Analysis of single- and cross-hole tests at the BK-site, Grimsel Test Site

Attempts are presented to apply the methodology described by Mishra to a number of pressure-recovery and constant-head injection tests which were performed in the fractured crystalline rock of the BK-area at the Grimsel Test Site. Results clearly show that the flow system at this site is not homogeneous and 2-D radial. Diagnostic plots and numerical simulations for the single-hole analysis show evidence of hydraulic boundaries which affect the pressure responses observed during the recovery period and in the injection intervals. The geometry of the flow system is seen to change from radial or sub-radial at early times to linear or bounded at late times due most probably to the presence of lamprophyre dykes which act as low-permeability boundaries. Analysis of the observation intervals (cross-hole analysis) reveals the presence of a high transmissivity feature, the location of which is in good agreement with existing geological information. The single- and cross-hole analysis are successful in providing estimates of transmissivities for all monitored intervals and of undisturbed hydraulic head for one interval. However, little confidence can be assigned to estimates of storativity due to severe uncertainty relative to the true migration path of the pressure-pulse. (author) figs., tabs