Geoelectric Sounding and Hydrochemical Analysis for Vulnerability Assessment of FUTA Campus Using Modified Le Grand Model

Abstract

The work is aim at assessing possible impact of FUTA dumpsite on groundwater resources within the campus. Vertical electrical sounding was done across the study area in 94 locations. Three to five geoelectric layers were delineated in the study area. The layers correspond to the topsoil, weathered layer (sandy clay and clayey sand), lateritic weathered layer, partially weathered basement/partially fractured basement and the presumed fresh bedrock. The layer’s resistivity varies respectively from 38 - 845 ohm-m, 9 - 7490 ohm-m, 41 - 90224 ohm-m, 60 - 15191 ohm, 162 - 99668 ohm-m, while the layer thickness ranges from 0.4 - 5.2 m, 0.9 - 24.1 m, 2.8 - 30.4 m and 4.3 - 41.6 m. The VES also results enabled the delineation of aquifer layer(s) where present, identification of the overlaying lithology above the aquifer layer across the area, determination of the transverse resistance, aquifer overburden longitudinal conductance, coefficient of anisotropy and VES distances from the dumpsite. These parameters were combined using the Le Grand model chart to evaluate and generate aquifer venerability model across the study area. The campus was classified into four zones of vulnerability; low, moderate, high, and very high. The current dumpsite is located in low vulnerability zones. The elevation map shows that the dump site is located at relatively low elevation to other areas, thus eliminating outward flow of leachate to other areas. The aquifer vulnerability model map (AVMM) was validated using physio-chemical analysis parameters (total dissolved solid, conductivity and total hardness) obtained from water samples from 8 different wells in the study area. The AVMM has 100% agreement with the water physio-chemical analysis. All water samples analysis results are within the WHO permissible limits.