Geological criteria to the 3D delimitation of groundwater bodies (GWB) in the hydrographic district of Sardinia

The Water Framework Directive 2000/60/EC (WFD), establishing a framework for Community action in the field of water, has introduced for all Member States the obligations relating to the identification of surface and groundwater bodies and their monitoring, classification and definition of programs of measures to achieve a good status of all water bodies. In compliance with this statement, the River Basin Management Plan of Sardinia (Regione Sardegna, 2015) has identified and delimited 114 groundwater bodies (GWB). Main criteria were the identification of geological boundaries at the scale of 1:200,000, hydrogeological divides, analysis of pressures, and chemical status of groundwater. In order to have a better knowledge of groundwater bodies boundaries, a more detailed delineation and characterization is in progress. As a first step of delineation the geological map of Sardinia at the 1:25,000 scale was used. Considering that the aim of this map was not for hydrogeological purpose, its reinterpretation was mandatory. Every geological context needs in-depth knowledges to describe and model it properly. A further hydrogeological analysis can allow new interpretation of existing model according to the most recent methodologies developed. Each GWB required a different investigation specific approach. For example, incoherent recent deposits (gravels, sands, silts, clays, etc.) hosting groundwater bodies are characterized by porous aquifers types. Thus, necessary to consider the geometric relationships between stratigraphic units and the depositional environment provides important information on the lateral variation of hydrogeological features. Otherwise, the groundwater bodies hosted in crystalline rocks show continuous lithological characteristics for wide zone, but the primary relationships with neighboring units are often modified by tectonics (Feroni Cerrina et al., 2008). The geological, hydrogeological and hydrogeochemical knowledge of GWBs becomes necessary to understand the quantitative state (extension and thickness of the area, yield, specific storage) and qualitative state (chemical state) for the correct delimitation of the GWB.