Fremont Siphon replacement project
March 13, 2015 Update
Praxair building demolition starts week of March 16
King County’s contractor for the Fremont Siphon Replacement project will begin demolishing the Praxair building located in the Fremont (north) project area. Removing the building makes room for the project’s north tunnel shaft. The microtunnel machine will be lowered 75 feet down the north shaft to bore holes under the Ship Canal for the new siphon’s two 60-inch diameter pipes. View project update (PDF, March 13, 2015).
Attend online open house now through Friday, March 20.
Click the link below to learn more about the project and leave comments.
Have a comment or question? Need more information about the project?
Click here to contact the project team.
Project areas in Fremont and Queen Anne.
Fremont Siphon service area
Building the Fremont Siphon Tunnel, 1913. Photo provided by Seattle Municipal Archives (external link)
King County will replace Fremont Siphon, a major sewer pipe running under the Ship Canal between Fremont and Queen Anne. The new siphon will be located west of the existing siphon to reduce project risks and impacts to the community. Construction begins in early 2015 and will continue until early 2017. The old siphon will be retained by King County for use by the Wastewater Treatment Division as necessary.
Why do we need this project?
The Fremont Siphon has provided safe, reliable sewer service to north Seattle and other cities in north King County for decades. Sewage and stormwater from more than 100 square miles of pass through the Fremont Siphon every year to be cleaned and safely discharged at the County’s treatment plant in Magnolia. During storms, the pipe carries up to 220 million gallons per day, making it one of the most heavily used pipes in the regional sewer system.
The existing Siphon is nearly 100 years old and has reached the end of its of service life. The new pipes will ensure north Seattle and northern King County continue to enjoy safe, reliable sewer service for decades.
How King County works with the community during construction
King County recognizes that its construction projects can disrupt the daily lives of those near them. During construction, the County’s project team update the community and local jurisdictions on the project’s progress and any unforeseen developments.
The County project team will also work directly with the community to minimize construction impacts to those living or working nearby. Information from the community helps to shape the County’s decisions about ways to address community disruptions, private property impacts attributable to the project and promote public safety around the work site.
Interested community members will have a number of ways to interact with the project, including:
- Community meetings with the contractor prior to construction
- Community briefings on project progress during construction
- Advance written notice of major construction activities
- Project status reports available via email and flyer
- Prompt response to all community inquiries
- 24/7 construction hotline
- News releases
What is a siphon and how does it work?
The Fremont Siphon is an inverted siphon. Inverted siphons use gravity to push liquids downhill. In this case, sewage and stormwater from north Seattle and elsewhere is pushed through the Fremont Siphon by having sewage and stormwater enter the pipe in Fremont Canal Park at a higher elevation than where it exits the pipe in Queen Anne.
To help keep the sewage and stormwater moving, inverted siphons in the sewer system are a smaller diameter pipe than those connecting to it on either side. The smaller diameter speeds up the passage of sewage and stormwater pass through the pipe to keep solids moving and avoid clogs.