ANALYSIS OF THE MIGRATION OF NONSORBING TRACERS IN A NATURAL FRACTUREIN GRANITE USING A VARIABLE APERTURE CHANNEL MODEL

A transport model has been used to describe the migration of nonsorbin g tracers in a non-uniform flow field in a natural fracture. A variabl e aperture channel model with particle tracking was used to characteri ze 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 blo ck of granite over a distance of 1 m. The hydraulic conductivity of th e fracture was determined from the pressure differential required to m aintain a given flow rate between pairs of boreholes. The results were used with a variable aperture channel model to map the aperture distr ibution. Pressure distribution and flow vector distribution are calcul ated for these experimental conditions. Groundwater containing (H2O)-H -3 and I-131 was injected into the fracture as a band at a flow rate o f 3 ml h(-1). The movement of the plume through the fracture was monit ored by Geiger-Muller probes inserted in the boreholes. The calculated results for the migration plume and elution profiles were compared wi th experimental results. (C) 1997 Elsevier Science B.V.