Urban geophysical studies on the groundwater environment in parts of Gangetic delta

Mixing of subsurface fresh and brackish/saline water has given rise to poll ution in the aquifer and consequent environmental problems in the urban and semi-urban areas of the Howrah District of West Bengal. Also, overdrawal o f groundwater has adversely affected the water table resulting in increase in salinity and possible threat to the civil structures. In order to sugges t some remedial measures to arrest further deterioration of the environment al problems due to excessive and random pumping of groundwater, vertical el ectrical soundings (VES) using Schlumberger configuration have been carried out at 70 locations. Geoelectrical sections, isoresistivity maps at differ ent depth levels as well as total transverse resistance (TTR) map of the ar ea have been prepared. Analysis of these interpreted sections and maps have been able to (1) ascertain the resistivity and geohydrological characteris tics of the subsurface layers, (2) map the aquifers and saline/brackish gro undwater zones and (3) suggest measures for safeguards against groundwater pollution. Further, prospective groundwater zones and an old channel of Bha girathi river are identified within the highly conducting brackish deltaic area. The lithe-sections brought out by the interpretation of survey data w ould be useful to the city planners for land use, foundation studies and re lated utilities.