INFILTRATION AND REDISTRIBUTION OF PERCHLOROETHYLENE IN STRATIFIED WATER-SATURATED POROUS-MEDIA

Although infiltration, redistribution, and drainage of dense nonaqueou s-phase liquids (DNAPLs) in water-saturated soils and aquifers are kno wn to be sensitive to stratifications of the solid phases of the porou s media, little experimental evidence is available to explain the beha vior of DNAPL movement. To improve our understanding of DNAPL movement under these conditions, physical simulations were conducted with vari ous perchloroethylene (PCE) spills in initially water-saturated, strat ified porous media in nominally one-dimensional glass columns and in a n intermediate scale, nominally two-dimensional laboratory now contain er. The columns and now container were packed with two distinct layers of coarse sand, with a fine sand layer in between. Volumetric water a nd DNAPL contents, as well as bulk densities, were determined with a d ual-energy gamma radiation system. To obtain additional information re quired for the explanation of the displacement processes, in-and outfl ow rates of water and PCE were measured during each experiment. Tn the sand columns, PCE accumulated on top of the fine layer, while in the now container, considerable lateral movement was observed just above t he fine sand layer. In general, these phenomena were attributed to the small conductivity values of the fine layers relative to those of the coarse layers rather than to displacement pressures not being exceede d. Overall our results suggest that in field situations, continuous PC E spills are more likely to penetrate horizontal fine layers than Shor t intermittent spills.