CONTAMINATION VULNERABILITY ASSESSMENT IN THEVOLTURNO RIVER ALLUVIAL AQUIFER

The study area is the upper part of the Campania alluvial plain (~ 343 km2), located in southern Italy. The plain's aquifer lies in the alluvial-pyroclastic and pyroclastic porous units underlying, in the northern sector, the "Campanian Ignimbrite" tuffs and oldest tuffs. The collection and the standardization of about 500 borehole stratigraphies permitted to define the spatial distribution of the hydrogeological units and their relationship in the subsoil. In fact, the hydrogeological setting is strongly related to the thickness and physical characteristics (granulometry, lithification, etc.) of the alluvial sediments and the tuffs. The aquifer is confined in the northern sector, semi-confined in the southern sector and phreatic in the central part. The aquifer is recharged by rainwater infiltration and by underflow from the adjacent reliefs: the limestone Mesozoic mountains (N and NE) and the Roccamonfina volcano (N).The piezometric surface (constructed on the basis of a monitoring network of almost 120 wells) stresses the groundwater flow directed towards W and SW. A hydrogeological database was purposely designed to satisfy the analytical needs of the vulnerability assessment studies. The geographic database (ILWIS, ARCGIS) has been drawn up supported by an alphanumeric database (ACCESS, EXCEL). In fact, the database combines significant hydrogeologic data for the study and is composed by two parts: the first is a spatial database containing various thematic maps (geological, hydrogeological, soil, etc. data).The second is a descriptive database including attribute data related to the lithology (borehole stratigraphies), to the hydrogeologic units (permeability, transmissivity, etc), to the groundwater points (monitoring network), etc.In order to make its management easier, a simple tabular structure was adopted for the descriptive database. Attribute data were organized, so that the information necessary for vulnerability assessment could be easily extracted and exported to a Geographic Information System. The parametric method SINTACS has been used in this study.For the construction of the seven SINTACS maps, different data input, collected during the last few years by the authors, have been used about topography, lithology, hydrology, climate, etc. The Aquifer Contamination Vulnerability Map highlights that:• the most widespread vulnerability degree is moderate (51 % of the area);• 34 % of the area presents a low vulnerability degree and it is localized in the confined sector for the protection exerted by the "Campanian Ignimbrite" or, in the semi-confined sector, by thick alluvial deposits (often more than 20 m) with fine granulometry, low-permeable;• in the coastal sector is present a wide zone (15 % of the area) with high vulnerability due to the poor “Depth to water” close to the sea and to the weak role played by the vadose zone and the soil in respect to the contaminants.