Versilia coastal plain aquifer system: a multidisciplinary approach to define qualitative and quantitative aspects of groundwater resources.

Pollution and wrong management of natural resources have led to an increasing attention of the public administration and a development of scientific research in environmental field. Following the Deliberation of the Regional Committee (no 939/2009) in the Tuscany territory, 66 Subterranean Groundwater Bodies (SGBs) were identified by regional Administration, which also promoted their geo-hydrological and geochemical characterization for reaching a better groundwater management. In this work a multidisciplinary geological-hydrogeological-geochemical approach has been applied to the study of Versilia SGB, that represents one of the major aquifer system of the Tuscany (Menichini, 2012). The study area is located in the extensional neogenic–quaternary Viareggio Basin, in the inner sector of the Northern Apennines, and it is encompassed from Serchio River (S), Carrara town (N), the Tyrrhenian Sea (W) and Apuan Alps (E). In the first phase of this study, the geometrical reconstruction of the subsurface geology has been performed through a sequence stratigraphic approach. Sedimentological and micropaleontological analysis of continuously cored boreholes were used as tools for facies definition. Furthermore a stratigraphic logs database allowed a detailed description of the hydrogeological units. During a second phase a 3D hydrostructural model was achieved by using Aquaveo Software and a computation of the total volume was performed for each hydrogeological unit. By means of the comparison among the elaborations of the water head and pumping test data and the 3D hydrostructural model, in the third phase the amount of the total water volume stored in the aquifer system was estimate, both in low-flow and high-flow conditions. Moreover, the piezometric surfaces, allowed to individuate the flow pattern and the most exploited zones of the aquifer. The fourth phase was the hydrogeochemical characterization, through deterministic and geostatistical approach, and through geochemical and isotopic data acquisition and processing. Main results pointed out that the Versilia SGB is constituted by multilayer aquifer system; a sequence of permeable, gravel and sand layers separated by impermeable silty-clayey deposits. This multi-layer system behaves similarly to a single-layer aquifer, as suggested by the reconstruction of the piezometric surfaces, owing to both the discontinuous nature of the impermeable deposits and the presence of several boreholes connecting the permeable layers situated at different depths. The chemical and water isotopes analyses allowed to identify and to characterise the main feeding components of multilayer aquifer system. The conceptual model is the starting point for flow and transport numerical models, which is a useful tool to define future groundwater management plans.