It belched methane into the sky over Los Angeles for 16 weeks straight until it was finally plugged on February 11. Now, a new study has confirmed what many thought was the case, that the Aliso Canyon gas well blowout was the largest methane leak in U.S. history, releasing over 90,000 tonnes (100,000 tons) of gas into the air. So big was the leak that researchers thought their equipment was faulty when first sampling the site, until they realized that this was actually just a massive event. 
“The methane releases were extraordinarily high, the highest we've seen,” explains Donald Blake, an atmospheric chemist from the University of California, Irvine, who coauthored the new paper published in Science. At its peak the well was leaking an astonishing 60 tonnes (66 tons) of methane per hour, creating the largest known human-caused source of methane in the entire U.S. The overall quantity of the gas being released doubled the methane emissions rate for Los Angeles while it was still flowing.
The researchers conducted flights over the blowout to sample the gas leaking out of the well, as well as sampling the air near the local Porter Ranch residential area. In these regions, they found above average levels of “dangerous compounds” including benzene, toluene, and xylenes. “Some of the volatile organic compounds have been linked to health effects if exposure is long-term,” says Blake. Over 11,000 people had to be evacuated from their homes after the blowout occurred, with many complaining of headaches, nose bleeds, and feeling nauseous.
While carbon dioxide hangs around in the atmosphere for longer, trapping the heat from the Sun and driving climate change, methane is considered by some estimates to be 80 times more powerful at trapping this heat over a 20-year period. At the peak of its four-month run, the blowout was California’s largest single source of greenhouse gas, equivalent to an extra half a million cars on the road, and despite it only being February it already looks like the state will miss its climate change targets for the year.
The disaster has been compared to the Deepwater Horizon oil spill in the Gulf of Mexico in terms of its size and environmental impact. So far, it is estimated to have cost SoCalGas, who operates the well (the fourth largest natural gas storage facility in the U.S.), around $250 million, though this figure is expected to grow significantly as lawsuits filed by the families forced from their homes, and environmental fines from the government, are enacted.
The researchers say that the event highlights the problem of unintended greenhouse gas emissions from natural gas storage and extraction, which is often not considered when looking at how environmentally friendly certain energy sources are. For example, while fracking might produce relatively “green” energy when compared to other fossil fuels, by itself, when taking in account the amount of methane released through extraction, some estimate it is as carbon intensive as other more traditional fossil fuels.
Main image: EARTHWORKS/Flickr CC BY 2.0
Image in text: Location of the gas well (SS25) compared to the residential area of Port Ranch, which had to be evacuated. Stephen Conley/UC Davis
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