MONITORING METHANE LEVELS AND SOURCES IN GROUNDWATER BEFORE AND AFTER THE ONSET OF FRACKING IN THE UTICA SHALE OF OHIO, USA

Hydraulic fracturing for natural gas provides a domestic energy source with potential environmental advantages over coal, but may negatively impact water resources and atmospheric methane emissions. Previous studies in the Marcellus Shale region of Pennsylvania have shown that thermogenic methane is present in water wells near fracking sites; however, these studies did not document the presence or source of methane in water wells prior to fracking. This study examines methane and its origins in private drinking water wells in the Utica Shale drilling region of eastern Ohio, focusing on the area of Carroll County, OH along a time series of fracking activity.

Between November 2012 and May 2014, water was sampled every three to four months from 22 private wells in Carroll County before, during, and after the onset of fracking. The first fracking permits were issued in this region in 2011. Over the course of the study period, one water well was within 10 kilometers 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 D), total dissolved organic carbon, total nitrogen, conductivity, and pH. In May 2014, 44 total wells were sampled in Columbiana, Belmont, Stark, and Harrison counties. 29 new wells were sampled in Carroll County along with 21 previously sampled wells.

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. The concentration of methane in groundwater ranged from less than 0.2 μg/L to 25.33 mg/L. Carbon isotope analysis from samples prior to May 2014 with CH₄ concentration values above 1.0 mg/L had δ¹³C values of -56.2 ‰ to -86.6 ‰. Hydrogen isotope analysis from samples prior to May 2014 had δD values of -66 ‰ to -223 ‰.

While four sampled wells had concentrations of methane above 10 mg/L, most wells had low levels of methane. Carbon and hydrogen isotope values indicated that methane in groundwater wells had biological origins. Future work will indicate whether increasing numbers of fracking wells in the region will cause methane migration into the aquifer.