[en] Short communication

[en] The Geological Survey of Sweden has carried out an investigation of the bedrock of the districts of Gaevleborg and Kopparberg. A study of intrusive gabbros has been made in the north of Sweden. The investigation aims at a detailed knowledge of the structure of the bedrock in selected parts of Sweden and of the zones of fracture with reference to ground water flow. The study will result in a proposition of areas for further geological and hydrological investigations. A number of maps are presented. (G.B.)

[en] The Svartboberget study site is an elongate hill, approx 2.5 km wide and 5 km long. The depth of the Quaternary sedimentary cover is small and the percentage of exposed rock is small. The main rock type is a migmatitic paragneiss with a great amount of neosome, granite, and subordinate veins. In the northern part of the area there is a 150 m thick layer of graphitic gneiss. The fracture frequency of the rock mass is 2.6 fractures per metre and the variation with depth is insignificant. The Svartboberget study site is situated between two north-northwest orientated valleys which are defined by regional fracture zones. The thickness of these zones are from 10 to more than 250 m. They dip 30 to 40 degrees towards the south-west and can be traced over long distances. The fracture zones consist of discrete sections, locally more than 30 m thick, of highly fractured and subordinate crushed rock. The regional fracture zones delimit a rock plinth, approx 5 km² large, consisting of the actual hill Svartboberget. Within this plinth there are local fracture zones with a mutual distance of 100-500 m. They contain minor parts of crushed rock. Common infilling in the fracture zones are calcite, chlorite, illite and zeolite. The hydraulic conductivity in the rock mass of Svartboberget decreases with depth. At 100 m depth, the conductivity is c. 4 x 10^-9 m/s and at 500 m c. 5 x 10^-11 m/s. The hydraulic conductivity of the local fracture zones in Svartboberget is at 500 m depth 8 x 10^-10 m/s. The topographic relief of the area implies that there is a high hydraulic gradient in the bedrock. This has also been confirmed by piezometric measurements where i.a. pressure differences of a 30 m water column have been registered in a drill hole. (author)

[en] The geologic and tectonic conditions of the Finnsjoen site and its surroundings have been studied on several scales ranging from regional to site scale. The Finnsjoen study is situated within a 50 square km shear lens. This lens is a part of a regional, c.20-30 km wide, WNW trending shear belt that was developed 1600-1800 million years ago. The final repository for reactor waste at Forsmark is also situated within this shear belt. The Finnsjoen Rock Block, bounded by regional and semi-regional fracture zones, constitute the main part of the Finnsjoen site. The size of the block is about 6 square km. A northeasterly trending fracture zone, Zone 1, divides this block into two lower order blocks, the northern and the southern block. In general, interpreted fracture zones, as well as the rock mass in general, are far better known in the northern Finnsjoen block compared to the southern block. This is due to extensive and detailed investigations of a gently dipping fracture zone, Zone 2, in the northern block. A tectonic model including 14 fracture zones is suggested for the Finnsjoen site and its surroundings. These zones have mainly been interpreted from lineament maps and to some extent from borehole measurements. The lack of borehole data implies that many of interpreted fracture zones, especially in the southern block outside the Finnsjoen site, should be regarded as tentative. The good general knowledge of the geologic and geohydrologic conditions in the northern Finnsjoen block, and possible stagnant groundwater conditions below Zone 2, makes the northern block the most suitable location for the generic repository at the Finnsjoen site. (authors)

[en] This report presents the results from a geological study of the layers of sedimentary rocks and their function as 'hydraulic barriers'. (35 refs.) (K.A.E.)

[en] The report covers the performance and interpretation of a series of hydraulic interference tests and a tracer test in fracture zone 2 within the Breandan area, Finnsjoen. The interference test were performed by pumping from isolated sections of one borehole and recording the resutling pressure changes in multiple-observation sections (generally five) in adjacent boreholes as well as in the pumping borehole. The tracer test was performed by pulse injection of tracers in isolated sections of the near-region observation boreholes and monitoring the break-trough of tracers in the pumping borehole. The interference tests showed that different response patterns were generated in the near-region and in the more distant region from the pumping borehole. In the near-region, primary responses in high-conductive, low-porosity flow paths between the boreholes generally dominate. The tracer test also indicates that the primary responses may be strongly influenced by local heterogeneities. At longer distances more averaged responses generally occurred with similar responses in the multiple-sections in the boreholes. The hydraulic interference test as well as the tracer test documented a very high transmissivity of zone 2, particularily in its upper part. The interference tests indicated hydraulic interaction between zone 2 and the over- and underlying rock. Zone 2 was found to be bounded and may be represented by a triangular-shaped area. Interflow to zone 2 occured during pumping, possibly via other fracture zones. Responses due to the pumping occurred at long distances (up to about 1.5 km) from the pumping borehole. A numerical model was used to simulate the responses of the interference tests. Good agreement was achieved between simulated and observed responses from the most distant boreholes but decreased agreement in the near-region boreholes. This fact was attributed to local heterogeneities in the near-region. (76 figs., 50 tabs., 36 refs.)

[en] In the present report all available data gathered from the Finnsjoen area of potential use for numerical modelling are compiled and discussed. The data have been collected during different phases during the period 1977-1989. This inevitably means that the quality of the measured and interpreted data varies in accordance with the continuous developments of improved equipments and interpretation techniques. The present report is an updated version of the SKB progress report 89-24 with the same title and authors, see introduction. (au)

[en] The large and small scale geometry of the fracture system at Stripa have been determined using regional scale remote imaging techniques and detailed data from drill core logging and drift mapping. These data identified two sub vertical dipping sets, a strong north-south striking set and a weaker set with a northwest-southeast strike, and two sub horizontal fracture sets. Fracture mapping showed a clear difference between fracture geometry in the average rock and that in the largest fracture zone, the H-zone, that was identified in the test site. The small scale fractures in the averagely fractured granitic rock at the Stripa mine site appear to mimic the large scale features, both in orientation and density. (authors). 14 refs., 2 tabs., 7 figs

[en] During the period from 1977-1986 SKB (Swedish nuclear Fuel and Waste Management Co.) performed surface and borehole investigations of 14 study sites for the purpose of assessing their suitability for a repository of spent nuclear fuel. The next phase in the SKB site selection programme will be to perform detailed characterization, including characterization from shafts and/or tunnels, of two or three sites. The detailed investigations will continue over several years to provide all the data needed for a licensing application to build a repository. Such an application is foreseen to be given to the authorities around the year 2003. It is presently not clear if anyone of the study sites will be selected as a site for detailed characterization. Other sites with geological and/or socio-economical characteristics judged more favourable may very well be selected. However, as a part of the background documentation needed for the site selection studies to come, summary reports will be prepared for most study sites. These reports will include scope of activities, main results, uncertainties and need of complementary investigations. This report concerns the Kamlunge study site. (79 refs.) (au)

[en] The proposed nuclear waste repository is to be constructed at Olkiluoto which is situated on the Precambrian rocks of the Fennoscandian shield. The rocks are made up of a complex mix of meta-sediments and meta-igneous units that have undergone several episodes of metamorphism and tectonic deformation. The latter have resulted in the formation of a variety of planar features including a regional fabric, ductile shear zones, fracture zones and discrete fractures. It is within this poly-metamorphosed foliated and fractured rockmass that the repository is to be sited. In order to position the repository appropriately it is necessary to determine the geometry, spatial organization and properties of these zones of weakness and the properties of the intact rock. This report critically examines the procedures and techniques used to determine these various parameters and the rational behind the proposed location of the underground rock characterization facility (ONKALO) and its access tunnels and shafts. Particular attention is given to understanding the current stress field operating in the rock, the effect of the zones of weakness on the stress orientation and the confidence levels with which the position, geometry and properties of the major planar zones are known at the depth of the proposed repository. (orig.)