Puget Sound safe despite sewage spill

SEATTLE—Last year’s sewage-treatment-plant disaster that sent nearly 250 million gallons of untreated stormwater and sewage into Puget Sound caused little to no damage to water quality, a scientific review by King County has found.

The plant was crippled in a catastrophic flood Feb. 9, 2017, so badly damaged it could perform only minimal settling of effluent and disinfection of waste in primary treatment for three months. Many thousands of tons of solids were deposited in Puget Sound via the plant’s outfall 240 feet under water.

But the discharge largely did not affect water quality, the scientists found. Swift currents diluted the pollution. Water quality did not slip below most required standards at the monitoring stations in Puget Sound, the scientists found in the report, which was approved by three external reviewers.

The largest effect documented so far of the plant’s greatly reduced capacity was during the emergency bypass of totally untreated sewage to the Sound, causing brief increases in bacteria counts at beaches near the plant at West Point, which were closed to protect public health. Those effects also quickly dissipated, with bacteria back to safe levels within three days, according to the report.

West Point, in Discovery Park, is the largest wet-weather plant of its type on the West Coast, and serves some 700,000 people.

The plant discharged 244?million gallons of untreated stormwater and sewage through a 40-foot-deep emergency bypass outfall during two separate events on Feb. 9 and 15-16, 2017. The bypasses consisted of approximately 85 to 90 percent stormwater.

But most measurements found the water samples met applicable water-quality standards even while the plant was under repair, with the exception of high bacteria counts and low dissolved oxygen at some sites in June. Those deficiencies were due to natural seasonal conditions, according to the report.

Analysis still is underway of samples taken from sediment near the outfall, as well as monitoring to search for metals and other pollution in intertidal sediments, clams, zooplankton and crab tissues.

Chris Wilke, executive director of Puget Soundkeeper Alliance, a water-quality-protection nonprofit, said he was not surprised by the results of the report.

“That is a very high-energy environment,” he said of the currents near the deep-water outfall. “There is a lot of mixing there.”

The report is the result of voluntary increased monitoring by King County’s Wastewater Treatment Division on the beach and in the water and sediments while the plant was unable to perform normally.

John Spencer said pre-treatment of industrial waste discharged to Puget Sound helped make the environmental impact less severe.