Application of the chlorine-36 method in the study of groundwater recharge by the Danube river in north-western Hungary (Szigetkoez area)

The gravel aquifer within the Sigetkoez Plain in Northern Hungary is mainly fed by the infiltration of the Danube River. As shown by previous studies this infiltration process away from the Danube in southern direction along distinct flow paths can be quantified with environmental isotope techniques. To a distance of about 30 km away from the infiltration area of the Danube the groundwater reflects also the evolution of the anthropogenic activities in the last decades as by nuclear bomb explosions in the atmosphere and the by the increased production and use of halocarbons. But as tritium has a relatively short half life (12.5 years) it was only possible by the combination with the Helium-3 technique to trace the exact position of the bomb peak corresponding to the highest tritium concentration in precipitation due to the infiltration of the Danube River. In the now presented study results of chlorine-36 analyses are demonstrated as additional isotope method. This natural radioisotope which was also produced by the nuclear bomb tests in the atmosphere behaves because of the much greater halve live of 300,000 years within this time span as an ideal stable constituent. It presents therefore an independent method to check the achieved model of aquifer recharge by river infiltration.