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West Duwamish Wet Weather Storage

King County’s plans to build a wet weather storage facility to hold stormwater and wastewater that currently overflows into the Duwamish River during large storms.

Project description

Aerial map displaying location of the new storage facility and associated structures (two underground structures and two outfall/overflows) next to the Duwamish River.

King County will build a 1.25-million-gallon underground storage tank near the intersection of Southwest Michigan Street and Second Avenue Southwest to hold stormwater and wastewater that currently overflows into the Duwamish River during large storms. The water in the storage tank will then flow to the West Point Treatment Plant for treatment before it is safely released into Puget Sound. This storage tank will reduce overflows and pollution into the Duwamish River. The County will also build supporting infrastructure underneath West Marginal Way Southwest.

The project design is nearly complete. Construction is anticipated to begin in summer 2025.

Project update

January 2025

Share your feedback on community engagement during project design!

Through project design, we have worked with project neighbors to develop a solution that reflects community priorities. Thanks to everyone who has participated! Take this short survey and let us know what you thought about our efforts to gather input and keep you informed: publicinput.com/westduwamishdesign

This survey will be open until Friday, February 28.

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Consultants, contractors & suppliers: learn about upcoming contract opportunities including the West Duwamish Wet Weather Storage Facility.

Project location

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