Aqueous surfactant washing of residual oil contamination from sandy soil

A laboratory study was conducted to determine the efficiency of different aqueous concentrations of an alcohol ethoxylate surfactant in washing residual levels of an oil from sandy soil. Five glass columns packed with the soil were prepared in a manner that simulated conditions leading to residual saturation in an actual oil leak. Each of four columns was washed continuously with 28 pore volumes of solution by pumping either 0.0% (water), 0.5%, 1.0%, or 2.0% aqueous surfactant solutions through the columns. The fifth column was washed intermittently with 28 pore volumes of a 1.0% surfactant solution. Water washed only 25.5% of the ATF from the column soil, while the 0.5%, 1%, and 2% surfactant solutions washed 55%, 60%, and 72.8% of the oil, respectively. In the case of water, the displacement of oil was the main washing mechanism, while all three mechanisms were operative during surfactant washing. Oil dispersion and solubilization were improved at higher surfactant concentrations. The column that was washed intermittently to pulse oil from dead end pores did not show a significant improvement over the column that was continuously washed with the same 1.0% surfactant solution. The results show promising potential for application in the field and will be further investigated in a two-dimensional model aquifer