Hydrogeochemical modeling and groundwater quality in coastal aquifers in Northeastern Brazil

Geochemical modeling is a central approach in hydrogeochemical assessments, enabling the identification of water-rock equilibrium conditions through mineral saturation indices and thereby increasing understanding of processes that control the chemical characteristics of groundwater. This study identified the main mechanisms governing hydrogeochemical behavior and evaluated the equilibrium conditions of the mineral species that comprise the hydrogeological framework of the northeastern coast of Brazil, using geochemical modeling to infer the processes controlling compositional and qualitative aspects from groundwater potable standards. The results indicate a predominance of sodium-chloride waters with concentrations of total dissolved solids, chloride, total hardness, sulfate, sodium, total iron, nitrate, turbidity, barium, and lead outside potable standards. Weathering induced by the interaction between groundwater and minerals of the infiltrated aquifers emerges as the principal hydrogeochemical control factor in the area. Geochemical modeling shows supersaturation for quartz, goethite, and hematite, and subsaturation for kaolinite, muscovite, illite, and calcite in the analyzed samples, explaining the high concentrations of elements from minerals prone to dissolution and the consequent addition of ions to solution, as well as the low concentrations of elements from minerals prone to precipitation, which are removed from solution. It is concluded that silicate weathering and carbonate dissolution are the main processes controlling the compositional state of groundwater in the region, with contributions from anthropogenic activities and marine influence. Keywords: contamination, Gibbs diagram, phreeqc, Potiguar Basin.