Author(s): Fritz Stauffer; Oscar Osorio; Wolfgang Kinzelbach
Keywords: Groundwater; Residual air saturation; Dissolution; Hydraulic conductivity; Inhomogeneity; Fingering; Analogy to NAPL-water systems
Abstract: The dissolution of immiscible fluid entrapped at residual saturation in porous media by flushing is investigated for the case of a water-air system, which represents an analogy to the dissolution of residual NAPLs in groundwater. A quasi-saturated sand packing at residual air saturation was horizontally flushed with deaerated water. Visible dissolution fronts could be discerned at the tank walls and their evolution was recorded. The dissolution fronts soon showed distinct fingers that increased in length from zero up to 19 cm over a total horizontal flow distance of 70 cm. These fingers were similar to the dissolution fingers described by Imhoff et al. (1996) for residual NAPLs. Tracer tests without dissolution effects were performed on the sand packing at residual air saturation. They showed that the packing was slightly horizontally layered and that the positions of the dissolution fingers in the sand packing coincided with zones of higher velocity. However the length of the dissolution fingers was more than two times larger than the length of the corresponding tracer fingers. Although similar results can be expected for the dissolution of residual NAPLs in groundwater, their applicability has to be further verified.