[en] Posiva Oy submitted am application for the Decision in Principle (the final disposal facility for spent nuclear fuel at Olkiluoto, Eurajoki) to the Finnish Government in May 1999. A positive decision was made at the end of 2000 by the Government The Finnish Parliament ratified the Decision in Principle in May 2001. The decision makes it possible for Posiva to focus the confirming bedrock investigations at Olkiluoto, where in the next few years an underground rock characterisation facility, ONKALO, will be constructed. The investigation programme on the influence of grouting in ground-water chemistry will be started by Posiva. The programme consists of long-term and short-term effects of grouting and the influence of grouting at different distances from the tunnel on groundwater conditions. As a part of this Suomen Malmi oy (Smoy) core drilled four boreholes in ONKALO. The identification numbers of thee boreholes are ONK-KR1, ONK-KR2, ONK-KR3 and ONK-KR4. An additional borehole ONK-PVA1 was core drilled for long-term monitoring purposes in a place where no grouting is planned to be done.The diameter of the borehole sis 75.7 mm A set of monitoring measurements and samplings from the drilling and returning water was carried out during the drilling. The volume of the drilling water and the returning water were recorded as well as the pressure of the drilling water. The objective of these measurements was to obtain more information about bedrock and groundwater properties. Sodium fluorescein was used as a label agent in the drilling water. The volume of the used drilling water was about 16 m³ and the measured volume of the returning water was about 11 dm³ in boreholes. The deviation of the boreholes was measured with the deviation measuring instrument EMS. The main rock types are migmatitic mica gneiss and granite. Filled fractures are most common type of fractures. The average fracture frequency of the boreholes varies from 0.6 to 3.1 pcs/m. The average RQD value of the boreholes varies from 95.6 to 100 %. In the boreholes two fractured zones were penetrated (orig.)