Reduction of hydraulic conductivity during the treatment of hydrocarbon polluted soils by using surfactants may be en inconvenience for a good recovery of the pollutant. The purpose of the present research work is to determine the main factorresponsible for this reduction and by the same way to give an application solution to this problem. Experimental studies on sand filled laboratory columns have shown that the reduction of hydraulic conductivity can be due neither to the precipitation ofthe anionic 8urfactants in the presence of calcium ions nor to the clay minerals present in small proportion in the porous medium. We point out that this phenomenon is essentially :due to the agglomeration of micelles and show that additon of 4 wt ofbutyl alcohol under specific conditions contributes to improving both the injectability of the surfactant solution and the efficiency of the treatment. The optimized surfactant formulation, containing a mixture Of two commercial surfactants and thiscosolvent, palliates the reduction of hydraulic conductivity and decreases the interfacial tension by a factor of 100. As a consequence, after three pore volumes of injected surfactant solution, 85 of the trapped oil is removed compared to 11.4 obtained without cosolvent.
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