Cape Fear TM BG Soils 2017-05-26

TECHNICAL MEMORANDUM
Date: May 26, 2017 File: 1026.103.27
To: John Toepfer (Duke Energy)
Cc: Kathy Webb (SynTerra), Ryan Czop (Duke Energy)
From: Chris Suttell
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Subject: Up-to-date Background Soil Data—Cape Fear Steam Electric Plant
The North Carolina Department of Environmental Quality (NCDEQ) provided a response letter
(Zimmerman to Draovitch, April 28, 2017) to the technical memorandum titled Statistical
Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash
Facilities (HDR Engineering, Inc. and Synterra Corporation, January 2017) requesting the following
technical issues be addressed in order to progress site assessments and corrective actions:
0 Collect a minimum of ten valid background soil samples, opposed to eight, prior to the
determination of background threshold values (BTVs) for constituents in soil; and
01 Provide updated spreadsheets of background data data for each facility.
Soil samples were collected from soil borings at the Cape Fear Steam Electric Plant (Site) in 2013
as part of a voluntary assessment, in 2015 during the Comprehensive Site Assessment (CSA),
and in 2016 as part of CSA data gap assessment. Table 1 provides a summary of the samples
(locations and depth intervals) which are considered for use in statistical calculations to
determine concentrations of naturally occurring (background) inorganic constituents in Site soil.
Statistical outliers omitted from the dataset are identified within Table 1. Figure 1 indicates the
location of soil samples to be used for statistical calculations.
Soil samples that meet the following criteria are considered valid for use in the statistic
calculations for background concentrations:
41, 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; and
h Soil sample is collected from the unsaturated zone, > 1 ft. above the seasonal high water
table elevation.
The background soil dataset satisfies the requirements for the minimum number of ten samples
to conduct statistical analysis for each constituent except antimony, selenium and thallium.
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 - Updated Background Data Spreadsheets for
NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\Cape Fear TM BG Soils 2017-05-26.docx

Up-to-date Background Soil Data
Cape Fear Steam Electric Plant
May 19, 2017
Page 2 of 2
Antimony, arsenic, cobalt, selenium, and thallium analytical results for samples collected
during CSA activities included in Table 1 had reporting limits greater than the PSRG for
Protection of Groundwater (POG), for some or all samples.
ATTACHMENTS: Table 1: Background Soil Data Summary
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 - Updated Background Data Spreadsheets for
NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\Cape Fear TM BG Soils 2017-05-26.docx