Gulf of Mexico
"The problem is that we have never, as a human society, engineered a hole to go four miles down in the Earth’s crust that we have complete confidence that it won’t leak," Doss said. "A perfect case-in-point is the 
 oil spill in 2010, that oil was being drilled at 18,000 feet but leaked at the surface. And that’s the concern because there’s no assurance that some of these unknown chemical cocktails won’t escape before it gets down to where they are trying to get rid of them."
Disposal of fracking wastewater poses potential environmental problems