A geochemical assessment and modeling of industrial groundwater contamination by orthophosphate and fluoride in the Gabes-North aquifer, Tunisia

In Tunisia, chemical industries are thought to be the cause of various environmental problems and more particularly the cause of groundwater quality deterioration and contamination. Within this scope, this study assesses the shallow-water quality of the Gabes-North aquifer with regard to the phosphate industry and also to model current and possible future contamination. This allows also the identification of factors that govern the spatial–temporal variation of the main sources of pollution. For that, 60 shallow groundwater samples were collected during the years 2013 and 2014 within and around the industrial chemical phosphate complex of Ghannouche–Gabes. Hydrogeochemical investigation permitted the detection of high concentrations of fluoride and orthophosphates in the sampled waters reaching 12 mg/l and 47 mg/l, respectively. The H₂PO₄⁻ and F⁻ ion transport model using the Visual MODFLOW software was calibrated and validated by the 2013 and 2014 observed data and was simulated for 6205 days up to the year 2030. The model showed that from 365 to 6205 days, the ions H₂PO₄⁻ and F⁻ migrated from 100 to 250 m and from 80 to 200 m, respectively, depending on groundwater flow direction. Predictive simulations indicate that the transport rate of these ions can go up to 2.5 times in 2030 compared to those detected in 2014. This integrated investigation in this current study proves that regular pollution constitutes a threat at a given local scale, but can also be used as a reference for reasonable water resources management on a larger scale.