NC0025542_Response to Notice_20230302

Public Utilities
February 20, 2023
Andrew H. Pitner
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-0085
Hickory -Catawba WWTP (NPDES Permit No. NC0025542)
Dear Mr. Pitner;
City of Hickory
PO Box 398
Hickory, NC 28603
Phone: [phone]
Email: [e-mail]
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The purpose of this correspondence is to provide additional information to the referenced Notice of Violation (NOV-2023-
LV-0085) for your consideration in evaluating and assessing possible enforcement actions against the City of Hickory.
After discussion with the Plant ORC, and assessing process controls, the following was determined:
The area experienced very cold temperatures during the month of December. 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 (CO610).
Remedial actions to correct this problem have been on -going. Soda ash is being added to increase the alkalinity. The
aerators are being cycled and we are experimenting with ways to try and warm the wastewater. We have discontinued
use of the supplemental carbon source after discovering it contains a small amount of methanol. We theorize that could
possibly be contributing to detectable amounts of methyl bromide in the effluent. We are currently researching
alternative non -methanol carbon sources as well as nitrifying bacteria blends to restore nitrification. 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.
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 0.160 MGD, the plant is discharging only 2.7 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