The aim of this research is to define a specific monitoring system in order to investigate the hydrogeological behaviour of a low permeability heterogeneous medium in a complex landslide. Case Pennetta active landslide is caused by roto-translational slides and complex active earth slides-earth flows and mainly involves sandstones and clays.
Piezometric levels were monitored, over two hydrogeological years, by two multilevel well systems. Discharge and physico-chemical parameters were monitored in several springs and artificial drains to understand the hydrogeological setting and its evolution over time. Mixing processes between groundwater and neo-filtration water were investigated by EC logs performed in the boreholes. In addition, isotopic analyses of δ18O and δD were carried out to define the recharge areas, and 3H analyses allowed to investigate the mean transit times.
Results showed the coexistence of different flowpath within the saturated zones at the slope scale. A shallow one, rapid and reactive to the rainfall regime is characterized by fast circuit, that shows EC values of less than 1000 µS/cm in high flow and up to 3700 µS/cm in depletion phase, according to local infiltration processes. The isotopic values also show a great variability over time (δ18O: -7,86 ÷ -6,95‰) and this variation is also observed in artificial drains and springs, according to a very shallow flowpath. 3H content values are indicative of a mixture between sub-modern and neo-infiltration water (mean value 2,95 UT).
Due to the heterogeneity of the medium, a deep, local and more conductive flowpath were found. This circuit shows smoother hydrograph, higher EC values (from 2500 up to 4200µS/cm without any influence by depletion/recharge phases) and more depleted isotope values with less variation. 3H content values underlines long transit times (mean value 0,34 UT).
The monitoring system developed in this study allowed a better understanding of the hydrogeological behaviour in this type of movement, where the heterogeneity of the material involved influences the groundwater dynamics.