Contribution to the Knowledge of Temperature and Reservoir Depth of Sulphurous Groundwater Aquifer Systems in the Dão River Basin, Portugal

The sulphurous groundwater aquifer systems of the Dão River basin in Portugal have been the subject of studies by some authors, as there are several Medical Spas, where over time there has been a need to increase their flow rates to guarantee more available mineral water and better quality. It is known that those waters resurface with anomalous temperatures, and that they are associated with very deep aquifer systems where the reservoir temperature is relatively high. Thus, the present work aims to contribute to the knowledge of the reservoir temperature and its depth, in the sense of taking to the planning of construction of deep wells, so that their results to be favourable, allow energy utilization, that function of the temperatures to be obtained, can allow from the production of electricity, to heating of buildings, heating of domestic water, to aqua-ludic uses in medical spas and leisure areas. After presenting the generic aspects of geomorphology, geology, climatic elements, and global conceptualization from the numerical models of the Dão River basin, the results of physical-chemical analyses of groundwater are presented. It should be noted that the groundwaters with the greatest geothermal potential are associated with deep aquifer systems, semi-confined to confined, fissured type (very localized), with sulphurous water, with pH values higher than 8.0, conductivity above 350 μS/cm, and surface temperatures between 15.7 and 50.9°C. It is important noting the occurrence of five main sectors with geothermal potential, which from upstream to downstream of the river basin are: Cavaca, Sezures, Alcafache, Sangemil and Granjal. By applying geothermal thermometers, in the results of physical-chemical analyses of the groundwaters of those sectors, the reservoir temperatures were obtained between 92 and 116°C and also reservoir depths generally greater than 2200m.