Until recently, there have not been scientifically grounded independent investigations that seek to fully understand the role of fracking in most groundwater contamination incidents . One exception is the investigation of the groundwater contamination in Bainbridge Township, Ohio, where the state found that one of the contributing factors was: “the frac communicated directly with the well bore and was not confined within the “Clinton” reservoir.”
http://switchboard.nrdc.org/blogs/amall/geochemistry_scientist_on_frac.html