MAPEAMENTO DOS AQUÍFEROS DO ESTADO DA BAHIA UTILIZANDO O ÍNDICE DE QUALIDADE NATURAL DAS ÁGUAS SUBTERRÂNEAS – IQNAS

This work presents maps of the State of Bahia groundwater quality, built with values of GNQI -Groundwater Natural Quality Index. The GNQI was developed similarly to the Water Quality Index - WQI (IQA-CETESB),to classify the surface water quality. The calculation of GNQI values were based on weights and graphs for theconcentration of the hydrochemical parameter versus water quality, or grade, defined by the authors of this work, with thesame criteria utilized for the IQA-CETESB, which are: 80-100, exceptional quality; 52-79, good; 37-51, acceptable; and 0-36, improper. The parameters utilized for GNQI calculations were: pH, chloride, total solids, hardness, nitrate and fluorite,obtained from chemical analysis of 1,899 wells, from CERB Data Bank, State of Bahia, Brazil, plus 05 samples of mineralwater from the Sedimentary Basin Recôncavo-Tucano, taken as water quality standard. The GNQI data were used toconstruct the maps of the following aquifer domains: Sedimentary, Metasedimentary, Karst and Crystalline. It was verifiedthat the maps with GNQI values adequately represented the groundwater quality of the studied regions, attesting theusefulness of the adopted methodology.