Asheville - GW BTV TM_Final

TECHNICAL MEMORANDUM
Date: September 5, 2017 File: 1026.102
To: John Toepfer (Duke Energy)
Cc: Kathy Webb (SynTerra)
From: Todd Plating (SynTerra)
Subject: Background Threshold Values for Groundwater
Asheville Steam Electric Plant — Arden, NC
An updated background groundwater dataset was provided to the North Carolina Department
of Environmental Quality (NCDEQ) for Asheville Steam Electric Plant (Asheville) 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:
,47 The highest value, or
,07 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
Asheville Steam Electric Plant Page 2 of 4
0 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;
'07 Sample turbidity is greater than 10 Nephelometric Turbidity Units (NTUs);
0 Result is a statistical outlier identified for background sample data presented to
NCDEQ on May 26,2017;
0 Sample collection occurred less than a minimum 60 days between sampling events;
and
[y Non -detect results are greater than 2L/IMAC.
Additional site-specific requirements related to groundwater background dataset for Asheville,
such as exclusion of data not approved by NCDEQ, groundwater as outlined in the July 7, 2017
NCDEQ letter have been incorporated into the groundwater background dataset. Duke Energy
provided an updated data set highlighting outliers to NCDEQ (email: Toepfer to Campbell,
August 14, 2017) to reflect the inclusion of the GW -1 cluster into the dataset. NC DEQ accepted
this dataset for use in determination of BTVs via email from Campbell to Toepfer on August 22,
2017.
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 four flow
zones — alluvium, saprolite, transition zone, 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.
ALLUVIUM
One well, MW -10, monitors background groundwater quality within the alluvium flow zone.
In the July 7, 2017 letter, NCDEQ concurred with the alluvium flow zone background dataset.
Samples collected less than 60 days between sampling events, statistical outliers, and invalid
data was omitted from use prior to statistical determinations. The background groundwater
dataset for the alluvium flow zone does not meet the minimum requirement of 10 samples after
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Background Threshold Values for Groundwater September 5, 2017
Asheville Steam Electric Plant Page 3 of 4
excluding these locations. Once the July 2017 groundwater sampling data is available and
validated, the alluvium flow zone should meet the minimum requirements of 10 samples. No
formal UTL statistics will be run at this time and the PBTV will be computed. Table 1 presents
the revised background dataset for the alluvium flow zone. PBTVs were calculated for
constituents monitored within the alluvium flow zone and are presented in Table 2.
SAPROLITE
Five wells - CB -1, CB -9, CB-9SL, GW -1, and MW -24S - monitor background groundwater
quality within the saprolite flow zone. In the July 7, 2017 letter, NCDEQ concurred with the
saprolite flow zone background dataset. Samples collected less than 60 days between sampling
events, statistical outliers, and invalid data was omitted prior to statistical determinations. The
background dataset for the saprolite flow zone meets the minimum requirement of 10 samples
for all constituents. The revised saprolite flow zone background dataset is presented in Table 1.
BTVs were calculated for constituents monitored within the saprolite flow zone using formal
UTL statistics. BTVs for the saprolite flow zone are presented in Table 2.
TRANSITION ZONE
Two wells - CB -11) and GW -011)- monitor background groundwater quality within the
transition flow zone. NCDEQ indicated in the July 7, 2017 letter that transition zone
background wells were appropriate for use in development of BTVs. With the exception of
radionuclides, the background groundwater dataset for the transition zone meets the minimum
requirement of 10 samples for all constituents. Once the July 2017 groundwater sampling data
is available and validated, radionuclides in the transition flow zone should meet the minimum
requirements of 10 samples. Samples collected less than 60 days between sampling events,
statistical outliers, and invalid data was omitted prior to statistical determinations. The revised
transition zone background dataset is presented in Table 1. BTVs were calculated for
constituents monitored within the transition zone using formal UTL statistics. BTVs for the
transition zone are presented in Table 2.
BEDROCK
Three wells - AMW-313, CB-09BR, and GW-01BR - monitor background groundwater quality
within the fractured bedrock. NCDEQ indicated in the July 7, 2017 letter that bedrock
background wells were appropriate for use in development of BTVs. Prior to statistical
determinations, samples collected less than 60 days between sampling events, statistical
outliers, and invalid data was omitted from use in statistical determinations. The background
groundwater dataset for bedrock meets the minimum requirement of 10 samples for all
constituents. The revised bedrock background dataset is presented in Table 1. BTVs were
calculated for constituents monitored within fractured bedrock using formal UTL statistics and
are presented in Table 2.
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Background Threshold Values for Groundwater September 5, 2017
Asheville Steam Electric Plant Page 4 of 4
LIST OF FIGURES:
Figure 1 Well Location Map
LIST OF TABLES:
Table 1 Background Groundwater Results through March 2017
Table 2 Background Threshold Values for Groundwater
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Background Threshold Values for Groundwater September 5, 2017
Asheville Steam Electric Plant
FIGURE
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MEMO\ Asheville\ Groundwater\ Asheville - GW BTV TM.docx

Background Threshold Values for Groundwater September 5, 2017
Asheville Steam Electric Plant
TABLES
P:\Duke Energy Progress.1026\Statistics_CAMA\Background Determinations for NCDEQ July 72017\BTV TECH
MEMO\ Asheville\ Groundwater\ Asheville - GW BTV TM.docx

TABLE 1
BACKGROUND GROUNDWATER RESULTS THROUGH APRIL 2017
ASHEVILLE STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, ARDEN, NC
Prepared by: LHQ Checked by: TDP
Now:
54 - Indicates value omitted from dataset.
® Indicates parameter not measured or analyzed.
-
Indicates data removes/identified as an outlier
- Indicates data removed due to autoaorrelation
- Indicates non -detect value greater than 2UIMAC and removed from dataset
mg/L - Milligrams per liter pCi/L - picocuries per liter
.g- 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
<concentration not detected at or above the adjusted reporting limit.
' - Interim Maximum Allowable Concentrations (IMACs) of the ISA NCAC 02L Standard, Appendix 1, April, 1, 2013.
- Hexavalent chromium does not have a NC 2UIMAC standard; therefore, the NC 2L standard for total chromium is relied upon as a surrogate.
B - Target analyte detected in method blank at or above the reporting limit Target analyte concentration In sample is less than 10X the concentration in the method blank. Analyte concentration in sample could be due to blank contamination.
el - Target analyte detected in method blank at or above the reporting limit. Target analyte concentration In sample was greater than lox the concentration in the method blank. Analyte concentration in sample is not affected by blank contamination.
82 - Target analyte was detected in blank(s) at a concentration greater than 1/2 the reporting limit but less than the reporting limit. Analyte concentration in sample is valid and may be used for compliance purposes.
B3 - Target analyte was detected in Continuing Calibration Blank(s) at a concentration greater than 1/2 the reporting limit but less than the reporting limit. Analyte concentration in sample is valid and may be used for compliance purposes.
B6 - Target analyte was detected in Continuing Calibration Blank(s) at a concentration greater than the reporting limit.
CL - The continuing calibration for this compound is outside of Pace Analytical acceptance limits. The results may be biased low.
D3 - Sample was diluted due to the presence of high levels of non -target analytes or other matrix interference.
Ll - Analyte recovery in the laboratory control sample (LCS) was above quality control (QC) limits. Results may be biased high.
L3 - Analyte recovery in the laboratory control sample (LCS) exceeded quality control (QC) limits. Analyte presence below reporting limits in associated samples. Results unaffected by high bias.
Ml - Matrix spike recovery was high: the associated Laboratory Control Spike (LCS) was acceptable.
N2 - The lab does not hold accreditation for this parameter.
P:\Duke Energy Progmss.1026\Statlstics_CAMA\Background Determinations for NCDEQ July 7 2817\13TV TECH MEMO\Asheville\Groundwater\Tables\TABLE 1 Asheville BG GW Data April2017_For TM.xIsxTABLE 1 - Asheville_BG GW Data Apn12017_For TM.xlsx Page 2 of 2
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Prepared by: LHQ Checked by: TDP
Now:
54 - Indicates value omitted from dataset.
® Indicates parameter not measured or analyzed.
-
Indicates data removes/identified as an outlier
- Indicates data removed due to autoaorrelation
- Indicates non -detect value greater than 2UIMAC and removed from dataset
mg/L - Milligrams per liter pCi/L - picocuries per liter
.g- 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
<concentration not detected at or above the adjusted reporting limit.
' - Interim Maximum Allowable Concentrations (IMACs) of the ISA NCAC 02L Standard, Appendix 1, April, 1, 2013.
- Hexavalent chromium does not have a NC 2UIMAC standard; therefore, the NC 2L standard for total chromium is relied upon as a surrogate.
B - Target analyte detected in method blank at or above the reporting limit Target analyte concentration In sample is less than 10X the concentration in the method blank. Analyte concentration in sample could be due to blank contamination.
el - Target analyte detected in method blank at or above the reporting limit. Target analyte concentration In sample was greater than lox the concentration in the method blank. Analyte concentration in sample is not affected by blank contamination.
82 - Target analyte was detected in blank(s) at a concentration greater than 1/2 the reporting limit but less than the reporting limit. Analyte concentration in sample is valid and may be used for compliance purposes.
B3 - Target analyte was detected in Continuing Calibration Blank(s) at a concentration greater than 1/2 the reporting limit but less than the reporting limit. Analyte concentration in sample is valid and may be used for compliance purposes.
B6 - Target analyte was detected in Continuing Calibration Blank(s) at a concentration greater than the reporting limit.
CL - The continuing calibration for this compound is outside of Pace Analytical acceptance limits. The results may be biased low.
D3 - Sample was diluted due to the presence of high levels of non -target analytes or other matrix interference.
Ll - Analyte recovery in the laboratory control sample (LCS) was above quality control (QC) limits. Results may be biased high.
L3 - Analyte recovery in the laboratory control sample (LCS) exceeded quality control (QC) limits. Analyte presence below reporting limits in associated samples. Results unaffected by high bias.
Ml - Matrix spike recovery was high: the associated Laboratory Control Spike (LCS) was acceptable.
N2 - The lab does not hold accreditation for this parameter.
P:\Duke Energy Progmss.1026\Statlstics_CAMA\Background Determinations for NCDEQ July 7 2817\13TV TECH MEMO\Asheville\Groundwater\Tables\TABLE 1 Asheville BG GW Data April2017_For TM.xIsxTABLE 1 - Asheville_BG GW Data Apn12017_For TM.xlsx Page 2 of 2

TABLE 2
GROUNDWATER BACKGROUND THRESHOLD VALUES
ASHEVILLE STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, LLC, ARDEN, NC
Parameter
Reporting
Unit
NCAC 02L
Standard
Alluviumt
Background Threshold Values
Saprolite Transition Zone
Bedrock
pH*
S. U.
6.5-8.5
4.6-5.1
4.3-5.8
3.9-7.0
4.1-8.1
Alkalinity
mg/L
NE
10.9
14.2
14.8
70.4
Aluminum
pg/L
NE
73
602
346
199
Antimony
Ng/L
1A
1
1
1
1
Arsenic
pg/L
10
1
1
1
1
Barium
ug/L
700
59
143
41
41.2
Beryllium
pg/L
4A
1
1
1
1
Bicarbonate
mg/L
NE
10.9
14.2
14.8
70.4
Boron
pg/L
700
50
50
50
50
Cadmium
Ng/L
2
1
1
1
1
Calcium
mg/L
NE
2.67
10.6
3.97
24.2
Carbonate
mg/L
NE
5
5
5
5
Chloride
mg/L
250
15
14
6.7
6.5
Chromium (VI) 1
ug/L
10
0.42
1.31
0.261
0.423
Chromium
pg/L
10
5
5
1.32
1.3
Cobalt
Ng/L
1A
4.29
5.65
4.61
1
Copper
Ng/L
1000
5
5
2.08
1
Iron
Ng/L
300
598
1050
1785
1246
Lead
pg/L
15
1
1
1
1
Magnesium
mg/L
NE
3.06
8.7
3.31
3.38
Manganese
pg/L
50
363
725
380
105
Mercury
ug/L
1
0.1
0.3
0.2
0.05
Methane
Ng/L
NE
230
10
10
10
Molybdenum
Ng/L
NE
1
1
1
3.7
Nickel
pg/L
100
5
10
9.83
1.77
Nitrate + Nitrite
mg-N/L
NE
0.113
2.8
0.872
0.422
Potassium
mg/L
NE
1.55
1.61
1.87
4.79
Selenium
Ng/L
20
1
1.88
1
1
Sodium
mg/L
NE
6.18
4.06
4.20
9.01
Strontium
Ng/L
NE
28
44
37.7
88
Sulfate
mg/L
250
4.6
50
5.47
5.6
Sulfide
mg/L
NE
0.1
0.1
0.1
0.1
TDS
mg/L
500
56
105
72.8
132
Thallium
Ng/L
0.2°
0.2
0.2
0.2
0.2
TOC
mg/L
NE
0.72
0.708
0.595
1.1
Vanadium
pg/L
0.3°
0.3
0.625
0.41
0.632
Zinc
pg/L
1000
22
45.4
27.6
5
Radium (Total)
pCi/L
NE
4.17
6.83
6.61t
6.55
Uranium (Total)
Ng/mL
NE
0.00035
0.00035
0.0004021
0.000454
Prepared by: JHG Checked by: ALA
Notes;
* - Upper and lower tolerance limits calculated for parameter
A - Interim Maximum Allowable Concentrations (IMACs) of 15A NCAC .02L 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
1 - Hexavalent chromium does not have a NC 2UIMAC 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
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