Granite fracturing and incipient pollution beneath a recent landfill facility as detected by geoelectrical surveys

Abstract

A resistivity survey using Wenner array was carried out in June 2000 in a granite region of Northern Portugal, where an active landfill is operating since 1998, to detect the possible spread of contamination. This survey was complemented with a self-potential (SP) survey, a dipole–dipole (DD) array profile and azimuthal Vertical Electrical Sounding arrays (VES). The location of these profiles was highly constrained by the available space in the landfill facility and by the available geological data, mainly fracturing. Significant groundwater circulation was detected, which is characterized by a low resistivity zone (<400 Ω m), with a fairly well defined configuration. Chemical analysis of water samples collected in boreholes inside the landfill facility and on springs around it confirmed the presence of water contamination. The presence of a very well delimited anomaly with low resistivity (<200 Ω m) just beneath the leachate collector system strongly suggests that the groundwater contamination is due to a landfill leak. Results of azimuthal VES are consistent with the structural data obtained outside the landfill, revealing that the strikes of the prevailing fracture systems inside the landfill are generally NW–SE to NNE–SSW, which seems to facilitate the downward propagation of contaminants.