Integrated geoelectrics and hydrogeochemistry investigation for potential groundwater contamination around a reclaimed dumpsite in Taraa, Ogbomoso, Southwestern Nigeria

An open dumpsite in Ogbomoso, Southwestern Nigeria was reclaimed to accommodate residential buildings due to increased population. Hence, possible groundwater contamination was investigated using electrical resistivity and hydrogeochemistry methods to ascertain the degree of potability of groundwater in the area. Twenty-two (22) depth sounding data were quantitatively interpreted along four traverses. The final layer parameters (resistivities and thicknesses) were used to construct geoelectric sections. Two-dimensional resistivity structures were generated along the traverses using dippro™ software package. Data from physicochemical properties and concentrations of anions, cations, and heavy metals of groundwater samples from nine (9) hand-dug wells around the dumpsite were determined and compared with World Health Organisation and Nigerian Industrial Standard baseline for potable water. The geoelectric strata identified were topsoil, laterite, weathered basement, partly weathered/fractured basement and fresh basement with layer resistivities and thicknesses between 11 and 493, 222 and 681, 6.0 and 369, 5.0 and 422, 558 and 53,037 Ωm; 0.3 and 3.0, 0.8 and 0.9, 7.7 and 17.5, 12 and 20 m thick, respectively. Depth to rock-head was between 2.0 and 20 m. Zones of relatively low-resistivity values (6–22 Ωm) suspected to be contaminant plumes at 0–6 m depth beneath the dumpsite were delineated. Concentrations (ppm) of anions, cations and hydrogeochemical parameters in the groundwater samples conformed to threshold for potable water, while excess ionic concentrations of Ni (av. 038), Cd (av. 0.03) and As (av. 0.02) were obtained in the groundwater samples. Further analyses showed that laterally dispersed of ions was possible at about 3–6 m depth. The concentration of elemental ions obtained in the water samples, however, portends potential groundwater contamination in the area.