Sanitary landfills are a well-planned engineering work for final disposal of municipal solid waste in order to minimize the environmental impacts in soil and groundwater. Therefore, several control systems are installed such as liners and leachate and biogas collectors. However, the establishment of landfill in vulnerable areas, the inadequate operations, and failures in collectors and liner systems can cause subsurface contamination. The discovery of eventual leachate leakage usually is based on chemical analyses of groundwater using monitoring wells; which may not be representative in spatial terms. This work involves a geophysical monitoring of the leachate percolation in a landfill waste cell closed in 2014, in which geomembrane boreholes and aquifer contamination have been proved. The DC resistivity method was applied by means of electrical resistivity tomography (ERT) in order to detect eventual contrasts in electrical properties. Twelve ERT lines have been carried out in a steady mesh during three years of study (2016, 2017, and 2018). The results of 2016 allowed a clear contrast between zones of leachate percolation into the aquifer and the natural environment. The comparative analyses of the three-year monitoring results reveal a gradual increase in resistivity values in the areas of leachate percolation. The absence of replacement of biodegradable organic matter after 2014 conditions the gradual decrease of leachate salinity. In this sense, the increase in resistivity is an indicator of the tendency for chemical stabilization of the organic waste and existence of natural attenuation processes.
Keywords: Contamination; Degradation; Geophysics; Monitoring; Resistivity.