HALOGENS AND AMMONIUM IN HYDRAULIC FRACTUING AND OIL AND GAS WASTEWATERS

The rapid expansion of unconventional shale gas and hydraulic fracturing has increased the volume of the oil and gas wastewater (OGW) generated in the US. Here we demonstrate that in addition to high chloride and bromide, OGW is characterized by elevated concentrations of iodide and ammonium. Systematic analysis of 75 Marcellus and Fayetteville hydraulic fracturing flowback fluids and conventional produced waters shows that the concentrations of iodide (a range of <1 to 56 mg/L) and ammonium (<1 to 420 mg/L) vary by geological formations and are controlled by geogenic processes with no systematic differences between OGW originated from hydraulic fracturing fluids and conventional produced waters. These results show that both conventional produced water and flowback and produced waters from unconventional drilling will contribute halides and ammonium to surface waters during disposal or accidental release. In addition to the environmental implications, this paper provides insight into the mechanism of ammonium enrichment in saline formation waters. Analysis of 17 effluents discharged to surface water from three disposal sites (Josephine, Franklin, Hart) in Pennsylvania and a spill site (Tyler County) in West Virginia show elevated levels of halides (I^- up to 28 mg/L) and ammonium that mimic the compositions of OGW. The ammonium contents in discharge effluents (12 to 106 mg/L) far exceed the EPA threshold values for chronic exposure in aquatic life (1.9 mg/L). Halides and ammonium were found to mix conservatively in surface waters downstream of the effluent discharge sites. Elevated bromide and iodide observed in downstream surface waters could promote the formation of the toxic brominated and iodinated analogues of disinfection by-products during disinfection at drinking water treatment plants, while ammonium can promote toxic nitrogen disinfection by-products and alter the disinfection process. Our findings indicate that the continued discharge and accidental spills of OGW to waterways in the USA pose risks to both human health and the environment.