Origin and Temporal Evolution of Groundwater Salinity in an Aquifer Complex: Case Study of Mila’s Province in North-Eastern Algeria

In Mila’s province (Algeria), the existing aquifer complex consists of a karstified limestone overlain by detrital formations. It provides more than 1.1 m3 s for drinking water allocation. A groundwater quality monitoring programme targeted main boreholes and covered the time span between 1993 and 2011. More than 100 groundwater samples were considered for field parameters and major elements analyses. The waters were found of the SO4‒Cl‒Ca type for the detrital aquifers, whereas they were of the HCO3‒Ca type for the karst system. During the monitoring period, an increase in Total Dissolved Solids (TDS) was quite noticeable. It concerned the groundwater from all the exploited aquifers. The increase in TDS reached 338 mg L−1 for the detrital aquifers and 138 mg L−1 for the karst waters. Moreover, abnormally high groundwater temperatures, exceeding the one inferred from the local geothermal gradient, were also recorded during some monitoring periods. The present work aimed at determining the origin and the evolution of groundwater salinization during the two decades (1993‒2011) of exploitation. Based on the use of geochemical tracers, it was brought to light complex hydro-geochemical processes. The latter are thought to be the main phenomena that are responsible for groundwater salinization in Mila’s region namely: the dissolution of evaporitic minerals, a congruous dissolution of carbonate minerals, an anthropogenic pollution, and a thermal water upwelling during some periods. The notable degradation of groundwater’s quality is not only attributed to climate change but more particularly to man-induced environmental changes. Groundwater recharge through normal rainfall percolation is no longer sufficient to maintain acceptable groundwater quality. Artificial recharge of the considered aquifers with surface water from the neighboring Beni Haroun dam would be a plausible remediation option. The results of the hydro-chemical monitoring could be preventive for the sustainability of the groundwater resource of the studied aquifer complex.