The company said about 4.5 miles of natural gas pipelines in the state were declared safe. It was later discovered, however, that the lines "may not have undergone proper integrity management assessments," the San Francisco Chronicle reports.
The newspaper notes that the company said those sections of pipeline were considered at risk of corrosion failures but cited faulty record-keeping for the testing oversight.
"PG&E took steps to ensure that this issue does not exist elsewhere in the system or occur again," a company statement read. "PG&E believes this issue does not exist elsewhere in the system."
A natural gas pipeline operated by PG&E exploded Sept. 9, 2010, in San Bruno, Calif., killing eight people and damaging 38 homes.
The National Transportation Safety Board said PG&E didn't know what kind of pipe was beneath San Bruno. A defective weld seam on the pipeline was blamed for the explosion.