Urban Geophysical Studies on the Groundwater Environment in Parts of Gangetic Delta

Mixing of subsurface fresh and brackish/saline water has given rise to pollution in the aquifer and consequent environmental problems in the urban and semi-urban areas of the Howrah District of West Bengal. Also, overdrawal of groundwater has adversely affected the water table resulting in increase in salinity and possible threat to the civil structures. In order to suggest some remedial measures to arrest further deterioration of the environmental problems due to excessive and random pumping of groundwater, vertical electrical soundings (VES) using Schlumberger configuration have been carried out at 70 locations. Geoelectrical sections, isoresistivity maps at different depth levels as well as total transverse resistance (TTR) map of the area have been prepared. Analysis of these interpreted sections and maps have been able to (1) ascertain the resistivity and geohydrological characteristics of the subsurface layers, (2) map the aquifers and saline/brackish groundwater zones and (3) suggest measures for safeguards against groundwater pollution. Further, prospective groundwater zones and an old channel of Bhagirathi river are identified within [he highly conducting brackish deltaic area. The litho-sections brought out by the interpretation of survey data uould be useful to the city planners for land use, foundation studies and related utilities.