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High concentrations of barium (Ba), strontium (Sr) and radium (Ra) are present in both the liquid and suspended solid portions of wastewater produced from hydraulic fracturing. These high concentrations often require special treatment in which the solid and liquid portions are separated and then independently treated prior to disposal. The solids are typically disposed in landfills while the liquids are further treated, recycled for future hydraulic fracturing, or disposed via injection wells. Finding optimal treatment methods of both the solid and the liquid fractions requires a thorough understanding of potential Ra mobility from both the raw suspended solids and mineral precipitates formed during treatment. Using a sequential extraction procedure, we found that, without treatment, more than 50% of Ra-226 in the suspended solids was associated with soluble salts and readily exchangeable fractions. When the liquid portion of the wastewater was treated by mixing with acid mine drainage (AMD), which contained high sulfate concentrations, approximately 80–97% of the total Ra-226 in the mixture solution is found in the insoluble sulfate fraction of the precipitate. The activity of Ra-226 sequestered in the precipitated solid sulfate fractions is positively correlated with the Sr/Ba ratio of the wastewater-AMD solution. We discuss implications of these findings for effective long-term management of elevated radium in both solid and liquid wastes. 

In the western U.S., produced water from oil and gas wells discharged to surface water augments downstream supplies used for irrigation and livestock watering. Here we investigate six permitted discharges on three neighboring tributary systems in Wyoming. During 2013–16, we evaluated radium activities of the permitted discharges and the potential for radium accumulation in associated stream sediments. Radium activities of the sediments at the points of discharge ranged from approximately 200–3600 Bq kg −1 with elevated activities above the background of 74 Bq kg −1 over 30 km downstream of one permitted discharge. Sediment as deep as 30 cm near the point of discharge had radium activities elevated above background. X-ray diffraction and targeted sequential extraction of radium in sediments indicate that radium is likely coprecipitated with carbonate and, to a lesser extent, sulfate minerals. PHREEQC modeling predicts radium coprecipitation with aragonite and barite, but over-estimates the latter compared to observations of downstream sediment, where carbonate predominates. Mass-balance calculations indicate over 3 billion Bq of radium activity ( 226 Ra + 228 Ra) is discharged each year from five of the discharges, combined, with only 5 percent of the annual load retained in stream sediments within 100 m of the effluent discharges; the remaining 95 percent of the radium is transported farther downstream as sediment-associated and aqueous species.