ASTM E2278-13(2019)

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.

4.2.2.1 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 H_{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.

4.3.1.1 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:

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.

4.3.2.1 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.

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.

4.3.3.1 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 (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.