Ballard Ship Canal Water Quality

What & Why

Seattle Public Utilities (SPU) and King County's Ship Canal Water Quality Project is a 2.7-mile, 18'10"-diameter tunnel that will capture and temporarily hold more than 29 million gallons of stormwater mixed with some sewage during heavy rains. When the storm passes, flows will be sent to the King County 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. Pier will be closed to the public until December 2024.

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.

Ballard Pump Station

  • Build a pump station to lift polluted stormwater and sewage from the tunnel and send it to the West Point Wastewater Treatment Plant.
  • Hold pump station stakeholder advisory group meetings about pump station building and site design. View the latest meeting materials here.


  • Build new pipes along 24th Ave NW, NW 56th St, and 28th Ave NW to connect Ballard’s existing pipes to the tunnel.

What's happening now?

Site preparation and 24th Avenue NW pier construction (Ballard Early Work) started in September 2018. The pump station and conveyance are currently in design.

Project goals and benefits

This project will keep more than 75 million gallons of polluted water out of the Lake Washington Ship Canal, Salmon Bay, and Lake Union on average each year. The project will limit CSOs to no more than one per outfall per year on average, in compliance with state and federal laws.

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 better fish habitat.