Timgad Basin is a part of the North-East Algerian Saharan Atlas. It is located at the northern of the Aurès Mountain. It is bordered in the North by Bou Arif, Amrane and Tagratine mountains, while in the South it is limited by Chelia, Rdam and Nerdi Bouhmar mountains. It is shaped as a synclinal gutter oriented East-West and covers an area of about 1000 Km2 . The climate is semi-arid (cold winter and hot summer) with average annual rainfall not exceeding 350 mm. The basin is composed by varied lithology, showing large folded structures down sloping towards the center, which favor groundwater storage. The Miocene sandstone aquifer is the most important. It is characterized by a wavy shape, which form series of shale-marl filling depressions. Recent wells drilled in the basin edges and center, put in evidence its artesian character. The piezometric survey shows a groundwater convergent flow oriented towards the basin east (Bou el Freis), likewise the sandstone aquifer is marked by the presence of a West-East drainage axis which separates the basin northern part characterized by a low reservoirs hydraulic capacity from the southern part distinguished by the groundwater relative abundance.

The basin of Timgad belongs to the North-Eastern Algerian Saharan Atlas; it is located at the northern extension of the Aures Mountains. The basin is an asymmetrical syncline oriented East-West covering an area of 1000 Km2. The climate is semi-arid (cold winter and hot summer) with average annual rainfall not exceeding 400 mm. Recently, the increasing agricultural activities led to an excessive exploitation of groundwater resources. In order to meet this rising water supply demands, implementing a water resources management policy is a priority which should be based on a basin hydrogeological study. Effectively, the geological and geophysical studies have confirmed the presence of permeable Miocene and Cretaceous formations (sandstone and carbonate); relatively resistant affected by fractures network, which are probably forming a confined aquifers. Indeed, recent wells drilled in the basin center and their boundaries; show that the aquifers are artesian. The sandstone aquifer of the Miocene is the most important, it is characterized by significant thickness which can exceed 200m, its extension as well as its particular corrugated geometry, characterized by a wavy shape, which forming a series of shale-marl filling depressions, influences the groundwater flow, actually, the piezometric surface illustrates groundwater convergent flow oriented to the east, towards Bou el freis, likewise the sandstone aquifer is marked by the presence of a West-East drainage axis which separates the basin northern part characterized by a low reservoirs hydraulic capacity from the southern part distinguished by the groundwater relative abundance. Groundwater is generally easily extracted, except the northern part of the basin where the top shale-marl layer is thickens to over 1000m.

The hydrochemical and multivariate statistical techniques such as the principal component analysis (PCA) and the cluster analysis (CA) were used to identify the hydrochemical processes and their relation with groundwater quality and also to get an insight into the hydrochemical Zana aquifer groundwater chemistry evaluation. Twenty-four samples during the wet season and even during the dry season are analyzed. The Piper diagram showed that water facies are magnesium bicarbonate on the sides of the western reliefs and magnesium chloride-sulfated at the north and the center of the plain. The PCA carried out on three factors revealed that on the factorial design F1-F3, nitrates negatively determine factor 3, indicating the presence of an agriculture pollution. On the factorial design F1-F2, HCO3− positively determine the factor 2, indicating the carbonated origin. However, the CA, based on variables, showed that the waters in the region can be classified into three groups according to flow direction while the CA, based on major ion contents, defined three groups, reflecting the same hydrochemical facies. The first group with dry residue varying between 360 and 1700 mg/l and characterized by Mg2+ and Cl−, HCO3−. Samples of this group are mostly located in the north and northeastern part of the region. The second group with highest dry residue (2080 to 3820 mg/l) characterized by Mg2+ and SO4−, Cl− is located near the Northwestern and western outcrops. The third group coincides with the central part, the lowest of the plain, with heightened dry residue (4140 to 13,950 mg/l), characterized by Mg2+ and SO4−. The hydrochemical study made it possible to allot the evaporitic origin to the elements Na+, Mg2+, K+, Cl−, and SO4−, while for element HCO3−, it results from the carbonated formations. These results showed that the presence of nitrates in the studied area is closely linked to the agricultural activity.

This paper was made in the region of M’daourouch-Dréa which is part of the high plains of northeastern Algeria, located southwest of the Souk-ahras Wilaya in eastern Algeria. It is a plain with agricultural vocation which requires for its development more water. Knowing that the rainfall is low (465mm/year) and not enough to meet the needs of farmers, the use of groundwater then becomes the only alternative to fill this lack of resources. Among the aquifers identified in this region is that contained in fissured limestones of lower Maestrichian age. In order to satisfy farmers and citizens in water it is necessary to have a good characterization of this aquifer. The objective of this paper is to improve the knowledge on the morphology and the extension of this aquifer and to locate its roof in space to help operators choose areas favorable to exploitation, so direct them to the nearest areas of the surface thus minimizing the cost of the drilling operation. To achieve this goal, we have exploited by exploiting several tools (geological map, logs of boreholes and geophysics survey), whose combination gave an idea on the geometry of the aquifer as well as the depth of its roof in different regions of the plain and shows by the occasion, the affectation of these limestones by several tectonic accidents generating thus a structure in collapsed blocks from where the very variable depth of the roof of these limestones of a place of the plain to other.

The hydrochemical and multivariate statistical techniques such as the principal component analysis (PCA) and the cluster analysis (CA) were used to identify the hydrochemical processes and their relation with groundwater quality and also to get an insight into the hydrochemical Zana aquifer groundwater chemistry evaluation. Twenty-four samples during the wet season and even during the dry season are analyzed. The Piper diagram showed that water facies are magnesium bicarbonate on the sides of the western reliefs and magnesium chloride-sulfated at the north and the center of the plain. The PCA carried out on three factors revealed that on the factorial design F1-F3, nitrates negatively determine factor 3, indicating the presence of an agriculture pollution. On the factorial design F1-F2, HCO3− positively determine the factor 2, indicating the carbonated origin. However, the CA, based on variables, showed that the waters in the region can be classified into three groups according to flow direction while the CA, based on major ion contents, defined three groups, reflecting the same hydrochemical facies. The first group with dry residue varying between 360 and 1700 mg/l and characterized by Mg2+ and Cl−, HCO3−. Samples of this group are mostly located in the north and northeastern part of the region. The second group with highest dry residue (2080 to 3820 mg/l) characterized by Mg2+ and SO4−, Cl− is located near the Northwestern and western outcrops. The third group coincides with the central part, the lowest of the plain, with heightened dry residue (4140 to 13,950 mg/l), characterized by Mg2+ and SO4−. The hydrochemical study made it possible to allot the evaporitic origin to the elements Na+, Mg2+, K+, Cl−, and SO4−, while for element HCO3−, it results from the carbonated formations. These results showed that the presence of nitrates in the studied area is closely linked to the agricultural activity.