Chemical Speciation of Sulfate in Groundwater of the Sedimentary Hydrogeological Domain of the State of Bahia – Brazil, using the Tableau Method

Abstract

Speciation consists of identifying the chemical forms of an element in aquatic environment to elucidate the origin, mobility and the impact of predominant species on water quality. This work used the Tableau method to obtain the chemical speciation of sulfate in groundwater of the sedimentary domain of the state of Bahia. Depending on the chemical species, groundwater may have a salty or bitter taste, and a laxative effect. Results from the CERB Hydrogeological Database, for wells drilled from 2003-2013, were the basis for this work. The choice was for wells with sulfate concentrations above the acceptable limit of 250 mg L-1 established by the Brazilian Ministry of Health in the Decree n°. 2914/2011. The Tableau method transforms a chemical problem into a mathematical set of equations, based on the chemical reactions and their equilibrium constants. After application of the method, higher concentrations were found for MgSO4(aq), followed by CaSO4(aq) and NaSO4-and lower concentrations for KSO4-. Although the presence of a chemical species depends on the occurrence of specific minerals in the lithology, this work did not verify the same concentration of chemical species in groundwater for the same lithology. In addition, it was not possible verify correlation between concentrations and local rainfall indices. Therefore, future research should consider other factors not studied here to determine the factors influencing the chemical speciation of sulfate in the groundwater of the State of Bahia.

Keywords

• Águas subterrâneas. Especiação química. Tableau. MINEQL +®