NC0026573_CEI Response_20240322

City of Morganton
Water Resources Department

March 22st, 2024

Daniel Boss, Assistant Regional Supervisor
Water Quality Regional Operations Section
Asheville Regional Office
Division of Water Resources, NCDEQ

Subject: Response to Feb 19th 2024 Letter from
August 25th 2023 Compliance Inspection Report
Catawba River Pollution Control Facility
NPDES WW Permit No. NC0026573
Burke County

Dear Mr. Boss,

On August 25th 2023, NC DEQ Division of Water Resources conducted an inspection of the
Catawba River Pollution Control Facility (CRPCF) and identified the following issues to be
addressed:
1. Prevention of solids loss during storm flows
2. Improvement and repair of solids removal processes
3. Control of solids and BOD loadings from SIUs
Prior to that inspection, on April 17, 2023, the City of Morganton had already issued a work
order for engineering services to evaluate flows and loadings to the CRPCF, hydraulic capacity,
treatment capacity, and solids processing capacity in order to identify capacity “bottlenecks”.
That evaluation was completed in late 2023 and on January 9, 2024 the engineer was directed to
develop alternatives for improvements to resolve the capacity “bottlenecks”. That work is on-
going and includes engineering tasks intended to resolve each of the three issues identified
during the August 2023 inspection as well as others.
1. Prevention of solids loss during storm flows
During high flows resulting from wet weather events the secondary clarifier solids loading
capacity may be exceeded resulting in an increase in sludge blanket depth and excessive TSS
discharge over the clarifier weirs. Three factors are combining to create this issue:
a. high I/I resulting from wet weather
b. insufficient secondary clarifier area
c. high influent BOD loading which then requires operation with a high MLSS in order to
maintain an SRT sufficient for stable nitrification
Factors a. and b. are being addressed via the on-going engineering work to identify capital
improvement projects for collection system rehabilitation and construction of additional new
clarifier area. Factor c. is currently being addressed through a special sampling program to
determine the source of excessive influent BOD and decrease it through cooperative efforts with
Telephone [phone] 305 East Union St. Post Office Box 3448
www.morgantonNC.gov Morganton, NC 28655 Morganton, NC 28680-3448
the potential source(s) as well as revisions to SIU permits, charge structure, and penalties for
discharge of excessive loadings. While engineering and permitting changes will be implemented
in the long and medium-term, short-term measures have also been identified. We are working
with our engineer to determine and operate with the minimum MLSS concentration that will
provide stable nitrification. By operating with no more than the MLSS necessary, the solids
loading to the clarifiers will be decreased so that higher flows can be treated without developing
excessive solids blankets. We are also working with our engineer to refine and implement an
SOP to use the downstream end of the aeration basins for solids storage during extreme peak
flows when solids blankets are increasing despite operating with the minimum MLSS. This
approach will further decrease the solids loading to the clarifiers by temporarily stopping
aeration at the last aeration basin diffuser grid so that some of the mixed liquor solids can settle
there and the MLSS going to the clarifiers will be decreased.
2. Improvement and repair of solids removal processes
The CRPCF uses both primary and secondary clarifiers for solids removal. Both processes are
effective when solids loadings are not excessive but performance declines when downstream
solids storage tanks are filled or out of service and pumping of underflow solids from the
clarifiers must be temporarily decreased or stopped. This has been the situation with the primary
solids concerning the storage tank at CRPCF where the tank has not been effectively utilized due
recently replaced pump station controls, grinders, valves, check valves and actuators.
Additionally the storage tank has a failing mixer. A new mixer has been ordered and we have
been notified that it has shipped and on its way to installer. Once installer receives, it will be
promptly installed and the primary solids pump station and storage tank will be returned to
automatic service. That additional primary solids storage will allow primary clarifier blankets to
be maintained at reasonable depth under all but the most extreme influent conditions.
Additionally, the capital improvement plan has identified that construction of additional primary
and secondary clarifier area will be included in an upcoming project. Improvements to solids
thickening and dewatering are also included in the recently developed CIP and will improve
overall solids removal capacity once implemented. Other improvements to solids management
are also being evaluated.
3. Control of solids and BOD loadings from SIUs
At times the BOD and TSS concentrations at the influent of the CRPCF are significantly higher
than the facility was designed to treat. Although the once monthly sampling of the SIUs has not
identified a consistent source, that it is coming from one or more of the SIUs remains the most
likely explanation. To better understand the source, we have recently (February and March
2024) conducted special sampling on a more frequent basis at our SIUs. Based on the results, we
are working with our engineer to develop a plan for more frequent SIU sampling on a permanent
basis as well as considering increasing the penalties assessed for violations. The intent is to
provide SIUs with both the monitoring and the incentive to achieve routine permit compliance.
Improved permit compliance by the SIUs is anticipated to decrease influent TSS and BOD which
will decrease solids loadings and solids production. Consequently, process overloads may be
less frequent in the short-term and required capital improvements can be sized and implemented
more rationally rather than on the basis of excessive loadings.

Telephone [phone] 305 East Union St. Post Office Box 3448
www.morgantonNC.gov Morganton, NC 28655 Morganton, NC 28680-3448

If there is any questions or if more information is needed, please reach me at
828-438-5375 or at [e-mail]

Sincerely,

Eli Self
Wastewater Plant Superintendent & ORC
City of Morganton NC