NC0004979_Other Correspondence_20180920

(, DUKE
ENERGY.
CAROLINAS
September 20, 2018
Mr. Ori Tuvia
North Carolina Dept. of Environmental Quality
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Subject: Allen Steam Station
NPDES Permit #:NC0004979
Gaston County
Dear Mr. Tuvia:
Allen Steam Station
253 Plant Allen Road
Belmont, NC 28012
RECEIVEDINCDENRIDWR
SEP 2 6 2018
WOROS
MOORESVILLE REGIONAL OFFICE
Duke Energy submits this written notification and status update of the Flue Gas Desulfurization
area Stormwater Basin (hereinafter "Stormwater Basin") overtopping that occurred at Allen
Steam Station on September 16, 2018 during tropical storm Florence, and as verbally reported
to the Agency on September 17, 2018.
Overtopping of the Stormwater Basin occurred during intense rainfall from tropical storm
Florence. Due to the intensity of rainfall, the two stormwater basin pumps could not displace
stormwater as quickly as in -flow arrived. Subsequently, stormwater from the event exited the
basin and crossed a vegetated Swale to an inlet surrounded by silt fencing and rock checks.
The inlet discharges to a vegetated landing, surrounded by an earthen berm, rip -rapped slope,
silt -fencing, and multiple rock checks. Due to the precipitation intensity and saturated
landscape, an accurate volume of the stormwater exceeding the basin rim cannot be
determined. The overflow occurred for approximately 2 hours.
Station personnel and environmental staff surveyed the areas, post storm event. Included in this
survey was a review of the nearest perennial stream that empties into the plants cooling water
discharge canal and is approximately 70 yards from the rock checks. No indication of
environmental impacts from the overtopping were observed.
Station personnel conducted testing of the Stormwater basin pumps and performed a visual
survey of inlet structures for damage or blockage. While it is believed this was an anomalous
event caused by a short duration intense rainfall associated with the tropical system, a
stormwater drainage assessment is being re -validated to assure current site construction
activities have not modified expected inflows beyond the design capacity of the Stormwater
Basin.
If you have any questions, please contact Ms. Elizabeth Glenn [phone] or
[e-mail].
t 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.
Sincerely, '
Terry W. Tuck
General Manager II
Allen Steam Station
Fossil/Hydro Operations - Carolinas Coal Generation
CC: Elizabeth Werner— NCDEQ Waste Management
BC: Terry W. Tuck
Randy Gantt
Richard Baker via email
Liz Glenn
Courtney Murphy via email
Shannon Langley via email