Objectives and Design Solutions of a 1000-year ... · PDF fileObjective #1: Meet or ... with...
Transcript of Objectives and Design Solutions of a 1000-year ... · PDF fileObjective #1: Meet or ... with...
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Objectives and Design Solutions of a 1000-year Evapotranspiration-Capillary Surface Barrier System
Z. FRED ZHANG, DAWN M. WELLMAN
May 17, 2017PNNL-SA-125146 1
Pacific Northwest National Laboratory2017 National Meeting of the American Society of Mining and Reclamation, Morgantown, WVWhat’s Next for Reclamation? April 9 - 13, 2017
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Background - Surface mining
Changes ecology of the site
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Alters the vegetation, soils, bedrock, and landformsChanges the surface hydrology, groundwater, and flow paths
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SurfaceLoss of vegetationLoss of soilErosionRunoffStream pollution
SubsurfaceAcid drainageGroundwater contamination
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Surface Mining -Problems
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Surface Barrier (Cover, Cap)
covers the exposed rocksisolates rockpile/tailingreduces erosionprovides a medium for vegetation growthreduces drainage
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Mine Land Reclamation with Surface Barriers
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Surface Barrier Use on Mine Land
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Continent Country Number of CasesNorth America Canada 40
United States 85 South America Brazil 4
Chile 2 Africa South Africa 13 Europe Sweden 6
United Kingdom 2 Germany 18
France, Czechoslovakia 1 eachGreece, Norway, Spain 1 each
Australia Australia 18 Asia Indonesia 5
China 1 Total 200
Soil covers for tailings impoundments, waste rock piles, backfilled pits and heap leach pads (Rykaart et al. 2006)
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Barrier Design Challenges
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Regulatory requirements
Recharge Control Wind Erosion Water Erosion
Animal Intrusion Plant Intrusion Human Intrusion
Waste isolation Maintenance
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Objectives
Introduce performance objectives and the design solutions for a long-term (1000 yr) surface barrier
The 2000-Year-Old Man-Made Grave Creek Mound in the Ohio River Valley, WV
10000-Year –Old Iceberg Deposited Mound (Berggmounds)
Evaluate the performance of the surface barrier after a demonstration of 20 years
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Performance Objectives of a Surface Barrier over a Nuclear Waste Site
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Objectives#1 Meet or exceed RCRA criteria#2 Function in a semiarid to
subhumid climate#3 Limit drainage to less than
0.5 mm yr-1
#4 Limit runoff#5 Minimize erosion#6 Minimize biotic intrusion#7 Have a design life of 1000 years#8 Be maintenance free
Regulatory Requirements:
Functionality Requirements:
Longevity Requirements:
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Objectives and Solutions - 1
Objective #1: Meet or exceed RCRA criteria
thickness > 0.91 m; design life: 30 years; conductivity: <32 mm/yr
Design Solutionthickness of 4.5 m; design life of 1000 year; drainage rate < 0.5 mm/yrcontaining a coated asphalt concrete (AC)
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4.5 m
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Objectives and Solution - 2
Objective #2: Function in a semiarid to subhumid climate
Design Solution: Use a ETC barrier with 2-m-thick silt loamThe compacted clay barrier may not work
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AI = P/PET
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Objective #3: Minimize drainage rate to <0.5 mm/yr
Design solution2-m thick ET barrierCapillary break2% slope of barrier surface
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Waste
Asphalt
Objectives and Solution - 3
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Objectives and Solution - 4
Objective #4: Limit runoffDesign solutions
Use soil with sufficient large permeability
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Warden silt loamKs = 36 mm/hr
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Objectives and Solution - 5
Objective #5: Minimize erosionDesign solution
15% gravel mixvegetation
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Objectives and Solution - 6
Objective #6: Minimize biotic intrusion
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Design solutions1.5-m riprap layerasphalt concrete layer
5 – 25 cm
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Objectives and Solution - 7
Objective #7: Have a design life of 1000 yearsObjective #8: Be maintenance free
Design solutionUse natural materials for barrier construction: soil and rockEstablish a natural ecological system: ETC BarrierInclude protective side slopes
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2:1 Basalt Riprap Side Slope10:1 Pit-Run Gravel
Side Slope
Asphalt concrete with a 5-mm-thick polymer-modified fluid-applied asphalt coating
Multi-Layered ETC Barrier
Compacted soil
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Barrier Design: 3D
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In Situ Soil
216-B-57 Waste Crib
Drainage Gravel:- Promote lateral drainage
Riprap Side Slope:- Intrusion control
Asphalt Concrete- Drainage interception- Noxious gas control
Silt Loam + Gravel:- Vegetation growth- Precipitation storage and release- Erosion control
Functions of Barrier Components
2X vertical exaggeration
Riprap layer:- Intrusion control
Compacted Soil- Settlement control
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Tests
Treatability testNov. 1994 to Oct. 1997Irrigated the north section to about 3x the average precipitation (3x160 = 480 mm/yr)
Controlled burnThe north section was burned in Sept. 2008
Monitoring: 1994 to 2013
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Once in 1,000,000
yr
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Results: Soil Water Content Dynamics(10/95-3/96, irrigated)
Water Content (m3/m3)
• Soil became wetter
• Top 0.7 to 1 m was very wet
• Lower portion was still moist in late spring
• Water was diverted away from the center line
Click to play video
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Soil Water Content Dynamics(4/96-10/96, irrigated)
Water Content (m3/m3)
• Soil became drier spring/summer
• Entire soil profile became dry
• ET used up all the stored water
Click to play video
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Summary - Design Barriers for Mine Lands
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Regulatory Requirements
Functionality Requirements
Longevity Requirements
Design lifeErosion controlMaintenance
ClimateMaximum drainage rateRunoff control
FederalState
Design surface barriers to achieve the objectivesType, Complexity
Determine barrier objectives
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