Fremont Siphon replacement project
April 12, 2016
Queen Anne Project site: W Ewing Alley closed between 3rd Avenue W and 6th Avenue W until fall
In late March, King County’s contractor for the Fremont Siphon Replacement project will start building the structure that will connect the new siphons to the existing sewer under the W Ewing Alley. W Ewing Alley will be closed to through traffic between 3rd Ave W and 6th Ave W beginning Friday, March 18 and will remain closed until the fall.
Vehicle traffic will be detoured off of W Ewing Alley onto W Ewing St or W Nickerson St. The Ship Canal Trail will remain open. Along with the closure, this work will increase noise and activity around the project site. The contractor will begin by installing shoring for excavation of the new connecting structure.
View project update (March 16, 2016).
Fremont Project Site: No alley access from 2nd Ave NW beginning Monday, April 11
Access to the alley north of NW Canal St will be routed through the parking lot of 123 NW 36th St. starting on Monday, April 11. Crews will be relocating a Puget Sound Energy (PSE) gas line to make room for a 9-foot diameter pipe that will connect the new siphon to an existing sewer pipe that runs under NW Canal St.
Access to the alley from 2nd Ave. NW will be closed for two weeks. The corner of 2nd Ave. NW and NW Canal St. will remain closed through the fall. Burke-Gilman Trail users should follow the trail detour just south of the normal trail to get around the Fremont Canal Park work area safely.
Along with the detours, these activities will increase noise and activity on 2nd Ave. NW. The contractor will begin by installing shoring for excavation of the new connecting structure.
View project update (April 7, 2016).
Have a comment or question? Need more information about the project?
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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.