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Brightwater Treatment System experiences brief loss of disinfection


King County quickly responded to a power outage at the Brightwater Treatment System’s disinfection facility on Monday, Jan. 16, restarting the plant's disinfection system within 15 minutes.


King County crews quickly responded to address an electrical malfunction affecting the disinfection facility in the Brightwater Treatment System. The shutdown led to a discharge of wastewater that was highly treated, but not disinfected, through an outfall one mile offshore and 650 feet deep in Puget Sound.

An equipment malfunction in the Brightwater Treatment Plant’s disinfection system temporarily shut down the plant’s disinfection system.

The problem occurred on Monday, Jan. 16, and was detected immediately by the plant’s monitoring systems. Within 15 minutes plant employees were able to restart the disinfection system. 

The electrical malfunction resulted in discharge of about 500,000 gallons of wastewater that was treated with an ultrafiltration system but not disinfected. The discharge mixed with treated and disinfected effluent in the pipeline that extends from the Brightwater plant in Woodinville to the marine outfall, which reaches one mile into Puget Sound off Point Wells and sits on the bottom of the sound at a depth of 650 feet deep.

King County reported the discharge to health and regulatory agencies.  Samples taken from the pipeline downstream did not contain bacteria, which are removed in the ultrafiltration step.

An investigation of the equipment malfunction is underway.

Detailed information about the Brightwater Treatment System is available online at