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Depth of detection of a target can be defined as that depth below which the target cannot be detected with a given electrode array assuming that the minimum detectable anomaly is 10%. Following this definition, physical modelling was carried out to determine depths of detection of conductive targets of limited lateral extent such as a vertical sheet, a horizontal cylinder and a sphere (infinitely conducting). It is seen that the two‐electrode array has the greatest depth of detection followed by the three‐electrode array, while a Wenner array has the smallest depth of detection, when the array spread is in‐line (i.e. perpendicular to the strike direction). On the other hand, the depth of detection with a Wenner array improves considerably and is almost equal to that of the two‐electrode array when the array spread is broadside (i.e. along the strike direction). With an increase in the depth extent of the vertical sheet from 10 to 20 times its thickness, there is an increase in the depth of detection with all arrays except for the three‐electrode array when the array spread is in‐line, and with the Wenner array when the array spread is broadside.

The groundwater quality detoriation due to various geochemical processes like saline water intrusion, evaporation and interaction of groundwater with brines is a serious problem in coastal environments. Understanding the geochemical evolution is important for sustainable development of water resources. A detailed investigation was carried out to evaluate the geochemical processes regulating groundwater quality in Cuddalore district of Tamilnadu, India. The area is entirely underlined by sedimentary formations, which include sandstone, clay, alluvium, and small patches of laterite soils of tertiary and quaternary age. Groundwater samples were collected from the study area and analyzed for major ions. The electrical conductivity (EC) value ranged from 962 to 11,824 µS/cm, with a mean of 2802 µS/cm. The hydrogeochemical evolution of groundwater in the study area starts from Mg–HCO3 type to Na–Cl type indicating the cation exchange reaction along with seawater intrusion. The Br/Cl ratio indicates the evaporation source for the ion. The Na/Cl ratios indicate groundwater is probably controlled by water-rock interaction, most likely by derived from the weathering of calcium–magnesium silicates. The plot of (Ca+Mg) versus HCO3 suggests ions derived from sediment weathering. The plot of Na+K over Cl reflects silicate weathering along with precipitation. Gibbs plot indicates the dominant control of rock weathering. Factor analysis indicates dominance of salt water intrusion, cation-exchange and anthropogenic phenomenon in the study.

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 Ωm. 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.