Pollutant transfer in the geological environment An understanding of the mechanisms by which water and pollutants are transferred to ground, rock and ground water is necessary for planning site development and future operations. This approach involves 3 steps: Natural system characterization. Testing. Simulation of the natural system and its development.   1 - Characterization of the natural system   Geology and hydrogeology of sites. Data collected in the field and from drill cores provides information about subsoil type and structure, together with water drainage direction and speed.     Example of 3D restoration of the geological character of the ground.   Observation of quartz grain surface through a scanning electron microscope. Water and soil geochemistry. In situ measurements and sampling are used to produce maps and profiles of sites for environmental monitoring purposes. Groundwater replenishment by rainy periods. Ground section and its radioactivity distribution map.   2 - Testing to build substantiated models   Laboratory characterization of the elemental mechanisms responsible for water drainage and pollutant migration; analog modeling of column migration. Curves showing sand column infiltration of tritium and uranium (x-axis = pore volume renewal number) Natural site instrumentation Physical and chemical monitoring of soil, rocks, and groundwater. Thermo-hydro-mechanical system study. Meteorology. Sequential sampling of infiltration water in an underground gallery. Diagram of a multiparameter station for continuous monitoring of interactions between the atmosphere, soil and groundwater.   3 - Simulation of the natural system and its development   Numerical modeling of hydrogeological transfers: Simulation of underground water drainage and transport of radionuclides from solid, liquid or gaseous waste in the ground or the atmosphere. Numerical modeling of the chemical behavior of radionuclides in the environment: determination of species in solution, dissolution and desorption reactions, and simulation of fluid-rock interactions. Combined hydrogeological and geochemical modeling of radionuclide transport into the ground and aquifers. Modeling of the 30-year development of tritium concentrations in an aquifer from a theoretical source. Modeling of hydrogeological processes provides a 3D-representation of the transfer of surface water into the groundwater. 2D simulation of the surface of groundwater given infiltration from the ground. Numerical model coupling can be used to simulate migration of a radionuclide to the natural environment, by integrating the set of processes responsible for transport, such as water drainage, radionuclide speciation and its interactions with ground components. Simulation of vertical uranium migration to siliceous soil from a point source.