Assessment of Aquifer Vulnerability to Groundwater Pollution by Multi-criteria Analysis in and around East Calcutta Wetlands,West Bengal,India

Abstract

The area lies between Hugli river in the northwest and Bidyadhari river in the east and includes the East Calcutta Wetlands, a Ramsar site. The area is flat in nature and a part of the lower deltaic plain of the Bhagirathi- Ganga river system. The sub-surface geology of the area is completely blanketed by the Quaternary fluviatile sediments comprising a succession of clay, silty clay, sand and sand mixed with occasional gravel. The Quaternary confined aquifer is made up of moderately well sorted sand and reflects fluviatile environment of deposition. Overlay analysis in GIS platform using multiple criteria such as height of piezometric surface above the base of top confining layer, hydraulic conductivity of the aquifer, groundwater velocity, thickness of top confining layer and water quality index have been utilized to understand vulnerability of the aquifer to groundwater pollution. The analysis indicates that 71% of the aquifer of the study area shows high to very high vulnerability to groundwater pollution. The aquifer below the sewage fed ponds and agricultural land shows high vulnerability to pollution. In these areas groundwater abstraction should be controlled to minimize surface water and groundwater interaction. Sensitivity analysis of the aquifer vulnerability assessment with the water quality indicates that in 70% of the total area vulnerability classes have matched with the present water quality distribution of the area. Artificial recharge to aquifer through roof top rainwater harvesting should be made mandatory for high-rise buildings and industries present in and around the wetlands.