A Control Volume Model of Solute Transport in a Single Fracture

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Abstract
A control volume model of solute transport through a single fracture in a porous matrix is developed. Application to problems of contaminant transport through fractured clay demonstrates several strong features of the method. The control volume approach inherently conserves mass and treats dispersivity at interfaces in a physically correct manner. By employing an upstream weighting scheme, based on the exact solution to the one‐dimensional steady state advection‐dispersion equation, the model proves to be more efficient than previous single‐fracture models. The significance of matrix diffusion in the direction parallel to the fracture axis is investigated. For the transport of a nonreactive tracer through a 20‐micrometer‐wide fracture in clay material, analytical solutions based on one‐dimensional matrix diffusion are erroneous for flow velocities of less than 1 m/day. The influence of boundary conditions on two‐dimensional matrix diffusion is considered, and the clean‐up of a contaminated fracture is simulated.