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1 Introduction On October 11, 2000, near Inez, Kentucky, a breakthrough occurred in which a 72-acre surface impoundment of waste materials from coal process- ing at Martin County Coal Corporation released approximately 250 million gallons of slurry into a nearby underground coal mine. The slurry flowed through the mine, into nearby creeks and rivers, flooding stream banks to a depth of 5 feet. The spill caused no loss of human life. However, environ- mental damage was significant, and local water supplies, taken from the rivers, were disrupted for days. This report develops numerous suggestions and recommendations to reduce the potential for similar accidents in the future. In this chapter, we review the processes that lead to the generation of coal waste and the impoundments used to store it, and then we turn to a description of accidents and incidents involving coal waste facilities. Finally, we review the tasks and activities of this committee. COAL PRODUCTION AND USE IN THE UNITED STATES Coal is the largest single source of fuel for domestic energy production. In the United States, 90 percent of the coal produced is used in power plants (Freme and Hong, 2000~. Coal accounts for about 33 percent of the total energy production (Chircop, 1999~. In 2000, coal accounted for 51.4 percent of electric power generation (Freme, 2001~. Industries and manufacturing plants also use coal directly, especially those that produce chemicals, cement, paper, ceramics, and various metal products. On average, about 20 pounds of coal are utilized per day per capita in the United States (Chircop, 1999~. The United States has approximately 26 percent of the world's coal reserves (BP Global, 2001) (Table 1.1~. More than 400 coalfields and small deposits underlie a total of 458,600 square miles in 38 states, nearly evenly 1, 7
18 TABLE 1.1 Major World Coal Reserves, 2000 Country Reserves in Percentage million short tons of world total United States 246,643 Former USSR 230,178 China 114,500 11.6 India 74,733 7.6 South Africa 55,333 5.6 Australia 90,400 9.2 Germany 67,000 6.8 Poland 14,309 1.5 Canada 8,623 0.9 Indonesia 5,220 0.5 United Kingdom 1,500 0.2 Mexico 1,211 0.1 Others 74,561 7.6 SOURCE: Data extracted from BP Global, 2001. COAL WASTEIMPOUNDMENTS split between the Eastern and Western regions (Chircop, 1999~. Although some 300 different coal beds are mined each year, almost 47 percent of total production comes from just 10 of the largest deposits. Important coal deposits east of the Mississippi, are found in 10 states (Alabama, Illinois, Indiana, Kentucky, Maryland, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia). In the West, the Wyodak coal bed, the nation's leading source of coal, underlies part of the Powder River Basin of Wyoming and Montana. Other active Western coal reserves are found in Colorado, Utah, New Mexico, Arizona, and Alaska (Chircop, 1999~. ~ the =
INTRODUCTION 19 interior states, coal occurs in several separate basins Tom Michigan to Texas. According to data Tom the U.S. Energy Information Administration, coal beds throughout the United States produced 1.08 billion tons of coal in 2000, the 12th consecutive year in which 900 million tons or more were mined. In recent years, U.S. coal production has exhibited the following trends: Western mines account for an increasing share of total production (Figure 1.1~. Fewer coal mines are operating, but those mines are larger. Surface mines produce all increased proportion of coal overall. · Longwall mining produces an increased Faction of coal mined underground. 1 ,200 1 ,000 ~ 800 o s 600 c 400 200 o US Appalachian Western Interior 1990 1992 1994 1996 1998 2000 FIGURE l.l Coal production by region, 1989-2000. From Energy Information Admini- stration, 2001.
20 COAL WASTEIMPOUNDMENTS ADVANCED COAL CLEANING Increased mechanization in the underground coal mining industry has decreased selectivity and increased the volume of refuse. Equipment, such as continuous miners or longwall shearers, often takes roof and floor rock in addition to in-seam partings (Sidebar 1.1~. Equipment currently used to mine and transport coal produces more fine coal particles than did earlier equipment. Rotating cutter heads, feeder-breakers, and transfer points in SIDEBAR 1.1 Underground Coal Mining Methods in the United States About 39 percent of coal produced in the' United States comes from underground mines (Chircop, 1999~. Underground coal is mined by the following methods: conventional, longwall, continuous, and shortwall. Longwall and continuous mining are used effectively in combination (Chircop, 1999~. Conventional mining processes include drilling and blasting the coal. This method, one of the oldest mining methods, can be effective in certain geologic areas. Today, it is used for only 5 percent of underground coal mining (Chircop, 1999~. More than 45 percent of underground coal is mined by longwall mining (Chircop, 1999~. This method is gaining in popularity because it can improve coal recovery to 80 percent, and it enhances miners' safety (Peterson et al., 2001~. Production rates depend on the width of the block, the thickness of the coal seam, and the technology used to transport the raw coal out of the mine. Rotating drums, steel plows, or mounted shearers traverse back and forth across the block width and excavate blocks 600 to 1,200 feet wide and 5,000 to 7,500 feet long (Chircop, 1999; Peterson et al., 2001~. Longwall length capabilities have been steadily increasing: some Western operations now achieve lengths of over 10,000 feet (e.g., Twentymile in Colorado and SUFCO in Utah). The miners and mining equipment are protected by moving hydraulic roof supports called shields (Chircop, 1999~. After an area has been mined, the roof collapses. Continuous mining is a mechanized method utilizing mechanical cutting machinery. Although longwall mining has moved to the forefront (Chircop, 1999; NRC, 2001), continuous mining is still important in coal production. Continuous mining equipment is used to develop the areas for longwall mining. The continuous mining method uses a room-and-pillar system, whereby mined-out "rooms" are supported by coal "pillars." An operator, who maintains visual contact with the machine, can control this machinery remotely, thereby increasing miners' safety. Shortwall mining refers to mining with a continuous mining machine, moving roof supports, and excavating blocks 150 to 200 feet wide and more than one half mile long (Chircop, 1999~. This method is currently not used to any appreciable extent. =
INTRODUCTION 21 conveyor belt systems all break up the coal, producing quantities of fine coal particles whose recovery requires special processing and cleaning techniques. The characteristics of the in-situ coal (e.g., ash and sulfur content) vary spatially. The product that emerges from a mine often includes, not only randomly distributed impurities and the non-coal material known as partings (see Sidebar 1.2 for a description of the processes that deposit coal and create the impunties), but also material Tom the roof and floor layers. Thus, the characteristics of mined coal vary considerably. End-use plants are engineered for optimal combustion to burn feedstock of a particular ash, sulfur, and energy content requirements rarely met by the n~n-of-mine coal or by coal from a single source (Figure 1.2~. These combustion requirements have been the impetus for all upstream process changes, including the search for coal of low sulfur content, improved coarse and fine coal cleaning processes, in addition to several disposal and environmental laws. SIDEBAR 1.2 Coal Geology Coal is a combustible material consisting of organic matter and minor amounts of inorganic materials. It is derived from a heterogeneous mixture of plant remains and associated minerals, which have undergone chemical and physical changes by geological and biological processes without free access to air. Coal has a highly variable composition, affecting both its chemical and physical properties. Except for the anthracite region in eastern Pennsylvania, coal beds usually occur as nearly horizontal or gently folded strata. A coal seam is a composite of several layers, each of which may consist of a different mixture of coal material and mineral matter. Occasionally, these layers may be completely inorganic, such as shale, or high in mineral matter. Such layers are referred to respectively as partings and bony coal. Coal and associated rocks may contain significant amounts of sulfur, arsenic, and other materials whose presence in the waste engenders environmental concems. The depositional environments that produced the coalfields of the Eastem United States were predominantly coastal-deltaic. Large volumes of sediment were deposited from the Appalachian Mountains into rivers, which emptied into bays and coastal seaways. These conditions engendered the development of vast, laterally extensive peat swamps along the coastlines and delta platforms. Periodically, sea level rose and shallow marine environ- ments flooded the swamps, depositing marine shales and limestones. The cyclic repetition of these sedimentary environments has resulted in some of the most complex stratigraphic sequences in the geologic record. SOURCE: Rice et al., 1979.
22 COAL WASTEIMPOUNDMENTS Resources Coal type Anthracite Bituminous Subbituminous Lignite Coal characteristics Sulfur Ash Moisture Heat content Minerals Coking index %~% Mining Underground Conventional Continuous Longwall Surface Open-pit Area Contour Auger Mountaintop Preparation Crushing Screening Conventional cleaning Deep cleaning Blending Transportation Train Regular freight Unit train Barge Truck Conveyor belt Slurry lines End Use Customer Utilities Metallurgical plants Industry Residential/commercial Environmental Issues Air Water Land Waste/residuals Wildlife Aesthetics Economy On-site Off-site FIGURE 1.2 Coal system components. Dotted arrows indicate important feedback to mining feasibility. Modified Tom Office of Technology Assessment, 1979. Limitations on sulfur dioxide (SO2) emissions from coal-fired power plants have also contributed to the need for advanced coal-cleaning tech- nology. Power plants require coal of consistent quality (e.g., sulfur, ash, and heat content) to comply with these regulations. In an effort to produce coals that allow power plant operators to comply win standards established by the Clean Air Act, various methods of removing pyrite (FeS2) from the coal have been developed. In the past, much of this material would have entered the combustion chamber with the coal and would have resulted in additional ash. Now, the pyrite is removed, but it adds to the waste the preparation plant generates. Finally' the quality of coal being mined in the Eastem United States has declined as higher quality reserves have been depleted. Therefore, tech- niques have been implemented to upgrade the coal product quality. Previously, coal was cleaned by dry methods; however, a combination of factors, such as particle size, dust, transport, health, safety, and noise, and the better performance of wet processes have contributed to the near =
INTRODUCTION 23 abandonment of dry coal cleaning processes in recent years. The increased use of water to control dust in underground mines, and the increased efficiency of wet cleaning methods have continued the sharp decline in dry coal cleaning methods. Coal preparation (colloquially referred to as "washing") separates non- combustible materials from coal. Processing the run-of-mine coal may include: removing extraneous materials, crushing, sizing, blending coal from several locations, and concentration. A coal preparation plant separates the material it receives into a product stream and a reject stream, which may be further divided into coarse and fine refuse streams. Depending on the source, 20 to 50 percent of the material delivered to a coal preparation plant may be rejected (Leonard, 1991~. One of the reject streams is slurry, a blend of water, coal fines, silt, sand, and clay particles, which is most commonly disposed of in an impoundment. COAL REFUSE IMPOUNDMENTS IN THE UNITED STATES Coal refuse disposal impoundments are constructed for the permanent disposal of any coal, rock, and related material removed from a coal mine in the process of mining. Standard classification of coal slurry impoundments includes the following: · Active In operation and receiving slurry. · InactiveNot in operation or receiving slurry. Inactive impound- ments may receive slurry in the future, becoming active again, and therefore have not been closed permanently. Abandoned Not in operation and closed. These impoundments usually have been filled to capacity and have been closed and reclaimed. Grandfathered or "Pre-law"Not in operation since promulgation of the 1977 Surface Mining Control and Reclamation Act (SMCRA) regulation. These impoundments are reclaimed under the Abandoned Mine Lands Program. As of August 2001, MSHA oversees 713 active fresh-water and slurry impoundments in the United States (T. Bentley, Mine Safety and Health Administration, personal communication, 2001~. Most coal waste impound- ments in the United States are found in the East, predominantly in West Virginia, Pennsylvania, Kentucky, and Virginia. The thicker Western coal seams being mined now contain fewer in-seam partings and out-of-seam
24 COAL WASTEIMPOUNDMENTS rock, and most of that coal is shipped raw without extensive processing. Consequently, coal waste impoundments are rarely used in the West. In the Eastem coalfields, however, the majority of the coal from underground mines is processed before sale. Of the 1.1 billion tons of coal mined in the United States per year, about 600-650 million tons are processed to varying degrees. Typically 350-400 million tons are handled in wet-processing systems that, on average, produce 70-90 million tons of fine refuse in a slurry. (C. Raleigh, CQ Inc., personal communication, 2001~. Much of that material is stored in coal waste impoundments. Disposal methods for coarse and fine coal refuse developed along separate lines. Even before the days of modern coal preparation plants, laborers picked rock from the run-of-mine coal and discarded it in refuse piles. Sometimes coarse refuse was resumed to the mine, but more commonly it was deposited on the surface. When fine coal cleaning came into widespread use, it became necessary to deal with the refuse. One way is to pump the slurry into an impoundment and allow the particles to settle. Another is to concentrate or dewater the slurry and/or to mix it with coarse refuse or other additives (e.g., lime, sodium silicate, elastomeric polymers, resinous adhesives) to provide stability (Osborne, 1988), and then dispose of it in a landfill or impoundment. DISPOSAL OF FINE REFUSE IN IMPOUNDMENTS To impound fine coal slurry, embankments are constructed with compacted coarse coal refuse material. Prior to an accident in 1972, the Buffalo Creek disaster (Sidebar 1.3), little consideration was given to control of water entering an impoundment from a preparation plant or as runoff from the watershed above. Indeed, the coarse coal refuse used for embankment construction provides a filter to limit impacts to the quality of the water entering nearby streams (D'Appolonia Consulting Engineers, 1975~. In most impoundments, the embankment is constructed of coarse coal refuse, according to a design that is approved by regulatory authorities (see Chapter 2~. In the mountainous Appalachian region, the coarse refuse embankments are usually constructed across a valley, enclosing a basin that holds the coal refuse. In flatter Midwestern terrain, beamed and incised impoundments may be constructed. They typically have a larger surface area and are shallower. The slurry is pumped into the impoundment, where the fine particles in the slurry settle by gravity beneath a pool of clear water. In many impoundments, this clear water is pumped back to the coal processing plant and is reused. ,_
INTRODUCTION SIDEBAR 1.3 February 26,1972: Buffalo Mining Company, Buffalo Creek, West Virginia On February 26, 1972, the most destructive flood in West Virginia's history occurred when a coal waste impounding structure collapsed on the Buffalo Creek tributary of Middle Fork. Shortly before 8:00 a.m., the impounding structure collapsed, releasing approximately 132 million gallons of water. The water passed through two more piles of coal waste blocking the Middle Fork. At that time, there were no federal standards requiring either impoundments or hazardous refuse piles to be constructed and maintained in an approved manner. Around 1957, as part of its surface mining operations, the Buffalo Mining Company (a subsidiary of the PiKston Coal Company) had begun depositing mine waste consisting of rock and coal in Middle Fork. Buffalo Mining constructed its first impounding structure, near the mouth of Middle Fork in 1960. Six years later, it added a second impounding structure, 600 feet upstream. By 1968, the company was depositing more waste another 600 feet upstream. By 1972, the height of this third impounding structure ranged from 45 to 60 feet. Between February 24 and 26, 1972, the National Weather Service measured 3.7 inches of rain in the area of Logan County and Buffalo Creek. The impounding structure probably failed because foundation deficiencies led to sliding and slumping of the front face of the refuse bank. The waterlogged refuse bank accelerated the failure. The slumping lowered the top of the refuse bank and allowed the impounded water to breach and then rapidly erode the crest of the bank. Upon failure of the refuse bank, the floodwater moved into pockets of burning coal waste. As result of the flood, 125 people were killed, 1,100 were injured, and more than 4,000 were left homeless. In addition, the flood completely demolished 1,000 cars and trucks, 502 houses, and 44 mobile homes, and damaged 943 houses and mobile homes to varying extents. Property damage was estimated at $50 million. SOURCE: W. E. Davies et al., 1972 FINES DISPOSAL PROBLEMS IN OTHER MINING SECTORS The problem of slurry disposal is not unique to the coal industry; it is a consideration for many base and precious metals industries, as well. For example, in the aluminum industry, disposal of massive quantities of bauxite tailings (called red mud) creates similar problems (Wagh and Desai, 1987~. Disposing of the red mud in settling ponds in dilute, fine mud-sar~d slurries of about 20 percent solids (Downs and Stocks, 1977) brings with it a number of problems including very slow settling time and low bearing strength. The 25
26 COAL WASTE IMPOUNDMENTS search for alternative disposal technologies (e.g., thickened t60 percent solids] high-density residue stacking), as well as for processing and utilization of the red mud, have been underway for some time (Wagh and Desai, 1987~. The disposal of the tremendous volume of waste sand and clay in the beneficiation process of phosphate mining is another example of these problems. The clay is pumped to a settling area in a dilute stream (3 percent solids) or sent to a Sickener to increase the solids content (15 percent solids) (Garlanger arid Fuleihan, 1983~. Fine sediment disposal also is a problem in base metal mining and smelting operations. COAL WASTE IMPOUNDMENT FAILURES Coal waste facilities have been involved in several accidents or incidents since 1972. She incidents reviewed here demonstrate Me range of the types of failures that can affect coal waste impoundments and of impacts of such failures. They are not a complete list of incidents. The first event was the Buffalo Creek accident (Sidebar 1.3), the most serious because it resulted in the loss of 125 lives and extensive damage to property down- s~eam of Me refuse piles and impoundments. Following that accident, regulations were promulgated to govern the design of the embankment structures used in figure impoun~nents. Since ~en, no engineered embar~k- ments have failed, although other incidents and accidents have occulted. Sidebars 1.4 to 1.12 describe selected events. SIDEBAR 1.4 August 14, 1977: Island Creek Coal Company, Boone County, West Virginia An embankment under construction failed at Island Creek Coal Company's impoundment in Boone County, West Virginia, on August 14, 1977. Heavy rainfall overflowed a temporary diversion ditch, causing the water level in the impoundment to rise. Because the embankment was still under construction, storage capacity had not yet reached the required minimum, and the sudden influx of additional water overtopped the embankment. Meanwhile, the water eroded the embankment, reducing its height 23 feet during a two-day period. During this time, 6.8 acre-feet of material was released, which clogged a drainage pipe downstream. SOURCE: Owens, 1977.
INTRODUCTION 27 SIDEBAR 1.5 December 18, 1981: Eastover Mining Company, Harlan County, Kentucky On December 18, 1981, Eastover Mining Company's Hollow No. 3 combined refuse disposal site failed, releasing about 25 million gallons of saturated coal refuse. The operation had been permitted to dispose of layers of coarse coal refuse and dewatered slurry "filter cake," which contained approximately 30 percent moisture, behind an embankment (see discussion of disposal techniques in Chapter 7) and, at a height of 192 feet, had reached 90 percent of its planned capacity. Several factors contributed to the increased pore water pressure in the dewatered fine refuse zone, including: (1 ) the filter cake layers had not been allowed sufficient time to dry before additional material was added; (2) layers of filter cake were not completely covered with coarse coal refuse; (3) a stream flowed into the impounded material, increasing saturation; and (4) material used in construction of the embankment did not allow water to seep out. The failure released a mudflow approximately 5 feet deep that traveled 4,400 feet downstream (500 feet in vertical distance) into the community of Ages, Kentucky. One resident was killed, three houses were destroyed, and 30 homes were damaged. SOURCE: Cannon, 1981. SIDEBAR 1.6 April 8, 1987: Peabody Coal Company, Raleigh County, West Virginia On April 8, 1987, a breach developed in the principal spillway pipe in the Lower Big Branch impoundment at Peabody's Montcoal No. 7 complex in Raleigh County, West Virginia. The 36-inch-diameter pipe ran through the impoundment and under part of the embankment at a depth of 55 feet. The rupture released nearly 23 million gallons of water, slurry, and fine coal refuse. The exact cause of the accident was not identified but was probably a combination of factors: (1) Heavy snowfall (16 inches of snow with a rainfall equivalent of 1.9 inches), followed by rapid temperature increases and snowmelt, sent excessive amounts of water through the pipe. (2) Two landslides occurred in the slope above the rupture. Although the relative timing of the landslides and the breach is not known, the slides could have caused the pipe to collapse or separate. (3) Erosion of particles near the pipe connections could have reduced the bearing strength of the pipe. (4) The strength of an "elbow" in the piping may have been exceeded by massive and rapid fluid flow. In addition, a sinkhole that developed from the rupture threatened the stability of the embankment. The sinkhole came within 100 feet of several upstream-constructed additions to the cross-valley embank- ment before stability was maintained through mitigation of the breach.
28 COAL WASTEIMPOUNDMENTS The impoundment, upstream from several communities, was rated at the time as high hazard. A 50-mile stretch of Coal River from Montcoal to its mouth at St. Albans was visibly affected, and five water plants were shut down. Although 1,700 customers' water supply was disrupted in the Racine Public Service District, no human injuries or fatalities occurred as a- result of this incident. SOURCE: Owens, 1987. SIDEBAR 1.7 January 28, 1994: Consolidation Coal Company, Morgantown, West Virginia On January 28, 1994, a 5-foot earthen berm failed at a slurry refuse impoundment at the Arkwright Mine in Granville, West Virginia. Heavy rain and melting snow resulted in 30 inches of water collecting behind the berm; it was determined that the 4-inch discharge pipe and rock underdrain at the site were insufficient to prevent water accumulation. The incident released 375,000 gallons of water into the town of Granville. Although no one was injured, three residences directly downstream were damaged. SOURCE: Betoney, 1994. SIDEBAR 1.8 May 22, 1994: Martin County Coal Corporation, Davella, Kentucky On May 22, 1994, a breakthrough occurred at Martin County Coal Corporation's Big Hollow slurry impoundment in Davella, Kentucky. Nearly 32 million gallons of black water inundated an abandoned and sealed-off portion of the mine. The breakthrough resulted either from collapse or water penetration of the Coalburg coal seam bordering the impoundment. Slurry had been impounded 32 feet higher than the coal seam's elevation. The mine's 16-inch concrete-block seals held the black water inundating the mine, but water broke through portal seals and a coal seam outcrop barrier. Although the slurry level dropped by 6 feet, the embankment structure was not damaged, and no injuries or fatalities occurred. SOURCE: Stewart and Robinson, 1994.
INTRODUCTION 29 SIDEBAR 1.9 August 9, 1996: Lone Mountain Processing Incorporated, St. Charles, Virginia On August 9, 1996, there was a breakthrough at Lone Mountain Processing's Miller Cove slurry impoundment. The evening before the failure, approximately 2.75 inches of rain had fallen, and most of it within an hour and a half. Approximately 1 million gallons of black water were released into Gin Creek through an abandoned mine. (Underground mines had operated in areas adjacent to the impoundment from the 1 920s to the 1 980s.) Excavation of the breach showed that the leak occurred in an area where available mine maps indicated a barrier of at least 25 feet of solid coal between the outcrop and the underground mine workings. Further exploration revealed that the barrier was in fact less than 2 feet thick. It is believed that hydrostatic pressure from the slurry opened cracks in the coal seam and began a piping-type failure. The thin coal barrier was progressively eroded, allowing slurry to flow uncontrolled into the abandoned mine. SOURCE: Michalek et al., 1996. SIDEBAR 1.10 October 24, 1996: Lone Mountain Processing Incorporated, St. Charles, Virginia On October 24, 1996, a second breakthrough occurred at Lone Mountain Processing's Miller Cove impoundment, but in another area of the abandoned mine. This release was more serious than the event in August (Sidebar 1.9) because the water contained more solids. Approximately 6 million gallons of water and slurry exited the abandoned mine into Gin Creek and flowed 11 miles, where it entered the Powell River's North Fork. Reportedly, the river was discolored for more than 40 miles. The failure resulted from two large sinkholes that had developed on the northwestern end of the impoundment. When the site was excavated to locate the breach, it was determined that the slurry had entered through a fracture in the mine roof that coincided with these sinkholes. SOURCE: Michalek et al., 1996.
30 COAL WASTEIMPOUNDMENTS SIDEBAR 1.11 November 26, 1996: Consolidation Coal Company, Oakwood, Virginia On November 26, 1996, the Buchanan No.1 impoundment in Buchanan County, Virginia, failed. In the 1 960s, the Kennedy coal seam at the site had been excavated by both surface area mining and underground auger mining. After the impoundment was constructed (1984), another company mining underground in the adjacent drainage area apparently intersected the historic auger mine workings, providing a conduit for the slurry. Coal refuse and slurry from the impoundment broke into an abandoned underground mine and discharged about 1,000 gallons per minute at its peak through two mine portals into the adjacent North Branch Hollow of the Levisa Fork of the Big Sandy River. There was no detrimental impact on the embankment, and no one was killed or injured. SOURCE: Michalek et al., 1996. SIDEBAR 1.12 October 11, 2000: Martin County Coal Corporation, Inez, Kentucky On October 11, 2000, a coal waste impoundment of the Martin County Coal's preparation plant near Inez, Kentucky, released slurry containing an estimated 250 million gallons of water and 31 million gallons of coal waste into local streams. Reportedly, the failure was caused by the collapse of the slurry pond into underground coal mine workings next to the impoundment. The slurry broke through an underground mine seal and discharged from mine entrances 2 miles apart into two different watersheds (wolf Creek and Coldwater Fork). Although no human life was lost, the release killed aquatic life along the Tug Fork of the Big Sandy River and its tributaries. Public water supplies were disrupted when communities along the rivers in both Kentucky and West Virginia shut down water plants to prevent contamination with black water. Anencan Electric Power had to close its massive generating plant, and numerous properties and residences were damaged. SOURCE: Vanous issues of the Herald Leader, the CounerMoumal, and the Charleston Gazette (2000, 2001~; Dennis Hatfield, Martin County Coal Corporation, personal communication, 2001. Two of the events resulted from leaks or failures of drainage pipes. However, the majority of the incidents involved failures in the basin area. Inaccurate mine maps and inadequate characterization of the basin area most
INTRODUCTION 31 likely contributed to at least some of these incidents. This report deals with both of these issues in detail (Chapters 4 and 5~. IMPOUNDMENT HAZARD RANKING SYSTEMS MSHA bases its hazard potential rating system on the height of the embankment, the volume of material impounded, and the downstream effects of an impoundment failure (MSHA, 1974, 1983~. The resulting three classifications are: Low Hazard Po ten tint Facilities in rural areas where failure would cause only slight damage, such as to farm buildings, forest, agricultural land, or minor roads. Moderate Hazard Potential Facilities in predominately rural areas where failure may damage isolated homes or minor railroads, disrupting services or important facilities. · High Hazardt Potential Facilities whose failure could reasonably be expected to cause loss of human life, serious damage to houses, industrial and commercial buildings, important utilities, highways, and railroads. The MSHA guidelines indicate that design criteria become more conservative as the hazard potential increases. For example, design criteria for the maximum precipitation (flood) event increase as the hazard classification moves from low to high. Thus, storm design criteria for a long- term high-hazard-potential impoundment require that the impoundment be designed to contain the probable maximum precipitation that is reasonable for the region (MSHA 1974, 1983~. In addition, piezometers are generally required to monitor and verify the water saturation conditions within the embankment for moderate and high hazard sites. MSHA guidelines further state that the stability of an embankment should normally have minimum static and seismic factors of safety of at least 1.5 and 1.2, respectively, under maximum anticipated phreatic condi- tions. The guidelines require extra attention to seismic events for high hazard impoundments in certain regions (MSHA, 1974, 1983~. On December 1, 1997, after two unintentional releases of slurry in Virginia in a two-month period, MSHA introduced a second classification system that addresses the potential for the unintentional release of water or slurry from impoundments into active or abandoned mines (Sidebars 1.9 and 1.10~. This classification system allows the coal mine operator to evaluate
32 COAL WASTEIMPOUNDMENTS the proximity of underground workings; to determine whether the recom- mendations of Bureau of Mines Information Circular 8741 (Babcock and Hooker, 1977), which provides guidelines for mining under bodies of water, are met; and to assess the potential impact if a breakthrough were to occur. For example, the impact may threaten the safety of miners or the safety of the general public (MSHA, 1997~. A priority rating is assigned to each impoundment based on its breakthrough potential- whether low, medium, or high and a potential impact of a breakthrough. The purpose of this classification system is to evaluate whether the impoundment plan adequately addresses the breakthrough potential (MSHA, 1997~. These ranking systems are based on the proximity of the basin to underground workings as well as the potential downstream impacts were a basin to fail. However, they do not assess the probability of failure. It is a completely separate ranking than that which is done for the embankment structure. In addition, the Federal Emergency Management Agency ranks embank- ments based on potential impacts should a failure occur (U.S. Bureau of Reclamation, 1988~. This inventory lists more than 76,000 dams. The Office of Surface Mines (OSM) and the state delegate programs use a similar system to rank earth dams and reservoirs by whether they are located in rural areas and the amount of damage failure could cause (U.S. Department of Agriculture, 1976~. Neither of these organizations has a ranking system for breakthrough potential. STUDY AND REPORT Concern about the potential for accidents like the one at Inez, Kentucky (October 2000), motivated Congress to direct MSHA to commission an independent study of current coal waste disposal methods and an exploration of alternatives for future disposal of coal waste. In addition, Congress directed that the study examine engineering standards for coal waste impoundments, and recommend ways to improve the stabilization of impoundment structures. The National Research Council (NRC) established the Committee on Coal Waste Impoundments to undertake this study. The committee consists of 14 experts from academia, industry, and state government with expertise in coal mining, geology, geophysics, geochemistry, hydrology, mining regulations, environmental law, mining health and safety, land-use planning, and geotechnical and geological engineering. Brief biographies of the committee members appear in Appendix A.
INTRODUCTION The overall objectives of this study are: . 33 to examine engineering standards for coal waste impoundments; · to provide recommendations for improving impoundment structure stabilization; to determine the adequacy of mine maps; and to evaluate potential alternatives for future coal waste disposal, including the benefits of each alternative. The Statement of Task lists the following specific tasks: Engineering Standards/Barrier Stability/Monitoring Examine current engineering practices for coal waste impound- ments and provide recommendations for improving engineering practices, including impoundment structure stabilization. What alternative means are available to evaluate or confirm the safety of the designed barriers protecting slurry impoundments? What options can be developed to effectively monitor the status of coal barriers left to protect slurry impoundments? Site Characterization Evaluate the adequacy of mine maps and explore ways to improve mapping and surveying practices in general for the mining industry. What is the best way to three-dimensionally conceptualize and delineate the impoundment area, including the extent of under- ground mine works beneath or adjacent to the slurry disposal area? Alternative Technologies Evaluate potential alternatives for future coal waste disposal, in- cluding the benefits of each alternative. Are there other methods to wash and process coal that would reduce the amount of slurry disposal needed? What are the options for the coal waste product to be refined further in order to produce a marketable product? To address the charge, the committee gathered, synthesized, and analyzed information by working in subgroups based on the three main topics in the Statement of Task (geotechnical aspects, site characterization, and alternative technologies). The committee held eight information- gathenng meetings, including six subgroup meetings, between March and June 2001. The meetings included presentations by, and discussions with the sponsor, personnel from other government programs, and representatives of
34 COAL WASTEIMPOUNDMENTS industry, academia, environmental organizations, labor organizations, and citizens' groups (Appendix B). To obtain input from the public, the com- mittee held eight town meetings throughout the Eastern coal-mining region. Finally, the full committee met twice in closed session for discussion and writing. As background material, the committee reviewed relevant govem- ment documents and materials, pertinent NRC reports, and other technical reports and literature published through July 2001. This report is intended for multiple audiences. It contains advice for MSHA, OSM, other federal agencies, and state regulatory agencies, as well as policy makers, the coal industry and its consultants, scientists, and engineers. Chapter 2 gives an overview of the regulatory framework for coal waste impoundments. Chapter 3 examines issues related to the engineering design for coal refuse facilities. Chapter 4 discusses site characterization, including mine mapping, map storage and preservation, and surveying. Chapter 5 addresses techniques, such as geophysical methods, to locate abandoned mines and other voids, and hydraulic testing to establish the thickness of barrier pillars. Chapter 6 discusses ways to limit potential failure modes for the embankment and basin area. Chapter 7 addresses alternatives to slurry impoundments, including alternative mining and coal preparation methods, direct utilization of slurry, and alternative disposal techniques. Chapter 8 summarizes the committee's conclusions and recom- mendations. Technical terms are defined in the glossary (Appendix C). It is important to recognize that this charge specifically directs the committee to focus its analysis on the engineering and characterization of coal waste impoundments. The committee was not asked to consider other factors related to potential impacts of disposing of coal wastes in an impoundment, or any other disposal option. For example, these factors might include potential long-term effects on water quality; land use issues, including long-term stewardship of closed impoundments; and economic and cost-benefit analyses of alternatives. The committee also was not asked to evaluate the risks of individual impoundments, examine the qualifications and training of inspectors, or comment on coal mining policy issues not directly related to impoundments. Although important, such issues are well beyond the charge to this committee. Furthermore, a comprehensive analysis of these issues would require considerably more time than was available for the present study. =
