A non destructive geophysical protocol for estimating near-surface porosity, water content and water conductivity

we present here an innovative non destructive geophysical protocol for the characterization and monitoring of various subsurface properties (lithology, porosity, water-content or water conductivity). The use of novel and original techniques of ,GPR processing (GPR velocity estimation by the Common Rellection Surface (CRS) method and the kriging method applied to 'GPR velocity) improved the estimate and the resolution of GPR velocity maps compared with the classical Normal MoveOut (NFrlO) and the linear interpolation. Velocity analysis of multioffset GPR data permits the determination of water-content froim the soil surface to the water table and the total porosity of the ground. The combination of GPR and electrical data permits to cstimate the water conductivity. This protocol was applied to an agricultural corn field where high concentration of nitrate and pesticides are present in the phreatic aquifer water whose water table fluctuates from 1.5 to 5 meters in depth. At the end of the inv'estigation period, boreholes were drilled along the profile every 5 meters. Cuttings were obtained and analysed and GPR velocity tomography is in progress. Chemical determinations were independently performed. The first results obtained with the:se complementary informations permit to validate the geophysical protocol and show the efficiency of non destructive geophysical method for providing accurate models of water -content, porosity or water conductivity down to a depth of several meters.