SELECTION AND FIELD TEST OF A PESTICIDE VULNERABILITY ASSESSMENT METHOD FOR COLORADO

In compliance with the United States Environmental Protection Agency’s 1991 groundwater protection strategy, a State Management Plan (SMP) is required to aid each state in managing pesticide contamination to groundwater. As part of this SMP a screening tool is needed for Colorado to delineate highly vulnerable areas of the state. This screening tool will aid evaluations of current soil conditions and land-use practices, allowing potential changes in practices to reduce the potential for contaminating groundwater. A transport-based analytical equation was chosen as the basis for the assessment method and adjusted to allow for input of parameters that were available in the state. Pesticide leachability classifications were also statistically generated to simplify the use of the method. The vulnerability assessment was then displayed spatially in a Geographical Information System (GIS). Land-use practices including tillage, irrigation, and application method were incorporated into the assessment as multiplying factors. These factors acted either to increase or decrease the vulnerability index based on reported effects of the various practices. The final vulnerability values indicate a low, moderate, or high vulnerability to pesticide contamination under current practices. This information can be used to alter farming practices to reduce the vulnerability for a given area. A validation of this method has been completed in Weld County, Colorado. Using 85 wells, the method successfully predicted areas of high vulnerability, with pesticides detected only in areas that were predicted to have high vulnerabilities.