Fracking for natural gas trapped in shale rock formations produces waste water that is toxic and needs to be disposed of properly. At first, the companies were hauling this back flow of radioactive and carcinogenic muck to waste water treatment plants ill eqipped to treeat it properly and it was being dumped into our drinking water supplies untreated. When the public pushed back we documented the dumping of it into out of the way streams, or on rural roads when they thought no one was looking. Now, because of courageous environmentalist voices, they can't do that anymore.
The problem remains. So the gas companies get the brainy idea to flood underground sandstone formations with millions and millions and millions of gallons of toxic waste water. And expecting it not to cause any issues. This water was formerly fresh water that was once on the surface in lakes and ponds and is now filling up the bowels of the earth. The cheapest solution they could think of is the cheap path of least resistance they chose, no surprise there.