Identification of Solubility-Controlling Solid Phases in a Large Fly Ash Field Lysimeter

Samples of pore fluids and leachates were obtained from a large fly ash field lysimeter in central Pennsylvania. The fly ash in the lysimeter was usually only partially saturated, and only 0.3 pore volumes of water leached through the lysimeter during the 3-year study period. The samples were analyzed for major and trace inorganic anions and cations. The resulting analyses were modeled by using an equilibrium speciation/solubility code to test the hypothesis that the solubilities of at least some species in the fly ash leachate were controlled by solid phases. Potential solubility-controlling solids were identified for Al, Ba, Ca, Cr, Cu, Fe, S, Si, and Sr in the pore waters and leachates. Solid solutions appear to play an important role in controlling the concentrations of Ba, Sr, and Cr. The activity relationships were independent of location within the lysimeter and time of sampling. A laboratory experiment showed that equilibration times between these nine elements and their solubility-controlling solids were on the order of days or less. Geochemical reactions controlling the concentrations of As, B, Cd, Mo, and Se were not identified

Identification of Solubility-Controlling Solid Phases in a Large Fly Ash Field Lysimeter

Samples of pore fluids and leachates were obtained from a large fly ash field lysimeter in central Pennsylvania. The fly ash in the lysimeter was usually only partially saturated, and only 0.3 pore volumes of water leached through the lysimeter during the 3-year study period. The samples were analyzed for major and trace inorganic anions and cations. The resulting analyses were modeled by using an equilibrium speciation/solubility code to test the hypothesis that the solubilities of at least some species in the fly ash leachate were controlled by solid phases. Potential solubility-controlling solids were identified for Al, Ba, Ca, Cr, Cu, Fe, S, Si, and Sr in the pore waters and leachates. Solid solutions appear to play an important role in controlling the concentrations of Ba, Sr, and Cr. The activity relationships were independent of location within the lysimeter and time of sampling. A laboratory experiment showed that equilibration times between these nine elements and their solubility-controlling solids were on the order of days or less. Geochemical reactions controlling the concentrations of As, B, Cd, Mo, and Se were not identified

HST-NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core

We report results from HST-NICMOS imaging of the extremely dense core of the globular cluster Terzan 5. This highly obscured bulge cluster has been estimated to have one of the highest collision rates of any galactic globular cluster, making its core a particularly conducive environment for the production of interacting binary systems. We have reconstructed high-resolution images of the central 19"x19" region of Terzan 5 by application of the drizzle algorithm to dithered NIC2 images in the F110W, F187W, and F187N near-infrared filters. We have used a DAOPHOT/ALLSTAR analysis of these images to produce the deepest color-magnitude diagram (CMD) yet obtained for the core of Terzan 5. We have also analyzed the parallel 11"X11" NIC1 field, centered 30" from the cluster center and imaged in F110W and F160W, and an additional NIC2 field that is immediately adjacent to the central field. This imaging results in a clean detection of the red-giant branch and horizontal branch in the central NIC2 field, and the detection of these plus the main-sequence turnoff and the upper main sequence in the NIC1 field. We have constructed an H versus J-H CMD for the NIC1 field. We obtain a new distance estimate of 8.7 kpc, which places Terzan 5 within less than 1 kpc of the galactic center. We have also determined a central surface-density profile which results in a maximum likelihood estimate of 7.9" +/- 0.6" for the cluster core radius. We discuss the implications of these results for the dynamical state of Terzan 5.Comment: 17 pages, 9 figures, accepted for publication in ApJ, for May 20, 200

Experimental Plan: Uranium Stabilization Through Polyphosphate Injection 300 Area Uranium Plume Treatability Demonstration Project

This Test Plan describes a laboratory-testing program to be performed at Pacific Northwest National Laboratory (PNNL) in support of the 300-FF-5 Feasibility Study (FS). The objective of the proposed treatability test is to evaluate the efficacy of using polyphosphate injections to treat uranium contaminated groundwater in situ. This study will be used to: (1) Develop implementation cost estimates; (2) Identify implementation challenges; and (3) Investigate the technology's ability to meet remedial objectives These activities will be conducted in parallel with a limited field investigation, which is currently underway to more accurately define the vertical extent of uranium in the vadose zone, and in the capillary fringe zone laterally throughout the plume. The treatability test will establish the viability of the method and, along with characterization data from the limited field investigation, will provide the means for determining how best to implement the technology in the field. By conducting the treatability work in parallel with the ongoing Limited Field Investigation, the resulting Feasibility Study (FS) will provide proven, site-specific information for evaluating polyphosphate addition and selecting a suitable remediation strategy for the uranium plume within the FS time frame at an overall cost savings

Project Work Plan Carbon Tetrachloride and Chloroform Attenuation Parameter Studies: Heterogeneous Hydrolytic Reactions

Between 1955 and 1973, an estimated 750,000 kg of carbon tetrachloride were discharged to the soil in the 200 West Area of the Hanford Site as part of the plutonium production process. Of this amount, some carbon tetrachloride reached the groundwater more than 70 m below the ground surface and formed a plume of 10 km2. Recent information has shown that the carbon tetrachloride plume extends to a depth of at least 60 m below the water table. Some carbon tetrachloride has been degraded either by the original process or subsequent transformations in the subsurface to form a co-existing chloroform plume. Although current characterization efforts are improving the conceptual model of the source area, more information is needed to effectively assess the fate and transport of carbon tetrachloride and chloroform to support upcoming remediation decisions for the plume. As noted in a simulation study by Truex et al. (2001), parameters describing porosity, sorption, and abiotic degradation have the largest influence on predicted plume behavior. The work proposed herein will improve the ability to predict future plume movement by better quantifying abiotic degradation mechanisms and rates. This effort will help define how much active remediation may be needed and estimate where the plume will eventually stabilize – key factors in determining the most appropriate remedy for the plume

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

The primary objective of this study is to summarize the laboratory investigations performed to evaluate short- and long-term effects of phosphate treatment on uranium leaching from 300 area smear zone sediments. Column studies were used to compare uranium leaching in phosphate-treated to untreated sediments over a year with multiple stop flow events to evaluate longevity of the uranium leaching rate and mass. A secondary objective was to compare polyphosphate injection, polyphosphate/xanthan injection, and polyphosphate infiltration technologies that deliver phosphate to sediment

Experimental Plan: 300 Area Treatability Test: In Situ Treatment of the Vadose Zone and Smear Zone Uranium Contamination by Polyphosphate Infiltration

The overall objectives of the treatability test is to evaluate and optimize polyphosphate remediation technology for infiltration either from ground surface, or some depth of excavation, providing direct stabilization of uranium within the deep vadose and capillary fringe above the 300 Area aquifer. Expected result from this experimental plan is a data package that includes: 1) quantification of the retardation of polyphosphate, 2) the rate of degradation and the retardation of degradation products as a function of water content, 3) an understanding of the mechanism of autunite formation via the reaction of solid phase calcite-bound uranium and aqueous polyphosphate remediation technology, 4) an understanding of the transformation mechanism, identity of secondary phases, and the kinetics of the reaction between uranyl-carbonate and –silicate minerals with the polyphosphate remedy under solubility-limiting conditions, 5) quantification of the extent and rate of uranium released and immobilized based on the infiltration rate of the polyphosphate remedy and the effect of and periodic wet-dry cycling on the efficacy of polyphosphate remediation for uranium in the vadose zone and capillary fringe, and 6) quantification of reliable equilibrium solubility values for autunite under hydraulically unsaturated conditions allowing accurate prediction of the long-term stability of autunite. Moreover, results of intermediate scale testing will quantify the transport of polyphosphate and degradation products, and yield degradation rates, at a scale that is bridging the gap between the small-scale UFA studies and the field scale. These results will be used to test and verify a site-specific, variable saturation, reactive transport model and to aid in the design of a pilot-scale field test of this technology. In particular, the infiltration approach and monitoring strategy of the pilot test would be primarily based on results from intermediate-scale testing. Results from this experimental plan will be documented in a PNNL report

Challenges Associated with Apatite Remediation of Uranium in the 300 Area Aquifer

Sequestration of uranium as insoluble phosphate phases appears to be a promising alternative for treating the uranium-contaminated groundwater at the Hanford 300 Area. The proposed approach involves both the direct formation of autunite by the application of a polyphosphate mixture, as well as the formation of apatite in the aquifer as a continuing source of phosphate for long-term treatment of uranium. After a series of bench-scale tests, a field treatability test was conducted in a well at the 300 Area. The objective of the treatability test was to evaluate the efficacy of using polyphosphate injections to treat uranium-contaminated groundwater in situ. A test site consisting of an injection well and 15 monitoring wells was installed in the 300 Area near the process trenches that had previously received uranium-bearing effluents. The results indicated that while the direct formation of autunite appears to have been successful, the outcome of the apatite formation of the test was more limited. Two separate overarching issues impact the efficacy of apatite remediation for uranium sequestration within the 300 Area: 1) the efficacy of apatite for sequestering uranium under the present geochemical and hydrodynamic conditions, and 2) the formation and emplacement of apatite via polyphosphate technology. This paper summarizes these issues

100-NR-2 Apatite Treatability Test: High-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization

Following an evaluation of potential strontium-90 (90Sr) treatment technologies and their applicability under 100-NR-2 hydrogeologic conditions, the U.S. Department of Energy (DOE), Fluor Hanford, Inc. (now CH2M Hill Plateau Remediation Company [CHPRC]), Pacific Northwest National Laboratory, and the Washington State Department of Ecology agreed that the long-term strategy for groundwater remediation at the 100-N Area should include apatite as the primary treatment technology. This agreement was based on results from an evaluation of remedial alternatives that identified the apatite permeable reactive barrier (PRB) technology as the approach showing the greatest promise for reducing 90Sr flux to the Columbia River at a reasonable cost. This letter report documents work completed to date on development of a high-concentration amendment formulation and initial field-scale testing of this amendment solution

Site Characterization Plan: Uranium Stabilization through Polyphosphate Injection

An initial feasibility study of options to treat the uranium plume at the 300-FF-5 Operable Unit considered hydraulic containment, slurry wall containment, and groundwater extraction as potential remedial action technologies. None were selected for interim action, and reduction of contamination levels by natural processes was considered a viable alternative while source removal actions continued. Subsequent planning for a Phase III feasibility study focused on methods that would reduce the concentration of uranium in the aquifer, including multiple methods to immobilize uranium using chemical-based technologies. Based on an initial technology screening, the polyphosphate technology was identified as the best candidate to treat the for further evaluation and selected for treatability testing. The overall objective of the polyphosphate treatability test is to evaluate the efficacy of using polyphosphate injections to treat uranium contaminated groundwater in situ. The objective of the work elements included in this site characterization plan is to collect site-specific characterization data that will be needed to design and implement a field-scale demonstration of the technology