California methane leak 'permanently sealed'
A leaking gas well near the US city of Los Angeles which has been polluting the air for four months has been "permanently sealed," officials say.
The Southern California Gas Company (SoCal Gas) had been pumping in heavy fluids and cement to seal the well.
The leak began in October in a vast underground storage field in Porter Ranch, on the outskirts of Los Angeles.
The natural gas leak, one of the largest in US history, has caused thousands to relocate.
The escaping gas at the Aliso Canyon storage field accounted for a fifth of all methane emissions - an extremely potent greenhouse gas - across the entire state of California.
"This has been among the worst environmental catastrophes in recent history," said Robin Greenwald, a senior attorney with Weitz & Luxenberg, a law firm which is taking legal action on behalf of some Porter Ranch residents.
"The public health crisis it caused is far from over," said Ms Greenwald, arguing that her clients still did not know if it was safe to return to their homes.
They were uncertain about the safety of the 114 other wells on the site and had not been given "assurances that the interior of their homes are safe," she said.
"The lack of transparency by all those involved is inexcusable."
Analysis - James Cook, BBC News, Los Angeles
The leak may be over but the blame game has only just begun. SoCal Gas and its regulators are squabbling over who was responsible for the catastrophic failure at Aliso Canyon.
The company insists it acted in accordance with the law. The state of California disagrees (although it has admitted that regulations might need tightening) and the battle is playing out in the courts.
Many residents of Porter Ranch and neighbouring communities, literally sick of the whole affair, think both sides are at fault, accusing them of an "incestuous" relationship. They have many outstanding questions.
What are the long-term health impacts of exposure to the gas? Will residents be compensated adequately for the nightmare of the past four months? Will SoCal Gas be allowed to continue operating the facility or will it be shut down?
There are questions too for the United States as a whole.
With gas in California's air and lead in Michigan's water, crumbling infrastructure and weak regulation are putting people at risk across the country, say environmental campaigners.
Action is needed at a national level, they argue, or the disasters will just keep happening.
Last week a crew from SoCal Gas injected heavy fluids into the well - in the Santa Susana mountains around a mile from the nearest homes - before pumping in cement to make a seal.
The gas company on Wednesday pleaded not guilty to criminal charges for allegedly waiting three days to report the huge leak back in October.
The latest estimate for the amount of methane emitted from the leaking well, taken on 13 February, is 94,067,040kg (94,100 metric tonnes), according to the California Air Resources Board.
Spokesman Stanley Young told the BBC this meant that during the leak California's entire emissions of methane rose "by roughly 20%", pushing up the state's total annual methane emissions by around 6%.
Mr Young said final figures for the amount of gas emitted would not be known for several weeks.
Aliso Canyon is a 3,600 acre site comprising 115 wells and is the second largest such facility in the US.
In early January, the company apologised but said it was not responsible for what environmental groups say is an environmental catastrophe.
Many living close to the site had been complaining of nausea, headaches and other symptoms. Environmental campaigner Erin Brockovich described it as the worst environmental disaster in the US since 2010.