Evaluation of aquifer vulnerability to contamination potential using the DRASTIC method

The unconfined shallow aquifer in the Eastern District of Abu Dhabi Emirate in the United Arab Emirates is showing signs of contamination from a wide variety of non-point sources (NPS). Assessing the fate and behavior of the NPS pollutants is a complex environmental problem due to heterogeneity of the subsurface system and the spread of NPS over large areas in relatively low concentrations. Vulnerability maps are used in this case as a tool to determine areas where groundwater protection or monitoring is critical. One of the widely used groundwater vulnerability mapping methods is DRASTIC. In the DRASTIC method, seven hydrogeological data layers are required, i.e., depth to groundwater, net recharge, soil texture, topography (slope), lithology of vadose zone, lithology of the aquifer, and hydraulic conductivity. For each cell, the DRASTIC rating for each input layer was multiplied by the DRASTIC and pesticide DRASTIC weight for that layer and summed to determine the DRASTIC index. The resulting pesticide DRASTIC vulnerability map indicates that the highest potential sites for contamination are along the area between the Jabel Hafit and Oman Mountains and in the northwest of the study area. To the northeast there is a small, rounded area which shows fairly high potential. Elsewhere, low to medium DRASTIC index values are observed, indicating areas of low vulnerability potential. The general DRASTIC index indicates that the potential for polluting groundwater is low. The pesticide DRASTIC index shows that the potential for polluting groundwater with pesticides is greater than with general DRASTIC index pollutants.