[A-HW19] Tracer Hydrology: Advances in Measurement and Modelling

[AHW19-P02] A snapshot of the current state and prospects of noble gas sampling methods, knowledge of natural artifacts, and synergies with numerical models

*Stephanie Musy^1,2, Roland Purtschert², Oliver S. Schilling^1,3 (1.Hydrogeology, Department of Environmental Sciences, University of Basel, Basel, Switzerland, 2.Climate and Environmental Physics, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland, 3.Eawag, Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland)

Keywords:Noble gas, Radioactive, Groundwater, Tracers

Noble gas radioisotopes (i.e. ³⁹Ar, ³⁷Ar, ⁸¹Kr, ⁸⁵Kr, ²²²Rn) are increasingly used as tracers of groundwater flow paths and residence times on scales from days to millions of years. Their inertness in the subsurface, combined with the continuous decrease in the amount of water required their analyses, and the improvement of measurement precision have placed them at the forefront of the tracer scene. Yet, with every vividly investigated topic, new questions and potential challenges arise. In this respect, we offer a tour d’horizon of the current knowledge and prospects for sampling methods, natural biases, and numerical modeling of radio-noble gases.
For instance, active and passive sampling methods offer different perspectives on the groundwater system. Therefore, the knowledge of their respective pros and cons is a prerequisite for choosing the method reflecting the purpose of an investigation. The long-held belief that underground production processes for ³⁹Ar, ⁸¹Kr, and ⁸⁵Kr are negligible was recently challenged by multiple field observations, leading to a re-evaluation of the subsurface production processes in rock and the water phases. Conversely, ³⁷Ar and ²²²Rn are indicators of residence times solely based on their accumulation rate in the subsurface and offer, in combination with numerical modeling, exciting new applications in the field of river–groundwater interactions and hence drastically increase the potential to understand complex hydrogeological systems in the future.