Friday, May 13, 2011
For those who did not see the article link on the Environmental Law Professors listserv, four Duke scientists have published a study in the Proceedings of the National Academy of Sciences that addresses possible connections between natural gas extraction (through drilling and hydraulic fracturing) and methane contamination of shallow groundwater in the Appalachian region. The study concludes that groundwater in areas with gas extraction activity has higher concentrations of thermogenic methane--methane from deep formations--than does the groundwater in areas without extraction activity. On average, the methane concentration in water wells sampled in the active extraction areas was seventeen times higher than the concentration in inactive areas. Most importantly, the study finds that "gas-phase transport of methane upward to the shallow groundwater zones sampled" may be occurring, suggesting that drilling and/or fracturing--not just naturally-occcuring methane around the groundwater--could be contributing to the methane contamination. The study cannot, however, pinpoint the exact causal mechanism for this apparent upward migration of methane. The most likely source of the methane in groundwater, the authors conclude, is gas that is transported in gas phase from shale formations to groundwater. Alternatively, "gas-rich solutions" from deep formations could be physically displaced in the extraction process and migrate upward to water, but the authors believe that this is unlikely. Secondly, "leaky gas-well casings" may allow methane to escape and to travel laterally and/or vertically to groundwater. Finally, hydraulic fracturing could expand fractures beyond the formation targeted by the fracturing. Then, according to the study, "The reduced pressure following the fracturing activities could release methane in solution, leading to methane exsolving rapidly from solution, allowing methane gas to potentially migrate upward through the fracture system." The study finds no evidence of brines or fracturing fluids contaminating groundwater. It concludes--unsurprisingly--that "[m]ore research is needed."