Geophysical and hydrochemical assessment of the risk posed by open dumpsite at Kaduna Central Market, Nigeria

Abstract

Open dumping is becoming a fast-spreading bad phenomenon across the globe. The groundwater systems and ambient soil remain the major hotspots of the dumpsite leachate plumes activities. An electrical resistivity survey and hydrochemical investigations were undertaken within and off-dumpsite to assess the environmental impacts of the dumpsite leachates. Schlumberger method was used to acquire twenty-nine (29) vertical electrical sounding (VES) points across two orthogonal traverses established within and off-dumpsite to investigate the level of impacts of the dumpsite leachate plumes on the soil and groundwater resources. While the protective overburden soil layers resistivity values vary between 2.4 and 217 Ωm within the dumpsite, the off-site varies between 117 and 1313 Ωm. The study indicates that the overburdened soil layers overlying the weathered/fractured unit, which constitute the aquifer systems of the region, were suspected to have been compromised by dumpsite leachate plumes as indicated by the low resistivity values characterizing the subsoil layers. The hydrochemical analysis of water samples from the investigated six hand-dug wells (HDWs) shows the presence of heavy metals (HMs). The results of the laboratory analysis of the water sample indicate a high content of electrical conductivity (0.699–1.221 mg/l), iron (0.782–1.9181 mg/l), lead (0.871–1.992 mg/l), chromium (0.333–0.512 mg/l), and cadmium (0.0211–0.0419 mg/l), while the high contents of chemical oxygen demand (COD) (459–561 mg/l), biological oxygen demand (BOD) (902–1017 mg/l), and total dissolved solids (TDS) (597–1301 mg/l). The high content of BOD and COD in the dumpsite leachate plumes shows high organic potency. However, it was noted that the concentration decreased as the pollutant source distance increased, while the shallow depth seems to have been more impacted. Geophysical and hydrochemical data show that the degree of the impacts of the dumpsite leachate plumes seeping the ground down the water table is a function of depth, source distance and subsurface properties. Both techniques confirmed the infiltration of leachate plumes into the soil and groundwater systems posing a great risk to public health. Therefore, to obtain clean and portable drinking water, it is suggested that HDWs/boreholes should be sited at least 100 m away from the dumpsite to at least a depth of 15 m.