A recent study of Marcellus Shale aquifers by researchers at Duke University in Durham, NC indicates that elevated levels of contaminants in areas overlaying certain shale-rich regions may be due to pre-existing natural pathways between the deep shale formations and shallower aquifers.
The study, published last week in the Proceedings of the National Academy of Sciences, examined current and historic groundwater samples from aquifers in six counties in northeastern Pennsylvania overlying the Marcellus shale formation. Overall, the groundwater samples showed elevated levels of shale “brine” (metal-rich saline solutions from the Marcellus shale formation itself) — not to be confused with flowback “brines” or fluids generated as part of the hydraulic fracturing process and disposed of primarily in deep injection wells. The Duke study highlighted this distinction, citing evidence that shale brine was present before shale drilling began and concluding that “the possibility of drilling and hydraulic fracturing causing rapid flow of brine to shallow groundwater in lower hydrodynamic pressure zones is unlikely but still unknown.”
As the Philadelphia Daily News recently noted, coverage of this report has been confused and to some degree politicized. The energy industry and homeowners/activists frequently have sparred as to whether elevated levels of methane and other constituents in groundwater are linked to nearby drilling activities. For example, controversies have flared regarding groundwater testing in nearby Dimock, PA and Pavilion, WY in the past year. To attempt to address this issue beforehand, state regulators (such as Ohio in its recently-passed Senate Bill 315) increasingly are requiring well operators to conduct pre-drilling baseline groundwater testing as a condition to their drilling permits.