Ship Canal Water Quality Project in Seattle Earns Envision Platinum Rating

The Ship Canal Water Quality Project includes a 2.7-mile, 18-ft and 10-in internal-diameter tunnel that will extend from Ballard to Wallingford. Left: Ballard Tunnel Segment. Right: Wallingford Shaft Site. Photos supplied in December 2022 courtesy Seattle Public Utilities.

Seattle Public Utilities’ Ship Canal Water Quality Project has been awarded Envision Platinum for sustainability. This project had verified achievements across several areas of the Envision framework, and in particular, it will bring significant water quality improvements to prevent 75 million gallons of polluted stormwater and sewage from entering the region’s waterways on average each year.

Public Utilities and King County’s Wastewater Treatment Division are completing an underground storage tunnel to reduce the amount of polluted stormwater runoff and sewage that flows in the Lake Washington Ship Canal, Salmon Bay, and Lake Union from the sewer system.

In some parts of Seattle (as with many other places), stormwater and sewage share a set of pipes — a combined sewer system which, during heavy storm/rain events, overflows when pipe capacity is exceeded. Untreated sewage and stormwater then flow directly into the Ship Canal, posing public health concerns and harming fish, wildlife, and the environment. The Ship Canal Water Quality Project is crucial for keeping the waterways clean and protecting human health and the environment over the long term.

This project is funded in part by the Washington State Department of Ecology and the Environmental Protection Agency through the State Revolving Fund and Water Infrastructure Finance and Innovation Act loans. The project’s 2.7-mile, 18’10”-diameter tunnel will be able to capture and temporarily hold more than 29 million gallons of stormwater and sewage during heavy rains. As the heavy rains subside, flows will be sent to King County’s West Point Wastewater Treatment Plant in Magnolia for treatment.

View the full announcement in our Project Directory.