Line 132 ruptured during hydrostatic testing on a knoll above Highway 280 near Farm Hill Boulevard at about 3:20 p.m., PG&E spokesman David Eisenhauer said.
A preliminary investigation indicated that the section of pipe had been damaged by a backhoe sometime after the line was installed in 1947. PG&E is looking into when that damage might have occurred and what agency might have been responsible, Eisenhauer said.
The explosion left a 5-foot-by-5-foot crater in the hillside, and water from inside the pipeline caused a mudslide that reached northbound Highway 280 and blocked two lanes for about four hours, California Highway Patrol Officer Art Montiel said. No one was injured.
The test was being conducted as part of an ongoing safety evaluation of natural gas transmission lines in "high consequence" or highly populated areas, Eisenhauer said.
"That's exactly why we do these type of safety tests, to find weaknesses in the pipeline," he said.
PG&E crews have conducted pressure tests on more than 120 miles of pipeline since April. Eisenhauer said no homes or buildings were damaged by Sunday's rupture and that the utility employs different testing strategies on pipelines that run directly through neighborhoods, such as placing cameras or "pigs" that run inside the pipes to detect corrosion or faulty seams.
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