عنوان مقاله [English]
This study has dealt with the groundwater pollution using Arc GIS 9.3 and has identified the areas with high, moderate, and low pollution risk by the help of modeling and some parameters of the DRASTIC method taking into account the population growth rate in the urban areas. Although DRASTIC is often applied to the large alluvial plains, the contamination rate of the aqufer can be assessed in the urban area with a semi-drastic model if some of DRASTIC parameters are modified and also other effective factors are taken into account. In this study the parameters of depth to water, net recharge, aquifer media, soil media, topography, impact of Vadose zone, and hydraulic conductivity were evaluated to assess the risk of groundwater contamination. The site specific conditions pertaining to the urban areas were also considered; the impact of the texture of surface soil on the contamination of aquifer in the urban areas has been highlighted. Considering the role of urban sewer in aquifer contamination the parameter of population density has also been determined as a vital parameter and has been added to the DRASTIC parameters. In general the findings showed that the most vulnerable areas in Mashhad city include central, southern, and southeastern parts of the city.