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Elliott West Wet Weather Treatment Station upgrade

King County is planning to upgrade the Elliott West Wet Weather Treatment Station (EWWTS). The upgrade will ensure compliance with stricter environmental regulations, meet the demands of a growing population, and handle a changing climate.

Project description

An aerial view of the Elliott West Wet Weather Treatment Facility.

The Elliott West Wet Weather Treatment Station (EWWTS) is a combined sewer overflow (CSO) facility that was first completed in 2005. Since then, it has stored and treated sewage and stormwater during periods of heavy rain. EWWTS now needs to be upgraded to meet stricter environmental standards and to adapt to changing climate.

This project will ensure that the upgraded facility meets its permit requirements. This is a major investment to ensure King County continues to protect public health and the environment for years to come.

More information about the upgrade plans will be available this summer and fall. To stay updated, subscribe to our email list.

Project update

May 2024

Our team is currently preparing a draft engineering report. This report describes the approach, technology, and the schedule for how King County will upgrade EWWTS. It will be sent to the Department of Ecology for review in summer 2024.

Learn more about design progress and other projects in the area! 

We are excited to share more information about our plans. In the coming months, there will be opportunities to provide some input on the project design. You can follow along by signing up for our email list using the link on the right side of this webpage. Please also feel free to contact us at any time during the project to ask questions, express concerns, or give feedback.

Our team is coordinating with other public works projects in the area. One of these projects is the Elliott Bay Connections Project. This project will impact the Elliott Bay waterfront area to the west of the EWWTS facility. The Elliott Bay Connections team is currently seeking input on their project designs. Visit their website for more information about the project, to sign up for project updates, and to take the survey, which is open through June 9, 2024.

Project schedule

The project schedule spans from 2023 to 2032. Design 2023-2027, and Construction 2027-2032. Community Outreach occurs the entire duration.

Our team is in the early stages of designing the needed upgrades to EWWTS. Project timelines may change due to a number of factors. We will provide updates as our work progresses and any schedule changes are needed.

Project location