Application of Geosciences Techniques for the Assessment of Dumpsite Leachates and Groundwater Pollution in Regolith Aquifers

Abstract

Groundwater in regolith aquifer around Awan-Nepa dumpsite in Keffi (north-central Nigeria) was assessed for contamination attributable to heavy metal leachates. The assessment was conducted by mapping elevation of static water table, geo-electric sounding, determining concentrations of heavy metal ions in filtrate created using the dumpsite soil colloid, and in water samples obtained from twenty wells dug manually into the regolith within the dumpsite vicinity. Contamination extent was evaluated using contamination factor (CF), index of pollution load (PLI), index of metal pollution (MPI), and index of geo-accumulation (1) Groundwater convergence zones were revealed at 2.5Km SW and 4Km NW of the dumpsite. Topsoil at the dumpsite was found to be thin (0.8-1m) and characterized with moderate resistivity (140-2400m) and transverse unit resistance (120-150m). These values indicate high permeability and hydraulic conductivity within the topsoil. Low resistivity (35 45 m) characterized the regolith at the dumpsite, indicating the presence of a contaminant plume. Surface runoff from rainfall dissolved some metal components of the dumpsite waste. Part of the dissolved metals infiltrated the regolith, and built up a contaminant plume. Concentrations of arsenic, chromium, manganese, nickel and lead is higher than 0.7 mg/l in water samples obtained from the regolith wells. This concentration value exceeds World Health Organization prescribed limit for potable water. Values of CF indicate moderate level contamination from arsenic and moderate to very high contamination level from cadmium and copper at the dumpsite. Less than 0.024 PLI value reveals that the area is free from heavy metals aggregate effects. Approximately 0.6 MPI value shows the dumpsite's vicinity is free from anthropogenic pollution attributable to heavy metals, in spite of some contamination at the dumpsite. The spatial concentration maps reveal a contamination plume at the dumpsite. and a gradual attenuation in contamination level outward from the dumpsite. The maps also show that the concentration of barium, chromium, arsenic and lead within the convergence is lower than 5% of the concentration in filtrate from the dumpsite's soil colloid Water in the groundwater convergence zones is fit for drinking