GEOCHEMISTRY AND HYDROGEOCHEMICAL PROCESSOFGROUNDWATERIN ARID REGION: A CASE STUDY OF THE WATER TABLE IN THE SOUF VALLEY (LOW SEPTENTRIONAL SAHARA, ALGERIA (original) (raw)

2014, African Journal of Geo-Science Research,

Groundwaters are the only hydrous resource exploited in the Souf valley, Algerian Sahara, principally, its water-table. Several techniques and conventional graphical plots were used to define the geochemical evaluation of this aquifer system based on the ioniccomponents, water hydrochemical facies and factors controlling groundwater quality. Groundwaters are highly salines (2361-14780 mg/L TDS) and show high contents in major ions that exceed, extensively, the admitted norms of potability. The relative abundance of major ions was Na+  Mg2+Ca2+ K+ for cations and Cl-SO42- HCO3- NO3-for anions. Two main waters families are identified; one is sodic facies rich in magnesium, the second is mixed facies. Their spatial distribution is strongly influenced by different parameters linked to the global aquifer system (lithology, structure, conditions and underground circulation directions). Dissolution of gypsum, salts, weathering of carbonate and silicate, ion exchange, mixing and nitrification of the organic matter are the main hydrogeochemical processes of waters mineralization. The conjugated action of the different mineralisation processes as well as their combinations had accentuated the salinity of these waters. Their identification allowed a better interrelationship between the different present ions. Indeed, the spatial chemical facies distribution observed is closely linked to the lithologic nature and to the geometry of the aquifer. The global scenario of mineralisation puts in evidence the roles played by the different natural parameters (internal and external) linked to the aquifer system, specifies the processes involved in the acquirement of the global saltiness of waters and can predict its probable evolution in the region. In this region deprived of treatment means and softening, when choosing captive fields and implantation of drilling of potable water supply, these results must guide decision makers in selecting the right sectors containing water less charged.