Silicon-32 in different aquifer types and implications for groundwater dating

The paper presents results of a study carried out in order to assess the applicability of 32Si for groundwater dating. Measurements of 32Si in soil samples of the unsaturated zone, of drainage waters and plant material give a basis for estimating the initial concentration of 32Si in groundwater. Different aquifers with groundwater of young and moderate ages have been selected for groundwater studies. For obtaining independent age information tritium was found to be a suitable reference isotope. A quantitative interpretation of the 32Si data is generally complicated by geochemical processes, mainly in the unsaturated zone. Favourable conditions for the use of 32Si in hydrogeology seem to exist in phreatic sand aquifers, in limestone aquifers, and, depending on the thickness and composition of the unsaturated zone, in sandstone aquifers. Further improvement of the 32Si method needs a better understanding of the geochemical processes affecting this isotope. (author). 16 refs, 7 figs, 2 tabs