NC0004979_FINAL_Allen_CSA_Report_2018_20180130

2018 Comprehensive Site Assessment Update January 2018
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Explanation of altered or items not initialed:

Item 1. The CSA was specifically designed to assess the coal ash management
areas of the facility. Sufficient information is available to prepare the
groundwater corrective action plan for the ash management areas of the
facility. Data limitations are discussed in Section 11 of the CSA report.
Continued groundwater monitoring at the Site is planned.
Item 2. Imminent hazards to human health and the environment have been
evaluated. The NCDEQ data associated with nearby water supply wells is
provided herein and is being evaluated.
Item 5. The groundwater assessment plan for the CSA as approved by NCDEQ
was specifically developed to assess the coal ash management areas of
the facility for the purposes of developing a corrective action plan for
groundwater. Other areas of possible contamination on the property, if
noted, are anticipated to be evaluated separately.

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WORK PERFORMED BY OTHERS

• HDR Engineering, Inc. (HDR) of the Carolinas prepared the reports
referenced herein under contract to Duke Energy.
• The reports were sealed by licensed geologists or engineers as
required by the North Carolina Board for Licensing of Geologists or
Board of Examiners for Engineers and Surveyors.
• The evaluations of hydrogeologic conditions and other information
provided in this updated Comprehensive Site Assessment (CSA) are
based in part on the work contained in the HDR documents and on
sampling activities performed by Pace Analytical Services after the
submittal of the HDR documents. The evaluations described in this
paragraph meet requirements detailed in 15A NCAC 02L .0106(g).
• SynTerra relied on information from the HDR reports as being
correct.
• The seal of the licensed geologist for this CSA applies to activities
conducted and interpretations derived after the HDR reports were
submitted. This submittal relies on the professional work
performed by HDR and references that work.

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EXECUTIVE SUMMARY
Source Information ES.1
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the coal-fired Allen
Steam Station (Allen, Plant, or Site), located in Belmont, Gaston County, North
Carolina. The Comprehensive Site Assessment (CSA) update was conducted to refine
and expand the understanding of subsurface conditions and evaluate the extent of
impacts from historical management of coal ash in accordance with the North Carolina
Coal Ash Management Act (CAMA). This CSA update contains an assessment of site
conditions based on a comprehensive interpretation of geologic and sampling results
from the initial site assessment and geologic and sampling results obtained after the
initial assessment. Available groundwater data from monitoring wells associated with
the Federal Coal Combustion Residuals Rule (CCR Rule) compliance program are also
considered in data interpretations. However, the CCR data has not been fully
incorporated into the analysis of this CSA due to the data only becoming available as of
mid- January 2018. For example, analytical results from CCR Rule-specific monitoring
wells are included on isoconcentration maps and analytical summary tables, but not
integrated into detailed mathematical analysis, such as piper plots, box-and-whisker
plots or background statistical calculations.
Operations began at Allen in 1957 with Units 1 and 2. Operations began at Unit 3 in
1959, followed by Unit 4 in 1960 and Unit 5 in 1961. The Plant remains in service. The
entire Allen site is approximately 1,009 acres in area and is owned by Duke Energy.
Duke Energy also owns property along the Discharge Canal to the east and west of
South Point Road (North Carolina Highway 273).
Coal combustion residuals (CCR) at Allen have been disposed of in the station’s ash
basins (the active ash basin and the inactive ash basin, which includes the ash storage
areas, structural fill areas, and the double-lined Retired Ash Basin [RAB] Ash Landfill
area). Both ash basins are located within natural drainage basins impounded by
earthen dams. Discharge from the active ash basin is permitted by the North Carolina
Department of Environmental Quality (NCDEQ) Division of Water Resources (DWR)
under the National Pollutant Discharge Elimination System (NPDES) Permit
NC0004979.
CCRs were deposited in the inactive ash basin by hydraulic sluicing operations until the
active ash basin was constructed and placed into operation in 1957. The Plant was
modified for dry fly ash (DFA) handling in the mid-2000’s, and dry ash handling began
in 2008. The dry fly ash is conveyed to silos on-site and then either sent off-site for
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beneficial reuse or disposed of at the RAB Ash Landfill permitted by the NCDEQ
Division of Waste Management (DWM) under Permit 3612-INDUS-2008. The RAB
Landfill is lined and constructed atop ash within the inactive ash basin. Since dry ash
handling commenced at Plant Allen, only de minimus quantities of fly ash are on
occasion sent to the ash basin system upon system start-up. The active ash basin still
receives bottom ash into three settling cells by hydraulic sluicing methods. Duke
Energy is in the process of converting to dry handling of bottom ash, which is
anticipated to commence in late 2018 or early 2019.
In borings installed in the inactive ash basin, ash was encountered to depths ranging
from 8 feet to 56 feet. In borings installed in the active ash basin, ash was encountered
to depths ranging from 1 foot to 54 feet. The majority of the ash in both basins is
saturated.
Assessment findings determined that CCR accumulated in the ash basins is a source of
impact to groundwater. The coal pile is likely another source of impact to groundwater.
The inferred extent of constituent migration from the ash basins and coal pile area
based on evaluation of constituent concentrations greater than both water quality
standards and background is shown on Figure ES-1. A detailed evaluation of
constituent migration is included in this CAMA CSA update report.
Initial Abatement and Emergency Response ES.2
Duke Energy has not conducted emergency responses because groundwater impacts
from the ash basins do not present an imminent hazard to human health or the
environment requiring emergency response. Abatement activities at the Allen Plant
related to the ash basins included conversion from wet handling (via sluicing to the
Active Ash Basin) to dry handling of fly ash in 2008. Duke Energy is also in the process
of converting to dry handling of bottom ash (anticipated by late 2018 or early 2019). In
preparation for closure of the ash basins, new holding and retention basin systems are
also being designed and constructed to handle certain water and wastewater streams.
Receptor Information ES.3
In accordance with NCDEQ direction, CSA receptor survey activities include listing and
depicting water supply wells (public or private, including irrigation wells and unused
wells) and surface water features within a 0.5-mile radius of the ash basin compliance
boundary. In 2017, the compliance boundary was revised; the compliance boundary
now encompasses the active ash basin, and not the entire inactive ash basin because the
inactive ash basin is no longer a permitted unit. However, the double-lined Retired Ash
Basin [RAB] Landfill constructed within the inactive ash basin is permitted and
encompassed by a compliance boundary offset 250 feet from the RAB Landfill
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boundary. The 0.5-mile radius, as it relates to this discussion of receptors, is in
reference to the previous, and larger, pre-2017 compliance boundary which
encompassed the active and inactive ash basins.
Public Water Supply Wells ES.3.1
Four public water supply wells have been identified within a 0.5-mile radius of
the pre-2017 compliance boundary. The public water supply wells serve several
residences in the vicinity of the Plant. The water supply wells are located
upgradient of the Allen Plant.
Private Water Supply Wells ES.3.2
HDR conducted receptor surveys and reported 219 private water supply wells
within a 0.5-mile radius of the pre-2017 compliance boundary.
HDR determined that 50 of the 219 identified private water supply wells
are recorded with Gaston and Mecklenburg counties. The Gaston County
Health and Human Services Department maintains records for 36 private
water supply wells, and Mecklenburg County’s online database maintains
records for 14 private water supply wells. The 50 private water supply
wells recorded with Gaston and Mecklenburg counties are identified as
“recorded” private water supply wells.
HDR determined that 93 of the 219 identified private water supply wells
were reported based on information provided in returned water supply
well questionnaires. Those 93 wells are identified as “reported” private
water supply wells.
Fifty-eight (58) private water supply wells were identified by HDR during
the site reconnaissance and are not considered “reported” or “recorded”
private water supply wells. HDR identified those 58 wells as “field-
identified” private water supply wells.
HDR reported that 18 private water supply wells are assumed to be 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. HDR determined
that 15 of the 18 assumed wells are located in Gaston County, and the
remaining three (3) assumed wells are located in Mecklenburg County.
Those 18 wells are identified as “assumed” private water supply wells.
In 2015, NCDEQ coordinated sampling of the water supply wells.
Approximately 125 samples were collected within a 0.5-mile radius of the pre-
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2017 ash basin compliance boundary. Additionally, Duke Energy voluntarily
collected approximately 23 samples in the vicinity of the Allen site from
background water supply wells located within an approximate 2- to 10-mile
radius of the Allen site boundary. NCDEQ also sampled seven private water
supply wells located in areas that are not hydraulically connected to
groundwater at Plant Allen, generally within an approximate 1- to 5- mile radius
of the Plant.
Available analytical data for the private wells generally show detected
concentrations less than Site-specific statistically derived provisional background
threshold values (PBTVs) of CCR-related constituents and not attributable to
CCR impacts. However, there were a few occasions when concentrations
reported were greater than current Site-derived PBTVs or 2L (sometimes both).
The use of water quality data from supply wells is one tool that can be used to
interpret whether the well has been influenced from the ash basin. However, the
Site-derived background values may not represent the natural variability of
background conditions within the 0.5-mile radius of the pre-2017 compliance
boundary. The water supply well data will also be effected by well construction
materials and equipment (e.g., galvanized piping, pump components) that the
site monitoring wells are not exposed that may influence the supply well
analytical results. Supply well data would also be affected by unknown land use
on the private properties. Therefore, the groundwater flow direction from the
source (ash basins) being away from the supply wells and toward Lake Wylie
and the discharge canal is a more reliable tool to infer that the supply wells have
not been impacted by the ash basins than the water quality data alone.
Boron (a key indicator of potential CCR influence) was not detected at
concentrations greater than the 2L in the private water supply well samples.
Boron was detected in a few water supply well locations at concentrations
greater than Site-derived PBTVs. These supply wells were at isolated locations
surrounded by other private supply or Site monitoring wells without detected
concentrations of boron. Therefore, the detection of boron in the wells does not
by itself conclusively indicate impact from the ash basin(s). Other constituents
that were detected in private supply wells at concentrations greater than
2L/IMAC were similar to Site-derived PBTVs and surrounded by wells with
concentrations less than applicable 2L or IMAC. There is limited supply well
construction information, such as depths and aquifer characteristics that would
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be helpful in interpretations. However, multiple lines of evidence indicate the
supply wells have not been impacted.
The land directly downgradient of the ash basins includes Lake Wylie/Catawba
River to the east and Duke Energy property to the north between the inactive ash
basin and the discharge canal. Therefore, there are no supply wells located
downgradient of the basins.
Surface Water Bodies ES.3.3
The Site is located adjacent to Lake Wylie (Catawba River), and groundwater
influenced by the ash basins flows toward the lake (east of the basins) and the
Discharge Canal (north of the basins). Results from surface water samples
collected from Lake Wylie/Catawba River do not indicate that impacted
groundwater associated with the Allen ash basins is causing 2B exceedances in
Lake Wylie/Catawba River. There are no surface water intakes in Lake Wylie in
the vicinity of the Site except for process water used by the Allen Plant.
Land Use ES.3.4
The area surrounding the Allen site generally consists of residential properties,
undeveloped land, and Lake Wylie (Catawba River). Properties located within a
0.5-mile radius of the Allen ash basin compliance boundary generally consist of
residential properties and undeveloped land in Gaston County to the north, west
and south, and residential properties and some undeveloped land in
Mecklenburg County to the east and southeast across Lake Wylie (Catawba
River). No change in land use surrounding the Allen Plant is currently
anticipated
Human Health and Ecological Risk Assessment ES.4
An update to the 2016 human health and ecological risk assessment was conducted.
There is no evidence of unacceptable risk to humans and wildlife at Allen attributed to
CCR constituent migration in groundwater from the ash basins. The only evidence of
potential unacceptable human related risks estimated in the 2016 risk assessment was
under the hypothetical subsistence fisherman scenario due to concentrations of cobalt in
fish tissue. This risk assessment update supports that the fisher risks were
overestimated based on conservative exposure (it is unlikely subsistence fishermen exist
in the area) and modeled fish tissue uptake assumptions (modeled concentrations likely
exceed actual fish tissue concentrations if measured), supporting a risk classification of
“Low” based upon groundwater related considerations.
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The Allen ash basins are currently designated as “Intermediate” risk under CAMA,
meaning that closure of the ash basins is required by 2024. The updated risk assessment
concluded no unacceptable risks to human health or wildlife exists from exposure to
groundwater and surface water.
Sampling/Investigation Results ES.5
This CAMA CSA includes evaluation of the hydrogeological and geochemical
properties of soil and groundwater at multiple depths and distances from the ash
basins.
Background Concentration Determinations ES.5.1
Naturally occurring background concentrations were determined using
statistical analysis for both soil and groundwater. Statistical determinations of
PBTVs were performed in strict accordance with the revised Statistical Methods
for Developing Reference Background Concentrations for Groundwater and Soil at Coal
Ash Facilities (statistical methods document) (HDR and SynTerra, 2017). The
current background monitoring well network consists of wells installed within
three flow zones — shallow, deep, and fractured bedrock. Background datasets
for each flow system used to statistically determine naturally occurring
concentrations of inorganic constituents in soil and groundwater are provided
herein. As of October 11, 2017, NCDEQ had approved a number of the
statistically derived background values; however, others are still under
evaluation and thus considered preliminary at this time. Therefore, it is
understood that valid background data may be greater than the currently
calculated PBTVs due to the limited dataset currently available and the statistical
nature of the determination. The statistically derived background threshold
values will continue to be adjusted as additional data become available.
Nature and Extent of Contamination ES.5.2
Site-specific groundwater constituents of interest (COIs) were developed by
evaluating groundwater sampling results with respect to 2L/IMAC and PBTVs.
The distribution of constituents in relation to the ash basin, co-occurrence with
CCR indicator constituents such as boron, and likely migration directions based
on groundwater flow direction are considered in determination of groundwater
COIs.
The following list of groundwater COIs at Allen has been developed:
Antimony Molybdenum
Arsenic Nickel
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Beryllium pH
Boron Selenium
Cadmium Strontium
Chromium (hexavalent) Sulfate
Chromium (total) Thallium
Cobalt Total Dissolved Solids (TDS)
Iron Vanadium
Manganese
Boron is a CCR-derived constituent in groundwater and is detected at
concentrations greater than the PBTV beneath and downgradient of the ash
basins. Boron, in its most common forms, is soluble in water and has a low
partitioning coefficient (Kd value), meaning the constituent is highly mobile in
groundwater. Therefore, the horizontal extent of boron concentrations greater
than PBTV approximates the leading edge of the CCR-derived plume from the
source areas (Figure ES-1). Arsenic is also included in the interpretation of the
extent of the plume on Figure ES-1 due to ash pore water concentrations greater
than the 2L across a broader area within the ash basins than boron and, although
it is relatively immobile, has less potential to migrate to groundwater beneath the
basins at concentrations greater than the 2L. Arsenic, in its most common forms,
is less soluble in water and has a greater Kd value meaning the constituent tends
to adsorb to solids and is relatively immobile in groundwater.
Boron is detected in groundwater at concentrations greater than the 2L and
PBTV in the shallow, deep, and bedrock flow layers, primarily in areas beneath
and east of the ash basins, within and beyond the compliance boundary (recent
revisions to the compliance boundary have resulted in a large majority of the
inactive ash basin being beyond the compliance boundary). Boron is not present
at concentrations greater than the PBTVs in wells to the west, north, or south of
the ash basins. Other COIs detected at concentrations greater than PBTVs are
primarily within the bounds of areas affected by boron. The coal pile is another
source of impact to groundwater north-northeast of the inactive ash basin as
indicated by a unique set of constituents detected in this area at concentrations
greater than applicable 2L/IMAC or PBTVs which were either not detected
elsewhere or detected at notably lower concentrations elsewhere. Boron
concentrations were either not detected or detected at concentrations less than
the 2L in the vicinity of the coal pile.
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Inactive Basin Summary
The compliance boundary around the inactive ash basin has been removed. The
area in the southern portion of the basin is encompassed by the active ash basin
compliance boundary.
Within the waste boundary of the inactive ash basin, samples from shallow
groundwater beneath the ash indicates arsenic, calcium, iron, manganese,
molybdenum, and strontium at concentrations greater than the 2L/IMAC or
PBTV, whichever is greater. Although boron was not detected at concentrations
greater than the 2L in valid samples from the existing shallow well network
beneath the inactive ash basin, boron concentrations are likely greater than the
PBTV and 2L in shallow groundwater beneath the eastern portion of the basin,
along Lake Wylie/Catawba River, based on groundwater flow and results from
samples further downgradient. Samples from deep groundwater indicate
antimony, calcium, manganese, strontium, and vanadium at concentrations
greater than, but similar to, applicable 2L/IMAC or PBTVs, whichever is greater.
Similar to the shallow flow zone, boron was not detected at concentrations
greater than the 2L in valid samples from the existing deep well network beneath
the inactive ash basin, however, boron concentrations are likely greater than the
PBTV and 2L in deep groundwater beneath the eastern portion of the basin,
along Lake Wylie/Catawba River, based on groundwater flow and results from
samples further downgradient. Valid samples from at least one well within the
bedrock flow zone indicate calcium, manganese, and strontium at concentrations
greater than, and similar to, applicable 2L or PBTVs, whichever is greater.
Similar to the deep monitoring zone, and based on groundwater flow and boron
concentrations detected in bedrock downgradient of inactive ash basin, boron
concentrations in bedrock are likely greater than the PBTV, and possibly the 2L,
beneath the eastern portion of the basin along Lake Wylie/Catawba River.
Downgradient of the inactive ash basin, samples from at least one well within the
shallow monitoring zone indicate boron and other constituents at concentrations
greater than applicable 2L or PBTVs, whichever is greater. Boron, calcium,
cobalt, iron, and manganese are primarily detected in areas east of the basin
indicating influence from the basin. North-northeast of the inactive basin, the
coal pile appears to be another source of impact to groundwater, as a unique set
of constituents is present in this area which are not detected in ash pore water at
concentrations greater than 2L (beryllium, cadmium, nickel, and zinc). Also in
the coal pile area, constituents common with those typically interpreted to be
associated with the ash basin (including arsenic, cobalt, manganese, sulfate,
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thallium, and TDS) are detected but at notably greater concentrations than
observed elsewhere on site indicating the coal pile may be the primary source of
those constituents in this area. Separate assessment of the coal pile as an
additional source is anticipated.
Deep groundwater downgradient of the inactive ash basin has boron and other
constituents at concentrations greater than applicable 2L/IMAC or PBTVs,
whichever is greater. Boron is primarily detected at locations to the east of the
inactive basin indicating influence from the basin. Deep groundwater north-
northeast of the basin is likely affected by the coal pile as indicated by sulfate and
TDS not observed elsewhere downgradient of the ash basin and by the notable
absence of boron at concentrations greater than the PBTV and 2L. Chromium
was detected at concentration 1.5 times greater than the 2L in a sample north of
the inactive basin, further downgradient of the coal pile. Nearby wells, including
those upgradient along the perimeter of the inactive basin, do not have
chromium concentrations greater than the 2L or PBTV, whichever is greater.
Chromium concentrations at locations closer to the coal pile and inactive ash
basin are typically less than the 2L or PBTV. These data indicate chromium at
this location is likely not derived from the ash basin or coal pile and the elevated
chromium concentration detected in this area is anomalous. The extent of
constituents in deep groundwater potentially related to the coal pile is likely
delineated to the north where constituent concentrations are less than applicable
2L/IMAC or PBTVs, with the exception of the anomalous chromium detection.
Bedrock groundwater downgradient of the inactive basin has boron (among
other constituents) at concentrations greater than the 2L east of the inactive basin.
The vertical extent of CCR-influence in bedrock has not been confirmed through
installation of a deeper monitoring well, however, an upward hydraulic gradient
in the area indicates bedrock groundwater discharges to Lake Wylie/Catawba
River and therefore the vertical extent should be limited. North of the inactive
ash basin, calcium, manganese, and strontium were detected in bedrock
groundwater at concentrations greater than, but similar to, applicable 2L/IMAC
or PBTVs, indicating the horizontal and vertical extent of migration in bedrock
has been adequately defined in this area.
Active Ash Basin Summary
Based on ash pore water concentrations, it is interpreted that shallow
groundwater beneath the active ash basin waste boundary is likely impacted by
CCR to some extent, although there are no shallow wells to confirm this. Samples
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from deep groundwater beneath the active ash basin indicate calcium, iron,
manganese, strontium, and vanadium at concentrations greater than, but similar
to, applicable 2L/IMAC or PBTVs, whichever is greater. Boron was detected
within the deep zone beneath the basin at a concentration greater than the PBTV,
but less than the 2L. However, based on boron concentrations within the deep
zone downgradient of the active basin and groundwater flow direction, boron
concentrations are likely greater than the PBTV and 2L at other areas beneath
basin. Samples from bedrock groundwater beneath the active ash basin indicate
calcium, strontium, manganese, and molybdenum at concentrations greater than,
but similar to, the 2L/IMAC or PBTVs, whichever is greater. Similar to the deep
monitoring zone, and based on boron concentrations detected in bedrock
downgradient of the active ash basin and groundwater flow direction, boron
concentrations in bedrock are likely greater than the PBTV, and possibly the 2L,
beneath the eastern portion of the basin.
Downgradient of the active ash basin, shallow groundwater to the south within
the compliance boundary contains only cobalt at concentrations greater than
applicable 2L/IMAC or PBTVs, whichever is greater, so the horizontal extent of
migration south of the basin has been adequately defined. Boron and other
constituents including aluminum, chromium, hexavalent chromium, cobalt, iron,
and manganese are detected at concentrations greater than the 2L/IMAC or
PBTVs within and east of the basin dam along Lake Wylie/Catawba River
(within the compliance boundary).
Deep groundwater east of the active ash basin within the compliance boundary
indicates influence from the basin as boron and other constituents including
calcium, iron, manganese, strontium and vanadium are detected in
concentrations greater than the 2L/IMAC or PBTVs, whichever is greater. South
of the basin within the deep groundwater, calcium and strontium were detected
at concentrations greater than, but similar to, applicable PBTVs. No other
constituents, including boron were detected in deep groundwater at
concentrations greater than 2L/IMAC or PBTVs, whichever is greater, south of
the basin. These data indicate the extent of migration has been defined in the
deep groundwater flow zone south of the active ash basin.
Bedrock groundwater east of the active ash basin within the compliance
boundary indicates influence from the basin as boron and other constituents
including calcium, iron, molybdenum, and strontium are detected at
concentrations greater than the 2L and PBTV, whichever is greater. East-
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southeast of the basin, boron concentrations are similar within wells screened in
upper and deeper bedrock indicating the vertical extent of boron concentrations
is not fully delineated downgradient of the active ash basin in this area. Upward
hydraulic gradients observed in wells in this area indicate bedrock groundwater
discharges to Lake Wylie/Catawba River. South of the active basin within the
compliance boundary, calcium and strontium are detected in bedrock
groundwater at concentrations greater than, but similar to, applicable PBTVs.
Boron or other constituents are not detected in bedrock groundwater greater
than PBTVs south of the basin indicating the ash basin has not affected bedrock
groundwater quality in this area and the horizontal and vertical extent of
migration in bedrock has been adequately defined in this area.
Soil Assessment Summary
Soil data indicates that COI migration from the source and sorption to soils
beneath and downgradient from the source is likely limited to areas immediately
adjacent to the ash basins, though difficult to decipher from natural distribution
of constituents. Concentrations of arsenic, barium, boron, calcium, chromium,
cobalt, iron, manganese, molybdenum, selenium, strontium, and vanadium in
soils beneath the ash basins are greater than their respective NCDEQ Preliminary
Soil Remediation Goals (PSRGs) Protection of Groundwater (POG) or PBTVs,
whichever is greater, however, only calcium and, to a lesser extent, strontium,
have consistent exceedances of respective PBTVs. Several soil samples collected
from upgradient locations (but not used in the current statistical determination of
PBTVs) also had sporadic detections of COIs. For strontium, all concentrations
that exceeded the PBTV, except two samples (which might have included some
ash within the sample aliquot), were similar to the PBTV. The exceedances likely
reflect natural variability in strontium concentrations across the Site. Other
constituent exceedances were sporadic and detected in just one or a few samples.
Constituent concentrations are similar at multiple sample depths within the same
boring locations, and higher concentrations do not directly correlate with
proximity to the ash basin elevation or the water table, therefore are likely
naturally occurring.
Maximum Contaminant Concentrations (Source ES.5.3
Information)
Maximum concentrations of COIs generally occur in the CCR material and pore
water accumulated in the ash basins. Ash pore water samples collected from
wells installed within the ash basins and screened in the ash layers have been
monitored since 2015. Concentrations of detected constituents have been
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relatively stable, with minor fluctuations. The coal pile is also a likely source of
constituents to groundwater.
Ash pore water within the inactive ash basin has concentrations of aluminum,
arsenic, boron, calcium, iron, manganese, molybdenum, strontium, sulfate, total
dissolved solids (TDS) and vanadium greater than 2L/IMAC or PBTVs,
whichever is greater (note comparison of pore water within the basins to 2B or
2L/IMAC is for source area information only). Ash pore water within the active
ash basin indicate concentrations of antimony, arsenic, boron, calcium, cobalt,
iron, manganese, molybdenum, strontium, thallium, total dissolved solids (TDS)
and vanadium greater than 2L/IMAC or PBTVs, whichever is greater.
Typically, the greatest COI concentrations are detected in either ash pore water
within the basins or shallow groundwater in the vicinity of the coal pile north-
northeast of the inactive basin. The greatest concentrations of antimony, arsenic,
boron, iron, molybdenum, strontium, vanadium, and total uranium were
detected within ash pore water. The greatest concentrations of beryllium,
cadmium, manganese, nickel, selenium, sulfate, TDS, and thallium were detected
in the vicinity of the coal pile. The greatest concentrations of the remaining
COIs, including chromium, hexavalent chromium, cobalt, and total radium, were
detected at various other locations downgradient of the ash basins.
Detections of COIs in soil samples at concentrations greater than PSRG POGs or
PBTVs were infrequent, sporadic, and at various locations and depth intervals.
Several PSRG POG exceedances were at background locations. This indicates
limited distribution and migration of COIs in soil potentially derived from the
ash basins. This also indicates that soils are not a secondary source to
groundwater beyond the waste boundaries of the ash basins.
Site Geology and Hydrogeology ES.5.4
Geology beneath the Allen Plant can be classified into three units: regolith
(shallow), transition zone (deep), and bedrock. Regolith is the shallowest
geologic unit and includes surficial residual soils, fill and reworked soil,
alluvium along the Lake Wylie stream valley, and saprolite. Saprolite is thick,
with a depth up to about 130 feet, and is typically saturated. The regolith is
primarily comprised of fine-grained material, such as silty clay and clayey sand.
The transition (deep) zone at the Allen Site is generally continuous throughout
the Allen Plant area and is comprised mostly of partially weathered rock that is
gradational between saprolite and competent bedrock. The transition zone is up
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to 65 feet in thickness. The change from partially weathered rock to competent
bedrock, is defined by subtle changes in weathering, secondary staining,
mineralization, core recovery, and the degree of fracturing in the rock.
Bedrock at the Site consists of meta-quartz diorite and meta-diabase. Based on
rock core descriptions, the meta-quartz diorite, which is the predominant rock
type at the Site, is very light gray to dark gray, fine- to coarse-grained, non-
foliated and massive to foliated, and is composed dominantly of plagioclase,
quartz, biotite, and hornblende. The meta-diabase is greenish black to very dark
greenish gray, is mostly non-foliated, and is noted as aphanitic to fine-grained,
although it is described as fine- to coarse-grained in some boring logs.
Shallow bedrock is fractured; however, only mildly productive fractures
(providing water to wells) were observed within the top 50 feet to 75 feet of
bedrock. The majority of fractures are relatively small (e.g., close and tight) and
appear to be limited in connectivity between borings. Yields from pumping or
packer testing are low.
The Allen groundwater system flow direction within each of the three layers is
generally consistent. Water levels fluctuate up and down with seasonal changes
in precipitation evapotranspiration, but the overall groundwater flow directions
do not change due to seasonal changes in precipitation.
The groundwater system at Allen is consistent with the regolith-fractured rock,
slope-aquifer system and is an unconfined, connected aquifer system. Typically,
groundwater flow within the slope-aquifer system mimics surface topography.
An elongated topographic high creates a groundwater divide that trends
approximately north to south and roughly follows NC Highway 273.
Groundwater to the east of the divide, including groundwater within the Allen
Plant, flows to the east toward Lake Wylie and to the northeast and north toward
Duke Energy property and the discharge canal, as confirmed by water level
measurements onsite. Groundwater to the west of the divide flows west toward
the South Fork Catawba River.
The hydraulic head created by the impounded water in the active ash basin
under current conditions creates a slight mounding effect that influences
groundwater flow direction in the immediate vicinity of the basin. Beyond the
area of impounded water, the forces of natural advective flow overcome the
mounding effect and groundwater flow continues toward the east and Lake
Wylie. Water level measurements from site wells indicate that the mounding
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effect does not extend beyond the ash basin boundary, indicating groundwater
does not flow toward the water supply wells in the vicinity of the basin.
Conclusions and Recommendations ES.6
The investigation described in the CSA presents the results of the assessments required
by the Coal Ash Management Act (CAMA) and 2L. The ash basin CCR material was
determined to be a source of the groundwater contamination. The assessment
investigated the Site hydrogeology, determined the direction of groundwater flow from
the ash basins, and determined the horizontal and vertical extent of impacts to
groundwater and soil sufficient to proceed with preparation of a CAP.
Assessment findings determined that CCR accumulated in the ash basins is the primary
source of impact to groundwater. Groundwater COIs migrate laterally and vertically
into and through surficial regolith (shallow flow zone), the transition zone (deep flow
zone), and fractured bedrock (bedrock flow zone). Boron, the primary ash basin plume
indicator parameter, is detected at concentrations greater than the 2L east of the ash
basins in the shallow, deep, and bedrock flow zones. Boron is not present at
concentrations greater than the PBTV in wells to the west and south of the active ash
basin compliance boundary. The extent of downgradient plume migration is limited to
the shores of Lake Wylie/Catawba River, where it discharges.
Boron is the primary constituent detected in groundwater at concentrations greater than
background and the 2L standard near or beyond the compliance boundary, as boron is
present at high concentrations, readily solubilizes and migrates with minimal retention.
In contrast, some COIs, such as arsenic and cobalt, readily adsorb to aquifer materials
and do not readily solubilize; thus, they are relatively immobile. Therefore, the extent
of boron concentrations greater than the PBTV, is interpreted to represent the extent of
ash basin influence on groundwater.
The coal pile (located north-northeast of the inactive basin) is another primary source of
impact to groundwater. Constituents such as beryllium, cadmium, nickel, and zinc that
are infrequently detected elsewhere at the site are detected at elevated concentrations,
and in addition, aluminum, arsenic, cobalt, manganese, sulfate, thallium, and TDS are
detected near the coal pile at greater concentrations than elsewhere at the Site. Boron
concentrations at locations immediately adjacent to the basin in this area are similar to,
if not less than other areas downgradient of the basins indicating the area is influenced
by the inactive ash basin, but it is not likely the primary source of the constituents
detected in this area.
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Soil samples collected beneath the ash basins indicate a few limited and sporadic
detections of COIs above PBTVs and PSRG POG values. Soils beneath the inactive and
active ash basin have constituent concentrations similar at multiple sample depths
within the same boring location, and higher concentrations do not directly correlate
with proximity to the base of the ash. This indicates detected constituent concentrations
are likely naturally occurring. This also indicates that there is limited potential for soil
to be a secondary source of constituents to groundwater.
Surface water data indicates constituent concentrations are typically greater at locations
downgradient of the ash basins compared to locations upgradient of the basins.
However, no constituent concentrations were greater than applicable 2B values for
protection of aquatic life and recreational uses. Results from surface water samples
collected from Lake Wylie/Catawba River do not indicate that impacted groundwater
associated with the Allen ash basins is causing 2B exceedances in Lake Wylie/Catawba
River. Additional surface water and sediment data collection is anticipated to support
the evaluation of potential monitored natural attenuation in the area of the
groundwater plume discharge into surface water.
Information evaluated as part of the updated CSA indicates that identified water
supply wells are not impacted by ash basin operations; constituent concentrations
detected in water supply wells are deemed to not be sourced from the ash basins.
The Allen ash basins are currently designated as “Intermediate” risk under CAMA,
meaning closure of the ash basins is required by 2024. The updated evaluation of risks
has determined that there are no unacceptable potential risks to human health or the
environment due to groundwater, surface water, or sediment impacts from the ash
basins. The private water supply wells located near the plant are not located in the ash
basin groundwater flow paths and analytical results of the water supply wells indicate
the ash basins have not affected water quality. A "Low" risk classification and closure
via a cap-in-place scenario are considered appropriate as alternative water supplies are
being provided in accordance with G.S. 130A-309.213.(d)(1) of House Bill 630.
A preliminary evaluation of groundwater corrective action alternatives is included in
this CSA to provide insight into the CAP preparation process. Primary source control
(closure) methods anticipated to be evaluated in the CAP include, but are not limited to:
Cap the residuals with a low permeability engineered cover system to minimize
infiltration.
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Excavate the ash to remove the source of the COIs from the groundwater flow
system.
Some combination of the above.
The source control (closure) options will be evaluated in the CAP based upon technical
and economical feasible means of removing or controlling the ash and ash pore water as
a source to the groundwater flow system. The evaluation will include predictive
groundwater modeling to evaluate the cost-benefit (including overall environmental
costs and sustainability) associated with various options. For basin closure, preliminary
modeling indicates reduction of the amount of water migrating from the basin to
groundwater will have a positive impact on groundwater and surface water quality
downgradient of the ash basin. If a “Low” risk classification is determined, a well-
designed capping system is expected to minimize ongoing migration to groundwater.
In addition to source control measures, the CAP will evaluate measures to address
groundwater conditions associated with the ash basins. It is anticipated that
groundwater corrective action by monitored natural attenuation (MNA) will be further
evaluated in the CAP. As warranted, a number of viable groundwater remediation
technologies, such as phytoremediation, groundwater extraction, and hydraulic
barriers, may be evaluated based on short-term and long-term effectiveness,
implementability, cost, and sustainability. Results of the evaluation, including
groundwater flow and transport modeling and geochemical modeling will be used for
remedy selection in the CAP.
Based on the assessment results, the CAP will focus on areas where boron
concentrations exceed the 2L, which is the primary indicator of CCR influence on
groundwater from the ash basins. These areas are primarily located east of the ash
basins and beneath the ash basins in the shallow, deep, and bedrock flow zones. The
CAP will also consider other constituents with concentrations likely attributable to CCR
from the ash basins such as arsenic. Additional monitoring wells may be installed in
shallow groundwater beneath the ash basins and deeper within bedrock downgradient
of the basins to evaluate the effectiveness of corrective measures.
Different remedial strategies may be applied to different portions of the Site, including
the area north-northeast of the inactive ash basin which may be influenced by the coal
pile. Remedial strategies in this area may be evaluated and implemented separately
from ash basin closure and corrective action, with a focus primarily on the shallow flow
zone and for different constituents such as arsenic, cadmium, cobalt, nickel, selenium,
sulfate, TDS, thallium, and zinc.
148 RIVER STREET, SUITE 220
GREENVILLE, SOUTH CAROLINA 29601
PHONE [phone]
www.synterracorp.com
PROJECT MANAGER:
LAYOUT:
DRAWN BY:
CHRIS SUTTELL
DATE:ADAM FEIGL
ES1
01/12/2018
01/25/2018 11:17 AM P:\Duke Energy Progress.1026\00 GIS BASE DATA\Allen\Map_Docs\CSA_Supplement_2\CSM3D\Allen_3D_ES1.dwg
FIGURE ES-1
APPROXIMATE EXTENT OF IMPACTS
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA
CAROLINAS
DISCH
A
R
G
E

C
A
N
A
L
REESE

W
I
L
S
O
N

R
DHIGHWAY 273 (SOUTHPOINT RD)LOWER
ARMSTRO
N
G

R
D
VISUAL AID ONLY -
DEPICTION NOT TO SCALE
DEEP
ASH BASIN WASTE BOUNDARY
NORTH
GENERALIZED GROUNDWATER FLOW DIRECTION
APPROXIMATE LANDFILL WASTE BOUNDARY
NOTE:
1.OCTOBER, 2016 AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON
DECEMBER 7, 2017. AERIAL DATED OCTOBER 8, 2016.
2.STREAMS OBTAINED FROM AMEC FOSTER WHEELER NRTR, MAY 2015.
3.GENERALIZED GROUNDWATER FLOW DIRECTION BASED ON SEPTEMBER 11, 2017
WATER LEVEL DATA.
4.PROPERTY BOUNDARY PROVIDED BY DUKE ENERGY.
5.GENERALIZED AREAL EXTENT OF MIGRATION REPRESENTED BY NCAC 02L
EXCEEDANCES OF MULTIPLE CONSTITUENTS (BORON AND ARSENIC) IN MULTIPLE
FLOW ZONES.
6.GENERALIZED AREAL EXTENT OF MIGRATION REPRESENTED BY NCAC 02L
EXCEEDANCES OF MULTIPLE CONSTITUENTS (BERYLLIUM, NICKEL, SULFATE, AND
THALLIUM) IN MULTIPLE FLOW ZONES. A SEPARATE ASSESSMENT IS PLANNED FOR
THE COAL PILE AREA.
WATER SUPPLY WELL LOCATION
SHALLOW
DUKE ENERGY PROPERTY BOUNDARY
LEGEND
BEDROCK
AREA OF CONCENTRATION IN GROUNDWATER
ABOVE NC2L (SEE NOTE 5)
STREAM WITH FLOW DIRECTION MECKLENBURG COUNTYCANAL RD
INACTIVE
ASH BASIN
LAKE WYLIE
(CATAWBA RIVER)GASTON COUNTYALLEN
PLANT
AREA OF CONCENTRATION IN GROUNDWATER ABOVE NC2L
POTENTIALLY ATTRIBUTABLE TO THE COAL PILE (SEE NOTE 6)STRUCTURAL FILLASHSTORAGEASHSTORAGESTRUCTURAL FILLRETIRED ASH BASIN
ASH LANDFILL
ACTIVE
ASH BASIN
PLANT ALLE
N

R
D
COAL
PILE
SLUICE LINES
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TABLE OF CONTENTS
SECTION PAGE
SOURCE INFORMATION ....................................................................................... ES-1 ES.1
INITIAL ABATEMENT AND EMERGENCY RESPONSE ................................ ES-2 ES.2
RECEPTOR INFORMATION .................................................................................. ES-2 ES.3
Public Water Supply Wells ................................................................................... ES-3 ES.3.1
Private Water Supply Wells ................................................................................. ES-3 ES.3.2
Surface Water Bodies ............................................................................................. ES-5 ES.3.3
Land Use .................................................................................................................. ES-5 ES.3.4
HUMAN HEALTH AND ECOLOGICAL RISK ASSESSMENT ...................... ES-5 ES.4
SAMPLING/INVESTIGATION RESULTS .......................................................... ES-6 ES.5
Background Concentration Determinations ...................................................... ES-6 ES.5.1
Nature and Extent of Contamination .................................................................. ES-6 ES.5.2
Maximum Contaminant Concentrations (Source Information) .................... ES-11 ES.5.3
Site Geology and Hydrogeology ....................................................................... ES-12 ES.5.4
CONCLUSIONS AND RECOMMENDATIONS .............................................. ES-14 ES.6
INTRODUCTION ......................................................................................................... 1-1 1.0
Purpose of Comprehensive Site Assessment ........................................................ 1-1 1.1
Regulatory Background ........................................................................................... 1-2 1.2
Notice of Regulatory Requirements ............................................................... 1-2 1.2.1
Coal Ash Management Act Requirements .................................................... 1-3 1.2.2
Coal Combustion Residuals Rule ................................................................... 1-4 1.2.3
1.3 Approach to Comprehensive Site Assessment ..................................................... 1-5
1.3.1 Notice of Regulatory Requirements Guidance ............................................. 1-5
USEPA Monitored Natural Attenuation Tiered Approach ........................ 1-6 1.3.2
ASTM Conceptual Site Model Guidance ....................................................... 1-6 1.3.3
1.4 Technical Objectives ................................................................................................. 1-6
1.5 Previous Submittals .................................................................................................. 1-7

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TABLE OF CONTENTS (CONTINUED)
SITE HISTORY AND DESCRIPTION ..................................................................... 2-1 2.0
2.1 Site Description, Ownership, and Use History..................................................... 2-1
2.2 Geographic Setting, Surrounding Land Use, Surface Water Classification ..... 2-1
2.3 Coal Ash Management Act -related Source Areas ............................................... 2-4
2.4 Other Primary and Secondary Sources .................................................................. 2-7
2.5 Summary of Permitted Activities ........................................................................... 2-8
2.6 History of Site Groundwater Monitoring .............................................................. 2-9
Ash Basin Voluntary Groundwater Monitoring .......................................... 2-9 2.6.1
Ash Basin NPDES Groundwater Monitoring ............................................. 2-10 2.6.2
2.7 Summary of Assessment Activities ...................................................................... 2-11
2.8 Summary of Initial Abatement, Source Removal, or other
Corrective Action .................................................................................................... 2-13
SOURCE CHARACTERISTICS ................................................................................. 3-1 3.0
3.1 Coal Combustion and Ash Handling System ....................................................... 3-1
3.2 General Physical and Chemical Properties of Ash............................................... 3-1
3.3 Site-Specific Coal Ash Data ..................................................................................... 3-3
RECEPTOR INFORMATION ..................................................................................... 4-1 4.0
4.1 Summary of Receptor Survey Activities................................................................ 4-2
4.2 Summary of Receptor Survey Findings ................................................................. 4-3
Water Supply Lines .......................................................................................... 4-4 4.2.1
Public Water Supply Wells .............................................................................. 4-4 4.2.2
Private Water Supply Wells ............................................................................ 4-4 4.2.3
4.3 Private Water Well Sampling .................................................................................. 4-5
4.4 Surface Water Receptors ........................................................................................ 4-12
REGIONAL GEOLOGY AND HYDROGEOLOGY ............................................... 5-1 5.0
5.1 Regional Geology ...................................................................................................... 5-1
5.2 Regional Hydrogeology ........................................................................................... 5-2
SITE GEOLOGY AND HYDROGEOLOGY ............................................................ 6-1 6.0
6.1 Site Geology ............................................................................................................... 6-1
6.1.1 Soil Classification .............................................................................................. 6-2
Rock Lithology .................................................................................................. 6-3 6.1.2
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TABLE OF CONTENTS (CONTINUED)
Structural Geology ............................................................................................ 6-4 6.1.3
Geologic Mapping ............................................................................................. 6-5 6.1.4
Effects of Geologic Structure on Groundwater Flow ................................... 6-5 6.1.5
Soil and Rock Mineralogy and Chemistry .................................................... 6-6 6.1.6
6.2 Site Hydrogeology .................................................................................................... 6-6
Hydrostratigraphic Layer Development ....................................................... 6-7 6.2.1
Hydrostratigraphic Layer Properties ............................................................. 6-8 6.2.2
6.3 Groundwater Flow Direction .................................................................................. 6-9
6.4 Hydraulic Gradient ................................................................................................. 6-10
6.5 Hydraulic Conductivity ......................................................................................... 6-12
6.6 Groundwater Velocity ............................................................................................ 6-12
6.7 Contaminant Velocity ............................................................................................. 6-13
6.8 Slug Test and Aquifer Test Results ...................................................................... 6-14
Fracture Trace Study Results ................................................................................. 6-15 6.9
Methods ............................................................................................................ 6-16 6.9.1
Results ............................................................................................................... 6-16 6.9.2
SOIL SAMPLING RESULTS ...................................................................................... 7-1 7.0
7.1 Background Soil Data ............................................................................................... 7-1
Synthetic Precipitation Leaching Procedure Results for 7.1.1
Background/Upgradient Soil........................................................................... 7-3
7.2 Facility Soil Data ....................................................................................................... 7-3
Soil Beneath Waste Boundaries of the Ash Basins ....................................... 7-3 7.2.1
Soil Beyond Waste Boundaries of Active and Inactive Ash Basins ........... 7-4 7.2.2
Synthetic Precipitation Leaching Procedure Results for Facility Soils ...... 7-5 7.2.3
Comparison of Partially Weathered Rock and Bedrock Results to 7.2.4
Background ........................................................................................................ 7-6
7.3 Secondary Sources .................................................................................................... 7-6
SEDIMENT RESULTS ................................................................................................. 8-1 8.0
8.1 Sediment/Surface Soil Associated with Areas Of Wetness ................................. 8-1

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TABLE OF CONTENTS (CONTINUED)
SURFACE WATER RESULTS .................................................................................... 9-1 9.0
9.1 Discussion of Results for Constituents Without Established
2B Standards .............................................................................................................. 9-2
9.2 Comparison of Exceedances of 2B Standards ....................................................... 9-4
9.3 Discussion of Surface Water Results ...................................................................... 9-4
GROUNDWATER SAMPLING RESULTS ............................................................ 10-1 10.0
10.1 Background Groundwater Concentrations ......................................................... 10-2
Background Dataset Statistical Analysis ..................................................... 10-3 10.1.1
Piper Diagrams (Comparison to Background) ........................................... 10-7 10.1.2
Downgradient Groundwater Concentrations..................................................... 10-8 10.2
Monitoring Wells Beneath the Ash Basins .................................................. 10-9 10.2.1
10.2.2 Monitoring Wells Sidegradient and Downgradient of the
Ash Basins ...................................................................................................... 10-12
Piper Diagrams (Comparison to Downgradient Well Samples) ............ 10-15 10.2.3
Radiological Laboratory Testing ................................................................. 10-17 10.2.4
10.3 Site-Specific Exceedances (Groundwater Constituents of Interest) ............... 10-17
Provisional Background Threshold Values ............................................... 10-17 10.3.1
Applicable Standards ................................................................................... 10-18 10.3.2
Additional Requirements ............................................................................. 10-18 10.3.3
Allen Steam Station Constituents of Interest ............................................ 10-20 10.3.4
HYDROGEOLOGICAL INVESTIGATION .......................................................... 11-1 11.0
11.1 Plume Physical and Chemical Characterization ................................................ 11-1
Plume Physical Characterization .................................................................. 11-1 11.1.1
Plume Chemical Characterization ................................................................ 11-8 11.1.2
11.2 Pending Investigation(s) ...................................................................................... 11-28
RISK ASSESSMENT .................................................................................................. 12-1 12.0
Human Health Screening Summary .................................................................... 12-2 12.1
Ecological Screening Summary ............................................................................. 12-4 12.2
Private Well Receptor Assessment Update ......................................................... 12-5 12.3
Risk Assessment Update Summary ..................................................................... 12-6 12.4

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TABLE OF CONTENTS (CONTINUED)
GROUNDWATER MODELING RESULTS........................................................... 13-1 13.0
13.1 Summary of Flow and Transport Modelling Results ........................................ 13-2
13.2 Summary of Geochemical Model Results ........................................................... 13-4
SITE ASSESSMENT RESULTS ................................................................................ 14-1 14.0
14.1 Nature and Extent of Contamination ................................................................... 14-1
14.2 Maximum Constituent of Interest Concentrations ............................................ 14-9
Contaminant Migration and Potentially Affected Receptors ......................... 14-14 14.3
CONCLUSIONS AND RECOMMENDATIONS ................................................. 15-1 15.0
15.1 Overview of Site Conditions at Specific Source Areas ...................................... 15-2
15.2 Revised Site Conceptual Model ............................................................................ 15-2
15.3 Interim Monitoring Program ................................................................................. 15-5
15.3.1 Interim Monitoring Program Implementation ........................................... 15-5
15.3.2 Interim Monitoring Program Reporting ...................................................... 15-6
15.4 Preliminary Evaluation of Corrective Action Alternatives............................... 15-6
15.4.1 Corrective Action Plan Preparation Process ............................................... 15-7
15.4.2 Summary .......................................................................................................... 15-9
REFERENCES ............................................................................................................... 16-1 16.0

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LIST OF TABLES
2.0 Site History and Description
Table 2-1 Well Construction Data
Table 2-2 NPDES Groundwater Monitoring Requirements
Table 2-3 Summary of Onsite Environmental Incidents
3.0 Source Characteristics
Table 3-1 Range (10th percentile - 90th percentile) in Bulk Composition of Fly Ash,
Bottom Ash, Rock, and Soil (Source: EPRI 2009a)
Table 3-2 Soil/Material Properties for Ash, Fill, Alluvium, and Soil/Saprolite
Table 3-3 Regional Background Soil SPLP Data
6.0 Site Geology and Hydrogeology
Table 6-1 Soil Mineralogy Results
Table 6-2 Soil Chemistry Results, Elemental Composition and % Oxides
Table 6-3 Solid Matrix Parameters and Analytical Methods for Soil, Ash, and Rock
Parameters and Constituent Analysis - Analytical Methods
Table 6-4 Ash Pore Water, Groundwater, Surface Water, and AOW
Analytical Methods
Table 6-5 Transition Zone Mineralogy Results
Table 6-6 Transition Zone Results, Elemental Composition and % Oxides
Table 6-7 Whole Rock Chemistry Results, Elemental Composition and % Oxides
Table 6-8 Petrographic Analysis Summary
Table 6-9 Historical Water Level Measurements
Table 6-10 Horizontal Groundwater Gradients and Velocities
Table 6-11 Vertical Hydraulic Gradients
Table 6-12 In-Situ Hydraulic Conductivity Results
Table 6-13 Allen Packer Tests Hydraulic Conductivity Results
Table 6-14 Hydrostratigraphic Layer Properties - Horizontal
Hydraulic Conductivity
Table 6-15 Hydrostratigraphic Layer Properties - Vertical Hydraulic Conductivity
Table 6-16 Estimated Effective Porosity/Specific Yield, and Specific Storage for
Upper Hydrostratigraphic Units (A, F, S, M1 and M2)
Table 6-17 Total Porosity, Secondary (Effective) Porosity/Specific Yield, and Specific
Storage for Lower Hydrostratigraphic Units (TZ and BR)
Table 6-18 Field Permeability Test Results
Table 6-19 Laboratory Permeability Test Results
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LIST OF TABLES (CONTINUED)
7.0 Soil Sampling Results
Table 7-1 Provisional Background Threshold Values for Soil
Table 7-2 Potential Secondary Source Soil Analytical Results
10.0 Groundwater Sampling Results
Table 10-1 Provisional Background Threshold Values for Groundwater
Table 10-2 Charge Balance Summary
Table 10-3 State and Federal Standards for COIs
11.0 Hydrogeological Investigation
Table 11-1 Data Inventory Summary Table
Table 11-2 Wells to Monitor Using Pressure Transducers
13.0 Groundwater Modeling Results
Table 13-1 Summary of Kd Values from Batch and Column Studies
15.0 Discussion - Conclusion and Recommendations
Table 15-1 Groundwater Interim Monitoring Program Analytical Methods
Table 15-2 Interim Monitoring Program List
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LIST OF FIGURES
Executive Summary
Figure ES-1 Approximate Extent of Impacts
1.0 Introduction
Figure 1-1 2016 USGS Topographic Map
2.0 Site History and Description
Figure 2-1 Allen Plant Vicinity Map
Figure 2-2 1948 Aerial Photograph
Figure 2-3 1973 Aerial Photograph
Figure 2-4 2015 Aerial Photograph
Figure 2-5 1949 USGS Topographic Map
Figure 2-6 NPDES Flow Diagram
Figure 2-7 Site Layout
Figure 2-8 Sample Location Map
3.0 Source Characteristics
Figure 3-1 Known Sample of Ash for Comparison (Source: Duke Energy 2014)
Figure 3-2 Elemental Composition for Bottom Ash, Fly Ash, Shale, and
Volcanic Ash (Source: EPRI 2009A)
Figure 3-3 Coal Ash TCLP Leachate Concentration Ranges Compared to
Regulatory Limits (Source: EPRI 2010)
Figure 3-4 Piper Diagram – Ash Pore Water
4.0 Receptor Information
Figure 4-1 USGS Map with Water Supply Wells
Figure 4-2 Water Supply Well Locations
5.0 Regional Geology and Hydrogeology
Figure 5-1 Regional Geologic Map
Figure 5-2 Site Geologic Map
Figure 5-3 Piedmont Slope-Aquifer System
6.0 Site Geology
Figure 6-1 General Cross Section A-A'
Figure 6-2 General Cross Section B-B'
Figure 6-3 General Cross Section C-C'
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LIST OF FIGURES (CONTINUED)
Figure 6-4 General Cross Section D-D'
Figure 6-5 General Cross Section E-E'
Figure 6-6 General Cross Section F-F'
Figure 6-7 Shallow Water Level Map - March 2017
Figure 6-8 Deep Water Level Map - March 2017
Figure 6-9 Bedrock Water Level Map - March 2017
Figure 6-10 Shallow Water Level Map - September 2017
Figure 6-11 Deep Water Level Map - September 2017
Figure 6-12 Bedrock Water Level Map - September 2017
Figure 6-13 Potential Vertical Gradient Between Shallow and Deep Zones
Figure 6-14 Potential Vertical Gradient Between Shallow and Bedrock Zones
Figure 6-15 Potential Vertical Gradient Between Deep and Bedrock Zones
Figure 6-16 Topographic Lineaments and Rose Diagram
Figure 6-17 Aerial Photography Lineaments and Rose Diagram
7.0 Soil Sampling Results
Figure 7-1 Potential Secondary Source Soil Analytical Results
9.0 Surface Water Results
Figure 9-1 Piper Diagram - AOW and Surface Water
10.0 Groundwater Sampling Results
Figure 10-1 Piper Diagram - Background and Upgradient Wells
Figure 10-2 Piper Diagram - Shallow Flow Layer
Figure 10-3 Piper Diagram - Deep Flow Layer
Figure 10-4 Piper Diagram - Bedrock Flow Layer
11.0 Hydrogeological Investigation
Figure 11-1 Isoconcentration Map - Antimony in Shallow Groundwater
Figure 11-2 Isoconcentration Map - Antimony in Deep Groundwater
Figure 11-3 Isoconcentration Map - Antimony in Bedrock Groundwater
Figure 11-4 Isoconcentration Map - Arsenic in Shallow Groundwater
Figure 11-5 Isoconcentration Map - Arsenic in Deep Groundwater
Figure 11-6 Isoconcentration Map - Arsenic in Bedrock Groundwater
Figure 11-7 Isoconcentration Map - Beryllium in Shallow Groundwater
Figure 11-8 Isoconcentration Map - Beryllium in Deep Groundwater
Figure 11-9 Isoconcentration Map - Beryllium in Bedrock Groundwater
Figure 11-10 Isoconcentration Map - Boron in Shallow Groundwater
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LIST OF FIGURES (CONTINUED)
Figure 11-11 Isoconcentration Map - Boron in Deep Groundwater
Figure 11-12 Isoconcentration Map - Boron in Bedrock Groundwater
Figure 11-13 Isoconcentration Map - Cadmium in Shallow Groundwater
Figure 11-14 Isoconcentration Map - Cadmium in Deep Groundwater
Figure 11-15 Isoconcentration Map - Cadmium in Bedrock Groundwater
Figure 11-16 Isoconcentration Map - Chromium (VI) and Chromium (Total) in
Shallow Groundwater
Figure 11-17 Isoconcentration Map - Chromium (VI) and Chromium (Total) in Deep
Groundwater
Figure 11-18 Isoconcentration Map - Chromium (VI) and Chromium (Total) in
Bedrock Groundwater
Figure 11-19 Isoconcentration Map - Cobalt in Shallow Groundwater
Figure 11-20 Isoconcentration Map - Cobalt in Deep Groundwater
Figure 11-21 Isoconcentration Map - Cobalt in Bedrock Groundwater
Figure 11-22 Isoconcentration Map - Iron in Shallow Groundwater
Figure 11-23 Isoconcentration Map - Iron in Deep Groundwater
Figure 11-24 Isoconcentration Map - Iron in Bedrock Groundwater
Figure 11-25 Isoconcentration Map - Manganese in Shallow Groundwater
Figure 11-26 Isoconcentration Map - Manganese in Deep Groundwater
Figure 11-27 Isoconcentration Map - Manganese in Bedrock Groundwater
Figure 11-28 Isoconcentration Map - Molybdenum in Shallow Groundwater
Figure 11-29 Isoconcentration Map - Molybdenum in Deep Groundwater
Figure 11-30 Isoconcentration Map - Molybdenum in Bedrock Groundwater
Figure 11-31 Isoconcentration Map - Nickel in Shallow Groundwater
Figure 11-32 Isoconcentration Map - Nickel in Deep Groundwater
Figure 11-33 Isoconcentration Map - Nickel in Bedrock Groundwater
Figure 11-34 Isoconcentration Map - pH in Shallow Groundwater
Figure 11-35 Isoconcentration Map - pH in Deep Groundwater
Figure 11-36 Isoconcentration Map - pH in Bedrock Groundwater
Figure 11-37 Isoconcentration Map - Selenium in Shallow Groundwater
Figure 11-38 Isoconcentration Map - Selenium in Deep Groundwater
Figure 11-39 Isoconcentration Map - Selenium in Bedrock Groundwater
Figure 11-40 Isoconcentration Map - Strontium in Shallow Groundwater
Figure 11-41 Isoconcentration Map - Strontium in Deep Groundwater
Figure 11-42 Isoconcentration Map - Strontium in Bedrock Groundwater
Figure 11-43 Isoconcentration Map - Sulfate in Shallow Groundwater
Figure 11-44 Isoconcentration Map - Sulfate in Deep Groundwater
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LIST OF FIGURES (CONTINUED)
Figure 11-45 Isoconcentration Map - Sulfate in Bedrock Groundwater
Figure 11-46 Isoconcentration Map - Thallium in Shallow Groundwater
Figure 11-47 Isoconcentration Map - Thallium in Deep Groundwater
Figure 11-48 Isoconcentration Map - Thallium in Bedrock Groundwater
Figure 11-49 Isoconcentration Map - Total Dissolved Solids in Shallow
Groundwater
Figure 11-50 Isoconcentration Map - Total Dissolved Solids in Deep Groundwater
Figure 11-51 Isoconcentration Map - Total Dissolved Solids in Bedrock
Groundwater
Figure 11-52 Isoconcentration Map - Total Radium in Shallow Groundwater
Figure 11-53 Isoconcentration Map - Total Radium in Deep Groundwater
Figure 11-54 Isoconcentration Map - Total Radium in Bedrock Groundwater
Figure 11-55 Isoconcentration Map - Total Uranium in Shallow Groundwater
Figure 11-56 Isoconcentration Map - Total Uranium in Deep Groundwater
Figure 11-57 Isoconcentration Map - Total Uranium in Bedrock Groundwater
Figure 11-58 Isoconcentration Map - Vanadium in Shallow Groundwater
Figure 11-59 Isoconcentration Map - Vanadium in Deep Groundwater
Figure 11-60 Isoconcentration Map - Vanadium in Bedrock Groundwater
Figure 11-61 Notes - Concentration Versus Distance From Source
Figure 11-62 Concentration Versus Distance From Source Antimony, Arsenic,
Beryllium, Boron, Cadmium, and Chromium Coal Pile Transect
(Sheet 1 of 4)
Figure 11-63 Concentration Versus Distance From Source Hexavalent Chromium,
Cobalt, Iron, Manganese, Molybdenum, and Nickel Coal Pile Transect
(Sheet 2 of 4)
Figure 11-64 Concentration Versus Distance From Source pH, Selenium, Strontium,
Sulfate, Thallium, and TDS Coal Pile Transect (Sheet 3 of 4)
Figure 11-65 Concentration Versus Distance From Source Total Radium, Total
Uranium, and Vanadium Coal Pile Transect (Sheet 4 of 4)
Figure 11-66 Concentration Versus Distance From Source Antimony, Arsenic,
Beryllium, Boron, Cadmium, and Chromium Northern Active Ash
Basin Transect (Sheet 1 of 4)
Figure 11-67 Concentration Versus Distance From Source Hexavalent Chromium,
Cobalt, Iron, Manganese, Molybdenum, and Nickel Northern Active
Ash Basin Transect (Sheet 2 of 4)
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LIST OF FIGURES (CONTINUED)
Figure 11-68 Concentration Versus Distance From Source pH, Selenium, Strontium,
Sulfate, Thallium, and TDS Northern Active Ash Basin Transect
(Sheet 3 of 4)
Figure 11-69 Concentration Versus Distance From Source Total Radium, Total
Uranium, and Vanadium Northern Active Ash Basin Transect
(Sheet 4 of 4)
Figure 11-70 Concentration Versus Distance From Source Antimony, Arsenic,
Beryllium, Boron, Cadmium, and Chromium Southern Active Ash
Basin Transect (Sheet 1 of 4)
Figure 11-71 Concentration Versus Distance From Source Hexavalent Chromium,
Cobalt, Iron, Manganese, Molybdenum, and Nickel Southern Active
Ash Basin Transect (Sheet 2 of 4)
Figure 11-72 Concentration Versus Distance From Source pH, Selenium, Strontium,
Sulfate, Thallium, and TDS Southern Active Ash Basin Transect
(Sheet 3 of 4)
Figure 11-73 Concentration Versus Distance From Source Total Radium, Total
Uranium, and Vanadium Southern Active Ash Basin Transect
(Sheet 4 of 4)
Figure 11-74 Antimony Analytical Results Cross Section B-B'
Figure 11-75 Antimony Analytical Results Cross Section D-D'
Figure 11-76 Antimony Analytical Results Cross Section E-E'
Figure 11-77 Antimony Analytical Results Cross Section F-F'
Figure 11-78 Arsenic Analytical Results Cross Section B-B'
Figure 11-79 Arsenic Analytical Results Cross Section D-D'
Figure 11-80 Arsenic Analytical Results Cross Section E-E'
Figure 11-81 Arsenic Analytical Results Cross Section F-F'
Figure 11-82 Beryllium Analytical Results Cross Section B-B'
Figure 11-83 Beryllium Analytical Results Cross Section D-D'
Figure 11-84 Beryllium Analytical Results Cross Section E-E'
Figure 11-85 Beryllium Analytical Results Cross Section F-F'
Figure 11-86 Boron Analytical Results Cross Section B-B'
Figure 11-87 Boron Analytical Results Cross Section D-D'
Figure 11-88 Boron Analytical Results Cross Section E-E'
Figure 11-89 Boron Analytical Results Cross Section F-F'
Figure 11-90 Cadmium Analytical Results Cross Section B-B'
Figure 11-91 Cadmium Analytical Results Cross Section D-D'
Figure 11-92 Cadmium Analytical Results Cross Section E-E'
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LIST OF FIGURES (CONTINUED)
Figure 11-93 Cadmium Analytical Results Cross Section F-F'
Figure 11-94 Chromium Analytical Results Cross Section B-B'
Figure 11-95 Chromium Analytical Results Cross Section D-D'
Figure 11-96 Chromium Analytical Results Cross Section E-E'
Figure 11-97 Chromium Analytical Results Cross Section F-F'
Figure 11-98 Chromium (VI) Analytical Results Cross Section B-B'
Figure 11-99 Chromium (VI) Analytical Results Cross Section D-D'
Figure 11-100 Chromium (VI) Analytical Results Cross Section E-E'
Figure 11-101 Chromium (VI) Analytical Results Cross Section F-F'
Figure 11-102 Cobalt Analytical Results Cross Section B-B'
Figure 11-103 Cobalt Analytical Results Cross Section D-D'
Figure 11-104 Cobalt Analytical Results Cross Section E-E'
Figure 11-105 Cobalt Analytical Results Cross Section F-F'
Figure 11-106 Iron Analytical Results Cross Section B-B'
Figure 11-107 Iron Analytical Results Cross Section D-D'
Figure 11-108 Iron Analytical Results Cross Section E-E'
Figure 11-109 Iron Analytical Results Cross Section F-F'
Figure 11-110 Manganese Analytical Results Cross Section B-B'
Figure 11-111 Manganese Analytical Results Cross Section D-D'
Figure 11-112 Manganese Analytical Results Cross Section E-E'
Figure 11-113 Manganese Analytical Results Cross Section F-F'
Figure 11-114 Molybdenum Analytical Results Cross Section B-B'
Figure 11-115 Molybdenum Analytical Results Cross Section D-D'
Figure 11-116 Molybdenum Analytical Results Cross Section E-E'
Figure 11-117 Molybdenum Analytical Results Cross Section F-F'
Figure 11-118 Nickel Analytical Results Cross Section B-B'
Figure 11-119 Nickel Analytical Results Cross Section D-D'
Figure 11-120 Nickel Analytical Results Cross Section E-E'
Figure 11-121 Nickel Analytical Results Cross Section F-F'
Figure 11-122 pH Analytical Results Cross Section B-B'
Figure 11-123 pH Analytical Results Cross Section D-D'
Figure 11-124 pH Analytical Results Cross Section E-E'
Figure 11-125 pH Analytical Results Cross Section F-F'
Figure 11-126 Radium Analytical Results Cross Section B-B'
Figure 11-127 Radium Analytical Results Cross Section D-D'
Figure 11-128 Radium Analytical Results Cross Section E-E'
Figure 11-129 Radium Analytical Results Cross Section F-F'
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LIST OF FIGURES (CONTINUED)
Figure 11-130 Selenium Analytical Results Cross Section B-B'
Figure 11-131 Selenium Analytical Results Cross Section D-D'
Figure 11-132 Selenium Analytical Results Cross Section E-E'
Figure 11-133 Selenium Analytical Results Cross Section F-F'
Figure 11-134 Strontium Analytical Results Cross Section B-B'
Figure 11-135 Strontium Analytical Results Cross Section D-D'
Figure 11-136 Strontium Analytical Results Cross Section E-E'
Figure 11-137 Strontium Analytical Results Cross Section F-F'
Figure 11-138 Sulfate Analytical Results Cross Section B-B'
Figure 11-139 Sulfate Analytical Results Cross Section D-D'
Figure 11-140 Sulfate Analytical Results Cross Section E-E'
Figure 11-141 Sulfate Analytical Results Cross Section F-F'
Figure 11-142 Thallium Analytical Results Cross Section B-B'
Figure 11-143 Thallium Analytical Results Cross Section D-D'
Figure 11-144 Thallium Analytical Results Cross Section E-E'
Figure 11-145 Thallium Analytical Results Cross Section F-F'
Figure 11-146 Total Dissolved Solids Analytical Results Cross Section B-B'
Figure 11-147 Total Dissolved Solids Analytical Results Cross Section D-D'
Figure 11-148 Total Dissolved Solids Analytical Results Cross Section E-E'
Figure 11-149 Total Dissolved Solids Analytical Results Cross Section F-F'
Figure 11-150 Uranium Analytical Results Cross Section B-B'
Figure 11-151 Uranium Analytical Results Cross Section D-D'
Figure 11-152 Uranium Analytical Results Cross Section E-E'
Figure 11-153 Uranium Analytical Results Cross Section F-F'
Figure 11-154 Vanadium Analytical Results Cross Section B-B'
Figure 11-155 Vanadium Analytical Results Cross Section D-D'
Figure 11-156 Vanadium Analytical Results Cross Section E-E'
Figure 11-157 Vanadium Analytical Results Cross Section F-F'
Figure 11-158 Proposed Coal Pile Assessment Sample Locations
Figure 11-159 Solid Phase - Groundwater Interaction Data Map
12.0 Screening-Level Risk Assessment
Figure 12-1 Ecological Exposure Areas
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LIST OF FIGURES (CONTINUED)
14.0 Discussion - Assessment Results
Figure 14-1 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Antimony
Figure 14-2 Time versus Concentration - Inactive Ash Basin Transect Antimony
Figure 14-3 Time versus Concentration - Active Ash Basin - North
Transect Antimony
Figure 14-4 Time versus Concentration - Active Ash Basin - South
Transect Antimony
Figure 14-5 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Arsenic
Figure 14-6 Time versus Concentration - Inactive Ash Basin Transect Arsenic
Figure 14-7 Time versus Concentration - Active Ash Basin - North
Transect Arsenic
Figure 14-8 Time versus Concentration - Active Ash Basin - South
Transect Arsenic
Figure 14-9 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Beryllium
Figure 14-10 Time versus Concentration - Inactive Ash Basin Transect Beryllium
Figure 14-11 Time versus Concentration - Active Ash Basin - North
Transect Beryllium
Figure 14-12 Time versus Concentration - Active Ash Basin - South
Transect Beryllium
Figure 14-13 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Boron
Figure 14-14 Time versus Concentration - Inactive Ash Basin Transect Boron
Figure 14-15 Time versus Concentration - Active Ash Basin - North
Transect Boron
Figure 14-16 Time versus Concentration - Active Ash Basin - South
Transect Boron
Figure 14-17 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Cadmium
Figure 14-18 Time versus Concentration - Inactive Ash Basin Transect Cadmium
Figure 14-19 Time versus Concentration - Active Ash Basin - North
Transect Cadmium
Figure 14-20 Time versus Concentration - Active Ash Basin - South
Transect Cadmium
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LIST OF FIGURES (CONTINUED)
Figure 14-21 Time versus Concentration - Coal Pile/Ash Storage Area Transect
Chromium (VI) and Chromium (Total)
Figure 14-22 Time versus Concentration - Inactive Ash Basin Transect
Chromium (VI) and Chromium (Total)
Figure 14-23 Time versus Concentration - Active Ash Basin - North Transect
Chromium (VI) and Chromium (Total)
Figure 14-24 Time versus Concentration - Active Ash Basin - South Transect
Chromium (VI) and Chromium (Total)
Figure 14-25 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Cobalt
Figure 14-26 Time versus Concentration - Inactive Ash Basin Transect Cobalt
Figure 14-27 Time versus Concentration - Active Ash Basin - North
Transect Cobalt
Figure 14-28 Time versus Concentration - Active Ash Basin - South
Transect Cobalt
Figure 14-29 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Iron
Figure 14-30 Time versus Concentration - Inactive Ash Basin Transect Iron
Figure 14-31 Time versus Concentration - Active Ash Basin - North
Transect Iron
Figure 14-32 Time versus Concentration - Active Ash Basin - South Transect Iron
Figure 14-33 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Manganese
Figure 14-34 Time versus Concentration - Inactive Ash Basin
Transect Manganese
Figure 14-35 Time versus Concentration - Active Ash Basin - North
Transect Manganese
Figure 14-36 Time versus Concentration - Active Ash Basin - South
Transect Manganese
Figure 14-37 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Molybdenum
Figure 14-38 Time versus Concentration - Inactive Ash Basin
Transect Molybdenum
Figure 14-39 Time versus Concentration - Active Ash Basin - North
Transect Molybdenum
Figure 14-40 Time versus Concentration - Active Ash Basin - South
Transect Molybdenum
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LIST OF FIGURES (CONTINUED)
Figure 14-41 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Nickel
Figure 14-42 Time versus Concentration - Inactive Ash Basin Transect Nickel
Figure 14-43 Time versus Concentration - Active Ash Basin - North
Transect Nickel
Figure 14-44 Time versus Concentration - Active Ash Basin - South
Transect Nickel
Figure 14-45 Time versus Concentration - Coal Pile/Ash Storage Area
Transect pH
Figure 14-46 Time versus Concentration - Inactive Ash Basin Transect pH
Figure 14-47 Time versus Concentration - Active Ash Basin - North Transect pH
Figure 14-48 Time versus Concentration - Active Ash Basin - South Transect pH
Figure 14-49 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Selenium
Figure 14-50 Time versus Concentration - Inactive Ash Basin Transect Selenium
Figure 14-51 Time versus Concentration - Active Ash Basin - North
Transect Selenium
Figure 14-52 Time versus Concentration - Active Ash Basin - South
Transect Selenium
Figure 14-53 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Strontium
Figure 14-54 Time versus Concentration - Inactive Ash Basin Transect Strontium
Figure 14-55 Time versus Concentration - Active Ash Basin - North
Transect Strontium
Figure 14-56 Time versus Concentration - Active Ash Basin - South
Transect Strontium
Figure 14-57 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Sulfate
Figure 14-58 Time versus Concentration - Inactive Ash Basin Transect Sulfate
Figure 14-59 Time versus Concentration - Active Ash Basin - North
Transect Sulfate
Figure 14-60 Time versus Concentration - Active Ash Basin - South
Transect Sulfate
Figure 14-61 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Thallium
Figure 14-62 Time versus Concentration - Inactive Ash Basin Transect Thallium
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LIST OF FIGURES (CONTINUED)
Figure 14-63 Time versus Concentration - Active Ash Basin - North
Transect Thallium
Figure 14-64 Time versus Concentration - Active Ash Basin - South
Transect Thallium
Figure 14-65 Time versus Concentration - Coal Pile/Ash Storage Area Transect
Total Dissolved Solids
Figure 14-66 Time versus Concentration - Inactive Ash Basin Transect
Total Dissolved Solids
Figure 14-67 Time versus Concentration - Active Ash Basin - North Transect
Total Dissolved Solids
Figure 14-68 Time versus Concentration - Active Ash Basin - South Transect
Total Dissolved Solids
Figure 14-69 Time versus Concentration - Coal Pile/Ash Storage Area Transect
Total Radium
Figure 14-70 Time versus Concentration - Inactive Ash Basin Transect
Total Radium
Figure 14-71 Time versus Concentration - Active Ash Basin - North Transect
Total Radium
Figure 14-72 Time versus Concentration - Active Ash Basin - South Transect
Total Radium
Figure 14-73 Time versus Concentration - Coal Pile/Ash Storage Area Transect
Total Uranium
Figure 14-74 Time versus Concentration - Inactive Ash Basin Transect
Total Uranium
Figure 14-75 Time versus Concentration - Active Ash Basin - North Transect
Total Uranium
Figure 14-76 Time versus Concentration - Active Ash Basin - South Transect
Total Uranium
Figure 14-77 Time versus Concentration - Coal Pile/Ash Storage Area
Transect Vanadium
Figure 14-78 Time versus Concentration - Inactive Ash Basin Transect Vanadium
Figure 14-79 Time versus Concentration - Active Ash Basin - North
Transect Vanadium
Figure 14-80 Time versus Concentration - Active Ash Basin - South
Transect Vanadium
Figure 14-81 Groundwater Concentration Trend Analysis Antimony In All Flow
Layers and AOWs
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LIST OF FIGURES (CONTINUED)
Figure 14-82 Groundwater Concentration Trend Analysis Arsenic In All Flow
Layers and AOWs
Figure 14-83 Groundwater Concentration Trend Analysis Beryllium In All Flow
Layers and AOWs
Figure 14-84 Groundwater Concentration Trend Analysis Boron In All Flow
Layers and AOWs
Figure 14-85 Groundwater Concentration Trend Analysis Cadmium In All Flow
Layers and AOWs
Figure 14-86 Groundwater Concentration Trend Analysis Chromium (VI) In All
Flow Layers and AOWs
Figure 14-87 Groundwater Concentration Trend Analysis Chromium (Total) In
All Flow Layers and AOWs
Figure 14-88 Groundwater Concentration Trend Analysis Cobalt In All Flow
Layers and AOWs
Figure 14-89 Groundwater Concentration Trend Analysis Iron In All Flow
Layers and AOWs
Figure 14-90 Groundwater Concentration Trend Analysis Manganese In All
Flow Layers and AOWs
Figure 14-91 Groundwater Concentration Trend Analysis Molybdenum In All
Flow Layers and AOWs
Figure 14-92 Groundwater Concentration Trend Analysis Nickel In All Flow
Layers and AOWs
Figure 14-93 Groundwater Concentration Trend Analysis pH In All Flow
Layers and AOWs
Figure 14-94 Groundwater Concentration Trend Analysis Selenium In All Flow
Layers and AOWs
Figure 14-95 Groundwater Concentration Trend Analysis Strontium In All Flow
Layers and AOWs
Figure 14-96 Groundwater Concentration Trend Analysis Sulfate In All Flow
Layers and AOWs
Figure 14-97 Groundwater Concentration Trend Analysis Thallium In All Flow
Layers and AOWs
Figure 14-98 Groundwater Concentration Trend Analysis Total Dissolved Solids
In All Flow Layers and AOWs
Figure 14-99 Groundwater Concentration Trend Analysis Total Radium
In All Flow Layers and AOWs
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LIST OF FIGURES (CONTINUED)
Figure 14-100 Groundwater Concentration Trend Analysis Total Uranium In All
Flow Layers and AOWs
Figure 14-101 Groundwater Concentration Trend Analysis Vanadium In All
Flow Layers and AOWs
Figure 14-102 Comprehensive Solids Data
Figure 14-103 Comprehensive Groundwater Data (Sheet 1 of 2)
Figure 14-104 Comprehensive Groundwater Data (Sheet 2 of 2)
Figure 14-105 Comprehensive Surface Water and Area of Wetness

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LIST OF APPENDICES
Appendix A Regulatory Correspondence
NCDEQ Expectations Document (July 18, 2017)
Completed NCDEQ CSA Update Expectations Check List
NCDENR NORR Letter (August 13, 2014)
NCDEQ Background Location Approvals (October 11, 2017)
NCDEQ Background Dataset Review (July 7, 2017)
NCDEQ PBTV Approval Attachments (September 1, 2017)
NCDEQ Correspondence – Revised Interim Monitoring Plan
(October 19, 2017)
Appendix B Comprehensive Data Table
Comprehensive Data Table Notes
Table 1 - Groundwater Results
Table 2 - Surface Water Results
Table 3 - AOW Results
Table 4 - Soil and Ash Results
Table 5 - Sediment Results
Table 6 - SPLP Results
Table 7- CCR Results
Appendix C Site Assessment Data
HDR CSA Appendix H – Hydrogeological Investigation
Soil Physical Lab Reports
Mineralogy Lab Reports
Slug Test Procedure
Slug Test Reports
Historic Permeability Data
Field Permeability Data
Fetter-Bear Diagrams – Porosity
Historic Porosity Data
Estimated Seasonal High Groundwater Elevations Calculation
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LIST OF APPENDICES (CONTINUED)
HDR CSA Supplement 2 Slug Test Report
UNCC Soil Sorption Evaluation – HDR CAP 1 Appendix D
Addendum to the UNCC Soil Sorption Evaluation - HDR CAP 2
Appendix C
Appendix D Receptor Surveys
Drinking Water Well and Receptor Survey Report
Supplement to Drinking Water Supply Well and Receptor Survey
Well Receptor Survey and Water Supplies per HB630
Dewberry Report – Permanent Water Supply Proposal to DEQ
Appendix E Supporting Documents
Stantec Report
WSP Maps
Appendix F Boring Logs, Construction Diagrams, and Lithographic Photographs
Appendix G Sample Characterization
Source Characterization – HDR CSA Appendix C
Soil and Rock Characterization – HDR CSA Appendix D
Surface Water and Sediment Characterization – HDR CSA Appendix F
Groundwater Characterization – HDR CSA Appendix G
Includes Duke Low Flow Sampling Plan
Field, Sampling, and Data Analysis Quality Assurance / Quality Control
HDR CSA Appendix E
Appendix H Background Determination
Site specific 2017 CSA PBTV Report
Appendix I Risk Assessment
Appendix J Lab Reports

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LIST OF ACRONYMS
2B NCDENR Title 15A, Subchapter 2B. Surface Water and Wetland
Standards
2L NCDENR Title 15A, Subchapter 2L. Groundwater Classification
and Standards
3D Three Dimensional
ADD Average Daily Dose
AOW Areas of Wetness
ASTM American Society for Testing and Materials
BG Background
CAMA Coal Ash Management Act
CAP Corrective Action Plan
CCR Coal Combustion Residuals
CFR Code of Federal Regulations
CNS Catawba Nuclear Station
COI Constituent of Interest
CS Clayey Sand
CSA Comprehensive Site Assessment
CSM Conceptual Site Model
DFA Dry Fly Ash
DORS Distribution of Residuals Solids
DWM Division of Waste Management
DWR Division of Water Resources
EMP Effectiveness Monitoring Plan
ESV Ecological Screening Value
FERC Federal Energy Regulatory Commission
FGD Flue Gas Desulfurization
GAP Groundwater Assessment Work Plan
GP Sand with Clay and Gravel
HAO Hydroxide Phases of Aluminum
HFO Hydroxide Phases of Iron
IHSB Inactive Hazardous Sites Branch
IMAC Interim Maximum Allowable Concentrations
IMP Interim Monitoring Plan

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LCS Leachate Collection System
LDS Leak Detection System
MCL Maximum Contaminant Level
MNA Monitored Natural Attenuation
MT3DMS Modular 3-D Transport Multi-Species
NCDENR North Carolina Department of Environment and Natural Resources
NCDENR DWM North Carolina Department of Environment and Natural Resources
Division of Waste Management
NCDEQ North Carolina Department of Environmental Quality
NCDEQ-DWR North Carolina Department of Environmental Quality – Division of
Water Resources
NORR Notice of Regulatory Requirements
NPDES National Pollution Discharge Elimination System
NURE National Uranium Resource Evaluation
PBTV Provisional Background Threshold Value
Plant/Site Allen Steam Station
POG Protection of Groundwater
PSRG Preliminary Soil Remediation Goal
PWR Partially Weathered Rock
RAB Retired Ash Basin
RBC Risk-Based Concentration
RCP Reinforced Concrete Pipe
REC Recovery
RQD Rock Quality Designation
RSL Regional Screening Level
SC Clayey Sand
SCM Site Conceptual Model
SM Silty Sand
SMCL Secondary Maximum Contaminant Level
SPLP Synthetic Precipitation Leaching Procedure
TCLP Toxicity Characteristic Leaching Procedure
TRV Toxicity Reference Values
TZ Transition Zone
UNC University of North Carolina
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UNCC University of North Carolina - Charlotte
USEPA United States Environmental Protection Agency
USGS United States Geological Survey
UTL Upper Tolerance Limit

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INTRODUCTION 1.0
Duke Energy Carolinas, LLC (Duke Energy) owns and operates the coal-fired Allen
Steam Station (Allen, Allen Plant, or Site), located in Belmont, Gaston County, North
Carolina (Figure 1-1). Power generating operations began at Allen in 1957 with Units 1
and 2. Operations began at Unit 3 in 1959, followed by Unit 4 in 1960 and Unit 5 in 1961.
Coal combustion residuals (CCR) and other liquid discharges from coal combustion
process at Allen have been disposed of in the station’s ash basins (including the active
and inactive ash basins, Retired Ash Basin [RAB] Ash Landfill area, ash storage areas,
and structural fill areas). Discharge from the active ash basin is permitted by the North
Carolina Department of Environmental Quality (NCDEQ) 1 Division of Water Resources
(DWR) under the National Pollutant Discharge Elimination System (NPDES) Permit
NC0004979.
Purpose of Comprehensive Site Assessment 1.1
This Comprehensive Site Assessment (CSA) update was conducted to refine and
expand the understanding of subsurface geologic/hydrogeologic conditions and
evaluate the extent of impacts from historical management of coal ash in the ash basins
in accordance with Coal Ash Management Act (CAMA) and 2L. This CSA update
contains an assessment of Site conditions based on a comprehensive interpretation of
geologic and sampling results from the initial CSA Site assessment and geologic and
sampling results obtained subsequent to the initial assessment. The report has been
prepared in coordination with Duke Energy and NCDEQ in response to requests for
additional information, including additional sampling and assessment of specified
areas in accordance with CAMA. Data associated with monitoring wells installed for
the purpose of compliance with 40 C.F.R. § 257.90 (the CCR Rule) is provided as
information. Groundwater data collected for the purpose of compliance with the CCR
Rule will be evaluated in accordance with the requirements and schedule provided
therein.
This CSA update was prepared in conformance to the most recently updated CSA table
of contents provided by NCDEQ to Duke Energy on September 29, 2017. In response to
a request from NCDEQ for an updated CSA report, this submittal includes the
following information.

1 Prior to September 18, 2015, the NCDEQ was referred to as the North Carolina Department of Environment and
Natural Resources (NCDENR). Both naming conventions are used in this report, as appropriate.
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Review of baseline assessment data collected and reported as part of CSA
activities
A summary of NPDES and Coal Ash Management Act (CAMA) groundwater
monitoring information
A summary of potential receptors, including results from water supply wells
A description and findings of additional assessment activities conducted since
submittal of the CSA Supplement report(s)
An update on background concentrations for groundwater and soil
Definition of horizontal and vertical extent of CCR constituents in soil and
groundwater based on NCDEQ approved background concentrations
An update to human health and ecological risk assessment to evaluate the
existence of imminent hazards to public health, safety, and the environment
The NCDEQ Expectations Document (July 18, 2017) and the completed NCDEQ CSA
Update Expectations Check List are included in Appendix A.
Regulatory Background 1.2
The CAMA of 2014 directs owners of CCR surface impoundments in North Carolina to
conduct groundwater monitoring, assessment, and remedial activities, if necessary. The
CSA was performed to collect information necessary to evaluate the horizontal and
vertical extent of impacts to soil and groundwater attributable to CCR source area(s),
identify potential receptors, and screen for potential risks to those receptors.
Notice of Regulatory Requirements 1.2.1
On August 13, 2014, North Carolina Department of Environment and Natural
Resources (NCDENR) issued a Notice of Regulatory Requirements (NORR) letter
notifying Duke Energy that exceedances of groundwater quality standards were
reported at 14 coal ash facilities owned and operated by Duke Energy. Those
groundwater quality standards are part of 15A NCAC 02L (2L) .0200
Classifications and Water Quality Standards Applicable to the Groundwaters of
North Carolina. The NORR stipulated that for each coal ash facility, Duke Energy
was to conduct a CSA. The NORR also stipulated that before conducting each
CSA, Duke was to submit a Groundwater Assessment Work Plan (GAP or Work
Plan) and a receptor survey. In accordance with the NORR requirements, 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 facility. The NORR letter is included in Appendix A.
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Coal Ash Management Act Requirements 1.2.2
The CAMA of 2014 — General Assembly of North Carolina Senate Bill 729
Ratified Bill (Session 2013) (SB 729) — requires that ash from Duke Energy coal
plant sites located in North Carolina 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 §130A-309.209 of the
CAMA ruling specifies groundwater assessment and corrective actions, drinking
water supply well surveys and provisions of alternate water supply, and
reporting requirements as follows:
(a) Groundwater Assessment of Coal Combustion Residuals Surface
Impoundments. – The owner of a coal combustion residuals surface
impoundment shall conduct groundwater monitoring and assessment as
provided in this subsection. The requirements for groundwater monitoring
and assessment set out in this subsection are in addition to any other
groundwater monitoring and assessment requirements applicable to the
owners of coal combustion residuals surface impoundments.
(1) No later than December 31, 2014, the owner of a coal combustion
residuals surface impoundment shall submit a proposed Groundwater
Assessment Plan for the impoundment to the Department for its
review and approval. The Groundwater Assessment Plan shall, at a
minimum, provide for all of the following:
a) A description of all receptors and significant exposure pathways.
b) An assessment of the horizontal and vertical extent of soil and
groundwater contamination for all contaminants confirmed to be
present in groundwater in exceedance of groundwater quality
standards.
c) A description of all significant factors affecting movement and
transport of contaminants.
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d) A description of the geological and hydrogeological features
influencing the chemical and physical character of the contaminants.
(2) The Department shall approve the Groundwater Assessment Plan if it
determines that the Plan complies with the requirements of this
subsection and will be sufficient to protect public health, safety, and
welfare; the environment; and natural resources.
(3) No later than 10 days from approval of the Groundwater Assessment
Plan, the owner shall begin implementation of the Plan.
(4) No later than 180 days from approval of the Groundwater
Assessment Plan, the owner shall submit a Groundwater Assessment
Report to the Department. The Report shall describe all exceedances of
groundwater quality standards associated with the impoundment.
Coal Combustion Residuals Rule 1.2.3
On April 17, 2015, the United States Environmental Protection Agency (USEPA)
published 40 Code of Federal Regulations (CFR) Parts 257 and 261: Hazardous
and Solid Waste Management System; Disposal of Coal Combustion Residuals
from Electric Utilities; Final Rule (USEPA, 2015). This regulation addresses the
safe disposal of coal combustion residuals (CCR) as solid waste under Subtitle D
of the Resource Conservation and Recovery Act and is referred to herein as the
CCR Rule. The CCR Rule became effective on October 19, 2015. The rule
provides national minimum criteria for “the safe disposal of CCR in new and
existing CCR landfills, surface impoundments, and lateral expansions, design
and operating criteria, groundwater monitoring and corrective action, closure
requirements and post closure care, and recordkeeping, notification, and internet
posting requirements. Monitoring wells have been installed and monitored in
accordance the CCR Rule. The most recent data available from the CCR
groundwater monitoring well network is provided on isoconcentration maps
and cross-sections herein. The CCR Rule data will otherwise be evaluated in
accordance with the requirements and schedule outlined therein.
The Final Rule establishes requirements for a phased groundwater monitoring
program consisting of detection monitoring and, if necessary, assessment
monitoring and corrective action. The first phase of monitoring to comply with
the CCR Rule is to include at least eight rounds of Detection Monitoring for
Appendix III and Appendix IV constituents (described below) prior to October
2017. This Detection Monitoring may be followed by Assessment Monitoring.
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The USEPA considers several parameters to be leading indicators that provide an
early detection of whether constituents are migrating from a CCR unit (i.e.,
Appendix III constituents). Appendix III constituents include: boron, calcium,
chloride, fluoride, pH, sulfate, and total dissolved solids.
If sampling results from the Detection Monitoring phase indicate that there are
statistically significant increases over background concentrations for Appendix
III constituents, the Final Rule requires the facility (or Site) to begin Assessment
Monitoring. The parameters required for Assessment Monitoring are antimony,
arsenic, barium, beryllium, cadmium, chromium, cobalt, fluoride, lead, lithium,
mercury, molybdenum, radium 226 and 228 (combined), selenium, and thallium
(USEPA, April 2015; Appendix IV constituents). If the results of assessment
monitoring indicate that corrective action may be warranted, the CCR Rule
requires additional assessment of corrective measures and potentially corrective
action monitoring.
1.3 Approach to Comprehensive Site Assessment
This CSA conducted in accordance with CAMA has been performed to meet NCDEQ
requirements associated with potential site remedy selection. The following
components were utilized to develop the assessment.
1.3.1 Notice of Regulatory Requirements Guidance
The NORR requires that site assessment provide information to meet the
requirements of 2L .0106 (g). This regulation lists the items to be included in site
assessments conducted pursuant to Paragraph (c) of the rule. These requirements
are listed below and referenced to the applicable sections of this CSA.
15A NCAC 02L .0106(g) Requirement CSA Section(s)
(1) The source and cause of contamination Section 3.0
(2) Any imminent hazards to public health and safety, as
defined in G.S. 130A-2, and any actions taken to
mitigate them in accordance with Paragraph (f) of this
Rule
Sections ES.2
and 2.8
(3) All receptors and significant exposure pathways Sections 4.0 and
12.0
(4) The horizontal and vertical extent of soil and
groundwater contamination and all significant factors
affecting contaminant transport
Sections 7.0, 8.0,
and 14.0
(5) Geological and hydrogeological features influencing the
movement, chemical, and physical character of the
contaminants
Sections 6.0,
11.0, and 15.0
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USEPA Monitored Natural Attenuation Tiered Approach 1.3.2
The assessment data is compiled in a manner to be consistent with “Monitored
Natural Attenuation of Inorganic Contaminants in Groundwater” (EPA/600/R-
07/139) (USEPA, October 2007). The tiered analysis approach discussed in this
guidance document is designed to align site characterization tasks to reduce
uncertainty in remedy selection. The tiered assessment data collection includes
information to evaluate:
Active contaminant removal from groundwater and dissolved plume
stability
The mechanisms and rates of attenuation
The long-term capacity for attenuation and stability of immobilized
contaminants
Anticipated performance monitoring needs to support the selected
remedy
ASTM Conceptual Site Model Guidance 1.3.3
The American Society for Testing and Materials (ASTM) E1689-95 generally
describes the major components of conceptual site models (CSMs), including an
outline for developing models. To the extent possible, this guidance was
incorporated into preparation of the Site Conceptual Model (SCM). The SCM 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).
1.4 Technical Objectives
The rationale for CSA activities fall into one of the following categories:
Determine the range of background groundwater quality from pertinent geologic
settings (horizontal and vertical) across a broad area of the Site.
Evaluate groundwater quality from pertinent geologic settings (horizontal and
vertical extent of CCR leachate constituents).
Establish perimeter (horizontal and vertical) boundary conditions for
groundwater modeling.
Provide source area information, including ash pore water chemistry, physical
and hydraulic properties, CCR thickness, and residual saturation within the ash
basin.
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Address soil chemistry in the vicinity of the ash basin (horizontal and vertical
extent of CCR leachate constituents in soil) compared with background
concentrations.
Determine potential routes of exposure and receptors.
Compile information necessary to develop a groundwater Corrective Action Plan
(CAP) protective of human health and the environment in accordance with 2L.
1.5 Previous Submittals
Detailed descriptions of the Site operational history, the Site conceptual model, physical
setting and features, geology/hydrogeology, and results of the findings of the CSA and
other CAMA-related work are documented in full in the following:
Comprehensive Site Assessment Report - Allen Steam Station Ash Basin (HDR, 2015a).
Corrective Action Plan Part 1 - Allen Steam Station Ash Basin (HDR, 2015b).
Corrective Action Plan Part 2 – Allen Steam Station Ash Basin (HDR, 2016a).
Comprehensive Site Assessment Supplement 2 – Allen Steam Station Ash Basin (HDR,
2016b).
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SITE HISTORY AND DESCRIPTION 2.0
An overview of the Allen Steam Station setting and operations is presented in the
following subsections.
2.1 Site Description, Ownership, and Use History
Allen is a coal-fired electricity generating facility with a capacity of 1,155 megawatts
(MW) along the Catawba River (specifically Lake Wylie). Commercial operations began
at the five-unit station in 1957 with operation of coal-fired Units 1 and 2 (330 MW total).
Unit 3 (275 MW) was placed into commercial operation in 1959, followed by Unit 4 (275
MW) in 1960, and Unit 5 (275 MW) in 1961.
The Allen site is located on the west bank of the Catawba River on Lake Wylie in
Belmont, Gaston County, North Carolina (Figure 1-1). The entire Allen site is
approximately 1,009 acres in area and is owned by Duke Energy. Duke Energy also
owns property along the Discharge Canal to the east and west of South Point Road (NC
273), as shown on Figure 2-1. In addition to the power plant property, Duke Energy
owns and operates the Catawba-Wateree Project (Federal Energy Regulatory
Commission [FERC] Project No. 2232). Lake Wylie reservoir is part of the Catawba-
Wateree Project and is used for hydroelectric generation, municipal water supply, and
recreation. The 1948 aerial photograph of the Site vicinity shows previous use as
undeveloped farm land (Figure 2-2). The 1973 and 2015 aerial photographs of the Site
vicinity show the development of the Site over the past 45 years (Figures 2-3 and 2-4).
The air pollution control system for the coal-fired units at Allen includes a flue gas
desulfurization (FGD) system that was placed into operation in 2009. Coal is delivered
to the station by a railroad line. Other areas of the site are occupied by facilities
supporting the production and transmission of power (two switchyards and associated
transmission lines), the FGD wastewater treatment system, and the gypsum handling
station (associated with the FGD system). A site features map is included as Figure 2-1.
2.2 Geographic Setting, Surrounding Land Use, Surface Water
Classification
The Allen Plant is situated in a residential and rural area approximately 4 miles south of
Belmont, North Carolina and approximately 9 miles southwest of Charlotte, North
Carolina on North Carolina Highway 273 (South Point Road; Figure 1-1). A description
of the physical setting of the Site is described in the following sections.
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Geographic Setting
The Allen ash basins are situated between the Allen powerhouse to the north and
topographic divides to the west (along South Point Road) and south (along Reese
Wilson Road) (Figure 2-1). The ash basin system is described further in Section
3.2. Natural topography at the site generally slopes downward and eastward
from that divide toward Lake Wylie. Topography at the Allen site ranges from
approximately 650 feet to 680 feet elevation near the west and southwest
boundaries of the site to an approximate low elevation of 570 feet at the shoreline
of Lake Wylie. Topography generally slopes from a west to east direction with an
elevation change of approximately 110 feet to 80 feet over an approximate
distance of 0.8 miles. A 1949 United States Geological Survey (USGS)
topographic map depicting the site prior to construction of ash basin features is
shown on Figure 2-5.
Surrounding Land Use
The area surrounding the Allen site generally consists of residential properties,
undeveloped land, and the Catawba River (Lake Wylie). Properties located
within a 0.5-mile radius of the Allen ash basin compliance boundary generally
consist of Duke Energy property including the coal pile, a discharge canal, power
production area, and undeveloped land to the north with residential properties
beyond, residential properties and some undeveloped land in Gaston County to
the west and south, and residential properties and some undeveloped land in
Mecklenburg County to the east and southeast across the Catawba River. Figure
2-4 depicts these properties surrounding the Allen site.
In addition to the power plant property, Duke Energy owns and operates the
Catawba-Wateree Project (Federal Energy Regulatory Commission [FERC]
Project No. 2232). Lake Wylie reservoir is part of the Catawba-Wateree Project
and is used for hydroelectric generation, municipal water supply, and recreation.
Duke Energy performed a review of property ownership of the FERC project
boundary property within the ash basin compliance boundary (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). The review indicated that Duke Energy owns all of the property
within the project boundary with the exception of one parcel located east of the
ash basin within the FERC boundary (Lake Wylie) and bisected by the ash basin
compliance boundary. Duke Energy has water rights for the parcel. The Duke
Energy property boundary and the ash basin compliance boundary are shown on
Figure 2-1.
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Meteorological Data
According to the U.S. Department of Agriculture Soil Conservation Service soil
survey (1989), the average summer temperature in Gaston County is 77°F and
the average daily maximum temperature is 88°F. During winter, the average
temperature is 43°F and the average daily minimum temperature is 32°F. The
average relative humidity in midafternoon is approximately 70 percent, with
humidity reaching higher levels at night. The prevailing wind is from the
southwest, and average wind speed is highest (9 miles per hour) in spring.
Average annual precipitation in the Piedmont ranges from 42 to 46 inches. Mean
annual recharge in the Piedmont ranges from 4.0 to 9.7 inches per year (Daniel
2001). The average annual precipitation for Belmont, North Carolina has been
approximately 41.5 inches over the past 30 years. The average for the State of
North Carolina is approximately 49 inches (Weather DB 2015).
Surface Water Classification
The Allen site is located in the Catawba River watershed, and the ash basin is
adjacent to the Catawba River and on the eastern side of a peninsula bounded by
the South Fork Catawba River. A topographic divide runs north to south along
Highway 273 (South Point Road). Surface water features on the peninsula
generally follow this topographic divide, with drainage features on the western
side of South Point Road draining west to South Point River and drainage
features on the eastern side draining east to the Catawba River. 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
the surface water classification for the South Fork Catawba River is Class WS-V.
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 WS-V waters are protected as water supplies, which are
generally upstream of and draining to Class WS-IV waters. No categorical
restrictions on watershed development or treated wastewater discharges are
required. However, the Environmental Management Commission or its designee
may apply appropriate management requirements as deemed necessary for the
protection of downstream receiving waters (15A NCAC 2B .0203) suitable for all
Class C uses. Surface water features located on the site are shown on Figure 2-1.
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2.3 Coal Ash Management Act -related Source Areas
CAMA provides for groundwater assessment of CCR surface impoundments defined as
topographic depressions, excavations, or diked areas formed primarily of earthen
materials, without a base liner, and that meet other criteria related to design, usage, and
ownership (Section 130A-309.201). At Allen, the groundwater assessment was
conducted for the active and inactive ash basins, including the ash storage areas,
structural fills and the Retired Ash Basin (RAB) Ash Landfill.
Coal ash residue from the coal combustion process has historically been disposed in the
Allen ash basins (the active ash basin and the inactive ash basin, which includes the
lined RAB Ash Landfill area, ash storage areas, and structural fill areas). The area
contained within the entire ash basins waste boundaries, which are shown on Figures 2-
1 and 2-5, encompasses approximately 322 acres. In general, the ash basins are located
in historical depressions formed from tributaries that flowed toward Lake
Wylie/Catawba River. The ash basins are operated as an integral part of the station’s
wastewater treatment system, which receives flows from the ash removal system, coal
pile runoff, landfill leachate, FGD wastewater, the station yard drain sump, and site
stormwater.
Ash Basins
The active ash basin, located on the southern portion of the property, is approximately
169 acres in area and contains an estimated 7,660,000 tons of ash. The inactive ash basin,
located between the generating units and the active ash basin, is approximately 132
acres in area and contains approximately 3,920,000 tons of ash.
There are two earthen dikes impounding the active ash basin: the East Dike, located
along the west bank of Lake Wylie/Catawba River, and the North Dike, separating the
active and inactive ash basins. The original ash basin at the Allen site (the inactive ash
basin), put into operation in 1957, was formed by constructing the earthen North Dike
and the north portion of the East Dike, where tributaries flowed toward Lake
Wylie/Catawba River. As the original ash basin capacity diminished over time, the
active ash basin was formed in 1973 by constructing the southern portion of the East
Dike. Ash has been sluiced to the active ash basin since 1973 and still receives bottom
ash into three settling cells by hydraulic sluicing methods.
In addition to the ash basins, two unlined dry ash storage areas, two unlined structural
fill units, and the RAB Ash Landfill are located on top of the inactive ash basin. The dry
ash storage areas were constructed in 1996. Construction of the structural fill units
began in 2003 and was completed in 2009. The double-lined RAB Landfill was
constructed in 2009.
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Fly ash precipitated from flue gas and bottom ash collected in the bottom of the boilers
was sluiced to the ash basins using conveyance water withdrawn from Lake
Wylie/Catawba River. During operations, the sluice lines discharge the water/ash
slurry (and other permitted flows) into the Primary Ponds of the northern portion of the
active ash basin. Primary Ponds 1, 2, and 3 were constructed in approximately 2004.
Currently, Primary Ponds 2 and 3 are utilized for settling purposes. Other inflows to
the ash basin include flows from coal pile runoff, landfill leachate, FGD wastewater, the
station yard drain sump, and stormwater flows. Due to variability in station operations
and weather, the inflows to the ash basin are highly variable.
The Plant was modified for dry fly ash (DFA) handling in the mid-2000’s and DFA
handling began in 2008. DFA is conveyed to silos on-site and then either sent off-site
for beneficial reuse or disposed of at the RAB Ash Landfill permitted by the NCDEQ
DWM under Permit 3612-INDUS-2008. Since dry ash handling commenced at Plant
Allen, only de minimus quantities of fly ash are on occasion sent to the ash basin system
upon system start-up. Duke Energy is in the process of converting to dry handling of
bottom ash, which is anticipated to commence in late 2018 or early 2019.
A majority of the ash contained in the active ash basin and approximately half of ash
contained in the inactive ash basin is saturated. Saturated ash levels were estimated
using the September 2017 24-hour water levels recorded from on-site monitoring wells.
Discharge from the ash basin system is permitted by the NCDEQ DWR under the
NPDES Permit NC0004979. Historically, permitted effluent from the ash basin was
discharged to Lake Wylie via a discharge tower and 42-inch diameter reinforced
concrete pipe (RCP) through Outfall 002. Following modifications in 2016, effluent
from the ash basin now discharges from a weir box structure located in the southeastern
portion of the ash basin via a 42-inch diameter high-density polyethylene (HDPE) pipe
to a concrete vault at the toe of the dam. The permitted effluent discharge then flows
through a 42-inch reinforced concrete pipe (RCP) to Lake Wylie. The water surface
elevation in the ash basin is controlled by the use of stop logs in the weir box structure.
Ash Landfill
The RAB Ash Landfill (NCDEQ DWM Solid Waste Section Permit No. 3612-INDUS), is
located on the eastern portion of the Allen site, on top of the inactive ash basin. The
landfill is bound to the north, east, and south by earthen dikes. The inactive ash basin
dam comprises the northern and eastern boundaries of the landfill. Lake
Wylie/Catawba River is located immediately to the east and below the landfill. To the
south of and adjacent to the RAB Ash Landfill is the active ash basin, and to the west is
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a structural fill area. The lined landfill is permitted to receive CCR materials, including
fly ash, bottom ash, boiler slag, mill rejects, and FGD waste generated by Duke Energy.
In addition to these CCR materials, the landfill is permitted to receive non-hazardous
sandblast material, limestone, coal, carbon, sulfur pellets, cation and anion resins,
sediment from sumps, and cooling tower sludge.
The RAB Ash Landfill is planned to contain two phases (Phase I and Phase II), and
when fully constructed will cover a total of 47 acres. Phase I has been constructed and
encompasses 25 acres on the southern half of the landfill footprint. The estimated gross
capacity of Phase I is 2,082,500 cubic yards. Phase II has not yet been constructed and is
planned to encompass 22 acres immediately north of the Phase I footprint. The
estimated gross capacity of Phase II is 3,958,200 cubic yards. The entire landfill facility,
including the waste footprint, associated perimeter berms, ditches, stormwater
management systems and roads, is projected to encompass an area of approximately 62
acres, when complete. The approximate boundary of the RAB Ash Landfill is shown on
Figure 2-1.
The Permit to Construct Phase I of the landfill was issued by NCDENR DWM in
September 2008. Its initial Permit to Operate was issued by NCDENR DWM in
December 2009, and the most recent Permit to Operate renewal was issued in December
2014. Prior to landfill construction, ash structural fill subgrade was placed beneath
Phase I (Cell 1 under Duke Energy’s Distribution of Residual Solids (DORS) Permit and
Cell 2 under both the DORS Permit and 15A NCAC 13B .1700 allowances). The landfill
was constructed with a leachate collection and removal system and a three-component
liner system consisting of a primary geomembrane, secondary geomembrane (with a
leak detection system between them), and clay soil liner. Placement of waste material in
the RAB Ash Landfill began in December 2009. Phase I contact stormwater and leachate
are collected in the leachate collection pipe system and then pumped to the discharge
location in the northeastern portion of the active ash basin. Since the landfill is situated
over the retired ash basin, the landfill was constructed with a double liner, leachate
collection system (LCS), and leak detection system (LDS). NCDENR DWM determined
that inclusion of the LCS, LDS, and leachate sampling is an acceptable alternative to
groundwater monitoring for the landfill, which would be difficult to assess with the
underlying retired ash basin. Landfill leachate samples are collected semi-annual with
analytical results reported to DWM.
Structural Fills
Two unlined DORS structural ash fills are located on top of the western portion of the
inactive ash basin, adjacent to and west of the RAB Ash Landfill. These fills were
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constructed of ponded ash removed from the active ash basin per Duke Energy’s DORS
Permit issued by NCDENR DWQ. Placement of dry ash in the structural fills began in
2003 and was completed in 2009. During and after the completion of filling, the
structural fill areas were graded to drain, and soil cover was placed on the top slopes
and side slopes, and vegetation was established. The eastern structural fill covers
approximately 17 acres and contains approximately 500,000 tons of ash. The western
structural fill covers approximately 17 acres and contains approximately 328,000 tons of
ash.
Ash Storage
Two unlined ash storage areas are located on top of the western portion of the inactive
ash basin, adjacent to and west of the two DORS structural fills. Similar to the two
DORS structural fills, the ash storage areas were constructed under Duke Energy’s
DORS Permit in 1996 by excavating ash from the northern portion of the active ash
basin in order to provide capacity for sluiced ash in the active ash basin and the future
construction of Primary Ponds 1, 2, and 3. After the completion of stockpiling, the ash
storage areas were graded to drain. A minimum of 18 inches of soil cover was placed
on the top slopes, a minimum of 24 inches of soil was placed on the side slopes, and
vegetation was established. Approximately 300,000 cubic yards of ash is stored in the
ash storage areas, which encompass an area of approximately 15-20 acres of the western
portion of the inactive ash basin.
2.4 Other Primary and Secondary Sources
Several environmental incidents or releases occurred at the site that required
notifications to NCDENR or subsurface investigations. 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 environmental incidents on-site is provided in Table 2-3.
In a letter dated March 16, 2012, NCDENR requested Duke Energy begin additional
assessment activities at stations where measured and modeled concentrations of
groundwater constituents exceed the 2L Standards at the compliance boundary. Duke
Energy submitted the Proposed Groundwater Assessment Work Plan, Duke Energy
Carolinas, LLC, Allen Steam Station Ash Basin, NPDES Permit NC 0004979, dated March
15, 2013, to address this request by NCDENR for Allen.
CSA activities included an assessment of the horizontal and vertical extent of
constituents related to ash management areas observed at concentrations greater than
2L, Interim Maximum Allowable Concentrations (IMAC) or PBTVs. If the CSA indicates
constituent exceedances are related to sources other than the ash basin, those sources
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will be addressed as part of a separate process in compliance with the requirements of
2L. To date, the coal pile appears to be another primary source of constituents to
groundwater and plans are underway to assess the area separately.
2.5 Summary of Permitted Activities
Duke Energy is authorized to discharge wastewater from Allen to receiving waters
designated as the Catawba River (i.e., Lake Wylie) and South Fork Catawba River that
has been adequately treated and managed in accordance with NPDES Draft Permit
NC0004979 dated May 15, 2015. Issuance of the final permit is pending.
The NPDES draft permit authorizes the following discharges in accordance with
effluent limitations, monitoring requirements, and other conditions set forth in the
permit:
Once-through cooling water (Outfall 001)
Septic tank and ash pond with pH adjustment and domestic wastewater
discharge, stormwater runoff, ash sluice, water treatment system wastewaters,
FGD system blowdown, landfill leachate, and miscellaneous cleaning and
maintenance wash waters (Outfall 002)
Coal yard sump overflow (Outfall 002A)
Powerhouse sump overflow (Outfall 002B)
Miscellaneous equipment non-contact cooling and sealing water (Outfall 003)
Miscellaneous non-contact cooling water, vehicle washwater, and intake screen
backwash (Outfall 004)
Seven potentially contaminated groundwater seeps (Outfall 010)
Toe drains (Outfall 011)
Discharge from the operation of the FGD wet scrubber wastewater treatment
system discharging to the ash settling basin through internal Outfall 005. The
FGD wet scrubber wastewater treatment system consists of:
A flow equalization tank and maintenance tanks
Feed systems for lime, sulfide, ferric chloride, polymer, hydrochloric acid, and
molasses-based nutrient
Two clarifiers
Dual heat exchangers
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A selenium reduction bioreactor
A sludge treatment system including three filter presses.
Discharge locations from the treatment works described above are shown in Figures 2-1
and 2-6.
One active lined landfill (Retired Ash Basin Ash Landfill), two unlined structural fill
units, and two unlined ash storage units are located at the site. Further details regarding
these ash management units are included in Section 3.2.
Duke Energy is permitted to discharge stormwater to the Catawba River and South
Fork Catawba River in accordance with the NPDES Draft Permit NCS000546 dated June
1, 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.
2.6 History of Site Groundwater Monitoring
Groundwater monitoring was performed prior to CAMA at Plant Allen under
voluntary and compliance monitoring programs that began in 2004 and 2011,
respectively. 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 Allen 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.
Ash Basin Voluntary Groundwater Monitoring 2.6.1
Monitoring wells AB-1, AB-2, AB-2D, AB-4S, AB-4D, AB-5, AB-6A, AB-6R, and
AB-8 were installed by Duke Energy in 2004 and 2005 as part of a voluntary
monitoring system. Voluntary monitoring well AB-8 was found damaged and
abandoned in 2010. Monitoring well AB-1 was abandoned when compliance
monitoring well AB-1R was installed in 2010. The existing voluntary wells are
shown on Figure 2-7. Duke Energy performed voluntary groundwater
monitoring around the Allen ash basin from May 2004 until November 2010.
During that period, the voluntary groundwater monitoring wells were sampled
two times per year and the analytical results were submitted to NCDEQ DWQ.
Since 2015, samples have been routinely collected from the voluntary wells for
CAMA monitoring and some wells are also used for NPDES compliance
monitoring.
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Ash Basin NPDES Groundwater Monitoring 2.6.2
Groundwater monitoring as required by the Allen NPDES Permit NC0004979
began in March 2011. NPDES Permit Condition A (11), Version 1.1, dated June
15, 2011, lists the groundwater monitoring wells to be sampled, the parameters
and constituents to be measured and analyzed, and the requirements for
sampling frequency and reporting results (Table 2-2). Locations for the
compliance groundwater monitoring wells were approved by NCDENR. A table
summarizing historical analytical results is included in Appendix B.
The compliance groundwater monitoring system for the Allen ash basin consists
of the following monitoring wells: AB-1R, AB-4S, AB-4D, AB-9S, AB-9D, AB-10S,
AB-10D, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, and AB-14D. All the
compliance monitoring wells were installed in 2010, with the exception of AB-
4S/D which were installed in 2004 as part of voluntary groundwater monitoring.
Compliance monitoring wells listed in Table 2-1 are sampled three times per
year (in March, July, and November). Analytical results are submitted to the
NCDEQ DWR on or before the last working day of the month following the
month of sampling for all compliance monitoring wells. The compliance
groundwater monitoring is performed in addition to the current NPDES
monitoring of the discharge flows from the ash basin.
From March 2011 through September 2017, the compliance groundwater
monitoring wells at Allen were sampled for compliance monitoring purposes at
least 21 times. During this period, samples have been collected at least three
times per year, with several wells being sampled more frequently as part of
CAMA groundwater monitoring.
As documented in NCDEQ’s NORR letter dated August 13, 2014, one or more 2L
Standards have been exceeded in groundwater samples collected at every
compliance monitoring well. Exceedances have occurred at least once for boron,
nickel, iron, manganese, sulfate, TDS, and pH in one or more wells across the
site. Exceedances measured from March 2011 through September 2017 are listed
in Appendix B, Table 1.
Monitoring wells AB-4S, AB-9S, AB-10S, AB-12S, and AB-13S were installed with
15-foot well screens placed above auger refusal to monitor the shallow flow
layer.
Monitoring wells AB-4D, AB-9D, AB-10D, AB-11D, AB-12D, AB-13D, and AB-
14D were installed with either 5-foot or 10-foot well screens placed in the
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uppermost region of the partially weathered rock transition zone (TZ) also
referred to as the deep flow or monitoring zone.
Monitoring well AB-1R is located to the northwest of the inactive ash basin. AB-
1R was installed with a 20 foot well screen placed above auger refusal to monitor
the shallow flow layer.
With the exception of monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D, the
ash basin monitoring wells were installed at or near the compliance boundary.
AB-11D is located to the south of the active ash basin. Monitoring wells AB-12S,
AB-12D, AB-4S, AB-4D, AB-13S, and AB-13D are generally located to the west of
the active ash basin. Monitoring well AB-14D is located to the southwest of a
portion of the inactive ash basin and near the western extent of the property.
Monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D are located along the Lake
Wylie/Catawba River compliance boundary and are east and downgradient from
the inactive and active ash basins. Monitoring wells AB-9S and AB-9D are
located to the southeast of the inactive ash basin and AB-10S and AB-10D are
located to the east of the active ash basin. Compliance with 2L Standards (at the
compliance boundary) for AB-9S, AB 9D, AB-10S, and AB-10D was historically
determined by using predictive calculations or an analytical groundwater model.
For these four monitoring wells, Duke Energy had used a groundwater model to
predict the concentrations at the compliance boundary. The predicted results
from the groundwater model and the analytical results for samples collected
during the sampling events were previously submitted to the DWQ; however,
the requirement for modeling was allowed to discontinue by DWQ, and the
wells continue to be sampled routinely. Sample results from these wells are still
reported triannually to NCDEQ DWR along with other compliance monitoring
data.
2.7 Summary of Assessment Activities
From 1993 to 2015, several environmental incidents (i.e., releases) occurred at the Site
that have initiated notifications to NCDENR or required subsurface investigations. 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.
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In a letter dated March 16, 2012, NCDENR requested that 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, Allen Steam Station Ash Basin, NPDES Permit NC 0004979 (dated
March 15, 2013) to address that request by NCDENR as it pertained to Allen.
CSA Activities
Groundwater monitoring wells were installed at multiple locations and depths across
the Site to monitor the horizontal and vertical constituent distribution. Monitoring wells
were installed at the active ash basin, inactive ash basin, RAB Ash Landfill, locations
inside and beyond the compliance area, and background areas. Groundwater
monitoring well locations are shown on Figure 2-1 and 2-7.
Background monitoring wells included fourteen pre-existing compliance groundwater
monitoring wells (AB-12S/D, AB-13S/D, GWA-16S/D, GWA-19S, GWA-21S/BR, GWA-
22S/D, GWA-23S, and GWA-26S/D) and ten wells (BG-1S/D*, BG-2S/D/BR*, and BG-
3S/D, BG-4S/D/BR) installed as part of the CSA effort. The background monitoring wells
were installed north, northwest, west, and southwest of the Site and are separated from
the source area by a series of topographic and/or groundwater divides. Well
abandonments (*) have occurred since the original CSA activities and are summarized
below.
Additional Assessment 2016
Thirty-three (33) additional monitoring wells were installed in 2016 to refine and
expand the understanding of horizontal and vertical extent of potential groundwater
impacts, the understanding of groundwater flow directions, and/or geochemical and
groundwater modeling predictions. Included in the 33 wells, were two additional
background well clusters (BG-1S/D and BG-4S/D/BR), installed to improve aerial
distribution and the understanding of constituent variability in background
groundwater quality at the Site.
Additional Assessment 2017
Additional monitoring wells were installed in 2017 for CAMA purposes in response to
NCDEQ requests. Monitoring wells AB-38BR, AB-22BRL, GWA-9BR, located within the
footprint of the active ash basin, were installed for additional vertical delineation of
potential groundwater impacts. BG-01DA, BG-02BRA-2, GWA-03BRA, GWA-05BRA,
GWA-06BRA, GWA-14DA, and GWA-21DA were installed as replacement wells where
potential grout contamination was present in pre-existing CSA monitoring wells. Well
GWA-24SA was installed deeper below the water table as the original well, GWA-24S,
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was too shallow to yield sufficient water for sampling. Boring logs and well
construction records for all of these recently installed wells are included in Appendix F.
Analytical results are included in Appendix B, Table 1.
Well Abandonments
Several wells installed for the initial CSA were determined to be impacted from possible
grout contamination associated with well construction. BG-1D, BG-2BR, BG-2BRA,
GWA-3BR, GWA-5BR, GWA-6BR, GWA-6D, GWA-14D, GWA-21D, and GWA-24S
were properly abandoned by an NC-licensed driller and replaced.
Additionally, several wells not installed for the initial CSA were abandoned. CCR-1D,
CCR-3D, CCR-4S, CCR-4D, CCR-11S, CCR-11D, CCR-11DA, PZ-1, PZ-2, PZ-3, PZ-4, PZ-
5, and PZ-6 were properly abandoned by an NC-licensed driller and replaced.
Well abandonment records are included in Appendix F.
2.8 Summary of Initial Abatement, Source Removal, or other
Corrective Action
Duke Energy has not conducted emergency responses because groundwater impacts
from the ash basins do not present an imminent hazard to human health or the
environment requiring emergency response. Abatement activities at the Allen Plant
related to the ash basins included conversion from wet handling (via sluicing to the
Active Ash Basin) to dry handling of fly ash in 2008. Duke Energy is also in the process
of converting to dry handling of bottom ash (anticipated by late 2018 or early 2019). In
preparation for closure of the ash basins, new holding and retention basin systems are
also being designed and constructed to handle certain water and wastewater streams.
Proposed correction action will be outlined in the updated CAP.

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SOURCE CHARACTERISTICS 3.0
For purposes of this assessment, the source areas are defined by the ash waste
boundaries as depicted on Figure 2-1. For the Allen Site, source areas include the ash
management areas comprised of active and inactive ash basins.
3.1 Coal Combustion and Ash Handling System
Coal ash is produced from the combustion of coal. The coal is dried, pulverized, and
conveyed to the burner area of a boiler. The smaller particles produced by coal
combustion, referred to as fly ash, are carried upward in the flue gas and are captured
by an air pollution control device, such as an electrostatic precipitator. The larger
particles of ash that fall to the bottom of the boiler are referred to as bottom ash.
Coal ash residue from the coal combustion process has historically been disposed in the
Allen 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 historically to the ash basin using
conveyance water withdrawn from the Catawba River, as further described in Section
3.2.
During operation of the coal-fired units, the sluice lines discharged the water/ash slurry
and other flows to the north portion of the inactive ash basin before the active ash basin
was constructed. Since construction of the active ash basin, the sluice lines have
discharged water/ash slurry and other flows to the north portion of the active ash basin.
Inflows to the ash basin are highly variable due to variability in station operations and
weather. Refer to Figure 2-7 for a depiction of these features.
3.2 General Physical and Chemical Properties of Ash
Coal ash consists of fly ash and bottom ash produced from the combustion of coal. The
physical and chemical properties of coal ash are determined by reactions that occur
during the combustion of the coal and subsequent cooling of the flue gas.
Physical Properties
Approximately 70 percent to 80 percent of the ash produced during coal combustion is
fly ash (EPRI, 1993). Typically, 65 percent 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 percent to 30 percent of ash produced is
considered 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 38 mm to 0.05 mm. In general, bottom ash has a grain size distribution
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similar to that of fine gravel to medium sand (EPRI, 1995). Physical properties of ash are
on Table 3-2.
Based on published literature not specific to Allen, the specific gravity of fly ash 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 soil with a similar gradation and density (EPRI, 1995).
Chemical Properties
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 one
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).
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
(considered representative of the ash at the Allen Plant) showing a mix of fly ash and
bottom ash at 10 µm and 20 µm magnifications. The glassy spheres can be observed in
the photograph. The glassy spheres are generally immune 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+) and sulfate (SO2-)], metals [e.g., copper (Cu) and 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 and calcium. Oxides of
magnesium, potassium, titanium and sulfur comprise approximately 4 percent of fly
ash by weight (EPRI, 1995). Trace elemental composition of fly ash typically is
approximately one percent by weight and may include arsenic, antimony, barium,
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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 (pH of 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 by weight. Calcium and iron 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, based on different coal types, different age of ash in the basin, etc., it is anticipated
that the chemical environment of the ash basin varies over time, distance, and depth.
EPRI (2010) reports that 64 samples of coal combustion products (including fly ash,
bottom ash, and flue gas desulfurization residue) from 50 different power plants were
subjected to United States Environmental Protection Agency (USEPA) Method 1311
Toxicity Characteristic Leaching Procedure (TCLP) leaching and no TCLP result
exceeded the TCLP hazardous waste limit (EPRI, 2010). Figure 3-3 provides the results
of that testing.
3.3 Site-Specific Coal Ash Data
Source characterization was performed to identify the physical and chemical properties
of the ash in the ash basins. The source characterization involved development of
selected physical properties of ash, identifying the constituents found in ash, measuring
concentrations of constituents present in the ash pore water, and performing laboratory
analyses to estimate constituent concentrations resulting from the leaching process. 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 and will also
be utilized as part of groundwater model development in the CAP.
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At the Allen Plant, 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.
The extent of coal ash within the active ash basin was evaluated by:
completing twenty-four (24) borings (AB-20S/D, AB-21S/SL/D/BR/BRL, AB-
23S/BRU, AB-24S/SL/D/BR, AB-25S/SL/BR/BRU, AB-27S/D/BR, AB-28S/D, SB-8,
and SB-9)
The extent of coal ash within the inactive ash basin was evaluated by:
completing thirty-four (34) borings (AB-29S/SL/D, AB-30S/D, AB-33S/D, AB-
34S/D, AB-35S/D/BR, AB-36S/D, AB-37S/D, AB-38S/D/BR, AB-39S/D, OW-3, OW-
7, OW-8, OW-9, OW-12, OW-18, OW-19, SB-1, SB-2, SB-3, SB-4, SB-5, and SB-6)
Ash and soil samples were collected from each boring for physical and chemical testing
in accordance with GAP Section 7.1.1 (HDR, 2014c) and as Site conditions allowed.
Laboratory results of ash samples are presented in Appendix B, Table 4.
The thickness of ash in the areas of investigation varied. Borings installed in the
inactive ash basin encountered ash from approximately 8 feet to 56 feet in thickness.
Borings installed in the active ash basin encountered ash from approximately one foot
to 54 feet in thickness. Boring logs indicate contact between ash and underlying soils
was distinct in each boring. Physical intrusion of ash into underlying soils appeared to
have been negligible.
Depth to saturated ash varies depending upon location within the basins, but generally,
the upper few feet of ash is unsaturated, based on HDR’s boring logs. Within the
inactive basin, saturated ash is typically encountered less than 10 feet bgs, with
exceptions at the DORS fill areas, where saturated ash is encountered between
approximately 15 and 40 feet and is unsaturated at AB-34S, located between the DORS
fill area and the RAB Ash Landfill. Ash is also likely unsaturated at AB-33S, located in
the north east portion of the inactive ash basin south of the coal pile. Within the active
ash basin, the depth to saturated ash is more consistent and is typically encountered
approximately 10 feet bgs. Ash is unsaturated at AB-28S, located within the active ash
basin between primary pond 2 and the inactive ash basin.
Physical Properties of Ash
Physical properties (grain size, specific gravity, and moisture content) and mineralogy
determinations were performed on samples from the ash basin. Table 3-3 presents the
laboratory test data. Physical properties were measured using ASTM methods and
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mineralogy was determined by X-ray diffraction (Appendix C). Bottom ash is generally
characterized as a loose, poorly graded (fine- to coarse-grained) sand. Fly ash is
generally characterized as a moderately dense silty fine sand or silt. Compared to soil,
fly ash exhibits a lower specific gravity.
Mineralogy analyses on three ash samples indicate that the ash is predominantly
mullite, with quartz, and one sample indicates 0.5 percent biotite content. Mullite is an
aluminosilicate mineral (Al6Si2O13) that is rare in nature but common in artificial melts
(Hurlbut, 1971). Presumably, the mullite formed from naturally occurring micas and
clays in the coal-fired boiler. Quartz (SiO2) is the primary mineral in most natural sand
deposits. Biotite (K(Mg,Fe) 3(AlSi3O10)(F,OH)2) is a main silicate found in coal (Zhang,
2013). Three ash samples were tested by Energy Dispersive X-Ray Fluorescence for
metal oxides and a suite of elements. The sample was comprised primarily of silicon
dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3). Cerium, copper, tin, and
zinc were the trace metals detected in highest concentrations in the sample.
Chemical Properties of Ash
Active Ash Basin
Ash samples were collected for chemical analyses from ten (10) borings (AB-20S/D, AB-
21D, AB-23BRU, AB-24D, AB-25SL, AB-27D, AB-28D, SB-8, and SB-9) installed within
the active ash basin boundary.
For information purposes, ash samples were compared to preliminary soil remediation
goals (PSRGs) for protection of groundwater (POG). Analytical results indicate arsenic,
boron, cobalt, iron, manganese, selenium, and vanadium concentrations were greater
than their respective PSRG POGs in one or more of the active ash basin ash samples (see
Table 7-2). Below is a summary of each constituent exceedance for ash samples
collected in the active ash basin:
Arsenic exceeded the POG PSRGs in all of the active ash basin ash samples.
Boron exceeded the POG PSRG in one sample from AB-21D.
Cobalt, iron, and vanadium exceeded the respective POG PSRGs in all of the
active ash basin ash samples.
Manganese exceeded the POG PSRG in ash samples from AB-25SL, AB-27D, and
AB-28D.
Selenium exceeded the POG PSRG in the majority of active ash basin ash
samples.
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Inactive Ash Basin
Ash samples were collected for chemical analyses from 13 borings (AB-29D, AB-30D,
AB-33D, AB-34D, AB-35D, AB-37D, AB-38D, AB-39S, SB-1, SB-3, SB-4, SB-5, and SB-6)
installed within the inactive ash basin boundary.
Note that two unlined ash storage areas and two ash structural fills are situated on top
of the inactive ash basin. Thus, shallow ash samples (3 feet to 5 feet below ground
surface [bgs] interval) collected from borings SB-1 and SB-3 represent ash within the ash
storage areas and shallow ash samples (3 feet to 5 feet bgs interval) collected from
borings AB-35D, SB-4, SB-5, and SB-6 represent ash within the structural fills. Ash
samples collected from deeper sample intervals (greater than 3 feet to 5 feet bgs)
represent ash within the underlying inactive ash basin.
For information purposes, ash samples were compared to PSRG for POGs. Analytical
results indicate arsenic, barium, boron, cobalt, iron, manganese, selenium, and
vanadium concentrations were greater than their respective POG PSRGs in one or more
of the inactive ash basin ash samples (see Table 7-2). Below is a summary of each
constituent exceedance for ash samples collected in the inactive ash basin:
Arsenic exceeded the POG PSRG in the majority of the inactive ash basin ash
samples.
Barium and boron exceeded the respective POG PSRGs in one sample collected
from AB-29D.
Cobalt and vanadium exceeded the respective POG PSRGs in the majority of the
inactive ash basin ash samples.
Iron exceeded the POG PSRGs in each of the inactive ash basin ash samples.
Manganese and selenium exceeded the respective POG PSRGs in approximately
half of the inactive ash basin ash samples.
Leaching Characteristics of Ash
Differences in the constituents leached and in concentrations of leached constituents
occur across the differing environments in which ash is stored at the Allen site. For
example, ash stored in the ash storage area would likely have 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 primarily saturated ash in the ash basin.
In general, infiltration in the ash storage areas and structural fills 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, runoff,
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grading, 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.
Thirteen ash samples were collected from borings within the active ash basin, inactive
ash basin, and the ash storage area for analysis for leachable inorganics using the
synthetic precipitation leaching procedure (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 SPLP is not intended to mimic
complete leaching processes and results are not necessarily indicative of resultant
concentrations in groundwater.
The ash samples collected from the active ash basin (five samples) and the inactive ash
basin (seven 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 ash sample collected from the ash storage area was collected from the
shallow ash sample in the boring before advancing into the inactive ash basin.
Analytical testing results are included in Appendix B, Table 4.
Although SPLP analytical results were compared to the 2L Standards, the levels of
constituents in these samples do not represent groundwater conditions at the site. The
results of SPLP analyses indicated that the following constituents exceeded their 2L
Standards or IMACs in one of more of the samples: antimony, arsenic, chromium,
cobalt, iron, lead, manganese, selenium, thallium, and vanadium. Detected constituents
in SPLP leachate data from the ash including cobalt, iron, manganese, and vanadium
are prevalent in samples from background soil locations. As discussed further in
Section 7, SPLP results from background/upgradient samples indicate cobalt, iron,
manganese and vanadium have the potential to leach from soil at concentrations greater
than their respective 2L/IMAC.
Chemistry of Ash Pore Water
Ash pore water refers to water samples collected from wells installed within the ash
basin and screened in ash. Data from these wells are not considered to be
representative of groundwater, but rather the source. Since installation as part of the
CSA in 2015, these wells have generally been sampled nine times up to the third quarter
of 2017 as part of the CAMA monitoring program. Pore water sample locations and
results are shown on Figures 2-7 and 2-8 and are listed in Appendix B, Table 1. Piper
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diagrams have been prepared for groundwater results from monitoring wells and are
discussed in Section 10.0.
Ash pore water analytical results are compared with 2L and/or IMAC standards for
source contribution reference purposes.
Active Ash Basin
Ten (10) ash pore water monitoring wells (AB-20S, AB-21S/SL, AB-23S, AB-24S/SL, AB-
25S/SL, AB-27S, and AB-28S) were installed within the active ash basin. Antimony,
arsenic, boron, calcium, cobalt, iron, manganese, molybdenum, pH, strontium, thallium,
TDS, and vanadium are consistently detected at concentrations greater than 2L/IMAC
or shallow zone PBTVs (further discussed in Section 10), whichever is greater, in pore
water samples collected from one or more wells within the active ash basin. The pore
water sampling results indicate stable concentrations with no consistent and notable
increases in constituent concentrations over time.
Chemical speciation samples were also collected from seven ash pore water monitoring
wells (AB-20S, AB-21S, AB-21SL, AB-24S, AB-24SL, AB-25S, and AB-25SL) within the
active ash basin. The speciation results are provided in Appendix B, Table 1.
Inactive Ash Basin
Seven ash pore water monitoring wells (AB-29S, AB-29SL, AB-30S, AB-35S, AB-37S, AB-
38S, and AB-39S) were installed within the inactive ash basin and screened within ash.
Arsenic, boron, calcium, cobalt, iron, manganese, molybdenum, pH, strontium, sulfate,
TDS, and vanadium are consistently detected at concentrations greater than 2L/IMAC
or shallow zone PBTVs (further discussed in Section 10), whichever is greater, in one or
more pore water samples collected from wells within the inactive ash basin.
Chemical speciation samples were also collected from six ash pore water monitoring
wells (AB-29S, AB-29SL, AB-35S, AB-37S, AB-38S and AB-39S) within the inactive ash
basin. The speciation results are provided in Appendix B, Table 1.
Concentrations of constituents detected consistently above 2L or IMAC in ash pore
water have been relatively stable.
Piper Diagrams
Piper diagrams are used to graphically depict the general chemical character of water
by plotting the relative concentrations of major ions on a series of tri-linear diagrams.
These points are then projected onto a central diamond plot to show the overall
chemical character of the water (Piper, 1944). Using these diagrams to understand both
source area water characteristics (ash pore water) and natural water characteristics
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(background water) provides the basis for useful evaluation of downgradient water. A
Piper diagram for ash pore water results is presented on Figure 3-4.
The Piper diagrams indicate ash pore water is characterized by two water types,
calcium-bicarbonate to calcium sulfate and that ash pore water is similar within the
inactive and active ash basins. These results are similar to findings in a 2006 EPRI study
of 40 ash leachate water samples collected from 20 different coal ash landfills and
impoundments which characterized bituminous coal ash leachate as calcium-
magnesium-sulfate water type. EPRI’s study also found subbituminous coal ash
leachate to be sodium-calcium-sulfate water type (EPRI, 2012), which is different from
the samples from the Allen plant, which were not sodium-rich.
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RECEPTOR INFORMATION 4.0
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 consideration of
whether surface water features have intakes for drinking water. Additional receptors
(described in Section 12.0) were evaluated as part of the risk assessment related to the
CSA effort.
The NORR CSA receptor survey guidance requirements include listing and depicting
water supply wells, public or private, including irrigation wells, and unused wells
(other than those that have been properly abandoned in accordance with 15A NCAC 2C
.0100) within a minimum of 1,500 feet of the known extent of contamination. In
NCDEQ’s June 2015 response to Duke Energy’s proposed adjustments to the CSA
guidelines, NCDEQ DWR acknowledged the difficulty in determining the known
extent of contamination at this time. DWR stated that it expected all drinking water
wells located 2,640 feet (0.5 mile) downgradient from the established compliance
boundary to be documented in the CSA reports as specified in the CAMA requirements.
The approach to the receptor survey in this CSA includes listing and depicting water
supply wells (public or private, including irrigation wells, and unused wells) and
surface water bodies within a 0.5-mile radius of the ash basin compliance boundary
(Appendix D). The compliance boundary used for the receptor surveys was the pre-
2017 compliance boundary, which included the inactive ash basin and active ash basin.
Properties located within a 0.5-mile radius of the ash basin compliance boundary (prior
to compliance boundary revisions in October 2017) are located predominantly in, and
south of Belmont, Gaston County, North Carolina. Those properties include residences
located upgradient of the Site to the west and southwest; sidegradient of the Site to the
south, and east and southeast of the Site across Lake Wylie/Catawba River in Charlotte,
Mecklenburg County, North Carolina. The City of Belmont provides potable water to
the Allen site and to some of the surrounding area within the City of Belmont, North
Carolina. However, properties in the vicinity of the Plant obtain potable water primarily
from a combination of private and public water supply wells.
The NORR CSA guidance requires that subsurface utilities be mapped within 1,500 feet
of the known extent of contamination in order to evaluate the potential for preferential
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pathways. Identification of piping near and around the ash basin was conducted by
Stantec in 2014 and 2015, and utilities at the Site were also included on a 2015
topographic map by WSP USA, Inc. (Appendix E, Figure 2-7).
4.1 Summary of Receptor Survey Activities
Surveys to identify potential receptors, including public and private water supply wells
(including irrigation wells and unused or abandoned wells), and surface water features
within a 0.5-mile radius of the compliance boundaries of the ash basins that were
current in 2015 have been reported to NCDEQ:
Allen Steam Station — Ash Basin Drinking Water Supply Well and Receptor Survey
(HDR, 2014a)
Allen Steam Station — Ash Basin Supplement to Drinking Water Supply Well and
Receptor Survey (HDR, 2014b)
These reports are included as Appendix D. Identified water supply wells are shown on
the USGS map on Figure 4-1 and on an aerial photograph on Figure 4-2.
The Allen Steam Station — Ash Basin Drinking Water Supply Well and Receptor Survey
(HDR, 2014a) included results of a review of publicly available data from NCDEQ
Division of Environmental Health, NC OneMap GeoSpatial Portal, DWR Source Water
Assessment Program online database, county geographic information system,
Environmental Data Resources, Inc. records review, and the USGS National
Hydrography Dataset, as well as a vehicular survey of public roads located within a 0.5-
mile radius of the ash basin compliance boundary.
The Allen Steam Station — Ash Basin Supplement to Drinking Water Supply Well and
Receptor Survey (HDR, 2014b) supplemented the initial report with additional
information obtained from questionnaires completed by property owners who own
property within the 0.5-mile radius of the ash basin compliance boundary. The report
included a sufficiently scaled map showing the coal ash facility location, the boundary
of the Site, the waste and compliance boundaries, all monitoring wells listed in the
NPDES permit, and the approximate location of identified water supply wells. A table
presented available information about identified wells, including the owner’s name,
address of the well with parcel number, construction and usage data, and the
approximate distance from the compliance boundary.
HDR summarized the receptor surveys in the 2015 CSA and stated that “No new wells
were identified by means of the water well survey questionnaires received after the
November 2014 supplement to the September 2014 receptor survey” (HDR, 2015a).
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A letter from Duke Energy (Mr. Harry K. Sideris) to NCDEQ (Mr. Donald R. van der
Vaart, Secretary) dated August 15, 2016, with the heading “Well receptor surveys and
water supplies per HB630” (Duke Energy, 2016) provided an updated summary of
water supply wells within a half-mile radius of the ash basin compliance boundary that
was current at the time of the letter. The letter also included a draft list of households
that may be eligible for an alternate supply of potable drinking water, based on the
updated survey results.
As required by G.S. 130A-309.211(c1) of House Bill 630 (HB630), Duke Energy evaluated
the feasibility and costs of providing a permanent replacement water supply to eligible
households. Households were eligible if any portion of a parcel of land crossed the line
representing 0.5-mile from the compliance boundary described in House Bill 630 and if
the household currently was using well water or bottled water (under Duke Energy’s
bottled water program) as the drinking water source. Undeveloped parcels were
identified but were not considered “eligible” because groundwater wells are not
currently used as a drinking source. In response to House Bill 630, a Potable Water
Programmatic Evaluation (Dewberry, Allen Steam Station Phase II Potable Water
Programmatic Evaluation - November 11, 2016, 2016) (Appendix D) was conducted.
That evaluation included a survey of eligible households, a preliminary engineering
evaluation, a cost estimate, and a schedule. The evaluation report also included a
listing of, and relevant information about, households and properties within the survey
area, as well as maps depicting property locations, including those properties for which
a replacement water supply would be provided. The cover letter provided by Duke
Energy also indicates that Duke Energy is evaluating an ion filtration treatment system.
4.2 Summary of Receptor Survey Findings
HDR’s receptor survey results reported that “no public or private drinking water wells
or wellhead protection areas were found to be located downgradient of the ash basins”
(HDR, 2015a). This finding was supported by field observations and a review of public
records. Based on the known current groundwater flow direction, none of the wells
identified in the water well survey are located downgradient of the ash basin. The
location and relevant information pertaining to suspected water wells located
upgradient of the facility, within 0.5 miles of the ash basin compliance boundary (as of
2015), were included in the survey reports as required by the NORR.
HDR’s November 2014 report supplemented the initial report with information
obtained from questionnaires sent to owners of property within the 0.5-mile radius of
the pre-2017 compliance boundary. Questionnaires were designed to collect
information regarding whether a water well or spring is present on the property, its use,
and whether the property is serviced by a municipal water supply. If a well is present,
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the property owner was asked to provide information regarding the well location and
construction information.
The November 2014 reports included a sufficiently scaled map showing the ash basin
location, the facility property boundary, the waste and pre-2017 compliance boundaries,
all monitoring wells, and the approximate location of identified water supply wells. A
table presented available information related to identified wells, including: the owner’s
name, the address of the well location with parcel number, construction information,
usage data, and the approximate distance of the well from the pre-2017 compliance
boundary.
Water Supply Lines 4.2.1
The City of Belmont has municipal water supply lines located along South Point
Road and Armstrong Road. As discussed in Dewberry’s November 2016 report
and the accompanying Duke Energy cover letter, connecting water supply lines
to properties in the vicinity of the Plant would require direct service lines from
existing municipal lines and also additional municipal lines along several roads
as extensions off the existing lines. Additional municipal lines would be
required along Canal Road (approximately 475 feet); Wildfire Lane (and
remaining roads in the subdivision with the furthest household approximately
1,750 feet from the current main); Warren Drive (and remaining roads in the
subdivision with the furthest household approximately 1,475 feet from the main);
Lake Mist Drive (and remaining roads in the subdivision with the furthest
household approximately 1,460 feet from the main); Wingpoint Drive (and
remaining roads in the subdivision with furthest household approximately 3,500
feet from the main), and Reese Wilson Road (and remaining roads in the
subdivision, with the furthest household approximately 4,660 feet from the main)
(Appendix D).
Public Water Supply Wells 4.2.2
HDR reported that four public water supply wells were identified within a 0.5-
mile radius of the pre-2017 ash basin (active and inactive combined) compliance
boundary (HDR, 2015a). Each of the wells is located upgradient of the Site, to
the west. Dewberry reported that three, not four, public water supply wells were
identified within the same radius (Dewberry, 2016).
Private Water Supply Wells 4.2.3
The fractured bedrock aquifer in the Piedmont, including the area surrounding
the Site, is commonly used for water supply purposes. However, based upon
water supply well depth information provided within questionnaire responses
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from private well owners, some wells in the area may be constructed within
unconsolidated residuum overlying bedrock.
In the 2015 CSA, HDR provided the following bulleted summary of private
water supply wells within 0.5-mile radius of the pre-2017 ash basin (active and
inactive combined) compliance boundary (HDR, 2015a):
• A total of 219 private water supply wells have been identified within a 0.5-mile
radius of the ash basin compliance boundary.
• Fifty of the 219 identified private water supply wells are recorded with Gaston
and Mecklenburg counties. The Gaston County Health and Human Services
Department maintains records for 36 private water supply wells, and
Mecklenburg County’s online database maintains records for 14 private water
supply wells. The private water supply wells recorded with Gaston and
Mecklenburg counties are identified as “recorded” private water supply wells.
• Ninety-three of the 219 identified private water supply wells have been reported
based on information provided in returned water supply well questionnaires.
These wells are identified as “reported” private water supply wells.
• A total of 58 private water supply wells were identified during the site
reconnaissance and are not considered “reported” or “recorded” private water
supply wells. Those wells are identified as “field-identified” private water supply
wells.
• A total of 18 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.
Fifteen of the 18 assumed wells are located in Gaston County, and the remaining
three (3) assumed wells are located in Mecklenburg County. These wells are
identified as “assumed” private water supply wells.
Dewberry indicated that private wells at households that connect to public water
supply through the City of Belmont are required to be abandoned to prevent
backflow potential, per verbal communication with City of Belmont (Appendix
D).
4.3 Private Water Well Sampling
Section § 130A-309.209 (c) of CAMA indicates that NCDEQ requires sampling of water
supply wells to evaluate whether wells may be adversely impacted by releases from
CCR impoundments. NCDEQ targeted sampling of all drinking water receptors within
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approximately 1,500 feet of the Allen compliance boundary in all directions. Between
February and August 2015, NCDEQ arranged for independent analytical laboratories to
collect and analyze water samples obtained from wells identified during the Drinking
Water Well Survey, if the owner agreed to have their well sampled. Tabulated results,
provided by Duke Energy, for the NCDEQ and Duke Energy sampling efforts, along
with exceedances of 2L/IMAC standards and other reporting limits, are included in
Appendix B, Table 1. The locations of the sampled wells are included on Figure 4-2.
In the 2016 CSA Supplement 2, HDR provided the following bulleted summary of
samples collected from private water supply wells located within 0.5-mile radius of the
pre-2017 ash basin compliance boundary:
• A total of 124 samples were collected within a 0.5-mile radius of the 2015 Allen ash basin
compliance boundary.
• A total of 23 samples were collected in the vicinity of the Allen site, and by Duke Energy,
from background water supply wells located within a 2- to 10-mile radius of the Allen
site boundary. (HDR, 2016)
The number of samples listed in the database provided to SynTerra in 2017 is 166,
which is different than HDR’s summary of 147. HDR provided a summary of the
analytical results in the 2016 CSA Supplement 2 as follows:
The concentrations of boron and other potential coal ash indicators were low and/or not
above screening levels in the water supply wells sampled by NCDEQ. Boron was detected in
27 of 124 samples in the NCDEQ-sampled water supply wells, and in four (4) of 23 samples
in the background water supply wells. Of the 124 wells sampled, there were exceedances of
the 2L Standard for the following constituents:
• Antimony – 1 exceedance
• Cobalt – 2 exceedances
• Copper – 4 exceedances
• Iron – 15 exceedances
• Lead – 1 exceedance
• Manganese – 1 exceedance
• Thallium – 1 exceedance
• Zinc – 2 exceedances (HDR, 2016)
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The database of private water supply well samples provided to SynTerra in 2017
indicated boron was detected in 28 of 166 samples, each at concentrations less than 2L,
and all but seven less than the PBTV for bedrock as estimated from wells installed on
Allen Plant property. Background values for bedrock are used for comparative
purposes, as most private supply wells are likely completed as open-holes within
bedrock. SynTerra tallied a total of 235 detections greater than applicable 2L/IMAC
values which included a slightly different constituent list than that tallied by HDR.
PBTVs had not been estimated when HDR provided their summary. SynTerra’s
summary of 2015 private well sample results with concentrations greater than 2L/IMAC
and PBTVs for bedrock, whichever is greater, is as follows:
Antimony – 1
Cobalt – 1
Iron – 9
pH – 71
Sulfate – 1
Strontium - 130
Thallium – 1
TDS – 1
Vanadium – 35
Concentrations of aluminum, bicarbonate, calcium, chloride, copper, lead, magnesium,
and sodium were detected greater than their respective PBTV, however, these
constituents are not identified as constituents of interest at Allen (Section 10.3.4).
Evaluation of water supply well analytical results using Piper diagrams are not
included due to charge balance differences beyond acceptable limits (10%). Greater
values of charge balance differences may indicate a missing analyte, laboratory error, or
elevated detection limit.
Boron (a key indicator of potential CCR influence) was not detected at concentrations
greater than the 2L in the private water supply well samples. Boron was detected in a
few water supply well locations at concentrations greater than the Site-derived PBTV.
However, these supply wells were at isolated locations surrounded by other private
supply or Site monitoring wells without detected concentrations of boron. Similarly,
other constituents detected in private supply wells at concentrations greater than
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2L/IMAC were typically within the range of Site-derived background concentrations
and surrounded by other wells with concentrations less than applicable 2L or IMAC.
Several of these wells were sampled twice within 2015. For such wells, the first set of
samples was collected in February, March, or April. The second set of samples was
collected primarily in either May or July, with a few collected in June, August, and
October. The analytical reporting limit was generally lower for samples collected
during the second event. Otherwise, analytical results between events were similar.
Notably, boron was detected in seven wells at concentrations greater than the Site-
derived PBTV (discussed in Section 10). All but one of those seven wells with boron
detections was resampled. In five out of these six resampled locations, boron was not
detected during the resampling event. At the remaining location, the boron
concentration decreased to a value below the PBTV.
HDR’s CSA Supplement 2 further stated the following (HDR, 2016a):
“Do Not Drink” letters were initially issued by DHHS for 141 water supply wells at
Allen, with hexavalent chromium and vanadium being the primary constituents listed in
the letters. After review of studies on how the federal government and other states
manage these elements in drinking water, state health officials withdrew the “Do Not
Drink” warnings for these two constituents. Letters were issued for other constituents as
follows: iron (13 wells), cobalt (1 well), lead (2 wells), sodium (1 well), strontium (1
well), sulfate (1 well), and thallium (1 well).
Based on data obtained during the NCDEQ water supply well sampling, Duke Energy
used a multiple-lines-of-evidence approach to evaluate whether the presence of
constituents in water supply wells near Allen are the result of migration of CCR-
impacted groundwater. This approach consisted of a detailed evaluation of groundwater
flow and groundwater chemical signatures.
The results of the groundwater flow evaluation confirmed that groundwater flow is
predominantly horizontal with flow to the east toward the Lake Wylie, and the north
portion of the inactive ash basin flowing to the northeast and north toward Duke Energy
property and the Station Discharge Canal. Thus, groundwater flow from areas associated
with the ash basins and the ash storage area is away from the water supply wells.
A review of groundwater elevations measured in monitoring wells at Allen found
evidence of mounding in the active ash basin. The net effect of the localized gradients
resulting from mounding is reflected in the current data set as well as previous CSAs.
The mounding appears to be caused by the variable discharge of water to the northern
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and western portions of the active ash basin. Mounding in this area of the active ash
basin is more apparent in the September 2015 groundwater elevation data compared with
May 2016 data. A review of historical groundwater analytical results for boron and
sulfate from NPDES compliance wells adjacent to the area where mounding is occurring
(AB-4S/D, AB-11D, AB-12S/D and AB-13S/D) does not indicate evidence of impacts
from coal ash indicator constituents, which suggests that overall groundwater flow is
away from the water supply wells. Although this data suggests that groundwater
between the area of mounding and the off-site water supply wells is not impacted by coal
ash, Duke Energy is installing additional assessment monitoring wells west of the ash
basin in the vicinity of the off-site water supply wells to further evaluate groundwater
quality and to better define the dominant groundwater flow direction west of the ash
basin.
Additional wells installed west of the ash basins included wells at the GWA-14, GWA-
21, and GWA-24 locations. Boron was not detected and sulfate concentrations were less
than the PBTV in samples collected from these wells.
HDR further stated in the CSA Supplement 2 that “the conclusion from the evaluation
is that there is no connection between the CCR-impacted groundwater [from the ash
basins] and the water quality exceedances found in the local water supply wells.”
(HDR, 2016a).
Duke Energy provided SynTerra with additional water supply well sample results in
January 2018. The results are from samples collected in 2016 and as recent as December
2017. Analytical results for those samples are included in Table 1 of Appendix B.
Preliminary review of that data indicates results are generally consistent with previous
data, which indicates the ash basins are not impacting water supply wells in the vicinity
of the plant as boron was detected in only one sample at a concentration less than the
PBTV. Other constituent concentrations are less than, or similar to, applicable PBTVs.
Further evaluation of the exceedances of PBTVs in private water wells must consider
the following:
Site-specific PBTVs for bedrock groundwater have been developed using
groundwater data from a set of two background wells from a geographically
limited area, all located at the Allen site. These wells are located within about 1
mile of each other. The geochemical data from these wells may not be
representative across the broader area encompassed by the private water supply
wells (spread across approximately 4 square miles).
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There is limited information available about the supply wells (e.g., date of
installation, drilling method, well depth, casing length, pump set depth, etc.).
Many private water supply wells in this part of the Piedmont are open-hole rock
wells. A shallow surface casing is installed, and then the well is drilled to a
depth that may be as shallow as 40 feet or 50 feet or as deep as several hundred
feet. When a groundwater sample is collected, it is unknown from what part of
the bedrock aquifer the groundwater is drawn.
It is common for wells in the Piedmont to be bored and installed within
residuum (soil or saprolite) or transition zone material partially weathered rock
(PWR) above bedrock. A review of the limited available well construction data
for the supply wells, based on questionnaire responses from property owners,
indicates a few wells are installed to relatively shallow depths (less than 100
feet) which indicates they may be installed within residuum or transition
zone/PWR material. Groundwater geochemistry in residuum, PWR, and
fractured bedrock aquifers can be quite variable. Boring logs for these private
wells are not available, so lithologic information at each location is unknown.
PBTVs are based on data collected from groundwater within discrete flow
zones. Water supply well data was compared to bedrock groundwater PBTVs,
but other PBTVs could be more appropriate.
Well construction and operation materials may influence analytical results. For
example, galvanized pipe can yield high zinc concentrations and brass
components in well pumps and valves can be a source of lead. Information
concerning well construction and piping materials is important to have before
attributing detections of ash-related constituents solely to the geochemistry of
the groundwater. Care must be taken when comparing geochemical data from
these wells with background concentrations derived from carefully drilled and
installed groundwater monitoring wells with machine-slotted wells screens,
proper filter pack installation, and proper well development.
Specific sample collection procedures employed are unknown. For groundwater
sample collection at Duke Energy facilities, detailed procedures planned and
executed to ensure proper sampling techniques are employed, such as purge
volume, field parameter stabilization, and turbidity minimization prior to
sample collection. Variations in sampling methodology can influence water
quality.
Land use on the private properties where the wells are located is unknown.
Historical and current land use and application of environmental contaminants
or nutrients can affect groundwater quality.
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Groundwater flow in the area around the Allen Plant is consistent with the
slope-aquifer model of groundwater flow in the Piedmont as described in
Section 5.2. This conceptual model of groundwater flow (LeGrand, 1988)
(LeGrand, 1989) describes each distinct Piedmont surface drainage basin as
similar to adjacent basins with the conditions generally repetitive from basin to
basin. Within a basin, movement of groundwater is generally restricted to the
area extending from the drainage divide to a perennial stream (Slope-Aquifer
System). Each distinct basin and slope-aquifer system may limit the area of
influence of wells. Groundwater flow from the source (ash basins) is
predominantly to the east toward Lake Wylie/Catawba River with a smaller
component of flow to the north toward the discharge canal from the northern
portion of the inactive basin. The closest private wells are situated to the west of
ash basins. Private water supply wells are either upgradient of the ash basins or
situated in distinct drainage basins/slope-aquifer systems where groundwater
likely flows toward the South Fork Catawba River, separate from the Plant area
and the ash basins.
Results of the groundwater chemical signature and groundwater flow direction
evaluation indicate that constituent concentrations in the water supply wells are
generally consistent with background concentrations, including boron, and that
groundwater flow is in the opposite direction of the water supply wells. Although
Piper diagrams could not be prepared using water supply wells, due to insufficient
charge balance, Piper diagrams prepared using data from Site background wells and
other upgradient and sidegradient wells (discussed further in Section 10) in the vicinity
of the water supply wells indicate a distinct difference between those wells and wells
located downgradient of the ash basins.
Use of water quality data from supply wells is one tool that can be used to interpret
whether the well has been influenced from the ash basin. However, the Site-derived
background values may not represent the natural variability of background conditions
within the 0.5-mile radius of the pre-2017 compliance boundary. The water supply well
data will also be effected by well construction materials and equipment (e.g.,
galvanized piping, pump components) that the site monitoring wells are not exposed to
that may influence the supply well analytical results. Supply well data would also be
affected by unknown land use on the private properties. Therefore, the groundwater
flow direction from the source (ash basins) being away from the supply wells and
toward Lake Wylie and the discharge canal is a more reliable tool to infer that the
supply wells have not been impacted by the ash basins than the water quality data
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alone. These multiple lines of evidence indicate the supply wells have not been
impacted.
4.4 Surface Water Receptors
The Site is located adjacent to Lake Wylie (Catawba River), and groundwater influenced
by the ash basins flows toward the lake (east) and the Discharge Canal (north). There
are no surface water intakes in Lake Wylie in the vicinity of the Site except for process
water used by the Allen Plant.
A surface water intake from Lake Wylie (Catawba River) is used to supply the City of
Belmont. This intake is located near Linestowe Dr. at the Catawba River (Lake Wylie)
approximately four miles upstream of the Allen ash basins, therefore, this intake is not
considered a receptor.
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REGIONAL GEOLOGY AND HYDROGEOLOGY 5.0
North Carolina is divided into distinct regions by portions of three physiographic
provinces: the Atlantic Coastal Plain, the Piedmont, and the Blue Ridge (Fenneman
1938). The Allen Plant is situated in the Piedmont physiographic 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 Piedmont is generally characterized by mature, well-rounded hills and northeast-
southwest trending ridges cut by small streams and drainages (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).
Elevations in the area of the Allen Plant range from 690 feet in the extreme southwest
portion of the Plant property (south of the active ash basin) to 570 feet along the west
bank of the Catawba River (Lake Wylie).
5.1 Regional Geology
The Allen site is within the Charlotte terrane, one of a number of tectonostratigraphic
terranes that have been defined in the southern and central Appalachians and is in the
western portion of the larger Carolina superterrane (Figure 5-1; Horton et al. 1989;
Hibbard et al. 2002; Hatcher et al. 2007). On the northwest side, the Charlotte terrane is
in contact with the Inner Piedmont zone along the Central Piedmont suture along its
northwest boundary and is distinguished from the Carolina terrane to the southeast by
its higher metamorphic grade and portions of the boundary may be tectonic (Secor et al.
1998; Dennis et al. 2000).
The Charlotte terrane is dominated by 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 including
phyllite, mica schist, biotite gneiss, and quartzite with marble along its western portion
(Butler and Secor 1991; Hibbard et al. 2002). The general structure of the belt is
primarily a function of plutonic contacts. A geologic map of the area around Allen is
shown in Figure 5-2.
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The fractured bedrock is overlain by a mantle of unconsolidated material known as
regolith. The regolith includes residual soil, 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 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 grade into bedrock. 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.
Until recently, most of the information supporting the existence of the TZ was
qualitative based on observations made during the drilling of boreholes and water
wells, although some quantitative data is available for the Piedmont region (Stewart
1964; Stewart et al. 1964; Nutter and Otton 1969; Harned and Daniel 1992). 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 (i.e., the new fractures developed during the
weathering process, and/or the enhancement of existing fracture systems). The
characteristics of the TZ 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; and 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).
Characteristics of 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. 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 (1992) 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). 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 5-3; LeGrand
1988; 1989; 2004). Rarely does groundwater move beneath a perennial stream to
another more distant stream or across drainage divides (LeGrand 1989). Crests of the
water table underneath topographic drainage divides represent natural groundwater
divides within the slope-aquifer system. The concave topographic areas between the
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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. Typically, the residual soil/saprolite is partially
saturated and the water table fluctuates within it. Water movement is generally
through the weathered/fractured and fractured bedrock. The near-surface fractured
crystalline rocks can form extensive aquifers. The character of such layers results from
the combined effects of the rock type, fracture system, topography, and weathering.
Topography exerts an influence on both weathering and the opening of fractures, while
the weathering of the crystalline rock modifies both transmissive and storage
characteristics.
The igneous and metamorphic bedrock in the Piedmont consist of interlocking crystals
and primary porosity is low, generally less than 3 percent. Secondary porosity of
crystalline bedrock due to weathering and fractures ranges from 1 percent to 10 percent
(Freeze and Cherry 1979); however, porosity values of 1 percent to 3 percent are more
typical (Daniel and Sharpless 1983). The porosity of the regolith ranges from 35 percent
to 55 percent near land surface but decreases with depth as the degree of weathering
decreases (Daniel, 1990).
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). Average annual precipitation in the
Piedmont ranges from 42 inches to 46 inches. Mean annual recharge in the Piedmont
ranges from 4.0 inches to 9.7 inches (Daniel 2001).
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SITE GEOLOGY AND HYDROGEOLOGY 6.0
Allen and its associated ash basin system are located in the Charlotte terrane. The
Charlotte terrane consists of an igneous complex of Neoproterozoic to Paleozoic ages
(Hibbard et al. 2002) that range from intermediate to mafic in composition (Butler and
Secor 1999). The Charlotte terrane is bordered on the east and southeast by the Carolina
terrane and to the west and northwest by the Inner Piedmont (Cat Square and Tugaloo
terranes) and the Kings Mountain terrane. The structural contact of the Inner Piedmont
and Charlotte terrane is the Central Piedmont Shear Zone. A regional geologic map for
the Allen Plant area is included as Figure 5-1 and a geological map of the Allen Plant
area is presented as Figure 5-2.
In general, three hydrogeologic units or zones of groundwater flow are described for
the Site. The zone closest to the surface is the shallow or surficial flow zone
encompassing saturated conditions, where present, in the residual soil, saprolite, or
alluvium beneath the Site. The transition zone (deep flow layer), encountered below
the shallow zone and above the bedrock, is characterized primarily by partially
weathered rock of variable thickness. The bedrock flow zone occurs below the
transition zone and is characterized by the storage and transmission of groundwater in
water-bearing fractures.
Site investigations included installation of soil borings, collection of soil and rock cores,
groundwater monitoring wells, borings in and through the ash basin, and installation of
wells for the sampling of ash pore water. Physical and chemical properties of soil
samples collected from the borings and wells are presented in Tables 6-1 and 6-2,
respectively. The analytical methods used with solid and aqueous samples are
presented in Table 6-3. Table 2-1 summarizes the well construction data for CAMA-
related wells and piezometers at the Site. Strategic locations for anchoring flow path
transects were selected and shown in Figures 6-1 to 6-6. Boring logs for CAMA-related
monitoring installations are included in Appendix F. Primary technical objectives for
the sampling locations included: the development of additional background data on
groundwater quality; the determination of horizontal and vertical extent of impact to
soil and groundwater; and the establishment of perimeter boundary conditions for
groundwater modeling that will be used to develop a CAP.
6.1 Site Geology
Geology beneath the Allen Plant is classified into three units: regolith (shallow),
transition zone (deep), and bedrock. Subsurface conditions vary with topography,
parent rock, and Site infrastructure. Regolith is the shallowest geologic unit and
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includes surficial residual soils, fill and reworked soil, alluvium along Lake
Wylie/Catawba River stream valley, and saprolite. Saprolite can be thick, with a depth
up to about 130 feet, and is typically saturated. Where present, the saprolite is the
lowest portion of the regolith. A transition zone of partially weathered rock underlies
the regolith and is generally continuous throughout the Allen Plant area. The transition
zone at the Allen Site is comprised mostly of partially weathered rock that is
gradational between saprolite and competent bedrock. The transition zone is up to 65
feet thick beyond the bottom of saprolite. The change from partially weathered rock to
the third unit, competent bedrock, is defined by subtle changes in weathering,
secondary staining and mineralization, core recovery, and the degree of fracturing in
the rock. Typically, mildly productive fractures (providing water to wells) were
observed within the top 50 feet to 100 feet of competent rock. More detail on the
hydrostratigraphic units is discussed in Section 6.2.1.
6.1.1 Soil Classification
Approximately 206 solid phase samples and approximately 140 monitoring well
locations were used as part of this CAMA assessment. The following
soils/materials were encountered in the boreholes:
• Ash – Ash was encountered in borings advanced within the ash basins
and ash storage areas, as well as in some borings advanced through the
basin perimeter and dikes. Ash was generally described as gray to dark
bluish gray, highly plastic to non-plastic, dry to wet, a silty to sandy
texture, consistent with fly ash and bottom ash.
• Fill – Fill material generally consisted of reworked silts, clays, and sands
that were borrowed from one area of the site and redistributed to other
areas. On the boring logs, fill was generally classified as silty sand (SM),
clayey sand (SC), and sand with clay and gravel (GP). Fill was used in the
construction of dikes, and as cover for ash storage areas.
• Alluvium – Alluvium was encountered in borings during the project
subsurface exploration activities and during geologic mapping. Alluvium
was classified as a well-sorted medium fine-grained sand, sand with silt
and gravel, and silty gravel.
• Residuum (Residual soils) – Residuum is the in-place weathered soil that
consists primarily of micaceous silty sand, micaceous silt, and clayey sand.
Residuum varied in thickness and was relatively thin at the Site.
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• Saprolite/Weathered Rock – Saprolite is soil developed by in-place
weathering of rock that retains remnant bedrock structure. Saprolite
consists primarily of dense to very dense silty sand, sand, silty sand, and
sand with gravel, noted as micaceous in some boring logs and not in
others. Saprolite thickness varies across the site from a very thin mantle
where bedrock is near the surface to as much as 130 feet in other areas.
• Partially Weathered/Fractured Rock – Partially weathered (slight to
moderate) and/or highly fractured rock encountered below refusal (auger,
casing advancer, etc.).
• Bedrock – Sound rock in boreholes, generally slightly weathered to fresh
and relatively unfractured.
Geotechnical index property testing of the above soil/materials was performed
for disturbed and undisturbed samples in accordance with ASTM standards.
Thirty-one (31) undisturbed (“Shelby Tube”) samples 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). The full suite of index property tests could not be
done for one undisturbed sample due to low recovery, wax and gravel mixed in
the tube, loose material, or a damaged tube. Twenty-three (23) disturbed (“Split
Spoon“ or ”Jar”) samples received grain size distribution with hydrometer
(ASTM D 422) and natural moisture content (ASTM D 2216). The results are
presented in Section 7.
Results from the geotechnical testing show little variation across the Site. Soils
present at the Site consist of clayey sand, silty sand, silty sand with gravel,
micaceous silty sand, and gravel with silt and sand.
Rock Lithology 6.1.2
Bedrock at the Site consists of meta-quartz diorite and meta-diabase. Based on
rock core descriptions, the meta-quartz diorite is very light gray to dark gray,
fine to coarse grained, non-foliated and massive to foliated, composed
dominantly of plagioclase, quartz, biotite, and hornblende. Epidote was not
noted in the cores. The meta-diabase is greenish black to very dark greenish
gray, is mostly non-foliated, and is noted as aphanitic to fine grained although it
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is described as fine to coarse grained in some logs. Figures 6-1 to 6-6 show the
extent of each unit. Meta-quartz diorite (Photograph 6-1) is the primary rock
type underlying the site with the meta-diabase occurring during a late syn-
plutonic stage similar to the relationships noted at the Catawba Nuclear Station
(CNS) located approximately 15 miles south of Allen (Gilbert et al. 1982).

Structural Geology 6.1.3
The Charlotte terrane is a meta-igneous terrane consisting of volcanic and
plutonic rocks that have been subjected to deformation and high grade
metamorphism due to tectonic stress during and after intrusion of the igneous
units. Foliation is noted in many of the boring logs, but it is not intense and is
not dominant with respect to structure of the rock mass.
Data from the rock core also show a number of joint dip angles that cannot be
properly defined as joint sets since no orientation information is available. For
the purpose of this discussion, the joints have been assessed based on dip angle
alone. Joint sets include a 40- to 50-degree dipping set, a horizontal to sub-
horizontal (10 degrees or less) set, a steeply dipping set 70 degrees to vertical, a
set dipping 20 degrees, and a set dipping 30-40 degrees. Based on the boring
logs, it is difficult to ascertain which sets are predominant. Iron and manganese
staining is noted on joints of all of the sets. The degree of openness (aperture) of
any of the joints is difficult to assess from rock core since the core is often broken
Photograph 6 - 1 : GWA - 22D ( 176 - 186 ft BGS). Meta - quartz diorite.
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at a joint and no longer retains its actual aperture. However, some of the logs
describe some joints as open. Geologic mapping was not successful in defining
any joint sets in outcrop that could help define the dip strike of any of the joint
sets.
The contacts of the meta-diabase dikes (and possibly sills) and the meta-quartz
diorite are an important structural feature of the Allen site. The orientations of
the contacts are not fully defined, but some of the contacts are described as
having significant clay along the contact. This indicates intense weathering and is
an indication of increased groundwater flow along the contact. The orientation of
the dikes at Allen is probably similar to that noted at Duke Energy’s CNS at the
southern end of Lake Wylie (Gilbert and others 1982), trending both northeast
and northwest and with minor shearing along the contacts and a secondary
foliation developing within the dikes from the shearing.
Geologic Mapping 6.1.4
Geologic mapping of outcrops was conducted in April 2015 at the site and within
a 2-mile radius of the site, utilizing a Brunton compass to characterize the
orientation (strike and dip) of structure such as foliation, joint sets, folds, and
shear zones. Due to limited outcrop, geologic mapping was not successful in
defining any structure other than two measurements of foliation in meta-quartz
diorite. Locations where outcrops were mapped are shown on Figure 5-2. In this
figure, the site location and well locations were overlain on the Geologic Map of
the Charlotte 1° x 2° Quadrangle, North Carolina and South Carolina (Goldsmith
et al. 1988). Field mapping and borehole data confirm the geologic units and
location of contacts of the units with no evidence for differing geologic units or
contact locations.
Effects of Geologic Structure on Groundwater Flow 6.1.5
An important potential effect of structural geology on groundwater flow is the
contact of the meta-diabase and the meta-quartz diorite and the likely
interconnected joint sets discussed in Sections 6.1.3 and 6.1.4. Based on the
regional site geologic maps (Figures 5-1 and 5-2), the contact is outside of the
evaluated area. However, site-specific boring logs indicate the presence of both
the meta-diabase and meta-quartz diorite within the plant. The logs indicate
meta-quartz diorite is prevalent beneath the majority of the site, while meta-
diabase is prevalent beneath the western portions of the site. However, the logs
also indicate the presence of both rock types within the same boring at several
locations with repeated sequences of meta-quartz diorite and meta-
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diabase. 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 and the impact of these contacts on flow is not fully understood.
Soil and Rock Mineralogy and Chemistry 6.1.6
Soil and mineralogy and chemistry results through August 19, 2015, are shown
in Table 6-1 (mineralogy), Table 6-2 (chemistry, % oxides, elemental
composition). The mineralogy and chemical composition of TZ materials are
presented in Table 6-5 (mineralogy), Table 6-6 (chemistry, % oxides, elemental
composition). Whole rock chemistry results (% oxides and elemental
composition) are shown in Table 6-7.
The dominant mineral constituents in the soils are quartz, feldspar (both alkali
and plagioclase feldspars), kaolinite, and illite. Soils exhibiting a higher degree of
weathering show an increase in kaolinite and illite. Other minerals identified
include biotite, dolomite, amphibole, and zeolite. The major oxides in the soils
are SiO2 (44.78% ‒ 65.69%), Al2O3 (12.91% ‒ 26.73%), and Fe2O3 (2.83% ‒
10.59%). MnO ranges from 0.05% to 0.15%. Major TZ minerals are quartz,
feldspar, illite, kaolinite, biotite, and amphibole. The major oxides are SiO2
(65.2% ‒ 68.15%), Al2O3 (12.87% ‒ 14.56%), and Fe2O3 (6.91% ‒ 8.56%). The
major oxides in the rock samples are SiO2 (49.29% ‒ 66.75%), Al2O3 (15.61% ‒
20.60%), and Fe2O3 (2.02% ‒ 12.28%).
Mineralogy and chemistry of the soil and rock encountered are presented in
Section 7.0.
6.2 Site Hydrogeology
Based on the site investigation, the groundwater system in the natural materials
(alluvium, soil, soil/saprolite, and bedrock) at Allen 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 Allen groundwater system is divided
into three layers referred to in this report as the shallow, deep (transition zone), and
bedrock flow layers to distinguish the flow layers within the connected aquifer system.
According to LeGrand (2004), the soil/saprolite regolith and the underlying fractured
bedrock represent a composite water-table aquifer system. The regolith provides the
majority of water storage in the Piedmont province, with porosities that range from 35
percent to 55 percent (Daniel & Dahlen, 2002). Calculated porosities specific to the Site
(21 percent to 54 percent) are more inclusive but capture the Piedmont province’s
porosity range.
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Hydrostratigraphic Layer Development 6.2.1
Hydrostratigraphic units were identified using the framework described by
LeGrand (2004) in which the soil/saprolite regolith and the underlying fractured
bedrock represent a composite water-table aquifer system. Continuous core
drilling techniques were employed to continually observe the subsurface for
saturated zones, weathered in-situ material, and characteristics of underlying
parent rock that may contribute to a water-bearing zone. Borings were advanced
to a depth of 50 feet beyond the top of competent bedrock to define water-
bearing zones within, adjacent to, and underlying the ash basin. Determination
of regolith saturation, transition zone thickness, and potential well yield were
made by the field geologist.
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 of Schaeffer (2014a) was 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, the Recovery (REC) and Rock Quality Designation (RQD)
collected during the drilling and logging of the boreholes. 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
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 (Fe/Mn staining).
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Layers M1 and M2 are combined and are evaluated as a single unit due to similar
hydrogeologic properties and no clear lithologic distinction between the two
based on boring logs and aquifer testing results.
Layer designations (saprolite (shallow), transition zone (deep), and bedrock) are
used on the geologic cross-sections presented in Figures 6-1 to 6-6.
In addition to these hydrostratigraphic units, a separate ash pore water unit is
present and confined to the area of the ash basins. A description of each is
provided in the following section.
Hydrostratigraphic Layer Properties 6.2.2
Soil conditions encountered in the borings showed minimal variation across the
site. Residual soil consists of clayey sand (SC), silty sand (SM), silty sand with
gravel (SM), micaceous silty sand (SM), and gravel with silt and sand (GP).
The following materials were encountered during the site exploration and are
consistent with material descriptions from previous site exploration studies.
Ash Pore Water
Ash pore water unit consists of saturated ash material. Ash depths range from a
few feet to approximately 90 feet within the active ash basin. Ash depths range
from a few feet within the inactive ash basin to approximately 70 feet in the
structural fill area. Generally the upper few feet of ash is unsaturated.
Shallow/Surficial Zone
The shallow/surficial flow zone consists of regolith (soil/saprolite) and alluvial
material. Thickness of regolith is directly related to topography, type of parent
rock, and geologic history. Topographic highs tend to exhibit thinner soil-
saprolite zones, while topographic lows typically contain thicker soil-saprolite
zones. Alluvium found along Lake Wylie/Catawba River stream valley is about
27 feet thick and directly overlies saprolite. Saprolite thickness at the Site ranged
from approximately 15 feet thick beneath the active ash basin to more than 130
feet thick at upgradient well pair GWA-22. Wells within the shallow flow zone
that are installed within alluvial and surficial (shallow) wells contain an “S”
designation. In addition, HDR designated wells installed within the ash with the
letter “S” or “SL”. Wells designated “SL” were typically installed at the base of
the ash, and deeper than an adjacent well within ash.
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Deep/Transition Zone
The deep/transition zone flow layer consists of a relatively transmissive zone of
partially weathered bedrock. Observations of core recovered from this zone
included rock fragments, unconsolidated material, and highly oxidized bedrock
material. Both saturated and unsaturated conditions occur in the transition zone
at Allen. Deep/transition zone wells are labeled with a “D” designation.
Fractured Bedrock
The fractured bedrock unit occurs within competent bedrock. Bedrock at the
Allen Plant is dominated by meta-quartz diorite and meta-diabase. The majority
of water-producing fracture zones were found within 50 to 75 feet of the top of
competent rock. Water-bearing fractures encountered are only mildly
productive (providing water to wells). Bedrock wells are labeled with a “BR”
designation.
North/south and east/west transects were selected to illustrate flow path conditions in
the vicinity of the ash basins. Sections A-A’ and B-B’ are transverse sections through
the ash basin, perpendicular to groundwater flow, in relation to the adjacent areas to the
west and east (Figures 6-1 and 6-2). Sections C-C’, D-D’, E-E’, and F-F’ illustrate
conditions upgradient (west) and along the flow path within the ash basin, then
downgradient to the bank of Lake Wylie/Catawba River (Figures 6-3 to 6-6).
6.3 Groundwater Flow Direction
Monitoring wells have been gauged within a 24-hour period for depth to water and
total well depth during several comprehensive groundwater elevation reading
(gauging) events since 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 those groundwater elevations.
Water levels were measured in Site wells and piezometers within a 24-hour period on
March and September 2017. These dates were selected based on a review of water level
data in the wells which indicated when depths to water were observed relatively
shallow (wet season) and deeper (dry season) (Table 6-9). Precipitation data from the
State Climate Office of North Carolina website (2017) that indicates relatively more
precipitation typically occurs during the spring of each year and less precipitation
during the fall of each year was also considered. Groundwater flow directions and the
overall morphology of the potentiometric surface vary little from the “dry” to “wet”
seasons. Water levels fluctuate up and down with significantly increased or decreased
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precipitation, but the overall groundwater flow directions do not change due to
seasonal changes in precipitation.
The groundwater system in the natural materials (alluvium, soil, saprolite, transition
zone, and bedrock) at Allen is consistent with the regolith-fractured rock, slope-aquifer
system and is an unconfined, connected aquifer system without confining layers.
Typically advective groundwater flow within the slope-aquifer system mimics surface
topography. An elongated topographic high runs approximately north to south in the
area and roughly follows NC Highway 273 creating a groundwater divide.
Groundwater to the east of the divide, including groundwater within the Allen Plant
flows from the highest topographic areas (at the west and southwest portions of the
site) to the east toward Lake Wylie/Catawba River and to the northeast and north
toward Duke Energy property and the discharge canal as confirmed by water level
measurements onsite. Groundwater to the west of the divide likely flows west toward
the South Fork Catawba River.
The potentiometric head created by the impounded water in the active ash basin —
particularly in the vicinity of where sluice lines discharge (typically Cell 2 and Cell 3) —
creates a slight mounding effect that influences the groundwater flow direction in the
immediate vicinity of the basin.
Shallow groundwater flow direction is shown on Figures 6-7 and 6-10. Groundwater
flow direction within the deep layer is shown of Figures 6-8 and 6-11. Groundwater
flow direction within the bedrock layer is shown on Figures 6-9 and 6-12. Groundwater
elevation, as determined by water level measurements, is generally consistent
topographic elevation.
The groundwater flow system at the Site serves both to store groundwater and provide
a means for groundwater movement. Regolith is generally saturated throughout the
Site. The porosity of the regolith is largely controlled by pore space (primary porosity),
whereas in bedrock, porosity is likely largely controlled by the number, size, and
interconnection of fractures (secondary porosity).
6.4 Hydraulic Gradient
Horizontal hydraulic gradients based on the September 2017 water-level measurements
in the various hydrogeologic zones vary across the Site and are listed on Table 6-10.
Horizontal hydraulic gradients were derived by calculating the difference in hydraulic
head over the length of the flow path between two wells with similar well construction
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(e.g., wells within the same water-bearing unit). The following equation was used to
calculate horizontal hydraulic gradient:
i = dh / dl i = hydraulic gradient; dh = difference between two hydraulic heads (measured in feet); and dl = flow path length between the two wells (measured in feet).
Generally horizontal gradients along the southern portion of the Site range from 0.013
feet/feet to 0.067 feet/feet. Horizontal gradients along the northern end of the Site range
from 0.011 feet/feet to 0.036 feet/feet. The greatest hydraulic gradient observed is
located along the southeastern portion of the Site. The high gradient, relative to the Site,
is driven by the high topographic relief between the active ash basin and Lake
Wylie/Catawba River.
Vertical hydraulic gradients were 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 downward flow and a negative
output indicates upward flow. Vertical gradients at select well pairs have been
calculated and are presented on Table 6-11 and visually presented in Figures 6-13 to 6-
15.
Eighty-six (86) pair locations, consisting of shallow to deep, deep to bedrock, or shallow
to bedrock groundwater monitoring wells, 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 6-11.
Throughout the Site, vertical gradients in saprolite, transition zone, and bedrock wells
are near equilibrium, indicating that there is no distinct horizontal confining layer
beneath the Allen Plant. The approximate range of vertical gradient varies from
0.211714 feet/feet to -0.07352 feet/feet. Generally, upward vertical gradients
predominate on the east side of the Site and along Lake Wylie where groundwater
discharges toward the lake. Downward hydraulic gradients (recharge) were observed
within the footprint of the ash basins downward gradients are more prevalent in the
northeast portion of the property. Upward vertical gradients from bedrock alongside
the Catawba River (Lake Wylie) reduce the potential for downward migration of
constituents of interest (COIs) into bedrock, thus reducing the potential of COIs
migrating downward under the river.
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6.5 Hydraulic Conductivity
Hydraulic conductivity (horizontal and vertical) of all layers was estimated utilizing
existing site data and historic 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 C). Field permeability and laboratory permeability test results are presented
in Tables 6-18 and 6-19, respectively.
The hydraulic conductivity parameters were developed by grouping the data into their
respective hydrostratigraphic unit and calculating the geometric mean, maximum, and
minimum.
Hydraulic conductivity values for wells screened in ash pore water have a geometric
mean of 8.04 x 10-4 cm/sec. Hydraulic conductivity values for shallow flow zone wells
have a geometric mean of 1.97 x 10-4 cm/sec. Hydraulic conductivity values recorded
for wells screened in the transition zone (deep flow zone) have a geometric mean of 4.96
x 10-4 cm/sec, while values based on packer tests have a geometric mean of 2.01 x 10-4
cm/sec. These measurements reflect the dynamic nature of the transition zone, where
hydrologic properties can be heavily influenced by the formation of clays and other
weathering by-products. Hydraulic conductivity results for bedrock wells across the
Site have a geometric mean of 1.31 x 10-5 cm/sec, while values based on packer tests have
a geometric mean of 3.13 x 10-5 cm/sec. The hydraulic conductivity measurements in
bedrock wells are regarded as a generalized representation of the localized bedrock
fractures in specific areas of a well cluster. Hydraulic conductivity results can be found
in Tables 6-12 and 6-13. Horizontal and vertical hydraulic conductivity values are
presented in Tables 6-14 and 6-15, respectively.
Further development of the above parameters and others required for the flow and
contaminant transport model will be provided in the CAP.
6.6 Groundwater Velocity
To calculate the velocity that water moves through a porous medium, the specific
discharge, or Darcy flux, is divided by the effective porosity, ne . The result is the
average linear velocity or seepage velocity of groundwater between two points.
Groundwater flow velocities for the surficial and transition flow zones were calculated
using Darcy's Law equation, which describes the flow rate or flux of fluid through a
porous media by the following formula: 𝐕𝐕𝐬𝐬=𝐊𝐊𝐊𝐊/ ne
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Vs = seepage groundwater velocity;
K = hydraulic conductivity;
i = the horizontal gradient; and
ne = effective porosity
Effective porosities were calculated using laboratory testing and physical soil data
presented in Table 3-2 and estimated on a Fetter-Bear diagram (Johnson, 1967). This
technique provides a simple method to estimate specific yield; however, there are
limitations to this method that may not provide an accurate determination of the
specific yield of a single sample (Robson, 1993). Estimated effective porosities and
secondary porosities are presented in Tables 6-16 and 6-17, respectively. Groundwater
velocities calculated for the Site range from approximately 8 to 3130 feet per year (Table
6-10). For each flow zone, the geometric mean from the calculated hydraulic
conductivity from slug tests was utilized to compute velocity (Appendix C).
Seepage velocities for groundwater were calculated using horizontal hydraulic
gradients established by grouping hydraulic conductivity (slug) test data into their
respective hydrostratigraphic units and calculating the geometric mean, maximum, and
minimum.
At Allen, groundwater movement in the bedrock flow zone is due primarily to
secondary porosity represented by fractures in the bedrock. Bedrock fractures
encountered at Allen tend to be isolated with sporadic interconnectivity. Hydraulic
conductivity values represent fractures immediately adjacent to a well screen, not
across the distance between two bedrock wells. Groundwater flow in bedrock fractures
is anisotropic and difficult to predict, and velocities change as groundwater moves
between factures of varying orientations, gradients, pressure, and size. For additional
information on the movement of groundwater around and downgradient of the ash
basin over time, refer to discussion concerning groundwater Flow and Transport
modeling (Section 13.0).
6.7 Contaminant Velocity
Contaminant velocity depends on physical and chemical properties such as the rate of
groundwater flow, the effective porosity of the aquifer material, and the soil-water
partitioning coefficient (Kd term). Soil samples were collected and analyzed for grain
size, total porosity, soil sorption (Kd), and anions/cations to provide data necessary for
completion of a flow and transport model.
Constituents enter the ash basin system in both dissolved and solid phases, and those
constituents may undergo phase changes that include dissolution, precipitation,
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adsorption, and desorption. Dissolved phase constituents may undergo these phase
changes as they are transported in groundwater flowing through the basin. Phase
changes are collectively addressed by specifying a linear soil-groundwater partitioning
coefficient (sorption coefficient [Kd]). In the flow and transport model, the entry of
constituents into the ash basin is represented by a constant concentration in the
saturated zone (pore water) of the basin, and is continually replaced by infiltrating
recharge from above. Laboratory Kd terms were developed by University of North
Carolina – Charlotte (UNCC) researchers via column testing of 12 Site-specific samples
of soil. The methods used by UNCC and Kd results obtained from the testing are
presented in Appendix C. The Kd data were used as an input parameter to evaluate
constituent flow and transport through the subsurface.
Boron is relatively mobile in groundwater and is associated with low Kd values. This is
primarily because boron is mostly inert, has limited potential for sorption, and lacks an
affinity to form complexes with other ions. In general, the low Kd measured for boron
allows the constituent to move with groundwater. The higher Kd values measured for
other constituents, like arsenic and cobalt, are consistent with the observed, limited
migration of these constituents. Constituents like cobalt and arsenic have much higher
Kd values and move at a much slower velocity than groundwater as it sorbs onto
surrounding soil. Geochemical mechanisms controlling the migration of constituents
are discussed further in Section 13.0. Groundwater modeling to be performed for the
updated CAP will include discussion of contaminant velocities for the modeled
constituents.
6.8 Slug Test and Aquifer Test Results
As previously discussed, hydraulic conductivity values for the various hydrogeologic
zones in which the wells are screened varied Site-wide as determined by the slug test
method conducted in accordance with GAP Section 7.1.4 (Table 6-3). Slug test field and
analytical methods are included in Appendix G, and results are presented in
Appendix C.
Slug tests were conducted for wells installed for the groundwater assessment except in
cases where there was not a sufficient amount of water in the well for the test.
Hydraulic conductivity results for the slug tests are summarized below. Where
multiple tests were conducted for the same well, the geometric mean result is used.
Slug test data was analyzed for CAMA and other regulatory wells were screened across
the surficial, transition, and bedrock zones throughout the Site. Hydraulic conductivity
values for wells screened in ash pore water have a geometric mean of 8.04 x 10-4 cm/sec.
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Hydraulic conductivity values for wells screened in the shallow zone have a geometric
mean of 1.97 x 10-4 cm/sec. Hydraulic conductivity values recorded for wells screened
in the deep zone have a geometric mean of 4.96 x 10-4 cm/sec. Hydraulic conductivity
results for bedrock wells across the Site have a geometric mean of 1.31 x 10-5 cm/sec.
Fracture Trace Study Results 6.9
Infiltration tests using Guelph permeameters were not performed because the
groundwater model developer indicated that those data would not be needed because
slug test data were available. Shelby tube samples were used for vertical hydraulic
conductivity tests, each conducted on media from five distinct zones: saprolite, residual
soil, ash, alluvium, and fill from the toe of the ash basin (Table 6-12). The vertical
conductivities were calculated to be, on average, two to twenty-two times smaller than
the horizontal results. Fracture Trace Analysis
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.
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Methods 6.9.1
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 by extensive land-surface modification owing to present
and past human activity. Aerial photography interpretation is most affected in
developed areas as identification of small-scale features can be rendered difficult
or impossible. Substantial surface alteration has occurred over an estimated 30
percent of the aerial photography study area for Allen.
Prior to performance of aerial photography and topographic map interpretation,
available geologic maps for the area were consulted to identify lithologies and
structures in the area, and likely fracture orientations. Low-altitude aerial
photography provided by Duke Energy (from WSP Global, Inc.) covering
approximately 5 square miles, and USGS 1:24000 scale topographic maps
covering an area of approximately 25 square miles, were examined.
Maps examined included portions of the Belmont N.C. S.C. and Charlotte West
N.C. USGS 7.5’ (1:24,000 Scale) topographic quadrangles. Digital copies of the
quadrangles were obtained and viewed on a monitor at up to 7x magnification.
Lineaments identified were plotted directly on the digital images.
Photography provided for review included 1 inch equals 600 feet scale, 9-inch by
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.
Rose diagrams were prepared for lineament trends identified from both aerial-
photography and topographic-map interpretation and are included as inserts on
the respective figures.
Results 6.9.2
Approximately 37 lineaments were identified from the topographic map. The
lineaments and trends indicated by a rose diagram are included on Figure 6-16.
These fall into two well-defined groups: one trending 30 to 50 degrees east of
north, and a second trending 60 to 70 degrees west of north. Both sets are well-
developed in areas underlain by high-grade metamorphic rocks, and less well-
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developed in the area east of the Catawba River underlain by younger
Ordovician to Devonian intrusives.
A total of 18 lineaments were identified from aerial photography. The lineament
trends indicated by a rose diagram are included on Figure 6-17. These were
generally in the form of subtle, small-scale features (linear outcrops and shallow
depressions) not recognizable at the scale of the topographic maps. The
lineament orientations vary from those identified from topographic map
interpretation. The dominant orientation is N20°W to N40°W, with less well-
defined groupings at orientations of approximately N25°E and N85°E.

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SOIL SAMPLING RESULTS 7.0
Soil samples, PWR samples, and bedrock samples were collected from background and
upgradient locations, from beneath the ash basins, and from locations sidegradient and
downgradient of the ash basins. The purpose of soil and rock characterization is to
evaluate the physical and geochemical properties in the subsurface with regard to
constituent presence, retardation, and migration.
Soil sampling was performed in general accordance with the procedures described in
the Work Plan (Appendix G). Variances from the proposed Work Plan are also
presented in Appendix G. Analytical methods for testing soil are summarized in Table
6-3, while the PBTV values are summarized on Table 7-1. Soil sampling locations are
shown on Figure 2-8. Total inorganic results for background soil samples, PWR
samples, and bedrock samples are provided in the comprehensive data table (Appendix
B, Table 4).
Boring logs (Appendix F) from soil boring and well installation borings indicate that
Site soils and saprolite are predominantly fine-grained and comprised of sandy clay to
clayey sand (Table 3-2). Mineralogical analysis of soil samples indicates clay minerals
(illite and kaolinite) comprise the bulk portion of Site soils, along with quartz, feldspars,
plagioclase, biotite, and amorphous minerals (Table 6-1).
7.1 Background Soil Data
Because some COIs are naturally occurring in soil and are present in the source areas,
establishing background concentrations is important for determining whether releases
have occurred from the source areas. Background (BG) boring locations were identified
based on the Site Conceptual Model at the time the Work Plan was submitted and
approved. Three borings (BG-1D, BG-2S, and BG-3D) were originally installed for use as
background soil and groundwater quality in areas believed not to be impacted by CCR
leachate based on existing knowledge of site conditions and hydrogeology. Soil
samples collected from additional locations (at well clusters GWA-08 and GWA-14D)
were later included in the background dataset.
A background soil dataset based on the 2015 CSA data was provided to NCDEQ on
May 26, 2017, for consideration of background soil concentrations. Additionally, the
revised Statistical Methods for Developing Reference Background Concentrations for
Groundwater and Soil at Coal Ash Facilities (HDR and SynTerra, 2017) was provided to
NCDEQ as a basis for determination. On July 7, 2017, NCDEQ provided a response
letter for each Duke Energy coal ash facility that identified soil and groundwater data
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appropriate for inclusion in the statistical analysis to determine PBTVs for both
media. NCDEQ requested that Duke Energy collect a minimum of 10 valid background
samples, rather than the previously planned eight, prior to the determination of PBTVs
for each constituent. In addition, soil samples meeting the following criteria are
considered valid for use in statistical determinations of PBTVs:
The sample was collected from a location that is not impacted by coal
combustion residuals or coal-associated materials.
The sample was collected from a location and depth that is not impacted by other
potential anthropogenic sources of constituents.
The sample was collected from the unsaturated zone, greater than one foot above
the seasonal high water table elevation.
NCDEQ determined that samples collected from several locations/depths did not meet
NCDEQ Inactive Hazardous Site Branch (IHSB) Guidance requirements; therefore,
those samples are not appropriate for use in determining PBTVs. The background soil
dataset included laboratory reporting limits for antimony and thallium above the
NCDEQ IHSB PSRG Protection of Groundwater values (dated October 2016). NCDEQ
requested that the values for antimony and thallium be reported below the PSRG
Protection of Groundwater values. In the interim, NCDEQ partially approved PBTVs
on October 11, 2017 (NCDEQ, October 2017; Appendix A). The partially approved
PBTVs in that letter are used for comparison for data presented in this document.
To address the request from NCDEQ for additional background data, additional soil
samples were collected from borings drilled in background locations on August 30 and
31, 2017, near six existing well cluster locations. These soil samples were designated as
BGSB-BG-01, BGSB-BG-02, BGSB-BG-03, BGSB-GWA-08, BGSB-GWA-23, and BGSB-
GWA-26 (Figure 2-8). Boring logs associated with the additional soil samples are
included in Appendix F. The updated background dataset was screened for outliers,
and PBTVs were recalculated. Proposed updated PBTVs for soils (and groundwater)
are included in a technical memorandum included as Appendix H. Exceedances of
current PBTVs detected in Site soils as discussed below are subject to change based on
further refinement of, and addition to, the soil PBTVs as additional data continues to be
added to the background data set. These updated values are subject to NCDEQ
approval prior to implementation.
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Synthetic Precipitation Leaching Procedure Results for 7.1.1
Background/Upgradient Soil
SPLP was used to determine the ability of simulated rainwater to leach site-
specific constituents out of the soil to groundwater at background or upgradient
locations. The 2L/IMAC standards are used for reference only in comparison to
the SPLP data; SPLP test results do not represent groundwater; therefore,
comparison with 2L/IMAC is used for potential source contribution information
only.
SPLP results from background/upgradient samples indicate cobalt, iron,
manganese and vanadium have the potential to leach from soil at concentrations
greater than their respective 2L/IMAC.
7.2 Facility Soil Data
Soil samples were collected from borings during CSA monitoring well installations and
the additional soil sampling in August 2017. Comparison of soil analytical results to
background is discussed below.
Soil Beneath Waste Boundaries of the Ash Basins 7.2.1
Based on boring logs, the contact between the ash and underlying soils in the ash
basin borings was distinct. Substantial migration of ash into underlying soils or
mixing of ash with those soils is not indicated on the logs.
Twenty-one (21) soil samples were collected from borings advanced beneath the
active ash basin at nine locations, including seven well clusters (AB-20D, AB-
21D, AB-23BRU, AB-24D, AB-25BRU, AB-27D, and AB-28D) and two other
boring locations (SB-8 and SB-9). Thirty (30) soil samples were collected from
borings advanced beneath the inactive ash basin at fourteen (14) locations,
including eight well clusters (AB-31D, AB-32S, AB-33S, AB-34S/D, AB-35S, AB-
36S, AB-37D, and AB-39S/D) and six other boring locations (SB-1 through SB-6).
Active Ash Basin
Arsenic, barium, calcium, chromium, cobalt, manganese, molybdenum,
selenium, and strontium were detected in soil at concentrations greater than
either the PBTV or PSRG POG, whichever is greater, in at least one soil sample
collected beneath the active ash basin. Of those constituents, only calcium,
chromium, selenium and strontium exceeded their respective PBTV in multiple
samples; other constituent exceedances were sporadic and detected in just one or
two samples. Constituent concentrations from multiple sample depths at the
same boring location were similar, and higher concentrations do not directly
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correlate with proximity to the base of the ash. This indicates detected
constituent concentrations are naturally occurring, especially for constituents
that are ubiquitous and relatively. The exception is at AB-25BRU, where
shallower soil sample concentrations were notably higher than the deeper
sample (for most constituents with PSRG POG or PBTV exceedances (in this case,
barium, cobalt, iron, manganese, and molybdenum); this may indicate influence
from the ash basin in this area. The single arsenic exceedance at SB-08 (33.5-35)
was collected from a location directly overlain by ash (based on the boring log)
and may have been partially comprised of ash.
Inactive Ash Basin
Arsenic, boron, calcium, chromium, cobalt, selenium, and strontium were
detected in soil at concentrations greater than either the PBTV or PSRG POG,
whichever is greater, in at least one soil sample collected beneath the inactive ash
basin. Each of these constituents exceeded their respective PBTV in multiple
samples; other constituent exceedances were sporadic and detected in just a few
samples. Similar to soils beneath the active ash basin, constituent concentrations
in samples collected beneath the inactive basin are similar at multiple sample
depths within the same boring location and higher concentrations do not directly
correlate with proximity to the base of the ash. This indicates that detected
constituent concentrations are naturally occurring, especially for constituents
that are ubiquitous across the Site and relatively immobile.
Soil Beyond Waste Boundaries of Active and Inactive 7.2.2
Ash Basins
Seventy-three soil samples were collected from 21 soil borings or monitoring well
borehole locations outside of the waste boundaries of the active and inactive ash
basins. Of these locations, nine (29 samples) were upgradient but not used in
current statistical calculations to determine background. The remaining samples
were collected at downgradient locations with the exception of one location
considered sidegradient.
One of the upgradient sample locations, SB-07, is at the western edge of the Cell
1 of the active ash basin. Boring logs indicate the boring was advanced through
soil, with no ash indicated. Due to it being adjacent to the basin, the results may
indicate potential influence from the basin. Arsenic, calcium, and selenium were
detected at concentrations greater than either the PBTV or PSRG POG, whichever
is higher, in the shallowest sample (8-10 feet bgs) and no COIs were detected at
elevated concentrations in the deeper sample (13.5-15 feet bgs).
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The other upgradient samples (not currently used for statistical determination of
background) were collected at locations more distant from the ash basins. At
those locations, calcium, chromium, cobalt, manganese, selenium, strontium, and
thallium were detected in soil at concentrations greater than either the PBTV or
PSRG POG, whichever is higher, in at least one of these soil samples. Several of
those constituents were also detected sporadically in soils beneath the ash basins
at similar concentrations, further indicating several of the constituents detected
beneath the ash basin may occur naturally at concentrations greater than the
PSRG POG or current PBTV.
Constituents detected in downgradient or sidegradient samples at concentrations
greater than the PSRG POG or PBTV, whichever is greater, included calcium,
chromium, cobalt, manganese, selenium, and strontium. Of those constituents,
only calcium and, to a lesser extent, strontium, exceed their respective PBTV in
multiple samples; other constituent exceedances were sporadic and detected in
just one or a few samples. Constituent concentrations were similar from multiple
sample depths at the same boring location, and higher concentrations do not
directly correlate with proximity to the ash basin elevation or the water table.
This indicates detected constituent concentrations are naturally occurring,
especially for constituents that are ubiquitous across the Site and relatively
immobile, and that soils are not likely to be affected by the ash basins beyond the
ash basins waste boundaries.
Synthetic Precipitation Leaching Procedure Results for 7.2.3
Facility Soils
SPLP was used to determine the ability of simulated rainwater to leach site-
specific constituents out of the soil to groundwater at downgradient locations.
The 2L/IMAC standards are used for reference only of SPLP data; SPLP test
results do not represent groundwater; therefore, comparison with 2L/IMAC is
used for potential source contribution information only.
SPLP analyses indicated that cobalt, iron, manganese, and vanadium leach from
soils beneath the active ash basin and, in addition, antimony, arsenic, chromium,
lead, and thallium leach from soils beneath the inactive ash basin at
concentrations greater than their respective 2L/IMAC values.
Available SPLP results for soils beyond the waste boundary were limited to only
one sidegradient sample collected at the GWA-15 well location. Results indicate
that chromium, cobalt, iron, manganese, and vanadium have potential to leach
from soils at concentrations greater than their respective 2L/IMAC values.
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Cobalt, iron, manganese, and vanadium appear to be ubiquitous in soils across
the Site, regardless of location (e.g., beneath ash, upgradient, downgradient) and
tend to leach at concentrations greater than the 2L/IMAC, even from soils not
beneath the ash basin, at background locations, and where compositional
concentrations are within the range of PBTVs.
Comparison of Partially Weathered Rock and Bedrock 7.2.4
Results to Background
Four samples were collected from the transition zone or bedrock and analyzed as
soil samples. Three samples were collected beneath the active ash basins, and
three samples were collected from locations downgradient of the ash basins.
Calcium, chromium, manganese, and strontium were detected in at least one of
those samples at concentrations greater than the POG or PBTV, whichever is
greater (elevated). Elevated concentrations of chromium and manganese were
detected only in the AB-25BR (143-143) sample. Strontium was not detected in
the AB-35BR (185-185) or GWA-03BR (147.5-147.5) samples at elevated
concentrations. The concentration and sporadic distribution of several of these
constituents in rock samples is relatively similar to that observed within the
overlying soils. Calcium and strontium concentrations in rock samples are
consistent with detected concentrations of those constituents in overlying soil.
7.3 Secondary Sources
Analysis of soil analytical data presented in Table 7-2 and Figure 7-1 show that COI
migration from the source and sorption to soils beneath and downgradient from the
source is difficult to decipher from natural distribution of constituents and may be
limited to areas immediately adjacent to the ash basins. Although concentrations of
arsenic, barium, boron, calcium, chromium, cobalt, iron, manganese, molybdenum,
selenium, strontium, and vanadium in soils beneath the ash basins were found to be
greater than their respective PSRG POG or PBTVs, whichever is greater, only calcium
and, to a lesser extent, strontium, exceed their respective PBTV in approximately one
third of the samples, other constituents exceed infrequently at sporadic locations. For
strontium, all concentrations that exceeded the PBTV except two samples (one near the
base of the inactive ash basin at AB-39S (45-45) and one at SB-1 (3-5), which may have
included some ash within the sample aliquot) were at similar concentrations as the
PBTV. The exceedances indicate natural variability in strontium concentrations across
the Site. Other constituent exceedances were sporadic and detected in just one or a few
samples. Constituent concentrations are similar at multiple sample depths within the
same boring locations, and higher concentrations do not directly correlate with
proximity to the ash basin elevation or the water table.
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Boron, an indicator parameter of constituent mobilization, was detected at elevated
concentrations only in samples from locations on the western and central portions of the
inactive ash basin (SB-02, SB-04, and SB-05) and is not at elevated concentrations at
locations farther downgradient.
Several soil samples collected from upgradient locations (but not used in the current
statistical determination of PBTVs) also had sporadic detections of calcium, chromium,
cobalt, manganese, selenium, strontium, and thallium at concentrations greater than
either the PBTV or PSRG POG, whichever is greater. This indicates these constituents
occur naturally at concentrations greater than the PSRG POG or PBTV and that soils are
not likely a secondary source to groundwater beyond the waste boundaries of the ash
basins. The fine-grained (clayey) nature of subsurface soils and saprolite are likely
retarding migration COIs potentially derived from the ash basins. Geochemical
modeling conducted for the CAP is anticipated to help in determining constituent
association with coal ash and an appropriate site remedy if necessary.
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SEDIMENT RESULTS 8.0
Sediment samples were collected from seven locations beyond the perimeter of the
active and inactive ash basins (Figure 2-8) during the 2015 CSA field effort. Sediment
sampling procedures and variances are provided in Appendix G and analytical results
are presented in Appendix B, Table 5.
8.1 Sediment/Surface Soil Associated with Areas Of Wetness
The seven sediment sampling locations were co-located with designated Areas of
Wetness (AOWs). It is assumed that the “sediment” collected was actually surface soil
over which water at the AOW was flowing or seeping. Sediment samples were
collected on July 1, 2015.
The sediment sample results were compared to North Carolina PSRGs for POG and soil
PBTVs, and are presented in Appendix B, Table 5. Sediment sample locations are
shown on Figure 2-8. Locations S-8 and S-9 were not sampled due to the locations
being at the end of an NPDES discharge culvert and safety/inaccessibility concerns,
respectively. A description of AOWs S-1 through S-7 and the results of sediment
analysis are provided below:
S-1: Located south of the Active Ash Basin, downhill of well AB-11D in a deeply
incised channel at the southern property line. Chromium, cobalt, iron,
manganese, and vanadium concentrations exceeded the PSRG Protection of
Groundwater (PSRG POG). The pH result for this sample exceeded the
respective soil PBTV, but was “j” flagged (estimated concentration above the
adjusted method detection limit and below the adjusted reporting limit).
S-2: Located approximately 200 feet south of the tree line near the Active Ash
Basin NPDES Outfall 002 discharge flume. Intermittent stream within a narrow,
shallow channel downgradient of the Active Ash Basin. Chromium, cobalt, iron,
manganese, and vanadium concentrations exceeded the PSRG POG. The boron
result for this sample exceeded the respective soil PBTV, but was j flagged.
Calcium, cobalt, and nickel concentrations exceeded the respective soil PBTVs.
S-3: Located approximately 50 feet east of the gravel access road behind a chain
link fence. A narrow channel that drains a wetland area at the toe of the Active
Ash Basin dam. Chromium, cobalt, iron, manganese, and vanadium
concentrations exceeded the PSRG POG. The pH result for this sample exceeded
the respective soil PBTV, but was j flagged. Calcium and zinc concentrations
exceeded the respective soil PBTVs.
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S-4: Located approximately 200 feet north of AOW S-3, East of the Active Ash
Basin. A narrow channel that drains a wetland area at the toe of the Active Ash
Basin Dam. Chromium, cobalt, iron, manganese, and vanadium concentrations
exceeded the PSRG POG. The pH and boron results for this sample exceeded the
respective soil PBTVs, but were j flagged. Calcium, manganese, nickel, and zinc
concentrations exceeded the respective soil PBTVs.
S-5: Characterized by a poorly defined low draw in a wooded area behind the
chain link fence that parallels the gravel access road downgradient of the Active
Ash Basin. Chromium, cobalt, iron, manganese, and vanadium concentrations
exceeded the PSRG POG. No concentrations exceeded the respective soil PBTVs.
Flow above the ordinary high water mark has not been observed since at least
2016.
S-6: Removed via disposition as flow, if present, emerges from below the
ordinary high water mark. Characterized by a poorly defined low draw in a
wooded area behind the chain link fence that parallels the gravel access road
downgradient of the Active Ash Basin. Chromium, cobalt, iron, manganese, and
vanadium concentrations exceeded the PSRG POG. No concentrations exceeded
the respective soil PBTVs. Flow above the ordinary high water mark has not
been observed since at least 2016.
S-7: Removed via disposition as flow, if present, emerges from below the
ordinary high water mark. Characterized by a poorly defined low draw in a
wooded area behind the chain link fence that parallels the gravel access road
downgradient of the Active Ash Basin. Cobalt, iron, manganese, and vanadium
concentrations exceeded the PSRG POG. No concentrations exceeded the
respective soil PBTVs. Flow above the ordinary high water mark has not been
observed since at least 2016.
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SURFACE WATER RESULTS 9.0
The Allen Plant ash basins, which include the inactive ash basin and active ash basin,
are located south of the plant operations area. The ash basins receive surface water
runoff from upland areas west of the basins. The basins receive groundwater recharge
from areas within the footprint of the basins. Groundwater in the vicinity of the ash
basins discharges downgradient into the Catawba River (Lake Wylie). Surface water
analytical results associated with samples collected from the Allen Plant are included in
Appendix B, Table 2. The surface water sample locations are included on Figure 2-8.
Aqueous matrix parameters and analytical methods are shown on Table 6-4.
Aqueous samples discussed within the following sections include three distinct types:
1) ash basin wastewater, 2) Areas of Wetness (AOWs), and 3) surface waters. For the
scope of this CSA, it is only appropriate to compare named surface waters to NCDEQ
Title 15A, Subchapter 02B Surface Water and Wetland Standards (2B) because AOWs,
wastewater, and wastewater conveyances (effluent channels) are evaluated and
governed separately in accordance with the NPDES Program administered by NCDEQ
DWR. This process, parallel to the CSA, is ongoing and subject to change.
Surface water and AOW analytical results are included in Appendix B, Tables 2 and 3.
The surface water sample locations are included on Figure 2-8.
Ash Basin Water Samples
Samples SW-01, SW-02, SW-03, and SW-04 were collected from within the active ash
basin. Sample locations SW-01 and SW-02 were collected directly from the water
column in the main water body of the active ash basin. The SW-03 sample was
collected from primary pond 2, and the SW-04 sample was collected from primary pond
3. Both SW-03 and SW-04 were collected directly from the water column. The ash basin
water is not considered surface water or groundwater, and the results are presented for
discussion purposes only. Ash basin water sample locations are shown on Figure 2-8
and analytical results are listed in Appendix B, Table 2.
Area of Wetness (AOW) Sample Locations
Eleven (11) AOWs have been identified and sampled routinely for monitoring
purposes. Nine AOWs (S-1, S-2, S-3, S-4, S-5, S-6, S-7, S-8, and S-9) were identified and
sampled as part of the 2015 CSA activities. The Allen Plant is inspected semi-annually
for the presence of existing and potentially new AOWs along the Catawba River (Lake
Wylie) and along and downgradient of the ash basins. Inspections include observations
of the ash basin along the toe of the dam; areas below full pond elevation for the ash
basin; between the ash basin and receiving waters; and drainage features associated
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with the basin, including engineered channels. Per the interim administrative
agreement, these inspections are governed by a Discharge Identification Plan until the
NPDES permit is issued. AOW locations S-8B and S-10 were identified after the 2015
CSA sampling effort.
These locations are being evaluated separately in accordance with the NPDES permit
and do not have applicable criteria. The analytical results of these samples are for
discussion purposes only. AOW sample locations are shown on Figure 2-8, and
analytical results are listed in Appendix B, Table 3.
Surface Water Sample Locations
Five surface water samples were also collected and analyzed (Figure 2-8). SW-05 was
collected west of the active ash basin from an unnamed body of water. SW-05, located
north of the GWA-9 well cluster, was first established in the CSA Supplement 1 to
evaluate potential migration from ash in the westernmost extent of the ash basin. SW-
06 and SW-07 were collected along the western bank of the Catawba River, and were
established to evaluate surface water quality in the direction of impacted groundwater
flow. SW-06 is located northeast of the coal pile, north of the ash basins. SW-07 is
located east of the ash basins, south of the AB-9 well pair. SW-U1 was established as an
upgradient sample and SW-D1 was established as a downgradient sample. SW-U1 is
located along the western bank of the Catawba River, north of the power plant. SW-D1
is also located along the western bank of the Catawba River, south of the active ash
basin.
NCDENR 2014 Sample Locations
NCDENR directed the sampling and analysis of AOWs in March 2014. The locations
and analytical results from this sampling event were provided by NCDENR to Duke
Energy and are assumed to be accurate. Assessment samples collected during the CSA
were analyzed for a more exhaustive constituent list than those collected in 2014 by
NCDENR and Duke Energy (for example, cobalt was not analyzed during the 2014
sampling efforts).
9.1 Discussion of Results for Constituents Without Established 2B
Standards
A 2B standard has not been established for a number of constituents. A summary of
results for COIs without 2B standards follows:
Antimony was not detected in the surface water samples at concentrations
greater than that of the upgradient surface water sample location (SW-U1).
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The reported beryllium concentrations of the Lake Wylie/Catawba River samples
did not exceed the laboratory reporting limit (0.1 µg/L).
Boron was reported in the upgradient sample location at a concentration of 60.5
µg/L. Concentrations of boron at SW-06 did not exceed the upgradient boron
values, while the concentrations at SW-07 did (120 µg/L).
Cadmium was not detected in Lake Wylie/Catawba River sample locations. The
concentration of cadmium at SW-07 in 2016 was reported at 0.18 µg/L, but
cadmium has not been detected since.
Chromium was detected at concentrations above the reporting limit (0.5 µg/L) at
SW-06 and SW-07 in 2016. Since 2016, all Lake Wylie/Catawba River surface
water sample locations have not exceeded the laboratory reporting limit,
possibly due to more consistent and careful sampling techniques, limiting
sample turbidity.
Hexavalent chromium was detected above the reporting limit (0.025 µg/L) at SW-
06, SW-07, SW-U1, and SW-D1. September 2017 concentrations of hexavalent
chromium at SW-07 (0.055 µg/L) exceeded the upgradient concentration of
hexavalent chromium of (0.03 µg/L).
Cobalt concentrations at SW-6 and SW-7 trend downwards since 2015. In
September 2017, SW-7 (0.17 µg/L) exceeded the upgradient concentration for
cobalt (0.12 µg/L).
Iron was detected in the upgradient sample at a concentration of 202 µg/L.
Historically; all surface water samples have concentrations that exceed the
upgradient sample concentration. In September 2017, the iron concentration at
SW-6 (178 µg/L) was less than the upgradient concentration, while SW-7 (333
µg/L) and SW-D1 (256 µg/L) were greater than the upgradient concentration.
Manganese was detected in the upgradient sample at a concentration of 44.3
µg/L. The most recent sampling event had exceedances of the upgradient
concentration at sample locations SW-07 (61.5 µg/L) and SW-D1 (44.9 µg/L).
Concentrations of molybdenum at all Lake Wylie/Catawba River samples were
below the laboratory reporting limit (0.5 µg/L) during September 2017 with the
exception of SW-D1 (0.89 B µg/L). Historically, SW-07 had the highest detected
value of the surface water samples (2.7 µg/L) in March 2017.
Strontium was detected in the upgradient sample at a concentration of 34.5 µg/L.
Concentrations of strontium at SW-06 (30.2 µg/L) are lower than that of the
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upgradient sample location, while SW-07 (42.2 µg/L) and SW-D1 (60.8 µg/L)
exceed the upgradient concentration.
Thallium concentrations were below the laboratory reporting limit (0.10 µg/L) in
all Lake Wylie/Catawba River samples.
Vanadium was detected in the upgradient sample at a concentration of 1.3 µg/L.
In the most recent sampling event, SW-06 (1.4 µg/L), SW-07 (1.6 µg/L), and SW-
D1 (1.4 µg/L) exceeded the concentration of the upgradient sample.
9.2 Comparison of Exceedances of 2B Standards
Surface water data represents a one-time, single sample; therefore, compliance with
either the acute or chronic 2B standard may not be determined based on 15A NCAC 02B
.0211 (11) (e). Surface water locations SW-D1, SW-U1, SW-06, and SW-07 are samples
collected along the shore of Lake Wylie/Catawba River area and the results of these
locations are compared with 2B (Class WS-IV) values. A summary of these results for
COIs and Field Parameters follows:
SW-D1 (Downgradient): No exceedances of 2B (Class WS-IV) values have been
detected.
SW-U1 (Upgradient): Turbidity was reported at 29.4 NTUs, which exceeds the
Class WS-IV standard of 25 NTUs. This exceedance may be a result of poor
sampling techniques and not a result of impact from the ash basins.
SW-06: One exceedance of 2B (Class WS-IV) values has been detected. Turbidity
was reported at 34.8 NTUs, which exceeds the standard of 25 NTUs, which may
have been a result of poor sampling technique. Additionally, one sample did not
meet the dissolved oxygen standard for 2B (Class WS-IV), which may also be a
result of poor sampling technique or field parameter performance and not a
result of impact from the ash basins.
SW-07: No exceedances of 2B (Class WS-IV) values have been reported for COIs;
however, two samples did not meet the dissolved oxygen standard for 2B (Class
WS-IV), which may be a result of sampling technique or field meter performance
and not a result of impact from the ash basins.
9.3 Discussion of Surface Water Results
Groundwater underlying the ash basins flows east toward Lake Wylie/Catawba River.
Groundwater in the northern portion of the inactive and active ash basins generally
flows to the northeast and east, while groundwater in the southern portion of the active
ash basin generally flows east and southeast. Of the 11 AOWs that were identified for
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routine monitoring, three locations (S-5, S-6, and S-7) are no longer monitored because
when flow is observed (rarely), it emerges from below the ordinary high water mark.
Additionally, two AOWs (S-9 and S-10) have been eliminated via engineered repair.
Flow is inconsistent and often insufficient for sampling at S-1 and S-2. These two
AOWs along with S-3, S-4, S-8, and S-8B emerge and discharge downgradient of the
active ash basin dam and contribute to the volume of water flowing into Lake
Wylie/Catawba River.
Surface water sample results from sample locations SW-06, SW-07, and SW-D1 are
compared with the upgradient sample location results of SW-U1. SW-U1 is considered
to be a reference location for the Allen Plant, as it is upgradient of any potential impacts
the Allen Plant ash basins may have on surface waters.
While surface water samples SW-06, SW-07, SW-D1, and SW-U1 are sampled from Lake
Wylie/Catawba River, sample SW-05 is sampled from water located west of the active
ash basin. The body of water SW-05 monitors is unnamed, immediately adjacent to ash,
is typically stagnant, and is not recognized as a stream by AMEC NRTR 2015.
Therefore, the concentrations of COIs reported at sample location SW-05 are not
diagnostic of typical surface waters in and around the Site.
While the concentrations of COIs at downgradient locations are generally greater than
the COI concentrations at the upgradient location, there were no exceedances of 2B
standards for COIs reported at the Catawba River sample locations (SW-U1, SW-06,
SW-07, and SW-D1). Elevated COI concentrations generally begin at sample location
SW-07 and continue to SW-D1. The surface water data show that sample locations SW-
U1 and SW-06 can be considered upgradient samples, as concentrations are less than
those observed at sample locations SW-07 and SW-D1.
Boron is a useful indicator of potential CCR impact. Boron concentrations indicate
influence related to the ash basins. Boron concentrations in surface water range from
60.5 µg/L at SW-U1 to 383 µg/L at SW-D1, with an increasing trend from upgradient to
downgradient. The increasing trend of boron and other constituents may be related in
part to NPDES Outfall 002, located upstream of surface water sample location SW-D1.
NPDES Outfall 002 is east of the active ash basin, along the bank of Lake
Wylie/Catawba River as shown on Figure 2-8.
Piper Diagrams
Piper diagrams, graphical representations of major water chemistry using two ternary
plots and a diamond plot, for AOWs and surface water are included as Figure 9-1. One
of the ternary plots shows the relative percentage of major cations in individual water
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samples, and the other shows the relative percentage of the major anions. Piper
diagrams for groundwater monitoring wells are presented and discussed in more detail
in Section 10.0. The piper diagram for AOWs and surface water locations is presented
as Figure 9-1. Observations based on the diagram include:
AOWs and surface waters at the Site are predominantly characterized as
calcium-sulfate waters with a few AOW samples plotting between calcium-
sulfate and calcium-bicarbonate.
Free water within the active ash basin is predominantly characterized as calcium-
magnesium-chloride-sulfate.
AOWs downgradient of the ash basins are primarily characterized by two water
types, calcium-bicarbonate to calcium-sulfate, similar to ash pore water.
Water at SW-05, collected from an unnamed body of water (a ditch adjacent to
the active ash basin) where flow is typically stagnant, plots as calcium sulfate-
type water, similar to free water within the basin, and notably differently than
surface water collected from Lake Wylie/Catawba River.
Samples from Lake Wylie/Catawba River plot between calcium-sodium plus
potassium-bicarbonate and calcium-chloride waters. These results plot similar to
surface water samples analyzed from Lake Norman in Iredell County, North
Carolina upstream of the Allen Plant (USGS, 2008).
AOW S-01, which is flow within a narrow, deeply incised channel with
intermittent flow sidegradient and south of the active ash basin, plots as
calcium–bicarbonate, similarly to background groundwater quality (further
discussed in Section 10). Groundwater from nearby well AB-11D also plots
similarly to background groundwater, indicating the active ash basin is not likely
influencing groundwater quality in this area, south of the active ash basin.
AOW S-02, which is intermittent flow within a narrow, shallow channel
downgradient of a wetland area and downgradient of the active ash basin, is
magnesium-chloride type water. This indicates mixing of background water with
ash basin-influenced water within the wetland.
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GROUNDWATER SAMPLING RESULTS 10.0
This section provides a summary of groundwater analytical results for the most recent
valid data available, primarily from the CAMA September 2017 (3Q2017) and
discussion of historical data results and trends. A comprehensive table with all media
analytical results is provided in Appendix B. A separate table is provided for the CCR
monitoring network. As indicated on the CAMA comprehensive data table, at the
request of NCDEQ, the groundwater results have been marked to indicate data points
excluded based on a measured turbidity greater than 10 NTUs; high pH values (above
8.5 S.U.) that may indicate possible grout intrusion into the well screen; and data that
may be auto-correlated because it was collected within 60 days of a previous sampling
event. The most recent valid data available are presented on the pertinent maps and
cross-sections.
Boring logs of CCR well construction information are presented as Appendix F. CCR
Rule related data are considered in the evaluation of the horizontal and vertical
distribution of constituents. However, evaluation of groundwater quality presented in
this report focuses on the data obtained for compliance with CAMA. The CCR Rule
data will be evaluated separately in accordance with the Rule.
One CAMA related comprehensive round of sampling and analysis was conducted
prior to, and reported in, the August 2015 CSA report. In addition, the following
CAMA monitoring events have been completed:
Round 2 – September 2015 (comprehensive and reported in November 2015
CAP, Part 1)
Round 3 – November 2015 (background wells only, reported in CSA Supplement
1 as part of February 2016 CAP Part 2)
Round 4 – December 2015 (background wells only, reported in CSA Supplement
1 as part of February 2016 CAP Part 2)
Round 5 – March 2016 (Q1 - comprehensive and reported in the August 2016
CSA Supplement 2)
Round 6 – May and June 2016 (Q2 - comprehensive)
Round 7 – September 2016 (Q3 - comprehensive)
Round 8 – December 2016 (Q4 - comprehensive)
Round 9 – March 2017 (Q1 - comprehensive)
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Round 10 - June 2017 (Q2 - comprehensive)
Round 11 – September 2017 (Q3 - comprehensive)
Groundwater sampling methods and the rationale for sampling locations were in
general accordance with the procedures described in the Work Plan (HDR, 2014c) and
are included in Appendix G. Variances from the proposed well installation locations,
methods, quantities, and well designations are presented in Appendix G. Analytical
data reports are included in Appendix K. A background summary report for
groundwater is included as Appendix H.
As described in the approved Work Plan, both unfiltered and filtered (0.45 um 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.
10.1 Background Groundwater Concentrations
Locations for background monitoring wells installed in 2015 for the initial CSA field
effort were chosen based on the SCM at the time the Work Plan was submitted,
including information from the previously installed monitoring well network,
horizontal distance from the waste boundary, and the relative topographic and
groundwater elevation difference compared with the elevation of the ash basin surface
water. After the background wells were installed and a sufficient number of samples
were collected, statistical analysis was used to confirm the analytical results represented
background conditions.
The following monitoring wells have been approved by NCDEQ as background
monitoring wells (Zimmerman to Draovitch, July 7, 2017; Appendix A). Background
monitoring wells are depicted on Figure 2-7.
BG-1S – Shallow
BG-2S – Shallow
BG-2D – Transition Zone/Deep
BG-4S – Shallow
BG-4D – Transition Zone/Deep
BG-4BR – Bedrock
GWA-19S – Shallow
GWA-21S – Shallow
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GWA-21BR – Bedrock
GWA-23S – Shallow
GWA-26S – Shallow
GWA-26D – Transition Zone/Deep
Evaluation of the suitability of each of these locations for background purposes was
conducted as part of the CAP 1 and in technical memoranda dated December 12, 2016,
and May 26, 2017 (Appendix H). Factors such as horizontal distance from the waste
boundary, the relative topographic and groundwater elevation difference compared to
elevation of the nearest ash basin surface or pore water, and the calculated groundwater
flow direction were considered to determine whether the locations represent
background conditions.
Additional monitoring wells upgradient of the ash basins and not influenced by COIs
from the ash basins are being further evaluated for inclusion in the background dataset.
Those wells include BG-3S, BG-3D, AB-12S, AB-12D, GWA-16S, and GWA-16D.
Rationale for including those wells and updated statistically-derived groundwater
PBTVs, which include those wells, is included in Appendix H.
Background Dataset Statistical Analysis 10.1.1
For CAMA evaluation purposes, currently accepted statistically-derived
background groundwater datasets and PBTVs are discussed below. The current
background monitoring well network consists of wells installed within three
flow zones – surficial, transition zone, and bedrock. Well locations are presented
on Figure 2-7. For groundwater datasets with less than 10 valid samples
available for determination of PBTVs, no formal upper tolerance limit (UTL)
statistics were run and the PBTV for a constituent and groundwater flow system
was computed to be one of the following (this procedure applies to the dataset
for the bedrock flow zone):
The highest value
If the highest value is above an order of magnitude greater than the
geometric mean of all values, then the highest value is considered to be an
outlier and removed from further use and the PBTV is computed to be the
second highest value.
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In addition, NCDEQ requested the updated background groundwater dataset
exclude data from the background data set due to one or more of the following
conditions:
Sample pH is greater than or equal to 8.5 standard units unless the
regional NCDEQ office has determined an alternate background threshold
pH for the Site.
Sample turbidity is greater than or equal to 10 NTUs.
Result is a statistical outlier identified for background sample data
collected through second quarter 2017.
Sample collection occurred less than a minimum 60 days between
sampling events.
Non-detected results are greater than 2L/IMAC.
Statistical determinations of PBTVs were performed in strict accordance with the
revised Statistical Methods for Developing Reference Background Concentrations for
Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR
and SynTerra, 2017).
Background datasets provided to NCDEQ on May 26, 2017, were revised based
on input from NCDEQ in the July 7, 2017, correspondence. The revised
background datasets for each flow system used to statistically determine
naturally occurring concentrations of inorganic constituents in groundwater are
provided in Table 10-1. Currently accepted PBTVs are based on data collected
through Q1 (March) 2017. Results for two additional sampling events (Q2 2017
and Q3 2017) are presented in (Appendix B) of this report, and another sampling
event Q4 2017) has also been conducted, with results to be included in a future
submittal. The following sections summarize the refined background datasets
along with the results of the statistical evaluations for determining PBTVs.
Several currently accepted PBTVs may underestimate the actual background
threshold, as Q3 2017 data indicates concentrations for several constituents from
accepted background locations are greater than the currently accepted PBTVs.
Inclusion of additional upgradient monitoring wells and more recent data from
wells currently included in the dataset will further refine PBTVs, and additional
evaluation of background groundwater and proposed updated PBTVs are
presented in Appendix H. Since the area of potentially affected groundwater is
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determined based on PBTVs, changes in PBTVs affect the area considered to be
potentially affected.
Shallow/Surficial Flow Unit
Seven wells that monitor background groundwater quality within the shallow
flow zone are accepted for use to statistically determine PBTVs, including wells
BG-1S, BG-2S, BG-4S, GWA-19S, GWA-21S, GWA-23S, and GWA-26S. Data
included in the currently accepted statistical calculations for the shallow flow
zone meets the minimum requirement of 10 samples for all constituents. Cobalt,
iron, manganese, and vanadium currently have a PBTV greater than the
2L/IMAC.
As discussed further in Appendix H, additional upgradient wells considered for
monitoring background groundwater quality in the shallow zone include BG-3S,
AB-12S, and GWA-16S.
Transition/Deep Zone Flow Unit
Three wells that monitor background groundwater quality within the
transition/deep flow zone are accepted for use to statistically determine PBTVs,
including wells BG-2D, BG-4D, and GWA-26D. However, this dataset does not
include any valid samples collected from BG-4D. Data included in the currently
accepted statistical calculations for the transition/deep flow zone do not meet the
minimum requirement of 10 samples for all constituents. Therefore, no formal
UTL statistics were performed and the PBTV was computed to be either the
highest value, or, if the highest value was above an order of magnitude greater
than the geometric mean of all values, the highest value was considered an
outlier and removed from further use and the PBTV was computed to be the
second highest value. Based on this limited dataset, iron, manganese, mercury,
and vanadium currently have a PBTV greater than the 2L/IMAC.
If additional data from Q2 and Q3 of 2017 were included in the background
dataset, there would be sufficient samples to meet NCDEQ’s requirements of 10
samples. Further, and as discussed in Appendix H, additional upgradient wells
are being considered for monitoring background groundwater quality in the
transition/deep zone, including wells BG-3D, AB-12D, and GWA-16D.
Fractured Bedrock Flow Unit
Two wells that monitor background groundwater quality within the bedrock
flow zone are accepted for use to statistically determine PBTVs, including wells
BG-4BR and GWA-21BR. However, this dataset does not include any valid
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samples collected from GWA-21BR. Data included in the currently accepted
statistical calculations for the bedrock flow zone do not meet the minimum
requirement of 10 samples for all constituents. Therefore, no formal UTL
statistics were performed and the PBTV was computed to be either the highest
value, or, if the highest value was above an order of magnitude greater than the
geometric mean of all values, the highest value was considered an outlier and
removed from further use and the PBTV was computed to be the second highest
value. Based on this limited dataset, only vanadium currently has a PBTV
greater than the 2L/IMAC.
If additional data from Q2 and Q3 of 2017 were included in the background
dataset, there would be sufficient samples to meet NCDEQ’s requirements of 10
samples. Further, and as discussed in Appendix H, bedrock well BG-2BRA2 is
being considered as an additional location to monitor background groundwater
quality in the bedrock flow zone.
Summary
Calculated groundwater PBTVs were less than applicable 2L/IMAC for every
constituent within each of the three flow units except:
Cobalt: PBTV of 4.3 µg/L (shallow) versus IMAC of 1 µg/L.
Iron: PBTVs of 835 µg/L (shallow) and 555 µg/L (transition/deep zone)
versus 2L of 300 µg/L.
Manganese: PBTVs of 578 µg/L (shallow) and 60.4 µg/L (transition/deep
zone) versus 2L of 50 µg/L.
Vanadium: PBTVs of 5.3 µg/L (shallow); 9.6 µg/L (transition/deep zone);
and 10.8 µg/L (bedrock) versus IMAC of 0.3 µg/L.
Groundwater PBTVs were calculated for the following constituents that do not
have a 2L, IMAC, or Federal Maximum Contaminant Level (MCL) established:
alkalinity, aluminum, bicarbonate, calcium, carbonate, magnesium, methane,
molybdenum, potassium, sodium, strontium, sulfide, and TOC.
Strontium concentrations in Site background wells are notably lower compared
with concentrations observed in several other Duke Energy facilities located
within the Piedmont physiographic province. As discussed below, strontium
was observed at several non-background locations across the Site at
concentrations greater than the current PBTV; other highly mobile CCR-indicator
parameters, such as boron and sulfate, were not observed at concentrations
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greater than applicable PBTVs at those locations. This indicates the current PBTV
for strontium may be too low and not representative of background groundwater
quality.
Background threshold values will continue to be evaluated and adjusted over
time as additional background data becomes available.
Additional wells are installed upgradient or sidegradient of the ash basins at
locations of well clusters AB-2, AB-4, AB-14, GWA-8, GWA-9, AB-13, GWA-15,
GWA-17, GWA-18, GWA-22, and GWA-24. These wells will continue to be
evaluated for consideration as background locations as more data become
available. Among the wells recently installed, well GWA-24SA was installed
(October 31, 2017) deeper to replace GWA-24S, which was frequently dry. The
well was initially sampled on November 17, 2017. Analytical results from the
first sampling event indicate cobalt, manganese, and vanadium concentrations
are greater than applicable 2L/IMAC values, but less than applicable PBTVs.
This indicates groundwater at this location represents naturally occurring
conditions.
Piper Diagrams (Comparison to Background) 10.1.2
A Piper diagram is a graphical representation of major water chemistry using
two ternary plots and a diamond plot. One of the ternary plots shows the
relative percentage of major cations in individual water samples, and the other
shows the relative percentage of the major anions. The apices of the cation plot
are calcium, magnesium, and sodium plus potassium. The apices of the anion
plot are sulfate, chloride, and carbonates. The two ternary plots are projected
onto the diamond plot to represent the major ion chemistry of a water sample.
The ion composition can be used to classify groundwater of particular character
and chemistry into sub-groups known as groundwater facies. Percentages of
major anions and cations are based on concentrations expressed in meq/L (EPRI,
2006). Plots of pore water and shallow groundwater, deep (transition)
groundwater, and bedrock groundwater — including background locations —
are shown on Figure 10-1, Figure 10-2, and Figure 10-3, respectively. Using
these diagrams to understand both source area water characteristics (ash pore
water) and natural water characteristics (background water) provides the basis
for useful evaluation of downgradient water.
Evaluation of the background groundwater Piper diagram (Figure 10-1) results
in the following observations:
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Generally, background groundwater at Allen is low in chloride and
sulfate, bicarbonate rich, and classified as a range from calcium-
bicarbonate to calcium-sodium plus potassium-bicarbonate type water.
Shallow groundwater tends to range from calcium-bicarbonate to calcium-
sulfate type waters.
Background groundwater has a smaller range of bicarbonate and sulfate
proportions and a larger range of chloride proportions than ash pore
water.
Background groundwater has a lesser proportion of calcium compared to
ash pore water.
Groundwater within the upgradient wells proposed to be included in the
expanded background dataset (Appendix H) to refine Site-specific
background threshold values, plot similar to groundwater from
background wells currently accepted by NCDEQ (Appendix A).
The USGS has conducted a “regionally significant hydrogeologic evaluation” of
groundwater flow and groundwater quality in the vicinity of Allen (USGS, 2008).
The five-year study was conducted at the Langtree Peninsula Research Station,
located in a similar geologic setting approximately 25 miles north of the Site. The
study provides additional information about background water quality
conditions in the region. Observations from that study indicate the majority of
samples collected were calcium-bicarbonate water type, consistent with
background wells located at Allen.
Downgradient Groundwater Concentrations 10.2
In order to best reflect current conditions at the Site, third quarter (July through
September) 2017 groundwater sample results provide a focus for data evaluation in this
report. Results from prior events are incorporated in data evaluation and summarized
as appropriate. The third quarter (Q3) 2017 data is the primary dataset used for
generating isoconcentration maps and graphical representation of data such as Piper
diagrams and cross-sections. At locations where Q3 2017 data were invalid or not
available, the most recent valid available sample result was used.
Measurements of pH indicated a number of locations with pH less than the 2L lower
limit of 6.5, or higher than the 2L upper limit of 8.5. The currently accepted PBTVs for
pH ranges from a low of 5.2 in the shallow flow layer to 8.4 in the deep flow layer. In
general, elevated pH measurements are interpreted as the result of grout-contaminated
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wells, and in accordance with DEQ guidance, the associated groundwater samples are
not used for evaluation of constituent concentrations.
Boron is observed at concentrations that are generally higher than background (but
usually below 2L), in and downgradient of the ash basins. As such, its presence is
indicative of CCR influence and is included in this section’s discussion of September
2017 groundwater sampling results. In general, constituent concentrations have
remained relatively stable in each well, with minor fluctuations. For some constituents,
those fluctuations are along the threshold of the 2L/IMAC or PBTVs.
Boron and sulfate are less sensitive to pH and turbidity and analytical results from
samples otherwise invalid, can help indicate the presence or absence of boron and
sulfate. For wells with high pH or turbidity due to well construction issues, boron and
sulfate values are considered with caution.
The following is a summary of groundwater analytical data collected for the CAMA
CSA for areas around the active and inactive ash basins. The CAMA comprehensive
groundwater analytical data table is included as Appendix B, Table 1. A data table for
the CCR Rule monitoring network is also provided in Appendix B, Table 7. The
following evaluations focus on CAMA CSA monitoring data.
Monitoring Wells Beneath the Ash Basins 10.2.1
Ten (10) well clusters are located within the active ash basin ash footprint (wells
installed within the dams are considered downgradient) and nine are located
within the inactive ash basin ash footprint. Most of the wells designated with
“S” or “SL” at those locations are constructed with screens within ash or partially
within ash. Discussion of source area wells screened within the ash to monitor
ash pore water concentrations is included in Section 3. Additional wells are
installed within the shallow, deep, and bedrock flow zones beneath the ash.
Wells at these clusters have been routinely monitored since being installed (most
were installed in 2015). Below is a summary of analytical results for these wells:
Shallow Flow Zone Beneath the Inactive Ash Basin — In Q3 2017, valid
samples were collected from one well (AB-36S) installed in the shallow flow zone
beneath the inactive ash basin below the ash soil interface. Arsenic, calcium,
iron, manganese, molybdenum, and strontium are consistently detected at
concentrations greater than the 2L/IMAC or PBTV, whichever is greater
(elevated) in this well. Although boron was not detected at concentrations
greater than the 2L in samples from AB-36S, boron concentrations are likely
greater than the PBTV and 2L in shallow groundwater beneath the eastern
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portion of the basin, along Lake Wylie/Catawba River, based on groundwater
flow and results from samples further downgradient.
Shallow Flow Zone Beneath the Active Ash Basin — No wells are installed
exclusively (without the well screen partially including ash) within the shallow
flow zone beneath the active ash basin. Boron, and possibly other constituent,
concentrations are likely greater than applicable 2L/IMAC and PBTVs in shallow
groundwater beneath the eastern portion of the basin, along Lake
Wylie/Catawba River, based on groundwater flow and results from samples
further downgradient.
Deep Flow Zone Beneath the Inactive Ash Basin — In Q3 2017, valid samples
were collected from eight wells (AB-29D, AB-30D, AB-33D, AB-34D, AB-36D,
AB-37D, AB-38D, and AB-39D) installed in the deep flow zone beneath ash of the
inactive ash basin. Only calcium and strontium are consistently detected at
concentrations greater than the applicable 2L/IMAC or PBTV in most of these
wells. Antimony and manganese are only detected at concentrations slightly
greater than applicable 2L/IMAC or PBTVs, whichever is greater at separate
isolated locations; antimony at AB-33D (1.6 µg/L) and manganese at AB-38D
(70.8 µg/L), both located in northern portions of the basin. Vanadium is also
detected at concentrations slightly greater than the PBTV at a few locations (AB-
30D, AB-34D, and AB-37D). Boron and sulfate are not detected at concentrations
greater than the 2L in any of the deep flow zone wells beneath the inactive ash
basin. Similar to the shallow zone, boron, and possibly other constituent
concentrations are likely greater than applicable 2L/IMAC and PBTVs in deep
groundwater beneath the eastern portion of the basin, along Lake
Wylie/Catawba River, based on groundwater flow and results from samples
further downgradient.
Boron and sulfate concentrations may be less than 2L at AB-33D and AB-35D
where pH values are high due to grout contamination.
Deep Flow Zone Beneath the Active Ash Basin — In Q3 2017, valid samples
were collected from two wells (AB-20D and AB-27D) installed in the deep flow
zone beneath ash of the active ash basin. Calcium, iron, manganese, strontium,
and vanadium are consistently detected at concentrations greater than the
2L/IMAC or PBTV in at least one of these two wells. Only vanadium and
calcium concentrations are elevated at AB-20D, located in upgradient portions of
the basin. Those constituents and the others identified above are detected at AB-
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27D located along the dike between the active and inactive basin. Similar to the
deep flow zone beneath the inactive ash basin, boron and sulfate are not detected
at concentrations greater than the 2L in the deep flow zone wells beneath the
active ash basin. Similar to the shallow zone, boron, and possibly other
constituent concentrations are likely greater than applicable 2L/IMAC and
PBTVs in deep groundwater beneath the eastern portion of the basin, along Lake
Wylie/Catawba River, based on groundwater flow and results from samples
further downgradient.
Boron and sulfate concentrations may be less than 2L at AB-24D and AB-28D
where pH values are high due to grout contamination.
Bedrock Flow Zone Beneath the Inactive Ash Basin — In Q3 2017, valid
samples were collected from two wells (AB-35BR and AB-38BR) installed in the
bedrock flow zone beneath ash of the inactive basin. Only calcium, strontium,
and manganese were detected at concentrations greater than the 2L/IMAC or
PBTV, whichever is greater, at AB-38BR. Strontium is the only constituent
detected at a concentration greater than 2L or PBTVs, whichever is greater, in
well AB-35BR. No other constituents, including boron or sulfate, are routinely
detected at concentrations greater than 2L/IMAC or PBTVs, whichever is greater,
in the bedrock flow zone monitoring wells beneath the inactive ash basin.
Bedrock Flow Zone Beneath the Active Ash Basin — In Q3 2017, valid samples
were collected from three wells (AB-21BR, AB-24BR, and AB-27BR) installed in
the bedrock flow zone beneath ash of the active basin. Only calcium, strontium,
manganese, and molybdenum were detected at concentrations greater than the
2L/IMAC or PBTV, whichever is greater (elevated), in one or more of these wells.
Only manganese was detected at elevated concentrations in each of the wells.
Molybdenum was the only other COI detected at an elevated concentration at
AB-21BR, located in the central portion of the basin. Strontium was detected at
elevated concentrations at AB-24BR and AB-27BR, both located in the northern
portion of the basin. Calcium was only detected at an elevated concentration at
AB27BR. No other constituents, including boron or sulfate, are routinely
detected at elevated concentrations in the bedrock flow zone monitoring wells
beneath the active ash basin.
Boron and sulfate concentrations may be less than 2L at AB-21BR, AB-23BRU,
AB-25BR, and AB-25BRU where pH values are high due to grout contamination.
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Updated PBTVs presented in Appendix H indicate some of the constituents
detected at concentrations greater than applicable PBTVs at locations beneath the
ash basins and discussed above, may actually be within the range of naturally
occurring background concentrations. Data from several deep and bedrock zone
monitoring wells beneath the basin is invalid due to grout contamination.
However, the lack of widespread detections at concentrations greater than the 2L
for CCR-influence indicator parameters such as boron and sulfate in wells in the
western portion of the basins beneath the ash, indicates the ash basins effect on
groundwater quality is limited to the eastern portion of the basins along Lake
Wylie/Catawba River.
10.2.2 Monitoring Wells Sidegradient and Downgradient of the
Ash Basins
Monitoring well clusters are installed in the shallow, deep, and bedrock flow
zones downgradient of the ash basins (wells installed within the dams are
considered downgradient). Wells at these clusters have been routinely
monitored since being installed (most were installed in 2015). A summary of
analytical results for these wells is provided below.
Shallow Flow Zone Downgradient of the Inactive Ash Basin — In Q3 2017,
valid samples were collected from 14 wells installed in the shallow flow zone
downgradient (AB-1R, AB-8, AB-9S, AB-31S, AB-32S, GWA-04S, GWA-05S,
GWA-06S, and GWA-07S) and sidegradient (AB-2, GWA-08S, GWA-15S, GWA-
17S, and GWA-18S) of the inactive ash basin. Sixteen (16) constituents —
aluminum, arsenic, beryllium, boron, cadmium, calcium, cobalt, iron,
manganese, nickel, selenium, strontium, sulfate, TDS, thallium, and zinc — were
detected in at least one sample at concentrations greater than applicable
2L/IMAC or PBTVs, whichever is greater. Most of those constituents are
detected at only one location, GWA-6 and primarily well GWA-6S installed
within the shallow monitoring zone. GWA-6 is located in close proximity to the
coal pile, which might be affecting groundwater quality. Separate assessment is
planned to better understand conditions around the coal pile. No other
monitoring locations have as many constituents or similar constituent
concentrations to those detected at GWA-6S. Only boron, calcium, strontium,
aluminum, cobalt, iron, and manganese (seven constituents) were detected at
concentrations greater than 2L/IMAC or PBTV, whichever is greater (elevated) at
other locations. Boron, cobalt, iron, and manganese are detected at elevated
concentrations east of the inactive ash basin. Elevated concentrations of cobalt,
iron, and manganese are also detected northeast of the basin in the vicinity of,
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and may represent influence from, the coal pile. Only aluminum, calcium, and
strontium were detected at elevated concentrations at locations northwest of the
inactive ash basin, and concentrations of those constituents likely represent
background groundwater quality in this area as they are similar to PBTVs.
Shallow Flow Zone Downgradient of the Active Ash Basin — In Q3 2017, valid
samples were collected from nine wells installed within the shallow flow zone
downgradient (AB-6A, AB-6R, AB-10S, AB-22S, AB-26S, GWA-1S, GWA-2S, and
GWA-3S) and sidegradient (AB-5S) of the active ash basin. Boron, aluminum,
chromium, hexavalent chromium, cobalt, iron, and manganese were detected in
at least one sample at concentrations greater than the 2L/IMAC or PBTV,
whichever is greater (elevated). Boron was detected at elevated concentrations in
only one well (AB-26S), which is located at the eastern edge (installed within the
east dam) of the basin. Elevated chromium concentrations were detected only at
the AB-6 cluster, located east of the dam. Elevated cobalt, iron, and manganese
were primarily detected east, and to a lesser extent, southeast of the active basin.
Deep Flow Zone Downgradient of the Inactive Ash Basin — In Q3 2017, valid
samples were collected from ten wells installed in the deep flow zone
downgradient (AB-9D, AB-32D, GWA-04D, GWA-05D, GWA-06DA, and GWA-
07D) and sidegradient (AB-2D, GWA-15D, GWA-17D, and GWA-18D) of the
inactive ash basin. Calcium, chromium, iron, manganese, strontium, sulfate, and
TDS were detected in at least one sample at concentrations greater than the
2L/IMAC or PBTV, whichever is greater (elevated). However, iron, manganese,
sulfate, and TDS were only detected at elevated concentrations in well GWA-
6DA located north of the basin. Chromium was only detected at an elevated
concentration at GWA-7D located north of the basin and further downgradient
of GWA-6DA. These detections indicate influence from the coal pile. Calcium
and strontium were detected at elevated concentrations in most wells
downgradient of the basin, however, at locations to the northwest, those detected
concentrations likely represent background groundwater quality. Boron was not
detected at concentrations greater than the 2L in the deep flow zone monitoring
wells downgradient of the inactive ash basin.
Boron and sulfate concentrations may be less than 2L at AB-31D and GWA-19D
where pH values are high due to grout contamination.
Deep Flow Zone Downgradient of the Active Ash Basin — In Q3 2017, valid
samples were collected from seven wells installed in the deep flow zone
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downgradient of the active ash basin: AB-10D, AB-11D, AB-22D, AB-26D, GWA-
1D, GWA-2D, and GWA-3D. Boron, calcium, iron, manganese, strontium,
sulfate, and vanadium were detected in at least one sample at concentrations
greater than the 2L/IMAC or PBTV, whichever is greater (elevated), in the deep
flow layer downgradient of the active ash basin. Boron was detected at elevated
concentrations in only one well (AB-22D), which is located at the eastern edge
(installed within the east dam) of the basin. Elevated iron and manganese
concentrations were detected in wells (AB-22D and AB-26D). Well AB-26D,
located at the eastern edge (installed within the east dam), was the only location
with an elevated vanadium concentration. Calcium and strontium were detected
at elevated concentrations in most wells downgradient of the basin. However, in
locations to the south of the basin, detected concentrations of calcium and
strontium likely represent background groundwater quality as they are similar to
applicable PBTVs.
Boron and sulfate concentrations may be less than 2L at GWA-14D, GWA-14DA,
GWA-21D, and GWA-23D where pH values are high due to grout
contamination.
Bedrock Flow Zone Downgradient of the Inactive Ash Basin — In Q3 2017,
valid samples were collected from three wells installed in the bedrock flow zone
downgradient of the inactive ash basin: GWA-04BR, GWA-05BRA, and GWA-
06BR. Aluminum, boron, calcium, iron, manganese, and strontium were
detected in at least one sample at concentrations greater than the 2L/IMAC or
PBTV, whichever is greater (elevated). However, aluminum, boron, and iron
were only detected at elevated concentrations in well GWA-5BRA located
northeast of the basin. Calcium, manganese, and strontium were detected at
elevated concentrations in each of the wells. In locations north of the basin, the
detected concentrations of calcium, manganese, and strontium likely represent
background groundwater quality as they are similar to applicable PBTVs.
Sulfate was not detected at elevated concentrations in any of the CAMA bedrock
wells downgradient of the inactive ash basin.
New well, GWA-6BRA was installed on October 26, 2017 as a replacement well
to GWA-6BR. GWA-6BRA was initially sampled on November 10, 2017.
Analytical results of the first sampling event indicate calcium, cobalt, manganese,
and strontium concentrations are similar to PBTVs and likely indicate
background concentrations.
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Boron and sulfate concentrations may be less than 2L at GWA-4BR and GWA-
5BR where pH and turbidity values are high due to well construction issues.
Boron may be less than, but sulfate greater than, the 2L at GWA-6BR where pH
values are high due to grout contamination.
Bedrock Flow Zone Downgradient of the Active Ash Basin — In Q3 2017, valid
samples were collected from two wells installed in the bedrock flow zone
downgradient of the active ash basin: AB-22BR and GWA-1BR. Boron, calcium,
iron, molybdenum, and strontium were detected at concentrations greater than
the 2L/IMAC or PBTV, whichever is greater (elevated) at AB-22BR, located at the
eastern edge (installed within the east dam) of the basin.
New well, AB-22BRL was installed on October 30, 2017 as a vertical extent
assessment well, installed deeper than AB-22BR. AB-22BRL was initially sampled
on November 10, 2017. Analytical results of the first sampling event indicate
boron, calcium, and strontium concentrations are greater than 2L or PBTVs
(whichever is greater). Boron concentrations are similar to the boron
concentrations detected within well AB-22BR, indicating the vertical extent of
boron concentrations is not fully delineated downgradient of the active ash basin
in this area. Vertical hydraulic gradients are upward in this area, indicating
groundwater is discharging to Lake Wylie/Catawba River, which should limit
migration further from the basin.
Only calcium and strontium were detected at elevated concentrations at GWA-
1BR, southeast of the basin. However, those detected concentrations are similar
to PBTVs and likely represent background groundwater quality.
Field pH measurements at well GWA-03BR and GWA-03BRA indicate these
wells are affected by grout contamination, so the samples are not considered
valid. However, available analytical results for boron (which is not likely
affected significantly by pH) indicate boron concentrations are less than the 2L,
but greater than PBTVs.
Boron and sulfate concentrations may be less than 2L at GWA-3BR and GWA-
3BRA, where pH values are high due to grout contamination.
Piper Diagrams (Comparison to Downgradient Well 10.2.3
Samples)
The Piper Diagrams included on Figures 10-1 to 10-4, display water chemistry to
allow comparison with background and ash pore water characteristics. Cation –
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anion charge balance calculations are an indicator of data quality. Samples with
a charge balance of greater than 10% are not included in the diagrams. Cation-
anion charge balance results are provided in Table 10-2. Generalized areas of the
ash pore water and background groundwater have been included on the figure
for comparative purposes. Upgradient wells not used as background and
sidegradient wells are plotted in blue and downgradient wells are plotted as
green on Figures 10-2 through 10-4. Evaluation of the Piper diagrams for wells
beneath and downgradient of the ash basins results in the following
observations:
Groundwater from upgradient and sidegradient locations in each flow
layer tends to plot as calcium-bicarbonate, similar to groundwater
characteristic of background.
Shallow groundwater tends have a broader range of calcium, chloride,
bicarbonate, and sodium plus potassium compared to deep and bedrock
groundwater.
Groundwater samples from downgradient locations generally fall
between calcium-bicarbonate type water and calcium-sulfate type water
and have a broader range of bicarbonate proportion compared to
background locations.
Groundwater at downgradient locations that plot similarly to background
are typically at locations where boron is detected at concentrations less
than the 2L or PBTV, such as the wells south of the active ash basin and in
deep and bedrock flow zones on the western side of the basins.
Groundwater downgradient of the basins where boron concentrations are
greater than or, close to the 2L, plot on the Piper diagrams similar to ash
pore water and are more sulfate- and calcium-rich, and with a wider
range of bicarbonate. This indicates influence from the ash basins by
mixing of groundwater and ash pore water.
Wells GWA-7D and GWA-6BR plot similar to typical ash pore water,
however boron is not detected in these locations. This indicates
groundwater may be influenced by another source, such as the coal pile.
Piper diagrams could not be made for GWA-6S and GWA-6D due to
charge balance differences beyond acceptable limits (10%).
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Radiological Laboratory Testing 10.2.4
Radionuclides may exist dissolved in water from natural sources (e.g. soil or
rock). The USEPA regulates various radionuclides in drinking water. Radium-
226, radium-228, total radium, uranium-238, and total uranium were analyzed in
approximately half of the samples collected from wells as part of the CAMA
sampling event in September 2017. Results for radiological laboratory testing are
presented in Table 1 in Appendix B. Radium and uranium isotopes were
detected below USEPA Maximum Contaminant Levels (MCLs) in all but one
(AB-21SL, an ash pore water well) of the samples analyzed.
10.3 Site-Specific Exceedances (Groundwater Constituents of
Interest)
Site-specific COIs were developed by evaluating groundwater sampling results with
respect to PBTVs, applicable regulatory standards, and additional regulatory
input/requirements. The approach to determining which constituents should be
considered constituents of interest (COIs) for the purpose of this assessment is
discussed in the following section.
Provisional Background Threshold Values 10.3.1
As presented in 2L .0202 (b) (3) — “Where naturally occurring substances exceed
the established standard, the standard shall be the naturally occurring
concentration as determined by the Director” — the following report was
provided to NCDEQ: Statistical Methods for Developing Reference Background
Concentrations for Groundwater and Soil at Coal Ash Facilities (HDR and SynTerra,
2017). NCDEQ (July 7, 2017) addressed each Duke Energy coal ash facility and
identified soil and groundwater data appropriate for inclusion in the statistical
analysis to determine BTVs and PBTVs. A revised and updated technical
memorandum that summarized revised background groundwater datasets and
statistically determined PBTVs for the Allen Site was submitted to NCDEQ on
September 5, 2017. A partial list of NCDEQ-approved groundwater PBTVs was
provided to Duke Energy on October 11, 2017 (Zimmerman to Draovitch;
Appendix A).
As discussed above, several currently accepted PBTVs underestimate actual
background threshold, as Q3 2017 data indicates concentrations for several
constituents from accepted background locations are greater than the currently
accepted PBTVs. Inclusion of additional upgradient monitoring wells and more
recent data from wells currently included in the dataset will further refine PBTVs
and further evaluation of background groundwater and proposed updated
PBTVs are presented in Appendix H. Since the area of potentially affected
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groundwater is determined based on PBTVs, changes in PBTVs affect the area
considered to be potentially affected. To account for potential changes in PBTVs,
contour lines shown on the isoconcentration maps show both the currently
accepted PBTVs and proposed updated and refined PBTVs.
Applicable Standards 10.3.2
As part of CSA activities at the Site, sampling and analysis for inorganic
constituents has been conducted for coal ash, ponded water in the ash basin, ash
pore water, AOW, surface water, sediment, soil, and groundwater
downgradient/sidegradient of the ash basin and in background areas. Based on
comparison of those sampling results from the multiple media to background
values and applicable regulatory values, potential lists of COIs were developed
in the 2015 CSA report, 2015 and 2016 CAPs, and 2016 CSA Supplement 2.
For the purpose of developing the groundwater COIs, constituent exceedances in
downgradient groundwater of PBTVs and 2L or IMAC are considered a primary
focus. Certain constituents, such as boron and sulfate, are included due to their
usefulness as indicators of coal ash influence. Additionally, NCDEQ requested
that hexavalent chromium be included as a COI at each CAMA-related site due
to public interest. As directed by a July 14, 2017, NCDEQ correspondence, a
comparative value of 10 µg/L is used for both total and hexavalent chromium.
Molybdenum and strontium do not have 2L or IMACs established; however,
these constituents are considered potential COIs with regard to CCR and are
evaluated as potential COIs for the Site at the request of NCDEQ.
The following constituents do not have a 2L/IMAC, or Federal MCL established:
alkalinity, aluminum, bicarbonate, calcium, carbonate, magnesium, methane,
potassium, sodium, sulfide, and TOC. Results from these constituents are useful
in comparing water conditions throughout the Site. For example, calcium is
listed as a constituent for detection monitoring in Appendix III to 40 CFR Part
257. Although these constituents are used to compare and understand
groundwater quality conditions at the Site, because there are no associated 2L,
IMACs, or MCLs, these constituents are not evaluated as potential COIs for the
Site.
Additional Requirements 10.3.3
NCDEQ requested that figures be included in the CSA that depict groundwater
analytical results for the constituents in 40 CFR 257, Appendix III detection
monitoring and 40 CFR 257, Appendix IV assessment monitoring (CCR Rule)
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(USEPA, 2015). Detection monitoring constituents in 40 CFR 257 Appendix III
are as follows:
Boron
Calcium
Chloride
Fluoride (limited historical data at this Site, not on assessment
constituent list)
pH
Sulfate
TDS
Constituents for assessment monitoring listed in 40 CFR 257
Appendix IV include:
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Cobalt
Fluoride (limited historical data at this Site, not on assessment
constituent list)
Lithium (not analyzed)
Mercury
Molybdenum
Selenium
Thallium
Radium 226 and 228 combined
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Aluminum, copper, iron, manganese, and sulfide were originally included in the
Appendix IV constituents in the draft rule; USEPA removed these constituents in
the final rule. Therefore, these constituents are not included in the listing above;
however, they are included as part of the current Interim Monitoring Plan (IMP;
Section 15.3). NCDEQ requested that vanadium be included as a COI.
Allen Steam Station Constituents of Interest 10.3.4
Exceedances of comparative values, the distribution of constituents in relation to
the ash basin, comparison with background concentrations, co-occurrence with
CCR indicator constituents such as boron, and likely migration directions based
on groundwater flow direction are considered in determination of groundwater
COIs. A constituent exceedance in an outlying area with no co-occurrence of
boron or similar CCR-related constituent is a reason to not retain the constituent
as a COI. A constituent exceedance based on a single sampling event when
previous results indicate a concentration trend below comparative values would
not warrant inclusion as a COI. Based on Site-specific conditions, observations,
and findings, the following list of COIs has been developed for the Allen Site:
Antimony
Arsenic
Beryllium
Boron
Cadmium
Chromium (total)
Chromium (hexavalent)
Cobalt
Iron
Manganese
Molybdenum
Nickel
pH
Selenium
Strontium
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Sulfate
Thallium
TDS
Vanadium
Tables 10-1 and 10-3 list the COIs and other constituents at the Allen Site along
with the currently accepted PBTVs and associated 2L/IMACs. Several of the
selected COIs are based on detections observed at concentrations greater than
2L/IMAC or PBTV, whichever is greater, only at well GWA-6S. COIs in that well
may be resultant from affects from the coal pile and not the ash basin. The COI
list may be further refined as additional information is obtained.
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HYDROGEOLOGICAL INVESTIGATION 11.0
Results from the hydrogeological assessment of the Allen Site, summarized in this
section, are primary components of the site conceptual model.2 Plume physical and
chemical characterization is detailed below for each groundwater COI. The horizontal
and vertical extent of constituent concentrations is presented on isoconcentration maps
and cross sections. These descriptions and depictions are based primarily on the most
recent comprehensive groundwater data set (September 2017), or the most recent valid
data available.
11.1 Plume Physical and Chemical Characterization

Plume Physical Characterization 11.1.1
The groundwater plume is defined as locations (in three-dimensional space)
where groundwater quality is impacted by the ash basins. Other COIs (defined
in Section 10.0) are used to help refine the extent and degree to which areas are
impacted by groundwater from the ash basins. The comprehensive groundwater
data table (Appendix B, Table 1) and an understanding of groundwater flow
direction (Section 6.2.3, Figures 6-1 to 6-6) were used to define the horizontal
and vertical extent of the plume. As discussed in Section 13.2 (Geochemical
Modeling), not all constituents with PBTV exceedances are attributed to the ash
basin. Naturally occurring groundwater contains varying concentrations of COIs
and other constituents including alkalinity, aluminum, bicarbonate, carbonate,
copper, lead, magnesium, methane, potassium, sodium, and TOC. Sporadic
detections and slight exceedances of 2L/IMAC or PBTVs (if determined) of these
constituents in the groundwater data do not necessarily demonstrate impacts
from the ash basins.
Isoconcentration Maps
The spatial distribution of groundwater concentrations for each COI in each flow
unit are shown on isoconcentration maps (Figures 11-1 to 11-60). These maps use

2 Pursuant to the CCR rule, owners and operators of CCR units must install the required groundwater
monitoring system; develop the required groundwater sampling and analysis program to include
selection of the statistical procedures to be used for evaluating groundwater monitoring data; and begin
detection monitoring, which requires owners and operators to have a minimum of eight samples for
each well and begin evaluating groundwater monitoring data for statistically significant increases over
background levels for the constituents listed in Appendix III of 40 C.F.R. Part 257. The data is posted to
Duke Energy’s publicly accessible Internet site as required under the CCR rule. The most recent data
available has been considered in this assessment for refinement of constituent distribution.
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valid groundwater analytical data to spatially and visually define areas where
groundwater concentrations are above the respective constituent PBTV and/or
2L/IMAC. For constituents for which the PBTV is greater than the 2L/IMAC,
only areas with concentrations greater than the PBTV are defined. Monitoring
data in the shallow zone beneath the ash basins is limited, therefore ash pore
water concentrations, while not representative of shallow groundwater, were
used to infer potential concentrations in the underlying shallow flow system for
generating isoconcentration figures.
The leading edge of CCR-related the plume from the ash basins, the furthest
downgradient edge, is within the existing well network as represented by arsenic
and boron concentrations in groundwater in the wells in each flow unit. Figures
11-4 to 11-6 and 11-10 to 11-12 depict the horizontal extent of arsenic and boron
in downgradient groundwater. The background contour line in the shallow flow
zone generally encompasses the perimeter of the ash basins to the north, south,
and west, as well as an inferred section encompassing the coal pile area. This
indicates that ash basin influence in the shallow flow zone is generally not
observed to the north, south, and west of the ash basins. In the deep flow zone,
the background contour line does not extend as far west as the shallow zone
contour line does. This indicates that ash basin influence in the deep/transition
flow zone is generally limited to the easternmost portion of the ash basin and
areas immediately downgradient to the east. In bedrock, the background
contour mimics the contour of the deep flow zone with the exception of the
northwest portion of the inactive ash basin. This indicates that ash basin
influence in the bedrock flow zone is generally limited to the easternmost portion
of the ash basin and areas immediately downgradient to the east. The plume
may extend some distance out into Lake Wylie/Catawba River, but upward
hydraulic gradients indicate that groundwater discharges to the lake, indicating
that it is unlikely that groundwater migrates to the other side of the lake. As
described in Section 6.0, there is no hydrogeologic confining unit at the Site;
therefore, under these unconfined conditions, groundwater moves freely across
each unit.
Concentration versus Distance Plots
Figure 11-61 to 11-73 depicts concentration versus distance graphs from the
sources along the plume centerlines for COIs. While PBTV values could not be
distinguished on these graphs because values differ by flow unit, the graphs
show constituent concentrations in source areas and downgradient and aid in
understanding plume distribution. Concentrations of each COI represent
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September 2017 conditions, or the most recent valid data available. The wells
used are consistent for each constituent represented. The graphs demonstrate
that COI concentrations generally decrease from the source area to downgradient
locations. The largest deviation from this trend is due to the GWA-06 and GWA-
07 well clusters. In the shallow and deep flow layers, these wells show a clear
trend of increasing concentrations. This is likely caused by the close proximity of
the coal pile to the wells. Transects in the active ash basin (Figures 11-66 to 11-
73) show a trend of decreasing concentrations with distance from the source area
for antimony, arsenic, barium, boron, molybdenum, strontium, and vanadium.
Chromium and hexavalent chromium concentrations along the transect in the
vicinity of the coal pile show an increasing trend. Other constituents show no
clear trend.
Vertical Extent Cross-Sections
The vertical extent of constituents along select centerlines within the inactive and
active ash basins are depicted in the cross-sectional views of the Site (Figures 11-
74 to 11-157). Cross-section B-B’ is partially cross-gradient with prevailing
groundwater flow, although flow along the northern portion of the section
follows the transect. Cross-sections D-D’, E-E’, and F-F’ depict vertical
conditions in areas upgradient and offsite (including water supply wells) as well
as conditions across the site to Lake Wylie. Cross Section D-D’ depicts vertical
conditions within the inactive basin. Cross-section E-E’ depicts vertical
conditions within the northern portion of the active basin including areas
beneath cells 1-3. Cross-section F-F’ depicts vertical conditions within the
southern portion of the active ash basin.
COIs have been contoured in the cross-sectional depictions. Constituent
isocontours reflect values greater than the 2L/IMAC standard, or the PBTV, if
greater than the 2L/IMAC. A detailed discussion of constituent distribution,
laterally and vertically is included in Sections 10 and 14 and summarized in
Section 15.
In summary, the horizontal extent of the plume has been defined. The vertical
extent is also defined except for an area around AB-22 located east of the active
ash basin and around GWA-5, located east of the inactive ash basin. Upward
hydraulic gradients indicated by wells located along Lake Wylie/Catawba River,
indicate groundwater discharges to the lake. Monitoring wells across the Site are
appropriately placed and screened to the correct elevations to monitor
groundwater quality. However, additional monitoring wells may be installed in
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shallow groundwater beneath the ash basins and deeper within bedrock
downgradient of the basins to evaluate the effectiveness of corrective measures
Monitoring wells installed for other regulatory programs 3 have added additional
details about the orientation and extent of the downgradient plume and have
helped refine an understanding of the vertical and horizontal distribution of the
plume.
Transects planned for use in the geochemical model are slightly different than
those shown in cross-section on current figures. Transects used for geochemical
modeling are planned to focus in on specific areas of interest to optimize
geochemical evaluation. Details of the geochemical model are further discussed
in Section 13. A description of each planned transect, purpose for the transect,
and data inventory for each of the four chosen flow transects for the geochemical
model is detailed subsections to follow (asterisks (*) shown below denote wells
screened within ash). The proposed geochemical flow transects are shown on
Figure 11-159 and discussed below. Data inventory associated with the
geochemical flow transects is summarized on Table 11-1.
Coal Pile / Ash Storage Area Transect
Wells that comprise the ash storage area/coal pile transect for geochemical
modeling, beginning with the upgradient wells and continuing down the flow
path are as follows: AB-38S*/D/BR, AB-39S*/D, CCR-4SA/DA, GWA-6S/DA/BRA,
and GWA-7S/D.
In the northeast corner of the ash storage area the groundwater in all flow zones
trends north-northeast. Elevated concentrations of several constituents are
observed along the northwest rim of the RAB Ash Landfill, with discrete
differences in concentration of the key CCR tracer, boron as well as distinct
differences of other constituents that are present only, or at concentrations only
observed, in areas north of the inactive basin in the vicinity of the coal pile. As
the location of those discrete constituent concentrations is adjacent to the coal

3 Pursuant to the CCR rule, owners and operators of CCR units must install the required groundwater
monitoring system; develop the required groundwater sampling and analysis program to include
selection of the statistical procedures to be used for evaluating groundwater monitoring data; and begin
detection monitoring, which requires owners and operators to have a minimum of eight samples for
each well and begin evaluating groundwater monitoring data for statistically significant increases over
background levels for the constituents listed in Appendix III of 40 C.F.R. Part 257. The data is posted to
Duke Energy’s publicly accessible Internet site as required under the CCR rule. The most recent data
available has been considered in this assessment for refinement of constituent distribution.
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pile, it is important to examine this northeastern transect in the updated
geochemical model. This north-northeast trending transect is primarily based on
uniquely elevated and localized concentrations of cadmium, cobalt, nickel,
selenium, and thallium in the surficial/shallow monitoring zone.
This flow transect consist of two wells screened within ash pore water (AB-38S*
and AB-39S*), three wells within the shallow flow zone (CCR-4SA, GWA-6S, and
GWA-7S), five wells within the deep flow zone (AB-28D, AB-39D, CCR-4DA,
GWA-6DA, and GWA-7D), and two wells within the bedrock flow zone (AB-
38BR and GWA-6BRA).
Concentrations of boron are only observed above the detection limit in the two
ash pore wells and in two of the five deep wells (AB-39D and GWA-6DA) along
the chosen flow transect, indicating the CCR material may not be the primary
source material along this flow path. The greatest concentrations of the five
constituents considered uniquely relevant to flow in this direction were located
in either CCR-4SA or GWA-6S with a decrease in concentration as groundwater
flows north toward GWA-7S. In light of this anomalous condition, the source or
starting location for the transect should be adjusted to assume an alternative
source (i.e., the coal pile) or a combination source area rather than a typical CCR
source beginning at and beneath an ash pore water well.
Of the 12 wells located along the proposed flow transect, three wells have less
than 6 valid sampling events; AB-38BR with four valid sampling events, GWA-
6BR with three valid sampling events, and GWA-6DA with five valid sampling
events, as of August 2017. Where wells remain (GWA-6BR is abandoned),
additional sampling events will increase the available data prior to the updated
geochemical model.
There are 14 wells located perpendicular to the proposed centerline of flow for
the ash storage area/coal pile. Of those 14 wells, seven are located within the
shallow flow zone and another seven within the deep flow zone.
Inactive Ash Basin Transect
Wells that comprise the Inactive Ash Basin Transect, beginning with the
upgradient wells and continuing down the flow path are as follows:
GWA-15S/D, AB-37S*/D, AB-36S/D, AB-35S*/D/BR, AB-34S*/D, AB-32S/D, and
GWA-5S/D/BRA.
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North of the Active Ash Basin groundwater generally flows west to east-
northeast through the Inactive Ash Basin, the Ash Storage areas, and the Retired
Ash Basin Landfill Permit No. 3612. The flow has an east-northeast trend with
the highest groundwater concentrations for most COIs located in wells along the
eastern portion of the waste boundaries adjacent to the Catawba River. This is
likely due to the lack of data within and beneath the basin. In the absence of
source area data, the 1-D geochemical model is limited to assumptions using
wells within the ash basin.
This flow transect consists of three wells screened within the ash pore water, four
wells within the shallow flow zone, seven wells within the deep flow zone, and
two wells within the bedrock flow zone. The highest concentrations of many
known CCR constituents along this transect are located at the GWA-5 well
cluster, adjacent to the Lake Wylie/Catawba River. The concentrations of boron
in GWA-5 wells indicate that there is CCR influence in the shallow, deep, and
bedrock zones in this area, however the concentrations in the deep and bedrock
wells do not exceed the 2L standard. Data from beneath the inactive ash basin
within the surficial/shallow flow would be useful for geochemical analysis
groundwater concentration along this flow transect.
Of the 16 wells along the centerline of this flow transect, four wells have less than
five valid sampling events: AB-35D with zero valid sampling events, GWA-
5BRA with two valid sampling events, and AB-35BR and AB-36D with four valid
sampling events. Additional sampling events will increase the available data
prior to the updated geochemical model.
There are 14 wells located perpendicular to the proposed centerline of flow for
the Inactive Ash Basins Transect. Of those 14 wells, three are screened in ash
pore water; four are screened in the shallow aquifer, six in the deep aquifer, and
one in the bedrock aquifer. Three of those wells have less than five valid
sampling events: AB-29SL* and AB-31D with zero valid sampling events and
GWA-4BR with one valid sampling event. All of those well have at least six valid
sampling events except AB-29SL* with zero valid sampling events, and GWA-
5BRA with two valid sampling events.
Active Ash Basin - North
The wells that comprise the active ash basin-north transect, beginning with the
upgradient wells and continuing down the flow path are as follows: AB-13S/D,
AB-24S*/SL*/D/BR, AB-25S*/SL*/BRU/BR, AB-26S/D, GWA-3S/D/BRA.
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In the active ash basin, groundwater is primarily flowing to the east towards
Lake Wylie/Catawba River with some flow to the north-northeast along the
northern rim of the three primary ponds. Two flow transects were chosen for the
active ash basin to account for the heterogeneity between the northern, primary
ponds and the southern portion of the basin. The wells chosen for the northern
active ash basin transect extend from upgradient location outside of the waste
boundary across the three Primary Ponds eastward toward Lake Wylie/Catawba
River.
This flow transect consists of four ash pore wells, three shallow wells, four deep
wells, one bedrock upper well(within the “deep” flow zone), and three bedrock
wells. However, of these 15 wells in this transect nine have less than five valid
groundwater sampling events, three of which are expected to result in more
successful sampling events based on recent trends, one of which has insufficient
data and the five of which are not likely to be useful for the updated geochemical
model due to likely grout contamination. As a result, the wells expected to have
sufficient, valid data prior to the updated geochemical model are AB-13S/D, AB-
24S*/BR, AB-25S*/SL*, AB-26S, and GWA-3S/D.
The greatest concentration of boron along the active ash basin-north transect is
within the two source wells AB-25S* and AB-25SL* located between Primary
Pond 2 and 3. Concentrations remain greater than the 2L in the shallow aquifer
AB-26S with concentrations dipping below the 2L beyond the waste boundary.
There are 12 wells located perpendicular to the proposed centerline of flow for
the active ash basin-north transect. Of those 12 wells, three are ash pore wells,
three are shallow wells, four are deep wells, one is a bedrock-upper well (located
within the deep flow zone), and one is a bedrock well. However, only eight are
anticipated to have at least five valid groundwater sampling events prior to the
CAP submittal.
Active Ash Basin -South
Wells that comprise the active ash basin-south transect, beginning with the
upgradient wells and continuing down the flow path are as follows: GWA-
9S/D/BR, AB-20S*/D, AB-21S*/SL*/D/BR/BRL, AB-22S/D/BR/BRL, and AB-10S/D.
The southern portion of the active ash basin contains the highest source area
concentrations of boron, as it may contain some of the most recently deposited
ash and receives water discharged from the three Primary Ponds. The flow
transect in this portion of the basin extends from an upgradient location to the
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west, through the centerline of the highest source area boron concentrations, and
downgradient toward Lake Wylie/Catawba River to the east. The geochemical
transect used in the 1-D PHREEQC model for the active ash basin-south transect
will begin at the AB-21 well cluster.
This flow transect consist of three wells screened in ash pore water, three within
the shallow flow zone, five within the deep flow zone, three within the bedrock
flow zone and two within the lower bedrock flow zone. Of these 16 wells, seven
have less than five valid sampling events as of August 2017 (AB-20D, AB-
21D/BR/BRL, AB-22BR/BRL, and GWA-9BR), two of which have positive trends
indicating successful future sampling events (AB-22BR and GWA-9BR), and two
of which were installed too recently to predict (AB-21BRL and AB-22BRL).
Boron trends along this transect start high to below detection limits at furthest
downgradient wells, AB-10S and AB-10D. While boron concentrations at AB-22S
have consistently remained below detection limits, the deep and bedrock wells at
this location have consistently resulted in concentrations between 1500 and 2000
µg/L. Additionally, adjacent wells within the surficial/shallow flow zone
indicate variable boron concentrations at approximately 1300 µg/L in CCR-17S
just north of AB-22S, and concentrations of 51.2 µg/L in CCR-18S just south of
AB-22S. This heterogeneity will be considered in the updated geochemical
model.
There are 14 wells located perpendicular to the proposed centerline of flow for
the active ash basin-south transect. Of those 14 wells, eight are screened in the
shallow flow zone and six are screened in the deep flow zone. All wells have at
least seven valid sampling events except for CCR-22DA which has no valid
sampling events to date.
Plume Chemical Characterization 11.1.2
Plume chemical characterization is detailed below for each COI. Analytical
results are based on the most recent groundwater sampling event which data are
available. The range of detected concentrations is presented with the number of
detections for the sampling event. Samples that have turbidity >10 NTUs or pH
greater than 9.0 (indicative of grout contamination in the well) have been
removed from the data set. Descriptions of the COIs identified for the Allen Site
are also provided. PBTVs and 2L/IMACs are included in Appendix B, Table 1.
Ash pore water (source) concentrations are discussed in Section 3.0.
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Arsenic
Detected Range: 0.052 j µg/L – 807 D3 µg/L; Number of Detections/Total Samples:
107/109
Concentrations in 33 samples (23 shallow; 2 deep; 8 bedrock) exceeded the
PBTV.
Concentrations in 15 samples (13 ash pore water; 2 surficial) exceeded the
2L of 10 µg/L.
Most sample locations that exceeded the 2L of 10 µg/L are ash pore water
wells, or are situated in or downgradient of the ash basins.
Arsenic is a trace element in the crust, with estimated concentrations ranging
from less than one mg/kg in mafic igneous rocks to 13 mg/kg in clay rich rocks
(Parker, 1967). It occurs in multiple valence states (As5+, As3+, and As3-). Arsenic in
coal occurs primarily in pyrite (iron sulfide, with arsenic replacing iron in the
crystal structure) (Finkelman, 1995). Arsenic condenses on fly ash as arsenate
(As5+) (Goodarzi, Huggins, & Sanei, 2008). Leaching tests on ash indicate that
trace quantities up to 50 percent of the arsenic present can be leached. In
addition to the solubility of the source, the concentration of calcium and presence
of oxides appear to limit the mobility of arsenic (Izquierdo & Querol, 2012). Both
natural and anthropogenic sources of arsenic can naturally attenuate on aquifer
solids. The primary attenuation mechanism for arsenic with aquifer solids are
precipitation of metal arsenates or arsenites or precipitation of arsenic sulfides,
co-precipitation with common soil/sediment minerals such as iron oxides and
iron sulfides, and adsorption to iron oxyhydroxides, iron sulfides, or other
mineral surfaces. The long-term stability of arsenic immobilized onto aquifer
solids will depend on the groundwater chemistry over time, specifically: pH,
redox potential (Eh), and the concentration of other anions competing for
sorption sites (EPA, 2007). The USEPA estimates that the amount of natural
arsenic released into the air as dust from the soil is approximately equal to the
amount of arsenic released by all human activities (EPRI, 2008).
Antimony
Detected Range: 0.1 j µg/L – 7.6 µg/L; Number of Detections/Total Samples:
53/109
Concentrations in 5 samples (3 shallow; 1 deep; 1 bedrock) exceeded the
PBTV.
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Concentrations in 2 samples (ash pore water) exceeded the IMAC of 1
µg/L.
Sample locations that exceeded the IMAC of 1 µg/L are ash pore water
wells located within the active ash basin.
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. 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 Count and other areas of the Carolina Slate Belt (Chapman, Cravotta,
III, Szabo, & Lindsey, 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, Cravotta III, Szabo, & Lindsey,
2013). Antimony is compared to an IMAC since no 2L Standard has been
established for this constituent by NCDEQ.
Beryllium
Detected Range: 0.01j µg/L – 38.6 D3 µg/L; Number of Detections/Total Samples:
73/109
Concentrations in 3 samples (3 shallow) exceeded the PBTV.
Concentrations in 1 sample (shallow) exceeded the IMAC of 4 µg/L. The
exceedance occurred in GWA-06S, which is located downgradient of the
inactive ash basin and adjacent to the coal pile.
Beryllium is a hard, gray metal that is very lightweight. In nature, it combines
with other elements to form beryllium compounds. Small amounts of these
compounds are naturally present in soils, rocks, and water. Emeralds and
aquamarines are gem-quality examples of a mineral (beryl) that is a beryllium
compound.
Beryllium combines with other metals to form mixtures called alloys. Beryllium
and its alloys are used to construct lightweight aircraft, missile, and satellite
components. Beryllium is also used in nuclear reactors and weapons, X-ray
transmission windows, heat shields for spacecraft, rocket fuel, aircraft brakes,
bicycle frames, precision mirrors, ceramics, and electrical switches (EPRI, 2008c).
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Most of the beryl occurring in North Carolina is along the south and southwest
sides of the Blue Ridge Mountains. The most notable mines include the
Biggerstaff, Branchand, and Poteat mines in Mitchell County; the Old Black mine
in Avery County; and the Ray mine in Yancey County. The beryl forms golden or
pale-green well-formed prismatic crystals ranging in size from a fraction of an
inch to about 3 inches in diameter. It is generally found near the cores of bodies
of pegmatites of moderate size that contain considerable amounts of perthitic
microcline. Production has been negligible, and no regular production appears
possible. Green beryl (aquamarine and emerald) was mined commercially many
years ago at the Grassy Creek emerald mine and the Grindstaff emerald mine on
Crabtree Mountain in Mitchell County. The Ray mine in Yancey County has also
produced some golden beryl and aquamarine (Brobst, 1962). Beryllium-
containing minerals are also common in granites and pegmatites throughout the
Piedmont; however, to a lesser degree than the Blue Ridge Mountains Province
(Brobst, 1962).
Beryllium is concentrated in silicate minerals relative to sulfides and in feldspar
minerals relative to ferromagnesium minerals. The greatest known naturally
occurring concentrations of beryllium are found in certain pegmatite bodies.
Beryllium is not likely to be found in natural water above trace levels due to the
insolubility of oxides and hydroxides at the normal pH range (Brobst, 1962). In
groundwater, beryllium concentrations are compared to IMAC since no 2L
Standard has been established for this constituent by NCDEQ.
Boron
Detected Range: 26.4 j µg/L – 6950 µg/L; Number of Detections/Total Samples:
45/109
Concentrations in 36 samples (22 shallow; 11 deep; 3 bedrock) exceeded
the PBTV.
Concentrations in 16 samples (8 ash pore water; 5 shallow; 1 deep; 2
bedrock) exceeded the 2L of 700 µg/L.
Boron exceeds the 2L in shallow groundwater beneath the ash basins, in
bedrock downgradient of the inactive ash basin, and in all flow layers
downgradient of the active ash basin.
Boron is a trace element in the crust, with estimated concentrations ranging from
as little as 1 mg/kg in mafic igneous rocks to hundreds of milligrams per
kilogram in clay rich rocks (Parker, 1967). It occurs only in the trivalent form
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(B3+) and is concentrated in sedimentary rocks (Urey & Mem, 1953). This
observation indicates that a mechanism exists to concentrate boron in minerals
because the oceans could dissolve all of the boron estimated to be present in the
crust (Fleet, 1965). Fleet (1965) presents both biogenic and mineralogical
processes to account for the preferential concentration of boron in the crust.
Boron is a micronutrient (Goldberg, 1997) that is concentrated in plant tissue,
including the plants from which coal formed.
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 associated with the carbon (fuel) in coal, and it tends to volatilize during
combustion and subsequently condense onto fly ash as a soluble borate salt
(Dudas, 1981). Boron leaches readily (up to 50 percent of total present) and
rapidly from fly ash (Cox, Lundquist, Przyjazny, & Schmulbach, 1978). Boron is
considered a marker COI for coal ash because boron is rarely associated with
other types of industrial waste products.
Boron is the primary component of a few minerals including tourmaline, a rare
gem mineral that forms under high temperature and pressure (Hurlbut, 1971).
The remaining common boron minerals, including borax that was mined in the
Mojave desert, in Boron, California, form from the evaporation of seawater in
deposits known as evaporites. For this reason, boron mobilized into the
environment will remain in solution until incorporation into plant tissue or
adsorption by a mineral.
Fleet (1965) describes sorption of boron by clays as a two-step process. Boron in
solution is likely to be in the form of the borate ion (B(OH)4-). The initial sorption
occurs onto a charged surface. Observations that boron does not tend to desorb
from clays indicates that it migrates rapidly into the crystal structure, most likely
in substitution for aluminum. Goldberg et al. (1996) determined that boron
sorption sites on clays appear to be specific to boron. For this reason, there is no
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need to correct for competition for sorption sites by other anions in transport
models (Goldberg, Forster, Lesch, & Heick, 1996).
Goldberg (1997) lists aluminum and iron oxides, magnesium hydroxide, clay
minerals, calcium carbonate (limestone), and organic matter as important
sorption surfaces in soils (Goldberg, 1997). Boron sorption on oxides is
diminished by competition from numerous anions. Boron solubility in
groundwater is controlled by adsorption reactions rather than by mineral
solubility. Goldberg concludes that chemical models can effectively replicate
boron adsorption data over changing conditions of boron concentration, pH, and
ionic strength.
Cadmium
Reported Range: 0.05 j µg/L – 9.3 D3 µg/L; Number of Detections/Total Samples:
17/109
Concentrations in 6 samples (6 shallow; 2 deep; 3 bedrock) exceeded the
PBTV.
Concentrations in 1 sample (shallow) exceeded the 2L of 2 µg/L.
Historic detections are stable for the two locations that exceed the 2L. The
exceedance occurred in GWA-06S, which is located downgradient of the
inactive ash basin and adjacent to the coal pile.
Cadmium is generally characterized as a soft, ductile, silver-white or bluish-
white metal, and is listed as 64th in relative abundance amongst the naturally
occurring elements. Cadmium is found principally in association with zinc
sulfide based ores and, to a lesser degree, as an impurity in lead and copper ores.
It is also found in sedimentary rocks at higher levels than in igneous or
metamorphic rocks, with the exception of the nonferrous metallic ores of zinc,
lead and copper (WHO 2011). Cadmium often co-occurs with zinc minerals like
sphalerite, and can substitute in the sphalerite crystal structure during
weathering (USGS 1985).
Cadmium is found throughout the environment from natural sources and
processes such as the erosion and abrasion of rocks and soils and from singular
events such as forest fires and volcanic eruptions (USGS 1985).
Cadmium occurs sporadically in the auriferous parts of the North Carolina
Charlotte and Carolina Slate Belts. Cadmium is widespread in the Carolina Slate
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Belt, but is found in the Charlotte Belt only near its southeastern boundary. A
cluster of cadmium sites marks the mineralized district in the northeast corner of
the Carolina Slate Belt, where cadmium was found in all zinc-rich samples.
The solubility of cadmium in water is influenced to a large degree by its acidity;
suspended or sediment-bound cadmium may dissolve when there is an increase
in acidity. In natural waters, cadmium is found mainly in bottom sediments and
suspended particles (WHO 2011).
Contamination of drinking water may occur as a result of the presence of
cadmium as an impurity in the zinc of galvanized pipes or cadmium-containing
solders in fittings, water heaters, water coolers and taps. Levels of cadmium
could be higher in areas supplied with soft water of low pH, as this would tend
to be more corrosive in plumbing systems containing cadmium. Cadmium is
used in battery production, dye and pigment manufacturing, coatings and
plating, as a stabilizing agent in plastic production, nonferrous alloys, and
photovoltaic devices (WHO 2011).
Chromium
Detected Range: 0.17 j,B µg/L – 26.9 µg/L; Number of Detections/Total Samples:
108/109
Concentrations in 9 samples (6 shallow; 3 deep) exceeded the PBTV.
Concentrations in 4 samples (2 shallow; 2 deep) exceeded the 2L of 10
µg/L. Three of four exceedances are located downgradient of the active
ash basin. GWA-22D exceeds the 2L of 10 µg/L as a background well,
indicating variability in naturally occurring chromium concentrations.
Chromium is a blue-white metal found naturally occurring in combination with
other substances. It occurs in rocks, soils, plants, and volcanic dust and gases
(EPRI, 2008c). Background concentrations of chromium in groundwater
generally vary according to the media in which they occur. Most chromium
concentrations in groundwater are low averaging less than 1.0 µg/L worldwide.
Chromium tends to occur in higher concentrations in felsic igneous rocks (such
as granite and metagranite) and ultramafic igneous rocks; however, it is not a
major component of the igneous or metamorphic rocks found in the North
Carolina Piedmont or the Blue Ridge (Chapman, Cravotta, III, Szabo, & Lindsey,
2013).
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In a statistical summary of groundwater quality in North Carolina, the
Superfund Research Program at UNC analyzed 1,898 private well water samples
in Gaston and Mecklenburg Counties. The samples were tested by the North
Carolina State Laboratory of Public Health from 1998 to 2012. The average
chromium concentrations were 5.1µg/L and 5.2 µg/L in Gaston and Mecklenburg
Counties respectively.
Hexavalent Chromium
Detected Range: 0.0089 j µg/L – 12.7 µg/L; Number of Detections/Total Samples:
93/109
Concentrations in 16 samples (2 shallow; 11 deep; 3 bedrock) exceeded the
PBTV.
Concentrations in 2 samples (2 shallow) exceeded the total chromium 2L
of 10 µg/L. Both exceedances occur in shallow wells located
downgradient of the active ash basin.
Chromium exists primarily in the +3 and +6 oxidation states under
environmental conditions (commonly written as Cr(III) and Cr(VI)). Hexavalent
chromium, Cr(VI), is relatively mobile with an acute toxicity, whereas trivalent
chromium, Cr(III) has a relatively low toxicity and is considered immobile in the
environment. The distribution of chromium species is largely controlled by the
pH and redox processes. Cr (VI) is the dominant form of chromium in shallow
aquifers where aerobic conditions exist, however the oxidation of Cr(III) to
Cr(VI) is considered poor with dissolved oxygen. In contrast, Cr(III) is readily
oxidized to the mobile Cr(VI) in the presence of solid MnO2 (Palmer & Puls,
1994). Thus, where elevated concentrations of manganese oxides exist in the
environment, Cr(III) is inclined to oxidize to the more mobile Cr(VI).
Alternatively, Cr(VI) can be reduced to Cr(III) by soil organic matter, S2- and Fe2+
ions under anaerobic conditions often encountered in deeper groundwater.
Major Cr(VI) species include chromate (CrO42-) and dichromate (Cr2O72-) which
precipitate readily in the presence of metal cations (especially Ba2+, Pb2+, and Ag+).
Chromate and dichromate also adsorb on soil surfaces, especially iron and
aluminum oxides. Cr(III) is the dominant form of chromium at low pH.
Chromium mobility depends on sorption characteristics of the soil, including
clay content, iron and manganese oxide content and the amount of organic
matter present. Chromium can be transported by surface runoff to surface
waters in its soluble or precipitated form. Soluble and unadsorbed chromium
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complexes can leach from soil into groundwater. The leachability of Cr(VI)
increases as soil pH increases. Most of chromium released into natural waters is
particle associated, however, and is ultimately deposited into the sediment
(Smith, Means, Chen, & others, 1995)
Cobalt
Detected Range: 0.012 j µg/L – 3640 D3,M6 µg/L; Number of Detections/Total
Samples: 109/109
Concentrations in 23 samples (15 shallow; 5 deep; 3 bedrock) exceeded the
PBTV.
Concentrations in 31 samples (9 ash pore water, 20 shallow, 1 deep, 1
bedrock) exceeded the IMAC of 1 µg/L.
15 of the 29 IMAC exceedances in the ash pore water and shallow flow
layer also exceed the PBTV. With the exception of two upgradient
exceedances at GWA-22S and GWA-9S which indicate natural variability
in cobalt concentrations, all locations are within or downgradient of the
ash basins.
Cobalt is a naturally occurring, silvery grey solid at room temperature and the
33rd most abundant element on earth. Cobalt occurs in the 0, +2, and +3 oxidation
states, with +2 being the most common under environmental conditions. In the
+2 oxidation state, cobalt forms hydroxide and sulfide solid phases and adsorbs
primarily iron and manganese oxides. The factors that affect the speciation and
mobility of cobalt in water, sediments, and soil include organic ligands such as
humic acids, anions, pH, and redox potential. Cobalt mobilizes in groundwater
in acidic oxidizing environments with relative ease, but does not undergo
extensive migration, since it combines with the hydroxides of iron and
manganese as well as silty minerals (Kim, Gibb, & Howe, 2006). As a cationic
species, Co2+ sorption will increase with increasing pH. This is a manifestation of
the attraction of Co2+ to mineral surfaces as the surface transitions from a net
positive charge to a net negative charge with increasing pH.
Cobalt can form a wide range of mineral phases including CoS2 (cattierite), CoSe
(freboldite), CoAs2 (safflorite), and CoFe2O4 (cobalt ferrite). Relatively high
concentrations of sulfide, selenium, and arsenic are required to form cattierite,
freboldite, and safflorite and in general these are not expected, except under
some anomalously high concentrations of Co and Se. Cobalt ferrite is predicted
to precipitate under conditions with high ferric iron concentrations. Geologically
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cobalt is normally associated with copper or nickel. A 1984 study to determine
the mineral potential of North and South Carolina, cobalt was found to be,
“particularly widespread in the Carolina Slate Belt,” and area which covers the
lower Piedmont of both North and South Carolina (Griffitts, Whitlow, Siems,
Duttweiler, & Hoffman, 1984).
Iron
Detected Range: 27.1 j µg/L – 108000 µg/L; Number of Detections/Total Samples:
95/109
Concentrations in 27 samples (21 shallow; 3 deep; 3 bedrock) exceeded the
PBTV.
Concentrations in 45 samples (13 ash pore water, 20 shallow, 9 deep, 3
bedrock) exceeded the 2L of 300 µg/L.
Iron exceeds the PBTV and 2L within and downgradient of the ash basins.
Iron is a naturally occurring element that may be present in groundwater from
the erosion of natural deposits (NCDHHS, 2010). A 2015 study by DENR
(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 µg/L. Iron is estimated to be the fourth most abundant
element in the Earth’s crust at approximately five percent by weight (Parker,
1967). Only Oxygen (46.60 weight percent), silicon (27.72 weight percent), and
aluminum (8.13 weight percent) occur in higher concentrations. Iron occurs in
divalent (ferrous, Fe2+), trivalent (ferric, Fe+3), hexavalent (Fe6+), and Fe2- oxidation
states. Iron is a common mineral forming element, occurring primarily in mafic
(dark colored) minerals including micas, pyrite (iron disulfide), and hematite
(iron oxide), as well as in reddish-colored clay minerals.
Clay minerals and pyrite are common impurities in coal. Under combustion
conditions in a coal-fired boiler, clay minerals would be dehydrated to mullite or
gibbsite, possibly liberating iron, and pyrite would oxidize to hematite or
magnesioferrite. Research summarized by Izquierdo and Querol (2012) indicates
that iron leaching from coal ash is on the order of 1 percent of the total iron
present due to the low pH required to solubilize iron minerals (Izquierdo &
Querol, 2012). Despite the low apparent mobilization percentage, iron is often
one of the COIs detected in the highest concentrations in ash pore water. The
extent to which iron dissolves in water depends on the amount of oxygen present
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in the water, and to a lesser extent, upon its degree of acidity (Stumm & Morgan,
1996). Fe(III) is the dominant oxidation state at high DO concentrations (greater
than 1-2 mg/L). As the DO is depleted, Fe(III) is reduced to the more mobile
Fe(II) species; pH values also play an important role in iron speciation and
mobility. At low pH values, both Fe(II) and Fe(III) are stable and mobile in
solution, as pH increases from ~2-~8 the dissolved concentrations of Fe(III)
decreases as Fe(III) forms hydroxide complexes and ultimately precipitating iron
bearing mineral phases.
Manganese
Detected Range: 2.6 j µg/L – 166000 µg/L; Number of Detections/Total Samples:
106/109
Concentrations in 37 samples (21 shallow; 8 deep; 8 bedrock) exceeded the
PBTV.
Concentrations in 53 samples exceeded the 2L of 50 µg/L.
Manganese exceeds the PBTV and 2L in shallow and deep flow layer
groundwater beneath the ash basins. Exceedances were also found in
downgradient wells all flow layers. Six upgradient wells (3 shallow; 2
deep; 1 bedrock) exceeded both the PBTV and 2L, indicating natural
variability in manganese concentrations.
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. High manganese
concentrations are associated with silty soils, and sedimentary, unconsolidated,
or weathered lithologic unit and low concentrations are associated with non-
weathered igneous bedrock and soils with high hydraulic conductivity
(Gillespie, 2013), (Polizzoto, 2014). Manganese is most readily released to the
groundwater through the weathering of mafic or siliceous rocks (Gillespie, 2013).
When manganese-bearing minerals in saprolite, such as biotite, are exposed to
acidic weathering, the metal can be liberated from the host mineral and released
to groundwater. It then migrates 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
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oxidized by microorganisms present in soil, leading to the precipitation of
manganese minerals (ATSDR, 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).
Manganese is estimated to be the twelfth most abundant element in the crust
(0.100 weight percent, (Parker, 1967)). Manganese exhibits geochemical
properties similar to iron with Mn7+, Mn6+, Mn4+, Mn3+, Mn2+, and Mn1- oxidation
states. Manganese substitutes for iron in many minerals. Similar to iron,
manganese leaching from coal ash is limited to less than 10 percent of the total
manganese present due to the low pH required to solubilize manganese minerals
(Izquierdo & Querol, 2012). Despite the low apparent mobilization percentage,
manganese can be detected in relatively high concentrations in ash pore water.
A 2016 study associated with the NC Division of Water Resources and the NC
Geological Survey used laboratory, spectroscopic, and geospatial analyses to
demonstrate how natural pedogenetic (soil forming) and hydrogeochemical
processes couple to export manganese from the near-surface to fractured bedrock
aquifers with the Piedmont. The study determined that manganese-oxides
accumulate near the water table within the chemically weathering saprolite.
Hydrologic gradients provide a driving force for the downward mobility to the
fractured-bedrock (Gillespie, 2013).
Molybdenum
Detected Range: 0.11 j µg/L – 2950 µg/L; Number of Detections/Total Samples:
84/109
Concentrations in 23 samples (9 shallow; 14 bedrock) exceeded the PBTV.
Molybdenum exceeds the PBTV in ash pore water and shallow flow layer
groundwater beneath the ash basin. Molybdenum does not have a 2L or
IMAC.
Molybdenum exceeds the PBTV in six bedrock wells sampled during
September 2017. Two PBTV exceedances are upgradient of the inactive
ash basin and two are upgradient of the active ash basin. These
concentrations are greater than most concentrations detected in bedrock
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wells beneath or downgradient of the ash basins. This indicates natural
variability in molybdenum concentrations at the Site.
Molybdenum is a trace element that exists predominantly as Mo(IV) and Mo(VI).
As a free metal, it is silvery gray, although it does not occur in this form in
nature. It is mined for use in alloys. Molybdenum commonly forms oxyanions in
groundwater that are affected by redox and pH (Ayotte, Gronbert, & Apodaca,
2011). Molybdenum has been observed to leach less from coal cleaning rejects in
acidic than neutral conditions, unlike many other metals (Jones & Ruppert, 2017).
Molybdenum has been shown to become more mobile in procedures that use
deionized water as a leachant, which may be similar to actual disposal conditions
unlike many other coal ash elements that are more mobile when subjected to
weak acid (Jones & Ruppert, 2017).
Nickel
Reported Range: 0.46 j µg/L – 821 D3 µg/L; Number of Detections/Total Samples:
94/109
Concentrations in 13 samples (10 shallow; 2 deep; 1 bedrock) exceeded the
PBTV.
Concentrations in 1 sample exceeded the 2L of 100 µg/L.
The sample location that exceeded the 2L, GWA-06S, is located
downgradient of the inactive ash basin and adjacent to the coal pile.
Nickel, like chromium and cobalt, is a base metal that exhibits geochemical
properties similar to iron and manganese. It occurs as a divalent and trivalent
ion. Finkelman (1995) reported evidence that nickel occurs in association with
organic matter in coal. Goodarzi et al. (2008) found nickel in the oxide form in
both coal and ash. Kim and Kazonich (2004) report association of nickel with the
silicate (likely clay) fraction in coal. Solubility of nickel from ash is pH sensitive,
with mobilization greatest under highly acidic conditions (Izquierdo and Querol,
2012).
Radium
Reported Range: 0.17 j pCi/L – 2.465 pCi/L; Number of Detections/Total Samples:
57/57
One concentration within ash pore water exceeds the PBTV.
Concentrations in 13 samples (2 shallow, 11 deep) exceed the PBTV.
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Radium is a naturally occurring radioactive element (or radionuclide) that
generally is present at low levels in all soil, water, and rocks. It is derived from
the decay of the common and long-lived radioactive elements uranium and
thorium. Three commonly occurring isotopes of radium are radium-224, radium-
226, and radium-228 (abbreviated as Ra-224, Ra-226, and Ra-228, respectively).
Each radium isotope varies in abundance because each decays at a different rate
(known as a “half-life”) to a daughter product or progeny (a different element).
Radium-226 is the most abundant radium isotope in the environment, primarily
because of its long half-life (about 1622 years). Ra-228 has a half-life of slightly
less than 6 years, and Ra-224 has a very short half-life of less than 4 days (USGS,
2014).
Like all rocks and soils, raw coal contains naturally occurring radionuclides.
Average concentrations of uranium and thorium in raw coals are 0.3–2.0 pCi/g
238U and0.35 pCi/g 232Th, respectively. Concentrations of these radionuclides
in raw coal are comparable to those in the earth’s crust (USGS, 1997). The
average amount of uranium and thorium in the earth’s crust is estimated to be
0.76 pCi/g 238U and 1.1 pCi/g 232Th, respectively. As the ash content of the coal
increases, the enrichment factor decreases. For bituminous and subbituminous
coals with 10–15% ash, it is reported that total radium activities in the ash were
7–10 times greater than in the original feed coal (EPRI, 2016).
The USGS found three geochemical conditions were associated with elevated
concentrations of radium in groundwater. These include 1) low levels of
dissolved oxygen (dissolved oxygen less than 1 milligram per liter) acidic water
(pH less than 6), and water with high concentrations of dissolved solids
(especially calcium, barium, magnesium, strontium, potassium, sulfate, or
bicarbonate). These water conditions can prevent radium from adsorbing to
aquifer sediments and increase its solubility in groundwater (USGS, 2014).
The somewhat greater frequency of occurrence of radium in anoxic conditions is
the most important factor controlling radium in aquifers used for drinking water
supply in the United States. The occurrence pattern, whether in the Appalachian
crystalline-rock aquifers or in the larger setting of the continental United States,
reflects the critical role that sorption processes, specifically to iron (and
manganese) oxyhydroxides, play in controlling the concentration of radium in
dilute groundwaters (USGS, 2013).
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Water treatment by adsorption and water-softening techniques are thought to be
effective in reducing radium in untreated drinking water. Therefore, it is likely
that radium in water does not migrate significantly from the area where it is
released or generated. Limited field data also support the generalization that
radium is not mobile in groundwater (USEPA, 1990).
Radium (Total)
Detected Range: 0.083 pCi/L – 2.465 pCi/L
Concentrations in 8 samples (3 shallow; 10 deep) exceeded the PBTV.
No concentrations exceeded the Federal MCL of 5 pCi/L.
Selenium
Reported Range: 0.32 j µg/L – 765 D3 µg/L; Number of Detections/Total Samples:
28/109
Concentrations in 14 samples (8 shallow; 6 deep) exceeded the PBTV.
Concentrations in 2 samples exceeded the 2L of 20 µg/L. The first
exceedance occurs in the ash pore water within the active ash basin (AB-
20S). The second exceedance occurs in GWA-06S, which is located
downgradient of the inactive ash basin and adjacent to the coal pile.
Historical analytical results for selenium have been called into question as
an improper analytical procedure was being used. Future analysis will
use the proper procedure and analytical results will provide more
accurate representation of selenium concentrations in groundwater.
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, 2008).
Groundwater containing selenium is typically the result of either natural
processes or industrial operations. Naturally, selenium’s presence in
groundwater is from leaching out of selenium-bearing rocks. It is most common
in shale ranging from 0.6 to 103 mg/kg. Anthropogenically, selenium is released
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as a function of the discharge from petroleum and metal refineries and from ore
mining and processing facilities. Ore mining may enhance the natural erosive
process by loosening soil, creating concentrations in erodible tailings piles, and
exposing selenium-bearing rock to runoff (Martens, 2002) (USEPA, 2017c).
In a statistical summary of groundwater quality in North Carolina, the
Superfund Research Program at UNC analyzed 399 private well water samples
in Stokes and Rockingham counties from 1998-2010. The values ranged from 2.5
to 26 µg/L, and no samples exceeded the 50 µg/L primary MCL for selenium
(NCDHHS, 2010). The mean concentration in both counties was 2.7 µg/L.
Selenium in the subsurface is primarily controlled by pH, redox potential (Eh),
and competition with other anions. Selenium can exist in the +6, +4, 0, and -2
oxidations states. Selenium exists as oxyanionic species under oxidizing
conditions as the +4 species, selenite (SeO32-) or the +6 species, selenate (SeO42-).
Similar to arsenic’s behavior, both selenite and selenate sorb to mineral surfaces
(primarily iron oxides) (EPA, 2007), (Strawn, Doner, Zavarin, & McHugo, 2002),
(Zawislandski & Zavarin, 1996)). It is important to note that while sorption to
iron oxides is an important sink for selenium in groundwater, changes in pH and
redox conditions could result in the dissolution of the host iron oxide and
mobilize sorbed selenium into groundwater. The oxidation of selenium from +4
(selenite) to the +6 (selenate) oxidation state could influence mobility, however
both are subject to competition from other oxyanions such as phosphate and
sulfate. Selenium is also readily reduced to zero valent Se0 (oxidation state of 0)
which is relatively stable (i.e., mobile) under mildly reducing conditions. At
increasingly reducing conditions, the formation of reduced -2 selenium species
can occur and can impact other metal ion concentrations such as through the
precipitation of CoSe(s).
Strontium
Detected Range: 3.9 j µg/L – 3490 µg/L; Number of Detections/Total Samples:
109/109
Concentrations in 49 samples (20 shallow; 21 deep; 8 bedrock) exceeded
the PBTV. Exceedances occur upgradient, sidegradient, within the ash
basins, and downgradient in all flow layers, indicating natural variability
in strontium concentrations at the Site. Strontium does not have a 2L or
IMAC.
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Strontium exceeds the PBTV in surficial, transition zone, and bedrock
groundwater beneath the ash basin.
Strontium is a soft silver-yellow alkaline earth metal. It is highly chemically
reactive and forms a dark oxide layer when it interacts with air. It is chemically
similar to Ca and replaces Ca or K in igneous rocks in minor amounts. Strontium
is generally present in low concentrations in surface waters but may exist in
higher concentrations in some groundwater (Hem, 1985).
Strontium is present as a minor coal and coal ash constituent. Strontium has been
observed to leach from coal cleaning rejects more in neutral conditions than
acidic, unlike many other metals (Jones & Ruppert, 2017). It has been shown to
behave conservatively in surface waters downstream of coal plants (Ruhl, et al.,
2012).
Sulfate
Detected Range: 0.54 j mg/L – 1790 mg/L; Number of Detections/Total Samples:
104/109
Concentrations in 57 samples (32 shallow; 14 deep; 11 bedrock) exceeded
the PBTV. Exceedances occur upgradient, downgradient, sidegradient,
within the ash basins, and in all flow layers, indicating natural variability
of sulfate in groundwater at the Site.
Concentrations in 3 samples exceeded the 2L of 250 mg/L. 2L exceedances
occur within the ash basin and downgradient in the shallow and deep
flow layers.
Sulfate is a naturally occurring substance found in minerals, soil, and rocks. It is
present in ambient air, groundwater, plants, and food. Primary natural sources
of sulfate include atmospheric deposition, sulfate mineral dissolution, and
sulfide mineral oxidation. 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). Anthropogenic sources include
coal mines, power plants, phosphate refineries, and metallurgical refineries.
Sulfate has a Secondary Maximum Contaminant Level (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). However,
adults generally become accustomed to high sulfate concentrations after a few
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days. It is estimated that about 3 percent of the public drinking water systems in
the United States may have sulfate concentrations of 250 mg/L or greater (Miao,
Brusseau, Carroll, & others, 2012). Sulfate is on the list of enforced regulated
contaminates that may cause cosmetic effects or aesthetic effects in drinking
water (USEPA, 2017a).
TDS
Detected Range: 36 D6 mg/L – 2670 mg/L; Number of Detections/Total Samples:
102/109
Concentrations in 41 samples (16 shallow; 18 deep; 7 bedrock) exceeded
the PBTV.
Concentrations in 6 samples exceeded the 2L of 500 mg/L.
TDS exceeds the 2L in shallow groundwater beneath the ash basin and in
GWA-06DA. GWA-06DA is located in a cluster with GWA-06S. These
wells are located adjacent to the coal pile and downgradient of the
inactive ash basin.
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
dissolved cation and anion particles (e.g., calcium, chlorides, nitrate, phosphorus,
iron, sulfur, and others) in varying concentrations. TDS is measured by weighing
the solid residue left after evaporating a measured volume of sample to dryness
(Freeze & Cherry, 1979). 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. The ions listed below are referred to as the major
ions as they make up more than 90 percent of the TDS in groundwater.
Sodium (Na+)
Magnesium (Mg2+)
Calcium (Ca2+)
Chloride (Cl-)
Bicarbonate (HCO3-)
Sulfate (SO4 2-)
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Minor ions in groundwater include: boron, nitrate, carbonate, potassium,
fluoride, strontium, and iron. 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 in water supplies originate from natural sources, sewage, urban and
agricultural run-off, and industrial wastewater. Salts used for road de-icing can
also contribute to the TDS loading of water supplies.
Reliable data on possible health effects associated with the ingestion of TDS in
drinking water are not available (WHO, 1996). TDS is on the list of “National
Secondary Drinking Water Regulations” which are non-enforced regulated
contaminates that may cause cosmetic effects or aesthetic effects in drinking
water (USEPA, 2017b).
Thallium
Reported Range: 0.016 j µg/L – 1.5 D3,B µg/L; Number of Detections/Total
Samples: 42/109
Concentrations in 8 samples (shallow) exceeded the PBTV.
Concentrations in 2 samples exceeded the IMAC of 0.2 µg/L. One
exceedance is attributed to ash pore water. The second exceedance occurs
in GWA-06S, located adjacent to the coal pile.
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 (Institute, 2008c).
Traces of thallium naturally exist in rock and soil. As rock and soil is eroded,
small amounts of thallium end up 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 range from <0.1 mg/kg to 8.8 mg/kg. Thallium is
compared to an IMAC since no 2L Standard has been established for this
constituent.
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In a study by the Georgia Environmental Protection Division 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 (MRL)=1 µg/L) (Donahue & Kibler, 2007).
Vanadium
Detected Range: 0.12 j µg/L – 35.2 µg/L; Number of Detections/Total Samples:
105/109
Concentrations in 20 samples (8 shallow; 10 deep; 2 bedrock) exceeded the
PBTV.
Concentrations in 102 samples exceeded the IMAC of 0.3 µg/L.
Vanadium exceeds the PBTV in groundwater in the shallow and deep
flow layers beneath the ash basins. Bedrock exceedances of the PBTV are
limited to upgradient wells, indicating natural variability in vanadium
concentrations at the Site.
Vanadium is estimated to be the 22nd most abundant element in the crust (0.011
weight percent, (Parker, 1967). Vanadium occurs in four oxidation states (V5+,
V4+, V3+, and V2+). It is a common trace element in both clay minerals and plant
material.
The National Uranium Resource Evaluation (NURE) program was initiated by
the Atomic Energy Commission in 1973 with a primary goal of identifying
uranium resources in the United States (Smith S. M., 2016). The
Hydrogeochemical and Stream Sediment Reconnaissance program (initiated in
1975) was one component of NURE. Planned systematic sampling of the entire
United States began in 1976 under the responsibility of four Department of
Energy national laboratories. Samples were collected from 5,178 wells across
North Carolina. Of these, the concentration of vanadium was equal to or higher
that the former IMAC of 0.0003 mg/L in 1,388 well samples (27 percent).
Uranium (Total)
Detected Range: 0.000072 j µg/mL – 0.0387 µg/mL ; Number of Detections/Total
Samples: 30/53
Concentrations in 8 samples (5 shallow; 3 deep; 4 bedrock) exceeded the
PBTV.
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A concentration in 1 sample exceeded the Federal MCL of 0.03 µg/mL and
was detected in ash pore water.
Uranium is a naturally occurring element that can be found in low levels within
all rock, soil, and water. Uranium is the 51st element in order of abundance in the
Earth's crust. Uranium is also the highest-numbered element to be found
naturally in significant quantities on Earth and is almost always found combined
with other elements. The decay of uranium, thorium, and potassium-40 in the
Earth's mantle is thought to be the main source of heat that keeps the outer core
liquid and drives mantle convection, which in turn drives plate tectonics.
Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and
it is about as abundant as arsenic or molybdenum. Uranium is found in
hundreds of minerals, including uraninite (the most common uranium ore),
carnotite, autunite, uranophane, tobernite, and coffinite. Significant
concentrations of uranium occur in some substances such as phosphate rock
deposits, and minerals such as lignite, and monazite sands in uranium-rich ores.
pH
Detected Range: 3.6 – 12.3 S.U.
Concentrations in 27 samples (5 shallow; 11 deep; 11 bedrock) exceeded
the PBTV maximum.
Concentrations in 19 samples exceeded the 2L maximum of 8.6 S.U.
Of the 19 exceedances of the 2L maximum, 11 sample locations are located
within an ash basin.
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 a 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, 2017b).
11.2 Pending Investigation(s)
Additional vertical extent monitoring wells are being evaluated for potential installation
at the GWA-5 and AB-22 well cluster locations. These wells would be installed at
depths greater than the deepest existing monitoring wells at these locations to evaluate
the vertical extent of CCR-derived constituents, primarily boron, in these areas and to
evaluate the effectiveness of corrective measures. Additional monitoring wells may
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also be installed in shallow groundwater beneath the basins to evaluate the
effectiveness of corrective measures.
In accordance with 15A NCAC 02L.0106( k)(5) and (l)(6), the CAP may include an
evaluation of whether groundwater migrating downgradient of the ash basin may have
contaminant concentrations that would result in violations of standards for surface
water. One means of accomplishing this objective is to collect surface water samples to
document existing conditions. Another method will be to conduct groundwater to
surface water modeling. It is anticipated that documenting current conditions through
the collection of the additional surface water samples will be coordinated with NCDEQ
guidance.
Assessment of the coal pile area is also pending to evaluate the horizontal and vertical
extent of constituents potentially derived from the coal pile. Preliminary plans for that
investigation include installation of approximately six well clusters at locations
surrounding the coal pile as shown on Figure 11-158. A coal pile assessment work plan
was submitted to NCDEQ for review on January 16, 2018. Wells are planned for
installation within the shallow and deep monitoring zones. Soil samples are planned
for each well location. Several periodic groundwater sampling events are planned from
the planned wells.
Additionally, water levels in select wells listed on Table 11-2 and shown on Figures 6-7
to 6-12 in the vicinity of the northern portion of the inactive basin and coal pile are
being monitored by transducers to evaluate the water level change from dewatering
being performed as part of a coal pile holding basin construction project. The coal pile
holding basin is being constructed within the eastern portion of the historical coal pile
footprint as shown on Figure 2-1. Groundwater sampling is planned for the wells listed
on Table 11-2 surrounding the area to be dewatered to evaluate potential constituent
concentration trends during and after groundwater extraction. Data from that
monitoring may be useful determine the groundwater response and radius of influence
groundwater extraction may have upon each flow zone. This information may be used
to supplement the coal pile assessment results and remedial alternative evaluation.
Finally, supplemental data collection to support groundwater modeling and long-term
monitoring is anticipated to support the CAP process. Additional data for metal oxy-
hydroxide phases of iron (HFO) and aluminum (HAO) are needed to support
geochemical modeling conducted as part of the CAP. A solid phase-groundwater
interactions data map was completed to indicate where solid and aqueous phase data
exist and where additional samples should be collected to address data needs for the
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updated geochemical model (Figure 11-159). Data distribution and results of
information related to soil/groundwater/COI interaction is presented on Figure 11-159.
Additional HFO samples are proposed to be collected for the following locations within
the screened interval (* indicates an ash pore water well):
Ash Storage Area/ Coal Pile Transect
AB-39S*, AB-39D, GWA-6S, GWA-6DA, GWA-6BRA, GWA-7S, and GWA-7D
Inactive Ash Basin Transect
AB-35BR, AB-34D, AB-32S, AB-32D, GWA-5S, GWA-5D, and GWA-5BRA
Active Ash Basin North Transect
AB-24S*, AB-24D, AB-24BR, AB-26S, AB-26D, GWA-3S, and GWA-3BRA
Active Ash Basin South Transect
AB-10S, AB-10D, AB-21SL*, AB-21D, AB-21BR, AB-21BRL, AB-22S, AB-22D, AB-
22BR, and AB-22BRL

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RISK ASSESSMENT 12.0
A baseline human health and ecological risk assessment was performed as a component
of CAP Part 2 (HDR 2016) and is included in Appendix J. For the purpose of aiding
corrective action decisions, the 2016 risk assessment characterized potential risks to
humans and wildlife exposed to coal ash constituents present in the environment.
Implementation of corrective action is intended to achieve future Site conditions
protective of human health and the environment, as required by CAMA.
This update to the risk assessment evaluates groundwater and surface water results
collected since the 2016 risk assessment (December 2015 to September 2017) in order to
confirm or update risk conclusions in support of remedial action. Data used in the 2016
risk assessment included groundwater samples from March 2011 through November
2015, surface water samples from August 27, 2014, through October 13, 2015, and AOW
soil and sediment samples collected on May 12 and May 13, 2015. This risk assessment
update uses sample data presented in Attachment A of the 2016 risk assessment (HDR
2016) along with groundwater and surface water data presented in Appendix B of this
report. As previously noted, AOW locations are outside the scope of this risk
assessment because AOWs, wastewater, and wastewater conveyances (effluent
channels) are evaluated and governed wholly separate in accordance with the NPDES
Program administered by NCDEQ DWR. This process, an effort parallel to the CSA, is
ongoing and subject to change. No new sediment or soil samples, other than for
background evaluations, have been collected that are applicable to the risk assessment;
therefore, risk estimates associated with those media have not been re-evaluated.
As part of the 2016 risk assessment, human health and ecological conceptual site models
(CSMs) were developed to guide identification of exposure pathways, exposure routes,
and potential receptors for evaluation in the risk assessment. The CSMs (CAP, Part 2;
Figures 2-3 and 2-4) describe the sources and potential migration pathways through
which groundwater beneath the ash basins may have transported coal ash-derived
constituents to other environmental media (receiving media) and, in turn, to potential
human and ecological receptors. Exposure scenarios and exposure areas were
presented in detail in the 2016 CAP, Part 2 risk assessment.
This risk assessment update included the following:
Identification of maximum constituent concentrations for groundwater and
surface water
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Inclusion of new groundwater and surface water data to derive overall average
constituent concentrations for exposure areas
Comparison of new maximum constituent concentrations to the risk assessment
human health and ecological screening values (ESVs)
Comparison of new maximum constituent concentrations to human health Risk-
Based Concentrations (RBC)
Incorporation of new maximum constituent concentrations into wildlife Average
Daily Dose calculations for comparison to ecological Toxicity Reference Values
(TRVs)
Evaluation of new groundwater and surface water data and the influence on the 2016
risk assessment conclusions are summarized below by exposure areas (Figures 12-1 and
12-2) at the Allen Plant.
Human Health Screening Summary 12.1
On-site Groundwater
Groundwater samples collected from 76 locations across the Site were used in the 2016
human health assessment (Figure 12-1). Samples from those locations were evaluated
because they represent the potential worker exposure area. No potential risks to
humans exposed to groundwater from the Site were identified in the 2016 assessment.
Groundwater analytical results are included in Appendix B, Table 1. Groundwater data
collected since the 2016 risk assessment were compared to USEPA’s human health
regional screening levels and risk-based concentrations (RBCs) from the 2016 risk
assessment. Inclusion of new data resulted in maximum concentrations greater than
the data presented in the 2016 assessment for several constituents (Appendix B, Table
1). The new maximum concentrations were less than their respective RBC for all
constituents. No evidence of potential unacceptable risk to receptors from exposure to
site groundwater were identified.
On-site Surface Water
Surface water samples were collected from three locations on-site (SW-05, SW-06, and
SW-07) during the 2016 risk assessment. Sample location SW-05 was collected from a
ditch west of the active ash basin, where water is typically stagnant. Because SW-05 is
not associated with a named water body, data for this sample location are not included
as part of this risk evaluation. SW-06 and SW-07 were collected from Lake
Wylie/Catawba River adjacent to the shore. These locations are considered on-site due
to their proximity to the property boundary and would likely not be indicative of
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concentrations further from the shore. Data for the on-site surface water sample
locations are included in Appendix B, Table 2.
The 2016 risk assessment found no evidence of unacceptable risk to humans exposed to
on-site surface water. The 2016 on-site surface water dataset included the AOW
samples that are outside the scope of this assessment which focused on exposure to
surface water bodies. Analytical results from sample locations SW-06, SW-07, and SW-
D1 in Lake Wylie/Catawba River (Figure 2-8) were evaluated as part of this assessment.
Surface water data collected since the 2016 risk assessment were compared to USEPA’s
human health RSLs and RBCs established for the most conservative exposure
scenario/receptor from the 2016 risk assessment. The new maximum concentrations in
surface water were less than their respective RBCs for all constituents.
No evidence of potential unacceptable risk to humans exposed to on-site surface water
was identified.
Off-site Surface Water
Off-site surface water samples that would accurately represent off-site water quality
and drinking water supply exposure were not collected from Lake Wylie/Catawba
River for the CAMA-related investigations. Off-site exposures were evaluated in the
2016 risk assessment using on-site surface water sample data (SW-05, SW-06, and SW-
07). This conservative approach was taken to provide an upper-bound estimate of
potential surface water concentrations. The 2016 risk assessment resulted in hazard
indexes (His) greater than 1 for cobalt for hypothetical recreational (HI=1.9) and
subsistence fisher (HI=55) scenarios. The EPC for cobalt used to derive the hazard
quotient was based on the maximum concentration at SW-05, located west of the active
ash basin. Because SW-05 is not associated with a named water body, data for this
sample location are not included as part of this risk evaluation. Use of on-site surface
water data as a surrogate for exposure and the use of conservative exposure
assumptions likely overestimate risk.
On-site surface water data from locations SW-06, SW-07 and SW-D1, collected in 2016-
2017 were used as a surrogate to evaluate off-site exposure scenarios. Surface water
data were compared with USEPA’s human health RSLs and RBCs established for the
most conservative off-site exposure scenario/receptor from the 2016 risk assessment.
The constituents with maximum concentrations in recent surface water data were less
than their respective RBCs for all constituents measured. With the exclusion of SW-05,
all cobalt concentrations in surface water samples are less than the surface water
screening value of 1 µg/L.
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No evidence of risks to humans exposed to off-site surface water was identified.
Ecological Screening Summary 12.2
The 2016 risk assessment included evaluation of potential ecological risk by exposure
area. Four exposure areas were established as presented on Figure 12-1 and include the
following:
Ecological Exposure Area 1, located between the ash basins and Lake
Wylie/Catawba River along the shoreline
Ecological Exposure Area 2, located west of the steam station
Ecological Exposure Area 3, located south of the active ash basin
Ecological Exposure Area 4, located west of the active ash basin
The 2016 ecological risk assessment included both surface water and AOW water in the
evaluation. The 2016 assessment resulted in no evidence of potential unacceptable
ecological risk for birds and mammals in all four Exposure Areas. Exposure Area 1 is
the only area with additional surface water samples collected since the 2016 assessment.
Area 1 Surface Water
Surface water samples were collected from two locations in exposure area 1 (SW-06 and
SW-07) during the 2016 risk assessment. The 2016 on-site surface water dataset
included the AOW samples, which are outside the scope of this updated assessment.
Results of on-site surface water samples are included in Appendix B, Table 2.
Analytical results from sample locations SW-06, SW-07, and SW-D1 (Figure 2-8) were
evaluated as part of this assessment. Surface water data collected since the 2016 risk
assessment were compared with the maximum detected concentrations in the 2016
assessment, along with ecological screening values (ESVs) and toxicity reference values
(TRVs). Cadmium was detected in a single sample collected from SW-07 (May 6, 2016)
at a concentration (0.18 µg/L) greater than the ESV (0.16 µg/L). Cadmium was not
detected in previous samples collected from this sample location or in two samples
collected in September 2017 from this location. Cadmium was not detected in the
surface water samples; therefore cadmium passed the initial screening phase of the 2016
risk assessment. Cadmium is not a constituent of concern for the ecological risk
assessment.
No potential unacceptable risks to wildlife exposed to surface water in Lake
Wylie/Catawba River were identified.
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Private Well Receptor Assessment Update 12.3
An independent study was conducted that evaluated 2015 groundwater data collected
by NCDEQ from approximately 120 private drinking water wells within close
proximity of the Allen Steam Station (CAP 2, Section 5.6; Haley & Aldrich, 2015).
Private well groundwater datasets evaluated in the study included:
Data collected by NCDEQ within a half-mile of the Duke Energy facility
properties where ash basins are located
Data collected by NCDEQ from areas identified as background locations
Data collected from locations within 2 to 10 miles of each Duke Energy facility in
North Carolina that manages or has managed coal ash on-site
The objectives of the study were to provide a review of private well data collected by
NCDEQ with respect to regulatory and risk-based screening levels and to review
background concentrations of constituents in groundwater in the vicinity of Duke
Energy facilities. A detailed summary of observations presented in the study was
included in the CAP 2 Risk Assessment which is included as Appendix J to this report.
The Haley & Aldrich report concluded that the constituents detected in the private
wells sampled by NCDEQ were consistent with background conditions and did not
indicate impact from constituents derived from coal ash.
Results from off-site water supply well samples collected in 2015 were compared to a
range of PBTVs (shallow and deep flow zones) recently developed for the Site.
Strontium was detected at concentrations greater than the range of PBTVs (200-286
µg/L) but below the North Carolina DHHS Screening Level and federal tap water RSL.
One private well sample had a detected concentration of magnesium greater than the
PBTV range of 4.58 µg/L to 5.61 µg/L. Magnesium, though, does not have a published
2L or a reported screening level used for comparison. Cobalt was detected above its
IMAC at one location but below the PBTV range. Of nine samples with iron
concentrations greater than the 2L, three were detected at concentrations greater than
the PBTV range of 555 µg/L to 834 µg/L. Zinc was detected in two samples at a
concentration greater than the 2L, with one sample greater than the PBTV range.
Vanadium was detected at concentrations greater than its IMAC and PBTV range.
Concentrations of vanadium and zinc were less than the federal tap water RSL. Private
wells at the Allen Site are located upgradient from the ash basins.
As discussed in Section 4, in January 2018, Duke Energy provided SynTerra with
additional water supply well data from samples collected in 2016 and 2017 (Appendix
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B, Table 1). Preliminary review of that data indicates results are generally consistent
with previous sample results.
Risk Assessment Update Summary 12.4
There is no evidence of unacceptable risks to humans and wildlife at Allen attributed to
CCR constituent migration in groundwater from the ash basins. The only evidence of
potential unacceptable human related risks estimated in the 2016 risk assessment was
under the hypothetical subsistence fisherman scenario due to concentrations of cobalt in
fish tissue. This risk assessment update supports that the fisher risks were
overestimated based on conservative exposure and modeled fish tissue uptake
assumptions, supporting a risk classification of “Low” based upon groundwater related
considerations.

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GROUNDWATER MODELING RESULTS 13.0
The Site-specific groundwater flow and transport models and the Site-specific
geochemical models are currently being updated for use in the CAP. Groundwater
flow, transport, and geochemical models simulate movement of COIs through the
subsurface to support the evaluation and design of remedial options at the Site. The
existing data inventory requested in Section 4.3 of “Monitored Natural Attenuation For
Inorganic Contaminants in Groundwater: Guidance for Developing Corrective Action Plans
Pursuant to NCAC 15A.0106(l)” (Appendix A) is summarized in Table 11-1. The models
will provide insights into:
COI mobility: Geochemical processes that affect chemical precipitation,
adsorption, and desorption onto solids will be simulated based on lab data and
thermodynamic principles. That simulation will support the prediction and
mobility in groundwater.
COI movement: Simulations of the groundwater flow system will be combined
with estimates of source concentrations, sorption, effective porosity, and
dispersion. That combination will support the prediction of the paths, extent, and
rates of constituent movement at the field scale.
Scenario Screening: The flow, transport, and geochemical models will be
adjusted to simulate how various ash basin closure design options and
groundwater remedial technologies will affect the short-term and long-term
distribution of COIs.
Design: Model predictions will be used to help design basin closure and
groundwater corrective action strategies in order to achieve compliance with 2L.
The groundwater flow model linked with the transport model will be used to establish
transport predictions that best represent observed conditions at the Site particularly for
the constituents, such as boron, that are negligibly affected by geochemical processes.
Information from the geochemical model will provide insight into the complex
processes that influence constituent mobility. Once the flow, transport, and geochemical
models for the Site accurately reproduce observed Site conditions, they will be used as
predictive tools to evaluate the conditions that would result from various remedial
options for basin closure.
The updated CAP will further discuss the purpose and scope of both the groundwater
and geochemical models. The CAP will detail model development, calibration,
assumptions, and limitations. The CAP will also include a detailed remedial option
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evaluation, based on observed conditions and the results of predictive modeling. The
evaluation of the potential remedial options will include comparisons of predictive
model results for long-term source concentration and plume migration trends toward
potential receptors. The model predictions will be used in combination with other
evaluation criteria to develop the optimal approach for basin closure and groundwater
remediation.
The following subsections provide a brief summary of modeling efforts completed to
date at Allen and present a description of the updated models to be submitted in the
updated CAP.
13.1 Summary of Flow and Transport Modelling Results
CAP Part 1 Model
The initial groundwater flow and transport models were developed by HDR, Inc. in
conjunction with University of North Carolina at Charlotte (UNCC) to gain an
understanding of COI migration after closure of the ash basins. The initial groundwater
model in the CAP Part 1 (HDR, 2015) included a calibrated steady-state flow model of
July 2015 conditions; a calibrated historical transient model of constituent transport to
match June/July 2015 conditions; and three potential basin closure scenarios. Those
basin closure simulation scenarios included:
No change in Site conditions (basin remains open, as is)
Cap-in-place (with existing ash configuration)
Ash removal (excavation of ash)
The initial model presented in the CAP Part 1 used antimony, arsenic, barium, boron,
chromium, hexavalent chromium, cobalt, selenium, sulfate, and vanadium as primary
modeling constituents. In addition, the remedial alternative evaluation simulations
were run to a total time of 100 years.
CAP Part 2 Model
The revised model in the CAP Part 2 (HDR, 2016) included a calibrated steady-state
flow model of July 2015 conditions and a calibrated historical transient model of
constituent transport to June/July 2015 conditions. In addition, CSA data was used to
refine the hydraulic conductivity values and recharge rates within the model. Bedrock
hydrostratigraphic layers were extended vertically downward to correlate to the
deepest reported off-Site private water supply well. The initial model did not include
any offsite wells since the domain was too small, however supply wells were added to
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the updated model, although the model only included approximately 50 of
approximately 185 wells within the pre-2017 compliance boundary. The revised model
also used antimony, arsenic, barium, boron, chromium, hexavalent chromium, cobalt,
selenium, sulfate, and vanadium as primary modeling constituents.
Two potential basin closure scenarios were considered in the revised model. Those
basin closure simulation scenarios included:
No change in Site conditions (basin remains open, as is)
Cap-in-place
Appendix B of the CAP Part 2 (HDR, February 19, 2016a) contains the report describing
the development and results from this modeling.
Updated CAP Model
The flow and transport model is currently being updated as a part of the updated CAP
and will include: development of a calibrated steady-state flow model that includes
data available through the fourth quarter of 2017; development of a historical transient
model of constituent transport; water supply wells within the 0.5-mile radius
(approximately 185 wells); and predictive simulations of basin closure plus
groundwater corrective action scenarios. The updated flow and transport model will
consider boron and additional COIs that are negligibly affected by geochemical
processes. Predictive remedial scenarios will have simulation times that will continue
until modeled COIs concentrations are below the 2L standard at the compliance
boundary.
The distribution of recharge, location of drains, and distribution of material will be
modified to represent the following different basin closure options in the
revised/updated models:
Complete Excavation with passive remediation
Complete Excavation with active remediation
Cap-in-place with passive remediation (MNA)
Cap-in-place with active remediation
The results of these simulations will be included as part of the updated CAP submittal.
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13.2 Summary of Geochemical Model Results
The Allen Steam Station geochemical model investigates how variations in geochemical
parameters affect movement of constituents through the subsurface. The geochemical
SCM will be updated as additional data and information associated with Site
constituents, conditions, or processes are developed, and will be updated based on
discussions and comments from NCDEQ. The geochemical modeling approach
presented in the following subsections was developed using laboratory analytical
procedures and computer simulations to understand the geochemical conditions and
controls on groundwater concentrations in order to predict how remedial action and/or
natural attenuation may occur at the Site and avoid unwanted side effects. The updated
geochemical model will be presented in the updated CAP.
CAP Part 2 Geochemical Model
The geochemical model presented in the CAP Part 2 (HDR, February 19, 2016a)
included:
Eh-pH (Pourbaix) diagrams showing potential stable chemical phases of the
aqueous electrochemical system, calibrated to encompass pH and redox
potentials at the Site
Sorption model in which the aqueous and surface speciation of constituents was
modeled using the USGS geochemical modeling program PHREEQC
Simulations of the anticipated geochemical speciation that would occur for each
COI in the presence of adsorption to soils and in response to changes in Eh and
pH
Attenuation calculations in which the potential capacity of aquifer solids to
sequester constituents of interest were estimated
Details on the development and results of the CAP Part 2 geochemical model are
presented in Appendix C of the CAP Part 2 (HDR, February 19, 2016a). The
groundwater, geochemical, and surface water models from the CAP Part 2 are
presented in Appendix I.
Updated Geochemical Model Development
The geochemical model in the updated CAP will contain refinements based on updated
data and on comments and discussions with NCDEQ.
The updated geochemical modeling will use hydraulically significant flow transects to
investigate the geochemical controls on groundwater concentrations in and around
source areas at the Site for selected constituents (Figure 11-159). The model will
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compare trends in the concentrations of each COI along transects with the model output
to verify that the conceptual and qualitative models can predict COI behavior. Then the
model will be used to evaluate the potential impacts of remediation activities. The
model will relate the COI concentrations observed in groundwater along flow transects
to key geochemical parameters influencing constituent mobility (i.e., Eh, pH, and
saturation/solubility controls).
The hydraulically significant flow transects that will be used in the geochemical model
were described in Section 11.1. These flow transects were determined by considering:
Associated source areas
Plume movement focusing on the centerline of the area(s) of impact (i.e., the
plume(s))
Geologically derived flow zones (geozones)
Hydraulic gradients
Downgradient receptors
Available data
The updated geochemical model will develop parameters for each aquifer or geozone
by considering the bulk densities, porosities, and hydraulic gradients used in the fate
and transport model. These parameters are used to constrain the sorption site
concentrations in the model input and will be incorporated in the 1-D ADVECTION
model to accompany the capacity simulations. The objective of these capacity
simulations is to determine the mass balance on iron and aluminum sorption sites when
simulating flow through a fixed region. Groundwater concentrations and initial solid
phase iron and aluminum concentrations will be fixed based on Site-specific data. Thus,
the model will be able to simulate the stability of the HFO and HAO phases assumed to
control constituent sorption.
The updated geochemical model report will include a Site-specific discussion of:
The model description
The purpose of the geochemical model
Modeling results compared with observed conditions
COI sensitivity to pH, Eh, and iron/aluminum oxide content
Model limitations
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The updated geochemical modeling will also present multiple methods of determining
constituent mobility at the Site. Aqueous speciation, surface complexation, and
solubility controls will be presented in the revised report. These processes will be
modeled using:
Pourbaix diagrams created with the Geochemist Workbench v10 software using
Site-specific minimum and maximum constituent concentrations
PHREEQC’s combined aqueous speciation and surface complexation model and
the 1-D ADVECTION function to gain a comprehensive understanding of
current geochemical controls on the system and evaluate how potential changes
in the geochemical system might affect constituent mobility in the future
Data Inventory
To appropriately characterize and model the geochemical behavior of constituents in
the subsurface requires a significant amount of data collection and analysis. In addition
to hydraulic controls and groundwater data, it is important to properly evaluate the
physical and chemical properties of the solid phase aquifer material in contact with
groundwater.
In preparation for the updated geochemical model to be presented with the CAP, a data
inventory was conducted to determine where additional data needs exist (Table 11-1).
As part of the data inventory, a solid phase-groundwater interactions data map (Figure
11-159) was completed to indicate where solid and aqueous phase data exist and where
additional samples should be collected to address data needs for the updated
geochemical model.
Data distribution and results of information related to soil/groundwater/COI interaction
is presented on Figure 11-159. This data map includes the following:
Boron plume within the shallow aquifer (boron is used as a proxy for the general
area of impact)
Geochemical flow transects
Soil-water pairs (i.e., where solid phase total metals analysis are available within
a screened interval of a well)
Currently available data and locations for HFO/HAO, Kd (Table 13-1), and
hydraulic conductivity (k) values
Proposed locations for additional HFO/HAO samples to be used in the updated
geochemical model as described in Section 11.1.1 and 11.2
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SITE ASSESSMENT RESULTS 14.0
A site conceptual model is an interpretation of processes and characteristics associated
with hydrogeologic conditions and constituent interactions. The site assessment results
in this section provide information for evaluating the distribution of constituents with
regard to Site-specific geological/hydrogeological properties within the SCM.
14.1 Nature and Extent of Contamination
The site assessment described in the CSA presents the results of investigations required
by CAMA and 2L regulations. Ash sluice water and ash in the basins was determined
to be a source of impact to groundwater. The site assessment investigated Site
hydrogeology, determined the direction of groundwater flow from the ash basins, and
determined the horizontal and vertical extent of impacts to groundwater and soil
sufficient to proceed with preparation of a CAP.
Constituents of Interest
COIs in groundwater identified as being associated with the Allen ash basins include
antimony, arsenic, beryllium, boron, cadmium, chromium, hexavalent chromium,
cobalt, iron, manganese, molybdenum, pH, selenium, strontium, sulfate, TDS, thallium,
and vanadium. Hexavalent chromium is evaluated as a COI at NCDEQ direction.
Some COIs are only routinely detected at concentrations greater than the 2L/IMAC or
PBTVs at specific areas of the Site. COIs arsenic, beryllium, cadmium, nickel, selenium,
sulfate, thallium, TDS and zinc are routinely detected at concentrations greater than
2L/IMAC and PBTVs at the GWA-6 location (between the inactive basin and coal pile).
Antimony is only routinely detected at concentrations greater than the IMAC at well
AB-33D, located beneath the inactive ash basin. Hexavalent chromium is routinely
detected at concentrations greater than the 2L (for total chromium) at AB-6, located east
of the active ash basin.
Hydrogeologic Conditions
Site hydrogeologic conditions were evaluated by installing and sampling groundwater
monitoring wells and piezometers; conducting in-situ hydraulic tests; sampling soil for
physical and chemical testing; and sampling surface water, AOW, and sediment
samples. Monitoring wells were completed in each hydrostratigraphic unit.
The groundwater flow system stores groundwater and provides a means for
groundwater movement. The effective porosity of the regolith is largely controlled by
pore space (primary porosity); whereas, in bedrock, the effective porosity is largely
secondary and controlled by the number, size, and interconnection of fractures. The
nature of groundwater flow across the Site is based on the character and configuration
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of the ash basins relative to specific Site features such as manmade and natural drainage
features, engineered drains, streams, and lakes; hydraulic boundary conditions; and
subsurface media properties.
Four hydrostratigraphic units were identified at the Site and were evaluated during the
CSA. A detailed description of each unit is provided in Section 6.2.2.
Ash – The ash pore water unit consists of saturated ash material.
Shallow/Surficial – The shallow/surficial unit consists of soil, saprolite, and
alluvial material that overlie the transition zone with bedrock. The shallow zone
is primarily saprolite and comprised of fine-grained materials like silt and clay.
Compared to the underlying transition/deep zone, the shallow zone is relatively
thick. An unsaturated vadose zone is present in the upper portions of the
shallow zone; otherwise, the shallow zone is saturated and extends continuously
across the Site, including areas beneath the ash basins.
Deep/Transition Zone – The transition zone flow unit lies directly above
competent bedrock and is a zone of partially weathered bedrock.
Fractured Bedrock – Fractures within competent bedrock. Most fracture zones
were found within 50 feet to 75 feet of the top of competent bedrock.
An elongated topographic high runs approximately north to south, roughly along
Southpoint Road (NC Highway 273), which forms a groundwater divide. Consistent
with the slope-aquifer system model (LeGrand, 1988) discussed in Section 5,
groundwater flow direction mimics surface topography at the Site. Groundwater to the
east of the divide and topographic high flows toward Lake Wylie/Catawba River, as
confirmed by water level measurements for onsite monitoring wells. Groundwater to
the west of the topographic divide flows toward the South Fork Catawba River. North-
northwest of the inactive ash basin, groundwater migrates north toward the discharge
canal.
Active sluicing into Primary Cells 1, 2, or 3 of the active basin increases the hydraulic
head in the north central portion of the active basin. The leachate collection system
within the south central portion of the adjacent inactive basin reduces infiltration of
meteoric water and lowers the hydraulic head in this area. The combined effect of these
two systems appears to induce a relatively strong hydraulic gradient northward from
the active ash basin toward the inactive ash basin. Beneath the inactive basin,
groundwater flow is generally toward the northeast and the discharge canal and east
toward Lake Wylie/Catawba River.
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Groundwater flow directions and the overall morphology of the potentiometric surface
vary little from “dry” to “wet” seasons. Water levels fluctuate up and down with
seasonal changes in precipitation and evapotranspiration, but the overall groundwater
flow direction does not change due to seasonal changes in precipitation.
Groundwater COIs migrate laterally and vertically into and through surficial regolith
(shallow flow zone), the transition zone (deep flow zone), and fractured bedrock
(bedrock flow zone). Constituent migration in groundwater occurs at variable rates
depending on a number of physical and chemical conditions and properties (e.g.,
constituent sorption properties, redox state, pH, hydraulic conductivity, etc.). Some
COIs, such as boron, readily solubilize and migrate with minimal retention. In contrast,
some COIs, such as arsenic, readily adsorb to aquifer materials; thus, they are relatively
immobile.
Horizontal gradients along the southern portion of the Site range from 0.013 feet/feet to
0.067 feet/feet. Horizontal gradients along the northern end of the Site range from 0.011
feet/feet to 0.036 feet/feet. The greatest hydraulic gradient observed is located along the
southeastern portion of the Site. The high gradient, relative to the Site, is driven by the
high topographic relief between the active ash basin and Lake Wylie/Catawba River.
Generally, upward vertical gradients predominate on the east side of the Site along
Lake Wylie/Catawba River, where groundwater discharges toward the lake/river.
Upward hydraulic gradients are also prevalent on the western portion of the Site.
Downward hydraulic gradients (recharge) were observed within the footprint of the
ash basins. Downward gradients are more prevalent in the northeast portion of the ash
basins than elsewhere on the property. Upward vertical gradients from bedrock
alongside Lake Wylie/Catawba River reduce the potential for downward migration of
COIs into bedrock, thus reducing the potential of COIs migrating under the river,
although migration may occur some distance beyond the lake shore before discharging
into the lake. Recent data from the newly installed well at AB-22BRL indicates boron
has migrated approximately 150 vertical feet into bedrock along the river east of the
active ash basin. Similarly, downgradient of the inactive ash basin, boron
concentrations in bedrock are at concentrations greater than the 2L. Additional
monitoring wells may be installed deeper within bedrock downgradient of the basins to
evaluate the effectiveness of corrective measures
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Horizontal and Vertical Extent of Impact
The groundwater plume is defined as locations (in three-dimensional space) where
groundwater quality is impacted by the ash basin. Naturally occurring groundwater
contains varying concentrations of COIs and a number of other constituents (e.g.,
alkalinity, aluminum, magnesium, sodium, etc.). Sporadic detections and slight
exceedances of 2L/IMAC or PBTVs (if determined) of these constituents in the
groundwater data do not necessarily demonstrate impacts from the ash basins. The
leading edge of CCR-related the plume from the ash basins, the furthest downgradient
edge, is within the existing well network as represented by arsenic and boron
concentrations in groundwater in the wells in each flow unit.
Boron, the primary CCR-derived constituent in groundwater at Allen, is detected at
concentrations greater than the PBTV and 2L standard beneath and downgradient (east)
of the ash basins. Boron has been detected in background groundwater, and at other
upgradient locations, however, concentrations are often less than the laboratories’
minimum detection limit. Boron, in its most common forms, is soluble in water, and
boron has a very low Kd value, meaning the constituent is highly mobile in
groundwater. Therefore, the presence/absence of boron in groundwater provides a
close approximation of the distribution of CCR-impacted groundwater.
Calcium, cobalt, iron, manganese, and strontium detections in groundwater may also
indicate impact from the ash basins. However, those constituents occur naturally in
area groundwater. PBTVs for some of them, including calcium and strontium, are
similar to concentrations observed downgradient of the ash basins. Further, the current
Site-specific PBTV for strontium is notably less than other PBTVs estimated at other
North Carolina Duke Energy facilities located within the Piedmont physiographic
province and with similar geologic settings. Therefore, areas farthest downgradient at
which boron is detected at a concentration greater than applicable PBTVs is interpreted
as the leading edge of the CCR-derived plume moving downgradient from the source
area.
Observations on the extent of CCR influence are as follows:
Flow and transport of constituents from the ash basins is toward the east and, to
a lesser extent, to the north, away from upgradient areas to the west and not
toward side-gradient areas to the south. With the inactive and active ash basins
being immediately adjacent to one another, it is difficult differentiate between
inactive versus active ash basin influence upon groundwater.
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Based on the extent of boron concentrations above background, the approximate
horizontal extent of CCR influence is assessed and limited to beneath the ash
basins and immediately downgradient of the ash basins to the east and a small
area north of the inactive basin within the Duke Energy property boundary.
North of the inactive ash basin, several other constituents (not boron) are
detected at concentrations greater than applicable 2L/IMAC or PBTVs, primarily
within the shallow flow zone, which indicate influence from a secondary source,
likely the coal pile. This area will be assessed separately.
The vertical extent of CCR-affected groundwater is limited to the transition zone
or upper portions of the bedrock in areas beneath and downgradient of the ash
basins with an exception of an area east-northeast of the inactive basin and east-
southeast of the active ash basin where, primarily boron, concentrations are
greater than 2L in recently installed lower level bedrock wells GWA-5BRA and
AB-22BRL. Upward hydraulic gradients in these areas indicate bedrock
groundwater discharges to Lake Wylie/Catawba River. Additional monitoring
wells may be installed deeper within bedrock downgradient of the basins to
evaluate the effectiveness of corrective measures.
Groundwater primarily flows and discharges toward Lake Wylie/Catawba River
to the east, with a smaller component of flow from the inactive ash basin
northward toward the discharge canal on Duke Energy property.
Boron was not observed in concentrations greater than 2L in groundwater
samples collected to the west, north, or south of the ash basins.
Seasonality does not appear to affect groundwater chemistry, as constituent
concentrations are relatively stable in most wells.
In general and with few exceptions, constituents detected at concentrations
greater than 2L/IMAC or PBTVs at locations where boron was not detected at
concentrations greater than the 2L, had concentrations similar to applicable
2L/IMAC or PBTVs. The presence of these other constituents detected at
concentrations greater than 2L/IMAC or PBTVs in these areas (where boron
concentrations are not greater than 2L) indicates natural variability in constituent
concentrations and that their presence is not be attributable to the ash basins.
Additional wells may be installed within the shallow flow zone beneath the ash
basins to support the evaluation of corrective measures and further refine the
vertical extent of groundwater potentially affected by the active ash basin.
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Inactive Ash Basin Observations Summary
Recent revisions to the compliance boundaries associated with the ash basins,
which removed the compliance boundary from the inactive basin, have resulted
in most of the inactive ash basin being outside of the compliance boundary.
Therefore, constituents detected at concentrations greater than 2L/IMAC or
PBTVs within and beyond the inactive ash basin waste boundary, with the
exception of the southern portion of the basin which is covered by the active ash
basin compliance boundary and the RAB Ash Landfill compliance boundary,
represent exceedances beyond the revised compliance boundary.
Beneath the inactive ash basin in the shallow zone, only one well (AB-36S) is
installed that is not partially screened within ash. Arsenic, calcium, iron,
manganese, molybdenum, and strontium are consistently detected at
concentrations greater than the 2L/IMAC or PBTV, whichever is greater
(elevated) in this well. Several of the above listed constituents, including arsenic,
iron, and strontium have concentrations in pore water less than the 2L or PBTVs
in upgradient areas within the basin (AB-37S) and also at a location further
downgradient within the central portion of the basin (AB-34S).
Beneath the inactive ash basin within the deep flow zone, calcium and strontium
are consistently detected in most wells at concentrations greater than applicable
PBTVs. Vanadium is also detected at concentrations slightly greater than the
PBTV in southwestern portions of the basin. Concentrations of antimony,
calcium, manganese and strontium are slightly greater than applicable 2L/IMAC
or PBTVs, whichever is greater. Boron and sulfate are not detected at
concentrations greater than 2L in deep flow zone wells beneath the inactive ash
basin. However, boron was detected at concentrations greater than the PBTV and
wells in the deep flow zone downgradient (east) of the basin have boron
concentrations greater than the 2L. This indicates that boron, and potentially
other COIs, are likely present at concentrations greater than 2L/IMAC or PBTVs
beneath the eastern portion of the inactive ash basin.
Beneath the inactive ash basin within the bedrock flow zone, calcium, strontium,
and manganese were detected at concentrations similar to, but greater than the
2L or PBTV. No other constituents, including boron or sulfate, are routinely
detected at elevated concentrations in the bedrock flow zone monitoring wells
beneath the inactive ash basin. However, similar to the deep zone, boron was
detected at concentrations greater than the 2L in bedrock groundwater
downgradient (east) of the basin. This, along with groundwater flow direction
information, indicates that boron, and potentially other COIs, are likely present
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at concentrations greater than 2L/IMAC or PBTVs beneath the eastern portion of
the inactive ash basin.
Downgradient to the east of the inactive ash basin, shallow groundwater has
boron concentrations greater than the 2L, indicating CCR in the ash basin is
affecting groundwater in this area. North of the basin, groundwater is likely
affected primarily by the coal pile as conditions observed in groundwater are
different than those observed elsewhere downgradient of the ash basins. Several
constituents including beryllium, cadmium, nickel, selenium, thallium, and zinc
are routinely detected at concentrations greater than 2L/IMAC and PBTVs only
in well GWA-6S, located between the inactive basin and coal pile. Sulfate and
TDS are also detected in this well at concentrations far greater than anywhere
else onsite. Notably, boron is not typically detected outside the waste boundary
in this area. This area will be further evaluated as part of separate assessment
currently being planned for the coal pile area.
Downgradient to the east of the inactive basin, deep groundwater is affected by
CCR as indicated by the distribution of boron detections at concentrations
greater than the PBTV and less than, but near the 2L. Deep groundwater north
of the basin may also be affected by the coal pile as indicated by concentrations
of other constituents (iron, manganese, sulfate, and TDS) not observed elsewhere
downgradient of the ash basins and by the notable absence of boron. Chromium
was detected at concentration greater than, but within the same order of
magnitude as, the 2L, at GWA-7D, located north of the basin and further
downgradient of GWA-6DA, suggesting the chromium detected at this location
may not be derived from the ash basin and the extent of constituents potentially
derived from the ash basin or coal pile may be delineated to the north.
Chromium concentrations at this location are typically less than the 2L.
Downgradient to the east of the inactive ash basin, bedrock groundwater is
affected by CCR as boron (among other constituents) was detected at
concentrations greater than the 2L at the GWA-5BRA location. North of the
basin, only calcium, manganese, and strontium were detected at concentrations
greater than applicable 2L/IMAC or PBTVs. Calcium and strontium
concentrations were similar to those detected in other upgradient samples.
Manganese concentrations were notably less than those detected shallower in the
deep flow zone. This indicates CCR within that the inactive ash basin is not
likely influencing groundwater north of the basin and that the horizontal and
vertical extent of migration is adequately defined in this area.
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Active Ash Basin Observations Summary
Based on ash pore water concentrations, it is interpreted that shallow
groundwater beneath the active ash basin waste boundary is likely impacted by
CCR to some extent, although there are no shallow wells to confirm this.
Beneath the active ash basin, deep groundwater contains calcium, iron,
manganese, strontium, and vanadium with concentrations greater than, but
similar to, applicable 2L/IMAC or PBTVs. Boron is not detected at
concentrations greater than 2L, but was at concentrations greater than the PBTV,
in deep flow zone wells beneath the active ash basin. Boron was detected at
concentrations greater than the PBTV and 2L in deep groundwater
downgradient (east) of the active ash basin. This indicates that boron, and
potentially other COIs, are likely present at concentrations greater than 2L/IMAC
or PBTVs beneath the eastern portion of the active ash basin.
Beneath the active ash basin, bedrock groundwater contains calcium, manganese,
molybdenum, and strontium at concentrations greater than, but similar to,
applicable 2L/IMAC or PBTVs, whichever is greater. Neither boron nor sulfate,
have been routinely detected at concentrations greater than the 2L. However,
similar to the deep zone, boron was detected at concentrations greater than the
2L in bedrock groundwater downgradient (east) of the basin. This, along with
groundwater flow direction information, indicates that boron, and potentially
other COIs, are likely present at concentrations greater than 2L/IMAC or PBTVs
beneath the eastern portion of the active ash basin.
Downgradient of the active ash basin, shallow groundwater to the south contains
only cobalt at a concentration greater than, but similar to, the PBTV (at GWA-2S).
Boron has not been detected in this well indicating CCR the cobalt concentration
likely represents natural variability. These data, along with groundwater flow
direction information, also indicate the active ash basin has not affected shallow
groundwater quality south of the basin and the horizontal extent of migration
south of the basin has been adequately defined. East of the basin, boron
concentrations greater than the 2L indicate CCR has affected shallow
groundwater quality downgradient of the basin.
Downgradient of the active ash basin, deep groundwater indicates influence
from CCR within the basin as boron has been detected at concentrations greater
than the PBTV and 2L.Only calcium and strontium were detected at
concentrations greater than 2L/IMAC or PBTVs in deep groundwater south of
the active ash basin. Those concentrations were similar to those observed
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elsewhere across the Site including upgradient locations. These data, along with
groundwater flow direction information, indicate the active ash basin has not
affected deep groundwater quality south of the basin and the horizontal extent of
migration south of the basin has been adequately defined.
Downgradient of the active ash basin, bedrock groundwater to the east indicates
influence from CCR as boron concentrations are greater than the 2L in both
upper (AB-22BR) and deeper (AB-22BRL) bedrock. Boron concentrations are
similar within both wells AB-22BR and AB-22BRL, indicating the vertical extent
of boron concentrations is not fully delineated downgradient of the active ash
basin in this area. Field pH measurements at wells GWA-03BR and GWA-
03BRA indicate these wells are affected by grout contamination, so the samples
are not considered valid. However, available analytical results for boron and
sulfate (which may not be affected significantly by pH) indicate boron and
sulfate concentrations are less than applicable 2L. South of the basin, only
calcium and strontium were detected at concentrations greater than applicable
PBTVs, at the GWA-1 location. Those concentrations were similar to those
observed elsewhere across the Site including upgradient locations. These data,
along with groundwater flow direction information, indicate the active ash basin
has not affected bedrock groundwater quality south of the basin and the
horizontal extent of migration south of the basin has been adequately defined.
14.2 Maximum Constituent of Interest Concentrations
Changes in COI concentrations over time are included as time-series graphs (Figures
14-1 to 14-80). Time series plots have been compiled in a matrix format to demonstrate
constituent occurrence through time in relation to depth and distance from source area
to receptor. The maximum historical detected COI concentrations in ash pore water,
groundwater in wells directly beneath the ash basins and groundwater in wells
downgradient of the waste boundary are included in the summary below. The 2L and
IMAC standards are not applicable to ash pore water. Also listed is the range of PBTVs
for the surficial, transition zone, and bedrock flow units. Samples with a pH of greater
than 8.5 S.U. or turbidity greater than 10 NTUs were considered invalid for the
compilation below.
Antimony – PBTV range: 0.5 µg/L - 0.876 µg/L; IMAC: 1 µg/L
• Active Ash Basin – Pore water: 7.6 µg/L (AB-25S); Outside Basin: 0.76 µg/L
(GWA-09BR);
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• Inactive Ash Basin – 1.6 µg/L (AB-33D); Outside Basin: 0.96 µg/L (GWA-
14DA)
Arsenic – PBTV range: 0.4 µg/L – 1.4 µg/L; 2L standard: 10 µg/L
• Active Ash Basin – Pore water: 1030 µg/L (AB-23S); Outside Basin: 1.6 µg/L
(GWA-21BR);
• Inactive Ash Basin – Pore water: 303 µg/L; Outside Basin: 137 µg/L (GWA-
06S)
Barium – PBTV range: 21 µg/L – 125.4 µg/L; 2L standard: 700 µg/L
• Active Ash Basin – Pore water: 419 µg/L (AB-21S); Outside Basin: 187 µg/L
(PH WELL);
• Inactive Ash Basin – Pore water: 339 µg/L (AB-30S); Outside Basin: 231 µg/L
(GWA-08S)
Beryllium – PBTV range: 0.1 µg/L – 0.2 µg/L; IMAC: 4 µg/L
• Active Ash Basin – Pore water: 0.054 j, B µg/L (AB-28S); Outside Basin: 0.15
µg/L (GWA-21S);
• Inactive Ash Basin – Pore water: 0.14 µg/L (AB-39D); Outside Basin: 38.6
D3 4 µg/L (GWA-06S)
Boron - PBTV range: Not Detected; 2L standard: 700 µg/L
• Active Ash Basin – Pore water: 6950 µg/L (AB-21SL); Outside Basin: 1550
µg/L (AB-22BR);
• Inactive Ash Basin – 1930 µg/L (AB-31S); Outside Basin: 2180 µg/L (GWA-
04S)
Cadmium – PBTV range: Not Detected; 2L standard: 2 µg/L
• Active Ash Basin – Pore water: 0.22 µg/L (AB-21SL); Outside Basin: 0.53
µg/L (AB-04BR);

4 D3 - Sample was diluted due to the presence of high levels of non-target analytes or other matrix
interference.
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• Inactive Ash Basin – 0.11 µg/L (AB-31S); Outside Basin: 9.3 D3 µg/L (GWA-
06S)
Chloride – PBTV range: 1.6 mg/L – 10.9 mg/L; 2L standard: 250 mg/L
• Active Ash Basin – Pore water: 61.8 µg/L (AB-21S); Outside Basin: 88.2 µg/L
(PH WELL);
• Inactive Ash Basin – Pore water: 13.6 µg/L (AB-39D); Outside Basin: 67.4
µg/L (GWA-08S)
Chromium – PBTV range: 5.6 µg/L – 6.927 µg/L; 2L standard: 10 µg/L
• Active Ash Basin – Pore water: 3.8 µg/L (AB-25S); Outside Basin: 26.9 µg/L
(GWA-22D);
• Inactive Ash Basin – 2.2 µg/L (AB-33D); Outside Basin: 15 µg/L (GWA-
06DA)
Chromium (hexavalent) – PBTV range: 0.23 µg/L – 7.742 µg/L; 2L standard (total
chromium): 10 µg/L
• Active Ash Basin – 0.94 µg/L (AB-20D); Outside Basin: 26.9 µg/L (GWA-
22D);
• Inactive Ash Basin – 0.97 µg/L (AB-35BR); Outside Basin: 6.2 µg/L (GWA-
07D)
Cobalt – PBTV range: 0.27 µg/L – 4.338 µg/L; IMAC: 1 µg/L
• Active Ash Basin – Pore water: 9.7 µg/L (AB-28S); Outside Basin: 17.5 µg/L
(GWA-22S);
• Inactive Ash Basin – Pore water: 25 µg/L (AB-29S); Outside Basin: 3640 D3
µg/L (GWA-05S)
Iron – PBTV range: 284 µg/L – 834.8 µg/L; 2L standard: 300 µg/L
• Active Ash Basin – Pore water: 13100 µg/L (AB-27S); Outside Basin: 9230
µg/L (GWA-03S);
• Inactive Ash Basin – Pore water: 108000 µg/L (AB-34S); Outside Basin: 32700
µg/L (AB-32S)
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Manganese – PBTV range: 39.1 µg/L – 577.9 µg/L; 2L standard: 50 µg/L
• Active Ash Basin – Pore water: 2920 µg/L (AB-AB-27S); Outside Basin: 2160
µg/L (GWA-03S);
• Inactive Ash Basin – Pore water: 8290 µg/L (AB-35S); Outside Basin: 166000
µg/L (GWA-06S)
Molybdenum – PBTV range: 0.849 µg/L – 30.2 µg/L
• Active Ash Basin – Pore water: 2950 µg/L (AB-21SL); Outside Basin: 16.3
µg/L (GWA-26D);
• Inactive Ash Basin – Pore water: 7.1 µg/L (AB-30S); Outside Basin: 13.6 µg/L
(AB-14BR)
Nickel – PBTV range: 3.4 µg/L – 8.1 µg/L; 2L standard: 100 µg/L
• Active Ash Basin – Pore water: 32.4 µg/L (AB-20S); Outside Basin: 20.8 µg/L
(GWA-22D);
• Inactive Ash Basin – Pore water: 7.4 µg/L (AB-36S); Outside Basin: 821 D3
µg/L (GWA-06S)
Selenium - PBTV range: Not Detected; 2L standard: 20 µg/L
• Active Ash Basin – Pore water: 0.33 µg/L (AB-28S); Outside Basin: 0.096 j
µg/L (GWA-22S);
• Inactive Ash Basin – 3.3 µg/L (AB-39D); Outside Basin: 765 D3 µg/L (GWA-
06S)
Strontium - PBTV range: 106 µg/L – 286 µg/L
• Active Ash Basin – Pore water: 3490 µg/L (AB-21S); Outside Basin: 380 µg/L
(AB-22D);
• Inactive Ash Basin – Pore water: 3380 µg/L (AB-33S); Outside Basin: 1670
µg/L (GWA-06S)
Sulfate – PBTV range: 2.9 mg/L – 16.2 mg/L; 2L standard: 250 mg/L
• Active Ash Basin – Pore water: 214 µg/L (AB-20S); Outside Basin: 72.6 µg/L
(AB-26S);
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• Inactive Ash Basin – Pore water: 383 µg/L (AB-33S); Outside Basin: 1790
µg/L (GWA-06S)
TDS – PBTV range: 126 mg/L – 180.957 mg/L; 2L standard: 500 mg/L
• Active Ash Basin – Pore water: 690 µg/L (AB-20S); Outside Basin: 314 µg/L
(PH WELL);
• Inactive Ash Basin – Pore water: 838 µg/L (AB-33S); Outside Basin: 2670
µg/L (GWA-06S)
Thallium – PBTV range: Not Detected; IMAC: 0.2 µg/L
• Active Ash Basin – Pore water: 0.33 µg/L (AB-28S); Outside Basin: 0.096 j
µg/L (GWA-22S);
• Inactive Ash Basin – Pore water: 0.13 µg/L (AB-36S); Outside Basin: 1.5 D3,
B µg/L (GWA-06S)
Vanadium – PBTV range: 5.33 µg/L – 10.8 µg/L; IMAC: 0.3 µg/L
• Active Ash Basin – Pore water: 35.2 µg/L (AB-25S); Outside Basin: 15.9 µg/L
(GWA-21BR);
• Inactive Ash Basin – Pore water: 12.3 µg/L (AB-30D); Outside Basin: 15.9
µg/L (AB-14BR)
pH - PBTV range: 5.2 S.U. – 8.4 S.U.; 2L standard: 6.5-8.5 S.U.
• Active Ash Basin – 8.4 S.U. (AB-21BRL); Outside Basin: 8.3 S.U. (GWA-
24BR);
• Inactive Ash Basin – Pore water: 7.6 S.U. (AB-30S); Outside Basin: 8.2 S.U.
(AB-14BR)
Radium (Total) – PBTV range: 0.613 pCi/L – 1.386 pCi/L; MCL: 5 pCi/L
• Active Ash Basin – Pore water: 1.525 µg/L (AB-21S); Outside Basin: 1.333
µg/L (GWA-09S);
• Inactive Ash Basin – Pore water: 1.277 µg/L (AB-35S); Outside Basin: 2.465
µg/L (GWA-05S)
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Uranium (Total) – PBTV range: .00039 µg/mL - .001937 µg/mL; MCL: 0.030
µg/mL
• Active Ash Basin – Pore water: 0.0387 µg/L (AB-21SL); Outside Basin: 0.0015
µg/L (GWA-01BR);
• Inactive Ash Basin – Pore water: 0.00061 µg/L (AB-33S); Outside Basin:
0.0061 µg/L (GWA-06S)
Contaminant Migration and Potentially Affected Receptors 14.3
The hydrogeologic characteristics of the ash basin environment are the primary control
mechanisms on groundwater flow and constituent transport. The ash basins were
constructed in distinct slope-aquifer systems in which flow of groundwater into and out
of the ash basin is restricted to the local flow regime. Groundwater flow from the ash
basins primarily discharges toward Lake Wylie (Catawba River) with a smaller
component of flow from the northern portions of the inactive basin toward the
discharge canal to the north. Boron and other COIs are present in groundwater beneath
and downgradient of the ash basins on the Site near or at the compliance boundary in
concentrations that exceed the 2L or PBTV.
The groundwater flow system at the Site stores groundwater and provides a means for
groundwater movement. The porosity of the regolith is largely controlled by pore
space (primary porosity), whereas in bedrock porosity is largely controlled by the
number, size, and interconnection of fractures. As a result, the effective porosity in the
regolith is normally greater than in the bedrock. The relatively thick (typically greater
than 100 feet) sequence of regolith is primarily comprised of fine-grained material (silts
and clays) and hinders migration of groundwater and COIs as indicated by relatively
lower hydraulic conductivity values within most portions of the shallow zone
compared with those from the transition/deep zone. Hydraulic conductivity values also
indicate a greater flow rate within the transition zone compared with the flow rate
within fractured bedrock.
Pore water and ash in the ash basins is the source of constituents detected above PBTVs
or 2L/IMAC in groundwater samples in the vicinity of the ash basins, although some
constituents may occur naturally at concentrations greater than 2L/IMAC or current
PBTVs. Pore water analytical results are compared with 2L or IMAC for reference
purposes only. Ash basin constituents become dissolved in pore water and migrate to
groundwater in response to hydraulic gradients. Gradients measured within the ash
basins support the interpretation that ash pore water mixes with shallow/surficial
groundwater and migrates downward into the shallow zone. Continued migration of
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groundwater laterally and vertically downgradient of the ash basins is indicated by
detected constituent concentrations in wells beyond the waste boundaries and within
deeper flow zones (deep and bedrock).
Migration of many constituents present in ash pore water is inhibited by geochemical
mechanisms such as sorption (measured by the distribution coefficient Kd) and
precipitation. Boron is relatively mobile in groundwater and is associated with low Kd
values. This is primarily because boron is mostly inert, has limited potential for
sorption, and lacks an affinity to form complexes with other ions. The low Kd measured
for boron and sulfate is consistent with observations of migration from the ash basins
(Figures 11-102 through 11-105), and the higher Kd values measured for other
constituents is consistent with the limited migration of these constituents. Selected soil
samples were analyzed using batch and column experiments to determine Kd values for
COIs (Table 13-2). Geochemical mechanisms controlling the migration of constituents
are discussed further in Section 13.0.
Groundwater migrates under diffuse flow conditions in the shallow zone in the
direction of the prevailing gradient. Groundwater advective flow is the primary
mechanism for migration of constituents to the environment. As groundwater under
the ash basin flows east toward the ash basin dams, the hydraulic impact of the ash
basin dams (which are likely less permeable than surrounding ash and soil) and the
hydraulic head exerted by the ash basin water forces groundwater downward into the
bedrock, increasing hydraulic pressure in the bedrock aquifer. As constituents enter the
transition zone and fractured bedrock flow systems, the rate of constituent transport has
the potential to increase.
Groundwater movement in the bedrock flow zone is due primarily to secondary
porosity represented by fractures in the bedrock. Bedrock fractures encountered at
Allen tend to be isolated with low interconnectivity. Further, hydraulic conductivity
values measure the fractures immediately adjacent to a well screen, not across the
distance between two bedrock wells. Groundwater flow in bedrock fractures is
anisotropic and difficult to predict, and velocities change as groundwater moves
between factures of varying orientations, gradients, pressure, and size.
Wells completed in the shallow, transition/deep, and bedrock zones proximate to the
ash basin dams are impacted by COIs. As groundwater and the plume migrate in the
downgradient direction, unimpacted groundwater enters the system from upgradient
recharge areas to the west, mitigating the concentration of some COIs.
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Concentration trends at all wells, surface water, and seep locations are graphically
depicted in plan view and included as Figure 14-81 through Figure 14-101. The figures
graphically depict the most recent data available (March-November 2017) valid COI
groundwater concentrations for monitoring wells, surface waters and AOWs. The
figures are color-coded to visually depict whether concentrations seem to be increasing,
decreasing, or stable, or whether a trend could not be determined.
Recent concentrations of COIs in solid media, groundwater, surface water, and AOWs,
as well as geochemical properties of soils are provided on Figures 14-102 to 14-105.
Potentially Affected Receptors
A baseline human health and ecological risk assessment, performed in 2016 as a
component of the CAP, Part 2 (HDR, 2016a), concluded that no unacceptable risks to
humans resulted from hypothetical exposure to constituents detected in the ash basin
area. The updated human health and ecological risk assessment presented in Section
12, which was based on review and analysis of groundwater, surface water, soil, and
sediment data collected since completing the human health and ecological risk
assessment in 2016, determined there is no evidence of potential unacceptable human
health or ecological risks at the Allen Site.
Water Supply Wells
Results from private water supply wells did not indicate human health risks to off-site
residents potentially exposed to groundwater associated with the ash basins. In
addition, no public or private drinking water wells, supply wells, or wellhead
protection areas were found to be located downgradient of the ash basin.
As discussed in Section 4, approximately 150 samples were collected in 2015 from
water supply wells located upgradient of the Allen Plant ash basins to the west,
southwest, and northwest, primarily located along NC Highway 273 and neighborhood
roads off of Highway 273 and also collected at sidegradient locations to the south,
primarily along Nutall Oak Lane. Additional water supply well samples were collected
in 2016 and 2017 and are provided in Appendix B, Table 1. The data is similar to the
2015 data.
Available analytical data for the private wells generally show detected concentrations
less than Site-specific statistically derived PBTVs for bedrock of CCR-related
constituents and not attributable to CCR impacts. However, there were a few occasions
when concentrations reported were greater than current Site-derived bedrock PBTVs or
2L (sometimes both). These exceedances and this data should be interpreted
considering the following factors:
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PBTVs were developed using groundwater data from a set of two bedrock
background wells located on the Site. Those wells are located within about 1 mile
from one another. The geochemical data from the wells may not be
representative across the broader area encompassed by the sampled 124 water
supply wells (spread across approximately 4 square miles).
Not all water supply wells may be installed in bedrock, some may be installed in
saprolite or transition zone materials which have different geochemical
properties and PBTVs.
There is limited information available about the sampled water supply wells.
Well construction procedures and equipment such as pipes, pumps, and fittings
may influence water quality.
Well construction may influence analytical results. There is limited information
about water supply well sampling methodology such as purge volume and field
parameter stabilization. Variations in sampling methodology can influence
water quality.
Land use on the private properties where the water supply wells are located is
unknown. Historical and current land use and application of environmental
contaminants or nutrients can affect groundwater quality.
Groundwater flow in the area around the Allen Plant is consistent with the
slope-aquifer model of groundwater flow in the Piedmont as confirmed by water
level measurements collected from Site monitoring wells. Groundwater flow
from the source (ash basins) is predominantly to the east toward Lake Wylie with
a smaller component of flow to the north from the northern portion of the
inactive basin toward the discharge canal. Water supply wells are upgradient or
situated in distinct separate drainage basins/slope-aquifer systems from the
Allen Plant and the ash basins where groundwater flows away from the Plant
toward the South Fork Catawba River.
Boron (a key indicator of potential CCR influence) was not detected at
concentrations greater than the 2L in the private water supply well samples.
Boron was detected in a few water supply well locations at concentrations
greater than Site-derived PBTVs. However, these supply wells were at isolated
locations surrounded by other private supply or Site monitoring wells without
detected concentrations of boron. Therefore, the detection of boron in the wells
does not by itself conclusively indicate impact from the ash basin(s). Other
constituents that were detected in private supply wells at concentrations greater
than 2L/IMAC were similar to Site-derived PBTVs and surrounded by wells with
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concentrations less than applicable 2L or IMAC. There is limited supply well
construction information, such as depths and aquifer characteristics that would
be helpful in interpretations. Therefore, multiple lines of evidence indicate the
supply wells have not been impacted.
Land directly downgradient topographically and hydraulically (as confirmed by onsite
measurements of water levels) of the ash basins includes Lake Wylie to the east and
Duke Energy property to the north between the inactive ash basin and the discharge
canal. This, combined with analytical results of samples collected from Site monitoring
wells and private water supply wells suggests the ash basins have not impacted the
water supply wells located upgradient of the basins.
No surface water intakes, other than the intake used to pump cooling tower make-up
water from Lake Wylie for the Allen Plant operations, are located in the vicinity of
Allen Plant. The closest public water supply intake is located within the Catawba River
approximately four miles north and upstream of the Plant.
Surface Water
Four surface water samples were collected from a named water body (Lake
Wylie/Catawba River) and analyzed, including one downstream of the ash basins and
one reference upstream location. Surface water sample data indicate that no 2B
standards were exceeded for COIs. 2B standards for field parameters were exceeded
twice for turbidity, while the 2B standards for dissolved oxygen were not met, which
may indicate improper sampling techniques or uncalibrated field equipment. The
majority of COI concentrations increase downgradient/downstream of the active ash
basin. While there are no 2B exceedances in the surface water samples, the downstream
sample location (SW-D1) concentrations are greater than the upstream sample location
(SW-U1) concentrations in thirteen (13) COIs. Of the thirteen (13) COIs found to be
greater in the downstream sample when compared with the upstream sample, only two
COIs (boron and sulfate) were greater than two times the concentrations in the
upstream sample. This may be due to NPDES Outfall 002, located slightly upstream
from SW-D1.
Additional surface water sampling is anticipated to be completed, and an evaluation of
potential impacts of groundwater on surface water will be presented in the CAP.

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CONCLUSIONS AND RECOMMENDATIONS 15.0
The assessment described in this CAMA CSA investigated the Site hydrogeology,
determined the direction of groundwater flow from the ash basin, and determined the
horizontal and vertical extent of impacts to groundwater and soil sufficient to proceed
with preparation of a CAP in accordance with the CAMA and 2L. The following
conclusions are based on evaluation described in this CAMA CSA report:
Ash sluiced to, and accumulated within, the ash basins is determined to be a
source and cause of groundwater impacts at the Site.
The updated CSA has determined no unacceptable risks to public health and
safety from exposure to groundwater, surface water, or sediment impacts related
to the ash basins. The ash basins are currently designated as “Intermediate” risk
under CAMA, meaning that closure of the ash basin is required by 2024. A
"Low" risk classification and closure via a cap-in-place scenario are considered
appropriate as alternative water supplies are being provided in accordance with
G.S. 130A-309.213.(d)(1) of House Bill 630.
Receptors including water supply wells and surface water bodies were identified
and found to be not impacted by the ash basins and generally in compliance with
applicable regulatory standards. Significant exposure pathways are understood
and constituent concentrations detected in water supply wells are deemed to not
be from the ash basins.
Impacts to groundwater in all three flow zones (shallow, deep, and bedrock)
have been identified beneath and downgradient of the ash basins. Supplemental
data collection to support groundwater modeling and long-term monitoring is
anticipated to support the CAP process.
Secondary sources have been identified in groundwater, likely attributable to the
coal pile adjacent to and north of the inactive ash basin. Additional assessment of
the coal pile area is being planned.
Soils beneath the ash basins are not likely to be a secondary source of impacts to
groundwater, based on soil sample analytical results.
Surface water receptors downgradient of the ash basin (e.g. Lake Wylie)
demonstrate compliance with 2B standards, with occasional exceptions for
dissolved oxygen. Additional surface water and sediment data collection is
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anticipated to support the evaluation of potential monitored natural attenuation
(MNA) in the area of the groundwater plume discharge to surface water.
The collection of additional data to support potential MNA as a groundwater corrective
action strategy and additional plume definition is anticipated. A discussion of
preliminary corrective action alternatives that may be appropriate to consider during
the updated CAP development are presented herein.
15.1 Overview of Site Conditions at Specific Source Areas
CCR material and sluice water in the ash basins were determined to be a source of
impact to groundwater. The coal pile has also likely contributed to groundwater
impact. Boron is the primary marker constituent detected in groundwater at
concentrations greater than background and the 2L near or beyond the compliance
boundary. Calcium and strontium also appear to be indicators of impact to
groundwater; however, distinction of downgradient concentrations from background
concentrations is not clear. The interpreted extent of boron concentrations greater than
the 2L standard is at or beyond the compliance boundary in the shallow,
transition/deep, and bedrock flow zones (Figures 11-10 to 11-12). Boron and other COI
concentrations are greater than the 2L/IMAC or PBTVs beyond the compliance
boundary at locations within and downgradient of the inactive ash basin, due to
compliance boundary revisions in 2017, which resulted in the compliance boundary no
longer encompassing the inactive basin waste boundary. Vertical migration of COIs
into bedrock is observed near the compliance boundary east of the ash basins.
15.2 Revised Site Conceptual Model
Site Conceptual Models (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. SCMs are a written and/or be a graphic
presentation of site conditions to reflect the current understanding of the site, identify
data gaps, and be updated as new information becomes available. SCMs can be used to
develop an understanding of the variable aspects of site conditions, such as a
hydrogeologic conceptual site model to help understand the site hydrogeologic
conditions affecting groundwater. SCMs can also be used in a risk assessment to
understand contaminant migration and pathways to receptors. Based on conclusions
within this CAMA CSA, the following is a brief description of the SCM for Allen.
The Allen Plant has two ash basins that contain CCR generated from historic coal
combustion at the Plant. The ash basins are located along Lake Wylie/Catawba River,
and portions of the ash basins occupy former unnamed stream valleys and coves along
the shoreline. These stream valleys comprise distinct slope aquifer systems encircled by
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topographic ridges resulting in a groundwater divide between the Site and surrounding
upgradient properties, or properties within separate slope aquifer systems. Lake
Wylie/Catawba River is located downgradient (east) of the ash basin and represents a
groundwater discharge zone for groundwater leaving the Site. Typically advective
groundwater flow within the slope-aquifer system mimics surface topography. An
elongated topographic high trends approximately north-south in the area, roughly
following NC Highway 273, creating a groundwater divide. As confirmed by water
level measurements onsite, groundwater to the east of the divide, including
groundwater within the Allen Plant flows from the highest topographic areas (at the
west and southwest portions of the site) to the east toward Lake Wylie/Catawba River
and to the northeast and north toward Duke Energy property and the discharge canal.
Groundwater to the west of the divide likely flows west toward the South Fork
Catawba River.
Groundwater flow and geochemical characteristics are the primary controls of
constituent migration across the Site. Coal ash sluiced to, and accumulated within, the
ash basin is the primary source of COIs in groundwater. Boron is a key indicator of
CCR groundwater impacts. Boron, in its most common forms, is soluble in water, and
has a low Kd value, indicating the constituent is highly mobile in groundwater. Boron is
detected in groundwater at concentrations greater than the 2L and PBTV in the shallow,
deep, and bedrock flow layers, in areas beneath and east of the ash basins, within and
beyond the compliance boundary (recent revisions to the compliance boundary have
resulted in a large majority of the inactive ash basin being beyond the compliance
boundary). Boron is not present at concentrations greater than the PBTVs in wells to
the west, north, or south of the ash basins. Other COIs detected at concentrations
greater than PBTVs are primarily within the bounds of areas affected by boron.
The coal pile is another source of impact to groundwater north-northeast of the inactive
ash basin as indicated by a unique set of constituents detected in this area at
concentrations greater than applicable 2L/IMAC or PBTVs. These constituents were
either not detected elsewhere at concentrations greater than 2L/IMAC or PBTVs
(beryllium, cadmium, nickel, and zinc) or, if detected at concentrations greater than
2L/IMAC or PBTVs, were detected at notably lower concentrations elsewhere
(aluminum, arsenic, cobalt, manganese, sulfate, thallium, and TDS). Boron
concentrations at locations immediately adjacent to the basin in this area are similar to,
if not less than other areas downgradient of the basins indicating the area is influenced
by the inactive ash basin, but it is not likely the primary source of the constituents
detected in this area.
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Boron was not detected at concentrations greater than the 2L in the private water
supply well samples. Boron was detected in a few water supply well locations at
concentrations greater than Site-derived PBTVs. However, these supply wells were at
isolated locations surrounded by other private supply or Site monitoring wells without
detected concentrations of boron. Similarly, other constituents detected in private
supply wells at concentrations greater than 2L/IMAC were typically within the range of
Site-derived background concentrations and surrounded by other wells with
concentrations less than applicable 2L or IMAC. There is limited supply well
construction information, such as depths and aquifer characteristics that would be
helpful in interpretations. However, multiple lines of evidence indicate the supply
wells have not been impacted by the basins.
Inconsistent detection of COIs in soil at concentrations greater than, but primarily
within the same order of magnitude of, PSRG POG or PBTVs beneath and adjacent to
the ash basins indicates limited impact to soil beneath the ash basins and also indicates
soils are not likely to contribute significant concentrations of COIs as a potential
secondary source to groundwater. Although concentrations of arsenic, barium, boron,
calcium, chromium, cobalt, iron, manganese, molybdenum, selenium, strontium, and
vanadium in soils beneath the ash basins were found to be greater than their respective
PSRG POG or PBTVs, whichever is greater at select locations, only calcium and, to a
lesser extent, strontium, exceed the respective PBTV at multiple locations. For
strontium, all concentrations that exceeded the PBTV except two samples (which might
have included some ash within the sample aliquot) were within the same order of
magnitude as the PBTV. These exceedances likely reflect natural variability in
strontium concentrations across the Site. Other constituent exceedances were sporadic
and detected in just one or a few samples. Constituent concentrations are similar at
multiple sample depths within the same boring locations, and higher concentrations do
not directly correlate with proximity to the ash basin elevation or the water table,
therefore are likely naturally occurring.
The fine-grained (clayey) nature of subsurface soils and saprolite is likely retarding
migration of COIs potentially derived from the ash basins and constraining distribution
of COIs in soil to close proximity of the ash basin, vertically and horizontally.
Geochemical modeling to be performed within the CAP will evaluate how the
occurrence of various constituents react to changes in the geochemical environment (Eh
and pH) along selected flow transects and through time.
Surface water data indicates constituent concentrations are typically greater at locations
downgradient of the ash basins compared to locations upgradient of the basins.
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However, no constituent concentrations were greater than applicable 2B values for
protection of aquatic life and recreational uses.
The SCM will continue to be refined after evaluation of the completed groundwater
models to be presented in the CAP and additional information obtained in subsequent
data collection activities.
15.3 Interim Monitoring Program
An Effectiveness Monitoring Program (EMP) is required by CAMA §130A-309.209
(b)(1)e. The EMP for the Allen Plant is anticipated to begin once the basin closure and
groundwater CAP have been implemented. In the interim, an Interim Monitoring Plan
(IMP) has been developed at the direction of NCDEQ. The CAP, and a proposed EMP,
will be submitted at a future date.
15.3.1 Interim Monitoring Program Implementation
An IMP has been implemented since CAMA CSA activities commenced and is
currently being implemented in accordance with NCDEQ correspondence
(NCDEQ, October 19, 2017; Appendix A) that provided an approved “Revised
Interim Monitoring Plans.” Sampling will be conducted quarterly until approval
of the CAP or as otherwise directed by NCDEQ. Groundwater samples will be
collected using low-flow sampling techniques in accordance with the Low Flow
Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment Program,
North Carolina, June 10, 2015 (Appendix G) conditionally approved by NCDEQ in
a June 11, 2015, email with an attachment summarizing its approval conditions.
Samples will be analyzed by a North Carolina certified laboratory for the
parameters listed in Table 15-1. The table includes targeted minimum detection
limits for each listed constituent. Analytical parameters and detection limits for
each medium were selected so the results could be used to evaluate the
effectiveness of a future remedy, conditions within the aquifer that may
influence the effectiveness of the remedy, and migration of constituents related
to the ash basin. Laboratory detection limits for each constituent are targeted to
be at or below applicable regulatory values (i.e., 2L, IMAC, or 2B).
Monitoring wells and surface water locations that will be sampled and
monitored as part of the IMP, as approved in NCDEQ correspondence (NCDEQ,
October 19, 2017; Appendix A), are included in Table 15-2.
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15.3.2 Interim Monitoring Program Reporting
Currently, data summary reports comprised of analytical results received during
the previous month are submitted to NCDEQ on a monthly basis. In addition,
NCDEQ directed that an annual IMP report be submitted by April 30 of the year
following the year in which data was collected. The reports shall include
materials that provide “an integrated, comprehensive interpretation of site
conditions and plume status.” The initial report was to be submitted to NCDEQ
no later than April 30, 2018; however, the October 19, 2017, correspondence
provides that the required date for an annual monitoring report will be extended
to a date in 2018 to be determined later.
15.4 Preliminary Evaluation of Corrective Action Alternatives
Closure of the ash basins is required by 2024 under CAMA (Intermediate Risk). The
updated risk assessment (Section 12.0) has determined there is no imminent risk to
human health or the environment due to groundwater, surface water, or sediment
impacts. Soil samples collected beneath the ash basins indicate a few, limited detections
of COIs above PBTVs and PSRG POGs. If needed, groundwater and surface water can
be remediated over time using a variety of approaches and technologies. Previous
groundwater modeling has indicated closure by excavation compared to a cap-in-place
closure does not substantively accelerate groundwater cleanup. For basin closure,
reduction of infiltrating water will have the greatest positive impact on groundwater
and surface water quality downgradient of the ash basins. Closure design can augment
an overall groundwater corrective action scenario, including cap-in-place or active
groundwater remediation, which will be evaluated in the CAP. Therefore, a “low”
groundwater risk classification is recommended.
This preliminary evaluation of corrective action alternatives is included to provide
insight into the updated CAP preparation process. The preliminary evaluation is based
on data available and the current understanding of regulatory requirements for the Site.
It is assumed a source control measure of implementation of an engineered cap system
(cap-in-place) to minimize infiltration, or excavation of the ash from the ash basins, or a
combination of the two, will be designed following completion of the risk classification
process. Groundwater currently presents minimal, if any, risk to receptors. A “Low”
risk classification and closure via a cap-in-place scenario are considered viable.
Potential groundwater remedial strategies are being considered as part of the closure
design.
Based on the assessment results, the CAP will focus on areas where boron
concentrations exceed the 2L, which is the primary indicator of CCR influence on
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groundwater from the ash basins. These areas are primarily located east of the ash
basins and beneath the ash basins in the shallow, deep and bedrock flow zones.
Remedial strategies may also focus on management of boron primarily, but also
consider other constituents with concentrations likely attributable to CCR from the ash
basins such as iron and manganese.
Different remedial strategies may be applied to different portions of the Site, including
the area north-northeast of the inactive ash basin which may be influenced by the coal
pile. Remedial strategies in this area may focus primarily on the shallow flow zone and
for different constituents such as arsenic, cadmium, cobalt, nickel, selenium, sulfate,
TDS, thallium, and zinc.
15.4.1 Corrective Action Plan Preparation Process
The CAP preparation process is designed to identify, describe, evaluate, and
select remediation alternatives with the objective of bringing groundwater
quality to levels that meet applicable standards, to the extent that the objective is
economically and technologically feasible, in accordance with 2L .0106
Corrective Action. Sections (h), (i), and (j) regarding CAP preparation read as
follows:
(h) Corrective action plans for restoration of groundwater quality, submitted pursuant
to Paragraphs (c), (d), and (e) of this Rule shall include:
(1) A description of the proposed corrective action and reasons for its selection;
(2) Specific plans, including engineering details where applicable, for restoring
groundwater quality;
(3) A schedule for the implementation and operation of the proposed plan; and
(4) A monitoring plan for evaluating the effectiveness of the proposed corrective
action and the movement of the contaminant plume.
(i) In the evaluation of corrective action plans, the Secretary shall consider the extent
of any violations, the extent of any threat to human health or safety, the extent of
damage or potential adverse impact to the environment, technology available to
accomplish restoration, the potential for degradation of the contaminants in the
environment, the time and costs estimated to achieve groundwater quality
restoration, and the public and economic benefits to be derived from groundwater
quality restoration.
(j) A corrective action plan prepared pursuant to Paragraphs (c), (d), or (e) of this
Rule shall be implemented using a remedial technology demonstrated to provide the
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most effective means, taking into consideration geological and hydrogeological
conditions at the contaminated site, for restoration of groundwater quality to the
level of the standards. Corrective action plans prepared pursuant to Paragraphs (c)
or (e) of this Rule may request an exception as provided in Paragraphs (k), (l), (m),
(r), and (s) of this Rule.
To meet these requirements and to provide a comprehensive evaluation, it is
anticipated that the CAP will include:
Corrective action objectives and evaluation criteria
Technology assessment
Formulation of remedial action alternatives
Analysis, modeling, selection, and description of selected remedial action
alternative(s)
Conceptual design elements, including identification of pre-design testing
such as pilot studies
Monitoring requirements and performance metrics
Implementation schedule
The following Site conditions significantly limit the effectiveness of a number of
possible technologies:
COIs in groundwater flow are distributed throughout the shallow flow
zone and into the transition/deep zone and upper fractured bedrock.
The proximity of the ash basin dams to the bank of Lake Wylie/Catawba
River constrain what can be feasibly constructed downgradient of the
basins.
The preliminary screening of potential groundwater corrective action included:
Source control by capping in place or excavation, and monitored natural
attenuation, will be vital components to the CAP.
Groundwater migration barriers. The depth and heterogeneity of the
impacted zone(s) must be considered to determine if this technology is
feasible.
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In situ chemical immobilization. This technology has been demonstrated
to be effective for a number of relevant COIs. It’s ability to achieve
required boron concentrations will require evaluation.
Permeable reactive barrier. Similar to in situ chemical immobilization,
permeable reactive barrier technology can be evaluated for all site COIs.
Groundwater extraction. Groundwater extraction appears to be most
likely and could potentially be a viable choice as a key element of
groundwater corrective action in combination with source control and
MNA. However, further analysis is required and will be addressed in the
updated CAP.
Potentially viable options will be further evaluated in the CAP with updated
flow and transport and geochemical modeling.
15.4.2 Summary
This preliminary evaluation of corrective action alternatives is intended to
provide insight into the revised CAP preparation process, as outlined in 2L. It is
based on data available and the current regulatory requirements for the Site. It
addresses potentially applicable technologies and remedial alternatives.
Potential approaches are based on the currently available information about Site
hydrogeology and COIs. In general, three hydrogeologic units or zones of
groundwater flow can be described for the Site: shallow zone, transition/deep
zone, and bedrock flow zone. The Site COIs include common coal ash related
constituents such as boron.
If required, the potentially applicable technologies to supplement source control
and MNA include groundwater extraction technologies such as conventional
vertical wells, angle-drilled wells, and horizontal wells. Migration barriers, in
situ chemical immobilization, and permeable reactive barriers are also identified
as potentially applicable remedial action alternatives. In the event that extracted
groundwater may require treatment prior to discharge, several water treatment
technologies for the relevant COIs would be evaluated, including pH
adjustment, metals precipitation, ion exchange, permeable membranes, and
adsorption technologies.
The CAP will further evaluate basin closure options for reducing potential
impacts to human health or the environment. The CAP will also: evaluate short-
and long-term effectiveness, implementability, and potential for attenuation of
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contaminants; determine time and cost to achieve restoration; consider public
and economic benefits; and comply with applicable laws and regulations.
The CAP evaluation process will be used to determine which approach, or combination
of approaches, will be most effective. Modeling will also be used to evaluate the
various options prior to selection.
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