Des Moines Selects HDR for Combined Sewer Project

The Des Moines Wastewater Reclamation Authority selected HDR, architectural, engineering and consulting firm to address significant combined sewer overflow issues, the groups said in a March 31 press release.

HDR will evaluate and select the most appropriate treatment technologies; design and provide construction phase engineering as well as observation services for a combined sewer solids separation facility. The project has an estimated cost of $40 million. Design plans are scheduled for completion in December 2009 and bids for construction should be received by March 2010 for a two-year construction period.

The overriding goal of the combined sewer overflow (CSO) reduction program is water quality improvement for the Des Moines River and the downtown riverfront area, while also helping the authority comply with a U.S. Environmental Protection Agency consent order that such facilities be in operation by June 30, 2012. In addition, the facility will be designed to reduce adverse impacts of wet weather flows to a nearby wastewater reclamation facility.

Several solids separation alternatives will be evaluated, including a baseline alternative that would have four primary clarifiers designed for 80 million gallons per day (mgd) with physical or chemical augmentation to achieve the desired wastewater quality. Other solids removal alternatives being considered include retention treatment basins and ballasted flocculation. Treated effluent will be discharged directly to the Des Moines River.

In addition to the solids separation process, the facility is expected to include:

• An influent pump station with capacity greater than 300 mgd
• A grit and screening facility to remove the substantial solids associated with combined sewer wet weather events
• A disinfection facility to reduce coliform bacteria concentrations to acceptable levels while complying with total chlorine limitations.

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