WQCS00011_Riverside Drive SSO Investigation Letter_20240213

North Carolina Department of Environmental Quality Division of Water Resources
Raleigh Regional Office 3800 Barrett Drive Raleigh, North Carolina 27609
919.791.4200

February 13, 2024

Mr. Keith Roger, Jr., City Manager
City of Rocky Mount
331 South Franklin Street
Rocky Mount, NC 27802
Subject: Rocky Mount Collectfon System – SSO
Collectfon System Permit: WQCS00011
Riverside Drive
Edgecombe County
Dear Mr. Roger,

On January 11, 2024, the NC Department of Environmental Quality - Division of Water
Resources (DWR) received a compliant regarding the frequency of sanitary sewer overflows
(SSO) from the City of Rocky Mount (City) wastewater collectfon system along Riverside Drive. In
response, the DWR - Raleigh Regional Office (RRO) conducted a file review and scheduled an
onsite meetfng with the city.

The file review identffied that the city reported 24 SSO between January 2021 and December
2023. Half of the SSO occurred on Riverside Drive totaling more than 1.9 million gallons spilled.
Riverside Drive accounted for 86% of the total SSO volume reported by the city during the
three-year period.

On January 31, 2024, Donald Smith, Kevin Fowler, and Danny Smith from the RRO meet with city
staff (Brenton Bent - Director of Water Resources, Brad Kerr – Director of Public Works, Scott
Miles – Assistant City Engineer, Nate Williams – Collectfon System Superintendent/ORC), and
Ken Orie, P.E., a city engineering consultant with Withers and Ravenel.

City staff provided the following informatfon during the meetfng:

1) Mapping/GIS: Withers and Ravenel has been collectfng informatfon/data to update the
wastewater collectfon system map. This includes identffying pipe material, diameter size,
pipe and manhole locatfons, pipe invert elevatfons and other mapping data necessary to
develop a more advanced/detailed GIS mapping layer of the collectf on system. These
efforts have been ongoing during this past year.
DocuSign Envelope ID: C446F406-A4D4-4A3E-B0DE-42655933BB90

North Carolina Department of Environmental Quality Division of Water Resources
Raleigh Regional Office 3800 Barrett Drive Raleigh, North Carolina 27609
919.791.4200

City of Rocky Mount, WQCS00011
February 13, 2024 Page 2 of 3

2) Modeling: Mr. Orie with Withers and Ravenel explained that the enhanced mapping
initfatfve/efforts, coupled with rain gage data and collectfon system flow data are
requisites for successful modeling development. The collectfon system modeling efforts
are intended to identffy effectfve approaches for abatfng SSO for different size/threshold
storm events. It was explained during the meetfng that model calibratfons are
antfcipated to be complete in approximately 2 months (early April).

3) SSO and I&I Reductions: The city has replaced or reconditfoned 4 out of 8 screw pumps
to improve influent wastewater pumping capacity to the wastewater treatment plant
(WWTP). The city indicated that the WWTP influent pumping and plant capacity is
generally not a concern during wet weather events, outside of extreme storms. Influent
pumping and WWTP capacity are downstream of the subject Riverside Drive SSO
locatfon.

Approximate 25,000 linear feet of the Beech Branch Outiall (27-inch diameter pipeline)
was rehabilitated/repaired. (The improvement helped with observed inflow and
infiltratfon during storm events due to structural integrity issues prior to its
replacement.)

4) Riverside Drive (SSO manhole location): While on site at Riverside Drive, city staff
explained that when the river level rises the stormwater culvert often receives flow from
the river and will back up onto the road. Once the flood water recedes, woody debris,
rack lines, trash, mud and silt coatfng the road, roadside areas and vegetatfon is left
behind. A SSO will initfally start to surcharge (discharge) from the manhole due to heavy
rain and high river flows flood the manhole and roadway. The adjacent/nearby storm
drain overflows due to “back flow” from the river.

Non-wet weather induced SSO events typically have solids, paper, and trash that is
common with wastewater discharges. SSO clean-up responses include barricading storm
drains and recovery of wastewater and clean-up rinse waters with use of pumps as well
as efforts to collect solids and treatment of the area soils with use of powdered hydrated
lime. For the Riverside Drive locatfon, city staff explained that due to the close proximity
of the storm drain to the manhole and respectfve flood waters subsidence, typically no
solids or trash is identffied or distfnguished from flood waters following an SSO at this
locatfon.

DocuSign Envelope ID: C446F406-A4D4-4A3E-B0DE-42655933BB90

North Carolina Department of Environmental Quality Division of Water Resources
Raleigh Regional Office 3800 Barrett Drive Raleigh, North Carolina 27609
919.791.4200

City of Rocky Mount, WQCS00011
February 13, 2024 Page 3 of 3

In response to the site visit and this letter, the RRO requests a follow up meetfng with you and
appropriate city staff in early May 2024 to discuss the next steps on how the city plans to
address the Riverside Drive SSO issue.

Specifically, this office would like an update on the following:

 On-going mapping/GIS efforts
 Data collectfon and assessment (flow, rainfall, river elevatfon/staff gauge, other) efforts
 Modeling and model calibratfon progress
 Hydraulic capacity and conditfon assessment of inverted siphons associated with
Riverside Drive overflow locatfon (include cleaning and inspectfon history)
 Proposed remedies, and schedules for addressing potentfal
rehabilitatfon/repair/constructfon needs to abate SSOs.

Please respond by e-mail to Donald Smith at [e-mail] confirming your and the
city staff availability for a follow up meetfng on Thursday, May 30 at 10:00 a.m. (If this proposed
meetfng does not work for you, please offer an alternatfve date and tfme with your e-mail
response.).

Thank you for your attentfon to these matters. If you have any questfons, please do not hesitate
to contact Donald Smith [phone] or me at [phone].

Sincerely,

Vanessa Manuel, Assistant Regional Supervisor
Water Quality Regional Operatfons Sectfon
Raleigh Regional Office
Division of Water Resources, NCDEQ

Cc: Laserfiche

DocuSign Envelope ID: C446F406-A4D4-4A3E-B0DE-42655933BB90