A VULNERABILIDADE NATURAL DE AQUÍFEROS FRATURADOS: AVALIANDO OS MODELOS DRASTIC E GOD, ORIGINAIS E ADAPTADOS:

Anthropogenic activities have always been a major groundwater concern. The understanding of the natural vulnerability of aquifers can aid decision makers for a better land use planning. This paper compares four methods for the classification of aquifer natural vulnerability, searching for the most adequate methodology, and determines the analytical differences among them. The original DRASTIC, modified DRASTIC, original GOD and the modified GOD methods were assessed by using geoprocessing software. Both DRASTIC methods presented the same vulnerability classes (insignificant, very low, low and moderate), but their spatial distribution and the values within each class were distinct. The GOD methods have revealed substantial difference in the classification of the vulnerability. The original GOD has presented insignificant and low vulnerability, respectively 0.96% and 99.04% of the studied area. Conversely, when testing the modified GOD, the vulnerability in the same area was classified as low and median, 25.80% e 74.19% respectively. The normalized results indicated that the original GOD has an incongruent classification towards the remaining methods. Both DRASTIC methods have indicated that soil, vadose zone, recharge and topography may be the responsible parameters for the underestimated or overestimated results. Lastly, the DRASTIC methods have shown better results as they presented enhanced detail and higher class variability, being more conservative and restrictive.