IMPACT ASSESSMENT OF AGIRIFON DUMPSITE LEACHATE ON THE AQUIFER SYSTEM AT ILUTITUN OSOORO, SOUTHWESTERN NIGERIA.

Abstract

The impact assessment of leachate from the Agirifon dumpsite on the aquifer system of Ilutitun was carried out using the integration of electrical methods (2-D Resistivity Imaging and Vertical Electrical Sounding) and hydro-physicochemical analysis on groundwater samples obtained at three (3) locations around the dumpsite. Six (6) traverses were occupied in the study area, on which the 2-D Resistivity Imaging and Vertical Electrical Soundings (VES) were carried out. A total of seventeen (17) Vertical Electrical Soundings were carried out in the study area in order to delineate depth to the various aquifer units and its level of contamination due to leachate contaminants. The 2-D resistivity structures, whose interpretation reveals upper 30 m of the subsurface geology, delineated virtually a single type of subsurface formation (coastal plain sand). The interpreted results from the vertical electrical soundings revealed a three- layer subsurface geoelectric units, which are the topsoil, clay/clayey/sand/sand units and pebbly sands (indurated sand stone). Generally resistivity range is between 27 Ωm and 10207 Ωm with the dumpsite characterized by low resistivity between 27 Ωm and 86 Ωm. The VES results were used to generate geoelectric sections, isoresistivity and isopach map of the topsoil, first and second aquiferous layers and the result revealed a radial migration of leachate around the vicinity of the dumpsite. The leachates are observed to have moved through porous and permeable layers into subsurface aquifers thereby contaminating them. The high resistivity intermediate/lower zone on the 2-D resistivity structure corresponds to the (probably unpolluted) sandy/pebbly sand units on the corresponding geoelectric sections. It could therefore be concluded that the leachates produced from the dumpsite is gradually infiltrating into the subsurface (shallow and deep) aquifers in the study area. However, the hydro- physicochemical analysis of water samples shows no major groundwater contamination.