Surfactant Flushing Technique for the Removal of Residual NAPL from the Heterogeneous Subsurface Media

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Once non-aqueous phase liquid remains behind into the soil pores as a small droplet after filtrating into the ground, it becomes extremely difficult to remove. Aims of this study are the development of the innovative technology that reduces interfacial tension between water and residual NAPL by injecting the surfactant solution into the ground, and that remove it by solubilizing and dispersing into aqueous phase as a micellar, or mobilizing NAPL phase itself. Researches were conducted to establish the formulation on the optimum surfactant solution for enhancement of NAPL mobilization, and to demonstrate the efficiency by applying the formulation to the model porous media.Results were obtained as follows :1. Mobilization of NAPL was dependent on the hydrophobic group length of surfactant. It is very important to have enough carbon chain length in the surfactant for forming the micell. And the existence of alcohol and sodium chloride is effective for enhancing the NAPL mobility. Qualitative description on the relationship between those concentration and interfacial tension was found.2. The formulation for deciding the optimum salinity, which minimizes interfacial tension, was constructed by examining the relationship between alcohol concentration and carbon number of the NAPL, surfactant type and concentration, temperature. And the examination was carried out on NAPL saturation (NAPL content), which was the important parameter that shows present state of NAPL in the porous media, as the result, optimization level of the formulation was developed.3. Applying the formulation to soil column test and two-dimensional soil tank test, it was shown that more than 95% of the residual NAPL could be mobilized and removed. And, using the image analysis that is non-contact and non-disturbing method, it was explained that the mobilization mechanism of NAPL largely depended on its residual situation, and the factor, which affects the optimization, was considered.