D.S. Kosson1, A.C. Garrabrants1, Hans van der Sloot2, Susan Thorneloe3, Richard Benware4, Greg Helms4, and Mark Baldwin4
1 Vanderbilt University, Nashville, TN2 van der Sloot Consultancy, Langedijk, the Netherlands3 U.S. EPA Office of Research and Development, RTP, NC
4 U.S. EPA Office of Resource Conservation & Recovery, Washington DC
19 June 2012
The Leaching Environmental Assessment Framework as a Tool for Risk‐informed, Science‐based Regulation
Introduction to Leaching Assessment
Overview of LEAF• Leaching Tests• Data Management
Overview of Interlaboratory Validation
Applicability to DOE Challenges
Conclusions
Presentation Outline
2
1960s-1990sProtection from hazardous wastes; waste minimization/conservation.
• Classification of “hazardous” waste (RCRA Subtitle C/D landfills)• Acceptance criteria for disposal of treated wastes (Universal Treatment Standards)• Best demonstrated available treatment (BDAT)
1990s – presentMove toward integrated materials management; balancing overall environmental performance with materials costs and long-term liability
• Global economic policy (resource costs, international trade)• Risk-informed waste management practices• Changing definition of waste materials (e.g., Dutch Building Materials Decree; U.S.
definition of solid waste)• Applications for waste delisting and alternative measures of treatment effectiveness • Re-use of waste materials (mine reclamation, alternative construction materials)
Materials Testing – Historically
3
Process by which constituents of a solid material are released into a contacting water phase
What is Leaching?
Percolation Release Water passes thru material Equilibrium High concentration
Mass Transfer Release Water flows around material Diffusion to material surface Lower concentration
4
Leaching - Controlling Factors
Physical Factors Particle size Rate of mass
transport
Site Conditions Flow rate of leachant Temperature Bed porosity Fill geometry Permeability Hydrological conditions
Chemical Factors Equilibrium/kinetic control pH Liquid-solid ratio Complexation Redox Sorption Biological activity
Trace elements
Soluble salts
TOC (at high pH) DOC
H+
CO2
O2
Erosion
ReleaseMechanisms
Wash OffDissolutionDiffusion
5
Total ContentTotal Content Does Not Correlate to Leaching
10-1
100
101
102
103
104
105
As
[µg/
L] -
Max
. Elu
ate
Con
cent
ratio
n
10-1 100 101 102 103
As - Total By Digestion [µg/g]
As
Fly Ash SDA Gypsum Scrubber Sludge Blended CCRs
Same total content with different eluateconcentrations
Same eluateconcentration with different total contents
6
Many Leaching Scenarios …
coastal protection
construction debris and run-off
roof runoff
municipal sewer system
drinking water welllandfill contaminated soil
road base
industrially contaminated soil
factory seepage basin
agriculture
mining
7
Common Assessment Approach
road base
C
B
A* A*
B
C
A CCR Leaching
Constituent Release from Use
Constituent Pt. of Compliance
Location DAF
Use Source TermCCR Leaching in Use Context
ThresholdDefinition
Total Content• Correlation to leaching?
Regulatory Tests• Comparison to limits• Does not consider
Release Scenario Time (kinetics) Mass Transport
Characterization Tests• Range of conditions• Comparisons between
Materials Treatments Scenarios
Leaching Tests
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Single Point Test
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Single Point Test
Regulatory Limit
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Single Point Test
Regulatory Limit
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Single Point Test
Characterization Test
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Regulatory Limit
Portland
Cemen
t
Characterization Test
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
enic
(m
g/L)
pH
Total Content
Regulatory Limit
Blen
ded Ce
men
tCharacterization Test
9
Leaching Method DevelopmentLeaching characterization applied to anticipated release conditions resulting in improved accuracy and more reliable environmental decision making
“An Integrated Framework for Evaluating Leaching in Waste Management and Utilization of Secondary Materials,” D.S. Kosson, H.A. van der Sloot, F. Sanchez, and A.C. Garrabrants, Environmental Engineering Science, 19(3): 159-204, 2002.
Parallel and coordinated methods development in the EU and US
Designed to address concerns of EPA Science Advisory Board• Form of the material (e.g., monolithic)• Leaching parameters (e.g., pH, liquid-solid ratio (L/S), release rate)
Intended for situations where TCLP is not required or best suited• Assessment of materials for beneficial reuse• Evaluating treatment effectiveness (determination of equivalent treatment)• Characterizing potential release from high-volume materials • Corrective action (remediation decisions)
10
Leaching Environmental Assessment FrameworkLEAF is a collection of …
• Four leaching methods• Data management tools• Geochemical speciation and mass transfer modeling • Quality assurance/quality control for materials production• Integrated leaching assessment approaches… designed to identify characteristic leaching behaviors for a wide range of materials and associated use and disposal scenarios.
LEAF facilitates integration of leaching methods which provides a material-specific “source term” release for support of material management decisions.
More information at http://www.vanderbilt.edu/leaching
11
LEAF Leaching MethodsMethod 1313 – Liquid-Solid Partitioning as a Function of Eluate pH using a
Parallel Batch Procedure
Method 1314 – Liquid-Solid Partitioning as a Function of Liquid-Solid Ratio (L/S) using an Up-flow Percolation Column Procedure
Method 1315 – Mass Transfer Rates in Monolithic and Compacted Granular Materials using a Semi-dynamic Tank Leaching Procedure
Method 1316 – Liquid-Solid Partitioning as a Function of Liquid-Solid Ratio using a Parallel Batch Procedure
Note: Incorporation into SW-846 is ongoing; method identification numbers are subject to change
12 12
Method 1313 Overview
nchemicalanalyses LnLBLA
n samples
S2 SnnBA
S1
0.01
0.1
1
10
100
1000
2 4 6 8 10 12 14Leachate pH
Cop
per [
mg/
L]
Titration Curve and Liquid-solid Partitioning (LSP) Curve as Function of Eluate pH
13
Equilibrium Leaching Test• Parallel batch as function of pH
Test Specifications• 9 specified target pH values plus natural conditions• Size-reduced material• L/S = 10 mL/g-dry • Dilute HNO3 or NaOH• Contact time based on particle size
18-72 hours
• Reported Data Equivalents of acid/base added Eluate pH and conductivity Eluate constituent concentrations
Equilibrium Leaching Test• Percolation through loosely-packed material
Test Specifications• 5-cm diameter x 30-cm high glass column• Size-reduced material• DI water or 1 mM CaCl2 (clays, organic materials)• Upward flow to minimize channeling• Collect leachate at cumulative L/S
0.2, 0.5, 1, 1.5, 2, 4.5, 5, 9.5, 10 mL/g-dry
• Reported Data Eluate volume collected Eluate pH and conductivity Eluate constituent concentrations
Method 1314 Overviewair lock
eluant collection bottle(s)(sized for fraction volume)
Luer shut‐offvalve
eluant reservoir
end cap
end cap
1‐cm sandlayers
pump
subjectmaterial
Luer shut‐offvalve
Luer fitting
Luer fitting
N2 or Ar (optional)
Liquid-solid Partitioning (LSP) Curve as Function of L/S; Estimate of Pore Water Concentration
14
Method 1315 OverviewMass-Transfer Test• Semi-dynamic tank leach test
Test Specifications• Material forms
monolithic (all faces exposed) compacted granular (1 circular face exposed)
• DI water so that waste dictates pH• Liquid-surface area ratio (L/A) of 9±1 mL/cm2
• Refresh leaching solution at cumulative times 2, 25, 48 hrs, 7, 14, 28, 42, 49, 63 days
• Reported Data Refresh time Eluate pH and conductivity Eluate constituent concentrations
1 Sample
nanalyticalsamples
A1
L1
A2 An
L2 Ln
∆t1 ∆tn
orMonolith
CompactedGranular
n Leaching Intervals
∆t2
Flux and Cumulative Release as a Function of Leaching Time
Granular
Monolithic
0.001
0.01
0.1
1
10
100
1000
0.01 0.1 1 10 100
Cr R
elea
se [
mg/
m2 ]
Leaching Time [days]
Availability
MDL
ML
15
Method 1316 OverviewEquilibrium Leaching Test• Parallel batch as function of L/S
Test Specifications• Five specified L/S values (±0.2 mL/g-dry)
10.0, 5.0, 2.0, 1.0, 0.5 mL/g-dry• Size-reduced material• DI water (material dictates pH)• Contact time based on particle size
18-72 hours• Reported Data
Eluate L/S Eluate pH and conductivity Eluate constituent concentrations
nchemicalanalyses LnLBLA
n samples
S2 SnnBA
S1
Liquid-solid Partitioning (LSP) Curve as a Function of L/S; Estimate of Pore Water Concentration
16
0
20
40
60
80
100
120
0 2 4 6 8 10
Mol
ybde
num
[µg/
L]LS Ratio [mL/g-dry]
Data Management ToolsData Templates
• Excel Spreadsheets for Each Method Perform basic, required calculations (e.g, moisture content) Record laboratory data Archive analytical data with laboratory information
• Form the upload file to materials database
LeachXS (Leaching eXpert System) Lite• Data management, visualization and processing program• Compare Leaching Test Data
Between materials for a single constituent (e.g., As in two different CCRs) Between constituents in a single material (e.g., Ba and SO4 in cement) To default or user-defined “indicator lines” (e.g., QA limits, threshold values)
• Export leaching data to Excel spreadsheets• Freely available at http://www.vanderbilt.edu/leaching
17 17
Data Templates
18
DRAFT METHOD 1313 (Liquid‐Solid Partitioning as a Function of pH) LAB DATA
Code Description (optional) Test conducted by: Extraction InformationProject ABC Example project LS Ratio 10 [mL/g‐dry
Material XYZ Exaple material Solids Information Liquid Volume / Extraction 200 [mL]Replicate A Maximum Particle Size 0.3 [mm] Recommended Bottle Size * 250 [mL]
Minimum Dry Equivalent Mass * 20.00 [g‐dry]Date Time Solids Content (default = 1) 0.901 [g‐dry/g] Nominal Reagent Information
Test Start 1/2/xx 2:00 PM Mass of "As Tested" Material / Extraction 22.20 [g] Acid Type HNO3Test End 1/3/xx 1:45 PM Acid Normality 2.0 [meq/mL]
Required Contact Time * 23‐25 [hr] * Data based on Draft Method 1313 Table 1. Base Type NaOHBase Normality 1.0 [meq/mL]
Schedule of Acid and Base AdditionTest Position T01 T02 T03 T04 T05 T06 T07 T08 T09 B01 B02 B03 totals
"As Tested" Solid [g] (±0.05g) 22.20 22.20 22.20 22.20 22.20 22.20 22.20 22.20 22.20 no solid no solid no solid 199.8Reagent Water [mL] (±5%) 147.80 167.80 185.80 197.80 195.80 193.80 189.80 185.80 178.80 200.00 181.00 150.00 2174.2Acid Volume [mL] (±1%) ‐ ‐ ‐ ‐ 2.00 4.00 8.00 12.00 19.00 ‐ 19.00 ‐ 64.0Base Volume [mL] (±1%) 50.00 30.00 12.00 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 50.00 142.0Acid Normality [meq/mL] ‐ ‐ ‐ ‐ 2.0 2.0 2.0 2.0 2.0 ‐ 2.0 ‐Base Normality [meq/mL] 1.0 1.0 1.0 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 1.0
Target pH 13.0±0.5 12.0±0.5 10.5±0.5 natural 8.0±0.5 7.0±0.5 5.5±0.5 4.0±0.5 2.0±0.5Acid Addition [meq/g] ‐2.5 ‐1.5 ‐0.6 0 0.2 0.4 0.8 1.2 1.9 Water Acid Base
Eluate pH 12.80 12.20 10.80 9.20 7.80 5.98 4.79 3.60 2.30Eluate EC [mS/cm]
Eluate Eh [mV] Save? (enter "a" or "r" )
Notes pH out of range
pH out of range
1) Enter particle sizeand solids content
2) Enter acid/base
type & normality
3) Enter target equivalents from titration curve
4) Follow “set-up” recipe
5) Record pH, conductivity, Eh (optional)
6) Verify that final pH is in acceptable range
LeachXS Lite
19
1) Set working materials database
2) Select material tests from database
3) Choose display options
4) Check comparison of materials for a single constituent
5) Bulk export one or more constituents to an
Excel spreadsheet
LEAF Methods Validation
20
Study MaterialsCoal Combustion Fly Ash
• Collected for EPA study• Selected for validation of … Method 1313 Method 1316
Solidified Waste Analog• Created at Vanderbilt University• Blast Furnace Slag, Class C Fly
Ash, Type I/II Cement, Metal Salts• Selected for validation of … Method 1313 Method 1316 Method 1315
Contaminated Field Soil• Copper smelter site• Selected for validation of… Method 1313 Method 1316 Method 1315 Method 1314
Brass Foundry Sand• Selected for validation of … Method 1315 Method 1314
21
Method 1313 Validation
22
1
10
100
1000
0 2 4 6 8 10 12 14S
e R
ep
rod
uci
bil
ity
(%)
Target pH
CFS RSD‐REaFA RSD‐RSWA RSD‐R
ICP‐OES RSD
1
10
100
1000
0 2 4 6 8 10 12 14
As
Re
pro
du
cib
ilit
y (%
)
Target pH
CFS RSD‐REaFA RSD‐RSWA RSD‐R
ICP‐OES RSD
ML
MDL
0.01
0.1
1
10
0 2 4 6 8 10 12 14
Se
len
ium
(m
g/L
)
Target pH
M1313 EaFA MeanOverall SDBetween Lab SDWithin Lab SD
ML
MDL0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
en
ic (
mg
/L)
Target pH
MeanOverall SDBetween Lab SDWithin Lab SD
ML
MDL0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ars
en
ic (
mg
/L)
Target pH
M1313 EaFA MeanOverall SDBetween Lab SDWithin Lab SD
ML
MDL
0.01
0.1
1
10
0 2 4 6 8 10 12 14
Se
len
ium
(m
g/L
)
Target pH
M1313 CFS MeanOverall SDBetween Lab SDWithin Lab SD
Coal Combustion Fly Ash Contaminated Field Soil Reproducibility
Data ProcessingLog10-Transform of Test Output
• Method 1313 – Eluate Concentration• Method 1314 – Eluate Concentration,
Cumulative Mass Release• Method 1315 – Interval Mass Flux,
Cumulative Mass Release• Method 1316 – Eluate Concentration
Linear Interpolation and Extrapolation• Collected Data Shows Variability• Brings Data to Specified pH, L/S or Time• Consistency in Comparisons
Implications for Compliance Standards
23
ML
MDL
0.01
0.1
1
10
0 2 4 6 8 10 12 14
Sele
niu
m (
mg/
L)
pH
ML
MDL
0.01
0.1
1
10
0 2 4 6 8 10 12 14
Sele
niu
m (
mg/
L)
target pH
LEAF Method Precision
24
Method Test Output RSDr(%)
RSDR(%)
Method 1313 Eluate Concentration (average over pH range) 10 26
Method 1314 Eluate Concentration (9th fraction at L/S=10)Mass Release (cumulative to L/S=0.5)Mass Release (cumulative to L/S=10)
1375
281814
Method 1315 Interval Flux (average excluding wash-off)Mass Release (cumulative to 7-days)Mass Release (cumulative to 63-days)
1196
281923
Method 1316 Eluate Concentration (average over L/S range) 7 17
Precision Comparison(pH-dependence Tests)
25
0
20
40
60
80
100
EaFA SWA CFS EN12457-2 TCLPR
SDR
(%)
Max CFSBa @ pH 13RSDR = 300%
Max SWASb @ pH 2
RSDR = 500%
Max RSDR = 124%
Max RSDR = 118%
0
20
40
60
80
100
EaFA SWA CFS EN12457-2
RSD
r(%
)
Max SWASb @ pH 2
RSDr = 130%
Max CFSBa @ pH 13RSDr = 114%
ReproducibilityRepeatability
Method Precision• Method 1314 Eluate Concentration (2 pH 13)• EN12457 Eluate Concentration (natural pH)• TCLP Eluate Concentration (acetic acid buffer)
Precision Comparison(Percolation Tests)
26
0
20
40
60
80
100
CFS JaFS DIN19528
RSD
r(%
)
0
20
40
60
80
100
CFS JaFS DIN19528 TCLPR
SDR
(%)
Max RSDR = 139%
Max RSDR = 118%
ReproducibilityRepeatability
Method Precision• Method 1314 Cumulative Release at L/S = 10 L/kg• DIN 19528 Cumulative Release at L/S = 4.0 L/kg• TCLP Eluate Concentration (L/S = 20 L/kg)
27
EPA Database Field leachate samples for fly ash only comparison withLEAF (EPA‐600/R‐09/151) All Fly Ash 5th, 50th, 95th percentiles and maximums
Comparison of Laboratory and Field Results
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
100
3 5 7 9 11 13pH
[Ni]
(mg/
kg)
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
100
0.0001 0.001 0.01 0.1 1 10 100L/S (l/kg)
Cum
. rel
ease
, [N
i] (m
g/kg
)
Lab
Lysimeter
Field
Consistent behaviour in different scales of testing
28
29
Generic Vault Disposal System
ReinforcingSteel
Waste Form
Clean Grout(high strength)
Muli-layer Cap and Infiltration Control
Drainage Layeror Capillary Break
PerchedWater
Seepage
Infiltration
29
30
Conceptual Model• Micro-cracks develop,
increasing solid-liquid surface area
• Bridging of micro-cracks create macro-cracks
• Through-cracks develop over time, leading to convective flow
• Ultimate end state may be permeable matrix – release based on local equilibrium
Physical Integrity & Water Contact
Monolithic MatrixFlow-aroundLow interfacial areaDiffusive release
Stressed MatrixFlow-around/throughHigher interfacial areaDiffusion-convection
Spalled MatrixHigh permeabilityVery high interfacial areaEquilibrium-based release
ImpactNeed to account for the sequence of physical states and rate of changes Influences chemical reactions and constituent releaseBoth “intact” & “degraded” cases are simplistic and may not be realistic
Processes and Impacts
30
31
Needed Information• External stresses
External loads
Differential settlement
• Material strength (e.g., Young’s Modulus)
• Material pore structure
• Internal stresses
Shrinkage/dehydration
Expansive reactions within pores
Physical Integrity & Water Contact
Monolithic MatrixFlow-aroundLow interfacial areaDiffusive release
Stressed MatrixFlow-around/throughHigher interfacial areaDiffusion-convection
Spalled MatrixHigh permeabilityVery high interfacial areaEquilibrium-based release
Processes and Impacts
31
32
Moisture Transport Conceptual ModelWaste form consumes water via hydration reactionsMoisture exchange w/environment
Evaporation/condensationCapillary suctionIntermittent wetting (precipitation)Percolation (degraded matrix)
Water content determines Gaseous degradation processes (oxidation, carbonation)Constituent diffusion pathways
ImpactSpatial & temporal moisture gradientsDiffusivities are not constant over moisture regimeFractional saturation
Increases the importance of gas phase transport & reactionsDecreases rate of liquid phase transport
Full SaturationCapillary Saturation
(a)Continuous LiquidDiscontinuous Gas
Transition Zone (b)Continuous Liquid Continuous Gas
Insular Saturation (c)Discontinuous LiquidContinuous Gas
Completely Dry
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
0 Saturation 1insular
saturationcapillary
saturation
Diffusivity
D/D
0
1
0GasLiquid
(a)
(c)
(b)
Processes and Impacts
32
33
Moisture TransportFull SaturationCapillary Saturation
Continuous LiquidDiscontinuous Gas
Transition ZoneContinuous Liquid Continuous Gas
Insular SaturationDiscontinuous LiquidContinuous Gas
Completely Dry
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH=100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
Hamb
RH<100%
RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
RH < 100%RH < 100%
Hamb
Needed InformationWater producing & water consuming reactions
Water retention curves (capillarity)
Relative humidity-material saturation equilibrium
Drying rates
Permeability (water)
Boundary conditions
Episodic infiltration
Relative humidity
0 Saturation 1insular
saturationcapillary
saturation
Diffusivity
D/D
0
1
0GasLiquid
Processes and Impacts
33
34
OxidationRates and Extent
Air Water Ratio (A/W)
DO2 [cm2/s] 0.21 0.000019 1.1E+04
Conc of O2 [mole/L] 8.9E-03 2.6E-04 1.4E+01
(1) Wilke and Chang, 1955(2) www.swbic.org/education/ env-engr/gastransfer/gastransf.html
oxidation front
O2
occludedpore
Conceptual ModelWaste form pores – two phase system of gas and liquid; depends on moisture content (saturation)O2 transport via gaseous diffusion may be important depending on saturation.Oxidation may lead to change in leaching behavior
Increased Tc-99 release; other redox sensitive constituents
ImpactGas phase transport must be considered
Flux of O2 (gas) ~105 > liquid phase flux
Processes and Impacts
34
35
OxidationRates and Extent
oxidation front
O2
occludedpore
Needed InformationReducing capacity & redox titrationMoisture statusGas phase diffusivity f(saturation)Liquid phase diffusivity f(saturation)Boundary conditions
Processes and Impacts
35
36
Carbonation
CO2
carbonation front
Conceptual ModelCO3
-2 + Ca+2 → CaCO3 (s)Gas phase diffusion of CO2Liquid phase diffusion of HCO3
-
Pore water pH decreased
Alters solubility of constituents (increase or decrease depending on species).
CarbonationExpansive precipitate – internal stress (cracking)Pore blocking – increases diffusional resistance (decreases oxidation, release rates).Extent and pore effects depend on waste form alkalinity and saturation
0.0001
0.001
0.01
0.1
1
10
100
2 4 6 8 10 12 14Leachate pH
As
[mg/
L]
NoncarbonatedCarbonated
ImpactPotential for speciation changes (e.g., As)Impact on sorption sitesPore structure changesMay have either positive (e.g., pore capping) or detrimental (i.e., increased solubility) impacts
Processes and Impacts
36
37
Conceptual Model• Transport described by moving
dissolution fronts• Precipitation/reaction processes near
external boundaries may significantly impact release (+ or -)
• Dissolution/diffusion of Ca(OH)2 and CSH control pore water pH pH gradients alter trace species
release• SO4 leaching from waste into vault
attacking concrete physical structure.• Source of SO4 may be waste or
external environmentImpact• Mass transport estimates may not
reflect the dynamic chemistry and mineralogy of the waste form.
• Release rates and extents mechanistically different from simplified assumptions, effecting predictability.
Leaching of Major Constituents
VaultWall
WasteForm
(high SO4)
leac
han
t
Ca moving front
effHD
CCa=CCa,0SCa=Sp,0
SSO4=SSO4,0=0
Ca(OH)2dissolution
pH
CCa=CCaSCa=0>0
effCaD
SO4 moving front
effSO4D
SO4 moving front
effSO4D
Sulfate species precipitate in cracks and large pores in vault concrete.
Processes and Impacts
37
38
Conceptual Model• Release based on coupled
chemistry and mass transport.• Release dependent on:
Moisture conditions pH gradients Redox chemistry Boundary layer formation
Impact• Performance assessments may
over- or under-predict release
Leaching of Trace Constituents
leac
han
t
Ca moving front
effHD
CCa=CCa,0SCa=Sp,0SMe=SMe,0=0
Ca(OH)2dissolutionpH
Me moving front
effHDeffMeD
CCa=CCaSCa=0
CMe=f{pH}
effCaD
AMD - Selenium
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0.01 0.1 1 10 100 1000Mean Interval [days]
Mea
n Fl
ux [m
g/m
2s]
AMD-AAMD-BMean
Simple Diffusion
Model predicts flux 102
greater than measured
after ~1 year
Processes and Impacts
38
39
Needed Information• pH dependent equilibrium
• Column test Pore water LS evolution
• Analysis of pH, EC, Eh Full suite of cations and
anions TOC, TIC, DOC, DIC
• Boundary Conditions!
Leaching of Major &Trace Constituents
leac
han
t
Ca moving front
effHD
CCa=CCa,0SCa=Sp,0SMe=SMe,0=0
Ca(OH)2dissolutionpH
Me moving front
effHDeffMeD
CCa=CCaSCa=0
CMe=f{pH}
effCaD
Processes and Impacts
39
A Possible Approach to Beneficial Use Screening LevelsStep 1: Select use application (includes engineering specifications)
Step 2: Select corresponding pH domain and perform Method 1313
Step 3: (a) Select corresponding fate and transport values(i) CCR fraction in engineered use (fCCR);(ii) Across‐the‐board engineered attenuation factor (EAF);(iii) Default constituent‐specific dilution attenuation factors (DAFs);(iv) Human or ecological benchmarks (federal and/or state); and
(b) Calculate screening levels
Step 4: Compare maximum LEAF result to screening levelsUse is protective of human health and the environment? (i.e., LEAF < screening level?)
Proceed with use
Conduct site‐specific IWEM modeling with
Method 1313 data from Step 2 or Method 1315
data (if available)
Can use application and/or engineering specifications be modified?Yes
No
Choose
Pass FailInappropriate for this use
Perform Method(s) 1314/1316 or 1315
Yes
No
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Supporting DocumentationH.A. van der Sloot, D.S. Kosson, A.C. Garrabrants and J. Arnold The Impact of Coal Combustion Fly Ash Used as a Supplemental Cementitious Material on the Leaching of Constituents from Cements and Concretes, draft report in administrative review (submitted Nov 2011).
A.C. Garrabrants, D.S. Kosson, L. Stefanski, R. DeLapp, P.F.A.B. Seignette, H.A. van der Sloot, P. Kariher and M. Baldwin Interlaboratory Validation of the Leaching Environmental Assessment Framework (LEAF) Leaching Tests for Inclusion into SW-846: Method 1313 and Method 1316, draft report in administrative review (submitted Nov 2011)
A.C. Garrabrants, D.S. Kosson, H.A. van der Sloot, F. Sanchez, and O. Hjelmar (2010) Background Information for the Leaching Environmental Assessment Framework Test Methods, EPA/600/R-10/170, December 2010; http://www.epa.gov/nrmrl/pubs/600r10170/600r10170.pdf.S.A. Thorneloe, D.S. Kosson, F. Sanchez, A.C. Garrabrants, and G. Helms (2010) “Evaluating the Fate of Metals in Air Pollution Control Residues from Coal-Fired Power Plants,” Environmental Science & Technology, 44(19), 7351-7356, http://pubs.acs.org/doi/pdfplus/10.1021/es1016558.
D. Kosson, F. Sanchez, P. Kariher, L. Turner, D. Delapp, P. Seignette and S. Thorneloe (2009) Characterization of Coal Combustion Residues from Electric Utilities - Leaching and Characterization Data, EPA-600/R-09/151, December 2009; http://www.epa.gov/nrmrl/pubs/600r09151/600r09151.html.
F. Sanchez, D. Kosson, R. Keeney, R. DeLapp, L. Turner, P. Kariher, and S. Thorneloe (2008) Characterization of Coal Combustion Residues from Electric Utilities Using Wet Scrubbers for Multi-Pollutant Control, EPA-600/R-08/077, July 2008; www.epa.gov/nrmrl/pubs/600r08077/600r08077.pdf.
F. Sanchez, R. Keeney, D. Kosson, R. Delapp and S. Thorneloe (2006) Characterization of Mercury-Enriched Coal Combustion Residues from Electric Utilities Using Enhanced Sorbents for Mercury Control, EPA-600/R-06/008, February 2006; http://www.epa.gov/ORD/NRMRL/pubs/600r06008/600r06008.pdf.
D.S. Kosson, H.A. van der Sloot, F. Sanchez, and A.C. Garrabrants (2002) “An integrated framework for evaluating leaching in waste management and utilization of secondary materials,” Environmental Engineering Science, 19(3), 159-204.
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Benefits to Use of LEAF• Provides standardization in leach testing and comparability in
resulting data for use across different materials and management scenarios
• Analytical work complete for all four methods as part of the interlaboratory validation for inclusion into SW-846
• Comparable methods being used abroad enable more robust data sets that provide better characterization across material types and management scenarios
• Provides data needed for binning materials into categories that enable more efficient beneficial use decisions (no or less stringent testing required depending upon the leaching behavior of the material)
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Benefits to Use of LEAF• Industry that generates CCRs and other industrial by-products has
clarity in what is required and access to labs across the U.S.
• Provides objective and independent analysis of claims made by producers or technologies
• LEAF allows one to understand the mechanistic behavior of materials across a range of management scenarios across long terms (can not use snap shot approach that doesn’t consider future environmental conditions)
• Provides robust source term for risk assessment by considering physical and chemical factors that control leaching behavior over time
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ConclusionsThe LEAF test methods
• Can be used to evaluate leaching behavior of a wide range of materials using a tiered approach that considers the effect of leaching on pH, liquid-to-solid ratio, and physical form
• Prepared for inclusion into SW846 – EPA’s compendium of test methods for waste and material characterization
• Supporting software (LeachXS-Lite) available for data entry, analysis, visualization, and reporting
• Demonstrated relevance for assessing release behavior under field conditions for use and disposal scenarios
Current efforts • Complete interlaboratory validation for Method 1314 and Method 1315• Provide information on
Relationship between the LEAF testing results and field leaching Application of LEAF test methods for evaluating CCR use and disposal
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AcknowledgementsParticipating Laboratories
• Oak Ridge National Lab• Pacific Northwest National Lab• Savannah River National Lab• ARCADIS-US, Inc.• Test America, Inc.• URS Corporation, Inc.
• Ohio State University• University of Wisconsin (Madison)• Missouri Univ. of Science & Tech.• Vanderbilt University• ECN• DHI
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Funding and Support• U.S. EPA, Office of Research and Development• U.S. EPA, Office of Resource Conservation and Recovery• U.S. DOE, Office of Environmental Management • Consortium for Risk Evaluation with Stakeholder Participation (CRESP)