Asheville Executive Summary CSA Rept Aug 2015

Comprehensive Site Assessment Report August 2015
Asheville Steam Electric Plant SynTerra
ASHEVILLE STEAM ELECTRIC PLANT
EXECUTIVE SUMMARY
On August 20, 2014, the North Carolina General Assembly passed Session Law 2014-
122, the Coal Ash Management Act of 2014 (CAMA). Section § 130A-309.211 of the act
requires the owner of a coal combustion residuals surface impoundment to submit a
Groundwater Assessment Work Plan (GAP or Work Plan) to the North Carolina
Department of Environment and Natural Resources (NCDENR) no later December 31,
2014 and a Groundwater Assessment Report (herein referred to as a Comprehensive
Site Assessment [CSA]) no later than 180 days following approval of the Work Plan.
Duke Energy Progress, LLC (Duke Energy) submitted a Work Plan to NCDENR for
assessment and characterization of the Asheville Steam Electric Plant (Asheville Plant,
Plant or Site) ash basin and ash storage areas on December 30, 2014. The Work Plan was
subsequently conditionally approved by the NCDENR in correspondence dated
February 24, 2015. This CSA report was prepared to comply with CAMA and is
submitted to NCDENR within the allotted 180 day timeframe. Data generated during
the CSA will be used in development of the Corrective Action Plan (CAP), due 90 days
after submittal of this CSA.
The purpose of this CSA is to characterize the extent of contamination resulting from
historical production and storage of coal ash, evaluate the chemical and physical
characteristics of the contaminants, investigate the geology and hydrogeology of the
Site including factors relating to contaminant transport, and examine risk to potential
receptors and exposure pathways.
NCDENR prescribed the list of monitoring parameters to be measured at the Asheville
Plant. Following receipt of the data, parameters were evaluated to assess those most
relevant for the Site. These parameters were determined by examining data from
monitoring wells installed in ash and seeps that drain from the ash, and then by
comparing these results to the North Carolina Groundwater Quality Standards found in
the North Carolina Administrative Code Title 15A, Subchapter 2L.0202 (2L or 2L
Standards) and the Interim Maximum Allowable Concentrations (IMAC) established by
NCDENR pursuant to 15A NCAC 02L.0202(c). If a constituent concentration exceeded
the North Carolina Groundwater Quality Standards in ash pore water wells, as
specified in the 2L Standards or the IMACs, it has been designated as a "Constituent of
Interest" (COI). COIs are constituents that display correlation to ash basin influence.
Some COIs are also present in background monitoring wells and thus require careful
examination to determine whether their presence on the downgradient side of the
basins is from natural sources (e.g., rock and soil) or the ash basin.
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The IMACs were issued in 2010, 2011 and 2012; however NCDENR has not established
a 2L for these constituents as described in 15A NCAC 02L.0202(c). For this reason,
IMACs noted in this report are for reference only.
The assessment addresses the horizontal and vertical extent of COIs in soil and
groundwater. Significant factors affecting constituent transport, and the geological and
hydrogeological features influencing the movement, as well as the chemical and
physical character of the COIs were evaluated.
Data presented in this assessment report will be the basis for the Corrective Action Plan
required within 270 days of the approved work plan to identify alternative strategies to
address groundwater impacts at the Site.
In accordance with Sections 3(b) and (c) of CAMA (Session Law 2014-122), Duke Energy
will fully excavate the ash basins at the Site, with the material to be safely recycled or
reused in a lined structural fill or disposed in a lined landfill. The Corrective Action
Plan will include groundwater modeling results of the anticipated ash removal to assess
the effects on groundwater. A groundwater monitoring plan will be provided to assess
changes in groundwater conditions over time.
Based on the scientific evaluation of historical and new groundwater assessment data
presented in this report, the following conclusions are drawn:
41' No imminent hazard to human health or the environment has been identified as
a result of groundwater migration from the ash basins.
47 Recent groundwater assessment results are consistent with previous results from
historical and routine compliance boundary monitoring well data.
'47 Upgradient, background monitoring wells contain naturally occurring metals
and other COIs at concentrations greater than 2L or IMAC concentrations. This
information is used to evaluate whether concentrations in groundwater
downgradient of the basins are also naturally occurring or might be influenced
by migration of constituents from the ash basin.
'61' The historical and new groundwater assessment data indicate the aerial extent of
impacted groundwater is limited to within the property boundary with the
exception of an area under I-26.
41' Groundwater in the surficial aquifer under the ash basin flows horizontally and
vertically to the west and discharges into the French Broad River. The river, with
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Asheville Steam Electric Plant SynTerra
tributaries to the north and south of the Site, provide hydrogeologic boundaries
for groundwater migration.
47 Boron is the primary constituent that can be identified at concentrations greater
than background concentrations and the 2L concentration in a three dimensional
area beneath and west (downgradient) of the ash basin in the surficial, transition,
and bedrock aquifers.
`1' Leakage from the lined flue gas desulfurization (FGD) wastewater treatment
wetlands was detected as evidenced by elevated FGD blowdown-related
constituents (e.g. chloride) to the northwest of the 1964 ash basin.
L1' Groundwater modeling to be provided with the Corrective Action Plan will be
used to evaluate the effects of the planned ash excavation.
L1' The approximate extent of horizontal migration of boron in the surficial aquifer
is shown on Figure ES -1.
Brief summaries of the essential portions of the Comprehensive Site Assessment Report
are presented in the following sections.
ES1. Source Information
Duke Energy Progress, LLC. (Duke Energy) owns and operates the Asheville Steam
Electric Plant (Asheville Plant) located near Asheville, in Buncombe County, North
Carolina. The Asheville Plant commenced operations in 1964 and is currently
operational. Mineralogical, physical, and chemical properties of the Asheville Plant ash
basins have been characterized for use in the hydrogeological Site Conceptual Model
(SCM). The ash basins were developed near original ground surface with excavation of
Site soils for construction of the earthen dams. The ash basins are situated upgradient
of the French Broad River and occupy two former tributary valleys. Ash pore water is
connected with the surficial aquifer and underlying transition zone and fractured
bedrock flow systems. Groundwater flow is toward the west and discharging into the
French Broad River.
ES2. Initial Abatement and Emergency Response
Duke Energy is currently planning to fully excavate the ash basins in accordance with
CAMA requirements with the material safely recycled or reused in a lined structural fill
or disposed in a lined landfill. Plans are underway to provide an alternate water
supply to nearby residences by extending a water line along Bear Leah Trail. This
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project is expected to be complete in early fall of 2015. Excavation of the 1982 ash basin
has been on-going since 2007.
ES3. Receptor Information
The Asheville Plant lies in a developed area approximately eight (8) miles southeast of
Asheville, North Carolina. Surrounding property uses include residential, commercial,
industrial and agricultural. Commercial and residential development dominates the
land use north and south of the property. Lake Julian is located east of the Plant and I-
26 and the French Broad River are located to the west.
ES.3-1 Public Water Supply Wells
Public water supply wells are located more than two miles from the Site. These
well locations are upgradient, side gradient or separated by a groundwater
discharge area (French Broad River) from the Asheville Plant. These production
wells are separated by topographic and groundwater divides; therefore, the
likelihood that groundwater from the Asheville Plant could be within the
drawdown zone of a well more than two miles away is extremely low.
ES.3-2 Private Water Supply Wells
Inventories of public and private water supply wells have been compiled.
NCDENR contacted nearby residents regarding private wells and managed the
sampling of the wells in accordance with CAMA. Water quality data indicate
that manganese, sulfate, and total dissolved solids (TDS) have been detected in
water from drinking water supply wells located on the west side of the French
Broad River from the Site. Elevated concentrations of iron and manganese are
cited in a USGS report as being the most common water quality issue in the Blue
Ridge and Piedmont Provinces (Daniel and Dahlen, 2002). The same study
indicates high sulfate (higher than the 2L) and TDS concentrations are
interrelated and are common with water from deep supply wells.
ES.3-3 Human and Ecological Receptors
Consumption of groundwater, recreational use of affected surface water, and
consumption of fish and game affected by contaminants are the primary
exposure pathways for humans in the vicinity of the ash basins.
Constituents of potential concern (COPCs) for human and ecological receptors
identified using screening level risk assessment methodology for receiving areas
at the Site include pH, aluminum, antimony, arsenic, barium, beryllium, boron,
cadmium, chloride, chromium, cobalt, copper, iron, manganese, mercury,
molybdenum, nickel, nitrate (as N), selenium, sulfate, thallium, TDS, vanadium,
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and zinc. This list is longer than the list of site specific COIs due to the
conservative approach of comparing analytical results to published reference
criterion in the risk assessment screening process.
ES4. Sampling / Investigation Results
The Asheville CSA was implemented as planned with a few modifications in well
placement due to access. Four wells were relocated due to underground utilities,
overhead utilities, or unsuitable terrain. Well locations MW -21 and MW -22 were
relocated to the I-26 right of way due to access not provided on private property. Wells
were installed in each saturated zone that was of sufficient thickness to discretely
monitor. Figure ES -1 shows the horizontal extent of groundwater impact to the
surficial aquifer which can be clearly attributed to migration of constituents from the
ash basin. The distribution of boron in groundwater best represents the extent of
impact. Other COIs (e.g., cobalt, iron, manganese, and vanadium) are not useful due to
their ubiquitous presence in samples from monitoring wells across the Site, including
hydraulically upgradient, background wells.
ES.4-1 Nature and Extent of Contamination
Antimony, arsenic, boron, chromium, cobalt, iron, manganese, pH, sulfate,
thallium, TDS and vanadium have been identified as Site-specific COIs based on
exceedances of the 2L or IMAC in ash pore water. Other metals (e.g. beryllium,
cadmium, nickel and selenium) have been detected above the 2L or IMAC and
are addressed herein, but are not considered COIs due to apparent isolation from
CCR leachate. For example, chloride is not present within ash pore water and is
not a COI, yet this constituent exceeds the 2L in areas downgradient from the
northwest corner of the 1964 ash basin and has been evaluated during this
assessment.
Cobalt, iron, manganese, and vanadium are detected in groundwater at
background locations at the Site. Calculation of proposed Site-specific
background concentrations will occur when a sufficient number of samples to
perform statistical analysis have been collected.
Data suggest antimony, arsenic, boron, chromium, sulfate, thallium, and TDS in
groundwater are limited to an area beneath and west of the basins. The
horizontal extent of migration is controlled by the French Broad River to the
west, which acts as a major groundwater to surface water discharge zone.
Field observations and test results indicate that the fractured bedrock flow
system is discontinuous across the Site. COIs have been detected in groundwater
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within bedrock wells downgradient of the ash basins prior to discharging into
the French Broad River.
ES.4-2 Maximum Contaminant Concentrations
For the COIs identified in groundwater, boron is the most prevalent constituent
detected above the 2L and background concentrations. The highest
concentration is detected in the surficial aquifer (saprolite) adjacent to the
northwest corner of the 1964 ash basin. The extent of boron is defined to the
downgradient portion of the Site between the ash basins and the French Broad
River. Seep sampling results verify groundwater is emerging at the French
Broad River, consistent with the current SCM. Refer to Figure ES -1 for extent of
boron concentrations in excess of the 2L concentration of 700 µg/L.
The highest concentration of thallium was detected near the northern waste
boundary of the 1964 ash basin inside the Compliance Boundary.
An area of maximum concentrations of chloride, selenium, sulfate, and TDS was
identified and defined during this assessment to the northwest of the 1964 ash
basin. The concentrations in this area are influenced by the FGD wastewater
treatment wetlands as evident by chemical analysis and hydraulic conditions in
the area.
Highest detections of arsenic, beryllium, and nickel occurred in the saprolite
below the 1964 ash basin. The CSA data indicate that these constituents have not
migrated in groundwater from the immediate vicinity of the ash basin.
The highest concentration of antimony, chromium, and nitrate were identified
near the southern corner of the 1982 basin. The CSA data indicate that these
constituents have not migrated in groundwater from the immediate vicinity of
the ash basin.
The highest concentration of cobalt was detected below the 1964 ash basin within
the transition zone. Iron was detected at the highest level within a bedrock well
along the French Broad River. Highest concentrations of manganese are found
within the saprolite beneath the 1964 ash basin. The highest concentration of
vanadium is found south of the 1982 basin. Cobalt, iron, manganese, and
vanadium are detected in groundwater at Site background locations at
concentrations greater than the 2L or IMAC. Calculation of proposed Site-
specific background concentrations will occur when a sufficient number of
samples to perform statistical analysis have been collected.
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ES.4-3 Source Characterization
Data indicates the ash within the 1964 and 1982 ash basins is the primary source
of COIs in nearby groundwater as shown on Figure ES -1. Naturally occurring
concentrations of cobalt, iron, manganese, and vanadium that exceed the 2L or
IMAC are found within Site background wells. Collectively these ash basins
encompass 78 acres. Ash placement within the 1964 basin ceased in the early
80's and dewatering and excavation of ash from the 1982 basin began in 2007.
Ash within the basins is between 36 and 59 feet thick. The bottom of the 1964 ash
basin is approximately 2,094 feet msl and the 1982 basin 2,097 msl near the
deepest portion of each basin. The basins continue to collect rainwater resulting
in saturated conditions near the base. In June 2015, approximately 35 feet of
saturated ash was measured in the 1964 basin. Dewatering of the 1982 basin to
facilitate excavation currently controls the groundwater level, resulting in 20 feet
of saturated ash measured in a small area of the basin not excavated at that time.
The toes of the dams are designed to allow ash pore water to discharge. Recently
the seepage flow through the dike from the 1964 basin was captured and routed
through NPDES Outfall 001. The seepage flow below the 1982 basin continues to
be monitored at an outfall structure with two weirs. The treatment wetlands
appear to be a secondary source of constituents in the groundwater. Design
information indicates it was lined. However, groundwater data from nearby
wells indicate some leakage from the FGD wastewater treatment constructed
wetlands.
ES.4-4 Receptor Survey
A receptor survey was conducted in accordance with CAMA during 2014 and
has been updated herein with additional available information. During 2015,
NCDENR managed the sampling of water supply wells in the area. Only
manganese, sulfate, and TDS were reported at concentrations greater than 2L or
IMAC. These constituents are known to cause water quality issues in the region
and cannot be directly attributed to the ash basins.
The three closest public water supply wells are over two miles from the Site.
Forty private supply wells have been identified within one half mile of the Site.
These private well locations are upgradient, side gradient or separated by a
groundwater discharge area (French Broad River) from the Asheville Plant. Five
private water supply wells are located to the south of the Site and east of the
French Broad River. These potential receptors are being mitigated by the
installation of a municipal water supply line to these residences. This project is
scheduled for completion by the fall of 2015.
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ES.4-5 Regional Geology and Hydrogeology
The Blue Ridge Physiographic province is dominated by the Blue Ridge geologic
belt. The Blue Ridge belt is an extensive thrust sheet separated from the
Piedmont geologic belt on the southeast by the Brevard zone and bounded from
the northwest by low angle thrust faults that have created the Valley and Ridge
Physiographic province in eastern Tennessee. The Brevard zone is characterized
by major faults trending SW -NE and associated cataclastic rocks with a typical
dip toward the SE. This zone, as marked by two major thrust faults in the
Skyland Quadrangle, passes approximately 1.3 miles to the southeast of the Site.
In a general perspective, the area underwent folding and faulting along with
several periods of metamorphism with igneous intrusion. Folding and faulting
of the bedrock creates preferential pathways that impact both groundwater flow
direction and velocity.
ES.4-6 Site Geology and Hydrogeology
Geology at the Site consists of overburden, also referred to as regolith, and
metamorphic bedrock. In stream valleys, fluvial deposits, also referred to as
alluvium, overlie the bedrock. The metamorphic bedrock, primarily schist and
gneiss, tends to be exposed on the ground surface along topographic ridges, road
cuts, and in stream or river valleys. Where metamorphic bedrock has been
weathered into saprolite, silt, sand and clay are found overlying the bedrock.
Due to the limited aerial and vertical extent of the alluvial deposits, alluvium and
saprolite are both categorized in the surficial flow regime. The transition zone, a
combination of partially weathered rock and saprolite, typically found above
competent bedrock, can be a significant hydrogeologic feature in the system.
Therefore, the transition zone is considered its own flow regime. The third flow
regime encountered at the Asheville Plant is composed of fractured bedrock,
which transports groundwater through secondary porosity. Each of the three
described flow regimes (surficial, transition zone, and bedrock) are present at the
Asheville Plant.
The groundwater table generally follows topography but will vary based on Site-
specific factors. Hydraulic data indicate groundwater flows to the west towards
the French Broad River. The first occurrence of water is heavily reliant upon the
nature of regolith (if present), since it is the primary storage unit that feeds
bedrock fractures. The regolith -fractured bedrock aquifer groundwater flow
regime of the Asheville Plant is bounded on the south and west by an unnamed
tributary and the French Broad River and to the north and east by Lake Julian
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and Powell Creek, which flows west and empties in the French Broad adjacent to
the NPDES Outfall 001.
ES.4-7 Existing Groundwater Monitoring Data
NPDES compliance groundwater monitoring data provide evidence that iron
and manganese are consistently detected above 2L concentrations in background
wells. Historical water level data indicate a lowering water table surface near the
southeast corner of the 1982 basin coincident with the dewatering for the ash
removal project.
ES.4-8 Development of Site Conceptual Model
The geologic and hydrogeologic framework for the Asheville Plant is consistent
with the basic slope -aquifer system SCM as defined by LeGrand (2004). This
hydrogeological SCM was developed with data generated during previous
assessments and confirmed with the 2015 groundwater assessment activities. In
general, the French Broad River and its tributaries are groundwater discharge
zones for groundwater at the Site. Groundwater under the ash basin source area
flows to the west towards the French Broad River where groundwater emerges
as seeps. The highest concentrations of COIs in groundwater occur to the
northwest of the 1964 ash basin and are likely due to leakage from the treatment
wetlands. This is the result of impacted groundwater flowing in that direction.
The Asheville Plant is bordered to the east by Lake Julian, to the north by Powell
Creek, to the south by an unnamed tributary and to the west by the French Broad
River. Powell Creek flows south to north to the confluence of Lake Julian. Below
the Lake Julian dam, Powell Creek flows east to west to the confluence of the
French Broad River. The unnamed tributary located to the south of the Plant also
flows east to west to the confluence of the French Broad River. Both streams
represent groundwater discharge zones and flow into the French Broad River.
The French Broad River flows south to north near the Site.
ESS. Identification of Data Gaps
The horizontal extent of groundwater impact has been defined and the vertical extent is
understood to be controlled by the depth of water -bearing zones in fractured bedrock.
Source area and groundwater characterization data will be used to support preparation
of flow and transport groundwater modeling for the Site. The SCM provided herein
will also support the modeling and the preparation of the Corrective Action Plan (CAP)
There are no data gaps that will be limiting factors in the execution of the groundwater
model or development of the CAP.
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However, the following additional information would be useful:
Speciation analysis was conducted for geochemical model input information. The
hexavalent chromium data is inconclusive with regards to source and extent.
Therefore, additional speciation analysis for hexavalent chromium is proposed
for the Asheville Plant; and
2. The installation of approximately 15 stream gauges will be used to further refine
the hydraulic conditions at the Site and provide useful input for the evolving
SCM and future performance monitoring.
ES6. Conclusions
1. The CSA evaluated the horizontal and vertical extent of groundwater
contamination at the Site, and found that the sources of contamination (shown on
Figure ES -1) are the coal ash contained in the ash basins and leakage from the
FGD wastewater treatment wetlands. The cause of contamination is the leaching
of constituents from the coal ash and FGD wastewater into the underlying soil
and groundwater.
2. Duke Energy plans to excavate the ash basins at the Site in accordance with
CAMA requirements. The impact of the ash excavation on long-term
groundwater quality will be evaluated as part of the groundwater flow and
transport modeling to be provided in the CAP.
3. Background monitoring wells contained naturally -occurring metals and other
constituents at concentrations that exceeded their respective 2L or IMAC values.
These constituents included cobalt, iron, manganese and vanadium.
4. Five private wells have been identified south of the Site on the east side of the
French Broad River. Prior to initiating this assessment, a plan was underway to
remove this potential hazard to receptors by extending a water line to these
properties. This project is expected to be complete in early fall of 2015.
5. The human health and ecological screening -level risk assessments did not
specifically identify the presence of health or environmental risks; however, the
results indicate that constituents in environmental media could be of concern
and further investigation by a Site-specific risk assessment may be warranted.
No imminent hazards to human health and the environment were identified
during the screening -level risk assessments.
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6. A plan for interim groundwater monitoring is presented in Section 16 of this
report. The CAP, based on the data presented in this report and subsequent
groundwater modeling, will be submitted within 90 days.
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