Background Soil Dataset Evaluation_20161213_20161213

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Technical Memorandum
Date:
Tuesday, December 13, 2016
Project:
Marshall Steam Station
To:
Tyler Hardin
From:
Chad Hearn
Subject: Quantification of Valid Background Soil Samples for Statistical Calculations
The purpose of this memorandum is to provide the basis for evaluation of soil samples proposed for use
in determining site -specific background concentrations using statistical methods. The soil samples
evaluated herein were principally collected during Comprehensive Site Assessment (CSA) fieldwork
conducted between May and July 2015. The locations of soil samples evaluated for use in background
statistical calculations are shown on Figure 1.
Viability of samples for use in statistical calculations was evaluated using the following criteria:
• Soil sample is collected from a location that is not impacted by coal combustion residuals or coal -
associated materials;
• Soil sample is collected from a location that is not impacted by other potential anthropogenic
sources of constituents;
• Soil sample is collected from the unsaturated zone, above the maximum groundwater elevation
measured in shallow wells during seven well gauging events conducted between July 2015 and
September 2016; and
• Soil sample collected from a location not impacted by periodic flooding.
A total of 46 soil samples were collected at Marshall during CSA activities. Of these 46 samples, 7
samples satisfy the four criteria listed above and are considered viable samples for use in statistical
calculations. These samples were collected from the following locations on -site: BG-31D is located beyond
the compliance boundary northeast of the ash basin; GWA-1 BR is located at the southern end of the ash
basin dam; GWA-41D is located beyond the compliance boundary northwest of the ash basin; GWA-5D is
located near the compliance boundary north of the ash basin; and MW-14BR located within the
compliance boundary of the Dry Ash Landfill (Phase 1). Note that viable samples collected from borings
near the waste boundary or down -gradient of ash management areas were collected at least one foot
above the maximum measured groundwater elevation and are assumed to have not been impacted by
groundwater migrating from ash sources.
Soil sampling data used in this evaluation, including the range of groundwater elevations for shallow wells
in each well cluster and analytical results per well are provided in Table 1. Note that laboratory reporting
limit for antimony, arsenic, boron, selenium, and thallium exceeded the North Carolina Protection of
Groundwater (POG) Preliminary Soil Remediation Goals, as revised in October 2016. Revised laboratory
reports that will provide the non -detect values and method detection limits are in the process of being
obtained from the lab.

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NOTES:
1. PARCEL DATA FOR THE SITE WAS OBTAINED FROM DUKE ENERGY REAL ESTATE AND IS APPROXIMATE.
2. WASTE BOUNDARY AND ASH STORAGE AREA BOUNDARY ARE APPROXIMATE.
3. AS -BUILT MONITORING WELL LOCATIONS PROVIDED BY DUKE ENERGY.
4. SHALLOW MONITORING WELLS (S) ARE SCREENED ACROSS THE SURFICIAL WATER TABLE.
5. DEEP MONITORING WELLS (D) ARE SCREENED IN THE TRANSITION ZONE BETWEEN COMPETENT BEDROCK AND THE REGOLITH.
6. BEDROCK MONITORING WELLS (BR) ARE SCREENED ACROSS A ROCK FRACTURE ZONE WITHIN COMPETENT BEDROCK.
7. ORTHOPHOTOGRAPHY WAS OBTAINED FROM WSP (DATED APRIL 2014).
8. THE COMPLIANCE BOUNDARY IS ESTABLISHED ACCORDING TO THE DEFINITION FOUND IN 15A NCAC 02L .0107 (a).
9. HYDROGRAPHY WAS OBTAINED FROM USGS 7.5-MINUTE SERIES TOPOGRAPHIC MAPS TROUTMAN, NC.
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ELEVATION 790 FT (APPROXI
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AB-5BR
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AB-5 AB-3S
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INA
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SCALE (FEET)
250' 0 250' 500'
I" = 500'
LEGEND:
DUKE ENERGY PROPERTY BOUNDARY
ASH BASIN WASTE BOUNDARY
LANDFILL/STRUCTURAL FILL BOUNDARY
LANDFILL COMPLIANCE BOUNDARY
ASH BASIN COMPLIANCE BOUNDARY
ASH BASIN COMPLIANCE BOUNDARY COINCIDENT
WITH DUKE PROPERTY BOUNDARY
STREAM
ASH BASIN COMPLIANCE
GROUNDWATER MONITORING WELL
ASH BASIN VOLUNTARY
GROUNDWATER MONITORING WELL
GROUNDWATER MONITORING
WELL LOCATION
SOIL BORING LOCATION
EXISTING LANDFILL GROUNDWATER MONITORING
WELL (ASH LANDFILLS AND FGD RESIDUE LANDFILL)
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MONITORING WELL AND SAMPLE LOCATION
DUKE ENERGY CAROLINAS, LLC
MARSHALL STEAM STATION ASH BASIN
CATAWBA COUNTY, NORTH CAROLINA
DATE
DECEMBER 2016
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