2012:37 Technical Note, Selective review of the hydrogeological aspects of SR-Site

This review of the hydrogeology is selective.  It focuses on the measurement, interpretation and modelling of the potential repository host rock, that is the rock domain FFM01<-400m.  It accepts as reasonably accurate the measurement and representation of the more transmissive parts of the hydrogeological system, particularly the near-surface 150m in the form presented by SKB. 

SKB have decided that their main field measurement method is the Posiva flow log.  The review notes the speed and efficacy of the method in identifying individual actively flowing features/fractures.  However, I have concern that the lower measurement threshold is too high and behaviour at low flows is insufficiently supported theoretically. 

The subsidiary method based on the ‘Pipe String System’ (PSS) (i.e. straddle packer injection testing) is strongly focussed on measuring hydraulic conductivity.  There is little or no emphasis on determining the independent ‘checking’ measurement, head.  In addition, the PSS method has produced an ‘unnatural’ looking dataset with a significant change of characteristic just below the measurement limit.

The method by which measurements produce parameters in the probabilistic ‘discrete fracture network’ (dfn) modelling is difficult to understand and different aspects of the same dataset are used as input and calibration.  There is a lack of sufficient independent checking methods.