Note that a third of the wells in the study had fecal coliform bacteria--indicating that they are not well isolated from potential surface contamination. It's not necessary to have downhole fracking fluids contaminating the well, as the threat via surface contamination is so great. The liners on sludge pits rupture or leak, there are blowouts, etc. Beyond the fracking issue, Pennsylvania has a well overdue, very strong need for well-construction standards (IMO). I imagine that study concludes that point (I haven't read it yet, but thanks for the link).
Also, much effort has been made to improve understanding in karst areas of PA. Sinkholes are not used as garbage disposals as much as in the past, and you can't use "blood and guts" as tracers like in the old days, but still, there's a lot of natural runoff going into these direct conduits to the groundwater, despite the thick soil covers over most of the areas.
Also note that Pennsylvania taxpayers are left holding the bag when gas companies closed up shop and left without plugging wells so there are countless thousands of open holes still out there. Former colleagues of mine are in on the contract to plug them, but there's enough money for only a few per year (though it's up to hundreds per year instead of tens).
When two companies claim they are no longer going to pump diesel fuel into underground sources of drinking water for fracking coalbed methane wells and then admit doing it for years after that agreement, it's difficult to claim we can just trust them to "do the right thing" without being monitored.
Things like 4-Nitroquinoline-1-oxide (CAS #56-57-5) are not naturally out there and just as healthful as an apple a day. The fact that it was detected in flowback solutions is pretty damning, in my mind. (What is 4-Nitroquinoline 1-oxide used for? As a "very potent mutagen and carcinogen," it's a very reliable means of creating cancerous tumors so anti-cancer drugs can be tested.) If there's no problems to worry about, then there should be no problem with appropriate regulation. I'm not for a ban, but just to be sure safeguards are in place as with other industries who could jeopardize others.