Aquifer vulnerability assessment in the Bengal alluvial tract, India, using GIS based DRASTIC model

In the present study, an attempt has been made to evaluate the aquifer vulnerability in the central part of Bengal alluvial tract, covering 5324 km 2 area by using DRASTIC model. Seven critical hydrogeological factors were taken into consideration. Initially, vulnerability index of individual factors were calculated on the basis of predefined weights and ratings. These indices were further combined to depict the actual vulnerability of the region. The model comprised of seven spatial parameters and their attributes and in handling of such diverse datasets, GIS played a significant role. For the depiction of the subsurface lithological characteristics, subsurface lotho-log data were used to generate 3 dimensional fence diagram of the entire region which was further helped in depicting the aquifer media condition. Entire eastern region of river Bhagirathi, a distributary of river Ganga, showed higher vulnerability index, which was about 29.65 % of the total study area, while the western portion had lesser vulnerability. Along with conventional modeling, map removal sensitivity analysis was also incorporated to examine the impact of different factors on the entire model. Depth to the water and impact of vadose zone were two important factors that contributed 46.93 % of the total variability of the model. Further, the generated model was incorporated with the locations of 156 groundwater samples, collected from the entire region and concentration of arsenic was determined to understand the probable relationship with the generated model through correlation coefficient. The model presented in the paper depicted recent hydrogeochemical condition of the aquifer which might help in further management of the region.