Sewer Work Eyed in California Gas Pipeline Explosion

The investigation into last week’s <"">San Bruno, California gas pipeline explosion is now focused on work that was performed on a sewer near the ruptured line back in 2008. According to the Los Angeles Times, the method used by the city to replace the sewer line is known to pose risks to nearby pipes.

The explosion, which occurred last Thursday around 6:00 p.m. local time, shot a fireball more than 1,000 feet in the air, and sent fire tearing across several blocks. According to a CNN report, the blast sent concrete flying, and the heat from the flames melted tail lights on cars blocks away from the blaze.

The blast killed at least four people, and three others are missing and presumed dead. About 60 people were injured. Fifty-six homes were either severely damaged or destroyed. The fire damage was estimated at $65 million.

It is not yet known what caused the Pacific Gas & Electric (PG&E) 30-inch pipeline to rupture. Christopher Hart, vice chairman of the National Transportation Safety Board, told the Los Angeles Times that the 2008 sewer project is among the factors investigators are looking at.

The work enlarged the diameter of the sewer pipe from 6 to 10 inches, and used a trenchless “pipe bursting” method that a 2001 study from the US Army Corps of Engineers found the method could potentially disturb, displace and compact soils. If the pipe bursting procedure damages nearby pipes, it usually occurs during the construction work, so the fact that two years passed before the San Bruno accident “diminishes the connection, but it doesn’t eliminate it,” the co-author of that report told the Los Angeles Times. It is possible that the soil could buckle over time.

According to the report, PG&E had inspected its gas line and found no problems after the sewer work

Meanwhile, the Los Angeles Times is also reporting that records released Wednesday showed that PG&E received approval in 2007 to spend $5 million of ratepayer money to replace a high-risk section of the 30-inch pipeline north of the San Bruno blast site, but never performed the work. It asked for another $5 million to do the same job this year.

According to an earlier CNN report, the ruptured line was installed in 1948, and had a “relatively high risk and likelihood of failure,” according to a PG&E document obtained by the network. The document recommended the line be replaced because of its proximity to a populated area. The Wall Street Journal reported that the gas line had an unusual construction, in that it contained a longitudinal seam and numerous welds indicating it had been made from many small segments of steel pipe.

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