Mayo - SOIL BTV_Tech Memo_20171005

TECHNICAL MEMORANDUM
Date: August 4, 2017 File: 1026.105
To: Kimberlee Witt (Duke Energy)
Cc: Kathy Webb (SynTerra)
From: Jerry Wylie (SynTerra)
Subject: Background Threshold Va ues for Soil
Mayo Steam Electric Plant — Roxboro, NC
An updated background soil dataset was provided to the North Carolina Department of
Environmental Quality (NCDEQ) for Mayo Steam Electric Plant (Mayo) 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 each media within 30
days from receipt of the NCDEQ letter for facilities submitting Comprehensive Site
Assessments (CSAs) by October 31, 2017, and 60 days from receipt of the NCDEQ letter for all
other facilities. The background threshold values 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 will be run and the provisional BTV (PBTVs) for a constituent
will be computed to be either:
4? The highest value, or
0 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.
P:\Duke Energy Progress.1026\Statistics_CAMA\Background Determinations for NCDEQ July 72017\BTV TECH
MEMO \ Mayo \ Soil \ Mayo - SOIL BTV_FINAL.docx

Background Threshold Values for Soil August 4, 2017
Mayo Steam Electric Plant Page 2 of 4
Soil samples meeting the following criteria are considered valid for use in statistical
determinations of BTVs:
Sample was collected from a location that is not impacted by coal combustion residuals
or coal associated materials;
'47 Sample was collected from a depth not less than 0.5 feet below ground surface;
'47 Sample was collected from a location that is not impacted by other potential
anthropogenic sources of constituents; and
,07 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 Mayo 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 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).
SOIL BACKGROUND DATA
Soil samples were collected from soil borings conducted at the Mayo 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 ft 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:
47 MW-03BR (0.8-1.25) and MW-15BR (0.5-1) — collected downgradient of the ash basin;
C7 MW-11BR and MW-13BR —per IHSB Guidance —collected from depth interval 0-2 ft
below ground surface and deemed too shallow (included sampled soil less than 0.5
below ground surface);
0 Samples collected at SB-02 and SB-03 — collected from borings possibly advanced
through coal ash;
E7 SB-05 and SB-06 — collected adjacent to the 1981 landfill.
P:\Duke Energy Progress. 1026\Statistics—LAMA\Background Determinations for NCDEQ July 72017\BTV TECH
MEMO \ Mayo \ Soil \ Mayo - SOIL BTV_FINAL.docx

Background Threshold Values for Soil August 4, 2017
Mayo Steam Electric Plant Page 3 of 4
Prior to statistical determinations, the background soil dataset was re -screened for outliers to
adjust for the removal samples from the dataset. A revised background soil dataset identifying
valid samples and statistical outliers are presented as Table 1. The revised background dataset
was used to determine PBTVs for naturally occurring inorganic constituent in Site soil.
Additional soil samples were collected on July 18, 2017 to satisfy the minimum number of soil
samples and to provide values for antimony, selenium and thallium below the PSRG Protection
of Groundwater values. The dataset will be screened for outliers once the additional samples
are included in the dataset. The analysis of the additional background soil samples are not
complete at the time of this technical memo. Therefore, as previously stated, PBTVs for soil
constituents were computed and are provided in Table 2. Boring logs associated with the
additional soil samples are included in Attachment 1. Additional analytical data 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.
LIST OF FIGURES
Figure 1- Background Soil Sample Locations - Mayo Steam Electric Plant
LIST OF TABLES
Table 1- Background Unsaturated Soil Data Summary - Mayo Steam Electric Plant
Table 2 - Background Threshold Values for Soil - Mayo Steam Electric Plant
LIST OF ATTACHMENTS
Attachment 1- Soil Boring Logs (Additional Samples)
P:\Duke Energy Progress. 1026\Statistics—LAMA\Background Determinations for NCDEQ July 72017\BTV TECH
MEMO \ Mayo \ Soil \ Mayo - SOIL BTV_FINAL.docx

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TABLE 1
BACKGROUND UNSATURATED SOIL DATA SUMMARY
MAYO STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, LLC, ROXBORO, NC
Analytical Parameter
pH
Aluminum
Antimony
Arsenic
Barium
Beryllium
Boron
Cadmium
Calcium
Chloride
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Cash;
Potassium
Selenium
Sodium
Strontium
Sulfate
Thallium
Vanadium
Zinc
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
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
Sample ID
Sample
Collection Date
Analytical Results
MW-08BR (0JS-1.25)
02/11/2015
6.0
14500
---
<3.2
147
0.82
-,63.4
<0.38
1120
<309
62.2
21.3
34.7
24700
8.9
10500
1230
<0.0096
<12.7
29.4
<30.9
6590
---
-12-78
13.2
<309
---
50.6
88.9
MW-08BR(25.5-26)
02/11/2015
7-4
23700
---
<2.7
193
0.39
31j
<0.33
3748
<272
449
32.9
45.7
31300
2j
29900
933
<0. 0089
<10.9
4 -57
<27.2
5450
---
173
33.6
<272
---
75.8
59.4
MW-10BR (0.75-1.0)
02/23/2015
6.3
7640
---
1.4
81.8
0.4
13.6j
0.1j
1210
NA
41.9
12.4
28.9
18600
9.8
5590
527
0.0053j
<0.57
16.3
NA
2660
1.4
93.4
9.4
---
---
35.1
61.3
MW-12D (1-2)
04/26/2015
4.9
11000
---
3.6j
19.6
<0.3
27.4
<0.72
<150
<302
43.6
<6
12.4
31200
6.8
139j
22.1
0.036
<3
0.83j
<30.2
182j
---
Q99
<3
<302
---
61
5.2j
MW-12D (25-26)
04/27/2015
5.9
3530
---
<6
67.4
<0.3
9.8j
<0.72
<149
<301
3.2
6
22.4
11900
7.2
1190
395
<0.0095
<3
<1.5
<30.1
1520
---
F299
<3
<301
---
8.2
15
SB-01 (1-2)
03/04/2015
6.3
7030
---
1.2j
49.6
0.24
9.6
<0.17
655
<362
15.7
3.7
8.8
12400
9.6
1670
104
0.033
<0.7
2.5
<36.2
881
<1.4
35.4j
6
<362
---
28.3
14.5
SB-01 (13.5-14.5)
03/04/2015
5.5
4960
---
1.2j
61.5
0.56
<15.9
<0.15
270
1 <312
1 <1.6
8.9
20.6
8490
1 2.9
1 2440
1 678
<0.01
<3.2
<1.6
<31.2
1550
1.4
40.7j
8.3
<312
---
17.8
13.2
Prepared by: JHG Checked by: JAW
Notes:
64 - Indicates values omitted from dataset.
--- - Value removed; non -detected concentration exceeds PSRG Protection of Groundwater.
Indicates data removed /identified as an outlier.
< - concentration not detected at or above the adjusted reporting limit.
j - Estimated concentration above the adjusted method detection limit and below the adjusted reporting limit.
mg/kg - milligrams per kilogram
NA - Not analyzed
NE - Not established
PSRG Protection of Groundwater - NCDEQ IHSB Preliminary Soil Remediation Soil Remediation Goals Table - October 2016
S.U. - Standard Units
P:\Duke Energy Progress. 1026\Statistics_CAMA\Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO\Mayo\Soil\TM Tables\TABLE 1 - MAYO_BG Soils -Highlighted Outliers.xlsx Page 1 of 1

TABLE 2
BACKGROUND THRESHOLD VALUES FOR SOIL
MAYO STEAM ELECTRIC PLANT
DUKE ENERGY PROGRESS, LLC, ROXBORO, NC
Parameter
Reporting Unit
PSRG Protection of
Groundwater
BTVt
pH*
S.U.
NE
4.9 - 6.3
Aluminum
mg/kg
NE
23700
Antimony
mg/kg
0.9
---
Arsenic
mg/kg
5.8
6
Barium
mg/kg
580
193
Beryllium
mg/kg
63
0.82
Boron
mg/kg
45
31
Cadmium
mg/kg
3
0.72
Calcium
mg/kg
NE
1210
Chloride
mg/kg
NE
362
Chromium
mg/kg
360,000
62.2
Cobalt
mg/kg
0.9
32.9
Copper
mg/kg
700
45.7
Iron
mg/kg
150
31300
Lead
mg/kg
270
9.8
Magnesium
mg/kg
NE
5590
Manganese
mg/kg
65
1230
Mercury
mg/kg
1
0.036
Molybdenum
mg/kg
NE
12.7
Nickel
mg/kg
130
29.4
Nitrate (as N)
mg/kg
NE
36.2
Potassium
mg/kg
NE
6590
Selenium
mg/kg
2.1
1.4
Sodium
mg/kg
NE
173
Strontium
mg/kg
NE
33.6
Sulfate
mg/kg
250
362
Thallium
mg/kg
0.28
---
Vanadium
ni
6
75.8
Zinc
mg/kg
1200
88.9
Prepared by: JHG Checked by: LWD
Notes:
S.U. = Standard Unit
mg/kg = milligrams per kilogram
* = Upper and lower threshold values calculated for parameter
NE = Not Established
= Not applicable; dataset contains zero valid samples
t Indicates value is provisional; dataset contains less than 10 valid samples
P:\Duke Energy Progress. 1026\Statistics_CAMA\Preli mi nary Background Determinations for NCDEQ July 7 2017\BTV TECH MEMO\Mayo\Soil\TM
Tables\TABLE 2 - Mayo PBG Soil Page 1 of 1

Background Threshold Values for Soil
August 4, 2017
Mayo Steam Electric Plant
ATTACHMENT 1
SOIL BORING LOGS (ADDITIONAL SAMPLES)
P: \ Duke Energy Progress.1026 \ Statistics_CAMA \ Background Determinations for NCDEQ July 7 2017\ BTV TECH
MEMO \ Mayo \ Soil \ Mayo - SOIL BTV_FINAL.docx

1%
PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-2
PROJECT NO: 1026.105
STARTED: 7/18/17 COMPLETED: 7/18/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1011195.19 EASTING: 2028866.64
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 15.0 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
v
= C�
co
co
W
d
O-
o
Cn_
z
OJ
o f
WELL
CONSTRUCTION
w v
Q O
DESCRIPTION
2
U
D
a Q
p
C�
<
�—
m0
MIL
Dense, brown orange, clayey sandy silt.
5
ML
Dense, brown orange, clayey sandy silt.
10
ML
Dense, brown orange, clayey sandy silt.
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
CLIENT: Duke Energy Progress, LLC.
SynTerra
148 River Street, Suite 220 PROJECT LOCATION: Roxboro, NC
ra Greenville, South Carolina 29601
�Ter•Phone:[phone] PAGE 1 OF 1

PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-3
PROJECT NO: 1026.105
STARTED: 7/18/17 COMPLETED: 7/18/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1011932.94 EASTING: 2029323.42
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 9.0 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
v
=
co
w
a
O^
a
U)
z
OJ
❑ E
WELL
CONSTRUCTION
w v
0
Q O
DESCRIPTION
g
U
❑
a s
❑
r
<
W"
m0
Orange brown, sandy silt with rock and white gray
ML
saprolite to partially weathered rock, dry, some relic
J.
structure present.
5
White gray saprolite, dry. Auger refusal at 9 feet below
ground surface.
10
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
f CLIENT: Duke Energy Progress, LLC.
ra
48 RPROJECT LOCATION: Roxboro, NC
148 River Street, Suite 220
���.ra Greenville, South Carolina 29601
Phone:[phone] PAGE 1 OF 1

PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-4
PROJECT NO: 1026.105
STARTED: 7/18/17 COMPLETED: 7/18/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1011758.59 EASTING: 2028843.84
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 15.0 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
v
=
co
w
a
O^
a
U)
z
OJ
❑ E
WELL
CONSTRUCTION
w v
0
Q O
DESCRIPTION
g
U
❑
a s
❑
r
<
W"
m0
ML
Brown sandy silt with vegetation, moist.
MILRed
orange, clayey sandy silt with highly weathered
rock, moist to dry.
5
MIL
Red orange, clayey sandy silt with highly weathered
J.
rock, moist to dry. Lighter color with depth.
10
ML
Orange brown, sandy silt, moist to dry.
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
f CLIENT: Duke Energy Progress, LLC.
ra
148 River Street, Suite 220 PROJECT LOCATION: Roxboro, NC
48 R
���.ra Greenville, South Carolina 29601
Phone:[phone] PAGE 1 OF 1

PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-5
PROJECT NO: 1026.105
STARTED: 7/24/17 COMPLETED: 7/24/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1012015.36 EASTING: 2028472.6
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 15.0 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
v
=
co
w
a
O^
a
U)
z
OJ
❑ E
WELL
CONSTRUCTION
w v
0
Q O
DESCRIPTION
g
U
LU
❑
a s
❑
(Q
m 0
OL
ML
Brown topsoil with vegetation, moist.
Light brown, sandy silt with clay lenses grading to
following depth description, dry.
Stiff, light orange brown, clayey silt, moist to dry.
ML
5
ML
Stiff, brown orange, clayey silt, moist to dry.
10
Same as above, grading to moderately stiff, brown
ML
orange, clayey silt, moist to dry saprolite with partially
weathered rock.
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
f CLIENT: Duke Energy Progress, LLC.
ra
148 River Street, Suite 220 PROJECT LOCATION: Roxboro, NC
48 R
���.ra Greenville, South Carolina 29601
Phone:[phone] PAGE 1 OF 1

PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-8
PROJECT NO: 1026.105
STARTED: 7/18/17 COMPLETED: 7/18/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1009163.72 EASTING: 2028830.52
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 9.5 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
U
= O
w
a
O^
U)
Oz
E❑
WELL
CONSTRUCTIONQOU)
W
DESCRIPTION
❑a
s
❑
_
<LU
0
ML
Brown silty sand with vegetation and rock fragments,
ML
Dense, brown orange, clayey silty sand, dry.
5
ML
Light brown orange, silty sand with rock, dry.
Light gray, sand and silt with rock. Geoprobe refusal at
BAML
9.5 feet below ground surface.
10
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
f CLIENT: Duke Energy Progress, LLC.
ra
48 RPROJECT LOCATION: Roxboro, NC
148 River Street, Suite 220
���.ra Greenville, South Carolina 29601
Phone:[phone] PAGE 1 OF 1

PROJECT: Mayo Steam Electric Plant
WELL / BORING NO: BGSB-9
PROJECT NO: 1026.105
STARTED: 7/18/17 COMPLETED: 7/18/17
DRILLING COMPANY: Geologic Exploration
NORTHING: 1009437.44 EASTING: 2029418.65
DRILLING METHOD: GeoProbe
G.S. ELEV: ft M.P. ELEV: NA ft
BOREHOLE DIAMETER: 3 IN
DEPTH TO WATER: NA ft TOC TOTAL DEPTH: 15.0 ft BGS
NOTES:
LOGGED BY: A. Lefitz CHECKED BY: E. Yurkovich
U
az 0
U
w
a
O o
U)
z
OJ
❑ E
WELL
CONSTRUCTION
W
Q O
U)
DESCRIPTION
g
U a
L
❑
a s
❑
_
<
m 0
SM
Dense, orange brown, silty sand with rock, saprolite
with relic structure, dry.
5
SM
Light gray, sandy silt, saprolite dry.
10
MIL
Light gray, sandy silt, dry, partially weathered rock at
12.5 feet below ground surface.
15
20
25
30
35
40
45
Coordinates obtained with hand held GPS unit.
f CLIENT: Duke Energy Progress, LLC.
ra
148 River Street, Suite 220 PROJECT LOCATION: Roxboro, NC
48 R
���.ra Greenville, South Carolina 29601
Phone:[phone] PAGE 1 OF 1