HomeMy WebLinkAboutNC0038377_GW Assessment WP_20141001Groundwater Assessment Work Plan September 2014
Mayo Steam Electric Plant SynTerra
TABLE OF CONTENTS
SECTION PAGE
Executive Summary
1.0 Introduction ......................................................................................................................1
2.0 Site History and Source Characterization ...................................................................3
2.1 Plant Description .........................................................................................................3
2.2 Ash Basin ......................................................................................................................3
2.3 Groundwater Monitoring System ............................................................................3
3.0 Receptor Information ......................................................................................................5
4.0 Regional Geology and Hydrogeology .........................................................................7
5.0 Site Geology and Hydrogeology ...................................................................................8
6.0 Groundwater Monitoring Results ................................................................................9
6.1 Groundwater Analytical Results ..............................................................................9
6.2 Preliminary Statistical Evaluation Results ..............................................................9
7.0 Assessment Work Plan..................................................................................................11
7.1 Anticipated Ash Basin Boring Locations ...............................................................11
7.2 Anticipated Soil Boring Locations ..........................................................................12
7.2.1 Inside Ash Basin ..................................................................................................12
7.2.2 Outside Ash Basin ...............................................................................................12
7.3 Anticipated Sediment and Surface Water Locations ...........................................13
7.4 Anticipated Groundwater Monitoring Wells .......................................................13
7.4.1 General Construction, Development, Aquifer Testing ..................................13
7.4.2 Background Wells ...............................................................................................15
7.4.3 Ash Basin Area ....................................................................................................15
7.4.4 Downgradient Assessment Areas ....................................................................15
7.4.5 Groundwater Sampling .....................................................................................16
7.5 Influence of Pumping Wells on Groundwater System ........................................16
7.6 Site Conceptual Model .............................................................................................17
7.7 Development of Groundwater Computer Model ................................................17
8.0 Implementation Schedule and Report Submittal ....................................................18
9.0 References ........................................................................................................................20
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List of Figures
Figure 1 - Site Location Map
Figure 2 - Site Layout
Figure 3 - Geology Map
Figure 4 - Anticipated Sample Locations
List of Tables
Table 1 - Summary of Concentration Ranges for Constituents Detected Greater than
2L Standards
Table 2 - Groundwater Assessment Parameter List
Table 3 - Assessment Sampling Plan
List of Appendices
Appendix A - NCDENR Letter of August 13, 2014
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EXECUTIVE SUMMARY
Duke Energy Progress, Inc. (Duke Energy), owns and operates the Mayo Steam Electric
Plant (Mayo Plant), located near Roxboro, in Person County, North Carolina. The coal
ash residue from the coal combustion process has been placed in the plant’s ash basin,
which is permitted by the North Carolina Department of Environment and Natural
Resources (NCDENR) Division of Water Resources (DWR) under the National Pollution
Discharge Elimination System (NPDES) #NC003837.
In a letter dated August 13, 2014, the DWR requested that Duke Energy prepare a
Groundwater Assessment Plan to identify the source and cause of contamination, any
imminent hazards to public health and safety and actions taken to mitigate them, all
receptors and significant exposure pathways. In addition, the plan should determine
the horizontal and vertical extent of soil and groundwater contamination and all
significant factors affecting contaminant transport and the geological and
hydrogeological features influencing the movement, chemical, and physical character of
the contaminants.
The following assessment plan anticipates:
• Implementation of a receptor survey to identify public and private water supply
wells (including irrigation wells and unused or abandoned wells), surface water
features, and wellhead protection areas (if present) within a 0.5 mile radius of the
Mayo Plant waste compliance boundary;
• Installation of borings within the ash basin and former 1981 landfill permit #73-B
for chemical and geotechnical analysis of residuals and in-place soils;
• Installation of background soil borings;
• Installation of monitoring wells and piezometers;
• Collection and analysis of groundwater samples from existing site wells and newly
installed monitoring wells;
• Statistical evaluation of groundwater analytical data; and
• Development of a groundwater model to evaluate the long term fate and transport
of constituents of concern in groundwater associated with the ash basin.
The information obtained through this Work Plan will be utilized to prepare a
comprehensive site assessment (CSA) report in accordance with the Notice of
Regulatory Requirements (NORR). In addition to the components listed above, a
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human health and ecological risk assessment will be conducted. This assessment will
include the preparation of a conceptual site model illustrating potential pathways from
the source to possible receptors.
During the CSA process if additional investigations are required, NCDENR will be
notified.
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1.0 INTRODUCTION
Duke Energy Progress, Inc. (Duke Energy), owns and operates the Mayo Steam Electric
Plant (Mayo Plant), located near Roxboro, in Person County, North Carolina (Figure 1).
The Plant is a single unit, coal-fired electricity-generating facility. Coal combustion
residues (CCR) have historically been managed in the Plant’s on-site ash basin. 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 Pollution Discharge Elimination System (NPDES). Dry ash has been
hauled and disposed in the lined dry flyash (DFA) landfill located at the nearby
Roxboro Steam Electric Plant (near Semora, NC). It is anticipated that beginning in Fall
2014, CCR from the Plant will be managed in a newly constructed on-site landfill.
Groundwater monitoring has been performed in accordance with the conditions of
NPDES Permit #NC0038377 beginning in December 2010. A monitoring network of 10
compliance wells is employed. Elevated concentrations greater than the North Carolina
Administrative Code (NCAC) Title 15A Chapter 02L (g) groundwater quality standards
(2L Standards) for iron (seven wells, including background wells), manganese (nine
wells, including background wells), total dissolved solids (TDS; two wells), and boron
(one well, CW-2) have been detected. The compliance boundary for the Mayo ash basin
is defined in accordance with NCAC Title 15A Chapter 02L.0107(a) (T15 A NCAC 02L
.0107(a)) as being established at either 500 feet from the waste boundary or at the
property boundary, whichever is closest. Monitoring wells CW-1, CW-1D, CW-2, CW-
2D, CW-3, CW-4, CW-5, and CW-6 are located at or near the compliance boundary.
Wells BG-1 and BG-2 are located southwest, upgradient, of the ash basin and are
considered background wells.
In a Notice of Regulatory Requirements (NORR) letter dated August 13, 2014, the DWR
of the NCDENR requested that Duke Energy prepare a Groundwater Assessment Plan
to conduct a Comprehensive Site Assessment (CSA) in accordance with 15A NCAC 02L
.0106(g) to address elevated groundwater concentrations greater than 2L Standards at
the compliance boundary. A summary of the concentrations is provided in Table 1 and
a copy of the DWR letter is provided in Appendix A.
SynTerra has prepared this Groundwater Assessment Plan on behalf of Duke Energy to
fulfill the DWR letter request and to satisfy the requirements of NC Senate Bill 729 as
ratified August 2014.
Specifically, this document describes the plans to meet the requirements of 15A NCAC
02L .0106(g) including;
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• Identify the source and cause of contamination;
• Identify any imminent hazards to public health and safety and actions taken to
mitigate them in accordance to 15A NCAC 02L .0106(f);
• Identify receptors and significant exposure pathways;
• Determine the horizontal and vertical extent of soil and groundwater
contamination and significant factors affecting contaminant transport; and
• Determine geological and hydrogeological features influencing the movement,
chemical, and physical character of the contaminants.
The information obtained through this Work Plan will be utilized to prepare a
comprehensive site assessment (CSA) report in accordance with the requirements of the
NORR. In addition to the components listed above, a human health and ecological risk
assessment will be conducted. This assessment will include the preparation of a
conceptual site model illustrating potential pathways from the source to possible
receptors.
During the CSA process if additional investigations are required, NCDENR will be
notified.
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2.0 SITE HISTORY AND SOURCE CHARACTERIZATION
2.1 Plant Description
The Mayo Plant is a coal-fired electricity-generating facility located in Person County,
North Carolina, near the city of Roxboro. The location of the plant is shown on Figure
1. The Mayo Plant became fully operational in June 1983.
The plant is located on Boston Road (US Highway 501) north of Roxboro. The northern
plant property line extends to the North Carolina/Virginia state line. The overall
topography of the Plant generally slopes toward the east (Mayo Reservoir) and
northeast (Crutchfield Branch).
2.2 Ash Basin
The Mayo Plant ash basin is approximately 153 acres in size with an earthen dike. Ash
generated from the plant’s coal combustion is contained in the ash basin. The Mayo
Plant NPDES permit (NC0038377) authorizes two discharges to Mayo Lake. Outfall 001
discharges cooling tower water and circulating water system discharge water. Outfall
002 is comprised of a number of streams including internal outfall 008 (cooling tower
blowdown), internal outfall 009 (FGD blowdown), ash transport water, coal pile runoff,
and other sources including water from wastewater treatment processes. Stormwater
outfalls are also authorized for the Mayo Plant.
2.3 Groundwater Monitoring System
Ten wells comprise the compliance monitoring well network for the Mayo Plant, two
background wells and eight downgradient wells. The locations of the compliance
monitoring wells, the waste boundary, and the compliance boundary are shown on an
aerial image, Figure 2, and on a geologic map, Figure 3.
Monitoring wells BG-1 and BG-2 represent background groundwater quality
upgradient (southwest) of the ash basin. The compliance boundary wells on the east
side of the ash basin are well pair CW-1/CW-1D. Monitoring well CW-5 is the
compliance boundary well for the west side of the ash basin. Monitoring wells CW-
2/CW-2D, CW-3, CW-4, and CW-6 are downgradient compliance boundary wells to the
north and northeast of the ash basin.
In accordance with the current NPDES permit, the monitoring wells are sampled three
times per year in April, July, and November. The analytical results for the compliance
monitoring program are compared to the 2L Standards or site-specific background
concentrations. A summary of the NPDES monitoring requirements is provided below.
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It is proposed that monitoring for aluminum be discontinued. Aluminum is a very
common, naturally-occurring element in soil and rocks of the area. A preliminary
statistical evaluation indicates that aluminum concentrations in downgradient
compliance monitoring wells are not statistically significant increases (SSIs) over the
background well data set for the most recent sampling event. Further, aluminum is not
consistently monitored across the entirety of Duke Energy facilities, and there is no 2L
Standard for aluminum.
NPDES Groundwater Monitoring Requirements
Well
Nomenclature Parameter Description Frequency
Monitoring
Wells BG-1,
BG-2, CW-1,
CW-1D, CW-2,
CW-2D, CW-3,
CW-4, CW-5,
CW-6
Aluminum Chloride Mercury TDS
April, July,
and
November
Antimony Chromium Nickel Thallium
Arsenic Copper Nitrate Water Level
Barium Iron pH Zinc
Boron Lead Selenium
Cadmium Manganese Sulfate
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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, SynTerra is in the process of
conducting a receptor survey to identify water supply wells, public water supplies,
surface water bodies, and wellhead protection areas (if present) within a 0.5 mile radius
of the Mayo Plant compliance boundary. The compliance boundary for groundwater
quality, in relation to the ash basins, is defined in accordance with 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 receptors include 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 Lee Plant compliance
boundary.
The survey consists of a review of publicly available data from NCDENR Department
of Environmental Health (DEH), Virginia Department of Environmental Quality, NC
OneMap GeoSpatial Portal, DWR Source Water Assessment Program (SWAP) online
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database, Person County GIS, Environmental Data Resources, Inc. (EDR) Records
Review, the USGS National Hydrography Dataset (NHD), as well as a vehicular survey
along public roads located within 0.5 mile radius of the compliance boundary.
Two primary surface water features are present within the 0.5 mile radius of the
compliance boundary. Mayo Lake, located to the east of the Plant, is a 2,800-acre lake
formed in 1977. Crutchfield Branch is a prominent fluvial surface water drainage
feature on the Plant. Crutchfield Branch originates near the base of the ash basin and
flows towards the north/northeast, crossing into Virginia, and eventually merging with
Mayo Creek.
Additional receptor information will be collected as part of the anticipated assessment
to comply with the CSA guidelines (NCDENR August 2014).
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4.0 REGIONAL GEOLOGY AND HYDROGEOLOGY
The Mayo Plant is situated in the eastern Piedmont Region of north-central North
Carolina. The Piedmont is characterized by well-rounded hills and rolling ridges cut by
small streams and drainages. Elevations in the area of the Mayo Plant range between
570 feet above mean sea level (msl) near the Plant entrance along Boston Road to 360
feet msl in the Crutchfield Branch stream area on the north side of the Plant.
Geologically, the Plant is located at the contact between two regional zones of
metamorphosed intrusive rocks: the Carolina Slate Belt (now referred to as Carolina
Terrane) on the east and the Charlotte Belt (or Charlotte Terrane) to the west (Figure 3).
The majority of the Mayo Plant, including the largest portion of the ash basin and Mayo
Lake are situated in the Carolina Terrane (USGS, 2007). The characteristics and genesis
of the rocks within these regional metamorphic belts have been the subject of intense
study to describe the geology in tectonic, structural, and/or litho-stratigraphic terms
(Hibbard, et. al., 2001).
Rocks of Charlotte Terrane are characterized by strongly foliated felsic mica gneiss and
schist and metamorphosed intrusive rocks. Carolina Terrane rocks in the vicinity of the
Plant are typically felsic meta-volcanics and meta-argillites. This is consistent with the
description of the geologic nature of the area according to the Geologic Map of North
Carolina (1985). The Geologic Map of North Carolina describes the felsic meta-volcanic
rock as metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray;
interbedded with mafic and intermediate volcanic rock, meta-argillite and meta-
mudstone. The felsic mica gneiss of the Charlotte Terrane is described as being
interlayered with biotite and hornblende schist. These general observations are
consistent with site-specific observations from well logs for the Mayo Plant, which
document the bedrock of the northwestern portion of the compliance boundary as
intermediate meta-volcanic rock and the bedrock of the remainder of the site as felsic
meta-volcanics or meta-argillites.
Rocks of the region, except where exposed in road cuts, stream channels, and steep
hillsides, are covered with unconsolidated material formed from the in-situ chemical
and physical breakdown of the bedrock. This unconsolidated material is referred to as
saprolite or residuum. Direct observations at the Mayo Plant confirm the presence of
residuum, developed above the bedrock, which is generally 10 to 30 feet thick. The
residuum extends from the ground surface (soil zones) downward, transitioning
through a zone comprised of unconsolidated silt and sand, downward through a
transition zone of partially weathered rock in a silt/sand matrix, down to the contact
with competent bedrock.
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5.0 SITE GEOLOGY AND HYDROGEOLOGY
Based on previous activities at the site, subsurface lithology beneath the Plant area is
comprised of tan, brown to orange sandy silt and fine to coarse sands grading into
partially weathered rock and then competent bedrock. The first occurrence of
groundwater tends to be within the partially weathered rock or competent bedrock at
depths ranging from nine to 20 feet below land surface (bls) along the downgradient
compliance boundary and greater than 30 feet bls upgradient of the ash basin. The
layout of the compliance boundary wells relative to the mapped geologic units is shown
on Figure 3.
Groundwater within the area exists under unconfined, also known as water table,
conditions within the residuum and/or saprolite zones and in the fractures and joints of
the underlying bedrock. The water table and bedrock aquifers are interconnected. The
residuum acts as a reservoir for water supply to the fractures and joints in the
underlying bedrock. Shallow groundwater generally flows from local recharge zones in
topographically high areas, such as ridges, toward groundwater discharge zones, such
as stream valleys. Ridge and topographic high areas may serve as groundwater
recharge zones. Groundwater flow patterns in recharge areas tend to develop a
somewhat radial pattern from the center of the recharge area outward toward the
discharge areas and are expected to mimic surface topography. The closest surface
water discharge for the plant is to the north-northeast at Crutchfield Branch and, for the
eastern portions of the property, to the east and Mayo Lake.
Routine water level measurements and corresponding elevations from the compliance
monitoring well network indicate that groundwater flows from upland areas
(southwestern portion of the property) towards the northeast and Crutchfield Branch.
The approximate groundwater gradient for July 2014 data was 135 feet (vertical
change) over 5,500 feet (horizontal distance) or 24.5 feet/1,000 feet as measured from
upgradient background well BG-2 to downgradient well CW-2. Groundwater elevation
data collected from the two well pairs indicate the vertical gradient tends to be
downward or neutral between the transition zone and upper bedrock.
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6.0 GROUNDWATER MONITORING RESULTS
6.1 Groundwater Analytical Results
July 2014 was the twelfth compliance monitoring event conducted in accordance with
the NPDES Permit. The routine analytical data indicates that boron, iron, manganese,
total dissolved solids (TDS) and pH tend to have concentrations greater than 2L
Standards. Boron tends to be detected near or greater than the 2L Standard in
compliance boundary well CW-2. Iron tends to be detected greater than the 2L
Standard in background wells BG-1 and BG-2 and compliance boundary wells CW-5
and CW-6. Manganese tends to be detected greater than the 2L Standard in
background well BG-2 and in compliance boundary wells CW-2, CW-2D, CW-5, and
CW-6. TDS tends to be similar to or greater than the 2L Standard in compliance
boundary wells CW-3 and CW-6. In general, the groundwater pH tends to be slightly
less than or within the 2L Standard range. The concentration ranges for the constituents
which are greater than the 2L Standards are provided in Table 1.
Antimony, barium, cadmium, chromium, lead, and thallium have each been detected in
at least one background or compliance boundary well at concentrations greater than the
2L Standard. However, these constituents have not been detected at elevated
concentration with regularity and are believed to be related to sample turbidity or
represent data outliers.
6.2 Preliminary Statistical Evaluation Results
As a preliminary evaluation tool, statistical analysis was conducted on the groundwater
analytical data collected between December 2010 and July 2014. The statistical analysis
was conducted in accordance with US EPA, Statistical Training Course for Ground Water
Monitoring Data Analysis, EPA530-R-93-003, 1992 and US EPA’s Statistical Analysis of
Groundwater Monitoring Data at RCRA Facilities; Unified Guidance EPA 530/R-09-007,
March 2009.
An inter-well prediction interval statistical analysis was utilized to evaluate the
groundwater data. The inter-well prediction interval statistical evaluation involves
comparing background well data to the results for the most recent sample date from
compliance boundary wells. Monitoring wells BG-1 and BG-2 are the upgradient
background wells. Monitoring wells CW-1, CW-1D, CW-2, CW-2D, CW-3, CW-4, CW-
5, and CW-6 are considered downgradient compliance boundary wells. Statistical
analysis was performed on the inorganic constituents with detectable concentrations for
the most recent routine sampling event (July 2014).
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The statistical analysis indicated statistically significant increases (SSIs) over
background concentrations for the following:
• CW-1 nitrate (however, the concentration is consistently much less than the 2L
Standard);
• CW-2 boron and sulfate (Concentrations for both constituents are consistently
less than the 2L Standard);
• CW-2D boron and sulfate (Concentrations for both constituents are consistently
less than the 2L Standard);
• CW-3 chloride and sulfate (Concentrations for both constituents are consistently
much less than the 2L Standard);
• CW-4 sulfate (however, the concentration is consistently much less than the 2L
Standard); and
• CW-6 chloride (which is consistently less than the 2L Standard), manganese
(which is consistently greater than the 2L Standard), and sulfate (which is
consistently less than the 2L Standard).
It is noteworthy that the current data for CW-5 indicates no SSIs over background
concentrations. Based upon topography and available water levels, CW-5 appears to be
located upgradient of the influence of the ash basin.
A more robust statistical analysis will be completed as part of the CSA using data from
additional background wells.
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7.0 ASSESSMENT WORK PLAN
The scope of work discussed in this plan is designed to meet the requirements of 15A
NCAC 02L .0106(g) which are:
• Identify the source and cause of contamination;
• Identify any imminent hazards to public health and safety and actions taken to
mitigate them in accordance to 15A NCAC 02L .0106(f);
• Identify all receptors and significant exposure pathways;
• Determine the horizontal and vertical extent of soil and groundwater
contamination and all significant factors affecting contaminant transport; and
• Determine geological and hydrogeological features influencing the movement,
chemical, and physical character of the contaminants.
The following sections generally describe anticipated assessment activities to fill data
gaps associated with the source, vertical and horizontal extent, in soil and groundwater,
for the constituents that are greater than the 2L Standards. The assessment may need to
be iterative with possible additional assessment activities prior to the preparation of the
CSA. Groundwater sample collected will generally be analyzed for the constituents
listed in Table 2. The following activities are anticipated at this time.
7.1 Anticipated Ash Basin Boring Locations
Borings are anticipated within the ash basin to determine the thickness of ash as well as
to determine the current residual saturation. Seven borings are anticipated in the ash
basin near the locations shown on Figure 4.
The borings may be conducted using Direct Push Technology (DPT) or Roto-Sonic
drilling (or other drilling methods), which is a core drilling method that employs
simultaneous high frequency vibration and low speed rotational motion along with
downward pressure to advance a recovery core barrel. The core barrel is generally
advanced at continuous intervals of 5 to 10 feet. The ash/soil core is then brought to the
surface and vibrated from the barrel into a plastic sleeve for visual classification, sample
collection, and optional storage in wooden core boxes. The Roto-Sonic cores will be
extended to approximately 20 feet below the bottom of the ash (if possible) to allow for
characterization of the underlying native soil, partially weathered rock or competent
bedrock.
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Ash samples will be collected for laboratory analysis of total metals and SPLP metals
plus various geotechnical parameters. To characterize the variation in ash composition,
two samples, a shallow and a deep, are anticipated at each location, if the ash thickness
is less than 20 feet. If the thickness is greater than 20 feet, three samples (shallow,
intermediate, and deep), may be collected. A summary of the boring details is provided
in Table 3. The depths at which the samples are collected will be noted on sample IDs.
7.2 Anticipated Soil Boring Locations
7.2.1 Inside Ash Basin
As discussed above, Roto-Sonic drilling (or similar technology) may be used to
conduct borings within the ash basin. These borings are anticipated to extend to
a depth of approximately 20 feet below the ash (if possible) to characterize the
native material below the ash basin.
Soil samples are anticipated at each of the boring locations immediately below
the ash and at the bottom of the borings to provide information on the vertical
distribution of metals beneath the basin. The soil samples will be analyzed for
total metals, SPLP metals, and geotechnical parameters (such as plasticity index,
grain-size w/ hydrometer, pH, and organic carbon content). A summary of the
anticipated boring details is provided in Table 3.
Following soil sample collection, the borings will be abandoned by filling with a
bentonite-grout mixture.
7.2.2 Outside Ash Basin
To characterize the vertical and horizontal extent of metals in soil or partially
weathered rock beyond the ash basin, background soil borings are anticipated at
the locations shown on Figure 4.
Hollow stem auger drilling (or similar technology) will be conducted along with
Standard Penetration Test (SPT) to complete the soil borings. Hollow stem auger
methods use continuous flight augers with a bit on the bottom that drives
cuttings to the surface during the drilling process. SPTs are generally performed
at five-foot intervals in the borings. Soil samples are obtained with a standard
1.4-inch ID/2-inch outside diameter (OD) split-tube sampler. In conjunction with
the SPTs, split-spoon soil samples can be examined for visual soil classification
and laboratory testing.
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Along with split-spoon samples, relatively undisturbed samples are anticipated
for potential laboratory testing. Samples may be collected using a Shelby Tube
sampler to obtain the undisturbed samples per ASTM D1587 (2008).
Shallow and deep soil samples are anticipated at each boring location if possible.
The shallow soil samples would be collected from the 1-2 foot interval and the
deep soil samples would be collected from immediately above the water table to
provide information on the vertical distribution of metals beyond the ash basin
and to be used as comparison with those soil samples collected below the ash
basin. The collected soil samples would be analyzed for total metals, SPLP
metals, and geotechnical parameters (Table 3). If the water table occurs below
the depth of competent bedrock, a soil sample near the depth of auger refusal
may be collected as the ‘deep’ soil sample.
Following collection of the soil samples, the borings will be abandoned by filling
with a bentonite-grout mixture.
7.3 Anticipated Sediment and Surface Water Locations
Surface water and sediment samples are not anticipated at this time. Data associated
with recent seep sampling will be used to infer preferential pathways and migration
from groundwater to surface water in various areas of the plant. Seep data analysis
may be used to guide the collection of additional sediment or surface water data in the
future.
7.4 Anticipated Groundwater Monitoring Wells
A number of monitoring wells, piezometers and former plant production wells are
present at the site. These existing wells will be supplemented with additional wells to
complete the CSA.
7.4.1 General Construction, Development, Aquifer Testing
Monitoring wells and piezometers will be constructed by North Carolina-
licensed well drillers. Drilling equipment will be decontaminated prior to use at
each location using a high pressure steam cleaner.
Monitoring wells will be constructed of 2-inch ID, National Sanitation
Foundation (NSF) grade polyvinyl chloride (PVC) (ASTM 2012a,b) schedule 40
flush-joint threaded casing and 0.010-inch machine-slotted screen.
Monitoring wells will be installed as nested Type II wells at each location. A
shallow well will be installed with the top of the well screen approximately 5 feet
below the water table if possible. Based upon available drilling logs, the
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residuum appears dry while drilling. Observable water tends to occur within the
partially weathered rock (transition zone) and within competent bedrock. The
deeper well will be installed to a depth of the first observed water bearing zone
below the shallow screened interval, likely in competent bedrock. This will
provide information on the vertical distribution of aquifer characteristics
(chemistry and aquifer parameters) as well was determining the vertical
hydraulic gradient.
For nested Type II wells, the well screen intervals will typically be a 10 foot
length for the shallow well and a 5 foot length for the deeper well. The deeper of
the nested wells will be installed first. The annular space between the borehole
wall and the well screens will be filled with clean, well-rounded, washed, high
grade No. 2 silica sand. The sand pack will be placed to approximately 2 feet
above the top of the slotted screen, and then a pelletized bentonite seal will be
placed above the filter pack to just below the elevation of the anticipated bottom
of the shallow well. The sand pack for the shallow well will then be placed to
approximately 2 feet above the slotted screen. At a minimum, a 2-foot pelletized
bentonite seal will be placed above the filter pack of the shallow screen. The
remainder of the annular space will be filled with a neat cement grout from the
top of the upper bentonite seal to near ground surface.
The monitoring wells will be completed with either steel above ground
protective casings with locking caps or steel flush-mount manholes with locking
expansion caps, and well tags. The protective covers will be secured and
completed in a concrete collar and 2-foot square concrete pad.
Following installation, the monitoring wells will be developed in order to
remove drill fluids, clay, silt, sand, and other fines which may have been
introduced into the formation or sand pack during drilling and well installation,
and to establish communication of the well with the aquifer. Well development
will be performed using a portable submersible pump, which will be repeatedly
moved up and down the well screen interval until the water obtained is
relatively clear. Development will be continued by sustained pumping until
monitoring parameters (e.g., conductivity, pH, temperature) are generally
stabilized; estimated quantities of drilling fluids, if used, are removed; and,
turbidity decreases to acceptable levels.
After the wells have been developed, hydraulic conductivity tests (rising head
slug tests) will be conducted on each of the wells. The slug tests will be
performed in general accordance with ASTM D4044-96 Standard Test Method
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(Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining
Hydraulic Properties of Aquifers and NCDENR Performance and Analysis of
Aquifer Slug Test and Pumping Test Policy, dated May 31, 2007.
The data obtained during the slug tests will be reduced and analyzed using
AQTESOLV™ for Windows, version 4.5, software to determine the hydraulic
conductivity of the soils in the vicinity of wells.
7.4.2 Background Wells
Existing background wells BG-1 and BG-2 are positioned to provide
representative data for comparison with background groundwater conditions.
Additional background well data will be useful to broaden the range of potential
background groundwater concentrations. Therefore, two additional background
well pairs (BG-3/BG-3D and BG-4/BG-4D) are anticipated along the southern side
of the property as shown on Figure 4. A summary of the boring details is
provided in Table 3.
7.4.3 Ash Basin Area
To provide residual ash saturation and the depth to groundwater information,
three piezometer pairs are anticipated within the ash basin as shown on Figure 4.
A shallow piezometer, screened at the base of the ash, will be used to monitor
residual saturation. A deeper piezometer, screened approximately 10 to 20 feet
below the basin, will be used to monitor the aquifer below the basin.
7.4.4 Downgradient Assessment Areas
A preliminary review of site data and existing monitoring well locations indicate
that horizontal and vertical coverage around the compliance boundary is mostly
adequate to complete a CSA of the Mayo Plant with the following exceptions.
Near the northwest corner of the property, a bedrock well will be installed
adjacent to compliance boundary well CW-5 to monitor groundwater conditions
in the shallow bedrock at this location. In addition, a sentinel well pair will also
be installed near the intersection of Hwy 501 and Mayo Lake Road to confirm the
direction of groundwater flow is toward the northeast as would be expected
based upon topography. A well pair will be installed on the west side of Boston
Road, due west of the ash basin to monitor groundwater conditions at this
location.
A well pair will be installed downgradient of existing compliance well pair CW-
2/2D to monitor downgradient groundwater quality along Crutchfield Branch.
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Toward the northeast, a well near the compliance boundary on the east side of
the former 1981 landfill (Permit #73-B) and two well pairs further toward the
northeast are anticipated to provide potentiometric data to refine the
groundwater flow regime and water quality in the area.
To the east, an additional well pair is anticipated to the northeast of the plant.
The approximate locations of the additional monitoring well pairs are shown on
Figure 4. A summary of the boring details is provided in Table 3.
7.4.5 Groundwater Sampling
It is anticipated that groundwater samples will be collected using a low-flow
sampling technique consistent with compliance monitoring well sampling
protocol. The groundwater samples will be analyzed for the parameters listed in
Table 2. Total and dissolved metals analysis will be conducted. In addition to
the groundwater samples collected from the new monitoring wells, it is
anticipated that groundwater samples will be collected from one or more of the
existing site monitoring wells, as well as from the existing site water supply
wells, if possible. A summary of the anticipated groundwater samples is
included in Table 3.
During groundwater sampling activities, water level measurements will be made
at the existing site monitoring wells, piezometers, and new wells. The data will
be used to generate water table and potentiometric maps of the transition zone
and upper bedrock aquifer.
7.5 Influence of Pumping Wells on Groundwater System
There are three former plant water supply wells located on the southern side of the
property near the entrance road. The wells are no longer in use.
Preliminary information indicates 21 potential water supply wells may be located
within a 0.5 mile radius of the compliance boundary. The wells are believed to be
located greater than 0.25 miles from the ash basin and in topographically upgradient
positions. It is anticipated that due to the distance from the ash basin and likely limited
withdrawal rates, the use of the off-site wells should not substantially affect the
groundwater flow system near the ash basin. The anticipated new well pairs near the
southern side of the property and near the northwest corner of the property will be
used to confirm this assumption. Additional information on the potential off-site water
supply wells will also be collected as part of the assessment.
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7.6 Site Conceptual Model
Using existing hydrogeological site data along with data that will be generated during
the CSA activities, a Site Conceptual Model (SCM) will be prepared. The SCM will be
prepared in accordance with Evaluating Metals in Groundwater at DWR Permitted
Facilities (July 2012) and the NCDENR memorandum, Hydrogeologic Investigation and
Reporting Policy (May 31, 2007). The SCM will define the groundwater flow systems at
the site, horizontally and vertically, and provide a better understanding of the fate and
transport of constituents of concern in groundwater. This information will be used to
develop a groundwater computer model for Mayo Plant. Figure 4 shows the proposed
locations for geologic cross sections anticipated for the SCM.
7.7 Development of Groundwater Computer Model
Data from existing and new monitoring wells will be used to develop a groundwater
computer model of the system. The groundwater modeling will be conducted in
accordance with the requirements of the May 31, 2007 NCDENR memorandum,
Groundwater Modeling Policy.
At this time, it is anticipated that a numerical groundwater flow model will be
developed using the MODFLOW finite difference model that was developed by the
USGS and is one of the most widely accepted and widely used groundwater flow
models. The MODFLOW model will be created as a multi-layer flow model to better
determine the vertical flow component of the aquifer system which will allow for more
accurate fate and transport modeling. Once the model is created, it will be calibrated to
site conditions by modifying model inputs, such as hydraulic conductivity, within
established limits based on actual site data, until a reasonable match between the model
and actual site conditions is accomplished.
After the MODFLOW model is calibrated, the modeled flow data will be imported into
MT3D or RT3D and a fate and transport model will be created. MT3D and RT3D are
three-dimensional numerical solute fate and transport model, which will be used to
predict the short and long-term movement of the constituents of interest in
groundwater at the site and under the various predictive scenarios discussed above.
Due to the data requirements of the computer modelling, the computer model will be
completed after the majority of the groundwater assessment activities. The results of
the groundwater modelling are anticipated as an appendix to the CSA Report.
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8.0 IMPLEMENTATION SCHEDULE AND REPORT SUBMITTAL
Implementation will take place immediately following approval of this Groundwater
Assessment Plan by DWR. The anticipated schedule of activities and project
completion following plan approval is provided below.
• 10 days to begin field activities upon approval of plan
(Including, but not limited to, notification of public utility locate services,
road access clearing, container requests from laboratories for the soil and
groundwater samples, assemble information on existing site wells and
piezometers in addition to compliance boundary well information)
• 60 days to complete field activities
• Complete drilling activities
• Conduct slug tests
• Survey soil borings, wells, and other assessment locations
• Collect groundwater and other assessment samples
• Collect site-wide water levels
• Setup groundwater computer model
• 30 days after completion of field activities receive analytical data
• 60 days after receipt of analytical data evaluate results, conduct statistical
evaluation, prepare summary tables, develop CSM, and calibrate computer
model.
• 20 days to complete Assessment Report, per NC Senate Bill 729, August 2014.
• 90 days (up to 180 days) to complete computer modeling and Corrective Action
Plan.
• Conduct additional work as may be required to complete the CSA.
• 90 days to complete CSA preparation, review, and submittal, in accordance with
NCDENR guidance (August 2014).
Project Assumptions Include:
• No more than one iterative assessment step will be required;
• No off-site assessment or access agreements are anticipated;
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• DEP will make a diligent effort to collect all receptor information in accordance
with NCDENR guidance (August 2014); however, it is anticipated that all such
information may not be available;
• If off-site water supply wells sampling is deemed necessary, NCDENR staff may
be requested to assist with access;
• No special permitting is anticipated;
• Data may not reflect all seasonal or extreme hydrologic conditions;
• During the CSA process, if additional investigations are required NCDENR, will
be notified; and
• In addition to the components listed above, a human health and ecological risk
assessment will be conducted.
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9.0 REFERENCES
ASTM, D4044-96 Standard Test Method (Field Procedure) for Instantaneous Change in
Head (Slug) Tests for Determining Hydraulic Properties of Aquifers.
Dicken, Connie L., Suzanne W. Nicholson, John D. Horton, Michael P. Foose, and Julia
A.L. Mueller, December 2007, Preliminary integrated geologic map databases for the
United States – Alabama, Florida, Georgia, Mississippi, North Carolina, and South
Carolina, Version 1.1: United States Geological Survey, USGS Open File Report
2005-1323, < http://pubs.usgs.gov/of/2005/1323>.
Hibbard, James P., Edward F. Stoddard, Donald T. Secor, and Allen J. Dennis, 2002, The
Carolina Zone: overview of Neoproterozoic to Early Paleozoic peri-Gondwanan terranes
along the eastern Flank of the southern Appalachians: Earth Science Reviews, v. 57.
North Carolina Geological Survey, 1985, Geologic map of North Carolina: North Carolina
Geological Survey, General Geologic Map , scale 1:500000.
North Carolina Department of Environment and Natural Resources, May 31, 2007,
Groundwater Modeling Policy.
North Carolina Department of Environment and Natural Resources, May 31, 2007,
Hydrogeologic Investigation and Reporting Policy.
North Carolina Department of Environment and Natural Resources, May 31, 2007,
Performance and Analysis of Aquifer Slug Tests and Pumping Test Policy.
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FIGURES
P:\Progress Energy.1026\10. NC Sites\01. Seep And NPDES Permit Assistance\MAYO\dwg\Groundwater Assessment Plan Figures\DUKE MAYO-GW Assessment Figures.dwg
PROJECT MANAGER:
LAYOUT:
DRAWN BY:
KATHY WEBB
DATE:S. ARLEDGE
FIG 1 (USGS SITE LOCATION)
2014-09-25
FIGURE 1
SITE LOCATION MAP
MAYO STEAM ELECTRIC PLANT
10600 BOSTON RD
ROXBORO, NORTH CAROLINA
CLUSTER SPRINGS, VA QUADRANGLE
2000
GRAPHIC SCALE
1000
IN FEET
10000CONTOUR INTERVAL:
MAP DATE:
10ft
1987
148 RIVER STREET, SUITE 220
GREENVILLE, SOUTH CAROLINA
PHONE 864-421-9999
www.synterracorp.com
SOURCE:
USGS TOPOGRAPHIC MAP OBTAINED FROM THE NRCS GEOSPATIAL DATA GATEWAY AT
http://datagateway.nrcs.usda.gov/
MAYO LAKE POWER PLANT
PERSON COUNTY
RALEIGH
WILMINGTON
GREENVILLE
GREENSBORO
CHARLOTTE FAYETTEVILLE
PROPERTY BOUNDARY
500' COMPLIANCE
BOUNDARY
WASTE
BOUNDARY
6000 600 1200GRAPHIC SCALEIN FEETFIG 2 (SITE LAYOUT)2014-09-25J. WYLIES. ARLEDGEPROJECT MANAGER:LAYOUT NAME:DRAWN BY:CHECKED BY:K. WEBBDATE:DATE:FIGURE 2SITE LAYOUTwww.synterracorp.com148 River Street, Suite 220Greenville, South Carolina 29601864-421-9999LEGEND2014-09-25500 ft COMPLIANCE BOUNDARYDUKE ENERGY PROGRESS MAYO PLANTWASTE BOUNDARYMAYO STEAM ELECTRIC PLANT10600 BOSTON RDROXBORO, NORTH CAROLINABACKGROUND MONITORING WELL (SURVEYED)COMPLIANCE MONITORING WELL (SURVEYED)CW-1BG-1SOURCES:1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY,NORTH CAROLINA OBTAINED FROM THE NRCSGEOSPATIAL DATA GATEWAY AThttp://datagateway.nrcs.usda.gov/2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY,VIRGINIA WAS OBTAINED FROM NRCS GEOSPATIALDATA GATEWAY AT http://datagateway.nrcs.usda.gov/3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSPFLOWN ON APRIL 17, 2014.4. DRAWING HAS BEEN SET WITH A PROJECTION OFNORTH CAROLINA STATE PLANE COORDINATE SYSTEMFIPS 3200 (NAD 83).NORTH CAROLINA-VIRGINIA STATE LINE (APPROXIMATE)BOSTON RD(US HWY 501)MAYO LAKE RDMAYO LAKE RDOLD US 501
MULLINS LNLOUISIANA PACIFICCORPORATION10475 BOSTON RD(TIED INTO THE CITY OFROXBORO WATER LINE)RT HESTER RDRAILROADRAILROADRAILROADRAILROAD
HUELL
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BPOWERPLANTBOSTON RD(US HWY 501)RAILROAD WOODY LOOPCRUTCHFIELDBRANCHMAYO CREEKMAYO RESERVOIRMAYOCREEKCRUTCHFIELDBRANCHEDR 1FORMER US HWY 501RAW WATERINTAKESTRUCTUREBG-1BG-2CW-1CW-1DCW-2CW-6CW-2DCW-3CW-4CW-5ACTIVE ASH BASIN
CZfg
CZbg
CZfg
CZfg
PzZg
CZfv
CZfv
CZfv
CZfv
CZve
MAYO RESERVOIR
MAYO CREEK
CRUTCHFIELD BRANCH
CZfg
BOWES BRANCH
PzZg
148 RIVER STREET, SUITE 220
GREENVILLE, SOUTH CAROLINA 29601
PHONE 864-421-9999
www.synterracorp.com
PROJECT MANAGER:
LAYOUT:
DRAWN BY:
KATHY WEBB
DATE:S. ARLEDGE
FIG 3 (GEOLOGY MAP)
2014-09-25
FIGURE 3
GEOLOGY MAP
DUKE ENERGY PROGRESS
MAYO STEAM ELECTRIC PLANT
10600 BOSTON RD
ROXBORO, NORTH CAROLINA
DISCLAIMER
The information on this map was derived from digital databases at the NC Department of Transportation Website. Care was
taken in the creation of this map. SYNTERRA cannot accept any responsibility for errors, omissions, or positional accuracy.
There are no warranties, expressed or implied, including the warranty of merchantability or fitness for a particular purpose,
accompanying this product. However, notification of any errors will be appreciated.
CZbg
LEGEND - UNIT NAME
CZg METAMORPHOSED GRANITIC ROCK (EASTERN SLATE BELT)
CZfg FELSIC MICA GNEISS (CHARLOTTE AND MILTON BELTS)
PzZg METAMORPHOSED GABBRO AND DIORITE (EASTERN SLATE BELT)
BIOTITE GNEISS AND SCHIST (INNER PIEDMONT)
GEOLOGY SOURCE NOTE:
GEOLOGY SHAPEFILES OBTAINED FROM THE USGS Preliminary integrated geologic map databases for the United
States - Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina, DATED 2007 AT
http://pubs.usgs.gov/of/2005/1323/
CZfv FELSIC METAVOLCANIC ROCK (EASTERN SLATE BELT)
CZv METAVOLCANIC ROCK (CHARLOTTE AND MILTON BELTS)
CZve METAVOLCANIC-EPICLASTIC ROCK (EASTERN SLATE BELT)
CW-1
CW-6
CW-5
BG-1
BG-2
CW-4 CW-3
CW-2
MAYO STEAM ELECTRIC PLANT
10600 BOSTON RD
PERSON COUNTY
NEAR ROXBORO, NC
1500 0 1500 3000
GRAPHIC SCALE
IN FEET
500 ft COMPLIANCE BOUNDARY
DUKE ENERGY PROGRESS MAYO PLANT
WASTE BOUNDARY
CW-3 COMPLIANCE MONITORING WELL
LEGEND
4804806000 600 1200GRAPHIC SCALEIN FEETFIG 4 (CROSS SECTIONS)(11X17)2014-09-25J. WYLIES. ARLEDGEPROJECT MANAGER:LAYOUT NAME:DRAWN BY:CHECKED BY:K. WEBBDATE:DATE:FIGURE 4ANTICIPATED SAMPLELOCATIONSwww.synterracorp.com148 River Street, Suite 220Greenville, South Carolina 29601864-421-9999LEGENDBACKGROUND MONITORING WELL (SURVEYED)COMPLIANCE MONITORING WELL (SURVEYED)2014-09-25500 ft COMPLIANCE BOUNDARYDUKE ENERGY PROGRESS MAYO PLANTWASTE BOUNDARYCW-1EDR 1EDR REPORTED SUPPLY WELL (APPROXIMATE)PARCEL LINE (PERSON CO GIS)FLOW DIRECTIONBG-1DUKE ENERGY PROGRESS PRODUCTIONWELL - NOT IN SERVICE (APPROXIMATE)DEP 1MAYO STEAM ELECTRIC PLANT10600 BOSTON RDROXBORO, NORTH CAROLINAAW-3ANTICIPATED MONITORING WELL LOCATIONANTICIPATED SOIL BORING LOCATIONANTICIPATED ASH/SOIL BORING LOCATIONANTICIPATED GEOLOGIC CROSS SECTION2007 LiDAR CONTOUR MAJOR420SOURCES:1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY, NORTHCAROLINA OBTAINED FROM THE NRCS GEOSPATIAL DATAGATEWAY AT http://datagateway.nrcs.usda.gov/2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY, VIRGINIAWAS OBTAINED FROM NRCS GEOSPATIAL DATA GATEWAYAT http://datagateway.nrcs.usda.gov/3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSPFLOWN ON APRIL 17, 2014.4. WELL SURVEY INFORMATION, PROPERTY LINE, LANDFILLLIMITS AND BOUNDARIES ARE FROM ARCGIS FILESPROVIDED BY S&ME AND PROGRESS ENERGY.5. PARCEL BOUNDARIES WERE OBTAINED FROM PERSONCOUNTY (NC) GIS DATA AT http://gis.personcounty.net6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTHCAROLINA STATE PLANE COORDINATE SYSTEM FIPS 3200(NAD 83).7. 10ft CONTOUR INTERVALS FROM NCDOT LiDAR DATED 2007https://connect.ncdot.gov/resources/gis/pages/cont-elev_v2.aspx8. VIRGINIA 10ft CONTOUR INTERVALS FROM USGSTOPOGRAPHIC MAP OBTAINED FROM THE NRCSGEOSPATIAL DATA GATEWAY AThttp://datagateway.nrcs.usda.gov/NOTE:1. CONTOUR LINES ARE USED FOR REPRESENTATIVEPURPOSES ONLY AND ARE NOT TO BE USED FOR DESIGNOR CONSTRUCTION PURPOSES.BG-1BG-2CW-1CW-1DCW-2CW-6CW-2DCW-3CW-4NORTH CAROLINA-VIRGINIA STATE LINE (APPROXIMATE)BOSTON RD(US HWY 501)MAYO LAKE RDMAYO LAKE RDOLD US 501
MULLINS LNLOUISIANA PACIFICCORPORATION10475 BOSTON RDRT HESTER RDRAILROADRAILROADRAILROADRAILROAD
RAILROAD
HUELL
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)PERSON COUNTYHALIFAX COUNTY1
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BACTIVE ASH BASINPOWERPLANTBOSTON RD(US HWY 501)RAILROAD WOODY LOOPCRUTCHFIELDBRANCHMAYO CREEKMAYO RESERVOIRMAYOCREEKCRUTCHFIELDBRANCHEDR 1DEP 1DEP 3DEP 2FORMER US HWY 501RAW WATERINTAKESTRUCTURECW-5BG-3BG-3DBG-4BG-4DAW-3DAW-3AW-2DAW-2CW-7AW-1DAW-1CW-5DCW-7DCW-6CW-6DAW-4DAW-4MONITORING WELLS / PIEZOMETERS / SOILBORINGS (APPROXIMATE)MW-2MW-2PZ-1PZ-1APZ-2PZ-2APZ-3PZ-3APZ-4PZ-4AMW-4GENERALIZED GROUNDWATER FLOWDIRECTION•SUPPORTED BY GROUNDWATER ELEVATION DATAPOINTS OR TOPOGRAPHIC DATA
TABLES
TABLE 1SUMMARY OF CONCENTRATION RANGES FOR CONSTITUENTS DETECTED GREATER THAN 2L STANDARDSMAYO STEAM ELECTRIC PLANT DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINAPARAMETER ANTIMONY BARIUM BORON CADMIUM CHROMIUM IRON LEAD MANGANESE THALLIUM TDS pH2L STANDARD (eff. 4/1/2013)1700 70021030015500.2500 6.5 - 8.5Units (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l) (ug/l)(ug/l) (mg/l) SUBG-1 Background 0.13 - 4.2 90 - 1040 <2L<2L 4.7 - 40.1 261 - 65700 2.3 - 33.1 8.9 - 2270 <0.1 - 0.35 <2L 5.2 - 7.0BG-2 Background<2L <2L <2L<2L 5.9 - 10.2 152 - 2660 <2L 27 - 248 <2L<2L 6.3 - 6.6CW-1CB<2L <2L <2L 0.082 - 2.19 <2L<2L<2L 7 - 104<2L<2L 5.6 - 6.7CW-1DCB<2L <2L <2L<2L <5 - 11 <2L<2L 5 - 422<2L<2L <2LCW-2CB<2L <2L 351 - 785 <2L<2L<2L<2L 11.4 - 535 <2L<2L 5.0 - 6.1CW-2DCB<2L <2L <2L<2L<2L 48 - 522 <2L 33.5 - 270 <2L<2L 6.1 - 6.8CW-3CB<2L <2L <2L<2L<2L 21 - 908 <2L 12.1 - 481 <2L 421 - 520 6.3 - 6.7CW-4CB<2L <2L <2L<2L<2L 28 - 784 <2L<2L<2L<2L 5.8 - 6.4CW-5CB<2L <2L <2L<2L<2L 98.9 - 1080 <2L 387 - 706 <0.1 - 0.361 <2L 6.4 - 7.0CW-6CB<2L <2L <2L<2L<2L 1220 - 1870 <2L 1090 - 1440 <2L 417 - 550 6.5 - 7.1Notes:Prepared by: RBI Checked by: MCMCB - Compliance Boundary< 2L - Constituent has not been detected above the 2L Standard or beyond range for pHShown concentration ranges only include concentrations detected above the laboratory's reporting limit.Well IDWell Location Relative to Compliance BoundaryConcentration RangePage 1 of 1P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 1 Summary Concentration Ranges Mayo.xlsx
TABLE 2
GROUNDWATER ASSESSMENT PARAMETER LIST
MAYO STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINA
PARAMETER UNITS FIELD EQUIPMENT/
LAB METHOD
pH SU YSI Professional Plus or YSI 556 MPS
Specific Conductivity S/cm YSI Professional Plus or YSI 556 MPS
Temperature CYSI Professional Plus or YSI 556 MPS
ORP mV YSI Professional Plus or YSI 556 MPS
Dissolved Oxygen mg/L YSI Professional Plus or YSI 556 MPS
Turbidity NTU Hach 2100Q
Antimony g/L EPA 200.8
Arsenic g/L EPA 200.8
Barium mg/L EPA 200.7
Boron mg/L EPA 200.7
Cadmium g/L EPA 200.8
Chromium g/L EPA 200.8
Copper mg/L EPA 200.7
Iron mg/L EPA 200.7
Lead g/L EPA 200.8
Manganese mg/L EPA 200.7
Mercury g/L EPA 245.1
Molydbenum g/L EPA 200.8
Nickel g/L EPA 200.8
Selenium g/L EPA 200.8
Thallium (low level)g/L EPA 200.8
Zinc mg/L EPA 200.7
Nitrate as Nitrogen mg-N/L EPA 300.0
Ferrous Iron mg/L (Field Test Kit)
Sulfate mg/L EPA 300.0
Sulfide mg/L SM 4500 Sd
Methane mg/L RSK 175
Chloride mg/L EPA 300.0
Calcium mg/L EPA 200.7
Magnesium mg/L EPA 200.7
Sodium mg/L EPA 200.7
Potassium mg/L EPA 200.7
Bromide mg/L EPA 300.1
Total Organic Carbon mg/l EPA 5310
Alkalinity (as CaCO3)mg/L SM 2320B
Total Dissolved Solids mg/L SM 2540C
Prepared by: RBI Checked by: JAW
Notes:
SU - Standard Units mg/L - milligrams per liter
S/cm - microsiemens per centimeter NTU - Nephelometric Turbidity Units
C - degrees Celsius g/L - micrograms per liter
mV - millivolts mg-N/L - milligrams nitrate (as nitrogen) per liter
Field Parameters
Lab Parameters - Inorganics (Total & Dissolved)
Lab Parameters - Anions/Cations
Page 1 of 1
P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 2
Assessment Parameter List Mayo.xlsx
TABLE 3
ASSESSMENT SAMPLING PLAN
MAYO STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, INC., ROXBORO, NORTH CAROLINA
ASH
MANAGEMENT
AREA
BORING /
WELL ID
ESTIMATED
BORING
DEPTH
(ft bgs)
ESTIMATED
NO. OF
SAMPLES
SAMPLE
MEDIA
SAMPLE
DEPTHS/INTERVALS/
TARGET ZONES
LAB ANALYSIS PURPOSE/NOTES
AB-1
(and piezometer
pair location)
40 5
Ash
Ash
Ash
Soil
Soil
Water
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Water Level
Refine ash thickness, determine
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-2 40 5
Ash
Ash
Ash
Soil
Soil
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Refine ash thickness, determine
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-3
(and piezometer
pair location)
40 5
Ash
Ash
Ash
Soil
Soil
Water
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Water Level
Refine ash thickness, determine
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-4 40 5
Ash
Ash
Soil
Soil
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Water Level
Refine ash thickness, determing
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-5
(and piezometer
pair location)
40 5
Ash
Ash
Ash
Soil
Soil
Water
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Water Level
Refine ash thickness, determing
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-6 40 5
Ash
Ash
Ash
Soil
Soil
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Water Level
Refine ash thickness, determing
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
AB-7 40 5
Ash
Ash
Ash
Soil
Soil
1-2'
Mid Depth
Above ash/soil contact
2' Below ash/soil contact
Bottom of boring
Total metals + SPLP
Total metals + SPLP
Total metals + SPLP
Total metals + Geotech
Total metals + Geotech
Refine ash thickness, determing
residual saturation of ash, characterize
ash chemistry and leachability,
characterize soil chemistry beneath
ash, geologic cross section,
groundwater modeling
SB-5 40 2 Waste
Soil TBD Total metals + SPLP
Define waste thickness, characterize
waste chemistry and leachability,
characterize soil chemistry beneath
landfill, groundwater modeling
SB-6 40 2 Waste
Soil TBD Total metals + SPLP
Define waste thickness, characterize
waste chemistry and leachability,
characterize soil chemistry beneath
landfill, groundwater modeling
SB-1 30 2 Soil
Soil
1-2'
Just above the water table
Total metals + Geotech
Total metals + Geotech
Background soil quality in felsic gneiss
and groundwater modeling data
SB-2 30 2 Soil
Soil
1-2'
Just above the water table
Total metals + Geotech
Total metals + Geotech
Background soil quality near geologic
contact and groundwater modeling
data
SB-3 3 2 Soil
Soil
1-2'
Just above the water table
Total metals + Geotech
Total metals + Geotech
Background soil quality near geologic
contact and groundwater modeling
data
SB-4 30 2 Soil
Soil
1-2'
Just above the water table
Total metals + Geotech
Total metals + Geotech
Background soil quality in meta
volcanic rock and groundwater
modeling data
BG-3/BG-3D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Background water quality
Groundwater modeling
Sentinel wells
BG-4/BG-4D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Background water quality
Groundwater modeling
Sentinel wells
CW-5D 60 3
Soil
Soil
Water
Just above the water table
Within lower screen interval
Bedrock
Total metals
Total metals
Table 2 List
Groundwater flow direction
Groundwater modeling
CW-7/CW-7D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater flow direction
Groundwater modeling
AW-1/AW-1D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Background water quality
Groundwater modeling
Sentinel wells
AW-2/AW-2D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater modeling Groundwater
flow direction Horizontal and vertical
extent
AW-3/AW-3D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater flow direction
Groundwater modeling Background
water quality
AW-4/AW-4D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater modeling Background
water quality Sentinel wells
AW-5/AW-5D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater modeling Groundwater
flow direction Horizontal and vertical
extent
AW-6/AW-6D 30
50 4
Soil
Soil
Water
Water
Just above the water table
Within lower screen interval
Transition zone
Bedrock
Total metals
Total metals
Table 2 List
Table 2 List
Groundwater modeling Groundwater
flow direction Horizontal and vertical
extent
Site Production
Wells DEP 1,2 &3 unknown 3 Water Screened interval Table 2 List
Confirm no influence in lower bedrock
fractures, groundwater modeling
Existing
Monitoring Wells TBD Variable TBD Water
Well Screen Interval
(variable)Table 2 List Groundwater modeling and statistical
evaluation
Notes:
SPLP (Synthetic Preciptation Leaching Procedure) Metals - As, B, Ba, Cd, Cr, Cu, Fe, Hg, Mn,Mo, Ni, Pb, Sb, Se, Tl, and Zn.
Total Metals - As, B, Ba, Cd, Cr, Cu, Fe, Hg, Mn,Mo, Ni, Pb, Sb, Se, Tl, and Zn.
Geotech - Geotechnical parameters include moisture content, particle size distribution, Atterberg limits, specific gravity, and permeability.
Prepared by: KWW Checked by: HJF
Ash Basin
Background
Soil
Permitted Landfill
New Monitoring
Wells
P:\Duke Energy Progress.1026\ALL NC SITES\DENR Letter Deliverables\GW Assessment Plans\Mayo\Tables\Table 3‐Assessment Sampling Plan.xlsx Page 1 of 1
APPENDIX A
NCDENR LETTER OF AUGUST 13, 2014