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About Interbay Sewer and Odor Control Upgrade

Find information about the Interbay Sewer and Odor Control Upgrade Project, including the project schedule and methods to upgrade the sewer pipes and control odors.

Project schedule 

Project timeline for the Interbay Sewer and Odor Control Upgrade

King County plans to begin work to upgrade one mile of aging sewer pipe in Seattle’s Interbay neighborhood in 2024. King County expects to hire a contractor as early as Fall 2023. Major construction, including excavation, pipe installation, and pipe relining, will begin as soon as January 2024 and ramp up during the summer months through early fall 2024.

Improving odor control and upgrading sewer pipes

King County’s project team has evaluated different methods for upgrading the sewer pipes and controlling odor, as not every method is right for every neighborhood.

Controlling Odor

Part of the sewer being upgraded consists of two parallel pipes. These pipes converge to become one larger pipe in a partially underground building, called a discharge structure, at the west end of the West Wheeler Street right-of-way (see project area map). Where the pipes converge, smells can be released into the air. To improve odor control, the County will install a pair of scrubbers (filters) at the discharge structure at the West Wheeler Street right-of way. 

Upgrading the sewer pipes

Most 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. Instead of digging up the entire length of pipe, repair crews can access the pipe at a few key locations and blow in the new liner.
A small section of the pipes near Magnolia Bridge will be completely replaced because the pipes in that area need to be increased in size. We are also upgrading approximately 2,000 feet of pipe north of the discharge structure. The 35-year-old lining in this section of pipe is aging and needs to be replaced. 



FM #1 - West

FM #2 - East


Where to find contract information

This project will be a Design-Bid-Build contract. The contract is expected to be advertised between early December 2023 and the end of January 2024. If you are a contractor interested in the project, please visit King County’s Upcoming contract opportunities page for updates.


Project area map

Interbay project site map