HAMPTON ROADS SANITATION DISTRICT VIRGINIA INITIATIVE PLANT
RAW WASTEWATER INFLUENT PUMP STATION

CLIENT: Hampton Roads Sanitation District

Northwest Hydraulic Consultants was retained by HDR Engineering Inc. to provide a conceptual design review of the Preliminary Treatment Facility Raw Wastewater Influent Pump Station for the Hampton Roads Sanitation District Virginia Initiative Plant, and then construct and test a physical hydraulic model of the preferred initial design. The overall objective of the model study was to optimize the hydraulic design of the screen channels and wet well to provide uniform flow to the pumps.

The proposed wastewater intake will be comprised of an influent pipe, which will convey the raw influent to a screening chamber before entering a trench type wet well. The screening chamber will be comprised of three mechanical screens. There will be four Raw Wastewater Intake Pumps rated at 34.7 mgd. Plant influent flows are expected to range from 14 mgd to 70mgd.

The 1:6 scale model study determined that the initial design was subject to unacceptable sub‑surface vortices entering all pumps. In addition, the velocity fluctuations measured at the pump impeller location were outside the specified criterion.

Modifications to the initial design were developed to produce more uniform flow in the screen channels and wet well, and reduce solids deposition in the screen channels. With these modifications installed, the surface and sub‑surface vortices, flow pre-swirl, and the velocity distribution and velocity fluctuations were all within acceptable limits.