Assessing the Probability of Inadvertent Human Intrusion. P. K. Black, L. P. Mathai, M. D. Neptune, M. M. Hooten, and K. J. Black, Neptune and Company, 1505 15th Street, Suite B, Los Alamos, NM 87544
The potential risk to human health from inadvertent intrusion into buried radioactive waste may be found to be unacceptable using standard risk assessment procedures that assume that such an intrusion occurs. However, assuming such an intrusion occurs may be overly conservative and may not adequately account for important site characteristics. Proper accounting for site characteristics results in a model that generates an expected risk as the product of the consequence of inadvertent intrusion and the probability of inadvertent intrusion. A number of factors may impact the probability of inadvertent intrusion. For example, if waste is buried sufficiently deep the mechanisms by which inadvertent intrusion can occur are limited; remoteness of the burial site impacts the potential for any form of intrusion; institutional control of the burial site impacts the availability of the site for intrusion; and, engineering designs may be used to deter intrusion. The example presented considers intrusion by way of drilling for water. Influence diagrams are used to model the various factors that may influence inadvertent intrusion through this mechanism. An elicitation of the model parameters is performed by convening an "expert panel." The inputs from the expert panel are used in the influence diagram model to generate a probabilistic estimate of the chance of inadvertent human intrusion into the buried waste. The approach developed may be applicable to any site for which burial of radioactive or toxic waste is under consideration.