Integrated Geophysical and Hydro-chemical Investigations of Impact of the Ijemikin Waste Dump Site in Akure, Southwestern Nigeria, on Groundwater Quality

Abstract

Background: Improper waste disposal can negatively impact the ecosystem and constitutes a major human health risk.

Objectives: The present study evaluated the environmental impact on groundwater quality of an open-air waste dump in Akure, southwestern Nigeria, using an integrated geophysical survey and hydro-chemical analysis of water samples.

Methods: The geophysical survey involved three dipole-dipole 2-D imaging profiles and seven vertical electrical soundings (VES) along three traverses. The dipole-dipole data were inverted using the Dipro for Windows software, while the VES data were quantitatively interpreted using partial curve matching and computer assisted 1-D forward modeling with the WINResist software. The VES interpretation results were used to generate geoelectric sections. For the hydro-chemical analysis, samples were taken from five hand-dug wells at various distances from the dumpsite. The samples were analyzed for temperature, pH, conductivity, total dissolved solids (TDS), and some major elements (calcium ion (Ca2+), magnesium ion (Mg2+), chloride ion (Cl-), nitrate (NO3-), sulfate (SO42-)) whose concentration values were compared with World Health Organization (WHO) and Nigerian Industrial Standard (NIS) standards for assessment of groundwater quality.

Results: The VES curves revealed three distinct geoelectric/geologic layers with thicknesses and resistivities in the range of 0.7 - 2.0 m and 31 - 55 Ωm for topsoil, 6.2 - 14.6 m and 13 - 114 Ωm for the weathered layer, and a fresh basement with resistivity values ranging from 344 -∞ Ωm.

In the hydro-chemical analysis, pH values ranged between 7.57 - 7.8, electrical conductivity ranged from 884 - 1510 μS/cm, and TDS ranged between 588 - 1008 mg/l. Concentration values of Ca2+ and Mg2+ ranged between 78 - 132 mg/l and 1.8 - 19 mg/l, respectively.

Conclusions: The results from the combined electrical resistivity methods showed relatively low resistivity values at the topsoil and weathered layers and the hydro-chemical assessment of water samples indicated that the topsoil and groundwater within the dumpsite may have been polluted by leachate.

Keywords: waste dump, leachate, geophysical investigation, hydro-chemical analysis, water quality