The Seepage of Leachate through Porous Layers with Different Values of Fluid Saturation

The migration of dense leachate through porous media was investigated under varying water saturation conditions by means of numerical simulations, which solved coupled flow and transport equations. The numerical approach couples generalized Darcy flow with advection-dispersion transport, incorporating the van Genuchten–Mualem model for relative permeability and density-concentration relationships for buoyancy-driven convection. The simulations reveal the complex interplay between saturation-dependent hydraulic conductivity and instability-driven transport, demonstrating that partially saturated conditions can enhance fingering development despite reduced permeability. A critical finding is the establishment of pronounced and persistent spatial heterogeneity in contaminant distribution. Simulations revealed that isolated regions of pristine pore water persist between high-concentration fingers, even over extended durations. The results emphasize the importance of accounting for density-driven instabilities in site characterization and monitoring strategies at contaminated sites.