Assessment of Aquifer-Protective Capacity of Orire Estate in Akure, Ondo State, Nigeria

Abstract

The amount and thickness of clay layers and surrounding organic elements have a direct impact on how well an aquifer protects itself. Thus, the purpose of this work was to evaluate Orire Estate's ability to preserve the aquifer in Akure, Ondo State, Nigeria, using a geophysical survey that used the Vertical Electrical Sounding (VES) and Very Low Frequency (VLF) Electromagnetic Technique. Throughout the course of the survey, seven traverses of various lengths were established, and VLF-EM measurements were made every five meters along the four main profiles. Thirteen vertical electrical soundings were also performed, with electrode spacings varying from one to one hundred meters. Computer-assisted modeling and partial curve matching approaches were used in the interpretation of the data. Four subsurface geological units were identified by the analysis: topsoil, worn layer, fractured basement, and fresh basement. The topsoil layer, with a thickness ranging from 0.9 to 1.5 meters, exhibited resistivity values between 57.0 and 198.4 Ω-m. The worn layer varied in thickness from 2.6 to 17 meters, with resistivity values from 87.0 to 978.7 Ω-m. The fractured basement layer's thickness ranged from 7.8 to 23.7 meters, showing resistivity values between 311 and 3041.8 Ω-m, while the fresh basement layer demonstrated resistivity values ranging from 1423.1 to 3790.57 Ω-m with infinite thickness. The presence of zones with poor aquifer-protective capacity throughout the study area indicates a heightened vulnerability to contamination from leachates and other pollutants. The subsurface conditions suggest an abundance of unconsolidated sand with limited clay, which prolongs the residence time of percolating pollutants and diminishes the necessary impediment to fluid movement for effective filtration.

Keywords

• Aquifer Protection; Groundwater Quality; Subsurface contaminants; Geophysical survey