From The National Geographic (Bill Chameides):
…a paper published this week in the journal Environmental Science and Technology by Nathaniel Warner formerly of Duke University and colleagues focuses on another of those environmental costs: disposal of wastewater.
Hydraulic fracturing, as the term implies, involves water — both at the front end with fracking fluid, the water-based chemical cocktail that is injected into the shale, and at the back end where there is flowback water and produced water.
Flowback water (which literally “flows back” during the fracking process) is a mixture of fracking fluid and formation water (i.e., water rich in brine from the targeted shale gas-rich rock). Once the chemistry of the water coming out of the well resembles the rock formation rather than the fracking fluid, it is known as produced water and can continue to flow as long as a well is in operation…
As a general rule, you would not want to take a shower much less drink flowback or formation water, nor would you want to just pour the stuff into a river or stream (although that has been known to happen, as described here and here). Fracking wastewater can contain massive amounts of brine (salts), toxic metals, and radioactivity. And so the gas companies have a problem: what to do with the stuff.
Ideally, the water would be reused or recycled, eliminating the need for immediate disposal. And indeed there is a lot of that. In the Marcellus Shale gas country of Pennsylvania, for example, a large percentage of the water, in the vicinity of 70 percent, is currently reused. And methods to reuse more are being developed. Even so, that leaves a massive amount of toxic wastewater to be disposed of.
One disposal route is injection into deep wells, and a good deal of flowback and produced water from the Marcellus Shale is transported to Ohio for just such a deep burial. But this method has its own problems — the injection process has the inconvenient habit of causing an earthquake every now and again.
Another alternative is waste treatment: removing the contaminants and then dumping the“clean” water into a nearby sewer or river. But you can’t use a standard municipal water treatment plant to treat flowback and produced water as those facilities are just not designed to handle the level of contamination, especially radioactivity, found in these waters.
But there are so-called brine treatment plants that are at least in principle equipped to handle that level of contamination. Although they’ve been in use for quite some time to treat water from conventional oil and gas operations, many facilities of this type have been found lacking and some have even incurred fines for failure to meet Clean Water Act or other regulatory standards.