LOS ANGELES — The utility whose leaking natural gas well has driven thousands of Los Angeles residents from their homes has publicly understated the number of times airborne levels of the cancer-causing chemical benzene have spiked over the past three months, the company’s own data suggests.
In trying to reassure the public there’s no long-term health risk from the leak, Southern California Gas Co. has said in news releases and FAQs on its website that since the crisis began, just two air samples briefly showed elevated concentrations of the substance.
But a closer look at the online data by The Associated Press and outside experts actually shows that a dozen samples from the Porter Ranch community contained at least twice the amount of benzene that Southern California air regulators consider the normal background level.
The possible reason for the discrepancy: SoCalGas apparently uses a different background level.
The company was given repeated opportunities to explain its conclusions but couldn’t.
“I don’t know what would explain it,” spokeswoman Melissa Bailey said.
Public health officials have sided with SoCalGas in saying they do not anticipate any long-term health problems. But some outside experts say the data is too scant to say that with any certainty. For one thing, it is unclear whether the benzene persisted long enough to exceed state exposure limits.
Seth Shonkoff, executive director of the energy science and policy institute at University of California, Berkeley, said he is surprised officials were so quick to discount the health risks.
“I have not seen anything convincing that it’s been proven to be safe,” Shonkoff said. “I’m not going on record as saying this is absolutely an unsafe situation; I’m saying there are a number of red flags.”
The leak at the biggest natural gas storage facility west of the Mississippi River was reported Oct. 23. The cause is unknown, but the leak has spewed huge amounts of methane, a potent greenhouse gas, and occasionally blanketed neighborhoods about a mile away with a sickening rotten-egg odor.
SoCalGas has run up more than $50 million in costs so far in trying to contain the leak and relocate families. Gov. Jerry Brown has declared an emergency, and some environmentalists are calling it the worst environmental disaster since the BP oil spill in the Gulf of Mexico in 2010.
Health officials and SoCalGas have said most of the gas has dissipated, though the odor from the chemical additive that makes the gas detectable is blamed for nausea, headaches and nosebleeds.
Natural gas also contains smaller amounts of other compounds, such as benzene, which is of greatest concern because it causes cancer as well as anemia and other blood disorders.
In the Los Angeles area, benzene is typically detected in minuscule levels between 0.1 and 0.5 parts per billion, according to the South Coast Air Quality Management District. But SoCalGas says on its website that typical community levels are 2 parts per billion.
Apparently relying on that standard, SoCalGas said that benzene was found in amounts slightly higher than background levels in just two samples, both on Nov. 10, and returned to normal the next day. The suspect readings were 5.6 parts per billion in one gated development near the facility and 3.7 parts per billion in the Porter Ranch Estates neighborhood of 1,100 homes.
However, a more detailed look at the data shows 10 other instances over seven days in November when benzene exceeded 1 part per billion. The clean-air agency also detected a reading of 3 parts per billion on Oct. 26.
Dr. Cyrus Rangan, a medical toxicologist from the Los Angeles County Department of Public Health, said the gas company’s website was incorrect.
“Don’t take cues from the gas company website of where the monitoring is and what the health risk is,” Rangan said.
The World Health Organization and U.S. government classify benzene as an undisputed cause of leukemia and other cancers. “No safe level of exposure can be recommended,” according to WHO.
California’s Office of Environmental Health Hazard Assessment in 2014 set a series of limits for the amount of benzene people could be exposed to without risking anemia and other noncancerous disorders.
Those limits are 8 parts per billion for a one-time exposure, 1 part per billion for repeated exposures for eight hours at a stretch, and 1 part per billion for several years or a lifetime.
Michael Jerrett, chairman of the environmental health department at the University of California, Los Angeles, said that because of the limited testing done by SoCalGas early on, it is impossible to know for sure whether there was repeated exposure in parts of the community. He said he believes there is a “high probability” the eight-hour standard was violated.
One problem with the testing is that it was done over very short periods that can indicate spikes but can’t provide meaningful data on long-term exposure.
Rangan, the county toxicologist, said it is unlikely state safety levels were exceeded because spot testing didn’t turn up a larger, more consistent pattern of such readings.
“You can’t take a 10-minute sample that’s 5.6 parts per billion and make any long-term risk assessment,” Rangan said. “If that was sustained over several months in a row, I’d be concerned about that, but we know that’s not happening.”
More comprehensive testing is underway. Not as much gas is being released because the pressure inside the field has subsided as the volume has dropped.
Since Dec. 21, the air district has been taking samples around the clock, and all but one showed benzene at 0.1 parts per billion, said spokesman Sam Atwood. One sample was 0.2 parts per billion.
The health department began more extensive testing at six sites on Monday and plans to add three more.
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