The Proceedings of the National Academy of Sciences has published a recent study on the impacts of shale development on surface water quality in Pennsylvania.  Of note:  "The density of shale gas wells upstream in a monitor’s watershed has a statistically insigni?cant effect on Cl- concentration downstream ***."  What does that mean?  From a related Council on Foreign Relations article:  "The team’s conclusions are fairly straightforward. They find enhanced chlorine concentrations downstream of waste water treatment facilities but not downstream of drilling sites. Chlorine is a good marker of contamination from well flowback. What the RFF analysis suggests is that leaks or spills aren’t statistically detectable, at least at the watershed level, but that impacts of poorly processed wastewater are."

Interesting ...