There have been a few cases where negligence has caused spills of fracking fluid being transported FROM a frack site. Not a single documented case of a well or a body of ground water being contaminated by fracking. Not a single one dude, believe me, natural gas is what pays my bills, I am up on this stuff.
There was one guy who famously took video of the water from his faucet catching fire. He of course was some sort of activist and there is also video of him and about 20 other activists sitting around his house when he received the letter from the EPA stating that his well was perfectly fine and had been temporarily contaminated by a pocket of naturally occurring methane gas. This ass threw a fit like a little girl.
Like I said earlier, there has been fracking in the US since as early as the teens and it has been a regular practice since the 40s and there is not a single documented case where fracking has been proven to be the cause of a contaminated well or water table. This is a manufactured crisis by people with an agenda, period.