Assessment of impact of leachate on hydrogeological repositories in Uyo, Southern Nigeria

Abstract

Electrical resistivity methods integrated with physico-chemical methods of water analysis were employed to assess the impact of dumpsite leachate on groundwater repositories in Uyo, Nigeria. The uneven distribution of the bulk resistivity, which range from 82·3 to 2705 Ω m, indicates the ingress of leachate from degraded materials into aquifer units for depths ranging from 15·8 to 60·1 m. The low longitudinal conductance of <0·5 Ω−1 indicates the susceptibility and vulnerability of the hydrogeological units to the leachate emanating from the dumpsite. The seemingly high bulk conductivity values also show the presence of organic contaminants in the arenaceous materials expected to have been characterised by freshwater. The results of the vertical electrical sounding (VES) and electrical resistivity tomography showed low resistivity to the depth extent of about 15 m, except in VES points away from the dumpsite. The analysis of water samples revealed a slightly acidic groundwater, which, on the average, falls below the World Health Organization (WHO) standard. The chemical parameters compared with the WHO standard were below the WHO standard for drinking water, and this suggests an interaction between the leachate and the geofluid. The sodium adsorption ratio, the magnesium adsorption ratio and Kelly’s ratio were also calculated in order to determine the suitability of the groundwater for agriculture (irrigation).