Contributions for the Understanding of the São Pedro do Sul (North of Portugal) Geohydraulic and Thermomineral System: Hydrochemistry and Stable Isotopes Studies

São Pedro do Sul thermomineral aquifer system is located in the North of Portugal. Hydrogeochemistry and isotopic studies were conducted order to improve knowledge this groundwater system, known since ancient Roman times for their therapeutic properties. One spring (NT) three boreholes (AC1, SDV1 SDV2) have a mean temperature around 68 °C. Currently, these waters are mainly used thermal spas geothermal energy supply. Major cations anions identify characterize different water types sub-systems. Stable isotopes composition, δ18O δ2H, been determine origin as first approach estimate preferential recharge altitude water. The results suggest single with relative composition similar mineralization values. δ2H values indicate meteoric no significant evaporation before infiltration. Besides, points areas at altitudes about 1000 m a.s.l. This suggests area Freita/Arada mountains NW poles.