Hydrochemistry of thermal waters in Northeast Tunisia: water-rock interactions and hydrologic mixing

This paper deals with the results of a geothermal study on the thermal waters of Northeast Tunisia, which has remarkable thermal springs that have been used for bathing since many years. Water temperature at the emergency varies between 18 and 57 degrees C and total dissolved solids (TDS) range from 1,742 to 18,542 mg/l. Hydrochemical approach recognized three different water types: (1) the poorly mineralized Ca-HCO3-SO42+ type characterizing the carbonate aquifer, (2) the mixed type influenced by the evaporate rocks, and (3) the highly mineralized Na-Cl- type representing the deep thermal waters. Furthermore, the estimated temperatures at depth, using various chemical geothermometers, range between 60 and 110 degrees C. A synthetic hydrogeothermal approach, applied on the study area, including hydrogeological, geological, hydrochemical, and geothermometrical data shows that the thermal water of Northeast Tunisia is of meteoric origin. This water infiltrates deeply into the Jurassic dolomite and reaches a high temperature before rising upwards to supply the hot springs and well discharge zones. The upward movement of hot water from the deep aquifers to the surface is essentially due to the tectonic disharmonies which affected the area.