Geochemistry and Natural Background Values of Waters in the Area Surrounding the Guamá Waste Treatment Landfill, Marituba (Pa), Amazon Region

The definition of natural background values is essential to distinguish natural geochemical processes from potential anthropogenic influences, thereby supporting the assessment of surface and groundwater quality. This study evaluates the hydrogeochemistry of waters surrounding the Central Waste Processing and Treatment Facility (CPTR) landfill in Marituba, Pará, Brazil, with the objective of establishing Natural Background Levels (NBL) and supporting the development of public policies in landfill-influenced areas. Sampling campaigns and statistical analyses of physicochemical parameters were conducted, including pH, temperature, electrical conductivity, redox potential, and inorganic and organic constituents. The results indicate slightly acidic pH (4.58–7.46), moderate temperatures (25.7–32.3°C), low electrical conductivity (≤ 274 µS/cm), and mildly oxidizing conditions. Elevated concentrations of iron and aluminum are attributed to water–rock interaction and intensified leaching driven by high Amazonian rainfall. Parameters such as phosphorus, color, and biochemical oxygen demand exceed drinking water standards, rendering the water unsuitable for consumption. Although localized variations in ammoniacal nitrogen were observed, systematic monitoring indicates that the CPTR landfill has not significantly altered regional water quality. These findings underscore the importance of continuous monitoring and the technical distinction between natural geochemical conditions and potential contamination sources in landfill-affected environments.