A recent study by the Division of Earth and Ocean Sciences at Duke University showed high concentrations of chloride, bromide, strontium, and radium in wastewater from hydraulic fracturing in Western Pennsylvania’s Marcellus Shale Formation, after undergoing wastewater treatment.

226Ra levels in stream sediments (544−8759 Bq/kg) at the point of discharge were ∼200 times greater than upstream and background sediments (22−44 Bq/kg) and above radioactive waste disposal threshold regulations, posing potential environmental risks of radium bioaccumulation in localized areas of shale gas wastewater disposal.

These potentially dangerous, high levels of sometimes radioactive pollutants were discovered in fracking water that had already been treated at a wastewater treatment plant. This poses serious concerns for treated fracking wastewater, let alone water from hydraulic fracturing that has been documented being dumped into nearby water supplies without first being treated.

The study is Impacts of Shale Gas Wastewater Disposal on Water Quality in Western Pennsylvania. Abstract below. 

Abstract: 

The safe disposal of liquid wastes associated with oil and gas production in the United States is a major challenge given their large volumes and typically high levels of contaminants. In Pennsylvania, oil and gas wastewater is sometimes treated at brine treatment facilities and discharged to local streams. This study examined the water quality and isotopic compositions of discharged effluents, surface waters, and stream sediments associated with a treatment facility site in western Pennsylvania. The elevated levels of chloride and bromide, combined with the strontium, radium, oxygen, and hydrogen isotopic compositions of the effluents reflect the composition of Marcellus Shale produced waters. The discharge of the effluent from the treatment facility increased downstream concentrations of chloride and bromide above background levels. Barium and radium were substantially (>90%) reduced in the treated effluents compared to concentrations in Marcellus Shale produced waters. Nonetheless, 226Ra levels in stream sediments (544−8759 Bq/kg) at the point of discharge were ∼200 times greater than upstream and background sediments (22−44 Bq/kg) and above radioactive waste disposal threshold regulations, posing potential environmental risks of radium bioaccumulation in localized areas of shale gas wastewater
disposal.