[en] Pacific Northwest National Laboratory assisted CH2M Hill Hanford Group, Inc., (CHG) by providing estimates of recharge rates for current conditions and long-term scenarios involving disposal in the Integrated Disposal Facility (IDF). The IDF will be located in the 200 East Area at the Hanford Site and will receive several types of waste including immobilized low-activity waste. The recharge estimates for each scenario were derived from lysimeter and tracer data collected by the IDF PA Project and from modeling studies conducted for the project. Recharge estimates were provided for three specific site features (the surface barrier; possible barrier side slopes; and the surrounding soil) and four specific time periods (pre-Hanford; Hanford operations; surface barrier design life; post-barrier design life). CHG plans to conduct a performance assessment of the latest IDF design and call it the IDF 2005 PA; this recharge data package supports the upcoming IDF 2005 PA

[en] Approximately 3 million liters of high temperature, Al-rich, hyperalkaline, and saline high-level waste fluids (HLWF) from the leaking tanks were deposited to the vadose zone at the Hanford Site, WA. The objective of this study was to investigate the effects of Al, hyperalkalinity and hypersalinity on dissolution in the Hanford sediments treated with solutions similar to HLWF..

[en] This paper details a new method to create permeable reactive barriers for the remediation of contaminated groundwater at the Hanford Site in Washington State

[en] The purpose of this laboratory study is to determine the influence of nitrate on the Hanford 100D Area in situ redox manipulation (ISRM) barrier longevity. There is a wide spread groundwater plume of 60 mg/L nitrate upgradient of the ISRM barrier with lower nitrate concentrations downgradient, suggestive of nitrate reduction occurring. Batch and 1-D column experiments showed that nitrate is being slowly reduced to nitrite and ammonia. These nitrate reduction reactions are predominantly abiotic, as experiments with and without bactericides present showed no difference in nitrate degradation rates. Nitrogen species transformation rates determined in experiments covered a range of ferrous iron/nitrate ratios such that the data can be used to predict rates in field scale conditions. Field scale reaction rate estimates for 100% reduced sediment (16 C) are: (a) nitrate degradation = 202 ± 50 h (half-life), (b) nitrite production = 850 ± 300 h, and (c) ammonia production = 650 ± 300 h. Calculation of the influence of nitrate reduction on the 100D Area reductive capacity requires consideration of mass balance and reaction rate effects. While dissolved oxygen and chromate reduction rates are rapid and essentially at equilibrium in the aquifer, nitrate transformation reactions are slow (100s of hours). In the limited (20-40 day) residence time in the ISRM barrier, only a portion of the nitrate will be reduced, whereas dissolved oxygen and chromate are reduced to completion. Assuming a groundwater flow rate of 1 ft/day, it is estimated that the ISRM barrier reductive capacity is 160 pore volumes (with no nitrate), and 85 pore volumes if 60 mg/L nitrate is present (i.e., a 47% decrease in the ISRM barrier longevity). Zones with more rapid groundwater flow will be less influenced by nitrate reduction. For example, a zone with a groundwater flow rate of 3 ft/day and 60 mg/L nitrate will have a reductive capacity of 130 pore volumes. Finally, long-term column experiments demonstrated the longevity of the reduced sediment barrier to reduce/immobilize 2 mg/L chromate in the presence of 8.4 mg/L dissolved oxygen (saturation), and 60 mg/L nitrate (maximums observed in the field). Initially the chromate reduction half-life was <0.1 h, 2.4 h by 120 pore volumes, and 17 h by 250 pore volumes. These chromate reduction rates are sufficiently fast relative to the 20-40 day residence time in the field for all chromate to be reduced/immobilized until the sediment is completely oxidized

[en] The oxidative dissolution of biogenic U(IV) precipitates was investigated in bioreduced sediment suspensions in contact with atmospheric O2 with an emphasis on the influence of Fe(II) and pH on the rate and extent of U release from the solid to the aqueous phase. The sediment was collected from the US Department of Energy (DOE) Field Research Center (FRC) site at Oak Ridge, Tennessee. Biogenic U(IV) precipitates and bioreduced sediment were generated through anaerobic incubation with a dissimilatory metal reducing bacterium Shewanella putrefaciens strain CN32. The oxidative dissolution of freshly prepared and aged biogenic U(IV) was conducted in 0.1 mol/L NaNO3 electrolyte with variable pH and Fe(II) concentrations. Biogenic U(IV)O2(s) was oxidized with the highest rate and extent at pH 4 and 9. U release to the aqueous phase was the lowest at circumneutral pH. Increasing Fe(II) significantly decreased the release of U(VI) to the aqueous phase. From 70 to 100% of the U in the sediments was extractable at the experiment termination (40-80 days) with a bicarbonate solution (0.2 mol/L), indicating that biogenic U(IV) was oxidized regardless of Fe(II) concentration and pH. Sorption experiments and modeling calculations indicated that the inhibitive effect of Fe(II) on U(IV) oxidative remobilization was consistent with the Fe(III) oxide precipitation and U(VI) sorption to this secondary phase

[en] The influence of sediment bioreduction and reoxidation on U(VI) sorption was studied using Fe(III) oxide-containing saprolite from the U.S. Department of Energy (DOE) Oak Ridge site. Bioreduced sediments were generated by anoxic incubation with a metal reducing bacterium, Shewanella putrefaciens strain CN32, supplied with an electron donor. The reduced sediments were subsequently reoxidized by air contact. U(VI) sorption was studied in Na-NO3-HCO3 electrolytes that were both closed and open to atmosphere, and where pH, U(VI) and carbonate concentration was varied. Moessbauer spectroscopy and chemical analyses showed that 50% of the Fe(III)-oxides were reduced to Fe(II) that was sorbed to the sediment during incubation with CN32. However, this reduction and subsequent reoxidation of the sorbed Fe(II) had negligible influence on the rate and extent of U sorption, or the extractability of sorbed U by 0.2 mol/L NaHCO3. Various results indicated that U(VI) surface complexation was the primary process responsible for uranyl sorption by the bioreduced and reoxidized sediments. A two-site, non-electrostatic surface complexation model best described U(VI) adsorption under variable pH, carbonate and U(VI) conditions. A ferrihydrite-based diffuse double layer model provided a better estimation of U(VI) adsorption without parameter adjustment than did a goethite-based model, even though a majority of the Fe(III)-oxides in the sediments were goethite

[en] The radioactive waste fluids stored in the tanks that have accidentally leaked into the vadose zone at the Hanford Site, WA, were high temperature, Al-rich, concentrated alkaline and saline solutions. In addition to dissolution, precipitation is likely to occur when these waste fluids contact the sediments..

[en] The purpose of this study was to quantify the influence of physical and/or geochemical heterogeneities in the Hanford 100D area In Situ Redox Manipulation (ISRM) barrier, which may be contributing to the discontinuous chromate breakthrough locations along the 65-well (2,300 ft long) barrier. Possible causes of chromate breakthrough that were investigated during this study include: (1) high hydraulic conductivity zones; (2) zones of low reducible iron; and (3) high hydraulic conductivity zones with low reducible iron. This laboratory-scale investigation utilized geochemical and physical characterization data collected on 0.5 to 1 foot intervals from four borehole locations. Results of this laboratory study did not provide definitive support any of the proposed hypotheses for explaining chromate breakthrough at the Hanford 100-D Area ISRM barrier. While site characterization data indicate a significant degree of vertical variability in both physical and geochemical properties in the four boreholes investigated, lateral continuity of high conductivity/low reductive capacity zones was not observed. The one exception was at the water table, where low reductive capacity and high-K zones were observed in 3 of four boreholes.Laterally continuous high permeability zones that contain oxic sediment near the water table is the most likely explanation for high concentration chromium breakthrough responses observed at various locations along the barrier. A mechanism that could explain partial chromate breakthrough in the ISRM barrier is the relationship between the field reductive capacity and the rate of chromate oxidation. Subsurface zones with low reductive capacity still have sufficient ferrous iron mass to reduce considerable chromate, but the rate of chromate reduction slows by 1 to 2 orders of magnitude relative to sediments with moderate to high reductive capacity.The original barrier longevity estimate of 160 pore volumes for homogeneous reduced sediment, or approximately 20 years, (with 5 mg/L dissolved oxygen and 2 ppm chromate) is reduced to 85 pore volumes (10 years) when the wide spread 60 ppm nitrate plume is included in the calculation. However, this reduction in barrier lifetime is not as great for high permeability channels, as there is insufficient time to reduce nitrate (and consume ferrous iron). If the cause of laterally discontinuous breakthrough of chromate along the ISRM barrier is due to oxic transport of chromate near the water table, additional dithionite treatment in these zones will not be effective. Treatment near the water table with a technology that emplaces considerable reductive capacity is needed, such as injectable zero valent iron

[en] Nine projects have been recently selected by the US Department of Energy (EM-22) to address groundwater contaminant migration at the Hanford Site. This paper summarizes the background and objectives of these projects. Five of the selected projects are targeted at hexavalent chromium contamination in Hanford 100 Area groundwater. These projects represent an integrated approach towards identifying the source of hexavalent chromium contamination in the Hanford 100-D Area and treating the groundwater contamination. Currently, there is no effective method to stop strontium-90 associated with the riparian zone sediments from leaching into the river. Phytoremediation may be a possible way to treat this contamination. Its use at the 100-N Area will be investigated. Another technology currently being tested for strontium-90 contamination at the 100-N Area involves injection (through wells) of a calcium-citrate-phosphate solution, which will precipitate apatite, a natural calcium-phosphate mineral. Apatite will adsorb the strontium-90, and then incorporate it as part of the apatite structure, isolating the strontium-90 contamination from entering the river. This EM-22 funded apatite project will develop a strategy for infiltrating the apatite solution from ground surface or a shallow trench to provide treatment over the upper portion of the contaminated zone, which is unsaturated during low river stage.

[en] Fluor Hanford is responsible for cleanup of legacy wastes, old production facilities, and environmental contamination that remain at the Hanford site. New technologies and technical information are being introduced to improve cost efficiency and assure safety. This paper presents recent advances in four of Fluor's projects. Supporting the Plutonium Finishing Plan Closure Project, laboratory evaluations and thermal analyses were conducted to quantify the potential for self-heating reactions that can develop in materials used to remove plutonium from contaminated equipment. Four commercial products were tested, and safe limits for packaging these wastes have been developed. The Groundwater Remediation Project is testing two technologies that show promise of preventing groundwater contaminants from reaching the Columbia River by innovative in situ methods. Laboratory tests are showing that the mineral apatite can sequester Sr-90, and current work to control in situ placement of the barrier is supporting a field deployment in late FY 06. In another location, a new approach using zero valent iron is being tested to 'mend' areas breached in the in situ redox manipulation barrier, which was installed to convert soluble chromium +6 to the less mobile +3 state. The Waste Stabilization and Disposition Project has successfully operated a process to grout sludge from spent fuel storage basins which controls the dose below contact handled limits. An in-line sensor and a nomogram that correlates dose to curies provide the operators with a simple and effective method to assure all waste drums meet WIPP acceptance specifications. The K Basins Closure Project will be transferring sludge containing fuel fragments using hoses and several pump booster stations. Selection of equipment fabrication materials required testing with a simulant, which in turn required laboratory evaluations of irradiated fuel hardness so that an appropriate non-radioactive material could be selected. A tungsten alloy was selected and used for testing system components