Electrical resistivity method is a versatile and economical technique for groundwater prospecting in different geological settings due to wide spectrum of resistivity compared to other geophysical parameters. Exploration and exploitation of groundwater, a vital and precious resource, is a challenging task in hard rock, which exhibits inherent heterogeneity. In the present study, two-dimensional Electrical Resistivity Tomography (2D-ERT) technique using two different arrays, viz., pole–dipole and pole–pole, were deployed to look into high signal strength data in a tectonically disturbed hard rock ridge region for groundwater. Four selected sites were investigated. 2D subsurface resistivity tomography data were collected using Syscal Pro Switch-10 channel system and covered a 2 km long profile in a tough terrain. The hydrogeological interpretation based on resistivity models reveal the water horizons trap within the clayey sand and weathered/fractured quartzite formations. Aquifer resistivity lies between ∼3–35 and 100–200 𝛺 m. The results of the resistivity models decipher potential aquifer lying between 40 and 88 m depth, nevertheless, it corroborates with the static water level measurements in the area of study. The advantage of using pole–pole in conjunction with the pole–dipole array is well appreciated and proved worth which gives clear insight of the aquifer extent, variability and their dimension from shallow to deeper strata from the hydrogeological perspective in the present geological context.

A comprehensive geophysical and petrological study was carried out at Giddalur area in Prakasam district, Andhra Pradesh, which is geologically a highly deformed area and is difficult to delineate the aquifer zone(s). The task was to find out the exact rock type in which aquifer is concealed as well as to delineate the aquifer zone, which can yield sufficient quantity of water. The resistivity models derived from geophysical dataset were interpreted in terms of hydrogeology and the results revealed substantial resistivity contrast of the geological formations within the study area. We have delineated two major groundwater potential zones based on this study. These zones were tapped at different depths in diverse rock types. Drilled hand specimens (rock cuttings) were not adequate, so these specimens were petrographically studied to reveal the exact contact zones of the rock type. On integration of the geophysical and the petrographic results, it was illustrated that two aquifer zones were struck at a depth of 92 and 122 m between shale-phyllite and phyllite-quartzite, respectively. These findings were correlated, which matched with the lithology of the drilled borehole. This integrated approach will be helpful in strategy for groundwater assessment as well as prospecting groundwater resources in different geological terrain.

Discovering and locating the source and availability of groundwater in a plateau region of Chhotanagpur gneissic complex, where there is a varied hydrogeological characteristics, is a crucial task for earth scientists. One such region located at Garh Khatanga near Ranchi, Jharkhand, India was closely studied for groundwater assessment and exploration. High resolution electrical resistivity tomography 2D data were acquired to probe deep inside the earth up to a maximum depth of 220 m using state-of-the-art electrical resistivity tomography technique and mapped geoelectrical subsurface images at 16 sites in three different blocks along a 7.2 km line for prospecting and exploration of groundwater resources. The geophysical inversion of the 2D resistivity data revealed prospect groundwater scenario at six sites based on the hydrogeological interpretation and the significant resistivity contrast between the highly weathered/fractured and the massive rocks. The modelled resistivity sections revealed different degree of weathered, fractured and saturated weathered/fractured strata as well as clearly indicated the presence of a totally hard massive rock within the subsurface lying between $\sim$30 and 220 m depths. The geophysical anomalies were confirmed and validated by borehole drilling at four sites up to a maximum depth of 215 m with yields ranging from 2.0 to 4.25 inch, which is equivalent to 5632–63769 l/hr of groundwaterexploitation. These yields of groundwater resources are rated as good aquifer(s) in the plateau region of Chhotanagpur gneissic complex. The characteristics resistivity for fracture zone varies from 140 to 1300 $\Omega$m, while for saturated weathered/fractured it ranges from 10 to 1000 $\Omega$m. On joint interpretation of the 2D resistivity models and the borehole lithology data, it clearly shows the average resistivity of the aquifer zone lies in the range 50–500 $\Omega$m. The present study along with the conceptual geological models provided a sound knowledge of hard rock hydrogeology in the plateau region with complex geological settings and these helped to achieve significant results for groundwater exploration and development of the resources of the studied area as well as take up such challenging work in exploring the prospect groundwater resources in other similar geological setting of the country.

Two-Dimensional (2D) Electrical Resistivity Tomography (ERT) survey was carried out at 11 sites within an area of $10 \rm{km}^{2}$ to delineate deeper potential groundwater zones in a complex geological terrain underlain by quartzite, shale and limestone formations with varied resistivity characteristics. The area is in medium rainfall zone in Tadipatri mandal of Anantapur district, Andhra Pradesh state, India. The investigation was carried out to meet the growing demands of water supply. Interpretation of the highdensity 2D resistivity dataset results revealed potential zones at only three sites in Tummalapenta, Ayyavaripalle and Guruvanipalle villages within the depth zone of 24–124 m. A major fault zone orientedin EW direction is mapped at Tummalapenta site. Based on high resolution geophysical data interpretation and significant anomalies, four boreholes were drilled in complex, viz., limestone, shale and quartzite formations up to a maximum depth of 192 m in the area with the yield ranging from $300$ to $\sim 5000$ liter per hour (lph). These four anomalous drilled borehole sites corroborates with the aquifer zone delineated through ERT technique. The aquifer parameters estimated from pumping tests show that the transmissivity varies between $\sim 0.3$ and $\rm{179.5 m^{2}/day}$ while the storage coefficient ranges from 0.137 to 0.5 indicating large variation in aquifer characteristics of the system in a smaller area. Suitable water conservation measures were suggested for improving the groundwater condition and yield of the pumping wells.