Hydrochemical assessment and groundwater pollution in the southern Hodna Chott region (Algeria): Characteristics, pollution levels and drinking water quality implications

Groundwater pollution has become a major issue of concern to both researchers and policymakers. Many climatic and anthropogenic factors impact groundwater. Groundwater is the sole source of water for all needs in a semi-arid area south of the Chott Hodna. Recently, the quality of drinking water has declined due to overexploitation of the aquifer and the presence of contaminating factors. This study aims to describe the hydrochemical characteristics of the aquifer, assess the level of groundwater pollution, and geographically locate the polluted areas. In 2019, we analyzed samples from 45 boreholes south of the Chott Hodna for 13 physicochemical parameters. The level of water pollution was assessed using the Groundwater Pollution Index (GPI). This index has proven effective in communicating information about water pollution to citizens and policymakers. We also used geographical approaches such as inverse distance weighting (IDW) and conventional kriging to present the polluted areas. It was found that calcium concentrations were all above health standards, and more than 93% of the samples had SO₄²⁻ and TH concentrations above the drinking water threshold. In addition, 58% of the samples had nitrate levels above the drinking water standard of 50 mg/L. The Piper diagram classifies groundwater into sulfate-calcium-magnesium-chloride hydrochemical facies, and these waters tend to become salinized. The Gibbs diagram reveals that the groundwater is younger and that evaporation is the dominant process. According to the GPI results, 18% of the samples fell into the insignificant pollution category, and 40% into the low pollution category, while only 22% fell into the moderate pollution category, 7% into the high pollution category, and 13% into the very high pollution category. The geographical presentation of the GPI index revealed that the agricultural zone of Maadher is the one with poor water quality. The analysis showed that borehole water near Sebkha has higher mineral contents and is not potable, compared to borehole water in the northern and eastern study areas.