12.1.5 NCDENR Receptor Well Investigation
Approximately 38 off -site private water supply wells were sampled and analyzed for constituents
as part of the NCDENR well testing program, as described in Section 4.0. NCDENR
recommended that 35 of the wells sampled not be utilized for drinking water due to the
presence of hexavalent chromium, iron, lead, and vanadium in the sampled wells.
In many of the wells sampled, vanadium exceeded its IMAC of 0.3 lag/L used by the NCDHHS
as a health screening level, leading NCDHHS to recommend these well owners not use the
water for drinking or cooking purposes. For reference, there is no federal drinking water
standard for vanadium, the California Health Advisory level for vanadium is 50 pg/L, and
NCDHHS toxicologists most recently calculated a new health screening level of 18 pg/L for
vanadium in Fall 2014 based on the USEPA's Integrated Risk Information System (IRIS)
database. Vanadium exceedances in the wells sampled ranged from 0.36 to 8 pg/L. In several
wells, iron was detected at concentrations exceeding its respective 2L Standard of 300 pg/L.
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Iron concentrations exceeding its 2L Standard ranged from 330 to 3,700 pg/L, although some
exceedances exhibited elevated turbidity/suspended solids and the majority of results were
below the laboratory reporting limit of 50 pg/L. Two wells contained lead concentrations of 22
pg/L and 32 pg/L, which exceeded the 2L Standard and federal primary MCL of 15 pg/L. These
concentrations may be the result of a turbid sample or corrosion of aged metal piping or well
casing. For purposes of the receptor sampling, the NCDHHS also used a level of 0.07 pg/L as a
health screening level for hexavalent chromium, calculated to be associated with an increased
lifetime cancer risk of 1 in 1,000,000. A significant fraction of wells exhibited concentrations
above this health screening level, with concentrations above this level ranging from 0.15 to 2.7
pg/L. The NCDHHS recommended that the majority of wells not be utilized for drinking water
due to the presence of one or more constituents, primarily hexavalent chromium, iron, and
vanadium; and in fewer instances, due to the presence of lead and manganese in the sampled
wells.
12.1.6 Human Health Risk Screening Summary
A human health CSM was developed to identify potential pathways of exposure from COPC
source to receptor populations; including several possible exposure scenarios. Maximum
concentrations of Cols were compared to media -specific screening levels; Cols exceeding
screening levels and those having no screening levels or issues with RLs were retained as
COPCs, in accordance with guidance.
• As a result of the screening, the majority of Cols were determined to be COPCs in
groundwater.
• Four COls exceeded their screening values in soil; sodium is retained by default
because it does not have a screening value.
• Only cobalt exceeded its surface water screening value; 11 COls are retained as
COPCs in surface water by default due to a lack of criteria being available for
comparison.
• Seven COls are determined to be COPCs based on exceedances of their screening
values in sediment and sodium is retained by default because of lack of screening value.
12.2 Ecological Screening
12.2.1 Introduction
This screening -level ecological risk assessment (SLERA) has been prepared in accordance with
the Guidelines for Conducting a Screening Level Ecological Risk Assessments within the North
Carolina Division of Waste Management (NCDENR 2003). An ecological CSM has been
developed for this site and is provided as Figure 12-2.
12.2.2 Ecological Setting
12.2.2.1 Site Summary
Refer to Section 2.0 for a description of the MSS site.
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12.2.2.2 Regional Ecological Setting
The site is located in the Southern Outer Piedmont eco-region of North Carolina adjacent to
Lake Norman; this eco-region is bordered by the Northern Inner Piedmont and Carolina Slate
Belt ecoregions (Griffith et al. 2002).
12.2.2.3 Description of the Eco-Region and Expected Habitats
The region consists of irregular plains and low to moderate gradient streams with less
precipitation and elevation than the Inner Piedmont. The common rock types include gneiss,
schist and granite covered by deep saprolite and mostly red, clayey subsoil. Land cover
consists of mixed white oak forests, croplands and pastures as well as pine plantations (Griffith
et al. 2002).
12.2.2.4 Watershed in which the Site is Located
The site is located in the Catawba River Basin watershed. The North Carolina portion of the
River Basin encompasses approximately 3,300 miles in all or in part of 11 counties.
12.2.2.5 Average Rainfall
The average annual precipitation for Sherrills Ford has been 45.28 inches over the past 30
years. The average for the State of North Carolina is 48.87 inches (Weather DB 2015).
12.2.2.6 Average Temperature
The average temperature for Sherrills Ford is 60.70 F. The average winter temperature is 48.1 °
F. The average spring temperature is 56.8° F. The average summer temperature is 75.60 F and
average fall temperature is 62.4° F (Weather DB 2015).
12.2.2.7 Length of Growing Season
According to the North Carolina State University Cooperative Extension, the average growing
season for Catawba County is 206 days, with a standard deviation of 16 days.
12.2.2.8 Threatened and Endangered Species that use Habitats in the Eco-Region
A list of threatened and endangered species for Catawba County is provided in Table 12-10.
12.2.2.9 Site -Specific Ecological Setting
An ecological checklist and habitat figure has been completed for this site and is provided in
Appendix I.
The June 2015 AMEC Natural Resources Technical Report identified 29 potential jurisdictional
wetland areas on the site measuring a total of approximately 9.42 acres. No open water areas
were identified. There were 17 potential jurisdictional drainage features; 10 intermittent and
seven perennial streams.
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The regulated 100-year floodplain occurs within the central and eastern portions of the ash
basin, including Holdsclaw Creek. Occurrences of the floodplain are generally limited to the
eastern boundary where Lake Norman (coves) are adjacent to the site (AMEC 2015).
Requests for information were submitted to several federal and state agencies, in accordance
with the North Carolina Guidelines for Performing Screening Level Ecological Risk Assessments
(NCDENR 2003). A copy of the requests and responses are provided in Appendix I and a
summary of the information is provided, as follows.
North Carolina Department of Cultural Resources
In a letter dated June 23, 2015 the North Carolina Department of Cultural Resources indicated
that there are "no historic resources which would be affected by the project."
North Carolina Natural Heritage Program
In a letter dated June 9, 2015 the North Carolina Natural Heritage Program (NCNHP) provided
information from their database, both for the site and within a one -mile radius. The NCNHP
database identified Lake Norman Slopes and Shores as a Natural Areas located within the site.
The NCNHP database shows no Natural Areas or Managed Areas within a one -mile radius.
North Carolina Wildlife Resources Commission
In a letter dated June 19, 2015, the North Carolina Wildlife Resources Commission reported the
following:
• The site drains to Lake Norman in the Catawba River basin.
• There are records for the state threatened bald eagle (Haliaeetus leucocephalus) near
the site. In addition, there are historical records for the federal species of concern and
state special concern — vulnerable Carolina birdfoot-trefoil (Acmispon helleri) near the
site.
• Bald eagles nest and forage in the area.
• There are records for a colonial wading bird colony (great blue heron) on or adjacent to
the site.
• There is recreational fishing in Lake Norman. Recreational species include: striped bass,
largemouth bass, spotted bass, catfish, crappie, sunfish, and white perch.
United States Department of Agriculture, National Forests in North Carolina
In an email dated May 28, 2015, it was reported that there are no Designated and Proposed
Federal Wilderness and Natural Areas, National Preserves and Forests, or Federal Land
Designated for the Protection of Natural Ecosystems with a half -mile of the site.
United States Department of the Interior, National Park Service
In an email dated June 3, 2015, the United States Department of the Interior, National Park
Service indicated that "the NPS has not identified any resource concerns at this time".
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12.2.2.10 On -site and Off -site Land Use
On -site land use is approximately 30% heavy industrial, 10% light industrial, 40% undisturbed,
and 20% water bodies and cleared areas. Land use within a one -mile radius of the site is 20%
undisturbed, 40% residential, 10% recreational and 30% waterbodies (including Lake Norman).
There are several areas for recreational use (boat launch and private docks) in the local area as
well.
12.2.2.11 Habitats within the Site Boundary
Based on HDR's June 30, 2015 site visit, the following habitats are present on site.
• 962 acres of Mixed Hardwoods
• 82.5 acres of Pine Plantation
• 19.4 acres of Bottomland Hardwoods
105 acres of Shrub/Scrub
• 240 acres of Open Fields
• Aquatic features including the ash basin, streams, and wetlands
For a description of habitats, refer to the Checklist for Ecological Assessments located in
Appendix I.
12.2.2.12 Description of Man-made Units that may Act as Habitat
A 382-acre ash basin is present on site and may act as man-made habitat.
12.2.2.13 Site Layout and Topography
Topography at the MSS site ranges from an approximate high elevation of 900 feet near the
intersection of Sherrills Ford Road and Island Point Road northwest of the site to an
approximate low elevation of 760 feet at the interface with Lake Norman on the southeastern
extent of the site. Topography generally slopes from a northwest to southeast direction with an
elevation loss of approximately 140 feet over an approximate distance of 1.8 miles. Surface
water drainage generally follows site topography and flows from the northwest to the southeast
across the site. Several unnamed drainage features are located on the north/northeast portion
of the site and drain southeast to Lake Norman. The full pond elevation for the MSS ash basin
is approximately 790 feet. The normal pond elevation of Lake Norman is approximately 760
feet.
12.2.2.14 Surface Water Runoff Pathways
Swales, drainage ditches, and groundwater seeps were observed during HDR's June 30, 2015
site visit.
12.2.2.15 Soil Types
Based on a review of soil boring and monitoring well installation logs (ash basin voluntary and
compliance wells) provided by Duke Energy, subsurface stratigraphy consists of the following
material types: fill, ash, alluvium, residual soil, saprolite, partially weathered/fractured rock
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(PWR), and bedrock. In general, saprolite, PWR, and bedrock were encountered on most areas
of the site. Bedrock was encountered across the site ranging in depth below ground surface
from 36 feet on the northwest extent of the site to 94 feet along the western extent of the site
and to approximately 85 feet on the southeastern extent of the site near Lake Norman (HDR
2014c).
AMEC's review of the National Resource Conservation Service (NRCS) Soil Survey indicated
the presence of fourteen soil map units within the study area. The study area is underlain by
Cecil sandy loam, 2 to 6 percent slopes, eroded (CmB2); Cecil sandy loam, 6 to 10 percent
slopes, eroded (CmC2); Cecil sandy loam, 10 to 15 percent slopes, eroded (CmD2); Cecil clay
loam, 10 to 25 percent slopes, severely eroded (CnE3); Enon fine sandy loam, 2 to 6 percent
slopes (EnB); Gullied land (Gu); Leveled clayey land (Lc); Madison gravelly sandy loam, 6 to 10
percent slopes, eroded (MgC2); Madison gravelly sandy loam, 10 to 25 percent slopes, eroded
(MgE2); Pacolet gravelly sandy loam, 25 to 45 percent slopes (PaF); Pacolet gravelly fine sandy
loam, 2 to 6 percent slopes (PcB); Pacolet gravelly fine sandy loam, 6 to 10 percent slopes
(PcC); Pacolet soils, 10 to 25 percent slopes (PeE); and Wilkes loam, 10 to 25 percent slopes
(WkE). The NRCS classifies the Enon fine sandy loam, 2 to 6 percent slopes (EnB) soil map
unit as a hydric soil (AMEC 2015).
12.2.2.16 Species Normally Expected to use Site under Relatively Unaffected Conditions
Terrestrial communities occur in both natural and disturbed habitats in the study area; these
may support a diversity of wildlife species. Information on the species that would normally be
expected to use this and similar sites in the Piedmont eco-region under relatively unaffected
conditions was obtained from relevant literature, mainly the Biodiversity of the Southeastern
United States, Upland Terrestrial Communities (Wiley and Sons 1993).
Mammal species that may be present include eastern cottontail (Sylvilagus floridanus), gray
squirrel (Sciurus carolinensis), various vole, rat and mice species, red (Vulpes vulpes) and gray
fox (Urocyon cinereoargenteus), raccoon (Procyon lotor), Virginia opossum (Didelphis
virginiana), and white-tailed deer (Odocoileus virginiana).
Avian species are the most diverse. Canopy dwellers include the great crested flycatcher
(Myiarchus crinitus), Carolina chickadee (Parus carolinensis), tufted titmouse (P. bicolor), white -
breasted nuthatch (Sitta carolinensis), blue -gray gnatcatcher (Polioptila caerulea), red -eyed
vireo (Vireo olivaceus), yellow -throated vireo (V. flavifrons), various warblers and tanagers, and
American redstart (Setophaga ruticilla).
Subcanopy species include a variety of woodpeckers, eastern pewee (Contopus virens),
Acadian flycatcher (Empidonax virescens), American crow (Corvus brachyrhynchos), blue jay
(Cyanocitta cristata) and Carolina wren (Thryothorus ludovicianus).
Catbirds (Dumetella carolinensis), brown thrashers (Toxostoma rufum), and mockingbirds
(Mimus polyglottos) are found along adjacent brushy edges, fields and thickets.
Understory species include wood thrush (Hylocichla mustelina), American robin (Turdus
migratorius), white -eyed vireo (Virea griseus), Kentucky warbler (Oporornis formosus), common
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yellow -throat (Geothlypis trichas), and yellow breasted chat (Icteria virens). Predatory birds
include several hawk and owl species, and the turkey vulture (Cathartes aura).
Amphibians and reptiles that tend to be associated with the terrestrial -aquatic interface in
streams, rivers, and open waters may include certain turtles, e.g., the Striped Mud and Gulf
Coast Spiny Softshell turtles; and frogs, snakes and amphibians such as the Three -lined
salamander. For a more detailed description, see Appendix I.
Streams of the southeastern Piedmont support a range of aquatic benthic macroinvertebrate
groups including mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera),
water beetles (Coleoptera), dragonflies and damselflies (Odonata), dobsonflies and alderflies
(Megaloptera), true flies (Diptera), worms (Oligochaeta), crayfish (Crustacea), and clams and
snails (Mollusca).
Streams, rivers, ponds, and reservoirs support populations of game fish that may include
redbreast sunfish (Lepomis auritus), bluegill (Lepomis macrochirus), warmouth (Lepomis
gulosus), and largemouth bass (Micropterus salmoides). The most widespread non -game fish
species are American eel (Anguilla rostrata), eastern silvery minnow (Hybognathus regius),
bluehead chub (Nocomis leptocephalus), golden shiner (Notemigonus crysoleucas), spottail
shiner (Notropis hudsonius), whitefin shiner (N. niveus), swallowtail shiner (N. procne), creek
chub (Semotilus atromaculatus), creek chubsucker (Erimyzon oblongus), silver redhourse
(Moxostoma anisurum), yellow bullhead (Ictalurus natalis), flat bullhead (l. platycephalus),
margined madtom (Noturus insignis), and tessellated darter (Etheostoma olmstedi).
12.2.2.17 Species of Special Concern
For a detailed list of species of special concern that may be present, see Table 12-10.
12.2.2.18 Nearby Critical and/or Sensitive Habitats
For a detailed description, see Section HID of the Ecological Checklist, provided in Appendix I.
12.2.3 Fate and Transport Mechanisms
Potential fate and transport mechanisms at/near the MSS include erosion, seeps, stormwater
runoff and flow of surface water bodies. An ecological CSM (Figure 12-2) has been prepared
illustrating potential exposure pathways from the source area to possible ecological receptors.
The information in the ecological CSM has been used in conjunction with the analytical data
collected as part of the CSA to develop an understanding of the sources, pathways and media
of exposure as well as the receptors potentially impacted by site -related COls.
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12.2.4 Comparison to Ecological Screening Levels
The sampling and analysis program completed as part of the MSS CSA investigation is
described earlier in this report. Media of primary concern for ecological receptors, i.e., sediment
and soil have been sampled in accordance with the NCDENR approved Work Plan. Surface
water and sediment sample collection was limited to one location (SW-6). Additional future
surface water and sediment sampling outside the ash basin waste boundary is recommended
(as described in Section 14.0). Pending the results of the additional sampling, ecological
receptors may be re-evaluated.
The results of the comparison of COI concentrations in various media to risk -based screening
levels are presented in the following tables:
• Table 12-6, a Comparison of Soil Sample Concentrations to USEPA Ecological Soil
Screening Levels and USEPA Region IV Recommended Ecological Screening Values;
• Table 12-7, a Comparison of Surface Water (Freshwater) Sample Concentrations to
USEPA Region IV Chronic Screening Values; and
• Table 12-8, a Comparison of Sediment Sample Concentrations to USEPA Region IV
Recommended Ecological Screening Values.
These tables include each COPCs' respective category 1-5 determination (as applicable) and
as described in Section 12.1.3 above. The potential for ecological risk was also estimated by
calculating screening hazard quotients (HQ) using the appropriate screening value of each
contaminant and comparing that value to the USEPA Region IV Ecological Screening Values.
COls having a HQ greater than or equal to 1 are identified as COPCs.
Table 12-9 presents a summary of the COls that were detected at concentrations exceeding
their relevant ecological screening media -specific or other criteria. Those COls exceeding the
relevant criteria are identified as ecological COPCs for purposes of the SLERA.
Note that NCDENR SLERA guidance does not allow for exclusion of COls as COPCs based on
a comparison to background concentrations.
NCDENR guidance requires a determination of which contaminant category the COPCs fall into
as a result of the data comparison to screening levels and is also presented in the ecological
COPC tables (Tables 12-6 through 12-8). These include:
• Category 1 — Contaminants whose maximum detection exceeds the media specific
ecological screening value included in the COPC tables.
• Category 2 — Contaminants that generated a laboratory sample quantitation limit (SQL)
that exceeds the USEPA Region IV media -specific ecological screening value for that
contaminant.
• Category 3 — Contaminants that have no USEPA Region IV ecological screening value,
but were detected above the laboratory SQLs.
• Category 4 — Contaminants that were not detected above the laboratory SQLs and have
no USEPA Region IV ecological screening value.
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In soil, all COls except cadmium and lead were detected at concentrations exceeding the
ecological soil screening levels. Sodium and strontium have no ecological criteria and are
retained by default. See Table 12-6 for detailed information, including the maximum
concentrations detected. For several COPCs, the exceedances are greater than one order of
magnitude above the screening levels; these include aluminum, boron, total chromium, iron,
manganese, selenium, and vanadium.
Based on the comparison of maximum detected concentrations to screening criteria, boron is
identified as an ecological COPC in surface water (freshwater). Barium, cobalt, manganese,
molybdenum, strontium and vanadium are retained by default due to the fact that there are no
ecological criteria available. Further information on the screening performed and
characterization as to the contaminant category each COPC falls into is provided in Table 12-7.
Nickel is identified as a COPC in sediment based on a comparison of maximum detected
concentrations to available criteria; aluminum, barium, beryllium, boron, cobalt, iron,
manganese, molybdenum, selenium, sodium, strontium thallium and vanadium were retained
due to there being no screening value available. Details on the COPC screening and
contaminant category are provided in Table 12-8.
COls were not screened out as COPCs based on a comparison to background concentrations,
as NCDENR SLERA guidance does not allow for screening based on background. Site -specific
background concentrations, discussed above in Section 12.1.3, will be considered in the
uncertainty section of the baseline ecological risk assessment, if determined to be necessary.
12.2.5 Uncertainty and Data Gaps
There are uncertainties inherent in any environmental investigation and risk evaluation that
involve the natural heterogeneity of the media, nature and extent of constituents in the
environment, due to their individual fate and transport characteristics and varied, site -specific
conditions. These uncertainties are considered in developing the sampling and analysis plan,
data quality assurance processes and understanding of the site.
These screening level assessments are designed to be very conservative in identifying potential
COPCs that would be carried forward into a baseline human health and/or ecological risk
assessment. They include all on- and off -site analytical data, and use the maximum
concentration detected as the comparison point to applicable screening criteria. Also, no COls
were eliminated as COPCs based on background levels; this will be evaluated in the baseline
risk assessment, if they are required to be performed. These are highly unlikely to be the actual
exposure concentrations, given the natural attenuation, dilution and distances to potential
receptors.
There is a high level of confidence that any constituent in groundwater, soil, or sediment with
potential to impact human health or ecological receptors has been identified as a result of these
assessments. Surface water COPCs will be re-evaluated when additional surface water
sampling analytical results are available.
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12.2.6 Scientific/Management Decision Point
If through the HQ analysis it is determined that COls have been detected at maximum
concentrations that exceed applicable screening criteria, additional assessment of potential
risks may be warranted. This does not mean that impacts are in fact, occurring; only that further
data collection or evaluation should be considered.
This determination is known as the Scientific/Management Decision Point and the conclusion
reached must be one of the following:
• There is adequate information to conclude that the ecological risks are negligible; or
• Site has inadequate data to complete the risk characterization. Data gaps need to be
filled prior to completion of the screening process; or
• The information indicates a potential for adverse ecological effects and a more thorough
assessment is warranted.
Given that several COPCs have been identified as having a HQ of greater than 1 in soil, surface
water and sediment, there is adequate information indicating a potential for adverse effects to
occur and a baseline ecological risk assessment (BERA) may be warranted.
12.2.7 Ecological Risk Screening Summary
The SLERA has identified that the potential exists for adverse ecological impacts due to
exposure to COPCs in soil, surface water and/or sediment. Cadmium and lead are the only
COls that have been excluded as COPCs in soil and numerous COPCs exceeded their
respective screening criteria by one or more orders of magnitude. Fewer COPCs have been
identified in surface water and sediment and most of those are retained by default for having no
criteria, not due to maximum concentrations actually exceeding screening criteria. Potential
impacts from limited ecological receptor groundwater exposure are minimal and have not been
evaluated. Further evaluation of potential ecological impacts appears to be warranted.
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13.0 Groundwater Modeling
Groundwater modeling will be performed and submitted in the CAP in accordance with
NCDENR's Conditional Approval letter (Appendix A). These activities will consist of groundwater
flow and fate and transport modeling, performed with MODLFOW and MT3DMS, and batch
geochemical modeling, performed with PHREEQC. This section presents an overview of the
fate and transport modeling, the batch geochemical modeling, and the site geochemical
conceptual model. The CAP will also discuss geochemical properties of the COls and how
these properties relate to the retention and mobility of the constituents.
13.1 Fate and Transport Groundwater Modeling
A three-dimensional groundwater fate and transport model (MODFLOW/MT3DMS Model) will
be developed for the site. The objective of the modeling process will be to predict the following
in support of the CAP:
• Predict concentrations of the COls at the compliance boundary or other locations of
interest over time,
• Estimate the groundwater flow and constituent loading to surface water discharge areas,
and
• Predict approximate groundwater elevations in the ash for the proposed corrective
action.
The modeling effort and report will be developed in general accordance with guidelines provided
in the memorandum Groundwater Modeling Policy, NCDENR DWQ, May 31, 2007.
The groundwater model will be developed from the hydrogeologic conceptual site model
presented in the CSA, from existing wells and boring information provided by Duke Energy, and
from information developed during the site investigation. The model will also be supplemented
with additional information developed from other Piedmont sites, as applicable.
Although the site is anticipated in general to conform to the LeGrand conceptual groundwater
model, due to the configuration of the ash basin, dry ash landfill (Phases I and ll), PV structural
fill, and the boundary conditions present, a three-dimensional groundwater model is warranted.
The groundwater modeling will be performed under the direction of Dr. William Langley, P.E.,
Department of Civil and Environmental Engineering, The University of North Carolina at
Charlotte (UNCC). Groundwater flow and constituent fate and transport will be modeled using
Visual MODFLOW 2011.1 (flow engine USGS MODFLOW 2005) and MT3DMS.
The modeling process, development of the model, development of the hydrostratigraphic layers,
model extent (or domain), and proposed model boundary conditions were described in Section
7.0 of the Work Plan. To date, no changes to the proposed model development are warranted
based on data collected during the site investigation.
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The MT3DMS model will use site -specific sorption Kd values developed from samples collected
along the major flow transects. The testing to develop the Kd terms is underway, but is not
complete at this time. Results of the testing will be presented in the CAP. The methods used to
develop the Kd terms were presented in Section 7.7.2 of the Work Plan.
13.2 Batch Geochemical Modeling
As described in the Work Plan, batch geochemical simulations using PHREEQC will be used to
estimate sensitivity of the proposed sorption constants used with MT3DMS and to assist in
understanding the mechanisms involved in attenuation of selected constituents. Geochemical
modeling using PHREEQC can be used to indicate the extent to which a COI is subject to
solubility constraints, a variable Kd, or other processes. PHREEQC can also identify postulated
solid phase calculations of their respective saturation indices. The specific locations where
batch geochemical modeling will be performed will be determined after developing the Kd terms
and reviewing site data.
13.3 Geochemical Site Conceptual Model
SCMs are developed to be a representation of what is known or suspected about a site with
respect to contamination sources, release mechanisms, transport, and fate of those
contaminants.9 SCMs can be a written and/or graphic presentation of site conditions to reflect
the current understanding of the site and identify data gaps, and be updated as new information
is collected throughout the project. SCMs can be utilized to develop understanding of the
different aspects of site conditions, such as a hydrogeologic SCM, to help understand the site
hydrogeologic condition affecting groundwater. SCMs can also be used in a risk assessment to
understand contaminant migration and pathways to receptors.
On June 25, 2015, NCDENR made the following request:
Since speciation of groundwater and surface water samples is a critical
component of both the site assessments and corrective action, the Division
expects a geochemical site conceptual model (SCM) developed as a subsection
in the Comprehensive Site Assessment (CSA) Reports. The geochemical SCM
should provide a summary of the geochemical interactions between the solution
and solid phases along the groundwater flowpath that impact the mobility of
metal constituents. At a minimum, the geochemical SCM will describe the
adsorption/desorption and mineral precipitation/dissolution processes that are
believed to impact dissolved concentrations along the aquifer flowpaths away
from the ash basin sources. The model descriptions should include the data upon
which the conceptual model is based and any calculations (such as mineral
saturation indices) that are made to develop the site -specific model.
Metal speciation analyses cover a broad aspect of metals' geochemistry,
including solution complexation with other dissolved species and specific
9 EPA MNA Volume 1
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association with aquifer solids, such as a metal adsorbed onto HFO or
precipitated as a sulfate mineral. A comprehensive speciation analysis that
requires a relatively complete groundwater analysis is expected that includes use
of an ion speciation computer code (such as PHREEQC) capable of calculating
solution complexes, surface complexation onto HFO, and mineral saturation
indices. This type of speciation calculation is necessary for the development of a
geochemical SCM and understanding metal mobility in an aquifer.
In previous correspondence, NCDENR agreed that the proposed geochemical modeling
described in the Work Plan, to be performed using PHREEQC, will be included in the CAP.
Specifically, the model descriptions and calculations, such as mineral saturation indices, will be
provided in the CAP. This approach will allow completion of the testing to develop the site -
specific Kd terms and site mineralogy, and will allow the geochemical modeling to be
coordinated with the groundwater flow and transport model.
Elements of the geochemical site conceptual model (GSCM) described below will be
incorporated into the fate and transport and the geochemical modeling performed for the CAP.
The GSCM will be updated as additional data and information associated with contaminants,
site conditions, or processes such as migration of contaminants are developed. The GSCM will
be useful in understanding the transport and attenuation factors that affect the mobility of
contaminants at the site and the long-term capacity of the site for attenuation and stability of
immobilized contaminants.
The GSCM will describe the geochemical aspects of the site sources that influence contaminant
transport. Site sources at MSS consist of the ash basin, dry ash landfill (Phases I and II), and
PV structural fill. These source areas are subject to different processes that generate leachate
migrating into the underlying soil layers and into the groundwater. For example, the dry ash
landfill and structural fill would generate leachate as a result of infiltration of precipitation, while
the ash basin would generate leachate based on the pond elevation in the basin. General
factors affecting the geochemistry of the site are as follows:
Factors Affecting Ash Formation (Primary Source):
• Chemical and mineralogical composition of coal
• Thermodynamics of coal combustion process
Factors Affecting Leaching in the Active Ash Basin (Primary Source Release
Mechanism):
• Chemical composition of ash
• Mineral phase of ash
• Physical characteristics of ash
• Inflow of water into/out of basin
• Period of time ash has been in basin
• Geochemical conditions in ash basin
• Precipitation -dissolution reactions
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• Sorptive properties of materials in ash
Factors Affecting Leaching in the Inactive Ash Basin (Primary Source Release
Mechanism):
• Chemical composition of ash in the inactive area
• Mineral phase of ash in the inactive area
• Physical characteristics of ash in the inactive area
• Inflow of precipitation in to ash in the inactive area
• Inflow of leachate amd contact stormwater from lined landfill
• Period of time ash has been in the inactive area
• Geochemical conditions of ash in the inactive area
• Precipitation -dissolution reactions
• Sorptive properties of materials in ash
Factors Affecting Sorption and Precipitation of Constituents onto Soil/Aquifer Materials
Beneath Ash (Secondary Source Release Mechanism):
• Chemical composition of soil
• Physical composition of soil
• Rate of infiltration/percolation of porewater
• Chemical composition of leachate infiltrating into soil
• Sorption capacity of soil
• Geochemistry of groundwater flowing beneath unit
Factors Affecting Desorption and Dissolution of Constituents From Soil/Aquifer Materials
Beneath Ash (Secondary Source Release Mechanism):
• Chemical composition of soil
• Physical composition of soil
• Rate of infiltration/percolation of porewater
• Attenuation capacity of soil
• Chemical composition of leachate or precipitation infiltrating into soil
• Geochemistry of groundwater flowing beneath unit
Results of the Kd testing, site mineralogy testing, and geochemical modeling developed in the
CAP will be used to refine the GSCM.
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14.0Data Gaps — Conceptual Site Model
Uncertainties
14.1 Data Gaps
The horizontal and vertical extent of impacted soil and groundwater has been delineated at the
site through completion of CSA field activities and evaluation of data. However, data gaps have
been identified, as described below, that will require further evaluation to refine the SCM and
complete the groundwater model, which will be included in the CAP. In addition, resolving data
gaps will provide valuable information for subsequent site monitoring. The data gaps have been
separated into two groups: 1) data gaps resulting from temporal constraints and 2) data gaps
resulting from evaluation of data collected during the CSA.
14.1.1 Data Gaps Resulting from Temporal Constraints
Data gaps identified in this category, as listed below, are generally 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 the CSA supplement, which will be submitted to
NCDENR following completion of the second comprehensive groundwater sampling event.
Petrographic Analysis of Rock Samples: Petrographic analysis of six rock samples is
incomplete as of the date of this report, and Duke Energy has not received all results of
this analysis. Results should be available for inclusion in the CSA supplement.
Speciation of Select Inorganics: To meet the NORR requirements, groundwater samples
were collected from monitoring wells located along inferred groundwater flow transects
for speciation of arsenic, chromium, iron, manganese, and selenium. These samples
were collected prior to conducting a review of laboratory data from total inorganic testing.
Analytical results for samples collected for total inorganics only (no speciation) indicate
that, for these select wells where speciation samples were not collected, total
concentrations of one or more speciation constituents are in excess of their respective
2L Standards. Adjustments to speciation sampling, as described in Section 15.0, will be
incorporated in the second comprehensive sampling event and results will be included in
the CSA supplement as needed.
14.1.2 Data Gaps Resulting from Review of Data Obtained During CSA Activities
New background monitoring well BG-2BR serves as the only background bedrock well
for the site. A deep background well was proposed at this location in the Work Plan.
However, due to rock being encountered at only 7 ft bgs at this location, a deep well was
not installed. Installation of one additional bedrock well (BG-4BR) and one deep well
(BG-4D) will be considered to improve the understanding of background groundwater
quality at the MSS site.
Background surface water samples were not collected as part of this CSA. A potential
location for background surface water is one of the two perrenial streams that flow
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toward the ash basin/PV structural fill in the northwest portion of the site. Flow from
these streams is routed via underground piping beneath the structural fill and discharges
to the ash basin. Surface water sampling will be considered northwest of the ash
basin/structural fill to refine background surface water constituent concentrations that
discharge to the ash basin.
• Boron concentrations exceeded the 2L Standard in the outermost wells located east and
downgradient of the ash basin and the dry ash landfill (Phase 1) in the shallow and deep
flow layers (MW-14S/D and AL-1 S/D). Boron was not reported above the 2L Standard in
the bedrock well MW-14BR. This suggests the bedrock is impeding vertical migration of
the groundwater and limiting the vertical extent of boron impacts at this location. Boron
was detected at a concentration of 2,200 tag/L in the surface water sample (SW-6)
collected from the unnamed tributary downgradient of these wells, indicating a
groundwater/surface water interaction is present. Note that there is no North Carolina 2B
Standard established for boron. To fully delineate the horizontal extent of boron
concentrations in groundwater in this area, additional assessment will be considered
downgradient and/or across the surface water feature.
14.2 Site Heterogeneities
Heterogeneities with regard to groundwater flow were not identified during the CSA. In general,
groundwater within the shallow, deep, and bedrock flow layers flows from the topographic highs
surrounding the ash basin to the ash basin and to the southeast toward Lake Norman.
Heterogeneities related to COI concentrations were not identified during the CSA. However,
heterogeneities may be identified following completion of the groundwater model for the site.
14.3 Impact of Data Gaps and Site Heterogeneities
Certain data gaps can generally be addressed with additional assessment activities including
installation of additional monitoring wells, ongoing groundwater sampling at the site, and surface
water sampling. As discussed in Section 15.0, a second comprehensive groundwater sampling
event is currently under discussion between NCDENR and Duke Energy. A plan for interim
groundwater sampling between submittal of the CSA and implementation of the anticipated CAP
is proposed in Section 16.0 and will further supplement the existing data.
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15.0 PLANNED SAMPLING FOR CSA SUPPLEMENT
15.0 Planned Sampling for CSA Supplement
A second round of groundwater and surface water sampling will be conducted to:
• Supplement data obtained during the initial sampling event; and
• Evaluate seasonal variation in groundwater results.
A summary of the proposed sampling program for the second sampling event is included in
Table 15-1.
15.1 Sampling Plan for Inorganic Constituents
The scope of the second sampling event will include the following:
• Collection of a second set of data for all groundwater monitoring wells installed during
the CSA, seeps, and surface water locations sampled during the intitial sampling;
• Samples will be collected and analyzed for CSA Work Plan parameters (including total
and dissolved consituents, as appropriate, using 0.45 prn filters);
• Re-evaluation and re -sampling of locations that were previously dry; and
• Collection of dissolved phase samples using 0.1 pm filters from select flow transect wells
to support geochemical modeling as part of the CAP.
15.2 Sampling Plan for Speciation Constituents
During the initial round of sampling for the CSA, samples were collected and speciation
analyses performed for arsenic (III), arsenic (V), chromium (III), chromium (VI), iron (II), iron (III),
manganese (II), manganese (IV), selenium (IV), and selenium (VI) at the following locations:
• Groundwater monitoring wells installed along anticipated groundwater flow transects
• Seeps
• Ash basin surface water samples
• Compliance wells that had previous groundwater exceedances
At the request of Duke Energy, NCDENR determined that additional analyses for speciation
during the second round of CSA sampling is not currently needed for CAP development or
further risk assessment unless required to fill data gaps, to provide data for geochemical
modeling, or to support the evaluation of corrective action measures.
Review of existing MSS speciation data has identified data gaps which require the collection of
additional speciation samples during the second round of groundwater and surface water
sampling at the locations listed below:
CSA monitoring wells AL-1 S/D and AL-2S/D/BR
Existing voluntary monitoring wells MW-7S/D
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16.0 INTERIM GROUNDWATER MONITORING PLAN
16.0Interim Groundwater Monitoring Plan
CAMA requires a schedule for continued / interim groundwater monitoring. As such, Duke
Energy plans to conduct interim groundwater monitoring at select wells identified in Table 15-1
to bridge the gap between completion of CSA activities and implementation of the proposed
CAP.
16.1 Sampling Frequency
Groundwater sampling as part of the interim monitoring is planned to occur two additional times
during 2015/early 2016 (timing will be such that the samples are not auto -correlated), then on a
quarterly basis until the CAP is approved by NCDENR and implemented by Duke Energy. This
sampling frequency will allow for evaluation of seasonal fluctuations in parameter
concentrations, as well as provide additional data for statistical analysis of site -specific
background concentrations.
16.2 Constituent and Parameter List
The proposed constituents and parameters for analysis remain the same and are presented in
Table 7-3.
16.3 Proposed Sampling Locations
The proposed sampling locations are the same as presented on Figure 6-2.
16.4 Proposed Background Wells
Final locations for proposed background wells BG-4D and BG-4BR will be considered at a later
date. Following the CSA supplemental sampling, the background wells installed as part of the
CSA assessment (BG-1 S/D, BG-2S/BR, and BG-3S/D) are planned be sampled a total of four
times in 2016.
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17.0 DISCUSSION
17.0Discussion
17.1 Summary of Completed and Ongoing Work
To date, the following activities have been completed in support of this CSA:
• Installation of 83 groundwater monitoring wells within the ash basin, dry ash landfill
(Phase ll), the PV structural fill, in locations upgradient and downgradient of the ash
basin waste boundary, and background locations;
• Completion of 13 soil borings within the footprint of the ash basin and PV structural fill;
• Completion of topographic and well/boring location surveys;
• Collection of ash samples from borings completed within the ash basin, dry ash landfill
(Phase ll), and PV structural fill boundaries, and analysis for total inorganics, total
organic carbon, anions/cations, SPLP, and physical properties;
• Collection of soil samples from borings completed within the ash basin, dry ash landfill
(Phase ll) and PV structural fill boundaries, outside the ash basin boundary, and
background locations, and analysis for total inorganics, total organic carbon,
anions/cations, and physical properties;
• Collection of PWR and bedrock samples from borings completed within the ash basin
boundary, beyond the ash basin boundary, and background locations and analysis for
total inorganics, total organic carbon, and anions/cations;
• Collection of soil samples for analysis of chemistry and mineralogy;
• Collection of rock samples for chemical analysis;
• Collection of rock samples for petrographic analysis (thin -sections);
• Performance of in -situ horizontal (open hole) and vertical (flush bottom) permeability
tests;
• Completion of packer tests in five bedrock borings;
• Completion of rising- and falling -head slug tests in 80 of the 83 newly installed
monitoring wells and three existing monitoring wells;
• Collection of groundwater samples from 95 monitoring wells (newly installed wells,
compliance wells, and voluntary wells) and analysis of samples for total and dissolved
inorganics and anions/cations;
• Speciation of groundwater samples for arsenic, chromium, iron, manganese, and
selenium in groundwater samples collected from 23 monitoring wells installed along
anticipated groundwater flow transects, existing compliance monitoring wells, and
background wells;
• Collection of one seep sample, one surface water sample, two sediment samples, two
NCDENR seep/water re -samples, and analysis for total inorganics and anions/cations;
• Speciation of the NCDENR seep/water re -samples for arsenic, chromium, iron,
manganese, and selenium;
• Evaluation of solid and aqueous matrix laboratory data;
• Completion of an updated receptor survey;
• Completion of fracture trace analysis; and
• Preparation of this CSA report.
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17.0 DISCUSSION
The following activities are on -going (as described further in Section 14.1.1) and will be provided
to NCDENR in the CSA supplement:
• Petrographic analysis of rock samples;
• Evaluation of the need for additional groundwater monitoring wells to better define the
horizontal extent of groundwater exceedances onsite and background groundwater
quality; and
• Evaluation of the need for additional speciation of constituents found to be in excess of
their respective 2L Standards.
17.2 Nature and Extent of Contamination
Soil and groundwater beneath the ash basin and the dry ash landfill (Phase 11), and groundwater
downgradient of the ash basin and the dry ash landfill (Phase 1) have been impacted by ash
handling and storage at the MSS site. Concentrations of several COls exceed their respective
2L Standards or IMACs in groundwater outside the ash basin, dry ash landfill (Phase 11), and PV
structural fill waste boundaries. However, the presence and magnitude of exceedances for
certain constituents may be attributed to naturally occurring conditions and not necessarily due
to ash handling at the MSS site, including antimony, barium, chromium, cobalt, iron, lead,
manganese, thallium, and vanadium.
Boron and sulfate are identified by the USEPA (2015) as selected constituents that would be
expected to migrate rapidly and provide early indications of contaminants migrating in
groundwater from a CCR unit. The horizontal and vertical migration of boron best represents the
the flow and potential transport system at the MSS 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 at the site are present in the shallow and deep flow layers beneath the dry
ash landfill (Phase 11), to the east and downgradient of the ash basin and dry ash landfill (Phase
1), and the southeast and downgradient of the ash basin. There are also boron exceedances
present in the deep flow layer beneath the central portion of the ash basin (AB-12D) and
beneath the western portion of the ash basin (AB-6D). Boron exceedances in bedrock are
limited to the area within the ash landfill (AL-2BR). Boron concentrations are generally higher in
the shallow and deep layers beneath the dry ash landfill (Phase 11) and in the deep layer
beneath the western portion of the ash basin. Bedrock is impeding vertical migration of
groundwater and limiting the vertical extent of boron impacts.
Figure ES-1 depicts the horizontal extent of 2L Standard exceedances for boron in the shallow,
deep, and bedrock groundwater flow layers at the site.
Based on data obtained during this CSA, groundwater flow direction, the extent of exceedances
of boron, and the other COls identified in groundwater, it appears that groundwater impacted by
the source area is contained within Duke Energy property and the ash basin compliance
boundary.
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17.0 DISCUSSION
17.3 Maximum Contaminant Concentrations
Maximum contaminant concentrations were determined for ash, soil, groundwater, and surface
water based on the results of sample analyses for each media. These concentrations were used
to perform screening -level human health and ecological risk assessments based on the
NCDENR Division of Waste Management guidelines (NCDENR 2003).
The Cols and maximum contaminant concentrations evaluated for groundwater samples are
included in Table 12-1 and those that exceeded their respective 2L Standards or IMACs are
shown on Figure 10-74. Based on the screening -level human health risk assessment, all COls
included in Table 12-1 except copper, lead, and zinc were identified as COPCs in groundwater
at the site.
COls and maximum contaminant concentrations evaluated for soil and sediment samples are
included in Table 12-2 and Table 12-4, respectively. The COls with North Carolina PSRG
exceedances are shown on Figure 8-1. Based on the screening -level human health risk
assessment, only three COls (arsenic, cobalt, and iron) exceeded their soil screening values
and were identified as COPCs in soil at the site. Sodium and thallium were also identified as
COPCs in soil due to a lack of screening values available for comparison. Four COls (antimony,
arsenic, cobalt, and iron) were identified as COPCs in sediment. Sodium and thallium were also
identified as COPCs in sediment due to a lack of screening values available for comparison.
For COls identified in ash basin porewater, maximum concentrations and sample locations are
listed below:
• Antimony: 26.6 pg/L (AB-20S)
• Arsenic: 6,380 pg/L (AB-12SL)
• Barium: 780 pg/L (AB-12SL)
• Beryllium: 23.5 pg/L (AB-5S)
• Boron: 73,400 pg/L (AL-3S)
• Cadmium: 6.3 pg/L (AL-3S)
• Chloride: 3,650,000 pg/L (AB-12S)
• Chromium: 71.6 pg/L (AB-20S)
• Cobalt: 423 pg/L (AB-20S)
• Iron: 2,300,000 pg/L (AB-5S)
• Lead: 28.7 pg/L (AB-20S)
• Manganese: 19,400 pg/L (AB-5S)
• Nickel: 333 pg/L (AB-5S)
• Selenium: 454 pg/L (AB-20S)
• Sulfate: 8,850,000 pg/L (AB-5S)
• TDS: 11,600,000 pg/L (AB-12S)
• Thallium: 14.8 pg/L (AB-20S)
• Vanadium: 163 pg/L (AL-3S)
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17.0 DISCUSSION
The maximum concentrations of COls in groundwater were mainly detected in shallow
monitoring wells AL-1 S, AL-2S, and MW-7S. The maximum concentration of boron (15,200
pg/L) was detected in deep monitoring well AL-4D. The maximum concentrations of sulfate
(979,000 pg/L) and TDS (1,610,000 pg/L) were detected in shallow monitoring well AL-2S.
Several other COls exhibited maximum concentrations in groundwater monitoring well AL-1 S,
including beryllium, cadmium, and manganese. Other COls with maximum concentrations in
groundwater monitoring well AL-2S include barium, selenium, and zinc.
COls with maximum concentrations in voluntary groundwater monitoring well MW-7S include
arsenic, cobalt, and thallium. Compliance groundwater monitoring well MW-14S only exhibited
maximum concentrations of one COI, nickel.
17.4 Contaminant Migration and Potentially Affected Receptors
In general, groundwater flows from the topographic highs surrounding the ash basin to the ash
basin and to the southeast toward Lake Norman. Based on data obtained during the CSA,
impacted groundwater is located beneath the ash basin, beneath the dry ash landfill (Phase II),
and has migrated with groundwater flow direction to the east and downgradient of the ash basin
and the dry ash landfill (Phase 1) and to the southeast and downgradient of the ash basin.
The human health and ecological CSMs, provided as Figures 12-1 and 12-2, illustrate
potentially affected receptors. These CSMs will be reviewed and revised as necessary based on
information indicated above.
Potentially affected receptors include those local residents identified by NCDENR whose private
supply wells may have potentially been impacted by a COI. These potentially affected receptors
are considered separately from the CSA under regulatory mechanisms being implemented by
NCDENR. Some COls are present in background and upgradient monitoring wells, and thus
require careful examination to determine whether their presence in private water supply wells is
naturally occurring or a result of the storage and handling of CCR in the ash basin, dry ash
landfill, or PV structural fill.
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18.0 CONCLUSIONS
18.0 Conclusions
18.1 Source and Cause of Contamination
The CSA identified the horizontal and vertical extent of groundwater contamination resulting
from the ash basin, dry ash landfill (Phases I and II), and the PV structural fill at the MSS site,
and found it is limited to within the ash basin compliance boundary. The source and cause of
impacts for certain parameters in some areas of the site, as shown on Figure ES-1, is the CCR
contained in the ash basin. The cause of contamination shown on Figure ES-1 is leaching of
constituents from CCR into the underlying soil and groundwater at the site. However, some
groundwater, surface water, and soil standards were also exceeded due to naturally occurring
elements found in the subsurface, including antimony, barium, chromium, cobalt, iron, lead,
manganese, thallium, and vanadium.
18.2 Imminent Hazards to Public Health and Safety and Actions
Taken to Mitigate them in Accordance to 15A NCAC 02L
.0106(f)
15A NCAC 02L.0106(g)(2) requires the site assessment to identify any imminent hazards to
public health and safety, and the actions taken to mitigate them in accordance with 2L.0106(f).
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 MSS site is required
to address soil and groundwater contamination discussed in Section 18.1. Proposed correction
action will be outlined in the CAP to be submitted in accordance with CAMA.
18.3 Receptors and Significant Exposure Pathways
The NORR and CAMA requirements concerning receptors were completed with the results
provided in Section 4.0. A screening -level human health risk assessment and screening -level
ecological risk assessment was performed with the results provided in Section 12.0. The
receptors and significant exposure pathways are identified in the human health and ecological
SCMs (Figures 12-1 and 12-2).
18.4 Horizontal and Vertical Extent of Soil and Groundwater
Contamination and Significant Factors Affecting
Contaminant Transport
The CSA identified the horizontal and vertical extent of soil and groundwater contamination
caused by leaching of COls from the ash basin. The horizontal extent of soil impacts is limited to
the area beneath the ash basin and one location east and downgradient of the dry ash landfill
(Phase 1). Where soil impacts were identified beneath the ash basin, the vertical extent of
contamination beneath the ash/soil interface is generally limited to the uppermost soil sample
collected beneath ash. Reported concentrations in soil samples were compared to background
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18.0 CONCLUSIONS
concentrations in addition to the North Carolina Industrial and POG PSRGs to delineate the
extent of contamination. Arsenic was the only COI with exceedances of background
concentrations and North Carolina PSRGs beneath the ash basin. In general, constituent
concentrations of barium, cobalt, iron, manganese, and vanadium were higher in soil compared
to ash, and are considered to represent naturally occurring background conditions.
The CSA found that COls found in groundwater at the site include antimony, arsenic, barium,
beryllium, boron, chloride, chromium, cobalt, iron, manganese, selenium, sulfate, thallium, TDS,
and vanadium, although many of these constituents are found above 2L Standards or IMACs
due to naturally occurring concentrations. The approximate horizontal extent of groundwater
impacts is limited to beneath the ash basin and dry ash landfill (Phase 11), east and
downgradient of the ash basin and dry ash landfill (Phase 1), and southeast and downgradient of
the ash basin, within the ash basin compliance boundary. The approximate vertical extent of
groundwater impacts is generally limited to the shallow and deep flow layers. Bedrock is
impeding vertical migration of groundwater and limiting the vertical extent of groundwater
impacts.
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. 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 limits the vertical migration of contaminants
in groundwater. The CSA found that the direction of mobile contaminant transport is to the
southeast toward Lake Norman and an unnamed tributary that flows to Lake Norman, and not
towards off -site receptors.
18.5 Geological and Hydrogeological Features influencing the
Movement, Chemical, and Physical Character of the
Contaminants
Based on the initial hydrogeologic SCM presented in the Work Plan, the geological and
hydrogeological features influencing the migration, chemical, and physical characteristics of
contaminants are related to the Piedmont hydrogeologic system present at the site. The
movement of the contaminants is related to the groundwater flow direction, the groundwater
flow velocity, and the rate at which a particular contaminant reacts with soil, TZ, and bedrock
materials. The rate of groundwater movement varies with the hydraulic conductivity and porosity
of the site soil, TZ, and bedrock materials.
The geological and hydrogeological features of the site influence the movement of the
contaminants by removal of constituents through sorption or precipitation of contaminants. The
degree and the rate at which these actions occur depend on many factors associated with the
solution containing the contaminant and the potentially sorbing soil or aquifer material. These
factors include redox conditions, the concentration of the solution, the chemical composition of
the solution and the contaminant, and the mineralogy of the soil or rock. The influence of these
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18.0 CONCLUSIONS
factors as determined by the chemical, physical, hydrologic, and mineralogical characterization
of the ash, ash basin porewater, groundwater, and site soil and rock will be incorporated into the
groundwater modeling discussed in Section 13.0. Geological and hydrogeological features at
the site do not influence the physical characteristics of the constituents other than through the
process of sorption and precipitation. The Kd term development and leaching tests results,
which will be presented in the CAP, will be key to understanding the influences of site soils and
rock on the constituents.
The groundwater model will facilitate evaluation of the site soil and rock material's capacity to
attenuate the loading imposed by the conditions modeled for the proposed corrective action.
18.6 Proposed Continued Monitoring
A plan for continued monitoring of select monitoring wells and parameters/constituents is
presented in Section 16.0 and will be implemented following NCDENR approval.
18.7 Preliminary Evaluation of Corrective Action Alternatives
In accordance with CAMA, Duke Energy is required to implement closure and remediation of the
MSS ash basin no later than August 1, 2029 (or sooner if classified by NCDENR as
intermediate or high risk). Closure for the MSS ash basin was not defined in CAMA.
In the subsequent CAP, Duke Energy will pursue corrective action under 15A NCAC 02L.0106
(k) or (1) depending on results of the groundwater modeling and evaluation of the site's suitability
to use MNA. This would potentially require evaluation of MNA using the approach found in
Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volumes 1 and 2
(USEPA 2007a, 2007b) and the potential modeling of groundwater surface water interaction. If
these approaches are found not to be satisfactory, additional measures such as active
remediation by hydraulic capture and treatment, among others, will be evaluated. When
properly applied, alternatives such as these can provide effective long-term management of
sites requiring corrective action.
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