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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

Eastgate Interceptor lining

This is part of the conveyance system program created to rehabilitate corroded conveyance pipelines throughout the county’s wastewater system. The first phase of this work is starting this summer; it includes lining of approx. 3,000 feet of sewer pipe located in the city of Bellevue.

Lake Hills and NW Lake Sammamish sewer upgrade

To keep up with a growing population, King County is looking at options to improve the sewer system in the Lake Hills and NW Lake Sammamish areas. Increasing sewer capacity will allow King County to continue to safely and reliably move wastewater flows to be treated at a regional treatment facility. King County will review project options over the next year and start design in 2016. Construction is expected to begin in 2018.

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

This project will increase the capacity of the existing North Mercer Island Interceptor and Enatai Interceptor components of the regional wastewater system in order to convey the 20-year peak wastewater flows projected through the year 2050.

Sunset and Heathfield Pump Stations upgrades

The Sunset and Heathfield Pump Stations Upgrade Project will ensure King County can efficiently and effectively accommodate Bellevue and Issaquah’s wastewater treatment needs into the next century.