ASSESSMENT OF GROUNDWATER AQUIFER VULNERABILITY TO SURFACE POLLUTION BY USING GIS-BASED DRASTIC MODEL IN GAZIPUR DISTRICT, BANGLADESH

Gazipur District is located in the Dhaka Division, a part of the floodplain region of Bangladesh, within the Ganges-Brahmaputra-Meghna delta (GBM). Most of the aquifers are localized within the alluvium consisting of thicker sandy units of Pliocene and Pleistocene age. Multi-layered aquifers punctuated by impermeable layers typify water-bearing strata in Gazipur. It is located between 23o˚53’ to 24˚o20’ North latitude and between the Industrial sector 90˚o09’ to 90o˚42’ east longitude with a total area of 1,806.36 km2. It is a growing industrial center with an increase of almost 1.13 million m3/d of water abstracted from the Gazipur district area for domestic and industrial purposes and 0.7 million m3/d for irrigation. The primary reason for excessive groundwater withdrawal is the increased rate of urbanization due to rapid infrastructure expansion, establishment of factories, and housing demands. Domestic and industrial sectors consume the most water in the district, with almost 85% of the urban water collected from groundwater and 15% from surface water. The groundwater reserve has a constant decline of >2 meters per year due to uncontrolled abstraction and chronically reduced recharge. There was a sharp drop in the water table between the years 2002 -2010, with the water slope dropping regularly over each decade. During the 80s the water table used to be at an average of 4 m below the surface. However, over time the water table has dropped almost 4 m below the surface per decade. Since the rate of groundwater recharge is much lower than the rate of drawdown, there is a diminishing trend in the groundwater level (GL) and with the progression of time, GL is also following similar trend. Hence, the cone of depression is becoming laterally extensive and deepening vertically. The vulnerability map was obtained using hydro-geological data layers in the ArcView GIS software environment. The calculated vulnerability values range from 79 to 137. These were classified into three vulnerability classes using the Natural Breaks (Jenks) classification method: low (79–97), moderate (97–117), and high (117–137). The vulnerability map indicates that the southwestern and southeastern parts have high vulnerability, coinciding with urban and industrial settings. It is necessary to link the impact of growing industrialization and urbanization with the deteriorating condition of groundwater.