Wintertime ozone is just one surprising air-quality problem that has appeared as gas fields balloon in size and creep closer to communities. "It's possible that emissions have been there all along," since the industry isn't new, says Ramón Alvarez, an Environmental Defense Fund air-quality expert. But with drilling under increasing scrutiny, he says, "People are appropriately wondering, 'What does this mean for my health?' "
The answer remains largely unknown. "To determine a health effect, you need a large number of exposures occurring, and for them to occur over a long enough time for people to develop an effect," says Alvarez. "When you're in a rural environment, those things are hard to match up."
Still, researchers are trying to get a handle on health risks. A study by the Colorado School of Public Health found that the risk of cancer and other illnesses in Garfield County, Colo., was greatest for residents within a half-mile of wells, where volatile organic compounds around homes were documented at five times safe levels.
Another important question concerns the industry's carbon footprint. This year, emissions of methane -- a powerful greenhouse gas -- from Colorado's Denver-Julesburg Basin were found to be about twice as high as the industry had reported, raising doubts over whether natural gas truly is a more climate-friendly fuel than coal.