Groundwater monitoring and control by using electromagnetic sensing techniques

Groundwater resources, which are exposed to overexploitation and pollution at regional and local levels, may take benefit from fast, nonintrusive, and inexpensive monitoring methods based on electromagnetic techniques. In fact, the available technologies can help to improve management and protection of the aquifers. This chapter deals with the role of electromagnetic sensing techniques in water monitoring with a specific focus to pollution surveys in groundwater bodies. Being sensitive to the presence of water in the subsoil and its electrical conductivity, which in turn depends on the ionic content, the electromagnetic sensing techniques are useful tools for groundwater identification and soil quality assessment. In fact, these sensing techniques offer advantages such as quickness, nonintrusivity, and the possibility of investigating large areas at reasonable costs. However, the appropriate use of these techniques implies an adequate knowledge of their working principles as well as of their on field application procedures, which mainly depend on the survey aim and the geological and logistic conditions of the site. This chapter also discusses the uncertainty in the interpretation of results, which is due to the fact that the electromagnetic sensing techniques are based on indirect inspections. Several strategies can be exploited to reduce ambiguity of results, such as the integration of different electromagnetic techniques and the comparison between field data and those provided by laboratory experiments. These issues are herein addressed through practical examples concerning two study cases, one referred to a site located in Serbia-Herzegovina and one located in Italy. In particular, we illustrate the physical concepts, the operative aspects, the data processing, and the integration of results concerning the following measurement techniques: electrical resistivity tomography (ERT), ground-penetrating radar (GPR), time-domain-induced polarization (time domain IP), and self-potential method (SP). The two study cases concerns an industrial site and a large waste dump structure. These sites represent specific examples of soil monitoring and have been selected in order to evaluate the performance of the proposed techniques. For each site, we provide a description of the survey results accounting for geological evidences, logistic constraints, and physical limitation of the used techniques. Finally, we highlight the advantages offered by a cooperative use of different techniques and suggest strategies to overcome intrinsic limitations of each one of the considered survey methods.