French approach to equivalence in landfill geological barriers
Résumé
Landfill barriers are essential for the protection of groundwater resources. With respect to landfill geological barriers, European legislation (Directive 1999/31/EC) specifies requirements in terms of minimal thickness and maximum permeability. For situations where requirements cannot be met under natural conditions, the Directive introduces the notion of "equivalence". While this notion has been transposed into member state regulations, its interpretation may vary however. This paper summarizes the French interpretation of the Directive with respect to equivalence in landfill geological barriers. Essential aspects of the French approach are the importance of demonstrating limited aquifer vulnerability through a detailed geological and hydrogeological investigation, a safety limit on the reduction of compacted clay barrier thickness and the importance of including qualitative reasoning in the assessment of equivalence in addition to the results of model calculations. The paper pinpoints some shortcomings of model calculations that neglect in particular the fact that reducing barrier thickness increases the risks associated with potential barrier material defects