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

Resumen

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.