Modification of DRASTIC Model with Two Different Methods for Assessing Groundwater Vulnerability in Ardabil Plain

Abstract

In the Ardabil Plain, groundwater is one of the most important sources of water supply. Therefore, quality protection and groundwater management are a research priority. Ardabil Plain is in danger due to agricultural activity's excessive consumption of fertilizers in the agricultural sector, livestock, and industrial centers effluent. Therefore, it is necessary to identify and monitor areas with high vulnerability potential. In this study, the vulnerability of the plain is first assessed using the DRASTIC method. The DRASTIC model is a general method and should calibrate in each area. So, this method was modified by two approaches. In the first approach, sensitivity analysis, and in the second approach, the amount of groundwater supply estimated by the WTF method was used. Then the vulnerability of Ardabil Plain was assessed. The results of the sensitivity analysis showed that the DRASTIC model in the Ardabil Plain area is susceptible to the parameters of Impact of vadose zone (I), Depth of groundwater (D), and aquifer media (A). The results also showed that the conventional model of the DRASTIC did not produce acceptable results compared to the Nitrate map. But calculating the amount of water recharge (R) by the WTF method, the correlation between the vulnerability maps and the Nitrate map was about 75%. In the second method, soil parameters (S) and hydraulic conductivity (C) did not have an acceptable correlation with the nitrate concentration in the groundwater of Ardabil Plain. These parameters were removed from the initial equation of the DRASTIC method, and the maps were prepared with the remaining parameters and with new weights and ratings, as a result of which the correlation between the new maps and the nitrate map reached about 30%. According to the WTF modified method for the DRASTIC model, the whole of the Ardabil Plain vulnerability maps in four areas was divided, including medium, high, very high, and infinitely highly vulnerable areas, and 25.8, 47.7, 15.1, and 11.4 percent, respectively.