Análise geoquímica das águas subterrâneas no município de Boquira, no semiárido baiano-Brasil

Abstract

The geochemical analysis was carried out in the center-south portion of the state of Bahia, in the semi-arid region of Bahia, where outcrop the Paramirim Complex, Boquira Unit, Boquira Granite, Veredinha Granite, Serra do Espinhaço, detritus coverings and alluvial deposits. The Boquira Unit is known for lead-zinc mineralization. In this unit operated the Boquira mine, considered the largest lead and zinc mine in Brazil, until it was suddenly abandoned, leaving significant environmental liabilities of toxic metals such as lead, zinc, silver, barium, copper, chromium and nickel. To characterize the groundwater 16 physical-chemical parameters from 24 wells were used, obtained from the Water and Sanitation Engineering Company of Bahia - CERB. Its classification was made in the Piper Diagram and the ionic relations in meq/L. To evaluate the quality of the water we used the Consolidation Ordinance no 5/2017 of the Ministry of Health and World Health Organization. With the PHREEQC 3.5 hydrochemical model, the saturation index of the analyzed elements was calculated. The results showed predominance of calcium chloride waters (71% of the samples), with ionic relations of type rCa2+> rMg2+>rNa+ and rCl->rHCO3->rSO42+. Geochemical modeling indicated calcite (CaCO3), dolomite (CaMg(CO3)2) and quartz (SiO2) as the main minerals with a tendency to precipitation. The first two were associated with the dissolution of the Boquira Unit ca rbonates and the third one with the quartzites of the Serra do Espinhaço Formation. The concentrations of calcium and chloride showed 54% and 25% of the samples above the Maximum Allowable Value for human consumption, respectively, representing a risk factor to the health of the population in the area. Keywords: Hydrochemistry, Saturation Index, Water-Rock Interaction.