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Project update

December 2019

Read the December Construction Update for recent highlights and information about upcoming work.

Ramp Night Closures

Construction to install the conveyance pipes on South Michigan Street and East Marginal Way South continues through the end of the year. To build the conveyance pipes, work in this area includes surveying in the roadway, moving utilities, trenching, placing pipes, backfilling, and temporarily restoring roadways.

Starting November 11, 2019, the southbound onboard ramp to SR-99 at the corner of East Marginal Way South and South Michigan Street will be closed during the permitted night shift hours, from 10 p.m. - 5 a.m. (Monday through Thursday). Occasional Sunday closures from 8 p.m. - 5 a.m. are also possible. The onboard ramp will remain closed during the night shift for approximately two months.

night time ramp closure map

Treatment Plant 

Crews continue to make progress building the underground tank (equalization basin). Concrete pours and rebar work will continue through the fall. Wastewater treatment works best when water flows into the system at a steady rate. However, this can be difficult to control especially during heavy rainfall.

An equalization basin helps adjust to the changes in the rate wastewater flows. The equalization basin also ventilates and mixes the stored stormwater to prevent it from becoming septic. Get an inside look at the construction of the equalization basin that will soon help to manage wastewater runoff at the Georgetown Wet Weather Treatment Station.

Inside view of equalization tank

View the latest project update .

King County’s Georgetown Wet Weather Treatment Station celebrates Platinum Achievement Award for Sustainability

King County’s Georgetown Wet Weather Treatment Station earned the coveted “Platinum” rating from the Institute for Sustainable Infrastructure’s Envision rating system. This is the first Platinum-awarded Envision project in Washington and recognizes the County’s commitment to sustainable communities and the environment. View news release.

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. (View other wet weather treatment facilities.)

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 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 construction contracts to three separate contractors.

In spring 2018, King County’s contractor Flatiron West, Inc. started treatment station construction. In the summer of 2018, Pacific Pile and Marine began the construction on the new outfall structure and in the fall of 2018, JW Fowler Company also began preparation work to construct the conveyance pipeline which will connect the treatment station to the outfall.

project timeline


Contact us

Construction hotline:

Contact Bibiana Ocheke-Ameh at:


 Feedback form

Facility Address:
6185 4th Ave S, Seattle, 98108

Sign up for email or text updates on the public involvement page.

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


Back to the capital projects overview map .

aerial map of the project area