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City: 'Thousand-year storm' cause of Factoria flood
City officials have a better understanding of the events that led up to localized flooding in Factoria on Aug. 13, which Utilities Director Nav Otal said was caused by high-intensity rainfall.
"It's the equivalent of a thousand-year storm," she said of the 2.65 inches of rain recorded by the Coal Creek rain gauge over a six-hour period during the flooding.
Police and fire were first to respond, with utility crews receiving the report around 3:20 a.m. Aug. 13, responding at 4:30 a.m. Waters began to recede at 5:30 a.m.
The storm flooded the Formula-1 Fast Lube shop on Factoria Boulevard, washing out oil onto the road. Flooding also was reported at several homes on West Lake Sammamish Parkway and at a condominium upstream from Richards Creek, which Otal said is believed to have been unrelated.
Otal said there was initially confusion, with reports of water socks being left in storm drains following a Factoria Boulevard overlay project, but the contractor reported to the city later that day those socks had been removed July 28-29. Formula-1 owner Bob Healy had blamed the city for causing the flooding by installing water sock filters in storm drains near his business.
"I think people took two unrelated events and, perhaps, made a tie," Otal said, adding water socks were used in catch basins following the flooding to absorb the oil.
Floodwaters reached as high as four feet along a portion of Factoria Boulevard. Oil mixed with the water complicated matters, but the city is confident most of the oil stuck to the roadway, said Joe Harbour, assistant director of operations and maintenance for the city's utilities department.
Harbour added no oil sheens were found running along Richards Creek, and oil boons were placed there to capture any potential runoff. The state Department of Ecology also was notified of the flood for further observation, should any contaminants have emptied into local waterways.
"Everything went as designed," Otal said. "The system worked as designed," but she said the system was designed to handle 100-year flooding, not 1,000-year flooding. She added she doesn't believe anyone uses such standards for storm drains. "… I don't think anybody foresaw the intensity."
The city is awaiting the release of a storm report, which should shed even more light on the Aug. 13 flooding event. The Reporter has requested a copy of the report and will post it online when it becomes available.