It is not known to be impossible for fluids to migrate to drinking watersources from deep hydraulic fracturing, but the likelihood of significant migration appears to be very low, especially when compared to the risk
of faulty casings or surface spills as a potential source of contamination. Finally, the relative risk of hydraulic fracturing varies substantially by local geological context, including the nature and depth of source rock, lithology of overlying rocks, and the nature of existing fractures and fault networks. Any comparison between the Marcellus Shale and another source
of natural gas must be well framed and consider these parameters