This study evaluates pesticide leachability on Long Island, New York, using the Theoretical Groundwater Ubiquity Score (TGUS) model, a theoretically based expansion of the empirical GUS model that includes soil properties, preferential flow, and dynamic degradation processes. Long Island's sandy soils and vulnerable aquifer systems offer a best-case study area for groundwater contamination risk assessment. The research provides improved calculations for the leaching risk of pesticides by introducing a Time of Leaching Risk Period (TLRP). TLRP is designed to forecast pesticides with a high risk of groundwater contamination by identifying a time window after application, following a rainfall that causes leaching risk and groundwater pollution. The results suggest that TLRP reliably predicts the leaching of pesticides in groundwater. Ninety-two percent of the pesticides that leached into groundwater were predicted correctly. One difficulty in the data analysis was that many pesticides were not found in the groundwater samples, including pesticides that were classified as leachers in other studies. Also, many of the pesticides were not applied on Long Island according to the Pesticide Use and Sales Reporting (PSUR) data. Using the PSUR that specified the pesticide use per zip code level in the risk analysis was only partially successful for predicting spatial leaching.