Duke University and the U.S. Geological Society (USGS) investigated the possible degradation of water quality in shallow aquifers overlying the Fayetteville Shale formation in north-central Arkansas, where approximately 4,000 wells have been drilled since 2004 to extract unconventional natural gas.
The study which was released in mid-May 2013 found no evidence of groundwater contamination from shale gas production in Arkansas. The scientists sampled 127 shallow drinking water wells in areas overlying the gas-producing Fayettevile Shale formation. The samples were taken at various locations by personnel from the Arkansas Oil and Gas Commission. The samples were analyzed for major and trace elements and hydrocarbons. Isotropic tracers were used to identify the sources of possible contamination. The chemical composition of any contaminants in the water samples was compared to those found in gas samples from the nearby shale gas drilling sites. The comparisons showed no spatial relationship between methane and salinity occurrences in the shallow drinking wells located in proximity to the sites. The low concentrations of methane that were found in the water did not match the isotopic fingerprint of the methane in the gas samples in all but two cases, showing that the methane in the water was primarily produced by biological activity in the shallow aquifers.
The scientists concluded that “systematic monitoring of multiple geochemical and isotopic tracers is necessary for assessing the possible groundwater contamination in areas associated with shale gas exploration as well as the possible hydraulic connectivity between shallow aquifers and deeper production zones.” The scientists indicated that variations in local and regional geology as well as human factors, such as drilling techniques and the integrity of the well bore, play major roles in determining the possible risk of groundwater impacts from shale gas development and in preventing or allowing gas leakage from drilling sites to shallow aquifers.