In-situ tracer experiment and solute transport characterization of a fracture in granitic rock

In-situ tracer experiment is considered an effective means of understanding the migration characteristics of groundwater solutes under actual underground environments. The authors have developed tracer test equipment applicable to mainly fractured rock masses, and methods for evaluating experimental results. To confirm their usefulness, a tracer experiment was conducted for a single fracture in a granitic rock mass at the Mizunami Underground Research Laboratory. A numerical analysis was performed for the breakthrough curves obtained from the experiment. As a result, we were able to estimate the solute transport characteristics of the target fracture, including the aperture, the dispersion length, and the sorption coefficients of the sorbing tracers on the fracture surface and the rock matrix. Batch sorption tests were also conducted for rock samples collected at the test site.The differences between the sorption coefficients estimated from in-situ tracer tests and those obtained from batch tests were shown for Toki granite.