Hydrogeological and hydrochemical character of the regolith aquifer, northern Obudu Plateau, southern Nigeria

Photogeological, geoelectrical, and drill-hole data were used to determine the hydrogeological conditions of the regolith layer mantling the Precambrian rocks in the northern Obudu plateau of southern Nigeria. The regolith thickness is 3.8-89.5 m (mean 38 m). Water for domestic purposes is extracted by dug wells < 15 m deep and shallow boreholes < 50 m. The mean value for permeability of the saturated regolith is 7.5 x 10(-1) m/d and for transmissivity, 3.8 x 10-1 m(2)/d. The regolith wells have a high specific capacity, 40-270 m(3)/d/m and a high yield, 700-4,050 m(3)/d. Using statistical analysis, well yields and specific capacities can be estimated if the saturated thickness and apparent resistivity of regolith layers are known from drill-hole data and vertical electrical sounding. Chemical data show that the major groundwater types are calcium-bicarbonate (Ca-HCO3) and sodium+potassium bicarbonate [(Na+K)-HCO3] and the water quality meets national and international standards for drinking, domestic and agricultural purposes. However, for future proper management of water resources in the area, care should be taken, that waste-disposal sites for both solid and human waste should not be located near waste sources.