Hydrogeochemistry zoning of the são paulo state aquifer systems as a groundwater management tool

Abstract

In São Paulo State, five aquifer systems (Bauru, Serra Geral, Guarani, Tubarão and Pré-Cambriano) are responsible for population supply. Despite the large knowledge about these aquifers, just a few studies have been done regarding the evaluation of the hydrochemical evolution of these waters as a tool for the responsible management of this resource. A geochemical zoning of the main aquifer systems of São Paulo State is proposed based on Chebotarev’s classical hydrochemical evolution by inferring residence times for groundwater, which can be associated with the aquifers renovation taxes and its sustainability facing growing exploitation. For this study, results from the groundwater quality monitoring program of São Paulo State, produced in 2015 by CETESB, were re-analyzed. Three categories for the São Paulo State groundwater were proposed, which correspond with the definition of hydrochemical parameters and the residence times. The Zone I represents unconfined aquifers, with low residence time, in CO2 open system, with groundwater average age between 1.000-5.000 year. The Zone II represents semi-enclosed aquifers, with medium residence time, in transition between an open-closed system, with groundwater ages between 5.000-70.000 years. The Zone III represents confined aquifers, with high residence time, in closed system, with groundwater ages between 15.000-834.000 years. Groundwater that shows low residence times is recommended to exploitation once the renovation is faster when compared to the waters from the other two zones. On the other side, these waters are more exposed to contamination. On the other hand, groundwater classified with high residence times can show higher quality and less risk of contamination. However, their renovation is relatively slow, and the overexploitation may result in scarcity or depletion of groundwater.