Groundwater chemistry in the vicinity of the Ouled Farès area, northern margin of the Cheliff Valley (N. Algeria)

Jacek Motyka, Stanisław Witczak


Chemizm wód podziemnych w okolicy Ouled Farès w północnym obrzeżeniu Kotliny Cheliffu (północna Algieria)

Detailed geological and hydrogeological mapping has been carried out in the northern, marginal part of the Cheliff Valley (area o f about 50 km2). Three groundwater systems have been identified. All the three circulation systems arc dominated by either brackish or saline waters (TDS 2-14 g/dm3). In general increased TDS content is accompanied by changes in chemical composition from the SO4 - Ca type through several multi-ion types to the Cl - Na one. Saturation index (SI) has been calculated for 23 samples in respect to various minerals. Waters from both the subsurface and shallow-circulation systems are close to equilibrium with both gypsum and calcium carbonates (aragonite and calcite) but tend to be supersaturated in respect to dolomite. Chemical composition of each groundwater system is critically influenced by mineralogy of rocks. It seems that an equilibration is quickly achieved between water and CaSO4, and followed by a slow, gradual enrichment in other ions, caused by leaching of small amounts of NaCl and MgSO4 from the gypsum beds.

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