Beach Open, but Bacteria Not Traced : Pollution: The source of contamination has county officials baffled. Because the levels quickly returned to normal, it is less likely that a broken sewage line is to blame.

Health officials and environmentalists expressed relief at the reopening this week of five miles of beach in Playa del Rey and Venice that had been closed for three days by pollution, but the relief was tempered by their continuing puzzlement over the source of the contamination.

A smaller stretch of beach, about half a mile south of Redondo Beach Municipal Pier, was also expected to reopen today. The resolution to that pollution problem was more clear-cut, as city officials capped a sewage pipe that had been forced open by vandals.

The cause of the larger beach closure is the source of a continuing investigation by the Los Angeles Bureau of Sanitation.

“The good news is that the bacterial counts are back down. The bad news is that they don’t know where it came from,” said Roger Gorke, research scientist for the environmental group Heal the Bay.

“If you don’t know the cause and where it came from, then it can happen again,” said Jack Petralia, director of environmental protection for the county Department of Health Services. “And that is an uneasy feeling.”

The pollution was discovered during routine testing Saturday morning in Ballona Creek, the giant concrete storm channel that empties into the ocean at Marina del Rey. Inspectors found extremely high concentrations of bacteria about seven miles up the creek, near Higuera Street in Culver City.

Such high concentrations are usually associated with sewage, but Petralia said it is unclear whether sewage or some other organic material caused the high bacterial readings. High concentrations as far away as Venice and Playa del Rey beaches indicated a sizable spill, perhaps as large as a million gallons, Petralia said.

In response, the county Department of Health Services on Saturday closed the beach on both sides of the mouth of the creek.

Yellow signs warned the public to avoid contact with the water, even as temperatures soared to their highest levels of the summer.

The signs were removed Tuesday, but officials remained perplexed by the source of the pollution.

“This has turned out to be a real hard one to play detective on,” said Sam Cheng, head of the sanitation bureau’s Environmental Monitoring Division. “We have been quite baffled.”

In the past, such massive spills have come when heavy rains caused sewers to overflow or when a sewage line broke and dumped waste into Ballona Creek.

But sanitation officials said a broken sewage line is unlikely in this case because the pollution disappeared as suddenly as it started. “It is very unlikely to be sewage leakage, because it would continue to flow until (the sewer) was fixed,” Cheng said.

Mark Gold, staff scientist for Heal the Bay, disagreed, saying the spill is too large to have come from other sources, such as a tanker truck making a one-time dump into the storm water system. Gold said he thinks the pollution probably came from either a broken sewer or a business illegally dumping into the storm water system.

“It’s kind of scary when you have a spill that big and you don’t know the source,” Gold said.

Tracking of the bacteria has been more difficult because the pollution diminished so quickly. But sanitation workers believe that it may come from a storm drain near Jefferson Boulevard, where bacteria measurements were taken this week.

If as yet uncompleted testing confirms high bacteria measurements in the drain, then a team will be sent to search for leaks or illegal hookups, Cheng said. A remote-controlled video camera is also available to probe into pipes too small for human exploration.

“It’s a complicated storm drain system, so to trace upstream is very difficult,” Cheng said. “We do want to get to the bottom of it. It’s unsolved for now and that is not good for anybody. It just means we can’t do the preventive things.”

Meanwhile, county health officials said they expect that testing results today will confirm that the ocean south of the Redondo Beach Municipal Pier is safe for swimming despite a sewage spill Monday morning.

A county health official was at the pier Monday for routine ocean testing when he noticed that a cap had been removed from a sewage line that carries waste from businesses on the pier.

The cap was replaced within half an hour, but the beach was closed as far south as Knob Hill Avenue as a precautionary measure.

The sewer cap will be replaced in the future with a more secure device that is less susceptible to vandalism, said Ray Koke, Redondo Beach’s assistant harbor director.