Fremont Siphon

Project description

Project map


Fremont Siphon service area


The Burke-Gilman trail passes over the north end of the Fremont Siphon.


Building the Fremont Siphon Tunnel, 1913. Photo provided by Seattle Municipal Archives (external link)

King County is planning to replace the existing Fremont Siphon, a wastewater conveyance system that extends from Fremont to Queen Anne under the Lake Washington Ship Canal. King County will install new pipelines in a separate crossing under the Ship Canal, just west of the existing siphon. After reviewing a range of options to rehabilitate or replace the Fremont Siphon in 2010, King County decided that replacing the existing pipelines in a new location reduces potential project risks and impacts, maintains operations during construction and provides safe, reliable service for years to come. The County will still retain the existing space in the Fremont Tunnel for Wastewater Treatment Division uses.

Why does King County need to do this project?

The Fremont Siphon is a critical conveyance line that carries wastewater from the county’s northeastern service area to the West Point Treatment Plant. The Fremont Siphon conveys wastewater from a service area of about 60 square miles year round, with an additional area of about 54 square miles during the summer. The siphon pipelines, which may convey up to 220 million gallons per day during storms, are located under the Lake Washington Ship Canal, west of the Fremont Bridge. The siphon was installed in the early 1900’s and has provided wastewater conveyance service for almost 100 years.

Next Steps

In Summer 2011, the Fremont Siphon Project team will begin the predesign phase. During this phase, the County’s project team develops the recommended project alternative and performs an environmental review under the State Environmental Policy Act (SEPA). The project team will also evaluate feasible options for odor control and acquire permits. Contract specifications will then be developed based on project design and permit conditions.

How King County works with the community during project design

During project design, King County will provide the Fremont and Queen Anne communities with information on project details including:

• Project plans and layout
• Major construction techniques
• Estimated construction duration
• Site restoration

The public can inform the County’s work by learning about the project and helping to identify reasonable solutions for construction impacts such as traffic disruptions.