Brightwater-to-Sound wastewater conveyance system begins full operation

  • Written by King County Dept. of Natural Resources and Parks
King County’s Brightwater Plant sent its first flows through 13 miles of new tunnel on Nov. 9, essentially completing the region’s largest clean-water project of the last half century.

The 600-foot-deep outfall, which rests on the floor of Puget Sound a mile off Point Wells, serves as the primary discharge point for the Brightwater treatment plant serving both south Snohomish County and north King County.

A 13-mile-long tunnel from the treatment plant north of Woodinville to Point Wells conveys highly treated wastewater to the outfall.

The outfall’s operation marks Brightwater’s commissioning as a fully operational facility. Phased construction on the $1.86 billion Brightwater project began in 2006 with the treatment plant, followed by four deep-bore tunnels that comprise the 13-mile-long conveyance line, and an influent pump station that conveys untreated wastewater to Brightwater from Bothell. Construction on the marine outfall was completed in 2008.

One of Brightwater’s most notable features is its membrane bioreactor technology that produces effluent that is 70 percent cleaner than conventional wastewater technologies.

The advanced treatment technology will also enable the plant to become a significant source of high-quality reclaimed water for non-drinking uses, such as irrigation and industrial processes.

King County selected the Brightwater outfall location after years of environmental review that included detailed study of Puget Sound oceanography and marine biology as well as an extensive permitting process involving state and federal agencies.

This release is also posted at

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