Untreated Wastewater Flows Into Puget Sound, Lake Washington

SEATTLE, WA — Power outages from Wednesday's storm sent millions of gallons of untreated sewage and stormwater flowing into Puget Sound and Lake Washington, according to the King County Wastewater Treatment Division.

In a news release published Wednesday night, officials said "a series of voltage fluctuations" at the West Point Treatment Plant in Seattle caused several of the facility's pumping stations to shut down between midnight and 2 a.m. Heavy rain lent to additional overflows at pump stations in Medina and Richmond Beach.

"The emergency caused an estimated 11 million gallons to overflow without treatment into Puget Sound. Approximately 80% was stormwater and 20% was sewage. Large volumes of rainfall throughout the day and into the night exceeded the capacity of the Richmond Beach pump station, and the volume of flow through the Medina Pump Station overwhelmed the station as it transitioned from line power to generator power and back to utility power. These two stations overflowed estimated volumes of 165,000 and 80,600 gallons respectively."

The county said quick action by crews on the scene prevented even more untreated water from flowing into Puget Sound from West Point. At least 17 pump stations across the county had to run on generator power during the storm.

"While county field operators worked to get the pumps running consistently, operators were able to mitigate the amount of the overflow by controlling the partial closing of the emergency bypass gate," officials wrote. "Equipment and operations worked as needed to protect the plant and employee safety from flooding. All systems were back online within 2 hours."

Officials said the county notified proper public health and regulatory agencies and posted beach closure signs at Discovery Park, Golden Gardens, Carkeek Park, and Richmond and Medina Park beaches warning visitors to avoid contact with the water as crews test water quality in the days ahead.

The West Point Treatment Plant suffered catastrophic flooding in 2017, sending 235 million gallons of untreated wastewater into Puget Sound and causing up to $57 million in damage. Other spills occurred as recently as last December.

King County will post further updates on Wednesday's spill on the DNRP website.