We developed a new soil washing method which can be used for silty or clayey oil-contaminated soil. The new method uses a combination of selected anionic surfactant and nonionic surfactant. This paper consists of two parts. Firstly, we describe laboratory tests to illustrate how we develop the new method and how it can significantly decrease TPH (Total Petroleum Hydrocarbon) of oil-contaminated soil by using selected surfactants. Secondly, we focused on environmental impact of recycling the washed soil since a small portion of surfactants is remained after treatment. In order to estimate the behaviour of the residual surfactants, we conduct laboratory tests and numerical analysis. The results suggested, although the movement of residual surfactants in the ground varies depending on types of soil, it is unlikely that surfactant leached from treated soil affects surrounding groundwater environment.
