C. Elliot Foutes, Dr. Kenneth Czyscinski, Al Colli and James Gruhlke
Office of Radiation and Indoor Air
Radiation Protection Division
USEPA

The potential benefits to be derived from using alternative disposal technologies for the disposal of mixed wastes minimally contaminated with radionuclides are being investigated by the Office of Radiation and Indoor Air (ORIA). While this assessment has only just begun, initially there appear to be benefits from such an approach. These benefits are in the form of savings for generators of these wastes by way of reduced disposal costs and increased regulatory flexibility for environmental restoration efforts. This preliminary analysis suggests that this can be done in an environmentally protective manner with no trade-offs in public health protection, given the use of proper controls and licensing requirements.

This paper discusses approaches being considered for the disposal of mixed waste in alternative disposal facilities. Mixed waste, conventionally and when used in the context of this paper, refers to Atomic Energy Act (AEA) radioactive waste with a hazardous chemical component under the purview of the Resource Conservation and Recovery Act (RCRA). Such hazardous components exhibit hazardous characteristics or are listed as hazardous under RCRA. This analysis focuses more specifically on mixed waste minimally contaminated with radionuclides generated by the commercial sector.

At such low concentrations, the overall hazard is presumed to be primarily from the hazardous component. Therefore, this paper examines the potential benefits of using disposal technology prescribed by RCRA hazardous waste disposal regulations for the disposal of minimally contaminated mixed waste. It should be noted that this effort is in a preliminary stage and does not represent EPA policy or guidance but rather an initial scoping of the technical, economic, and regulatory aspects of such an approach.

In a related effort, the Agency has, for some time, been looking into the potential of using low-level radioactive waste technology for the disposal of chemically hazardous materials. As a part of the Hazardous Waste Identification Rulemaking (HWIR), EPA's Office of Solid Waste is considering the disposal of certain chemically hazardous mixed waste with minimal concentrations of hazardous constituents in Atomic Energy Act regulated low-level waste disposal facilities . The approach described in this paper is a logical extension and perhaps mirror image to that effort, i.e. the use of alternative disposal technology for mixed wastes. The approach the Agency is examining is currently intended to be restricted to mixed wastes and not to encompass the broader and higher activity spectrum of waste compositions currently captured under the classification of low-level wastes (1).

The Agency is considering alternative disposal technologies to alleviate well-known mixed waste management and disposal problems in the commercial sector. Numerous commercial radioactive waste generators produce small volumes of mixed waste, some with very low levels radioactivity. Such waste fall under a dual regulatory framework, having to meet both the AEA and RCRA requirements. Management and storage costs are high and disposal options are limited. The RCRA hazardous waste disposal technology is a proven and tested approach for the disposal of chemically hazardous wastes, and if it can provide and environmentally sound approach for the disposal of mixed waste, a significant new disposal alternative would become available for commercial mixed waste.

The possibility also exists that at some point some use might be made of RCRA disposal technology to assist in addressing the national challenge to restore numerous facilities and lands contaminated by mixed wastes. This effort is particularly challenging with the large variety of existing contaminated site scenarios, some lacking clear-cut cleanup solutions, and decreasing Federal budgets. One of the activities of ORIA is to investigate new and innovative approaches for dealing with the massive, expensive job of cleanup and associated waste disposal. We believe it is important that we use a common sense approach with an eye towards regulatory streamlining and more cost-effective disposal solutions. This paper will discuss some of the approaches ORIA is considering to further these goals.

The contemplated facilities, at a minimum, would have a liner designed, constructed, and installed to prevent any migration of waste out of the facility to the adjacent subsurface soil, ground water or surface water during its active life, including the closure and post-closure periods. The liner must be constructed of materials with appropriate chemical properties and sufficient strength and thickness to prevent failure due to pressure gradients (including static head and external hydrogeologic forces), physical contact with wastes or leachates, climatic conditions, and the stress of installation and daily operation. The liner would be placed upon a foundation capable of providing support to the liner and resistance to pressure gradients above and below the liner, prevent failure of the liner due to settlement, compression, or uplift; and installed to cover all surrounding soils likely to come in contact with wastes or leachates.

Also mandated would be a leachate collection and removal system (LCRS) that would collect and remove leachates from the facility. The LCRS would be constructed of materials chemically resistant to wastes and expected leachate constituents. The materials would also be of sufficient strength and thickness to prevent collapse under the pressures exerted by overlying wastes, cover materials, and by any equipment used at the facility. In addition, the LCRS would be designed and operated to function through the scheduled closure of the facility. The facility would contain a surface water run-on control system.

Mixed wastes in the commercial sector arise largely from the nuclear power industry, hospitals and radio pharmaceutical development, manufacturing, R&D work, laboratory analyses, routine maintenance, and decontamination activities. A national profile of mixed waste volumes and characteristics developed by the Nuclear Regulatory Commission indicates that, based on 1990 practices, commercial facilities generated several thousand cubic meters of mixed waste and held in storage an equally large amount (2). Much of the commercial mixed wastes are from small volume generators. The paucity of treatment and disposal options for these generators poses operational problems, increased management costs and prolonged storage of these wastes.

Commercial activities do not create new hazardous substances, rather mixed waste are generated when chemicals are used in medical research or assay, as cleaning agents or solvents and become commingled with radioactive materials. Finally, the types of mixed waste and the amounts being generated are known to vary significantly among industry sectors and practices.

The national profile was developed by conducting a survey of facilities. It should noted that the generation rates, as reported by the NRC, were weighted on a national basis to account for facilities which did not respond to the survey and those that were not queried during the survey. The profile divides mixed waste properties and generation into five sectors of generators including: nuclear power plants, medical facilities, academic institutions, government institutions and facilities, and industrial facilities.

For each sector, the waste streams were categorized into 10 groups. The grouping also provides a listing of the most often reported radionuclides. The waste streams are summarized in Table I and are compiled from NRC data (3).

Tables II and III summarize the results of the profile for all five categories of waste generators and are also abstracted from NRC data. The summary presents estimates of generation rates and volumes held in storage and treated. As shown in table II, the amounts that were treated are nearly equal to the amounts being generated nationally. However, this profile varies significantly among waste generator sectors.

Table III presents waste volume distributions by waste streams. Of the amounts of waste being generated and treated, liquid scintillation fluids capture about 72 and 84% of the total, respectively. Three waste streams account for nearly 65% of the waste volume being held in storage. In decreasing volume, they are cadmium wastes (35%), liquid scintillation fluids (17%), and chlorinated fluorocarbons (12%).

Based on 1990 industry practices, the commercial sector generated about 3,950 m³ of mixed waste and held another 2,120 m³ in storage. In addition, waste generators treated about 3,990 m³ of mixed waste, using both on and off-site facilities. A total of about 500 m³ of mixed waste being generated annually cannot be treated or disposed of using conventional methods. This waste is being stored indefinitely. This waste volume is an extremely small fraction of that being generated by DOE, under current and future Environmental Restoration Program activities.

The intent of the disposal approach being described here is to increase the available options for mixed waste disposal, while protecting public health with controls on the disposal process. Results of the preliminary modeling assessments reported here indicate that RCRA’s hazardous waste disposal technology can offer long-term protective disposal of mixed waste if radionuclide waste concentrations are maintained below defined limits. In implementing such an alternative disposal option, requirements for maximum waste radionuclide concentrations would be established and used essentially as waste acceptance criteria. For wastes containing a chemically hazardous waste component as well, i.e., mixed wastes, requirements for hazardous waste disposal would also apply (for example, treatment requirements for mixed wastes as required under the hazardous waste regulatory regimes). The radionuclide component of mixed wastes would require controls to be in place under AEA requirements. An NRC licensing process could be envisioned where the controls necessary for radioactive wastes are also imposed. In this manner, assurance would be provided that disposal would be governed by requirements and limitations appropriate to the nature of the wastes involved. Commercial generators might make use of this new disposal approach taking into account practical and economic considerations.

Since RCRA-C disposal cells are designed to provide waste containment and isolation, many of the requirements for satisfying the 10 CFR Part 61 licensing process for low-level radioactive waste disposal may already be satisfied through the RCRA permitting process. With a recognized overlap in waste containment requirements between RCRA and the Part 61 licensing process, a more streamlined NRC licensing process for such a disposal facility may be possible. This is in total congruence with the spirit of current Federal efforts to redesign the regulatory process and minimize the regulatory burden, as recommended by the National Performance Review. Since the approach addresses the presence of hazardous materials, it recognizes that the disposal technology being considered here is already governed by Federal and State authorities under RCRA. Accordingly, this disposal approach is not seen as potentially relieving the commercial sector from having to comply with all applicable regulatory requirements addressing the presence of hazardous materials. State authority would ultimately determine where and how disposal of theses wastes could be executed in RCRA facilities. RCRA authority would be exerted over the hazardous components of these wastes, and controls imposed by the NRC licensing process (particularly waste inventory tracking and control) would apply to the radionuclides in these wastes. It should be noted that the approach would probably limit the annual dose to any member of the public from all exposure pathways, including ground water. The application of a very low dose limit would seem necessary, given that the approach permits the disposal of mixed waste using an alternate technology designed to meet different performance objectives than those required for radioactive wastes alone. A lower dose limit would also take into account that for a given site or region, there is the possibility of colocating multiple sites, which could result in cumulative exposures. Wastes containing radionuclide concentrations in excess of what would be permissible under this approach would have to be disposed of either at a low-level waste disposal facility that accepts mixed waste in accordance with existing standards, treated, or held in storage.

To examine the long-term protection offered by RCRA hazardous waste disposal technology, computer modeling has been conducted to project performance under a variety of climatic and hydrogeologic conditions. Using the basic RCRA-C cell design, the scenarios modeled included both an anticipated case scenario and a post-closure intrusion scenario. For the anticipated performance scenario, rainfall infiltrates the disposal trench after a predetermined time (simulating eventual failure of the liners); removes and transports radionuclides through the ground water pathway to a receptor well located 50 meters from the disposal cell boundary. In the intrusion case, a well is drilled adjacent to the disposal trench into the underlying geologic media. In addition to the ground water pathway, doses to the off-site receptors are calculated from surface spillage of the wastes during facility operation. To perform these assessments, the PRESTO-EPA-CPG code (4) was used. This code has been extensively tested and reviewed and provides sufficient capabilities to assess the doses arising from the scenarios under consideration.

The ultimate intent of the modeling was to determine what limiting radionuclide concentrations could be present in the wastes to assure public health protections. The modeling approach is a typical "inverse problem" wherein a desired answer is assumed (a maximum reference dose level to the receptor - 1 mrem/yr) and the conditions necessary to arrive at this answer are derived, in this case the maximum concentration of radionuclides in the wastes. These concentrations could then be considered as part of the acceptance criteria for wastes that could be safely disposed of using the alternative technology. For scoping calculations, an assumed waste radionuclide concentration of 1 pCi/gm for each of 70-80 radionuclides reported in environmental restoration wastes was used. The resultant dose to the receptors was calculated using the PRESTO code, from which waste concentrations that would produce a reference dose level of 1 mrem/yr are calculated by scaling the calculated dose numbers and waste radionuclide concentrations to the reference dose level.

To assess the projected performance of RCRA hazardous waste technology disposal cells, site-specific hydrologic and geologic data for 10 sites across the country were compiled from published sources and used to model each site individually. The 10 sites were selected based the existence of sufficient site characterization data in the technical literature. These sites range from arid locations to humid sites and cover a broad range of real-world hydrogeologic conditions.

The results of these modeling calculations for the anticipated case indicated that the ground-water pathway is by far the dominant source for doses to the receptor. Doses from spillage and surface transport were calculated to be very low and in the near-term. Results showed that doses to the receptors arise from only a small number of the 70-80 radionuclides modeled. Over the period of hundreds of years doses to the receptors arise primarily from I-129, Tc-99, Np-237 and isotopes of uranium, with the arid sites showing the lowest doses reflecting the lower rates of rainfall and longer distances between the disposal trench bottoms and the ground water tables below the cells. For some humid climate sites, small doses also result from C-14. These results are consistent for both the expected case and the intrusion case, with higher doses for the intrusion case as would be expected. Although higher doses are found for the intrusion case, the differences are not dramatic. This observation indicates that the scenario for expected performance is very conservative in that little dilution/dispersion of the contaminants takes place between the disposal cell and the well located 50 meters away. Sensitivity analyses of the modeling scenarios show that a relatively small number of parameters strongly influence the calculated doses. These parameters include the fraction of disposal cell cap failure assumed over time, permeability of the wastes, ground water velocity and aquifer thickness, partition coefficients ( Kd numbers) in the vadose zone and its permeability, and the distance to the receptor well. Identifying these "driver" parameters is important for assessing the technical strength of the disposal approach, determining the need for modifications to the standard disposal trench design or siting requirements to improve performance, and other considerations involved in assessing how well the approach could be implemented in practice. Further modeling efforts will examine the effects of these "driver" parameters in more detail relative to implementation of the approach.

From the dose assessments under the expected case and post-closure intrusion scenarios, maximum waste radionuclide concentrations can be calculated and compared against "generic" radionuclide concentrations in low-activity waste streams in the DOE and commercial sectors. These "generic" waste compositions can be derived from descriptive waste characterization data for wastes in the DOE sector (2, 5, 6). Preliminary results of such comparisons suggest that the alternative disposal sites in arid regions offer better containment potential than sites in humid regions, not a surprising conclusion considering the relatively limited rainfall and generally larger vadose zones in humid versus arid areas. To increase the potential use of this disposal approach in humid areas, additions to the basic RCRA hazardous waste disposal design are being examined, such as modified cap designs, ground water flow modification techniques, sorption barriers, etc. Research and development activities on these techniques are underway and the results of these efforts will be examined for their potential application to the disposal approach described here.

As part of the overall review of the alternative approaches to the disposal of mixed waste, a generic analysis was performed of the benefits of select alternatives. The focus here, as in the rest of the paper, is the hypothetical use of a RCRA C type cell design for the disposal of mixed wastes. This analysis was meant to support an a priori assumption that an effort in this area might produce significant reductions in waste disposal costs.

There are, of course, both quantifiable and non-quantifiable benefits of this disposal approach. And in this instance, the benefits that we have not been able to address in a quantitative fashion are equally as important, if not more so, than the quantitative benefits. These benefits are believed to include providing the commercial sector the flexibility to manage specific types of wastes in a more cost-effective manner; and freeing up limited disposal capacity at facilities specifically designed to receive more hazardous low-level and mixed wastes by allowing the disposal of low activity waste in alternate and equally protective facilities. Accordingly, the approach is expected to expedite the remediation of some contaminated sites and reduce their clean-up costs, and to provide commercial generators of mixed waste another disposal alternative. While these non-quantifiable benefits are considered equally important, they cannot be addressed here.

Quantifiable benefits are the savings to be realized due to the cost differential in disposal methods. As presented here, this differential is that between our alternative disposal technology as opposed to using facilities specifically designed to accept mixed waste or those meeting Federal Standards governing the disposal of conventional low-level waste. Disposal costs used to derive the conclusions of this paper are selected from DOE studies and engineering estimates that are assumed to reflect current DOE strategies in managing such wastes (7). The costs reflect full life cycle cost components. The cost discounting method used for this analysis was the concept of levelized cost. The levelized cost is defined to be the hypothetical charge per unit of waste disposed of that would exactly recover the present value of DOE's cost of disposal. The unit disposal costs were adjusted for facilities with disposal capacities of 250,000 cubic meters for low-level waste, mixed waste, and hazardous waste. This approach was used since it is assumed most likely that larger disposal facilities would be built to benefit from economy of scale and minimize the total number of disposal sites.

The assumed unit waste disposal cost for the comparative alternative disposal technology, given a 250,000 cubic meter disposal site, is $226 per cubic meter. Using the same techniques to develop costs for conventional LLW disposal or for mixed waste disposal, we derived a per cubic meter disposal cost of $2330. The differential between these estimates is striking - an order of magnitude. Estimates in the past for the volume of waste generated by commercial generators would imply a modest but important savings in disposal costs between the two methods.

It is imperative to also mention that any potential savings in disposal costs are directly dependent upon on the actions of waste generators, as well as on legal constraints arising from other Federal and State regulations and how the Nuclear Regulatory Commission would implement the approach within the commercial sector.

This analysis suggests that there are savings, both quantitative and qualitative, to be realized by the use of alternative disposal technologies for commercial mixed waste, with no reduction in public health protection. While the absolute amount of these saving are likely to be small given the relatively small volumes of commercial waste (compared to either commercial low-level waste or DOE low-level waste) they are nonetheless significant, particularly to small generators. Expedited and inexpensive access to approved disposal facilities would also be expected to provide an inducement to the many generators currently storing such waste in many facilities around the Country.

1. U.S. Nuclear Regulatory Commission, 10 CFR Part 61, Licensing Requirements for Land Disposal of Radioactive Waste, Title 10, CFR Part 61, U.S. Federal Register, Vol.46, No.142, July 24, 1987.
2. U.S. Nuclear Regulatory Commission, Characterization of Class A Low-Level Radioactive Waste 1986-1990, NUREG/CR-6147, January 1994.
3. Nuclear Regulatory Commission, National Profile on Commercially Generated Low Level Radioactive Mixed Waste, NUREG/CR-5938, December 1992, Washington, DC.
4. User's guide for PRESTO-EPA-CPG Operation System, Version 2.1, EPA report, EPA 402-R-96-013, June 1996.
5. U.S. Department of Energy, The 1966 Baseline Environmental Management Report, DOE/EM-0290, Office of Environmental Management, June 1996.
6. U.S. Department of Energy, Integrated Data Base for 1995: Spent Fuel and Radioactive Waste Inventories, Projections, and Characteristics, DOE/RW-0006, Rev. 12, December 1996.
7. Idaho National Engineering Laboratory, Waste Management Facilities Cost Information for Low-Level Waste, INEL-95/0013, Rev. 0, June 1995, Lockheed Idaho Technologies Company.

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