Tritium/3He dating of river infiltration: An example from the Danube in the Szigetköz area, Hungary

³H, He, ⁴He, and Ne data were obtained from a shallow ground-water system being recharged by bank infiltration from the Danube River in northwestern Hungary. After correting for excess air, ⁴He and Ne concentrations reflect a recharge temperature of about 9° C., close to the mean annual temperature of the Danube (10.4° C). Values of H plus ³Hetrit (“initial tritium”) as a function of the tritium/He age are consistent with time series measurements of tritium in the Danube. Tritium/ He ages increase linearly as a function of distance from the Danube along ground-water flow lines. A horizontal flow velocity of about 530 m yr¹ was derived from the age gradient. Most of the deviations between measured Danube tritium data and ground-water tritium/He data can be explained by dispersive mixing.