About

Treating combined stormwater and sewage on rainy days is one way to prevent combined sewer overflows. With this project, extra water will go to the wet weather treatment station when pipes get too full. The station will remove solids and kill germs before the water is released. The station will work in big storms, which is when we need it most to protect Puget Sound.

This project includes a new wet weather treatment station in SODO. The proposed site covers about eight acres. It is near South Spokane Street and First Avenue South.

This project is part of King County’s Mouth of Duwamish Wet Weather Facilities program. The program will reduce combined sewer overflows from five combined sewer outfall pipes. They will keep more than 400 million gallons of polluted water out of the Duwamish River and Elliott Bay each year. This work helps King County meet state and federal clean water laws. Learn more about the program at KingCounty.gov/MDWetWeatherFacilities.

The SODO Wet Weather Treatment Station project includes these proposed clean water facilities:

• A wet weather treatment station in SODO. It will treat stormwater and sewage during heavy storms.
• A new outfall pipe to the Duwamish River. This pipe will safely release treated water from the wet weather treatment station into the Duwamish River. The proposed location of the new pipe is between SODO and Harbor Island.
• New pipes and support buildings. They will connect the treatment station to the regional sewer system and help everything work together.

All communities deserve a fair chance to do well. To support this, King County makes equity and fairness a priority in every stage of our projects.

• We listen to people and work with neighbors. We ask for feedback and use it in our plans when possible.
• We focus on communities most affected by our work.
• We plan and build projects that protect public health and the environment.

We share regular project updates and provide opportunities for community feedback. We do this in each phase of the project.

Location matters. The proposed plan places the station close to existing sewer pipes and the Duwamish River. This means we need fewer new pipes. Fewer new pipes means less time spent building, lower costs, and fewer disruptions to nearby roads and neighborhoods. 

Before construction, you may see our team gathering information about the project area. This may include soil and groundwater testing. We will notify nearby businesses and community members before this work starts. We usually do this notification 48 to 72 hours in advance. 

Construction could start as early as 2029 and last about five years. The facilities could begin operating as soon as 2034. As construction gets closer, we will share updates about what to expect and how we will stay in touch. 

This project is currently in the design phase.

During the design phase, we will:

• Create detailed plans for building each facility
• Apply for permits to start building
• Write contracts that will explain the work and who will do it
• Study soil and groundwater samples to learn more about the project area
• Identify environmental impacts and plan ways to address them