(CNN) -- Investigators only recently were told that a natural gas pipeline that ruptured last year in San Bruno, California, killing eight people, had a leak more than 20 years before, federal officials said Wednesday.
Deborah Hersman, chairwoman of the National Transportation Safety Board, made the disclosure during a visit to the blast site, where she announced new safety recommendations meant to address problems with emergency notification procedures.
"We are glad to see it," Hersman said of the document on the 1988 incident nine miles away from San Bruno, "but we expected to see it sooner."
The information was discovered May 20 during a search of millions of documents by hundreds of employees, PG&E spokesman Brian Swanson told CNN. It was turned over to federal investigators immediately, he said.
"We acknowledged several times that our record-keeping practices are not where they should be," said Swanson, adding the utility has made improvements and will become an industry leader in making records available to assure the public it is operating safely.
According to Swanson, the 1988 incident involved a "trace" leak. Crews replaced a 12-foot pipe section, he said.
Hersman, who said the recent discovery of the PG&E document raises questions about its ability to conduct proper risk assessments, met Wednesday with several affected families.
The massive explosion in the pipeline created a 72-foot long, 26-foot-wide crater, and residents of the San Francisco suburb originally thought an airliner had crashed there. A 28-foot pipe segment was found about 100 feet away from the crater. The blast and fire destroyed 38 homes.
The NTSB expects to release its final report on the probable cause in the next few months. It made several recommendations in January, and announced three more Wednesday.
It recommended PG&E employees call 911 when a possible pipeline rupture is suspected. The NTSB also said the Pipeline and Hazardous Materials Safety Administration should issue similar guidelines to other utilities and companies. And the board recommended PHMSA urge pipeline operators to provide emergency response agencies with details about their systems.
PG&E welcomed the recommendations and has made improvements, Swanson said. Workers in the field are verifying records, making visual inspections and pressure-testing pipelines similar to the one that exploded September 9 in San Bruno, he said.
In April, Transportation Secretary Ray LaHood announced Monday that the Obama administration will push legislation designed to overhaul and upgrade America's aging oil and gas pipeline network.
The initiative is partly a response to a series of deadly pipeline explosions, including the one in San Bruno. A February pipeline explosion in Allentown, Pennsylvania, resulted in the deaths of five people.
San Bruno's faulty pipeline was installed in 1956; Allentown's was installed in 1928.
LaHood called on the major pipeline companies to conduct a review of their oil and gas delivery systems to identify the lines with the highest risk. He also urged them to speed up the most critical repair work.
CNN's Phil Gast contributed to this report.