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Table 5-1: 90th Percentile Fly Ash Concentration with Different Non-Detect Treatments (mg/kg)....... 5-7 vi List of Figures Figure 1: Diagram of generic coal combustion processes.
Figure 2-1: Comparison of cumulative leaching of antimony from concrete.
Figure 2-2: Comparison of cumulative leaching of arsenic from concrete.
Figure 2-3: Comparison of cumulative leaching of boron from concrete.
Figure 2-4: Comparison of cumulative leaching of cadmium from concrete.
Figure 2-5: Comparison of cumulative leaching of chromium from concrete.
Figure 2-6: Comparison of cumulative leaching of lead from concrete.
Figure 2-7: Comparison of cumulative leaching of molybdenum from concrete.
Figure 2-8: Comparison of cumulative leaching of selenium from concrete.
Figure 2-9: Comparison of cumulative leaching of thallium from concrete.
Figure 3-1: Human conceptual exposure model for fly ash concrete.
Figure 3-2: Ecological conceptual exposure model for fly ash concrete.
Figure 3-3: Human conceptual exposure model for FGD gypsum wallboard.
vii Abbreviations and Acronyms AASHTO American Association of State Highway and Transportation Officials ACAA American Coal Ash Association ACH Air Changes per Hour AEA Air Entrainment Admixture ANSI American National Standards Institute ASHRAE American Society of Heating, Refrigerating and Air Conditioning Engineers ASTM American Society for Testing and Materials ATSDR Agency for Toxic Substances and Disease Registry AWQC Ambient Water Quality Criteria BCF Bioconcentration Factor CalEPA California Environmental Protection Agency CASRN Chemical
Service Registry Number CCR Coal Combustion Residual COPC Constituent of Potential Concern CPSC Consumer Product Safety Commission CV-AFS Cold Vapor Atomic Fluorescence Spectrometry DOE United States Department of Energy DOT United States Department of Transportation EC European Commission Eco-SSL Ecological Soil Screening Levels EERC University of North Dakota Energy and Environmental Research Center EPA United States Environmental Protection Agency EPRI Electric Power Research Institute FBC Fluidized Bed Combustion FGD Flue Gas Desulfurization FHWA Federal Highway Administration HBN Health-Based Number HEI Highly Exposed Individual HELP Hydrologic Evaluation of Landfill Performance HPS Health Physics Society HQ Hazard Quotient IAEA International Atomic Energy Agency IBC International Building Code ICC International Code Council ICP Inductively Coupled Plasma ICRP International Commission on Radiological Protection IRIS Integrated Risk Information System IWEM Industrial Waste Evaluation Model LEAF Leaching Evaluation Assessment Framework LOI Loss of Ignition viii MCL Maximum Contaminant Level MDL Method Detection Limit ML Minimum Level of Quantitation NJDEP New Jersey Department of Environmental Protection NCRP National Council on Radiological Protection NOAA National Oceanic and Atmospheric Administration NOAEL No Observable Affects Evaluation Level NPDWR National Primary Drinking Water Regulation NRC Nuclear Regulatory Commission OSWER Office of Solid Waste and Emergency Response PCA Portland Cement Association PFA Pulverized Fuel Ash PPRTV Provisional Peer Reviewed Toxicity Values for Superfund PSI Pounds per Square Inch RAGS Risk Assessment Guidance for Superfund RfC Reference Concentration SMM Sustainable Materials Management SPLP Synthetic Precipitation Leaching Procedure T3 Third Trophic Level T4 Fourth Trophic Level TCLP Toxicity Characteristic Leaching Procedure TEL Threshold Effect Level TENORM Technologically-Enhanced, Naturally Occurring Radioactive Materials TL Trophic Level UNSCEAR United Nations Scientific Committee on the Effects of Atomic Radiation U.S. United States UKHPA United Kingdom Health Protection Agency UKNRPB United Kingdom National Radiation Protection Board USGS United States Geological Survey ix Introduction Coal combustion residuals (CCRs) are the byproducts of coal combustion that are captured from plant effluent and flue gases prior to discharge to the environment. Once generated, CCRs may be either disposed of or beneficially used. Beneficial use, as defined in this document, is the reuse of CCRs in a product that: 1) provides a functional benefit; 2) meets relevant product specifications and performance standards for the proposed use; and 3) may replace virgin raw materials in a product on the market (referred to as an “analogous product” or “analogous non-CCR product”), thus conserving natural resources that would otherwise need to be obtained through other practices, such as extraction. The reason CCRs can be used to replace virgin materials is that they possess physical and chemical properties similar to those of the virgin materials.
The United States Environmental Protection Agency (“EPA” or “the Agency”) Sustainable Materials Management (SMM) Program supports the productive and sustainable use/reuse of resources throughout all stages of their life cycles, from resource acquisition through disposal. The SMM Program seeks to avoid or minimize impacts to the environment while accounting for economic efficiency and social considerations. The beneficial use of CCRs, when done in a manner protective of human health and the environment, can advance these goals. The purpose of this beneficial use evaluation is to determine whether environmental releases of constituents of potential concern (COPCs) from these encapsulated 1 CCR products are comparable to or lower than those from analogous products made without CCRs, or are at or below relevant regulatory and health-based benchmarks for human and ecological receptors, during use by the consumer. This document details the evaluation process as well as the findings and conclusions of this beneficial use evaluation.
Selection of Beneficial Uses for Evaluation CCR is a broad term used to refer to the byproducts generated either directly by coal combustion or as a result of applying certain pollution control devices to emissions from coal-fired combustion units.
Types of CCRs generated from coal combustion include fly ash, bottom ash, boiler slag, flue gas desulfurization (FGD) waste, and fluidized bed combustion (FBC) waste. All coal-fired electric utility plants in the United States generate at least one of these types of CCRs. Each different type of CCR has unique properties and, as a result, different potential uses. This evaluation chose to examine those encapsulated beneficial uses that divert the greatest quantity of CCRs from disposal and have been most extensively studied in the literature. The following text provides the rationale for the selection of the CCR products evaluated.
In the June 2010 Proposed Rule, Hazardous and Solid Waste Management System; Identification and Listing of Special Wastes; Disposal of Coal Combustion Residuals from Electric Utilities (“the 2010 Proposed CCR Disposal Rule”) (75 FR 35127), the Agency defined encapsulated beneficial use as one that binds the CCRs into a solid matrix that minimizes their mobilization into the surrounding environment. Examples of encapsulated uses are concrete, wallboard, and brick. In contrast, unencapsulated beneficial uses include road embankments, structural fills, or agricultural applications (e.g., substitute for lime).
The American Coal Ash Association (ACAA) conducts a voluntary, annual survey of the coal-fired electric utility industry to track the quantities of CCRs generated and beneficially used. According to the latest survey, the electric utility industry generated nearly 110 million tons of CCRs during the 2012 calendar year. Approximately 39 million tons of these CCRs were identified by ACAA as beneficially used in either encapsulated or unencapsulated products. An additional 12.8 million tons were placed in mine-fill operations, while the remaining 57.8 million tons were disposed of in landfills and surface impoundments (ACAA, 2013). 2 Based on the beneficial use rates reported by ACAA, the evaluation chose fly ash used as a direct substitute for portland cement during the production of concrete (referred to as “fly ash concrete”) and FGD gypsum used as a replacement for mined gypsum in wallboard (referred to as “FGD gypsum wallboard”) during use by the consumer. Specifically, the 2012 ACAA survey indicates that the largest encapsulated beneficial uses of CCRs, by more than a factor of two, are fly ash used in “concrete/concrete products/grout” (11.8 million tons) and FGD gypsum used in “gypsum panel products” (7.6 million tons). That is, these two beneficial uses make-up nearly 50 percent of the total amount of CCRs beneficially used on an annual basis. While fly ash and FGD gypsum may not be the only CCR or industrial material that may be beneficially used in concrete or wallboard, this evaluation does not address the beneficial use of other industrial materials. This evaluation also draws no conclusions about other beneficial uses of fly ash and FGD gypsum.
Properties of Fly Ash and FGD Gypsum The following subsection describes the production process and properties of fly ash and FGD gypsum as well as the associated beneficial uses evaluated in this document. Figure 1 illustrates a generalized layout of a coal-fired plant and the collection points for fly ash and FGD gypsum.
Fly Ash Fly ash is the fraction of combusted coal that becomes suspended in plant flue gases. The fly ash available for beneficial use is captured primarily by mechanical particulate collection devices, such as an electrostatic precipitator or baghouse. The remaining fly ash that passes through these particulate collection devices either escapes into the atmosphere or is captured through sulfur dioxide [SO2] control devices (i.e., scrubbers), resulting in its incorporation into the FGD solids. The chemical composition of the beneficially used fly ash is variable and dependent on multiple factors, such as the geographic source of the coal burned.
In 2012, the survey response rate was equivalent to 59 percent of the total US coal-fired electric generation capacity. This estimated response rate is based on a ratio of the generating capacity of the individual plants reporting and the total United States coal-fired generation capacity reported by the Energy Information Administration (EIA) in 2012. These data are available online at: http://www.eia.gov/coal/data.cfm. Reported beneficial use rates were extrapolated for the entire industry sector using the 2012 survey data, historical ACAA survey data, EIA data, and other miscellaneous data sources.
The survey groups similar beneficial uses into generalized categories. As a result, a given ACAA category may include some data on beneficial uses beyond those evaluated in this document.
Figure 1: Diagram of generic coal combustion processes.
Fly ash may be used as a partial substitute for the portland cement in concrete because it is a pozzolan, a material that reacts with calcium oxide [CaO], also known as lime, in the presence of water to produce a cementitious compound. Silica dioxide [SiO2], aluminum trioxide [Al2O3], and iron oxide [Fe2O3] are the primary chemical constituents that may contribute to this reaction. In addition, fly ash may contain significant amounts of lime, causing it to be self-cementing in the presence of water. The American Society for Testing and Materials (ASTM) classifies fly ashes based on the amount of lime present as either Class F (low lime/high iron) or Class C (high lime/high calcium) (ASTM C618).
Depending on the composition of the fly ash and the intended use of the fly ash concrete, a wide range of cement substitution rates may be considered. Class F fly ash is often used to replace portland cement at rates between 15 percent and 25 percent by mass, while Class C fly ash is often used to replace portland cement at rates between 15 percent and 40 percent by mass (PCA, 2003). However, specific replacement rates vary based both on the characteristics of the specific fly ash and on the desired characteristics of the concrete. ASTM specifies a maximum cement replacement rate of 40 percent for blended fly ash-cement mixtures based on engineering specifications (ASTM C595). Therefore, the findings of this evaluation are limited to portland cement replacement rates at or below 40 percent by mass.
Flue Gas Desulfurization Gypsum Coal-fired plants employ a number of different air pollution control devices (generally referred to as “flue gas desulfurization units” or “scrubbers”) to reduce sulfur dioxide emissions. These devices differ in how they remove sulfur dioxide, but all generate FGD waste. This waste ranges from a dry powder to a wet sludge. FGD gypsum is a subset of the wet sludges produced by FGD units. During the generation of FGD gypsum, fly ash is initially removed from flue gas to the extent practicable using mechanical collection devices. Next, the flue gas is sprayed with a wet limestone-based reagent. This reagent reacts with the sulfur dioxide in the flue gas, limiting the amount of the sulfur dioxide and remaining fly ash that can escape into the atmosphere. The chemical composition of the resulting sludge is dependent on the amount of oxygen available during the reaction. In the absence of oxygen, the reaction produces calcium sulfite hemihydrate [CaSO3•½H2O]. In the presence of oxygen, the reaction produces calcium sulfate dihydrate [CaSO4•2H2O], also known as gypsum. To convert as much of the sludge to gypsum as possible, the sludge may undergo forced oxidation, driven by air pumped into the chamber during the reaction.
FGD gypsum may be used as a full substitute for mined gypsum in wallboard (i.e., drywall) because the primary chemical constituent, calcium sulfate dihydrate, is identical in both materials. The generation of FGD gypsum may allow greater control over the chemical composition of the final gypsum product and, as a result, FGD gypsum may have higher gypsum purity than mined gypsum.
However, FGD gypsum may contain some impurities that are not found in mined gypsum. Fly ash is one such impurity, and can result in accelerated wear to the production machinery and physical defects in the final products. As a result, common market specifications established by North American wallboard manufactures limit the amount of fly ash allowed in the FGD gypsum used in wallboard to one percent by mass (Henkels and Gaynor, 1996).