http://video.nytimes.com/video/2011/11/18/magazine/100000001177838/fracking-in-one-town.html
"Five years ago, no one in Amwell Township knew anything about fracking."
Correlation isn't causation. Yet it suggests something. When a plague of illness, gagging smells and death shows up at your doorstep only after fracking moved in, maybe, just maybe, there's a link that deserves to be investigated. In the words of Randall Munroe, it waggles its eyebrows suggestively and mouths, "look over there".
The unwillingness of Pennsylvania's DEP do its job, dismissing the flood of complaints with such responses as "[there was] a 'strong odor' at the impoundment but not [directly] on her property, or deal with Range Resources' amnesia with recording complaints, makes one suspect the cause. Frequently, blind eyes at agencies are correlated with corruption. But that's correlation. Perhaps as the lawsuit against the DEP progresses one might ascertain a cause.