Geo-electrical Method Applied to Evaluation of Groundwater Potential and Aquifer Protective Capacity of Overburden Units
N. K. Abdullahi *
Department of Applied Science, College of Science and Technology, Kaduna Polytechnic, Kaduna, Nigeria
E. E. Udensi
Department of Physics Federal University of Technology, Minna, Niger State, Nigeria
A. Iheakanwa
Department of Applied Science, College of Science and Technology, Kaduna Polytechnic, Kaduna, Nigeria
B. E. Eletta
Department of Applied Science, College of Science and Technology, Kaduna Polytechnic, Kaduna, Nigeria
*Author to whom correspondence should be addressed.
Abstract
Aims: This study was designed to determine different subsurface Geo-electric layers, the aquifer units, determination of Dar-Zarrouk parameter (Longitudinal conductance(S) and Transverse resistance (R)) as well as identifying suitable areas with poor, weak, moderate and excellent aquifer protective capacity rating.
Study Design: The study area, Sabo in Kaduna state lies approximately between latitudes 10º25’N and 10º30’N and longitudes 7º25’E and 78º30’E covering an area of about 500,000m2.
Methodology: A total of sixty-six (66) vertical electrical soundings (VES) using Schlumberger electrode array were acquired with a maximum electrode separation of AB/2=100 m, using the ABEM Terrameter SAS 300C.
Results: Maximum of five lithologies were identified namely, topmost layer which consists of lateritic clay, river sand and gravel, clayey sand, weathered transition zone/ fractured layer and the fresh basement. Qualitative interpretation indicates that the weathered layer and weathered/fractured basement constitutes the main aquifer units. These aquifers are characterized by thick overburden found within basement depressions with maximum value of 65 m and resistivity values between 10 ohm.m and 756 ohm.m. The Dar-Zarrouk parameters evaluated are total longitudinal unit conductance (S) and total transverse resistance (T) with values ranging from 0.005 – 0.65 mhos and 2000 – 32000 ohm.m2.
Conclusion: The results show that the lithology of the aquifer is dominated by clay/clayey sand and sandy materials with attendant low and high transmissivity. About 80 % of the area has longitudinal conductance value greater than 0.3 mhos due to high content of clay/lateritic clay indicating moderate protective capacity rating, hence vulnerable to contamination.
Keywords: Schlumberger, dar-zarrouk, aquifer, contamination