NC0036269_Pretreatment_HWA_Response_20240905

North Carolina Department of Environmental Quality Division of Water Resources
512 North Salisbury Street 1611 Mail Service Center Raleigh, North Carolina 27699-1611
919.707.9000

Via Electronic Mail ([e-mail])

Beverly Metcalf
Environmental, Health & Safety Compliance Manager
Water & Sewer Authority of Cabarrus County
6400 Breezy Lane
Concord, NC 28025

Subject: Pretreatment Review of Head Works Analysis
Response to WSACC Letter 07/23/2024
Program: Water & Sewer Authority of Cabarrus County (WSACC)
Wastewater Treatment Plant: Rocky River Regional WWTP
NPDES #: NC0036269, Cabarrus County

Dear Beverly Metcalf:

The Municipal Unit of the Division of Water Resources has reviewed the response from WSACC for the updated
Headworks Analysis (HWA) and the Allocation Table (AT) for WSACC’s Rocky River Regional WWTP
(NC0036269). The response letter was received by the Division on 07/23/2024. The Long Term Monitoring Plan
(LTMP), HWA, and AT are approved for the 30 MGD NPDES flow tier.
Below is the Division’s response to each bullet point presented in the letter from WSACC.
 HWA and AT Corrections and Observations
o Pass-Through Loading Calculations
 For the mercury detection levels WSACC is responsible for performing a year of sampling
(at least quarterly, but the Division recommends monthly) the influent at the lower level
(EPA Method 1631) and send the results into the Division. The Division understands the
concerns that WSACC has, and once the results have been sent in if there are issues with
interference it can be noted and kept on record. Since there are no effluent violations, the
Division encourages WSACC to maintain the mercury levels currently set for industries.
Please submit the additional mercury sampling data with the 2025 PAR in March 2026.
 Thank you for clarifying and using the literature value for silver.
 The values for the instream calculated dissolved metals values can be taken from the
calculator spreadsheet that the Division provides, therefore the data was interpreted
correctly. As a note for future reference, dissolved metals values can also be taken from
the Fact Sheet RPA table, which can save some time for the POTW. Thank you for
clarifying how the values were calculated.
o Inhibition Loading Calculations
 Thank you for clarifying the use of the literature value and that it was in the drop box.
o Maximum Allowable Industrial Loadings Calculations
Docusign Envelope ID: B2A36DA2-52C6-4DBB-8253-C6623B88CC65
9/5/2024

North Carolina Department of Environmental Quality Division of Water Resources
512 North Salisbury Street 1611 Mail Service Center Raleigh, North Carolina 27699-1611
919.707.9000

 For all four bullet points under this section the Division acknowledges and accepts the
explanations for MAIL calculations. The Division asked so that we could be aware of why
values were chosen to have a better understanding of what is going on at the POTW.
o Ammonia
 Thank you for including the ammonia correspondence.

Thank you for your continued cooperation with the Pretreatment Program. If you have any questions or comments,
please contact Natalie Gorensek [email: [e-mail]] at [phone] or Octavio Henriquez at
[phone] [email: [e-mail]].

nhg/cab_rocky_hwa_response_2024
Ec: Municipal Unit File
Wes Bell, MRO
Central Files (Laserfiche)
Sincerely,

Karen Preston, Municipal Unit Supervisor
Division of Water Resources

Docusign Envelope ID: B2A36DA2-52C6-4DBB-8253-C6623B88CC65