ABSTRACT:

Four Wenner apparent pscudoscclions and a vertical electrical sounding were made at the Orita Aperin refuse dump site, Ibadan, Soulh West Nigeria, to map the gross layered stmcture of the refuse as well as the extent of groundwater contamination. Wood, leaves. newspaper, cloth, polythene bags, plastics, glass and metal rethse interspersed with soil exhibited resistivity of l l.6 ohm-m and layer thickness of 0. 7m as obtained from tlie inversion of the sounding. The unsaturated layer has a resistivity of 6.8 ohm-m and thickness of O.7m while lcachate-saturated is characterised by low resistivity of 2. 9 ohm-m; l.2 m thickness.'Pim .fractured saturated layer exhibited resistivity of 49.6 ohm-m. The accurate determination of the refuse thickness in geoclectrical model is primarily due lo a strong resistivity contrast between the leachate s,ituratcd (2. 9 ohm-m) and u,1derlying saturated fractured rock ( 49.6 ohm·rn). Despite this contrast, models generated from electrical resistivity soundings arc reasonably accurate in their depictions of internal structure of the dump site. The hydrochemical analysis of the surface and groundwater samples collected within the vicinity of the dump site were analysed for physico .. chemical parameters. The results produced higher concentration of TDS. total hardness. er. N03-, Mg2'_ Na K' and pH value for water collected at  close locations the dump site than those far away from the site:an evidence for a quantitative assessment of groundwater contamination.