Theories Arise on Pipe Burst’s Cause

Computer software problems, inadequate training or human error likely caused this week’s catastrophic water-main failure that disrupted supplies to more than 700,000 south Orange County customers, water officials said Friday.

At the same time, officials announced that initial inspections of the 69-inch-diameter prestressed concrete pipe--similar to those that have failed in other water districts around the nation--uncovered no signs of corrosion that could have led to the breach.

Investigators did find problems in the computer programs that made a control valve open faster than operators anticipated, said Jill T. Wicke, manager of water systems operations for the Metropolitan Water District of Southern California. The operators reacted by quickly closing the valve, which made for a combination of actions that led to a surge of backward pressure in the Allen-McColloch Pipeline, Wicke said.

“It looks like the valve opened quickly and closed quickly [within] a couple of minutes,” Wicke said.

Among questions yet to be answered is whether the operators responded appropriately, and if not, whether they had been properly trained, officials said.

The pressure, which exceeded the pipe’s capacity, blew out a 10-foot section of the buried steel-and-concrete conduit. Some 5 million gallons of water, along with concrete chunks, churned up from 25 feet underground in a pressurized torrent that flooded a nearby strawberry field.

Workers will operate valves manually until the computer programs can be analyzed, said Ronald R. Gastelum, MWD’s general manager. He put the cost of repairs at $750,000 but said it would not lead to a rate increase.

MWD engineers also will inspect the 26-mile Allen-McColloch Pipeline as soon as it can be arranged. And MWD officials will review staff training procedures for operating the pipeline, he said.

The computer problem arose with MWD’s 1995 takeover of the pipeline from the Municipal Water District of Orange County, Gastelum said. Valves controlling flow in that system were operated by a computer system that was incompatible with MWD’s existing system.

MWD officials have tried to reconcile the systems, and will not use the old Municipal computer program until they are sure they have resolved the problem, Gastelum said.

The rupture began with a routine request through the Santa Margarita Water District to the MWD for more water to be diverted to a branch line called the South County Pipeline through a set of valves in Lake Forest, Wicke said.

The opening and closing of the valve led pressure to back up in the pipeline, causing it to rupture at a low point near the Portola Parkway north of the former El Toro Marine Corps Air Station, said Eddie Rigdon, MWD’s assistant water system manager.

The pipe is designed to withstand a spike in pressure to 227 pounds per square inch, or psi. Normal running pressure is 131 to 162 psi, said Adan Ortega Jr., Gastelum’s executive assistant. At the time of the rupture, the pressure had increased to up to 250 PSI, he said.

Officials said the location of the rupture--in the lower third of the pipe--is consistent with a pressure-caused break rather than a weakness or defect in the pipe itself--the cause officials initially considered.

Prestressed concrete pipes are built in layers of concrete, steel tubing and steel reinforcing wire. When placed in soils high in sulfates, the cement can deteriorate and crack, allowing water to seep into the layers of steel, leading to corrosion and weakening.

That has caused ruptures in water systems across the country, including San Diego, Simi Valley and San Francisco. Districts in San Diego and San Francisco have retrofitted portions of their concrete pipelines with steel sleeves to prevent ruptures.

Because of the problems, MWD stopped installing the pipes and now inspects all of its 160 miles of prestressed concrete pipe, about one-fifth of the 770-mile system, on a five-year schedule.

“We wanted to assure ourselves that ours was in good condition,” said Gordon Johnson, the agency’s engineering services manager. “We know that it has the potential, under certain conditions, to have problems, but there is a lot of it that is perfectly good.”

MWD officials also said that soil within their jurisdiction is not high in the corrosive sulfates, reducing the risk of corrosion-related ruptures. The agency has retrofitted 1,000 feet of pipeline near the Dominguez Channel in Carson after finding signs of corrosion and other deterioration.

In Irvine, repair crews have been working around the clock and are expected to reopen the pipeline by Monday evening, Wicke said. Crews are replacing three 20-foot sections of the damaged water main with new steel segments, which they began welding into place Friday.

Once the segments are lined with cement, the water main will be disinfected and put back into service, Wicke said.

Local water officials said a potential water emergency was averted thanks to water transfers from unaffected cities and the overwhelming response to a plea for water conservation by more than 700,000 South County residents.

Water supplies should be adequate through the weekend as the conservation measures remain in effect, said Karl Seckel, assistant general manager for the Municipal Water District of Orange County.

Water use has dropped by about half in the Santa Margarita and Los Alisos water districts, the two districts most affected by the break. They serve Lake Forest, Mission Viejo, Rancho Santa Margarita, Coto de Caza, Ladera Ranch and Talega Valley.

Neighboring cities connected to the South County’s second main water pipeline have transferred 23.6 million gallons of water to those needy areas since Monday, actually increasing water reserves in Los Alisos and Santa Margarita by 5.7 million gallons from Thursday to Friday, officials said.

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How the Pipeline Broke

Computer or human error is believed to have caused a catastrophic water main failure in south Orange County. How it happened:

1. Computer glitch opens valve too quickly

2. Operator closes valve, triggers backward surge

3. Rupture at low point of concrete pipe

Water main break on Monday.

Maximum water pressure in pounds per squre inch

162, Sustained flow

227, Spike

250, Monday’s spike

Graphics reporting by BRADY MacDONALD / Los Angeles Times

Source: Orange County Municipal Water District