GEOCHEMICAL CHARACTERIZATION OF THE BAKKEN OIL AND GAS PRODUCED WATERS AND ASSOCIATED SURFACE WATER SPILLS IN NORTH DAKOTA

The rapid rise of oil and gas production in the Williston Basin in North Dakota raises concerns relating to surface water contamination associated with the accidental release of oil and gas wastewaters, including flowback and produced waters, to the environment following leaks and spills. Williston Basin brines in particular are known to be highly saline (>300 g/L TDS) and contain a number of toxic trace elements. In this study, we evaluate the chemistry of produced and flowback waters (n=5) from the Bakken Formation of the Williston Basin. We found elevated concentrations of chloride (up to 120,000 mg/L), bromide (370 mg/L), calcium (15,000 g/L), sodium (up to 61,000 mg/L), boron (260 mg/L), lithium (37 mg/L), ammonium (2,500 mg/L), and toxic trace elements such as vanadium (1700 mg/L), selenium (1600 mg/L), and lead (3,500 mg/L). Preliminary radium measurements indicate total radium (²²⁸Ra + ²²⁶Ra) activities in Bakken produced waters of ~70 Bq/L. We also collected 30 surface water samples in western North Dakota, which include surface waters where three major brine spill events have been identified. In these areas, elevated salinity (TDS up to 34,000 mg/L), halides (Cl, Br), major cations (Ca, Mg, Na) and trace elements, including environmentally toxic contaminants of NH₄, Se, V, and As, were found. Evidence for brine contamination was found even in spill sites that were affected over a year ago, in some cases. Future research will aim to evaluate the accumulation of radioactive and toxic elements in the spill sites and their long-term preservation in the environment.