SURFACTANT EFFECTS ON RESIDUAL WATER AND OIL SATURATIONS IN POROUS MEDIA

A series of soil column tests were performed to determine surfactant effects on residual water and oil saturations in porous media. In particular, these tests focused on the impact of sub-micellar surfactant solutions and the potential application of these low concentration systems to LNAPL contamination in the vadose zone. One set of tests involved surfactant flushing in soil-filled columns followed by drainage to residual water saturation and LNAPL injection to determine the subsequent residual LNAPL saturation. Another set of tests involved surfactant application to a soil-filled column already holding residual LNAPL saturation to promote the release of the previously trapped LNAPL. Test results showed surfactant systems could reduce both residual water and oil saturations by up to 50%. In addition, sub-micellar surfactant systems were equally effective as supra-micellar solutions in reducing residual water saturations and potentially more effective at reducing residual oil saturations. Sub-micellar surfactant applications to a medium-grained (20-40 mesh) soil containing residual LNAPL saturations were effective at releasing up to 50% of the previously trapped residual LNAPL. These applications were less successful in a fine-grained soil as full drainage of water and LNAPL was unachievable due to high capillary pressures. Overall observations suggest low concentration surfactant solutions may have the ability to release significant amounts of previously trapped LNAPL in the vadose zone, potentially increasing free-product recovery rates and lowering LNAPL saturations to levels more favorable for biodegradation. The decrease in overall saturations (both water and oil) in a contaminated vadose zone could also present an increase in air permeability, thus enhancing other vadose zone treatment technologies such as bioventing or soil vapor extraction.