EVALUATION OF NATURAL VULNERABILITY TO CONTAMINANTS APPLYING DRASTIC INDICES

The characterization of environmental susceptibility to pollution is fundamental for decision making on land use and occupation. The vulnerability indices constitute useful tools to help protecting the quality of the groundwater, given the technical and economic limitations to remediate the existing contamination. The DRASTIC index was used here to evaluate the natural vulnerability of aquifer constituted by the weathered basaltic rocks of the Serra Geral Formation. The DRASTIC method was chosen in this evaluation for its simplicity, low cost, easy application and because it has been widely used for analysis of the natural vulnerability. The weathered layers of basalt consist of silt-clay, providing aquifer protection. However, a large number of wells crosses extremely fractured weathered basalts (saprolite), favoring groundwater flow. Hydraulic conductivity obtained from slug tests range from 213,4 to 25,6 m/d, averaging 110,4 m/d. In general, the vulnerability of the studied area can be classified as moderate, while that in the water divide region and in the vicinity of ribeirão Lindóia are ranked low and high, respectively.