Integrated Surface/Borehole GPR and high resolution seismic for site characterization

The evaluation of contaminated soil and waste disposal sites is a crucial step in any remediation project. Effective methods for site characterization are urgently needed in industrial countries, where the rise in population claims the recovery of brown- fields for residential land use or for new industrial plants. We exploit a combination of Ground Penetrating Radar (GPR) and seismic techniques to obtain enhanced re- construction of subsurface conditions. The primary objectives of this study are the improvement of non-invasive subsurface imaging and characterization and the con- sequential optimisation and cost reduction of sampling and invasive surveys. Three GPR techniques are jointly utilized: linear multi-fold (LMF), Vertical Radar Profil- ing (VRP), cross-well radar tomography (CWRT). LMF allows enhanced imaging of shallow reflectors and provides information about radar wave velocities that is further refined by VRP and CWRT. Strong attenuation of radar waves due to conductivity in the range between 0.04 and 0.5 S/m and highly heterogeneous shallow materials at the selected test sites prevents from a complete characterization of the study areas and encourages the application of alternative geophysical methods. Our choice is the in- tegration with high-resolution multi-component seismics and Multi-channel Analysis of Surface Waves (MASW). The latter technique (MASW) is an effective solution to bridge over the blind zone between seismic and GPR data. The integration of GPR and seismic methods is effective for waste disposal sites characterization, where elas- tic and EM properties exhibit strong lateral and vertical variations. The integrated GPR-Seismic method is further fit to provide a full reconstruction of waste volumes in most conditions. We use pre-stack depth migration algorithms for GPR imaging, 3-D interpretation for a constrained subsurface reconstruction, attribute analysis to classify the radar and seismic response and obtain quantitative indicators for subsur- face characterization. The validation of the joint GPR-seismic prospecting results by means of excavations and boreholes in the depth range between 0 and 14 m indicates that the method is fit for environmental applications and provides the penetration and resolution required for remediation planning and monitoring.