Low-level Radioactive Waste Disposal Sites Research Articles

Adsorption of U(VI) on the natural soil around a very low-level waste repository

The behaviors of U(VI) in environmental media around radioactive waste disposal site are important for safety assessment of geological repositories. However, the estimation of environmental behaviors of U(VI) in natural media was insufficient. This work aimed to determine the adsorption of U(VI) on natural soil surrounding a candidate very low-level radioactive waste (VLLW) disposal site in southwest China. Results showed that the adsorption process of U(VI) on soils could be well supported by pseudo-second-order kinetic and Freundlich model. The adsorption of U(VI) was pH-dependent but temperature-independent. High ionic strength (NaCl) strongly affected the adsorption process at low pH (2.0–5.5). CO32− remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO43− and SO42−. Naturally occurred soil organic matters (SOMs) showed high affinity for U(VI), while the presence of additional humic acid (HA) strongly inhibited U(VI) adsorption. The occurrence of ferrous iron could result in the reduction of U(VI) at low pH values (pH < 4), leading to the promotion of immobilization of U(VI). These findings would provide some guidance for the safety assessments of the VLLW disposal as well as the remediation of contaminated soil.

Use of Routine Environmental Monitoring Data to Establish a Dose-based Compliance System for a Low-level Radioactive Waste Disposal Site.

A dose-based compliance methodology was developed for Waste Control Specialists, LLC, low-level radioactive waste facility in Andrews, Texas, that allows routine environmental measurement data to be evaluated not only at the end of a year to determine regulatory compliance, but also throughout the year as new data become available, providing a continuous assessment of the facility. The first step in the methodology is a screening step to determine the potential presence of site emissions in the environment, and screening levels are established for each environmental media sampled. The screening accounts for spatial variations observed in background for soil and temporal fluctuations observed in background for air. For groundwater, the natural activity concentrations in groundwater wells at the facility are highly variable, and therefore the methodology uses ratios for screening levels. The methodology compares the ratio of gross alpha to U + U to identify potentially abnormal alpha activity and the ratio of U to U to identify the potential presence of depleted uranium. Compliance evaluation is conducted for any samples that fail the screening step. Compliance evaluation uses the radionuclide-specific measurements to first determine (1) if the dose exceeds the background dose and if so, (2) the dose consequences, so that the appropriate investigation or action occurs. The compliance evaluation is applied to all environmental samples throughout the year and on an annual basis to determine regulatory compliance. The methodology is implemented in a cloud-based software application that is also made accessible to the regulator. The benefits of the methodology over the existing system are presented.

A study on waterproof capabilities of the bentonite-containing engineered barrier used in near surface disposal for radioactive waste

Study of nuclear fuel cycle in Vietnam at the aspect of domestic production, the exploitation and process of uranium ore were began. These processes generated large amounts of radioactive waste overtiming. The naturally occurring radioactive material and technologically enhanced radioactive material (NORM/TENORM) waste, which would be large, needs to be managed and disposed reasonably by effective methods. It was therefore very important to study the model of the radioactive waste repository, where bentonite waterproofing layer would be applied for the low and very low level radioactive waste in disposal site. The aim of this study was to obtain the preliminary parameters for low-level radioactive waste disposal site suitable with the conditions of Vietnam. The investigation of the ratio between soil and bentonite was interested in the safety of the uranium tailings disposal site. The experiments with some layers of waterproofing material with the ratio of soil and bentonite are 75/25; 50/50; 25/75 were carried out to test the moving of uran nuclide through these waterproofing material layers. Waterproofing layers containing bentonite combined with soil were compacted into PVC pipes. One end of the plastic tube is sealed, the other end is embedded in a solution containing uranium nuclide. Analyzing the uranium content in each layers (0,1 cm) of material pipe is to determine the uranium nuclide adsorption from solution into the material in the different ratios at the different times: 1, 2 and 3 month. The results showed that the calculated average speeds of the migration of uranium nuclide into the soil- bentonite layer are 5.4.10-10, 5.4.10-10 and 3,85.10-10 m/s and thickness waterproofing layer (for 300 years) are 4,86 m, 4,86 m and 3,63 m for layer with the ratio of soil and bentonite are 75/25; 50/50; 25/75 respectively

壁面歩行型コンクリート非破壊品質評価試験ロボットの開発

Concrete used for low-level radioactive waste disposal sites must be managed to satisfy the required quality for performance assurance and accountability after construction. However, it is not easy to ensure the quality of concrete due to environmental factors and human factors under construction. In Central Research Institute of Electric Power Industry, nondestructive inspection techniques has been studied and a nondestructive air-permeability tester called ”TCAPT” has been developed. In order to perform this test for concrete with large wall surface more efficiently.,combination of a wall-walking robot with the TCAPT is effective. We have been developing a concrete wall inspection robot by fusion of a wall-walking robot with the TCAPT. In this paper, we propose a new mechanism to increase the reliability of adhesion with validation of the eectiveness.

Influences of specific ions in groundwater on concrete degradation in subsurface engineered barrier system.

Many disposal concepts currently show that concrete is an effective confinement material used in engineered barrier systems (EBS) at a number of low-level radioactive waste (LLW) disposal sites. Cement-based materials have properties for the encapsulation, isolation, or retardation of a variety of hazardous contaminants. The reactive chemical transport model of HYDROGEOCHEM 5.0 was applied to simulate the effect of hydrogeochemical processes on concrete barrier degradation in an EBS which has been proposed to use in the LLW disposal site in Taiwan. The simulated results indicated that the main processes that are responsible for concrete degradation are the species induced from hydrogen ion, sulfate, and chloride. The EBS with the side ditch drainage system effectively discharges the infiltrated water and lowers the solute concentrations that may induce concrete degradation. The redox processes markedly influence the formations of the degradation materials. The reductive environment in the EBS reduces the formation of ettringite in concrete degradation processes. Moreover, the chemical conditions in the concrete barriers maintain an alkaline condition after 300 years in the proposed LLW repository. This study provides a detailed picture of the long-term evolution of the hydrogeochemical environment in the proposed LLW disposal site in Taiwan.

Environmental risks of radioactive discharges from a low-level radioactive waste disposal site at Dessel, Belgium

The potential radiological impact of releases from a low-level radioactive waste (Category A waste) repository in Dessel, Belgium on the local fauna and flora was assessed under a reference scenario for gradual leaching. The potential impact situations for terrestrial and aquatic fauna and flora considered in this study were soil contamination due to irrigation with contaminated groundwater from a well at 70 m from the repository, contamination of the local wetlands receiving the highest radionuclide flux after migration through the aquifer and contamination of the local river receiving the highest radionuclide flux after migration through the aquifer. In addition, an exploratory study was carried out for biota residing in the groundwater.All impact assessments were performed using the Environmental Risk from Ionising Contaminants: Assessment and Management (ERICA) tool. For all scenarios considered, absorbed dose rates to biota were found to be well below the ERICA 10 μGy h−1 screening value. The highest dose rates were observed for the scenario where soil was irrigated with groundwater from the vicinity of the repository. For biota residing in the groundwater well, a few dose rates were slightly above the screening level but significantly below the dose rates at which the smallest effects are observed for those relevant species or groups of species. Given the conservative nature of the assessment, it can be concluded that manmade radionuclides deposited into the environment by the near surface disposal of category A waste at Dessel do not have a significant radiological impact to wildlife.

Using Geographic Information Systems to Determine Site Suitability for a Low-Level Radioactive Waste Storage Facility.

Radioactive waste is an inevitable product of using radioactive material in education and research activities, medical applications, energy generation, and weapons production. Low-level radioactive waste (LLW) makes up a majority of the radioactive waste produced in the United States. In 2010, over two million cubic feet of LLW were shipped to disposal sites. Despite efforts from several states and compacts as well as from private industry, the options for proper disposal of LLW remain limited. New methods for quickly identifying potential storage locations could alleviate current challenges and eventually provide additional sites and allow for adequate regional disposal of LLW. Furthermore, these methods need to be designed so that they are easily communicated to the public. A Geographic Information Systems (GIS) based method was developed to determine suitability of potential LLW disposal (or storage) sites. Criteria and other parameters of suitability were based on the Code of Federal Regulation (CFR) requirements as well as supporting literature and reports. The resultant method was used to assess areas suitable for further evaluation as prospective disposal sites in Louisiana. Criteria were derived from the 10 minimum requirements in 10 CFR Part 61.50, the Nuclear Regulatory Commission's Regulatory Guide 0902, and studies at existing disposal sites. A suitability formula was developed permitting the use of weighting factors and normalization of all criteria. Data were compiled into GIS data sets and analyzed on a cell grid of approximately 14,000 cells (covering 181,300 square kilometers) using the suitability formula. Requirements were analyzed for each cell using multiple criteria/sub-criteria as well as surrogates for unavailable datasets. Additional criteria were also added when appropriate. The method designed in this project proved to be sufficient for initial screening tests in determining the most suitable areas for prospective disposal (or storage) sites. Cells above 90%, 95%, and 99% suitability include respectively 404, 88, and 4 cells suitable for further analysis. With these areas identified, the next step in siting a LLW storage facility would be on-site analysis using additional requirements as specified by relevant regulatory guidelines. The GIS based method provides an easy, economic, efficient and effective means in evaluating potential sites for LLW storage facilities where sufficient GIS data exist.

Durability Analysis on Reactive Powder Concrete as Barrier Materials for Low-Level Radioactive Waste Disposal

Reactive powder concrete (RPC) has been proposed as barrier materials for the construction of engineered barrier in a low-level radioactive waste disposal site. The durability characteristics of RPC in such applications become paramount for the success of the containment of the wastes. The adverse environmental conditions at the disposal site could attack concrete barrier material and result in degradation of the material. Laboratory tests were conducted on RPC with various compositions to investigate the physical and durability properties of RPC. The effects of the addition of cement, silica fume, quartz powder, silica sand, steel fiber, and 2 levels of water-to-binder ratio (W/B = 0.25 and 0.30) on the properties of RPC specimens were investigated. Experimental results indicate that the long-term durability of RPC is significantly improved with the hydration of pozzolanic materials, which produces a very dense structure and thus exhibiting improved durability. The coefficient of permeability of RPC matrix determined using gas permeability apparatus demonstrated that RPC has much lower permeability than that of ordinary concrete. Heat-treating of concrete at 80°C accelerates the hydration process of RPC and shows enhanced physical and durable characteristics, as demonstrated by the chloride penetration test results.

Physical modelling of in-ground waste repository capping systems

This paper describes a series of geotechnical centrifuge tests carried out to investigate aspects of landfill capping system performance, in the context of a low-level radioactive waste disposal site. The effects of the basic cap geometry (sloping or flat) and the subsidence pattern imposed as the underlying waste degrades (ramp or step, i.e. slope or displacement discontinuity) are shown to influence cap performance. The effect of moving the toe of a sloping cap outside the landfill subsidence zone, thereby increasing the depth of inert fill below the cap, is also shown to be effective in limiting the displacements transmitted to the resistive layer. Analysis of the runoff from sloping capping systems shows that if the resistive layer fails, there is the potential for the infiltration rate through the cap to increase from near zero to almost 100% of the incident rainfall.

Movement of a tritium plume in shallow groundwater at a legacy low-level radioactive waste disposal site in eastern Australia

Between 1960 and 1968 low-level radioactive waste was buried in a series of shallow trenches near the Lucas Heights facility, south of Sydney, Australia. Groundwater monitoring carried out since the mid 1970s indicates that with the exception of tritium, no radioactivity above typical background levels has been detected outside the immediate vicinity of the trenches. The maximum tritium level detected in groundwater was 390 kBq/L and the median value was 5400 Bq/L, decay corrected to the time of disposal. Since 1968, a plume of tritiated water has migrated from the disposal trenches and extends at least 100 m from the source area. Tritium in rainfall is negligible, however leachate from an adjacent landfill represents a significant additional tritium source. Study data indicate variation in concentration levels and plume distribution in response to wet and dry climatic periods and have been used to determine pathways for tritium migration through the subsurface.

Fe(III) Reduction in the Subsurface at a Low-level Radioactive Waste Disposal Site

The low-level radioactive waste (LLW) repository located near to the village of Drigg, Cumbria is the principal site for disposal of LLW in the United Kingdom. To gain a better understanding of the potential microbial processes that could control radionuclide mobility in the LLW repository, we studied of a range of anaerobic processes in microcosms constructed from sediments at the site. Sediment samples taken from both former disposal trenches and the far-field region of the site were analyzed for the presence of Fe(II) and bioavailable Fe(III) using chemical extractions and assays. Near-field (trench) sediments were found to have undergone some microbial reduction of iron, with acid-extractable Fe(II) present and 16S rRNA genes affiliated to known Fe(III)-reducing microorganisms detected in clone libraries constructed by PCR using broad-specificity primers. In far-field material, no Fe(II) was detectable although poorly crystalline Fe(III) was present. No 16S rRNA genes affiliated with known Fe(III)-reducing microorganisms were observed in clone libraries prepared with broad-specificity primers, suggesting that they were not numerically dominant in the far-field sediments. Time-course microcosm experiments were set up by amending the near- and far-field material with 10 mM acetate. The utilization of nitrate, poorly crystalline Fe(III) and sulfate was monitored to identify the sequence of terminal electron accepting processes in the sediments. Analysis of the microbial community after Fe(III) reduction had terminated revealed a large increase in 16S rRNA gene sequences affiliated to known Fe(III)-reducing bacteria, with a close relative to Ferribacterium limneticum accounting for 55% of the community. 16S rRNA analysis of the sediments post-Fe(III) reduction revealed the presence of some Fe(III)-reducing microorganisms such as a close relative of Rhodoferax ferrireducens. Nitrate, iron and sulfate data were then modeled with a biogeochemical reactive transport computer model that includes representation of microbial growth kinetics, and which is used to simulate the evolution of the subsurface geochemistry at the repository site. The potential impact of these processes on radionuclide mobility at LLW sites is discussed.

Evaluation of geogrid as a reinforcement layer in clay based engineered barriers

Imperviousness of clay based barrier, which is provided in cover system of low-level radioactive waste disposal sites, is essential to mitigate the environmental hazard. The objective of this paper is to examine the influence of geogrid reinforcement on the deformation behaviour of clay based cover systems subjected to differential settlements. A series of centrifuge tests were performed on model clay barriers with and without the inclusion of geogrid reinforcement at 40 gravities. Motor-based differential settlement simulator was custom designed and developed for inducing continuous differential settlement in high gravity environment. By maintaining type and location of the geogrid within the clay barrier as constant, the thickness of clay barrier is varied. The performance of the clay barrier with and without geogrid layer having an overburden pressure equivalent to that of cover system was monitored by measuring water breakthrough at the onset of differential settlements. It was observed that both 0.6 m and 1.2 m thick clay barriers with and without overburden experienced cracks extending up to full depth. In comparison, geogrid reinforced clay barrier was found to sustain large distortions with an enhanced imperviousness. With the provision of an overburden equivalent to that of cover system, integrity of geogrid reinforced clay barrier was found to be retained even after inducing a distortion level of 0.125. This implies that provision of thickness of clay barrier equal to 0.6 m reinforced with a suitable geogrid may be adequate in sustaining higher distortion levels.

Effects of meteorological models on the solution of the surface energy balance and soil temperature variations in bare soils

summary A complete evaluation of the soil thermal regime can be obtained by evaluating the movement of liquid water, water vapor, and thermal energy in the subsurface. Such an evaluation requires the simultaneous solution of the system of equations for the surface water and energy balance, and subsurface heat transport and water flow. When only daily climatic data is available, one needs not only to estimate diurnal cycles of climatic data, but to calculate the continuous values of various components in the energy balance equation, using different parameterization methods. The objective of this study is to quantify the impact of the choice of different estimation and parameterization methods, referred together to as meteorological models in this paper, on soil temperature predictions in bare soils. A variety of widely accepted meteorological models were tested on the dataset collected at a proposed low-level radioactive-waste disposal site in the Chihuahua Desert in West Texas. As the soil surface was kept bare during the study, no vegetation effects were evaluated. A coupled liquid water, water vapor, and heat transport model, implemented in the HYDRUS-1D program, was used to simulate diurnal and seasonal soil temperature changes in the engineered cover installed at the site. The modified version of HYDRUS provides a flexible means for using various types of information and different models to evaluate surface mass and energy balance. Different meteorological models were compared in terms of their prediction errors for soil temperatures at seven observation depths. The results obtained indicate that although many available meteorological models can be used to solve the energy balance equation at the soil–atmosphere interface in coupled water, vapor, and heat transport models, their impact on overall simulation results varies. For example, using daily average climatic data led to greater prediction errors, while relatively simple meteorological models may significantly improve soil temperature predictions. On the other hand, while models for the albedo and soil emissivity had little impact on soil temperature predictions, the choice of the atmospheric emissivity models had a greater impact. A comparison of all the different models indicates that the error introduced at the soil atmosphere interface propagates to deeper layers. Therefore, attention needs to be paid not only to the precise determination of the soil hydraulic and thermal properties, but also to the selection of proper meteorological models for the components involved in the surface energy balance calculations.

Disruption or Convention? A Process-based Explanation of Divergent Repertoires of Contention Among Opponents to Low-level Radioactive Waste Disposal Sites

Violence, disruption and convention constitute three well established categories of collective action repertoires available to contemporary social movements. What factors shape differences in repertoire selection across social movement groups? I take a process-based approach to answer this question, examining two grassroots opposition movements to the disposal of low-level radioactive waste in the United States. The two rural New York State counties I consider each faced a state-imposed low-level radioactive waste site proposal in 1988. Activists in each county mounted vigorous collective opposition to the proposed facility, while exhibiting distinct repertoires of collective action. Activists in Allegany County pursued disruptive civil disobedience, while activists in Cortland County pursued a conventional repertoire of citizen lobbying and litigation efforts. Similarities across a variety of demographic, political, and social characteristics in these two counties leave the standard explanations for repertoire selection put forth in the social movement literature wanting. I argue that the relationship developed between the respective county governments and citizen activists during the waste-site proposal dispute had a dramatic effect on the dominant repertoire of collective action adopted by each community. More specifically, identifying the presence or absence of the social mechanism of brokerage between local government and activists is crucial to understanding the different trajectories of these movement groups. This article highlights the utility of fine-grained process-based analysis as a complement to variable-based approaches for explaining social movement activity, and the importance of the mechanism of brokerage among local government and activists for understanding bottom-up movements responding to proximate grievances, such as the environmental justice movement.

Centrifuge model tests on clay based engineered barriers subjected to differential settlements

The objective of this paper is to investigate the influence of thickness of the clay barrier and overburden pressure on the integrity of the clay barrier, which is provided in the cover system of low low-level radioactive waste disposal sites. A series of centrifuge tests were performed on model clay barrier subjected to continuous differential settlement at 40 g. The model clay barrier material has been selected in such a way that it envelopes the material characteristics of the clay barriers. The model clay barriers were moist-compacted on the wet side of its optimum moisture content. The performance of the clay barrier as an effective hydraulic barrier was monitored throughout the deformation process and attempts have been made to arrive at strain distribution along the top surface of clay barrier with the help of marker based digital image analysis. A 1.2 m thick clay barrier with a nominal overburden pressure of the order of 12.5 kPa was found to experience multiple cracking extending up to its full depth; whereas with overburden pressure of the order of 25 kPa, it was observed to have suppression of cracks. A catastrophic nature of water breakthrough was registered for a 0.6 m thick clay barrier with an overburden equal to that of a closure system of a low-level radioactive waste disposal site, once settlement ratio attains 0.6. This indicates that provision of thickness of clay barrier equal to 0.6 m may not be adequate.

Development of a Novel Depleted Uranium Treatment Process at Lawrence Livermore National Laboratory

A three-stage process was developed at Lawrence Livermore National Laboratory to treat potentially pyrophoric depleted uranium metal wastes. The three-stage process includes waste sorting/rinsing, acid dissolution of the waste metal with a hydrochloric and phosphoric acid solution, and solidification of the neutralized residuals from the second stage with clay. The final product is a solid waste form that can be transported to and disposed of at a permitted low-level radioactive waste disposal site.

A Generic Method to Evaluate the Reasonable Upper-Bound Dose from Near-Surface Radioactive Waste Disposal Facilities Through Drinking Water Pathway

A generic method has been developed to evaluate the reasonable upper-bound (RUB) dose from near-surface radioactive waste disposal facilities through a drinking water pathway. This generic method has been developed by applying a safety assessment model to seven near-surface radioactive waste disposal sites in India. The concentrations and effective radiation dose rates due to different radionuclides are evaluated at different distances from the disposal facilities. The peak dose rates received by members of the public at these distances are given per unit nuclear power capacity at the site [mSv/yr per GW(electric)·yr]. The product of these normalized peak dose rates and the total existing or projected nuclear power capacity at a site [GW(electric)·yr] will indicate the RUB dose rates from the near-surface disposal facility through a drinking water pathway at different distances. Results indicate that the sites can be grouped into two categories: (a) sites having groundwater velocity >10 cm/day (category 1) and (b) sites having groundwater velocity <10 cm/day (category 2). The variation in the dose rates between each category of sites is found to be small. Based on this finding, a generic method has been developed to evaluate the RUB dose rates to members of the public from the near-surface radioactive waste disposal facilities as a function of distances and nuclear power capacity. It is observed that the RUB dose rates at 1, 2, and 3 km are ~0.03, 0.02, and 0.01 mSv/yr, respectively, for category 1 sites for a nuclear power capacity of 1 GW(electric). These dose rates are reduced by a factor of 2 for category 2 sites. This generic method is found useful for the screening analysis of proposed low-level radioactive waste disposal sites as it estimates the RUB effective dose rates as a function of distance and nuclear power capacity for different categories of sites.

Treatment of uncertainty and developing conceptual models for environmental risk assessments and radioactive waste disposal safety cases

The common approach to performing quantitative risk assessments in the contaminated land industry in the UK lacks a formal methodology for the treatment of the full range of uncertainties and for documenting decisions regarding the development of conceptual models and the selection of computer codes. The approach presented here represents an alternative, more detailed, and systematic approach for developing conceptual models and addressing uncertainties when undertaking contaminated land risk assessments. It is intended that the advantages of this approach are recognised by practitioners in the contaminated land industry and adopted, where appropriate, to help improve the quality of contaminated land risk assessments. The identification of features, events, and processes (FEPs) has been applied to safety assessments of deep geological and near-surface disposal of radioactive wastes. One of the primary benefits of using this approach is in the development of conceptual models. The approach identifies the FEPs that need to be addressed during the development of conceptual models and in the selection of suitable computer codes that can be used to represent the conceptual models. This approach has been applied by BNFL at the low-level radioactive waste disposal site at Drigg in Cumbria and is currently being adopted for a contaminated land study at the Sellafield site, also in Cumbria. This paper presents the advantages of using FEPs in the development of conceptual models and the treatment of uncertainties. The paper also discusses the application of this approach to contaminated land studies and provides an example to demonstrate the application of the approach. BNFL's approach at the Drigg site involves the identification of components (features) and phenomena (events and processes) that govern interactions and dependencies between the components by arranging them in a matrix format.

Navigated control in dental implantology

Monitoring and restoration activities at low-level radioactive waste disposal sites have identified complicated mixtures of inorganic and organic contaminants in soil and groundwater. Metallic contaminants are generally complexed with various chelating agents and organic acids which alter the geochemical behavior of the contaminants in subsurface media. The objective of this study was to provide an improved understanding of the geochemical processes controlling the subsurface transport of radioactive 60Co complexed with ethylenediaminetetraacetic acid (EDTA). Specifically, we investigated the kinetics and mechanisms of Co(II) EDTA2− oxidation to Co(III)EDTA− by the soil mineral pyrolusite (β-MnO2). A column displacement technique was utilized to investigate Co(II)EDTA2− reactivity and oxidation rates through packed beds of pyrolusite-coated SiO2. The interaction of Co(II)EDTA2− with the porous media was characterized by a MnO2-induced oxidation of the Co (II)EDTA2− to Co(III)EDTA−. The oxidation of Co(II)EDTA2− appeared to involve the reduction of Mn (IV) to both an aqueous Mn2+ species and a theorized Mn(III)-oxide solid phase. The redox reaction was catalytic since the reduction products were gradually reoxidized in the presence of dissolved O2 to form a Mn(IV)-oxide phase. Oxidation of surface-bound Mn2+ and the theorized Mn(III)-oxide was slow relative to Co(II)EDTA2− oxidation, and a reversible loss in the oxidative ability of the β-MnO2 occurred when exposed to CO(II)EDTA2−. The reduction in catalytic activity of the MnO2 was not the result of direct surface poisoning by Mn2+ but rather was believed to result from the formation of an intermediate Mn(III)-oxide solid phase whose oxidative potential was significantly less than MnO2. Thus, the kinetics of Co(II)EDTA2− oxidation to Co(III)EDTA− by MnO2 was dependent on the rate of MnO2 surface regeneration. The environmental implications of this redox reaction are pronounced, since any Co(III)EDTA− produced is extremely stable, and this enhances the persistence and transport of 60Co in subsurface environments.

Radionuclides in soil and water near a low-level disposal site and potential ecological and human health impacts.

Material Disposal Area G is the primary low-level radioactive waste disposal site at Los Alamos National Laboratory, New Mexico, and is adjacent to Pueblo of San Ildefonso lands. Pueblo residents and Los Alamos scientists are concerned about radiological doses resulting from uptake of Area G radionuclides by mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus), then consumption of deer and elk meat by humans. Tissue samples were collected from deer and elk accidentally killed near Area G and were analyzed for 3H, 90Sr, total U, 238Pu, 239,240Pu, 241Am, and 137Cs. These data were used to estimate human doses based on meat consumption of 23 kg y(-1). Human doses were also modeled using RESRAD, and dose rates to deer and elk were estimated with a screening model. Dose estimates to humans from tissue consumption were 2.9 x 10(-3) mSv y(-1) and 1.6 x 10(-3) mSv y(-1) from deer and elk, respectively, and RESRAD dose estimates were of the same order of magnitude. Estimated dose rates to deer and elk were 2.1 x 10(-4) mGy d(-1) and 4.7 x 10(-4) mGy d(-1), respectively. All estimated doses were significantly less than established exposure limits or guidelines.