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Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

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Staff Contacts

Ballard Siphon Replacement Project

Project construction

April 2, 2014 Project Update –

North site: King County’s contractor finished work on the 80-year old sewer pipe in south Ballard about a month ahead of schedule.

Shilshole Avenue N.W. will be fully open to traffic on the night of Friday, April 4.

The work had closed the Shilshole Avenue N.W. westbound lane near N.W. Dock Place since January..

View project update (March 31, 2014).  
South site: Crews are repairing the Salmon Bay Marine Center parking lot where equipment used to pull a new lining through the 80-year old sewer pipe was located. Crews will continue restoring the project site and West Commodore Way’s southern sidewalk through April. (April 2, 2014).    
Take a video tour of the tunnel!
Take a video tour of the tunnel!
(WTD YouTube channel) 

Typical work hours: 7:00 a.m. – 6:00 p.m. weekdays
Horas normales de trabajo: De lunes a viernes de las 7:00 a.m. a las 6:00 p.m.
24-hour project hotline/Para más información*: 206-296-3848 
Para más información sobre el proyecto las 24 horas, llame  al 206-296-3848
Seleccione su idioma para solicitar hablar con un intérprete, este servicio es gratuito.

Project description

Ballard Siphon Project Map
Project map. Click map to enlarge view
. Also available as PDF

Construction at the South site along West Commodore Way
View construction photos at the South site and North site.

Shilshole Avenue Northwest traffic detour
North Site – Shilshole Ave NW traffic detour map
 (PDF), January 15, 2014

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

August 2011
Mobilize site
Traffic detours begin on Shilshole Avenue Northwest and West Commodore Way 
Fall 2011
Site preparation
Existing building demolished
Shaft shoring installed
Fall 2011 Summer 2012
Tunnel Boring Machine shafts excavated
Summer/Early Fall 2012
Junction structure constructed
(West Commodore Road closed)
Fall 2012 – Summer 2013
Spring – Summer 2013
Regulator structure added
Summer Fall 2013
New siphon connected to conveyance system
Early 2014
Existing siphon relined (Shilshole Avenue Northwest detour)
Complete restoration
Final inspection
Project closeout

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.

More information

Ballard Siphon replacement tunnel into final phases, produced by TunnelTalkVideos, October 30, 2013

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