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About the West Duwamish Wet Weather Storage Facility

Get information about the West Duwamish Wet Weather Storage Facility schedule and design elements.

Project schedule

Timeline graphic showing that 2016 to 2018 is planning, 2018 to 2025 is design, and 2025 to 2028 is construction.

Read the most recent project newsletter or visit our online open house to learn more.

Project need

Like many cities around the country, older parts of King County’s sewer system use the same set of pipes to carry both sewage and stormwater to a treatment plant. During storms, the pipes can fill with stormwater that runs off roofs, driveways and streets. When the system is overwhelmed, it is designed to overflow. These overflows are called Combined Sewer Overflows, or CSOs.

To keep the sewer system working and to prevent sewer backups, the excess water and sewage is released into our local water bodies through CSOs. However, CSOs pose a risk to public health and the environment. Over the past several years, King County has been planning a project to reduce CSOs from the South Park drainage basin into the Duwamish River. Our requirement is to reduce CSOs to no more than one overflow per year on average.

Our commitment to sustainability

The storage tank and surrounding site will incorporate many sustainable elements. Some examples of design elements already added include new trees, solar panels, and rain gardens. Visit our online open house to learn more about other sustainability features this site will have.

Rendering of the storage facility and elements of design influenced by public input.