Abstract

CASTRO, Alejandrina et al. Geochemical and geoelectric characterization of a site contamined by hydrocarbons in the state of Puebla, Mexico. Bol. Soc. Geol. Mex [online]. 2013, vol.65, n.2, pp.405-418. ISSN 1405-3322.

Two methods are used to characterize a site contaminated with hydrocarbons: soil sampling and chemical analysis as direct methods, and electrical resistivity tomography (ERT) as an indirect method. The application of the direct method was based on the NOM-138-SEMARNAT/SS-2003; 42 soil samples were collected, including 4 duplicates, concluding that the main contaminant in the subsoil is diesel and that the volume of affected soil is approximately 1301 m³. The ERT method was carried out in two stages: six profiles in the first stage, parallel to each other, with a distance of 4 m between them, using a dipole-dipole arrangement with a distance of 0.5 m between electrodes. In the second stage, two profiles located in the northwest and southeast ends of the site using a Wenner-Schlumberger array with a separation of 0.75 m between electrodes (near the points PUE1 and PUE18, which are the most polluted)may provide the possible delineation of the contaminant in correspondence to the granulometric analysis performed in soil samples, which indicates the existence of a sandy soil of high permeability. Eventhough the location and length of the ERT profiles in both stages were affected by the accesibility of the industrial site, the results clearly show anomalies of high resistivity (ρ > 600 Ohm-m) associated with the presence of recent hydrocarbon contamination. Moisture changes in the compound stratigraphy of the sandy sediments cause resistivity variations between 25 and 150 Ohm-m. Both soil sampling and chemical analyses, and the ERT results, indicate that the hydrocarbon contamination has generally low horizontal extension; however, two ERT profiles show a conductive layer of greater extension with resistivity values lower than 10 Ohm-m, indicating the possible presence of mature contamination, eventhough new drilling and soil sampling are required to confirm this assumption.

Keywords : characterization; punctual contamination; hydrocarbons; electrical tomography.

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