Electromagnetic methods application for characterizing a site contaminated by leachates

Two electromagnetic geophysical methods, very low frequency (VLF) and low induction number coils (EM-LIN) were used to obtain the response to the presence of leachates from a waste disposal site used for more than 24 years, covering an area of 0.16 km². This landfill is located in fractured shale and sandstone associated with the Oaxaca Fault. The study was performed on six profiles, four of which were common to both methods, with lengths of 325, 320, 300 and 645 m, in two others only the VLF method was used. The interpretation of VLF data using the Hjelt and Karous filter resulted in current density sections. The current density variation was assumed to indicate the presence of fractures, along which the infiltration of leachate takes place. The interpretation of EM-LIN data provided two-dimensional models showing the distribution of the conductivity of the subsoil. The integration of these results shows a main conductive anomalous zone in the southeastern part of the landfill that increases in thickness towards the middle and with a depth up to 30-40 m. Correlation with natural surface runoff enables to infer that the conductive anomalous body indicates the presence of leachates. Both electromagnetic methods provided a good response in fractured zones.