An integrative approach to characterize hydrological processes and water quality in a semi-arid watershed in Northeastern Brazil

Abstract:

Arid and semi-arid regions face serious challenges in the management of scarce water resources. This situation tends to become worse with the increasing population growth rates and consequently increasing water demand. Groundwater is the most important water resource in these areas and, therefore, the sustainability of its use depends on the effectiveness in which it is managed, both in terms of quantity and quality. The Caetité Experimental Basin (CEB), located in a semi-arid region of Northeastern Brazil, faces not only the challenges associated with water scarcity, but also changes in landscape and potential contamination processes due to mining activity. The only active uranium production center in Brazil (URA) is located in this watershed and the sustainability of mining and milling operations as well as the survival of the local community are highly dependent on the availability of groundwater resources. Hydrogeological studies in this area are scarce, and the potential contamination and overexploitation of groundwater can not be ruled out. Therefore, a national project was launched in order to improve the understanding and quantification of the interaction between the hydrogeological system and human health. The methodological approach involved hydrological and geochemical monitoring and characterization of the CEB, use of isotopic techniques, groundwater modeling, water quality diagnosis and human health risk assessment due to water ingestion. The results suggested that the groundwater in the CEB are not totally connected, with evidence of a mixture of recent and old waters. The Na-Ca-HCO₃-Cl is the dominant water type (50%) followed by Ca-Na-HCO₃-Cl water type (17%). The relevant non-radioactive contaminants are Mn, F, NO₃ and Ba, mostly from natural origin, with the exception of NO₃ that could be associated with the livestock activities. The estimated effective doses due to groundwater ingestion containing radionuclides are below the recommended reference level (1 mSv/year) for drinking water in existing exposure situation and do not represent significant radiological impact.