Hydrogeology and hydrogeochemistry of the plain between Mt. Massico and the river Volturno (Campania).Idrogeologia ed idrogeochimica della Piana compresa tra il M.te Massico ed il F. Volturno (Campania).

The study covers the sector of the Campanian Plain between the River Volturno and Mt. Massico. The hydrogeological system was defined in detail by analysing data from borehole stratigraphies and piezometric surveys. The extensive stratigraphic data acquired (more than 450 items) helped create the hydrogeological sections reported in the Map of Plate I. What emerges is the almost continuous presence throughout the area of Campanian Grey Tuff (IC): a greyish ashy rock associated with black scoriae and molten lava, with a variable degree of diagenesis and generally low permeability. IC crops out especially on the margin of the plain with fairly significant thickness (40-50 m) which become thinner, so as to almost disappear, towards the River Volturno. Chemical analysis of the water sampled from wells are indicated in the Plate II, which also reports the relevant groundwater chemistry maps. The Chemical Conductivity Map shows the predominance of values between 500 and 1000 μS/cm; lower values were obtained in aquifer sectors where there is no significant input from the limestone mountains and/or where the underground flow is coming from the Roccamonfina groundwater. Along the coast and in line with the bed of the River Volturno, saltwater contamination led to higher conductivity values. On the basis of the analytical data several areas with homogeneous chemical properties were able to be identified in the plain groundwater: - Zones a, stretching in discontinuous sectors at the foot of the limestone reliefs, collect the water from recent underground flows, which still bear the clear imprint of these aquifers. - Zones b, conditioned by the leaching of pyroclastic soils. - Zones c, located in the remaining part of the plain show a contributions, in different proportions, of the firsts two components. - Zones c', close to the river is a new zone substantially similar in lithology and sited downstream of the former (in terms of groundwater flow): nevertheless, the previous waters appear changed insofar as the local water has small quantities of sulphates and increases in the bicarbonate ion, due to reducing conditons. Contamination by nitrates, with values > 50 mg/L, is observed in the plain’s vast north/north-eastern sectors; towards the River Volturno the groundwater nitrates have fairly low concentrations, amounting to a few mg/L. The same distribution of values occurs for the SO4 ion which decreases from 30-40 mg/L to about one mg/L in the areas close to the river; in the same area, however, CO2 (and HCO3), Fe and Mn increase. Finally, the Aquifer Contamination Vulnerability Map stressed the importance of the depth to water and the vadose zone in the unconfined sectors.