A study in the Marcellus Shale region of western Pennsylvania has shown that even after being treated, wastewater from hydraulic fracturing operations left significant contamination in a waterway downstream of treatment plants. 

Researchers from Penn State University, Colorado State University, and Dartmouth College studied sediments from Conemaugh River Lake — a dammed reservoir east of Pittsburgh — and found that they were contaminated with endocrine-disrupting chemicals called nonylphenol ethoxylates; polycyclic aromatic hydrocarbons, which are carcinogens; and elevated levels of radium. 

The study, published in the journal Environmental Science & Technology, said that the highest concentrations of these pollutants were found in lake sediment layers deposited five to ten years ago during a peak period of fracking wastewater disposal. The high radium levels were found as far as 12 miles downstream of treatment plants.