Waste classification system bases

Development of a waste classification system based on considerations of risks to the public requires assumptions about generic exposure scenarios (i.e., exposure scenarios that are generally applicable at any disposal site). 

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. 

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... 

Establishing a Waste Classification System Based on the Framework and Risk Index... 

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 ... 

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 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. 

Exempt Radioactive Wastes. The radioactive waste classification system in the United States does not include a general class of exempt waste (see Table 1.1). Rather, many products and materials that contain small amounts of radionuclides (e.g., specified consumer products, liquid scintillation counters containing 3H and 14C) have been exempted from requirements for use or disposal as radioactive material on a case-by-case basis. The various exemption levels are intended to correspond to low doses to the public, especially compared with dose limits in radiation protection standards for the public or doses due to natural background radiation. However, the exemption levels are not based on a particular dose, and potential doses to the public resulting from use or disposal of the exempt products and materials vary widely. 

Deficiencies in the Radioactive Waste Classification System. The classification system for radioactive waste in the United States summarized in Table 1.1 is based primarily on the earliest descriptions of different classes of waste that arises from chemical reprocessing of spent nuclear fuel and subsequent processing of nuclear materials that were developed beginning in the late 1950s. These wastes were considered to be the most important in regard to potential radiological impacts on workers. 

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. 

NCRP s approach to addressing these difficulties is to develop a single hazardous waste classification system that is comprehensive and risk-based. 

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. 

Legal impediments to development of a new waste classification system would be ignored. These include, for example, the distinction between radioactive waste that arises from operations of the nuclear fuel-cycle and NARM waste, which is based on provisions of AEA, the distinction between radioactive and hazardous chemical wastes, which is based on provisions of AEA and RCRA, and the provision in the National Energy Policy Act that prohibits NRC from establishing a general class of exempt radioactive waste. 

Thus, NCRP s recommendations focus on the technical foundations for a generally applicable and risk-based waste classification system. 

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.

Risk Index for Mixtures of Hazardous Substances. For the purpose of developing a comprehensive and risk-based hazardous waste classification system, a simple method of calculating the risk posed by mixtures of radionuclides and hazardous chemicals is needed. The method should account for the linear, nonthreshold dose-response relationships for radionuclides and chemical carcinogens (stochastic effects) and the threshold dose-response relationships for noncarcinogenic hazardous chemicals (deterministic effects). 

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. 

A general class of exempt waste, which could be regulated as nonhazardous material, would be established. Development of an exempt class of waste that contains low levels of hazardous substances has been controversial and currently is banned by law in the case of radioactive waste. Some radioactive and hazardous chemical wastes have been exempted on a case-by-case basis, but general principles for exempting radioactive or hazardous chemical wastes have not been established. In spite of these difficulties, however, a meaningful risk-based waste classification system must include a general class of exempt waste. 

Under current laws and regulations, many radioactive and hazardous chemical wastes are classified based on their source, rather than their radiological or toxicological properties. Development of a risk-based waste classification system would require elimination of source-based waste classifications. 

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... 

Numerous formal waste classification systems, or, equivalently, boundaries between classes of waste and rules for using them, have been developed over the years (see Section 4 for an extensive discussion). The bases for the boundaries also are numerous, with the following being the most common ... 

Establishing the boundaries in a risk-based waste classification system requires that one or more values of acceptable risk be specified. The values of acceptable risk are then used to establish the values of parameters that define the boundaries of the different waste classes. The process of establishing the value(s) of acceptable risk is part of risk management. Risk management is an essential aspect of establishing a waste classification system, but it has an important nontechnical component that reflects societal values. 

Report thus, the phrase risk-based waste classification system. The desirability of basing a waste classification system on risk has been recognized for many years (DOE, 1980). While risk will be defined more precisely in subsequent sections, the following general definition is useful at this point (Garrick and Kaplan, 1995) ... 

This means that development of a risk-based waste classification system must consider the events that could result in exposing biological organisms e.g., humans) to hazardous substances placed in a disposal facility, the probability that each event will occur, and the consequences of the event if it does occur. 

Significant portions of existing waste classification systems are not based on the primary objective of ensuring that the risk that arises from waste disposal is acceptable. 

DOE s high-level wastes as if they were among the most hazardous of all radioactive wastes. However, the concentrations of hazardous substances in some of these wastes are similar to those in low-level radioactive waste that is normally intended for disposal in near-surface facilities. In contrast, some chemical wastes that are highly hazardous, compared with other wastes, and nondegradable are being sent to near-surface disposal facilities. Both of these situations occur largely because of the source-based aspects of existing waste classification systems. 

The existing waste classification systems are becoming increasingly complex as additional waste streams are incorporated into a patchwork system that is not based on a consistent set of principles. Some wastes are classified based on their source (i.e., the nature of the process or facility that produces them), some based on their composition, and some based on their physico-chemical characteristics. 

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... 

The waste classification system developed in this Report includes a general class of exempt waste. Waste in this class would contain sufficiently small amounts of hazardous substances that it could be managed in all respects as if it were nonhazardous (e.g., as household trash). NCRP intends that exempt materials could be used or disposed of in any manner allowed by laws and regulations addressing disposition of nonhazardous materials. However, exempt waste would not necessarily be exempt for purposes of beneficial use without further analysis of the risks associated with anticipated uses. Materials could be exempted for purposes of disposal or beneficial use based on similar considerations of acceptable risk. However, based on differences in exposure scenarios for the two dispositions, limits on the amounts of hazardous substances that could be present in exempt materials intended for beneficial use could be substantially lower than the limits for disposal as exempt waste. Thus, disposal may be the only allowable disposition for some exempt materials based on considerations of risk. In addition, some exempt materials may consist of trash, rubble, and residues from industrial processes that would have no beneficial uses and must be managed as waste. 

The discussions in Section 2.1 outline the logic leading to the need for, and scope of, a risk-based waste classification system. Despite this presentation, there is the potential for confusion and misunderstanding concerning the limits of developing the foundations of a risk-based waste classification system and its relationship to other aspects of waste management. The following sections address these limits and relationships. 

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. 

Establishment of a risk-based waste classification system requires that one or more levels of acceptable risk be specified. A determination of acceptable risks depends on societal values, and is a task appropriately left to governmental policy makers and the public. As a result, this Report will not attempt to select or justify specific values for acceptable risk. However, in Sections 6 and 7, values of... 

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. 

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. 

Section 5 discusses the desirable attributes of a waste classification system and evaluates present classification systems with respect to these attributes. These discussions essentially summarize the rationale for the development of a comprehensive and risk-based hazardous waste classification system. 

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