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Inventory and Characteristics of DOE Mixed Waste

To support the selection of treatment technology and waste forms, the inventory and characteristics of stored waste material must be known with a reasonable degree of confidence. This section reviews documentation provided by the Mixed Waste Focus Area (MWFA) and discusses the adequacy of the present knowledge about the inventory of mixed waste under responsibility of the Department of Energy (DOE) Office of Environmental Management (EM). Two sources supplied most of the inventory information: the National 1995 Mixed Waste Inventory Report (MWIR) (DOE, 1995a) and the Mixed Waste Focus Area Technical Baseline Report (DOE, 1996a, 1997a).

The MWFA estimates that the quantity of mixed low-level waste (MLLW) and mixed transuranic (MTRU) waste presently in EM's inventory is 167,000 cubic meters (m3).1 Approximately two thirds of the waste is MLLW and the remainder is MTRU. Projections of mixed waste generation during the next few years indicate that the inventory will increase to about 250,000 m3. This does not include the waste that will require treatment as a result of remediation of closed sites under the Comprehensive Environmental Response, Compensation, and Liability

1  

The measure of waste by volume rather than weight is industry practice. All waste quantities and percentages given in this report are volumetric.



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--> 2 Inventory and Characteristics of DOE Mixed Waste To support the selection of treatment technology and waste forms, the inventory and characteristics of stored waste material must be known with a reasonable degree of confidence. This section reviews documentation provided by the Mixed Waste Focus Area (MWFA) and discusses the adequacy of the present knowledge about the inventory of mixed waste under responsibility of the Department of Energy (DOE) Office of Environmental Management (EM). Two sources supplied most of the inventory information: the National 1995 Mixed Waste Inventory Report (MWIR) (DOE, 1995a) and the Mixed Waste Focus Area Technical Baseline Report (DOE, 1996a, 1997a). The MWFA estimates that the quantity of mixed low-level waste (MLLW) and mixed transuranic (MTRU) waste presently in EM's inventory is 167,000 cubic meters (m3).1 Approximately two thirds of the waste is MLLW and the remainder is MTRU. Projections of mixed waste generation during the next few years indicate that the inventory will increase to about 250,000 m3. This does not include the waste that will require treatment as a result of remediation of closed sites under the Comprehensive Environmental Response, Compensation, and Liability 1   The measure of waste by volume rather than weight is industry practice. All waste quantities and percentages given in this report are volumetric.

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--> Act2 regulations, which will add significantly to the total waste volume. While these additions will increase the total inventory, the current inventory is believed to be representative of all the various types of mixed wastes that must be treated and stabilized (Kolts, 1996).3 In its current inventory, EM distinguishes the following waste groups: (1) waste waters, (2) combustible organic waste, (3) homogeneous solids, sludges, and soils, (4) debris, and (5) unique wastes. The following page gives a list of these groups and describes the materials that comprise each group. To characterize individual waste types, the MWIR-1995 database uses 119 codes (DOE, 1995a). These codes cover acidic aqueous liquids, pond and other sludges, waste solvents, discarded equipment, discarded protective clothing, paint wastes, used air filters, discarded chemicals, lead shielding, contaminated soil, debris, and many other categories. The waste is stored in containers such as large storage tanks, 200 liter drums, boxes (up to 4 m3), and numerous small containers of various shapes, sizes, and methods of construction. The containers are made from various types of wood, metal and plastic, but the specific container materials are not included in MWIR-1995. The inventory includes wastes from 45 locations, however the following seven locations account for 96% of the total (DOE, 1995a). The locations of these seven sites are shown on Figure 1. Idaho National Engineering and Environmental Laboratory—35% (includes much of the MTRU waste); Oak Ridge, including the laboratory, K-25 site and Y-12 plant—30%; Rocky Flats Plant—9%; 2   Enacted by Congress in 1980 to require cleanup of sites contaminated by past activities, including "closed" sites where contamination by hazardous and toxic chemicals exists. 3   Present-day operating practice applies the concept of waste minimization to production processes. In addition to process changes to reduce the quantity of waste generated, this concept includes segregation of wastes to simplify treatment and allow recycle of useful materials. Waste minimization is required by DOE order 5820.2A that is described in Chapter 3. It is expected that current and future wastes will be easier to treat than the older wastes, which as noted in this report, are heterogeneous and inadequately characterized.

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--> List of Mixed Waste Groups that Comprise the EM Inventory Waste Waters Aqueous Liquids and Slurries. This group includes waste waters and slurries having acidic, basic, and neutral characteristics, as well as cyanide-containing waste waters and slurries. Combustible Organics Organic Liquids This group includes aqueous streams containing both halogenated and nonhalogenated organic compounds, as well as pure organic streams containing halogenated and nonhalogenated compounds. Organic Homogeneous Solids Organic particulate matter (resins, organic absorbents), organic sludges (biological sludges, halogenated and nonhalogenated sludges), and organic chemicals are included in this group. Inorganic Homogeneous Solids and Soils Inorganic Homogeneous Solids These wastes include particulate matter—ash, sandblasting media, inorganic particulate absorbents, absorbed organic liquids, ion-exchange media, metal chips/turnings, glass/ceramic materials, and activated carbon. Inorganic Sludges Waste water treatment sludges, pond sludges, off-gas treatment sludges, plating waste sludges, and reprocessing sludges constitute this group. Other Inorganic Waste This group includes paint waste (paint chips and solids, paint sludges), salt waste containing chlorides, sulfates, nitrates, and metal oxides/hydroxides, and inorganic chemicals. Solidified Homogeneous Solids This group includes soil, soil/debris, and rock/gravel. Debris Metal Debris Metal debris with or without lead or cadmium constitute this category. Inorganic Nonmetal Debris Concrete, glass, ceramic/brick, rock, asbestos, and graphite debris are included in this category. Organic Debris This category includes plastic/rubber, leaded gloves/aprons, halogenated plastics, nonhalogenated plastics, wood, paper, and biological debris. Heterogeneous Debris Composite filters, inorganic and organic debris, asphalt, and electronic equipment constitute this category. Unique Waste Lab Packs Organic, aqueous, and solid lab packs and scintillation cocktails are included. Special Wastes Included in this category are elemental mercury, elemental hazardous metals (activated and non-activated lead, elemental cadmium), beryllium dust, batteries (lead acid, mercury, cadmium), reactive metals (bulk and reactive metal-contaminated components), pyrophoric fines explosives/propellants, and compressed gases/aerosols. All others Materials placed in a final waste form are included in this category. SOURCE: (DOE, 1995a)

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--> Figure 1 The seven locations where 96% of the total mixed waste inventory is stored. SOURCE: DOE, 1995a.

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--> Savannah River Site - 8%; Los Alamos National Laboratory - 5%; Portsmouth Gaseous Diffusion Plant - 5%; Richland Site - 4%. The MWFA has identified 58 radionuclides that account for most of the radioactivity in the present inventory of EM's mixed wastes. Because the shorter-lived radionuclides have mostly decayed, those remaining range from 60Co having a half-life of 5.27 years to 232Th having a half-life of 14 billion years. While the radionuclide content varies widely among waste streams, the available data indicate that it is unusual for more than about six or eight nuclides to be present in any individual stream. In accord with the U.S. Environmental Protection Agency (EPA) regulations, much of EM's waste inventory has been declared hazardous based on the processes that produced it, or other historical knowledge, but actual analyses are generally not available. Data from MWIR-1995 show that more than 80% of the inventory has been declared hazardous because it is suspected to be contaminated with waste solvents, electroplating and metal treating wastes, or waste from leachate treatment (DOE, 1995a). Solvent contamination is believed to occur in two thirds of the inventory. Lead contamination is suspected in more than half the inventory. Wastes regulated by the Toxic Substance Control Act (TSCA), such as polychlorinated biphenyls (PCBs), are suspected in about 6% of the mixed waste inventory, but may be present in up to half of the combustible organic waste.4 TSCA-regulated combustible wastes can be burned only in incinerators with a TSCA permit to operate. In addition to the available inventory data contained in MWIR-1995 (DOE, 1995a), the database includes a qualitative description of MWFA's confidence in the data. The confidence levels for the waste type, and the hazardous and radioactive waste components are presented as "high," "medium," "low" or, in a few cases, not available. Overall the confidence level in the type of waste is rated medium or high for about 84% of the inventory. Confidence in the radioactive component 4   The Toxic Substances Control Act (TSCA) includes special management provisions for handling and cleaning up materials that are considered to present imminent hazards. TSCA is described in Chapter 3.

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--> characterization is medium or high for 64% of the inventory. In the absence of actual analyses for most of the hazardous components, high or medium confidence in their characterization drops to about 29% of the overall inventory. The portion of the inventory for which confidence levels on both hazardous and radioactive components is medium or high is only about 25%. In the remaining 75%, confidence in one or both components is rated as low (or not available). In spite of the uncertainties for the hazardous components in the inventory, the percent of the inventory that displays EPA hazardous characteristics can be estimated from MWIR-1995. Table 1 summarizes the hazardous characteristics of the entire inventory. Almost 60% of the inventory displays the toxicity characteristic, essentially all of which is due to heavy metals (58%).5 Lead is present is most of this inventory (54%). Mercury contamination, which is difficult to treat as will be discussed in Chapter 4, is present in about 26% of the inventory. It should be emphasized, however, that the confidence level in the hazardous component characterization is generally low. Possible measures to reduce the amount of waste that must be treated as mixed waste, such as better waste characterization and the establishment of "below regulatory concern" criteria are described in the committee's findings and recommendations in the following section. The EPA's procedure for de-listing waste and its proposed Hazardous Waste Identification Rule are mentioned in Chapter 3. Findings, Discussion, and Recommendations The committee found that EM's mixed waste inventory is sufficiently characterized that conceptual design of treatment processes and waste form selection can proceed. However, the inventory is insufficiently characterized for detailed engineering design of treatment processes or process optimization. Better characterization is necessary to reduce risks of technology failures and allow cost-effective design and operation of treatment processes. 5   The Toxicity Characteristic Leaching Procedure is discussed in Ch 3.

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--> TABLE 1 Hazardous Characteristics as a Percent of the EM Mixed Waste Inventory Hazardous Characteristic Percent of Inventory Volume Ignitable 22 Corrosive 21 Reactive 7 Toxic Chemicals 59 Heavy Metals 58 Mercury 26 Lead 54 Chromium 31 Cadmium 27 Organics 30 Non-specific Listed Contamination 82 Solvents 64 Electroplating Waste 34 Cyanide 15 Leachate Treatment 11   SOURCE: DOE (1995a). The mixed waste inventory is stored in a variety of forms and conditions. Inventory diversity results from past waste management practices (e.g., poor segregation of wastes, and discharge to ponds or retention basins that now must be remediated) and past storage practices (e.g., drums of material having only generic identification of contents). The MWFA is confronted with complex, often poorly defined mixtures of waste materials.6 6   The committee noted that at present there is no lower limit for contamination by radioactive nuclides below which the waste would simply be considered as hazardous, i.e., not mixed. Definition of de minimis, below regulatory concern, and exemption levels has been discussed by U.S. and international regulatory agencies for many years (IAEA, 1996). EPA is proposing a new risk-based "Hazardous Waste Identification Rule" that would allow waste containing only small amounts of hazardous waste to be removed from its system for regulating hazardous wastes. Although the committee did not receive information that would allow it to quantify the effects of such definitions, it appears that proper selection of lower limits for contamination could reduce the total volume of material considered as mixed waste, resulting in considerable cost savings.

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--> Although qualitative information sufficient, in the committee's view, to support conceptual design of treatment processes is available for most mixed waste streams, quantitative analyses are incomplete, as discussed in this chapter. Considerable effort will be required to quantify the radiological and hazardous constituents in many waste streams. MWFA appears to have reasonably good descriptive knowledge about the waste types (e.g., paint waste or pond sludge), and fair knowledge about its radioactivity characteristics (e.g., nuclides present and radiation levels), but MWFA is lacking specific analytical knowledge about the hazardous chemical content of the waste. In the absence of chemical analyses, much of EM's waste has been declared hazardous based on the process that produced it or other historical knowledge. Hazardous waste requires special, licensed facilities for treatment, storage and disposal (see Chapter 3) that significantly increase costs. Actual analyses may show that some of this declared inventory is not hazardous and thus reduce overall costs. The MWFA has recognized the need for improved waste characterization by listing it as the number one priority on its list of technology needs.7 The committee agrees that characterization should have high priority in the MWFA. However, the committee also recognizes that detailed chemical analysis of such heterogeneous wastes can be very expensive and time consuming and that the nature and storage conditions of the waste present risks to operators who must obtain representative samples for analysis. The committee, therefore, recommends the following: The MWFA should develop simplified methods to characterize the waste, with emphasis on nondestructive examination and assay techniques.8 According to available inventory data, emphasis should be placed on developing better methods to determine heavy metals and solvent contamination in the waste. 7   The MWFA's technical needs list is reproduced in Appendix C and is discussed in the committee's findings in Chapter 4. 8   The committee is aware that similar efforts are underway by EM to certify compliance with acceptance criteria for waste disposal at the Waste Isolation Pilot Plant. Radiography and waste drum head-space testing are included.

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--> The MWFA should continue to develop, demonstrate, and encourage deployment of techniques and procedures to ensure that all new waste streams are adequately characterized. The MWFA should strive for a balance between the risks, benefits, and cost of detailed characterization and the risks, benefits, and cost to adapt or to develop more robust treatment technologies that can handle a wide variety of waste compositions. Both characterization and technology development efforts should be pursued. Neither detailed characterization nor robust technology provides the total answer to treatment of the EM inventory.