San Antonio's ozone levels have violated federal standards dozens of times since the drilling began. Ozone is also one of several greenhouse gases, including methane, released or created through drilling operations. Experts are particularly concerned about methane because it's a powerful greenhouse gas and large-scale leakage could undermine natural gas' reputation as a cleaner alternative to coal.
Even the EPA doesn't know much about methane emissions or the other pollutants from oil and gas production. An inspector general's report last year concluded that the agency's air emissions database is incomplete and "likely underestimates" those emissions. The lack of reliable data, the report said, "hampers EPA's ability to accurately assess risks and air quality impacts from oil and gas production activities."
Environmental groups have tried to collect their own air-quality data in the Eagle Ford, but the process is so expensive and time-consuming that they've had little success.
Last March, Wilma Subra, an environmental consultant from Louisiana, and Sharon Wilson of the advocacy group Earthworks, accompanied Calvin Tillman, who runs a nonprofit called ShaleTest, as he took air samples near Mike and Myra Cerny's one-acre tract, about a half-mile from the Buehrings.
There are at least 17 oil wells within a mile of the Cernys' small house. Their teenage son, Cameron, gets frequent nosebleeds, and the fumes make his parents dizzy, irritable and nauseous. "This crap is killing me and my family," said Mike, a former oil company truck driver. "We went from nice, easy country living to living in a Petri dish."
Myra complained to the TCEQ in 2012, and the agency cited Marathon Oil for operating a broken flare and failing to report thousands of pounds of unauthorized emissions at its Sugarhorn Central gas processing plant. But Marathon paid no penalty. "I feel like we're expendable," Myra said.
The Cernys have sued Marathon, hoping to get enough money to move away from the drilling.
Marathon spokeswoman Lee Warren said in an email that the company "took corrective actions" after receiving the state citation and engaged in "good faith discussions with [the Cernys] to listen to and address their concerns."
Marathon had monitoring done around the family's house in 2012, prior to the filing of the lawsuit, and found "no levels of air contaminants in excess of regulatory limits," Warren wrote. "The TCEQ conducted further visits to the Sugarhorn site in 2013 and has closed out that case."
The air samples the environmental groups took near the Cerny home detected 14 VOCs, including benzene, toluene and xylene, but none in concentrations the TCEQ considers immediately dangerous. Subra said that doesn't mean the air is safe, because the data came from a "grab sample" that represented only a snapshot in time.
She and other scientists say there's another factor that state and federal health guidelines don't consider: the added risks of breathing many chemicals at once.
Guidelines are set for one compound at a time without considering what happens when people are simultaneously exposed to multiple chemicals. To add to the confusion, scientists don't know much about some of the chemicals emitted, and certain proprietary compounds are hidden from public scrutiny.
Neil Carman, who spent 12 years as an investigator with a predecessor to the TCEQ and now works for the Sierra Club, said any of the chemicals could cause illness but they become more pernicious when combined. "What you get is a toxic soup," he said. "I would be very concerned about people living there day after day and getting a semi-continuous toxic exposure."
One way to reduce emissions is to identify and crack down on the worst offenders, said Jackson, the Duke scientist. His research in parts of Pennsylvania's Marcellus Shale has shown that while most of the gas wells have relatively low emissions, a small group—1 percent, 5 percent, or even a tenth of a percent—release an enormous amount of pollutants.
In Texas, however, the fast pace of drilling and the TCEQ's shrinking budget make it difficult to find the culprits.