7. Aquifer Vulnerability and Contamination Risk

Water supply systems must be designed in such a way to ensure groundwater extraction sustainability. In addition, the quality of pumped water must also be guaranteed, and this entails protecting the groundwater source from contamination. To do so, it is necessary to identify the physical and hydraulic characteristics of the soil, the unsaturated medium and the aquifer itself that influence the migration of contaminants spilled at the surface towards the aquifer, and hence potentially towards sensitive targets (i.e., drinking water pumping wells). The susceptibility of an aquifer to become polluted following a contaminant spill is called vulnerability, and its assessment is the focus of this chapter. Of the four categories of vulnerability assessment methods, i.e., overlay, index and statistical methods, and process-based simulation models, this chapter presents examples of the former two, which are of easier implementation and are widely used. Overlay methods define aquifer vulnerability on the basis of groundwater circulation and rely on the superposition of maps of the hydrogeologic, structural and morphologic setting. Index methods, instead, are based on the assignment of scores (sometimes weighed) to sets of parameters that are likely to affect the degree of vulnerability. Specific methods of these two categories described in detail in this chapter are the one developed by the Bureau de Recherches Géologiques et Minières in France, the Italian CNR-GNDCI and SINTACS methods, the US-EPA DRASTIC method and the British GOD method. The suitability of different methods is discussed, and how vulnerability assessment can be used to determine the risk of contamination is presented. On this basis, an example of contamination risk reduction strategies is illustrated.