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A conceptual hydrogeological model of the Viterbo thermal area (central Italy) has been developed. Though numerous studies have been conducted on its geological, geochemical and geothermal features, there is no generalized picture defining the origin and yield of the hydrothermal system. These latter aspects have therefore become the objectives of this research, which is based on new hydrogeological and geochemical investigations. The geological setting results in the coexistence of overlapped interacting aquifers. The shallow volcanic aquifer, characterized by fresh waters, is fed from the area around the Cimini Mountains and is limited at its base by the semiconfining marly-calcareous-arenaceous complex and low-permeability clays. To the west of Viterbo, vertical upflows of thermal waters of the sulphate-chloridealkaline- earth type with higher gas contents, are due to the locally uplifted carbonate reservoir, the reduced thickness of the semiconfining layer and the high local geothermal gradient. The hot waters (30–60°C) are the result of deep circulation within the carbonate rocks (0.5–1.8 km) and have the same recharge area as the volcanic aquifer. The upward flow in the Viterbo thermal area is at least 0.1 m3/s. This flow feeds springs and deep wells, also recharging the volcanic aquifer from below

The conceptual hydrogeological model of the Viterbo thermal area in central Italy and the yield of the groundwater sys- tem have been examined. This area is of great geothermal interest. Through new investigations, three overlapping aquifers have been found. This study examines in detail the two shallower aquifers, characterized by different hydraulic and chemical characteristics. The first aquifer is related to the regional groundwater flow of the Cimino-Vico volcanic system and is generally characterized by cold, fresh waters used for irrigation and drinking water supply. The second aquifer, <i>i.e.</i> the thermal aquifer, supply thermal spas and public pools; it is present where the local hydrostratigraphic, structural and geothermal conditions permit a relatively active flow of higher salinity thermal waters (40?C - 62?C). These two aquifers interact vertically and laterally, giving rise to mixed waters circulating in the first aquifer. The first aquifer is recharged by direct infiltration and inflow from regional groundwater, as well as inflow from the second aquifer. The yield of the thermal aquifer is at least 170 L/s, discharging into thermal springs and wells, besides feeding the shallow aquifer vertically and laterally. Even if a future development of the second aquifer is potentially achievable on a global scale, the exploitation of the thermal waters is strictly dependent on the specific local hydrogeological equilibrium between the overlapping aquifers, different from place to place. The case study highlights that, in the volcanic hydrogeological environment, one of the most stringent constraints in determining the correct usage of a resource is the variable level of interaction of groundwater with different qualities

Abstract. The paper illustrates some results of research carried out to assess factors triggering debris flows which involve the pyroclastic overburdens covering carbonate mountains around Vesuvius. The aims of the research were to reconstruct a relationship between rainfall and debris flow occurrence and to highlight empirical hydrological thresholds through rainfall pattern analysis. The research was also aimed at investigating hydrogeological features of a pyroclastic cover-carbonate bedrock system to analyse factors inducing temporary hydraulic flow, critical for pyroclastic soil stability. The results of research are the following: i) rainfall pattern highlights empirical hydrological thresholds that differentiate the Lattari and Salerno Mountains from the Sarno Mountains; ii) in some sample areas of the Sarno Mountains close to the trigger zones of the landslides of May 1998 strong variation in hydraulic conductivity has been found in the first few meters below the surface; iii) these permeability variations would seem to justify temporary perched water tables that might affect the stability of the pyroclastic mantle.