It’s been a week since the Southern California Gas Company permanently sealed off the leaking natural gas well in Aliso Canyon near Porter Ranch, capping months of methane and other gases spilling into the air.
But just how much was lost?
Researchers from UC Irvine, UC Davis and elsewhere took dozens of air samples over the course of the nearly four month spill, some from the ground and some from a plane flying above the area.
They estimate that all told, the blowout spewed around 100,000 tons of methane into the air, which would make it the nation's single largest release of that gas.
“This was just a huge event,” said study co-author Stephen Conley of Scientific Aviation and UC Davis in a statement.
At its peak, the leak doubled the methane emissions rate for the entire Los Angeles basin. Another way to think of it: on average the well lost enough gas every day to fill a balloon the size of the Rose Bowl.
"A lot of natural gas, I mean the Rose Bowl is a big place," said UC Irvine researcher and co-author Donald Blake.
Methane is a powerful greenhouse gas and the largest contributor to global warming after carbon dioxide. There is plenty of naturally occurring methane in Southern California, some blowing in from the ocean and some coming from farms. Landfills and cars also emit the gas.
Blake estimated that the pollution put out by the gas leak was the equivalent to the annual emissions from half a million vehicles.
That sounds bad, and it is, but there are around 33 million registered vehicles in California alone and our atmosphere is vast. Blake said even a leak this size wasn't large enough to significantly raise background levels of methane around Los Angeles.
Still, he said any unnecessary emissions is a bad thing for the environment, calling it "death by a thousand cuts."
At times during the spill local areas saw a tenfold uptick in the background amount of methane, the study found. Methane is not known to harm humans, but other gases detected during the spill, like benzene, have been linked to long term health problems.
In the readings taken, benzene levels did increase during the spill, but the amount detected was low.
"Amazingly low, I was shocked," Blake said.
Still, he said some pockets of the Porter Ranch community may have experienced higher levels than what appeared in his samples.
Another study from UCI published this week highlighted several recurring methane hotspots throughout the Los Angeles basin, including power plants, water treatment facilities and even a “clean ports” truck refueling facility near the Port of Long Beach.
“Our surveys demonstrate the prevalence of unwanted methane emissions across the Los Angeles urban landscape and show that two-thirds of the gas comes from fossil fuel origins,” said lead author Francesca Hopkins in a written statement.
Still, given the size of the Aliso Canyon spill, California may have trouble meeting its greenhouse gas reduction targets for the year.
The state is asking Southern California Gas Company to pay to offset the pollution. It's unclear how the company will do that.
A spokesperson said the gas company is working on its own calculations of how much gas was lost and doesn't have a comment on the researchers' numbers.
"Until we complete our own calculation of how much gas was lost, we are not in a position to comment on or otherwise confirm the accuracy of any other researcher," a statement read.
The UCI/UC Davis methane study appeared in the journal Science.