GEOCHEMICAL EVIDENCE FOR POSSIBLE NATURAL MIGRATION OF MARCELLUS FORMATION BRINE TO SHALLOW AQUIFERS IN PENNSYLVANIA
Many of the brines in the northern Appalachian Basin likely share a common origin as the expelled remnants of the formation of the Silurian Salina evaporite deposits. To determine the ultimate source of the diluted brine we compared the observed geochemistry to over 80 brines produced from northern Appalachian Basin formations. The shallow salinized groundwater most closely resembles diluted produced water from the Middle Devonian Marcellus Formation. The 18O/16O and 2H/H of the salinized groundwater indicate that the brine is likely diluted with post-glacial (<10,000 ybp) meteoric water. Combined, these data indicate that hydraulic connections allowed cross formational migration of brine from deeper formations (1-2 kilometers below ground surface) and subsequent dilution. The occurrence of the saline water does not appear to be correlated with the location of shale-gas wells. Also, salinized groundwater with similar chemistry was reported prior to the most recent shale-gas development in the region. Instead brine likely migrated into the shallow aquifers and was recently diluted through natural pathways and processes. However, the presence of natural hydraulic connections to deeper formations suggests specific structural and hydrodynamic regimes where shallow drinking water resources are at greater risk of contamination with fugitive gases during drilling and hydraulic fracturing of shale gas.