Hydraulic properties and modelling of potential repository sites in Swedish crystalline rock

Hydraulic properties of crystalline rock from four potential sites in Sweden have been measured and analyzed. The hydraulic conductivity of the bedrock has been established by transient water-injection tests with constant head followed by a pressure fall-off period. When evaluating the hydraulic conductivity, the continuum approach has been utilized. From the transient tests, the piezometric head in each section has also been calculated. Based on geological, geophysical and hydrogeological data, the sites have been divided into different hydraulic units comprising regional fracture zones, local fracture zones and rock mass. The calculated effective hydraulic conductivity based on the geometric mean values has been found to decrease with depth in all different hydraulic units. According to the Swedish concept a repository will be sited in the rock mass at 500 m depth. On repository depth, the effective hydraulic conductivity is about 5.10-11 m/s. Model calculations have been performed utilizing a numerical 3-dimensional FEM-model. The size of the modelled areas is 2-5 km2. The influence of the fracture zones on the groundwater flow at repository depth has been illustrated by alternative modelling