Environmental Sciences Electrical resistivity soundings to determine subsurface contamination in the vicinity of

Abstract

Four Wenner apparent pseudosections and a vertical electrical sounding were made at the Orita Aperin refuse dump site, Ibadan, South West Nigeria, to map the gross layered structure of the refuse as well as the extent of groundwater contamination. Wood, leaves, newspaper, cloth, polythene bags, plastics, glass and metal refuse interspersed with soil exhibited resistivity of 11.6 ohm-m and layer thickness of 0.7 m as obtained from the inversion of the sounding. The unsaturated layer has a resistivity of 6.8 ohm-m and thickness of 0.6 m while leachate-saturated is characterized by low resistivity of 2.9 ohm-m; 1.2 m thickness.


The fractured layer exhibited resistivity of 49.6 ohm-m. The accurate determination of the refuse thickness in geoelectrical model is primarily due to a strong resistivity contrast between the leachate saturated (2.9 ohm-m) and underlying saturated fractured rock (49.6 ohm-m). Despite this contrast, models generated from electrical resistivity soundings are 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, Cl-, NO3-, Mg2+, Na+, K+ and pH value for water collected at close locations to the dump site than those far away from the site: an evidence for a quantitative assessment of groundwater contamination.

Global Journal of Pure and Applied Sciences Volume , No 1 January (2001) pp. 127-132



KEY WORDS:

Resistivity, groundwater, leachate-saturated, contamination, layer.