Seattle Public Utilities and King County Wastewater Treatment Division are building an underground storage tunnel to significantly reduce the amount of polluted stormwater (from rain) and sewage that flows into the Lake Washington Ship Canal, Salmon Bay, and Lake Union from our sewer system.

Learn more about the project

In some parts of Seattle, sewage and stormwater (rain) share a set of pipes; this is called a combined sewer. During heavy rains (What? Rain? Here?) the water often exceeds the pipes’ capacity (known as an overflow to us sewer nerds), sending untreated sewage (yep, that means poop) and stormwater into the Ship Canal. These overflows can harm fish, wildlife, and the environment, and can contain pollution.

During a heavy storm, the new tunnel will capture and temporarily store more than 30 million gallons of untreated stormwater and sewage until the treatment plant is ready for it. The tunnel will improve water quality regionally by keeping more than 75 million gallons of polluted stormwater (from rain) and sewage on average each year from flowing into the Lake Washington Ship Canal, Salmon Bay, and Lake Union. Based on data from the last five years, the Ship Canal Water Quality Project would have removed about 70% of SPU’s total combined sewer overflow volume.

This storage tunnel (completed) and the conveyance pipes in Wallingford (under construction) are two of several components that comprise the Ship Canal Water Quality Project. The total cost for the overall Ship Canal Water Quality Project is around $710 million dollars.  

Check out this video, made in 2020, for an overview of the project. 

 

 

Learn more about the Ballard site

Ballard is home to the western end of the tunnel and above-ground facilities supporting the tunnel. Tunnel boring started at this site before it made its way to Wallingford.

We started work at our site near 24th Ave NW and Shilshole Ave NW in 2018 to prepare for tunneling. This work included soil remediation, utility relocation, 24th Ave Pier replacement, and replacing a sewer outfall pipe.

Project elements in Ballard include:

• A new pipe in Ballard that will convey polluted stormwater and sewage from the Ballard neighborhood into the storage tunnel. This pipe will run along 24th Ave NW, NW 56th St, and 28th Ave NW.
• A new 80-ft tall pump station at the 107-ft deep, 80-ft diameter vertical shaft that was used for tunneling. The pump station will take flows from the tunnel to the West Point Treatment Plant.
• A new 24th Ave NW Pier containing art inlays by artist Christian French (This pier is completed, publicly accessible, and managed by Seattle Department of Transportation.)

After construction is completed at the Ballard site, you can expect to see:

• Ballard Pump Station (not publicly accessible):
  • 80-ft illuminated tower with above- and below-ground mechanical equipment and odor control
  • Maintenance yard with vehicle access
  • An urban tree farm 
  • Landscaping 
  • Fencing
• 24th Ave NW Restoration 
  • Green stormwater infrastructure
  • Pedestrian improvements, including seating and bike racks  
  • Parking improvements 
  • Street-end improvements
  • Public art by artist Jeffrey Veregge

To learn more about the Ballard project site, read our fact sheet.

Learn about the Fremont site

The 8-ft diameter conveyance tunnel boring machine reached its destination in Queen Anne in early February 2023! Crews are installing piping and an air duct inside the 8-ft diameter tunnel casing and working on the diversion structure.

Project elements in Fremont include:

• A new 85-ft deep, 32-ft diameter vertical shaft, also called a drop shaft, to carry sewage and stormwater into the new storage tunnel
• A new diversion structure and conveyance pipe to connect the existing sewer and stormwater overflow pipes to the storage tunnel 
• A new 8-ft diameter conveyance tunnel under the Ship Canal to carry flows from Queen Anne to the storage tunnel
• A new underground structure to house mechanical, electrical, and odor control equipment

Artists Preston Singletary and David Franklin collaborated on artwork for the Fremont and Queen Anne sites. This artwork is planned to be installed in 2024.

To learn more about the Fremont project site, read our fact sheet.

Learn about the Wallingford site

Wallingford marks the eastern end of the Ship Canal Water Quality Project and the location where tunneling ended underneath N 35th St and Interlake Ave N in June 2023. Construction will continue to take place on Stone Way N, N 34th St, N 35th St, and Interlake Ave N.

Project elements in Wallingford include:

• A new 56-ft deep, 32-ft diameter vertical shaft, also called a drop shaft, near Stone Way N and N 35th St to convey stormwater and sewage into the tunnel
• New conveyance pipe installation along Stone Way N and N 35th St to connect the existing sewer and stormwater overflow pipe to the storage tunnel 
• A new small, above-ground electrical building near 3500 Interlake Ave N
• New underground structures to house mechanical, electrical, and odor control equipment
• Site and roadway restoration 
• Public art by Ryan! Feddersen

Once construction at the Wallingford site is complete, SPU will retain ownership of the southern portion of the site. The site will be mostly fenced to secure utility equipment. The fenced area will house an aboveground electrical building, and several large, underground structures attached to the storage tunnel.

The design for the Wallingford site is complete. During design, our landscape architects reviewed the planting schemes for the North Transfer Station and the Carr Place Play Area. Their goal was to create a site that was unique to the neighborhood but still complemented the aesthetic of nearby open spaces.

Artist Ryan! Feddersen will design and install the artwork at this project site.

To learn more about the Wallingford project site, read our fact sheet.