Análise estatística R-modal e modelo geoquímico inverso no estudo da qualidade da água subterrânea na região metropolitana de Fortaleza-CE

Abstract

Hydrochemical analyses were made for 250 groundwater samples from Dunes, Palaeodunes, the Barreiras Formation and the Migmatitic Complex, in strategic areas of the Metropolitan Region of Fortaleza, for quality assessment and processes of salinization. With respect to limits of potability, chloride was acceptable in 73% of the wells, nitrate in 86% and TDS was below limit in 82%. Piper and Expanded Durov diagrams were used for classification according predomination of ions and also as indicators for their origin. For obtaining more significant informations on the origin, Factor Analysis was applied. It showed that in the major part of the areas the dominant factor (Factor 1) represents sodium chloride from marine aerosol. Reverse Geochemical Modeling with PHREEQC identified internal processes in each of the aquifer systems, showing that ion concentrations in waters vary locally, depending on the lithology. Dissolution and/or precipitation of the minerals calcium carbonate, magnesium carbonate, sylvite, gibbsite, calcium sulfate and contribution from marine aerosol are the predominant geohydrochemical processes. Also cation exchange of the types CaX2, MgX2, NaX e KX was identified in the waters from different storages. In the Migmatitic Complex ion concentrations are influenced by the presence of aluminum silicates through dissolution or precipitation of biotite, Na-montmorillonite, kaolinite and Camontmorillonite.