Characterization of Aquifers Using Geo-electrical Methods in parts of Abia State, Southeastern Nigeria

This study was carried out to map and characterize the water bearing formations (aquifers) in Abia State, southeastern Nigeria. Vertical electrical resistivity depth sounding for inferring the resistivity and thicknesses of the vertical succession of different conducting zones in the subsurface was employed in characterization of the subsurface aquiferous units. The depth of the boreholes drilled varies from 21.02m - 250m, while the static water level (SWL) varies between 4.57m around Ukwa-West to about 35.97m around Aba South. The depth range of 9.15m to 53.05m to the aquiferous zone for Umuahia Local Government Area is in agreement with the value of 35.0m. Very productive aquifers in Abia State are limited to the alluvial deposits and the Coastal Plain Sands lithologies comprising: fine, medium and coarse-grained and often pebbly sands with some intercalations of clays. The alluvium occurs mainly in Ukwa West and East Local Government Areas. Drilling depths in this aquifer range from 30 to 140m. Prolific production is expected from this alluvium which has an approximate permeability of 35m2/day. The High production rate (Permeability = 35m2/day) is expected in the Coastal Plain Sands sediments found in all Local Government Areas stretching south of Umuahia and Bende. Drilling depths ranging from 40 to 250 m are recommended for boreholes in these LGAs. However, more precise drilling depths must be confirmed by hydro-geophysical site survey, because the geology of Abia State becomes more complicated north of Umuahia and Bende LGAs. This complication in geology affects all other LGAs north of Umuahia.