The SS-25 natural gas well in Aliso Canyon, the source of the October 2015 gas leak. | Wikimedia Commons/ Scott L/ CC BY-SA 2.0
A new study provides one of the first quantitative estimates of the methane leak rate from the blowout of a natural gas well in California in 2015, suggesting that emissions from this event temporarily doubled those from all other sources in the entire Los Angeles Basin, including landfills, dairies, and other leaks.
"The magnitude of the event really surprised me," said lead author Stephen Conley, president of Boulder-based Scientific Aviation and an atmospheric scientist at University of California, Davis. "It was 20 times larger than any leak I had ever seen before."
Its impact on climate, the authors say, will be equivalent to the effect of the annual greenhouse gas emissions from over half a million cars. What's more, the disaster will substantially affect California's ability to meet greenhouse gas emission targets for the year, the researchers noted.
The blowout spewed more than 100,000 tons of methane to the atmosphere, the study in the 26 February issue of Science reports, making it the biggest methane leak from anthropogenic sources in the United States. "Some might argue that the underground storage facility in Moss Bluff, Texas, released more methane," Conley said, referring to a 2004 event, "but methane there was mostly consumed in the fire, so very little of it was actually released to the atmosphere."
Globally, underground natural gas storage facilities hold reserves representing 10% of the world's annual gas consumption. On 23 October 2015, when a blowout occurred at a well connected to the Aliso Canyon underground storage facility outside Los Angeles — the fourth largest facility of its kind in the U.S. — a substantial amount of natural gas was released. This prompted evacuations of more than 11,000 residents in the nearby San Fernando Valley. In January 2016, Governor Jerry Brown declared a state of emergency.
In the days that followed, using airborne and surface measurements at and around the blowout site, Conley and colleagues quantified the gas release to the atmosphere.
View of Well SS-25 and the town of Porter Ranch, taken from an aircraft measuring methane and ethane emissions. | Stephen Conley
Conley had the airborne estimates as early as two weeks after the leak sprung. He explained how he was able to mobilize so quickly. "My company has two dedicated research aircraft — always ready on a moment's notice," he said. "When the initial call came in, I was at the airport preparing to conduct a research flight for the California Energy Commission, part of an effort with UC Davis to search for pipeline gas leaks."
But Conley quickly changed gears and flew over Aliso Canyon.
Processed natural gas is composed primarily of methane, a powerful greenhouse gas, and ethane. As part of this work, Conley and colleagues analyzed methane and ethane data from 13 research aircraft flights between 7 November 2015 and 13 February 2016 — two days after the leak was finally plugged.
During the flights, Conley tracked atmospheric data in real time. At first he thought something was wrong with the instruments on his plane because he'd never seen measurements so large.
Using his measurements and those from land-based efforts, he and his coauthors suggest that atmospheric leak rates from the blowout were up to 66 tons of methane and 4.9 tons of ethane per hour at times.
The researchers' analysis included finding above-normal levels of several potentially dangerous compounds present in natural gas, including benzene, toluene, and xylenes. "Some of the volatile organic compounds have been linked to health effects if exposure is long-term," said co-author Donald Blake, an atmospheric chemist at University of California, Irvine.
Their report emphasizes the utility of rapid-response airborne chemical sampling in providing leak rate data, and it reveals how single vulnerabilities in the natural gas infrastructure can impact local and federal climate policies.