Soil TM_20170526

Date: May 26, 2017
TECHNICAL MEMORANDUM
File: 1026.105
To: John Toepfer (Duke Energy); Kim Witt (Duke Energy)
Cc: Kathy Webb (SynTerra)
From: Jerry Wylie (SynTerra) 1(r
Subject: Up-to-date Background Soil Data —Mayo 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:
41' 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
y Provide updated spreadsheets of background data data for each facility.
Soil samples were collected from soil borings at the Mayo Steam Electric Plant (Site) in 2015
during the Comprehensive Site Assessment (CSA). 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.
Soil samples that meet the following criteria are considered valid for use in the statistic
calculations for background concentrations:
47 Soil sample is collected from a location that is not impacted by coal combustion
residuals or coal associated materials;
y Soil sample is collected from a location that is not impacted by other potential
anthropogenic sources of constituents; and
47 Soil sample is collected from the unsaturated zone, > 1 ft. above the seasonal high water
table elevation.
Based on the minimum ten sample dataset requirement established by NCDEQ no additional
background soil samples are projected for the Site.
Antimony 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, for some
or all samples, as revised in October 2016.
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 - Updated Background Data Spreadsheets for
NCDEQ \ Tech Memo - Response to NCDEQ 04282017 Letter \ Final \ Mayo - Soil TM 05262017.docx

Up-to-date Background Soil Data
May 19, 2017
Mayo Steam Electric Plant
ATTACHMENTS: Table 1: Unstaturated Background Soil Data Summary
Page 2 of 2
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 - Updated Background Data Spreadsheets for
NCDEQ \ Tech Memo - Response to NCDEQ 04282017 Letter \ Final \ Mayo - Soil TM 05262017.docx