Explanation of Water Distribution variations in the Landfill Using Electrical Resistivity Tomography

Abstract

The continuous accumulation of solid waste has posed a great threat to the environment of our future generations. A novel approach that is currently under development is to treat the waste collected in an engineered landfill in order to reduce the emission potential to an environmentally acceptable level. The main topic for this research is to improve the understanding of how leachate is distributed throughout the landfill Kragge and how this distribution varies in time. This is important for identifying the long-term behavior of the landfill and for managing landfill waste.

At the start of this project, we have a number of water level measurements obtained from various wells in the landfill. Straightforward spatial interpolation of this data leads to unexpected results. Most likely this is caused by the highly complex heterogeneity in this porous system. For this reason, this research aims to apply Electrical Resistivity Tomography (ERT) technology to explain the water distribution variations between wells. The apparent resistivity along several lines are measured over depth using different arrays. Some scripts written in Python with 'pyBERT' and 'pyGIMLi' packages are used to get electrical resistivity inversion results from the apparent resistivity. It is known that the decrease in the water content leads to a significant increase in the resistivity. Therefore, the possible existence of saturated and unsaturated blocks in the waste body can be visualized from the inversion maps.

Initially, the interface between the saturated and unsaturated zones is expected to be identified from Laplacian edge detection, while the results indicate that this technique fails to represent the area boundaries under highly-heterogeneous situations. Subsequently, Archie's law and van Genuchten equation are coupled to give a relation between the resistivity and water pressure head. Archie's law is used to compute the resistivity from water content and van Genuchten equation is used to compute the water content from the water pressure head. There are two hypotheses during this analysis: (a) where the resistivity is 20(ohm-m) gives the interface of dry and wet zones; and (b) the landfill leachate is under hydrostatic condition. Then the water pressure head is the distance from the interface, which can be read from the inversion maps. By selecting a certain range of empirical parameters, the computed resistivity-pressure head curves provide relatively good fits to the measured results.