http://www.scientificamerican.com/ar...lic-fracturing
In Dimock's case, Houston-based Cabot Oil and Gas has spilled fracturing fluid, diesel and other fluids, according to Pennsylvania's Department of Environmental Protection. And elsewhere in the state fracturing fluid contamination has been detected in the Monongahela River, which is a source of drinking water. In more common practice, companies dump used fracking fluid back beneath the surface, usually injecting it into other formations beneath the shale. For example, in the case of the Barnett Shale, disposal wells send that water into the deeper Ellenburger Formation.

But there's also the problem of what's actually in the fracking fluid. EPA tests in Wyoming have found suspected fracking fluid chemicals in drinking water wells, and a study by the New York State Department of Environmental Conservation identified 260 chemicals used in the process—a review undertaken as the state decides whether to allow such drilling on lands comprising the watershed providing New York City with its drinking water. And Dow Chemical notes that it sells biocides—antimicrobial poisons—to be included in the mix. But companies zealously guard the secret of what exactly makes up their individual "special sauce." It is one of the ways the companies distinguish themselves.