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Completed Fall 2018

Exterior of the Rainier Valley Wet Weather Storage facility

King County built this project to keep sewage and stormwater out of the Duwamish River. We installed a new sewer pipe near the intersection of Rainier Avenue South and South Bayview Street to send sewage and stormwater from a pipe that gets full during storms to another pipe that has more room.

We also built a storage tank at the intersection of South Hanford Street and South 27th Avenue. This tank can store extra sewage and stormwater that may otherwise be released into the Duwamish River.

New and reused pipe at S. Bayview St.New and reused pipe at South Bayview Street (  , May 2014)

new storage tank at S. Hanford St.Underground storage tank at South Hanford Street (  , May 2015)

Project schedule

Construction on the Rainier Valley Wet Weather Storage project began in early 2016. Project restoration was completed in Fall 2018.

24-hour emergency and odor reporting:

Contact West Point Treatment Plant at  206-263-3801.


Project location


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Combined sewer systemWhy does sewage overflow on the rainiest days?

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Protect public health

Like many cities around the country, the older parts of King County's wastewater system uses a single set of pipes to carry untreated sewage and stormwater to a treatment plant. To prevent sewer backups into homes and streets, the system includes safety valves called “combined sewer overflows” that route excess sewage and polluted stormwater flow directly into the Duwamish River and Puget Sound during storms. Although CSOs reduce potential exposure to untreated sewage, they pose significant public health concerns.

Clean up the Duwamish River

Every day, sewage flows through pipes under Rainier Valley to a King County treatment plant in Magnolia. During a storm, these pipes fill up with sewage and stormwater. When this happens, some wastewater must be released into the Duwamish River. These releases are called “combined sewer overflows” or CSOs. This is unhealthy for both people and the river. The new pipes and 340,000 gallon storage tank will reduce the number of CSOs into the Duwamish by storing wastewater until the pipes have room and the wastewater can be pumped back into the system to be sent for treatment.

Before finalizing the design, King County interacted with hundreds of people who live and/or work in Rainier Valley through interviews, presentations, an open house and a survey. We asked questions about the proposed design and safety features for the new Rainier Wet Weather Storage facility.

The community told King County that the project should support: 

  • Walkability 
  • Safety 
  • Opportunities for development 
  • Open space Attractive appearance 
  • No disruption to businesses or traffic on Rainier and MLK Jr Way

The final design reflected input from the community, including new sidewalks and lighting for safer passage around the facility, trees & landscaping that are adjusted for safety and visual effect, and a small facility footprint to leave as much room as possible for future uses of the rest of the property.

Station property and project office on adjacent propertyThe building and property next to the Rainier Valley Wet Weather Storage facility that King County used as a project office will be part of a redevelopment planning process that the City of Seattle is coordinating.

Please see below for more information from the City about this process:

The Mount Baker Station Area has been the focus of several planning processes in the past ten years in which the Mt. Baker community articulated a vision for a thriving, diverse, sustainable, and affordable town center. As public-sector capital investments and private sector developments occur, there is an opportunity for interdepartmental collaboration to best meet the community’s vision and develop near-term recommendations.

In late 2018, several agencies (including Seattle Office of Planning and Community Development, Seattle Department of Transportation, Seattle Parks and Recreation, Sound Transit, King County Metro, and King County Wastewater Treatment) formed a partnership to work with the Urban Land Institute to convene a Technical Assistance Panel (TAP). The TAP is an objective team of seasoned professionals who will develop recommendations and identify next steps toward implementing the community’s vision. We expect to have more to share on recommendations and next steps in summer 2019.

For more information, please contact Qualin Hu at