Did the Pipe’s Bubble Burst? : The mystery of the San Diego spill deepens

When one of the nation’s worst sewage spills began off the San Diego coastline nearly two weeks ago, city officials said they believed the accident resulted from external forces: settlement of the ocean floor and unusual wave action, which knocked a big sewage pipe off its rock base. Since then, 180 million gallons a day of partially treated sewage has been flowing into the Pacific, 3,150 feet offshore, resulting in the initial closure of 4 1/2 miles of coastline.

City officials also said the 29-year-old pipe had been checked last fall and was found to be structurally sound.

But then it was learned that engineers had warned the city two years ago about serious corrosion in the 2.2-mile-long pipe after a study requested by the Regional Water Quality Control Board, which had concerns about the integrity of the pipe.

San Diego maintained, however, that corrosion did not cause the pipe to break in 21 places.

That was the first indication that city officials might be trying to distance this incident from sewage system problems that have plagued San Diego for years, resulting in hundreds of thousands of dollars in fines and lawsuits by the state and federal governments.

Now, five workers at the Point Loma sewage treatment plant say that a huge air bubble developed in the pipe just two days before the break was discovered. They said the bubble caused the plant, and the pipe, to shake violently.

The workers, who include a plant operator but no engineers, contend the incident was caused by an incorrect procedure. They think it is likely the incident caused the pipe rupture. City engineers vigorously dispute that claim.

After the plant workers’ comments were aired, the city manager’s office ordered a full investigation. So has the regional water quality board. That is certainly needed, if only to ascertain precisely what happened.

But any investigation of the spill needs to be done openly and without trying to downplay either its seriousness or its underlying causes. What is learned from this accident could prevent future disasters.