HomeMy WebLinkAboutNC0004979_Allen Assessment Work Plan_Final_20140925
Allen Steam Station Ash Basin
Proposed Groundwater
Assessment Work Plan
NPDES Permit NC0004979
September 25, 2014
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
Table of Contents
i
Table of Contents
Executive Summary .............................................................................................................. ES-1
1.0 Introduction .......................................................................................................................... 1
2.0 Site History........................................................................................................................... 2
2.1 Plant Description ...................................................................................................... 2
2.2 Ash Basin Description ............................................................................................... 2
2.3 Regulatory Requirements ......................................................................................... 3
3.0 Receptor Information ............................................................................................................ 5
4.0 Regional Geology and Hydrogeology ................................................................................... 6
5.0 Site Geology and Hydrogeology ........................................................................................... 7
6.0 Groundwater Monitoring Results .......................................................................................... 8
7.0 Assessment Work Plan ........................................................................................................ 9
7.1 Ash and Soil Sampling Plan ...................................................................................... 9
7.1.1 Boring and Sampling Methods ...................................................................... 9
7.1.2 Proposed Soil and Ash Sampling Locations and Depths ..............................10
7.2 Groundwater Sampling Plan ....................................................................................11
7.2.1 Well Installation and Development ...............................................................11
7.2.2 Hydrogeologic Evaluation .............................................................................12
7.2.3 Groundwater Sampling.................................................................................12
7.3 Surface Water Sampling Plan ..................................................................................12
7.3.1 Ash Basin Surface Water Samples ..............................................................12
7.3.2 Seep Samples ..............................................................................................13
7.4 Site Hydrogeologic Conceptual Model .....................................................................13
7.5 Site-Specific Background Concentrations ................................................................13
7.6 Groundwater Model .................................................................................................13
8.0 Proposed Schedule .............................................................................................................15
9.0 References..........................................................................................................................16
Appendix A – Notice of Regulatory Requirements Letter from John E. Skvarla, III, Secretary,
State of North Carolina, to Paul Newton, Duke Energy, dated August 13, 2014.
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
Table of Contents
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List of Figures
1. Site Location Map
2. Site Layout Map
3. Proposed Well and Sample Locations
List of Tables
1. Groundwater Monitoring Requirements
2. Monitoring Well Locations
3. Exceedances of 2L Standards
4. Environmental Exploration and Sampling Plan
5. Soil and Ash Parameters and Analytical Methods
6. Groundwater, Surface Water, and Seep Parameters and Analytical Methods
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
Executive Summary
ES-1
Executive Summary
Duke Energy Carolinas, LLC (Duke Energy), owns and operates the Allen Steam Station
(Allen), located along the Catawba River in Gaston County near the town of Belmont, North
Carolina (see Figure 1). Allen began operation in 1957 as a coal-fired generating station and
currently operates five coal-fired units. The coal ash residue from Allen’s coal combustion
process has historically been disposed in the station’s ash basin located to the south of the
station and adjacent to the Catawba River. The discharge from the ash basin is permitted by
the North Carolina Department of Environment and Natural Resources (NCDENR) Division of
Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES)
Permit NC0004979.
On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter to
Duke Energy, pursuant to Title 15A North Carolina Administrative Code Chapter (15A NCAC)
02L.0106. The NORR stipulates that for each coal-fueled plant owned, Duke Energy will
conduct a comprehensive site assessment (CSA) that includes a Groundwater Assessment
Work Plan (Work Plan) and a receptor survey. In accordance with the requirements of the
NORR, HDR is in the process of completing a receptor survey to identify all receptors within a
0.5-mile radius (2,640 feet) of the Allen ash basin compliance boundary. This receptor survey
will also address the requirements of the General Assembly of North Carolina Session 2013
Senate Bill 729 Ratified Bill (SB 729).
Soil and groundwater sampling will be performed to provide information pertaining to the
horizontal and vertical extent of potential soil and groundwater contamination. This will be
performed by sampling select existing wells, installing and sampling approximately 32 nested
monitoring well pairs (shallow and deep), and collecting soil and ash samples. This work will
provide additional information on the chemical and physical characteristics of site soils and ash,
as well as the geological and hydrogeological features of the site that influence groundwater
flow and direction and potential transport of constituents from the active ash basin and inactive
ash basin. Samples of ash basin water will be collected and used to evaluate potential impacts
to groundwater and surface water. In addition, seep samples will be collected from locations
identified in August 2014 (as part of Duke Energy’s NPDES permit renewal application) to
evaluate potential impacts to surface water.
The information obtained through implementation of this Work Plan will be utilized to prepare a
CSA report in accordance with the requirements of the NORR. If it is determined that additional
investigations are required during the review of existing data or data developed from this
assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating
additional sampling or investigations.
HDR will also perform an assessment of risks to human health or safety and to the
environment. This assessment will include the preparation of a conceptual site model
illustrating potential pathways from the source to possible receptors.
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
1.0 Introduction
1
1.0 Introduction
Duke Energy Carolinas, LLC (Duke Energy), owns and operates the Allen Steam Station
(Allen), located along the Catawba River in Gaston County near the town of Belmont, North
Carolina (see Figure 1). Allen began operation in 1957 as a coal-fired generating station and
currently operates five coal-fired units. The coal ash residue from Allen’s coal combustion
process has historically been disposed in the station’s ash basin located to the south of the
station and adjacent to the Catawba River. The discharge from the ash basin is permitted by
the North Carolina Department of Environment and Natural Resources (NCDENR) Division of
Water Resources (DWR) under the National Pollutant Discharge Elimination System (NPDES)
Permit NC0004979.
On August 13, 2014, NCDENR issued a Notice of Regulatory Requirements (NORR) letter to
Duke Energy, pursuant to Title 15A North Carolina Administrative Code (15A NCAC) Chapter
02L.0106. The NORR stipulates that for each coal-fueled plant owned, Duke Energy will
conduct a comprehensive site assessment (CSA) that includes a Groundwater Assessment
Work Plan (Work Plan) and a receptor survey. In accordance with the requirements of the
NORR, HDR is in the process of completing a receptor survey to identify all receptors within a
0.5-mile radius (2,640 feet) of the Allen ash basin compliance boundary. The NORR letter is
included as Appendix A.
On behalf of Duke Energy, HDR has prepared this proposed Work Plan for performing the
groundwater assessment as prescribed in the NORR. If it is determined that additional
investigations are required during the review of existing data or data developed from this
assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating
additional sampling or investigations.
HDR will also perform an assessment of risks to human health or safety and to the
environment. This assessment will include the preparation of a conceptual site model
illustrating potential pathways from the source to possible receptors.
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
2.0 Site History
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2.0 Site History
2.1 Plant Description
Allen is a five-unit, coal-fired, electric generating plant with a capacity of 1,140 megawatts
located on the west bank of the Catawba River on Lake Wylie, in Belmont, Gaston County,
North Carolina. The site is located east of South Point Road (NC 273) and the surrounding area
generally consists of residential properties, undeveloped land, and Lake Wylie (Figure 1). The
station’s ash basin is situated between the Allen station to the north and surface water divides to
the west (along South Point Road) and south (along Reese Wilson Road), which both drop in
elevation to the east toward Lake Wylie. The surface water divide along South Point Road likely
functions as a groundwater divide. The topography at the site generally slopes downward from
that divide toward Lake Wylie. The entire Allen site is approximately 1,009 acres in area.
2.2 Ash Basin Description
The station’s ash basin consists of an active ash basin and an inactive ash basin. The active
ash basin was commissioned in 1973 and is currently in operation.1 The inactive ash basin is
located to the north of the active ash basin and is not in operation. A large portion of the area
on top of the inactive ash basin is permitted as an industrial landfill by the NCDENR Division of
Waste Management (Permit No. 3612). The area contained within the ash basin waste
boundary, which is shown on Figures 2 and 3, is approximately 322 acres in area.
There are two earthen dikes impounding the active ash basin; the East Dike, located along the
west bank of Lake Wylie, and the North Dike, separating the active and inactive ash basins.
The surface area of the active ash basin is approximately 169 acres1 with an operating pond
elevation of approximately 633.5 feet. The full pond elevation of Lake Wylie is approximately
568.7 feet.
The ash basin is operated as an integral part of the station’s wastewater treatment system,
which receives flows from the ash removal system, coal pile runoff, landfill leachate, flue-gas
desulfurization (FGD) wastewater, the station yard drain sump, and stormwater flows. Due to
variability in station operations and weather, the inflows to the ash basin are highly variable.
The inflows from the ash removal system and other plant discharges are discharged through
sluice lines to the ash basin. Prior to 2009, all of the fly ash produced was sluiced to the ash
basin. Since 2009, fly ash has been dry-handled and is infrequently sluiced to the ash basin.
All of the bottom ash produced by the station is sluiced to the ash basin.
Effluent from the ash basin is discharged from the discharge tower via a 42-inch-diameter
reinforced concrete pipe, to Lake Wylie. The water surface elevation in the ash basin is
controlled by the use of stop logs in the discharge tower.
1 Information obtained from Duke Energy Carolinas, LLC CERCLA 104(e) Request for Information to US
Environmental Protection Agency, Allen Steam Station, dated March 26, 2009
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
2.0 Site History
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2.3 Regulatory Requirements
The NPDES program regulates wastewater discharges to surface waters, to ensure that surface
water quality standards are maintained. Allen operates under NPDES Permit NC0004979,
which authorizes Duke Energy to discharge once-through cooling water (Outfall 001); operate a
septic tank and ash pond with pH adjustment and domestic wastewater discharge, stormwater
runoff, ash sluice, water treatment system wastewaters, FGD system blowdown, landfill
leachate, and miscellaneous cleaning and maintenance wash waters (Outfall 002); coal yard
sump overflow (Outfall 002A); power house sump overflow (Outfall 002B); miscellaneous
equipment for non-contact cooling and sealing water (Outfall 003); and miscellaneous non-
contact cooling water, vehicle washwater, and intake screen backwash (Outfall 004) to the
Catawba River in accordance with effluent limitations, monitoring requirements, and other
conditions set forth in the permit. Furthermore, the NPDES Permit authorizes Duke Energy to
continue operation of the FGD wet scrubber wastewater treatment system discharging to the
ash settling basin through internal Outfall 005.
The NPDES permitting program requires that permits be renewed every five years. The most
recent NPDES permit renewal at Allen became effective on March 1, 2011, and expires May 31,
2015.
In addition to surface water monitoring, the NPDES permit requires groundwater monitoring.
Groundwater monitoring has been performed in accordance with the permit conditions
beginning in March 2011. NPDES Permit Condition A (11), Version 1.1, dated June 15, 2011,
lists the groundwater monitoring wells to be sampled, the parameters and constituents to be
measured and analyzed, and the requirements for sampling frequency and reporting results.
These requirements are provided in Table 1.
The compliance boundary for groundwater quality at the Allen ash basin site is defined in
accordance with Title 15A NCAC 02L .0107(a) as being established at either 500 feet from the
waste boundary or at the property boundary, whichever is closer to the waste. The location of
the ash basin compliance monitoring wells, the ash basin waste boundary, and the compliance
boundary are shown on Figure 2.
The locations for the compliance groundwater monitoring wells were approved by the NCDENR
DWR Aquifer Protection Section (APS). All compliance monitoring wells included in Table 2 are
sampled three times per year (in March, July, and November). Analytical results are submitted
to the DWR before the last day of the month following the date of sampling for all compliance
monitoring wells except AB-9S, AB-9D, AB-10S, and AB-10D.
The compliance groundwater monitoring system for the Allen ash basin consists of the following
monitoring wells: AB-1R, AB-4S, AB-4D, AB-9S, AB-9D, AB-10S, AB-10D, AB-11D, AB-12S,
AB-12D, AB-13S, AB-13D, and AB-14D (shown on Figures 2 and 3). All the compliance
monitoring wells were installed in 2010.
One or more groundwater quality standards (2L Standards) have been exceeded in
groundwater samples collected at monitoring wells AB-1R, AB-4S, AB-4D, AB-9S, AB-9D, AB-
10S, AB-10D, AB-11D, AB-12S, AB-12D, AB-13S, AB-13D, and AB-14D. Exceedances have
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
2.0 Site History
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occurred for boron, iron, manganese, pH, and nickel. Table 3 presents exceedances measured
from March 2011, through July 2014.
Monitoring wells AB-4S, AB-9S, AB-10S, AB-12S, and AB-13S were installed with 15-foot well
screens placed above auger refusal to monitor the shallow aquifer within the saprolite layer.
Monitoring wells AB-4D, AB-9D, AB-10D, AB-11D, AB-12D, AB-13D, and AB-14D were installed
with either 5-foot or 10-foot well screens placed in the uppermost region of the fractured rock
transition zone.
Monitoring well AB-1R is located to the northwest of the inactive ash basin and is considered by
Duke Energy to represent background water quality at the site. AB-1R was installed with a 20-
foot well screen placed above auger refusal to monitor the shallow aquifer within the saprolite
layer.
With the exception of monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D, the ash basin
monitoring wells were installed at or near the compliance boundary. AB-11D is located to the
south of the active ash basin. Monitoring wells AB-12S, AB-12D, AB-4S, AB-4D, and AB-13S,
AB-13D are generally located to the west of the active ash basin. Monitoring well AB-14D is
located to the south of a portion of the inactive ash basin and near the western extent of the
property.
Monitoring wells AB-9S, AB-9D, AB-10S, and AB-10D are located inside of the compliance
boundary downgradient from the inactive and active ash basins (where it was not possible to
access the compliance boundary). Monitoring wells AB-9S and AB-9D are located to the
southeast of the inactive ash basin and AB-10S and AB-10D are located to the east of the
active ash basin. Compliance with 2L Standards (at the compliance boundary) for AB-9S, AB-
9D, AB-10S, and AB-10D is determined by using predictive calculations or a groundwater
model. For these four monitoring wells, Duke Energy uses a groundwater model to predict the
concentrations at the compliance boundary. The predicted results from the groundwater model
and the analytical results for samples collected during the sampling events are to be submitted
to the DWR annually.
Note that monitoring wells AB-1, AB-2, AB-2D, AB-5, AB-6A, AB-6R, and AB-8 were installed by
Duke Energy in 2004 and 2005 as part of a voluntary monitoring system.2 Voluntary monitoring
well AB-8 was found damaged and abandoned in 2010. No samples are currently being
collected from the voluntary wells. The existing voluntary wells are shown on Figure 3.
2 AB-1 and AB-8 were abandoned in 2010.
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
3.0 Receptor Information
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3.0 Receptor Information
The August 13, 2014 NORR states:
No later than October 14th, 2014 as authorized pursuant to 15A NCAC 02L
.0106(g), the DWR is requesting that Duke perform a receptor survey at each of
the subject facilities and submitted to the DWR. The receptor survey is required
by 15A NCAC 02L .0106(g) and shall include identification of all receptors within
a radius of 2,640 feet (one-half mile) from the established compliance boundary
identified in the respective National Pollutant Discharge Elimination System
(NPDES) permits. Receptors shall include, but shall not be limited to, public and
private water supply wells (including irrigation wells and unused or abandoned
wells) and surface water features within one-half mile of the facility compliance
boundary. For those facilities for which Duke has already submitted a receptor
survey, please update your submittals to ensure they meet the requirements
stated in this letter and referenced attachments and submit them with the others.
If they do not meet these requirements, you must modify and resubmit the plans.
The results of the receptor survey shall be presented on a sufficiently scaled
map. The map shall show the coal ash facility location, the facility property
boundary, the waste and compliance boundaries, and all monitoring wells listed
in the respective NPDES permits. Any identified water supply wells shall be
located on the map and shall have the well owner's name and location address
listed on a separate table that can be matched to its location on the map.
In accordance with the requirements of the NORR, HDR is in the process of completing a
receptor survey for Allen to identify all receptors within a 0.5-mile radius (2,640 feet) of the ash
basin compliance boundary to be submitted to NCDENR no later than October 1, 2014. This
receptor survey will also address the requirements of the General Assembly of North Carolina
Session 2013 Senate Bill 729 Ratified Bill (SB 729). The receptors include, but are not limited
to, 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 Allen ash basin compliance
boundary. The compliance boundary for groundwater quality, in relation to the ash basin, is
defined in accordance with Title 15A NCAC 02L .0107(a) as being established at either 500 feet
from the waste boundary or at the property boundary, whichever is closer to the source.
The receptor survey will include a map showing the coal ash facility location, the facility property
boundary, the waste and compliance boundaries, and all monitoring wells listed in the NPDES
permit. The identified water supply wells will be located on the map and the well owner's name
and location address listed on a separate table that can be matched to its location on the map.
During completion of the CSA, HDR will update the receptor information as necessary, in
general accordance with the CSA receptor survey requirements. If necessary, an updated
receptor survey will be submitted with the CSA report.
Duke Energy Carolinas, LLC | Proposed Groundwater Assessment Work Plan
Allen Steam Station Ash Basin
4.0 Regional Geology and Hydrogeology
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4.0 Regional Geology and Hydrogeology
North Carolina is divided into distinct regions by portions of three physiographic provinces: the
Atlantic Coastal Plain, Piedmont, and Blue Ridge (Fenneman, 1938). Allen is located in the
Charlotte terrane within the Piedmont province. The Piedmont province is bounded to the east
and southeast by the Atlantic Coastal Plain and to the west by the escarpment of the Blue Ridge
Mountains, covering a distance of 150 to 225 miles (LeGrand, 2004).
The topography of the Piedmont region is characterized by low, rounded hills and long, rolling,
northeast-southwest trending ridges (Heath, 1984). Stream valley to ridge relief in most areas
range from 75 to 200 feet. Along the Coastal Plain boundary, the Piedmont region rises from an
elevation of 300 feet above mean sea level, to the base of the Blue Ridge Mountains at an
elevation of 1,500 feet (LeGrand, 2004).
Charlotte terrane bedrock consists primarily of igneous and metamorphic bedrock. The
fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The
regolith includes, where present, the soil zone (a zone of weathered, decomposed bedrock
known as saprolite) and, where present, alluvium. Saprolite, the product of chemical and
mechanical weathering of the underlying bedrock, is typically composed of clay and coarser
granular material up to boulder size and may reflect the texture of the rock from which it was
formed. The weathering product of granitic rocks are quartz rich and sandy textured; whereas,
rocks poor in quartz and rich in feldspar and other soluble minerals form a more clayey
saprolite. The regolith serves as the principal storage reservoir for the underlying bedrock
(LeGrand 2004).
A transition zone may occur at the base of the regolith between the soil-saprolite and the
unweathered bedrock. This transition zone of partially weathered rock is a zone of relatively
high permeability compared to the overlying soil-saprolite and the underlying bedrock (LeGrand
2004).
Groundwater flow paths in the Piedmont are almost invariably restricted to the zone underlying
the topographic slope extending from a topographic divide to an adjacent stream. LeGrand
describes this as the local slope aquifer system. Under natural conditions, the general direction
of groundwater flow can be approximated from the surface topography (LeGrand 2004).
Groundwater recharge in the Piedmont is derived entirely from infiltration of local precipitation.
Groundwater recharge occurs in areas of higher topography (i.e., hilltops) and groundwater
discharge occurs in lowland areas bordering surface water bodies, marshes, and floodplains
(LeGrand 2004).
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Allen Steam Station Ash Basin
5.0 Site Geology and Hydrogeology
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5.0 Site Geology and Hydrogeology
Based on a review of soil boring and monitoring well installation logs provided by Duke Energy,
subsurface stratigraphy consists of the following material types: fill, ash, residuum, saprolite,
partially weathered rock (PWR), and bedrock. In general, residuum, saprolite, and PWR were
encountered on most areas of the site. Bedrock was encountered sporadically at a range of
depths across the site. Bedrock was encountered at approximately 10 feet below ground
surface (bgs) in areas on the southern extent of the site, approximately 29 feet bgs in areas on
the western extent of the site, and as deep as approximately 108 feet bgs in areas on the
eastern extent of the site near the Catawba River. In addition, alluvium is expected to be
present beneath the southern portion of the active ash basin where, based on historic USGS
topographic maps, two streams existed and flowed toward the Catawba River prior to
construction of the active ash basin. The general stratigraphic units, in sequence from the
ground surface down to boring termination, are defined as follows:
Fill – Fill material generally consisted of re-worked silts and clays that were borrowed from
one area of the site and re-distributed to other areas. Fill was used in the construction of
dikes and presumably as cover for the ash storage area and as cover for the Retired Ash
Basin Ash Landfill.
Ash – Of the logs reviewed, borings were advanced through ash in the area of the Retired
Ash Basin Ash Landfill only. Although previous exploration activities, for which Duke Energy
provided boring logs, did not evaluate the inactive portions of the retired ash basin, the ash
storage areas and the active ash basin, ash is expected to be present in these ash
management areas.
Alluvium – Alluvium was not encountered in the boring information provided to HDR.
However, alluvium is expected to be present beneath the southern portion of the active ash
basin where two streams previously existed and flowed toward the Catawba River prior to
construction of the active ash basin. Alluvium is unconsolidated soil and sediment that has
been eroded and redeposited by streams and rivers.
Residuum – Residuum is the in-place weathered soil that generally consists of white,
yellow, red, brown, gray, or olive sandy clay to silty sand. This unit was encountered in
various thicknesses across the site.
Saprolite – Saprolite is soil developed by in-place weathering of rock similar to the bedrock
that consists of brown, tan, or green silty sand with trace mica. The primary distinction from
residuum is that saprolite typically retains some structure (e.g., mineral banding) from the
parent rock. This unit was found in areas across the site and was described as white,
yellow, red, or brown silty extremely weathered rock with relict rock structure.
Partially Weathered Rock (PWR) – PWR occurs between the saprolite and bedrock and
contains saprolite and rock remnants. This unit was described as white to reddish yellow to
olive brown to dark gray with quartz and potassium feldspar fragments.
Bedrock – Bedrock was encountered in borings completed around the western, southern,
and eastern extents of the ash basin. Depth to top of bedrock ranged from 10 to 108 feet
below ground surface. Bedrock was described as granite, quartzite, and gabbro.
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Allen Steam Station Ash Basin
6.0 Groundwater Monitoring Results
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6.0 Groundwater Monitoring Results
From March 2011 through July 2014, the compliance groundwater monitoring wells at Allen
have been sampled a total of 11 times. During this period, these monitoring wells were sampled
in:
March 2011
July 2011
November 2011
March 2012
July 2012
November 2012
March 2013
July 2013
November 2013
March 2014
July 2014
With the exception of boron, iron, manganese, pH, and nickel, the results for all monitored
parameters and constituents were less than the 2L Standards. Table 3 lists the range of
exceedances for boron, iron, manganese, pH, and nickel for the sampling events listed above.
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Allen Steam Station Ash Basin
7.0 Assessment Work Plan
9
7.0 Assessment Work Plan
Soil and groundwater sampling will be performed to provide information pertaining to the
horizontal and vertical extent of potential soil and groundwater contamination. Based on readily
available site background information, and dependent upon accessibility, HDR anticipates
collecting soil and/or ash samples from 6 soil boring locations and during installation of
approximately 32 nested monitoring well pairs (shallow and deep). Groundwater samples will
be collected from the proposed monitoring wells. The proposed well and boring locations are
listed in Table 4 and shown on Figure 3. HDR may also resample select existing monitoring
wells to supplement groundwater quality data. This work will provide additional information on
the chemical and physical characteristics of site soils and ash, as well as the geological and
hydrogeological features of the site that influence groundwater flow and direction and potential
transport of constituents from the active ash basin and inactive ash basin.
Samples of ash basin water will be also be collected and used to evaluate potential impacts to
groundwater and surface water. If conditions allow for representative sampling, water samples
will be collected from seep sample locations (S-1 through S-9) identified in August 2014 (as part
of Duke Energy’s NPDES permit renewal application) to evaluate potential impacts to surface
water.
A summary of the proposed exploration plan, including estimated sample quantities and depths
of soil borings and monitoring wells, is presented in Table 4. If it is determined that additional
investigations are required during the review of existing data or data developed from this
assessment, Duke Energy and HDR will notify the NCDENR regional office prior to initiating
additional sampling or investigations.
7.1 Ash and Soil Sampling Plan
7.1.1 Boring and Sampling Methods
Prior to drilling each boring, all down-hole equipment and tools will be cleaned by washing with
high pressure hot water. A designated remote cleaning area will be established in the field.
Water for cleaning will be obtained from a tap or hydrant (to be designated) at Allen, or supplied
by the drilling contractor from an off-site source. Cleaning water will not require collection,
treatment, or disposal.
Borings will be advanced using hollow stem auger or roller cone drilling techniques to facilitate
collection of down-hole data. Standard Penetration Testing (SPT) (ASTM D 1586) and split-
spoon sampling will be performed at 2.5-foot to 5-foot increments using an 18-inch split-spoon
sampler. The sampler will be decontaminated with a non-phosphate detergent wash between
sampling depths. Ash and soil samples will be collected by the Project Scientist/Engineer.
Borings will be logged by the Project Scientist/Engineer and ash/soil samples will be observed,
visually classified, and photographed in the field for origin, consistency/relative density, color,
and soil type in accordance with the Unified Soil Classification System (ASTM D2487/D2488).
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Allen Steam Station Ash Basin
7.0 Assessment Work Plan
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Samples will be identified with a unique boring number and approximate collection depth (e.g.,
AB-21 (20-22’)). Sample containers will be provided by HDR’s contracted laboratory prior to
commencement of the on-site investigation. Samples will be delivered to the analytical
laboratory in time to extract the samples within their specified hold times (to be provided by the
laboratory). HDR will provide the name, phone number, and email address of the laboratory
project manager to facilitate sample analysis coordination.
Boring locations will be surveyed for horizontal and vertical control upon completion of the field
exploration program.
7.1.2 Proposed Soil and Ash Sampling Locations and Depths
HDR anticipates collection of soil and ash samples for laboratory analysis at 9 locations within
the active ash basin and on the north and east dikes (i.e., from monitoring well borings
designated as AB-20 through AB-28), 11 locations within the inactive ash basin and on the east
dike (i.e., from monitoring well borings designated as AB-29 through AB-39), and 6 soil boring
locations in the ash storage area (designated as SB-1 through SB-6). The borings located
within the waste boundary will extend approximately 20 feet below the ash/native soil interface
or to refusal, whichever is encountered first. In addition, HDR anticipates collection of soil
samples at three background locations (designated as BG-1 through BG-3).
Soil samples will not be collected for laboratory analysis during installation of monitoring wells
located outside the waste boundary (designated as GWA-1 through GWA-9). No borings will be
advanced within the footprint of the double-lined ash landfill located in the east portion of the
inactive ash basin. Proposed boring locations are shown on Figure 3.
CONSTITUENT SAMPLING AND ANALYSES
In general, ash is expected to be encountered in AB-series and SB-series borings. Ash
samples will be collected from shallow and deeper vertical intervals to evaluate variations in
type (e.g., fly ash or bottom ash) and chemical profile of the ash. In locations where ash
thickness is expected to be greater than 30 feet, a third ash sample may be collected from a
depth mid-way between the shallow and deeper intervals in a particular boring. Shallow ash
samples will be collected from the 4-foot to 5-foot intervals and deeper ash samples will be
collected from the 1-foot to 2-foot intervals overlying the ash/native soil interface. The depth of
deeper ash samples is expected to vary based on ash thickness at each specific boring
location. Ash samples will be analyzed by HDR’s subcontract laboratory for total and leachable
inorganic compounds, as presented in Table 5.
Soil samples will be collected below the ash/native soil interface and from the terminus of each
boring to characterize soil quality beneath the ash management areas. Soil samples will be
analyzed by HDR’s subcontract laboratory for total inorganics using the same constituents list
proposed for the ash samples.
INDEX PROPERTY SAMPLING AND ANALYSES
Physical characteristics of ash and soil will be tested both in the field and in the laboratory to
provide data for use in groundwater modeling. The location and depth of the index property
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samples will be based on site-specific geology and decided upon in the field. Based on HDR’s
current understanding of site-specific geology, five hydrostratigraphic units are present on-site.
In general, a minimum of five in-situ permeability tests, either falling or constant head tests, will
be performed in each of the hydrostratigraphic units. In addition, a minimum of five packer tests
will be performed in bedrock.
Laboratory testing of soil and ash collected from SPT samples will include tests for grain size
(with hydrometer), specific gravity, and porosity (calculation).
7.2 Groundwater Sampling Plan
Groundwater samples will be collected from the proposed wells shown on Figure 3.
Groundwater quality data may be supplemented through evaluation of historical data or re-
sampling of select existing monitoring wells. The purpose and anticipated construction details
of the proposed monitoring wells are as follows:
AB-series Wells – One shallow well screened across the water table (15-foot well
screen) and one deep well with screen installed in the transition zone (5-foot well screen
in weathered rock below auger refusal) will be installed at each location. The AB-series
well locations were selected to provide water quality data in, beneath, and adjacent to
the ash basin.
GWA-series Wells – One shallow well screened across the water table (15-foot well
screen) and one deep well with screen installed in the transition zone (5-foot well screen
in weathered rock below auger refusal) will be installed at each location. The GWA-
series well locations were selected to provide water quality data beyond the waste
boundary for use in groundwater modeling (i.e., to evaluate the horizontal and vertical
extent of potentially impacted groundwater around the ash basin).
BG-series Wells – One shallow well screened across the water table (15-foot well
screen) and one deep well with screen installed in the transition zone (5-foot well screen
in weathered rock below auger refusal) will be installed at each location. The
background well locations were selected to provide additional physical separation from
possible influence of the ash basin on groundwater. These wells will also be useful in
the statistical analysis to determine the site-specific background water quality
concentrations (SSBCs).
7.2.1 Well Installation and Development
SHALLOW MONITORING WELLS
At each monitoring well location specified on Figure 3 with an “S” qualifier in the well name (e.g.,
AB-21S), a shallow well will be constructed with a 2-inch-diameter, schedule 40 PVC screen
and casing. Each of these wells will have a 10-foot to 15-foot well screen (0.010-slot) set to
bracket the water table at the time of installation.
DEEP MONITORING WELLS
At each monitoring well location specified on Figure 3 with a “D” qualifier in the well name (e.g.,
AB-21D), a double-cased deep well will be constructed with a 6-inch-diameter PVC outer casing
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and a 2-inch-diameter PVC inner casing and well screen. The purpose of installing cased wells
at the site is to restrict vertical mixing within the shallow and deeper portions of the unconfined
aquifer during well installation. Outer well casings (6-inch casing) will be advanced to auger
refusal and set approximately 1 foot into PWR. Note that location-specific subsurface geology
will dictate actual casing depths on a per-well basis. Air rotary drilling will be used to advance
the borehole a minimum of 10 feet into PWR or bedrock with the intent of setting a 5-foot well
screen at least 10 feet below the bottom of the outer casing.
All newly installed monitoring wells will be developed using appropriate measures (e.g.,
agitation, surging, pumping, etc.). Water quality parameters (specific conductance, pH,
temperature and turbidity) will be measured and recorded during development and should
stabilize before development is considered complete. Development will continue until
development water is visually clear (target < 50 Nephelometric Turbidity Units (NTU) Turbidity)
and sediment free. Following development, sounding the bottom of the well with a water level
meter should indicate a “hard” (sediment free) bottom. Development records will be prepared
under the direction of the Project Scientist/Engineer and will include development method(s),
water volume removed, and field measurements of temperature, pH, conductivity, and turbidity.
7.2.2 Hydrogeologic Evaluation
Hydraulic conductivity (slug) tests will be completed in select monitoring wells under the
direction of the Project Scientist/Engineer. Slug tests will be performed to meet the
requirements of the NCDENR Memorandum titled, “Performance and Analysis of Aquifer Slug
Tests and Pumping Tests Policy,” dated May 31, 2007. Water level change during the slug
tests will be recorded by a data logger.
In addition, approximately 5 to 10 packer tests will be conducted during installation of the Type
III wells to facilitate permeability testing of the upper five feet of rock.
7.2.3 Groundwater Sampling
Subsequent to monitoring well installation and development, each newly installed well will be
sampled using low-flow sampling techniques. During low-flow purging and sampling,
groundwater is pumped into a flow-through chamber at flow rates that minimize or stabilize
water level drawdown within the well. Indicator parameters are measured over time (usually at
5-minute intervals). When parameters have stabilized within ±0.2 pH units and ±10 percent for
temperature, conductivity, and dissolved oxygen (DO), and ±10 millivolts (mV) for oxidation
reduction potential (ORP) over three consecutive readings, representative groundwater has
been achieved for sampling. Turbidity levels of 10 NTU or less will be targeted prior to sample
collection. Groundwater samples will be analyzed by a North Carolina certified laboratory for
the constituents included in Table 6. Select constituents may be analyzed for total and
dissolved concentrations.
7.3 Surface Water Sampling Plan
7.3.1 Ash Basin Surface Water Samples
Surface water samples will be collected from the active ash basin at the approximate open
water locations shown on Figure 3 (SW -1 through SW -4). At each location two water samples
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will be collected – one sample close to the surface (i.e., 0 to 1 foot from surface) and one
sample at the approximate middle depth of the water body. The middle depth sample will vary
based on the water level in the water body. In areas where the water body is less than 5 feet
deep, one water sample will be collected from the location at the approximate middle depth of
the water body. Ash basin surface water samples will be analyzed for the same constituents as
groundwater samples (Table 6). Select constituents may be analyzed for total and dissolved
concentrations.
7.3.2 Seep Samples
Water samples will be collected from the seep sample locations shown on Figure 3 (S-1 through
S-9). The seep samples will be collected for laboratory analysis of the constituents listed in
Table 6. Select constituents may be analyzed for total and dissolved concentrations. Duke
Energy collects surface water samples from Lake Wylie from upstream and downstream
locations for their existing NPDES permit requirements. If seep analytical results indicate
potential for impacts to Lake Wylie, then surface water quality data collected in Lake Wylie will
be reviewed.
7.4 Site Hydrogeologic Conceptual Model
The data obtained during the proposed assessment will be supplemented by available reports
and data on site geotechnical, geologic, and hydrologic conditions to develop a site
hydrogeologic conceptual model (SCM). The NCDENR document, “Hydrogeologic Investigation
and Reporting Policy Memorandum,” dated May 31, 2007 (Reference 6), will be used as general
guidance. In general, the SCM will utilize site information to characterize the geologic and
hydrogeologic characteristics of the area of interest, and, where appropriate, lead directly to the
proper construction of a groundwater flow and transport model.
7.5 Site-Specific Background Concentrations
Statistical analysis will be performed to determine the SSBCs to assess whether or not
exceedances can be attributed to naturally occurring background concentrations or attributed to
potential contamination. Specifically, the relationship between exceedances and turbidity will be
explored to determine whether or not there is a possible correlation due to naturally occurring
conditions and/or well construction.
7.6 Groundwater Model
Groundwater flow and chemical constituent fate and transport at the site will be modeled in
three dimensions using the MODFLOW -2005 groundwater flow numeric engine and the MT3D
transport model with linear isotherm sorption to predict chemical constituent concentrations over
time at the compliance boundary.
The groundwater model layers will be developed based on hydrogeologic properties and other
data obtained during the site investigation and the SCM. The model will include the effects of
recharge from precipitation.
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Site soil samples will be collected and used to develop site-specific distribution coefficient, Kd,
terms using batch methods (US EPA Batch-type procedures for estimating soil adsorption of
chemicals Technical Resource Document 530/SW-87/006-F).
The selection of the initial concentrations and the predictions of the concentrations for
constituents with respect to time are to be developed with consideration of the following data:
Site-specific analytical results from leach tests and from total digestion of ash samples
taken at varying locations and depths within the ash basin and ash storage piles (if
present),
Analytical results from appropriate groundwater monitoring wells or surface water
sample locations outside of the ash basin,
Analytical results from monitoring wells installed in the ash basin pore-water (screened
in ash), and
Published or other data on sequential leaching tests performed on similar ash.
The groundwater modeling will be conducted in general conformance with the requirements of
the May 31, 2007, NCDENR Memorandum titled, Groundwater Modeling Policy.
The groundwater model and the report on the results of the groundwater modeling will be
prepared by Dr. William Langley, P.E., Department of Civil and Environmental Engineering,
University of North Carolina at Charlotte. Dr. Langley will perform the work under contract with
HDR and the groundwater model report will be included as an attachment to the CSA. The
groundwater model will be used, as required, to evaluate options for potential corrective action
in the subsequent phase of work.
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8.0 Proposed Schedule
Duke Energy will submit the CSA Report within 180 days of NCDENR approval of this Work
Plan. The anticipated schedule for implementation of field work, evaluation of data, and
preparation of the Work Plan is presented in the table below.
Activity Start Date Duration to Complete
Field Exploration Program 10 days following Work Plan approval 75 days
Receive Laboratory Data 14 days following end of Exploration Program 15 days
Evaluate Lab/Field Data, Develop SCM 5 days following receipt of Lab Data 30 days
Prepare and Submit CSA 10 days following Work Plan approval 170 days
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9.0 References
16
9.0 References
1. Fenneman, Nevin Melancthon. “Physiography of eastern United States.” McGraw-Hill.
1938.
2. Heath, R.C., 1984, “Ground-water regions of the United States.” U.S. Geological Survey
Water-Supply Paper 2242, 78 p.
3. LeGrand, Harry E. 2004. “A Master Conceptual Model for Hydrogeological Site
Characterization in the Piedmont and Mountain Region of North Carolina, A Guidance
Manual,” North Carolina Department of Environment and Natural Resources Division of
Water Quality, Groundwater Section.
4. NCDENR Memorandum “Performance and Analysis of Aquifer Slug Tests and Pumping
Tests Policy,” May 31, 2007.
5. NCDENR document, “Hydrogeologic Investigation and Reporting Policy Memorandum,”
dated May 31, 2007.
6. US EPA Batch-type procedures for estimating soil adsorption of chemicals Technical
Resource Document 530/SW -87/006-F.
Figures
Tables
Table 1 – Groundwater Monitoring Requirements
Well Nomenclature Constituents and Parameters Frequency
Monitoring Wells: AB-1R, AB-4S,
AB-4D, AB-9S*, AB-9D*, AB-10S*,
AB-10D*, AB-11D, AB-12S, AB-12D,
AB-13S, AB-13D, AB-14D
Antimony Chromium Nickel Thallium
March, July,
November
Arsenic Copper Nitrate Water Level
Barium Iron pH Zinc
Boron Lead Selenium
Cadmium Manganese Sulfate
Chloride Mercury TDS
Note: Monitoring wells marked with * are located inside of the compliance boundary.
TABLE 2 – MONITORING WELL LOCATIONS
Monitoring Well Locations Monitoring Well
At or Near the Compliance
Boundary
AB-1R, AB-4S, AB-4D, AB-11D,
AB-12S, AB-12D, AB-13S,
AB-13D, AB-14D
Inside of the Compliance
Boundary
AB-9S, AB-9D, AB-10S, AB-10D
TABLE 3 – EXCEEDANCES OF 2L STANDARDS MARCH 2011 – JULY 2014
Parameter Boron Iron Manganese Nickel pH
Units µg/L µg/L µg/L µg/L SU
2L Standard 700 300 50 100 6.5 - 8.5
Well ID Range of Exceedances
AB -1R No
Exceedances 381 No
Exceedances
No
Exceedances 5.9 – 6.2
AB-4S No
Exceedances 314 – 555 64 – 285 No
Exceedances 5.8 – 6.1
AB -4D No
Exceedances
No
Exceedances
No
Exceedances
No
Exceedances 5.8 – 6.3
AB-9S 708 – 740 5,600 – 10,500 9,320 – 10,200 No
Exceedances 6.1 – 6.4
AB -9D No
Exceedances 356 – 909 95 No
Exceedances 6.4
AB -10S No
Exceedances 333 - 704 373 - 526 No
Exceedances 5.9 – 6.3
AB-10D No
Exceedances 307 – 881 53 – 144 No
Exceedances 5.9 – 6.4
AB-11D No
Exceedances 355 – 844 No
Exceedances
No
Exceedances 5.5 – 6.1
AB -12S No
Exceedances 573 53 – 56 No
Exceedances 4.7 – 5.2
AB-12D No
Exceedances 307 – 823 No
Exceedances
No
Exceedances 6.1 – 6.4
AB -13S No
Exceedances 324 – 817 55 – 165 No
Exceedances 5.3 – 5.9
AB-13D No
Exceedances 391 – 3,100 57 – 240 No
Exceedances 5.9 – 6.4
AB-14D No
Exceedances 301 – 8,350 52 – 945 104 – 544 5.2 – 6.2
TABLE 4 – ENVIRONMENTAL EXPLORATION AND SAMPLING PLAN
ALLEN STEAM STATION
Exploration
Area Soil Borings Shallow Monitoring Wells Deep Monitoring Wells Surface Water
Boring IDs Quantity
Estimated
Boring Depth
(ft bgs)
Well IDs Quantity
Estimated
Well Depth
(ft bgs)
Screen
Length
(ft)
Well IDs Quantity
Estimated
Casing Depth
(ft bgs)
Estimated
Well Depth
(ft bgs)
Screen
Length
(ft)
Quantity of
Locations
Quantity of
Samples
Active Ash
Basin
AB-20 through
AB-28 9 70-120 AB-20S through
AB-28S 9 15-50 10-15 AB-20D through
AB-28D 9 55-105 70-120 5 4 8
Inactive Ash
Basin
AB-29 through
AB-9, SB-1
through SB-6
17 45-110 AB-29S through
AB-39S 11 15-60 10-15 AB-29D through
AB-39D 11 30-95 45-110 5 N/A N/A
Beyond Waste
Boundary N/A 0 N/A GWA-1S through
GWA-9S 9 20-35 15 GWA-1D through
GWA-9D 9 30-75 45-90 5 N/A N/A
Background BG-1, BG-2,
and BG-3 3 60-120 BG-1S, BG-2S,
and BG-3S 3 30-55 15 BG-1D, BG-2D,
and BG-3D 3 45-105 60-120 5 N/A N/A
Notes:
1. Estimated boring and well depths based on data available at the time of work plan preparation and subject to change based on site -specific conditions in the field.
2. Laboratory analyses of soil, ash, groundwater, and surface water samples will be performed in accordance with the constitu ents and methods identified in Tables 5 and 6.
3. Additionally, soils will be tested in the laboratory to determine grain size (with hydrometer), specific gravity, and perm eability.
4. During drilling operations, downhole testing will be conducted to determine in-situ soil properties such as horizontal and vertical hydraulic conductivity.
5. Actual number of field and laboratory tests will be determined in field by Field Engineer or Geologist in accordance with project specifications.
TABLE 5 – SOIL AND ASH PARAMETERS AND ANALYTICAL METHODS
INORGANIC COMPOUNDS UNITS METHOD
Antimony mg/kg EPA 6020
Arsenic mg/kg EPA 6020
Barium mg/kg EPA 6010
Boron mg/kg EPA 6010
Cadmium mg/kg EPA 6020
Chloride mg/kg SM4500-Cl-E
Chromium mg/kg EPA 6010
Copper mg/kg EPA 6010
Iron mg/kg EPA 6010
Lead mg/kg EPA 6020
Manganese mg/kg EPA 6010
Mercury mg/kg EPA Method 7470A/7471
Nickel mg/kg EPA 6010
pH SU EPA 9045
Selenium mg/kg EPA 6020
Thallium (low level) mg/kg EPA 6020
Zinc mg/kg EPA 6010
Notes:
1. Soil samples to be analyzed for Total Inorganics using USEPA Methods 6010/6020
and pH using USEPA Method 9045, as noted above.
2. Ash samples to be analyzed for Total Inorganics using USEPA Methods 6010/6020
and pH using USEPA Method 9045; select ash samples will also be analyzed for
leaching potential using SPLP Extraction Method 1312 in conjunction with USEPA
Methods 6010/6020. SPLP results to be reported in units of mg/L for comparison to
2L Standards.
1
TABLE 6 – GROUNDWATER, SURFACE WATER, AND SEEP PARAMETERS AND ANALYTICAL
METHODS
PARAMETER UNITS METHOD
FIELD PARAMETERS
pH SU Field Water Quality Meter
Specific Conductance mmho/cm Field Water Quality Meter
Temperature ºC Field Water Quality Meter
Dissolved Oxygen mg/L Field Water Quality Meter
Oxidation Reduction Potential mV Field Water Quality Meter
NPDES CONSTITUENTS
Antimony µg/L EPA 200.8 or 6020
Arsenic µg/L EPA 200.8 or 6020
Barium µg/L EPA 200.7 or 6010
Boron µg/L EPA 200.7 or 6010
Cadmium µg/L EPA 200.8 or 6020
Chloride mg/L EPA 300.0
Chromium µg/L EPA 200.7 or 6010
Copper mg/L EPA 200.7 or 6010
Iron µg/L EPA 200.7 or 6010
Lead µg/L EPA 200.8 or 6020
Manganese µg/L EPA 200.7 or 6010
Mercury µg/L EPA 245.1
Nickel µg/L EPA 200.7 or 6010
Nitrate as Nitrogen mg-N/L EPA 300.0
Selenium µg/L EPA 200.8 or 6020
Sulfate mg/L EPA 300.0
Thallium (low level) µg/L EPA 200.8 or 6020
Total Dissolved Solids mg/L EPA 160.1 or SM 2540C
Zinc mg/L EPA 200.7 or 6010
ADDITIONAL GROUNDWATER CONSTITUENTS
Alkalinity (as CaCO3) mg/L SM2320B
Calcium mg/L EPA 200.7
Ferrous Iron mg/L SM4500-Fe
Magnesium mg/L EPA 200.7
Potassium mg/L EPA 200.7
Sodium mg/L EPA 200.7
Sulfide mg/L SM4500S-F
Total Organic Carbon mg/L SM5310
Note:
1. Select constituents may be analyzed for total and dissolved concentrations.
Appendix A
Notice of Regulatory Requirements Letter from
John E. Skvarla, III, Secretary, State of North
Carolina, to Paul Newton, Duke Energy, dated
August 13, 2014.