Das Projekt "Untersuchung der hydrogeologischen und geochemischen Prozesse, die mit Tiefenkreislaeufen entlang des Jura verbunden sind, auf der Grundlage von neuen Bohrloechern in Delemont, Yverdon, Genf und Aix-les-Bains" wird vom Umweltbundesamt gefördert und von Universite de Neuchatel, Institut de Geologie, Centre d'Hydrogeologie durchgeführt. Leading Questions: Evaluation of the hydraulic parameters. Determination of the recharge basins. Estimation of the groundwater transit time. Assessment of the chemical reactions taking place at depth. Conceptual modeling of the global groundwater circulations. Abstract: The study of the hydrogeological and hydrochemical processes in the deep Malm aquifers along the Jura Range has started in 1992. This project is focused on the sites of recent deep boreholes reaching the limestones aquifers of the Malm (430 to 2530 m) in Delemont (JU), Yverdon (VD), Geneva (GE) and Aix-les-Bains (France). The main objectives are to evaluate the origin and hydraulic characteristics of these deep groundwater flows, to determine their extension and their link with other hydrogeological systems, to estimate their underground transit time, and to assess the water-rock interactions governing their chemical and isotopic composition. Numerous measurements and analyses have been performed on 35 springs and boreholes, as well as on limestones samples. For each site, mixing processes have been deciphered between the original fluid of the Malm aquifer and one or several components of diverse origin. The latter ones come either from shallow, cold, dilute and recent groundwaters, or from deeper, warmer, more mineralized and older end-members. The complexity of the flow systems is obviously proportional to the intricacy of the geological and tectonic environments. Consequently, groundwater transit time is very variable from site to site. On the contrary, all the fluids sampled in the Malm limestones and analyzed show a low mineral content (300 to 1000 mg/l), whatever are the temperature (12 to 72 degree C) and the underground transit time (deeper 10 high 0 to higher 10 high 3 y).