Carbonate chemistry and isotope analysis of the groundwater were performed to acquire new hydrogeological data, which should serve as a base for improvement of hydrogeological conceptual models of both aquifers. The radioactive isotope tritium was used to estimate the age of groundwater. Major carbonate ions and the stable isotope of oxygen were used to identify differences in the recharging areas of aquifers. Four groups of groundwater were identified.
Horizontal and vertical variations in the distribution of radiocarbon, d13C and d18O in groundwater of the Žitný island (Rye island) at the Danube River Basin, which is the largest groundwater reservoir in the Central Europe (about 10 Gm3), has been carried out using the geostatistical analysis of experimental isotope data. The core of the subsurface C14 profile represents contemporary groundwater with C14 values above 80 pMC, except a small area on the east of the island where C14 values down to 40 pMC were observed, indicating a groundwater source outside of the direct Danube River influence. This has been for the first time when vertical distributions of isotopes in different groundwater horizons have been studied.
A computerized procedure for analyzing high-resolution gamma-ray spectra was improved in three regards: the peak areas having large relative uncertainties were corrected for the possible contribution of statistical fluctuations in the continuous background, the peaks having a negative net peak area after background subtraction were included in the activity calculations and the primary measurement results were converted to the best estimate using an application of the Bayes theorem. It was proven empirically that the improvements that were introduced diminish the probability and severity of type-I errors and that they improve the consistency and accuracy of the measurement results near the decision threshold.