Groundwater vulnerability assessment in Savar upazila of Dhaka district, Bangladesh — A GIS-based DRASTIC modeling

Abstract

Revealing the status of groundwater contamination before it reaches a critical level is crucial to effective groundwater management. With this in mind, the research primarily aims to identify vulnerable aquifers of Savar upazila (sub-district), a highly industrialized zone of Dhaka district, by analyzing existing hydrological attributes through a GIS-based DRASTIC model. Seven DRASTIC attributes viz., depth to aquifer, net recharge, aquifer media, soil media, topography, impact of vadose zone, and hydraulic conductivity of aquifer were created and integrated using a weighted-overlay method in a GIS interface. The resultant vulnerability map reveals that about 34% of the study area is in low-vulnerability zones, 45% is moderately vulnerable and 21% highly vulnerable to groundwater contamination. The results also reveal that aquifers contiguous to floodplain areas are highly vulnerable whereas those adjacent to terrace areas have low vulnerability. The model outcomes affirm that the depth to aquifer, topography and soil media had the greatest link to vulnerability. A positive correlation was also noticed, while validating the final DRASTIC map, between the vulnerability classes and the three groundwater quality parameters-electrical conductivity, nitrate and chromium concentrations. Though the current levels of contamination are within permissible limits, the risk of further contamination cannot be ruled out, and is indeed rather likely. Information on the current status of contamination of groundwater might act as an early warning for the responsible authorities to take prudent measures to prevent further stress on this invaluable resource.