Geochemical Journal, Vol. 51 (No. 5), pp. 423-437, 2017
Jakub Jankovec,1 Tomáš Vitvar,1 Martin Šanda,1* Takuya Matsumoto2 and Liang-Feng Han2
1Czech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7, CZ-16629 Prague, Czech Republic
2International Atomic Energy Agency, Isotope Hydrology Section, Division of Physical and Chemical Sciences, Vienna International Centre, P.O. Box 100, A-1400 Vienna, Austria
(Received October 14, 2015; Accepted December 30, 2016)
Groundwater recharge amounts and residence times were estimated in the quaternary aquifer of the Jizera Mountains, Czech Republic, using noble gases, 2H, 18O, 3H and CFCs. Tracer ages from years to decades were determined for water in a shallow sedimentary aquifer (three boreholes of 10, 20 and 30 m depth). Approximately 90–180 mm of precipitation (7–14% of annual precipitation) infiltrates to deep percolation. A mean percolation velocity of 0.6 m/y in the sedimentary Uhlířská aquifer was estimated based on an apparent groundwater age of 40 years at 30 m depth. A lumped parameter approach was used to calculate groundwater residence times based on synoptic evaluation of 3H/3He, 3H and CFCs. Groundwater apparent ages in the shallowest borehole (10 m depth) determined by 3H/3He are younger than those determined by CFCs. This discrepancy is caused by partial re-equilibration of water with modern air, and by admixing of water that has zero age. The pronounced variations of δ18O values in the borehole may be ascribed to a young component quickly recharged from the air-exchanged stream water or through preferential flowpaths.
Key words: apparent age, deep percolation, groundwater dating, environmental tracers, mountain catchment