Natural gas was discovered leaking in 38 places, including from high-pressure pipelines, during the first phase of a Pacific Gas and Electric Company inspection program ordered after the San Bruno explosion and fire.
The company also discovered a section of pipeline casing that might be damaged beneath Highway 101 in San Bruno.
Gas escaping from a 30-inch-wide gas transmission pipeline beneath San Bruno ignited Sept. 9, causing an explosion and fire that killed eight people, federal investigators found. It was the company’s 10th pipeline accident this year.
The cause of the leak has not been determined but investigators found that pipeline pressure spiked slightly before the blast.
After the disaster, the California Public Utilities Commission ordered the utility company to take a number of safety-related measures, including assessing its pipelines in the San Bruno area and surveying its entire gas transmission network.
On Monday, PG&E provided the CPUC with the preliminary results of its survey work and other documents.
Gas was discovered leaking from transmission pipelines beneath the Northern California cities of Hollister, Gridley, American Canyon and Napa, PG&E reported.
Transmission pipelines are wide pipes that carry large amounts of gas from one area to another.
The leaks were repaired either by replacing a pipeline segment, tightening pipeline bolts or greasing a pipeline valve.
Click on the markers to see details from PG&E's report for each location.
Another 34 leaks were discovered and repaired in gas distribution lines and other smaller pipelines operated by the company.
The inspection work is expected to be finished by Dec. 15.
Mindy Spatt, spokeswoman for the nonprofit watchdog group The Utility Reform Network, said PG&E should not have waited for the San Bruno disaster to undertake the inspection work.
“We’re wondering, ‘Why did it take this tragedy to alert them to the fact that they had 38 leaks?’” she said. “They’ve had the money to inspect these lines and repair them, so we’re wondering why these leaks were left for so long.”
During special San Bruno area inspections, PG&E surveyed 16 miles of pipeline and discovered one potential problem: A section of transmission pipeline passing beneath Highway 101 might have come into contact with its casing.
Non-pressurized casings are used to surround and protect pipelines as they cross railway lines, streets and other rights-of-way.
“PG&E will excavate the area immediately surrounding the detected casing/pipeline contact, conduct a visual examination to confirm contact, and take remedial actions if necessary,” Brian Cherry, vice president for regulatory relations at PG&E, wrote in the report.
Also on Monday, PG&E told the CPUC that it had identified 300 manual gas transmission valves that could be replaced with automatic valves in 565 miles of pipeline passing beneath populated areas.
The San Bruno fire was fueled after the explosion with enough compressed natural gas to fill the Louisiana Superdome, because PG&E took 89 minutes to close manual pipeline valves at either side of the blast site.
The massive gas-fueled fire led lawmakers and regulators to call on PG&E to install automatic valves, which can be remotely opened and closed, throughout its gas distribution network.
The 300 automatic valves would cost between $100,000 and $1.5 million each to install, the company found.
The cost to install automatic valves would likely be paid by PG&E’s natural gas customers through increased rates.