Groundwater quality and human health risks in the Setifian high plains, Algeria

Groundwater is crucial for socio-economic development, serving as the primary source of drinking water in some countries. In North Africa, it is the main resource for freshwater extraction. This study aims to describe the hydrochemistry of the aquifer system and to assess water quality for drinking and irrigation using the Water Quality Index (WQI) and Soil Pollution Index (SPI) in a section of the Setifian High Plain in northeastern Algeria. Additionally, the research evaluates human health risks in areas affected by nitrate contamination through an integrated approach that combines hydrochemical data from 210 groundwater samples with spatial risk modelling. The groundwater is a mixture of a type of Ca-Mg-SO₄-Cl and Ca-HCO₃, primarily dominated by calcium, chloride, and sulfate ions. The salinity of the groundwater is mainly influenced by processes such as the dissolution of carbonate and evaporite formations, as well as the intrusion of saline water from the sabkha (salt lakes). Water quality assessment using the Water Quality Index (WQI) showed the following classifications: 10.47% of samples were excellent, 54.76% were good, 29.52% were poor, 3.80% were very poor, and 1.42% were unsuitable for drinking. The majority of nitrate concentrations are classified as high (above 50 mg/L), suggesting potential groundwater pollution resulting from human activities. In contrast, the Synthetic Pollution Index (SPI) revealed that 58.57% of the samples were unfit for use, with 36.19% classified as highly polluted, 4.28% as moderately polluted, and 0.95% as slightly contaminated. Most groundwater samples are appropriate for irrigation because they are classified as 'good' or 'suitable' based on water assessment indicators such as Sodium Absorption Ratio, Soluble Sodium Percentage, Residual Sodium Carbonate, Permeability Index, Magnesium Hazard, and Kelly Ratio. Non-carcinogenic risk values (Hazard Index, HI) ranged from 0 to 1.47 for adult males and 0 to 2.08 for adult females, with even higher levels for children (up to 2.69). These findings highlight that nitrate-contaminated water poses significant health risks, especially for pediatric populations, highlighting the urgent need for treatment and monitoring measures.