Classification of hazardous wastes

Hazardous waste identification To facilitate the proper identification and classification of hazardous waste, RCRA begins with hazardous waste identification procedures. 

Second, waste that contains hazardous substances is classified based on considerations of health risks to the public that arise from waste disposal. The existing classification systems for radioactive and chemical wastes in the United States are not based primarily on considerations of health risks to the public. Rather, classification of hazardous wastes has been based primarily on the source of the waste or the presence of particular hazardous substances. The absence of risk-based waste classifications has had a number of undesirable ramifications ... 

Over the last several decades, separate classification systems have been developed for radioactive and hazardous chemical wastes based on a variety of considerations, the most prevalent being the source of the waste. These classification systems have served their intended purpose of facilitating development of health-protective strategies for waste management and disposal reasonably well. However, they have exhibited a number of shortcomings and undesirable ramifications, which indicate that a new approach to classification of hazardous wastes would be beneficial. 

This Report is concerned with classification of hazardous wastes. Wastes are materials deemed to have no further beneficial use to their present custodian, although these materials may be useful to others. Unless otherwise indicated, the term hazardous as used in this Report refers to the presence of radionuclides, hazardous chemicals, or both. This term also may refer to certain characteristics of materials that pose a hazard, such as ignitability, corrosivity, or reactivity. 

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. 

This Report is concerned with classification of hazardous waste for purposes of disposal. However, the principles and concepts embodied in the waste classification system could be applied in classifying hazardous materials for any other purpose. The classification system is intended to be applied to hazardous waste prior to disposal. It is not intended to be applied to screening or ranking of contaminated sites, including existing hazardous waste disposal sites, because these activities involve site-specific considerations that cannot be included in a generally applicable waste classification system. However, any wastes exhumed from contaminated sites that then require disposal would be included in the waste classification system. 

NCRP s recommendations on classification of hazardous wastes are intended to address deficiencies and inconsistencies in the separate systems for classification and disposal of radioactive and hazardous chemical wastes in the United States summarized previously. The most important of these include ... 

Each of these issues is addressed in presenting NCRP s recommendations on classification of hazardous waste in the following section. 

Waste classification systems are not transparent or defensible. There exist numerous classification systems for different wastes having a variety of bases and implementation rules that are not tied to any consistent set of principles. As a consequence, the overall classification of hazardous waste is not transparent to... 

Classification of hazardous waste based on risk requires assumptions about allowable risks from exposure to hazardous substances. Therefore, an understanding of current approaches to risk management for radionuclides and hazardous chemicals, especially their differences and how they can be reconciled, is important in classifying waste. 

Fig. 6.2. Decision diagram for classification of hazardous waste using the risk index (RI).

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. 

Despite the best efforts of pollution prevention and recycling programs, hazardous wastes are being, and will continue to be, generated. Classification of hazardous waste is necessary for cost-effective waste management. 

The most appropriate primary basis for classification of hazardous waste is the risk to human health posed by waste. Furthermore, the health risks of primary concern in classifying hazardous wastes are risks to the public that arise from waste disposal, since permanent disposal is the intended disposition of most waste materials having no further use to their present custodian. 

MEHLHAFF, L.C., COOK, T. and KNUDSON, J. (1979). A quantitative approach to classification of hazardous wastes, Solid Waste Manage. 21, 70-86. 

Hazardous Waste Advisement Program Bureau of Regulation and Classification Division of Hazardous Waste Management New Jersey Department of Environmental Protection... 

Management and disposal of the wide variety of hazardous wastes has been aided by the development of waste classification systems. The term waste classification refers to broadly defined waste categories related, for example, to properties of waste materials, potential risks to human health that arise from waste management or disposal, or the source of the waste. Ideally, hazardous wastes in the same class should pose similar risks to human health and, thus, require similar approaches to safe management and disposal. 

The system for classification and disposal of hazardous chemical waste developed by EPA under RCRA does not apply to all wastes that contain hazardous chemicals. For example, wastes that contain dioxins, polychlorinated biphenyls (PCBs), or asbestos are regulated under the Toxic Substances Control Act (TSCA). In addition, the current definition of hazardous waste in 40 CFR Part 261 specifically excludes many wastes that contain hazardous chemicals from regulation under RCRA, including certain wastes produced by extraction, beneficiation, and processing of various ores and minerals or exploration, development, and use of energy resources. Thus, the waste classification system is not comprehensive, because many potentially important wastes that contain hazardous chemicals are excluded, and it is not based primarily on considerations of risks posed by wastes, because the exclusions are based on the source of the waste rather than the potential risk. 

Basic Elements of Hazardous Waste Classification System... 

For the purpose of developing the waste classification system described in Section 1.4.1, a simple method of evaluating risks to the public posed by radionuclides and hazardous chemicals in waste is needed. The term risk generally refers to the probability of harm, combined with the potential severity of that harm. In the context of hazardous waste disposal, risk is the probability of a response in an individual or the frequency of a response in a population taking into... 

NCRP undertook a study of waste classification because of the importance and visibility of hazardous waste management in the United States coupled with the observation that the existing classification systems for hazardous wastes are increasingly complex and inefficient. This determination led to the independently conceived alternative approach to hazardous waste classification described in this Report. 

The principles of waste classification presented in this Report do not address a framework for subclassification of hazardous wastes. However, the relationship of existing subclassifications to the proposed framework is discussed. 

Wastes have been classified for decades for a variety of purposes. This Section discusses the historical development of classification systems for radioactive and hazardous chemical wastes and the resulting classification systems in use at the present time. The relationship between waste classification and requirements for disposal of different classes of hazardous waste is emphasized. The framework for this discussion is the top-level system for waste classification in the United States shown in Figure 4.1. Within this framework, it is first determined whether a waste is nonhazardous (e.g., municipal waste) these wastes are not addressed in this Report. If a waste is deemed hazardous, it is so classified due to the presence of radionuclides or hazardous chemicals. Mixed radioactive and hazardous chemical waste is not a separate class of waste. However, mixed waste has been an important concern as a result of differences in requirements for management and disposal of radioactive and hazardous chemical wastes. Section 4.1 addresses classification and disposal of radioactive waste, and is followed by discussions of classification and disposal of hazardous chemical waste in Section 4.2 and approaches to management of mixed radioactive and hazardous chemical waste in Section 4.3. Finally, Section 4.4 summarizes previous NCRP recommendations relevant to waste classification. 

The states of Washington and California have considered a classification of hazardous chemical waste based on risk and have developed a category of extremely hazardous waste (California, 1999 Mehlhaff et al., 1979 NAS/NRC, 1999b). However, the requirements for treatment and disposal of extremely hazardous waste differ little from those applied to other hazardous waste. Thus, the designation of a class of extremely hazardous waste based on relative hazard has had little effect on waste management and disposal. 

Under current EPA regulations, a chemical waste is either hazardous or it is not, and there is no further classification of hazardous chemical waste with respect to the degree of hazard. Some states have defined classes of hazardous chemical waste (e.g., extremely hazardous waste) but, in practice, the requirements on management and disposal of all hazardous wastes have resulted in essentially the same approaches being used regardless of hazard. When a hazardous chemical waste is mixed with a nonhazardous solid waste, the entire waste is classified as hazardous unless the former is a characteristically hazardous waste that does not contain any listed waste and mixing with the nonhazardous waste removes the hazardous characteristic. 

There are two possible alternatives to using risk directly as the basis for waste classification non-risk-based systems and surrogate systems. Non-risk-based systems could use any conceivable attribute of hazardous waste as a basis for classification, including its source (see Sections 4.1 and 4.2 for examples) or the date it was produced. These bases are at best somewhat related to risk and at worst are totally unrelated. Because of this variable relationship, the use of non-risk-based approaches to waste classification could result in an unacceptable risk if the waste is managed in a way that does not provide adequate long-term protection, or an inappropriate allocation of resources if relatively innocuous wastes are managed in the same way as much more hazardous wastes. 

The existing waste classification systems for radioactive and hazardous chemical wastes clearly are not comprehensive. At a fundamental level, entirely separate and quite different classification systems have been developed for the two types of hazardous waste. In addition, each classification system is not comprehensive in the context of the general type of waste to which each system applies. In the existing radioactive waste classification system, waste that arises from operations of the nuclear fuel cycle is classified separately from NARM waste. The existing classification system for hazardous chemical waste excludes many potentially important wastes that contain hazardous chemicals. 

Unfortunately, however, it is difficult for anyone to fully comprehend the existing classification systems for radioactive and hazardous chemical wastes. These systems are not based on clearly stated principles from which a logical and transparent classification system might follow, and the two systems approach classification and disposal of hazardous waste in different ways. The systems intermix legal and technical considerations in ways that sometimes defy logic. A few examples of the incongruities in the waste classification systems that result in a lack of transparency and difficulties in comprehension are described below. 

NCRP recognizes that if the waste classification system described in this Report is to gain acceptance, it must be broadly compatible with current approaches to management and disposal of hazardous wastes. However, NCRP believes that development of a new waste classification system to address deficiencies in the existing systems should not be constrained by provisions of current laws or regulations... 

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. 

As indicated by the current subclassifications of existing waste classes summarized above, a variety of waste properties could be used to develop meaningful subclassifications of broadly defined waste classes. These properties include, for example, waste volumes, levels of decay heat and external radiation, and the long-term persistence of the hazard posed by waste constituents. Subclassifications of waste classes also could be based on the presence of particular hazardous substances. However, if the broadly defined waste classes are based on risk, as in the classification system proposed in this Report, the intrinsic toxicity of hazardous substances normally would not provide a basis for subclassification, because this property already is accounted for in determining the basic classification of any waste. Examples of possible approaches to subclassifying the basic waste classes are discussed in the following paragraphs. 

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