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Project update

April 17, 2018

More activities begin on site; Crews building Secant Pile Wall 

Starting in mid-April 2018, crews will begin building the wall of the facility’s underground Influent Pump Station. Work will include drilling holes about 90 feet into the ground and installing four-foot wide concrete cylinders. The cylinders are called secant piles.

Secant piles lock together to create a structurally stable ring. This ring will be nearly 100 feet wide and is part of the Influent Pump Station’s structural wall.

Read the latest project update for more information and view the video below to learn more about secant pile walls (ring).

Project description

Georgetown Wet Weather Treatment StationSite 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.

This year, King County’s contractor completed demolition and site preparation activities. Demolition activities included removing buildings, underground structures, asphalt, and utilities. The site has been graded and prepared for treatment station construction.

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. Major construction will start in 2018. Through two additional competitive processes, the County will award two construction contracts to build the new pipes and outfall structure into the Duwamish River in late 2017 and early 2018. 

Project timeline


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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.

Project location


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