Vine Basin Combined Sewer Overflow Control

Photo the west end of Vine Street near Elliott Bay and the outfall structure
The west end of Vine Street near Elliott Bay and the outfall structure where overflows occur. The Vine Basin CSO Control project will make improvements in the Vine Basin to limit the number of polluted combined stormwater and sewage overflows into the Bay. 


This project will make improvements in the Vine Basin, which is in Belltown. The exact location of improvements will be determined in design, but we'll likely have impacts on Elliott Ave between Vine and Bay streets.

What's happening now?

In 2019, we received feedback from several community groups, completed sewer system flows modeling work, and analyzed the cost-effectiveness and efficiency of several design solutions. At this time, we're recommending moving forward with a King County partnership solution. This solution involves sending more City sewer system flow to King County's Elliott Bay Interceptor sewer pipe and would likely include:

  • Installing new sewer pipe under Elliott Ave between Vine and Bay streets
  • Installing a new connection to King County's Interceptor pipe
  • Restoring the right-of-way to Seattle Department of Transportation's standards

Additionally, we may partner with other City agencies to install additional community benefits like green stormwater infrastructure and pedestrian improvements. We'll continue to work with the community throughout design.

Community benefits

Sewer pipes in Seattle carry sewage (wastewater) away from homes and buildings for treatment at King County's treatment plants before discharging into Puget Sound. In some neighborhoods, like Belltown (Vine Basin), the same sewer pipes also carry untreated rain water (stormwater) from roofs, drains and streets. During heavy rains, if the amount of sewage and stormwater exceeds the sewer system capacity, the excess flows overflow into nearby water bodies through an outfall pipe. These overflows can harm fish, wildlife and swimmers. This is called a combined sewer overflow (CSO).

The Vine Basin CSO Control project will make changes to the combined wastewater and stormwater system in the Vine Basin to reduce CSOs and improve water quality and public health.

Community engagement

SPU is committed to providing timely information and updates on project activities. Updates may be available in multiple formats: the website, emails, drop-in sessions, briefings, and/or public meetings. There will be several opportunities for the public to engage and provide feedback throughout the project. Check back for more information about upcoming opportunities to get engaged and sign up for the project listserv.

Construction could begin as early as 2022, pending input from our regulatory agencies, such as the Department of Ecology. We will keep the community informed as the schedule develops.

Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.