U.S. Geological Survey Scientific Investigations Report 2005-5026—ONLINE ONLY

Review of the Transport of Selected Radionuclides in the Interim Risk Assessment for the Radioactive Waste Management Complex, Waste Area Group 7 Operable Unit 7-13/14, Idaho National Engineering and Environmental Laboratory, Idaho

By Joseph P. Rousseau, Edward R. Landa, John R. Nimmo, L. DeWayne Cecil, LeRoy L. Knobel, Pierre D. Glynn, Edward M. Kwicklis, Gary P. Curtis, Kenneth G. Stollenwerk, Steven R. Anderson, Roy C. Bartholomay, Clifford R. Bossong, and Brennon R. Orr


Prepared in cooperation with the
Idaho Operations Office
U.S. Department of Energy
under Interagency Agreement DE-AI07-97ID13556


Idaho Falls, Idaho

February 2005


This report is available as a pdf.



Table of Contents


Executive Summary

J.P. Rousseau

1.0 Introduction

J.P. Rousseau

1.1 Purpose

1.2 Scope

1.2.1 Task 1: Review of radionuclide sampling data at the Radioactive Waste Management

1.2.2 Task 2: Radionuclide transport processes

1.2.3 Task 3: Distribution coefficients (Kds) and their application to transport analysis

1.2.4 Task 4: Transport model analysis

1.2.5 Task 5: Further work

1.3 Acknowledgments

1.4 Report Organization

2.0 Conceptual model of aqueous-phase fluid flow and contaminant transport

J.R Nimmo, S.R. Anderson, R.C. Bartholomay, J.P. Rousseau, L.L. Knobel

2.1 Regional setting

2.2 Conceptual models

2.3 Geologic framework

2.3.1 Geologic data

2.3.2 Stratigraphy

2.3.3 Basalt flows Typical basalt-flow characteristics Typical basalt-flow geochemistry Fractures

2.3.4 Surficial sediment and sedimentary interbeds Depositional environments Lithologic variations Physical characteristics and mineralogy Pedogenesis Thickness and areal extent Hydraulic conductivity

2.3.5 Hydrologic pathways

2.4 Hydrologic framework

2.4.1 Meteorology

2.4.2 Surface water and local runoff Areal infiltration Stream infiltration

2.4.3 Unsaturated-zone flow Flow in a homogeneous medium Flow and perching in stratified unsaturated zones Preferential flow Macropore flow—heterogeneity of the porous medium Funneled flow—heterogeneity of the porous medium Unstable flow—heterogeneities in the condition of the medium Quantitative treatment of preferential flow Effective properties Dual-modality and multi-modality Additional considerations in the quantification of unstable flow Contentions and ambiguities concerning preferential flow Flow in the unsaturated zone at and near the Subsurface Disposal Area Surficial sediments Basalts Sedimentary interbeds Current qualitative understanding of flow in the unsaturated zone at the Idaho National Engineering and Environmental Laboratory Vertical flow of local origin Combined vertical and lateral flow Summary of unsaturated-zone flow

2.4.4 Flow in the saturated zone

2.5 Contaminant transport

2.5.1 Source-term description Point sources Nonpoint sources

2.5.2 Summary of geochemical processes at the Subsurface Disposal Area Lithology and mineralogy Water chemistry

2.5.3 Description of contaminant transport processes Solute transport Colloid transport

2.6 Summary

3.0 Task 1: Review of radionuclide sampling program and available data at the Subsurface Disposal Area

L.D. Cecil, L.L. Knobel, E.R. Landa

3.1 Introduction

3.1.1 Background

3.1.2 Purpose and scope

3.2 Detection limits, statistical screening criteria, and reporting of data

3.3 Sampling methodology

3.3.1 Sampling location, frequency, and media

3.3.2 Sample identification

3.3.3 Sampling equipment and procedures

3.3.4 Sample handling, packaging, and shipping

3.3.5 Documentation

3.3.6 Handling and disposition of investigation-derived waste

3.4 Analytical methods and laboratory techniques

3.5 Quality assurance and quality control protocols

3.6 Reported detections in sediments and water

3.6.1 Surficial sediments and sedimentary interbed data

3.6.2 Perched-water and ground-water data

3.6.3 Significance of reported detections

3.7 Summary

4.0 Task 2: Actinide transport processes

G.P. Curtis, P.D. Glynn, K.G. Stollenwerk, R.C. Bartholomay

4.1 Introduction

4.2 Summary of geochemical characteristics at the Subsurface Disposal Area

4.3 Potential effects of speciation on actinide transport

4.3.1 Am, U, Np, and Pu chemistry and speciation Am U Np Pu

4.3.2 Speciation calculations for aqueous Am, U, Np, and Pu in INEEL waters Speciation calculations for aqueous Am Speciation calculations for aqueous U Speciation calculations for aqueous Np and Pu Additional speciation calculations for Np and Pu

4.3.3 Summary

4.4 Applicability of the local equilibrium concept to actinide transport

4.4.1 Chemically-mediated kinetics

4.4.2 Transport-controlled kinetics

4.5. Colloid-facilitated transport of actinides

4.5.1 Colloid definition and mobility

4.5.2 Previous studies of actinide colloid formation and transport Batch experiments Column experiments Field studies

4.5.3 Evidence for colloid-facilitated transport of actinides at the Idaho National Engineering
and Environmental Laboratory Field evidence Laboratory column experiments

4.5.4 Summary of colloid-facilitated transport of actinides

4.6 Summary

5.0 Task 3: Distribution coefficients (Kds) and their application to transport analysis

E.R. Landa, P.D. Glynn, K.G. Stollenwerk, G.P. Curtis

5.1 Introduction

5.2 Literature review

5.2.1 Kd basics

5.2.2 Sorption processes Alternatives to single Kd values Importance of secondary minerals Role of Fe2+-bearing minerals Influence of organic compounds on subsurface migration of actinides

5.3 Evaluation of the Kds for Am, U, and Pu used in the Interim Risk Assessment model—experimental data

5.3.1 Materials and methods Solid phases Interbed sediments Basalt Aqueous phase Column experiments Crushed basalt and interbed sediments—saturated Intact basalt—saturated Crushed basalt—unsaturated Batch experiments

5.3.2 Results and discussion Batch experiments Am U PU Risk assessment Kds for Am, U, and Pu Column experiments Interbed sediment columns Crushed-basalt columns Enhanced mobility fraction Additional experiments ph and ionic-strength variability Reproducibility of Kds Solid:liquid ratio Crushed basalt versus intact basalt Unsaturated column experiments

5.3.3 Summary of the evaluation of Kds for Am, U, Np, and Pu used in the Interim RiskAssessment

5.4 Evaluation of the Kds for Np used in the Interim Risk Assessment model—literature review

5.4.1 Studies of potential relevance to the Idaho National Engineering and Environmental Laboratory

5.4.2 Summary of Kds for Np used in the Interim Risk Assessment model

5.5 Use and limitations of the Kd concept as applied to actinide transport at the Idaho National Engineering and Environmental Laboratory

5.5.1 Advantages and limitations of the Kd approach in modeling contaminant retardation Advantages of the Kd approach Limitations of the Kd approach Applicability of the Kd approach to ground-water systems in chemical steady state

5.5.2 Advantages and limitations of speciation-based approaches in modeling sorption reactions

5.5.3 Uncertainties at the Idaho National Engineering and Environmental Laboratory site and their potential effects on simulation of radionuclide sorption and retardation

5.5.4 One-dimensional transport simulations for U and Np U(VI) transport calculations Calibration of the reactive-transport mode Application of the surface complexation model to ground water at the Idaho National Engineering and Environmental Laboratory Comparison of one-dimensional transport simulations and calculated Krs Np transport calculations Description of the Np transport simulations Np infiltration results Np cleanup results Np sorption isotherms for the PHREEQC surface complexation models

5.6 Evaluation of the uncertainties associated with selected Kds

5.7 Summary

6.0 Task 4: Transport model analysis

J.R. Nimmo, E.M. Kwicklis, J.P. Rousseau, S.R. Anderson, C.R. Bossong, G.P. Curtis

6.1 Introduction

6.2 Review of significant Interim Risk Assessment assumptions and simplifications

6.2.1 Hydrogeologic framework—geometrical aspects Definition and description of the model domain Geostatistical applications Variogram construction Kriging results

6.2.2 Nature of materials Means used to determine hydraulic properties Fractured basalts in the unsaturated zone Surficial sediments Sedimentary interbeds Aquifer properties Heterogeneity and anisotropy of hydraulic properties

6.2.3 Unsaturated-zone flow Infiltration Percolation Lateral flow

6.2.4 Contaminant input and transport Source term Solute transport Colloid transport

6.2.5 Saturated-zone flow

6.3 Review of the numerical simulator

6.3.1 Description of the numerical simulator Discretization and grid refinement

6.3.2 Model calibration Calibration for unsaturated-zone hydraulics Perched water Travel time Calibration for saturated-zone hydraulics Calibration for contaminant transport Nitrate Carbon tetrachloride Detected contaminants of potential concern

6.4 Model utilization

6.4.1 Sensitivity analyses

6.4.2 Predictions

6.5 Summary

7.0 Summary and conclusions

J.P. Rousseau

References Cited

Appendix: Task 5

J.P. Rousseau, B.R. Orr


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