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Lagoons upgraded to help Winthrop Wastewater Treatment Plant meet ammonia, E. coli limits


The City of Winthrop, Iowa, has a three-cell aerated lagoon Wastewater Treatment Plant. The treatment plant was struggling to meet ammonia and E. coli limits set in its National Pollutant Discharge Elimination System permit. The sanitary sewer collection system also had issues with excessive infiltration and inflow. The City hired Fehr Graham to prepare a Facility Plan to determine options for meeting limits, and then retained Fehr Graham for design and construction engineering services for recommended improvements.

Improvements included replacing the pumps in the main lift station to increase capacity, replacing surface aerators with submerged diffusers, covering lagoons with a floating insulated cover to retain heat to promote ammonia removal, and installing a polishing reactor to remove additional ammonia following the lagoon and ultraviolet disinfection system to reduce E. coli. 

Blowers were replaced in one building, and an operations building was constructed. Several sanitary sewer mains were rehabbed with cured-in-place pipe (CIPP) to reduce infiltration into the collection system.

Fehr Graham recommended the treatment plant lagoons to help keep costs and user rates low. Our team worked with the City to secure funding from a Community Development Block Grant and a State Revolving Fund loan.

March 2017 to July 2020


$2.4 million

» Wastewater Facility Plan.
» Lagoon upgrades.
» Polishing reactor.
» Ultraviolet disinfection.
» CIPP line sewer mains.
» Main lift station upgrade.

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