Roxboro Executive Summary CSA September 2015

Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
ROXBORO STEAM ELECTRIC PLANT
EXECUTIVE SUMMARY
North Carolina General Assembly Session Law 2014-122, the North Carolina Coal Ash
Management Act (CAMA) of 2014, requires the owner of a coal combustion residuals
surface impoundment to submit a Groundwater Assessment Work Plan (GAP or Work
Plan) to the North Carolina Department of Environment and Natural Resources
(NCDENR) no later than December 31, 2014 and a Groundwater Assessment Report
[herein referred to as a Comprehensive Site Assessment (CSA) Report] for each
regulated facility within 180 days of approval of the Work Plan. Data generated by this
CSA will be used in development of a Corrective Action Plan (CAP) for each regulated
facility. This report addresses the Roxboro Steam Electric Plant (the Roxboro Plant,
Plant or Site) owned by Duke Energy Progress, LLC (Duke Energy). The assessment
was performed within 180 days of the approval of the GAP by NCDENR dated March
6, 2015.
The purpose of the CSA is to characterize the extent of impact resulting from historical
production and storage of coal ash, evaluate the chemical and physical characteristics of
detected constituents, investigate the geology and hydrogeology of the Site including
factors relating to contaminant transport, and examine risk to potential receptors and
exposure pathways.
NCDENR prescribed the list of monitoring parameters to be measured at the Site. Once
the sampling portion of the CSA was complete, the data were examined to select those
parameters that were most relevant for the Site. These parameters were determined by
examining data from monitoring wells installed in ash (ash pore water), and then by
comparing these results to the North Carolina Groundwater Quality Standards found in
the North Carolina Administrative Code (NCAC) Title 15A, Subchapter 2L.0202 (2L or
2L Standards) and the Interim Maximum Allowable Concentrations (IMAC) established
by NCDENR pursuant to 15A NCAC 02L.0202(c). If a constituent concentration
exceeded the North Carolina Groundwater Quality Standards in ash pore water wells,
as specified in the 2L Standards or the IMACs, it has been designated as a "Constituent
of Interest" (COI). COIs are constituents that display correlation to ash basin influence.
The IMACs were issued in 2010, 2011, and 2012; however NCDENR has not established
a 2L for these constituents as described in 15A NCAC 02L.0202(c). For this reason,
IMACs noted in this report are for reference only.
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Roxboro Steam Electric Plant SynTerra
Based on detections in ash pore water or groundwater samples at concentrations greater
than 2L or IMAC at the Site, COIs identified include antimony, arsenic, beryllium,
boron, cobalt, iron, manganese, nickel, pH, sulfate, thallium, total dissolved solids
(TDS) and vanadium. Some constituents (e.g., antimony, chromium, cobalt, iron,
manganese, TDS and vanadium) are also present in background monitoring wells and
thus require careful examination to determine whether their presence in groundwater
on the downgradient side of an ash 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 COIs and the other constituents monitored.
Data presented in this assessment report are the basis for the Corrective Action Plan
(CAP) required within 270 days of the approved Work Plan and within 90 days of CSA
submittal to identify alternative strategies to address groundwater impacts at the Site.
Duke Energy is investigating a hybrid closure approach to address the Roxboro ash
basin, where a portion of the basin may be capped and the remainder may be
excavated. The excavated material may be re -positioned within the basin footprint in
accordance with the hybrid cap -in-place design, or safely recycled, or reused in a lined
structural fill or disposed in a lined landfill.
The CAP, as required by CAMA, will include groundwater model results of potential
ash removal and capping closure options to assess the effects on groundwater. A
groundwater monitoring plan will be provided to assess changes in groundwater
conditions over time.
Based on the evaluation of both historical groundwater data and recently obtained CSA
information, the following conclusions are provided:
0 No imminent hazard to human health or the environment has been identified as
a result of groundwater migration from the ash basins
Recent groundwater assessment results are consistent with previous results from
historical and routine compliance boundary monitoring well data.
Based on empirical data, no off-site impact to private or public water supply
wells is evident.
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
Background monitoring wells contain naturally occurring metals 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, antimony, chromium, cobalt, iron,
manganese, pH, TDS and vanadium are present in the background monitor well
samples at concentrations at or above their applicable 2L or IMAC.
47 Regional groundwater flow is to the west/northwest toward the Hyco Reservoir.
The water table at the Site is typically located within a transition zone above
bedrock or within bedrock. Groundwater in both zones generally flows
north/northwest across the Site to the Hyco Reservoir. A discharge canal and
topographic ridge located west of the Site ash basins limits groundwater flow in
that direction. Localized groundwater high zones are centered around the ash
basins, with radial flow in these areas.
�7 The seeps and springs intended to monitor groundwater quality as it discharges
to Hyco Reservoir were too dry during the 2015 CSA sampling event to be
clearly representative of groundwater and likely reflect the surface water quality
of the lake below the Plant's National Pollution Discharge Elimination System
(NPDES) permitted outfall. As such, this is a data gap that will require
additional monitoring of these spring and seep locations to assess the effects of
groundwater discharge to Hyco Reservoir.
L? Cobalt, iron and manganese are present in background groundwater monitoring
well locations; however the concentrations are considerably higher in ash pore
water samples. The CSA data indicate the migration of metals is limited to seeps
and groundwater in the transition zone and bedrock downgradient between the
ash basins and the reservoir. The approximate extent of horizontal migration of
COIs in groundwater is shown on Figure ES -1.
Boron concentrations are the highest in the ash pore water and its occurrence is
attributable to the ash basins. Migration of boron, the most mobile of the COIs, is
also limited to the groundwater beneath the basins and in limited areas
downgradient to the East Ash Basin. The boron concentrations in seeps indicate
potential preferential pathways.
47 The ash basins appear to be hydrologically bounded by drainage features to the
northeast and southwest, by the Hyco Reservoir to the north/northwest and by
topographic upgradient areas to the east and southeast. Groundwater modeling
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
as part of the CAP will provide further insight to Site hydrogeology and will
allow an evaluation of potential ash removal and capping closure options to
assess the impact to groundwater.
�7 A decreasing trend of COI concentrations for boron, chromium, iron and
manganese is evident in downgradient landfill monitoring wells GMW-06,
GMW-10 and GMW-11. Since the lined landfill began operation in 2003, iron,
manganese and chromium concentrations have decreased to below 2L and/or
below detection limits. These data indicate the lined landfill is reducing
migration of COIs to Site groundwater.
'67 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.
Brief summaries of portions of the CSA 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 the two ash basins: the semi -active East Ash Basin, and the adjacent gypsum pad, the
active West Ash Basin and a lined landfill. The approximate size of the combined ash
basins is 495 acres. An unlined landfill was constructed on top of the semi -active East
Ash Basin in the late 1980s. The thickness of the ash in the East Ash Basin is
approximately 55 to 80 feet thick and in the West Ash Basin the ash was approximately
80 feet thick. Both ash basins are located within natural drainage basins. Currently the
top of the lined landfill is approximately 100 to 120 feet above grade of the East Ash
Basin. The ash basins are impounded by earthen dams. Surface water runoff from the
East Ash Basin and the lined landfill are routed into the West Ash Basin to allow
settling. Water discharges from the West Ash Basin at the filter dike located on the
south end, and is directed northward toward the Hyco Reservoir via a man-made canal.
Seeps discharge from the East Ash Basin on the east and north sides and the West Ash
Basin are equipped with toe drains at the base of the northern berm. Groundwater
mounding is apparent in the immediate area of each ash basin.
ES.2 Initial Abatement and Emergency Response
15A NCAC 02L .0106(8) (2) requires the site assessment to identify imminent hazards to
public health and safety and actions taken to mitigate them in accordance with
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Roxboro Steam Electric Plant SynTerra
Paragraph (f) of .0106(g). Paragraph (f) provides requirements for corrective action.
The CSA found no imminent hazard to public health and safety; therefore, no actions to
mitigate or abate imminent hazards are required. However, Duke Energy is
investigating closure options for Roxboro, including a hybrid cap -in-place approach
where ash is consolidated and capped. This approach may require some ash to be
excavated and either relocated either to a different portion of the ash basin or be safely
recycled or reused in a lined structural fill or disposed in a lined landfill.
ES.3 Receptor Information
The requirement contained in the NORR and the CAMA concerning receptors was
completed with the results provided in Section 4.0. A screening level HHRA and
SLERA were conducted with the results provided in Section 12.0.
Land use surrounding the Site includes forest, pasture or rural residential properties
and limited commercial/industrial.
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. Based on
empirical data, no impact to private or public drinking water wells is evident.
ES.3-1 Public Water Supply Wells
No public supply wells were located by the receptor survey in the Site area
except a well located at the dry wall plant located east of the Plant and an
elementary school located west of the Site. The dry wall plant well, is located 785
feet east of the compliance boundary and the school is located 2,700 feet west and
upgradient of the compliance boundary.
ES.3-2 Private Water Supply Wells
Inventories of 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; however they are located upgradient to the
ash management areas. While 2L or IMAC were exceeded in some samples for
manganese and vanadium, these constituents are common to groundwater in the
region and their occurrence is not attributable to the ash basins.
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
ES.3-3 Human and Ecological Receptors
The exposure media for human receptors includes potentially impacted
groundwater, seeps, surface water, soil and sediments. The exposure routes
associated with the potentially completed exposure pathways evaluated for the
Site include ingestion, inhalation and dermal contact of environmental media.
Potential human receptors, current or future, include recreational users and
construction/industrial workers and residents.
The potential exposure media for ecological receptors includes impacted soil,
surface water, and sediments. Direct contact with groundwater does not present
a complete exposure pathway to ecological receptors. Exposure routes associated
with potentially completed exposure pathways include dermal contact,
incidental ingestion, and ingestion of prey or plants.
Constituents of potential concern (COPCs) for human and ecological receptors
identified using screening level risk assessment methodology for receiving areas
at the Site include: pH, aluminum, antimony, arsenic, barium, beryllium, boron,
chromium (total and hexavalent), cobalt, copper, iron, manganese, mercury,
molybdenum, nickel, selenium, sulfate, thallium, 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 criteria in the risk
assessment screening process.
ES.4 Sampling / Investigation Results
ES.4-1 Nature and Extent of Contamination
Antimony, arsenic, beryllium, boron, cobalt, iron, manganese, nickel, thallium,
sulfate, vanadium, pH and TDS have been detected in excess of the 2L or IMAC
in the saturated ash pore water or groundwater. The majority of the exceedances
occur in the ash pore water or bedrock samples. Cobalt, iron, manganese and
vanadium were also detected in the ash pore water; however these are also
naturally -occurring metals common to regional groundwater that were also
detected in several background wells at the Site, and therefore their occurrence at
the Site cannot be wholly attributed to the ash basins.
Nickel was detected above 2L in only one ash pore water sample and in the
bedrock sample from the same location in the West Ash Basin. The occurrence of
thallium was also limited, exceeding IMAC in only one location outside of the
ash basin area.
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
Sulfate above 2L is limited to the ash pore water and wells beneath and adjacent
to the ash basins. TDS is also limited to the ash basins and adjacent wells with the
exception of the upgradient well location MW -18.
MW -18 is a background well location approximately one mile southeast and
upgradient of the West Ash Basin. This well is located upgradient both
topographically and hydrologically from the ash basins and the majority of the
Site; as such it represents a background location. It differs from the other
background locations in that, in addition to concentrations of cobalt, iron,
manganese and vanadium exceeding 2L or IMAC, antimony, chromium and TDS
were also detected above 2L or IMAC at this location and cobalt was
considerably higher than at other locations. Additional data are needed to
understand this anomaly, although these results are unlikely to be from
migration of constituents from the ash basin.
ES.4-2 Maximum Contaminant Concentrations
Of the metals detected at the highest concentrations in ash pore water, cobalt,
iron, manganese and vanadium are the most prevalent in groundwater. Cobalt,
iron, manganese and vanadium were also detected in background wells and the
occurrence of these metals can also be somewhat attributed to regional
groundwater quality although, the iron and manganese concentrations in ash
pore water were considerably higher than background. Nickel and thallium are
limited in their occurrence. Arsenic, boron, nickel and thallium are COIs that
were not observed in background conditions and are likely attributable to the ash
basins. The occurrence of nickel and thallium are very limited.
Arsenic is detected only in ash pore water samples above 2L. It was detected
above 2L in every ash pore water sample. It is not detected in seeps, surface
water or groundwater outside of the ash basin. The concentrations of arsenic in
the ash pore water range from 10.4 µg/l to 976 µg/1.
The highest concentration of boron was detected in the ash pore water sample
AMBW-04 at 36,800 µg/1. Boron is only detected above 2L in two wells outside of
the ash basins, downgradient wells MW -51) and MW-3BR. Boron was detected
above 2L in bedrock wells within the ash basins at ABMW-5D, ABMW-3BR,
GMW-8 and GMW-11 and in transition zone well GMW-06. The highest boron
concentration detected in groundwater was 4,060 pg/l in ABMW-3BR. The
highest concentration of boron in seep samples was 9,540 µg/l at S-09 east of the
East Ash Basin.
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
The highest concentration of iron in ash pore, groundwater or seep samples was
62,000 µg/l in ABMW-03. The highest concentration of iron in groundwater
outside of the ash basins was 4,000 µg/1 at MW-13BR, upgradient of the ash
basin. The highest iron concentration in designated background wells was 898
µg/1.
The highest concentration of manganese was 5,880 µg/l in ABMW-03. The
highest concentration of manganese in groundwater was 18,800 µg/l at ABMW-
3BR, beneath the West Ash Basin and the highest concentration of manganese in
groundwater outside the ash basins was 2,500 µg/l at MW-1BR, east of the East
Ash Basin. The highest manganese concentration in designated background
wells was 690 µg/1.
The highest concentration of cobalt in groundwater, ash pore water or seeps was
369 µg/l in ABMW-03BR. The highest concentration of cobalt in groundwater
outside the ash basins was 4.2 µg/l at MW-2BR, between the East and West Ash
Basins. The highest cobalt concentration in designated background wells was
20.1 µg/l in MW-18BR.
The highest concentration of TDS was 4,300 µg/l in ash pore water from ABMW-
03BR. The highest concentration of TDS in groundwater outside the ash basins
was 2,100 µg/l at MW-3BR. The highest TDS concentration in designated
background wells was 580 µg/l in MW -18D.
The highest concentration of sulfate was 3,400 mg/l in ABMW-03BR. The highest
concentration of sulfate in groundwater outside the ash basins was 1,200 mg/l at
MW-2BR. The highest sulfate concentration in designated background wells was
130 mg/l in MW -18D.
ES.4-3 Source Characterization
The approximate size of the combined ash basins is 495 acres; the East Ash Basin
covers a slightly larger area than does the West Ash Basin. The total estimated
CCR inventory in both basins is 19,420,000 tons. The ash basins are located in
naturally -formed drainage basins, which are oriented roughly south to north,
and are impounded by earthen dams. Surface water runoff from the East Ash
Basin and the lined landfill are routed into the West Ash Basin to allow settling.
The ash in the West Ash Basin is approximately 80 feet thick with the base
elevation of approximately 390 feet mean sea level (msl), and the ash in the East
Ash Basin is approximately 55 to 80 feet thick with a base elevation of
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
approximately 410 msl. Ash was also used as structural fill below the lined
gypsum pad and is included in the inventory of ash stored at the Site.
The CCR includes fly ash and bottom ash. Overall, the ash was generally found
to be sand -sized with abundant silt and clay size particles. The CCR consists of
predominately quartz, feldspar and chlorite.
The ash samples from both basins were found to contain barium, beryllium,
copper, lead, mercury, and selenium above the United States Environmental
Protection Agency (USEPA) Mid -Atlantic Risk Assessment Regional Screening
Levels (RSL) — Protective of Groundwater (Table 7-3). Ash samples from the
West Ash Basin were also found to contain manganese above the protective of
groundwater RSL. Concentrations of aluminum, cobalt, iron, manganese and
vanadium were detected in ash basin samples above the residential health RSL.
Arsenic was detected above the industrial health RSL in most ash samples.
The USEPA Synthetic Precipitation Leaching Procedure (SPLP, Appendix C)
analyses indicated leachate concentrations exceeding 2L or IMAC for antimony,
arsenic, chromium, cobalt, iron, manganese, nitrate, and vanadium in samples
from both ash basins.
Antimony, arsenic, boron, cobalt, iron, manganese, sulfate, thallium, TDS and
vanadium were detected in ash pore water samples from both the ash basins
above the corresponding 2L or IMAC.
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.
No public supply wells were located by the receptor survey in the Site area
except a well located at the dry wall plant located east of the Site and two located
at an elementary school located west of the Site. The dry wall plant well, is
located 785 feet east of the compliance boundary and the school is located 2,700
feet west and upgradient of the compliance boundary.
No private drinking water wells, or wellhead protection areas, were found to be
located within the potential area of interest downgradient of the ash basins.
Private water wells were identified along Dunnaway Road, Johnson Road and
Archie Clayton Road and to the south on Daisy Thompson Road and Semora
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Comprehensive Site Assessment Report September 2015
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Road. Based on the anticipated groundwater flow path, none of the wells
identified in the water well survey are located downgradient of the ash basins.
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, cobalt, copper, iron, manganese, nickel,
sulfate, turbidity, 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 criteria in the risk assessment screening process.
ES.4-5 Regional Geology and Hydrogeology
The Geologic Map of North Carolina (1985) places the rocks of the Plant area in
the Charlotte Terrane: a belt of metamorphic rock trending generally southwest
to northeast characterized by strongly foliated felsic mica gneiss and schist and
metamorphosed intrusive rocks. The rocks of the area near the Plant are
described as biotite gneiss and schist with abundant potassic feldspar and garnet,
and interlayered and gradational with calc-silicate rock, silliminite-mica schist
and amphibolite.
Groundwater within the Site area exists under unconfined, or water table,
conditions within the residuum and/or saprolite zone and in fractures and joints
of the underlying bedrock. The water table and bedrock aquifers are
interconnected. The residuum acts as a reservoir for supplying groundwater to
the fractures and joints in the bedrock. Shallow groundwater generally flows
from local recharge zones in topographically high areas, such as ridges, toward
groundwater discharge zones, such as stream valleys.
ES.4-6 Site Geology and Hydrogeology
The subsurface at the Site is composed of regolith/saprolite, a transition zone and
bedrock. Alluvium was encountered at a few locations but was not common
across the Site. The dominant rock type was crystalline bedrock consisting of
biotite gneiss, felsic gneiss or granitic gneiss. Top of bedrock ranges from 8 to 48
feet below ground surface (bgs).
Groundwater at the Site exists under unconfined, or water table, conditions
within the regolith/saprolite zone, the transition zone and/or in fractures and
joints of the underlying bedrock. The water table and bedrock aquifers are
interconnected. Groundwater within the regolith/saprolite at the Site is limited,
with only three wells screened within this zone. While groundwater within the
transition zone was more common, it is not present across the entire Site. The
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Comprehensive Site Assessment Report September 2015
Roxboro Steam Electric Plant SynTerra
majority of the groundwater at the Site occurs within bedrock. Depth to water in
the saprolite and transition zone wells generally range from 40 to 50 feet bgs in
the upland background wells and 5 to 10 feet below top of casing (TOC) in the
downgradient wells.
Groundwater flow within both the saprolite/transition zone and bedrock aquifers
is to the north/northwest at the Site. Localized groundwater high zones are
centered around the ash basin, with radial flow in these areas.
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 BG -01, and
intermittently at CW -02, and CW -03. Chromium has exceeded the 2L in BG -01
intermittently. Sulfate and TDS consistently exceeds 2L in CW -05.
ES.4-8 Development of Site Conceptual Model
The hydrogeologic SCM is based on the configuration of the ash basins relative
to Site features including canals, and other surface water bodies. Based on a
review of soil boring data, monitoring well and piezometer installation logs
provided by Duke Energy, subsurface stratigraphy consists of the following
material types: topsoil, ash, structural fill, saprolite, partially
weathered/fractured rock (PWR), and bedrock. In general, saprolite, PWR, and
bedrock were encountered on most areas of the Site.
Groundwater beneath the Site occurs within the regolith/partially weathered
rock or competent bedrock with potentiometric levels ranging from 3 to 20 feet
below ground surface (bgs) along the downgradient compliance boundary and
greater than 35 feet bls upgradient of the ash basin. Water level measurements
indicate that groundwater generally flows from upland areas along the south,
west, and eastern boundaries to the north and west towards Hyco Reservoir.
Groundwater generally flows from the south to the north along the western
portion of the Site and from the east-southeast to the north-northwest across the
remainder of the Site.
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
SCM provided herein will also support the modeling and the preparation of the CAP.
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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. Additional groundwater sampling to refine background concentrations
statistically.
2. Monitoring of the natural seeps and springs to assess the impact of groundwater
discharging to surface water bodies.
ES.6 Conclusions
No imminent hazard to human health or the environment has been identified as a result
of groundwater migration from the ash basins.
Duke Energy is investigating closure options at the Site, including a hybrid cap -in-place
scenario. The impact of these closure options on long term groundwater quality will be
evaluated as part of the groundwater flow and transport modeling to be provided in the
CAP.
Data indicate that groundwater impact from ash pore water seepage is limited to
beneath the ash basins and downgradient in the areas between the ash basins and Hyco
Reservoir and the intake canal. Seeps represent preferential pathways of ash pore
water migration to surface water. A plan for future groundwater monitoring is
presented in Section 16 of this report. The CAP, based on the data presented in this
report and subsequent groundwater modeling, will be submitted within 90 days of this
report.
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