reflected in the interpolated values of the spatial and nonspatial attributes.

Dozier (1992) points out the synergism between model development—that is, for the purposes of this discussion, assessment techniques—and data collection efforts. He observes that ''Modeling and data collection each drive and direct each other. Better models illuminate the type and quantity of data that are required to test hypotheses. Better data, in turn, permit better and more complete models and new hypotheses." Most research efforts to date have been concerned primarily with the representation of environmental processes involved in contaminant transport and transformations. Considerable progress has been made in development of increasingly sophisticated simulation models. However, less attention has been paid to collection, entry, and management of the data required to estimate the model inputs at the appropriate spatial/temporal scales. The need for appropriate computing environments (i.e., integration of data bases, model computations, display of model outputs) needed in vulnerability assessments has also received little attention. These limitations have resulted in models (or techniques) that may describe relevant processes at a local scale (e.g., field plots), but are impractical to implement at larger spatial scales (e.g., watersheds, regional, national). On the other hand, paucity of data and a lack of understanding of the relevant processes at the requisite spatial and temporal resolution has led to development of models or techniques that may not be appropriate for larger scales at which vulnerability assessments are being conducted.

Since public funds are limited, many federal agencies currently are interested more in maintaining and improving the usefulness, accuracy, and availability of existing databases than in embarking on new programs of data collection. This chapter reviews the status of existing information, and describes several databases, their availability, and their use in ground water vulnerability assessments. The focus here is on federally developed and managed databases, with some reference to state and local databases. Although many state and local databases may be valuable in helping to assess the vulnerability of ground water to contamination for state, county, and watershed areas, no comprehensive listing of state geographic databases exists. The lack of this information makes it impractical for this committee to specifically cite or assess state and local databases. Appendix A contains a listing of sources of digital resource databases.

Federal Data Management Activities

Multiple federal agencies collect and use spatially-referenced attribute and nonattribute data required for vulnerability assessments. Over the past several decades, many scientists with diverse scientific backgrounds were



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