There is considerable handwringing over hydraulic fracturing fluids and their potential effects on “the environment”. I use quotes in ironic fashion because I see very little parsing of the issue into relevant components. The chemical insult to the environment is highly dependent on both the substances and the extent of dispersion. But I state the obvious.
There are surface effects at the drill site and there are subsurface effects. A spill on the surface is going to be relatively small due to the limited size of the available tankage on site. I drive by these sites almost daily and can see with my own eyes the scale of the project. A surface spill of materials will be limited in scope.
The subsurface effects are complex, however, and the magnitude of consequences will depend on both the extent of the fluid penetration into aquifers and the nature of the materials in the fluid. Much criticism has been dealt, rightfully I think, over the secrecy claims on the composition of these fluids. The default reply from drillers has rested on trade secrecy. To be sure, the matter of government forcing a company to reveal its art is a serious matter. But the distribution of chemical substances into the environment requires some oversight. Especially when substances are injected into locations where they cannt be readily remediated. The remediation of an aquifer is a serious undertaking which may or may not be effective.
If you want to see what is potentially in frac fluids, go to Google Patents and search “hydraulic fracturing fluid”. A great many patents will be found. This will give the length and breadth of the compositions patented. Of this large list only a few are used in current practice. The potential carrier fluids vary from water to LPG (!). Water is a common component, but brine is said to be preferred. Additives include hydrochloric acid and surfactants. The MSDS documents may be a good source of info. Consider that a substantial threat to ground water may be that it is rendered non-potable rather than outright toxic.