Will, it's not the same. With an injection well you are pumping under the water table. There is an insoluble barrier between the levels.
Heck if the water is so far down there I guess I will just dump my used oil on the ground, bury my old tv in the yard.
There is another way. It's called flowback and produced water recycling. A company called Fountain Quail is setting up shop in Kenedy and already operates in the Barnett Shale area of Ft. Worth and the Marcellus Shale of Pennsylvania. Flowback and produced water is filtered down to salt water, which can be reused for drilling or fracking, or it can be distilled to 99.9% water which can be mixed with fresh water for fracking or discharged into a stock tank or river. This keeps the water in the hydrologic cycle instead of permanently disposing of it underground.
Recycling also lessens the requirement for groundwater in fracking, which may be 4 to 5 million gallons per frack job. Recycling some 80% of that obviously would put much less drawdown and strain on the aquifer.
There has also been controversy over all these abnormal earthquakes around the country and their potential association with shallow injection wells. In fact, four disposal wells in Arkansas were recently shut in after more than 200 earthquakes.
Then there's the issue of being good neighbors. If your next door neighbor stays up all night banging on the drums with all the lights on, you can call the cops if it's disturbing you. Not so with a disposal well. There's no shortage of land around here, so to build a disposal well next to a subdivision just doesn't have much merit.
Location, location, location...
If you want to use your gasoline powered equipment then the disposal wells are needed. That is the only way we have to get rid of the waste water (salt water) that the wells will produce while also producing Oil and Gas. Some oil is brought to the disposal site but is not injected into the ground. It too, is sold for a profit. With all the disposal wells in the state I have not heard of one contaminating the ground water supply. Simply put, we need disposal wells to continue to produce oil.