Heavy metal assessment on groundwater quality around abandoned borrow pit environment: evidence from hydrogeology and geochemistry

Abstract

Selected heavy metal, Chromium (Cr), Lead (Pb), Nickel (Ni), and Iron (Fe) based on their health index has been determined in Asoro, Otofure, and Ikhueniro satellite towns in Benin Metropolitan City (BMC), Nigeria. The areas are heavily populated and depend on groundwater for drinking purposes. Literature review showed that groundwater quality in the study areas is adversely affected due to rapid urban and economic growth. The study combines hydrogeological and geochemical techniques in evaluating the subsurface geology, the interrelationship between abandoned borrow pit, contaminants transportation, and the concentration of Cr, Pb, Ni, and Fe in groundwater in and around the study vicinity. The results obtained showed that the excavated average depth of the borrow pits in the area is 27 m deep, whereas the depths to the aquifer were 53.22 m, 77 m, and 50 m at Ikhueniro, Otofure, and Asoro, respectively. The mean value of Cr in the groundwater samples was, 2.23, 0.04, and 0.03 mg/L with a corresponding Coefficient of Variation (CV) of 150%, 22.24% and166.67% in Asoro, Ikhueniro, and Otofure, respectively. It was observed that groundwater around Asoro and Ikhueniro were impacted with Cr when the result was compared to the WHO and SON permissible limit of 0.05 mg/L except in Otofure where the mean value of 0.03 mg/L was below the tolerable limit for potable water. Based on the results obtained in the study, the groundwater in the study areas cannot be consumed unless routine treatment is administered considering the health impact of the selected metals.