French approach to equivalence in landfill geological barriers

Landfill barriers are essential for the protection of groundwater resources. With respect to landfill geological barriers, European legislation (Directive 1999/31/EC) specifies minimal requirements in terms of thickness and reduced 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 approach to the notion of equivalence in landfill geological barriers. Essential aspects of this approach are the importance of demonstrating limited aquifer vulnerability through a detailed geological and hydrogeological investigation, a protective limit to 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 influence of reduced barrier thickness on the risks related to possible barrier material defects.