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Project update

March 2021

King County to upgrade regional sewer pipelines in Interbay neighborhood

King County is planning to upgrade approximately one mile of its pipeline system extending from the Magnolia Bridge to just south of Seattle Parks and Recreation’s Interbay Athletic Complex. This work will enhance odor control and assure the reliability of this portion of our wastewater system for the next 50 years or more. Construction for the project is expected to begin in 2022.

What happens during final design?  

The project is now in the final design phase. The design process is a multi-step process with several inputs, and final design will continue through 2021. During this phase the project team will add detail to the design and generate plans for constructing the two main elements of the project: improved odor control and upgraded sewer pipes.

This project will improve odor control by installing scrubbers (filters) at a building where sewer pipes converge. During final design, the project team will refine details of what this new facility looks like and how it functions. 

A portion of the sewer will be repaired by lining the inside of the pipe using an innovative approach that involves blowing the new liner into the pipe with water pressure. The new liner covers any cracks or holes and strengthens the existing pipes. Lining the pipe is more efficient and less expensive than replacing it and minimizes construction impacts on surrounding neighborhoods.

During the design phase, we will continue to:

  • Gather information to understand the project’s physical constraints and opportunities. 
    We have been conducting fieldwork and other studies to develop an initial understanding of the physical conditions along the route, including soils, groundwater levels, slopes, existing utilities, and other structures. We will continue to conduct fieldwork as we finalize design. 
  • Conduct environmental review and obtain the necessary permits. 
    We are taking an inventory of the natural and built environment near the project area. We will use this information to minimize disruptions during construction and plan for construction and restoration. For example, we are working closely with the National Guard Armory, as we will need access to their property during construction.  
  • Coordinate with partner agencies  
    The pipeline is in an area where multiple agencies have jurisdiction and there are overlapping project areas. The project team is coordinating with other agencies, including Seattle Department of Transportation, Seattle Parks and Recreation, Sound Transit and Seattle City Light, to get feedback on the developing design. We will continue to work with our partners during final design.
  • Share information with the public
    The project team will continue to reach out to neighbors and organizations in the project area. We want to hear from you anything we should be keep in mind as we plan for construction.

More information about this project:

Whether you work, live or recreate in the area, we know you may have questions or concerns. As the project proceeds, we’d like to get to know you better. The project team continues to reach out to neighbors and organizations in the project area. Interested in scheduling an individual meeting or briefing to learn more about the project? Contact Dana West at or call 206-477-5536 or TTY 711.

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Be sure to sign up for project updates to stay up-to-date on the latest project information and upcoming events. To sign up for text alerts, text KING INTERBAY to 468-311.

Project description

King County plans to upgrade an aging sewer pipe in Seattle’s Interbay neighborhood. The existing pipe was built in 1967 and is nearing the end of its service life. New odor control technology will be added to the system while the sewer pipe upgrade is underway. When complete, the sewer will provide reliable service for another 50 years or more.

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Project Timeline for Full Project

project timeline

planning phase

Contact us

Contact Kelly Foley Kruse at:

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Project location

Interbay-Sewer-location-mapView higher resolution version.

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