South Magnolia CSO Control Project

May 2012 Update
King County’s project team invites you to a community meeting on June 13 at 6 pm at the Discovery Park Environmental Learning Center. The purpose of the meeting is to provide a project update and information about the design concept for the new Combined Sewer Overflow (CSO) control facility at the Port of Seattle’s West Yard. View meeting invitation (PDF).

South Magnolia basin and project location.


South Magnolia CSO basin project area
How will the new CSO facility work? View animation.

Project description

King County is designing and building an underground storage tank in the Port of Seattle’s Terminal 91 West Yard south of the Magnolia Bridge. This facility will store peak combined sewer flows so that CSOs are limited to no more than one per year on a long-term average.

Why does King County need to do this project?

In 2008, King County reported that the South Magnolia combined sewer overflow (CSO) facility has 19 overflows per year on average that discharge a total of 31 million gallons of untreated wastewater and stormwater into Puget Sound off of South Magnolia. King County is working to meet current regulations set by the Washington Department of Ecology that require no more than one untreated discharge per year on a long term average.

What is next?

• King County will continue to work with the Magnolia community throughout siting, design and construction.

Project schedule

View meeting calendar for upcoming public meetings, and South Magnolia CSO Control Project Timeline (PDF).