Reply on RC1 [* Cross-Reference *]

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.