Delineation of Leachate Plume and Subsurface Characterization Using Geophysical Method of Sisdol Landfill Site, Nepal

Leachate generated from landfill sites represents a major environmental threat, particularly to surface and groundwater resources. Conventional leachate monitoring using boreholes is a one-dimensional approach and does not adequately define the lateral and vertical extent of leachate plume migration. To address this limitation, an integrated geophysical and physico-chemical investigation was carried out at the Sisdol landfill site to delineate the depth and spatial extent of leachate plume migration. The study employed a two-dimensional electrical resistivity survey using Wenner and Wenner–Schlumberger array configurations, complemented by physico-chemical analysis of leachate and surface water samples. A total of six electrical resistivity survey lines were conducted within the landfill site, and five water samples were collected from upstream, on-site, and downstream locations. The resistivity images clearly distinguish leachate plumes, saturated and unsaturated waste zones, and the landfill base. The leachate exhibits very low resistivity values ranging from 0.47 Ωm to 6 Ωm, consistent with its high electrical conductivity of 35010 μS/cm. Physico-chemical analysis indicates elevated concentrations of heavy metals such as manganese, copper, zinc, nickel, iron, and lead in downstream water samples, while upstream samples remain uncontaminated. Lead concentrations exceeding permissible limits were detected at one downstream site. These findings confirm that the poorly managed Sisdol landfill site poses a serious risk to nearby water resources due to leachate percolation and direct discharge into the Kolpu Khola without proper treatment.