Westside Equalization Basin and Pumping Station

This project upgraded the largest wastewater pumping station in the City of Des Moines. The project included installation of new pumps, bar screens and piping, electrical instrumentation and controls, new sewer forcemain, and structural modifications to the existing building.

The Westside Equalization Basin and Pumping Station is a very deep facility, with sewers entering the wet wells more than 50 feet underground – well into solid bedrock. Additionally, the project site is located on a limited tract of land, which the City leases from the U.S. Army Corps of Engineers, near the Des Moines River. Because of these site restrictions, HR Green aimed to avoid further excavation or horizontal expansion of the Westside facility, contrary to recommendations for such measures in the client’s 2004 Facility Plan. HR Green hoped instead to contain all the necessary improvements within the existing facility’s footprint, thus saving the client money and hastening the project’s completion.

The goals of no expansion and no interruption were achieved by a careful redesigning of the Westside station’s piping system, selection of an entirely different kind of pump, and a creative construction sequence. The old pumps were 200 hp pumps of the long-shaft variety. These pumps required frequent attention by operators, who had to descend more than 50 feet of stairways to inspect the couplings on the spinning shafts. HR Green selected 335 hp dry-pit submersible style pumps, thus eliminating the spinning shafts. Modifications to the roof were also designed, to provide a hatch system for installation and future maintenance of the new pumps.

Most notably, HR Green authored a detailed sequence of construction operations to ensure that no interruption of the facility’s service would occur during construction. This sequence required the procurement process for new pumps to begin in June before the design was complete, in order to install them during early winter, when sewage flows to the station are at their annual ebb.

Other improvements designed by HR Green for this project included:

1. Extensive electrical, instrumentation and control upgrades, including variable frequency drives, touch-screen operator interfaces, new backup generator, new main switchgear, and closed-circuit TV monitoring.
2. A new 1,100-ft., 30-in. diameter sewer forcemain in parallel with an existing forcemain.
3. Structural modifications to the pumping station interior to accommodate the greater weight of new equipment.
4. Wet well modifications, in accordance with Hydraulic Institute Standards (HIS), including a dispersion shelf to reduce turbulence and prevent cavitation at the pump volutes.
5. New self-cleaning bar screens.