This report describes a procedure to develop a risk assessment methodology for contaminated sites with respect to the risk of dispersal in groundwater. The methodology was originally intended for landfills, but is for example also usable for risk assessment of contaminated industrial sites and sludge depots or to determine the priority of remediation. A Geographic Information System database can be constructed from available databases and preliminary modelling studies, which should then be ranked according to a fuzzy logic system, and incorporated into a Decision Support System. The final product, the Decision Support System, is a flexible instrument for making environmental policy decisions where the available data is vaguely defined and/or incomplete.