Dc resistivity method applied in the monitoring of diesel leakage in a railway accident in SÃo Manuel city, SÃo Paulo state (Brazil)

Abstract

This paper presents an integrated analysis of geochemical and geophysical data in a contaminated site by a leakage of 240.000L of diesel in 1999, currently under environmental monitoring. The main objective is to assess the presence of contaminants in residual and dissolved phase in the subsurface, using the technique of Electrical Resistivity Tomography (ERT), understand the effects of natural attenuation process in the degradation of hydrocarbons and changes in electrical properties in soil and groundwater. The results allowed for the definition of two distinct patterns of resistivity in region with presence of dissolved phase, defined in a historical of chemical analyzes. The intermediate values (260Ω.m and 511Ω.m) are indicative of the coexistence of hydrocarbons in residual and dissolved phase. The region of high values (>1000Ω.m) reveal the prevalence of residual phase with incipient degradation, possibly in concentrations of high toxicity for effective action of the biodegradation processes. The generation of 3D visualization models from 2D sections allows the use of the isosurface modeling technique and definition of a high resistivity body, consistent with conceptual models of hydrocarbons dispersion in the subsurface. The diagnostic of an area with potential accumulation of hydrocarbons in residual phase can subsidize the planning of remediation techniques and promote the complete attenuation of the area.