Hydrochemistry of Tubarão and Crystalline Aquifers in Indaiatuba-Rafard Region, São Paulo State

Abstract

This paper presents a hydrochemical and groundwater quality characterization of the aquifers Tubarão (sedimentary, granular) and Crystalline (fissural) in the southern portion of the Basin of Piracicaba, Capivari and Jundiaí Rivers (UGRHI 05) which involves the municipalities of Indaiatuba, Salto , Monte Mor, Elias Fausto, Capivari and Rafard, São Paulo State. The Crystalline Aquifer waters are predominantly calcium and sodium bicarbonate, with pH average of 7.35, while the waters of Tubarão Aquifer are sodium bicarbonate, with pH average of 8.15, and occurrence of sodium sulfate waters. The sodium concentration and salinity of these groundwaters tend to rise usually in the direction of groundwater flow, from recharge areas to discharge areas in the main rivers. The correlation of isotopic data δD and δ¹⁸O demonstrated an influence of rainwater on the composition of both aquifers, but also indicated that certain portions of the Tubarão Aquifer are confined with the presence of older recharged waters associated with a cold weather period of time. Chemical analyzes of sampled well waters and of well reports, indicate some parameters that exceeded potability standard values: fluoride, total dissolved solids, total iron, manganese and nitrate. The occurrence of high levels of F- and TDS is associated with natural anomalies of the region; Fe(t) and Mn²⁺ may be related to the characteristics of the geological formations, although additional studies are necessary to investigate the influence of sources of contamination or well construction problems. Contamination cases by NO₃ ^- are still punctual and indicate a potential influence of sewage loads associated with the urban occupation and must be monitored.