Evaluation of groundwater resources protection within mega school, Ayeka, Southwestern Nigeria

Abstract

Electrical Resistivity method involving Vertical Electrical Sounding (VES) was carried out within the Maga school, Ayeka, southwestern Nigeria. This was carried out with aim of evaluating the protective capacity of the layers overlying the aquifers in preventing pollution from getting to the groundwater resources within the area. A total of twelve Vertical Electrical Soundings (VES) were acquired using the Schlumberger configuration. The half-current electrode spacing (AB/2) of the Schlumberger configuration was varied from 1 to 225 m. The sounding curves derived from the VES data were quantitatively interpreted using partial curve matching and further refined using computer assisted program. From the interpreted geoelectric result, four lithological layers were delineated; the topsoil, the sandy clay, the lateritic sand and the clayey sand/sand. The topsoil resistivity ranges from 89 to 162 Ωm and its thickness varies from 0.9 to 2.0 m, the sandy clay resistivity varies from 215 to 512 Ωm and its thickness ranges from 3.1 to 7.6 m, the lateritic sand resistivity varies from 1025 to 2611 Ωm and thickness ranges from 13.3 to 23.9 m and the clayey sand/sand resistivity ranges from 183 to 522 Ωm with a depth range from 19.7 to 30.4 m. The protective capacity map revealed that all the parts of the study area fall within a weak protective capacity zone. This is informed by the low longitudinal conductance which suggests a weak protective capacity rating. As a result of this, the study area is therefore vulnerable to pollution if it is exposed to contaminant sources which could come from septic tanks, underground petroleum storage tanks, industrial waste and landfills.