May 17, 2021

California Environmental Protection Agency Air Resources Board

On October 23, 2015, Southern California Gas (SoCalGas) informed the State of a natural gas leak at its Aliso Canyon natural gas storage facility. Natural Gas is composed primarily of methane which is a potent greenhouse gas. Methane is in a category of greenhouse gases known as short-lived climate pollutants. These types of gases remain in the atmosphere much shorter than longer-lived climate pollutants, such as carbon dioxide (CO2); but when measured in terms of how they heat the atmosphere, their impacts can be tens, hundreds, or even thousands of times greater than that of carbon dioxide. In order to quantify the methane release rate from the Aliso Canyon gas leak, state agencies in collaboration with the research community are collecting measurements near the ground at the well site, and from towers, airplanes and satellites.

A complete calculation of the total methane emitted from Aliso Canyon based on a full set of data and an assessment of any changes in methane release rate over the duration of the leak will take several months to complete. In the interim, periodic updates on measurements and associated emission estimates have been posted to keep stakeholders informed. The preliminary measurements suggest a total of 94, 500 tons of methane was released from the leak.

On February 11, 2016 SoCalGas temporarily controlled the leak by injecting mud from a relief well intersecting the bottom of the leaking well. Gaining control of the leak has drastically reduced the amount of leaking methane. A permanent seal of the well was announced by The Department of Conservation, Division of Oil, Gas, and Geothermal Resources (DOGGR) on . Since the well was controlled the methane levels in the community has been drastically reduced (see graph below). ARB and the South Coast Air Quality Management District (SCAQMD) are jointly making ground level measurements around the sealed well to understand how residual methane still in the soil after the well has been sealed continues off gassing releasing small amounts of methane into the atmosphere. SCAQMD is posting maps of mobile surveys (external site) done at the Aliso Canyon natural gas storage facility. Infrared (IR) camera videos are also able to see very small amounts of methane off gassing. These small amounts seen with IR cameras very near the surface surrounding the SoCalGas well site SS-25, are consistent with off gassing of natural gas from the soil. ARB and SCAQMD will continue to monitor the off gassing methane.

ARB is providing additional information at the following links:

Aliso Canyon Climate Impacts Mitigation Program

Pursuant to the Governor's Proclamation of January 6, 2016, ARB has developed a Climate Impacts Mitigation Program to mitigate the methane emissions from the Aliso Canyon natural gas leak.