WQCS00055_SSO Compliance Evaluation Inspection_20240315

DocuSign Envelope ID:B3ED6A46-OB02-4693-9BD1-262875EDDFOF
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ROY COOPER
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ELIZABETH S.BISER
Secretary `$` "�"`�
RICHARD E.ROGERS,JR. NORTH CAROLINA
Director Environmental Quality
March 15, 2024
Mr. Terrell Blackmon, City Manager
City of Henderson
PO Box 1434
Henderson, NC 27536
Subject: Henderson Wastewater Collection System
Collection System Permit: WQCS00055
Wet Weather Sanitary Sewer Overflows
Vance County
Dear Mr. Blackmon,
The NC Department of Environmental Quality - Division of Water Resources (DWR), Raleigh
Regional Office (RRO) recently conducted a review of the City of Henderson's sanitary sewer
overflow (SSO) reporting records for January 2022 to January 2024 (25 months). The file review
identified 49 reported SSO totaling more than 1 million gallons of wastewater released from the
collection system. Eighty-six (86) percent of the total reported SSO causes were due to
inflow/infiltration or severe natural conditions and more than 39 percent were associated with
Rock Mill Road and the Sandy Creek interceptor and pump station.
On Friday, March 1, 2024, Donald Smith, and Danny Smith from the RRO met with city staff,
Christy Lipscomb —Water Resources Director, Joey Long—Assistant Water/Sewer Director/ORC,
and Seth Davidson —Water Reclamation Facility Maintenance Supervisor. Following the meeting
to discuss the SSOs and system operations, the Sandy Creek Pump Station and a few manholes
associated with two parallel 12-inch gravity sewer lines were visited.
City staff provided the following information during the meeting:
Collection System: The Henderson wastewater collection system consists of 163 miles of
pipeline with 147 miles of gravity sewer and 15 miles of force main. There are 13 duplex
pump stations. The city has a population of approximately 14,900 residents. City staff
identified the Sandy Creek Sewer Basin to be an area of the system that backs-up and has
capacity issues during heavy rainfall events. Likewise, the wastewater treatment plant
also experiences high flow conditions (10-13 MGD), more than 10 times the average daily
flow of 1.6 million gallons per day (MGD) during heavy rainfall events. The collection
North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh,North Carolina 27609
o p,n, m e ;o may ni oai\ r 919.791.4200

DocuSign Envelope ID: B3ED6A46-OB02-4693-9BD1-262875EDDFOF
City of Henderson, WQCS00055
March 15, 2024 Page 2 of 4
system consists of a variety of different pipeline materials including PVC, vitreous clay and
cast-iron pipe. Manholes are constructed in a variety of pre-cast, brick and mortar
designs.
SSO and Inflow and Infiltration (I&I) Reduction Efforts: The city has worked with WK
Dickson, a consulting firm in 2021 and 2022 to acquire a total of $7.5 million of state
revolving funds and grants to work on I&I reduction. City staff conducted some in-house
flow monitoring and smoke testing around the same time-period to identify sources of
I&I. Some I&I and stormwater system connections were found and corrected. The city
has a project kickoff meeting scheduled for March 22, 2024, with HG Reynolds, a
contractor to assist with finding and fixing I&I problems in the collection system. It was
also explained by the city staff, that the contractor will especially help in areas of the
system that are difficult to access due to wet easement conditions.
Sandy Creek Basin and Pump Station Visit: City staff indicated that the Sandy Creek Pump
Station has a current average daily flow of 0.5 MGD with a firm capacity of approximately
4 MGD. The pump station is a wet pit/dry pit design consisting of a bar screen, wet well,
(2) variable frequency drive - 300 Hp horizontal split case centrifugal pumps, weight
assisted check valves, magnetic flow meter,force main emergency bypass connection, 16-
inch force main, and approximately 8 to 10 air release valves (ARV). The Sandy Creek
Pump Station receives sewer flow from three upstream pump stations (Industrial Park,
HV2, and Martin's Creek). The pump station has programmable logic control (PLC) and
supervisory control and data acquisition (SCADA) telemetry and is monitored by
wastewater treatment plant personnel.
In 2018 Charles Underwood (contractor) performed maintenance at the pump station that
included conducting a drawdown, flushed the force main, and repaired/replaced 8-10
ARV. Staff indicated that no additional pump drawdowns or ARV maintenance has
occurred since Charles Underwood's maintenance.
While onsite city staff placed pump #1 in hand and operated the pump at 55 hertz (92%
speed) with an observed flow rate of approximately 1,730 gallons per minute (GPM), or
2.49 MGD. City staff explained that the pump controls are adjusted to 55 of 60 hertz due
to vibration at 100% speed. City staff also indicated that only one pump is operated at a
time as when two pumps are used, they "fight" each other's discharge and a lower
discharge rate is observed. The Sandy Creek Pump Station is listed in the collection system
permit as having a capacity of 2,750 GPM or 3.96 MGD.
North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh,North Carolina 27609
NORTH GARO�INA _
m� Mnme 0"INII 919.791.4200

DocuSign Envelope ID:B3ED6A46-OB02-4693-9BD1-262875EDDFOF
City of Henderson, WQCS00055
March 15, 2024 Page 3 of 4
GreenAcres Gravity Sewer (parallel 12-inch sewer lines with crossover):
Parallel 12-inch gravity sewer line identified as "Green
Acres" was visited and manholes opened to observe
system flow and manhole conditions. At the time of the
inspection, one of the 12-inch sewer lines appeared to +. f
be flowing at approximately 50-60%full while the other
sewer line was flowing in the 30-40% full in junction Flow Direction
manhole where flows combine. There was no
measurable rainfall the day prior to the system
inspection. (Note: These observations occurred prior to
the late afternoon/evening precipitation event for
March 1.) The parallel 12-inch sewer lines combine with
(50-60?Zfl
an estimated 18-inch sewer line that expands to 24-inch
as it flows to the Sandy Creek Pump Station. The
manholes were brick and mortar construction and the
sewer lines appeared to be vitreous clay pipe that GreenAcres-Gravity Sewer Junction Manhole
transitions to ductile iron pipe in the area visited.
In response to the site visit and this letter, the RRO requests a follow up meeting with the City of
Henderson and appropriate engineering and city staff in June 2024 to discuss how the city plans
to address the wet weather Sandy Creek SSO issues. Prior to the follow up meeting, please
provide this office by May 31, 2024, with a letter from the city engineer/management with
updates on items 1-4 listed below, and any additional information you wish to provide:
1) Summary of data collection and assessment (flow monitoring, rainfall, smoke testing, sewer
line assessment,other)efforts used to identify I&I and system capacity in areas of the Sandy Creek
Sewer Shed and any other areas affected by wet weather SSOs.
2) Hydraulic capacity and condition assessment of the Sandy Creek Pump Station. This
assessment/account should include information on pump drawdowns,vibration assessment, and
results of force main/ARV evaluation(s).
3) Please describe any additional or new monitoring efforts that are planned to help
systematically identify hydraulic pinch points and I&I sources that could account for WWTP
hydraulic loading.
4) Also, provide a proposed plan and schedule for how acquired funding will be used to remedy
and address rehabilitation/repair/construction needs to abate sewer overflows.
D E Q�� North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh,North Carolina 27609
NORTH CAROUNA _
Dopwbnwd„F r��,�wla,\ /./ 919.791.4200

DocuSign Envelope ID:B3ED6A46-OB02-4693-9BD1-262875EDDFOF
City of Henderson, WQCS00055
March 15, 2024 Page 4 of 4
Please respond by e-mail to Donald Smith at [e-mail] confirming city staff
availability for a follow up meeting on Wednesday, June 5 at 10:00 a.m. (If this proposed meeting
does not work for Henderson, please offer an alternative date and time with your e-mail
response.
Thank you for your attention to these matters. If you have any questions, please do not hesitate
to contact Donald Smith [phone] or me at [phone].
Sincerely,
DocuSigned by:
Va1n t,SS -e. M can lit,(
B2916E6AB32144F...
Vanessa Manuel, Assistant Regional Supervisor
Water Quality Regional Operations Section
Raleigh Regional Office
Division of Water Resources, NCDEQ
Cc: Laserfiche
D E Q�� North Carolina Department of Environmental Quality I Division of Water Resources
Raleigh Regional Office 13800 Barrett Drive I Raleigh,North Carolina 27609
NORTH CAROUNA _
Depwbnwd„F r��,�w10ua\ /./ 919.791.4200