Groundwater quality assessment for drinking and irrigation purposes by utilizing integrated water quality indexes in a semi-arid region, SE Sfax area, Tunisia

The region of Sfax, with a population of over 1.2 million inhabitants, has experienced significant demographic, agricultural, and industrial development in recent decades. This situation has intensely strained water resources, particularly the groundwater and led to water quality and quantity deterioration. The use of quality indices constitutes a synthesis of various parameters for water use and allows for an informed and straightforward decision on water usage. The aims of the study are to evaluate groundwater geochemistry evolution over 10 years, from 2005 to 2014, and its suitability for drinking and irrigation purposes using Integrated Water Quality Index in the phreatic aquifer in the South East of Sfax City in southern Tunisia. This index is influenced by the levels of cations such as calcium, magnesium, sodium, and potassium, along with anions like chloride, sulfate, and nitrate, as well as pH and total dissolved solids (TDS). The drinking index map for 2005 shows a dominant "unsuitable" class over the study area; however, for 2014, the groundwater becomes unsuitable for drinking. The irrigation index takes into account EC, Na+, HCO3-, Cl-, and SAR. According to mapped results, five classes varying from no-restriction to severe-restriction quality levels are found. From 2005 to 2014, the natural recharge in the upstream area of the aquifer resulted in improvement of groundwater quality in its surroundings but in the southern coastal aquifer part, the water quality is affected by infiltration of treated wastewater used in irrigation.