DRINKING WATER AND SHALE GAS EXTRACTION: EVIDENCE FOR WATER CONTAMINATION IN SOME LOCATIONS BUT NOT OTHERS

Unconventional energy extraction is expanding rapidly in the United States and around the world. Accompanying this expansion in energy production are concerns about air and water quality and, potentially, human health. In this presentation we compare our results for the Marcellus and Fayetteville Shales with those of other shale gas plays, including the Barnett shale in Texas. In the Marcellus, our most recent sampling showed no increases in salt concentrations or radioactivity in water of homeowners living near natural gas wells. It did show elevated methane concentrations in the water of some homes within 1km of a gas well. Additionally, ethane was 23 times higher in homes located less than 1 km from shale gas wells (P =0.0013), and propane was found in only 10 water wells, all of them within 1 km or so of a gas well (P = 0.01). Isotopic signatures (δ13C-CH₄, δ13C-C₂H₆, and δ2H-CH₄), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas ⁴He to CH₄ in groundwater were characteristic of a Marcellus-like gas source in some, but not all, cases. In contrast to our work in the Marcellus, our new results in the Fayetteville Shale of Arkansas in collaboration with the USGS found no evidence of increased salts, radioactivity, or stray gases in drinking water aquifers for 127 homeowners. Methane was detected in two thirds of the drinking-water wells (32 of 51 samples), but only six wells had concentrations >0.5 mg CH₄/L. Possible explanations for the differences in results for the Fayetteville and Marcellus shales include local geology and, potentially, human error.