The plant suffered catastrophic damage on Feb. 9 and will not return to regular service for many weeks, according to Mark Isaacson, director of the King County’s wastewater-treatment division.

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King County has stopped dumping raw sewage into Puget Sound from its crippled West Point treatment plant for now — but the county will likely start dumping again when rainy weather returns.

The plant, which treats sewage from 1.7 million people around the Seattle region, suffered catastrophic damage on Feb. 9 and will not resume regular service for many weeks, according to Mark Isaacson, director of the King County’s wastewater-treatment division.

Beaches at Discovery Park are closed, with no date yet for reopening, because of the risk to public health from raw sewage pumped from the plant into the Sound. “We are here for the health of the environment, and for public health, and right now, we are compromising that,” said Isaacson.

The trouble started when the pump station that sends treated wastewater out of the plant failed, according to a letter from plant managers sent Wednesday to King County’s regulators.

Staff on duty about 2:15 a.m., Feb. 9, worked to reduce the incoming flow while attempting — unsuccessfully — to restart the 2,250-horsepower motors on the pumps. As water levels in the plant continued to rise, staff next worked to manually intervene to stop pumps bringing more incoming flow.

That caused the upstream levels of sewage entering the plant to rise, triggering an emergency bypass gate to automatically open. That diverts raw sewage away from the plant and into an emergency outfall pipe to Puget Sound, as a desperate measure to save the plant.

By then the plant was already flooded, with a barrage of some 15 million gallons of water barreling through it, powerful enough to buckle and break down 25-foot-high garage doors, mangle equipment and leave a fur of untreated sewage 12 feet up the walls. Cavernous rooms filled with pumps and other equipment were flooded to the ceiling and steeped in muck.

“Water is impatient,” said operations and maintenance section manager Robert Waddle. “And the water won.”

Tens of millions of dollars of equipment, including more than 200 motors and more than 100 electrical panels, were destroyed. An uncounted number of pumps have to be taken apart, cleaned and repaired. Industrial-scale boilers, used in the treatment process, need to be replaced.

Since the flood, hazardous-materials crews have been steam-cleaning the plant, and electricians have been working their way, room by room, to make them safe to enter after water swamped the electric circuitry.

Next comes the slow process of cleaning and replacement and repair of motors, pumps, and electrical wiring and panels, expected to take many weeks.

King County has a $250 million insurance policy that is expected to cover the cost.

Isaacson, during a tour of the plant with reporters Thursday afternoon, said the event was catastrophic. It’s so damaging that the plant, which turned 50 years old this year, cannot perform secondary treatment that is required by its wastewater permit. That puts the county out of compliance with state regulators and facing possible fines.

The plant normally provides intensive treatment of up to 450 million gallons per day of sewage, wastewater and stormwater.

But right now, the plant is limping along at half capacity and is treating stormwater and raw sewage flowing to the plant with primary treatment only. That means solids are screened and settled out, and the rest is disinfected with chlorine, then dechlorinated before discharging the water offshore of the beach at West Point to Puget Sound.

Worse, when rain swells the amount of water entering the system because of stormwater from roads, roofs and other hard surfaces, the plant, operating at reduced capacity, bypasses what it can’t shed to other plants for treatment and sends it directly to Puget Sound.

Environmentally, untreated flows cause temporarily elevated levels of bacteria in some areas, spot tests by the Wastewater Treatment Division show. Currents dissipate the pollution. Large amounts of stormwater in the effluent also mean the sewage is greatly diluted.

The plant bypassed 260 million gallons of untreated flows to Puget Sound beginning early in the morning Feb. 9 and stopped about 19 hours later, said Doug Williams, spokesman for the county.

Dumping of untreated flows began again about 3:30 a.m. Wednesday because of the wet weather and lasted until about 10:30 a.m., spilling an estimated six to 10 more million gallons of untreated effluent into Puget Sound from an emergency overflow pipe 35 feet below the surface, nearly 500 feet offshore. Most of the effluent is stormwater, but about 10 percent is raw sewage.

The emergency overflows resumed from 4 p.m. Wednesday and continued overnight until about 6:30 a.m. Thursday, when heavy rain resumed. Totals from that bypass event had not yet been calculated.

The county has notified its regulators at the state Department of Ecology and Department of Health of the situation, and has also informed tribes with treaty-fishing rights.

The trouble comes just as the region is experiencing record heavy rains that are expected to continue into the middle of next week. That is sure to mean more raw sewage bypassed to Puget Sound.

Isaacson said right now the county’s top priorities are worker safety and getting the plant back in working order. Still to come is what he promised would be a “deep dive” to figure out exactly what went wrong. “We owe that to ourselves and to the region. We are going to learn from this.”

King County operates a far-flung and diverse network of pipes, vaults and treatment plants from large, regional facilities, such as Brightwater and West Point, that collect and treat flows from local sewer agencies to a community septic system on Vashon Island.

The county’s Wastewater Treatment Division serves about 1.7 million people within a 424-square-mile service area, which includes most urban areas of King County and parts of south Snohomish County and northeast Pierce County.