Revision of the hydrogeological conceptual models of two Portuguese thermomineral water systems: similarities and differences

This paper aims to highlight the role that the assessment of hydrogeological conceptual models of the thermomineral water systems of a given region plays in the sustainable management and protection of its resources (e.g., possible drilling plans to capture thermomineral waters with higher flow rate and/or temperature) and development (use of thermomineral waters in the various forms). Therefore, a multi and interdisciplinary approach from a variety of scientific fields of the domain of geoscience such as geology, geochemistry, hydrogeology, and isotope hydrology was applied. Despite the contrasting features of the two thermomineral systems studied, namely, different geochemical signatures ascribed to distinct geological environments (e.g., the Caldas do Moledo system HCO₃-Na with 8 < pH < 9, and the Cabeço de Vide system Na-Cl/Ca-OH with pH ≈ 11.5), the respective hydrogeological conceptual models show clear similarities. Regional/local higher altitude areas associated with highly fractured rocks play an important role in conducting the infiltrated meteoric waters towards the discharge zones near the Thermal Spas. The discharge zones are mainly related to the intersection of the main local/regional fault lineaments and conjugate structures, responsible for promoting the ascent of the thermomineral waters. The use of thermomineral waters in spas, bottling industries, or low-temperature geothermal facilities often promote social and economic development at local and/or regional scale. In many cases, it is even a major, if not the main, source of local/regional development. Thus, the importance of such multidisciplinary studies for the sustainable management of these important types of georesources is obvious.