GEOCHEMISTRY OF SPRINGWATERS IN MOLASSE AQUIFERS - TYPICAL MINERAL TRACE-ELEMENTS

Water investigations have been conducted throughout the Molasse basin between Chambery (France) and Lint (Austria), but mainly in the Swiss Molasse basin, in order to provide an overview of the spatial distribu tion of inorganic water compounds in different Tertiary aquifer lithol ogies. The data set comprises more than a hundred water analyses from different springs with catchments that completely drain a single, lith ologically most ly homogenous Molasse terrain unit. Recharge areas of selected springs were generally not affected by runoff from urban wate rs, waste deposits, agricultural activities or roads. The chemical mar king due to various sorts of metallic water pipe materials was taken i nto account. Such spring water should be free of major human influence s and represent the most natural conditions possible. Leachate tests o f crushed rocks and comparison with precipitation and soil water compo sitions allowed to identify the geogene origin of the dissolved ions i n natural groundwaters. The water analyses have been evaluated by inte grating sedimentological, stratigraphical and structural data. With th is procedure, about 30 different aquifer sub-types could be defined wi thin the Molasse deposits according to their sedimentary petrography ( sediment feeder system, ''Schuttung''), to their tectonical structure (hydraulic conductivity) and to their grain size distribution (deposit ional environment). Complete analyses comprising 33 inorganic compound s have been executed and contribute to a definition of natural groundw ater quality. Due to the very low detection limits of the HR-ICP-MS in the order of magnitude of mu g/l, multielement trace analyses, such a s those of chromium, uranium, lithium, molybdenum and barium, have pro ven to be of interest for the determination of the geological water or igin in Molasse deposits. Moreover, the presented results show, that t he great variety of the Molasse basin sediments forming aquifer hostro cks is reflected by the chemical groundwater composition. Thus, a grea t number of springwater, usually classified as calcium-magnesium-bicar bonate type, can chemically be clearly distinct with respect to the ge ological nature of the aquifer as well as the flow system to which the studied waters belong.