Hydrochemistry and geothermometry of an Albian aquifer from Oued Righ region in northeastern Algerian Sahara

Abstract

The area of Oued Righ is one of the important geothermal areas in northeastern Algerian Sahara. It is characterized by a hot arid climate with intense dryness and very high evaporation rates. These various climatic characteristics are reflected on the hydrography of the study area. The water requirements of the Oued Righ region are provided by groundwater resources contained in the two aquifers: the complex terminal and the deeper confined continental intercalaire aquifer. Twenty-seven samples were taken in November 2010 and April 2012; Water samples were analyzed for major and minor dissolved chemical constituents. Samples collected from the CI aquifer are characterized by high temperatures varying from 40°C to 60°C and conductivities of 2110 to 3370 µS/cm. The total dissolved solids (TDS) of the thermal waters range from 1488 to 5480 mg/l. The waters are generally of sodium and magnesium sulfated and sodium chlorinated types. The results of mineral equilibrium modeling indicate that the thermal waters of Oued Righ are undersaturated with respect to evaporite minerals and oversaturated or nearly in equilibrium with respect to dolomite, calcite, and aragonite. This paper presents ternary diagrams of Na-K-Mg1/2 and Cl-SO4-HCO3 and a calculation model, which allows location of geothermal water with the two diagrams, involving knowledge of their chemical composition. Groundwater in the Albian aquifer of Oued Righ shows a change in its chemical properties between the two sampling periods, resulting from water-rock interactions and mixing processes.