Southern California air quality regulators have issued a violation notice against the Southern California Gas Co. (SoCalGas) Aliso Canyon underground natural gas storage facility north of Los Angeles, alleging that a leak that lasted about 50 minutes last week at the 3,600-acre facility caused a public nuisance for nearby Porter Ranch residents.

SoCalGas late on Dec. 18 in a community notification said there was an “unplanned” gas release during a routine operation to pressurize equipment following maintenance.

The South Coast Air Quality Management District (SCAQMD) received 15 odor complaints from residents of the upscale Porter Ranch residential community that is about one mile south of the 86 Bcf capacity storage field, the state’s largest.

SCAQMD Executive Officer Wayne Nastri said the Sempra Energy utility and all the facilities in its four-county territory “have an obligation to protect residents from foul odors.”

One of the continuous methane monitors at Aliso Canyon on its fence line measured peak concentrations of 66 parts per million (ppm), which SCAQMD said was more than 30 times the typical background methane concentration of 2 ppm.

The notice to SoCalGas requires the utility to provide by Tuesday (Dec. 26) all fence line monitoring data during the day of the leak.

SCAQMD said since last January SoCalGas has been cited with nine violation notices at various locations around Southern California. Two violations were for causing a public nuisance and the other seven were for violating various district rules and regulations.

SoCalGas said the equipment involved in the methane leak is used in the dehydration process that removes water from natural gas. A flange gasket on the equipment did not function properly, causing the release that was stopped within an hour and did not present a health or safety risk to the community, according to the utility.

Since the prolonged leak at Aliso Canyon that began in October 2015, Porter Ranch residents, environmental groups and elected officials have urged the state to close the storage facility, which sits in a former oilfield in the Santa Susana Mountains.

Meanwhile, Save Porter Ranch and Food & Water Watch last week staged protests near the Aliso Canyon entrance to demand that the California Public Utilities Commission (CPUC) investigate whether SoCalGas isdeliberately manipulating winter gas supplies to force increased operations at the facility, whose use has been tightly restricted the past two years.

Aliso Canyon and the state’s other 11 underground gas storage facilities have been under close scrutiny by state legislators and regulators.

SCAQMD, the CPUC and the Division of Oil, Gas and Geothermal Resources have placed numerous requirements on the SoCalGas facility in terms of testing, upgrading, monitoring and operational restrictions.