Hydrogeologic Studies on the Regional Scale: Risk Assessment and Decision Analysis

Doktorsavhandling, 1999

Regional hydrogeologic studies are important components of environmental policy-making and as a basis of large construction projects. The structure of hydrogeologic studies on the regional scale is often complex, with a large number of steps and considerations. The aim is to provide sufficiently accurate results to meet the objectives of each specific step. The precision of the results is dependent on the data utilised and, subsequently, the selection of adequate input data is crucial. The steps involved include defining objectives, compilation of existing information, design of pre-investigations, modelling and evaluation of both data and results. These studies are commonly iterative, where two or more steps are repeatedly performed. Not only aspects of the hydrogeologic system must be considered, but also other environmental and economic issues. Inevitably, uncertainty is inherent in all hydrogeologic studies which implicates that economic risks cannot be ignored. Therefore, if the uncertainties are not properly accounted for, decisions of low cost-efficiency may be taken. In this thesis, existing, available data from several sources have been evaluated for uses in early stages of hydrogeologic studies with emphasise on conceptual modelling. Simulations of uncertainty in existing soil and land-use data have been performed on the European scale for risk assessment. Furthermore, a conceptual framework for risk-based decision analysis was developed and applied in two study areas to analyse the importance of: (1) hydrogeologic uncertainties, and (2) the valuing of groundwater resource in the process of evaluating the societal economic relevance of alternatives to reduce groundwater nitrate and aluminium contamination. The actions designed for nitrate and aluminium reduction included: (1) alternative agricultural practices, and (2) alternative atmospheric emission scenarios for nitrogen, sulphur and ammonia. Results show that uncertainty of existing, available data in the studied cases is typically large. However, the accuracy can be considered as sufficient to meet the objectives of many hydrogeologic studies conducted in the early stages, in particular to increase conceptual understanding of the studied hydrogeologic environment. In the risk-based decision analysis, hydrogeologic uncertainty and the valuing of groundwater have considerable impact on the results. The economic uncertainty increases with higher groundwater values. Despite the large degree of uncertainty inherent in the decision analysis, the results indicate that the suggested approach is useful and feasible for environmental policy-making. Furthermore, the described conceptual framework for risk-based decision analysis provides a means of finding the most cost-effective alternative, handling complex information, improving communication between stakeholders of different backgrounds regarding societal decision-making on the European level and displaying the degree of uncertainty.