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[en] An ongoing treatability test is evaluating in situ biostimulation at the 100-D Area of the Hanford Site in Richland, Washington. This test is part of a strategy to couple multiple technologies to accelerate cleanup of hexavalent-chromium contaminated groundwater discharging into the Columbia River. A permeable chemical reducing barrier was previously applied as the primary treatment to prevent the chromium plume from reaching the river at concentrations that exceed regulatory standards. In situ biostimulation is intended to provide supplemental treatment upgradient of this chemical treatment barrier by reducing the concentration of the primary oxidizing species in groundwater (i.e., nitrate and dissolved oxygen) and chromium, thereby increasing the longevity of the chemical barrier and helping to diminish the chromium plume.
[en] A tight cluster of 35 new wells was installed over a former waste site, the South Process Pond (316-1 waste site), in the Hanford Site 300 Area in summer 2008. This report documents the details of the drilling, sampling, and well construction for the new array and presents a summary of the site hydrogeology based on the results of drilling and preliminary geophysical logging.
[en] A groundwater plume containing uranium, originating from a combination of purposeful discharges of wastewater to cribs, trenches and ponds, along with some accidental leaks and spills during nuclear fuel fabrication activities, has persisted beneath the Hanford Site 300 Area for many years. Despite the cessation of uranium releases and the removal of shallow vadose zone source materials, the goal of less than 30 (micro)g/L has not been achieved within the anticipated 10-year time period. Polyphosphate technology has been demonstrated to delay the precipitation of phosphate phases for controlled in situ precipitation of stable phosphate phases to control the long-term fate of uranium. Precipitation occurs when polyphosphate compounds hydrolyze to yield the orthophosphate molecule. Based on the hydrolysis kinetics of the polyphosphate polymer, the amendment can be tailored to act as a time-released source of phosphate for lateral plume treatment, immediate and sustained remediation of dissolved uranium, and to preclude rapid precipitation which could result in a drastic change in hydraulic conductivity of the target aquifer. Critical to successful implementation of polyphosphate remediation technology is a site specific evaluation and optimization of multi-length polyphosphate amendment formulations. A multi-faceted approach has been taken to provide key fundamental science knowledge regarding optimization of the polyphosphate remedy through: (1) phosphorus-31 nuclear magnetic resonance to quantify the effects of Hanford groundwater and sediment on the degradation of inorganic phosphates, (2) static tests to quantify the kinetics, loading, and stability of apatite as a long-term sorbent for uranium, and (3) single-pass flow through testing to quantify the stability of autunite and apatite under relevant site conditions. Dynamic column tests were utilized to (1) optimize the composition of the polyphosphate formulation for the formation and emplacement of apatite and autunite, (2) understand the rate and extent of reaction between polyphosphate and uranium-bearing phases, (3) evaluate the effect of chemical microenvironments on the degradation of polyphosphate and the formation of autunite, and (4) quantify the mobility of polyphosphate as a function of water content. These activities are being conducted in parallel with a limited field investigation, to more accurately define the vertical extent of uranium in the vadose zone, and in the capillary fringe laterally throughout the plume
[en] A labortory testing program has been conducted to optimize polyphosphate remediation technology for implementation through a field-scale technology infiltration demonstration to stabilize soluble, uranium-bearing source phases in the vadose zone and capillary fringe. Source treatment in the deep vadose zone will accelerate the natural attenuation of uranium to more thermodynamically stable uranium-phosphate minerals, enhancing the performance of the proposed polyphosphate remediation within the 300 Area aquifer. The objective of this investigation was to develop polyphosphate remediation technology to treat uranium contamination contained within the deep vadose zone and capillary fringe. This paper presents the results of an investigation that evaluated the rate and extent of reaction between polyphosphate and the uranium mineral phases present within the 300 Area vadose zone and capillary fringe and autunite formation as a function of polyphosphate formulation and concentration. This information is critical for identifying the optimum implementation approach and controlling the flux of uranium from the vadose zone and capillary fringe to the underlying aquifer during remediation. Results from this investigation will be used to design a full-scale remediation of uranium at the 300 Area of the Hanford Site.
[en] Sr-90 present in groundwater and the vadose zone at the Hanford 100N area due to past waste disposal practices has reached the nearby Columbia River, as evidenced by Sr-90 concentrations in near river wells and aquifer tubes and near shore sediments. Sr-90 is currently being remediated by adsorption onto apatite (55 times stronger than Sr-90 adsorption to sediment), followed by incorporation of the Sr-90 into the apatite structure. If the Sr-90 can remain immobilized for 300 years (∼ten 29.1-yr half-lives of Sr-90 decay), it will have decayed below regulatory limits to Y-90 and to stable Zr-90. Apatite (Ca10(PO4)6(OH)2) is being precipitated in situ in saturated zone sediments by injection of a aqueous solution of Ca-citrate and Na-phosphate through a series of 16 wells. For the treatability study, field scale demonstration of the technology was implemented through injection of a low-concentration, apatite-forming solution, followed by high concentration solution injections as required to emplace sufficient treatment capacity to meet treatability test objectives. Analysis of field cores collected after the low concentration injections indicates that targeted apatite contents were achieved and that ∼25% of the Sr-90 associated with the sediment was incorporated in the apatite structure. Aqueous Sr-90 monitoring in four compliance monitoring wells over a year following the high concentration injections indicates 84% to 95% decrease in Sr-90 concentrations (relative to the low and high end of the baseline range, respectively). Cores are currently being analyzed to confirm the apatite mass and Sr-90 substitution in apatite after these high concentration injections.
[en] A site specific treatability test was conducted to optimize polyphosphate remediation technology for implementation through a field-scale technology demonstration to accelerate monitored natural attenuation of the uranium plume within the Hanford 300 Area aquifer. A focused application of polyphosphate was conducted in a source or 'hot spot' area to reduce the inventory of available uranium that contributes to the groundwater plume through direct precipitation of uranyl-phosphate solids and secondary containment via precipitation of apatite acting as a long-term sorbent for uranium. The general treatability testing approach consisted of initial site characterization and setup, a polyphosphate injection test, and post-treatment performance assessment. Fundamental science studies were conducted with site specific sediment and groundwater to develop an effective remediation scheme for deployment of polyphosphate technology. In addition to remediating a portion of the plume, the data from this test provides valuable information for designing a full-scale remediation of uranium in the aquifer at the 300 Area of the Hanford Site. It will also provide a detailed understanding of the fundamental underpinnings necessary to evaluate the efficacy and potential utilization of polyphosphate technology at other sites with varying geochemical and hydrodynamic conditions.
[en] Pacific Northwest National Laboratory is conducting a treatability test designed to demonstrate that in situ biostimulation can be applied to help meet cleanup goals in the Hanford Site 100-D Area. The in situ biostimulation technology is intended to provide supplemental treatment upgradient of the In Situ Redox Manipulation (ISRM) barrier by reducing the concentration of the primary oxidizing species in groundwater (i.e., nitrate and dissolved oxygen) and chromate, and thereby increasing the longevity of the ISRM barrier. This report summarizes the initial results from field testing of an in situ biological treatment zone implemented through injection of a soluble substrate. The field test is divided into operational phases that include substrate injection, process monitoring, and performance monitoring. The results summarized herein are for the substrate injection and process monitoring phase encompassing the first approximately three months of field testing. Performance monitoring is ongoing at the time this report was prepared and is planned to extend over approximately 18 months. As such, this report is an interim data summary report for the field test. The treatability testing has multiple objectives focused on evaluating the performance of biostimulation as a reducing barrier for nitrate, oxygen, and chromate. The following conclusions related to these objectives are supported by the data provided in this report. Substrate was successfully distributed to a radius of about 15 m (50 ft) from the injection well. Monitoring data indicate that microbial growth initiated rapidly, and this rapid growth would limit the ability to inject substrate to significantly larger zones from a single injection well. As would be expected, the uniformity of substrate distribution was impacted by subsurface heterogeneity. However, subsequent microbial activity and ability to reduce the targeted species was observed throughout the monitored zone during the process monitoring period, and low nitrate and oxygen concentrations were maintained. Chromate concentrations in the treatment zone began to increase about two months after substrate injection, up to about 30 percent of the background concentration upgradient of the test site. The performance monitoring phase will provide additional data to interpret the performance of the biostimulation process and information for scale-up as a reducing barrier.
[en] This report presents results from bench-scale treatability studies conducted under site-specific conditions to optimize the polyphosphate amendment for implementation of a field-scale technology demonstration to stabilize uranium within the 300 Area vadose and smear zones of the Hanford Site. The general treatability testing approach consisted of conducting studies with site sediment and under site conditions, to develop an effective chemical formulation and infiltration approach for the polyphosphate amendment under site conditions. Laboratory-scale dynamic column tests were used to (1) quantify the retardation of polyphosphate and its degradation products as a function of water content, (2) determine the rate of polyphosphate degradation under unsaturated conditions, (3) develop an understanding of the mechanism of autunite formation via the reaction of solid phase calcite-bound uranium and aqueous polyphosphate remediation technology, (4) develop an understanding of the transformation mechanism, the identity of secondary phases, and the kinetics of the reaction between uranyl-carbonate and -silicate minerals with the polyphosphate remedy under solubility-limiting conditions, and (5) quantify 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 smear zone
[en] The Integrated Field Research Challenge (IFRC) at the Hanford Site 300 Area uranium (U) plume addresses multi-scale mass transfer processes in a complex subsurface biogeochemical setting where groundwater and riverwater interact. A series of forefront science questions on reactive mass transfer motivates research. These questions relate to the effect of spatial heterogeneities; the importance of scale; coupled interactions between biogeochemical, hydrologic, and mass transfer processes; and measurements and approaches needed to characterize and model a mass-transfer dominated biogeochemical system. The project was initiated in February 2007, with CY 2007, CY 2008, CY 2009, and CY 2010 progress summarized in preceding reports. A project peer review was held in March 2010, and the IFRC project acted upon all suggestions and recommendations made in consequence by reviewers and SBR/DOE. These responses have included the development of 'Modeling' and 'Well-Field Mitigation' plans that are now posted on the Hanford IFRC web-site, and modifications to the IFRC well-field completed in CY 2011. The site has 35 instrumented wells, and an extensive monitoring system. It includes a deep borehole for microbiologic and biogeochemical research that sampled the entire thickness of the unconfined 300 A aquifer. Significant, impactful progress has been made in CY 2011 including: (i) well modifications to eliminate well-bore flows, (ii) hydrologic testing of the modified well-field and upper aquifer, (iii) geophysical monitoring of winter precipitation infiltration through the U-contaminated vadose zone and spring river water intrusion to the IFRC, (iv) injection experimentation to probe the lower vadose zone and to evaluate the transport behavior of high U concentrations, (v) extended passive monitoring during the period of water table rise and fall, and (vi) collaborative down-hole experimentation with the PNNL SFA on the biogeochemistry of the 300 A Hanford-Ringold contact and the underlying redox transition zone. The modified well-field has functioned superbly without any evidence for well-bore flows. Beyond these experimental efforts, our site-wide reactive transport models (PFLOTRAN and eSTOMP) have been updated to include site geostatistical models of both hydrologic properties and adsorbed U distribution; and new hydrologic characterization measurements of the upper aquifer. These increasingly robust models are being used to simulate past and recent U desorption-adsorption experiments performed under different hydrologic conditions, and heuristic modeling to understand the complex functioning of the smear zone. We continued efforts to assimilate geophysical logging and 3D ERT characterization data into our site wide geophysical model, with significant and positive progress in 2011 that will enable publication in 2012. Our increasingly comprehensive field experimental results and robust reactive transport simulators, along with the field and laboratory characterization, are leading to a new conceptual model of U(VI) flow and transport in the IFRC footprint and the 300 Area in general, and insights on the microbiological community and associated biogeochemical processes influencing N, S, C, Mn, and Fe. Collectively these findings and higher scale models are providing a unique and unparalleled system-scale understanding of the biogeochemical function of the groundwater-river interaction zone.
[en] The Old Rifle Site is a former vanadium and uranium ore-processing facility located adjacent to the Colorado River and approximately 0.3 miles east of the city of Rifle, CO. The former processing facilities have been removed and the site uranium mill tailings are interned at a disposal cell north of the city of Rifle. However, some low level remnant uranium contamination still exists at the Old Rifle site. In 2002, the United States Nuclear Regulatory Commission (US NRC) concurred with United States Department of Energy (US DOE) on a groundwater compliance strategy of natural flushing with institutional controls to decrease contaminant concentrations in the aquifer. In addition to active monitoring of contaminant concentrations, the site is also used for DOE Legacy Management (LM) and other DOE-funded small-scale field tests of remediation technologies. The purpose of this laboratory scale study was to evaluate the effectiveness of a hydroxyapatite (Ca10(PO4)6(OH)2) permeable reactive barrier and source area treatment in Old Rifle sediments. Phosphate treatment impact was evaluated by comparing uranium leaching and surface phase changes in untreated to PO4-treated sediments. The impact of the amount of phosphate precipitation in the sediment on uranium mobility was evaluated with three different phosphate loadings. A range of flow velocity and uranium concentration conditions (i.e., uranium flux through the phosphate-treated sediment) was also evaluated to quantify the uranium uptake mass and rate by the phosphate precipitate.