||Environmental Research Lab., Athens, GA. ;Computer Sciences Corp., Athens, GA. ;Union Carbide Agricultural Products Co., Inc., Research Triangle Park, NC.
A Monte-Carlo numerical simulation procedure for making regional assessments of pesticide leaching has been developed. The procedure uses probability density functions for organic matter, field capacity, and wilting point developed from information on approximately 3,000 soils. Variations in climatic conditions were incorporated by random selection of yearly rainfall data. The procedure was demonstrated for aldicarb applied to corn grown in Ohio. The simulation results indicated that convergence of the 90th, 95th, and 99th percentiles for movement past 0.3, 0.6, 0.9, and 1.5 meters was obtained after 500 simulations. The relative uncertainty associated with these percentiles was approximately 50 percent after 1,500 simulations. The downward movement of aldicarb residues was most sensitive to changes in field capacity. These simulations, coupled with additional soil-specific simulations, indicated no significant movement of aldicarb residues beyond 1.8 meters for applications to Ohio corn.