NC0025542_Response to Notice_20230421

Public Utilities
City of Hickory
PO Box 398
Hickory, NC 28603
Phone: [phone]
Email: [e-mail]
RECEIVED/NCDEO/DWR
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April 17, 2023 WQROS
Andrew H. Pitner MOORESVILLE REGIONAL OFFICE
Water Quality Regional Operations Section
Mooresville Regional Office
610 East Center Ave., Suite 301
Mooresville, NC 28115
RE: Notice of Violation & Intent to Assess Civil Penalty
Tracking Number: NOV-2023-LV-0251 Hickory -Catawba WWTP (NPDES Permit No. NC0025542)
Dear Mr. Pitner;
The purpose of this correspondence is to provide additional information regarding Notice of Violation (NOV-2023-LV-0251) for your
consideration.
After discussion with the Plant ORC, and assessing process controls, the following was determined:
The area experienced very cold temperatures during the month of February. The cold weather, current plant flow and the size of
the oxidation ditch at the Hickory -Catawba WWTP create a very low Food to Mass Ratio and very long Mean Cell Residence Time
which makes maintaining the biomass needed for nitrification very challenging. A slight temperature, flow, or influent loading
variation can cause a disruption in the nitrification process. When this occurs, it makes it extremely difficult to meet the Nitrogen,
Ammonia Total (as N) — Concentration (C0610).
Remedial actions to correct this problem have been on -going. Soda ash is being added to increase the alkalinity. The aerators are
being cycled to increase the dissolved oxygen. The plant was also reseeded with several loads of seed sludge from other WWTP's.
Additional influent sampling is also being conducted to determine if there are any interferences. Unfortunately, weather
conditions are beyond our control and cold weather can inhibit the nitrification process. During the winter months, the
temperature in the plant will drop below 10 degrees Celsius, which can inhibit the nitrification process and cause effluent limits
violations. The facility demonstrated a return to compliance the week of 2/19/2023 and has remained in compliance with its NH3
limit since.
We believe the City of Hickory acts proactively to achieve compliance. Historically, NH3 has only been a challenge during the winter
months. As permitted, the plant can discharge up to 25 lbs. per day of NH3 at 1.5 MGD. At the current flow of 0.156 MGD, the
plant is discharging only 2.6 lbs. per day. We ask that this be considered as we feel that this NH3 discharge will not impair or disrupt
the receiving stream.
The City of Hickory takes all violations seriously and works diligently in promoting and protecting the environment, health and
natural resources. The City hopes you will consider the above factors when evaluating possible enforcement actions. Should
you have additional questions or desire additional information, please do not hesitate contacting me at [phone].
Sincerely,
Keith D. Rhyne
WWTP Superintendent
PC: M. Shawn Pennell, Public Utilities Director
Andrew Foy, Assistant Public Utilities Director
David Cox, Public Utilities Environmental Manager
Josh Archambault, Hickory -Catawba WWTP