Vulnerability of the aquifer system: considerations on a methodological approach.

The worldwide development of past civilisations as well as the recent socio-economical evolution of Nations is based and strongly controlled by the availability of water. The Mediterranean Basin that during the last decades has been characterised by a semi-arid climate is not an exception. In this area, the occurrence of wide aquifers both in limestone rocks and alluvial deposits favour the accumulation of important amounts of water resources. However, this opulence in underground waters is often compromised by an abuse of pumping and by local but diffused polluting phenomena having several causes (urban, farming, facto-ries, etc.). In Italy, only the 40% of the total amount of the potentially exploitable water re-sources, both superficial and underground, is effectively exploited. In fact, the remaining 60% is in practice not used because of qualitative and economical problems. Due to the general setting and the specific characteristics, the aquifers are frequently vulnerable to superficial polluting sources. In particular, the vulnerability of the underground resources is a function of a) the hydrolithological, hydrostructure and hydrogeological conditions of the system; b) the pedological characteristics of the soils; c) the recharge conditions; d) the groundwater inflow-outflow processes and e) the physical and hydrochemical processes that influence the natural quality of waters (Civita and De Maio, 1977). In the last decades, several methods to evaluate the intrinsic vulnerability of the aquifer system have been development based on a) the zona-tion of homogeneous areas with a similar degree of vulnerability (e.g. Albinet and Margat, 1970) and b) the parametric systems separated in a matrix system, a point count system, a point count system model and an environmental evaluation system (Foster, 1987; Aller et al., 1987; Dee et al., 1973; Civita and De Maio, 1997). The present research is devoted to the evaluation of the intrinsic vulnerability to pollution for two case studies characterised by a different density and overall quality of basic information. The first area is represented by the carbonate aquifer of the High Basento Valley (Basilicata, Southern Italy), while the second case study is the alluvial system surrounding the town of Ferrara, characterised by an unconfined aquifer (Eastern Po Plain, Northern Italy). For both areas, we define the conceptual hydrogeological model before applying the more suitable methodological approach allowing us to recognise the sectors characterised by the higher degree of pollution risk