Evaluation of aquifer hydraulic conductivity and transmissivity of Ezza/Ikwo area, Southeastern Nigeria, using pumping test and surficial resistivity techniques

Aquifer hydraulic parameters including hydraulic conductivity and transmissivity play a very important role in the assessment and management of groundwater. Conventionally, these parameters are best estimated employing pump test, which is usually expensive and time-consuming. The use of surficial electrical resistivity data integrated with few available pumping test data provides a cost-effective and efficient alternative. A total of thirty-five (35) vertical electrical soundings with a maximum half-current electrode spacing of 150 m using the Schlum-berger array were used in this study. Five (5) of these soundings were parametric soundings carried out in the vicinity of monitoring wells for correlation and comparative purposes. The empirical relationships between the hydraulic parameters derived from the pump test data and the aquifer resistivity data were established for the Ebonyi and Abakaliki Formations, respectively, and, in turn, used to estimate aquifer hydraulic parameters in areas away from wells. Aquifer hydraulic conductivity estimated across the study area varies from 0.49 to 1.5735 m/day with a mean value of 0.9205 m/day for the Ebonyi Formation, while the Abakaliki Formation has hydraulic conductivity values that vary from 0.0775 to 1.3023 m/ day, with a mean value of 0.2883 m/day. The transmissivity values estimated across the study area range between 0.29 and 57.27 m(2)/day with a mean value of 6.59 m(2)/day. Transmissivity values obtained were interpreted with Krasnrs transmissivity classification, and this delineated the study area into three groundwater potential zones: very low, low, and intermediate zones. The study shows that the areas underlain by the Ebonyi Formation have a higher groundwater potential than those underlain by the Abakaliki Formation. These findings are supported by the geology of the area, which revealed that the Abakaliki Formation is dominated by shales with very low permeability, while the Ebonyi Formation consists of shales with alternations of sand/sandstones, which statistical analysis of the different model equations used in estimating the hydraulic parameters of the study area revealed that the new model empirical equations proposed and used in the present study proved to be the best alternatives to pumping test data.