Avaliação do índice de vulnerabilidade do Sistema Aqüífero Guarani no perímetro urbano da cidade de Sant’Ana do Livramento-RS

Abstract

Groundwater is a natural resource of great importance for humanity, which abundance varies according to the local geology. In spite of its importance, it is also vulnerable to the contamination provoked by man himself. This study has as main objective to evaluate the vulnerability index of the Guarani Aquifer system in the urban perimeter of the city of Sant'Ana do Livramento, South Brazil. It was used data from 145 wells and three springs of that city classified in its majority by CPRM/1995, based on the GOD methodology developed by Foster and Hirata (1993) and Foster et al. (2003). From the 145 wells and three springs were obtained 15 samples that were later submitted to complete chemical analysis: 10 of the samples were obtained from a study performed by CPRM/1995, four from a study by the Laboratory of Industrial and Environmental Chemistry at UFSM (LAQIA) for the Guarani Aquifer Project, and one from hydrogeological field work, geological mapping of an area around 49km², measurements of static levels, water samples collecting and data bank of the head points of contamination. The results obtained will work as subsidies for an integrated management of the underground hydric resources for public and private managers. As final products were elaborated three maps of the studied area: a geological one, a slope classes and a map of the vulnerability index, in which variability degree was classified as vulnerability classes obtained described in the mentioned methodology. The map of the area was digitalized from topographical letters in the Spring 4.1 software, and later put upon by the cartogram of vulnerability obtained with Surfer 8 software, through the use of kriging interpolator to spatialize the static levels, the wells' depth, the flows, the electric conductivity and the vulnerability index, as well as the potentiometric surface. After this process, the cartograms were then re-edited in Corel Draw 11 software. As results were obtained the classification of the area in classes according to its vulnerability levels, whose most part of the area was inserted in the high and extreme classes. Those results are worrying due to the occupation of the referred areas by enterprises that are potentially pollutants, such as three cemeteries and 22 gas stations.