California Air Resources Board

SACRAMENTO - State and local air quality officials today announced criteria for determining whether air contaminants in Porter Ranch and surrounding communities have returned to typical levels prior to the massive natural gas leak from the nearby SoCalGas Aliso Canyon natural gas storage facility.

The South Coast Air Quality Management District (SCAQMD) and the California Air Resources Board (CARB) – two agencies that have been monitoring air quality in Porter Ranch since late October -- jointly developed the criteria.

“This will help assure residents that the massive leak from the Aliso Canyon gas storage facility is no longer affecting air quality in their community,” said Barry Wallerstein, SCAQMD’s executive officer. “We are committed to continuing our intensive air monitoring efforts in and around Porter Ranch for an extended period of time to provide the community with specific information regarding their air quality.”
“The California Air Resources Board is committed to continuing to make available to Aliso Canyon area residents comprehensive monitoring data about the air quality around their homes,” said CARB Executive Officer Richard Corey. “We are also working to ensure that Southern California Gas fully mitigates the climate impact from the leak.”

SCAQMD and CARB officials recommend that the air quality criteria be met for a period of consecutive days before residents return home.
The air quality criteria include four pollutants of chief concern from the leak: methane, mercaptans, benzene and hydrogen sulfide. If any measurements exceed the thresholds set in the criteria, air quality officials will determine whether it is due to the Aliso Canyon facility gas leak or another unrelated source of emissions.

The full air quality criteria are posted to http://www.aqmd.gov/home/regulations/compliance/aliso-canyon-update.
In addition to monitored air quality levels, SCAQMD and CARB will use infrared cameras and aircraft measurements to confirm that well SS-25 is no longer leaking natural gas.

Methane is not considered toxic to humans but is a potent greenhouse gas. Mercaptans and hydrogen sulfide can cause foul odors at extremely low levels and can result in short-term symptoms including headaches and nausea. Benzene is a known cancer-causing compound, although levels measured by air quality officials since the leak started are in the same range or lower than levels found in other areas of the Los Angeles Basin.

SCAQMD and CARB have been operating eight monitoring stations in Porter Ranch for months and will continue to run monitoring equipment for a period after residents return home to ensure that air quality remains at typical levels prior to the gas leak.

The current monitoring stations include dozens of instruments for measuring methane and benzene in real time; equipment to capture samples for analysis of dozens of volatile organic compounds including benzene, as well as analysis for sulfur compounds including hydrogen sulfide and mercaptans. Mercaptans are added to natural gas as odorants so gas leaks can be readily detected. In addition SCAQMD will continue to operate an SUV equipped with a real-time methane monitor throughout Porter Ranch and nearby communities.
On Feb. 11, SoCalGas announced that it had temporarily stopped the leak from its SS-25 well after it had continuously leaked large amounts of methane and other gases for more than 3 ½ months. The concentrations of methane measured by SCAQMD and CARB, both off-site in the Porter Ranch and surrounding communities, and on-site within the Aliso Canyon facility have significantly decreased since Feb. 11.

The well that leaked is one of 115 in the company’s Aliso Canyon underground natural gas storage facility -- one of the largest in the country with a working capacity of more than 86 billion cubic feet of natural gas. The working capacity of the gas has been reduced down to about 15 billion cubic feet due to the leak from the SS-25 well as well as a continuous withdrawal of natural gas by SoCalGas for use by customers.

Last month, based on a petition filed by SCAQMD, the SCAQMD’s independent Hearing Board adopted an Order for Abatement requiring several actions by SoCalGas to protect public health, including an enhanced leak detection and reporting program for all wells at its Aliso Canyon site, and an independent health study of potential health effects to residents from exposure to the leaking gas.
SCAQMD’s air monitoring, enforcement, health impact estimates and other activities regarding Aliso Canyon are reported on its website at http://www.aqmd.gov/home/regulations/compliance/aliso-canyon-update.

CARB’s Aliso Canyon information is at http://www.arb.ca.gov/research/aliso_canyon_natural_gas_leak.htm.
The SCAQMD is the air pollution control agency for Orange County and major portions of Los Angeles, San Bernardino and Riverside counties.

ARB’s mission is to promote and protect public health, welfare, and ecological resources through effective reduction of air pollutants while recognizing and considering effects on the economy. The ARB oversees all air pollution control efforts in California to attain and maintain health based air quality standard