Waste classification system recommendations

Based on these principles, the hazardous waste classification system recommended by NCRP includes three classes of waste exempt, low-hazard, and high-hazard waste. Each waste class is defined in relation to the type of disposal system (technology) that is expected to be generally acceptable in protecting public health as follows ... 

This Report presents the foundations and technical principles for development of a generally applicable and risk-based hazardous waste classification system. Recommendations on suitable approaches to establishing boundaries of different waste classes are discussed these boundaries could be expressed, for example, in terms of limits on concentrations of hazardous substances. However, a particular implementation of the proposed waste classification system in terms of quantifying the boundaries of different waste classes is not presented. 

The radioactive waste classification system recommended by IAEA differs from the existing classification system in the United States in the following respects. 

Development of the generally applicable and risk-based waste classification system recommended by NCRP would have a number of important implications with regard to current laws and regulations ... 

The hazardous waste classification system recommended by NCRP is depicted in Figure 6.1 at the beginning of Section 6. This proposal was developed with two fundamental objectives in mind. First, all wastes that contain radionuclides, hazardous chemicals, or mixtures of the two should be included in the same classification system. A comprehensive hazardous waste classification system should be developed to replace the separate, and quite different, classification systems for radioactive and hazardous chemical wastes, as well as the separate classification systems for radioactive waste that arises from operations of the nuclear fuel cycle and NARM waste. Second, all hazardous wastes should be classified based on considerations of risks to the public that arise from disposition of the material. In this Report, permanent disposal in a permitted facility for hazardous or nonhazardous waste is the assumed disposition of waste containing hazardous substances that has no further use to its present custodian. An important consequence of these two objectives is that the same rules should apply in classifying any waste that contains hazardous substances. 

The principal elements of an approach to establishing the hazardous waste classification system recommended in this Report should include the following ... 

The primary purpose of this Report is to present NCRP s recommendations on classification of hazardous wastes. The Report is directed at a multidisciplinary audience with different levels of technical understanding in the fields of radiation and chemical risk assessment and radioactive and chemical waste management. Anew hazardous waste classification system is proposed that differs from the existing classification systems for radioactive and hazardous chemical wastes in two fundamental respects. First, hazardous waste would be classified based on considerations of health risks to the public that arise from disposal of waste. Hazardous waste would not be classified based, for example, on its source. Second, the classification system would apply to any hazardous waste, and separate classification systems for radioactive and hazardous chemical wastes would not be retained. In the proposed system, waste would be classified based only on its properties, and the same rules would apply in classifying all hazardous wastes. 

As part of this study, proposed radioactive waste classification systems that differ from the existing classification system in the United States were reviewed and evaluated. Of particular interest is the classification system currently recommended by the International Atomic Energy Agency (IAEA). This classification system and the disposal options for each waste class are summarized in Table 1.2. The basic waste classification system consists of exempt waste, low-and intermediate-level waste, and high-level waste. 

The waste classification system should be based on the distinct concepts of negligible and acceptable ii.e., barely tolerable) risks to the public that arise from waste disposal. Precedents for specifying negligible or acceptable risks that could be used in classifying waste, such as other NCRP recommendations, would be cited, but specific recommendations would not be presented in this Report. 

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

Fig. 1.2. Depiction of waste classes defined in relation to acceptable disposal systems in recommended risk-based waste classification system.

The recommended risk-based waste classification system has important implications in three areas (1) the resulting classification of existing radioactive and hazardous chemical wastes, (2) subclassification of the basic waste classes, and (3) changes in existing laws and regulations that would be required to implement such a classification system. 

As part of this study, NCRP investigated how the recommended waste classification system would affect the current classifications of radioactive and hazardous chemical wastes. The results of this investigation are summarized as follows ... 

Further Development of the Recommended Waste Classification System... 

In addition to the effort required to develop a comprehensive and risk-based hazardous waste classification system based on NCRP s recommendations, several legal and regulatory impediments would need to be addressed. However, the resulting classification system would be more transparent and understandable than the separate classification systems for radioactive and hazardous chemical wastes... 

Section 4 presents detailed information on existing classification systems for radioactive and hazardous chemical wastes, the relationships between waste classification and requirements for waste disposal, and the impacts of waste classification systems on management and disposal of mixed wastes. This Section also summarizes previous NCRP recommendations relevant to waste classification. 

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... 

Section 7 then addresses the implications of the recommended risk-based waste classification system. By assuming key parameters (e.g., values of acceptable risk, characteristics of exposure scenarios) and applying the system to a variety of example waste streams, the question of how existing wastes would be classified in the new system is investigated. This Section also summarizes the legal and regulatory ramifications of the proposed hazardous waste classification system. 

This Section discusses the historical development and current approaches to classification and disposal of radioactive waste. Classification and requirements for disposal of different radioactive wastes in the United States are emphasized, particularly the relationship between waste classification and requirements for disposal much of this discussion is adapted from a previous paper (Kocher, 1990). Proposals for alternative radioactive waste classification systems are reviewed. Classification systems developed by the International Atomic Energy Agency (IAEA) and the relationship between waste classification and disposal requirements in IAEA recommendations are discussed in some detail. Waste classification systems developed in other countries are briefly mentioned. 

Not discussed in this Section are radioactive waste classification systems developed in other countries, particularly in Europe. Waste classification systems in European countries are discussed, for example, in a report of the Commission of the European Communities (CEC, 1990), and waste classification systems in a number of countries have been reviewed by Numark et al. (1995). The waste classification systems developed in other countries often have been based, at least in part, on the source-based classification system in the United States or the various IAEA recommendations discussed in this Section they generally do not include any new concepts of waste classification. 

To address the limitations of the waste classification system described above, new recommendations on waste classification were developed (IAEA, 1994). A particular aim of the new system was to associate waste classes with intended disposal technologies (options), at least to some degree. The recommended classification system includes the following three major classes of waste exempt waste, low- and intermediate-level waste, and high-level waste. These waste classes and the associated disposal options are summarized in Table 4.2 and described as follows. 

In its recommendations, IAEA emphasizes that waste classification, even if it focuses on waste disposal, does not provide an adequate substitute for site-specific safety assessments of particular disposal systems to ensure the acceptability of waste disposal. IAEA also recognizes the role of national authorities in implementing waste classification systems and ensuring the safety of waste disposal, and that different countries may choose to classify waste in different ways depending on their particular situations. However, IAEA believes that, if for no other reason than to facilitate communication, it would be desirable to achieve some level of uniformity of waste classification systems in different countries. IAEA recommends that it is particularly important to obtain an international consensus on the boundary for determining unconditionally exempt material that may be transferred from one country to another, especially for purposes of recycle/reuse. 

This Section briefly reviews previous recommendations of NCRP that are potentially relevant to the development of a risk-based waste classification system. The topics discussed include NCRP s recommendations on radiation protection of the public and the comparative hazards of ionizing radiation and chemicals. 

Application of NCRP Recommendations to Waste Classification. NCRP s recommendations on dose limits and a negligible dose for individual members of the public, and their associated cancer risks, could be used in developing a risk-based waste classification system. Specifically, the dose limits applicable to all man-made sources of exposure combined could be used in establishing concentration limits of radionuclides or hazardous chemicals in dedicated hazardous waste disposal facilities based on assumed scenarios for exposure of the public. Similarly, the negligible individual dose could be used in establishing concentration limits of radionuclides in disposal facilities for nonhazardous waste. These applications are discussed in Sections 6.2 and 6.3 where NCRP s recommendations on risk-based waste classification are presented. 

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. 

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. 

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. 

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. 

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 ... 

The risk index defined in Equation 6.1 (see Section 6.2.1) is intended to provide a measure of the potential risk that arises from disposal of any waste that contains hazardous substances. In Section 6.3, the general definition of the risk index is elaborated and recommendations on suitable approaches to calculating the risk index for individual hazardous substances are presented. For purposes of developing a comprehensive and risk-based waste classification system, a simple method of calculating the risk from disposal of mixtures of hazardous substances is needed. The method must take into account that the allowable concentrations of particular hazardous substances in waste of a given class generally will be lower when multiple substances are present than when only a single substance is present. Such a method is presented and discussed in this Section. 

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. 

This Section provides example applications of the recommended risk-based waste classification system to a variety of hazardous wastes to illustrate its implementation and potential ramifications. Disposal is the only disposition of waste considered in these examples. In Section 7.1.1, a general set of assumptions for assessing the appropriate classification of hazardous wastes is developed, including a variety of assumed exposure scenarios for inadvertent intruders at waste disposal sites and assumed negligible and acceptable risks or doses from exposure to radionuclides and hazardous chemicals. Subsequent sections apply the methodology to several example wastes. 

It is not NCRP s intent to recommend specific boundaries between waste classes. Rather, the examples illustrate that the recommended framework has the potential to be practical and to result in an implementable waste classification system when a variety of plausible assumptions are used. Many assumptions are made in developing the examples. NCRP endorsement or disapproval should not be construed from the use or absence of specific assumptions about exposure scenarios and allowable doses or risks. It is the responsibility of the appropriate regulatory authorities to develop and guide implementation of any waste classification system. 

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