A decision tree tool supporting the assessment of groundwater vulnerability

The Water Framework Directive and Groundwater Directive aim at preserving and improving the groundwater status. Groundwater bodies are classified as being or not being at risk of failing to meet these objectives. Those at risk are subject to more precise risk assessment where the concept of vulnerability is considered in the pathway part of the source–pathway–receptor scheme. However, no further details on implementation strategies are provided. In order to support groundwater managers and decision-makers in implementation of programs protecting groundwater, a systematic operational approach based on a decision tree is proposed, which leads the user through the stages of vulnerability assessment. First, a problem has to be formulated related to a threatening of the quantitative and/or qualitative status of a groundwater body. Next, the stated problem needs to be related to the intrinsic or specific vulnerability. Methods used for the intrinsic vulnerability assessment belong to two categories: subjective rating and objective methods. Method selection depends primarily on: data availability, knowledge and available resources. A key issue is the lag time associated with transport between a source/event of contamination and the water body. This lag time is primarily controlled by the temporal scale of water flow. It provides information about flow processes and at the same time also about timescales required for the implementation of strategies. Effects of any measures taken cannot be observed immediately but at the earliest after these estimated lag times emphasizing the need to also proactively safeguard groundwater resources and preserve their good status.