The main objective of this study was to assess the environmental impact of the Nam Son Landfill on the subsurface geological structure studied using 3D electrical imaging and self-potential investigations. The map of the equipotential was based on self-potential data and was indicative of concentrations of redox-active components, and the map of the electrical conductivity provided information about the mineralization of the groundwater. The electrical conductivity of the subsurface was obtained from 3D-electrical imaging analysis conducted using a Wenner-based array configuration. An inversion of the data was carried out using 3D regularized least-squares optimization methods with robust model constraints. Three profiles of 3D electrical imaging and 180 self-potential data points, scattered within the study area near the disposal site, were implemented. The self-potential method supports the results of the geoelectrical method relating to a contaminated zone in the survey area with a large negative self-potential anomaly of ∼−260 mV with respect to the reference of a contaminant plume. Interpretations of geophysical data showed a low resistivity zone (<10 Ω m), which appeared to be a fully saturated zone with leachate from the Nam Son open dumpsite. The correlation between geophysical investigations and hydrochemical analysis proved to show high conductivity zones related with landfill leachate.