Spatial and temporal analysis of shallow groundwater quality using GIS, Grombalia aquifer, Northern Tunisia

This study aimed to analyze the spatial and temporal variations of water quality from 2000 to 2015 in the Grombalia basin aquifer, northern Tunisia. Some physicochemical parameters of collected samples were measured and processed in a GIS environment. Quantitative assessments of their distribution patterns and spatio-temporal variability were performed. Inverse distance weighting (IDW) interpolator and map algebra procedures were the used GIS tools. During 2000, 2015 campaigns 21 groundwater samples were collected from georeferenced boreholes and analyzed for Ca2+, Na+, Mg2+, K+, SO42-, HCO3-, Cl-, EC, pH, T degrees, O-2, and Salinity. Hydrochemical indices were also estimated such as sodium adsorption ratio, total dissolved solids, and soluble-sodium percentage. Findings were examined in terms of water quality, salinization degree and deterioration rate. During the considered interval, a mixed facies of Cl-SO4-Na-Ca, which remained roughly unchanged, characterizes the aquifer. While the spatial distribution of almost all ions is the same, the obtained spatio-temporal maps (2000-2015) for each ion indicate different patterns. Significant variations of concentration were observed in the pediplain area. This region is susceptible to contain most suitable sources for irrigation purposes; it represents 23.8% of groundwater samples that are among the good and safe category. Also, there is no significant variations of water quality indices are observed in the aquifer, except for some northern samples (coastal area). Therefore, a slow hydrochemical process maintains the aquifer quality with a moderate variability while an ongoing salinization hazard locally induces the deterioration level.