Fremont Site: Burke-Gilman Trail detour begins week of July 6
King County's contractor for the Fremont Siphon Replacement Project finished building the watertight ring around the tunnel launch shaft at the Fremont site. The ring will control groundwater to protect against settlement of nearby buildings, streets and utilities when the tunnel shaft is dug. Crews will begin digging out the shaft next week.
The contractor will also begin work to move a City of Seattle Combined Sewer Overflow drain pipe during the week of Monday July 6. To allow safe passage around the project site, the Burke-Gilman Trail will be detoured on to a temporary paved path, just north of the existing trail (see map). The detour will be in effect through mid-August.
Queen Anne site: W. Ewing Alley and Ship Canal Trail close the week of July 20 as pipe installation begins.
King County’s contractor for the Fremont Siphon will begin installing a 9-foot diameter pipe to connect the new siphon and the existing sewer system on July 20. W. Ewing Alley and the Ship Canal Trail will be closed between 6th Ave NW and 3rd Ave NW in Queen Anne while this work occurs (see map). Vehicles, cyclists, and pedestrians will be detoured to nearby streets through August.
Video -- Learn how King County Wastewater Treatment Division creates safe underground work environments using a construction technique called secant piles. Similar to a project in West Seattle, King County will use interlocking concrete cylinders called secant piles to create a watertight ring. The ring keeps groundwater out while the inside of the ring is excavated, which protected nearby homes, streets and utilities from settlement. King County will replace Fremont Siphon, a major sewer pipe running under the Ship Canal between Fremont and Queen Anne.
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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
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.
Project updates / news
Project updates and news releases are located on the library page.