In Washington State, nitrogen groundwater contamination is a growing concern. Several contaminants have been reported, but nitrogen is the most prevalent and most frequently documented groundwater contaminant in the state. The process has been caused by irrigation development and increased use of fertilizers. A significant concentration of the problem is located in the Quincy-Pasco area (Q-P), where 29% of the wells have exceeded the EPA MCL. A study oriented to provide a long-term quantification of the magnitude of this problem and avenues for mitigation was conducted using a computer simulation-based approach. Cropsyst, a cropping systems simulation model was used to perform the simulations. Interactions between soils, crops, weather, and irrigation and fertilization management scenarios were simulated. The site selected was Richland, WA from where 30 years of weather data were used. A sandy soil was selected as representative. A three-year crop rotation including potato, winter wheat and maize was simulated. The principal conclusions were that management practices and weather variability were the most important factors in determining the potential for nitrogen leaching from the simulated potato system. Precipitation variability modulated the accumulation-leaching cycle producing some large nitrogen leaching events. Excess irrigation did not significantly affect the bulk of nitrogen leaching, which occured principally during fall-winter time. The potato growing season appeared to be the principal contributor to nitrogen leaching due to the use of fertilization rates above the crop requirements and its shallow rooting depth. This study establishes a base of understanding to suggest that fertilization rates could be reduced from the current practices without affecting yields but increasing the risk of yield reductions. Some economic incentivo to account for the environmental risks of nitrogen leaching, may need to be granted to farmers to compensase for this risk