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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

East King County Projects

Eastside interceptor lining

This work is part of a program to restore corroded sewer lines throughout the regional wastewater system. Pipe lining is a cost-effective way of maintaining the sewer lines. It saves on materials and energy use, when compared to installing new sewer lines.

Eastgate sewer pipeline lining (Phase 3)

This is part of the conveyance system program created to rehabilitate corroded conveyance pipelines throughout the county’s wastewater system.

Lake Hills and NW Lake Sammamish sewer upgrade

King County is beginning design on a project to upgrade 21,000 feet of aging pipeline in Redmond that has been in service for as long as 60 years. The new pipeline will increase system reliability and accommodate population growth.

Loop® Vehicle Maintenance Facility

King County is designing a new vehicle maintenance and staging facility for transporting Loop biosolids. The new facility, expected to be open in winter 2018, will be located in North Bend (exit 34 off I-90) on County-owned land.

North Lake Sammamish flow diversion

Currently, flows from the North Lake Sammamish basin are routed to the South Treatment Plant through the East Side Interceptor (ESI). This project will divert up to 43 million gallons per day of wastewater from the North Lake Sammamish basin and send these flows to the Brightwater Treatment Plant. This project is necessary to maintain the ability of the ESI to convey peak flows during a 20-year storm event. The ESI is expected to reach peak flow capacity in 2021. Construction is scheduled to begin in 2017.

North Mercer Island and Enatai sewer upgrade

King County will continue project planning and design to replace sewer pipelines that have served neighborhoods in North Mercer Island, southwest Bellevue and the town of Beaux Arts Village since 1970. The new pipeline is being designed to serve these communities for the next 60 years 

Sunset and Heathfield Pump Stations upgrades

King County plans to upgrade two pump stations in Bellevue as well as connecting sewer pipelines. The project also entails upgrading the Eastgate Trunk structure near I-90, which enables wastewater from these pump stations to get to King County’s South Treatment Plant in Renton.