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About the Elliott West Wet Weather Treatment Station

Exterior view of the Elliott West Wet Weather Treatment Station

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. This combined wastewater goes to the West Point Treatment Plant in the Magnolia neighborhood to be treated.

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 into waterways. These overflows are called Combined Sewer Overflows, or CSOs. To keep the sewer system working and to prevent sewer backups into homes and businesses, the excess water and sewage is released into our local water bodies through CSOs. This is when EWWTS is called into action.

In service since 2005, EWWTS provides partial treatment to sewage and stormwater during large storms to reduce untreated overflows of combined wastewater into Elliott Bay. 
Without wet weather treatment stations like EWWTS, polluted stormwater runoff and sewage is discharged into our waterways with no treatment. However, EWWTS needs an upgrade to ensure compliance with stricter environmental regulations, meet the demands of a growing population, and handle a changing climate. 

This is a major investment to ensure King County continues to protect public health and the environment for years to come.

More about the upcoming project

This project has been selected to pursue a collaborative delivery method known as General Contractor/Construction Manager or GC/CM. This delivery method differs from the Design-Bid-Build (DBB) project delivery method in several ways. DBB hires a design consultant first to help design the project and then a construction contractor wins the bid to build the project. GC/CM brings in the construction contractor into the design process. This allows the construction contractor to offer input and feedback during the design process. GC/CM can reduce constructability challenges and reduce risks for all parties helping to deliver the project.

EWWTS is using the GC/CM project delivery method because the facility needs to be upgraded quickly. EWWTS is a regulated CSO facility under the West Point Treatment Plant’s National Pollutant Discharge Elimination System, or NPDES permit. The Environmental Protection Agency (E.P.A.) issues the NPDES permit, and the Washington Department of Ecology (Ecology) enforces it. Ecology is currently reviewing and updating West Point’s NPDES permit.

The NPDES permit allows West Point and its associated facilities to treat and/or release wastewater into bodies of water like rivers, lakes, and the Puget Sound. The permit contains restrictions and requirements to ensure permittees are not causing or contributing to water quality problems.

The EWWTS project will bring the facility into compliance with the new, stricter regulations. 

A draft engineering report that describes the type of method and schedule for how King County will upgrade the facility will be sent to Ecology for review by June 30, 2024. This has placed the EWWTS project on an accelerated schedule.

Where to find contract information

The GC/CM Request for Proposals (RFP) is expected to be advertised between January and March 2024, pending CPARB Project Review Committee approval. If you are a contractor interested in the project, please visit King County’s Upcoming contract opportunities page for updates.