I remember years ago the Rocky Mountain Arsenal was pumping things deep into the ground to dispose of them. It was causing all kinds of earthquakes too and they had to stop doing it.

When driving through the area it smelled a bit different from all the chemicals and refining being done.

I don't think it is healthy to be pumping things deep into the ground - they usually have to come out sometime as we know from some sources of spring water that come out after many years of underground travel.