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|Colonial map of Ohio Valley and surrounding areas. Some researchers claim producing natural gas from shale gas formations can lead to contamination of drinking water. (Fuse/Thinkstock)|
Elevated levels of methane and other stray gases have been found in drinking water near natural gas wells in Pennsylvania's gas-rich Marcellus shale region, according to new research, reports NBC News and other news sources.
In the case of methane, concentrations were six times higher in some drinking water found within one kilometer of drilling operations.
Robert Jackson, an environmental scientist at Duke University in Durham, N.C., told NBC News the just-published research is “strong evidence” that the likeliest explanation for the gas found in drinking water is leaky wells."
Producing natural gas from shale rock formations involves a technique called hydraulic fracturing, or fracking, which shoots several million gallons of water laced with chemicals and sand deep underground to break apart chunks of shale, freeing trapped gas to escape through cracks and fissures into wells.
The technique has unlocked the potential to usher in a new era of energy independence and may serve as a bridge to a clean energy future. But the fast-developing industry has raised a host of environmental concerns, including the potential for drinking water near natural gas wells to become contaminated, according to the NBC News report.
Earlier research from Jackson and his colleagues also found high concentrations of methane near natural gas wells. In this new study, Jackson's team analyzed 141 drinking water samples from private wells across northeastern Pennsylvania.
In addition to the higher methane concentrations, the new study documented higher ethane and propane concentrations. Ethane concentrations were 23 times higher at homes within a kilometer of a shale gas well. Propane was detected in 10 samples, all from wells within one kilometer of drilling.
All the gases appear to be fossil in origin. Jackson said the ethane and propane results support this view as these gases are not generated by microbes that can live in the ground and affect well water.
The researchers also conducted chemical analyses of hydrocarbon and helium that suggest the gas found in some instances comes from leaky steel pipes used in the extraction system.
The methane contamination may be a result of cracks in the cement that surrounds the outside of the steel tubing and serves as a barrier between the rock that is drilled through and the well. An improper cement job, Jackson explained, could permit gas from a pocket at mid-depth to move into the space outside the well, and move up to the drinking water.
The biggest known risk of high methane concentrations in drinking water is an explosion or fire due to the buildup of the gas in a confined space such as a basement or a shed, Jackson noted.
Naturally occurring methane is "ubiquitous" in water wells throughout the study region, Steve Everley, with the natural gas industry group Energy-in-Depth, writes in a blog post that characterizes the study as full of flaws. Chief among them, Everley argues that methane is ubiquitous in the region, and that the Duke University research team found methane in water wells "nowhere near natural gas wells."
The group also notes that the new research does not find evidence of fluids used during fracking in the groundwater.
The new research appears in a paper published online by the Proceedings of the National Academy of Sciences.