Leachate modeling for a municipal solid waste landfill for upper expansion

Abstract

This study sought to predict leachate levels within a municipal solid waste landfill and evaluate design alternatives for landfill expansion using the U.S. Geological Survey modular flow model with new flow and contaminant transport packages (MODFLOW-SURFACT). This was used to overcome the drawbacks of the more widely used Hydrologic Evaluation of Landfill Performance (HELP) model in predicting leachate levels and movement within a landfill. The valley landfill in this study had two imminent issues regarding leachate management. One was its current high leachate levels, and the other was the selection of a design option for the bottom of the expanded landfill above it. According to the model calibration, relatively high leachate levels in the current landfill were attributed to unsatisfactory leachate removal efficiency by the leachate collection system. Additional leachate pumping was necessary to prevent possible leachate level increase after the landfill expansion over the current landfill. Based on numerical investigations of the design options of the expanded landfill bottom, the separation of leachate generated in the upper (expanded) landfill from the lower (existing) one is recommended, indicating that a low permeable layer such as a liner is an essential component. MODFLOW-SURFACT can be successfully used to calibrate landfill properties and predict hydraulic performance with given landfill conditions, particularly for a valley landfill.