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.
Aquifer types and the geoelectric/hydrogeologic characteristics of part of the central basement terrain of Nigeria (Niger State)
Abstract A study of lithological logs from forty (40) wells drilled in twelve (12) localities in parts of the Niger State of Nigeria and the interpretation results of the parametric vertical electrical soundings (VES) were carried out to identify the geoelectric/hydrogeologic characteristics of the basement complex area. Five (5) aquifer types were identified. These include the weathered aquifer; the weathered/fractured (unconfined) aquifer; the weathered/fractured (confined) aquifer; the weathered/fractured (unconfined)/ fractured (confined) aquifer and the fractured (confined) aquifer. The mean groundwater yield for the aquifer types varies from 0.83 L/S for the weathered layer aquifer to 3.0 L/S for the weathered/fractured (unconfined)/ fractured (confined) aquifer. The fracture frequency increases with depth and reaches a maximum at between 25–35 m for granite, gneiss and schist but decreaseswith further increase in depth. The cumulative fracture frequency is maximum in granite and minimum in schist. The fracture thicknesses are maximum (greater than 3 m) and occur most frequently within the depths of 10–40 m. Minimum fracture thicknesses (≤ 1 m) occur most frequently between the depths of 50–70 m. Fractures rarely occur at depths greater than 90 m An optimum borehole depth for the study area is 60–70 m.
GROUNDWATER EXPLORATION IN HARD-ROCK TERRAIN—A CASE HISTORY*
The utility of electrical resistivity and magnetic measurements to locate suitable wellsites in hard-rock terrains intruded by dykes is illustrated. The example is taken from a highly hilly terrain of Karnataka State situated in the Western Ghat hills of Peninsular India. Electrical resistivity profiles and soundings, S.P., and total magnetic field measurements are discussed. Of the fifteen recommended sites, nine have been drilled, eight of which are reported to yield between 6–12 m3/hr (1500 to 3000 gals./hr), which is considered satisfactory in this region.