Des Moines WRA Eastside Interceptor

The Des Moines Metropolitan Wastewater Reclamation Authority (WRA) maintains a vast wastewater collection system that serves the City of Des Moines and its suburbs. The Westside Pump Station and Equalization Basin is the system’s largest wastewater pumping facility, along with a buried tank equalization basin. The Westside Pump Station and force main were a “bottleneck” for an extensive network of sewers that converge at its twin 55-foot-deep wet wells. Improvements constructed in 2007 increased the pump station capacity to match the downstream force main capacity. However, since 2007, upstream expansion and plans for extension of the tributary trunk sewers again pushed the limits of the existing capacity, and the WRA Eastside Interceptor project was developed to increase the capacity of the system.

There were eight major segments of construction projects broken out for the overall project. Segments 1 through 5 encompass a gravity interceptor sewer from Union Park, through the east side of Des Moines, to the Wastewater Reclamation Facility (WRF). Segments 6 and 7 encompass a 42” diameter pressure force main from the Westside Pumping Station site to the gravity sewer at Union  Park. Segment 8  involved the construction of a new High Flow Pump Station on the Westside Pumping Station property and was designed to provide an additional capacity of 40 mgd. HR Green provided engineering services for the $24.8M Segments 6-8.

The selected alternative for the pump station configuration was a separate dry-pit structure that houses four 300 HP pumps. The pumps have suction lines extending into an adjacent quadrant of the existing Equalization Basin tank. The pump electrical equipment was housed at grade in a new building constructed above the below-grade dry pit structure.

The Segment 8 improvements also included a new screening facility with three mechanical bar screens. All incoming wastewater, whether it is being handled by the existing pump station, or the new High Flow Pump Station, undergoes screening prior to pumping or equalization. A Valve Vault structure was constructed as part of the Segment 8 improvements, which allows the WRA operational flexibility to combine flows from the existing pump station with the new High Flow Pump Station, or pump from either station to either force main.

The discharge force main (Segments 6&7) was sized as a 42” ductile iron pipe to allow for both sets of pumping stations to discharge satisfactorily into the force main while also providing favorable velocities. The project included a new 1,000 kW diesel generator to provide backup power for the new High Flow Pump Station. Miscellaneous improvements were also included on the existing pump station to tie the discharge into the new valve vault, convert space into an electrical room for the new screening facility, and change an existing room into a non-rated space available for storage.

The alignment for the force main crosses the Des Moines River and follows Birdland Drive prior to crossing the Birdland Marina and discharging into the gravity sewer (Segments 1-5) along E. Jefferson Avenue for an overall length of approximately 8,500 linear feet. The alignment was chosen to avoid levee crossings, minimize dewatering costs, and avoid impacts to a regional bike trail.

The WRA Eastside Interceptor helps address known capacity deficiencies of the Westside Interceptors and increase the system’s capacity to effectively and efficiently convey the flow of wastewater for the Des Moines metro area for decades to come.