Projects

The proposed wet weather treatment station will control overflows from four of the project outfalls (called Hanford #2, Lander, Kingdome, and King Street). The proposed location is on about eight acres of land near the intersection of South Spokane Street and First Avenue South. 

During periods of heavy rain, stormwater and wastewater that currently overflow into the Duwamish River will be directed to the wet weather treatment station. There, the combined stormwater and wastewater will be cleaned before it is discharged into the Duwamish River.

King County recently built a similar facility in Georgetown. The Georgetown Wet Weather Treatment Station can treat up to 70 million gallons of combined stormwater and wastewater per day. To put the proposed wet weather treatment station in context, it will have the capacity to treat up to about 240 million gallons of combined stormwater and wastewater per day during heavy rains. That is nearly four times as much as the Georgetown Wet Weather Treatment Station. Learn more about that facility by visiting kingcounty.gov/GeorgetownWWTS.

The storage tank will control overflows from the fifth project outfall (called Chelan). It will be underground near the intersection of Southwest Dakota Street and West Marginal Way Southwest. 

The storage tank will help control CSOs by holding combined stormwater and wastewater that would otherwise overflow into the Duwamish River during large rainstorms. Once heavy rain subsides, the combined stormwater and wastewater held in the storage tank will flow back into pipes and on to West Point Treatment Plant for cleaning. The proposed storage tank would be able to hold up to 7.5 million gallons of combined stormwater and wastewater. That is more than 10 Olympic-sized swimming pools!

King County is preparing to build a similar storage tank in South Park. The West Duwamish Wet Weather Storage project will be able to hold up to 1.25 million gallons of combined stormwater and wastewater. Learn more about that project by visiting kingcounty.gov/WestDuwamish-cso.

After leaving the new wet weather treatment station, clean water will be released into the Duwamish River from a new outfall between SODO and Harbor Island. The outfall will be underwater and will not be visible from the shore.

To connect the new wet weather treatment station and storage tank to the existing system serving homes and businesses, we will install new pipes along the following roads in SODO and West Seattle (Industrial District West):

• Utah Avenue South from South Lander Street to South Hinds Street
• South Hinds Street from Utah Avenue South to the Duwamish River
• West Marginal Way Southwest from Chelan Avenue Southwest to Southwest Dakota Street

Supporting facilities will connect the wet weather treatment station and storage tank to the existing system and direct flows on rainy days. These facilities will be above-ground buildings with a footprint between the size of a two-car garage and a basketball court. The proposed solution includes supporting facilities at the following intersections:

• Alaskan Way South and South King Street
• First Avenue South and South Royal Brougham Way
• Utah Avenue South and South Lander Street
• Utah Avenue South and South Hanford Street
• Chelan Ave Southwest and West Marginal Way Southwest