Aliso Canyon methane leak 6. (credit: Earthworks / Flickr) 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.