A recent study conducted by the University of Texas found no evidence to support claims of groundwater contamination from hydraulic fracturing operations:  "Researchers found no evidence of aquifer contamination from hydraulic fracturing chemicals in the subsurface by fracturing operations, and observed no leakage from hydraulic fracturing at depth."  Just as interesting (and something that many farmers already know):  "Methane found in water wells within some shale gas areas (e.g., Marcellus) can most likely be traced to natural sources, and likely was present before the onset of shale gas operations."

For more, see here.