Biodegradable natural surfactants obtained from plants can be an attractive alternative to synthetic surfactants in the remediation of contaminated soils. In this research, a plant-based surfactant obtained from the fruit pericarp of Sapindus mukurossi, a tree generally grown in tropical regions of Asia, is tested. A simple and economical method for the preparation of the surfactant is developed. An empirical formula for the surfactant was determined to be (C26H31O10) n . The aqueous solubilities of hexachlorobenzene (HCB) and naphthalene in the natural surfactant solutions were found to vary linearly with the concentration of the surfactant showing trends comparable to that of typical com mercial surfactants. Natural surfactant solutions were also employed for flushing HCB from one-dimensional soil columns. HCB recoveries after 12 pore volumes of flushing with 0.5 and 1% natural surfactant solutions were 20 and 100 times more than that recovered by water flooding. These promising results warrant further research to establish the usefulness of plant-based surfactants for soil washing applications.

The use of magnetic resonance imaging (MRI) for monitoring multiphase displacement experiments for quantitative characterization of fluid saturations is demonstrated. Displacements are conducted with one fluid phase in a porous medium being immiscibly displaced by another. Our objective is to accurately measure porosity and saturation distributions corresponding to one spatial dimension. Measures for the accuracy and resolution, with which the properties are identified, are developed. IntroductionNoninvasive imaging methods, such as X-ray CT scanning and magnetic resonance imaging (MRI), are providing exciting new opportunities for determining accurate rock characterizations and fluid-phase distributions corresponding to local regions within porous media. While much of the work reported for imaging methods have centered around the use of X-ray C T scanning (Potter and Groves, 1989;Vinegar, 1986), the versatility of MRI provides some unique opportunities for even more accurate and complete characterization of many properties associated with fluid-solid systems. Most of the work to date has dealt with static or nonflowing situations. When the porous media contain a single fluid phase, the void volume of the media can be characterized by imaging (Edelstein et al., 1988). MRI can also be used to characterize the distribution of one or more fluid phases in multiphase situations (Hall and Rajanayagam, 1987;Chen et al., 1988;Baldwin and Yamanashi, 1986;. In previous studies, fluid distributions have typically been expressed by a quantity proportional to the intensity of the signal. While these experiments demonstrate the use of imaging, they provide at best only a semiquantitative measure of rock properties and fluid-phase distributions. Porosity and fluid saturations, which are desired for quantitative analysis of fluid transport and storage in porous media, have been reported only as averages for whole samples (Edelstein et al., 1988), rather than resolved spatially in one or more dimensions.Several studies that deal with experiments involving transient multiphase flow in porous media have been reported (Baldwin and Yamanashi, 1986;Chen et al., 1988). Standard twodimensional (slice) imaging procedures were typically used. In some cases, such as the absorption of water by nylon (Blackband and Mansfield, 1986), the flow process is sufficiently slow so that the time required for imaging is not a critical issue. In other cases, the flow has been disrupted to perform the imaging under static conditions (Chen et al., 1988;Baldwin and Yamanashi, 1986). This generally is not desired for quantitative work since some redistribution of fluid phases is to be expected.In this work, we investigate the use of MRI for monitoring multiphase displacement experiments. In our experiments, one fluid phase is immiscibly displaced from a porous medium by a second fluid phase. Our objective is to accurately measure quantities that may be used to characterize the porous media and transport processes-specifically, the porosity and saturation p...

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