Hydrostratigraphic framework and physicochemical status of groundwater in the Gioia Tauro coastal plain (Calabria--southern Italy)

In this study, we analysed the Gioia Tauro Plain (Tyrrhenian coast, southern Italy) interms of hydrostratigraphy and the physicochemical status of groundwater. We investigated thehydrostratigraphic framework of the area identifying a deep aquifer (made by late Miocene succession), an aquitard (consisting of Pliocene clayey and silty deposits) and a shallow aquifer (includingLate Pleistocene and Holocene marine and alluvial sediments) using subsoil data (boreholes andgeophysics). Our reconstruction showed that the structural geology controls the spatial patternof the aquitard top and the shallow aquifer thickness. Furthermore, we evaluated the hydraulicconductivity for the shallow aquifer using an empirical method, calibrated by slug tests, obtainingvalues ranging from 10-4to 10-5 m/s with a maximum of 10-3 m/s located close to inland dunefields. The piezometric level of the shallow aquifer recorded a significant drop between the 1970sand 2021 (-35 m as the worst value). It is the effect of climate and soil use changes, the latter beingthe increased water demand for kiwi cultivation. Despite the overexploitation of the shallow aquifer,shallow groundwater is fresh (736 µS/cm as mean electrical conductivity) except for a narrow coastalarea where the electrical conductivity is more than 1500 µS/cm, which can be due to the seawaterintrusion. What was more complex was the physicochemical status of the deep aquifer characterisedby high temperature (up to 25.8 oC) and electrical conductivity up to 10,520 µS/cm along the northernand southern plain boundaries marked by tectonic structures. This issue suggested the dominant roleof the local fault system that is likely affecting the deep groundwater flow and its chemical evolution.