GEOSTATISTICAL INTEGRATION OF GEOPHYSICAL MEASUREMENTS FOR HYDROGEOLOGICAL INVESTIGATIONS

Abstract

Most often, the integration of geophysical measurements for hydrogeological investigations is performed manually and is limited to the stratigraphic contacts. However, this approach fails to use most of the information contained in the geophysical data. This study shows a geostatistical approach that integrates geophysical data in a plausible hydrostratigraphic model that takes into account borehole information and correlations between physical parameters and hydrogeological parameters. The proposed approach is applied to a site located in St-Lambert, Quebec. At the study site, leachate from a landfill is a problematic that has been studied extensively through the years. Despite those efforts, conventional hydrogeological investigations have failed due to their incapacity to characterize small to medium scale heterogeneities that controls the groundwater flow at the site. To address this issue, a hydrogeophysical characterization was done using ground penetrating radar (GPR) surveys, cone penetration tests (RCPT) and electrical resistivity imaging (ERT). In order to integrate this information for contaminant transport modeling, reflections were identified on the GPR profiles and were converted to depth using available information from boreholes and CPTs. This information was then interpolated to obtain a 3D stratigraphic model. To perform groundwater flow simulations, a plausible hydraulic conductivity (K) field must be defined for every cell in the model. To achieve this, meaningful correlations between the CPT electrical resistivity and the hydraulic conductivity were obtained from 26 multilevel slug tests and the available GPR and ERT images. Those correlations were used along the ERT profiles and the stratigraphic model to perform Sequential Gaussian Simulations (SGS) of the K field. This resulted in several plausible hydraulic conductivity 3D models that exhibit realistic textures and heterogeneities. In conclusion, the proposed approach integrates all the information from geophysical measurements, CPTs and boreholes and give much more realistic models to perform groundwater flow and transport simulations.