NC0004774_Modification to wastewater treatment process._20200709

('DUKE
ENERGY
July 9, 2020
Division of Water Resources
WQ Permitting Section - NPDES
Attn: Sergei Chernikov
1617 Mail Service Center
Raleigh, NC 27699-1617
ELECTRONIC SUBMITTAL
Subject: Buck Combined Cycle Station
NPDES Permit NC0004774
New Wastewater Retention Basin
Buck Combined Cycle Station
1385 Dukeville Rd.
Salisbury, NC 28146
With reference to the attached notification of the start-up of the new wastewater
retention basin (WWRB) it has experienced algae growth. Once the algae bloom was
noted the discharge ceased and flow from the station went back to the previous flow
path. It is planned to operate the WWRB in a batch mode going forward. When
in -process monitoring indicates that the WWRB is out of specification, instead of
incorporating chemical treatment, the station's preference is to pump the water to the
station clarifier to be recirculated as station process water. The flowrate from the
WWRB to the site clarifier is planned to be 200 gpm or approximately 10 times less than
the normal process water flowrate to the clarifier from the river.
This operation should not result in a change of any significance in the characteristics of
the final discharge at outfall 001 A. This mode of operation will be infrequent. It will just
be used when in process monitoring indicates the need to be sent to the station process
water system. It does have the added benefit of water reuse.
Please advise if this proposal is acceptable to you. If you have questions or need
additonal information, please contact Robert Wylie at [phone]_
Sincerely,
Kris Eisenrieth, General Manager II
Buck Combined Cycle
Attachments
cc: Roberto Scheller

NKE
RGY,
March 11, 2020
Division of Water Resources
WQ Permitting Section - NPDES
Attn: Sergei Chernikov
1617 Mail Service Center
Raleigh, NC 27699-1617
Division of Water Resources
Attn.: Corey Basinger
Mooresville Regional Office
610 East Center Avenue, Suite 301
Mooresville, NC 28115
ELECTRONIC SUBMITTAL
Subject: Buck Combined Cycle Station
NPDES Permit NC0004774
Start -Up of Wastewater Retention Basin
Buck Combined Cycle Station
1385 Dukeville Rd.
Salisbury, NC 28146
With reference to paragraph C. (9) of the subject permit, this letter provides notification
to you that the start-up of the new wastewater retention basin (WWRB) is currently
scheduled for March 25, 2020. Attachment 1 provides a description of the WWRB.
Attachment 2 provides a water flow schematic diagram that shows where the new
treatment basin is located within the station's wastewater processes. During station
operation this system will primarily receive wastewater from the site wastewater sump
system. If the water chemistry of the cooling tower blowdown system is in specification,
and no additional treatment is needed, then the system has the option to send the
blowdown directly to outfall 001 A by way of the wastewater sump, as it currently does.
During outages cleanout material from the cooling tower basin and the clarifier is
planned to be sent to the WWRB.
If you have any questions, please contact Robert Wylie at [phone] or
[e-mail].
Sincerely,
Kris Eisenneth, General Manager II
Buck Combined Cycle
Attachments
cc: Roberto Scheller

Attachment 1
New Wastewater Retention Basin Description
NPDES Permit NC0004774

New Wastewater Retention Basin Description
NPDES Permit NCOOO4774
Duke Energy (Duke) is building a new wastewater retention basin at the Buck Combined Cycle Station located
on Dukeville Road in Rowan County, North Carolina. The wastewater retention basin is intended to hold and
treat wastewater from the combined cycle wastewater sump, cooling tower blowdown, clarifier
cleaning/draining and the future ash beneficiation facility. Normal operation is to route the water currently
going directly to outfall 001A to the new wastewater retention basin for additional treatment or if it is
determined that no additional treatment is warranted the water could be sent from the sump directly to
Outfall 001A.
The new wastewater retention basin provides Buck Combined Cycle Station the option to close the outlet
structure and treat the wastewater if the plant has a known process upset and the flow into the basin has
qualities that would exceed the permit limits for outfall 001A. The plant could then continue to route water
into the basin or bypass the basin straight to the NPDES outfall if the quality of that water meets the
requirements of the NPDES permit.
The final basin design has a maximum berm height of 24 feet with a maximum of storage volume of 47.6 acre-
feet. The basin capacity is 7.4 mgals. The basin will have a 20 foot wide emergency spillway on the southwest
corner to prevent berm overtopping. The basin is to be lined to prevent infiltration of wastewater into the
ground. The final basin design includes a 60 mil HDPE liner with a protective geotextile below and above the
HDPE liner. This liner is covered with 18 inches of stone.
The basin flow path is designed to maximize retention time and increase settling efficiency. The final basin
design includes three floating baffles with alternating flow openings. The basin is also designed to adjust pH if
needed with caustic or acid to ensure compliance with the NPDES permit limits of >_ 6.0 and <_ 9.0 standard
units.
A description for the inputs to the new wastewater retention basin are as follows:
Combined Cycle Wastewater Sump: The flow rate from the combined cycle wastewater sump varies
depending on the number of pumps running in parallel. The wastewater sump has three pumps, but rarely
does more than one pump is run. The average daily flow (ADF) from the wastewater sump is approximately
350 gpm. The average daily flow rate includes the pump cycling on and off. The maximum flow rate while one
pump is running is approximately 660 gpm.
Cooling Tower Blowdown Cleaning: The estimated volume of water that is drained from the cooling tower
blowdown basin when it is cleaned is 1.5 mgal. The cooling tower blowdown is cleaned once every four years.
Clarifier Cleaning and Draining: The estimated volume of water that is drained from the clarifier when it is
cleaned is 1 mgal. The clarifier is cleaned once a year.
Future Flows from Ash Beneficiation Facility: The flow rate from the future ash beneficiation facility was
estimated to be 100 gpm. It is designated as internal outfall 008.

Attachment 2
Buck Combined Cycle Station
Water Flow Schematic Diagram
NPDES Permit NC0004774

x
Y
c
0 E
Y cu
yL
U
N N
a, 3
u o
u W
W
p1 Y
c 3
v
E Y
o
u 3
Y
V UJ
:3 W
m o
O_
Z