The EPA Office of Pesticide Programs (OPP) Environmental Fate and Effects Division (EFED) uses a tiered approach to risk assessment. The tiered approach screens out low-risk pesticides and focuses refined assessments and resources on pesticides most likely to pose a risk of concern. This approach utilizes modeling in conjunction with available water monitoring data from both surface water and groundwater to compensate for the fact that monitoring data for most pesticides is usually insufficient to estimate exposure to aquatic organisms under all potential use conditions and geographic scales. 

• Evaluation and Use of Water Monitoring Data in Pesticide Aquatic Exposure Assessments (PDF)(6 pp, 82 K)