Submitted to: Water Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 7, 1997
Publication Date: N/A
Interpretive Summary: Three methods for assessing groundwater vulnerability to pesticides and nitrate are being applied to information from the Midwest. Methods that use statistics, map overlays and indices, and leaching models are combined in a geographic information system. Information used in the assessments include soil characteristics, crops, chemical use, tillage and other management practices, hydrologic information, and climatic variables. The results of these assessments are being used to map the potential for contamination of groundwater by herbicides and nitrate. A system with the capability to assess vulnerability from the geographic distribution of crops, land management, and chemical use factors will allow policy makers to estimate the potential effects on groundwater of changes in these factors.
Agrichemicals are significant sources of diffuse pollution for groundwater contamination. Indirect methods are needed to assess the potential for groundwater contamination and to define the extent of contamination at a regional or national scale. Examples of statistical, overlay and index, and simulation modeling methods for groundwater vulnerability assessments are included using a variety of data from the Midwest. The principles of vulnerability include both intrinsic and specific vulnerability of a location. Statistical methods use the frequency of contaminant occurrence, contaminant concentration, or contamination probability as a response variable. Statistical assessments are particularly useful for defining relations among explanatory and response variables. Multivariate statistical analyses are useful for ranking variables critical to estimating water-quality responses. Overlay and index methods involved intersecting maps of intrinsic and specific vulnerability properties and indexing ranging from equal weighting of variables to sophisticated scores and weights. While these methods provide insight into causes of contamination, they do not completely incorporate processes affecting vulnerability. Process-based models simulate contaminant transport and are distinguished from other methods in their potential to predict contaminant transport in both space and time. An example linking a one-dimensional leaching model to a geographic information systems (GIS) to define a regional metamodel is being developed to assess vulnerability in the Midwest. Comprehensive assessments of groundwater vulnerability will require the application of multiple approaches to address a variety of questions, available data, and scales of assessments.