Seattle Public Utilities

Wallingford Ship Canal Water Quality


The Wallingford site for the Ship Canal Water Quality Project.

What & Why

Seattle Public Utilities (SPU) and King County’s Ship Canal Water Quality Project is a 2.7-mile, approximately 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 includes the following activities in Wallingford:

  • Building the eastern end of the new storage tunnel (the tunnel boring machine will complete tunneling at this location)
  • Building a drop shaft to collect flows entering the tunnel and a small above-ground maintenance building near 3500 Interlake Avenue N
  • Installing new pipes to convey polluted stormwater and sewage to the tunnel
  • Providing odor control equipment to minimize odor

What’s happening now?

Elements of the Ship Canal Water Quality Project in Wallingford are currently in design and are expected to be complete in 2019. Construction is expected in 2020.

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.