California regulators on Thursday confirmed that Southern California Gas Co., a subsidiary of Sempra Energy, had permanently sealed the leaking natural gas well in Aliso Canyon that drove thousands of residents from their homes.

The leak, which began Oct. 23, released methane and chemical additives that add odor to the gas. Those chemicals reportedly have causes nausea, headaches and nosebleeds among residents of nearby Porter Ranch.

The Department of Conservation said tests confirmed that SoCal Gas’ efforts to seal the leaking well with cement were successful on Feb. 17. State investigators are still determining the cause of the leak and whether SoCal Gas violated any regulations, the DOC said. Air quality in Porter Ranch has now returned to normal, according to the California Air Resources Board.

SoCal Gas said relocated residents in short-term housing have eight days to return home, while those in rental housing have until their leases expire.

In a Feb. 11 regulatory filing, Sempra said the relocation of 6,400 residents, sealing the leak, mitigating community impacts and the lost gas would cost $250 million to $300 million. It said four insurance policies would likely cover those expenses, minus a $4 million deductible.