HR: 0800h
AN: H51B-0458    [Abstracts]
TI: Hydrogeochemical modelling of a saline pollution in alluvial groundwater: the example of the Rhine aquifer
AU: * lucas, y
EM: Yann.Lucas@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AU: clement, a
EM: aclement@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AU: fritz, b
EM: bfritz@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AU: chabaux, f
EM: fchabaux@illite.u-strasbg.fr
AF: Centre de Geochimie de la Surface, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AB: One of the newest challenges to the earth science is to build numerical approaches that are able to combine both hydrological and geochemical constraints. The objectives are broad and may concern both the water quality and the determination of reaction rates at the water/rock interface. To explore the hydrogeochemical behavior of groundwater, we focused on the alluvial water table of the Upper Rhine valley because it has undergone a huge pollution related to the exploitation of the Alsace potash mines during the XXth century. This offers the opportunity to know with precision the nature of the pollution by infiltration of saline waters and point zero in space and time. Examination of Na+ and Ca2+ concentration values revealed that a loss of Na compared to Cl occurs together with a gain in Ca. This chemical observation is not consistent with a single dilution process and strongly advocate for ion exchanges at the water-rock interface. The hypothesis of cation exchange in the aquifer clays has been done, as it contains Montmorillonite which enables such an exchange. We have then modelled the water chemistry along on few kilometres downstream from a salt dirt heap. The 1D model is built after the existing hydrochemical numerical code KIRMAT. The aquifer rock is modelled by 1% of Montmorillonite and 99% of inert rock. KIRMAT deals with clays as solid solutions, in the present case with a Na- pole and a Ca-pole. Through the history pollution modelling over approximately hundred years, the calculated values show a good agreement with measurements relating to the spatialized chloride concentrations, pH, sodium and calcium concentrations. These results validate the cation exchange hypothesis: they enhance our understanding of the aquifer system submitted to a saline pollution; they also show the interest of the coupled hydrogeochemical approach for natural systems.
DE: 0496 Water quality
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2007 Fall Meeting