Estimation of geohydraulic parameters from fractured shales and sandstone aquifers of Abi (Nigeria) using electrical resistivity and hydrogeologic measurements

Geohydraulic parameters are essential elements in groundwater resource management and conservation. Most of these parameters especially the hydraulic conductivity and transmissivity are usually estimated from pumping test carried out on drilled boreholes. This paper presents a study conducted in Abi area of the Ikom-Mamfe Embayment with the objective of estimating aquifer parameters from 30 evenly distributed vertical electrical soundings using the Schlumberger configuration and hydrogeologic measurements from 28 boreholes within the area as an alternative way of generating an initial data for groundwater characterisation and quality assessment in the area. The results showed low resistivity 45 Om, hydraulic conductivity 2.0 × 10-5 m/s ( 1.7 m/day) and transmissivity 5.2 × 10-4 m2/s ( 45 m2/day) for the water-bearing aquifer horizons in the northeastern and northwestern parts of the study area due to the nature of the aquifer system that were predominantly fractured shale. The sand based aquifers had higher values in the neighbourhood of ~100–800 Om, ~4.0 × 10-5–1.0 × 10-4 m/s (~3.46–9.04 m/day) and ~6.94 × 10-4–3.81 × 10-3 m2/s (~60–330 m2/day) for the respective parameters mentioned above. The potability of the groundwater system as observed from hydrogeologic measurements of water samples from most boreholes were relatively poor, having electrical conductivity and total dissolved solids values of ~250–931.0 µS/cm and ~500–623.77 mg/l respectively due to the influence of clay minerals within the aquifer horizon. Some of the vertical electrical sounding points were taken in the vicinity were pumping tests and lithologic data were available for adequate comparison of the results.