(AP) — A utility asked California regulators Tuesday to resume operations at the largest underground gas storage facility in the West a year after a well blowout spewed methane uncontrollably for months and drove thousands of residents from their Los Angeles homes.

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Southern California Gas Co. said about a quarter of its wells at the Aliso Canyon facility had passed rigorous testing ordered by the state in the wake of the disruptive leak that persisted for four months and led to widespread complaints of nausea, nosebleeds, headaches and other vexing symptoms.

The utility request to resume injecting gas into the field — where it is piped into abandoned oil wells more than a mile underground — comes as the utility needs to store gas for winter heating, cooking and electricity needs throughout the greater Los Angeles area.

Before the company can resume storage operations, wells must be inspected, the facility must meet current regulations and state agencies will hold a hearing and take comment from the public. That process is expected to take several weeks.

“Safety is our top priority,” State Oil and Gas Supervisor Ken Harris said in a statement.

“We will thoroughly review all the information and data, conduct independent site inspections, seek public feedback and the opinion of outside experts before making any determination.”

The four-month blowout was the largest-known release of climate-changing methane in U.S. history and led to a federal task force last month recommending dozens of safety changes for the nation’s 400 underground natural gas storage facilities.

It also led to criminal charges against the company for failing to immediately report the leak to state agencies when it was discovered Oct. 23, 2015.

SoCalGas, a division of Sempra Energy, pleaded no contest to a criminal charge and agreed to pay $4 million — most of it in facility improvements such as a leak-monitoring system — in a settlement with prosecutors.

As of late July, the disaster had cost SoCalGas an estimated $717 million, most of that to temporarily relocate about 8,000 families. The company still faces investigations from several local, state and federal agencies, as well as more than 180 lawsuits.

Of the 114 wells in the field that didn’t leak, only 29 have passed tougher tests required to inject gas underground.

The remaining 85 wells are temporarily plugged and will be permanently plugged if they don’t pass state-ordered tests within a year.

All the wells that passed testing had inner metal tubing replaced that is now required to be used for injection and withdrawal of gas in the field.

SoCalGas had been withdrawing and injecting gas using both the inner pipe and an outer steel casing that is designed as a safety barrier. The practice is used in the industry to move larger volumes of gas, but it is considered risky because the outer pipe can corrode or crack, experts said.

The cause of the blowout remains under investigation, but experts who reviewed state records said it appeared the casing failed under high pressure, allowing gas to escape.

Since the leak, SoCalGas has improved the safety, infrastructure and technology at Aliso Canyon, spokesman Chris Gilbride said.

Many residents, environmentalists and others want to see the facility shutdown.