LAUSR

In recent years DRASTIC method has been used to map groundwater vulnerability to pollution in very areas. As this method is used in different places without any evolution, it cannot bring up the effects of pollution type and characteristics. Hence, the method needs to be calibrated and reformed for a specific aquifer and pollution. In the present resent research, the rates of DRASTIC parameters have been reformed so that the vulnerability potential to pollution can be determine more exactly. The new rates were calculated using the relationships between each parameter and the nitrate concentration in the groundwater. The suggested methodology was applied to Asadabad aquifer located in western of Iran. The measured nitrate condensation values were used to correlate the pollution potential in the aquifer to DRASTIC index. The results showed that the modified DRASTIC is better than the original method for nonpoint source pollutions in agricultural zones. Application of the new rates, a new DRASTIC map was expanded that shows that 2.1 percent of the area fall in high vulnerability class. This percentage was 2.5 before the modification. The assessed area was 34.2% and 58.19% for moderate class and, for low vulnerability class, 63.7% and 31.39% respectively, before and after using of the new rates.