NC0004979_Supplement_202030126_Renewal Application_20240429

DUKE
ENERGY
April 25, 2024
Sergei Chernikov, PhD.
North Carolina Division of Environmental Quality
1617 Mail Service Center
Raleigh, NC 27699-1617
Subject: Duke Energy Carolinas, LLC.
Allen Steam Station
Allen Steam Station
253 Plant Allen Road
Belmont NC, 28012
704-829-2587
RECEIVED
APR 2 9 2024
NCDEQ/DWR/NPDES
NPDES Permit NC0004979
Supplement to January 26, 2023 Application for Permit Renewal
Dear Dr. Chernikov:
Duke Energy Carolinas, LLC (Duke Energy) is submitting supplemental information to update the
January 26, 2023, NPDES permit renewal application. This submittal is necessitated due to significant
changes that are planned in 2025 after the station is retired. The current proposed station retirement date
is December 31, 2024.
After the January 26, 2023, permit renewal application submittal, it was decided that Plant Allen would
be retired earlier than previously expected. With the acceleration of the station retirement and the need
for a new site landfill, it was determined that the land occupied by the lined retention basin (LRB) will
make a suitable location for a new landfill. Prior to this decision the LRB (NPDES Outfall 006) was to
be the primary on -site station wastewater treatment system (WWTS) as the ash basin closure progressed.
The LRB is now planned to be decommissioned and demolished in 2025 with its location being replaced
by the construction of the new landfill (Canal Road Landfill), which is needed to support closing out the
ash basin. With the station shutting down and the LRB being decommissioned the other existing on -site
WWTS that discharges to NPDES Outfall 002 will become the primary on -site WWTS.
With the station retirement, many of the current outfalls will transition to no longer discharge and will
eventually be physically removed and/or plugged. Included in this submittal is a narrative that describes
the transition phase and long-term plans for each NPDES outfall. Two flow diagrams are also included.
The first flow diagram shows all the outfalls during the decommissioning transition phase after the
station is retired and the second diagram shows the remaining outfalls after the transition phase is
finished. An updated site map locating each outfall is also included.
The current WWTS classification for Allen Steam Station is PC-2/WW-2. The WW-2 was due
primarily to the Flue Gas Desulfurization WWTS (Internal Outfall 005), which includes a biological
treatment component. With this WWTS and also the domestic septic system being decommissioned, it
is requested that the WWTS for Outfall 002 be reassigned its classification accordingly, once these
systems are decommissioned.

Allen Steam Station
NPDES Permit NC0004979
Page 2 of 2
In the January 26, 2023 application cover letter, a reduction in the monitoring frequency was
requested for the Catawba River in -stream monitoring, the toe drain outfalls and Outfall 002.
Historical in -stream river data was included in the January 26, 2023 application. For your
consideration attached are summaries of analytical data for Outfall 002 and the toe drains. A
WWTS was built and then began operation in May 2022 for Outfall 002. The data summary for
Outfall 002 ranges from May 2022 through February 2024.
Should you have any questions please contact Robert Wylie at either 704 562-8258 or
Robert.Wylie(@,duke-energy.com.
CERTIFICATION
V certify, under penalty of law, that this document and all attachments were prepared
under my direction or supervision in accordance with a system designed to assure
that qualified personnel properly gather and evaluate the information submitted.
Based on my inquiry of the person or persons who manage the system, or those
persons directly responsible for gathering the information, the information submitted
is, to the best of my knowledge and belief, true, accurate, and complete. I am
aware that there are significant penalties for submitting false information,
including the possibility of fines and imprisonment for knowing violations. "
Yours truly,
Jeffrey D. Flanagan
General Manager III
Allen Steam Station
Attachments

Allen Steam Station Post Retirement Plans for Each NPDES Outfall
The current proposed retirement date for Allen Steam Station is December 31, 2024. Once retired the
site will begin a transition process. The following provides a description for each NPDES
permitted outfall during this transition period and thereafter.
Outfall 001: Once through cooling water. The primary flow historically from this outfall is the
Condenser Cooling Water (CCW). The CCW system will remain operational for a time period after
station retirement to allow for a source of water to support decommissioning of the station
powerhouse, basin closure dust suppression and the Groundwater Corrective Action Plan
(GWCAP) water infiltration system. A new service water system is planned to be installed in the
future to support these activities. Once this new service water system is installed Outfall 001 will
no longer discharge.
Outfall 002: Wastewater Treatment System (WWTS). This outfall will include treated landfill
leachate, extracted groundwater from GWCAP remediation, and ash basin dewatering. This
WWTS currently treats the ash basin dewatering by clarification, filtering, and pH control. In the
fall of 2024 additional components are to be installed in preparation for the three mentioned waste
streams. These components will include equalization tanks and sludge/sediment removal. The ash
basin dewatering will also include rainwater. The WWTS is designed to treat a maximum daily
discharge of 3 mgd.
Outfall 002A: Coal Yard Sump overflow (discharge from coal handling and storage areas). This
outfall is discharged when a rare event occurs such as loss of power to the pumps. As part of
decommissioning the Coal Yard Sump will be removed and this outfall will no longer discharge.
Outfall 00213: Powerhouse Sump overflow (floor wash water, boiler blowdown, water treatment
waste, condensates, equipment cooling water, sealing water and miscellaneous leakage). This
outfall is discharged when a rare event occurs such as loss of power to the pumps. As part of
decommissioning the Powerhouse Sump will be removed and this outfall will no longer discharge.
Outfall 003: Miscellaneous equipment non -contact cooling and sealing water. This system is also a
source for service water that is to be used to support decommissioning of the station powerhouse,
basin closure dust suppression and the GWCAP water infiltration system. This outfall will stop to
discharge as part of the decommissioning after the station retires.
Outfall 004: Miscellaneous non -contact cooling water, vehicle wash water, and intake screen
backwash. This outfall will stop to discharge as part ofthe decommissioning.
Outfall 005: Internal outfall for Flue Gas Desulfurization (FGD) Wastewater Treatment
System (WWTS). This system will stop to discharge as part of the decommissioning after the
station retires. As part of decommissioning, the FGD WWTS will be physically removed.
Page 1 of 7

Outfall 006: Lined Retention Basin (LRB). The LRB treats wastewater by flow equalization, settling,
chemical coagulation and pH neutralization. Waste streams that enter the LRB include wastewater from
the Holding Basin, component washdowns, domestic sanitary wastewater, stormwater from the coal
pile area, miscellaneous stormwater flows, CCR landfill leachate, FGD blowdown, yard drain sump,
water treatment filter backwash, bottom ash purge from the submerged flight conveyers, extracted
groundwater, laboratory wastes, and the powerhouse sump at Unit 5. The domestic waste is pre-treated
by a septic tank. The septic tank is planned to be removed and replaced with a collection tank that will
need to be pumped out and hauled to an off -site WWTS. During station decommissioning the LRB
will be receiving wastewater as noted above until each of the sources are decommissioned and stop to
discharge. The GWCAP extracted groundwater remediation system and the landfill leachate
collection basin will be diverted to the WWTS for Outfall 002. Other waste streams will no longer
exist. The inputs to the LRB are anticipated to cease to cease around June 2025. Once the inputs no
longer are entering the LRB the LRB will be decommissioned, removed and a landfill will be
constructed in the area the LRB previously existed. It is projected that the final discharge from the
LRB will occur in July 2025.
Outfall 007: Emergency spillway of the Lined Retention Basin. The spillway is designed for a flood
greater than a 100-year event. Sampling of this spillway is waived due to unsafe conditions associated
with sampling during an overflow event. This spillway will be removed as part of the
LRB decommissioning.
Outfall 008: Emergency spillway of the retired Ash Pond. The spillway is designed for a flood
greater than a 100-year event. Sampling of this spillway is waived due to unsafe conditions associated
with sampling during an overflow event.
Toe Drain Outfalls:
There are four toe drain outfalls that are in place to assist in maintaining the phreatic water levels
within the ash basin dam. These are four toe drains that are monitored quarterly if a discharge occurs.
Outfalls 108 and 108B rarely discharge. These outfall locations are identified on the following
attached site map.
Page 2 of 7

Catawba
River
Condenser
Cooling Water
Closed Loop
Bottom Ash
System
Water
Treatment
Boiler Room
Sumps
Flow Diagram #1
Allen Steam Station Post Retirement Water Flow Schematic Transition Phase
Sanitary
Waste
New Landfills
Leachate
Storage Basin
Outfall 001
79.9 MGD South Fork River
Outfall 002A
—
------ — — — ——O-———————— — — —-jo�( Catawba River
Intermittent
Coal Yard
Leachate
Sump
4
7Atmosphere
FGD
FGDWWTS
I
Boiler
Turbine Room
Sumps
Yard Drainage
Sump
Stormwater
Coal Handling
Sumps Outfall002
1.6 MGD avg
(3.0 MGD max)
Holding basin Catawba River
Wastewater I I
Treatment I I
System I
;As�hBasln � I
Outfall 103 I I
0.0022 MGD i I
l I
Toe Drains Outfall 104
1 0.0018 MGD I I
I
I L — — — — — — — — — —-Outfall 108 - Intermittent- I
I— — — — — — — — — — — — —-Outfall 108E - Intermittent)
FGD Ash Silo Outfall 007 LRB
Storrwater Emergency
Sump Sump Overflow
Lined
Retention Outfall006
Basin 0.1 MGD avg Catawba River
3.5 MGD max
0.5 MGD
Misc Equipment
Outfall 003
South Fork River
Cooling & Seals
4.5 MGD
Limestone
Stormwater
Retired Ash
Sump
Groundwater
Groundwater
Basin
Outfall
--► Catawba River
Infiltration
Extraction
Emergency
(Emergency)
Wells
Wells
Overflow
Powerhouse
Sump
Outfall002B
—--——
—————————————————
——————————————
— — — — — ——
(Intermittent)
=Catawba
Intake Screen
Outfall 004
—�
Catawba River
Backwash
6.5 MGD
Asiatic Clam/
Debris Filter------------------------------------------------------------- Catawba River
Notes: Backwash
1. Flows are estimated averages.
2. Red blocks and lines indicate systems being decommissioned. Page 3 of 7
3. Dashed lines indicate intermittent flows.

Flow Diagram #2
Allen Steam Station Post Decommission of Station Water Flow Diagram
Landfill Leachate
0.4 MGD
Basin
Ash Basin
0.7 MG
Dewatering
GCAP Wells 0.5
- -I
Wastewater
Treatment System
MGD
Notes:
1. Flows are estimated averages.
2. Dashed lines indicate intermittent flows. Page 4 of 7
Outfall 002
1.6 MGD avg
(3.0 MGD max)
Outfall 008
Emergency Overflow
Outfall 103
0.0022 MGD
Outfall 104
0.0017 MGD
Outfall 108
0.00008 MGD
Outfall 108B
0.00001 MGD
9

'0
Qpx.'L oW—
Outfa1007 • r.f �s ^.,1� .lam"/ _.
Outfall 006
Facility Location
-'. - • �. 6`- Legend
1
NPDES Outfall Locations
Active Outfall
��a_ ~ • * Outfall 602s Outfall to be Decommissioned
•�� - - - State sGrid/Quad: G14NE/Belmont
Outfall 60141
`s ,� j ° •'�. oU / - - - Receiving Streams: Catawba and South
\_' "`•✓ !! •' • j �V� Fork Catawba Rivers
Outfall 004 _ -'
QylrCfp(aptQ �• ,. Stream Class: WS-IV B & WS-V B
8-Diait HUC: 03050102
�W1 ! •Outfa11,002A � - - Drainage Basin: Catawba River Basin
Sub -Basin: 03-08-34
A4;
•����;"t I` __ ; I •• �: '. .�.,.��---(- •. �Outfall 008 .
\\'\.., .• - �` _ y,,... .. Outfall 108 �..
Outfalls
001 - Lat: 35°11'21.323"N / Long: 81°0'42.841"W
002 - Lat: 35°10'30.037"N / Long: 81°0'21.195"W
002A - Lat: 35"11'12.345"N / Long: 81"0'20.949"W
002B - Lat: 35*11'26.734"N / Long: 81°0'27.714"W
003 - Lat: 35*11'22.184"N / Long: 81°0'44.809"W
004 - Lat: 35°31'16.158"N / Long: 81°0'19.719"W
006 - Lat: 35°11'42.477"N / Long: 81°0'30,296"W
007 - Lat: 35"11'51.086"N / Long: 81°0'33.125"W
008 - Lat: 35"10'55.250"N / Long: 81"0'22.794"W
103 - Lat: 35"10'44.427"N / Long: 81°0'23.040"W
104 - Let: 35010'37.416"N / Long: 81°0'21.810"W
108 - Lat: 35°30'52.175"N / Long: 81'0'21.933"W
108B - Lat: 35*10'48.362"N / Long: 81°0'22.671"W
isrn�.r.�icr:�-3rtn�Rn; rrnam
�'-"'' ' -��� • •� Outfall 108B '
Outfall 103 ' ' X, I",
i • ( Outfall 104
Figure 1
Outfall Location Ma
0utfau 002! NPDES Permit No. NC0004979
Allen Steam Station
"�' : rC ! o soo 000 000 Duke Energy Corporation
Fee Gaston County, North Carolina
Page 5 of 7

Allen Steam Station - Outfall 002 Data Summary
May 2022 through February 2024
# of
Samples
Min.
Avg.
Max.
Parameter
Units
76
<5
<5
<5
O&G
mg/L
76
<0.5
1.69
5.55
Hg
ng/L
76
0.2
0.8
1.3
Bromide
mg/L
76
8.4
18.6
30.3
Calcium
mg/L
76
0.123
0.518
5.49
Iron
mg/L
76
3.01
6.1
9.88
Magnesium
mg/L
76
33.3
71.6
113
Total Hardness
mg/L
76
<1
1.6
2.44
Arsenic
ug/L
76
<1
<1
<1
Cadmium
ug/L
76
<1
<1
<1
Chromium
ug/L
76
<2
<2
<2
Copper
ug/L
76
<1
<1
<1
Lead
ug/L
76
1.04
2.04
4.36
Nickel
ug/L
76
2.3
9.6
21.4
Selenium
ug/L
76
<0.3
<0.3
<0.3
Silver
ug/L
76
<5
<5
<5
Zinc
ug/L
73
83
141
205
TDS
mg/I
76
0.04
0.26
0.64
Total Nitrogen
mg-N/L
74
<2.5
7.8
32
TSS
mg/L
75
0.53
3.81
35.5
Turbidity
NTU
76
<0.05
0.30
17.0
Total Phosphorus
mg/L
Page 6 of 7

Allen Steam Station Maximum Analytical Value Measured for Outfalls 103, 104 and 108 for
Timeframe from August 2021 Through March 2024
Parameter
Units
103
Oil and Grease
mg/L
<5
Mercury
ng/L
1.1
Chloride
mg/L
54.6
Flouride
mg/L
0.103
Nitrate
mg/L
0.752
Nitrate as Nitrogen
mg-N/L
0.17
Sulfate
mg/L
39.9
Barium
mg/L
0.059
Iron
mg/L
1.29
Manganese
mg/L
0.42
Total Hardness (CaCO3)
mg/L
247.09
Zinc
mg/L
0.01
Arsenic
ug/L
<1
Cadmium
ug/L
<0.1
Chromium
ug/L
<1
Copper
ug/L
<2
Lead
ug/L
<1
Lead (low level)
ug/L
<0.2
Nickel
ug/L
<1
Selenium
ug/L
<1
TDS
mg/L
359
T55
mg/L
13.9
104
108
<5
<5
2.0
5.88
46.6
3.278
<0.1
<0.2
0.333
1.762
0.07
0.39
38.82
j
78.7
0.127
0.54
7.17
0.466
1.75
0.005
299.80
176.99
<0.005
0.0059
<1
<1
<0.1
<0.1
<1
I <1
<2
10.46
<1
No Results
0.349
<0.2
<1
1.44
<1
<1
378
231
40.8
<2.5
NOTE: Outfall 108 only had two sampling events. Outfall 108B did not discharge during this timeframe.
Page 7 of 7