Review: origin, heating process, and groundwater flow system of non-volcanic thermal aquifers in Tunisia

Thermal groundwater is of great economic and social importance. Tunisia is characterized by its hot groundwater spread over several regions. Hydrothermal resources need further investigation and diagnosis to determine their local, Mediterranean, or regional thermal sources and flow regimes. This study aims to differentiate origin and heating process of non-volcanic thermal aquifers. For this, three thermal provinces in Tunisia were reviewed and studied: Cap Bon thermal province (Korbous), Fluorinated Province of Zaghouan (Zriba Hammam), and Southern thermal province (El Hamma). A multidisciplinary approach, integrated with hydrogeological, geochemical, and isotopic data from the various studied provinces, was used. Results reveal that the studied thermal waters are of meteoric origin heated by deep circulation and acquire their thermal energy from the Earth’s heat during long-time residence. The thermal waters of El Hamma are the oldest and the northern waters are younger, influenced by the recent recharge. Thermal groundwater chemistry is influenced by minerals related to rock-water interaction. This study confirms that thermal waters, in non-volcanic areas, are of meteoric origin; their temperature and salinity depend on the residence time and their depth of circulation. This makes it possible to rationalize for their use in the appropriate sectors and ensure sustainable management.