NC0026051_Response to NOV-2024-LV-0800_20240920

Engineering and
Environmental Services
Utilities Division
September 20, 2024
RETURN RECEIPT REQUESTED
CERTIFIED MAIL # 70163010000113387256
Ms. Vanessa Manuel
NCDEQ— Division of Water Resources
Attn: Raleigh Regional Office
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: Notice of Violation, NOV-2024-LV-0800
Dear Ms. Manuel:
This is in response to the Notice of Violation dated September 13, 2024, and received by Durham
County on September 19, 2024. The Triangle Wastewater Treatment Plant (TWWTP) is an
exceptionally performing facility and was granted reduced monitoring in February 2013. TWWTP
prides itself on operating efficiently and remaining compliant to ensure protection of human health
and the environment.
On August 12, 2024, Mr. Cheng Zhang was notified in writing that TWWTP, NCO026051, had a
BOD permit limit violation for the week of July 22, 2024, and had exceeded the monthly limit.
On July 24, 2024, there was a BOD result of 13.9 mg/l. The sample two days prior for BOD was
2.6 mg/l calculating out to a weekly average of 8.25 mg/l. Our weekly permit limit is 7.5 mg/l;
therefore, exceeding the weekly permit limit. The monthly permit limit is 5.0 mg/l, and the
monthly average was 5.71 mg/l; therefore, resulting in a monthly limit violation. All data was
reviewed which included certified parameters, process control data, and data logged on the
SCADA system, as well as reviewing operational changes, maintenance activities, and weather
patterns. Leading up to the permit violation, TWWTP received high flows due to record rain totals.
TWWTP was operating with three filters because two were down for repair. Backwash and
washwater pumps had been ordered but delivery had been delayed resulting in routine cleaning of
the filters being decreased. During this period of high flows, operational changes were made that
included placing an additional train online and continually backwashing the three filters in
operation. Additional clarifiers were placed into operation which decreased the detention time,
driving pH levels below 6.0 mg/1 and causing the rotors to struggle with keeping the dissolved
oxygen above 1.5 mg/l. We believe all this combined contributed to the violation.
Since this event, repairs have been completed and all filters are currently operational. Spare
backwash and washwater pumps have been. ordered to ensure replacement pumps are readily
available. To the best of my knowledge and based on laboratory results received to date, TWWTP
has remained in compliance since the above -mentioned violations.
5926 NC Highway 55 East, Durham, North Carolina 27713
[phone] 1 Fax [phone] ( dconc.gov
Equal Employment/Affirmative Action Employer

TWWTP is an exceptionally performing facility, reporting was conducted in a timely manner as
required, and repairs were made as soon as the equipment arrived onsite. Based on the information
provided, I request that the Division of Water Resources not pursue further enforcement action.
For future correspondence from the Division of Water Resources to Durham County concerning
permits NC0026051, WQCS00038, WQ0032821, and NCGI10054 please copy me so I can
respond to any request in a timely manner. If you have any questions, contact me at
sbrixey_(i0conc.gov or 919-560-9034.
Sincerely,
Stephanie Brixey
Deputy Director of E&ES/POTW Director
Cc: Dr. Kimberly Sowell, County Manager (via email)
Julio Delgado, Assistant County Manager (via email)
Jay Gibson, Director of E&ES (via email)
Wade Shaw, Utilities Superintendent/ORC (via email)