The importance of reduced-scale experiments for the characterization of porous media

In order to reduce threats to the quality of groundwater resources, prevention and control are the most important activities to carry out. In general, these activities require the ability to model the flow and solute transport phenomena in the aquifer. Thus, it is essential to collect information about potential contamination sources, boundary conditions, hydrological forcing, and the magnitudes and spatial distributions of the hydrodynamic and hydrodispersive parameters of the porous media. Measurements of such parameters, available only at a finite number of locations, are often obtained by means of different techniques and can be representative of various measurement scales. The use of available data, necessarily distributed on different scales, for characterizing porous media at a defined scale is a key question of great interest. With the aim to investigate on the hydraulic conductivity scale effect on a homogeneous porous medium, several experiments were carried out at the Hydrogeosite Laboratory (Marsico Nuovo, Italy). This laboratory is a large scale model sized 10 × 7 × 3 m3, filled with a homogeneous medium made up of quartz-rich sand. The results are described by separating the two important scale-ambits under consideration, obtaining two scale power laws. Moreover, the scale effect of the hydraulic conductivity has been detected by considering the water flow type (uniform or radial) into the porous medium. However, the results, either considering the only scale law or multi-scale laws, confirm what was proved by several authors for heterogeneous porous media, that is the trend of hydraulic conductivity to reach a higher limit when the measurement scale increases and, in our opinion, regardless of the heterogeneity of the porous medium. Finally, a hydrogeophysical approach is described in this chapter, in order to show how a passive geophysical method as self-potential can estimate the hydraulic conductivity. It is an important step when large site should be characterized and few direct borehole data are available. These aspects are important because the hydraulic conductivity estimation is the first step for the characterization of a site.