It's actually sort of unclear what the status is. The problem is that "Gasland" has muddied the water, so you spend so much time vetting sources that it's slow going.
There is a movie from .. 1940? titled "Tulsa" where Robert Preston's character "invents" fracking - a column of water and dynamite. It got safer :)
I'm sure there are incidents. But it's not like an incident goes without recourse. I think there's one case where a formation in Wyoming is physically entangled with the water table. That operation should never have been approved ( and yes, these things have to be approved ). After a decade of reading, that's the only remotely credible one I know of. Generally, water is at, say 400 feet and oil/gas/shale is at 10,000 feet.
Even then, while it's not easy to clean it up, it's doable.
J. Larry Nichols is a founder of and on the board of Devon Energy, one of the companies that pioneered fracking for shale. He's on record saying "show me one case where fracking caused environmental damage."
But, of course, he's not considered reliable by people interested in environmentalism, usually. And I haven't found a demonstration (other than the one) that proves him wrong yet. I'm a lot more concerned that oil in general will get the USA v. RJR treatment which sets off some sort of scarcity cascade that could destabilize the Third World.
IMO, gas at the pump ougtha be $10 a gallon and $5 of that should go to alts research but I doubt that's possible.
IMO, and this is also just IMO, the whole thing is a proxy for AGW fear because nat. gas is a bridge technology while we wait for Elon Musk to save us from fossil fuels. But that's psychlogizing, really.
Fracking is a pretty high-energy activity. But most of the fuss seems at least to be mostly confirmation bias by both sides.