A SOLUTE TRANSPORT MODEL FOR CHANNELIZED FLOW IN A FRACTURE

Recent experimental and theoretical investigations of transport in fractures indicate that water flows preferentially through channels in the fracture plane. This channeling of flow may imply that solutes transported in large-aperture channels have limited exposure to the bulk of the rock matrix surface which contacts the fracture. We present a solute transport model for large-aperture channels that includes both mass transfer to small-aperture regions of the fracture and the adjacent rock matrix to investigate the interaction of solute in large-aperture channels with the surrounding rock mass. Modeling channels similar to those observed in the crystalline rock at the Stripa mine show that solute can be retarded considerably due to mass exchange between the channels, the small-aperture regions of the fracture, and the rock matrix. The extent of solute retardation is insensitive to the solute capacity in the small-aperture regions and the areal spacing between channels in the fracture plane but is very sensitive to the mass transfer rates between the channel and the small-aperture region.