A sandbox experiment of self-potential signals associated with a pumping test

The flow of water in a charged porous material is the source of an electrical field called the streaming potential. The origin of this coupling is associated with the drag of the excess of charge contained in the vicinity of the pore-water interface by the pore fluid flow. In this paper, we present a sandbox experiment to study this "hydroelectric" in the case of a pumping test. A relatively thin Plexiglas tank was filled with homogeneous sand and then infiltrated with tapwater. A pumping test experiment was performed in the middle of the tank with a peristaltic pump. The resulting electrical potential distribution was measured passively at the top of the tank with a network of 27 nonpolarizable electrodes related to a digital multichannel multimeter plus an additional electrode used as a reference. A electrical field was produced at the ground surface and analyzed with analytical solutions of the coupled hydroelectric problem. After the shutdown of the pump, the electrical potential and the piezometric level exhibit similar relaxation times in the vicinity of the pumping well. This means that the electrical potential measured at the ground surface can be used to track the flow of the groundwater and possibly to invert the distribution of the hydraulic transmissivity of the ground.