Groundwater Vulnerability Zonation Using DRASTIC and SI models in GIS (Case Study: Ajabshir Plain)

Ajabshir Plain is located in the eastern Azerbaijan province and in the north-west of Iran. This plain provides the water for drinking, agriculture, and industry in Ajabshir city. In this research, regarding the hydrology and hydrogeology conditions of the study area, the vulnerability of the aquifer against the pollutants was zoned using DRASTIC and SI models and geographical information system. In DRASTIC model 7 factors including depth to water, net recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity are used to generate the vulnerability map. The vulnerability assessment of aquifer is also affected by 5 factors including depth of groundwater, net recharge, lithology of the aquifer, topography and land use in the SI model. After preparing information layers and rating in ArcGIS software, the final map of aquifer vulnerability to pollution was prepared through integrating layers. Regarding the SI vulnerability map, about 2.24% of the study area is located in very low vulnerability area, 5.27% in low vulnerability area, 45.08% in moderate to low vulnerability area, 39.09% in moderate to high vulnerability area, and 8.3% in high vulnerability area. According to the DRASTIC model, 13.4% of the study area was allocated to very low vulnerability, 55.43% to low vulnerability, 28.69% to moderate to low vulnerability, and 3.08% to moderate to high vulnerability. The evaluation of two models by TDS element indicated that SI model (correlation coefficient= 0.76) is more accurate than DRASTIC model in terms of preparing vulnerability map for the study area. Moreover, both prepared vulnerability maps showed that conservation of groundwater resources of Ajabshir plain by managers and planners is necessary to control and prevent the aquifer from pollution and its stability for the future generation.