Vulnerabilidade natural e risco à contaminação do Sistema Aquífero Parecis no estado de Mato Grosso

Abstract

The mapping of areas susceptible to contamination has been applied worldwide and in Brazil is no different. To this end, methods of vulnerability of aquifers are widely used, serving as a tool for the management of groundwater resources. This research aims to evaluate the natural vulnerability by the MAIA method (method of intrinsic evaluation of aquifers) and the risk to the contamination of the Parecis Aquifer System (SAP) in the State of Mato Grosso. This method uses the following parameters: groundwater depth, specific capacity of wells, transmissivity of the aquifer, soil thickness, terrain slope and average annual rainfall. The data from 2,570 wells used in the survey were obtained mainly from public agencies. It was structured a database in “Access” to facilitate its manipulation and the other results of the research were obtained through the application of techniques of geoprocessing and remote sensing. The indexes of vulnerability calculated by the MAIA equation resulted in 96% of the wells classified as medium vulnerability, 3% low and 1% high and extreme vulnerabilities. The factors that most influenced the results of high and extreme vulnerability were the low water depth, the specific high capacity of the wells and the high value of annual average rainfall combined with the low slope of the terrain, favoring the infiltration of water into the soil and so may carry with it contaminants. In the analysis about the use and occupation of the 290,022 km2 land occupied by the SAP, 67.4% of the surface is covered by forests and reforestation, 20.4% are agricultural areas, 9.5% are extensive cattle ranching, 2, 6% are from water slides and 0.1% from urbanized areas. Studies of the current use and occupation of soils crossed with potentially contaminating sources and excluding indigenous lands indicated that 24% of the area has a high risk of groundwater contamination, 14% medium risk, 53% low risk and 9% very low risk. The knowledge of the most sensitive areas allows the establishment of specific control and monitoring programs to maintain groundwater quality of this granular aquifer system, which covers almost the entire Parecis sedimentary basin, considered as one of the main underground water resources in Brazil and becoming a strategic and vital reserve for the public supply in the State of Mato Grosso.