Ten years after the Aliso Canyon natural gas blowout, what’s changed?

Ten years ago today, what became the largest known gas leak in U.S. history was discovered in the foothills of the Santa Susana Mountains above the San Fernando Valley.

The source — one of the 114 underground wells at Southern California Gas Co.’s Aliso Canyon storage facility, the largest in the state. The leak lasted nearly four months.

Natural gas is primarily composed of methane, a powerful greenhouse gas that heats up the planet far more quickly than carbon dioxide. The leak released a quarter of the entire state’s methane emissions in 2015, equivalent to a year of pollution from half a million cars.

Outdoor air monitoring and sampling inside nearby homes during and after the leak also found elevated levels of carcinogens such as benzene, as well as toxic heavy metals.

As the smel