Characterization of legacy landfills with electrical resistivity tomography; a comparative study

Abstract

Historic landfills that were constructed to standards that would not meet current regulations represent environmental and human-health risks. The adequate characterization of legacy landfills is paramount to manage the risks they pose effectively. In this study, the non-invasive geophysical technique of electrical resistivity tomography has been used to characterize two sites that have been identified as posing risks to the local environment. The sites are significantly different in the type of waste present, moisture content, type of bedrock and shape and distribution of the waste; although they have in common that neither site is lined.The results of the resistivity imaging have allowed defining the boundaries of the landfill and the depth of the waste. Different types of waste and their distribution have been identified. Additionally, a relationship between the resistivity distribution and the release of residual gas from the landfill has been described; where the presence of saturated clay in the waste prevents the release of said gasses. This is be associated with locations with higher resistivity and lower clay content. That relationship is not observed when the clay is dry.When interpreting the results, the heterogeneous nature of the waste can lead to misinterpretations due to resistivity overlap between the bedrock and the waste materials. Therefore, comparison of the resistivity models with direct information like borehole logs can significantly improve the reliability of the interpretations. However, the resistivity survey should predate the installation of bores to identify the most suitable locations for them.