Unveiling groundwater flow connection in carbonate aquifers through the combined use of hydrochemical and isotopic data and water budget evaluation: a case study in Southern Italy

Carbonate rocks cover about 15% of the global continental surface and represent important water resources in terms of water quality and availability. The understanding of groundwater flows in karst aquifers is beneficial for satisfying human water demand, avoiding potential conflicts among users and preserving groundwater dependent ecosystems, that is for a sustainable management of water resources. The consequences of water utilization in karst areas are revealed through monitoring activities of hydrochemical characteristics and water utilization (withdrawals and piezometric levels).We investigated the hydrogeological relationship between two neighboring carbonate aquifers, which were considered as two separate aquifer units in the past. Archival and newly acquired data on groundwater availability, hydrochemical and isotopic features were considered. Their combined use led to the proposal of new hypotheses regarding the connection between these aquifers. This issue is not only of scientific relevance but also has practical implications; indeed, there are important springs and well fields providing water to about 3.8 million inhabitants.The aquifers examined in this study are the carbonate mountains of Mt. Maggiore and Mt. Tifata located in Campania Region in Southern Italy. The mountains are geographically separated by the Volturno River valley, filled with alluvial-pyroclastic deposits. The aquifers have been exploited for drinking purposes since the late 1980s. The exploitation of these aquifers and the availability of historical and recent data (i.e., long-term monitoring) revealed their hydrogeological connection. This connection would be induced by the strong groundwater withdrawals from the well fields at Mt. Tifata (located south of the Volturno River). In fact, the exploitation provoked the depletion of the groundwater table and the disappearance of the major spring. The connection, with groundwater flowing from Mt. Maggiore to Mt. Tifata, can explain the absence of signs of overexploitation in the groundwater of Mt. Tifata even in the presence of withdrawals that exceed the natural recharge of the aquifers. As a consequence of the connection, a recall of mineralized waters characteristic of the southern portion of Mt. Maggiore has been observed in well fields at Mt. Tifata. At Mt. Maggiore the mineralization of groundwater is related to local faults, while moving away from them the mineralization is greatly reduced. This opens broader prospects for water utilization, for example, a more specific use for mineralized waters (such as bottling, balneotherapy, etc.) and a potable use in areas distant from the mineralized zone. In conclusion, as revealed in this study, stakeholders and water managers need to consider these carbonate aquifers as a whole groundwater body (i.e., not anymore as separated aquifers) when planning their utilization.