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Progress puts West Point Treatment Plant on a path to resume normal operation April 30


King County officials today announced details of plan to restore normal operation at West Point Treatment Plant beginning April 30, as well as the intent to commission an independent review of the sewer utility’s operation and maintenance procedures. Forensic analysis pinpoints an unprecedented combination of electrical system failure and equipment malfunction as the cause of severe flooding that damaged the treatment plant during a storm in the early hours of Feb. 9.


As progress continues on the repair of critical systems damaged by severe flooding Feb. 9 at the West Point Treatment Plant, King County officials today announced plans to restore full treatment capability beginning April 30.

King County also presented a preliminary forensic analysis for what caused the plant damage, and announced the hiring of a firm to conduct an independent review of the incident and the county’s response, and to offer recommendations. 

“The firm of Woodard and Curran has assembled a team of experts who have wide ranging experience with large wastewater treatment plants,” said Christie True, Director of the Department of Natural Resources and Parks, which manages the Wastewater Treatment Division. “These experts will prepare findings and recommendations that the Wastewater Treatment Division can implement to ensure we continue to operate at the highest standards possible.” 

True said the independent review will begin by evaluating the equipment failures and subsequent actions on Feb. 9 followed by a comprehensive look at the West Point control systems, asset management, preventive and routine maintenance programs, redundancy and relatability policies and standards, operating procedures at high flows, and operator training.

The flooding on Feb. 9 damaged electrical and mechanical equipment, reduced the plant’s treatment capacity by almost half, and halted its ability to treat wastewater to the secondary level, a biological process in which beneficial micro-organisms break down and remove organic pollutants in wastewater that’s ultimately disinfected, dechlorinated and sent to Puget Sound.   

With cleanup completed in late February and substantial repair of pumps and electrical equipment well underway, workers are now focused on repairing boilers that provide heat necessary for the secondary treatment process biology. 

Once boiler heat is restored by March 17, experts in wastewater treatment systems and biology will be tasked with assessing the health of the micro-organisms, which have been without needed heat for several weeks. Cultivating the micro-organisms in the digesters will require a delicate balance of time, testing and biological expertise. The estimated date to resume treating to the secondary level required under state and federal permits is April 30.

Engineering firm CH2M conducted an independent forensic analysis to piece together the sequence of events that occurred Feb. 9.

The problem began with an instantaneous fault in the electrical systems in the effluent pumping station. This caused one of the power feeds to shut down, which led to all the pumps shutting down. These pumps help move treated wastewater – or effluent – out of the treatment plant and into Puget Sound. 

Plant operators were trying to contain flows inside the plant to allow time to restart the pump station and avoid a stormwater-sewage bypass. Operators were relying on an automated system that triggers the shutdown of the raw sewage pumps and opens the emergency bypass gates, but float switches that act as water level sensors failed. 

Forensic analysis determined the switches failed due to bent rods that occurred during many cycles of routine maintenance. If the float switches worked properly, the flooding of the wastewater plant would not have occurred. 

With the combination of power failure and rapid flooding, the plant was manually put into bypass mode, sending 180 million gallons of untreated stormwater mixed with small amounts of sewage into Puget Sound through an emergency outfall. 

Crews stopped the stormwater-sewage bypass after 19 hours and restored limited primary treatment and disinfection on Feb. 10. Aside from two smaller bypasses on Feb. 15 and 16, the plant continues limited treatment that removes trash and debris, settles out some of the solids, and disinfects and dechlorinates the flow before it’s discharged to Puget Sound. 

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