May 25, 2019

The Aliso Canyon gas leak was a massive natural gas leak that was discovered by SoCalGas employees on October 23, 2015. Gas was escaping from a well within the Aliso Canyon’s underground storage facility in the Santa Susana Mountains near Porter Ranch, Los Angeles. This second-largest gas storage facility of its kind in the United States belongs to the Southern California Gas Company, a subsidiary of Sempra Energy. On January 6, 2016, Governor Jerry Brown issued a state of emergency. The Aliso gas leak’s carbon footprint is said to be larger than the Deepwater Horizon leak in the Gulf of Mexico. On February 11, 2016, the gas company reported that it had the leak under control. On February 18, 2016, state officials announced that the leak was permanently plugged.
The final leak—which spewed 109,000 metric tons of methane into the air over five months between 2015 and 2016—was the biggest methane leak in US history.
It was widely reported to have been the worst single natural gas leak in U.S. history in terms of its environmental impact.
According to a press release from the California Public Utilities Commission, Blade Energy Partners found that the leak came from a seven-inch outer well casing which had corroded due to exposure to microbes from groundwater. The natural gas storage facility at Aliso Canyon is made up of dozens of vast underground caverns which were previously filled with oil before they were pumped and emptied decades ago. Since then, the caverns have been used to store natural gas to supply the Southern California area.
The indirect cause of the leak, according to Blade, was a failure on the part of SoCal Gas to conduct detailed inspections of the well equipment. “Blade identified more than 60 casing leaks at Aliso Canyon before the October 2015 incident going back to the 1970s, but no failure investigations were conducted by SoCalGas,” the CPUC wrote. The company also failed to do any risk assessment focused on well failure.
(Source: nbc Los Angeles Wikipedia/ARS technical – Aliso Canyon blow out/PBS)