3D electrical resistivity tomography geophysical monitoring of the effectiveness of an environmental remediation system by pure oxygen injection

Abstract

A polluted site with hydrocarbons is being actively treated by an innovative approach consisting of improving the effect of aerobic bacteria to depollute the soil. To do so, pure oxygen is added into the ground by an injection borehole. In order to complement soil, water and gas sampling made directly from adjacent monitoring boreholes, a 3D electrical resistivity tomography (ERT3D) geophysical imaging analysis has been conducted on a monthly basis. The setup consists of 286 electrodes positioned on a 75m x 75m grid centered on the injection borehole. The acquisition is made with more than 45000 apparent resistivity points collected over 4 different array types: Dipole-Dipole, Pole-Dipole, Wenner and Wenner Schlumberger. Over the 5 months survey we have observed that changes in resistivity are mainly located around the injection borehole, especially in the northern and eastern part of the site. The geophysical survey allows a better understanding of the localization, shape and evolution over time of the main pollutants with respect to the injection of O2. This survey demonstrate that 3D electrical resistivity imaging is an efficient tool to quickly map a polluted site and to allow for a better definition of corrective remediation measures.