GUEST,Iain, The modern fracking technique is responsible for a host of documented health and environmental issues (and certainly some we don't know about yet) as energy companies increasingly use it in more populous areas and in environmentally sensitive areas. It's rapid expansion has found many states without up to date regulations in place to deal with problems like well integrity, ground water monitoring and usage of toxic chemicals (which energy companies seem to be very secretive about) just to mention just a few.
Plenty of info can be found on the link that gnu provides at 23 Apr 15 - 06:57 PM above or with a simple google search.