Southern California Gas Co. says there was a leak at the Aliso Canyon natural gas storage facility during a routine operation to pressurize equipment after maintenance.
In a community alert, the company said the leak occurred about 4:55 p.m. Monday and didn't pose any health risks, though it did produce a noticeable odor.
But Andrew Krowne, a Northridge resident who developed a cellphone application for those within 18 miles of the facility to report health issues, said 34 people reported symptoms including headaches, nosebleeds, and burning of the eyes and throat, the Los Angeles Times reported.
The leak was shut off within about 50 minutes and residents were notified about 7:40 p.m., according to the utility's alert.
Since Krowne's app became available in October, more than 150 users have reported 2,200 symptoms, he said, according to The Times.
The facility is the site of the largest methane leak in U.S. history.
Starting in 2015, a ruptured well spewed tens of thousands of tons of gas, forcing roughly 8,000 families in the northwest San Fernando Valley from their homes. Many complained of health issues that included cancer, nausea and nosebleeds.
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The blowout took more than four months to plug and prompted demands from residents and elected officials that the facility be shut down.