Subsurface Disposal Area Research Articles

237Np analytical method using 239Np tracers and application to a contaminated nuclear disposal facility

Environmental 237Np analyses are challenged by low 237Np concentrations and lack of an available yield tracer; we report a rapid, inexpensive 237Np analytical approach employing the short lived 239Np (t1/2 = 2.3 days) as a chemical yield tracer followed by 237Np quantification using inductively coupled plasma-mass spectrometry. 239Np tracer is obtained via separation from a 243Am stock solution and standardized using gamma spectrometry immediately prior to sample processing. Rapid digestions using a commercial, 900 W “Walmart” microwave and Parr microwave vessels result in 99.8 ± 0.1% digestion yields, while chromatographic separations enable Np/U separation factors on the order of 106 and total Np yields of 95 ± 4% (2σ). Application of this method to legacy soil samples surrounding a radioactive disposal facility (the Subsurface Disposal Area at Idaho National Laboratory) reveal the presence of low level 237Np contamination within 600 m of this site, with maximum 237Np concentrations on the order of 103 times greater than nuclear weapons testing fallout levels.

Mechanical environmental transport of actinides and 137Cs from an arid radioactive waste disposal site

Aeolian and pluvial processes represent important mechanisms for the movement of actinides and fission products at the Earth's surface. Soil samples taken in the early 1970's near a Department of Energy radioactive waste disposal site (the Subsurface Disposal Area, SDA, located in southeastern Idaho) provide a case study for studying the mechanisms and characteristics of environmental actinide and 137Cs transport in an arid environment. Multi-component mixing models suggest actinide contamination within 2.5 km of the SDA can be described by mixing between 2 distinct SDA end members and regional nuclear weapons fallout. The absence of chemical fractionation between 241Am and 239+240Pu with depth for samples beyond the northeastern corner and lack of 241Am in-growth over time (due to 241Pu decay) suggest mechanical transport and mixing of discrete contaminated particles under arid conditions. Occasional samples northeast of the SDA (the direction of the prevailing winds) contain anomalously high concentrations of Pu with 240Pu/239Pu isotopic ratios statistically identical to those in the northeastern corner. Taken together, these data suggest flooding resulted in mechanical transport of contaminated particles into the area between the SDA and a flood containment dike in the northeastern corner, following which subsequent contamination spreading in the northeastern direction resulted from wind transport of discrete particles.

137Cs activities and 135Cs/137Cs isotopic ratios from soils at Idaho National Laboratory: a case study for contaminant source attribution in the vicinity of nuclear facilities.

Radiometric and mass spectrometric analyses of Cs contamination in the environment can reveal the location of Cs emission sources, release mechanisms, modes of transport, prediction of future contamination migration, and attribution of contamination to specific generator(s) and/or process(es). The Subsurface Disposal Area (SDA) at Idaho National Laboratory (INL) represents a complicated case study for demonstrating the current capabilities and limitations to environmental Cs analyses. (137)Cs distribution patterns, (135)Cs/(137)Cs isotope ratios, known Cs chemistry at this site, and historical records enable narrowing the list of possible emission sources and release events to a single source and event, with the SDA identified as the emission source and flood transport of material from within Pit 9 and Trench 48 as the primary release event. These data combined allow refining the possible number of waste generators from dozens to a single generator, with INL on-site research and reactor programs identified as the most likely waste generator. A discussion on the ultimate limitations to the information that (135)Cs/(137)Cs ratios alone can provide is presented and includes (1) uncertainties in the exact date of the fission event and (2) possibility of mixing between different Cs source terms (including nuclear weapons fallout and a source of interest).

Transuranic waste remediation in Idaho: Pit 9, failed contracts, and lawsuits

AbstractThe U.S. Department of Energy (US DOE) remediation responsibilities include its Idaho National Laboratory. In 1989, the U.S. Environmental Protection Agency placed the Idaho site on its National Priority List for environmental cleanup. The site's contamination legacy from operations included inactive reactors and other structures, spent nuclear fuel, high‐level liquid radioactive wastes, calcined radioactive wastes, and transuranic wastes. Documents governing cleanup include a 1995 Settlement Agreement between the US DOE and the US Navy as responsible parties, and the State of Idaho. The Subsurface Disposal Area contains buried transuranic wastes, lies above the East Snake River Plain Aquifer, and could be the “site's most nettlesome cleanup issue,” according to an outside observer. This article describes the technical and legal difficulties that have been encountered in remediating this area. © 2010 Wiley Periodicals, Inc.

Distribution of uranium, plutonium, and 241Am in soil samples from Idaho National Laboratory

Soil materials used were collected in the early 1970s at Idaho National Laboratory near the Subsurface Disposal Area (SDA). Samples from a depth of 0–4 and 4–8 cm at two different sites located on the northeast corner of the SDA perimeter were analyzed. The concentration of 234U, 235U, 236U, and 238U in soil digests were measured by mass spectrometry. Uranium isotopic composition of the soil at the two sample sites and depths is compared to previously measured concentrations of 238Pu, 239Pu, 240Pu, 241Pu, and 241Am. Implications for remediation of contaminated soils surrounding the SDA are discussed.

Radioanalytical approach to determine 238Pu, 239+240Pu, 241Pu and 241Am in soils

The simultaneous determination of multiple actinide isotopes in samples where total quantity is limited can sometimes present a unique challenge for radioanalytical chemists. In this study, re-determination of 238Pu, 239+240Pu, and 241Am for soils collected and analyzed approximately three decades ago was the goal, along with direct determination of 241Pu. The soils had been collected in the early 1970’s from a shallow land burial site for radioactive wastes called the Subsurface Disposal Area (SDA) at the Idaho National Lab (INL), analyzed for 238Pu, 239+240Pu, and 241Am, and any remaining soils after analysis had been archived and stored. We designed an approach to reanalyze the 238Pu, 239+240Pu, and 241Am and determine for the first time 241Pu using a combination of traditional and new radioanalytical methodologies. The methods used are described, along with estimates of the limits of detection for gamma-and alpha-spectrometry, and liquid scintillation counting. Comparison of our results to the earlier work documents the ingrowth of 241Am from 241Pu, and demonstrates that the total amount of 241Am activity in these soil samples is greater than would be expected due to ingrowth from 241Pu decay.

Use of a Paraffin-Based Grout to Stabilize Buried Beryllium and Other Wastes

The long-term durability of WAXFIX, a paraffin-based grout, was evaluated for in situ grouting of activated beryllium wastes in the subsurface disposal area (SDA), a radioactive landfill at the Radioactive Waste Management Complex, part of the Idaho National Laboratory (INL). The evaluation considered radiological and biological mechanisms that could degrade the grout using data from an extensive literature search and previous tests of in situ grouting at the INL. Conservative radioactive doses for WAXFIX were calculated from the “hottest” (i.e., highest-activity) Advanced Test Reactor beryllium block in the SDA. These results indicate that WAXFIX would not experience extensive radiation damage for many hundreds of years. Calculation of radiation-induced hydrogen generation in WAXFIX indicated that grout physical performance should not be reduced beyond the effects of radiation dose on the molecular structure. Degradation of a paraffin-based grout by microorganisms in the SDA is possible and perhaps likely, but the rate of degradation will be at a slower rate than found in the literature reviewed. The calculations showed the outer 0.46-m (18-in.) layer of each monolith, which represents the minimum expected distance to the beryllium block, was calculated to require 1000 to 3600 yr to be consumed. The existing data and estimations of biodegradation and radiolysis rates for WAXFIX/paraffin do not indicate any immediate problems with the use of WAXFIX for grouting beryllium or other wastes in the SDA.

Regulatory Modeling for the Idaho National Engineering and Environmental Laboratory's Subsurface Disposal Area and Conceptual Model Uncertainty Treatment

The Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL) contains low‐level, hazardous, and transuranic wastes and is the subject of ongoing environmental assessments. The buried waste is in shallow land burial overlying a 180‐m‐thick vadose zone comprised of fractured basalts and sedimentary interbeds. Applied simulation studies to predict future contaminant concentrations from this buried waste have been conducted as part of ongoing regulatory‐driven environmental assessments for the SDA. An overview of the most recent numerical simulation study is presented along with a treatment of conceptual model uncertainty. The main premise of this paper is that conceptual uncertainty likely dominates parametric uncertainty, and this dominance should be considered when designing characterization studies. Given that the current modeling is uncalibrated due to inconsistent monitoring data in the vadose zone, it is only appropriate to consider conceptual model uncertainty. Conceptual model uncertainty was addressed by modeling different scenarios. Scenarios presented in this paper are the assignment of infiltration boundary conditions, a simplistic approximation to represent facilitated transport, and alternative representations of the moisture characteristic curve for fractured basalts. Results of this subsurface transport modeling have been used in part to guide additional field characterization activities. Eventually, predicted concentrations from this applied model will be used to estimate human health risks for a potential future receptor as part of the environmental assessment process.

Fate of Brine Applied to Unpaved Roads at a Radioactive Waste Subsurface Disposal Area

Between 1984 and 1993, MgCl2 brine was used to suppress dust on unpaved roads at a radioactive waste subsurface disposal area. Because Cl− might enhance corrosion of buried metals in the waste, we investigated the distribution and fate of Cl− in the vadose zone using pore water samples collected from suction lysimeters and soluble salt concentrations extracted from sediment samples. The Cl/Br mass ratio and the total dissolved Cl− concentration of pore water show that brine contamination occurs primarily within 13 m of treated roads, but can extend as much as 30 m laterally in near-surface sedimentary deposits. Within the deep vadose zone, which consists of interlayered basalt lava flows and sedimentary interbeds, brine has moved up to 110 m laterally. This lateral migration suggests formation of perched water and horizontal transport during periods of high recharge. In a few locations, brine migrated to depths of 67 m within 3 to 5 yr. Elevated Cl− concentrations were found to depths of 2 m in roadbed material. In drainage ditches along roads, where runoff accumulates and recharge of surface water is high, Cl− was flushed from the sediments in 3 to 4 yr. In areas of lower recharge, Cl− remained in the sediments after 5 yr. Vertical brine movement is directly related to surface recharge through sediments. The distribution of Cl− in pore water and sediments is consistent with estimates of vadose zone residence times and spatial distribution of surface water recharge from other investigations at the subsurface disposal area.

Regulatory Modeling for the Idaho National Engineering and Environmental Laboratory's Subsurface Disposal Area and Conceptual Model Uncertainty Treatment

Regulatory Modeling for the Idaho National Engineering and Environmental Laboratory's Subsurface Disposal Area and Conceptual Model Uncertainty Treatment

Fate of Brine Applied to Unpaved Roads at a Radioactive Waste Subsurface Disposal Area

Between 1984 and 1993, MgCl2 brine was used to suppress dust on unpaved roads at a radioactive waste subsurface disposal area. Because Cl− might enhance corrosion of buried metals in the waste, we investigated the distribution and fate of Cl− in the vadose zone using pore water samples collected from suction lysimeters and soluble salt concentrations extracted from sediment samples. The Cl/Br mass ratio and the total dissolved Cl− concentration of pore water show that brine contamination occurs primarily within 13 m of treated roads, but can extend as much as 30 m laterally in near‐surface sedimentary deposits. Within the deep vadose zone, which consists of interlayered basalt lava flows and sedimentary interbeds, brine has moved up to 110 m laterally. This lateral migration suggests formation of perched water and horizontal transport during periods of high recharge. In a few locations, brine migrated to depths of 67 m within 3 to 5 yr. Elevated Cl− concentrations were found to depths of 2 m in roadbed material. In drainage ditches along roads, where runoff accumulates and recharge of surface water is high, Cl− was flushed from the sediments in 3 to 4 yr. In areas of lower recharge, Cl− remained in the sediments after 5 yr. Vertical brine movement is directly related to surface recharge through sediments. The distribution of Cl− in pore water and sediments is consistent with estimates of vadose zone residence times and spatial distribution of surface water recharge from other investigations at the subsurface disposal area.

Regulatory Modeling for the Idaho National Engineering and Environmental Laboratory's Subsurface Disposal Area and Conceptual Model Uncertainty Treatment

The Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL) contains low-level, hazardous, and transuranic wastes and is the subject of ongoing environmental assessments. The buried waste is in shallow land burial overlying a 180-m-thick vadose zone comprised of fractured basalts and sedimentary interbeds. Applied simulation studies to predict future contaminant concentrations from this buried waste have been conducted as part of ongoing regulatory-driven environmental assessments for the SDA. An overview of the most recent numerical simulation study is presented along with a treatment of conceptual model uncertainty. The main premise of this paper is that conceptual uncertainty likely dominates parametric uncertainty, and this dominance should be considered when designing characterization studies. Given that the current modeling is uncalibrated due to inconsistent monitoring data in the vadose zone, it is only appropriate to consider conceptual model uncertainty. Conceptual model uncertainty was addressed by modeling different scenarios. Scenarios presented in this paper are the assignment of infiltration boundary conditions, a simplistic approximation to represent facilitated transport, and alternative representations of the moisture characteristic curve for fractured basalts. Results of this subsurface transport modeling have been used in part to guide additional field characterization activities. Eventually, predicted concentrations from this applied model will be used to estimate human health risks for a potential future receptor as part of the environmental assessment process.

Fate of Brine Applied to Unpaved Roads at a Radioactive Waste Subsurface Disposal Area

Fate of Brine Applied to Unpaved Roads at a Radioactive Waste Subsurface Disposal Area

Hybrid empirical—theoretical approach to modeling uranium adsorption

An estimated 330 metric tons of U are buried in the radioactive waste Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL). An assessment of U transport parameters is being performed to decrease the uncertainty in risk and dose predictions derived from computer simulations of U fate and transport to the underlying Snake River Plain Aquifer. Uranium adsorption isotherms were measured for 14 sediment samples collected from sedimentary interbeds underlying the SDA. The adsorption data were fit with a Freundlich isotherm. The Freundlich n parameter is statistically identical for all 14 sediment samples and the Freundlich K f parameter is correlated to sediment surface area ( r 2=0.80). These findings suggest an efficient approach to material characterization and implementation of a spatially variable reactive transport model that requires only the measurement of sediment surface area. To expand the potential applicability of the measured isotherms, a model is derived from the empirical observations by incorporating concepts from surface complexation theory to account for the effects of solution chemistry. The resulting model is then used to predict the range of adsorption conditions to be expected in the vadose zone at the SDA based on the range in measured pore water chemistry. Adsorption in the deep vadose zone is predicted to be stronger than in near-surface sediments because the total dissolved carbonate decreases with depth.

Neptunium and plutonium sorption to Snake River Plain, Idaho soil

SummaryThe behavior of Np and Pu on soil collected from the subsurface disposal area at the Idaho National Engineering and Environmental Laboratory was investigated by performing short-duration, sorption experiments to measure sorption isotherms. Neptunium sorption can be described with a Freundlich isotherm; however, Pu sorption can only be described in this fashion as a conservative estimate of minimum sorption. Geochemical modeling predictions suggest that initial sorption of Np is controlled predominantly by surface complexation on clay minerals, while Pu is controlled by a competition between complexation with iron oxyhydroxides and the precipitation of hydrolysis products. Longer-term sorption is governed by the transformation of these species to oxide minerals. Solution ionic strength and carbonate alkalinity did not significantly affect Np or Pu soil sorption.

Kilometer‐Scale Rapid Transport of Naphthalene Sulfonate Tracer in the Unsaturated Zone at the Idaho National Engineering and Environmental Laboratory

To investigate possible long‐range flow paths through the interbedded basalts and sediments of a 200‐m‐thick unsaturated zone, we applied a chemical tracer to seasonally filled infiltration ponds on the Snake River Plain in Idaho. This site is near the Subsurface Disposal Area for radioactive and other hazardous waste at the Idaho National Engineering and Environmental Laboratory. Within 4 mo, we detected tracer in one of 13 sampled aquifer wells, and in eight of 11 sampled perched‐water wells as far as 1.3 km away. These detections show that (i) low‐permeability layers in the unsaturated zone divert some flow horizontally, but do not prevent rapid transport to the aquifer; (ii) horizontal convective transport rates within the unsaturated zone may exceed 14 m d−1, perhaps through essentially saturated basalt fractures, tension cracks, lava tubes, or rubble zones; and (iii) some perched water beneath the Subsurface Disposal Area derives from episodic surface water more than 1 km away. Such rapid and far‐reaching flow may be common throughout the Snake River Plain, and possibly occurs in other locations that have a geologically complex unsaturated zone and comparable sources of infiltrating water.

Kilometer-Scale Rapid Transport of Naphthalene Sulfonate Tracer in the Unsaturated Zone at the Idaho National Engineering and Environmental Laboratory

To investigate possible long-range flow paths through the interbedded basalts and sediments of a 200-m-thick unsaturated zone, we applied a chemical tracer to seasonally filled infiltration ponds on the Snake River Plain in Idaho. This site is near the Subsurface Disposal Area for radioactive and other hazardous waste at the Idaho National Engineering and Environmental Laboratory. Within 4 mo, we detected tracer in one of 13 sampled aquifer wells, and in eight of 11 sampled perched-water wells as far as 1.3 km away. These detections show that (i) low-permeability layers in the unsaturated zone divert some flow horizontally, but do not prevent rapid transport to the aquifer; (ii) horizontal convective transport rates within the unsaturated zone may exceed 14 m d−1, perhaps through essentially saturated basalt fractures, tension cracks, lava tubes, or rubble zones; and (iii) some perched water beneath the Subsurface Disposal Area derives from episodic surface water more than 1 km away. Such rapid and far-reaching flow may be common throughout the Snake River Plain, and possibly occurs in other locations that have a geologically complex unsaturated zone and comparable sources of infiltrating water.

Gas Contaminant Mobility at Subsurface Disposal Area

ABSTRACTBeginning in 1952, waste materials, including volatile organic compounds (VOCs)contaminated with transuranic radionuclides, were generated during the fabrication, assembly, and processing of nuclear weapons components in the US Department of Energy (DOE) weapons productions complex at the Rocky Flats Plant (RFP). Following processing and containerization, drums were shipped to the Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL). During 1968 approximately 9,691 drums were buried there.In subsequent years, observations made during drum retrieval studies indicated that many of the drums were compromised on impact or suffered physical damage by compaction equipment shortly after burial. Corrosion also appears significant on drums buried for a few years. A large vadose-zone contaminant plume composed of solvents buried in the drums has been found beneath the burial area.Phase partitioning calculations show it unlikely that separate-phase solvent has leaked from the compromised drums deep into the soil profile or that solvents have dissolved into infiltrating water. Rather, it appears that the solvents are evaporating out of the barrels into the air phase and further partitioning from there throughout the subsurface.This paper describes the history of mixed wastes buried at the SDA, phase partitioning, and preliminary computer simulation results on gas contaminant mobility in the vadose zone.

Kilometer-Scale Rapid Transport of Naphthalene Sulfonate Tracer in the Unsaturated Zone at the Idaho National Engineering and Environmental Laboratory

To investigate possible long-range flow paths through the interbedded basalts and sediments of a 200-m-thick unsaturated zone, we applied a chemical tracer to seasonally filled infiltration ponds on the Snake River Plain in Idaho. This site is near the Subsurface Disposal Area for radioactive and other hazardous waste at the Idaho National Engineering and Environmental Laboratory. Within 4 mo, we detected tracer in one of 13 sampled aquifer wells, and in eight of 11 sampled perched-water wells as far as 1.3 km away. These detections show that (i) low-permeability layers in the unsaturated zone divert some flow horizontally, but do not prevent rapid transport to the aquifer; (ii) horizontal convective transport rates within the unsaturated zone may exceed 14 m d−1, perhaps through essentially saturated basalt fractures, tension cracks, lava tubes, or rubble zones; and (iii) some perched water beneath the Subsurface Disposal Area derives from episodic surface water more than 1 km away. Such rapid and far-reaching flow may be common throughout the Snake River Plain, and possibly occurs in other locations that have a geologically complex unsaturated zone and comparable sources of infiltrating water.

Safety risk analysis of an innovative environmental technology.

The authors describe a decision and risk analysis performed for the cleanup of a large Department of Energy mixed-waste subsurface disposal area governed by the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). In a previous study, the authors worked with the site decision makers, state regulators, and U.S. Environmental Protection Agency regional regulators to develop a CERCLA-based multiobjective decision analysis value model and used the model to perform a screening analysis of 28 remedial alternatives. The analysis results identified an innovative technology, in situ vitrification, with high effectiveness versus cost. Since this technology had not been used on this scale before, the major uncertainties were contaminant migration and pressure buildup. Pressure buildup was a safety concern due to the potential risks to worker safety. With the help of environmental technology experts remedial alternative changes were identified to mitigate the concerns about contaminant migration and pressure buildup. The analysis results showed that the probability of an event with a risk to worker safety had been significantly reduced. Based on these results, site decision makers have refocused their test program to examine in situ vitrification and have continued the use of the CERCLA-based decision analysis methodology to analyze remedial alternatives.