An old memo, recently revealed by PG&E, indicates the company had noted weld defects on the same line that exploded in San Bruno, more than two decades before the fatal blast.
According to the San Francisco Chronicle, PG&E said the 1989 memo, found during a search of 11 million documents, summarized an investigation into a leak about 9 miles south of where the 2010 explosion occurred -- an explosion that killed eight people and destroyed 38 homes.
Both state and federal investigations into the explosion have been completed, but PG&E said it only recently found the memo and turned it over to pipeline regulators last month.
The memo said a PG&E investigation determined the likely cause of the October 1988 leak was a defective seam weld: the same problem that contributed to the San Bruno blast.
PG&E said the findings of the 1989 leak investigation were not definitive, and therefore did not require it to test the entire 51-mile-long pipeline.
Federal investigators have determined that the segment of the line that exploded in 2010 had a defective weld that dated back to 1956, when it was installed. If the company had done pipeline-wide testing after the 1988 leak, it may have discovered this defect.
Pipeline safety experts said the fact that the company just turned over this document to the state raises questions about PG&E's record keeping and safety practices, the newspaper reports.
"If you have seam weld risk of this magnitude, you have to assess it - that means a hydro test," Richard Kuprewicz, a pipeline safety consultant, told the Chronicle.