A method for a precautionary assessment of aquifer vulnerability to pollution

The assessment of aquifer vulnerability to pollution is an important tool for protecting groundwater resources. Vulnerability may be underestimated due to uncertainties affecting this assessment, with potential adverse consequences for pollution prevention policies; in order to reduce the likelihood of vulnerability underestimation and protect the efficacy of such policies, a precautionary vulnerability value may be used as a reference for planning and design. This paper illustrates an approach for selecting such a precautionary vulnerability value, applied to the vulnerability point count system SINTACS R5 developed by the Italian National Research Council. The method uses possibility theory and fuzzy mathematics in order to: 1) define quantitative models of the uncertainties ; including those of a subjective nature ; regarding the parameters and partial ratings used to assess vulnerability; 2) to propagate the uncertainty to the final degree of vulnerability; 3) to calculate how much each vulnerability degree among the possible ones can be considered precautionary, starting from the definition of the level of precaution related to each degree. Vulnerability maps that correspond to different precaution degrees and can be generated automatically are illustrated, and some possible criteria for selecting an optimal degree are outlined.