2012:33 Technical Note, Review of Groundwater Chemistry in SKB’s Safety Assessment SR-Site

This initial review examined SKB’s characterization of groundwater chemistry at the Forsmark site and its evolution during long time periods under different possible climates in the future. The review considered whether the geochemical data provided by SKB are reasonable and sufficient and whether the methods used by SKB for projecting geochemical conditions into the future are appropriate.  The review is based on information provided by SKB in the main report of the SR-Site project and in various main and supporting references for the safety report.

Overall, SKB’s acquisition and interpretation of groundwater chemistry data as part of the Forsmark site characterization appear to be adequate.  For example, SKB identified sulphide concentrations as an important but uncertain contributor to a safety function and appropriately dedicated additional effort to screening and improving the usefulness of the collected data.  Despite the difficulty of collecting representative groundwater samples under low flow conditions at depth, SKB has obtained numerous water samples of at least reasonable quality throughout the candidate site area.  However, there are particular regions of the candidate repository volume that have little or no high quality hydrochemical data, and an effort should be made to supplement the available data with new data from those regions.  Also, the reviewers had some difficulty tracing data-based conclusions to their original source.  The review determined that the SKB modelling to describe the evolution of groundwater chemistry is reasonable though the model has not been fully verified by comparison with chemical analyses and field observations.  The review has also identified potential uncertainties about the contribution of site characterization and construction activities to localized microbial production of sulphides.