Regional estimation of ground water vulnerability to nonpoint sources of agricultural chemicals

The potential for ground water contamination by agricultural chemicals exists in many regions of the world. A collaborative effort between Hungarian and United States scientists has developed a general strategy to estimate the regional vulnerability of ground water to agricultural chemicals. The midwest U.S. and most of Hungary are major agricultural regions with similar hydrogeologic settings. Many areas where ground water provides public drinking water supplies in these regions are vulnerable to ground-water contamination. The vulnerability of shallow, unconsolidated aquifers and thinly-covered bedrock aquifers to agricultural chemicals is being investigated in an initial application of the strategy. This strategy integrates elements of overlay methods of vulnerability estimation, process-based modeling methods, and statistical methods. Strategy steps include: identifying characteristics of ground water needed to classify regional ground water resources; mapping the spatial distribution of aquifer classes (unconsolidated and bedrock) using a regional geographic information system; and estimating the occurrence of agricultural contaminants by applying leaching models to representative conditions in each aquifer class. In the U.S. project, pedologic data bases are being used for both mapping aquifer classes and model input. Estimated vulnerability will be evaluated against data from a regional survey of shallow aquifers recently completed in the Midwest. The Hungarian project is developing new maps of basic hydrogeologic characteristics with data that can be used to model vulnerability of the 1-meter root zone, the unsaturated zone, and the saturated zone.