Geo-electrical Method Applied to Evaluation of Groundwater Potential and Aquifer Protective Capacity of Overburden Units

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.