Evaluating the quality of groundwater from aquifers in São Paulo State, Brazil: scenarios revealed by hydrochemical, stable isotopes, and radionuclides data.

Abstract

Historically, in the past years, the Pardo River watershed in the Brazilian State of São Paulo has provided enough water resources for people living there. However, with an increasing population, growing urbanization, industrialization, and higher living standards, groundwater became extensively exploited from bores that reached various aquifer systems occurring in that hydrographic basin. Hydrogeochemical surveys involve the acquisition of mandatory parameters to evaluate the water quality and to understand some processes taking place in the aquifers. Despite such importance, they are incipient at the Pardo River watershed, in which a previous investigation pointed out the diffuse pollution of lead and motivated the development of this study. Eleven deep tubular wells drilled there have been selected from the Information System of Groundwater (SIAGAS) sustained by the Brazilian Geological Survey (CPRM), which exploits groundwater from different aquifer systems of the Paraná Sedimentary Basin (PSB). A large hydrogeochemical dataset was obtained for the groundwater sampled, involving measurements of temperature, DO-dissolved oxygen, pH, Eh-redox potential, EC-electrical conductivity, SiO₂, Na⁺, K⁺, Ca²⁺, Mg²⁺, alkalinity, Cl^-, NO₃^-, SO₄^2-, F^-, PO₄^3-, Br^-, NO₂^-, N-NH₃, Fe, Sr, Ni, Cu, Zn, Mn, Cr, Ba, Pb, stable isotopes in water (H-2 and O-18), stable isotopes in dissolved inorganic carbon (C-13 and O-18), radioactive cosmogenic C-14, radioactive potassium (K-40), and radionuclides occurring in the decay series of uranium (U-238, U-234, Ra-226, Rn-222, Pb-210, and Po-210) and thorium (Ra-228 and Ra-224). Several analytical methods were utilized for data acquisition, for instance, potentiometry, colorimetry, Total Reflection X-Ray Fluorescence Spectroscopy (TXRF), Mass Spectrometry, Accelerator Mass Spectrometry (AMS), gamma-ray spectrometry, and alpha-spectrometry. The results obtained have been interpreted taking into account the lithologies of the aquifers and highlighting parameters relevant to assure the water quality for human consumption as those waters are chiefly utilized for such purposes.