Crosshole radiowave imaging survey was conducted late in 2005 at Eurajoki Olkiluoto in Finland. Work belongs to site characterization process for spent nuclear fuel disposal into Finnish bedrock, which is run by Posiva Ltd. Crosshole radiowave imaging (RIM) was performed as a joint operation of Geological Survey of Finland and FGUNPP Geologorazvedka from Russia, using FARA-MCH tool. Pöyry Environment reviewed the results and compared the material to existing background information. The field work performed successfully between two borehole pairs at surface collar distances of 250-300 m. Recorded amplitude data were processed to resistivity images using crosshole tomographic reconstruction. The results prove that the method can be used in 100-400 m scale between boreholes to delineate and follow sulphide-bearing horizons, which are controlled by ductile and brittle geological processes in the site. Obtained results indicate that the location and geometry of resistive and conductive units in bedrock correlate rather well with data from geological mapping and geophysical logging from boreholes. The obtained projected geometry correlates also rather well with one subset of seismic 3-D reflections, and with geophysical electrical and electromagnetic results from the site.


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