Applied geophysics for regeneration of past metallurgical sites

Ancient metallurgical sites, such as those found in post-industrial cities, present both challenges and opportunities for the development of resilient cities. The legacy of these industries, including mining, smelting, and blast furnace, has left behind vast quantities of residues in the form of unrecorded slag heaps. The challenge of those ancient metallurgical sites is to combine the remediation of the polluted soil while leveraging the valuable resources it contains to support sustainable economic development. This requires a detailed understanding of the structure and composition of the slag heaps in order to safely and effectively extract valuable materials while minimizing environmental impacts.For decades, the regeneration of past metallurgical sites has relied on extensive drilling surveys and geochemical analysis. However, this approach has proven to be costly, time-consuming, and potentially hazardous for the operators involved. In this context, we present an integrated methodology for characterizing slag heaps using non-invasive geophysics. Developed as part of the NWE-REGENERATIS Interreg project, our approach consists of four main steps: (i) historical studies of the site activities and deposits to identify areas of interest, (ii) electromagnetic induction mapping of the identified areas of interest; (iii) 2D electrical resistivity tomography (ERT) and induced polarization (IP) to image the structure of the slag heap; and (iv) conducting a limited sampling survey to validate the geophysical interpretation and define the bulk composition of the deposit. Our approach is not only less time-consuming and less costly than the traditional method but also safer for the operators.This study has been applied to a former zinc production site nearby Liège city in Wallonia, Belgium. The application of the NWE-REGENERATIS methodology has allowed the imaging of the 3D structure of the anthropogenic deposits. The combination of ERT and IP measurements has revealed the presence of two types of residues, with the main part of the deposit composed of inert waste, and metallic slag lenses are present on the surface. These insights provide valuable information for assessing the feasibility of urban mining and developing effective regeneration plans for the site. The application of the NWE-REGENERATIS methodology in this study has proven to be a valuable tool for understanding the complexities of ancient metallurgical sites. Our approach is not only less time-consuming and less costly than the traditional method but also safer for the operators.