4.1 General—CCPs can effectively be used to reclaim surface mines (5-10). First, CCPs are ideally suited for use in numerous reclamation applications. Any type of CCP may be evaluated for use in mine reclamation. Project specific testing is necessary to ensure that the CCPs selected for use on a given project will meet the project objectives. Second, the use of CCPs can save money because they are available in bulk quantities and reduce expenditures for the manufacture and purchase of Portland cement or quicklime. Third, large-scale use of CCPs for mine reclamation conserves valuable landfill space by recycling a valuable product to abate acid mine drainage and reduce the potential for mine subsidence, provided that the CCP is environmentally and technically suitable for the desired use. The availability of CCPs makes it possible to reclaim abandoned mineland that could not otherwise be reclaimed. The potential for leaching constituents contained in CCPs should be evaluated to ensure that there is no adverse environmental impact.

4.2 Physical and Chemical Properties and Behavior of CCPs—Fly ash, bottom ash, boiler slag, FGD material and FBC ash, or combinations thereof, can be used for mine reclamation. Each of these materials typically exhibits general physical and chemical properties that must be considered in the design of a mine reclamation project using CCPs. The specific properties of these materials vary from source to source so environmental and engineering performance testing is recommended for the material(s) or combinations to be used in mine reclamation projects.

4.2.1 Physical Properties: 

4.2.1.1 Unit Weight—Unit weight is the weight per unit volume of material. Fly ash has a low dry unit weight, typically about 50 to 100 pcf (8 to 16 kN/m³). Bottom ash is also typically lighter than coarse grained soils of similar gradation. Stabilized FGD material from a wet scrubber and FGD material from a dry scrubber are also relatively lightweight, with unit weights similar to fly ash.

4.2.1.2 Strength—Shear strength is the maximum resistance of a material to shearing stresses. The relatively high shear strength of fly ash is beneficial for CCP flowable fill formulations requiring strengths sufficient to prevent mine subsidence. The shear strength of non-self-hardening fly ash is primarily the result of internal friction. Cementitious CCPs experience a cementing action that is measured as cohesion and increases over time, which results in high compressive strength. Unconfined compressive strengths in excess of 1000 psi can be achieved for cementitious CCPs.

4.2.1.3 Specific Gravity—Specific gravity is the ratio of the weight in air of a given volume of solids at a stated temperature to the weight in air of an equal volume of distilled water at a stated temperature. The particle specific gravity of fly ash is relatively low compared to that of natural materials, and generally ranges from 2.1 to 2.6.

4.2.1.4 Grain-Size Distribution—Grain-size distribution describes the proportion of various particle sizes present in a material. Fly ash is a uniformly-graded product with spherical, very fine grained particles.

4.2.1.5 Moisture Content—Moisture content is the ratio of the mass of water contained in the pore spaces of soil or rock material to the solid mass of particles in that material, expressed as a percentage. CCPs have almost no moisture when first collected after the combustion of coal. Power plant operators sometimes add moisture to facilitate transport and handling, a process termed “conditioning.”

4.2.1.6 Coefficient of Permeability—Permeability is the capacity of a material to transmit a liquid. When compacted to its maximum dry density, fly ash can have permeabilities ranging from 10 to 10^-3 gpd/ft² (10^-4 to 10^-7 cm/s). These permeabilities are comparable to natural silty soils.

4.2.2 Chemical Properties: 

4.2.2.1 Elemental Composition—The major elemental components of CCPs are silica, aluminum, iron, calcium, magnesium, sodium, potassium, and sulfur. These elements are present in various amounts and combinations dependent primarily on the coal and type of CCP. The elements combine to form amorphous (glassy) or crystalline phases. Trace constituents may include elements such as arsenic, boron, cadmium, chromium, copper, chlorine, mercury, manganese, molybdenum, selenium, or zinc.

4.2.2.2 Phase Associations—The primary elemental constituents of CCPs are present either as amorphous (glassy) phases or crystalline phases. Coal combustion fly ash is typically 70+ % amorphous material. FGD and FBC products are primarily crystalline, and the crystalline phases typically include lime (CaO), portlandite (Ca(OH)₂), hannebachite (CaSO₃ · ¹/₂ H₂O), and forms of calcium sulfate.

4.2.2.3 Free Lime Content—Free lime content varies among CCP sources and other potential activators (for example, lime kiln dust, cement kiln dust, quicklime, or Portland cement). Variability of free lime content in CCP sources is due to the type and efficiency of the emissions control technology that is used. FBC products typically contain up to 10 % free lime, while most Class F fly ash has no free lime content. The free lime content of other potential activators is also variable. For example, cement kiln dust typically ranges from 20 to 30 % free lime whereas quicklime contains 100 % free lime.

4.2.2.4 Pozzolanic Activity—Most CCPs, with the exception of FGD material, are characterized as pozzolans due to the presence of siliceous or siliceous and aluminous materials that in themselves possess little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.

4.2.2.5 Buffer Capacity—The buffer capacity of the CCP is important in maintaining the high pH that generally is a requirement for neutralizing acidic materials such as acid mine drainage or for minimizing acid formation from acid forming materials. The CCP must have enough buffer capacity to maintain the pH of the treated areas so the area remains stable over time and under environmental stresses. Test Methods C400 can be applied to evaluate the buffer capacity of the CCP. Determine the basicity factor for the CCP as noted in Test Method B of Test Methods C400.

4.3 Environmental Considerations: 

4.3.1 Regulatory Framework: 

4.3.1.1 Federal—The U.S. Department of the Interior Office of Surface Mining (OSM) is charged with the responsibility of ensuring that the national requirements for protecting the environment during coal mining are met and making sure the land is reclaimed after it is mined. When the use of CCPs happens at surface coal mines, state or federal coal-mining regulators are involved to the extent that SMCRA (Surface Mining Control and Reclamation Act) requires the mine operator to ensure that:

(1) All toxic materials are treated, buried, and compacted, or otherwise disposed of, in a manner designed to prevent contamination of ground or surface water (30 CFR 816/817.41).

(2) The proposed land use does not present any actual or probable threat of water pollution (30 CFR 816/817.133).

(3) The permit application contains a detailed description of the measures to be taken during mining and reclamation to ensure the protection of the quality and quantity of surface and ground water systems, both on- and off-site, from adverse effects of the mining and reclamation process (30 CFR 780.21 and Sections 401.402, or 404 of the Clean Water Act).

(4) The rights of present users of such water are protected (30 CFR 816/817.41).

(5) Any disposal of CCPs at mine sites must be in accordance with those standards and with applicable solid waste disposal requirements (30 CFR 816/817.89).

SMCRA gives primary responsibility for regulating surface coal mine reclamation to the states, and 24 coal-producing states have chosen to exercise that responsibility. On federal lands and Indian reservations (Navajo, Hopi, and Crow) and in the coal states that have not set up their own regulatory programs (Tennessee and Washington), OSM issues the coal mine permits, conducts the inspections, and handles the enforcement responsibilities. As a result of the activities associated with the SMCRA, coal mine operators now reclaim as they mine, and mined lands are no longer abandoned without proper reclamation. OSM also collects and distributes funds from a tax on coal production to reclaim mined lands that were abandoned without being reclaimed before 1977. OSM has a Coal Combustion Residues Management Program that focuses on providing expert technical information on the use of CCPs in mine reclamation for the mining industry, regulatory agencies, and other stakeholders. Use of CCPS in reclamation procedures should be proposed in the mining permit application if possible, detailing the type and characteristics of the proposed CCP and the specific beneficial use for the location proposed. In 1999, U.S. Environmental Protection Agency (EPA) completed a two-phased study of CCPs for the U.S. Congress as required by the Bevill Amendment to RCRA. At the conclusion of the first phase in 1993, EPA issued a formal regulatory determination that the characteristics and management of the four large-volume fossil fuel combustion waste streams (that is, fly ash, bottom ash, boiler slag, and flue gas emission control waste) do not warrant hazardous waste regulation under RCRA and that utilization practices for CCPs appear to be safe. In addition, EPA “encourage[d] the utilization of coal combustion by-products and support[ed] state efforts to promote utilization in an environmentally beneficial manner.” In the second phase of the study, EPA focused on the by-products generated from FBC boiler units and the use of CCPs from FBC and conventional boiler units for mine reclamation, among other things. Following completion of the study, EPA issued a regulatory determination that again concluded that hazardous waste regulation of these combustion residues was not warranted. However, EPA also decided to develop national solid waste regulatory standards for CCPs, including standards for placement of CCPs in surface or underground mines, either under RCRA, SMCRA, or a combination of the two programs (65 CFR 32214, May 22, 2000).

4.3.1.2 State and Local—There is considerable variation in state-mandated permitting and other regulatory requirements for CCP utilization. Some states have specific beneficial use policies, while other states have no regulations or guidance addressing beneficial use. Although the NEPA (National Environmental Policy Act) strictly applies only to federally funded projects, many states have similar mechanisms for assessing the environmental impacts of non-Federal projects. These mechanisms may require state permits that address any or all of the following issues: wetlands/waterways, National Pollutant Discharge Elimination System (NPDES) discharge, underground injection, erosion and sediment control, air quality considerations, and storm water management.

4.3.2 Water Quality—When planning to use CCPs for mine reclamation, one should consider the potential impacts on ground water and surface water to ensure protection of human health and the environment.

4.3.2.1 Ground Water—The design and implementation of a mine reclamation project should consider the potential ground water impacts of CCPs to ensure the protection of human health and the environment. Considerable research has been conducted to assess and predict the potential impacts of CCP utilization on ground water quality. An assessment of ground water quality impacts should be performed by a qualified professional and should take into account project-specific considerations such as composition of CCPs, the typical leachability of CCPs, presence of acid forming materials or acid mine drainage, placement of CCPs relative to the ground water table, rates of infiltration, the type of placement used for the CCP, and constituent migration, attenuation in ground water, and location of sensitive receptors (that is, wells). Where protection of ground water is a special concern, the leaching characteristics of the CCP should be evaluated as part of the assessment of constituent migration and attenuation. Consideration should be given to the leachability of the CCP in the presence of AMD.

Note 1: It is highly recommended that up-gradient and down-gradient wells be installed to determine background groundwater conditions prior to CCP placement. Then, following placement of CCPs, periodic monitoring of these wells should be done to determine any potential groundwater impact.]

4.3.2.2 Surface Water—CCPs may affect surface water bodies during and after placement activities as a result of erosion and sediment transport. The engineering and construction practices recommended to minimize these effects on surface waters (in accordance with the requirements of the 30 CFR 816.43 through 816–49 and any applicable federal or state permit) include storing the CCPs in stockpiles employing effective storm water management controls to maximize runoff and minimize run-on. Impacts could also be minimized by limiting size of active working face of area being reclaimed.

4.3.3 Air Quality—When planning to use CCPs for mine reclamation, one should consider the potential impacts to air quality including dusting and emissions.

4.3.3.1 Dust Control—Dusting must be controlled during the transport and handling of CCPs in order to avoid fugitive dust and to ensure worker safety. Dust control measures routinely used on earthwork projects are effective in minimizing airborne particulates at CCP storage sites. Typical controls include appropriate hauling methods, use of windbreaks, moisture conditioning of the CCPs, storage in bins or silos, covering the CCPs with large tarpaulins, wetting or covering exposed CCP surfaces, and paving or wetting unpaved high-traffic haul roads with coarse materials.

4.3.3.2 Radionuclides—Coal and fly ash are not significantly enriched in radioactive elements or in associated radioactivity compared to common soils or rocks (11). Certain radioactive elements including radium and uranium are known to occur naturally in CCPs (12) and other fill materials. The U.S. Department of Energy estimated the radium concentration of fly ash to be no more than 3.0 pCi/g (13). Radon emissions from the CCPs are not likely to exceed the naturally occurring ambient emissions.

4.4 Economic Benefits—The use of CCPs for mine reclamation can have economic benefits. These benefits are affected by local and regional factors, including production rates, processing and handling costs, transportation costs, availability and cost of competing materials, environmental concerns, and the experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators, and other professionals. CCPs are competing as manufactured materials and not as waste products. Since CCPs are produced in the process of manufacturing electricity, these materials can present an advantage when utilized as raw products for finished goods. This is primarily due to the low overheads involved with the material production cost and the fact that some, but not all coal-fired power plants have immediate access to low-cost transportation. The transport of coal to the power plant can provide an excellent opportunity to return CCPs to a mine site to aid in mine reclamation projects.

1.1 This guide covers the beneficial use of coal combustion products (CCPs) for abatement of acid mine drainage and revegetation for surface mine reclamation applications related to area mining, contour mining, and mountaintop removal mining. It does not apply to underground mine reclamation applications. There are many important differences in physical and chemical characteristics that exist among the various types of CCPs available for use in mine reclamation. CCPs proposed for each project must be investigated thoroughly to design CCP placement activities to meet the project objectives. This guide provides procedures for consideration of engineering, economic, and environmental factors in the development of such applications.

1.2 The utilization of CCPs under this guide is a component of a pollution prevention program; Guide E1609 describes pollution prevention activities in more detail. Utilization of CCPs in this manner conserves land, natural resources, and energy.

1.3 This guide applies to CCPs produced primarily from the combustion of coal.

1.4 The testing, engineering, and construction practices for using CCPs in mine reclamation are similar to generally accepted practices for using other materials, including cement and soils, in mine reclamation.

1.5 Regulations governing the use of CCPs vary by state. The user of this guide has the responsibility to determine and comply with applicable regulations.

1.6 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.