Inversion of synthetic and measured 3D geoelectrical data to study the geomembrane below a landfill

The aim of this work is to explore the potential of ERT to study the geometry and soundness of the geomembrane that is commonly placed below the waste deposits to prevent leachate propagation into the subsurface. We compare the results obtained from 3D inversion of synthetic and measured geoelectrical data starting from homogeneous and heterogeneous initial models. Real data were collected in an actual landfill site with loop-like electrode spreads and according to different quadrupole configurations. Synthetic data were modelled considering field conditions and performed surveys thanks to an open-source software capable of handling models created with unstructured meshes. Although a priori information obviously guides the inversion process, the inversion results using a homogeneous initial model indicate that measured data are not able to reconstruct a (relatively) high-resistivity volume below the landfill, differently from what is found with synthetic data. This may suggest potential issues related to the soundness of the geomembrane. Yet, chi2 values associated to different initial models are very similar. Therefore, further tests are necessary both using modelling software and by performing controlled field experiments, possibly exploring different conditions of the insulating liner, of the waste deposit as well as of leachate propagation.