ENVIRONMENTAL DIMENSIONS OF SHALE GAS EXTRACTION AND STRAY GAS MIGRATION

Shale gas extraction is growing rapidly in the United States and elsewhere, developed in part through advances technologies such as horizontal drilling and hydraulic fracturing (also called “fracking). Concerns over potential environmental impacts have accompanied the boom in natural gas extraction around the country. For several years we have studied drinking water quality, asking the question, “Is water quality different for homeowners living near natural gas wells?” We have sampled shallow groundwater systems of >200 homeowners, the majority of them in the Marcellus formation of Pennsylvania and New York, for brines, dissolved gases, and other attributes.

In our first study published in May of 2011 (Osborn et al. 2011, PNAS 108:8172-8176), we found no evidence of increase salt concentrations or fracturing fluids with distance to gas wells for 68 sampled homes. However, dissolved methane concentrations were 17 times higher on average for water wells found within 1km distance of them. Higher chain hydrocarbons (ethane, propane, and butane) were detected more often in active areas (21, 8, and 3, respectively) compared to non-active areas (3, 0, and 0, respectively), indicating a more thermogenic methane character. The carbon isotope values of 13C-CH4), in active extraction areas were on average less negative (-37±7 ‰) than non-active extraction areas (-54±11‰). We conclude from these, and newer follow-up results, that there are important differences in methane concentration and isotopic (13C-CH4 and 2H-CH4) values in some shallow groundwater wells near natural gas extraction areas. Furthermore, the dissolved gas geochemistry nearer gas wells appears to be consistent with a more thermally mature source of organic matter. This presentation will include results from additional sampling in 2011 and 2012.