The Ground Water Protection Council (GWPC) has issued a report on agency groundwater investigation findings in two states, Ohio and Texas.  It has interesting things to say regarding alleged groundwater contamination from well stimulation activities.  From the Executive Summary, for example:

Neither state has documented a single occurrence of groundwater pollution during the site preparation or well stimulation phase of operations. Despite this, Ohio has implemented more detailed notification, inspection, record keeping, and reporting requirements in response to the national debate on the process of hydraulic fracturing. Texas is currently placing summary data online for new completions, has implemented new disposal well requirements in the Barnett Shale play, and recently enacted statutes requiring public disclosure of hydraulic fracturing chemicals.  (Emphasis is ours.)

For a copy of the report, see here (generally) and here (a copy of the report).