Principaux processus physico-chimiques et biologiques intervenant dans l'infiltration des produits polluants et leur transfert vers les eaux souterraines

Main physico-chemical and biological processes in pollutants percolation and their transfer towards groundwater

Service Eau, BRGM, Orléans

Abstract

Water is a transportation vector towards groundwater for various mineral and organic compounds, whatever are their origin or nature: gas, dissolved solids, colloids or particles. As the water percolates through the soil, different chemical, physical and biological processes modify the original water quality through reactions with soil, rocks and organic matter. Mechanisms occurrence and intensity vary in the three compartments of an aquiferous system: soil, unsaturated zone, and groundwater. A large range of natural and biological processes occurs in the soil zone, together with different orders of magnitude. In the unsaturated zone instead, biological activity occurs at a lesser extent than in the soil zone, and the physical and chemical processes are also predominant. Little reactive processes take place in the saturated zone, where solution, dilution and hydrodynamic dispersion are most effective in the attenuation of contaminants. Each of these three layers play their own role in the attenuation, the time of transfer; the propagation level and the final retention of the different transported products. This paper presents some major geochemical processes such as adsorption-desorption, solution-precipitation reactions, oxidation-reduction phenomena, complexation affecting contaminant transport like heavy metals, organic chemicals, bacteria.