Environmental Monitoring Using Electrical Resistivity Tomography (ERT) in the Subsoil of Three Former Petrol Stations in SE of Spain

Abstract

Electrical resistivity tomography (2D ERT) is a powerful tool for the diagnosis of the subsoil state and to pursue an environmental monitoring in time to detect and follow a temporal evolution of plumes in hydrocarbon-contaminated soils. In situ, 2D ERT was conducted to investigate the electrical properties of the subsoil in three petrol stations in Murcia semiarid Region (SE Spain), which have been active for many years, in order to look for anomalous areas that could be related to the presence of a non-aqueous phase liquid (NAPL) contaminant plume in the subsoil. A total of 18 ERT profiles in wet and dry season were conducted to study the seasonal effects in the resistivity values of the subsoil. Dipole–dipole array was set up to make the soil diagnosis, achieving a good vertical and lateral resistivity distributions for the sites investigated. Interpretations obtained from ERT pseudo-sections, after a processing and inversion data process with PROSYS II and RES2DINV software, show delimited highly resistive regions above 2,000 Ω·m at 2 m deep related to the underground storage tanks (USTs) position and the filling ports and anomalous resistivity areas where boreholes and further GC–FID determination in soil samples have been done. No significant differences have been found between results obtained in dry and wet seasons. Thus, the geo-electrical non-destructive technique ERT is presented as a tool to delineate the USTs positions and to point out anomaly in the subsoil that could contain NAPL, helping to design sampling strategies, saving cost and time.