Geoelectric Evaluation of Aquifer Potential and Vulnerability of Northern Paiko, Niger State, Nigeria
This study was carried out using vertical electrical sounding (VES) to evaluate the groundwater potential and the aquifer protective capacity of Northern Paiko. Sixty vertical electrical soundings were obtained across the study area using Schlumberger electrode configuration. Three to four geoelectric layers were delineated from the interpreted results. The stratigraphy of the subsurface shows: topsoil (62.8–3082 Ωm), weathered layer (15.2–80 368 Ωm), fractured layer (191–236 672 Ωm), and the fresh basement (79.9–308 865 Ωm). The weathered layer was delineated as the major aquiferous horizon. From the results, the resistivity, thickness, and longitudinal conductance maps were drawn. It was observed that groundwater potential is low in about 76.7% of the study area. This study has also shown that the aquifer protective capacity of most parts of the study area is poor (83.3%), thus rendering the aquifer vulnerable to contamination.
Delineation of contaminant zone through electrical imaging technique
Electrical imaging technique has been found to be a powerful tool to delineate sub-surface contaminated zone, when there is sufficient resistivity contrast. Electrical tomography (imaging) involves measuring a series of constant separation traverses with the electrode spacing being increased with each successive traverse. Since increasing separation leads to information from greater depths, the measured apparent resistivities have been used to construct a pseudo-section displaying the variation of resistivities, both laterally and vertically over the section. Normally, the pseudosection contains geometrical effects, geological noise and the distorting effects of near-surface lateral changes in resistivities, which occur close to the electrodes (electrode effects). In order to remove geometrical effects as well as to produce an image of true depths and true formation resistivities, the inversion technique is used. This technique was successfully demonstrated near Dindigul town, where groundwater was contaminated due to untreated tannery effluents.
GEOPHYSICAL STUDIES IN DETERMINING HYDRAULIC CHARACTERISTICS OF AN ALLUVIAL AQUIFER
M. Senthil KumarD. GnanasundarL. ElangoCentre for Geoscience and EngineeringAnna UniversityChennai, IndiaThe vertical electrical sounding (VES) data obtained from 70 locations in the unconsolidatedsandy formation south of Chennai was interpreted, and layer parameters such as trueresistivity and thickness were determined. Formation factor was calculated from the resistiv-ity data. Three empirical relationships were established: they are (i) the relationship betweenhydraulic conductivity and formation factor, (ii) hydraulic conductivity and modified aquiferresistivity, and (iii) transmissivity and transverse resistance. The aquifer parameters of thisalluvial aquifer have been estimated with a reasonable accuracy using the relations betweenhydraulic properties and electrical resistivity parameters. This study implies that geoelectricaltechniques offer an alternate approach for estimating the hydraulic characteristics of alluvialaquifers.