CONICET | Buscador de Institutos y Recursos Humanos

The goal of this work was to study a contaminated soil due to a gasoline spill produced by fissures in a concrete purge chamber located along a gas transmission line. A monitoring well drilled 16 m from the chamber in the direction of the descendent topographic slope reveled the presence of a gasoline layer of 0.5 m thick at 1.5 m depth, floating over the water table. A second well, drilled 30 m apart from the other, in the same direction, did not present evidences of contaminants. To face this problem, we performed a geoelectrical prospecting, combining dipole-dipole and Wenner arrays. First, four dipole-dipole profiles in a direction perpendicular to the longitudinal axis were carried out. The electrical tomographies obtained from the 2D inversion of the data shown that the contaminant region extent is laterally about 6-8 m, and was located at a depth between 1 to 2 m. The longitudinal extension was less than 20 m, since the last profile located 30 m farther of chamber do not present this kind of anomaly. To better determine the longitudinal extension, we performed a dipole-dipole line along this direction. The inverse model confirmed that the extension of the contaminated section was about 16 m. To complete the study of the deeper layer, we carried out Wenner soundings. The results of the inversion process indicated that at least up to 20 m the soil was very conductive, associated with the presence of clays as main constituents and confining the contaminant within this impermeable surrounding. To improve the inverse model, we performed a joint inversion of dipole-dipole and Wenner data. Analysis of the depth of penetration showed that it increased to 25 m and comparing the resulting model with the ones obtained from each array separately, we concluded that the joint inversion improves the depth reached by the prospection, maintaining the shallow lateral resolution.

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