A procedure is described for making regional assessments of pesticide residue loadings and movement in groundwater underneath and downgradient from treated fields. A Monte-Carlo numerical simulation technique is performed using the Pesticide Root Zone Model linked to a simple groundwater solute transport model. The procedure is useful for evaluating the potential for producing pesticide residues in drinking water wells before actual field applications are made. The procedure was used to assess aldicarb levels in North Carolina groundwater resulting from application of the pesticide to peanuts. Probability density functions for selected soil characteristics were developed using a direct-access soils information data base. Probability density functions for selected groundwater characteristics were developed from available data for the study area. Simulation results indicated that mass fluxes to groundwater exceeded 0.01 and 0.1 kg/ha approximately 6.9 and 1.0 percent of the time, respectively. No fluxes exceeded 0.1 kg/ha at a distance of 60 m downgradient in any of the cases evaluated.