Mapping of Ground Water Vulnerability Using DRASTIC and Empirical Assessment of Unsaturated Zone in GIS, Varamin Plain

The vulnerability of ground water pollution in Varamin plain, located in the southeast of Tehran, has been evaluated using DRASTIC method in GIS environment. The DRASTIC parameters have been calibrated with respect to migration of nitrate ion in the aquifer. The weights of depth to groundwater, soil, unsaturated zone, and hydraulic conductivity have been modified accordance to observed data of nitrate concentrations. This study produced a pollution potential map for the area and classified 9% as having very low pollution potential, 38% as having low pollution potential, 26% as having moderate to low pollution potential, 17% as having moderate to high pollution potential, 8% as having high pollution potential, 1.94% as having very high pollution potential, and 0.06% as having complete vulnerability. The northeast and southwest areas of Varamin plain have more pollution potential rather than middle parts of the plain. The unsaturated adsorption coefficients have been modeled as surface 2D parameter in GIS environment for evaluation of vulnerability of aquifer with respect to adsorb able contaminants. Assessment of adsorption in the unsaturated zone shows that the west and south of Varamin plain have very high pollution potential and the northwest areas of the plain have lowest vulnerability indices. The central parts of the plain have moderate to high adsorption indices and therefore have lower risk of ground water pollution. In general, the results of DRASTIC have relative correlation with the results of the model of unsaturated zone evaluation, in Varamin plain.