Drilling for natural gas locked deep in a shale formation has seriously contaminated shallow groundwater supplies  beneath far northeastern Pennsylvania with flammable methane. That’s the conclusion of a new study, published today in the Proceedings of the National Academy of Sciences. The analysis gives few clues, however, to how pervasive such contamination might be across the wide areas of the Northeast United States, Texas, and other states where drilling for shale gas has taken off in recent years.
Problems with shale gas drilling have already gotten attention in less scientifically rigorous arenas. The documentary film Gasland , nominated for an Oscar this year, dramatized the issue by showing a homeowner set fire to well water gushing from a faucet. The implication was that nearby drilling into shale 1000 meters or more deep had somehow unleashed natural gas—mostly methane—that ended up in groundwater less than 100 meters deep. The obvious culprit, in the film at least, was “fracking.” That’s the essential process of pressurizing a wellbore until the shale shatters in innumerable fractures, releasing the tightly bound gas.
So shale gas and fracking were getting plenty of public attention, but environmental scientist Robert Jackson of Duke University in Durham, North Carolina, found it “surprising how little peer-reviewed data there is” on well water contamination near shale gas drilling. So he and three Duke colleagues, including geologist Stephen Osborn, sampled well water across 175 kilometers of far northeast Pennsylvania centered on the town of Dimock, made infamous by Gasland. A few samples were also taken in an area 75 kilometers from Pennsylvania in adjacent New York.
Analyses of 60 wells paint a picture of contamination near active gas wells. Almost all water wells more than a kilometer from an active gas well had only a few parts per million methane in their water. But most wells 1 kilometer or less from a gas well produced water with 19 to 64 parts per million methane. That’s at and above the “action level” of federal safety guidelines for methane, which can displace air’s oxygen to cause asphyxiation. The higher levels are also in the flammable range. “I watched one homeowner light his water on fire,” Jackson says.
Crucially, additional chemical and isotopic analyses in effect “fingerprinted” the well water methane. Those results, the authors say, suggest that the gas from high-methane, close-in water wells was produced in the deep shale. The low-level, background methane from more distant water wells would have come from methane-generating bacteria living in shallow rock.
“There’s a strong indication something’s going on,” says geologist Adam Schoonmaker of Utica College in New York. “I would be concerned.” He would also consider more sampling before and after shale gas drilling over a broader area, as the paper’s authors recommend in a white paper  released today. One concern is that shale gas formations vary greatly one to the next. They extend continuously from upstate New York to Alabama and in patches across Texas and up the Rocky Mountain states to Montana. Each shale formation will have its own distinct geologic setting that could be crucial to the release of gas during drilling and fracking. In response to the many unknowns, U.S. Energy Secretary Steven Chu announced on 5 May the formation of a blue-ribbon panel to recommend ways to improve the safety and environmental performance of shale gas fracking. Any immediate recommendations are due in 90 days.