Enhanced LNAPL Remediation in Heterogeneous Soil with Surfactant Foam

Soil washing with surfactants has been proven to enhance in-situ LNAPL recovery in contaminated soils. However, in heterogeneous soils, injected fluids mostly flow in high permeability soil layers, leaving lower permeability zones bypassed and untreated. One technique that can improve the sweep efficiency of the entire contaminated zone is the injection of air with the surfactant, which causes the formation of foam that will block preferential flow channels and divert subsequent flow through low permeability zones. The main objective of this study is to evaluate the efficiency of foam for the treatment of a heterogeneous soil contaminated with a LNAPL and containing low permeability soil layers. Several surfactant solutions were compared based the results of laboratory tests: the pendent drop test was used to evaluate their interfacial tension with the LNAPL, batch tests showed their potential to dissolve the LNAPL and the Ross Miles test evaluated their foamability and the time needed for the foam to collapse. The Ross Miles test showed similar results for most of the surfactants tested but one candidate did stand out because its interfacial tension (IFT) with the LNAPL was 20 orders of magnitude lower than water-LNAPL IFT. This surfactant solution was therefore selected for further testing. Several series of tests were run on homogeneous 1D silica sand columns with different grain sizes. Adsorption tests were run for each type of sand with the surfactant solution in the liquid form. Also, the surfactant solution sweep and displacement efficiencies were measured for both liquid and foam. Results of the 1D column tests will be used to design experiments in a 2D physical model (sand tank) filled with layers of both low and high permeability silica sands in order to measure the mobility control obtained with foam injection compared to liquid surfactant injection.