3619_3620_3621_DukeAllen_GWVertSeparation_LeachateBasin_FID1715806_20220830

(' DUKE
ENERGY-.
August 30, 2022
North Carolina Department of Environmental Quality (NCDEQ)
Division of Waste Management (DWM)
Solid Waste Section (the Section)
1646 Mail Service Center
Raleigh, North Carolina 28778
Attn: Ms. Sarah Moutos
526 S. Church Street
EC13K
Charlotte, NC 28202
Re: Groundwater Information to Demonstrate Vertical Separation and REQUEST FOR APPROVAL to Place
CSL — Leachate Basin
Reference No.: 3619-INDUS, 3620-INDUS, 3621-INDUS
Allen Steam Station
Gaston County
Dear Ms. Moutos,
As part of the requested information under item number (1.) of the Section's letter dated December 15,
2021 with subject Vertical Separation and Hold of PTC at South Starter Landfill, Duke Energy Carolinas
(Duke Energy) previously submitted on January 14, 2022 a drawing that depicted the Allen Steam Station
(Allen) Leachate Basin compacted soil liner (CSL) subgrade with two sets of overlain groundwater contours:
the adjusted modeled long-term seasonal high shallow groundwater contours and the November 29, 2021
shallow groundwater contours.
Although it was not specifically requested in the December 15, 2021 letter, the Section notes in their review
of the January 14, 2022 submittal, (Section letter dated January 26, 2022), that Duke Energy did not provide
accompanying analysis, determination of the groundwater separation, or comment on the constructability
of the current design.
The enclosed current submittal includes Drawing 1, a similar drawing to that submitted for the Allen
Leachate Basin on January 14, 2022; however, the previous site -wide shallow groundwater contour set
dated November 29, 2021 has been replaced/updated with a site -wide shallow groundwater contour set
dated May 31, 2022, and the viewport scale has been reduced in order to display additional area
surrounding the Leachate Basin footprint to show additional shallow wells.
Additionally, Attachment 1 of the current submittal includes a table with hydrographs summarizing
quarterly groundwater information collected from three piezometers (LB-PZ-1, LB-PZ-2, and LB-PZ-3) in
closest vicinity to the Allen Leachate Basin. The quarterly data ranges from August 31, 2020 through May
31, 2022. As observable from the enclosed table and hydrographs, shallow groundwater levels in the
vicinity of the Allen Leachate Basin appear to have achieved adequate vertical separation over a year ago
(May/June 2021 timeframe) and continue on a decreasing trend.
Page 1 of 2

Groundwater Information for Vertical Separation
Allen Steam Station — Leachate Basin
August 30, 2022
Duke Energy believes the enclosed information provides sufficient analysis of groundwater levels to
demonstrate that adequate vertical separation between groundwater and liner is achieved for the Allen
Leachate Basin, and groundwater levels are not anticipated to impact constructability of the current design
for the Allen Leachate Basin.
Upon the Section's review and concurrence with the enclosed information, Duke Energy respectfully
requests approval to begin placing CSL for the Allen Leachate Basin.
This information is only being provided electronically, but hard copies are available upon request. If you
have any questions or comments regarding this submittal, please contact me at Courtney.Murphy@duke-
energy.com or [phone].
Respectfully submitted,
&AU&A"
Courtney W. Murphy, P.G.
Environmental Services
Enclosures (2): Drawing 1— Groundwater Overly— Leachate Basin Compacted Soil Liner Subgrade (AECOM,
August 24, 2022)
Attachment 1—Allen Steam Station — Leachate Basin Groundwater Level Summary (Duke
Energy, August 22, 2022)
Cc: Jordan Russ — NCDEQ
Elizabeth Werner —NCDEQ
Claire Osborn — NCDEQ
Tyler Hardin — Duke Energy
Kim Witt — Duke Energy
Ashley Healy — Duke Energy
Kyle Baucom — Duke Energy
Henry Duperier— Duke Energy
Jay Mokotoff — AECOM
Chris Suttell - SynTerra
Page 2 of 2

1 1 REV. 0
/- �\
GWA-22S ;
\ ,\` EL.632.55'
x
o �
r r
1
I I
1
-------------
LLJ
0
- -----
::
------ lu 0
o
O�, = \ II I jl 1 \ \ 1� 1 W / _ —� --_- I �__-_ -_____ -- _-__--- _____ _—
Lj
LLY
II \ \ ------- �___�� — — —
\ \ I 1 \ \ / \t 1 \\ \\ \ J - L_ -__---- 1� / il�� %x '' ''/!'� _�=___=ram___--
_--__-
`�i
AB-28S i
Imi i l l l l I I l l 1 I \I /' I ' / �i%�630'
I I I I I //
1 \ of ROw1 1 / / / t t I I I �\ 1 1 I / III II I I I \ - ROW/wWI / ' / ; I I 1 , ; Ibei„ I IRow
�/I0�./1\/\\lIJI OE/�OE �,I I ROwOE
OE'�of I//., �� RowUE
/
_------- --------- - - - _ / ,.,////ROWS / OE , �I- / / / I w�
—' w \�\ w — —�' — _ = — _ ___-- _ == _ — — — - � � ,;;;•,'��, , f�OW , OE / / �E I , / p i
dE
�O ,' / ROW,- ISO' o
-�---------------- -----EX. SLUICE - �� E
-_- 30==- / kOlflh' / PIPES =
/ \ / / / / �_���� _ __ ___ / 15' X 20' LEACHATE / , , �, I / _
i i ,� \\ \ \/ II / ltl, /' % ' BASIN PUMP STATION ------- / . ' / ,/ ! / Q/ r-
/ / J ! _ / !
1 w I t / o \ \ \ / / / / ' I I // /' ' / ROW
\ /W I 640 10' x 6' LEACHATE BASIN - — — — — —— ,/ , \
,� /' LDS SIDESLOPE RISER
\ -
�.' I _ I .'- ! � • I � Jc ,/ � .. ,' � ACCESS PAD ------------' ! .' I,
w LB-PZ-0
EL: 624.38 /'/
,-------
640=
/ / \ ' I I / BASIN SUMP
O
1 ' / �i�-- It I I I / EL. 634.94' ��\ / T0" AB=24S
r-J/ EL. 623.43'
/
LLk
If
w / 1 / b / W
�'` k
��s
-� O IIf{
`Z/ / / I II I I 1 I, `\
"LU
ZF
LLJ
LLJ'' O 4' ' it 1 11, :�, 11 \\\
I iIf
o
IfJ I ► I I 1 ,� rn� , 1' �c'
LEACHATE I / ,, �/ / // // / /
w / I Lu
O BASIN I II
AB-13S / \ �i' L w li i I II I ii
EL. 637.27' ��_- O ' ./ I O//-
'
Lj
CO
W
0p'If
EL:622.85 xl I
\ 1 I I I
w \ cc
O
X �r W W I I 162iS
�— X `._n \ w Ld
O`IN
-625-
-------- 625 --------
625
LEGEND
EXISTING MAJOR CONTOUR (10 FOOT)
EXISTING MINOR CONTOUR (2 FOOT)
HISTORIC MAJOR CONTOUR (10 FOOT)
HISTORIC MINOR CONTOUR (2 FOOT)
PROPOSED MAJOR CONTOUR (10 FOOT)
PROPOSED MINOR CONTOUR (2 FOOT)
DUKE ENERGY PROPERTY BOUNDARY
APPROXIMATE ASH BASIN WASTE BOUNDARY
BRUSH AND TREE LINE
OE EXISTING OVERHEAD TRANSMISSION LINES
625 ADJUSTED LONG-TERM SEASONAL HIGH GROUNDWATER (SEE NOTE 3)
625 — EXISTING GROUNDWATER ELEVATION (MAY 31, 2022)
GUARDRAIL
GROUNDWATER MONITORING WELL
WATER LEVEL MONITORING PIEZOMETER
KInTr_:C
1. BOTTOM OF LEACHATE BASIN ELEVATIONS HAVE BEEN SET TO MAINTAIN A MINIMUM
VERTICAL SEPARATION OF 1 FOOT FROM MARCH 2O21 GROUNDWATER ELEVATIONS.
2. GRADES SHOWN OUTSIDE THE LIMITS OF THE EXISTING ASH BASINS ARE EXISTING
GRADES. GRADES SHOWN INSIDE THE LIMITS OF THE EXISTING ASH BASINS ARE
HISTORICAL BOTTOM OF ASH GRADES.
3. INCLUDES A FACTOR OF SAFETY OF 2.5 FEET ADDED TO THE ESTIMATED LONG TERM
SEASONAL HIGH GROUNDWATER ELEVATION DEVELOPED AND MODELED BY SYNTERRA
(2020) USING APPROVED METHODOLOGY AS DESCRIBED IN APPENDIX VI OF THE
GEOLOGICAL AND HYDROGEOLOGICAL REPORT - ALLEN STEAM STATION - CCR CLOSURE
LANDFILL UNITS (3619-, 3620- AND 3621-INDUS) - REVISION 0 (AECOM, 2020).
\ - _ `I- I 1� I 1 1 II I _-,� 1 -___ - _ --_ \\ I \ \ `\ ` \ `\ \\ \\ 6" CAST -IN -PLACE CONCRETE
- \ LLI I \ \ _ \ \ \ \
\\ `\ \\ I I '\
, \`\ `\ � \ \\ \\ I I \ \ \ ` I `\ `\ 4 CUSHION GEOTEXTILE
HAUL N\ 'I, \ \ \ \ I ` \ \\ \ I I \ \ \ \ 4 4 4
1 w I 1 \ \ \ \ \ \ \
__--,--- _\ `_`\� '•`� \ - \ \\\ O \ ; ROAD i I II I I Y' ! ` \` \`� \ `\ \`\ \��� \�_� \\ �\ I \ \� \`\ \\ \\ 4 4 `� 4 60-MIL HDPE
`\ �o 111,� 11 - x� `\ \\ I t\ \
PRIMARY GEOMEMBRANE
\`j \ I
`W \ \ \ - - \
II I `\ \ I 30_ \ \ \ \ ` \ _, ` \ \ \I I `\\ ��\ �`\ \`\ �`\\ �\\ � �����X����'����C���X���C�'��X��X����'��X��X � GEONET LEAK DETECTION SYSTEM
w--- I II I 1 `\ — �\ P I \`
LLJ
IN IN
��LEACHATE BASIN ',''. \\ \\
Y \ OE p ACCESS RAMP `�
-_� \\ \ \ , \\oW `. w , _ \ \\ \\ \ `\ \ \ , \, % I I \I \ \ CURRENT LAYER SHOWN
C �: y� y
LjLj IN
Lu
PERIMETER BERM
EL. 647.75'
If
w LLJ
1\ AB-23S \ �/
1 WA-23S \I `\ I I lash \��\ - _1 ` / / / / / \1 \ I ,
\ EL. -23S' - / ; \\`\ I , / / / ' //" _ / --- EL. 629.01
W-23S EL. 630.85' r \\ Il I / /
! I LLJ
O I ClF WELL
v 1 � ► I 1 , I / l l / 1, . l /
W ► I
W �7 I / / l l I I I 111 / l// / I � ' I / If
O (D l� I I ,
/
ZE If
r
W / /
/ \ --- / - \ W W
0 If
pw
------ _ - _ - \�
O
--- -- ----�\ \` .. - /' I♦ �l � `� i , � iii'/ // lll,/l//l/, I \ I' / / i l .--' -/ -----/i' // �� �,� � �,' � / / /
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
- 60-MIL HDPE
SECONDARY GEOMEMBRANE
- GEOSYNTHETIC CLAY LINER
12" COMPACTED SOIL LINER
NATURAL SOIL OR STRUCTURAL FILL
(COMPACTED EMBANKMENT)
TYPICAL LEACHATE BASIN CROSS-SECTION ON BASE
NOT TO SCALE
1 REV 1 DATE 1 APPD 1 DESCRIPTION I
0 80 160 240
GRAPHIC SCALE (IN FEET)
TITLE
GROUNDWATER OVERLAY - LEACHATE
BASIN COMPACTED SOIL LINER SUBGRADE
loim=mcom NSLF(3619-INDUS) AND SSLF(3620-INDUS)
ALLEN STEAM STATION
GASTON COUNTY, NORTH CAROLINA
N.C. ENGINEERING LICENSE NO. FOR ISSUED FOR REVIEW
F-0342
SEAL SCALE: AS SHOWN DES: MLM DUKE
DWG TYPE:.DWG DFTR: RES
JOB
�. ENERGY® DATE: : 8- 4-2204 ENGR: JDM
FILENAUE0VERLAY 034 - LEACHATE POND - BASE OF SOIL LINER GRADING PLAN 02 P_PRIWGJDM
DWG SIZE DRAWING NO. REVISION
ANSI O
22.0"x34.0"
o
0
INCHES 1 2 5 ITENTHS 1`0 20 30
1

ATTACHMENT 1 - ALLEN STEAM STATION - LEACHATE BASIN - GROUNDWATER LEVEL SUMMARY
Approx. CSL Approx. Inferred Approx. Inferred
Measurement WL Depth WL Elev Subgrade Elev for GW Elev for LB GW Vertical
Location ID TOC Elev Separation from
Date (ft-TOC) (ft-MSL) LB Zone Zone
CSL Subgrade for
(ft-MSL)1 (ft-MSL)1 LB Zone (ft)l
LB-PZ-1
8/31/2020
647.73
18.55
629.18
634.94
(LB Low End -sump)
625
10
LB-PZ-1
11/30/2020
14.62
633.11
LB-PZ-1
3/1/2021
12.20
635.53
LB-PZ-1
6/1/2021
17.21
630.52
LB-PZ-1
8/30/2021
20.29
627.44
LB-PZ-1
11/29/2021
22.43
625.30
LB-PZ-1
2/28/2022
18.20
629.53
LB-PZ-1
5/31/2022
23.35
624.38
LB-PZ-2
8/31/2020
646.77
14.36
632.41
638
(LB Mid -Section)
625
13
LB-PZ-2
11/30/2020
10.84
635.93
LB-PZ-2
3/1/2021
9.54
637.23
LB-PZ-2
6/1/2021
13.50
633.27
LB-PZ-2
8/30/2021
16.66
630.11
LB-PZ-2
11/29/2021
17.98
628.79
LB-PZ-2
2/28/2022
13.83
632.94
LB-PZ-2
5/31/2022
23.92
622.85
LB-PZ-3
8/31/2020
656.72
22.23
634.49
(LB High 0 End)
630
10
LB-PZ-3
11/30/2020
20.12
636.60
LB-PZ-3
3/1/2021
18.03
638.69
LB-PZ-3
6/1/2021
21.54
635.18
LB-PZ-3
8/30/2021
23.68
633.04
LB-PZ-3
11/29/2021
24.24
632.48
LB-PZ-3
2/28/2022
23.14
633.58
LB-PZ-3
5/31/2022
25.87
630.85
TOC = Top of PVC Casing Elev = Elevation MSL = Mean Sea Level CSL = Compacted Soil Liner
WL = Water Level ft = feet LB = Leachate Basin GW = Groundwater
Approx. = Approximate
1 Inferred from AECOM Drawing No. 1 - Groundwater Overlay - Leachate Basin Compacted Soil Liner Subgrade dated 8 24 2022
LB-PZ-1 (LB Low End)
638
636
J
�n 634
632
> 630
w 628
-1 626
624
622
6/2020 9/2020 1/2021 4/2021 7/2021 10/2021 2/2022 5/2022 8/202:
Date (M/YYYY)
LB-PZ-2 (LB Mid -Section)
f Water Level
Measurements (ft-MSL)
4-ft below LB Sump CSL
Subgrade EIev=630.94
• • • • • • Linear Trendline
638 f Water Level
636 Measurements (ft-MSL)
Ln 634
4 632
4-ft below Approx. CSL
630
2se
Subgrade Elev for LB Mid-
LU 628
A
Section=634
J 626
624
• Linear Trendline
622
6/2020 9/2020 1/2021 4/2021 7/2021 10/2021 2/2022 5/2022 8/2022
Date (M/YYYY)
LB-PZ-3 (LB High End)
640
639 -
638 -
637 -
636 -
635
v 634
LL' 633
631
630
6/2020 9/2020 1/2021 4/2021 7/2021 10/2021 2/2022 5/2022 8/2022
Date (M/YYYY)
0 Water Level
Measurements (ft-MSL)
4-ft below Approx. CSL
Subgrade Elev for LB
High End=636
• • • • • • Linear Trendline
Prepared By: CWM
Date: 8/22/2022
Page 1of1