NC0024112_Staff Comments_20220829

DocuSign Envelope ID: 16879A0E-249F-4960-B700-0005C1133374
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHARD E. ROGERS, JR.
Director
NORTH CAROLINA
Environmental Quality
8/29/2022
City of Thomasville
Attn: Misty Conder, Laboratory Supervisor
P.O. Box 368
Thomasville, NC 27361
Email: [e-mail]
Subject: HWA-AT and LTMP Review
Program Name: Thomasville
NPDES Permit No NC0024211, 6.0 MGD
Biosolids to Uwharrie Landfill, Troy NC
Hamby Creek WWTP
Davidson County, WSRO
Dear Permittee:
The Municipal Unit of the Division of Water Resources is currently reviewing the Headworks
Analysis (HWA) and allocation table (AT) for the City of Thomasville's wastewater treatment
plant (WWTP) working under the NPDES Permit No NC0024211 (effective on April 1, 2022).
The HWA was initially received by the Division on November 1, 2020, followed by more
information received on November 22, 2021. We regret the delay in providing this review.
Please review the corrections and observations, and address the requests discussed below in
the enclosed spreadsheet. Please follow the color code in the spreadsheet and submit a cover letter
outlining the main changes. Please submit the revised HWA-AT with supporting documents and
the updated Long -Term Monitoring Plan (LTMP) by October 17, 2022.
1. HWA Corrections
a. Water Quality Stream Standards: The HWA was updated to use site -specific water
quality standards (WQS) for arsenic, cadmium, chromium, copper, cyanide, lead, nickel,
silver, and zinc (Source: `RPA Input (WQS)' Tab in the HWA Sheet).
b. NPDES Limits for copper and TP were included/updated.
c. Design value for TSS was updated from 215 to 200 according to the Design Criteria
documentation.
d. The use of Design Criteria Loading for BOD and TP has been removed to use the
NPDES BOD and TP loadings. The NPDES BOD and TP loadings are less than the
Design BOD loading; the lowest loading must be used.
e. Silver: The HWA showed a calculated over allocation based on the dissolved metals
stream standard. Recently, DWR has decided to allow POTWs the option of using zero
as uncontrolled concentration and the use of the next most limiting factor (Acute WQS)
when all silver data is reported as below the best available PQL. All recent WWTP
influent and effluent silver data was below 0.5 ug/1. Therefore, the use of zero and site -
specific acute WQS is allowed.
2. HWA Observations.
a. Total Nitrogen (TN) WWTP Design Values: The Facility based the TN design value
on the TKN design value. This approach is acceptable at this time, since there is no TN

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NPDES limitation. If an NPDES TN limit is assigned, the Facility must develop a site -
specific TN Design Value.
3. HWA-AT Requests
a. The sludge was reported to be taken to the Uwharrie Landfill in Troy NC, please provide
a copy of the Landfill Permit and their last annual report.
b. Because your NPDES was recently reissued, please revise the Plan Removal Rate (%)
calculations with the influent and effluent data collected beyond 8/2020 up to today and
update the HWA-AT sheet as necessary. Also, if there are new SIUs or changes in
industrial discharges occurred since the HWA-AT was submitted, please revise the
uncontrolled concentrations and update the HWA-AT sheet as necessary.
c. Please provide the HWA Narrative.
d. Selenium: The AT showed a calculated over allocation. Please revise the IUPs' selenium
limits to solve overallocation.
e. Mercury: The HWA showed a calculated over allocation based on the stream standard.
The literature uncontrolled concentration was larger than the MAHL leaving no
allocation for the SIUs. The Division recommends collecting uncontrolled sampling to
assess the uncontrolled concentration and the local limits. If the City attempts to solve
the overallocation through uncontrolled sampling, DWR will allow 12 months to collect
the necessary mercury information at the lower Practical Quantification Level (PQL).
f. Total Nitrogen: The HWA showed a calculated over allocation based on the minimum
inhibition loading. The mass balance uncontrolled concentration was larger than the
MAHL. The Division recommends collecting uncontrolled sampling to assess the
uncontrolled concentration and will allow 12 months to collect the necessary nitrogen
information.
4. AT Corrections/Updates
a. Allocation Table (AT): In the HWA review process, the Permittee dropped 029-Custom
Drum Services and included 032 HER. Permits 028, 008, and 018 were renewed in
February 2022. The AT has been updated to reflect those changes and includes all IUPs'
limits.
5. LTMP Observations and Requests
a. As outlined in the NPDES permit renewal, please submit the updated Long -Term
Monitoring Plan (LTMP) addressing the following:
i. Review pollutants of concern (POCs) and update the LTMP to reflect all
pollutants limited in industrial user permits (IUPs), sludge management
permit, NPDES permit, and assess recommendations in the POC review form.
1. Sample LTMP addressing emerging compounds is included.
ii. The target Practical Quantification Level (PQLs) for the following parameter
shall be updated in the LTMP: silver (from 5.0 to 1.0 µg/1).
iii. The Division recommends updating the PQL for the following parameters in
the LTMP: cadmium (from 2 to 0.5 µg/1), lead (from 10 to 2.0 µg/1), and
mercury (from 0.2 to 0.001 µg/1).
iv. Ensure effluent mercury samples are analyzed using Method 1631E.
v. Please include a revision history section for the LTMP.
Federal and State pretreatment regulations require the local delegated pretreatment program to
effectively control and document the discharge of wastewater from Significant/Categorical
Industrial Users to the POTW. It is the POTW's responsibility to ensure that these objectives are
consistently met.
Thank you for your continued support of the Pretreatment Program. If you have any questions or

DocuSign Envelope ID: 16879A0E-249F-4960-B700-0005C1133374
comments, please contact the Pretreatment Coordinator Keyes [[e-mail]], or the
Unit Supervisor, Michael at[[e-mail]].
Sincerely,
DocuSigned by:
C464531431644FE...
for Richard E. Rogers Jr., Director
Division of Water Resources
dy/Thomasville.24112 hwa.review 2022
Attachments:
Thomasville.24112. HWA-AT.2022 (under review) .xlsx and pdf
Sample LTMP
POC review form
cc with attachments:
DWR Winston-Salem Regional Office — Pretreatment/ Jim Gonsiewski
Municipal Unit File and Central Files (Laserfiche)