Hydrogeochemical evaluation and modelling performed within the Swedish site investigation programme

Site studies for SKB’s (Swedish Nuclear Fuel and Waste Management Co.) programme of deep geological disposal of nuclear fuel waste currently involve the investigation of two locations, Forsmark and Laxemar–Simpevarp situated on the eastern coast of Sweden, to determine their geological, hydrogeochemical and hydrogeological characteristics. Present work describes hydrogeochemical methods such as conceptual postglacial modelling, explorative analysis, mathematical modelling and construction of site descriptive models. The complex groundwater evolution and patterns at Forsmark and Laxemar–Simpevarp are a result of many factors such as: (a) the present-day topography and proximity to the Baltic Sea; (b) past changes in hydrogeology related to glaciation/deglaciation, land uplift and repeated marine/lake water regressions/transgressions; and (c) organic or inorganic alteration of the groundwater composition caused by microbial processes or water/rock interactions. The major conclusion is that changes from glacial rebound and hence hydrogeology seems to have a major influence on the groundwater chemistry. These complex data require a multidisciplinary approach to their interpretation which is based on 25 years of experience within the SKB radioactive waste site investigation programme.