Hydrogeological site characterization of marly-silici-calcareous rocks through surveys of discontinuities and pumping tests

Abstract

One of the challenges in the characterization of fractured aquifers is to define whether the approximation to a porous medium is valid or not. In this context, the present study concerns the hydrogeological characterization of a small area constituted by densely fractured marly-silici-calcareous rocks. The hydrogeological investigations included fracture network surveys and pumping tests. The survey of the outcrops showed a rock mass characterized by a high number of persistent discontinuities with a wide spatial distribution, high frequency and a wide range of values of the aperture in the different systems. These characteristics imply the possibility of considering the rock mass as an equivalent porous medium at the outcrop scale. Pumping tests highlighted a consistent reaction of the various monitoring points and a similar trend of the drawdown-time curve, resulting in considering the aquifer as continuous medium at the scale of the volume influenced by pumping. The drawdown maps seems to be related to a weak anisotropy of the aquifer in the horizontal plane with the major axis of the ellipse aligned along the direction NE-SW, consistent with the directions of the principal components of the hydraulic conductivity resulting from the hydraulic model of the rock mass. Although the aquifer can be considered an equivalent anisotropic porous medium at the scale of the study, the comparison between the results of pumping tests and of the rock mass survey indicates that this approach would be not sufficient to characterize groundwater movement.