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 found no living bacteria, probably as a result of the advanced filtration system.

An investigation is underway to identify why the circuit protection device did not prevent the equipment shutdown.