NC0026689_HWA review_20220829

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ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHARD E. ROGERS, JR.
Director
NORTH CAROLINA
Environmental Quality
8/29/2022
Town of Denton
Attn: Troy B. Branch, ORC - Pretreatment Coordinator
P.O. Box 306
Denton, NC 27239
Email: [e-mail]
Subject: HWA-AT and STMP Review
Program Name: Denton
NPDES Permit No NC0026689, 0.8 MGD
Class B Biosolids Permit No WQ00016966
Town of Denton WWTP
Davidson County, RRO
Dear Permittee:
The Municipal Unit of the Division of Water Resources is currently reviewing the Headworks
Analysis (HWA) and Allocation Table (AT) for the Town of Denton's wastewater treatment plant
(WWTP) working under the NPDES Permit No NC0026689 (effective on October 1, 2021). The
HWA was initially received by the Division on August 30, 2021.
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 updated HWA-AT with supporting documents and
the updated Short -Term Monitoring Plan (STMP) by October 14, 2022.
1. HWA Corrections
a. Water Quality Stream Standards (WQS): The HWA was updated to use site -specific
WQS for cadmium, copper, lead, silver, and zinc (Source: `RPA Input (WQS)' Tab in
the HWA Sheet). The WQS for dichlorobromomethane and bis(2-ethylhexyl) phthalate
were included as well.
b. NPDES Limits for copper and bis(2-ethylhexyl) phthalate were included.
c. Plant Removal Rate for copper was updated from 86 (Literature value) to 81.8 to use
the site -specific value. The Literature value shall be used if > 50% of the data is below
the detectable level (BDL).
d. Sludge to Disposal Flow was updated from 0.00087 to 0.00034 MGD based on the 2021
Sludge Annual Report. The 2021 Annual Land Application Field Summary Form
reported 123,500 gallons of solids applied.
e. Minimum Sludge Loading (lbs/day) for arsenic [Cell F111] was corrected to use the
calculated value.
f. Uncontrolled (formerly Uncontrollable) source for ammonia, arsenic, cyanide,
mercury, nickel, and silver was updated to Literature. The uncontrolled literature
values for cyanide and mercury were updated to 0.015 and 0.0003 mg/l. Please correct
this in your uncontrolled spreadsheet.

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2. HWA Requests
a. Please revise the SIU Uncontrolled Mass Balance Spreadsheet to ensure that the
uncontrolled concentration to be used in the HWA (mg/L) matches any of the available
values (mass balance or literature).
b. Please provide the WWTP Design Criteria source document.
c. Please provide the HWA Narrative. Include discussions for calculations or assumptions
for:
i. The Sludge Site Area (acres) and Sludge Site Life (years)
d. Silver: The HWA showed a calculated over allocation based on the dissolved metals
stream standard. The uncontrolled load was larger than the MAHL. There are no current
limits set for silver in the AT. Recently, DWR has decided to allow POTWs the option
of using zero as uncontrolled for data reported as below PQL (Practical Quantitation
Limit) data when the PQL is sufficiently low (best available PQL). All recent WWTP
influent and effluent silver data was below 5 ug/1 PQL. Therefore, the Division will
allow 12 months to collect the necessary silver information at the lower Practical
Quantification Level (PQL) (1.0 ug/1).
e. Selenium could be overallocated based on sludge ceiling. There are no current IUP
limits set for selenium in the AT. Upon reviewing the HASL calculations and the
effluent data (all below PQL, < 10.0 ug/L), the HASL can be used to solve the potential
overallocation concentration of selenium.
f. Zinc: The AT showed a calculated over allocation based on sludge ceiling. The current
IUP limit is 0.25 mg/L. By using the HASL calculation, the overallocation for zinc could
be resolved in the HWA. To assess the use of HASL, the Division recommends
collecting uncontrolled sampling for zinc. If the City attempts to solve the overallocation
through uncontrolled sampling, DWR will allow 12 months to collect the necessary zinc
information.
3. AT Requests
a. The AT showed a calculated over allocation for zinc based on sludge ceiling. The POTW
should revise the IUPs' zinc limit to resolve this overallocation.
4. STMP Observations and Requests
a. The Division recommends updating the PQL for the following parameters in the
STMP: arsenic (at 2.0 ug/1), cadmium (at 0.5 ug/1), lead (at 2.0 ug/1), molybdenum (at
10.0 µg/1), and silver (at 1.0 µg/1)
b. Include POC limited by the NPDES permit in the STMP POC Table and sampling
plan (i.e., Dichlorobromomethane, Bis(2-Ethylhexyl) Phthalate, TN, and TP)
c. Please include a revision history section for the STMP.
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 comments, please contact the Pretreatment Coordinator Keyes
[[e-mail]] , or the Unit Supervisor, Michael at
[[e-mail]].

DocuSign Envelope ID: 14AB1 E68-C62D-4BF8-8F64-217F0648C28E
Sincerely,
,—DocuSigned by:
`— C464531431644 F E...
for Richard E. Rogers Jr., Director
Division of Water Resources
dy/Denton.266 89_hwa.review_2022
Attachments:
Denton.26689.HWA-AT.2022 (under review)
cc with attachments:
DWR Winston-Salem Regional Office — Pretreatment/ Jim Gonsiewski
Municipal Unit File and Central Files (Laserfiche)