CONDUCTIVE GEOPHYSICAL ANOMALIES ASSOCIATED WITH PETROLEUM HYDROCARBON BIODEGRADATION PROCESS IN A NON-SATURATED ZONE

Abstract

Geophysical surveys using eletroresistivity methods and hidrochemical analyses were applied aiming the characterization of geoelectrical signatures in hydrocarbon contaminated sites located in an industrial site in Sao Paulo, Brazil. There have been accomplished six vertical electric soundings (VESs) and three 2D electrical imaging, which identified conductive geophysical anomalies. It was verified that the presence of conductive anomalies within the non-saturated zone coincided with the occurrence of free phase on the monitoring wells. In those wells, lower values for nitrate (NO3-) concentration and increased ammonium (NH4+) contents suggest the occurrence of dissimilatory nitrate reduction process. Additionally, reduced concentrations observed for sulfate (sO(4)(2-)) and ferrous (Fe-2(+)) ions in the free phase contaminated groundwater generated the hypothesis that they were, respectively, biologically reduced to sulfide (S2-) and precipitated as iron sulfide (FeS). Based on those results, it was concluded that the conductive anomalies detected inside the non-saturated zone were directly associated with the presence of hydrocarbon residual phase, which is undergoing a biodegradation process. Therefore, the geophysical methods applied in this study, coupled with hidrochemical data, allowed the identification of areas under petroleum hydrocarbons influence.