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| Citation |
- Permanent Link:
- https://ufdc.ufl.edu/UFE0025067/00001
Material Information
- Title:
- Study of Pore Water Pressure Impact and Fluid Conductance of a Landfill Horizontal Liquids Injection System
- Creator:
- Kumar, S
- Place of Publication:
- [Gainesville, Fla.]
- Publisher:
- University of Florida
- Publication Date:
- 2009
- Language:
- english
- Physical Description:
- 1 online resource (137 p.)
Thesis/Dissertation Information
- Degree:
- Master's ( M.E.)
- Degree Grantor:
- University of Florida
- Degree Disciplines:
- Environmental Engineering Sciences
- Committee Chair:
- Townsend, Timothy G.
- Committee Members:
- Motz, Louis H.
Annable, Michael D.
- Graduation Date:
- 8/8/2009
Subjects
- Subjects / Keywords:
- Bedding ( jstor )
Bioreactors ( jstor )
Flow velocity ( jstor )
Fluids ( jstor )
Landfills ( jstor )
Liquids ( jstor )
Porosity ( jstor )
Pressure ( jstor )
Pressure sensors ( jstor )
Transducers ( jstor )
Environmental Engineering Sciences -- Dissertations, Academic -- UF
bioreactor, distribution, horizontal, injection, landfills, leachate, lines, pore, pressure, recirculation
Polk County ( local )
- Genre:
- Electronic Thesis or Dissertation
born-digital ( sobekcm )
Environmental Engineering Sciences thesis, M.E.
Notes
- Abstract:
- 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 STUDY OF PORE WATER PRESSURE IMPACT AND FLUID CONDUCTANCE OF A LANDFILL HORIZONTAL LIQUIDS INJECTION SYSTEM By Sendhil Kumar August 2009 Chair: Timothy G. Townsend Major: Environmental Engineering Sciences Moisture distribution in landfilled waste plays a very important role in waste stabilization. Liquid addition systems are designed and buried inside landfilled waste to distribute moisture at different depths. Pressure is required to inject leachate through these systems. Landfill operators often add liquids under pressure to achieve higher liquid addition rates which speeds up waste stabilization. In this process, slope stability of the landfill becomes a subject of concern. When liquids are present under pressure in the landfilled waste, an increase in the pore water pressure can decrease the shear strength and the geotechnical stability of side slopes. Though modeling techniques are available to predict the possible build up of pressures inside the landfill, very little is known about the real pressures that result from adding liquids under pressure. Two field investigations were conducted at a bioreactor landfill in Polk County, Florida: (1) Measurement of the spatial variation of pore water pressure resulting from pressurized leachate injection through the horizontal injection lines (HILs), and (2) evaluation of the performance of HILs in terms of fluid conductance Pressure transducers were buried in and around three buried HILs in the landfill to study the pressure distribution resulting from prolonged liquids addition. Each of the three HILs was constructed with different bedding media: crushed glass, tire chips, and no bedding media. Moisture distribution was more uniform among the trenches with bedding media than in the one which did not have any bedding media. Pore pressure dissipated over a short distance from the HILs. It was observed that the pore pressure impact was similar both in the horizontal and vertical direction from the HIL. The fluid conductance values (flow rate per unit length of HIL per unit of applied pressure head) for 31 HILs of varying, length, bedding media, and overburden depth of waste were monitored over a large range of cumulative linear-injected volumes. Pressure and flow for the operated HILs were monitored and recorded using the supervisory control and data acquisition (SCADA) system. In general, the HILs with bedding media had higher fluid conductance values than those without bedding media. Variation of flow rates during the operation of these HILs had negligible impact on the fluid conductance. The fluid conductance values of all the HILs decreased with increased cumulative injection volume and decreased with increased overburden depth of waste. This decrease in fluid conductance, which varied from 0.01 to 0.1 gpm/ft/ft of w.c, is hypothesized to be the result of decreasing hydraulic conductivity of the surrounding waste due to increasing volume of leachate injection and overburden depth. ( en )
- General Note:
- In the series University of Florida Digital Collections.
- General Note:
- Includes vita.
- Bibliography:
- Includes bibliographical references.
- Source of Description:
- Description based on online resource; title from PDF title page.
- Source of Description:
- This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
- Thesis:
- Thesis (M.E.)--University of Florida, 2009.
- Local:
- Adviser: Townsend, Timothy G.
- Electronic Access:
- RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-08-31
- Statement of Responsibility:
- by S Kumar.
Record Information
- Source Institution:
- University of Florida
- Holding Location:
- University of Florida
- Rights Management:
- Copyright Kumar, S. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
- Embargo Date:
- 8/31/2010
- Resource Identifier:
- 489120312 ( OCLC )
- Classification:
- LD1780 2009 ( lcc )
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2.2.3 Data Management
All the instruments were connected to six multiplexers that were connected to a Geokon
CR10X datalogger. The responses from the 81 pressure transducers were recorded by the
datalogger; a laptop was used to connect to the datalogger and periodically download the raw
frequency and temperature data for all the pressure transducers. The datalogger was programmed
to record data every 30 minutes, the raw data were converted to pressure in psi using the
calibration reports specified for each pressure transducer using the manufacturer's instructions.
The equation used to convert the raw data and the calibration constants for each transducer
(Tables C-l and C-2) are presented in Appendix C. Pressure readings recorded with 60 minutes
interval were chosen to represent the results, figures with the results show the change in pressure
with days of operation. A contour plot using a software called SURFER, was made to present the
pressure distribution around the trench with transducers buried 3 ft away from the trench, the
highest pressures reached by the end of the experimental duration was used to represent the
impact due to pressurized leachate injection. The data analyzed and presented for this thesis
represent an experimental duration of 4 months, Jul 2007 to Oct 2007 during which all the three
injection lines were operated. Results from only 50 out of the 81 pressure transducers were found
to be useful to study the pore pressure distribution, as the rest of the transducers recorded
negative frequency readings during the experimental period that suggested the transducer had
failed. The reason for the transducers to fail is presumed to be the harsh landfill conditions.
2.2.4 Leachate Injection Experiment
The three HILs around which the experimental setup was constructed were operated to
meet the objectives of the experiment. The Table 2-1 shows the duration and volume of leachate
injected through each HIL; HIL A was chosen to be operated first, resulting in impacting the
pore pressures in the surrounding. To avoid any overlap of response from the pressure
Miller 1998) found that the flow rate to applied pressure ratios, described by Larson (2007) as
"fluid conductance", decreased with increasing injection time and varied depending upon the
depth within the landfill and the construction of the HIL. The objective of the research described
in this thesis is to evaluate the performance of horizontal injection lines for leachate recirculation
based on the fluid conductance; fluid conductance can be used as one of the design inputs for
similar systems at future bioreactors.
Larson (2007) presented preliminary results of fluid conductance for design and
operational variables at the Polk County North Central Landfill. This study aims to continue and
build upon this past study by examining the flow rate to applied pressure ratio for design and
operational variables such as the length of a HIL, effect of HIL depth within the landfill and the
effect of HIL bedding media.
3.2 Methods and Materials
3.2.1 Site Description
The Polk County North Central landfill is in Winter Haven, Florida (figure B-l) and was
opened in 1976. The facility has a total area of approximately 2,200 acres, of which 700 acres are
permitted for landfill use. As shown in the aerial view of the Polk NCLF facility in figure B-2,
the facility has the following on site: a household hazardous waste collection area, a materials
recycling facility (MRF), a closed unlined Class I and III landfill, closed unlined landfill cells,
and three lined Class I landfill cells, Phase 1, 2 and 3. Phase 1 is temporarily capped, Phase 2
stopped accepting waste in November 2007 and Phase 3 is the currently active cell. The facility
accepts waste from the entire Polk County community at a daily average of 1,250 tons of
municipal solid waste (MSW), 88 tons of construction and demolition waste, and 180 tons of tire
and wood ash. Phases 1, 2 and 3 in the facility generate about 30,000 gallons/day of leachate.
10
Pressure transducer Al
Pressure transducer A2
Pressure transducer A3
3 ft HILA
Injection
o Tire chips
6 A3 -A2 Al
180 ft 180 ft
2
0.0 0.5 1.0 1.5 2.0
Days
Figure 2-9. Initial responses from pressure transducers buried along the trench of HIL A with tire
chips as bedding media.
2009 Sendhil Kumar
20
180
180
50
40
30
PI
20
10
-0
220
Linear cumulative volume injected (gallons/ft)
Figure B-61. Flow-pressure variation with linear cumulative volume injected through HIL 101.
(Media = Crushed glass; Length = 1080 ft; Overburden depth = 41 ft)
0.05
S0.04
0.03
t 0.02
0o
0.01
180 190 200 210 220
Linear cumulative volume injected (gallons/ft)
Figure B-62. Fluid conductance variation with linear cumulative volume injected through HIL
101.
119
-+- Flowrate
-- Pressure head
1 .t~
The study described in this document was carried out in the Phase 2 landfill unit; Phase 2
cell was actively accepting waste from March 2000 to November 2007. The Phase II landfill as
shown in figure B-2 is a 43-acre cell divided into eight equal-size subcells of a saw tooth design.
This site uses a state-of-the-art supervisory control and data acquisition (SCADA) system to
operate and monitor the liquid distribution system in Phase 2. All Phase 2 subcells, except for
Subcell 1, are recirculated with leachate using Horizontal Injection Lines (HILs) installed at
different elevations within the cells. Subcells 2 to 7 each have a hydrant/header assembly that is
connected to the force main at the south toe of the landfill as shown in figure B-3. Each
hydrant/header assembly branches into a group of standpipes to connect to the HILs. Each
standpipe has a manual butterfly valve that is outfitted as shown in figure B-4. Each hydrant
assembly is equipped with a pressure gauge, flow meter, and flow control valve.
3.2.2 Horizontal Injection Line Construction
There are 106 HILs connected to the standpipes as shown in figure B-4 at different
subcells. These 106 HILs enter the landfill from the south side at various elevations, a drawing
showing the cross section of the south side of phase 2 landfill with the HILs is attached in the
Appendix B. The HILs have different configurations; most of them are single lines having
different lengths. A few recently constructed lines are "branched lines" which means that several
HILs within the landfill were connected to a single inlet manifold, most of which are located at
higher elevations in the landfill. Each HIL was constructed by excavating trenches
approximately 3 to 4 ft wide and 5 ft deep using hydraulic excavators. The trenches were
backfilled with a layer of porous bedding media, a perforated pipe was placed, and then the
remainder of the trench was backfilled again with the same porous bedding media. All the HILs
have perforations starting at 100 ft inside the landfill from the point of entry on the side slope;
the first 100 ft would be solid-walled pipe where the trench was backfilled with clay so as to
ACKNOWLEDGMENTS
I would like to thank my committee members for their guidance and comments on this
thesis. I would like to specially thank Professor Timothy Townsend for constantly supporting
me through the research work. Thanks go out to Drs Brajesh Dubey, Pradeep Jain, Jae Hac Ko
and Hwidong Kim for their assistance throughout my graduate studies. Additional thanks to my
fellow graduate students who helped me while carrying out the experiments.
I also thank the Polk County Board of County Commissioners, Hinkley center for solid and
hazardous waste management and U.S. Environmental Protection Agency for funding this
research as well as the Polk County Solid Waste Division for their support. Special thanks to
Brooks Stayer, Allan Choate, and Sharon Hymiller for their support and guidance. Further
gratitude is offered to the administration staff and operators of the Polk County Solid Waste
Division.
I would like to mention my appreciation to those I worked with and learned from while
working at the Polk North Central landfill, especially Dennis Davis and George Reinhardt of
Jones Edmunds & Associates; Eric Sullivan of Curry Controls; and everyone at Eclipse
Construction. Further thanks to those who offered advice from afar via phone or e-mail from
Geokon, Inc. and Multilogger Inc.
Lastly, I can never thank my parents enough for their support and encouragement
throughout my life and the greatest thanks to my friends, for their friendship, encouragement,
and advice.
APPENDIX A
SUPPLEMENTAL FIGURES FOR CHAPTER 2
This appendix presents graphs of the data collected from all the pressure transducers
present in the landfill that were used to analyze data. The results cover a period from July 2007
to June 2008.
Flowrate
Pressure head
100
80
60
40
20
190 200 210 220
190 200 210 220
50
40
30
20
10
-0
230
Linear cumulative volume injected (gallons/ft)
Figure B-25. Flow-pressure variation with linear cumulative volume injected through HIL 61.
(Media = Tire chips; Length = 520 ft; Overburden depth = 60 ft)
0.0080
-- Fluid conductance
0.0075
8 0.0070
g 0.0065
r4 0.0060 -
0.0062
0.0055 -
0.0050 i
190 195 200 205 210 215 220 225
Linear cumulative volume injected (gallons/ft)
Figure B-26. Fluid conductance variation with linear cumulative volume injected through HIL
61.
Townsend, T. G. and Miller W. L. (1998). Leachate recycle using horizontal injection.
Advances ofEnvironmental Research, 2(2) 1995, 129-138.
Townsend, T. G., Wise, W. R., and Jain, P. (2005). One dimensional gas flow model for
horizontal gas collection systems at municipal solid waste landfills. Journal of
Environmental Engineering, ASCE, 131(12), 1716-1723.
Watson, R.P. (1987). "A case study of leachate generation and recycling at two sanitary
landfills" in Proceedings from the Technical Sessions of the GRCDA 25th Annual
International Seminar, Equipment, Services, and Systems Show. Vol. 1, August 11-13,
Saint Paul, MN.
Warith, M. (2002). Bioreactor Landfills: experimental and field results. Waste Management 22
(2002), 7-17.
Warith, M.A., Evgin, E., Benson, P. A. S (2004). Suitability of shredded tires for use in landfill
leachate collection systems. Waste Management 24 (2004), 967-979.
Clay Plug
Leachate Storage Tanks
Figure B-3. Schematic view of the phase 2 leachate pumping setup.
Table C-l Initial readings and calibration constants for the pressure transducers
Initial Readings Calibration Constants
Gauge R, To S. A B C K
(hz) (0 C) (hz) (pressure/digit2) (pressure/digit2) (pressure/digit2) (pressurelC)
Al 8768 21.60 994.40 -5.40701E-09 -0.01725 151.74 -0.01571
A2* 9040 22.40 991.80 -1.57052E-08 -0.01618 147.40 -0.02690
A2 8729 24.60 991.80 1.05023E-08 -0.01590 137.92 -0.01155
A3 8707 22.60 991.80 -5.35972E-09 -0.01675 146.12 -0.02378
A4 8905 22.60 991.80 -3.41020E-08 -0.01876 169.63 -0.00572
A5 9272 22.00 990.18 -3.59765E-09 -0.01659 154.00 -0.01879
A6 8655 21.80 991.80 2.16509E-08 -0.01605 137.15 -0.01282
A6* 8687 24.40 991.80 7.14185E-09 -0.01737 150.31 -0.01417
A7 8754 23.10 994.40 -5.86632E-09 -0.01684 147.70 -0.01537
A8 8804 21.60 1002.74 9.76917E-09 -0.01536 134.36 -0.01971
A8* 8754 22.10 996.70 -1.86265E-08 -0.01589 140.37 -0.01475
A9 8694 22.60 994.40 -1.70334E-08 -0.01753 153.70 -0.00889
A9* 8605 22.70 991.80 8.38216E-10 -0.01689 145.16 -0.02507
A10 8781 22.70 991.80 1.37404E-08 -0.01576 137.17 -0.01583
All 8824 20.80 991.80 2.48634E-08 -0.01567 136.24 -0.01371
All* 8742 22.50 994.40 7.91103E-09 -0.01572 136.72 -0.01431
A12 8750 22.40 994.40 1.01788E-08 -0.01556 135.30 -0.02456
A13 8781 22.90 991.80 3.14503E-08 -0.01655 142.81 -0.00838
A14 8808 24.70 991.80 -1.67472E-08 -0.01727 153.34 -0.02143
A15 8739 21.00 991.80 4.93877E-09 -0.01604 139.65 -0.02540
BI 8840 21.20 991.80 -3.04300E-09 -0.01633 144.48 -0.01943
B2 8651 22.80 991.80 2.18668E-09 -0.01718 148.41 -0.01729
B2* 8578 23.70 991.80 -3.85094E-10 -0.01643 140.88 -0.00861
B3 8619 21.80 994.40 2.13540E-08 -0.01689 143.82 -0.02380
B4 8773 22.50 994.40 5.14225E-09 -0.01667 145.76 -0.01970
B5 8884 24.10 991.80 -1.88008E-08 -0.01792 160.51 -0.00931
B6 8790 22.00 1005.02 -3.15315E-08 -0.01787 159.32 -0.01489
B6* 8692 21.80 1005.87 -3.69290E-09 -0.01674 145.68 -0.01895
B7 8832 22.40 994.40 1.84816E-09 -0.01530 134.93 -0.01710
B8 8957 22.60 996.73 1.49087E-08 -0.01707 151.60 -0.02762
B8* 8643 24.20 1004.18 -7.95127E-09 -0.01599 138.68 -0.01496
B9 8650 23.30 991.80 3.67142E-09 -0.01623 140.05 -0.01503
B9* 8696 23.80 991.80 3.62757E-10 -0.01613 140.45 -0.01147
B10 8762 21.80 994.40 -3.14806E-08 -0.01747 155.50 -0.01121
Bl1 8749 22.20 994.40 -3.39356E-10 -0.01576 137.82 -0.01603
Bll* 8721 22.30 994.40 3.68740E-08 -0.01732 148.19 -0.01991
B12 9060 22.00 994.40 -9.73143E-09 -0.01826 166.28 -0.01538
B13 8701 22.80 991.80 -2.60550E-09 -0.01707 148.64 -0.01578
B14 8789 21.90 994.40 6.09440E-10 -0.01914 168.12 -0.01523
B15 8687 20.80 994.40 -1.45253E-08 -0.01716 150.03 -0.02402
CHAPTER 4
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
4.1 Summary
An understanding of the in-situ pore pressure distribution in a landfill resulting from
pressurized liquid addition would be extremely helpful to bioreactor landfill engineers. The pore
pressure value within the landfilled waste is a very important input in estimating factors of safety
for geotechnical stability. The present study measured the in situ pore pressures with the use of
buried pressure transducers. Originally, data from 81 buried pressure transducers were to be used
for the study. However, it was discovered that 31 of these instruments had stopped working
before the experiment was started. The results were analyzed based upon data collected from the
50 reliable pressure transducers. It was found that the pore pressure values within the landfill due
to pressurized injection of liquids ranged from 0 6.5 psi and that the pressure dissipated over a
small distance around the horizontal trenches. It was observed that there was little to no impact
on pore pressures in the waste surrounding the HIL with no bedding media because of low
conductivity of waste media. This range of pore pressure reported was observed for a maximum
of 5 psi injection pressure through each horizontal trench as per the permit conditions. Pore
pressures increased before the injection experiments were started as more lifts of waste was
added over the experimental area due to build of landfill gas and pore space compression.
Another field study evaluated the effect of different design and operational variables upon the
fluid conductance (i.e., flow-rate-to-applied-pressure ratio) of HILs at the same landfill. Thirty
one HILs were examined and fluid conductance values were determined for similar cumulative
linear-injected volumes in this study. Results from the study confirmed that the fluid
conductance values for HILs decreased with increasing overburden depth, cumulative volume
injected; similar results were observed in a study at a different site by Townsend and Miller
3 inches but with larger and smaller pieces at times, having a hydraulic conductivity that ranged
from 0.67 to 13.4 cm/sec (Warith et al. 2004). The crushed glass was derived onsite from broken
bottles that were collected at the Polk County materials recycling facility. To evaluate the effect
of bedding media on fluid conductance, injection tests were performed on HILs at the same
depths within the landfill that contained either type of media. The effect of no bedding media
was also tested in this fashion.
To test the effect of HIL length, injection tests were performed on multiple HILs of
different lengths and with approximately the same depth of overburden pressure above. The
resulting fluid conductance data were compared for the same values of cumulative linear-injected
volume.
3.2.5 Data Management
Fluid conductance values were observed to be higher for all the HILs when first operated,
as the volume of leachate injected through them increased, the difference due to HIL
configuration could be seen in terms of fluid conductance. Therefore, fluid conductance values
of HILs were compared at an approximate cumulative linear injected volume of 200 gallons per
foot of the HIL. Only 31 HILs of the 106 had been operated to inject over 200 gallons/ft of
leachate, those were used in this study (table 2). Flow-pressure data for the HILs were
downloaded from the SCADA server and processed to determine the fluid conductance. These
data were logged every minute. Fluid conductance for the injection run was then plotted as a
function of cumulative linear-inj ected volume. The plots will show the impact of prior use of the
HIL presented. Box plots were used to represent the fluid conductance of HILs to compare for
the design parameters. This was accomplished plotting the HILs on the y-axis with the fluid
conductance of the last day's injection run of HIL where the injected volume was close to a
cumulative linear-injected volume of 200 gallons/foot of HIL on x-axis (log scale). The averages
04 50 ft 04
3a----- 3
I
o13 14
0 0
12
I
60
I
13 14
O
8 2
7 0
60
131 14
12
0
8 9
7 I 0'
6
I
* Pressure transducers suitable for the analysis
0 Pressure transducers not suitable for the analysis
15
10
10
Figure 2-1. Plan view of the experimental area with buried pressure transducers.
50 ft
100
80
60
40
20
0
19
0 195
200 205 210 215
- Flowrate
- Pressure head
lo p 'tI
,, r,/i
Linear cumulative injected volume (gallons/ft)
Figure B-23. Flow-pressure variation with linear cumulative volume injected through HIL 59.
(Media = No media; Length = 480 ft; Overburden depth = 75 ft)
0.010
-
0.008
-*
S0.006
-
S 0.004 -
0
S0.002 -
-
0.000
190 195 200 205 210 215 220
Linear cumulative volume injected (gallons/ft)
Figure B-24. Fluid conductance variation with linear cumulative volume injected through HIL
59.
100
50
40
30
20
10
0
220
-- Fluid Conductance
0.0036
I I
2.2 Materials and Methods
2.2.1 Site Description
The Polk County North Central Landfill (NCLF) is located in Winter Haven, Florida as
shown in the figure B-1. Phase 2, shown in figure B-2, is a lined landfill site that accepted waste
from March 2000 to November 2007. The Phase 2 landfill received approximately 2,500 metric
tons of waste per day, which consisted of mixed residential, commercial, and industrial waste.
The site also contains several closed landfill units.
One hundred and six HILs were installed in seven out of eight subcells in the Phase 2
landfill and were connected to seven main pipes at their respective subcells. These main pipes
were all connected to the storage tanks where the leachate was pumped to the HILs. The HILs
are 4-inch-diameter high-density polyethylene (HDPE) pipe with two perforations at every 2
linear ft of the pipe. The perforations were each oriented at 450 from either side of vertical and
were placed facing downward. The trenches were constructed by excavating approximately 3-
foot-wide-and-3-foot-deep trenches and backfilling them with a layer of porous bedding media,
laying a perforated pipe, and backfilling the rest of the trench with the bedding media.
The liquid distribution system was operated and monitored by a SCADA system. The
HILs were operated individually or sometimes as a cluster of two or more HILs in the same
subcell. HILs were selected to achieve maximum leachate recirculation. The permitted maximum
daily limit for leachate injection is 50,000 gallons. The leachate distribution system was operated
only when an operator was present on site (8 hours per day for 5 to 7 days a week depending on
how urgent the need to reduce the leachate levels in the storage tanks). The permit also states that
the HILs can be operated only at a maximum of 5-psi injection pressure. The pressure limit was
set for slope stability reasons. The applied pressure is the difference between the elevation head
and the recorded pressures measured at the base of the landfill. After a chosen HIL is operated at
0 -
200
50
40
30
20
10
0
205 210 215 220 225
Linear cumulative volume injected (gallons/ft)
Figure B-13. Flow-pressure variation with linear cumulative volume injected through HIL 30.
(Media = Crushed glass; Length = 720 ft; Overburden depth = 121 ft)
0.0001 I II
200 205 210 215 220 225
Linear cumulative volume injected (gallons/ft)
Figure B-14. Fluid conductance variation with linear cumulative volume injected through HIL
30.
120
20
--- Flowrate
--- Pressure head
wP"t
- I
0.007
7 0.006
0.005
S0.004-
-
m 0.003-
S0.002
S0.001 -
E oo-
I-N- Fluid Conductance
0.0024
60
40
20
0
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-59. Flow-pressure variation with linear cumulative volume injected through HIL 91.
(Media = No media; Length = 360 ft; Overburden depth = 15 ft)
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-60. Fluid conductance variation with linear cumulative volume injected through HIL
91.
S Pressure transducer B1
3 f Pressure transducer B2
_/ Pressure transducer B3
0* No media
B3 >I -B2 B1
18 ft 180 ft
HIL B
Injection
0 -I---
0.6 0.8
Days
Figure A-11. Response from the pressure transducers in the trench of HIL B with no bedding
media.
6 -
0 0
4 (
= =
.
<, .< = =
Bl B2 B3
Pressure transducers
Figure A-12. Response over time from the pressure transducers after the injection was stopped.
- Pressure transducer Al
- Pressure transducer A2
Pressure transducer A3
|o _ _ Tire chips
A3 ~ A2 <> Al
180 ft 180 ft
i ^ ^A
tart of injection
14 day operation End of injectionI
Days
Figure 2-7. Response from pressure transducers buried along the trench HIL A with tire chips as
bedding media.
3ft
HIL A
. Injection
~I I
The pressure data recorded after the experimental duration were analyzed to understand the
change in pore pressure after the injection was stopped; figure 2-6 shows the response from the
transducers (Cl, C2 and C3) along the HIL C with crushed glass. It can be seen that the pore
pressures reduce greatly over time after the injection is stopped; similar results are presented in
Appendix A.
2.3.2 Measurement of Pore Pressures Within the Trenches
The results in figures 2-7 through 2-10 show the response of the transducers that are buried
along the trench of the three HILs. There is negligible pressure loss and a uniform pressure
distribution along the trenches with tire chips and crushed glass as seen in figures 2-7 and 2-9;
this is due to the higher porosity of the bedding media compared to the surrounding waste. A
good pressure distribution within the trench is a great advantage to spread out the injected liquids
in the surrounding area. Pressure transducer responses were analyzed to check the time taken to
attain uniform leachate flow through the trench. The response from pressure transducers (Al, A2
and A3) buried along HIL A with tire chips in the trench as seen in figure 2-9, indicate that there
is only a small delay of 3 to 4 hrs in reaching steady state flow through the whole trench with
bedding media after the injection is started. There is a slight difference in pressures on the first
day of injection, whereas by the second day the pressures along the whole trench seem to have
attained uniformity (figure 2-9).
Figure 2-10 shows the response from the transducers (B B2 and B3) buried along the
trench of HIL B (figure 2-1) which does not have any bedding media around it. There is a great
loss in the injection pressure along the trench, which is likely the result of the lower hydraulic
conductivity of waste surrounding the line. The HILs with no media were found to have a better
fluid conductance (discussed in the next chapter) at shallower depths of about 20 to 40 ft in the
landfill and as the overburden depth increased it required very high pressures to inject leachate
10
Pressure transducer B1
| Pressure transducer B2
8 / Pressure transducer B3 Injecton
of- 1No media
B3 1----B2 -- B
B3 18I ft B2 180 ft B1
6-
6 Start of injection End of injection
1 day duration
4
2
0 ,-* '-* *
0.4 0.6 0.8
Days
Figure 2-10. Response from pressure transducers buried along the trench HIL B with no bedding
media.
2 -
0 5 10 15 20
Days
Figure A-21. Response of pressure transducers 3 ft away on the left of HIL C with crushed glass
as bedding media.
7 -
6 -
5 -
2 8 8*
| 3- C
2 8 8*
Pressure transducers
Figure A-22. Response over time from the pressure transducers after the injection was stopped.
60
40
20
0
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-11. Flow-pressure variation with linear cumulative volume injected through HIL 27.
(Media = Crushed glass; Length = 720 ft; Overburden depth = 80 ft)
0.10
S0.08
1 0.06
S 0.04
U
0.02
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-12. Fluid conductance variation with linear cumulative volume injected through HIL 27.
14
12
10
U,
8
6
4
2
0
0 10 20 30 40
LInear cumulative volume injected (gallons/ft)
Figure C-2. Flow-pressure response for a HIL operation
Judd La;ion
M1zirerl Itg ive
sMtiudc(nt
Pirliinminni. Iluid
conductince %tlldi
(Jniiu;n March)
1 clarl
Pol 4 imonthll
Poiv pmvsuir Mhtu l
Seulliil K Pim;"r (1J ul Oclober)
iit(lInt Fluid conliduc-iIncc
tIlldl
Figure C-3. Timeline for the studies at the phase 2 bioreactor landfill
Table C-2 Continuation of Table C-l
Initial Readings Calibration Constants
Gauge Ro T. S. A (pressure/digit2) B C K (pressure/ C)
(hz) (0 C) (hz) (pressure/digit2) (pressure/digit2)
Cl 8499 22.30 994.40 -7.86816E-10 -0.01641 139.58 -0.01624
C2 8502 21.50 991.80 -2.94946E-09 -0.01500 127.57 -0.01841
C2* 8756 22.20 994.40 -3.93869E-08 -0.01734 154.71 -0.01285
C3 8782 21.60 994.40 -1.37782E-08 -0.01743 154.03 -0.01800
C4 8801 21.30 991.80 1.28473E-08 -0.01518 132.49 -0.01494
C5 8872 21.60 994.40 1.50457E-08 -0.01667 146.68 -0.01830
C6 8434 24.40 991.80 -9.17820E-09 -0.01510 128.00 -0.01733
C6* 8748 24.50 991.80 1.84417E-08 -0.01670 144.67 -0.01692
C7 8756 22.10 991.80 3.19346E-09 -0.01605 140.09 -0.01138
C8 8783 22.00 991.80 6.88460E-09 -0.01393 121.63 -0.01706
C8* 8939 23.90 991.80 1.27517E-08 -0.01649 146.28 -0.01508
C9 8543 22.00 1004.26 -3.89146E-09 -0.01704 145.77 -0.01685
C9* 8690 21.30 995.84 -1.16148E-08 -0.01613 140.91 -0.01776
C10 8767 24.10 991.80 4.01470E-09 -0.01621 141.72 -0.00659
C11 8715 23.40 991.86 1.78469E-08 -0.01712 147.69 -0.01531
C11* 8628 22.00 994.40 8.06401E-09 -0.01605 137.73 -0.02101
C12 8740 24.10 991.80 4.13024E-09 -0.01636 142.61 -0.01512
C13 8629 23.50 991.80 -9.98118E-09 -0.01629 141.21 -0.01499
C14 8828 22.50 1008.77 -7.53833E-09 -0.01650 146.13 -0.03129
C15 8739 21.10 994.46 -8.27269E-09 -0.01701 149.07 -0.02417
C16 8678 21.70 983.06 1.48209E-08 -0.01606 138.13 -0.01769
C17 8874 20.90 992.50 -2.94248E-09 -0.01689 150.11 -0.01264
Barometer 4992 21.50 1002.28 5.13403E-09 0.00077 -3.72 -0.00188
Pressure transducers were buried in and around three buried HILs in the landfill to study
the pressure distribution resulting from prolonged liquids addition. Each of the three HILs was
constructed with different bedding media: crushed glass, tire chips, and no bedding media.
Moisture distribution was more uniform among the trenches with bedding media than in the one
which did not have any bedding media. Pore pressure dissipated over a short distance from the
HILs. It was observed that the pore pressure impact was similar both in the horizontal and
vertical direction from the HIL.
The fluid conductance values (flow rate per unit length of HIL per unit of applied pressure
head) for 31 HILs of varying, length, bedding media, and overburden depth of waste were
monitored over a large range of cumulative linear-injected volumes. Pressure and flow for the
operated HILs were monitored and recorded using the supervisory control and data acquisition
(SCADA) system. In general, the HILs with bedding media had higher fluid conductance values
than those without bedding media. Variation of flow rates during the operation of these HILs had
negligible impact on the fluid conductance. The fluid conductance values of all the HILs
decreased with increased cumulative injection volume and decreased with increased overburden
depth of waste. This decrease in fluid conductance, which varied from 0.01 to 0.1 gpm/ft/ft of
w.c, is hypothesized to be the result of decreasing hydraulic conductivity of the surrounding
waste due to increasing volume of leachate injection and overburden depth.
50
40
30
20
10
0
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-55. Flow-pressure variation with linear cumulative volume injected through HIL 89.
(Media = No media; Length = 360 ft; Overburden depth = 15 ft)
0.08
S 0.06
g 0.04
0.02
-J
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-56. Fluid conductance variation with linear cumulative volume injected through HIL
89.
116
Table 2-1. Injection details
HIL# Bedding Media Operation duration Volume of leachate
added (gallons)
A Tire chips 14 days 81,700
B Excavated waste 1 day 6,200
C Crushed Glass 12 days 74,200
o O
0 4 0 I
04 LO
/ BB19 J ,,V" ,- \ 0 ,
LO -, O 'O L6
SM n
B*- -- -- 02 C4- N~ *^-i-B^j-- --- -
gcat -- rCW.7t* NCE
---------.----------i?
Figure 2-17. Contour plot representation of the maximum pressure reached around the three
HILs by the end of the experiment.
--- Flowrate
Pressure head
190 200 210 220 230 240
190 200 210 220 230 240
Linear cumulative volume injected (gallons/ft)
Figure B-19. Flow-pressure variation with linear cumulative volume injected through HIL 46.
(Media = Crushed glass; Length = 400 ft; Overburden depth = 101 ft)
0.04
o 0.03
S0.02-
I
0.01
-V
0.00 1 II I iI
190 200 210 220 230 240 250
Linear cumulative volume injected (gallons/ft)
Figure B-20. Fluid conductance variation with linear cumulative volume injected through HIL
46.
50
40
30
20
10
0
250
-- Fluid Conductance
C
0.0044
65 3 .14~B r
S S S
1 2
0 S
Subcell 3
57 5B 5-
i1
16 16
* *
IC13
0
tri 61 l2
6 0 0
Sub ell
185 1 187
64 65 ., 6 67 858 6g 7
46 4 50 51 Ib
S24 25 26 272
21 22 23 0 0
LEGEND
O COORDINATES KNOWN reed re ip
Crushed Glass
* KNOWN COORDINATES No Bed1mg Material
Crushed Concrtte
O DESIGN COORDINATES No Perforate Pipe
LINIVERSiTY OF FLORIDA POLK COUNTY
SOLID AND HA-ZADOUS WASTE MANAGEMENT ACHATE I
ENVIRONMENTAL ENGINEERING SCIENCES LEACHATE INJ
125
bU 52
Ar
20
72 73 74
85gQ 8
75
@S
29 30 31 32 33 34 35
0 0 e a 0 0
.CU
BIOREACTOR
SECTION UNE CROSS SECTION
Subcell 4
TH'aP
91 (360 ft)
89 (360 ft)
88 (360 ft)
87 (360 ft)
81 (360 ft)
86 (360 ft)
80 (200 ft)
Lines with 15 ft of overburden depth
(for a cumulative volume of 200 gallons/ft)
+ No media
On a No media
M*s No media
# No media
4H No media
STire chips
4243 Crushed glass
0.001 0.01 0.1
Fluid Conductance (gpm/ft/ft of w.c)
Figure B-67. Fluid conductance of HILs with different bedding media.
Lines with 30-50 ft of overburden depth
(for a cumulative volume of 200 gallons/ft)
112 (1080 ft)
101 (1080 ft)
72 (520 ft)
90 (360 ft)
73 (200 ft)
58 (200 ft)
69 (200 ft)
0.001 0.01
Fluid Conductance (gpm/ft/ft of w.c)
Figure B-68. Fluid conductance of HILs with different bedding media.
Tire chips *
Crushed glass m
Tire chips +
Crushed glass -
Tire chips
Crushed glass
Crushed glass
Lines with 70-90 ft of overburden depth
(for a cumulative volume of 200 gallons/ft)
42 (300 ft)
84 (360 ft)
82 (360 ft)
2 (440 ft)
25 (720 ft)
27 (720 ft)
0.001 0.01 0.1
Fluid conductance (gpm/ft/ft of w.c)
Figure 3-3. HILs having same overburden depth showing the effect of length on fluid
conductance.
Crushed glass
Crushed glass
Tire chips
Tire chips
Tire chips
Crushed glass
0-0
Days
Figure A-5. Response from the pressure transducers 3 ft below on right ofHIL A with tire chips.
10 -
68 -
4 -
2 -
0 -
A9* A10* All*
Pressure transducers
Figure A-6. Response over time from the pressure transducers after the injection was stopped.
HIL A Pressure transducer A9*
I $ ft 5 5 ft o0 Pressure transducer All*
2 t A9 A10 All
Tire chips '5 ft o 10 ft
A2* A9* All*
Townsend and Miller 1998, Doran 1999, Larson 2007). Townsend (1995) studied the variation
of fluid conductance for several types of horizontal injection lines (HILs) in a landfill in Florida
and found that the fluid conductance decreased with an increase in operation time and changed
with elevation in the landfill. The effects of other design and operational parameters such as
injection flow rate, HIL length, and HIL bedding media type are still uncertain. Larson (2007)
studied the variation of fluid conductance for a few HILs at the Polk County landfill in Florida
and presented preliminary results that suggested that while the fluid conductance did not change
greatly with varying flow rates, fluid conductance did change with bedding media and elevation.
Part of the work presented in this thesis is a continuation of Larson's (2007) work with more
results evaluating the HILs in the same landfill unit.
One of the important concerns at any landfill where liquids are present under pressure is
slope stability. An increase in pore water pressure can result in a decrease in shear strength. If
liquids are added to a landfill in a manner where excessive pressures develop, it is possible that
slope failures may result for some configurations. Modeling techniques allow the engineer to
predict possible pressure buildup and factors-of-safety for slope failure, but very little is known
about what pressures actually develop within landfills as a result of added liquids. The studies
described in this document will help in understanding the impact on pore pressure due to
pressurized leachate injection and the efficiency of the HILs, one of the commonly used leachate
injection systems.
1.2 Objectives
The objectives of the research presented in this thesis are to:
Measure the pore pressure distribution around three HILs with different bedding media as
a result of pressurized leachate injection through the HILs.
8 (200 ft)
62 (200 ft)
61 (520 ft)
63 (520 ft)
109 (1080 ft)
66 (1560 ft)
Lines with 50-70 ft of overburden depth
(for a cumulative volume of 200 gallons/ft)
No media
4 Tire chips
e Tire chips
SCrushed glass
-No media
-.-A Tire chips
0.001 0.01 0.1
Fluid conductance (gpm/ft/ft of w.c)
Figure 3-4. HILs having same overburden depth showing the effect of length on fluid
conductance.
Equations to convert the raw data collected from the transducers to pressure data
The frequency data from the vibrating wire transducers were converted to pressure data by
using the factory-supplied calibration constants and equations. The equations are the following:
Digit = 1 (C-l)
1000
AbsolutePressure = ARmeasured+ BR measured+ C + K (Measured- To S (C-2)
Where Hz is the vibrating frequency measurement (Hertz), A, B, and C are the factory
supplied polynomial gauge factors (pressure/digits2, pressure/digit, pressure respectively); Ro is
the reading taken at the time of installation (digits), Rmeasured is the measured vibrating wire
reading (digits), K is the factory supplied thermal factor (pressure/C), Tmeasured is the measured
temperature (C), To is the temperature recorded at installation (C), and So is the barometric
pressure recorded at installation (pressure). To correct for thermal effects to the material of the
vibrating wire of each instrument, they are all equipped with thermistors with a range of -20C to
80C.
Barometric pressure was eliminated from the equation C-2 and the gauge pressure was
presented in the results for the thesis as the change in barometric pressure seemed to have no
effect on the pore pressures during the experimental period.
CHAPTER 1
INTRODUCTION
1.1 Background and Problem Statement
Bioreactor landfills have become popular among some landfill owners for the advantages
of faster stabilization of waste. Faster waste stabilization means an increase in both airspace and
the rate of methane generation (Eliassen 1942, DeWalle et al. 1978, Rees 1980, and Pohland
1980). Usually, the leachate generated by the landfill is added back to the landfill using designed
liquid distribution systems to create anaerobic conditions. Operating these liquid distribution
systems successfully can save the landfill owners money in treating the leachate and enhances
waste stabilization.
To build an efficient bioreactor, it is important to understand liquids addition system
design and operation, including moisture distribution within the landfilled waste, the impact on
slope stability, the performance of bedding media around the injection lines, and the resulting
injection pressures. This document focuses on evaluating a liquids addition system consisting of
buried horizontal trenches. Such an evaluation will help resolve some of the problems landfill
owners have encountered distributing moisture inside the landfill. Evaluating the liquid
distribution system and studying its impacts on the landfill play a major role in the progress
towards building an efficient bioreactor.
Since only limited knowledge is available regarding the characteristics of in-place
municipal solid waste (MSW), numerical modeling has been performed to predict pore water
pressures surrounding liquids addition devices in response to pressurized injection (Jain 2005).
Because of the natural heterogeneity in landfilled MSW and because of uncertainty describing
waste characteristics, the accuracy of these modeled predictions are uncertain. Field studies have
been carried out to evaluate the performance of liquid addition systems (Townsend 1995,
10
HIL A
HL Pressure transducer A2
I A2 -I Pressure transducer A2*
Tire chips-es_
A2*
6
,0
2
0 5 10 15
Days
Figure 2-15. Initial responses from pressure transducers buried at different depths under HIL A
(tire chips)
10
SPressure transducer C1
3 t Pressure transducer C2 HIL C
o Pressure transducer C3 _Injection
o* _ _ Crushed glass *
C3 C2 C1
180 ft 180 ft
6
.t
; 4
2-
Start of injection 12 day operation End of injection
0 i .
0 5 10 15 20
Days
Figure 2-8. Response from pressure transducers buried along the trench HIL C with crushed
glass as bedding media.
20
0--
190
--- Flowrate
-- Pressure head
.+ ji +
Linear cumulative volume injected (gallons/ft)
Figure B-17. Flow-pressure variation with linear cumulative volume injected through HIL 45.
(Media = Tire chips; Length = 300 ft; Overburden depth = 100 ft)
0.25
-
' 0.20
S0.15
0.10
-J
0.00
200
210
230
Linear cumulative volume injected (gallons/ft)
Figure B-18. Fluid conductance variation with linear cumulative volume injected through HIL
45.
50
40
30
20
10
-0
230
-- Fluid Conductance
S0.0082
'-L = --- ~
20
0--
180
190 200 210 220
50
40
30
20
10
-0
230
Linear cumulative volume injected (gallons/ft)
Figure B-65. Flow-pressure variation with linear cumulative volume injected through HIL 112.
(Media = Tire chips; Length = 1080 ft; Overburden depth = 48 ft)
0.020
0.015
0.010
0.005
0.000
180 190 200 210 220 230
Linear cumulative volume injected (gallons/ft)
Figure B-66. Fluid conductance variation with linear cumulative volume injected through HIL
112.
-+- Flowrate
-- Pressure head
IWm -
-- Fluid Conductance
0.0066
I I I I
2-V
Cl C2 C3
Pressure transducers
Figure 2-6. Response over time from the pressure transducers buried along HIL C with Crushed
glass, after the injection was stopped.
10
0- Pressure transducer Al
Pressure transducer A2
3 ft Pressure transducer A3 HIL A
8 ---------------- ----Injection
0 Tire chips *.
A3- A2 Al
180 ft 180 ft
6-
2
tart of injection 14 day operation End of injection
0 5 10 15
Days
Figure 2-4. Response from pressure transducers buried along the trench HIL A with tire chips as
bedding media.
2-
/ I uy
0.4 0.5 0.6 0.7 0.8
Figure A-13. Response from the pressure transducers buried at different depths under HIL C
with no bedding media.
B2 B2*
Pressure transducers
Figure A-14. Response over time from the pressure transducers after the injection was stopped.
LIST OF REFERENCES
Barber, C., and Maris, P. J. (1984). Recirculation of leachate as a landfill management option:
Benefits and operational problems. Quarterly Journal of Engineering Geology, 17, 19-29.
DeWalle, F. B., E. S. K. Chian, and E. Hammerberg (1978). Gas production from solid
waste in landfill. Journal of the Environmental Engineering Division, ASCE, 104, 415.
Doran, F. (1999). Lay leachate lay. Waste Age; Apr 1999; 30, 4; ABI/INFORM Global pg. 74
Eliassen, R. (1942). Decomposition of Landfills. American Journal of Public Health.
32, 1029.
Haydar, M and Khire, M. (2004). Evaluation of heterogeneity and anisotropy of waste
properties on leachate recirculation in bioreactor landfills. Journal of Solid Waste
Technology andManagement, 30(4), 233-242.
Haydar, M., and Khire, M. (2005). Leachate recirculation using horizontal trenches in bioreactor
landfills. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 131(7),
837-847.
Geokon, Inc. (Doc Rev S 4/07). Model 4500 VW Piezometer Instruction Manual.
Jain, P. (2005). Moisture Addition at Bioreactor Landfills Using Vertical Wells: Mathematical
Modeling andFieldApplication. Ph.D. Dissertation, University of Florida, Gainesville,
FL, USA.
Jain, P., Powell, J. T., Townsend, T. G., and Reinhart, E. R. (2005). Air permeability of waste in
a municipal solid waste landfill. Journal ofEnvironmental Engineering, ASCE, 131(11),
1565-1573.
Jain, P., Powell, J. T., Townsend, T. G., and Reinhart, E. R. (2006). Estimating the hydraulic
conductivity of landfilled municipal solid waste using the borehole permeameter test.
Journal ofEnvironmental Engineering, ASCE, 132(6), 645-652.
Jain, P., Larson, J., Townsend, T.G. and Tolaymat, T. (2007). "Design of vertical wells for
introduction at bioreactor landfill: Guidelines based on mathematical modeling" Submitted
to Journal ofEnvironmental Engineering, ASCE.
Koerner, R. M., and Soong, T.-Y. (2000). "Leachate in landfills: The stability issues." Geotext.
Geomembrane, 18 5 293-309.
Larson, J. A. (2007). Investigations at a Bioreactor Landfill to Aid in the Operation and Design
of Horizontal Injection Liquids Addition Systems. Master's Thesis, University of Florida,
Gainesville, FL, USA.
Leckie, J.D., Pacey, J.G. and Halvadakis C.P. (1979). Landfill management with moisture
control. Journal ofEnvironmental Engineering Division, ASCE EE2, 105, 337-355.
vertical and horizontal directions. As mentioned earlier the results from figure 2-15 show that
the response of the transducer (A2*) buried 3 ft under the trench in the waste responds slower
than the one in the trench with media (A2). A contour plot representing the pressure distribution
for the cross section of the HILs in the center is presented in figure 2-17. It can be seen from
figure 2-17 that the transducers around the trench of HIL C and HIL A have been impacted
almost equally irrespective of the direction. It could be expected that the pressure distribution is
greater in the horizontal direction compared to the vertical direction due to the anisotropic nature
of the waste, but the results indicate there is an equal impact around the HIL. The change in pore
pressure in the horizontal direction is only due to injection pressure, where as the change in pore
pressure in the vertical direction is a result of injection pressure and the gravitational force for
the liquid movement. Also, importantly the small radial distance about 3 ft in the current study,
does not help in understanding the anisotropic nature of waste. There is little change around the
trench of HIL B as shown in figure 2-16 and in the contour plot figure 2-17.
2.3.5 Implications
The stability of a landfill structure is influenced by the internal shear strength of the
waste material in each layer and the pore pressures that develop due to gas or pressurized liquid
addition. Increase in pore pressure decreases the shear strength that might lead to a slope failure.
Stability analysis for landfills that practice pressurized liquid addition is important; pore pressure
is a primary input in this analysis. The influence of leachate under pressure on the stability of
landfilled waste mass has been discussed by Koerner and Soong (2000), by calculating the factor
of safety. The research described in this thesis is an attempt to provide an insight into actual pore
pressures that result from pressurized leachate addition and their behavior within landfilled
waste. It was found that the pore pressure decreased over a short distance, there was a decrease
of about 4 psi over a distance of 25 ft from the HILs. Apart from the liquid addition it was found
CHAPTER 2
A FIELD STUDY TO MEASURE THE PORE PRESSURES IN LANDFILLED WASTE AS A
RESULT OF PRESSURIZED LIQUIDS ADDITION
2.1 Introduction
Anaerobic bioreactor landfills are becoming popular as their advantages become
increasingly well documented (Pohland, 1975; Leckie et al., 1979; Watson, 1987; Townsend et
al., 1996; Warith et al., 2001, Warith, 2002; and Jain, 2005, Larson, 2007,). Bioreactor landfill
operators often try to recirculate as much leachate as possible into their landfills, requiring
liquids addition under pressure. However, injection of liquids with pressure raises concern over
the slope stability because the pore water pressure increase can decrease the shear strength that
will result in a slope failure (Koerner and Soong, 2000; Jain et al., 2007).
Evaluating landfill stability becomes a priority to successfully operate the bioreactor when
liquids are being added with pressure. Pore pressure is one of the primary inputs to evaluate the
stability. A focus of research at several landfills in Florida is the development and evaluation of
methodologies for safe design and operation of bioreactor landfills. Having this in mind, the
impact of liquids addition via vertical wells on pore water pressure in the surrounding waste was
mathematically modeled by (Jain 2005, Jain et al 2007); however, there are no field data
available measuring how the pore water pressure changes due to the liquid addition. The
objective of the experiment discussed in this paper is to study the spatial variation of pore water
pressure in the waste as a result of pressurized liquid addition through horizontal trenches. In this
experiment, pressure was measured from transducers buried in landfilled waste surrounding the
horizontal leachate injection trenches.
Table 3-4. Fluid conductance values for similar cumulative linear-injected volume of
approximately 100 gallons/ft
Perforated Bedding Approximate Fluid conductance Cumulative
Perforated Bedding Cumulative
HIL Design Length (f) media overburden depth (gpm/ft/ft of w.c) at gallons injected
Length (ft) media gallons injected
(ft) (100 gallons/ft)
80 Single pipe 200 Glass 15 0.12840 40,000
69 Single pipe 200 Glass 35 0.05070 40,000
58 Single pipe 200 Glass 35 0.02550 40,000
90 Single pipe 360 Glass 35 0.02590 72,000
27 Single pipe 720 Glass 80 0.00670 144,000
86 Single pipe 360 Tires 15 0.03340 72,000
73 Single pipe 200 Tires 35 0.02850 40,000
72 Single pipe 520 Tires 35 0.03040 104,000
25 Single pipe 720 Tires 80 0.00520 144,000
81 Single pipe 360 Nothing 15 0.01900 72,000
87 Single pipe 360 Nothing 15 0.01200 72,000
88 Single pipe 360 Nothing 15 0.01700 72,000
89 Single pipe 360 Nothing 15 0.01590 72,000
91 Single pipe 360 Nothing 15 0.00710 72,000
HIL A
loft 5 ft 5 t -
A5 A6 A7 A8 2ft
A2
Tire chips
S I ;lI \ -
ij \I '\ .-
Pressure transducer A5
Pressure transducer A7
Pressure transducer AS
- Pressure transducer A2
blrI~vr:I
Days
Figure 2-11. Response from pressure transducers buried in waste on the left side of the HIL A
(tire chips)
-- Flowrate
-- Pressure head
196 198 200 202 204 206 208
50
40
30
20
10
0
210
Linear cumulative volume injected (gallons/ft)
Figure B-5. Flow-pressure variation with linear cumulative volume injected through HIL 2.
(Media = Tire chips; Length = 440 ft; Overburden depth = 86 ft)
0.008
0.007 -
-
0.006 -
-
S0.005 -
-
g 0.004 -
-
: 0.003 -
0.002 -
0.001 -
0.000
196 198 200 202 204 206 208 210
Linear cumulative volume injected (gallons/ft)
Figure B-6. Fluid conductance variation with linear cumulative volume injected through HIL 2.
-- Fluid Conductance
0.0030 ----
-50
-40
-30
20
- 20
- 10
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-37 Flow-pressure variation with linear cumulative volume injected through HIL 72.
(Media = Tire chips; Length = 520 ft; Overburden depth = 35 ft)
0.20
' 0.15-
g 0.10
0.05
0.05-
1
-- Fluid Conductance
S0.0304 0.0293
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-38 Fluid conductance variation with linear cumulative volume injected through HIL 72.
--- Flowrate
- Pressure head
I v v I '
1 r V
+ ) 1--- -
or plateaued, was determined to be the elevation head of the HIL from the pressure gauge and the
point of zero applied pressure.
3.2.4 Experimental Method
The leachate recirculation system was operated only when an operator was present.
Therefore, leachate was injected for approximately 8 hours a day, 5 to 7 days a week, depending
upon the necessity to lower the leachate level in the storage tanks. The performance of the HILs
differed in terms of fluid conductance only at higher cumulative volumes injected through them,
majority of the HILs installed were not used or had only been operated for a small cumulative
volume. The maximum cumulative volume injected per foot of HIL studied by Larson (2007)
was 200 gallons, fourteen HILs presented in table B-l (Appendix B) were operated to measure
the fluid conductance in the previous study. Seventeen individual HILs that reached a linear
cumulative volume of 200 gallons/ft of HIL presented in table B-2 (Appendix B) were tested for
durations that were necessary for the objectives of this research or were run until the injection
pressure reached the permitted 5 psig for the desired operational flow rate. Fluid conductance
values were evaluated at a linear cumulative injected volume of 200 gallons/ft of HIL for the
convenience of comparing the HILs studied in the previous study. All injection tests were
designed to evaluate the effect of multiple design and operational variables upon HIL fluid
conductance values. Therefore, a total of 31 HILs are evaluated in this thesis, based on fluid
conductance for the parameters mentioned before.
The effects of overburden depth of waste over the HIL fluid conductance was studied by
choosing HILs of same length and bedding media but buried at different elevations, these HILs
were compared after they were injected with similar volumes of leachate through them.
The effects of bedding media upon HIL fluid conductance was studied using two types of
bedding media; shredded tire chips and crushed glass. The shredded tire chip size was usually of
Table 2-2. Estimated times to fill the HIL trenches
M a Trench Assumed Volume of trench Time to fill trench
Media 3
dimensions (ft) Porosities (ft3) (hours)
0.3 972 8.1
Crushed glass 360 x 3 x 3 0.4 1296 10.8
0.5 1620 13.5
0.3 972 8.1
Tire chips 360 x 3 x 3 0.4 1296 10.8
0.5 1620 13.5
0.2 648 5.4
MSW 360 x 3 x 3 0.3 972 8.1
0.4 1296 10.8
HIL A
10Oft 5f 51 5F
A5 A6 A7 A8 2 ft
SA2
Tire chips
Pressure transducer A5
Pressure transducer A7
Pressure transducer AS
- Pressure transducer A2
I
" I \ I gI
; I I\
\ -J~-ll5~~J~
4-13*
Days
Figure A-7. Response from the pressure transducers on left of HIL A with tire chips as bedding
media.
8
14I I ll III
2
0 ,
A5 A6 A7 A8
Pressure transducers
Figure A-8. Response over time from the pressure transducers after the injection was stopped.
l
50
40
30
20
10
0
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-57. Flow-pressure variation with linear cumulative volume injected through HIL 90.
(Media = Crushed glass; Length = 360 ft; Overburden depth = 35 ft)
0 .0 "1------
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-58. Fluid conductance variation with linear cumulative volume injected through HIL
90.
-- Fluid Conductance
0.0137
U{
0.0259
iV
ul
I
HIL A
loft 5 ft5 --1
A5 A6 A7 A8 2 ft
A2
Tire chips
54. ii
Pressure transducer A5
Pressure transducer A7
Pressure transducer AS
- Pressure transducer A2
I
i I i~
'I I'
I~ I\~\:\~
I\IlJ ~, \
E~~~ I11 1~
It' I\ \i
~I\ Ij ______-~-
Days
Figure 2-5. Response from pressure transducers buried in waste on the left side of the HIL A (tire
chips)
Determination of elevation head for HIL operation
During the operation of the HILs studied in this thesis, the injection pressure was not to
exceed 5 psi according to the site permit. Injection pressure (P) was determined by the equation
"P = P1 P2". As shown in the figure C-l, pumping pressure (Pi) was recorded by the gage at
the foot of the landfill and elevation head (P2) was initially obtained from the elevation survey
data for each HIL. Later, In order to account for settlement of the HIL after waste placement,
flow pressure data for the first day operation (figure C-2) that was recorded on SCADA was used
to determine the elevation head of the HILs. The point at which the pressure starts becoming
constant (figure C-2) after the first few minutes of HIL operation is considered as the elevation
of the HIL.
MSW Landfill
Injection pressure P
HIL
Flow-pressure gage
P2 = Elevation head
Pumping pressure Pi NC /
Figure C-1. Schematic diagram of the HIL in the landfill with elevation, injection and pumping
pressure representation
LIST OF TABLES
Table page
2-1 Injection details .................................................................... ......... 28
2-2 Estim ated tim es to fill the HIL trenches ........................................ ........................ 29
2-3 Initial pressures of the transducers used in the experiment. ............................................30
3-1 Fraction of HILs that reached the 200 gallons/ft for the study ........................................59
3-2 H IL specifications ......... ....... ....................................................................... ...... 60
3-3 Fluid conductance values for a cumulative linear-injected volume of approximately
2 0 0 g allo n s/ft ........................................................................... 6 1
3-4 Fluid conductance values for similar cumulative linear-injected volume of
approxim ately 100 gallons/ft ................................................. ................................ 62
Examine the influence of HIL length on fluid conductance.
Examine the influence of using shredded tire chips or crushed glass as bedding media on
fluid conductance.
Examine the influence of using no bedding media on fluid conductance.
Examine the influence of HIL depth within the landfill on fluid conductance with respect
to prior injected volumes.
1.3 Research Approach
Two field studies were carried out with the objective of understanding and evaluating the
process of pressurized liquid addition and its impact on pore pressure in the landfilled waste. In
the first study, 81 vibrating wire pressure transducers were buried in the center of the landfill
around a series of HILs and connected to a data logger station. These instruments were installed
to measure pore water pressure resulting from different injection pressures applied to those
nearby HILs. When the injection experiment was about to begin, the initial pressures were noted
and the HILs were operated one at a time. Three HILs with different bedding media (crushed
glass, tire chips, and excavated waste) were examined. Pressure transducers were buried around
each HIL. Each HIL was operated until the HIL reached its maximum halting pressure of 5 psi.
Data in the form of frequency from these instruments were processed to pressure in psi using
Microsoft Access. Pressure change in these buried transducers indicated the distance which the
liquids had reached and the extent to which the pore pressure changed at different distances.
These pressure values provide field pore pressures due to pressurized injection of liquids that can
be compared to that of numerical modeling.
For the second study in this document, the performance of 31 HILs installed in the Polk
County Phase 2 landfill was evaluated. These HILs were used as part of the liquid distribution
system within the landfill and were monitored and operated through the Supervisory Control and
of the injection run close to 200 gallons/ft of HIL were taken to represent the fluid conductance
and compare for the different overburden depths of waste. Similarly, fluid conductance values
were compared at a cumulative linear-injected volume of 100 gallons/foot of HIL, for 14 of the
31 HILs (table 4).
3.3 Results and Discussion
3.3.1 Fluid Conductance Results
More than 20 million gallons of leachate has been intermittently injected into 106 HILs in
Phase 2 landfill. Pressure and flow rate data were collected from a set of 31 HILs for their
respective injection runs. As discussed in the study by Larson (2007) the HILs in this study had
the same behavior for a typical operation, with each injection run fluid conductance values
started high, as back pressures were low, and then decreased with continued operation, as back
pressures rose more slowly (See figure 2 for a reminder of this behavior). With every renewed
injection run, fluid conductance values initially rebounded but then, less gradually than before,
decreased to yet a lower amount than previously reached for the same volume of liquid
previously added. At the end of each injection run, fluid conductance values appeared to have
reached a steady-state value, but still decreased at a small rate. Table 3 and 4 compares the fluid
conductance values for the end of an injection run as close as possible to a cumulative linear-
injected volume of 200 and 100 gallons/foot of HIL respectively. The fluid conductance values
presented in the tables can be used for the design and operation of a HIL system in a landfill, a
design engineer can determine the pressure required for a desired flowrate or vice versa.
3.3.2 The Effect of Continuous Leachate Injection
The HILs were all operated for long periods intermittently. All injection lines show a
general decrease in fluid conductance values with increasing cumulative linear-injected volume.
HIL C
loft 5ft1 ft 5 t -F
C5 C6 C7 C8 I $2It
CC2
Crushed glass
Pressure transducer C6
Pressure transducer C7
Pressure transducer CS
- Pressure transducer C2
I J
I I kr\
I *x vj
U i .i I II
0 5 10 15 20
Days
Figure 2-12. Response from pressure transducers buried in waste on the left side of the HIL C
(crushed glass)
TABLE OF CONTENTS
page
A C K N O W L E D G M E N T S ..............................................................................................................4
L IS T O F T A B L E S ................................................................................. 7
L IST O F FIG U R E S ............................................................................... 8
ABSTRACT ...... ..... .................. .............. ............ ..... 10
CHAPTER
1 INTRODUCTION ................. ............................ ............................ 12
1.1 Background and Problem Statem ent ........................................ .......................... 12
1 .2 O bje ctiv e s ...................................... ................................................... 13
1.3 Research A approach .................. .................. ................. ........... .. ............ 14
1.4 Organization of Thesis ................. ............... ......... ............... .. ...... 15
2 A FIELD STUDY TO MEASURE THE PORE PRESSURES IN LANDFILLED
WASTE AS A RESULT OF PRESSURIZED LIQUIDS ADDITION ..............................16
2 .1 In tro du ctio n ............................ ................................................................. ............... 16
2 .2 M materials and M methods ........................................................................... ....................17
2.2.1 Site D description .......................... ................ ....... .. ......17
2.2.2 Experimental Setup and Materials.........................................................18
2.2.3 D ata M anagem ent ................................. ........................ ...............19
2.2.4 Leachate Injection Experim ent......... ......................................................... 19
2.3 R results and D discussion ........................ .................... ... .... ........ ......... 20
2.3.1 Pressure Transducer Responses......... ........... ..........................20
2.3.2 Measurement of Pore Pressures Within the Trenches......................................... 22
2.3.3 Measurement of Pore Pressures Away From the Trenches Horizontally .............23
2.3.4 Measurement of Pore Pressures Away From the Trenches Vertically .................23
2 .3.5 Im plications .........................................................................24
2 .3 .6 L im itatio n s............................. ....................................................... ............... 2 5
2 .4 C o n clu sio n s........................................................ ................ 2 6
3 FACTORS IMPACTING FLUID CONDUCTANCE OF HORIZONTAL TRENCHES
USED FOR LEACHATE RECIRCULATION IN A LANDFILL .......................................48
3 .1 In tro d u ctio n ........................................................ ................ 4 8
3.2 M methods and M materials .......................................................................... .....................49
3.2 .1 Site D description ..................... ............................................ .......... ... ........... 49
3.2.2 Horizontal Injection Line Construction..... .......... ...................................... 50
3.2.3 System Operation and M monitoring ........................................ ...... ............... 51
3.2 .4 E xperim mental M ethod ..................................................................... ..................52
20
180
180
-50
-40
-30
20
- 20
- 10
0
200 220 240
Linear cumulative volume injected (gallons/ft)
Figure B-29. Flow-pressure variation with linear cumulative volume injected through HIL 63.
(Media = Crushed glass; Length = 520 ft; Overburden depth = 61 ft)
0.025
0.020
0.015
0.010
0.005
0.000 ..i
160 180 200 220 240 260
Linear cumulative volume injected (gallons/ft)
Figure B-30. Fluid conductance variation with linear cumulative volume injected through HIL
63.
-+- Flowrate
-- Pressure head
X -X- Fluid Conductance
0.0068
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
STUDY OF PORE WATER PRESSURE IMPACT AND FLUID CONDUCTANCE OF A
LANDFILL HORIZONTAL LIQUIDS INJECTION SYSTEM
By
Sendhil Kumar
August 2009
Chair: Timothy G. Townsend
Major: Environmental Engineering Sciences
Moisture distribution in landfilled waste plays a very important role in waste
stabilization. Liquid addition systems are designed and buried inside landfilled waste to
distribute moisture at different depths. Pressure is required to inject leachate through these
systems. Landfill operators often add liquids under pressure to achieve higher liquid addition
rates which speeds up waste stabilization. In this process, slope stability of the landfill becomes a
subject of concern. When liquids are present under pressure in the landfilled waste, an increase
in the pore water pressure can decrease the shear strength and the geotechnical stability of side
slopes. Though modeling techniques are available to predict the possible build up of pressures
inside the landfill, very little is known about the real pressures that result from adding liquids
under pressure.
Two field investigations were conducted at a bioreactor landfill in Polk County, Florida:
(1) Measurement of the spatial variation of pore water pressure resulting from pressurized
leachate injection through the horizontal injection lines (HILs), and (2) evaluation of the
performance of HILs in terms of fluid conductance
40 -
30-
20 -
10
50 100
-50
-40
30
20
- 20
- 10
- 0
150 200 250
Linear cumulative volume injected (Gallons/ft)
Figure B-41. Flow-pressure variation with linear cumulative volume injected through HIL 80.
(Media = Crushed glass; Length = 200 ft; Overburden depth = 15 ft)
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-42. Fluid conductance variation with linear cumulative volume injected through HIL
80.
109
--- Flowrate
-- Pressure head
1I ~- -- -- I
Irr+MP-
*_ ~t
SIrSSIt ssuI tLaIISUUCCIti DL
0 3 ft -- Pressure transducer B8
5 ft No media
B8* B2*
6
2
0 0.
0.4 0.5 0.6 0.7 0.8
Days
Figure 2-16. Response from pressure transducers 3ft away on the left of HIL B (no media)
have significantly less fluid conductance values than those with bedding media. The effect of
increasing overburden stress was observed to have a negative impact upon fluid conductance at
lower cumulative injected volumes. This observation was part of the overall effect of fluid
conductance values decreasing with increasing cumulative linear-injected volume. This is
hypothesized to be caused by changes in the hydraulic conductivity of the waste surrounding the
HILs by either the presence of landfill gas, the changing structure of the waste from decay, or
both. This effect could also be caused by HIL clogging from fines within the waste or from a
still-expanding wetting front of liquid from the HIL.
Overall, it was found that liquids addition into a HIL system requires larger pressures as
these systems are operated for a longer period. During early operation of these systems, fluid
conductance values for all types of HILs are greater. However, it is important to remember that
the whole experiment here was conducted at a fixed injection pressure of 5 psig. Higher
operational pressures for these HILs might help getting more liquids into the landfill.
Table B-2 HILs evaluated during the current research study.
Perforated Bedding
HIL Design(f) media
Length (ft) media
63
101
42
46
30
65
84
2
61
62
45
66
82
112
8
59
109
Single pipe
Tri branched
Single pipe
Single pipe
Single pipe
Only media
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Tri branched
Single pipe
Tri branched
Single pipe
Single pipe
Tri branched
520
1080
300
400
720
0
360
440
520
200
300
1560
360
1080
200
480
1080
Approximate
overburden
depth (ft)
61
41
75
101
121
72
84
86
60
55
100
53
78
48
65
75
53
Cumulative
gallons injected
104000
216000
60000
80000
144000
93600
72000
88000
104000
40000
60000
312000
72000
216000
40000
96000
216000
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Nothing
Nothing
Nothing
0.06
Z 0.05
-
0
S0.04
U 0.03
I 0.02
0
S 0.01*
Impact of overburden depth
(for a cumulative volume of 100 gallons/ft)
Crushed glass
A Tire chips
0 No media
A
A
A
0
8
0
o 6
10 20 30 40 50 60 70 80
Overburden depth of waste (ft)
Figure 3-6. Fluid conductance values at a cumulative linear injected volume of approximately
100 gallons/ft for HILs with different bedding media at different depths in the landfill
STUDY OF PORE WATER PRESSURE IMPACT AND FLUID CONDUCTANCE OF A
LANDFILL HORIZONTAL LIQUIDS INJECTION SYSTEM
By
SENDHIL KUMAR
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING
UNIVERSITY OF FLORIDA
2009
a minimum flowrate of 15-25 gpm for a few minutes, a steady increase in pressure at the
pressure gauge is observed. When the pressure starts becoming constant, that point is determined
as the elevation head.
In a study of waste composition carried out in the summer of 2003 and the winter of 2004
with 30 grabbed samples from the Phase 2 cell, the density of the landfilled waste has been
estimated at approximately 1500 lb/yd3(R.W. Beck, Inc. 2004).
2.2.2 Experimental Setup and Materials
The experimental area is approximately 560 ft x 200 ft on Subcell 5 of the Phase 2 cell and
consists of three horizontal trenches each with a different bedding media (tire chips, glass, and
excavated waste). The HILs are surrounded by 81 pressure transducers. Three transducers are
installed in each trench and the rest are installed at different distances from the HILs. As shown
in Figure 2-1, the transducers were installed in a V formation around the HILs to minimize short-
circuiting and to have undisturbed waste in the fluid path from the injection line to the
transducers. The injection lines have a perforated length of 360 ft. Figures 2-1 and 2-2 show the
plan view and the cross section of the pressure transducers experiment layout. Eighty-one
Geokon model 4500S vibrating wire pressure transducers were used for the experiment. The
transducers were factory calibrated to a gauge pressure range of 0 psi to 50 psi with a reported
accuracy and resolution of 0.05 psi and 1.25 psi, respectively. The standard used to calibrate
was a Pressure Controller Model PPC2 made by DH instruments with an accuracy of 0.02%
FS. The Geokon accuracy figure of 0.1% of full scale is a conservative estimate of the accuracy
after accounting for any possible errors during the calibration process. Therefore, any calculation
of pressure using the calibration factor and the transducer reading will be within 0.1% (0.05
psi) of full scale of the true value. Also, the transducers were designed with thermistors with a
range of -20C to 80C to correct for the effects of temperature (Geokon, Inc. 2007).
transducer below the HIL C had failed before the experiment began; this gives only limited idea
of how pressure varies over distance vertically when the HILs are operated. The pressure values,
horizontally and the area of impact due to injection from this study can only be valid for that
fixed depth of waste (80 ft in the current study) over the experimental area. The pressure
distribution and area of impact due to injection will change when the overburden depth of waste
will vary. It can be presumed that the initial pore pressures in the waste before starting the
injection would be higher as the overburden depth of waste increases.
2.4 Conclusions
In-situ pore pressures within landfilled waste resulting from pressurized leachate
injection were studied. It was observed that the pore pressures in the waste increase slowly as the
waste lifts are being constructed. In the experimental area with an overburden depth of 80 ft of
waste, the pressures as shown by the transducers, before the experiment was started were
between 0 to 4 psi. The transducers which were towards the center were noted to have higher
pressures than the ones closer to the slopes. These initial pressures can be higher when the
overburden depth of waste increases due to landfill gas and further compression of pores.
When the injection through the HILs commenced it was observed that the trenches having
bedding media of crushed glass or tire chips performed better in terms of the amount of total
leachate intake. The bedding media being more porous than the surrounding waste helps the
leachate fill up the trench quickly. There is a negligible pressure loss along the trenches with the
bedding media (tire chips and crushed glass) and this in turn is advantageous to achieve good
distribution of moisture in the surrounding area. The HIL which did not have any bedding media
was operated only for a day as it reached the 5 psi injection pressure limit. There was a
significant loss in pressure along the trench with no bedding media after the injection was
started. The pore pressure due to pressurized injection decreased over the distance and was
APPENDIX B
SUPPLEMENTAL FIGURES AND TABLES FOR CHAPTER 3
This appendix presents tables and graphs of the data collected from the 31 horizontal
injection lines in the Phase 2 landfill that were evaluated in the research experiment described in
this thesis. The results cover a period from January 2006 to August 2008.
Figure 2-2. Cross section of the HIL A trench with buried pressure transducers.
Figure B-1. Location of the Polk North Central Landfill Facility
160 180 200 220 240 260 280
50
40
30
20
10
-0
300
Linear cumulative volume injected (gallons/ft)
Figure B-7. Flow-pressure variation with linear cumulative volume injected through HIL 8.
(Media = No media; Length = 200 ft; Overburden depth = 65 ft)
0.05
-- Fluid Conductance
C..
S0.04
S0.03
,..
| 0.02-
0.01 0.0103 -
0.00
160 180 200 220 240 260 280 300
Linear cumulative volume injected (gallons/ft)
Figure B-8. Fluid conductance variation with linear cumulative volume injected through HIL 8.
-- Flowrate
--- Pressure head
APPENDIX C
SUPPLEMENTAL DATA FOR CHAPTER 2
This appendix presents graphs of the data collected from all the pressure transducers
present in the landfill that were used to analyze data. The results cover a period from July 2007
to June 2008.
3 .2 .5 D ata M anagem ent............................................................... ........................ .... 53
3.3 R results and D discussion ........................ .................... .. .... ............. ......... 54
3.3.1 Fluid Conductance Results ............ ................. ...... ............... 54
3.3.2 The Effect of Continuous Leachate Injection................................. ... ................ 54
3.3.3 The Effect of HIL Length ......... ........................................ ............... 55
3.3.4 The Effect of HIL Bedding Media ............. .................................. 56
3.3.5 The Effect of Overburden Depth ................................................................ 57
3 .4 C o n c lu sio n s ................................................................................................................. 5 7
4 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS ......................................69
4 .1 S u m m a ry ..................................................................................................................... 6 9
4 .2 C o n c lu sio n s ................................................................................................................. 7 0
4.3 Recom m endations....... .............. .......................... .. .. ..................70
APPENDIX
A SUPPLEMENTAL FIGURES FOR CHAPTER 2..................................... .................72
B SUPPLEMENTAL FIGURES AND TABLES FOR CHAPTER 3 ....................................84
C SUPPLEMENTAL DATA FOR CHAPTER 2 ........................................ .....................127
L IST O F R E F E R E N C E S .................................................................................. ..................... 133
B IO G R A PH IC A L SK E T C H ......................................................................... .. ...................... 136
of waste above them were not able to receive enough liquid to evaluate because the pressures
necessary to inject even the smallest allowable flow rate the SCADA system could achieve were
above the regulatory limit of 5 psig. Townsend and Miller (1998) used average pressures higher
than 10 psig to add liquid to the HILs with no bedding media and had about 30 feet of
overburden waste above them. They also found that the fluid conductance for HILs with no
bedding media was significantly less than those with bedding media. The linear cumulative
volumes for the study by Townsend and Miller (1998) were greater than 400 gallons/ft.
3.3.5 The Effect of Overburden Depth
We can see from the figures 5 and 6 that the fluid conductance decreases as the
overburden depth increases. Townsend and Miller (1998) too found that the HILs that were
buried shallow within the landfill had larger fluid conductance values than those that were buried
deeper within the landfill. This phenomenon was explained to be the result of larger effective
stresses causing lower hydraulic conductivities of waste deeper within the landfill. The overall
trend from the figures 5 and 6 show that crushed glass and tire chips media has equal and a
higher fluid conductance than the no media. In general the reason for the decrease in fluid
conductance is likely due to the hydraulic conductivity of the waste surrounding the HIL being
reduced by either landfill gas accumulation, structural changes in the waste from decay, or both.
It could also simply be the result of damages in the pipe or clogging due to fines in the waste.
3.4 Conclusions
This study examined the effects of different operation and design parameters upon the
fluid conductance of HILs. The effect of HIL length from this study cannot be concluded based
on fluid conductance. There was not a big difference found in fluid conductance between tire
chips and crushed glass media; however, the fluid conductance value for crushed glass was
slightly higher than the tire chips in some cases. The HILs with no bedding media were found to
Pressure transducer C1
3 ft Pressure transducer C2 HIL C
PI pressure transducer C3_ Injection
S Crushed glass *
C3 > C2 C1
180 ft 180 ft
Start of injection 12 day operation End of injection
0 5 10 15
Days
Figure A-17. Response from the pressure transducers in the trench of HIL C with crushed glass
as bedding media.
6 -
2 -
0 4
Cl C2 C3
Pressure transducers
Figure A-18. Response over time from the pressure transducers after the injection was stopped.
Table 3-2. HIL specifications
HIL
2
7
8
59
61
62
63
101
42
45
46
65
66
82
84
109
30
74
112
80
69
58
90
27
29
86
73
72
24
25
81
87
88
89
91
Date of
construction
Mar-01
Feb-02
Feb-02
May-05
Apr-05
Apr-05
Apr-05
Aug-06
Mar-05
Aug-05
Aug-05
Jun-06
Jan-04
Mar-05
Jun-06
Sep-05
Mar-05
May-05
Jul-05
Dec-03
Jan-04
Aug-05
Mar-05
Mar-05
Nov-03
Nov-03
Sep-05
Aug-05
Aug-05
Jul-05
Jul-05
SDR
Pipe I.D.
(in)
3.949
3.949
3.949
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.649
3.949
3.649
3.649
3.649
3.649
3.649
3.649
3.949
3.949
3.649
3.649
3.649
3.949
3.949
3.649
3.649
3.649
3.649
3.649
Perforated
Length (ft)
440
200
200
480
520
200
520
360
300
300
400
0
520
360
360
360
720
520
360
200
200
200
360
720
720
360
200
520
720
720
360
360
360
360
360
Bedding
media
Tires
Tires
Nothing
Nothing
Tires
Tires
Glass
Glass
Glass
Tires
Glass
Glass
Tires
Tires
Glass
Nothing
Glass
Glass
Tires
Glass
Glass
Glass
Glass
Glass
Glass
Tires
Tires
Tires
Tires
Tires
Nothing
Nothing
Nothing
Nothing
Nothing
Approximate
overburden depth (ft)
86
43
65
75
60
55
61
41
75
100
101
72
53
78
84
53
121
57
48
15
35
35
35
80
80
15
35
35
80
80
15
15
15
15
15
0.30
S0.25
4-
0.20
0.15
0.10
0.05
0.00
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure 3-1. Injection runs for HIL 58 with crushed glass showing the effect of cumulative
volume injected on fluid conductance.
can be seen that the fluid conductance is almost the same for HILs 2 and 82 which have different
lengths. HIL 65 in figure 3 shows a higher fluid conductance though it has no perforated length.
Similar results can be seen with HILs in figure 4 and Appendix B. The results suggest three
possibilities for the effect of HIL length. From these results it is difficult to conclude the effect of
HIL length. This could be because of the heterogeneity of the surrounding MSW or HILs with a
bigger length might have greater possibilities of breaking due to overburden depth of waste. The
fluid conductance values presented in the graphs are for the last run when the linear cumulative
injected volume got close to 200 gallons/ft of HIL.
3.3.4 The Effect of HIL Bedding Media
Figures 5 and 6 show the resulting fluid conductance values for injection runs of HILs
with different bedding media and with the different depth of overburden waste above. The fluid
conductance values presented are when the HILs reached a linear cumulative injected volume of
200 gallons/ft of HIL and 100 gallons/ft of HIL where available. The single points shown in the
figures were picked when the fluid conductance values reached a steady state (Appendix B)
during the operation. The reason for not having many data points for HILs without any media is
that they are very poor performers as compared to the HILs with media. The majority of the
HILs that did not reach the 200 gallons/ft volume are the ones without media.
It was observed that the HILs with crushed glass and tire chips as bedding media had higher fluid
conductance at shallower depths in the landfill (figures 5 and 6). Crushed glass seemed to have
slightly greater fluid conductance value compared to tire chips in some cases. The bedding media
crushed glass or tire chips have greater hydraulic conductivity than the surrounding waste. HILs
using no bedding media could be said to fall into the category of a HIL with a bedding media
that has the same hydraulic conductivity as the surrounding waste (Larson 2007). In fact, all of
the HILs that were constructed with no bedding media but had greater than 15 feet of overburden
An example of this behavior is shown in figure 1; similar results are presented in the Appendix
B. Fluid conductance reduces as the injected cumulative volume increases, pressure required in
forcing the liquid in to the pore spaces of the surrounding waste increases. This is a result of pore
spaces being filled up. Landfill gas could also occupy the pore spaces and cause a decrease in
fluid conductance by resisting the leachate flow. There is a resiliency of fluid conductance with
each injection run that is a function of the length of time between injections (Larson 2007). It is
expected that each time injection is halted, the liquid within the HIL trench and a portion of the
liquid within the pore spaces of the compacted MSW surrounding the HIL drain by gravity to
another area within the landfill. This causes the fluid conductance to be slightly higher when the
injection is resumed and quickly reduces after the pore spaces are occupied as seen in the figure
1 at the beginning of every operation. The liquids can drain through the waste to the bottom liner
which is collected by the collection sumps, a portion of the liquid might be caught in
impermeable zones creating small perched aquifers within the landfill (Bleiker et al. 1993).
Some percentage of the liquid volume is stored in the pore spaces of the compacted waste which
helps in the anaerobic decomposition of the MSW which is the main goal of a bioreactor.
3.3.3 The Effect of HIL Length
The flow-pressure data was analyzed to study and compare the performance of HILs with
different lengths. Branched lines which have many HILs within the landfill connected to a
standpipe using a single pipe were considered to be HILs of different length, the lengths of HILs
that were connected were summed. Box plots were made with the fluid conductance data points
for the last injection run close to a cumulative linear injected volume of 200 gallons per foot of
HIL. Figures 3 and 4 illustrate the impact of HIL length on fluid conductance. Each graph
represents HILs of common depth in the landfill during their injection tests. Figure 3 shows that
the fluid conductance value is higher for HIL 25 which has a greater length than HIL 2, also it
HIL A
1 5 ft
I A14 A15
Tire chips
Tire chips
- Pressure transducer A14
- Pressure transducer A15
Days
Figure A-9. Response from the pressure transducers on right of HIL A with tire chips as bedding
media.
8 -
A14 A15
Pressure transducers
Figure A-10. Response over time from the pressure transducers after the injection was stopped.
8-
S6-
S4-
2-
0-
72 (520 ft)
G-
" 90 (360 ft)
'5
a 73 (200 ft)
* 58 (200 ft)
69 (200 ft)
Lines with 30-50 ft of overburden depth
(for a cumulative volume of 100 gallons/ft)
Tire chips
P Crushed glass
-;-- Tire chips
-IM 0* Crushed glass
4 -4 Crushed glass
0.01 0.1
Fluid Conductance (gpm/ft/ft of w.c)
Figure B-71. Fluid conductance of HILs with different bedding media.
Lines with 70-90 ft of overburden depth
(for a cumulative volume of 100 gallons/ft)
29 (720 ft)
G-
S27 (720 ft)
'-
S25 (720 ft)
24 (720 ft)
0.001 0.01
Fluid conductance (gpm/ft/ft of w.c)
Figure B-72. Fluid conductance of HILs with different bedding media.
124
M K Crushed glass
* Crushed glass
STire chips
S Tire chips
HIL C
10 ft 5 ft 5fti5
C5 C6 C7 C8I 2f
Crushed C2
Crushed glass
I
L AX
Pressure transducer C6
Pressure transducer C7
Pressure transducer CS
- Pressure transducer C2
t l I
5 10 15
Days
Figure A-19. Response from the pressure transducers on the left of HIL C with crushed glass as
bedding media.
6 -
4= -
2 -
I I C
I I1 I
C6 C7 C8
Pressure transducers
Figure A-20. Response over time from the pressure transducers after the injection was stopped.
the resulting pressures presented in the subsequent graphs in this chapter represent values after
the initial pressures were zeroed.
The peaks seen in figure 2-4 represent each day's operation of HIL A. The flowrate was
first fixed at 15 gpm and was lowered until 10 gpm whenever the injection pressure reached the
5 psi pressure limit. The flow-pressure was measured at the foot of the landfill with a pressure
gauge connected to the standpipe, and then the elevation head of the HIL was subtracted to get
the injection pressure at the point where the HIL entered the landfill. As seen in figure 2-4, the
increase in pressure at the pressure transducer locations occurs as soon as operation of the HIL
starts and decreases immediately when injection is stopped, similar results of pressure change
due to pressurized operation of HILs are presented in the Appendix A.
During the operation of the HIL, the responses of the transducers clearly show that the
pressure does not decrease back to the initial pressure condition before the next day operation
begins (figure 2-4). The pressure increases to a higher value than the previous day's pressure at
the end of the operation. The bedding media (crushed glass and tire chips) used in the trenches
has well connected and larger pore spaces compared to the surrounding waste. The trenches are
hydraulically more conductive than the surrounding waste, thus the leachate flow through these
trenches seem to have negligible resistance. Figure 2-4 illustrates that the pore pressure response
in the trench with bedding media is quick, and the transducers respond immediately when the
injection operation begins or is stopped. The response from the transducers buried in waste at
varying distances horizontally from the HIL A is shown in figure 2-5. The pressure transducers
in the waste do not show a sharp increase or decrease compared to the transducer in the media.
There is a delay in the pressure impact due to the operation, which is a result of the poor
conductivity of waste that is surrounding the injection trench.
Table 3-1. Fraction of HILs that reached the 200 gallons/ft for the study
Overburden depth (ft) Glass Tires Nothing
20 1/2 1/3 5/5
40 4/8 3/5 0/2
60 1/2 2/9 2/4
80 4/8 4/10 1/3
100 1/2 1/3 0/3
120 1/1 0/0 0/0
Table 3-3. Fluid conductance values for a cumulative linear-injected volume of approximately
200 gallons/ft
Perforated Bedding
HIL Design Length (ft) media
63
101
42
84
46
65
30
80
69
58
90
27
2
61
62
45
66
82
112
86
73
72
25
8
59
109
81
87
88
89
91
Single pipe
Tri branched
Single pipe
Single pipe
Single pipe
Only media
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Tri branched
Single pipe
Tri branched
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
Tri branched
Single pipe
Single pipe
Single pipe
Single pipe
Single pipe
520
1080
300
360
400
0
720
200
200
200
360
720
440
520
200
300
1560
360
1080
360
200
520
720
200
480
1080
360
360
360
360
360
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Glass
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Tires
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Nothing
Approximate
overburden depth
(ft)
61
41
75
84
101
72
121
15
35
35
35
80
86
60
55
100
53
78
48
15
35
35
80
65
75
53
15
15
15
15
15
Fluid conductance
(gpm/ft/ft of w.c) at
(200 gallons/ft)
0.00680
0.00860
0.00410
0.00470
0.00440
0.00430
0.00240
0.05000
0.02480
0.01390
0.01370
0.00420
0.00300
0.00620
0.01520
0.00820
0.01160
0.00400
0.00660
0.03180
0.02100
0.02930
0.00470
0.01030
0.00360
0.00510
0.01300
0.01000
0.01900
0.00870
0.00410
Cumulative
gallons injected
104,000
216,000
60,000
72,000
80,000
93,600
144,000
40,000
40,000
40,000
72,000
144,000
88,000
104,000
40,000
60,000
312,000
72,000
216,000
72,000
40,000
104,000
144,000
40,000
96,000
216,000
72,000
72,000
72,000
72,000
72,000
Table B-l HILs evaluated by Larson (2007).
Perforated Bedding approximate Cumulative
HIL Design overburden depth
SLength (ft) media rr d gallons injected
(ft)
80 Single pipe 200 Glass 15 40,000
69 Single pipe 200 Glass 35 40,000
58 Single pipe 200 Glass 35 40,000
90 Single pipe 360 Glass 35 72,000
27 Single pipe 720 Glass 80 144,000
86 Single pipe 360 Tires 15 72,000
73 Single pipe 200 Tires 35 40,000
72 Single pipe 520 Tires 35 104,000
25 Single pipe 720 Tires 80 144,000
81 Single pipe 360 Nothing 15 72,000
87 Single pipe 360 Nothing 15 72,000
88 Single pipe 360 Nothing 15 72,000
89 Single pipe 360 Nothing 15 72,000
91 Single pipe 360 Nothing 15 72,000
--- Flowrate
--- Pressure head
304 '?
180
Linear cumulative volume injected (gallons/ft)
Figure B-15. Flow-pressure variation with linear cumulative volume injected through HIL 42.
(Media = Crushed glass; Length = 300 ft; Overburden depth = 75 ft)
0.025
0.020
4.
S0.010 -
-J
0o.o00
-
0 .L
U o
0.000
160 180 200
Linear cumulative volume injected (gallons/ft)
Figure B-16. Fluid conductance variation with linear cumulative volume injected through HIL
42.
50
40
30
20
10
0
220
I -X- Fluid Conductance
0.0041
50
40
30
20
10
0
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-9. Flow-pressure variation with linear cumulative volume injected through HIL 25.
(Media = Tire chips; Length = 720 ft; Overburden depth = 80 ft)
0.10
S0.08
0
S0.06
t 0.04
0 0
0.02
0.00
0 50 100 150 200 250
Linear cumulative volume injected (gallons/ft)
Figure B-10. Fluid conductance variation with linear cumulative volume injected through HIL 25
--- Flowrate
-- Pressure head
9 2
190 195 200 205 210 215
50
40
30
20
10
-0
220
Linear cumulative volume injected (gallons/ft)
Figure B-45. Flow-pressure variation with linear cumulative volume injected through HIL 82.
(Media = Tire chips; Length =360 ft; Overburden depth = 78 ft)
0.008
-- Fluid Conductance
0.006
8 0.004 0.0040
0.002 0
SJ
0.000
*I.
190 195 200 205 210 215 220
Linear cumulative volume injected (gallons/ft)
Figure B-46. Fluid conductance variation with linear cumulative volume injected through HIL
82.
Table 2-3. Initial pressures of the transducers used in the experiment.
Initial Pressure range (psi) Number of pressure transducers
0-1 4
1-2 12
2-3 16
3-4 14
>4 1
50
40
30
0 50 100 150 200 250
Linear cumulative volume injected
(Gallons/ft)
Figure B-35 Flow-pressure variation with linear cumulative volume injected through HIL 69.
(Media = Crushed glass; Length = 200 ft; Overburden depth = 35 ft)
0
DS
Fluid conductance
C
0.0507 0.0248
i,
0 50 100 150 200 250
Linear cumulative injected volume
(Gallons/ft)
Figure B-36 Fluid conductance variation with linear cumulative volume injected through HIL 69.
106
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PAGE 1
1 STUDY OF PORE WATER PRESSURE IMPACT AND FLUID CONDUCTANCE OF A LANDFILL HORIZONTAL LIQUIDS INJECTION SYSTEM By SENDHIL KUMAR A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF TH E REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2009
PAGE 2
2 2009 Sendhil Kumar
PAGE 3
3 To my parents
PAGE 4
4 ACKNOWLEDGMENTS I would like to thank my committee members for their guidance an d comments on this thesis. I would like to specially thank Professor Timothy Townsend for constantly supporting me through the research work. Thanks go out to Drs Brajesh Dubey, Pradeep Jain, Jae Hac Ko and Hwidong Kim for their assistance throughout my g raduate studies. Additional thanks to my fellow graduate students who helped me while carrying out the experiments. I also thank the Polk County Board of County Commissioners, Hinkley center for solid and hazardous waste management and U.S. E nvironment al Protection Agency for funding this research as well as the Polk County Solid Waste Division for their support. Special thanks to Brooks Stayer, Allan Choate, and Sharon Hymiller for their support and guidance. Further gratitude is offered to the admin istration staff and operators of the Polk County Solid Waste Division. I would like to mention my appreciation to those I worked with and learned from while working at the Polk North Central landfill, especially Dennis Davis and George Reinhardt of Jones Edmunds & Associates; Eric Sullivan of Curry Controls; and everyone at Eclipse Construction. Further thanks to those who offered advice from afar via phone or e mail from Geokon, Inc. and Multilogger Inc. Lastly, I can never thank my parents enough f or their support and encouragement throughout my life and the greatest thanks to my friends, for their friendship, encouragement, and advice.
PAGE 5
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 4 LIST OF TABLES ................................ ................................ ................................ ........................... 7 LIST OF FIGURES ................................ ................................ ................................ ......................... 8 A BSTRACT ................................ ................................ ................................ ................................ ... 10 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 12 1.1 Background and Problem Statement ................................ ................................ ................ 12 1.2 Objectives ................................ ................................ ................................ ......................... 13 1.3 Research Approach ................................ ................................ ................................ ........... 14 1.4 Organization of Thesis ................................ ................................ ................................ ...... 15 2 A FIELD STUDY T O MEASURE THE PORE PRESSURES IN LANDFILLED WASTE AS A RESULT OF PRESSURIZED LIQUIDS ADDITION ................................ 16 2.1 Introduction ................................ ................................ ................................ ....................... 16 2.2 Material s and Methods ................................ ................................ ................................ ..... 17 2.2.1 Site Description ................................ ................................ ................................ ...... 17 2.2.2 Experimental Setup and Materials ................................ ................................ .......... 18 2.2.3 Data Management ................................ ................................ ................................ ... 19 2.2.4 Leachate Injection Experiment ................................ ................................ ............... 19 2.3 Results and Discussion ................................ ................................ ................................ ..... 20 2.3.1 Pressure Transducer Responses ................................ ................................ .............. 20 2.3.2 Measurement of Pore Pressures Within the Trenches ................................ ............ 22 2.3.3 Measurement of Pore Pressures Away From the Trenches Horizontally ............... 23 2.3.4 Measurement of Pore Pressures Away From the Trenches Vertically ................... 23 2.3.5 Implications ................................ ................................ ................................ ............ 24 2.3.6 Limitations ................................ ................................ ................................ .............. 25 2.4 Conclusions ................................ ................................ ................................ ....................... 26 3 FACTORS IMPACTING FLUID CONDUCTANCE OF HORIZONTAL TRENCHES USED FOR LEACHATE RECIRCULATION IN A LANDFILL ................................ ........ 48 3.1 Introduction ................................ ................................ ................................ ....................... 48 3.2 Methods and Materials ................................ ................................ ................................ ..... 49 3.2.1 Site Description ................................ ................................ ................................ ...... 49 3.2.2 Horizontal Injection Line Construction ................................ ................................ .. 50 3.2.3 System Operation and Monitoring ................................ ................................ ......... 51 3.2.4 Experimental Method ................................ ................................ ............................. 52
PAGE 6
6 3.2.5 Data Management ................................ ................................ ................................ ... 53 3.3 Results and Discussion ................................ ................................ ................................ ..... 54 3.3.1 Fluid Conductance Results ................................ ................................ ..................... 54 3.3.2 The Effect of Continuous Leachate Injection ................................ ......................... 54 3.3.3 The Effect of HIL Length ................................ ................................ ....................... 55 3.3.4 The Effect of HIL Bedding Media ................................ ................................ ......... 56 3.3.5 The Effect of Overburden Depth ................................ ................................ ............ 57 3.4 Conclusions ................................ ................................ ................................ ....................... 57 4 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS ................................ ......... 69 4.1 Summary ................................ ................................ ................................ ........................... 69 4.2 Conclusions ................................ ................................ ................................ ....................... 70 4.3 Recommendations ................................ ................................ ................................ ............. 70 APPENDIX A SUPPLEMENTAL FIGURES FOR CHAPTER 2 ................................ ................................ 72 B SUPPLEMENTAL FIGURES AND TABLES FOR CHAPTER 3 ................................ ....... 84 C SUPPLEMENTAL DAT A FOR CHAPTER 2 ................................ ................................ .... 127 LIST OF REFERENCES ................................ ................................ ................................ ............. 133 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ....... 136
PAGE 7
7 LIST OF TABLES Table page 2 1 Injection details ................................ ................................ ................................ .................. 28 2 2 Estimated times to fill the HIL trenches ................................ ................................ ............ 29 2 3 Initial pressures of the transducers used in the experiment. ................................ .............. 30 3 1 Fraction of HILs that reached the 200 gallons/ft for the study ................................ .......... 59 3 2 HIL specifications ................................ ................................ ................................ .............. 60 3 3 Fluid conductance values for a cumulative linear injec ted volume of approximately 200 gallons/ft ................................ ................................ ................................ ..................... 61 3 4 Fluid conductance values for similar cumulative linear injected volu me of approximately 100 gallons/ft ................................ ................................ ............................. 62
PAGE 8
8 LIST OF FIGURES Figure page 2 1 Plan view of the experimental area with buried pressure transduce rs. .............................. 31 2 2 Cross section of the HIL A trench with buried pressure transducers. ............................... 32 2 3 Pore pressure increase at the center of each trench for seventeen months before the experiment began. ................................ ................................ ................................ .............. 33 2 4 Response from pressure transducers buried along the trench HIL A with tire chips as bedding media. ................................ ................................ ................................ ................... 34 2 5 Response from pressure transducers buried in waste on the left side of the HIL A (tire chips) ................................ ................................ ................................ .......................... 35 2 6 Response over time from the pressure tran sducers buried along HIL C with Crushed glass, after the injection was stopped. ................................ ................................ ................ 36 2 7 Response from pressure transducers buried along the trench HIL A with tire chips as bedding media. ................................ ................................ ................................ ................... 37 2 8 Response from pressure transducers buried along the trench HIL C with crushed glass as bedding media. ................................ ................................ ................................ ...... 38 2 9 Initial respons es from pressure transducers buried along the trench of HIL A with tire chips as bedding media. ................................ ................................ ................................ ..... 39 2 10 Response from pressure transducers buried along the trench HIL B with no bedding media. ................................ ................................ ................................ ................................ 40 2 11 Response from pressure transducers buried in waste on the left side of the HIL A (tire chips) ................................ ................................ ................................ .......................... 41 2 12 Response from p ressure transducers buried in waste on the left side of the HIL C (crushed glass) ................................ ................................ ................................ ................... 42 2 13 Response from pressure transducers 3 ft away on the right of HIL A (tire chips) ............ 43 2 14 Response from pressure transducers 3 ft away on the left of HIL C (crushed glass) ........ 44 2 15 Initial responses from pressure transducers burie d at different depths under HIL A (tire chips) ................................ ................................ ................................ .......................... 45 2 16 Response from pressure transducers 3ft away on the left of HIL B (no media) ................ 46 2 17 Contour plot representation of the maximum pressure reached around the three HILs by the end of the experiment. ................................ ................................ ............................. 47
PAGE 9
9 3 1 Injection runs for HIL 58 with crushed glass showing the ef fect of cumulative volume injected on fluid conductance. ................................ ................................ .............. 63 3 2 A typical fluid conductance, pressure and flow rate behavior when an HIL is operated ................................ ................................ ................................ .............................. 64 3 3 HILs having same overburden depth showing the effect of length on fluid conductance. ................................ ................................ ................................ ....................... 65 3 4 HILs having same overburden depth showing the effect of length on flu id conductance. ................................ ................................ ................................ ....................... 66 3 5 Fluid conductance values at a cumulative linear injected volume of approximately 200 gallons/ft for HILs with different bedding media at different depths in the landfil l ................................ ................................ ................................ ................................ 67 3 6 Fluid conductance values at a cumulative linear injected volume of approximately 100 gallons/ft for HILs with different bedding media at different depths in the landfill ................................ ................................ ................................ ................................ 68
PAGE 10
10 A bstract 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 STUDY OF PORE WATER PRESSURE IMPACT AND FLUID CON DUCTANCE OF A LANDFILL HORIZONTAL LIQUIDS INJECTION SYSTEM By Sendhil Kumar August 2009 Chair: Timothy G. Townsend Major: Environmental Engineering Sciences Moisture distribution in landfilled waste plays a very important role in waste stabilization. Li quid addition systems are designed and buried inside landfilled waste to distribute moisture at different depths. P ressure is required to inject leachate through these systems. Landfill operators often add liquids under pressure to achieve higher liquid ad dition rates which speeds up waste stabilization. In this process, slope stability of the landfill becomes a subject of concern. When liquids are present under pressure in the landfilled waste an increase in the pore water pressure can decrease the shear strength and the geotechnical stability of side slopes. Though modeling techniques are available to predict the possible build up of pressures inside the landfill, very little is known about the real pressures that result from adding liquids under pressure Two field investigations were conducted at a bioreactor landfill in Polk County, Florida : (1) M easure ment of the spatial variation of pore water pressure resulting from pressurized leachate injection through the horizontal injection lines ( HILs ), and (2 ) evaluation of the performance of HILs in terms of fluid conductance
PAGE 11
11 Pressure transducers were buried in and around three buried HILs in the landfill to study the pressure distribution resulting from prolonged liquids addition. Each of the three HILs was constructed with different bedding media : crushed glass, tire chips and no bedding media. Moisture distribution was more uniform among the trenches with bedding media than in the one which did not have any bedding media. Pore pressure dissipated over a sh ort distance from the HILs. It was observed that the pore pressure impact was similar both in the horizontal and vertical direction from the HIL. The fluid conductance values (flow rate per unit length of HIL per unit of applied pressure head) for 31 HILs of varying length, bedding media and overburden depth of waste were monitored over a large range of cumulative linear injected volumes. Pressure and flow for the operated HILs were monitored and recorded using the supervisory control and data acquisitio n ( SCADA ) system In general, the HILs with bedding media had higher fluid conductance values than those without bedding media. Variation of flow rates during the operation of these HILs had negligible impact on the fluid conductance. The fluid conductance values of all the HILs decreased with increased cumulative injection volume and decreased with increased overburden depth of waste. This decrease in fluid conductance, which varied from 0. 01 to 0. 1 gpm/ft/ft of w.c, is hypothesized to be the result of dec reasing hydraulic conductivity of the surrounding waste due to increasing volume of leachate injection and overburden depth
PAGE 12
12 CHAPTER 1 INTRODUCTION 1.1 Background and Problem Statement Bioreactor landfills have becom e popular among some landfill owners for the advantages of faster stabilization of waste. Faster waste stabilization means an increase in both airspace and the rate of methane generation (Eliassen 1942, DeWalle et al. 1978, Rees 1980, and Pohland 1980) Usually, the leachate generated by the landfill is added back to the landfill using designed liquid distribution systems to create anaerobic conditions. Operating these liquid distribution systems successfully can save the landfill owners money in treating the leachate and enhances waste stabil ization. To build an efficient bioreactor, it is important to understand liquids addition system design and operation, including moisture distribution within the landfilled waste, the impact on slope stability, the performance of bedding media around the injection lines and the resulting injection pressures. This document focuses on evaluating a liquids addition system consisting of buried horizontal trenches Such an evaluation will help re solve some of the problems landfill owners have encountered distr ibut ing moisture inside the landfill. Evaluating the liquid distribution system and studying its impacts on the landfill play a major role in the progress towards building an efficient bioreactor. Since only limited knowledge is available regarding the ch aracteristics of in place municipal solid waste (MSW), numerical modeling has been performed to predict pore water pressures surrounding liquids addition devices in response to pressurized injection (Jain 2005). Because of the natural heterogeneity in land filled MSW and because of uncertainty describing waste characteristics, the accuracy of these modeled predictions are uncertain. Field studies have been carried out to evaluate the performance of liquid addition systems (Townsend 1995,
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13 Townsend and Mill er 1998, Doran 1999, Larson 2007 ). Townsend (1995) studied the variation of fluid conductance for several types of horizontal injection lines ( HILs ) in a landfill in Florida and found that the fluid conductance decreased with an increase in operation time and changed with elevation in the landfill. The effects of other design and operational parameters such as injection flow rate, HIL length, and HIL bedding media type are still un certain Larson (2007 ) studied the variation of fluid conductance for a few HILs at the Polk C ounty landfill in Florida and presented preliminary results that suggested that while the f luid c onductance did not change greatly with varying flow rates, fluid conductance did chang e with bedding media and elevation. Part of the work presen ted in this thesis is ) work with more results evaluating the HILs in the same landfill unit. One of the important concerns at any landfill where liquids are present under pressure is slope stability. An increase in pore w ater pressure can result in a decrease in shear strength. If liquids are added to a landfill in a manner where excessive pressures develop, it is possible that slope failures may result for some configurations. Modeling techniques allow the engineer to p redict possible pressure buildup and factors of safety for slope failure, but very little is known about what pressures actually develop within landfills as a result of added liquids. The studies described in this document will help in understanding the im pact on pore pressure due to pressurized leachate injection and the efficiency of the HILs one of the commonly used leachate injection systems. 1.2 Objectives The objectives of the research presented in this thesis are to : Measure the pore pressure distr ibution around three HILs with different bedding media as a result of pressurized leachate injection through the HILs.
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14 Examine the influence of HIL length on fluid conductance. Examine the influence of using shredded tire chips o r crushed glass as beddi ng media on fluid conductance Examine the influence of using no bedding media on fluid conductance. Examine the influence of HIL depth within the landfill on fluid conductance with respect to prior injected volumes. 1.3 Research Approach Two field stu dies were carried out with the objective of understanding and evaluating the process of pressurized liquid addition and its impact on pore pressure in the landfilled waste. In the first study, 81 vibrating wire pressure transducers were buried in the cente r of the landfill around a series of HILs and connected to a data logger station. These instruments were installed to measure pore water pressure resulting from different injection pressures applied to those nearby HILs. When the injection experiment was about to begin the initial pressures were noted and the HILs were oper ated one at a time. T hree HILs with different bedding media ( crushed glass, tire chips and excavated waste ) were examined. P ressure transducers were buried around each HIL Each HIL w as operated until the HIL reached its maximum halting pressure of 5 psi. Data in the form of frequency from these instruments were processed to pressure in psi using Microsoft Access. Pressure change in these buried transducers indicated the distance which the liquids had reached and the extent to which the pore pressure changed at different distances. These pressure values provide field pore pressures due to pressurized injection of liquids that can be compared to that of numerical modeling. For the secon d study in this document the performance of 31 HILs installed in the Polk County Phase 2 landfill was evaluated. These HILs we re used as part of the liquid distribution system within the landfill and we re monitored and operated through the Supervisory Con trol and
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15 Data Acquisition (SCADA) system The experiment studied HIL fluid conductance and the impact on the fluid conductance of changing depth, design, bedding media and prior injected cumul ative volumes. The SCADA recorded the pressure and flow rate of all of the HILs ; these were later analyzed for fluid conductance. The HILs were all operated at a flowrate ranging from 10 50 gpm depending on their lengths ; the halting pressure for all these HIL s was 5 psi as the permit conditions require Fluid conduc tance values for these HIL s were studied by analyzing the flow pressure data recorded. The fluid conductance of the HILs was then compared for effect of different bedding media, overburden depth and le ngth based on fluid conductance. 1.4 Organization of T hesis Chapter 2 presents the results of measured pore pressure changes in the landfill as a result of pressurized leachate injection through the HILs. Buried pressure transducers around the HILs record the pressures when the HILs are operated at high press ures. The data from these transducers are downloaded to understand the pressure distribution in the landfilled waste. Chapter 3 discusses fluid conductance of the HILs with various depths, bedding media and length of HIL The fluid conductance is calculat ed by the flow pressure field data based on injection experiments on the subsurface HIL liquid distribution system. The thesis ends with C hapter 4, a summary and a set of conclusion s from C hapters 2 and 3 and includes reco mmendations for future research Appendix A presents supplemental figures with change in pressure during and after the experimental period for all the pressure transducers. Appendix B presents the tables and supplemental f igures, which include flow, pressure, and fluid conductance data for all the HILs analyzed for the study presented in this thesis.
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16 CHAPTER 2 A FIELD STUDY TO MEA SURE THE PORE PRESSU RES IN LANDFILLED WA STE AS A RESULT OF PRESSURIZE D LIQUIDS ADDITION 2.1 Introduction Anaerobic bioreactor landfills are becoming popular as their advantages become increasingly well documented (Pohland, 1975; Leckie et al., 1979; Watson, 1987; Townsend et al., 1996; Warith et al., 2001, Warith, 2002; and Jain, 2005 Larson 2007 ,). Bioreactor landfill operators often try to recirculate as mu ch leachate as possible into their landfills, requiring liquids addition under pressure. However, i njection of liquids with pressure raises concern over the slope stability because the pore water pressure increase can decrease the shear strength that will result in a slope failure ( Koerner and Soong 2000 ; Jain et al., 200 7 ) Evaluating landfill stability becomes a priority to successfully operate the bioreactor when liquids are being added with pressure. Pore pressure is one of the primary inputs to eva luate the stability. A focus of research at several landfills in Florida is the development and evaluation of methodologies for safe design and operation of bioreactor landfills. Having this in mind, the impact of liquids addition via vertical wells on por e water pressure in the surrounding waste was mathematically modeled by (Jain 2005, Jain et al 2007); however there are no field data available measuring how the pore water pressure changes due to the liquid addition. The objective of the experiment discu ssed in this paper is to study the spatial variation of pore water pressure in the waste as a result of pressurized liquid addition through horizontal trenches. In this experiment pressure was measured from transducers buried in landfilled waste surroundi ng the horizontal leachate injection trenches
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17 2.2 Materials and Methods 2.2.1 Site Description The Polk County North Central Landfill (NCLF) is located in Winter Haven, Florida as shown in the figure B 1 Phase 2 shown in figure B 2, is a lined landfill site that accepted waste from March 2000 to November 2007. The Phase 2 landfill received approximately 2,500 metric tons of waste per day which consisted of mixed residential, commercial, and industrial waste. The site also contains several closed landfi ll units. One hundred and six HILs were installed in seven out of eight subcells in the Phase 2 landfill and were connected to seven main pipes at their respective subcells T hese main pipes were all connected to the storage tanks where the leachate was pumped to the HILs. The HILs are 4 inch diameter high density polyethylene (HDPE) pipe with two perforations at every 2 linear ft of the pipe. The perforations were each oriented at 45 0 from either side of vertical and w ere placed facing downward. The tren ches were constructed by excavating approximately 3 f oo t wide and 3 f oo t deep trenches and backfilling them with a layer of porous bedding media, laying a perforated pipe and backfilling the rest of the trench with the bedding media. The liquid distributi on system was operated and monitored by a SCADA system. The HILs were operated individually or sometimes as a cluster of two or more HILs in the same subcell. HILs were selected to achieve maximum leachate recirculation T he permitted maximum daily limit f or leachate injection is 50,000 gallons The leachate distribution system was operated only when an operator was present on site ( 8 hours per day for 5 to 7 day s a week depending on how urgent the need to reduce the leachate levels in the storage tanks ) T he permit also states that the HILs can be operated only at a maximum of 5 psi injection pressure. The pressure limit was set for slope stability reasons. The applied pressure is the difference between the elevation head and the record ed pressures measured at the base of the landfill. After a chosen HIL is operated at
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18 a minimum flowrate of 15 25 gpm for a few minutes, a steady increase in pressure at the pressure gauge is observed. W hen the pressure starts becoming constant, that point is determined as the elevation head. In a study of waste composition carried out in the summer of 2003 and the winter of 2004 with 30 grabbed samples from the Phase 2 cell, the density of the landfilled waste has been estimated at approximately 1500 lb/yd 3 (R.W. Beck, Inc. 20 04). 2.2.2 Experimental Setup and Materials The experimental area is approximately 560 ft x 200 ft on S ubcell 5 of the P hase 2 cell and consists of three horizontal trenches each with a different bedding media (tire chips, glass and excavated waste). The HILs are surrounded by 81 pressure transducers. Three transducers are installed in each trench and the rest are installed at different distances from the HIL s A s shown in Figure 2 1 t he transducers were installed in a V formation around the HIL s to minim ize short circuiting and to have undisturbed waste in the fluid path from the injection line to the transducers. The injection lines have a perforated length of 360 ft. Figures 2 1 and 2 2 show the plan view and the cross section of the p ressure transducer s experiment layout. Eighty one Geokon model 4500S vibrating wire pressure transducers were used for the experiment. The transducers were factory calibrated to a ga u ge pressure range of 0 psi to 50 psi with a reported accuracy and resolution of 0.05 psi a nd 1.25 psi respectively. The standard used to calibrate was a Pressure Controller Model PPC2 made by DH instruments with an accuracy of 0.02% FS. The Geokon accuracy figure of 0.1% of full scale is a conservative estimate of the accuracy after accountin g for any possible errors during the calibration process. Therefore, any calculation of pressure using the calibration factor and the transducer reading will be within 0.1% (0.05 psi) of full scale of the true value. Also, the transducers were designed w ith thermistors with a range of (Geokon, Inc 2007).
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19 2.2.3 Data Management All the instruments were connected to six multiplexers that were connected to a Geokon CR10X datalogger. The responses from the 81 pressure transd ucers were recorded by the d atalogger; a laptop was used to connect to the datalogger and periodically download the raw frequency and temperature data for all the pressure transducers. The datalogger was p rogrammed to record data every 3 0 minutes, th e raw data were converted to pressure in psi using the calibration reports specifi ed for each pressure transducer using the manufacturer instructions. The equation used to convert the raw data and the calibration constants for each transducer (Tables C 1 and C 2) are presented in Appendix C Pressure readings recorded with 60 minutes interval w ere chosen to represent the results, figures with the results show the change in pressure with days of operation. A contour plot using a software called SURFER, was made to present the pressure distribution around the trench with transducers buried 3 ft away from the trench, the highest pressures reached by the end of the experimental duration was used to represent the impact due to pressurized leachate injection. T he data analyzed and presented for this thesis represent an experimental duration of 4 months Jul 2007 to Oct 2007 during which all the three injection lines were operated. Results from only 50 out of the 81 pressure transducers w ere found to be useful to study the pore pressure distribution as the rest of the transducers recorded negative frequency readings during the experimental period that suggested the transducer had failed. The reason for the transducers to fail is presumed to be the harsh landfill conditi ons. 2.2.4 Leachate Injection Experiment The three HILs around which the experimental setup was constructed were operated to meet the objectives of the experiment. The Table 2 1 shows the durat ion and volume of leachate injected through each HIL; HIL A was chosen to be operated first, resulting in impacting the pore pressures in the surrounding. To avoid any overlap of response from the pressure
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20 transducers near HIL A, the farthest line HIL C was chosen next. HIL B was chosen to be operated last (30 to 40 d ays after operation of HIL C was stopped). The reason for choosing this order of operation was to prevent any impact on the transducers due to injection into more than one HIL The HILs were operated at a flowrate of 15 gpm to achieve prolonged leachate in jection before they reached the maximum injection pressure (halting pressure) of 5 psi. At a flowrate of 15 gpm (112 ft 3 per min) the time taken to fill the three trenches is presented in table 2 2, for a porosity range from 0.2 to 0.5. The chosen line was operated through SCADA during the working hours of the Polk County division. There was a gap of 30 to 40 days between operations of each HIL to prevent any overlap of impact on the pressure transducers by the operation of HIL s. 2.3 Results and Discussion 2.3.1 Pressure Transducer Responses The pressure transducers were monitored over the period of 16 months from January 2006 to June 2007 before the experiment was started. Larson (2006) studied the vertical air permeability with the data from the buried pr essure transducers during January 2006 through March 2006 as shown in figure 2 3. A steady increase in pressure among all the transducers during the 1 6 months period was observed. A sample of this pressure increase is presented in figure 2 3 with one press ure transducer from the center of each trench. This increase in pore pressure is presumed to mainly be the result of subsequent placement of waste material over the experimental area, which would have resisted the landfill gas to escape and thus resulting in a pore pressure increase in the experimental area due to build up of landfill gas. Compaction after placing the waste lifts might have also contributed towards the pore pressure increase by compressing the pore space. Due to this increase, the initial p ressures of the transducers when the experiment was started were not zero and ranged from 0 to 5 psi as shown in table 2 3 However,
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21 t he resulting pressures presented in the subsequent graphs in this chapter represent values after the initial pressures wer e zeroed. The peaks seen in figure 2 first fixed at 15 gpm and was lowered until 10 gpm whenever the injection pressure reached the 5 psi pressure limit. The flow pressure was measured at the foot of the landfill with a pressure gauge connected to the standpipe, and then the elevation head of the HIL was subtracted to get the injection pressure at the point where the HIL entered the landfill. As seen in f igure 2 4, the increase in pressure at the p ressure transducer locations occurs as soon as operation of the HIL starts and decreases immediately when injection is stopped similar results of pressure change due to pressurized operation of HILs are presented in the Appendix A During the operation of the HIL, the responses of the tr ansducers clearly show that the pressure does not decrease back to the initial pressure condition before the next day operation begins (figure 2 4) T at the end of the operation. The bedding media (crushed glass and tire chips) used in the trenches has well connected and larger pore spaces compared to the surrounding waste. The trenches are hydraulically more conductive than the surrounding waste, thus the leachate flow through these trenches seem to have negligible resistance. Figure 2 4 illustrates that the pore pressure response in the trench with bedding media is quick, and the transducers respond immediately when the injection operation begins or is stopped. The response from the transducers buried in waste at varying distances horizontally from the HIL A is shown in figure 2 5. The pressure transducers in the waste do not show a sharp increase or decrease compared to the transducer in the media. The re is a delay in the pressure impact due to the operation, which is a result of the poor conductivity of waste that is surrounding the injection trench.
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22 The pressure data recorded after the experimental duration were analyzed to understand the change in po re pressure after the injection was stopped; figure 2 6 shows the response from the transducers (C1, C2 and C3) along the HIL C with crushed glass. It can be seen that the pore pressures reduce greatly over time after the injection is stopped; similar resu lts are presented in Appendix A. 2.3.2 Measurement of Pore Pressures W ithin the Trenches The results in figures 2 7 through 2 10 show the response of the transducers that are buried along the trench of the three HILs. There is negligible pressure loss and a uniform pressure distribution along the trenches with tire chips and crushed glass as seen in figures 2 7 and 2 9; this is due to the higher porosity of the bedding media compared to the surrounding waste A good pressure distribution within the trench is a great advantage to spread out the injected liquids in the surrounding area. Pressure transducer responses were analyzed to check the time taken to attain uniform leachate flow through the trench. The response from pressure transducers (A1, A2 and A3) buried along HIL A with tire chips in the trench as seen in figure 2 9, indicate that there is only a small delay of 3 to 4 hrs in reaching steady state flow through the whole trench with bedding media after the injection is started. There is a slight diff erence in pressures on the first day of injection, whereas by the second day the pressures along the whole trench seem to have attained uniformity (figure 2 9). Figure 2 10 shows the response from the transducers (B1, B2 and B3) buried along the trench of HI L B (figure 2 1) which does not have any bedding media around it. There is a great loss in the injection pressure along the trench, which is likely the result of the lower hydraulic conductivity of waste surrounding the line. The HILs with no media were found to have a better fluid conductance (discussed in the next chapter) at shallower depths of about 20 to 40 ft in the landfill and as the overburden depth increased it required very high pressures to inject leachate
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23 through these lines. HIL B had an ove rburden depth of approximately 80 ft during this study. The maximum injection pressure according to the permit conditions for the phase 2 landfill unit is 5 psi. The injection pressure for operating the HIL B reached its 5 psi limit within the first day of leachate injection which is because of the increased overburden depth 2.3.3 Measurement of Pore Pressures Away F rom the Trenches Horizontally The results in figure 2 11 show the responses from transducers placed horizontally farther from the trench of H I L A, the pressure decreases with increasing distance The overburden depth of waste and the low conductivity of waste are presumed to be the main factors that make the pressure dissipate over this distance. A pressure drop of around 4 psi can be seen with in a distance of 25 ft from the trench having bedding media of tire chips. Figure 2 12 also shows that the pressure on the side of HI L C horizontally decreases over the distance. From f igure 2 2, shows the transducers on the side of HIL B and has no beddin g media in the trench there is no change in pressure at all during the injection period. This is due to less intake of leachate through that HIL; the reason being the absence of bedding media to spread the pressure in the trench which helps greatly in spr eading the leachate around. Figure 2 9 shows that the pressures decrease over the length of the HIL in the trench itself. From all the responses from the transducers, there is no impact on any transducer away from the trench due to injection into HIL B (fi gures A 14 to A21 in Appendix A) 2.3.4 Measurement of Pore Pressures Away F rom the Trenches Vertically When the injection through the HIL start s leachate spread s through the waste from the trench. To understand the pore pressure distribution in the hor izontal direction from the HIL versus vertical direction the results from the transducers were evaluated There are 5 transducers placed 3 ft away from the trench of HIL A horizontally, vertically and diagonally (figure 2 2) From figures 2 13 and 2 14 it can be seen that the pore pressure increase is the same, both, in the
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24 vertical and horizontal directions. As mentioned earlier the results from figure 2 15 show that the response of the transducer (A2*) buried 3 ft under the trench in the waste responds slower than the one in the trench with media (A2). A contour plot representing the pressure distribution for the cross section of the HILs in the center is presented in figure 2 17. It can be seen from figure 2 1 7 that the transducers around the trench of HIL C and HIL A have been impacted almost equally irrespective of the direction. It could be expected that the pressure distribution is greater in the horizontal direction compared to the vertical direction due to the anisotropic nature of the waste, but t he results indicate there is an equal impact around the HIL. The change in pore pressure in the horizontal direction is only due to injection pressure, where as the change in pore pressure in the vertical direction is a result of injection pressure and the gravitational force for the liquid movement. Also, importantly the small radial distance about 3 ft in the current study, does not help in understanding the anisotropic nature of waste. There is little change around the trench of HIL B as shown in f igure 2 1 6 and in the contour plot figure 2 17. 2.3.5 Implications The stability of a landfill structure is influenced by the internal shear strength of the waste material in each layer and the pore pressures that develop due to gas or pressurized liquid additio n. Increase in pore pressure decreases the shear strength that might lead to a slope failure. Stability analysis for landfills that practice pressurized liquid addition is important; pore pressure is a primary input in this analysis. The influence of leach ate under pressure on the stability of landfilled waste mass has been discussed by Koerner and Soong (2000), by calculating the factor of safety. The research described in this thesis is an attempt to provide an insight into actual pore pressures that resu lt from pressurized leachate addition and their behavior within landfilled waste. It was found that the pore pressure decreased over a short distance, there was a decrease of about 4 psi over a distance of 25 ft from the HILs. Apart from the liquid additio n it was found
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25 that the pore pressures before liquid addition, ranged from 0 5 psi which is presumed to be due to landfill gas generation. As the landfill gas builds up there will be more resistance to liquid additions requiring higher injection pressure s. Pore pressures were found to decrease significantly over time after the injection through the HILs were stopped. These learning from the field data can be used by geotechnical engineers to account for pore pressure effects in the stability analysis. It was also observed that the pore pressure increased with everyday operation and the rate of decrease in pressure was very slow after injection was stopped, however the results indicated that the pore pressure does dissipate over time and liquid injection ca n be resumed in these areas. 2.3.6 Limitations This method involves laborious field work initially in installing the transducers. But once the field work is completed, it only involves downloading the data from the data logger and managing the data. This m ethod can be used to study pressure distribution at different elevations provided transducers have been installed at different elevations. The method can be used around different sets of HIL s to have multiple values. The experiment was run only once until the HIL s reached the 5 psi pressure limit set in the permit. This can be repeated again when the transducers pressure drop back to the initial pressures. The transducers to come back to their initia l pressures take a long time There is a risk of having s ome of the transducers not work due to the harsh landfill conditions. Installation process also can damage the instruments. Thirty one out of eighty one transducers ( 38% ) that were installed stopped working during this study. Using instruments that are des igned for such rough conditions could help the study. Most of the transducers in this study were installed at varying distances from the injection line horizontally. Vertically there is only one transducer which is 3 ft below each trench, and the
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26 transduc er below the HIL C had failed before the experiment began ; this gives only limited idea of how pressure varies over distance vertically when the HILs are operated. The pressure values horizontally and the area of impact due to injection from this study ca n only be valid for that fixed depth of waste (8 0 ft in the current study) over the experimental area. The pressure distribution and area of impact due to injection will change when the overburden depth of waste will vary. It can be presumed that the initi al pore pressures in the waste before starting the injection would be higher as the overburden depth of waste increases. 2.4 Conclusions In situ pore pressures within landfilled waste resulting from pressurized leachate injection were studied. It was obser ved that the pore pressures in the waste increase slowly as the waste lifts are being constructed. In the experimental ar ea with an overburden depth of 8 0 ft of waste, the pressures as shown by the transducers, before the experiment was started were betwee n 0 to 4 psi. The transducers which were towards the center were noted to have higher pressures than the ones closer to the slopes. These initial pressures can be higher when the overburden depth of waste increases due to landfill gas and further compressi on of pores When the injection through the HILs commenced it was observed that the trenches having bedding media of crushed glass or tire chips performed better in terms of the amount of total leachate intake. The bedding media being more porous than the surrounding waste helps the leachate fill up the trench quickly. There is a negligible pressure loss along the trenches with the bedding media (tire chips and crushed glass) and this in turn is advantageous to achieve good distribution of moisture in the surrounding area. The HIL which did not have any bedding media was operated only for a day as it reached the 5 psi injection pressure limit. There was a significant loss in pressure along the trench with no bedding media after the injection was started. Th e pore pressure due to pressurized injection decreased over the distance and was
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27 observed to have impacted a distance of 30 ft horizontally. However, the distance of impact can decrease as the overburden depth of waste increases.
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28 Table 2 1 Injection deta ils HIL# Bedding Media Operation duration Volume of leachate added (gallons) A Tire chips 14 days 81, 700 B Excavated waste 1 day 6,2 00 C Crushed Glass 12 days 74, 200
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29 Table 2 2 Estimated times to fill the HIL trenches Media Trench dimensions (ft) A ssumed Porosities Volume of trench (ft 3 ) Time to fill trench (hours) Crushed glass 360 x 3 x 3 0.3 972 8.1 0.4 1296 10.8 0.5 1620 13.5 Tire chips 360 x 3 x 3 0.3 972 8.1 0.4 1296 10.8 0.5 1620 13.5 MSW 360 x 3 x 3 0.2 648 5.4 0.3 972 8.1 0.4 1296 10.8
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30 Table 2 3 Initial pressures of the transducers used in the experiment. Initial Pressure range (psi) Number of pressure transducers 0 1 4 1 2 12 2 3 16 3 4 14 >4 1
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31 Figure 2 1 Plan view of the experimental area w ith buried pressure transducers
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32 Figure 2 2. Cross section of the HIL A trench with buried pressure transducers.
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33 Figure 2 3. Pore pressure increase at the center of each trench for seventeen months before the experiment began.
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34 Figure 2 4. Resp onse from pressure transducers buried along the trench HI L A with tire chips as bedding media.
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35 Figure 2 5. Response from pressure t ransducers buried in waste on the left side of the HI L A (tire chips)
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36 Figure 2 6. Response over time from the pressur e transducers buried along HIL C with Crushed glass, after the injection was stopped.
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37 Figure 2 7. Response from pressure transducers buried along the trench HI L A with tire chips as bedding media.
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38 Figure 2 8. Response from pressure transducers burie d along the trench HI L C with crushed glass as bedding media.
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39 Figure 2 9. Initial responses from pressure transducers buried along the trench of HIL A with tire chips as bedding media
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40 Figure 2 10. Response from pressure transducers buried along th e trench HI L B with no bedding media.
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41 Figure 2 11. Response from pressure t ransducers buried in waste on the left side of the HI L A (tire chips)
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42 Figure 2 12. Response from pressure t ransducers buried in waste on the left side of the HI L C (crushed glass)
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43 Figure 2 13. Response from pressure t ransducers 3 ft away on the right of HIL A (tire chips)
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44 Figure 2 14. Response from pressure t ransducers 3 ft away on the left of HIL C (crushed glass)
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45 Figure 2 15. Initial responses from pressure tran sducers buried at different depths under HIL A (tire chips)
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46 Figure 2 16. Response from pressure t ransducers 3ft away on the left of HIL B (no media)
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47 Figure 2 17. Contour plot representation of the maximum pressure reached around the three HILs by the end of the experiment
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48 CHAPTER 3 FACTORS IMPACTING FL UID CONDUCTANCE OF H ORIZONTAL TRENCHES U SED FOR LEACHATE RECIRCU LATION IN A LANDFILL 3.1 Introduction Munic ipal solid waste (MSW) landfill operators commonly practice l eachate recirculation to create a naerobic bioreactor conditions that will enhance MSW stabilization (Pohland 1980; Barber and Maris 1984; Townsend et al. 1995, 1996; Reinhart and Townsend 1997; Townsend and Miller 1998; Meh ta et al. 2002). B ioreactor landfill s are designed to control, mon itor, and optimize the waste stabilization process compared to landfills acting just as containment units for the waste (Reinhart and Townsend, 1997, Reinhart et al., 2002). One of the common methods of leachate recirculation is horizontal injection via su bsurface horizontal injection lines (HILs). Subsurface leachate injection techniques are widely practiced as they are less likely to produce offensive odors that are associated with surface applications such as the use of infiltration ponds and spray irrig ation and allow better control of liquids distribution at different depths within a landfill (Townsend and Miller 1998) Evaluation of such recirculation systems become an important part of designing successful bioreactor landfills in the future. The impo rtant inputs that are used to design the recirculation system are the range of flow rates achievable, associated pumping pressures required, recirculation line spacing, and long term system performance Hydrodynamic modeling techniques have been used to st udy the efficiency of HILs in terms of moisture distribution within the landfill (McCreanor and Reinhart 1996 ; McCr eanor 1998; McCreanor and Reinh art 2000; Haydar and Khire 2004, 2005 ) but there are only a few published field performance studies on these moisture addition systems (Townsend and Miller 1998, Doran 1999) A field study that measured the flow to pressure ratio as a function of injection time for 11 HILs at a landfill in North Central Florida ( Townsend and
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49 Miller 1998 ) found that the flow rate to applied pressure ratios described by Larson (2007) as decreased with increasing injection time and varied depending upon the depth within the landfill and the construction of the HIL. The objective of the research described in this thesis is to evaluate the performance of horizontal injection lines for leachate recirculation based on the fluid conductance; fluid conductance can be used as one of the design inputs for similar systems at future bioreactors Larson (2007 ) presented pr eliminary results of fluid conductance for design and operational variables at the Polk County North Central Landfill. This study aims to continue and build upon this past study by examining the flow rate to applied pressure ratio for design and operationa l variables such as the length of a HIL, effect of HIL depth within the landfill and the effect of HIL bedding media. 3.2 Methods and Materials 3.2.1 Site Description The Polk County North Central landfill is in Winter Haven, Florida ( f igure B 1) and was opened in 1976. The facility has a total area of approximately 2,200 acres, of which 700 acres are permitted for landfill use. As shown in the aerial view of the Polk NCLF facility in f igure B 2, the facility has the following on site: a household hazardou s waste collection area, a materials recycling facility (MRF), a closed unlined Class I and III landfill, closed unlined landfill cells, and three lined Class I landfill cells, Phase 1, 2 and 3. Phase 1 is temporarily capped Phase 2 stopped accepting wast e in November 2007 and Phase 3 is the currently active cell. The facility accepts waste from the entire Polk County community at a daily average of 1,250 tons of municipal solid waste (MSW), 88 tons of construction and demolition waste, and 180 tons of tir e and wood ash. Phases 1, 2 and 3 in the facility generate about 30,000 gallons/day of leachate.
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50 The study described in this document was carried out in the Phase 2 landfill unit; Phase 2 cell was actively accepting waste from March 2000 to November 200 7. The Phase II landfill as shown in f igure B 2 is a 43 acre cell divided into eight equal size subcells of a saw tooth design. This site uses a state of the art supervisory control and data acquisition (SCADA) system to operate and monitor the liquid dist ribution system in Phase 2 All Phase 2 subcells, except for S ubcell 1, are recirculated with leachate using Horizontal Injection Lines (HIL s ) installed at different elevations within the cells Subcells 2 to 7 each have a hydrant/header assembly that is c onnected to the force main at the south toe of the landfill as shown in f igure B 3. Each hydrant/header assembly branches into a group of standpipes to connect to the HILs Each standpipe has a manual butterfly valve that is outfitted as shown in f igure B 4. Each hydrant assembly is equipped with a pressure gauge, flow meter, and flow control valve. 3.2.2 H orizontal I njection L ine Construction There are 106 HILs connected to the standpipes as shown in f igure B 4 at different subcells. These 106 HIL s enter t he landfill from the south side at various elevations, a drawing showing the cross section of the south side of phase 2 landfill with the HILs is attached in the Appendix B. The HILs have different configurations; most of them are single lines having diffe rent lengths. A few recently constructed lines are branched lines HILs within the landfill were connected to a single inlet manifold, most of which are located at higher elevation s in the landfill. Each HIL was constructed by exc avating trenches approximately 3 to 4 ft wide and 5 ft deep using hydraulic excavators. The trenches were backfill ed with a layer of porous bedding media, a perforated pipe was placed, and then the remainder of the trench was backfilled again with the same porous bedding media All the HILs have perforation s starting at 100 ft inside the landfill from the point of entry on the side slope ; the first 100 ft would be solid walled pipe where the trench was backfilled with clay so as to
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51 minimize side seeps durin g injection Table 1 presents the HILs that could be used for the study from the HILs that were installed and operated. Table 2 were evaluated for this study. The pipes were 4 inch diameter high density polyethylene (HD PE). The perforated pipe consisted of two 0.375 in diameter perforations w ith a frequency were always placed in the downward direction. The HILs were placed in a 5 ft deep trench with 2 ft of bedding media in the bottom and 1 ft of bedding media on top of the HIL and the rest 2ft backfilled with excavated waste. The end of each perforated pipe was capped. The HILs were surveyed using a Global Positioning System (GPS) device, an AutoCAD drawing that shows the plan view of the HIL s buried in the phase 2 landfill is attached in the Appendix B. 3.2.3 System Operation and Monitoring The recirculation of leachate into phase 2 was operated and monitored by SCADA system. Flow rates were monitored by Bailey Fischer & Porter model 10DX311 1E series magnetic flow meters. The range of these flow meters is 0 250 GPM and the accuracy is 0.5% of the measured flow rate. Injection pressures were monitored with ABB model 264HS digital pressure gauges. These gauges have a range of 0 150 psi g and an accuracy of 0.1125 psig. The SCADA operating system recorded and saved the flow rate and pressure values every minute. In accordance with permit requirements for slope stability concerns injection pressure limit was set to be 5 psig at the p oint perforated pipe began. The applied pressure was determined by the difference between elevation head and the recorded pressures measured at the toe of the landfill. The minor pressure losses were considered negligible for the flow rates used. The el evation head was determined for each HIL by pumping at the lowest flow rate achievable by the system (25 GPM) for at least 10 minutes. The point where the pressure stayed constant,
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52 or plateaued, was determined to be the elevation head of the HIL from the pressure gauge and the point of zero applied pressure. 3.2.4 Experiment al Method The l eachate recirculation system was operated only when an operator was present. Therefore, leachate was injected for approximately 8 hours a day, 5 to 7 days a week, depend ing upon the necessity to lower the leach ate level in the storage tanks. The performance of the HILs differed in terms of fluid conductance only at higher cumulative volumes injected through them, majority of the HILs installed were not used or had only be en operated for a small cumulative volume. The maximum cumulative volume injected per foot of HIL studied by Larson (2007) was 200 gallons, fourteen HILs presented in table B 1 (Appendix B) were operated to measure the fluid conductance in the previous stu dy. Seventeen i ndividual HILs that reached a linear cumulative volume of 200 gallons/ft of HIL presented in table B 2 (Appendix B) were test ed for durations that were necessary for the objectives of this research or were run until the injection pressure re ached the permitted 5 psig for the desired operational flow rate. Fluid conductance values were evaluated at a linear cumulative injected volume of 200 gallons/ft of HIL for the convenience of comparing the HILs studied in the previous study. All injectio n tests were designed to evaluate the effect of multiple design and operational variables upon HIL fluid conductance values. Therefore, a total of 31 HILs are evaluated in this thesis, based on fluid conductance for the parameters mentioned before. The ef fects of overburden depth of waste over the HIL fluid conductance was studied by choosing HILs of same length and bedding media but buried at different elevations, these HILs were compared after they were injected with similar volumes of leachate through t hem. The effects of bedding media upon HIL fluid conductance was studied using two types of bedding media ; shredded tire chips and crushed glass. The shredded tire chip size was usually of
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53 3 inches but with larger and smaller pieces at times having a hy draulic conductivity that ranged from 0.67 to 13.4 cm/sec (Warith et al. 2004) The crushed glass was derived onsite from broken bottles that were collected at the Polk County materials recycling facility. To evaluate the effect of bedding media on fluid conductance, injection tests were performed on HILs at the same depths within the landfill that contained either type of media. The effect of no bedding media was also tested in this fashion. To test the effect of HIL length, injection tests were perfo rmed on multiple HILs of different lengths and with approximately the same depth of overburden pressure above. The resulting fluid conductance data were compared for the same values of cumulative linear injected volume. 3.2.5 Data Management Fluid conduct ance values were observed to be higher for all the HILs when first operated, as the volume of leachate injected through them increased, the difference due to HIL configuration could be seen in terms of fluid conductance. Therefore, fluid conductance values of HILs were compared at an approximate cumulative linear injected volume of 200 gallons per foot of the HIL. Only 31 HILs of the 106 had been operated to inject over 200 gallons/ft of leachate, those were used in this study (table 2). F low pressure data for the HILs were downloaded from the SCADA server and processed to determine the fluid conductance. These data were logged every minute. Fluid conductance for the injection run was then plotted as a function of cumulative linear injected volume. The plots will show the impact of prior use of the HIL presented. Box plots were used to represent the fluid conductance of HILs to compare for the design parameters. This was accomplished plotting the HILs on the y axis with the fluid conductance of the last injection run of HIL w h ere the injected volume w as close to a cumulative linear injected volume of 200 gallons/foot of HIL on x axis (log scale) The averages
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54 of the injection run close to 200 gallons/ft of HIL were taken to represent the fluid conductanc e and compare for the different overburden depths of waste Similarly, fluid conductance values were compared at a cumula tive linear injected volume of 1 00 gallons/foot of HIL for 14 of the 31 HILs (table 4). 3.3 Results and Discussion 3.3.1 Fluid Conduct ance Results More than 20 million gallons of leachate has been intermittently injected into 106 HILs in Phase 2 landfill. Pressure and flow rate data were collected from a set of 31 HILs for their respective injection runs. As discus sed in the study by L arson (2007 ) the HILs in this study had the same behavior for a typical operation, with each injection run fluid conductance values started high, as back pressures were low, and then decreased with continued operation, as back pressure s rose more slowly (S ee figure 2 for a reminder of this behavior). With every renewed injection run, fluid conductance values initially rebounded but then, less gradually than before, decreased to yet a lower amount than previously reached for the same volume of liquid previou sly added. At the end of each injection run, fluid conductance values appeared to have reached a steady state value, but still decreased at a small rate. Table 3 and 4 compares the fluid conductance values for the end of an injection run as close as poss ible to a cumulative linear injected volume of 200 and 100 gallons/foot of HIL respectively The fluid conductance values presented in the tables can be used for the design and operation of a HIL system in a landfill, a design engineer can determine the pr essure required for a desired flowrate or vice versa. 3.3.2 The Effect of Continuous Leachate Injection The HILs were all operated for long periods intermittently. All injection lines show a general decrease in fluid conductance values with increasing c umulative linear injected volume.
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55 An example of this behavior is shown in figure 1; similar results are presented in the Appendix B. Fluid conductance reduces as the injected cumulative volume increases, pressure required in forcing the liquid in to the p ore spaces of the surrounding waste increases. This is a result of pore spaces being filled up. Landfill gas could also occupy the pore spaces and cause a decrease in fluid conductance by resisting the leachate flow There is a resiliency of fluid conducta nce with each injection run that is a function of the length of time between injections (Larson 2007 ). It is expected that each time injection is halted, the liquid within the HIL trench and a portion of the liquid within the pore spaces of the compacted MSW surrounding the HIL drain by gravity to another area within the landfill. This causes the fluid conductance to be slightly higher when the injection is resumed and quickly reduces after the pore spaces are occupied as seen in the figure 1 at the beginn ing of every operation. The liquids can drain through the waste to the bottom liner which is collected by the collection sumps, a portion of the liquid might be caught in impermeable zones creating small perched aquifers within the landfill (Bleiker et al. 1993). Some percentage of the liquid volume is stored in the pore spaces of the compacted waste which helps in the anaerobic decomposition of the MSW which is t he main goal of a bioreactor. 3.3.3 The Effect of HIL Length The flow pressure data was analyze d to study and compare the performance of HILs with different lengths. Branched lines which have many HILs within the landfill connected to a standpipe using a single pipe were considered to be HILs of different length, the lengths of HILs that were connec ted were summed. Box plots were made with the fluid conductance data points for the last injection run close to a cumulative linear injected volume of 200 gallons per foot of HIL. Figures 3 and 4 illustrate the impact of HIL length on fluid conductance Ea ch graph represents HILs of common depth in the landfill during their injection tests. Figure 3 shows that the fluid conductance value is higher for HIL 25 which has a greater length than HIL 2, also it
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56 can be seen that the fluid conductance is almost the same for HILs 2 and 82 which have different lengths HIL 6 5 in figure 3 shows a higher fluid conductance though it has no perforated length. Similar results can be seen with HILs in figure 4 and Appendix B. The results suggest three possibilities for the effect of HIL length. From these results it is difficult to conclude the effect of HIL length. This could be because of the heterogeneity of the surrounding MSW or HILs with a bigger length might have greater possibilities of breaking due to overburden de pth of waste. The fluid conductance values presented in the graphs are for the last run when the linear cumulative injected volume got close to 200 gallons/ft of HIL 3.3.4 The Effect of HIL Bedding Media Figures 5 and 6 show the resulting fluid conductan ce values for injection runs of HILs with different bedding media and with the different depth of overburden waste above. The fluid conductance values presented are when the HILs reached a linear cumulative injected volume of 200 gallons/ft of HIL and 100 gallons/ft of HIL where available The single points shown in the figures were picked when the fluid conductance values reached a steady state (Appendix B) during the operation. The reason for not having many data points for HILs without any media is that they are very poor performers as compared to the HILs with media The majority of the HILs that did not reach the 200 gallons/ft volume are the ones without med ia. It was observed that the HILs with crushed glass and tire chips as bedding media had highe r fluid conductance at shallower depths in the landfill (figures 5 and 6). Crushed glass seemed to have slightly greater fluid conductance value compared to tire chips in some cases. The bedding media crushed glass or tire chips have greater hydraulic cond uctivity than the surrounding waste. HILs using no bedding media could be said to fall into the category of a HIL with a bedding media that has the same hydraulic conductivity as th e surrounding waste (Larson 2007 ). In fact, all of the HILs that were cons tructed with no bedding media but had greater than 15 feet of overburden
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57 of waste above them were not able to receive enough liquid to evaluate because the pressures necessary to inject even the smallest allowable flow rate the SCADA system could achieve w ere above the regulatory limit of 5 psig. Townsend and Miller (1998) used average pressures higher than 10 psig to add liquid to the HILs with no bedding media and had about 30 feet of overburden waste above them. They also found that the fluid conductan ce for HILs with no bedding media was significantly less than those with bedding media. The linear cumulative volumes for the study by Townsend and Miller (1998) were greater than 400 gallons/ft. 3.3. 5 The Effect of O verburden D epth We can see from the fig ures 5 and 6 that the fluid conductance decreases as the overburden depth increases. Townsend and Miller (1998) too found that the HILs that were buried shallow within the landfill had larger fluid conductance values than those that were buried deeper with in the landfill. This phenomenon was explained to be the result of larger effective stresses causing lower hydraulic conductivities of waste deeper within the landfill. The overall trend from the f igure s 5 and 6 show that crushed glass and tire chips medi a has equal and a higher fluid conductance than the no media In general the reason for the decrease in fluid conductance is likely due to the hydraulic conductivity of the waste surrounding the HIL being reduced by either landfill gas accumulation, struct ural changes in the waste from decay, or both. It could also simply be the result of damages in the pipe or clogging due to fines in the waste. 3.4 Conclusions This study examined the effects of different operation and design parameters upon the fluid con ductance of HILs. The effect of HIL length from this study cannot be concluded based on f luid conductance. There was not a big difference found in fluid conductance between tir e chips and crushed glass media; however the fluid conductance value for crushe d glass was slightly higher than the tire chips in some cases The HILs with no bedding media were found to
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58 have significantly less fluid conductance values than those with bedding media. The effect of increasing overburden stress was observed to have a n egative impact upon fluid conductance at lower cumulative injected volumes. This observation was part of the overall effect of fl uid conductance values decreasing with increasing cumulative linear injected volume. This is hypothesized to be caused by cha nges in the hydraulic conductivity of the waste surrounding the HILs by either the presence of landfill gas, the changing structure of the waste from decay, or both. This effect could also be caused by HIL clogging from fines within the waste or from a st ill expanding wetting front of liquid from the HIL. Overall, it was found that liquids addition into a HIL system requires larger pressures as these systems are operated for a longer period. During early operation of these systems, fluid conductance val ues for all types of HILs are greater. However, it is important to remember that the whole experiment here was conducted at a fixed injection pressure of 5 psig. Higher operational pressures for these HILs might help getting more liquids into the landfill.
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59 Table 3 1 Fraction of HILs that reached the 200 gallons/ft for the study Overburden depth (ft) Glass Tires Nothing 20 1/2 1/3 5/5 40 4/8 3/5 0/2 60 1/2 2/9 2/4 80 4/8 4/10 1/3 100 1/2 1/3 0/3 120 1/1 0/0 0/0
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60 Table 3 2 HIL specifications
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61 Ta ble 3 3 Fluid conductance values f or a cumulative linear injected volume of approximately 200 gallons/ft
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62 Table 3 4 Fluid conductance values for similar cumulative linear in jected volume of approximately 1 00 gallons/ft
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63 Figure 3 1. Injection run s for HIL 58 with crushed glass showing the effect of cumulative volume injected on fluid conductance.
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64 Figure 3 2. A typical fluid conductance, pressure and flow rate behavior when an HIL is operated
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65 Figure 3 3. HILs having same overburden depth sh owing the effect of length on fluid conductance.
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66 Figure 3 4. HILs having same overburden depth showing the effect of length on fluid conductance.
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67 Figure 3 5. Fluid conductance values at a cumulative linear injected volume of approximately 200 gallons /ft for HILs with different bedding media at different depths in the landfill
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68 Figure 3 6. Fluid conductance values at a cumulative linear injected volume of approximately 100 gallons/ft for HILs with different bedding media at different depths in the l andfill
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69 CHAPTER 4 SUMMARY, CONCLUSIONS AND RECOMMENDATION S 4.1 Summary An understanding of the in situ pore pressure distribution in a landfill resulting from pressurized liquid addition would be extremely helpful to bioreactor landfill engineers. The po re pressure value within the landfilled waste is a very important input in estimating factors of safety for geotechnical stability. The present study measured the in situ pore pressures with the use of buried pressure transducers. Originally, data from 81 buried pressure transducers were to be used for the study. However, it was discovered that 31 of these instruments had stopped working before the experiment was started. The results were analyzed based upon data collected from the 50 reliable pressure tra nsducers. It was found that the pore pressure values within the landfill due to pressurized injection of liquids ranged from 0 6.5 psi and that the pressure dissipated over a small distance around the horizontal trenches. It was observed that there was l ittle to no impact on pore pressures in the waste surrounding the HIL with no bedding media because of low conductivity of waste media. This range of pore pressure reported was observed for a maximum of 5 psi injection pressure through each horizontal tren ch as per the permit conditions. Pore pressures increased before the injection experiments were started as more lifts of waste was added over the experimental area due to build of landfill gas and pore space compression. Another field study evaluated the effect of different design and operational variables upon the fluid conductance (i.e., flow rate to applied pressure ratio) of HILs at the same landfill. Thirty one HILs were examined and fluid conductance values were determined for similar cumulative li near injected volumes in this study. Results from the study confirmed that the fluid conductance values for HILs decreased with increasing overburden de pth, cumulative volume injected; similar results were observed in a study at a different site by Townsen d and Miller
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70 (1998). Fluid conductance values for HILs with no bedding media were found to be significantly lower than HILs with bedding media at the same depths within the landfill. The effect of HIL length upon fluid conductance was found to be inconclus ive as there were instances where HILs with different lengths had close fluid conductance values for similar cumulative injected volumes; this is presumed to be the result of highly heterogeneous waste. Finally, no consistent difference in fluid conductanc e values for HILs with either tire chips or glass chips was noted. 4.2 Conclusions The conclusions from this research are the following: Pore pressure resulting from pressurized injection of liquids through HILs dissipates over a short distance from the in jection trench. Pressure loss along the trench that has bedding media is very negligible; uniform distribution of pressure is achieved within the first few minutes of operation. Pore pressure inside the trench is affected as soon as the injection is sta rted and stopped, whereas there is a delay in response in the surrounding waste. Pore pressure change due to pressurized leachate injection is similar both in the horizontal and vertical direction of the HIL. Fluid conductance values decrease with incre asing cumulative linear injected volume. Fluid conductance values decrease with increasing overburden depth of waste. Both tire chips and crushed glass as HIL bedding media perform similarly in terms of fluid conductance. HILs without bedding media have significantly lower fluid conductance values compared to ones with bedding media. 4.3 Recommendations The spatial variation of pore pressure due to pressurized injection was studied in the horizontal direction from the HILs; the pore pressure change in the vertical direction from the
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71 HIL would be very useful to fully understand the impact of pressurized liquid addition. Pressure transducers installed at different depths within the landfill will help in understanding the spatial variation around the HIL w ith different overburden depth of waste. The Phase 2 landfill contains a few HILs buried above the pressure transducer experimental area that can be operated with the objective of studying the pore pressure change in the vertical direction. Computer genera ted modeling techniques can be used to estimate the pore pressures around the HILs and can be compared with the in situ measured values. Future studies evaluating the performance of HILs buried in the landfill should be carried out for higher injection pre ssures.
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72 APPENDIX A SUPPLEMENTAL FIGURES FOR CHAPTER 2 This appendix presents graphs of the data collected from all the pressure transducers present in the landfill that were used to analyze data. The results cover a period from July 2007 to June 2008.
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73 Figure A 1 Response from the p ressure t ransducers in the t rench of HIL A with t ire c hips as b edding m edia. Figur e A 2. Response over time from the pressure t ransducers after the injection was stopped
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74 Figure A 3 Response from the p ressure transduce rs on right of HIL A with tire chips as m edia. Figure A 4 Response over time from the pressure t ransducers after the injection was stopped
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75 Figure A 5 Response from the p ressure transducers 3 ft below on right of HIL A with tire chips Figure A 6 Response over time from the pressure t ransducers after the injection was stopped
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76 Figure A 7 Response from the p ressure transducers on left of HIL A with tire chips as bedding media. Figure A 8 Response over time from the pressure t ransducers after the injection was stopped
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77 Figure A 9. Response from the p ressure transducers on right of HIL A with tire chips as bedding media. Figure A 10. Response over time from the pressure t ransducers after the injection was stopped
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78 Figure A 11. Response f rom the p ressure transducers in the trench of HIL B with no bedding media. Figure A 12. Response over time from the pressure t ransducers after the injection was stopped
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79 Figure A 13. Response from the p ressure transducers buried at different depths und er HIL C with no bedding media. Figure A 14. Response over time from the pressure t ransducers after the injection was stopped
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80 Figure A 15. Response from the p ressure transducers on left of HIL B with no bedding media. Figure A 16. Response from the p ressure transducers on the right of HIL B with no bedding media.
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81 Figure A 17. Response from the p ressure transducers in the trench of HIL C with crushed glass as bedding media. Figure A 18. Response over time from the pressure t ransducers after the injection was stopped
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82 Figure A 19. Response from the p ressure transducers on the left of HIL C with crushed glass as bedding media. Figure A 20. Response over time from the pressure t ransducers after the injection was stopped
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83 Figure A 21. Response of p ressure transducers 3 ft away on the left of HIL C with crushed glass as bedding media. Figure A 22. Response over time from the pressure t ransducers after the injection was stopped
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84 APPENDIX B SUPPLEMENTAL FIGURES AND TABLES FOR CHAPT ER 3 This app endix presents tables and graphs of the data collected from the 31 horizontal injection lines in the Phase 2 landfill that were evaluated in the research experiment described in this thesis. The results cover a period from January 2006 to August 2008.
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85 Tab le B 1 HILs evaluated by Larson (2007 ).
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86 Table B 2 HILs evaluated during the current research study
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87 Figure B 1 Location of the Polk North Central Landfill Facility
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88 Figure B 2 NCLF facility aerial view
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89 Figure B 3 Schematic view of the phase 2 leachate pumping setup.
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90 Figure B 4 HILs connected to standpipes.
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91 Figure B 5. Flow pressure variation with linear cumulative volume injected through HIL 2 (Media = Tire chips; Length = 440 ft; Overburden depth = 86 ft) Figure B 6. Fluid conductance variation with linear cumulative volume injected through HIL 2
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92 Figure B 7. Flow pressure variation with linear cumulative volume injected through HIL 8 (Media = No media; Length = 200 ft; Overburden depth = 65 ft) Figure B 8. Fluid conductance variation with linear cumulative volume injected through HIL 8
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93 Figure B 9. Flow pressure variation with linear cumulative volume injected through HIL 25 (Media = Tire chips; Length = 720 ft; Overburden depth = 80 ft) Figure B 10. F luid conductance variation with linear cumulative volume injected through HIL 25
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94 Figure B 11. Flow pressure variation with linear cumulative volume injected through HIL 27. (Media = Crushed glass; Length = 720 ft; Overburden depth = 80 ft) Figure B 12 Fluid conductance variation with linear cumulat ive volume injected through HIL 27.
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95 Figure B 13. Flow pressure variation with linear cumulative volume injected through HIL 30 (Media = Crushed glass; Length = 720 ft; Overburden depth = 121 ft) Figure B 14. Fluid conductance variation with linear cumulative volume injected through HIL 30
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96 Figure B 15. Flow pressure variation with linear cumulative volume injected through HIL 42 (Media = Crushed glass; Length = 300 ft; Overburden depth = 75 ft) F igure B 16. Fluid conductance variation with linear cumulative volume injected through HIL 42
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97 Figure B 17. Flow pressure variation with linear cumulative volume injected through HIL 45 (Media = Tire chips; Length = 300 ft; Overburden depth = 100 ft) Figure B 18. Fluid conductance variation with linear cumulative volume injected through HIL 45
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98 Figure B 19. Flow pressure variation with linear cumulative volume injected through HIL 46 (Media = Crushed glass; Length = 400 ft; Overburden depth = 101 ft) Figure B 20. Fluid conductance variation with linear cumulative volume injected through HIL 46
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99 Figure B 21. Flow pressure variation with linear cumulative volume injected through HIL 58 (Media = Crushed glass; Length = 200 ft; Overburden depth = 35 ft) Figure B 22. Fluid conductance variation with linear cumulative volume injected through HIL 58
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100 F igure B 23. Flow pressure variation with linear cumulative volume injected through HIL 5 9. (Media = No media; Length = 480 ft; Overburden depth = 75 ft) Figure B 24. Fluid conductance variation with linear cumulative volume injected through HIL 59.
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101 Figure B 25. Flow pressure variation with linear cumulative volume injected through HIL 61 (Media = Tire chips; Length = 520 ft; Overburden depth = 60 ft) Figure B 26. Fluid conductance variation with linear cumulative volume injected through HIL 61
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102 F igure B 27. Flow pressure variation with linear cumulative volume injected through HIL 62 (Media = Tire chips; Length = 200 ft; Overburden depth = 55 ft) Figure B 28. Fluid conductance variation with linear cumulative volume injected through HIL 62
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103 Figure B 29. Flow pressure variation with linear cumulative volume injected through HIL 63 (Media = Crushed glass; Length = 520 ft; Overburden dep th = 61 ft) Figure B 30. Fluid conductance variation with linear cumulative volume injected through HIL 63
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104 Figure B 31. Flow pressure variation with linear cumulative volume injected through HIL 65 (Media = Crushed glass; Length = 0 ft; Overburden d epth = 72 ft) Figure B 32. Fluid conductance variation with linear cumulative volume injected through HIL 65
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105 Figure B 33. Flow pressure variation with linear cumulative volume injected through HIL 66 (Media = Tire chips; Length = 1560 ft; Overburden depth = 53 ft) Figure B 34. Fluid conductance variation with linear cumulative volume injected through HIL 66
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106 Figure B 35 Flow pressure variation with linear cumulative volume injected through HIL 69. (Media = Crushed glass; Length = 200 ft; Overbur den depth = 35 ft) Figure B 36 Fluid conductance variation with linear cumulati ve volume injected through HIL 6 9.
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107 Figure B 37 Flow pressure variation with linear cumulative volume injected through HIL 72. (Media = Tire chips; Length = 520 ft; Overburd en depth = 35 ft) Figure B 38 Fluid conductance variation with linear cumulative volume injected through HIL 72.
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108 Figure B 39. Flow pressure variation with linear cumulative volume injected through HIL 73. (Media = Tire chips; Length = 200 ft; Overburde n depth = 35 ft) Figure B 40. Fluid conductance variation with linear cumulative volume injected through HIL 73.
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109 Figure B 41. Flow pressure variation with linear cumulative volume injected through HIL 80. (Media = Crushed glass; Length = 200 ft; Overb urden depth = 15 ft) Figure B 42. Fluid conductance variation with linear cumulative volume injected through HIL 80.
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110 Figure B 43. Flow pressure variation with linear cumulative volume injected through HIL 81 (Media = No media; Length = 360 ft; Overbu rden depth = 15 ft) Figure B 44. Fluid conductance variation with linear cumulative volume injected through HIL 81.
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111 Figure B 45. Flow pressure variation with linear cumulative volume injected through HIL 8 2 (Media = Tire chips; Length = 360 ft; Overb urden depth = 78 ft) Figure B 46. Fluid conductance variation with linear cumulative volume injected through HIL 82
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112 Figure B 47. Flow pressure variation with linear cumulative volume injected through HIL 8 4 (Media = Crushed glass; Length = 360 ft; O verburden depth = 84 ft) Figure B 48. Fluid conductance variation with linear cumulative volume injected through HIL 8 4
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113 Figure B 49. Flow pressure variation with linear cumulative volume injected through HIL 86. (Media = Tire chips; Length = 360 ft; Overburden depth = 15 ft) Figure B 50. Fluid conductance variation with linear cumulative volume injected through HIL 86.
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114 Figure B 51. Flow pressure variation with linear cumulative volume injected through HIL 87. (Media = No media; Length = 360 ft; Ov erburden depth = 15 ft) Figure B 52. Fluid conductance variation with linear cumulative volume injected through HIL 87.
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115 Figure B 53. Flow pressure variation with linear cumulative volume injected through HIL 88. (Media = No media; Length = 360 ft; Ove rburden depth = 15 ft) Figure B 54. Fluid conductance variation with linear cumulative volume injected through HIL 88.
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116 Fi gure B 55. Flow pressure variation with linear cumulative volume injected through HIL 89. (Media = No media; Length = 360 ft; Over burden depth = 15 ft) Figure B 56. Fluid conductance variation with linear cumulative volume injected through HIL 89.
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117 Figure B 57. Flow pressure variation with linear cumulative volume injected through HIL 90. (Media = Crushed glass; Length = 360 ft; O verburden depth = 35 ft) Figure B 58. Fluid conductance variation with linear cumulative volume injected through HIL 90.
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118 Figure B 59. Flow pressure variation with linear cumulative volume injected through HIL 91 (Media = No media; Length = 360 ft; Ove rburden depth = 15 ft) Figure B 60. Fluid conductance variation with linear cumulative volume injected through HIL 91
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119 Figure B 61. Flow pressure variation with linear cumulative volume injected through HIL 101 (Media = Crushed glass; Length = 1080 f t; Overburden depth = 41 ft) Figure B 62. Fluid conductance variation with linear cumulative volume injected through HIL 101
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120 Figure B 63. Flow pressure variation with linear cumulative volume injected through HIL 109 (Media = No media; Length = 1080 ft; Overburden depth = 53 ft) Figure B 64. Fluid conductance variation with linear cumulative volume injected through HIL 10 9.
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121 Figure B 65. Flow pressure variation with linear cumulative volume injected through HIL 112 (Media = Tire chips; Length = 1080 ft; Overburden depth = 48 ft) Figure B 66. Fluid conductance variation with linear cumulative volume injected through HIL 112
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122 Figure B 67. Fluid conductance of HILs with different bedding media. Figure B 68. Fluid conductance of HILs with dif ferent bedding media.
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123 Figure B 69. Fluid conductance of HILs with different bedding media. Figure B 70. Fluid conductance of HILs with different bedding media.
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124 Figure B 71. Fluid conductance of HILs with different bedding media. Figure B 72. Flu id conductance of HILs with different bedding media.
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125
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127 APPENDIX C SUPPLEMENTAL DATA FOR CHAPTER 2 This appendix presents graphs of the data collected from all the pressure transducers present in the landfill that were used to analyze data. The results c over a period from July 2007 to June 2008.
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128 Equations to convert the raw data collected from the transducers to pressure data The frequency data from the vibrating wire transducers were converted to pressure data by using the factory supplied calibration c onstants and equations. The equations are the following: (C 1) (C 2) Where Hz is the vibrating frequency measurement (Hertz), A, B, and C are the factory supplied polynomial gauge factors (pressure/ digits 2 pressure/digit, pressure respectively); R o is the reading taken at the time of installation (digits), R measured is the measured vibrating wire measured is the measured temp o o is the barometric pressure recorded at installation (pressure). To correct for thermal effects to the material of the vibrating wire of each instrument, they are all equipped with t hermistors with a range of Barometric pressure was eliminated from the equation C 2 and the gauge pressure was presented in the results for the thesis as the change in barometric pressure seemed to have no effect on the pore pressures duri ng the experimental period.
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129 Table C 1 Initial readings and calibration constants for the pressure transducers
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130 Table C 2 Continuation of Table C 1
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131 Determination of elevation head for HIL operation During the operation of the HILs studied in this t hesis, the injection pressure was not to exceed 5 psi according to the site permit. Injection pressure (P) was determined by the equation 1 P 2 As shown in the figure C 1, pumping pressure (P 1 ) was recorded by the gage at the foot of the landfill and elevation head (P 2 ) was initially obtained from the elevation survey data for each HIL. Later, In order to account for settlement of the HIL after waste placement, flow pressure data for the first day operation (figure C 2) that was recorded on SCADA was used to determine the elevation head of the HILs. The point at which the pressure starts becoming constant (figure C 2) after the first few minutes of HIL operation is considered as the elevation of the HIL. Figure C 1. Schematic diagram of the HIL in the landfill with elevation, injection and pumping pressure representation
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132 Figure C 2. Flow pressure response for a HIL operation Figure C 3. Timeline for the studies at the phase 2 bioreactor landfill Elevation head P 2
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133 LIST OF REFERENCES Barber, C., and Mar is, P. J. (1984). Recirculation of leachate as a landfill management option: Benefits and operational problems. Quarterly Journal of Engineering Geology 17, 19 29. DeWalle, F. B., E. S. K. Chian, and E. Hammerberg (1978). Gas production from solid waste in landfill. Journal of the Environmental Engineering Division, ASCE 104, 415. Doran, F. (1999). Lay leachate lay Waste Age; Apr 1999; 30, 4; ABI/INFORM Global pg. 74 Eliassen, R. (1942). Decomposition of Landfills. American Journal of Public Health 32 1029. Haydar, M and Khire, M. (2004). Evaluation of heterogeneity and anisotropy of waste properties on leachate recirculation in bioreactor landfills. Journal of Solid Waste Technology and Management 30(4), 233 242. Haydar, M., and Khire, M. (2005). Leachate recirculation using horizontal trenches in bioreactor landfills. Journal of Geotechnical and Geoenvironmental Engineering ASCE, 131(7), 837 847. Geokon, Inc. (Doc Rev S 4/07). Model 4500 VW Piezometer Instruction Manual. Jain, P. (2005). Moi sture Addition at Bioreactor Landfills Using Vertical Wells: Mathematical Modeling and Field Application Ph.D. Dissertation, University of Florida, Gainesville, FL, USA. Jain, P., Powell, J. T., Townsend, T. G., and Reinhart, E. R. (2005). Air permeabil ity of waste in a municipal solid waste landfill. Journal of Environmental Engineering ASCE, 131(11), 1565 1573. Jain, P., Powell, J. T., Townsend, T. G., and Reinhart, E. R. (2006). Estimating the hydraulic conductivity of landfilled muncipal solid was te using the borehole permeameter test. Journal of Environmental Engineering ASCE, 132(6), 645 652. introduction at bioreactor landfill: Guidelines based on mathe to Journal of Environmental Engineering ASCE. Koerner, R. M., and Soong, T. Geotext. Geomembrane 18_5_, 293 309. Larson, J. A. (2007). I nvestigations at a Bioreactor La ndfill to Aid in the Operation and Design Gainesville, FL, USA. Leckie, J.D., Pacey, J.G. and Halvadakis C.P. (1979). Landfill management with moisture control. Jour nal of Environmental Engineeri ng Division ASCE EE2, 105, 337 355.
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134 Lin, J., and Hildemann, L. (1995). A nonsteady state analytical model to predict gaseous emissions of volatile organic compounds from landfills. Journal of Hazardous Material 40, 271 295 McCreanor P. T. (1994). Hydrodynamic modeling of Leachate Recirculation Thesis, University of Central Florida, Orlando, FL, USA. McCreanor, P. T. (1998). Landfill leachate recirculation systems: mathematical modeling and validation. Ph.D. Dissertation University of Central Florida, Orlando, FL, USA. McCreanor, P. T., and Reinhart, D. R (1996). Hydrodynamic modeling of leachate recirculating landfills. Water Science and Technology 34(7 8), 463 470. McCreanor, P. T., and Reinhart, D. R. (2000). Ma thematical modeling of leachate routing in a leachate recirculating landfill. Water Research 34(4), 1285 1295. Mehta, R., Barlaz, M. A., Yazdani, R., Augenstein, D., Bryars, M., and Sinderson, L. (2002). Refuse decomposition in the presence and absence of leachate recirculation. Journal of Environmental Engineering ASCE, 128(3), 228 236. Pohland, F.G. (1975). Sanitary landfill stablization with leachate recycle and residual treatment. EPA 600/2 75 043. USEPA, Washington DC, USA. Pohland, Fredrick (1980 ). Leachate recycle as landfill management option. Journal of Environmental Engineering ASCE, 106 (EE6), 1057 1069. Rees, J. F. (1980). Optimisation of methane production and refuse decomposition in landfills by temperature control. Journal of Chemica l Technology and Biotechnology 30, 458. Reinhart, D. R., and Townsend, T. G. (1997). Landfill Bioreactor Design and Operation Boca Raton, FL: Lewis Publishers. R.W. Beck. (2004, April). Final Report: Composition of Municipal Solid Waste Disposal in P olk County, Florida Winter Haven, FL. Sellers, B. (2005). Truth about accuracy. Geotechnical News 23 (2). Townsend, T. G., (1995). Leachate recycle at solid waste landfills using horizontal injection. Ph.D. Dissertation, University of Florida, Gain esville, FL, USA. Townsend, T. G., Miller W. L., and Earle, J. F. K (1995). Leachate recycle infiltration ponds. Journal of Environmental Engineering ASCE, 121(6), 465 471. Townsend, T. G., Miller, W. L, Lee, H. J., and Earle, J. F. K (1996). Accelera tion of landfill stabilization using leachate recycle. Journal of Environmental Engineering ASCE, 122(4), 263 268.
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135 Townsend, T. G. and Miller W. L. (1998). Leachate recycle using horizontal injection. Advances of Environmental Research 2(2) 1995, 129 138. Townsend, T. G., Wise, W. R., and Jain, P. (2005). One dimensional gas flow model for horizontal gas collection systems at municipal solid waste landfills. Journal of Environmental Engineering ASCE, 131(12), 1716 1723. Watson, R.P. (1987). "A case study of leachate generation and recycling at two sanitary landfills" in Proceedings from the Technical Sessions of the GRCDA 25th Annual International Seminar, Equipment, Services, and Systems Show. Vol. 1, August 11 13, Saint Paul, MN. Warith, M. (2002 ). Bioreactor Landfills: experimental and field results. Waste Management 22 (2002), 7 17. Warith, M.A., Evgin, E., Benson, P. A. S (2004). S uitability of shredded tires for use in landfill leachate collection systems Waste Management 24 (2004), 967 979.
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136 BIOGRAPHICAL SKETCH Sendhil Kumar was born in 1982, to B. Sampath Kumar and S. Bhagya Lakshmi in Bangalore, India. He studied mathematics, physics and chemistry as his major subjects and graduated from pre university college in 2001. He attended the R ashtreeya V idyalaya College of Engineering (R. V. C. E) Bangalore, India where he earned his Bachelor of Engineering degree in Chemical engineering in 2005. In August 2006, he enrolled in graduate school in the Environmental Engineering Sciences Departm ent at the University of Florida, to study solid and hazardous waste management under the advisement of Dr. Timothy Townsend.
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