Prediction of Pesticide Leaching on a Watershed Basis: Methodology and Application

Abstract

Abstract Methodology consisting of a numerical solute transport model (LEACHM), combined with geostatistical analysis (kriging) and a geographic information system (GIS), was developed to predict and characterize low-level, nonpoint source pesticide contamination of groundwater on a watershed basis. A preliminary test and evaluation of the methodology was conducted by applying it to the prediction of atrazine contamination of groundwater in the Grand River watershed in Southern Ontario. Atrazine loading to the groundwater was predicted to be highly variable spatially (CV = 164%), but low-level (0 to 2.5 mg atrazine/m2/year) and less than 2% of the surface application (150 mg atrazine/2/year). The predicted concentration of atrazine in the groundwater never exceeded the Canadian drinking water guideline of 60 ppb, but exceeded the 3 ppb U.S. EPA standard in about 27% of the watershed area. These predictions were in general agreement with recent groundwater survey results, which found that nonpoint source atrazine contamination of groundwater in the watershed was highly variable spatially and generally low-level, but occasionally exceeding the U.S. EPA standard. Although these preliminary results are encouraging, more development and testing of the methodology is required.