Dipole tracer experiment in a low-angle fracture zone at Finnsjoen - results and interpretation. The fracture zone project -phase 3

摘要

This report described a large scale tracer experiment performed in a dipole flow geometry in the upper highly transmissive part of a low angle fracture zone, called zone 2, at the Finnsjoen study site. The experiment was performed as a part of phase 3 of the fracture zone project aiming to characterize a major fracture zone. The purpose of the experiment was to determine transport parameters for zone 2 and to test the applicability of the experimental method for characterization of major fracture zones. The dipole experiment involved a total of 15 tracer injections including 14 short-lived radionuclides and 5 inactive tracers. Both sorbing and non-sorbing tracers were injected and some of them several times. Tracer breakthrough was monitored both in the pumping hole at a distance of 168 m and in two observation holes inside the flow field at distances 157 and 223 m, respectively. The evaluation of the results included both 1-D modelling of individual flow paths as well as 2-D modelling of the entire flow system. Inverse modelling technique was applied for both models including regression statistics. The statistics were used to assess the uniqueness and goodness of the model fits. The 1-D modelling was used to study effects of multiple flow paths and to determine transport parameters such as mean travel times and dispersivity. The purpose of the 2-D modelling was to study effects of the magnitude and direction of the natural gradient, anisotropy, and leakage. Comparison with previous prediction was also made with the 2-D model. The report also contains a comparison of all three tracer experiments performed in the upper part of zone 2. 34 refs. (Atomindex citation 25:049290)