COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES

THROUGH THE VADOSE ZONE

A Proposal Submitted to

U.S. Department of EnergyO�ce of Science, Grants and Contract Division

Germantown, MD 20874-1290

ATTN: Program Notice 02-03

By

Markus Flury

Department of Crop and Soil Sciences

Washington State University, Pullman, WA 99164

(Phone: 509-335-1719, Fax: 509-335-8674, Email: flury@mail.wsu.edu)

James B. Harsh

Department of Crop and Soil Sciences

Washington State University, Pullman, WA 99164

(Phone: 509-335-3650, Fax: 509-335-8674, Email: harsh@mail.wsu.edu)

John M. ZacharaEnvironmental Molecular Science Laboratory

Pacific Northwest National Laboratories, Richland, WA 99352

(Phone: 509-376-3254, Fax: 509-376-3650, Email: john.zachara@pnl.gov)

John F. McCarthy

Center for Environmental Biotechnology

University of Tennessee, Knoxville, TN 37996

(Phone: 865-974-8039, Fax: 865-974-8086, Email: jmccart1@utk.edu)

Peter C. Lichtner

Geoanalysis|Earth and Environmental Sciences

Los Alamos National Laboratory, Los Alamos, NM 87545

(Phone: 505-667-3420, Fax: 505-665-8737, Email: lichtner@lanl.gov)

Application Category:

Field of Scienti�c Research: Hydrogeology

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Contents

1 Project Abstract 1

2 Budget 2

2.1 Forms DOE F4620.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Budget Justi�cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2.1 Washington State University . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.2.2 University of Tennessee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3 Project Description 14

3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3 Signi�cance of Project to EM Mission . . . . . . . . . . . . . . . . . . . . . . . . . . 153.4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4.1 Sources of Mobile Colloidal Particles in Subsurface Environments . . . . . . . 163.4.2 In situ Formation of Colloids at the Hanford Site . . . . . . . . . . . . . . . . 173.4.3 In situ Colloid Mobilization and Transport at Hanford . . . . . . . . . . . . . 183.4.4 Fate and Transport of Radionuclides in the Subsurface . . . . . . . . . . . . . 183.4.5 Selection of Cs, Eu, and Am . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.4.6 Stability of Sodalite and Cancrinite in the Subsurface Environment . . . . . . 203.4.7 Colloid Transport and Colloid-facilitated Contaminant Transport . . . . . . . 203.4.8 Preferential Flow in Intact Monoliths . . . . . . . . . . . . . . . . . . . . . . 223.4.9 Modeling of Colloid, Contaminant, and Colloid-facilitated Transport . . . . . 22

3.5 Major Results from Previous EMSP Project and Outlook . . . . . . . . . . . . . . . 243.6 Research Design and Methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.6.1 Overall Research Concept and Outcomes . . . . . . . . . . . . . . . . . . . . 253.6.2 Sediment Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.6.3 Colloidal Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.6.4 Formation and Characterization of Colloids . . . . . . . . . . . . . . . . . . . 263.6.5 Colloid and Colloid-facilitated Transport in the Vadose Zone . . . . . . . . . 303.6.6 Characterization of Colloids and Colloid Transport Using X-Ray Computed

Tomography and Nuclear Magnetic Resonance Techniques . . . . . . . . . . . 363.6.7 Reactive Transport Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.7 Student Training Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.8 Project Management and Time Schedule . . . . . . . . . . . . . . . . . . . . . . . . . 39

4 References 40

5 Collaborative Arrangements 50

6 Biographical Sketches 51

7 Facilities and Resources 63

7.1 Washington State University . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637.2 Paci�c Northwest National Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . 64

7.2.1 The Radiochemistry Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . 64

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7.2.2 W.R. Wiley, EMSL|Environmental Dynamics & Simulation . . . . . . . . . 647.2.3 NMR Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

7.3 University of Tennessee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657.4 Los Alamos National Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

8 Current and Pending Support 67

9 Assurance and Certi�cations 69

A Accomplishments of Previous EMSP Project 75

A.1 Project Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75A.2 Alteration of Mineralogical and Surface Properties of Hanford Sediments contami-

nated with Tank Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75A.3 Alteration of Mineralogical and Surface Properties of Reference Minerals . . . . . . . 77A.4 Cesium Sorption on Altered Hanford Sediments . . . . . . . . . . . . . . . . . . . . . 77A.5 Colloid Transport through Unsaturated Hanford Sediments . . . . . . . . . . . . . . 77A.6 Colloid-facilitated Transport of Cesium through Hanford Sediments . . . . . . . . . . 79A.7 Anticipated Non-Expended Funds from Previous EMSP Project . . . . . . . . . . . . 80

B Los Alamos DOE Field Work Proposal and Budget 81

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1 Project Abstract

Radioactive and hazardous wastes stored in the underground tanks at the Hanford site have leakedinto the vadose zone. Many of these waste streams were highly caustic. Waste sediment interactionhas resulted in a wide array of dissolution and precipitation reactions, resulting in secondary solidsthat have sorbed or coprecipitated with contaminants. Characterization activities in the tankfarms have clearly shown that the waste plumes are being driven to depth in the vadose zoneby the in�ltration of low-ionic strength meteoric waters and the leakage of dilute Columbia Riverwater from ubiquitous process-water supply lines. This scenario of concentrated, reactive waste,followed by low ionic strength water, encourages colloid mobilization. Other, less electrolyte-concentrated waste streams, like cribs and French drains, are also conducive to in situ colloidmobilization, when meteoric water dilutes and displaces the waste plumes. The goal of this projectis to elucidate the role, and quantify the relevance, of colloids in facilitating the transport ofcontaminants in the Hanford vadose zone. We will focus on (1) thermodynamic stability andmobility of colloids formed by reactions of sediments with highly alkaline tank waste solutions,(2) colloid-contaminant interactions, and (3) in situ colloid mobilization and colloid-facilitatedcontaminant transport occurring in both contaminated and uncontaminated Hanford sediments.As contaminants to study colloid-facilitated transport, we have selected Cs, Eu, and Am. We willconsider two di�erent types of colloids that can potentially facilitate the movement of radionuclides:newly-formed colloidal materials due to reactions of tank waste with subsurface sediments, andnative colloidal material present in the sediments. The newly-formed colloidal phases, identi�ed aszeolites and feldspathoids, may not be stable when geochemical conditions change at which theywere formed. We will determine the thermodynamic stability of the zeolites and feldspathoidsunder conditions representative for the Hanford subsurface. The interactions of Cs, Eu, and Amwith newly-formed and native colloidal particles isolated from the sediments will be investigatedwith batch sorption and spectroscopic techniques. In column tests using representative sedimentsamples from the Hanford site, we will examine the potential for in situ mobilization of colloids.Waste plume displacement by typical meteoric and pore water will be simulated in packed columnsas well as in undisturbed soil monoliths. Experiments will be carried out under variably saturated,steady-state and transient water ow to study the e�ect of water content and ow-interruptions oncolloid mobilization and transport. We will use X-ray tomography and NMR to visualize colloidalmovement in the porous media. We will also study colloid mobilization from selected contaminatedsediment samples from the Hanford site. Thermodynamic stability, sorption, and column studieswill be analyzed with a two-phase reactive transport model in which relevant processes for colloid-facilitated transport of radionuclides will be incorporated. The results of the proposed research willlead to a better understanding of colloid-formation, colloid-contaminant-soil interactions, colloidmigration, and colloid-facilitated transport in the vadose zone. The experiments proposed hereuse conditions speci�c to various waste streams at the Hanford site, and the results are thereforedirectly applicable to clean-up strategies and procedures for Hanford contamination problems. Wewill provide conclusive evidence under what conditions colloid-facilitated transport can be expectedat the Hanford site, and what the quantitative magnitude of this transport process will be.

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2 Budget

2.1 Forms DOE F4620.1

� Main Budget

{ Year 1

{ Year 2

{ Year 3

{ Summary

� Subcontract University of Tennessee

{ Year 1

{ Year 2

{ Year 3

{ Summary

2

2.2 Budget Justi�cation

2.2.1 Washington State University

1. Personnel

� Principal Investigator. One month summer salary per year for the two PIs is requested.

� Postgraduate Researcher. Salary for one postgraduate researcher per year is requested.The postgraduate researcher will be responsible for analysis and modeling of experimen-tal data, and will assist in the design and performance of the experiments.

� Graduate Students. Salary for two graduate students at the Ph.D. level is requested.Salary per student for the �rst year will be $16,127 with an increase of 4% per year foryears 2{3. Quali�ed Tuition Reduction in the amount of $10,698 for year 1, $6,527 foryear 2, and $6,853 for year 3 per student is included in the fringe bene�ts. This amounthas been excluded, along with other excludable costs, from Modi�ed Total Direct Costsbase when computing Facilities and Administrative costs.

� Undergraduate Student (Lab Assistant). Salary is requested for one undergraduatestudent to assist with laboratory column experiments. The salary includes wages at$12.00/hr for 10 hours per week during the academic year and 2-months full-time (40hours per week) salary for the summer. Fringe bene�ts are calculated at 9%.

2. Equipment: Funds ($70,000) are requested to purchase the following equipment:

� ThermoLink (Decagon Devices) and TDR sensors for measurement of volumetric watercontent in sediment columns ($3,500).

� Peristaltic Pump (Ismatec) ($2,500).

� Surface Area Analyzer ($31,000) for characterization of colloidal particles (Micromerit-ics).

� Field-Flow Fractionation System ($33,000) for separation and characterization of col-loidal particles (FFFractionation, LLC).

3. Travel: Travel funds are requested for the PI to attend the initial kicko�-meeting, the NationalEMSP workshop or Focus-Area-speci�c Mid-Year Review, visit the Hanford site, and presentthe research results at one national meeting per year.

4. Materials and Supplies:

� Year 1: The expendable funds will be used to purchase materials for batch experiments,constructing the columns (including pressure transducers and tensiometer cups), lab-ware, reagents, uranium/neptunium analysis, etc.

� Year 2 and 3: Similar expenses as in year 1 are expected for years 2 and 3.

5. Publication Costs: Page charge and/or reprints for 3{4 papers.

6. Subcontract: Refer to budget justi�cation from University of Tennessee.

7. Indirect Costs: The indirect cost rate at Washington State University is 45% (Modi�ed TotalDirect Cost) plus 45% of the �rst $25,000 of the subcontract. Indirect costs are charged ontotal direct costs excluding permanent equipment and tuition.

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2.2.2 University of Tennessee

1. Personnel

� Principal Investigator. Funds are requested for 3 months of e�ort by John McCarthyduring the �rst two years of the project, and for 2 months of e�ort in the third yearto complete data analysis and manuscript preparation. Dr. McCarthy is a non-salariedResearch Professor and his e�ort must be supported through the grant.

� Graduate Student. Funds are requested for a support of a full-time M.S. or Ph.D.graduate research assistant for two years of the project. Tuition costs for the graduatestudent are $3,700 per year.

2. Fringe Bene�ts. Fringe bene�ts at the University of Tennessee are set at 28% of the cost ofsalary and wages.

3. Equipment: Funds are requested for a fraction collector required to sample the e�uent of theintact monoliths.

4. Travel: In the �rst year, $4,000 is requested for travel by the PI and graduate student totravel to Richland, WA to collect core material from the Hanford Site, and for the PI topresent preliminary results of the project at a national meeting. In the second and third year,$2,000 per year is requested for travel to meet with project collaborators and present resultsat a national meeting.

5. Materials and Supplies: The cost of initial acquisition, transport and setup of the laboratorycolumn system and material and supplies for detecting the colloids is expected to be $5,000in the �rst year. The costs decline to $2,000 in the second year. In the �nal year of the grant,we anticipate that data collection will be coming to a �nish, so material costs drop to $1,000.

6. Indirect Costs: On-site indirect costs are 45% of the modi�ed total direct costs.

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3 Project Description

3.1 Motivation

A considerable amount of radioactive and hazardous waste stored in the underground tanks at theHanford site has leaked into the vadose zone. Radionuclides that are normally considered to bestrongly sorbed under natural subsurface conditions (e.g., Pu and Cs) have been found to migratefarther than anticipated. While in some cases extreme solution chemistry has been identi�ed asone reason for decreased sorption and consequently enhanced transport [Zachara et al., 2002],in other cases preferential ow and colloid-facilitated transport are likely to cause acceleratedmigration in the subsurface. In this proposal we will focus on colloid-facilitated transport. There isstrong indication that contaminants can be transported via colloids. Most experimental evidencefor colloid-facilitated transport of contaminants has been obtained from saturated porous media,either saturated laboratory column studies or groundwater studies. A recent article published inNature [Kersting et al., 1999] strongly suggests that colloidal particles are responsible for migrationof plutonium in groundwater at the Nevada Nuclear Test Site. There is little information availableabout colloid-facilitated transport in the vadose zone. Colloids may sorb at liquid-air interfaces inan unsaturated porous medium, and may therefore behave di�erently in the vadose zone than inthe phreatic zone. At the Hanford site, contaminants leaking from the storage tanks are releaseddirectly to the vadose zone, and therefore the fate and behavior of these contaminants in theunsaturated zone need to be speci�cally addressed.

Based on results of our previous EMSP project, we know that zeolite, feldspathoid, and silicacolloids are formed in situ when Hanford Waste tank solutions representative for SX Tank Farmscontact sediments of the Hanford formation. In addition, native colloidal material is altered throughreaction with tank waste. Our results have shown that these newly-formed and altered colloidsstrongly associate with radionuclides like Cs, and that the colloids can indeed move through thevadose zone. Not known at this time, however, is what happens with these colloids when thechemical and physical conditions, under which they have been formed, change. It is anticipatedthat colloidal material formed at high pH will not necessarily be stable at lower pH values, and thesolids may dissolve or transform to another type of mineral phase. Furthermore, while we knowthat the colloids bind Cs strongly, we do not have information about their reactions with otherradionuclides of concern at the Hanford site.

The waste streams at Hanford are very complex and range from the extremely alkaline SXTank Farm supernatants to less aggressive waste solutions disposed of in cribs and trenches. Whileour previous EMSP project has focused on the high alkaline chemistry of the SX Tank Farms,colloid-facilitated transport of radioncuclides will likely be of importance for other waste streamsat Hanford as well. In the chemically less aggressive waste streams, we do not anticipate mineralalterations to occur, but we expect that in situ colloid mobilization will be very likely in the coarsesediments of the Hanford site.

Although colloid-facilitated transport is a potentially important mechanisms to accelerate themovement of otherwise deemed rather immobile contaminants, little is known about the factorscontrolling in situ colloid release. The chemistry and physics of both contaminant-colloid interac-tions and their transport through the vadose zone bears detailed investigation, both for immediateremediation schemes as well as for long-term risk assessment.

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3.2 Objectives

This project seeks to improve the basic understanding of the role of colloids in facilitating the trans-port of contaminants in the vadose zone. We will focus on three major thrusts: (1) thermodynamicstability and mobility of colloids formed by reactions of sediments with highly alkaline tank wastesolutions, (2) colloid-contaminant interactions, and (3) in situ colloid mobilization and colloid-facilitated contaminant transport occurring in both contaminated and uncontaminated Hanfordsediments. As contaminants to study colloid-facilitated transport, we have selected Cs, Eu, andAm. The speci�c objectives that will be addressed are:

1. Determine the lability and thermodynamic stability of colloidal materials, which form afterreacting Hanford sediments with simulated Hanford Tank Waste, under a range of conditionsexpected in both reacted and unreacted zones relevant for Hanford subsurface sediments.

2. Determine the potential of Hanford sediments for in situ mobilization of colloids for di�erenttypes of sediments and di�erent leaching scenarios.

3. Characterize the interactions between initially-formed colloids, their dissolution/alterationproducts, and native colloidal particles with contaminants in batch experiments under variousionic strength and pH conditions. We will investigate the nature of the solid-liquid interactionsand the kinetics of the reactions.

4. Evaluate mobility of dissolution/alteration products and native colloids through sedimentsunder di�erent degrees of water saturation in packed and undisturbed sediment columns.

5. Determine the potential of initially-formed colloids, their dissolution/alteration products, andnative colloids to act as carriers to transport the model contaminants through the vadose zone,and verify the results through comparison with �eld samples collected under leaking tanksand other waste streams.

6. Verify experimental results obtained in uncontaminated sediments with in situ colloid mobi-lization experiments in contaminated sediment samples.

7. Implement colloid-facilitated contaminant transport mechanisms and thermodynamic stabil-ity constants for colloids into a reactive chemical transport model, and verify model simula-tions with experimental transport data.

8. Improve conceptual characterization of colloid-contaminant-soil interactions and colloid-facili-tated transport for clean-up procedures and long-term risk assessment.

3.3 Signi�cance of Project to EM Mission

The results of the proposed research will lead to a better understanding of colloid-formation, colloidstability, colloid-contaminant-soil interactions, colloid migration, and colloid-facilitated transportin the vadose zone. We will speci�cally investigate the potential of colloids to act as carriers forcontaminants found in Hanford waste. The experiments proposed use conditions speci�c to theHanford site, and the results are therefore directly applicable to clean-up strategies and proce-dures for Hanford contamination problems. We expect to provide conclusive evidence under whatconditions colloid-facilitated transport can be expected at the Hanford site, and what the quanti-tative magnitude of this transport process will be. As such, the project|although basic researchin nature|will contribute to the clean-up mission of DOE at the Hanford site. The basic nature

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of the research will serve to provide data that is more broadly related to contaminant transportby facilitated-transport in a variety of environments. We anticipate providing data that lead to animprovement of conceptual models of colloid-facilitated transport at the Hanford site and expectto improve reactive transport models to allow prediction of colloid-facilitated transport. Resultsobtained from the project will be a prerequisite for a sound and successful remediation and clean-upprotocol at Hanford.

Recent assessments of research needs and knowledge gaps by the Environmental ManagementScience Program [U.S. DOE, 2000] and the DOE Complex-Wide Vadose Zone Science & TechnologyRoadmap [U.S. DOE, 2001] have identi�ed a better understanding of the factors controlling long-term fate and transport of radionuclides, including colloid and colloid-facilitated transport, asone of the future research priorities. Colloid and colloid-facilitated transport of contaminants areimportant, yet not well-understood, processes in the vadose as well as saturated zone. As long asthe role of colloidal process and colloid-facilitated transport is poorly understood, uncertainties insubsurface fate and transport cannot be reduced.

3.4 Background

3.4.1 Sources of Mobile Colloidal Particles in Subsurface Environments

Colloids are commonly de�ned as small particles or other entities with dimensions between 1 nmto 1 �m [Hiemenz and Rajagopalan, 1997; Hunter, 2001]. These include dissolved macromoleculeson one side and larger suspended particles on the other side. Several potential sources of mobilecolloidal particles in subsurface media have been identi�ed. Such sources include in situ mobi-lization of particles (both inorganic and organic) that are naturally present, formation of colloidalparticles by precipitation from supersaturated solutions, and direct introduction of colloidal parti-cles into the subsurface through waste management procedures, such as land�lls, septic tanks, orgroundwater recharge.

The most common source of mobile colloids in soils and groundwater aquifers is in situ particlerelease as a result of changes in solution chemistry [McCarthy and Degueldre, 1993; Ryan andGschwend, 1994; Ryan and Elimelech, 1996]. In situ mobilization and transport of colloidal materialin natural porous media has been demonstrated for various subsurface materials, such as non-calcareous silt loam soil [Grolimund and Borkovec, 1999], sand soil [Kaplan et al., 1993], andhighly-weathered aquifer sand [Seaman et al., 1995, 1997]. The major factors inducing mobilizationand subsequent transport are a change in solution ionic strength and pH; however, pH is often notthat important for permanently charged clay minerals [Grolimund and Borkovec, 1999], unlessthe pH changes span several orders of magnitude or the pH change occurs close to the particles'zero point of charge. Concentrations of mobilized particles can be large; up to a few hundreds ofmilligrams per liter have been reported for laboratory column out ow [Grolimund and Borkovec,1999]. The experimental evidence suggests that, upon disturbance of ionic strength, in situ colloidmobilization may be an important transport mechanism for contaminant species. If the disturbanceof ionic strength occurs in combination with the presence of sorbing contaminants, the mobilizedparticles may also likely act as vectors for accelerated contaminant movement [Flury et al., 2002].

In most natural subsurface environments colloid formation by precipitation is unlikely to beimportant because soil solutions tend to be either undersaturated or in equilibrium with respect tothe mineral phase present. However, human activities such as waste disposal, groundwater pumping,or arti�cial recharge can induce quite drastic changes in water chemistry. Such hydrogeochemicalperturbations can lead to conditions that favor colloid formation by precipitation. One example isthe in�ltration of oxygen-rich water into an anoxic aquifer, a situation that may result from arti�cial

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recharge. Liang et al. [1993] demonstrated in a �eld experiment that injection of oxygenated waterinto a anoxic sandy aquifer, in which dissolved Fe(II) was present, resulted in rapid precipitation ofFe(III) hydroxide colloids. In another �eld investigation, Gschwend and Reynolds [1987] collectedgroundwater samples near a secondary-sewage in�ltration site and found that colloidal particleswere formed by precipitation of sewage-derived phosphate with ferrous iron released from the aquifersolids.

Although it is known and documented that changes in solution chemistry lead to release ofcolloidal particles from soil and sediment matrices, the particle generation process is not wellunderstood on a mechanistic level, so that in situ particle mobilization is di�cult to predict apriori. Particle release has been found to follow �rst-order kinetics in some cases [Laegdsmandet al., 1999], but multiple �rst-order kinetics with a distribution of release rate coe�cients in othercases [Grolimund et al., 2001]. In the vadose zone, the particle release is also a�ected by wettingand drying e�ects, superimposing the e�ect of the solution chemistry.

3.4.2 In situ Formation of Colloids at the Hanford Site

A special situation exists at the Hanford tank farms, where solutions of high pH, high alkalinity,and high aluminate concentrations have leaked into the subsurface. It has been postulated, andthen experimentally demonstrated, that when simulated Hanford Tank solutions contact subsurfacesediments, silica is solubilized from native minerals. Certain minerals, like quartz and kaolinite,are releasing silica and are dissolving under the extreme chemical conditions [Bickmore et al.,2001; Mashal et al., 2001; Zhao et al., 2002]. The high silica concentrations from the sedimentstogether with the high aluminate concentrations from the tank solutions lead to the precipitation ofsecondary mineral phases, which have been identi�ed as zeolite, cancrinite, and sodalite [Buhl et al.,2000; Bickmore et al., 2001; Chorover et al., 2001; Mashal et al., 2001; Zhao et al., 2002]. Thesemineral phases occur in a speci�c sequence, and transform from more labile to more stable phases.It has recently been shown that reacting aluminosilicate minerals with solutions of high pH willlead to mineral transformations in the following sequence: aluminosilicate species ! amorphousphase ! poorly-crystalline zeolite ! sodalite ! cancrinite [Barnes et al., 1999a].

It has further been shown that this sequence of mineral transformations is a�ected by theSi to Al ratio. A larger Al to Si ratio favors the formation of sodalite and cancrinite, whereasat a lower Al to Si ratios more zeolite-type minerals are formed [Bickmore et al., 2001; Mashalet al., 2001]. Calculations performed to estimate supernatant concentrations in the SX Tank Farmindicate saturation with respect to cancrinite [Lichtner and Felmy, 2002], using the data fromBickmore et al. [2001] for experiments conducted at 89�C using a high pH tank simulant.

These �nding have important implications for fate and transport of radionuclides below theHanford waste tanks. First, zeolite, sodalite, and cancrinite have a porous aluminosilicate frame-work structure consisting of cages or channels. Sodalite has interlocking cages, whereas cancriniteconsists of a series of channels [Gerson and Zheng, 1997]. These cages and channels are knownto sorb cations, like Ca, Na, and K [Ballirano et al., 2000], and likely will also sorb radionculides.Zeolites are well known, and commercially used, for their suitability as catalysts, ion exchangers,and molecular sieves in waste water treatment [Bostick et al., 2001]. Second, some of the trans-formation products can be in the colloidal size fraction and can become potentially mobile in thesubsurface [Wan et al., 2001; Zhao et al., 2001, 2002], thereby facilitating the transport of stronglysorbing radionuclides.

Little is known about the thermodynamic stability of sodalite, cancrinite, and its mixtures. Itis expected that the minerals formed under high pH conditions will not be stable at low pH, but it

17

is di�cult to predict what the stability is as a function of pH. Solubility of sodalite and cancrinitein sodium aluminate and silicate solutions with high pH have been determined for temperaturesbetween 90 and 220�C [Barnes et al., 1999b]. It was found that the solubility of the mineralsincreased linearly with increasing temperature, and that sodalite had a consistently higher solubilitythan cancrinite [Barnes et al., 1999b]. For the conditions at Hanford, we would need to haveinformation for much lower temperatures and pH values.

3.4.3 In situ Colloid Mobilization and Transport at Hanford

Hydrologic and geochemical conditions in many of Hanford's single-shell tank (SST) farms havebeen conducive to colloid formation and mobilization. Over 60 of Hanford's 140 SSTs have leakedhigh level wastes (HLW) into the Hanford vadose zone. These HLWs have been highly variable inchemical composition because of the multiple, Pu, U, Sr, and Cs recovery processes employed bythe site. Many of these waste streams, however, were highly caustic, and some contained molarconcentrations of dissolved Al, Na, Fe, OH, and PO4. Waste sediment interaction has resulted in awide array of dissolution and precipitation reactions, resulting in secondary solids that have sorbedor coprecipitated with contaminants. Characterization activities in the tank farms have clearlyshown that these concentrated HLW waste plumes are being driven to depth in the vadose zone bythe in�ltration of low-ionic strength meteoric waters and the leakage of dilute Columbia River waterfrom ubiquitous process-water supply lines. This scenario of concentrated, reactive waste, followedby dilute water encourages colloid formation and dispersion. Other, less electrolyte-concentratedwaste streams may also be susceptible to in situ colloid mobilization, when meteoric water dilutesand displaces the waste plumes.

3.4.4 Fate and Transport of Radionuclides in the Subsurface

Radionuclides that are normally considered to be strongly sorbed (e.g., Cs and Pu), have been de-tected at much deeper depth than predicted based on current theories of vadose zone contaminanttransport. Three main mechanisms that can contribute to increased transport of contaminants areion exchange, preferential ow, and colloid-facilitated transport. In this proposal we will focus oncolloid-facilitated transport, although the importance of ion exchange processes will be implicitlyexamined through both batch and column experiments performed in solutions varying in salt con-centration and composition. In a column experiment using sediment from the Hanford Formation,we showed that both ion exchange and colloid-facilitated transport of Cs is important: the mainmass of Cs was transported via an ion exchange process in molar NaNO3, but a fraction of re-maining Cs was eluted with colloidal material at millimolar Na concentration [Flury et al., 2002].Many contaminants, such as Cs, exhibit \�xation" behavior, in which at least some fraction of theion is chemisorbed to sorption sites and not easily subject to ion exchange [Zachara et al., 2002].Other metals may form colloidal polymers, e.g., PuO2(H2O)x (amorphous or crystalline), such thatsuspended particles may be mobile where precipitation of immobile solids is predicted or assumed[Kim et al., 1985; Kersting et al., 1999]. Complexes with organic matter can result in humic colloidsthat are transported under favorable conditions of solution composition and water content [Klotzet al., 1997; Randall et al., 1994; Warwick et al., 2000; Luhrmann et al., 1998]. Contardi et al.[2001] show that inclusion of colloids into a conceptual model of contaminant transport can resultin a several order of magnitude reduction in the retardation factor for strongly retained ions likeAm and Th. We will study the formation and transport of colloidal forms of Cs, Eu(III), andAm(III) under conditions similar to those expected at the Hanford site in Washington state.

18

3.4.5 Selection of Cs, Eu, and Am

We selected Cs in our previous study for a number of reasons. The 137Cs radionuclide is a majorcontaminant in the tank waste, exists primarily in the aqueous phase of the waste, and has a ten-dency to form inner sphere complexes with aluminosilicate colloids [Kim and Kirkpatrick, 1997].The latter feature satis�es one of the criteria for colloid-facilitated transport-that a strong inter-action must exist between contaminant and colloid. This appears to be likely for several colloidalmaterials that might exist or could form at the Hanford site. Kaolinite [Saiers and Hornberger,1996], zeolites [Bray and Fullam, 1971; Shih and Chang, 1996], clay minerals [Kim and Kirkpatrick,1998], boehmite, and silica gel [Kim and Kirkpatrick, 1997] have all been shown to strongly sorbCs at some fraction of sites.

We have performed sorption experiments on altered sediments of the Hanford site and �ndonly small changes in their Cs sorption properties [Zhao et al., 2001]. Parallel experiments on puremineral systems indicate that Cs sorption is signi�cantly increased on kaolinite after transformationto hydrous feldspathoids [Zhao et al., 2002], but changed little or even lowered on mica-type minerals[Zhao et al., 2001]. In the current study, we will continue to examine the sorption and exchangeproperties of Cs on altered sediment colloids and synthesized sodalite and cancrinite.

In this project, we will extend our examination of the potential for contaminant transport toAm(III) and Eu(III). Americium and europium are likely to be present in carbonated sediments,such as the Hanford formation, as trivalent cations. In their soluble forms, both are stronglysorbed by phyllo- and tecto-silicates [Bish et al., 2000; Nagasaki et al., 1997; Vandergraaf et al.,1997], although the sorption mechanism is likely to be di�erent than that of Cs+ and stronglya�ected by pH and carbonate concentration [Clark et al., 1998; Luckscheiter and Kienzler, 2001].Interaction of Eu(III) and Am(III) to speci�c aluminosilicates has not been studied in detail. Aknowledge of the nature of such interactions is important not only because Am(III) and Eu(III)are radioactive contaminants at Hanford and other DOE sites, but because they serve as analogsto Pu(III), whose multiple oxidation states make it di�cult to work with from an experimentalstandpoint [Krauskopf, 1986; Choppin, 1999]. The use of both Eu(III) and Am(III) serves anotherpurpose of allowing a comparison between lanthanide (4f) and actinide (5f) homologues. The 5forbitals are less shielded than the lighter lanthanide elements and, as a result, can be considered\softer" elements and more likely to form covalent bonds [Choppin, 1983]. Di�erences in softness,even among species considered to be hard cations, can have signi�cant e�ects on adsorption orexchange selectivity depending on the sorbent involved [Xu and Harsh, 1990a,b; 1992].

The purpose of the studies on synthesized sodalite and cancrinite is to determine the selectivityand potential hysteresis of exchange on these materials. Exchange hysteresis is known to occur onzeolites and feldspathoids due to the sizes of cages and channels in the tectosilicate structure and the(hydrated) radii of the exchanging cations [Barrer and Falconer, 1956; Dyer et al., 1993]. Some ofthis hysteresis is expected to arise from the di�erence in structure between cancrinite and sodalite.The former is made up of series of channels [Zheng et al., 1998], which should be easily accessible forion exchange, whereas sodalite consists of an array of cages [Zheng et al., 1998], in which ions couldbe trapped. Further, stacking faults in cancrinite could conceivably lead to stacking faults thatblock the channels [Bickmore et al., 2001]. Selectivity and reversibility of exchange will ultimatelydetermine the distribution of cations between exchange sites on sodalite and cancrinite and thesolution. This equilibrium is of concern not only because of the potential formation of sodaliteand cancrinite below leaking waste tanks at Hanford, but because of the suggested use of suchmaterials for containment of radioactive elements [Barney, 1975; Morss et al., 2000]. Furthermore,cement-based systems for waste containment, consisting of Portland cement, y ash, clay minerals,

19

etc., form sodalite-type minerals when subjected to alkaline radioactive waste [Olson et al., 1997].

3.4.6 Stability of Sodalite and Cancrinite in the Subsurface Environment

Sodalite and cancrinite form readily from alkaline solutions of high NaOH (>�0.5 M), Si, and Alor caustic solutions in contact with aluminosilicate minerals [Henmi, 1987; Barth-Wirsching et al.,1993; Gerson and Zheng, 1997; Su et al., 1997; Zheng et al., 1998; Baccouche et al., 1998]. Theyhave been synthesized under conditions designed to simulate the conditions occurring under theleaking alkaline waste tanks at the Hanford site [Su et al., 1997; Mashal et al., 2001; Bickmoreet al., 2001], but have not been found in sediment cores removed from below the SX tank farm(J. Serne, personal communication). The solubility of both sodalite and cancrinite has been studiedin alkaline solutions [Gerson and Zheng, 1997; Zheng et al., 1998; Bickmore et al., 2001] and thethermodynamic parameters for sodalite have been determined for sodalite from 15 K to 1000 K[Komada et al., 1995]; however, their stability and lability under less caustic conditions in thesubsurface environment have not been examined. The failure to �nd feldspathoids as componentsof the sediment cores below the SX tanks may be due to a failure to successfully isolate and identifythe minerals or it may be they are unstable under conditions of lower pH, temperature, and Naconcentration and may have transformed to other crystalline or noncrystalline aluminosilicates.The stability of these minerals needs to be examined other the conditions prevailing long afterleaking of alkaline tank waste occurred.

3.4.7 Colloid Transport and Colloid-facilitated Contaminant Transport

Transport of colloidal particles has been observed to occur in di�erent types of subsurface environ-ments including soils, groundwater aquifers, and fractured rocks [McDowell-Boyer et al., 1986; Mc-Carthy and Zachara, 1989; Ryan and Elimelech, 1996]. A classical example of colloid transportin soils is evident in Al�sols and Spodosols, soil types that are characterized by migration ofclay minerals and humic material. Colloidal particles are present in most groundwater samples.The abundance and composition of groundwater colloids was extensively reviewed by McCarthyand Degueldre [1993]. The concentrations of colloidal particles found in groundwaters can varyconsiderably. Groundwaters with higher colloid concentrations were found primarily at samplingsites where some physical or chemical perturbations of the natural system had occurred that likelyresulted in mobilization of colloidal particles. Such perturbations can be a result of arti�cial ground-water recharge, waste disposal, sewage e�uent, irrigation, groundwater pumping, and even groundwater sampling. In most groundwaters, colloids are composed of minerals that are naturally occur-ring in the aquifer, suggesting that in situ mobilization is the primary source of mobile colloidalparticles [Degueldre et al., 1989; Ryan and Gschwend, 1990; Freedman et al., 1996].

Despite growing research e�orts during the past decade, the majority of evidence for colloid-facilitated transport of contaminants is mainly based on indirect �eld observations, model calcu-lations, and laboratory scale column experiments. Earlier studies on colloid-facilitated transportwere conducted to provide a better scienti�c basis for long-term risk assessment of high-level ra-dioactive waste repositories or radionuclide migration at former nuclear test sites [Saltelli et al.,1984; Buddemeier and Hunt, 1988]. Some radionuclide elements have the tendency to undergohydrolysis reactions to form colloidal particles by precipitation. In addition, many radionuclidesare strongly sorbed to colloidal particles consisting of clay minerals, oxides, and humic substances.Thus, mobile colloidal particles potentially play a signi�cant role as carriers of radionuclides insoils, groundwater aquifers, and rock fractures [Smith and Degueldre, 1993; Saiers and Hornberger,1996]. In a recent study, strong experimental evidence points to colloid-facilitated movement of

20

Pu in groundwater [Kersting et al., 1999]. Using the ratio 240Pu to 239Pu, Kersting and her col-leagues could unequivocally identify the source of the Pu as more than one kilometer away from thesampling site. Filtration of contaminated groundwater samples removed 99% of the Pu, indicatingtheir association with colloidal material.

The role of in situ mobilized colloids in mobilization and transport of contaminants has alsobeen addressed recently. Faur�e et al. [1996] conducted packed column experiments with sand and5% bentonite clay to study colloid and radionuclide transport induced by a salinity gradient. Atsalt (NaCl) concentration > 0.16 M no colloid particles were leached from the column and 137Cswas transported as the dissolved species. When the salt concentration was decreased below thecritical threshold concentration of 0.16 M, particles started to be mobilized and colloid-facilitated137Cs transport was observed. The potential of natural in situ mobilized colloids for facilitating thetransport of strongly sorbing contaminants in natural porous media was con�rmed by Grolimundet al. [1996]. In columns packed with a non-calcareous soil material, they observed signi�cantcolloid release and mobilization of Pb when feed solution was switched from 50 mM NaCl to0.15 mM CaCl2.

Transport in the Vadose Zone

Radionuclide wastes at the Hanford site have leaked into the vadose zone. In addition to move-ment due to preferential ow, colloid-facilitated transport may be another reason for acceleratedtranslocation of radionuclides in the subsurface. Until recently, most research on colloid and colloid-facilitated transport has been focused on the saturated zone and the in uence of water content oncolloid transport and deposition has been neglected. Several recent studies have demonstrated theimportance of the gas-water interface for the transport and deposition of colloidal particles in un-saturated porous media [Wan and Wilson, 1994; Wan et al., 1994; Powelson and Mills, 1996; Wanand Tokunaga, 1997; Chu et al., 2001].

The importance of the gas-water interface for deposition of colloidal particles in unsaturatedporous media was demonstrated by Wan and Wilson [1994] using two-dimensional glass micro-models. Sorption of hydrophobic and hydrophilic particles of clay and polystyrene latex as well asbacteria, to the surface of air bubbles was directly visualized using uorescent microscopy [Wanand Wilson, 1994; Wan et al., 1994]. Particle adsorption at the gas-water interface increased withincreasing particle hydrophobicity and solution ionic strength, and was not reversible when theionic strength of the bulk solution was reduced. The e�ect of a gas-water interface on microbialtransport and the causes of increased retention of bacteria in unsaturated porous media have alsobeen investigated and quanti�ed in column experiments [Wan et al., 1994]. In their study, prefer-ential sorption (up to 52% of total mass) of the bacteria to the gas-water interface was observedand the sorption appeared to be due to hydrophobic forces. It should be noted, however, that thesetransport experiments were conducted under conditions highly unfavorable for colloid depositionat the solid-water interface.

A �lm-straining theory proposes that transport of suspended colloids can be retarded dueto physical restrictions imposed by thin water �lms in partially saturated porous media [Wan andTokunaga, 1997]. In this model, the concepts of \critical matric potential" and \critical saturation"are introduced, at which thick �lm interconnections between pendular (capillary) rings are brokenand �lm straining begins to become e�ective. The modeled magnitude of colloid transport throughwater �lms depends on the ratio of colloid size to �lm thickness and on ow velocity.

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3.4.8 Preferential Flow in Intact Monoliths

In the sand and gravel soils at the Hanford site we expect water (and associated contaminants) tomove preferentially through soils in a few ow paths (�ngers) at high moisture content [Glass et al.,1989; Selker et al., 1992; Liu et al., 1994; Ritsema et al., 1998]. Preferential ow paths not onlycarry water and solutes more rapidly to groundwater but also have a much higher moisture contentthan that would be predicted by the traditional convective-dispersive ow. The higher moisturecontent is easily understandable if we consider that the same amount of recharge is carried througha few paths down to the groundwater rather than being uniformly distributed. Thus, under lowmoisture conditions the thickness of water �lms within the preferred ow paths may be muchgreater than that predicted based on the bulk moisture content. This consideration makes it lesslikely that �lm straining [Wan and Tokunaga, 1997] is signi�cant as a mechanism to retard colloidsunder low moisture conditions when preferential ow occurs. Higher rates of water application arepostulated to result in the formation of more preferential ow paths that then would transport alarger total mass of water, although the rate and depth of penetration of each ow path would besimilar. Thus, a larger mass of colloids is expected to be released, but the rate of release is notexpected to change substantially at higher water in�ltration rates.

The length of time between in�ltration events is expected to have a signi�cant e�ect on themobilization of colloids. In in�ltration experiments in a sandy loam soil [Jacobsen et al., 1997;Jacobsen et al., 1998], the mobilization of in situ colloids was not in uenced by ow velocity, butwas in uenced by the time between in�ltration events. As the time delay between water applicationincreased, the mass of mobilized colloids increased. This pattern is consistent with depletion of a�nite pool of readily detached colloids, and a time-dependent re-supply of that detachable pool.Schelde et al. [2002] postulate that re-supply is controlled by di�usion of colloids from the soilmatrix to the active ow path, but it may also involve di�usion of colloids across the boundarylayer between the grain surface and the bulk uid in the water �lm [Ryan and Gschwend, 1994].We hypothesize that the detachable colloids accumulate at the gas-water interface. A rechargeevent that generates an advancing saturated �ngertip will translocate colloids in water �lms andthe gas-water interface, thus causing a local depletion of colloid concentrations in the water �lmthat remains after drainage. The bulk uid in the water �lm will again be re-supplied in a time-dependent manner with colloids by rate-limited detachment and di�usion from the mineral phase.Over time, a steady state will be established in the concentration of colloids at the two interfaces,determined by the interaction energy governing the association of the colloid with mineral surfacesor the gas-water interface. The mass of colloids mobilized by a subsequent recharge event willthus be in uenced by its a�nity for mobile or immobile interfaces and the length of time betweenin�ltrations.

3.4.9 Modeling of Colloid, Contaminant, and Colloid-facilitated Transport

A considerable literature exists on modeling the in uence of colloid-facilitated transport of ra-dionuclides involving reversible and irreversible sorptive processes in porous and fractured media[van der Lee et al., 1992; Harber and Brenner, 1993; Nuttall and Long, 1993; Jiang and Corap-cioglu, 1993; Smith and Degueldre, 1993; Kessler and Hunt, 1993; Wan and Wilson, 1994; Ibarakiand Sudicky, 1995; Baek and Pitt, 1996; Grindrod and Lee, 1997; Marty et al., 1997; Corapciogluet al., 1999; James and Chrysikopoulos, 1999; Contardi et al., 2001].

Mathematical models for colloid and colloid-facilitated transport are usually based on theadvection-dispersion equation (ADE). The ADE is then coupled with di�erent types of colloid{contaminant{soil-matrix interactions. Colloid interactions with the stationary solid phase are usu-

22

ally described with �ltration theory, where the overall reaction can be formulated as �rst-orderkinetics. According to classical �ltration theory, colloidal particles attach usually strongly andirreversibly to sediments and soil minerals, and therefore migration of colloids is assumed to belimited to several tens of meters [Honeyman, 1999]. As �eld evidence has proven, this presumptionis often not valid. Other than �rst-order reactions have to be considered in conceptual models todescribe colloid transport. Recent advances have been made by considering two-site attachment,Langmuir-type reaction kinetics [Lindqvist et al., 1994; Saiers et al., 1994], sorption site blocking[Johnson and Elimelech, 1995; Ko and Elimelech, 2000], and solid phase heterogeneity [Song et al.,1994].

Transport under unsaturated conditions di�ers considerably from transport under saturatedconditions, as experimental evidence presented above clearly demonstrated. Only few attempts havebeen made to quantify and predict colloid and colloid-facilitated transport in the presence of an air-phase. Corapcioglu and Choi [Corapcioglu and Choi, 1996; Choi and Corapcioglu, 1997] presenteda modeling approach that considers the air-phase as an additional sorption site for colloids, withthe sorption reaction described as an irreversible rate-limited process.

Colloid-facilitated transport of contaminants is only going to be an important transport mech-anisms if contaminants sorb strongly to colloidal particles. For reversible sorption the e�ectiveretardation coe�cient, taking into account sorption on colloids and mineral surfaces in the rockmatrix, has the form

Rj = 1 +Kr

j

1 +Kcj

; (1)

where Krj and Kc

j denote dimensionless distribution coe�cients for sorption of the species j onthe rock matrix and colloids, respectively. It should be emphasized that the above relation forretardation in terms of distribution coe�cients is only valid provided radionuclides are present intrace amounts and the solution composition remains approximately uniform along the ow path.For these circumstances, under reversible conditions when retardation is large (Kr

j � 1) in theabsence of colloids, in order for colloids to have a signi�cant e�ect on retardation it is necessarythat the colloid distribution coe�cient be comparable to sorption on the rock matrix: Kc

j ' Krj � 1.

For this relation to occur, however, requires that colloids compete e�ectively with the rock matrixfor radionuclides. This only can happen if colloids are present in su�cient numbers or they havemore favorable properties that enhance radionuclide sorption compared to the rock matrix.

Alternatively, low colloid concentrations can also be e�ective at reducing retardation of ra-dionuclides through irreversible sorption processes or through formation of intrinsic radionuclidecolloids. In either of these cases, Eq. (1) does not apply. Filtration mechanisms involving colloidattachment and detachment processes become the dominant factor in limiting the e�ectiveness ofcolloid-facilitated transport.

Modeling redistribution of moisture, heat, and solutes in the vicinity of the Hanford tanksinvolves a number of complicating processes including in�ltration, umbrella e�ects caused by thetank shadow, heat released from the tanks, and leakage of high salinity uids with internal heatgeneration from radioactive decay [Pruess et al., 2002b]. A number of two-phase ow codes havebeen used to model these processes including FLOTRAN [Lichtner, 2001], NUFT [Nitao, 1998],STOMP [White and Oostrom, 1996], and TOUGH2 [Pruess et al., 2002a]. The codes describe si-multaneous ow of aqueous and gas phases coupled to heat ow under gravity, capillary, and viscousforces based on Darcy's law incorporating relative permeability and capillary e�ects. Constitutiverelations for relative permeability and saturation represented as functions of capillary suction arebased on phenomenological considerations such as the van Genuchten relations [van Genuchten,1980].

23

Two phase conditions for ow and transport for variably saturated media incorporating mul-ticomponent chemical processes have been modeled as sequentially coupled processes [Lichtner,1996]. Volatile species such as CO2 can exchange between the gaseous and aqueous phases. For sit-uation involving generation of CO2 from, e.g., calcite dissolution or degradation of organic matter,a more tightly coupled scheme than currently implemented may be necessary.

High temperature conditions encountered near the base of several of the Hanford tanks resultin heat pipe e�ects with counter ow of liquid and vapor and concentration of solutes resultingfrom evaporative e�ects [Pruess et al., 2002b]. Because of the extreme conditions, such locationscould be an e�ective source for colloid generation.

3.5 Major Results from Previous EMSP Project and Outlook

Our previous EMSP project has focused on the special conditions occurring at the SX Tank Farm.1

We have found that that 3 di�erent types of colloidal materials form when highly alkaline tanksupernatant solutions contact Hanford sediments:

1. Altered native minerals in the colloidal size fraction.

2. Newly formed, secondary mineral phases identi�ed as mixtures of sodalite and cancrinite.

3. Precipitates formed during titration of the supernatant solutions after reaction with Hanfordsediments.

We have identi�ed the reaction products mineralogically using XRD, SEM/TEM, FTIR, and NMR.Colloidal properties, assessed by electrophoretic mobility measurements, showed that the newlyformed colloids had di�erent surface properties than the unaltered native minerals of the sediments:we observed a zero-point of charge around pH 6.5 to 7.5; however, at the ambient pH of the Hanfordsediments (pH 8 to 8.5), the newly formed mineral phases have a negative electrophoretic mobilitysimilar to that of the unaltered native sediments. Sorption of Cs to newly-formed mineral phaseswas slightly less than to native colloidal material. We have further shown that the conditions atthe SX Tank Farm, i.e., high ionic strength plumes displaced by low ionic strength meteoric water,is conducive to in situ colloid mobilization and transport.

The new EMSP project will build upon, and extend, the previous project in three main areas:

1. Thermodynamic stability of newly-formed colloidal phases: While we know what the productsare that form under the speci�c conditions of the SX Tank Farm, we do not know how stablethese new materials are. What will happen to these colloids when they move downwardthrough the sediments and encounter di�erent geochemical conditions?

2. Colloid-contaminant interactions: A strong colloid-contaminant interaction is pre-requisitefor colloid-facilitated transport. How do Cs, Eu, and Am associate with colloidal phases?

3. In situ mobilization and colloid-facilitated contaminant transport under di�erent waste streamsat Hanford: We know that the speci�c conditions at the SX Tank Farm are conducive to col-loid mobilization and transport, when meteoric water or Columbia River water displaces wasteplumes. Similar conditions may arise at other, less chemically extreme, waste streams, suchas cribs, trenches, or French drains. We will systematically study in situ mobilization andtransport under a variety of sedimentary and chemical conditions.

Figure 1 summarizes the main thrusts of the previous and planned research activities.

1A more detailed description of the previous project goals and accomplishments is given in Appendix A.

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Previous EMSP Project

Reaction of tank waste with Hanford sediments

Colloid-association with Cs

Colloid transport under SX Tanks

Formation of zeolite, sodalite, cancrinite colloids

Colloids associate with Cs

Colloids move through vadose zone

New EMSP Project

Expected OutcomesOutcomes

Thermodynamic stability of zeolite, sodalite, cancrinite

Colloid-association with Cs, Eu, Am

In situ mobilization and transport of colloids withpacked, undisturbed, and contaminated sediments

Conceptual model for colloid-facilitated transport atHanford incorporated into reactive transport code

Relevance and quantification of colloid-facilitatedtransport of radionuclides under different waste streams

Cs

SX Tanks SX, TXTanks

Cribs, French Drains

Cs, Eu, Am

Figure 1: Schematic overview of previous and new EMSP projects including outcomes.

3.6 Research Design and Methodologies

3.6.1 Overall Research Concept and Outcomes

The three main foci of this proposal, (1) the thermodynamic stability and mobility of colloids formedby reactions of sediments with highly alkaline tank waste solutions, (2) the colloid-contaminant in-teractions, and (3) the in situ colloid mobilization and mobility of native colloids occurring in bothcontaminated and uncontaminated Hanford sediments, will be accomplished through laboratoryexperiments and numerical analyses. For the �rst focus area, we will build upon the results ofour previous EMSP project and extend the characterization of cancrinite/sodalite colloids, whichare forming when highly alkaline tank waste solutions react with Hanford sediments, and deter-mine their thermodynamic stability and mobility with batch and column experiments. For thesecond focus area, we will use ion-exchange and spectroscopic methods to determine the nature ofcolloid-contaminant associations. For the third focus area, we will use a series of colloid mobiliza-tion scenarios to determine whether, and to what extent, in situ colloid mobilization in Hanfordsediments can occur. These colloid mobilization experiments involve saturated as well as unsat-urated transport experiments in packed and undisturbed soil monoliths. We will also use somecontaminated sediment material to verify whether in situ colloid mobilization can results in ac-celerated movement of radionuclides. The experimental data will be analyzed with a two-phase,multicomponent reactive transport model. The modeling will not only allow to develop a concep-tual model for colloid mobilization and colloid-facilitated contaminant transport, but also extendsthe experimental results to conditions not explicitly covered during the experimentation.

As a result of this project, we anticipate to provide clear conclusions on whether, and underwhat conditions, colloid-facilitated transport of radionuclides at the Hanford site can occur, andwhat the quantitative magnitude of this process will be. We will cover a variety of di�erent wastestreams and subsurface sediments, and will therefore obtain representative results for conditions atHanford. Colloids are suspected to be important vectors for strongly sorbing radionuclides, but littleis know about in situ mobilization and transport through the vadose zone. Here, we systematically

25

address these questions, with special emphasis on the conditions at the Hanford site. As such, ourexperimental and modeling e�orts will lead to an improvement of the understanding of the basicfactors controlling long-term fate and transport of radionuclides at the Hanford site.

3.6.2 Sediment Materials

We recognize that the vadose zone at Hanford is heterogeneous and that colloid transport will bea�ected by this heterogeneity. When tank waste solutions leak into the vadose zone, the aggressivesolutions are neutralized by reactions with the sediments underlying the tanks. We anticipate thatthese dissolution precipitation reactions take place close to the tanks, and that the waste solutionswill be neutralized during deeper migration through the vadose zone. Formation of zeolite andfeldspathoid colloids is therefore con�ned to the immediate neighborhood of the tanks; however, asthese colloids move downward, they not only dissolve and transform in new mineral phases, but alsoencounter the di�erent stratigraphy of the sediments of the Hanford and Ringold formations. It istherefore important to investigate transport of the colloids and their products in di�erent types ofsediments characteristic for the Hanford and Ringold formations. We have consulted with geologicexperts of the Hanford site (Bruce Bjornstad and Stephen Reidel, Paci�c Northwest NationalLaboratory) which stratigraphic units would be most representative for colloid characterization andtransport experiments. We anticipate to use at least four di�erent sediment samples, originatingfrom the cataclysmic ood deposits, the uvial/aolian deposits, the caliche layer, and the uvialoverbank deposits. A 4-inch diameter split-spoon core (299-E24-21) drilled in the 200 East Area isavailable for experimental purposes and can be used for characterization and transport experiments.

3.6.3 Colloidal Materials

We will work with two types of colloidal material (de�ned as material < 2 �m diameter): (1) insitu colloids separated from di�erent types Hanford sediments mentioned above, and (2) colloidsseparated from Hanford sediments, representative for the sediments underlying the SX Tank Farm,after reaction with simulated tank waste solutions. From our previous EMSP project we know thatthe latter type of colloids consist themselves of three di�erent materials, namely (1) altered in situcolloids, (2) newly-formed mineral phases, and (3) Si-rich precipitates from supernatant solutions.We have extensively characterized these latter materials with XRD, FTIR, NMR, TEM/SEM,electrophoretic mobility, and Cs sorption. Similar characterizations will be performed for thedi�erent in situ, unreacted, colloids.

3.6.4 Formation and Characterization of Colloids

Characterization of Colloidal and other Solid Phases

Colloids will be separated from coring material, batch synthesis procedures, and columns by particlesize fractionation, selecting, at least, the <0.2 �m and 0.2{2.0 �m fractions for characterization.We will use photon correlation spectroscopy to determine particle size distribution of the <0.2�m fraction and static laser scattering for the larger fractions. Electrophoretic mobility will bedetermined as a function of pH and ionic strength in a NaNO3 background [Su et al., 1994; Suand Harsh, 1994]. The particle-size isolates will be analyzed by X-ray di�raction (XRD) and IRspectroscopy for identi�cation of mineral components. Standard clay mineralogical methods ofsaturating with index cations (K+, Mg2+) and solvation with polar organics will be used to identifythe discrete phyllosilicates (smectite, kaolinite, illite, vermiculite) by their characteristic di�ractionmeasurements.

26

We will identify less crystalline materials IR spectroscopy and an FTIR microscope. FTIRhas been shown to be a particularly useful means for characterizing both crystalline and poorly-crystalline aluminosilicates [Flanigen et al., 1971; Farmer et al., 1979; Hlavay et al., 1985; Farmerand Russell, 1990; Diaz et al., 2002]. In addition, far-IR can provide speci�c information regardingsite occupancy by alkali metal cations, such as Cs, Na, and K, in zeolites [Godber et al., 1989]and micas [Diaz et al., 2002]. In this study, will obtain far-IR spectra of Cs-, Am-, Eu-, and Na-exchanged colloidal aluminosilicates to determine if any are ordered enough to allow characterizationof metal cation translatory modes. This would allow identi�cation of speci�c metal-occupied sitesin complex matrices by far-IR. Electron probe microanalysis (EPMA) also will be used to obtainchemical compositions of the particle size isolates, as well as morphologic analysis. Large samplingsize (N) and careful statistical analyses of compositional and morphologic information will beperformed to ensure accurate mineralogic characterization.

We will measure the speci�c surface area of the colloidal material by gas absorption using theBET method. The surface area measurements will be a key parameter for assessing sorption andcolloidal properties of the material.

Thermodynamic Stability and Products of Feldspathoid Transformations

The stability of sodalite will be examined both from a modeling and experimental approach. Thethermodynamic properties of sodalite (�Ho, �Go, heat capacity, �So298) have been determinedand can be used to calculate the solubility at equilibrium as a function of pH and temperature.Thermodynamic parameters are not available for cancrinite, but it may be possible to use linearfree energy approximations from observed di�erence in solubility to develop a reasonable estimateof the free energy of formation for cancrinite. Cancrinite is known to be less soluble than sodalite inalkaline solutions [Zheng et al., 1998]. Stability diagrams will be constructed comparing sodalite toother aluminosilicate phases including smectite and illite end-members as well as metastable phasessuch as \allophanes" and imogolite [Su and Harsh, 1994,1995,1998; Xu and Harsh, 1994,1995].

The stability and lability of synthetic sodalite and cancrinite [Zheng et al., 1998] will bedetermined experimentally under the range of conditions expected in the subsurface below theHanford site. We will determine the concentrations of Al, Si, Na, and NO3 as well as the pH insuspensions of colloidal material with solid:solution ratios � 1. Equilibrium will be approachedfrom expected over- and under-saturation and Si(OH)4 activity and pH will be used to index theapproach to equilibrium or steady state. The initial pH will range from 6 to 8.3; the upper limitmaintained by equilibrium with CaCO3 and atmospheric CO2 and lower pH's will be adjusted asneeded with HNO3 or NaOH. Stability will also be determined as a function of temperature from20 to 80�C to simulate conditions both near �eld and far �eld with respect to a leaking tank.

We suspect that these minerals may be thermodynamically unstable but nonlabile within thetime frame of these experiments. To estimate the long-term lability of the feldspathoid materi-als, we will perform solubility experiments at elevated temperatures and equilibrium water vaporpressure in Parr bombs with Te on reaction vessels [Su and Harsh, 1998]. This will both decreasethe time of approach to equilibrium dissolution and formation of possible reaction products. Byperforming experiments over a range of temperature and extrapolating to a selected temperature,we can estimate the stability of a given phase. Although we cannot assume that reaction productsformed under conditions of elevated temperature and pressure will be the same as what would formunder environmental conditions, this experiment will give us the ability to identify potential solidphases and estimate their rate of formation; something that may not be possible with short-termexperiments at ambient temperature. Selected solubility experiments will be performed on theproducts of simulated tank waste to compare the products with the synthetic feldspathoids.

27

Ion Exchange Selectivity and Sorption Reversibility

Ion exchange isotherms will be obtained with Cs+, Na+, and Ca2+ on synthetic sodalite and cancri-nite, reaction products of simulated tank waste with Hanford sediments, and with selected reactionproducts of solubility experiments, if enough material can be generated in the latter case. Thepurpose of these experiments is to determine how the capacity of the materials changes with al-teration relative to the original sediment materials [Zachara et al., 2002]. It is also necessary todetermine the extent of chemisorption and other \irreversible" sorption processes. In the case ofCs+, this is expected to come from sorption to frayed edge sites (FES) on hydrous micas. Theconcentration and number of such sites should change, at least in the clay fraction of the sedimentsfollowing reaction with simulated tank wastes. For this reason, we will compare selectivity coe�-cients and irreversibility as a function of Cs+ site occupancy in the clay fraction of altered sedimentsto unaltered sediment clay, selected clay minerals (illite, smectite, kaolinite and vermiculite), andfeldspathoids.

Similar experiments will be performed with Eu(III) and Am(III), but sorption will be deter-mined as a function of pH and ionic strength at equilibrium atmospheric CO2 partial pressures. AtpH values selected to represent much of the subsurface volume at the Hanford site (7 to 10), it isexpected that Eu(III) and Am(III) will chemisorb to clay surfaces. Sorption may be inhibited atthe higher pH values (> 8.5) as a result of carbonate complexation, but cation exchange will not bethe sorption mechanism. High ionic strength solutions of NaNO3 will be used to assess the extentof chemisorption relative to adsorption by electrostatic forces alone. The main purpose of thesesorption experiments will be to determine sorption capacities, dependence on solution parameters,and the most likely sites of sorption. For the latter purpose, we will use the same microscopic toolsdescribed above for the characterization of metal sorption to contaminated sediments.

A third set of experiments will be performed to determine the lability of metal ions copre-cipitated with feldspathoids. Low levels of radio-labelled Cs, Eu, and Am (< 10�5 M) will bedissolved in the alkaline solutions used to synthesize cancrinite and sodalite and in the reactionswith Hanford Formation sediments. We will determine the fraction of metal incorporated into thesolid phase by solution analysis of the radioisotope and by selective extraction of the solid. Sodalitecan be completely dissolved from a clay fraction containing aluminosilicates and metal oxides withtwo extractions of 0.5 M HCl [Singh and Gilkes, 1991]. Extraction with 1 M Na and Ca salt so-lutions will be used to determine the exchangeability of coprecipitated metals compared to metalsadsorbed to synthesized and altered feldspathoids and clays. A dilute acid extraction will removeeasily desorbed metals from surface sites. For a more direct analysis of the location of metals inthe mineral matrix, will apply microbeam techniques as described above.

Surface Chemical Composition

The structural locations where Am, Eu, and Cs associate on strongly sorbing Hanford mineralfractions, the new solid phases formed from reaction with simulated tank waste, and synthesizedaluminosilicate colloids will be identi�ed by energy-dispersive x-ray emission analysis (EDX) onthe TEM. The EDX will allow us to \map\ the distribution of metals on a broad range of particlesizes, if necessary, ranging from clay (<2.0 �m) to silt (2{50 �m), and to determine areas of metallocalization down to the scale of 10{20 nm. The EDX is not a quantitative-analysis tool, but itprovides a wealth of semi-quantitative information. In particular, it will allow us to assess theextent to which metals associate with colloids that may be mobilized under suitable conditions.

One or two of several potential microbeam methods will be used to interrogate metal (Cs, Am,Eu, Al, Fe, Si, etc.) concentrations on speci�c areas of metal-sorbing particles. These analyseswill document microscopic regions of dissolution or precipitation (e.g., Al and Si composition)

28

and will quantify metals within speci�c mineral phases. Such phases may include newly formedcolloids or clay minerals from the original matrix. The elegant early study of Le Roux et al. [1970]used microbeam analysis to show Rb exchange occurred primarily at step edges, cracks, and othersuch features on 500-�m mica particles. Signi�cant technology advances in microbeam analyticalequipment, as contained in Environmental Molecular Sciences Laboratory (EMSL), will allow usto perform improved microanalytical measurements on silt and possibly clay sized particles. Ouravailable techniques and beam diameters are (1) small area X-ray photoelectron spectroscopy (XPS,8{10 �m); (2) electron probe microanalysis (EPMA, 1{2 �m); (3) time-of- ight secondary-ion massspectrometry microprobe (TOF-SIMS, 100 nm), and (4) �ne beam Auger electron spectroscopy(AES, 30 nm).

Our methods of choice for select area chemical analysis probably will be EPMA and TOF-SIMS, and these will limit us to 0.1{1 �m areas on particles. The project team is su�cientlyexperienced with these methods [Zachara et al., 1989, 1995] to allow their successful application inthis project.

HRTEM has long been a technique of choice to interrogate nm-scale features of layer-silicates[Ahn and Peacor, 1986; Bell, 1986; Klimentidis and Mackinnon, 1986; Srodon et al., 1990; Whitneyand Velde, 1993] and will be a valuable source of nanoscale features of the newly formed alumi-nosilicates. The EMSL HRTEM has a point-to-point resolution of 2 nm and software for imageanalysis of particle size and other features. D-spacings of small spatial areas also can be obtainedby selected area di�raction (SAD) and software exists for the immediate initial interpretation ofthe resulting Laue spot pattern. We have previously used TEM to quantify the particle-size distri-bution of clay-sized 2:1 layer-silicates isolated from soil and to correlate their size, mineralogy, andmorphology with chemical reactivity [Zachara et al., 1993].

Atomic-force microscopy (AFM) is a relatively new technique that holds great potential forthe measurement of the dimensions of clay-sized particles [Lindgreen et al., 1991; Blum and Eberl,1992]. With appropriate mounting techniques (such as on muscovite plates as described by Blum,1994), thickness can be measured as well as surface steps and other microstructures at an accuracyof approximately 0.4 nm; this distance is less is 50% of the thickness of one mica layer (1.0 nm).Surface topological mapping can be correlated with chemical analysis by other techniques to helpdetermine particular phases where Cs may reside. The direct atomic imaging of dehydrated Cs+

sorbed within ditrigonal cavities on the surface of clinochlore was shown by Wicks et al. [1994],underscoring the potential usefulness of this technique.

Chemical Modeling

The GMIN code will serve as our repository for equilibrium, macroscopic-reaction parametersdescribing metal sorption, exchange, aluminosilicate stability, and other controlling geochemicalreactions developed during the course of research. Additionally, it will include other relevantsolubility or aqueous complexation equilibria parameterized by the project or found to be necessaryfor experimental interpretation. Examples include the high ionic-strength solubility and aqueousspeciation reactions of the Si(IV) oxide and Al(III)-oxide systems. By project end, it will containbinary ion-exchange parameters to describe equilibrium Cs ion-exchange sorption over the range inchemical parameters and temperature addressed by experiment. Functional relationships will alsobe established between selectivity and solid-phase composition for a given structure (e.g., Al/Siratio in a zeolite or hydrous feldspathoid). As such, it will function as a predictive model withcapability to forecast the extent of Cs adsorption that may occur to the colloidal aluminosilicatefraction in the reaction products formed from Hanford sediments subjected to supernatant solutionsof various in-tank and subsurface-reacted compositions.

29

Colloidal Stability

The stability of colloidal suspensions against aggregation is an important parameter to determinethe behavior of the colloids in the subsurface. We will determine the stability ratio W of colloids|formed after reactions with simulated tank waste solutions and in situ colloids separated from thesediments|using di�erent types of electrolytes (NaCl, KCl, CsCl, CaCl2, MgCl2). The stabilityratio W will be determined by measuring the rate of particle aggregation using PCS [Hiemenzand Rajagopalan, 1997; Hunter, 2001], where the aggregation rate constant is calculated from theinitial slope of a plot of hydrodynamic radius versus time [Virden and Berg, 1992]. The criticalcoagulation concentration (ccc) will result directly from the stability ratio at the concentrationwhere W = 1. We will also independently measure the ccc with the test tube method [Hunter,2001].

3.6.5 Colloid and Colloid-facilitated Transport in the Vadose Zone

Our overall purpose is to test whether and to what extent colloid-facilitated transport of stronglysorbing contaminants, represented by Cs, Eu(III), and Am(III), occurs in Hanford sediments. Ex-periments will be conducted in both, packed and undisturbed, sediment materials. In a series ofcolumn experiments we will investigate:

� in situ colloid mobilization from sediments

� the impact of water content on colloid and colloid-facilitated transport

� the e�ect of solution chemistry and hydrodynamics on mobilization of colloids

� the consequences of wetting-drying cycles on colloid and colloid-facilitated transport

Selected contaminated samples from SX, TW, and TX Tank Farms will be used to verify the resultsobtained from uncontaminated samples.

Setup of Packed Sediment Columns and Undisturbed Monoliths

We will study transport of colloids and contaminants through both packed sediment columns andundisturbed monoliths. In the previous EMSP project we have developed a sophisticated columnsetup for studying colloid transport through packed sediments (Figure 2). The system allows usto control water contents, and corresponding water potentials, to an accuracy of 10% e�ectivewater saturation during steady-state water ow. The columns are custom-designed and have aninner diameter of 7 cm and are 20 cm long. Five high- ow ceramic tensiometers are insertedinto the column in spiral-shaped arrangement. The water potential at lower boundary conditionof the column is controlled with a sintered-glass porous plate with a bubbling pressure of about70-cm H2O. Our tests have shown that the e�ective saturation of coarse Hanford sediments at asuction of 70-cm H2O is less than 10%. The suction is controlled by a hanging water column. Theupper boundary condition is controlled by a sprinkler head made out of a Plexiglas head piecein which 12 hypodermic needles are inserted. Flow is maintained by a high-precision peristalticpump. The column out ow is routed online through an UV-VIS spectrophotometer and out owis �nally collected in a fraction collector. In ow, out ow, and the column itself are placed onload-cells to monitor weight changes. Tensiometers, load-cells, and UV-VIS spectrophotometerare interfaced to a computer via a Campbell Scienti�c data logger. We have found that the deadvolume in the in- and out- ow portion of the column will a�ect the breakthrough curves, and wehave consequently minimized the volume comprised in in- and out ow tubing and connections.

30

Colloidsuspension

Eliuent solution

Datalogger

Peristaltic pumpThree-way valve

Column

Pressure transducers

Loadcell

Loadcell

Sprinkler head

Fraction collector

Hanging watercolumn}CR-7Campbell Scientific Inc.

3 0 0

.0132000

Perkin-Elmer

LC-95

Response time

Absorbance/1 cm Inj. MarkA/ZRec. Range

msec

Loadcell

Spectrophotometer

Tensiometers with

Figure 2: Column setup for unsaturated ow and transport experiments in packed sediments.

The standard ow-through cell of the spectrophotometer has been replaced with a custom-built,low-volume ow-through cell. Colloid and tracer (NO3) concentrations can be measured accuratelywith the spectrophotometer and recorded at any desired time interval. Our results have shown thatthis experimental system allows excellent control of water contents and potentials during steady-state ow experiments. A critical advantage of our system is that we do not require a vacuumchamber at this time. If a vacuum chamber would be used, we could not measure breakthroughcurves over prolonged periods of time, because vacuum chambers have a limited capacity to collectsamples in the enclosed fraction collector.

For the work proposed here, we will further re�ne this experimental setup by including ow-through pH and electrical conductivity cells in the out ow portion, and by inserting TDR waveg-uides into the column next to the tensiometers. Depending on the type of sediments used, we willreplace the sintered-glass porous plate with another appropriate suction-control device.

Undisturbed monoliths will be taken from the sediments of the Hanford formation. We antici-pate to take the monoliths from the submarine pit at the Hanford site. Since the sediments of thisformation are coarse and unconsolidated, sampling an undisturbed monolith is challenging. We willadapt the approach used by Buchter et al. [1995], which uses liquid nitrogen to freeze a block ofsediments in place, followed by excavation and enclosure in para�n. Although the liquid nitrogentreatment might not necessarily preserve the natural spatial colloidal distribution, it seems to bethe only way we can obtain least disturbed monoliths from the Hanford sediments. The monolithssampled will be 80 to 100 cm in height and 50 to 60 cm in diameter. We anticipate to take twosuch monoliths.

The monolith setup in the laboratory will be similar to that for the packed column study.However, we recognize that the water potential is unlikely uniformly distributed within the monolithdue to formation of preferential ow paths. The bottom end of the monoliths will be �tted withfritted glass plates that are positioned in low volume Plexiglas holders and bolted together to holdthe plates against the soil monolith ends. Numerous air vents will be drilled along the distance ofthe monolith in order to open the system to surrounding atmosphere [Jardine et al., 1993]. Thisprocedure does not disturb the soil core. The outlet pressure head will be maintained with a hanging

31

water column. The selection of imposed negative pressure-head at the bottom will be dictated bythe need to avoid a capillary fringe at the bottom. A sprinkler head similar to that described forthe packed columns will control the upper boundary condition. A high precision peristaltic pumpwill control the ow rate. The column e�uent will be routed to a fraction collector. Water contentwill be monitored with a large capacity balance.

In Situ Mobilization of Colloidal Material from Hanford Sediments

Besides the postulated, newly formed colloidal particles and their alteration and dissolution prod-ucts, the native in situ colloidal particles may cause colloid-facilitated contaminant transport. The�rst condition for colloid-facilitated transport to occur is that the in situ colloids become dispersed.At Hanford, colloid dispersion and mobilization is likely to occur when contaminant plumes of highionic strength and high pH are diluted by dispersion during downward migration or when theplumes are displaced by in�ltrating rainwater. We will experimentally simulate these conditions incolumns �lled packed Hanford sediments. In a series of experiments, we will initially equilibrate thesediments with a solution of high ionic strength (1 M, representing a contaminant plume) and dis-place this solution with a solution of low ionic strength (1 to 20 mM, representing uncontaminatedsoil solution). We will use NaNO3 as contaminant electrolyte and displace it with 1:1 (NaNO3 andKNO3) and 2:1 (Ca(NO3)2 or CaCl2) electrolytes. We will bu�er the pH close to the native pHof the sediments (about pH 8.5). We will also use displacement solutions representative for thepore water in Hanford sediments. The out ow will be routed through a ow-through pH cell, andcollected in a fraction collector. The change of ionic strength will cause an increase in pH due to ionexchange of electrolyte cations with protons, which has to be considered in the interpretation theresults. Colloids in the out ow will be characterized in terms of mineralogy and colloidal propertiesas described above.

We will choose two cases where we observe (1) no or little colloid mobilization and (2) muchcolloid mobilization to verify the results in undisturbed sediment monoliths. All these experimentswill be conducted under saturated conditions under unit gradient or smaller hydraulic head. It isknown that colloid mobilization is ow-rate dependent, and high ow rates tend to mobilize morecolloidal material [Ryan and Elimelech, 1996]. It is therefore important to control ow rates atconditions natural for the vadose zone.

Impact of Water Content

Hanford sediments will be packed into columns of the experimental system described above. Exper-iments will be carried out under saturated and unsaturated, steady-state water ow to study thee�ect of water content on colloid transport. The water ow rates will be di�erent for the variouswater contents, and are given by the unsaturated hydraulic conductivity function. Thus, water owrates and water content of the columns are not independently adjustable, except for the saturatedcolumns where we will use the saturated hydraulic conductivity as ow rate. Thus, we will usea unit hydraulic gradient in all the ow experiments. This condition corresponds to the naturalcondition in the vadose zone. Realizing that the water contents in the vadose zone at the Hanfordsite can vary from very wet to very dry, we will study transport under a series of water contentsranging from 10% to 100% e�ective saturation. Our preliminary results have indicated that weshould be able to control water contents in 10% increments, so that we can run the experiments inthe following sequence:

1. E�ective water saturation of 100, 90, 80, 70, 60, 50, 40, 30, 20, 10%

2. E�ective water saturation of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100%

32

We expect that Hanford sediments have a heterogeneous particle size distribution and it is thereforedi�cult to predict at which water content the water �lms become small enough to inhibit colloidtransport. The careful control of the water content in small increments will therefore be necessaryto assess the impact of water saturation on colloid transport. The sequence shows that we willstart with a saturated column, lower the water contents in steps, and then increase the watercontent again until we reach saturation. Doing so will obtain a complete hysteresis loop along theprimary drainage and imbibition curves of the water characteristic. Several sets of experiments atthe proposed water contents will be conducted as described below.

In a �rst set of experiments, transport of the contaminants in absence of colloids is investigated.These experiments will provide the benchmark behavior of each contaminant in the soil columns.The columns will be pre-conditioned with 0.01 M CaCl2 solution for about 100 pore volumes torepresent typical background ionic strength as found in most soils. The contaminant will be fed tothe columns in the in uent and out ow collected in a fraction collector. Contaminant concentrationsin the out ow will be analyzed by atomic emission spectroscopy, ICP-MS, and liquid scintillationcounting. We anticipate that the \free" contaminant ions will be signi�cantly retarded in thecolumns in the absence of colloids and will not leach out of the columns readily.

In a second set of experiments, the potential for colloid transport in the columns will beevaluated. The columns will be pre-conditioned with 0.01 M CaCl2 as described above. Colloidsand dissolution/alteration products formed in batch studies will be fed in the in ow solution to thecolumns, and colloid concentrations in the out ow will be measured on-line with the ow-throughUV-VIS detector. Out ow will then �nally be collected with a fraction collector and analyzed forparticle size distributions and electrophoretic mobility with dynamic light-scattering.

In a third set of experiments, we will investigate the potential for colloid-facilitated contaminanttransport through the sediments. In this case contaminants are already associated with colloidswhen they enter the columns. The columns will again be preconditioned with 0.01 M CaCl2 solution.Then, a solution containing colloids and contaminants will be fed to the columns. Column out owwill be collected with a fraction collector. Samples will be analyzed for both total contaminantconcentration (dissolved and particulate) and solution-phase contaminant concentration. Columnout ow will be split in three aliquots. The �rst aliquot will be used to determine electrophoreticmobility and particle sizes, and morphology. Electrophoretic mobilities and particle sizes willbe measured with dynamic light scattering. For the dynamic light scattering measurements, thebackground electrolyte concentration used will be the same as the one eluted from the column.The second aliquot will be occulated with a few drops of 1 M NaNO3 and centrifuged. We willverify that the supernatant is free of colloidal particles by dynamic light-scattering and transmissionelectron microscopy, and would accordingly adjust centrifugation time and speed. The supernatantwill then be analyzed for solution phase contaminants. The third aliquot will be analyzed for totalcontaminant concentrations.

Our experience has shown that a full sequence of these experiments is very time-consuming,particularly because the ow rates become very small at low water saturations, but a successfulcompletion is feasible within the time frame of this study.

Colloid and Colloid-facilitated Transport in Undisturbed Sediment Monoliths

Sediment heterogeneity is also considered in the experiment with the undisturbed soil monolith.Two types of experiments will be conducted. The �rst will focus on the mobilization of native (insitu) colloids from the undisturbed monolith and the e�ect of wetting and drying cycles on colloidmobilization. The second set of experiments will introduce colloids and dissolution/alterationproducts formed in batch studies. These colloids will be associated with the contaminants. We

33

hypothesize that

1. Colloid transport in the undisturbed monoliths is dominated by preferential ow in paths thatare wetter than the surrounding media. Because the entire ux of water occurs through onlya small fraction of the total soil volume, thick water �lms and mobile gas-water interfacesfacilitate colloid movement.

2. The maximum velocity of colloid transport in the vadose zone is equal to the velocity of thefastest water moving in the preferred ow path, not that predicted by conventional modelsthat distribute water through the entire volume of soil.

3. The mass of colloids transported is a function of the recharge rate, and the time delay betweenrecharge events. A higher recharge rate increases the mass ux of colloids, but not necessarilythe depth of colloid penetration. The mass ux of colloids mobilized by wetting fronts willincrease as the time delay between recharge events increases. This is a consequence of atime-dependent equilibration of colloids between the solid-water and gas-water interfaces.

In the �rst set of experiments, we will determine the e�ect of ionic composition, in�ltrationrate, and wetting and drying cycles on colloid mobilization. Based on the results of the colloidmobilization studies in the packed columns, the experiments will compare two electrolyte solutionswhere there was either very little mobilization or a large degree of mobilization. In any case, wewill use one solution that is representative for pore water in Hanford sediments. Mobilization attwo in�ltration rates will also be compared. For a given set of conditions ( ow rate and solutioncomposition) the in�ltration experiments will be repeated with di�erent lengths of time betweenwetting events

The experimental sequence (Table 1) will start by in�ltrating the aqueous solution that pro-motes mobilization (we anticipate that this will be a low ionic strength solution). Initially, thesolution will be applied at a low in�ltration rate. We expect that there will be an initial peak ofcolloid mobilization, which will decline with continued in�ltration. When colloid release reachesa relative constant low concentration, in�ltration will be interrupted for di�erent periods of time.After a 1-day delay, in�ltration of the same solution at the same ow rate will resume and continueuntil colloid release again reaches a relative constant low concentration. In�ltration will then beterminated to allow the monolith to drain for a period 10 days before the in�ltration is resumed.This will be followed by a ow interruption of 30 days before the next in�ltration event. The secondexperimental sequence will repeat the in�ltration cycles, but at a higher in�ltration rate. Finally,the third experimental sequence will change the in�ltrating solution to the one that is expected toresult in very little colloid release (presumably high ionic strength and divalent cations). Becausewe do not expect a substantial amount of colloids to be released, only the 30-day delay interval isshown in Table 1. The timing can be re-evaluated if results warrant.

The concentrations of colloids in each fraction will be determined using UV-VIS spectropho-tometry, after appropriate calibration [Flury et al., 2002]. We will also characterize the mobilizedcolloids in terms of their mineralogy and colloidal properties as described above.

In the second set of experiments will we will investigate the potential for transport of colloidsassociated with Pu analogues. Colloids and dissolution/alteration products formed in batch studieswill be mixed with contaminants (separately with Cs, Eu, and Am). As with the experiments inthe packed columns, the monolith will be preconditioned with 0.01 M CaCl2 solution. The ow ratewill be selected based on the results of the previous studies on colloid mobilization. When the owsystem stabilizes, the labeled colloids will be input to the column. The transport of the introduced

34

Table 1: Experimental Sequence for Mobilization of in situ Colloids in Monolith.

Sequence Ionic In�ltration Delay In�ltration Delay In�ltration Delay In�ltrationstrength rate (days) rate (days) rate (days) rate

1 low low 1 low 10 low 30 low2 low high 1 high 10 high 30 high3 high high 30 high � � � �

colloids through the monolith will be assessed by analysis of the contaminant concentration in thee�uent, as described above for the packed column studies.

We will then evaluate the potential for remobilization of labeled colloids that were initiallyretained in the monolith. When the initial colloid breakthrough is complete, in�ltration will beinterrupted, and the monolith allowed to dry for a period of time before in�ltration is resumed. Thelength of the delay will be chosen based on the previous studies on mobilization of in situ colloids.Two cases will be compared: (1) a delay period that results in a small but measurable release ofcolloids, and (2) a delay that results in mobilization of a large mass of colloids. We anticipate thatboth in situ colloids and colloids with bound contaminants will be mobilized, demonstrating thepotential for continued downward migration of radionuclides with subsequent recharge events.

At the end of the transport experiments, the location of the ow paths and colloids will bedetermined. The location of the ow paths will be established by adding Brilliant Blue FCFdye [Flury and Fl�uhler, 1994; Flury and Wai, 2002] to the in�ltrating water near the end of anin�ltration series. Horizontal slices of the column will then be removed successively, starting fromthe top and working down, taking photographs at each level. The column should be dissectedshortly after the dye injection is completed because the dye may di�use with time and blur thelocation of the ow paths. Alternatively, the column could be frozen to minimize the e�ects ofdi�usion. This information can be assembled to form a 3-D image of the preferential ow paths.The information can be used to evaluate how large an area the in�ltrating water owed through.This will help estimate the water content of the conductive ow paths.

Concurrently with the recording of the dye patterns, the location of radiolabeled colloids fromthe colloid-facilitated transport experiments can be determined by autoradiography. A sheet ofX-ray �lm is placed over each slice, and location of the ionizing radiation from the colloids willbe recorded on the �lm. Comparison of the photograph of the dye and the autoradiograph willindicate which ow paths are associated with transport of the colloids.

Colloid Mobilization from Contaminated Material

We plan to investigate whether mobile, contaminant-bearing colloids exist in Hanford sedimentscontaminated with three di�erent types of tank waste. Research will focus on strongly sorbingradionuclides with potential for colloid facilitated migration (137Cs+, 239;240;241Pu, 241Am, and154Eu3+). The research will be performed using three di�erent sediments that have been con-taminated with HLWs enriched in these radionuclides: (1) 137Cs-REDOX waste, SX Tank Farm(SX-108 slant borehole); (2) Pu/Am-undi�erentiated tank waste TW-1/TW-2 soil site groupings;and (3) 154Eu B Plant High Level Waste, TX Tank Farm (TX-107 borehole). The contaminatedsediments will be obtained by Dr. J.M. Zachara from the River Protection Program{Tank FarmCharacterization Project and from the 200 Area Soil Site Characterization Project managed byBechtel, Hanford.

35

The Cs and Pu/Am-containing samples have already been received by Dr. Zachara. The Cs-sediments have been characterized (106 pCi/g) and studied from the perspective of 137Cs desorption[Liu et al., 2002a,b]. The Pu/Am-containing sediments (5 samples) have been characterized fromthe standpoint of radionuclide concentration. The �ve samples range from 102{106 pCi/g and showdecreasing counts with depth over an approximate 7.5 m vertical column. The 154Eu-containingsamples are scheduled for collection in early FY03. The Pu/Am and Eu containing samples will bewell characterized in terms of mineralogy and geochemistry by Zachara and coworkers with Hanfordfunds before use by this project.

Both batch and column experiments will be performed with these materials in Zachara's radio-chemical laboratories at PNNL to ascertain (1) whether the three target sorbates are associated withcolloidal material in the sediment, (2) the geochemical and mineralogic nature of the contaminant-bearing solids, and (3) whether the colloids are dispersable and mobile through Hanford sedimentsunder realistic and expected porewater composition conditions. Two general types of experimentswill be performed. In the �rst, contaminated sediments will be equilibrated in batch mode withelectrolytes ranging in ionic strength, Na/Ca ratio, and pH (7.5�10). These will be gently agitatedfor approximately 24 hours, and then gravel, sand, and silt will be allowed to settle. The suspended,dispersed clay fraction will be removed, characterized for radionuclide content, and saved for lateranalysis. The second experiment series will utilize small, undisturbed core segments and repackedcolumns of contaminated sediment. These will be linked to secondary �ltration columns �lled withpristine sand-textured Hanford sediment by te on tubing containing an intermediary sampling cellwhere e�uent from the contaminated columns/cores may be collected for analysis before enteringthe second column. The column series will be leached with two di�erent electrolyte solutions vary-ing in ionic strength and/or Na/Ca ratio that were shown to disperse in batch systems. E�uentfrom both the primary and secondary columns will be monitored with time for radionuclide andcolloid concentrations and other relevant parameters.

The experiments above will determine whether mobile contaminant-bearing colloids exist inHanford sediment, the conditions promoting their mobilization, and potential contaminant uxesassociated with water-borne microparticulates with high potential scienti�c impact to the HanfordSite will be characterized in PNNL's radiochemical facilities. The analyses of radioactive colloids isexpensive, especially those involving Pu, and characterization activities will be carefully selected.Characterization methods available include X-ray di�raction, scanning, and transmission electronmicroscopy with wavelength dispersion analysis and electron di�raction, electron microprobe, elec-trophoresis, and others.

A signi�cant portion of the research and characterization to be performed with these contam-inated sediments will be performed at PNNL with support from Hanford Science and TechnologyProgram. The reason for this is the high cost and ES&H concerns associated with HLW contami-nants. Washington State University sta� and students will play an integral part in the design andinterpretation of these challenging experiments.

3.6.6 Characterization of Colloids and Colloid Transport Using X-Ray Computed

Tomography and Nuclear Magnetic Resonance Techniques

X-ray computed tomography (XCT) allows for the nondestructive, noninvasive three-dimensionalmapping of electron density in a natural porous sample. It provides unambiguous, spatially-resolvedmedium properties and co-registered time-resolved transport measurements. The transport mea-surements are in the form of time-resolved local saturation values, where the saturation value fora uid is the local volume fraction of the pore space that is occupied by that uid. XCT provides

36

medium porosity [Peters and Afzal, 1992], uid saturations [Peters and Hardham, 1990], air satura-tion [Chen et al., 1996], and particulate distributions [Lin and Miller, 2000] at multiple time steps.Washington State University is acquiring a X-ray computed tomography (XCT) system (from asuccessful NSF-MRI grant) that will be available for colloid transport studies in porous media. Theinstrument will be an ACTIS 600-420 CT/DR System (Bio-Imaging Research, Inc.) with a spatialresolution of 100{200 �m, and is expected to be fully operational at the beginning of 2003. We willexamine the feasibility of using this system to study three-phase (water-air-colloid) transport in anatural porous medium.

In practice, the porous medium is imaged by XCT while both dry and fully water saturated,and the sample holder is imaged while containing only water. After conventional back-projectionreconstruction to yield a series of spatial intensity images I(x; y; z), the appropriate combinationof image intensity data (computed for each pixel) provides a map of sample porosity �, i.e.,

�(x; y; z) = (ISaturated � IDry)=IWater (2)

Subsequent transport measurements are performed by imaging the sample at multiple time-steps,and the resulting uid saturation and colloid distribution determined by taking the appropriatelinear combination of image data. For example, the air saturation Sa (the volume fraction of thepore space that is occupied by air) for a sample that is subsequently sparged with air is determinedby

Sa(x; y; z) = (ISaturated � ISparged)=ISaturated (3)

The contrast can be optimized as necessary by the addition of electron-rich elements to the wateror colloid, e.g., barium salts, to increase its X-ray attenuation. We will use the system to mapunsaturated ow pathways and colloid transport pathways.

In a related project, we will investigate the feasibility of employing multinuclear nuclear mag-netic resonance (NMR) techniques for the study of colloid mobility and transport in a porousmedium environment. The colloid will be modi�ed by the covalent attachment of uorine atomswhich will serve as a 19F NMR spin probe. 19F has a large relative NMR sensitivity (83% relativeto 1H NMR) which makes it well suited for imaging at moderate concentrations. Further, thereis no background uorine concentration from which to discern the spin probe. Our preliminaryexperiments have shown that 1H NMR, using Cu-tagged colloids, su�ered from serious magneticbackground contamination from the sediments. We will investigate the feasibility of using 19F NMRimaging [Doughty and Tomutsa, 2000] to map the colloid distribution in a porous medium. It isestimated that 19F concentrations of the order of 100 mM or greater are required to map the localcolloid concentrations with sub-millimeter spatial resolution. We will also attempt to study colloidmobility and aggregation in a porous medium environment. Other researchers [Kanetakis et al.,1997] have applied rotational correlation techniques to colloidal solutions. This technique involvesthe characterization of rotational di�usion of the spin-labeled colloid spheres. These measurementsare used to derive the colloidal rotational activation energy, e.g., as a function of colloid concen-tration and medium water content. 19F has a large chemical shift anisotropy (�� > 100 ppm),which makes it a good candidate for motional studies. These studies would allow to see whether,and if yes, at which water content, the rotational di�usion of colloidal particles is hindered. Thisinformation would provide important information regarding the mobility of colloidal particles inporous media as a function of water content. No funds are requested for the NMR study; the studywill be separately funded through an EMSL User Proposal, and conducted in collaboration withPaul Majors from the Macromolecular Structure and Dynamics Group at the NMR facility of theEnvironmental Molecular Science Laboratory (EMSL) in Richland, WA.

37

3.6.7 Reactive Transport Modeling

The computer code FLOTRAN [Lichtner, 2001] will be used to carry out model calculations involv-ing transport of radionuclides with and without the presence of colloids. FLOTRAN is a Fortrancode with standard ASCII I/O interface. FLOTRAN applies to isothermal and nonisothermal,heterogeneous, variably saturated porous media. The code describes two-phase ow and vapordi�usion sequentially coupled to transport of aqueous, gaseous and colloid species with multicom-ponent chemical reactions. Homogeneous aqueous complexing reactions and heterogeneous mineralprecipitation/dissolution, ion exchange, surface complexation, and Monod biodegradation reac-tions are included in the code. Thermodynamic data for equilibrium constants, stoichiometriccoe�cients, molar volumes, and Debye-H�uckel activity coe�cient parameters are read from an ex-tensive database. A separate database is available for use of the Pitzer model for high ionic strength uids. Both ion exchange and surface complexation reactions can be implemented either in termsof mineral-speci�c properties or in terms of bulk properties of the porous medium. The formerapproach provides for changes in sorption properties as minerals and colloids precipitate and dis-solve. A dual continuum formulation is implemented in FLOTRAN which can be used to accountfor mobile and immobile water. Mass transfer between mobile and immobile water is described bya �rst-order reaction, i.e., di�usive mass transfer between the two regions.

The reactive transport model will be calibrated against column experiments for breakthroughof a tracer and colloids. In addition, to determine the exchange properties of the column: cationexchange capacity, surface site density, and selectivity coe�cients; observed breakthrough of re-active species will be compared to the model predictions. Colloid-transport speci�c mechanismswill be incorporated into FLOTRAN. In an unsaturated porous medium, colloids can attach tothe solid-liquid as well as to the liquid-gas interface. Colloid attachment to these interfaces will beimplemented based on experimental data, presumably as �rst-order type reactions with or with-out site blocking mechanisms. Several methods have been proposed to estimate the liquid-gasinterfacial area [Cary, 1994; Choi and Corapcioglu, 1997; Or and Tuller, 1999]. We will use thepore-scale based approach by Or and Tuller [1999] to estimate the liquid-gas phase interfacial areaas a function of water saturation.

We will integrate FLOTRAN with PEST [Doherty et al., 1994] for inverse modeling capabili-ties. Any of the input parameters to FLOTRAN can be varied using the versatile PEST interface.PEST can also be used in conjunction with massively parallel computing architectures for increasedthroughput.

3.7 Student Training Opportunities

The proposed project will provide education and research training for three graduate students and apostdoctoral scholar. Two of the graduate students will be located at Washington State University(WSU). We anticipate that the students make an internship at the Environmental Molecular ScienceLaboratory (EMSL). Undergraduate students can collaborate in many di�erent aspects of theproject, such as the characterization of hydraulic properties, colloid-contaminant-soil interactions,column studies, and colloid characterization. Undergraduate students can participate in the projectduring the academic year as well as during the summer months.

Drs. Flury and Harsh teach at WSU, which is located about 130 miles east of the Hanford site.The courses taught|soil science, soil chemistry, soil physics, contaminant ow and transport|arerelevant for vadose zone issues, and can be applied to Hanford and other DOE sites. We have usedour current EMSP project in our courses as examples and illustrations. We continue to incorporateour research activities in the education of both undergraduate and graduate students.

38

3.8 Project Management and Time Schedule

The project will be coordinated by Markus Flury in close collaboration with the other PIs. MarkusFlury and Jim Harsh have their o�ces next to each other and interact almost on a daily basis. Wewill set up weekly meetings with the research group at Washington State University (Postdoc andStudents), and we will interact with our collaborators in Los Alamos, PNNL, and Tennessee on aregular basis via phone conferences and e-mail. As WSU and PNNL are located closely to eachother, travel between the two sites is easy. We have budgeted travel expenses to meet with eachother, and we also plan to meet during national workshops and meetings. A brief time schedule forthe project is shown below.

Activity Year 1 Year 2 Year 3

1{6 6{12 13{18 18{24 25{30 31-36

Characterization of Porous Media

Colloid Formation

Colloid Characterization

Colloid and Colloid-Facilitated Transport

Mobilization in Contaminated Sediments

X-ray Tomography

NMR Characterization

Reactive Transport Modeling

39

4 References

Ahn, J. H., and D. R. Peacor, Transmission and analytical electron microscopy of the smectite-to-illite transition, Clays Clay Miner., 34, 165{179, 1986.

Baccouche, A., E. Srasra, and M. El Maaoui, Preparation of Na-P1 and sodalite octahydrate zeolitesfrom interstrati�ed illite-smectite, Appl. Clay Sci., 13, 255{273, 1998.

Baek, I., and W. W. Pitt, Colloid-facilitated radionuclide transport in fractured porous rock, WasteManagement, 16, 313{325, 1996.

Ballirano, P., E. Bonaccorsi, A. Maras, and S. Merlino, The crystal structure of franzite, the ten-layer mineral of the cancrinite group, Can. Mineralogist, 38, 657{668, 2000.

Barnes, M. C., J. Addai-Mensah, and A. R. Gerson, The mechanism of the sodalite-to-cancrinitephase transformation in synthetic spent Bayer liquor, Microporous Mesoporous Mat., 31, 287{302, 1999a.

Barnes, M. C., J. Addai-Mensah, and A. R. Gerson, The solubility of sodalite and cancrinite insynthetic spent Bayer liquor, Colloids Surf. Physicochem. Eng. Aspects, 157, 101{116, 1999b.

Barney, G. S., Immobilization of aqueous radioactive cesium wastes by conversion to aluminosilicateminerals, Nucl. Sci. Abstr., 32, Abstract No. 24713, 1975.

Barrer, R. M., and J. D. Falconer, Ion exchange in felspathoids as a solid-state reaction, Proc. Roy.Soc. (London), A236, 227{249, 1956.

Barth-Wirsching, U., H. Hoeller, D. Klammer, and B. Konrad, Synthetic zeolites formed fromexpanded perlite: type, formation conditions, and properties, Mineral. Petrol., 48, 275{294,1993.

Bell, T. E., Microstructure in mixed-layer illite/smectite and its relationship to the reaction ofsmectite to illite, Clays Clay Miner., 34, 146{154, 1986.

Bickmore, B. R., K. L. Nagy, J. S. Young, and J. W. Drexler, Nitrate-cancrinite precipitation onquartz sand in simulated Hanford tank solutions, Environ. Sci. Technol., 35, 4481{4486, 2001.

Bish, D. L., D. T. Vaniman, R. S. Runberg, K. Wolfsberg, W. R. Daniels, and D. E. Broxton, Proc.Int. Conf. Radioact. Waste Manag., 3, 415{432, 2000.

Blum, A. E., Determination of illite/smectite particle morphology using scanning force microscopy,in CMS Workshop Lectures, Scanning Probe Microscopy of Clay Minerals, edited by K. L.Nagy, and A. E. Blum, , Clay Minerals Society, Boulder, CO, 1994.

Blum, A. E., and D. D. Eberl, Determination of clay particle thicknesses and morphology usingScanning Force Microscopy, In Proc. 7th International Symposium Water-Rock Interaction,Park City, Utah pp. 133{136, A. A. Balkema, Rotterman, 1992.

Bostick, D. T., S. M. DePaoli, and B. Guo, Treatment of low-level radioactive wastewaters withIonsiv(TM) IE-911 and cabazite zeolite, Separation Sci. Technol., 36, 975{998, 2001.

Bray, L. A., and H. T. Fullam, Recovery and puri�cation of cesium-137 from purex waste usingsynthetic zeolites, Adv. Chem Series, 101, 450{455, 1971.

40

Buchter, B., C. Hinz, M. Flury, and H. Fl�uhler, Heterogeneous ow and solute transport in anunsaturated stony soil monolith, Soil Sci. Soc. Am. J., 59, 14{21, 1995.

Buddemeier, R. W., and J. R. Hunt, Transport of colloidal contaminants in groundwater: Radionu-clide migration at the Nevada Test Site, Appl. Geochem., 3, 535{548, 1988.

Buhl, J. C., F. Stief, M. Fechtelkord, T. M. Gesing, U. Taphorn, and C. Taake, Synthesis, x-raydi�raction and MAS NMR characteristics of nitrate cancrinite Na7[AlSiO4]6(NO3)1:6(H2O)2,J. Alloys Compounds, 305, 93{102, 2000.

Cary, J. W., Estimating the surface area of uid phase interfaces in porous media, J. Contam.Hydrol., 15, 243{248, 1994.

Chen, M. R., R. E. Hinkley, and J. E. Killough, Computed tomography imaging of air sparging inporous media, Water Resour. Res., 32, 3013{3024, 1996.

Choi, H., and M. Y. Corapcioglu, Transport of non-volatile contaminant in unsaturated porousmedia in the presence of colloids, J. Contam. Hydrol., 25, 299{324, 1997.

Choppin, G. R., Comparison of the solution chemistry of the actinides and lanthanides, J. Less-Common Metals, 93, 323{330, 1983.

Choppin, G. R., Utility of oxidation state analogs in the study of plutonium behavior, Radiochim.Acta, 85, 89{95, 1999.

Chorover, J., K. Mueller, K. G. Karthikeyan, A. Vairavamurthy, and R. J. Serne, Interfacial SoilChemistry of Radionuclides in the Unsaturated Zone, EMSP Principal Investigator Workshop,Paci�c Northwest National Laboratory, Richland, WA, 2001.

Chu, Y., Y. Jin, M. Flury, and M. V. Yates, Mechanisms of virus removal during transport inunsaturated porous media, Water Resour. Res., 37, 253{263, 2001.

Clark, S. B., A. L. Bryce, A. D. Lueking, J. Gariboldi, and S. M. Serkiz, Factors a�ecting trivalentf-element adsorption to an acidic sandy soil, in Adsorption of Metals by Geomedia, edited byE. A. Jenne, pp. 149{164, Academic Press, San Diego, 1998.

Contardi, J. S., D. R. Turner, and T. M. Ahn, Modeling colloid transport for performance assess-ment, J. Contam. Hydrol., 47, 323{333, 2001.

Corapcioglu, M. Y., and H. Choi, Modeling colloid transport in unsaturated porous media andvalidation with laboratory column data, Water Resour. Res., 32, 3437{3449, 1996.

Corapcioglu, M. Y., J. Shiyan, and S.-H. Kim, Comparison of kinetic and hybrid-equilibriummodelssimulating colloid-facilitated contaminant transport in porous media, Transp. Porous Media,36, 373{390, 1999.

Degueldre, C., B. Baeyens, W. Goerlich, J. Riga, J. Verbist, and P. Stadelmann, Colloids in waterfrom a subsurface fracture in granitic rock, Grimsel Test Site, Switzerland, Geochim. Cos-mochim. Acta, 53, 603{610, 1989.

Diaz, M., V. Laperche, J. B. Harsh, and R. Prost, Far infrared spectra of K+ in dioctahedral andtrioctahedral mixed-layer minerals, Am. Mineralogist, pp. (in press), 2002.

41

Doherty, J., B. Lindsay, and P. Whyte, PEST: Model Independent Parameter Estimation, Water-mark Computing, Brisbane, Australia, 1994.

Doughty, D. A., and L. Tomutsa, Multinuclear NMR microscopy of two-phase uid systems inporous rock, Magnetic Resonance Imaging, 14, 869{873, 2000.

Dyer, A., S. Amini, H. Enamy, H. A. El-Naggar, and M. W. Anderson, Cation-exchange in syntheticzeolite L: the exchange of hydronium and ammonium ions by alkali metal and alkaline earthcations, Zeolites, 13, 281{290, 1993.

Farmer, V. C., A. R. Fraser, and J. M. Tait, Characterization of the chemical structures of naturaland synthetic aluminosilicate gels and sols by infrared spectrometry, Geochim. Cosmochim.Acta, 43, 1417{1420, 1979.

Farmer, V. C., and J. D. Russell, Structures and genesis of allophanes and imogolite and theirdistribution in non-volcanic soils, in Soil colloids and their association in aggregates, edited byD. Broodt, pp. 165{178, 1990.

Faur�e, M. H., M. Sardin, and P. Vitorge, Transport of clay particles and radioelements in a salinitygradient|experiments and simulations, J. Contam. Hydrol., 21, 255{267, 1996.

Flanigen, E. M., H. A. Szymanski, and H. Khatami, Infrared structural studies of zeolite frame-works, Adv. Chem. Series, 101, 201{229, 1971.

Flury, M., and H. Fl�uhler, Brilliant Blue FCF as a dye tracer for solute transport studies|Atoxicological overview, J. Environ. Qual., 23, 1108{1112, 1994.

Flury, M., and N. N. Wai, Dyes as tracers for vadose zone hydrolgy, Rev. Geophys., pp. (submitted),2002.

Flury, M., J. B. Mathison, and J. B. Harsh, In situ mobilization of colloids and cesium transportin Hanford sediments, Environ. Sci. Technol., pp. (submitted), 2002.

Freedman, Y. E., D. Ronen, and G. L. Long, Determination of Cu and Cd content of groundwatercolloids by solid sampling graphite furnace atomic absorption spectrometry, Environ. Sci.Technol., 30, 2270{2277, 1996.

Gerson, A. R., and K. L. Zheng, Bayer process plant scale: Transformation of sodalite to cancrinite,J. Crystal Growth, 171, 209{218, 1997.

Glass, R. J., T. S. Steenhuis, and J.-Y. Parlange, Wetting front instability. 2. Experimental deter-mination of relationships between system parameters and two-dimensional unstable ow �eldbehavior in initially dry porous media, Water Resour. Res., 25, 1195{1207, 1989.

Godber, J., M. D. Baker, and G. A. Ozin, Far-IR spectroscopy of alkali-metal and alkaline-earthcations in faujasite zeolites, J. Phys. Chem., 93, 1409{1421, 1989.

Grindrod, P., and A. J. Lee, Colloid migration in symmetrical non-uniform fractures: particletracking in three dimensions, J. Contam. Hydrol., 27, 157{175, 1997.

Grolimund, D., and M. Borkovec, Long-term release kinetics of colloidal particles from naturalporous media, Environ. Sci. Technol., 33, 4054{4060, 1999.

42

Grolimund, D., K. Barmettler, and M. Borkovec, Release and transport of colloidal particles innatural porous media. 2. Experimental results and e�ects of ligands, Water Resour. Res., 37,571{582, 2001.

Grolimund, D., M. Borkovec, K. Barmettler, and H. Sticher, Colloid-facilitated transport of stronglysorbing contaminants in natural porous media: a laboratory column study, Environ. Sci.Technol., 30, 3118{3123, 1996.

Gschwend, P. M., and M. D. Reynolds, Monodisperse ferrous phosphate colloids in an anoxicgroundwater plume, J. Contam. Hydrol., 1, 309{327, 1987.

Harber, S., and H. Brenner, E�ect of entrained colloidal particles in ehhancing the transport ofadsorbable chemical contaminants, J. Colloid Interface Sci., 155, 226{246, 1993.

Henmi, T., Synthesis of zeolite and its related minerals from coal ash waste, Nippon Dojo HiryogakuZasshi, 58, 378{380, 1987.

Hiemenz, P. C., and R. Rajagopalan, Principles of Colloid and Surface Chemistry, 3rd ed., Marcel-Dekker, New York, 1997.

Hlavay, J., I. Vassanyi, and J. Inczedy, Quantitative determination of the mordenite content ofnatural zeolite rocks by infrared spectroscopy, Spectrochim. Acta, 41A, 1457{1458, 1985.

Honeyman, B. D., Colloidal culprits in contamination, Nature, 397, 23{24, 1999.

Hunter, R. J., Foundations of Colloid Science, 2nd ed., Oxford University Press, Oxford, 2001.

Ibaraki, M., and E. A. Sudicky, Colloid-facilitated transport in discretely fractured porous medium:I. Numerical formulation and sensitivity analysis, Water Resour. Res., 31, 2945{2960, 1995.

Jacobsen, O. H., P. Moldrup, C. Larson, L. Konnerup, and L. W. Petersen, Particle transport inmacropores of undisturbed soil columns, J. Hydrol. (Amsterdam), 196, 185{203, 1997.

Jacobsen, O. H., P. Moldrup, H. de Jonge, and L. W. de Jonge, Mobilization and transport ofnatural colloids in a macroporous soil, Phys. Chem. Earth., 23, 159{162, 1998.

James, S. C., and C. V. Chrysikopoulos, Transport of polydisperse colloid suspensions in a singlefracture, Water Resour. Res., 35, 707{718, 1999.

Jardine, P. M., G. K. Jacobs, and G. V. Wilson, Unsaturated transport processes in undisturbedheterogeneous porous media, I. Inorganic contaminants, Soil Sci. Soc. Am. J., 57, 945{953,1993.

Jiang, S., and M. Y. Corapcioglu, A hybrid equilibrium model of solute transport in porous mediain the presence of colloids, Colloids Surf. Physicochem. Eng. Aspects, 73, 275{286, 1993.

Johnson, P. R., and M. Elimelech, Dynamics of colloid deposition in porous media: blocking basedon random sequential adsorption, Langmuir, 11, 801{812, 1995.

Kanetakis, J., A. T�olle, and H. Sillescu, Rotational di�usion of colloid spheres in concentratedsuspensions studies by deuteron NMR, Phys. Rev. E., 55, 3006{3013, 1997.

Kaplan, D. I., P. M. Bertsch, D. C. Adriano, and W. P. Miller, Soil-borne mobile colloids asin uenced by water ow and organic carbon, Environ. Sci. Technol., 27, 1193{1200, 1993.

43

Kersting, A. B., D. W. Efurd, D. L. Finnegan, D. J. Rokop, D. K. Smith, and J. L. Thompson,Migration of plutonium in ground water at the Nevada Test Site, Nature, 397, 56{59, 1999.

Kessler, J. H., and J. R. Hunt, Dissolved and colloidal contaminant transport in a partially cloggedfracture, Water Resour. Res., 30, 1195{1206, 1993.

Kim, J. I., W. Treiber, C. Lierse, and P. O�erman, Solubility and colloid generation of plutoniumfrom leaching of a HLW glass in salt solutions, Mat. Res. Soc. Symp. Proc., 44, 359{368, 1985.

Kim, Y., and R. J. Kirkpatrick, 23Na and 133Cs NMR study of cation adsorption on mineralsurfaces: Local environments, dynamics, and e�ects of mixed cations, Geochim. Cosmochim.Acta, 61, 5199{5208, 1997.

Kim, Y., and R. J. Kirkpatrick, NMR T1 relaxation study of 133Cs and 23Na adsorbed on illite,Amer. Mineralogist, 83, 661{665, 1998.

Klimentidis, R. E., and I. D. R. Mackinnon, High-resolution imaging of ordered mixed layer clays,Clays Clay Miner., 34, 155{164, 1986.

Klotz, D., H. Lang, A. Hartmann, and P. Zeh, The e�ect of suspended particles on the transportof pollutants in aquifers, GSF-Ber., 3, 81{98, 1997.

Ko, C.-H., and M. Elimelech, The \Shadow e�ect" in colloid transport and deposition dynamics ingranular porous media: measurements and mechanisms, Environ. Sci. Technol., 34, 3681{3689,2000.

Komada, N., E. F. Westrum, B. S. Hemingway, M. Y. Zolotov, Y. V. Semenov, I. L. Khodakovsky,and L. M. Anovitz, Thermodynamic properties of sodalite at temperatures from 15 K to 1000K, J. Chem. Thermodynamics, 27, 1119{1132, 1995.

Krauskopf, K. B., Thorium and rare-earth metals as analogs for actinide elements, Chem. Geol.,55, 323{335, 1986.

Laegdsmand, M., K. G. Villholth, M. Ullum, and K. H. Jensen, Processes of colloid mobilizationand transport in macroporous soil monoliths, Geoderma, 93, 33{59, 1999.

Le Roux, J., C. I. Rich, and P. H. Ribbe, Ion selectivity by weathered micas as determined byelectron microprobe analyses, Clays Clay Miner., 18, 333{338, 1970.

Liang, L., J. F. McCarthy, L. W. Jolley, J. A. McNabb, and T. L. Mehlhorn, Iron dynamics:Transformation of Fe(II)/Fe(III) during injection of natural organic matter in a sandy aquifer,Geochim. Cosmochim. Acta, 57, 1987{1999, 1993.

Lichtner, P., and A. Felmy, Estimation of Hanford SX tank waste compositions from historicallyderived inventories, Computers Geosci., pp. (in press), 2002.

Lichtner, P. C., Continuum formulation of multicomponent-multiphase reactive transport, Reviewsin Mineralogy, 34, 1{81, 1996.

Lichtner, P. C., FLOTRAN User Manual, LA-UR-01-2349, Los Alamos National Laboratory report,Los Alamos, New Mexico, 2001.

44

Lin, C. L., and J. D. Miller, Pore structure and network analysis of �lter cake, Chem. Eng. J., 80,221{231, 2000.

Lindgreen, H., J. Garnaes, P. L. Hansen, F. Besebacher, E. Laegsgaard, I. Stensgaard, S. A. C.Gould, and P. K. Hansma, Ultra�ne particles of North Sea illite/smectite clay minerals inves-tigated by STM and AFM, Amer. Mineralogist, 76, 1218{1222, 1991.

Lindqvist, R., J. S. Cho, and C. G. En�eld, A kinetic model for cell density dependent bacterialtransport in porous media, Water Resour. Res., 30, 3291{3299, 1994.

Liu, C., J. M. Zachara, and S. C. Smith, A cation exchange model to describe Cs sorption at highionic strength in subsurface sediments at Hanford site, USA, Environ. Sci. Technol., pp. (inpress), 2002a.

Liu, C., J. M. Zachara, S. Smith, J. P. McKinley, and C. Ainsworth, Desorption kinetics of ra-diocesium from subsurface sediments at the Hanford site, USA, Geochim. Cosmochim. Acta,pp. (submitted), 2002b.

Liu, Y., T. S. Steenhuis, and J.-Y. Parlange, Formation and persistence of �ngered ow �elds incoarse grained soils under di�erent moisture contents, J. Hydrol. (Amsterdam), 159, 187{195,1994.

Luckscheiter, B., and B. Kienzler, Determination of sorption isotherms for Eu, Th, U, and Am onthe gel layer of corroded HLW glass, J. Nucl. Mater., 298, 155{162, 2001.

Luhrmann, L., U. Noseck, and C. Tix, Model of contaminant transport in porous media in thepresence of colloids applied to actinide migration in column experiments, Water Resour. Res.,34, 421{426, 1998.

Marty, R. C., D. Bennett, and P. Thullen, Mechanism of plutonium transport in a shallow aquiferin Mortandad canyon, Los Alamos National Laboratory, New Mexico, Environ. Sci. Technol.,31, 2020{2027, 1997.

Mashal, K., H. Zhao, J. B. Harsh, and M. Flury, Colloid formation in Hanford sediments con-taminated with tank waste, Abstracts, 222nd ACS National Meeting August 26{30, Chicago,Illinois, 2001.

McCarthy, J. F., and C. Degueldre, Sampling and characterization of groundwater colloids forstudying their role in the subsurface transport of contaminants, in Environmental Particles,vol. II, edited by J. Bu�e, and H. van Leeuwen, pp. 247{315, Lewis Publisher, Chelsea MI,1993.

McCarthy, J. F., and J. M. Zachara, Subsurface transport of contaminants, Environ. Sci. Technol.,23, 496{502, 1989.

McDowell-Boyer, L. M., J. R. Hunt, and N. Sitar, Particle transport through porous media, WaterResour. Res., 22, 1901{1921, 1986.

McKinley, J. P., C. J. Zeissler, J. M. Zachara, R. J. Serne, R. M. Lindstrom, H. T. Schaef, andR. D. Orr, Distribution and retention of Cs-137 in sediments at the Hanford Site, Washington,Environ. Sci. Technol., 35, 3433{3441, 2001.

45

Morss, L. R., M. L. Stanley, C. D. Tatko, and W. L. Ebert, Corrosion of glass-bonded sodalite asa function of pH and temperature, Mater. Res. Soc. Sympos. Proc., 608, 733{738, 2000.

Nagasaki, S., S. Tanaka, and A. Suzuki, Interfacial behavior of actinides with colloids in the geo-sphere, J. Nucl. Mater., 248, 323{327, 1997.

Nagy, K., S. Yabusaki, and R. J. Serne, Reactivity of Primary Soil Minerals and Secondary Precipi-tates Beneath Leaking Hanford Waste Tanks, EMSP Principal Investigator Workshop, Paci�cNorthwest National Laboratory, Richland, WA, 2001.

Nitao, J., Reference Manual for the NUFT Flow and Transport Code, Version 2.0, Lawrence Liv-ermore National Laboratory Report UCRL-MA-130651, Livermore, CA, 1998.

Nuttall, H. E., and R. L. Long, Mobility of radioactive colloidal particles in groundwater, Radioac-tive Waste Manag. Nuclear Fuel Cycle, 17, 237{251, 1993.

Olson, R. A., P. D. Tennis, D. Bonen, H. M. Jennings, T. O. Mason, B. J. Christensen, A. R.Brough, G. K. Sun, and J. F. Young, Early containment of high-alkaline radioactive waste inblended cement, J. Hazard. Mater., 52, 223{236, 1997.

Or, D., and M. Tuller, Liquid retention and interfacial area in variably saturated porous media:Upscaling from single-pore to sample-scale model, Water Resour. Res., 35, 3591{3605, 1999.

Peters, E. J., and N. Afzal, Characterization of heterogeneities in permeable media with computedtomography imaging, J. Petroleum Sci. Eng., 7, 283{296, 1992.

Peters, E. J., and W. D. Hardham, Visualization of uid displacements in porous media usingcomputed tomography imaging, J. Petroleum Sci. Eng., 4, 155{168, 1990.

Powelson, D. K., and A. L. Mills, Bacterial enrichment at the gas-water interface of a laboratoryapparatus, Appl. Environ. Microbiol., 62, 2593{2597, 1996.

Pruess, K., C. Oldenburg, and G. Moridis, TOUGH2 User's Guide, Version 2.0, Lawrence BerkeleyNational Laboratory Report LBNL-43134, Berkeley, CA, 2002a.

Pruess, K., S. Yabusaki, C. I. Steefel, and P. C. Lichtner, Fluid ow, heat transfer, and solutetransport at nuclear waste storage tanks in the hanford vadose zone, Vadose Zone J., pp. (inpress), 2002b.

Randall, A., P. Warwick, P. Lassen, L. Carlsen, and P. Grindrod, Transport of europium and iodinethrough sand columns in the presence of humic acids, Radiochim. Acta, 66/67, 363{368, 1994.

Ritsema, C. J., L. W. Dekker, J. L. Nieber, and T. S. Steenhuis, Modeling and �eld evidence of�nger formation and �nger recurrence in a water repellent sandy soil, Water Resour. Res., 34,555{567, 1998.

Ryan, J. N., and M. Elimelech, Colloid mobilization and transport in groundwater, Colloids Surf.,107, 1{56, 1996.

Ryan, J. N., and P. Gschwend, Colloid mobilization in two Atlantic coastal plain aquifers|�eldstudies, Water Resour. Res., 26, 307{322, 1990.

46

Ryan, J. N., and P. M. Gschwend, Chemical conditions conducive to the release of mobile colloidsfrom Ultisol pro�les, Environ. Sci. Technol., 28, 1717{1726, 1994.

Saiers, J. E., and G. M. Hornberger, The role of colloidal kaolinite in the transport of cesiumthrough laboratory sand columns, Water Resour. Res., 32, 33{41, 1996.

Saiers, J. E., G. M. Hornberger, and L. Liang, First- and second-order kinetics approaches formodeling the transport of colloidal particles in porous media, Water Resour. Res., 30, 2499{2506, 1994.

Saltelli, A., A. Avogardo, and G. Bidoglio, Americium �ltration in glauconitic sand columns, Nucl.Technol., 67, 245{254, 1984.

Schelde, K., P. Moldrup, O. H. Jacobsen, H. de Jonge, L. W. de Jonge, and K. Komatsu, Di�usion-limited mobilization and transport of natural colloids in unsaturated macroporous soil, VadoseZone J., 1, (in press), 2002.

Seaman, J. C., P. M. Bertsch, and R. N. Strom, Characterization of colloids mobilized from south-eastern coastal plain sediments, Environ. Sci. Technol., 31, 2782{2790, 1997.

Seaman, J. C., P. M. Bertsch, and W. P. Miller, Chemical controls on colloid generation andtransport in a sandy aquifer, Environ. Sci. Technol., 29, 1808{1815, 1995.

Selker, J. S., T. S. Steenhuis, and J.-Y. Parlange, Wetting front instability in homogeneous sandysoils under continuous in�ltration, Soil Sci. Soc. Am. J., 56, 1346{1350, 1992.

Shih, W. H., and H. L. Chang, Conversion of y ash into zeolites for ion-exchange applications,Materials Letters, 28, 263{268, 1996.

Singh, B., and R. J. Gilkes, Concentration of iron oxides from soil clays by 5 M sodium hydroxidetreatment: the complete removal of sodalite and kaolin, Clay Miner., 26, 463{472, 1991.

Smith, P. A., and C. Degueldre, Colloid-facilitated transport of radionuclides through fracturedmedia, J. Contam. Hydrol., 13, 143{166, 1993.

Song, L., P. R. Johnson, and M. Elimelech, Kinetics of colloid deposition onto heterogeneouslycharged surfaces in porous media, Environ. Sci. Technol., 28, 1164{1171, 1994.

Srodon, J., C.Andreoli, F. Elsass, and M. Robert, Direct high-resolution transmission electronmicroscopic measurement of expandability of mixed layer illite/smectite in bentonite rock,Clays Clay Miner., 38, 373{379, 1990.

Su, C. M., and J. B. Harsh, Gibbs free energies of formation for imogolite and gibbsite fromsolubility measurements, Geochim. Cosmochim. Acta, 58, 1667{1677, 1994.

Su, C. M., and J. B. Harsh, Solubility of interlayer-Al(OH)3 and imogolite in a spodosol, Soil Sci.Soc. Am. J., 59, 373{379, 1995.

Su, C. M., and J. B. Harsh, Dissolution of allophane as a thermodynamically unstable solid in thepresence of boehmite at elevated temperatures and equilibrium vapor pressures, Soil Sci., 163,299{312, 1998.

47

Su, C. M., J. Harsh, and P. M. Bertsch, Sodium and chloride sorption by imogolite and allophanes,Clays Clay Miner., 40, 280{286, 1994.

Su, Y., L. Wang, B. C. Bunker, and C. F. Windisch, Spectroscopic studies of aluminosilicateformation in tank waste simulants, 1997.

U.S. DOE Research Needs in Subsurface Science, U.S Department of Energy's EnvironmentalManagement Science Program, National Academy Press, Washington DC, 2000.

U.S. DOE A National Roadmap for Vadose Zone Science & Technology. Understanding Monitoring,and Predicting Fate and Transport in the Unsaturated Zone, U.S Department of Energy, IdahoFalls, ID, 2001.

van der Lee, J., E. Ledoux, and G. de Marsily, Modelling of colloidal uranium transport in afractured medium, J. Hydrol. (Amsterdam), 139, 135{158, 1992.

van Genuchten, M. T., A closed-form equation for predicting the hydraulic conductivity of unsat-urated soils, Soil Sci. Soc. Am. J., 44, 892{898, 1980.

Vandergraaf, T. T., D. J. Drew, D. Archambault, and K. V. Ticknor, Transport of radionuclidesin natural fractures: some aspects of laboratory migration experiments, J. Contam. Hydrol.,26, 83{95, 1997.

Virden, J. W., and J. C. Berg, The use of photon correlation spectroscopy for estimating the rateconstant for doublet formation in an aggregating colloidal suspension, J. Colloid Interface Sci.,141, 528{535, 1992.

Wan, J. M., and J. L. Wilson, Colloid transport in unsaturated porous media, Water Resour. Res.,30, 857{864, 1994.

Wan, J. M., and T. K. Tokunaga, Film straining of colloids in unsaturated porous media: conceptualmodel and experimental testing, Environ. Sci. Technol., 31, 2413{2420, 1997.

Wan, J. M., J. L. Wilson, and T. L. Kieft, In uence of the gas-water interface on transport ofmicroorganisms through unsaturated porous media, Appl. Environ. Microbiol., 60, 509{516,1994.

Wan, J., T. K. Tokunaga, E. Saiz, K. Olsen, and R. Coutoure, Secondary colloids formed duringleaking of Hanford waste tank solutions into vadose zone sediments, Abstracts, 222nd ACSNational Meeting August 26{30, Chicago, Illinois, 2001.

Warwick, P. W., A. Hall, V. Pashley, N. D. Bryan, and D. Gri�n, Modelling the e�ect of humicsubstances on the transport of europium through porous media: a comparison of equilibriumand equilibrium/kinetic models, J. Contam. Hydrol., 42, 19{34, 2000.

White, M. D., and M. Oostrom, STOMP|Subsurface Transport over Multiple Phases: TheoryGuide, Paci�c Northwest National Laboratory Report PNNL-11217, Richland, WA, 1996.

Whitney, G., and B. Velde, Changes in particle morphology during illitization: An experimentalstudy, Clays Clay Miner., 41, 209{218, 1993.

48

Wicks, F. I., G. S. Henderson, and G. A.Vrdoljak, Atomic and molecular scale imaging of layeredand other mineral structures, in CMS Workshop Lecture, Scanning Probe Microscopy of ClayMinerals, edited by K. L. Nagy, and A. E. Blum, , Clay Minerals Society, Boulder, CO, 1994.

Xu, S., and J. B. Harsh, Hard and soft acid base model veri�ed for monovalent cation selectivity,Soil Sci. Soc. Am. J., 54, 1596{1601, 1990a.

Xu, S., and J. B. Harsh, Monovalent cation selectivity quantitatively modeled according to hard/softacid/base theory, Soil Sci. Soc. Am. J., 54, 357{363, 1990b.

Xu, S., and J. B. Harsh, Alkali cation selectivity and surface charge of 2:1 clay minerals, ClaysClay Miner., 40, 567{574, 1992.

Xu, S., and J. B. Harsh, Labile and nonlabile silica in acid solutions: Relation to the colloidalfraction, Soil Sci. Soc. Am. J., 57, 1271{1277, 1994.

Xu, S., and J. B. Harsh, In uence of measurement errors and autocorrelation on interpretation ofsolubility diagrams, Soil Sci. Soc. Am. J., 59, 1549{1557, 1995.

Zachara, J. M., J. A. Kittrick, L. S. Dake, and J. B. Harsh, Solubility and surface spectroscopy ofzinc precipitates on calcite, Geochim. Cosmochim. Acta, 53, 9{19, 1989.

Zachara, J. M., P. L. Gassman, S. C. Smith, and D. Taylor, Oxidation and adsorption ofCo(II)EDTA2� complexes in subsurface materials with iron and manganese oxide grain coat-ings, Geochim. Cosmochim. Acta, 59, 4449{4463, 1995.

Zachara, J. M., S. C. Smith, J. P. McKinley, and C. T. Resch, Cadmium sorption on specimen andsoil smectites in sodium and calcium electrolytes, Soil Sci. Soc. Am. J., 57, 1491{1501, 1993.

Zachara, J., S. C. Smith, C. Liu, J. P. McKinley, R. J. Serne, and P. L. Gassman, Sorption of Cs+

to micaceous subsurface sediments from the Hanford Site, USA, Geochim. Cosmochim. Acta,66, 193{211, 2002.

Zhao, H., J. B. Harsh, and M. Flury, Alteration of surface and cesium retention properties ofkaolinite in Synthetic Hanford Tank Wastes, Clays Clay Miner., pp. (submitted), 2002.

Zhao, H., J. B. Harsh, M. Flury, and K. Mashal, Alteration of mineralogical and surface propertiesof Hanford sediments contaminated with tank waste, Abstracts, 222nd ACS National MeetingAugust 26{30, Chicago, Illinois, 2001.

Zheng, K., R. S. C. Smart, J. Addai-Mensah, and A. Gerson, Solubility of sodium aluminosilicatesin synthetic Bayer liquor, J. Chem. Eng. Data, 43, 312{317, 1998.

49

5 Collaborative Arrangements

The project team consists of two universities (Washington State and Tennessee) and two NationalLaboratories (PNNL and Los Alamos). The di�erent project groups complement each other intheir expertise and capabilities. In the following, we summarize individual responsibilities of eachgroup.

� Washington State University (Markus Flury and Jim Harsh): Physical and chemical charac-terization of sediments, formation and characterization of colloids, thermodynamic stability ofcolloids, contaminant-colloid interactions, in situ colloid mobilization, transport, and colloid-facilitated transport of contaminant in packed sediment columns under water-saturated andunsaturated conditions.

� Paci�c Northwest National Laboratories (John Zachara and Paul Majors): In situ colloidmobilization in contaminated sediment material, characterization of contaminated colloidsand quanti�cation of radionuclides (John Zachara). Characterization of colloid stability andporosity using NMR (Paul Majors). No funds are requested for these studies. The contami-nated sediment work will be separately funded through the Hanford Science and TechnologyProgram, the NMR work through an EMSL User Proposal.

� University of Tennessee (John McCarthy): Colloid transport and colloid-facilitated contam-inant transport in undisturbed soil monolith under water-saturated and unsaturated condi-tions, 3-D imaging of ow pathways in soil monoliths.

� Los Alamos National Laboratory (Peter Lichtner): Mathematical modeling of batch and col-umn experiments, including thermodynamic stability of colloids, colloid- and colloid-facilitatedtransport through saturated and unsaturated sediments. The budget portion for Los Alamosis attached as Appendix B.

50

6 Biographical Sketches

Markus Flury

Education

� Ph.D. Natural & Environmental Sciences, 1993, Swiss Federal Institute of Technology, ETH,Z�urich, Switzerland

� M.S. Geosciences, 1988, University of Z�urich, Switzerland

Professional Experience

� Associate Professor, Department of Crop & Soil Sciences, Washington State University, Pull-man, 2001{present

� Assistant Professor, Department of Crop & Soil Sciences, Washington State University, Pull-man, 1997{2001

� Post-Doctoral Research Associate, Department of Soil & Environmental Sciences, Universityof California, Riverside, 1994{1997

Awards and Services

� Associate Editor, Vadose Zone Journal, 2001{present

� WSU, College of Agriculture Excellence in Research Award, 2001

� Award for best poster presentation at the annual German Soil Science Society meeting inKiel, Germany, 1994

� ETH Medal for outstanding dissertation, 1993

Research

Research Interests

Dr. Flury's principal research interest is in the area of water ow and chemical movement andreactions in porous media. Speci�c areas include: (1) Characterization of water ow in soils, (2)measurement and modeling of transport of conservative and reactive tracers in �eld soils, (3) mod-eling sorption kinetics and transport of organic chemicals and viruses, (4) characterization andevaluation of dye tracers for solute transport studies, (5) colloid-facilitated transport of radionu-clides in unsaturated porous media.

Selected Peer-Reviewed Publications

Flury, M. and N. N. Wai, 2002. Dyes as tracers for vadose zone hydrology, (submitted to Rev.Geophys.).

Zhao, H., J. B. Harsh, and M. Flury, 2002. Alteration of surface and cesium retention propertiesof kaolinite in Synthetic Hanford Tank Wastes, (submitted to Clays Clay Miner.).

Flury, M., J. B. Mathison, and J. B. Harsh, 2002. In situ mobilization of colloids and cesiumtransport in Hanford Sediments, (submitted to Environ. Sci. Technol.).

Jin, Y., and M. Flury, 2001. Fate and transport of viruses in porous media, Adv. Agron. 77: (inpress).

51

Posadas, A.N.D., D. Gim�enez, M. Bittelli, C.M.P. Vaz, and M. Flury, 2001. Multifractal charac-terization of soil particle-size distributions, Soil Sci. Soc. Am. J. 65: 1361{1367.

Chu, Y., Y. Jin, M. Flury, and M.V. Yates, 2001. Mechanisms of virus removal during transportin unsaturated porous media, Water Resour. Res. 37: 253{263.

Bittelli, M., M. Flury, G.S. Campbell, and E.J. Nichols, 2001. Reduction of transpiration throughfoliar application of Chitosan, Agric. For. Meteorol. 107: 167{175.

German-Heins, J., and M. Flury, 2000. Sorption of Brilliant Blue FCF in soils as a�ected by pHand ionic strength, Geoderma 97: 87{101.

Guo, L., W. A. Jury, R. J. Wagenet, and M. Flury, 2000. Dependence of pesticide degradationon sorption: nonequilibrium model and application to soil reactors, J. Contam. Hydrol. 43:45{62.

Flury, M., and W. A. Jury, 1999. Solute transport with resident-time-dependent sink/source re-action coe�cients, Water Resour. Res. 35: 1933{1938.

Forrer, I., R. Kasteel, M. Flury, and H. Fl�uhler, 1999. Longitudinal and lateral dispersion in anunsaturated �eld soil, Water Resour. Res. 35: 3049{3060.

Bittelli, M., G. S. Campbell, and M. Flury, 1999. Characterization of particle-size distributions insoils with a fragmentation model, Soil Sci. Soc. Am. J. 63: 782{788.

Flury, M., Q. J. Wu, L. Wu, and L. Xu, 1998. Analytical solution for solute transport with depth-dependent transformation or sorption coe�cients, Water Resour. Res. 34: 2931{2937.

Thompson, S. S., M. Flury, M. V. Yates, and W. A. Jury, 1998. Role of the air-water-solid interfacein bacteriophage sorption experiments. Appl. Environ. Microbiol. 64: 304{309.

Fortin, J., M. Flury, W. A. Jury, and T. Streck, 1997. Rate-limited sorption of simazine in saturatedsoil columns. J. Contam. Hydrol. 25: 219{234.

Flury, M., 1996. Experimental evidence of transport of pesticides through �eld soils|A review.J. Environ. Qual. 25: 25{45.

Flury, M., and H. Fl�uhler, 1995. Modeling solute transport in soils by di�usion-limited aggregation|Basic concepts and application to conservative solutes. Water Resour. Res. 31: 2443{2452.

Flury, M., and H. Fl�uhler, 1995. Tracer characteristics of Brilliant Blue FCF. Soil Sci. Soc. Am.J. 59: 22{27.

Flury, M., J. Leuenberger, B. Studer, and H. Fl�uhler, 1995. Transport of anions and herbicides ina loamy and a sandy �eld soil. Water Resour. Res. 31: 823{835.

Buchter, B., C. Hinz, M. Flury, and H. Fl�uhler, 1995. Heterogeneous ow and solute transport inan unsaturated stony soil monolith. Soil Sci. Soc. Am. J. 59: 14{21.

Flury, M., H. Fl�uhler, W. A. Jury, and J. Leuenberger, 1994. Susceptibility of soils to preferential ow of water: A �eld study. Water Resour. Res. 30: 1945{1954.

52

James B. Harsh

Education

� Ph.D. Soil Chemistry, 1983, University of California, Berkeley

� M.S. Soil Chemistry, 1980, University of California, Berkeley

� B.S. Conservation of Natural Resources, 1974, University of California, Berkeley

Professional Experience

� Professor, Department of Crop and Soil Sciences, Washington State University, 2000{present

� Associate Professor, Department of Crop and Soil Sciences, Washington State University,1990{2000

� Assistant Professor, Department of Agronomy and Soils, Washington State University, 1983{1990

� Graduate Research/Teaching Assistant, Department of Plant and Soil Biology, University ofCalifornia, Berkeley, 1977{1983

Awards

� WSU, College of Agriculture Excellence in Research Award, 2000

� UC Berkeley Academic Senate Citation, Distinguished Teaching Assistant, 1983

� Clay Minerals Society Best Student Paper Award, 1982 Annual Meeting, Hawaii

� Caroline Meeks Memorial Scholarship, July-August, 1982

� UC Berkeley Chancellor's Patent Fund Dissertation Research Grant, 1982

Research

Research Interests

The chemistry of soil mineral surfaces; physicochemical factors a�ecting the availability and mobil-ity of ions; the chemistry of non-crystalline soil materials; the synthesis of soil mineral analogues;the chemistry of saline and sodic soils; far-infrared spectroscopy of silicates; colloid formation andcharacterization.

Selected Peer-Reviewed Publications

Zhao, H., J. B. Harsh, and M. Flury, 2002. Alteration of surface and cesium retention propertiesof kaolinite in Synthetic Hanford Tank Wastes, (submitted to Clays Clay Miner.).

Flury, M., J. B. Mathison, and J. B. Harsh, 2002. In situ mobilization of colloids and cesiumtransport in Hanford Sediments, (submitted to Environ. Sci. Technol.).

Diaz, M., V. Laperche, J. B. Harsh, and R. Prost, 2002. Far infrared spectra of K+ in dioctahedraland trioctahedral mixed-layer minerals, Am. Mineralogist (in press).

53

Dion, H. M., J. B. Harsh, H. H. Hill, 2001. Competitive sorption between glyphosate and inorganicphosphate on clay minerals and low organic matter soils. J. Radioanal. Nuclear Chem. 249:385{390.

Harsh, J. B., 2000. Poorly Crystalline Aluminosilicate Clays. In: M.E. Sumner (ed.) Handbook ofSoil Science, CRC Press, Boca Raton, pp. F169{F182.

Rochette, E. A., J. B. Harsh, and H. H. Hill, 1998. Supercritical uid extraction of 2,4-D fromsoils: pH and organic matter e�ects. Soil. Sci. Soc. Am. J. 62: 602{610.

Su, C. M., and J. B. Harsh, 1998. Dissolution of allophane as a thermodynamically unstable solidin the presence of boehmite at elevated temperatures and equilibrium vapor pressures. SoilSci. 163: 299{312.

Guo, C., W. Sun, J. B. Harsh, and A. Ogram, 1997. Hybridization analysis of microbial DNAfrom fuel oil-contaminated and noncontaminated soil. Microbial Ecol. 34: 178-187.

Xu, S., and J. B. Harsh, 1997. In uence of autocorrelation and measurement errors on interpre-tation of solubility diagrams|Reply. Soil. Sci. Soc. Am. J. 61: 331{332.

Rochette, E. A., J. B. Harsh, and H. H. Hill, 1996. Soil component interactions with 2,4-D undersupercritical uid conditions. Environ. Sci. Technol. 30: 1220{1226.

Su, C. M., and J. B. Harsh, 1996. In uence of soluble aluminosilicate complex formation onimogolite solubility determination. Geochim. Cosmochim. Acta 60: 4275{4277.

Su, C. M., and J. B. Harsh, 1996. Alteration of imogolite, allophane and acidic soil clays bychemical extractants. Soil Sci. Soc. Am. J. 60: 77{85

Su, C. M., and J. B. Harsh, 1995. Solubility of interlayer-Al(OH)3 and imogolite in a spodosol.Soil Sci. Soc. Am. J. 59: 373{379.

Xu, S., and J. B. Harsh, 1995. In uence of measurement errors and autocorrelation on interpre-tation of solubility diagrams. Soil Sci. Soc. Am. J. 59: 1549{1557.

Xu, S., and J. B. Harsh, 1994. Labile and nonlabile silica in acid solutions: Relation to the colloidalfraction. Soil Sci. Soc. Am. J. 57: 1271{1277.

Su, C., and J. B. Harsh, 1994. The electrophoretic mobility of allophane and imogolite in thepresence of inorganic anions and citrate. Clays and Clay Miner. 41: 461{471.

Su, C., and J. B. Harsh, 1994. Gibbs free energies of formation for imogolite and gibbsite fromsolubility measurements. Geochim. Cosmochim. Acta 58: 1667{1677.

Xu, S., and J. B. Harsh, 1992. Alkali cation selectivity and surface charge of 2:1 clay minerals.Clays Clay Miner. 40: 567{574.

Pan, W. L., R. A. Black, J. B. Harsh, J. H. Bassman, and J. S. Boyle, 1991. Morphology, root con-ductivity, and mineral accumulation of Northwest tree species in response to acid depositionin arti�cial soil. In: R.J. Wright et al. (eds.) Plant soil interactions at low pH. pp. 25{33.

54

John M. Zachara

Education

� Ph.D. Soil Chemistry, 1986, Washington State University� M.S. Soil/Watershed Chemistry, 1979, University of Washington� B.S. Chemistry, 1973, Bucknell University

Professional Experience

� Chief Scientist (Grade V); Associate Director Environmental Dynamics & Simulation Group,William R. Wiley, Environmental Molecular Sciences Laboratory, Paci�c Northwest NationalLaboratories

Professional Activities

� Member of AGU Groundwater Hydrology Advisory Panel (1991 to 1992, and 1994 to present)� Associated Western Universities Distinguished Lecturer, FY 94� Research coordinator and principal scientist for the DOE's, Subsurface Science Program Co-Contaminant Chemistry research

� Associate editor of the Journal of Contaminant Hydrology� Member of the Stanford University Synchrotron Radiation Laboratory (SSRL) proposal re-view panel (1994{present)

Research

Research Interests

Dr. Zachara has performed extensive experimental research on adsorption reactions of organic,metal, and radionuclide contaminants to organic materials, mineral matter, and subsurface mate-rials from di�erent geochemical environments. The research has ranged from fundamental surfacechemical and spectroscopic studies in the laboratory to site evaluations of solute mobilization andtransport in the �eld. He has been active in evaluating complex co-contaminant interactions thatoccur in contaminant mixtures and in applying multi-component adsorption models to contaminantbinding in mineralogically complex natural materials. Dr. Zachara's current research is focused onthe geochemical behavior of metals and radionuclides, the in uence of subsurface microbial pro-cesses on mineral surface chemistry, contaminant binding in groundwaters, and the application ofM�ossbauer spectroscopy to iron biomineralization.

Selected Peer-Reviewed Publications

Dr. Zachara has published over 110 journal articles and 30 technical reports. Most recent publica-tions are listed below.

Zachara, J. M., R. K. Kukkadapu, S. C. Smith, and P. L. Gassman. 2002. Bacterial changes tothe Fe(II/III) mineralogic suite in petroleum contaminated aquifer sediments. (submitted toGeochim. Cosmochim. Acta).

Zachara, J. M., G. E. Brown, Jr., C. C. Ainsworth, S. J. Traina, J. P. McKinley, J. E. Szecsody,O. Qafoku, J. Catalano, and S. C. Smith. 2002. Chromium speciation and mobility in a highlevel nuclear waste vadose zone plume. (submitted to Environ. Sci. Technol.).

55

Liu, C., J. M. Zachara, S.C. Smith, J. P. McKinley, and C.C. Ainsworth. 2002. Desorptionkinetics of radiocesium from subsurface sediments at the Hanford site, USA. (submitted toGeochim. Cosmochim. Acta).

Zachara, J. M., R. K. Kukkadapu, J. K. Fredrickson, Y. A. Gorby, and S. C. Smith. 2002.Biomineralization of poorly crystalline Fe(III) oxides by dissimilatory metal reducing bacteria(DMRB). Geomicrobiology J. (in press).

Liu, C., J. M. Zachara, and S. C. Smith. 2002. A cation exchange model to describe Cs sorptionat high ionic strength in subsurface sediments at Hanford site, USA. Environ. Sci. Technol.(in press).

Fredrickson, J. K., J. M. Zachara, D. W. Kennedy, C. Liu, M. C. Du�, D. B. Hunter, and A.Dohnalkova. 2002. In uence of Mn oxides on the reduction of U(VI) by the metal-reducingbacterium Shewanella putrefaciens. Geochim. Cosmochimica Acta (in press).

Zachara, J. M., S. C. Smith, C. K. Liu, J. P. McKinley, R. J. Serne and P. L. Gassman, 2002.Sorption of Cs+ to micaceous subsurface sediments from the Hanford site, USA. Geochim.Cosmochim. Acta 66: 193{211.

Kukkadapu, R. K., J. M. Zachara, S. C. Smith, J. K. Fredrickson, J. K. and C. X. Liu, 2001. Dis-similatory bacterial reduction of Al-substituted goethite in subsurface sediments. Geochim.Cosmochim. Acta 65: 2913{2924.

McKinley, J. P., C. J. Zeissler, J. M. Zachara, R. J. Serne, R. M. Lindstrom, H. T. Schaef, andR. D. Orr, 2001. Distribution and retention of Cs-137 in sediments at the Hanford Site,Washington. Environ. Sci. Technol. 35: 3433{3441.

Yeh, G. T., W. D. Burgos, and J. M. Zachara, 2001. Modeling and measuring biogeochemicalreactions: system consistency, data needs, and rate formulations. Adv. Environm. Res. 5:219{237.

Liu, C. X., S. Kota, J. M. Zachara, J. K. Fredrickson, and others, 2001. Kinetic analysis of thebacterial reduction of goethite. Environ. Sci. Technol. 35: 2482{2490.

Liu, C. G. and J. M. Zachara, Y. A. Gorby, J. E. Szecsody, and C. F. Brown, 2001. Microbialreduction of Fe(III) and sorption/precipitation of Fe(II) on Shewanella putrefaciens strainCN32. Environ. Sci. Technol. 35: 1385{1393.

Zachara, J. M., J. K. Fredrickson, S. C. Smith, and P. L. Gassman, 2001. Solubilization ofFe(III) oxide-bound trace metals by a dissimilatory Fe(III) reducing bacterium. Geochim.Cosmochim. Acta 65: 75{93.

Zachara, J.M., S. C. Smith, and J. K. Fredrickson, 2000. The e�ect of biogenic Fe(II) on thestability and sorption of Co(II)EDTA(2-) to goethite and subsurface sediment. Geochim.Cosmochim. Acta 64: 1345{1362.

Brown, G. E., Jr., V. E. Henrich, W. H. Casey, D. L. Clark, C. Eggleston, A. R. Felmy, D. W.Goodman, M. Gratzel, G. Maciel, M. I. McCarthy, K. H. Nealson, D. A. Sverjensky, M. F.Toney, and J. M. Zachara, 1999. Metal Oxide Surface and Their Interactions with AqueousSolutions and Microbial Organisms. Chem. Rev. 99: 77{174.

56

John F. McCarthy

Education

� Ph.D., University of Rhode Island, Oceanography, 1975

� B.S., Fordham University, Biology, 1969

Professional Experience

� Research Professor, Research Center of Excellence for Environmental Biotechnology, Univer-sity of Tennessee, Knoxville, Tennessee, 2001

� Distinguished Research Scientist, Environmental Sciences Division, Oak Ridge National Lab-oratory, Oak Ridge, Tennessee, 1995-2001

� Research Sta� Member and Senior Scientist, Environmental Sciences Division, Oak RidgeNational Laboratory, Oak Ridge, Tennessee, 1980-1995

� Research Associate, University of Tennessee, 1979-1980

� Postdoctoral Investigator, Graduate School of Biomedical Sciences, Biology Division, OakRidge National Laboratory, 1976-1979

Research

Research Interests

Dr. McCarthy has conducted extensive research on the transport of inorganic colloids and naturalorganic matter (NOM) in subsurface systems, and the potential for enhanced transport of contam-inants by colloids and NOM. This research has included fundamental studies on the mechanismsof attachment, colloid and NOM transport studies in packed and intact columns, and �eld-scaletracer experiments to evaluate the migration of colloids, NOM, and colloid-facilitated transport ofradionuclides.

Selected Peer-Reviewed Publications

McCarthy, J. F., D. D. Bruner and L. D. McKay, 2002. In uence of Ionic Strength and CationValence on Transport of Colloidal Particles in Fractured Shale Saprolite. Environ. Sci.Technol. (submitted).

Shevenell, L and J. F. McCarthy, 2002. E�ects of precipitation events on colloids in a karst aquifer.J. Hydrol. 255(1/4): 50{68.

McCarthy, J. F., K. M. Howard, and L. D. McKay, 2000. E�ect of pH on the sorption andtransport of uorobenzoic acid groundwater tracers in shale saprolite. J. Environ. Qual. 18:1806{1817.

McCarthy, J. F., and L. Shevenell, 1999. Sampling colloids in a fractured and karst aquifer.Ground Water 36: 251{260.

McCarthy, J. F and L. Shevenell, 1998. Processes controlling colloid composition in a fracturedand karstic aquifer in eastern Tennessee, USA. J. Hydrol. 206(3-4): 191{218.

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McCarthy, J. F., W. E. Sanford, and P. L. Sta�ord, 1998. Lanthanide �eld tracer demonstrateenhanced transport of transuranic radionuclides by natural organic matter. Environ. Sci.Technol. 32: 3901{3906.

McCarthy, J. F., K. R. Czerwinski, W. E. Sanford, P. M. Jardine and J. D. Marsh, 1998. Mo-bilization of transuranic radionuclides from disposal trenches by natural organic matter. J.Contam. Hydrol. 30: 49{77.

McCarthy, J. F., 1998. Colloid-facilitated transport of contaminants in groundwater: mobilizationof transuranic radionuclides from disposal trenches by natural organic matter. Physics Chem.Earth 23: 179{185.

McCarthy, J. F., B. Gu, L. Liang, J. Mas-Pla, T. M. Williams and T.-C. J. Yeh, 1996. Fieldtracers tests on the mobility of natural organic matter in a sandy aquifer. Water Resour.Res. 32: 1223{1228.

Gu, B., T. Mehlhorn, L. Liang and J. F. McCarthy, 1996. Competitive adsorption, displace-ment, and transport of organic matter on iron oxide: I. competitive adsorption. Geochim.Cosmochim. Acta. 60: 1943{1950.

Gu, B., T. Mehlhorn, L. Liang and J. F. McCarthy, 1996. Competitive adsorption, displacement,and transport of organic matter on iron oxide: II. Displacement and transport. Geochim.Cosmochim. Acta. 60: 2977{2992.

Yeh, T.-C., J. Mas-Pla, T. M. Williams, and J. F. McCarthy, 1995. Observation and three-dimensional simulation of chloride plumes in a sandy aquifer under forced gradient conditions,Water Resour. Res. 31: 2141{2159.

Yeh, T.-C., J. Mas-Pla, T. M. Williams, and J. F. McCarthy, 1995. Modeling of natural organicmatter transport processes in groundwater. Environ. Health Perspect. 103: 41{46.

Gu, B., J. Schmitt, Z. Chen, L. Liang and J. F. McCarthy, 1995. Adsorption-desorption of di�erentorganic matter fractions on iron-oxide. Geochim. Cosmochim. Acta 59: 219{229.

Liang, L. and J. F. McCarthy, 1995. Colloidal transport of metal contaminants in ground water.In: Metal Speciation and Contamination of Soil. H.E. Allen, C.P. Huang, G. W. Bailey, A.R. Bowers (eds), Chapter 4. Lewis Publishers, Boca Raton; p. 87{112.

McCaulou, D. R., R. C. Bales and J. F. McCarthy, 1994. Use of short-pulse experiments to studybacteria transport through porous media. J. Contamin. Hydrol. 15: 1{14.

McCarthy, J. F. and C. Degueldre, 1993. Sampling and characterization of groundwater colloidsfor studying their role in the subsurface transport of contaminants. In: J. Bu�e and H. vanLeeuwen (Eds.) Environmental Particles, Volume II. Lewis Publishers, Chelsea MI. Chapter6, pp. 247{315.

Liang, L., J. A. McNabb, J. M. Paulk, B. Gu and J. F. McCarthy, 1993. Kinetics of Fe(II)oxygenation at low partial pressure of oxygen and in the presence of natural organic matter.Environ. Sci. Technol. 27: 1864{1870.

McCarthy, J. F., T. M. Williams, L. Liang, P. M. Jardine, A. V. Palumbo, L. W. Jolley, L.W. Cooper, and D. L. Taylor, 1993. Mobility of natural organic matter in a sandy aquifer.Environ. Sci. Technol. 27: 667{676.

58

Peter C. Lichtner

Education

� Habilitation, Geochemistry, 1989, University of Bern, Bern, Switzerland

� Ph.D. Physics, 1974, Universitity of Mainz, Mainz, Germany

� M.S. Physics, 1970, University of Maryland

� B.S. Mathematics and Physics, 1965, University of Wisconsin-Milwaukee

Professional Experience

� Sta� Scientist, Earth and Environmental Sciences, EES-6 Los Alamos National Laboratory

Professional A�liations

� American Geophysical Union (AGU)

Research

Research Interests

Dr. Lichtner is experienced in numerical modeling of uid ow and transport combined with chem-ical reactions of minerals, aqueous species and gases in porous and fractured media that has led tofundamental research in this �eld. His research has ranged from theoretical investigations to mod-eling �eld and laboratory studies. He has co-edited a book on reactive transport entitled \ReactiveTransport in Porous Media", published by the Mineralogical Society of America. Dr. Lichtner'scurrent research interests include modeling reactive transport in heterogeneous and fractured me-dia, modeling dispersion in axisymmetric media, upscaling microscale and mesoscale descriptionsof transport and chemical reactions, and developing parallel computing techniques.

Selected Peer-Reviewed Publications

Dr. Lichtner has published over 30 articles and 10 technical reports in Earth sciences and 19publications in the �eld of theoretical nuclear physics. Recent publications are listed below.

Callahan, T. J., P. W. Reimus, P. C. Lichtner, and R. S. Bowman, 2002. Multicomponent E�ectson the Transport of Cations Undergoing Ion Exchange in Fractured Media, 2002 InternationalGroundwater Symposium in Berkeley, CA, in press.

Hammond, G. H., A. J. Valocchi, and P. C. Lichtner, 2002. Modeling Multicomponent ReactiveTransport on Parallel Computers Using Jacobian-Free Newton Krylov with Operator-SplitPreconditioning, XIV International Conference on Computational Methods in Water Re-sources, June 23-28, 2002, Delft, The Netherlands., 2002, in press.

Kechagia, P., I. N. Tsimpanogiannis, Y. C. Yortsos, and P. C. Lichtner, 2002. On the Upscalingof Reaction-Transport Processes in Porous Media with Fast or Finite Kinetics, Chem. Eng.Sci., in press.

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Lichtner, P. C., S. Kelkar, and B. Robinson, 2002. New Form of Dispersion Tensor for Axisym-metric Porous Media with Implementation in Particle Tracking, Water Resour. Res., in press.

Lichtner, P. C., 2000. Critique of Dual Continuum Formulations of Multicomponent ReactiveTransport in Fractured Porous Media, Dynamics of Fluids in Fractured Rock, GeophysicalMonograph 122: 281{298.

Kechagia, P., Y. C. Yortsos, and P. C. Lichtner, 2001. Nonlocal Kardar-Parisi-Zhang Equation toModel Interface Growth, Phys. Rev. E 64: 016315-1-016315-15.

Lichtner, P. C., 1998. Modeling Reactive Flow and Transport in Natural Systems, Eds. G.Ottonello and L. Marini, Environmental Geochemistry, Pacini Editore, Pisa, Italy, 5{72.

Steefel C. I. and P. C. Lichtner, 1998. Multicomponent Reactive Transport in Discrete Fractures:I. Controls on Reaction Front Geometries, J. Hydrology 209: 186{199.

Steefel C. I. and P. C. Lichtner, 1998. Multicomponent Reactive Transport in Discrete Fractures:II: In�ltration of Hyperalkaline Groundwater at Maqarin, Jordan, a Natural Analogue Site,J. Hydrology 209: 200{224.

Connor, C. B., P. C. Lichtner, F. M. Conway, B. E. Hill, A. A. Ovsyannikov, I. Federchenko, Y.Doubik, V. N. Shapar, and Y. A. Taran, 1997. Cooling of An Igneous Dike Twenty YearsAfter Intrusion, Geology 25: 711{714.

Lichtner, P. C., R. T. Pabalan, and C. I. Steefel, 1997. Model Calculations of Porosity ReductionResulting from Cement-Tu� Di�usive Interaction, Scienti�c Basis for Nuclear Waste Man-agement XXI, eds. I. G. McKinley and C. McCombie, Mat. Res. Symp. Proc., Davos,Switzerland, 506, 709{718.

Lichtner, P.C., 1996. Continuum Formulation of Multicomponent-Multiphase Reactive Transport,In: Reactive Transport in Porous Media (eds. P. C. Lichtner, C. I. Steefel, and E. H. Oelkers),Reviews in Mineralogy 34: 1{81.

Steefel, C. I. and P. C. Lichtner, 1994. Di�usion and Reaction in Rock Matrix Bordering aHyperalkaline Fluid-Filled Fracture, Geochim. Cosmochim. Acta 58: 3595{3612.

Lichtner, P.C., 1994. Time{Space Continuum Formulation of Supergene Enrichment and Weath-ering of Sul�de-Bearing Ore Deposits, In: C. N. Alpers and D. W. Blowes (eds.), Environ-mental Geochemistry of Sul�de Oxidation: American Chemical Society, Washington D. C.,Am. Chem. Soc. Symp. Ser., 550: 153{170.

Matsunaga, T., G. Karametaxas, H. R. von Gunten, and P. C. Lichtner, 1993. Redox Chemistryof Iron and Manganese Minerals in River{Recharged Aquifers: A Model Interpretation ofColumn Experiments, Geochim. Cosmochim. Acta 57: 1691{1704.

Lichtner, P. C., 1993. Scaling Properties of Kinetic Mass Transport Equations, American Journalof Science 293: 257{296.

Lichtner, P.C. and V. N. Balashov, 1993. Metasomatic Zoning: Appearance of Ghost Zones inLimit of Pure Advective Mass Transport, Geochim. Cosmochim. Acta 57: 369{387.

60

Paul D. Majors

Education

� Ph.D. Physical Chemistry, 1985, University of South Carolina, Columbia SC

� M.S. Chemistry/Math, 1979, University of Maryland

� B.S. Mathematics and Physics, 1965, Frostburg State University, Frostburg MD

Professional Experience

� Sr. Research Scientist, Paci�c Northwest National Laboratory, Richland WA, 2001{present

� AWU Faculty Fellow, Paci�c Northwest National Laboratory, Richland WA, 1999{2001

� Research Scientist, University of Texas, Austin TX, 1991{1999

� Adjunct Research Professor, Lovelace Medical Foundation, Albuquerque NM, 1989{1991

� Research Assistant Professor, University of New Mexico, Albuquerque NM, 1989{1991

� Postdoctoral Fellow, Lovelace Medical Foundation, Albuquerque NM, 1985{1989

Honors and Awards/A�liations

� Discover Award|Health Category (contributing member of the PNNL combined optical/magneticresonance microscopy instrument development team), 2001

� American Chemical Society

Research

Research Interests

Dr. Majors is experienced in using NMR to investigate biological and hydrological systems. Hehas worked in the past in visualization of ow processes in porous media, in imaging of bio�lms,imaging miscible displacement in porous media, and measurements of aperture and multiphase owin fractures.

Selected Peer-Reviewed Publications

Wind, R. A., P. D. Majors, K. R. Minard, E. J. Ackerman, G. R. Holtom, B. D. Thrall, andT. J. Weber, 2002. Combined confocal and magnetic resonance microscopy, Appl. MagneticResonance (submitted).

Majors, P. D., G. R. Holtom, K. R. Minard, R. A. Wind, E. J. Ackerman, D. F. Hopkins, C. I.Parkinson, 2002. Development of an integrated confocal uorescence optical and magneticresonance microscope for the study of live cells, Review Scienti�c Instruments (submitted).

Zuluaga, E., P. D. Majors and E. J. Peters, 2002. A simulation approach to validate petrophysicaldata from Nuclear Magnetic Resonance Imaging, SPE J. (in press).

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Majors, P. D., T. J. Weber, G. R. Holtom, K. R. Minard, and R. A. Wind, 2001. Combined opticaland Magnetic Resonance Microscopy of heterogeneous JB6 Tumor Spheroid Populations,Proc. ISMRM 9: 725.

Hoskins, B. C., L. Fevang, P. D. Majors, M. M. Sharma, and G. Georgiou, 2001. Selective imagingof bio�lms in porous media by NMR Relaxation, J. Magnetic Resonance 139: 67{73.

Wind, R. A., K. R. Minard, G. R. Holtom, P. D. Majors, E. J. Ackerman, S. D. Colson, D. G.Cory, D. S. Daly, P. D. Ellis, N. F. Metting, J. M. Price, and X.-W. Tang, 2000. An integratedconfocal and Magnetic Resonance Microscope for cellular research, J. Magnetic Resonance147: 371{377.

Butler, J. E., P. D. Majors, and R. T. Bonnecaze, 1999. Observations of shear-induced particlemigration for oscillatory ow of a suspension within a tube, Physics Fluids 11: 2865{2877.

McLean, R. J. C., M. Whiteley, B. C. Hoskins, P. D. Majors, and M. M. Sharma, 1999. Labora-tory Techniques for Studying Bio�lm Growth, Physiology, and Gene Expression in FlowingSystems and Porous Media, Methods in Enzymology, Vol. 310 Ch. 20, Academic Press.

Majors, P. D., P. Li, and E. J. Peters, 1997. NMR Imaging of immiscible displacements in porousmedia, SPE Formation Evaluation 12: 164{169.

Kumar, A. T. A., P. D. Majors, and W. R. Rossen, 1997. Measurement of aperture and multiphase ow in fractures using NMR Imaging, SPE Formation Evaluation 12: 101{107.

Lewandowski, Z., S. A. Altobelli, P. D. Majors and E. Fukushima, 1992. NMR Imaging of hydro-dynamics near microbially colonized surfaces, Water Sci. Technol. 26: 577{584.

Majors, P. D., D. M. Smith and P. J. Davis, 1991. E�ective di�usivity measurement in porousmedia via NMR Radial Imaging, Chem. Eng. Sci. 46: 3037{3043.

Majors, P. D., and A. Caprihan, 1991. Fast Radial Imaging of circular and spherical objects byNMR, J. Magnetic Resonance 94: 225{233.

Majors, P. D., J. L. Smith, F. S. Kovarik and E. Fukushima, 1990. NMR Spectroscopic Imagingof oil displacement in dolomite, J. Magnetic Resonance 89: 470{478.

Altobelli, S. A., A. Caprihan, E. Fukushima, E.E. Benitez-Read, R. H. Gri�ey, and P. D. Ma-jors, 1990. NMR ow studies by phase methods, in Noninvasive Techniques in Biology andMedicine, S.E. Freeman, E.Fukushima, and E.R. Greene (eds.), San Francisco Press, 91.

Majors, P. D., R. C. Givler and E. Fukushima, 1989. Velocity and concentration measurementsin multiphase ows by NMR, J. Magnetic Resonance, 85: 235{243.

Majors, P. D. and P. D. Ellis, 1987. Surface site distributions by solid-state Multi-Nuclear NMRspectroscopy. Pyridine Binding to Alumina by 15N and 2H NMR, J. Am. Chem. Soc. 109:1648{1653.

Majors, P. D., T. E. Raidy and P. D. Ellis, 1986. A multinuclear solid-state NMR investigationof the chemisorption of ammonia on Alumina, J. Am. Chem. Soc. 108: 8123{8129.

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7 Facilities and Resources

7.1 Washington State University

The laboratories of James Harsh and Markus Flury are equipped with most of the instrumentationneeded to carry out the research. Standard chemical laboratory instrumentation is available. TheDepartment of Crop and Soil Sciences has HPLC's that are available for bromide and nitrateanalyses, a MasterSizer (static light scattering) for particle size analysis, a Zetasizer (dynamiclight scattering) to determine electrophoretic mobilities and particles sizes of colloids, and liquidscintillation counters.

Dr. Flury's laboratory space consists of a wet chemistry lab and a soil physics laboratory. Thewet chemistry laboratory is equipped to carry out saturated and unsaturated column experiments.The facilities relevant for the proposed research are the wet chemistry laboratory with two fumehoods, fraction collectors to collect column out ow, plexiglass and glass columns for column ex-periments, and peristaltic pumps. Chemical equipment include a variety of constant temperatureshakers, pH meters, balances, ion selective electrodes, centrifuges, and a HP photospectrometer.The physical laboratory contains most standard soil physical instrumentation, including a pressureplate apparatus, various forms of psychrometers, tension in�ltrometers, tensiometers, TDR sensors,and a -ray apparatus. In the previous EMSP project, we have developed a unsaturated column ow column apparatus to study colloid and colloid-facilitated contaminant transport, which will beused in this new project as well. The laboratory has several computer workstations where transportmodels to analyze column experiments are implemented.

The laboratory of Dr. Harsh has a Varian atomic absorption spectrophotometer, Malvern Ze-tasizer, Isco SFX 2-10 supercritical uid extractor with 260D syringe pump, HP gas chromatographwith ame ionization detector, 100-650 rpm tubing pump, 8-line peristaltic pump, Phillips X-raydi�ractometer, and other equipment conducive to a well-equipped chemistry laboratory includ-ing balances, pH meters, IBM compatible computers, centrifuges, glassware, te onware, etc. Dr.Harsh has access to a modern Siemens X-ray di�ractometer and ICP mass spectrometer in theGeoanalytical Laboratory at WSU.

At Washington State University, Drs. Flury and Harsh have access to the Electron MicroscopyCenter (EMC), a research and training facility for the study of biological and non-biological mate-rials. The EMC provides electron microscopy and light microscopy equipment for observation andanalysis of a diverse array of specimens. The EMC maintains two TEMs, a STEM, a SEM andvarious light microscopes. Three of the electron microscopes also have EDX analyzers for elemen-tal analysis. All necessary ancillary equipment, computers for image processing and analysis, andthree photographic darkrooms are also maintained for student and faculty use. The center providesproject consultation and has a skilled sta� capable of assisting students and faculty in a wide rangeof research projects.

Washington State University is acquiring a X-Ray Tomography System, funded through a NSFMRI grant. The system will be an ACTIS 600-420 CT/DR System (Bio-Imaging Research, Inc.)with a spatial resolution of 100{200 �m, and will be located in the College of Engineering andArchitecture at WSU. The system will be speci�cally designed and dedicated for porous mediaresearch (i.e., ow and transport, stuctural stability). Drs. Flury and Harsh have participated inthe NSF-MRI proposal, and will have access to this new facility.

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7.2 Paci�c Northwest National Laboratory

Research at PNNL will be performed in three primary locations that are described below, the Ra-diochemistry Laboratory, the Environmental Dynamics and Simulation (ED&S), Thin Film Labo-ratories, and the NMR facility in the W.R. Wiley, Environmental Molecular Sciences Laboratory,(EMSL).

7.2.1 The Radiochemistry Laboratory

Four fully equipped, \wet" radiochemistry laboratories (over 2400 ft2) are available for projectresearch. The laboratories enable batch and column geochemical interaction studies of varyingscale using radioactive tracers or contaminated waters and sediments. The labs have pH meters,balances, ovens, shakers, centrifuges, wet sieving machines, and controlled atmosphere chambers forstudies with desired gas compositions. The radiochemistry laboratory maintains a fully equippedradiocounting room (750 ft2) with state-of-the-art detectors for counting alpha, beta, and gammaemitters. Six high e�ciency intrinsic Ge or Ge(Li) detectors are individually housed in speciallow background steel and lead caves. All detectors are hooked to a computer controlled masterdata acquisition system that handles all data, QA, and QC manipulations. The tracer experimentsproposed herein will be readily counted on this system at minimal cost. Other necessary analyticalinstrumentation is also available including: inductively coupled plasma emission spectrometers(ICP) and ICP-MS (ICP linked to a mass spectrometer) for measuring major cations and tracemetals, ion chromatographs and automatic titrators to measure major anions and free hydroxide insolution, multiple X-ray di�ractometers for mineral analyses, carbon analyzers, and BET surfacearea analyzers.

7.2.2 W.R. Wiley, EMSL|Environmental Dynamics & Simulation

The Environmental Dynamics and Simulation Research Facility (ED&S) of the EnvironmentalMolecular Science Laboratory (EMSL) consists of integrated laboratories in environmental spec-troscopy, analytical chemistry, physical chemistry, radiochemistry, and graphics and visualization.These laboratories provide spectroscopic and computational capabilities that link molecular scaleresearch to research on natural environmental systems and materials. Instrumentation includes u-orescence excitation and laser-induced uorescence (LIF) spectrometry, visible and UV, and pulsedlaser systems, confocal and optical uorescence imaging microscopes, atomic force microscopy(AFM), scanning tunneling microscopy (STM) and near-�eld scanning optical microscopy (NF-SOM) systems, time-resolved uorescence and transient absorption spectroscopy (ps and fs), UVresonance Raman spectroscopy, high sensitivity FTIR spectrometer, including far and near IR capa-bility and IR microscope, Inductively Coupled Plasma (ICP) analysis, Mossbauer spectroscopy withcryogenics and controlled atmosphere environmental chambers. The nearby Materials and InterfaceLaboratory contains �eld emission-SEM, HRTEM with GIF-ELS �ltration for nm scale chemicalimaging, high-resolution XPS spectroscopy, Auger and TOF-SIMS microprobes with sub-micronscale resolution, and other high vacuum techniques useful in mineral and surface characterization.Various types of ultramicrotomy are available for preparation of TEM thin sections that retainchemical integrity.

7.2.3 NMR Facility

There is a suite of 12 multinuclear NMR spectrometers at the Environmental Molecular SciencesLaboratory (EMSL) at PNNL. A Varian Instruments model Unity+ NMR spectrometer with a

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wide (89 mm i.d.) bore Oxford superconducting magnet operating at a proton Larmor frequencyof 300 MHz will serve as the primary NMR instrument for the proposed research. Available testequipment include network analyzers, oscilloscopes, and rf-impedance measurement devices for usein strument construction and maintenance. Standard wet laboratory facilities are available for theproposed research.

7.3 University of Tennessee

The Center for Environmental Biotechnology (CEB) was established in 1986 by the TennesseeHigher Education Commission and a $1,000,000 equipment grant from the U.S. Department ofEducation to provide multidisciplinary graduate and undergraduate training in EnvironmentalBiotechnology. The CEB focuses on cross-training scientists and engineers in a collaborative re-search e�ort. There are 12 faculty and adjunct faculty members, 7 senior research associates, andapproximately 30 graduate students from the departments of Chemical Engineering, Civil and Envi-ronmental Engineering, Ecology, Environmental Toxicology, Geology, Microbiology, Plant and SoilScience, and the Oak Ridge National Laboratory participating in CEB activities. The CEB labo-ratory presently occupies 26,000 sq. ft. in the newly constructed Science and Engineering ResearchFacility on the main campus of the University of Tennessee, Knoxville. Specialized equipmentavailable for this project includes, but is not limited to the following:

Shimadzu TOC-V Total Organic Carbon AnalyzerBeckman LH-80 Ultra Centrifuge (1)Beckman J2-High Speed Centrifuges (3)Beckman TL100 Ultra-Centrifuge(1)Sorval RC-5 High Speed Centrifuge (1)Beckman Scintillation Counters (2)Bio101 FastPrep FP120 Membrane Disruptor(1)BioRad VersaFlur FluormeterBeckman Oligo 1000 DNA Synthesizer (1)Perkin Elmer Thermal Cycler 480 (2)Perkin Elmer Thermal Cycler 2400 (1)MJ Research DNA Engine PTC-2000 Peltier Ther-mocycler (1)Molecular Dynamics Storm 840 PhosphoImager(1)Nikon Phase Contrast Microscope w/Javelin Cameraand Monitor (1)Nikon Optiphot Microscope w/Nikon FX 35A Cam-eraOlympus Inverted Microscope w/MicromanipulatorPlas-Labs Anaerobic ChamberVG GM-MS System with Thermospray (1)Fotodyne Transilluminator (1)LKB HPLC (1)Desorption Chemical Ionization Probe (1)Microtox Assay System (1)Bioengineering 2 Liter Fermenters (2)Hewlett Packard 5973 Mass Spectrometer with HP6890 Gas ChromatographHewlett Packard 5890 Gas Chromatograph with ECDand FID

Beckman Oligo 1000 DNA SynthesizerSDS-PAGE Electrophoresis ApparatiLKB HPLC (1)Waters HPLC with Electrochemical and RefractiveIndex UV DetectorsPerkin Elmer HPLC (1)Shimadzu GC-9A w/FIDShimadzu GC-14A, ECD (1)Wallac 1450 Microbeta PlusScintillation CounterDohrmann 80 Total Organic Carbon AnalyzerLabline 1 Liter Fermenters (3)Genomyx Long Read Sequencer (1)New Brunswick Bio o Fermenters, 300 ml, 1L (8)IMCO 60 Liter Air Lift Fermenters (2)Laser Confocal Microscope (1)Bioimage Computer Scanner (1)Oriel Photomultiplier Detection System Model 7070w/Light Pipe (10)Rayonet Model RPR-200 Photochemical Chamber(1)Coulter Multisize Particle Counting System (1)Metrohm Titroprocessor (1)GSI Lumonics ScanArray 5000Engineering Services, Inc. DNA Micro-Arrayer(SDDC)BioRad iCycler QPCRCepheid SmartCyclerMJ Research Opticon SystemABI Model 370 Capilary Sequenator

65

The Program in Microscopy at the University of Tennessee is a core resource facility in theDivision of Biology. The facility serves as a campus wide support group for electron, optical, andscanned probe microscopies, and for microanalysis. Instrumentation includes Scanning ElectronMicroscopes (Hitachi S-800 and Hitachi S-3000), Transmission Electron Microscopes (Hitachi H-600 and Hitachi H-800), a Scanning Tunneling Microscope (Burleigh STM), Optical Microscopes(Nikon Eclispe 600 Light Microscope and Noran Tandem Scanning Optical Miroscope), as well asancillary equipment (Balzers Freeze Fracture Device and Reichert Ultramicrotome). The Universityalso maintains the Biology Services Facility with machine and electronics fabrication/repair services.

7.4 Los Alamos National Laboratory

High performance computing resource is available at Los Alamos National Laboratory at no charge.The machine is a 144-processor linux cluster called lambda.lanl.gov. In addition, workstations arealso available. No other resources will be needed for the modeling study.

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8 Current and Pending Support

Markus Flury

1. E�ect of Microbial Activity on Water Flow in Soils, USDA-CREES, NRI. July 2002{June2004. Funds requested $197,000 (PI) (pending).

2. Transgenic Barley Expressing Phytases in Roots, USDA-CREES, NRI. July 2002{June 2005.Funds requested $369,000 (Co-PI) (pending).

3. Colloid-facilitated Transport of Radionuclides through the Vadose Zone, US Department ofEnergy, EMSP. September 1999{September 2002. Funds awarded $700,000 (PI).

4. Education of the Next Generation of Environmental Scientists and Engineers. National Sci-ence Foundation, IGERT. October 1999{September 2004. $2,664,848 (Co-PI).

James B. Harsh

1. Transgenic Barley Expressing Phytases in Roots, USDA-CREES, NRI. July 2002{June 2005.Funds requested $369,000 (Co-PI) (pending).

2. Sorption of Cesium in Natural Sediments, Inland Northwest Research Alliance. October2000{September 2003. Funds awarded $157,000 (PI).

3. Colloid-facilitated Transport of Radionuclides through the Vadose Zone, US Department ofEnergy, EMSP. September 1999{September 2002. Funds awarded $700,000 (Co-PI).

John M. Zachara

1. Hanford Groundwater/Vadose Zone Integration Project-Representative Sites Studies, DOE/RichlandOperations. Exp. Date 9/31/02. Funds awarded $300,000 (PI).

2. The In uence of Calcium Carbonate Grain Coatings on Contaminant Reactivity in VadoseZone Sediments, DOE/EMSP. Exp. Date 9/31/02. Funds awarded $370,000/yr (PI).

3. Fixation Mechanisms and Desorption Rates of Sorbed Cs in High Level Waste ContaminatedSubsurface Sediments: Implications to Future Behavior and In-Ground Stability, DOE/EMSP.Exp. date 9/31/03. Funds awarded $340,000/yr (PI).

4. Biogeochemical Coupling of Fe and Tc Speciation in Subsurface Sediments: Implications toLong-Term Tc Immobilization, DOE/OBER - NABIR Program. Exp. date 9/31/03. Fundsawarded $500,000/yr (PI).

5. Interactions Between Fe(III)-Reducing Bacteria and Fe(III) Oxides: Microbial and Geo-chemical Dissolution Controls, DOE/BES-Geosciences. Exp. date 9/31/03. Funds awarded$200,000/yr (PI).

John F. McCarthy

1. Humic Adsorption and Desorption in Sandy Coastal Plain Soils. US Department of Energy,March 2002{December 2002. $49,000.

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2. Program Development in Environmental Applications. University of Tennessee Research Cen-ter of Excellence in Environmental Biotechnology, November 2001{July 2003. $80,000.

3. Evaluating risks and remediation of pathogen transport from point and nonpoint sources. Ten-nessee Department of Environmental Conservation, 2002{2003. $75,000 (pending).

4. Identifying Successful Strategies for Development and Implementation of the Total MaximumDaily Load (TMDL) Approach to Water Pollution Reduction, Water Resources Research In-stitute Program, 2001{2003. $25,000 (pending).

5. The Structural and Chemical Basis of Soil Microaggregate Formation and Stability. USDA-CREES, October 2002{September 2005. $299,000 (pending).

Peter Lichtner

1. Science and Technology Modeling Project for the Hanford Vadose Zone. US Department ofEnergy, Exp. Date 9/30/2002. $135,000, (Co-PI).

2. Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling. US Depart-ment of Energy, EMSP. Exp. Date 9/30/2005. $360,000 (Co-PI, pending).

3. Immobilization of Radionuclides in the Hanford Vadose Zone by Incorporation in Solid Phases.US Department of Energy, EMSP. Exp. Date 9/30/2005. $235,400 (Co-PI, pending).

4. When are Colloids (Including Nanoparticles) Important in Subsurface Contaminant Trans-port? US Department of Energy, EMSP. Exp. Date 9/30/2005. $156,800 (Co-PI, pending).

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9 Assurance and Certi�cations

� Assurance of Compliance

� Certi�cations regarding Lobbying

69

A Accomplishments of Previous EMSP Project

A.1 Project Goals

In our previous EMSP project we hypothesized that colloidal material is formed in situ when Han-ford tank supernatants are reacting with the sediments underlying the waste tanks. We anticipatedthat the newly formed products are composed of allophane, feldspathoid, and zeolite-like material,and that the material is of colloidal size fraction. The colloids would then strongly sorb the ra-dionculide Cs and potentially move through the subsurface, thereby facilitating the transport ofCs. The speci�c objectives of the previous EMSP project were to (1) determine whether, and, ifso, what colloids are formed from reaction between simulated tank waste and Hanford sediments,(2) determine the sorption of Cs to the formed colloids, (3) determine colloid characteristics thatgovern their mobility through the vadose zone, and (4) determine the potential of colloids to actas carriers to transport Cs through the vadose zone.

A.2 Alteration of Mineralogical and Surface Properties of Hanford Sedimentscontaminated with Tank Waste

Hanford sediments representative for the materials underlying the Hanford waste tanks were reactedwith simulated tank waste solutions. Experiments were carried out with tank waste solutionsvarying in NaOH and aluminate concentrations, at temperatures of 25 and 50�C. Aliquots weresamples as a function of time. After reaction, colloidal material (<2 �m) was separated from thesediments and characterized in terms of electrophoretic mobility, SEM/TEM, EDAX, FTIR, XRD,NMR, and particle size.

We found that three di�erent types of colloidal materials were formed upon reactions of tankwaste solutions with sediments: (1) altered native minerals in the colloidal size range, (2) newlyprecipitated phases, and (3) precipitates formed during titration of supernatant solutions. Di�erentminerals in the Hanford sediments reacted di�erently with simulated tank solutions: some minerals,like kaolinite, were completely or partially dissolved, others, like quartz and feldspar, were partiallydissolved, and others, like biotite, were fairly resistant towards tank waste solutions. The newlyformed colloidal phases were identi�ed as zeolites, sodalites, and cancrinites (Figure 3). While wehave worked with bulk sediments, other EMSP Projects have used pure mineral phases, like quartzand aluminosilicates, and have also observed formation of sodalite/cancrinite mineral phases [Nagyet al., 2001; Bickmore et al., 2001; Chorover et al., 2001].

Compared with the presence of native colloids, de�ned as particles <2 �m, the reaction withsimulated tank waste resulted in a mass increase of the colloidal size fraction, ranging from 80 to220% depending on reaction time and the chemistry of the tank solutions. The treated materialshad a zero-point of charge between pH 5 and 8, again depending on time of reaction and solutionchemistry (Figure 4). This contrast with the colloids from the untreated sediments, which hadonly negative charges between pH 2 and 11. We also formed colloidal material by using pure silicasolutions instead of Hanford sediments. The colloids formed from pure silica solutions were similarto those formed from the sediments, but the electrophoretic mobility depended on pH and Al:Siratio of the initial solutions.

The negative charge of the colloids at pH values typical for the Hanford vadose zone (pH >7) suggests that the colloids likely form stable, mobile suspensions, that they are not electrostati-cally attracted to the dominantly negatively charged Hanford sediments, and cations, like Cs, willelectrostatically attach to the colloids.

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6 mµ 0 2 4 6 8 10

Energy (keV)

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nsity

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Na KCa Fe

Figure 3: Sodalite/cancrinite particle formed during reactions of tank waste solutions with Hanfordsediments and associated EDAX spectrum.

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)

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0.01 M NaNO40 days50 C

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o

Figure 4: Electrophoretic mobility measured in 0.01 M NaNO3 of colloids formed under di�erenttank solution chemistry (Colloid 1 to 4) compared to untreated sediments (Colloid 0).

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A.3 Alteration of Mineralogical and Surface Properties of Reference Minerals

Hanford sediments consist of a variety of primary and secondary minerals. As it is expected thatdi�erent minerals will react di�erently with simulated tank waste, the bulk sediments will likelyreact as a selective mixture of minerals, some minerals will dissolve more readily than others. Toelucidate which mineral phases are susceptible to dissolution, we reacted pure mineral phases withsimulated tank solutions. The minerals tested were kaolinite, montmorillonite, illite, vermiculite,chlorite, biotite, and quartz. Results for kaolinite and montmorillonite indicated that upon reactionwith tank waste solutions, the clay minerals dissolve in part, and new mineral phases are formed.Kaolinite was almost quantitatively dissolved by the tank solutions over a time period of twomonths. The new mineral phases were identi�ed by FTIR, XRD, and SEM to be mixtures ofsodalite and cancrinite. Micrographs show that the morphologies of the newly formed particles issimilar to those of particle formed from Hanford sediments (Figure 5).

Cesium sorption studies showed that the colloids formed from pure mineral phases had highersorption a�nity for Cs than the original minerals. This result indicates that the experiments withthe bulk Hanford sediments, where Cs sorption slightly decreased after reactions, are a�ected bythe presence of additional minerals which were not yet studied as pure phases. Related studieswith pure mineral phases are in progress [Chorover et al., 2001; Nagy et al., 2001].

By and large, the results from the pure mineral reactions corroborate the results from bulksediments, namely that the main particles formed are mixtures of sodalites and cancrinites. Pure-mineral and bulk-sediment-derived colloids possessed similar colloidal properties in terms of elec-trophoretic mobility.

A.4 Cesium Sorption on Altered Hanford Sediments

One of the conditions for colloid-facilitated transport is that the contaminant strongly sorbs to thecolloidal particles. We have determined Cs sorption to three di�erent colloidal materials present inreacted Hanford sediments, namely the native colloids, the colloids formed after reaction with tankwaste solutions, and the colloids formed from the supernatant solutions. The results show that afterreactions with tank waste, the sorption a�nity for Cs has decreased compared to the unreactedsediments; however, the Cs sorption is still considerable (Figure 6a). Cesium sorbs strongly to thecolloids formed by titration of the supernatant solutions; the supernatant colloids sorb even moreCs than the native and reacted minerals (Figure 6b).

A.5 Colloid Transport through Unsaturated Hanford Sediments

As one would expect, colloid transport through Hanford sediments is a�ected by the ionic strengthand the water ow rate. The quantitative magnitude of these e�ects was investigated in water-saturated column experiments using colloids formed by reacting waste solutions with Hanfordsediments. Colloids were transported unretarded through the sediment, and a portion seems to beirreversibly attached to minerals inside the column.

Transport under unsaturated conditions clearly caused more colloidal particles to be trappedinside the column than under saturated conditions. Interestingly, the colloid breakthrough curves donot show a plateau, but rather the concentrations in the out ow slowly, but steadily, increase afterinitial breakthrough (Figure 7). Model analyses assuming physical non-equilibrium and mobile-immobile ow regions inside the columns, revealed that the steady increase is due to physicalnon-equilibrium. Under unsaturated conditions, the initial colloid breakthrough still occurs atabout one pore volume, indicating that colloids are not retarded inside the column, and travel with

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2.5 mµ2.5 mµ

(a)

5 mµ 2.5 mµ

(b)

Figure 5: SEM images of (a) kaolinite and (b) montmorillonite before (left) and after (right) reactionwith simulated tank waste solutions.

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Figure 6: (a) Cesium sorption isotherms measured in 0.01 M NaNO3 for colloids formed underdi�erent tank solution chemistry (Colloid 1 to 4) compared to untreated sediments (Colloid 0). (b)Cesium sorption isotherms in 0.01 M NaNO3 for colloids formed from supernatant solutions aftertitration to two di�erent pH values.

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0 1 2 3 4 5 6 7 8 9 100.0

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Figure 7: Colloid transport in unsaturated Hanford sediments. (a) Experimental data, and (b)experimental data plus model simulations with a two-region non-equilibrium transport model. Col-loids used were obtained by reacting simulated waste solutions with Hanford sediments (Colloid 3.)

the velocity of the water. No size exclusion e�ects were observed. Quantitatively less colloids weretransported as the water content decreased.

Native, unreacted, colloids showed a di�erent behavior than the reacted colloids. Colloidconcentrations in the out ow also showed also, steady increase after initial fast breakthrough, butthe model simulations revealed that only part of this increase can be explained by physical non-equilibrium. At this time, we hypothesize that, in case of the native colloids, attachment sitesfor colloids inside the column get blocked, thereby causing the in owing colloids to become moremobile.

A.6 Colloid-facilitated Transport of Cesium through Hanford Sediments

We have studied transport of Cs through water-saturated Hanford sediments in the absence andpresence of colloidal material. Cesium as well as colloid transport are strongly a�ected by the ionicstrength of the background solution. However, the e�ect of the ionic strength in terms of mobilityof soluble Cs and colloids is opposite: while Cs sorption decreases with increasing ionic strengthand consequently Cs migration is enhanced, colloids occulate under high ionic strength and arenot mobile. These complementary e�ects were quanti�ed in a saturated column experiment using1 M and 1 mM NaNO3 solutions to simulate a Hanford tank leak with 0.1 mM Cs as contaminant.Cesium breakthrough curves were measured in both 1 M and 1 mM NaNO3 electrolytes, as well asduring colloid mobilization.

Colloidal particles were mobilized during the change of ionic strength (Figure 8). Mobilizedcolloids consisted mainly of quartz, mica, illite, kaolinite, and chlorite. Mobilized colloids carrieda fraction of the cesium along. Total concentrations of Cs in the out ow varied between 0.5 and0.8 �mol/L, and dropped to below 0.03 �mol/L after 110 pore volumes (Figure 8). The onlysigni�cant concentrations in the solution phase were measured within the �rst 15 pore volumesfollowing colloid elution when solution phase concentrations reached up to 0.1 �mol/L. The bulkportion of the Cs was associated with the colloidal phase. Based on studies on contaminatedsediments from the Hanford Site, it is likely that the Cs was mainly carried by biotite and to alesser degree by vermiculite [McKinley et al., 2001].

We calculated the mass balance of Cs for the mobilization experiment based on the concentra-tions measurements in the out ow. Most of the Cs introduced into the column was eluted during

79

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Figure 8: Column out ow after eluent change from 1 M to 1 mM NaNO3. The pore volume axisstarts when the ionic strength of the in ow was changed. (a) Colloid concentration breakthroughcurve, (b) colloid breakthrough curve in semi-log scale, (c) Cs concentration breakthrough.

the Cs breakthrough experiment (1 M NaNO3), accounting for 99.5% of the Cs mass. After thechange of the ionic strength, an additional 0.432% of the Cs was eluted. The colloid-associatedCs amounted to 0.428%. A negligible amount of Cs (0.004%) was detected in the solution phaseduring the colloid mobilization experiment. Based on the mass balance calculation, the 0.428% ofcolloid-associated Cs might not seem signi�cant; however, considering the portion of Cs remaininginside the column after the �rst Cs breakthrough curve, the eluted colloid-associated Cs accountsfor 42% of the Cs remaining in the column. A considerable amount of the Cs residing in the columnwas therefore mobilized via colloidal particles.

A.7 Anticipated Non-Expended Funds from Previous EMSP Project

At the end of the previous EMSP project we do not anticipate to have a signi�cant amount offunds left. As our Postdoc has taken a position at Sandia National Laboratories during the courseof our project, and the re-hiring of a new Postdoc has taken about 3 months of time, we will beable to extend the employment of the new Postdoc by 3 months after the project o�cially ends viaa no-cost extension application.

80

B Los Alamos DOE Field Work Proposal and Budget

81