Biggest US Gas Leak Followed Years of Problems, State Says

Construction continues on one of many local gated communities as people continue to be affected by a massive natural-gas leak in the Porter Ranch neighborhood of the of the San Fernando Valley region of Los Angeles, Calif., on Dec. 22, 2015. David Mcnew/AFP/Getty Images

The worst natural gas leak in U.S. history, which broke out at a Sempra Energy storage field near Los Angeles almost four years ago, was caused by corrosion, according to a report commissioned by California regulators.

The rupture of a 7-inch (18-centimeter) well casing at Sempra Energy’s Aliso Canyon storage complex was due to “microbial corrosion” brought on by contact with groundwater, an independent analysis conducted by Blade Energy Partners and commissioned by two state agencies found.