Hydrochemical investigations in crystalline bedrock in relation to existing hydraulic conditions: experiences from the SKB test-sites in Sweden

This report represents the compilation, discussion and interpretation of hydrochemical and hydraulic data resulting from the SKB test-site investigations carried out over a period of three years (1982-84). By systematically applying hydrological and geological considerations to each sampled horizon, it has been possible to differentiate between those groundwaters which are reasonably representative for the depth sampled, from those which have been subject to contamination from different sources. Groundwaters which are here considered representative are defined as those which show no evidence of mixing with other water sources, whether from drilling water, younger, near-surface water, or other deeper groundwaters. As a consequence, only a few sampled horizons can be considered with serious hydrochemical attention. The lack of representative groundwater samples, whilst often due to technical problems or sampling from non-conductive sections of the boreholes, also illustrate the extremely complex geometry of the premeable fracture systems in crystalline bedrock, and thus the difficulty of establishing the nature and depth relation of the groundwater tapped. Although the main findings of this study have revealed gross inadequacies in the hydrochemical programme, valuable experience has nevertheless been gained. Consequently, some of the improvements recommended in Section 7 of this report have been already implemented resulting in higher sampling standards and thus water samples which are much more representative for the hydrogeological environment under investigation. (author)