"In Pennsylvania, the closer you live to a well used to hydraulically fracture underground shale for natural gas, the more likely it is that your drinking water is contaminated with methane. This conclusion, in a study published in the Proceedings of the National Academy of Sciences USA in July, is a first step in determining whether fracking in the Marcellus Shale underlying much of Pennsylvania is responsible for tainted drinking water in that region." (Quoted from article)