Geophysical Survey for Delineation of Subsurface Saline Water Zones in Southeastern Part of Kolkata Megacity

A number of saline/brackish water zones are present in the subsurface around the Kolkata metropolis. Mixing of fresh and brackish groundwater has created environmental problems in certain areas. Vertical Electrical Soundings (VES) employing Schlumberger configuration have been deployed in the eastern and southern Kolkata metropolis for delineating the subsurface saline water zones. Interpretation of VES data has brought out disposition of saline/brackish and fresh water zones at different depth level which would be useful in the proper drawal of groundwater with minimum risk of saline contamination. Resistivity surveys have also delineated clay formations which act as barriers for saline water percolation or transmission. Aquifer zone at some depths south of Bhangar canal is vulnerable for saline water contaminations large part of this area is occupied by brackish/saline water in the subsurface. It has been found that the area north of the canal does not contain any appreciable saline water in the subsurface and may be considered environment friendly it is further inferred that the saline water was trapped inland in the Holocene times during marine transgressions causing salinity of groundwater at several places.