Development and evaluation of GIS-based ArcPRZM-3 system for spatial modeling of groundwater vulnerability to pesticide contamination

The objectives of this study were to develop and evaluate a GIS-based modeling system called ArcPRZM-3 for spatial modeling of pesticide leaching potential from soil surface towards groundwater. The ArcPRZM-3 was developed by coupling a commonly used FORTRAN-based Pesticide Root Zone Model version 3 (PRZM-3) with user-friendly input and output interfaces through links to GIS using customized programming. A Visual PRZM-3 interface simplifies the entry of model inputs and links to the databases of crops, soils, and pesticides. The ArcPRZM-3 produces user-friendly outputs from the PRZM-3 batch simulations in the form of tables, charts, and maps. The Visual PRZM-3 can be used to run a single simulation for site-specific studies or simultaneous multiple simulations for spatial distributed modeling. The ArcPRZM-3 was applied to simulate maximum dissolved bentazon concentration at 0.75 m soil depth for a period of 2 years. These simulation results were used to develop a health risk map for Woodruff County, Arkansas, based on the U.S. Environmental Protection Agency's Lifetime Health Advisory Level (USEPA-LHA) of bentazon in drinking water. The ArcPRZM-3 was evaluated by comparing the bentazon detection data from monitoring wells from the same area with the predicted bentazon health risk map. The results showed that 100% of the wells where bentazon was detected were within the high risk category based on the ArcPRZM-3 predictions. However, uncertainty in the ArcPRZM-3 model and the timing of groundwater well monitoring could both complicate the interpretations of the ArcPRZM-3 simulation results.