Operator error led to spill
Rains overwhelmed a Mill Valley, Calif. treatment plant Jan. 31, causing about 2.7 million gallons of partially treated sewage to spill into Richardson Bay, the Marin Independent Journal reported.
The sewage was filtered of most solids, but it was not disinfected with chlorine, releasing bacteria into the bay.
Marin County’s Office of Emergency Services did not issue a press release until the early afternoon of Feb. 1, when the public learned of the spill. According to officials, miscommunication among local agencies delayed notification, the paper reported.
Officials posted signs at beaches and waterfronts along Richardson Bay warning people of the contamination, said Marin County sheriff's Lt. Doug Pittman, and San Francisco officials posted signs on numerous beaches, warning that they were unsafe for swimming.
According to Stephen Danehy, general manager of the Sewerage Agency of Southern Marin, the problem started when an operator at the plant decided to leave only two of six pumps on when he left for the day about 4 p.m. on Jan. 31, the paper reported.
"Essentially, we had more water coming in than we could pump out," Danehy said. "We just didn't have enough pumps set up. We should of had four pumps going instead of two. It was one of those errors in judgment."
Redwood Security Systems, Inc., of Mill Valley, responded to an alarm that went off at 4:30 p.m., but due to miscommunication, the plant operators did not receive notification until later that evening when a plant operator checked his computer online at home and saw the rising flow levels, the paper reported. He went to the plant and turned on the extra pumps at 8:30 p.m.
Some 2.7 million gallons of the partially treated sewage, containing the equivalent of up to 80,000 gal of raw sewage, flowed into the Arroyo Corte Madera del Presidio Creek and Richardson Bay for three hours, the paper reported.
"It was partially treated, but bacterial levels were higher, obviously," Danehy said. "Should we have done something differently? Yeah, we should have made sure all pumps were ready to run. Our person is an experienced operator who has been with us for 15-plus years. It was an error in judgment."
The fact that the sewage had not been treated with a final chlorine treatment may have been good and bad, according to Lila Tang, chief of the wastewater division for the state Regional Water Quality Control Board.
"It wasn't disinfected, so it wouldn't kill wildlife--but it would have bacteria, which could be a problem from a public health standpoint," Tang said.
County health officials advised the public to avoid contact with bay water or sport fishing in and around Richardson Bay until further notice.
It appeared animal life was not harmed, according to the paper.