Exposure Scenarios for Waste Classification

Assumptions about exposure scenarios are required in developing a risk-based waste classification system. These scenarios would be used to calculate potential risks posed by hazardous wastes for purposes of waste classification. An exposure scenario essentially is a set of assumptions about events and processes that could result in exposure of humans. 

In principle, for any type of disposal system that could be assumed for purposes of classifying waste, such as a near-surface disposal facility for hazardous wastes, a multitude of exposure scenarios might be considered. However, NCRP believes that only a single type of exposure scenario should be considered in classifying waste. Specifically, NCRP believes that the concept of a hypothetical inadvertent intruder at waste disposal sites provides a suitable basis for 

The general concern about limiting off-site releases of hazardous substances is the primary reason why classification of waste based on risks to hypothetical inadvertent intruders at waste disposal sites does not provide a substitute for site-specific risk assessments when determining acceptable disposal practices. Nonetheless, experience with risk assessments at near-surface disposal sites for low-level radioactive waste has indicated that, for most radionuclides, disposal limits that provide adequate protection of future inadvertent intruders should provide adequate protection of the public and the environment at off-site locations as well. Exceptions are expected to occur only in unusual cases of long-lived and highly mobile radionuclides. 

Similar conclusions should apply to hazardous chemical waste, especially waste that contains heavy metals. Thus, basing waste classification on scenarios for inadvertent intrusion should not result in large quantities of waste that would not be acceptable for disposal using the intended disposal technology for the particular waste class at well chosen sites. 

The types of scenarios for inadvertent intrusion that could be used in classifying waste are discussed further in Section 6.3.2. 

---