[en] To measure movements in the rock, TGB Borrteknik AB installed two micro seismic sensors, a k a geofones, in borehole OL-PR10 in Olkiluoto, Finland. The drilling was performed with DTH technique (hole diameter 115 mm) to a depth of 253.5 meters. Water flowing zones were passed at 53-60 meters and water flows were estimated to be more than 6 000 l/h. To prevent water inflow, the hole was completely injected at 113 meters, and thereafter re-drilled before drilling continued. During drilling, three deviation surveys were conducted with Flexit MultiSmart instrument, to ensure that the position of the borehole was within given limits. Finally the complete borehole was measured. The geofones were successfully installed at 150 and 250 meters and the hole was injected with cement. (orig.)