Use of electrical resistivity tomography in the study of soil pollution caused by hydrocarbons: Case study in Puebla (Mexico)

摘要

The use of electrical resistivity tomography in the study of soils contaminated by hydrocarbons has had a substantial impact since it gives valuable information on the spatial distribution of pollutants in the subsoil. This methodology was applied to characterize an area contaminated by middle fraction hydrocarbons located at the east of the city of Puebla (central México) in order to probe its effectiveness. Additionally, chemical sampling was conducted in order to identify contaminated areas. Concentrations were determined in five samples in the zone based on the Official Mexican Standard NOM-138-SEMARNAT-SS-2003 (SEMARNAT, 2005). The geophysical survey consisted of six profiles of 20 m length, using a dipole-dipole array with a separation of four m between profiles and 50 cm of electrode spacing. Later, the geoelectrical models were computed using an inversion scheme in order to determine the resistivity distribution and its relationship with possible contamination. Results obtained from chemical sampling depicted that the contaminated area was between 0 and 1.3 m depth; three of the five analyzed samples showed a concentration above the allowed standard limit. Comparison between chemical and geophysical data allow us to assess the sensitivity of the physical property to the presence of the contaminant, and it was possible to visualize that electrical resistivity varies depending on volume and residence time of the hydrocarbon in the ground. Finally, comparison between geoelectrical models and hydrocarbon isoconcentrations showed a relationship between low resistivity of the northern portion of the study area and the highest concentration of hydrocarbon detected in the same zone.