Age and recharge area of thermal waters in La̧dek Spa (Sudeten, Poland) deduced from environmental isotope and noble gas data

Abstract Environmental isotope and noble gas data are shown to identify the global parameters of the thermal water system in Ladek Zdroj (Spa), Sudeten, Poland. The mean 14 C age is about 5 ka, and the δ 18 O and δD data are assumed to yield the mean altitude of recharge by making use of the altitude effect known for the Sudeten area. The natural discharge rate multiplied by the 14 C age gives the total volume of water, whereas the volume of the host rock is roughly estimated for three scenarios of system dimensions. For these scenarios, the ratio of these two volumes yield a total porosity in the range of about 0.005–0.014, which, in a good approximation, should be equal to the matrix porosity. Laboratory determinations of unaltered rock samples yield a matrix porosity of 0.008 ± 0.001. For the three scenarios, the tracer age and matrix porosity are shown to yield a hydraulic conductivity for the whole system in the range 0.8–1.6 × 10 −8 m s −1 , without any knowledge of the fissure network parameters. Noble gas temperature compared with known temperature dependence yields the mean altitude of the recharge area equal to that found from the δ 18 O and δD data. The radiogenic 4 He excess and 40 Ar 36 Ar ratios are consistent with the mid-Holocene age determined from the 14 C data.