Vulnerability Assessment of Kordkandi- Duzduzan Plain Groundwater Using Calibrated DRASTIC Model

The land use in Kordkandi- Duzduzan plain mainly occurs by agricultural activities so; the possibility of aquifer contaminations is very high by irrigation returned water contaminated with chemical fertilizers. Thus, vulnerability assessment of the aquifer seems to be essential for the land use management and preventing groundwater contaminations of the area. The main aim of this study is mapping the region's vulnerability by DRASTIC method and then calibration of DRASTIC model with nitrate data to improve this method. Groundwater vulnerability affecting factors such as Depth of groundwater, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity, which were prepared with raster format in GIS media. Two nitrate data sets were used for validation and calibration of DRASTIC model. The results showed that the determination coefficient between nitrate concentration and the corresponding vulnerability increased from 0.6783 to 0.7903 by modifying layer weights. Based on calibrated DRASTIC vulnerability map, vulnerability index for the study area calculated between 66.56 to 148.89. The determination coefficient between nitrate concentration values and calibrated DRASTIC vulnerability map were increased in compare with the original DRASTIC map which confirms the validity of calibration process.