Geochemical and isotopic variations in surface waters of the monongahela river basin: An area of accelerating marcellus shale development in West Virginia

Abstract

Water samples were collected from fifty streams in the Monongahela River basin of West Virginia at baseflow condition. The study area was divided into different Marcellus Shale production categories based the amount of Marcellus Shale gas production in a particular HUC-12 sub-watershed. All samples were analyzed for selected major and minor geochemistry, as well as stable isotopes of δ 2 H H2O , δ 18 O H2O , δ 13 C DIC , δ 18 O SO4 and δ 34 S SO4. The geochemical and isotopic characteristics of the 50 water samples collected show no clustering based on production category. Extremely high concentrations of total dissolved solids (TDS) are characteristic of produced water from Marcellus Shale production. All of our samples have TDS concentrations less than 1000 mg/L, with a direct correlation between TDS and dissolved sulfate concentration. The area with the greatest density of Marcellus Shale development has also undergone extensive coal mining. Hence geochemical and isotopic characteristics were used to decouple the effects of coal mining from shale gas development in the area. Elevated dissolved sulfate concentrations are interpreted to be the result of contribution from coal mine drainage. The stable isotopic composition of δ 2 H H2O and δ 18 O H2O lie along to meteoric water line and show expected trends with altitude indicating that this is meteoric water. The geochemical and isotopic characteristics of the waters also does not indicate that the streams are receiving any significant contribution from produced waters associated with Marcellus Shale drilling or natural structural pathways. However, the water samples collected represent synoptic, or one-time sampling, and continued site-specific monitoring might better assess the impact of shale gas drilling on water quality of streams.