Los Angeles County sanitation officials said Monday that they were unable to explain a chain of failures that led to what they are calling the largest sewage spill into Santa Monica Bay in a decade.
About 2 million gallons of untreated sewage spewed out of manhole covers and some residential pipes Sunday after a power failure shut down a pumping station in Manhattan Beach.
Nearby beaches will remain closed for days.
A day after the spill, the reason for the power outage remained a mystery: The station, which is supposed to pump raw sewage to a treatment station in Carson, has connections to Southern California Edison lines as well as a backup generator, but all of them failed.
An alarm system is supposed to warn the Los Angeles County Sanitation Districts when the pumping station shuts down, but it also failed.
Not until an hour later did officials sense that something was wrong -- they discovered that the alarm systems at about 21 pumping stations were not communicating with the central alarm center.
More hours passed before officials could take effective steps to stop the sewage flow.
Ultimately, about 100,000 gallons of sewage flowed into the Pacific Ocean, according to the sanitation agency.
"This is a very severe event for us," said Philip Friess, the head of the sewage department of the agency, which serves 78 cities.
"I don't believe we've had an event this severe in many years," he said.
Agency officials said they would investigate, exploring whether aging equipment played a role or recent rains damaged electrical connections.
On Monday, an area the size of a baseball field at Manhattan Beach was covered with dried bits of toilet paper and black scum. A plume of foul debris spread out to the ocean with flecks of toilet paper bobbing in the surf.
One resident recalled asking firefighters Sunday what was going on and being stunned by the response.
"Wow, we live in a world of technology and fail-safe systems in place and so many different scenarios. How can this happen?" asked Jason Walker, 30, who lives on the Strand in Manhattan Beach.
Mark Gold, the longtime leader of the environmental group Heal the Bay, said he was concerned that the sanitation district's alarm network had failed and was anxious to find out what had caused the malfunction.
"I'm upset the backup generator didn't kick in," Gold said. "Major pumping stations don't go out a lot, but when they do, they cause the biggest spills in the region."
