California attorney general sues gas company over 'unprecedented' methane leak
Porter Ranch residents Danielle Michaels (L) and Michelle Theriault (R) hold signs outside Los Angeles City Hall during a demonstration ahead of the testimony before the Los Angeles City Council on the ongoing natural gas leak in the Porter Ranch area of Los Angeles, California December 1, 2015. REUTERS/Gus Ruelas

California's attorney general sued Southern California Gas Co on Tuesday over a huge methane leak near Los Angeles, escalating legal action sparked by an underground pipeline rupture that has forced thousands of residents from their homes since October.

The latest civil complaint accuses the utility, a division of San Diego-based Sempra Energy of violating state health and safety laws by failing to promptly control the escaping gas and report the leak to authorities.

The lawsuit also cites environmental damage caused by the uncontrolled release of 80,000 metric tons of methane, the prime component of natural gas and a far more potent greenhouse gas than carbon dioxide.

The leak stems from an underground pipeline rupture at the company's 3,600-acre (1,457-hectare) Aliso Canyon natural gas storage field. The largest such leak ever in California, at its height it accounted for a fourth of all methane emissions statewide.

"The impact of this unprecedented gas leak is devastating to families in our state, our environment and our efforts to combat global warming," Attorney General Kamala Harris said.

The lawsuit in Los Angeles County Superior Court amends a civil complaint brought in December by the Los Angeles city attorney and later joined by Los Angeles County. It seeks unspecified civil penalties and court orders requiring the utility to immediately take all steps necessary to mitigate the leak, repair the damage and prevent future discharges.

Several attempts to halt the methane release have failed, but the company said it hopes to finally plug the leak by the end of the month through a relief well now being drilled.

"We are working hard to both stop the leak and to address our neighbors' concerns," the company said in a statement, adding it would "respond to the lawsuit "through the judicial process."

Last week, the South Coast Air Quality Management District filed a separate suit against SoCal Gas seeking civil penalties of up to $250,000 a day for each of six pollution-related health and safety code violations.

The stench of methane fumes has sickened scores of people and was prompting the relocation of more than 6,600 households from the Porter Ranch community at the edge of the crippled underground gas storage field.

More than 20 private lawsuits have been filed on behalf of some of those residents.

The company also has accelerated the withdrawal of surplus gas supplies stored beneath the site to diminish underground pressure on the ruptured well pipe.

(Reporting and writing by Steve Gorman; Additional reporting by Dan Levine in San Francisco and Brendan Pierson in New York; Editing by David Gregorio and Tom Brown)