GEOPHYSICAL INVESTIGATION OF GROUNDWATER RESOURCES USING ELECTRICAL RESISTIVITY AND INDUCED POLARIZATION METHOD

Abstract

Identifying potential groundwater is crucial, especially in the area that faced water stress issue. Geophysical surveys are one of the most reliable ways to find a groundwater supply. However, when performing a resistivity survey, there is uncertainty in distinguishing between soil particles and groundwater. Therefore, this study combines the electrical resistivity and induced polarization method to distinguish the saturated zones between an aquifer and unconsolidated sediments and the results were validated with borehole data. The pole-dipole array was used to build up two resistivity survey lines. According to the results of the 2-D resistivity and IP survey, low resistivity values between 10 and 100 m (Ohm-m) and low chargeability values between 0 and 1 millisecond can be used to identify potential groundwater areas in the subsurface (msec). Silty sand and sandy clay make up alluvium, which has a resistivity range of 125 to 255 m and a chargeability range of 7 to 10 msec. The reflection coefficient (Rc) values generally range between 0.41 and 0.70 and suggest a highly fractured formation with respect to the hardrocks. A comparison between the depth to bedrock as predicted by electrical resistivity tomography (ERT) and the borehole logs was in strong agreement with the correlation coefficient value (R² = 0.9478). On the other hand, the study revealed a relatively week correlation (R² = 0.4351) between the final drilled depth and the borehole yield. The study therefore has demonstrated the efficacy of the ERT and IP technique as a tool in delineating groundwater potential zones for the drilling of boreholes.