Saline Water Contamination of the Aquifer Zones of Eastern Kolkata

A number of saline/brackish water zones are present in the subsurface around the Kolkata metropolis. Mixing of fresh and brackish ground water has created environmental problems in certain areas. Vertical Electrical Soundings (VES) employing Schlumberger configuration have been deployed in the eastern and south eastern Kolkata metropolis for delineating the subsurface saline water zones. Interpretation of VES data has indicated disposition of saline / brackish and fresh water zones at different depth level which would be useful in the ground water management 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 contamination as 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. It is further inferred that the sea water was trapped inland in the Holocene times during marine transgression causing salinity of ground water at several places.