Evaluation of the Potential for DNAPL Mobilization During the Delivery of Partitioning Alcohol for in situ Density Conversion

Low interfacial tension mobilization through surfactant flushing has shown to be an effective treatment for remediation of entrapped non-aqueous phase liquids (NAPLs) in the subsurface. Mobilization approaches, however, are problematic for dense NAPLs (DNAPLs) because of the strong gravitational component to flow. The Density-Modified Displacement (DMD) method employs partitioning alcohols to mitigate the potential for downward migration during NAPL mobilization and recovery. However, partitioning of alcohol into NAPL causes swelling and reduces the interfacial tension between the organic and aqueous phases. Reductions in interfacial tension may lead to pre-mature mobilization of DNAPLs. This research evaluated the relative influence of swelling and interfacial tension reduction during the alcohol delivery phase of DMD. One- dimensional column experiments were conducted to investigate the mobilization potential during the partitioning of alcohol into trichloroethene- and tetrachloroethene-DNAPL entrapped within sandy media. The mobilization potential of the entrapped NAPL was determined through compositional analysis of the organic and aqueous phases following a n-butanol flush that was designed to approach the point of NAPL density conversion. Results from the column experiments conducted with a relatively permeable (k = 6 x 10-7 cm2), sandy medium suggest that the partitioning of n-butanol during the alcohol delivery phase of DMD did not mobilize the entrapped NAPL.