Analysis of the migration of nonsorbing tracers in a natural fracture in granite using a variable aperture channel model

A transport model has been used to describe the migration of nonsorbing tracers in a non-uniform flow field in a natural fracture. A variable aperture channel model with particle tracking was used to characterize the aperture width of the fracture and to simulate solute transport. This model was validated using results obtained from a radionuclide migration experiment performed in a natural fracture in a quarried block of granite over a distance of 1 m. The hydraulic conductivity of the fracture was determined from the pressure differential required to maintain a given flow rate between pairs of boreholes. The results were used with a variable aperture channel model to map the aperture distribution. Pressure distribution and flow vector distribution are calculated for these experimental conditions. Groundwater containing 3H2O and 131I was injected into the fracture as a band at a flow rate of 3 ml h-1. The movement of the plume through the fracture was monitored by Geiger-Miiller probes inserted in the boreholes. The calculated results for the migration plume and elution profiles were compared with experimental results.