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-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 includes the following projects and activities in Ballard:

Site preparation

  • Remove contaminated soil
  • Relocate utilities before construction
  • 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

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.

Gravity 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

Ballard conveyance

  • 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 other elements are currently in design.

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.