Embed Size (px)
Citation preview
1
FEASIBILITY OF PHOSPHOGYPSUM AS MSW LANDFILL STRUCTURAL MATERIAL AND SHEAR STRENGTH OF MSW WITH DIFFERENT FOOD WASTE CONTENT
By
YONGQIANG YANG
A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2011
2
© 2011 Yongqiang Yang
3
To my wife Huisuo Huang; my son Allen Yang; and my parents, Guoan Yang and Junying Xia
4
ACKNOWLEDGMENTS
I would like to thank my academic advisor and committee chairman, Dr. Timothy
Townsend, for sharing his knowledge and experience. I was very lucky to work with
him. He gave me the wonderful experience of working on these valuable projects, and
his tireless endeavors toward academic accomplishment inspired me. He put great
effort to train me as a researcher and engineer. I would also like to thank my other
committee members, Dr. Frank Townsend, Dr. Michael Annable, and Dr. David
Bloomquist for their guidance in assisting me in completing my graduate studies. Also, I
am very thankful for the Mosaic Company and Caterpillar Inc. for their support.
Furthermore, I would like to thank my friends and colleagues, Dr. Hwidong Kim,
Dr. Jae Hac Ko, Dr. Yu Wang, Dr. Shrawan Singh, and Dr. Young Min Cho for providing
me with wonderful advice and support. I acknowledge the support from my friends,
Jianye Zhang, Antonio Yaquian, Wesley Gates, and Shabnam Mostary. Also I would
like to thank my friend Dan Pitocchi in the Florida Department of Transportation,
Gainesville, FL.
I would especially like to thank my parents-in-law. In my last semester they came
to the United States to help us with the daily responsibilities of house-work and caring
for our son so we could have more time to work on our projects and research.
At last, I would like to thank my wife, son, parents, and my brother, and for their
love, support, and encouragement.
5
TABLE OF CONTENTS
ACKNOWLEDGMENTS .................................................................................................. 4
page
LIST OF TABLES ............................................................................................................ 7
LIST OF FIGURES .......................................................................................................... 9
LIST OF ABBREVIATIONS ........................................................................................... 11
ABSTRACT ................................................................................................................... 12
CHAPTER
1 INTRODUCTION .................................................................................................... 14
Research Background ............................................................................................ 14 Research Objectives ............................................................................................... 16 Research Approach ................................................................................................ 16 Outline of Thesis ..................................................................................................... 17
2 GEOTECHNICAL ENGINEERING PROPERTIES OF PHOSPHOGYPSUM ......... 18
Materials and Methods ............................................................................................ 19 PG Samples Collection, Storage and Safety .................................................... 19 Test Methods .................................................................................................... 20
Results and Discussion ........................................................................................... 22 Test Results ..................................................................................................... 22 Comparison with Previous Studies ................................................................... 23
Summary ................................................................................................................ 25
3 COMPATIBILITY TEST OF PHOSPHOGYPSUM WITH MSW LANDFILL LEACHATE AND GEOSYNTHETIC CLAY LINERS ............................................... 39
Materials and Methods ............................................................................................ 40 Test Materials ............................................................................................ 40 Test Methods ............................................................................................. 41
Results and Discussion ........................................................................................... 43 Test Results ............................................................................................... 43 Compatibility with MSW Landfill Leachate ................................................. 45 Compatibility with GCLs ............................................................................. 46
Summary ................................................................................................................ 47
4 SHEAR STRENGTH OF MSW WITH DIFFERENT FOOD WASTE CONTENT ..... 59
Materials and Methods ............................................................................................ 60
6
MSW Specimen Preparation ............................................................................ 60 Direct Shear Test ............................................................................................. 61 Data Analysis ................................................................................................... 62
Results and Discussion ........................................................................................... 63 Stress-Displacement Response ....................................................................... 63 Change of Internal Friction Angle ..................................................................... 63 Application to Landfill Slope Stability Design .................................................... 65
Summary ................................................................................................................ 65
5 SUMMARY AND CONCLUSIONS .......................................................................... 75
APPENDIX
A SUPPLEMENTAL TABLES .................................................................................... 77
B SUPPLEMENTARY FIGURES ............................................................................. 103
LIST OF REFERENCES ............................................................................................. 108
BIOGRAPHICAL SKETCH .......................................................................................... 113
7
LIST OF TABLES
Table
page
2-1 PG sieve analysis test results ............................................................................. 26
2-2 PG standard compaction test results .................................................................. 27
2-3 PG direct shear test results ................................................................................ 28
2-4 PG hydraulic conductivity test results ................................................................. 29
2-5 PG hydraulic conductivity in this study and previous tests ................................. 30
3-1 Hydraulic conductivity of GCL permeant chemical properties ............................ 49
3-2 GCL Hydraulic conductivity in this study and the previous researchs ................. 50
4-1 Composition of MSW specimens ........................................................................ 67
4-2 Sizes and moisture contents of each waste component ..................................... 68
4-3 Average moisture contents and dry densities of the MSW specimens ............... 69
4-4 Mobilized internal friction angle and cohesion values ......................................... 70
A-1 PG sieve analysis test data ................................................................................ 77
A-2 PG standard compaction test data ..................................................................... 78
A-3 Hydraulic conductivity test data for SWPG ......................................................... 79
A-4 Hydraulic conductivity duplicate test data for SWPG .......................................... 80
A-5 Hydraulic conductivity test data for WWPG ........................................................ 81
A-6 Hydraulic conductivity duplicate test data for WWPG ......................................... 82
A-7 Hydraulic conductivity test data for NWPG ......................................................... 83
A-8 Hydraulic conductivity duplicate test data for NWPG .......................................... 84
A-9 Hydraulic conductivity test data for EWPG ......................................................... 85
A-10 Hydraulic conductivity duplicate test data for EWPG .......................................... 86
A-11 Cations concentration in batch leaching solution of SWPG of with MSW Leachate ............................................................................................................. 87
8
A-12 Cations concentration in batch leaching solution of WWPG of with MSW Leachate ............................................................................................................. 88
A-13 Cations concentration in batch leaching solution of NWPG of with MSW Leachate ............................................................................................................. 89
A-14 Cations concentration in batch leaching solution of EWPG of with MSW Leachate ............................................................................................................. 90
A-15 Cations concentration in batch leaching solution of GCL bentonite with DI water ................................................................................................................... 91
A-16 Cations concentration in batch leaching solution of GCL bentonite with MSW landfill leachate ................................................................................................... 92
A-17 Cations concentration in batch leaching solution of GCL bentonite with simulated SWPG leachate .................................................................................. 93
A-18 Cations concentration in batch leaching solution of GCL bentonite with simulated WWPG leachate ................................................................................. 94
A-19 Cations concentration in batch leaching solution of GCL bentonite with simulated NWPG leachate ................................................................................. 95
A-20 Cations concentration in batch leaching solution of GCL bentonite with simulated EWPG leachate .................................................................................. 96
A-21 GCL hydraulic conductivity test results with DI water ......................................... 97
A-22 GCL hydraulic conductivity test results with MSW landfill leachate .................... 98
A-23 GCL hydraulic conductivity test results with simulated SWPG leachate ............. 99
A-24 GCL hydraulic conductivity test results with simulated WWPG leachate .......... 100
A-25 GCL hydraulic conductivity test results with simulated NWPG leachate ........... 101
A-26 GCL hydraulic conductivity test results with simulated EWPG leachate ........... 102
9
LIST OF FIGURES
Figure
page
2-1 PG particle size distribution ................................................................................ 31
2-2 Standard compaction curves of SWPG .............................................................. 31
2-3 Standard compaction curves of WWPG ............................................................. 32
2-4 Standard compaction curves of NWPG .............................................................. 32
2-5 Standard compaction curves of EWPG .............................................................. 33
2-6 Standard compaction and modified compaction curves of SWPG. ..................... 33
2-7 Shear strength versus horizontal displacement for the SWPG ........................... 34
2-8 Residual shear strength versus normal stress to determine the interface friction angle and cohesion for the SWPG .......................................................... 34
2-9 Shear strength versus horizontal displacement for the WWPG .......................... 35
2-10 Residual shear strength versus normal stress to determine the interface friction angle and cohesion for the WWPG ......................................................... 35
2-11 Shear strength versus horizontal displacement for the NWPG ........................... 36
2-12 Residual shear strength versus normal stress to determine the interface friction angle and cohesion for the NWPG .......................................................... 36
2-13 Shear strength versus horizontal displacement for the EWPG ........................... 37
2-15 Compacted PG hydraulic conductivity under different confining pressures ........ 38
3-1 Calcium concentrations in the batch leaching soultions of PG with MSW landfill leachate ................................................................................................... 51
3-2 Sulfate concentrations in the batch leaching solutions of PG with MSW landfill leachate ................................................................................................... 51
3-3 TDS in the batch leaching solutions of PG with MSW landfill leachate ............... 52
3-4 Hydraulic conductivity, pH, and specific conductivity of the SWPG in column test. ..................................................................................................................... 53
3-5 Hydraulic conductivity, pH, and specific conductivity of the WWPG in column test ...................................................................................................................... 54
10
3-6 Hydraulic conductivity, pH, and specific conductivity of the NWPG in column test ...................................................................................................................... 55
3-7 Hydraulic conductivity, pH, and specific conductivity of the EWPG in column test ...................................................................................................................... 56
3-8 Calcium concentrations in batch leaching test of GCL bentonite with DI water, MSW landfill leachate, and simulated PG leachate ............................................ 57
3-9 Sodium concentrations in batch leaching test of GCL bentonite with DI water, MSW landfill leachate, and simulated PG leachate ............................................ 57
3-10 Potassium concentrations in batch leaching test of GCL bentonite with DI water, MSW landfill leachate, and simulated PG leachate ................................. 58
3-11 GCL hydraulic conductivity to simulated PG leachate, MSW landfill leachate, and DI water ....................................................................................................... 58
4-1 Stress-displacement response curves of direct shear tests with 0, 20, 50, and 70% of food waste specimens under 96 kPa of effective normal stress ............. 71
4-2 Stress-displacement response curves of direct shear tests with 0, 20, 50, and 70% of food waste specimens under 192 kPa of effective normal stress ........... 71
4-3 Stress-displacement response curves of direct shear tests with 0, 20, 50, and 70% of food waste specimens under 287 kPa of effective normal stress ........... 72
4-4 Mohr-Coulomb failure envelopes of direct shear tests ........................................ 72
4-5 Impact of food waste contents in synthetic fresh MSW on friction angles at different displacement levels .............................................................................. 73
4-6 Relationship of MSW internal friction and cohesion by direct shear test with different food waste contents .............................................................................. 73
4-7 Comparison of values of internal friction angle and cohesion values in this study to those of in previous studies ................................................................... 74
B-1 PG stack and sample location. ......................................................................... 103
B-2 PG samples were stored in solid and hazard waste management laboratory .. 104
B-3 Schematic diagram of PG column test ............................................................. 105
B-4 Compacted PG and GCL hydraulic conductivity test devices ........................... 106
B-5 Large-scale direct shear test device ................................................................. 107
11
LIST OF ABBREVIATIONS ASTM American Society for Testing and Materials
DI Deionized
EPA U.S. Environmental Protection Agency
EW East wall of PG stack
FIPR Florida Industrial and Phosphate Research Institute
GCL Geosynthetic clay liner
MSW Municipal solid waste
NW North wall of PG stack
PG Phosphogypsum
SW South wall of PG stack
TDS Total dissolved solids
WW West wall of PG stack
12
Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering
FEASIBILITY OF PHOSPHOGYPSUM AS MSW LANDFILL STRUCTURAL MATERIAL AND SHEAR STRENGTH OF MSW WITH DIFFERENT FOOD WASTE CONTENT
By
Yongqiang Yang
May 2011
Chair: Timothy G. Townsend Major: Environmental Engineering Sciences
Research related to the potential landfill structural material of phosphogypsum
(PG) and the shear strength of municipal solid waste (MSW) was conducted. The
geotechnical engineering properties of PG, the compatibility of PG with MSW landfill
leachate and geosynthetic clay liners (GCLs), and the shear strength of MSW with
different food waste contents were all explored.
The maximum dry density of PG ranged from 1450 to 1560 kg/m3 in standard
compaction tests. Interface friction angles of compacted PG ranged from 33.8˚ to 39.7˚
under drained conditions. PG compaction and shear test results supported the
hypothesis that compacted PG has sufficient geotechnical properties to serve as a
foundation base layer under landfills. In this study, the hydraulic conductivity of
compacted PG ranged from 2.9 x 10-5 to 7.3 x 10-5 cm/sec under a confining pressure of
69 to 345 kPa, higher than the 10-5 cm/sec required by Florida Landfill Rules for double
lined landfills.
Elevated concentrations of Ca2+, SO42-, and total dissolved solids (TDS) were
observed in batch leaching solutions of PG with MSW landfill leachate. Elevated
concentrations of Ca2+ and SO42- may impact landfill leachate and gas quality. In
13
column tests, the hydraulic conductivity of compacted PG with MSW landfill leachate
ranged from 2.8 x 10-5 to 6.6 x 10-5 cm/sec, slightly higher than hydraulic conductivity
measured using deionized (DI) water, which ranged from 1.8 x 10-5 to 2.7 x 10-5 cm/sec,
but they were in the same order of magnitude of 10-5 cm/sec. The impact of MSW
landfill leachate to compacted PG hydraulic conductivity was not significant.
Significant cation exchange of Na+ and K+ was found in the batch leaching
solutions of GCL bentonite with MSW landfill leachate. A more significant exchange of
Ca2+ occurred in the batch leaching tests of GCL bentonite with simulated PG leachate.
In the GCL hydraulic conductivity tests, the hydraulic conductivity of GCLs with
simulated PG leachate ranged from 1.2 x 10-6 to 3.6 x 10-9 cm/sec, whereas with MSW
landfill leachate the hydraulic conductivity ranged from 6.4 x 10-6 to 1.8 x 10-7 cm/sec.
Both of these were higher than with DI water, which gave a hydraulic conductivity
ranging from 2.3 x 10-9 to 4.1 x 10-9 cm/sec.
The impact of food waste content on the MSW shear strength was studied by
large-scale (430 mm×430 mm) direct shear test using synthetic MSW with different food
waste contents (0, 20, 50, and 70%). In the shear tests with different food waste
contents, the internal friction angle of MSW ranged from 15˚ to 35˚, and cohesion
ranged from 5 to 12 kPa. The bi-linear internal friction angle envelope showed that if
the food waste content in MSW is higher than 50%, the internal friction angle could drop
dramatically.
14
CHAPTER 1 INTRODUCTION
Research Background
Phosphogypsum (PG) is a solid by-product produced during the wet
manufacturing process of phosphoric acid. PG is composed of calcium sulfate
dihydrate (CaSO4·2H2O), trace elements (TE), rare earth elements (REE), and naturally
occurring radioactive elements such as Radium-226 (226Ra) and Uranium-238 (238U).
In 1992, U.S. Environmental Protection Agency (USEPA) issued the rule prohibiting the
offsite use of PG with average radium concentration greater than 10 picocuries per
gram (pCi/g), requiring this PG to be placed in large piles or stacks to prevent it from
entering the environment. These stacks are normally built on unused or excavated land
on the processing site. According to USEPA (2010), about 30 million tons of PG are
produced annually in Central Florida, and are stockpiled indefinitely in stacks. In total,
about 7.7 billion metric tons were generated in the United States from 1910 to 1981.
The surface area covered by individual stacks ranges from about 5 to 740 acres. In
1989, the total surface area covered by stacks was about 8,500 acres, of which more
than half is in Florida (USEPA, 2010). In 1999, USEPA modified its regulations,
allowing the use of 317 to 3175 kg of PG for indoor research and development, thus
giving researchers opportunities to develop practical applications for PG.
Many research projects have been conducted to investigate a variety of practical
applications of PG. These included using PG as a road fill material (FIPR, 1983; FIPR,
1989; FIPR, 1990), soil stabilizer (Degirmenci, et al. 2006), and embankment material
(Moussa et al. 1984). In the PG application areas surveyed in FIPR, 1993, (roads and
parking lots in Florida and Texas), there were no environmental or health impacts
15
reported from exposure to radioactive materials in PG. In the present study, a potential
beneficial use for PG is explored: as part of municipal solid waste (MSW) landfill
construction and operation activities. The options include use of PG as landfill daily
cover material, and, at new landfill sites, use as a substitute for the large volume of soil
required to be placed under the liner to provide the needed grades for leachate
drainage.
Although the above applications would offer benefits, many technical questions
have to be addressed to make sure necessary regulatory requirements are met and
long-term environmental protection is ensured. The research reported here provides
information helpful for making preliminary assessments of the feasibility of these
approaches. The topics covered in this thesis include evaluating the PG geotechnical
engineering properties and the compatibility of PG with MSW landfill leachate and
geosynthetic clay liners (GCLs) as landfill foundation and daily cover material.
In recent years, with the rising demand for landfill capacity, there has been a drive
towards vertical expansion, resulting in a number of landfill slope failures. Thus,
estimating the geotechnical properties of MSW has become an ever more important
need for landfill design (Stark et al. 2009). MSW shear strength has been evaluated by
many researchers (Kavazanjian et al. 1995; Kavazanjian et al. 1999; Machado et al.
2002; Mahler and Netto 2003; Harris et al. 2006; Gabr et al. 2007; Zhan et al. 2007;
Zekkos et al. 2007; Kavazanjian 2008; Zekkos et al. 2008; Reddy et al. 2009; Cho et al.
2011). However, most of these researchers performed experiments on waste sourced
from western countries. In Asian countries the MSW composition is typically different
from western countries. For example, the average food waste content of U.S. MSW is
16
approximately 12.5% (USEPA, 2005), while that of China has been reported to be up to
73% (The World Bank, 1999; Wang and Nie, 2001). High food waste content MSW,
such as that which is found in Asian countries, could impact the waste shear strength
(Cho et al. 2011). Thus, it is necessary to evaluate MSW shear strength with different
food waste contents to help in landfill slope stability design.
Research Objectives
One objective of this study was to evaluate the feasibility of utilizing PG as a
structural material for lined MSW landfills. The applicability has been judged by testing
PG geotechnical engineering properties and PG compatibility with MSW landfill leachate
and GCLs. Another objective was to measure the shear strength of MSW with different
food waste contents to contribute to MSW landfill slope stability design.
Research Approach
Objective 1. Evaluating PG geotechnical engineering properties as landfill
construal material
Approach. A series of classical soil geotechnical engineering properties tests,
adopted from ASTM, were performed on PG. Sieve analysis was used to determine PG
particle distribution; compaction tests were performed to evaluate PG compaction
properties; PG shear strength was tested by direct shear test; and hydraulic conductivity
of compacted PG was measured in triaxial cells.
Objective 2. Testing PG compatibility with MSW landfill leachate and GCLs as
landfill construal material
Approach. Batch leaching tests, column tests, and GCL hydraulic conductivity
tests were conducted to evaluate the compatibility of PG with MSW landfill leachate and
GCLs. PG leaching tests were performed to evaluate the impact of PG on the quality of
17
MSW landfill leachate. GCL leaching tests were used to analyze the exchange of
cations in the leaching solution with MSW landfill leachate and simulated PG leachate.
Column tests were used for long term monitoring of PG compatibility with MSW landfill
leachate. GCL hydraulic conductivity tests were performed in triaxial cells using MSW
landfill and simulated PG leachate as test liquids.
Objective 3. Estimating the shear strength of MSW with different food waste
contents contribute to landfill slope stability design
Approach. Direct shear tests were conducted on synthetic MSW samples with
food waste contents of 0, 20, 50, and 70%. Eight representative waste components
were combined to prepare a reproducible specimen: food waste, paper, plastic, metal,
wood, textile, glass, and ash. These were placed in a stress-controlled direct shear box
testing device (430 mm length × 430 mm width) with a maximum 16 cm horizontal
displacement and normal pressures of 96, 192, and 287 kPa were applied.
Outline of Thesis
This thesis is organized into 5 Chapters, Appendices, and References. Chapter 1
presents the introduction, objectives, and research approach. Chapter 2 presents the
PG geotechnical engineering properties tests. Chapter 3 presents results from PG
compatibility experiments. Chapter 4 presents the shear strength of MSW with different
food waste content. Chapter 5 provides the comprehensive summary and conclusion of
the entire research of this thesis. Supplementary Tables and Figures are provided in
the Appendices. Cited references are included at the end of this thesis.
18
CHAPTER 2 GEOTECHNICAL ENGINEERING PROPERTIES OF PHOSPHOGYPSUM
The design of a MSW landfill bottom liner includes placing a low permeability
barrier layer, compacted clay usually, at the bottom of the landfill and grading the barrier
layers to promote gravity drainage of the leachate to low points from which leachate can
be removed. Given the relatively flat topography in Florida, it is necessary to either
excavate in order to achieve the needed grade, or to bring in extra fill material. For
landfills with large base areas, the amount of soil that is needed may be very large,
which may necessitate the purchase and delivery of soil from off site. Phosphogypsum
(PG) could potentially be utilized as a base layer for a newly lined MSW landfill in order
to help reach needed grades. The use of PG for this purpose would result in savings to
the landfill operator if soils needed to be hauled in from long distances. It would also be
a benefit to the PG producers, as it would provide the opportunity for beneficial use of
the material.
To achieve these aims geochemical engineering assessments have to be
conducted to evaluate whether PG has sufficient geochemical properties to serve as a
foundation base layer. For example, Florida Landfill Rules (FDEP, 2010) requires that,
in the double liner systems for a MSW landfill, the lower geomembrane is placed directly
on a sub-base which is a minimum six inches thick and has a saturated hydraulic
conductivity of less than or equal to 10-5 cm/sec. In this chapter, a series of
geochemical tests, consisting of sieve analysis, compaction, hydraulic conductivity
measurements, and shear strength tests, were carried out to evaluate the engineering
properties of PG as sub-base material for MSW landfills.
19
Materials and Methods
PG Samples Collection, Storage and Safety
Collection. PG was sampled from the top of a Mosaic’s Bartow Facility, South PG
stack located in Mulberry, Florida. Samples were collected from four locations: the
south, west, north, and east, wall of the top PG stack. (These samples are henceforth
referenced as SWPG, WWPG, NWPG, and EWPG respectively.) Samples were
collected at approximately 30 to 60 cm depths from the top of the stack wall. PG
samples were then transported to the University of Florida Solid and Hazard Waste
Management Research Laboratory. A chain-of-custody record was kept from the point
of sample collection to the laboratory.
Storage. The PG samples were stored in closed containers in the lab at room
temperature. To perform research on PG, requirements of 40 CFR 61.205 were
followed; all PG samples were accompanied by certified documents that conformed to
the requirements of 40 CFR 61.208. The total quantity of PG at this research facility did
not exceed 3182 kg. Containers of PG were labeled with the following warning:
“Caution: Phosphogypsum Contains Elevated Levels of Naturally Occurring
Radioactivity.”
Safety. U.S. Occupational Safety and Health Administration health and safety
instructions were followed in all phases of the project which were involved with PG.
Field and laboratory personnel were made aware of the common exposure routes for
chemicals, such as, inhalation, ingestion, and contact. They were instructed in the
proper use of safety equipment such as protective clothing and respiratory equipment.
Basic first-aid kits were made accessible to all personnel involved in this research.
20
Test Methods
Sieve analysis. Sieve analysis tests were performed to classify the grain size
distribution of the PG by following ASTM D421. The smallest sieve used in these tests
was a No. 200 sieve with a 0.075 mm opening size. This size corresponds to the
Unified Soil Classification System’s size for distinguishing between sand and silt. Prior
to sieve analysis, a 200 g of PG was dried in an oven at 60°C for 24 hours. The dried
PG was gently crushed by mortar and pestle. A total of 100 grams of PG were placed
in the sieve stack and shaken for 10 minutes. The retained PG in each sieve was
weighed to calculate the retaining and passing percentage for each grain size range.
Compaction. Compaction methods described in ASTM method D421 were
employed to determine PG compaction properties. Approximately 2,500 g of PG which
passed a No. 4 sieve were dried at 60°C for 24 hours. The desired moisture content
was achieved by mixing the PG samples with a known amount of water and each
sample was left undisturbed overnight before compacting. Then PG was compacted
into a 10 cm diameter mold in three layers. During the compaction procedure, each
layer was subjected to 25 blows with a 2.5 kg hammer dropped from a height of 30.5
cm. In addition, for more effort compaction tests, each layer was subjected to 50 blows
of a 2.5 kg hammer dropped from a height of 30.5 cm. The compaction tests were
repeated 10 times with different values of soil water content for each PG sample.
Compaction curves were drawn of the resulting relationship of dry weight density versus
water content. Specimen water contents were determined by oven drying for 24 hours
at 60°C according to ASTM D2216. PG samples specific gravity were determined by
ASTM D854.
21
Direct shear test. Direct shear tests, adopted from ASTM D3038, were used to
determine the shear strength properties of internal friction and cohesion of compacted
PG under drained condition. The maximum dry density and optimum water content
were obtained for each PG specimen from the standard compaction tests. The direct
shear apparatus is a 10 cm diameter circular shear box with separated lower and upper
halves. The lower half of the box is fixed to a frame while the upper half is capable of
moving horizontally relative to the lower one. Each PG sample was tested at four
different normal loads, 144, 287, 431, and 575 kPa. A 0.018 cm/min shearing rate was
used for the test to permit a good drainage (Moussa et al. 1984). Horizontal
displacement, vertical displacement, and shear load measurements were recorded
during each test. Compacted PG internal frictions and cohesions were determined
busing Mohr-Coulomb Equation 2-1.
τ’ = c’ + σ’ tan( Φ’) (2-1)
Where τ’ = (Effective) shear stress; c’ = (Effective, or apparent) cohesion; σ’ =
(Effective) normal stress; Φ’ = (Effective, or drained) angle of internal friction.
Hydraulic conductivity. Hydraulic conductivities of the compacted PG were
measured in accordance with ASTM D5084 using a flexible wall permeameter,
composed of triaxial cells and pressure providing flexpanels. DI water was used as the
test liquid. PG specimens were compacted in a 7.1 cm diameter compaction mold at
optimum moisture content in three layers.
Three steps of back pressure saturation, consolidation, and permeation were used
to complete hydraulic conductivity tests. Compacted PG specimens were set up in the
flexible-wall permeameter with a pair of saturated porous stones on the bottom and top.
Then, specimens were saturated using a 483 kPa backpressure, taking 7 to 10 days to
22
achieve a complete saturation. Before permeation, specimens were consolidated under
confining pressures of 69, 207, and 345 kPa. Consolidation was completed in 3-5 days
under each confining pressure. The hydraulic conductivity was tested using a falling
head rising tail test method. Hydraulic conductivity, k, was determined by using the
Equation 2-2.
1
2
ln( )( )
in out
in out t
a a L hka a A h
=+ ∆
(2-2)
Where, k = hydraulic conductivity (cm/s), ain = cross-sectional area of the inflow
stand pipe (cm2), aout = cross-sectional area of the outflow stand pipe (cm2), L = height
of specimen (cm), A= cross-sectional area of specimen (cm2), h1 = head loss across the
specimen at t1, (cm of water), h2 = head loss across the specimen at t2 (cm of water), ln
= natural logarithm (base e = 2.71828), and ∆t = interval of time (t1-t2) (seconds).
Results and Discussion
Test Results
Sieve analysis. Sieve analysis test results for the PG samples are presented in
Table 2-1 and Figure 2-1. The sieve analysis results showed that the percentage of PG
passing #200 sieve ranged from 44 to 71%. According to American Association of
State Highway and Transportation Officials (AASHTO) M-145, PG samples were
classified as silt-clay materials as more than 35% pass a sieve # 200 (0.075mm). More
sieve analysis test data was present in Table A-1.
Compaction. Laboratory compaction test results of PG were presented in Table
2-2. The test results of standard compaction showed that maximum dry density of PG
samples ranged from 1450 to 1560 kg/m3 while the optimum moisture content ranged
from 16.4 to 19.0%. More effort compaction test results showed that maximum dry
23
density was 1620 kg/m3 with an optimum moisture content of 14.2% for SWPG, which
was only slightly higher than in the standard compaction test (Figure 2-6). Thus,
compaction energy, defined as the potential energy of the falling hammer times the
number of falls, had little influence on the values of maximum dry density and optimum
water content of the PG samples. Table 3-1 showed that PG compaction behavior is
also dependent on its fine percentage (passing sieve # 200). It was found that higher
fine percentage correlates with lower maximum dry density after compaction and flatter
dry density curves (Figures 2-1 to 2-4). This indicates that PG dry density would be less
sensitive to water content
Direct shear test. Direct shear test results are presented in Table 2-3. Test
results showed that the interface friction angle of the PG samples ranged from 33.8˚ to
39.7˚ and that the cohesion ranged from 10 to 68 kPa. Figures 2-6 to 2-13 show the
plots of shear stress versus horizontal displacement and residual shear strength versus
normal stress, which was used to determine the interface friction angle and cohesion.
Hydraulic conductivity test. Hydraulic conductivity test results of compacted PG
are presented in Table 2-4. Hydraulic conductivities of PG samples ranged from 2.9 x
10-5 to 7.3 x10-5 cm/sec under confining pressures of 69, 207, and 345 kPa. Figure 2-
14 shows that hydraulic conductivities of compacted PG samples slightly decreased
with increasing confining pressure. More hydraulic conductivity test data is presented in
Tables A-4 to A-11.
Comparison with Previous Studies
Particle size distribution of PG tested in this study was similar to that found in the
previous investigations (FDOT, 2008). The percentage of PG passing through a # 200
24
Sieve in this study ranged from 44.2 to 73.2%, which was similar to the results reported
by FDOT (2008), (41.5 to 73.9%). FDOT (2008) reported that PG samples should be
classified as an A-4 material in the AASHTO Soil Classification System. A-4 material
could serve well as a pavement component when properly compacted and drained.
In standard compaction tests we found that PG had maximum dry density range of
1450 to 1560 kg/m3. These results are comparable to those found in the previous
studies (Moussa et al. 1984; FDOT, 2008). On the PG stack in the Mosaic Fertilizer
Greenbay Facility, dry densities of undisturbed PG collected from different depths in the
East and West walls ranged from 1232 to 2000 kg/m3 (Ardaman & Associates, Inc.
2007), which showed that PG undergoes compression as the weight of the overlying PG
increases and dry density of PG increased.
Shear strength parameters determined for PG samples were also similar to the
results of previous studies (Moussa et al. 1984; FDOT, 2008). In this study, PG
samples internal friction angle ranged from 33.8˚ to 39.7˚ at standard compaction and
optimum water content. PG direct shear tests conducted by Moussa et al. (1984)
showed internal friction angles ranging from 30˚ to 40˚ at water contents ranging from 3
to 28%. FDOT, (2008) reported an internal friction angle of 44.34˚ for a compacted PG
specimen on the ultimate loads in triaxial shear tests.
PG hydraulic conductivity research has also been reported by some researchers
(Moussa et al. 1984; Ardaman & Associates, Inc, 2007; FDOT, 2008). Ardaman &
Associates Inc. (2007) reported vertical permeability of undisturbed PG samples
collected in PG stacks at Mosaic Fertilizer Greenbay Facility, obtained from four borings
on the PG stack ranged from 5.0 x 10-6 to 4.6 x 10-4 cm/sec. FDOT, (2008) and Moussa
25
et al. (1984) reported laboratory-compacted PG hydraulic conductivities ranging from
1.8 x 10-6 to 1.3 x 10-4 cm/sec. The hydraulic conductivities measured in this study, 2.9
x 10-5 to 7.3 x10-5 cm/sec, were similar to their test results. PG hydraulic conductivity
values from this study and previous studies are summarized in Table 2-5.
Summary
In this study, PG dry densities in standard compaction tests are in the typical
range of fine-grained soil dry densities, 1280 to 2080 kg/m3 (Holtz and Kovacs, 1981),
and shear strength parameters of the PG samples show slightly greater internal friction
angles than the typical 25˚ - 30˚ of fine-grained soil. These test results showed that PG
had good geotechnical properties to serve as landfill sub-base material in comparison to
compacted clay.
However, hydraulic conductivities of compacted PG, 2.9 x 10-5 to 7.3 x 10-5
cm/sec, were found to be higher than the typical range of hydraulic conductivities of
compacted clays, which is less than 10-7 cm/sec (Benson et al. 1994). According to
Florida Landfill Rules (FDEP, 2010), MSW landfill sub-base soil must have a saturated
hydraulic conductivity of less than or equal to 10-5 cm/sec. Compacted PG, hydraulic
conductivity higher than 10-5 cm/sec, could not singly serve as sub-base material. A
geosynthetic clay liner (GCL) with a hydraulic conductivity not greater than 1x10-7
cm/sec could be placed on the top of compacted PG layer under landfill.
26
Table 2-1. PG sieve analysis test results
Sample Passing # 10 (%)
Passing # 20 (%)
Passing # 30 (%)
Passing # 50 (%)
Passing # 100 (%)
Passing # 200 (%)
Diameter (mm) 2.000 0.850 0.420 0.250 0.150 0.075 SWPG 100.0 99.1 96.1 89.2 70.6 44.2 WWPG 99.9 98.6 95.2 88.1 69.4 44.6 NWPG 100.0 98.2 92.6 88.2 82.7 69.4 EWPG 100.0 99.0 95.7 93.0 86.4 66.3 Average 100.0 98.7 94.9 89.6 77.3 56.1
27
Table 2-2. PG standard compaction test results
Sample Maximum dry (kg/m3)
Optimum water content (%)
Passing # 200 sieve (%)
GBSW 1560.0 16.4 43.7
GBWW 1530.0 17.0 46.7
GBNW 1460.0 19.0 71.3
GBEW 1450.0 19.0 66.5
Average 1500.0 17.9 57.1
28
Table 2-3. PG direct shear test results Sample internal frication (˚) Cohesion (kPa) Passing # 200 sieve (%)
SWPG 39.7 43 43.7
WWPG 33.8 68 46.7
NWPG 39.4 10 71.3
EWPG 38.0 13 66.5
Average 37.7 33.5 57.1
29
Table 2-4. PG hydraulic conductivity test results
Sample Hydraulic conductivity (cm/sec) Pass # 200
sieve (%) 69 kPa 207 kPa 345 kPa SWPG 5.9E-05 4.9E-05 4.1E-05 43.7 WWPG 6.2E-05 6.0E-05 5.3E-05 46.7 NWPG 3.7E-05 3.6E-05 3.2E-05 71.3 EWPG 5.7E-05 5.3E-05 4.9E-05 66.5 Average 5.4E-05 5.0E-05 4.4E-05 57.1
30
Table 2-5. PG hydraulic conductivity in this study and previous tests
Test method PG specimen Confining pressure (kPa)
Hydraulic conductivity (cm/sec) References
ASTM 5084, flexible wall Laboratory-compacted 69-345 2.9 x 10-5-7.3 x10-5 In this study
Constant head Laboratory-compacted na* 1.8 x 10-6-3.5 x 10-5 Moussa et al. 1984
ASTM 5084, flexible wall Laboratory-compacted 35-276 8.4 x 10-5-1.3 x10-4 FDOT, 2008
ASTM 5084, flexible wall Undisturbed na 5.0 x 10-6-4.6 x 10-4 Ardaman & Associates, Inc.,
2007 *Not available
31
40
50
60
70
80
90
100
0.010.101.0010.00
SWPG
WWPG
EWPG
EWPG
Per
cent
pas
sing
(%)
Grain size (mm)
Figure 2-1. PG particle size distribution
1,400
1,500
1,600
1,700
1,800
1,900
10 12 14 16 18 20 22 24
Dry unit weight
100% saturated
Water content (%)
Uni
t wei
ght (
kg/m
3 )
Figure 2-2. Standard compaction curves of SWPG
32
1,300
1,400
1,500
1,600
1,700
1,800
12 14 16 18 20 22 24 26
Dry unit weight100% saturated
Water content (%)
Uni
t wei
ght (
kg/m
3 )
Figure 2-3. Standard compaction curves of WWPG
1,300
1,400
1,500
1,600
1,700
1,800
12 14 16 18 20 22 24 26
Dry unit weight
100% saturated
Water content (%)
Uni
t wei
ght (
kg/m
3 )
Figure 2-4. Standard compaction curves of NWPG
33
1,300
1,400
1,500
1,600
1,700
1,800
12 14 16 18 20 22 24 26
Dry unitweight
Water content (%)
Uni
t wei
ght (
kg/m
3 )
Figure 2-5. Standard compaction curves of EWPG
1,400
1,500
1,600
1,700
1,800
1,900
2,000
8 10 12 14 16 18 20 22
100% saturatedDry unit weight-standardDry unit weight-more effort
Water content (%)
Uni
t wei
ght (
kg/m
3 )
Figure 2-6. Standard compaction and modified compaction curves of SWPG, more
effort compaction is done by adding more compaction effort of 50 blows per layer comparing to standard 25.
34
0
100
200
300
400
500
600
0.0 0.5 1.0 1.5 2.0
144 kPa
144 kPaduplicate287 kPa
287 kPaduplicate431 kPa
431 kPaduplicate575 kPa
575 kPaduplicate
Horizontal displacement (%)
She
ar s
treng
th (k
Pa)
Figure 2-7. Shear strength versus horizontal displacement for the SWPG
y = 0.83x + 42.53R² = 0.99
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
Normal stress (kPa)
She
ar s
tress
(kP
a)
Figure 2-8. Residual shear strength versus normal stress to determine the interface
friction angle and cohesion for the SWPG
35
0
100
200
300
400
500
600
0.0 0.5 1.0 1.5 2.0
144 kPa
144 kPaduplicate287 kPa
287 kPaduplicate431 kPa
431 kPaduplicate575 kPa
575 kPaduplicate
Horizontal displacement (%)
She
ar s
treng
th (k
Pa)
Figure 2-9. Shear strength versus horizontal displacement for the WWPG
y = 0.67x + 67.50R² = 0.99
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
Normal stress (kPa)
She
ar s
tress
(kP
a)
Figure 2-10. Residual shear strength versus normal stress to determine the interface
friction angle and cohesion for the WWPG
36
0
100
200
300
400
500
600
0.0 0.5 1.0 1.5 2.0
144 kPa
144 kPaduplicate287 kPa
287 kPaduplicate431 kPa
431kPaduplicate575 kPa
575 kPaduplicate
Horizontal displacement (%)
She
ar s
treng
th (k
Pa)
Figure 2-11. Shear strength versus horizontal displacement for the NWPG
y = 0.82x + 9.98R² = 0.99
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
Normal stress (kPa)
She
ar s
tress
(kP
a)
Figure 2-12. Residual shear strength versus normal stress to determine the interface
friction angle and cohesion for the NWPG
37
0
100
200
300
400
500
600
0.0 0.5 1.0 1.5 2.0
144 kPa
144 kPaduplicate287 kPa
287 kPaduplicate431 kPa
431 kPaduplicate575 kPa
575 kPaduplicate
Horizontal displacement (%)
She
ar s
treng
th (k
Pa)
Figure 2-13. Shear strength versus horizontal displacement for the EWPG
y = 0.78x + 12.50R² = 0.98
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
Normal stress (kPa)
She
ar s
tress
(kP
a)
Figure 2-14. Residual shear strength versus normal stress to determine the interface
friction angle and cohesion for the EWPG
38
1.0E-05
3.0E-05
5.0E-05
7.0E-05
9.0E-05
0 100 200 300 400
SWPGWWPGNWPGEWPG
Hyd
raul
ic C
ondu
ctiv
ity (c
m/s
ec)
Confining pressure (kPa)
Figure 2-15. Compacted PG hydraulic conductivity under different confining pressures of 69, 207, and 345 kPa
39
CHAPTER 3 COMPATIBILITY TEST OF PHOSPHOGYPSUM WITH MSW LANDFILL LEACHATE
AND GEOSYNTHETIC CLAY LINERS
PG is mainly composed of calcium sulfate dihydrate (CaSO4·2H2O). Moussa, et
al. (1984) reported that PG could dissolve in DI water about 2.4 g/L at pH 6. VanGulck
et al. (2003) researched calcium precipitation from leachate and its accumulation within
the pore space of the drainage medium causes scaling. Lee et al. (2005) reported that
in construction and demolition (C&D) landfills a biological conversion of sulfate from
disposed gypsum drywall to hydrogen sulfide (H2S) could happen in the anaerobic
landfill environment. Concerns over this issue arise when discussing use of PG as a
landfill nonstructural material such as daily cover soil. In order to address these
concerns, batch leaching and column tests on PG were conducted to test the
compatibility of PG with MSW landfill leachate.
Previous tests, in Chapter 2 of this thesis, showed that compacted PG could not
singly serve as sub-base material under landfill. Geosynthetic clay liners (GCLs) could
be used in MSW landfill composite bottom liners placing on compacted PG. Many
laboratory studies have been conducted on the evolution of GCLs in contact with
various types of chemical permeates containing cations that may impact the
performances of the hydraulic conductivity of the GCL (Petrov and Rowe 1997; Ruhl
and Daniel 1997; Shackelford et al. 2000; Jo et al. 2001). GCLs may contact with PG
leachate or MSW landfill leachate, in the case that geomembrane overlying the GCL is
damaged, or the groundwater table increase and submerges compacted PG. As MSW
leachate usually contains cations, cation exchange may occur in the GCL following the
flow of leachate (Touze-Foltz et al. 2006). PG dissolved in water or MSW leachate may
40
cause cation exchange with GCL bentonite, which could impact GCL hydraulic
conductivity performances. Here, GCL bentonite batch leaching tests with MSW landfill
leachate and simulated PG leachate, and GCL hydraulic conductivity tests were
conducted to test the PG compatibility GCLs.
Materials and Methods
Test Materials
MSW landfill leachate. MSW landfill leachate was collected from Polk County
North Central Class III landfill, FL. MSW landfill leachate was stored in the University of
Florida Solid Waste Management laboratory coolers and used for batch leaching tests
with PG samples, GCL bentonite batch leaching tests, and GCL hydraulic conductivity
tests.
Simulation of PG leachate. In this study, PG leachate was created by mixing a
100 g PG sample with 2 L DI water in a 2.2 L glass jar. The mixture was agitated using
a rotator for 16 to 20 hours. After tumbling, the slurry was filtered to separate PG
leachate from the slurry. Simulated samples of PG leachate was used for bentonite
batch leaching tests and GCL hydraulic conductivity tests. Simulated PG leachate and
MSW landfill leachate chemical properties are summarized in Table 3-1.
Geothynthetic clay liners. Geosynthetic clay liners (GCLs) are factory-
manufactured clay liners consisting of a layer of bentonite clay encased by geotextiles
or glued to a geomembrane. In this study, the GCL contained granular sodium encased
by two geotextiles bounded by needles. The average thickness of GCL used in the
hydraulic conductivity tests was 8.4 mm and the mass per unit area of air-dried
bentonite in the GCL was 3.64 kg/m2. GCL bentonite retrieved from GCL was used in
GCL betonite batch leaching tests.
41
Test Methods
Batch test with MSW landfill leachate. The batch test of PG with MSW landfill
leachate was conducted by adding 100 g PG to 2 L of MSW leachate and then mixing
the aggregate on a rotary extractor for 18 ± 2 hours at 30 rpm. The mixture of MSW
landfill leachate and PG was filtered using 0.7 μm glass fiber filters. Sulfate (SO42-)
concentrations in the filtered leaching solution were determined using a
spectrophotometer (DR/4000 UV-VIS, HACH, Loveland, CO) with HACH Method 8051.
Cation concentrations were analyzed by ICP-AES after acid digestion according to
USEPA test methods 6010C and 3010A. Total dissolved solids (TDS) were analyzed
by USEPA test method of 160.1.
Column test. Column tests were conducted in accordance with ASTM D5856 and
following the procedures of the drainage column tests conducted by Chapuis et
al.(2006). The present test was used to evaluate the impact of MSW landfill leachate on
the hydraulic conductivity and other chemical parameters of compacted PG. In this test,
twelve columns were made from 10 cm diameter PVC pipes. PG samples were
compacted in the column 12.7 cm deep in order obtain the optimum water content
determined from previous PG standard compaction test. No confining pressure was
applied for the tested PG specimens.
MSW landfill leachate was used to fill in the columns. The test liquid in the column
was maintained at 30.5 cm constant head above PG specimens in the columns. Test
liquid flow direction was opposed to compaction direction. Effluent liquid passing the
PG samples was collected to measure the change of hydraulic conductivity of
compacted PG and then measurements of pH and specific conductivity of the liquid
were taken. Duplicate tests were performed for MSW landfill leachate filled columns,
42
and DI water was used for a control to compare with MSW landfill leachate. Figure B-3
illustrated a column test.
Batch test with GCL betonite. Leaching tests were conducted using bentonite
from the GCL to evaluate the effect of cation exchange on GCL hydraulic conductivity.
This test method was adopted from Benson and Meer (2009). MSW landfill leachate, DI
water, and simulated PG leachate were used as extract solutions. For this test, 12.5 g
of bentonite were mixed with 250 mL extract solutions and rotated for 18 ± 2 hours. The
mixture of extract solutions and GCL betonite were filtered using 0.7μm glass fiber filters
after rotation. Cation concentrations were analyzed by ICP-AES after acid digestion
according to USEPA test methods 6010C and 3010A. TDS was analyzed by USEPA
test method 160.1.
GCL Hydraulic conductivity test. Falling head rising tail hydraulic conductivity
tests were conducted on GCL in flexible-wall permeameters according to methods
described in ASTM D6766. An average hydraulic gradient of 170 and a confining
pressure of 69 kPa were applied in this test. Simulated PG leachate, MSW landfill
leachate, and DI water were used as the permeate solutions. A large backpressure of
583 kPa was used to achieve saturation in the GCL specimens.
GCL specimens were prepared by using 105 mm diameter stainless steel cutting
ring and a sharp cuter. The cutting edge was immediately hydrated by testing liquid to
minimize bentonite loss. Bentonite paste, the permeate liquid, and silicon grease were
applied around the perimeter of the GCL to reduce the potential for sidewall leakage. A
483 kPa back pressure and a 550 kPa cell pressure were used for GCL specimens’
saturation, hydration, swell, and consolidation in 72 hours. During permeation, a
43
pressure of 15 kPa across the specimen was maintained. The ratio of the rate of inflow
to the rate of outflow was between 0.75 and 1.25 for the last three consecutive flow
measurements. Hydraulic conductivity was calculated as per ASTM D 5084 using the
Equation 2-1.
Results and Discussion
Test Results
Batch leaching test with MSW landfill leachate. Batch leaching test solutions
were analyzed for cations, anions of SO42-, and TDS concentration changes. The
results are presented in Figures 3-1 to 3-3. The quantities of most cations in the batch
leaching test solutions were similar to those in MSW Landfill leachate, except calcium
and strontium. Ca2+ concentrations in the batch leaching test solutions were 100 times
higher than those in the MSW landfill leachate values presented in Figure 3-1. SO42-
concentrations in the leachate ranged from 3,000 to 3,250 mg/L, 15 times higher than
those from the MSW landfill leachate, which had a sulfate concentration of 195 mg/L.
TDS measured in the batch leaching test solutions ranged from 9,350-9,500 mg/L,
which is slightly higher than the TDS concentrations of 6,300 mg/L found in the MSW
leachate. More cations exchange data of the batch leaching solution are presented in
Table A-12 to A-15.
Column test. The column test results of compacted PG samples with MSW landfill
leachate and DI water are presented in Figures 3-4 to 3-7. The hydraulic conductivity of
compacted PG to MSW landfill leachate increased for the first four pore volumes of
MSW leachate. After four pore volumes of MSW leachate passed through the columns,
hydraulic conductivity of PG samples stabilized at 6.6 x 10-5 cm/sec or lowered into the
range of 2.8 x 10 -5 to 6.6 x 10-5 cm/sec. The hydraulic conductivity values achieved
44
using DI water were relatively lower, and ranged from 1.8 x 10 -5 to 2.7 x 10-5 cm/sec.
The test results showed that the hydraulic conductivity of compacted PG specimen
when using MSW landfill leachate as a permeate are higher than values achieved when
using DI water as a permeate. The hydraulic conductivity of PG samples when exposed
to DI water in column tests was similar to the values calculated in the triaxial
permeameter tests in the Section 3 of Chapter 2. The average saturation degree of PG
specimens, after test, with MSW landfill leachate in the column test was 91%, and with
DI water was 78%.
In the column test with MSW landfill leachate, the pH and specific conductivity of
the effluent solutions also changed over the range of pore volumes passing the PG
specimens. In the first pore volume of MSW landfill leachate passing the PG specimen
the pH was lower, at 3.1, than the MSW landfill leachate pH of 8.1. After the second
pore volume passed, the effluent solution pH stabilized at 7.4, and specific conductivity
increased from 2,000 to 11,500 μs/cm. The test solution of MSW landfill leachate had a
specific conductivity of 9,500 μs/cm. In contrast to the results with MSW leachate, all
parameters measured with DI water showed relatively stable values over the period of
the test. The average pH of effluent with DI water was about 3.5. The average specific
conductivity was about 2,300 μs/cm, which was comparable to simulated PG leachate
values.
Batch leaching test with GCL bentonite. The concentrations of Ca2+, Na+, and
K+ changed significantly after the GCL bentonite batch leaching tests with DI water,
MSW landfill leachate, and simulated PG leachate. The cation exchange results for
Ca2+, Na+, and K+ are presented in Tables 3-1, 3-2, and 3-3. The concentration of Ca2+
45
in simulated the PG leachate was reduced during the batch test with GCL bentonite.
Initial Ca2+ concentrations in simulated PG leachate ranged from 745 mg/L to 861 mg/L,
however as result of GCL batch leaching tests, the concentrations decreased to a range
of 166 -303 mg/L. In contrast, Na+, and K+ concentrations in simulated PG leachate
increased significantly. During this test, Na+ concentrations increased by 400-500 mg/L
from an initial average value of 9 mg/L. Sodium concentrations increased in MSW
leachate and DI water as well but the change was not as significant as in the simulated
PG solutions. Additionally, potassium concentrations in increased DI water and PG
leachate solutions, yet decreased in MSW leachate solutions.
GCL hydraulic conductivity test. The test results of GCL hydraulic conductivities
when permeated by DI water, MSW landfill leachate, and simulated PG leachate are
presented in Figure 3-11. Compared to GCL hydraulic conductivity tested using DI
water as a permeate, MSW landfill leachate and simulated PG leachate had an
increased hydraulic conductivity. GCL hydraulic conductivity with DI water ranged from
2.3 x 10-9 to 4.1 x 10-9 cm/sec. GCL hydraulic conductivities with simulated PG leachate
varied from 1.2 x 10-6 to 3.6 x 10-9 cm/sec. Most hydraulic conductivities with simulated
PG leachate were greater than those with DI water. The highest GCL hydraulic
conductivities were observed with MSW landfill leachate. GCL hydraulic conductivities
with MSW leachate ranged from 6.4 x 10-6 to 1.8 x 10-7 cm/sec. Chemical properties of
the permeates are summarized in Table 3-1.
Compatibility with MSW Landfill Leachate
The batch test of PG samples with MSW landfill leachate showed increased
calcium, sulfate, and TDS concentrations in batch leaching solution. Increased calcium
could cause scaling problems within the leachate collection and removal system.
46
VanGulck et al. (2003) researched calcium carbonate (CaCO3) precipitation from
leachate and its accumulation within the pore space of the drainage medium. Calcium
precipitation is caused by the anaerobic fermentation of volatile fatty acids, which adds
carbonate to and raises the pH of the leachate. Another major concern in the batch test
was the increased sulfate in the leaching solution. Under anaerobic conditions sulfate
could be converted to hydrogen sulfide (H2S) which results in odor problems and
possible health concerns at many disposal facilities. In Lee et al. (2005) research on
C&D landfills showed biological conversion of sulfate from disposed gypsum drywall to
H2S in the anaerobic C&D landfill environment. However, Shieh (1999) reported that
concentrations of calcium and sulfate were higher than in the typical landfill leachate,
but no elevated level of H2S in the gas composition was found. The Increased TDS
values in the batching solution showed that PG samples dissolved in MSW landfill
leachate and released cations which could affect landfill leachate quality.
In the column test, the hydraulic conductivity of the compacted PG with MSW
landfill leachate was slightly higher than DI water after stabilization. That indicated that
test liquid chemical properties, such as, pH, specific conductivity, could affect
compacted PG hydraulic conductivity. In this test, the hydraulic conductivity of PG with
MSW landfill leachate and DI water were in the same order of magnitude of 10-5 cm/sec.
Compatibility with GCLs
The key cations typically found in GCL batch leaching solutions were sodium,
potassium, calcium, magnesium (Mg2+), and aluminum (Al3+). Sodium and potassium
exchange in GCL bentonite in contact with simulated PG leachate and MSW landfill
leachate could have an impact on hydraulic conductivity of GCLs. These changes in
47
cation concentrations are influenced by multiple factors of MSW leachate and PG
leachate quality such as ionic strength, pH, and the presence of organic compounds.
Chemical interactions and their effect on the hydraulic conductivity of bentonite in
GCLs have been studied by many researchers (Jo et al. 2001; Wang and Benson,
1999; Petrov et al. 1997; Petrov and Rowe, 1997). The results are summarized in
Table 3-2. Concentrations of cations in permeate are known to be very influential on
hydraulic conductivity of GCLs. Kolstad et al. (2004) concluded that hydraulic
conductivity of GCLs is a function of ionic strength and RMD of chemical solution or
leachate. Simulated PG leachate has a low RMD, i.e., a low ratio of monovalent, such
as, sodium or potassium concentrations relative to the concentration of divalent, such
as, calcium. Thus high concentrations of calcium in PG leachate, and high ionic
strength of MSW landfill leachate caused adverse effects on GCL bentonite, i.e., GCL
bentonite swelling, leading to effects on GCL hydraulic conductivity. However, there
was no evidence, in this study, showed that PG leachate could increase hydraulic
conductivity of GCLs greater than MSW landfill leachate did.
Summary
In the batch test PG with MSW landfill leachate, elevated Ca2+, SO42- and TDS
levels were observed in batch leaching solutions. High concentrations of Ca2+ in landfill
leachate could cause clogging in the leachate collection removal system, and high
levels of SO42- could cause landfill gas odor and possible health concerns. The batch
test results do not suggest that PG could be used as daily or intermediate cover soil
layers as part of the operation of a MSW landfill. In the column test, hydraulic
conductivity of compacted PG samples with MSW landfill leachate are slightly higher
than those with DI water, but they are in the same order of magnitude of 10-5 cm/sec.
48
Hydraulic conductivities of GCL increased with simulated PG leachate (1.2 x 10-6
to 3.6 x 10-9 cm/sec) and MSW landfill leachate (6.4 x 10-6 to 1.8 x 10-7 cm/sec)
compared to the tests with DI water (2.3 x 10-9 to 4.1 x 10-9 cm/sec). GCL betonite
batch leaching tests showed that cation concentrations in simulated PG leachate and
MSW landfill leachate influence GCL hydraulic conductivity. These test results showed
that PG leachate could impact the hydraulic conductivity of GCLs when it applied as
landfill sub base material, but no evidence was found that PG leachate could increase
hydraulic conductivity of GCLs greater than that of MSW landfill leachate.
49
Table 3-1. Hydraulic conductivity of GCL permeant chemical properties Permeate type pH Specific Conductivity
(µs/cm) Ionic strength (M)
Monovalent concentration (M)
Divalent concentration (M)
RMDb (mM1/2)
MSW Landfill Leachate 7.97 12,670 0.17 0.0894 0.0036 1.4803
SW PG leachate 6.25 2,582 0.03 0.0004 0.0203 0.0028
WW PG leachate 6.20 2,571 0.03 0.0008 0.0207 0.0053
NW PG leachate 4.61 2,233 0.03 0.0006 0.0219 0.0038
EW PG leachate 5.55 2,256 0.03 0.0003 0.0199 0.0020
DI water 7.16 4 naa na na na a Not available b RMD: RMD is defined as Mm/(Md1/2), where Mm = total molarity of monovalent cations and Md = total molarity of multivalent cations in the solution, and represents the relative abundance of monovalent and multivalent cations at a given ionic strength.
50
Table 3-2. GCL Hydraulic conductivity in this study and the previous researchs
Test Method Permeability (cm/sec) Permeate type Confining pressure (kPa)
Hydraulic gradient References
ASTM D5084, D6766
2.3 x 10-9 - 4.1 x 10-9 DI water
69 149 - 194 In this study 6.4 x 10-6 - 1.8 x 10-7 MSW landfill leachate
1.2 x 10-6 - 3.6 x 10-9 Simulated PG leachate
ASTM D5084, D6766 1.0x10-5 - 8.9x10-10 Chemical solution na* 100 Jo et al. 2001
ASTM D6766
1.0 x 10-7 simulated MSW leachate
35 100 - 200 Ruhl et al. 1997 2.0 x 10-8 MSW landfill leachate
9.0 x 10-10 Tap water
Constant flow rate fixed ring 2.6x10-5 - 7.3x10-10 NaCl na 18 - 2,142 Petrov et al. 1997
ASTM D6766 4.2x10-12 - 2.7x10-9 DI water 41 175 - 440 Wang et al. 1999
Fixed ring Double-ring 1.4x10-8 - 7.1x10-10 DI/tap water 3-117 318 - 893 Petrov et al. 1997
* Not available
51
Cal
cium
(mg/
L)
0
200
400
600
800
1000
1200
1400
SWPG + MSWlandfill leachate
WWPG + MSWlandfill leachate
NWPG + MSWlandfill leachate
EWPG + MSWlandfill leachate
MSW landfill leachate
Figure 3-1. Calcium concentrations in the batch leaching soultions of PG with MSW
landfill leachate
Sul
fate
(mg/
L)
0
1000
2000
3000
4000
5000
SWPG + MSWlandfill leachate
WWPG + MSWlandfill leachate
NWPG + MSWlandfill leachate
EWPG + MSWlandfill leachate
MSW landfill leachate
Figure 3-2. Sulfate concentrations in the batch leaching solutions of PG with MSW
landfill leachate
52
TDS
(mg/
L)
0
2000
4000
6000
8000
10000
12000
SWPG + MSWlandfill leachate
WWPG + MSWlandfill leachate
NWPG + MSWlandfill leachate
EWPG + MSWlandfill leachate
MSW landfill leachate
Figure 3-3. TDS in the batch leaching solutions of PG with MSW landfill leachate
53
1E-5
2E-5
3E-5
4E-5
5E-5
DI waterMSW landfill leachateMSW landfill leachate-duplicateH
ydra
ulic
Con
duct
ivity
(cm
/sec
)
1
2
3
4
5
6
7
8
pH
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16 18Accumulated pore volume
Spec
ific
Con
duct
ivity
(mS/
cm)
Figure 3-4. Hydraulic conductivity, pH, and specific conductivity of the SWPG in column
test. One pore volume of the SWPG specimen equals to 344 mL.
54
1E-5
2E-5
3E-5
4E-5
5E-5
6E-5
7E-5
DI waterMSW landfill leachateMSW landfill leachate-duplicateH
ydra
ulic
Con
duct
ivity
(cm
/sec
)
1
2
3
4
5
6
7
8
pH
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16 18 20 22Accumulated pore volume
Spec
ific
Con
duct
ivity
(mS/
cm)
Figure 3-5. Hydraulic conductivity, pH, and specific conductivity of the WWPG in column
test. One pore volume of the WWPG specimen equals to 357 mL.
55
9E-6
2E-5
3E-5
4E-5
5E-5
DI waterMSW landfill leachateMSW landfill leachate-duplicateH
ydra
ulic
Con
duct
ivity
(cm
/sec
)
1
2
3
4
5
6
7
8
pH
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16Accumulated pore volume
Spec
ific
Con
duct
ivity
(mS/
cm)
Figure 3-6. Hydraulic conductivity, pH, and specific conductivity of the NWPG in column
test. One pore volume of the NWPG specimen equals to 381 mL
56
1E-5
2E-5
3E-5
4E-5
5E-5
6E-5
7E-5
DI waterMSW landfill leachateMSW landfill leachate-duplicateH
ydra
ulic
Con
duct
ivity
(cm
/sec
)
1
2
3
4
5
6
7
8
pH
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14 16 18 20 22Accumulated pore volume
Spec
ific
Con
duct
ivity
(mS/
cm)
Figure 3-7. Hydraulic conductivity, pH, and specific conductivity of the EWPG in column
test. One pore volume of the EWPG specimen equals to 387 mL
57
10
100
1000
GCL+DIwater
GCL+MSWlandfill leachate
GCL+NWPGleachate
GCL+SWPG leachate
GCL+EWPGleachate
GCL+ WWPGleachate
Cal
cium
(mg/
L)MSW landfill leachate= 113mg/L
PG leachate= 791mg/L
Figure 3-8. Calcium concentrations in batch leaching test of GCL bentonite with DI
water, MSW landfill leachate, and simulated PG leachate
1
10
100
1000
10000
GCL+DIwater
GCL+MSWlandfill leachate
GCL+NWPGleachate
GCL+SWPG leachate
GCL+EWPGleachate
GCL+ WWPGleachate
Sod
ium
(mg/
L)
MSW landfill Leachate= 1630 mg/L
PG Leachate= 9 mg/L
Figure 3-9. Sodium concentrations in batch leaching test of GCL bentonite with DI water,
MSW landfill leachate, and simulated PG leachate
58
1
10
100
1000
GCL+DIwater
GCL+MSWlandfill leachate
GCL+NWPGleachate
GCL+SWPG leachate
GCL+EWPGleachate
GCL+ WWPGleachate
Pot
assi
um (m
g/L)
MSW landfill Leachate= 744 mg/L
PG Leachate= 3 mg/L
Figure 3-10. Potassium concentrations in batch leaching test of GCL bentonite with DI
water, MSW landfill leachate, and simulated PG leachate
DI water
Hyd
raul
ic c
ondu
ctiv
ity (c
m/s
ec)
1e-10
1e-9
1e-8
1e-7
1e-6
1e-5
1e-4
MSW landfillleachate
SWPGleachate
WWPGleachate
NWPGleachate
EWPGleachate
Permeant type Figure 3-11. GCL hydraulic conductivity to simulated PG leachate, MSW landfill
leachate, and DI water
59
CHAPTER 4 SHEAR STRENGTH OF MSW WITH DIFFERENT FOOD WASTE CONTENT
Landfill slope stability design requires the evaluation of compacted MSW shear
strength properties, e.g., the internal friction angle and cohesion. Research
investigating appropriate MSW internal friction angles and cohesions have been
reported, with most values reported in the range of 15˚ to 36˚ and 0 to 60 kPa
(Kavazanjian et al. 1995; Kavazanjian et al. 1999; Machado et al. 2002; Mahler et al.
2003; Harris et al. 2006; Gabr et al. 2007; Zhan et al. 2007; Zekkos et al. 2007;
Kavazanjian 2008; Zekkos et al. 2008; Reddy et al. 2009; Cho et al. 2011). The wide
range of values is caused by numerous factors such as the test methods, test
conditions, waste composition, waste age, decomposition degree, and pre-processing
methods.
The composition of MSW varies with geographical, cultural, and seasonal
differences. Food waste content, for example, can vary dramatically among countries.
The food waste content of U.S. MSW is approximately 12.5% as determined by its
water content (USEPA, 2005), while that of China has been reported to be as high as
73% (The World Bank, 1999; Wang et al. 2001). Most of the studies referenced earlier
were focused on waste from western countries. As other parts of the world with
different waste compositions begin to utilize large sanitary landfills, it is important to
better understand how different factors, such as high food waste content waste, might
impact the waste shear strength properties.
This study investigated the relationship between the MSW internal friction angle
and food waste content. Laboratory direct shear tests were performed on synthetic
MSW with different food waste contents, under a maximum 16 cm displacement.
60
Materials and Methods
MSW Specimen Preparation
Sample collection. In this study, synthetic MSW samples were prepared to
represent common waste characteristics. Eight representative components were
selected: food waste, paper, plastic, metal, wood, textile, glass, and ash (Table 4-1).
Here, paper, plastic, aluminum, and glass components were collected from the
University of Florida recycling center. Chipped wood mulch of appropriate sizes was
collected from a local waste transfer station. Textiles used were discarded clothes.
Coal ash was collected from a local coal-fueled power plant (Gainesville Regional
Utilities, FL US). Food waste was collected from the University of Florida dining halls.
A visual observation was used to ascertain that the general characteristics of all waste
components.
Sample processing. The target sizes, methods of size reduction, and average
moisture contents for the different waste components are summarized in Table 4-2.
Paper components consisted of 50% office paper and 50% newspaper which were cut
to 14 cm length and 22 cm width pieces. Plastics consisted of 50% plastic bottles and
50% plastic film. Plastics, aluminum beverage cans, glass and textile were reduced to
less than 15 cm. Food waste consisted primarily of discarded meats, pizza, bread, and
vegetables. The average food waste moisture was 63.5%. Size reduction was not
performed on food waste.
Specimen preparation. Direct shear test specimens were prepared by mixing all
waste components and compacting in the shear box. All waste components were
thoroughly mixed with shovels in a stainless steel tank to promote a homogenous
composition for the shear tests. Then the mixture was placed and compacted in the
61
shear box. All test specimen and waste components were determined on a wet weight
basis. Drying temperature was set at 60°C to avoid combustion of volatile material
(Reddy et al. 2009). The average moisture contents of each waste component and
specimen are presented in Tables 4-2 and 4-3, respectively. The initial moisture
content of each specimen, before consolidation occurred, was estimated by taking the
weighted average moisture content of each component.
Direct Shear Test
Direct shear tests were conducted to determine the angle of internal friction and
cohesion of fresh MSW at different food under drained condition. Tests were performed
in accordance with ASTM D3080 in a large-scale rectangular shear box with dimensions
43cm width, 43 cm length, and 61cm height. The shear box includes an upper fixed
shear box (43-cm length × 43-cm width × 46-cm height) and a movable lower shear box
(43-cm length × 43-cm width × 16-cm height). The maximum displacement level of the
large-scale device is approximately 40% of the shear box length (16 cm of horizontal
displacement). For normal stress and shear stress applications, hydraulic jacks
equipped with hand pumps (SIMPLEX® P42 and P82, Broadview, Illinois, U.S.) and
pressure gauges (GD1 SIMPLEX®, Broadview, Illinois) were used. The stress-
controlled direct shear box was designed as shown in Figure B-4 (Stewart & Associates
Manufacturing Corporation, Gainesville, Florida, U.S.).
Each direct shear test was initiated by placing and compacting a well-mixed MSW
specimen in the shear test box. The normal stresses applied on the specimen were 96,
192, and 287 kPa, respectively. The applied normal stresses on the MSW specimens
were treated as the effective normal stresses under drained conditions. Shear test
specimens were consolidated under effective normal stress within a 24 hour period until
62
vertical deformation rates were less than 0.5% per hour. The normal stress was
continuously monitored and maintained at a constant value during the consolidation and
testing procedures. Shear stress was applied at the constant shear speed 0.5 cm/min,
and shear stress and horizontal displacement were monitored and recorded. Each
shear test was terminated after maximum horizontal displacement of 16 cm was
reached. Densities of the specimens after consolidation and before shearing are
provided in Table 4-3. Dry density was calculated by subtracting the moisture weight
from the total weight of a specimen.
Data Analysis
In direct shear tests internal friction angle and cohesion were estimated using
peak or ultimate shear strength values produced during the test. That is to say, the
highest value within the relevant range was used, although sometimes the process was
terminated while the shear strength was still increasing. In this latter case, the final
measured values were used. The Mohr-Coulomb failure criterion expressed as
Equation 2-1 was used to calculate the shear strength parameters. To develop a Mohr-
Coulomb failure criterion envelope for each set of direct shear test data, a best-fit linear
regression was performed. For all 24 tests duplicates were conducted at each normal
stress and food waste content. All of the replicate data points for each set of tests were
used to develop the regression line. The cohesion values were also determined from
shear strength vs. normal stress plots.
Mobilized shear strength, cohesion, and internal friction angle at various
displacements were calculated to investigate the relationship between displacement
and mobilized shear-strength parameters. Based on the stress-displacement data,
mobilized internal friction angles of MSW were estimated at horizontal displacements of
63
22 mm (or 5% of the total), 43 mm (10%), 65 mm (15%), 86 mm (20%), 108 mm (25%),
and 129 mm (30%).
Results and Discussion
Stress-Displacement Response
Stress-displacement curves are presented in Figures 4-1, 4-2, and 4-3. Twelve
out of 24 direct shear tests, with 50% and 70% food waste content, showed the fully
mobilized, well-defined peak shear strength. Under a stress of 297 kPa, peak shear
strengths were achieved at 8 cm (17%) and 16 cm (27%) respectively. In the remaining
12 tests, with 0 and 20% food waste content, the stress-displacement response did not
reach their peak shear strengths even at the maximum displacement of 16 cm (37%),
which were similar with previous results (Pelkey et al. 2001; Vilar and Carvalho 2004;
Reddy et al. 2009). For these tests the maximum shear strength values at a
displacement of 16 cm (37%) were considered as the peak shear strength and those
were used to develop Mohr-Coulomb failure criteria envelopes.
Change of Internal Friction Angle
Mohr-Coulomb criteria envelopes were plotted using the peak or maximum shear
strength values produced in the 24 direct shear tests. In Figure 4-4 the envelopes
showed that mobilized internal friction angles decreased with increasing food waste
content. The increasing degrees varied for different food waste content MSW. The
internal fiction angle decreased from 35 to 33˚ with MSW food waste content increasing
from 0 to 20%. The internal fiction angle decreased from 33 to 30˚ with 20% to 50%.
When the food waste continued increasing from 50 to 70%, internal frication
dramatically dropped from 30 to 15˚. The reason could be that as the ratio of food to
64
other components became more dominant, internal friction angles changed more
significantly.
The values of the mobilized internal friction angle and the mobilized cohesion at
different displacement levels with different food waste contents were summarized in
Table 4-5. At each displacement level from 5 to 30% the internal friction angle
decreased with increasing food waste content, as shown in Figure 4-4. However, there
was no evidence that there was an overall change of cohesion by increasing food waste
content. This was different with the test results from Cho et al. (2011) who reported that
overall cohesion increased with increasing displacement level.
Relationship of internal friction angle and cohesion with food waste content was
attempted to be determined based on results of this study and Cho et al. (2011) test
results. Figure 4-6 showed that there was a significant trend of the internal friction
angle decreasing with the food waste content increasing in MSW. The “best fit” internal
friction angle envelope is plotted in Figure 4-6. To summary the relationship of the
internal friction angle with the food waste content the bilinear envelope should be used.
The bi-linear internal friction angle envelope showed that: if food waste contents less
than 50%, an additional 10% of food waste causes a decrease of approximately 1.7
degrees of internal friction (Equation 4-1), and if higher than 50%, an additional 10% of
food waste cause a decrease of approximately 6 degrees of internal friction (Equation 4-
2).
Φ = 36.5-0.17(100x) (4-1)
Φ = 58.0-0.60(100x) (4-2)
Where, Φ = internal friction angle, x = food waste content (%), by wet base.
65
Application to Landfill Slope Stability Design
MSW Internal friction angle and cohesion in the this study were compared to those
from previous tests (Kavazanjian et al. 1999; Machado et al. 2002; Harris et al. 2006;
Reddy et al. 2009; Cho et al. 2011). Reported internal friction angles ranged from 7 to
39° and cohesion ranged from 0 to 65 kPa as shown in Figure 4-7. This wide range of
values can be caused by numerous factors which influenced the test results including
the test methods, test conditions, waste composition, waste age, decomposition degree,
and pre-processing methods.
Internal friction angle values of 20 to 40˚ are often considered as a typical range
for MSW from western countries where the waste is more dominated by packaging
materials and discarded domestic goods, and less by food waste. The design engineer
would use an internal friction angle estimate as an input for a landfill slope stability
design. Considering the food waste content in some regions has been reported as high
as 70% (The World Bank, 1999; Wang et al. 2001) the typical friction angle values used
for the design of a landfill in the U.S. could not be used properly. At very high food
waste contents, internal friction angle does decrease to levels lower than expected for
wastes with lower food contents. The results suggest that at food waste contents up to
50%, the friction angle will be close to the lower end of the typical range, with contents
up to 70% the angle will be lower than the typical ranges used for design.
Summary
The shear strength properties of MSW with different food waste contents were
investigated by conducting direct shear tests with large-scale direct-shear testing
devices. In the direct shear tests, the stress-displacement response plots showed
relatively well-defined peak shear strengths for all tested MSW with high food waste
66
contents. Test results showed that the peak shear strength decreased with the
increasing in food waste content under a given normal stress. Also, increasing food
waste content resulted in a decreasing of the internal friction angles. The internal
friction angle decreased down to 15˚ with an increased food waste content of up to
70%.
The relationship of internal friction angle decrease with food waste content
increase was summarized as bi-linear relationship. The bi-linear internal friction angle
envelope showed that if the food waste content in MSW is higher than 50%, the internal
friction angle could drop more significant. These results suggest that the impact of high
food waste content MSW on the internal friction angle should be considered when
designing for landfill slope stability.
67
Table 4-1. Composition of MSW specimens Component Content (%) by wet weight Food 0.0 20.0 50.0 70.0 Paper 24.0 19.2 12.0 7.2 Plastic 22.7 17.8 11.2 6.8 Metal 4.0 3.2 2.0 1.2 Wood 11.3 8.9 5.6 3.4 Glass 6.0 5.0 3.1 1.8 Textile 8.7 6.9 4.3 2.6 Ash 23.3 19.0 11.8 7.0 Total 100.0 100.0 100.0 100.0
68
Table 4-2. Sizes and moisture contents of each waste component
Component Size limit Size reduction method
Moisture content (%)
Food No reduction 63.5 Paper 140 mm x 220mm Scissors 5.8 Plastic < 150 mm Scissors 3.7 Metal < 150 mm Scissors 1.8 Wood < 150 mm Hammer 32.5 Glass < 150 mm Hammer 2.9 Textile < 150 mm Scissors 6.0 Ash No reduction 27.2
69
Table 4-3. Average moisture contents and dry densities of the MSW specimens
Food waste content
Moisture content (%) Dry density (kg/m3)c
Initiala Finalb 96 kPa 192 kPa 287 kPa
0% 13.0 9.8 242 321 269
20% 23.1 25.1 282 356 403
50% 38.3 41.3 327 396 472
70% 48.4 51.6 319 457 550 a Measured before consolidation b Measured after testing shear strength c Measured after consolidation and before shearing
70
Table 4-4. Mobilized internal friction angle and cohesion values Relative displacementa Parameter
Food waste content (%) 0 20 50 70
5% Internal friction (˚) 21 24 21 16 Cohesion (kPa) 4 0 4 0
10% Internal friction (˚) 27 29 27 16 Cohesion (kPa) 6 1 2 6
15% Internal friction (˚) 30 31 29 16 Cohesion (kPa) 6 1 2 9
20% Internal friction (˚) 33 32 30 16 Cohesion (kPa) 3 3 0 10
25% Internal friction (˚) 35 34 29 15 Cohesion (kPa) 0.5 2 5 11
30% Internal friction (˚) 36 34 27 16 Cohesion (kPa) 0.5 3 9 8
Peakb Internal friction (˚) 35 33 30 15 Cohesion (kPa) 6 7 5 12
a Relative displacement represents the relative horizontal displacement of a specimen b Peak represents the peak shear strength values or maximum shear strength
71
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18
0%0% duplicate20%20% duplicate50%50% duplicate70%70% duplicate
Horozontal displacement (cm)
shea
rstre
ss (
kPa)
Figure 4-1. Stress-displacement response curves of direct shear tests with 0, 20, 50,
and 70% of food waste specimens under 96 kPa of effective normal stress
0
40
80
120
160
200
240
0 2 4 6 8 10 12 14 16 18
0%0% duplicate20%20% duplicate50%50% duplicate70%70% duplicate
Horozontal displacement (cm)
shea
rstre
ss (
kPa)
Figure 4-2. Stress-displacement response curves of direct shear tests with 0, 20, 50,
and 70% of food waste specimens under 192 kPa of effective normal stress
72
0
50
100
150
200
250
300
0 2 4 6 8 10 12 14 16 18
0%0% duplicate20%20% duplicate50%50% duplicate70%70% duplicate
Horozontal displacement (cm)
shea
rstre
ss (
kPa)
Figure 4-3. Stress-displacement response curves of direct shear tests with 0, 20, 50,
and 70% of food waste specimens under 287 kPa of effective normal stress
c = 6, Φ = 35˚
c = 7, Φ = 33˚
c = 5, Φ = 30˚
c = 12, Φ = 12˚
0
50
100
150
200
250
300
0 100 200 300 400
0% Food waste20% Food waste50% Food waste70% Food waste
Normal stress (kPa)
shea
r stre
ss (
kPa)
Figure 4-4. Mohr-Coulomb failure envelopes of direct shear tests. Data points
correspond to peak shear strengths under each effective normal stress and at each waste composition; each line was derived by a best-fit linear regression
73
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70 80
5%10%15%20%25%30%
Inte
rnal
fric
tion
(˚)
Food waste content (%)
Relative displacement
Figure 4-5. Impact of food waste contents in synthetic fresh MSW on friction angles at
different displacement levels
y = -0.17x + 36.49R² = 0.75
y = -0.60x + 58.00R² = 0.86
0
10
20
30
40
50
0 10 20 30 40 50 60 70 80 90 100
Internal friction (˚) in this study
Internal friction (˚) Cho et al. 2011
Inte
rnal
fric
tion
(˚)
Food waste content (%)
Figure 4-6. Relationship of MSW internal friction and cohesion by direct shear test with different food waste contents
74
0
10
20
30
40
50
60
70
0 10 20 30 40 50
0% food waste, in this study
20% food waste, in this study
50% food waste, in this study
70% food waste, in this study
Cho et al. 2011, fresh waste,0%-80% food wasteReddy et al. 2009, fresh waste
Harris 2008, < 2 years
Harris et al. 2006, >10 years
Machdo et al. 2002,about 15 years, at 20% strainKavazanjian et al. 1999, 11-35years
Internal friction angles ( ˚ )
Coh
esio
n (k
Pa)
Figure 4-7. Comparison of values of internal friction angle and cohesion values in this
study to those of in previous studies
75
CHAPTER 5 SUMMARY AND CONCLUSIONS
In Chapters 2 and 3 of this thesis, the feasibility of utilizing phosphogypsum (PG)
in lined MSW landfills structural material was evaluated. Applications could include use
of PG as daily landfill cover material, and, at new landfill sites, compacted PG could
possibly substitute for the large volume of soil required to be placed under the liner to
provide the needed grades for leachate drainage. The applicability has been judged by
testing PG geotechnical engineering properties and PG compatibility with MSW landfill
leachate and geosynthetic clay liners (GCLs).
Test results of PG geotechnical properties showed that PG has the geotechnical
properties to serve as landfill foundation material as compared to compacted clay. PG
dry unit densities are in the typical range of fine-grained soil unit dry densities, and the
internal friction angles of compacted PG are slightly greater than those typical of
compacted clay. However, PG hydraulic conductivity test results didn’t support the idea
that compacted PG could singly serve as sub-base soil. A GCL with a hydraulic
conductivity not greater than 1x10-7 cm/sec could be used on top of PG.
The batch leaching test results didn’t suggest that PG could be used as daily cover
soil layers as part of the operation of a MSW landfill. In the PG with MSW landfill
leachate solution, elevated calcium, sulfate, and TDS concentrations were observed
which could clog landfill leachate collection systems, causing landfill gas odor or
possible health concerns. In the column test, the hydraulic conductivity of compacted
PG when permeated with MSW landfill leachate is slightly higher than that of DI water,
but is in the same order of magnitude of 10-5 cm/sec. GCL batch leaching tests with PG
leachate results showed that calcium cation exchange with GCL bentonite could impact
76
the GCL hydraulic conductivity. Hydraulic conductivities of GCLs increased with
simulated PG leachate (1.2 x 10-6 to 3.6 x 10-9 cm/sec), and this range overlapped with
Florida Landfill Rules (FDEP, 2010) required limit of the 10-7 cm/sec. These test results
showed that PG leachate could impact the hydraulic conductivity of GCLs when it
applied as landfill sub base material, but no evidence showed that PG leachate could
increase hydraulic conductivity of GCLs greater than that of MSW landfill leachate.
In Chapter 4, the impacts of food waste content on the shear strength properties
of MSW were investigated by conducting large-scale direct shear tests. In the 24 direct
shear tests, the residual shear strength decreased with increasing in food waste
contents for a given normal stress. Also, increases in food waste content resulted in
decreases in the internal friction angles. The internal friction angle decreased to 15˚
with an increased food waste content of 70%. The bi-linear internal friction angle
envelope showed that if the food waste content in MSW is higher than 50%, the internal
friction angle could drop dramatically.
77
APPENDIX A SUPPLEMENTAL TABLES
Table A-1. PG sieve analysis test data
Sample Sieve No.
Diameter (mm)
Mass of sieve (g)
Mass of sieve +soil (g)
Retained Soil (g)
Retained percent (%)
Passing percent (%)
SWPG
10 2.000 416.9 417.0 0.1 0.0 100.0 20 0.850 399.5 402.1 2.6 0.8 99.1 40 0.420 462.9 472.4 9.5 3.1 96.1 60 0.250 328.7 349.9 21.2 6.8 89.2 100 0.150 343.6 401.3 57.7 18.6 70.6 200 0.075 339.0 420.8 81.8 26.4 44.2 Pan 0 370.8 507.9 137.1 44.2 0.0
WWPG
10 2.000 417.0 417.7 0.7 0.2 99.8 20 0.850 399.6 404.4 4.8 1.5 98.2 30 0.420 409.5 412.5 3.0 1.0 97.3 50 0.250 364.5 375.4 10.9 3.5 93.8 100 0.150 343.8 401.4 57.6 18.4 75.4 200 0.075 339.0 422.0 83.0 26.5 48.9 Pan 0 370.9 523.9 153.0 48.9 0.0
NWPG
10 2.000 417.0 417.0 0.0 0.0 100.0 20 0.850 399.6 403.0 3.4 1.0 99.0 30 0.420 409.5 414.3 4.8 1.5 97.5 50 0.250 364.5 374.5 10.0 3.1 94.4 100 0.150 343.7 364.5 20.8 6.4 88.0 200 0.075 339.0 387.0 48.0 14.8 73.2 pan 0 370.9 608.0 237.1 73.1 0.0
EWPG
10 2.000 417.0 417.1 0.1 0.0 100.0 20 0.850 399.6 404.2 4.6 1.4 98.6 30 0.420 409.4 413.5 4.1 1.2 97.4 50 0.250 364.5 370.4 5.9 1.8 95.6 100 0.150 343.8 368.1 24.3 7.3 88.4 200 0.075 339.0 411.4 72.4 21.6 66.7 pan 0 371.0 593.5 222.5 66.5 0.0
78
Table A-2. PG standard compaction test data Sample Specimen No. 1 2 3 4 5 6 7 8 9 10
SWPG
Weight of mold (g) 2018 2018 2018 2018 2018 2018 2018 2018 2019 2018
Weight of mold + soil (g) 3620 3646 3678 3703 3738 3722 3705 3711 3672 3685
Weight of soil in mold (g) 1602 1629 1660 1686 1720 1704 1687 1693 1653 1667
Dry unit weight (kg/m3) 1520 1548 1536 1507 1457 1512 1535 1559 1509 1464
Zero air void (kg/m3) 1768 1711 1650 1622 1580 1809 1737 1670 1617 1571
Water content (%) 13.8 15.6 17.8 18.9 20.5 12.5 14.8 17.1 19.0 20.9
WWPG
Weight of mold (g) 2016 2018 2016 2018 2016 2018 2016 2018 2019 2016
Weight of mold + soil (g) 3618 3646 3664 3703 3708 3722 3702 3705 3672 3649
Weight of soil in mold (g) 1602 1629 1648 1686 1691 1704 1686 1687 1653 1633
Dry unit weight (kg/m3) 1497 1504 1516 1494 1450 1498 1517 1534 1505 1406
Zero air void (kg/m3) 1769 1709 1657 1615 1572 1782 1727 1677 1627 1517
Water content (%) 13.9 15.9 17.8 19.3 21.0 13.5 15.3 17.0 18.9 23.3
NWPG
Weight of mold (g) 2017 2017 2018 2017 2018 2017 2018 2018 2018 2018
Weight of mold + soil (g) 3544 3588 3600 3632 3648 3668 3657 3651 3633 3636
Weight of soil in mold (g) 1526 1570 1582 1615 1630 1650 1639 1633 1615 1618
Dry unit weight (kg/m3) 1424 1436 1454 1464 1429 1439 1455 1436 1393 1376
Zero air void (kg/m3) 1714 1649 1603 1558 1518 1633 1576 1524 1479 1442
Water content (%) 13.8 16.1 17.9 19.7 21.4 16.7 18.9 21.1 23.1 24.8
EWPG
Weight of mold (g) 2018 2017 2018 2017 2017 2017 2017 2017 2017 2017 Weight of mold + soil (g) 3543 3567 3580 3616 3614 3656 3654 3640 3644 3621 Weight of soil in mold (g) 1525 1551 1563 1599 1597 1639 1637 1623 1627 1604 Dry unit weight (kg/m3) 1422 1432 1436 1453 1423 1425 1444 1461 1429 1381 Zero air void (kg/m3) 1712 1657 1600 1559 1517 1665 1612 1572 1536 1475 Water content (%) 13.9 15.8 18.0 19.6 21.4 15.6 17.5 19.1 20.6 23.3
79
Table A-3. Hydraulic conductivity test data for SWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 91.1% 72.0 0.0 6.3 70.0 24.0 17.7 184 15.06 5.7E-05 2 80.0 70.0 91.1% 72.0 6.3 11.9 70.0 17.7 12.1 184 13.93 5.5E-05 3 80.0 70.0 91.1% 72.0 11.9 17.0 70.0 12.1 6.9 184 12.91 5.5E-05 Average 5.6E-05 4 100.0 70.0 91.1% 72.0 0.0 5.0 70.0 24.0 19.0 183 15.18 4.5E-05 5 100.0 70.0 91.1% 72.0 5.0 9.7 70.0 19.0 14.3 183 14.26 4.5E-05 6 100.0 70.0 91.1% 72.0 9.7 14.0 70.0 14.3 10.0 183 13.40 4.4E-05 Average 4.5E-05 7 120.0 70.0 91.1% 72.0 0.0 4.4 70.0 24.0 19.6 183 15.24 4.0E-05 8 120.0 70.0 91.1% 72.0 4.4 8.5 70.0 19.6 15.5 184 14.43 3.9E-05 9 120.0 70.0 91.1% 72.0 8.5 12.3 70.0 15.5 11.7 183 13.68 3.8E-05 Average 3.9E-05 a PG specimen final water content (%), 20.2; length (cm), 10.52; and diameter (cm), 7.10 b Water height in burette
80
Table A-4. Hydraulic conductivity duplicate test data for SWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 91.1% 72.0 0.0 7.0 70.0 24.0 17.1 185 14.67 6.5E-05 2 80.0 70.0 91.1% 72.0 7.0 13.2 70.0 17.1 10.8 186 13.44 6.3E-05 3 80.0 70.0 91.1% 72.0 13.2 18.7 70.0 10.8 5.3 184 12.35 6.1E-05 Average 6.3E-05 4 100.0 70.0 91.1% 72.0 0.0 5.7 70.0 24.0 18.3 182 14.78 5.4E-05 5 100.0 70.0 91.1% 72.0 5.7 10.9 70.0 18.3 13.1 183 13.77 5.2E-05 6 100.0 70.0 91.1% 72.0 10.9 15.7 70.0 13.1 8.3 182 12.84 5.2E-05 Average 5.3E-05 7 120.0 70.0 91.1% 72.0 0.0 4.7 70.0 24.0 19.2 183 14.87 4.4E-05 8 120.0 70.0 91.1% 72.0 4.7 9.1 70.0 19.2 14.8 183 14.02 4.3E-05 9 120.0 70.0 91.1% 72.0 9.1 13.2 70.0 14.8 10.7 184 13.23 4.3E-05 Average 4.3E-05 a PG specimen final water content (%), 19.3; length (cm), 10.75; and diameter (cm), 7.09 b Water height in burette
81
Table A-5. Hydraulic conductivity test data for WWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 92.0% 72.0 0.0 7.8 70.0 24.0 16.2 121 21.79 7.4E-05 2 80.0 70.0 92.0% 72.0 7.8 14.5 70.0 16.2 9.5 120 19.77 7.0E-05 3 80.0 70.0 92.0% 72.0 14.5 20.5 70.0 9.5 3.6 121 18.02 6.8E-05 Average 7.1E-05 4 100.0 70.0 92.0% 72.0 0.0 7.4 70.0 24.0 16.5 120 21.84 7.1E-05 5 100.0 70.0 92.0% 72.0 7.4 14.0 70.0 16.5 9.9 120 19.89 6.9E-05 6 100.0 70.0 92.0% 72.0 14.0 19.8 70.0 9.9 4.1 120 18.16 6.6E-05 Average 6.9E-05 7 120.0 70.0 92.0% 72.0 0.0 6.8 70.0 24.0 17.2 121 21.93 6.4E-05 8 120.0 70.0 92.0% 72.0 6.8 12.8 70.0 17.2 11.1 120 20.14 6.2E-05 9 120.0 70.0 92.0% 72.0 12.8 18.2 70.0 11.1 5.7 121 18.55 6.0E-05 Average 6.2E-05 a PG specimen final water content (%), 21.5; length (cm), 7.20; and diameter (cm), 7.15 b Water height in burette
82
Table A-6. Hydraulic conductivity duplicate test data for WWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 85.0% 72.0 0.0 5.9 70.0 23.0 17.1 121 21.96 5.5E-05 2 80.0 70.0 85.0% 72.0 5.9 11.2 70.0 17.1 11.8 121 20.41 5.3E-05 3 80.0 70.0 85.0% 72.0 11.2 16.1 70.0 11.8 6.9 120 18.99 5.4E-05 Average 5.4E-05 4 100.0 70.0 85.0% 72.0 0.0 5.7 70.0 24.0 18.2 121 22.13 5.4E-05 5 100.0 70.0 85.0% 72.0 5.7 10.9 70.0 18.2 13.0 121 20.60 5.2E-05 6 100.0 70.0 85.0% 72.0 10.9 15.6 70.0 13.0 8.3 120 19.22 5.1E-05 Average 5.2E-05 7 120.0 70.0 85.0% 72.0 0.0 4.8 70.0 24.0 19.1 120 22.25 4.5E-05 8 120.0 70.0 85.0% 72.0 4.8 9.3 70.0 19.1 14.6 120 20.95 4.5E-05 9 120.0 70.0 85.0% 72.0 9.3 13.4 70 14.6 10.5 120 19.75 4.3E-05 Average 4.4E-05 a PG specimen final water content (%), 21.6; length (cm), 7.18; and diameter (cm), 7.15 b Water height in burette
83
Table A-7. Hydraulic conductivity test data for NWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 92.2% 72.0 0.0 4.3 70.0 24.0 19.7 121 22.45 4.0E-05 2 80.0 70.0 92.2% 72.0 4.3 8.3 70.0 19.7 15.7 122 21.28 3.9E-05 3 80.0 70.0 92.2% 72.0 8.3 12.0 70.0 15.7 11.9 120 20.20 3.9E-05 Average 3.9E-05 4 100.0 70.0 92.2% 72.0 0.0 4.3 70.0 24.0 19.6 120 22.44 4.0E-05 5 100.0 70.0 92.2% 72.0 4.3 8.4 70.0 19.6 15.5 120 21.26 4.0E-05 6 100.0 70.0 92.2% 72.0 8.4 12.1 70.0 15.5 11.7 121 20.16 3.8E-05 Average 4.0E-05 7 120.0 70.0 92.2% 72.0 0.0 3.7 70.0 24.0 20.3 120 22.53 3.4E-05 8 120.0 70.0 92.2% 72.0 3.7 7.2 70.0 20.3 16.8 120 21.52 3.4E-05 9 120.0 70.0 92.2% 72.0 7.2 10.4 70.0 16.8 13.6 122 20.58 3.2E-05 Average 3.3E-05 a PG specimen final water content (%), 23.7; length (cm), 7.15; and diameter (cm), 7.13 b Water height in burette
84
Table A-8. Hydraulic conductivity duplicate test data for NWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 91.0% 72.0 0.0 3.9 70.0 24.0 20.1 120 22.55 3.6E-05 2 80.0 70.0 91.0% 72.0 3.9 7.6 70.0 20.1 16.4 120 21.48 3.6E-05 3 80.0 70.0 91.0% 72.0 7.6 11.1 70.0 16.4 12.9 120 20.47 3.5E-05 Average 3.6E-05 4 100.0 70.0 91.0% 72.0 0.0 3.5 70.0 24.0 20.4 121 22.60 3.2E-05 5 100.0 70.0 91.0% 72.0 3.5 6.9 70.0 20.4 17.0 121 21.62 3.2E-05 6 100.0 70.0 91.0% 72.0 6.9 10.1 70.0 17.0 13.8 121 20.70 3.2E-05 Average 3.2E-05 7 120.0 70.0 91.0% 72.0 0.0 3.3 70.0 24.0 20.6 120 22.63 3.1E-05 8 120.0 70.0 91.0% 72.0 3.3 6.4 70.0 20.6 17.5 120 21.72 3.0E-05 9 120.0 70.0 91.0% 72.0 6.4 9.4 70.0 17.5 14.6 120 20.87 2.9E-05 Average 3.0E-05 a PG specimen final water content (%), 21.6; length (cm), 7.13; and diameter (cm), 7.16 b Water height in burette
85
Table A-9. Hydraulic conductivity test data for EWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 89.0% 72.0 0.0 7.0 70.0 24.0 17.0 120 21.62 6.7E-05 2 80.0 70.0 89.0% 72.0 7.0 13.4 70.0 17.0 10.6 120 19.78 6.7E-05 3 80.0 70.0 89.0% 72.0 13.4 19.0 70.0 10.6 5.0 120 18.14 6.4E-05 Average 6.6E-05 4 100.0 70.0 89.0% 72.0 0.0 6.5 70.0 24.0 17.5 121 21.69 6.2E-05 5 100.0 70.0 89.0% 72.0 6.5 12.3 70.0 17.5 11.7 120 20.00 6.0E-05 6 100.0 70.0 89.0% 72.0 12.3 17.5 70.0 11.7 6.5 120 18.50 5.8E-05 Average 6.0E-05 7 120.0 70.0 89.0% 72.0 0.0 5.9 70.0 24.0 18.1 121 21.77 5.6E-05 8 120.0 70.0 89.0% 72.0 5.9 11.2 70.0 18.1 12.8 121 20.24 5.4E-05 9 120.0 70.0 89.0% 72.0 11.2 16.1 70.0 12.8 7.9 121 18.84 5.4E-05 Average 5.4E-05 a PG specimen final water content (%), 25.0; length (cm), 7.29; and diameter (cm), 7.25 b Water height in burette
86
Table A-10. Hydraulic conductivity duplicate test data for EWPGa
Test No.
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Saturation degree (%)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1 80.0 70.0 89.0% 72.0 0.0 5.4 70.0 24.0 18.6 121 22.24 5.0E-05 2 80.0 70.0 89.0% 72.0 5.4 10.4 70.0 18.6 13.6 120 20.79 5.0E-05 3 80.0 70.0 89.0% 72.0 10.4 14.8 70.0 13.6 9.2 121 19.48 4.6E-05 Average 4.9E-05 4 100.0 70.0 89.0% 72.0 0.0 5.1 70.0 24.0 18.9 121 22.28 4.7E-05 5 100.0 70.0 89.0% 72.0 5.1 9.7 70.0 18.9 14.2 121 20.92 4.6E-05 6 100.0 70.0 89.0% 72.0 9.7 14.0 70.0 14.2 9.9 121 19.67 4.5E-05 Average 4.6E-05 7 120.0 70.0 89.0% 72.0 0.0 4.9 70.0 24.0 19.1 121 22.31 4.5E-05 8 120.0 70.0 89.0% 72.0 4.9 9.4 70.0 19.1 14.6 120 21.00 4.4E-05 9 120.0 70.0 89.0% 72.0 9.4 13.6 70.0 14.6 10.3 120 19.78 4.4E-05 Average 4.5E-05 a PG specimen final water content (%), 24.5; length (cm), 7.16; and diameter (cm), 7.16 b Water height in burette
87
Table A-11. Cations concentration in batch leaching solution of SWPG of with MSW
Leachate (mg/L)
Cation MSW landfill leachate Leaching test 1 Leaching test 2 Leaching test 3
Ag BDL* BDL BDL BDL Al 0.2 0.19 0.23 0.24 As 0.16 0.15 0.15 0.16 B 6.47 6.76 6.93 6.99 Ba 0.05 0.03 0.04 0.04 Be BDL BDL BDL BDL Ca 85 1061 1175 1217 Cd BDL BDL BDL BDL Co 0.03 0.03 0.03 0.03 Cr 0.08 0.08 0.08 0.08 Cu 0.02 0.05 BDL 0.02 Fe 5.96 2.57 3.50 3.66 K 847 903 903 933 Mg 36.43 37.2 37.11 38.13 Mn 0.14 0.12 0.12 0.13 Mo BDL 0.02 BDL 0.03 Na 1558 1639 1638 1700 Ni 0.11 0.10 0.10 0.12 Pb BDL BDL BDL BDL Sb 0.11 BDL BDL BDL Se BDL BDL BDL BDL Sn BDL 0.05 BDL 0.06 Sr 0.27 2.95 3.19 3.32 V 0.05 0.06 0.05 0.05 Zn 0.05 0.03 0.03 0.04 *BDL = below detection limit
88
Table A-12. Cations concentration in batch leaching solution of WWPG of with MSW
Leachate (mg/L)
Cation MSW landfill leachate Leaching test 1 Leaching test 2 Leaching test 3
Ag BDL* BDL BDL BDL Al 0.2 0.19 BDL 0.14 As 0.16 0.14 0.13 0.15 B 6.47 6.79 6.27 6.3 Ba 0.05 0.04 0.06 0.03 Be BDL BDL BDL BDL Ca 85 1169 1034 903 Cd BDL BDL BDL BDL Co 0.03 0.03 0.02 0.02 Cr 0.08 0.07 0.06 0.07 Cu 0.02 BDL BDL BDL Fe 5.96 2.62 2.41 2.75 K 847 889 819 816 Mg 36.43 36.9 34.34 34.36 Mn 0.14 0.1 0.09 0.1 Mo BDL BDL BDL BDL Na 1558 1620 1485 1480 Ni 0.11 0.1 0.17 0.12 Pb BDL BDL BDL BDL Sb 0.11 BDL BDL BDL Se BDL BDL BDL BDL Sn BDL BDL BDL BDL Sr 0.27 3.22 2.87 2.56 V 0.05 0.05 0.05 0.05 Zn 0.05 0.04 0.16 0.13
*Below detection limit
89
Table A-13. Cations concentration in batch leaching solution of NWPG of with MSW
Leachate (mg/L)
Cation MSW landfill leachate Leaching test 1 Leaching test 2 Leaching test 3
Ag BDL* BDL BDL BDL Al 0.2 BDL BDL BDL As 0.16 0.14 0.16 0.15 B 6.47 6.59 6.97 6.43 Ba 0.05 0.05 0.04 0.04 Be BDL BDL BDL BDL Ca 85 1051 1170 1080 Cd BDL BDL BDL BDL Co 0.03 0.03 0.03 0.03 Cr 0.08 0.08 0.08 0.07 Cu 0.02 BDL BDL BDL Fe 5.96 2.60 3.53 2.99 K 847 858 928 853 Mg 36.43 36.09 38.76 35.86 Mn 0.14 0.12 0.13 0.17 Mo BDL 0.07 0.08 0.09 Na 1558 1574 1711 1558 Ni 0.11 0.11 0.12 0.13 Pb BDL BDL BDL BDL Sb 0.11 BDL 0.04 0.04 Se BDL BDL 0.03 BDL Sn BDL BDL BDL 0.04 Sr 0.27 3.16 3.48 3.2 V 0.05 0.05 0.05 0.04 Zn 0.05 0.03 0.02 0.03 *Below detection limit
90
Table A-14. Cations concentration in batch leaching solution of EWPG of with MSW
Leachate (mg/L)
Cation MSW landfill leachate Leaching test 1 Leaching test 2 Leaching test 3
Ag BDL* BDL BDL BDL Al 0.2 0.18 0.13 BDL As 0.16 0.16 0.14 0.14 B 6.47 7.00 6.34 6.37 Ba 0.05 0.06 0.05 0.03 Be BDL BDL BDL BDL Ca 85 1119 1154 1157 Cd BDL BDL BDL BDL Co 0.03 0.03 0.03 0.03 Cr 0.08 0.08 0.07 0.07 Cu 0.02 BDL BDL BDL Fe 5.96 2.96 2.74 2.51 K 847 917 869 855 Mg 36.43 37.72 36.06 35.57 Mn 0.14 0.11 0.1 0.1 Mo BDL BDL 0.02 0.03 Na 1558 1670 1577 1550 Ni 0.11 0.11 0.10 0.09 Pb BDL BDL BDL BDL Sb 0.11 BDL BDL BDL Se BDL BDL BDL BDL Sn BDL BDL BDL 0.03 Sr 0.27 3.32 3.38 3.38 V 0.05 0.05 0.04 0.04 Zn 0.05 0.03 0.03 BDL
*Below detection limit
91
Table A-15. Cations concentration in batch leaching solution of GCL bentonite with DI
water (mg/L) Cation Test 1 Test 2
Ag BDL* BDL Al 245.37 234.67 As BDL BDL B 0.79 0.77 Ba 0.16 0.16 Be 0.01 0.01 Ca 21.23 21.65 Cd BDL BDL Co 0.01 BDL Cr BDL BDL Cu 0.12 0.31 Fe 48.4 46.66 K 9.23 4.92 Mg 53.49 50.86 Mn 0.05 0.05 Mo 0.09 0.10 Na 159.51 145.20 Ni 0.04 0.06 Pb 0.06 0.06 Sb BDL BDL Se BDL BDL Sn 0.07 0.07 Sr 0.51 0.47 V BDL BDL Zn 0.14 0.30
*Below detection limit
92
Table A-16. Cations concentration in batch leaching solution of GCL bentonite with
MSW landfill leachate (mg/L) Cation Test 1 Test 2 Ag BDL* BDL Al 1.05 1.10 As BDL BDL B 5.40 5.32 Ba 0.17 0.18 Be BDL BDL Ca 134.82 124.35 Cd BDL BDL Co 0.04 0.04 Cr 0.22 0.22 Cu 0.16 0.13 Fe 2.06 2.01 K 537.45 496.31 Mg 61.84 62.46 Mn 0.08 0.07 Mo 0.04 0.04 Na 1828.65 1823.42 Ni 0.26 0.41 Pb 0.07 0.08 Sb BDL 0.03 Se BDL BDL Sn BDL BDL Sr 3.3 3.45 V 0.05 0.04 Zn 0.24 0.19 *Below detection limit
93
Table A-17. Cations concentration in batch leaching solution of GCL bentonite with
simulated SWPG leachate (mg/L) Cation Test 1 Test 2 Test 3 Ag BDL* BDL BDL Al 2.88 1.23 0.86 As BDL BDL BDL B 0.3 0.48 0.36 Ba 0.05 0.05 0.04 Be BDL BDL BDL Ca 235.92 187.32 271.81 Cd BDL BDL BDL Co BDL BDL BDL Cr BDL BDL BDL Cu 0.08 0.07 0.07 Fe 1.1 BDL BDL K 19.06 19.03 18.39 Mg 21.83 19.03 22.12 Mn BDL BDL BDL Mo 0.03 0.04 0.03 Na 415.36 434.91 394.98 Ni 0.01 0.02 BDL Pb BDL BDL BDL Sb BDL BDL BDL Se BDL BDL BDL Sn 0.04 0.03 BDL Sr 2.26 1.95 2.42 V BDL BDL BDL Zn 0.09 0.06 0.08 *Below detection limit
94
Table A-18. Cations concentration in batch leaching solution of GCL bentonite with
simulated WWPG leachate (mg/L) Cation Test 1 Test 2 Test 3 Ag BDL* BDL BDL Al 0.92 0.8 0.62 As BDL BDL BDL B 0.41 0.37 0.27 Ba 0.05 0.05 0.05 Be BDL BDL BDL Ca 193.38 214.44 302.83 Cd BDL BDL BDL Co BDL BDL BDL Cr BDL BDL BDL Cu 0.06 0.07 0.08 Fe BDL BDL BDL K 18.32 18.4 16.45 Mg 19.18 20.1 22.1 Mn BDL BDL BDL Mo 0.03 0.03 0.03 Na 437.23 442.74 380.49 Ni BDL BDL BDL Pb BDL BDL BDL Sb BDL BDL BDL Se BDL BDL BDL Sn BDL BDL BDL Sr 2.05 2.17 2.6 V BDL BDL BDL Zn 0.06 0.06 0.09 *Below detection limit
95
Table A-19. Cations concentration in batch leaching solution of GCL bentonite with
simulated NWPG leachate (mg/L) Cation Test 1 Test 2 Test 3 Ag BDL* BDL BDL Al 0.6 0.97 1.7 As BDL BDL BDL B 0.3 0.36 0.66 Ba 0.04 0.05 0.07 Be BDL BDL BDL Ca 204.3 189.95 189.23 Cd BDL BDL BDL Co BDL BDL BDL Cr BDL BDL BDL Cu 0.08 0.09 0.07 Fe BDL BDL BDL K 18.07 21.36 18.23 Mg 19.77 19.28 19.42 Mn BDL BDL BDL Mo 0.04 0.03 0.03 Na 433.47 512.24 438.08 Ni 0.02 BDL BDL Pb 0.02 BDL BDL Sb BDL BDL BDL Se 0.02 BDL BDL Sn BDL BDL BDL Sr 2.14 2.07 2.09 V BDL BDL BDL Zn 0.08 0.07 0.09
*Below detection limit
96
Table A-20. Cations concentration in batch leaching solution of GCL bentonite with
simulated EWPG leachate (mg/L) Cation Test 1 Test 2 Test 3 Ag BDL* 0.34 BDL Al 0.99 1.55 0.76 As BDL BDL BDL B 0.43 0.53 0.32 Ba 0.05 0.05 0.04 Be BDL BDL BDL Ca 166.36 181.25 182.02 Cd BDL BDL BDL Co BDL BDL BDL Cr BDL BDL 0.01 Cu 0.09 0.08 0.07 Fe BDL BDL BDL K 17.82 18.21 18.9 Mg 17.21 18.55 18.16 Mn BDL BDL BDL Mo 0.04 0.03 0.08 Na 440.5 451.83 479.29 Ni 0.02 BDL BDL Pb BDL 0.02 BDL Sb BDL BDL 0.04 Se BDL BDL BDL Sn BDL BDL 0.06 Sr 1.82 1.93 1.92 V BDL BDL BDL Zn 0.08 0.07 0.06
*Below detection limit
97
Table A-21. GCL hydraulic conductivity test results with DI water
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 13.4 18.3 70.0 17.8 13.5 76500 162.19 4.5E-09 80.0 70.0 72.0 18.3 19.8 70.0 13.5 12.2 28440 155.26 3.8E-09 80.0 70.0 72.0 10.0 13.4 70.0 20.0 17.1 57600 170.33 3.9E-09
Average 4.0E-09
2b 80.0 70.0 72.0 10.0 11.1 70.0 20.0 19.2 61200 188.33 2.1E-09 80.0 70.0 72.0 11.1 12.9 70.0 19.2 17.8 93120 185.12 2.4E-09
Average 2.3E-09
3c 80.0 70.0 72.0 0.0 3.2 70.0 24.0 20.7 84360 175.89 2.5E-09 80.0 70.0 72.0 3.2 7.2 70.0 20.7 16.7 109560 167.99 2.5E-09 80.0 70.0 72.0 7.2 10.5 70.0 16.7 13.4 69900 160.03 3.3E-09
Average 2.8E-09 a Duplicate test 1, specimen final water content (%), 105.1; thickness (cm), 0.87; diameter (cm), 10.30 b Duplicate test 2, specimen final water content (%), 111.2; thickness (cm), 0.80; diameter (cm), 7.04 c Duplicate test 3, specimen final water content (%), 127.0; thickness (cm), 0.92; diameter (cm), 10.60
98
Table A-22. GCL hydraulic conductivity test results with MSW landfill leachate
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 10.0 13.2 70.0 20.0 16.8 1200 175.94 1.8E-07 80.0 70.0 72.0 13.2 16.5 70.0 16.8 13.5 1200 168.19 1.9E-07 80.0 70.0 72.0 16.5 19.8 70.0 13.5 10.8 1290 160.67 1.7E-07
Average 1.8E-07
2b 80.0 70.0 72.0 0.0 7.1 70.0 24.0 16.8 61 219.15 6.3E-06 80.0 70.0 72.0 7.1 14.0 70.0 16.8 9.9 63 199.60 6.4E-06 80.0 70.0 72.0 14.0 20.4 70.0 9.9 3.5 61 181.10 6.8E-06
Average 6.5E-06
3c 80.0 70.0 72.0 5.0 10.9 70.0 20.0 14.1 60 180.88 6.2E-06 80.0 70.0 72.0 10.9 16.6 70.0 14.1 8.4 60 166.87 6.5E-06 80.0 70.0 72.0 16.6 21.9 70.0 8.4 3.2 60 153.65 6.5E-06
Average 6.4E-06 a Duplicate test 1, specimen final water content (%), 95.0; thickness (cm), 0.84; diameter (cm), 10.35 b Duplicate test 2, specimen final water content (%), 105.1; thickness (cm), 0.72; diameter (cm), 10.42 c Duplicate test 3, specimen final water content (%), 83.1; thickness (cm), 0.83; diameter (cm), 10.54
99
Table A-23. GCL hydraulic conductivity test results with simulated SWPG leachate
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 0.0 3.0 70.0 24.0 20.9 1260 170.60 1.7E-07 80.0 70.0 72.0 3.0 6.1 70.0 20.9 17.8 1260 164.11 1.8E-07
Average 1.7E-07
2b 80.0 70.0 72.0 11.0 12.7 70.0 19.0 17.3 1242 161.18 2.1E-07 80.0 70.0 72.0 12.7 14.4 70.0 17.3 15.6 1202 157.46 2.2E-07
Average 2.1E-07
3c 80.0 70.0 72.0 5.0 10.8 70.0 20.0 14.2 600 170.87 6.6E-07 80.0 70.0 72.0 10.8 15.0 70.0 14.2 10.0 600 159.47 5.2E-07 80.0 70.0 72.0 15.0 18.1 70.0 10.0 6.9 605 151.15 4.0E-07
Average 5.3E-07 a Duplicate test 1, specimen final water content (%), 118.5; thickness (cm), 0.95; diameter (cm), 10.42 b Duplicate test 2, specimen final water content (%), 122.8; thickness (cm), 0.91; diameter (cm), 7.24 c Duplicate test 3, specimen final water content (%), 104.4; thickness (cm), 0.88; diameter (cm), 10.42
100
Table A-24. GCL hydraulic conductivity test results with simulated WWPG leachate
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 10.0 20.4 70.0 20.0 10.4 600 179.82 1.1E-06 80.0 70.0 72.0 10.0 21.0 70.0 20.0 9.0 603 178.54 1.2E-06 80.0 70.0 72.0 10.0 21.6 70.0 20.0 8.4 602 177.77 1.3E-06
Average 1.2E-06
2b 80.0 70.0 72.0 10.0 11.5 70.0 20.0 18.5 601 173.25 3.5E-07 80.0 70.0 72.0 11.5 13.5 70.0 18.5 16.4 602 169.13 4.9E-07 80.0 70.0 72.0 13.5 15.8 70.0 16.4 14.1 602 164.07 5.7E-07
Average 4.7E-07
3c 80.0 70.0 72.0 10.0 11.1 70.0 20.0 18.9 1800 188.34 3.8E-08 80.0 70.0 72.0 11.1 12.1 70.0 18.9 17.9 1830 185.70 3.5E-08 80.0 70.0 72.0 10.0 10.7 70.0 20.0 19.2 1808 188.78 2.6E-08
Average 3.3E-08 a Duplicate test 1, specimen final water content (%), 115.0 thickness (cm), 0.78; diameter (cm), 10.42 b Duplicate test 2, specimen final water content (%), 108.4; thickness (cm), 0.86; diameter (cm), 7.24 c Duplicate test 3, specimen final water content (%), 104.4; thickness (cm), 0.88; diameter (cm), 10.42
101
Table A-25. GCL hydraulic conductivity test results with simulated NWPG leachate
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 5.0 6.6 70.0 20.0 18.4 9600 153.57 1.2E-08 80.0 70.0 72.0 6.6 9.7 70.0 18.4 15.4 29640 148.94 7.8E-09
Average 1.0E-08
2b 80.0 70.0 72.0 5.0 5.9 70.0 20.0 19.3 39600 166.14 3.0E-09 80.0 70.0 72.0 5.9 6.9 70.0 19.3 18.1 65760 164.11 2.6E-09
Average 2.8E-09
3c 80.0 70.0 72.0 5.0 8.5 70.0 20.0 16.7 66780 165.61 3.5E-09 80.0 70.0 72.0 8.5 12.8 70.0 16.7 12.6 85260 157.35 3.6E-09
Average 3.6E-09 a Duplicate test 1, specimen final water content (%), 93.6 thickness (cm), 1.03; diameter (cm), 10.63 b Duplicate test 2, specimen final water content (%), 98.8; thickness (cm), 0.93; diameter (cm), 7.13 c Duplicate test 3, specimen final water content (%), 98.7; thickness (cm), 0.92; diameter (cm), 10.54
102
Table A-26. GCL hydraulic conductivity test results with simulated EWPG leachate
Test
Chamber readings Inflow burette Outflow burette Test time (sec)
Gradient Hydraulic conductivity, K, (cm/sec.)
Cell pressure (psi)
Back pressure (psi)
Pressure (psi)
Ht. H2O initial (cm)b
Ht. H2O final (cm)
Pressure (psi)
Ht. H2O initial (cm)
Ht. H2O final (cm)
1a 80.0 70.0 72.0 5.0 8.3 70.0 20.0 16.7 180 173.38 1.2E-06 80.0 70.0 72.0 8.3 11.6 70.0 16.7 13.4 180 165.87 1.3E-06 80.0 70.0 72.0 11.6 14.9 70.0 13.4 10.1 180 158.36 1.3E-06
Average 1.3E-06
2b 80.0 70.0 72.0 5.0 8.4 70.0 20.0 16.6 182 194.44 1.1E-06 80.0 70.0 72.0 8.4 12.7 70.0 16.6 12.3 189 184.61 1.4E-06 80.0 70.0 72.0 12.7 17.4 70.0 12.3 7.5 182 173.05 1.7E-06
Average 1.4E-06
3c 80.0 70.0 72.0 10.0 13.2 70.0 20.0 16.8 1200 175.94 1.8E-07 80.0 70.0 72.0 13.2 16.5 70.0 16.8 13.5 1200 168.19 2.0E-07 80.0 70.0 72.0 16.5 19.8 70.0 13.5 10.8 1290 160.67 1.7E-07
Average 1.8E-07 a Duplicate test 1, specimen final water content (%), 102.5 thickness (cm), 0.88; diameter (cm), 10.61 b Duplicate test 2, specimen final water content (%), 106.4; thickness (cm), 0.78; diameter (cm), 10.57 c Duplicate test 3, specimen final water content (%), 114.1; thickness (cm), 0.84; diameter (cm), 10.33
103
APPENDIX B SUPPLEMENTARY FIGURES
Figure B-1. PG stack and sample location, Mosaic’s Batow Facility - South PG stack located in Mulberry, Florida. (Provided by Mosaic Fertilizer, LLC.)
104
Figure B-2. PG samples were stored for research purposes in solid and hazard waste management laboratory
105
Compacted PG 12.7 cm
10.2 cm
30.5 cm constant head
above PG
Influent
Effluent
Liquid
Figure B-3. Schematic diagram of PG column test
106
Figure B-4. Compacted PG and GCL hydraulic conductivity test devices
107
Figure B-5. Large-scale direct shear test device
108
LIST OF REFERENCES
ASTM (American Society of Testing and Materials), 2004. Standard test method for direct shear test of soils under consolidated drained conditions. West Conshohocken, Pennsylvania.
ASTM (American Society of Testing and Materials), 2004. Standard test methods for laboratory compaction characteristics of soil using standard effort. West Conshohocken, Pennsylvania.
ASTM (American Society of Testing and Materials), 2004. Standard test methods for measurement of hydraulic conductivity of saturated porous materials using a flexible wall permeameter. West Conshohocken, Pennsylvania.
ASTM (American Society of Testing and Materials), 2004. Standard test method for evaluation of hydraulic properties of geosynthetic clay liners permeated with potentially incompatible liquids. West Conshohocken, Pennsylvania.
ASTM (American Society of Testing and Materials), 2004. Standard test method for measurement of hydraulic conductivity of porous material using a rigid-wall, compaction-mold permeameter. West Conshohocken, Pennsylvania.
Ardaman & Associates, Inc., 2007. Gypsum consolidation and drainage volume estimates for the unlined and lined phosphogypsum stacks Mosaic Fertilizer, LLC Green Bay Facility Polk County, Florida. Provided by Mosaic Fertilizer, LLC.
Benson, C.H., John. M.T., 1994. Hydraulic conductivity of thirteen compacted clays, Clays and Clay Minerals, 43 (6) 669-681.
Benson, C.H., Meer, S.R., 2009. Relative abundance of monovalent and divalent cations and the impact of desiccation on geosynthetic clay liners. Geotechnical & Geoenvironmental Engineering, 135 (3), 349-358.
Chapuis, C., Masse, I., Aubertin, M., 2006. A drainage column test for determining unsaturated properties of coarse materials. Geotechnical Testing Journal, 30 (2) 1-7
Cho Y. M., Ko, J. H., Chi. L., Townsend, T.G., 2011. Food waste impact on municipal solid waste angle of internal friction. Waste Management, 31(1), 26-32.
Degirmenci, N., Okucu, A., Turabi, A., 2006. Application of phosphogypsum in soil stabilization. Building and Environment, 42(9), 3393-3398.
FDEP (Florida Department of Environmental Protection), 2010. Solid waste management facilities: chapter 62-701 solid waste management facilities table of contents. http://www.dep.state.fl.us/waste/quick_topics/rules/documents/62-701.pdf.
109
FDOT (Florida Department of Transportation), 2008. Summary of Phosphogypsum Laboratory Test Results. Provided by Mosaic Fertilizer, LLC.
FIPR (Florida Institute of Phosphate Research), 1983. Use of Florida phosphogypsum in synthetic construction aggregate. http://fipr1.state.fl.us/fipr/fipr1.nsf/a1380a2dc3df745f85256b4b006398eb/548768214d42a80a85256b25006cf204/$FILE/01-008-026Final.pdf.
FIPR (Florida Institute of Phosphate Research), 1989. Phosphogypsum for secondary road construction. http://www1.fipr.state.fl.us/fipr/fipr1.nsf/129fc2ac92d337ca85256c5b00481502/3e4ac1d74250acc085256b2e005b1632/$FILE/01-033-077Final.pdf.
FIPR (Florida Institute of Phosphate Research), 1990. Proceedings of the third international symposium on phosphogypsum. http://www1.fipr.state.fl.us/FIPR/FIPR1.nsf/.../01-060-083v1Final.pdf.
FIPR (Florida Institute of Phosphate Research), 1993. Environmental monitoring of Polk and Columbia counties experimental phosphogypsum roads. Bartow (FL). http://fipr1.state.fl.us/fipr/fipr1.nsf/9bb2fe8f45c4945e85256b58005abaec/d6a0b29584170e7685256b2f005bfeff/$FILE/05-033-101Final.pdf.
Gabr, M.A., Hossain, M.S., Barlaz, M.A., 2007. Shear strength parameters of municipal solid waste with leachate recirculation, Geotechnical and Geoenvironmental Engineering, 133(4), 478-484.
Harris, J. M., Shafer, A. L., DeGroff, W., Hater G. R., Gabr M., and Barlaz, M. A., 2006. Shear strength of degraded reconstituted municipal solid waste, Geotechnical Testing 29 (2), 1-8.
Holtz, R.D., Kovacs W.D.,1981. An Introduction to Geotechnical Engineering, Prentice Hall, Englewood Cliffs, NJ.
Jo, H.Y., Katsumi,T., Benson,C.H., Edil, T.B., 2001. Hydraulic conductivity and swelling of nonprehydrated GCLs permeated with single species salt solutions, Geotechnical And Geoenvironmental Engineering, 127 (7), 557-567.
Kavazanjian, E. 2008. The impact of degradation on MSW shear strength. Proceedings of GeoCongress 2008, Geotechnics of Waste Management and Remediation, ASCE, New Orleans, Louisiana, 224-231.
Kavazanjian, E. JR., Matasovic, N. Bachus, R.C., 1999. Large-diameter static and cyclic laboratory testing of municipal solid waste. Proceedings of Sardinia 99, 7th Int. Waste Management and Landfill Symposium, CISA-Environ. Sanitary Engineering, Cagliari, Italy, 437–445. http://www.infomine.com/publications/docs/Kavazanjian1999b.pdf
110
Kavazanjian, E., Matasovic, N., Bonaparte, R., Schmertmann, G., 1995. Evaluation of MSW properties for seismic analysis. Proceedings of Specialty Conference, Geoenvironmental 2000, ASCE Geotechnical Special Publication No. 46(2), 1126-1141.
Kolstad, D., Benson, C., Edil, T., 2004. Hydraulic conductivity and swell of nonprehydrated GCLs permeated with multispecies inorganic solutions. J. Geotech. Geoenviron. Eng., 130(12), 1236-1249.
Lee S., Xu Q., Booth M., Townsend T.G., Chadik P., Bitton G., 2006. Reduced sulfur compounds in gas from construction and demolition debris landfills. Waste Management, 26 (5), 526-533.
Machado, S.L., Carvalho, F.M., Vilar, O.M., 2002. Constitutive Model for municipal solid waste. Journal of Geotechnical and Geoenvironmental Engineering, 128 (11), 940-951.
Mahler, C.F., Netto, A.D.L., 2003. Shear resistance of mechanical biological pre-treated domestic urban waste. Proceedings of Sardinia 2003, 9th International Waste Management and Landfill Symposium, CISA-Environ. Sanitary Engineering, Cagliari, Italy. http://www.getres.ufrj.br/artigos/Mahler%20et%20Neto%20(2003b).pdf.
Moussa, D., Crispel, J.J., Legrand, C., Thenoz, B., 1984. Laboratory study of the structure and compactibility of Tunisian phosphogypsum (SFAX) for use in embankment construction, Resources and Conservation, 11 (2), 95-116.
Pelkey S.G., Valsangkar A.J., Landva A., 2001. Shear displacement dependent strength of municipal solid waste and its major constituent. Geotech Test J ASTM 24(4):381-390
Petrov, R.J., Rowe, R.K., 1997. Geosynthetic clay liner (GCL)-chemical compatibility by hydraulic conductivity testing and factors impacting its performance, Can. Geotech. J. 34, 863-885.
Petrov, R.J., Rowe, R.K., Quigley, R.M., 1997. Selected factors influencing GCL hydraulic conductivity, Journal of geotechnical and geoenvironmental engineering, 123 (8), 683-695.
Reddy, K. R., Hettiarachchi, H., Parakalla, N. S., Gangathulasi, J., Bogner J. E., 2009. Geotechnical properties of fresh municipal solid waste at Orchard Hills landfill, USA. Waste Management, 29, 952-959.
Ruhl, J.L., Daniel, D.E., 1997. Geosynthetic clay liners permeated with chemical solutions and leachates. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 123 (4), 369-381.
111
Shackelford C.D., Benson C.H., Katsumi T., Edil T.B., Lin L., 2000. Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids. Geotextiles and Geomembranes, 18 (2-4), 133-161.
Shieh, C. S., 1999. Application of Phosphogypsum in Landfills. http://www.fipr.state.fl.us/5b_Shieh_testimony.pdf.
Stark, T. D., Huvaj-Sarihan, N., Li, G., 2009. Shear strength of municipal solid waste for stability analyses, Environmental Geology, 57(8), 1911-1923.
The World Bank, 1999. Urban development sector unit and east asia and pacific region, what a waste: solid waste management in Asia. The International Bank for Reconstruction and Development, 4-24. http://web.mit.edu/urbanupgrading/urbanenvironment/resources/references/pdfs/WhatAWasteAsia.pdf
Touze-Foltz, N., Duquennoi, C., Gaget, E., 2006. Hydraulic and mechanical behavior of GCLs in contact with leachate as part of a composite liner. Geotextiles and Geomembranes, 24 (3), 188-197.
USEPA, 2007. Municipal solid was in the United States: 2007 Facts and Figures. http://www.epa.gov/epawaste/nonhaz/municipal/pubs/msw07-rpt.pdf.
USEPA, 2010. About phosphogypsum. http://www.epa.gov/rpdweb00/neshaps/subpartr/about.html
VanGulck, J.F., Rowe, K.R., Rittmann B. E., Cooke A. J., 2003. Predicting biogeochemical calcium precipitation in landfill leachate collection systems, Biodegradation, 14 (5), 331-346.
Vilar O.M., Carvalho M.F., 2004. Mechanical properties of municipal solid waste. Geotech Test J ASTM 32(6):1-12
Wang, H., Nie, Y., 2001. Municipal solid waste characteristics and management in China, Air & Waste Management Association, 51, 250-263.
Wang, X.D., Benson, C.H., 1999. Hydraulic conductivity testing of geosynthetic clay liners (GCLs) using the constant volume method, Geotechnical Testing Journal, 22(4): 277-283.
Zekkos, D., Bray, J.D., Stokoe, K., Kavazanjian, E., Rathje, E., Athanasopoulos, G.A., Riemer, M., Matasovic, N., Lee, J.J., Seos, B., 2008. Recent findings on the static and dynamic properties of municipal solid waste. http://www.infomine.com/publications/docs/Zekkos2008.pdf.
Zekkos, D., Bray, J.D., Athanasopoulos, G.A., Riemer, M.F., Kavazanjian, E. Jr., Founta, P.A., Grizi, A.F., 2007. Compositional and loading rate effects on the shear strength of municipal solid waste. http://waste.geoengineer.org/files/1525_zek.pdf.
112
Zhan, T.L.T., Chen, Y.M., Ling, W.A., 2008. Shear strength characterization of municipal solid waste at the Suzhou landfill, China, Engineering Geology, 97, 97-111.
113
BIOGRAPHICAL SKETCH
Yongqiang Yang was born in 1979 in China to Guoan Yang and Junying Xia. He
enrolled in the Heibei Normal University of Science and Technology, Qinhuangdao,
China, in September 2001, and graduated with a Bachelor of Science in Food Science
& Engineering in July 2005. He also enrolled in the University of Findlay, Ohio in fall of
2007 and graduated with a Master of Science in Environmental, Health and Safety
Management in spring of 2009. He received his Master of Science in Environmental
Engineering Sciences from the University of Florida in spring of 2011.
