Magnetic resonance sounding for the estimate of hydrogeologic characteristics of chalk aquifers (North of France)

Abstract

The hydrogeological characteristics are required for investigating the modelling processes. The transmissivity and hydraulic conductivity values which are obtained from the inverse methods and pumping tests are not representative in the northern part of France where the major aquifer is composed of the chalk deposits. In addition, these methods are costly and time-consuming. In the north of the Paris Basin and by using the magnetic resonance sounding (MRS), the chalk aquifer reveals the vertical distribution of the porosity, the hydraulic conductivity, and the transmissivity. The decay constants of the MRS signal which have been identified from the MRS analysis are considered parameters which control the permeability and the transmissivity values. Five MRS surveys were realized and performed by the electrical resistivity tomography (ERT) aiming to characterize the lithology variation and the thickness of the hydrogeological units. This comparison shows the power of MRS methods of the chalk aquifer in the characterization of the hydrogeological system in the north of France. The water content which is deduced from the MRS highlights a heterogeneous distribution in the aquifer and the water content can reach 35%. Results which are deduced from the pumping test and the MRS are consistent. Indeed, the transmissivity values vary generally between 10−3 and 10−2 m2/s. This comparison shows the utility of the multidisciplinary approaches in the characterization of the chalk system in the north of France.