NC0003468_Review of Thermal Model Verification Study Plan_20230714

DocuSign Envelope ID:6B8E156F-DB16-42DC-851D-5C411567A068
ROY COOPER _
Governor d C
ELIZABETH S.BISERr
Secretary •E .
RICHARD E.ROGERS,JR. NORTH CAROLINA
Director Environmental Quality
July 14,2023
Mr.Kristopher Eisenrieth,General Manager II-Regulated Stations
Duke Energy Carolinas,LLC
864 S. Edgewood Rd
Eden,NC 27288
Subject: Review of Thermal Model Verification Study Plan
Dan River Combined Cycle Station
NPDES Permit No. NC0003468
Rockingham County
Dear Mr. Eisenrieth:
The Division of Water Resources(DWR)reviewed the modeling report"Dan River Thermal
Verification Study Plan" submitted to the NPDES Permitting Branch on March 28, 2023. The report
was submitted in accordance with permit Condition A. (6.)(d).
Duke Energy's consultants,Water Environment Consultants(WEC)developed an Environmental
Fluid Dynamics Code(EFDC)thermal model to analyze effluent mixing from the discharge to the
Dan River at Outfall 001. The goal of the study plan is to document the methodology for data
collection and/or adjust the previously approved thermal mixing zone model. The study plan outlines
the use of a biodegradable dye(Rhodamine WT) in Outfall 001 to determine instream dilution. The
goal of the review is to determine if the proposed use of biodegradable tracer dye would cause any
issues for benthos and would be acceptable for verifying the model predictions.
Overall,there were no concerns with the selection of the biodegradable dye to verify the model
predictions. However,DWR's Biological Assessment Branch commented that the ecotoxicity of
intermittently released tracer dye should be relatively low for fish, so long as exposure periods are
brief.
Regarding the benthos below the discharge,DWR has four(4)distinct benthos stations below the
discharge (at varying distances), comprising a total of nine(9) samples and going as far back as 1983,
and as recent as 2021. Given this existing dataset,we will be in the position to provide some analysis
of the effects of this discharge on the benthos community. The Division will be sampling at least one
of these downstream locations next year since we have the Roanoke Basin up for assessment in 2024.
The dye study certainly has the potential to give us a better understanding of how this discharge might
impact the benthos.
The Division would expect when you move forward with the Thermal Verification Study that Duke
Energy will: (1)Apprise the NCDEQ Permit Writer when the study commences; (2)Continue to
adhere to all existing permit conditions; (3)and adhere to all applicable regulations throughout the
study. In accordance with Permit Condition A. (6.)(d),after 12 months of temperature data are
collected the permittee shall submit a report to the Division to verify the Cormix model predictions.
North Carolina Department of Environmental Quality I Division of Water Resources
NORTMcna 512 North Salisbury Street 11617 Mail Service Center I Raleigh,North Carolina 27699-1617
a Effi 919.707.9000
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DocuSign Envelope ID:6B8E156F-DB16-42DC-851D-5C411567A068
The report shall include field verification of assumptions used in the model and a summary of
temperature data for effluent,upstream and downstream and shall be submitted to:
Division of Water Resources
WQ Permitting Section-NPDES
1617 Mail Service Center
Raleigh,NC 27699- 1617
Please note,in accordance with Permit Condition A. (6.) (f),the permit may be reopened to
implement alternative temperature limits or requirements based on the data collected.
Should you have any questions,please feel free to contact Derek Denard at(919) 707-3618/
[e-mail] or Doug Dowden at(919) 707-3605/[e-mail].
Respectfully,
IV
DocuSigned by:
64 V bW D 'V'
CE9CD2D3C45B4D4...
Doug Dowden
Supervisor,NPDES Industrial Permitting Unit
ec: NPDES Files[Laserfiche]
Duke Energy/Kris Eisenrieth[[e-mail]];Joyce Dishmon [e-mail]];
DWR/Michael J Montebello[[e-mail]];Doug Dowden[[e-mail]];
Kristen Litzenberger[[e-mail]];Derek Denard[[e-mail]];
Sergei Chernikov[[e-mail]]
WSRO/Shuying Wang[[e-mail]];Jenny Gramak [e-mail]];
Lon Snider[[e-mail]]
DWR/WSS Biological Assessment Branch/Eric Fleek[[e-mail]]
D E Q�� North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh,North Carolina 27699-1611
NORTH CAROUNA _ 919.707.9000