Environmental Risk Assessment of Subsurface Corrosion Severity as Aids to Pollution Level of Proliferated Petrol Stations in Abeokuta Metropolis Using Geophysical Technique (Published)
Twenty (20) Vertical Electrical Sounding (VES) Method of Geophysical Investigation was carried out in Abeokuta, South-West Nigeria adopting the Schlumberger configuration with maximum electrode separation (AB/2) of 100 m and minimum of 32m with a linear electrodes array (AMNB) in order to delineate the subsurface geologic layers and determine both their corrosion severity and overburden Protective capacity rating (OPCR) as aids to evaluating the vulnerability and pollution level in groundwater system of the study area. The acquired data were interpreted with WinRESIST software with identified curve types; KH and HKH curves among others are in many instances indicative of fracturing which serve as favourable zones for groundwater abstraction. The VES data interpretation delineated four (4) major lithological units in the order of the lateritic topsoil, weathered material, fractured basement/fresh bedrock with delineated low resistivity water absorbing, clayey, linear fracture zones at varying depths. It was concluded that the very low resistivity of the area investigated indicates that the subsurface structure is highly corrosive. Depths of burial of the storage tanks varied from the maximum depth of 5.0m to the minimum depth of 4.0m with an average depth of 4.7m while the overburden thickness to the aquiferous zone in the study area as determined from the electrical resistivity inversion ranged from the maximum depth of 22.4m (VES5) to the minimum thickness of 3.3m (VES19) with an average thickness of 4.7m. This investigation revealed that 10% of the locations comprising VES17 and VES19 are extremely corrosive; 10% are highly corrosive; 35% are corrosive; 25% are moderately corrosive; 5% are mildly corrosive and 15% are non-corrosive. No VES location exhibited Very Good to Excellent OPCR while only 5% exhibited Good OPCR. 65% of the stations fell within Moderate OPCR; this is due to their relatively high overburden thickness compared to other locations.
Keywords: Proliferation, clay sections, corrosion severity, lethal effects, vulnerability status