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Western Ave Stormwater Outfall Treatment

Saint Johnsbury, VT

The Western Avenue Stormwater Outfall Treatment project was designed to divert flow from a previously separated stormwater collection system into a new Vortechs Separating structure.  The project was funded by a Grant made possible by the Caledonia County Natural Resources Conservation District.


Vortechs Stormwater Treatment system is a hydrodynamic separator that combines swirl concentration and flow controls into a shallow precast concrete treatment unit that traps and retains trash, debris, sediment, and hydrocarbons from stormwater runoff without the use of filters that need to be replaced.


During the preliminary engineering phase of the project, Dufresne Group evaluated four possible treatment devices, but given the limiting area of the site and large volume of stormwater to be treated the Vortechs system was selected.  Treatment volume was determined by Dufresne Group using hydraulic modeling in the program HydroCAD for the WQv (0.9-inch) storm event.


Dufresne Group provided engineering services for preliminary and final design, as well as on-site construction engineering services.

Key Features

  • Design provides treatment for WQv storm event for approximately 54.1 acres of impervious surface.

  • Design provides a compact size that allowed an existing easement to be used.

  • Design has low maintenance requirements with not replacement of internal parts.

  • Bypass structure installed to allow additional stormwater to be treated by a previously installed HDPE treatment device or direct discharge to the Sleepers River.

Chad Whitehead, Town Manager
Pomerleau Building, Suite 3
51 Depot Square
St. Johnsbury, VT 05819
Phone: 802.748.3926

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