Hydrogeochemical and pollution characterization of a shallow glauconitic sandstone aquifer in a peri-urban setting of Bobo-Dioulasso, southwestern Burkina Faso

Abstract

Groundwater resources are often exposed to multiple sources of pollution, which may make them unfit for human consumption. As a result, comprehensive geochemical studies on groundwater status and evolution are required for a sustainable management of water resources. In the present study, 38 water samples from hand-dug wells were collected in a peri-urban area, and their physico-chemical parameters, viz. pH, electrical conductivity (EC), turbidity, dissolved oxygen (DO), total dissolved solids (TDS), major ions (Ca2+, Mg2+, K+, Na+, NO3−, Cl−, HCO3− and SO42−) and heavy metals (Cd, Cu, total Fe, Ni and Zn) were measured. Because of the short residence time of the groundwater and already advanced weathering stage of the aquifer materials, major ion concentrations, EC and TDS were low and within the World Health Organization (WHO) recommended guideline values for drinking water. However, turbidity, Cd, Ni and, to a lesser degree, total Fe had concentrations greater than the WHO acceptable limits. Piper and Durov diagrams showed that the aquifer is vulnerable to anthropogenic activities, as the groundwater is dominated by a mixed Ca–Mg–Cl–SO4-type water. Bivariate diagrams, correlation and factor analyses indicated that glauconite weathering during water–rock interactions within the aquifer contributed to Ca2+, Mg2+ and SO42− loadings into the groundwater. In contrast, K+ and Na+ can be derived from both chemical weathering and anthropogenic sources such as agricultural activities and landfill leachate. Anthropogenic environmental pollution was mainly associated with turbidity, NO3−, Cd, Ni and Zn. Under the current pH and potential redox conditions, Cu was naturally removed from the water column through adsorption onto Fe-oxydroxides; whereas, Cd, Ni and Zn were remained in their free ionic states. This study showed that hydrogeochemical characterization can be a robust tool in assessing groundwater evolution and its pollution status under the influence of multiple anthropogenic sources.