A research programme has been undertaken at ENEA with the financial support of the Ministry for the Environment in the aim at evaluating the environmental impact of hazardous waste disposal. Experimental tests have been carried out in order to obtain a series of data on which models for the prediction of future contamination are based, in the frame of such programme. The release of toxic elements from solidified wastes, as well as the release mechanisms, were evaluated. The interaction between conditioned wastes and soil was assessed in labo. scale with the help of lysimeters using siliceous sand or natural pozzolan as simultants of ground soil. Moreover, the relative mobility of different cations travelling through the soil was determined by measuring the linear distribution coefficient. Finally the permeabilities of both conditioned waste and backfill material were taken into account and related to each other. Due to the strict relationship existing between water permeability and cement capillary pores, measurements of cement porosity by mercury intrusion porosimetry were also performed.