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 29 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 (currently under construction) is one of several projects that comprise the Ship Canal Water Quality Project. The Storage Tunnel construction contract value is $255M. The total cost for the overall Ship Canal Water Quality Project is $570M and right now there is a 65% chance that our total cost will be at or below $570M. As the project moves forward, the team will update the cost model and the confidence level will change over time.

 

 

Learn more about the Ballard site

Ballard will be home to the western end of the tunnel and above-ground facilities supporting the tunnel. Tunnel boring will start at this site and move toward Fremont and 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 107-ft deep, 80-ft diameter shaft to hold pump station equipment and carry sewage and stormwater into the new storage tunnel
• New pipes along NW 56th St, 28th Ave NW, and 24th Ave NW to connect the shaft to Ballard’s existing combined sewer system overflow pipe
• A large pump station that will take the flows from the tunnel and send them to West Point for treatment
• A new 24th Ave Pier containing art inlays by artist Christian French

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 (publicly accessible)
  • Green stormwater infrastructure
  • Pedestrian improvements, including seating and bike racks  
  • Parking improvements 
  • Street-end improvements
  • Public art by artist Jeffrey Veregge

Learn about the Fremont site

We anticipate construction of the tunnel to take place until early summer. During this time, there will be a large crane on-site and an uptick in deliveries for the casing pipe construction.

Additionally, in late spring, we’ll begin construction of the diversion structure in 2nd Ave NW. We anticipate 2nd Ave NW will be closed south of Leary Way NW for at least six months.

Project elements in Fremont include:

• A new 86-ft deep, 32-ft diameter vertical shaft to carry sewage and stormwater into the new storage tunnel
• A new diversion structure and conveyance pipe to connect the new shaft to the existing combined sewer system overflow pipe
• 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 late 2023.

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 will end underneath N 35th St and Interlake Ave N. Construction will take place on Stone Way N, N 35th St, and Interlake Ave N.

Project elements in Wallingford include:

• A new 56-ft deep, 32-ft diameter vertical shaft near Stone Way N and N 35th St to convey stormwater and sewage into the tunnel
• New pipe installation along Stone Way N and N 35th St to connect the current combined sewer system overflow pipe to the new vertical shaft
• Removing tiebacks underneath N 35th St
• A new small, above-ground electrical building near 3500 Interlake Ave N
• New underground structures to house mechanical and odor control equipment
• Site restoration and restoration of impacted roadways
• Public art by Ryan! Feddersen

After 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 a number of 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.