Colloid-facilitated contaminant transport in discretely fractured porous media .1. Numerical formulation and sensitivity analysis

A two-dimensional numerical model is developed that incorporates the mechanism of colloid-facilitated transport in discretely fractured porous media. The numerical model accounts for aqueous phase contaminant transport in the fractures and the porous matrix, colloid transport in the fractures, and sorption of the solute. Deep-bed filtration of the colloids is accounted for, and the solute is allowed to sorb on both the mobile and filtered colloids. The numerical formulation allows for either equilibrium or kinetic sorption reactions onto the fracture walls, the matrix solids, and the mobile and filtered colloids according to either a Langmuir or a Freundlich isotherm. The results of a series of simulations involving a system of parallel fractures explore the importance of mobile colloids on contaminant migration and indicate that if sorption onto the colloids is a slow kinetic process, then the mobile colloids may lead to significantly enhanced contaminant migration.