Geophysical and hydrogeochemical evaluation of a spring In Ado-Ekiti,South-Western Nigeria

Abstract

Very Low Frequency Electromagnetic (VLF-EM), Electrical Resistivity (ER) hydrogeological, hydrochemical and hydrobiological methods were used to evaluate a spring with a view to determine its feasibility for development in Ado Ekiti, South-western, Nigeria.Three-200 m long traverses and one 120 m long traverse cutting through the three traverses were established with stations at 5 m intervals. Components of the VLF-EM and ER were measurements were conducted. The ER utilized pole-pole and Schlumberger electrode arrays for profiling and Vertical Electrical Soundings (VES) respectively. A hand-dug well was sited at higher elevation and ten meters away from the spring. Microbial and physicochemical analyses were conducted on water samples from the spring and the well. The yield of the spring was determined using the “below-ground” method. The VLF-EM results indicated the relatively conductive zones suspected to be faults/fracture zones while the VES interpretation results delineated three main lithologic layers which include the topsoil, weathered layer and the basement bedrock. The resistivities and thicknesses of the topsoil and weathered layer varied from 116 m to 1710 m, 69 m to 96 m and 0.51 m to 1.19 m and 3.95 m to 9.17 m respectively. The fresh basement bedrock had resistivity > 1000 m. The Total Heterotrophic Bacteria count was 1.8 x 10⁵ CFU/ml and fungal and Coli counts were 1.0 CFU/ml each in the spring. The TDS and pH were 60 mg/l and 8.00 respectively while the cationic concentrations of the metals were 0.014, 1.758, 0.020, 0.013, 0.0773, 0.808, 3.558, 8.79, 0.0651, 0.237, 0.001, and 0.007 mg/l for Cr²⁺ , Fe²⁺  , Cd²⁺  , Zn²⁺  , Ni²⁺  , Mg²⁺  , K⁺  , Na⁺  , Pb²⁺  , Ca²⁺  , Mn²⁺  and Cu²⁺  respectively in the spring. The yield was 0.021 L/s. The study concluded that though the yield of the spring was relatively low, its quality is good enough and its development was feasible.

 Keywords: Spring, Measurements, Analyses, Yield, Feasibility, Development.