4.1Significance and Use—CCPs can be
effective materials for use for reclamation of surface mines.
Following are key scenarios in which CCPs may be utilized
beneficially in a mined setting:
Structural fill
Road construction
Soil modification or amendment for
revegetation (5-9)
Isolation of acid forming materials
(5)
Reduction of acid mine drainage (AMD)
(5,10-15)
Highwall mining 4.1.1 These options represent most, but
not all, scenarios under which CCPs would be returned to the mine.
This guide discusses issues related to highwall mining and
recontouring. Because of the chemical and physical characteristics
of CCPs and the benefits derived from the use of CCPs in these
applications, placement of CCPs in a surface mine setting qualifies
as a beneficial use as defined in Terminology E2201.
4.1.2 CCPs are ideally suited for use in
numerous fill applications. Structural fills and other high-volume
fills are significant opportunities for placement of CCPs in mine
situations for reclamation, recontouring, and stabilizing slopes.
These applications are the focus of this guide.
4.1.3 Any type of CCP may be evaluated
for use in mine reclamation, even fly ash with high carbon content.
Project-specific testing is necessary to ensure that the CCPs
selected for use on a given project will meet the project
objectives. The use of CCPs can be cost effective because they are
available in bulk quantities and reduce expenditures for the
manufacture and purchase of borrow material, Portland cement, or
quicklime. Large-scale use of CCPs for mine reclamation conserves
landfill space by recycling a valuable product, provided that the
CCP is environmentally and technically suitable for the desired
use.
4.2Use of
CCPs for Mine Reclamation—E2201 the Standard on 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. Guidance in evaluating the physical,
engineering, and chemical properties of CCPs is given in Sections
6 and7.
4.3Engineering Properties and
Behavior—Depending on the mine reclamation application, fly
ash, bottom ash, boiler slag, FGD material, FBC fly ash, FBC bottom
ash, or combinations thereof may have suitable and/or advantageous
properties. Each of these materials typically exhibits general
engineering properties that must be considered in engineering
applications. These general engineering properties are discussed in
the following subsections; however, it should be noted that the
specific engineering properties of these materials can vary greatly
from source to source and must be evaluated for each material, or
combination of materials, to be utilized for a structural fill.
4.3.1Unit
Weight—Many CCPs have relatively low unit weights. This is
sometimes referred to as “bulk density” in the literature. The low
unit weight of these materials can be advantageous for some
structural fill applications. The lighter-weight material will
reduce the load on weak layers or zones of soft foundation soils
such as poorly consolidated or landslide-prone soils. Additionally,
the low unit weight of these materials may reduce transportation
costs, since less tonnage of material is hauled to fill a given
volume. Lower density fills of equal internal angle of friction
will exert less lateral pressure on retaining structures.
4.3.1.1 Fly ash is typically lighter than
the fill soil it replaces, with unit weight ranging from about 50
to 100 pcf (8 to 16 kN/m3).
4.3.1.2 Bottom ash is also typically less
dense than coarse-grained soils of similar gradation, with unit
weight ranging from about 70 to 90 pcf (11 to 14
kN/m3).
4.3.1.3 Boiler slag is typically as heavy
as, if not heavier than, natural soils of similar gradation, with
unit weight ranging from about 90 to 110 pcf (14 to 18
kN/m3).
4.3.1.4 Oxidized and/or fixated FGD
materials are also relatively lightweight, with unit weights
ranging from about 50 to 100 pcf (8 to 16 kN/m3).
4.3.2Compaction Characteristics—Most CCPs can
be placed and compacted in a manner very similar to soil and
aggregate fill materials. In fact, most CCPs exhibit very little
cohesion and are not as sensitive to variations in moisture content
as are natural soils.
4.3.2.1 Fly ash, FGD material, and FBC
ash are typically placed and compacted in a manner similar to
noncohesive fine-grained soils. Smooth-drum vibratory rollers or
pneumatic tired rollers typically compact these materials most
effectively. Although not always, fly ash and FGD material
typically exhibit a measurable moisture-density relationship that
can be utilized for compaction quality control. To take full
advantage of the self-hardening properties of some fly ash, FGD
material, and FBC ash, compaction soon after the addition of water
is recommended. If hardening or cementation has occurred prior to
compaction, cementitious bonds may need to be disrupted to relocate
the grains into a more dense state 4.3.2.2 Bottom ash is generally placed
and compacted in a manner similar to noncohesive coarse-grained
soils or fine aggregate. Smooth-drum vibratory rollers typically
are most effective for the compaction of these materials. Bottom
ash may or may not exhibit consistent moisture-density
relationships. Bottom ash typically compacts best when saturated.
Bottom ash should be compacted to a specified density.
4.3.2.3 Boiler slag is generally placed
and compacted in a manner similar to noncohesive coarse-grained
soils or fine aggregate. Smooth-drum vibratory rollers typically
are most effective for the compaction of these materials. As with
bottom ash, boiler slag may or may not exhibit consistent
moisture-density relationships. Boiler slag typically compacts best
when saturated.
4.3.3Strength:
4.3.3.1Shear Strength—For non-self-hardening fly
ash and bottom ash, shear strength is derived primarily from
internal friction. Typical values for angles of internal friction
for non-self-hardening fly ash are higher than those for many
natural soils. These ashes are non-cohesive, and although the ash
may appear cohesive in a partially saturated state, this effect is
lost when the material is either completely dried or saturated.
(1) Because of its angular
shape, the shear strength of bottom ash is typically greater than
that of fly ash and is similar to the shear strength of natural
materials of similar gradation. However, friable bottom ash may
exhibit lower shear strength than natural materials of similar
gradation.
(2) The shear strength of
boiler slag may be higher than that of natural materials of similar
gradation, owing in part to the typically angular shape and
hardness of the particles.
4.3.3.2Compressive Strength—Self-hardening CCPs
and stabilized FGD material undergo a cementing process that
increases with time. Hydration of dry self-hardening CCPs commences
immediately upon exposure to water and can cement the CCP particles
in a loose state, reducing the compacted density and strength. High
compressive strengths can be achieved if the CCPs are compacted
immediately after incorporation of water. Unconfined compressive
strengths greater than 2000 psi have been reported for a
cementitious ash-water mixture after 248 days (18).
4.3.4Consolidation Characteristics—Structural
fills constructed of fly ash or FGD material typically exhibit
small amounts of time-dependent, postconstruction consolidation.
This is because excess pore water pressures dissipate relatively
rapidly, and thus most of the embankment settlement or deformation
occurs as a result of elastic deformation of the material rather
than by classical consolidation. Most deformation due to the mass
of the fill or structure thereof generally occurs during
construction.
4.3.4.1 Bottom ash and boiler slag are
free-draining materials that can be compacted into a relatively
dense, incompressible mass. For this reason, structural fills
constructed of bottom ash or boiler slag also typically exhibit
small amounts of time-dependent, postconstruction consolidation or
deformation, with the most deformation occurring during
construction.
4.3.4.2 Self-hardening fly ash and FGD
material typically exhibit minimal postconstruction consolidation
or deformation because of cementing and solidification of the
CCPs.
4.3.5Permeability—The values for permeability
of CCPs range greatly depending on the type of CCP, the degree of
compaction, and other placement variables.
4.3.5.1 The permeability values for
non-self-hardening fly ash are similar to those observed for
natural silty soils.
4.3.5.2 Self-hardening fly ash and FGD
material are relatively impermeable, with permeability values
similar to those for natural clays. Self-hardening fly ash and some
FGD material may be susceptible to cracking in the environment.
Cracking can produce a conduit for liquids through the placed
material and change the measured permeability.
4.3.5.3 Bottom ash and boiler slag are
typically as permeable as granular soils of similar gradation.
4.3.6Erosion Characteristics:
4.3.6.1Internal Erosion
(Piping)—Non-self-hardening fly ash is subject to internal
erosion because of its fine-grained, noncohesive nature. Internal
erosion can be controlled by providing adequate surface water
controls to minimize infiltration and by providing internal
drainage when warranted.
(1) Bottom ash and boiler
slag typically are well graded and capable of being compacted to a
stable mass. These attributes usually preclude any problems arising
from internal piping of material.
(2) Self-hardening fly ash
and FGD material are usually not subject to internal erosion.
4.3.6.2Surface Erosion—All CCPs may be eroded by
wind or water and require use of erosion controls similar to those
commonly used on earthwork construction projects. Wind erosion may
be controlled by use of wind breaks. Dusting may be controlled by
addition of water, or conditioning, to non-self-hardening
materials. Water erosion can be limited by controlling water at the
site by using sedimentation, sloping, and run-off controls meeting
regulatory requirements. These controls should be put in place
under the supervision of a qualified professional.
4.3.7Swelling—Some self-hardening CCPs may
swell with time. Paragraph 6.3.8 provides guidance on evaluating the
swelling potential of CCPs.
4.3.8Liquefaction and Frost Heave—Although
fine-grained and noncohesive materials such as fly ash are
susceptible to liquefaction and frost heave when saturated, these
problems are readily controlled by design practices that allow for
drainage away from the ash fill. Because of fly ash sensitivity to
moisture, it is standard practice to design fills to be well
drained. Typically, drainage blankets to provide internal drainage
and serve as a capillary barrier are included at the base of fills.
Also, locating fills in areas where they are not subject to
saturation or infiltration by surface water or ground water is
normally considered in design. Self-hardening and stabilized fly
ash and FGD material are not susceptible to liquefaction.
Non-stabilized wet FGD material is highly susceptible to frost
heave.
4.3.8.1 Well-compacted bottom ash and
boiler slag are not typically susceptible to either liquefaction or
frost heave. However, some of the finer bottom ash materials may
behave quite similarly to fly ash and would require the same
consideration for design as fly ash embankments.
4.3.9Specific 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 4.3.10Grain-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.
4.3.11Moisture 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. Most CCPs have almost no moisture when
first collected after the combustion of coal. Nonstabilized wet FGD
material has a high moisture content. Power plant operators
sometimes add moisture to facilitate transport and handling, a
process termed conditioning.
4.3.12Thixotropy—The property of some gels to
become fluids when disturbed by energy events such as vibration.
This property may be exhibited by some FGD materials.
4.4Chemical Properties:
4.4.1Elemental Composition—The major elemental
components of CCPs are silicon, aluminum, iron, calcium, magnesium,
sodium, potassium, and sulfur. These elements are present in
various amounts and combinations dependent primarily on the coal
type (bituminous, subbituminous, or lignite) and type of CCP (coal
fly ash, FBC fly ash, FGD material, and so forth). Trace
constituents may include trace elements such as arsenic, boron,
cadmium, chromium, copper, chlorine, mercury, manganese,
molybdenum, selenium, or zinc 4.4.2Phase 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
calcium-based minerals.
4.4.3Pozzolanic Activity—Most fly ash is
characterized as pozzolanic because of 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.
4.4.4Hygroscopy—Most CCPs are captured and
then handled in conditions that either create or preserve
dehydrated conditions. Some CCPs have distinctive stable states of
hydration. This stable hydration state needs to be considered in
some applications of CCPs.
4.5Environmental Considerations:
4.5.1Regulatory Framework:
4.5.1.1Federal—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
occurs 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 assure 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).
(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).
(a) 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.
(b) 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 byproducts and support[ed] State efforts to promote
utilization in an environmentally beneficial manner.” In the second
phase of the study, EPA focused on the byproducts 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).
4.5.1.2State 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.
4.5.2Water 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.
4.5.2.1Ground 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 typically limited 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. Some states may require a
groundwater protection plan be prepared outlining controls that
will limit potential impact to groundwater.
4.5.2.2Surface 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
include storing the CCPs in stockpiles employing effective storm
water management controls to maximize runoff and minimize
run-on.
4.5.3Air
Quality—When planning to use CCPs for mine reclamation, one
should consider the potential impacts to air quality including
dusting.
4.5.3.1Dust 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.
4.5.3.2Radionuclides—Coal and fly ash are not
significantly enriched in radioactive elements or in associated
radioactivity compared to common soils or rocks (21). Certain radioactive elements
including radium and uranium are known to occur naturally in CCPs
4.6Economic 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, however in the event that CCPs do not meet
beneficial use requirements or cannot be utilized, they should be
managed at an appropriate waste facility. 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. Scope
1.1 This guide covers the use of coal
combustion products (CCPs) for surface coal mine reclamation
applications, as in beneficial use for reestablishing land
contours, highwall reclamation, and other reclamation activities
requiring fills or soil replacement. The purpose of this standard
is to provide guidance on identification of CCPs with appropriate
engineering and environmental performance appropriate for surface
mine re-contouring and highwall reclamation applications. It does
not apply to underground mine reclamation applications. There are
many important differences in physical and chemical characteristics
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, and should be used in conjunction with
professional judgement. This guide is not intended to replace the
standard of care by which the adequacy of a given professional
service must be judged, nor should this guide be applied without
consideration of a project's unique aspects.
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. For guidance on
structural fills to be constructed at mine sites, see applicable
ASTM guide for coal ash structural fills.
1.5 Regulations governing the use of CCPs
vary by state. The user of this standard 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.
1.7This 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.
1.8This 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.
Standard Test Method for Repetitive
Static Plate Load Tests of Soils and Flexible Pavement Components,
for Use in Evaluation and Design of Airport and Highway
Pavements
Standard Test Method for Nonrepetitive
Static Plate Load Tests of Soils and Flexible Pavement Components,
for Use in Evaluation and Design of Airport and Highway
Pavements
Standard Test Methods for Measurement of
Hydraulic Conductivity of Saturated Porous Materials Using a
Flexible Wall Permeameter (Includes all amendments and changes
12/27/2016).
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