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Stability of U(VI)- and Tc(VII) reducing microbial communities to environmental perturbation: a thermodynamic network model and intermediate-scale experiments

Description: The project is a collaborative task with a larger project headed by Jack Istok at Oregon State University, which is conducted under the same title. The project was conceptualized as follows. A ''geochemical'' model of microbial communities was hypothesized, in which microbes were characterized as mineral species according to the chemical transformations they used for metabolic function. The iron-reducing bacteria, for example, would be represented by the iron reducing chemical reaction, including a specific electron donor, the fraction of the consumed donor used for biomass maintenance or growth, and a free energy for the reaction. The pseudomineral species would then be included in a standard geochemical model, and community succession could be calculated according to the thermodynamically favored microbially mediated reactions under progressive consumption of electron donors and receptors, and evolving geochemical conditions. The project includes relatively minor participation by the University of Oklahoma and Pacific Northwest National Laboratory, with the major component at OSU. The PNNL project was funded to provide assistance to Dr. Istok in formulating the appropriate modeling approach and geochemical constraints on the modeling effort.
Date: June 1, 2006
Creator: McKinley, James P.; Liu, Chongxuan; Istok, Jack & Krumholz, Lee
Partner: UNT Libraries Government Documents Department

Stability of U(VI) and Tc(VII) Reducing Microbial Communities to Environmental Perturbation: Development and Testing of a Thermodynamic Network Model

Description: Previously published research from in situ field experiments at the NABIR Field Research Center have shown that cooperative metabolism of denitrifiers and Fe(III)/sulfate reducers is essential for creating subsurface conditions favorable for U(VI) and Tc(VII) bioreduction (Istok et al., 2004). The overall goal of this project is to develop and test a thermodynamic network model for predicting the effects of substrate additions and environmental perturbations on the composition and functional stability of subsurface microbial communities. The overall scientific hypothesis is that a thermodynamic analysis of the energy-yielding reactions performed by broadly defined groups of microorganisms can be used to make quantitative and testable predictions of the change in microbial community composition that will occur when a substrate is added to the subsurface or when environmental conditions change. An interactive computer program was developed to calculate the overall growth equation and free energy yield for microorganisms that grow by coupling selected combinations of electron acceptor and electron donor half-reactions. Each group performs a specific function (e.g. oxidation of acetate coupled to reduction of nitrate); collectively the groups provide a theoretical description of the entire natural microbial community. The microbial growth data are combined with an existing thermodynamic data base for associated geochemical reactions and used to simulate the coupled microbial-geochemical response of a complex natural system to substrate addition or any other environmental perturbations.
Date: June 1, 2005
Creator: McKinley, James P. & Istok, Jonathan
Partner: UNT Libraries Government Documents Department

In situ Microbial Community Control of the Stability of Bio-Reduced Uranium

Description: In aerobic aquifers typical of many Department of Energy (DOE) legacy waste sites, uranium is present in the oxidized U(VI) form which is soluble and thus mobile compared to U(IV). Previous work at the Old Rifle Uranium Mill Tailings Remedial Action (UMTRA) site demonstrated that biostimulation by acetate injection promoted growth of Geobacteraceae and stimulated the microbial reduction of U(VI) to less soluble U(IV) (1, 4). Despite the potential for oxidative dissolution of bio-reduced U(IV), field experiments at the Old Rifle site show that although the rate of U(VI) reduction decreases following the on-set of sulfate reduction, U(VI) reduction continues even following the cessation of acetate injection (1, 4). However, U(VI) reduction is reversible and the basis for the observed maintenance of U(VI) reduction post-stimulation is a critical but as yet unresolved issue for the application of biostimulation as a treatment technology. The continued U(VI) reduction and the maintenance of reduced U(IV) may result from many factors including U(VI) reduction by sulfate reducing bacteria (SRB), generation of H2S or FeS0.9 which serves as an oxygen sink, or the preferential sorption of U(VI) by microbial cells or biopolymers. The overall goal of the project is to develop an understanding of the mechanisms for the maintenance of bio-reduced uranium in an aerobic aquifer under field conditions following the cessation of electron donor addition.
Date: June 1, 2006
Creator: Long, Phillip E.; McKinley, James P. & White, David C.
Partner: UNT Libraries Government Documents Department

Fixation Mechanisms and Desorption Rates of Sorbed Cs in High-Level Waste Contaminated Subsurface Sediments: Implications to Future Behavior and In-Ground Stability

Description: Research is investigating mineralogic and geochemical factors controlling the desorption rate of 137Cs+ from subsurface sediments on the Hanford Site contaminated with different types of high level waste. The project will develop kinetic data and models that describe the release rates of 137Cs+ from contaminated sediments over a range of potential geochemical conditions that may evolve during waste retrieval from overlying tanks, or in response to meteoric water infiltration. Scientific understanding and computational techniques will be established to predict the future behavior of sorbed, in-ground 137Cs+.
Date: June 1, 2002
Creator: Zachara, John M.; McKinley, James P.; Ainsworth, Calvin C. & Serne, R. Jeff
Partner: UNT Libraries Government Documents Department

Fixation Mechanisms and Desorption Rates of Sorbed Cs in High-Level Waste Contaminated Subsurface Sediments: Implications to Future Behavior and In-Ground Stability

Description: The high-yield fission product 137Cs is a major contaminant of the vadose zone at Hanford and other DOE sites. Over 100 kCi of 137Cs was discharged to the vadose zone in the S-SX tank farm at Hanford through the leakage of high-level waste from tanks SX-108 and SX-109. Although 137Cs is strongly sorbed by subsurface sediments, certain waste characteristics, such as high Na+, can expedite its migration and reduce its retardation to low values. This project is focused on defining the in-ground geochemistry of sorbed 137Cs released from high-level waste tanks, so that better future projections can be made of Cs mobility in the vadose zone. The project will study Cs-contaminated subsurface sediments from various Hanford tank farms to (1) determine the mineralogic and surface site residence of sorbed Cs in contaminated sediments varying in current Cs content and original waste composition, (2) establish geochemical factors and processes controlling Cs desorbability and desorption kinetics from contaminated sediment and Cs-enriched sediment particles, and (3) define and parameterize a kinetic model for Cs desorption that incorporates multi-site behavior and heterogeneous intraparticle Cs distribution.
Date: June 1, 2001
Creator: Zachara, John M.; McKinley, James P.; Ainsworth, Calvin C. & Serne, R. Jeff
Partner: UNT Libraries Government Documents Department

Geochemical Characterization of Chromate Contamination in the 100 Area Vadose Zone at the Hanford Site - Part 2

Description: At the Hanford Site, chromate was used throughout the 100 Areas (100-B, 100-C, 100-D/DR, 100-F, 100-H, and 100 K) as a corrosion inhibitor in reactor cooling water. Chromate was delivered in rail cars, tanker trucks, barrels, and local pipelines as dichromate granular solid or stock solution. In many occasions, chromate was inevitably discharged to surface or near-surface ground through spills during handling, pipeline leaks, or during disposal to cribs. The composition of the liquids that were discharged is not known and it is quite possible that Cr(VI) fate and transport in the contaminated sediments would be a function of the chemical composition of the waste fluids. The major objectives of this investigation which was limited in scope by the financial resources available, were to 1) determine the leaching characteristics of hexavalent chromium [Cr(VI)] from contaminated sediments collected from 100-D Area spill sites; 2) elucidate possible Cr(VI) mineral and/or chemical associations that may be responsible for Cr(VI) retention in the Hanford Site 100 Areas through the use of macroscopic leaching studies, and microscale characterization of contaminated sediments; and 3) provide information to construct a conceptual model of Cr(VI) geochemistry in the Hanford 100 Area vadose zone that can be used for developing options for environmental remediation. The information gathered from this research effort will help to further improve our understanding of Cr(VI) behavior in the vadose zone and will also help in accelerating the 100 Area Columbia River Corridor cleanup by providing valuable information to develop remedial action based on a fundamental understanding of Cr(VI) vadose zone geochemistry. A series of column experiments were conducted with contaminated sediments to study Cr(VI) desorption patterns. Column experiments used the field size fraction of the sediment samples and a simulated Hanford Site groundwater solution. Periodic stop flow events were applied to evaluate the change ...
Date: January 4, 2011
Creator: Qafoku, Nikolla; Dresel, P. Evan; McKinley, James P.; Ilton, Eugene S.; Um, Wooyong; Resch, Charles T. et al.
Partner: UNT Libraries Government Documents Department

Geochemical Characterization of Chromate Contamination in the 100 Area Vadose Zone at the Hanford Site

Description: The major objectives of the proposed study were to: 1.) determine the leaching characteristics of hexavalent chromium [Cr(VI)] from contaminated sediments collected from 100 Area spill sites; 2.) elucidate possible Cr(VI) mineral and/or chemical associations that may be responsible for Cr(VI) retention in the Hanford Site 100 Areas through the use of i.) macroscopic leaching studies and ii.) microscale characterization of contaminated sediments; and 3.) provide information to construct a conceptual model of Cr(VI) geochemistry in the Hanford 100 Area vadose zone. In addressing these objectives, additional benefits accrued were: (1) a fuller understanding of Cr(VI) entrained in the vadose zone that will that can be utilized in modeling potential Cr(VI) source terms, and (2) accelerating the Columbia River 100 Area corridor cleanup by providing valuable information to develop remedial action based on a fundamental understanding of Cr(VI) vadose zone geochemistry. A series of macroscopic column experiments were conducted with contaminated and uncontaminated sediments to study Cr(VI) desorption patterns in aged and freshly contaminated sediments, evaluate the transport characteristics of dichromate liquid retrieved from old pipelines of the 100 Area; and estimate the effect of strongly reducing liquid on the reduction and transport of Cr(VI). Column experiments used the < 2 mm fraction of the sediment samples and simulated Hanford groundwater solution. Periodic stop-flow events were applied to evaluate the change in elemental concentration during time periods of no flow and greater fluid residence time. The results were fit using a two-site, one dimensional reactive transport model. Sediments were characterized for the spatial and mineralogical associations of the contamination using an array of microscale techniques such as XRD, SEM, EDS, XPS, XMP, and XANES. The following are important conclusions and implications. Results from column experiments indicated that most of contaminant Cr travels fast through the sediments and appears as Cr(VI) ...
Date: July 16, 2008
Creator: Dresel, P. Evan; Qafoku, Nikolla; McKinley, James P.; Fruchter, Jonathan S.; Ainsworth, Calvin C.; Liu, Chongxuan et al.
Partner: UNT Libraries Government Documents Department

Remediation of Uranium in the Hanford Vadose Zone Using Gas-Transported Reactants: Laboratory Scale Experiments in Support of the Deep Vadose Zone Treatability Test Plan for the Hanford Central Plateau

Description: This laboratory-scale investigation is focused on decreasing mobility of uranium in subsurface contaminated sediments in the vadose zone by in situ geochemical manipulation at low water content. This geochemical manipulation of the sediment surface phases included reduction, pH change (acidic and alkaline), and additions of chemicals (phosphate, ferric iron) to form specific precipitates. Reactants were advected into 1-D columns packed with Hanford 200 area U-contaminated sediment as a reactive gas (for CO2, NH3, H2S, SO2), with a 0.1% water content mist (for NaOH, Fe(III), HCl, PO4) and with a 1% water content foam (for PO4). Uranium is present in the sediment in multiple phases that include (in decreasing mobility): aqueous U(VI) complexes, adsorbed U, reduced U(IV) precipitates, rind-carbonates, total carbonates, oxides, silicates, phosphates, and in vanadate minerals. Geochemical changes were evaluated in the ability to change the mixture of surface U phases to less mobile forms, as defined by a series of liquid extractions that dissolve progressively less soluble phases. Although liquid extractions provide some useful information as to the generalized uranium surface phases (and are considered operational definitions of extracted phases), positive identification (by x-ray diffraction, electron microprobe, other techniques) was also used to positively identify U phases and effects of treatment. Some of the changes in U mobility directly involve U phases, whereas other changes result in precipitate coatings on U surface phases. The long-term implication of the U surface phase changes to alter U mass mobility in the vadose zone was then investigated using simulations of 1-D infiltration and downward migration of six U phases to the water table. In terms of the short-term decrease in U mobility (in decreasing order), NH3, NaOH mist, CO2, HCl mist, and Fe(III) mist showed 20% to 35% change in U surface phases. Phosphate addition (mist or foam advected) showed inconsistent ...
Date: January 4, 2010
Creator: Szecsody, James E.; Truex, Michael J.; Zhong, Lirong; Williams, Mark D.; Resch, Charles T. & McKinley, James P.
Partner: UNT Libraries Government Documents Department

SERDP ER-1421 Abiotic and Biotic Mechanisms Controlling In Situ Remediation of NDMA: Final Report

Description: This laboratory-scale project was initiated to investigate in situ abiotic/biotic mineralization of NDMA. Under iron-reducing conditions, aquifer sediments showed rapid abiotic NDMA degradation to dimethylamine (DMA), nitrate, formate, and finally, CO2. These are the first reported experiments of abiotic NDMA mineralization. The NDMA reactivity of these different iron phases showed that adsorbed ferrous iron was the dominant reactive phase that promoted NDMA reduction, and other ferrous phases present (siderite, iron sulfide, magnetite, structural ferrous iron in 2:1 clays) did not promote NDMA degradation. In contrast, oxic sediments that were biostimulated with propane promoted biomineralization of NDMA by a cometabolic monooxygenase enzyme process. Other monooxygenase enzyme processes were not stimulated with methane or toluene additions, and acetylene addition did not block mineralization. Although NDMA mineralization extent was the highest in oxic, biostimulated sediments (30 to 82%, compared to 10 to 26% for abiotic mineralization in reduced sediments), large 1-D column studies (high sediment/water ratio of aquifers) showed 5.6 times higher NDMA mineralization rates in reduced sediment (half-life 410 ± 147 h) than oxic biomineralization (half life 2293 ± 1866 h). Sequential reduced/oxic biostimulated sediment mineralization (half-life 3180 ± 1094 h) was also inefficient compared to reduced sediment. These promising laboratory-scale results for NDMA mineralization should be investigated at field scale. Future studies of NDMA remediation should focus on the comparison of this in situ abiotic NDMA mineralization (iron-reducing environments) to ex situ biomineralization, which has been shown successful in other studies.
Date: September 30, 2009
Creator: Szecsody, James E.; McKinley, James P.; Crocker, Fiona H.; Breshears, Andrew T.; Devary, Brooks J.; Fredrickson, Herbert L. et al.
Partner: UNT Libraries Government Documents Department

Technetium Attenuation in the Vadose Zone: Role of Mineral Interactions

Description: High-level waste (HLW) has leaked into the vadose zone from buried single-shell tanks at the Hanford Site. Contaminant plumes containing radionuclides are slowly migrating toward the groundwater table. The accepted model of contaminant migration places technetium (Tc) at the leading edge of the plume due to the high mobility of the anionic species, TcO{sub 4}{sup -}, in its oxidized state. However, recent drilling and sampling programs at the B-BX-BY and S-SX Hanford Site tank farms have revealed that the Tc distribution within the contaminant plume is more complex than anticipated and some Tc may be retained in the vadose zone as insoluble precipitates. This research project investigates possible mechanisms by which Tc associated with HLW leakages can be attenuated in the vadose zone. It also will provide fundamental information on surface mediated reduction/precipitation reactions of Tc on Fe{sup II}-containing mineral surfaces and the stability of Tc precipitates under conditions in the va dose zone at the Hanford Site. This information will provide much needed data for the development of models of Tc mobility in the vadose zone following closure of the tank farms. With reliable models, a major cost reduction in remediation efforts may be achieved by selecting sites that present the greatest environmental threat and designing remediation methods with the greatest efficacy.
Date: June 1, 2002
Creator: Hess, Nancy J.; Conradson, Steven D.; Rai, Dhanpat; McKinley, James P.; Wildung, Raymond E. & Krupka, Kenneth M.
Partner: UNT Libraries Government Documents Department

Technetium Attenuation in the Vadose Zone: Role of Mineral Interactions

Description: In the subsurface environment, the pertechnetate ion, Tc{sup VII}O{sub 4}{sup -}, forms only weak surface complexes with hydroxylated surface sites on clays and Al and Fe{sup III} oxides, and consequently, is weakly sorbed by most sediments and subsurface materials. Thus, adsorption of Tc{sup VII} onto these surfaces is not a viable mechanism for the attenuation of Tc in unsaturated subsurface environments or the vadose zone. Only the reduction of Tc{sup VII} to Tc{sup IV}, which results in the precipitation of low-solubility solids, will result in retention of Tc in the vadose zone. Possible reduction mechanisms are (1) homogeneous reduction, (2) microbial reduction, and (3) heterogeneous reduction on mineral surfaces. The redox conditions in the vadose zone in the western United States are likely too oxidizing for homogeneous reduction of Tc{sup VII} or to support a viable, widely distributed population of Fe-reducing organisms that can reduce Tc directly or indirectly. Thus, the purpose of this research is the investigation of heterogeneous reduction of Tc{sup VII} on Fe{sup II}-containing mineral surfaces and the stability of the resulting precipitated Tc solids.
Date: June 1, 2001
Creator: Hess, Nancy J.; Conradson, Steven D.; McKinley, James P.; Rai, Dhanpat; Wildung, Raymond E. & Krupka, Kenneth M.
Partner: UNT Libraries Government Documents Department

Hanford 100N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr-90 Immobilization in 100N Sediments

Description: This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to sediments by ion exchange (99% adsorbed, < 1% in groundwater) in the upper portion of the unconfined aquifer and lower vadose zone. Although primarily adsorbed, Sr-90 is still considered a high mobility risk as it is mobilized by seasonal river stage increases and by plumes of higher ionic strength relative to groundwater. This remediation technology relies upon the Ca-citrate-PO4 solution forming apatite precipitate [Ca6(PO4)10(OH)2], which incorporates some Sr-90 during initial precipitation and additionally slowly incorporates Sr-90 by solid phase substitution for Ca. Sr substitution occurs because Sr-apatite is thermodynamically more stable than Ca-apatite. Once the Sr-90 is in the apatite structure, Sr-90 will decay to Y-90 (29.1 y half-life) then Zr-90 (64.1 h half-life) without the potential for migration into the Columbia River. For this technology to be effective, sufficient apatite needs to be emplaced in sediments to incorporate Sr and Sr-90 for 300 years (~10 half-lives of Sr-90), and the rate of incorporation needs to exceed the natural groundwater flux rate of Sr in the 100N area. A primary objective of this study is to supply an injection sequence to deliver sufficient apatite into subsurface sediments that minimizes initial mobility of Sr-90, which occurs because the injection solution has a higher ionic strength compared to groundwater. This can be accomplished by sequential injections of low, then high concentration injection of Ca-citrate-PO4 solutions. Assessment of low concentration Ca-citrate-PO4, citrate-PO4, and PO4 solutions show greater Sr and Sr-90 incorporation during initial ...
Date: October 1, 2007
Creator: Szecsody, James E.; Burns, Carolyn A.; Moore, Robert C.; Fruchter, Jonathan S.; Vermeul, Vincent R.; Williams, Mark D. et al.
Partner: UNT Libraries Government Documents Department

Remediation of Uranium in the Hanford Vadose Zone Using Ammonia Gas: FY 2010 Laboratory-Scale Experiments

Description: This investigation is focused on refining an in situ technology for vadose zone remediation of uranium by the addition of ammonia (NH3) gas. Objectives are to: a) refine the technique of ammonia gas treatment of low water content sediments to minimize uranium mobility by changing uranium surface phases (or coat surface phases), b) identify the geochemical changes in uranium surface phases during ammonia gas treatment, c) identify broader geochemical changes that occur in sediment during ammonia gas treatment, and d) predict and test injection of ammonia gas for intermediate-scale systems to identify process interactions that occur at a larger scale and could impact field scale implementation.Overall, NH3 gas treatment of low-water content sediments appears quite effective at decreasing aqueous, adsorbed uranium concentrations. The NH3 gas treatment is also fairly effective for decreasing the mobility of U-carbonate coprecipitates, but shows mixed success for U present in Na-boltwoodite. There are some changes in U-carbonate surface phases that were identified by surface phase analysis, but no changes observed for Na-boltwoodite. It is likely that dissolution of sediment minerals (predominantly montmorillonite, muscovite, kaolinite) under the alkaline conditions created and subsequent precipitation as the pH returns to natural conditions coat some of the uranium surface phases, although a greater understanding of these processes is needed to predict the long term impact on uranium mobility. Injection of NH3 gas into sediments at low water content (1% to 16% water content) can effectively treat a large area without water addition, so there is little uranium mobilization (i.e., transport over cm or larger scale) during the injection phase.
Date: December 1, 2010
Creator: Szecsody, James E.; Truex, Michael J.; Zhong, Lirong; Qafoku, Nikolla; Williams, Mark D.; McKinley, James P. et al.
Partner: UNT Libraries Government Documents Department

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Description: Uranium (U) is an important risk-driving contaminant at the Hanford Site. Over 200,000 kg have been released to the vadose zone over the course of site operations, and a number of vadose zone and groundwater plumes containing the uranyl cation [UO22+, U(VI)] have been identified. U is recognized to be of moderate-to-high mobility, conditions dependent. The site is currently making decisions on several of these plumes with long-lasting implications, and others are soon to come. Uranium is one of nature’s most intriguing and chemically complex elements. The fate and transport of U(VI) has been studied over the long lifetime of the Hanford Site by various contractors, along with the Pacific Northwest National Laboratory (PNNL) and its collaborators. Significant research has more recently been contributed by the national scientific community with support from the U.S. Department of Energy’s (DOE) Office of Science through its Environmental Remediation Sciences Division (ERSD). This report represents a first attempt to integrate these findings into a cohesive view of the subsurface geochemistry of U at the Hanford Site. The objective is to inform all interested Hanford parties about the in-ground inventory of U and its geochemical behavior. This report also comments on the prospects for the development of a robust generic model to more accurately forecast future U(VI) migration at different Hanford waste sites, along with further research necessary to reach this goal.
Date: October 26, 2007
Creator: Zachara, John M.; Brown, Christopher F.; Christensen, J. N.; Davis, Jim A.; Dresel, P. Evan; Liu, Chongxuan et al.
Partner: UNT Libraries Government Documents Department

In Situ Microbial Community Control of the Stability of Bio-reduced Uranium

Description: In aerobic aquifers typical of many Department of Energy (DOE) legacy waste sites, uranium is present in the oxidized U(VI) form which is more soluble and thus more mobile. Field experiments at the Old Rifle UMTRA site have demonstrated that biostimulation by electron donor addition (acetate) promotes biological U(VI) reduction (2). However, U(VI) reduction is reversible and oxidative dissolution of precipitated U(IV) after the cessation of electron donor addition remains a critical issue for the application of biostimulation as a treatment technology. Despite the potential for oxidative dissolution, field experiments at the Old Rifle site have shown that rapid reoxidation of bio-reduced uranium does not occur and U(VI) concentrations can remain at approximately 20% of background levels for more than one year. The extent of post-amendment U(VI) removal and the maintenance of bioreduced uranium may result from many factors including U(VI) sorption to iron-containing mineral phases, generation of H2S or FeS0.9, or the preferential sorption of U(VI) by microbial cells or biopolymers, but the processes controlling the reduction and in situ reoxidation rates are not known. To investigate the role of microbial community composition in the maintenance of bioreduced uranium, in-well sediment incubators (ISIs) were developed allowing field deployment of amended and native sediments during on-going experiments at the site. Field deployment of the ISIs allows expedient interrogation of microbial community response to field environmental perturbations and varying geochemical conditions.
Date: March 28, 2008
Creator: Baldwin, Brett, R.; Peacock, Aaron, D.; Resch, Charles, T.; Arntzen, Evan; Smithgall, Amanda, N.; Pfiffner, Susan et al.
Partner: UNT Libraries Government Documents Department

Multi-Scale Mass Transfer Processes Controlling Natural Attenuation and Engineered Remediation: An IFRC Focused on Hanford’s 300 Area Uranium Plume

Description: The Integrated Field-Scale Subsurface Research Challenge (IFRC) at the Hanford Site 300 Area uranium (U) plume addresses multi-scale mass transfer processes in a complex hydrogeologic setting where groundwater and riverwater interact. A series of forefront science questions on mass transfer are posed for research which 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 system. The project was initiated in February 2007, with CY 2007 and CY 2008 progress summarized in preceding reports. 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 2009 with completion of extensive laboratory measurements on field sediments, field hydrologic and geophysical characterization, four field experiments, and modeling. The laboratory characterization results are being subjected to geostatistical analyses to develop spatial heterogeneity models of U concentration and chemical, physical, and hydrologic properties needed for reactive transport modeling. The field experiments focused on: (1) physical characterization of the groundwater flow field during a period of stable hydrologic conditions in early spring, (2) comprehensive groundwater monitoring during spring to characterize the release of U(VI) from the lower vadose zone to the aquifer during water table rise and fall, (3) dynamic geophysical monitoring of salt-plume migration during summer, and (4) a U reactive tracer experiment (desorption) during the fall. Geophysical characterization of the well field was completed using the down-well Electrical Resistance Tomography (ERT) array, with results subjected to robust, geostatistically constrained inversion analyses. These measurements along with hydrologic characterization have yielded 3D distributions of hydraulic properties that have been incorporated into an updated and ...
Date: February 1, 2010
Creator: Zachara, John M.; Bjornstad, Bruce N.; Christensen, John N.; Conrad, Mark E.; Fredrickson, Jim K.; Freshley, Mark D. et al.
Partner: UNT Libraries Government Documents Department

Multi-Scale Mass Transfer Processes Controlling Natural Attenuation and Engineered Remediation: An IFRC Focused on Hanford’s 300 Area Uranium Plume January 2010 to January 2011

Description: 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 hydrogeologic setting where groundwater and riverwater interact. A series of forefront science questions on reactive mass transfer focus 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 system. The project was initiated in February 2007, with CY 2007, CY 2008, and CY 2009 progress summarized in preceding reports. A project peer review was held in March 2010, and the IFRC project has responded to 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. 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 2010 including the quantification of well-bore flows in the fully screened wells and the testing of means to mitigate them; the development of site geostatistical models of hydrologic and geochemical properties including the distribution of U; developing and parameterizing a reactive transport model of the smear zone that supplies contaminant U to the groundwater plume; performance of a second passive experiment of the spring water table rise and fall event with a associated multi-point tracer test; performance of downhole biogeochemical experiments where colonization substrates and discrete water and gas samplers were deployed to the lower aquifer zone; and modeling of past injection experiments for model parameterization, deconvolution of well-bore flow effects, system understanding, and ...
Date: February 1, 2011
Creator: Zachara, John M.; Bjornstad, Bruce N.; Christensen, John N.; Conrad, Mark S.; Fredrickson, Jim K.; Freshley, Mark D. et al.
Partner: UNT Libraries Government Documents Department

Multi-Scale Mass Transfer Processes Controlling Natural Attenuation and Engineered Remediation: An IFRC Focused on Hanford’s 300 Area Uranium Plume January 2011 to January 2012

Description: 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 ...
Date: March 5, 2012
Creator: Zachara, John M.; Bjornstad, Bruce N.; Christensen, John N.; Conrad, Mark S.; Fredrickson, Jim K.; Freshley, Mark D. et al.
Partner: UNT Libraries Government Documents Department

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

Description: The objective of this project is to develop a method to emplace apatite precipitate in the 100N vadose zone, which results in sorption and ultimately incorporation of Sr-90 into the apatite structure. The Ca-citrate-PO4 solution can be infiltrated into unsaturated sediments to result in apatite precipitate to provide effective treatment of Sr-90 contamination. Microbial redistribution during solution infiltration and a high rate of citrate biodegradation for river water microbes (water used for solution infiltration) results in a relatively even spatial distribution of the citrate biodegradation rate and ultimately apatite precipitate in the sediment. Manipulation of the Ca-citrate-PO4 solution infiltration strategy can be used to result in apatite precipitate in the lower half of the vadose zone (where most of the Sr-90 is located) and within low-K layers (which are hypothesized to have higher Sr-90 concentrations). The most effective infiltration strategy to precipitate apatite at depth (and with sufficient lateral spread) was to infiltrate a high concentration solution (6 mM Ca, 15 mM citrate, 60 mM PO4) at a rapid rate (near ponded conditions), followed by rapid, then slow water infiltration. Repeated infiltration events, with sufficient time between events to allow water drainage in the sediment profile can be used to buildup the mass of apatite precipitate at greater depth. Low-K heterogeneities were effectively treated, as the higher residual water content maintained in these zones resulted in higher apatite precipitate concentration. High-K zones did not receive sufficient treatment by infiltration, although an alternative strategy of air/surfactant (foam) was demonstrated effective for targeting high-K zones. The flow rate manipulation used in this study to treat specific depths and heterogeneities are not as easy to implement at field scale due to the lack of characterization of heterogeneities and difficulty tracking the wetting front over a large subsurface area. However, the use of real-time ...
Date: March 1, 2009
Creator: Szecsody, James E.; Rockhold, Mark L.; Oostrom, Martinus; Moore, R. C.; Burns, Carolyn A.; Williams, Mark D. et al.
Partner: UNT Libraries Government Documents Department