3D Resistivity Model of a Lubricant Oil Waste Disposal Area in the City of Ribeirão Preto, São Paulo, Brazil

The present work presents results of geophysical investigations in a lubricant oil waste area located in the municipality of Ribeirão Preto, São Paulo State, Brazil. In the study area the waste was disposed of in four trenches with a total volume of about 25.000 m3, in an area of sandstone outcroppings of the Botucatu Formation and in basalts of the Serra Geral Formation. The trenches were totally filled with waste over approximately 25 years and no protection liners were used in the bottom or laterals of the trenches. The goal of the study was the acquisition and modeling of 3D data with the electroresistivity method for the environmental characterization of the study area. The acquisition of 3D data, from a series of 2D electrical surveys, was effective in mapping variations of resistivity in three dimensions, showing in the subsurface the behavior of contaminants. The conductive anomalies in the saturated zone and unsaturated zone were related to contamination generated by the biodegradation process. A direct analysis of the soil and groundwater samples confirmed the contamination. In the soil analysis, low concentrations of several polycyclic aromatic hydrocarbons were found, mainly naphthalene and phenanthrene. In the water samples, there was confirmed contamination of the groundwater by lead (Pb). The biodegradation process was confirmed by the presence of microorganisms (bacteria), as evidenced in a biological analysis of soil samples collected at a specific point, where geophysical signatures suggested contamination.