20 Jun 2023
 | 20 Jun 2023
Status: this preprint is currently under review for the journal HESS.

Short high-accuracy tritium data time series for assessing groundwater mean transit times in the vadose and saturated zones of the Luxembourg Sandstone aquifer

Laurent Gourdol, Michael K. Stewart, Uwe Morgenstern, and Laurent Pfister

Abstract. While in the southern Hemisphere a single water sample can be sufficient for tritium-based young groundwater dating, several tritium measurements spanning over multiple years are still needed in the northern Hemisphere. Although it is advised to focus tritium-based groundwater age dating on sites where long chronicles of tritium data are available, we tested in this study the potential for short high-accuracy tritium data series (~4 years) to date groundwater from 35 springs draining the Luxembourg Sandstone aquifer (Central Western Europe). We determined groundwater mean transit times by using the lumped parameter model approach in a Monte Carlo uncertainty estimation framework to provide uncertainty ranges inherent to the low number of tritium data at hand and their related analytical errors. Our results show that unambiguous groundwater mean transit time assessments cannot be determined solely based on such recent short tritium time series, given that several ranges of mean transit times appeared theoretically possible. Nonetheless we succeeded in discriminating groundwater mean transit times in the vadose and saturated zones of the aquifer through a stepwise decision process guided with several supplementary data. Our findings are consistent with both the tritium measurements of individual springs and the hydrogeological context of the study area. We have been able to improve our understanding of the water transit times in the Luxembourg Sandstone aquifer. We particularly highlighted a horizontal-vertical water velocity anisotropy in the Luxembourg Sandstone - a key feature that deserves to be explored further.

Laurent Gourdol et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2023-152', Anonymous Referee #1, 24 Jul 2023
  • RC2: 'Comment on hess-2023-152', Anonymous Referee #2, 18 Sep 2023

Laurent Gourdol et al.

Laurent Gourdol et al.


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Short summary
Determining water transit times in aquifers is key to a better understanding of groundwater resources and their sustainable management. For our research, we used high-accuracy tritium data from 35 springs draining the Luxembourg Sandstone aquifer. We assessed the mean transit times of groundwater and found that water moves on average more than ten times slower vertically in the vadose zone of the aquifer (~12 m/year) than horizontally in its saturated zone (~170 m/year).