When the massive methane gas leak in Aliso Canyon was discovered in California last year, it was quickly projected to be the largest gas leak in U.S. history. Now, a week after the failed well was plugged, new research finds that’s exactly the case.
Through the 112-day leak, the Aliso Canyon Storage Facility — located about 30 miles northwest of downtown Los Angeles — released 97,100 metric tons of methane, creating the largest known human-caused source of methane in the country, according to the study published Thursday in the journal Science. It also doubled the leak rate of all other methane sources in the Los Angeles Basin combined.
At its peak, the leak rate exceeded that of the next largest point source of methane in the U.S. — an underground coal mine in Alabama — by a factor of two, and it was comparable to total emission rates of entire oil and gas production regions in the country. “Aliso Canyon will be, certainly, the biggest single source of the year,” said co-lead author Stephen Conley, a researcher at the University of California Davis and Scientific Aviation, to the Los Angeles Times. “It’s definitely a monster.”
The study establishes the full extent and damage of an unprecedented leak that sickened Los Angeles, prompted the evacuation of 6,000 people and sparked myriad lawsuits. It also raised serious problems for the regional environment, since methane is a greenhouse gas 86 times more potent than carbon dioxide over a 20-year period.
To gather the data, researchers flew a single-engine plane equipped with sensors a total of 13 times from early November — about two weeks after the leak was found — to February 13, just five days before the well was plugged. Through the flights, researchers measured methane and ethane to quantify the atmospheric leak rate and to assess air quality of the leaking well. But aside from methane and ethane, researchers also documented some traces of benzene, toluene and other toxic substances in the invisible plume of gas.
Methane is not associated with long-term health effects in humans, but benzene is carcinogenic, according to the Environmental Protection Agency. These toxic substances, however, came out to just a few parts per trillion for every part-per-million of methane. Researchers told the LA Times that while elevated, these are very low concentrations.
In the last 15 years there have been at least two other major methane leaks in the country. In 2001 gas leaked from an underground storage facility near Hutchinson, Kansas, sparking an explosion and fire which destroyed two downtown buildings and, a day later, blew up a trailer home killing two people. And in 2004, natural gas released after the collapse of an underground storage facility in Moss Bluff, Texas, also caused explosions and evacuations.
The methane leak accident in Texas was technically larger than the Aliso Canyon accident, researchers noted in their study, yet the most recent leak has the largest climate impact. During the Texas leak, the explosions combusted most of the methane, turning it into CO2 and preventing the more potent greenhouse gas from reaching the atmosphere.
Southern California Gas Company, which owns the failed well, has estimated that the leak could cost between $250 to $300 million. Aside from clean-up, relocation costs and civil suits, SoCalGas is looking at criminal charges levied by Los Angeles County for failing to immediately notify state authorities about the leak.