NCS000574_Cape Fear Modification Request Response Letter_20200427

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
BRIAN WRENN
Acting Director
Mr. Issa J. Zarzar
General Manager, East Region
Duke Energy Progress, LLC
Cape Fear Steam Electric Plant
500 CP&L Road
Moncure, NC 27559
Dear Mr. Zarzar:
NORTH CAROLINA
Environmental Quality
April 27, 2020
Subject: NPDES Stormwater Permit
Permit No. NCS000574
Modification Request
Cape Fear Steam Station
Chatham County
The Division of Energy, Mineral, and Land Resources' Stormwater Program received your
request to modify permit no. NCS000574 on December 3, 2019. The Division has reviewed
your request to add a stormwater outfall for the proposed emergency overflow spillway that
must be constructed for the 1956 Ash Basin at the Cape Fear Plant to meet NC DEQ Dam Safety
regulatory requirements. The letter asserted that the new discharge point to the Haw River is
designed to divert flow from the full Probable Maximum Flood (PMF) storm event, and that the
spillway will be set at an elevation sufficient to ensure the basin will contain the 100-year, 24-
hour storm without discharging.
The Stormwater Program has determined that a permit modification is not necessary. The
determination is based on the agency's practice of considering exemptions for stormwater
retention ponds from NPDES stormwater permitting requirements when they are designed to
hold at least the 25-year, 24-hour storm event. That threshold is consistent with the most
conservative design storm event criteria in the federal effluent guidelines for BAT (Best
Available Technology) for wastewater impoundments and with non -discharging surface
disposal unit treatment design criteria in North Carolina's 15A NCAC 02T rules. The proposed
spillway would prevent potential discharge well above this performance baseline.
This letter acknowledges the company's notification that the emergency spillway point will be
added to the 1956 Ash Basin. If flow routing or other circumstances change that introduce the
potential for stormwater discharge from this spillway, the company will be required to reapply
for a permit modification.
D E Q�� North Carolina Department of Environmental Quality I Division of Energy, Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center I Raleigh, North Carolina 27699-1612
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If you have any questions or comments concerning this correspondence, contact Bethany
Georgoulias at [phone] or atbethany. eg_or.og u�kncdenr. og_v.
Sincerely,
for Brian Wrenn, Acting Director
Division of Energy, Mineral, and Land Resources
cc: Raleigh Regional Office, DEMLR Stormwater Program (via email)
Joyce Dishmon, Duke Energy (via email)
DEMLR Stormwater Program Electronic Document Repository