Groundwater quality assessment for different uses using various water quality indices in semi-arid region of central Tunisia.

ABSTRACT

The Hajeb Layoun-Jelma basin, located in the central Tunisia, is the principal source of water supply for Sidi Bouzid and Sfax region. The over-abstraction from this groundwater, since 1970, and the intensive agriculture activities led to the degradation of the water quantity and quality. The quality evaluation for this groundwater is very important tool for sustainable development and decision for water management. A total of 28 groundwater samples, from shallow, springs, and deep aquifers, were collected, storage and analyzed to evaluate its quality suitability for domestic and agriculture purposes using geographic information system and geochemical methods. For the both aquifers, the abundance of cations Na > Mg > Ca > K, and of anions in the order Cl > HCO3 > SO4. The dominant hydrochemical facies, for the shallow aquifer and springs, are Na-Cl and Ca-Mg-Cl; for the deep aquifer, the geochemical facies are Na-Cl, Ca-Mg-Cl, and Ca-Cl. The comparison of the major parameters and the chemical data with the World Health Organization standards and the national standards indicate that this groundwater is suitable for drinking, except in some samples, with high salinity concentrations. The water quality was assessed, for drinking uses, using "water quality index," "entropy," and "improved water quality index." The results mentioned that the improved water quality index is the best method which indicated that the poor water quality coincide with the Na-Cl water type. The entropy method and the water quality index present the optimistic methods. The irrigation suitability assessment was made using various parameters (SAR, TH, % Na, PI, MH, KR, EC). The results revealed that the majority of samples in Hajeb Layoun-Jelma basin are not appropriate for irrigation uses.