NC0026573_NOVNOI-2024-LV-0176_20240321_response

City of Morganton
Water Resources Department
March 21 ", 2024
Daniel Boss, Assistant Regional Supervisor
Water Quality Regional Operations Section
Asheville Regional Office
Division of Water Resources, NCDEQ
Subject: Response to NOV-2024-LV-0176
Dear Mr. Boss,
We have reviewed the permit violation NOV-2024-LV-0176 for Permit NC0026573. It
has been determined the cause of the violations to be hydraulic overloading due to high peak
flow from named winter storm Fynn with very young sludge characteristics following the rain
event, compromising Ammonia removal.
On January Bch — 91h (week #2) 4.2 inches of rain fell in a 12-hour period with Morganton
area experiencing flash flooding. The max of 30.5 MGD was pumped through facility for 14
hours. All available storage was placed online and oxygen production was halted in the aeration
basins in an attempt to capture solids inside. Hydraulic overloading from secondary clarifiers
occurred once all storage was filled causing TSS & BOD exceedances.
Following the major flow disruption, the facility struggled to recover its sludge volume to
effectively remove BOD and Ammonia from the waste stream. Facility experienced very young
sludge characteristics after rain event. Due to the young sludge, effective Ammonia removal was
compromised which caused the exceedance for the month.
ORC contacted our engineer team that is currently evaluating process capacity and
designing improvements for the facility. After consulting, a recover strategy was implemented
and ORC implemented steps a & b with increased dissolved oxygen setpoints prior to
consultation:
a) Stop sludge wasting
o To build MLSS as rapidly as possible
b) Operate with just one of the two aeration basins until MLSS increased to 2500-3000
mg/L
o To avoid very low MLSS that decreases flocculation effectiveness
c) Split MLSS between two basins when MLSS > 3000 mg/L
o To avoid excessively high MLSS and solids loading rate
d) Sample and analyze for ammonia-N within the process to monitor recovery of
nitrification
e) Return to controlled wasting after two basins are operating at over 3000 mg/L
The recovery process continued into the first 2 weeks of February before facility was back to
normal operations.
Telephone [phone] East Union St. Post Office Box 3448
www.morgantonNC.gov Morganton, NC 28655 Morganton, NC 28680-3448

Exert from engineer strategy: "That strategy has proved effective, and rapidly restored
the lost MLSS solids. But because nitrifier growth is slow, the return to consistent ammonia
removal required weeks rather than days. As a result, the plant could not meet the monthly
average ammonia-N limit for January 2024." — Sean Scuaras, PhD PE BCEE
If there is any questions or if more information is needed, please reach me at
828-438-5375 or at eself(cmorgantonNC.gov
Sincerel
y,
Eli Self
Wastewater Plant Superintendent & ORC
City of Morganton NC
Telephone [phone] East Union St. Post Office Box 3448
www.morgantonNC.gov Morganton, NC 28655 Morganton, NC 28680-3448