A massive natural gas leak at a storage facility in Southern California was caused by microbial corrosion of well equipment, according to a new independent report from analysis firm Blade Energy Partners. The report blames the storage facility owner, Southern California Gas (SoCalGas) for failing to conduct follow-up inspections of equipment, despite knowing about 60 smaller leaks at the facility that had occurred since the 1970s.
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. (A larger loss of methane occurred in 2004 in Texas, but a corresponding fire immediately combusted the methane into carbon dioxide.) But the California leak at the Aliso Canyon Natural Gas Storage Field was particularly devastating because methane, unfortunately, is a far more potent greenhouse gas than carbon dioxide.
The new report (PDF) was commissioned three years earlier to find the root cause of the leak. According to a press release from the California Public Utilities Commission (CPUC), 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.