Quality and evolution of groundwater in the west-central region of RS: an applied hydrogeochemical approach

Abstract

Hydrochemistry is essential for assessing groundwater quality, identifying geochemical processes, and supporting the sustainable management of water resources. This study conducted the hydrochemical characterization of tubular wells in the municipalities of São Vicente do Sul, Cacequi, Rosário do Sul, and Vila Nova do Sul, aiming to evaluate groundwater quality, salinity risk, hydrogeochemical processes, and potential for mineral water exploitation. The evaluated parameters included pH, hardness, total dissolved solids, electrical conductivity, and concentrations of major, minor, and trace ions. Hydrochemical classification was performed using Piper, Stiff, and U.S. Department of Agriculture diagrams, while water quality assessment followed the standards established by Ordinance GM/MS No. 888/2021. The potential for mineral water was assessed based on the Brazilian Mineral Water Code. The results indicated a predominance of calcium-bicarbonate and mixed waters, typical of recharge areas and recent flow systems, as well as sodium-rich waters associated with confined zones and hydrochemical evolution. Concentrations exceeding the permissible limits were identified for fluoride, nitrate, aluminum, iron, and manganese, the latter mainly from natural processes, while nitrate suggests anthropogenic contamination. Spatial analysis indicated greater confinement and salinization in the Sanga do Cabral/Pirambóia Aquifer System, especially in São Vicente. There is potential for natural fluoridated mineral water and alkaline-earth waters rich in calcium and magnesium. Most waters were classified as fresh and suitable for human consumption, livestock watering, and irrigation. This study reinforces the importance of continuous monitoring for the safe and sustainable management of groundwater resources.