Non Destructive Geophysical Monitoring of Water Content and Fluid Conductivity Anomalies in the Near Surface at the Border of an Agricultural

Abstract

We use in this paper advanced geophysical techniques for the characterization and monitoring of subsurface properties such as porosity, water content and electrical conductivity of water. Ground Penetrating Radar (GPR) and electrical conductivity measurements were recorded monthly during one year at the border of a corn field. Velocity analyses of multioffset GPR data were conducted to determine total porosity and to monitor vertical transport of water from the soil surface to the water table. The use of novel and original techniques for GPR processing (GPR velocity estimation by the Common Reflection Surface (CRS) method, kriging applied to GPR velocity) improved the estimate and the resolution of GPR velocity maps compared with the classical Normal MoveOut (NMO) and the bi-linear interpolation. Electrical resistivities were used to determine the effective porosity. The combination of GPR and electrical data permitted to estimate the electrical conductivity of water and to highlight high conductivity zones, possibly due to contamination by agricultural fertilizers. Independent determinations (grain size fractions, electrical conductivity, major ion content of water samples and porosity) were obtained, that validate our geophysical investigation. This study demonstrates the efficiency of non destructive geophysical approaches for providing accurate models of water content, porosity and electrical conductivity of water down to a depth of several meters in a poorly conductive soil.