Présentations Colloques

    Oral Presentation
    Session 8.04: Isotopic and residence time tracers
    Alazard Marina
    Origin of groundwater and CO2 in the crystalline environment of Saint Galmier, France
    The Badoity natural mineral water in Saint Galmier, France was investigated in order to determine the origin of the water, the carbonic gas and the residence time of groundwater in the fractured granite aquifer. **Two distinct populations of sparkling natural mineral water were identified based on groundwater geochemistry (major ions, delta18O-2H, delta13C, 3He 4He, noble gases)- i) a relatively low-mineralized and young (below 30 years) groundwater and (ii) highly mineralized, CO2-rich, deeper and older groundwater. The residence time of groundwater was estimated using radio-chronometers (14C, 3H, SF6, 39Ar and 85Kr). However, in our study area the use of such tracers is complicated by a series of factors- (i) degassing of upwelling water due to high pCO2 pressures may lead to a decoupling of the gas (age) and water (age) and makes 14C dating very difficult+ (ii) the fractured crystalline basement with various degree of weathering causes very heterogeneous hydraulic and geochemical conditions+ (iii) high water temperatures at greater depth and elevated U contents in the rocks facilitate the release of radiogenic isotopes. Most of these factors were overcame by the completing combination of suitable methods e.g is the 85Kr dating method much less sensitive to degassing compared to other gas based tracers. ****


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