Overview of geological and hydrogeological conditions of the Aspo Hard Rock Laboratory site

The site of the underground facility, the Aspo Hard Rock Laboratory, was ex cavated at a depth of 450 m below the island of Aspo and has been extensive ly investigated by geological, hydrogeological and hydrochemical methods as part of the geoscientific research for disposal of nuclear waste in Sweden . The geological history of the area dates back to 1.85 Ga and is dominated by granitoids belonging to the Trans-Scandinavian Igneous Belt but also in cludes basic sheets and xenoliths and dikes of fine-grained granite. Seven tectonic episodes, giving rise to fracture mineralization, are recognised. The major discontinuities and fracture zones were characterised from surfac e investigations before the tunnel construction work started. These structu ral features were also identified in the tunnel and are, as predicted, the major water conducting features. Sets of open fractures in the NNW-NW and N -S directions and the brittle fine-grained granite are other important wate r conductors. Groundwater flow modelling shows that the location of Aspo is land has a major impact on the current distribution of groundwater salinity due to varying hydraulic/boundary/conditions in the late and post glacial period. (C) 1999 Elsevier Science Ltd. All rights reserved.