Groundwater quality of shallow aquifers in the Municipality of Rio Claro (SP): influence of natural and anthropogenic processes

Abstract

This study assessed the groundwater quality at 33 sampling sites, 23 springs and 10 shallow wells, distributed across the Rio Claro, Passa Dois (Corumbataí Formation), and Guarani aquifer systems in the municipality of Rio Claro (São Paulo, Brazil). A comprehensive hydrochemical and isotopic analysis, along with geochemical modeling, was conducted to calculate the saturation indices of dissolved minerals and to identify the main natural and anthropogenic processes influencing groundwater composition. The results revealed significant hydrochemical differences among the aquifers, with Ca-HCO₃-type waters and higher mineralization prevailing in the Passa Dois System, indicating intense water–rock interaction. In contrast, the Rio Claro Aquifer mineralogy exhibited lower geochemical reactivity and a stronger anthropogenic influence, evidenced by elevated concentrations of NO₃⁻, SO₄²⁻, and Cl⁻, particularly in urban areas. Isotopic signatures indicated recent meteoric recharge, with no evidence of significant isotopic fractionation None of the samples exceeded drinking water standards established by the Brazilian Ministry of Health (Ordinance GM/MS No. 888/2021) for nitrate, fluoride, or trace metals, suggesting that, despite anthropogenic inputs, groundwater remains suitable for consumption. The study underscores the value of springs as strategic monitoring points and highlights the importance of integrated groundwater management to ensure water quality preservation in shallow aquifers.