Numerical modeling of reactive solute transport in a single fracture with matrix diffusion under complex boundary condition

A numerical model using finite volume QUICK scheme has been developed for simulating the transport behavior of solutes in a coupled fracture-matrix system for pulse-type boundary condition as against the conventional constant continuous source-type boundary condition, which essentially reflects the reality better, as it is practically not feasible for any source type to discharge it continuously with the same magnitude for a very long period. The sensitivity of fracture and rock matrix parameters, namely fracture aperture thickness, matrix porosity, and matrix diffusion coefficient have been analyzed under this complex boundary condition. In addition, the role of nonlinear sorption as well as decay has also been investigated. Numerical results suggest that the reduction in relative concentration within the fracture resulting from pulse-type boundary condition should always not be mistaken for matrix diffusion. It has been concluded from the present numerical study that segregating and quantifying the role on individual components, namely (a) source exhaustion (pulse-type boundary condition); (b) matrix diffusion; (c) sorption; and (d) decay in characterizing the resultant transport behavior of solutes in a single fracture with matrix diffusion under a pulse-type boundary condition remains challenging and needs further research.