Mapping groundwater contamination around a landfill facility using the VLF-EM method — A case study

An electromagnetic survey to detect leachate flow and to map its spatial distribution using the VLF-EM method was carried out around a landfill that is operating since 1998. The survey comprised twelve, roughly E–W, VLF-EM profiles in the western part of the landfill where conductive anomalies had been detected in a previous resistivity survey (Wenner and dipole–dipole arrays). The VLF-EM data were interpreted qualitatively, using the Fraser and the Karous–Hjelt filters. The quantitative interpretation of the data was done with a 2-D code that performs the inversion of the tipper data, using the results of the previous resistivity survey to constrain the inversion. Fraser filtered data and relative current density pseudosections indicate the presence of shallow and deep conductive zones that cross the landfill facility along known fracturing directions. The 2-D resistivity models calculated from tipper data indicate that these zones may have resistivity lower than 400 Ω m that is in a good agreement with the results obtained from the previous resistivity data. Chemical analysis of both surface and groundwater collected inside and outside the landfill confirms the presence of a halo of water contamination around the landfill location. This enables to infer that the anomalies detected by VLFEM data are due to contaminated groundwater flowing in connected fractures.