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Designs, Natural Succession, and LTS&M of Disposal Cell Covers for Uranium Mill Tailings WJ Waugh

Designs, Natural Succession, and LTS&M of Disposal Cell Covers for Uranium Mill Tailings WJ Waugh S.M. Stoller Corporation LTS&M Conference November 16-18, 2010. U.S. Department of Energy Office of Legacy Management (LM) Sites.

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Designs, Natural Succession, and LTS&M of Disposal Cell Covers for Uranium Mill Tailings WJ Waugh

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  1. Designs, Natural Succession, and LTS&M of Disposal Cell Covers for Uranium Mill Tailings WJ Waugh S.M. Stoller Corporation LTS&M Conference November 16-18, 2010

  2. U.S. Department of Energy Office of Legacy Management (LM) Sites

  3. U.S. Department of Energy Office of Legacy Management (LM) Sites Remedies at most LM sites includedisposal cells for U mill tailings. Broad range of climates, soils, and ecology.

  4. Presentation Topics • Purpose of disposal cell covers • Cover designs, natural succession, and performance • Cover renovation – improving sustainability by accommodating natural succession • Summary

  5. Presentation Topics • Purpose of disposal cell covers • Cover designs, natural succession, and performance • Cover renovation – improving sustainability by accommodating natural succession • Summary

  6. UraniumMill Tailings • Uranium Mill Tailings Radiation Control Act (UMTRCA) of 1978 • limit radon escape • contain tailings source • clean up and protect ground water (came later) • last for 200-1000 years! RADON GAS U TAILINGS VADOSE ZONE PLUME GROUND WATER

  7. Remedy: EngineeredCover • Slow radon flux < 20 pCi m-2 s-1 (< 0.74 Bq m-2 s-1) • Control percolation and mobilization of contaminants —satisfy GW standards • Control erosion and bio-uptake • Last for 200-1000 years RADON GAS Cover U TAILINGS VADOSE ZONE PLUME GROUND WATER

  8. Presentation Topics • Purpose of disposal cell covers • Cover designs, natural succession, and performance • Cover renovation – improving sustainability by accommodating natural succession • Summary

  9. 30 cm Rock Riprap 15 cm Bedding Low-Permeability Radon Barrier 60 cm Tailings Early Disposal Cell Cover Design

  10. Natural Succession and Performance Lesson 1: Rock covers increase water storage and create habitat for deep-rooted woody plants for a broad range of climates and ecology Accumulation of water in the bedding layer and low-permeability radon barrier favors germination and establishment of shrubs and trees.

  11. Rock Riprap 30 cm 15 cm Bedding Low-Permeability Radon Barrier 60 cm Tailings Burrell, PA Precip > 1000 mm/yr (> 40 in/yr) Sycamore Tree-of-heaven Japanese knotweed

  12. Rock Riprap 30 cm Bedding 200 cm Low- Permeability Radon Barrier Tailings Shiprock, NM Precip ~ 180 mm/yr (~ 7 in/yr) Russian thistle Kochia Tamarisk Rabbitbrush Saltbush

  13. Rock Riprap 30 cm 15 cm Bedding 45 cm Protection Layer Low-Permeability Radon barrier 45 cm Tailings Fourwing saltbush Grand Junction, CO Precip < 200 mm/yr (< 8 in/yr) Fourwing Saltbush Shadscale Spiny Hopsage Rabbitbrush Halogeton

  14. 15 cm Soil Rock Riprap 30 cm 15 cm Bedding Low-Permeability Radon barrier 45 cm Tailings Lakeview, OR Precip ~ 380 mm/yr (15 in/yr) Rabbitbrush Sagebrush Bitterbrush

  15. Natural Succession and Performance Lesson 2: Roots of woody plants can penetrate compacted soil layers overlying tailings Plant roots were excavated at several sites to determine rooting depths. • Primary roots extend vertically through rock and bedding layers and then branch laterally at the radon barrier surface • Secondary and tertiary roots extend vertically in the radon barrier as root mats following soil structural planes

  16. Lakeview, OR Sagebrush

  17. Test Dye and Sagebrush Roots in Radon Barrier Lakeview, OR Sagebrush

  18. Burrell, PA Japanese knotweed Grand Junction, CO Fourwing Saltbush

  19. Burrell, PA Japanese knotweed Grand Junction, CO Fourwing Saltbush Saltbush Root Mat in Radon Barrier

  20. Burrell, PA Japanese knotweed

  21. Burrell, PA Japanese knotweed

  22. Natural Succession and Performance Lesson 3: Windblown dust in semiarid West and organic litter in humid East are creating soils in rock riprap and drainage layers • Soil development in rock enhances plant habitat and drives plant succession • Soil development in drainage layer may limit lateral shedding of precipitation

  23. Grand Junction Cover Dust has filled the basalt riprap layer on leeward side of the cover

  24. Test dye shows structural planes Lesson 4:Different types of soil development (pedogenic) processes may be causing preferential flow in CSLs: • Soil structure developing faster than expected • Plant roots and burrowing animals • Freeze-thaw cracking and desiccation • Borrow soil structure retained after construction Roots follow structural planes

  25. Cover Soil Development andSaturated Hydraulic Conductivity (Ks) Lesson 5: Root intrusion and soil development increase the KS of the low-permeability radon barrier Assumed saturated hydraulic conductivity (KS): Ks≤ 1x10-7 cm/s In situ Ks measured using air-entry permeameters (AEPs) D.B. Stephens Air-Entry Permeameter

  26. Rock Riprap 30 cm 15 cm Bedding Low-Permeability Radon Barrier 60 cm Tailings Burrell, PA In-situ Ks 1996AEP Study

  27. Lakeview, OR In-situ Ks 1998 AEP Study 15 cm Soil Rock Riprap 30 cm 15 cm Bedding Low-Permeability Radon barrier Manual AEP on side slope Automated AEPs on topslope 45 cm Tailings

  28. Rock Riprap 30cm Bedding 200 cm Low- Permeability Radon Barrier Tailings Shiprock, NM In-situ Ks 1999 AEP Study

  29. Tuba City, AZ In-situ Ks 1999 AEP Tests Rock Riprap 30 cm Bedding 15 cm Low-Permeability Radon barrier 107 cm Tailings

  30. Rock Riprap 30 cm 15 cm Bedding 45 cm Protection Layer Low-Permeability Radon Barrier 45 cm Tailings Fourwing saltbush Grand Junction, CO In-situ Ks 2005 AEP Tests

  31. ACAP initial Ks < 1 x 10-7 cm/s Burrell, PA Polson, MT Omaha, NE Albany, GA Altmont, CA Tuba City, AZ Shiprock, NM Lakeview, OR Grand Jct, CO Apple Valley, CA EPA ACAP Sites Bill Albright, Desert Research Institute Low-Permeability Radon Barrier Ks Means 1 x 10-3 1 x 10-4 1 x 10-5 Ks (cm/s) 1 x 10-6 1 x 10-7 1 x 10-8 DOE LM Sites

  32. Lesson 6: High saturated hydraulic conductivity (Ks) may cause significant percolation through the cover Lakeview, Fall 2005 Water fluxmeters Installed below CSL

  33. Lakeview Water Flux Meter Results(November 2005 – September 2007)

  34. Lesson 7:Inadequate revegetation planning and poor soil edaphic properties can compromise performance Lakeview, OR edge of cover Thin soil layers overlying rock are poor habitat for grasses

  35. Lesson 8:Water balance cover designs accommodate natural succession (plant ecology and soil development) and perform better than low-permeability covers 60 cm Water Storage Layer (Sponge) 40 cm 30 cm 30 cm 38 cm 60 cm Monticello, Utah Disposal Cell Cover

  36. Soil Water Balance Monitoring (3-hectare embedded lysimeter) Fine Soil Capillary Barrier Drainage collection system Percolation and Runoff: Dosing siphons Soil Moisture Monitoring: - Water content TDR - Water potential HDU

  37. Upper Storage Limit Embedded Lysimeter Water Balance On-Site Evapotranspiration Average Percolation ~ 0.5 mm/yr

  38. Cover Percolation Comparison Average Percolation Site Average Cover Precipitation Percolation as % of EPA ACAP Type (mm) (mm) Precipitation DOE LM Low- Albany, GA 849 26.0 265.0 Permeability Apple Valley, CA 61 4.1 2.5 Cover Cedar Rapids, IA 449 8.8 39.5 Lakeview, OR 319 9.4 30.1 Water Apple Valley, CA 167 0.3 0.5 Balance Boardman, OR 181 0.0 0 Cover Polson, MT 349 0.1 0.2 Monticello, UT 387 0.1 0.5

  39. Cover Water Balance: Role of Plants Estimated Ranges of Annual Recharge (mm/yr) ~380 Shrubs 380 mm (15 in) 100-200 Wheatgrass Cheatgrass Bare / Rock Soil Depth (1.5 m) Loam Soil <1 0-20 20-100 100-200

  40. 250 50 1.0 225 45 0.9 200 40 0.8 175 35 0.7 150 30 0.6 Percent Cover Shrub Density (#/Acre) Leaf Area Index 125 25 0.5 100 20 0.4 75 15 0.3 50 10 0.2 25 5 0.1 0 0 0 Monticello Vegetation Monitoring 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

  41. June 2008 Preliminary LAI Map for Monticello CoverJune 2008 LAI 5.432 John Gladden SRNL 0

  42. Presentation Topics • Purpose of disposal cell covers • Cover designs, natural succession, and performance • Cover renovation – improving sustainability by accommodating natural succession • Summary

  43. Shrub encroachment and soil development may be the solution, not the problem! Grand Junction, Colorado

  44. Shrub encroachment and soil development may be the solution, not the problem! Without intervention, natural succession processes may eventually transform conventional low-permeability covers into ET-type covers. • LTSM Options: • Control plant growth • Let plants grow • Enhance soil development and ecological succession Cover Renovation! Grand Junction, Colorado

  45. Cover Renovation Research Goal:Enhance natural transformation of conventional covers into ET covers • Reduce soil bulk density (compaction) • Increase soil water storage capacity • Blend soil and rock to imitate natural analogs • Enhance establishment of favorable vegetation Test:Construct pair of large drainage lysimeters, identical to actual cover, and compare water balance of existing and renovated designs Renovation Concept:Rip the rock, drainage, and protection layers on the contour, and transplant native shrubs in rip rows

  46. Rock Riprap 30 cm 15 cm Bedding 45 cm Protection Layer 45 cm Low-Permeability Radon Barrier Fourwing saltbush Tailings Control Renovate Cover Renovation Lysimeters 2008 46

  47. 20 700 Control Lysimeter 600 Precipitation 15 Soil Water Storage 500 400 Cumulative Runoff and Percolation (mm) 10 Cumulative Precipitation and Evapotrasnpiration, and Soil Water Storage (mm) Evapotranspiration 300 200 5 Percolation 100 Surface Runoff 0 0 10/31/07 5/1/08 10/31/08 5/1/09 10/31/09 5/1/10 10/31/10 Baseline Water Balance Monitoring: ‘Renovate’ and ‘Control’ Lysimeters 20 700 Renovate Lysimeter Precipitation 600 Soil Water Storage 15 500 400 Cumulative Runoff and Percolation (mm) 10 and Soil Water Storage (mm) Cumulative Precipitation and Evapotrasnpiration, Evapotranspiration 300 Percolation 200 5 100 Surface Runoff 0 0 10/31/07 4/30/08 10/30/08 5/1/09 10/30/09 5/1/10 10/31/10

  48. Presentation Topics • Purpose of disposal cell covers • Cover designs, natural succession, and performance • Cover renovation – improving sustainability by enhancing natural succession • Summary

  49. Cover LTSM Questions • Why did we cover uranium mill tailings? • How were the covers designed to work and how were they constructed? • How have natural succession processes altered cover performance? • What are the risks to HH&E if the covers are not performing as designed? • What types of maintenance are required—and at what cost—to keep covers performing as designed? • Could we design sustainable repairs or renovations if needed to reduce LTSM costs and risks? • Can we expect covers to continue working as designed for the long term—200 to 1000 years?

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