Sempra Energy’s Southern California Gas Co. (SoCalGas) unit announced Friday that it will be sampling the indoor air quality for methane and mercaptans in homes near the Aliso Canyon underground natural gas storage facility that was closed in the aftermath of a four-month storage well leak that ended last month (see Daily GPI, Feb. 18).

Volunteer homeowners were sought last Friday, and sampling was scheduled to begin Monday.

SoCalGas officials said that a sampling of households will be invited to participate in third-party screening to provide reassurances for those Porter Ranch residents returning home after choosing to move from their homes during the prolonged leak that state and local public health officials have concluded poises no long-term health risks. About 20% of the residents in the upscale residential area nearest the storage field chose to move at the utility’s expense (see Daily GPI, March 3).

Outdoor air in the area has returned to typical background levels, according to analysis of more than 3,500 outdoor air samples by independent agencies, a SoCalGas spokesperson said. The new initiative to test indoor air quality is consistent with a request from Mike Antonovich, the Los Angeles County Board of Supervisors member whose district includes Aliso Canyon.

“It is vital that our residents have proper air quality sampling to determine whether their houses are safe and livable,” said Antonovich, who earlier also forced the Sempra Energy gas-only utility to extend the period residents have to give up utility-paid-for housing and return to their homes. As of the end of February, SoCalGas had paid $36 million to cover temporary housing and related expenses for the displaced families (see Daily GPI, March 7), and more than 2,700 households are still in temporary quarters.

The indoor air screening will seek to detect any level of methane or the natural gas odorant mercaptan that is higher than what would typically be expected inside a home, the utility spokesperson said.

The president of the local homeowners association endorsed the SoCalGas plans, noting that families returning home want assurances that everything is safe.

Gillian Wright, SoCalGas vice president for customer services, said the people in Porter Ranch “deserve peace of mind in knowing the air is normal and we are taking action to enable a smooth transition back.” Wright said 75 randomly selected residents will be invited to participate in the indoor air screening.

A third-party contractor will do the work and a California registered professional engineer will oversee the work, which will deploy a flame ionization detector to evaluate any detectable levels of methane, along with Tedlar bags to capture indoor air samples.

Since Oct. 30, seven days after the storage well leak was identified, 3,500 outdoor air samples have been taken in the Porter Ranch area by state, regional and local agencies, including the South Coast Air Quality Management District (SCAQMD), California Air Resources Board (CARB), Los Angeles County Department of Health, and the Office of Environmental Health Hazard Assessment.

Since the leaking well was permanently sealed Feb. 18, CARB and SCAQMD have continued to provide real-time methane monitoring.

Earlier this month returning residents complained about oily film found on and around their homes and vehicles, and two local public parks were also found to have the residue. In response to Antonovich’s concerns, SoCalGas dispatched cleaning crews to take care of the problem. County health officials warned residents not to get the residue on their skin or clothing.

The cleanup effort was complete as of Monday, SoCalGas officials reported.