THE PREVALENCE OF METHANE, SALINITY AND TRACE METALS IN SHALLOW GROUND WATER CONSUMED IN NORTHEASTERN PENNSYLVANIA AND SOUTHWESTERN PENNSYLVANIA, NORTHERN WEST VIRGINIA, AND EASTERN OHIO: IMPLICATIONS FOR REGULATORY ASSESSMENT OF BACKGROUND WATER QUALITY

Natural gas produced from the Marcellus and Utica Formations of the Appalachian Basin constitutes a large part of United States gas reserves. Recently, a series of published scientific papers using dispersed small data sets have suggested that dissolved methane concentrations in shallow aquifers may increase because of this gas production. We herein present the results of a geochemical synthesis of more than 20,000 samples of shallow ground water obtained in northeastern and western parts of the Appalachian Basin prior to drilling for Marcellus Shale gas. Given this sampling density, our geochemical characterization in shallow Pennsylvanian drinking water may be as rigorous as can be done in the context of regulatory protocol. We also report the results of detailed studies on the variability of methane and other parameters in ground water over time in 11 water wells in different hydrogeologic settings in northeastern Pennsylvania. One-time baseline samples cannot characterize whether a single measurement of ground water quality reflects the natural range of what might occur at that location.

Fundamentally, our study shows that the spatial and temporal variability in concentrations of constituents of regulatory interest related to shale gas production (e.g. Na, CH₄, Fe, Mn, Sr, and Ba) span more than an order of magnitude, and commonly exceed regulatory MCLs because of natural geochemical evolution along flow paths and local geochemical conditions. The potential for regulatory false positives is high if only based on increasing solute and gas concentrations after gas well drilling. Rather, a suite of diagnostic forensic geochemical approaches needs to be used to properly identify actual geochemical changes potentially caused by gas drilling.