decision makers of the need for or consequences of their actions, to providing direction for allocating resources, to informing decisions about land use activities, to educating the general public about ground water contamination potential. Existing uses of and needs for vulnerability assessments can be grouped into four broad categories. First, assessments can be used in policy analysis and development to identify the potential for ground water contamination and the need for protection and to aid in examining of the relative effects of alternative ways to control contamination. Second, when scarce resources prevent uniform and costly expenditures, vulnerability assessments can be used in program management to allocate resources to areas where the greatest effort is warranted. Third, vulnerability assessments can be used in some instances to inform land use decisions such as site selection, alteration of land use activities to reflect the potential for ground water contamination, or voluntary changes in behaviors of land owners as they become more aware of the ground water impacts of their land-based activities. Finally, and perhaps most important, is the use of vulnerability assessments to improve general education and awareness of a region's hydrologic resources.
Often policy makers will not find the objective, scientific, and accurate product they need for the decisions identified above. Rather, they will find that the usefulness of a vulnerability assessment may be severely constrained by scientific unknowns or lack of suitable data. Hence, policy makers and managers need to become intelligent consumers of vulnerability assessments since the selection and use of assessments are significantly affected by several technical and institutional factors.
Several key factors will affect both the technical conduct of an assessment and its effectiveness in use. The more consideration given to these technical and institutional issues, the more likely are the needs for a vulnerability assessment to be matched with a useful, scientifically-based technique.
Vulnerability assessments can be used to aid in the development and analysis of policies to respond to potential or actual ground water contamination. In this early stage of the policy making process, assessments can be used to predict, at least qualitatively, potential ground water quality outcomes of different policy scenarios. Vulnerability assessments can also be used as a tool in assessing the effectiveness of alternative responses to a problem.