Seattle Public Utilities Mami Hara, General Manager/CEO

Ballard Ship Canal Water Quality


The existing 24th Avenue NW pedestrian pier will be replaced.

What & Why

Seattle Public Utilities (SPU) and King County’s Ship Canal Water Quality Project is a 2.7-mile, approximately 14-18-foot diameter tunnel that will capture and temporarily hold more than 15 million gallons of stormwater mixed with some sewage during heavy rains. When the storm passes, flows will be sent to King County’s West Point Wastewater Treatment Plant in Magnolia.

The Ship Canal Water Quality Project will be completing a number of projects in Ballard. These projects center on Seattle Public Utilities’ property at 24th and Shilshole avenues NW. To learn more about projects and activities in Ballard check out the latest project fact sheets and read below:

The Ship Canal Water Quality Project includes the following projects and activities in Ballard:

Site preparation

  • Remove contaminated soil
  • Install water, electrical, gas, drainage, and wastewater utilities in 24th Avenue NW
  • Replace existing combined sewer outfall pipes at 24th Avenue NW street end

24th Avenue NW pier

  • Replace the 24th Avenue NW public access pier

Storage tunnel

  • Begin tunneling
  • Build the western end of the tunnel

Site Master Plan

  • Develop a master plan for the Ship Canal Water Quality Project’s Ballard site, located at 24th and Shilshole avenues NW. SPU will use a portion of the site to build and operate the Ship Canal Water Quality Project.

Ship Canal Water Quality pump station

  • Build a pump station to pump polluted stormwater and sewage from the tunnel
  • Hold pump station stakeholder advisory group meetings about pump station building and site design. View the latest meeting materials here.

Shilsole pipe

  • Build new pipes along Shilshole and 24th avenues NW to carry flows from the tunnel to King County’s West Point Wastewater Treatment Plant
  • Seattle Public Utilities is coordinating Seattle Department of Transportation to have this pipe constructed as part of the Burke-Gilman Missing Link.


  • New pipes to connect Ballard’s existing pipes to the tunnel

What's happening now?

Site preparation and 24th Avenue NW pier construction is expected in 2017. The storage tunnel, pump station, and Shilshole pipe are currently in design. The site master plan and conveyance are in options analysis.

Project goals and benefits

Once complete the Ship Canal Water Quality project will prevent nearly 60 million gallons of raw sewage and polluted stormwater from flowing into Lake Union, the Ship Canal, and Salmon Bay each year.

The 24th Avenue NW Pier will provide pedestrian access to the waterfront and feature public art. The construction of the new pier will also remove creosote-treated wood pilings from Salmon Bay which will improve water quality and create a better fish habitat.