PG&E's highest-risk gas pipelines in the Bay Area are in the East Bay, according to a regulatory filing last year.

In making its case for customer rate increases, PG&E told regulators some of the money was needed to replace its riskiest pipelines, including one in Fremont and another between Livermore and Sunol.

The documents filed with the California Public Utilities Commission don't explain exactly why the company rated the two East Bay pipelines as the highest- and second-highest-risk natural gas transmission lines in the Bay Area. Nor do they state the age of the pipelines.

But the risk was ranked by combining the likelihood they would fail and the consequences to life and property if they did fail.

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Typically, engineers consider the population density of communities, the age of the pipelines and other factors, such as nearby earthquake faults, when assessing pipeline risk, said Bob Bea, a professor of engineering at UC Berkeley.

Bea, who has worked extensively on natural gas and oil pipelines, including recent studies of the BP blowout in the Gulf of Mexico, said he was not surprised that the two East Bay lines are considered top risks because the one in Fremont is near the Hayward Fault and the one south of Livermore crosses the Calaveras Fault, two of California's most dangerous earthquake zones.

"Many of the existing pipelines we have in this part of the world were engineered before the days of recognizing how you cross a fault with a pipeline," Bea said. "That makes one hell of a big difference. Crossing a fault at right angles is asking to have the pipeline sheared -- much like cutting a straw with scissors."

The eight-mile segment of Line 107 between Livermore and Sunol, "is the highest-risk pipeline in the Bay Area," PG&E told the state agency. Replacing it would cost $35.1 million.

It would cost $13.4 million to replace a 4.3-mile segment of Line 131 in Fremont, the second-highest-risk pipeline in the Bay Area.

The 30-inch gas line that blew up in a San Bruno residential tract last week killed seven people and destroyed 37 homes.

"We understand that customers can be concerned," said Matt Nauman, a spokesman for PG&E. "And obviously we are continually monitoring and upgrading our gas system."

Nauman said for security reasons he could not discuss specifics, but that if people want to know how close a transmission pipeline is to their homes, they can call PG&E and the utility will provide the information in writing.

He also noted that PG&E will examine the two East Bay pipelines for leaks as part of the statewide inspection of all its transmission lines in the next month.

Livermore officials were never informed of the pipeline risk, said a Livermore official who described his attempts to get information this week from PG&E as "frustrating."

"If they're rating things as high risk, they should be working with local jurisdictions to inform them of that," said Livermore assistant city manager Troy Brown. "We have a right to know that information."

The segment in Livermore skirts the city's southern edge, starting around Greenville Road and heading southwest toward Highway 84, Brown said.

The Fremont pipeline goes from the Sunol Grade near Interstate 680 west to Interstate 880 near Auto Mall Parkway. It was unclear what section of that pipeline needed to be replaced, said Fremont fire Chief Bruce Martin.

"Is this simply a prioritizing of maintenance projects or does this represent an imminent problem?" Martin said. "That's an unanswered question."

Martin said he was seeking information from PG&E to determine the severity of the pipeline risk, but, in any case, he said, it would have been "a welcome gesture" had PG&E provided that information earlier.

The filing mentioned a third pipeline, a 7.9-mile segment of Line 108 between Stockton and Ripon that is PG&E's highest-risk pipeline in the San Joaquin Valley.

All three segments are scheduled for replacement from 2011 to 2014 under a risk-management program regulators approved in 2000.

At that time, PG&E ranked the risk of its 6,438 miles of gas transmission lines by determining how vulnerable its pipelines were to breaking and how much a break would endanger people and property.

PG&E did not disclose the age of the two East Bay pipelines. But in the same filing with the Public Utilities Commission last year, it described a section of line about three miles north of the San Bruno explosion site as "high risk." It was built in 1948.

Bea said pipeline engineering has advanced in recent years. Now, he said, many gas pipelines in earthquake areas are built in trenches surrounded with foam or slurried clay, to absorb seismic shaking without the pipe breaking. Or they are designed to break in earthquakes like links of a chain, with automatic shut-off valves at either end of the link. Older pipelines lack those safeguards, he said.

Still, he noted that natural-gas pipeline accidents in the Bay Area have been rare. His advice for people who live near the high-risk lines? Pressure lawmakers and the Public Utilities Commission to make sure PG&E is inspecting and maintaining its lines.

"I think they should be concerned," Bea said. "That doesn't mean panicked, but concerned, so that they turn to the governments that are supposed to be 'of, by and for the people' and say that we expect to have our infrastructure properly maintained and configured so it serves the public interest."

Pipelines are considered the safest way to move large amounts of gas and fuel, but the catastrophic San Bruno blast and fire is forcing pipeline regulators to consider new safety measures.

"The Livermore line is a real concern because it's a major line coming in from the Central Valley," said Rep. John Garamendi, D-Walnut Grove. "PG&E has got to get on with it. "... There is a major infrastructure investment that is going to have to be made."

Garamendi said he would address the San Bruno explosion during a congressional hearing today that was scheduled to examine pipeline safety after a July spill from a pipeline that polluted the Kalamazoo River in Michigan with as much as 1 million gallons of crude oil.

Late Monday, California's top utility regulator ordered PG&E to conduct an expedited inspection of its pipelines and to reduce by 20 percent the pressure of gas in Line 132, which included the segment that exploded in San Bruno, among other measures.

Mike Taugher covers the environment. Contact him at 925-943-8257 or mtaugher@bayareanewsgroup.com.