Information provided by SDOT

To protect public health and the environment, King County is building a new 85-inch siphon pipe under Salmon Bay between the Ballard and Interbay areas of Seattle. The new siphon will be installed more than 120 feet underground and connect the Ballard Regulator Station at 5110 Shilshole Avenue Northwest in Ballard to the North Interceptor at West Commodore Way and 24th Avenue West intersection in Interbay (see project map).

After excavating vertical shafts at the Shilshole Avenue and Commodore Way sites, King County’s contractor will install a tunnel boring machine to bore a pipe corridor for the new siphon roughly 60 feet beneath Salmon Bay. The existing siphon will be cleaned out and relined as part of this project. Additional equipment supporting the new pipe will also be installed at the Ballard Regulator.

Project need:
The new pipe is needed to accommodate growth in north Seattle. The new pipe replaces two 36-inch wooden stave pipes which have served the Ballard community since the 1930’s. The new pipe will meet north Seattle’s wastewater conveyance needs through the end of the century.
Wastewater from homes and businesses in Ballard now flows through the 36-inch siphons and across the bay, moving from the higher elevated pipes on the north side of the canal to the lower elevation on the south side, for treatment at the West Point Treatment Plant in Magnolia.
Project schedule

What to Expect:
• Noise and other activity typical of a construction site at the intersection of Shilshole Avenue Northwest and Northwest 20th Avenue in Ballard and at the intersection of West Commodore Way and 24th Avenue West in Interbay.
• Crews, trucks and heavy equipment at the Ballard and Interbay sites
• Traffic detours near the construction sites on Shilshole Avenue Northwest and West Commodore Way.
• Increased truck traffic on Shilshole Avenue Northwest, 15th Avenue Northwest, Northwest Leary Street, West Nickerson Street and Aurora Avenue.

North site: Beginning Monday, January 20, westbound traffic on Shilshole Avenue Northwest will be detoured to Leary Avenue Northwest for approximately four months. This week SDOT reassessed the traffic detour based on community feedback and revised the detour route as shown in the map below. The new route directs westbound traffic to 14th Ave NW, NW Leary Way, NW Market St and south on Shilshole Ave NW. Eastbound traffic will remain on Shilshole Avenue Northwest. The detour is necessary to reline the existing 80-year-old Ballard Siphon sewer line that runs underneath Salmon Bay. Access to businesses on Shilshole Ave NW will be maintained at all times.

South site: Crews will demolish concrete from the top of the south shaft with a concrete breaker December 23-24 and 26-27. This work will be noisy. Crews will remove shoring from the south site December 30, 31 and January 2. Near neighbors may experience noise and vibration during shoring removal.