Origin of shallow groundwater of Csepel Island (south of Budapest, Hungary, River Danube): isotopic and chemical approach

Abstract

AbstractThe shallowest aquifer of the alluvial Csepel Island is used for drinking water supply for Budapest and the surrounding villages. A previous two‐dimensional hydraulic model failed to explain many observations; therefore, a three‐dimensional hydraulic model was constructed using the software application MODFLOW. Isotopic and hydrogeochemical investigations were carried out during the period 1998 to 2002 in order to provide model data. Four water sources have been identified, having different isotopic (and chemical) characteristics. Danube water is characterized by seasonally varying δ18O values: its unweighted mean δ18O value is −10·9‰ for the years 1998 to 2002. The most negative δ18O values occur in late spring and summertime. Average tritium content is 20 TU. Infiltrated precipitation has δ18O values between −9·0 and −9·5‰. The average tritium content of the precipitation is 10 TU, and that of infiltrated precipitation must be close to this value and about half that of the Danube. The δ18O value of lake water is > −9·0‰. Its stable isotope composition plots on the right side of the local meteoric water line on the δD–δ18O diagram. Ascending deep groundwater (sampled depth of 20–140 m) has δ18O values between −12·0 and −13·5‰. Its radiocarbon age is between 16 000 and 30 000 years BP, probably infiltrated during and around the last glacial maximum (Würm III) period of the latest glaciation. Copyright © 2005 John Wiley & Sons, Ltd.