The Stripa mine test site, located approximately 200 km west-northwest of Stockholm, Sweden, is the focal point of a detailed fracture-hydrology study. Preliminary results from three of the five main components of this program are discussed in this paper. These three components are
a detailed borehole testing program to determine the directional permeabilities of the fractured granite,
a macro permeability experiment - an attempt to measure the average permeability of a large volume of the fractured granite, and
a detailed study of the groundwater geochemistry to determine the origin and age of the groundwater both in and around the immediate mine area.
Preliminary analysis of the borehole tests gave equivalent porous media hydraulic conductivities that ranged from 10−5 to 10−10 cm/sec. Preliminary results from the macro permeability experiment suggests bulk rock mass hydraulic conductivities of about 10–9cm/sec. Environmental isotope and chemical analysis of waters collected from water bearing fractures in the granite show that the groundwaters are many thousands of years old and their salinity increases with depth. It is not yet clear whether the deep groundwaters (>338m) belong to local or regional flow systems.
Fractured crystalline and argillaceous rocks have been proposed as alternative host rocks for storage or disposal of high-level radioactive waste. To evaluate this proposal, one must obtain an accurate description of the hydrology of fractured rocks. Thus, one must begin to develop data bases that permit one to answer questions such as:
what is the role of fractures in determining the nature (isotropic or anisotropic) of fractured rock permeability? and
under what conditions, if any, can fractured rock masses be treated as porous media or equivalent porous media?
The first question dictates that we must develop methods of characterizing a fracture system and its role in determining the hydrology of fracture systems in order to provide a framework within which to interpret local and large scale flow systems in fractured rock masses. Answers to the second question determine the type of borehole testing programs that will be undertaken in concept verification studies. Borehole testing programs must provide the data needed to develop hydraulic parameters that clearly describe how fluids move and the rate at which they move through fractured rocks. based on porous media concepts will not provide sufficient data if, as is permeability of fractured rocks is highly anisotropic.
Borehole testing programs generally agreed, the The volumes and rates of groundwater movement through fractured rock masses, predicted from borehole tests, must be supported by data obtained from other field studies. Such supporting data can be obtained from large-scale tunnel or shaft pumping tests, that perturb a volume of the rock mass many times larger than that tested by a single borehole, and through detailed studies. of the geochemistry and isotopic composition of the groundwaters. Groundwater flow systems configuration, calculated from measured distributions of permeabilities, porosities and hydraulic head boundary conditions, must be consistent with data of the evolution of groundwater geochemistry in fractured rocks and the distribution of ages inferred from isotope analysis.
