Skip to main content

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 has recently reached the 90 per cent design milestone. At 90 per cent design, the project details are determined including equipment, architecture, landscaping, and contractor documents (design drawings and specifications). The project team is now focused on finalizing design details and preparing for construction, which will begin in 2025.

Project update

Project design is nearing the finish line. Construction will start in 2025!

Explore our project newsletter and online open house to learn more about the West Duwamish Wet Weather Storage Facility project’s design progress, public art, work force development opportunities.

Read the newsletter and online open house:

Leer el boletín y Jornada de puertas abiertas en línea:

Đọc bản tin và Nhà mở trực tuyến:

閱讀時事通訊 和 網上開放日:

阅读时事通讯 和 网上开放日 :

Sign up for project updates

Construction is quickly approaching! Select the "Subscribe for project updates by email or text" button in the Stay informed box to get updates, surveys, notices, and other information by email and/or text. You can unsubscribe anytime.

Previous project updates

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

Project location