Comparison between the water quality indexes Cetesb and Bascarán applied to the hydrographic basin of the São Domingos River, Northwest of Rio de Janeiro

Abstract

Water is an essential good for life and for many economic activities. However, its degradation occurs in rapidly, making it unsuitable for multiple uses of society. The São Domingos river watershed (SDRW), in the municipalities of São José de Ubá and Itaperuna, has high rates of deforestation, extensive agriculture, urban centers with low levels of basic sanitation and intense groundwater extraction for household use and irrigation. The present article aims to analyze the quality of the groundwater of this basin using two Water Quality Indexes (WQI): WQICETESB and WQIBASCARÁN. For this purpose, groundwater samples were obtained in 19 sites in the basin in 2004 and 2005. The parameters evaluated and used to compose the indices were: dissolved oxygen, thermo-tolerant coliforms, pH, biochemical oxygen demand, temperature, visual appearance of water, total nitrogen, total phosphorus, turbidity and total residue. The WQI were interpolated to the SDRW area. The WQICETESB index presented more positive and homogeneous results, with most samples classified as “good”, whereas, bythe WQIBASCARÁN index, the water quality of the SDRW presented worse quality, the samples were predominantly classified as “median” and “bad”, with a few “very bad” samples. When the k constant present in the WQIBASCARÁN was not applied, the results of this index were similar to that of WQICETESB. When the constant was used, the classification were more distinct among the indexes. The general results show that from 2004 to 2005 the water quality deteriorated. As there is direct consumption of groundwater by the SDRW population, and water consumption is highly related to the health of consumers, WQIBASCARÁN is recommended for the monitoring of groundwater quality in this watershed, because it describes more strictly the quality of water, thus ensuring greater health security for the population.