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Project update

September 2018

Construction continues for outfall and treatment station; Conveyance contractor onboard

Treatment Station - Secant piling is complete!

The structural wall for the underground Influent Pump Station, which will help to move flows into the station, is in place. Crews placed 104 secant piles to complete the wall. The wall will keep soil in place as excavation for the pump station begins in September. Around the site, crews are pouring concrete where pipes will be placed. The concrete will support the pipes underground and keep them in place. Before the pour, rebar forms are installed to hold the concrete. 

Outfall Pipe installation and sheet piling continue

Construction continues on the Outfall structure. Right now, crews are working on the structure that will help control water flows into the Duwamish River and prevent erosion. Concrete pours to form the structure have begun. Sheet piling activities are planned to continue intermittently through the fall as surrounding pipes are installed. 

Concrete pours and excavation activities for the station and outfall are planned to continue through fall 2018. Increased truck traffic in and out of the site is expected during concrete pours.

Conveyance Pipes Contractor Onboard

James W. Fowler Company has been awarded the contract to build the underground conveyance pipes that will connect the station to the new outfall structure. We’ll share more information later this year as we begin to prepare for construction, expected to start in late 2018.

Concrete being pouredCrews are pouring concrete at the station and outfall construction sites through fall 2018.

Read the project update for more information.

Now posted: Project overview fact sheet , June 2018; Summer 2018 newsletter , August 2018

Project description

Rendering of Georgetown Wet Weather Treatment SystemSite of future Georgetown Wet Weather Treatment Station at the corner of 4th Avenue South and South Michigan Street.

The Georgetown Wet Weather Treatment Station Project includes the construction of a combined sewer overflow (CSO) wet weather treatment station between the Brandon Street and South Michigan Street Regulator Stations, related pipes and a new outfall structure to release the treated water into the Duwamish River. When constructed, the station can treat up to 70 million gallons of combined rain and wastewater a day that would otherwise have discharged directly to the Duwamish without treatment during storm events.

Earlier this year, King County’s contractor Flatiron West Inc. started treatment station construction. This summer, construction on the new outfall structure will begin.

This project will help clean up the Duwamish River by treating stormwater runoff and sewage during heavy rains. Right now, heavy rains can fill up our sewer pipes, sending polluted runoff and sewage through a pipe into the river. King County began on-site work in April 2017 and expects to finish construction in 2022.

Wet Weather Treatment StationWet weather treatment stations clean overflows locally on-site during heavy rain storms.


Through a competitive process, King County awarded the Treatment Station construction contract to Flatiron West Inc. Through an additional competitive process, Pacific Pile & Marine was awarded the contract to construct the new outfall structure. Major construction on the treatment station started in April, and outfall construction will begin this summer. Later this year, King County will select a contractor to build the new pipes to connect the station to the outfall structure.

Project timeline


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Contact Bibiana Ocheke-Ameh at:


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King County partnered with Nature Consortium and Seattle Public Schools to teach 5th graders at Maple Elementary about water conservation and create art for the construction fence. View more project videos in the Library.

Project location


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