METHANE LEVELS AND SOURCES IN GROUNDWATER OVER A TIME SERIES OF FRACKING ACTIVITY IN THE UTICA SHALE OF OHIO, USA

Shale oil and gas development has recently flourished in the Utica Shale region of Ohio. While natural gas may provide U.S. energy independence and a bridge between fossil fuels and renewables, the environmental impacts of hydraulic fracturing are largely unknown. Previous studies in the Marcellus Shale have found evidence of natural gas contamination in Pennsylvanian drinking water wells within 1 km of shale gas extraction, but no study has assessed the concentration or source of methane in drinking water wells before fracking. Our study evaluates CH₄ and its origins in private drinking water wells in the Utica Shale drilling region of eastern Ohio, focusing on Carroll County, Ohio, along a time series of shale gas development.

Over a two-year study period beginning in November 2012, water was sampled every three to four months from 22 private wells in Carroll County before, during, and after the onset of fracking. Carroll County received its first fracking permit in 2011. Over the course of the study, one water well was within 10 km of a producing or drilled well pad, five wells were within 5 km, 13 wells were within two km, and three water wells were within one km. Samples were measured for CH₄ concentration, stable isotope composition of CH₄ (¹³C and ²H), total dissolved organic carbon, total nitrogen, conductivity, and pH. In May 2014, 96 water wells were sampled in a regional field study from Belmont, Carroll, Columbiana, Harrison, and Stark counties.

Conductivity values of groundwater samples ranged from 35 to 1664 microsiemens per centimeter. pH ranged from 5.33 to 8.88. Total dissolved organic carbon measurements ranged from 0.3 to 1.7 mg/L, while total nitrogen measurements ranged from 0.01 to 6.22 mg/L. Dissolved methane concentration measurements ranged from less than 0.2 μg/L to 25.33 mg/L. δ¹³C-CH₄ values ranged from -43.2 ‰ to -87.8 ‰, and δ²H-CH₄ values ranged from -66 ‰ to -260 ‰.

While certain wells have consistently contained greater than 10 mg/L of CH₄ over the course of the study period, most wells had low levels of methane. Carbon and hydrogen isotope values indicate that methane in sampled groundwater wells had biological sources. Future work will focus on evaluating the specific source of elevated biogenic CH₄ in particular wells, including the possibility of coal bed methane.