A paper recently published in the Proceedings of the National Academy of Sciences investigated the potential impacts to surface water quality from shale gas development. The researchers used data from more than 20,000 surface water quality monitors in Pennsylvania and found evidence of impacts from two of the pathways tested.
The monitoring results suggest that:
(a) the treatment of shale gas waste by treatment plants in a watershed raises downstream chloride; and
(b) the presence of shale gas wells in a watershed raises downstream concentrations of total suspended solids.
You can read more about this study in a blog post from one of the researchers, Lucija Muehlenbachs of Resources for the Future.