ABSTRACT
Groundwater is the major source for irrigation in the Eastern District of Abu Dhabi Emirate in United Arab Emirates with an area of 15890-square kilometer. The main geomorphologic features are the mountains, piedmonts, and the desert sand dunes. The soil is composed mainly of alluvial and Aeolian deposits poor in organic matter. Fertilizers and agricultural chemical compounds are being intensively used to maintain the productivity of the soil. Consequently, The unconfined shallow aquifer is showing signs of contamination from a wide variety of non point sources (NBS). 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 NBS over large areas in relative low concentrations. Vulnerability maps are used in this case as a tool determines areas where groundwater protection or monitoring is critical. One of the widely used groundwater vulnerability mapping methods is DRASTIC. Developed by the United State Environmental Protection Agency (EPA) as method for assessing groundwater pollution potential (Aller et al., 1987). The DRASTIC system is divided into two portions: the designation of mapable units termed hydrogeologic settings; and the application of a scheme for relative ranking of hydrogeologic parameters herein named as the DRASTIC rating. In the DRASTIC method, seven hydrogeological data layers are required; depth to groundwater, net recharge, soil texture, topography (slope), lithology of vadose zone, lithology of the aquifer, and hydraulic conductivity. Preprocessing of the information included digitizing, data formatting, and geo-referencing. Later each hydrogeological parameter was rated and weighted according to DRASTIC specified ranges. 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. Overlying the seven hydrogeological parameters produced DRASTIC generated final map. The resulting Pesticide DRASTIC vulnerability map indicates that the highest potential areas 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 that 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.
