The treatment plant in Seattle’s Discovery Park partially shut down as peak levels of sewage and stormwater funneled into the facility amid a rainstorm about 2:30 a.m. Thursday.

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A wastewater-treatment plant that malfunctioned amid downpours Thursday — causing millions of gallons of raw sewage and untreated stormwater to be dumped into Puget Sound — is back operating and close to fully functional again, a King County spokesman said Friday afternoon.

The problem with the West Point Treatment Plant in Discovery Park appears to lie with an effluent pump station that shut down amid heavy rains, said Doug Williams, a spokesman for the King County Department of Natural Resources and Parks.

The treatment plant in Seattle’s Discovery Park had partially shut down as peak levels of sewage and stormwater funneled into the facility amid a rainstorm about 2:30 a.m. Thursday. As the facility became flooded with wastewater and stormwater, a circuit blew for reasons still unknown, causing the pump station to shut down, Williams said.

The malfunction forced the plant to operate under “emergency bypass mode” until about 9 p.m. Thursday, meaning that most sewer and stormwater coming into the plant for treatment was instead piped offshore and dumped into the Sound.

In all, about 260 million gallons of untreated discharge — a mix of about 85 percent to 90 percent stormwater and 10 percent to 15 percent raw sewage — poured into the Sound, Williams said. Up to another 200 million gallons of raw sewage and stormwater was diverted to other area plants for treatment.

Repair crews were still assessing the cause of the problems and damages to the facility Friday, Williams said. High tides off Discovery Park that coincided with the downpours early Thursday may not have factored into the malfunction as previously thought, he added.

Water-quality sampling continued near the plant and warning signs remained on beaches Friday, Williams said.

An executive director for the environmental watchdog Puget Soundkeeper Alliance called the dumping of untreated discharges into the Sound “a major event” that in one day comprised about one-fifth of the typical overflow amount for the area’s sewers annually.