Can’t is easy to disprove. Accepting for a moment your premise that these chemicals will stay put in the ground on a geological time scale (think of the children), these chemicals can and do find their way into water on the surface where they are stored, disposed of, and yes, sometimes even spilled.
With respect to the broader debate on carbon, I am constantly baffled by the taker mentality on the right. Cheap energy is great, but if it’s only cheap because you’re not paying for the externalities, that’s outright theft.
A truly conservative position would be to accept responsibility for the externalities (process fracking water, pay for carbon impact, etc), which as far as I can tell would make fracking uneconomical almost everywhere, and thus makes the water pollution question somewhat moot.
Forgive my rant on personal responsibility, the value of well-functioning markets, and the harm of indirect government subsidies, it’s the conservative in me ;).