Bent equipment caused wastewater treatment plant failure

A bent rod on a switch float at the West Point treatment plant prevented the device from rising and sounding an alarm as the water rose.
↓ Advertisement ↓

Devices likely bent through normal maintenance procedures caused a massive failure at a King County wastewater treatment plant, according to an initial forensic report presented Tuesday to the King County Council.

The West Point Treatment Center in Discovery Park suffered a historic failure in early February, causing a massive flood that led to electrical damage which is still not repaired. That failure sent hundreds of millions of gallons of stormwater and raw sewage into Puget Sound.

Related: Skepticism meets assurance at meeting on wastewater treatment plant

The focus of the flood assessment was equipment called a switch float, which operates similarly to home toilet systems. The switch floats are supposed to rise as water rises. Instead, all eight of the devices had bent rods, preventing them from rising and signaling the alarm.

"The floats suspended by 8-inch rods failed to execute their design function. That caused a flood event of tragic proportions," said David Kelly, a CH2M engineer.

↓ Advertisement ↓

Kelly has overseen the recovery effort since the beginning. He expects the facility will be running at full capacity earlier than the expected finish date of April 24.

"The rate at which the facility is being brought back far exceeds what we would've estimated could be done in the available time," he said.

Since the flood on February 9, the plant has sent 250 gallons of wastewater everyday into Puget Sound that has only passed through primary treatment.

"This is a catastrophe of epic proportions for the county. It's polluting Puget Sound, something we don't like to do. It endangered, it sounds like, the lives of our employees. For those reasons, we want to make sure we understand why it occurred, what occurred and take steps to make sure it never happens again," said County Councilman Rod Dembowski.

Kelly told councilmembers that the switch floats were reported to have similar damage in 2008. The bending of the rods is most likely caused by regular cleaning.

"I think I want to look at that and understand if there were recommendations at that time to change those switches, and if there were, why didn't we? These are open questions. We don't know the answers, but we're going to find them out," Dembowski said.

The county council is planning to perform its own independent investigation of the West Point failure. It will also discuss upgrading the float switches to a different kind of device.