Low-hazard waste

2 Low-Hazard Waste. Waste classified as low-hazard would be generally acceptable for disposal in a dedicated near-surface facility for hazardous wastes. Limits on concentrations of hazardous substances in low-hazard waste would be derived based on an assumption that the risk or dose to a hypothetical inadvertent intruder at a disposal site should not exceed acceptable (barely tolerable) levels. 

Acceptable (barely tolerable) risks or doses used to classify low-hazard waste could be established based on a variety of considerations, consistent with the different approaches to risk management for radionuclides and hazardous chemicals described in Section 1.5.3. For noncarcinogenic hazardous chemicals, NCRP recommends that an acceptable dose should be set at a nominal threshold for deterministic responses in humans obtained as described in Section 1.5.5.3, or slightly below the threshold (e.g., by a factor of two or three) if an additional margin of safety is warranted. For 

As an alternative, multiples of RfDs established by EPA could be used to define acceptable (barely tolerable) doses of noncarcinogenic hazardous chemicals, because RfDs normally are intended to be well below nominal thresholds for deterministic responses in humans. However, the cautions about using RfDs discussed in the previous section, especially when RfDs are based on data of poor quality, also apply in establishing acceptable doses. As in establishing negligible doses of noncarcinogens, NCRP prefers an approach in which acceptable doses are based directly on nominal thresholds in humans and application of small safety factors, as appropriate, to promote transparency and consistency in waste classification. 

Acceptable risks or doses for radionuclides and chemical carcinogens also could be established based on considerations of unavoidable risks from natural background as noted previously, these lifetime risks are about 10 2. For example, an acceptable risk could be set at a value corresponding approximately to the geographical variability in the background risk, because people normally do not consider this variability in deciding where to live. 

The assumed disposal systems for exempt waste and low-hazard waste both involve near-surface disposal, and either type of waste often would be emplaced sufficiently close to the surface that inadvertent intrusion into the waste could occur as a result of normal human activities. However, there are differences in the two types of disposal systems that should be taken into account in developing appropriate scenarios for inadvertent intrusion. Disposal facilities for low-hazard waste frequently include engineered barriers to deter inadvertent intrusion, impenetrable waste forms, or deliberate emplacement of more hazardous wastes at locations where access to the waste during normal human activities would be less likely. Most importantly, as noted previously, current plans call for institutional control to be maintained over hazardous waste disposal sites for a considerable period of time after facility closure, which allows for substantial 

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The Agency s aulhorily lo regulate certain high-volume, low-hazard wastes (known as "special wastes was restricted... 

Eventnal reclassification of these types of low-hazard wastes could increase the qnantities of regulated wastes severalfold. 

Low-hazard waste any nonexempt waste that is generally acceptable for disposal in a dedicated near-surface facility for hazardous wastes. 

Waste that exceeds concentration limits for exempt waste would be classified as low-hazard if it poses no more than an acceptable (i.e., barely tolerable) risk to a hypothetical inadvertent intruder at a dedicated near-surface disposal facility for hazardous wastes, with the important condition that an acceptable risk or dose used to determine low-hazard waste should be substantially higher than a negligible risk or dose used to determine exempt waste. 

Waste that exceeds concentration limits for low-hazard waste would be classified as high-hazard. 

High-hazard waste Any nonexempt waste that generally requires disposal system more isolating than dedicated near-surface facility for hazardous wastes1 Concentrations of any hazardous substances that exceed limits for low-hazard waste... 

In developing generic scenarios for inadvertent intrusion into near-surface disposal facilities used to determine limits on concentrations of hazardous substances in exempt and low-hazard waste, consideration must be given to the question of how far into the future the scenarios should be applied, as well as the earliest time at which the scenarios could occur. This issue arises because the potential risk posed by some radionuclides e.g., uranium) increases with time, due to the long-term buildup of radiologically significant decay products, and some hazardous chemicals could be transformed over time into more hazardous forms. NCRP believes that scenarios for inadvertent intrusion used to classify waste should be applied over a time period consistent with the time period for applying standards for protection of members of the public beyond the boundaries of waste disposal sites. 

The risk index for any hazardous substance in Equation 1.1 or 1.2 (see Section 1.5.1) is calculated based on assumed exposure scenarios for hypothetical inadvertent intruders at near-surface waste disposal sites and a specified negligible risk or dose in the case of exempt waste or acceptable (barely tolerable) risk or dose in the case of low-hazard waste. Calculation of the risk index also requires consideration of the appropriate measure of risk (health-effect endpoint), especially for carcinogens, and the appropriate approaches to estimating the probability of a stochastic response per unit dose for carcinogens and the thresholds for deterministic responses for noncarcinogens. Given a calculated risk index for each hazardous substance in a particular waste, the waste then would be classified using Equation 1.3. 

Most radioactive waste currently classified as low-level waste and most hazardous chemical waste would be classified as low-hazard waste, based on the expectation that these wastes would be generally acceptable for disposal in dedicated near-surface facilities for hazardous wastes. A possible exception is hazardous chemical waste that contains relatively high concentrations of heavy metals, which could be classified as high-hazard waste. 

Most uranium and thorium mill tailings that contain elevated levels of naturally occurring radionuclides could be classified as low-hazard waste, but only under conditions of perpetual... 

Low-Hazard Waste - Risk from disposal in dedicated near-surface hazardous waste facility would not exceed acceptable (barely tolerable) levels... 

Nonexempt Waste. NCRP recommends that nonexempt waste—i.e., waste that contains amounts of radionuclides, hazardous chemicals, or both greater than the allowable amounts in exempt waste—be placed in one of two classes, called low-hazard waste and high-hazard waste. 

Low-hazard waste. NCRP recommends that low-hazard waste be defined as any nonexempt waste that is generally acceptable for disposal in a dedicated near-surface facility for hazardous wastes. Examples of such facilities include licensed or permitted for disposal of low-level radioactive waste under AEA (1954) or disposal of hazardous chemical waste under Subtitle C of RCRA (1976). 

The use of an acceptable (barely tolerable) risk to classify nonexempt waste can be justified, in part, on the following grounds. Disposal facilities for exempt and low-hazard waste both are located near the ground surface, and many scenarios for inadvertent intrusion into municipal/industrial landfills for nonhazardous waste also would be credible occurrences at disposal sites for low-hazard waste. However, these types of scenarios should be less likely to occur at hazardous waste sites, compared with sites for disposal of nonhazardous waste, given the intention to maintain institutional control and records of past disposal activities for a considerable period of time after closure of hazardous waste sites and the possibility that societal memory of disposal activities will be retained long after institutional control is relinquished. Thus, the risk to future inadvertent intruders at dedicated hazardous waste disposal sites, taking into account the probability that exposures according to postulated scenarios would actually occur, should be comparable to the risk at disposal sites for nonhazardous waste. 

Establishing an acceptable risk or dose. There also are a number of precedents for establishing an acceptable (barely tolerable) risk or dose of substances that cause stochastic responses for the purpose of classifying waste as low-hazard or high-hazard. For radionuclides, the annual dose limit for the public of 1 mSv currently recommended by ICRP (1991) and NCRP (1993a) and contained in current radiation protection standards (DOE, 1990 NRC, 1991) could be applied to hypothetical inadvertent intruders at licensed near-surface disposal facilities for low-hazard waste. This dose corresponds to an estimated lifetime fatal cancer risk of about 4 X 10 3. Alternatively, the limits on concentrations of radionuclides in radioactive waste that is generally acceptable for near-surface disposal,... 

In general, calculation of the risk or dose from waste disposal in the numerator of the risk index in Equation 6.2 or 6.3 involves the risk assessment process discussed in Section 3.1.5.1. As summarized in Section 6.1.3, NCRP recommends that generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites should be used in calculating risk or dose for purposes of waste classification. Implementation of models describing exposure scenarios for inadvertent intruders at waste disposal sites and their associated exposure pathways generally results in estimates of risk or dose per unit concentration of hazardous substances in waste. These results then are combined with the assumptions about allowable risk discussed in the previous section to obtain limits on concentrations of hazardous substances in exempt or low-hazard waste. 

For the purpose of illustrating how the composite risk index in Equation 6.6 would be used to classify a hypothetical waste, it is helpful to simplify Equations 6.4 and 6.5. This is done by assuming that the summation over all responses (index r) has been calculated, that only one waste classification boundary represented by the index j is being considered (i.e., the boundary between exempt and low-hazard waste, based on a negligible risk, or the boundary between low-hazard and high-hazard waste, based on an acceptable risk), and that the modifying factor (F) is unity. Further, the calculated dose in the numerator of the risk index is denoted by D and the allowable dose in the denominator is denoted by L. Then, the composite risk index for all hazardous substances in the waste, expressed in the form of Equation 6.6, can be written as ... 

Establish generic exposure scenarios for inadvertent human intrusion into a municipal/industrial landfill for disposal of exempt waste and intrusion into a dedicated near-surface facility for disposal of low-hazard waste. 

Divide the negligible and acceptable doses of each hazardous substance by the corresponding doses per unit concentration, resulting in limits on the concentrations of each hazardous substance in exempt and low-hazard waste, respectively. Waste that contains concentrations of hazardous substances greater than the limits in low-hazard waste would be classified as high-hazard. 

Promulgate tables of concentration limits of hazardous substances that cause stochastic or deterministic effects in exempt and low-hazard waste and the rules for using the tables. For example, concentration limits of substances that cause deterministic effects should include an identification of the organ or organs at risk from exposure to each substance, so that the risk index for multiple substances that cause deterministic effects can be evaluated properly. 

The question of appropriate time frames for risk assessments to be used in classifying waste is discussed, in part, in Section 6.3.2, where the types of exposure scenarios that could be used in classifying exempt and low-hazard waste are described. These discussions and other considerations by NCRP may be summarized as follows ... 

By defining low-hazard waste as any radioactive or hazardous chemical waste that is generally acceptable for disposal in a dedicated near-surface facility for hazardous waste, NCRP expects that this class would include most radioactive waste presently classified in the United States as low-level waste. Because low-hazard waste would include radioactive waste from any source, this class also should include most NARM waste. 

NCRP also expects that many hazardous chemical wastes presently generated in the United States would be classified as low-hazard waste. Indeed, for hazardous chemical waste, low-hazard waste essentially would correspond to the one waste class presently defined in the United States—namely, solid hazardous waste (see Section 4.2.1). 

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