Each raw sewage pump has a firm capacity of 110 million gallons per day of wastewater.
Each raw sewage pump has a firm capacity of 110 million gallons per day of wastewater.

There are a lot of moving parts that keep wastewater flowing in and out of the West Point Treatment Plant, and numerous enhancements and redundancies have been added over the years to ensure systems remain online.

A number of improvements were made in response to a catastrophic system failure in 2017 that resulted in the plant going offline and losing treatment capabilities for three months, and now the King County Wastewater Treatment Division is assessing, in partnership with Seattle City Light, how to improve electrical reliability at the plant following an unpermitted discharge that occurred to prevent flooding during a voltage sag back in July.

People rarely think about how the system works until it doesn’t, said Bruce Kessler, deputy director for King County’s Wastewater Treatment Division (WTD).

The Queen Anne News joined Kessler and several WTD employees for a tour of the West Point Treatment Plant on Friday, Oct. 25, to better understand the process, what’s been improved in the last two years, and what’s on the horizon.

Unlike most wastewater treatment facilities in the state, West Point is designed to take in and treat both stormwater and raw sewage.

There are two influent lines into West Point. The Fort Lawton tunnel comes down the hillside from Discovery Park and is 144 inches in diameter. The Old Fort Lawton tunnel is 84 inches, and it runs down from the north point of the park.

Wastewater is combined at the influent control structure, and then transferred through six bar screens, which capture debris of all shapes and sizes; two screens are used during dry weather.

The water continues through four raw sewage pumps to preaeration tanks, where grit and sand is removed by gravity.

At the time of the Feb. 9, 2017 flooding event inside the plant, a heavy rain storm was sending flows of 440 million gallons per day (MGD), which was pushing the plant at its peak.

West Point Treatment Plant supervisor Tom Bauer said that event resulted in making plans for maintaining firm capacity to match 440 MGD, which would involve increasing pump capacity, either adding a pump or increasing the capacity for the existing pumps.

The raw sewage pumps operate on gas-powered engines, and the generated heat is captured and circulated to other parts of the plant, Bauer said.

During the 2017 electrical systems failure that caused the other pumps to shut down, emergency float switches in the preaeration tanks were supposed to trigger a shutdown of the raw sewage pumps and open the emergency bypass gates. This was a critical failure in the system, Bauer said, and caused flooding in the raw sewage pump station.

Now the preaeration tanks have been upgraded with an independent float system on a stainless steel rod that can better detect water levels and activate an emergency shutdown of the raw sewage pumps, he said. The floats are tested twice a year, and a high-level alarm will sound before a shut down is triggered.

The wastewater then goes through 12 primary sedimentation tanks, where the primary sludge is removed. Fats and oils rise to the top and are skimmed out.

“Thanksgiving gets pretty greasy down there,” Bauer said.

Primary effluent combines at a flow diversion structure, which can divert flows of more than 300 million gallons of wastewater in a day, which is roughly what the plant was handling on July 19.

The secondary diversion pushes some wastewater around various systems and back down for chlorination and other treatment before it’s sent to the effluent pump station to be released into Puget Sound. The water goes through a dechlorination process before it’s pumped out of the plant. The plant is permitted to bypass flows of more than 300 MGD around the secondary process.

Wastewater not sent through secondary diversion is lifted into six aeration tanks via three pumps at the intermediate pump station. Oxygen is pumped into the aeration tanks, which stimulates microbes that feed on organic material (raw sewage). More sludge gets sorted out of the wastewater in the tanks, and then the water is sent to 13 secondary sedimentation tanks, where more solids settle to the bottom and are removed. Cleaner water gets channeled out for chlorination and then dechlorination.

Bauer said the challenge during the 2017 flooding event was that pumping couldn’t take place, and so the biological process of getting the microbes working on digesting the raw sewage couldn’t occur. The digesters were back in action 100 days after the electrical failure.

Not only was the plant flooded, but 235 million gallons of wastewater was released into Puget Sound through the emergency bypass gate. The Washington Department of Ecology fined King County $361,000. Damages sustained in the flood event amounted to more than $23 million.

Following the 2017 plant failure, the wastewater treatment division (WTD) engaged consulting firm AECOM to develop an independent assessment of the West Point Treatment Plant. AECOM generated 98 potential mitigation strategies, of which WTD has completed 63 and is working on completing 26 more. On top of the $800,000 in investments made after the 2017 flood, WTD has identified $200 million in long-term projects to increase capacity and redundancies at West Point.

The upgrades and protocol changes at the West Point Treatment Plant are credited for preventing flooding during a July 19 voltage sag that also knocked pumps offline, including the intermediate and effluent pump stations.

“The equipment here has to be manually reset,” Bauer said.

The emergency bypass gates opened for 27 minutes due to high wastewater levels in the raw sewage pumps and influent control structure. It takes 17-19 seconds to open the gates.

“A gate this big, in 17 seconds, is pretty fast,” Bauer said.

The gate is now online at all times, and so it opened quickly after high wastewater levels triggered the July 19 emergency bypass, Bauer said.

A draft report for an independent study of the electrical systems powering the treatment plant is expected by February at the latest, Kessler said, at which point there will likely be more evaluation.

“I’m hopeful there are some quick, simple things we can do — some minor tweaking — but there will be some longer-term projects too,” he said.

Where does the sludge go?

Raw sludge from the primary sedimentation, aeration and secondary sedimentation tanks drops down to a blending tank before heading to a series of gravity belt thickeners. There it is mixed with a polymer, and water falls through a porous belt, Bauer said. About four of the 10 gravity belt thickeners are run during average flows.

The thickened sludge is blended again and transferred to five digester tanks where microbes feed and produce methane gas, a portion of which is transferred to a cogeneration facility that produces electricity. Seattle City Light uses the electricity generated. Under this partnership, the treatment plant generates about $5,000 a day in revenue, Bauer said.

Remaining solids head from the digester tanks to a blending tank, and then to four dewatering centrifuges. The biosolids are then recycled for composting, forestry and agriculture.

Bauer said the treatment plant hauls five truckloads — at 30 tons each — of biosolids out every day.