BORON AND STRONTIUM ISOTOPES AS SENSITIVE TRACERS FOR INDICATING POTENTIAL SHALLOW GROUNDWATER CONTAMINATION FROM MARCELLUS FORMATION BRINES

Development of the Marcellus Shale as a natural-gas resource in areas of northeastern Pennsylvania has increased dramatically in the past four years with the advent of horizontal drilling and hydraulic fracturing technologies. Even though the Marcellus Shale lies 1-4 kilometers underground, its development has raised concerns for contaminating the overlying surficial aquifers used as drinking water sources. This potential contamination may occur from either hydraulic fracturing fluids containing toxic chemicals or highly saline (TDS>100,000mg/L) formation water that contains high naturally occurring radioactive materials (NORM).

Recent findings of Duke University researchers have shown that in northeastern Pennsylvania shallow drinking water wells near natural gas wells can be contaminated with methane that has a deep thermogenic geochemical and isotopic signatures. However, that study did not show chemical contamination and increased concentrations of major dissolved constituents or NORM. To develop diagnostic tools for delineating possible contamination of fracing fluids and produced waters, we present new data on the isotopic compositions of strontium and boron in brines and surficial aquifers of the Marcellus, Catskill and Lockhaven Formations in northeastern Pennsylvania. Our data show that the Marcellus brines have distinct isotopic compositions of strontium (⁸⁷Sr/⁸⁶Sr range of 0.7101 and 0.7115) and boron (d¹¹B 28-32‰) compared to shallow regional groundwater. These variations indicate that boron and strontium isotopes can be used as very sensitive tracers (>1%) to track possible contamination of shallow groundwater and surface water from Marcellus brine and to distinguish this contamination from natural background and/or other possible sources of contamination (i.e., acid mine drainage, road salt, sewage/animal waste).