Printed on recycled paper DRAFT Characterization and Evaluation of Landfill Leachate September 2000 Submitted to:

U. S. Environmental Protection Agency 2800 Crystal Drive Arlington, VA 22202 Submitted by:

Science Applications International Corporation 11251 Roger Bacon Drive Reston, Virginia 20190 EPA Contract No. 68 W6 0068 SAIC Project No. 06 5240 08 9957 000 Work Assignment No. 2 14 September 2000 i 1 Draft INTRODUCTION This report results from a broad based effort to collect and review data on landfill leachate. This effort included the following:

  A review of existing scientific literature on landfill leaching processes and the factors that influence leachate generation and characteristics.

  A quantitative analysis of leachate generation rates in landfills managing various types of waste.

  Development of a comprehensive database describing the physical properties and chemical characteristics of leachate from landfills managing various types of waste.

  Detailed case studies describing the operation and environment of example landfills representing the various types included in the characterization database.

The report is organized as follows:

  Section 1 provides information on the mobility of inorganic and organic constituents that may be present in waste, primarily based on review of the scientific literature.

  Section 2 presents the results of the quantitative analysis of the available data on leachate generation rates.

  Section 3 discusses the properties and characteristics of landfill leachate. This discussion includes presentation of summary statistics from the characterization database for various categories of landfill. It further compares these characteristics across landfill types, based on the empirical data and the scientific literature.

  Section 4 summarizes the landfill case studies.

  Section 5 is the bibliography of sources reviewed from the literature. September 2000 i 2 Draft TABLE OF CONTENTS SECTION 1. MOBILITY OF INORGANIC AND ORGANIC CONSTITUENTS 1.1 Inorganic Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 1.1.1 Trends in Solubility of Metal Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 Soluble Compounds pH Control Oxidation Reduction Potential ( redox potential) and Electron Activity 1.1.2 Behavior of Specific Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 13 Copper, Cadmium, and Lead Arsenic and Selenium Chromium Mercury 1.2 Organic Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 19 1.2.1 Effects of pH on Leachability Of Organics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 20 Acid Leachable Organics Alkali Leachable Organics Polyfunctional Organics SECTION 2. LEACHATE GENERATION QUANTITIES IN LANDFILLS 2.1 Information Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 2.2 Values of Liquid to Solid Ratio and Leachate Generation Rate Found . . . . . . . . . . . . . . . . . . . 2 4 2.2.1 Summary of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 2.2.2 EPA Office of Water Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 Operational Status Landfill Type Precipitation 2.2.3 Use of Other Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 11 SECTION 3. LEACHATE COMPOSITION AND PROPERTIES 3.1 Characterization Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 3.2 Municipal Solid Waste Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 3.2.1 Overall Composition of MSW Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 Trace Inorganics Organics 3.2.2 Temporal Variability in MSW Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 Stages of a MSW Landfill Significance of Phases Towards Leaching 3.2.3 Factors Affecting Contaminant Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 8 pH Redox Potential and Sulfate Organic Content: Overview BOD and COD Volatile Fatty Acids and COD Alkalinity Summary of Significant Findings for Indicator Parameters in MSW Landfill Leachate September 2000 i 3 Draft TABLE OF CONTENTS ( continued)

SECTION 3. LEACHATE COMPOSITION AND PROPERTIES ( continued) 3.3 Construction and Demolition Debris Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 21 3.3.1 Overall Composition of C& D Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 21 General Parameters Trace Inorganics Organics 3.3.2 Temporal Variability and Indicator Parameters in C& D Landfills . . . . . . . . . . . . . . . 3 22 pH Redox and Sulfate Alkalinity COD and BOD 3.4 Industrial Codisposal Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 26 General Parameters Trace Inorganics Organics 3.5 Hazardous Waste Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 28 General Parameters Trace Inorganics Organics 3.6 Comparison of Leachate Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 30 3.6.1 Overview of Factors Affecting Leaching Medium Composition . . . . . . . . . . . . . . . . 3 30 Infiltrating Liquid Waste Composition Landfill Operations 3.6.2 Comparison of Factors Affecting Leaching Medium Composition . . . . . . . . . . . . . . 3 32 Composition of Infiltrating Liquid Waste Composition Landfill Operations 3.6.3 Comparison of Factors Affecting Contaminant Mobility . . . . . . . . . . . . . . . . . . . . . . 3 33 pH Redox Potential and Sulfate TOC, COD, and BOD Alkalinity 3.6.4 Comparison of Other Major Physical and Chemical Parameters . . . . . . . . . . . . . . . . 3 39 3.6.5 Comparison of Trace Inorganics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 43 3.6.6 Comparison of Organic Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 49 3.7 Summary Statistics for Captive Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3.7.1 Paper Mill Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3.7.2 Combustion Waste Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3.7.3 Foundry Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 SECTION 4. QUANTITATIVE LANDFILL CASE STUDIES SECTION 5. BIBLIOGRAPHY September 2000 i 4 Draft TABLE OF CONTENTS ( continued)

APPENDIX A: REVIEW OF STATE LANDFILL LEACHATE DATA AVAILABILITY APPENDIX B: RELEVANT CONVERSION FACTORS APPENDIX C: LIQUID TO SOLID RATIOS AND LEACHATE GENERATION RATES REPORTED IN LITERATURE APPENDIX D: LIQUID TO SOLID RATIOS AND LEACHATE GENERATION RATES CALCULATED FROM CASE STUDIES APPENDIX E: LEACHATE QUANTITY DATABASE APPENDIX F: QUALITY ASSURANCE ANALYSIS AND ADJUSTMENT OF STATE OF WISCONSIN LEACHATE CHARACTERIZATION DATA LIST OF TABLES Table 1 2. Metal Salt Speciation Under Oxidizing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 1 10 Table 1 3. Metal Salt Speciation Under Reducing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 11 Table 1 4. Leaching characteristic as a function of acidity of the contact solution and the L/ S ratio. 1 12 Table 1 5. Compounds Whose Leachability Changes In Acidic Media . . . . . . . . . . . . . . . . . . . . 1 22 Table 1 6. Compounds Whose Leachability Changes in Alkaline Media . . . . . . . . . . . . . . . . . . 1 25 Table 1 7. Compounds More Leachable in Acidic and Alkaline Media . . . . . . . . . . . . . . . . . . . 1 26 Table 2 1. Summary of Liquid to Solid Ratios for all Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 Table 2 2. Summary of Leachate Generation Rates for all Sources . . . . . . . . . . . . . . . . . . . . . . . . 2 5 Table 2 3. Leachate Generation Rates by Operational Status from Office of Water Data . . . . . . . 2 6 Table 2 4. Liquid to Solid Ratios by Operational Status from Office of Water Data . . . . . . . . . . 2 6 Table 2 5. Leachate Generation Rates by Landfill Type from Office of Water Data . . . . . . . . . . 2 7 Table 2 6. Liquid to Solid Ratios by Landfill Type from Office of Water Data. . . . . . . . . . . . . . 2 7 Table 2 7. Leachate Generation Rates by Precipitation Rate from Office of Water Data. . . . . . . . 2 9 Table 3 1. Composition of MSW Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 Table 3 2. Behavior of Indicator Parameters in MSW Landfill Leachate: Summary . . . . . . . . . . 3 20 Table 3 3. Composition of C& D Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 22 Table 3 4. Composition of Industrial Codisposal Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . 3 27 Table 3 5. Composition of Hazardous Waste Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . 3 29 Table 3 6. Composition of Paper Mill Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 Table 3 7. Composition of Combustion Waste Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . 3 54 Table 3 8. Composition of Foundry Landfill Leachate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 Table 4 1. Landfill Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 September 2000 i 5 Draft LIST OF FIGURES Figure 1 1. Solubilities of metal hydroxides as a function of pH . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 Figure 1 2. Solubilities of metal hydroxides and sulfides as a function of pH . . . . . . . . . . . . . . . . 1 8 Figure 1 3. Simplified pe pH diagram for the system As O H2O at 25b C and one atm. . . . . . . . 1 14 Figure 1 4. Simplified pe pH diagram for the system Se O H2O at 25bC and one atm. . . . . . . . . 1 15 Figure 1 5. pe pH diagram for the system Cr O H2O at 25bC and one atm. . . . . . . . . . . . . . . . . . 1 16 Figure 1 6. pe pH diagram for the system Hg S O H2O at 25bC and one atm . . . . . . . . . . . . . . . 1 17 Figure 1 7. Stability regions of mercury species in the sulfur carbonate water system . . . . . . . . . 1 18 Figure 1 8. Volatile concentration and solubility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 19 Figure 1 9. Semi volatile concentration and solubility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 20 Figure 1 10. Volatile concentration and Kow values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 21 Figure 2 1. Leachate Generation Rates by Landfill Type and Operational Status. . . . . . . . . . . . . . 2 8 Figure 2 2. Liquid to Solid Ratio by Landfill Type: Both Active and Inactive. . . . . . . . . . . . . . . . 2 8 Figure 2 3. Leachate Generation Rates by Precipitation Rate and Operational Status. . . . . . . . . . 2 10 Figure 2 4. Liquid to Solid Ratio by Precipitation Rate: Both Active and Inactive. . . . . . . . . . . . 2 11 Figure 3 1. Cumulative Frequency of pH in Wisconsin MSW Landfills by Age Group . . . . . . . . 3 11 Figure 3 2. pH Observed in Wisconsin MSW Landfills by Age . . . . . . . . . . . . . . . . . . . . . . . . . . 3 12 Figure 3 3. pH Trends for Individual Landfills ( increasing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 13 Figure 3 4. pH Trends for Individual Landfills ( decreasing or varying) . . . . . . . . . . . . . . . . . . . . 3 13 Figure 3 5. Relationship between VFA and COD in Landfill Leachate . . . . . . . . . . . . . . . . . . . . 3 17 Figure 3 6. COD Observed in Wisconsin MSW Landfills by Age . . . . . . . . . . . . . . . . . . . . . . . . 3 18 Figure 3 7. Cumulative Distribution of pH by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 34 Figure 3 8. Cumulative Distribution of Sulfate by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . . . 3 35 Figure 3 9. Cumulative Distribution of Total Organic Carbon ( TOC) by Landfill Type . . . . . . . 3 36 Figure 3 10. Cumulative Distribution of Chemical Oxygen Demand ( COD) by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 37 Figure 3 11. Cumulative Distribution of Biochemical Oxygen Demand ( BOD) by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 37 Figure 3 12. Cumulative Distribution of BOD/ COD Ratio by Landfill Type . . . . . . . . . . . . . . . . . 3 38 Figure 3 13. Cumulative Distribution of Alkalinity by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . 3 38 Figure 3 15. Cumulative Distribution of Other Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 41 Figure 3 16. Trace Inorganics Found in the Highest Concentrations in Hazardous Waste Landfills 3 44 Figure 3 17. Trace Inorganics Found in the Highest Concentrations in Both Hazardous Waste and Industrial Codisposal Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 46 Figure 3 18. Cumulative Distribution of Other Trace Inorganics by Landfill Type . . . . . . . . . . . . 3 47 Figure 3 19. Cumulative Distribution of Organics by Landfill Type . . . . . . . . . . . . . . . . . . . . . . . 3 49 September 2000 1 1 Draft 1. MOBILITY OF INORGANIC AND ORGANIC CONSTITUENTS Leachate characteristics are a function of the constituents contained in the disposed wastes and the waste management environment. The mobility of both inorganic and organic constituents is dependent upon many interrelated factors. These factors include most importantly the waste type, waste management unit, and climate of the intended disposal unit. Physical characteristics of the waste type may increase or decrease the mobility of constituents. For example, a cementitious solidified waste is less likely to release toxic constituents because those constituents are bound within the cementitious matrix. On the other hand, a granular waste such as combustion ash residues, may be more likely to release toxic constituents due to increased surface area and a matrix that allows more easily for dispersibility.

The waste management environment will also contribute to the mobility or immobility of certain constituents. Effects of co disposal with other wastes, the chemical characteristics, and rainfall may all play a part in the leaching of constituents from wastes.

Regardless of the waste's physical form or disposal environment there are a number of observed and theoretical chemical relationships that are considered underlying or basic to the discussion of leaching. These relationships are discussed in the following sections. Inorganic mobility and the chemical factors that tend to increase or decrease mobility are explored in the Section 1.1. The mobility of organics is discussed in Section 1.2. It should be noted that the discussion is theoretical; however, real world examples are provided. While certain conditions may increase the mobility of certain constituents, those conditions in conjunction with other factors may yield different results. Therefore the following discussion is meant to act as a basis for initial consideration of how certain waste types may behave in a given waste management scenario. September 2000 1 2 Draft 1.1 Inorganic Mobility Inorganic constituent mobility has been well studied for a select group of wastes; however, the speciation concepts have been well explored for a wide variety of inorganic constituents. These concepts and real world examples are discussed below.

Determining which inorganic waste constituents will dissolve and be leached from waste depends on a multitude of factors. Factors affecting solubility of inorganic contaminants reviewed for this discussion include acid base equilibria, oxidation reduction reactions, coordinated metal anion pair solubility, and pH. Metals described below include barium, beryllium, chromium, cobalt, nickel, arsenic, selenium, cadmium, antimony, mercury, and lead.

To summarize metal speciation and mobilization in waste environments, the following categories will be used in combination to describe the conditions under which chemical species become mobile: ( 1) oxidizing, ( 2) reducing, ( 3) acidic, ( 4) neutral, and ( 5) basic. Acid base equilibria, solubility, oxidation reduction, and pH were chosen because they are the most influential factors affecting mechanisms related to leaching. However, though these factors control many dissolution and mobilization mechanisms ( i. e., precipitation reactions, complexation, adsorption, chemisorption, passivation, ion exchange, molecular transport), this study is based on simple solutions containing one cation anion pair at specified redox and pH conditions. Reaction rates are not included in this discussion.

To compare solubilities of metals, experimentally measured or estimated solubility values were collected for the compounds of metals with the following anions:

° sulfides ° phosphates ° hydroxides ° chlorides ° oxides ° carbonates ° sulfates ° cyanides.

These compounds were chosen because they represent some common waste forms in which metals occur and they demonstrate a distinct gradient in solubility. By examining trends in the pH and redox effects that contribute to metal dissolution and mobility, the conditions that cause metal release and environmental transport in a waste management scenario may be described. Because most metals' behavior varies similarly under most conditions, a general discussion of solubility is followed by metal specific discussions. September 2000 1 3 Draft 1.1.1 Trends in Solubility of Metal Species To discuss the solubility of a metal and to understand the processes regulating dissolved ion concentrations, all possible ionic and covalent species present in the system should be considered. However, for this study, solubility trends are discussed with regard to simple systems. Some examples of metal solubility and mobility from actual waste studies are also provided.

One of two values was used to observe the solubilities of metal compound, experimental or estimated values derived using solubility product constants ( Ksp). Published experimental values were used whenever they were available. When deriving solubility using Ksp, it was assumed that the metal compound undergoes a dissociation when it dissolves, and the undissociated compound does not contribute to the concentration in the solution. This can introduce a negative bias, to varying degrees, in the solubility estimate. Table 1 1 provides some metal compound solubilities. Experimental and estimated solubilities are indicated.

Some general observations about soluble inorganic species in water are demonstrated by the following representation of increasing/ decreasing solubility:

least soluble most soluble sulfides < phosphates< hydroxides < oxides < carbonates < sulfates < cyanides < chlorides Soluble Compounds   Metal halide ( Cl, Br , I ) salts are generally soluble ( except for Ag+, Hg2+, Pb2+)

  Nitrates, perchlorates, and acetates are soluble ( except for acetates of Ag+ and Hg2+ which are moderately soluble)

  Sulfates are soluble ( except for Sr2+, Ba2+, Pb2+, not soluble) ( Ca2+ and Ag+ are moderately soluble)

Additionally, Benefield et al. ( 1982) show that extensive systematic treatment of equilibria using Ksp, pH and acid base equilibria in conjunction with redox can be used to graphically represent metal compound speciation over a range of pH and Eh ( volts). This becomes increasingly complex as the number of metal anion pairs increases in the matrix. September 2000 1 4 Draft Table 1 1. Solubilities of Metal Anion Compounds in Water Metal Anion Species Compound g/ L Solubility Rating Experimental/ Estimated Value Antimony Sulfide Sb2S3 1.75E 03 M Experimental Chloride SbCl3 2390* H Experimental Arsenic Sulfide As2S3 6.65E 04** L Experimental Sulfide AsS5 1.36E 03 M Experimental Oxide As2O3 1.77E+ 01** H Experimental Barium Phosphate Ba3( PO4) 2 4.27E 04 L Estimated Hydroxide Ba( OH) 2 3.98E+ 01 H Estimated Sulfite BaSO3 1.07E 01** M Experimental Sulfate BaSO4 1.01E 02** M Experimental Beryllium Oxide BeO 4.17E+ 02 H Experimental Cadmium Hydroxide Cd( OH) 2 1.57E 03 L Experimental Oxide CdO 2.43E 03** M Experimental Carbonate CdCO3 2.72E 05 L Estimated Cyanide Cd( CN) 2 2.47E 03 M Experimental Chromium Sulfate Cr2( SO4) 3 860* H Experimental Cobalt Sulfide Co2S3 2.58E 23 L Estimated Hydroxide Co( OH) 3 3.18E 03 M Experimental Carbonate CoCO3 1.06E 04 L Estimated Copper Sulfide CuS 2.18E 13 L Experimental Sulfide Cu2S 6.70E 15 L Estimated Hydroxide Cu( OH) 2 2.10E 07** L Experimental Oxide CuO 1.40E 08 L Experimental Oxide Cu2O 8.60E 05 L Experimental Cyanide CuCN 1.60E 08 L Estimated Chloride CuCl 4.32E 02 M Estimated Chloride CuCl2 637* H Experimental September 2000 1 5 Draft Table 1 1. Solubilities of Metal Anion Compounds in Water ( continued)

Metal Anion Species Compound g/ L Solubility Rating Experimental/ Estimated Value Lead Sulfide PbS 7.70E 04** L Experimental Phosphate Pb3( PO4) 2 6.81E 07 L Estimated Hydroxide Pb( OH) 2 9.90E 04 L Estimated Oxide PbO 1.41E+ 00** H Experimental Carbonate PbCO3 1.70E 03 M Experimental Sulfate PbSO4 4.07E 02 M Experimental Chloride PbCl2 4.49E+ 00 H Estimated Mercury Sulfide HgS 1.25E 05 L Experimental Hydroxide Hg2( OH) 2 4.31E 07 L Estimated Hydroxide Hg( OH) 2 5.90E 02 M Experimental Oxide HgO 2.58E 02** M Experimental Carbonate Hg2CO3 1.30E 03 M Estimated Sulfate HgSO4 3.90E 01 M Experimental Sulfate Hg2SO4 2.75E+ 00 H Estimated Cyanide Hg( CN) 2 9.30E+ 01 H Experimental Chloride Hg2Cl2 4.25E 06*,** L Experimental Chloride HgCl2 65.0 H Experimental Nickel Sulfide NiS beta 9.08E 12 L Estimated Hydroxide Ni( OH) 2 1.27E 02 M Experimental Carbonate NiCO3 9.25E 02 M Experimental Cyanide Ni( CN) 2 5.92E 02 M Experimental H = Highly soluble M = Moderately soluble L = Slightly soluble to insoluble * g/ L calculated from wt% assuming no loss in volume when the salt was dissolved in water ** Mean of two reported values Source: compiled by SAIC from the sources listed in Section 5 of this report. September 2000 1 6 Draft pH Control pH largely controls metal containment in a solid matrix influenced by a solvent. Predicting any constituent's solubility as a function of pH must be done carefully. Though redox conditions largely influence solubility, the solubility of some metals is more dependent on pH than on redox potential ( e. g., Pb).

Generally, metal cations are more soluble/ mobile at low pH. Some metal anionic species are more soluble at high pH. Adsorption of metal cations and anions generally increases as pH increases thus reducing solubility. Metal hydroxides and oxides have low solubility in the range of pH 7.5 11, as depicted in Figures 1 1 and 1 2 ( Conner, 1990). At higher pH (> 12), in the absence of a strong reducing agent, metal hydroxides may become soluble. Greater effects on solubility of certain metals occur at extreme low and high pH (< 2 and > 12), respectively. Solubility over " transition" pH ranges ( 5 9) varies for most metal compounds and is more dependent on the overall influence of the waste environment. Amphoteric metals ( e. g., chromium, lead) have higher solubility at both low and high pH.

Anions of weak bases become more soluble at low to mid range pH ( e. g., carbonates, sulfides, and phosphates). It is generally observed that hydrolysis occurring under strongly alkaline conditions leads to the precipitation of salts, and hydrolysis ( hydrogen bonding/ protonation) occurring under acidic conditions leads to the solubilization of salts. Hydrolyzed metals at low to mid range pH act as weak acids, thus acidifying the solution and increasing the solubility of slightly soluble salts ( Benefield, Judkins, and Weand, 1982).

pH greatly influences the reactions that occur at the surface of solids in contact with the solvating solution via the charge induced on solid and particle surfaces. Charged surfaces in turn influence hydration, adsorption, and complexation reactions. Thus the influence of the electro chemical environment as a function of pH and redox potential should be observed together when predicting the stability boundaries, considering all possible metal cation and anion species.

Oxidation Reduction Potential ( redox potential) and Electron Activity In simple and multi component systems, the solubility gradient for many metals is largely dependent on the electro chemical environment of solid and liquid phases ( redox) in conjunction with pH. The solubility of polyvalent metals is more complex than for metals that have a strong tendency to exist in one oxidation state in solution, when bonded, and during chemical reactions ( i. e., Cu, Zn, Cd, Pb, Ba, Co, Ni). Dissolution mechanisms are complex because a variety of redox influencing chemical species may exist at all ranges of pH. Furthermore, some metals are capable of anionic speciation and demonstrate different solubilities and amphoteric properties over varying pH ( As, Se, Sb, Cr). September 2000 1 7 Draft Figure 1 1. Solubilities of metal hydroxides as a function of pH ( Adapted from Connor, 1990).

6 9 10 11 12 8 7 pH 0.0001 0.001 0.01 0.1 1.0 10 100 Solubility ( mg/ L)

Fe+ 3 Cu Ni Cd Fe+ 2 Ag Pb Zn Metal Hydroxides September 2000 1 8 Draft Metal Hydroxides/ Sulfides Figure 1 2. Solubilities of metal hydroxides and sulfides as a function of pH ( Adapted from Connor, 1990). September 2000 1 9 Draft In addition to the metals that have more than one valence state, other species in their elemental or ionic form ( such as sulfur) have more than one valence state which also influences the redox process. Metals such as Cu and Cd, even though they have mainly one oxidation state, can be strongly influenced by redox processes.

In order to use the electrical potential to assess the likelihood of a reaction proceeding in the direction of metal dissolution, the species required for redox processes must be available in the system. In addition, since redox reactions involve the transfer of electrons, the use of electron activity ( pe) is used as an approach ( Drever, 1997). The activity of electrons does not correspond to a concentration, but the tendency of the system to provide electrons to any electron acceptor. Redox potential is a measure of the electrical charge required for a reaction involving a redox pair to proceed in the direction of oxidation or reduction. Thus a conventional means of discussing redox reactions can be done by using pe pH and Eh pH diagrams which conveniently display solubility transition boundaries based on speciation.

Oxidizing conditions are characterized by the redox potential of the system such that the dissolution of the metal species of concern is favored in the ionic environment, indicated by a positive electrical potential. Some natural oxidizing species include iron ( III) oxide, manganese dioxide, and dissolved oxygen recharge water. Oxidizers found in wastes include peroxides, dichromates, and nitric acid. Some reducing species are iron( II) hydroxide and sulfides.

Knowledge of the redox potential of a system allows estimation of the possible speciation of the metal and its leachability at varying pH. This area, however, needs much more investigation in complex systems to understand what species are being affected by the overall redox potential of a system. In the following discussion, observations were made according to oxidation state classifications ( e. g., + 1, + 2, + 3, etc.).

The + 2 metals ( Cu, Zn, Cd, Pb, Ba, Co, and Ni) tended to show similar trends in solubility along pH and redox gradients. The + 2 metals are generally more soluble in oxidizing conditions and less soluble under reducing conditions.

Two metals have unique oxidation states of + 3 and + 5, arsenic and antimony. Information was available for arsenic. Selenium is shown together with arsenic in the tables that follow, because both form anionic species over a range of conditions. However, Se and As solubilities are influenced differently by adsorption at varying pH.

In general, amphoteric metals in high pH environments are capable of being reduced and forming soluble metal anions from their higher oxidation state complexes ( e. g., As, Sb). The contrary holds true as well. Amphoteric metals complexed at a low oxidation state are capable of being oxidized and solubilizing the metal ion at low pH. However, the mobility of these species is higher in acidic environments. Chromium and mercury behave uniquely compared to other metals due to their complex redox chemistry at varying pH. September 2000 1 10 Draft Soluble Moderately Soluble Tables 1 2 and 1 3 show metal solubilities at general pH ranges under oxidizing and reducing conditions. These tables are only a general guide and may not predict the true solubility of a compound in a complex environment. Metal solubility and mobility information obtained from studies on simple systems is presented in Tables 1 2 and 1 3 in conjunction with information obtained from leaching studies of actual wastes ( e. g., fly ash, bottom ash, municipal waste combustion ash) that supports these conclusions.

Table 1 2. Metal Salt Speciation Under Oxidizing Conditions Acidic  Oxidizing Neutral  Oxidizing Basic  Oxidizing  CrO4 2 and CrO7 2 form stable and mobile anion  all salts of Pb2+, Cu2+, Cd2+, Ba2+, Co2+, Ni2+

 As5+, SeO4 2

 salts of Hg  Pb2+ salts  salts of Hg  Cu2+, Cd2+, Pb2+ at high pH (> 12)

 anionic species of As  salts of Hg  Gradient to higher pH: the salt solubilities of Pb2+, Cu2+, Cd2+, Ba2+, Co2+, Ni2+ are limited by the formation of carbonates and hydroxides.

 SeO3 2

Source: compiled by SAIC from the sources listed in Section 5 of this report. September 2000 1 11 Draft Soluble Moderately Soluble Table 1 3. Metal Salt Speciation Under Reducing Conditions Acidic  Reducing Neutral  Reducing Basic  Reducing  When no sulfide is present, salts of Cd2+, Ba2+, Co2+, Pb2+

 Cr( OH) 3 3+

 salts of As and Sb remain soluble until strong reducing conditions are achieved.

 salts of Ni2+ when no sulfide is present  with increase in pH the solubilities of Pb2+, Cu2+, Cd2+, Ba2+, Co2+, Ni2+ salts are limited by the formation of carbonates and hydr/ oxides.

Source: compiled by SAIC from the sources listed in Section 5 of this report.

According to de Groot et al. ( 1989) pH is the main factor in controlling leachability [ in fly ash], as illustrated in Table 1 4. The elements present in the form of anionic species ( for example, As, Sb, Se, Mo and V) behave similarly. In contrast with literature information, limited solubility of anions at high pH (> 11) has been observed. The metals Pb, Cu, Cd, and Zn show minimum solubility at high pH. To verify the pH dependence of all major elements normally found in fly ash extracts at pH 4 and liquid to solid ( LS) ratio of 5, have been performed. By stepwise increase of the pH, by adding calcium oxide, the relation between pH and element concentrations in the solution has been established. Trace elements such as As, Sb, Se, Mo, and V show a characteristic maximum at neutral pH and a decrease in concentration towards lower and higher pH. September 2000 1 12 Draft Table 1 4. Leaching characteristic as a function of acidity of the contact solution and the L/ S ratio.

Concentration in Leachate Trace elements form of anion L/ S= 5 pH Observed solubility Formation of insoluble compounds Decrease As, Sb, Se, Mo, V > 7 minimum With calcium or precipitation / sorption as barium arsenate. < 7 minimum Solid phases , arsenic oxide, antimony oxide, molybdenum oxide, vanadium oxide Pb, Cu, Cd, Zn > 11 minimum Hydroxide compounds Mg > 8 limited Magnesium hydroxide Maximum As, Sb, Se, Mo, V 7 Al 6 7 minimum Caused by gibbsite formation 10 maximum Related to pozzolanic activity > 11 minimum Ettringite formation ( 3 CaO. Al2O3.3CaSO4.31 H2O ) Si 10 minimum 12 maximum Increase Ca high limited Calcium sulfate SO4 high limited Calcium sulfate Source: compiled by SAIC from the sources listed in Section 5 of this report.

Comans and Meima ( 1987) show that the Ca chemistry of municipal solid waste bottom ash can exert a strong influence on the leaching of potential contaminants. Leaching of the heavy metals Cd, Cu and Pb is probably controlled by ( hydr) oxide or carbonate minerals. The solubility minimum for these heavy metals lies between pH 8 and 9, and the solubility may increase as pH rises or decreases from the pH of minimum solubility. September 2000 1 13 Draft 1.1.2 Behavior of Specific Elements Copper, Cadmium, and Lead ( Drever, 1997)

The expected behavior of these metals in the environment can be summarized as follows: Under oxidizing conditions at low pH, they are all soluble and mobile. As the pH rises, their concentrations tend to decrease, first because of adsorption ( particularly for Pb and Cu), and then because of the limited solubility of carbonates and oxides/ hydroxides. Under reducing conditions, if sulfur is present, all should be immobilized as sulfides. If sulfur is absent, for Cd and Pb the solubility control will be the same as under oxidizing conditions; Cu should be insoluble at all pH values. Adsorption is generally less important in soil under reducing conditions because the most important substrates in soil for adsorption, Fe and Mn oxyhydroxides, tend themselves to dissolve.

Arsenic and Selenium ( Drever, 1997)

Under oxidizing conditions, the dominant form of arsenic is the + 5 oxidation state, which is present as arsenic acid and its anions ( arsenate), corresponding closely to phosphoric acid and phosphate species. For selenium, the dominant form under oxidizing conditions is selenate, which is closely analogous to sulfate. As conditions become reducing, As ( V) is reduced to As ( III) arsenious acid and arsenite anions. When sulfate reduction occurs, As precipitates as a sulfide; if sulfur is absent, it remains in solution as arsenious acid or an arsenite. Elemental arsenic should be a stable species under highly reducing conditions. For selenium, selenite species ( analogous to sulfite) occur at intermediate redox levels, followed by elemental selenium and hydrogen selenide ( analogous to hydrogen sulfide) species under strongly reducing conditions. Both arsenic and selenium may be incorporated into iron sulfides under reducing conditions. Figures 1 3 and 1 4 present pe pH diagrams for arsenic and selenium, respectively. September 2000 1 14 Draft Figure 1 3. Simplified pe pH diagram for the system As O H2O at 25b C and one atm. Total activity of sulfur species = 10 2. Solubility is defined as a dissolved As species activity of 10 6. ( Adapted from Drever, 1997)

1.0 0.5 0  0.5 Eh ( v) 20 15 10 5 0  5  10 pe 12 2 HAsO4 2 H3AsO4 H2AsO4

H3AsO3 As 4 8 6 10 pH AsO4 3

As 2 S 3 H 2 AsO 3  HAsO3 2

AsS Arsenic September 2000 1 15 Draft Figure 1 4. Simplified pe pH diagram for the system Se O H2O at 25bC and one atm. Solubility is defined as a dissolved Se activity of 10 6. ( Adapted from Drever, 1997)

1.0 0.5 0  0.5 Eh ( v) 20 15 10 5 0  5  10 pe 12 2 SeO 4 2 H2SeO3 HSeO3

SeO4 2

Seelemental HSe

H2Se 4 8 6 10 pH Selenium Chromium ( Drever, 1997)

Under highly oxidizing conditions, the hexavalent form ( chromate) is stable as an anion. It is not strongly adsorbed ( adsorption edge at about pH 7) and is therefore mobile in the environment. Under intermediate and reducing conditions, Cr ( III) is the stable oxidation state. It is insoluble in the neutral and alkaline pH ranges. It is soluble ( largely as Cr( OH) 2+) under acid conditions. In general, Cr ( III) species are strongly adsorbed. Figure 1 5 presents a pe pH diagram for chromium. September 2000 1 16 Draft Figure 1 5. pe pH diagram for the system Cr O H2O at 25bC and one atm. Solubility is defined as a dissolved Cr activity of 10 6. ( Adapted from Drever, 1997)

1.0 0.5 0  0.5 Eh ( v) 20 15 10 5 0  5  10 pe 12 2 HCrO4

4 8 6 10 pH CrO4 2

Cr2O3 Cr3

Cr( OH) 2 Chromium Mercury The chemistry of mercury in the environment is highly complex. The common soluble form is the oxidized ( mercuric) Hg2+ ion and its hydrolysis product Hg( OH) 2 ( neutral species), with the reduced ( mercurous) Hg2 2+ dication being less important. Elemental mercury has a large stability field. The elemental form is volatile and slightly soluble in water. Mercury sulfide is not mobile except in extreme alkaline conditions. Figure 1 6 presents a pe pH diagram for mercury. ( Drever, 1997). September 2000 1 17 Draft Figure 1 6. pe pH diagram for the system Hg S O H2O at 25bC and one atm. Solubility is defined as a dissolved Hg activity of 10 6. Total activity of sulfur species = 10 2. The diagram is the same in the absence of S species, with the HgS ( cinnabar) field replaced by Hg ( metal). In the presence of chloride, the Hg2 2+ may be replaced by the insoluble mercurous chloride ( calomel). ( Adapted from Drever, 1997)

2 1 0  1  2 2 4 6 10 14 8 12 Eh ( v) HgCO3 Hg HgS Hg Hg2 2+ Hg2SO4 HgS2 2 HgO pH Mercury In a metal contaminated site, mercury exists in mercuric form ( Hg2+), mercurous form ( Hg2 2+), elemental form ( Hg0), or alkylated form ( e. g., methyl and ethyl mercury). Hg2 2+ and Hg2+ under oxidizing conditions are more stable than metallic mercury. Under mildly reducing conditions, both organically bound mercury and inorganic mercury compounds may be degraded to elemental mercury that can be converted readily to methyl or ethyl mercury by biotic and abiotic processes. Methyl and ethyl mercury are the most toxic forms of mercury. The alkylated mercury compounds are both volatile in air and soluble in water ( Smith, 1995).

Mercury ( II) forms relatively strong complexes with Cl and CO3  2. Mercury ( II) also forms complexes with other inorganic ligands such as F, Br, I, SO4  2, S 2, and PO4  3. The insoluble HgS is formed under mildly reducing conditions ( Smith, 1995). The stability of some mercury compounds under various Eh and pH conditions is shown in Figure 1 7. September 2000 1 18 Draft Figure 1 7. Stability regions of mercury species in the sulfur carbonate water system. Hg = 0.001 M; S = 0.1 M; C = 0.1 M. ( From USEPA, 1984. Mercury Health Effects Update: Health Issue Assessment, Final Report. EPA/ 600/ 8 84/ 019F.)

1.0 0.5 0  0.5 Eh ( v) 20 15 10 5 0  5  10 pe 12 2 Hg2+

4 8 6 10 pH Hg( OH) 2 0 Hg metal Hg 2 2+

HgS cinnabar Hg September 2000 1 19 Draft 1.2 Organic Mobility The mobility of organic constituents has received less study than the behavior of inorganics; however, there is a theoretical body of work that addresses the behavior of many organic compounds. For the purposes of this discussion, organic counpounds included in the Hazardous Waste Identification Rule ( HWIR) organics list were evaluated to explored for potential mobility using both theoretical and real world examples. The relationship of chemical properties to leachate characteristics is best identified by properties such as octanol water coefficients, pH, and solubility.

For many organic compounds, solubility often determines the leachate concentration. The solubility of some volatile constituents have been found to indicate that increasing solubility is related to increasing leachate concentration ( Pavelka et al., 1993). Alcohol constituents and halogenated hydrocarbons, ketones, and aromatics were found to follow this trend. Figure 1 8 shows the relationship for solubility and leachate concentration. Figure 1 9 indicates a strong correlation of leachate concentrations and solubility of the semi volatile constituents.

Figure 1 8. Volatile concentration and solubility. ( Adapted from Pavelka et al., 1993)

100 1000 10000 100000 1000000 · · · · · · · · · · · · · · · Isobutyl Alcohol Butyl Alcohol Methanol 1,1 Dichloroethane Benzene 1,2 Xylene 1,3 Xylene Toluene Trichloroethne Chloroform 1,1,1 Trichloroethane Methyl Chloride Methyl Isobutyl Ketone Methyl Ethyl Ketone Acetone Chemical Solubility ( mg/ L) 10 100 10 1000 10000 1000000 Leachate Concentration ( ug/ L) September 2000 1 20 Draft Figure 1 9. Semi volatile concentration and solubility. ( Adapted from Pavelka et al., 1993)

· · · · · · · · · · · · · · · · · 10 3 10 1 10 103 105 105 104 103 102 10 100 10 1 Chemical Solubility ( mg/ L) Leachate Concentration ( ug/ L)

1.2.1 Effects of pH on Leachability Of Organics Many organic compounds can become more leachable if they are exposed to an acidic or alkaline leachant. The leachability of an organic in a neutral ( pH = 7) aqueous leachant can be estimated by the organic's octanol/ water partition coefficient ( Kow). However, new species can be formed from some organics in acid or alkali, usually cationic or anionic forms of the organic, with different Kow and different leachability. The Kow of a chemical should be related to the leachate concentration in an inverse way. Since the Kow is a measure of a chemical hydophobicity, the more hydrophobic a chemical is, the less soluble it should be. Pavelka et al. ( 1993) found that with volatile constituents leachate concentrations decreased as Kow increased. Two distinct groups were identified by the study: alcohols; and halogenated hydrocarbons, aromatics and ketones. The semi volatile constituents were also found to behave similarly to the volatiles ( Figure 1 10). Constituents with low Kow values were characterized as having high leachate concentrations ( e. g., phthalic acid, phenol, and aniline). September 2000 1 21 Draft Figure 1 10. Volatile concentration and Kow values. ( Adapted from Pavelka et al., 1993).

· · · · · · · · · · · · · · · · · 104 103 102 10 100 Log KOW Leachate Concentration ( ug/ L)

0 2 4 6 8 · 10 Acid Leachable Organics In general, amines ( R NH2, R NH R, R( R) N R), amides ( R C(= O) NH R), and other nitrogencontaining organics can form very water soluble salts in the presence of strong acids like hydrochloric, nitric, phosphoric, or sulfuric. The amine or amide nitrogen becomes protonated, forming a cation that is much more water soluble than the neutral compound.

Table 1 5 lists compounds that react with strong acid containing leaching media, changing their leachability and environmental mobility. Most of the compounds become protonated, forming a more mobile cation. Note, however, that two compounds in Table 1 5, endothall and the sodium salt of fluoroacetic acid are already very water leachable salts. ( Endothall is the disodium salt of a dicarboxylic acid.) In the presence of acid, they are rendered neutral, and become less mobile in acidic media. September 2000 1 22 Draft Table 1 5. Compounds Whose Leachability Changes In Acidic Media CAS # Chemical Acid Mobility 145 73 3 Endothall Less mobile 62 74 8 Fluoracetic acid, sodium salt Less mobile 53 96 3 Acetylaminofluorene, 2 More mobile 79 06 1 Acrylamide More mobile 116 06 3 Aldicarb More mobile 92 67 1 Aminobiphenyl, 4 More mobile 504 24 5 Aminopyridine, 4 More mobile 61 82 5 Amitrole More mobile 62 53 3 Aniline More mobile 2465 27 2 Auramine More mobile 225 51 4 Benz[ c] acridine More mobile 92 87 5 Benzidine More mobile 357 57 3 Brucine More mobile 86 74 8 Carbazole More mobile 106 47 8 Chloroaniline, p More mobile 5344 82 1 Chlorophenyl thiourea, 1 o More mobile 50 18 0 Cyclophosphamide More mobile 2303 16 4 Diallate More mobile 226 36 8 Dibenz( a, h) acridine More mobile 224 42 0 Dibenz[ a, j] acridine More mobile 194 59 2 Dibenzo[ c, g] carbazole, 7H More mobile 91 94 1 Dichlorobenzidine, 3,3' More mobile 60 51 5 Dimethoate More mobile 60 11 7 Dimethylaminoazobenzene, p More mobile 119 93 7 Dimethylbenzidine, 3,3' More mobile 122 09 8 Dimethylphenethylamine, alpha, alpha More mobile 119 90 4 Dimethyoxybenzidine, 3,3' More mobile 122 39 4 Diphenylamine More mobile 122 66 7 Diphenylhydrazine, 1,2 More mobile 51 79 6 Ethyl carbamate More mobile 96 45 7 Ethylene thiourea More mobile 151 56 4 Ethyleneimine ( aziridine) More mobile 52 85 7 Famphur More mobile 640 19 7 Fluoracetamide, 2 More mobile 302 01 2 Hydrazine More mobile 123 33 1 Maleic hydrazide More mobile 91 80 5 Methapyrilene More mobile 16752 77 5 Methomyl More mobile 101 14 4 Methylenebis, 4,4' ( 2 chloroaniline) More mobile 1615 80 1 N, N Diethylhydrazine More mobile 86 88 4 Naphthyl 2 thiourea, 1 More mobile 134 32 7 Naphthylamine, 1 More mobile September 2000 1 23 Draft Table 1 5. Compounds Whose Leachability Changes In Acidic Media ( continued) CAS # Chemical Acid Mobility 91 59 8 Naphthylamine, 2 More mobile 54 11 5 Nicotine More mobile 88 74 4 Nitroaniline, 2 More mobile 99 09 2 Nitroaniline, 3 More mobile 100 01 6 Nitroaniline, 4 More mobile 55 86 7 Nitrogen mustard More mobile 126 85 2 Nitrogen mustard N Oxide More mobile 99 55 8 Nitro o toluidine, 5 More mobile 56 57 5 Nitroquinoline 1 oxide, 4 More mobile 55 18 5 Nitrosodiethylamine More mobile 62 75 9 Nitrosodimethylamine More mobile 924 16 3 Nitrosodi n butylamine More mobile 10595 95 6 Nitrosomethylethylamine More mobile 1116 54 7 N Nitrosodiethanolamine More mobile 621 64 7 N Nitrosodi n propylamine More mobile 86 30 6 N Nitrosodiphenylamine More mobile 4549 40 0 N Nitrosomethyl vinyl amine More mobile 59 89 2 N Nitrosomorpholine More mobile 615 53 2 N Nitroso N methylurethane More mobile 100 75 4 N Nitrosopiperidine More mobile 930 55 2 N Nitrosopyrrolidine More mobile 103 85 5 N Phenylthiourea More mobile 297 97 2 O, O Diethyl O pyrazinyl phosphorothioate More mobile 152 16 9 Octamethylpyrophosphoramide More mobile 108 45 2 Phenylenediamine,   More mobile 106 50 3 Phenylenediamine, p More mobile 25265 76 3 Phenylenediamines ( N. O. S.) More mobile 109 06 8 Picoline, 2 More mobile 23950 58 5 Pronamide More mobile 107 10 8 Propylamine,   More mobile 110 86 1 Pyridine More mobile 50 55 5 Reserpine More mobile 57 24 9 Strychnine More mobile 62 55 5 Thioacetamide More mobile 79 19 6 Thiosemicarbazide More mobile 62 56 6 Thiourea More mobile 137 26 8 Thiram More mobile 95 80 7 Toluenediamine, 2,4 More mobile 823 40 5 Toluenediamine, 2,6 More mobile 496 72 0 Toluenediamine, 3,4 More mobile 95 53 4 Toluidine, o More mobile 106 49 0 Toluidine, p More mobile Source: compiled by SAIC from the sources listed in Section 5 of this report. September 2000 1 24 Draft Alkali Leachable Organics Phenols ( Ar OH) and imides ( R C(= O) NHC(= O) R) are the two organic functional groups represented on the HWIR list that can form an ionic species in the presence of an alkaline leachant. They are both weak acids, capable of giving up a proton in the presence of hydroxide, to form an organic anion, which is much more soluble than the neutral species.

Table 1 6 lists compounds that react with strong alkali containing leaching media, changing their leachability and environmental mobility. Most of the compounds lose a proton, forming a more mobile anion. Note, however, that four compounds in Table 1 6, all acid salts, are already very water leachable. In the presence of alkali, they are rendered neutral, and become less mobile in alkaline media.

Polyfunctional Organics Organics with multiple functional groups, including one that can be protonated in acid leachant, and one that can lose a proton in alkaline leachant, will be more leachable in both acids and alkalis. There are at least ten such compounds on the list. They are listed in Table 1 7. ( A number of drugs and antineoplastic agents on the list have not been included, considering their low probability of occurrence in significant concentrations in industrial hazardous wastes.) September 2000 1 25 Draft Table 1 6. Compounds Whose Leachability Changes in Alkaline Media CAS # Chemical Alkali Mobility [ 54 11 5] Nicotine salts Less mobile 51 75 2 Nitrogen mustard hydrochloride salt Less mobile 302 70 5 Nitrogen mustard N Oxide, HCl salt Less mobile 636 21 5 Toluidine hydrochloride, o Less mobile 106 51 4 Benzoquinone, p More mobile 88 85 7 Butyl 4,6 dinitrophenol, 2 sec ( Dinoseb) More mobile 59 50 7 Chloro m cresol, p More mobile 95 57 8 Chlorophenol, 2 More mobile 108 39 4 Cresol,   More mobile 95 48 7 Cresol, o More mobile 106 44 5 Cresol, p More mobile 131 89 5 Cyclohexyl 4,6 dinitrophenol, 2 More mobile 120 83 2 Dichlorophenol, 2,4 More mobile 87 65 0 Dichlorophenol, 2,6 More mobile 94 75 7 Dichlorophenoxyacetic acid, 2,4 ( 2,4 D) More mobile 56 53 1 Diethylstilbestrol More mobile 105 67 9 Dimethylphenol, 2,4 More mobile 534 52 1 Dinitro o cresol, 4,6 More mobile 51 28 5 Dinitrophenol, 2,4 More mobile 64 18 6 Formic Acid More mobile 130 15 4 Naphthoquinone, 1,4 More mobile 88 75 5 Nitrophenol, 2 More mobile 100 02 7 Nitrophenol, 4 More mobile 13256 22 9 N Nitrososarcosine More mobile 87 86 5 Pentachlorophenol More mobile 108 95 2 Phenol More mobile 108 46 3 Resorcinol More mobile 58 90 2 Tetrachlorophenol, 2,3,4,6 More mobile 108 98 5 Thiophenol More mobile 95 95 4 Trichlorophenol, 2,4,5 More mobile 88 06 2 Trichlorophenol, 2,4,6 More mobile 93 76 5 Trichlorophenoxyacetic acid, 2,4,5 ( 245 T) More mobile 93 72 1 Trichlorophenoxypropionic acid, 2,4,5 ( Silvex) More mobile 81 81 2 Warfarin More mobile Source: compiled by SAIC from the sources listed in Section 5 of this report. September 2000 1 26 Draft Table 1 7. Compounds More Leachable in Acidic and Alkaline Media\

CAS # Chemical Acid Mobility Alkali Mobility 591 08 2 Acetyl 2 thiourea, 1 More mobile More mobile 2763 96 4 Aminomethyl 3 isoxazolol, 5 More mobile More mobile 115 02 6 Azaserine More mobile More mobile 541 53 7 Dithiobiuret More mobile More mobile 148 82 3 Melphalan More mobile More mobile 70 25 7 Methyl nitro nitrosoguanidine ( MNNG) More mobile More mobile 50 07 7 Mitomycin C More mobile More mobile 759 73 9 N Nitroso N ethylurea More mobile More mobile 684 93 5 N Nitroso N methylurea More mobile More mobile 62 44 2 Phenacetin More mobile More mobile Source: compiled by SAIC from the sources listed in Section 5 of this report. September 2000 2 1 Draft 2. LEACHATE GENERATION QUANTITIES IN LANDFILLS Various processes affect the rate of leachate generation and its composition. The four factors listed below represent the ones most significantly affecting leachate quantity ( Lu et al., 1985):

° Quantity of water at landfill surface. This includes effects such as climate ( e. g., precipitation), topography ( e. g., stormwater runon), and irrigation ( e. g., leachate recirculation).

° Landfill surface conditions. Not all of the water hitting the landfill surface will percolate through the landfill. Water can also evaporate ( influenced by climate and cover material), or run off ( influenced by cover material and topography). Indirectly, some of these effects are determined by whether the landfill is active or inactive with a cap.

° Refuse effects. Most of the landfills examined in the literature have been municipal solid waste landfills. However, there are differences both within MSW and between different waste types ( e. g., industrial, hazardous, C& D). These include moisture retention effects and permeability.

° Underlying soil. Similarly to refuse effects, the moisture retention and permeability of underlying soil affects the rate at which leachate migrates to the ground water. This principally influences the quantity of leachate entering the subsurface rather than the quantity of leachate generated by the landfill.

Two relative metrics of leachate generation are reported most frequently in the literature: leachate generation per unit landfill area and liquid to solid ( L/ S) ratio. Leachate generation is commonly reported as a field observation while L/ S is commonly reported as a laboratory or experimental leaching metric. These two metrics have significant differences and are not easily related to or correlated with one another. As discussed later leachate generation per unit area and time are a relatively consistent benchmark among landfills. Field observations of L/ S ratios range more widely than leachate generation values and where reported are often calculated on differing bases. Most often, however, L/ S ratios are reported as the abscissa ( x axis) in leaching experiments or methods development studies.

L/ S ratios are of particular interest in such studies because of their significance for the design and interpretation of laboratory leaching tests. Specifically, leaching tests require the addition of liquid to a solid ( usually waste) matrix. Comparing the quantity of liquid added per unit of solid material in the test procedure to L/ S ratios observed in actual landfills is critical to interpreting test results.

From a practical standpoint, L/ S ratio can be calculated by dividing the total leachate generated over a period of time by the total quantity of waste in the landfill. The total quantity of leachate September 2000 2 2 Draft generated is dependent on time, since liquid could percolate through the landfill indefinitely and also at different rates due to the factors described above. For an active landfill, both the leachate generation rate and the waste quantity are dynamic ( i. e., leachate generation changes as the landfill is expanded, while waste volume increases daily). For a closed landfill, the waste volume is constant but, as time goes on, the cumulative quantity of leachate generated from the landfill increases. For purposes of this analysis we have defined L/ S as the ratio of annual mass of leachate generated by a landfill or landfill cell to the cumumlative mass of waste disposed in that landfill or landfill cell. The analysis that follows serves ( 1) to identify values of leachate generation rates and L/ S ratios found in the literature and other case studies, and ( 2) to quantitatively evaluate, using a database of approximately 250 landfills developed by EPA's Office of Water, the way a number of factors influence leachate generation rate. September 2000 2 3 Draft 2.1 Information Sources Four types of information sources are presented here: ( 1) recent data from EPA's Office of Water's effluent guidelines development work, ( 2) data previously developed from EPA's Subtitle D survey from the 1980s, ( 3) data from the literature, and ( 4) data taken from various case studies. Each of these sources presents data representing different landfill designs, waste types, climate, etc., allowing for an examination of the various factors influencing generation rate. The four data sources are discussed below.

Effluent guidelines for the landfills point source category were proposed on February 6, 1998 ( 63 Federal Register 6425). In developing these standards, EPA's Office of Water collected data specific to landfills using a questionnaire ( among other data sources), with 1992 as the base year. Approximately 250 landfills are represented in the survey results, representing hazardous, municipal, and Subtitle D landfills. These data are presented in Appendix E.

For comparison to the data obtained from EPA's Office of Water, another large scale database available is the distribution of Subtitle D landfills collected by EPA in the late 1980' s. These data are still used by EPA, for example in the Monte Carlo framework of the hazardous waste identification rule ( 64 Federal Register 63382, November 19, 1999). These data predominantly represent private or captive industrial landfills ( i. e., landfills managing waste from a single industrial plant or several industrial plants owned by the same company). Complete landfill dimension data are available for approximately 500 landfills. As an estimate to determining leachate generation rate, each landfill is identified with 1 of 97 climatic areas of the U. S., which correspond to a fixed infiltration rate through a " look up" table. The infiltration rates are calculated using various assumptions and the HELP model.

Data from individual sites from the literature are extracted. Although in most cases the researchers did not make the investigation of L/ S ratio or leachate generation rate a principal effort, sufficient information exists from these sources to calculate this quantity. Specifically, five papers were identified that allowed the calculation of L/ S ratios for thirteen different sites, while three papers were used in calculating normalized leachate generation rates ( rate per area) at eight sites. These sites were exclusively municipal landfills. Appendix C presents the citations and more detailed data concerning these sites.

Finally, SAIC has initiated the collection of data from " case studies." These data are from various sources including past EPA programs and more current information from states where leachate characteristics from a single landfill are identified. Appendix D presents the data in a " site by site" format. September 2000 2 4 Draft 2.2 Values of Liquid to Solid Ratio and Leachate Generation Rate Found 2.2.1 Summary of Data Tables 2 1 and 2 2 present an overview of the data from the sources discussed above. Table 2 1 summarizes liquid to solid ( L/ S) ratios, which are calculated as annual leachate generation ( in volume per year) divided by total waste accumulated ( in volume), resulting in units of 1/ years ( or years 1). The calculated liquid to solid ratios are fairly consistent between the four various data sources ( i. e., within the same order of magnitude), and they are all much less than the L/ S ratio of 20: 1 used in the TCLP. The TCLP laboratory procedure uses a L/ S ratio of 20: 1. As shown in Table 2 1, the quantity of leachate generated in a fixed period of time ( one year), as compared to the quantity of waste in the landfill, is much less than 20: 1 ( with differences of two or more orders of magnitude). Therefore, if anything, the 20: 1 ratio is representative of the quantity of leachate generated after hundreds of years.

In Table 2 2 provides leachate generation rates are provided for the various sources. These data are calculated as leachate generation ( in gallons per day) divided by landfill area ( in acres), resulting in units of gallons/ acre day. The median generation rates between sources are similar. These summaries demonstrate that the values obtained from one source are of the same magnitude as data obtained from other sources.

Table 2 1. Summary of Liquid to Solid Ratios for all Sources Source of Data Number of Data Points Liquid to Solid Ratio ( years 1) Additional Data Analysis Performed Median Range ( 10th to 90th Percentiles)

Office of Water 234 0.012 0.0004 to 0.23 Landfill type, operational status, and precipitation HWIR/ HELP 487 0.06 0.02 to 0.13 None ( data set lacks flexibility)

Case Studies 6 0.05 0.0003 to 0.15 Operational status Literature 13 0.04 0.003 to 1.9 Operational status TCLP  20  For comparison September 2000 2 5 Draft Table 2 2. Summary of Leachate Generation Rates for all Sources Source of Data Number of Data Points Leachate Generation Rate ( gallons/ acre day) Additional Data Analysis Performed Median Range ( 10th to 90th Percentiles)

Office of Water 252 290 1 to 2,100 Landfill type, operational status, and precipitation HWIR/ HELP 487 410 70 to 1,100 None Case Studies 8 320 40 to 2,100 Operational status Literature 8 130 30 to 620 Operational status 2.2.2 EPA Office of Water Data Operational Status When a landfill is closed, cover materials are placed over it to reduce infiltration. These materials include natural soil, clay, synthetics, and/ or vegetation. Several studies in the literature have shown that infiltration rate is in fact reduced after a landfill is closed in this way ( these cases are in Appendices C and D). Table 2 3 shows data extracted from the Office of Water database for active and inactive cells, showing a similar reduction. This table presents leachate generation rate in units of gal/ ac day.

Table 2 4 presents L/ S ratios using two different computational methods. All data are from the Office of Water survey. In the first set of data, the L/ S ratio is calculated by dividing the landfill's leachate generation rate ( given in units of gal/ ac d) by average cell depth. In the second set of data, the L/ S ratio is calculated by dividing the leachate flow rate ( in gal/ d) by the total waste volume ( in units of cubic yards). The purpose of this comparison is to show if certain data elements in the survey yield vastly different results, which would imply some level of inconsistency in the data. As shown in Table 2 4, however, the data are consistent. September 2000 2 6 Draft Table 2 3. Leachate Generation Rates by Operational Status from Office of Water Data Type of Landfill Number of Data Points Leachate Generation Rate ( gallons/ acreday Statistical Significance A Median Range ( 10th to 90th Percentile)

Active 191 500 30 to 3500 Active and inactive rates are statistically different at 95th% significance level Inactive 127 67 0 to 1000 A. Statistical significance was determined using the t test for differences between two population means.

Table 2 4. Liquid to Solid Ratios by Operational Status from Office of Water Data Type of Data Number of Data Points Liquid to Solid Ratio ( years 1) Statistical Significance A Median Range ( 10th to 90th Percentile)

Normalized leachate flow/ landfill depth active 178 0.014 0.00044 to 0.17 Active and inactive rates are statistically different inactive 97 0.005 0.00040 to 0.049 Leachate flow/ landfill volume active B 185 0.016 0.00034 to 0.22 Statistical significance not determined inactive B 49 0.0067 0.00051 to 0.41 A. Statistical significance was determined using the t test for differences between two population means at the 95% level. B. " Inactive" indicates a landfill with only inactive cells. " Active" indicates a landfill with at least one active cell; it may or may not also have inactive cells.

Landfill Type The three categories of landfills used in this analysis of the Office of Water survey are municipal, Subtitle D, and hazardous. These same distinctions were used in developing the proposed effluent guidelines. It should be noted that, in order to provide a sufficient sample size for analysis, the latter two categories are broader than those discussed in Section 3 of this report. Specifically, Subtitle D landfills include non hazardous industrial waste landfills ( both codisposal and monofill) and construction and demolition ( C& D) landfills. Hazardous waste landfills include both commercial Subtitle C landfills and captive hazardous waste landfills from various industries.

Leachate generation rates and L/ S ratios may vary due to differences in landfill type. Tables 2 5 and 2 6 present data for these parameters based on distinctions between hazardous, industrial, and municipal landfills, and their operational status. Figures 2 1 and 2 2 display the data in graphical form. The data show that differences are apparent between active and inactive landfills for each landfill type. Differences between landfill types, however, are not as apparent. September 2000 2 7 Draft Table 2 5. Leachate Generation Rates by Landfill Type from Office of Water Data Type of Landfill Number of Data Points Leachate Generation Rate ( gallons/ acre day) Statistical Significance A Median Range ( 10th to 90th Percentile)

Hazardous active 33 493 11 to 2600 Active and Inactive rates are not statistically different inactive 43 88 0 to 1400 Municipal active 122 500 33 to 2300 Different at a 95th% significance level inactive 69 58 0 to 840 Subtitle D active 36 509 8 to 5400 Different at a 95th% significance level inactive 15 100 0 to 500 All ( from Table 2 3) active 191 500 30 to 3400 Different at a 95th% level inactive 127 67 0 to 1000 A. Statistical significance was determined using the t test for differences between active and inactive population means.

Table 2 6. Liquid to Solid Ratios by Landfill Type from Office of Water Data.

Type of Landfill Number of Data Points Liquid to Solid Ratio ( years 1) Statistical Significance A Median Range ( 10th to 90th Percentile)

Hazardous 61 0.008 0.00038 to 0.41 L/ S ratio for Subtitle D landfill is statistically higher than population as a whole Municipal 132 0.010 0.00036 to 0.098 Subtitle D 41 0.060 0.0012 to 0.62 All ( from Table 2 1) 234 0.012 0.00038 to 0.23 A. Statistical significance was determined using the t test for differences between two population means at the 95% level. September 2000 2 8 Draft Figure 2 1. Leachate Generation Rates by Landfill Type and Operational Status.

1 10 100 1,000 10,000 100,000 0 10 20 30 40 50 60 70 80 90 100 Cumulative Distribution Leachate Generation Rate ( gal/ acre day)

Haz Active Haz Inactive MSW Active MSW Inactive Sub Active Sub Inactive Source: Effluent Guidelines for Landfills Point Source Figure 2 2. Liquid to Solid Ratio by Landfill Type: Both Active and Inactive.

1.0E 06 1.0E 05 1.0E 04 1.0E 03 1.0E 02 1.0E 01 1.0E+ 00 1.0E+ 01 0 10 20 30 40 50 60 70 80 90 100 Cumulative Distribution Liquid to Solid Ratio ( l/ kg yr) Hazardous MSW Subtitle D S ource: Effluent Guidelines for Landfills P oint S ource September 2000 2 9 Draft Precipitation Leachate generation rates and L/ S ratios also vary due to differences in landfill location. Tables 2 7 and 2 8 present data for these parameters based on distinctions between precipitation. Distinctions are also made between active and inactive cells. Figures 2 3 and 2 4 display the data in graphical form.

Figure 2 3 shows that leachate generation rate increases with increasing precipitation in inactive landfills. Figure 2 4 shows that L/ S ratio also increases with increasing precipitation.

Table 2 7. Leachate Generation Rates by Precipitation Rate from Office of Water Data.

Amount of Precipitation Number of Data Points Leachate Generation Rate ( gallons/ acre day) Statistical Significance A Median Range ( 10th to 90th Percentile)

< 40 inches active 83 340 4 to 1800 Different at a 95th% significance level inactive 50 40 0 to 720 40 to 60 inches active 84 610 46 to 2600 Different at a 90th% significance level inactive 53 92 0 to 700 >= 60 inches active 24 970 33 to 5600 Different at a 95th% significance level inactive 24 200 0 to 1350 All active 191 500 30 to 3500 Different at a 95th% significance level inactive 128 67 0 to 1000 A. Statistical significance was determined using the t test for differences between two population means. September 2000 2 10 Draft Table 2 8. Liquid to Solid Ratio by Precipitation Rate from Office of Water Data.

Amount of Precipitation Number of Data Points Liquid to Solid Ratio ( years 1) Statistical Significance A Median Mean Standard Deviation < 40 inches 192 0.0095 0.062 0.19 Precipitation is significant for active landfills ( at a 90% level).

Precipitation is not significant for inactive landfills. 40 to 60 inches 208 0.015 0.10 0.31 >= 60 inches 68 0.022 0.26 0.50 All ( from Table 2 1) 234 0.012 0.11 0.31 A. Regression analysis was performed to examine the relationship between precipitation and leachate generation. Because of the significant differences found between active and inactive landfills, the analysis was performed separately for each group. In both cases, precipitation was found not to be a very strong predictor of leachate generation ( i. e., the coefficient of determination, R2, was on the order of 0.01). For active landfills, however, the relationship between precipitation and leachate generation still was found to be statistically significant at the 90 percent level ( i. e., based on analysis of variance of the regression and significance tests on the regression estimators). The relationship was not significant for inactive landfills. These results suggest that, for active landfills, precipitation does influence leachate generation, although other factors appear to have a more substantial effect. Further analysis would be required to isolate the effects of these other factors.

Figure 2 3. Leachate Generation Rates by Precipitation Rate and Operational Status.

1 10 100 1,000 10,000 100,000 0 10 20 30 40 50 60 70 80 90 100 Cumulative Distribution Leachate Generation Rate ( gal/ acre day)

< 40"  A ctive < 40"  Ina ctive 40 60"  Active 40 60"  Ina ctive > 60"  A ctive > 60"  Ina ctive Source: Effluent Guidelines for Landfills Point Source September 2000 2 11 Draft Figure 2 4. Liquid to Solid Ratio by Precipitation Rate: Both Active and Inactive.

1.0E 06 1.0E 05 1.0E 04 1.0E 03 1.0E 02 1.0E 01 1.0E+ 00 1.0E+ 01 0 20 40 60 80 100 Cumulative Distribution Liquid to Solid Ratio ( l/ kg yr < 40"

40 60"

> 60"

Source: Effluent Guidelines for Landfills Point Source 2.2.3 Use of Other Data Other data sources were investigated to verify or supplement the data from the EPA Office of Water data set. As shown in Tables 2 1 and 2 2, these other data sets presented results of similar magnitude, and therefore confirm the reasonableness of the EPA Office of Water data.

These data sources could also be used in identifying the effect of parameters such as landfill operation on L/ S ratio and leachate generation rate. The Office of Water data showed that the values of both variables are lower for inactive landfills than for active landfills. Similar anecdotal conclusions are available from the literature and case study information in the Appendices C and D. September 2000 3 1 Draft 3. LEACHATE COMPOSITION AND PROPERTIES This section presents summary statistics on leachate composition from the characterization database developed in conjunction with this report. It also discusses some of the more fundamental of these characteristics based on the available literature on contaminant leaching processes. Where the data are sufficient to do so, it compares leachate characteristics across landfill types.

This section begins with a description of the characterization database and the sources combined to create the database ( Section 3.1). It then presents summary statistics and discusses leaching processes for several types of landfills. Municipal solid waste ( MSW) landfills and leachate characteristics are discussed first ( in Section 3.2) because of the extensive body of literature available. Sections 3.3 through 3.5 discuss the leachate characteristics of three other types of landfill that are well represented in the database. These landfill types are as follows:

° Construction and demolition debris ( C& D) landfills, ° Industrial codisposal landfills ( these are a set of older landfills that have managed multiple types of waste from multiple generating sites throughout their history, including non hazardous industrial waste, hazardous waste, and municipal solid waste), and ° Commercial hazardous waste landfills ( Subtitle C landfills).

Section 3.6 presents comparative statistics for these four types of landfills, with discussion of the apparent fundamental differences. Section 3.7 presents summary statistics for other types of landfills represented in the database. The landfills discussed in Section 3.7 all are captive landfills managing waste from a single industrial plant or several industrial plants owned by the same company. Statistics in Section 3.7 are presented according to the waste generating industry. September 2000 3 2 Draft 3.1 Characterization Database An integral part of this study was the development of a comprehensive database of landfill leachate characteristics. The search for data to incorporate into the database encompassed industry and Federal and State government sources. Data were accepted into the database if they met the following criteria:

° They represented leachate characteristics on an individual sample basis. ° They included at least some information regarding the type of landfill from which the data were taken. ° They were from a reliable source. ° They were available in an electronic form that could be incorporated into the database without extensive modification or manual data entry.

The search for data did not attempt to employ any statistical sampling approach. That is, the data are not necessarily a representative sample by geographic region, landfill type, or any other criterion. The database simply includes all of the readily available data that met the acceptance criteria above.

Each of the data sets resulting from the search was combined into a single electronic database that accompanies this report. The resulting database ( entitled LEACH 2000) includes data for conventional pollutants, metals, and organics in leachate from a variety of landfill types. The LEACH 2000 data is the basis for the summary statistics presented in the sections below. In order to represent typical landfills of each type, rather than extreme conditions, the summary statistics presented in this report exclude statistical outliers found in the data. These statistical outliers ( with the exception of certain outliers in the Wisconsin data set, discussed below), however, have been retained in the electronic database to allow for possible future investigation of their sources. The following paragraphs describe the specific data that was collected and incorporated in the LEACH 2000 database.

Two data sets were obtained from industry sources: data representing 60 MSW landfills from Browning Ferris Incorporated ( BFI) and data from a 1992 Chemical Waste Management ( CWM) study of leachate quality. The CWM study includes data from 47 landfills, including commercial hazardous waste landfills, industrial codisposal landfills, and MSW landfills.

Two data sets also were obtained from previous EPA research efforts. The first was a set of data for 21 C& D landfills compiled by ICF Incorporated for the Office of Solid Waste. The second was the EPA Office of Water database, discussed in Section 2, which was derived from data collecting during development the effluent guidelines for landfills. The EPA Office of Water database includes characterization data for 35 landfills of various types. Twenty three of these landfills could be conclusively identified according to type ( 21 MSW landfills and two commercial hazardous waste landfills). The remaining Office of Water landfills could be categorized as managing Subtitle D ( either industrial or C& D) waste or Subtitle C hazardous waste, but it could not be determined whether they were captive to a specific industry or accepted waste on a commercial basis from multiple generating sources. Data from this latter set of landfills are included in the electronic database accompanying this report, but are not included in the summary statistics provided in the remainder of this section. September 2000 3 3 Draft To locate data from state government sources, contact was initiated with cognizant agencies in all 50 states. In general, limited automated data, other than capacity summary data, were found. The summary table describing the leachate data collection programs in each state is presented in Appendix A. Data from two states, however, were available for combining into the LEACH 2000 database. The first data set, from the State of Florida, comprises leachate characterization data for 65 MSW landfills. The second data set represents 70 landfills from the State of Wisconsin. The Wisconsin data includes 39 MSW landfills, 18 paper mill landfills, 6 combustion ash landfills, and 7 landfills of other types.

In analyzing the Wisconsin data, certain patterns of statistical outliers were discovered. These patterns were consistent with intermittent misreporting of analytical units. Therefore, a detailed analysis was undertaken to identify and correct data points in the Wisconsin data suspected of having this problem. This analysis is described in detail in Appendix F. Separate data tables have been included in the LEACH 2000 database representing the original and adjusted Wisconsin data. The Wisconsin data included in the combined data table in LEACH 2000 and used in this report represent the adjusted data.

Another relevant characteristic of the Wisconsin data is that, for a number of landfills, it was possible to identify the date of first operation. The Wisconsin data, therefore, were instrumental in the analysis of temporal variability in fundamental leachate characteristics in MSW landfills presented in Sections 3.2.2 and 3.2.3. September 2000 3 4 Draft 3.2 Municipal Solid Waste Landfills The discussion of MSW leachate and leaching processes in this report is more extensive than that for other types of landfills for several reasons. First, prior scientific review of MSW landfills has been extensive. Second, the data available for MSW landfills in the characterization database are more extensive than for any other type of landfill. Third, EPA has traditionally viewed the MSW landfill as the default mismanagement scenario for hazardous waste ( e. g., in the TCLP analysis the leaching medium is intended to simulate those acids present in an MSW landfill), so leaching processes in these landfills are of particular interest. Finally, the discussion of leaching processes in MSW landfills provides a basis for the comparison of leachate from different types of landfills in Section 3.6.

Section 3.2.1 provides a general overview of the composition of MSW leachate, based primarily on the extensive data available in the characterization database. Later sections discuss both the circumstances under which these parameters are known to change in value and the significance of these parameters to accelerating or inhibiting the leaching of toxic constituents. Section 3.2.2 discusses temporal changes known to occur in a MSW landfill and how this affects the composition and properties of leachate generated over time. Section 3.2.3 isolates parameters which can be variable in MSW leachate and which are known to affect contaminant mobility.

3.2.1 Overall Composition of MSW Leachate Municipal solid waste ( MSW) landfills receive waste primarily from residential, commercial, and institutional sources. Some MSW landfills may receive quantities of construction and demolition debris, non hazardous industrial waste, and even hazardous waste from household sources or other exempt small quantity generators. The quantities of these types of waste, however, typically are small compared to the quantities of municipal waste managed. Several specific examples of MSW landfill operations may be found in Section 4 of this report ( case studies 6, 9, 11, 15, and 18 through 22).

In part because of the large number of sources and resulting heterogenous nature of the waste, MSW leachate is a complex mixture of inorganic and organic constituents. The specific composition of MSW leachate also varies both spatially ( within a single landfill and between landfills) as well as temporally. While research has identified some of the reasons for this variability, it is useful to first identify what some of these parameters are and the values that can be expected in landfill leachate. The data presented in Table 3 1, below, are from the more than 200 MSW landfills represented in the LEACH 2000 database.

As discussed in Section 3.1 above, although a large number of MSW landfills are represented, they do not necessarily constitute a statistically representative sample of MSW landfills by geographic region or any other criterion. Nevertheless, these MSW landfills do represent a variety of locations, ages, and other factors which are expected to result in variation between landfills. Such variation results from the many factors affecting leachate composition which will be discussed in Sections 3.2.2 and 3.2.3. Specifically, these and other sections focus on explaining the conditions wherein low, high, or median values will most likely be encountered.

The constituents included in Table 3 1 ( and similar, subsequent tables for other types of landfills in other sections of this report) represent the parameters most frequently analyzed for in the September 2000 3 5 Draft characterization data included in the LEACH database. They are not a complete set of all the constituents for which data are available in the database. Constituents not included in the tables have fewer samples from which to draw statistics than those constituents represented in the tables.

Table 3 1 organizes constituents into three categories: major physical/ chemical parameters ( e. g., pH, chemical oxygen demand ( COD), major anions), trace inorganics ( e. g., RCRA metals), and organics. The paragraphs below discuss the available characterization data for MSW landfills in each of these categories.

General Parameters Parameters commonly analyzed in wastewaters are also commonly analyzed in MSW leachate. Unfortunately, data for other parameters known to be critical in leaching assessments, such as oxidation reduction potential, are not well represented in the characterization data or the scientific literature. Conventional pollutants for which data are available include pH, alkalinity, biochemical oxygen demand ( BOD), chemical oxygen demand ( COD), total organic carbon ( TOC), and common anions. Typical ranges for these pollutants cover several orders of magnitude even with a single landfill.

Trace Inorganics The inorganics most frequently detected in MSW leachate are, in order of detection frequency: manganese, boron, barium, zinc, aluminum, nickel, arsenic, chromium, copper, and lead. These constituents were detected in more than 50 percent of the MSW landfill leachate samples.

Organics Most organic compounds such as volatiles, semivolatiles, pesticides, PCBs, herbicides, and insecticides are detected in MSW landfill leachate with less frequency than other parameters such as metals. For example, a four year, six landfill Waste Management Inc. study analyzed leachate samples for these parameters and found the following frequency of detection as follows:

° Volatiles: 10 percent ° Semivolatiles: 2 percent ° Pesticides: 3 percent ° PCBs: 0 percent ° Herbicides: 5 percent ° Insecticides: 6 percent.

These figures may be misleading with regard to certain specific organic compounds because they are an average of relatively frequently detected compounds and many other compounds detected rarely or not at all. Both the Waste Management study and the data compiled in Table 3 1 show that certain specific organic compounds are detected with some frequency. For example, in the LEACH 2000 database, acetone, benzene, ethylbenzene, phenol, and xylene are detected in greater than 50 percent of the samples. The Waste Management study similarly found toluene ( 79 percent), m & p cresol ( 79 percent), methyl ethyl ketone ( 71 percent), phenol ( 67 percent), acetone ( 63 percent), xylene ( 63 percent), and methylene chloride ( 58 percent) in greater than 50 September 2000 3 6 Draft percent of the samples. In general, however, organic compounds are detected much less frequently than metals in MSW leachate.

Table 3 1. Composition of MSW Landfill Leachate Analyte N % Detected 5th % ile 10th % ile Median Mean 90th % ile 95th % ile MAJOR PHYSICAL/ CHEMICAL PARAMETERS ( mg/ L, except pH in Standard Units) Alkalinity 3,697 96.5 182 304 2,080 2,689 5,470 7,220 B. O. D. 4,645 94.2 7.05 16.9 536 2,548 7,276 11,800 Calcium 839 99.5 32.9 73.4 220 466 860 1,516 Chloride 4,392 99.4 19.2 43 704 5,024 2,800 4,610 C. O. D. 4,252 95.5 35 93 1,200 4,709 9,550 15,000 Cyanide 1,429 31.3 0.005 0.006 0.018 4.10 0.166 0.71 Fluoride 1,041 91.7 0.11 0.15 0.4 6.93 1.9 14.9 Iron 4,284 98.0 0.31 0.97 17.0 308 259 530 Magnesium 829 99.8 13 25 155 511 320 430 Nitrogen 3,482 93.1 0.45 1.2 145 7,367 625 901 pH 6,965 100.0 5.88 6.20 7 7.05 7.94 8.29 Sodium 2,321 98.5 18 49 539 2,290 1,910 3,010 Sulfate 2,930 87.6 6 11 92.7 314 514 1,000 T. O. C. 1,444 99.6 8.6 21 282 1,534 3,850 7,270 TRACE INORGANICS ( µ g/ L) Aluminum 366 86.1 73 160 800 15,046 24,700 107,000 Antimony 710 25.5 3 4 13 70.0 190 360 Arsenic 2,444 71.1 4 6 20 441 100 260 Barium 1,779 93.4 50 84 405 866 1,700 2,800 Beryllium 653 11.2 0.3 0.5 4 39.5 55 143 Boron 764 96.5 190 490 4,500 87,541 16,000 27,000 Cadmium 2,351 31.5 0.5 1 10 28.3 79 110 Chromium 2,776 63.0 9 10 51 235 341 592 Copper 2,064 57.1 7.4 10 33 139 200 384 Lead 2,539 50.2 2 4 21 133 250 500 Manganese 2,371 97.4 51 99 744 6,076 15,000 37,000 Mercury 2,078 18.0 0.09 0.14 0.59 7.15 4.6 16 Nickel 1,889 80.9 20 30 120 679 489 740 Selenium 1,754 18.2 1 1.7 10 58.5 180 310 Silver 1,830 17.8 1 2 11.3 53.7 56 110 Thallium 632 12.2 1 2 15 149 516 815 Zinc 2,282 89.6 14 24 160 5,103 2,300 7,300 ORGANICS ( µ g/ L) 1,1 Dichloroethane 1,768 39.9 1.5 2.2 19 66.1 122 195 1,1 Dichloroethene 1,155 1.9 0.6 1 15.5 134 176 251 Acenaphthene 677 8.7 1 1 6.15 11.22 32 55 Acetone 815 61.7 16 33 770 3,299 9,200 12,000 Benzene 2,169 52.3 1 1.7 6.69 32.5 51 117 Chloroethane 1,771 19.9 2 3 12 24.1 50 100 Ethylbenzene 1,897 65.8 2 4.43 34 1,502 150 290 Methyl Isobutyl Ketone 844 44.4 4 10 120 3,631 970 1,740 Naphthalene 1,190 46.7 2.40 3.90 16.6 48.1 120 256 Phenol 1,624 71.9 10 17 190 45,900 4,100 34,000 Trichloroethylene 1,845 20.6 0.604 1 7.51 22.9 53 86.4 Vinyl Chloride 1,952 20.7 0.9 1.1 6.6 2,409 70 542 Xylene 2,285 68.0 3 5.8 53.3 1,452 239 390 Source: Characterization data from the more than 200 MSW landfills included in the LEACH 2000 database. September 2000 3 7 Draft 3.2.2 Temporal Variability in MSW Landfill Leachate Stages of a MSW Landfill The quality and rate of leachate generation at a landfill changes over time. This is caused by changes in the dimensions of the waste inside the landfill, its potential for oxidation or degradation, etc. These changes in leachate quality in turn affect the mobility of toxicants.

The municipal waste landfill has been described as an anaerobic microbial process during much of its active life, a process which can be modeled or conceptualized as a batch digester with inputs of refuse and moisture and outputs of gas and leachate. Pohland ( 1986) has described the municipal waste landfill in five phases.

° Phase I: Initial Adjustment. This period represents the beginning of the operating life of the landfill where refuse is initially placed and moisture enters the cell.

° Phase II: Transition. This period represents the beginning of leachate generation ( i. e., the available moisture exceeds the capacity of the surrounding soils or refuse itself). The landfill changes from aerobic conditions to anaerobic microbial stabilization. This is due to the presence of carbon dioxide rather than oxygen in surrounding gas. With this change from aerobic to anaerobic conditions, critical electron accepting molecules change from oxygen to nitrates and sulfates and an overall reducing environment is encountered. The increased moisture also enhances microbial activity. Metabolic by products such as volatile organic fatty acids and alcohols appear in the leachate and increase its organic strength ( Farquhar, 1989).

° Phase III: Acid Formation. Volatile organic fatty acids become predominant in the leachate, with the continuation of conditions described for Phase II. Nutrients such as nitrogen and phosphorous are released and utilized in support of the growth of biomass. Decreases in pH are observed in the leachate as a result of the presence of the organic acids.

° Phase IV: Methane Formation ( or methanogenic). Nutrients continue to be consumed and intermediates such as volatile organic fatty acids are converted to methane and carbon dioxide. This gives several results. First, the leachate organic strength is reduced and gas generation increases. As a result of the decrease in fatty acids, the pH changes; the pH becomes representative of a bicarbonate buffered system rather than the organic acid buffered system. The landfill continues to represent a reducing environment, with oxidation reduction potential at the lowest level.

The methanogenic phase of a MSW landfill is expected to be best demonstrated under the following conditions ( Ehrig, 1983): Moisture content A50%; Temperature > 15bC ( 60bF); Good buffering capacity of leachate: alkalinity 2,000 mg/ L as CaCO3, and ratio of volatile fatty acids to alkalinity @ 0.8 September 2000 3 8 Draft ° Phase V: Final Maturation. In this phase, nutrient availability may become limiting due to the consumption of the readily available organic constituents in the waste and leachate; microbially resistant organic materials may be slowly converted. As a result of the decrease in activity, measurable gas production decreases. Oxygen and oxidized species may reappear with a corresponding increase in oxidation reduction potential.

Significance of Phases Towards Leaching While five steps in an MSW landfill life are listed above, anaerobic activity is only present in two of them ( phases III and IV). These are the times of a landfill's life which are most dynamic, and therefore of interest to many researchers. The phases are chronological but the corresponding length of time for each stage is site specific. However, researchers ( Ehrig, 1983; Farquhar, 1989) have generally found this period to be relatively short (< 10 years or even as little as several months) as compared to the length of time that the landfill is actively accepting wastes ( e. g., 20 years or more) or generating leachate ( many years following closure). These sitespecific factors influencing the time for these stages to proceed include landfilling procedures, the nature of the wastes, the quantity of moisture entering the landfill, and closure conditions ( Pohland, 1986). Additionally, individual cells within a landfill may be at different stages and exhibit different phenomenon, such that the overall landfill becomes a complex characterization of the above processes.

The different stages of activity within a landfill result in differences in certain indicator parameters. For example, the presence of organic fatty acids and varying values of oxidationreduction potential were described in general terms for these different stages. The variation of these parameters are discussed below. Not only are these parameters indicative of conditions within a landfill, but they result in differences in mobility, precipitation, and speciation of metals in the waste and leachate. Pohland ( 1986) lists many factors that are associated with the different stages listed above. Of particular interest are parameter ratios, such as the ratio of BOD to TOC , for which the value of the ratio changes as do values of the parameters themselves.

Some of these factors, such as changes in pH, are well studied factors which are known to affect the leaching behavior of metals such as lead. Other factors, such as total solids, may indeed be reflective of the different stages in landfill life but have little impact on the mobility of contaminants.

3.2.3 Factors Affecting Contaminant Mobility Researchers have historically analyzed MSW landfill leachate for a wide variety of parameters, and a wide body of literature exists with these results. However, their reasons for research have been equally varied, including wastewater treatment concerns and methane gas generation concerns. While these areas of study can supplement and provide critical input to work regarding contaminant leaching processes, it also means that parameters that are often presented in the literature may or may not have relevance to contaminant leaching. Unfortunately, because leaching fundamentals is such a complex topic it is difficult or impractical to conclude that a given parameter is ` unimportant.' Nevertheless, this section attempts to isolate several parameters that are known or suspected of the most significant affects of the mobility for toxic metals and other contaminants of concern to human health and the environment. September 2000 3 9 Draft The effect of extract properties upon contaminant mobility has been researched for a wide variety of wastes and even for industrial processes such as liquid liquid extraction. A number of factors affect the degree of mobilization or fixation of contaminants in the waste. Usually several factors are in operation simultaneously ( e. g., in the case of microbial activity in MSW leachate). Conner ( 1990) listed many factors in their application to hazardous waste stabilization processes; not all of these factors are relevant to environmental leaching phenomena. Other researchers have suggested additional factors. Some of these major factors as applied to MSW landfill conditions include the following:

° pH. The solubility of metal species as a function of pH is well studied in the physical sciences as well as the waste treatment literature. For example, when studying a single species such as lead hydroxide, the concentration of lead in solution is lowest at pH 9.5 ( Conner, 1990).

° Redox potential ( oxidation reduction potential). The presence of strong oxidants or reductants can change the valence state of metals such as chromium and arsenic. This in turn affects their speciation and their solubility. High values indicate an oxidizing environment; low or negative values represent a reducing environment. Chemical species are often stable in one area of pH and redox potential; changes in one or both of these variables may result in a different species being stable and creating a driving force for conversion between the species ( Conner, 1990). Redox also affects the presence of anionic species such as sulfate/ sulfite, which differ in their solubilities towards metals.

° Organic leachant composition ( e. g., total volatile acids). Leachants such as EDTA and acetic acid are generally believed to be more aggressive than distilled water ( Van der Sloot, 1997). This is due to the presence of acid as well as its buffering capacity to counter the effects of alkalinity and hold the pH at this lower value. Metal species may be complexed with dissolved organic carbon and affect mobility.

° Biological Oxygen Demand ° Chemical Oxygen Demand ° Ratio of Biological Oxygen Demand to Chemical Oxygen Demand ° Total alkalinity ° Sulfate and sulfide. The presence of anionic species such as sulfate and sulfite differ in their solubilities towards metals.

These factors are discussed in greater detail below. These are the parameters which are known to be present in leachate, and which also affect mobility of contaminants. Field leachate is a complex mixture of parameters and while some factors are well studied and their importance has previously been isolated ( such as some of these above factors), other parameters present may exert synergistic effects, no effects, or even countering effects towards contaminant leaching behavior. September 2000 3 10 Draft Additional parameters are present in landfill leachate at levels different than ambient conditions, or change over time, but their effect on contaminant leaching is not well known or not well studied. Such factors, listed below but could include others, are not extensively discussed in this report.

° Conductivity. An increase in conductivity indicates an increase in ionic strength of the solution. For some ionic species, the effect is an increase in solution concentration ( Frampton, 1998). ° Total Organic Carbon ° Ratio of Chemical Oxygen Demand to Total Organic Carbon ° Total Kjeldahl Nitrogen ° Nitrate ° Ammonia ° Ratio of Ammonia to Total Kjeldahl Nitrogen ° Total phosphate ° Total solids ° Chloride. Chloride may form stable soluble complexes with certain metals, such as cadmium.

pH In the literature, low leachate pH has been associated with increased microbial activity and therefore are an indication of additional processes occurring: organic acid formation, increases in alkalinity, changes in oxidation reduction potential, etc. Higher values of pH ( i. e., greater than 7) are generally associated with more mature landfills with less bioactivity.

Poland ( 1986) identifies an early stage of a landfill where pH is low due to acid formation ( e. g., 4.7 to 7.7), rising above 7 in later stages. Data from Ehrig ( 1983) support this assessment. Specifically, pH values between 4.5 and 6 were most often found in the first two years of landfill operation; after approximately two years the lowest pH values were no lower than 6. The highest pH values from Ehrig ( 1983) were 8 to 9.

Data from Farquhar ( 1989) also show that relatively young landfills have lower pH. Leachate from landfills of less than 5 years exhibit typical pH of 5 to 6; this rises to 7.5 after 20 years. Time series data from a single cell in a South African landfill shows a similar trend, with a value of 5.9 after five months increasing to 7.8 after 42 months ( Ross, 1990).

MSW landfill leachate data from the LEACH 2000 database also show a correlation between pH and landfill age. Specifically, the Wisconsin data included in the database allow identification of landfill age. Using data for Wisconsin MSW landfills, Figure 3 1 presents cumulative frequency distributions of pH for MSW landfills in various age categories. The median ( 50th percentile) pH shifts upwards for landfills of age 2 and older. Approximately 20 percent of landfills less than 2 years old had leachate pH less than 6. However, for landfills between 2 and 9 years old only approximately 5 percent of landfills exhibit pH less than this value. The frequency of lower pH ( i. e., pH of 5 or lower) is very infrequent for any landfill age ( a maximum of approximately 3 percent), and conclusions regarding the effect of landfill age at this low range are difficult to make. September 2000 3 11 Draft At the other pH extreme, pH values above 8 were most common in the landfills of age 6 to 9 years according to the Wisconsin data ( approximately 10 percent of the cases). For the remaining landfills ( aged 5 years or less), approximately 5 percent of the landfills had pH values above 8.

Figure 3 1. Cumulative Frequency of pH in Wisconsin MSW Landfills by Age Group 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Cumulative Distribution pH Year 0 Year 1 Years 2 5 Years 6 9 Using the same data, it is possible to perform regression analysis of pH versus age to further examine the relationship between pH and landfill age. While the relationship does not explain all of the observed variation in pH, the trend is statistically significant at the 1 percent level. Figure 3 2 shows the scatter plot of pH versus age for the Wisconsin MSW landfills with the regression line indicated. Further examination of Figure 3 2 further supports the observation that low pH is more frequent in young landfills. Observations below pH of 6 become less frequent for landfills older than approximately 5 years ( see the detail expanded in Figure 3 2). September 2000 3 12 Draft Figure 3 2. pH Observed in Wisconsin MSW Landfills by Age 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 0 1 2 3 4 5 6 7 8 9 10 Year pH Detail show n below Detail from above 5.25 5.5 5.75 6 6.25 6.5 6.75 7 7.25 7.5 7.75 0 1 2 3 4 5 6 7 8 9 10 Year pH R squared = 0.08 Significant at 1% September 2000 3 13 Draft A review of time series data at individual landfills appears to indicate that the trends seen in the overall data hold true for many individual landfills, but not all. Figures 3 3 and 3 4 present trend lines based on regression analysis of pH versus age for each of the individual landfills represented in the Wisconsin data. More than half of the individual landfills display statistically significant increasing trends ( Figure 3 3). Statistically significant trends could not be found for three landfills. The other landfills displayed trends that were decreasing or variable ( Figure 3 4)

Figure 3 3. pH Trends for Individual Landfills ( increasing)

5.5 6 6.5 7 7.5 8 8.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Year pH Brow n ( other sample pts) Marathon Mar oco Monroe Outagamie Sauk Superior Mocassin Mike Superior Cranberry Creek Superior Seven Mile Creek Vernon WMWI Pheasant Run ( other sample pts) WMWI Ridgeview ( sample pts 22& 42) WMWI Valley Trail Winnebago Figure 3 4. pH Trends for Individual Landfills ( decreasing or varying)

4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Year pH Abbotsford Door Brow n ( sample pt 95) Dane Juneau Lincoln WMWI Timberline Trail WMWI Pheasant Run ( sample pt 285) WMWI Ridgeview ( sample pts 23& 61) September 2000 3 14 Draft Redox Potential and Sulfate While a theoretically important parameter in identifying the stability of individual metal species, and therefore mobility, redox potential is not often reported in the literature. Further, the analytical measurement can be prone to significant error. In one study ( Chian, 1977), analysis for redox potential was made immediately following collection, and then frequently for a twelve day period. After 24 hours the measurement was 100 mV higher ( i. e., representing a more oxidizing environment) than immediately following sampling, even under refrigerated conditions. Redox potential showed the largest dependence on analysis time of any of the parameters measured. This study shows that reports of redox potential in the literature may or may not be reflective of the actual conditions in the leachate depending on whether the analysis occurs in the field or following delivery to a laboratory.

One study ( Chian, 1977) identified redox potential as a function of landfill age. The results were plotted with pH and showed that as pH increased, redox potential increased. As discussed above, different researchers have found that pH rises slightly as a landfill ages. During the early years of a landfill life (< 2 years), redox potential ranges from  200 to 150 mV. Later ( 5 to 15 years), the upper end of the range is still 150 mV while the range has narrowed somewhat. Low values of redox potential have been cited as due to a high degree of anaerobiosis in the landfill, while higher readings reflect a steady state situation. Low redox potential values are associated with reducing conditions, high values with oxidizing conditions.

These data are consistent with information from Pohland ( 1986). In the second phase of a landfill ( initial formation of leachate), the redox potential ranges from 40 to 80 mV. The third phase ( acid formation) and fourth phase ( gas formation) show the lowest values of redox potential:  240 to 80 in Phase III and  240 to  70 in Phase IV. Redox potential in Phase V is reported as 97 to 163.

Based on these two studies by Pohland ( 1986) and Chian ( 1977), low redox values ( reducing conditions) are most likely to be present during the acid generation and methane formation phases of a landfill, with redox potential reaching its lowest value in the methane generation phase. Therefore, in cases where such redox data are not available it may be possible to extrapolate, qualitatively, what these conditions may be based on other properties indicative of Phase II and Phase III behavior.

Sulfate concentration is one possible parameter to use as a surrogate. Chian ( 1977) presents sulfate concentration data as a function of landfill age, plotted as the ratio sulfate to chloride concentration. This trend is compared to trends in pH and redox potential over time. As the landfill ages, the sulfate/ chloride ratio decreases, redox potential increases, and pH increases. The decrease in the sulfate/ chloride ratio is attributed to anaerobic conditions where sulfate is reduced to sulfide. There is an inverse correlation between redox potential and sulfate concentration which is explained by Chian ( 1977) as low ORP readings ( reducing conditions) correspond to falling sulfate levels. In addition to its indication of reducing conditions, the presence of sulfides may result in lower metal solubilities. Species of cadmium, copper, lead, mercury, nickel, and zinc are insoluble in their sulfide form ( Conner, 1990). Conversely, sulfate forms are much more soluble. September 2000 3 15 Draft Ehrig ( 1983) has presented data for sulfate concentration as a function of landfill age in laboratory scale experiments, where the acid formation and methane fermentation stages are condensed to a period of days rather than years, as well as from an operating landfill. For the laboratory scale study, in comparing these results to other parameters, the highest sulfate concentrations were present early, followed by a drop in concentration for the remainder of the study period. The time of the drop corresponded to a rise in pH and lagged the fall in concentration of COD and BOD ( as discussed below). These results, therefore, are similar to the Chian ( 1977) results that show decreasing sulfate levels over time and increasing pH over time. Because sulfur is still present in the system, the sulfur would likely be converted to sulfide as sulfate concentrations fall.

The operating landfill data presented in Ehrig ( 1983) suggest similar findings. Sulfate concentration decreases from approximately 1,300 mg/ L at the beginning of the study ( when the landfill is 1 ½ years old) to less than 100 mg/ L after 6 ½ years. The fall is sulfate concentrations parallel the fall in COD and BOD levels, and a rise in pH.

Similar results are available from Farquhar ( 1989) which summarizes data from previous studies, showing the effect of landfill age on parameters including sulfate; the data were presented in tabular format grouping the landfill ages into five or ten year increments: 0 to 5 years, 5 to 10 years, 10 to 20 years, and greater than 20 years. As expected, landfills greater than 20 years had the lowest levels of sulfate (< 100 mg/ L). Conversely, these parameters exhibited the highest levels in the range of 0 to 5 years ( 500 to 2,000 mg/ L) and decreasing in the range of 5 to 10 years ( 200 to 1,000 mg/ L).

Organic Content: Overview The organic content of leachate is measurable by several parameters, including volatile fatty acids, chemical oxygen demand ( COD), and biological oxygen demand ( BOD). Volatile fatty acids ( e. g., acetic acid) are the product of biological activity. Chemical oxygen demand is a test to quantify the oxidizable contents of a wastewater and represents the ultimate value of the oxygen that the wastewater could consume in oxidizing species that are present as reduced species. Biological oxygen demand is indicative of the degree to which the contents of the water is amenable to biological activity. It is measured by adding oxygen and bacteria and allowing equilibration for five days. The ratio of BOD to COD can not be greater than 1; values close to 1 indicate that biological degradation is favorable while values much less than 1 indicate that some oxidizable material is not biodegradable ( Stephenson, 1998).

Each of these parameters are indicator parameters, which do not measure any one species or compound but a class of compounds.

BOD and COD The measurement of the ratio of BOD to COD in landfill leachate, as well as absolute values of these parameters, is provided by several researchers. Ehrig ( 1983) measures these parameters in landfills aged up to 7 years. In one landfill, these parameters behaved similarly such that elevated levels of COD generally corresponded to instances of elevated levels of BOD, and elevated levels of the ratio between BOD and COD. Specifically, these levels were elevated and stayed at these levels from year 1 ½ ( initial measurement) until year 3, with the exception of a September 2000 3 16 Draft sharp dip and rise shortly after measurements began. Following year 3 there was a gradual decrease in the values of these parameters to year 6 ½ when the activity was at its lowest. Interestingly, the behavior of pH in this same period of time was a gradual increase from 6 to approximately 8.

The results of the single landfill study by Ehrig ( 1983) correlate well to results from many landfills presented in the same paper as generated using data from a variety of previous studies ( mostly from studies initiated in the United States) and from data from landfills in Germany. The effect of age on COD measurements shows a very uniform steady state concentration of COD after year 8 ( approximately 3,000 to 5,000 mg/ L). Prior to this year the data are much more scattered with many of the values higher than this ( as consistent with the single landfill study) but several of the values lower ( ranging from 100 to 40,000). Similar results are obtained in a laboratory scale experiment, where concentrations of BOD and COD are initially high ( approximately 10,000 to 15,000 mg/ L for BOD and 15,000 to 25,000 for COD) but, together with the BOD to COD ratio, drop following a rise in pH.

The findings of Ehrig ( 1983) are consistent with the data presented by Pohland ( 1986). Pohland ( 1983) indicated that the ratio of BOD to COD increases during Phases II and III of the landfill life ( transition and acid formation), then drops in later phases ( e. g., gas production). Absolute values of biological oxygen demand and chemical oxygen demand have similar behavior, in that these values increase in Phases II and III and drop in later phases.

Similar results are available from Farquhar ( 1989) which summarizes data from previous studies, showing the effect of landfill age on parameters such as COD and BOD; the data were presented in tabular format grouping the landfill ages into five or ten year increments: 0 to 5 years, 5 to 10 years, 10 to 20 years, and greater than 20 years. As expected, landfills greater than 20 years had the lowest levels of BOD and COD. Conversely, these parameters exhibited the highest levels in the range of 0 to 5 years and decreasing in the range of 5 to 10 years.

While the above sources suggest that relatively young municipal waste landfills have higher levels of BOD, COD, and BOD/ COD ratios, conflicting data are available from Waste Management's study of leachate generated from six of its municipal waste landfills, each varying in age and characteristics. In comparing the average values of organic indicator parameters ( BOD, TOC, and COD) to the start date of the landfill, no clear trends are apparent. Average levels of COD and BOD are highest in the oldest landfill, a finding in contradiction to the Farquhar ( 1989) and Ehrig ( 1983) results. However, average values from the Waste Management data are relatively low in comparison to the data from these two previous papers. The average values of COD from Waste Management ranged from 227 to 4,645 mg/ L; Ehrig ( 1983) identifies the range of 3,000 to 5,000 mg/ L as typical of long term steady state conditions.

Volatile Fatty Acids and COD The correlation of volatile fatty acid concentration to COD concentration was also demonstrated by Ehrig ( 1983), who used the result to theorize that the volatile fatty acids are responsible for the chemical oxygen demand ( see Figure 3 5). Specifically, samples with low COD also had low concentrations of volatile fatty acids, a correlation which was generally linear over a range of 0 to COD of 60,000 mg/ L. September 2000 3 17 Draft Figure 3 5. Relationship between VFA and COD in Landfill Leachate ( from Ehrig, 1984)

Information from Pohland ( 1986) support this correlation to an extent. Specifically, COD concentration, TOC concentration, and volatile fatty acid concentrations all increase during the acid formation phase of the landfill. During the methane fermentation phase, the volatile fatty acid concentration decreases because of its bioconversion to methane; COD and TOC similarly decrease. These matching trends are due to the overlap of volatile acids as analytically measured by each of these three parameters. However, later in the life of a landfill volatile fatty acids are essentially absent. This decline in COD is confirmed using time series data from Wisconsin ( Figure 3 6) however these data do not proceed long enough ( i. e., beyond 20 years) to evaluated hypotheses regarding the later stages of landfill life. COD and TOC measurements, while low, are non zero due to the presence of higher molecular weight residual organics. Together, the Ehrig ( 1983) and Pohland ( 1986) data imply that high values of COD are the result of high values of volatile fatty acids, but lower values of COD may reflect negligible concentrations of volatile fatty acids. September 2000 3 18 Draft Figure 3 6. COD Observed in Wisconsin MSW Landfills by Age 0.01 0.1 1 10 100 1000 10000 100000 1000000 0 5 10 15 20 Year COD ( mg/ L) R squared = 0.01 Significant at 1%

Characterization of volatile fatty acids has been conducted by several researchers and summarized by Frampton ( 1998). During the acid generation phase, volatile fatty acids can comprise up to 87 percent of total organic carbon in MSW landfill leachate. Following this period, other sources of organic carbon dominate including fulvic acid, humic acid, and high molecular weight (> 10,000) organic compounds.

The significance of volatile fatty acids towards contaminant leaching has been the focus of leaching test development, including which acids should be incorporated into the test fluid and their effects on leaching. Volatile fatty acids such as acetic acid can form stable ( and soluble) complexes with metal cations ( Frampton, 1998). In contrast, when analyzing for metals in a mixture of low molecular weight ( volatile fatty acids) and higher molecular weight (> 500) organic molecules following ultrafiltration, the metals magnesium, calcium, and zinc were associated with the low molecular weight organic fraction ( Chian, 1977). This shows that volatile fatty acids may be more significant than higher molecular weight species in mobilizing metals.

Alkalinity Alkalinity reflects the acid neutralizing capacity of an aqueous solution, measured as the equivalent sum of the bases that are titratable with strong acid to an equivalence point. It represents the sum of all such bases, such as hydroxides ( OH), carbonate ( CO3 2), bicarbonate ( HCO3 ), and other anions that may be present to react with excess protons ( H+) ( Stumm, 1981). Therefore, alkalinity is used as an indication of the buffering capacity and the ability of a solution to maintain a pH, rather than to identify the exact anionic species in a solution.

The general behavior of alkalinity in a landfill over time is expressed by Pohland ( 1983). The highest levels of alkalinity are found in the acid formation phase of the landfill, Phase III. This is due to the formation of volatile acid which results in dissolution of bicarbonate. As volatile acids September 2000 3 19 Draft are removed due to their conversion to methane and carbon dioxide, residual alkalinity determines the resulting pH of the system. If alkalinity is relatively high the pH of the system becomes controlled by the anions contributing to alkalinity; low alkalinity makes the system more susceptible to changes affecting pH.

Ehrig ( 1983) also presents information regarding alkalinity. The ratio of volatile fatty acid concentration to alkalinity is presented, and observed that gas production is initiated when the ratio drops below 0.8 ( i. e., the landfill enters Phase IV), which occurred in the sixth year of landfill activity. Unfortunately, this paper does not present the actual values of alkalinity as well. As shown above, volatile fatty acid concentration drops in Phase IV, but based on data by Farquhar ( 1989) and the above discussion by Pohland ( 1983) alkalinity decreases over time as well. High pH values ( i. e., greater than 7) were also correlated with low ratios of volatile fatty acids to alkalinity, showing that high levels of volatile fatty acids are associated with low pH.

Farquhar ( 1989) presents information regarding alkalinity as a function of time ( years of landfill operation). Values are highest ( 10,000 to 15,000 mg/ L) in the period 0 to 5 years. Values steadily decrease over the ranges 5 to 10 years, 10 to 20 years, and greater than 20 years where the value is less than 500 mg/ L. Data reflecting the first 10 years of MSW landfill operations from Wisconsin do not indicate any significant decline in alkalinity but his pattern may be more visible in later stages of landfill development.

This decrease in alkalinity over time may be the result of simple mass balance effects: additional alkalinity is no longer generated by bioactivity, and it is removed continuously in leachate. Therefore its concentration in leachate decreases.

Summary of Significant Findings for Indicator Parameters in MSW Landfill Leachate Many researchers have found temporal differences for certain parameters present in MSW landfill leachate. These findings are summarized in Table 3 2 and reflect the body of literature discussed above. Some of these parameters may or may not have a direct affect on contaminant leaching. For example, high COD by itself may not significantly affect mobility. However, high COD levels are indicative of the acid generation phase of an MSW landfill where many different effects are happening simultaneously. One or a combination of these other parameters, however, may be indicative of contaminant mobility. September 2000 3 20 Draft Table 3 2. Behavior of Indicator Parameters in MSW Landfill Leachate: Summary Parameter Result pH Initially low ( 5 to 6) due to the presence of organic acids forming during biodegradation. As these acids are removed by additional bioprocesses and converted to gas, pH rises slightly ( to 8) to reflect new equilibrium conditions by residual alkalinity.

Redox potential Lowest during the acid generation phase; values of  200 mV are encountered ( reflective of reducing conditions). These levels rise slightly during gas production and remain above zero for the remainder of landfill life.

Sulfate concentration may be a surrogate indicator of redox potential if redox potential is not measured. Sulfate concentrations decrease over time from up to 2,000 to < 100 mg/ L; they convert to sulfides under the reducing conditions of the acid generation phase. Alternatively, the measurements can be used in conjunction to assess bioactivity.

BOD and COD Indicative of bioactivity. These parameters typically display a peaking behavior ( initially low, rising, then low. High levels of each parameter indicate acid production; during gas production the levels fall. Additionally, the ratio of BOD to COD is indicative. High ratios indicate organic acid production, where most of the organic matter is biologically active. This ratio also exhibits peaking behavior.

Volatile Fatty Acids and COD Volatile fatty acids have been shown to be a significant source of COD in MSW landfill leachate. Their presence demonstrates biological activity ( acid formation) in MSW landfills. Other sources contribute to COD such as nonbiodegradable organic material.

Alkalinity Highest during acid formation phase; bioactivity creates species contributing to acid content ( e. g., formation of organic acids) and alkalinity ( e. g., formation of bisulfide ion); alkalinity is also increased by acids solubilizing carbonate ion ( which contributes to alkalinity). Alkalinity drops over time, perhaps due to the elimination of acid generation and subsequent ` washing out' of the ions. September 2000 3 21 Draft 3.3 Construction and Demolition Debris Landfills Construction and demolition debris ( C& D) landfills are less studied in the literature than municipal waste landfills. Based on the available literature, however, the cycle of a MSW landfill ( e. g., acid formation, methane fermentation) may occur with less intensity or not at all in a C& D landfill. Section 3.3.1 provides a general overview of the composition of C& D landfill leachate based on the data available in the LEACH 2000 database. Section 3.3.2 discusses the information available on temporal changes in C& D landfill environments.

3.3.1 Overall Composition of C& D Landfill Leachate C& D landfills, in general, receive materials associated with land clearing ( soil, rock, trees), exterior structure demolition ( concrete and asphalt rubble, roofing, brick), interior structure demolition ( painted wallboard, framing, piping), and similar materials ( Townsend, 1998). Two specific examples of C& D landfill operations may be found in Section 4 of this report ( case studies 8 and 13). Section 4 also includes an example of a landfill receiving a mixture of MSW and C& D wastes ( case study 17).

The data presented in Table 3 3, below are from the 22 C& D landfills represented in the LEACH 2000 database. As discussed in Section 3.1 above, these landfills do not necessarily constitute a statistically representative sample of C& D landfills by geographic region or any other criterion. As with the MSW landfill leachate data presented in Table 3 1, the constituents included in Table 3 3 represent the parameters most frequently analyzed for in the characterization data included in the database. Constituents are organized into three categories: major physical/ chemical parameters, trace inorganics, and organics. The paragraphs below discuss the data for C& D landfill leachate in each of these categories.

General Parameters For C& D landfills, data are available for most of the parameters commonly analyzed in wastewaters. Unfortunatly, data are unavailable for some parameters critical to leaching analyses, particularly oxidation reduction potential. Of the analytes for which data are available, alkalinity, chloride, chemical oxygen demand, iron, nitrogen, and sodium are the most highly variable. Magnesium is rarely detected in C& D landfill leachate.

Trace Inorganics A number of inorganics are found in C& D landfill leachate. Inorganics detected in 50 percent or more of samples are, in order of detection frequency: barium, boron, manganese, aluminum, zinc, copper, lead, chromium, arsenic, cadmium, and mercury.

Organics Organic species are less frequently analyzed in C& D landfill leachate than other constituents. When organics are sampled, they are less frequently detected than other parameters such as metals. Only phenol, xylene, and acetone were detected in more than 50 percent of the C& D landfill leachate samples. The available acetone data, furthermore, consist only of nine samples. September 2000 3 22 Draft Table 3 3. Composition of C& D Landfill Leachate Analyte N % Detected 5th % ile 10th % ile Median Mean 90th % ile 95th % ile MAJOR PHYSICAL/ CHEMICAL PARAMETERS ( mg/ L, except pH in Standard Units) Alkalinity 94 98.9 54.5 110 1,450 2,202 4,540 5,300 B. O. D. 45 91.1 5.7 9 40 110 170 320 Calcium 35 97.1 44 96.4 205 237 480 578 Chloride 107 100.0 8 13 400 603 1,400 1,630 C. O. D. 90 97.8 24 32 438 1,661 3,730 11,200 Cyanide 30 50.0 0.01 0.011 0.022 0.0665 0.3 0.34 Fluoride 14 92.9 0.05 0.05 0.22 0.63 0.52 5 Iron 54 66.7 4.92 8.6 33.5 89.5 320 680 Magnesium 46 4.4 0.0003 0.0003 0.00465 0.00465 0.009 0.009 Nitrogen 15 100.0 1.59 28.8 156 160 380 400 pH 90 100.0 6.20 6.33 6.90 6.90 7.35 7.70 Sodium 69 100.0 17 20 191 356 953 1,430 Sulfate 65 96.9 21 26 99 289 770 1,000 T. O. C. 30 96.7 6.1 15 180 296.68621 620 1080 TRACE INORGANICS ( µ g/ L) Aluminum 18 83.3 100 130 200 676 590 6,350 Arsenic 48 54.2 5 8 32.5 34.9 75 77.3 Barium 27 100.0 100 100 300 638 1,000 1,500 Beryllium 7 14.3 20 20 20 20 20 20 Boron 2 100.0 1,400 1,400 2,650 2,650 3,900 3,900 Cadmium 68 50.0 0.2 2 10 73.1 30 54 Chromium 51 56.9 5 5 18 35.8 100 120 Copper 55 72.7 5.2 7.15 35 75.9 170 465 Lead 68 60.3 2.9 4 40 122 220 360 Manganese 64 100.0 80 620 3450 9,416 17,000 22,000 Mercury 24 50.0 10 20 50 63.8 100 170 Selenium 42 14.3 2 2 3 3.3 5 5 Silver 41 17.1 9 9 10 14.9 30 30 Zinc 41 80.5 10 23 91 575 1,420 2,600 ORGANICS ( µ g/ L) 1,1 Dichloroethane 23 26.1 0.048 0.048 5.9 7.47 17 17 1,1 Dichloroethene 19 5.3 3,000 3,000 3,000 3,000 3,000 3,000 Acenaphthene 16 18.8 2 2 3 3 4 4 Acetone 9 66.7 31 31 155 992 5,100 5,100 Benzene 23 30.4 0.8 0.8 2.7 3.71 7 7 Chloroethane 23 21.7 5 5 18 82.1 353 353 Ethylbenzene 23 47.8 0.8 1.9 18 26.3 61 79 Methyl Isobutyl Ketone 11 27.3 8.9 8.9 59 106 250 250 Naphthalene 19 21.0 1.4 1.4 5.9 19.0 63 63 Phenol 25 56.0 2.6 11 36.5 323 700 2,990 Trichloroethylene 27 25.9 2 2 6 848 3,000 3,000 Vinyl Chloride 5 40.0 3 3 12.5 12.5 22 22 Xylene 24 58.3 2.3 5.6 69.5 95.2 210 270 Source: Characterization data from the 22 C& D landfills included in the LEACH 2000 database.

3.3.2 Temporal Variability and Indicator Parameters in C& D Landfills As presented above, the stages of activity in a MSW landfill are well researched. These stages include a leachate generation phase, an acid generation phase, a gas fermentation phase, and a steady state maturation phase. Corresponding time stages of C& D landfills have not been September 2000 3 23 Draft postulated. However, several researchers provide time series data for C& D wastes which allow for the opportunity to draw parallels between these different landfills. For MSW landfills, the following factors are indicative of the onset of biological activity:

° Increase in COD and BOD ° Increase in alkalinity ° Drop in sulfate and rise in redox potential ° Drop in pH and increase in volatile acids Such indications of biological activity have been monitored by Townsend ( 1998). Findings indicate that some of these effects are evident in C& D waste leachate. Not all of the above indications were present, which may be indicative that different types or degrees of biological activity was taking place. Findings for each parameter are discussed below.

pH Research has found that the individual components comprising C& D wastes affect pH in different ways. Significant findings include the following:

° The pH from a lysimeter consisting exclusively of concrete was a constant 11 to 12 over time. In contrast, the pH from lysimeters containing only wood, cardboard, or wallboard were relatively constant 4 to 6 over time. This compares to a time dependence of pH in a lysimeter with a more typical mix of C& D waste, where pH was initially 10 11 then dropping to 7 ( Townsend, 1998).

° This influence of materials on pH is consistent with previous lysimeter tests in 1980 by other researchers and reported in Townsend ( 1998); in this 1980 test the pH of a lysimeter containing high masonry C& D mix was 7.45 while the pH of a lysimeter containing high wood mix was 6.9.