NC0005363_Weatherspoon CSA Report 08-04-2015_20150805

(� DUKE
�C ENERGY.
August 4, 2015
Mr. Donald R. van der Vaart, Secretary
North Carolina Department of Environment and Natural Resources
1601 Mail Service Center
Raleigh, North Carolina 27699-1601
Subject: COMPREHENSIVE SITE ASSESSMENT REPORT
Duke Energy W.H. Weatherspoon Power Plant
Lumberton, Robeson County, North Carolina
NPDES Permit No. NC0005363
Dear Mr. van der Vaart:
Harry K. Sideris
Senior Vice -President
Environmental, Health & Safety
526 South Church Street:
Mail Code ECUP
Charlotte, North Carolina 28202
704-382-4303
In accordance with the North Carolina Department of Environment and Natural Resources
Division of Water Resources' February 6, 2015 letter (Conditional Approval of Revised
Groundwater Assessment Work Plan), Duke Energy hereby submits the Comprehensive Site
Assessment (CSA) Report for the W.H. Weatherspoon Power Plant. As indicated below, Duke
Energy is also providing the CSA Report to additional NCDENR Central Office personnel, the
NCDENR Fayetteville Regional Office, and the Coal Ash Management Commission.
We consider development and submittal of this CSA Report to satisfy the directives of your
Conditional Approval letter as well as the requirements of Section 130A-309.209(a)(4) and
Section 130A-309.209(d) of the Coal Ash Management Act of 2014.
If you have comments and/or questions, please direct them to me at 704-382-4303 or Ed
Sullivan, Manager of Waste & Groundwater Programs, at 980-373-3719.
Sincerely,
/177
Harry K. Sideris
Senior Vice -President
Environmental, Health & Safety
Enclosure: Comprehensive Site Assessment Report, W.H. Weatherspoon Power Plant
cc: Stanley (Jay) Zimmerman, Director, Division of Water Resources, Central Office
Steven Lanter, Hydrogeologist, Water Quality Regional Operations Section, Central Office
Tom Reeder, Assistant Secretary for Einvornment
NCDENR Fayetteville Regional Office
Coal Ash Management Commission

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synTerra
COMPREHENSIVE
SITE ASSESSMENT REPORT
Site Name and Location:
Groundwater Incident No.:
NPDES Permit No.:
Date of Report:
Permittee and Current
Property Owner:
Consultant Information:
Latitude and Longitude of Facility:
W.H. Weatherspoon Power Plant
491 Power Plant Road
Lumberton, North Carolina 28358
Not Assigned
NC0005363
August 5, 2015
Duke Energy Progress, Inc.
526 South Church St
Charlotte, NC 28202
[phone]
SynTerra Corporation
148 River Street
Greenville, South Carolina
[phone]
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DIVISION OF WATER RESOURCES
Certification for the Submittal of a Comprehensive Site Assessment
Responsible Party and/or Permittee: Duke Energy Progress, Inc.
Contact Person: Harry Sideris
Address: 526 South Church Street
City: Charlotte State: NC Zip Code: 28202
Site Name: W.H. Weathers oon Power Plant
Address: 491 Power Plant Road
City: Lumberton State: NC Zip Code: 28358
Groundwater Incident Number (applicable): NA/ Coal Ash Management Act CSA
I, Mark Taylor, a Professional Engineer/Professional Geologist (circle one) for
S nTerra Corporation (firm or company of employment) do hereby certify that the
information indicated below is enclosed as part of the required Comprehensive Site
Assessment (CSA) and that to the best of my knowledge the data, assessments,
conclusions, recommendations and other associated materials are correct, complete
and accurate.
(Each item must be initialed by the certifying licensed professional)
1. The source of the coal combustion residuals (contamination) has been identified. A list
of all potential sources of the coal combustion residuals (contamination) is attached.
2. Imminent hazards to public health and safety have been evaluated but none were
identified.
3.Potential receptors and significant exposure pathways have been identified.
4. —4-Zr Geological and hydrogeological features influencing the movement of groundwater have
been identified. The chemical and physical character of the contaminants have been
identified.
5. `-441 4 The CSA sufficiently characterizes the cause, significance and extent of groundwater and
soil contamination associated with the regulated coal ash management areas such
that a groundwater Corrective Action Plan can be developed.
If any of the above statements have been altered or items not initialed,
provide a detailed explanation.
Failure to initial any item or to provide written justification for the lack
thereof will result in immediate return of the CSA to the responsible party.
(Please Affix Seal and Signature)
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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 area of the
facility. Data limitations are discussed in Section 14 of the CSA report.
Continued groundwater monitoring at the site will refine the understanding
of the following:
1. Distribution of constituent of interests (COls) along the major flow
transect to the southeast of the ash basin toward the cooling pond, to
the northeast toward Jacob Swamp, and vertically.
2. Continued monitoring of background monitoring wells will generate
sufficient data for calculation of site specific background concentrations.
3. Analysis of chromium speciation in ash pore water will provide
reference data to confirm that the ash basin is not a source of
hexavalent chromium in groundwater.
Item 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.
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
fresh water from upstream and unaffected groundwater from the opposite
side and the confining layer prevents vertical migration of constituents of
interest.
Item 5. The groundwater assessment plan for the CSA as approved by NCDENR
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 were
not evaluated.
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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,
ES-i
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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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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
ES -iv
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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
ES-v
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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.
ES5. 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
W.H. Weatherspoon Power Plant SynTerra
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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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
TABLE OF CONTENTS
SECTION PAGE
W.H. Weatherspoon Power Plant Executive Summary..................................................ES-i
ES1. Source Information............................................................................................. ES-iii
ES2. Initial Abatement and Emergency Response ..................................................
ES-iii
ES3. Receptor Information......................................................................................... ES-iii
ES3.1 Public Water Supply Wells..........................................................................ES-iii
ES3.2 Private Water Supply Wells........................................................................ ES-iii
ES3.3 Human and Ecological Receptors............................................................... ES -iv
ES4. Sampling / Investigation Results...................................................................... ES -iv
ES4.1 Nature and Extent of Contamination......................................................... ES -iv
ES4.2 Maximum Contaminant Concentrations.................................................... ES-v
ES4.3 Source Characterization............................................................................... ES-vi
ES4.4 Receptor Survey............................................................................................ ES-vi
ES4.5 Regional Geology and Hydrogeology...................................................... ES-vii
ES4.6 Site Geology and Hydrogeology............................................................... ES-vii
ES4.7 Existing Groundwater Monitoring Data .................................................
ES-viii
ES4.8 Development of Site Conceptual Model ..................................................
ES-viii
ESS. Identification of Data Gaps..............................................................................ES-viii
ES6. Conclusions.......................................................................................................... ES -ix
1.0 Introduction.....................................................................................................................1
1.1 Purpose of Comprehensive Site Assessment.........................................................1
1.2 Regulatory Background............................................................................................ 2
1.2.1 NCDENR Requirements..................................................................................... 2
1.2.2 NORR Requirements........................................................................................... 2
1.2.3 CAMA Requirements.......................................................................................... 2
1.3 NCDENR-Duke Energy Correspondence.............................................................. 3
1.4 Approach to Comprehensive Site Assessment...................................................... 3
1.4.1 NORR Guidance................................................................................................... 3
1.4.2 USEPA Monitored Natural Attenuation Tiered Approach ........................... 4
1.4.3 ASTM Site conceptual model............................................................................. 4
1.5 Technical Objectives.................................................................................................. 5
2.0 Site History and Description........................................................................................ 6
I
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2.1
Site Location, Acreage, and Ownership................................................................. 6
2.2
Plant Description........................................................................................................ 6
2.3
General Site Description........................................................................................... 6
2.4
Adjacent Property, Zoning, and Surrounding Land Uses ................................... 6
2.5
Adjacent Surface Water Bodies and Classifications .............................................. 7
2.6
Meteorological Setting............................................................................................... 7
2.7
Hydrologic Setting..................................................................................................... 7
2.8
Permitted Activities and Permitted Waste............................................................. 7
2.9
History of NPDES and Surface Water Monitoring ............................................... 7
2.10 History of NPDES Groundwater Monitoring........................................................ 8
2.11
Assessment Activities or Previous Site Investigations ......................................... 9
2.12 Plans for Decommissioning....................................................................................
11
3.0
Source Characteristics..................................................................................................12
3.1
Coal Combustion and Ash Handling System......................................................12
3.2
Physical Properties of Ash......................................................................................
12
3.3
Chemical Properties of Ash....................................................................................12
3.4
Description of Ash Basins and Other Ash Storage Areas..................................14
4.0
Receptor Information...................................................................................................15
4.1
Summary of Receptor Survey Activities...............................................................
15
4.2
Summary of Receptor Survey Findings................................................................
16
4.2.1 Public Water Supply Wells...............................................................................16
4.2.2 Private Water Supply Wells.............................................................................
17
5.0
Regional Geology and Hydrogeology......................................................................18
5.1
Regional Geology.....................................................................................................18
5.2
Regional Hydrogeology..........................................................................................19
6.0
Site Geology and Hydrogeology................................................................................
20
6.1
Site Geology..............................................................................................................
23
6.1.1 Soil Classification...............................................................................................
23
6.1.2 Rock Lithology...................................................................................................
24
6.1.3 Structural Geology.............................................................................................
24
6.1.4 Soil and Rock Mineralogy and Chemistry.....................................................
24
6.2
Site Hydrogeology...................................................................................................
24
6.2.1 Groundwater Flow Direction...........................................................................
25
ii
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6.2.2 Hydraulic Gradients..........................................................................................
26
6.2.3 Hydraulic Conductivity....................................................................................
26
6.2.4 Groundwater Velocity.......................................................................................
27
6.3
Hydrogeologic Site Conceptual Model.................................................................
27
6.4
Geochemical Site Conceptual Model....................................................................
28
6.4.1 Iron.......................................................................................................................
28
6.4.2 Vanadium............................................................................................................29
6.4.3 Manganese..........................................................................................................
29
6.4.4 Boron....................................................................................................................30
6.4.5 Arsenic.................................................................................................................
31
6.4.6 Chromium, Cobalt, and Nickel........................................................................
31
6.5
Electrochemical Charge Balance............................................................................
32
6.6
Equilibrium...............................................................................................................
32
7.0
Source Characterization...............................................................................................
34
7.1
Identification and Description of Sources............................................................
34
7.1.1 Coal Combustion and Ash Handling System ................................................
34
7.1.2 Description of Ash Basin...................................................................................
35
7.2
Characterization of Sources....................................................................................
35
7.2.1 Physical Properties of Ash................................................................................
36
7.2.2 Chemical Properties of Ash..............................................................................
37
7.2.3 Chemistry of Ash Pore Water..........................................................................
38
7.2.4 Hydrology of the Ash Basin.............................................................................
39
7.3
Piezometers and Seeps............................................................................................
39
7.4
Constituents of Potential Concern.........................................................................
39
8.0
Soil and Rock Characterization..................................................................................
40
8.1
Background Soil.......................................................................................................
40
8.2
Soil..............................................................................................................................
40
8.2.1 Soils beneath the Ash Basin..............................................................................
41
8.2.2 Site Soils...............................................................................................................
42
8.2.3 Surficial Soils.......................................................................................................
42
8.3
Comparison of Results to Applicable Levels .......................................................
42
9.0
Sediment, Seep, and Surface Water Characterization ...........................................
44
9.1
Review of NCDENR March 2014 Sampling Results ...........................................
44
iii
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9.2 Comparison of Exceedances to 2B Standards......................................................
45
9.3 Discussion of Results for Constituents without 2B Standards ..........................
45
10.0 Groundwater Characterization...................................................................................
46
10.1 Background Monitoring Wells...............................................................................
46
10.2 Discussion of Redox Conditions............................................................................
48
10.3 Regional Groundwater Data for Constituents of Potential Concern ................
49
10.4 Groundwater Analytical Results...........................................................................
49
10.5 Comparison of Results to 2L Standards...............................................................
53
11.0 Hydrogeological Investigation ...................................................................................54
11.1 Hydrostratigraphic Layer Development..............................................................
54
11.2 Hydrostratigraphic Layer Properties....................................................................
54
11.2.1 In -Situ Tests...................................................................................................
54
11.2.2 Slug Tests.......................................................................................................
54
11.2.3 Porosity..........................................................................................................
55
11.3 Groundwater Flow Direction.................................................................................
55
11.4 Hydraulic Gradient..................................................................................................
55
11.5 Groundwater Velocity.............................................................................................
55
11.6 Contaminant Velocity..............................................................................................
55
11.7 Characterization of COI Distribution....................................................................
55
11.8 Groundwater / Surface Water Interaction............................................................
55
11.9 Confining Layers......................................................................................................
56
12.0 Screening -Level Risk Assessment.............................................................................
57
12.1 Human Health Screening........................................................................................
57
12.1.1 Introduction...................................................................................................
57
12.1.2 Conceptual Exposure Model.......................................................................
58
12.1.2.1 Current/Future Construction Workers ................................................
59
12.1.2.2 Current/Future Maintenance Workers .................................................
59
12.1.2.3 Current/Future Resident (Adult/Child)...............................................
59
12.1.2.4 Current/Future Recreational User (Adult/Child) ...............................
59
12.1.3 Risk -Based Screening Levels.......................................................................
59
12.1.4 Site Specific Risk Based Remediation Standards .....................................
78
12.2 Ecological Screening................................................................................................
78
12.2.1 Introduction...................................................................................................
78
iv
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12.2.2 Ecological Setting..........................................................................................
78
12.2.2.1 Facility Site Summary.............................................................................
78
12.2.2.2 Regional Ecological Setting....................................................................
78
12.2.2.3 Description of Ecoregion and Expected Habitats ...............................
79
12.2.2.4 Watershed in which the Site is Located ...............................................
79
12.2.2.5 Average Rainfall......................................................................................
79
12.2.2.6 Average Temperature.............................................................................
79
12.2.2.7 Length of Growing Season.....................................................................
79
12.2.2.8 Threatened and Endangered Species that use Habitats in the
Ecoregion...................................................................................................................
80
12.2.2.9 Site -Specific Ecological Setting..............................................................
80
12.2.2.10 On -site and Off -site Land Use.............................................................
80
12.2.2.11 Habitats within the Site Boundary......................................................
80
12.2.2.12 Description of Man-made Units that May Act as Habitat ...............
80
12.2.2.13 Site Layout and Topography...............................................................
81
12.2.2.14 Surface Water Runoff Pathways.........................................................
81
12.2.2.15 Soil Types................................................................................................
81
12.2.2.16 Species Normally Expected to Use Site under Relatively Unaffected
Conditions.................................................................................................................
81
12.2.2.17 Species of Special Concern...................................................................
81
12.2.2.18 Nearby Critical and/or Sensitive Habitats .........................................
81
12.2.3 Fate and Transport Mechanisms................................................................
81
12.2.4 Preliminary Exposure Estimate and Risk Calculation ............................
83
12.2.5 Comparison to Ecological Screening Levels .............................................
83
12.3 Uncertainty and Data Gaps....................................................................................
93
12.4 Scientific/Management Decision Point.................................................................
94
12.5 Risk Assessment Summary.....................................................................................
94
13.0 Groundwater Modeling...............................................................................................
95
13.1 Groundwater Modeling to be Performed in CAP ...............................................
95
13.2 Description of Kd Term Development...................................................................
96
13.3 Description of Flow Transects................................................................................
96
13.4 Other Model Inputs.................................................................................................
97
14.0 Data Gaps — Site conceptual model Uncertainties.................................................
98
v
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14.1 Data Gaps.................................................................................................................. 98
14.2 Site Heterogeneities.................................................................................................
98
14.3 Impact of Data Gaps and Site Heterogeneities....................................................
99
15.0 Planned Sampling for CSA Supplement...............................................................100
16.0 Interim Groundwater Monitoring Plan..................................................................101
16.1 Sampling Frequency..............................................................................................
101
16.2 Constituent and Parameter List...........................................................................
101
16.3 Proposed Sampling Locations..............................................................................
101
16.4 Proposed Background Wells................................................................................101
17.0 Discussion....................................................................................................................102
17.1 Maximum COI Concentrations............................................................................
102
17.2 Summary of Completed and Ongoing Work.....................................................102
17.3 Contaminant Migration and Potentially Affected Receptors ..........................103
18.0 Conclusions and Recommendations.......................................................................104
18.1 Source and Cause of Contamination...................................................................104
18.2 Imminent Hazards to Public Health and Safety and Actions Taken to Mitigate
Them 104
18.3 Receptors and Significant Exposure Pathways .................................................
104
18.4 Horizontal and Vertical Extent of Soil and Groundwater Contamination ....
105
18.5 Geological and Hydrogeological Features influencing the Movement,
Chemical, and Physical Character of the Contaminants..............................................106
18.6 Proposed Continued Monitoring.........................................................................
107
18.7 Preliminary Evaluation of Corrective Action Alternatives ..............................
107
19.0 References.....................................................................................................................108
v1
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Comprehensive Site Assessment Report August 2015
W.H. Weatherspoon Power Plant SynTerra
LIST OF FIGURES
Executive Summary
Figure ES-1 Site Conceptual Model - Plan View
1.0 Introduction
Figure 1-1 Site Location Map
2.0 Site History and Description
Figure 2-1 Site Layout Map
Figure 2-2 Predevelopment USGS Topographic Map
Figure 2-3 NPDES Flow Diagram
3.0 Source Characteristics
Figure 3-1 Coal Ash TCLP Leachate Concentration Ranges Compared to
Regulatory Limits
Figure 3-2 Known Sample of Ash for Comparison
Figure 3-3 Elemental Composition for Bottom Ash, Fly Ash, Shale, and
Volcanic Ash
Figure 3-4 Trace Element Concentration Ranges in Fly Ash Compared to EPA
Residential Soil Screening Levels
4.0 Receptor Information
Figure 4-1 Subsurface Utility Location Map
6.0 Site Geology and Hydrogeology
Figure
6-1
Geologic Cross -Sections
Figure
6-2
Geologic Cross -Section A -A' with Photographs
Figure
6-3
Geologic Cross -Section B-B' with Photographs
Figure
6-4
Geologic Cross -Section C-C' with Photographs
Figure
6-5
Water Level Map - Surficial Aquifer Wells
Figure
6-6
Potentiometric Surface - Lower Yorktown Formation Wells
Figure
6-7
Potentiometric Surface - Pee Dee Formation Wells
Figure
6-8
Cross -Section - Site Conceptual Model
7.0 Source Characterization
Figure 7-1 Aerial Photographs -1950 and 1951
Figure 7-2 Aerial Photographs - 1958 and 1964
Figure 7-3 Aerial Photographs - 1974 and 1980
vii
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W.H. Weatherspoon Power Plant SynTerra
LIST OF FIGURES (CONTINUED)
8.0 Soil and Rock Characterization
Figure 8-1 Geologic Cross -Sections with COI Analytical Results
Figure 8-2 Site Map with Soil Exceedances
10.0 Groundwater Characterization
Figure
10-1
Site Layout with 2L Exceedances - Ash Pore Water
Figure
10-2
Site Layout with 2L Exceedances - Surficial Aquifer
Figure
10-3
Site Layout with 21, Exceedances - Lower Yorktown Wells
Figure
10-4
Site Layout with 2L Exceedances - Pee Dee Wells
Figure
10-5
Isoconcentration Map - Arsenic in Ash Pore Water
Figure
10-6
Isoconcentration Map - Boron in Ash Pore Water
Figure
10-7
Isoconcentration Map - Cobalt in Ash Pore Water
Figure
10-8
Isoconcentration Map - Iron in Ash Pore Water
Figure
10-9
Isoconcentration Map - Manganese in Ash Pore Water
Figure
10-10
Isoconcentration Map - Thallium in Ash Pore Water
Figure
10-11
Isoconcentration Map - Total Dissolved Solids in Ash Pore Water
Figure
10-12
Isoconcentration Map - Vanadium in Ash Pore Water
Figure
10-13
Isoconcentration Map - Arsenic in Surficial Wells
Figure
10-14
Isoconcentration Map - Boron in Surficial Wells
Figure
10-15
Isoconcentration Map - Cobalt in Surficial Wells
Figure
10-16
Isoconcentration Map - Iron in Surficial Wells
Figure
10-17
Isoconcentration Map - Thallium in Surficial Wells
Figure
10-18
Isoconcentration Map - Manganese in Surficial Wells
Figure
10-19
Isoconcentration Map - Total Dissolved Solids in Surficial Wells
Figure
10-20
Isoconcentration Map - Vanadium in Surficial Wells
Figure
10-21
Isoconcentration Map - Arsenic in Lower Yorktown Wells
Figure
10-22
Isoconcentration Map - Boron in Lower Yorktown Wells
Figure
10-23
Isoconcentration Map - Cobalt in Lower Yorktown Wells
Figure
10-24
Isoconcentration Map - Iron in Lower Yorktown Wells
Figure
10-25
Isoconcentration Map - Manganese in Lower Yorktown Wells
Figure
10-26
Isoconcentration Map - Thallium in Lower Yorktown Wells
Figure
10-27
Isoconcentration Map - Total Dissolved Solids in Lower Yorktown
Wells
Figure 10-28
Isoconcentration Map
- Vanadium in Lower Yorktown Wells
Figure 10-29
Isoconcentration Map
- Arsenic in Pee Dee Wells
Figure 10-30
Isoconcentration Map
- Boron in Pee Dee Wells
Figure 10-31
Isoconcentration Map
- Cobalt in Pee Dee Wells
viii
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Comprehensive Site Assessment Report August 2015
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LIST OF FIGURES (CONTINUED)
10.0 Groundwater Characterization (Continued
Figure
10-32
Isoconcentration Map - Iron in Pee Dee Wells
Figure
10-33
Isoconcentration Map - Manganese in Pee Dee Wells
Figure
10-34
Isoconcentration Map - Thallium in Pee Dee Wells
Figure
10-35
Isoconcentration Map - Total Dissolved Solids in Pee Dee Wells
Figure
10-36
Isoconcentration Map - Vanadium in Pee Dee Wells
Figure
10-37
Detection Monitoring Constituent Map - Ash Pore Water
Figure
10-38
Detection Monitoring Constituent Map - Surficial Aquifer
Figure
10-39
Detection Monitoring Constituent Map - Lower Yorktown Wells
Figure
10-40
Detection Monitoring Constituent Map - Pee Dee Wells
Figure
10-41
Assessment Monitoring Constituent Maps - Ash Pore Water
Figure
10-42
Assessment Monitoring Constituent Maps - Surficial Aquifer
Figure
10-43
Assessment Monitoring Constituent Maps - Lower Yorktown Wells
Figure
10-44
Assessment Monitoring Constituent Maps - Pee Dee Formation
Figure
10-45
Ash Pore Water Piper Diagrams
Figure
10-46
Surficial Aquifer Piper Diagrams
Figure
10-47
Lower Yorktown Piper Diagrams
Figure
10-48
Pee Dee Piper Diagrams
Figure
10-49
Time versus Concentration - BW-01
Figure
10-50
CW-3 Time versus Concentration - CW-03
Figure
10-51
Compliance Well Box and Whisker Plots - Arsenic, Barium, Boron,
Cadmium
Figure
10-52
Compliance Well Box and Whisker Plots - Chloride, Iron,
Manganese, Nitrate
Figure
10-53
Compliance Well Box and Whisker Plots - Sulfate, TDS, Thallium,
Zinc
Figure
10-54
Seep Piper Diagram
Figure
10-55
Surface Water Piper Diagram
11.0 Hydrogeological Investigation
Figure 11-1 Geologic Cross -Sections with Arsenic and Boron
Figure 11-2 Geologic Cross -Sections with Manganese and Vanadium
Figure 11-3 Geologic Cross -Sections with Lead, Thallium, and TDS
In
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LIST OF FIGURES (CONTINUED)
12.0 Screening -Level Risk Assessment
Figure
12-1
Human Health Conceptual Exposure Model
Figure
12-2
COPC Locations Flagged - Groundwater - Ash Pore Water - Human
Health
Figure
12-3
COPC Locations Flagged - Groundwater - Surficial Aquifer -
Human Health
Figure
12-4
COPC Locations Flagged - Groundwater - Lower Yorktown -
Human Health
Figure
12-5
COPC Locations Flagged - Groundwater - Pee Dee - Human Health
Figure
12-6
COPC Locations Flagged - Soils (0-2 feet) - Human Health
Figure
12-7
COPC Locations Flagged - Sediment - Human Health
Figure
12-8
COPC Locations Flagged - Surface Water / Seeps - Human Health
Figure
12-9
Ecological Conceptual Exposure Model
Figure
12-10
COPC Locations Flagged - Surface Water / Seeps - Ecological
Figure
12-11
COPC Locations Flagged - Soils (0-2 ft) - Ecological
Figure
12-12
COPC Locations Flagged - Sediment - Ecological
16.0 Interim Groundwater Monitoring Plan
Figure 16-1 Proposed Groundwater Monitoring Locations
x
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LIST OF TABLES
2.0 Site History and Description
Table 2-1 NPDES Groundwater Monitoring Requirements
Table 2-2 Compliance Well 2L Exceedances
3.0 Source Characteristics
Table 3-1 Ash, Rock, and Soil Composition
6.0 Site Geology and Hydrogeology
Table 6-1 Exploration and Sampling Plan
Table 6-2 Soil, Sediment, and Ash COIs and Analytical Methods
Table 6-3 Ash Pore Water, Groundwater, Surface Water, and Seep COIs &
Analytical Methods
Table 6-4 Well Construction Data
Table 6-5 Water Level Measurements - June 2015
Table 6-6 Local Groundwater Gradients and Flow Velocities
Table 6-7 In -Situ Hydraulic Conductivity Test Results
Table 6-8 Vertical Hydraulic Conductivity of Undisturbed Soil Samples
7.0 Source Characterization
Table 7-1
Physical Properties of Ash
Table 7-2
Mineralogy of Ash
Table 7-3
Chemical Properties of Ash
Table 7-4
Leaching Properties of Ash
Table 7-5
Whole Rock Metal Oxide Analysis of Ash
Table 7-6 Whole Rock Elemental Analysis of Ash
Table 7-7 Ash Pore Water Analytical Results
Table 7-8 2L Exceedances in Ash Pore Water
Table 7-9 Ash Basin Perimeter Ditch Sediment Analytical Results
8.0 Soil and Rock Characterization
Table 8-1
Physical Properties of Soil
Table 8-2
Mineralogy of Soils
Table 8-3
Chemical Properties of Soil
Table 8-4
Leaching Properties of Soil
Table 8-5
Whole Rock Metal Oxide Analysis of Soil
Table 8-6
Whole Rock Elemental Analysis of Soil
xi
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LIST OF TABLES (CONTINUED)
9.0 Sediment, Seep, and Surface Water Characterization
Table 9-1 Sediment Analytical Results
Table 9-2 Seep Analytical Results
Table 9-3 Surface Water Analytical Results
Table 9-4 NCDENR 2014 Seep Analytical Results
Table 9-5 2B Exceedances in Seeps and Surface Water
10.0 Groundwater Characterization
Table 10-1 Groundwater Analytical Results
Table 10-2 2L Exceedances in Groundwater
Table 10-3 Valence Speciation of Groundwater
Table 10-4 Charge Balance Summary
12.0 Screening -Level Risk Assessment
Table 12-1 Risk Screening Table: Ash Pore Water Data
Table 12-2 Coal Ash COPC Determination
Table 12-3 Risk Screening Table: Yorktown and Pee Dee Aquifer Background
Groundwater Data
Table 12-4
Risk Screening Table: Yorktown Aquifer Downgradient
Groundwater Data
Table 12-5
Risk Screening Table: Pee Dee Aquifer Downgradient Groundwater
Data
Table 12-6
Soils (0-2) Analytical Results with Screening Criteria Residential and
Industrial Soils - Human Health
Table 12-7
Sediment Analytical Results with Screening Criteria - Residential
and Industrial Soils - Human Health
Table 12-8
Surface Water Analytical Results - EPA Recommended Water
Quality Criteria and 15 NCAC 2B Standards- Human Health
Table 12-9
Seep Analytical Results with Screening Criteria - EPA
Recommended Water Quality Criteria and 15 NCAC 2B Standards -
Human Health
Table 12-10
Matrix for Determination of Constituents of Potential Concern -
Human Health
Table 12-11
Threatened and Endangered Species in Robeson County
xu
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LIST OF TABLES (CONTINUED)
12.0 Screening -Level Risk Assessment (Continued)
Table 12-12 Surface Water and Seep Analytical Results with Screening Criteria -
15NCAC 2B andEPA Recommended Water Quality Criteria for
Aquatic Life (Acute and Chronic) - Ecological
Table 12-13 Soils (0-2) Analytical Results with Screening Criteria - EPA Region 4
Recommended Screening Values for Soil - Ecological
Table 12-14 Sediment Analytical Results with Screening Criteria - EPA Region 4
Recommended Screening Values for Soil and Effects Value -
Ecological
Table 12-15 Matrix for Determination of Constituents of Potential Concern -
Ecological
16.0 Interim Groundwater Monitoring Plan
Table 16-1 Recommended Groundwater Monitoring Parameters
Table 16-2 Recommended Groundwater Monitoring Locations
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LIST OF APPENDICES
Appendix A Regulatory Correspondence
NCDENR to DEP, 7/7/2015
NCDENR CSA Guideline Adjustment, Final Addendum 1, June 2015
NCDENR to DEP, 2/6/2015
NCDENR to DEP, 11/4/2014
NCDENR to DEP, 8/13/2013
NCDENR Hydrogeologic Investigation and Reporting Policy
Appendix B Water Well and Receptor Survey
Table B-1 Analytical Results for DEP#2 (PW-01)
Table B-2 NDENR 2015 Water Well Data
Table B-3 NCDENR Water Supply Well Tracking Information
Table B-4 Public and Private Water Supply Wells (0.5 Mile Radius)
Table B-5 Parcel Ownership Information
Well Construction Data - DEP#1 and DEP#2
Figure B-1 Receptor Vicinity Map
NCDENR 2015 Water Well Sample Laboratory Results and Chain of
Custody Forms (CD)
Appendix C Methodology
SynTerra Field Procedures
Appendix D Quality Control Data
Table D-1 Rinse Blank Analyses for Soils
Table D-2 Rinse Blank Analyses for Groundwater -TOTAL
Table D-3 Rinse Blank Analyses for Groundwater -DISSOLVED
Appendix E 2015 Groundwater Assessment Documentation
Boring Logs and Well Construction Diagrams
Driller Well Construction Record
Historical Boring Logs and Well Construction Diagrams
Appendix F Soils Test Data
Whole Rock Metal Oxides, Whole Rock Elemental Analysis,
X-ray Diffraction
Grain Size Distribution and Specific Gravity
Moisture Content
Vertical Hydraulic Conductivity
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LIST OF APPENDICES (CONTINUED)
Appendix G In -Situ Hydraulic Conductivity Measurements
Slug Test Results
Appendix H Statistical Analysis of Compliance Well Groundwater Results
March 2015
June 2015
Figure H-1 Time versus Concentration - Comparison Between
Compliance & Background Wells - Arsenic, Barium
Figure H-2 Time versus Concentration - Comparison Between
Compliance & Background Wells - Chloride, Iron
Figure H-3 Time versus Concentration - Comparison Between
Compliance & Background Wells - Manganese, Sulfate
Figure H-4 Time versus Concentration - Comparison Between
Compliance & Background Wells - Total Dissolved Wells
"Figure H-5 Time versus Concentration - Comparison Between
Compliance & Background Wells - Turbidity and Water Level
(BW-01, CW-01)"
"Figure H-6 Time versus Concentration - Comparison Between
Compliance & Background Wells - Turbidity and Water Level
(CW-02, CW-03)"
Appendix I Screening Level Risk Assessment
Ecological Assessment Checklist
Weatherspoon Plant Jurisdictional Delineation
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LIST OF ATTACHMENTS
Attachment 1 Topographic, Underground Utility Maps, and EDR Reports (CD)
Attachment 2 Drinking Water and Receptor Survey Reports (CD)
Attachment 3 Comprehensive Analytical Results Tables (CD)
Attachment 4 Laboratory Reports - Chemical Analyses (CD)
Attachment 5 Photographs (CD)
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LIST OF ACRONYMS
ARAR
Applicable or Relevant and Appropriate Requirements
ASTM
American Society for Testing and Materials
BW
Background Well
BGS
below existing ground surface
CAMA
Coal Ash Management Act
CAP
Corrective Action Plan
CCR
Coal Combustion Residuals
CEM
Conceptual Exposure Model
COI
Constituent of Interest
COPC
Constituents of Potential Concern
CSA
Comprehensive Site Assessment
DEP
Duke Energy Progress, Inc.
DO
Dissolved Oxygen
DPT
Direct Push Technology
DWR
Division of Water Resources
EDXRF
Energy Dispersive X-ray Diffraction
ESV
Ecological Screening Value
GAP
Groundwater Assessment Plan
GIS
Geographic Information System
HHRA
Human Health Risk Assessment
HQ
Hazard Quotient
IMAC
Interim Maximum Allowable Concentrations
MCL
Maximum Contaminant Level
MSL
Mean Sea Level
MW
Monitoring Well
NCAC
North Carolina Administrative Code
NCDENR
North Carolina Department of Environment and Natural Resources
NORR
Notice of Regulatory Requirements
NPDES
National Pollution Discharge Elimination System
NTU
Nepthalic Turbidity Unit
ORP
Oxidation -Reduction Potential
OW
Observation Well
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LIST OF ACRONYMS
Plant
W. H. Weatherspoon Plant
PVC
Polyvinylchloride
PZ
Piezometer
RSL
USEPA Regional Screening Level
SCM
Site Conceptual Model
SLERA
Screening Level Risk Assessment
SPLP
Synthetic Precipitation Leaching Procedure
SW
Surface Water
NCDENR/DWR Title 15, Subchapter 2B. Surface Water and
213
Wetland Standards
NCDENR/DWR Title 15, Subchapter 2L. Groundwater Quality
2L
Standards
TCLP
Toxicity Characteristic Leaching Procedure
TDS
Total Dissolved Solids
TOC
Total Organic Carbon
USACE
US Army Corps of Engineers
USEPA
United States Environmental Protection Agency
USFWS
United States Fish and Wildlife Service
USGS
United States Geological Survey
WQC
Water Quality Criteria
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1.0 INTRODUCTION
Duke Energy Progress, Inc. (Duke Energy), owns and operates the W.H. Weatherspoon
Power Plant (Weatherspoon Plant), located near Lumberton in Robeson County, North
Carolina (Figure 1-1). Electrical power generation operations, situated on the northern
portion of a 1,015 acre tract, included coal-fired steam generating units until retired in
October 2011. Ash from the coal-fired boilers was sluiced to an on -site ash basin. The
discharge from the ash basin through the cooling pond to the Lumber River is
permitted by the North Carolina Department of Environment and Natural Resources
(NCDENR) Division of Water Resources (DWR) under the National Pollution Discharge
Elimination System (NPDES).
Duke Energy performed voluntary groundwater monitoring around the ash basin from
March 1990 to March 1998 and December 2006 until March 2010. The voluntary
groundwater monitoring wells were sampled two times a year and the analytical results
were submitted to DWR. Groundwater monitoring as required by the NPDES permit
began in November 2010. The compliance groundwater monitoring wells required for
the NPDES permit are sampled three times a year and the analytical results are
submitted to DWR. Concentrations of iron, cadmium, thallium, and manganese in
excess of North Carolina Administrative Code (NCAC) Title 15A Chapter 02L.0202
groundwater quality standards (2L) have been measured in groundwater samples
collected at compliance monitoring wells BW-1, CW-1, CW-2, and CW-3.
Duke Energy recommended in June 2015 that all of the ash in the Weatherspoon ash
basin would be excavated from the ash basin (htti2s://www.duke-
energy. com/pdfs/SafeBasinClosureUpdate Weatherspoon.pdf., accessed on July 28,
2015).
1.1 Purpose of Comprehensive Site Assessment
The Comprehensive Site Assessment (CSA) was conducted to collect information
necessary to understand the ash basin as a source of potential contamination, determine
horizontal and vertical extent of soil and groundwater contamination, identify potential
receptors of contamination, evaluate risks to receptors, and ultimately develop a
Corrective Action Plan (CAP). Constituents of interest (COIs) and constituents of
potential concern (COPCs) for the Weatherspoon site were identified based on the
chemical analytical results from ash basin samples and a screening level risk
assessment. A site conceptual model (SCM) and associated physical properties and
chemical data are to be used as the basis for a groundwater flow model and an
associated COPC fate and transport model for the ash basin. The subsequent CAP for
the site is to be based on the results of risk assessments and groundwater models.
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1.2 Regulatory Background
In a Notice of Regulatory Requirements (NORR) letter dated August 13, 2014, DWR
requested that Duke Energy prepare a Groundwater Assessment Plan to conduct a
Comprehensive Site Assessment (CSA) in accordance with 15A NCAC 02L .0106(g) to
address groundwater constituents for which concentrations were detected above 2L
groundwater quality standards at the compliance boundary.
1.2.1 NCDENR Requirements
NCDENR issued site specific requirements for the Weatherspoon site in letters
dated November 4, 2014 and February 6, 2015. Specific NCDENR requirements
for the CSA attached to the February letter were modified after issuance of the
letter and were finalized in June 2015.
1.2.2 NORR Requirements
The NORR required Duke Energy to comply with 15A NCAC 02L .0106(g),
DWR's Groundwater Modeling Policy, May 31, 2007, and various site specific
requirements.
1.2.3 CAMA Requirements
In addition, the Coal Ash Management Act (CAMA) 2014 — General Assembly of
North Carolina Senate Bill 729 Ratified Bill (Session 2013) (SB 729) revised North
Carolina General Statute 130A-309.209(a) to require the following:
(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.
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c. A description of all significant factors affecting movement and transport
of contaminants.
d. A description of the geological and hydrogeological features influencing
the chemical and physical character of the contaminants.
e. A schedule for continued groundwater monitoring.
f. Any other information related to groundwater assessment required by the
Department.
(2) The Department shall approve the Groundwater Assessment Plan if it determines
that the Plan complies with the requirements of this subsection and will be
sufficient to protect public health, safety, and welfare; the environment; and
natural resources.
(3) No later than 10 days from approval of the Groundwater Assessment Plan, the
owner shall begin implementation of the Plan.
(4) No later than 180 days from approval of the Groundwater Assessment Plan, the
owner shall submit a Groundwater Assessment Report to the Department. The
Report shall describe all exceedances of groundwater quality standards associated
with the impoundment.
1.3 NCDENR-Duke Energy Correspondence
SynTerra submitted to NCDENR a proposed Groundwater Assessment Plan (GAP) for
the Weatherspoon Plant dated September 2014 on behalf of Duke Energy.
Subsequently, NCDENR issued a comment letter dated November 4, 2014 containing
both general comments applicable to the Duke Energy ash basin facilities and site -
specific comments for the Weatherspoon Plant (Appendix A). In response to these
comments, SynTerra prepared and submitted a revised Groundwater Assessment Work
Plan (Revision 1) on December 30, 2014, for performing the groundwater assessment as
prescribed in the NORR and SB 729, and to address the NCDENR review of the work
plan dated November 4, 2014 and subsequent meetings among Duke Energy, SynTerra,
and NCDENR. Conditional approval of the Work Plan was dated February 6, 2015.
Final approval was issued on July 7, 2015 (Appendix A).
1.4 Approach to Comprehensive Site Assessment
The approach to the CSA was developed to meet NCDENR's requirements.
1.4.1 NORR Guidance
This CSA was conducted in accordance with the conditionally approved Work
Plan to meet the requirements of 15A NCAC 02L .0106(g). This rule requires:
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(g) The site assessment conducted pursuant to the requirements of
Paragraph (c) of this Rule, shall include:
(1) The source and cause of contamination;
(2) Any imminent hazards to public health and safety and actions taken
to mitigate them in accordance with Paragraph 69 of this Rule;
(3) All receptors and significant exposure pathways;
(4) The horizontal and vertical extent of soil and groundwater
contamination and all significant factors affecting contaminant
transport; and
(5) Geological and hydrogeological features influencing the movement, chemical, and
physical character of the contaminants.
1.4.2 USEPA Monitored Natural Attenuation Tiered Approach
The assessment data is also compiled in a manner to be consistent with
"Monitored Natural Attenuation of Inorganic Contaminants in Groundwater"
(EPA/600/R-07/139). 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:
1. Evaluate active contaminant removal from ground water and dissolved
plume stability,
2. Evaluate the mechanisms and rates of attenuation,
3. Evaluate the long-term capacity for attenuation and stability of immobilized
contaminants, and
4. Evaluate anticipated performance monitoring needs to support the selected
remedy.
This assessment information will be used to develop a Corrective Action Plan
(CAP) for the site. The CAP will provide a demonstration of these criteria in
support of the recommended site remedy.
1.4.3 ASTM Conceptual Site Model
ASTM E1689-95 generally describes the major components of site conceptual
models, including an outline for developing models. To the extent possible, this
guidance was incorporated into preparation of the Weatherspoon site conceptual
model (SCM).
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1.5 Technical Objectives
The rationale for borings and wells installed and sampled during the assessment fall
into one of the following categories:
'610 Evaluate the range of background groundwater quality from pertinent geologic
settings (horizontal and vertical) across a broader area of the site and a greater
distance from the ash basin.
'610 Evaluate groundwater quality from pertinent geologic settings (horizontal and
vertical extent of coal ash constituents) at a greater distance down gradient of the
ash basin than previously available
t1' Establish perimeter (horizontal and vertical) boundary conditions for a
comprehensive groundwater model
Provide source area information including pore water chemistry, coal ash
thickness, and residual saturation within the ash basin
Fill soil chemistry data gaps in the vicinity of the ash basin (horizontal and
vertical extent of coal ash constituents in soil) and a comparison to background
concentrations.
The following report presents the information obtained from the field investigation to
address the requirements of 15A NCAC 02L .0106(g), the conditional approval letter,
and CSA guidance document (revised June 2015).
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2.0 SITE HISTORY AND DESCRIPTION
An overview of the W.H. Weatherspoon Plant setting and operations is presented in the
following sections.
2.1 Site Location, Acreage, and Ownership
The Weatherspoon Plant is a former coal-fired electrical power generation facility
located on 1,015 acres near the city of Lumberton in Robeson County (Figures 1-1 and 2-
1). Duke Energy Progress, Inc. owns the site and has owned the site for decades.
Records available from Environmental Data Resources, Inc. (Attachment 1) do not
contain any information prior to construction of the Weatherspoon Power Plant. A 1957
USGS topographic map of the site indicates that the ash basin site was undeveloped
rural land at that time (Figure 2-2).
2.2 Plant Description
The Weatherspoon Plant became operational in 1949 with a Babcock & Wilcox boiler.
Two additional coal-fired units were added in the 1950s. Four oil and natural gas
fueled combustion turbines were added in the 1970s. All of the coal-fired units were
retired by October 2011. The four oil and natural gas fueled units continue to operate
on an intermittent basis.
2.3 General Site Description
The Weatherspoon Plant utilizes an approximate 225-acre cooling pond located adjacent
to the Lumber River. The cooling pond remains in service. Coal ash, the potential
source of contamination at the site, is no longer generated at the site. Duke Energy has
recommended that coal ash be excavated from the ash basin, and is in the process of
developing a detailed closure plan for the ash basin.
Reportedly, from 1949 to 1955 coal ash was sluiced to a low area that was eventually
encompassed by the existing ash basin. Examination of historic United States
Geological Survey (USGS) aerial photography shows that a small diked impoundment
had been constructed by 1958. The basin was enlarged in stages to its current size by
early 1981. No other areas of coal ash management (other than possible de minimis
quantities) are known to exist at the site.
2.4 Adjacent Property, Zoning, and Surrounding Land Uses
The Weatherspoon Plant site is surrounded by commercial, rural residential,
agricultural, and forest land.
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2.5 Adjacent Surface Water Bodies and Classifications
The Lumber River, designated as a 'Natural and Scenic River" by the North Carolina
General Assembly in 1989, borders the plant to the south. Jacob Creek, a tributary to
the Lumber River, borders the ash basin and cooling pond on the east.
2.6 Meteorological Setting
The site lies within the southeastern United States coastal plain climate zone that
exhibits a humid subtropical climate type (NOAA, 2013). The high rainfall amounts
and substantial seasonal temperature variations in this region promote rapid
weathering of surficial geologic formations.
2.7 Hydrologic Setting
Topography at the site ranges from approximately 140 feet above mean sea level (MSL)
north of the site to approximately 110 feet MSL at the cooling pond to the east and south
and the Lumber River to the southwest. The plant, cooling pond, and ash basin are
located on the northeast side of the Lumber River. Jacob Creek flows south toward the
Lumber River along the east side of the cooling pond. Groundwater flow from the site
discharges to the cooling pond, Jacob Creek, and the Lumber River.
2.8 Permitted Activities and Permitted Waste
The ash basin, operating under NPDES Permit NC005363, is located north and west of
the cooling pond (northeast of the plant, shown with a 500 foot compliance boundary
on Figure 2-1). The ash basin is impounded by an earthen embankment system
approximately 6,600 feet long, with a dam height of 28 feet and a crest height of 12 feet
(143 foot elevation) (Dewberry & Davis, 2011). The basin area is approximately 36 acres
and contains approximately 1,530,000 tons of ash (https://www.duke-
energy.com/pdfs/duke-energy-ash-metricLpdf, accessed on July 17, 2015).
2.9 History of NPDES and Surface Water Monitoring
The ash basin was constructed in phases using a combination of basin excavation and
earthen dike construction beginning in 1955. Additional excavation and earthen dike
construction occurred south of the original basin as the plant expanded and ash volume
increased. The last of the perimeter earthen dikes was constructed in 1979. The basin
was also expanded vertically in the northwestern portion of the basin by the use of
interior dikes constructed of large diameter geotextile tubes filled with ash. Interior ash
dike construction began in 2001 (S&ME, 2012).
The majority of the ash placed into the basin was conveyed hydraulically by sluicing.
Limited quantities of bottom ash removed from structures in the plant were hauled to
the basin by truck. Overflow from the northeast corner of the ash basin discharged into
the northwest corner of the cooling pond within the 500 foot compliance boundary.
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NPDES permit NCO05363 authorizes discharge of recirculated cooling water, ash sluice
water (from the ash basin), domestic wastewater, chemical metal cleaning water, and
categorical low volume wastewater from the cooling pond to the Lumber River via
Outfall 001 under severe weather conditions and cooling pond maintenance (Figure 2-
3).
2.10 History of NPDES Groundwater Monitoring
On July 1, 2010, DWR conducted an on -site review of the compliance well locations
selected by DEP and subsequently provided Duke with written approval to construct
the proposed compliance well network and to initiate compliance boundary
groundwater monitoring. For purposes of this monitoring, the applicable groundwater
reference criterion is the Groundwater Quality Standard (21, or Interim Maximum
Allowable Concentration (IMAC)) referenced in 15A NCAC 02L.0202. 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.
In August 2010, DEP installed background monitoring well BW-1 and compliance
boundary wells CW-1, CW-2, and CW-3 around the ash basin (Figure 2-1). Well BW-1
was installed to the north and hydraulically upgradient from the ash basin to monitor
background water quality conditions. Wells CW-1, CW-2, and CW-3 were located
along the downgradient ash basin compliance boundary area. Wells BW-1, CW-1, CW-
2, and CW-3 comprise the current groundwater monitoring network for the ash basin
(superseding use of the wells noted elsewhere). Duke initiated routine compliance
boundary monitoring in November 2010.
Currently, Duke conducts routine compliance boundary monitoring during March,
June, and October each year for the parameters listed in Table 2-1. At the direction of
NCDENR, Duke has adjusted the parameter list to support the CSA process as of June
2015.
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TABLE 2-1. Groundwater Monitoring Requirements*
Well
Identification
parameter Description
Frequency
Antimony
Chromium
Nickel
Thallium
Arsenic
Copper
Nitrate
Water Level
Monitoring
Wells BW-01,
Barium
Iron
pH
Zinc
March, June,
CW-01, CW-02,
CW-03
Boron
Lead
Selenium
and October
Cadmium
Manganese
Sulfate
Chloride
Mercury
TDS
*Updated to include CAMA parameters in 2015
2.11 Assessment Activities or Previous Site Investigations
According to EDR (Attachment 1), a fuel oil release occurred at the Weatherspoon Plant
site in March 1995. It was assigned NCDENR Incident Number 13884.
In the ash basin area, Duke Energy installed one background well (MW-1) and paired
downgradient monitoring wells at two locations (MW-2/MW-3 and MW-4/MW-5)
during 1989. Groundwater samples from these wells were collected and analyzed as
part of an NPDES permit requirement from approximately 1990 through 1998 and as
part of a voluntary monitoring program from fall 2006 through spring 2010. During
May 2010, Duke Energy installed well pair MW-6/MW-7 near the cooling pond to
further evaluate compliance well locations.
Exceedances of or variances from the applicable groundwater reference criterion
included boron (MW-4), iron (all wells), and pH (MW-1) (Table 2-2). Isolated one-time
exceedances included antimony (MW-3) and chromium (MW-5). All other analytes
were non -detect or less than regulatory standards. During 2009, DWR requested maps
depicting site topography and boundaries of the ash basin to aid in delineation of a
compliance boundary for the ash basin and to select proposed locations for compliance
monitoring wells. The compliance boundary was established 500 feet from the outer toe
of the ash basin dike, in accordance with 15A NCAC 2L .0107.
S&ME (2012) conducted an initial assessment to begin planning closure of the
Weatherspoon ash basin. The geotechnical, hydrogeologic, and environmental
characterization consisted of subsurface borings, well and piezometer installations,
water level measurements, slug tests, an aquifer pump test, field sampling, and
geotechnical and analytical laboratory testing of ash, soil, groundwater, and surface
water.
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Groundwater monitoring wells installed in 2012 are located in close proximity to the
ash basin (Figure 2-1). Preliminary observations from 2012 work and monitoring of
NPDES compliance wells follow:
'611 Saturated soils occur at shallow depths in the immediate vicinity of the
Weatherspoon Plant.
'611 The oxidation state of shallow soils ranges from oxidized (characterized by red
and brown coloration) in upland areas to reduced (characterized by gray
coloration) in low-lying areas.
'610 Ash pore water mounded within the ash basin exhibits a radial flow pattern
away from the ash basin.
'611 Ditches surrounding the ash basin control the gradient of pore water mounded
within the basin.
General shallow (water table condition) groundwater flow in the immediate
vicinity of the Weatherspoon Plant is to the southeast (toward Jacob Creek) and
south (toward the Lumber River).
Iron is ubiquitous in groundwater samples from the site and occurs above the
2L of 300 µg/L in samples from monitoring wells upgradient of the ash basin as
well as monitoring wells downgradient of the ash basin.
Arsenic, barium, boron, chromium, iron, manganese, and total dissolved solids
(TDS) concentrations greater than the corresponding 2L were detected in at
least one sample of ash pore water collected from wells screened within the
ash.
TDS, nitrate, sulfate, arsenic, boron, chromium, iron, and manganese
concentrations greater than the corresponding 2L and antimony greater than
IMAC were detected in samples from one or more locations representative of
the shallow, intermediate, or deep aquifers.
Potential receptors include on -site groundwater supply wells, ditches, ponds,
and streams, as well as several nearby residential groundwater supply wells.
The Groundwater Assessment Plan (GAP) developed in response to the NORR was
based on these observations.
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2.12 Plans for Decommissioning
Duke Energy has recommended excavation of the 1.5 million tons of ash located in the
Weatherspoon Plant ash basin (https://www.duke-
energy.com/pdfs/SafeBasinClosureUl2date Weatherspoon.pdf., accessed on July 28,
2015). Studies identified that soils under the basin embankments could be susceptible
to movement and settling in a large earthquake, so excavation was recommended to be
the best option for long-term safe storage of the material.
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3.0 SOURCE CHARACTERISTICS
The following overview of coal ash was prepared by HDR Incorporated and supplied
for this report.
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 or boiler
slag.
3.2 Physical 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. In general,
coal is dried, pulverized, and conveyed to the burner area of a boiler for combustion.
As described in Section 3.1, material that forms larger particles of ash and falls to the
bottom of the boiler is referred to as bottom ash or boiler slag. Smaller particles of ash,
known as fly ash, are carried upward in the flue gas and are captured by an air
pollution control device.
Approximately 70 to 80 percent of the ash produced during coal combustion is fly ash
(EPRI 1993). Typically 65 to 90 percent of fly ash has particle sizes that are less than
0.010 millimeter (mm). In general, fly ash has a grain size distribution similar to that of
silt. The remaining 30 to 40 percent of ash produced is considered to be bottom ash.
Bottom ash consists of angular particles with a porous surface and is normally gray to
black in color. Bottom ash particle diameters can vary from approximately 38 to 0.05
mm. In general, bottom ash has a grain size distribution similar to that of fine gravel to
medium sand (EPRI 1995).
Specific gravities of fly ash range from 2.1 to 2.9. The specific gravities of bottom ash
typically range 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). Permeability and other physical properties of the ash found in
the Weatherspoon ash basin are presented later in this report.
3.3 Chemical Properties of Ash
The specific mineralogy of coal ash varies based on many factors including the chemical
composition of the coal, which is directly related to the geographic region where the
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coal was mined, the type of boiler where the combustion occurs (i.e., thermodynamics
of the boiler), and air pollution control technologies employed.
The overall chemical composition of coal ash resembles that of siliceous rocks from
which it was derived, particularly shale. Oxides of silicon, aluminum, iron, and calcium
make up more than 90 percent of most siliceous rocks, soils, fly ash, and bottom ash.
Other major and minor elements (sulfur, sodium, potassium, magnesium, titanium)
make up an additional 8 percent, while trace constituents account for less than 1
percent. The following constituents are considered to be trace elements: arsenic,
barium, cadmium, chromium, lead, mercury, selenium, copper, manganese, nickel,
lead, vanadium, and zinc (Figure 3-1, EPRI 2010).
Duke Energy has typically burned bituminous coal from Appalachian sources.
The majority of fly ash particles are glassy spheres mainly composed of amorphous or
glassy aluminosilicates, crystalline matter, and carbon. Figure 3-2 presents a
photograph of ash collected from the ash basin at Duke Energy's Cliffside Steam Station
showing a mix of fly ash and bottom ash at 10 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 (Ca +z), sulfate (SO-2), metals (copper (Cu), zinc (Zn),
and other minor elements (e.g., boron (B), selenium (Se), and arsenic (As)) (EPRI 1994).
The major elemental composition of fly ash (approximately 95 percent by weight) is
composed of mineral oxides of silicon, aluminum, iron, and calcium. Oxides of
magnesium, potassium, titanium, and sulfur comprise approximately 4 percent by
weight (EPRI 1995). Trace elemental composition typically is approximately 1 percent
by weight and may include arsenic, antimony, barium, boron, cadmium, chromium,
copper, manganese, mercury, nickel, lead, selenium, silver, thallium, zinc, and other
elements. For comparison, Figure 3-3 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 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,
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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 USEPA Method 1311 Toxicity Characteristic Leaching Procedure (TCLP)
leaching and no TCLP result exceeded the TCLP hazardous waste limit. Figure 3-1
provides the results of that testing. The report also presents the trace element
concentrations for fly ash and bottom ash compared to USEPA Residential Soil
Screening Levels (RSLs) for ingestion and dermal exposure. Figure 3-4 shows the 10th to
90th percentile range for trace element concentrations (mg/kg) in fly ash and the
associated USEPA RSLs. The trace element concentrations for arsenic were greater than
the RSL for arsenic. The RSLs of the remaining constituents were greater than or within
the 10th to 90th percentile range for their trace element concentrations.
The second page of Figure 3-4 shows similar data for bottom ash. As with fly ash, the
trace element concentrations for arsenic in bottom ash were greater than the RSL for
arsenic. The RSL for chromium was within the range of concentrations for chromium in
bottom ash and the trace element concentrations for the remaining constituents were
below their respective RSLs.
3.4 Description of Ash Basins and Other Ash Storage Areas
Refer to Sections 2.3 and 7.1 for site specific information.
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4.0 RECEPTOR INFORMATION
The Weatherspoon Plant lies in a rural area southeast of Lumberton. Commercial and
industrial facilities are located along Highway 72 west of the plant. Pockets of
residences occur along Old Whiteville Road to the north. Agriculture dominates the
land use east of the property, and undeveloped floodplain lies south of the Lumber
River that borders the plant to the southwest. Duke Energy plans to maintain electricity
production at the site.
The Weatherspoon ash basin is surrounded by engineered perimeter ditches that drain
the toe of the dam. Culverts, abandoned ash sluice pipe, the ash basin discharge pipe,
and miscellaneous subsurface utilities were located (Figure 4-1). Locations of
subsurface utilities in the plant area to 1,500 feet beyond the basin boundary are
exhaustive and difficult to complete and map with certainty. Due to the isolation of the
ash basin from the plant area, subsurface utilities in the plant area are not expected to
be major contaminant flow pathways. Identification of piping near and around the ash
basin was conducted by Stantec in 2014 and utilities around the plant property were
also included on a 2014 topographic map by WSP (Attachment 1) to meet this NCDENR
requirement. These maps encompass most of the 1,500 foot perimeter around the ash
basin with the exception of areas beyond the property line.
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 Weatherspoon Plant compliance boundary have been
reported to NCDENR (SynTerra, Drinking Water Well and Receptor Survey, September
2014, and Supplement to Drinking Water Well and Receptor Survey, November 2014). The
first report included results of a review of publicly available data from NCDENR
Department of Environmental Health, NC OneMap GeoSpatial Portal, DWR Source
Water Assessment Program (SWAP) online database, county geographic information
system, Environmental Data Resources, Inc. records review, the United States
Geological Survey National Hydrography Dataset (NHD), as well as a vehicular survey
along public roads located within 0.5 mile radius of the compliance boundary.
The first report indicated that two supply wells, DEP #1 and #2, located on the plant
property are the only public or private drinking water wells or wellhead protection
areas located within the potential area of interest (Appendix B and Attachment 2).
Possible water wells located within 0.5 mile of the compliance boundary upgradient of
the facility were noted in the report for completeness. A sample from well DEP #2
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(identified as PW-01) was collected for chemical analysis during the site assessment
(there is no electrical power to DEP #1).
The second report supplemented the initial report with information obtained from
questionnaires sent to owners of property within the 0.5 mile radius of the compliance
boundary. The report included a sufficiently scaled map showing the ash basin
location, the facility property boundary, the waste and compliance boundaries, all
monitoring wells, and the approximate location of identified water supply wells. A
table presented available information about identified wells including the owner's
name, address of well location with parcel number, construction and usage data, and
the approximate distance from the compliance boundary.
The 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, the property owner was asked to
provide information regarding the well location and construction information. The
results from the questionnaires indicated approximately 21 wells might be located
within or in close proximity to the survey area (reported wells, observed wells, and
possible wells), not including the two on -site production wells at the plant.
4.2 Summary of Receptor Survey Findings
Aquifers beneath the site, including the shallow subsurface aquifer, are used for water
supply in the vicinity of the Weatherspoon site (Section 5.0). The ash basin is likely a
recharge area for these aquifers.
4.2.1 Public Water Supply Wells
Public water systems in the Lumberton area extract groundwater from the Black
Creek aquifer (http://co.robeson.nc.us/departments-p-z/public-works/water-
s stems , accessed on June 19, 2015). The distance to the nearest three wells was
measured using the NCDENR Public Water Supply (PWS) Sections website
(http://swap.ncwater.org/website/swap/viewer.htm, accessed on June 23, 2015):
'610 PWS ID 0378055, Well #30 (County Jail): 4.2 miles west
'01P PWS ID 0378010, Well #8: 3.2 miles northwest
�1' PWS ID 0378055, Well #14: 5.7 miles north
Assuming that groundwater flow in the Black Creek aquifer is to the southeast
(from the upland toward the Atlantic Ocean), all three well locations are
upgradient of the Weatherspoon site. Because these production wells are
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screened in a confined aquifer, the likelihood that water from the surficial aquifer
at Weatherspoon could be within the drawdown zone of a well more than three
miles away is extremely low.
4.2.2 Private Water Supply Wells
Private water supply wells have been identified within or in close proximity to
the half mile offset from the compliance boundary. Updated information
regarding these wells, including analytical results for samples collected by
NCDENR is included in Appendix B. Information reported by well owners
indicates a range in well depth from 21 to 173 feet below ground surface.
The plant also used two production wells, DEP #1 and #2. DEP #2 was sampled
as part of the CSA (reference sample description PW-1). There is currently no
power to DEP#1 and therefore it was not sampled. Both are reportedly screened
within the Black Creek aquifer at depths of 193 and 220 feet below ground
surface.
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5.0 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
Coastal Plain regional aquifer system. The following sections contain a synopsis of the
geologic and hydrogeologic characteristics of the area.
The North Carolina Coastal Plain is approximately 90 to 150 miles wide from the
Atlantic Ocean westward to its boundary with the Piedmont province (Winner and
Coble, 1989). Two natural subdivisions (Tidewater Region and Inner) of the Coastal
Plain were described by Stuckey (1965). The Weatherspoon Plant is located within the
Inner Coastal Plain, which consists of the gently rolling land surface between the
Tidewater region and the Fall Line (Winner and Coble, 1989). Weatherspoon is located
northeast of the Lumber River within a subdivision of the Inner Coastal Plain that is
typified by swampy areas in the flat uplands between major river systems. Jacob Creek
flows toward the Lumber River along the eastern edge of the cooling pond.
5.1 Regional Geology
The Coastal Plain comprises a wedge shaped sequence of stratified marine and non -
marine sedimentary rocks deposited on crystalline basement. The sedimentary
sequences range in age from recent to lower Cretaceous (Winner and Coble, 1989). In
this region, units of confined aquifers divided by confining layers overlay the crystalline
bedrock. The confining units at the top of these aquifers consist of laterally extensive
silt and clay rich layers. The Lower Cape Fear and Upper Cape Fear aquifers are the
lower -most (deepest) marine sediment units in Robeson County (Winner and Coble,
1989). The Upper Cape Fear aquifer is overlain by the Black Creek aquifer which is in
turn overlain by the Pee Dee aquifer. In the Inner Coastal Plain region, the confining
unit between the Pee Dee aquifer and the overlying Yorktown or Coastal Plain deposits
(the surficial aquifer) is reported to be discontinuous, meaning that the Yorktown and
Pee Dee are semi -confined aquifers.
The surficial aquifer is comprised primarily of Coastal Plain sands with inter -bedded
silts and clays. The Yorktown Formation generally consists of fine-grained sands, shell
material, and bluish -gray silts and clays. The Pee Dee Formation generally consists of
gray or light brown, silty, fine to very fine grained quartz sand with traces of
glauconite, phosphorite, oyster shells, and pyrite. The Black Creek Formation generally
consists of gray to black lignitic clay, thin beds and laminae of fine-grained micaceous
sand, and thick lenses of cross -bedded sand. Glauconitic, fossiliferous clayey sand
lenses are also reported in the upper part of the Black Creek Formation.
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Borings installed at the site indicate that surficial deposits are either Coastal Plain or
Yorktown Formation. Coastal Plain sediments are clearly present in upland areas. It is
unclear whether oxidized sequences in low-lying areas along Jacob Creek and the
Lumber River are of Coastal Plain origin (as interpreted by S&ME, 2012) or are
weathered Yorktown Formation sediments (the interpretation in this report). It is
evident that the geologic map showing outcropping of the Black Creek Formation in the
Weatherspoon Plant vicinity (based on US Geological Survey data at
httl2://pubs.usgs.gov/of/2005/1323/) presented in the Proposed Groundwater
Assessment Workplan (SynTerra, December 2014) is not accurate.
5.2 Regional Hydrogeology
Groundwater is obtained from the surficial, Yorktown, Pee Dee, and Black Creek
aquifers in Robeson County. The Coastal Plain aquifers are comprised of permeable
sands, gravels, and limestone separated by confining units of less permeable sediment.
According to Winner and Coble (1989), the surficial aquifer consists primarily of fine
sands, clays, shells, peat beds, and scattered deposits of coarse -grained material in the
form of relic beach ridges and floodplain alluvium. The areal extent of the surficial
aquifer in the Coastal Plain is approximately 25,000 square miles with an average
thickness of 35 feet. Average recharge to the surficial aquifer is between 12 and 20
inches per year. The average estimated hydraulic conductivity is 29 feet per day
(Winner and Coble, 1989).
In the Inner Coastal Plain in the vicinity of Weatherspoon, a surficial aquifer comprised
of approximately 60 feet of Coastal Plain and Yorktown Formation sediments is the
saturated zone that underlies the land surface. It is the first aquifer to receive recharge
from precipitation. The recharge water is stored in the surficial aquifer as the
groundwater migrates toward local discharge points (lakes, rivers, streams, etc.). A
portion of the groundwater in the surficial aquifer migrates vertically to recharge semi -
confined aquifers. On average, only a fraction of the surficial aquifer recharge reaches
the semi -confined aquifers due to the substantial amount of time it takes for
groundwater to reach these units (Giese et al., 1997).
The Pee Dee confining unit, with an average thickness of 25 feet across the region,
underlies the surficial aquifer (Giese et al., 1997). The Pee Dee aquifer is composed of
fine to medium grained sand interbedded with gray to black marine clay and silt (Giese
et al., 1997). Shells are common throughout the aquifer. The aquifer thickness ranges
from 10 feet at its eastern edge to greater than 300 feet (Giese et al., 1997).
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6.0 SITE GEOLOGY AND HYDROGEOLOGY
Four layered geologic units (Coastal Plain surficial deposits, Yorktown Formation, Pee
Dee Formation, and Black Creek Formation) have been encountered in exploratory
borings installed at the site (Figure 6-1). Subsurface lithology at the plant is comprised
of thin isolated deposits of sub -angular to well-rounded gravel alluvium or Coastal
Plain surficial deposits that consist of black, gray, brown, light red, tan, or white silty
fine sand, sandy silt, clayey silt, or sandy clay. These deposits vary in thickness from
approximately three to 30 feet.
The site investigation conducted in accordance with the GAP (Section 3.2) included
installation of soil borings, groundwater monitoring wells, borings in and through the
ash basin, and installation of an additional well to sample ash pore water (Table 6-1
[revision of Table 9 from the GAP]). Physical and chemical properties of soil samples
collected from the borings and wells and sediment samples collected from ditches and
streams were determined (Table 6-2). Chemical analyses of a broad list of potential
constituents of interest were conducted on samples of groundwater, water from seeps,
and surface water (Table 6-3).
Fifteen groundwater monitoring wells (five sets of three vertically nested wells) and one
ash basin pore water well were installed in February 2015 in accordance with GAP
Sections 7.1.2 and 7.1.3 (Table 6-1, Table 6-4, Appendices C and E). The primary
technical objectives for the new well locations was to develop additional background
data on groundwater quality, confirm horizontal and vertical extent of impact to soil
and groundwater and to establish perimeter boundary conditions for the groundwater
modeling that will be used to develop the Corrective Action Plan (CAP) for the site.
These well installations were selected to anchor strategically positioned flowpath
transects to facilitate model analysis (Figure 6-1). Flow from the ash basin to potential
receptor areas is radial in an arc from the northeast to the southwest of the ash basin.
Three transects were selected for the Weatherspoon site to illustrate flowpath
conditions in the vicinity of the ash basin. Section A -A' provides the best illustration of
the ash basin source area (basin dams, engineered perimeter ditch, and ash) in relation
to the upland area to the west and receptor area to the east. Section B-B' illustrates
conditions from the wetlands across the Lumber River from the plant through the plant
area and ash basin to the Jacob Creek wetlands to the east. A transverse section from
the upland area north of the ash basin to the plant area is illustrated on Section C-C'.
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Specific objectives for each location follow:
'611 BW-02: An upland location north of the ash basin to provide site -wide variance
information on background groundwater concentrations. "The well cluster
(BW-2S/I/D) will be used to provide a more robust data set for evaluating
background groundwater quality across all hydrostratigraphic units"
(NCDENR site specific conditional approval letter last comment).
BW-03: A low-lying location across the Lumber River from the Weatherspoon
Plant to provide site -wide variance information on background groundwater
concentrations. "The well cluster (BW-3S/I/D) will be used to provide a more
robust data set for evaluating background groundwater quality across all
hydrostratigraphic units" (NCDENR site specific conditional approval letter
last comment).
1611 AW-01 and AW-02: Locations along the southern perimeter of the plant area
near the Lumber River and cooling pond to access the groundwater quality at
multiple depths hydraulically downgradient of the ash basin.
AW-03: A low-lying location northeast of the ash basin adjacent to the Jacob
Creek floodplain to access the groundwater quality at multiple depths beyond
the compliance boundary (NCDENR November 2014 site specific comment).
Three wells were installed at each location. The deep well was drilled first at each
location (GAP Section 7.1.3). A shallow well ('S' designation) was installed with the top
of the well screen approximately five feet below the groundwater surface. In the
upland location (BW-02), the shallow well was installed in the Coastal Plain sediments
(Figure 6-1). The two shallow wells installed in the plant area (AW-01 and AW-02)
were installed in Coastal Plain sediments or imported fill material. Ten -foot pre -packed
screens were installed in the shallow well at these three locations. It appears that the
shallow wells installed in low-lying areas (BW-03 and AW-03) are screened in the
Yorktown Formation. Five-foot pre -packed screens were installed in BW-03S and AW-
03S to avoid overlap with the well screen in the accompanying 'I' well.
A monitoring well with a pre -packed five-foot screen was constructed in the lower
Yorktown Formation at all five locations ('I' designation). At the two low-lying
locations, these well screens are immediately beneath the shallow well screens. At the
two plant locations, the 'I' wells are screened beneath a low permeability layer (clay or
siltstone).
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Similarly, five 'D' wells with pre -packed five-foot screens were installed immediately
below the confining layer that separates the Pee Dee Formation from the overlying
Yorktown Formation. Deep wells were installed with an outer casing grouted into the
overlying confining layer (GAP Section 7.1.3). These wells were installed in sand
horizons that exhibited fining -upward stratigraphy.
All pre -pack well screens were filled with high grade 12/40 mesh silica sand that is
comparable to the 20/40 sand mentioned in the work plan. All 16 wells were installed
with steel above ground protective casings and bollards. The hydraulic conductivity of
each GAP well was tested by the instantaneous change in head or "slug" test method in
accordance with GAP Section 7.1.4 (ASTM D4044-96, Appendix C). The list of
constituents of interest (COI) for chemical analysis of samples collected under the GAP
was expanded significantly from previous assessment and monitoring activities (Tables
6-2 and 6-3).
Drinking water purchased from Robeson County was used for drilling fluid. A sample
of the "source water" was analyzed for the full set of GAP parameters (Attachments 3
and 4). No exceedances of reference criteria were detected. GAP COIs arsenic, boron,
cobalt, manganese, and vanadium were undetected in the sample. Iron was detected at
34 micrograms per liter (µg/L).
Rinse blanks from sample collection equipment were collected each day. Rinse blanks
for most soil samples collected by pouring deionized water through the sonic drill bit.
COIs detected in these samples indicate that rust that would collect on the bit overnight
was rinsed into the sample bottle (Appendix D). Apparently a considerable quantity of
this material plus some dust (source of aluminum) was on the bit the first day of
drilling (February 10, 2015). Samples from this day have been analyzed to evaluate for
potential contamination by the bit. The first two samples collected from SB-04 indicate
that there was no contamination because the first sample (SB-04(0-2)) collected with a
decontaminated hand auger contained nearly two orders of magnitude more iron than
the first sample collected with the drill bit (SB-04(4-5)).
Although various constituents were detected at low level concentrations in several of
the equipment blanks associated with the soil and groundwater samples as well as a
number of the filter blanks, the overall quality of the sample data is not impacted. The
constituents found in the blank samples were either not detected in the associated soil
and groundwater samples or were detected at concentrations significantly higher than
that found in the blanks.
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Rinse blanks from the pumps and filters used to collect groundwater samples yielded
negligible detections of COIs (Appendix D).
6.1 Site Geology
Limited exposures of surface geology are available at the Weatherspoon site. Areas in
the plant and associated impoundments have been constructed by mass grading
resulting in disturbed or possibly imported geologic materials. Undisturbed areas are
wooded and electric transmission line corridors are maintained with grass. Siltstone
that is resistant to weathering has been observed in ditches around the ash basin during
site reconnaissance work. These outcrops have been correlated with indurated
Yorktown Formation siltstone layers encountered at locations AW-02 and BW-03.
Photographs of sonic drill core from all of the monitoring wells (Appendix E) and
several of the soil borings are displayed on the geologic cross -sections to illustrate the
geology of the site (Figures 6-2, 6-3, and 6-4). The full set of photographs is included as
Attachment 5.
6.1.1 Soil Classification
Yorktown Formation deposits (identified based on the characteristic color and
content described for the Formation) approximately 14 to 35 feet thick underlie
the surficial deposits. The Yorktown Formation deposits at the Weatherspoon
Plant consist of blue, green, gray, and white fossiliferous sand and sandy silty
clay. The Yorktown Formation occurs unconformably on the eroded surface of
the Pee Dee Formation.
Pee Dee sediments at Weatherspoon Plant are gray,
dark green, olive, brown, and light gray silty clay,
sandy clay and silty fine to medium sand. The
thickness of the Pee Dee Formation ranges from
approximately 22 to 42 feet. Sediments identified as
Black Creek Formation with characteristic dark gray
to black micaceous clay and sand seams with
abundant mica were encountered below the Pee Dee.
Substantial fines content in the sand units in the
Coastal Plain, Yorktown, and upper Pee Dee
Formations were evident in the continuous
formation cores during well drilling (Appendix F).
Zones of clean sand were limited. In general, sand
horizons in the Coastal Plain deposits were loose
and the fines appeared to be associated with pore
Photograph 1. Sonic core from BW-
02, 7 to 11 BGS. Note brown water
draining from sand by upper right
of marker board.
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water more than the lithologic formation. This condition was most evident at
location BW-02 (Photograph 1) from 7.0 to 13.5 feet below ground surface, and
similar conditions were encountered at locations BW-03 and AW-03. The
prevalence of fine grained solids in the saturated shallow formations resulted in
turbidity measurements in excess of 10 Nephelometric Turbidity Units (NTU) in
one or both of the 2015 samples from AW-03S, BW-02S, BW-02I, BW-03S, and
BW-03I.
Sand units in the Yorktown Formation range in grain size from gravel to clay.
Numerous fining upward sequences were observed. Additionally, sand units
were interlayered with clay and siltstone horizons at most locations. These
conditions were prominent at location AW-02, and observed at AW-01 and BW-
03. The upper Yorktown Formation at location BW-03 consists of saturated clay
rich soils, resulting in elevated turbidity readings in one or both of the 2015
samples from BW-03S and BW-03I. Monitoring well AW-02I was constructed in
a sand layer between two clay rich layers. Based on recharge rates measured in
weeks, this sand layer is apparently isolated from other sand layers at this
elevation and recharges from the overlying clay.
Observations of core from the uppermost Pee Dee Formation (where each of the
deep monitoring wells designated by "D" were constructed) indicate that the
sands are very firm and fine upward to clay or fine grained calcium carbonate
(indicated by pH above 7 standard units). These conditions are reflected in the
pH and turbidity readings for March and June 2015 samples collected from the
five "D" monitoring wells.
6.1.2 Rock Lithology
There are no rocks within the CSA area.
6.1.3 Structural Geology
Unlithified sediments were encountered in all the borings on the site. There are
no indications that deep seated features in the sedimentary column or bedrock
directly affect these sediments. For this reason, structural geology is not a factor
in the SCM for the site.
6.1.4 Soil and Rock Mineralogy and Chemistry
Mineralogy and chemistry of the soils encountered are presented in Section 8.
6.2 Site Hydrogeology
The surficial unconfined aquifer is the first major hydrostratigraphic unit at the
Weatherspoon site. The upper portion of this aquifer consists of thin isolated deposits
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of sub -angular to well-rounded gravel alluvium or Coastal Plain surficial deposits that
consist of black, gray, brown, light red, tan, or white silty fine sand, sandy silt, clayey
silt, or sandy clay. These deposits vary in thickness from approximately 3 to 30 feet.
The lower portion of the surficial aquifer consists of Yorktown deposits (identified
based on the characteristic color and content described for the formation) that range
from approximately 14 to 35 feet thick.
The Yorktown deposits at Weatherspoon consist of blue, green, gray, and white
fossiliferous sand and sandy silty clay. A clay rich confining unit, which appears to be
continuous across the site separates the Yorktown deposits from the underlying Pee
Dee sediments. Pee Dee sediments at Weatherspoon are gray, dark green, olive, brown,
and light gray silty clay, sandy clay and silty fine to medium sand. The thickness of the
Pee Dee Formation ranges from approximately 22 to 42 feet. Below the Pee Dee lie
sediments of the Black Creek Formation with characteristic dark gray to black
micaceous clay and sand seams with abundant mica (S&ME, 2012).
The first occurrence of groundwater at Weatherspoon is in the surficial aquifer at
depths ranging from three to ten feet below land surface. Groundwater elevations in
June 2015 (Table 6-5) indicate the groundwater flow direction in the upper portion of
the surficial aquifer beneath the ash basin follows topography to the southeast toward
the cooling pond. Water level data from the lower portion of the surficial aquifer
(Yorktown) and Pee Dee aquifers indicate a similar flow direction with some localized
mounding under the ash basin.
6.2.1 Groundwater Flow Direction
The initial zone of saturation is comprised of pore water within the ash basin (if
present) and shallow sediment. Groundwater gradients in the surficial aquifer
are affected by manmade features (rail cuts, plant area, and ponds), ditches, the
ash basin, and site geology (Figures 6-1 and 6-5).
The surface of groundwater (water table) at Weatherspoon is typically located at
depths of three to 10 feet below ground surface, depending on antecedent
precipitation and topography. The surficial aquifer groundwater flow regime of
the Weatherspoon Plant is bounded on the southwest by the Lumber River and
to the south and east by the cooling pond and Jacob Creek, which flows
southwest toward the Plant and then flows along the southern side of the cooling
pond to its junction with the Lumber River. Based on site topography,
groundwater on the eastern side of Jacob Creek would be expected to flow west
toward the creek.
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Wells screened above the confining layer near the base of the Yorktown
Formation mimic the configuration of the initial zone of saturation, including a
mounding effect beneath the ash basin (Figure 6-6). Data from wells screened in
the Pee Dee Formation indicate a general northwest to southeast flow direction
(Figure 6-7).
6.2.2 Hydraulic Gradients
Horizontal hydraulic gradients for the June 2015 water level measurements in
the surficial aquifer vary substantially around the ash basin (Table 6-6 and
Figure 6-5). Seepage flow velocities were calculated for primary flow directions
using applicable hydraulic conductivities from slug test results, a porosity
measurement for the Lower Yorktown Formation, and the gradient measured at
either end of the transect (Table 6-6).
TABLE 6-6. Local Groundwater Gradients and Flow Velocities
Area
Bearing
Data Points
Gradient
(foot per foot)
Velocity
(feet per year)
Northwest
NE - SW
BW-02 to Lumber River
0.007
11.4
Northeast
NW - SE
BW-02 to AW-03
0.011
3.3
Plant
NE - SW
ABMW-01 to Cooling Pond
0.013
10.1
Ash Basin
NW-- SE
ABMW-1 to Ditch
0.025
19.4
Prepared by: JHG Checked by: RLP
6.2.3 Hydraulic Conductivity
Hydraulic conductivity values of the sandy formations in which the wells are
screened are relatively low as determined by the slug test method in accordance
with GAP Section 7.1.4 (Table 6-7, Appendix G). Infiltration tests using Guelph
permeameters were not performed because the groundwater model developer
indicated that those data would not be used because the slug test data were
available.
Hydraulic conductivity results from slug tests on groundwater monitoring wells
screened in the surficial aquifer range from 3.6 x 10-z to 1.4 x 10-5 cm/sec (Figure
6-1). Values for wells screened in the lower Yorktown average 3.5 x 10-3 cm/sec
and values for wells screened in the upper Pee Dee Formation average 2.2 x 10-4
cm/sec. Vertical hydraulic conductivity results for undisturbed samples of sand
(from well screen intervals) and clay are very low (1 x 10-5 cm/sec to 1 x 10-7
cm/sec, Table 6-8). The discrepancy between these values can be explained by
the smaller undisturbed sample size and the fact that the slug test measures
hydraulic conductivity in three dimensions.
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These data indicate that, despite the forces of gravity, lateral groundwater flow
will predominate over downward vertical flow at the site because of the
confining layer. Accordingly, lateral migration of COIs would be expected
relative to vertical migration.
TABLE 6-8. Vertical Hydraulic Conductivity of Undisturbed Soil Samples
Sample
Depth
(feet BGS)
Hydraulic
Conductivity
(cm/sec)
Percent
Sand
Content
Comment
From
To
AW-01
27
29
1.8 x 10-6
89.7
Well screen interval
AW-02
48
50
1.7 x 10-7
77.9
Confining layer
BW-02
68
70
1.2 x 10-5
90.8
Well screen interval
BW-03
1 37
39
1.2 x 10-7
81.5
Confining layer
Prepared by: MT Checked by: RLP
6.2.4 Groundwater Velocity
Groundwater velocities calculated for the four flow paths described in Section
6.2.2. range from 3.3 to 19.4 feet per year. The lowest hydraulic conductivity
along the path was used to calculate the velocity since groundwater flow is
limited to the slowest rate. Flow rates from the ash basin to surrounding areas
are the highest due to the hydraulic gradient from the elevated basin to the
surrounding areas.
6.3 Hydrogeologic Site Conceptual Model
The hydrogeologic site conceptual model is based on the configuration of the ash basin
relative to site features including drainage ditches, ponds, and stream, and rivers
(Figure 6-8). The presence of the confining layer at the base of the Yorktown Formation
figures significantly in this model.
Ditches along the rail siding to the west of the basin intercept groundwater and control
the groundwater elevation to the east of the siding, including the area of the ash basin.
Monitoring wells, soil borings, and piezometers show that the western end of the ash
basin is situated above the water table.
Infiltration of rainwater that falls onto the basin causes ash pore water mounding in the
eastern end of the basin. That mounding combined with the drop in the elevation of the
bottom of the basin to the southeast results in the intersection of the saturated zone in
the ash basin with the groundwater surface.
Groundwater flow in the vicinity of the basin is generally to the east and south.
Mounding of the pore water in the basin results in perturbation of the easterly flow
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resulting in localized radial flow to the northeast, southeast, and southwest. This flow
is intercepted by the perimeter ditch around the basin, yet likely extends beyond the
perimeter ditches.
A downward gradient of 6.43 feet resulting from the mounding in the ash basin was
measured using water levels in MW-44S and deeper well MW-44SA. As indicated by
the distribution of boron, groundwater flow carries COIs from the ash basin downward
and to the southeast. The zone of elevated boron concentrations sinks as it moves east,
possibly due to surface water infiltration from Jacob Swamp.
There is no recent evidence that the downward migration of contaminants extends
beneath the confining layer at the base of the Yorktown formation. Boron was not
detected in samples collected from wells screened in the Pee Dee Formation beneath the
zone of impact in the overlying Yorktown Formation (MW-53D, MW-54D, and MW-
55D, Table 10-1).
6.4 Geochemical Site Conceptual Model
This section contains geochemical information on the primary COIs for the
Weatherspoon Plant groundwater assessment. This information provides a necessary
context for the data collected to characterize the ash basin source area and potential
receptors. Data from published sources address the relative abundance of each COI in
the rocks at the earth surface ("crust"), the occurrence of the elements in coal, the
leaching characteristics of ash, and fate and transport of COIs that might be released to
the environment. Based on exceedances of 2L or IMAC in samples of ash pore water
and groundwater, iron, vanadium, manganese, boron, arsenic, beryllium, chromium,
cobalt, and nickel (listed in order of prevalence) are addressed in the following
paragraphs.
6.4.1 Iron
Iron has been detected in a sample above the 2L in nearly every monitoring well
on the property, including background wells. Iron is estimated to be the fourth
most abundant element in the Earth's crust at approximately five weight percent
(Parker, 1967, Table 18 and Figure 3). 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, Fe+z), trivalent (ferric, Fe+3),
hexavalent (Fe+6), and Fe-2oxidation 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.
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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 one percent of the total iron
present due to the low pH required to solubilize iron minerals. Despite the low
apparent mobilization percentage, iron can be one of the COIs detected in the
highest concentrations in ash pore water.
Ferric iron is soluble at pH less than 2 at typical surface conditions (25°C and 1
atmosphere total pressure, Schmitt, 1962). For this reason, dissolved iron in
surficial waters is typically oxidized to the trivalent state resulting in formation
of ferric iron oxide that exhibits a characteristic reddish tint.
6.4.2 Vanadium
Analysis for vanadium in groundwater samples from the Weatherspoon site was
initiated with the 2015 groundwater assessment. Exceedances of IMAC of 0.3
µg/L were detected in samples from each of the well locations and each of the
depth horizons sampled. 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 (V+S, V+4, V+3, and V+z). It is a common trace element in both
clay minerals and plant material. Concentrations in samples of ash pore water
were above IMAC (1.99 µg/L total, 0.455 µg/L dissolved). The discrepancy
between the total and dissolved results indicates that much of the vanadium was
associated with suspended solids in the pore water.
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 (httj2://12ubs.usgs.gov/of/1997/ofr-97-
0492 accessed on June 8, 2015). The Hydrogeochemical and Stream Sediment
Reconnaissance (HSSR) 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 than IMAC of 0.3 µg/L in 1,388
well samples (27 percent).
6.4.3 Manganese
Manganese is estimated to be the 12th most abundant element in the crust (0.100
weight percent, Parker, 1967). Manganese exhibits geochemical properties
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similar to iron with Mn+' Mn+6 Mn+4 Mn+3 Mn+z and Mn-1 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
and Querol, 2012). Despite the low apparent mobilization percentage,
manganese can be detected in relatively high concentrations in ash pore water.
6.4.4 Boron
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, Table 19). It occurs only in the trivalent
form (B+3). Boron is concentrated in sedimentary rocks like those that underlie
the Weatherspoon Plant (Urey, 1953). This observation indicates that a
mechanism exists to concentrate boron in minerals since the oceans could
dissolve all of the boron estimated to be present in the crust (Fleet, 1965). Fleet
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.
Because boron is associated with the carbon (fuel) in coal, 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 et al., 1978). Boron is considered a marker COI for coal
because boron is rarely associated with other types of industrial contamination.
Boron is the primary component of very few minerals. Tourmaline, a rare gem
mineral, forms under high temperature and pressure (Hurlbut, 1971). The
remaining common boron minerals, including borax that was mined for laundry
detergent in Death Valley, 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 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 (1997) lists aluminum and iron oxides, magnesium hydroxide, clay
minerals, calcium carbonate (limestone), and organic matter as important
sorption surfaces in soils. 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 (p. 43).
6.4.5 Arsenic
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, Table 19). It occurs in multiple valence states (As+5, As+3, and As-3).
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 (As+5) (Goodarzi et al., 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 and Querol, 2012).
6.4.6 Chromium, Cobalt, and Nickel
Chromium, cobalt, and nickel are base metals that exhibit geochemical properties
similar to iron and manganese. Each occurs as a divalent and trivalent ion.
Chromium also exhibits a hexavalent (Cr+6) valence state that is substantially
more toxic than the other two forms. Cobalt can occur as Co-1. In terms of
distribution in the crust, all three metals exhibit a strong affinity for mafic
igneous and volcanic rocks and deep-sea clays (Parker, 1967, Table 19).
Chromium occurs as Cr+3 in coal, apparently in association with the clay mineral
illite. Chromium in fly ash appears to be associated with glass or aluminosilicate
phases in the Cr+3 valence state (Goodarzi et al., 2008).
Cobalt occurs in clay minerals and substitutes into the pyrite crystal structure.
There is also evidence that it is organically bound in coal (Finkelman, 1995).
Izquierdo and Querol (2012) report limited leaching of cobalt from coal,
attributing this observation to incorporation into iron oxide minerals.
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
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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).
6.5 Electrochemical Charge Balance
Constituents dissolved in solution exhibit either positive (called cations, such as Fe+2) or
negative (anions, such as HCO3) charges because they are not chemically bound in a
solid. Comparison of the concentration of major cations and anions in a solution such
as a groundwater sample can be used for two purposes. First, charge balance within a
small tolerance (five to ten percent) provides an indication that all of the major
constituents have been identified. Second, lack of charge balance in a well characterized
sample can be an indication of disequilibrium.
Electrochemical charge balance is calculated by converting concentrations of major
cations (calcium, potassium, sodium, magnesium, iron, and manganese) and major
anions (chloride, bicarbonate + carbonate, sulfate + sulfide, and nitrate + nitrite) to molar
equivalents, summing the total of each, and comparing the results as a percentage off
equality. Groundwater that is in equilibrium with the soil or rock that surrounds it
should exhibit equal concentrations of cations and anions (refer to Section 6.4.5). Lack
of charge balance can be an indication that other chemical constituents are "major"
cations or anions.
Lack of charge balance can also be an indication of disequilibrium. The chemical
weathering that occurs as rainwater infiltrates into the ground everywhere in the
southeastern United States is the result of chemical disequilibrium. If the rainwater
were in equilibrium with soil and rock, weathering would not occur. Similarly,
discharge of contaminants from a source can cause disequilibrium in affected
groundwater as reactions initiated by the introduced contaminants proceed.
Groundwater samples collected for the CSA were analyzed for a large suite of cations
and anions. It is unlikely that anions in particular have not been fully characterized.
Deviations in solution chemistry indicated by charge balance calculations are evaluated
in this report to identify a cause.
6.6 Equilibrium
The conditions under which chemical reactions such as the binding of dissolved arsenic
into an iron oxide can be determined by experiments conducted under highly
controlled, or equilibrium, conditions (Nash, 1971, p. 101-107). These experimental data
yield powerful predictive capabilities regarding the results of chemical reactions so long
as the assumption of equilibrium can be made.
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Equilibrium is attained over time when the entropy (S, defined as the chemical capacity
for change) of the reaction reaches a maximum for the conditions (e.g., temperature,
pressure, concentration, etc.) under which the reaction is occurring. Equilibrium
calculations do not address the time required for entropy to reach a maximum
(Denbigh, 1971, p.40-42). In general, conditions at the surface of the earth are not
conducive to driving reactions to the maximum level of entropy, or equilibrium. It is
for this reason that chemists use reactors to create conditions of elevated temperature
and pressure to convert a mixture of chemicals into a product in a short period of time.
For these reasons, use of equilibrium equations to predict the results of chemical
reactions in an ash basin or in the shallow subsurface of the earth is at best an
approximation. These equations are a proper and appropriate starting point to predict
the chemical reactions that will occur over time as ash sluice water accumulates in a
basin, becomes ash pore water, and subsequently migrates from the basin. However,
because the assumption that equilibrium will be attained cannot be supported, the
predictions in this report and subsequent documents based on such calculations are
approximations and must be critically evaluated with professional judgment.
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7.0 SOURCE CHARACTERIZATION
As described in the following sections, the groundwater assessment was focused on the
single ash basin at the Weatherspoon Plant as the primary potential source of
groundwater contamination, as described in the following sections. Methods used to
characterize the source materials are described in Appendix C.
7.1 Identification and Description of Sources
Coal ash from the Weatherspoon Plant boilers included bottom ash and fly ash. Coal is
formed from plant material that accumulated in settings comparable to modern day
swamps. Coalification is the process by which plant material is converted to coal by
elevated heat and pressure that result from burial beneath overlying soil and rock.
Varying amounts of inorganic sediment such as sand, silt, and clay are deposited in
swamps with the dead plant material. Additional inorganic impurities such as pyrite
likely formed from interstitial liquids as the plant material was converted to coal. The
chemical character of coals evolves in a regular manner with increasing depths of burial
and passage of time. Depth ranges up to 2,000 meters (6,560 feet) below ground surface
and temperature ranges of 70' to 80°C (158' to 176°C) are accepted as the conditions
under which coals form (Kisch, 1969, p. 407-425; Turner, 1981, p. 303-305).
7.1.1 Coal Combustion and Ash Handling System
Coal was pulverized prior to combustion in the boilers. Bottom ash is comprised
primarily of the inorganic impurities in coal that did not burn in the boiler. The
grain size or specific gravity of this material prevents entrainment in the flue gas.
Fly ash is very fine material that was removed from the flue gas stream by
electrostatic precipitators at Weatherspoon. Ash was conveyed hydraulically
from the Weatherspoon boilers to the ash basin. During operation, ash laden
sluice water flowed by gravity to a pump pit for conveyance by pipe to the ash
basin. Hydraulic placement of ash was accomplished by moving the influent
pipe to different locations along the western end of the basin. The volume of the
ash basin was increased over time by using ash and large diameter geotextile
tubes filled with ash to form internal containment berms.
Ash particles settled in the basin while the water was impounded. Decant water
from the ash basin discharged into a small basin on the east corner of the basin
prior to discharge to the cooling pond. In general, the eastern end of the basin
will contain finer ash particles than areas close to the discharge pipe to the west.
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7.1.2 Description of Ash Basin
The Weatherspoon ash basin appears to have been mostly constructed above the
original ground elevation. It is possible that the basin was started in low lying
ground, but the vast majority of the ash is currently elevated above the
surrounding topography. Examination of historic USGS aerial photography
(Figures 7-1, 7-2, and 7-3) indicates that the site was wooded or open pasture
prior to use for ash settling. Water covered much of the cleared area on the ash
basin site in a 1951 photograph. By 1958, a small diked basin had been
constructed at the northwest end of the ash basin site. Successive aerial
photographs show that the diked basin was expanded in stages to the southeast.
The February 1980 photograph shows the footprint of the basin in the current
configuration.
The perimeter of the basin has been altered by substantial excavation for a rail
spur. The rail spur and adjacent drainage ditches extend along the southwest
perimeter of the basin. It is unclear how much excavation was required to install
these features. A drainage ditch has been excavated along the northeast
perimeter of the basin. A ditch also runs along the southeastern perimeter of the
basin between the toe of slope and what appears to have been original low lying
ground.
The ash basin embankments are well vegetated and armored with riprap in
areas. Soil has been used to construct some or all of the perimeter levees. Within
the ash basin, ash or large diameter geotextile tubes filled with ash have been
used to construct roadways and containment embankments. The elevation of
both the top of the ash basin dike and the bottom of the ash basin is highest on
the northwest end and lowest on the southeast end.
The ash basin covers an area of approximately 55 acres. Borings installed in the
ash basin encountered ash from 18 to 34 feet in thickness. The ash basin contains
an estimated 1,530,000 tons of ash (Duke Energy, June 23, 2015). Since plant
operations ceased late in 2011, a limited area of standing water has occupied the
eastern corner of the basin (Figure 2-1). No other ash storage facilities have been
identified on the Weatherspoon Plant property.
7.2 Characterization of Sources
Prior characterization of the ash basin by S&ME (Figure 6-1) was supplemented by four
borings and installation of a monitoring well during the current assessment. The
borings were installed using direct push technology (DPT) drilling methods with
continuous sample recovery (Appendix C). Each boring penetrated the bottom of the
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basin. Two ash samples and two soil samples were collected from each boring for
physical and chemical testing in accordance with GAP Section 7.1.1. Ash thickness
exceeded 30 feet only at the location of ABMW-1. Two ash samples were collected at
that location, including a large volume sample for sorption property testing that
required nearly all the ash from the boring.
The contact between ash and underlying soils was distinct in each boring (Photograph
2). Physical intrusion of ash into the underlying soils appeared to have been limited.
Photograph 2. Geoprobe core from AB-03 showing
one inch diameter sample in acrylic tube. Soil (left
of arrows) contact with saturated ash (right) is
distinct with little vertical migration of ash.
7.2.1 Physical Properties of Ash
Physical properties (grain size, specific gravity, and moisture content) and
mineralogy determinations were performed on samples from the ash basin.
Physical properties were measured using ASTM methods and mineralogy was
determined by X-ray diffraction (Appendix C). With the exception of the sample
from AB-2, the ash is fine grained (primarily silt and clay size particles) and
exhibits a lower specific gravity than soils which typically range from 2.5 to 2.7
(Table 7-1).
TABLE 7-1. Physical Properties of Ash
Moisture
Gravel
Sand
Silt
Clay
Specific
Sample
Content
(percent)
(percent)
(percent)
(percent)
Gravity
(percent)
AB-1 (3-5)
52.2
0
8.8
87.4
3.8
2.174
AB-2 (18-22)
42.9
18
56.1
23.1
2.8
2.385
AB-3 (14-15)
64.5
0
12.6
80.2
7.2
2.154
AB-4 (3-5)
56.4
1.7
23.4
58.2
16.7
2.194
Prepared by: MT Checked by: RLP
Mineralogy was determined for an ash sample from 30 to 32 feet BGS in ABMW-
01 (Table 7-2). The sample tested was predominately quartz (40.7 percent),
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mullite (43.3 percent), and oxides of iron and magnesium (9.5 percent). Quartz
(SiO2) is the primary mineral in most natural sand deposits. Mullite is an
aluminosilicate mineral (Al6Si2O13) that is rare in nature but common in artificial
melts (Hurlbut, 1971, p.385). Presumably, the mullite formed from naturally -
occurring micas and clays in the coal-fired boiler. Hematite (Fe3O4) and
magnesioferrite (MgFe2O4) are also presumed to have formed in the boiler from
minerals that contained reduced iron (such as pyrite) and magnesium.
7.2.2 Chemical Properties of Ash
Ten samples of ash were analyzed for total metals, total organic carbon (TOC),
and metals susceptible to leaching by the USEPA Synthetic Precipitation
Leaching Procedure (SPLP, Appendix C). Arsenic was detected at quantifiable
concentrations above the USEPA Soil Regional Screening Level (RSL,
http://www.epa. og v/reg3hwmd/risk/human/rb-
concentration table/Generic Tables/index.htm, accessed on July 26, 2015) for
industrial health in all the samples tested (Table 7-3). Cobalt was detected above
the industrial health RSL in one sample, and above the residential RSL in the
remaining samples. Vanadium was detected above the residential RSL in all ash
samples.
The residential RSL concentration in ash was exceeded for aluminum (six
samples), barium (one sample), iron (four samples), manganese (one sample),
and strontium (one sample). The RSL for protection of groundwater was
exceeded at quantifiable concentrations in ash for antimony (three samples),
barium (nine sample), beryllium (seven samples), copper (one sample), lead
(nine samples), and selenium (10 samples). Boron was detected in the samples
from an estimated concentration of 16.5 mg/kg to 248 mg/kg. Residual carbon
(measured as TOC) in the samples ranged from 0.143 to 12.3 percent (1,430 to
123,000 mg/kg).
Of the 25 metals analyzed, all were detected in the SPLP leachate from one or
more samples except mercury and silver (Table 7-4). Aluminum, iron, sodium,
calcium, and potassium were the only COIs detected at concentrations exceeding
1 milligram per liter (mg/L) in leachate from the samples. The remainder of the
metals leached at concentrations less than one milligram per liter of leachate.
Comparison of the total metals data and the SPLP leachate data for ash indicate
that barium, boron, selenium, and strontium are most prone to leaching under
SPLP conditions. Conversely, aluminum, arsenic, cadmium, calcium, cobalt,
copper, lead, and nickel are less susceptible to leaching from ash.
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A single ash sample was tested by Energy Dispersive X-Ray Fluorescence
(EDXRF) for metal oxides (Table 7-5) and a suite of elements (Table 7-6). The
sample was comprised primarily of silicon dioxide (SiO2), aluminum oxide
(Al2O3), carbon (C), and iron oxide (Fe2O3). Copper (144 mg/kg), zinc (110
mg/kg), nickel (93 mg/kg), and arsenic (55 mg/kg) were the trace metals detected
in highest concentrations in the sample.
7.2.3 Chemistry of Ash Pore Water
Two samples of pore water collected from ABMW-01 and one sample from MW-
44S were analyzed for the expanded list of COIs (Table 6-3). The pore water was
slightly turbid (3.51 to 13.7 NTU) with an elevated concentration of dissolved
constituents (Total Dissolved Solids from 660 to 1,100 mg/L, Table 7-7). Five
metals were detected above the corresponding 2L or IMAC (Table 7-8).
Molybdenum, a metal for which a reference criterion has not been assigned, was
detected at a concentration of 0.255 mg/L.
Elevated concentrations of calcium, potassium, magnesium, sodium, bicarbonate,
chloride, and sulfate were also detected in the sample of ash pore water (Table 7-
7). Calcium appears to limit the mobility of arsenic and other COIs from ash
(Izquierdo and Querol, 2012).
Sediments accumulated in the perimeter ditch contain numerous COIs (Table 7-
9). This is likely the result of precipitation due to the change in chemical
conditions (primarily pH and oxidation state) from the subsurface pore water to
the surface water.
Sorption characteristics (Kd) for arsenic, boron, cobalt, iron, molybdenum, nickel,
and vanadium are being measured for the ash. Sorption factors were determined
for these metals for the following reasons:
'07 Arsenic, boron, iron, and vanadium were detected above 2L or IMAC
criterion in ash basin pore water
Cobalt and nickel were detected above the 2L or IMAC in a sample from
one or more of the monitoring wells
'07 Molybdenum, a metal without an established reference criterion, was
detected at a relatively high concentration in ash basin pore water
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7.2.4 Hydrology of the Ash Basin
Boring data indicate that the bottom of the ash basin slopes from west to east
(Figure 6-1, Section A -A'). Saturated conditions were observed in the eastern
portions of the ash basin during the 2015 assessment. Observation wells OW-1,
OW-3, and OW-8 (Figure 2-1) were dry in February and June 2015. An area of
internal drainage on the eastern side of the basin near PZ-2 appears to feed a
seep at the toe of the slope. Saturated conditions within the basin provide as
much as 15 feet of vertical head on the bottom of the basin.
Standing water in ditches to the west of the ash basin indicate that the cut for the
rail spur into the plant intersects shallow groundwater and controls the elevation
at which groundwater flow from the upland area to the west passes beneath the
ash basin (Figure 6-1). Seep sample locations around the perimeter of the ash
basin provide an indication of the elevation of the zone of saturation within the
basin and the eastward discharge of ash pore water to the perimeter ditch.
The hydraulic conductivity of the ash in the screened interval of ABMW-01 was
determined to be 3.6 x 10-4cm/sec (Appendix G). This value will be used as an
input to the site -wide groundwater model.
7.3 Piezometers and Seeps
Ash pore water discharges from the dike on the southeastern end of the basin. Three
piezometers are located in the northeastern dike of the ash basin to monitor water
levels. Ash pore water samples were collected from the piezometers and designated
seep locations. Additionally, sediment samples were collected from the perimeter ditch
in conjunction with the seep samples.
7.4 Constituents of Potential Concern
COIs identified in conjunction with the Weatherspoon ash basin include arsenic, boron,
cobalt, iron, manganese, thallium, TDS, and vanadium. The majority of the ash pore
water samples collected from the pore water wells, piezometers, and seeps (Table 7-7)
exceed 2L for arsenic, boron, iron, manganese, and IMAC for vanadium. Eleven of the
14 samples fall within the pH range of 6.5 to 7.4, while three samples exhibited pH from
6.0 to 6.4. Additional exceedances of 2L or IMAC include barium (two samples),
chromium (one sample), cobalt (four samples above IMAC), lead (one sample), thallium
(one sample above IMAC), and TDS (five samples).
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8.0 SOIL AND ROCK CHARACTERIZATION
Four soil borings were conducted to collect soil samples from the unsaturated zone and
the zone of saturation in areas unaffected by the ash basin. Soil samples were also
collected from borings at five monitoring well sites. These samples were analyzed for
total metals, TOC, and leaching characteristics to determine naturally occurring
constituents.
Fifteen groundwater monitoring wells were installed at five locations. Three wells at
each location were constructed to provide groundwater samples from the following
saturated zones:
41' Shallow saturated zone ("water table" conditions)
410 Lower portion of the Yorktown Formation aquifer
'61' Upper portion of the Pee Dee aquifer
Soil samples from these locations were analyzed to determine mineralogy, physical, and
chemical properties conditions (Appendix F).
Geologic cross -sections illustrating groundwater and soil COI concentrations are shown
on Figure 8-1. The location of analytical results for soils is shown on Figure 8-2.
Discussion of groundwater sample results is presented in Section 10 of this document.
8.1 Background Soil
Soil samples collected from background locations are discussed in conjunction with
soils from the remainder of the site in the following section. Shallow soils at
background location BW-03 are similar to the soils in monitoring wells downgradient of
the ash basin. These soils are either relatively recent surficial materials deposited on top
of an eroded Yorktown Formation surface or are weathered and reworked Yorktown
Formation.
Shallow soils at background locations MW-1, BW-1, and BW-02 are clearly Coastal Plain
deposits that overly a full Yorktown section. Due to the lower elevation of the plant
area, these soils are either limited in thickness or not present in the vicinity of the ash
basin.
8.2 Soil
Soils from the site were tested in accordance with Work Plan Section 7.1.1. Physical
property testing of soil samples indicates that site soils are predominately sand (Table
8-1). This includes materials identified in the field as plastic clay and siltstone.
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Mineralogical determinations indicate that feldspar, muscovite (a mica), and clay
minerals (kaolinite, illite, and smectite) accompany quartz in soil samples from the site
(Table 8-2). Chlorite, an aluminosilicate mineral similar to mica, and lepidococite, an
iron oxide, were each detected in one sample.
8.2.1 Soils beneath the Ash Basin
The contact between the ash and underlying soils in the ash basin borings was
visually distinct. There was no visible evidence of substantial migration of ash
into underlying soils or mixing of ash with those soils (Photograph 2, Section
7.2).
Comparison of chemical analytical data for soils beneath the ash basin with the
chemistry of the ash as revealed in both total (Table 7-3) and leaching data
(Table 7-4) yields the following observations:
410 Aluminum concentrations in the soils are comparable to the aluminum
content of the ash, indicating that aluminum has not been added to the
soils by migration of large amounts of aluminum into soil.
'410 Calcium, magnesium, and sodium concentrations in soil beneath the ash
basin are an order of magnitude lower than those in the ash, indicating
that these constituents have not migrated in large concentrations into soil.
410 Cadmium, chromium, cobalt, copper, lead, manganese, and nickel occur
at part per million concentrations in ash and leach at very low
concentrations, indicating that they have not migrated in large
concentrations into soil.
410 Iron occurs in soils beneath the basin at concentrations comparable to that
at background locations as well as in ash and exhibits leaching properties
that indicate it has not migrated in large concentrations into soil.
410 Vanadium concentrations in ash and soil are comparable (although soils
beneath the basin are consistently lower than ash), and leaching data
indicate that it has not migrated in large concentrations into soil.
410 Arsenic leaching results indicate that it should exhibit relatively low
potential for migration, but the presence of low levels of arsenic in soils
beneath the basin suggests that it has migrated into soil.
'610 Boron concentrations in soil beneath the ash basin are comparable to those
from other areas of the site, indicating that boron detected in solution in
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groundwater samples beneath the basin does not precipitate or adsorb at
appreciable levels in soil, and is therefore expected to be transported in
groundwater.
8.2.2 Site Soils
Observations from the chemical data provide several insights. COIs detected
above a 2L or IMAC in groundwater samples were detected in soils and SPLP
leachate from soils at background locations over a range of depths.
Chemical analysis of soil samples (Tables 8-3, 8-4, 8-5, and 8-6 and Figures 8-1
and 8-2) indicate that oxides of silicon (74 to 96 percent) and aluminum (1.4 to 16
percent) are the predominate chemicals present. Trace metals (potential COIs)
detected in appreciable concentrations include iron (78.5 to 20,600 mg/kg),
manganese (non -detect to 276 mg/kg), and vanadium (non -detect to 150 mg/kg).
The whole rock analyses of aluminum (Al) indicate that the USEPA method for
analyzing aluminum in soil underestimates the true value. Aluminum oxide
(Al2O3) is 52 percent Al. Samples tested by whole rock X-ray fluorescence were
determined to contain up to 16.23 weight percent (wt. pct.) Al2O3 (8.44 wt. pct.
Al), which is approximately equivalent to 84,400 mg/kg (Table 8-5). None of the
soil samples tested by USEPA methodology yielded results of this magnitude.
Apparently, the digestion process for the USEPA method does not capture all the
Al in the solid material.
All of the metals analyzed in SPLP leaching tests were detected in leachate from
one or more soil sample. Inspection of these results indicates that aluminum,
calcium, iron, potassium, and sodium would be mobilized from natural soils at
the site in the highest concentrations.
8.2.3 Surficial Soils
Soil samples from the surface to two feet below ground surface (BGS) were
collected at nine locations (four soil borings and five monitoring well locations).
Four COIs (aluminum, arsenic, barium, and iron) were detected at quantifiable
concentrations above a soil screening level. These results are discussed in greater
detail in Section 12.2.5.
8.3 Comparison of Results to Applicable Levels
Qualitative evaluation of the soil chemistry data suggest that surficial soils at locations
SB-03 (immediately southeast of the ash basin) might be affected by coal ash and SB-04
(material laydown yard in the plant area) might be affected by industrial activity other
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than the ash basin. Quantifiable soil concentrations in excess of an RSL in sample SB-
03(0-2) include arsenic (7.2 mg/kg), barium (157 mg/kg), and iron (11,400 mg/kg).
Metals detected above the industrial RSL in sample SB-04(4-5) include antimony (136
mg/kg), arsenic (139 mg/kg), cobalt (152 mg/kg), and thallium (146 mg/kg). Metals
detected above the residential screening level in sample SB-04(4-5) include cadmium
(14.1 mg/kg), selenium (140 mg/kg), and vanadium (150 mg/kg). The RSL for protection
of groundwater was exceeded in this sample for beryllium (13.8 mg/kg) and lead (155
mg/kg). This sample was described as tan fine to medium grained sand, silty with
rounded gravel. This is the only location where antimony and thallium were detected
in soil. The SB-04 location is also anomalous in the low concentrations of iron and
manganese. Lead and total organic carbon were moderately elevated in the sample.
The rail spur was present between the ash basin area and the location of SB-04 in the
1951 aerial photograph. There is no indication on the aerial photographs that ash was
managed south of the rail spur. Possible operations other than coal ash management
that might have produced these soil analytical results include coal handling and
equipment maintenance. The 1995 fuel oil release is another possible source.
Quantifiable detected values in soil samples from location AW-02 exceeded one or more
RSL for aluminum (13,000 mg/kg), arsenic (5.3 mg/kg), cobalt (3.5 and 45.8 mg/kg), lead
(20.1 mg/kg), and selenium (7.4 mg/kg). This location is between the coal pile for the
former coal-fired boilers and the cooling pond. As noted throughout this report, the
location and chemical data for samples from this site indicate that coal ash is not the
source of elevated COI concentrations in soil and groundwater.
Arsenic was detected above one or more RSLs in samples from new background and
downgradient monitoring well locations BW-02 (1.5 mg/kg), BW-03 (2.0 mg/kg), and
AW-03 (3.2 and 3.2 mg/kg) (Figures 8-1 and 8-2). Cobalt was detected above an RSL in
samples from BW-02 (5.1 mg/kg) and AW-03 (3.7 mg/kg). Iron was detected above the
residential RSL at concentrations ranging from 7,820 to 17,400 mg/kg in samples from
locations AW-01, AW-03, SB-01, and SB-02.
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9.0 SEDIMENT, SEEP, AND SURFACE WATER CHARACTERIZATION
Sediment samples were collected during the CSA from four locations beyond the
perimeter of the ash basin. Two seeps at locations distant from the ash basin were
sampled, as were two surface water locations. These data are discussed in the context
of samples collected by NCDENR in 2014.
The industrial RSL was exceeded for arsenic in sediment from location S-15 in the ditch
that drains from the ash basin to the cooling pond (Table 9-1). Residential RSLs in
samples detected at quantifiable concentrations were exceeded for aluminum, arsenic,
barium, iron, manganese, and vanadium in the sediment samples. All but three of the
exceedances were detected in sediment sample S-15. The RSLs for protection of
groundwater in samples detected at quantifiable concentrations were exceeded for lead
and mercury.
One seep sample (S-20) was collected from Jacob Creek upstream of the plant, a second
(S-07) was collected from drainage from an area west of the plant, and a third (S-15) was
collected from the ditch immediately downstream of the ash basin that drains ash pore
water to the cooling pond. The upstream seep sample (collected from the outfall from a
beaver dam) was more acidic than 2L for groundwater and the North Carolina Section
2B surface water criteria for surface water (Table 9-2).
Criteria exceeded in the sample from S-15 follow:
10' Aluminum (113 µg/L / <5 µg/L dissolved, greater than 2B of 87 µg/L total
recoverable)
'67 Boron (1,650 µg/L / 1,680 µg/L dissolved, greater than 2L of 700 µg/L)
'j Vanadium (0.592 µg/L / 0.529 µg/L dissolved, greater than IMAC of 0.3 µg/L)
The surface water samples were collected from drainages near the ash basin. Sample
SW-01 was collected from Jacob Creek east of the cooling basin. SW-02 was collected
from a flowing portion of the discharge from a wetland area northeast of the ash basin.
Both samples exceeded the 2B criteria for aluminum (Table 9-3). The aluminum result
for SW-01 (193 µg/L) was lower than the upstream Jacob Creek seep result (252 µg/L).
9.1 Review of NCDENR March 2014 Sampling Results
NCDENR directed the sampling and analysis of seeps in March 2014 (Table 9-4). The
majority of these samples were collected from the ash basin toe drains and perimeter
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ditch and are therefore representative of ash basin pore water (Section 7.0 of this
report).
9.2 Comparison of Exceedances to 213 Standards
Exceedances of a 2B criteria were measured for pH and aluminum. The pH of samples
collected from Jacob Creek (also known as Jacob Swamp) were 5.7 upstream of the ash
basin (S-20) and 5.1 downstream (SW-02). This is consistent with slow -flowing,
blackwater creeks are colored by tannic, humic, and fulvic acids.
Aluminum was detected above the criteria in the upstream sample (SW-20: 252 µg/L /
186 µg/L dissolved) as well as both downstream samples (SW-01: 193 µg/L / 146 µg/L
dissolved; SW-02: 598 µg/L / 475 µg/L dissolved). Data summarized in Section 8.2
indicate that aluminum does not leach appreciably from the ash to and mobilize soil.
SPLP leaching tests indicate that aluminum would be mobilized from natural soils at
the site at relatively high concentrations. Therefore, the aluminum detected in these
surface water and seep samples appears to be naturally occurring.
9.3 Discussion of Results for Constituents without 213 Standards
COIs for which a 2B Standard has not been established include boron, iron, manganese,
TDS, and vanadium (Table 9-5). Boron was detected only in the filtered (dissolved)
sample from SW-01 at 54 µg/L. This result is questionable since it was detected in only
one of a paired set of samples.
Iron was detected in both surface water samples (1,050 µg/L / 828 µg/L dissolved in SW-
01 and 1,140 µg/L / 749 µg/L dissolved in SW-02). These concentrations are consistent
with the slow -flowing, blackwater wetland and creek from which the samples were
collected.
Manganese was detected in seep samples S-07 and S-07 DUP (35 µg/L / 34 µg/L
dissolved in both), S-20 (77 µg/L / 74 µg/L dissolved), SW-01 (69 µg/L / 66 µg/L
dissolved), and SW-02 (59 µg/L / 38 µg/L dissolved). These concentrations of
manganese are on the order of 10 percent the concentration of iron in the samples,
which is a common ratio for natural waters.
TDS was detected in a range of 33 to 130 µg/L, and vanadium was detected in upstream
sample S-20 (0.592 µg/L / 0.529 µg/L dissolved) and the duplicate sample from S-07
(0.312 µg/L / <0.3 µg/L dissolved). These values do not appear to be indicative of
impact.
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10.0 GROUNDWATER CHARACTERIZATION
Groundwater samples from the 15 new monitoring wells and 20 existing monitoring
wells were analyzed for the GAP COIs (Table 10-1). Fourteen COIs were detected in
groundwater samples above 2L or IMAC (Table 10-2) all on Duke Energy property.
Comparison of ash pore water analytical results to groundwater 2L or IMAC is shown
on Figure 10-1. Of the 14, pH (2L), chromium (2L), cobalt (IMAC), iron (2L), lead (2L),
manganese (2L), TDS (2L), and vanadium (IMAC) were detected above 2L or IMAC in
wells located both upgradient and downgradient of the ash basin. Vanadium and iron
appear to be associated with suspended solids based on inspection of the dissolved
analytical results. Manganese was primarily detected above 2L in samples collected
from wells screened in the Lower Yorktown Formation above the confining layer and
the Pee Dee Formation beneath the confining layer.
The data presented in this section indicate that some detected values, particularly for
iron, manganese, and vanadium, above 2L or IMAC are naturally occurring. Many of
the remaining detections above reference criteria occur in samples collected from
monitoring wells beneath the ash basin or within 250 feet of the ash basin perimeter
ditch.
10.1 Background Monitoring Wells
Monitoring wells MW-01 and BW-01 were installed prior to 2015. Samples have been
collected intermittently from MW-01 since 1990. Monitoring well BW-01 is currently
used as the background well for NPDES compliance monitoring. Due to historic
mounding of the ash basin potentially influencing data from these two wells, both are
under evaluation for use in comparisons to naturally occurring background conditions.
Both wells are screened as surficial aquifer wells and are hydraulically upgradient of
the ash basin and the rail spur (Figure 6-1). Ditches on both sides of the rail spur
between these wells and the ash basin intersect the water table and are therefore
discharge points for shallow groundwater. As such, the ditches separate MW-01 and
BW-01 from the ash basin, meaning that both MW-01 and BW-01 should be reliable
sources of "background" information in the future. This tentative conclusion will be
reevaluated with the results of the groundwater modeling to be performed for the CAP.
The chemical characteristics of groundwater samples from these two monitoring wells
differ considerably. The pH of samples from MW-01 exhibit a broad range from 3.8 to
6, while samples collected from BW-01 is consistently lower between 3.9 and 4.6.
Antimony has been detected above IMAC in one historic sample from MW-01, as has
cadmium (2L) in a historic sample from BW-01. Iron has been consistently detected
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above 2L in samples from both wells. However, one recent filtered sample from MW-01
was below the detection limit for iron while seven of 15 samples from BW-01 have been
above 2L for iron. Vanadium has only been tested in one sample from each well, and
was not detected in the sample from MW-01 but was detected in both unfiltered and
filtered samples from BW-01.
During the CSA, new monitoring wells were installed at locations BW-02 and BW-03 to
better characterize background groundwater quality. Background location BW-02 is
hydraulically upgradient of the ash basin in terms of the water table ('S' monitoring
wells), the potentiometric surface at the base of the Yorktown Formation ('I' monitoring
wells), and the potentiometric surface in the confined Pee Dee Formation ('D'
monitoring wells) (Figures 6-5, 6-6, and 6-7). Geologically, BW-02S is screened in
Coastal Plain sediments and BW-02I is screened near the base of the Yorktown
Formation. Samples drawn from BW-02S and BW-02I exhibit elevated turbidity due to
the nature of the water in the vicinity (refer to Section 6.1).
Chemically, groundwater from BW-02S exhibits pH less than 6.5 with iron (total and
dissolved), lead (total only), and vanadium (total only, IMAC) in excess of reference
criteria. Groundwater from BW-02I contains chromium in excess of 2L, cobalt and
vanadium in excess of IMAC, and iron in excess of 2L in both unfiltered and filtered
samples. Anomalous high pH and TDS results from BW-02D indicate that this well
might be compromised by bentonite or grout contamination. Continued development
during future sample collection events will occur if this monitoring well is deemed
necessary for future monitoring.
Background location BW-03 is across the Lumber River from the Weatherspoon Plant.
Because the Lumber River is a groundwater discharge point for surficial groundwater
(Figure 6-5), this well location can be considered a background monitoring site for the
surficial and Lower Yorktown wells (BW-03S and BW-03I). The configuration of the
potentiometric surface in the Pee Dee Formation (Figure 6-7) indicates that BW-03D is a
suitable background monitoring location for the Pee Dee Formation due to the distance
from the ash basin and comparable water level measurements relative to Pee Dee wells
at the ash basin.
Chemically, groundwater from BW-03S exhibits pH less than 6 with iron (total and
dissolved) in excess of 2L and vanadium (total only) in excess of IMAC. Groundwater
from BW-03I also exhibits pH less than 6 with iron (total and dissolved), manganese
(total only), and vanadium (total only, IMAC) in excess of reference criteria.
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Based on these results, it appears that site specific background values for iron,
manganese, and vanadium merit further evaluation after sufficient samples for
statistical analysis have been collected. Inspection of the data from upgradient
monitoring wells indicates that background concentrations for groundwater in the
surficial aquifer would be on the order of the following:
'611 Iron at two to five times 2L of 300 µg/L
�� Manganese slightly higher than 2L of 50 µg/L
t1' Vanadium in the range of 1 to 3 µg/L (compared to IMAC of 0.3 µg/L)
BW-02 and BW-03 clusters were installed to potentially replace current background
well BW-01 as representative of naturally occurring conditions in areas beyond
potential historical mounding from the ash basin. Detailed evaluation of groundwater
gradients discussed in this report indicates that both BW-01 and MW-01 are
hydraulically upgradient of the ditches along the rail spur west of the ash basin and
therefore isolated from mounding of pore water in the ash basin. Continued
monitoring of these locations is recommended to determine if these locations are useful
indicators of background groundwater quality. Eight sets of data from the new
background wells will be collected for statistical evaluation of naturally occurring
background concentrations. Until more sample sets are available for statistical analysis,
the data from these wells can be used for general understanding of background
conditions.
10.2 Discussion of Redox Conditions
For the most part, shallow monitoring well screens were set in soils that exhibit
oxidizing conditions such as reddish color. Two wells installed near wetland areas
(BW-03 and AW-03) were saturated to within a few feet of the surface resulting in
relatively reducing conditions. Despite this current condition, shallow soils at these
locations exhibit characteristics of chemical weathering by oxygenated waters in the
past.
The lower Yorktown Formation and Pee Dee Formation exhibited evidence of reducing
conditions that include gray color and strongly negative oxidation / reduction potential
(ORP) readings in groundwater.
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Valence speciation determinations were performed on groundwater samples from
shallow monitoring wells installed in 2015, compliance wells, and select existing wells
located in close proximity to the ash basin (Table 10-3). General observations follow:
'611 Trivalent arsenic (As+3) was the dominant species detected for each sample.
Samples from BW-01, AW-03S, and the two wells screened beneath the ash basin
(MW-08I and MW-44SA) contained appreciable As+5.
Hexavalent chromium was detected at concentrations less than or comparable to
the tapwater standard of 0.037 µg/L
(http://www.el2a.gov/reg3hwmd/risk/human/rb-
concentration table/Generic Tables/index.htm, accessed on July 28, 2015) with
the highest concentration occurring in background sample BW-02S (0.04 µg/L)
indicating that hexavalent chromium detected in groundwater samples at the
Weatherspoon Plant site is naturally occurring.
�� Reduced iron was the dominant species in each sample with the exception of
AW-02S and AW-03S. The geologic settings for these two wells are very
different and the reason for these deviations is not evident.
Mn+4 was detected at only four locations. With the exception of the sample from
BW-02S and AW-01S, Mn+4 occurred at roughly 10 percent of the concentration of
Mn+2. BW-02S is screened in the most upland location of all the wells in highly
oxidized soils. AW-01S is screened beneath recently disturbed soils in the plant
area.
10.3 Regional Groundwater Data for Constituents of Potential
Concern
Iron, manganese, and vanadium are detected across the Weatherspoon site, including at
the background location across the Lumber River. It is anticipated that site specific
background levels will be calculated for these COIs after eight sets of groundwater data
are available.
NURE data on vanadium were discussed in Section 6.3.2 of this report. These data have
not been analyzed in detail, but they make it clear that vanadium is common in North
Carolina groundwater. Calculation of a site specific background concentration for
vanadium will include an effort to incorporate NURE data from Robeson County.
10.4 Groundwater Analytical Results
The largest number of 2L or IMAC exceedances occurred in samples from monitoring
well location AW-02S. The coal pile that fed the combustion boilers was situated
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immediately northwest of this monitoring well location. A preliminary conclusion is
that this monitoring well is affected by remnants from the coal pile that was located
nearby rather than migration of constituents from the ash basin.
Iron, manganese, and vanadium were detected in monitoring wells across the site
(Figures 10-2,10-3, and 10-4). While certain impact from the ash basin is indicated at
some locations (refer to Section 11), site specific background levels need to be
determined when sufficient analytical data from new wells are available. Elevated TDS
was encountered in samples from several background monitoring wells as well as
samples from several monitoring wells in the vicinity of the ash basin.
Boron is the most mobile of the COIs (refer to Section 6.3.3), with lateral migration more
prevalent than vertical movement. Arsenic appears to have migrated limited distances
vertically and horizontally from the ash basin. While cobalt and thallium have been
designated COIs for the site due to a detection above the reference criterion, it is not
clear that they have migrated from the ash basin. Cobalt was detected in only four
samples and thallium was detected in only one (excluding samples from AW-02S in the
plant area).
Isoconcentration maps illustrate the distribution of COIs in ash pore water (Figures 10-5
through 10-12), the surficial aquifer (Figures 10-13 through 10-20), wells screened in the
lower Yorktown Formation (Figures 10-21 through 10-28), and wells screened in the Pee
Dee Formation (Figures 10-29 through 10-36).
Samples from the upland background well BW-02S and a monitoring well beneath the
ash basin (MW-44SA) were analyzed for isotopes of uranium and radium (Attachment
4). Uranium-238 (U238) was the only isotope detected in the samples, with the
concentration in the background well slightly higher (0.00332 µg/mL) than that in the
well beneath the ash basin (0.00179 µg/mL).
Both isotopes of radium were detected in both samples. The concentration of Ra228 was
1.95 picoCuries per liter (pCi/L) in the background well sample and 2.02 pCi/L in the
sample from beneath the ash basin. Ra226 was detected at 0.88 pCi/L in the background
well sample and 6.69 pCi/L in the sample from beneath the basin.
Maps of ash pore water and groundwater analytical results related to detection
monitoring constituents and inorganic parameters as identified in the USEPA April
2015 Final Ruling 40 CFR Parts 257 and 261 (CCR Rule), including boron, calcium,
chloride, conductivity, pH, sulfate, and total dissolved solids are included as Figures
10-37, 10-38, 10-39, and 10-40. Maps of ash pore water and groundwater analytical
results related to assessment monitoring constituents as identified in the USEPA April
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2015 Final Ruling 40 CFR Parts 257 and 261, including aluminum, antimony, arsenic,
barium, beryllium, cadmium, chromium, copper, iron, lead, manganese, mercury,
molybdenum, selenium, sulfate, sulfide, thallium, and vanadium are included as
Figures 10-41, 10-42, 10-43, and 10-44. Certain constituents listed in 40 CFR Parts 257
and 261 are not included on Figures 10-37 through 10-44 because they were not
included in the GAP approved by NCDENR.
Distributions of major cations and anions in ash pore water and groundwater from the
surficial, lower Yorktown, and Pee Dee monitoring wells plotted on Piper diagrams
provide an indication of the characteristics of each zone. Ash pore water is dominated
by calcium, magnesium, carbonate, and sulfate (Figure 10-45). Ion ratios vary
substantially in the surficial zone across the site, with the water in AW-02S as a clear
outlier (Figure 10-46). Conversely, major ion ratios in samples from the lower
Yorktown and Pee Dee monitoring wells exhibit limited variation (Figures 10-47 and
10-48).
Electrochemical charge balance calculations (Table 10-4) indicate that many of the
samples are within the expected range (less than 10 percent deviation). All samples are
anion deficient (i.e., positively charged ions outnumber negatively charged ions). This
is to be expected since the electrochemical effects of hydroxyl radicals (OH-) cannot be
evaluated because there is no analytical method for that parameter. Inspection of the
data yields the following observations:
'61' Leaching (disequilibrium) and the likely presence of metal hydroxides in the
sample turbidity in the ash basin monitoring wells and seeps is indicated by
charge balance differences of 11.6,14.1, 16.1, and 27.8 percent.
'61' The two shallow monitoring wells installed in the area of the plant that was
recently regraded after plant demolition (AW-01 and AW-02) reflect apparent
disequilibrium due to the disturbed soils (58.5 and 64.1 percent).
'61' Samples collected from monitoring wells BW-01 (20.4 percent), BW-03S (10.9
percent), and BW-03I (12.0 percent) that are located near wetlands (and therefore
prone to seasonal variations) show indications of disequilibrium.
'61' Charge imbalance in the sample from BW-02I (14.3 percent) is likely due to solids
(turbidity = 413 NTU).
'61' At this time, the only potential explanation of the charge imbalance in the sample
from MW-01 is modification of natural conditions, such as the rail cut or the ash
basin.
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Compliance groundwater monitoring has been performed at Weatherspoon since 2010.
Time versus concentration diagrams of TDS, sulfate, and chloride indicate considerable
seasonality in the samples collected from BW-01 and CW-03 (Figures 10-49 and 10-50).
Both wells are located in or adjacent to wetland areas, indicating that a mechanism
related to the shallow water table is involved. Absolute concentrations are higher in the
samples from CW-03 than those from BW-01. Variations of constituent concentrations
through time are illustrated on Figures 10-51,10-52, and 10-53.
For comparison purposes, Piper diagrams for seep and surface water are included as
Figures 10-54 and 10-55.
Groundwater monitoring data collected for the four compliance monitoring wells are
evaluated using interwell prediction limits (parametric, nonparametric, and Poisson) to
compare background well data (BW-01) to the results for the most recent sample data
from compliance wells. Based on recommendations from ASTM (2012) guidance and
USEPA (2007), nondetected values were replaced with half of the detection limit for the
parametric and Poisson prediction limit procedures, and the detection limit for the
nonparametric prediction limit procedure.
Confidence levels were set at 99 percent for the parametric and Poisson prediction
interval. Confidence levels for the nonparametric prediction limit are given by n/(n+k)
were n is the number of background samples and k is the number of comparisons. The
false positive rate is given by 1-[n/(n+k)]. The number of comparisons is defined by the
number of recent sample dates multiplied by the number of compliance wells
(background wells).
Prior to conducting the interwell statistical analysis, the data set was "screened" and
"treated." The Shapiro-Wilks goodness -of -fit test was used to evaluate the statistical
distribution of data sets because they contain less than 50 measurements. Each data set
was initially tested to determine whether the distribution is normal. If a data set fails
the test of normality, the natural logarithms of the data are taken and the procedure is
repeated. If the transformed data passes, the data set is designated as lognormal. If a
logtransformed data set fails the test of normality, the data set is designated as non -
normal.
The parametric prediction limit was used to analyze data that were normally or
lognormally distributed with less than or equal to 50 percent nondetects (ASTM D6312-
98, Section 6.1.1). The nonparametric prediction interval test was performed on normal
and lognormal data sets with greater than 50 percent nondetects and for data sets with
non -normal distributions with fewer than 90 percent nondetects (ASTM D6312-98,
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Section 6.1.1). The nonparametric prediction limit compares each individual
downgradient concentration for the selected dates to the maximum concentration in
background samples. The Poisson prediction limit statistic was utilized to evaluate data
with greater than 90 percent nondetects (ASTM D6312-98, Section 6.1.1).
Groundwater statistics for samples collected from the compliance wells in March and
June 2015 also reflect the variation (Appendix H). Concentrations of boron and
chloride in the March sample from monitoring well CW-03 exhibited statistically
significant increases over the results for the sample from monitoring well BW-01. The
June samples for boron and chloride were statistically indistinguishable.
10.5 Comparison of Results to 2L Standards
Exceedances of 2L for iron and manganese, and IMAC for vanadium are most common
across the site (Table 10-2, Figures 8-2, 10-2, 10-3, and 10-4). Each element is naturally
occurring and common in shallow wells in this hydrogeologic setting. In most cases for
iron, comparison of total concentrations to a corresponding "dissolved" (filtered)
concentration indicates that iron is associated with solids. Vanadium appears to be
attributable to solids in samples from BW-02I, BW-03I, MW-03, and MW-44SA. Site
specific background concentrations should to be calculated for all these COIs when a
sufficient number of analytical results are available for the statistical calculations.
Exceedances of the reference criterion for arsenic, cobalt (IMAC), and thallium in the
complete data set are rare and limited to the immediate vicinity of the ash basin
(Figures 8-2, 10-2, 10-3, and 10-4). Boron exceedances occur beneath the ash basin and
to southeast of the basin. The distribution of COIs is discussed in more detail in the
next section of the report.
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11.0 HYDROGEOLOGICAL INVESTIGATION
Results of the hydrological investigation summarized in this section are the primary
components of the site conceptual model (SCM).
11.1 Hydrostratigraphic Layer Development
The surficial aquifer and the Pee Dee aquifer are the two distinct hydrostratigraphic
layers discussed in this CSA report. Data from previous reports (S&ME, 2012)
document the presence of the Black Creek aquifer below the Pee Dee at the site, but it
was not included in the GAP because there is no evidence of COI migration to that
depth. The surficial aquifer (initial zone of saturation) beyond the limits of the ash
basin occurs in Coastal Plain sediments and the Yorktown Formation (Figure 6-1). It
ranges in thickness from less than 20 feet to nearly 60 feet depending on topography.
The saturated portion of the ash basin is superimposed on this aquifer.
Evidence from previous investigations (S&ME, 2012) and the 2015 CSA indicate that the
confining layer between the Yorktown Formation and the Pee Dee Formation is
contiguous across the Weatherspoon site. The confining layer strata which vary from
plastic soils to stiff "siltstone" (Figures 6-2, 6-3, and 6-4) have been encountered in every
deep boring at the site. The thickness of this layer varies from a few feet to nearly 20
feet across the site.
11.2 Hydrostratigraphic Layer Properties
Properties of the hydrostratigraphic layers plotted on the geologic cross -sections
illustrate the relationship of the materials to groundwater quality data (Figures 11-1,11-
2, and 11-3).
11.2.1 In -Situ Tests
Infiltration tests using Guelph permeameters were not performed because the
groundwater model developer indicated that those data would not be used
because the slug test data were available. Testing of undisturbed soil samples
collected using Shelby tubes confirms that the vertical hydraulic conductivity of
Weatherspoon soils is low for materials with such high sand content (Table 6-8).
11.2.2 Slug Tests
Slug testing is described in Section 6.2.3 and summarized in Table 6-7 and on
Figure 6-1. Slug testing within the ash basin exhibits flow properties typical of a
fine sand or silt soil (4.1 x 10-4 cm/sec). The screened intervals for the majority of
the groundwater monitoring wells exhibit hydraulic conductivity values
between 3 x 10-3 and 3 x 10-5 cm/sec. The shallow well at location BW-03 along
the Lumber River is on the order of 1 x 10-2 cm/sec.
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11.2.3 Porosity
Porosity was calculated for the four undisturbed samples collected. Two
confining layer samples were calculated to have 32.1 (BW-03(37-39)) and 34.5
(AW-02(48-50)) percent porosity. A sample of the Lower Yorktown aquifer (AW-
01(27-29)) was determined to have 38.7 percent porosity, and a sample of the Pee
Dee Formation (BW-02(68-70)) was calculated to have 37.6 percent porosity.
11.3 Groundwater Flow Direction
Groundwater at the site flows east and south toward Jacob Creek and the Lumber River
from upland areas to the west and north (Figures 6-5, 6-6, and 6-7). Mounding of ash
pore water within the eastern portion of the ash basin creates radial flow from the basin
to the northeast, southeast, and southwest.
11.4 Hydraulic Gradient
The hydraulic gradient from the ash basin to surrounding areas ranges from 0.013 to
0.025 foot per foot (Figures 6-5, 6-6, and 6-7, Table 6-8).
11.5 Groundwater Velocity
Groundwater flows from the ash basin to surrounding areas at approximately 3.3 to
19.4 feet per year (Table 6-6).
11.6 Contaminant Velocity
Based on preliminary site specific sorption coefficients not included in this report, most
COIs would migrate at rates lower than the groundwater velocity. Boron is likely an
exception to this generalization and would migrate at approximately the same rate as
groundwater. Site specific sorption coefficients will be available for incorporation into
the groundwater modeling that will be performed for the CAP.
11.7 Characterization of COI Distribution
Distributions of COIs from the ash basin to the surrounding area are illustrated on the
primary flow transect (Section A -A', Figures 11-1,11-2, and 11-3). Horizontal extent to
the southeast is defined to the cooling pond and Jacob Creek, the groundwater
discharge zones for the surficial aquifer.
11.8 Groundwater / Surface Water Interaction
A ditch on the west side of the rail spur adjacent to the ash basin intercepts
groundwater and controls the elevation of groundwater flow to the southeast from this
feature (Figure 6-1). Perimeter ditches around the ash basin divert considerable
amounts of pore water to ditches that drain to the south and east (toward the cooling
pond). These ditches vary from being gaining streams to losing streams depending
upon location and seasonal wetness.
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Groundwater discharges to the wetland areas to the northeast and east of the ash basin.
Groundwater that discharges to the southeast and south of the ash basin discharges to
the cooling pond (Figures 6-5, 6-6, and 6-7).
11.9 Confining Layers
The confining layer that separates the base of the Yorktown Formation from the Pee Dee
Formation has been described as semi -continuous on a regional basis. A primary
objective of the CSA is to determine if the confining layer is continuous on the
Weatherspoon Plant site. To accomplish this objective, borings were installed at
locations peripheral to the ash basin to supplement existing data collected in the
immediate vicinity of the basin.
The Lower Yorktown confining layer was encountered at every location that a boring
was installed (refer to Section 6). The thickness of the confining layer ranged from a 3.5
feet (AW-01) to as much as 19 feet (BW-03). Hydraulic conductivity measurements of
two undisturbed samples of the confining layer (Table 6-8) were 1.7 x 10-7 cm/sec and
1.2 x 10-7 cm/sec. The confining layer ranged in consistency from plastic clay to a stiff
siltstone. At the five locations that well nests were installed, the integrity of the
confining layer is also indicated by the differing configuration between the
potentiometric surface in the confined Pee Dee Formation wells relative to the overlying
unconfined Lower Yorktown wells (Table 6-5, Figures 6-6 and 6-7).
The most recent groundwater monitoring samples from the Pee Dee Formation did not
detect boron (Figure 11-1). Boron was detected in samples collected in February and
March 2012. Whether these results reflect a laboratory artifact or short term impacts
from well installation, they do not appear to be representative of current conditions.
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12.0 SCREENING -LEVEL RISK ASSESSMENT
To support the groundwater assessment and inform corrective action decisions,
potential risks to human health and the environment have been assessed in accordance
with applicable federal and state guidance, as described in Section 8 of the Proposed
Groundwater Assessment Work Plan (SynTerra, December 2014). Screening level
human health assessments and ecological risk assessments have been performed to
serve as the foundation for evaluating potential risks to human and ecological receptors
at the site. NCDENR has managed sample collection from nearby private water supply
wells. Data from these samples are contained in Appendix B.
Preliminary COPCs have been identified based on evaluations performed in accordance
with NCDENR recommendations regarding coal ash constituents. Both screening level
risk assessments compare maximum constituent concentrations to appropriate risk -
based screening values as a preliminary step in evaluating the potential for
unacceptable risks to receptors. When appropriate, site- and media -specific risk -based
remediation standards may be derived as part of the corrective action plan.
For the purpose and scope of this report, sample locations have been segregated into
two groups: source locations and receiving locations. Source locations are defined as
sample locations that are either (a) in/on the ash basin or its containment structures (e.g.,
berms, dikes) or (b) directly adjacent to the ash basin or its containment structures (e.g.,
drainage ditches, swales, and/or adjacent creeks that receive seep water from the ash
basin). Receiver locations, not to be confused with human or ecological receptors, are
defined as sample locations that are located in areas of the site that are separated either
spatially or hydrologically from ash basin influence. The screening -level risk
assessment is not designed to characterize the horizontal and vertical extent of potential
contamination, but rather to identify coal ash related constituents that exceed published
human or ecological health screening criteria and warrant further consideration with
respect to corrective action.
12.1 Human Health Screening
12.1.1 Introduction
This screening level human health risk assessment (HHRA) has been prepared in
accordance with Section 8 of the Proposed Groundwater Assessment Work Plan
(SynTerra, December 2014) and USEPA guidance for human health risk
assessment, including the USEPA Region 4 2014 Draft Final Human Health Risk
Assessment Supplemental Guidance, as applicable.
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12.1.2 Conceptual Exposure Model
Consistent with standard risk assessment practice for developing conceptual
models, separate Conceptual Exposure Models (OEMs) were developed for the
human health and ecological risk evaluations. Figure 12-1 has been prepared
illustrating potential exposure pathways from the source area to possible human
receptors. The information in the CEM has been used in conjunction with the
analytical data collected as part of the CSA.
The human health CEM is based on characterization of primary and secondary
sources and corresponding release mechanisms, the COPC for each affected
environmental medium, and the possible migration and transport potential of
this constituent to potentially exposed populations (receptors). Figure 12-1
identifies the source and release mechanisms for the site along with exposure
medium and route. Potential receptors at the site are identified, with
consideration of current land use scenarios. The individual components of the
human health CEM are further described in the following sections.
Primary Constituent Source
Historical coal ash management activities conducted at the site is the source of
constituents addressed in this assessment. Potentially impacted groundwater,
soil, surface water and sediment in the vicinity of the ash basin are the exposure
medium.
Primary Release and Transport Mechanisms
Consistent with the focus of this assessment on migration of ash basin
constituents into water, the primary potential constituent release and transport
pathways at the site are as follows:
y Desorption of constituents from coal ash to coal ash pore water.
41' Infiltration of coal ash pore water to underlying groundwater.
y Infiltration of coal ash pore water through ash basin dikes to form seeps.
161, Formerly discharged sluice water from the ash basin to cooling pond.
Secondary Release Mechanisms
Secondary potential constituent release and transport pathways at the site follow:
h Transport of coal ash constituents from groundwater to seeps, surface
water body sediments, and surface water.
h Transport of coal ash constituents from seeps to surface soils, surface
water bodies, and surface water body sediments.
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Exposure Medium, Pathways, and Exposure Routes
The exposure medium includes potentially impacted groundwater, soil, surface
water and sediments at the site. The exposure routes associated with the
potentially completed exposure pathways evaluated for the site include
ingestion, inhalation and dermal contact of environmental media.
12.1.2.1 Current/Future Construction Workers
The potential exists for current and/or future construction workers to be
exposed to COPCs at the site. Construction work activity, including soil
excavation and grading, is considered in the risk screening scenario.
12.1.2.2 Current/Future Maintenance Workers
The potential exists for current and future maintenance workers to be
exposed to COPCs at the site. Maintenance work may include routine
outdoor maintenance activities such as mowing, landscaping and manual
excavation. This exposure scenario is considered in the risk screening.
12.1.2.3 Future Resident (Adult/Child)
There are no residences onsite. There is the potential that the site could be
redeveloped for residential use in the future and future residents could
potentially be exposed to COPCs at the site. This exposure scenario is
considered in the risk screening.
12.1.2.4 Current/Future Recreational User (Adult/Child)
The potential exists for current and future recreational users. Current
users include adults and adolescent trespassers hunting, fishing, or
swimming onsite. The site could be made available for public recreational
use in the future. Recreational users under these current and future use
scenarios could potentially be exposed to COPCs at the site. These
exposure scenarios are considered in the risk screening.
12.1.3 Risk -Based Screening Levels
The human health risk assessment includes an initial comparison of constituent
concentrations in various media to risk -based screening levels. A comparison of
constituent concentrations in various media to the following risk -based screening
levels is presented in the following sections. The screening criteria include
chemical -specific screening levels based on concentrations that are Applicable or
Relevant and Appropriate Requirements (ARARs) [e.g., Safe Drinking Water Act
maximum contaminant levels (MCLs)] and concentrations resulting from risk -
based calculations that set concentration limits using carcinogenic or systemic
toxicity values under specific exposure conditions. These include:
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h Coal Ash Constituents — Regional screening level (RSLs) for soil
protective of groundwater and human health under residential -use
scenarios and industrial -use scenarios
(httl2://www.el2a. og v/reg3hwmd/risk/human/rb-
concentration table/Generic Tables/index.htm, accessed on July 26, 2015).
h Coal Ash Pore Water - NCDENR Title 15A, Subchapter 2L.
h Groundwater - NCDENR Title 15A, Subchapter 2L Standards, Interim
Maximum Allowable Concentrations (IMACs; 15A NCAC 02L.0202), and
USEPA Screening Level for Hexavalent Chromium in Residential Tap
Water (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015).
167 Soil and Sediments - USEPA Residential and Industrial Soil Regional
Screening Levels (RSLs) Target Cancer Risk 1x10-6/Target Hazard Quotient
of 0.1 (USEPA Regional Screening Levels (RSLs) rev., June 26, 2015).
101 Surface Water and Seeps - North Carolina Surface Water Standards
(Subchapter 2B) and USEPA National Recommended Water Quality
Criteria for Human Health for the consumption of water and organisms
(NCDENR 2007-2014 Triennial Review; USEPA National Recommended
Water Quality Criteria; 2004).
Soil, sediment and groundwater will be compared to available local, regional and
national background data, as available.
Coal Ash and Coal Ash Pore Water
Coal ash and water retained within the coal ash basin is the sole source of
constituents addressed by this risk screening process. Constituents impacting
groundwater from other onsite sources, offsite sources, or naturally occurring
sources, may be acknowledged but are beyond the scope of this risk screening
process. Consequently, COPCs going forward will be attributable only to the
coal ash.
Coal Ash
Coal ash COPC are, by definition, constituents of coal ash. Ten ash samples were
collected from five borings installed within the Weatherspoon ash basin. The
coal ash samples were analyzed for 28 inorganic constituents and total organic
carbon (TOC). Coal ash analytical results are summarized in Table 7-3 and
compared with constituent soil regional screening levels (RSLs) derived for the
protection of groundwater as well as the protection of human health under
residential -use and industrial -use scenarios. Constituents that have at least one
soil screening criteria and were detected at concentrations below all applicable
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RSLs, or were not detected and their analytical method detection limits where
below their respective RSLs, may not be considered a coal ash COPC. Coal ash
constituents that may not be coal ash COPCs are listed below:
h Beryllium
y Cadmium
h Copper
10 Lead
h Mercury
161, Molybdenum
,611 Nickel
10 Strontium
y Zinc
Conversely, the following coal ash constituents are retained as preliminary coal
ash COPCs for the reasons indicated (Table 7-3):
Coal Ash Constituent Concentrations
Greater Than One Or More Soil RSLs
y
Aluminum
y
Antimony
,611
Arsenic
y
Barium
41,
Boron
y
Cobalt
h
Iron
h
Manganese
y
Selenium
,611
Thallium
y
Vanadium
Coal Ash Constituents
That Have No Soil RSLs
y
Calcium
,611
Chloride
,01
Chromium
01
Magnesium
y
Nitrate (as N)
h
Potassium
,6j
Sodium
y
Sulfate
101
TDS
Coal Ash Pore Water
Coal ash pore water is precipitation that has infiltrated through the coal ash and
is retained within the ash basin (Figure 12-2). Coal ash pore water above the
ash/soil interface results in saturated conditions within disposed ash. Desorption
of coal ash constituents into precipitation that has infiltrated into the coal ash is
expected to be greatest wherever the coal ash is under saturated conditions for
extended periods of time. The coal ash pore water and solubilized inorganic
constituents will eventually infiltrate into the underlying groundwater.
Consequently, coal ash pore water can potentially impact groundwater quality
when solubilized inorganic constituents are present at concentrations above 2L
or IMAC. Conversely, solubilized inorganic constituents present in ash pore
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water at concentrations below 2L or IMAC do not pose unacceptable risk to the
quality of underlying groundwater.
A total of 15 coal ash pore water samples were collected from two monitoring
wells screened within the coal ash, three piezometer wells installed along the
immediate perimeter of the coal ash basin, and nine seeps immediately adjacent
to the base of the ash basin containment. Ash pore water samples were analyzed
for 28 inorganic constituents. Analytical results of ash pore water analyses are
presented in Table 12-1 along with 2L or IMAC, where applicable.
Ash pore water constituents that have 2L or IMAC and were detected at
concentrations below 2L or IMAC, or were not detected and their analytical
method detection limits where below their respective 2L or IMAC, are not coal
ash COPCs because they do not pose an unacceptable risk to the quality of
underlying groundwater. These constituents are listed below:
y
Antimony
y
Nickel
,67
Beryllium
61,
Nitrate (as N)
y
Cadmium
67
Selenium
y
Chloride
y
Sulfate
01
Copper
611
Thallium
01
Mercury
67
Zinc
Conversely, coal ash constituents that are at concentrations that exceed their
groundwater screening criteria or have analytical method detection limits greater
than their groundwater screening criteria, or have no groundwater screening
criteria may adversely affect the quality of underlying groundwater. The
following coal ash constituents are retained as preliminary coal ash COPCs for
the reasons indicated:
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Coal Ash Constituent
Concentrations Greater than Coal Ash Constituents
2L or IMAC
that have no 2L or IMAC
01
Arsenic
h
Aluminum
0
Barium
h
Calcium
0
Boron
y
Magnesium
h
Chromium
h
Molybdenum
h
Cobalt
y
Potassium
h
Iron
h
Sodium
01
Lead
h
Strontium
Ol
Manganese
�i
TDS
1j Thallium
167 Vanadium
Calcium/Magnesium/Potassium/Sodium
Calcium, magnesium, potassium, and sodium analyses were conducted for the
purpose of characterizing the geochemistry of different aquifers. These
constituents are found in abundance in natural groundwater systems and are
routinely quantified by geochemists to generate Piper diagrams or plots of major
cations and anions. Cation and anion data collected at the Weatherspoon site has
been used to generate Piper diagram plots that categorize geochemical
characteristics of the coal ash pore water, the Yorktown Formation, and the Pee
Dee Aquifer (Section 10). Furthermore, these naturally occurring constituents do
not pose unacceptable risks to human health when present in groundwater at
moderate concentrations. This is one reason why these constituents have no
established numerical limits (e.g., 2L, IMACs, Safe Drinking Water Act maximum
contaminant levels) in groundwater for the protection of human health.
Calcium, the most abundant mineral in the body, is found in many foods and is
available as an over-the-counter dietary supplement. Magnesium, potassium,
and sodium are also present in many common foods and are also available as, or
included in, over-the-counter dietary supplements. Although calcium,
magnesium, potassium, and sodium are coal ash constituents, it is unlikely that
they will be significant contributors to potential human health risk posed by coal
ash constituents. For these reasons, calcium, magnesium, potassium, and
sodium will not be considered coal ash COPCs (Table 12-2).
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Seep Sample S-10
Seep sample S-10 is unique because it contained elevated concentrations of total
recoverable lead (161 µg/L) and thallium (2.82 µg/L) when all other seep and ash
pore water samples contained no quantifiable concentrations of total recoverable
lead (<1 µg/L) and thallium (<1 µg/L). Similarly, seep sample S-10 contained
elevated concentrations of total recoverable chromium (67.4 µg/L) when only one
ash pore water sample collected from well ABMW-01 in March contained 1.22
µg/L total recoverable chromium. Total recoverable chromium was not
quantifiable (<1 µg/L) in the ABMW-01 sample collected in June. Elevated
concentrations of total recoverable lead, thallium, and chromium detected in the
S-10 seep sample is attributed to high sample turbidity in excess of 1000 NTU
(Table 12-1). Dissolved lead, thallium, and chromium concentrations in the field
filtered S-10 seep sample and all other ash pore water and seep samples were
below the analytical method detection limit (<1 µg/L). Lead, thallium, and
chromium will not be designated a coal ash COPCs on the basis of a single turbid
seep sample when all other lines of evidence indicate that these constituents are
at unquantifiable concentrations in less turbid, more representative seep samples
(Table 12-2). If conditions allow, a more representative, less turbid, surface
water sample will be collected from seep sample location S-10 for total metals
analysis.
Coal Ash COPC Determination
Coal ash COPC determinations are summarized in Table 12-2 along with the
rationale for the determination. Constituents that are coal ash COPCs will be
evaluated as to whether they are groundwater, soil, sediment or surface
water/seeps COPCs that are potentially attributable to coal ash. Constituents
that are not coal ash COPCs will not be evaluated going forward.
Groundwater
Site groundwater meets the definition of Class GA groundwater (15A NCAC
02L.0201). Consequently, the 15A NCAC 02L.0202 and IMAC groundwater
quality standards (2L or IMAC) apply. The concentrations of groundwater
constituents that have 2L or IMAC are compared to those screening criteria.
Groundwater constituents having concentrations below their respective 2L or
IMAC in all groundwater samples do not pose an unacceptable risk to human
health. Groundwater constituents having concentrations above their respective
2L or IMAC warrant further evaluation. The source of groundwater constituents
detected above 2L or IMAC could be naturally occurring conditions (e.g.,
elevated metals in saturated subsurface matrix), high turbidity groundwater
samples, an offsite contaminant release, the coal ash, or other site related source
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of groundwater constituents. A constituent that exceed 2L or IMAC or has no
2L or IMAC and is a coal ash COPC will be a designated groundwater COPC
potentially attributable to coal ash. Conversely, a constituent in groundwater
that exceed 2L or IMAC or has no 2L or IMAC but is not a coal ash COPC will
not be a groundwater COPC potentially attributable to coal ash.
The following groundwater constituents are not groundwater COPCs potentially
attributable to coal ash because they are not coal ash COPCs (Table 12-2):
h
Antimony
161,
Beryllium
h
Cadmium
y
Calcium
y
Chloride
,611
Total Chromium
y
Copper
h
Lead
y
Magnesium
h
Mercury
,611 Molybdenum
,611 Nickel
1611 Nitrate (as N)
1611 Potassium
y Selenium
h Sodium
'61, Sulfate
161, Thallium
y Zinc
Thirty-six on -site groundwater wells were sampled in 2015. Nineteen of the
wells were sampled twice (March and June) in 2015 and seventeen wells were
sampled only in June. The Duke Energy Ash Basin Groundwater Assessment
Program Low Flow Sampling Plan (May 22, 2015) was employed to collect the
groundwater samples. Two primary objective of the low flow sampling
methodology was to determine when sampling field parameters were stable
before collecting a sample and to minimize sample turbidity.
The following field parameters were monitored and recorded in accordance with
the Low Flow Sampling Plan:
10 pH (s.u.)
y Dissolved Oxygen (DO; mg/L)
h Temperature (OC)
y Specific Conductivity (µS/cm)
h Oxidation/Reduction Potential (ORP; mV)
167 Turbidity (NTU)
y Water Level (Ft. Below TOC)
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In addition, ferrous iron concentration (mg/L) in groundwater was estimated
using a colorimetric field screening procedure.
The groundwater samples were submitted to Duke Energy Environmental
Analytical Laboratory and analyzed for up to 37 analytical parameters including
25 metals (total and dissolved). Groundwater samples submitted for dissolved
metals analyses were field filtered.
Field parameters and analytical results are assimilated on risk assessment
screening Tables 12-1, 12-3, 12-4, and 12-5. In addition, groundwater analytical
results are evaluated against 2L, IMAC, and EPA Regional Screening Levels
(RSLs) for tapwater, where applicable.
Background Groundwater
2015 Yorktown and Pee Dee Aquifer Background Sample Analytical Results
(Table 12-3) includes five background monitoring wells installed within the
surficial and Lower Yorktown Formation and two background monitoring wells
installed within the Pee Dee Aquifer.
Background Groundwater — Surficial and Lower Yorktown
Formation
Analytical results of groundwater samples collected in 2015 from the surficial
and Lower Yorktown Formation background wells indicate that the following
constituents were detected at concentrations above their respective 2L and
IMAC:
h Chromium 167 Manganese
y Cobalt '47 Total Dissolved Solids
0 Iron (TDS)
y Lead y Vanadium
Chromium was not detected above 2L (10 µg/L) in samples collected from
monitoring wells BW-02S and BW-02I in March 2015; however, chromium was
detected in groundwater samples collected from these wells at concentrations
above 2L in June 2015. The turbidity of the samples collected during the June
2015 sampling event was approximately four times higher than the turbidity
measured during the March sampling event (Table 12-3). In addition, chromium
was not detected in any of the field filtered samples collected from those wells. It
appears that elevated chromium concentrations detected in new background
monitoring wells BW-02S and BW-02I may be attributed to sample turbidity.
New monitoring wells tend to have higher turbidity in early monitoring events
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followed by lower turbidity with time and aquifer stabilization. Continued
monitoring of the wells will be conducted to evaluate this condition, with
additional well development if necessary.
Speciation analysis was conducted on samples collected from Yorktown
Formation background groundwater monitoring wells BW-01, BW-02S, and BW-
03S (Table 10-3). The only exceedance of the EPA screening level for hexavalent
chromium Cr(VI) for residential tap water (0.035 µg/L) occurred in the BW-02S
sample (0.04 µg/L). The hexavalent chromium concentration in groundwater
samples collected from wells BW-01 and BW-03S were 0.017 µg/L and 0.034 µg/L,
respectively.
Cobalt was detected above IMAC (1 µg/L) in the sample collected from BW-02I in
June 2015 (1.31 µg/L) but cobalt concentrations in all other background samples
were below their respective reporting limit (1 µg/L). Cobalt detected in the BW-
02I sample collected in June 2015 may be attributed to high turbidity (413 NTU).
As previously discussed, the turbidity of samples from the new monitoring wells
should decrease over time and the effects on the data evaluated accordingly.
Iron was detected in all Yorktown Formation background samples collected in
2015. Total iron concentrations in 8 of 11 samples exceeded 2L (300 µg/L) and
dissolved iron concentrations in 8 of 9 samples exceeded 2L. Background iron
concentrations appear to be naturally occurring because there is no known
anthropogenic source of iron hydraulically upgradient of the background wells
and iron was consistently detected in all background groundwater samples. The
occurrence of naturally occurring constituents above 2L is addressed in the
North Carolina groundwater Class GA classification:
Class GA groundwaters are considered suitable for drinking in their natural
state, but which may require treatment to improve quality related to natural
conditions (15A NCAC 02L.0201).
Total lead was detected above 2L (15 µg/L) in the BW-02S sample analyzed in
June 2015 (42.1 µg/L); but, total lead in the March BW-02S sample (7.85 µg/L) was
below 2L. Total lead was detected in six out of 11 samples below 2L.
Furthermore, dissolved lead was not detected above the reporting limit in any of
the field filtered samples including the BW-02S sample. This single incidence of
total lead exceeding 2L may be attributed to elevated sample turbidity (>1,000
NTU) in the BW-02S sample collected in June. For new well BW-02S in
particular, well development seemed to continue to introduce fine grained
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formation material. Therefore, it appears time will be required for the formation
to stabilize and to subsequently produce less turbid groundwater samples.
Manganese was detected above 2L (50 µg/L) in the March 2015 sample collected
from BW-03I. The presence of total manganese above 2L cannot be attributed
solely to elevated turbidity (58.3 NTU) since dissolved manganese concentration
in the field filtered sample collected from the same well during the same
sampling event was also above 2L. Total and dissolved manganese
concentrations in the BW-03I samples collected in June were below 2L. Total and
dissolved manganese was detected in every background groundwater sample at
an average concentration of 33 µg/L. Dissolved and total manganese appears to
be naturally occurring at concentrations just below 2L (50 µg/L).
Total dissolved solids (TDS) in the BW-02S sample (520 mg/L) collected in June
was the only sample that exceeded 2L for TDS (500 mg/L). TDS in all other
samples, including the BW-02S sample collected in March, were below 2L.
Elevated TDS in the June BW-02S sample may be attributed to elevated sample
turbidity (>1,000 NTU). As previously discussed, for new well BW-02S in
particular, well development seemed to continue to introduce fine grained
formation material. Therefore, it appears time will be required for the formation
to stabilize and to subsequently produce less turbid groundwater samples
Vanadium was detected above IMAC (0.3 µg/L) in eight of eight unfiltered
background samples and in nine of nine filtered samples. There are no known
sources of vanadium hydraulically upgradient of the site background wells
installed in the Yorktown Formation. Vanadium is naturally occurring and it
appears that it is present within the Yorktown aquifer at concentrations above
IMAC.
Downgradient Groundwater — Surficial and Lower Yorktown
Formation
Analytical results of groundwater samples collected in 2015 from wells installed
within the surficial and Lower Yorktown Formation hydraulically downgradient
of the coal ash basin (Table 12-4) indicate that the following constituents were
detected at concentrations above their respective 2L or IMAC:
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Yorktown Formation COPC
Potentially Attributable To Coal Ash
0 Arsenic
h
Boron
y
Cobalt
0
Iron
y
Manganese
h
TDS
y
Vanadium
Not A Coal Ash COP01)
h
Beryllium
y
Total Chromium
,611
Nickel
y
Sulfate
y
Thallium
Note (1): See Table 12-2
In addition, hexavalent chromium was detected in one groundwater sample
collected from MW-44SA that exceeded the EPA screening level for residential
tap water for hexavalent chromium Cr(VI) in residential tap water (0.035 µg/L).
MW-44SA was sampled once in June 2015 and the concentration of hexavalent
chromium in that groundwater sample was 0.037 µg/L (Table 10-3).
Beryllium, chromium, nickel, sulfate and thallium were detected above their
respective 2L groundwater screening criteria in groundwater samples collected
from the surficial and Lower Yorktown Formation; however, these exceedances
are not attributed to the coal ash because these constituents are not coal ash
COPCs. Consequently, these constituents will not undergo further evaluation.
Arsenic was detected in 8 out of the 34 samples collected from Yorktown
Formation downgradient wells installed downgradient of the coal ash basin. The
only sample where total or dissolved arsenic concentrations were above 2L (10
µg/L) was collected from groundwater monitoring well MW-44SA. Otherwise,
arsenic concentrations in all other groundwater samples were below 2L. Arsenic
is a Yorktown Formation groundwater COPC potentially attributable to coal ash.
Total and dissolved boron concentrations were above 2L (700 µg/L) in
groundwater samples collected from five Yorktown Formation wells constructed
within the compliance boundary. Total and dissolved boron concentrations were
below 2L in all groundwater samples collected from wells installed at, or beyond,
the compliance boundary. Boron is a Yorktown Formation COPC potentially
attributable to coal ash.
Total and dissolved cobalt concentrations were above IMAC (1 µg/L) in
groundwater samples collected from five downgradient Yorktown Formation
wells. Four of these wells were constructed within the compliance boundary.
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Groundwater monitoring well AW-02S is the only downgradient Yorktown
Formation well at or beyond the compliance boundary where total and dissolved
cobalt was detected above the analytical reporting limit. The average
concentration of total and dissolved cobalt detected in the AW-02S groundwater
samples is 65.7 µg/L and 69.7 µg/L, respectively. In contrast, the average
concentration of total and dissolved cobalt detected in the four downgradient
Yorktown Formation wells constructed within the compliance boundary is 3.1
µg/L and 2.5 µg/L, respectively. Similarly, the average concentration of total and
dissolved cobalt detected at the coal ash pore water wells MW-44S and PZ-02
and seep sample S-09A is 2.3 µg/L and 2.0 µg/L, respectively (Table 12-4). The
order of magnitude (10x) increase in total and dissolved cobalt concentrations at
groundwater monitoring wells approximately 1,000 feet downgradient of the
closest compliance boundary strongly suggests that the source of cobalt detected
at AW-02S may be the coal pile that was maintained in the vicinity of well AW-
02S before coal burning operations were terminated, not the coal ash basin.
Although iron is naturally occurring in the Yorktown Formation at
concentrations above 2L (300 µg/L), total and dissolved iron concentrations in
groundwater samples collected from wells downgradient of the coal ash basin
are significantly higher than naturally occurring iron concentrations in samples
collected from Yorktown Formation background wells (Table 12-3). The average
dissolved iron concentrations at downgradient groundwater monitoring wells
within the compliance boundary (4,080 µg/L) is almost two times the average
dissolved iron concentration at the Yorktown background groundwater
monitoring wells (2,398 µg/L). Similarly, the average dissolved iron
concentrations at downgradient groundwater monitoring wells at or beyond the
compliance boundary (5,035 µg/L) is two times the average dissolved iron
concentration at the Yorktown background groundwater monitoring wells (2,398
µg/L). Consequently, iron is a Yorktown Formation COPC potentially
attributable to coal ash because dissolved iron concentrations exceed 2L at 19 out
of 23 downgradient groundwater monitoring wells and dissolved iron
concentrations are considerably higher than naturally occurring iron
concentrations.
Manganese is naturally occurring in the Yorktown Formation at average
concentrations (33 µg/L) below 2L (50 µg/L). Total and dissolved manganese
concentrations exceeded 2L at only one background groundwater monitoring
well (BW-03I) installed in the Yorktown Formation. In contrast, dissolved
manganese exceeded 2L at eight out of 14 groundwater monitoring wells
installed within the compliance boundary and at five out of nine groundwater
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monitoring wells installed at or beyond the compliance boundary. The average
dissolved manganese concentration for all samples collected from downgradient
wells where manganese concentrations were quantifiable is 195 µg/L.
Manganese is a Yorktown Formation COPC potentially attributable to the coal
ash.
TDS is a coal ash pore water COPC. The TDS concentrations in groundwater
samples collected from four out of 14 Yorktown Formation downgradient wells
constructed within the compliance boundary were above 2L (500 mg/L). In
contrast, TDS concentrations in groundwater samples collected from only one
out of nine Yorktown Formation downgradient wells constructed at or beyond
the compliance boundary was above 2L. The average TDS concentration of three
groundwater samples collected from AW-02S is 520 while the average TDS
concentration of the other 17 groundwater samples collected from Yorktown
Formation downgradient wells constructed at or beyond the compliance
boundary is 124 mg/L. It appears that elevated TDS concentrations at AW-02S
may be attributed to the coal pile that was maintained in the vicinity of well AW-
02S before coal burning operations were terminated; not the coal ash basin.
However, TDS is a Yorktown Formation COPC potentially attributable to the
coal ash within the compliance boundary.
Vanadium was detected in 17 out of 27 Yorktown Formation groundwater
samples at concentrations above IMAC (0.3 µg/L). Vanadium is a Yorktown
Formation COPC potentially attributable to coal ash.
Surficial and Yorktown Formation groundwater samples containing COPCs
potentially attributable to coal ash are presented on Figures 12-3 and 12-4,
respectively.
Background Groundwater — Pee Dee Aquifer
Analytical results of groundwater samples collected in 2015 from background
wells installed within the Pee Dee Aquifer (Table 12-3) indicate that the
following constituents were detected at concentrations above their respective 2L
or IMAC:
41, Chromium 161, Total Dissolved Solids (TDS)
y Iron y Vanadium
Total and dissolved chromium was detected in the new background well BW-
02D samples collected in March at concentrations of 24.5 µg/L and 22.3 µg/L,
respectively (Table 12-3). In both instances, chromium exceeded 2L of 10 µg/L.
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However, total and dissolved chromium was detected in the BW-02D samples
collected in June at concentrations of 1.32 µg/L and 1.33 µg/L, respectively.
Chromium was not detected above the reporting limit in any of the samples
collected from background well BW-03D. Turbidity does not appear to be a
factor. Further evaluation of chromium in the background Pee Dee Aquifer does
not appear warranted unless chromium is subsequently confirmed to be present
at concentrations above 2L in the Pee Dee Aquifer downgradient of coal ash.
Total and dissolved iron was detected above 2L (300 µg/L) at new background
well BW-03D during the March and June sampling events (Table 12-3).
However, dissolved iron concentrations at well BW-02D were below the
reporting limit and total iron was detected only at well BW-21) during the March
sampling event (17 µg/L). Like the Yorktown Formation, it appears that
naturally occurring iron is also present in the Pee Dee Aquifer but at lower
concentrations.
TDS in the BW-02D sample (740 mg/L) collected in March was the only sample
that exceeded 2L for TDS (500 mg/L). Elevated TDS was not confirmed at BW-
02D during the June (240 mg/L) sampling event (Table 12-3). Furthermore, TDS
in all other Pee Dee Aquifer background samples were below 2L.
Total and dissolved vanadium was detected above IMAC (0. 3 µg/L) at BW-02D
during the March and June sampling events (Table 12-3). Vanadium was not
detected in any of the samples collected from BW-03D. Natural sources of
vanadium are likely responsible for the vanadium detected in the BW-02D
samples.
Downgradient Groundwater — Pee Dee Aquifer
Analytical results of groundwater samples collected in 2015 from wells installed
within the Pee Dee Aquifer (Table 12-5) hydraulically downgradient of the coal
ash basin indicate that the following constituents were detected at concentrations
above their respective groundwater screening criteria:
h Iron 611 Vanadium
01 Manganese
Iron, manganese, and vanadium are coal ash COPCs. Iron, manganese, and
vanadium are also Pee Dee Aquifer COPCs potentially attributable to coal ash
because they were detected above 2L in multiple groundwater samples collected
from multiple wells.
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COPCs associated with the Pee Dee Aquifer that are being considered to evaluate
potential risks to human health are presented on Figure 12-5.
Soils and Sediments
Soils and sediment analytical results were evaluated relative to USEPA soil
Regional Screening Levels (RSLs) protective of human health under residential -
use and industrial -use scenarios (USEPA 2015). The following constituents are
not soil or sediment COPCs potentially attributable to coal ash because they are
not coal ash COPCs (Table 12-2):
y
Antimony
h
Beryllium
y
Cadmium
h
Calcium
161,
Chloride
h
Total Chromium
h
Copper
0
Lead
y
Magnesium
47 Mercury
y Molybdenum
41, Nickel
,611 Nitrate (as N)
47 Potassium
y Selenium
167 Sodium
y Sulfate
h Thallium
y Zinc
Consequently, these constituents are not considered soil or sediment COPCs
attributable to coal ash and therefore, will not be evaluated further.
Soils
Soil samples were evaluated separately from sediments in order to appropriately
evaluate risk exposure scenarios for potential human receptors. Surface soil
samples were collected from the top two feet of soil borings conducted at the
Weatherspoon facility. Analytical results are summarized in Table 12-6 and soil
boring locations are identified on Figure 2-1. Soil COPCs under considertion to
evaluate potential risks to human health are presented on Figure 12-6.
Constituent concentrations in surficial soil samples are compared with EPA
residential -use and industrial -use RSLs. The following inorganic constituents
were detected in surficial soil samples at concentrations above their respective
soil RSLs:
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Soil COPC
Potentials Attributable To Coal Ash
h
Aluminum
y
Arsenic
,67
Cobalt
y
Iron
Not A Coal Ash COPCM
,67 Thallium
Note (1): See Table 12-2
Aluminum was detected in all nine samples, with two soil samples having
detected concentrations above the soil residential -use RSL (7,700 mg/kg).
Aluminum concentrations in all surficial soil samples were detected at
concentrations below the soil industrial -use RSL (110,000 mg/kg). Aluminum
concentrations ranged from 343 mg/kg to 14,400 mg/kg.
Arsenic was detected in four of the nine soil samples, with detected
concentrations ranging from 2 mg/kg to 15.3 mg/kg. Arsenic concentrations
exceeded the soil residential -use RSL (0.67 mg/kg) at four locations and the
industrial -use RSL (3 mg/kg) at two locations. In addition, the analytical method
limit for arsenic analysis of five soil samples was higher than the residential -use
RSL but below the residential -use RSL.
Cobalt was detected in one sample at a concentration estimated (J-flagged) to be
equal to the residential -use RSL (2.3 mg/kg) but below the industrial -use RSL (35
mg/kg). However, three of the samples reported cobalt concentrations below
analytical detection limits that were greater than the residential -use RSL but
below the industrial -use RSL. Because cobalt was not detected at a quantifiable
concentration, it was eliminated as a soil COPC potentially attributable to coal
ash.
Iron was detected in all nine soil samples with concentrations ranging from 178
mg/kg to 11,400 mg/kg. Four of these samples had iron concentrations greater
than the residential -use RSL (5,500 mg/kg) but less the industrial -use RSL (82,000
mg/kg).
Sediment
Sediment samples consist of samples collected at co -located surface water and
seep sample locations identified on Figure 2-1. Analytical results are
summarized in Table 12-7 and sediment sampling locations are identified on
Figure 2-1. COPCs in sediment that are being considered to evaluate potential
risks to human health are presented on Figure 12-7.
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Constituent concentrations in sediment samples are compared with EPA
residential -use and industrial -use RSLs. The following inorganic constituents
were detected in sediment samples at concentrations above their respective RSLs:
Sediment COPC
Potentially Attributable To Coal Ash
h Aluminum
41,
Arsenic
h
Cobalt
y
Iron
,61,
Manganese
47
Vanadium
Not A Coal Ash COPC«>
,611
Antimony
��
Molybdenum
,611
Selenium
��
Thallium
Note (1): See Table 12-2
Aluminum was detected in all 14 sediment samples at concentrations ranging
between 1,230 mg/kg to 16,800 mg/kg. Aluminum concentrations in five of the
sediment samples were above the residential -use RSL (7,700 mg/kg) but all
aluminum concentrations were below the industrial -use RSL (110,000 mg/kg).
Arsenic was detected in eight sediment samples ranging in concentrations
between 8.7 mg/kg to 1,090 mg/kg. Arsenic concentrations in all eight sediment
samples were above the residential -use (0.68 mg/kg) and industrial -use (3 mg/kg)
RSLs. In addition, arsenic concentrations in six sediment samples were not
detected above their analytical method detection limits which also were above
the residential -use (0.68 mg/kg) and industrial -use (3 mg/kg) RSLs.
Cobalt was estimated to be present in three of the 14 sediment samples at
concentrations ranging between 6.8J mg/kg to 16.4J mg/kg. These concentrations
are above the residential -use RSL (2.3 mg/L) but below the industrial -use RSL (35
mg/kg). The analytical method detection limits of ten sediment samples were
above the residential -use RSL and the analytical method detection limits of one
sediment sample was above the industrial -use RSL.
Iron was detected in all 14 sediment samples ranging in concentrations between
474 mg/kg to 82,000 mg/kg. Iron concentrations in seven sediment samples were
above the residential -use RSL (5,500 mg/kg) and the iron concentration in two
sediment samples were above the industrial -use RSL (82,000 mg/kg).
Manganese was detected in 13 out of 14 sediment samples ranging in
concentrations between 9.3 mg/kg to 811 mg/kg. Manganese concentrations in
two sediment samples were above the residential -use RSL (180 mg/kg) but no
manganese concentrations were above the industrial -use RSL (2,600 mg/kg).
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Vanadium was detected in 10 out of 14 sediment samples ranging in
concentrations between 4.5J mg/kg to 73.5 mg/kg. Vanadium concentrations in
two sediment samples were above the residential -use RSL (39 mg/kg) but no
manganese concentrations were above the industrial -use RSL (580 mg/kg).
Surface Water and Seeps
Surface water and seep analytical results were evaluated against the North
Carolina surface water standards (Subchapter 213) and USEPA National
Recommended Water Quality Criteria (WQC) protective of human consumption
of water and organisms (NCDENR 4/22/15; USEPA 2009).
Surface water samples were evaluated separately from seeps in order to
appropriately evaluate receptor source and risk exposure scenarios for potential
human receptors. Surface water sample locations are shown on Figure 2-1. The
locations of surface water and seep COPCs potentially attributable to coal ash are
presented on Figure 12-8.
Surface Water
Surface water analytical results are summarized in Table 12-8 where they are
compared to their respective 2B Standards and the EPA National Recommended
WQC, as applicable. Only aluminum was detected in surface water samples at
concentrations above a surface water RSL. Four other coal ash COPCs (boron,
iron, manganese, vanadium) have no 2B standard or EPA National
Recommended WQC. Consequently, boron, iron, manganese, and vanadium are
retained as surface water COPCs that are potentially attributable to coal ash.
These constituents may be eliminated as surface water COPCs that are
potentially attributable to coal ash if site specific surface water criteria protective
of human health are developed for these compounds.
Aluminum is a coal ash COPC and it was detected in both surface water samples
(dissolved and total phases) at concentrations greater than the National
Recommended Water Quality Criteria for the protection of human health (6.5
µg/L). Consequently, aluminum is a surface water COPC potentially attributable
to coal ash. The 2B standards do not have a criterion for aluminum in surface
water that is protective of human health.
Seeps
Seep samples were evaluated separately from surface water in order to
appropriately evaluate receptor source and risk exposure scenarios for potential
human receptors. For this analysis, seeps in both the source area and the
receiving area are discussed. Seep data are compared to surface water criteria
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identified above (Table 12-9). Seep sample locations are shown on Figure 2-1.
COPCs in seeps that are being considered to evaluate potential risks to human
health are presented on Figure 12-8.
Constituent concentrations in seep samples are compared to their respective 2B
Standards and the EPA National Recommended WQC, as applicable. The
following inorganic constituents were detected in seep samples at concentrations
above their respective surface water criterion:
Seep COPC
Potentially Attributable To Coal Ash
�i Aluminum
y Arsenic
161, Barium
0 Cobalt
Not A Coal Ash COPCM
h Thallium
Note (1): See Table 12-2
Aluminum was detected in all twelve seep samples at concentrations ranging
between 9 µg/L to 66,000 µg/L. Aluminum concentrations in every seep sample
were above the EPA National Recommended WQC protective of human
consumption of water and organisms (6.5 µg/L). The 2B standards do not have a
criterion for aluminum in surface water that is protective of human health.
Arsenic was detected in 10 of the 12 seep samples at concentrations ranging
between 1.12 µg/L to 1,530 µg/L. Arsenic concentrations in five of the seep
samples were above the 2B Standard (10 µg/L). EPA National Recommended
WQC protective of human health have not established a criterion for arsenic in
surface (seep) water that is protective of human health.
Barium was detected in all twelve seep samples at concentrations ranging
between 30 µg/L to 1,950 µg/L. The barium concentration in only one seep
sample was above the EPA National Recommended WQC protective of human
consumption of water and organisms (1,000 µg/L). The 2B Standards do not
have a criterion for barium in surface water that is protective of human health.
Cobalt was detected in two seep samples at concentrations of 2.04 µg/L and 32.1
µg/L. The cobalt concentration in only one seep sample was above the EPA
National Recommended WQC protective of human consumption of water and
organisms (3 µg/L). The 2B Standards do not have a criterion for cobalt in
surface (seep) water that is protective of human health.
COPCs potentially attributable to coal ash that have been retained for each media
are summarized in Table 12-10. Figures 12-2 through 12-8 show sample
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locations where these COPCs have been identified. Additional refinement of
COPCs for site -specific considerations will be included as part of a corrective
action plan.
12.1.4 Site Specific Risk Based Remediation Standards
Based on the results of the preliminary comparison to risk -based screening
levels, media -specific remediation standards may be warranted in accordance
with the Eligibility Requirements and Procedures for Risk -Based Remediation of
Industrial Sites Pursuant to NC General Statutes 130A-310.65 to 310.77 as part of
a corrective action plan. These standards will be calculated as part of corrective
action planning based on the COPCs defined by the screening level risk
assessment.
12.2 Ecological Screening
12.2.1 Introduction
This screening level ecological risk assessment (SLERA) has been prepared in
accordance with the guidelines for conducting a SLERA for sites under the
authority of NCDENR Division of Waste Management. The objective of the
SLERA is to evaluate the likelihood that adverse ecological effects may result
from exposure to environmental stressors associated with conditions at the site.
This scope of work is equivalent to Step 1- preliminary problem formulation and
ecological effects evaluation (USEPA, 1998) and Step 2 — estimation of the level of
a constituent exposure to a plant or animal at the site and comparison of the
maximum constituent concentrations to Ecological Screening Values (ESVs).
12.2.2 Ecological Setting
The site ecological setting is described in the following paragraphs.
12.2.2.1 Facility Site Summary
The Weatherspoon Plant is a former coal-fired electricity -generating
facility located at 491 Power Plant Road, Lumberton, Robeson County,
North Carolina. The location of the Plant is shown on Figure 2-1. The
approximate coordinates of the site are latitude N34.592931 and longitude
W-78.978587. The Plant utilizes an approximate 225-acre cooling pond
located adjacent to the Lumber River. The ash basin is located north of the
cooling pond.
12.2.2.2 Regional Ecological Setting
The Weatherspoon Plant facility is located in the Southeastern Plains
ecoregion of North Carolina, further divided into the Atlantic Southern
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Loam Plains ecoregion, with the Lumber River lying within the
Southeastern Floodplains and Low Terraces ecoregion (Griffith et al.,
2002).
12.2.2.3 Description of Ecoregion and Expected Habitats
This region is a major agricultural area and generally has well -drained
soils. Carolina bays are not uncommon in this region, within which are
often found rare and/or endangered flora and fauna. The bottomland
hardwood forests are often oak, and may contain some swamp areas of
cypress and tupelo (Griffith et al., 2002). This region also typically includes
large, slow rivers with swamps, ponds, and oxbow lakes often found in
the immediate vicinity. Oak -dominated bottomland hardwood forests,
and some river swamp forests of bald cypress and water tupelo are quite
common.
12.2.2.4 Watershed in which the Site is Located
The Lumber River watershed (hydrologic unit 03040203030010)
encompasses approximately 3,343 square miles in all or part of 10
counties. There are four smaller watersheds that feed into the Lumber
River watershed: the Lumber River, the Waccamaw River, the headwaters
of the Little Pee Dee, and the coastal watershed of the
Shalotte/Lockwoods/Folly Rivers. There is one named tributary to the
Lumber River, Mill Branch, and then, after crossing into South Carolina,
the Lumber River drains into the Little Pee Dee River. The Lumber River
is state designated as a Natural and Scenic Water, and 81 miles have also
been designated as National Wild and Scenic Water
(httl2://12ortal.ncdenr.org/web/eep/rbri2s/lumber, accessed on July 29,
2015).
12.2.2.5 Average Rainfall
Total annual precipitation in this region is approximately 48 inches.
12.2.2.6 Average Temperature
The annual average high temperature is 73°F and the annual average low
temperature is 51°F.
12.2.2.7 Length of Growing Season
The growing season in Lumberton, NC is approximately 173 days (with 95
percent probability)
(www.erh.noaa.gov/ilm/climate/freeze/Lumberton.html, accessed on July
29, 2015).
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12.2.2.8 Threatened and Endangered Species that use
Habitats in the Ecoregion
A list of threatened and endangered species for Robeson County is
provided in Table 12-11.
12.2.2.9 Site -Specific Ecological Setting
A Checklist for Ecological Assessments/Sampling has been completed for
this site (Appendix I).
12.2.2.10 On -site and Off -site Land Use
The Weatherspoon Plant facility was commissioned in 1949 and the coal-
fired generating units were retired in 2011 and demolished in 2013. The
facility included three coal-fired steam units. Four combustion turbine
units were added in 1970 and 1971. The approximate size of the property
is 1,015 acres, and consists primarily of several modular office buildings
and various other metal buildings, including the structures that house the
combustion turbine units. The original coal-fired plant structures have
been demolished and are no longer present onsite. The property is
dissected by several power line rights -of -way, with substations onsite.
There is an approximately 55 acre area with a decommissioned ash basin
and an approximately 225 acre cooling pond. The Lumber River divides
the parcel in a northwest/southeast direction, and flows south along the
west side of the former plant site and along the west side of the cooling
pond. The area bordered by the Lumber River and the western parcel line
primarily consists of forested/shrub wetlands.
Existing ecological studies publically available for the site were reviewed.
In 2014, a wetland delineation of the site was conducted by ESI (Appendix
I). The delineation identified six wetland areas and two jurisdictional
tributary segments based on current wetland and stream criteria
established by the United States Army Corps of Engineers (USACE) and
North Carolina Division of Water Resources (DWR).
12.2.2.11 Habitats within the Site Boundary
The Checklist for Ecological Assessments/Sampling contains a detailed
description of habitats (Appendix I).
12.2.2.12 Description of Man-made Units that May Act as
Habitat
The 225 acre cooling pond may act as a man-made aquatic habitat.
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12.2.2.13 Site Layout and Topography
A general site layout can be found in Figure 2-1, and the topography is
consistent with the typical parameters of the Southeastern Plains
Ecoregion (e.g., relatively flat with areas of moderate to steep terraces
leading down to the Lumber River).
12.2.2.14 Surface Water Runoff Pathways
The site has been graded to manage or divert runoff (e.g., stormwater)
using features such as swales, ditches, and culverts into nearby water
bodies (e.g., Lumber River, Jacob Creek,).
12.2.2.15 Soil Types
The Southeastern Coastal Plain Ecoregion is generally composed of
alluvium and deposits of sand, silt, and gravel (Griffith et al., 2002). For a
detailed description of site lithology, see Section 6.1.1 of this report.
12.2.2.16 Species Normally Expected to Use Site under
Relatively Unaffected Conditions
Wildlife expected to be in the area of the site would potentially include
those listed in Table 12-11, and also other game and non -game wildlife
endemic to the Atlantic Southern Loam Plains and Southeastern
Floodplains and Low Terraces ecoregions (Appendix I).
12.2.2.17 Species of Special Concern
The Lumber River supports two unique fish species designated of "special
concern" by the state of North Carolina. These species are the pinewoods
darter (Etheostoma mariae) and the sandhills chub (Semotilus lumbee).
Threatened and Endangered Species for the site are listed in Table 12-11.
12.2.2.18 Nearby Critical and/or Sensitive Habitats
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). There are also wetland areas on -site that are listed in
the 2014 wetland delineation and the USFWS National Wetland Inventory
(Appendix I).
12.2.3 Fate and Transport Mechanisms
Fate and transport mechanisms at this site would include: erosion, seeps, storm
water runoff, and flow of surface water bodies.
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Conceptual Exposure Model
Consistent with standard risk assessment practice for developing conceptual
models, separate Conceptual Exposure Models (CEMs) were developed for the
human health and ecological risk evaluations. Figure 12-9 has been prepared
illustrating potential exposure pathways from the source area to possible
ecological receptors. The information in the CEM has been used in conjunction
with the analytical data collected as part of the CSA.
The ecological CEM is based on characterization of primary and secondary
sources and corresponding release mechanism sources, the COPC for each
affected environmental medium, and the migration and transport potential of
this constituent to potentially exposed populations (receptors). Figure 12-9
identifies the source and release mechanisms for the site along with exposure
medium and route. Potential receptors at the site are identified, with
consideration of current and future potential land use scenarios. The individual
components of the ecological CEM are further described in the following
sections.
Primary Constituent Source
The primary known source of site related constituents in groundwater at the site
is from historical activities conducted in the ash basin. The affected soil, surface
water, seeps, and sediment in the vicinity of the ash pond serves as a secondary
source.
Release and Transport Mechanisms
The potential constituent release and transport pathways at the site are as
follows:
'610 Infiltration to groundwater
1611 Seeps to soil and surface water bodies
Secondary Release Mechanisms
The secondary potential constituent release and transport pathways at the site
are as follows:
01 Seeps from the groundwater beneath the ash pond
,610 Storm water runoff
,610 Infiltration/percolation
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Exposure Medium, Pathways, and Exposure Routes
The exposure medium includes potentially impacted soil, surface water and
sediments at the site. Groundwater does not present a complete exposure
pathway to ecological receptors.
The exposure routes associated with the potentially completed exposure
pathways evaluated for the site include incidental ingestion and ingestion of
prey or plants.
Completed exposure pathways are the means by which potential receptors come
into contact with site -related COPCs. The completed exposure pathways under
current and future land use scenarios (Figure 12-9) include the following:
y Terrestrial mammals
16
7 Aquatic mammals
y Birds (including waterfowl)
'67 Benthic invertebrates
,67 Herptiles
410 Fish
y Insects
0 Aquatic vegetation
41 Algae/moss
y Woody plants
4' Herbaceous plants
12.2.4 Preliminary Exposure Estimate and Risk Calculation
Exposure estimates used in the screening level risk assessment are represented
by maximum concentrations of analytes detected in surface water, sediment, soil,
and groundwater samples. Hazard quotients (HQ) are defined as the ratio of
exposure estimates to ecological screening values (i.e., HQ = maximum analyte
concentration: ecological screening value). If exposure estimates exceeded an
ecological screening value (i.e., HQ>1), analytes were retained as a COPC for
further consideration at the site. COPCs are identified in the next section.
12.2.5 Comparison to Ecological Screening Levels
A comparison of constituent concentrations in various media to the following
risk -based screening levels has been made and is presented in Tables 12-12
through 12-14. These include species -specific screening levels based on
constituent concentrations that are Applicable or Relevant and Appropriate
Requirements (ARARs), designed for protection of ecological receptors from
specific exposure conditions that elicit toxic responses. These screening levels
are derived from risk -based calculations that set concentration limits using
USEPA and state standards for the following media:
,61P Groundwater: Not applicable, as groundwater has no direct pathway to
ecological receptors
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411 Surface water: 2B Criteria for Aquatic Life (NCDENR 2015b) and/or
USEPA National Recommended Water Quality Criteria for Aquatic Life
(USEPA 2009) and/or USEPA Region 4 Surface Water Quality Criteria —
Chronic (USEPA 2001)
h Seeps: 2B Criteria for Aquatic Life (NCDENR 2015b)and/or USEPA
National Recommended Water Quality Criteria for Aquatic Life (USEPA
2009) and/or USEPA Region 4 Surface Water Quality Criteria — Chronic
(USEPA 2001)
h Soil: USEPA Region 4 Recommended Ecological Screening Values for Soil
(USEPA 2015b)
h Sediment: USEPA Region 4 Recommended Ecological Screening Values
for Soil (USEPA 2015b) and/or USEPA Region 4 Effects Value — Sediment
(USEPA 2001)
Surface water, seep, soil, and sediment background sample data from prior
investigations are considered, as well as regional and national background data,
as available.
Groundwater
Direct exposure pathways of groundwater to ecological receptors are incomplete,
and therefore do not pose any appreciable risk. Ash pore water samples, as well
as groundwater samples from the perimeter of the site, were collected and
analyzed (Table 12-2) to aid in determination of groundwater COPCs. As ash
pore water emerges as a seep, however, it is subject to USEPA or 213 Aquatic Life
Criteria instead of USEPA or 2L Groundwater Standards. This can potentially
cause some constituents that were not considered COPCs in ash pore water (i.e.,
groundwater) to be deemed COPCs in surface waters and/or seeps.
Surface Water
Surface water samples were evaluated in order to appropriately evaluate risk
exposure scenarios for potential ecological receptors. Surface water samples
consist of samples collected from the water column (below the water/air interface
when feasible) at selected sample locations at the Weatherspoon facility. Figure
2-1 displays the locations of the surface water sample locations.
As detailed Tables 12-12 and 12-15, the following inorganic constituents are
excluded from the list of ecological COPCs for surface water because either (a)
their maximum detected concentrations were less than their respective
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comparison criteria, or (b) the constituents were not detected in the sample and
their detection limit values were less than all comparison criteria (2B Criteria for
Aquatic Life and/or USEPA National Recommended Water Quality Criteria for
Aquatic Life and/or USEPA Region 4 Surface Water Quality Criteria - Chronic):
y
Antimony
h
Arsenic
,611
Boron
01
Chloride
y
Chromium
y Copper
h Mercury
y Nickel
,67 Selenium
Aluminum will be retained as a COPC for further evaluation because the
maximum detected concentrations were greater than its respective comparison
criteria (2B Criteria for Aquatic Life and/or USEPA National Recommended
Water Quality Criteria for Aquatic Life and/or USEPA Region 4 Surface Water
Quality Criteria - Chronic). Total aluminum was detected in both surface water
samples at concentrations greater than USEPA National Recommended Water
Quality Criteria for Aquatic Life - Chronic (87 µg/L) and USEPA Region 4
Surface Water Quality Criteria - Chronic (87 µg/L).
COPCs not retained because their detection limits values were greater than their
respective comparison criteria were added to the list of uncertainties requiring
further investigation to follow:
h Beryllium
y Cadmium
161, Lead
1i Sulfide
h Zinc
Dissolved beryllium was not detected in any surface water samples, but
detection limit values for both sample analyses were greater than USEPA Region
4 Surface Water Quality Criteria - Chronic (0.53 µg/L).
Cadmium was not detected in any surface water samples, but detection limit
values for both sample analyses were greater than USEPA Region 4 Surface
Water Quality Criteria - Chronic (0.66 µg/L), USEPA National Recommended
Water Quality Criteria for Aquatic Life - Chronic (0.25 µg/L), and 2B Criteria for
Aquatic Life - Acute and Chronic (0.82 µg/L and 0.15 µg/L, respectively).
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Dissolved lead was not detected in either surface water sample, but detection
limit values for both sample analyses were greater than 2B Criteria for Aquatic
Life — Chronic (0.54 µg/L).
Dissolved sulfide was not detected in any surface water samples, but detection
limit values for both sample analyses were greater than USEPA Region 4 Surface
Water Quality Criteria — Chronic (0.002 mg/L).
Dissolved zinc was detected in one surface water sample at a concentration
greater than all comparison criteria. This is likely an anomalous result, however,
as total zinc in the same sample location was non -detect (MDL = 0.005 mg/L).
This sample location will be resampled to confirm or refute zinc as a COPC.
The following constituents will be added to the list of COPC uncertainties since
they are not subject to published 2B Criteria for Aquatic Life or USEPA National
Recommended Water Quality Criteria for Aquatic Life:
y
Barium
y
Cobalt
,611
Manganese
,01
Methane
,61
Molybdenum
y Nitrite/Nitrate
y Strontium
,611 Sulfate
h Thallium
161, Vanadium
Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs
as they have no applicable criteria, are ubiquitous in nature, and are considered
to be macrominerals with negligible toxicity to ecological receptors. These
constituents were quantified as a component of the water characterization
process.
Seeps
Seep samples were evaluated separately from surface water in order to
appropriately evaluate potential source and receptor risk exposure scenarios.
For this analysis, seeps in both the source area and the receiving area are
discussed. Seep data are compared to surface water criteria identified above.
Seep sample locations are shown on Figure 2-1.
As detailed on Tables 12-12 and 12-15, the following inorganic constituents are
excluded from the list of ecological COPCs for seeps because either (a) their
maximum detected concentrations were less than their respective comparison
criteria, or (b) the constituents were not detected in the sample and their
detection limit values are less than all comparison criteria (15A NCAC 2B
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Criteria for Aquatic Life and/or USEPA National Recommended Water Quality
Criteria for Aquatic Life and/or USEPA Region 4 Surface Water Quality Criteria -
Chronic):
h Antimony
y Arsenic
h Chloride
y Chromium
4-11 Copper
,611 Mercury
47 Nickel
y Selenium
Aluminum, boron, iron, and zinc will be retained as COPCs for further
evaluation because the maximum detected concentrations were greater than its
respective comparison criteria (2B Criteria for Aquatic Life and/or USEPA
National Recommended Water Quality Criteria for Aquatic Life and/or USEPA
Region 4 Surface Water Quality Criteria - Chronic).
Total aluminum was detected in six seep samples at concentrations greater than
the USEPA National Recommended Water Quality Criteria for Aquatic Life -
Chronic (87 µg/L) and USEPA Region 4 Surface Water Quality Criteria - Chronic
(87 µg/L). Total aluminum was detected in one seep sample (S-10) at a
concentration greater than USEPA National Recommended Water Quality
Criteria for Aquatic Life - Acute (750 µg/L). The S-10 location is confined within
the engineered structure and within the wastewater treatment system.
Dissolved boron was detected in seven seep samples at concentrations greater
than the USEPA Region 4 Surface Water Quality Criteria - Chronic (750 µg/L).
Dissolved iron was detected in three seep samples at concentrations greater than
USEPA National Recommended Water Quality Criteria for Aquatic Life -
Chronic (1000 µg/L) and USEPA Region 4 Surface Water Quality Criteria -
Chronic (1000 µg/L).
Dissolved zinc was detected in one seep sample (S-02) at a concentration greater
than the 15A NCAC 2B Criteria for Aquatic Life - Acute and Chronic (0.036
mg/L) and one seep sample (S-03A) at a concentration greater than USEPA
Region 4 Surface Water Quality Criteria - Chronic (0.059 mg/L).
The following constituents will be added to the list of uncertain COPCs for
further evaluation because detection limit values were greater than comparison
criteria:
0 Beryllium
h Cadmium
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0 Lead
167 Sulfide
y Zinc
The detection limit values for all beryllium sample analyses were greater than
USEPA Region 4 Surface Water Quality Criteria — Chronic (0.53 µg/L).
The detection limit values for dissolved cadmium sample analyses were greater
than the USEPA National Recommended Water Quality Criteria for Aquatic Life
— Chronic (0.25 µg/L), USEPA Region 4 Surface Water Quality Criteria — Chronic
(0.66 µg/L), and the 15A NCAC 2B Criteria for Aquatic Life — Acute and Chronic
(0.82 µg/L and 0.15 µg/L, respectively).
The detection limit values for dissolved lead sample analyses were greater than
the 15A NCAC 2B Criteria for Aquatic Life — Chronic (0.54 µg/L).
Dissolved sulfide was not detected in any seep samples, but detection limit
values for all sample analyses were greater than the USEPA Region 4 Surface
Water Quality Criteria — Chronic (0.002 mg/L).
The following will be added to the list of COPCs for further investigation since
they are not subject to published 2B Criteria for Aquatic Life or USEPA National
Recommended Water Quality Criteria for Aquatic Life:
y
Barium
161,
Cobalt
01
Manganese
h
Methane
y
Molybdenum
y Nitrite/Nitrate
,611 Strontium
h Sulfate
y Thallium
y Vanadium
Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs
as they have no applicable criteria, are ubiquitous in nature, and are considered
to be macrominerals with negligible toxicity to ecological receptors. These
constituents were quantified as a component of the water characterization
process (e.g., hardness).
Soils
Soil samples were evaluated separately from sediments in order to appropriately
evaluate risk exposure scenarios for potential ecological receptors. Surface soil
samples were collected from the top two feet of soil borings conducted at the
Weatherspoon facility (Figure 2-1).
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The following inorganic constituents (Tables 12-13 and 12-15) are excluded from
the list of ecological COPCs for surface soils because their maximum detected
concentrations were less than their respective comparison criteria for soils, or (b)
the constituents were not detected in the sample and their detection limit values
were less than all comparison criteria (USEPA Region 4 Recommended
Ecological Screening Values for Soil):
167
Antimony
41,
Lead
0
Barium
y
Manganese
h
Beryllium
y
Mercury
47
Cadmium
h
Molybdenum
h
Cobalt
h
Nickel
y
Copper
167
Zinc
The following constituents will be retained as COPCs for further evaluation
because their maximum detected concentrations in soil were greater than their
respective comparison criteria for soils (USEPA Region 4 Recommended
Ecological Screening Values for Soil):
y Aluminum
h Arsenic
47 Boron
y Chromium
0 Iron
y Vanadium
Aluminum was detected in all soil samples at concentrations greater USEPA
Region 4 Recommended Ecological Screening Values for Soil (50 mg/kg).
Arsenic was detected in one sample (SB-04) at a concentration greater than
USEPA Region 4 Recommended Ecological Screening Values for Soil (10 mg/kg).
Boron was detected in three of the nine soil samples at concentrations greater
than USEPA Region 4 Recommended Ecological Screening Values for Soil (0.5
mg/kg). The remaining seven samples were non -detect, but the detection limits
for these analyses were greater than USEPA Region 4 Recommended Ecological
Screening Values for Soil (0.5 mg/kg).
Chromium was detected in all soil samples at concentrations greater USEPA
Region 4 Recommended Ecological Screening Values for Soil (0.4 mg/kg).
Iron was detected in eight of the nine soil samples at concentrations greater than
USEPA Region 4 Recommended Ecological Screening Values for Soil (200
mg/kg). Sample BW-02 DUP, with a detected concentration of 178 mg/kg, did
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not exceed; however, sample BW-02, with a detected concentration of 407 mg/kg,
did exceed. One of these results may be anomalous, or there may have been an
issue with sample collection. This sample location will be resampled to confirm
or refute iron as a COPC.
Vanadium was detected in seven of the nine soil samples at concentrations
greater than USEPA Region 4 Recommended Ecological Screening Values for
Soil (2 mg/kg).
Selenium and thallium will be added to the list of COPC uncertainties due to lack
of quantifiable analytical results. Selenium was detected below the quantitation
level (i.e., result was greater than the MDL, but less than reporting limit) in one
of the nine soil samples (3.7J mg/kg). This concentration exceeded USEPA
Region 4 Recommended Ecological Screening Values for Soil (0.81 mg/kg). The
remaining sample analyses had detection limits greater than this criterion.
Thallium was not detected in any soil samples. It will be added to the list of
COPC uncertainties because all sample analyses had detection limits greater than
USEPA Region 4 Recommended Ecological Screening Values for Soil (1 mg/kg).
The following constituents will be added to the list of COPC uncertainties since
they are not subject to published USEPA Region 4 Recommended Ecological
Screening Values for Soil:
0 Chloride
h Nitrate
0, Strontium
0, Sulfate
Calcium, magnesium, potassium, and sodium are omitted from the list of COPCs
as they have no applicable criteria, are ubiquitous in nature, and are considered
to be macrominerals with negligible toxicity to ecological receptors. These
constituents were quantified as a component of the soil characterization process.
Sediment
Sediment samples consist of samples collected at co -located surface water and
seep sample locations (Figure 12-3). As summarized on Tables 12-14 and 12-15,
the following inorganic constituents are excluded from the list of ecological
COPCs for sediment because either (a) their maximum detected concentrations
were less than their respective comparison criteria (USEPA Region 4
Recommended Ecological Screening Values for Soil and/or USEPA Region 4
Effects Values for Sediment), or (b) the constituents were not detected in the
sample and detection limit values were less than both comparison criteria:
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0 Chromium
y Copper
h Nickel
The following constituents will be retained as COPCs for further evaluation
because their maximum detected concentrations in soil were greater than their
respective comparison criteria for soils (USEPA Region 4 Recommended
Ecological Screening Values for Soil and/or USEPA Region 4 Effects Values for
Sediment):
167 Aluminum
0 Arsenic
h Barium
y Beryllium
h Boron
,611 Iron
h Lead
y Manganese
h Mercury
,0, Molybdenum
,611 Selenium
h Vanadium
y Zinc
Aluminum was detected in all sediment samples at concentrations greater than
USEPA Region 4 Recommended Ecological Screening Values for Soil (50 mg/kg).
Arsenic was detected in seven of the 14 sediment samples, six of which exceed
USEPA Region 4 Recommended Ecological Screening Values for Soil (10 mg/kg)
and USEPA Region 4 Effects Values for Sediment (7.24 mg/kg), and one that
exceeded USEPA Region 4 Effects Values for Sediment (7.24 mg/kg). Arsenic
was not detected in any other samples, but due to dilution requirements during
analysis, the detection limits for five other sample analyses were greater one or
both screening criteria. Sample S-01 was non -detect, with a detection limit value
less than both criteria.
Barium was detected in three of the 14 sediment samples at concentrations
greater than USEPA Region 4 Recommended Ecological Screening Values for
Soil (165 mg/kg). All other samples did not exceed this criterion.
Beryllium was detected in two of the 14 sediment samples at concentrations that
exceed USEPA Region 4 Recommended Ecological Screening Values for Soil (1.1
mg/kg). Beryllium was detected in four other samples (S-02, S-03B, S-09A, and S-
10) at levels at or below this criterion, and the remainder of the sample analyses
had detection limits greater than this criterion.
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Boron was detected in six of the 14 sediment samples at concentrations that
exceed USEPA Region 4 Recommended Ecological Screening Values for Soil (0.5
mg/kg). Boron was not detected in any other samples, but due to dilution
requirements during analysis, the detection limits for the remaining sample
analyses were greater than this criterion.
Iron was detected in all sediment samples at concentrations greater than USEPA
Region 4 Recommended Ecological Screening Values for Soil (200 mg/kg).
Lead was detected in one sediment sample at a concentration greater than
USEPA Region 4 Effects Values for Sediment (30.2 mg/kg). Two sample locations
(S-05 and SW-01) were non -detect for lead, but due to dilution requirements
during analysis, sample S-05 had a detection limit greater than USEPA Region 4
Effects Values for Sediment (30.2 mg/kg) and sample SW-01 had a detection limit
greater than USEPA Region 4 Recommended Ecological Screening Values for
Soil (50 mg/kg).
Manganese was detected in five samples that exceed USEPA Region 4
Recommended Ecological Screening Values for Soil (100 mg/kg).
Mercury was detected in two samples that exceed USEPA Region 4
Recommended Ecological Screening Values for Soil (0.1 mg/kg) and one sample
that exceeds both USEPA Region 4 Recommended Ecological Screening Values
for soil (0.1 mg/kg) and USEPA Region 4 Effects Values for Sediment (0.13
mg/kg).
Molybdenum was detected in eight of the fourteen sediment samples at
concentrations that exceed USEPA Region 4 Recommended Ecological Screening
Values for Soil (2 mg/kg). Molybdenum was not detected in any other samples,
but due to dilution requirements during analysis, the detection limits for the
remaining sample analyses were greater than this criterion.
Selenium was detected in two of the fourteen sediment samples, both of which
exceeded USEPA Region 4 Recommended Ecological Screening Values for Soil
(0.81 mg/kg). All other sample analyses were non -detect for selenium, but due to
dilution requirements during analysis, these detection limits were greater than
this criterion.
Vanadium was detected in ten of the fourteen sediment samples at
concentrations exceeding USEPA Region 4 Recommended Ecological Screening
Values for Soil (2 mg/kg). The remaining samples were non -detect for
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vanadium, but due to dilution requirements during analysis, these detection
limits were greater than this criterion.
Zinc was detected in two of the fourteen sediment samples (S-15 and S-20) at
concentrations exceeding the USEPA Region 4 Recommended Ecological
Screening Values for Soil (50 mg/kg).
Antimony, cadmium, cobalt, and thallium will be added to the list of COPC
uncertainties due to lack of quantifiable detections. Antimony was not detected
in any samples, but detection limits for all sample analyses were greater than
USEPA Region 4 Recommended Ecological Screening Values for Soil (3.5 mg/kg)
and USEPA Region 4 Effects Values for Sediment (2 mg/kg).
Cadmium was not detected in any samples, but detection limits for all sample
analyses were greater than one or both screening criteria.
Cobalt did not exceed USEPA Region 4 Recommended Ecological Screening
Values for Soil (20 mg/kg). Three sample detection limits were greater than this
criterion due to dilution requirements during analysis.
Thallium was not detected in any samples, but detection limits for all sample
analyses were greater than USEPA Region 4 Recommended Ecological Screening
Values for Soil (1 mg/kg).
The following constituents will be retained as sediment uncertain COPCs for
further evaluation because they do not have a published USEPA Region 4
Recommended Ecological Screening Values for Soil:
y Chloride
h Nitrate
41' Strontium
h Sulfate
Ecological COPCs retained for each medium are summarized in Table 12-15.
Figures 12-10,12-11, and 12-12 show sample locations with COPCs.
12.3 Uncertainty and Data Gaps
This screening level risk assessment was conducted as part of the groundwater
assessment under the primary assumption that sampling locations, sample media, and
analytes, as defined in the Work Plan, were sufficient for screening human health and
ecological risks at the Weatherspoon site. All proposed samples were collected, and
analyses completed as planned. However, due to analytical constraints (e.g., method
detection limits and dilution effects during sample preparation for analysis) or
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anomalous results, there are numerous constituents for which (a) detection limits were
greater than one or more screening criteria, (b) reported results were greater than
detection limits, but less than reporting limits (i.e., estimated), or (c) reported results
seemed anomalous (e.g., dissolved metal concentration greater than total metal
concentration). This presents the possibility that the actual concentration of a given
constituent might exceed one or more screening criteria while not being detected by
instrumentation, result was incorrectly estimated, or some unknown error occurred
which interfered with accurate reporting. For this reason, these particular instances
have been noted and affected constituents flagged as COIs that require further
consideration. The COIs flagged for these reasons include aluminum, arsenic, barium,
beryllium, boron, cadmium, chloride, chromium, cobalt, iron, lead, manganese,
molybdenum, nitrite/nitrate, selenium, strontium, sulfate, sulfide, thallium, vanadium,
and zinc.
12.4 Scientific/Management Decision Point
Based on the results of the human health and ecological screen, media -specific
remediation standards will be calculated in accordance with the Eligibility
Requirements and Procedures for Risk -Based Remediation of Industrial Sites Pursuant
to NC General Statutes 130A-310.65 to 310.77 after additional sample collection.
12.5 Risk Assessment Summary
The Screening Level Human Health and Ecological Risk Assessments conducted as part
of this groundwater assessment resulted in the identification of the following COPCs
(in groundwater, surface water, seeps, sediment, and/or soil) at the W.H. Weatherspoon
Power Plant: pH, aluminum, arsenic, barium, beryllium, boron, chromium, iron, lead,
manganese, mercury, molybdenum, selenium, TDS, vanadium, and zinc (Tables 12-10
and 12-15). Calcium, magnesium, potassium, and sodium are omitted from the list of
COPCs as they have no applicable criteria, are ubiquitous in nature, and are considered
to be macrominerals with negligible toxicity to ecological receptors. These constituents
were quantified as a component of the water, soil, and sediment characterization
processes. To summarize: the potential exists for exposure of the COPCs listed above to
human or ecological receptors, as identified in the CEMs (Figures 12-1 and 12-9), at
levels exceeding those listed in one or more screening criteria.
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13.0 GROUNDWATER MODELING
A brief synopsis of the groundwater modeling effort is included in the following
sections.
13.1 Groundwater Modeling to be Performed in CAP
The proposed numerical modeling involves development of a groundwater flow model
and a chemical transport model. The groundwater modeling will be conducted in
accordance with the requirements of the May 31, 2007 NCDENR Memorandum titled
Groundwater Modeling Policy.
The numerical groundwater flow model will be developed using MODFLOW, a three-
dimensional finite difference groundwater model created by the United States
Geological Survey (USGS). In MODFLOW, Darcy's law and the conservation of mass
are used to derive balance equations for each finite difference cell. MODFLOW
considers three-dimensional transient groundwater flow in confined and unconfined
heterogeneous systems, and it can included dynamic interaction with pumping wells,
recharge, evapotranspiration, rivers, streams, springs, lakes, and swamps.
The numerical model will be used as a quantitative conceptual model of the site where
flow features such as boundary conditions, sources and sinks, material zones,
hydrologic parameters, and external stresses will be defined. The boundaries of the
flow model will be located far (several miles) away from the site so that boundary
conditions do not dominate the modeled flow regime. The boundary conditions will
depend on the type of boundary, but will be either specified head (for surface water
boundaries), or no -flow (for groundwater divides). Parts of the boundary may be
modeled using a specified or head -dependent flux.
The Weatherspoon model sources and sinks will consist of drains, springs, rivers,
swamps and ponds. Drains adjacent to the ash basin were field surveyed (points
labeled "CLDI" in the table on Figure 2-1) and will be integrated into the model.
Material zones or hydrostratigraphic layers will be defined from fifty-seven (57)
existing boring logs and twenty-nine (29) boring logs generated during the 2015
assessment. Recharge, evapotranspiration, and precipitation are representations of
external stresses that are used in the model. Recharge will be initially estimated using
the average characteristics of the regional hydrogeology. These initial estimates will
then be refined during a model calibration process where the model parameters are
adjusted to provide a better match with site field data.
To further define heterogeneities, a 2-D scatter point set will be used to define specified
hydraulic values within vertical or horizontal zones. Specified hydraulic values will be
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given set ranges that reflect field conditions from core measurements, historical slug
and pump tests from SM&E (2012), and recent slug tests from the 16 wells installed
under the GAP. The model will be calibrated in part by adjusting the specified
hydraulic value distribution to minimize the residuals between the predicted hydraulic
heads and the observed values, thereby adjusting for the considerable anisotropy of the
hydraulic conductivity. Historical hydraulic heads and recent June 2015 measurements
from 38 wells will be used as observed values.
The chemical transport model will use the Modular 3-D Transport Multi -Species
(MT3DMS) model. MT3DMS uses the groundwater flow field from MODFLOW to
simulate three-dimensional advection and dispersion of the dissolved COIs including
the effects of retardation due to COI adsorption to the soil matrix. The COC source
terms will consist of initial distributions of the COIs in the subsurface that are estimated
from site boring and observation well data. During the calibration process, these source
terms, and to a lesser extent some of the transport parameters will be adjusted to
provide a best match with the field COI data.
Model limitations will be primarily related to uncertainties in field data. Model
confidence will always be higher in areas where a high density of field data can
constrain the model. Numerical model errors are easily recognizable and minimized by
experienced users.
13.2 Description of Kd Term Development
An adaptation of the column method described by Daniels and Das (2014) to develop
Kd estimates was used on Weatherspoon soil samples. Soil samples with measured dry
density and maximum particle size of 2 mm were placed in lab -scale columns
configured to operate in the up -flow mode. A solution with measured concentrations of
the COI was pumped through each column and the resulting effluent samples were
collected at regular intervals over time.
When constituent breakthroughs are verified, a "clean" solution (no COIs) was pumped
through the columns and effluent samples will be collected as well. Samples were
analyzed by inductively coupled plasma -mass spectroscopy (ICP-MS) and ion
chromatography (IC). Plots of effluent COI concentration versus cumulative pore
volumes exchanged were analyzed to estimate Kd values and to confirm reversibility of
COI sorption. Kd factors for boron, iron, manganese, and vanadium were utilized in the
transport model.
13.3 Description of Flow Transects
Groundwater flow from the ash basin to potential receptor areas is radial in an arc from
the northeast to the southwest of the ash basin (Figure 6-5). Three transects were
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selected for the Weatherspoon site to illustrate flowpath conditions in the vicinity of the
ash basin (Figures 2-1 and 6-1). Section A -A' provides the best illustration of the ash
basin source area (basin dams, engineered perimeter ditch, and ash) in relation to the
upland area to the west and receptor area to the east. Section B-B' illustrates conditions
from the wetlands across the Lumber River from the plant through the plant area and
ash basin to the Jacob Creek wetlands to the east. A transverse section from the upland
area north of the ash basin to the plant area is illustrated on Section C-C'.
13.4 Other Model Inputs
At a Coastal Plain site such as Weatherspoon, the stratigraphy of the sedimentary units
in the subsurface is the primary component of the model. Key components of the
model include the confining layer at the top of the Pee Dee Formation and the
characteristics of the Yorktown Formation. This confining layer appears to effectively
isolate the Pee Dee from vertical migration of COIs. While the confining layer appears
to vary across the Weatherspoon property from indurated siltstone to highly plastic
clayey sand, hydraulic conductivity tests on undisturbed samples yield values typical of
clay (1 x 10-7 cm/sec).
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14.0 DATA GAPS — SITE CONCEPTUAL MODEL UNCERTAINTIES
The horizontal and vertical extent of COIs have been determined for soil and
groundwater. Source area and groundwater characterization data will be used to
support preparation of flow and transport groundwater modeling for the site. The Site
Conceptual Model provided in this report will also support the modeling and the
preparation of the CAP. There are no data gaps that will be limiting factors in the
execution of the groundwater model or development of the CAP.
14.1 Data Gaps
Data that would be useful in developing a better understanding of site conditions
include the following:
1. Continued monitoring of COI migration along the major flow transect to the
southeast of the ash basin toward the cooling pond.
2. Continued monitoring of COI migration beneath the perimeter ditch to the
northeast toward CW-03.
3. Continued monitoring of COI migration vertically in the area immediately
adjacent to the southeast perimeter of the ash basin near the cooling pond.
4. Analysis of chromium speciation in ash pore water to confirm the ash basin is
not a source of hexavalent chromium in groundwater.
5. Continued monitoring of COIs in new background wells relative to turbidity and
to develop a sufficient data set for statistical analysis.
14.2 Site Heterogeneities
A discrete area of COIs in the vicinity of AW-02S has been identified. Based on a
variety of geochemical characteristics, including major cation and anion ratios and the
wide range of COI exceedances of reference criteria, this area does not appear to be
related to migration from the ash basin. It is in the vicinity of the former coal pile,
adjacent to the cooling pond, and downgradient of other historical plant operations.
For these reasons, the vicinity of AW-02 does not merit further assessment for
groundwater impacts attributed to coal ash.
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14.3 Impact of Data Gaps and Site Heterogeneities
The ash basin data gaps can be addressed with additional groundwater monitoring of
existing wells. Sampling for submittal as a Supplemental CSA is planned. Following
that, data collection through an annual cycle will be especially important to evaluate the
seasonal effects. Additional shallow groundwater monitoring wells are anticipated for
compliance with the new CCR rule.
Additional groundwater monitoring data from existing wells is also important to
address the question regarding vertical migration east of the ash basin.
Investigation of other areas of the plant site is beyond the scope of this assessment. The
land use in those areas remains industrial and is intended to remain in the capacity for
the long term. There does not appear to be an imminent threat to receptors from the
vicinity of monitoring well site AW-02 due to its proximity to the cooling pond.
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15.0 PLANNED SAMPLING FOR CSA SUPPLEMENT
Two sampling activities are planned for the near future with results to be submitted as a
CSA Supplement, as follow:
1. Collection of a groundwater sample from monitoring well MW-55I along the
primary northwest to southeast flow transect to further refine the horizontal
extent of impacts to groundwater.
2. Collection of ash pore water samples from ABMW-01 and MW-44S in the ash
basin for determination of hexavalent chromium.
These activities will be completed in time to include the results in the groundwater
model. The results will be submitted to NCDENR as a CSA Supplement.
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16.0 INTERIM GROUNDWATER MONITORING PLAN
The outline for an interim groundwater monitoring plan is contained in this section.
Wells at all background locations will be sampled to collect sufficient data to calculate
site specific background concentrations. Wells immediately peripheral to the ash basin
will be sampled to confirm the extent of impact and develop an understanding of the
effects of seasonality. MW-55I will be added to the monitoring program to assess
horizontal extent of impact. Three Pee Dee Formation wells (MW-53D, MW-54D, and
MW-55D) beneath the zone of impact will be monitored to confirm the conclusion
regarding absence of vertical migration through the confining layer.
16.1 Sampling Frequency
Interim groundwater sampling would occur on an accelerated schedule to allow for
calculation of site specific background concentrations by the end of 2016. One sample
collection event would occur in the fourth quarter of 2015 and sample collection would
occur quarterly in 2016. Sample collection events would occur a minimum of five
weeks apart.
Should interim monitoring continue past 2016, monitoring would shift to the NPDES
compliance monitoring schedule. The schedule followed for the existing compliance
sampling has yielded meaningful seasonal data that can assist in the refinement of the
SCM.
16.2 Constituent and Parameter List
The proposed list of constituents for analysis is included as Table 16-1.
16.3 Proposed Sampling Locations
Proposed groundwater monitoring wells to be included in the interim groundwater
sampling program are listed in Table 16-2 and shown on Figure 16-1.
16.4 Proposed Background Wells
Of the monitoring wells listed in Table 16-2, wells at locations BW-01, MW-01, 13W-02,
and BW-03 would be designated background wells.
Current hydraulic data suggest BW-01 is not under the influence of mounding from the
ash basin and therefore will continue to be referenced as a background well for NPDES
monitoring and for the purpose of this assessment. Modeling data to be provided in the
CAP will be used to determine whether this condition.
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17.0 DISCUSSION
All aspects of the GAP were accomplished, with the exception of the infiltration tests
that were superseded by in -situ hydraulic conductivity testing. The SCM for the site
entails the following major components:
10' The ash basin sits atop Coastal Plain and Yorktown Formation sediments north
of the main plant area.
41' Regional groundwater flow is from upland areas north and west of the ash basin
and plant area to the south and east.
'61P Ash pore water in the eastern portion of the ash basin discharges vertically into
the ground beneath the basin and radially to the northeast, southeast, and
southwest into a perimeter ditch and the subgrade beyond the ditch.
Ash pore water is concentrated by the ditches into the vicinity of the eastern tip
of the ash basin.
'41' Hydraulic loss from the ditches conveys COIs into the subsurface.
Infiltration of surface water from Jacob Swamp appears to have established a
lens of fresh water above groundwater affected by ash basin COIs.
17.1 Maximum COI Concentrations
COI concentrations at the groundwater monitoring compliance boundary are below
reference criteria for all parameters except iron (2L) and vanadium (IMAC). Both iron
and vanadium are COIs for which development of a site specific background
concentration is appropriate. For the remaining parameters, COI concentrations above
the reference criteria occur immediately adjacent to the ash basin. At the present time,
there is no indication of off -site migration of COIs.
Results from monitoring location AW-02 in the plant area are not included in this
discussion because the COIs detected appear to related to past industrial activity rather
than migration from the ash basin.
17.2 Summary of Completed and Ongoing Work
Work anticipated under the GAP was completed. Supplemental sample collection is
proposed to provide additional input into the CAP.
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17.3 Contaminant Migration and Potentially Affected Receptors
No receptors with impact from the ash basin have been identified. All impact identified
to date is located on Duke Energy property.
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18.0 CONCLUSIONS AND RECOMMENDATIONS
The conclusions developed during the CSA are summarized in this section.
18.1 Source and Cause of Contamination
The CSA found that the unlined ash basin is a source of impact to the underlying
groundwater. The cause of impact is leaching of constituents from the coal ash into the
ash pore water and its migration to underlying groundwater.
18.2 Imminent Hazards to Public Health and Safety and Actions
Taken to Mitigate Them
15A NCAC 02L .0106(g)(2) requires the site assessment to identify any imminent
hazards to public health and safety and the actions taken to mitigate them in accordance
with Paragraph (f) of .0106(g). Paragraph (f) provides requirements for corrective
action. The CSA found no imminent hazards to public health and safety. No actions to
mitigate imminent hazards are required for this reason.
18.3 Receptors and Significant Exposure Pathways
The requirement contained in the NORR and the CAMA concerning receptors was
completed with the results provided in Section 4. A screening level human health risk
assessment and screening level ecological risk assessment was performed with the
results provided in Section 12.
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. 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 county wells are located upgradient of the site based on
regional groundwater gradients.
Inventories of public and private water supply wells have been compiled. Nearby
residents have been contacted regarding private wells and two have been sampled. The
samples, which were split and analyzed by two laboratories, from one of the two wells
exceeded IMAC for cobalt (1.51 µg/L and less than 5 µg/L, compared to IMAC of 1 µg/L)
and vanadium (0.5 µg/L and 0.335 µg/L, compared to IMAC of 0.3 µg/L).
With regard to ecological resources, 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
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mariae) and the sandhills chub (Semotilus lumbee), two unique fish species designated of
"special concern" by the state of North Carolina.
18.4 Horizontal and Vertical Extent of Soil and Groundwater
Contamination
The CSA identified the horizontal and vertical extent of groundwater impact. Chemical
analytical data for soils that indicate apparent areas of soil contamination are shown on
Figures 8-1 and 8-2. Soil contamination is possible at locations where analytical results
were in excess of soil screening levels protective of groundwater. With the exception of
the area immediately southeast of the ash basin, soils with elevated COI concentrations
appear to be related to prior industrial site activities.
The horizontal and vertical extent of groundwater impact is shown on Figures 10-5
through 10-36 and Figures 11-1,11-2, and 11-3. Groundwater impact is considered to
be present where the analytical results were in excess of the site background
concentrations and in excess of 2L or IMAC. Lateral migration of COIs southeast
toward Jacob Creek and the cooling pond has been identified. Continued groundwater
monitoring using existing wells (most notably MW-55I) is planned to assess
concentration changes in this area over time. The extent of groundwater impact shown
on these figures is limited to an area on Duke Energy property.
Arsenic, boron, cobalt, iron, manganese, thallium, total dissolved solids (TDS), and
vanadium have been identified as site specific constituents of interest (COIs) based on
concentrations in excess of 2L or IMAC in ash pore water. Aluminum has been
identified as a site specific COI on the basis of concentrations detected in surface water.
Constituent transport is dependent on leaching from the coal ash source that results
from solubility due to chemical disequilibrium (the dissolved phase is more stable than
the solid phase under the conditions at the time). Factors that affect reactions with
material along the flow path resulting in removal of the constituents from groundwater
control the extent of migration. These factors vary by constituent and vary based on the
properties of the soil or aquifer materials along the flow path.
Sorption and precipitation are the primary mechanisms that immobilize cations
(aluminum, arsenic, boron, cobalt, iron, manganese, thallium, and vanadium), as
described in Section 6.4. A number of factors specific to constituent and to the site
conditions are involved in determining which of these mechanisms occur and how
much of the constituent is partitioned out of the groundwater.
The results of testing performed to determine the chemical, physical, and mineralogical
characteristics of the soil and aquifer materials and the site groundwater are presented
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in Sections 7, 8, 9, and 10. Additional testing is being performed to determine the
adsorptive capacity of the site soils and aquifer materials to the specific groundwater
constituents by development of site specific partition coefficient Kd terms, as described
in Section 13. The Kd testing will provide site specific values for the ability and capacity
of site soils to remove constituents from groundwater and will assist in understanding
the mechanisms affecting transport at the site. Kd tests and the associated groundwater
modeling will also allow for evaluation of the long-term constituent loading and the
capacity of the site soil and aquifer material to attenuate this loading. The results of this
testing, the groundwater modeling, and the evaluation of the long term groundwater
conditions at the site will be presented in the CAP.
Iron, manganese, and vanadium are commonly detected in shallow groundwater in the
coastal plain region of North Carolina. Calculation of proposed site specific
background concentrations will occur when a sufficient number of samples to perform
statistical analysis have been collected. Arsenic, cobalt, and thallium in groundwater
are limited in extent to a small area beneath and east of the basin. Boron and TDS are
more prevalent southeast of the basin than at depth beneath it.
Data collected to date indicate that vertical migration is limited to the lower portion of
the surficial aquifer (wells screened in the lower Yorktown Formation). Field
observations indicate that the confining layer at the top of 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.
18.5 Geological and Hydrogeological Features influencing the
Movement, Chemical, and Physical Character of the
Contaminants
As anticipated in the initial site conceptual hydrogeologic model presented in the Work
Plan dated December 30, 2014, the primary feature that influences migration of
contaminants is the confining layer at the base of the Yorktown Formation. This
confining layer appears to be continuous on the Weatherspoon site based on its
presence at every boring installed to the depth to encounter it.
The movement of the contaminants is related to the groundwater flow direction, the
groundwater flow velocity, and the rate at which a particular contaminant reacts with
materials in the aquifer. The direction of the movement of the constituents confirmed
by the CSA is toward the east and south, as anticipated. The rate of groundwater
movement varies with the hydraulic conductivity and porosity of the site soil and rock
materials and ranges from 3.3 feet per year to 19.4 feet per year.
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Data collected during the CSA, coupled with Kd data to be supplied at a later date, will
be used to build groundwater flow and transport models for the site. The groundwater
model will provide information to allow evaluation of the capacity of the site soil and
aquifer material to attenuate the loading imposed by the conditions modeled for the
proposed corrective action.
18.6 Proposed Continued Monitoring
Interim groundwater monitoring is proposed in Section 16.
18.7 Preliminary Evaluation of Corrective Action Alternatives
Duke Energy has recommended excavation of the ash from the basin (Duke Energy,
June 2015). Further assessment will determine whether monitored natural attenuation
of groundwater will be appropriate or if other corrective action will be necessary.
Groundwater modeling will provide an estimate of the degree of residual groundwater
impact over time. In the subsequent CAP, Duke Energy will pursue corrective action
under 15A NCAC 02L .0106 (k) or (1) depending on the results of the groundwater
modeling and the evaluation of site suitability for monitored natural attenuation.
Evaluation of monitored natural attenuation would be performed using the approach
found in Monitored Natural Attenuation of Inorganic Contaminants in Groundwater,
Volumes 1 and 2 (EPA Reference) and potential modeling of interaction between
groundwater and surface water.
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