SOIL BTV MEMO_FINAL_20170907

TECHNICAL MEMORANDUM
Date: September 5, 2017 File: 1026.19
To: Melonie Martin (Duke Energy)
Cc Kathy Webb (SynTerra)
From: Jerry Wylie and Ted Volskay (SynTerra)
Subject: Background Threshold Values for Soil
Dan River Steam Station — Eden, NC
An updated background soil dataset was provided to the North Carolina Department of
Environmental Quality (NCDEQ) for Dan River Steam Station (Dan River) 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 groundwater are provided under
separate cover.
The revised background soil datasets provided to NCDEQ on May 26, 2017 incorporated
comments provided in a letter by NCDEQ (Zimmerman to Draovitch, April 28, 2017). NCDEQ
requested that Duke Energy collect a minimum of 10, rather than the previously planned eight,
valid background samples prior to the determination of BTVs for each constituent. For soil
datasets with less than 10 valid samples available for BTV determination, no formal upper
tolerance limit (UTL) statistics could be run and the provisional BTV (PBTVs) for a constituent
was computed to be either:
t0 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.
Soil samples meeting the following criteria are considered valid for use in statistical
determinations of BTVs:
t' Sample was collected from a location that is not impacted by coal combustion
residuals or coal associated materials;
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Background Threshold Values - Soil September 5, 2017
Dan River Steam Station Page 2 of 3
0 Sample was collected from a depth not less than 0.5 feet below ground surface;
,07 Sample was collected from a location that is not impacted by other potential
anthropogenic sources of constituents; and
t7 Sample is collected from the unsaturated zone, greater than one foot (ft) above the
seasonal high water table elevation.
Additional site-specific requirements related to the Dan River background soil dataset as
outlined in the July 7, 2017 NCDEQ letter have been incorporated into the soil background
dataset.
This technical memorandum summarizes the revised background soil 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).
SOIL BACKGROUND DATA
Soil samples were collected from soil borings conducted at the Dan River Plant during the 2015
Comprehensive Site Assessment (CSA). Background soil sample locations are presented in
Figure 1. The background dataset provided to NCDEQ on May 26, 2017 included pooled soil
samples collected from multiple depth intervals. Only samples collected from background
locations at depth intervals greater than one foot above the seasonal high water table were
included in the dataset. The background soil dataset has been further revised from the May 26,
2017 submittal based on input from NCDEQ in the July 7, 2017 letter. NCDEQ determined the
following samples are not appropriate for use in determining BTVs:
0 BG -1D (0-2) -collected too shallow;
,67 GWA-3D (5-6.5) - collected in close proximity to Ash Storage 1;
47 GWA-6S (9-11) - collected downgradient of Ash Basin Primary Cell;
0 GWA -10D (19-20) and GWA-10D (25) - collected downgradient of Ash Storage 2;
0 GWA-11D (10-11.5) - collected downgradient of Ash Storage 1.
After these samples were removed from the dataset, the remaining background soil dataset was
re -screened for outliers prior to statistical determinations. A revised background soil dataset
identifying valid samples and statistical outliers are presented as Table 1. The revised
background dataset satisfies the minimum requirement of 10 samples to use formal statistics to
derive BTVs for all constituents except antimony, selenium, and thallium. The background soil
dataset for these constituents included laboratory reporting limits above the NCDEQ IHSB
Preliminary Soil Remediation Goals (PSRG) Protection of Groundwater standards (dated
October 2016). NCDEQ requires that the analytical practical quantitation limit (PQL) for
P:\Duke Energy Carolinas\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH
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Background Threshold Values - Soil September 5, 2017
Dan River Steam Station Page 3 of 3
antimony, selenium, and thallium be less than the PSRG Protection of Groundwater for the data
to be valid for calculating BTVs.
BTVs were calculated using formal UTL statistics for constituent datasets meeting the minimum
requirement of 10 samples. Antimony and thallium datasets were comprised of zero valid
samples and selenium datasets contained two valid samples. PPTVs are not presented at this
time for antimony and thallium. The PBTV for selenium was determined to be either the
maximum value, or, if the maximum value was above an order of magnitude greater than the
geometric mean of all values, the second highest value. Therefore, PBTVs for selenium was
computed. BTVs and PBTVs for constituents in site soil are provided in Table 2.
Additional soil samples will be collected to satisfy the minimum number of soil samples for
analysis of antimony, selenium, and thallium by a method whereby the PQL is below the PSRG
Protection of Groundwater values. Once the planned additional samples are included in the
dataset, the dataset will be screened for outliers and BTVs computed. Sampling and analysis of
additional background soil samples is not complete at this time of this technical memo.
Therefore, as previously stated, PBTVs for selenium, was computed and is provided in Table 2.
Boring logs and analytical data for subsequent collection of background soil samples will be
submitted to the NCDEQ Regional Office if received and processed in sufficient time for review
prior to the preparation of the updated CSA report. If sufficient time is not available, the data
will be provided in the updated CSA report based on the locations presented in this technical
document.
LIST OF FIGURES:
Figure 1 Background Soil Sample Location Map Dan River Steam Station
LIST OF TABLES:
Table 1 Background Unsaturated Soil Data Summary
Table 2 Background Threshold Values for Soil
P:\Duke Energy Carolinas\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH
MEMO \Dan River \ Soil \ Dan River- SOIL BTV MEMO_FINAL.docx

Background Threshold Values - Soil
Dan River Steam Station
FIGURE
September 5, 2017
P:\Duke Energy Carolinas\ Statistics_CAMA \Background Determinations for NCDEQ July 7 2017\BTV TECH
MEMO \Dan River \ Soil \ Dan River- SOIL BTV MEMO_FINAL.docx

NOTES:
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FIGURE 1
GRAPHIC SCALE IN FEET BACKGROUND SOIL
148 RIVER STREET, SUITE 220
GREENVILLEW.r,SOUTH CAROLINA 29601 SAMPLE LOCATION
PHONE [phone] DAN RIVER STEAM STATION
synTerra PROJECT
ROJECTM A. MANAGER:
J.
DATE 08/07/2017 EDEN, NORTH CAROLINA
PROJECT MANAGER: J. MAHAN
CHECKED BY: B. WYLIE

Background Threshold Values - Soil
Dan River Steam Station
TABLES
September 5, 2017
P:\Duke Energy Carolinas\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH
MEMO \Dan River \ Soil \ Dan River- SOIL BTV MEMO_FINAL.docx

TABLE 1
BACKGROUND UNSATURATED SOIL DATA SUMMARY
DAN RIVER STEAM STATION
DUKE ENERGY CAROLINAS, LLC, EDEN, NC
Analytical Parameter
pH
Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Calcium
Chloride
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Nitrate
Potassium
Selenium
Sodium
Strontium
Sulfate
Thallium
Vanadium
Zinc
PSRG Protection of Groundwater
NE
NE
0.9
5.8
580
63
45
3
NE
NE
360000
0.9
700
150
270
NE
65
1
NE
130
NE
NE
2.1
NE
NE
NE
0.28
6
1200
Reporting Units S.U.
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
Sampel ID
Sample
Collection Date
Analytical Results
BG -5D (1-2)
5/27/2015
5.1 j
13200
---
3.9 j-
57.8 j+
0.56
15.7 Uj
0.75 Uj
248
325 U
40.2 j-
6.8 j-
21.7
30400
15.1
1110
113
0.026
3.1 U
7.4
32.5 Uj
684
6.3 R
314 U
6.5
325 U
---
45.9
26.7
GWA-2D (19-20)
5/12/2015
6.7 j
19500
---
3.8 j
297
2
14.4 U
0.69 Uj
908
277 U
30.6
18.6
41
48300
13.5
4520
468
0.006 j
2.9 U
29.9
27.7 Uj
1790
3.2 j
288 U
19.5
277 U
---
30.2
139
GWA-9D (20-21.5)
5/13/2015
5.2 j
9620
---
5.4 U
34.2
0.64
13.4 U
0.64 Uj
77.4 j+
276 U
18.8
10.5
6.4
16500
11.6
930
267
0.0094
1-6-1
6.7
27.6 Uj
579
---
269 U
2.3 j
276 U
---
15.5
23.5
GWA-10D (9-10)
5/5/2015
5.5j
19900
---
5.7 U
103
2.9
14.3 U
0.69 U
185
287 U
14.9
18.6
12.5
27500
13.5
3300
247
0.0096 U
2.9 U
19.4
28.7 Uj
1950
---
286 U
7.7
287 U
---
26.6
67
SB -1 (1-2)
5/2/2015
4.6 j
22200
---
4 j-
63.6 j+
0.72
17 Uj
0.81 U
172
338 U
21.9
7j+
21.9
41800
13.9 j-
1560 j+
113
0.047
3.4 U
9
33.8 Uj
635
---
339 U
8.6
338 U
---
39.9
40.1
SB -1 (10-11.5)
5/2/2015
4.9j
33200
---
4.6j
59.6
3.9
14 U
0.67 U
140 U
267 U
32.7
18.9
1 44.6
95986
1 25.9
6110
418
0.0069j
2.8 U
52.2
26.7 Uj
168j
---
280 U
1.9j
267 U
---
49.5
178
SB -1 (15-16.5)
5/2/2015
5.3 j
23600
---
3.1 j
51.6
2.7
15.1 U
0.72 U
151 U
287 U
19.9
16.2
25.1
54700
18.4
4050
202
0.0052 j
3 U
27.5
28.7 Uj
247 j
---
301 U
3.2
287 U
---
38.7
107
SB -1 (20-21.5)
5/2/2015
5.4 j
27600
---
5.3 j
74.8
2.2
14.8 U
0.71 U
269
285 U
28.5
14.6
47.9
54800
14.9
4050
145
0.04
3 Uj
17.1
28.5 Uj
605
---
297 U
21.8
285 U
---
54.4
70.5
SB -1 (25-26.5)
5/2/2015
4.5j
18700
---
28
73.8
1.7
14.1 U
9.44j
9488
293 Uj
17
26.2
79.5
39300
31.3
4690
328
0.038
7.4
38.9
29.3 Uj
1340
---
282 U
78
243 j-
---
19.1
178
SB -2 (1-2)
4/14/2015
7.2j
14000
---
---
110
2
15.7 U
0.76 U
429
300 U
20.3
13
27.7
30300
12.3
2360
233
0.0092 Uj
3.1 U
12.6
30 Uj
1280
---
315 U
10.3
300 U
---
21.3
51.1
SB -2 (10-11.5)
4/15/2015
5.5j
27700
---
5.8 U
110
2.1
14.5 U
0.69 U
145 U
284 U
30.9
12
57
49100
21.5
4490
256
0.012
2.9 U
19.1
28.4 Uj
2730
---
289 U
4.4
284 U
---
41.4
83.5
SB -2 (20-21.5)
4/15/2015
5.3 j
24300
---
10.6
244
1.9
14.8 U
0.71 U
1930
289 U
111
42-6
66.1
1 60300
18.9
4790
3436
0.024
5.4
36.3
28.9 Uj
2100
---
297 U
7-39
289 U
---
33.8
104
SB -2 (30-31.25)
4/15/2015
6.5j
17400
---
9.2
71.3
1
14.7 U
0.71 U
4166
285 U
34.7
20.1
68.4
42700
18.2
8470
395
0.0086j
3.2
32.4
28.5 Uj
2200
---
295 U
36.4
145-j
---
24.2
113
SB -2 (35-36)
4/15/2015
8.6j
19800
---
5.4 U
61.9
0.59
13.5 U
0.65 U
9858
279 U
27.1
12
30.2
37100
11.4
10800
837
0.0073j
1-911
19.4
27.9 Uj
1800
---
269 U
52-8
279 U
---
26.2
74.1
SB -2 (65-65.3)
4/15/2015
8.6 j
24600
---
8.6
74.4
0.86
15.2 U
0.73 U
i8266
291 U
36.1
21.8
57.8
49200
16.5
12700
433
0.011
4-6-1
31.9
29.1 Uj
1970
---
4H8}
69.7
291 U
---
34.1
91.4
SB -3 (1-2)
4/17/2015
4.2j
14300
---
7j
102
1.6
16.5 U
0.79 U
680
322 U
18
8.9 j-
26.9
33600
1 21.9
1830 j-
200
0.017
3.3 Uj
9
32.2 Uj
1390
---
329 U
7.1
564
---
37.3
58.2
SB -3 (10-11)
4/18/2015
5 j
15000
---
---
104
1.2
16U
0.77 U
1480
322 U
19.3
16.1
23.3
27700
23
3060
601
0.03
3.2 U
12
32.2 Uj
1700
---
320 U
13
322 U
---
35
46.5
SB -3 (20-21.5)
4/18/2015
6j
17700
5.8 U
63
1.5
14.5 U
0.7 U
433
280 U
17.7
7.5
23.4
28800
17.8
2330
82.7
0.0052]
2.9 U
16.9
28 Uj
308
290 U
2.5j
280 U
34.3
61.1
SB -3 (35-36.5)
4/18/2015
7.1j
12100
89.7
0.75
35-9-j
0.79 U
2010
339 U
12.8
22.6
15.6
34400
22.9
2430
2846
0.011 U
3.3 U
21.9
33.9 Uj
313j
327 U
24.2
339 U
---
21.5
47.8
Prepared by: LWD Checked by: JAW
Notes:
54 Indicates values omitted from dataset.
--- Not applicable; non -detect concentration greater than PSRG Protection of Groundwater; value omitted
Indicates data removed /identified as an outlier
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.
mg/kg - milligrams per kilogram
NE - Not established
PSRG Protection of Groundwater - NCDEQ IHSB Preliminary Soil Remediation Soil Remediation Goals Table - October 2016
R - Relative Percent Difference (RPD) indeterminate due to low concentration in the parent sample.
S.U. - Standard Units
U - Results not detected at concentrations which equal the laboratory's method reporting limit.
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TABLE 2
BACKGROUND THRESHOLD VALUES FOR SOIL
DAN RIVER STEAM STATION
DUKE ENERGY CAROLINAS, LLC, EDEN, NC
Parameter
Reporting Unit
PSRG Protection of
Groundwater
BTV
pH*
S. U.
NE
2.3 - 9.4
Aluminum
mg/kg
NE
34,500
Antimony
mg/kg
0.9
NA
Arsenic
mg/kg
5.8
12.4
Barium
mg/kg
580
133
Beryllium
mg/kg
63
3.31
Boron
mg/kg
45
ND
Cadmium
mg/kg
3
ND
Calcium
mg/kg
NE
2,276
Chloride
mg/kg
NE
ND
Chromium
mg/kg
360,000
44.5
Cobalt
mg/kg
0.9
29.2
Copper
mg/kg
700
87.3
Iron
mg/kg
150
68,009
Lead
mg/kg
270
30.9
Magnesium
mg/kg
NE
12,119
Manganese
mg/kg
65
802
Mercury
mg/kg
1
0.04
Molybdenum
mg/kg
NE
ND
Nickel
mg/kg
130
45.6
Nitrate (as N)
mg/kg
NE
ND
Potassium
mg/kg
NE
3,160
Selenium
mg/kg
2.1
NA
Sodium
mg/kg
NE
ND
Strontium
mg/kg
NE
85
Sulfate
mg/kg
NE
ND
Thallium
mg/kg
0.28
NA
Vanadium
mg/kg
6
58.7
Zinc
mg/kg
1,200
192
Prepared by: LWD Checked by: TME
Notes:
* - Upper and lower threshold values calculated for parameter
mg/kg - milligrams per kilogram
NA - Not applicable; dataset contains zero valid samples
ND - Not Detected
NE - Not Established
S.U. - Standard Unit
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