Weatherspoon CSA Executive Summary 08-04-2015

Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
W.H. WEATHERSPOON POWER PLANT
EXECUTIVE SUMMARY
The North Carolina Coal Ash Management Act (CAMA) requires the preparation of a
Comprehensive Site Assessment Report for each regulated facility within 180 days of
approval of the work plan. This report addresses Duke Energy's W.H. Weatherspoon
Power Plant. The purpose of this assessment was to identify the source and cause of
exceedances of regulatory standards, potential hazards to public health and safety, and
identify receptors and exposure pathways.
NC Department of Environment and Natural Resources (NCDENR) prescribed the list
of monitoring parameters to be measured at Weatherspoon. Once the sampling portion
of the Comprehensive Site Assessment (CSA) was complete, the data were examined to
pick those parameters that were 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 NCDENR/DWR Title 15,
Subchapter 2L and Interim Maximum Allowable Concentrations (IMAC) criterion.
Appendix 1 of 15A NCAC Subchapter 02L Classifications and Water Quality Standards
Applicable to The Groundwaters of North Carolina lists IMACs. The IMACs were issued in
2010 and 2011, however NCDENR has not established a 2L standard for these
constituents as described in 15A NCAC 02L.0202(c). For this reason, IMACs noted in
this report are for reference only.
If a parameter was greater than 2L or IMAC, it was designated a 'Constituent of
Interest' (COI). Some COIs (e.g., iron and manganese) 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.
The assessment also 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, chemical, and physical character of
the COIs.
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.
Duke Energy recently recommended that the basin be fully excavated with the material
safely recycled or reused in a lined structural fill (https://www.duke-
energ3�.com/12dfs/SafeBasinClosureUl2date Weatherspoon.pdf., accessed on July 28,
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
2015). 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 can be drawn:
�� No imminent hazard to human health or the environment has been identified as
a result of groundwater migration from the ash basin.
'610 Recent groundwater assessment results are consistent with previous results from
historical and routine compliance boundary monitoring well data.
Upgradient, background monitoring wells contain naturally occurring metals
and other COIs at concentrations greater than 2L or IMAC. This information is
used to evaluate whether concentrations in groundwater downgradient of the
basin are also naturally occurring or might be influenced by migration of
constituents from the ash basin.
'610 The historical and new groundwater assessment data provide no indication that
the ash basin has influenced groundwater quality beyond the property
boundary.
'61' Groundwater in the surficial aquifer under the ash basin generally flows
horizontally to the southeast and discharges into the onsite cooling pond, Jacob
Creek or the Lumber River. This flow direction is away from the nearest private
water wells. The surficial aquifer groundwater discharge to surface water
provides a boundary for migration beyond the plant property.
Downward flow from the surficial aquifer to deeper regional aquifers (the Pee
Dee and the Black Creek) is prevented by a clay confining layer. There is no
indication of persistent migration of COIs through the confining layer to the Pee
Dee Formation and Black Creek water supply aquifer beneath the Pee Dee.
The groundwater flow direction in the deep regional aquifers is also generally
toward the south and southeast, away from the nearest public and private wells.
Boron is the primary constituent that can be identified at concentrations greater
than background concentrations and 2L in a three dimensional area beneath and
southeast (downgradient) of the ash basin in the surficial aquifer.
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
h Groundwater monitoring results from wells screened in the Pee Dee aquifer
beneath the clay confining unit indicate that there has not been persistent
migration of COIs through the confining layer to the Pee Dee Formation and the
Black Creek water supply aquifer beneath the Pee Dee.
161' The groundwater modeling to be provided with the Corrective Action Plan will
be used to evaluate the effects of the planned ash excavation.
Brief summaries of the essential portions of the CSA report are presented in the
following sections.
ES1. Source Information
Mineralogical, physical, and chemical properties of the Weatherspoon Plant ash basin
have been characterized for use in the hydrogeological site conceptual model. The ash
basin was developed near original ground surface with excavation of site soils for
construction of the perimeter dikes. Ash pore water in the eastern end of the basin is
hydraulically upgradient of surrounding areas to the northeast, southeast, and
southwest, resulting in radial migration of ash pore water to groundwater in a
predominately southeast direction.
ES2. Initial Abatement and Emergency Response
No imminent threat to human health or the environment has been identified therefore
initial abatement and emergency response actions have not been required. Discharge of
ash to the basin ceased in 2011. Certain measures to further stabilize the ash basin dike
have also been implemented since 2011.
ES3. Receptor Information
Land use surrounding the Weatherspoon site includes commercial, light industrial,
rural residential, agricultural, and forest land. Jacob Creek and the Lumber River
border the Weatherspoon Plant and cooling pond.
ES.3-1 Public Water Supply Wells
Robeson County water supply wells are located more than three miles from the
site. These wells produce water from the Black Creek Formation that is
separated from the shallow groundwater at the site by a geologic confining layer.
The Robeson County wells are located upgradient of the site based on regional
groundwater gradients.
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
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
sampling of the wells in accordance with CAMA. The water quality data do not
indicate that water from a drinking water supply well has been affected by
constituents from the ash basin, therefore provisions for replacement of a
drinking water supply well with an alternate supply of potable drinking water
has not been required in the area.
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 basin.
The Lumber River is a protected habitat, as it is designated as a state 'Natural
and Scenic Water' (115 miles) and a 'National Wild and Scenic Water' (81 miles).
Wetlands adjacent to the river and Jacob Creek are potentially sensitive habitat
areas. The Lumber River supports the pinewoods darter (Etheostoma mariae) and
the sandhills chub (Semotilus lumbee), two unique fish species designated of
"special concern" by the state of North Carolina.
ES4. Sampling / Investigation Results
The Weatherspoon CSA was implemented as planned. All wells and borings were
installed at the planned locations and attained the depths necessary to accomplish the
sample collection and well installation objectives at each location. The horizontal extent
of groundwater impact to the surficial aquifer that can be clearly attributed to migration
of constituents from the ash basin is shown on an aerial photograph (Figure ES -1). The
distribution of boron in groundwater best represents the extent of impact. Other COIs
(e.g., iron) are not useful due to the ubiquitous presence in samples from monitoring
wells across the site, including hydraulically upgradient, background wells.
ES.4-1 Nature and Extent of Contamination
Arsenic, boron, cobalt, iron, manganese, thallium, total dissolved solids (TDS),
and vanadium have been identified as site specific COIs based on concentrations
in ash basin pore water being greater than a 2L or IMAC should these
constituents migrate and cause similar concentrations in groundwater.
Historic groundwater monitoring has shown that values for iron and
occasionally manganese can be greater than 2L in upgradient background and
compliance boundary wells (500 feet downgradient of the basin). Site specific
historic data is not available for vanadium. However, iron, manganese, and
vanadium are known to be commonly occurring in natural, background shallow
groundwater in the coastal plain region of North Carolina. Calculation of
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
proposed site specific background concentrations will occur when a sufficient
number of samples to perform statistical analysis have been collected from
upgradient background wells not influenced by historic mounding of water from
the ash basin.
Data suggest arsenic, cobalt, and thallium in groundwater are limited in extent to
a small area beneath and southeast of the basin. Boron and TDS are more
prevalent southeast of the ash basin than beneath the basin.
Field observations and test results indicate that the clay confining layer below
the surficial aquifer and above the Pee Dee Formation is continuous across the
site. There is no indication of persistent migration of COIs through the confining
layer to the Pee Dee Formation and Black Creek water supply aquifer beneath
the Pee Dee.
ES.4-2 Maximum Contaminant Concentrations
For the COIs identified on the basis of ash basin pore water concentrations,
boron is the most prevalent in groundwater with the highest concentration being
detected in the surficial aquifer beneath the southeast corner of the ash basin
(above the confining layer). While boron is prevalent at the site, it is limited in
area and depth (refer to Figures 10-14 and 11-1 for extent of concentrations in
excess of 2L). Groundwater affected by boron discharges to the plant cooling
pond, Jacob Creek, and the Lumber River. The maximum concentration of boron
in soil was detected in a sample collected two feet below the ash basin (20 to 21
feet below ground surface).
The highest concentration of arsenic in groundwater occurs beneath the central
portion of the ash basin. The CSA data indicate that arsenic has not migrated in
groundwater from the immediate vicinity of the ash basin. The highest
concentration of cobalt in groundwater was detected in an isolated sample near
the cooling pond. Cobalt was also detected in an area of historical plant
operations that is clearly unrelated to the ash basin. As with boron, arsenic and
cobalt detected in groundwater samples are limited in area and extent.
The highest concentration of iron in groundwater was detected in a sample from
a shallow monitoring well located adjacent to a wetland area northeast of the ash
basin. The iron concentration at this location is interpreted to be naturally
occurring due to the proximity to the wetlands rather than due to migration from
the ash basin. The highest concentration of manganese in groundwater was
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
detected in a sample from an area of historical plant operations between the
former coal pile and the cooling pond that is clearly unrelated to the ash basin.
The highest concentrations of TDS and vanadium in groundwater were detected
in upgradient, background monitoring wells.
The highest concentrations of arsenic, cobalt, and vanadium in soil occur in an
area of the plant that historic aerial photographs indicate was not used to
manage ash. The highest concentration of iron in soil occurs in a sample of clean
reddish silty sand collected from the wooded area northeast of the ash basin.
The highest concentration of manganese in a soil sample was collected from
shallow soils immediately southeast of the ash basin.
ES.4-3 Source Characterization
The ash within the 55 acre ash basin is the primary source of COIs in
groundwater. Sluicing of ash to the basin was discontinued in 2011. Historical
plant operations may represent a secondary source. The ash within the basin is
approximately 18 to 34 feet thick. The bottom of the ash basin is approximately
134 feet above mean sea (MSL) in the northwest and slopes to roughly 112 MSL
on the east. The water table elevation is controlled by ditches on either side of
the rail spur that borders the ash basin to the northwest and southeast at
elevations ranging from 129 MSL on the northwest end to 108 MSL on the
northeast and southeast corners of the ash basin. Mounding of ash pore water
within the ash basin results in discharge from the basin dikes to the perimeter
ditches around the ash basin and to groundwater beneath the unlined basin.
The basin continues to collect rainwater resulting in saturated conditions near
the base. In June 2015, approximately 15 feet of saturated ash was measured on
the eastern side of the basin. The ash on the western side of the basin was dry.
The toe of the dike is designed to allow ash pore water to discharge to a
perimeter ditch that flows to the cooling pond. When the ash basin was
operational, the discharge from the ash basin was routed to the cooling pond.
The cooling pond outfall to the Lumber River is regulated under a National
Pollution Discharge Elimination System (NPDES) permit.
ES.4-4 Receptor Survey
A receptor survey was conducted in accordance with CAMA during 2014. No
additional water supply wells or surface water bodies have been identified.
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
Public water supply wells in Robeson County draw water from the Black Creek
aquifer. The closest public water supply wells are three to five miles from the
site in the regional upgradient direction. Arsenic, boron, cobalt, thallium, and
vanadium (ash basin COIs) were not detected in a sample from a Weatherspoon
plant water supply well also screened within the Black Creek aquifer. Therefore,
there is no indication that public water supplies are affected by the ash basin.
The private water supply wells identified within one half mile of the compliance
boundary are located either upgradient of the site or on the opposite side of the
surficial aquifer discharge zone, Jacob Creek. The private water supply well data
collected at the direction of the North Carolina Department of Environment and
Natural Resources (NCDENR) during 2015 are consistent with background
conditions.
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, arsenic, barium, boron, chromium, iron,
manganese, mercury, TDS, vanadium, 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.
ES.4-5 Regional Geology and Hydrogeology
The vicinity of the Weatherspoon Plant is generally characterized by shallow
water table conditions occurring in surficial soils and unconsolidated sediments
underlain by the Coastal Plain regional aquifer system. Sediments of the
Yorktown Formation are part of the surficial aquifer. The confined Pee Dee and
Black Creek aquifer systems lie beneath the Yorktown Formation in the area.
ES.4-6 Site Geology and Hydrogeology
Sediments exposed at the surface in the Weatherspoon Plant area are either
relatively recent Coastal Plain sediments or exposed Yorktown Formation
sediments. Siltstone in the Yorktown Formation is exposed at the surface in
limited areas.
Groundwater flows across the Weatherspoon site toward Jacob Creek on the
east, the cooling pond to the east and south, and the Lumber River to the south
from upland areas north and west of the property. The water table occurs within
a few feet of the surface to as much as 15 feet below ground surface in upland
areas. A confining layer that separates the Yorktown Formation from the
underlying Pee Dee Formation was encountered consistently across the site.
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
ES.4-7 Existing Groundwater Monitoring Data
NPDES compliance groundwater monitoring data provide evidence of seasonal
pulses of chloride, sulfate, iron, and TDS. Boron and chloride in the March 2015
sample from CW -03 were identified as statistical outliers. This condition was not
repeated for the June 2015 data.
ES.4-8 Development of Site Conceptual Model
A hydrogeological site conceptual model was developed from data generated
during previous assessments, existing groundwater monitoring data, and 2015
groundwater assessment activities. In general, the ash basin source area
discharges ash pore water to perimeter ditches at the toe of the basin dam and to
the subsurface beneath the basin. Groundwater flows in a radial pattern to the
southeast in close proximity to the ash basin. The highest concentrations of COIs
in groundwater occur beneath ash basin in the lower Yorktown Formation above
the Pee Dee confining layer. There is no indication of migration through the
confining layer.
ESS. Identification of Data Gaps
The horizontal and vertical extent of COIs have been evaluated for soil and
groundwater. Source area and groundwater characterization data have been used to
develop hydrogeologic and geochemical site conceptual models that will support
preparation of flow and transport groundwater modeling for the site. There are no data
gaps that will be limiting factors in the execution of the groundwater model or
development of the Corrective Action Plan. The following additional information
would be useful:
1. Additional data from recently installed background wells will assist in
confirming the background concentration ranges in groundwater for the COIs.
Over time, the turbidity of the new assessment wells should decrease allowing
for greater reliance on the total concentrations as true naturally occurring
background concentrations.
2. Groundwater data between the ash basin boundary and the compliance
boundary is limited. Monitoring of wells within this zone will be helpful to
assess natural attention of COIs with distance from the source area.
3. Analysis of chromium speciation in ash pore water is proposed to determine if
the ash basin is a source of hexavalent chromium detected in groundwater
samples.
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Comprehensive Site Assessment Report August 2015
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ES6. Conclusions
1. Duke Energy recently recommended that the basin be fully excavated with the
material safely recycled or reused in a lined structural fill. The impact of this
recommendation on groundwater quality will be evaluated in the Corrective
Action Plan.
2. No imminent hazards to human health and the environment requiring
immediate action were identified by the CSA. The data indicate that the geologic
confining layer beneath the ash basin is continuous on the plant site, and is
effectively preventing impact to underlying regional aquifers. Interpretation of
the CSA results indicate that there is little possibility that private water supplies
would be impacted by the ash basin because the cooling pond and adjacent
surface water bodies lying immediately to the east and south of the basin are
groundwater discharge areas that receive surface water from upstream and
groundwater from the opposite side and the confining layer prevents vertical
migration of COIs.
3. A plan for interim groundwater monitoring is presented in Section 16 of this
report. The Corrective Action Plan, based on the data presented in this report
and subsequent groundwater modeling, will be submitted within 90 days.
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NOTES:
DUKE
ENERGY
PROGRESS
FIGURE ES -1
SITE CONCEPTUAL MODEL - PLAN VIEW
WEATHERSPOON POWER PLANT