Determination of soil hydraulic properties of potential low and intermediate level waste disposal sites in Bulgaria. Assistance to site selection and site evaluation for low- and intermediate level waste disposal in Bulgaria

In the framework of selecting a suitable site for final disposal for low- and intermediate level short-lived radioactive waste in Bulgaria, a determination of soil hydraulic properties of two potential sites was made. The investigated samples are from the vadoze zone of the unsaturated deep soil profiles, which are considered as a pathway of eventual radionuclide migration from the disposal facility to the biosphere. The hydraulic parameters are determined from the relationship ”soil water content – pressure head” (soil water retention curve). We established a series of equilibria between water in the soil sample and a body of water at known potential. According to the pressure head value, two types of apparatuses were used – a sand bath and a pressure cell. The hydraulic parameters of the samples were obtained by implementing the optimization procedure for retention curves available in the computer code RETC. The resulting hydraulic parameters can now be used in the simulation models for the prediction of variably saturated water flow and concomitant radionuclide transport in the deep unsaturated sediments of the potential disposal sites. This is important input to an evaluation of the suitability of potential sites for developing a near surface disposal facility.