[en] As part of its research and development programme on the possible burial of solidified radioactive waste in a clay formation (Boom clay) the Nuclear Research Centre at Mol is conducting studies aimed at determining the characteristics of the potential site at Mol more precisely. The studies involve field measurements, laboratory tests and experiments on samples, and mathematical simulations. Geological (drilling), geophysical (seismic campaign) and hydrological investigations (installation of piezometers and periodic measurements of groundwater) have confirmed the geological and hydrological structure of the Mol site. A number of internal parameters of the Boom clay have been determined from samples taken at different levels during drilling, namely, the chemical and mineralogical composition, the ion exchange potential, physical properties in general and geomechanical characteristics in particular. Various mathematical models have been constructed to help assess the magnitude of certain technical and safety problems. The migration of ions through a sorbant medium has been evaluated in this way, taking into account the numerical values obtained in the field or in the laboratory. The various factors studied, the methods of data acquisition and the results obtained are reviewed in the paper. (author)