Prior to October 2015, many homeowners in the Porter Ranch neighborhood of Los Angeles were unaware that they lived next door to one of the largest natural gas storage facilities in the nation.  Then the largest methane gas leak in U.S. history happened.   A 61-year-old wellhead, buried 8,500 feet underground at the Southern California Gas Company’s Aliso Canyon storage site cracked.  It began spewing gas into the atmosphere at astonishing pressure and the leak was not contained for three months.

At its peak, the leak of the powerful greenhouse gas spewed the equivalent pollution of 4.5 million cars every day.   The Division of Oil and Gas has confirmed that the leak in the Aliso Canyon storage field has now been permanently sealed.  The news put an end to four months of foul air that sickened many residents and forced thousands of people to relocate to temporary housing far from the leaking well. Crews reached the leak last week and injected heavy fluids and then cement to seal it.

Activists and residents are calling for the permanent closure of all 114 wells at the facility.  Dennis Arriola, president and chief executive of Southern California Gas, said the company would develop a plan to mitigate the damage the leaking well did to the environment and will support “forward-looking” regulations.

“To the residents of Porter Ranch and the surrounding communities, I want to tell you I recognize the disruption that this gas leak has caused to your lives,” Arriola said. “I know there is nothing that I can say that will change the past, but I know that measurable actions actually speak louder than words.”

Residents who moved out of their homes were notified by phone, text and email Thursday morning that they have eight days to vacate their temporary housing that the gas company has been paying for. By early Thursday, residents of 1,800 households had returned to their homes.  An estimated 4,000 reimbursement checks were to be issued on Thursday to residents who incurred expenses related to the gas leak.

As residents return home, attention will turn to the full scope of the damage done to the San Fernando Valley community of 30,000 people.  A major concern of homeowner  are the effects that the worst natural gas leak in U.S. history will have on property values and residents’ long-term health — despite assurance from public officials that the noxious fumes posed no permanent health risks.

The gas company will be required to do a full inspection and testing of the other wells at Aliso Canyon before injections can resume. State authorities will continue to look into the cause of the leak, which was first reported Oct. 23.  The South Coast Air Quality Management District and the California Air Resources Board will continue to monitor the air in the coming weeks, looking at the levels of methane, mercaptans, benzene and hydrogen sulfide.