Effectiveness of resistivity monitoring for unsaturated water flow in landfill sites

The waste layers of landfill sites are stabilized by the washout of the permeate flow, and understanding the permeate flow allows us to indirectly identify zones where stabilization has been delayed. Using leachate and gas monitoring or borehole surveys to assess the stability of waste layers in landfill is limited, and they are largely uneconomical. Therefore, in this study, we followed an electrical resistivity method to provide non-destructive, three-dimensional visualizations of the leachate movement in the landfills, as the resistivity is correlated with leachate conductivity, porosity and water saturation. Water injected into the fills was tap water for simulated landfill (laboratory experiment) and salt water for two actual landfills (field experiment). Their resistivity change profiles were compared and evaluated with the soil test results. It was found that resistivity monitoring can effectively visualize unsaturated water flow in both laboratory and field experiments. In addition, the results of the simulated landfill show that vertical osmosis from the rough holes driven by gravity is the main path of water in the fills, and the water saturation rate at that time is about 35–40%. The results obtained by this method provide effective information for promoting stabilization of landfills.