Washington Highway Pumping Station & Force Main Replacement

BETA completed the planning, design, and construction administration for the replacement of the Washington Highway pumping station and force main for the Narragansett Bay Commission as the existing pumping station was beyond its useful life. During the preliminary design process, a number of alternatives were considered to address existing station issues including poor access, maintenance problems, variable flow conditions, and resulting odor concerns due to extended retention times in the existing 16-inch force main.

BETA designed a dual pumping system consisting of four (4)-pumps with dual force mains to handle the large variation in dry weather/wet weather flows and reduce odors. This system allows the lower flow range to be managed more effectively with smaller capacity pumps. Since the reduced pumping flow rate requires a smaller diameter force main to maintain proper scouring velocities, two force mains were designed to provide sufficient station capacity. The force mains are designed to automatically drain by gravity back to the station when not in use.

To reduce the need for employee entry into the wet well, BETA designed a “self-cleaning,” trench-type wet well. The wet well configuration relies on the influent pipe for storage, thereby reducing the amount of wet well storage volume required, and utilizing wet well geometry to produce a scouring flow pattern during cleaning cycles. The cleaning cycles consist of a periodic drawdown of the wet well utilizing the raw sewage pumps.

The new facility was positioned adjacent to the existing station which was demolished upon completion of the new pumping station. The project included:

• Four (4) dry pit submersible pumps (1,500 gpm, 40 hp each), with a total station pumping capacity of 5.0 mgd.
• 2,900 Feet of dual 12-inch force mains
• Separate enclosure for generator