Duke Energy-Allen - Gypsum Pad Assessment Work Plan Tech Memo Final 2019 06 12

41P
synTerm TECHNICAL MEMORANDUM
Date: June 12, 2019 File: 1026.17.23A
To: Courtney Murphy (Duke Energy)
Cc: Kathy Webb (SynTerra)
From: Chris Suttell C:75
Subject: Allen Steam Station Gypsum Pad Assessment Work Plan
This technical memorandum provides a work plan for proposed groundwater and soil
assessment activities related to the gypsum pad area at the Allen Steam Station (Allen,
Station, or Site). The Station, owned and operated by Duke Energy Carolinas, LLC
(Duke Energy), is located in Belmont, Gaston County, North Carolina (Figure 1). The
Site encompasses approximately 1,009 acres. The gypsum pad assessment area
encompasses approximately 8 acres in the northern portion of the Site (Figure 2).
BACKGROUND
In 2014, the North Carolina General Assembly passed the Coal Ash Management Act
(CAMA). CAMA requires the owner of a coal combustion residuals (CCR) surface
impoundment to conduct a detailed assessment of site groundwater and soil within and
around the CCR surface impoundment. Primary sources of CCR-related constituents at
Allen were identified during the CAMA-compliant Comprehensive Site Assessment
(CSA). The constituents were related to the retired ash basin (RAB) and the active ash
basin (AAB).
In an April 5, 2019 letter from the North Carolina Department of Environmental Quality
(NCDEQ) to Duke Energy, NCDEQ listed and requested assessment of additional
potential sources at the Station. Per the letter, all potential sources hydrologically
connected to the ash basins, including the ash basins, are to be assessed and included in
an updated Corrective Action Plan (CAP). The coal pile was included as an additional
potential source hydrologically connected to the ash basins and an assessment of the
coal pile area is ongoing.
Page 1 of 4

Technical Memorandum - Gypsum Pad Assessment Work Plan June 12, 2019
Duke Energy Carolinas, LLC - Allen Steam Station SynTerra
The gypsum pad was identified in the April 5, 2019 letter as a potential source not
associated with the ash basins, as it is located approximately 1,800 feet north of the RAB
and coal pile and within a groundwater flow system separated from the ash basins by
the discharge canal. Per the April 5, 2019 letter, all potential sources not hydrologically
connected to the ash basins are to be assessed and included in a CSA in 2020. There is
no current evidence indicating storage of gypsum on the pad has affected soil or
groundwater. However, no existing monitoring wells are located within approximately
1,000 feet of the gypsum pad area. Therefore, assessment of inorganic constituents in
soils and groundwater in the gypsum pad area is planned.
GYPSUM PAD DESCRIPTION
Power generating operations began at Allen in 1957, and the Station is currently active.
Coal-fired power generation produces sulfur dioxide emissions. A flue gas
desulfurization (FGD) system, located north of the Station, directs flue gas into an
absorber, where a limestone (calcium carbonate) slurry is sprayed. The sulfur dioxide in
the flue gas reacts with the limestone slurry to produce gypsum (calcium sulfate).
Gypsum produced from this process is temporarily staged in an area referred to as the
gypsum pad. The gypsum pad, which covers approximately 3.5 acres, is lined with 60-
millimeter high -density polyethylene (HDPE) geomembrane and a concrete pad.
Gypsum was first placed on the pad in 2009, and use of the pad to stage gypsum
continues. Gypsum produced at Allen is either sold for beneficial reuse or placed in the
double -lined RAB Ash Landfill, located within the footprint of the RAB.
GYPSUM PAD AREA ASSESSMENT OBJECTIVES
Objectives of the gypsum pad area assessment include the following:
• Characterize inorganic constituent concentrations in soil and groundwater.
• Determine groundwater flow direction.
• Compare inorganic constituent concentrations in the gypsum pad area with Site
background concentrations evaluated during the CAMA ash basins assessment
and with other applicable regulatory criteria.
Page 2 of 4

Technical Memorandum - Gypsum Pad Assessment Work Plan June 12, 2019
Duke Energy Carolinas, LLC - Allen Steam Station
SOIL ASSESSMENT
SynTerra
Soil samples would be collected at proposed monitoring well locations (GP-1 through
GP-6) as part of well installation activities (Figure 2). Soil samples would be collected at
intervals of approximately 3 feet to 5 feet until reaching the top of the groundwater
table (estimated to range from approximately 10 feet to 25 feet below ground surface) as
summarized on Table 1. Additional soil samples would be collected below the water
table within well screened intervals. The soil samples would be analyzed for inorganic
parameters listed on Table 2 with adjusted reporting limits appropriate for comparison
of soil analytical results to the Preliminary Soil Remediation Goals (PSRG) Protection of
Groundwater (POG).
A synthetic precipitation leaching procedure (SPLP) would be used to evaluate
potential leaching effects from the solid media. Soil SPLP samples would be collected at
a frequency of two per well cluster location, with one unsaturated sample collected
from 2 to 3 feet below ground surface, and one saturated sample collected from within
the well screen interval. Soil SPLP samples would be analyzed for inorganic parameters
listed on Table 2.
GROUNDWATER ASSESSMENT
Twelve (12) monitoring wells would be installed to characterize the gypsum pad area
groundwater in shallow and deep groundwater zones. The shallow zone is considered
groundwater within soil and saprolite material. The deep zone is considered
groundwater within partially weathered rock transition zone material underlying the
shallow zone and overlying competent bedrock. Six shallow (S) and six deep (D)
groundwater monitoring wells (GP-1S/D through GP-6S/D) would be installed as well
pairs. Proposed gypsum pad area well installation locations are shown on Figure 2, and
proposed well details are provided as Table 1. Specific well locations may be shifted
depending on access and field conditions at the time of installation.
Well installation procedures and well construction materials and lengths would be
consistent with ongoing CAMA assessment activities and in general accordance with
the NCDEQ approved Proposed Groundwater Assessment Work Plan (Rev. 1) (HDR, 2014).
During boring installation, soil/rock cuttings would be described for lithologic
information, including color and soil/rock type. Each well would be constructed in
accordance with NCAC Title 15A, Subchapter 2C, Section .0100 Well Construction
Standards and consist of 2-inch diameter NSF schedule 40 PVC flush -joint threaded
casings and prepacked screens.
Page 3 of 4

Technical Memorandum - Gypsum Pad Assessment Work Plan June 12, 2019
Duke Energy Carolinas, LLC - Allen Steam Station SynTerra
After installation, the monitoring wells would be developed in order to remove drill
fluids, soils, and other fines that might have been introduced into the formation or sand
pack during drilling and well installation. Development helps establish communication
of the well with the aquifer. Newly installed wells would be surveyed for location and
elevation.
Groundwater samples would be collected using low -flow sampling techniques per the
groundwater sampling procedures provided in the Low Flow Sampling Plan, Duke Energy
Facilities, Ash Basin Groundwater Assessment Program, North Carolina, June 10, 2015 (Duke
Energy, 2015). Groundwater samples would be analyzed for constituent parameters in
Table 3.
GYPSUM PAD ASSESSMENT REPORTING
The gypsum pad area assessment findings will be presented in a CSA report that will be
submitted to the North Carolina Department of Environmental Quality (NCDEQ) on
March 31, 2020, as requested in an April 5, 2019, letter from NCDEQ to Duke Energy.
ATTACHMENTS:
Figure 1: Site Location Map
Figure 2: Proposed Gypsum Pad Assessment Sample Locations
Table 1: Proposed Gypsum Pad Assessment Soil Samples and Monitoring Wells
Table 2: Soil Analytical Parameters
Table 3: Groundwater Analytical Parameters
REFERENCES:
April 5, 2019 letter from Holman (NCDEQ) to Draovitch (Duke Energy)
Proposed Groundwater Assessment Work Plan (Rev. 1) (HDR, 2014)
Low Flow Sampling Plan, Duke Energy Facilities, Ash Basin Groundwater Assessment
Program, North Carolina, June 10, 2015 (Duke Energy, 2015)
Page 4 of 4

Technical Memorandum - Gypsum Pad Assessment Work Plan June 12, 2019
Duke Energy Carolinas, LLC - Allen Steam Station
ATTACHMENTS
SynTerra

n
` !
ALLEN STEAM STATION
PARCEL LINE
6
IGYPSUM PAD
DISCHARGE CANAL
t
111 ¢p I
GP
5
POWER PLANT
v
COAL PILE AREA___f__
b
a �NPDES OUTFACE 001 tJ p
ALA
I
PLp�T
a .
r
�
RETIRED ASH BASIN
ASH LANDFILL
I
1
(COMPLIANCE BOUNDARY)RETIRED
ASH BASINf
LANDFILL
_ASH
-KUN
RETIRED ASH BASIN
RETIRED ASH BASIN
ASH LANDFILL
BOUNDARY V
RETIRED ASH BASIN
1
WASTE BOUNDARY
! yY
+
yyflflLfFE-R 0...
CYPRVS.kD
y°
ACTIVE ASH BASIN
C
NPDES OUTFALL 002
ACTIVE ASH BASIN _
WASTE BOUNDARY y
ACTIVE ASH ASIN
�� wi7tA 11P C�
&NCOMPLIANCE BOUN ARYL 1
a
SOURCE:
WATER FEATURES DEPICTED WITHIN WASTE BOUNDARIES
OF THE ASH BASINS ON THE 2016 USGS TOPOGRAPHIC MAP
DO NOT REPRESENT CURRENT CONDITIONS. THE CONDITIONS
DEPICTED ARE SIMILAR TO THOSE SHOWN ON THE 1968 AND
1973 USGS TOPOGRAPHIC MAPS OF THE AREA (1968 WEST
CHARLOTTE (1:24000) AND 1973 BELMONT (1:24000).
2016 USGS TOPOGRAPHIC MAP, BELMONT & CHARLOTTE WEST
QUADRANGLE, OBTAINED FROM THE USGS STORE AT
hftps://store.usgs.gov/map-locator.
,0'
synTerra
[7 ASHEVILLE
DUKE
-ENERGY, GASTON
CAROLINAS COUNTY
m
41
2
V
FIGURE 1
SITE LOCATION MAP
GYPSUM PAD ASSESSMENT
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC
IRLOTTE BELMONT, NORTH CAROLINA
DRAWN BY: K. KING DATE: 5/9/2019
PROJECT MANAGER: C. SUTTELL CONTOUR INTERVAL: 10 FT 95; 0 950 1,900
CHECKED BY: L. DRAGO MAP DATE: 2016 GRAPHICSCALE IN FEET

N'�
♦
♦
1
6z6/
�666/
4
I
1
I ♦.0
000 1 ,.00
o+
LEGEND
PROPOSED GYPSUM PAD ASSESSMENT SOIL
1 BORING AND MONITORING WELL
EXISTING MONITORING WELL
APPROXIMATE EXTENT OF GYPSUM PAD AREA
* — — — — TRANSMISSION LINES FROM WSP SURVEY
10' TOPOGRAPHIC CONTOUR FROM WSP SURVEY
2' TOPOGRAPHIC CONTOUR FROM WSP SURVEY
DUKE ENERGY CAROLINAS ALLEN PLANT
- - SITE BOUNDARY
90 0 90 180
1 oo ♦ ♦ GRAPHIC SCALE IN FEET
1 PosynTerra 148 RIVER STREET, SUITE 220
GREENVILLE, SOUTH CAROLINA 29601
11 io PHONE [phone]
D www.svnterracoro.com
�ccR-2ss/D/BR f DUKE
i DRAWN BY: B. MANAGER:
DATE: 06/12/2019
1 1 1 �� �' ENERGY PROJECT MANAGER: C. SUTTELL
' I t I CAROLINAS CHECKED BY: L. DRAGO
� � o ♦ ♦ I I
PADuke Energy Progress. 1026\00 GIS BASE DATA\Allen\M
NOTES:
PROPOSED WELL AND SOIL BORING LOCATIONS ARE APPROXIMATE AND MAY BE
ADJUSTED BASED ON ACCESSIBILITY AND FIELD CONDITIONS.
WSP SURVEY CONDUCTED APRIL 17, 2014.
AERIAL PHOTOGRAPHY OBTAINED FROM GOOGLE EARTH PRO ON MAY 6, 2019.
AERAL WAS COLLECTED ON APRIL 26, 2018.
DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM RIPS 3200 (NAD83).
FIGURE 1
PROPOSED GYPSUM PAD
ASSESSMENT SAMPLE LOCATIONS
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA

TABLE 1
PROPOSED GYPSUM PAD ASSESSMENT SOIL SAMPLES AND MONITORING WELLS
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
Monitoring
Well ID
Estimated
Well Depth
(feet bgs)
Soil Sample ID
(Estimated Depth
Interval in feet bgs)
Comments
-
GP-iSB 2-3
Near -surface unsaturated soil sample, water table —25 feet bgs
-
GP-1S6 8-9
Unsaturated soil sample, water table —25 feet bgs
-
GP-iSB 13-14
Unsaturated soil sample, water table —25 feet bgs
-
GP-1S6 18-19
Unsaturated soil sample, water table —25 feet bgs
-
GP-iSB 23-24
Unsaturated soil sample, water table —25 feet bgs
GP-1S
65
GP-iSB (61-62)
Soil sample from shallow well screened interval
GP-11)
110
GP-1SB (106-107)
Soil sample from deep well screened interval
-
GP-2SB 2-3
Near -surface unsaturated soil sample, water table —25 feet bgs
-
GP-2SB 8-9
Unsaturated soil sample, water table —25 feet bgs
-
GP-2SB 13-14
Unsaturated soil sample, water table —25 feet bgs
-
GP-2SB 18-19
Unsaturated soil sample, water table —25 feet bgs
-
GP-2SB 23-24
Unsaturated soil sample, water table —25 feet bgs
GP-2S
65
GP-2SB (61-62)
Soil sample from shallow well screened interval
GP-21D
110
GP-2SB (106-107)
Soil sample from deep well screened interval
-
GP-3SB 2-3
Near -surface unsaturated soil sample, water table —25 feet bgs
-
GP-3SB 8-9
Unsaturated soil sample, water table —25 feet bgs
-
GP-3SB 13-14
Unsaturated soil sample, water table —25 feet bgs
-
GP-3SB 18-19
Unsaturated soil sample, water table —25 feet bgs
-
GP-3SB 23-24
Unsaturated soil sample, water table —25 feet bgs
GP-3S
65
GP-3SB (61-62)
Soil sample from shallow well screened interval
GP-3D
110
GP-3SB (106-107)
Soil sample from deep well screened interval
-
GP-4SB 2-3
Near -surface unsaturated soil sample, water table —25 feet bgs
-
GP-4SB 8-9
Unsaturated soil sample, water table —25 feet bgs
-
GP-4SB 13-14
Unsaturated soil sample, water table —25 feet bgs
-
GP-4SB 18-19
Unsaturated soil sample, water table —25 feet bgs
-
GP-4SB 23-24
Unsaturated soil sample, water table —25 feet bgs
GP-4S
55
GP-4SB (51-52)
Soil sample from shallow well screened interval
GP-41D
100
GP-4SB (96-97)
Soil sample from deep well screened interval
GP-5SB 2-3
Near -surface unsaturated soil sample, water table —10 feet bgs
GP-5SB 5-6
Unsaturated soil sample, water table —10 feet bgs
-
GP-5SB 8-9
Unsaturated soil sample, water table —10 feet bgs
GP-5S
40
GP-5SB (36-37)
Soil sample from shallow well screened interval
GP-5D
85
GP-5SB (81-82)
Soil sample from deep well screened interval
-
-
GP-6SB 2-3
Near -surface unsaturated soil sample, water table -10 feet bgs
-
-
GP-6SB 5-6
Unsaturated soil sample, water table —10 feet bgs
-
GP-6SB 8-9
Unsaturated soil sample, water table "10 feet bgs
GP-6S
40
GP-6SB (36-37)
Soil sample from shallow well screened interval
GP-61D
85
GP-6SB (81-82)
Soil sample from deep well screened interval
Prepared by: LWD Checked by: CJS
Notes:
bgs = below ground surface
— = Approximately
SynTerra recommends rotosonic drilling methods for boring and well installation
Continuous cores from sonic drilling provide sufficient material for soil sampling and lithologic description.
Estimated well and soil sample depths based on data from the CCR-26S/D and LRB-07S.
Number of soil samples shown is approximate. A shallower water table will result in fewer samples, and a deeper water table will result in additional samples.
SynTerra recommends each well screen be submerged beneath the water table and have a length of at least 10 feet
SynTerra proposes soil samples be collected from well screen intervals for potential use in future analyses.
P:\Duke Energy Carolinas\17.ALLEN\23.Gypsum Pad Assessment\Work Plan\
Table 1 - Proposed Gypsum Pad Assessment Soil Samples and Monitoring Wells
Page 1 of 1

TABLE 2
SOIL ANALYTICAL PARAMETERS
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
INORGANIC COMPOUNDS
PSRG POG
UNITS
METHOD
Aluminum
110000
mg/kg
EPA 6010D
Antimony
0.9
mg/kg
EPA 6020B
Arsenic
5.8
mg/kg
EPA 6020B
Barium
580
mg/kg
EPA 6010D
Beryllium
63
mg/kg
EPA 6020B
Boron
45
mg/kg
EPA 6010D
Cadmium
3
mg/kg
EPA 6020B
Calcium
NE
mg/kg
EPA 6010D
Chloride*
NE
mg/kg
EPA 9056A
Chromium
3.8
mg/kg
EPA 6010D
Cobalt
0.9
mg/kg
EPA 6020B
Copper
700
mg/kg
EPA 6010D
Iron
150
mg/kg
EPA 6010D
Lead
270
mg/kg
EPA 6020B
Magnesium
NE
mg/kg
EPA 6010D
Manganese
65
mg/kg
EPA 6010D
Mercury
1
mg/kg
EPA 7471B or 7470A
Molybdenum
7.1
mg/kg
EPA 6010D
Nickel
130
mg/kg
EPA 6010D
Nitrate as Nitrogen*
NE
mg/kg
EPA 9056A
pH*
NE
S.U.
EPA 9045D
Potassium
NE
mg/kg
EPA 6010D
Selenium
2.1
mg/kg
EPA 6020B
Sodium
NE
mg/kg
EPA 6010D
Strontium
1500
mg/kg
EPA 6010D
Sulfate*
NE
mg/kg
EPA 9056A
Thallium low level
0.28
rril
EPA 6020B
Total Organic Carbon*
NE
rril
EPA 9060A
vanadium
350
rril
EPA 6020B
Zinc
1200
1 rril
EPA 6010D
Prepared by: RBI Checked by: C]S
Notes:
1. Soil samples to be analyzed for Total Inorganics using USEPA Methods 6010/6020 and pH using USEPA Method 9045, as noted above.
Select soil samples will also be analyzed for leaching potential using SPLP Extraction Method 1312 in conjunction with USEPA Methods
6010/6020.
2. Analytical methods as presented were applicable as of May 6, 2019. Analytical methods are updated periodically and applied as
appropriate.
*Select constituents are not analyzed for leaching potential.
PSRG POG - Primary Soil Remediation Goals Protection of Groundwater
mg/kg - Milligrams per kilogram
S.U. - Standard Unit
P:\Duke Energy Carolinas\17.ALLEN\23.Gypsum Pad Assessment\Work Plan\Table 2 - Soil Analytical Parameters Page 1 of 1

TABLE 3
GROUNDWATER ANALYTICAL PARAMETERS
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
PARAMETER
RL I UNITS METHOD
FIELD PARAMETERS
pH
NA
S.U.
Field Water Quality Meter
Specific Conductance
NA
PS/cm
Field Water Quality Meter
Oxidation Reduction Potential
NA
mV
Field Water Quality Meter
Temperature
NA
0C
Field Water Quality Meter
Eh
NA
mV
Field Water Quality Meter and Calculation
Dissolved Oxygen
NA
m L
Field Water Quality Meter
Turbidity
NA
NTU
Field Water Oualltv Meter
INORGANICS (total and dissolved)
Aluminum
S
/L
EPA 200.7
Antimony
1
/L
EPA 200.8
Arsenic
1
L
EPA 200.8
Barium
5
L
EPA 200.7
Beryllium
1
L
EPA 200.8
Boron
50
L
EPA 200.7
Cadmium
0.1
L
EPA 200.8
Chromium
1
L
EPA 200.8
Chromium VI
0.025
L
EPA 218.7
Cobalt
1
/L
EPA 200.8
Copper
1
/L
EPA 200.8
Iron
10
/L
EPA 200.7
Lead
1
/L
EPA 200.8
Lithium
2.5
L
EPA 200.8
Manganese
5
L
EPA 200.7
Mercury
0.00005
m L
EPA 245.1 or 7470A
Molybdenum
1
/L
EPA 200.8
Nickel
1
/L
EPA 200.8
Phosphorus
0.0005
/L
EPA 365.1
Selenium
1
/L
EPA 200.8
Silver
0.3
/L
EPA 200.8
Strontium
5
/L
EPA 200.7
Thallium low level
0.2
/L
EPA 200.8
Vanadium low level
0.3
/L
EPA 200.8
Zinc
5
L
EPA 200.7
RADIONUCLIDES
Radium 226
1
Ci/L
EPA 903.1 Modified
Radium 228
1
Ci/L
EPA 904.0/SW846 9320 Modified
Uranium 233 234 236 238
Varies by isotope
mL
SW846 3010A 6020A
ANIONS/CATIONS/OTHER
Alkalinity (as CaCO3)
5
m /L
SM 2320E
Bicarbonate
5
m /L
SM 2320B
Calcium
0.01
m /L
EPA 200.7
Carbonate
5
m /L
SM 2320B
Chloride
0.1
m /L
EPA 300.0
Fluoride
0.1
m /L
EPA 300.0
Magnesium
0.005
m L
EPA 200.7
Nitrate + Nitrite
0.01
m -N/L
EPA 353.2
Potassium
0.1
m /L
EPA 200.7
Sodium
0.05
m /L
EPA 200.7
Sulfate
0.1
mg/L
EPA 300.0
Sulfide
0.1
mg/L
SM 4500-S2D
Total Dissolved Solids
25
mg/L
SM 2540C
Total Organic Carbon
0.1
mg/L
SM531013EPA9060A
Total Suspended Solids
2.5
mq1L
SM 2540D
Prepared by: REB Checked by: KHG
Notes:
1. Select constituents will be analyzed for total and dissolved concentrations.
2. Analytical methods and reporting limits as presented were applicable at time of CSA field implementation in 2015. Analytical
methods and reporting limits are updated periodically and applied as appropriate.
RL - reporting limit
NA - Not analyzed
S.U. - Standard Unit
pS/cm - micro -Siemens per centimeter
mV - Millivolts
°C - Degrees Celsius
mg/L - Milligrams per liter
NTU - Nephelometric turbidity unit
pg/L - Micrograms per liter
pCi/L - Picocuries per liter
pg/mL - Micrograms per milliliter
mg - N/L - Milligrams nitrogen per liter
PADuke Energy Carolinas\17.ALLEN\23.Gypsum Pad Assessment\Work Plan\Table 3 - Groundwater Analytical Parameters Page 1 of 1