Citing the threat of earthquakes, Los Angeles County on Wednesday filed a lawsuit against state regulators to force them to keep closed California’s largest underground natural gas storage facility at Aliso Canyon.

County and city health and fire officials increasingly have beenexpressing concerns about Southern California Gas Co.’s (SoCalGas) 86 Bcf capacity, 3,600-acre facility. Theprolonged storage well leak that spewed large amounts of methane for four months last year has still not had its root cause identified by state authorities, they contend.

LA County’s lawsuit now accuses the state Department of Conservation’s Division of Oil, Gas and Geothermal Resources of ending a safety review without knowing the seismic risk of SoCalGas’ Aliso Canyon facility.

A spokesperson for SoCalGas dismissed the latest legal action, noting that the Sempra Energy utility has met the state’s comprehensive safety review requirements. She lamented any more “unnecessary delays” in resuming injections at the state’s largest storage facility.

Since 2006, the county alleges that 16 quakes have occurred at Aliso Canyon, ranging in magnitude from 2.0 to 4.7 on the Richter Scale. They said that the Santa Susana fault with the Sierra Madre fault zone runs directly underneath and next to the SoCalGas storage field, which is located in the Santa Susana Mountains.

Past designations by the state have indicated concerns about earthquakes in the area, according to the county lawsuit.

Citing, a web and mobile app that estimates seismic hazards and claims to help identify steps to lower quake risks, the county said its “hazard rank” for Aliso Canyon is 81 and Temblor’s Global Earthquake Activity Rate model forecasts a quake magnitude in the 6.5-6.75 magnitude is likely for Aliso Canyon in the span of an average person’s current lifetime.

“Such an earthquake could cause significant damage to the gas storage facility and result in the release of natural gas,” according to Temblor’s David Jacobson, writing on the app’s blog.

The SoCalGas spokesperson noted that “according to a federal report, the leak occurred in the outer casing of the SS-25 well. Regardless of what the root cause analysis finds, the state’s Comprehensive Safety Review has already demonstrated that the outer casings of every well approved for use are safe.

“Moreover, under new regulations, gas will no longer flow through the outer casing. Gas will only flow through newly installed and pressure-tested, inner steel tubing. The outer casing will now serve only as a secondary layer of protection.

“Unnecessary delays in resuming injections needlessly puts more than 20 million people and thousands of businesses and critical facilities at risk of natural gas and electricity service interruptions.”