CAPILLARY BARRIER PERFORMANCE IN HETEROGENEOUS POROUS-MEDIA

The effects of heterogeneities on the performance of capillary barrier s is investigated by numerically simulating three systems comprised of a fine soil layer overlying a coarse gravel layer with (1) homogeneou s, (2) layered heterogeneous, and (3) random heterogeneous property fi elds. The amount of lateral diversion above the coarse layer under ste ady state infiltration conditions is compared among the simulations. R esults indicate that the performance of capillary barriers can be sign ificantly influenced by the spatial variability of hydraulic propertie s. In the layered heterogeneous systems, realizations with highly stra tified regions within the fine layer performed best and resulted in lo calized capillary barriers that delayed breakthrough into the coarse l ayer. In contrast, realizations of the random heterogeneous system per formed worst because of channeled flow that produced numerous localize d regions of breakthrough into the coarse layer. Results of the homoge neous model were comparable to the mean results of the layered heterog eneous realizations, but homogeneous results underpredicted the freque ncy and amount of breakthrough for all realizations of the random hete rogeneous system. These results indicate that homogeneous models can b e used to estimate the average behavior of layered heterogeneous syste ms with reasonable accuracy. In addition, engineered capillary barrier s may be improved through emplacement and packing methods that induce highly stratified features within the fine layer of a capillary barrie r system.