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8
Conclusions and Recommendations
The charge to the committee includes three major components. First, the
committee was asked to examine engineering practices and standards currently
being applied to coal waste impoundments and to consider options for evalu-
ating, confirming, improving, and monitoring the various barriers that retain
coal waste material within impoundments. Second, the committee was
charged with evaluating the accuracy of mine maps and exploring ways to
improve surveying and mapping for underground coal mines with the goal of
delineating more accurately how underground mines relate to current or
planned slurry impoundments. The third committee task was to evaluate
alternative technologies that could reduce the amount of coal waste generated
or allow productive use of the waste. This chapter summarizes the commit-
tee's conclusions, outlines the rationale for those conclusions, and reviews
the recommendations that follow from them.
ENGINEERING STANDARDS,
BARRIER STABILITY, AND MONITORING
The regulatory structure that governs the design process is outlined in
Chapter 2, and a detailed review of the current engineering practices used in
the design of coal waste impoundments is given in Chapter 3. A substantial
regulatory structure exists, and a detailed regulatory review process that
covers many key aspects of the design, construction, and operation of coal
waste impoundments is in place. The review of the impoundment basin has
been less detailed and rigorous, and the series of incidents that involved
releases of coal slurry material from impoundment basins (see Sidebars 1.3
to 1.11) indicates that more investigation of the potential for loss of integrity
of an impoundment in the basin area is appropriate. Special attention should
be given to the potential for breakthrough of coal slurry into underground
coal mines. The authority for review of basin characterization and design
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COAL WASTEIMPOUNDMENTS
appears to be covered in general language authorizing investigation of all
relevant issues with respect to the impoundment. The committee recom-
mends that MSHA and OSM should have clear authority to review basin
design. It is not evident to the committee whether specific legislation to
authorize more detailed examination of basin issues is required or whether
these issues can be handled by additional rulemaking under existing
authority.
The regulatory approach taken by MSHA and OSM with respect to the
design, construction, and operation of the embankment portion of impound-
ments has been effective in general. The incidents that have occurred
involving impoundments have generally not been the result of significant
failures of the embankment structure. Similar guidance should now be
provided for the basin portion of impoundments. The committee recom-
mends that MSHA and OSM develop and promulgate guidelines for the
site evaluation, design, construction, and operation of basins. They
should be comparable in scope to the guidelines used in embankment design.
The guidelines should include methods for mitigation of any potential
pathways for release of coal slurry. Many of these mitigation measures will
involve established procedures for grouting, sealing of fractures, or
construction of embankments that line the basin rim, for example. At the
same time, the question of engineered bulkhead barriers used to isolate
underground coal mines from the coal slurry in the basin should be
addressed. Current regulations specify the design of bulkheads that are
intended to protect miners from underground explosions, but they do not
provide for bulkheads intended to support the high hydraulic heads that can
arise in coal waste impoundments. Hence, the committee recommends
that MSHA review its current practice and develop guidelines for the
design of bulkheads intended to withstand hydraulic heads associated
with slurry impoundments.
While the embankments designed and constructed under the current
regulatory system have generally performed according to design, the
committee believes that prudence requires that MSHA and OSM continue to
evaluate worldwide experience with impounding structures, and to stay
abreast of lessons learned from failures experienced in other mining
applications so that their design criteria reflect the latest experience in all the
mine sectors. The committee recommends that MSHA and OSM continue
to adopt and promote the best available technology and practices with
regard to the site evaluation, design, construction, and operation of
impoundments. MSHA and OSM should commission periodic reviews of
existing technical procedures and practices, with particular attention to the
basin. Results of the reviews should be disseminated to industry. Based on
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CONCLUSIONS AND RECOMMENDS TIONS
167
the outcome, MSHA and OSM may need to revise guidelines that establish
minimum expectations and levels of investigation for site characterization,
design, construction, operation, and closure of coal refuse impoundments.
If underground mine workings are near the basin area of an existing or
proposed impoundment, it is important to assess the status of coal barriers
that separate the mined-out area from the surface. Currently, no federal
regulations address the amount of outcrop coal barrier to be left or the depth
and nature of the overburden that is required. OSM has studied the problem
of outcrop barriers but has not published conclusions to date. The com-
mittee recommends that MSHA and OSM jointly pursue the issue of
outcrop coal barrier width and overburden thickness and its competence
and develop minimum standards for them.
Procedures in place for monitoring embankment structures, which
include visual inspections and instrumentation, appear to be performing as
envisioned in the regulations MSHA implemented. For monitoring to be
successful, it should be applied to all potential failure modes. The committee
believes, however, that there are opportunities for additional, continuous
monitoring that may offer timely warning of potential failure of an
embankment or basin. The committee recommends that MSHA and OSM
consider requiring additional continuous monitoring in specific instances
and evaluate automation of monitoring instruments.
SITE CHARACTERIZATION
The committee examined two parts of the question of site characteri-
zation, the accuracy of mine maps and the use of geophysical techniques to
delineate the extent of underground mine workings In situations where maps
do not exist or may not be sufficiently accurate.
The committee notes that the accuracy of mine maps has improved win
the use of modem surveying equipment and practices, but also concludes
that additional improvements in surveying practices, recording information
on maps, and storage of maps and related information are necessary and
possible. Therefore, the committee recommends that MSHA work with
OSM and state agencies to establish standards for mine surveying and
mapping. These should include the following:
.
=
Determining surface coal outcrop locations by aerial topographic
measurements, where adjacent to existing or proposed refuse
impoundments,
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COAL WASTEIMPOUNDMENTS
Implementing a coordinated and assertive approach to collecting
and archiving mine maps,
Scanning paper copies of mine maps into electronic data files
upon receipt,
Setting standards for minimum closure error for all underground
closed-loop surveys and that a closed-loop survey be maintained
within a standard distance (to be determined by MSHA),
Recording the depth of the last cut taken to a level of accuracy
to be determined by MSHA,
Using state plane coordinates or latitude and longitude and
bottom-of-seam elevations as the map base reference,
Listing of appropriate coordinate transformation equations) on
the mine map,
· Adding a qualifying statement to accompany any coordinate
transformation that is based upon the alignment of surface
features,
Improving and maintaining the location of surface controls,
· Determining which mine permit documents should be retained,
in what form, and for how long,
· Avoiding the use of coal seam names as the sole basis for
determining the vertical location of an abandoned mine.
In situations where no mine maps are available or there is reason to
doubt the accuracy of maps that do exist, additional investigation of the
relative location of underground mine workings with respect to an existing
or proposed impoundment is warranted. Chapter 5 reviews a variety of
geophysical techniques that can be used to obtain additional inflation.
Some drilling of boreholes is likely to be of value in most site characten-
zation efforts, but the use of geophysical techniques along with drilling has
potential to provide additional useful information. The committee concludes
that geophysical techniques have been underutilized in the coal-mining
industry and could benefit from additional research. The committee recom-
mends that demonstration projects using modern geophysical techniques
be funded, and that the results be widely conveyed to the mining industry
and to government regulatory personnel through workshops and contin-
uing education. Continuing education could include the opportunity to attend
short courses and seminars that present the latest technology along with case
histories to support its use.
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CONCLUSIONS AND RECOMMENDS TIONS
ALTERNATIVE TECHNOLOGIES
169
Coal waste impoundments are part of the system for mining and
processing coal to produce energy. In order to assess alternatives, the whole
system of mining, preparation, refuse disposal, transportation, and power
generation should be explored through an in-depth life-cycle assessment,
including cost assessment, with the goal of optimizing the system to
generate less fine coal waste while maintaining the performance and
economics of the system. The committee recommends that the total
system of mining, preparation, transportation, and utilization of coal
and the associated environmental and economic issues be studied in a
comprehensive manner to identify the appropriate technologies for each
component that will eliminate or reduce the need for slurry impound-
ments while optimizing the performance objectives of the system. The
committee concludes that a similar analysis of the waste use and disposal
technologies that make up the coal system would have value. The com-
mittee recommends incorporating life-cycle assessment of the costs and
environmental impacts of the alternatives to evaluate them on a more
objective, comprehensive basis. In addition, a detailed analysis of the
economic and environmental impact of the various policy alternatives
should be performed.
The opportunities for reducing slurry volume include mining alterna-
tives and coal processing alternatives. However, modem methods of surface
and underground coal mining offer only a limited possibility for quality
control during mining. Slurry volume can be reduced by improving fine coal
recovery, minimizing the mass of solids for disposal, and dewatering. Many
dewatering technologies are currently available for specific applications,
though none is likely to be universally applicable. The committee believes
that the research and development currently being performed by equipment
vendors will lead to improvements in these technologies.
Slurry refuse can be utilized directly for power generation, either in
conventional boilers or in advanced combustion and gasification technol-
ogies, some of which can reduce coal-cleaning requirements. But, the use of
low quality coal feed may increase the amount of waste generated at the
power plant. The utilization of fine coal waste in conventional coal-fired
power plants offer near-term opportunities for the reduction of fine coal
waste disposed of in impoundments. However, the coal produced is more
expensive than cleaned coal, as a result of capital and operating costs of
additional equipment, and, in the case of coal water slurry, the additional
cost of transportation. To compare technologies, the avoided costs of slurry
impoundments must be included in a cost comparison.
,_
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170
COAL WASTEIMPOUNDMENTS
Fluidized-bed combustion and gasification show promise for recovering
the heat content of fine coal waste while avoiding some of the operational
problems that limit use of coal fines in conventional pulverized coal-fired
boilers. The combustion of fine coal waste in advanced combustion technol-
ogies, such as fluidized-bed combustion and gasification, is- an alternative
that also shows considerable long-term promise. Further research is needed
on the use of fine coal waste slurries as feeds; incentives may be needed if
these technologies are to be utilized widely for fine coal waste combustion.
While coal combustion wastes from power plants are already being used for
a number of purposes, the issue of the safe handling of coal combustion
waste from these advanced combustion technologies should be studied
further.
Both surface and underground methods are available for the disposal of
coal slurry other than in impoundments. Alternative surface methods include
incised ponds, slurry cells, combined refuse piles, and co-disposal of fine
and coarse refuse. In many instances, these methods are influenced by
topography, geology, and mining and coal preparation characteristics and are
therefore site specific. The two primary methods for injecting fine coal refuse
into underground mines are controlled flushing, where the underground
workings are accessible, and blind or uncontrolled flushing, where the
underground workings are abandoned or have caved in. A number of issues
related to underground injection of slurry such as adequate supply of
water, surface ownership, permits, surface layout, and surface drainage are
independent of the method of slurry injection.
Although there are alternatives to disposing of coal waste in impound-
ments, no specific alternative can be recommended in all cases. Furthermore,
the alternatives that have been identified are in varying stages of
technological development and implementation. A factor limiting imple-
mentation to this point is the cost associated with the various alternatives.
Additional research is needed to develop these alternatives farther and to
evaluate the economics of these processes. The committee recommends
that a screening study be conducted that (1) establishes ranges of costs
applicable to alternative disposal options, (2) identifies best candidates
for demonstration of alternative technologies for coal waste impound-
ments, and (3) identifies specific technologies for which research is war-
ranted. Input from MSHA and OSM regarding regulatory issues will be
valuable to such a study. The committee recommends that the use of
economic incentives be explored as a way of encouraging the develop-
ment and implementation of alternatives to slurry impoundments. The
development of incentives should be based on the full range of the portfolio
of technologies as well as the economics of the technologies. The incentives
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CONCLUSIONS A ND RECOMMENDATIONS
171
should be linked directly to the reduction in slurry production of the
utilization of slurry.
One way to reduce the volume of material in older slurry impoundments
is to recover or remine the fine coal. Profitable remitting may be possible if
impoundments contain at least 1 million tons of in-situ slurry material, at an
expected recovery rate of a marketable fine coal product of not less than 30
percent. The committee concludes that, as advances are made in the use of
low value coal or coal water slurry, remitting of slurry impoundments can be
an attractive source of fuel.
ADDITIONAL RECOMMENDATIONS
In its deliberations, the committee identified several issues that cut
across the elements of the statement of task. In addition, related areas
warrant additional study, in the committee's view.
The committee notes that MSHA uses two systems to classify coal
waste impoundments. One system classifies impoundments as high, medium,
or low hazard, based on the magnitude of the potential consequences of a
failure of the embankment structure- an embankment where people live and
structures have been built immediately downstream would be classified as
high hazard, regardless of the likelihood of failure of the embankment. A
second system, which deals with basin failures, includes assessments of the
proximity of underground mine workings, the potential for failure that would
release slurry or water into those workings, and the potential impacts of a
release. The second classification system comes closer to the standard
definition of risk. Using different methodologies for classifying embankment
and basins is inappropriate. Therefore, the committee recommends that:
(1) MSHA and OSM review activities related to risk assessment for
existing impoundments (including both embankments and basins) to
ensure that they are consistent and that they distinguish appropriately
between hazard and consequence assessment in the methodologies
adopted; and (2) MSHA and OSM establish a single, consistent system,
which should be used to assign both embankments and basins to risk
categories. The ranking should be based on the combination of hazards arid
consequences, such as loss of life, cost, and environmental impact. This can
be accomplished using qualitative risk assessment techniques.
A consistent risk assessment system would allow decisions on
impoundments to be based on their relative risks. The committee recom-
mends that MSHA and OSM oversee a thorough assessment of potential
mitigation measures for those impoundments that fall in the highest risk
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COAL WASTEIMPOUNDMENTS
category and should determine which mitigation measures should be
applied to reduce this risk to an acceptable level.
The committee also concludes that the design process for impoundments
would be improved by a more formal risk analysis. Proposed new impound-
ments should also be assigned to risk categories, based on a combination of
hazards and consequences, as was suggested for existing impoundments. To
maximize the potential for risk reduction, the committee recommends
that all impoundment designs be accompanied by a risk analysis
utilizing qualitative methods. Examples of such methods include Potential
Problem Analysis and Failure Modes and Effects Analysis.
The committee believes there is a limit to risk tolerance, for both
existing and new impoundments. When risk is high, and when mitigation
either through more reliable characterization or barrier construction is
impossible, of limited precedent, or so expensive that it is infeasible, then a
substantial change in operation of the impoundment is warranted. This may
range from minimizing slurry fluidity to cessation of operation. Impound-
ments that fail risk-assessment criteria and where risk cannot be mitigated
should be phased out or alternatives considered.
The committee heard repeatedly that the current review process for
impoundment approval could take 2 years or more to complete. The com-
mittee believes that an efficient and coordinated regulatory review process
would have substantial public benefit. A well-coordinated technical review
process would protect health and safety of both miners and the public, and
would foster protection of the environment. Therefore, the committee
recommends that the review process for both new permits and existing
permits be overhauled to include the following elements:
· A formal joint review that would coordinate the currently
fragmented and inefficient collection of reviews into a single
process.
Sufficient staff for engineering and other reviews in the agencies
that participate in the joint process so that the time required to
complete the review can be reduced significantly.
The committee found that only very limited information was available
concerning the quantities of trace elements in the slurry and the associated
water. The committee heard repeatedly that citizens are concerned about
ground and surface water quality and the impacts of impoundments on them.
While a detailed review of the environmental impacts of coal waste
impoundments is beyond the scope of this study, the committee identified
this area as one needing further study. In addition, the character of the
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CONCLUSIONS AND RECOMMENDA TIONS
173
effluents will change with time as the coal and associated minerals including
sulfides gradually oxidize. The committee recommends that research be
performed to identify the chemical constituents contained in the liquid
and solid fractions of coal waste, and to characterize the hydrogeologic
conditions around impoundments. Information obtained from such research
would have value for monitoring impoundments as well as for analyzing
environmental impacts.
The committee also heard numerous comments indicating citizens'
concern about emergency response and evacuation plans, which the operator
of a coal waste impoundment must prepare to obtain a permit to build the
impoundment. The committee recognizes the importance of the manner in
which emergency and evacuation plans are developed, communicated with
communities close to an impoundment, and coordinated with local emergency
response authorities. Better communication among the companies operating
impoundments, local emergency response authorities, and local citizens
would allow the authorities and the citizens to understand the risks, the steps
taken to mitigate them, and the appropriate responses in case of an accident.
SUMMARY
The conclusions and recommendations offered above reflect the com-
mittee's judgments concerning ways to improve the design process for coal
waste impoundments, ways to improve mapping of mines and the charac-
terization of sites of existing and future impoundments, and ways to improve
the assessment and mitigation of risks associated with impoundments. The
committee believes that implementation of those recommendations will
substantially reduce the potential for uncontrolled release of coal slurry from
impoundments, particularly through the mechanism of breakthrough into
nearby underground Nine workings. In addition, the committee believes that
an appropriate way to balance alternatives for creating, handling, and
disposing of wastes and to understand and mitigate the impacts of failure of
any element of those systems is to view the designs of embankment and
basins, as well as the entire process of handling and burning coal, as systems
of interlinked components that operate together. The safe operation of these
systems depends on effective engineering design, construction, and
operation of facilities in addition to appropriate monitoring. With He
recommended improvements in each of these areas, the potential for
incidents like that at Inez, Kentucky, can be reduced.
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174
COAL WASTE IMPOUNDMENTS
. ~
Secondary air
Coal and
limestone
Ash
At'
Cyclones
=~1
it,
~1: ~ _
~ , , -, ~ , To baghouse
—~ ~ · 1 ~ 1
., Fluidizing bed
l treat exchangers
l ~ i
l
l
Primary air Fluidizing air
FIGURE 7.4 Typical circulating fluidized bed arrangement Reprinted with
permission, from, Rousaki and Couch, 2000. Copyright 2000, by IEA
Coal Research.
recirculating nearly all the bed material with adjacent high-volume, hot
cyclone separators. The relatively clean flue gas goes on to the heat
exchanger. This approach theoretically simplifies feed design, extends
the contact between sorbent and flue gas, reduces likelihood of heat
exchanger tube erosion, and improves SO2 capture and combustion
efficiency (DOE, 2001~. With all these features, second-generation
pressurized fluidized-bed combustion is expected to achieve a 52 percent
fuel-to-elec~icity efficiency level and have near-zero NOX, SO2, and
Prepublication Version - Subject to Further Editorial Correction
Representative terms from entire chapter:
fine coal
