Investigators in southern California said they're focusing their efforts on the causes behind a methane leak now that a faulty well is sealed.

California regulators and the Southern California Gas Co. said a faulty well at the Aliso Canyon storage facility was permanently sealed with cement and taken out of service.

"Now that California Division of Oil, Gas and Geothermal Resources has confirmed that the well is permanently sealed, the operations focus will shift to determining the cause of the leak," Dennis V. Arriola, the top executive at the California utility company said in a statement.

SoCalGas workers started drilling a relief well to stem the leak in late January and temporarily stemmed the flow of natural gas last week. State authorities said the leak appeared to be the result of damage to well infrastructure located about 500 feet underground.

Methane is a non-toxic greenhouse gas that's more potent than carbon dioxide. California Gov. Jerry Brown in 2015 signed an executive order to reduce greenhouse gas emissions by 40 percent from their 1990 levels by 2030, which the government is the most ambitious target in North America.

Other gases associated with the mix may contain chemicals linked to cancer risks.

The site near Los Angeles has been leaking since late October. Residents in the area were forced to relocate to temporary housing while state, federal and SoCalGas officials worked to control the leak.

"While the leak has been stopped and the well permanently sealed, we have much work to do, partnering with state and local agencies to help the local community and impacted residents return to normal," Arriola said.