In only 30 minutes, about a mile of tunnels full of vital equipment were flooded at West Point Treatment Plant in Seattle


Thirty minutes — that’s all it took for an unprecedented flooding event to almost incapacitate a major Seattle-area wastewater treatment plant and leave operators picking up the pieces for weeks afterward.

On Feb. 9, the West Point Treatment Plant in King County, Washington, experienced severe flooding caused by power and equipment failures. The resulting bypass led to about 180 million gallons of storm water and sewage being discharged into Puget Sound, and damage to the plant temporarily reduced its capacity and treatment capability. Officials estimate the event caused at least $25 million in damage to the facility.

But now, after weeks of almost ceaseless labor, crews remain on track to restore full wastewater treatment function at the plant by April 30 — something that didn’t seem likely six weeks ago.

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“Basically, we flooded a mile of tunnels, the average dimensions of which are probably 15 feet wide by 10 feet high,” says Robert Waddle, divisions operations manager for the King County Wastewater Treatment Division. “We estimated we put about 15 million gallons of sewage, rain water and sludge into those tunnels — and all the way to the ceiling.”

The West Point system serves about 700,000 people, mostly in Seattle and its northwestern suburbs. It has 20 pump stations, 23 regulator stations and three wet-weather treatment plants. The West Point Treatment Plant, which serves Seattle’s combined stormwater and sewer system, averages 90 mgd during dry months, but has a wet-weather design capacity of 440 mgd — a capacity that was put to the test Feb. 9.

At about 2:30 a.m. that day, an intense storm with heavy rain sent maximum flows into the plant. According to a King County frequently-asked-questions document, problems began with an instantaneous fault in the electrical systems of the effluent pumping station. That caused a power feed to shut down, which led to all the pumps shutting down. Those pumps help move treated wastewater out of the plant and into Puget Sound.

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The operations manager for the King County Wastewater Treatment Division says the equipment failures during the storm caused about a mile of tunnels to become flooded. —Photos Contributed By King County


“During this time, the plant operators were trying to hold flows inside the plant to allow the electricians to restart the pump station and avoid a raw-sewage bypass,” the document says. “One of the operators was relying on an automated system that was measuring the level of the water in the primary treatment tanks. When this automated system senses levels are within 1 foot of the top of the tanks, the raw sewage pumps automatically shut down, and the emergency bypass gates automatically open. However, these level sensors, also called float switches, did not work. If they had worked properly, the flooding would not have happened.”

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An independent forensic analysis later determined the staff that night properly followed procedures, and the incident resulted from equipment and electrical failure.

Twelve minutes after the electrical failure, the primary tanks started to overflow. Workers were forced to open an emergency bypass gate for 19 hours, during which about 180 million gallons of stormwater and wastewater overflowed into Puget Sound.

Waddle received a call at about 3 a.m. and arrived at the plant at about 5 a.m. The scene was chaotic.

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“We couldn’t enter the tunnels,” he says. “You could get down the stairwells to the tunnels, but couldn’t see the tops of the doors down the stairs. We’ve had a flooding event before but nothing of this magnitude, so you can’t imagine training for this scenario.”

And the news got worse. The submerged tunnels contained 149 electric motors, ranging from a few horsepower to 100 horsepower, plus 127 pumps, 125 electrical panels and hundreds of miles of conduit with thousands of miles of electrical wiring.

Waddle says it took three days to remove the water from the tunnels. Then, mechanics and electricians had to ensure that the area was safe to enter. Finally, after four days, crews could start restoration efforts.

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“We were pushing it pretty much 24/7 for the first couple of weeks,” Waddle says. “Because in addition to getting all the contaminated stuff out before we could touch anything, we had to get in and get it cleaned.”

Plant staff hosed down the affected area, and then decontamination crews steam-cleaned the entire mile of tunnel. Then, workers further sanitized the area with bleach. Afterward, crews began electro-mechanical replacement and repair work. Meanwhile, the plant diverted flows to other facilities, and crews posted beaches and monitored water quality to protect the public.


A West Point Treatment Plant employee vacuums some equipment after the cleaning process.


Waddle says West Point’s 158 staff members, plus up to 40 employees from other plants, were more than up to the task.

“They were engaged, they saw the challenge and they stepped up to it,” he says. “There was no complaining. About the only complaining I heard about it was some people didn’t get more of a chance for overtime. Most of the people were plugging ahead and moving ahead. For the first two weeks, I had guys here who hadn’t missed a single day, and they were working 12- to 16-hour days, and no one was forcing them to do it. I didn’t have to come up with a mandate. The people coming in on their own made that a moot point.”

And that effort has paid off. Two smaller bypasses occurred Feb. 15 and 16. However, area beaches reopened in late February, and the cleanup and dewatering of the plant is complete. The plant’s capacity had been restored to about 250 mgd, and workers continue to repair and replace pumps, motors and other electrical equipment, along with other building damage. Also, they have completed removing contaminated insulation from the plant pipes that carry and circulate hot water to the digester system and continued to install new insulation.


Crews remove contaminated fiberglass insulation from the pipes before installing new insulation. While the face shields and suits weren't required, the workers wore them for comfort.


Further, the solids handling systems has been restored, so sludge generated from the primary treatment process can be collected and put into anaerobic digesters. And officials were planning to re-seed the plant’s secondary treatment process with microorganisms. Full wastewater treatment function was on schedule to be restored by April 30.

Waddle says he is especially proud of one fact: no one was injured during the February incident, which, considering the rapid flooding, is remarkable.

“This all happened in 30 minutes,” he says. “I don’t think I need to describe what would have happened if it had been 9 in the morning instead of 2 in the morning. Statistically, how much more likely would it have been for someone to be in the tunnels and get hurt?”

Thankfully, crews won’t have to answer that question as they continue pressing forward to full operational capacity and an improved West Point Treatment Plant.

For another in-depth look at the West Point Treatment Plant flooding, take a look at this article from The Seattle Times.


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