ALLEN - GW BTV MEMO_FINAL

TECHNICAL MEMORANDUM
Date: September 5, 2017 File: 1026.17
To: Sean DeNeale (Duke Energy)
Cc: Kathy Webb (SynTerra)
From: Chris Suttell (SynTerra)
Subject: Background Threshold Values for Groundwater
Allen Steam Station- Belmont, NC
An updated background groundwater dataset was provided to the North Carolina Department
of Environmental Quality (NCDEQ) for Allen Steam Station (Allen) on May 26"2017.
Additionally, the revised Statistical Methods for Developing Reference Background Concentrations for
Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR Engineering, Inc.
and SynTerra Corporation, May 2017) was provided to NCDEQ. On July 7, 2017, NCDEQ
provided a response letter (Zimmerman to Draovitch, July 7, 2017) for each Duke Energy coal
ash facility that identified soil and groundwater data appropriate for inclusion in the statistical
analysis to determine background threshold values (BTVs) for both media. As outlined in the
NCDEQ July 7, 2017 letter, Duke Energy is required to provide BTVs for both media within 60
days from receipt of the NCDEQ letter for facilities submitting Comprehensive Site
Assessments (CSAs) later than October 31, 2017. BTVs for soil are provided under separate
cover.
The updated background groundwater dataset provided to NCDEQ on May 26, 2017 addressed
comments provided in a letter by NCDEQ (Zimmerman to Draovitch, April 28, 2017). NCDEQ
requested Duke Energy collect at least 10, rather than the previously planned eight, valid
samples from background monitoring wells prior to determination of BTVs for constituents
within each flow system. For groundwater datasets with less than 10 valid samples available
for determination of BTVs, no formal upper tolerance limit (UTL) statistics could be run and the
provisional BTV (PBTV) for a constituent and groundwater flow system was computed to be
either:
y The highest value, or
h If the highest value is above an order of magnitude greater than the geometric mean
of all values, then the highest value should be considered an outlier and removed
from further use and the PBTV is computed to be the second highest value.
NCDEQ requested that the updated background groundwater dataset exclude data from the
background data set due to one or more of the following conditions:
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Background Threshold Values for Groundwater September 5, 2017
Allen Steam Station Page 2 of 3
y Sample pH is greater than or equal to 8.5 standard units (S.U.) unless the regional
DEQ office has determined an alternate background threshold pH for the site;
01 Sample turbidity is greater than 10 Nephelometric Turbidity Units (NTUs);
y Result is a statistical outlier identified for background sample data presented to
NCDEQ on May 26,2017;
y Sample collection occurred less than a minimum 60 days between sampling events;
and
h Non -detect results are greater than 2L/IMAC.
Additional site-specific requirements related to groundwater background dataset for Allen,
such as exclusion of data not approved by NCDEQ, as outlined in the July 7, 2017 NCDEQ letter
have been incorporated into the groundwater background dataset.
This technical memorandum summarizes the revised background groundwater datasets and
statistically determined BTVs. Statistical determinations of BTVs were performed in accordance
with the revised Statistical Methods for Developing Reference Background Concentrations for
Groundwater and Soil at Coal Ash Facilities (statistical methods document) (HDR Engineering, Inc.
and SynTerra Corporation, May 2017).
GROUNDWATER BACKGROUND DATA
The current background monitoring well network consists of wells installed within three flow
zones - shallow, deep, and bedrock. Well locations are presented on Figure 1. Background
datasets provided to NCDEQ on May 26, 2017 were revised based on input from NCDEQ in the
July 7, 2017 letter. Revised background datasets for each flow system used to statistically
determine naturally occurring concentrations of inorganic constituents in groundwater are
provided in Table 1. The following sections summarize the refined background datasets along
with results of statistical evaluations for determining BTVs.
SHALLOW
Seven wells - BG -1S, BG -2S, BG -4S, GWA-19S, GWA-21S, GWA-23S, and GWA-26S - monitor
background groundwater quality within the shallow flow zone. In the July 7, 2017 letter,
NCDEQ identified AB -4S as not appropriate for use in the shallow flow zone background
dataset. Samples collected less than 60 days between sampling events, statistical outliers, and
invalid data were omitted prior to statistical determinations. The resulting shallow background
dataset meets the minimum requirement of 10 samples for all constituents. The revised shallow
flow zone background dataset is presented in Table 1. BTVs were calculated for constituents
monitored within the shallow flow zone using formal UTL statistics and are presented in Table
2.
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Background Threshold Values for Groundwater September 5, 2017
Allen Steam Station Page 3 of 3
DEEP FLOW ZONE
Three wells - BG -21), BG -41), and GWA-26D - monitor background groundwater quality within
the deep flow zone. NCDEQ indicated in the July 7, 2017 letter that these three deep flow zone
background wells were appropriate for use in development of BTVs. In the July 7, 2017 letter,
NCDEQ identified BG -11), AB -4D and GWA-21D as not appropriate for use in the
determination of BTVs for the deep flow zone and should be removed from the background.
Currently, no valid samples have been collected from BG -4D. Samples collected less than 60
days between sampling events, statistical outliers, and invalid data were omitted prior to
statistical determinations. The background groundwater dataset for the deep flow zone does
not meet the minimum requirement of 10 samples after excluding these locations. Table 1
presents the revised background dataset for the deep flow zone. No formal UTL statistics were
performed and the PBTV was computed to be either the highest value, or, if the highest value
was above an order of magnitude greater than the geometric mean of all values, the highest
value was considered an outlier and removed from further use and the PBTV was computed to
be the second highest value. PBTVs were calculated for constituents monitored within the deep
flow zone and are presented in Table 2.
BEDROCK
Two wells - BG-4BR and GWA-21BR - monitor background groundwater quality within the
fractured bedrock. In the July 7, 2017 letter, NCDEQ identified BG-2BR and AB-4BR as not
appropriate for use in the bedrock background dataset. Currently, no valid samples have been
collected from GWA-21BR. Samples collected less than 60 days between sampling events,
statistical outliers, and invalid data were omitted prior to statistical determinations. The
bedrock background groundwater dataset does not meet the minimum requirement of 10
samples after excluding these locations. Table 1 presents the revised background dataset for
the deep flow zone. No formal UTL statistics were performed and the PBTV was computed to
be either the highest value, or, if the highest value was above an order of magnitude greater
than the geometric mean of all values, the highest value was considered an outlier and removed
from further use and the PBTV was computed to be the second highest value. PBTVs were
calculated for constituents monitored within fractured bedrock and are presented in Table 2.
LIST OF FIGURE:
Figure 1 Well Location Map
LIST OF TABLES:
Table 1 Background Groundwater Results through March 2017
Table 2 Background Threshold Values for Groundwater
P: \ Duke Energy Carolinas \ 17.ALLEN \ 05.EHS CAMA Compliance
Support\ Assessment\ Background\ Groundwater\ Tech Memos\ 2017-09 \ALLEN - GW BTV MEMO_FINAL.docx

Background Threshold Values for Groundwater September 5, 2017
Allen Steam Station
FIGURE
P: \ Duke Energy Carolinas \ 17.ALLEN \ 05.EHS CAMA Compliance
Support\ Assessment\ Background\ Groundwater\ Tech Memos\ 2017-09 \ALLEN - GW BTV MEMO_FINAL.docx

Background Threshold Values for Groundwater September 5, 2017
Allen Steam Station
TABLES
P: \ Duke Energy Carolinas \ 17.ALLEN \ 05.EHS CAMA Compliance
Support\ Assessment\ Background\ Groundwater\ Tech Memos\ 2017-09 \ALLEN - GW BTV MEMO_FINAL.docx

TABLE 1
BACKGROUND GROUNDWATER RESULTS THROUGH MARCH 2017
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
Prepared by: LM Checked bv:QS
Notes,
54 - Indicates value omitted from dataset.
Indicates parameter not measured or analyzed.
Indicates data removed/identified as an outlier
- Indicates data removed due to autocorrelation
mg/L - Milligrams per liter pCVL - picocuries per liter
mg - N/L - Milligrams nitrogen per liter S.U. - Standard Unit
NE - Not established ug/mL - micrograms per milliliter
NTU - Nephelometric turbidity unit ug/L - Micrograms per liter
* - Interim Maximum Allowable Concentrations (IMACs) of the 15A NCAC 02L Standard, Appendix 1, April, 1, 2013.
j - Estimated concentration above the adjusted method detection limit and below the adjusted reporting limit.
j- -Estimated concentration, biased low.
j+ - Estimated concentration, biased high.
U - Results not detected at concentrations which equal the laboratory's method reporting limit.
- Hexavalent chromium does not have a NC 2L/IMAC standard; therefore, the NC 2L standard for total chromium is relied upon as a surrogate.
P:\Duke Energy Carolinas\17.ALLEN\05.EHS CAMA Compliance Supportyssessment\Background\Groundwater\Tech Memos\2017-09\Tables\TABLE I - Allen BG GW Data_NEW Page 1 of 1
Analytical
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Prepared by: LM Checked bv:QS
Notes,
54 - Indicates value omitted from dataset.
Indicates parameter not measured or analyzed.
Indicates data removed/identified as an outlier
- Indicates data removed due to autocorrelation
mg/L - Milligrams per liter pCVL - picocuries per liter
mg - N/L - Milligrams nitrogen per liter S.U. - Standard Unit
NE - Not established ug/mL - micrograms per milliliter
NTU - Nephelometric turbidity unit ug/L - Micrograms per liter
* - Interim Maximum Allowable Concentrations (IMACs) of the 15A NCAC 02L Standard, Appendix 1, April, 1, 2013.
j - Estimated concentration above the adjusted method detection limit and below the adjusted reporting limit.
j- -Estimated concentration, biased low.
j+ - Estimated concentration, biased high.
U - Results not detected at concentrations which equal the laboratory's method reporting limit.
- Hexavalent chromium does not have a NC 2L/IMAC standard; therefore, the NC 2L standard for total chromium is relied upon as a surrogate.
P:\Duke Energy Carolinas\17.ALLEN\05.EHS CAMA Compliance Supportyssessment\Background\Groundwater\Tech Memos\2017-09\Tables\TABLE I - Allen BG GW Data_NEW Page 1 of 1

TABLE 2
GROUNDWATER BACKGROUND THRESHOLD VALUES
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
Parameter
Reporting Unit
NCAC 02L Standard
Shallow
Background Threshold Values
Deept
Bedrockt
pH*
S. J.
6.5-8.5
5.2 - 7.5
6.7 - 8.4
7.5 - 7.8
Alkalinity
mg/L
NE
189
74
83.4
Aluminum
pg/L
NE
427
540
301
Antimony
pg/L
1A
0.9
0.7
0.5
Arsenic
pg/L
10
0.42
1.4
0.4
Barium
Ng/L
700
78
52.4
21
Beryllium
pg/L
4A
0.127
0.2
0.1
Bicarbonate
mg/L
NE
189
74
83.4
Boron
pg/L
700
50
50
50
Cadmium
pg/L
2
0.08
0.08
0.08
Calcium
mg/L
NE
20
14.2
20.4
Carbonate
mg/L
NE
5
5
5
Chloride
mg/L
250
10.9
6
1.6
Chromium (VI) 1
Ng/L
10
7.7
1.2
0.23
Chromium
pg/L
10
6.93
6.8
5.6
Cobalt
pg/L
1A
4.3
0.5
0.27
Copper
pg/L
1000
2.3
1.7
1.2
Iron
pg/L
300
835
555
284
Lead
pg/L
15
0.17
0.1
0.1
Magnesium
mg/L
NE
5.6
4.6
4.8
Manganese
pg/L
50
578
60.4
39.1
Mercury
Ng/L
1
0.2
2.4
0.2
Methane
pg/L
NE
11.4
38.9
10
Molybdenum
pg/L
NE
0.85
30
4.7
Nickel
pg/L
100
4.02
8.1
3.4
Nitrate + Nitrite
mg-N/L
NE
1.8
0.94
0.41
Potassium
mg/L
NE
5.24
9.89
6.06
Selenium
pg/L
20
0.5
0.5
0.5
Sodium
mg/L
NE
15.2
28.3
7.71
Strontium
Ng/L
NE
286
200
106
Sulfate
mg/L
250
3.64
16.2
2.9
Sulfide
mg/L
NE
0.1
0.12
0.1
TDS
mg/L
500
181
126
147
Thallium
pg/L
0.2"
0.1
0.1
0.1
TOC
mg/L
NE
18
11
5.6
Vanadium
pg/L
0.3A
5.3
9.6
10.8
Zinc
pg/L
1000
80
17.3
15.3
Radium (Total)
pCi/L
NE
1.39
0.613
1.1
Uranium (Total)
Ng/mL
NE
0.002
0.0005
0.0004
Prepared by: LWD Checked by: KLS
Notes:
* - Upper and lower tolerance limits calculated for parameter
A - Interim Maximum Allowable Concentrations (IMACs) of 15A NCAC .021 Standard, Appendix 1, April 1, 2013
pg/L - micrograms per liter
pg/mL - micrograms per milliliter
t - Provisional; dataset contains less than 10 valid samples
' - Hexavalent chromium does not have a NC 2L/IMAC standard; therefore, the NC 2L standard for total chromium is relied upon as a surrogate.
mg - N/L - Milligrams nitrogen per liter
mg/L - milligrams per liter
NE - Not Established
pCi/L - picocuries per liter
Radium (Total) - Radium -226 and Radium -228 combined
S.U. - Standard Unit
TDS - Total Dissolved Solids
Uranium (Total) - Uranium -233, Uranium -234, Uranium -236, and Uranium -238 combined
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