A large part of the water we drink is transported through the ground through pipes and other methods. The plastics in the dumpsite will mix, resulting in high impact plastic and seep into the ground and into most sources of ground water. The harmful effects of plastics can be passed through the ground to the body through various ways like the water explained here. For most people, ground water is assumed to be safe for drinking when the reality is far from that. Unless it has been treated and approved for human consumption, do not attempt to drink it as you will be taking in lots of poisons.