geo-scientific indicators for safety

Working Group A was continuation of Working Group B of AMIGO-1, but participants explored more deeply the issues surrounding geo-scientific indicators for safety. The following outcomes were expected. - List different geo-scientific arguments or indicators for safety (with motivation) for various host rocks and sites. Consider dividing the arguments into those that support isolation or retention and discuss their applicability for different time frames. - What actual measurable field evidence supports these arguments/indicators? - What kind of field evidence would go counter to these safety arguments? - What key messages are the most promising in terms of scientific credibility to contribute to the safety case? Possibly examine the same message but in terms of potential ease of communication. The session started with two introductory presentations: - Following the presentations, in discussion the Working Group listed: - Safety Functions where geo-scientific support is needed; - Commonly used chains of argument for supporting these safety functions; - Whether the applicability of the arguments are host rock or site specific and how they apply for different time frames; - Field evidence or other issues that would go counter to the safety arguments; - Key messages most promising in terms of scientific credibility to contribute to the safety case. Overall it was concluded by the Working Group that: - The most important argument is to present a clear understanding of past geological evolution at the particular site, consistent with the global understanding of geological evolution. Efforts should be made to achieve a broad consensus on this from many independent experts. - The supporting arguments are seldom based on a single piece of evidence. It is the chain of arguments rather than individual arguments that is important. - We are primarily interested in 'reasonable' predictability of the geological system. We recognize that most geological systems evolve with time, but all details of this are not needed for demonstrating safety. However, there is a need to find well-reasoned bounds for the future evolution. - Generally, the same type of arguments can be applied for different rock types. The strength of arguments and the time scale of validity, however, vary between host rocks and types. The arguments work better in 'simple' systems. - Sharing experiences between different programmes is crucial in assessing strengths and weaknesses in 'own' arguments. (authors)