Sutton CSA Executive Summary 08-05-2015

Comprehensive Site Assessment Report August 2015
L.V. Sutton Energy Complex SynTerra
L.V. SUTTON ENERGY COMPLEX
EXECUTIVE SUMMARY
The North Carolina Coal Ash Management Act (CAMA) requires the preparation of a
Comprehensive Site Assessment (CSA) Report for each regulated facility within 180
days of approval of the Work Plan. This report addresses Duke Energy's L.V. Sutton
Energy Complex (Site). The Work Plan for the Site was approved on February 6, 2015.
The purpose of this assessment is to identify the source and cause of exceedances of
regulatory standards, potential hazards to public health and safety, receptors and
exposure pathways.
NC Department of Environment and Natural Resources (NCDENR) prescribed the list
of monitoring parameters to be measured at the Site. Once the sampling portion of the
CSA was complete, data were examined to pick those parameters that were most
relevant to the Site. These parameters were determined by examining data from
monitoring wells installed in ash, and then by comparing these results to 2L or the
former Interim Maximum Allowable Concentrations (IMACs). 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.
Parameters detected in ash pore water samples at values greater than 21, or IMAC, were
designated as 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 a basin is from natural
sources (e.g., rock and soil) or the ash basin.
This assessment addresses the horizontal and vertical extent of COIs in soil and
groundwater, significant factors affecting groundwater flow conditions, and the
geological and hydrogeological features influencing the movement, chemical, and
physical character of Cols.
Data presented in this assessment report is the basis for the Corrective Action Plan
(CAP) required within 270 days of the approved Work Plan to identify alternative
strategies to address groundwater impacts at the site.
The Corrective Action Plan, as required by CAMA, will include groundwater model
results of the anticipated ash removal to assess the effects on groundwater. A
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groundwater monitoring plan will be provided to assess changes in groundwater
conditions over time.
In accordance with CAMA Section 3(b), Duke Energy will fully excavate the ash basins
at the Site, with the material to be safely recycled or reused in a lined structural fill or
disposed in a lined landfill. Additionally, a Groundwater Mitigation and Monitoring
Plan was submitted to NCDENR in July 2015 which proposed a groundwater extraction
system as an interim corrective action to address the migration of COIs.
Based on the evaluation of both historical and recently obtained CSA data, the
following conclusions are provided:
41' Recent groundwater assessment results are consistent with previous results from
historical and routine compliance boundary monitoring well data.
41' Background monitoring wells contain naturally occurring COIs at concentrations
greater than 2L or former IMAC. This information is used to evaluate whether
concentrations in groundwater downgradient of the basins are naturally
occurring, from another source or influenced by migration of constituents from
an ash basin. As examples, iron, manganese, cobalt and vanadium are present in
the background monitor well samples at concentrations at or above their
applicable 2L or IMAC.
Regional groundwater flow is to the west toward the Cape Fear River, to the east
toward the Northeast Cape Fear River or to the south toward the convergence of
the two rivers. In the vicinity of the 1971 and 1984 ash basins, groundwater
flows radially. A groundwater divide is located northeast of the ash basins and
groundwater north of the basins flow west toward the cooling pond.
Groundwater east and south of the basins flows east, southeast and south. In the
Former Ash Disposal Area (FADA), groundwater flows to the southwest.
'61' Data indicate the water quality of the Cape Fear River has not been impacted by
the ash basins.
41' Migration of COIs, primarily boron, above the 2L, has occurred in the lower
surficial aquifer at a depth of approximately 25 to 50 feet below ground surface.
Concentrations of boron in the ash pore water and groundwater adjacent to the
1971 ash basin are higher than elsewhere on the Site. Also, boron concentrations
are not observed in surficial aquifer background wells and concentrations
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decrease downgradient of the basins; thus, boron serves as a good indicator of
the maximum extent of ash constituent migration. However, boron has also been
detected in deeper Pee Dee formation wells at the site. This is likely a result of
saltwater intrusion (boron is the 10111 most prevalent constituent in sea water).
Regional groundwater data supports this.
41' Boron is detectable above the 2L in offsite monitoring wells downgradient and
east of the basins. The horizontal extent of the boron concentrations above the 2L
has been defined. Boron concentrations greater than 2L do not extend southeast
to the public water supply wells located beyond the property boundary
southeast of the basins. The approximate extent of horizontal migration of boron
is shown on Figure ES -1.
41' The flow paths for COIs indicate a preference for lateral migration, rather than
vertical migration, as a result of contrasting hydraulic conductivities between the
surficial and Pee Dee formations. A clay confining unit was not observed in the
monitoring wells or soil borings within the study area. While no confining unit
is present above the Pee Dee Formation, the lower permeability of the Pee Dee
Formation reduces vertical migration of COIs.
`7 The CSA characterizes the horizontal and vertical extent of COIs and
groundwater gradients which now facilitate development of the Site Conceptual
Model (SCM) (i.e., the groundwater flow and constituent migration model). This
then facilitates development of a CAP due within 90 days of submittal of this
CSA report.
�7 The horizontal extent of boron in the lower surficial aquifer at levels exceeding
the 2L has extended beyond the site boundary to the east. Mitigating actions to
address this horizontal extent are already initiated.
o An interim corrective action plan has been prepared and submitted to
NCDENR. The interim plan proposes 12 groundwater extraction wells
along the downgradient property line to intercept the groundwater in the
area of boron migration.
o Data indicate boron concentrations in nearby water supply wells are less
than the 2L.
o The approximate extent of horizontal migration of boron in the surficial
aquifer is shown on Figure ES -1.
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Brief summaries of portions of the Comprehensive Site Assessment report are presented
in the following sections.
ES.1 Source Information
Mineralogical, physical, and chemical properties of the Site ash basins have been
characterized for use in the hydrogeological SCM. The ash management area consists
of three locations; the FADA, the 1971 ash basin and the 1984 ash basin. The FADA,
which contains a depth of ash less than 15 feet, is located in a low-lying area and was
developed near original ground surface. The 1971 ash basin was excavated to a depth
of approximately 40 feet below ground surface (bgs) and contains approximately 80
vertical feet of ash at its deepest point. The 1984 ash basin was constructed near
original ground surface and contains a clay liner. Groundwater within the 1971 and
1984 basins is mounded and hydraulically upgradient of the surrounding land surface
to the northeast, east and southeast and the normal pool elevation of the cooling pond
located to the west. Seepage of water from within the 1971 and 1984 ash basins to
groundwater under the basins migrates in a radial pattern.
ES.2 Initial Abatement and Emergency Response
Duke Energy is currently planning to fully excavate the ash basins in accordance with
CAMA requirements; with the material safely recycled or reused in a lined structural
fill or disposed in a lined landfill. A Groundwater Mitigation and Monitoring Plan was
submitted to NCDENR in July 2015 to address offsite migration of constituents of
concern, primarily boron. Twelve extraction wells are proposed along the eastern site
boundary to intercept groundwater in the surficial aquifer. Plans to discontinue the use
of the nearby municipal water supply wells are underway and Duke has taken
proactive steps to replace these water supply wells with a new water line extension.
Completion of the replacement well field water system is anticipated by December
2015.
ES.3 Receptor Information
Land use surrounding the Site includes commercial, industrial, mining (sand quarry),
residential, and forest land. The Site is located on a small peninsula formed by the Cape
Fear River bordering the Site to the west and the Northeast Cape Fear River located
approximately one mile to the east. The two rivers converge in the City of Wilmington
south of the Site.
Well inventories of public and private wells have been compiled. Nearby property
owners have been contacted regarding private wells and a number of water supply
wells have been sampled at the direction of NCDENR. Inventories of public and
private water supply wells have been updated as part of this assessment. The
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groundwater model being developed for the Site will provide additional information on
the likelihood of private and public wells being impacted by the Site.
ES.3-1 Public Water Supply Wells
Four Cape Fear Public Utility Authority (CFPUA) municipal water supply wells
are located near the southeastern property boundary of the site. Two of these
wells are not in use. Analyses on samples collected routinely from the wells
indicate concentrations of manganese slightly above the 2L. Data indicate these
exceedances are not related to the ash basins. The CFPUA wells are
approximately 50 feet deep within the surficial sand aquifer. These two wells
will be eliminated once the new water line is completed in December 2015. After
which, all four wells will be properly abandoned.
ES.3-2 Private Water Supply Wells
Inventories of other smaller public and private water supply wells have been
compiled. NCDENR contacted nearby property owners regarding water supply
wells and managed the sampling of the wells in accordance with CAMA. Water
supply wells are located within 0.5 mile of the site, including on-site wells used
for plant operations and wells for commercial and industrial developments.
Some of the wells are production wells that might also be used as a source of
drinking water as there are no public water lines to these facilities.
While some of these wells are potentially located downgradient to the site, and
2L or IMAC were exceeded in some samples for iron, manganese, cobalt and
vanadium, these constituents are common to groundwater in the region and
their occurrence cannot be conclusively attributed to the ash basins. Where
industrial water supply wells are located in the area mapped with boron 2L
exceedances based upon monitoring well data, the water supply well sample
data provided by NCDENR indicate the boron concentrations are not greater
than the 2L for the production well samples.
ES.3-3 Human and Ecological Receptors
Consumption of groundwater, recreational use of affected surface water
(particularly 'Lake Sutton' located west of the ash basins, built as the plant
cooling pond but open to the public for fishing) and consumption of fish and
game potentially affected by these waters are the primary potential exposure
pathways for humans in the vicinity of the ash basins.
The ecological exposure medium includes potentially impacted soil, surface
water and sediments at the site. Groundwater does not present a complete
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exposure pathway to ecological receptors. Potentially complete pathways
evaluated for the Site include incidental ingestion of soil or sediment, and
ingestion of prey or plants.
The Cape Fear River Basin supports over 95 species of commercial and
recreational fish, including 42 rare aquatic species. The Cape Fear shiner
(Notropis mekistocholas), a federally endangered fish species, is known only to
inhabit this river basin. The shortnose sturgeon (Acipenser brevirostrum), red -
cockaded woodpecker (Leuconotopicus borealis), Saint Francis' satyr (Neonympha
mitchellii francisci), and the West Indian manatee (Trichechus manatus) (in
estuarine areas) are also known species in the Cape Fear River and are federally
listed as endangered. The American alligator (Alligator mississippiensis) and the
loggerhead turtle (Caretta caretta) are federally listed as threatened.
ES.4 Sampling / Investigation Results
ES.4-1 Nature and Extent of Contamination
Arsenic, barium, boron, cobalt, iron, manganese, selenium, thallium, vanadium
and total dissolved solids (TDS) have been identified as site specific COIs based
on concentrations in excess of the 2L or IMAC in the saturated ash (pore) water
or groundwater. Iron, manganese and vanadium were detected in the ash pore
water, however these are naturally -occurring metals common to regional
groundwater and their occurrence at the Site cannot be wholly attributed to the
ash basins. Cobalt and thallium were not detected in ash pore water samples,
therefore the concentrations in groundwater appear to be naturally occurring.
Selenium occurs in groundwater in an isolated area north of the ash basins;
however it was not detected in the 1971 ash basin pore water. Groundwater data
immediately north of the 1984 ash basin can be collected to determine if it is the
source of the selenium in this area of the Site.
Historical groundwater monitoring has shown that values for iron and
occasionally manganese can be greater than the 2L in background wells. Site
specific historical data are not available for vanadium. However, iron,
manganese and vanadium are known to be commonly occurring in background
shallow groundwater in the coastal plain region of North Carolina. Manganese
and cobalt were detected in background wells MW-37B/C and MW -5C and iron
and vanadium were detected in MW-37B/C at concentrations greater than 2L or
IMAC. Arsenic in groundwater at concentrations greater than the 2L is limited
to an area southeast of the 1971 ash basin and below the FADA.
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Boron is detectable above the 2L in offsite monitor wells directly east and
downgradient of the basins. The horizontal extent of the boron concentrations
above the 2L has been defined. Boron concentrations greater than the 2L do not
extend southeast to the public water supply wells located beyond the property
boundary. The horizontal extent of boron in groundwater greater than the 2L is
shown on Figure ES -1. Field observations indicate that the Pee Dee formation is
not associated with a clay -confining layer at the site; however the low
permeability of the Pee Dee formation, based on hydraulic conductivity values,
contrasts with that of the overlying surficial sands and acts as an aquitard to
downward vertical flow.
ES.4-2 Maximum Contaminant Concentrations
For the COIs identified on the basis of basin ash pore water concentrations,
boron, iron, manganese and vanadium are the most prevalent in groundwater.
Iron, manganese and vanadium were also detected in background wells and the
occurrence of these metals can also be attributed to regional groundwater
quality. Of these, boron is the only COI that is not typical of surficial aquifer
background conditions and attributed to the ash basins in the surficial aquifer
wells.
The highest concentration of boron in groundwater was detected in MW -23C, a
compliance boundary well screened in the lower surficial aquifer and located 500
feet east of the 1971 ash basin. The boron concentration in MW -23C was 3,060µg/l
in March 2015 and 2,050µg/l in June 2015.
The highest concentration of arsenic in groundwater occurs beneath the FADA.
Higher concentrations were detected in the 1971 ash basin pore water well,
which is screened below the water table but is not considered groundwater. The
CSA data indicate that arsenic migration in groundwater is limited to the FADA
waste boundary and an area just southeast of the 1971 ash basin (MW -21C).
The highest concentration of iron in groundwater was detected in a sample from
SMW-2B, an offsite monitoring well screened in the upper surficial aquifer and
located approximately 800 feet east of the site property boundary. The iron
concentration at this location is interpreted to be unrelated to the ash basins
based on the distribution of iron concentrations across the site. Similar high iron
concentrations were also detected in other offsite monitor wells and wells located
along the eastern site boundary or upgradient to the ash basins; suggesting the
iron is naturally -occurring or related to an offsite source.
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The highest concentration of manganese in groundwater was also detected in a
sample from an offsite well, SMW-3C, screened in the lower surficial aquifer and
located approximately 900 feet east of the site property boundary. The
distribution of manganese is similar to that of iron and is also considered to be
unrelated to the ash basins.
The highest concentrations of TDS in groundwater were detected in the Pee Dee
Formation wells and in surficial wells located along the eastern property
boundary. The highest concentration of vanadium in groundwater was 39.6 µg/l
detected in a sample collected from MW -20, a well screened in the upper surficial
aquifer located southwest and downgradient of the FADA.
Cobalt was not detected in the ash pore water and as such its occurrence in
several wells at the site is not considered related to the ash basins. The highest
concentration of cobalt in groundwater, 93.1 µg/1, was detected in SMW-2C; an
offsite well which is screened in the lower surficial aquifer and located east of the
site property boundary.
Selenium was not detected in the ash pore water and is only detected in two
wells. Additional data associated with the 1984 basin is needed to rule it out as a
possible source of the selenium.
Exceedances of 2B concentrations were detected in the surface water samples for
aluminum, copper, iron and zinc. Aluminum and copper exceedances were
detected in samples collected from the cooling pond. Aluminum was detected
above the 2B concentration in samples collected from the Cape Fear River at
locations upgradient, adjacent and downgradient to the ash basins, while zinc
was detected above the 2B concentration in upgradient samples.
ES.4-3 Source Characterization
Ash within the basins and the FADA are the source of COIs in groundwater,
primarily boron. Ash disposal in the FADA ended in 1971 and sluicing of ash to
the 1971 and 1984 basins was discontinued in 2013. The ash within the FADA is
less than 15 feet thick and groundwater in the FADA is approximately three feet
bgs. The underlying soils in the FADA consist of the medium -fine grained sands
of the surficial aquifer.
The ash in the 1971 basin is approximately 80 feet thick. The 1971 ash basin area
appears to have been excavated below grade to a depth of approximately 40 feet
and all but the lower couple of feet of the surficial sands were removed prior to
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placement of the ash. The Pee Dee Formation underlies the remnant surficial
aquifer sands below the ash basin. The water level recorded in the 1971 basin
was approximately 34 feet bgs and therefore ash below this depth is saturated.
When the 1971 ash basin was operational, the discharge was routed to the
cooling pond. The cooling pond outfall to the Cape Fear River is regulated
under a NPDES permit. The 1971 ash basin continues to receive rainwater and
storm water runoff from the plant, which infiltrates into the subsurface of the ash
basin. No runoff or discharge occurs from the ash basin.
The 1984 ash basin was constructed with a 12 -inch thick clay liner. Therefore,
drilling into or through the clay liner to collect similar data for the 1984 basin
was not conducted.
ES.4-4 Receptor Survey
A receptor survey was conducted in accordance with CAMA during 2014 and
has been updated herein with additional available information.
Public water supply wells in New Hanover County draw water from the surficial
aquifer. The closest public water supply wells are two active wells located to the
southeast of the ash basins and the property line. These wells are routinely
sampled. No COIs are detected above the 2L in the public supply wells with the
exception of manganese. Based on data obtained during the assessment, the
occurrence of manganese in the area of the public supply wells cannot be
conclusively attributable to the ash basins.
Other water supply wells identified within lh mile of the compliance boundary
are located east and southeast of the site. During 2015, NCDENR managed the
sampling of water supply wells in the area. Only iron, manganese, cobalt, and
vanadium were reported at concentrations greater than 2L or IMAC. Based on
data obtained during the assessment, the occurrence of iron, manganese and
cobalt in the wells cannot be directly attributed to the ash basins. Vanadium is
also a naturally -occurring element in groundwater and assessment data does not
definitively indicate a connection between the detection of vanadium in the
supply wells and the ash basins. Boron results for the water supply wells
sampled at the direction of NCDENR were reported to be less than the 2L.
Constituents of potential concern (COPCs) for human and ecological receptors
identified using screening level risk assessment methodology include aluminum,
antimony, arsenic, barium, beryllium, boron, cadmium, sulfide, TDS, chromium,
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copper, iron, lead, manganese, molybdenum, selenium, thallium, vanadium, and
zinc. This list is longer than the list of site COIs due to the conservative approach
of comparing analytical results to published reference values in the risk
assessment screening process. Additional risk evaluation will be provided as
part of the CAP.
ES.4-5 Regional Geology and Hydrogeology
The Site lies within the Coastal Plain Physiographic Province. The Coastal Plain
comprises a wedge shaped sequence of stratified marine and non -marine
sedimentary material deposited on crystalline basement. In the eastern part of
the North Carolina Coastal Plain, groundwater is obtained from the surficial,
Castle Hayne, and Pee Dee aquifers, although the Castle Hayne is not present in
the area of the Site. The Coastal Plain groundwater system consists of aquifers
comprised of permeable sands, gravels, and limestone separated by confining
units of less permeable material.
ES.4-6 Site Geology and Hydrogeology
Soils exposed at the surface in the Site area are relatively recent Coastal Plain
sediments. Sediments of the surficial aquifer are underlain unconformably by
the unconfined Pee Dee Formation at approximately 50 feet below land surface.
No confining unit was found between the surficial aquifer and the Pee Dee
Formation at the site. However, data indicate lower hydraulic conductivities in
the Pee Dee formation than in the overlying surficial aquifer, indicating the Pee
Dee acts as an aquitard to vertical migration.
The site is located on a peninsula of land defined by the Cape Fear River,
adjacent to the west and the Northeast Cape Fear River, located approximately
one mile to the east. Based on regional topography and drainage features,
groundwater flow within this peninsula would be either west or east to one of
the two rivers or to the south where the rivers converge. At the site, the current
interpretation of groundwater flow indicates that in close proximity to the 1971
and 1984 ash basins, groundwater flows radially; toward the west along the edge
of the cooling pond and to the east, southeast and south on the east side of the
1971 ash basin. In the FADA, groundwater flow is to the southwest. A
groundwater divide or ridge is located northeast of the ash basins. Areas where
shallow water levels appear to be influenced by operating water wells occur near
the plant production wells, which are used for industrial purposes, the CFPUA
(public water supply) wells, located southeast of the site, and the Wooten plant
production wells, located directly to the east of the ash basins.
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Depth to the water table is approximately 7 to 18 feet below land surface. The
potential influence of on-site production wells, off-site municipal and industrial
production wells is being evaluated with the groundwater flow model to be
presented with the CAP. The model results will be used to further assess the
groundwater flow directions at the site. As the model is being prepared,
additional groundwater and surface water elevation data may be collected.
ES.4-7 Existing Groundwater Monitoring Data
The compliance monitoring data indicate that iron has been consistently detected
at concentrations greater than the 2L for background well MW -4B, while
manganese has been detected at a concentration greater than 2L intermittently.
Manganese is consistently detected at a concentration greater than the 2L at the
southern compliance well MW -7C.
Manganese is typically the only constituent detected at a concentration greater
than the 2L at background well MW -5C, to the north of the basins. Manganese
and selenium are consistently detected at concentrations greater than the 2L at
the northern compliance boundary well MW -27B.
Boron, iron, and manganese have been detected at concentrations greater than
the 2L in eastern compliance wells MW -19, MW -21C, MW -22B, MW -23C and
MW -24C.
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 pore water seeps
directly into the porous sands of the surficial aquifer underneath the unlined
1971 ash basin and the FADA. It is anticipated that some migration may occur
from the lined basin, however to a lesser extent. The contrast of permeabilities
across the surficial/Pee Dee contact reduces downward vertical groundwater
flow. The highest concentrations of COIs are detected in the lower surficial
aquifer at a depth of approximately 45 feet, above the surficial/Pee Dee contact.
The horizontal extent of boron in the surficial groundwater flow zone greater
than 2L is shown on ES -1.
ES.5 Identification of Data Gaps
The horizontal and vertical extent of COIs have been sufficiently 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
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conceptual model provided herein 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.
However, the following additional information would be useful:
1. Determination of background COI concentrations for deep (Pee Dee formation)
groundwater.
2. Evaluation of potential offsite sources or natural conditions related to the
concentrations of iron and manganese.
3. Further evaluation of the 1984 basin as a potential source of the selenium in the
groundwater north of the ash basin.
ES.6 Conclusions
Duke Energy plans to excavate the ash basins at the Site in accordance with CAMA
requirements. The impact of the ash excavation on long term groundwater quality will
be evaluated as part of the groundwater flow and transport modeling to be provided in
the Corrective Action Plan.
Data indicate groundwater has been impacted by the seepage of ash pore water from
the unlined 1971 ash basin and FADA. The lined ash basin may also contribute to this
impact, but to a lesser extent. Detectable boron concentrations have migrated offsite to
the east. However, the 2015 data collected by NCDENR indicate the boron
concentrations in the public and private water supply wells sampled are less than 2L.
The extent of the boron concentrations greater than 2L in the surficial aquifer has been
defined. The anticipated horizontal and vertical extent of potential migration will be
further evaluated by the groundwater modeling to be provided in the CAP.
A Groundwater Mitigation and Monitoring Plan has been submitted to protect water
supply wells located east of the site. The plan includes the installation of 12
groundwater extraction wells along the eastern property boundary. Groundwater
modeling to be provided in the CAP will also evaluate this action combined with
removal of the ash from the basins.
A plan for future 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 of this report.
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