Asheville - Tech Memo 05262017

TECHNICAL MEMORANDUM
Date: May 26, 2017 File: 1026.102
To: John Toepfer (Duke Energy)
Cc: Kathy Webb(S erra)
From: Todd Platingz�=4 ✓��
Subject: Up-to-date Bd Groundwater Data—Asheville 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:
y Collect a minimum of ten valid background groundwater samples, opposed to eight,
prior to the determination of background threshold values (BTVs) for constituents in
each flow lower; and
y Provide updated spreadsheets of background groundwater data for each facility.
NCDEQ requests that the updated background data spreadsheets contain strike-throughs of
data that may be omitted from the background data set due to one or more of the following
conditions:
y Sample pH is greater than or equal to 8.5 standard units (S.U.);
0 Sample turbidity is greater than or equal to 10 Nephelometric Turbidity Units (NTUs);
411 Result is a statistical outlier identified for background sample data collected through
March 2017;
y Sample collection occurred less than a minimum 60 days between sampling events; and
y Non-detected results are greater than 2L/lMAC.
Table 1 provides a summary of existing background well data for each flow system and
indicates which samples are considered for use in statistical calculations to determine
concentrations of naturally occurring (background) inorganic constituents in groundwater. The
following discussion quantifies the number of valid results collected through January 2017
within each flow zone. Sample results designated as statistical outliers or were collected less
than 60 days between sampling events are identified in Table 1. Groundwater sampling was
recently completed in April 2017 and when available these results will be able to augment the
dataset provided herein.
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 -Updated Background Data Spreadsheets for
NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\ Final\ Asheville - Tech Memo 05262017.docx

Quantification of Valid Background Groundwater Samples for Statistics May 26, 2017
Asheville Steam Electric Plant Page 2 of 2
BACKGROUND WELL NETWORK
The current background monitoring well network consists of wells installed within four flow
zones: alluvial, saprolite, transition zone, and bedrock.
ALLUVIAL
One background well (MW -10) is screened within the alluvial flow zone. MW -10 has been
sampled eleven times since March 2014. Potentially autocorrelated data, outliers, and and an
evolving parameter list result in the number of valid events ranging from four to eight
depending on the constituent. Additional samples will be collected to bring the total number of
valid samples to ten for all constituents by the end of first quarter (Q1) 2018. An analysis of the
potentially autocorrelated datasets is recommended and may demonstrate the dataset is
currently sufficient to perform statistical calculations. Subsequent outlier screening of the
alluvial background dataset may warrant additional sample collection.
SAPROLITE
Five background wells (CB -1, CB -9, CB-09SL, and MW -24S) are screened in the saprolite flow
zone. The data set currently satifies the requirements for the minimum number of samples to
conduct statistical analysis for all constituents.
TRANSITION ZONE
One background well (CB -01D) is screened within the transition zone. Six valid sample events
have occurred since April 2015. With the exception of radionuclides (Radium -226, Radium -228,
Uranium -233, Uranium -234, Uranium -236, and Uranium -238), the transition zone background
data set will satisfy the requirements for the minimum number of samples to conduct statistical
analysis by the fourth quarter (Q4) 2017 based upon a two month sampling frequency.
BEDROCK
Two wells (AMW-3B and CB-09BR) are screened in the bedrock flow zone. With the exception
of radionuclides the bedrock background data set currently satisfies the requirements for the
minimum number of samples to conduct statistical analysis. The data set will be sufficient to
conduct statistical analysis on all parameters following the Q3 2017 sampling event.
RECOMMENDATION OF ADDITIONAL BACKGROUND WELLS — GW -1
CLUSTER
Historical analytical data results of select coal ash indicator parameters for wells within the
GW -1 cluster indicate values of boron, strontium, sulfate, and TDS are consistent with other
background location results and similar to previously developed provisional proposed
background concentrations. This information was presented in a December 15, 2016 Technical
Memorandum. The inclusion of the GW -1 cluster in the statistical background evaluation
would provide nineteen additional sample events in the saprolite flow system, four additional
valid sample events in the transition zone (achieving the desired 10 discrete sample events) and
three additional sample events in the bedrock flow system. Once formally approved by DEQ
the GW -1 cluster will be incorporated into the background dataset.
ATTACHMENTS: Table 1: Background Analytical Results through March 2017
P: \ Duke Energy Progress.1026 \ Statistics _CAMA \ May 26 2017 -Updated Background Data Spreadsheets for
NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\ Final\ Asheville - Tech Memo 05262017.docx