Geochemical and isotopic characterization of groundwater in the alluvial aquifer of Guelma (north-eastern Algeria)

This study aims at determining the factors and the processes controlling groundwater quality, origin, and chemistry in the alluvial aquifer of Guelma northeastern of Algeria. Hydrochemical and isotopic investigations were carried out on 21 points, including boreholes, wells, springs, and surface waters in June 2016. A thorough hydrogeological investigation has revealed that groundwater is Ca-Mg/SO4-Cl facies. The combined use of geochemical tools and multivariate statistical analysis indicates that groundwater composition is largely governed by water-rock interactions, particularly the dissolution of evaporitic minerals as well as ion exchange processes. This study reports for the first time the isotopic contents (delta O-18, delta H-2) of the alluvial aquifer and the surface water. The stable isotope composition for the ground- and surfacewater samples has shown a homogeneous isotopic signature and reveals non-evaporated waters in the northern and central parts of the aquifer. This is the indication of the presence of a significant recharge by modern rainfall. Evaporated waters that are characterized by relatively enriched delta O-18 and delta H-2 contents are located in the western part of the plain. This suggests the occurrence of partial evaporation at the surface prior to, during, or after infiltration through the unsaturated zone.