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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 = 165
166 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
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,
168 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. =
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. ,_
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
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 =
172 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 =
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. =
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
