EPA/600/R-07/060 September 2006



# Landfill Bioreactor Performance
Second Interim Report Outer Loop Recycling & Disposal Facility Louisville, Kentucky

National Risk Management Research Laboratory Office of Rese arch and Development U.S . Environmental Protection Agency Cin cinnati, Ohio 45268ii

## Notice

The U.S. Environmental Protection Agency through its Office of Research and Development partially funded and collaborated in the research activities described herein under Cooperative Research and Development Agreement Number 0 189-00 with Waste Management In c. and under contract number EP06C000146 with GeoSyntec Consultants. This report has been subject to both internal and external Agency review and has been approved for publication as an U.S. EPA document.



### iiiiv

## Acknowledgments

The report presented herein is collaborative in nature. Considerable effort has been devoted to the Outer Loop Landfill Bioreactor project. Over the past five years, the following individuals and organizations have assisted in the design, construction, operation, and data collection and analysis aspects of the project:

U.S. EPA Thabet Tolaymat Ph.D. Fra n Kremer Ph.D. Davi d Carson W endy Davis-Hoover Ph.D.

Was te Management Gary Hater Roger Green John Barbush Chad Abel Rick Barr Kevin Meiczkowski Greg Cekander, PE Chuck Williams, PE
GeoSyntec Consultants Jon Powell Mazen Haydar Ph.D. Robert Bachus Ph.D., PE Michael Houlihan, PE Jeremy Morris Ph.D., PE

Alternative Natu ral Technologies C. Douglas Goldsmith Ph.D.
North Carolina State University Morton Barlaz Ph.D., PE
Neptune Inc. Paul Black Ph.D. Doug Bronson Ph.D. David Gratson Ph.D.
University of Cincinnati Robert Grosser Ph.D. David Feldhake Brian Morris

vvi

## Foreword

The U.S. Environmental Protection Agency (U.S. EPA) is charged by Congress with protecting the Nation’s land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural systems to support and nurture life. To meet this manda te, U.S. EPA’s research program is providing data and technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecol ogical resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future. The National Risk Management Research Laboratory (N RMRL) is the Agency’s center for investigation of technological and management approaches for preventing and reducing risks from pollution that threaten human health and the environment. The focus of the Laboratory’s re search program is on methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that reduce the cost of compliance and to anticipate emerging problems. NR MRL’s research provides solutions to environmental problems by: developing and promoting technologies that protect and improve the environment; advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical support and information transfer to ensure implementation of environmental regulations and strategies at the national, state, and community levels. This publication has been produced as part of the Laboratory’s strategic long-term research plan. It is published and made available by U.S. EPA’s Office of Research and Development to assist the user community and to link researchers with their clients. Sally Gutierrez, Director National Risk Management Research Laboratory

viiviii

## Executive Summary

A bioreactor landfill is a landfill that is operated in a ma nner that is expected to increase the rate and extent of waste decomposition, gas generation, and settlement compared to a traditional landfill. This Second Interim Report was prepared to provide an interpretatio n of field data collected as part of a multi-year Cooperative Research and Development Agreement ( CRADA) between the U.S. Environmental Protection Agency (U.S. EPA) and Waste Management, Inc. (W M). The CRADA was established to evaluate the performance of landfill bioreactor units at the WM Ou ter Loop Landfill, located in Louisville, Kentucky. This report follows the September 2003 U.S. EPA document Landfills as Bioreactors: Research at the Outer Loop Landfill, Louisville, Ke ntucky, First Interim Report (i.e., the First Interim Report, EPA/600/R03/097), which presented a complete description of th e landfill study sites and the data collection procedures. The Outer Loop Landfill Bioreactor (OLLB) project considers solid waste decomposition, moisture balance, landfill gas generation, and leachate quality to evaluate the effect of bioreactor operations on municipal solid waste (MSW) decomposition. Three ty pes of landfill cells were evaluated in the OLLB study: (i) a Control cell, in which no liquids were adde d; (ii) a cell in which liquids were added after the cell had been completely filled with waste (i.e., the Retrofit cell); and (iii) a cell in which liquids and air were added as the waste was placed in the landfill (i .e., the As-Built cell). The monitoring data were sequentially evaluated to identify trends in solid wa ste decomposition, moisture retention, landfill gas quality and quantity, and leachate quality. One must recognize the limitation of data presented in this report in establishing long-term tre nds in the operation of bioreactor land fills. Below is a brief description of data evaluation presented in this report. Operations

• The results of the moisture balance calculations indicate an increase in moisture content of six to seven percent in the As-Built cells, an increase of approxima tely one percent in the Retrofit cells and a slight decrease in the Control cells during the study period;

• Data regarding leachate head in the sump , which was used as an indirect indicator of leachate head on the liner, indicated that operating a landfill as a bioreact or caused an overall increase in leachate head in the sump compared to the Control cells. Howeve r, in all cases, the average leachate level on the liner was well below the required 0.3 m (1 ft);

• To date, there is no indication that the bottom liner system of the test cells was compromised while installing liquid application features, or while applying liquid through those features;

• Although leachate breakouts occurred intermittently in the bioreactor landfill cells, no significant leachate breakout occurred that would result in any surface-water quality impacts;

• The lack of significant leachate breakouts (breakouts resulting in surface water quality impact) and the lack of landfill gas emission problems (methane surface emissions were detected, however at concentrations less than 500 ppm) suggest that, to date, the Oute r Loop Bioreactor Landfill has been operated in a manner that will minimize problems related to excessive pressures in the cells;

• There were indications of “watering-out” of gas collection wells and trenches which was addressed by using submersible pumps to pump out the free standing liquid;

• During the period of the study, there was an incr ease in landfill gas collected from the bioreactor areas. Therefore, it is not possible to conclusively know what affects the watering-out of the collection features have on the gas collection efficiency;

• During the period of the study, there were no sign s that “watering-out” of the gas collection wells posed a geotechnical instability problem at the site;

• There was no indication of clogging in the leachate collection system during the study period; and

ix• Overall, the bioreactor landfill cells generally met the criteria of Sub title D of the Resource Conservation and Recovery Act for design and op eration of MSW landfills. Data, from this site, suggest that other well-designed and well-operated bioreactor landfills can also be operated in compliance with the requirements of Subtitle D. Solids Decomposition

• The solids composition data support conclusions reached by previous research that the operation of an MSW landfill as a bioreactor results in accelerated solids decomposition. All solid waste monitoring parameters showed accelerated waste decomposition in one of the As-Built bioreactor landfill cells relative to the Control cells. However, results were as not as conclusive for the second As-Built bioreactor landfill cell. The relatively young age of the solid waste made definitive decay rate estimates difficult.
Landfill Gas

• Results indicate that, although it is variable, the rate of landfill gas generation in the As-Built bioreactor landfill cells was greater than that of the Control cells, poten tially providing a greater rate of energy production if collection occurred early and consistently;

• The landfill gas decay constant for As-Built bior eactor landfill cells was evaluated to be 0.16 yr -1 while the Retrofit cells and the Control cells had a k value of approximately 0.061 yr -1 ; and

• Although the concentration (ppmv) of non methane organic carbon (NMOC) in the collected landfill gas did not appear to be higher in the landfill bioreact or cells compared to the Control cells, the overall production was higher because of the higher gas flow rate. Leachate Quality

• The leachate quality test results were generally well correlated to the age of the waste for each cell for the study period. However, no strong correla tions were found between leachate quality and accelerated waste decomposition in the bioreactor land fill cells, as the bottom, most degraded part of the solid waste mass has the larges t impact on the leachate quality;

• Evaluation of the biochemical oxygen demand to chemical oxygen demand ratio (which is generally a strong indicator of organic solids decomposition) revealed that waste decomposition in the As-Built bioreactor landfill cells may have been acceler ated compared to the Control cells; and

• Liquids that were added to the Retrofit cells were pre-treated to decrease ammonia concentrations. This was effective since leachate quality test results from this study showed a decrease in ammonia concentration during the study period in the Retrofit bioreactor landfill cells. Overall, the analysis of the data collected during the first five years indicate that the addition of liquids increased the moisture content of waste in the landf ill bioreactor cells and accelerat ed waste degradation. Leachate quality and solid waste decomposition data indi cate that waste degradation was enhanced in the As-Built landfill bioreactor cells. Landfill gas quantity data indicate that the decay rate was highest in the As-Built cells and lowest in the Control cells as expected.
Future Activities
To substantiate the effectiveness of landfill bioreactors, research is focused in the following areas:

• Evaluate and adjust sampling frequency of the various monitoring/operational parameters;

• Examine NMOC emissions through various landfill covers;

• Evaluate alternative approaches to assess an d engineer controls for fugitive emissions;

• Determine shear strength as a function of age of the wastes and assessment of landfill stability;

• Identify the effectiveness of landfill bioreactors in enhancing carbon sequestration; and

• Identify the effectiveness of bioreactors in treating/co ntaining nanoparticles.

xIt is anticipated that the data collected throughout the remainder of the CRADA test period will further support the conclusions reached in this report and a llow better definition of the correlations described. Finally, it is concluded that, if the trends illustrated in th is report for all of the monitored media (i.e., solids, liquids, and gases) are confirmed at the end of the CRADA test period, then there will be a significant increase in our understanding of bioreactors and in creased potential to predict their performance.

xixii

## Table of Contents

Notice

......................................................................................................................... ................................... iii
Acknowledgments

................................................................................................................ .......................... v

Foreword

....................................................................................................................... ............................... vii
Executive Summary

.............................................................................................................. ......................... ix

Table of Contents

.............................................................................................................. .......................... xiii
List of Figures

................................................................................................................ .............................. xv

List of Tables

................................................................................................................. .............................. xix
List of Acronyms............................................................................................................... .......................... xxi
Chapter 1. In troduc tion

........................................................................................................ ........................... 1 1.1 Landfill Bioreact or Technology

................................................................................................. ..... 1 1.2 Outer Loop Land fill Bioreactor

................................................................................................. ...... 1 1.3 Project Ob jectives

............................................................................................................. ............... 1 1.4 Report Orga nization

............................................................................................................ ............ 2
Chapter 2. Overview of Bioreactor Landfills

.................................................................................... ............. 3 2.1 Introduction to Land fill Biore actors

........................................................................................... ..... 3 2.2 Regulatory Overview

....................................................................................................................... 4 2.3 Anaerobic Decompositi on Fundamentals

........................................................................................ 5 2.3.1 Phase I (Initial Adjustment)

................................................................................................... .... 6 2.3.2 Phase II (Transition)

.................................................................................................................. 6 2.3.3 Phase III (Aci d Forma tion)

........................................................................................................ 6 2.3.4 Phase IV (Methane Fermentation)

............................................................................................. 7 2.3.5 Phase V (Final Maturatio n and Stabilization)

............................................................................ 7 2.4 Key Monitoring Parameters fo r MSW Landfill Bioreactors

........................................................... 7 2.4.1 Physical Monitori ng Parameters

................................................................................................ 8 2.4.2 Analytical Monitori ng Parameters

........................................................................................... 10
Chapter 3. Site Descriptio n and Analyti cal Methods

............................................................................. ...... 19 3.1 Site Description an d System Design

............................................................................................. . 19 3. 1.1 Control Landfill Ce lls

......................................................................................................... ..... 19 3.1.2 As-Built Landfill Bi oreactor Cells

........................................................................................... 21 3.1.3 Retrofit Landfill Bi oreactor Cells

............................................................................................ 2 5 3. 2 Sample Procedures and Methods

.................................................................................................. . 29 3. 2.1 Leachate Sa mpling

.............................................................................................................. .... 29 3.2.2 Municipal Solid Wa ste Sampling

............................................................................................ 30 3.2.4 Landfill Se ttleme nt

............................................................................................................ ...... 34 3.2.5 Landfill Gas Samplin g

.......................................................................................................... ... 34 3.3 Data Processing and Statistical Analysis

....................................................................................... 36 3.3.1 Sample Dating and Sta tistical An alysis

................................................................................... 36 3.3.2 Moisture Balance Calculations

................................................................................................ 37 3.3.3 Statistical Analysis of Leachate Parameters

.............................................................................. . 38

x iiiChapter 4. Solid Waste and Moisture Cont ent Analysis

........................................................................... ... 39 4.1 Solid Waste Analys is

........................................................................................................... .......... 39 4.1.1 Results

........................................................................................................................ ............. 39 4.1.2 Multiple Linear Regr ession Models

........................................................................................ 47 4.1.3 Summary of Solids Decomposition

......................................................................................... 48 4.1.4 Solid Waste Surf ace Settleme nt

............................................................................................... 54 4.1.5 Landfill Temperature and Oxidati on Reduction Pote ntial (O RP)

............................................ 54 4.1.6 Solid Waste Sl ope Stability

.................................................................................................... . 54 4. 2 Moisture Additio n

.............................................................................................................. ............ 55 4.2.1 Moisture Balance

............................................................................................................... ...... 55 4.2.2 Leachate Head on Liner

......................................................................................................... .. 59 4.2.3 Measured Waste Mois ture Content

.......................................................................................... 65 4.2.4 Evaluation of Calculated and M easured Moisture Content

..................................................... 66 4.2.5 Moisture Content An alysis Summary

...................................................................................... 69
Chapter 5. Land fill Gas (LFG)

.................................................................................................. ................... 71 5.1 Landfill Gas (LFG ) Composition

................................................................................................. . 71 5. 1.1 Control cells

.................................................................................................................. ........... 71 5.1.2 As-Built cells

................................................................................................................. .......... 71 5.1.3 Retrofit Cells

................................................................................................................. .......... 74 5.1.4 Landfill Gas (LFG) Com position Summary

............................................................................ 75 5.2 Measured Methane Production an d LandGEM Model Predictions

............................................... 77 5.3 Comparison of Field Gas Results of Control and Landfill Bioreactor Cells

................................. 83 5.3.1 Summary of LFG Generation

................................................................................................ ......... 86 5.4 None Met hane Organic Carbon (NMO C) Concentrations in LFG

................................................ 87 Where:

......................................................................................................................... ........................ 91 5.5 Methane Surfa ce Emissions

...................................................................................................... ..... 93
Chapter 6. Leac hate Qu ality

.................................................................................................... ..................... 95 6.1 Temperature

.................................................................................................................... ............... 95 6.2 pH

.................................................................................................................................................. 97 6.3 Volatile Organic Acids (VOAs)

.................................................................................................. .. 99 6.4 Total Organic Ca rbon (TOC)

..................................................................................................... .. 101 6.5 Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)

.......................... 103 6.6 Nitrogen Content

............................................................................................................... .......... 108 6.7 Meta ls

.......................................................................................................................................... 112 6.8 Volatile and Semi-Volatile Organic Compounds

........................................................................ 113 6.9 Phosphorous Content

............................................................................................................ ....... 115 6.10 Chloride

....................................................................................................................... ................ 118 6.11 Leachate Qual ity Summary

....................................................................................................... .. 119
Chapter 7. Landfill Bioreact or Performan ce Anal ysis

............................................................................ .... 123 7.1 Slope St ability

................................................................................................................ ............. 123 7.2 Liner and Final Cover Integrity

................................................................................................ ... 123 7.3 Liquids Addition System Performance

........................................................................................ 124 7.4 Leachate Collection Syst em Performance

................................................................................... 124 7.5 Landfill Gas Productio n and Emi ssion

........................................................................................ 125
Chapter 8. Conclusion s and Recommendations

..................................................................................... .... 127 8.1 Conclusions

.................................................................................................................... ............. 127 8.2 Recommendations

................................................................................................................ ....... 130 8.3 Landfill Bioreactor Monitoring Para meters

................................................................................. 131
Chapter 9. References

.......................................................................................................... ....................... 133

xiv

## List of Figures

Figure 2-1 Phases of Solid Waste Decom position (source: Pohl and et al . 1993)

......................................... 6
Figure 2-2 Changes in VFA in a Si ngle Pass (Conventional) Reactor versus Bioreactor9 and Bioreactor21

o ver Time (Source: Sponza and A ğ da ğ , 2004)

........................................................ 13
Figure 3-1 Outer Loop Landfill S ite Map

........................................................................................ ........... 20
Figure 3-2 Solid Waste Placement in the As-Built Landfill Bioreactor Cells

............................................ 22
Figure 3-3 Solid Waste Placement in As-Built Landfill Bi oreactor Cells

.................................................. 22
Figure 3-4 Cumulative Industrial and To tal Added Liquids in As-Built Cell A

........................................ 24
Figure 3-6 Solid Waste Placement in the Retrofit Landfill Bioreactor Cells

............................................. 26
Figure 3-7 Bottom Liner Config uration of the Retrofit Unit

..................................................................... . 27
Figure 3-8 Cross-Sectional Layout of Liquid Intro duction Trench

............................................................ 28
Figure 3-9 Cumulative Liquid In troduction into Retrofit Bioreact or Landfill Unit by Subcell

.................. 28
Figure 3-10 Liquid Intro duction and Gas Collection System in Retrofit Landfill Bioreactor Cells

........... 30
Figure 4-1 Summary of Waste Age for Retrofit Cells A (5.1 ) and B (5.2)

................................................ 40
Figure 4-2 Relationship between CH:L an d Waste Age in the Retrofit Ce lls

............................................ 42
Figure 4-3 Relationship between Moisture Content and Solids Decomposition in the Retrofit Cells

........ 43
Figure 4-4 Waste Age Profile for the Contro l Cell A (7.3A) and C ontrol Cell B (7.3B)

........................... 43
Figure 4-5 Moisture Content Profile for th e Control cells at E ach Sampling Time

................................... 44
Figure 4-6 Relationship between Moisture Content and Solids Decomposition in the Control Cells

........ 44
Figure 4-7 Waste Age Profile for As-Built Ce lls A and B

........................................................................ . 46
Figure 4-8 Relationship between Moisture Content and Solids Decomposition in As-Built Cell A

.......... 47
Figure 4-9 Relationship between Moisture Content and Solids Decomposition in As-Built Cell B

.......... 48
Figure 4-10 Comparison of Moisture Content in the Control, Retrofit, and As-Built Cells

....................... 50
Figure 4-11 Trends in CH:L as a Function of Waste Age

.......................................................................... 51
Figure 4-12 Trends in BMP as a Function of Waste Age

........................................................................... 52
Figure 4-13 Trends in Organic So lids as a Function of Waste Age

........................................................... 53
Figure 4-14 Cumulative and M ean Monthly Pr ecipitatio n

......................................................................... 5 6

xvFigure 4-15 Moisture Balance and Calculated Waste Moisture Content of the Control Cells

................... 57
Figure 4-16 Moisture Balance and Calculated Waste Moisture Content of Retrofit Landfill Unit

............ 58
Figure 4-17 Moisture Balance and Calculated Waste Moisture Content of As-Built Cell A

..................... 58
Figure 4-18 Moisture Balance and Calculated Waste Moisture Content of As-Built Cell B

..................... 59
Figure 4-19 Mean Monthly Leachate H ead on Liner of th e Control Cell

.................................................. 60
Figure 4-20 Mean Monthly Leachate Head and Leac hate Volumes Generated in the Control Cell

........... 61
Figure 4-21 Mean Monthly Leachate H ead on Liner for th e Retrofit Cells

............................................... 62
Figure 4-22 Mean Monthly Leachate Head and L eachate Generated Volumes in Retrofit Cells

............... 62
Figure 4-23 Mean Monthly Leachate H ead on Liner of As-Built Ce ll A

................................................... 63
Figure 4-24 Mean Monthly Leachate H ead on Liner of As-Built Ce ll B

................................................... 63
Figure 4-25 Mean Monthly Leachate Head and Leac hate Generated Volumes in As-Built Cell A

........... 64
Figure 4-26 Mean Monthly Leachate Head and Leac hate Generated Volumes in As-Built Cell B

........... 64
Figure 4-27 Calculated and Measured Wast e Moisture Content in the Control Cells

................................ 67
Figure 4-28 Calculated and Measured Wast e Moisture Content in the Retrof it Cells

................................ 68
Figure 4-29 Calculated and Measured Wast e Moisture Content in As-Built Cell A

.................................. 68
Figure 4-30 Calculated and Measured Wast e Moisture Content in As-Built Cell B

.................................. 69
Figure 5-1 Monthly Average of Ga s Composition for Co ntrol Cell A

....................................................... 72
Figure 5-2 Monthly Average of Ga s Composition for Co ntrol Cell B

....................................................... 73
Figure 5-3 Monthly Average of Gas Composition for As -Built Ce ll A

..................................................... 74
Figure 5-4 Monthly Average Gas Co mposition for As-B uilt Ce ll B

.......................................................... 75
Figure 5-5 Monthly Average of Ga s Composition for Re trofit Ce ll A

....................................................... 76
Figure 5-6 Monthly Average of Ga s Composition for Re trofit Ce ll B

....................................................... 76
Figure 5-7 Cumulative Methane Gas Collection Data versus LandGEM-Predicted Gas Generation for the Contr ol Cells

............................................................................................................ 79
Figure 5-8 Cumulative Methane Gas Collection Data versus LandGEM-Predicted Gas Generation for AsBuilt Cell A

.............................................................................................................. 80
Figure 5-9 Cumulative Methane Gas Collection Data versus LandGEM-Predicted Gas Generation for AsBuilt Cell B

.............................................................................................................. 80
Figure 5-10 LFG Generation Rate Pr ediction for As-Bu ilt Cell A an d B

.................................................. 81

xviFigure 5-11 Cumulative Methane Gas Collection Data versus LandGEM-Predicted Gas Generation for the Retrofit Cells

............................................................................................................ 82
Figure 5-12 Monthly Average LFG Flow Rate for Re trofit Cells

.............................................................. 83
Figure 5-13 Modeled LFG Generation Ra te for Waste in th e Retrofit Cells

.............................................. 84
Figure 5-14 Normalized Comparison of Gas Collection in Control and Retrof it Cells

.............................. 85
Figure 5-15 Normalized Comparison of Gas Collection in Control and As-Bu ilt Cells

............................ 86
Figure 5-16 Normalized Comparison of Gas Co llection in Control cells and As-Built Cells

.................... 87
Figure 5-17 NMOC Producti on in the C ontrol Cells

............................................................................... ... 89
Figure 5-18 NMOC Produc tion in As-B uilt Ce ll A

................................................................................. ... 90
Figure 5-19 NMOC Produc tion in As-B uilt Ce ll B

................................................................................. ... 90
Figure 5-20 NMOC Producti on in the Re trofit Cells

.............................................................................. ... 91
Figure 6-1 Leachate Temperature as a Fu nction of Time in th e Control Cells

........................................... 96
Figure 6-2 Leachate Temperature as a Fu nction of Time in th e Retrofit Cells

.......................................... 96
Figure 6-3 Leachate Temperature as a Function of Time in As-Built Cells

............................................... 97
Figure 6-4 Leachate pH as a Functio n of Time in th e Control Cells

.......................................................... 98
Figure 6-5 Leachate pH as a Functio n of Time in th e Retrofit Cells

.......................................................... 98
Figure 6-6 Leachate pH as a Functio n of Time in th e As-Built Cells

........................................................ 99
Figure 6-7 Volatile Organic Acids as a F unction of Time in Control Ce ll B

........................................... 100
Figure 6-8 Volatile Organic Acid as a Fu nction of Time in th e As-Built Cells

....................................... 100
Figure 6-9 Total Organic Carbon as a Func tion of Time in the Control Cells

......................................... 101
Figure 6-10 Total Organic Carbon as a F unction of Time in th e Retrofit Cells

....................................... 102
Figure 6-11 Total Organic Carbon as a F unction of Time in th e As-Built Cells

...................................... 102
Figure 6-12 Biochemical Oxygen Demand as a Function of Time in the Control Cells

.......................... 104
Figure 6-13 Chemical Oxygen Demand as a Function of Time in the Control Cells

............................... 104
Figure 6-14 BOD/COD Ratio as a Functio n of Time in the Control Ce lls

............................................... 105
Figure 6-15 Biochemical Oxygen Demand as a Function of Time in the Retrofit Cells

.......................... 105
Figure 6-16 Chemical Oxygen Demand as a Function of Time in the Retrofit Cells

............................... 106
Figure 6-17 BOD/COD Ratio as a Functio n of Time in the Retrofit Ce lls

............................................... 106

xviiFigure 6-18 Biochemical Oxygen Demand as a Function of Time in the As-Built Cells

......................... 107
Figure 6-19 Chemical Oxygen Demand as a Function of Time in the As-Built Cells

............................. 107
Figure 6-20 BOD/COD Ratio as a Functio n of Time in the As-Built Ce lls

............................................. 108
Figure 6-21 Total Kjeldahl Nitrogen as a Function of Time in the Control Cells

.................................... 109
Figure 6-22 Ammonia as Nitrogen as a Fu nction of Time in th e Control Cells

....................................... 110
Figure 6-23 Total Kjeldahl Nitrogen as a Function of Time in the Retrofit Cells

.................................... 110
Figure 6-24 Ammonia as Nitrogen as a Fu nction of Time in th e Retrofit Cells

....................................... 111
Figure 6-25 Total Kjeldahl Nitrogen as a Function of Time in the As-Built Cells

................................... 111
Figure 6-26 Ammonia as Nitrogen as a Fu nction of Time in th e As-Built Cells

..................................... 112
Figure 6-27 Total Iron as a Function of Time in the Control Ce lls

.......................................................... 113
Figure 6-28 Total Iron as a Function of Time in the Retrofit Ce lls

.......................................................... 114
Figure 6-29 Total Iron as a Function of Time in the As-Built Ce lls

......................................................... 114
Figure 6-30 Ortho-Phosphate as a Func tion of Time in th e Control Cells

............................................... 116
Figure 6-31 Total Phosphorous as a Func tion of Time in th e Control Cells

............................................ 116
Figure 6-32 Ortho-Phosphate as a Func tion of Time in th e Retrofit Cells

............................................... 117
Figure 6-33 Total Phosphorous as a Func tion of Time in th e Retrofit Cells

............................................ 117
Figure 6-34 Ortho-Phosphat e as a Function of Time in the As-Bu ilt Cells

.............................................. 118
Figure 6-35 Total Phosphorous as a Func tion of Time in th e As-Built Cells

........................................... 118
Figure 6-36 Chloride Concentrations as a Function of Time in the Control Cells

................................... 120
Figure 6-37 Chloride Concentrations as a Function of Time in the Retrofit Cells

................................... 120
Figure 6-38 Chloride Concen trations as a Function of Ti me in the As-B uilt Cells

.................................. 121

xviii

## List of Tables

Table 2-1 Mass Balance Monitoring Parameters and Frequencies

............................................................... 9

Table 4-3 Summary of Waste Composition Data for the Control cells and Assessment of Cell Replication45
Table 4-4 Summary of Waste Composition Data for th e As-Built cells and Assessment of Cell Replication Table 2-2 Liquid Addition Monitoring Parameters

................................................................................ .... 10

Table 2-3 Tier 1 Landfill Bioreactor Leachate Monitoring Parameters and Frequency

............................. 11

Table 2-4 Tier 2 Landfill Bioreactor Leachate Monitoring Parameters and Frequency

............................. 11
Table 2-5 Organic Composition of Fresh Residential Refuse (% of Dry Weight)

..................................... 16
Table 2-6 Chemical Composition of Paper Products Present in Municipal Waste

..................................... 16

Table 2-7 Landfill Bioreactor So lids Monitoring Parameters

.................................................................... 1 7

Table 3-1 Chemical Propertie s of Industrial Liquids

............................................................................ ...... 23
Table 3-2 Leachate Sampling Parameters an d Schedule

............................................................................ 31
Table 3-3 Volatile Organic Compound s Examined in La ndfill Leach ate

................................................... 31
Table 3-4 Semi Volatile Organic Compou nds Examined in La ndfill Leach ate

......................................... 32
Table 3-5 Municipal Solid Waste Sampling Schedule

.............................................................................. . 33

Table 3-6 LFG Sampling Schedule

................................................................................................ ............ 35
Table 3-7 HAPs Analyzed in Quarterly LF G Sampling

............................................................................. 3 5

Table 3-8 Moisture Balance Pa rameters

.......................................................................................... ........... 38

Table 3-9 Area Distribution of As-B uilt ce lls

.................................................................................. .......... 38

Table 3-10 Area Distribution of Retrofit and Control Units

..................................................................... .. 38
Table 4-1 Summary of Waste Compos ition Data for the Retrofit cell

....................................................... 40
Table 4-2 Slopes and Their 95% Confiden ce Intervals for Linear Regressions

......................................... 42

............................................................................................................................... ... 49

Table 4-5 Summary of Calculated and Fiel d Measured Waste Moisture Content

..................................... 67
Table 5-1 Summary Statistics for Gas Co mposition for Control Cells A and B

........................................ 72
Table 5-2 Summary Statistics of Gas Co mposition for As-Built Cells A and B

........................................ 73
Table 5-3 Notable Air Injection Da tes for As-Built Ce lls A and B

............................................................ 74

xixTable 5-4 Summary Statistics of Ga s Composition for Retrofit Cells

........................................................ 75

Table 5-11 LandGEM-Predicted Mass Production Rate of NMOCs in Different Landfill Units (Mg/yr).92

Table 8-2 Evidence of Accelerated Waste Decomposition Across All Me dia Analyzed Between Control Table 5-5 Summary of Waste Mass In puts for LandGEM, Mg (tons)

....................................................... 78
Table 5-6 Optimized Landfill Decay Constant (k) for Control Cell

........................................................... 79
Table 5-7 Optimized Landfill Decay Consta nt (k) for As-Built Bioreactor Cells

...................................... 81
Table 5-8 Summary of Dates Used for Retrofit and Control Cells CH 4 Flow Comparison

....................... 85
Table 5-9 Summary of Dates Used for As-Built and Control Cells CH 4 Flow Comparison

...................... 85

Table 5-10 NMOC Concentration for Each Sub Cell (ppm as Hexane)

..................................................... 88

Table 5-12 LandGEM Model Input Values for NMOC Side-by- Side Analysis

......................................... 93

Table 5-13 LandGEM Predicted Mass Productio n Rate of NMOCs Em issions (Mg/yr)

........................... 93
Table 8-1 OLLB Obj ectives Assessment

........................................................................................... ...... 127

and Bioreactor La ndfill Ce lls

................................................................................. 130

xx

## List of Acronyms

ANOVA Analysis of Variance BMP Biochemical Methane Potential BOD Biological (or Biochemical) Oxygen Demand C&D Construction and Demolition CAA Clean Air Act CE Collection Efficiency CFR Code of Federal Regulations CH:L Cellulose plus Hemicellulose to Lignin COD Chemical Oxygen Demand CQA Construction Quality Assurance CRADA Cooperative Research And Development Agreement DOC Dissolved Organic Carbon FML Flexible Membrane Liner GEM Gas Emissions Model GPS Global Positioning System HAP Hazardous Air Pollutant HDPE High Density Polyethylene HELP Hydrologic Evaluation of Landfill Performance ID Inner Diameter LCS Leachate Collection System LFG Landfill Gas MACT Maximum Achievable Control Technology MSL Mean Sea Level MSW Municipal Solid Waste NCSU North Carolina State University NESHAP National Emission Standards for Hazardous Air Pollutants NMOC Non-Methane Organic Compound NRMRL National Risk Management Research Laboratory NSPS New Source Performance Standards OLLB Outer Loop Landfill Bioreactor OLRDF Outer Loop Recycli ng and Disposal Facility OP-FTIR Open Path Fourier Transform Infrared ORD Office of Resear ch and Development ORP Oxidation Reduction Potential PCF Pounds Per Cubic Foot PSF Pounds Per Square Foot QAPP Quality Assurance Project Plan RCRA Resource Conservation and Recovery Act RD&D Research, Development, and Demonstration RPD Relative Percent Deviation SBR Sequential Batch Reactor SDR Standard Dimension Ratio SM Standard Methods SVOC Semi-Volatile Organic Compound TKN Total Kjeldahl Nitrogen TOC Total Organic Carbon

xxi

### List of Acronyms (continued)

TVA Total Volatile Acid UCL Upper Confidence Level U.S. EPA United States Envi ronmental Protection Agency VFA Volatile Fatty Acid VOA Volatile Organic Acid VOC Volatile Organic Compound VS Volatile Solid WM Waste Management, Incorporated XL eXcellence and Leadership

xxii

## Chapter 1. Introduction

1.1 Landfill Bioreactor Technology
In 2005, more than 230 million tons of municipal so lid wastes (MSW) were generated in the United States with 57 percent of that waste managed via disposal in MSW landfills (U.S. EPA 2006a). The majority of these landfills are permitted under Subtitle D of the Resource Conservation and Recovery Act (RCRA) and are managed as “dry tombs” where explicit controls are implemented to minimize liquid introduction and infiltration into the solid waste mass. Since the 197 0s, the potential benefits of moisture addition, or leachate recirculation, into MSW landfills have been examined by the U.S. EP A as well as many other researchers. These potential benefits include the rapid decomposition of degradable organics, the rapid generation of landfill gas (LFG), and the stabilization (e .g., low concentration of organics, metals, etc.) of landfill leachate. Since the 1990s, the coupled e ffects of controlled introdu ction of leachate and groundwater (and sometimes air) as well as LFG extract ion have been incorporated into the concept of what is known as the “landfill bioreactor”. The concept is particularly appealing since under th e current Subtitle D regulations landfill owners are financially responsible for the environmental care and management of their landfills for a minimum of 30 years after closure. If a landfill bioreactor can be demonstrated to consistently enhance/accelerate waste degradation and reduce to long term risk associated w ith the site to an acceptable level, then reduced post closure care may be considered for such sites. Although the technology related to landfill bioreactors has been investigated since the 1970s, full-scale implementation and the corresponding performance monitoring results have been limited. Under a Cooperative Research and Development Agreement (CRADA) between the U.S. EPA and Waste Management, Inc. (WM), long-term performance monitoring of MSW bioreactor landfill cells was initiated at th e Outer Loop Landfill in Louisville, Kentucky. In addition to confirming/refuting the results of previous laboratory and pilot-scale studies, the Outer Loop Landfill Bioreactor (OLLB) study also focused on defining the obstacles and limitations to the full-scale implementation of the landfill bioreactor tech nology concepts at working MSW landfills.


### 1.2 Outer Loop Landfill Bioreactor
The study presented in this document was conducted at the Outer Loop Recycling and Disposal Facility, (OLRDF), which is located in Louisville, Jefferson County , Kentucky. The site has a total property area of approximately 316 hectares (780 acres) and is located on the north side of Outer Loop Road, immediately west of Interstate 65. The OLDRF is owned and operated by WM and has been used for waste disposal for approximately 35 years. The OLRDF comprises eight individual and separate landfill units, designated Units 1 through 8. Units 1, 2, 3, and 6 are inactive la ndfill units that are not cu rrently receiving waste. Unit 4 is permitted as a construction and demolition (C&D ) debris landfill that is currently active, and Unit 8 is a newly permitted active bioreactor landfill cell (not included in this report) . This study focuses on portions of Unit 5 and Unit 7, which are both permi tted Subtitle D landfill units. During the study, Unit 5 was inactive, while Unit 7 actively received waste.
The bioreactor demonstrations at the OLLB represent large-scale research efforts at a full-scale operational landfill. The study covers approximately 20.2 hectares (50 acres) in three types of lined landfill units. The first was a Subtitle D landfill that was retrofitted with moisture addition piping to allow the recirculation of liquids (Unit 5). The second type of units in this st udy was a landfill that had a piping network (for liquids and air addition) installed as waste was being placed (U nit 7.4). The third unit was a Control cell that was developed and filled as a typical Subtitle D landfill with out any intent of supplemental liquid addition (Unit 7.3). Each of the three units was divided into sub ce lls to provide a quasi-“dup licate” of each test cell for data quality purposes.


### 1.3 Project Objectives
The overall objectives for the OLLB project, previously presented in the First Interim Report, are as follows:

1• Extensive monitoring of bioreactor landfill cells to understand the physical, chemical, and biological activities and changes over time within th e landfill bioreactors, with particular emphasis given to characteristics of in-place solid waste, leachate, LFG, as well as waste settlement;

• Compare and contrast measured information with that of a conventional Subtitle D landfill to evaluate differences caused by the bioreactor landfill treatments;

• Incorporate statistical techniques to assess the effectiveness and protectiveness of the landfill bioreactor operational technique;

• Establish best practices and procedures re quired to operate landfill bioreactors;

• Establish the important and indicative parameters th at should be monitored with respect to landfill bioreactor operations (i.e., critical and non-critical measurements); and

• Obtain sufficient research data to enable improvements that may be applied to future bioreactor landfills, both in an experimental capacity and as an alternative design and management method for MSW landfills.


### 1.4 Report Organization
This report provides a summary and interpretation of the monitoring results from 2001 to the second quarter of 2006 for the OLLB project. This report is a follow-up to the September 2003 U.S. EPA document Landfills as Bioreactors: Research at the Ou ter Loop Landfill, Louisville, Kentucky, First Interim Report , which presented a complete description of the landfill study sites, the distinction between the study units, and the data collection procedures. A lthough this document is a follow-up to the earlier report, this Second Interim Report is intended to be a stand-alone document. The document is organized as follows:

• Chapter 1. Provides a brief back ground related to landfill bioreactor technology and introduction to the OLLB project,

• Chapter 2. Summarizes previous findings regardin g landfill bioreactor tech nology. The findings presented were usually obtained at laboratory-or p ilot-scale level and served as the springboard for the OLLB project,

• Chapter 3. Provides a description of the various test cells at the OLLB site and explains the rationale for selecting the specific cells for study,

• Chapter 4. Focuses on solids decomposition and moisture balance calculations,

• Chapter 5. Focuses on landfill gas generation as well as non-methane organic carbon emissions,

• Chapter 6. Focuses on leachate quality and how they relate to waste decomposition,

• Chapter 7. Provides an evaluation of several performance criteria at the site as well as a discussion of results compared to regulato ry thresholds for MSW landfills,

• Chapter 8. Presents conclusion s from the study, as well as recommendations regarding ongoing and future monitoring activities at the site,

• Chapter 9. Provides a list of the cited references from the report,

• Appendix A. Provides the data validation report generated by Neptune and Company, Inc.,

• Appendix B. Provides supplemental figures related to MSW solids analysis,

• Appendix C. Presents statistical analyses of measured waste moisture content,

• Appendix D. Presents statistical analyses of meas ured versus calculated waste moisture content,

• Appendix E. Presents summary statistics for th e hazardous air pollutant (HAP) analysis; and

• Appendix F. Presents a statistical analys is of the leachate monitoring results.



### 2

## Chapter 2. Overview of Bioreactor Landfills

This chapter presents a brief overvi ew of previous research and studie s related to the bioreactor landfill concept. Many of the topics covered in this section were presented and evaluated as part of an earlier U.S. EPA document titled “ Monitoring Parameters for Landfill Bioreactors” (U.S. EPA 2004). That document outlines monitoring at MSW bioreactor landfills based on the OLLB ex perience. The main purpose of that document was to provide a regulatory and research-based rationale for the various parameters that were monitored during the project. The main reason for reintroducing those parameters is to provide a basis for the re-evaluation of the effectiveness of these para meters that are presented in later chapters.


### 2.1 Introduction to Landfill Bioreactors
More than 230 million tons of MSW is generated in the United States annually with 57 percent of that waste disposed of in MSW landfills (U.S. EPA 2006a). Most of the MSW landfills currently in service are permitted under Subtitle D of the RCRA or Subtitle D regulations (U.S. EPA 2006a). The main purpose of MSW landfill regulations (just like other environmental regulations), is to minimize risk to human health and the environment. In the case of MSW land fills, this was accomplished by reducing possible contamination from the migration of leachate and LFG from landfill s ites. Thus, Subtitle D landfill regulations outline a system that minimizes liquid infiltration into the solid waste mass by controlling the amount of moisture allowed into these landfills. Because the Subtitle D “dry tomb” landfill design incorporates features to minimize the potential for th e introduction of liquids into the waste, the resulting waste mass is often maintained at relatively low moisture content. As a result, the conventional Subtitle D “dry tomb” landfill design does not promote the solid waste decomposition process. Therefore, the risk associated with environmental emissions from dry to mb MSW landfills may exist longer, justifying the need for long-term monitoring at MSW landfill sites. Current re gulations require leachate and LFG emissions to be monitored for at least 30 years after cl osure of a landfill site or as long as environmental risk are present. Numerous small-scale and large-scal e projects have demonstrated that the rate of solid waste decomposition at MSW landfills can be improved by increasing the moisture content of the waste, thereby potentially reducing the duration of the requir ed post-closure care requirements. Increasing the moisture content of MSW by may provide the necessary liquids to accelerate wa ste decomposition. In addition, leachate recirculation is an economical means for leachate mana gement at landfill sites (Pohland 1975). Initially, most of the research examining the effects of moisture addition on solid waste degradation concentrated on leach ate recirculation as a means of economical ly managing MSW landfill leachate. In a conventional dry tomb landfill, landf ill leachate is mainly generated by rain water percolation through the solid waste. As a result, the volume of the leachate generated depends larg ely upon the climate, the type of waste present in the landfill, th e landfill morphology, the landfill su rface conditions, and the types of operations at the facility (Reinhart and Townsend 1998). Research has demonstrated that enhanced degradation of MSW is possible use leachate recircul ation (Pohland et al. 1993; Townsend et al. 1996; Reinhart and Townsend 1998). Enhanced degradation in a landfill where liquids are recirculated compared to a conventional landfill, is also characterized by enhanced LFG production. When operated in a fashion that includes controlled introduction of liquids, the landfill appears to operate like a “biological reactor” or “bioreactor”, as the recirculated liquids increase the moisture content of the waste and enhance the distribution of nutrients and bacteria, buffer the pH, and dilute inhibitory compounds (Reinhart and Townsend 1998; Kim and Pohland 2 003). Recirculation of leachate also reduces the need and cost associated with the collection and subsequent removal of leachate from the landfill to some other on-site or off-site location for treatment through conventional biological and/or physical-chemical processes. Research has also shown that liqui ds recirculated in landfill bioreact ors tend to act as a medium for nutrients, provide microbial transport, and enhance th e establishment of anaerobes. As a result of the increase in moisture content, a more rapid rate of so lid waste decomposition is achieved when compared to conventional MSW landfills. The enhanced rate of d ecomposition, facilitated by the increase in moisture content, often leads to an increase in the LFG generation rate with a corresponding reduction in biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total

3volatile acids (TVA), and metals co ntent in the leachate (Pohland et al. 1993; Reinhart and Townsend 1998; Sponza and Agdag 2004). The enhanced rate of landfill decomposition typically results in an increase in the rate of landfill settlement (El-Fadel 1998; Hossain et al. 2003), which may provide additional airspace. As a result, the total amount of solid waste placed in landfill bioreactors may be more than the amount placed in a dry tomb landfill of sim ilar size. Enhancing the rate of LFG production may also improve the economics associated with gas-to-ene rgy facilities at landfill bioreactor sites (Barlaz et al. 1990; Mehta et al. 2002). As a re sult of these comb ined effects, landfill bior eactors may reduce the longterm environmental impacts associated with the disposal of MSW in landfills.


### 2.2 Regulatory Overview
Solid waste regulations were established fairly recently relative to other environmental regulations. Most MSW landfills in the U.S. operate under regulations identified in Subtitle D of RCRA. The specific regulatory criteria for MSW landfills are presented in 40 CFR Part 258, which was promulgated in 1991. The main goal of these regulations is to ensure protection of human health and the environment through the establishment of minimum national criteria for MSW la ndfills. Subtitle D regulation specifies performance standards for the location, design, groundwater monito ring, and corrective actions for MSW landfills. In the preamble to the Subtitle D regulations, the U.S. EPA r ecognized that landfills are, in effect, biological systems that require moisture for decomposition to occur. The U.S. EPA further acknowledged that the increase in moisture content of solid waste landf ills may provide specific benefits, which may include increasing the rate of waste stabilization, improv ing leachate quality, and incr easing LFG production for potential energy recovery. At the time Subtitle D regu lations were promulgated, however, the U.S. EPA believed that many landfills, particularly those in humid areas, already had sufficient liquid for decomposition. Therefore, the conventional opinion was that the intentional addition of liquids was unnecessary. Furthermore, it was hypothesized that intentional liquid introduction may result in operational problems, including: (i) an increase in l eachate production; (ii) clogging of the leachate collection system; (iii) buildup of hydraulic head with in the landfill; (iv) an increase in LFG emissions and odor problems; and (v) an increase in the potential for the leachate to be released as a pollutant due to leachate breakouts and/or run-off. These operational problems, should th ey occur, would likely result in adverse impacts on human health and the environment (Ikem et al. 2002). Subtitle D regulations included provisions to prohibit th e addition of liquids to MSW landfills. Specifically 40 CFR 258.27 states “bulk or no n-containerized bulk liquid waste ma y not be placed in MSW landfill units.” Subtitle D regulations, howev er, allow for recirculation of leach ate and gas condensate generated from the gas recovery process as long as the landfill design includes certain liner requirements. Because of the lack of data on the performance of landfill bottom liners, the U.S. EPA initially required (at a minimum) that MSW landfills that recirculate leachate and gas condensa te use single composite liners to contain leachate and prevent it from contaminating the underlying soil and grou ndwater. MSW landfill liner systems typically consist of high density polyethylene (HDPE) geomembranes, geosynthetic clay materials, or compacted clay (Foose et al. 2002). In addition to requiring composite liners, the regulations require that a demonstration be provided to assure that the added volume of liquid will not increase the liquid (i.e., hydraulic) head on the lin er to more than the allowable 30 cm (1 ft). Because of the selfimplementing nature of the regulations, the permitting of leachate recirculation systems for MSW landfills was delegated to the approved state regulatory agency or tribal community. Thus, regulations regarding MSW landfills tend to vary between states, which allo w various degrees of flexibility within the law. The U.S. EPA provided limited regu latory flexibility to allow landfill bioreactors because of promising results from research regarding la ndfill bioreactors. Most notable was the introduction by U.S. EPA in 1995 of Project XL (eXcellence and Leadership). Fo r the case of MSW landfills , Project XL allowed for leachate, as well as other industrial liquids, to be added to Subtitle D landfills that do not meet the composite liner criterion. In turn, the designers of the Project XL landfill bioreactors hoped that the leachate recirculation/LFG recovery requirements would enhance groundwater protection and provide for additional capacity to accommodate more waste at indi vidual landfills, thus extending the life of existing landfill cells. Unfortunately, because of difficulty in obtaining a Project XL landfill bioreactor permit, only five landfills were permitted under th is effort nationwide before the U.S. EPA ceased accepting Project XL proposals in 2003.

4In 2003, the U.S. EPA defined landf ill bioreactors as MSW landfills that utilize liquids other than leachate and gas condensate to achieve an average moisture conten t of more than 40 percent on a wet weight basis. In its final rule on National Emissions Standards fo r Hazardous Air Pollutants (N ESHAP) for landfills and the Maximum Achievable Control Technology (MAC T) regulations, the U.S. EPA required landfill bioreactors with a total disposal capacity equal to or greater than 2.5 x 10 6 Mg (or m 3 ) to include a system to actively collect and control LFG that will commence operation within 180 days after liquids addition or after the average landfill moisture co ntent reaches 40 percent, whiche ver occurs later (FR 2003). Realizing the potential benefits of adding moisture to reduce the long-term risk associated with MSW landfills, the U.S. EPA promulgated the Research, De velopment, and Demonstration Permits for Municipal Solid Waste Landfills (RD&D rule) in 2004 (FR 2004). Under this rule, the U.S. EPA allowed approved states to permit landfill bioreactors under Subtitle D regulations. The RD&D rule deviates from the Subtitle D regulations in that it allows approved stat es to waive some provisions of the Subtitle D landfill operating criteria (excluding hazardou s waste prohibition and explosive ga s control), design criteria, and final cover criteria. RD&D permits, as well as the ru le itself, are temporary modifications to the original Subtitle D regulations. The RD&D permit for a given MSW landfill is initially approved for three years, with optional three year renewals for a maximum of 12 years. Landfill bioreactors permitted under the RD&D rule are required to submit annual reports that summarize data obtained duri ng each year and assess progress towards ultimate solids stabilization. Approved states may issue landfill permits under the RD &D rule to allow the addition of non-hazardous industrial liquids to MSW landfills that use conventional composite liners or alternative liner systems. The landfill owner must also demonstrate to the appropri ate State Director that the MSW landfill that is designed and operated as a landfill bioreactor under the RD&D rule does not pose an additional risk to human health or the environment beyond what can result from its operation as a dry tomb Subtitle D MSW landfill. Just like the Subtitle D regulations, the RD&D rule is self-implementing, giving each state or tribal community the authority to permit landfill bioreactors that may otherwise not have been allowed previously under Subtitle D regulations.
There are insufficient data on the be havior of landfills that use industrial liquids as a source of moisture. Since the RD&D rule is temporary (i.e., 12 years) , the U.S. EPA Office of Research and Development (ORD) is actively gathering data that may help in supporting many of the concepts envisioned by this rule. The data gathered by ORD will not only concentrate on the performance of the containment system (e.g., leachate and LFG collection, liners, slope stability, etc.) but also on th e microbial stabilization within the landfill unit. Data are currently being collected from four Project XL landfills and the two MSW landfills that have CRADAs with the U.S. EPA. More information regarding the other Project XL landfills can be found on the webpage http://www.epa.gov/projectxl.


### 2.3 Anaerobic Decomposition Fundamentals
Waste in an MSW landfill does not have a single age b ecause waste is placed incrementally in the various cells throughout the life of the facility. Rather, waste of different ages is associated with the various cells within the landfill and their respective “stabilization” st age or phase (Pohland et al. 1993). As can be seen in Figure 2-1, the different MSW la ndfill stabilization phases often overlap and can be viewed collectively, which tends to limit the industry’s understanding of th e various phases and their interaction. As shown in Figure 2-1, the initial phase results in aerobic decomposition followed by four stages of anaerobic decomposition. Thus, the majority of MSW landfill decomposition occurs under anaerobic conditions. It is noted that virtually all MSW landfills undergo these five stages of stabilization and that operating an MSW landfill as a landfill bioreactor ha s an effect only on the rate and not the sequence (and potentially the duration) of the stabilization phases (Pohland and Al-Yousfi 1994; Reinhart and Townsend 1998; Kim and Pohland 2003). Thus, it is important to understand each of the

5Figure 2-1 Phases of Solid Waste Decomposition (source: Pohland et al. 1993) stabilization phases individually. After a short-duration aerobic phase, it is generally recognized that there are four more steps involved in th e anaerobic solid waste degradation and stabilization process, with each step involving a set of separate and distinct microbial populations. These steps/ph ases are shown in Figure 2-1 and further described below. Successful conversi on and stabilization of th e waste is dependent on microorganisms performing their respective functions in syntrophic relationships. The application of these phases to an MSW landfill setting is briefly disc ussed below (Pohland 1975; Pohland et al. 1993).

2.3.1 Phase I (Initial Adjustment) This phase is sometimes referred to as the lag phase. As the waste is placed in th e landfill, the void spaces contain oxygen (O 2 ). With compaction, the O 2 content of the landfilled solid waste gradually decreases. As moisture becomes available and the microbial population density increases, biochemical decomposition under aerobic conditions is initiated.

2.3.2 Phase II (Transition) The transition phase is relatively short-lived as the O 2 is rapidly consumed by the bacteria present, resulting in a transition from aerobic to an aerobic conditions. During this ph ase, the primary electron acceptors become nitrates and su lfates, rather than O 2 , with the displacement of O 2 by carbon dioxide (CO 2 ) in the effluent gas.

2.3.3 Phase III (Acid Formation) This phase is marked by the onset of the hydrolysis of the biodegradable fraction of the solid waste, leading to a rapid increase in the concentration of volatile fatty acids (VFAs) in the leachate. This also corresponds to a decrease in pH from approximately 7.5 to 5.6 (Pohland et al. 1993). During this phase, the decomposition intermediates such as VFAs contribute to a high COD and the long-chain volatile organic acids (VOAs) are converted to acetic acid (C 2 H 4 O 2 ), CO 2 , and hydrogen (H 2 ). The presence of high levels of VFAs in the le achate will increase both BOD and VOAs, leading to the onset of H 2 production by fermentative bacteria and H 2 -oxidizing bacteria. The H 2 generation phase is comparatively short-lived as it terminates by the end of this phase. This phase is also marked by an increase in the biomass of acidogenic bacteria as well as a rapid consumption of substrates and nutrients.

6The drop in pH may cause concomitant mobilization and the possible complexation of metal species that are more soluble at a low pH.

2.3.4 Phase IV (Methane Fermentation) Intermediary products appearing during the acid forma tion phase (i.e., mainly acetic, propionic, and butyric acids) are converted to methane (CH 4 ) and CO 2 by methanogens. As a result of the consumption of VFAs by methanogens, the pH moves back to neutrality. Th e organic strength of the l eachate (as characterized by high BOD) is dramatically decreased in correspondence with increases in gas (i.e., CH 4 and CO 2 ) production. This phase also signifies the longest overall time duration and represents the period when the majority of the waste decomposes.

2.3.5 Phase V (Final Maturation and Stabilization) The final stage of solid waste decomposition is character ized by a lower rate of biological activity due to the limiting nutrients such as phosphorus. During this stage, landfill CH 4 production is almost negligible. O 2 and oxidized species may slowly reappear as O 2 permeates from the atmos phere with a corresponding increase in oxidation-reduction potential (ORP) in the leachate. It is hypothesized that residual organic materials may slowly be converted to gas in this phase, with the possible production of humic-like substances. To date, the U.S. EPA has no doc umentation of an MSW landfill exhibiting such characteristics.


### 2.4 Key Monitoring Parameters for MSW Landfill Bioreactors

The landfill bioreactor RD&D rule a llows for the controlled introductio n of liquids into Subtitle D MSW landfills to accelerate the decomposition of biodegradable organics. To understand the decomposition process, it is important to understand the type and role of microorganisms that contribute to this process. The anaerobic waste degradation proces s requires at least four different groups of microorganisms (Parkin and Owen 1986; Pohland et al. 1993). These microorg anisms occur naturally in MSW but require different conditions to achieve optimal perfor mance. The kinetics of microorgan isms in landfill bioreactors have not been widely investigated, likely becau se these groups of microorganisms (and other anaerobes in general) are harder to culture compared to aerobes. In fact, it is now rec ognized that the majority of the microorganisms in environmental systems cannot be easily cultured (Amman et al. 1995; Hugenholtz et al. 1998; Jjemba 2004). As a result, there is a need to use molecular-based non-culture techniques to study the microbial populations in MSW landfills as solids decom position progresses. Therefor e, instead of directly studying the “cause” or source of the decomposition, re searchers are often forced to indirectly study waste stabilization by monitoring the “effect” of the decomposition process. As a demonstration of this, Lay, et al. (1998), examined the abundance and activity of methanogens in simulated landfill columns. In that study, both the cumulative CH 4 production and moisture content were higher in the columns that included recirculated leachate. Recirculation of leachate al so shortened the initial lag phase. The specific microbes responsible for these mechanisms (i.e., the cause) were not thoroughly investigated, but the results of the microbial activity (i.e., the eff ect) were demonstrative. In addition to the biological parameters that can be monitored, there are some physical and chemical parameters that can be monitored that collectively confirm the optimal operatio n of landfill bioreactors. The remainder of this section presents results from previous studies that focus on these parameters. It should be noted that the optimal ranges presented in this review may not apply to all landfills as the composition of waste varies greatly. Therefore, in response to the heterogeneous nature of MSW, waste stream variability, and differences in environmental an d climate conditions, the use of “Control cells” (i.e., conventional dry tomb cells) at operating landfill bioreact or facilities is encouraged to help understand the site-specific performance of landfill bioreactors compared to the conventional landfill units. Unfortunately, the literature does not include numerous example projects where Control cells were systematically constructed and operated; while Control cells were in tegral to the study at th e OLRDF. For research purposes, it is recommended that landfill cells used as a control be comparable to the landfill bioreactor cells in age, depth, and composition of waste so that specific differences in monitoring parameters may be evaluated more effectively. They should be monitored separately whenever possible to demonstrate specific impacts of landfill bioreactor operations on the volume and qua lity of leachate, the volume and

7composition of LFG generated, changes in the waste ma ss, and effects on the l eachate collection system. While it is believed that the use of Control cells asso ciated with landfill bioreactor are beneficial and that use of the Control cells will likely help in the assessment of site-specific data, it is understood that the use of Control cells may not be feasible in all cases.

2.4.1 Physical Monitoring Parameters

2.4.1.1 Geotechnical Considerations Slope stability is an important parameter in MSW land fill design, particularly with regard to landfill bioreactors. Often landfill slope st ability focuses on the stability of th e final landfill configuration. Operating landfills as bioreactors increases the importanc e of a slope stability assessment as part of the overall design, not only for the final configuration but also for when the landfill is at interim grades. Large changes in liquid levels in the landfill impact the deve lopment of pore pressures, which can influence slope stability. Pore pressures may increas e in landfill bioreactors because of the addition of liquids and the concurrent increase in the rate of LFG production. However, there are little well documented field data available to substantiate this possibility. Several approaches for predicting and periodically assessing stability in landfills have been proposed (Bachus et al. 2004). Stability calculations can be conducted using the strength properties of the waste and foundation soils, the geometry of the waste mass, an d the pore pressures within the waste and foundation soils. Unit weight, shear strength and frictional charact eristics of MSW vary widely because of differences in waste characteristics and compaction techniques. The unit weight of MSW was reported by Landva and Clark (1990) to range from 320 to 1580 kg/m 3 (20 to 99 pcf). As expected, the shear strength of the waste and the calculated stability of the landfill depend on the composition of the waste. MSW may have an internal friction angle of 1 degree with cohesion as large as 2200 psf to a friction angle as high as 36 degrees with no cohesion (Singh and Murphy 1990). Kavazanjian et al. (1995) reviewed the technical literature and recommended design shear strength for wa ste that is represented as a bilinear Mohr-Coulomb failure envelope exhibiting a friction angle of 33 degr ees with minimum shear strength of 550 psf. Largescale laboratory direct shear tests conducted on “conventional” and bioreactor landfill wastes indicate similar strength parameters. Leachate levels in the waste and liquid in the subs urface also affect slope stability. In conjunction with a slope stability study, it is recommended that operators follow simple guidelines to promote landfill bioreactor slope inte grity. Operators should avoid any excavation at the toe of the slope that can create local zones of high stress that may potentially lead to instability. Operators should also avoid filling waste in cells at steep grades [i.e., great er than 3 horizontal to 1 vertical (3H:1V)]. The placement of fill for on-site roads and a component of the cover may also l ead to a translational or veneer instability, and should be considered during design (Stark et al. 2000). As required under Subtitle D regulations, leachate head on a landfill bottom liner should not exceed 30 cm (1 ft). The addition of moisture into the landfill ma y cause excess amounts of l eachate to build up on the bottom liner if the liquids are not effectively removed. Before the addition of moisture into a landfill bioreactor, therefore, the ability of the leachate collection system (LCS) to effectively minimize the potential impacts of increased leachat e flow must be explicitly consider ed. Performance of the LCS and resistance to clogging should also be examined during design and monitored during operation. Potential clogging of the LCS may lead to a buildup of leachate within the drainage layer, causing the head on the liner to exceed 30 cm (1 ft). As described previously, this may increase the potential for slope instability. Alkalinity, hardness, iron, and manganese compounds, total organic carbon, COD, and BOD are all involved in reactions that can result in buildup of precipitates that could potentially lead to LCS clogging (Fleming et al. 1999; Rowe et al. 2000; Cook et al. 2001; Rittmann et al. 2003). Monitoring the concentration of these parameters may provide an indication as to whether leachate concentrations approach saturation levels for calcium carbonate and other compounds that contribute to clogging and poor LCS efficiency. LCS clogging may also be caused by the settling of su spended particles from the leachate and biological growth on or in the LCS (Koerner and Koerner 1995).

82.4.1.2 Mass Balance It is important that the mass of th e landfilled solid waste within each landfill bioreactor cell be identified and recorded. Conducting regular su rveys of in-place volume and total disposed mass can be helpful in estimating the density of solid waste placed and may provide insight into wast e decomposition. As the solid waste decomposes, the density of the landfill tends to increase (Tiquia et al. 2002). Parameters that may assist with mass loading calculations are presented in Table 2-1. With regard to the total disposed mass, it is recognized that soil used as daily cover ne eds to be considered in an y mass calculation. It has been recommended to avoid daily cover materials with a low permeability to minimize perched leachate zones within the landfill (U.S. EPA 2002). Efforts may be made during site operations to remove temporary cover, temporary roadways, and piles of so ils used for daily cover prior to the placement of waste in a particular part of the cell. Additionally, using materials other than soil (e.g., temporary tarps, foams, etc.) as daily cover may be an effective a lternative in preventing perched leachate zones.
Table 2-1 Mass Balance Monitori ng Parameters and Frequencies Parameter Frequency Units Visual Landfill Inspection Daily

- Mass of Landfilled MSW Daily Mg (tons) Mass of Landfilled Construction and Demolition Waste Daily Mg (tons) Mass of Soil (other than daily cover) Daily Mg (tons) Type of Daily Cover Daily Mass or Volume of Daily Cover Daily Mg (tons) or m 3 (yd 3 ) Landfill volume Quarterly m 3 (yd 3 ) Settlement Quarterly m (ft)

2.4.1.3 Moisture Balance A key component in operating a landf ill as a bioreactor is the introductio n of moisture from internal (i.e., leachate) and external (e.g., preci pitation, stormwater, groundwater, an d industrial liquid waste streams) sources into the landfill. In general, the decompositi on and select stabilization rate of biodegradable solid wastes increases with increasing mois ture content of the waste (El-Fadel 1998; Olayinka 2003). Research has shown that the optimum moisture content for biologic al degradation is greater than 40 percent (Pohland et al. 1993; Reinhart and Townsend 1998). Deliberate moisture addition to the landfill should be applied uniformly to the extent practicable to evenly wet the waste and to reduce differential settlement. Typical moisture addition techniques incl ude applying liquids to the surface and to the subsurface. Surface applications include spray irrigatio n and surface ponds. Subsurface tech niques include horizontal trenches and vertical wells, in addition to other methods such as permeable blankets, which have been described elsewhere (Haydar and Khire 2006). Limited research has been performed at full-scale landfills regarding design guidelines for subsurface application techniques; however, hydraulic properties of waste were estimated using leachate recirculation via vertical wells (Jain et al. 2006) . Similarly, hydraulic properties while using horizontal injection have been reported (Townsend and Miller 1998, Haydar and Khire 2005). As described previously, an increase in landfill moisture content that results in a build-up of pore pressure may decrease slope stability. Assuming the volume of water consumed to be negligible during waste hydrolysis, moisture balance can be calculate d as presented in the following equation:
Δ S = Moisture in – Leachate out Equation 2-1

Where:
Δ S = net moisture storage; Leachate out = leachate generated by the landfill; and Moisture in = liquids added into the landfill, including precipitation. As mentioned previously, liquids addition occurs in various forms including, but not limited to, the introduction of leachate, stormwater , liquid waste, and municipal and i ndustrial wastewater. Parameters that assist in performing a water balance are presented in Table 2-2. These should be monitored daily when

9liquids are being introduced into the waste. It is also important to take into account the moisture content of the incoming waste when using the moisture content of the waste to quantify or to assess moisture balance. Table 2-2 Liquid Addition Monitoring Parameters Parameter Frequency Units Volume of Leachate Added Daily L (gal) Rainfall Daily mm (inch) Volume Outside Liquid Added (e.g., Groundwater, Industrial Wastewater) Daily L (gal)

Volume of Leachate Generated Daily L (gal) of leachate generated by the landfill bioreactor cells only Mass of Sludge Addition Daily Mg (tons) Wet Basis Moisture Content of Sludge Added Daily Percent (M/M)

2.4.2 Analytical Monitoring Parameters

2.4.2.1 Leachate Monitoring Leachate monitoring parameters presen ted in this section may be used to enhance the operational control of MSW landfill bioreactors. These parameters are categorized as either “Tier 1” or “Tier 2”, shown in Tables 2-3 and 2-4, respectively. Tier 1 parameters are relatively inexpensive to obtain. Tier 2 parameters are usually more time intensive to assess and, as a result, the testing is incrementally more expensive than testing for Tier 1 parameters. The extent and frequen cy of leachate monitoring at each site will ultimately be dependent on local, state, and federal regulations. It is, however, recognized th at the value of some of the individual parameters can change significantly over the life of the landfill biore actor cell. It is noted that the constituents listed in Table 2-3 and 2-4 are simply suggested monitoring parameters, and the specific leachate monitoring needs and requirements ofa bioreactor landfill should be evaluated on a sitespecific basis. Because of their importance in un derstanding the decomposition process and therefore attaining a properly functioning land fill bioreactor, some of these monito ring parameters are discussed in detail below.
2.4.2.1.1 Leachate Temperature Research suggests that anaerobic pr ocesses are optimized when the wast e is within either the mesophilic (30 to 38 ° C (86 to 100 °F)) or thermophilic (50 to 60 ° C (122 to 140 °F)) temperature range (Parkin and Owen 1986). The higher thermophilic temperatures enha nce the rate at which organic matter is converted to VOAs but lead to a lower yield of CH 4 compared to the lower mesophilic temperatures (Pohland et al. 1993). This trend is possibly attributed to an incr ease in the activity of acetogens and a decrease in the activity of methanogens. Optimum CH 4 generation from solid wastes, however, was found to occur at 41 ° C (105.8 °F ) (Hartz et al. 1982). It is recogni zed that operating temperatures in the landfill at the thermophillic range may present concerns regarding fire, health and safety issues, and sustained vitality of the microorganisms. The maintenance of a uniform l eachate temperature is believed to be a fundamental monitoring parameter that is indicative of an efficient anaerobic stabili zation process. Since landfill temperature is not typically controlled by the operator, the temperature ranges stated above reflect a combination of effects due to ambient temp erature conditions, microbial activity, and the extent and effectiveness of insulation provided by the specific landfill configuration. In a study conducted at the Outer Loop Landfill in Louisville, Kentucky, the temper atures of the leachate were initially approximately 7 ° C (45 °F) but steadily increased to 30 ° C (86 °F) or higher within a few months after operating the landfill as a bioreactor (U.S. EPA 2003). While an incr ease in leachate temperature may be reflective of waste degradation in a landfill, it is not solely indicative of biological activity. Leachate temperature may also be affected by ambient temperature as well, depending on the leachate sampling location.

10Table 2-3 Tier 1 Landfill Bioreactor Leac hate Monitoring Parameters and Frequency 

### Parameter Method Frequency
Static head on Liner Pressure Transducer (1) Temperature Thermometer Monthly pH U.S. EPA (2) 9045C Monthly Conductance ( μ Sm/cm) Field Electrode Monthly Total Dissolved Solids (mg/L) SM (3) 160.1 (C) Monthly Alkalinity (mg/L as CaCO 3 ) SM (3) 310.1 Monthly Anions (mg/L) SM (3) 300.1 Monthly Cations (mg/L) Monthly Chemical Oxygen Demand (mg/L) SM (3) 410.4 Monthly Biochemical Oxygen Demand (mg/L) SM (3) 405.1 Monthly Total Organic Carbon (mg/L) EPA (2) 9060 Monthly Total Phosphorous (mg/L) SM (3) 365.2 (C) Monthly Ortho Phosphate (mg/L) SM (3) 365.2 (C) Monthly Ammonia (mg/L) SM (3) 350.1 (C) Monthly Nitrite (mg/L) SM (3) 300.1 Monthly Nitrate (mg/L) SM (3) 300.1 Monthly Notes: 1. Head on the liner should be monitored continuously, howev er, it is suggested that a w eekly average is reported. 2. U.S. EPA SW-846 Test Methods for Evaluating Solid Wastes. 3. U.S. EPA Methods for Chemical Analysis of Water and Wastes.

Table 2-4 Tier 2 Landfill Bioreactor Leac hate Monitoring Parameters and Frequency Parameter Method Frequency Volatile Organic Compounds (1) (VOCs) ( μ g/L) SW-846 8260 (B) Quarterly Semi-Volatile Organic Compounds (SVOCs) ( μ g/L) SW-846 8270 (B) Quarterly Volatile Fatty Acids (mg/L) GC MS Quarterly Arsenic (mg/L) SW-846 6010(prepared per SW-846 3005) Quarterly Barium (mg/L) SW-846 6010 (pre pared per SW-846 3005) Quarterly Cadmium (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Calcium (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Copper (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Chromium (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Iron (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Lead (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Magnesium (mg/L) SW-846 7470 (prepared per SW-846 3005) Quarterly Mercury ( μ g/L) SW-846 7470 (prepared per SW-846 3005) Quarterly Potassium (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Sodium SW-846 6010 (prepared per SW-846 3005) Quarterly Selenium (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Silver (mg/L) SW-846 6010 (prepared per SW-846 3005) Quarterly Zinc (mg/L) SW-846 6010 (prepa red per SW-846 3005) Quarterly Note: 1. Constituents listed in 40 CFR 258 Appendix I.

112.4.2.1.2 Leachate pH The optimum pH for anaerobic systems ranges betwee n 6.8 and 7.4 (Parkin and Owen 1986). Initially, the leachate pH may be neutral; but after the onset of anae robic conditions there is ge nerally a noticeable drop in the pH especially during the acid forming phase, as discussed previously. The drop in pH is caused by the accumulation of VFAs in the leach ate. However, the pH will eventu ally increase to neutral conditions as methanogens consume these acids. Studies conducte d to compare leachate pH in conventional dry tomb MSW landfills and landfill bioreactors have shown that there may not be a significant difference in pH between the two systems. As described previously, the pH is expected to vary with time in all landfills, depending on the initial waste composition and the phase of waste degradation in the areas where the leachate passes before it is collected in the LCS.
2.4.2.1.3 Volatile Fatty Acids and Volatile Organic Acids VFAs and VOAs affect microorganisms and the degradation processes in two primary ways. First, they have a low ionization constant (i.e., low pK a) and can readily dissociate, releasing H + ions that cause the pH of the system to decrease and therefore beco me destabilized. Second, when the acids are nondissociated (as is typical at low pH levels), the acids are able to penetrate microbial cell membranes, establishing a pH gradient by actively transporting prot ons out of the cell and redu cing the internal cell pH (Zoetemeyer et al. 1982; Aguilar et al . 1995). The decrease in intracellular pH in turn leads to an increased energy demand by the cell to restore pH levels leaving less energy for growth (Yamaguchi et al. 1989; Gonzalez et al. 2005). These processe s lead to reduction in the rate of solid waste degradation. VOA concentrations that are in excess of 6,000 mg/L can inhibit microbial processes (Pohland et al. 1993). However, most research regarding solid waste degradation has not focused on VOAs, but rather has investigated the effect of VFAs on the menthanogenic population within the landfill. Acidic leachate typically correlates with a high VFA content and a low CH 4 production for prolonged periods. Most common among these VFAs are acetic acid, propionic acid, and butyr ic acid (Barlaz et al. 1989; Kim and Pohland 2003). The amou nt of leachate that is recirculated affects the quantity of VFAs. If VFAs are high, methanogenesis can be inhibited by the low pH that is induced. Therefore, the volume of recirculated leachate has to be properly adjusted to minimize a buildup of VFAs. Lab-scale study results presented in Figure 2-2 demonstrate this. Figure 2- 2 shows the effects of leachate recirculation on VFA accumulation in comparison to VFA generation under conventional landf ill management. The leachate in “Reactor 9” was recirculated at 9 L/day (2.4 gpd) which was 13 perc ent of the reactor volume, whereas leachate in “Reactor 21” was recirculat ed at 21 L/day (5.5 gpd, 30 percent of the reactor volume). It is interesting to note that VFA buildup in the reactor with a higher leachate recirculation rate of 21 L/day (5.5 gal/day) was nearly as high as th e VFAs generated in the single-pa ss (i.e., conventional) reactor. Furthermore, at 21 L/day (5.5 gpd), the bioreactor had a spike of almost 30,000 mg VFA/L within 30 days which can be detrimental to methanogens. This is apparent when comparing the CH 4 production in Reactor 21 to Reactor 9 (Figure 2-2). A further demonstration of the affect on degradation is that waste settlement was greater in Reactor 9 than Reactor 21 (Sponza and A ğ da ğ 2 004). Settlement may be related to CH 4 production in anaerobic landfill systems as it is an indication of mass loss and waste degradation. At high leachate volumes, saturation, washou t of the methanogens and/or ponding may occur in the reactor, thus contributing to the noted detrimental effects of the acidic condition. At this time, models that adequately predict the correct amount of leachate to recirculate have not been developed and determinations of what recirculation volume is adequate (or optimal) are generally made on a case-by-case assessment of performance.
2.4.2.1.4 Leachate Biochemical and Chemical Oxygen Demand BOD consists of biologically degr adable dissolved organics in the leachate. COD is a measure of chemically oxidizable components in leachate and reflects the amount of O 2 that is required by the bacteria to metabolize the existing organic substrate as well as the O 2 required by other oxidizable chemical compounds. One of the main conseq uences of operating a landfill bior eactor is the rapid reduction of BOD in the leachate. BOD values reported in the litera ture for conventional landfills ranged between 20 and 152,000 mg/L (Krung and Ham 1991; Chu et al. 1994; Kjeldsen et al. 2002; U.S. EPA 2003), whereas COD values range between 500 and 60,000 mg/L (Pohland et al. 1993; Reinhart and Townsend 1998; U.S. EPA 2003). By comparison, BOD values for landfill bioreactors were found to range between 20 and 28,000 mg/L (Pohland et al. 1993; Reinhart and Townsend 1998; U.S. EPA 2003).

12Figure 2-2 Changes in VFA in a Single Pass (Conventional) Reactor versus Bioreactor9 and Bioreactor 21 over Time (Source: Sponza and A ğ da ğ , 2004) While the values of BOD and COD may change individu ally as a function of decomposition, the ratio of BOD to COD may be used to assess the relative biodegra dability of the leachate substrate. Variations in BOD and COD may be closely related to the variations observed with VFA production. As a result, the BOD/COD ratio may act as an indicator of the biodegradability of organics present in MSW. At the time of initial waste placement within the landfill, the BOD and COD concentrations were relatively low. The initial low BOD and COD concentration is thought to be caused by the initial aerobic stabilization of the MSW or by a delay in the hydrolysis of the waste. During the acid formation ph ase, the majority of the O 2 demand (both BOD and COD) is caused by the presence of high concentrations of VFAs. BOD and COD concentrations decrease after the onset of the CH 4 fermentation phase and the conversion of VFAs. Landfill bioreactors have a higher BOD/COD ratio during the acid forming phase relative to conventional landfills (Reinhart and Al-Yousfi 1996; Reinhart and Townsend 1998). However, research suggests that this ratio decreases during the phase that follows (i.e., during the CH 4 fermentation phase (Phase IV)). After waste stabilization, COD may be influenced by hi gh molecular weight organics such as humics and fulvics present in the leachate (Pohland et al. 1993). These residuals tend to elevate COD to a higher level than BOD and reduce the BOD/COD ra tio. For instance, leachate BOD/CO D ratios are usually higher than 0.5 for acid formation phases of decomposition but may decline to less than 0.1 for well-decomposed waste. It should be noted that COD is also influe nced by an increase in the concentration of ammonia which has implications that are outlined later in this document.
2.4.2.1.5 Leachate Total Organic Carbon Similar to the phenomenon observed for COD and BO D, the TOC levels increase after initial waste placement as a result of microbial solubilization of the organics. During the acid forming phase, TOC increases rapidly. An increase in TOC may also be observed soon after the introduction of waste containing high concentrations of organics. Because of the conversion of the VFAs to CH 4 , TOC concentration tends to decrease during the CH 4 fermentation phase. TOC of conventional landfills has been reported to range between 30 and 30,000 mg/L (Pohland and Harper 1987; Krung and Ham 1991; Pohland et al. 1993; Chu et al. 1994; Kjeldsen et al. 2002). As an indication of the similarity in the decomposition mechanism, the TOC in landfill bioreactor systems ranges between 70 and 28,000 mg/L (Pohland et al. 1993).

132.4.2.1.6 Leachate Nitrogen Content Nitrogen is mainly present in MSW leachate in th e following forms: total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH 4 -N), and nitrate nitrogen (NO 3 -N). Ammonia is the most important of the three forms of nitrogen since at high concentrations (i.e.,1,500 - 2,500 mg/L) it tends to inhibit methanogens (Hashimoto 1986; Hansen et al. 1998) and therefore reduces the potential for waste degradation. Under anaerobic conditions, ammonia tends to accumulate in the leachate, especially when the leachate is recirculated. While the ammonia concentration in co nventional landfills ranges between 2 and 2,200 mg/L (Krung and Ham 1991; U.S. EPA 2003), concentrations in landfill bioreactors range between 6 and 20,000 mg/L (Krung and Ham 1991; Pohland et al. 1993; Chu et al. 1994; Reinhart and Townsend 1998; U.S. EPA 2003). The accumulation of ammonia in the leachate from landfill bior eactors may adversely affect the methanogenic population. Ammonia concentrations of 1,500-3,000 mg/L are inhibitory to anaerobic processes at high pH levels, whereas concentrations above 3,000 mg/L can be toxic to most microorganisms in the waste (Pohland et al. 1993). Increasingly higher concentrations of ammonia in the leachate may indicate the potential for adverse effects on the methanogenic popula tion, but these elevated values may also be an indication of an advanced stage of waste decomposition.
2.4.2.1.7 Leachate Metals and Metalloids Content Heavy metals and metalloids exert toxicity to microorganisms influencing their biochemical activities, cell morphology, and growth (Hughes and Poole 1989; Gadd 1992; Jjemba 2004). Unlike organic compounds, metals do not degrade as the waste in the landfill de composes, but rather they are transformed from one chemical state to another. Metals may also be precipitated under anaerobic conditions as carbonates, hydroxides, or sulfides; they may also bind to orga nic waste ligands. Metals can also be chelated or subjected to ion exchange within the landfilled waste matrix.
Most of what is known about metal transformations in la ndfills is based on chemical rather than biological analyses. Thus, there is limited information about the role of microorganisms on such transformations under the anaerobic conditions that are typical of la ndfills with progressively changing redox potential, moisture content, temperature, and pH. Beyond the adverse effects of metals in the leachate from a microorganism perspective, metals concentration in the leachate is an important parameter as it can affect the cost of off-site leachate treatme nt (e.g., a wastewater treatment plant may reject leachate if metals concentration (e.g., arsenic) is too high, thus causing the landfill to send the leachate elsewhere for treatment). The lower pH and higher organic conten t of the leachate during th e initial landfill stabilization phases may mobilize some metals during the acid forming phase (Pohland et al. 1993). However, after the onset of the CH 4 fermentation phase, metal concentrations in th e leachate tend to decrease. The decrease in these concentrations is a result of metal reducti on, formation of metal sulfides, precipitation, and complexation within the waste matrix. Operators should recognize that the introduction of large concentrations of heavy metals, throug h either solid or liquids placed in the landfill, may retard or inhibit the solid waste degradation process and should be avoided in landfill bioreactors.
2.4.2.1.8 Semi-Volatile and Volatile Organic Compounds SVOCs and VOCs may represent parameters that are of particular importance for monitoring as there is a potential for the introduction of complex organic constituents into the landfill, particularly when various industrial wastes are applied. The ability of microorganisms to assimilate and transform potentially toxic organic compounds in landfill bioreactors has been documented. For example, in-situ reductive dehalogenation of organic compounds (e.g., tric hloroethylene and hexachlorobenzene) has been demonstrated in bench-scale landfill bioreactor studies (Kim and Pohland 2003). However, additional data are needed to compare and contrast the volatilizati on potential for specific VOCs and SVOCs that are most likely to appear in leachate for both conventional and bioreactor landfills.
2.4.2.1.9 Leachate Phosphate Concentration The carbon to phosphate (C:P) ratio is important as the presence of low phosphorus quantities will slow down microbial growth and decomposition. A C:P ratio of 60:1 is deemed optimal for microorganisms to actively assimilate substrate carbon. Reducing the C:P ratio to this range in landfills may require adding commercial phosphorous-rich fe rtilizers together with the recirculation leachate. The beneficial effects of adding phosphates to laboratory-scale landfill bioreactor cells have been document ed (Sheridan 2002). To the authors’ knowledge, this practice has not been further examined in the field.

142.4.2.2 Solids Monitoring
2.4.2.2.1 Refuse Composition Cellulose and hemicellulose are the principal biodegradable components of MSW. While the anaerobic biodegradation of refuse in landfills requires the coordinated activity of several trophic groups of microorganisms, the conversion of cellulose and hemicellulose to CH 4 can be described by the following reactions: (C 6 H 10 O 5 )n + nH 2 O → 3nCO 2 + 3nCH 4 Equation 2-2 (C 5 H 8 O 4 )n + nH 2 O → 2.5nCO 2 + 2.5nCH 4 Equation 2-3 The other major organic compound in refuse is lignin, which is, at best, only slowly degradable under the anaerobic conditions that prevail in landfills (Colberg 19 88). In addition to its recalcitrance, lignin interferes with the decomposition of cellulose and he micellulose by physically impeding microbial access to the more easily degradable carbohydrates. Thus, th e complete conversion of cellulose and hemicellulose to LFG is not expected. Research to date from both field-scale and labora tory-scale systems has not established a lower level of cellulose and hemicellulose biodegradation as many components of waste contain cellulose, hemicellulose, and lignin and each waste component has unique biodegradation characteristics (Barlaz 2006). The cellulose, hemicellulose, and lignin concentrations fo r a series of waste samples collected over the past 14 years are summarized in Table 2-5. Some of the samples represent fresh residential refuse while others were collected at a landfill. The samples collected at a landfill may not be comparable to the residential waste samples that do not include the large quantities of office paper or wood waste that are typically generated in the commercial and construction sectors, respectively. The relatively large range in cellulose, hemicellulose, and lignin concentrations is indicative of their variability in refuse composition. Unfortunately there is not a single factor to which this variability can be attributed . The last row in Table 2-5 represents values for the aggregate composition of waste entering a Canadian landfill. These values were calculated from measurement of the cellulose, hemicellulose, and lignin content of individual waste components and a waste composition survey. The com position of the aggregated waste stream includes some inert wastes that dilute the cellulose, hemicellulose, and lignin concentrations. The precise composition of waste that enters a landfill is never known and can vary over time and with the landfill location (e.g., proximity to urban, residential, or rural waste streams). Nonetheless, it is generally agreed that the major sources of organic matter in la ndfills are paper, food wast e, and yard waste. Of course, the disposal of yard waste in landfills is bann ed in many states, thus decreasing its importance as a source of CH 4 production. The U.S. EPA published an estimate of the composition of MSW based on the materials flow methodology (U.S. EPA 2006a). Using these data, coupled with data on th e fraction of each MSW component that is recycled, it is estimated that paper makes up approximately 26.3 percent of the mass of MSW entering landfills. In that other waste st reams (i.e., those that do not contain food waste, paper, and yard waste) are typically buried in landfills , the actual paper content in a landfill is lower than 26.3 percent. This is consistent with the lower cellu lose content of waste entering the Canadian landfill as presented in Table 2-5. Available data on the cellulose, hemicellulose, and lignin concentrations in fresh paper and wood waste are summarized in Table 2-6. It is noted that a relativel y large difference in the cellu lose content exists for the two office papers that were tested. The office paper described in Wu et al. (2001) had an ash content of 11.6 percent compared to a 1.4 percent ash content in the sample obtained by Eleazer et al. (1997). This difference is likely due to the presence of inorganic coatings in the sample obtained by Wu et al. (2001).

15Table 2-5 Organic Compositio n of Fresh Residential Refuse (% of Dry Weight)
Reference Cellulose (C) Hemicellulose (H) Lignin (L) (C + H) / L VS. Source (6)
Ham and Bookter, 1982 42.4 nm 10.9 3.89 nm (5) L Jones et al., 1983 (1) 25.6 6.6 7.2 4.5 59.6 L Bookter and Ham, 1982 (2) 63.4 nm 15.7 4.04 nm L Barlaz et al, 1989 (3) 51.2 11.9 15.2 4.15 78.6 R Eleazer et al. 1997 28.8 9 23.1 1.64 75.2 R Rhew and Barlaz, 1995 38.5 8.7 28 1.68 nm R Ress et al., 1998 48.2 10.6 14.5 4.06 71.4 R Price et al., 2003 43.9 10 25.1 2.15 nm R Barlaz unpublished (4) 22.4 5.8 11 2.57 nm L 1. Refuse recovered from a landfill in the UK. The type of refuse and sampling strategy were not specified. The samples also contained 2.3% starch and 5% protein. Analyses were conducted using detergent fiber techniques. 2. Average of ten samples from th e working face of a NY landfill. 3. The following additional analyses were performed on this sample: protein – 4.2%, soluble sugars – 0.35%, starch – 0.6% and pectin - <3%. 4. These values represent the composition of waste entering a Canadian landfill as described in the text. 5. nm = not measured. 6. (L) = landfill and (R) = residential refuse.

Table 2-6 Chemical Composition of Pap er Products Present in Municipal Waste
Source Newsprint Office Paper Corrugated Cardboard Coated Paper Branches

R eference Wu et al. 2001 Eleazer et al. 1997 Wu et al. 2001 Eleazer et al. 1997 Eleazer et al. 1997 Eleazer et al. 1997 Eleazer et al. 1997
Cellulose 48.3 48.5 64.7 87.4 57.3 42.3 35.4
H emicellulose 18.1 9 13.0 8.4 9.9 9.4 18.4
L ignin 22.1 23.9 0.93 2.3 20.8 15.0 32.6
V olatile solids 98.0 98.5 88.4 98.6 92.2 74.3 96.6
In summary, although the exact composition of waste that is buried in landfills varies, it is well established that the waste contains large concentrations of cellulose-containing materials. Paper is the major contributor to the cellulose and hemicellulose concentrations in landfills, followed by contributions from wood, yard debris and food waste. Therefore, regardless of initial concentrations of cellulose, hemicellulose, and lignin, it may be a useful measure of decomposition to track the relative changes in cellulose, hemicellulose, and lignin during the life of the facility.
2.4.2.2.2 Solids Monitoring Parameters In the previous sections, discussions were presented regarding the physical and analytical measurements that can be made to demonstrate waste decomposition. Ultimately, it is the degradation of the waste solids themselves that is the true measure of decomposition. The values of the parameters presented in this section can vary widely due to heterogeneity of the wa ste, variations in the degree of decomposition, and moisture content. Unlike leachate and LFG sampling (where “weighted average va lues” may be obtained), it is physically difficult and expensive to obtain representative individual samples of waste for analysis. Table 2-7 presents suggested solids monitoring parameters for landfill bi oreactors. More data from other bioreactor landfills regarding solids m onitoring are needed; monitoring of the parameters shown in Table 2­ 7 (with the exception of moisture content) may not be necessary during routine operation.

16Table 2-7 Landfill Bioreactor Solids Monitoring Parameters
Parameter Method Frequency Optimum Range Average Temperature Thermometer (1) 35 - 55 °C Average pH (2) U.S. EPA 9045C (1) 6.5 - 7.6 Average Volatile Solids (percent M/M) (3) U.S. EPA 1684 (1) Decreasing Trend Average Wet-Based Moisture Content (percent M/M) - (1) < 45 %

Notes: 1. Frequency of solids monitoring should be dete rmined on a site- and project-specific basis. 2. U.S. EPA, 2003. 3. Mehta et al., 2002. 2.4.2.2.3 Temperature Temperature of the waste mass may be determined by thermocouples or thermistors within the waste mass and monitored electronically (via a data logging station) or by using portable meters. Temperature monitoring in bioreactor landfills ope rating aerobically is essential, as the regulation of temperature is critical to preventing el evated waste temperatures resulting from aerobic waste decomposition.
2.4.2.2

. 4 Volatile Solids Adding moisture to the MSW stimul ates biological activity in landfill bioreactors. This increase in biological activity may directly translate into an incr ease in the degradation of cellulose and hemicellulose, which may translate into a measurable increase in the rate of waste settlement. A three-year study at the Yolo County Landfill in California demonstrated that the abundance of cellulose, hemicellulose, and lignin are strongly correlated to the volatile solids (VS) cont ent of MSW (Mehta et al. 2002). VS content in MSW is expected to decrease as the refuse decomposes because of cellulose and hemicellulose content loss from the waste. The main disadvantage of using VS as an indicator, however, is that, unlike cellulose, hemicellulose, and lignin, the analysis of VS offers a lower level of accuracy and is affected by daily cover application (Mehta et al. 2002).
2.4.2.2

. 5 Moisture Content Moisture content of MSW should be examined to ensure relatively uniform distribution of the liquids that are added to the landfill bioreactor. The moisture co ntent of the “fresh” incoming solid waste needs to be evaluated to calculate moisture ad dition requirements. Moisture addition requirements (i.e., volumes) will likely dictate the liquids addition rate required for landfill bioreactors.
2.4.2.3 Landfill Gas Monitoring Parameters During the process of anaerobic solid waste decompos ition, landfills generate significant quantities of CH 4 and CO 2 . Both of these gases are undesirable greenhouse gases (Conrad 1995; Jjemba 2004), with CH 4 having a global warming potential approximately 20 times that of CO 2 (IPCC 2001). Controlling and monitoring the emissions of these gases is an essential element of any controlled landfill operation. Estimates of gas production rates in bioreactor landfills relative to conventional (i.e., Subtitle D) landfills vary, but previous investigations have indicated rates of landfill ga s production at landfill bioreactors between two (Reinhart and Townsend 1998) and seven (U.S. EPA 2005b) times higher than that at conventional landfills. As a result, it is critical to design gas collection systems at landfills operating as bioreactors to capture the expected additional LFG. The rate and quan tity of LFG generated is dependent on the mass and composition of waste as well as the moisture conditions within the landfill. Equation 2-4 describes the relationship of the predicted CH 4 generation over time with regard to the composition of the waste, disposed waste mass, and time.

17c Q CH 4 = L o R 

# ( e − kc

− e − kt 

# ) Equation 2-4 Where: Q CH4 = methane generation rate at time t (m 3 /yr); L o = methane generation potential of the waste (m 3 CH 4 /Mg waste); R = average annual refu se acceptance rate during the active life of the landfill (Mg/yr); k = methane generation rate constant (yr -1 ); = time since landfill closure (yr) and t = time of initial waste acceptance (yr), respectively.
As will be discussed later in ch apter 5, LFG generally consists of approximately 50 percent CH 4 and 50 percent CO 2 by volume, so to calculate the total LFG generated at a specific time, Equation 2-4 should be multiplied by 2. Of particular interest when assessing LFG generation with regard to la ndfill bioreactors are the parameters L o and k. The capacity to generate CH 4 generally depends on the organic content and moisture content of the waste (U.S. EPA 1998). As de scribed previously, operation as a landfill bioreactor by increasing moisture content of the waste may accelerate the deco mposition of the waste and therefore increase the value of k. These parameters can be estimated on a site-specific basis and implemented in the Landfill Gas Emissions Model Version 3.02 (LandGEM), developed by U.S. EPA, to predict LFG generation based on waste placement data and kinetic parameters. Since landfills operated as bioreactors are expected to generate LFG at a greater rate than dry tomb landfills , gas recovery systems at landfill bioreactors need to be designed to handle larger flow rate s than those at conventional landfills. The discussion thus far has mainly been on the anaerobic reactions that occur in landfill bioreactors. It is recognized that landfill bioreactor s can be operated as aerobic units by the controlled introduction of air into the waste after placement. Po tential issues regarding air additio n in bioreactor landfills include hydraulic limitations as well as subsurface fires. Jain et al. (2005) found that leachate recirculation had a significant impact on the air permeabili ty of MSW. One of th e regulatory concerns associated with aerobic landfill bioreactors has been the potential for subsurf ace fires from spontaneous combustion. Literature suggests that carbon monoxide (CO) production may be an indicator of subsurf ace fires (U.S. EPA 1998). The U.S. EPA’s Compilation of Air Po llutant Emission Factors (AP-42) cite s a default CO concentration of 142 ppm for MSW landfills; ho wever, it is noted that this value was based on data collected from a limited number of sites, and the data were classified with a qualifier of “poo r” (U.S. EPA 1998). A study at a landfill undergoing leachate recirculation and air addition in Florida found CO concentrations between 0-30 ppm in areas operating under anaerobic conditions, and CO concentrations up to 1,200 ppm in areas operating under aerobic conditions (Powell et al. 2006) . However, areas showing higher CO concentrations did not have elevated temperatures indicative of a su bsurface fire. A combination of CO and temperature monitoring is likely the most effective approach in evaluating the presence of subsurface fire.
MSW landfills with an actual or desi gn capacity equal to or greater than 2.5 million Mg of waste (or 2.5 million m 3 ) are subject to New Source Performance Standard s (NSPS) for air emissions, which require the collection of LFG and 95% destruction (by weight) of non-methane organic compounds (NMOCs), a class of compounds that depletes stratospheric ozone, cont ributes to global warming, and includes hazardous air pollutants (HAPs). Curren tly, specific regulations re garding anaerobic landfill bi oreactor LFG collection requirements are found in 40 CFR Part 63, Subpart AAAA. As a resu lt of these requir ements, landfill bioreactor facilities must comply with LFG collecti on requirements sooner than dry tomb landfills. Because of limited data availabl e for LFG emissions at aerobic land fill bioreactors, these systems are regulated in a similar manner to dry tomb landf ills under NSPS. The com pounds included in the monitoring program and the monitoring frequency may be determined on a site-specific basis and guided by local, state, and federal regulati ons pertaining to the site or by the goals of the landfill bioreactor owner/operator.

18

## Chapter 3. Site Description and Analytical Methods

3.1 Site Description and System Design
The OLRDF is located in Louisville, Jefferson County, Kentucky. The site , shown in Figure 3-1, is located on the north side of Outer Loop Road, immediately west of Interstate 65 with an approximate area of 316 hectares (780 acres). The site comp rises eight landfill units, designated Un its 1 through 8. Units 1, 2, 3, and 6 are inactive. Un it 4 is an active, permitted C&D debris land fill. Unit 8 is an active bioreactor landfill unit that is located to the north of Unit 7 and overlays parts of Units 7 and 4 (not shown in Figure 3-1). Waste placement in Unit 8 just started and will not be discus sed in this report. The fo cus of this study is on portions of Unit 5 and Unit 7, which are both Sub title D landfill cells; Unit 5 did not receive any waste during the study, while portions of Unit 7 received waste until 2005, as described later. The landfill bioreactor permit approval for this site was receive d from the Commonwealth of Kentucky, Kentucky Natural Resources and Environmental Protection Cabi net, Department for Environmental Protection in 2001 under Permit No. 056-00028. The OLDRF is owned and operated by WM and has b een used for waste disposal for approximately 35 years. The site is situat ed within the alluvial valley of the Ohio River; approximately nine miles southwest of River Mile 614. The area is generally flat with elevations averaging 139 m (456 ft) above mean sea level (MSL). The region is effectively enclosed by topographically elevated areas on the west, east, and south. Elevations range up to 229 m (750 ft) above MSL in areas surrounding the site. Topography and stream development in the area ha ve been modified by constructio n and development activities of the region. Because of the flat topography, the clayey nature of the soil, and the relatively low elevation, the area is naturally poorly drained. To enhance surface drainage for the development of the region, several engineered drainage channels have been constructed in the vicinity of the landfill. The channels drain toward the southwest, eventu ally discharging into the Ohio River. So me of the cells on the site are unlined and the entire site utilizes pumps to provide an inward gradient to groundwater flow into the site. The average yearly regional temperature is 13o C (55° F), ranging from -30 to 40o C (-21 to 103° F). Average annual precipitation is approximately 113 cm (44 in.) of rainfall, plus approximately 38 cm (15 in.) of snow (U.S. Department of Commerce 2004). The average number of days with precipitation is 125 annually, with 47 days being associ ated with thunderstorms. The prevailing wind in the area is generally from the south. Details regarding the meteorological conditions at the site, w ith particular focus on precipitation as it relates to the moistu re balance analysis at the site, will be presented in la ter sections.
In contrast to some of the landfill bioreactor research described in Chapter 2, the demonstrations at the OLLB are large-scale research efforts at a full-scale operational la ndfill. The study covers a total of approximately 20.2 hectares (50 acres ) in lined landfill units. In this study, three types of landfill units were studied. The first unit was a control that was developed and filled as a conventional Subtitle D landfill without any intent of supplemental liquid addition (Control ce lls). The second type of unit in this study was a landfill that had a piping network (for liquids and air add ition) installed as waste was being placed (As-Built landfill bioreactor ce lls). The third was a Subtitle D landfill that was retrofitted with a moisture addition piping network to allow the recirculation of liquids (Retrofit landfill bioreactor cells). Each of the three units was divided into subcells to provid e a quasi-“duplicate” of th e test cell, which will be discussed in more detail in subsequent sections.

3.1.1 Control Landfill Cells

3.1.1.1 General Unit 7 is located in the western por tion of the OLDRF as shown on Figure 3-1. Portions of that Unit, designated 7.3A and 7.3B, have been designated as the Control cells for the study. These cells have been operated as conventional Subtitle D (i.e., dry tomb) la ndfills since initial waste placement began in 1998.

19Figure 3-1 Outer Loop Landfill Site Map

The cells were monitored and sampled in a similar manner to the landfill bior eactor units. The Control cells consist of two paired landfill cells (i.e., Contro l cell A and Control cell B) that are not hydraulically separated. However, a barrier layer was installed between the Control and As-Built units. The layer consists of low permeability clay along with an additional layer of permeable tire chips.
The Control cells were selected to represent waste decomposition in a conventional Su btitle D landfill without liquids addition and with st andard vertical LFG extraction wells . Waste placement in the Control cells commenced in 1998 and ceased in 2004. At the start of the la ndfill bioreactor project in 2001, solid waste in the Control cells was approx imately three years old. Prior to the start of the project in 2001, approximately 342,000 Mg (380,000 tons) of solid wast e was present in the Contro l cells. Additional waste was placed in Control cell A and Control cell B during the project to bring the cells to final grade.

3.1.1.2 Leachate Coll ection System (LCS) The Control cells were lined with a smooth 60 mil HDPE geomembrane on the base areas while textured 60 mil HDPE geomembrane was used on the perimeter slopes (2.5H:1V). A 10 oz . non-woven geotextile cushion layer was placed over the bottom liner and a double-sided geocomposite was placed over the side slope. A 0.3 m (1 ft) granular leach ate drainage blanket covered the base areas, and was constructed with non-carbonate coarse gravel. In swal es in the valleys in the Control cells , an 8 in. standard dimension ratio (SDR) 11 perforated HDPE pipe was laid on a gravel bed then covered with gravel. This coarse 3⁄4 in. to 1 1⁄2 in. gravel material had the same basic characteristic s as the remainder of the leachate drainage blanket, except it was a larger grade. Each leachate collection line terminated on the west side of the Control cells into a sump underlain by the compos ite liner system. A pumping system was installed at each sump, which

20provides a means to pump leachate that accumulates. These pumping systems discharge into a force main that terminates at the site’s leachate treatment plant.

3.1.1.2 Gas Collection As with any “dry tomb” landfill cell, each Control cell contained two vertical gas collection wells installed in the center of the solid waste ma ss. LFG collection wells were connected to header lines that connect to the flare station. The LFG collection headers maintained separate gas coll ection fields in the Control cell. The first gas collection header collects landfill gas mainly generated in Control cell A, while the second collects the gas generated in Control cell B. Before merging together, gas flow in each header line is measured via an orifice plate installed within the pi pe. A probe was also installed in each gas collection well to allow for LFG sample collection, as will be discussed in Section 3.3.

3.1.2 As-Built Landfill Bioreactor Cells

3.1.2.1 General
The As-Built cells are also located w ithin Unit 7, designated 7.4A and 7.4B, as shown in Figure 3-1. The cells were designed as a sequential aerobic-anaerob ic landfill bioreactor (also refe rred to as “hybrid”). The rationale behind the sequential ap proach was to promote the rapid decomposition of eas ily degradable organic matter in the aerobic stage of treatment with the intent of reducing the amount of fermentable organic matter entering the anaerobic stage. This strategy may shorten the acid-generating phase of anaerobic waste decomposition and result in a more rapid onset of methanogenesis. Thus, the objective of these cells was to examine the impact of increased mo isture content and waste aer ation on the degradation of recently placed MSW. It is no ted that the aim of this research is not to examine the performance of WM’s patented design (U.S. Patent No. 6,283,676 B1) but rather the effect of liquid addition and sequential aerobic/anaerobic operation on th e solid waste de gradation. The As-Built cells were divided to provide quasi-“dupli cates” that are hydraulically separated with a clay barrier [0.3 m (1 ft)]. A layer of shredded tires wa s placed onto the clay barrier to act as a conduit for leachate to reach the bottom liner. The placement of shredded tires was discontinued in the first quarter of 2004 since the layer acted as a conduit for LFG and rainwater migration. A schematic of the configuration discussed here is presented in Figure 3-2. The initial waste placement in As-Built cell A and As-Bu ilt cell B occurred during June and October of 2001, respectively as presented in Figure 3-3. As of June 2005, approximately 1,461,000 Mg (1,610,000 tons) of solid waste had been placed in the two As-Built cells [i.e., 59 0,000 Mg (650,000 tons) in As-Built cell A and 871,000 Mg (960,000 tons ) in As-Built cell B]. The cells we re constructed in 4.6 m (15 ft) vertical lifts for a total of seven different lifts. Based on mass, solid waste comprised approximately 71 % while biosolids from a municipal wastewater tr eatment plant, C&D debris, and soil accounted for approximately the remaining 13%, 9.2% and 6.8%, respectively.

3.1.2.2 Leachate Collection System Since the As-Built cells are a part of Unit 7, the LCS is similar to that of the Control cells as described in section 3.1.1.2. Each leachate collection line drains into a sepa rate sump underlain by the composite liner system. A pumping system was installed at each sump, which provides a means to pump leachate from each sump as it accumulates to a designated depth. As with the Control cells, these pumping systems discharge into a force main that terminates at the site’s leachate treatment plant.

3.1.2.3 Piping Network Installation The design of the As-Built cells li quid addition, air injection, and LF G extraction piping network utilized one piping network for delivering liquids and a second piping network for distributing air and extracting LFG. The sequence and method of placing the pipes is described below. The first 4.6 m (15 ft) thick lift of waste was placed on top of the leachate collection system, followed by placement of the first pipe layer (comprised of 10.2 cm (4 in.) ID perforated HD PE) on the top surface of the first lift. The pipes were placed at approximately 18. 5 m (60 ft) wide intervals across the top surface of

21Figure 3-2 Solid Waste Placement in th e As-Built Landfill Bioreactor CellsCumulative Mass (tons)

0 2e+5 4e+5 6e+5 8e+5 1e+6

As-Built Cell A As-Built Cell B

3/1/01 9/1/01 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
Date Figure 3-3 Solid Waste Placement in As -Built Landfill Bioreactor Cells

22the waste. The length of these pipes was dependent on the length of the individual lift within th e cell. The pipes were perforated with three 1 cm (0.4 in.) diameter holes at 120° intervals around th e pipe, with holes spaced at 0.3 m (1 ft) intervals along the length of the pipe. The pipes were covered with a permeable media generally consisting of tire ch ips; however, an alte rnative design was intr oduced in the second quarter of 2004 that involved placi ng a thin horizontal layer of perm eable material on top of each lift to facilitate liquid recirculation, air addition, and LFG collection. Each end of the perforated piping has a section of solid pipe of the same diameter that is su bsequently connected to a common 10.2 cm (4 in.) ID manifold pipe. After placement and installation of the first lift and pipe layer, a second lift was placed, followed by a second piping layer. In this design , the uppermost lift of wast e is aerated, while the lift immediately below this lift receives liquid, and LFG is extracted from all deeper lifts.

3.1.2.4 Air Introduction Air addition began once a completed lift was placed on t op of the piping layer (e.g., the second lift was aerated by injecting air through the fi rst layer of piping). Each 4.6 m ( 15 ft) lift of waste received injected air beginning approximately 30 days after lift placement. This was accomplished by connecting the header pipe for a particular lift to a high-volume air compressor. Compressed air was continuously pumped into each new lift at a maximum rate of 57 m 3 /min (2,000 ft 3 /min) for a period ranging from 30 to 90 days. The following three set points were desi gnated as the threshold points for the cessation of air introduction: (i) waste mass temperature of 71 °C (160 °F); (ii) net change in waste mass temperature of 6.7 °C (12 °F) within 24 hours; and/or ( iii) after 90 days of air introduction. Se t points (i) and (ii) were established to prevent elevated waste temperatures and potential subsu rface fire caused by aerobic decomposition. In all cases, air introduction stoppe d whenever one of these se t points was reached. Un til January of 2006, 9.6 × 10 7 m 3 (3.4 × 10 9 ft 3 ) of air was injected into As-Built cell A while 4.8 × 10 7 m 3 (1.7 × 10 9 ft 3 ) of air was injected into As-Built cell B. Based on the total mass of solid waste placed in the cells, As-Built cell A received almost five times more air per unit mass of waste [162 m 3 /Mg (6,300 ft 3 /ton)] compared to AsBuilt cell B [32 m 3 /Mg (1,260 ft 3 /ton)].

3.1.2.5 Liquids Addition Liquids addition into the As-Built cells was accomplished through the piping network previously described. Liquids were gravity-fed through one of four on-site ta nks to the lift of waste di rectly below the lift being aerated. The addition of liquids was controlled and included intermittent dosing depe nding on several daily and seasonal factors including the apparent moisture c ontent of the in-place waste, forecasted precipitation events, and recent moisture additions. Liquids added into the As-Built cells included a combination of industria l liquids as well as recirculated leachate obtained from other lined units at the OLDRF site. The indus trial liquids added to the As-Built cells consisted mainly of beverage waste (75 percen t); oily wastewater (10 percent); paint waste (9 percent); ink water (2 percent); and other (4 percent). Volu mes and chemical proper ties of the industrial liquids are presented in Table 3-1. A summary of th e liquids injection history as related to moisture balance in the As-Built cells is pr ovided in Section 4.2. Figures 3-4 and 3-5 presen t the volume of industrial liquids added to As-Built cell A and As-Built cell B, respectively. Figures 3-4 and 3-5 show that the majority of industrial liquids were ad ded to the As-Built cells after March 2004. Table 3-1 Chemical Properties of Industrial Liquids Liquid Type State Percent of Total 1 pH BOD (mg/L) COD (g/L) NH 3 -H (mg/L) Beverage waste Liquid 75 NA NA NA NA Oily wastewater Liquid 10 5.7 – 8.1 NA 19 – 134 1 - 95 Paint waste Liquid & Sludge 9 5.0 – 9.1 NA 2.4 – 16 1 - 550 Ink water Liquid 2 9.9 NA 38 163 Food waste Liquid & Sludge 1 4 1,800 33 NA Other (septic, municipal, food, beverage, cleaning) Liquid & Sludge 3 3.6 -7 NA NA NA

1: This represents the approximate percentage of th e total industrial liquids added to the As-Built cells.

231.6e+7 60000Cumulative Added Liquid Volumes (cubic meters)

50000

40000

30000

20000

10000

0Cumulative Added Liquid Volumes (gallons) 1.4e+7

1.2e+7

1.0e+7

8.0e+6

6.0e+6

4.0e+6

2.0e+6

0.0 Total Added Liquids Industrial Liquids

3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/ 04 3/1/05 9/1/05
DateCumulative Added Liquid Volumes (cubic meters) 1.6e+7 60000

50000

40000

30000

20000

10000Cumulative Added Liquid Volumes (gallons) 1.4e+7

1.2e+7

1.0e+7

8.0e+6

6.0e+6

4.0e+6

2.0e+6

0.0 Total Added Liquids Industrial Liquids

0 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
Date Figure 3-4 Cumulative Industrial and Total Added Liquids in As-Built Cell A

Figure 3-5 Cumulative Industrial and Total Added Liquids in As-Built Cell B

3.1.2.6 Gas Collection LFG was collected in deeper waste lifts through the pipes previously u tilized for air addition. In general, a series of LFG collection pipes were connected to the active gas collection sy stem once air addition and liquids addition were no longer occurring in a particular lift. The LFG collection started in April of 2003 for the As-Built cells.

243.1.3 Retrofit Landfill Bioreactor Cells As part of this research, an exis ting “dry tomb” MSW landfill cell was re trofitted with a piping network to operate as a bioreactor landfill cell. Apart from the main objective of examining the effect of liquids on solid waste degradation, research in the cell aimed to assess the effects of n itrate-enriched leachate on landfill bioreactor performance. Previous research co ncluded that leachate r ecirculation was shown to increase the ammonia concentration within landfill bioreactor cells. Ammonia rich leachate from the OLRDF was treated in a sequencing ba tch reactor aerobically to convert a mmonia to nitrate. This leachate containing nitrate was then recirculated in the Retrofit area. As nitrate-containing liquid moves through the upper sections of the landfill bioreactor cells, denitrifying bacteria convert nitrate to N 2 gas, resulting in a net loss of nitrogen fr om the landfill. The Retrofit bioreactor landfill Unit (Un it 5) is located in the northern portion of the OLRDF complex, as shown in Figure 3-1. The Unit consists of four separate landfill subce lls (designated 5.1A, 5.2A, 5.1B and 5.2B) and is permitted as a Subtitle D cell with a single composite clay liner . Each subcell is equipped with its own leachate collection line, which allows sampli ng at each distinct leachate sump. To provide for hydraulic separation between the test areas and because of geometric similarities, Unit 5.1A (the most southern cell, referred to as Retrof it cell A) and Unit 5.2B (the most nort hern cell, referred to as Retrofit cell B) were selected for this st udy. Liquid introduction also occurred in the two middle cells of the Retrofit unit (5.1B and 5.2A) as will be discussed later. Leachate analysis results presented in Section 4.4 is for the leachate collected from the sump of cell 5.1A and 5.2B (referred in Section 4.4 as Retrofit cell A and Retrofit cell B, respectively). Waste placement was initiated in July 1995. Approximately 1,752,000 Mg (1,931,000 tons) of solid waste were in place by October 1997, of which 32 percent wa s special waste consisting mainly of contaminated soils, while the remaining 68 percent was MSW. Between October 2000 and March 2001, an additional 136,000 Mg (150,000 tons) of MSW was placed in th e cell to adjust the final top deck elevations as presented in Figure 3-6. During 2004, daily cover ma terial was stockpiled on the western side of the cell, as presented in Figure 3-6. Since the cell did not receive new waste during the study, a 1 m thick long-term clay cover was placed on the Unit. A 5 cm thick laye r of cover soil was then placed on top of the clay cover and the cell was seeded with grass for erosion control.

3.1.3.1 Leachate Collection System The LCS consists of a collection layer (Figure 3-7), se parator geotextile, collection pipe, and cleanout riser. The collection layer consists of a 0.3 m (1 ft) thic k layer of sand on the 10H:1V cell floor and 2H:1V intercell berms, and geocomposite on the 3H:1V perime ter berms. Perforated pipes used to collect the leachate were surrounded with coarse aggregate an d wrapped by a nonwoven geotextile. The collection pipes discharge via perforations in the pipe into the Retrofit cell’s sumps. Also, collection pipe cleanout risers connect to the collection pipes in the cell sumps. The pumped discharge from the sumps is connected into the site’s leachate management system via a for ce main. Underlying the LCS in the Retrofit unit is a geomembrane that was constructed of 60 m il HDPE that was smooth on both sides.

3.1.3.2 Liquids Addition
Construction of the Retrofit bior eactor cells took place between Ma rch and May 2001 and included installation trenches, moisture distribution and gas co llection piping, thermocouples, and ORP probes. To increase the moisture content of the Retrofit cells, 26 horizontal infiltration galle ries were constructed. The trenches were 4.6 to 6 m (15 to 20 ft) deep, 1 m (3.3 ft) wide and were constructed just below the surface of the landfill (Figure 3-8). The trenches were spaced approximately 18.3 m (60 ft ) apart as presented in Figure 3-8. Each trench contains two 7.6 cm (3 in.) ID HDPE pipes, one for liquid introduction and the other for gas collection. Each pipe was perforated with 0.95 cm (0.4 in.) holes every 0.3 m (1 ft) along the length of the pipe. The trenches we re bedded with tir e chips and backfilled with permeable material like shredded tires to allow for liquid an d gas flow as illustrated in Figure 3-8. The liquid introduction lines were then connected through a solid 7.6 cm (3 in.) ID riser pipe to a valve and then to an HDPE liquid distribution header. Temperature and ORP probes were also installed at the end of each horizontal trench.

25Figure 3-6 Solid Waste Placement in the Retrofit Landfill Bioreactor Cells

26Figure 3-7 Bottom Liner Configuration of the Retrofit Unit

Nitrified leachate was added intermittently depending on daily and seasonal factors, apparent moisture content of the in-place waste, forecasted precipitation ev ents, recent moisture add itions as well as operator judgment. The ultimate goal was to achieve uniform in filtration while avoiding l eachate outbreaks, seeps, and the reduction of performance of the LFG collectio n. Initial liquid intro duction commenced in March 2002 and additions oc curred steadily until October 2002 when liquid introductio n stopped for a period of about 10 months. During that time, no liquids were added to the cells except for limited amounts of infiltration from pr ecipitation through the long-t erm cover system. After this 10-month period, the injection episodes continued until spring 2006 (with the exception of a 4-month period between January 2005 and April 2005). The cumulative liquids injection is presented in Fi gure 3-9, and is discussed in more detail in Section 4.2.
The main source of moisture added to the Retrofit cells was nitrified leachate which was treated ex-situ by

- chemolithotrophic bacter ia that converts NH 4 + to NO 3 as presented in Equation 3-1.
NH 4 + + 2O 2 → NO 3 − + 2H + + H 2 O Equation 3-1 Laboratory research suggests that denitrifying bacteria that are al ready present in the waste mass will utilize the NO 3 - as a terminal electron acceptor to form both N 2 and small amounts of N 2 O gases. Liquid sources other than leachate, including water from the landfill underdrain, sedimenta tion pond, and other liquid waste streams as allowed by the permit, were used to augment the supply of leach ate. These liquid sources were pumped from the sequential batch reactor (SBR) pr etreatment plant to holding tanks that were then used to distribute leachate to the trench es via a force main and manifold system.

275e+6Cumulative Added Liquid Volume (cubic meters)

15000

10000

5000Cumulative Added Liquid Volume (gallons)

4e+6

3e+6

2e+6

1e+6 Retrofit Cell 5.1A Retrofit Cell 5.1B Retrofit Cell 5.2A Retrofit Cell 5.2B

0 0 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
Date Figure 3-8 Cross-Sectional Layout of Liquid Introduction Trench

Figure 3-9 Cumulative Liquid Introduction into Retrofit Bioreactor Landfill Unit by Subcell

283.1.3.3 Gas Collection In addition to the horizontal gas collection trenches disc ussed previously, there are 17 vertical gas collection wells installed in the Retrofit cells, as shown in Figure 3-10. These ve rtical LFG collection wells served the dual purpose of collecting LFG and penetratin g layers of daily soil cover. Probes for measuring temperature and ORP were installed during ver tical gas well installati on in 2000. Additional thermocouples and ORP probes were installed during 2001 when the Retr ofit cells were retrofitted with the additional gas collection and the li quid distribution piping network.
LFG collection wells and trench es were connected to two header lines th at connect to the flare station. The LFG collection headers main tained separate gas collection fields in the Retrofit unit. The first gas collection header collects landfill gas mainly generated in cells 5.1A and 5.1B, while the second collects the gas generated in cells 5.2A and 5.2B. Before merging together, gas flow in each header line can be measured via an orifice plate installed within the pipe . A probe was also installed in each header pipe to allow for LFG sample collection, as will be discussed in Section 4.3.


### 3.2 Sample Procedures and Methods
The primary objective of this research was to assess the effect of liquids addition on wast e decomposition. The type and frequency of each analysis follows most of the guidelines presented in Chapter 2, as well as in the First Interim Report. A discussi on is presented herein of the sa mpling locations and sample handling and analysis protocols. Methods used in the project meet specifications for U.S. EPA-approved methodologies and are appropriate for the parameter a nd matrix of interest. The methods are generally either from SW 846 (U.S. EPA 1996) or Standard Methods for the Examination Water and Wastewater (APHA 1999). Equipment used for field sampling is calibrated and maintained acc ording to manufacturer's guidelines. Redundant solid waste probes (i.e., temper ature and ORP) were empl oyed to circumvent any premature instrument failure. Coll ected leachate samples were placed in a cooler and maintained at 4  ̊ C (40 °F) using crushed ice and were shipped overnight to the appropriate laboratory for analysis. During the study, inclement weather and component equipment failure affected sampling frequency and the sampling periods were altered to accom modate such occurrences.

3.2.1 Leachate Sampling Leachate was collected monthly from each of the landfill bioreactor and Control cells. The design of the landfill units (i.e., paired cells) was such that, w ith the exception of the Control cells, each cell was hydraulically separated at the base from the surrounding cells. The Retrofit cells were separated by approximately 305 m (1,000 ft) late rally. The As-Built cells were cons tructed with a clay barrier to hydraulically separate As-Built cell A and As-Built cell B. Leachate samples were collected directly from the tap on the leachate riser line fo r each subcell. Switching the riser pump from automatic mode to manual mode (i.e., turning the pump on manually) prior to purging and sampling was shown to be an effective method for ob taining an adequate volume of leachate. Leachate sample bottles were collected in the following sequence: COD, BOD, VFAs, pH, temperature, VOCs, SVOCs, TKN, ammonia-N, nitrate-N, nitrite-N, metals, calcium, sodium , ortho phosphate, total phosphate, chloride, sulfate, TOC, DOC, TDS and specific conductance. Methods used to analyze for these parameters are presented in Table 3-2, while the list of VOCs and SVOCs examined ar e presented in Tables 3-3 and 3-4, respectively. To obtain a repr esentative sample, effluent was purged prior to actual sample collection in accordance with the approved sampling protocol in the QAPP.

29Figure 3-10 Liquid Introduction and Gas Collection System in Retrofit Landfill Bioreactor Cells

3.2.2 Municipal Solid Waste Sampling MSW samples were collected biennia lly (every two years) through discrete borings advanced into the landfill units. The sampling lo cation protocol requir ed dividing the cell into six sections and then dividing each section into approximately 3 m × 3 m (10 ft × 10 ft) grids and randomly choosing a square within the grid. This boring location protocol was used for assi gning the sampling locations in the remaining sections. Within each unit, the same 3 m × 3 m (10 ft × 10 ft) grid was used for subsequent sampling events. Sampling at the edges of the cell was avoided. In addition, if drilling at a selected location could not be initiated (e.g., known location of asbestos placement) or if the boring could not be comp leted (e.g., an impenetrable object was encountered) at a selected location, a randomly selected square adjacent to the original location was selected. The following protocol was used for MSW sampling during the study: (i) the surface elevation of the sampling location was established; (ii) a drill rig equipped with an ap proximately 0.9 m (3 ft) diameter bucket auger was used to drill into the solid waste ma ss; (iii) each location was sampled in approximately 3 m (10 ft) long vertical sections; (iv) a composite sa mple was obtained at each 3 m (10 ft) long depth interval at each boring location; (v) the initial 3 m (10 ft) of material at each location was generally discarded as it predominantly contained cover soil (or at least a disproportionate amou nt of soil); (vi) as the boring advanced, each 3 m (10 ft) long sample was ex tracted from the auger and the appearance of the waste was observed and recorded; and (vii) at least fi ve composite samples were collected from each of six sampling locations in each sampling tim e period. As such, a minimum of 30 MSW samples were collected for each cell on a biennial basis. This sa mpling schedule is summarized in Table 3-5. Temperature and ORP of the in-place MSW were measured by Type T-thermocouple probes connected to a PC-driven data collection system. The data communications system for the probes was designed to record the temperature and ORP for each probe once every 30 minutes. These data were used to construct a control chart for each probe. Probes installed in the Retrofit cells were mostly temporary, and as such were removed, inspected, reconnected, and replaced (as necessary).

30Table 3-2 Leachate Sampling Parameters and Schedule Parameter Frequency Method Head on liner Continuous Pressure Transducer Leachate production Continuous Flow Meter COD Monthly SM 410.4 (1) BOD Monthly SM 405.1 Ammonia-nitrogen (NH3-N) Monthly SM 350.1 Ortho Phosphate / Total Phosphate Monthly SM 365.2 (c) Nitrate-nitrogen (NO3-N) Monthly SM 300.1 Nitrite-nitrogen (NO2-N) Monthly SM 300.1 Total volatile fatty acids Monthly GC MS Temperature Monthly Thermometer TOC and DOC Monthly U.S. EPA 9060 pH Monthly U.S. EPA 9045 VOC Quarterly SW-846 8260(B) SVOC Quarterly SW-846 8270(B) TKN Quarterly Total dissolved solids Quarterly SM 160.1(C) Sulfate Quarterly SM 300.1 Chloride Quarterly SM 300.1 Potassium Quarterly Conductance Monthly Electrode Metals (As, Ba, Cd, Ca, Cu, Cr, Fe, Pb, Mg, Hg, K, Na, Se, Ag, Zn) Quarterly SW-846 6010

Notes: Standard Methods (APHA 1999).

Table 3-3 Volatile Organic Compound s Examined in Landfill Leachate Chemical Compound Name Chemical Compound Name Chemical Compound Name Ethylbenzene Carbon Tetrachloride 1,1,1-Trichloroethane Styrene 2-Hexanone Bromomethane cis-1,3-Dichloropropene 1,1,1,2-Tetrachloroethane Chloromethane trans-1,3-Dichloropropene Acetone Iodomethane 1,4-Dichlorobenzene Chloroform Dibromomethane 1,2-Dibromoethane (EDB) Benzene Bromochloromethane Acrolein 1,1,2,2-Tetrachloroethane Chloroethane 1,2-Dichloroethane 1,2-Dichlorobenzene Vinyl chloride Acrylonitrile 1,2-Dibromo-3-Chloropropane DBCP Methylene chloride Vinyl acetate 1,2,3-Trichlorop ropane Carbon Disulfide Methyl Isobutyl Ketone Et hyl methacrylate Bromoform Toluene Methyl Ethyl Ketone Dichlorobromomethane Chlorobenzene 1,1,2-Trichloroethane 1,1-Dichloroethane trans-1,4-Dichloro-2-butene Total Xylenes 1,1-Dichloroethene 2-Chloroethylvinyl ether cis-1,2-Dich loroethene Trichlorofluoromethane Dibromochloromethane Dichlorodi fluoromethane Trichloroethene Tetrachloroethene 1,2-Dichloropropane trans-1,2-Dichloroethene

31Table 3-4 Semi Volatile Organic Comp ounds Examined in Landfill Leachate Chemical Compound Name Chemical Comp ound Name Chemical Compound Name
4-Nitroaniline Thionazin Pentachlorophenol 4-Nitrophenol Methyl parathion 2,4,6-Trichlorophenol Benzyl alcohol Phor ate 2-Nitroaniline N-Nitrosopiperidine Disu lfoton 2-Nitrophenol 4-Bromophenyl phenyl ether Isodrin 2-sec-Butyl-4,6-dinitrophenol 2,4-Dimethylphenol Benzo(a)pyrene Naphthalene N-Nitrosomethylethylamine 2,4-Dinitrophenol 2-Methylnaphthalene Cresol, p- Chlorobenzilate 2-Chloronaphthalene 1,4-Dichlorobenzene Famphur 2-Naphthylamine 4-Chloroaniline Dibenzo(a,h) anthracene Methapyrilene p-Phenylenediamine 2-Acetylaminofluorene 3,3'-Dichlorobenzidine Cresol, m- Cresol, 4,6-Dinitro-O­ 4-Aminobiphenyl 2,2'-Oxybis(1-Chloropropane) 1,3-Dichlorobenzene N-Nitrosodi-n-butylamine Phenol N-Nitrosodiethylam ine N-Nitros opyrrolidine Bis(2-chloroethyl) ether Parathion Safrole Bis(2-chloroethoxy) methane 3-Methylcholanthrene Cresol, oBis(2-ethylhexyl) phthalate Benzo( a)anthracene 1,2-Dichlorobenzene
Di-n-octyl phthalate 7,12­ Dimethylbenz(a)anthracene o-Toluidine Hexachlorobenzene 2,3,4,6-Tetrachlorophenol 2-Chlorophenol 3,3'-Dimethylbenzidine Cresol, p-Chloro-m- 1,2,4,5-Tetrachlorobenzene Anthracene p-Dimethylaminoazobenzene 2,4,5-Trichlorophenol Isosafrole Dimethoate Acetophenone 1,2,4-Trichlorobenzene 2,6-Dinitrotoluene Nitrobenzene 2,4-Dichlorophenol Pentachlo robenzene 3- Nitroaniline 2,4-Dinitrotoluene Phenacetin sym-Trinitrobenzene Diphenylamine Ethyl methane su lfonate 5-Nitro-o-toluidine 1,4-Dioxane N-Nitrosodimethylamine m-Dinitrobenzene 0,0,0-Triethylphosphorothioate N-Nitroso-Di-n-propylamine N-nitrosodiphenylamine Pyrene Methyl methanesulfonate Fluorene 1,4-Naphthoquinone Hexachloroethane 2,6-Dichlorophenol Dimethyl phthalate 4-Chlorophenyl phenyl ether Hexachlorobutadiene Dibenzofuran Hexachlorocyclopent adiene Benzo(k)fluoranthene 1-Naphthylamine Isophorone Acenaphthylene Kepone Pentachloronitr obenzene Chrysene Hexachloropropene Acenaphthene Diallate Benzo(ghi)perylene Diet hyl phthalate Pronamide Indeno(1,2,3-cd)pyrene Di-n-butyl phthalate Butyl benzyl phthalate Benzo(b)fluoranthene Phenanthrene Fluoranthene

32Table 3-5 Municipal Solid Waste Sampling Schedule Parameter Collection Frequency ORP Daily Temperature Daily Solid waste settlement Quarterly Waste moisture Biennially pH Biennially Cellulose and lignin content Biennially Organic solids Biennially BMP Biennially

3.2.2.1 Analytical Methods for Solids Analysis The procedures that were used to process solid samples have been fully described in the QAPP presented in the First Interim Report, and are summarized here. Samples were excavated as described above. After excavation, a composite sample was mixed and then gr ab samples were placed in a 19 liter (5 gallon) bucket for shipment for analysis. U pon receipt, samples were stored at 4 °C (40 °F) to preclude additional biodegradation. Samples were initially shredded to a width of about 20 mm (0.8 in.) and a length of 50 to 100 mm (2 to 4 in.). Afte r shredding, samples were ag ain stored at 4 °C (40 °F) until they could be dried. Approximately 1 to 2 kg (2.2 to 4.4 lb) of each sample was dried for analysis of moisture content and solids composition. After drying, samples were ground using a Wiley Mill to pass a 1 mm (0.04 in.) screen and then re-dried prior to anal ysis. When pieces of metals and/or textiles were encountered in the sample, the materials were cut into small pieces prior to grinding. Alternately, small pieces of metal were substituted for larger pieces to maintain a similar metal concentration.
The concentrations of cellulose and hemicellulose were analyzed by subjecting a sample to a two-stage acid hydrolysis (Petterson and Schwandt 1991). After wa shing a sample with a 2:1 mixture of toluene and 95 percent ethanol to remove lip ids, a solid sample was su bjected to a 72 percent H 2 SO 4 primary hydrolysis followed by a 28 fold dilu tion for the secondary hydrolysis. These hydrolyse convert the cellulose and hemicellulose to their component simp le sugars. Cellulose is a polymer of glucose, while hemicellulose is a polymer of arabinose, galactose, mannose, and xylose. The solubilized sugars were analyzed by using a high performance liquid chromatograph equipped with a pulsed amperometric detector. Sugars were separated with a Carbo-Pac PA1 co lumn manufactured by Dionex Corp., Sunnyvale, CA. The mobile phase was 50 percent NaOH with 40 .4 mL of 1.5 M sodium acetate added per liter of 50 percent NaOH eluent. Water was circulated around the column to damp en temperature variations. Fucose was used as an internal standard to correct for losses during the hydrolysis procedure (Davis 1998). A new high performance liquid chromatograph system was used for the samples analyzed in 2005. The same procedure was used although th e detector was a pulsed electrochemi cal detector. In addition, it was no longer necessary to circulate wate r to maintain column temperature wi th the new liquid chromatograph. The solids that remain ed after the acid hydrolysis consisted of organic and inorganic materials. These solids were then combusted for 2 hrs at 550 °C (1,022 °F) with the weight loss on combustion considered lignin (Petterson and Schwandt 1991). In all likelihood, this procedur e slightly over predicted the amount of lignin as the material “counted” as lignin also in cluded some plastic, rubber, and leather that were not removed during the acid hydrolyses. Organic solids concentrations were de termined by the weight loss of the dried samples after combustion for 2 hrs at 550° C (1,022 °F). All so lids analyses were perfor med in duplicate and aver age data were utilized for the regression analyses described below. Samp les were reanalyzed in a ll cases where the relative percent deviation (RPD), as defined in equation 3-2, exceeded 20 percent.
standard deviation RPD = × 100 Equation 3-2 mea n

333.2.2.2 Biochemical Methane Potential Samples were placed in 160 mL capacity serum bottle s after which a biochemical methane potential (BMP) medium was added (Wang et al. 1994) . Bottles were then inoculated using 15 mL of a methanogenic consortium that were maintained on freshly ground MSW. Serum bottle s were filled and maintained under anaerobic conditions with an 80/20 mixture of N 2 and CO 2 gas and incubated at 37 °C (99 °F). After 60 days of incubation, the majority of the gas volume was measured by using a 60 mL capacity plastic syringe. A 5 mL capacity wetted glass syringe was then used to measure the remaining overpressure. BMP results were corrected for CH 4 production attributable to the inoculum and to standard temperature and pressure. The concentration of CH 4 was measured by using a gas chromatograph equipped with a thermal conductivity detector and a CTR1 co lumn manufactured by Alltech, De erfield, IL. BMP assays were conducted in triplicate and five rep licates were conducted to measure CH 4 production associ ated with the inoculum. If the RPD exceeded 20 percent, then sa mples were reanalyzed unless two replicates were consistent, in which case th e outlier was discarded.

3.2.2.3 Use of Cellulose Plus Hemicellulose to Lignin Ratios Historically, daily and inte rmediate covers were applied to each landfill cell a nd the amount of soil was estimated to range from 10 to 25 percent of the waste volume. Thus, there is the potential to include soil in refuse samples that are excavated from landfills. The soil component of the sample will dilute the cellulose, hemicellulose, and lignin concentrations in th e sample. The most effective way to eliminate the effect of soil dilution is to analy ze data based on the cellulose plus hemicellulose to lignin (CH:L) ratio rather than the concentration of either the cellulose or hemicellulo se. While advantageous from the perspective of eliminating the influe nce of the soil, this method has th e disadvantage that the initial CH:L ratio of the buried refuse is often unknown or only know n within a range. The va riation in the CH:L ratio for fresh refuse was presented in Table 2-5. This ra tio may be different when all of the different waste streams entering a land fill are considered.

3.2.4 Landfill Settlement
Settlement of the landfill was monito red on a quarterly basis as a se condary indication of decomposition and stability using a GPS measurement of surface el evation. GPS surveyin g was performed using a Trimble Model 4800 for the settlement plates within each cell using the followi ng protocol: (i) every sampling event was initialized from a known point that was controlled at ± 5 cm (2 in.) for horizontal and vertical control (if sampling within a cell was interr upted, the system was reinitialized from the known point before sampling resumed); (ii) sampling was initiated if the root mean square reading from the system

was ≤ 10 cm (4 in.); and (iii) the positional dilution of precision as measured on the device was ≤ 6 before the GPS system could be used. In addition, one of every 20 settlement plates measured by the GPS unit was randomly selected and re-tested. These results we re compared to the limits established in the QAPP presented in the First Interim Report. If the thre e aforementioned conditions were met, the positional accuracy of the GPS readings was reported to be suffic ient to meet the analytical needs of the study. A detailed landfill settlement analysis is not included in Chapter 4, as waste filli ng occurred con tinuously in the Control cells until 2004, and waste filling occurred in the As-Built cells until 2005. Since waste filling occurred in these cells thro ughout the monitoring period, an assess ment of total settlement and a correlation between waste decomposition and settle ment could not be made. Monito ring of the settlement points will continue at the site and a correlation between waste settlement and waste degradation will be investigated as part of the Final Report.

3.2.5 Landfill Gas Sampling

3.2.5.1 Gas Collection System Sampling The LFG sampling schedule is presented in Ta ble 3-6. Primary LF G constituents (i.e., CH 4 , CO 2 and O 2 ) were measured weekly, whereas trace gases (i.e., NMOCs, including individua l HAPs) were measured quarterly. Surface emissions monitoring of CH 4 was conducted quarterly, if required. Table 3-7 indicates the specific HAPs (which are a subset of NMOCs) that were analyzed fo r in each sample. Similar to the leachate sampling protocol, LFG sampling occurred at one point per cell. The LFG extraction wells are

34located systematically across the cell, approximately equidistant from each other, to provide relatively uniform extraction coverage. Table 3-6 LFG Sampling Schedule Parameter Collection Frequency LFG flow Weekly LFG percent composition (CH 4 , CO 2 , O 2 ,) Weekly HAPs Quarterly Surface emission monitoring (CH 4 ) Quarterly

LFG analysis was also performed for CH 4 , CO 2, and O 2 using a CES Landtec GEM 2000 as outlined in the QAPP. This instrument is a portab le field gas analyzer and uses a se lf-compensating infrared detector. After calibration, the instrument wa s connected to a gas sampling port on the selected gas header using flexible plastic tubing. Gas was drawn into the instru ment by an internal pump. Results are date and time stamped and logged by the instrument. Gas standards for CH 4 , CO 2 and O 2 were also analyzed twice daily on the day of sampling to evaluate accuracy objectives as outlined in the QAPP. Concentration readings for CO 2 and CH 4 were to be within 15 percent of the actual concentration or of the sample duplicate; the tolerance for O 2, was to be ± 30 percent. LFG analyses were made by electronically logging three consecutive measurements at a freq uency of one measurement per minute of LFG composition and flow. Flow rate, differential pressure, static pressure, and te mperature were recorded on the field instrument at each sample location (i.e., well, late ral, header, and flare). The mean value for each of these measurements was recorded and selected as the reported value for each parameter of interest. LFG samples were also collected for laboratory analysis of CH 4 , CO 2 , N 2 and O 2 by U.S. EPA Method 3C, NMOCs were sampled and analyzed by U.S. EPA Met hod 25C, and HAPs were an alyzed as identified in U.S. EPA Method TO-14. For the gas samples obtaine d for external laboratory analysis, samples were collected in 6 liter capacity SUMMA® pa ssivated stainless steel canisters.

Table 3-7 HAPs Analyzed in Quarterly LFG Sampling Chemical Compound Chemical Co mpound Chemical Compound Dichlorodifluoromethan e Toluene Vinyl acetate Chloromethane trans-1,3-Dichloropropene cis-1,2-Dichloroethene 1,2-Dichloro-1,1,2,2­ tetrafluoroethane 1,1,2-Trichloroethane 2-Butanone (MEK) Vinyl chloride Tetrachloroethene Chloroform Bromomethane 2-Hexanone 1,1,1-Trichloroethane Chloroethane Dibromochloromet hane Carbon tetrachloride Trichlorofluoromethane 1,2-Dibromoethane (EDB) Benzene 1,1-Dichloroethene Chlorobe nzene 1,2-Dichloroethane Carbon disulfide Ethylbenzene Trichloroethene 1,1,2-Trichloro-1,2,2­ trifluoroethane Xylenes (total) 1,2-Dichloropropane
Acetone Styrene Br omodichloromethane Methylene chloride Bromoform 1,3,5-Trimethylbenzene trans-1,2-Dichloroethene 1,1,2,2-Tetr achloroethane 1,2,4-Trimethylbenzene 1,1-Dichloroethane Benzyl chloride 1,3-Dichlorobenzene 1,2,4-Trichlorobenzene 4-Ethyltoluene 1,4-Dichlorobenzene
Hexachlorobutadiene 4-Methyl-2-pentanone (MIBK) 1,2-Dichlorobenzene cis-1,3-Dichloropropene

35

### 3.3 Data Processing and Statistical Analysis

3.3.1 Sample Dating and Statistical Analysis The primary goal of the study at the OLLB was to evaluate the extent to which the operation of a landfill as a bioreactor accelerated refuse decomposition. The CH :L will be used as a metric to compare samples excavated from different landfill cells . However, waste age must also be considered as refuse decomposes over time, resulting in a change in th is ratio (Barlaz 2006). Thus, six year old refuse from a Control cell may (or may not) be more decomposed than six mont h old refuse from a bioreactor landfill cell. To evaluate the effect of decomposition over time, it was necessary to establish the age of the solid waste at the time of sample collection. The age of the wast e represented by each sample was estimated from site survey data that were specific to the location of each boring. The survey data provided historical waste placement information that allowed an estimate of th e age of each sampling interval for each boring. Typically, survey data were available to document the date of waste filling through th e entire depth of the landfill. In some cases, it was not possible to estimat e the age of waste from a specific boring. In such cases, that data were excluded from the analyses presen ted in this section. Over the entire data set, 3.4 percent of the samples were excluded because of a lack of information regarding waste age. To evaluate reproducibility between ce lls, a given characteristic of the refu se (e.g., moisture content) was initially compared between cells by using a t-test in Microsoft Excel®. All of these analyses were conducted using a two-sided t-test, assuming unequal varian ce in the data. In genera l, data sets were only considered significantly diffe rent if the results of the t-test indicat e a probability (p-value ) of less than 0.05, meaning that there is a 95% probability that a difference is rele vant in consideration of sample variability. To evaluate decomposition as a function of time, the CH:L, BMP and organic solids data for a specific cell were plotted as a function of waste age, and a linear regression was conducted. The slope of the best fit line from the linear regression was then evaluated to determine whether the slope was significantly different from zero by calculating the 95 percent conf idence intervals for each slope using the regression analysis tool in Microsoft Excel. If the 95 percent confidence interval included a slope of zero, then the slope was judged to be sta tistically similar to zero. A slope of zer o means that there was not a significant decrease in the measured parameter (e.g., BMP) with re spect to waste age. Slope s for all linear regressions and the corresponding 95 percent c onfidence intervals are pr esented in Section 4.1. The same procedure has been used in previous research (Barlaz et al. 2004). Diagnostic plots were anal yzed to ensure linear regression model assumptions were met and to investigate the influence of individual points upon the fit. A plot of residuals versus fitted values was used to assess the assumption of constant error variance. A normal qua ntile-quantile plot was used to assess the assumption that errors were distributed normally. A re siduals-versus-leverage plot was used to investigate the influence of individual points on the regression fit. As illustrated by Equations 2-2 and 2- 3, the biodegradation of cellulose and hemicellulose is linked to CH 4 production. As described in Section 4.3, the predictive CH 4 generation model is exponential. Thus, the CH:L and BMP are more likely to de crease exponentially as the remaini ng substrate (i.e., cellulose and hemicellulose) becomes less bioavailable. In this respect, a first order decay model may be a more appropriate mathematical representation of solids decomposition as a function of waste age. A linear regression model was used here only as a method to rapidly assess a large amount of data and to assess statistically whether the calculated slopes were signif icantly less than zero. The calculated model is not intended for use in a predictive mode based on the analys es presented in this secti on. It should also be noted that a linear model is not id eal when working with a ratio (CH: L). However, of the three solids decomposition parameters evaluated (C H:L, BMP, and organic solids), CH:L is the onl y one that eliminates the influence of soil dilution. Thus, it was judge d important to use this ra tio in a linear regression. A multiple linear regression analysis was also conducted . Five variables were considered (waste age, sampling date, sample elevation, moisture content, and temperature). First, the correlation between the five variables was investigated. Next, multiple parameters were evaluated, incl uding both indivi dual parameters (e.g., moisture content), and parameter interactions (e .g., sampling date × elevatio n). Best-fit models were developed using R, a statistical modeling software ( www.r-project.org ), and the results were inspected

36qualitatively using both the adjusted R 2 and the significance of the parameter modeled. The adjusted R 2 is comparable to R 2 for the linear regression analys is in that it is corrected for the used multiple parameters.

3.3.2 Moisture Balance Calculations As a part of this study a moisture balance was conducted to provide confirmation of the “apparent” or “anticipated” increase in the bulk moisture content of th e waste. Waste moisture content was also directly measured during the biennial solid waste sampling events. An evaluation wa s made to compare the calculations to the measured values. The Control and Retrofit cells were each considered as a single unit due to the lack of any hydraulic se paration between their sub cells. As-Built cells A and B, howe ver, were considered as individual units because of the cl ay barrier separating them. The moisture balance calculations were performed for the all the cells between March 2002 and December 2005. Parameters used in preparing the moisture bala nce included: (i)volumes of recircul ated leachate; (ii) supplemental liquid addition; (iii) estimated infiltration; (iv) estimated surface run-on; and (v) measured leachate generation. Moisture generated as a re sult of biological or chemical in teractions within the landfill cells was neglected as a source of additional liquids in the moisture balance calculations . Moisture leaving the landfill through the ga s collection system as conde nsate was also not included in the moisture balance calculations. These two sources were not expected to si gnificantly influence the resu lts of the analysis (less than approximately 1500 cubic meters per cell) expressed in %.
March 2002 was chosen as the start date because solid waste samples were collected from each cell during that month and analyzed for (among other parame ters) moisture content. Since the sampling was conducted prior to liquids addition in the bioreactor cells, the mean moisture content from the March 2002 solid samples was used as the initial moisture conten t in the moisture balance calculations. Thus, the estimated initial moisture content (on a wet weight basi s) was 32.5 percent for th e Control cells, 37 percent for the Retrofit cells, 42 pe rcent for As-Built cell A, an d 43 percent for As-Built cell B. Typical moisture content on a wet weight basis (i.e., mass of water divided by mass of wet waste) of incoming waste can range from 15 to 40 percent (Tchobanoglous 1998). It is acknowledged that these moisture content values are on the high end of the “typical ” range of waste moisture content reported by Tchobanoglous (1998). Given the relatively wet climate of Lo uisville and the fact that the data utilized are from a single sampling event, the actual moisture content of as-received wast e may be less than what was measured in the March 2002 samples. However, using these data provided the best startin g point for estimating an initial moisture content amount for use in the mo isture balance calculations. With regard to the parameters used in performing the mo isture balance, the volume of recirculated leachate, the volume of supplemental liquids added, and the volume of the generated leachate were recorded daily. Precipitation at the site was recorded daily at an on-site weather statio n. To account for infiltration, runoff and evapotranspiration, paramete rs were estimated using the H ydrologic Evaluation of Landfill Performance (HELP) model (Schroeder et al. 1994). The type of cover material, thickness of the cover material, slope of the waste surface, an d slope length were selected as input parameters to the HELP model. Only the surface of each landfill cell was modeled in HELP to calcu late runoff, evapotranspiration, and infiltration. Details regarding sel ection of the specific input paramete rs were obtained using available survey maps and by communication with the OLRDF’s si te manager. For the Control cells, Retrofit cells, and sloped surfaces of the As-Built cells, the cover material was assumed to be clay with a hydraulic conductivity of 1 x 10 -6 cm/s (4 x 10 -7 in/s). The thickness of the clay cover was assumed to be approximately 1 m (3 ft). The flat areas of the As-Built cells consiste d of a cover material made of an approximately 0.3 m (1 ft) thick layer of compost with a hydraulic conductivity of about 4 x 10 -2 cm/s. The compost cover material was replaced by a 1 m (3 ft) thick layer of clay in August 2004. The slope of the landfill units was 4 horizontal to 1 vertical (4H:1V) and the length of the slope was assu med to be 76 m (250 ft). Additional details on the moisture balance parameters for th e different units are presented in Table 3-8. The topography of the landfill units and the ra tio of the sloped versus flat areas of the landfill units was estimated using contour inte rvals from the survey maps that we re available from March 2002 to December 2005. These estimates are presented in Tabl e 3-9 (As-Built cells) and Ta ble 3-10 (Retrofit and Control cells). It is noted that because the day-to-day details of waste filling and covering were not available, the inputs to the HELP model are best es timates, and the results shoul d be treated as such. Run-on was the only parameter that was not recorded or calculated directly; rather, it was estimated based on runoff values output by the HELP model and the geometry of each cell. Run-on from Unit 7.2 (located

37to the north of As-Built cell A) to As-Built cell A, run-on fr om Control cell A to Control cell B, and run-on from the Control cell to As-Built cell B was included in the estimated/calculated in filtration volumes. Runon percentage was estimated using the parameters presented in Table 3-8. Run-on from unit 7.2 to Control cell A was assumed to be 25 percent of rainfall. This was based on an average value of runoff in the sloped and flat surfaces of unit 7.2. It is noted that prior to late 2003, mo st of the run-on volu me did not infiltrate to the As-Built cells, but rather wa s channeled directly to the LCS, as presented in survey maps and reported by WM. This was due to the inclusion of a “column” of rubber tire chips that were placed between: (i) unit 7.2 and As-Built ce ll A; (ii) As-Built cell A and As-Bu ilt cell B; and (iii) As-Built cell B and Control cell B. The channeling was assumed to cease after the first quarter of 2004 when tire chips were no longer placed at the edges of the cells.
Table 3-8 Moisture Balance Parameters

Parameter Control & Retrofit Sloped Area Control & Retrofit Flat Area As-Built Sloped Area As-Built Flat Area Runoff (percent) 51 49 51 3.5 Evapotranspiration (percent) 47 48.5 47 60 Infiltration (percent) 2 2.5 2 36
Table 3-9 Area Distributi on of As-Built cells
Date\Units As-Built cell A Sloped Area, m 2 (acres) As-Built cell A Flat Area, m 2 (acres) As-Built cell B Sloped Area, m 2 (acres) As-Built cell B Flat Area, m 2 (acres) Mar 02-Oct 02 12141(3.0) 39659 (9.8) 0 36017 (8.9) Nov 02-Feb 03 10117 (2.5) 18211 (4.5) 3237 (0.8) 38850 (9.6) Mar 03- May 03 12950 (3.2) 16187 (4.0) 8094 (2.0) 32375 (8.0) Jun 03-Nov 03 12141 (3.0) 18211 (4.5) 14164 (3.5) 32375 (8.0) Nov 03-Oct 04 12141 (3.0) 18211 (4.5) 14164 (3.5) 46539 (11.5) Nov 04 – Apr 05 12141 (3.0) 18211 (4.5) 40469 (10) 22662 (5.6) June 05-Dec 05 566 (1.4) 13759 (3.4) 40469 (10) 22662 (5.6)
Table 3-10 Area Dist ribution of Retrofit and Control Units Date\Units Retrofit Sloped Area, m 2 (acres) Retrofit Flat Area, m 2 (acres) Control Sloped Area, m 2 (acres) Control Flat Area, m 2 (acres) Mar 02-Dec 05 99553 (24.6) 19425 (4.8) 33994 (8.4) 0

3.3.3 Statistical Analysis of Leachate Parameters Multiple linear regressions were utili zed to quantify trends in the leach ate parameters of interest. Two explanatory variables were used in the regression fits, sampling date and a phase-shifted sine function of the sampling date (to capture a possible seasonal componen t). The sine variable was phase-shifted to have a maximum on September 1st and minimum on March 1st. For the regression fits, the parameter Sampling Date is the number of days between the sampling date and 1/1/1970. While not presented, several diagnostic plots were an alyzed to ensure linear re gression model assumptions were met and to investigate the influence of individual po ints upon the fit. A plot of residuals versus fitted values was used to assess the assu mption of constant error variance. A normal quantile-quantile plot was used to assess the assumption that er rors are distributed normally. Resi dual versus leverage plot was used to investigate the influen ce of individual points on the regression fit.

38

## Chapter 4. Solid Waste and Moisture Content Analysis

A data validation report, which confirms that data presented herein were collected according to the specifications outlined in the QAPP in the First Interim Report and provide s validation of data presented in this section, is included as Appendix A.


### 4.1 Solid Waste Analysis
The objective of Section 4.1 is to present and analyze data on the composition of solids excavated from the Control, As-Built, and Retrofit cells of the OLLB between 2000 and 200 5. Major samplin g events were conducted in 2000, 200 2, 2003, and 2005. In add ition, fresh waste entering th e Control and As-Built cells was characterized in 2001 and 2004. The solids co mposition data from the OLLB are presented and discussed in Section 4.1.1. To the authors’ knowledg e, the data presented in this section represent the largest data set of refuse samples from a single site available to date.

4.1.1 Results The primary focus of this section is to present and analyze data on th e composition of the solids excavated from the Control, As-Built, and Re trofit areas. The discussion focu ses on the followi ng two questions:
1. Do the solids composition data s upport the assumption that repli cate cells actually behaved as replicates? This applies to a comparison of results from replicate areas of the Retrofit, Control, and As-Built cells. Data from cells 5. 1A and 5.1B are referred to as Retrofit cell A, and data from cells 5.2A and 5.2B are referred to as Retrofit cell B.
2. Do the solids composition data s upport the hypothesis that the ope ration of a landfill cell as a bioreactor accelerates the biodegradation of orga nic matter as described by equations 2-2 and 2-3. It is recognized that there are inherent differences in the Retrof it and As-Built landfill bioreactors. As such, some caution is wa rranted in analysis of the results.
The discussion in this section addr esses these two questions from the perspective of the solids composition data only. Later in this report, the solids, gas, and leachate data are considered together to evaluate whether there is evidence that operation as a bioreactor landfill resulted in accelerated refuse decomposition.

4.1.1.1 Solids Decompositio n in the Retrofit cell The first assessment of “data reproducibility” is to compare the calcula ted waste age from Retrofit cells A and B (i.e., 5.1 and 5.2). If there is a significant difference in the wa ste age between cells that cannot be explained by the cells’ fill histories, it suggests that the procedure used to date the waste is not entirely appropriate. In comparing the inte rcell variability, the waste age in Retrofit cell A was older than that in Retrofit cell B by 222, 89 and 89 days in 2000, 2002 and 2005, respectively (Table 4-1). This difference was only significant (p < 0.05) in 2000 when the waste was youngest and small differences would be more significant. The actual difference may be important fo r waste less than five years old, but becomes less important over time. The waste age da ta are encouraging as they are reasonably consis tent. This suggests that the solids decomposition data can be assessed with respect to the calcu lated waste age. Another way to assess differences in waste age between cells would be to evaluate the distribution of the sample age data as presented in Figure 4-1. As described in Chapter 3, the Retrof it cells are reported to be composed of approximately 32 percent soil. While this will not affect the CH:L, it will reduce the BM P, which is expre ssed on a “per dry mass” basis. As presented in Table 4-1, there are significant differences between Retrofit cells A and B in 2005 for CH:L, BMP, and organic solids. The 2005 trends ar e consistent in that all three measures of solids decomposition suggest that the solids from Retrofit cell A are more decomposed relative to samples from Retrofit cell B. However, this observ ation is not consistent with the m easured moisture contents, which are statistically similar between Retrofit cells A and B in 2005. The decomposition rate data, which are described below, do not support the hypothesis that the rate of decomposition is different between Retrofit cells A and B.

39Table 4-1 Summary of Waste Composit ion Data for the Retrofit cell
Sampling

Year Subcell Statistical Parameter Waste Age at Time of Sampling

(days) Moisture (%) CH:L BMP (mL CH 4 /dry

gm) Organic Solids

(%)2000 A (5.1) average 1,470 34.7 1.17 31.3 37.3 stnd. dev. 191 6.3 0.69 21.5 12.6 B (5.2) average 1,248 35.0 1.31 43.2 43.6 stnd. dev. 135 6.0 0.88 34.9 15.8 p-value 9.38E-08 0.87 0.44 0.087 0.0632002 A (5.1) average 2,077 37.7 1.20 25.9 33.1 stnd. dev. 612 7.5 0.65 20.4 10.4 B (5.2) average 1,988 36.5 1.12 23.5 32.7 stnd. dev. 342 7.7 0.46 15.4 10.6 p-value 0.41 0.49 0.53 0.56 0.882005 A (5.1) average 3,044 38.0 0.72 15.5 25.0 stnd dev. 537 6.4 0.29 11.4 8.2 B (5.2) average 2,955 40.1 0.98 25.4 31.6 stnd. dev. 296 6.52 0.55 20.4 13.0 p-value 0.44 0.21 0.02 0.02 0.0155.1 (2000)5.2 (2000)5.1 (2002)5.2 (2002)5.1 (2005)5.2 (2005)1000 2000 3000 4000Waste Age (days) n=34 n=42 n=45 n=44 n=36 n=27

Note: The boxes encompass data between the 25 th and 75 th percentiles and the solid line in the box is the median. As illustrated, while the medians are close, there is more vari ability in the waste age in Retrofit cell A relative to Retrofit cell B in 2005. The whiskers represent the highest and lowest data points that are less than 1.5 × (75 th percentile – 25 th percentile) from the edges of the box, while the open circles represent data outside of this range. Figure 4-1 Summary of Waste Age for Retrofit Cells A (5.1) and B (5.2)

40A graphical depiction of trends in the relationship between waste age and CH:L, BMP, and organic solids are presented in several figures, included in Appendix B. Figure 4-2 depicts the combined Retrofit cell data, with no distinction between Retrofit cells A and B. This was done to utilize the largest data set possible, minimizing the confounding effects of other variables that may affect refuse decomposition. Additional analysis of the CH:L and BMP results in which the data were separated by area are presented in Appendix B. The statistics associated with the linear regressi on analysis are presented in Table 4-2. For analysis purposes, regression modeling was chosen. There are several limitati ons to the use of linear regression models including whethe r a linear model is most appropriate, whether waste age is the most important independent variable, and whether multiple variables should be consid ered concurrently. As discussed in Chapter 3, a first order decay model may be a more appropriate mathematical representation of solids decomposition. However, as illustrated in Figure 4-2, the calcula ted exponential function is similar to the linear model for CH:L. Further assessment of exponential models is beyond the scope of this interim report, as the results suggest that ad ditional data collection and analysis ov er the next severa l years is more critical.
When all of the CH:L data are comb ined for the Retrof it Unit, the slope of the regression is significantly less than zero at the 95% confidence le vel despite the high degree of scatte r. This is also the case for the combined data for BMP and organic solids. A negative slope means that there is a statistically significant decrease in the value of a solids decomposition parameter with waste age. The BMP is a more sensitive measure of decomposition as it tracks changes in biodegradable solids only, while the organic solids includes both biodegradable organics (e.g., cellulose) and non-degradable organic solids (e.g., HDPE). With respect to the trends in decomposition as presen ted in Figure 4-2, the low correlation coefficients indicate that a single variable linear regression m odel does not completely characterize the measured trends. This is reasonable as th ere are many other variables affec ting refuse decomposition. Multiple parameter regressions are discussed below.
When Retrofit cells A and B are analyzed separately (as presented in Table 4-2) for CH:L and BMP, the slopes are significantly less than zero for both measures in Retrofit cell A but only for BMP in Retrofit cell B. The results do not provide sufficient evidence to pursue further analyses of the data in which Retrofit cells A and B are treated differently as the larger data set associ ated with the combined area is more robust. Many factors other than waste age are expected to be correlated with refuse decomposition including, for example, moisture content, pH, subs trate quality and temperature. To evaluate whether moisture content alone was a better indicator of decomposition, the BMP and CH:L were plotted as a function of moisture content in Figure 4-3. As illustrated, moisture content was not a good pred ictor of the extent of decomposition. Two explanations for this result are that (i) the samples that contained elevated moisture were not wetter long enough for moistu re to influence decomposition at the time of sampling; and (ii) other confounding variables precluded a clear trend. Ultimately, when all of the data from the Retrofit cells are considered, the increase in the average moisture content between 2000 and 2005, from 34.7% to 38.6%, was statistically significant (p<0.05) but not so dramatic as to be the only variable controlling either the CH:L or BMP. The use of multiple parameter regression models is discussed in Sec tion 4.1.2.

4.1.1.2 Solids Decompositio n in the Control cell As presented in Table 4-3, there was not a significant difference in waste age between samples obtained from Control cells A and B in 2000, 2003, and 2005. Both the median waste age and the range were quite similar (Figure 4-4). The 225-day difference associat ed with the 2002 sampling, as well as the different ranges for Control cells A and B, was surprising and likely reflects some imprecision in the sample dating process (Figure 4-4). There were no significant differe nces in any of the waste monitoring parameters at any of the sampling periods, with th e exception of the moisture content in 2005, when the average moisture content of samples from Control cell B was about four percent higher than samples from Control cell A (Figure 4-5). The moisture data fo r Control cell A in 2000 shows some particularly wet samples relative to Control cell B. The two wettest samples have moistu re contents of 49.6 an d 56.4%, respectively. However, the corresponding CH:L (2.84 and 1.49) and BMP (114.9 and 75.8 ml CH 4 /dry gm) do not suggest that these two samples were well decomposed relative to the bulk of the samples (Figures presented in Appendix B). As the characteris tics of Control cells A and B were quite similar, all subsequent analyses

41CH:L

0 1 2 3 4 5 y = -0.0002x + 1.5695 R 2 = 0.0738

y = 1.3524e -0.0002x R 2 = 0.0601

1000 2000 3000 4000

Linear Waste Age (days) Exponential Table 4-2 Slopes and Their 95% Confid ence Intervals for Linear Regressions Between W aste Age and CH:L, BMP, and Organic Solid s in the Retrofit, Control, and As-Built Cells

Cell CH:L BMP Organic Solids Lower Level Slope Upper Limit Lower Level Slope Upper Limit Lower Level Slope Upper Limit
Retrofit cells (A

& B) -3.3E-4 -2.3E-4 -1.E-4 -1.4E-2 -9.7E-2 -5.8E-3 -8.3E-3 -6.2E-3 -4.1E-3

Retrofit cell A -3.9E-4 -2.6E-4 -1.2E-4 -1.3E-2 -8.8E-3 -4.5E-3 Not Analyzed Retrofit cell B -3.4E-4 -1.5E-4 -3.0E-5 -1.7E-2 -9.7E-3 -2.5E-3

Control

cells -2.6E-4 -9.5E-4 -7.0E-5 -1.8E-2 -1.1E-2 -4.5E-3 -5.3E-3 -2.1E-3 1.2E-3

As-Built cells (A

& B) -8.3E-4 -5.1E-4 -1.9E-4 -1.6E-2 -3.2E-2 9.2E-3 -1.4E-2 -8.1E-3 -2.4E-3

As-Built

cell A -1.2E-3 -7.2E-4 -2.5E-4 -3.5E-2 -1.9E-2 -2.6E-3 -1.7E-2 -1.0E-2 -3.3E-3

As-Built

cell B -7.5E-4 -3.0E-4 -1.5E-4 -2.3E-2 -4.3E-3 1.4E-3 -1.5E-2 -6.0E-4 3.3E-3

Figure 4-2 Relationship between CH:L and Waste Age in the Retrofit Cells

42BMP (mL CH4/dry gm)

0 50 100 150 200CH:L

0 1 2 3 4 5

CH:L y = 0.0143x + 0.5663 R 2 = 0.0243 BMP y = 0.6568x + 3.2994 R 2 = 0.0373

20 40 60 80 Moisture Content (%)

BMP CH:L Linear - CH:L Linear - BMP500 1000 1500 2000 2500 3000Waste Age (days) n=59 n=27 n=40 n=31 n=40 n=29 n=30 n=287.3A (2000)7.3B (2000)7.3A (2002)7.3B (2002)7.3A (2003)7.3B (2003)7.3A (2005)7.3B (2005) Figure 4-3 Relationship between Moisture Content and Solids Decomposition in the Retrofit Cells

Figure 4-4 Waste Age Profile for the Contro l Cell A (7.3A) and Control Cell B (7.3B)

43BMP (mL CH4/dry gm)

0 20 40 60 80 100 120 140 160 180 200CH:L

0 1 2 3 4 5 CH:L y = 0.0292x + 1.1404 R 2 = 0.0366 BMP y = 1.927x + 3.9506 R 2 = 0.0888

10 20 30 40 50 60 70 Moisture Content (%)

BMP CH:L Linear - CH:L Linear - BMP20 30 40 50 60 70 80% Moisture n=59 n=30 n=39 n=31 n=40 n=31 n=30 n=287.3A (2000)7.3B (2000)7.3A (2002)7.3B (2002)7.3A (2003)7.3B (2003)7.3A (2005)7.3B (2005)

Figure 4-5 Moisture Content Profile for th e Control cells at Each Sampling Time

Figure 4-6 Relationship between Moisture Content and Solids Decomposition in the Control Cells

44Table 4-3 Summary of Waste Co mposition Data for the Control cells and Assessment of Cell Replicatio n
Sa mpling

Year Subcell Statistical Parameter Waste Age at Time of Sampling (days) Moisture (%) CH:L BMP (mL CH 4 /dry gm) Organic Solids

(%)2000 A average 479 35.3 2.63 102.3 67.19 stnd. dev. 50 6.8 0.93 37.5 16.35 B average 470 33.9 2.52 96.93 63.54 stnd. dev. 30 6.15 1.10 38.15 16.84 p-value 0.44 0.33 0.63 0.53 0.332002 A average 1,000 32.4 1.34 34.4 41.7 stnd. dev. 509 5.3 0.58 24.0 11.6 B average 1,225 32.6 1.42 37.8 46.0 stnd. dev. 366 4.6 0.45 22.2 15.0 p-value 0.042 0.84 0.50 0.55 0.182003 A average 1,526 36.4 2.05 59.54 44.7 stnd. dev. 422 6.0 0.69 29.58 12.4 B average 1,534 36.2 2.23 68.4 49.7 stnd. dev. 463 6.0 0.65 25.8 13.8 p-value 0.94 0.91 0.18 0.19 0.112005 A average 1,657 36.0 2.68 88.6 71.2 stnd. dev. 750 4.9 0.88 30.2 12.1 B average 1,655 40.1 2.52 82.5 73.0 stnd. dev. 730 5.6 0.86 30.1 11.9 p-value 0.99 0.01 0.47 0.45 0.57 of trends presented in this section are based on the comb ined data set (i.e., all of the data from the Control cells were combined to form a single data set). The relationship between waste age and CH:L, BMP, and organic solids are presented in Appendix B, and the statistics associated with the linea r regression analyses presented in these figures are presented in Table 4-2. The slopes of the regressions are only significan tly less than zero at the 95 % confidence level for the BMP, but not for the CH:L and organic solids. The limitations to the linear regr ession model that were described in the previous section apply to the solids da ta in the Control cells as well. As was the case for the Retrofit cells, moisture conten t was not a better predictor of wa ste composition than was waste age (Figure 4-7). The major purpose of the Control cells was to compare tr ends to the Retr ofit and As-Built landfill bioreactor cells. Further disc ussion of these results are presented later in this section.

4.1.1.3 Solids Decompositio n in the As-Built cells A comparison of the waste age, moisture content, CH:L, BMP, and or ganic solids for As-Built cells A and B is presented in Table 4-4. In contrast to the Control area, there were several significant differences between As-Built cells A and B. With reference to Table 4-4, any compar ison that exhibits a p-value of < 0.05 is considered to represent significantly differe nt data sets. Thus, the waste age was consistently different and all measures of solids decomposition were different in 2003 and 2005. As described in Section 3.1.2.2, As -Built cell A received approximately five times more air than As-Built cell B. Given all of the differences, the data for As-Built cells A and B will be analyzed separately throughout this section. In 2001 (and early 2002) and 2004, samples were only collected to characterize the fresh refuse added to each cell. As such, the samples sets were small (n=6) and tren ds with respect to samp le date should not be inferred. These samples, howeve r, were used to calculate L o (methane generation potential of the waste (m 3 CH 4 /Mg waste)) for gas generation model as is pres ented in Chapter 5. There was a significant

45difference in the moisture content in 2004 between the refuse added to As-Built cells A and B. Although both sets of samples were collected in May, 2004, thei r age is different and pres umably more moisture was added to As-Built cell B over the 76-day residence time of these samples in the landfill. The waste age increased in As-Bu ilt cell A between 2003 and 2005, whereas the average waste age was statistically similar between 2003 an d 2005 in As-Built cell B. This wa s consistent with the addition of fresh waste to As-Built cell B betwee n 2003 and 2005. A co mparison of the waste age profiles for As-Built cells A and B is presented in Figure 4-7. Trends in the relationship between waste age and CH:L, BMP, and organic solids are presented in Appendix B, and the statistics associat ed with the linear regre ssion analysis for these figures are presented in Table 4-2. For As-Built cell B, the linear regression slopes were not significantly different from zero for any of the monitoring parameters (i.e., CH:L, BMP, and organic solids). As the calculated average waste age in As-Built cell B was only 545 days, thus a clear trend was not apparent. Th is is a very short time interval over which to observe any refuse decomposition. For As-Built cell A, the sl opes of all measures of decomposition, CH:L, BMP and organic solids were significantly less than zero (Table 4-2) which indicates that decreases in CH:L, BMP and organic solids with waste age were all statistically significant ev en though the average waste age was relatively young (730 days). The steeper slopes for the solids data for As-Built cell A relative to As-Built cell B were consistent with the fact that As-B uilt cell A received more air. The pr esence of air would have stimulated aerobic decomposition which is faster than anaerobic decomposition. Thus, the data suggest that the additional air added to As-Built cell A accelerated de composition. As was the case for the Retrofit and Control cells, the moisture content was not a useful predictor of waste decomposition (Figures 4-8 and 4-9). This is not to suggest that moisture content is not a significant vari able, but rather that the relatively young waste age coupled with other confounding variables mask a simple statistical relationship. As for the other test areas, these results suggest that additional monitoring in the coming years is warranted to be able to assess results and trends over a longer time period.7.4A (2002)7.4B (2002)7.4A (2003)7.4B (2003)7.4A (2005)7.4B (2005)0 500 1000 1500Waste Age (days) n=24 n=27 n=42 n=52 n=32 n=31

Figure 4-7 Waste Age Profile for As-Built Cells A and B

46BMP (mL CH4/dry gm)

0 50 100 150 200CH:L

0 1 2 3 4 5 CH:L y = -0.0221x + 2.5792 R 2 = 0.057 BMP y = -0.4149x + 68.86 R 2 = 0.017

15 25 35 45 55 65 Moisture Content (%)

BMP CH:L Linear - CH:L Linear - BMP 4.1.2 Multiple Linear Regression Models Linear regression analyses using eith er waste age or moisture content as the independent variable indicated that neither of these parameters was able to explain th e observed variation in CH:L, BMP or organic solids. This is reflected in the correlation coefficients pres ented with each linear regression. These coefficients were typically below 0.1 and never exceeded 0.13. In conducting a methodical search of potential single parameter relationships using moisture content, waste age, sampling date, sample elevation, and temperature, it was found th at all variables except temperature were about the same in their ability, or inability in this case, to explain the observed trends in CH:L , BMP or organic solids. As a result, multiple linear regression analyses were conducted in an atte mpt to better explain the observed variation in solids decomposition monitoring parameters. Subsequent work with temperature as a third variable did not improve the two variable (age, moisture) models, while the use of elevation offered slight impr ovements. Specifically, when elevation was used as the third variable for the same twenty four models, six had an adjusted R2 below 0.1, twelve had an adjusted R2 of 0.1 to 0.2 and six had an adjusted R2 of 0.27 to 0.50. Finally, work was conducted to explore models that included a sample date and an elev ation term. The logic for this interaction was that it might account for waste settlement. While this mode l did offer an improved ad justed R2, the physical meaning of this term is not clear and the extent of settlement would actually re flect decomposition of waste under the sample, and not the sample itselfs. Thus, no further discussion of this model is presented. The best multiple linear regression model was determined to be: Decomposition Parameter = f (Moisture Percen t + Waste Age + Elevation) Equation 4-1 In summary, the use of multip le linear regression analysis validates th e significance of mo isture content as a parameter that controls waste decomposition. However, given th e number of other factors that affect decomposition, even a multiple parameter model could not account for most of th e variability in the solids decomposition parameters.

Figure 4-8 Relationship between Moisture Conten t and Solids Decomposition in As-Built Cell A

47BMP (mL CH4/dry gm)

0 50 100 150 200CH:L

0 1 2 3 4 5 BMP y = 0.0527x + 49.567 R 2 = 0.0006 CH:L y = 0.0009x + 1.6349 R 2 = 0.0003

20 40 60 80 Moisture Content (%)

BMP CH:L Linear - CH:L Linear - BMP Figure 4-9 Relationship between Moisture Conten t and Solids Decomposition in As-Built Cell B

4.1.3 Summary of Solids Decomposition The objectives of this section were to: (i) assess reproducibility between the cells and (ii) evaluate whether the solids composition data support the concept that operation of a bior eactor landfill can accelerate solids decomposition relative to a traditional landfill. The waste age is signi ficantly older in the Retrofit cell relative to the As-Built and Control ce lls. As such, trends th at include the influence of waste age should be most apparent in the Retrofit cells. However, as refuse decomposes the nature of the remaining degradable organic matter changes. Thus, the refuse in th e As-Built and Retrofit bior eactor landfills cannot be assumed to be the same. Analysis of cell reproducibility was important as it sh owed significant differences between As-Built cells A and B. Given the impracticalities associ ated with the operation of a full-scale landf ill as a research site, it is not surprising that the cells were not perfect replicat es however, this project will continue utilizing during the lifetime of this CRADA. As all solids data could be analyzed as a function of waste age, the need for replication was less important than cases where waste age is difficult to a ssess. In the case of the OLLB, it was possible to assign a waste age to individual sample s on the basis of landfill f ill records, a capability not afforded at many other study sites. The available solids compositio n data document significan t decreases in degradable solids as a function of waste age in the Retrofit cell. The average waste age in Retrofit cells A and B in 2005 was 3,044 and 2,955 days, respectively. In contrast, the average waste age for Control cells A and B in 2005 was 1,657 and 1,655 days, respectively. Thus, there is less time for trends to become apparent in the Control cell relative to the Retrofit cells. In 2005, the average moisture contents were similar in the Retr ofit and the Control cells, although the recirculation of leachate in the Retrofit cells woul d be expected to provide some stimulation even if the average mo isture contents are similar. The slope of the CH:L and organic solids linear regressi on lines for the Retrofit ce lls were greater (i.e., more negative) than that for the Control cells as woul d be expected given that the Control cells were not operated to accelerate decomposition. However, the slopes of the BMP linear regression lines for these two

48Table 4-4 Summary of Waste Comp osition Data for the As-Built cells and Assessment of Cell Replicatio n

Sa mpling

Year Subcell Statistical Parameter Waste Age at Time of Sampling

(days) Moisture (%) CH:L BMP (mL CH 4 /dry

gm) Organic Solids

(%)2001 & Early2002 A average 36 40.0 1.54 57.7 62.4 stnd. dev. (1) 4.5 0.77 18.5 12.1 B average 72 45.8 3.10 84.2 82.6 stnd. dev. (1) 7.0 0.66 22.3 4.2 p-value (1) 0.12 0.00 0.05 0.002002 A average 290.3 41.9 0.96 26.6 41.9 stnd. dev. 155.01 9.19 0.39 12.20 5.96 B average 207.5 41.5 1.00 20.3 37.5 stnd. dev. 115.3 9.48 0.43 11.89 9.03 p-value 0.05 0.90 0.76 0.08 0.0542003 A average 418 41.1 2.12 68.8 49.9 stnd. dev. 175.48 8.3 0.55 25.0 11.0 B average 562 48.4 1.62 49.0 42.5 stnd. dev. 123.4 16.7 0.51 21.7 10.1 p-value 1.05E-05 0.0114 1.53E-05 9.05E-05 0.0012004 A average 22 28.1 2.99 75.9 56.4 stnd. dev. (1) 4.7 0.80 15.7 11.3 B average 76 39.5 2.40 97.8 58.9 stnd. dev. (1) 6.38 0.62 22.56 16.13 p-value (1) 0.0055 0.186 0.080 0.7692005 A average 730 39.9 1.46 44.2 40.4 stnd. dev. 321.3 7.6 0.63 19.7 9.8 B average 545 39.0 1.79 62.9 51.9 stnd. dev. 405.3 9.6 0.63 26.5 12.5 p-value 0.048 0.708 0.045 0.002 0.00014 1. The 2001/early 2002 and 2004 sample sets were only six samples pe r cell. All samples were collected on the same day so the standard deviation is zero and a t-test is not appropriate. These samples were collect ed to characterize fresh refuse used to fill the cells. test cells were similar. As will be discussed in Chap ter 5, the LFG collected in the Retrofit cells appears to be greater than that collected in the Control cells, indicating that de composition in the Retrofit cells may have been accelerated relative to the Control cells. With regard to the behavior of samples from the As-Built cells, the calculated averag e waste age in AsBuilt cell A (730 days) and As-Built ce ll B (545 days) were si gnificantly different an d much lower than the average age in the Cont rol cell (1,656 days). The young waste age in the As-Bu ilt cells makes it difficult to compare decomposition as trends would be expected to emerge over a period of five years or more. Nonetheless, As-Built cell A, which received more injected air than Cell B, exhibited more rapid decomposition (steeper slop es) than both As-Built ce ll B and the Control cell fo r all three measures of decomposition (CH:L, BMP, or ganic solids). This was also consistent with the higher mo isture content in As-Built cell A (Figure 4-10). With respect to As-B uilt cell B, the linear regression slopes were not significantly different from zero which means that ther e was not a statistically significant decrease in CH:L, BMP or organic solids with waste age. Given the young age in As-Built cell B, it is difficult to document accelerated solids decomposition on the basis of the solids data alone. It is expected that if additional

49sampling and testing is performed in su bsequent years, consistent trends with regard to the solids data will become apparent. Finally, while the emphasis of this section has been to examine statistical evidence for accelerated biodegradation in the bioreactor landf ill cells, it is also important to cons ider visible trends. Trends over time, in which the data were grouped by year, are presented in Figures 4-11 through 4-13. These figures illustrate trends in CH:L, BMP, an d organic solids for both the As-B uilt A and Retrofit cells that are encouraging and support the supposition that the operation of a landf ill as a bioreactor results in accelerated solids decomposition. Thus, while the statistical analyses were not overwhelming, this is likely a result of limited data, time period of sample collection, an d waste heterogeneity, not the absence of accelerated decomposition. This observat ion is made in full recognition that the data set from the OLLB is perhaps the most comprehensive available to date. These data sugge st the need for waste samples that are at least five years old to document decomposition. Going forward, it may be cost-effe ctive to collect a smaller set of targeted samples of known waste age to provide information for a compar ison of the effect of bioreactor landfill operation on solid s decomposition.Control CellsRetrofit CellsAs-Built Cell AAs-Built Cell B20 30 40 50 60 70 80% Moisture n=58 n=64 n=32 n=31

Figure 4-10 Comparison of Mois ture Content in the Control, Retrofit, and As -Built Cells

506CH:LCH:L0 1 2 3 4 5 60 1 2 3 4 5 n=14 n=104 n=13 n=67 n=23 n=62 n=00 1 2 3 4 5 6CH:L n=0 n=7 n=8 n=47 n=32 n=86 n=43

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)

Control cells Retrofit cells

n=47 n=43 n=15 n=5 n=0 n=0 n=00 1 2 3 4 5 6CH:L n=49 n=54 n=8 n=4 n=0 n=0 n=0

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)
As-Built cell A As-Built cell B Figure 4-11 Trends in CH:L as a Function of Waste Age

51BMP (mL CH4/dry g)BMP (mL CH4/dry g)0 50 100 150 2000 50 100 150 200 n=14 n=103 n=13 n=67 n=23 n=62 n=00 50 100 150 200BMP (mL CH4/dry g) n=0 n=7 n=8 n=47 n=32 n=85 n=41

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)

Control cells Retrofit cells

n=47 n=43 n=15 n=5 n=0 n=0 n=00 50 100 150 200BMP (mL CH4/dry g) n=50 n=54 n=8 n=4 n=0 n=0 n=0

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)

As-Built cell A As-Built cell B

Figure 4-12 Trends in BMP as a Function of Waste Age

52Organic Solids (%, dry wt.)Organic Solids (%, dry wt.)0 20 40 60 80 1000 20 40 60 80 100 n=14 n=104 n=13 n=67 n=23 n=62 n=00 20 40 60 80 100Organic Solids (%, dry wt.) n=0 n=7 n=8 n=47 n=32 n=86 n=43

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)

Control cells Retrofit cells

n=47 n=43 n=15 n=5 n=0 n=0 n=00 20 40 60 80 100Organic Solids (%, dry wt.) n=50 n=54 n=8 n=4 n=0 n=0 n=0

<1 1-2 2-3 3-4 4-5 5-8 8-11 <1 1-2 2-3 3-4 4-5 5-8 8-11 Waste Age (yr.) Waste Age (yr.)

As-Built cell A As-Built cell B

Figure 4-13 Trends in Organic So lids as a Function of Waste Age

534.1.4 Solid Waste Surface Settlement Accelerating waste settlement in a landfill unit is one of the key objectives of operating a landfill as a bioreactor. Moisture addition to the waste is intended to increase the rate of waste decomposition, resulting in accelerated waste settlement (and therefore a gain in airspace). Surface elevation data was collected for the different landfill units using G PS measurements. As discussed in Section 3.2.4, settlement in the Control and As-Built cells could not be estimated, sin ce these units received waste for most of the study period, making an assessm ent of settlement as a function of waste decomposition alone difficult. Additional waste placement is not planned for the test areas. Periodic monitoring of settlement will continue at the site, and a di scussion of settlement will be presented in the final report.

4.1.5 Landfill Temperature and Oxidation Reduction Potential (ORP) As discussed in Chapter 3, instrumentation for meas uring in-situ temperature of the waste and ORP was installed in the Retrofit and As-Bu ilt cells. Because of an installa tion defect, the majority of the thermocouples installed to measure temperature were heavily influe nced by ambient temperature. As a result, the data collected for the Retrofit and As -Built cells were not representative of the waste temperature, and these data are not presented. Additiona lly, the majority of ORP pr obes returned data that indicated the probes did not function co rrectly; as a result, an analysis of ORP data is not presented in this report.

4.1.6 Solid Waste Slope Stability A slope stability study for the Retr ofit and As-Built cells was complete d in March 2000. Results were presented in a report prep ared by Vector Engineer ing, Inc. (Vector) titled: Stability Analyses for Unit 7.4A/7.4B and Area 5 at the Outer Loop RDF, Louisville, Kentucky . For the stability analyses, both the intermediate and final waste filling conditions were analyzed. Two potentia l stability failures were considered. The first failure conditio n assumes the failure surface to be based within the leachate collection system/geomembrane liner/compacted clay liner syst em interfaces. The second failure condition assumes failure to occur in the subgrade soils beneath the cells. For the intermediate waste filling co nditions, waste grades of 3H:1V and 3.5H:1V (horizontal to vertical) were analyzed for both static and pseudo-static conditions. For these analyses, a unit weight of 1041 kg/m 3 (65 pcf) was assumed and a fricti on angle of 33° for the waste was used. For the final waste filling conditions, the final design waste grade was assumed to be 4H:1V fo r both static and pseudo-static conditions. For these final conditions, a unit weight of 1361 kg/m 3 (85 pcf) and a friction angle of 25° for the waste were assumed. For the stability analyses in the Retrofit cells, both existing (i.e., before stockpiling) and proposed final conditions (i.e., after stockp iling) were evaluated. Th e western slope of the stockpiled material intersected the existing eastern slope of the Re trofit cells. Stability analyses were evaluated for both the eastern and western side slopes unde r static conditions. Based on the assumptions made in the stability study, it was concluded that selected waste grades for intermediate and final conditions in As-Built cell A an d As-Built cell B are stable under static and pseudostatic conditions. Similarly, the ex isting and proposed conditions for wast e grades in the Retrofit cell were stable under drained and undrained static conditions. Liquid addition to the Retrofit and As-Built cells wa s initiated early in 2002 an d is ongoing. For the monitoring period between 2002 and 2005, approximately 65,000 m 3 (17.4 million gallons) and 105,000 m 3 (27.8 million gallons) of liquid we re introduced to the Retrofit and As-Built cells, respectively. Approximately 20 L (5.3 gallons) of nitrified leachate per Mg of in-place waste was applied in the Retrofit cells. Approximately 206 L (55 gal) of liquid per Mg of in-place waste was added to the As-Built cells. No stability problems have been reported for any of the landfill units at the OLLB to date. A slope stability analysis was not performed as part of this report. However, a follow-on study that utilizes data in this report may be beneficial and prov ide valuable information as to th e potential for stability problems. A general discussion on slope stability is presented in Chapter 7

54

### 4.2 Moisture Addition
The purpose of this section is to provide a summary of the moisture balance assessments and a discussion of the calculated waste moisture content, liquid head on the liner, and measured mo isture content within the study cells. In this section, “calcu lated moisture content” refers to the moisture content as determined using methods described in the U.S. EPA document Example Moisture Mass Balance Calculations for Bioreactor Landfills (U.S. EPA 2005c). The “measured moisture content” is the percent moisture content measured in the solid waste samples collected from th e site throughout the study period (presented in Section 4.1). The discussion includes an assessment of the moisture balance calculations in the cells followed by a discussion regarding the leachate head in the LCS sump, which was used as an indicator of head on the landfill liner.

4.2.1 Moisture Balance
A moisture balance for each of the landfill cells was performed. Mo isture balance calculations were performed for the Control, Retrofit, and As-built cells for the time period ranging from March 2002 to December 2005. The bulk waste moisture content was calculated for each of the landfill units. Furthermore, this calculated moisture content was co mpared to the one measured from field-collected samples of waste. The addition of leachate and liquids to the Retrofit and As-Built cells was expected to increase the moisture content of the waste. Field-meas ured moisture content was expected to exhibit large variability because of the spatial variation in waste hydraulic properties (i.e., wa ste heterogeneity) and the non-uniform wetting of the waste. It is noted that the method of solid waste sampling described in Chapter 3 may have impacted the liquid distribution in the bi oreactor landfill cells. The advancement of the 0.9-m boreholes may have drilled through perched liquid zones, possibly leading to an improved liquid distribution. The degree, to which this occurred, if at all, is unknown. For the moisture balance pres ented in this section, the “Liquid In” value is the summation of the estimated infiltration from rainfall, recirculated leachate, and added liqui ds. The procedure for incorporating infiltrated rainfall into th e moisture balance was described in Chap ter 3. The “Liquid Out” value is the leachate collected at the leachate collection sump. The difference between Liquid In and Liquid Out, Δ S, represents the change in moisture content due to liquids in troduction. The bulk waste moisture content is calculated as follows:

Moisture content = M i M Δ S

w + 100 × Equation 4-2

Where: M i = Initial moisture content (%); Δ S = Change in storage (tons of water); and M w = Wet weight of waste (tons). Equation 4-2 was used to assess the moisture balance of the landfill units, and calcu late moisture content of the waste for each landfill unit.

4.2.1.1 Precipitation Rainwater infiltration into the solid waste is typically governed by the type of cover material and vegetation on the surface of the waste. At the OLLB, a vegetativ e cover was not constructed with the exce ption of the Retrofit cells. Precipitation data was collected by an on-site weather stat ion. Figure 4-14 presents the mean monthly precipitation and the cumu lative precipitation that was recorded at the site during the period from March 2002 to December 2005. The annual averag e precipitation at the OLLB is about 100 cm (40 in.). However, it is important to no te that evapotranspiration is believed to be relatively high, ranging from 40 to 70 percent (based on HELP input para meters) depending on surface soil conditions.

553/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05 0 2 4 6 8 10 12
Cumulative Precipitation Mean Monthly Precipitation 200 300 5000

180 4500Mean Monthy Precipitation (inches)Mean Monthy Precipitation (mm) 250

200

150

100 160

140

120

100

80

60

40Cumulative Precipitation (inches) 4000

3500

3000

2500

2000

1500

1000Cumulative Precipitation (mm)

50

0 0 20

0 500

Date Figure 4-14 Cumulative and Mean Monthly Precipitation

4.2.1.2 Control Cells
The Control cells did not receive an y supplemental liquids addition du ring the study. Control cell A and Control cell B were combined in this analysis because there was no hydraulic separation between the cells. However, since the cells were filled until 2004, in filtration from precipitati on occurred during the monitoring period. The moisture balance and the calculated bulk moisture content of the waste in the Control cells are presented in Figure 4-15. The cumulative infiltrated volu me reached about 3,000 m 3 (800,000 gallons) by Decembe r 2005 in this area. In filtration to the Control ce lls was relatively low after waste acceptance ceased. The leachate generation in the Control cells was also relatively low and steady compared to the other land fill units during the monito ring period. Figure 4-15 shows no general seasonal patterns and indicates no general trends during the monitoring period. Prior to the middle of 2003, the calculated value of Leachate Out was higher than Leachate In, resulting in a net decr ease in the calculated bulk waste moisture content from 32 to about 29.5 percen t. However, after mid-200 3, the rate of Leachate Out decreased, resulting in a relatively constant calcula ted bulk moisture content of about 29.5 percent. With infiltration being almost the sole source for Li quid In for the Control ce lls, the calculated moisture content showed a slight decrease over the study peri od. This decrease may be attributed to the small amount of infiltration that occurred following the co mpletion of waste filling, as well as the increase in vertical stress from added waste, causing compression and release of the pore liquids. During the study period, the calculated mean and standa rd deviation of Liquid In per Mg of in-place waste for the Control cells were 2.8 liters/Mg (0.7 gallons/ton) and 1.5 lite rs/Mg (0.39 gallons/ton), resp ectively. The measured mean and standard deviation of Liquid Out per ton of in-place waste were 22.7 liters/Mg (6.0 gallons/ton) and 7.8 liters/Mg (2.1 ga llons/ton), respectively.

561.6e+5 4e+7Calculated Waste Moisture Content (percent by mass)

3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05 20 30 40 50 60

Moisture Content Liquid Out Liquid InCumulative Liquid Volumes (cubic meters)Cumulative Liquid Volumes (gallons) 1.4e+5

1.2e+5

1.0e+5

8.0e+4

6.0e+4 3e+7

2e+7

2.0e+4

0 0.0

Date 4.0e+4 1e+7

Figure 4-15 Moisture Balance and Calculated Waste Moisture Content of the Control Cells

4.2.1.3 Retrofit Cells The Retrofit cells received nitrified leachate as well as the infiltrated liquids. There was no addition of waste into the Retrofit cells during the monitoring period. The mois ture balance and the calculated bulk moisture content of the waste in th e Retrofit cells are presented in Figu re 4-16. Cumulative Liquid In reached about 76,000 m 3 (20.2 million gallons, approximately 15% infiltration) by December 2005, while cumulative Liquid Out was steady during the monitoring period and reached about 62,000 m 3 (16.2 million gallons) by December 2005. Infiltr ation volume for the Retrofit cells was relatively low compared to the As-Built cells because of the clay cover. Figure 4-16 shows no general seasonal patterns and indicates no cyclical trends during the monitoring period. Since Liquid In and Liqu id Out were nearly identical, there was a small change in the calculated moisture cont ent. The calculated bulk waste moisture content increased from approximately 37 to 38 percent as of December 2005. During the monitoring period, the calculated mean and standard deviation for Liquid In per Mg of in-place waste for the Retrofit cells were 20 liters/Mg (5.3 gallons/ton) and 9. 5 liters/Mg (2.5 gallons/ton), respect ively. The mean and standard deviation of the measured Liquid Ou t per ton of in-place waste were 13 .5 liters/Mg (3.6 gallons/ton) and 8.8 liters/Mg (2.3 gallons /ton), respectively.

4.2.1.4 As-Built Cells
The As-Built cells received moisture through the addition of liquids and infiltration from precipitation. Liquids addition and infiltration occurred as waste wa s being placed as presente d in Figure 4-17. The moisture balance and the calculated bulk moisture content of the waste in As-Built cell A and B are presented in Figure 4-17 and Figure 4-18, respectively. Infiltration vo lumes in the As-Built cells were the highest compared to the other landf ill units. The primary reas ons for the high infiltration volume were that waste placement occurred until 2005 and relatively high permeability compost was used as daily cover, in addition to the large volume of run- on because of the location of As-Built cells relative to the other units. The location of the As-Built cells re sulted in a high percentage of ru n-on volumes to the As-Built cells, particularly from Unit 7.2 toward As-Built cell A and from the Control cells to As-Built cell B. The infiltration volumes comprise d about 65 percent of th e total liquid added to eac h of the As-Built cells. Cumulative Liquid In was greater than that of Liquid Out in the As-Built cells resu lting in an increase in the calculated bulk moisture content of the waste.

571.6e+5 4e+7Calculated Waste Moisture Content (percent by mass)

20 30 40 50 60

Moisture Content Liquid Out Liquid In

3e+7

2e+7

1e+7Cumulative Liquid Volume (gallons) 1.4e+5

1.2e+5

1.0e+5

8.0e+4

6.0e+4

4.0e+4

2.0e+4

0 0.0Cumulative Liquid Volume (cubic meters)

3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
DateCalculated Waste Moisture Content (percent by mass)

20 30 40 50 60

Moisture Content Liquid Out Liquid In 1.6e+5 4e+7

3e+7

2e+7

1e+7Cumulative Liquid Volume (gallons) 1.4e+5

1.2e+5

1.0e+5

8.0e+4

6.0e+4

4.0e+4Cumulative Liquid Volume (cubic meters)

2.0e+4

0 0.0 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
Date Figure 4-16 Moisture Balance and Calculated Wa ste Moisture Content of Retrofit Landfill Unit For As-Built cell A, cumulative Li quid In reached about 152,000 m 3 (40.2 million gallons, approximately 62% infiltration) by December 2005, while cu mulative Liquid Out r eached about 80,000 m 3 (20 million gallons). Figure 4-17 shows no general seasonal pa tterns and indicates no cyc lical trends during the monitoring period. A fluctuation in the calculated waste moisture content was observed in As-Built cell A. A rapid increase in the moisture c ontent was noted around the middle of 2002 when the total waste mass was generally unchanged while the liquids introduction rate remained high. During the monitoring period, the mean and standard deviation of the calculated Li quid In per Mg of in-place waste for As-Built cell A were 247 liters/Mg (65.3 gallons/ton ) and 47.2 liters/Mg (12.5 gallons/to n), respectively. The mean and standard deviation of the measured Liquid Out pe r Mg of in-place waste we re 175.8 liters/Mg (46.5 gallons/ton) and 46.1 liters/Mg (12. 2 gallons/ton), re spectively.

Figure 4-17 Moisture Balance and Calculated Waste Moisture Content of As-Built Cell A

58For As-Built cell B, cumulative Liquid Out was rela tively constant during the monitoring period. Cumulative Liquid In reached about 147,000 m 3 (39.0 million gallons, approximately 68% infiltration) by December 2005, while cumulative Liqu id Out reached about 80,000 m 3 . Figure 4-18 shows no general seasonal patterns and indicates no general trends durin g the monitoring period. The calculated bulk waste moisture did not show large fluctua tions which increased from 43 percent to about 50 percent by December 2005. During the monitoring period, the calculated mean and standard deviation of Liquid In per Mg of inplace waste for the As-Built cell B were 164.0 L/ton (43.4 gallons/ton) and 52.9 L/ton (14 gallons/ton), respectively. The measured Liquid Out per ton of in-place waste mean and standard deviation were 106.2 L/ton (28.1 gallons/ton) and 34.0 L/ton (9.0 gallons/ton) , respectively. The mean and standard deviation of the calculated bulk moisture content for As-Built cell B were 47.8 percen t and 2.3 percent, respectively. It is important to note that the calculated net increase in bulk moisture content in the As -Built cells above was conservative, based on the high liquid addition volumes. As desc ribed in Chapter 3, a layer of shredded tires was used between As-Built cell A and As -Built cell B during the co nstruction of these cells until the first quarter of 2004, when it was noted th at the shredded tires we re acting as a conduit for leachate to drain quickly into the leach ate collection system thus the use of shredded tires was discontinued. As shown on Figures 4-17 and 4-18 , approximately 66% of the total l eachate generation during the study period occurred prior to the first qu arter of 2004 in the As-Built cells. Furthermore, the difference between the rates of increase for Liquid In versus Liquid Out is much more pronounced after the first quarter of 2004. Therefore, a portion of the Liquid Out us ed in the moisture bala nce calculation was likely overestimated, resulting in an underestimation of the Δ S.Calculated Waste MoistureContent (percent by mass) 60 1.6e+5

3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05Cumulative Liquid Volume (gallons)

0 1e+7 2e+7 3e+7 4e+7

Moisture Content Liquid Out Liquid In 1.4e+5

1.2e+5

1.0e+5

8.0e+4

6.0e+4

4.0e+4

2.0e+4

0.0 50

40

30

20

DateCumulative Liquid Volume (cubic meters)

Figure 4-18 Moisture Balance and Calculated Waste Moisture Content of As-Built Cell B

4.2.2 Leachate Head on Liner Under RCRA regulations, the head on the bottom liner of an MSW landfill should not exceed 0.3 m (1 ft). The main purpose of this regulation was to reduce risks associ ated with leakage of leachate from a landfill unit that could cause groundwater cont amination. The potential for leachate head to build up on the bottom liner typically correlates with l eachate generation, given that great er leachate generation rates would logically increase the potential for leachate accumulati on of liquids on the liner. As mentioned previously, the leachate head presented in this s ection is the leachate head measured in the sump and not on the bottom liner itself. Caution must be take n when examining head on the liner data in this section since it is recognized that leachate head in the sump can be influenced by th e size of the pump used to convey leachate from the leachate collection system, as well as the pump control system. Furthermore, the leachate

59head level in the sump may be affected by precipitation events (e.g., runoff from th e landfill into either the sump or the vaults connected to the sump). The OLLB was permitted to ha ve the leachate head in the sump temporarily exceed the regulatory limit of 0.3 m on da ys following heavy rainfa ll events, per the site’s permit issued by Kentucky. Recognizing that the Contro l cells were considered as a whole in the moisture balance, leachate head in the sump of Control cells A and B were averaged for this assessment. Similarly, leachate head measured in the sump in the Retrofit cells was also averaged for these calculations.

4.2.2.1 Control Cells The Control cells received liquids fr om infiltration only (i.e., the cells did not receive any supplemental liquids). Thus, leachate in the collec tion system is expected to be genera ted from infiltration and trends of leachate head are expected to correlate well with pr ecipitation. The mean mont hly leachate head in the Control cells is presented in Fi gure 4-19. The mean monthly leachate head was mostly below the regulatory limit. The mean and standard deviation of leachate head in the sump were 14 and 7.4 cm (5.5 and 2.9 in.), respectiv ely. The leachate head and generation were generally higher prior to mid-2003, while waste was still being placed in the Control cells. Once waste placement ceased in 2003, both leachate head measurements and leachate generation decreased, as sh own in Figure 4-20. The higher leachate head and generation rates prior to mid-2003 were likely caused by a portion of the runoff from the landfill being routed to the sump.Mean Monthly Leachate Head (inches)

0 2 4 6 8 10 12 14 16Mean Monthly Leachate Head (cm)

0 10 20 30 40

Leachate Head Regulatory Limit

3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/ 04 3/1/05 9/1/05


### Date Figure 4-19 Mean Monthly Leachate Head on Liner of the Control Cell

6016 1.4e+6 40 50000 Leachate Head 14 1.2e+6 Leachate GeneratedLeachate Generated Volume (cubic meters)

30

20

10Mean Monthly Leachate Head (inches)Leachate Generated Volume (gallons)

40000

30000

20000

10000Mean Monthly Leachate Head (cm)
12 1.0e+6

10 8.0e+5
8
6.0e+5 6

4.0e+5 4

2.0e+5 2

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Date Figure 4-20 Mean Monthly Leachate Head and Leachate Volumes Generated in the Control Cell

4.2.2.2 Retrofit Cells
The Retrofit cells received moisture through the addition of nitrified l eachate (beginning in March 2002) and infiltration from precip itation. The clay cap that was placed on the Retrofit cells resulted in a low infiltration volume relativ e to the As-Built cells. Since there wa s no hydraulic sepa ration between the Retrofit cells with respect to liquid ad dition, the leachate head values as recorded from Re trofit cells A and B were averaged. Since the pressure transducers are located in the sumps of all cells, it is necessary to account for the elevation head in the sump. In the case of the Retrofit ce lls, the leachate sump was located at an elevation that added a pressure head of approximately 97 cm (40 in .). Thus, an “equ ivalent regulatory limit” is noted on Figure 4-21. The equivalent regulatory limit accounts for the additional 97 cm (40 in.) added to the transducer’s measurement caused by the higher elevation of the sump. The mean monthly leachate head in the Retrofit cells was generally below the regulatory limit. The mean and standard deviation of the leachate head were 95 cm and 25 cm (37.4 and 9.8 in.), respectively. The leachate head in the Retrofit cells was consider ably higher than in the Control cells. The leachate head in the Retrofit cells is expected to be greater than in the Control cells since the Retrofit cells received additional liquids. The mean monthly leachate head correlates well with volumes of generated leachate in the Retrofit cells as presented in Figure 4-22. A tem porary increase in leac hate head correlated well with an increase in leachate generation towards the end of 2002 and at the beginning of 2005, as shown in Figure 4-22.

4.2.2.3 As-Built Cells
The As-Built cells received moisture through the addition of industrial liquids and infiltration from precipitation. Infiltration volumes fo r the As-Built cells were higher than those in the Control and Retrofit cells. This was the result of high infiltration allowed by the compos t cover used for the As-Built cells during waste filling, as well as the higher volume of ru n-on from surrounding cells. Figure 4-23 and Figure 4-24 present the mean monthly leachate head in As-Built cells A and B, respectively. The mean monthly leachate head in the As-Built cells was below the 30 cm (1 ft) leachate head regulatory limit and similar to values measured in the Control cells . For As-Built cell A, the leachate head mean and standard deviation were 16 cm (6.4 in.) and 6.9 cm (2.7 in.), respectively. For As-B uilt cell B, the leachate head mean and standard deviation were 14.5 cm (5.7 in.) and 6 cm (2 .35 in.), respectively. When compared to the Control cells, the addition of industrial liqui ds and the relatively larg e infiltration volumes did not have a significant effect on the head measured in the sump – Figures 4-19, 4-23, 4-24 indicate the number of times the 0.3 m (1 ft) threshold was exceeded (four, four, and one in the Control and As -Built cells A and B, respectively) during the study period. This is likely due to effective drainage of leachate in the cells’

6180 200 Leachate Head

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DateLeachate Generated Volume (cubic meters) Figure 4-21 Mean Monthly Leachate Head on Liner for the Retrofit Cells

Figure 4-22 Mean Monthly Leachate Head and Leachate Generated Volumes in Retrofit Cells

62Mean Monthly Leachate Head (inches)

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Date Figure 4-24 Mean Monthly Leachate Head on Liner of As-Built Cell B

63Date 3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05 2 4 6 8 10 12 14 16

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Figure 4-26 Mean Monthly Leachate Head and Leachate Generated Volumes in As-Built Cell B

leachate collection system that was specifically designed to handle the excess flow rate. Similar to the Control and Retrofit cells, the trend of leachate head of As-Built cell A and As-Built cell B appears to correlate well with trends in the generated leachat e as presented in Figure 4-25 and Figure 4-26, respectively. An increase in leachate head correlated well with an increase in leachate generation for AsBuilt cell A at the end of 2002 and at the beginning of 2005. For As-Built cell B, an increase in leachate head correlated well with an increase in leachate gene ration in March 2002 and at the beginning of 2005. The elevated leachate generation in As-Built cell A and As-Built cell B was likely caused by a combination of: (i) a portion of the runoff being r outed to the LCS during cell filling prio r to the end of 2004; and (ii) the layer of shredded tires that was in use between As-Built cell A and As-Bu ilt cell B until the first quarter of 2004, which acted as a conduit for th e injected liquids to enter the leach ate collection system more quickly.

644.2.3 Measured Waste Moisture Content
This section describes statistical an alyses that were conducted to eval uate moisture cont ent trends with respect to waste age and sampling date. The moisture content of the waste was assessed on samples collected from each of the la ndfill units during the study period, as described in Section 4.1. The frequency of solid waste sample collection varied between the different landfill units. Samples collected from the Control and Retrofit cells in 2000 were included in this analysis. Waste age and moisture content were assessed using time plots and running linear regression f its of the data. Moisture content and sampling data were evaluated using box plots and performing multiple comparisons using Tukey’s procedure. Details of the statistical analysis of these two methods are provided in Appendix C.

4.2.3.1 Measured Moisture Content versus Waste Age Linear regression fits and time plots were used to ev aluate the measured moisture content versus age and are presented in Appendix D. Inspec tion of the time plots indicates larg e variability in moisture content in all cells. This is also ev idenced in the low adjusted-R 2 values, even though waste age is a significant predictor for all cells. The linear regression fits indicate that all cells had an increasing trend in moisture content with waste age. However, only the Retrofit cells’ time plots indi cate a definitive linear trend. Linear regression assumptions may not be met in the Control and As-Built cells. The time plots for the As-Built cells appear to show mo isture content levels incr easing and then decreasing as waste age increases. It appears that the collec tion of additional older waste samples is needed to determine if a trend exists. The diagnostic plots show the residuals were not rand om in the As-Built cells. The diagnostic plots also show the residuals may not have been normally distributed in As-Built cell B. These characteristics make it difficult to definitively conclude if there wa s an increasing trend in moisture content with waste age in th e Control and As-built cells.

4.2.3.2 Measured Moisture Content versus Sampling Date For the analysis of measured moisture content versus sampling date, it was assume d that all sampled waste is similar for a specific sampling date and that the age difference in sampled waste between sampling dates is equal to the difference in sampling dates. One viol ation of this assumption woul d be if waste sampled in 2002 is actually older than waste sampled in 2003. Analysis of va riance (ANOVA) summary tables and box plots were used in this analysis and are presented in Appendix C. The ANOVA summary tables present th e F-test of the null hypothesis th at all means are equal versus the alternative hypothesis that there are at least two significantly di fferent means. The other part of the summary tables provid es Tukey multiple comparisons (i.e., compar isons of mean moisture content between each pair of sampling dates). A multiple compar ison method is necessary to control the overall significance level since more than one significance test is being performed. Box plots are also provided to allow a qualitative assessment of each trend with sampling date. For the Control cells, the F-test p-va lue indicates that at least two m ean moisture content levels were significantly different. Th e Tukey multiple comparisons analysis i ndicates that mean moisture content levels were relatively consta nt across sampling dates except for the drop in 2002. In addition, the box plots did not provide evidence of a trend. Therefore, ther e is no evidence of a trend in the measured mean moisture content with sampling date in the Control cells. For the Retrofit cells, the F-test p-value indicates that at leas t two mean moisture content levels were significantly different. Th e Tukey multiple comparisons indicated th at the 2002 and 2 005 mean moisture content levels were equal and both are significantly greater than the 2000 mean moisture content. The box plots did not provide any evidence of a trend. These re sults indicate there is no tr end in the mean measured moisture content with sampling date in the Retrofit unit. For As-Built cell A, the F-test p-valu e indicates there were no differences between mean moisture content levels. The box plots also indicated no differences present. Th erefore, there is no evidence of a trend in the mean measured moisture content with sampling date in the As-Built cell A. For the As-Built cell B, the F-test p-value indicates th at at least two mean moisture content levels were significantly diffe rent. The Tukey multiple comparisons and the box plots indicate the 2003 mean was

65higher than the 2002 mean and the 2005 mean. Theref ore, there is no evidence of a trend in the mean measured moisture content with sa mpling date in the As-Built cell B.

4.2.4 Evaluation of Calculated and Measured Moisture Content Because solid waste samples analyzed for moisture cont ent were measured for a given year with collection obtained in a single month, it was decided to compare these measured values to the calculated values for the entire given year. The calculated moisture content showed no pattern s within a given year; therefore, the entire year is considered comparab le to the measured values collected in a single month of that year. A qualitative comparison of the distributions by year consisted of summary statistics and box plots. A quantitative comparison of the distributions by year consisted of a two- sample t-test and a nonparametric Wilcoxon Rank Sum test. The qu alitative comparison is of the whol e distribution while the quantitative comparison is of the mean of the distributions. The qualitative and quantit ative comparison of the distributions is includ ed in Appendix D. Both the qualitative and quantitative co mparisons indicate that measured mo isture content was higher than the calculated moisture content for all years in the Control cells. A ll comparisons indicate that the measured moisture content and calcula ted moisture content we re equivalent in both 2002 and 2005 in the Retrofit cells. The box plots and hypothesis tests indi cate that the average calculated moisture content was higher than measured moisture content in the As-Built cells in all years except for As-Built cell B in 2002. While the box plots indicate the measured distributions span was smaller than the calculated distributions, the general conclusion must be that calculated moisture content was highe r than measured moisture content in the As-Built cells. A statistical summary including: (i) numb er of samples; (ii) mean moisture content; (iii) sta ndard devi ation; and (iv) coefficient of variation is presented in Table 4-5. The relatively large standard deviation in the measured waste moisture content is believed to be caused by a combination of the heterogeneous nature of the waste, the spatial variation in waste composition, and the varying macro-pore structure and resulting hydraulic properties within a given cell. As shown in Figure 4-27, there was an overall incr ease in the mean measured moisture content in the Control cells of about five percen t during the monitoring period, while the calculated moisture content showed a slight decrease. The amount of measured in crease is unlikely to have occurred since the Control cells did not receive any addition of liquids. This ma y indicate that calculated values of the bulk waste moisture content are more accurate than the measured mo isture content of discrete solid waste samples, or may be indicative of the inherent va riability in the waste moisture conten t in different loca tions within the area. The mean measured waste moisture content sh owed an increase of about 2 percent for the Retrofit cells during the monitoring period. Figure 4-28 indicates that there was good correlation between calculated and measured waste moisture content in the Retrofit cells. This may ha ve been due to the welldefined geometry of the Retrofit cells that resulted in relatively more accurate estimates of rainwater infiltrated volumes. However, it is recognized that the sampling fre quency of solid wast e samples in the Retrofit cells was relatively low as compared to other units. In the As-Built cells, the measured mo isture content revealed large spatial variation. The distribution of injected liquids will likely result in relatively wetter areas where the injected liqui ds follow preferential flow paths and accumulate, and the addition of air may have formed dry areas within the waste and removed some moisture via aerobic decomposition of the waste. The difference in calculated and measured moisture content of the As-Built cells may be caused by the assumptions taken for calculating the bulk waste moisture content. Inf iltration and run-on volu mes (estimated using HELP) to estimate the moisture balance of these cells in specific portions of the cells were difficult to estimate due to cell geometry. The measured waste moisture content show ed large fluctuations with an average decrease of about 2 percent in the mean waste mo isture content, as shown in Figure 4-29 (As-Built cell A) and Figure 4-30 (As-Built cell B). A d ecrease in the moisture content of the As -Built cells is doubtful because of the addition of relatively large liquid volumes into these cells. The calculated bulk waste moisture content appears to be a more realistic representation of the As-Built moisture content than the measured moisture content from waste samples taken from those cells.

66As expected, there was lowe r variability in the measured moisture content of the Control cells as compared to the Retrofit cells and As-Built cells (refer to Table 4-1) sin ce no additional liquids we re added. Leachate generation and liquid addition to the Retrofit and As-Built cells resulted in large spatial variation of the moisture content, likely du e to the non-uniform wetting of the waste. Thus, the variability in the measured moisture content in the bioreactor landfill cells was greater than that in the Control cells.

Table 4-5 Summary of Calculated and Field Measured Waste Moisture Content Parameters\Date 2002 2003 2005ControlCells Number of Samples 70 73 60 Mean Measured Waste MC ± Stdev Coefficient of Variation (percent) 32.5 ± 5; 15.3 36.1 ± 5.9; 16.3 38 ± 5.3; 13.9 Mean Calculated Bulk Waste MC ± Stadev Coefficient of Variation (percent) 31.5 ± 0.4; 1.2 29.7 ± 0.4; 1.3 29.6 ± 0.1; 0.3RetrofitCells Number of Samples 84 NA 64 Mean Measured Waste MC ± Stdev Coefficient of Variation (percent) 37.0 ± 7.5; 20.1 NA 38.8 ± 6.6; 17.0 Mean Calculated Bulk Waste MC ± Stadev Coefficient of Variation (percent) 37.7 ± 0.2; 0.5 37.6 ± 0.1; 0.2 37.7 ± 0.1; 0.2As-BuiltCell A Number of Samples 24 42 32 Mean Measured Waste MC ± Stdev Coefficient of Variation (percent) 41.9 ± 9.2; 21.9 41.1 ± 8.3; 20.2 39.9 ± 7.6; 19.0 Mean Calculated Bulk Waste MC ± Stadev Coefficient of Variation (percent) 49.3 ± 3.4; 6.9 46.1 ± 2.3; 5.0 50.3 ± 1.2; 2.4As-BuiltCell B Number of Samples 31 56 31 Mean Measured Waste MC ± Stdev Coefficient of Variation (percent) 41.6 ± 9.0; 21.6 48.6 ± 16; 33.5 39 ± 9.6; 24.6 Mean Calculated Bulk Waste MC ± Stadev Coefficient of Variation (percent) 44.2 ± 1.1; 2.5 47.6 ± 1.7; 3.6 49.1 ± 0.5; 1.0Waste Moisture Content (percent by mass)

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3/1/02 9/1/02 3/1/03 9/1/03 3/1/04 9/1/04 3/1/05 9/1/05
Date 1. NA = Not Applicable.

Figure 4-27 Calculated and Measured Wa ste Moisture Content in the Control Cells

67Waste Moisture Content (percent by mass)

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Figure 4-28 Calculated and Measured Wast e Moisture Content in the Retrofit CellsWaste Moisture Content (percent by mass)

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### Date Figure 4-29 Calculated and Measured Wa ste Moisture Content in As-Built Cell A

68Waste Moisture Content (percent by mass)

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Date Figure 4-30 Calculated and Measured Wa ste Moisture Content in As-Built Cell B

4.2.5 Moisture Content Analysis Summary
A moisture balance of the different landfill units indicated an increase in the calculated bulk waste moisture content in the Retrofit and As-Built cells. The time plots for the calculated bulk waste moisture content showed no general seasonal patterns and indicated no general trends during the monitoring period. A decrease in the moisture content of about two percent was calculated for the Control cells, as a result of a larger Liquid Out volume versus Liquid In. By the en d of December 2005, the calculated waste moisture content increased by about one percen t in the Retrofit cells. The rate of increase in moisture content was relatively consistent over time. There was a relatively large variati on in the calculated waste moisture content of the As-Built cells, as a result of the various assumptions considered in the estimate of infiltrated volumes into these cells, the ongoing waste placement in the cells, and the effects of air addition to the waste. By the end of December 2005 , the calculated bulk waste moisture content had increased by six to seven percent in As-Built cell A and B, respectively. In making mois ture balance computations, several estimates had to be made regarding the factors that in fluence infiltration. While it is believed that a net increase in moisture content occurr ed in the Retrofit and As-Built cells , it is difficult to verify the magnitude of the phenomenon, even moisture content data from solid waste samples. Leachate head in the sump of the diffe rent landfill units was consistent with trends of leachate generation. Leachate head measurements were generally below re gulatory limits and correlat ed well with trends of leachate generation. Overall, the mean leachate head measurements for all cells were below the regulatory limit of 30 cm (1 ft).
Trends in measured moisture conten t were assessed in two ways – mois ture content versus waste age and moisture content versus sampling date. The first method provided some evidence of a trend in the measured moisture content with waste age, but the second method did not provide evidence of a trend in the mean measured moisture content with sampling date . The measured waste moisture content revealed a large variability because of the spatial variation in th e waste. This variability was greater in the Retrofit cells and the As-Built cells comp ared to the Control cells. The calculated bulk moisture content appeared to provide a more realistic estimation of the actual moisture content increase compared to the measured moisture content data. It appeared that on-going waste filling and the construction of tire chip layers at the edge s of the As-Built cells reduced the magnitude of the expected moisture content increas e, based on the estimated infiltra tion volume and the liquid addition volume. Overall, the results emphasize the large liquid volumes required to increase the moisture content of a landfill to the level cited in the literature as ideal for an aerobic waste decomposition.

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## Chapter 5. Landfill Gas (LFG)

LFG quality and quantity were measured on an approximately weekly ba sis in accordance with procedures identified in Section 3 and the QAPP. This section consists of th e following: (i) pres entation of the LFG composition and flow data; (ii) comparison of fiel d data and predicted LFG generation based on U.S. EPA’s LandGEM at various waste decay rates; (iii) comparison of LFG fl ow data between the Control cells and the landfill bioreactor cells; (iv) presentation of non-methane organic carbon (NMOC) concentration data; (v) calculation of NMOC production based on LFG flow data; and (v i) calculation of NMOC production based on in-place waste data using LandGEM.


### 5.1 Landfill Gas (LFG) Composition

The quantity and composition of LFG is anticipated to vary with the st age of solid waste decomposition. However, since solid waste decomposition was believed to be occurring predominantly under anaerobic conditions at the time the gas measur ements were obtained, LFG at the OLLB was expected to consist of approximately 55 percent by volume CH 4 , 40 percent CO 2 , 5 percent N 2, and trace amounts of NMOCs (U.S. EPA, 1998). Often however, LFG is assumed to consist of only methane and carbon dioxide at 50% ratio. LFG was monitored on site using a LandGEM 2000 landfill gas analyzer. Sampling was performed approximately once per week during active gas coll ection for each cell. In accordance with the QAPP, triplicate gas readings were made for each sampling ev ent at each sampling point. In this analysis, the mean of the triplicate readings is presented, and samples in which the gas flow was zero were eliminated from the analysis.

5.1.1 Control cells
As presented earlier in Chapter 3, LFG collection sampling at the Control cells began in January 2002. The data and analysis presented here show gas samples collected through February 2006. Gas samples were analyzed at two gas collection wells (GW) for each ce ll (GW A-1, GW A-2, GW B-1, and GW B-2). The number of triplicate sets of sample data evaluated va ries between 116 (Control cells A-2 and B-2) and 147 (Control cell A-1). Summary statistics for the field ga s samples taken from the Co ntrol cells are shown in Table 5-1. Statistically, the LFG composition was simila r in each of the Control ce lls (GW A-1 and 2, B-1 and 2) and across duplicate ce lls (Control cells A and B).
The data presented in Table 5-1 shows LFG concen trations indicative of anaerobic decomposition; furthermore, the data ar e generally consistent (i .e., there was minimal variation in gas composition throughout the sampling period ). To show the variation of gas co mposition over time within the Control cells, data collected between 2002 and 2006 were aggr egated for each month. The results are shown in Figures 5-1 and 5-2 for Control cells A and B, respec tively. The figures indicat e that the gas composition of the primary LFG constituents was generally consistent th roughout the sampling period. Additionally, the concentrations of O 2 and balance gas (i.e., N 2 ) were generally low for bo th cells throughout the sampling period, indicating minimal air intrusion and prop er balancing of the gas collection system. It is also noted that the sampling loca tion (well heads) may have play ed a role in minimizing the O 2 and N 2 concentrations by minimizing the effects of br eaks and leaks in the header piping system.

5.1.2 As-Built cells
In As-Built cells A and B, LFG was sampled from the LFG extraction head er pipe of each subcell starting in April 2003. Summary of gas composition sta tistics for As-Built cells A and B are presented in Table 5­ 2. Figures 5-3 and 5-4 summarize the temporal variation of the data presented in Table 5-2, and indicate substantial variability, particularly in comparison to the relatively consiste nt results from the Control cells. This variability is unusual given air injections into the cell. Potential sources of the erratic behavior include: (i) effects of air injection activities in the cells; (ii) leakage and air intrusion aroun d the header pipes; (iii) air intrusion through the cover; and (iv) “over- pulling” of the well field.

711 / 1 / 0

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Sub Cell Parameter CH 4 (%) CO 2 (%) O 2 (%) Balance (%)
GW A-1 (N = 147) Mean ± Stdev 58±3 41±3 0.6±1 0.5±3 Median 57 42 0.1 0.2 Range 45-65 31-44 0-4.6 0-18
GW A-2 (N = 116) Mean ± Stdev 58±34 42±3 0.2±0.3 0±3 Median 57 42 0 0.2 Range 48-68 33-48 0-2.4 0-11
GW B-1 (N = 116) Mean ± Stdev 58±3 41±2 0.4±0.7 1.3±3 Median 58 41 0.1 0.2 Range 46-66 34-43 0-3.7 0-15
GW B-2 (N = 130) Mean ± Stdev 57±2 41±1 0.2±0.4 0.8±2 Median 57 41 0.1 0.3 Range 43-62 38-44 0-1.9 0-10

72 Note: Each sample represents th e mean of triplicate readings collected at gas collection well

Figure 5-1 Monthly Average of Gas Composition for Control Cell A1 / 1 / 0

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Figure 5-2 Monthly Average of Gas Composition for Control Cell B

The cause of this erratic behavior is likely a combination of the effects of air injection and sampling location. LFG sampling in the As-Bu ilt cells occurred in a h eader pipe, compared to the well heads in the Control cells, which allowed for leak s to play a role in LFG compositio n. The second reason is the aerobic/anaerobic operation of these cells. While air injection occurred at various times throughout the study period, it is likely that the months where more air was injected had an e ffect on the overall LFG composition. For example, in As -Built cell A, large-scale air inj ection activities occu rred at various occasions as presented in Table 5- 3. Figure 5-3 shows reduced CH 4 and CO 2 and elevated O 2 and balance gas during the same month where large air injection oc curred. Large-scale air in jection activities occurred in As-Built cell B. Again, Fi gure 5-4 shows that the CH 4 and CO 2 percentages were reduced, while the balance gas and O 2 concentrations were elevated at these times. It is interesting to point out that the O 2 to N 2 ratio during these times (assuming balance gas consists of only N 2 ) is (1 to 4) similar to that in ambient air. Table 5-2 Summary Statistics of Gas Composition for As-Built Cells A and B
Sub Cell Parameter CH 4 (%) CO 2 (%) O 2 (%) Balance (%)
Cell A (N = 127) Mean ± Stdev 51±11 37±6.4 2.4±3 9.7±13 Median 55 39 0.9 2.9 Range 21-63 18-45 0-12 0.1-48
Cell B (N = 125) Mean ± Stdev 52±9 37±6 2.1±3 9±11 Median 54 39 1.1 5.5 Range 5-82 4.2-45 0-18 0.1-73 Note: Each sample represents th e mean of triplicate readings co llected at gas collection header

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Figure 5-3 Monthly Average of Gas Composition for As-Built Cell A Table 5-3 Notable Air Injection Dates for As-Built Cells A and B Cell Month Air Injected, m 3 (ft 3 )

As-Built cell A 11/2003 2.8x10 5 (9.9x10 6 ) 6/2004 2.1x10 6 (7.5x10 7 ) 1/2005 1.1x10 6 (3.9x10 7 )

As-Built cell B 8/2003 5.7x10 5 (2.0x10 6 ) 7/2004 7.7x10 6 (2.7x10 7 ) 8/2005 * 9.2x10 6 (3.210 8 )

* Air injection occurred over a period of 6 m onth ending with the da te indicated. Air injection occurred in equal volumes over that time period.

5.1.3 Retrofit Cells
In the Retrofit cells A and B, there was a single samp le collection point in each cell. LFG sampling from the Retrofit cells began in November 2001 and summary statistics are presented in Table 5-4. Figures 5-5 and 5-6 show significant va riability and inconsistency, although bot h cells seem to be exhibiting similar behavior. Potential sources of the erratic behavior include: (i) leakage and air intrusion around LFG header pipes; (ii) “over-pullin g” of the well field and subseq uent air intrusion through th e cover; and (iii) watering out of gas collection wells. The most likely explanatio n is a combination of thes e factors, since watering out of gas collection wells can cause an imbalance in the vacuum applied to the landfill, resu lting in overpulling of the well field and subsequent air intrusion. These effects will be discussed in mo re details in Section 5.2.3. As with the As-Built cells, the O 2 to N 2 (assuming balance gas consists of only N 2 ) ratio is (1 to 4) is similar to ambient air throughout the monitoring period.

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Figure 5-4 Monthly Average Gas Composition for As-Built Cell B Table 5-4 Summary Statistics of Gas Composition for Retrofit Cells
Sub Cell Parameter CH 4 (%) CO 2 (%) O 2 (%) Balance (%)
Cell A (N = 177) Mean ± Stdev 49±9 35±6 3.3±3 11±12.3 Median 51 36 2.7 7.2 Range 4-63 3.2-46 0-19 0-74
Cell B (N = 140) Mean ± Stdev 43±13 32±9.3 4.9±4.3 19±19 Median 46 34 4 13 Range 4-62 3.2-46 0-19 0-74 Note: Each sample represents th e mean of triplicate readings co llected at the header pipe of each cell

5.1.4 Landfill Gas (LFG) Composition Summary
In general, duplicate cells had statisti cally similar LFG composition, with CH 4 and CO 2 constituting the bulk of the LFG stream. Oxygen co ncentrations in LFG of the As-Bu ilt bioreactor landfill cells may not necessarily indicate a problem with the gas collection system. While some oxygen can be consumed in the process of aerobic degradation, the rate of air injection is much larger than what is needed for stoichiometric co nversion; thus the majority of O 2 will pass through the system . However, the ratio of concentration of O 2 to N 2 in LFG of the Retrofit system at 1:4 (ratio of O 2 to N 2 ) is evidence of LFG collection problems. It is most likely that leaks in the header piping system played a large role in air intrusion as well as wate ring-out of LFG wells.

758 / 1 / 0

1 2 / 1 / 0 2 8 / 1 / 0 2 2 / 1 / 0 3 8 / 1 / 0 3 2 / 1 / 0 4 8 / 1 / 0 4 2 / 1 / 0 5 8 / 1 / 0 5 2 / 1 / 0 6Gas Concentration (%)

0 10 20 30 40 50 60 70 CH 4 CO 2 O 2 Balance

9 / 1 / 0

1 3 / 1 / 0 2 9 / 1 / 0 2 3 / 1 / 0 3 9 / 1 / 0 3 3 / 1 / 0 4 9 / 1 / 0 4 3 / 1 / 0 5 9 / 1 / 0 5 3 / 1 / 0 6Gas Concentration (%)

0 10 20 30 40 50 60 70 CH 4 CO 2 O2 Balance Figure 5-5 Monthly Average of Gas Composition for Retrofit Cell A

Figure 5-6 Monthly Average of Gas Composition for Retrofit Cell B

76

### 5.2 Measured Methane Production and LandGEM Model Predictions

For this section, the actual LFG coll ection rates (i.e., field data) were compared to predicted gas generation rates modeled in the U.S. EPA’ s LFG production model, LandGEM. LandGEM models landfill gas generation using a first-order decay equation. Detailed informati on regarding the parameters and assumptions used in LandGEM can be found on the U.S. EPA’s website ( http://www.epa.gov/ttn/catc/dir1/landgem-v302-guide.pdf ). The equation used by the model to calculate LFG generation is similar in mathem atical form to Equation 5-1:

n 1 − kt i, j Q = 2 

# ∑ ∑ kL o ⎛ ⎜ M i ⎞ ⎟ e Equation 5-1
i = 1 j = 0.1 ⎝ 10 ⎠

Where: Q = LFG generated (m 3 /yr); k = first order waste decay rate (yr -1 ); L o = CH 4 generation potential (m 3 /Mg waste); M i = waste mass placement in year i (Mg); and t i,j = time (yr).

LandGEM allows the user to input various parameters, including waste mass placement (M i ), waste decay rate (k), and the CH 4 generation potential (L o ). One cited benefit of land fill bioreactors is the acceleration of the waste decomposition rate (i.e., higher k) (R einhart and Townsend 1998). The objectives of the analysis presented in t his section are to: (i) estimate an approximate k for each cell based on gas collection data; (ii) c ompare the actual landfill gas generation rates to those predicted using LandGEM; and (iii)
com pare the k values based on field data to the expected k values for landfill bioreactors as reported in the literature.
For the purposes of this analysis, waste mass inputs used in LandGEM for each cell are presented in Table 5-5. These values were calculated using waste r eceipts at the site. Mode l default values of L o or sitespecific estimates of L o may be used in LandGEM. The U.S. EPA’s compilation of pollutant emission factors, AP -42, states “Estimation of the potential CH 4 generation capacity of refuse (L o ) is generally t reated as a function of the moisture and organic content of the refuse.” Moisture content and BMP (i.e., a

m easure of the CH 4 yield of an organic material during an aerobic decomposition) data from fresh waste
sam ples taken at the site in 2004 were available and were used to calculate a site-specific L o . Since the waste placed in each cell at OLLB was pr imarily MSW, it was assumed that the BMP and moisture content results of the fresh waste were indicativ e of waste placed in all cells. It is noted that the site specific L o (59 m 3 /Mg-wet) is lower than the LandGEM default L o values for wet and conventional land fills (96 and 100 m 3 /Mg (3,000 and 3,200 ft 3 /ton), respectively).
The LFG flow rate and volume collected at OLLB, like any other landfill, represents the fraction of the gas captured by t he LFG collection system. Thus, the coll ected LFG is generally less than the LFG generated since c ollection systems do not operate at 100 percent co llection efficiency (CE). Rather, AP-42 states that reported CEs typically range from 60 to 85 percent, with a 75 percent CE being the value that is most
com monly assumed. To this end, each of the subse quent sections will comp are the following to the LandGEM -predicted gas generation rate: (i) the raw field data collected; and (ii) transformed field data, usin g the assumption that the gas samples represent a collection system operating at 75% CE. To
accom plish this latter comparison, the collected LFG wa s divided by 0.75 to calculate the landfill gas gene ration rate. It is noted that this procedure does not follow U.S. EPA Method 2E for estimating a sitespecific gas ge neration rate. The sites actual CE can be higher or lower than 75%, but for the purposes of this analysis 75 % will be used.

To ca rry out the comparison using field LFG data, the cumulative CH 4 generation for each cell was calculated by (i) averaging the triplicate total gas flow readings for each date of co llection; (ii) multiplying the m ean of the daily readings by the mean of the CH 4 percentage for that day; (iii) taking the average of

77

### ⎛ 2 ⎛ ⎞ 

### ⎞ 

# ∑ d 

### ⎜ ⋅



### kL d

− i

− k ⎜ ⎟ 0 

### M e ⎝ 10 ⎠



### − Q ⎟

d 

### ⎜ 

# ∑ 10 i d 

### ⎟ ⎝ i = 0 

### ⎠ Equation 5-3 the weekly readings for each month; (iv) multiplying th e monthly average flow rate by the number of days in the month; and (v) summing the total monthly gas collection amounts. Dates with a zero gas flow reading were eliminated. It is also noted that La ndGEM typically provides gas generation estimates on an annual basis, so the equations were entered manua lly to provide monthly results as necessary.
In order to optimize the CH 4 production equation from LandGEM (as presented in Equation 5-1) for the waste decay parameter k using annual wa ste mass placement data and monthly CH 4 generation volume, the sum of squared errors was used. Since on ly two to four complete years of CH 4 flow data exists, optimization had to be performed on a deciyear basis (decimal year). This required stating Equation (1) in terms of decimal year production (as presented in Equation 5-2). 

# ∑

i 0 = d

− i ⎛ ⎜ ⎝ ⎞ ⎟ ⎠ d 

### kL

− k

⋅ 0 10 

### Q M i 

### e = d 

### 10 Equation 5-2
Where d is the number of deciyear s since initial waste placement, M i is the waste mass placed in deciyear i, and Q d is the methane production for deciyear d. Estimat ion of the waste decay rate parameter, k, for a particular cell proceeded by minimizing the sum of squa red errors of Equation 2 (as presented in Equation 5-3).

Where d varies over the deciyear me thane data for the cell. The actual data for the minimization consisted of monthly methane observations and annu al waste mass values. Therefore, the Q d values were interpolated and the M i values were the annual waste mass observations divided by 10, so it was assumed that waste was placed uniformly thr oughout a given year. A quasi-Newton method was used to minimize this function. Table 5-5 Summary of Waste Mass Inputs for LandGEM, Mg (tons)

Year Control Cells Retrofit Cells As-Built Cell A Cell B 1995 424,810 (467,287) 1996 745,369 (819,898) 1997 585,133 (643,640) 1998 1999 193,771 (213,148) 2000 148,131 (162,944) 112,263 (123,489) 2001 35,801 (39,381) 28,577 (31,435) 2002 49,398 (54,338) 183,680 (202,048) 256,247 (281,872) 2003 58,456 (64,302) 100,574 (110,631) 2,188 (2,407) 2004 27,139 (29,853) 178,424 (196,267) 289,747 (318,722) 2005 56,759 (62,435) 250,641 (275,705)

5.2.1 Control Cells
Waste placement began in the Control cells in 1999; however, gas collection and measurement did not commence until 2003. As a result, onl y LandGEM results from 2003 onward were used for comparison to field data to estimate k. Since no hydraulic barrier ex ists between the subcells of the Control cells, the data from each subcell were aggregated to compare to th e LandGEM prediction. In general, the cumulative methane generation for Control cells appears to follow the expected landfill gas generation rate as predicted for a typical “dry tomb” landfill scenario in LandGEM. Without accounting for gas collection inefficiencies, the optimized k value (0.043) matches up very well with the curve representative of the dry

781 / 1 / 0

1 1 / 1 / 0 2 1 / 1 / 0 3 1 / 1 / 0 4 1 / 1 / 0 5 1 / 1 / 0 6 1 / 1 / 0 7 1 / 1 / 0 8 1 / 1 / 0 9 1 / 1 / 1 0 16

14

12

10

8

6

4

2

0 LandGEM k=0.04 LandGEM k=0.05 LandGEM k=0.15 Collected LFG Generated LFG Assuming CE=75%Cumulative Methane (Million m3) tomb case of k = 0.04 yr -1 as presented in Table 5-6. When assuming a gas CE of 75 percent, the transformed field data indicate a waste decay rate of 0.061 yr -1 , greater than the AP-42 default k value of 0.04 yr -1 . It is noted that the actual CE of the Control ce lls is not known, so the actual waste decay rate may be more or less than 0.061 yr -1 . It is also recognized that the ti me period of data collection may not necessarily be indicative of long-term LFG generation trends. Table 5-6 Optimized Landfill Deca y Constant (k) for Control Cell L 0 = 59 L 0 = 96 Collected Methane Generated Methane 1 Collected Methane Generated Methane 1 0.043 0.061 0.025 0.035 1.Assumed a collection efficiency of 75%

Figure 5-7 Cumulative Methane Gas Collection Da ta versus LandGEM-Predicted Gas Generation for the Control Cells

5.2.2 As-Built Cells
Data from As-Built cells A and B were analyzed separately since detailed waste placement data were available for each cell (see Table 5-5) and because of the hydraulic separation of these cells. LFG collection data for the As-Built cells began in April 2003. Since LandGEM provid es an annual output, the output for 2003 was scaled such that it represented nine months of predicted generation (i.e., representing April 2003 to December 2003 rath er than the entire year).
Cumulative methane generation predictions using La ndGEM with mass input based on the available waste acceptance data (Table 5-5), beginni ng with a k value of 0.04 yr -1 (the AP-42 default for “dry tomb” landfills), and incrementally increas ing up to a k value of 0.25 yr -1 are presented in Figures 5-8 and 5-9. A decay rate (k value) of 0.25 yr -1 represents the expected decay rate for wet landfills according to the U.S. EPA report “ First-Order Kinetic Gas Generation Model Parameters for Wet Landfills” (U.S. EPA 2005). As demonstrated by the figures, the cumulative collected methane for both As-Built bioreactor landfill cells (as presented in Table 5-7) indicate a k value of between 0.15 yr -1 and 0.20 yr -1 in As-Built cells. The optimization of the decay constant k indicated that the k value for bot h bioreactor cells are statistically similar at 0.11 yr -1 . Moreover, if it is assumed that the collect ed gas represents 75% of the methane being

791 / 1 / 0 2 1 / 1 / 0 3 1 / 1 / 0 4 1 / 1 / 0 5 1 / 1 / 0 6 1 / 1 / 0 7 1/ 1 / 0 8 1 / 1 / 0 9 1 / 1 / 1 0Cumulative Methane (Million m3)

0 5 10 15 20 25
LandGEM k= 0.04 LandGEM k = 0.15 LandGEM k =0.20 LandGEM k = 0.25 Collected LFG Generated LFG Assuming CE = 75%

1 / 1 / 0 2 1 / 1 / 0

3 1 / 1 / 0 4 1 / 1 / 0 5 1 / 1 / 0

6 1 / 1 / 0 7 1 / 1 / 0

8 1 / 1 / 0

9 1 / 1 / 1 0Cumulative Methane (Million m3)

0 5 10 15 20 25 30 35 LandGEM k = 0.04 LandGEM k = 0.15 LandGEM k = 0.20 LandGEM k = 0.25 LandGEM k = 0.28 Collected LFG Generated LFG Assuming CE = 75% Figure 5-8 Cumulative Methane Gas Collection Da ta versus LandGEM-Predicted Gas Generation for As-Built Cell A

Figure 5-9 Cumulative Methane Gas Collection Da ta versus LandGEM-Predicted Gas Generation for As-Built Cell B

80Table 5-7 Optimized Landfill Decay Consta nt (k) for As-Built Bioreactor Cells
Landfill

Cell L 0 = 59 L 0 = 96 Collected Methane Generated Methane Collected Methane Generated Methane As-built A 0.11 0. 16 0.064 0.089 As-built B 0.11 0. 15 0.062 0.086
generated (i.e., a CE of 75 percent), the k value fo r As-Built cells is optimized at a value of 0.16 yr -1 which falls within the range that was visually estimated before and that is statistically higher than that observed for the control cells.
These results suggest that based on gas collected at the site between 2003 and 2006, the As-Built cells appeared to generate LFG at a rate that is clearly higher th an would be expected at traditional “dry tomb” landfills. As described earlier, the waste decay ra te in the Control cells is approximately 0.06 yr -1 which is much lower than that of the As-Built cells. As illustra ted in Figure 5-10, LFG generated in the early stages of the landfill’s life was significantly greater in the As-Built bioreactor cells relative to the Control and dry tomb cells.
Modeling of LFG generation rates for 50 years based on current loading rates and k of 0.16 (yr -1 ) indicates the effectiveness of bioreactor landfills at generating methane at a faster rate relative to a “dry tomb” cells as presented in Figure 5-10. The higher LFG generati on rate, especially in the early stages of landfill development, has implications for potential benefici al reuse of LFG. Furthermore, the As-Built LFG curves, shown in Figure 5-10, indicate that LFG genera tion declines to very low rates after approximately 25 years; this has the potential to reduce long-term concerns regarding LFG management during postclosure. These results should be viewed with caution since the developed k values are based on only 3 years worth of landfill gas collection data.Flow Rate (m3/min)

0 2 4 6 8 10 12

As-Built Cell A k = 0.04 As-Built Cell B k = 0.04 As-Built Cell A k = 0.16 As-Built Cell B k = 0.16

2000 2010 2020 2030 2040 2050
Figure 5-10 LFG Generation Rate P rediction for As-Built Cell A and B

811 / 1 / 0 0 1 / 1 / 0

1 1 / 1 / 0 2 1 / 1 / 0

3 1 / 1 / 0 4 1 / 1 / 0 5 1 / 1 / 0

6 1 / 1 / 0 7 1 / 1 / 0

8 1 / 1 / 0 9 1 / 1 / 1 0Cumulative Methane (Million m3)

0 10 20 30 40 50

LandGEM k = 0.04 LandGEM k = 0.07 LandGEM k = 0.15 Collected LFG Generated LFG Assuming CE = 75% 5.2.3 Retrofit cells

Unlike the As-Built bioreactor landf ill cells, the Retrofit cells were not hydr aulically separated. As a result, the LFG collected from the two collection points was aggregated to calculate methane collection for further use in modeling the Retrofit unit. LFG collection star ted in November 2001. For LandGEM modeling of the Retrofit cells, a k for a “dry tomb” landfill case (i.e., k = 0.04 yr -1 ) in addition to higher k values were explored. Results presented in Figure 5-11 show that direct field measurements of LFG generally fall just above (k = 0.041 yr -1 ) the expected gas generation in “dry tomb” landfill. However, when a CE of 75% was applied, methane generation approximately matched the curve corresponding to a k = 0.061 yr -1 which is slightly higher than “dry tomb” landfill but not high er than that of the Control cell. The U.S. EPA document regarding k values for wet landfills indicated th at modeled landfill sites had a k value that ranged between 0.11 and 0.3 yr -1 . Even with the assumption of 75 percen t CE, the data for the Retrofit unit fall well below the lower bound of that range.
As discussed previously, LFG collectio n in the Retrofit cells exhibited erratic behavior with regard to CH 4 , CO 2 , and O 2 concentrations during the sampling period. It is believed that this trend can be attributed to a combination of watering out of gas we lls, air leakage, air intrusion, and operator error. Upon review of Figures 5-5 and 5-6, it is noted that each figure shows LFG concentration for Retrofit cells A and B as expected for the first four months of operation (i.e., November 2001 through February 2002). Figure 5-12 depicts the average LFG collection flow rate for the Retrof it cells during the study. This figure shows that the LFG generation was highest during the first four mont hs before starting a precipi tous decline in flow for the first few months of 2002, when the installation of new vertical gas wells was stopped. As a result, it appears that the erratic behavior in terms of LFG co mposition began as the LFG collection rate decreased, indicating that the existing vertical gas collection wells may have been affected. It is likely that the wells filled with either the liquids that were being applied during this time period and/or with gas condensate. The magnitude of the impact on LFG CE is not know n, since the determination of specific gas collection efficiency was beyond the scope of this project. Furthe rmore, the fluctuation of LFG flow rate beginning in

Figure 5-11 Cumulative Methane Gas Collection Data versus LandG EM-Predicted Gas Generation for the Retrofit Cells

821/1/ 2001 1/ 1/2002 1/1/ 2003 1/ 1/2004 1/ 1/2005 1/1/2006 1/ 1/2007Monthly Average LFG Flow Rate (m3/min) 70

60

50

40

30

20

10

0

Monthly Average LFG Flow Rate Date Figure 5-12 Monthly Average LFG Flow Rate for Retrofit Cells
late 2004 (see Figure 5-12) may be the result of an increase in the vacuum on the Retrofit cells. The comparison of Figures 5-5 and 5-6 to Figure 5-12 i ndicates that the increase in gas flow rate generally coincides with a decrease in CH 4 and an increase in O 2 , indicating over-pulling on the LFG well field. Furthermore, operators for LFG well monitoring were replaced at the same time and this may have contributed to the erratic readings after that time.
Figure 5-13 compares the modeled LFG genera tion rate for the Retrofit unit (k = 0.061 yr -1 ) to the decomposition rate in the AP-42 default. The results indicate that the decomposition rate in the Retrofit unit was greater than the modeled LFG production ba sed on the decomposition rate of the regulatory default value. The difference in LFG generation is not as dramatic in the Retrofit cells compared to the AsBuilt cells (assuming similar loading rate). It is impor tant to note that the Retrofit Unit was not operated as a bioreactor landfill until 2001, appr oximately six years after initial waste placement. Based on the firstorder decay LFG production model for MSW, fresher (i.e ., newly placed) waste generates LFG at a greater rate than older waste. Therefore, the timing of la ndfill bioreactor operations and the time period of collected LFG field data (2001 to 2006) is not perfec tly comparable to the Cont rol cell. In addition, the older refuse in the Retrofit cell may have contributed to a lower decay rate.

5.3 Comparison of Field Gas Results of Control and Landfill Bioreactor Cells
A comparison of the CH 4 flow rates between the Control (i.e., dry tomb) cell and the experimental (i.e., landfill bioreactor) cells is critical in understanding the effectiveness of landfill bioreactor operations. The hypothesis is that with the greater degradation rate in bioreactor landfi ll cells, compared to dry tomb cells, landfill gas will be generated at a greater rate. Since waste placement and mass in the test cells varied, a direct side-by-side comparison over the entire monitori ng period was not possible. Comparisons were only made in months for which gas collection data for wa ste of similar age was available as summarized in Table 5-8 and 5-9. The mass of waste in each cell wa s normalized to the mass in the Control cell as the rate and amount of CH 4 generated, over time, is proportional to the mass in the cell. The waste age, shown in Tables 5-8 and 5-9, is relative to the year of in itial waste placement for each cel l (e.g., a waste age of six

83Flow Rate (m3/min) 12

10

1990 2000 2010 2020 2030 2040 2050 0 2 4 6 8 k = 0.061yr -1 k = 0.04 yr -1

Figure 5-13 Modeled LFG Generation Ra te for Waste in the Retrofit Cells
is compared in Table 5-8 since waste filling began in 1999 and 1995 for the Control and Retrofit cells, respectively). To carry out th e comparison, the ratio of CH 4 generated in a bioreactor landfill cell to that generated in the Control cell on these dates was calcula ted and plotted as presented in Figures 5-14 and 5­ 15. The observation number listed in the tables corresponds to the observation number located on the xaxis of each of the figures. The dashed horizontal line at a ratio of one indicates no difference in gas generation (based on collected gas data) between the Control cells and the landfill bioreactor cells.
Figure 5-14 shows that the data for the comparison of the Control and Retrofit Unit fell below the ratio of 1.0 for the first two observations and above the line fo r the last two observations. As presented earlier in Chapter 3, liquid introduction into the Retrofit landfill Unit did not started until May 2001. As a result, there was not adequate time for good moisture dist ribution, between May and November, to see an enhancement in the LFG generation rate in the Retrofit Unit. The increasing trend in the ratio over time, observed in Figure 5-14 suggest that, with time, the Retrofit Unit was able to produce more gas. This observation is inline with the solids data results (prese nted in Chapter 4) that suggested that the Retrofit cells are potentially decomposing at a rate higher than the Control cells. However, as with the solids data, more data are needed to better document trends.
Because of the filling schedule, more gas observations were available fo r the comparison of the bioreactor landfill cells and Control cells as presented in Table 5-9. As shown in Figure 5-15, the ratios of the landfill gas generated in the bioreactor landfill cells to that gene rated in the Control cells were often higher than 1, suggesting that the rate of degradat ion was greater in the As-Built bioreact or landfill. This conclusion is further supported by the solids data (see Chapter 4) th at show more rapid solids decomposition in the AsBuilt cells.

84Retrofit/Control Ratio

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0 1 2 3 4 5
Observation Number

CH 4 Flow Rate Ratio Table 5-8 Summary of Dates Used for Retrofit and Control Cells CH 4 Flow Comparison Observation # Waste Age (Yr) Control Month Retrofit Month 1 6 11/2005 11/2001 2 12/2005 12/2001 3 7

1/2006 1/2002 4 2/2006 2/2002 Table 5-9 Summary of Dates Used for As-Built and Control Cells CH 4 Flow Comparison Observation # Waste Age (yr) Control Month As-Built Month 1 1/2002 1/2005 2 2/2002 2/2005 3 3/2002 3/2005 4 4/2002 4/2005 5 5/2002 5/2005 6 3

6/2002 6/2005 7 7/2002 7/2005 8 8/2002 8/2005 9 9/2002 9/2005 10 10/2002 10/2005 11 11/2002 11/2005 12 12/2002 12/2005 13 4

1/2003 1/2006 14 2/2003 2/2006

Figure 5-14 Normalized Compar ison of Gas Collection in Control and Retrofit Cells

85As-Built Cell A or B/Control Ratio

0 1 2 3 4 5 6 7 8

0 2 4 6 8 10 12 14 16
Observation Number

CH 4 Flow Ratio - As-Built Cell A CH 4 Flow Ratio - As-Built Cell B Figure 5-15 Normalized Compar ison of Gas Collection in Control and As-Built Cells

5.3.1 Summary of LFG Generation
The measured LFG generation rates, the decay constant (k), and the solids data presented in the previous sections indicate that there is an increase in solid waste degradation in bioreactor landfills compared to Control cells. The enhanced LFG generation rate indicat es that the majority of LFG production will occur in the early stages of landfill development (in the case of the As-Built cells in this study, within the first ten years following initial waste placement). Figure 5-16 s hows the percent of LFG gene rated as a function of years after waste placement for the various k values es timated earlier in this section. Based on this analysis, 50% of LFG is generated within 7 years of waste placement at a k of 0.16 yr -1 . This trend has significant implications for potential beneficial us e options for LFG at MSW landfills operated as a bioreactor during and after waste filling since the rapid LFG generation would mean more recoverable energy is available sooner. The trend further un derscores the importance of having a LFG collection system in place in the early stages of landfill development for: (i) ambien t emission control if a landfill is tobe operated as a bioreactor and (ii) an increase in LFG collected if a beneficial use of the LFG (e.g., LFGto-energy) is considered for the site. If a LFG collection system is not in place du ring the early stages of landfill development, the most LFG-productive years will be missed, resulting in greater emissions and lower cumulative LFG utilization.
These trends also have an implication for post closure care. Based on LandGEM model data presented in Figure 5-16, more than 90% of LFG is produced wi thin 12 years after wast e placement in bioreactor landfill cells as compared to less than 50% in the Co ntrol Units. Thus, if the potential for LFG generation is low (e.g., 90% of LFG has alr eady been produced) in MSW landfills operated as bioreactors, then an argument could be made that the duration of post cl osure care monitoring for LFG may be reduced.

860.1 1 10 100LFGGd(%) 0 20 40 60 80 100

k = 0.04 /yr k = 0.061 / yr k = 0.16 / yr k = 0.7 /yr



### Year After Waste Placement Figure 5-16 Normalized Comparis on of Gas Collection in Cont rol cells and As-Built Cells


### 5.4 None Methane Organic Carbon (NMOC) Concentrations in LFG
Samples for analysis of total NMOCs and a number of speciated HAPs that are a subset of NMOCs were collected for all cells on a quarterly basis and sent under chain-of-custody protocol to Severn Trent Laboratories as outlined in the QAPP presented in the First Interim Report. Summary statistics for the HAP data are provided as Appendix E. Non-detected constituents were not included in the statistical analysis represented in the tables. In evaluating th e air pollutant concentrations , a correction was used to account for air infiltration. Furthermor e, only constituents detected in mo re than 50 percent of the samples were included; these constituents were then corrected for air infiltration using the following equation from U.S. EPA’s AP-42 guidance document:

C P,u (1x10 6 ) C p = Equation 5-4 C CH 4 + C CO 2 

### Where: Cp = Corrected concentration of pollutant P in LFG, ppmv; C P,u = Uncorrected concentration of pollutant P in LFG, ppmv; 1 x 10 6 = Constant used to correct concentration of P to units of ppmv; C CH4 = CH 4 concentration in collected gas, (ppmv); and C CO2 = CO 2 concentration in collected gas, (ppmv).
Currently, littl e is known a bout the kinetics of NMOC emissions from MSW landfills, specifically as the NMOC em issions relate to waste type, waste age, and other factor s. NMOCs are generated in MSW landfills from volatilization of orga nic compounds and, to a limited degree, by biological and chemical

87processes (U.S. EPA, 1998; Staley et al., 2006). The Clean Air Act (CAA) default concentration for NMOCs in MSW LFG is 4,000 ppm as hexane. This value was developed for compliance purposes, but AP-42 indicates that NMOC concentr ations greater than this default concentration can exist at MSW landfills. AP-42 defaults for NMOCs are 600 ppm for MSW landfills with minimal co-disposal occurred at the site.
When considering a comparative analysis of NMOC production, the use of only NMOC concentration data from a landfill cell may be misleading. NMOC concentrat ions must be tied in with the LFG flow rate to evaluate production. Additionally, the mass of waste and the composition of waste would likely affect the magnitude of NMOCs produced. In this section, the an alytical data (i.e., NMOC concentrations) will be tied into available LFG flow rate data to calculate the mass flow rate of NMOCs from the different cells. Only total NMOC data are analyzed in this section, since the individual compounds listed in the QAPP and analyzed in the laboratory (i.e., HA Ps) are a subset of NMOCs. The da ta will be analyzed to present the analytical results on a unit (i.e., mass) basis. Summ ary statistics for total NMOCs are presented in Table 5­ 10.

The mean NMOC concentration (presented in Table 5-10) varied between cells. Differences between concentrations ranged from a factor of approximately 4. 5 (e.g., Retrofit cells versus Control cell A) to as little as approximately 1 (e.g., As-Built cell B versus Retrofit cells). It is noted that higher NMOC concentration in a particular cell does not necessary mean higher emissions since NMOC production rate depends on the volume of LFG generated by each ce ll. Furthermore, the ca lculated NMOC production averages do not directly account for the differences in the mass of waste in the cell or waste age. Thus, a direct between-cell comparison of NMOC production is inaccurate. Th e aforementioned lack of accurate predictive methods of NMOC production does not allow for any meaningful conclusions to be drawn based on NMOC concentration alone. Furthe rmore, the differences between the cells with regard to the time of waste placement, coupled with the NMOC sampling frequ ency outlined in the QAPP, limits the pool of data that can be compared.

Table 5-10 NMOC Concentration for Each Sub Cell (ppm as Hexane) Subcell Number of Detects Range (minmax) Median Mean ± Standard Deviation Control cell A 14 383-1,608 1,146 1,060±368 Control cell B 14 450-867 633 611±117 As-Built cell A 10 97-633 458 393±177 As-Built cell B 10 85-467 233 242±100 Retrofit cell A 15 63-350 250 246±73 Retrofit cell B 14 143-383 250 237±71

5.4.1 Landfill Gas (LFG) Flow-Based NMOC Production Analysis
As noted in Chapter 3, the Control and Retrofit cells were sampled at more than one location; however, there was no hydraulic separation between the cells, and therefore the LFG flow data was combined for comparison with LandGEM. In this section, a simila r approach will be used in evaluating the mass flow rate of NMOCs in the Control and Retrofit cells as wa s used for methane production. Since samples were taken from more than one point for NMOC analysis, th e mean of the concentration at each selected date will be used to calculate the NM OC mass emission rate. Equation 5-5 depicts the approach for calculating the NMOC mass emission rate:

881 / 1/2002

7 / 1 /20

0 2

1 / 1 /2 00

3
7 / 1/2003 1/1/2004 7/ 1 /20

0 4 1/ 1 /20

0 5
7 / 1 /2 00

5

1 / 1/2006 0.03

0.02

0.01

0.00NMOC Emission Rate (kg/min)

Date m = C p × Q LFG × 1 × 86.17 × 0 .454 × 10 − 6 Equation 5-5 385.4

Where:
m = mass flow rate of NMOC, kg/min; C p = concentration of NMOC corrected for air intrusion, ppmv as hexane; Q LFG = flow rate of LFG, scfm; 3 85.4 = conversion of ft 3 per lb-mol of gas at STP; 86.17 = molecular weight of hexane, lb/lb-mol; 0.454 = conversion of lb into kg; and 10 -6 = conversion factor from ppm to volume fraction.

Sin ce NMOC samples were collected quarterly, the monthly average flow rate corresponding to the month that the NMOC sample was collected was used in calculating the mass flow rate. These calculated NMOC production rates were plotted over time to evaluate potential temporal trends in NMOC production. Figures 5-17 through 5-20 depict the results for the Control, Retrofit, and As-Built cells A and B and demonstrate somewhat erratic behavior in NMOC production rate.
The NMOCs from the Control cells appear to increase and decrease randomly while showing an overall decreasing trend during the sample collection period. Th e As-Built cells also appear to fluctuate during the sample collection period. Overall, it do es not appear to be a strong temporal trend for each cell. In general, the production rate for each cell falls between 0.002 an d 0.035 kg/min (0.004 and 0.07 lb/min). The meanNMOC production rate that takes into account the cell’s LFG flow rate for the Control, Retrofit, and AsBuilt A and B cells is 0.012, 0.012, 0.010, and 0.008 kg/min (0.026, 0.026, 0.022, and 0.018 lb/min), respectively.

Figure 5-17 NMOC Production in the Control Cells

891 / 1 / 2 0 0 3
7 / 1 / 2 0 0 3

1 / 1 / 2 0 0 4
7 / 1 / 2 0 0 4

1 /1/2005

7 / 1 / 2 0 0 5

1 / 1 / 2 0 0 6 0.03

0.02

0.01

0.00NMOC Emission Rate (kg/min)

Date

1 /1/20 0 3 7/1 / 2 0 03 1/1/2004 7/1 / 2 0 04 1/1/2 0 05
7 /1/2005 1/1 / 2 0 0 6NMOC Emission Rate (kg/min) 0.03

0.02

0.01

0.00

Date Figure 5-18 NMOC Production in As-Built Cell A

Figure 5-19 NMOC Production in As-Built Cell B

901 /1/200 1 7/1/200 1 1/1/2 00

2 7/1/ 200

2

1 /1/200 3 7/1/200 3 1/1/2 00

4 7/1/20 0 4 1/1 /200

5 7/1 /200

5 1/1/200 6 0.03

0.02

0.01

0.00NMOC Emission Rate (kg/min)

Date Figure 5-20 NMOC Production in the Retrofit Cells

5.4.2 Waste Mass-Based NMOC Production Analysis
The regulatory requirements for installing a LFG collec tion and control system are based on the mass flow rate of NMOCs, which is based on a tiered system. If a landfill’s design capacity is 2.5 million Mg or 2.5 million m 3 , a LFG collection and control system must be put in place. However, this is based on a regulatory default NMOC concentration of 4,000 ppm. If it can be demonstrated that a landfill’s NMOC concentration is less than 4,000 ppm, the NMOC prod uction rate may be modeled using the site-specific NMOC concentration and Equation 5-6.

n

− kt i − 9 M NMOC = 

# ∑ 2kL

o M i (e )(C NMOC )(3.6 × 10 ) Equation 5-6

i = 1

Where: M NMOC = Mass emission rate of NMOC (Mg/yr); k = CH 4 generation rate constant (yr -1 ); L o =CH 4 generation potential (m 3 /Mg); M i = Mass of MSW placed in year i (Mg); t i = age of the i th section of waste (yr); C NMOC = Concentration of NMOC (ppm); and 3. 6×10 -9 = Conversion factor.

After calculating the annual mass of NMOC production, th e result is compared to a regulatory threshold of 50 Mg/yr. If the calculated NMOC production exceeds this amount, then a LFG collection system must be installed in acc ordance with 40 CFR Subpart WWW. The site-specifi c NMOC concentr ation (i.e., C NMOC ) is determined by performing Tier 2 testing, which is described in Subpart WWW.

The calc ulation of NMOC production depicted in Equati on 5-6 differs from Equation 5-5 in that it is based on the m ass of waste in place as well as the parameters k and L o of the landfill cell instead of actual LFG collection data. Equation 5-6 can be modeled in Land GEM using site-specific waste placement data and a

91representative NMOC concentrati on (based on the sampling guidelines stated in Subpart WWW). The parameters k and L o can either be the Clean Air Act regulatory default values of 0.05 yr -1 and 170 m 3 /Mg or determined on a site-specific basis using U.S. EPA Method 2E.
The NMOC generation rate was modeled for each cel l based on available waste placement data, the regulatory default k and L o , and the mean NMOC concentration duri ng the study period. The mean NMOC concentration for each cell was presented in Table 5-10. Table 5-11 depicts the LandGEM-predicted NMOC production for each cell using the waste placement data presented in Table 5-5, k=0.05 yr -1 and L o =170 m 3 /Mg.
Typically, a demonstration of whether a landfill is abov e or below the 50 Mg/yr threshold is performed by summing the NMOC production rate for ea ch landfill unit at a site for a particular year. Since this report focuses on a portion of the OLRDF, a comparison to the 50 Mg/yr threshold would be incomplete, based on available NMOC concentration data (i.e., no NMOC data were available for the cells that were not part of this study). It is not feasible to make a strong comparison of NMOC production between the Control cells and the landfill bioreactor cells usin g the method prescribed by the regu lations (i.e., using Equation 5-6). The data presented in Table5-11 are a reflection of the waste placement data (time of waste placement and total in-place waste mass) and the NMOC concentratio n based on several sampling events. Since all of these data are incorporated in th e LandGEM model, it is difficult to establish a cause-and-effect relationship between operation as a bioreactor landfill and NMOC production. Section 5.3, which investigated relationships between waste placemen t, NMOC concentration, and LFG collection data, indicated that there was no clear distinction between the NMOC productions in the Control cells versus the landfill bioreactor cells. However, it is noted that th e increased waste decomposition rates discussed earlier may necessitate the early collection of LFG (regard less of predicted NMOC pr oduction) for bioreactor landfills, especially if the landfill owner/operator seeks to capture LFG for beneficial reuse (e.g., gas-toenergy).
Table 5-11 LandGEM-Predicted Mass Production Rate of NMOCs in Different Landfill Units (Mg/yr) Year Control Cell Retrofit Cell As-Built Cell A As-Built Cell B 1995

- 0.0

- - 1996

- 6.1

- - 1997

- 16.6

- - 1998

- 24.2

- - 1999 0.0 23.0

- - 2000 9.7 21.9

- - 2001 16.6 22.5

- - 2002 17.5 21.8 0.0 0.0 2003 19.1 20.7 4.3 3.7 2004 21.1 19.7 6.4 3.5 2005 21.4 18.7 10.3 7.6 2006 20.4 17.8 11.1 10.8 2007 19.4 17.0 10.6 10.3 2008 18.5 16.1 10.1 9.8 2009 17.6 15.3 9.6 9.3 2010 16.7 14.6 9.1 8.8 Note: A dash ( - ) indicates NMOC production was not modeled for that year since no waste was in place. To directly compare cells, the NMOC generation rate for each cell was based on normalized mass placement and site specific L o , k and the 95 percentile upper confidence level on the mean (as a conservative estimate of the mean) of the NMOC conc entration for each cell during the study period as presented in Table 5-12. Results of the analysis ar e presented in Table 5-13. Although the NMOC UCL 95 for the bioreactor cells was much lower than the Control cell (less than half), bioreactor cells produced more NMOC per year when compared to the Control cell. This observation is a direct result of the increase

92in LFG generation rate (higher k va lues) of bioreactor landfill cells . However, the amount of NMOC generated (Mg/year) drops quickly to levels below that of the Control cell within a few years of operations (7 years in the case of OLLB).
These results shed light on the importance of a LFG management system for bioreactor landfills. Bioreactor landfills are expected to emit NMOCs more rapidly than dry tomb cells. However, bioreactor landfill NMOC emissions tend to drop much quicker than dry tomb cells, thus reducing long-term
concerns.

Table 5-12 LandGEM Model Input Values for NMOC Side-by-Side Analysis Parameter Control cell Retrofit cell As-Built cell A As-Built cell B k (year -1 ) 0.061 0.061 0.16 0.16 L o (m 3 /Mg) 59 59 59 59

NMOC UCL 95 (ppm) 993 271 495 300

Table 5-13 LandGEM Predicted Mass Production Rate of NMOCs Emissions (Mg/yr) Year After Waste Placement Control Cells Retrofit Cells As Built Cell A As Built Cell B 1 0 0 0 0 2 4.83 1.32 6.05 3.66 3 8.24 2.25 9.79 5.92 4 8.64 2.36 9.46 5.72 5 9.36 2.56 9.60 5.81 6 10.27 2.81 10.01 6.06 7 10.34 2.82 9.38 5.67 8 9.72 2.66 7.99 4.84 9 9.15 2.50 6.81 4.12 10 8.61 2.35 5.80 3.51 20 4.68 1.28 1.17 0.71 30 2.54 0.69 0.24 0.14 60 0.41 0.11 0.00 0.00



### 5.5 Methane Surface Emissions

Methane emissions were measured on using a CEC-Landtec SEM-500 field instrument. Surface concentrations were monitored around the perimeter of the collection area and along a pattern that traversed the landfill at 30 m intervals and where visual observations indicated elevated concentrations of landfill gas. Emissions were monitored and recorded separately for Unit 5 and 7. The climatic conditions and the background methane concentration up and downwind were recorded for each sampling event. Background concentrations averaged 5.82 ppm upwind and 9.97 ppm downwind for Unit 5, and 2.98 ppm upwind and 21.73 ppm downwind for Unit 7, for the period December 2001 to June 2006. Permit requirements necessitate a methane concentration greater than 500 ppm above the measured background level to be marked, adjustments made to reduce the surface emissi ons at that location, and the location to be reanalyzed within 10 days. If an exceedance exists on reanalysis, additional adjustments and/or cover maintenance must be performed and the location reanal yzed within 10 days. On a third exceedance, the Air Pollution Control District (APCD) must be notified, an d either a new well installed within 120 days of the initial exceedance, or an alternative remedy submitted for approval to the APCD.

93During the period from December 2001 to June 2006, Unit 5 recorded the following permit response actions:

• Reported twenty occasions of exceedances which were resolved within 10 days via adjustment of the gas collection system;

•

 Seven exceedances where additional soil cover was added; and

• Installation of one new gas collection well.
During the period from December 2001 to June 2006, Unit 7.3 recorded the following permit response actions:

• 

### • Reported fifteen exceedances which were resolved within 10 days via adjustment to the gas collection system;

• Fourteen exceedances where additional soil cover was added; and

• Five instances that required maintenance of leachate risers or changes to the gas collection header to resolve the issue



### . During this same period, Unit 7.4 record ed the following permit response actions:

• Reported four exceedances which were resolved within 10 days via adjustment to the gas collection system;

• Four exceedances where additional cover soil was added; and

• One instance that required modification of the gas collection header to resolve the issue.

94

## Chapter 6. Leachate Quality

This section considers the following parameters for the leachate quality analysis and the interpretation of the treatment performance in the different landfill un its: temperature, pH, volatile organic acids (as acetic acid), BOD, COD, BOD/COD ratio, TOC, TKN, ammonia nitrogen (NH 3 /NH 4 -N), total iron, total phosphorous, total metals, VOCs, SVOCs, and chloride. Leachate quality changes over time as a landfill ma tures and the waste characteristics change due to changes from waste decomposition. Ho wever, often that quality is gover ned by the bottom, most degraded, portion of the landfill (Kjeldsen et al., 2002). In this section, leachate quality over time (not waste age) is evaluated. As the statistical analys is of the solids samples demonstrated in Section 4.1, both waste age and sample date were found to have an equivalent im pact in demonstrating trends or changes in waste characteristics (and therefore leachat e characteristics). As such, an ex amination of leachate quality over time was deemed to be an appropriate context in which to view the data. Trends of leachate parameters versus time were plo tted for leachate parameters with detection frequencies exceeding 50 percent. Descriptive statistical summaries are presented in the analysis for each of the leachate parameters discussed below: (i) number of sa mples; (ii) percent detected; (iii) minimum number of samples detected; (iv) maximum number of samples detected; (v) mean and standard deviation of the detected samples; (vi) 95 percent UCL; (vii) 75 th percentile; and (viii) 95 th percentile. When the percentage detected was less than 100 percent, detection limits we re noted in the summary statistics. Multiple linear regressions were used to quantify trends of the leachate parameters. When linear regression assumptions were not met, a qualitative assessment was utilized. Details on the quantitative and qualitative assessment of the leachate parameters are included in Appendix F. The 95 percent confidence interval for the mean is the range of values that will contain the true mean (i.e., the average of the full statistical population of all possible data) 95 percent of the time. The 75 th and 95 th percentiles represent values that are less than or equal to the selected value, 75 percent and 95 percent of the values respectively.


### 6.1 Temperature
Leachate temperature may be an indicator of microbial activity in a landfill. However, temperature alone cannot predict the stages of waste decomposition. For example, temperature may also reflect seasonal variation and, to a lesser extent, the effectiveness of insulation provided by the landfill configuration. Anaerobic processes are favorable at mesophilic (30 to 38 oC) and ther mophilic (50 to 60 oC) temperature ranges. Leachate temperatures as a function of time in the Co ntrol, Retrofit, and As-Built cells are presented in Figures 6-1 through Figure 6-3, respectively. Based on the multiple regression analysis conducted, leachate temperature exhibited a statistically significant positive trend in the Control and As-Built cells. The same analysis, however, indicated that the leachate temperature in the Retrofit cell A had a statistically significant decreasing trend while Retrofit cell B did not display any trends. The detailed statistical analysis is presented in Appendix F. These trends can graphically be observed in Figures 6-1 through 6-3. Overall leachate temperature in the As-Built cells (average 33 oC) was higher than in Retrofit cells (average 27 oC), and Control cells (average 22 oC), potentially indicating a higher waste decomposition rate in the As-Built cells relative to the other treatments as a result of air and liquids injection that likely had stimulated and increased microbial activity. It is no ted that a decrease in temperature of about 7 oC was observed in Control cell A compared to Control cell B following the end of 2004. Reasons for such a change are currently under investigation and will be further discussed in later reports.

95Temperature (oC)

20

10

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date 50

Control Cell A Control Cell B 40

30Temperature (oC) 50

Retrofit Cell A Retrofit Cell B 40

30

20

10

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-1 Leachate Temperature as a Function of Time in the Control Cells

Figure 6-2 Leachate Temperature as a Function of Time in the Retrofit Cells

9650

As-Built Cell A As-Built Cell B 40

30

20

10

0Temperature (oC)

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-3 Leachate Temperature as a Function of Time in As-Built Cells


### 6.2 pH
The leachate pH is typically measured in landfill l eachate to assist in identifying the stabilizing phase (see Chapter 2). For optimal anaerobic activ ity, the leachate pH is expected to range from 6.8 to 7.6 (Parkin and Owen 1986). Although the initial pH may drop, because of the production and accumulation of VOAs, it tends to rise back to the neutral range in the CH 4 fermentation phase when methanogens start consuming the VOAs. The air addition, in the As-Built cells, is expected to shorten the acid-forming phase and cause a rapid progression towards the CH 4 fermentation phase. As with temperature, there are sign ificant increasing pH trends (Figures 6-4 through 6-6) in the Control cells and As-Built cells, and significant decreasing trends in the Retrofit cell s. The model fits are only fair as seen in the adjusted-R 2 values (See Appendix F). The pH time plots indicate that a seasonal component may be present, but when this component was added to the model, the regression fits did not improve. Although in both the Control and As-Bu ilt cells, the pH reached neutral valu es by the end of 2003, a clearly defined acid forming phase was not observed. The aci d forming phase occurs at the early stages of a landfill’s life and may last for a relatively short period. In this study, the introduction of air may have also shortened the period of acid forming phase in the As -Built cells. Thus, in future study, measurement of leachate pH may be needed at a greater sampling freq uency to identify small or sudden changes resulting from air addition. During the monitoring period, the mo stly likely reason for the neutral pH values was that the characteristics of the bottom porti on of well degraded solid waste influenced the overall pH of the leachate, as described earlier in this document. A good fraction of the industrial liquid introduced into the As-Built bioreactor Cells was carbonated beverage waste which tends to be acidic in nature. Ba sed on the leachate pH values, the addition of these types of liquids did not result in a decrease of the m easured leachate pH in the As-Built bioreactor landfill cells. A sudden drop in pH to about 5.2 was observed in As-Built cell B during September 2004. This, however, was not observed in As-Built cell A, and so the limited and short-peri od drop in leachate pH could not be attributed to the addition of beverage waste. Once again it is noted that a decrease in pH of about 0.4 was observed in Control cell A relative to Control cell B following the end of 2004. This decrease was consistent with trends of other parameters.

97pH (-log H+) 10

Control Cell A Control Cell B 9

8

7

6

5 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05
DatepH (-log H+) 10

Retrofit Cell A Retrofit Cell B 9

8

7

6

5 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05
Date Figure 6-4 Leachate pH as a Function of Time in the Control Cells

Figure 6-5 Leachate pH as a Function of Time in the Retrofit Cells

98pH (-log H+)

5 6 7 8 9 10

As-Built Cell A As-Built Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-6 Leachate pH as a Function of Time in the As-Built Cells


### 6.3 Volatile Organic Acids (VOAs)
The production and accumulation of VOAs is an indicator of the acid formation phase of a landfill. The concentration of VOAs decreases over time as th ese acids are consumed by methanogens in the CH 4 fermentation phase. At this phase, pH is expected to increase and to stabilize around neutral values. VOAs measured in the leachate included: acetic acid, butyric acid, formic acid, lactic acid, propionic acid, and pyruvic acid. For the purposes of this report, rather than reporting the concentration of each VOA by itself, the total VOAs concentra tions were calculated as acetic aci d using the following equation:


### [Total VOAs] = 

## [ Acetic 

## ] + 60 × ⎜ ⎛ 

## [ Butyric 

## ] + 

## [ Lactic 

## ] + 

## [ Pyruvic 

## ] + 

## [ Propionic 

## ] ⎟ ⎞ Equation 6-1 

### ⎝ 88 90 110 74 ⎠ where: numerals indicate the molecular weight of each compound in grams; brackets indicate concentration in mg/L; and total VOAs are expressed in mg/L as acetic acid. Of the VOAs examined in the leachate, only ace tic and propionic acids were detected above their respective detection limit at sufficient frequencies. Because of the large per centage of non-detects, statistical analysis and comparisons were rather difficult to conduct. Leachate VOA concentration as a function of time in the Control and As -Built cells are presented in Figure 6-7 and Figure 6-8, respectively. VOAs in the Retrofit cells were detected at a rela tively low frequency, thus will not be graphically presented in this section. VOAs concentrations exhib ited a spike in the leachate of the Control cells in late 2003. Since then, with a few exceptio ns, concentrations of VOAs in th ese cells remained below 100 mg/L during the monitoring period suggesting that the CH 4 fermentation phase in the Control cells had already started. This observation is further supported by the leachate pH measured in the Control cells,

99Volatile Organic Acid as Acetic Acid (mg/L)

0 1000 2000 3000 4000 5000

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-7 Volatile Organic Acids as a Function of Time in Control Cell B

6/1/01 12/1/01 6/1/02 12/1 /02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateVolatile Organic Acid as Acetic Acid (mg/L)

0 1000 2000 3000 4000 5000

As-Built Cell A As-Built Cell B

Figure 6-8 Volatile Organic Acid as a Fu nction of Time in the As-Built Cells

100which is consistent with on-going waste decomposition in the CH 4 fermentation phase. For the As-Built cells, concentrations of VOAs were relatively high with a large degree of variability from approximately 4,000 mg/L prior to mid 2004 before stabilizing below 10 0 mg/L at a later time. This correlated well with leachate pH increasing to reach a neutral value followi ng the end of 2003 in the As-Built cells. It is particularly interesting to recognize that the As-B uilt cells generated high volumes of LFG, as was presented in Chapter 5, even during times with high VOA concentration in the leachate. The existence of this phase “accelerated methane phase” suggests that for bioreact or landfills, because of the increase in the degradation rate, it is possible to have high VOA concentration as the methane generation starts. Compared to Control cells, higher concentrations of VOAs (about five-fold) we re observed in leachate from As-Built cells until mid 2004.


### 6.4 Total Organic Carbon (TOC)
TOC includes a variety of organic compounds, including humic and fulvic acids, VOAs, and carbohydrates. TOC measur ement was not included as a leachate monitoring parameter until early 2004. A statistical summary of the TOC measurements in th e leachate of the landfill units is presented in Appendix F. Leachate TOC concentrations as a function of time in the Control, Retrofit, and As-Built cells are presented in Figures 6-9 through 6-11, respectively. Statistically, the TOC concentrations in the leachate sh owed no apparent trends in any of the treatment cells. The addition of beverage waste to the As-Bui lt cells was likely respons ible for the higher TOC concentrations (about three-fold) obse rved in this unit as compared to the Control and Retrofit cells. TOC measurements increased from about 800 to 1,500 mg/L in the As-Built cells while it ranged from 500 to 800 mg/L in the Control cells. Higher TOC concentrations could also have been caused by an increase in the rate of waste decomposition in the As-Built cells, wh ich may have resulted in higher concentrations of VOAs, as discussed earlier. TOC concentrations in th e Retrofit cells were lower compared to the other two treatment units and appeared to be stable ranging from 200 to 500 mg/L, which is again consistent with a stable phase of CH 4 production. A decrease in TOC concentration of about 600 mg/L was observed in Control cell A following the end of 2004.Total Organic Carbon, TOC (mg/L)

0 500 1000 1500 2000

Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-9 Total Organic Carbon as a Function of Time in the Control Cells

101Total Organic Carbon, TOC (mg/L) 2000

Retrofit Cell A Retrofit Cell B

1500

1000

500

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Organic Carbon, TOC (mg/L) 2000

As-Built Cell A As-Built Cell B

1500

1000

500

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-10 Total Organic Carbon as a Function of Time in the Retrofit Cells

Figure 6-11 Total Organic Carbon as a Function of Time in the As-Built Cells

102

### 6.5 Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)
BOD is generally higher in younger leachate and it decreases more rapidly than COD over time. COD includes the recalcitrant organic compou nds (e.g., high molecular weight compounds as well as synthetics). Consequently, as waste ages, the ratio between BOD and COD decreases (i.e., more COD in relation to BOD). Leachate generated from waste with relativ ely low biodegradability was reported to have a BOD/COD ratio lower than 0.5 (Christensen et al. 2001, Reinhart and Alyousfi 1996). A statistical summary of the BOD and COD measurements in the leachate of the diff erent landfill units is presented in appendix F. Leachate BOD, COD, and BO D/COD ratios as a function of time in the Control, Retrofit, and As-Built cells are presented in Figu res 6-12 through Figure 6-20, respectively. BOD concentrations showed an increasing trend in th e Control cells and a decreasing trend in the Retrofit and As-Built cells. Leachate from the As-Built cells exhibited BOD concentrations that were substantially higher (about five-fold) than in the Control and Retrofit cells. This could be a consequence of the high BOD in the beverage waste added to the As-Built cells. Retrofit cells displayed lower concentrations of BOD than both Control and As-Built ce lls, which is indicative of the more mature waste in the Retrofit cells. BOD concentrations in the C ontrol cells ranged from 20 to 1,000 mg/L. The BOD concentration in the Retrofit cells was typically belo w 200 mg/L. BOD concentrations in the As-Built cells ranged from 300 to 10,000 mg/L prior to early 2004 before stabilizing at about 250 mg/L. COD concentrations showed an increasing trend in the Control cells, a decreasing trend in the Retrofit cells and no apparent trend in the As-Built cells. Similar to BOD concentrations, the highest COD concentrations were found in the leachate from As-B uilt cells, followed by the Control cells and the Retrofit cells. COD concentration in the Control cells was typically below 1,000 mg/L prior to September 2003 before increasing to about 2,000 mg/L. COD con centration in the Retrofit ce lls decreased from about 2,000 to 1,000 mg/L during the monitoring period. COD concentration in the As-Built cells increased from about 2,000 to 5,000 mg/L during the monitoring period. The BOD/COD ratios are comparable between the As-Built and Control cells as they both appear to show a decreasing trend early on with a more stable ratio as the waste ages. The BOD/ COD ratio in leachate from the As-Built cells dropped below 0.5 at the end of 2003 , almost two years after initiating landfill bioreactor activities. Similarly, the BOD/COD ratio in the Cont rol cells dropped below 0.5 after June 2002, almost four years after initial waste placement. These result s indicate that the As-Built cells exhibited a more rapid rate of decomposition relative to the Control cells. The BOD/COD ratio in both the As-Built and Control cells reached about 0.1 in December 2005. The BOD/COD ratio in Retrofit cells generally remained constant throughout the monitoring period. The ratio ranged from 0.05 to 0.08, which is indicative of mature leachate generated from less degradab le (i.e., more mature) waste. Similar to the other parameters previously discussed, there is a clear difference between Control cell A and Control cell B following the end of 2004 with respect to BOD and COD. Control cell A has distinctly lower concentrations of BOD and COD compared to Control cell B.

103Biochemical OxygenDemand, BOD (mg/L) 10000

1000

100

10 Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateChemical Oxygen Demand, COD (mg/L) 10000

1000

100

Control Cell A Control Cell B

10 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-12 Biochemical Oxygen Demand as a Function of Time in the Control Cells

Figure 6-13 Chemical Oxygen Demand as a Function of Time in the Control Cells

104BOD/COD Ratio 1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0 Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateBiochemical Oxygen Demand, BOD (mg/L)
10000

1000

100

10 Retrofit Cell A Retrofit Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-14 BOD/COD Ratio as a Function of Time in the Control Cells

Figure 6-15 Biochemical Oxygen Demand as a Function of Time in the Retrofit Cells

105Chemical Oxygen Demand, COD (mg/L) 10000

1000

100

10 Retrofit Cell A Retrofit Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date

1.6

Retrofit Cell A 1.4 Retrofit Cell B

1.2BOD/COD Ratio 1.0

0.8

0.6

0.4

0.2

0.0

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-16 Chemical Oxygen Demand as a Function of Time in the Retrofit Cells

Figure 6-17 BOD/COD Ratio as a Function of Time in the Retrofit Cells

10610000

1000

100

As-Built Cell A As-Built Cell B

10 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateBiochemical Oxygen Demand, BOD (mg/L)

100

As-Built Cell A As-Built Cell B
10 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date 10000

1000Chemical Oxygen Demand, COD (mg/L) Figure 6-18 Biochemical Oxygen Demand as a Function of Time in the As-Built Cells

Figure 6-19 Chemical Oxygen Demand as a Function of Time in the As-Built Cells

107BOD/COD Ratio

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
As-Built Cell A As-Built Cell B



### Date Figure 6-20 BOD/COD Ratio as a Function of Time in the As-Built Cells


### 6.6 Nitrogen Content
TKN is the sum of organic nitrogen plus ammonia. Ammonia concentrations should not be higher than TKN concentrations, since they are a subset of TKN. Ammonia is the reduced, inorganic form of nitrogen and is formed as a result of the release of organic nitr ogen in waste. The conversion of organic nitrogen to ammonia is called ammonification. As waste degrad es, ammonia concentrations in leachate generally increase as the nitrogen-b earing compounds in waste (e.g., proteins, amino aci ds, etc.) mineralize (i.e., become ammonified). As leachate matures, most of the organic nitrogen is mineralized and TKN is (almost) equivalent to ammonia. The conversion of ammonia to nitrate (nitrification) under aerobic conditions produces nitrite as a short-lived intermediary. Due to th e anaerobic nature of leachate, nitrite and nitrate are generally not detected. However, it is noted that the Retrofit cells were injected with nitrified leachate as an additional source of liquids, which could lead to the detection of these compounds in the leachate. Furthermore, the As-Built cells we re injected with air, which would be expected to facilitate nitrification and therefore increase the detection of nitrate in the leachate. A statistical summary of the nitrogen content in the leachate of the differ ent landfill units is presented in appendix F. It is noted that nitrate was not detected at a frequency greater than 50 percent in any of the landfill units. Nitrite was detected at greater than 50 percent frequency in the As-Built cells, but not in the Retrofit or Control cells. This was likely caused by th e introduction of air into the waste in the As-Built cells. However, while nitrate also br iefly spiked in the As-Built cells, it was detected at lower frequencies than nitrite, potentially indicating in complete nitrification. Furthermor e, this effect occurred over a brief period that quickly disappe ared as conditions returned to anaerobic . Leachate nitrogen content (TKN and ammonia) as a function of time in the Control, Retrof it, and As-Built cells, is presented in Figures 6-21 through 6-26.
Ammonia concentration trends often reflect those of TK N. TKN concentration trends in the As-Built cells and Control cell B were similar and showed an increasin g trend. TKN concentrati ons increased from about 250 mg/L to 1,500 mg/L an d from about 100 mg/L to 1,500 mg/L in the Control cell B and As-Built cells during the study period, respectively. An increase in TKN concentrations may be an indicator of additional waste degradation in the Control and As-B uilt cells. TKN concentrations showed a decreasing trend in Retrofit cell A and no trend in Retrofit cell B. Ammonia concentrations showed a significantly

108decreasing trend in the Retrofit cells. A decrease in TKN concentrations of about 1,200 mg/L was observed in Control cell A following the end of 2004. The As-Built cells and Control cell B exhibited an increasing trend of ammonia with a similar magnitude as TKN. Ammonia concentrations increased from about 250 mg/L to 1,800 mg/L and from about 500 mg/L to 1,800 mg/L in Control cell B and the As-Built cells, respectively. A decrease in ammonia concentrat ions of about 1,200 mg/L was observed in Control cell A following the end of 2004, which is consistent with the decrease in TKN concentrations. The Retrofit cells were injected with nitrified leachate and exhibited decreasing trends of TKN and ammonia concentrations. The decrease in ammonia conc entrations was likely related to the nitrification process where ammonia in leachate was converted into nitrate, which counteracted the build-up of ammonia concentrations in leachate from the Retrofit cells. However, no spike in nitrate (or nitrite) concentrations was observed in these cells as a consequence of the additional liquids injection. This could be expected given the strongly anaerobic nature of l eachate in these cells and th e relatively low volume of nitrified leachate introduced as compared to generate d leachate. It was expected that denitrification (therefore an increase in N 2 gas) of the nitrified l eachate upon injection would o ccur; however changes in N 2 gas concentration in the Retrofit cells appeared to be intermittent and short-lived, which may be indicative of changes in N 2 concentration that were caused by oper ational issues (e.g., over-pulling on the gas well field and watering out of gas wells) rather th an a result of denitrification. The results discussed above are again consistent with the more stable and ma ture waste in the Retrofit cells. TKN concentrations in the Retrofit cells gradually decreased from about 1,000 mg/L to stabilize around 500 mg/L. It is expected that the TKN concentrations in the Retrofit cells will remain at this level for decades, since research using leaching tests on MSW has shown that th e nitrogen content in leachate will be substantial for centuries (Christensen et al. 2001). The Retrofit cells display a decreasing trend in ammonia concentrations from about 1,500 mg/L to 500 mg/L; these concentrations are generally lower compared to the Control and As-Built cells, indicating more stable concentrations, which is indicative of a more mature and stable waste.Total Kjeldahl Nitrogen, TKN (mg/L)

0 500 1000 1500 2000 2500 3000

Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-21 Total Kjeldahl Nitrogen as a Function of Time in the Control Cells

109Ammonia as Nitrogen (mg/L) 3000

Control Cell A Control Cell B 2500

2000

1500

1000

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date 500Total Kjeldahl Nitrogen, TKN (mg/L) 3000

Retrofit Cell A Retrofit Cell B 2500

2000

1500

1000

500

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-22 Ammonia as Nitrogen as a Function of Time in the Control Cells

Figure 6-23 Total Kjeldahl Nitrogen as a Function of Time in the Retrofit Cells

1103000
Retrofit Cell A Retrofit Cell B 2500

2000

1500Ammonia as Nitrogen (mg/L)

1000

500

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-24 Ammonia as Nitrogen as a Function of Time in the Retrofit Cells

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Kjeldahl Nitrogen, TKN (mg/L)

0 500 1000 1500 2000 2500 3000

As-Built Cell A As-Built Cell B

Figure 6-25 Total Kjeldahl Nitrogen as a Function of Time in the As-Built Cells

111Ammonia as Nitrogen (mg/L) 3000

2500

2000

1500

1000

500

0 As-Built Cell A As-Built Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-26 Ammonia as Nitrogen as a Function of Time in the As-Built Cells


### 6.7 Metals
Addition of industrial liquids into the As-Built cells may have caused an increase in the heavy metals content of the leachate. Paint and ink waste made up about 11 percent of the total liquids added to the AsBuilt cells. Metals that are typically constituents of paint and ink waste include arsenic, barium, cadmium, chromium, mercury, selenium and silv er. Elevated concentrations of trace heavy metals in wastewater streams have been reported to retard or inhibit biol ogical processes (U.S. EPA 1987). In general, aerobic processes are more sensitive to elevated trace metal concentrations compared to anaerobic processes, and inhibition of biological processes (and therefore waste degradation) in MSW landfills, as a consequence of elevated trace metal concentrations, is very unlikely si nce metals concentrations are well below the ranges reported to inhibit biological processes (U.S. EPA 1 987). Trace metal concentrations are generally low in leachate from MSW landfills and are not very useful leachate parameters for a geochemical evaluation. Iron concentrations, on the other hand, are generally substantial in leachate and may be more useful as a monitoring parameter. Under anaerobic conditions, it is expected that more iron gets mobilized since the reduced form of iron (Fe 2+ ) is more soluble than the oxidized form (Fe 3+ ), which precipitates out as oxides and hydroxides. A statistical summary of leachate metals, as presented in Appendix F, show that trace metal concentrations generally do not appear to exhibit a trend. However, it is noted that aluminum, cadmium, copper, and lead were observed at greater frequency and concentration in the As-Built cells compar ed to the other landfill units. This may have been caused by the injection of industrial liquids containing paint waste and ink waste into those cells. Arsenic and chromium were detected at 100 percent frequency in both the Retrofit and As-Built cells. Arsenic concentr ations appeared to be slightly higher in leach ate from the Retrofit cells. Arsenic is more mobile under anaerobic conditions since it is present in its more mobile (and more toxic) trivalent state (As 3+ ) compared to its pentavalent oxidation state (As 5+ ). Conversely, chromium concentrations appeared to be higher in leachate from the As-Built cells. This is consistent with the fact that chromium is more mobile and so luble in its oxidized state (i.e., Cr 6+ ) as compared to its reduced trivalent oxidation state (i.e., Cr 3+ ). This difference could also be the consequence of higher concentrations of dissolved organic carbon (which is captured in the TOC measurements), which has been shown to increase metal mobility th rough the formation of DOC-metal complexes.

112Total iron concentrations in leachate as a function of time in the Control, Retrofit, and As-Built cells are presented in Figures 6-27 through 6-29, respectively. Iron concentrations showed a decreasing trend with concentrations gradually decreasing from about 15 mg/L to 5 mg/L and from about 30 mg/L to 5 mg/L in the Control and As-Built cells, respectively. In the Retr ofit cells, iron concentrations showed an increasing trend in Retrofit cell A and no significant trend in Retrofit cell B and ranged from approximately 10 to 20 mg/L. Iron concentrations were high er in the Retrofit cells as compared to the Control and As-Built units. This is consistent with more reducing conditions in the Retrofit cells compared to the Control and As-Built cells. This is also consistent with the interpretation of arsenic concentrations abov e. Injection of air into As-Built cells appears to have had a fairly long-lasting effect as iron concentrations are low. The iron levels are likely to rebound as the waste matures an d the potential effect of the aeration dissipates. However, a longer monitoring period is required to support more conclusive interpretations with respect to iron concentrations.


### 6.8 Volatile and Semi-Volatile Organic Compounds
The occurrence of VOCs and SVOCs in leachate may be of use in evaluating the landfill bioreactor’s capacity for microbial assimilation and transformation of organic and potentially toxic compounds. A list of VOCs and SVOCs that were measured in the leachat e of the different landfill units is presented in Chapter 3. A statistical summary of the VOCs and SVOCs detected at grea ter than 50 percent frequency in the different landfill units is presented in Appendix F. Similar to the discussion regarding trace metals, VOCs and SVOCs were generally only detected at fairly low concen trations in leachate from MSW landfills and meaningful trends are generally hard to di scern. Overall, the concen trations of VOCs detected in leachate of the different treatment units were consis tent with similar landfill settings. Acetone, MEK, and toluene were detected at a greater frequency and co ncentrations in the As-Built cells compared to other units. However, these compounds are generally quickly degraded under aerobic conditions and do not pose challenges for leachate management.Total Iron (mg/L)

0 10 20 30 40 50

Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-27 Total Iron as a Function of Time in the Control Cells

113Total Iron (mg/L) 50

Retrofit Cell A Retrofit Cell B 40

30

20

10

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Iron (mg/L) 50

As-Built Cell A As-Built Cell B 40

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date 30

20

10 Figure 6-28 Total Iron as a Function of Time in the Retrofit Cells

Figure 6-29 Total Iron as a Function of Time in the As-Built Cells

114Similarly, leachate from MSW landfills may contai n some SVOCs including phenolic compounds such as phenols and cresols. Low concentr ations of cresols were detected in the As-Built cells at higher frequencies and concentrations compared to the other ce lls. This may be a consequence of the addition of paint waste. SVOCs and VOCs may have a small effect on COD measurements. In general, the VOC and SVOC concentrations were relatively low and there were no observed trends of VOC and SVOC concentrations in the leachate samples.


### 6.9 Phosphorous Content
Phosphorous may be one of the rate-controlling macro nut rients in landfills. Since leachate samples were not filtered prior to analysis, a high phosphorous concen tration may be an indicator of microbial growth as it was incorporated into the microb ial cell mass, which was analyzed as total phosphorous. Mineralization of organic phosphorous in the waste generates inorga nic phosphorous. In its inorganic form, phosphorous is typically measured as ortho-phosphate. Leachate ortho-phosphate an d phosphorous concentrations as a function of time in the Control, Re trofit, and As-Built cells, are presente d in Figures 6-30 through Figure 6­ 35. Phosphate concentration trends in th e As-Built cells and Control cell B are similar; both show an increase over time with concentrations in th e As-Built cells being slightly higher. The Retrofit cells exhibited a slightly increasing trend with lower concentrations when compared to the As-Built and Control cells. Phosphate concentrations were below 3 mg/L before th ey gradually increased up to 15 mg/L after the end of 2003 in the Control cells. The increase in phosph ate may be an indicator of increased decomposition following the end of 2003 as or ganic phosphorous in waste became mineralized. On the other hand, microbial growth may account for an increase in total phosphorous concentrations, which would also be an indirect measurement of increased decomposition as an increase in microbial cell mass, suggesting an increase in waste decomposition. Total phosphorous concentration trends are generally a reflection of phosphate concentrations. Similar to phosphate, phosphorous concentrations in the Control cells increased from below 5 mg/L to about 15 mg/L following the end of 2003. Similar to other parameters discussed above, a decrease in phosphate and phosphorous concentrations of about 5 mg/L was observed in Control cell A following the end of 2004. The Retrofit cells displayed a sli ghtly increasing trend with lower concentrations of phosphate and phosphorous compared to Control cell B and the As-Bui lt cells. Phosphate and phosphorous concentrations were at or slightly below 5 mg/L in the Retrofit cells. The As-Built cells displayed an increasing trend of phosphate and phosphorous concentrations, similar to that in the Control cells. Phosphate concentrations were mostly below 5 mg/L before they increased up to 18 mg/L following mid 2004. Similarly, total phosphorous concentrations were below 10 mg/L before increasing up to 25 mg/L following mid 2004. Th e increase in phosphate an d phosphorous may be an indicator of increased waste decomposition and microbial growth following mid 2004. However, it cannot be excluded that the addition of the beverage waste to the As-Bui lt cells increased the phosphorous concentrations in these cells, since many beverage s contain phosphoric acid; however, this cannot be verified with the available analyti cal data for the beverage waste Leachate carbon to phosphate ratio (C: P) was determin ed for the different treatme nt units. For the Control cells, the C:P ratio mean and standard deviation were 124.1 ± 6 9.5 (Control cell A) and 124.2 ± 53.3 (Control cell B). For the Retrofit cells, the C:P ratio mean and standard deviation were 105.3 ± 40.4 (Retrofit cell A) and 121.2 ± 53.4 (Retrofit cell B). For the As-built cells, the C:P ratio mean and standard deviation were 160.1 ± 77.7 (As-Built ce ll A) and 181.0 ± 58.5 (As-Built cell B). A C: P ratio of 60:1 is deemed optimal for microorganisms to ac tively assimilate substrate carbon.

115Ortho-Phosphate (mg/L)

0 5 10 15 20 25 30

Control Cell A Control Cell B

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-30 Ortho-Phosphate as a Function of Time in the Control Cells

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Phosphorous (mg/L)

0 5 10 15 20 25 30

Control Cell A Control Cell B

Figure 6-31 Total Phosphorous as a Function of Time in the Control Cells

116Ortho-Phosphate (mg/L) 30

Retrofit Cell A Retrofit Cell B 25

20

15

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5

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Phosphorous (mg/L) 30

Retrofit Cell A Retrofit Cell B 25

20

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5

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-32 Ortho-Phosphate as a Function of Time in the Retrofit Cells

Figure 6-33 Total Phosphorous as a Function of Time in the Retrofit Cells

117Ortho-Phosphate (mg/L) 30
As-Built Cell A As-Built Cell A 25

20

15

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5

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateTotal Phosphorous (mg/L) As-Built Cell A As-Built Cell B 25

20

15

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5

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date 30 Figure 6-34 Ortho-Phosphate as a Function of Time in the As-Built Cells

Figure 6-35 Total Phosphorous as a Function of Time in the As-Built Cells


### 6.10 Chloride
Chloride is a useful leachate parameter since it is present at substantial concentrations in MSW landfill leachate behaves like a conservative tracer (i.e., it does not get attenuated). Chloride concentrations are expected to show a peak due to an initial period of leaching and mobilization and remain relatively constant thereafter. Thus, chloride concentra tions are generally considered to be fairly stable over time (except if

118the nature of the landfilled waste changes). Furthermore, chloride is not redox sensitive and should not change much as a result of the di fferent treatment approaches.
Leachate chloride concentrations as a function of time in the Control, Retrofit, and As-Built cells are presented in Figures 6-36 through Figure 6-38. Interestingly, chloride concentrations appeared to show an increasing trend over time in both the Control and the As-Built cells, although it is observed that the initial chloride concentration in the Control cells was lo wer than the other cells. Changes in chloride concentrations are generally more a reflection of diluti on rather than a result of waste decomposition. Chloride concentrations in the Control cells were be low 1,000 mg/L prior to mid 2003 and increased to a peak at about 5,000 mg/L before decreasing again at the end of 2004. Consistent with most parameters presented in this section, chloride concentrations in Control cell A decreased compared to Control cell B following mid 2004. In the Retrofit cells, chloride concentrations showed no trend and ranged between 1,000 mg/L to 2,000 mg/L. Chloride concentrations in the As-Built cells showed an increasing trend with concentrations increasing from about 1,000 mg/L to 3,000 mg/L. The increase in chloride concentrations in the Control and As-Built cells may have been cause d by the ongoing waste placement in those cells until 2004 and 2005, respectively. It is expected that these concentrations will stabilize over time.


### 6.11 Leachate Quality Summary
In summary, all parameters measured provide a consis tent geochemical picture for each cell with respect to each cell’s waste age and waste decomposition phase. The As-Built cells, which received air and liquids injection, have the youngest waste age and appear to display the most active phase of decomposition. Trends are generally not mu ch different in the bioreactor landfill cel ls compared to the Control cells, even though concentrations of some parameters appear to be higher. The substantial difference in temperature, however, may indicate more active decomposition in As -Built cells, possibly reflective of the exothermic nature of aerobic MSW decomposition. Although the ov erall waste age in the As-Built cells is less than that of the Control cells, the geochemical analysis of the leachate indicates that the cells are approximately at the same stage of waste decomposit ion. Judging from the reviewed data, it can be hypothesized that the combined treatment of air and liquids appears to have accelerated waste decomposition in this investigation. The Retrofit cells, which received n itrified leachate, did not sh ow any significant signs of accelerated waste decomposition based on the leachate chem istry. This is likely the result of waste age (as much as six years old when treatment began), which is significantly older than both the Control and AsBuilt units. The waste in the Retrofit cell may have already reached a more mature stage prior to the addition of supplemental liquids, which is reflected in stable and lower concentr ations of many leachate parameters reviewed. From a geochemical persp ective, it appears the waste may have already gone through most of its decomposition; thus, the injection of liquids did not increase waste decomposition in the Retrofit cells. The addition of nitrified leachate to th e Retrofit cells resulted in a significant decrease of ammonia concentrations in the leachate of the Retrofit cells.

1196000
Control Cell A Control Cell B 5000

4000

3000

2000

1000Chloride (mg/L)

0 6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### Date Figure 6-36 Chloride Concentrations as a Function of Time in the Control Cells

6/1/01 12/1/01 6/1/02 12/1/02 6/1/03 12/1/03 6/1/04 12/1/04 6/1/05 12/1/05


### DateChloride (mg/L)

0 1000 2000 3000 4000 5000 6000

Retrofit Cell A Retrofit Cell B

Figure 6-37 Chloride Concentrations as a Function of Time in the Retrofit Cells

120Chloride (mg/L) 6000
As-Built Cell A As-Built Cell B 5000

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### Date Figure 6-38 Chloride Concentrations as a Function of Time in the As-Built Cells

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## Chapter 7. Landfill Bioreactor Performance Analysis

As described in Chapter 1 of this report, one of the primary objectives of the OLLB study was to evaluate whether the benefits of landfill bioreactors as report ed in laboratory- and pilo t-scale projects could be realized at a full-scale and operating MSW landfill. The previous chapters of this interim report focused on describing the tests that were performed to evaluate the performance of the OLLB and presenting an interpretation of the test results. This chapter prov ides a general discussion of the overall performance of the OLLB with respect to certain permitting issues that are relevant to landfill bioreactors. The issues addressed in this chapter are slope stability, liner and cover integrity, liquids addition system performance, LCS performance, and LFG production and emissions. Relevant sections of the “ Solid Waste Disposal Facility Criteria Technical Manual ” (U.S. EPA, 1993) are referenced, where appropriate.


### 7.1 Slope Stability
MSW Landfills must be designed and operated in a ma nner that maintains the stability of natural and waste slopes. Based on evaluations of past failures of bot h natural slopes and waste slopes, it is widely known that excessive amounts of liquids within soils or waste can contribute to failure and/or movement of slopes. The failure to control liquids within a slope or a landfill could result in problems related to slope stability. Because bioreactor landfill operati ons involve adding liquid to the wa stes, it is appropriate to pay particularly close attention to the potential destabilizi ng effects of liquids at such facilities. Excess liquids can result in saturation and a decrease in the effective stress within the waste, with a corresponding decrease in effective shear strength. Control of excess liquid (i.e., “por e”) pressures in a bioreactor landfill is provided by minimizing the potential for large portions of the landfilled waste to become saturated. This can be provided by: (i) controlling liquid applicati on rates; (ii) maintaining the LCS operation and preventing the LCS from being overloaded; and (iii ) controlling exit gradients (i.e., seeps), usually achieved by providing a minimum of 15 – 30 m (50 to 100 ft) between landfill slopes and the end of an injection pipe and/or trench. As described in Section 4.2 (i.e., Mois ture Addition) of this report, the data from th e OLLB collected under the CRADA to date show that: (i) liq uid application rates resulted in increased moisture content but not saturation of the waste as some of the solid waste sa mples examined had low moisture content; (ii) the LCS remained functional and showed no signs of excessive head buildup; and (iii) there was no evidence of excessive seeps occurring. Based on these findings, it is concluded that operation of the OLLB has not caused conditions that would decrease the stability of natural or waste slopes resulting from the development of excess pore pressures. Note that adding liquid increases the weight of the waste and, therefore, could reduce the overall st ability of the waste. Although ev aluation of this aspect of slope stability is beyond the scope of this report, it is likely that the increas ed weight resulting from moisturecontent increases (which are reported in Section 4.2 to be about, on average, six to seven percent in the AsBuilt cells and one percent in the Retrofit cells) would no t have a significant adverse effect on stability if the slopes were originally designed having a factor of safety meeting the recommendations provided in U.S. EPA (1993).


### 7.2 Liner and Final Cover Integrity
The integrity of the base liner is of particular concer n for bioreactor landfills because of the need to contain the additional amount of liquid that is collected and removed from atop the liner of a bioreactor landfill. In addition, the integrity of the final cover is of concern for a bioreactor land fill because it may be exposed to more seeps and differential settlement than a non-bioreact or landfill. The study reported in this document was not designed to evaluate liner and final cover integrity, and so this study does not directly provide information for evaluating effects of bioreactor operations on liner or cover integrity. However, it is important to note that a recent U.S. EPA study on th e performance of Subtitle D landfill liner systems of landfills that are younger than 15 years old (U.S . EPA 2002) confirmed that the integrity of wellconstructed liner systems that are properly monitored during construction is not jeopardized over the operating life of the facility. Leakage in the base liner is usually associated with poor construction,

123inadequate construction quality assurance (CQA) monitoring, and construction of features near the liner. The best assurance that the liner system will perform well for operating landfill bioreactors is to provide a high-quality construction and CQA monitoring (pay ing particular attention to sealing around all penetrations) and installing liquid a pplication features in a manner that does not damage the liner (e.g.,not installing liquid application wells to a depth near the li ner). Based on a review of the installation of the liquid application features for the O LLB project, there is no indication th at the base liner system at the OLLB was compromised while installing liquid applicatio n features or while applying liquid through those features at this point of the project. The integrity of the final cover could be compromised if excessive differential settlement occurs or if slope instability occurs. These problems could be worsened if landfill bior eactor operations increase the amount of differential settlement or increase the pressure on the bottom of the cover system (e.g., liquid pressure or gas pressure acting on the bottom of the geomembrane or clay barrier layer), which could lead to instability. Because final cover has not yet been installed over the cells that were part of the OLLB study, an evaluation of these potential eff ects. However, the lack of leachate breakout problems and the lack of landfill gas emission problems suggest that the OLLB has been operated in a manner that will minimize problems related to excessive pressures under the liner. Although no similar information is available to evaluate the potential for significant differential settlem ents, such settlements (if they were to occur) could be easily repaired. Based on these considerations, im pacts on the integrity of the OLLB final cover are not expected to be a problem.


### 7.3 Liquids Addition System Performance
The performance of the liquid addition system can have a significant effect on ot her systems present at a landfill. Systems that could be affected include th e surface-water management system (which could be affected if seeps from the landfill im pinge on drainage features), LFG ma nagement system (which could be affected if gas extraction wells beco me filled with liquid), or the LCS (which is discussed separately in Section 7.4). Based on observations at the site, no significant leachat e breakout problems were reported that would have resulted in surface-w ater quality effects. Therefore, the operational practices used at the OLLB appear to have been successful in preventing su rface-water quality problems. Also, although there were indications of “watering-out” of gas collection wells and trenches during some periods of the study, there was also an increase in landfill gas collected from the bioreactor areas and so it is not possible to conclude whether the watering-out of the collection featur es would be expected to have an impact on future stability of the landfill cover system; see Section 8 for recommendations on future monitoring and performance evaluation of the LFG management system. Finally, as discussed in the body of the report, wastes having a low pH and/or high sugar levels are expected to have an adverse effect on waste degradation and should be avoided unless lab- or benc h-scale testing is performed to assess the potential effects of the candidate liquid waste stream on the mi crobial populations and resulting performance of the landfill environmental protection systems.


### 7.4 Leachate Collection System Performance
If liquid application activities promote microbial activity within LCS featur es, then it is conceivable that those features could become clogged. In that case, the LCS features might no t function as originally intended and cease to transmit leachate from the landfill as designed. Upon achieving field capacity or if preferential flow paths develop in the solid waste, ther e is a concern that the amount of liquids that pass into and through the LCS will increase, thus raising th e concern regarding the integrity of the LCS. This concern could extend from an increase in flow volum e or flow rate in the drainage materials or the premature “fouling” of the pores in either the prot ective geotextile or the hy draulically transmissive granular drainage component of the LCS. Although it is certainly recognized that this can be a potential problem, the authors are not aware of any case where the concern has been suspected, studied, and confirmed. It is encouraging to note that the effect of the landfill bioreactor performance is to merely accelerate the waste degradation processes, not introd uce new mechanisms or pr ocesses. Therefore, components or construction techniques that are effect ive for the LCS systems for conventional landfills are anticipated to be effective for land fill bioreactor landfills. Because of the likelihood for additional microbial activity and higher flows ra tes in landfill bioreactors compared to conventional landfills, it may

124be advisable to consider increasing LCS hydraulic conductivity and transmissivity for landfills bioreactor projects. In addition to the construction and materials selection controls, it is recommended that operating practices that result in the potential for clogging or blinding of the LCS components be avoided. For example, if waste streams are identif ied that may react and introduce pr ecipitates (e.g., aluminum dross), these waste streams should be avoided. Similarly, the use of fine-grained soils near the bottom of the waste mass should not be used, as they have the potential for migration into the LCS. Signs of clogging of the LCS can include reduced leachate collecti on rates, watered-out landfill gas collection wells, or breakouts at the sides of the landfill. At the OLLB, none of these conditions was observed to the degree that would imply clogging of the LCS features. However, this finding should be confirmed again in future studies.



### 7.5 Landfill Gas Production and Emission
A final concern regarding landfill bioreactors is the emi ssions from the facility th at result from enhanced LFG generation. If LFG emissions at a bioreactor landfill are greaterbefore capping than for a nonbioreactor landfill, then it could be exp ected that a greater quantity of la ndfill gases would be emitted to the atmosphere from the bioreactor landfill. Chapter 5 i ndicates that, at the OLLB, LFG production in the AsBuilt cells was significantly higher than would be expect ed for a conventional dry tomb landfill and slightly higher in the Retrofit cell. However, despite the highe r gas production rates during bioreactor operations, there does not appear to have been excessive surface (surface scans with greater than 500 ppm CH 4 ) emissions from the facility.

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## Chapter 8. Conclusions and Recommendations

8.1 Conclusions
The data set from the five-year study at the OLLB re presents one of the most comprehensive compilations of information regarding the performance of landfill bioreactors. The study was conducted at a full-scale operating MSW landfill and, as such, was faced with th e challenges of performing leading-edge research at an operating landfill site. The objectives of the OLLB study were presented in Chapter 1; a summary of these objectives and their status (i.e., “met”, “not met”, or “on-going”) as of the date of this Second Interim Report is presented in Table 8-1. Table 8-1 OLLB Objectives Assessment Objective Met / Not Met / On-going Comment Design and implement two alternative large-scale bioreactor operations. Met The Retrofit and As-Built cells represent the two alternative bioreactor operations. Monitor sufficient parameters to understand the physical, chemical, and biological activities within the landfill bioreactors. On-going Several conclusions are presented in this report; however, research and performance monitoring continues at the site. Compare and contrast monitoring results with the requirements for a Subtitle D Landfill. On-going Many comparisons between the bioreactor and Control cells are provided in this report; however, research at the site is on-going. Incorporate statistical techniques to assess effectiveness of the landfill bioreactor operation. On-going Statistics were utilized to evaluate data for all three media (solid, liquid, and gas). More data are being collected at the site for future statistical assessment. Establish best practices and procedures required to operate landfill bioreactors. On-going Additional data collection and analysis will further refine conclusions reached in this report, leading to a complete evaluation of the operational techniques used. Establish important and indicative parameters that should be monitored with respect to landfill bioreactor operations. On-going Monitoring parameter recommendations for bioreactor landfills in general are provided below in Section 8.2. Ongoing work at the site will expand on these recommendations. Obtain sufficient data to enable improvements that may be applied to future bioreactor landfills, in both an experimental and practical capacity. On-going Recommendations for additional data collection parameters are provided in Section 8.3.

8.1.1 Solids Analysis The intent of the solids decomposition analysis was to assess the reproducibility of the data between the cells and their replicates (i.e., Control cells A and B, Retrofit cells A and B, and As-Built cells A and B) and to evaluate whether th e solids decomposition data support the co ncept that operation as a bioreactor landfill accelerates waste decomposition relative to operat ion as a conventional landfill. The assessment of cell replicates indicated that the waste in the Retrofit and Control cell replicates were similar, but As-Built cells A and B were found to be significantly differe nt. The differences between As-Built cell A and AsBuilt cell B were attributed to the fact that th e waste in the two cells was relatively young. The three primary parameters used to assess the extent of decomposition were BMP, CH:L, and organic solids content. Generally, a decr ease in these parameters indicates an increase in the degree of waste decomposition. CH:L and organic solids content were found to be significantly different in the Retrofit

127cells compared to the Control cells; however, linear regressions of the da ta indicated that BMP was similar in the Retrofit and Control cells. All three decomposition parameters we re less in As-Built cell A relative to both the Control cells and As-Built cell B, indicat ing more rapid waste decomposition. The accelerated waste decomposition in As-Built cell A relative to As-Built cell B was attri buted to the much larger volume of air injected into As-Built cell A (approximately five times great er on a mass basis). However, regressions of solids data for As-Built cell B did no t indicate a difference when compared to the Control cells. One limitation of the analysis of the As-Built cells was the young age of the waste, which precluded significant trends in waste decomposition to develop. An additional limitation in developing strong trends in decomposition was the inherent heterogeneity of th e MSW. Despite nearly five years of operation, the solids analysis results still indicate that, although there are statistical differences in waste decomposition between the three distinct cells, the waste has not un dergone significant solids decomposition. It is expected that data from sampling and testing of solid waste from these cells in subsequent years will show more consistent solids decomposition trends.

8.1.2 Liquids Analysis The liquids analysis involved assessing the moisture balance of the different landfill cells, evaluating leachate head on the liner, and evaluating leachate quality data. Data showed an inconsistent trend in moisture content with respect to waste age and the type of landfill cell. For instance, the mean measured moisture content for the Control cells showed an overall increase of approximately six percent between 2002 and 2005, which is a large incr ease considering that no moisture wa s added to the Control cells during the study period. Overall, measured waste moisture content data as obtained from moisture content measurements on discrete waste samples should be interpreted with caution; variability in waste composition, hydraulic properties, compaction rates, and other factors likely contributed to the inconsistent behavior of the measured moisture content data. A moisture balance was conducted using a combination of information related to rainfall, liquids addition, and leachate generation quantities. The initial moisture content percentage used in the calculation was based on the measured moisture content of samples coll ected in 2002, prior to in itiation of liquids addition in the bioreactor landfills cells. This assumption has obvi ous limitations in that it represents data based on discrete samples from a single sampling event. As de scribed earlier, the measured moisture content data showed inconsistent trends in all cells during the study period; however, this was assumed to be a more appropriate starting point co mpared to literature-reported moisture c ontent values. Liquid addition rates of 5.3, 65.3, and 43.4 gallons/ton in the Retrofit cells, As-Built cell A, and As-Built cell B resulted in a calculated moisture content increase (on a wet weight ba sis) of approximately one, six, and seven percent, respectively. The slight increase observ ed in the Retrofit cells is attribut ed to a low liquid injection volume at those cells relative to the overall mass of the cells, as well as the cover system that minimized infiltration of rainfall. The six and seven percent moisture cont ent increase in As-Built cell A and As-Built cell B is believed to be conservative relative to the “Liquid In” volumes that likely infi ltrated the waste mass in these cells. Prior to the first quarter of 2004, a 0.3m (1 ft) thick layer of tire chips was installed between the As-Built cells, resulting in short-circuiti ng of injected liquids to the LCS. This led to an overall increase in the “Liquid Out” value used in the moisture balance cal culation prior to the first qu arter of 2004. When the practice of installing the tire chip layer between th e As-Built cells ceased following the first quarter of 2004, the rate of leachate generation slowed significant ly, indicating that a greater increase in moisture content may have occurred in the As-Built cells (based on the Liquid In volumes) if the tire chip layer had not been installed prior to 2004. Data following the first quarter of 2004 indicat ed a significantly lower leachate generation rate in the As-Bui lt cells. Nevertheless, the moisture balance calculation results for the bioreactor landfill cells underscore the fact that very la rge volumes of liquid are required to significantly increase the moisture content of a land fill. Despite efforts to significan tly increase the moisture content, it appears that additional liquids could have been assimilated by the waste if the operation procedures had been different. Leachate head in the sump for each cel l was measured to provide an indica tion of the leachate head on the liner. The mean leachate head in the sump for each cell was below the regulatory threshold of 0.3 m (1 ft). However, exceedances of head on the liner did occur occasionally in all cells; the exceedances generally corresponded with th e active filling phase of a particular landf ill cell, and the frequency of exceedances

128decreased after the final lift of waste had been placed . The exceedances during waste filling were primarily attributed to inadvertent routing of runoff from the cell to the sump. The leachate quality analysis results were generally co nsistent with the corresponding calculated age of the waste for each cell throughout the study period. However, the results of the l eachate quality analysis for the majority of the parameters did not reveal a str ong trend that would indicat e significantly accelerated waste decomposition in the bioreactor landfill cells. St ill, the results of some of the parameters were encouraging. For example, the B OD/COD ratio in the As-Built cells decreased to below 0.5 within two years of initial waste placement, which is indicativ e of waste decomposition. In comparison, the BOD/COD ratio for the Control cells did not decrease to below 0.5 until approximately four years after initial waste placement, supporting the premise of acceler ated waste decomposition in the As-Built cells. Additionally, Chapter 2 described the ex-s itu nitrification pr ocess that was used to treat the leachate prior to injection into the Retrofit cells; this process, impl emented with the intent of decreasing the ammonia concentration, was expected to have an increasing benefit over time as a result of increased waste decomposition. The mean ammonia concentration in th e Retrofit cells showed a strongly decreasing trend during the study period, which indicates that treating the leachate ex-situ was effective at decreasing the ammonia concentration in the leachate.

8.1.3 LFG Analysis The goals of the LFG analysis were to evaluate the LFG kinetics in each cell, draw comparisons between the cells, and assess the NMOC concentration data for each cell. Using the field-collected LFG data and in-place waste mass as inputs, the U.S. EPA model LandGEM was used to estimate waste decay rates for each cell. Assuming a 75 percent LFG collection syst em efficiency, waste decay rates of approximately 0.16, 0.061, and 0.06 yr -1 were estimated for As-Built cells, the Retrofit cells, and the Control cells, respectively. It is noted that there are some limitati ons to the estimation of these decay rates. First, the LFG collection efficiency was assumed based on the AP-42 recommended value of 75 percent. Second, the estimation of the decay rates was based on only th ree years (As-Built cells) or four and a half years (Retrofit cells) of field-coll ected data. Third, the CH 4 generation potential, L o , used in LandGEM was assumed to be constant and was selected based on the analysis of fresh waste, although this value likely does not remain constant over time as waste degrad es. Despite these limitations, the results strongly indicate that the LFG generation rate was accelerated in the As-Built cells relative to the Control cells. The results also indicate that the LFG generation rate in th e Retrofit cells appeared to be somewhat greater than in the Control cells; however, the LFG flow and compos ition data from the Retrofit cells indicated a degree of variability that was attributed to the watering out of LFG collection wells. As a result, the LFG collection efficiency in the Retrofit cells may be less than the assumed 75 percent, which would indicate that the waste decay rate in the Retr ofit cells may be greater than 0.061 yr -1

. The NMOC concentration data were evaluated in two ways: (i) NMOC production based on the measured NMOC concentration and LF G flow data from each cell; and (ii) NMOC production based on the NMOC concentration data and mass of in-place waste for each cell. The first method was developed to tie in the years of field gas data to the NMOC concentration and to investigate an y trends. The second method was similar to the method prescribed in a typical Tier 2 NSPS analysis, in which a site-specific NMOC concentration is used in LandGEM to predict NMOC production based on waste placement data. Analysis of NMOC production using the firs t method indicated little difference between the cells, resulting in a mean NMOC production rate of 0.012, 0.012, 0.010, and 0.008 kg/min for the Control cells, Retrofit cells, As-Built cell A, and As-Built cell B, respectively. Analysis of NMOC production using waste placement data and the mean NMOC concentration for each cell indicated NMOC production rates of less than 50 Mg/yr for each cell; it is noted that the predicte d NMOC production usi ng LandGEM was performed primarily to observe whether each cell exceeded the regulatory threshold of 50 Mg/yr of NMOCs.

8.1.4 Summary Overall, the performance monitoring results are very en couraging. The most significant conclusion is that, despite the five-year duration of the study, two of the three media analyzed (i.e., solids and LFG) indicated that waste decomposition was accelerated in the As-Built and Retrofit cells relative to the Control cell. Table 8-2 summarizes a comparison of the different waste decomposition indicators for each media (solid, liquid, or gas) between the Control cells and the bioreactor landfill cells.

129For the Retrofit cells, two of the three solids monitoring parameters indicated accelerated decomposition relative to the Control cells; therefore the results were believed to be inconclusive. Furthermore, for the Retrofit cells, the generally stable leachate data did not indicate that waste decomposition was accelerated as a result of liquids addition. The LFG results indicated a waste decay rate that was similar to that of the Control cells; the authors believe that if the actual LFG collection efficien cy in the Retrofit cells could be established, it would likely reveal an efficiency of le ss than 75 percent, thereby resulting in a greater estimated waste decay rate. For As-Built cell A, all three solids monitoring parameters indicated a trend of accelerated waste decomposition relative to the Control cells. The B OD/COD ratio of the leachate indicated that perhaps waste decomposition was accelerated, bu t that ratio alone is not enough to conclude that the leachate indicated accelerated waste decomposi tion. At the other extreme, the waste decay rate as estimated by using the LFG collection data in th e As-Built cells was several times greater than the Control cells. Not all of the solids monitoring parameters indicat ed accelerated waste decom position in As-Built cell B relative to the Control cells. The authors believe th at future solid waste sampling will likely indicate accelerated decomposition of waste in this cell. Si milar to As-Built cell A, As-Built cell B exhibited a decrease in BOD/COD ratio, indicating that waste deco mposition was accelerated relative to the Control cells, but as stated above this is not enough to conclude that the leach ate results (by themselves) indicated accelerated waste decomposition. LFG data from As-Bui lt cell B indicated a waste decay rate several times that of the Control cells. Table 8-2 Evidence of Accelerated Waste Decomp osition Across All Media Analyzed Between Contro l and Bioreactor Landfill Cells Bioreactor La ndfill Cell Solid Liquid Gas
Retrofit cells I No TBD As-Built cell A Yes I Yes As-Built cell B TBD I Yes Notes: 1. TBD - To be determined; a conclusion will likel y be reached after additional data is collected. 2. I - The results of the waste decomposition data were positive, but inconclusive.


### 8.2 Recommendations
As Table 8-2 shows, and as described in Sections 8.1.1 through 8.1.3, ongoing performance monitoring is anticipated (and is recommended) to continue at the OLLB. The parameters reported in Chapter 2 will continue to be monitored for the next several years. The authors recommend that additional analyses be considered. The results of these additional analyses co uld support the conclusions presented in this report. Additional recommendations are provided below:

• Collect data that can be used to estimate LFG coll ection efficiency for each cell. This could be accomplished by using U.S. EPA Method 2E to es timate the LFG generation rate and indirectly estimating the CE by comparing the LFG gene ration rate with the LFG collection rate. Alternatively, the fugitive emissions for each cell may be estimated using a technology such as open path Fourier-transform infrared spectrometr y. Fugitive emissions at the OLLB were previously reported using this technique (U.S. EPA 2005), but the measurements were taken in 2002 and 2003, prior to the end of waste plac ement in the As-Built and Control cells.

• Continue collecting topographic survey data of the Control, Retrofit, and As-Built cells. The authors note that it may take several more years before a quantitative correlation between waste decomposition and settlement can be made for the landfill bioreactor cells.

• Provide more detailed sample identification in formation during the collection of solid waste samples, especially with regard to the sample pr oximity of a liquid addition pipe or trench. The authors believe this information may provide insight related to th e variability of the measured moisture content data. For example, during solid waste sample collection, note the distance of the borehole to the nearest injection pipe/trench, an d identify the volume of liquids added to the corresponding trench/pip e, if that information is available.

130It may only be necessary to collect one more set of solid waste samples over the next approximately five years to analyze the various decompos ition parameters. As noted in Section 4.1, a high degree of scatter seen in the data may be attributable to the relati vely short time window during which the samples were collected, resulting in relatively young waste.


### 8.3 Landfill Bioreactor Monitoring Parameters
The OLLB will continue to monitor the parameters (presented in Chapter 2) at the same frequency for the next several years under its RD&D permit. As a re sult, the trends of solids decomposition, moisture balance, LFG composition and flow, and leachate quality will be further developed. It is expected that the variability seen in some trends (e.g., solids decompos ition) will tend to decrease during this period, as the study cells are no longer ac tive (i.e., the study cells no longer recei ve new waste). Based on the results from the first five years of monitoring at the OLLB, the following observations can be made regarding the monitoring parameters and frequency described in Chapter 2. The mass balance and liquid addition monitoring parameters listed in Tables 2-1 and 2-2 are considered to be a fundamental part of the OLLB program and any la ndfill bioreactor project. The liquids added and the nature and amount of the deposited material in the landfill cell provide the basic information for conducting moisture balancing and predicting LFG generation using LandGEM. The monitoring frequency listed in Tables 2-1 and 2-2 was appropriate for the first five years of the OLLB project. LFG monitoring of CH 4 , CO 2 , O 2 , and balance gas once per week appeared to be an appropriate monitoring frequency for the OLLB study. Monitoring at this frequency minimized significant variability that may have occurred with less frequent monitoring; however, even with weekly sampling, there was a relatively high degree of variability in the As-Built and Retr ofit bioreactor landfill cel ls. NMOC monitoring, however, appeared to be more frequent than needed. The comparison of NMOC production between cells did not indicate a significant difference between the biore actor landfill cells data and the Control cell data. The authors believe an NMOC sampling frequency of once per year is adequate to further develop the trends (or lack thereof) seen in the first five years of the OLLB project. Furthe rmore, the authors believe that an NMOC sampling frequency of once per year at other landfill bioreactor sites may be appropriate. Solid waste sampling and analysis parameters used for quantifying solid waste decomposition were appropriate; however, the period of the study (i.e., onl y five years) appears to have been too short to see significant trends, even in cells where large decom position rates were anticipated. There was significant variability in BMP, CH:L, and organi c solids between the three sampling periods; the authors believe that the scatter observed in these parameters may have been caused by the relatively short time window analyzed in this study. For bioreactor landfills in general, the authors beli eve that it is critical to obtain a sufficient number of solid waste samp les for characterization at the outset of a bioreactor landfill project and less frequent monitoring (e.g., every five years) be conducted following the initial sampling period. Analyses on samples of solid waste are important as they provide the most direct evidence of waste decomposition. However, the solids analyses are perform ed on discrete samples a nd the inherent variability in waste composition may “mask” the indicators of deco mposition during the shor t monitoring time period that has elapsed so far for the OLLB.

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