Hydrochemical Investigation and Quality Assessment of Groundwater in the BouHafna-Haffouz Unconfined Aquifers, Central Tunisia

Abstract

Multivariate statistical techniques were applied to improve the understanding of the aquifers hydrodynamic and to identify the natural and anthropogenic processes that control the BouHafna and Haffouz groundwater quality. Some other parameters, such as sodium adsorption ratio (SAR), percent sodium (%Na), residual sodium carbonate (RSC), and permeability index (PI), were used to examine the suitability of groundwa - ter for irrigation applications. Groundwater samples are classified into Ca-Mg-HCO 3 and Ca-Mg-SO 4 water-type. The statistical investigation permits to identify three dif - ferent groups. The first group reflects the influence of water-rock interaction in relation with the dissolution of evaporatic minerals, the cation exchange process with phyllo - silicates and the dedolomitization. The second and third groups, including the weakly mineralized groundwater samples, suggest, firstly, that the return flow of irrigation waters has a small, but not negligible contribution to the groundwater contamination, and secondly, the reduction of nitrate (NO 3 ) to nitrogen gas (N 2 ). Furthermore, it has been demonstrated that the majority of the groundwater samples are suitable for irriga tion uses. mineralization. This investigation reveals the predominance of Ca-Mg-HCO 3 and Ca-Mg-SO 4 water-types. These water facies are derived mainly from water-rock interaction processes, i.e., the dissolution of halite, gypsum, the dedolomitization, and the cation exchange. On the other hand, return flow of irrigation water has resulted in elevated nitrate concentrations in groundwater especially in the agricultural zones, which are characterized by an exces sive use of fertilizer. Thus, it is important to protect the aquifers against overexploitation and groundwater quality deterioration related to the evaporate dissolution and agricultural contamination. For these reasons, in the BouHafna and Haffouz regions where groundwater resources are under the great development stress and environmental pressure, some pre ventive measures should be taken. These are (1) control the exploitation groundwater; (2) the definition of special groundwater resources protection zones; (3) control the potential processes and sources of salinization; and (4) improvement of diffuse source groundwater pollution.