Submitted to: Water Science and Technology
Publication Type: Proceedings
Publication Acceptance Date: 5/16/1997
Publication Date: N/A
Technical Abstract: Ground-water vulnerability is characterized by using intrinsic and anthropogenic properties. Intrinsic vulnerability is described using pedologic and hydrologic data. Anthropogenic vulnerability uses the amount, timing, and methods of agrichemical applications. An overlay and index method was used in a GIS as well as a process-based modeling method. Both methods centered on defining areas with hydrogeologic characteristics that make the ground water intrinsically vulnerable to surface application of soluble chemicals. Variables from the State Soil Geographic Data Base were used to define three classes of shallow aquifers: unconsolidated alluvial aquifers, other unconsolidated aquifers, and bedrock aquifers. Alluvial aquifers were mapped using flood frequency variables that identified alluvial soils and flood plains. Other unconsolidated aquifers were mapped by selecting soils that have high sand content, and relatively large permeability. The shallow bedrock aquifers were identified by selecting soils where bedrock was less than 1.5 meters from the land surface. Anthropogenic vulnerability properties include the application rates of atrazine, nitrogen fertilizer use rates, and conservation tillage adoption rates. A flexible weighted ranking system was used to provide a composite vulnerability index. Boundaries of the aquifer classes were also intersected with the National Resources Inventory data to extract parameters for input to a leaching model. The robust yet flexible strategy to estimate ground-water vulnerability will be a useful tool to evaluate proposed or contemplated changes in agricultural policies, practices, and land in areas identified as having intrinsic vulnerability to ground-water contamination.