On the track of contamination

The understanding of the physico-chemical mechanisms of pollutant migration in the ground implies first to know the structure of aquifers and that of geological layers in which water flows and secondly to be able to model the water flow. The flow of water is driven by 2 basic equations: the Darcy law and the conservation of mass. The migration of pollutants is led by 4 mechanisms: advection that is the transport by water, kinematic transfer (passage from a flow line to another due essentially to heterogeneities), molecular diffusion such as Brownian movement for instance and chemical reactions between pollutants themselves or with the rock components. The great difficulty comes from the non-linear coupling between advection-transfer-diffusion processes and chemical reactions. (A.C.)