Integrated geophysical investigation of groundwater potential and bedrock structure in Precambrian basement rocks of Ife, southwest Nigeria

Abstract

Telluric profiling (TP) and vertical electrical sounding (VES) techniques were employed for subsurface geophysical investigation at a new development site in Ife, southwest Nigeria. The study was carried out to provide geological data to assist in identifying locations of high potentials for good groundwater resource development and map suitable locations for infrastructural development in the area. Interpreted results of the two techniques (2-D profile map and geoelectric sections) are in good agreement, TP technique probes far deeper depth into the subsurface than VES technique. 2-D cross-section maps generated from TP data reveals zones of weathered/fractured bedrock delineated up to a depth of about 20 m in most locations with the exception of few locations showing outcrops close to the surface. TP cross-section also depict the presence of fault zones at the latter segment of the second traverse. Geoelectric sections generated from VES analysis and interpretation revealed a maximum of four subsurface strata which are topsoil (71–371 Ωm), weathered layer (22–94 Ωm), fractured/intensely fractured bedrock (453–496 Ωm and 122–311 Ωm respectively) and fresh bedrock (533–1088 Ωm). Weathered layer composed of clayey material originating from underlying schist rock occurred at depth below 5 m mainly along the first two traverses with thickness in the range 1.44–5.17 m. These clayey zones are unsuitable for groundwater abstraction. This medium is a less permeable bed of aquitard, with permeability not sufficient to allow the completion of production wells. Fractured zone is prevalent across all the traverses at varying thicknesses (3.65–12.2 m) and at depth range of 2.38–5.82 m. The regions with fractured zone are delineated at several spots for groundwater resource development and areas underlain by competent fresh bedrock at considerable depth identified for future infrastructural development in the study location.