Dramatic increase in the use of pesticides since the World War II has helped to make the United States the largest producer of the food in the world. However this has also raised many concerns about potential adverse effects on the environment and human health. About 1.1 billion pounds of pesticides are used each year in the United States for agricultural production (USGS, 1999). The greatest potential for adverse effects of pesticides is through the contamination of the Earth's hydrologic systems. Water is considered one of the primary media in which pesticides are transported. The transport of a chemical compound in the environment also depends on its persistence (USGS, 1999). Microorganisms do not break down some pesticides in the natural environment. For example, DDT and cholorodane can remain in soil, water, and animal tissues for years and even decades. Some pesticides, such as Carbyl, are relatively unstable in water and break down to other compounds in days. The environmental monitoring programs of the mid-70s have revealed widespread detection of organic chemicals (e.g., pesticides) and microbial pathogens (e.g., bacteria and viruses) in the nation's ground water. Extensive herbicide use in agricultural areas, accounting for about 70 percent of total national use of pesticides, has resulted in widespread occurrence of herbicides in agricultural streams and shallow ground water (USGS, 1999). The highest rates of detection for the most heavily used herbicides-atrazine, metolachlor, alachlor, and cyanazine- were found in streams and shallow ground water in agricultural areas (USGS, 1999). Non-point source pollutants (NPS) such as pesticides, nitrates, salts and trace elements are often the result of agricultural activities and can cause ground water contamination. Nearly 50% of the drinking water needs and 40% of the irrigation water needs in the United States are met using ground water supplies (USGS, 1999). Non-point source pollution is considered to be the major contributor to surface and ground water contamination worldwide (Duda, 1993). It is estimated that 30-50% of the earth's surface is affected by NPS pollutants (Pimental, 1993). As the world's population continues to grow, it is important thing to meet the world's food demand. However sustainable agriculture needs a balance among crop production, environmental impact, and economics. There is a need to optimize crop production while maintaining economic stability and minimizing impacts on the environment. Yet, agriculture remains the single greatest contributor of NPS pollutants to soil and water resources. The degradation of ground water particularly by NPS pollutants has become a growing public concern primarily because of the concern over long-term health effects. Non-point source pollutants pose a tremendous threat to soil and ground water resources because of the areal extent of their contamination and the difficulty of effective remediation once soils and ground water are contaminated (Corwin, 1996). According to National Water-Quality Assessment (NAWQA) Program, about 50 percent of the wells sampled contained one or more pesticides, with the highest detection frequencies in shallow ground water beneath agricultural and urban areas and the lowest frequencies in major aquifers, which generally are deeper (USGS, 1999). Although streams and rivers are more vulnerable than ground water to rapid and widespread contamination, ground water contamination is extremely difficult to reverse because of the slow rate of ground water flow (USGS, 1999). Fig. 1 illustrates the percentage of pesticides found in fish, streams and shallow groundwater (USGS, 1999). The President's Water Quality Initiative was launched in 1989 due to the concern that agricultural activities contribute to the contamination of the ground water. The purpose of this initiative was to relate agricultural activities to ground water quality and develop farm management programs to protect ground water. Therefore it justifies the need to develop ArcPRZM-3. Assessing the environmental impact of NPS pollutants at different scales is a key component to achieve sustainability of agriculture. Assessment involves the determination of change of some constituent over time, which can be measured in real time or predicted with a model. Real-time measurements could reflect current and past activities, and a model may predict future trends. Because of the volume of the needed data, the spatial heterogeneity of the earth's surface and subsurface, and the complexity of solute transport processes, a multidisciplinary and integrated approach is required to assess the impacts of NPS pollutants (Corwin, 1996). The objectives of this study were three-fold. First to develop a user-friendly modeling system for pesticide transport, called ArcPRZM-3, through coupling integrated spatial Geographic Information System (GIS) and Pesticide Root Zone Model (PRZM-3). The use of advanced information technologies in this system will help users generate and synthesize the required information quickly, easily, and cheaply. The system will also be able to display results in the form of maps, charts, and tables. The second objective of the study was to evaluate the effectiveness of ArcPRZM-3 to predict pesticide contamination in ground water of Woodruff County, Arkansas. To accomplish this, ArcPRZM-3 was tested for two pesticides, bentazon and acifluorfen, and the results were compared with actual well monitoring data. Sensitivity and uncertainty analyses were performed to evaluate the system. The third objective was the application of ArcPRZM-3 in three counties in the Arkansas Delta and its comparison with DRASTIC model. The purpose was to determine the applicability and efficiency of a coupled GIS simulation model on a regional scale as compared to a simple overlay and index method.