INTEGRATION OF ENVIRONMENTAL ISOTOPES, HYDROCHEMICAL AND MINERALOGICAL DATA TO CHARACTERIZE GROUNDWATERS FROM A POTENTIAL REPOSITORY SITE IN CENTRAL SWITZERLAND

摘要

An understanding of the origin, evolution and model ages of groundwater is important in evaluating the suitability of sites proposed for radioactive waste repositories. Such understanding cannot be derived from hydrochemical or isotopic data alone, but requires integration of both, with mineralogical, chemical and isotopic data on the host rock. This paper describes such an integrated study being carried out by Nagra at the Wellenberg, a potential repository site south of Lake Lucerne in central Switzerland. The repository host rock is a strongly deformed, slightly metamorphosed, Cretaceous marl of the Helvetic Drusberg nappe. Studies involve five boreholes to depths from 470 m to 1870 m, with geological and geophysical logging, packer testing, fluid logging and water and gas sampling during drilling. Multipacker systems are now in place for long term formation pressure measurements and fluid sampling.Water samples were analysed for the composition of their dissolved solids and for ~2H, ~3H and ~(18)O, for ~(13)C and ~(14)C in dissolved organic carbon, for the ~(87)Sr/~(86)Sr ratio of dissolved Sr, for the ~2H and ~(13)C concentrations of hydrocarbon gases, and for ~(37)Ar, ~(39)Ar and ~(85)Kr. In most cases all isotopic data can be explained consistently; for one water, however, discrepancies between some data have not yet been accounted for.