Total vulnerability estimation for the Tabriz aquifer (Iran) by combining a new model with DRASTIC

Groundwater vulnerability mapping is an important key for improving the planning and decision-making processes in order to prevent groundwater contamination. The main objective of this research was to delineate the groundwater total vulnerable zones within the Tabriz aquifer in the northwest of Iran. So, the groundwater intrinsic vulnerability map was created by overlaying the layouts obtained from the DRASTIC parameters. In this research, a new method for evaluation of specific vulnerability was also applied. In this method, five parameters (density of population, recharge by rivers, agriculture, industry and abstraction) were determined and assigned a suitable weight and rates to each parameter to obtain the specific vulnerability index of the aquifer. Finally, the intrinsic and specific vulnerability maps were combined to develop the groundwater total vulnerability map. The resulting map shows that the east and northeast of the Tabriz aquifer is more vulnerable than the other parts. To confirm the vulnerability distribution, 53 samples of groundwater nitrate concentration were plotted on the resulting total vulnerability map which showed that the northeast and east parts of Tabriz aquifer (High and moderate vulnerability zones) have higher nitrate concentration relative to the rest of the Tabriz aquifer which is located in the low vulnerability zones. Application of DRASTIC+DRAIA method to another aquifer confirmed the good accuracy of this method in evaluation of the total vulnerability.