The Mio-pliocene aquifer system of the South Auresian Trough, Low Septentrional Sahara, Algeria: aquifer geometry and groundwater characterization

Abstract

In the South auresian trough, Low Septentrional Sahara, Algeria, the sands aquifer is contained in the Mio-pliocene deposits in which several sedimentary sets have identified and contain two independent aquifer levels. Their relationship is determined by data correlation of several cross-sections surveyed on outcrops and boreholes that permit us a 2D construction of the multi-layer aquifer formations and to specify its geometry. The latter shows an asymmetrical synclinal structure with greater depth to the south and an unconformity of the upper unit (upper aquifer) on the base unit (lower aquifer) with a reduction in thickness from south to north. The upper aquifer, commonly designated “undifferentiated Mio-pliocene aquifer” is the most exploited. Its water is moderate to strongly charged and presents two families at evolutional hydrochemical facies. Their spatial distribution is strongly influenced by the natural context and the aquifer geometry. The hydrochemical analysis reveals that the dissolution of carbonate (CaCO₃ or CaMgCO₃), sulfate (CaSO₄) and salt (NaCl) were the major sources of ions in the studied groundwaters. In this region deprived of treatment means and softening of water, the exploitation of the study results can help the decision makers, preferentially, to choose the captive fields principally destined for potable water supply in sectors containing the water less charged.