Neilson WTP Modernization - 2- Narrative

STORMWATER MANAGEMENT NARRATIVE | NEILSON WTP MODERNIZATION PROJECT

2 OCTOBER 2018
Project and Site Description
The subject application involves the Modernization of the existing Neilson Water Treatment Plant
(WTP). The original facility was constructed in 1961 with major plant additions in 1982 and 1988. It is
located in Clemmons, NC, just west of Muddy Creek in the Yadkin Pee-Dee River Basin, and is owned and
operated by Winston-Salem/Forsyth City/County Utilities Commission (CCUC). The Neilson WTP sits on a
66-acre property along Frye Bridge Rd. The site topography within the construction limits includes
moderately sloped terrain that drains mostly south to north, as well as steep sloped terrain that drains
east to west along the north-west portion of the site. Most drainage flows towards the adjacent
drainage ditch which discharges to the Yadkin River Basin(s). The existing site consists of existing built
upon area (BUA), as well as maintained vegetated/grass areas and wooded areas around the perimeter.
Approximately 13-acres are expected to be disturbed in construction.
This project is a modernization of the existing facilities to improve plant hydraulics, process equipment,
chemical feed storage system, operations building, wash water and residuals management facilities,
power distribution systems, control systems, and site work and ensure process reliability.
Stormwater Management
With this project, the existing stormwater management system will remain in tact, with
maintenance/replacement to existing catch basins frames & grates as needed. All new stormwater
runoff will be treated through infiltration of overland sheet flow and vegetative conveyance. The
majority of improvements occur within the existing BUA, increase to BUA is less than 0.25%. At
minimum, stormwater runoff will travel via overland sheet flow 180 before discharging to the drainage
ditch along the north-west corner of the property. On Average, runoff will travel 400 feet or more.
Exterior alterations to the existing site include demolition of existing pipe, retrofitting existing yard
structures, adding new piping, expanding the gravel drive, and creation of new treatment structures,
such as the Equalization Basin, Washwater Clarifier, Backwash Supply Tank, Backwash Supply Tank Valve
Vault, Switchgear Building, Plant Effluent Collection Box, and Residuals Electrical Building. All demolition
work and installation of new piping will result in temporary land disturbance that will be restored upon
completion of the project. Erosion & sediment control permit shall be obtained for runoff during
construction.
This project will only increase the existing BUA by 0.24%, adding roughly 6,900 square feet of impervious
surfaces. These impervious areas are due to new yard structures spaced throughout the property. The
locations and dimensions of these structures can be seen in the attached plans sheets. Runoff from
these structures will be overland sheet flow and will be treated through infiltration. Of the new
structures being created, the Equalization Basin and Washwater Clarifier will be open to the atmosphere
to collect and store stormwater which will be discharged as process water to the existing residuals
lagoons and existing NPDES outfall. Therefore, these structures will not create additional runoff to be
handled by the current or proposed stormwater system and are not considered new impervious area.
These structures are shown in blue on the attached “New Built Upon Area” drawing.