High-hazard waste, disposal

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 ... 

High -hazard waste any nonexempt waste that generally requires a disposal system more isolating than a dedicated nearsurface facility for hazardous wastes (e.g., a geologic repository). 

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... 

HIGH-HAZARD WASTE (GEOLOGIC DISPOSAL OR EQUIVALENT)... 

High-Hazard Waste. Waste classified as high-hazard would contain such high concentrations of radionuclides or hazardous chemicals that it would not be generally acceptable for nearsurface disposal in a dedicated facility for hazardous waste, but would require disposal in a facility located well below the ground surface. At the present time, geologic repositories are intended for... 

An important characteristic of acceptable disposal facilities for high-hazard waste is that inadvertent intrusion into a facility, such as by drilling, must be unlikely. Therefore, assessments of risk or dose to hypothetical inadvertent intruders based on exposure scenarios that are assumed to occur do not provide a suitable basis for determining acceptable disposals in facilities located well below the ground surface. 

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. 

The best example of this is wastes that are classified based solely on the nature of the generating process or facility e.g., high-level radioactive waste, chemical wastes from certain industries), irrespective of the content and concentration of hazardous substances. This results in resources being used unnecessarily on lower-risk situations when they could be better applied to higher-risk situations (hazardous waste disposal or otherwise). For example, billions of dollars have been spent in managing... 

High-Hazard Waste - Risk from disposal in dedicated near-surface hazardous waste facility would exceed acceptable levels... 

The basic definitions of exempt, low-hazard, and high-hazard waste shown in Figure 6.1 are considered in the following sections. Recommendations on approaches to calculating the risk from waste disposal in the numerator of the risk index and recommendations on specifying allowable risks in the denominator of the risk index for the purpose of classifying waste are discussed in Section 6.3. 

High-hazard, waste. NCRP recommends that high-hazard waste be defined to include any nonexempt waste with concentrations of hazardous substances greater than those that are generally acceptable for disposal in a dedicated near-surface facility for hazardous wastes. High-hazard waste would require a disposal system considerably more isolating than a near-surface facility for hazardous waste. 

Classification as High-Hazard Waste. Waste that would not be generally acceptable for near-surface disposal in dedicated... 

Recommendations on subclassifications of the basic classes of exempt, low-hazard, and high-hazard waste defined in Section 6.2.2 are not developed in this Report. However, NCRP acknowledges that subclassifications of basic waste classes would be reasonable, particularly in the case of low-hazard and high-hazard wastes. NCRP believes that any such subclassifications should be consistent with the physical, chemical, radiological, and toxicological properties of waste, and with requirements for safe management and disposal. NCRP believes that extrinsic and non-risk-related factors, such as the source of a waste, should not be used in subclassifying risk-based waste classifications. 

The exposure scenario described in the previous example of domestic uranium mill tailings was used to classify the high-radium residues. The risk and dose assessments indicated a probability of radiation-induced cancer incidence of about 0.6, potential doses in excess of 10 Sv, and a risk index between 50 and 100. Thus, these residues would be classified as high-hazard waste, even under conditions of perpetual institutional control over near-surface disposal sites, and they would require some form of greater confinement disposal well below the ground surface. This conclusion is consistent with recommendations for disposition of these residues (NAS/ NRC, 1995b). 

Okrent and Xing (1993) estimated the lifetime cancer risk to a future resident at a hazardous waste disposal site after loss of institutional control. The assumed exposure pathways involve consumption of contaminated fruits and vegetables, ingestion of contaminated soil, and dermal absorption. The slope factors for each chemical that induces stochastic effects were obtained from the IRIS (1988) database and, thus, represent upper bounds (UCLs). The exposure duration was assumed to be 70 y. Based on these assumptions, the estimated lifetime cancer risk was 0.3, due almost entirely to arsenic. If the risk were reduced by a factor of 10, based on the assumption that UCLs of slope factors for chemicals that induce stochastic effects should be reduced by this amount in evaluating waste for classification as low-hazard (see Section 7.1.7.1), the estimated risk would be reduced to 0.03. Either of these results is greater than the assumed limit on acceptable risk of 10 3 (see Table 7.1). Thus, based on this analysis, the waste would be classified as high-hazard in the absence of perpetual institutional control to preclude permanent occupancy of a disposal site. 

---