Request for Information - Mouth of Duwamish CSO Program

Background
King County is issuing a Request for Information (RFI) to gather insights from qualified firms regarding Architectural/Engineering (A/E) and Construction Services for the Mouth of Duwamish Combined Sewer Overflow (MDCSO) Program.

This initiative aims to control the discharge of five Combined Sewer Overflow (CSO) outfalls during wet weather events, fulfilling a consent decree with the US Environmental Protection Agency and the Washington State Department of Ecology.

The project area includes sections of the Elliott Bay shoreline and waterways of the Duwamish River, specifically in the SODO neighborhood.

Work Details
The MDCSO Program will construct infrastructure to convey, store, and treat combined sewer flow during storm events. Key components include:
- Wet weather treatment facilities
- Wet weather storage facilities
- Diversion structures
- Conveyance pipelines
- A new outfall
- System integration and SCADA.

The program aims to deliver facilities that comply with regulatory standards, incorporate King County initiatives on equity and climate action, and manage multiple projects in a coordinated manner. The construction packages may include:
1) Wet Weather Treatment Station (WWTS)
2) Effluent Conveyance and Outfall
3) Influent Conveyance
4) Chelan storage tank.

Period of Performance
Preconstruction services are targeted to start between 2026 and 2027, with construction services expected to begin between 2028 and 2029 depending on the specific package.

Place of Performance
The contract work will be performed in Seattle, Washington, specifically in the SODO neighborhood and along the Elliott Bay shoreline as well as the east and west waterways of the Duwamish River.