Blame Laid in Pipe Rupture

Operator error and computer-system flaws caused the massive pipeline burst that disrupted water supplies to more than 700,000 South County customers in December, officials said Monday.

An inspection of the 26-mile water main also uncovered possible evidence of corrosion in the prestressed concrete segments of the water main, similar to defects that led to ruptures elsewhere in the nation.

Although corrosion was not a factor in the December rupture, the finding has created “some cause for concern,” said Jill T. Wicke, manager of water systems operations for the Metropolitan Water District of Southern California.

The agency will do a detailed inspection of the pipeline in early February, a year ahead of a planned inspection, and shut down the main for a week, Wicke said.

The closure is not expected to disrupt service to residents, since county water agencies will be asked to store more water first, agency officials said.

Investigators found that an employee in the MWD’s operations center in Los Angeles caused the Dec. 13 rupture by taking the wrong steps in opening, then shutting, valves while sending water down branch lines to the Santa Margarita Water District, Wicke said.

By closing both valves by mistake, the operator caused a backward pressure surge that exceeded the main line’s capacity. That blew out a 10-foot section of the buried concrete and steel pipe on the outskirts of Irvine, Wicke said.

About 5 million gallons of water, along with chunks of concrete, churned up from 25 feet underground in a torrent that flooded over Portola Parkway and nearby strawberry fields.

Crews worked around the clock to replace 60 feet of damaged pipe, and the main was back in operation within eight days. Drought-like water restrictions were imposed throughout South County for the duration. The repairs cost an estimated $650,000, Wicke said.

Wicke presented a four-page report on the findings of the investigation to members of the MWD’s board of directors Monday morning. The report confirmed the MWD’s preliminary inquiry, released in late December.

The MWD is considering disciplinary action against the operator, although no further steps will be taken until the employee’s role is investigated further, said MWD spokesman Bob Muir. Punishment could range from a reprimand or added training requirements to dismissal, depending on the employee’s track record and culpability, Muir said.

The operator, who went unnamed, has been an “exemplary employee with an unblemished performance record,” Muir said.

A contributing factor was the computer system that controls the Orange County pipeline’s valves, which the MWD took over in 1995 from the Municipal Water District of Orange County, Wicke said.

The MWD has been operating the water main using software incompatible with the pipeline’s system, Wicke said. Because of that, MWD operators transferring water to agencies served by the pipeline must open and close more valves in this region than anywhere else in the MWD system.

“It was definitely not just operator error,” Wicke said. “There were some flaws in the system that we need to make sure are corrected.”

In fact, all other water agencies served by the MWD operate their own valves, Wicke said.

The MWD already has reconfigured the valves on the Orange County line, called the Allen-McColloch Pipeline, to ensure that similar problems don’t occur, she said. The MWD also is providing more training to make employees aware of Orange County’s pipeline operational system, and the agency is reevaluating operator practices and communications, Wicke said.

While the pipeline was being repaired, inspectors using a newly developed, high-tech voltage testing method found evidence of possible corrosion in 2,300 feet of prestressed concrete pipe that was tested to the south of the rupture, Wicke said. Roughly a third of the 26-mile line consists of prestressed concrete segments, with welded steel segments making up the rest.

The tests on the pipeline showed that the steel wire coiled around and strengthening the pipe had snapped in some spots, Wicke said.

However, Wicke said the testing method itself may have been flawed, so the MWD will reinspect the water main in February.

The MWD stopped installing that type of water main about five years ago after the corrosion factor was blamed for disastrous ruptures in California and elsewhere.

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

How the Pipeline Broke

1. More water was requested via branch lines, so large line was opened to supplement small line.

2. Large line was fully opened by accident; small line was closed to reduce flow, causing back-flow pressure.

3. Large line was fully closed by accident, causing even more back-flow; main line ruptured.

Source: Metropolitan Water District