Approximately 260 million gallons of combined stormwater and wastewater flowed into Puget Sound over a period of almost 20 hours last week, after an equipment failure at the West Point Treatment Plant in Magnolia.
The combination of 85-90 percent stormwater, and 10-15 percent sewage had to be diverted to an emergency bypass outfall on Feb. 9 after a pump failure around 2 a.m. that morning. The failure occurred during a period of heavy rainfall and high tides, and when the treatment plant was operating at maximum capacity (440 million gallons a day). In order to protect the treatment plant from significant flooding — which could cause significant damage to its equipment — the plant operated in that bypass mode while crews worked to fully restore operations.
During that time, crews pumped flooded areas of the plant to clean, inspect, and repair equipment. The bypass discharges offshore by the North Beach in Discovery Park, and currents travel northward from that point. Flows were also diverted to other treatment facilities during that time.
By 9 p.m. that night, wastewater flows were again being sent through the treatment plant, receiving primary treatment and disinfection before going through the deepwater outfall, with some still diverted to other plants in the system to ensure the safe, systematic restoration of operations.
Water quality monitoring is ongoing by King County’s Environmental Laboratory, and warning signs were placed on several area beaches to warn of the potential health hazards of coming into contact with the water. The most recent water quality sampling results for fecal coliform bacteria, released on Saturday, showed a bacteria level above the threshold for beach closure at several locations at West Point. Results for testing at Golden Gardens and Carkeek Park showed levels below that threshold, indicating that the current did not transport the discharge very far.
The warning signs will remain until Public Health - Seattle & King County, reviews the water quality testing results, and approves their removal.
When in full service, the plant treats wastewater from Seattle, Shoreline, north Lake Washington and north King County, along with portions of south Snohomish County.
To comment on this story, write to QAMagNews@nwlink.com.