Colloid-facilitated contaminant transport in discretely fractured porous media .2. Fracture network examples

Numerical simulations of colloid-facilitated contaminant transport in fractured porous media were performed to examine the influence of mobile colloids on contaminant migration through a network of fractures. Simulations involving transport through fracture networks in a clay and a sandstone rock indicate that colloid-facilitated contaminant transport can be an important factor leading to the rapid exceedance of water quality standards at large distances from the contaminant source. If the colloids are highly mobile in open fractures and there is a strong affinity for a reactive contaminant to remain adsorbed onto them, then low but environmentally significant contaminant concentration levels can quickly propagate through an interconnected network of fractures. The total concentration plumes that are produced are highly irregular in regions in advance of the zone of bulk aqueous phase contaminant transport. Because of this feature, colloid-enhanced solute transport is likely to increase prediction uncertainty compared to the case when colloids are absent because field data on fracture network interconnectivity, aperture values, and values of parameters such as colloid filtration coefficients in the fractures are typically lacking.