Evaluation of the Vulnerability to Contamination of Groundwater in the Central Amazon, Santarém Region

ABSTRACT In a context of rapid deforestation and agricultural expansion, the GOD (Groundwater type, Overall lithology of aquifer, and Depth of groundwater) approach can be used to identify areas most susceptible to diffuse contamination of the aquifer. We applied this approach to evaluate the intrinsic vulnerability to pollution of the Alter do Chão Aquifer System, located in the Santarém region (Pará State, Brazil). The parameters G (hydraulic confinement), O (lithology of overlying layers) and D (water table depth) were estimated using data from 41 boreholes from SIAGAS (Sistema de Informações de Águas Subterrâneas) and spatialized with interpolation via kriging. Results reveal predominantly low to moderate vulnerability (79% of the study area), with critical zones near the Tapajós and Amazon rivers (high to extreme vulnerability, 2.2%). The presence of Belterra clay significantly reduces risks in the central plateau. Methodological limitations, associated to data availability, highlight the need for enhanced monitoring networks. This mapping provides a decision-support tool for integrated groundwater management in the Amazon.