3620_DukeAllen_ReqAbandonPZ_FID_20240821

DUKE
ENERGY,
August 21, 2024
North Carolina Department of Environmental Quality
Division of Waste Management
Solid Waste Section
2090 U.S. 70 Highway
Swannanoa, NC 28778-8211
Attn: Ms. Sarah Moutos
525 S. Tryon Street
Mail Code: DEP-36A
Charlotte, NC 28202
Re: Additional Groundwater Data and Piezometer Abandonment REQUEST FOR APPROVAL —
South Starter Landfill
Reference No.: 3620-INDUS
Allen Steam Station
Gaston County, North Carolina
Dear Ms. Moutos,
On July 12, 2024, Duke Energy Carolinas, LLC (Duke Energy) submitted Technical Memorandum: Allen
Steam Station — South Starter Landfill (Permit No. 3620-INDUS) Groundwater Vertical Separation
Evaluation, prepared by SynTerra, to demonstrate regulatory requirements for groundwater vertical
separation from the South Starter Landfill (SSLF) liner were satisfied. The North Carolina Department
of Environmental Quality (NCDEQ), Division of Waste Management, Solid Waste Section (Section)
concurred that the requirements had been met in a letter dated July 31, 2024.
As required per the Section's June 16, 2023 Memorandum, Duke Energy collected additional
groundwater elevation data from water level observation piezometers located within the footprint of the
Allen SSLF after receiving the Section's approval of groundwater vertical separation and is hereby
providing the additional groundwater information and requesting approval to abandon four of the six
SSLF footprint piezometers as soon as possible due to SSLF liner deployment progression,
namely SSLF-PZ-1 R, SSLF-PZ-4R, SSLF-PZ-S, and SSLF-PZ-6.
Two other SSLF footprint piezometers, SSLF-PZ-2R and SSLF-PZ-3R, are expected to be able to
remain in -place a short time longer before liner progression warrants their abandonment. Duke Energy
will continue to monitor water levels at SSLF-PZ-2R and SSLF-PZ-3R and submit that additional
groundwater data and request for abandonment approval separately.
Locations of groundwater monitoring locations in and around the SSLF area, including the six SSLF
footprint piezometers, are shown on the enclosed Figure 2.
The Technical Memorandum submitted July 12, 2024 contained SSLF area groundwater
measurements through July 1, 2024. The enclosed Table 1 (groundwater elevation summary) and
Figure 1 (hydrographs) have been updated to provide groundwater elevation data collected from July
1, 2024 through August 7, 2024 (most recent measurement) from the four SSLF footprint piezometers
that Duke Energy is currently seeking abandonment approval for: SSLF-PZ-1 R, SSLF-PZ-4R, SSLF-
PZ-5, and SSLF-PZ-6.
Page 1 of 2

Additional Groundwater Data & PZAbandonment Request
Allen Steam Station — SSLF 3620-INDUS August 21, 2024
If you have any questions or comments regarding this submittal and request, please contact me at
Courtney.Murphy(a-)_duke-energy.com or [phone].
Respectfully,
a 111
WAYW-ffk1Ptj
Courtney W. Murphy, P.G.
Environmental Services
Enclosures (3): Table 1 — Well Construction and Groundwater Elevation Summary, Allen Steam Station,
South Starter Landfill, Gaston County, North Carolina (SynTerra, August 21, 2024)
Figure 1 — Hydrographs for SSLF Area Monitoring Locations, Allen Steam Station,
Gaston County, North Carolina (SynTerra, August 21, 2024)
Figure 2 — Site Features and Monitoring Locations, South Starter Landfill, Allen Steam
Station, Gaston County, North Carolina (SynTerra, July 12, 2024)
Cc: Jordan Russ — NCDEQ
Sherri Stanley — NCDEQ
Ed Sullivan — Duke Energy
Tyler Hardin — Duke Energy
Kim Witt — Duke Energy
Preston McCloud — Duke Energy
Sheila Westcott — Duke Energy
Jay Mokotoff — AECOM
Chris Suttell - SynTerra
Page 2 of 2

TABLE 1
WELL CONSTRUCTION AND GROUNDWATER ELEVATION SUMMARY
GROUNDWATER VERTICAL SEPARATION EVALUATION
ALLEN STEAM STATION - SOUTH STARTER LANDFILL
DUKE ENERGY CAROLINAS, LLC, GASTON COUNTY, NC
7/1/2024
7/10/2024
7/16/2024
7/23/2024
7/30/2024
8/7/2024
Approximate
Calculated Vertical
Target
Top of Well
Ground
Screened
Separation from
Location ID
Monitoring
Casing
Surface
Interval
Northing
Easting
Groundwater
Depth
p
Groundwater
Depth Groundwater
p
Depth
p
Groundwater
De
Depth
Groundwater
Depth
Groundwater
Depth
Groundwater
Target Elevation as
Flow Zone
(Ft-NAVD 88)
Elevation
(Ft-BGS)
Elevation^
to Water
Elevation
to Water Elevation
to Water
Elevation
to Water
Elevation
to Water
Elevation
to Water
Elevation
of 8/7/2024
(Ft-NAVD 88)
(Ft-NAVD 88)
(Ft-BTOC)
(Ft-NAVD 88)
(Ft-BTOC) (Ft-NAVD 88)
(Ft-BTOC)
(Ft-NAVD 88)
(Ft-BTOC)
(Ft-NAVD 88)
(Ft-BTOC)
(Ft-NAVD 88)
(Ft-BTOC)
(Ft-NAVD 88)
(Ft)
SSLF-PZ-01R
Shallow
609.36
606.69
5.00
20.00
524110.00
1399614.45
603
7.22
602.14
6.80[6602.56
7.33
602.03
6.74
602.62
6.52
602.84
6.84
602.52
0.48
SSLF-PZ-04R
Shallow
622.07
619.40
5.00
20.00
523485.74
1399046.62
617
14.60
607.47
14.525
14.86
607.21
14.88
607.19
14.63
607.44
14.85
607.22
9.78
SSLF-PZ-05
Shallow
610.98
608.19
5.00
20.00
523689.45
1399580.96
605
14.00
596.98
13.61
14.12
596.86
12.19
598.79
13.27
597.71
13.57
597.41
7.59
SSLF-PZ-06
Shallow
619.67
617.26
5.00
20.00
523827.66
1399117.56
613
8.90
610.77
8.561
9.10
610.57
8.73
610.94
8.25
611.42
8.54
611.13
1.87
Notes:
-Groundwater elevation is at least 4 feet below the target groundwater elevation
^ - Target groundwater elevation for a minimum of 4 feet of vertical separation of the water table from the CSL, based on revised SSLF base grades (see AECOM Permit to Construct Modification Request dated 5/5/2023)
BGS - below ground surface
BTOC - below top of casing
CSL - compacted soil liner
Ft - feet
NAVD 88 - North American Vertical Datum of 1988.
SSLF - South Starter Landfill
Prepared by:LVS Checked by:C1S
Page 1 of 1

SSLF-PZ-01R
SSLF-PZ-04R
607
4
620
4
t SSLF-PZ-01R
3.5 Groundwater Elevation
♦SSLF-PZ-04R
3.5 Groundwater Elevation
605
(Ft NAVD)
615
(Ft NAVD)
0
3
3
z 603
—Model Prediction
2.5 c (Ft NAVD-88)
610
—Model Prediction
2.5 (Ft NAVD-88)
0
601
0
2
i0
1
4
2
w
599
1.5 ` —Target Elevation
a (603 Ft NAVD-
88)
605
1.5 a —Target Elevation
(617 Ft NAVD-
88)
1
1
600
597
0.5 —Rainfall (in)
-
A�A
0.5 —Rainfall (in)
595
0
595
— 1�
0
7/5/2024
7/10/2024
7/15/2024 7/20/2024 7/25/2024 7/30/2024 8/4/2024
6/30/2024 7/5/2024 7/10/2024 7/15/2024 7/20/2024 7/25/2024 7/30/2024 8/4/2024
6/30/2024
Date
Date
SSLF-PZ-05
SSLF-PZ-06
610
4
620
4
605
3.5 SSLF-PZ-05
Groundwater Elevation
(Ft NAVD)
615
3.5 ♦SSLF-PZ-06
Groundwater Elevation
(Ft NAVD)
3
3
600
o
2.5 c —Model Prediction
" (Ft NAVD-88)
a
610
o
2.5 —Model Prediction
- (Ft NAVD-88)
0
'
2 «
n
2 -
w 595
1 5
W 605
1.5 c` —Target Elevation
—Target Elevation
(613 Ft NAVD-
(605 Ft NAVD-
1 88)
88)
1
590
600
0.5
0.5 —Rainfall (in)
—Rainfall (in)
&
%/,\
A
585
0
595
/
\—A
—
A
7/5/2024 7/10/2024 7/15/2024 7/20/2024 7/25/2024 7/30/2024 8/4/2024
7/5/2024
7/10/2024 7/15/2024 7/20/2024 7/25/2024 7/30/2024 8/4/2024
6/30/2024
6/30/2024
Date
Date
Notes:
in -inches
SSLF -South Starter Landfill
Elevation of feet is in reference to North American Vertical Datum of 1988 (NAVD-88)
Ft - Feet
Model predictions based on SynTerra's July 11, 2023 report titled Groundwater
+.
if,
V ENERGY
DRAWN BY: C. SUTTELL DATE: 8/21/2024
REVISED BY:
CHECKED BY: L. DRAGO DATE: 8/21/2024
APPROVED BY: C. SUTTELL DATE: 8/21/2024
PROJECT MANAGER: C. SUTTELL
FIGUREI
HYDROGRAPHS FOR SSLF AREA
MONITORING LOCATIONS
GROUNDWATER VERTICAL SEPARATION
EVALUATION
Modeling to Support Vertical Separation -South Starter Landfill 36201NDUS
'
ALLEN STEAM STATION
www.synterracorp.com
synTerra
GASTON COUNTY, NORTH CAROLINA