The King County Wastewater Treatment Division announced that construction for the installation of a new 84-inch siphon pipe under Salmon Bay will start this month. The new pipe will run between Seattle’s Ballard and Interbay areas to reduce the potential for sewer overflows into the Ship Canal and to meet north Seattle’s wastewater conveyance needs into the next century.

The new siphon will lie 120 feet underground and connect the Ballard Regulator Station to the North Interceptor in Interbay (see map). Wastewater from north Seattle will be conveyed through the new pipe to King County’s West Point wastewater treatment plant in Magnolia.

King County contractors have been preparing the Shilshole Avenue Northwest and West Commodore Way work sites for construction since July, and will begin mobilizing equipment and personnel at both sites this month.

After excavating vertical shafts at each site, the contractor will use a tunnel boring machine to dig the new siphon’s pipe corridor roughly 60 feet beneath Salmon Bay. The existing siphon will be cleaned out and relined during this project, and support equipment for the new pipe will be installed at the Ballard Regulator.

Work hours will typically be weekdays from 7:00 a.m. – 5:30 p.m. Construction will finish in late 2013.

Traffic impacts:

The Shilshole Avenue Northwest northern sidewalk is closed between 20th Avenue Northwest and Northwest Dock Place. Additional detours along Shilshole Avenue Northwest will be necessary in 2013. Traffic detours will also be necessary on West Commodore Way at the south project site in summer 2012. More information about these detours will be provided later.

What to expect this month:

North site (Shilshole Avenue Northwest)
• Crews, equipment and noise typical of a construction site
· Building on site demolished
• Sidewalk closed between Northwest Dock Place and 20th Avenue Northwest
• Additional truck traffic on Shilshole Avenue Northwest

South site (West Commodore Way)
• Crews and equipment on site to install contractor facilities and sedimentation/erosion control equipment

Schedule:

August 2011
• Mobilize site
• Traffic detours begin

Fall 2011
• Building on north site demolished
• Tunneling machine access shaft shoring installed at both sites

Fall 2011 – Summer 2012
• Access shafts excavated

Summer/Early Fall 2012
• Junction structure constructed at south site

Summer 2012 – Winter 2013
• Tunneling

Spring – Summer 2013
• Regulator structure added at north site

Fall 2013
• Existing siphon relined
• New siphon connected to conveyance system

December 2013
• Complete restoration
• Final inspection
• Project closeout

For more informatiom, visit the project's website, here.