The King County Wastewater Treatment Division and Seattle City Light expect to have a draft report evaluating the electrical systems powering the West Point Treatment Plant and recommending potential ways to improve reliability completed by mid-January.

The independent study is being commissioned as a response to a voltage sag at the treatment plant that occurred during a July 19 storm and required emergency bypass gates to be opened, releasing 2.1 million gallons of stormwater and sewage into Puget Sound.

This was the largest unpermitted discharge of untreated wastewater from West Point since the Feb. 9, 2017 plant failure, which resulted in 235 million gallons being released into Puget Sound. That incident was far more serious, and resulted in a loss of treatment abilities for three months and a $361,000 fine by the Washington Department of Ecology.

King County Department of Natural Resources and Parks director Christie True said equipment and control systems upgrades were made following the 2017 plant failure, and employee training and emergency protocols were updated.

“And we do believe that our employees followed the protocols as they should have to prevent flooding at the West Point Treatment Plant during this incident,” True told the King County Board of Health during a status update on Oct. 18.

Consulting firm AECOM performed an independent assessment of West Point following the 2017 event, and generated 98 potential mitigation strategies, of which WTD has completed 63 and is working on completing 26 more.

Seattle City Light reported the July 19 storm event caused a surge and resulting fire to break out on a power pole adjacent to the Canal Street Substation. The pole broke off and struck additional power lines, cutting power to more than 10,000 City Light customers.

West Point has a dedicated underground feeder from the Canal Substation and a backup source at the Broad Street Substation. The dedicated feeder experienced a 0.75-second voltage sag, where it dipped to 64.5 percent of nominal voltage, which resulted in pumps turning off, including an intermediate pump station and an effluent pump station.

The plant was dealing with roughly 300 million gallons of wastewater that night; that’s about six times more wastewater than usual during the summer, True said.

West Point operators attempted to slow the flow of wastewater at the Interbay pump station and at the first pumps accessed at the treatment plant while attempting to get the downed pumps back online, True said.

“But they were not able to get everything up and running before we had too high a flow in the plant,” she said, “and so, to protect our employees and to protect the plant, what is known as the emergency bypass gates were opened.”

The emergency bypass gates opened for 27 minutes due to high wastewater levels in the raw sewage pumps and influent control structure. King County reports about 80 percent of the 2.1 million gallons of discharge into Puget Sound was stormwater while the other 20 percent was sewage. Subsequent water testing did not find any negative impacts from the discharge.

Now King County and Seattle City Light have entered a memorandum of agreement to prioritize the quality of power coming into West Point, and independent consultants will look at City Light and West Point’s systems to find ways to improve reliability.

“We’re never going to eliminate the risk of either voltage dips or power outages, but what we can do is better understand what’s causing those and what we can do with our equipment to mitigate the impacts that they cause,” said Mike Haynes, Seattle City Light chief operations officer.

Even when a backup feeder kicks in, there will be a temporary gap, he said, which has a greater impact on large industrial customers than residential consumers. Similarly, True said switching from one power feed to another in the plant would still mean a 15-second delay. If a large generator were set up at West Point, there would not only be a delay in switching sources, but it would also require around 10 megawatts of power to fuel it. The pumps also needed time to startup , she said.

There are 47 pump stations with backup generators in King County’s collection system, and at least one every week needs to make the switch, True said, and during normal flows it goes unnoticed.

“If it had not been raining that night, we would not be here talking about this,” she said.

Haynes said the team focused on the electrical quality and reliability assessment would begin the formal process with consultants on Oct. 22.