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Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

Seattle projects

Fremont Siphon replacement

King County is designing a new pipeline to transport untreated wastewater from Seattle’s Fremont neighborhood to Queen Anne, and eventually to the West Point Treatment Plant in Magnolia. The current pipeline, which runs beneath the Lake Washington Ship Canal, has been in service for more than 100 years. 

Georgetown Wet Weather Treatment Station

King County is planning for a combined sewer overflow (CSO) facility to control South Michigan and Brandon Street combined stormwater and wastewater overflows. 

Highland Park and South Park Green Stormwater Infrastructure Project (West Michigan and Terminal 115 CSO Control)  

King County is exploring the feasibility of controlling combined sewer overflows (CSOs) using Green Stormwater Infrastructure (GSI) or a combination of GSI and storage for sewer overflows.

Lower Duwamish Waterway Superfund

King County will maintain involvement in the Lower Duwamish Waterway Group (external link), which is currently working with EPA and the state Department of Ecology to identify a Superfund cleanup strategy to address historically contaminated sediments in the waterway.

North Beach force main maintenance

King County is carrying out a project to assess the condition of the North Beach Force Main, installed in 1963.

North Beach outfall assessment 

King County is assessing the condition and looking at repair/replacement options for the North Beach Outfall.

Puget Sound Beach CSO Control 

King County is making it a priority to control combined sewer overflows, or CSOs, that occur during heavy rains near popular recreation beaches in West Seattle, North Beach and Magnolia:

Rainier Valley Wet Weather Storage (Hanford #1 CSO Control) 

King County is building a new combined sewer overflow (CSO) storage tank and sewer pipeline to keep sewage and polluted stormwater from Mt. Baker and the northern Rainier Valley out of the Duwamish River.

Sediment Management Program

This program enables King County to address sediment contamination near CSO locations in Puget Sound. The county is continuing its efforts to remove historic CSO contamination and restore habitat at locations in Elliott Bay and the Waterway.

West Point Treatment Plant improvements 

Several projects are planned for West Point Treatment Plant to improve plant efficiency and operations and insure compliance with regulations.