What happens on ranch X may affect the groundwater on farm Y or in town Z, a few kilometers away. I have no idea about the distances involved, and presumably they vary a lot depending on a number of factors that you'd have to ask scientists about.

Ideally, you would be able to detect pollutants moseying off the property underground, just as you would cattle wandering off the ranch above ground, and your property system would work fine ("Bob, yer frackin' byproducts done cross over into mah property yesterday, an I cain't abide by that") , but presumably it's not easy.

Wow, you just solved everything!

Seriously though, water tables don't respect property borders, and runoff doesn't stop at fence lines. If that happened, there would be no issue.

These people aren't stupid, and the last thing they want to do is ostracize themselves from their peers by raising environmental concerns. They're forced into these positions by a lack of alternatives.

Property rights often do not include 'mineral rights' and they definately don't include neighboring properties' (mineral) rights.

Edit: The owners of mineral rights may legally drill a well in your front yard, if they comply with current laws & ordinances.