Multi-Geophysical Characterization of Karst Landfills in Croatia: Mapping the Waste–Bedrock Interface and Assessing Waste Volume

Landfills situated in karst terrains pose unique sustainability challenges due to the complex geological characteristics of these environments. This is mainly due to the well-developed underground drainage systems, including discontinuities and caves that can quickly transport contaminants over long distances, reaching the water sources and ecosystems. The focus of this study is on multi-geophysical assessment incorporating electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) to evaluate the volume of the waste and to delineate the contact between the waste material and the karst, offering a more comprehensive view of subsurface conditions. The presented examples include geophysical mapping of the landfills Sodol and Sorinj, situated in the immediate vicinity of sensitive water bodies, increasing the potential risk of environmental contamination. At both sites, the boundary between waste material and bedrock was clearly delineated. Bedrock was identified with P-wave velocities of approximately 3000 m/s at Sodol Landfill and 2000 m/s at Sorinj Landfill. Waste material, observed at both sites, exhibited electrical resistivity values up to 120 Ω·m. The combined use of ERT and SRT provides extensive coverage of the landfill area, surpassing what can typically be achieved through traditional methods such as boreholes or excavations. Overall, the obtained results show promising potential for using integrated geophysical methods to accurately characterize landfill sites in karst terrains, thereby improving environmental protection strategies in karst regions and contributing to sustainable waste management.