Framework for Risk-Based Waste Classification

This Section presents NCRP s recommendations on a framework for a comprehensive and risk-based hazardous waste classification system. These recommendations focus primarily on the concepts and principles embodied in the new system. Approaches to implementing the waste classification system by specifying quantitative boundaries of different waste classes in the form of limits on concentrations of hazardous substances are discussed in this Section and in Section 6.4.5, and numerical examples are developed in Section 7.1. However, NCRP believes that the task of specifying such boundaries is properly the role of regulatory authorities, and specific recommendations on limits on concentrations of hazardous substances in different waste classes are not presented. 

1978 King and Cohen, 1977). The possibility of defining subclasses of the three basic waste classes is discussed in Section 6.6. 

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Recommended Framework for Risk-Based Waste Classification... 

In most cases, evaluations of ecological impacts are site-specific and, as a consequence, are not considered when establishing a generally applicable waste classification system. These impacts normally are addressed in disposal site selection, design, and operation, and they may be used in establishing waste acceptance criteria for the site. To the extent that ecological impacts can be evaluated generi-cally, NCRP believes that the principles and framework for risk-based waste classification presented in this Report are sufficiently flexible to take them into account. 

Use of the foundations and framework for risk-based waste classification as a blueprint for an improved classification system ... 

Table 1.4—Framework for the recommended risk-based waste classification system. 

This Report culminates in the presentation of the principles and framework for a comprehensive and risk-based hazardous waste classification system. NCRP does not propose a particular implementation of the proposed classification system (e.g., a particular quantification in terms of limits on concentrations of hazardous substances in each waste class) this is most appropriately left to governmental policy organizations. The relationship of the proposed risk-based waste classification system to existing regulations is discussed in Section 7.2. 

A risk-based waste classification system must focus on the inherent characteristics of waste, representative facilities, and generic events, because the system necessarily presumes that specific disposal sites and related waste treatment and disposal technologies have not yet been identified and characterized. NCRP emphasizes that the principles, framework, and implementation details of a risk-based waste classification system do not provide a substitute for site-specific risk assessments. The two most important cases where site-specific risk must be estimated are (1) an assessment of risk for the spectrum of actual wastes at a specific disposal site for the purpose of establishing site-specific waste acceptance criteria, and (2) an assessment of risk posed by a prior waste disposal at a site for the purpose of determining whether the risk is unacceptable and, thus, whether remedial action is required at the site. 

A risk index for waste classification to be used in conjunction with the framework is then developed, the combination of these constituting the recommended risk-based waste classification system and... 

The framework for the comprehensive and risk-based waste classification system developed in this Report is depicted in Figure 6.1 at the beginning of Section 6. Classification of waste is based on specific objectives and the fundamental principle of defining waste classes in relation to acceptable disposal systems, and these lead to the definitions of three basic waste classes. 

The basic element of the recommended framework for a comprehensive and risk-based waste classification system is the assumption that any waste that contains sufficiently small amounts of radionuclides or hazardous chemicals should be classified as exempt, or essentially nonhazardous. Waste that contains greater amounts of hazardous substances then would be classified as nonexempt, and further classification of nonexempt wastes, based also on the amounts of hazardous substances present, would be appropriate. 

The proposed framework for risk-based classification of all radioactive and hazardous chemical wastes developed in Section 6.2.2 represents waste classification in its broadest, most general terms. Thus, this classification system can be viewed as the highest level of a possible hierarchy of hazardous waste classifications (e.g., see Figure 4.2). Further subclassification of these broadly defined waste classes may be desirable for such purposes as protection of workers during waste operations, protection of public health and the environment following waste disposal, and development of efficient methods of waste management taking into account the characteristics of actual wastes. 

In many respects, the foundations and framework of the proposed risk-based hazardous waste classification system and the recommended approaches to implementation are intended to be neutral in regard to the degree of conservatism in protecting public health. With respect to calculations of risk or dose in the numerator of the risk index, important examples include (1) the recommendation that best estimates (MLEs) of probability coefficients for stochastic responses should be used for all substances that cause stochastic responses in classifying waste, rather than upper bounds (UCLs) as normally used in risk assessments for chemicals that induce stochastic effects, and (2) the recommended approach to estimating threshold doses of substances that induce deterministic effects in humans based on lower confidence limits of benchmark doses obtained from studies in humans or animals. Similarly, NCRP believes that the allowable (negligible or acceptable) risks or doses in the denominator of the risk index should be consistent with values used in health protection of the public in other routine exposure situations. NCRP does not believe that the allowable risks or doses assumed for purposes of waste classification should include margins of safety that are not applied in other situations. 

Many details would need to be considered in developing a new waste classification system based on the framework presented in this Report. Assumptions about generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites to be used in classifying waste and the time frames for applying the scenarios would be required. Decisions would need to be made about negligible and acceptable (barely tolerable) doses or risks that would be used in classifying waste as exempt or low-hazard, respectively. 

The purpose of this Report is to set forth the technical principles and framework for a comprehensive and risk-based hazardous waste classification system. In this context, waste is any material that has insufficient value to justify further beneficial uses, and thus must be managed at a cost. Hazardous waste is waste that can be harmful to biological organisms, due to the presence of radioactive substances or chemicals that are deemed hazardous, to the extent that it must be regulated. Hazardous waste excludes material that is simply useless (e.g., typical household trash). This work is comprehensive because it considers all hazardous wastes irrespective of their source.1... 

Section 6 then establishes and discusses the principles and framework for a comprehensive and risk-based hazardous waste classification system in a number of steps ... 

Principles and Framework for a Comprehensive and Risk Based Hazardous Waste Classification System... 

This Section develops NCRP s recommendations on the principles and framework for a comprehensive and risk-based hazardous waste classification system. Implementation of the system also is discussed. These recommendations focus on classification of waste that contains hazardous substances for purposes of permanent disposal. The proposed waste classification system was developed to address deficiencies in the existing waste classification systems discussed in Sections 2, 4 and 5. 

The basic framework for the waste classification system developed in this Report is depicted in Figure 6.1. Starting with the objectives that the classification system should apply to any waste that contains radionuclides or hazardous chemicals and that all such waste should be classified based on risks to the public posed by its hazardous constituents, the fundamental principle of the proposed system is that hazardous waste should be classified in relation to disposal systems (technologies) that are expected to be generally acceptable in protecting public health. This principle leads to the definitions of three classes of waste, and to quantification of the boundaries of the different waste classes based on considerations of risks that arise from different methods of disposal. The boundaries normally would be specified in terms of limits on concentrations of hazardous substances. At the present time, nearly all hazardous and nonhazardous wastes are intended for disposal in a near-surface facility or a geologic repository, and these are the two types of disposal systems assumed in classifying waste. The three waste classes and their relationship to acceptable disposal systems are described in more detail in Section 6.2. 

Previous sections of this Report have discussed concepts, precedents, and technical information that are important to development of NCRP s recommendations on a comprehensive and risk-based hazardous waste classification system. This Section discusses selected aspects of this background information that are critical to establishing the principles and framework for the recommended hazardous waste classification system. The topics discussed involve technical aspects of risk assessment and issues of risk management. 

Limits on amounts of hazardous substances in each waste class would be calculated based on values of the so-called risk index for each hazardous substance in the waste and the composite risk index for mixtures of hazardous substances. For the purpose of describing the recommended framework for a risk-based hazardous waste classification system, the risk index is generally defined as ... 

Process of Implementing the Waste Classification System. Taken together, the framework for waste classification discussed in Section 6.2 and the risk index developed in Section 6.3 and this Section constitute the foundations of a comprehensive and risk-based hazardous waste classification system. Such a waste classification system could be established by regulatory authorities using the following general process ... 

Development and implementation of the comprehensive and risk-based hazardous waste classification system presented in this Report would be facilitated by changes in the current legal and regulatory framework for managing radioactive and hazardous chemical wastes in the United States. A number of examples have been discussed previously in this Report and are summarized below. 

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