Natural contamination vulnerability of the Bauru Aquifer System in the urban area of the municipality of Bauru, São Paulo

Abstract

This work assesses the natural vulnerability of the Bauru Aquifer System (BAS) to contamination in the urban area of the Municipality of Bauru (São Paulo State). The vulnerability of the BAS has been evaluated by applying the GOD and DRASTIC methods, in combination with Geographic Information System (GIS). The results obtained from the GOD method allowed the identification of three vulnerability classes: low-high, moderate-low and moderate-high. The moderate-low class has the greater coverage in the area (79.3%), followed by moderate-high (20.0%) and low-high (0.7%). In the DRASTIC method, the vulnerability was defined as low, moderate or high. Areas of moderate vulnerability constitute 67.0% of the study area, whereas areas of low and high vulnerability correspond to 30.0% and 3.0%, respectively. The maps created by both methods show that the areas of the BAS most vulnerable to contamination are those located close to the Bauru and Batalha rivers and their tributaries, coincident with the discharge areas of this aquifer system. This is confirmed when nitrate concentrations, resulting from anthropic activity, are correlated with the vulnerability maps. Generally, the highest contents of this contaminant, often exceeding the alert value (5 mg/L N-NO3-) or even the drinking water standard (10 mg/L N-NO3-), are located in moderate to high vulnerability areas. Another important factor is that districts not covered by water and sewage networks comprise the areas with moderate vulnerability. In order to protect the Bauru Aquifer System in the study area, it is important to point out the necessity of implanting a sanitary sewer system in the areas of moderate vulnerability and the special care that must be taken with the land use and occupation in places close to the discharge areas of the SAB.