High Uranium Concentrations in Groundwater in Burundi

Abstract

Uranium occurs naturally in groundwater and frequently exceeds maximum admissible concentration levels. Here we present the results of a study from Burundi where dissolved uranium concentrations can exceed 700 μg/L. A conceptual model is proposed that relates these high levels to strong evapotranspiration of groundwater where uranium appears by dissolution of minerals from the granitic host rock. The proposed model is consistent with water balance considerations and corroborated by simulations using the geochemical code PHREEQC. Varying degrees of evapotranspiration, mineral dissolution and uranium concentrations of the source rock account for the large variation of the chemical composition of groundwater observed in the study area. These findings highlight the need for caution when developing water supply systems in the vicinity of groundwater discharge zones characterized by strong evapo-concentration.