Resistivity measurements and water quality analysis for the assessment of the impact of Ile-Oluji waste dumpsite in Ondo State, Southwestern Nigeria, on the environment

Abstract

In this study, soil resistivity measurements and water quality analysis were carried out as a means of assessing the impact of Ile-Oluji dumpsite on the environment. Resistivity measurements were made on radially established traverses adopting 2D dipole-dipole profiling and Schlumberger depth sounding techniques. Physicochemical and microbial analyses for parameters including color, turbidity, temperature, pH, total dissolved solids (TDS), conductivity, hardness, major ions, total coliform, and E.coli were performed on surface and groundwater samples. The underlying geologic layers were topsoil, laterite, weathered layer, partly weathered/fractured basement, and fresh bedrock. Indication of subsoil contamination and by extension the groundwater was observed from contrasting geoelectric characteristics of the area within and outside the waste dump. Relatively low resistivities (< 78 Ωm) defined the leachate contaminated zone to depth extent of > 25 m and a distance > 50 m beyond the waste boundary, including a nearby stream. Leachate migration was aided by the surface topographic dip and groundwater flow in the north and northeastern directions and through basement fractures/faults. The concentrations of major pollution indicators like conductivity, TDS, hardness, chloride, magnesium, calcium, potassium, E.coli exceeded standard thresholds for potable water quality and were at least 10 times more within the contaminated zone than in samples at control locations. All the water samples were fecal contaminated having E.coli of 6–95 CFU/100 ml counts. The results showed that the environment around the dumpsite had been significantly polluted and the level of pollution raised an intermediate to high public health safety risk that requires high action priority.