Combined radiogenic (87Sr/86Sr, 234U/238U) and stable (δ88Sr) isotope systematics as tracers of anthropogenic groundwater contamination within the Williston BasinUSA

Using these isotopic systematics we confirm previous conclusions that surface water and shallow groundwater in two studied sites are variably contaminated by produced water and estimate the degree of the contamination at ∼7% in a sample collected close to a brine tank and <0.5% in most other samples. The U isotope analyses in combination with the Sr isotope results help outline variable groundwater pathways and uncontaminated end-members. Also, U isotopes show no appreciable groundwater contamination from U-enriched P-fertilizers. Our study in the Williston Basin demonstrates the potential of using combined radiogenic (87Sr/86Sr, 234U/238U) and non-traditional stable (δ88Sr) isotopic systematics as tracers of anthropogenic contamination in surface and groundwater systems.