http://www.scientificamerican.com/ar...lic-fracturing
"...From compressor stations emitting known human carcinogens such as benzene to the poor lining of wells after drilling that has led some water taps to literally spout flames, the full set of activities needed to produce natural gas gives rise to a panoply of potential problems. The EPA study may examine everything from site selection to the ultimate disposal of the fluids used in fracking..."