Strontium Isotopes as Tracers for Contamination from Potential Marcellus Shale Waters

Abstract:

Mineralogical and geochemical conditions vary significantly in natural water systems, including groundwater aquifers and rivers. In addition, contamination events are often elusive. As a result, it is often challenging to pinpoint the contamination of natural waters by specific types of water sources. The strontium isotope ratio R⁸⁷Sr, defined as ⁸⁷Sr/⁸⁶Sr, has shown promise in discerning contamination from different types of wastewaters related to Marcellus Shale development. The R⁸⁷Sr of potential end members, including Marcellus shale produced water (0.710-0.712) and Upper Devonian/Lower Mississippian formation brine (0.720-0.721), have been shown to be distinct from those in natural waters. Here we use reactive transport modeling (CrunchFlow) to understand key process and factors that govern the evolution of R⁸⁷Sr, and the conditions under which we can discern contamination sources in natural water systems. Simulation results show that ion exchange reaction plays an important role in the evolution of R⁸⁷Sr while release rate has a relatively minor impact on R⁸⁷Sr evolution. Even with large dilution factor where the volumetric flow rate of natural waters is orders of magnitude higher than the release rates of contamination source water, the R⁸⁷Sr is still sensitive to different types of source contamination waters. Insights gained here suggest that strontium isotopes can potentially be used as a tracers for different type of water contamination. The modeling tool developed can offer a powerful tool for understanding, predicting, monitoring of natural water contamination.