EGU2020-5022
https://doi.org/10.5194/egusphere-egu2020-5022
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Untangling transient groundwater mixing and travel times with noble gas time series and numerical modeling

Andrea L. Popp1,2,3, Álvaro Pardo-Álvarez4, Oliver S. Schilling5,6, Stéphanie Musy7, Andreas Scheidegger1, Morgan Peel4, Rolf Kipfer1,2, and Philip Brunner4
Andrea L. Popp et al.
  • 1Eawag, Department of Water Resources and Drinking Water, Switzerland
  • 2ETH Zurich, Department of Environmental Systems Science, Switzerland
  • 3Now at University of Oslo, Department of Geosciences, Norway (andrea.popp@geo.uio.no)
  • 4University of Neuchâtel, Centre d’Hydrogéologie et de Géothermie, Switzerland
  • 5Université Laval, Département de géologie et de génie géologique, Canada
  • 6Now at Flinders University, National Centre for Groundwater Research and Training, Australia
  • 7University of Bern, Climate and Environmental Physics, Switzerland

The quality and quantity of alluvial groundwater in mountainous areas are particularly susceptible to the effects of climate change, as well as increasing pollution from agriculture and urbanization. Understanding mixing between surface water and groundwater as well as groundwater travel times in such systems is thus crucial to sustain a safe and sufficient water supply. We used a novel combination of real-time, in-situ noble gas analysis to quantify groundwater mixing of recently infiltrated river water (Frw) and regional groundwater, as well as travel times of Frw during a two-month groundwater pumping test carried out at a drinking water wellfield in a prealpine valley in Switzerland. Transient groundwater mixing ratios were calculated using helium-4 concentrations combined with a Bayesian end-member mixing model. Having identified the groundwater fraction of Frw consequently allowed us to infer the travel times from the stream to the wellfield, estimated based on radon-222 activities of Frw. Additionally, we compared and validated our tracer-based estimates of Frw using a calibrated surface water-groundwater model. Our findings show that (i) mean travel times of Frw are in the order of two weeks, (ii) during most of the experiment, Frw is substantially high (~70\%), and (iii) increased groundwater pumping only has a marginal effect on groundwater mixing ratios and travel times. The high fraction of Frw in the abstracted groundwater and its short travel times emphasize the vulnerability of mountainous regions to present and predicted environmental changes.

How to cite: Popp, A. L., Pardo-Álvarez, Á., Schilling, O. S., Musy, S., Scheidegger, A., Peel, M., Kipfer, R., and Brunner, P.: Untangling transient groundwater mixing and travel times with noble gas time series and numerical modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5022, https://doi.org/10.5194/egusphere-egu2020-5022, 2020.

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