Análise dos dados de monitoramento de qualidade da água e de sedimentos de reservatórios situados a jusante do rompimento da barragem de rejeitos de minério de ferro situada na Bacia Hidrográfica do Rio Paraopeba

Abstract

Mining activities are extremely important for the State of Minas Gerais, however, they can cause several damages to the environment. On January 25, 2019, the B1 iron ore tailings containment dam at the Córrego do Feijão Mine, in Brumadinho/MG, burst, releasing 12 Mm³ of tailings into the environment, a portion of this tailings was dissipated by the Paraopeba River. Data from the Special Program for Monitoring the Quality of Water and Sediments of the Três Marias and surroundings (PMQS-TM), carried out by Vale SA, in the hydrographic basins of the Paraopeba River (SF3) and the surroundings of the Três Marias Reservoir (SF4). Several statistical tools were used, such as: a) non-parametric U of Mann-Whitney (MW) and Kruskal-Wallis (KW) tests, to verify if there is a significant difference between the median values of the parameters analyzed in the dry and rainy seasons; b) analysis of compliance with current legislation standards or existing reference values; c) Cluster Analysis (CA) and Factor Analysis (FA) to verify the variations in water quality at the various monitoring points and which parameters were responsible for the impacts. The database was pre-processed, and criteria were adopted for the selection of monitoring points, parameters and data period to be considered. The analyzes were carried out considering: the different compartments (water and sediments); lentic and lotic ecosystems; dry and rainy periods; besides this the depth of the water column was also considered, in the case of lentic ecosystems. As a result, it was found that: i) through the MW test, the predominance of significant differences in the data referring to the evaluation of water quality in the rainy season was verified; ii) high percentages of non-compliance of water quality parameters were observed to the limits in force in the legislation and of the sediment quality parameters to the reference values existing in the literature; iii) through the CA, the grouping of points by similarity in the different ecosystems was observed; iv) through FA it was possible to verify which parameters explain the greater variability of data in water and sediments; v) through the non-parametric tests mentioned above, the parameters that presented significant differences between the different compartments were identified, based on the groups previously formed; vi) the comparison of pre- and post-disruption data indicated significant differences, both in the dry and in the rainy season, in the station located upstream of the Retiro Baixo HPP reservoir; vii) the spatial analysis of the stations immediately upstream and downstream of the HPP Retiro Baixo indicated that the total iron showed a difference in both periods under study, as the total manganese only in the rainy season.