Sutton-GW Tech Memo_Final_20170526

Date: May 26, 2017
To: John Toepfer (Duke Energy)
Cc: Kathy Webb (Sy erra �'
From: Perr Waldr � �Gu' �
Y
Subiect: Up-to-date Ba round Q�'ot
TECHNICAL MEMORANDUM
water Data — L.V. Sutton
File: 1026.108
The North Carolina Department of >f`nvironmental Quality (NCDEQ) provided a response letter
(Zimmerman to Draovitch, Apri128, 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:
h 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
h Provide updated spreadsheets of background groundwater data for each facility.
NCDEQ requests that the updated background data spreadsheets contain strike-throughs of
data sets that may be omitted from the background data set due to one or more of the following
conditions:
�� Sample pH is greater than or equal to 8.5 standard units (S.U.);
h Sample turbidity is greater than or equal to 10 Nephelometric Turbidity Units (NTUs);
h Result is not a statistical outlier identified for background sample data collected through
March 2017;
h Sample collection occurred at a minimum 60 days between sampling events; and
h 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. 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\GROUNDWATER\Sutton\Sutton - GW Tech Memo_Final.docx

Up-to-date Background Groundwater Data May 26, 2017
L.V. Sutton Energy Complex Page 2 of 3
BACKGROUND WELL NETWORK
The current background monitoring well network consists of wells installed within four flow
zones: upper surficial, lower surficial, upper Pee Dee, and lower Pee Dee.
UPPER SURFICIAL ZONE
Five background wells (MW -4, MW4A, MW -5A, MW -5B and MW -37B) are screened within the
upper surficial flow zone. Table 1 presents analytical results for the upper surficial flow zone.
Sample results designated as statistical outliers or were collected less than 60 days between
sampling events are identified in Table 1. All constituents within the upper surficial
background groundwater dataset, with the exception of bromide (which is not a designated
constituent of interest); satisfy the requirements for the minimum number of ten samples to
conduct statistical analysis for each constituent. Additional samples will be collected which
could bring the total number of valid bromide samples to ten for all constituents by third
quarter 2017. Subsequent outlier screening of the upper surficial background dataset may
warrant additional sample collection to achieve at least ten valid bromide results.
LOWER SURFICIAL ZONE
Four background wells (MW -4B, MW -5C, MW -8, and MW -37C) are screened in the lower
surficial flow zone. Table 1 presents analytical results for the lower surficial flow zone. Sample
results designated as statistical outliers or were collected less than 60 days between sampling
events are identified in Table 1. All constituents within the lower surficial background
groundwater dataset except for chromium (VI) satisfy the requirements for the minimum
number of ten samples to conduct statistical analysis for each constituent. Additional samples
will be collected which could bring the total number of valid chromium (VI) samples to ten for
all constituents by second quarter 2017. Subsequent outlier screening of the lower surficial
background dataset may warrant additional sample collection to achieve at least ten valid
chromium (VI) results.
UPPER PEE DEE ZONE
Four background wells (MW-5CD, MW -5D, MW-37CD and MW -37D) are screened within the
upper Pee Dee zone. As discussed in SynTerra's Technical Memorandum dated December 14,
2016, conditions within upper and lower Pee Dee zones (i.e., presence of calcium carbonate and
occurrence of sea water intrusion) result in naturally -occurring higher pH values. Based on
results obtained from upper and lower Pee Dee background wells, a pH of less than or equal to
(<) 9.7 S.U. is proposed as the upper threshold for these zones.
Table 1 presents analytical results for the upper Pee Dee flow zone. Sample results designated
as statistical outliers or were collected less than 60 days between sampling events are identified
in Table 1. The upper Pee Dee background groundwater dataset does not satisfy the
requirement for the minimum number of ten samples to conduct statistical analysis for each
constituent. Additional samples will be collected which could achieve the desired sample size
by the end of second quarter 2017. Subsequent outlier screening of the lower surficial
P: \Duke Energy Progress.1026 \ Statistics_CAMA \May 26 2017 -Updated Background Data Spreadsheets for
NCDEQ\GROUNDWATER\Sutton\Sutton - GW Tech Memo_Final.docx

Up-to-date Background Groundwater Data May 26, 2017
L.V. Sutton Energy Complex Page 3 of 3
background dataset may warrant additional sample collection to achieve at least ten valid
results.
LOWER PEE DEE ZONE
Table 1 presents analytical data from two wells, MW -5E and MW -37E, screened in the lower
Pee Dee flow zone. Sample results designated as statistical outliers or were collected less than
60 days between sampling events are identified in Table 1. The lower Pee Dee background
groundwater dataset does not satisfy the requirement for the minimum number of ten samples
to conduct statistical analysis for each constituent. Three of the four samples from MW -5E had
pH levels above 12 S.U., indicating likely grout influence. This well has been replaced by Mw -
5R -E. Two additional lower Pee Dee wells (MW -8E & MW -41E) were also installed at
background locations north of the MW -5 cluster (see attached Figure). These three wells, along
with MW -37E, were sampled again in April with pH and turbidity levels within acceptable
ranges (< 9.7 S.U. as noted above). Additional samples will be collected in June 2017 which
could achieve the desired sample size by the end of the second quarter 2017. Subsequent outlier
screening of the lower surficial background dataset may warrant additional sample collection to
achieve at least ten valid results.
ATTACHMENTS:
Table 1: Background Analytical Results through March 2017
Figure 1-2: Site Layout Map
P: \Duke Energy Progress.1026 \ Statistics_CAMA \May 26 2017 -Updated Background Data Spreadsheets for
NCDEQ\GROUNDWATER\Sutton\Sutton - GW Tech Memo_Final.docx

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LEGEND
GEOSYNTEC EXTRACTION �-�-r� RAILROAD ASH BASIN
WELLS BOAT ROAD � . _ . _ _ � COMPLIANCE BOUNDARY
CCR MONITORING WELL PHASE 1 - - HALF -MILE OFFSET FROM
(SURVEYED) � - - - - COMPLIANCE BOUNDARY
MONITORING WELL INTERCELL ALIGNMENT
(SURVEYED) LANDFILL FINAL COVER (10' _ DUKE ENERGY PROGRESS
INTERVAL) � - _� SUTTON PLANT SITE
�, COMPLIANCE MONITORING BOUNDARY
WELL (SURVEYED) ASH LOADING
CAMA MONITORING WELL � PHASE 1 SURFACE WATER
(SURVEYED) PONDS
� BACKGROUND COMPLIANCE
MONITORING WELL
(SURVEYED)
PRIVATE WATER SUPPLY WELL
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FIGURE 1 2
148 RIVER STREET, SUITE 220 PROGRESS SITE LAYOUT MAP
GREENVILLE, SC 29601
864-421-9999 L.V. SUTTON ENERGY COMPLEX
www.synterracorp.com WILMINGTON, NORTH CAROLINA
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1 . ��`\,,,, - 1983 � �' .. � � ,n '� `:\� '•� � �. f
ii ,-�, : EXTENSION \�i '. 1 � ��.,' ` r f ' ', .� �..
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FORMER ASH �,� �:: ,�,. °, py "'��,
.---
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AREA � �,;, NHC-SVV2 (NOT IN USE) �DW-18 .; •". "�
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LEGEND
GEOSYNTEC EXTRACTION �-�-r� RAILROAD ASH BASIN
WELLS BOAT ROAD � . _ . _ _ � COMPLIANCE BOUNDARY
CCR MONITORING WELL PHASE 1 - - HALF -MILE OFFSET FROM
(SURVEYED) � - - - - COMPLIANCE BOUNDARY
MONITORING WELL INTERCELL ALIGNMENT
(SURVEYED) LANDFILL FINAL COVER (10' _ DUKE ENERGY PROGRESS
INTERVAL) � - _� SUTTON PLANT SITE
�, COMPLIANCE MONITORING BOUNDARY
WELL (SURVEYED) ASH LOADING
CAMA MONITORING WELL � PHASE 1 SURFACE WATER
(SURVEYED) PONDS
� BACKGROUND COMPLIANCE
MONITORING WELL
(SURVEYED)
PRIVATE WATER SUPPLY WELL
..
• � Y{
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,� - � � - Sutton Steam Plant Rd -�� - _ .. - -�° � ...
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. � �- .�
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0 500 1,000 2,000 3,000
GRAPHIC SCALE IN FEET
DRAWN BY: A. FEIGL DATE: 05/17/2017
�� CHOEC ED BYNP. WALDREPLDREP DATE: 05/17/2017
arra
E�JERY� _
FIGURE 1 2
148 RIVER STREET, SUITE 220 PROGRESS SITE LAYOUT MAP
GREENVILLE, SC 29601
864-421-9999 L.V. SUTTON ENERGY COMPLEX
www.synterracorp.com WILMINGTON, NORTH CAROLINA