Fluoride in the Serra Geral Aquifer System: Source Evaluation Using Stable Isotopes and Principal Component Analysis

Abstract

Groundwater with anomalous fluoride content and water mixture patterns were studied in the fractured Serra Geral Aquifer System, a basaltic to rhyolitic geological unit, using a principal component analysis interpretation of groundwater chemical data from 309 deep wells distributed in the Rio Grande do Sul State, Southern Brazil. A four-component model that explains 81% of the total variance in the Principal Component Analysis is suggested. Six hydrochemical groups were identified. δ18O and δ2H were analyzed in 28 Serra Geral Aquifer System samples in order to identify stable isotopes patterns and make comparisons with data from the Guarani Aquifer System and meteoric waters. The results demonstrated a complex water mixture between the Serra Geral Aquifer System and the Guarani Aquifer System, with meteoric recharge and ascending water infiltration through an intensive tectonic fracturing.