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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

Brightwater project

Facility operations

Brightwater Treatment System Banner

Completed fall 2012

In response to increased growth in our region, King County has built a new $1.86 billion regional wastewater treatment system called Brightwater to serve the northern portion of the King County service areaTreatment plant operations began in September 2011. The conveyance system and outfall began full operations in fall 2012.

Map of Brightwater project facilities
Brightwater Treatment System
(PDF). View more detailed 11x17 inches map (PDF).

The new facilities include:

  • The Brightwater wastewater treatment plant is located in unincorporated Snohomish County, north of Woodinville. The plant is designed to have the capacity to treat an average of 36 million gallons of wastewater per day (mgd). By 2040, treatment capacity could be expanded to 54 million mgd.
  • The conveyance system is the tunnels, pipes, and other facilities that carry wastewater to and from the treatment plant. The Brightwater system includes 13 miles of pipeline built in underground tunnels, shallower connector pipes, and an influent pump station to send wastewater to the plant.
  • The marine outfall consists of twin, 5-foot-diameter pipes with a diffuser at the end where highly treated wastewater from the Brightwater treatment plant is discharged into Puget Sound. The mile-long, 600-foot-deep outfall extends off of Point Wells.

Brightwater Treatment Plant opening (September 24, 2011) from King County DNRP on Vimeo.

Background - siting the Brightwater facilities

Beginning in the summer of 2000, the County began searching for and analyzing sites. In May, 2001 the King County Council selected six sites and eight marine outfall sites for further evaluated as “systems” (including a plant site, conveyance system and outfall).

In June 2001, the County began a second round of evaluation. Based on this, the County Council selected two systems - including conveyance options and four marine outfall zones – to continue on into the environmental review process.  

King County conducted a formal environmental review of the Brightwater project under the State Environmental Policy Act (SEPA). On November 19, 2003, a Final Environmental Impact Statement (Final EIS) was issued for this project. See Environmental Review for more details. 

Project siting decision - on December 1, 2003, the King County Executive made a decision on the location for the Brightwater Treatment System (PDF).

On July 27, 2005 the King County Executive reaffirmed his earlier selection of the Route 9 - 195th Street system alternative for the Brightwater project. To learn more, download the Regional Wastewater Services Plan: Summary of the Executive's Process to Update the Brightwater System Siting Decision, July 2005 (PDF).

In December 2005, King County completed a systemwide mitigation package (PDF).

Project photos

The following links point to WTD Flickr sets.

Aerial view of one the outfall pipes with just the end section not yet submerged (September 2008)
Marine outfall

(off of Point Wells)

Transporting segments in the west tunnel
Conveyance facilities

(pipelines and portals)

Solids area digesters with energy building (in the foreground)
Treatment plant

(near Woodinville, WA)

Reclaimed water lines at North Creek Pump Station
Reclaimed water system

Visitors at boardwalk entry to North Mitigation Area
North mitigation area

(north end of treatment plant site)

Environmental Education and Community Center (viewed from the West), December 2010
Environmental education center

(north end of treatment plant site)

Trained divers harvest eelgrass to be grown in tanks during construction of the Brightwater Marine Outfall.
Marine restoration

(at the marine outfall) 

Project videos

The following links point to DNRP Vimeo videos.

Video: First flow of clean test water to come into the Brightwater Plant from the Influent Pump Station in Bothell, 2.8 miles away! (May 2011) Brightwater Plant test (May 2011)
Video length: 17 seconds
Video: installation of membrane bioreactor filters (MBRs) at the treatment plant (April 2011).

Installation of membrane bioreactor filters (MBRs) at the treatment plant (April 2011)
Video length: 2 minutes, 32 seconds

Video: Earth Week at Brightwater Center (April 2011)

Earth Week at Brightwater Center (April 2011)
Video length: 2 minutes, 4 seconds

Smooth sailing for Brightwater outfall pipelines (September 2008)

Smooth sailing for Brightwater outfall pipelines (September 2008)
Part 1 - the first outfall pipeline was submerged on September 10, 2008 (video length: 1 minute, 46 seconds)
Part 2 - the second outfall pipeline was submerged on September 12, 2008 (video length: 1 minute, 35 seconds)

Brightwater treatment plant introduces tunneling equipment (September 2007) Brightwater treatment plant introduces tunneling equipment (September 2007)
Video length: 1 minute, 46 seconds
Brightwater habitat restoration tours, April 2007 Take a tour of the Brightwater habitat restoration (April 2007)
Video length: 4 minute, 16 seconds