HF Lee - Tech Memo_05-26-2017_20171006

Date: May 26, 2017
To: Ryan Czop (Duke Energy)
Cc: Kathy We b (S;��
From: Judd Mahan
TECHNICAL MEMORANDUM
File: 1026.104
Up-to-date BaAground Groundwater Data—H.F. Lee Ener
Complex
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 support of site assessment and corrective action activities:
0 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 layer; and
,01 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:
,01 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);
,01 Result is a statistical outlier identified for background sample data collected through
March 2017;
,01 Sample collection occurred less than a minimum 60 days between sampling events; and
,01 Non -detected results are greater than 2L/IMAC.
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 March 2017 within
each flow zone.
P: \ Duke Energy Progress.1026 \ Statistics_CAMA \ May 26 2017 - Updated Background Data Spreadsheets for
NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\HF Lee - Tech Memo_05-26-2017.docx

Up-to-date Background Groundwater Data May 26, 2017
H.F. Lee Energy Complex Page 2 of 2
BACKGROUND WELL NETWORK
The current background monitoring well network consists of wells installed within the surficial
and Cape Fear flow zones.
SURFICIAL
Eight background monitoring wells (IMW-IS, IMW-3S, AMW-11S, AMW-125, AMW-13S,
AMW-17S, SMW-2 and CCR-100S) are screened within the surficial flow zone. Table 1 presents
analytical results for the surficial flow zone. Sample results designated as statistical outliers or
those samples collected less than 60 days between sampling events are identified in Table 1.
The surficial background groundwater dataset satisfies the requirements for the minimum
number of ten samples to conduct statistical analysis for each constituent.
CAPE FEAR
Seven background monitoring wells (IMW-IBC, IMW-02BC, IMW-03BC, AMW-11BC, AMW-
12BC, AMW-13BC, and AMW-16BC) are screened in the Cape Fear flow zone. Table 1 presents
analytical results for the Cape Fear flow zone. Sample results designated as statistical outliers
or those samples collected less than 60 days between sampling events are identified in Table 1.
The Cape Fear background groundwater dataset satisfies the requirements for the minimum
number of ten samples to conduct statistical analysis for each constituent.
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\HF Lee - Tech Memo_05-26-2017.docx