David S. Kosson1 and Hans A. van der Sloot2 1Vanderbilt University
2Hans van der Sloot Consultancy
Laboratory-to-Field Relationships and Recommendations for Leaching Assessment Using the Leaching Environmental Assessment Framework (LEAF)
May 29, 2014
A Decision Support System for Beneficial Use and Disposal Decisions in the United States and Internationally…
• Four leaching test 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 scenarios &
… provide a material & scenario-specific “source-term”. More information at http://www.vanderbilt.edu/leaching
2
Objectives for Laboratory-to-Field Evaluation (EPA-600/R-14/061, 2014)
Evaluate applicability and limitations of using LEAF laboratory
leaching tests for estimating leaching of COPCs from a broad range
of materials under field disposal and beneficial use scenarios.
• Compare testing “as produced” and “field aged” materials using
LEAF methods, and results from field leaching studies.
• Interpret LEAF leaching data within the context of a defined
conceptual model for leaching
• Use chemical speciation modeling as a tool to facilitate evaluation
of scenarios beyond the conditions of common laboratory testing
Provide recommendations on the selection and use of LEAF testing
for different types of materials or wastes when evaluating disposal or
use scenarios.
3
Materials and Cases Evaluated
Coal Fly Ash • Multiple Landfills (US)
• Large-scale Lysimeters (DK)
• Roadbase & Embankments (NL)
Fixated Scrubber Sludge • coal fly ash + FGD scrubber sludge + lime
• Landfill (US)
Municipal Solid Waste Incinerator (MSWI)
Bottom Ash • Landfill (DK)
• Roadbase (SE)
4
Materials and Cases Evaluated
Predominantly Inorganic Waste Mixture • Lysimeters and Landfill (NL)
Municipal Solid Waste • Bioreactor Landfill (leachate recirculation, NL)
• Multiple Landfills (multiple countries)
Cement-Stabilized MSWI Fly Ash • Pilot Test Cells & Landfill (NL)
Portland Cement Mortars and Concrete • Recycled Concrete Used in Roadway (NO)
• Field Samples (multiple countries)
5
LEAF Leaching Methods*
Method 1313 – Liquid-Solid Partitioning as a Function of Eluate pH
using a Parallel Batch Procedure (pH dependence)
Method 1314 – Liquid-Solid Partitioning as a Function of Liquid-
Solid Ratio (L/S) using an Up-flow Percolation
Column Procedure (percolation column)
Method 1315 – Mass Transfer Rates in Monolithic and Compacted
Granular Materials using a Semi-dynamic Tank
Leaching Procedure (mass transport)
Method 1316 – Liquid-Solid Partitioning as a Function of Liquid-
Solid Ratio using a Parallel Batch Procedure
(L/S dependence)
*Posting to USEPA SW-846 as “New Methods” completed August 2013
6 6
LEAF and EU Methods
WASCON, Gothenburg, Sweden
Parameter LEAF EU Method EU Applications
pH-
dependence
Method
1313
PrEN 14429
PrEN 14997
ISO/TS 21268-4
Waste, mining waste, construction
Waste, mining waste
Soil, sediments, compost, sludge
Percolation Method
1314
PrEN 14405
FprCENTS 16637-3
NEN 7373 (NL)
ISO/TS 21268-3
Waste, mining waste
Construction products
Waste, construction products
Soil, sediments, compost, sludge
Mass
Transport
Method
1315
PrEN 15863
FprCENTS 16637-2
NEN 7375 (NL)
NEN 7347 (NL)
Monolithic waste
Monolithic & granular construction
Monolithic waste
Granular waste and construction
L/S
dependence
Method
1316
EN12457-2 Waste
7
Conceptual Model for Leaching
Primary factors that effect leaching
Relationships between results from multiple leaching tests
Definition of field scenarios • Range of applicable field conditions (pH, pE)
• Useful simplified source-term models & chemical speciation models
Relationships between leaching test results & field
conditions • Screening assessments
• Sensitivity analysis
• Site-specific evaluations
• Regional probabilistic evaluations
8
Factors Influencing Material Leaching
Leaching Factors Equilibrium or Mass Transport
pH
Liquid-to-solid ratio
Redox conditions
Rates of mass transport (flux)
Physical Factors Hydraulic
conductivity (water
contact mode) Physical Degradation
(Erosion, Cracking)
Moisture Transport
Water,
Acids,
Chelants,
DOC
Leachant Composition
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1,000
6 8 10 12 14
pH
Me
tal (m
mo
l/L
)
Pb
Zn
Cd Cu Ni
Co
Chemical Reactions (Sulfate, Oxygen, Carbon Dioxide)
1.E-12
1.E-11
1.E-10
1.E-09
0.01 0.1 1 10 100 1000
Leaching Time (days)
Flu
x (m
g/m
2 s
)
9
pH-dependent Leaching • Liquid-solid partitioning ≈ chemical equilibrium
• Interpreted with respect to relevant pH range for a material
• Available Content = Maximum leaching (mg/kg) over 2 ≤ pH ≤ 13
Relevant pH Range
Should Consider
• Natural pH of the material (no acid or base addition)
• Life cycle pH (fresh to end-of-life)
• Blending of materials
• External sources (leachant composition)
Relevant pH Range
10
0.1
1
10
100
1000
10000
0 2 4 6 8 10 12 14
Le
ach
ed
Qu
an
tity
(m
g/k
g)
pH
TOTAL CONTENT
AVAILABLE CONTENT
MEASURED RELEASE(cationic metal)
min
eral
ogy
solu
tio
n c
hem
istr
y
rem
iner
aliz
atio
nWasteSludge
Contaminated Soil
Natural Soil
Compost&
Sediment
Stabilized Wasteand Concrete
What about TCLP and SPLP?
Acetic Acid • TCLP solution is
not a relevant leaching condition
Liquid-to-Solid Ratio (mL/g) • TCLP/SPLP at
L/S 20
• M1313 at L/S 10
• M1316 at L/S 0.5-10
Final pH • TCLP and SPLP
recording final pH is not required
ML
MDL
0.0001
0.001
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ch
rom
ium
(m
g/L)
pH
TC Limit
TCLP
SPLP
Stabilized Waste
11
ML
MDL
0.0001
0.001
0.01
0.1
1
10
100
1000
0 2 4 6 8 10 12 14
Ars
en
ic (
mg
/L)
pH
TC Limit
SPLPTCLP
M1316Stabilized Waste
ML
MDL
0.0001
0.001
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Ch
rom
ium
(m
g/L)
pH
TC Limit
SPLP
TCLP
ML
MDL
0.0001
0.001
0.01
0.1
1
10
100
1000
0 2 4 6 8 10 12 14
Ars
en
ic (
mg
/L)
pH
TC LimitTCLP
SPLP
M1316
Smelter Soil
Smelter Soil
Comparison of
Treatment Processes
Min-Max
0.3-1.7% Min-Max
0.4-0.5%
Min-Max
0.2-3.2%
0
5
10
15
20
25
30
Untreat. Am soil
Untreat. Eu soil
Vendor 3
Vendor 4
Vendor 2
Hg
Re
lea
se
[%
]
Min-Max
0.0003-7.7%
Min-Max
0.001-29.6%
Percolation scenario
0.04%
0.002% 0
0.05
0.1
0.15
0.2
0.25
0.3
Untreat. Am soil
Untreat. Eu soil
Vendor 3
Vendor 4
Vendor 2
Hg
Re
lea
se
[%
]
0.2%
0.04%
0.09%
TCLP
0.4% 0.4%
0.004% 0
0.2
0.4
0.6
0.8
1
1.2
1.4
Untreat. Am soil
Untreat. Eu soil
Vendor 3
Vendor 4
Vendor 2
Hg
Re
lea
se
[%
]
1.2%
0.2%
Mass transfer scenario
Mercury-contaminated Soil • 2 untreated soils (Am, Eu)
• 3 treated Am soils S/S: Vendors 2,3
SPC: Vendor 4
12
Effects of Redox Conditions (pH+pE)
13
FeS
Fe3+
Ferrihydrite (HFO)Fe2+
FeSO4
pH+pE=13
pH+pE=4
pH+pE=5.5
Fe2[OH]24+ O2
H2
Pyrite (FeS2)
pE
pH1.0
19
.0-1
2.0
13.07.0
pH+pE=20.75
pH+pE=0
Cr(OH)3
pH+pE=13
pH+pE=4
pH+pE=5.5Cr(OH)2+
Cr3+
CrO42-
Cr2O72-
HCrO4-
CrO2-
O2
H2
pH+pE=20.75
pH+pE=0
pE
pH1.0
19
.0-1
2.0
13.07.0
Iron Chromium
Assessment Approach
C
B
A
B
C
Constituent Release from Application Scenario
Constituent Conc./Release at Point of Compliance
DAF or Model Scenario
Use as Source Term
Material Leaching in Context of Application
A
road base
14
Leaching represents the “source term” for
contaminant release into the near-field environment.
LeachXS™
Test Methods Support
Data Management
Statistical Analysis
Quality Control
Chemical Speciation
Scenario Modeling
LeachXS Lite
developed as free
simplified version for
data management in
support of LEAF
Methods use
15
Multiple, Flexible Base Models Available in
LeachXS/ORCHESTRA
16
• Select general field or laboratory scenario to model
• Select from existing reference materials or customize materials
• Select interface conditions (e.g., fixed volume, continuous flow or intermittent flow/ exchange & solutions (e.g., “Hanford infiltration”)
• Resulting model transferable to GoldSIM simulations
Case 9 – Stabilized MSWI Fly Ash
Sustainable Landfill Project
• Cement stabilized monolithic wasteform
• S/S plant operating in Maasvlakte, The Netherlands
Project Goals
• Evaluate test methods for assessing long-term release behavior
• Functionality of current operational practices
• Development of a quality control procedure
• Chemical reaction/transport modeling (i.e., reactive transport modeling) to understand release controlling processes (chemical and physical)
• Evaluation of field leachate and testing at laboratory, pilot and field scale to improve prediction capabilities of long-term release
17
Sustainable Landfill Project (The Netherlands) http://www.duurzaamstorten.nl/wawcs0122289/Home-page.html
Pilot Experiment Preparation A&G, Maasvlakte, The Netherlands
18
Pilot Experiment (front view)
Geotextile – provides
vertical drainage pathway
Soil Layer - provides
buffering against high pH
and metal binding
19 19
Weathered Stabilized Waste
pH Profile measured after 4-yrs of atmospheric exposure
Weathered layer • Carbonation effects
Neutralization to pH 8-9
CaOH2 converted to CaCO3
• Plant growth
-30
-25
-20
-15
-10
-5
0
8 9 10 11 12
pH
De
pth
(c
m)
20
pH Development in Solidified Waste
21
-60
-50
-40
-30
-20
-10
0
8 9 10 11 12
-60
-50
-40
-30
-20
-10
0
8 9 10 11 12 13pH
Dep
th (
cm
)
Covered Cell (4 yrs)
Exposed (1 week)
Exposed (4 months)
Exposed (1.3 yrs)
Exposed (4 yrs)
Integration of test results from lab, lysimeter, core sample leaching, field percolate and modelling
22
[Ba+2]
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1 2 3 4 5 6 7 8 9 10 11 12 13 14
[Ca+2]
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Co
nc
en
tra
tio
n (
mo
l/l)
[Mg+2]
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1 2 3 4 5 6 7 8 9 10 11 12 13 14
[Zn+2] 1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH
Co
nc
en
tra
tio
n (
mo
l/l)
[MoO4-2]
1.0E-10
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH
[K+]
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH
Red dots: pH dependence test TS14429 fresh Blue square: percolation test TS14405 fresh Purple triangle: Aged core material exposed TS14429 Green diamond: Aged core material sealed TS 14429 Open triangle: Core samples EN 12457-2 Open diamond: Core samples EN 12457-2
Red line: model prediction fresh
Purple broken line: model exposed cell
Green dotted line: modeling sealed cell
22
January 27, 2014 LEAF Short Course 23
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
1 3 5 7 9 11 13
Co
nce
ntr
ati
on
(m
g/L)
pH
pH dependent concentration of Pb
0.0001
0.001
0.01
0.1
1
10
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Co
nce
ntr
ati
on
(m
g/L)
14
Cu as function of pH
Cu(OH)2
Tenorite
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Co
nce
ntr
ati
on
(m
ol/
l)
pH
Partitioning liquid-solid, Cu
Free DOC-bound POM-bound
FeOxide Cu[OH]2[s]
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
1 2 3 4 5 6 7 8 9 10 11 12 13
Co
nce
ntr
ati
on
(m
g/L)
pH
Pb as function of pH
Pb(OH)21.0E-10
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Co
nce
ntr
ati
on
(m
ol/
l)
pH
Partitioning liquid-solid, Pb
Free DOC-bound POM-bound
FeOxide Corkite Pb[OH]2[C]
Pb2V2O7 Pb3[VO4]2 PbMoO4[c]
0.0001
0.001
0.01
0.1
1
10
100
1 3 5 7 9 11 13
Co
nce
ntr
ati
on
(m
g/L)
pH
pH dependent concentration of Cu
0.0001
1000
2 4 6 8 10 12 14
Co
nce
ntr
ati
on
(m
g/L)
pH
pH dependent concentration of ZnCore sample composite Cell B (4 yrs) Individual core sample Cell B (L/S=10; 4 yrs)
Core sample composite Cell C (covered; 4 yrs) Individual core sample Cell C (L/S=10; 4 yrs)
Leachate Cell B Leachate Cell C
Leachate Cell D Individual core sample Cell D (L/S=10; 4 yrs)
Fresh stabilised waste NL Individual core samples full scale monofill (L/S=10; 10 yrs)
Leachate full scale stabilised waste monofill
Case 1 - Coal Fly Ash - Landfill Disposal
Compared pH dependent relationships for field leachates and pore
water to laboratory test results from a wide range of samples.
Results
Applicable field leachate pH domain: 6 - 13.
Testing a wide range of samples within a class of materials can be
used to define the anticipated field characteristic leaching
behavior (pH dependent leaching and range of field of
concentrations, or bandwidth).
Can be considered a conservative estimate of the upper limit of
field concentrations, but laboratory concentrations of highly
soluble constituents must be adjusted based on a correction
factor between laboratory L/S and field pore water L/S.
Field leachate concentrations lower than anticipated may be a
consequence of either (i) reducing conditions (e.g., Cr, Se),
(ii) common ion effects (e.g., Ba), (iii) preferential flow.
24
Case 1 - Comparison of field leachates to pH-dependent leaching for Mg and V release from CCRs
LEAF Short Course 25
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
0 2 4 6 8 10 12 14
Ma
gn
esiu
m (
mg
/L)
pH
0.0001
0.001
0.01
0.1
1
10
100
0 2 4 6 8 10 12 14
Va
na
diu
m (
mg
/L)
pH
0.001
10
0 2 4 6 8 10 12 14Ars
en
ic
(mg/
L)
pH
EPRI-38575 Core EPRI-38575 Leachate EPRI-38575 Lysimeter
EPRI-49003B Leachate EPRI-50207 Lysimeter EPRI-50207 Well Leachate
EPA-14093 Well Leachate EPA-23214 Leachate Collection EPA-27413 Well Leachate
EPA-50211 Leachate Collection EPA-50212 Leachate Collection EPA-50213 Lysimeter
EPA-SX-BAG Porewater EPA Lab - All CFAs - 5th, 95th % EPA Lab - All CFAs - Median
Case 2 – Coal Fly Ash - Field Lysimeters
Compared large-scale lysimeters (7 years) to percolation column tests.
Results
Applicable field pH domain: 11 – 12.8
Percolation column testing can provide a good estimate of initial
leachate concentrations under field conditions.
Percolation column testing provides a good approximation of the
evolution of leaching profiles as a function of L/S that would be
expected under field conditions in the absence of preferential flow
and establishment of strong reducing conditions.
January 27, 2014 LEAF Short Course 26
Case 2 – Coal Fly Ash - Field Lysimeters
and Laboratory Column Testing
LEAF Short Course 27
0,001
0,01
0,1
1
0,001 0,01 0,1 1 10
Elu
ate
co
ncen
trati
on
(m
g/L
)
L/S (L/kg)
As
0,01
0,1
1
10
100
0,001 0,01 0,1 1 10
Elu
ate
co
ncen
trati
on
(m
g/L
)
L/S (L/kg)
Cr
0,01
0,1
1
10
100
0,001 0,01 0,1 1 10
Elu
ate
co
ncen
trati
on
(m
g/L
)
L/S (L/kg)
Mo
10
11
12
13
0,001 0,01 0,1 1 10
pH
L/S (L/kg)
pH
Lysimeter-4
Lysimeter-9
Lysimeter-14
Column-4
1
10
100
1000
10000
0,001 0,01 0,1 1 10
Elu
ate
co
ncen
trati
on
(m
g/L
)
L/S (L/kg)
Na
Lysimeter-4
Lysimeter-9
Lysimeter-14
Column-4
Case 3 – Fixated Scrubber Sludge Landfill
Compared field leaching, field pore water samples, and laboratory
leaching test results on landfill core samples, and on fresh “as
disposed” material
Results
Applicable field pH domain: 6 – 9.5
Carbonation during field aging can have a significant impact on the pH
dependent leaching behavior of periodic table Group II elements
(i.e., Ca, Sr) and some trace elements (i.e., arsenic).
Water samples (i.e., landfill porewater) are more susceptible to
carbonation because of air contact and low buffering capacity.
Higher concentrations of highly soluble species (i.e., K, Na, Cl) can be
anticipated in porewater compared to laboratory testing. Elevated
concentrations can be readily estimated based (L/S effect).
28
Case 3 – FSSL – Effect of L/S
LEAF Short Course 29
1
10
100
1000
0 2 4 6 8 10 12 14
Po
tassiu
m (
mg
/L)
pH
1
10
100
1000
10000
0 2 4 6 8 10 12 14
So
diu
m (
mg
/L)
pH
10
100
1000
10000
0.1 1 10
Po
tassiu
m (
mg
/L)
L/S (L/kg)
L/S=10 L/kg; Conc=40 mg/L
L/S=0.5 L/kg;Conc=20*40 mg/L=800 mg/L
10
100
1000
10000
0.1 1 10
So
diu
m (
mg
/L)
L/S (L/kg)
L/S=0.5 L/kg;Conc=20*30 mg/L=600 mg/L
L/S=10 L/kg; Conc=30 mg/L
Case 4 – Coal Fly Ash Road base and Embankment
Compared the results of field leaching over 2 years from a road base
and embankment to percolation column results.
Results
Combined use of pH dependent leaching and percolation column
leaching in combination with chemical speciation simulations to
understand field performance.
Reducing conditions and carbonation impact leaching of major species
(e.g., Ca, Sr) and oxyanions (e.g., Cr).
Percolation column testing provided a realistic estimate of the upper
bound concentration for leaching of COPCs.
An initial delay in the field before peak leaching concentrations were
observed was attributed to the mass transport delay and attenuation
associated with drainage materials
30
Case 4 – Coal Fly Ash Road base and Embankment
LEAF Short Course 31
Road Base
Embankment
Case 4 – CFA Road Base and Embankment
Effect of Redox Conditions
LEAF Short Course 32
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.01 0.1 1 10 100
Ch
rom
ium
(m
ol/
L)
L/S (L/kg)
Coal Fly Ash; pH+pE=15
Percolation Column
[CrO4-2] (continuous)
[CrO4-2] (fraction average)
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.01 0.1 1 10 100
Ch
rom
ium
(m
ol/
L)
L/S (L/kg)
Coal Fly Ash; pH+pE = 12.8
Percolation Column
[CrO4-2] (continuous)
[CrO4-2] (fraction average)
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.01 0.1 1 10 100
Ch
rom
ium
(m
ol/
L)
L/S (L/kg)
Coal Fly Ash; pH+pE = 12
Coal fly ash NL (column)
[CrO4-2] (continuous)
[CrO4-2] (fraction average)
Embankment
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.00 3.33 6.67 10.00 13.33
Ch
rom
ium
(m
ol/
L)
Depth (m)
Partitioning Profile; L/S=1.3, pH+pE=15
Free
POM-bound
FeOxide
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.00 3.33 6.67 10.00 13.33
Ch
rom
ium
(m
ol/
L)
Depth (m)
Partitioning Profile; L/S=1.3, pH+pE=12.8
Free
POM-bound
FeOxide
Cr(OH)3 [A]
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0.00 3.33 6.67 10.00 13.33
Ch
rom
ium
(m
ol/
L)
Depth (m)
Partioning Profile; L/S=1.3, pH+pE = 12
Free
POM-bound
FeOxide
Cr(OH)3 [A]
Conclusions
LEAF can be used to provide a reasonably conservative (upper-
bound) source-term for a wide range of materials in use and disposal
scenarios.
Interpretation of the leaching test results should be in the context of
the controlling physical and chemical mechanisms of the field
scenario.
Leaching test results should be evaluated with consideration of the
potential for changes in leaching conditions
• pE changes (oxidation of reduced materials, reduction of oxidized material)
• Carbonation
• DOC from external sources
Chemical speciation modeling can be used to consider field
conditions beyond the domain of laboratory test conditions.
33
Selecting Methods and Data Use
Acceptable
Impact?
Treatment
Option
Mgmt
Scenario
Fundamental leaching properties
Equilibrium data
Site information*
Assessment model
Fundamental leaching properties
Availability data, Equilibrium
data, Mass Transfer data
Site information*
Assessment model
Material
Yes
Release Estimate
Exit Yes No
Flow - around Percolation
* Site - specific information or Default scenarios
Acceptable
Impact?
Treatment
Option
Mgmt
Scenario
Fundamental leaching properties
Equilibrium data
Site information*
Assessment model
Fundamental leaching properties
Availability data, Equilibrium
data, Mass Transfer data
Site information*
Assessment model
Material
Yes
Release Estimate
Exit Yes No
Flow - around Percolation
Acceptable
Impact?
Treatment
Option
Mgmt
Scenario
Fundamental leaching properties
Availability, Equilibrium data,
Site information*
Assessment model
Fundamental leaching properties
Availability data, Equilibrium
data, Mass Transfer data
Site information*
Assessment model
Material Material
Yes
Release Estimate
Exit Yes No
Flow - around Percolation
* Site - specific information or Default scenarios
34
Conclusions
The leaching source term should be used in conjunction with
additional assessment steps that include consideration of
• the location that serves as the basis for exposure assessment
(e.g., point of compliance),
• dilution and attenuation from the point of release to the point of
compliance, and
• appropriate exposure scenarios or reference thresholds
(e.g., human health or ecological thresholds).
Field testing of new use or disposal scenarios or new classes of
materials to be used or disposed in new ways is very beneficial to
understanding the factors that control leaching for the specific
scenario.
LEAF Short Course 35
Conclusions
Individual sources of similar materials based on process origin and
leaching behavior can be grouped into material classes for
assessment purposes
Accumulation of LEAF testing data for a range of materials and over
time can provide useful estimates of uncertainty and variability
associated with material classes.
Creation of one or more databases containing leaching data used in
regulatory decision making and monitoring can facilitate efficient use
of leaching data in future assessments
• More robust assessments
• Reduced testing and evaluation costs
LEAF Short Course 36
Conclusions
Single point leaching tests and other common leaching assessment
approaches cannot provided needed insights into the expected
leaching performance of materials under the range of expected field
conditions.
The combination of results from pH-dependent leaching tests and
percolation column tests (or monolith leach tests) can be used to
provide reliably conservative estimates of field leachate
concentrations under both disposal and use scenarios.
LEAF Short Course 37
Vanderbilt University research team and collaborators:
D.S. Kosson (USA lead)1, A.C. Garrabrants1*, H.A. van der Sloot2 (EU Lead),
R. DeLapp1, D. DeLapp1, S. Sarkar1, K. Brown1, P. Seignette3,
O. Hjelmar4, J.C.L. Meeussen3
EPA development team and collaborators:
Susan Thorneloe5 (Lead), Mark Baldwin6, Richard Benware6,
Greg Helms6, Jason Mills6, Tim Taylor6, Peter Kariher7
1 Vanderbilt University, Nashville, TN *CH2M-Hill as of Jan. 2014 2 Hans van der Sloot Consultancy, Langedijk, The Netherlands 3 Energy Research Centre of The Netherlands, Petten, The Netherlands 4 DHI, Hørsolm, Denmark 5 U.S. EPA Office of Research and Development, RTP, NC 6 U.S. EPA Office of Resource Conservation & Recovery, Washington DC 7 ARCADIS-US, Inc., RTP, NC
Acknowledgements
38
Thank you
for your attention and invitation to
participate in this workshop!
Questions?
39
40
Additional Supporting Information
Method 1313 Overview
n chemical analyses
Ln LB LA
n samples
S2 Sn n B A
S1
0.01
0.1
1
10
100
1000
2 4 6 8 10 12 14 Leachate pH
Co
pp
er
[mg/
L]
Titration Curve and Liquid-solid Partitioning (LSP) Curve as Function of Eluate pH
41
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 KOH
• 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 Overview air lock
eluant collection bottle(s) (sized for fraction volume)
Luer shut-off valve
eluant reservoir
end cap
end cap
1-cm sand
layers
pump
subject material
Luer shut-off valve
Luer fitting
Luer fitting N2 or Ar
(optional)
Liquid-solid Partitioning (LSP) Curve as Function of L/S; Estimate of Pore Water Concentration
42
Method 1315 Overview
Mass-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
n
analytical
samples
A1
L1
A2 An
L2 Ln
Δt1 Δtn
or
Monolith
Compacted Granular
n Leaching Intervals
Δt2
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
Rele
ase [
mg
/m2]
Leaching Time [days]
Availability
MDL
ML
43
Method 1316 Overview
Equilibrium Leaching Test
• Parallel batch as function of L/S
Test Specifications
• Five specified L/S values (±0.2 mL/g-dry) 10, 5, 2, 1, 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
n chemical analyses
Ln LB LA
n samples
S2 Sn n B A
S1
Liquid-solid Partitioning (LSP) Curve as a Function of L/S; Estimate of Pore Water Concentration
44
0
20
40
60
80
100
120
0 2 4 6 8 10
Mo
lyb
den
um
[µ
g/L
]
LS Ratio [mL/g-dry]
Tiered Approach in Testing
Goal: Efficient use of testing to
minimize cost
• Different users and evaluation
steps have different information
needs.
• Once the release characteristics
of a product type or class are
established, simpler screening or
conformity testing will suffice for
critical parameters.
• Testing frequency based on the risk of exceeding limit values.
• Using a limited part of the full characterization testing for screening
or compliance simplifies evaluation
45
Quality Control/ Compliance
Initial Characterization
Frequency of testing
Level of detail
Monolith Diffusion
46
• Laboratory and field simulations
• Variable water contacting sequence, chemistry
• Saturated or unsaturated
• Carbonation, oxidation ingress
• Sulfate attack with leaching
Percolation with Mobile-Immobile Zones
47
• Laboratory and field simulations
• Variable water flow rate, chemistry
• Effects of preferential flow
Percolation with Radial Diffusion
48
• Laboratory and field simulations
• Cracked materials or packed beds
• Effects of preferential flow
• Variable water flow rate, chemistry
Data Flow
49
• Results may be used empirically or with chemical speciation based models
• Screening is often based on peak concentration
• Definition of range of field conditions is critical
