Groundwater Investigation and Shallow Subsurface Evaluation of Granite Gneiss Formation using Electrical Resistivity Tomography Survey of Mauranipur Block, Jhansi District, Uttar Pradesh, India

Geophysical methods employ indirect, nonintrusive observations to characterize and map variations in the physical properties of what lies concealed beneath the ground surface. The apparent resistivity (ρa) of the ground can be calculated using Electrical resistivity method. Using electrical properties of ground subsurface to characterize and map the granite gneiss hard rock formation of study area. The apparent resistivity (ρa) of the ground can be calculated, and since low porosity bedrock usually exhibits an electrical resistivity higher than overlying sediment, the buried topography can be interpreted. Electrical resistivity can map lateral and vertical variations in apparent resistivity of geologic material. Resolution is a function of electrode spacing and resistivity contrast between lithologically different earth materials. The resolution of electrical resistivity tomography (ERT) profile defines the accuracy of interpretation of subsurface conditions. Because of variability in resistivities of earth materials, interpretation of electrical resistivity tomography (ERT) data must be handled with caution. During ERT survey, when current is induced to flow through deeper layers, the distance between current and potential electrodes is gradually increased. This affects the sensitivity of the ERT method. Gradually increasing the distance between electrodes lowers the intensity of current flow, and accordingly the sensitivity of ERT survey. Thus, interpretation of smaller scale objects at greater depths becomes increasingly difficult. Factors such as temperature, porosity, conductivity, salinity, clay content, saturation and lithology generally affect the resistivity of earth materials and can affect the ability of different materials to conduct electrical current. For instance, dry soil usually has much higher resistivity than saturated soil. The same situation appears with weathered and unweathered rock. Weathered rock is usually more porous and fractured, and it becomes more saturated with groundwater; as a result, weathered rock has lower resistivity than intact rock. Total 15 ERT profile carried out in different geomorphological formation of study area. It is observed that the apparent resistivity value of weathered zone occurs less than 100 Ω-m in the northwest region of study area and the apparent resistivity value of water saturated weathered zone is varies from 100 Ω-m to 200 Ω-m. The resistivity value of fractured zone is greater than 200 Ω-m with varying depth from 80 m to 100 m. In north-west region of study area occurs in good water potential zone with high yield and southeast region of study area having low groundwater potential zone with low yield. The most part of study area occurs in poor to moderate groundwater potential zone. The methods provided a more precise hydrogeomorphologic model for the study area. Results from this study area useful for technical groundwater managements and they clearly identified suitable borehole for long term groundwater prospecting. 2D electrical resistivity imaging method provides promising input to Groundwater evaluation in complex geology weathered environment