## 4 Discussion and Conclusions  
The results obtained from the simulated data on the blocky model show that the volumetric distribution of the inverse model resolution changes considerably depending on the chosen electrode areal arrangement. With the same number of electrodes, their arrangement on a single polygon does not allow an adequate resolution of the zones inside the polygon. In fact, the resistive or conductive blocks are not identified with sufficient accuracy by the inverse models. The choice, if possible, to arrange electrodes along two concentric or contiguous polygons significantly improves the resolution in the center of the investigated area, while maintaining an acceptable detail also in the peripheral areas. However, arrangement \(B\) with concentric squares allows obtaining models in which the lengths of the two non-centered prisms are identified more accurately, probably because this arrangement guarantees a more homogeneous coverage than arrangement \(C\). Considering the same electrode areal arrangement, the choice of the electrode array configuration also affects the quality and reliability of the inverse model, albeit to a lesser extent. In this context, the \(\beta\) and \(\gamma\) arrays give inverse models that are more similar to the starting model than that obtained by the \(\alpha\) array. However, the \(\gamma\) array is preferable because it allows for a shorter measurement time for about the same amount of data acquired, thanks to the high value of potential measurements that can be carried out for each current dipole. Figure 10: Landfill of Bellolampo: 3D rendering of the inverse models of electrical resistivity and induced polarization, limited upward by the waterproof membrane and relating to the bedrock below the landfill: (**a**) log (resistivity) model; (**b**) log (resistivity) model cut by vertical sections; (**c**) chargeability model; (**d**) chargeability model cut by vertical sections. The test carried out on the Bellolampo landfill (Palermo, Italy) allowed the results obtained through the simulations to be validated in the field. The choice of a landfill site was suggested by the need to obtain a highly detailed three-dimensional representation of the electrical resistivity and chargeability in an area with high criticality regarding access and operability, also in consideration of carrying out the measurements in the shortest time possible for health and safety reasons. In a landfill, it is not possible to arrange the electrodes regularly, but field operations are limited by the access paths to the various sectors. In this context, the choice of arranging the electrodes along summarily concentric polygons appeared to be the only practicable one. Furthermore, the choice of the FRG array allowed us to carry out the measurements in the shortest possible time while guaranteeing adequate coverage and good resolution, at least in the landfill area above the water-proofing membrane. In the 3D ERT results, the resistive zones, close to the external surface, indicate a dry waste material, not permeated by leachate. By highlighting the volumes with very low resistivity and/or very high chargeability values (Figure 11), it is possible to delimit the zones where the leachate accumulates inside the landfill and to identify the areas where the leachate could potentially spill below the waterproofing membrane. The zones with resistivity lower than 3 \(\Omega\)m are highlighted inside the waste (Figure 11a) and in the rock bottom under the membrane (Figure 11b). These conductive zones, more localized and extended further down, are an indication of a high concentration of leachate which, due to gravitational effects, tends to accumulate at the bottom of the landfill. Similarly, the zones with chargeability greater than 300 ms are shown inside the waste (Figure 11c), and below the waterproofing membrane (Figure 11d).