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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

King County's Wastewater treatment process

The process used at our three regional treatment plants provides secondary treatment (preliminary, primary and secondary treatment, and disinfection). The graphic below shows the basic steps in the treatment process.

Note: Stormdrains are connected to the sewer system only in the combined sewer system in parts of Seattle.

2016_RR-treatment-process_1000
Source: Ratepayer ReportPages 4 and 5 (PDF).


Besides our principal work of treating wastewater, we provide odor control, investigate and assess new wastewater treatment technologies, and strive to be a good neighbor during construction.

To find out more about King County's wastewater system:

Learn more about wastewater treatment