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3 COAL MINING An understanding of coal-mining processes is germane to determining the significance and redistribution of trace elements in the environment resulting from coal mining. Current government regulations require that before any physical activity begins at the mine, plans must be developed to assure optimum mine operation, reclamation, and conservation of the environment. National and state regulations now require that the objectives of complete reclamation and conservation of the environment be a mandatory part of mine operations (Office of the Federal Register, 1979). Environmental inventories are also required so that the site-specific concerns may be alleviated in mine planning and reclamation planning. With greater development of the western coal, a greater proportion of U.S. coal production will come from surface mines. This report has therefore given more attention to the effects on trace elements in the environment from surface mining than from underground mining. A brief description of the relevant phases of mining as practiced in the coal provinces of the United States follows. The general, net effects of surface mining are a few-hundred-meter relocation of the overburden, the earth materials above the coal, accompanied by a reduction of its density. As a result, permeation of groundwater through it occurs more readily. The major force for the redistribution of trace elements in the environment of a surface mine is thereby related to the changed physical properties of the overburden. In an underground mine, the density of the overburden is reduced by subsidence that results in greater porosity and permeation by groundwater and air, which brings about microenvironmental changes and redistributions of the contained trace elements. Similarly, in surface mines, the removal and handling of the overburden provides for the dissolution and migration of the contained trace elements. SURFACE MINING Surface mines in the three western coal provinces (Northern Great Plains, Rocky Mountain, and Gulf Coastal Plain) are generally set in a rangeland environment. To a lesser extent, potential sites may occur on high, sloping plateau areas and even less frequently, on agricultural 39
40 land. In the two Appalachian provinces (North and South), the environmental setting is typically hilly to mountainous. In the remaining two provinces (Eastern and Western Interior), surface mines occur in mostly agricultural environments and, to a much lesser extent, in undeveloped areas. Surface mining processes are summarized below. Coal Extraction The first stage of surface mining is removal of the native soil referred to as a natural soil in 91 Stat. 487 (7) (U.S. Congress, 1977). Trees and large shrubs are removed first; those of sufficient size are used as timber. Smaller vegetation is removed by dragging a chain between two bulldozers. This vegetation becomes a solid waste and is buried in the spoil area of a mine or burned on site. Soil, known as the "A horizon" in Public Law 95-87, 91 Stat. 487 (U.S. Congress, 1977) or the "natural earth materials at or vertically adjacent to the land surface with physical and chemical characteristics suitable for support of vegetation" in Title 30 CFR 211.2 (Office of the Federal Register, 1978) is removed next. This material is segregated for replacement during reclamation. The B horizon, or a combination of it and other, lower strata, is next removed and segregated for replacement as root zones. If either material must be stored, it is protected from wind and water erosion and noxious plant species in Title 30 CFR 211.40(a) (4) (Office of the Federal Register, 1978; U.S. Congress, 1977). Normal practice is to use self-loading pan scrapers (Brown, 1977). If bulldozers and front-end loaders are used, trucks transport these soils to active reclamation areas or to storage. The next step is overburden removal. In mine areas where the overburden rock is dense and consolidated, a pattern of holes is drilled nearly to the depth of the coal. These holes are charged with explosives, which are detonated to fracture the overburden or actually move it into an adjacent, open pit. Various combinations of ammonium nitrate and fuel oil are the most commonly used explosives. Other blasting agents such as aluminum slurry mixes, gelatins, and dynamites may be used in fracturing harder formations. Following this blasting operation, overburden can be removed. In the coal provinces of the Northern Great Plains, Rocky Mountains, Gulf Coastal Plain, and the Eastern and Western Interior, many economically significant coal beds are nearly horizontal beneath level to gently rolling surface terrain. Mining normally begins near where the coal outcrops at the surface, where the overburden is thin, then continues into thicker overburden until physical or economic limits of mining are reached. overburden from each cut is placed in the previous cut after removal of the coal. Operation in this manner advances in much the same way as in plowing a farm field (Cassidy, 1973, p. 386). A typical section view for this operation appears in Figure 7, which shows a horizontal section of a mine plan to mine the Wadge coal seam, the uppermost coal seam (about 8 ft thick) that occurs in some portions of Routt County, Colorado (L. G. Shearer, 1975, Peabody Coal Company, Denver, Colorado, personal communication). The upper portion of Figure 7 shows a section of a surface-mine pit looking from the highwall toward the regraded spoil. At the left end of
41 17% . ·nal surface 16'1!. - - - - - - ons~------ . ------ Smut and wadQeSeam Soft Coal Typical 18Ction parallel to pits Original Surface 25% , /' ' . . r: , Typical 18Ction perpendicular to pits FIGURE 7 Typical cross sections of a surface-mine operation in Routt County, Colorado. (Source: Peabody Coal Company.) the cut the depth of the coal eventually reaches a level beyond which it is uneconomical to dig. The lower portion of Figure 7 is perpendicular to the cut. The difference between the dashed line (representing the spoil as overburden is removed from above the coal and cast into empty cuts where coal has already been extracted) and the upper solid line (representing the original surface) indicates the large amount of grading that is required to meet the standards for restoration in Part 816.102 of the 1977 Surface Mining Control and Reclamation Act (Office of the Federal Register, 19781 U.S. Congress, 1977). Figure 8 is an artist's concept of the overall operation of a surface mine. Portions of a railroad loop and coal loading layout appear near the upper left (1). Area (2) is where topsoil has been removed and set aside for later replacement on the regraded spoil. Area (3) is a bench from which the dragline will cast the underlying overburden into the adjacent cut where coal has been removed. Haul roads (4), connecting inclines (5), and topsoil storage areas (6) are shown. A fully reclaimed area (7), where vegetation has already been re-established, is now self-sustaining. A somewhat rougher area in the regrading reclamation plan (8) has been left deliberately to serve as wildlife habitat and cover. Figure 9 is an aerial view of a coal mine that is planned and operated according to the scheme depicted in Figures 7 and 8. At the extreme left of Figure 9 is an unmined area with vegetation, a few large rock formations (which will be avoided in future mine progress), gently rolling topography, and a natural drainage channel near the top of the photo. Running vertically through the center of the photo is a strip where topsoil has been removed. In the center of the photo, a dragline
42 FIGURE 8 Artist's concept of a surface-mine operation. (Source: After P. Schirmer, du Quoin, Illinois.) can be seen removing interburden (earth material lying between two coal seams) and casting it toward the right. Actual coal extraction is occurring immediately below the dragline in the darkest strip in the photo. Partially graded spoil appears in a vertical line to the right of the dragline. Completely graded spoil occurs on the right third of the photo. Inclines run across the graded spoil into the cut. This area is ready for reseeding at the next available planting season. At the extreme right of the photo, some fully reclaimed areas are partially visible (top right). Figure 10 shows a dragline in operation on an interburden bench; it is casting spoil to its right. In other coal provinces or where the terrain is hilly, contour mining prevails. Contour mining commences where the coal bed and surface elevations coincide and proceeds along the outcrop of the coal bed. overburden from the first cut is commonly hauled to a nearby mine pit. A second cut, and any subsequent cuts, may be made and overburden placed in earlier cuts as described above. In such instances, the cuts parallel the contact between the coal bed and the surface of the ground, unlike the plowing procedure illustrated in Figure 7. overburden removal by dragline or shovel mandates transfer into adjacent, open cuts. Use of bucket-wheel excavators, or other equipment using conveyor handling of dug overburden, permits moving the spoil material considerable distances from the active cut. If such an
44 I FIGURE 10 Dragline on an interburden bench casting spoil to its right. potentials exists, which may cause dissolution and migration of trace elements in this zone. Migration of and altered chemical forms of traci elements in this zone are not believed to be consequential, but this fact suggests the need for further research on the environmenta1 impact of mining. Investigations of this impact will be conducted as a result of the environmental regulations mentioned earlier (U.S. Congress, 1977). In all coal provinces, most coal beds are drilled and blasted to fracture them for easier loading. The practices and explosives used ar similar to those described for overburden removal. Coal extraction in surface mine is almost exclusively accomplished by small shovels cbucke capacity up to about 30 ml). The universal practice is to haul coa.1 away from the active pit in trucks. Drainage Water Control Rain falling upslope of a surface mining area will be diverted by ditches around the active mining areas but will rejoin the naturai downslope drainage pattern. Standard practice is to design the di~chei: -
45 to handle a 50-year flood (the maximum flood expected in a 50-year period). Streams that normally flow at <5 ft 3 /s (<0.14 ml/s) will also be diverted around the mining area. Streams that normally flow at greater volumetric rates are usually left undisturbed and the mine designed around them. Runoff water resulting from precipitation directly onto the active mining area joins groundwater seeping into the mine. Groundwater seepage occurs from the highwall, the pit ends, and, to a lesser extent, the spoil side of the pit. Such water is collected in sumps and pumped to settling ponds, where it is treated as necessary to conform to the National Pollutant Discharge Elimination System (NPDES) [Federal Water Pollution Control Act, Amendments of 1972, Public Law 92-500 (U.S. Congress, 1972)] prior to release to the natural downslope drainage pattern. UNDERGROUND MINING Coal Extraction In an underground mine, some digging operations are required, such as shaft construction, that produce rock but not coal. This ordinary mine rock generally must be brought to and handled on the surface. Further, some roof and floor rocks are extracted with the coal during mining underground to assure maximum coal recovery. A crushing, grinding, and screening operation at the mine separates most of the roof-and-floor rock from the coal. This roe~ is generally disposed of with the other rock produced at the mine, commonly to piles on or near the mine site, or it is used for roadfill and building low dams for water impoundments. The volume of rock thus affected, with its trace-element loading, is small in comparison with the volume of rock similarly disturbed in a surface-mine operation. This waste rock, however, may contain some waste coal. If it does, such waste is heaped into piles, and drainage from upslope is diverted around them. They are covered with earth and the sides of the piles may be further sealed with clay. Covering and sealing prevent spontaneous combustion of waste coal that may be present. Rolling and compacting the ends and sides reduce erosion and slumping, which might otherwise expose waste coal. Subsidence Subsidence commonly occurs following coal extraction by underground mining. In a few places, subsidence occurs relatively soon, as a result of controlled roof collapse, during long-wall mining. In other places, as in some old mining areas, subsidences may continue for several decades after mining has ceased. In some mines, the floors of underground mines heave upward, thereby reducing the amount of subsidence, but subsidence, in some degree, occurs above practically all underground coal mines. As controlled roof caving occurs, subsiding rock fills the void left from coal extraction with less dense material. Subsequently, additional overlying material, but with less volume, settles into the void left in
46 collapse of the immediate roof. This sequence repeats. As the effect propagates to the surface, broken rock gradually fills the void. This generally accepted picture of how subsidence occurs produces at least one significant result with respect to the impact on trace elements from coal extraction from an underground mine, that is, the reduced density of the geologic zone immediately above the extracted coal. The reduced density results in greater porosity and therefore greater surface area of solid exposed to groundwater. The consequence is a greater potential for dissolution and then migration of trace elements in the immediate environment of the mine. As in the case of surface mining discussed above, this phenomenon bears further investigation to determine its quantitative effects on trace elements as a result of coal extraction. These investigations will be conducted in the future because of environmental factors reporting required by current regulations governing coal mining. Groundwater Control Dewatering of underground mines requires collection of mine water in a sump and pumping it to settling basins (which now commonly include water treatment), either outside the mine or in abandoned workings. The pumping of mine water to mined-out areas is possible in relatively dry mines, and such action may serve eventually to recharge aquifers. In new mines with water passing through undisturbed earth, the effects of this operation on the redistribution of trace elements may be no more significant than from a well in an undisturbed area. On the other hand, if seepage eventually occurs from old workings to surface streams, the effect is about the same as the pumping of such water to surface settlement basins, with the added leachates from any earth filling in the old works. The effects of this latter process on trace-element redistribution appear similar to those of subsidence. Acid Mine Drainage Trace elements from acid mine drainage (AMD) may be mobilized into subsurface water systems, lakes, and streams. In the late 1960's, AMD was especially serious in the eastern half of the country, where over 10,500 miles of waterways were being degraded by acid drainage and 200,000 acres of land became barren or infertile because of refuse disposal and acid runoff (Ohio Basin Regional Federal Water Pollution Control Administration, 1969). By 1977, these figures were reduced to 5700 miles (nearly half of the waterway mileage) and to only tens of thousands of acres of land (Kendrick, 1977). Today, AMD is primarily effluent from abandoned underground mines. A survey in Appalachia indicated that inactive underground mines contributed 52 percent of the total acid drainage in the region; active underground mines contributed 19 percent. The acid drainage may continue to flow from inactive mines as long as air, water, and sulfide materials are available. The areas most seriously affected are those where mining has been extensive and where pyritic materials are abundantly exposed to oxidation. Western coals generally contain small
47 amounts of pyritic materials, so wastes are usually nonacidic (Ohio Basin Regional Federal Water Pollution Control Administration, 19691 Wewerka et al., 1976b). The burgeoning use of coal is not expected to reverse this favorable trend in controlling AMO because current regulations applicable nationally do not allow degradation of existing, receiving-water quality. The Surface Mining Control and Reclamation Act of 1977 on 91 Stat. 488 (U.S. Congress, 1977) specifically prohibits discharge of water from a mine that does not meet local stream water- quali ty standards. Thus, governmental regulations have greatly reduced the possibility of increased AMO. The iron sulfide minerals, pyrite and marcasite, exposed to air produce ferrous sulfate and sulfuric acid. The oxidation of one molecular weight of pyrite (FeS 2 ) ultimately leads to the release of two molecular weights of sulfuric acid. Secondary reactions of sulfuric acid with minerals and organic compounds produce concentrations of a wide variety of elements in the drainage that may persist long after acidity has been neutralized. The AMO control methods fall into two categories: those directed at preventing the formation of AMO and those that treat AMO after it has formed. Although these methods are usually concerned more with reducing acidity than with reducing metal concentrations, concentrations of many metals are correspondingly reduced as the solution pH is raised above neutrality. Techniques for controlling air and water influx--such as compacting or sealing the wastes, grading and covering the wastes with soil, and burying the wastes in underground or strip mines--reduce the levels of dissolved or suspended trace metals in the runoff. Neutralization of wastewaters with alkaline agents, including limestone, lime, and caustic soda, is the moat widespread treatment method, with some 300 plants operating in the United States. These treatments are designed primarily to treat acidity1 only those ions, such as iron and aluminum, and certain trace elements whose solubilities are sensitive to pH in the acid to neutral range will be removed by the alkaline neutralization process. The solubilities of other ions, such as calcium, magnesium, sodium, potassium, and sulfate, are not highly dependent on solution pH (Wewerka et al., 1976a) and will not be reduced1 they may even be increased. Methods of treating AMO using ion exchange, reverse osmosis, flash distillation, and dissolved ions, which have been developed, are not currently used on a wide scale commercially. The sludges produced by ion-exchange methods appear to be easier to dewater than those produced by alkaline neutralization, but the methods are limited in application to drainage with medium- to low-level solids (<1000 ppm). Surface mines may also be sources of AMO, though much less so than underground mines. Inactive surface mines contributed 11 percent of the AMO in the Appalachia inventory, and active surface mines contributed 1 percent (Ohio Basin Regional Federal Water Pollution Control Administration, 1969).
48 RECLAMATION Overburden and Soil After grading of the overburden, topsoil is replaced on the area. The topsoil may originate either from storage or from immediate salvage. The topsoil is smoothed by grading also. At this point the area is ready for revegetation at next planting season. The first step in reclamation is the development of a plan for postmining land use. In the western coal provinces, the typical postmining land use is currently rangeland and wildlife habitat. To a lesser extent, water storage and recreational uses are intended. In other coal provinces, however, a combination of crop production, pasture and rangeland, wildlife habitat, and recreational area is typically negotiated among several community groups. The specific combination of uses dictates the overall objective of the spoil-grading plan and influences the redistribution of trace elements therein. Reclamation of spoil to produce pasture or rangeland for grazing can be accomplished with less grading than for crop production. Coamonly, ponds are included in reclamation plans based on pasture uses for domestic-animal water supplies. Topsoil is also replaced and smoothed over the graded spoil. Reclamation to produce wildlife habitat requires rougher terrain in the spoil. These rougher areas approximate natural draws or gullies and thereby provide protection from visibility for wildlife. Location of such draws will coincide with spoil drainage channels so that water supply to vegetation is assured, further protecting wildlife by additional cover, as well as providing food. The extent of grading required to provide recreational areas depends on the type of recreational use intended. Rougher terrain suits camping and hiking1 smoother terrain must be produced for park-like areas. Large water impoundments may be included and stocked with game fish. Postmining Spoil and Overburden Drainage Final or initial cuts can serve the useful purpose of surface water storage. In this case, the edge of the coal seam at the base of a "highwall" is covered by impermeable sediment to prevent direct contact between the coal and the stored water. Exchange between the stored water and the coal seam is only through the groundwater regime. Where upslope runoff or spoil-area runoff is directed to these catch basins, they serve the subsidiary, useful purpose of sediment entrapment. Grading of the spoil must create channelization of runoff to the area planned for water impoundments. Knowledge of groundwater production and movement in the area and of local precipitation patterns is necessary to plan a grading pattern for this purpose. To maximize retention of runoff water as aquifer recharge, grading must create a series of smaller catchment basins. Catchment basins are smaller and shallower than impoundments. Wide distribution of such catchment basins encourages percolation of collected runoff into the groundwater regime. Acid- or toxic-producing materials occurring in the
49 spoil are buried deeply to avoid contact with runoff water. Exclusion of water contact can be through burial under (or within) an impervious material such as clay in Title 30, CFR 211.40(a)(l) (Office of the Federal Register, 1978; U.S. Congress, 1976, 1977). Refuse and Waste Disposal Reclamation in coal mining includes disposal of refuse and waste from mining. Refuse is generated from ancillary processes, which may accompany coal extraction, such as crushing, sizing, and washing (i.e., coal preparation). In addition, office, shop, and maintenance areas generate waste. Coal preparation produces a slurry composed of finely ground coal and inorganic minerals in the coal, such as quartz and pyrite. Typically, this slurry is pumped to settling basins where solids are retained and the clarified water is discharged if or when it conforms to NPDES regulations [Federal Water Pollution Control Act Amendments of 1972 (FWPCA) Public Law 92-500 (U.S. Congress, 1972)). As slurry settling basins become filled with sediment, they are drained and covered with natural earth material from the surrounding terrain. Slopes on the burial areas (shown in cross-sectional view in Figure 11) are compacted with rollers. The mining process, apart from overburden removal, coal extraction, and coal preparation, also produces wastes that must be handled. In a surface mine, these wastes result from cleaning the top of an exposed coal seam before the coal is removed. Extraneous rock and coal refuse are scraped from the top of the seam with a bulldozer and pushed into the adjacent pit; this material is then covered with spoil as the excavation machine makes its next cut to remove the overburden. This material is relocated vertically and horizontally by only a matter of meters but is broken up in the process. The included trace elements are exposed to a new microenvironment just as in the case for overburden and topsoil. T COMPACTED CLAY (6+-ml ( 15-34m) SLURRY SOLIDS FIGURE 11 Cross section of buried slurry settling basin.
so Final Abandonment By the time of final abandonment, the area of active surface mininq should be completely reclaimed to the state of a self-sustaininq ecosystem. Structures are demolished or removed for reuse elsewhere. Waste materials from abandonment of facilities are disposed of in a manner similar to a sanitary landfill. Once they are buried in the sanitary landfill, reveqetation proceeds by seedinq, plantinq, fertilizinq, and irriqation, as necessary. Compacted areas are scarified, soil amendments are added as necessary, and seedinq re- establishes veqetative cover. Other alternative land uses may dictate continued use of certain of the access roads or facilities. In this case, continued concern for redistribution of trace elements in the environment passes from mininq to new uses of such facilities. Reveqetation Processes Some trace elements are undoubtedly redistributed as a result of steps taken to reveqetate areas disturbed by mininq. New or different sources and amounts of trace elements are made available to veqetation, and their potential beneficial or detrimental effects should be assessed throuqh controlled environmental or aqricultural studies on test plots on reclaimed land with careful sequential chemical analysis of product qrowth. Disturbed areas include not only reqraded areas of actual surface mininq but also areas at abandoned mines where facilities and haul roads and/or access roads are removed. Such disturbed areas also include areas at underqround mines where surface use was required durinq operation of the mine. Dissolution of trace elements by percolatinq surface water or qroundwater makes them available to uptake by veqetation. The siqnificance of trace-element uptake by veqetation depends on the type of veqetation and the intended use of the veqetation. The role of the veqetation from reclaimed areas in the human food chain is a further factor influencinq this siqnificance. Reclamation plans for mininq areas do not always call for reveqetation because some reclaimed areas may be used as urban or industrial sites. However, most reclaimed areas are to be used as aqricultural or recreational areas. Redistribution of trace elements as a result of reveqetation on aqricultural or recreational areas qenerally beqins with the increased availability of trace elements to the new veqetation because of soil and rock disturbance. Dissolved salts of trace elements in the soil are subject to uptake by veqetation throuqh the depth of root penetration, which will vary with different types of veqetation; rarely will such a depth be qreater than 20 ft (6 m). Where veqetation is not removed from the site throuqh aqricultural crop harvestinq, further redistribution of trace elements will be limited to airborne scatterinq of dead and dried veqetation. This redistribution would be minor in comparison with redistribution throuqh aqricultural crop harvestinq. A crop such as hay, corn, or other similar veqetation would be harvested, removed from the site with its component trace elements, and fed to livestock or people. In any case,
51 man is at the end of this food chain, and his inqestion of the trace elements removed from the mine site is of ultimate concern. Veqetation on the reclaimed site also may serve as a food source for wildlife, and the wildlife, in turn, may be eaten by manr for example, deer or antelope may eat the veqetation and then be consumed by man. The maqnitude of this redistribution of trace elements from the mine site would probably be small in comparison with consumption of veqetation by livestock and thereby introduction into man's diet. REDISTRIBUTION OF TRACE ELEMENTS IN MINING Trace elements that occur in coal will be removed from their in situ location, transported to a coal preparation site, and thence to the site of coal utilization. Topsoil handlinq, overburden removal and replacement, coal extraction, reveqetation, and subsidence may influence trace-element redistribution. Redistribution can occur throuqh one or more of the followinq processes: ⢠Physical relocation. ⢠Mechanical breakup (fraqmentation) of previously consolidated material that increases the surface area of rock so the rock and minerals are more exposed to weatherinq and subsequent possible trace- element mobility. ⢠Major chanqe in porosity and permeability of rock material, with a consequent increase in the rate and amount of water that moves throuqh near-surface aquifers. ⢠Chanqe from chemically reducinq conditions to oxidizinq conditions, which alter the solubility by conversion to the oxidized forms of the trace elements. ⢠Oxidation of pyrite and release of acid, thereby enhancinq solubility and mobilization of trace elements. All of these processes may influence the availability of trace elements to the biota. Each of the mininq phases produces a new microenvironment for the trace elements. The creation of this new microenvironment is the sinqle most important factor influencinq redistribution of trace elements in the mine environment. This section addresses the potential means for redistribution of trace elements in the environment as a result of mininq. First, there is a simple relocation of the trace elements in situ in native soil by topsoil salvaqe, overburden removal, and reclamation. Several subprocesses involved in this part of coal mininq are identified. There is, in qeneral, inadequate information available to evaluate the importance of these subprocesses individually. Additional empirical and theoretical evaluation of the contribution of each subprocess to the overall redistribution of trace elements is required. The new microenvironment results in part from juxtaposition of strata that were not so located before mininq. New information about the potential contribution to redistribution from the new microenvironment is needed. The phases of mininq described cause chanqes in the environment of tl:e miner these mobilization processes can redistribute trace elements.
52 Topsoil Handlinq The replacement of topsoil from salvaqe site or active mininq site to qraded spoil is, in itself, a redistribution of intrinsic concentrations of trace elements. The topsoil may be picked to remove stones above a certain diameter, say 15 cm. Pickinq of stones and their burial in the mine pit are a secondary-level redistribution of intrinsic concentrations of trace elements. The deqree of consolidation, or density, of replaced topsoil will be less than that of in-place topsoil. Further, the chemical and physical nature of subsoil on which the topsoil is placed may be different from that at its oriqinal site. Because of the slope, the exposure to the sun may also be different. Finally, the moisture conditions may be changed in the topsoil as a result of both surface water and qroundwater chanqes. Salvaqed topsoil that is placed in storaqe can be leached of some trace elements. The factors that affect leachinq from stored topsoil include: ⢠qeometry of the storaqe pile, ⢠amount of precipitation, ⢠rate of precipitation, ⢠chemical nature of precipitation, ⢠availability of qroundwater below the pile, ⢠drainaqe away from the pile, and ⢠lenqth of time in storaqe. The qeometry of a topsoil storaqe pile affects absorbency and the percolation of the precipitation fallinq on it. Conically shaped piles reduce absorbency and thereby percolation of runoff water into the pile. Where the qeometry of the pile presents more surface area to runoff water, it follows that absorbency would be increased. Trace elements can also be transferred from topsoil storaqe durinq wind erosion associated with dust blown away from the stored topsoil. Normal practice in the mininq industry now is to contrc! such dust by sprayinq the surface of storaqe areas with water until temporary veqetation can be established to hold the surface soil in place. Overburden Removal and Replacement At most surface mines, spoil piles are qraded to a qently rollinq contour. The qradinq operation relocates trace elements occurrinq in the oriqinal overburden. This relocation is a minor effect, as is overburden removal, compared to the potential and actual redistribution of trace elements by oxidation and water-solubilization processes occurrinq at the microenvironmental levels. In any method of overburden removal, the density of the spoil will be less than that in the overburden. The qeneral rule is that overburden will swell by approximately 20 percent. Thus, as the density decreases with swell, the surface area per unit of volume of the overburden, or spoil, increases. As the surface area increases, the potential for oxidation and redistribution of trace elements from the spoil also increases.
53 The decreased density in spoil may chanqe the mode by which water moves throuqh the space oriqinally occupied by overburden. Water moves more readily by percolation throuqh the qreater porosity (resultinq from decreased density) of the spoil than throuqh in situ overburden. More particle surfaces of spoil are in direct contact with the percolatinq water, hence the potential for redistribution of trace elements is further enhanced. Actual redistribution of trace elements will depend not only on the chemical nature of the overburden but also on the chemical nature of the qroundwater. The principal mechanism for redistribution of trace elements in a mininq environment is thouqht to be dissolution of their salts from the spoil, followed by miqration of the trace elements via qroundwater. The primary phenomena that cause redistribution of trace elements via qroundwater are the solubility of the trace-element salts and their movement with the qroundwater (Bird et al., 1960). The qroundwater may seep out of the area and add to downslope drainaqe and flow. Such downslope drainaqe miqht eventually contribute to drinkinq-water supplies for either man or livestock. In either case, the trace elements carried from the mine site by qroundwater seepaqe eventually may be consumed by man, livestock, or wildlife as drinkinq water. Dissolution of trace-element salts in qroundwater permeatinq the spoil depends on the chemical nature of the qroundwater. The definition of this relationship throuqh an application of well-known thermodynamic and kinetic principles and data in available reports miqht assist the mininq industry in predictinq the concentration of trace-element salts in qroundwater seepinq out of the mine area. The interdependence of overburden characteristics, the availability and composition of qroundwater as a transport medium, and the method of overburden removal and replacement make the analysis of potential redistribution of trace elements a site-specific problem. HEALTH EFFECTS Occupational Health Inhalation of coal dust and concomitant trace-metal exposure from surface mininq have not been shown to be hazardous. The U.S. Public Health Service surveyed 1438 surface coal miners to determine the prevalence of Coal Workers' Pnewnoconiosis (CWP), chronic bronchitis, and ventilatory impairment. Four percent of miners showed some x-ray evidence of CWP, but all had previously worked in underqround mines over prolonged periods. The study concluded that employment in surface mines was not likely to cause CWP or clinically siqnif icant respiratory impairment (Fairman et al., 1977). There is, however, some current concern reqarding possible detrimental effects from exposure to exhaust fumes and noise qenerated by the heavy equipment used in surface coal mininq. Possible effects from these exposures are now under study by several federally funded projects. Coal Workers' Pnewnoconiosis is a well-recoqnized hazard of underqround coal mining. The multiple respiratory disorders associated with CWP vary in prevalence and severity accordinq to geoqraphic area, deqree of occupational exposure, and apparent individual susceptibility
54 (Naeye, 1972). Study of 1455 bituminous coal workers from six mines revealed a 47 percent prevalence of x-ray evidence of CWP and a 2.4 percent prevalence of proqressive massive fibrosis (PMF), as compared with 60 percent and 14 percent prevalence rates of CWP and PMF, respectively, for 518 anthracite miners from two anthracite mines (Morqan et al., 1972). The National Coal Board followed 4122 coal mine-face workers at 20 collieries, relatinq total dust concentration and mineral content of dust to x-ray evidence of CWP and proqression to PMF and to lunq patholoqy at autopsy (Davis et al., 19771 Walton et al., 1977). The amount of total dust exposure was the most siqnif icant factor in determininq probability of proqression to PMF. Mineral content was a lesser factor, but the probability of proqression appeared to fall with increasinq mineral content. Mineral content in this study was predominantly quartz. The authors suqqested that the apparent fall in toxicity of the dust with increasinq mineral content miqht alternatively be explained by a diminishinq effect of coal of decreasinq rank (Walton et al., 1977). Several CWP-related disorders lead to pulmonary fibrosis. In some cases the fibrosis is clearly related to mine dust1 in others the pathoqenesis is unclear. There is extensive literature documentinq the toxicity and fibroqenecity of free silica on cells in culture, and the silica content of miners' lunqs is directly related to the collagen content of the macules and nodules (Naeye, 19721 Waqner, 1972). Certain trace elements could act as factors or cofactors in fibroqenesis. A lonq-ranqe study of lunq tissue from deceased bituminous coal miners from West Virqinia compared metal concentrations between miners and nonminers and examined the relationship of total dust, free silica, and trace-metal concentrations to severity of CWP (Sweet et al., 1974). The concentrations of iron, nickel, titanium, and vanadium in miners' lunqs were markedly hiqher than in lunqs of lonq- term residents (nonminers) of the same county as the miners. The miner:nonminer concentration ratios were 2:1 for iron, 4:1 for nickel, 4.5:1 for titanium, and 4:1 for vanadium. A statistical test for trends in classification means (Duncan's multiple ranqe test) indicated a continuously increasinq trend in the means of maqnesium, beryllium, vanadium, free silica, and coal dust with increasinq deqrees of lunq damaqe. There was no relationship between the severity of CWP and means of chromium, copper, iron, manqanese, nickel, titanium, zinc, and noncoal dust. An analysis of variance indicated that vanaditim was more stronqly associated with CWP than either beryllium or maqnesium. Compositional differences have been found between the characteristic areas of heavy and liqht piqmentation of pneumoconiotic lunqs. Bismuth, maqnesium, manqanese, and qermanium were more concentrated in the areas of heavily piqmented tissue from two pneumoconiotic lunqs than in the liqhtly piqmented tissue (Sweet et al., 1978). An earlier report showed that only silica and vanadium, but not coal dust, total dust, iron, nickel, lead, zinc, manqanese, beryllium, titanium, copper, maqnesium, or chromium, were siqnificantly more concentrated in hilar lymph nodes than in lunqs (Carlberq et al., 1971). Silica was found to be more concentrated by a factor of 3.6, and vanadium by a factor of 1.63. These findinqs suqqest that vanadium is present in an insoluble, stable form.
55 Vanadium in coal is present not only in inorganic forms but also in vanadyl porphyrin chelates (stable five- and six-member rings) associated completely with the organic fraction of coal. The toxicity via the inhalation pathway of this form of vanadium is not known, although vanadium pentoxide is severely irritating to the mucous membranes of the eyes, nose, throat, and respiratory tract (Waters, 1977). While there is clearly enrichment of certain minerals and elements in the lungs, cause and effect are difficult to determine. The differential enrichment may be a result of differential retention caused by the disease, rather than a cofactor in causing the disease (Davis et al. I 1977) o It may be that incidence of CWP and PMF is determined partly by susceptibility in the miners. Heise et al. (1977) showed that the relative risk of PMF was approximately 300 percent less in miners who possessed antigen Wl8 than in those lacking this antigen. The predominant radionuclide emission from coal mining is radon, released into the air during exposure of the seam and breakup of the coal. A survey of the presence of 222Rn and 220Rn daughters in the range of 0 to 0.3 working levels in 223 operating mines in 15 states concluded that there was no apparent occupational health hazard from inhalation of the ambient levels of zzzRn or zzoRn daughters (Rock et al. I 1975) ⢠Public Health Acid mine drainage (AMD) can adversely affect water supplies. Effects may include increased acidity, discoloration, and increased concentrations of iron, manganese, silt, coal fines, and sulfates. The high acidity and increased corrosiveness might interfere with water treatment processes, such as coagulation and softening, although the mineral content can usually be reduced by additional treatment. The direct public-health effects of increased metal concentrations in drinking water are unclear, especially as only a small fraction of the daily intake of elements reaches the human body through drinking water (Table 12), as the amounts reaching man via bioaccumulation through the food chain and relative uptakes from various sources have not been quantified. Surveys by the EPA Effluent Guidelines Division have confirmed the presence of several organic petroleum and solvent types of compounds in drainage water affected by mining operations. The pollutants, among which are several suspect carcinogens, are believed to originate in equipment-servicing operations. Research on coal, trace elements, and mortality is being attempted by Kagey et al. (1978) to determine whether the identity and geographic distribution of dissolved trace elements in water can be correlated with epidemiological data. Trace-element air emissions from surface mining result from diesel- fuel combustion and windblown coal fines. The regional emissions are low, ranging from l0-2 ton/yr to lo-⢠ton/yr for various metals (Appendix C). Strip mining is most prevalent in the Northern Plains and the Southwest, but the public health risks are attenuated by the low population densities in these areas.
56 a TABLE 12 Total Daily Intakes of Various Elements from Food and Water Average Proportion of Total Intake from Water Intake from Intake from Water Median Maximum Food and Median Maximum Element (mg/day) (mg/day) Water (mg/day) (percent) (percent) Essential Calcium 52 100 800 6.5 11.8 Magnesium 12.5 40 210 5.9 16.8 Sodium 24 100 4400 0.5 2.2 Potassium 3.2 10 3300 0.09 0.3 Vanadium <0.008 0.02 2 0.6 1.0 Chromium 0.001 0.01 0.1 1.0 9.2 Manganese 0.01 o.~ 3 0.3 6.3 Iron 0.09 0.3 15 0.6 2.0 Cobalt 0.006 0.01 0.3 2.0 3.3 Nickel 0.005 0.02 0.4 1. 3 4.8 Copper 0.02 0.2 2.5 0.8 7.5 Zinc 0.5 2.1 13 3.8 14.4 Selenium <0.02 0.15 <13.3 Fluorine 0.4 1.0 1.8 22.2 41. 7 Molybdenum 0.003 0.02 0.34 0.9 5.6 Nonessential Silicon 14.2 60 <20 <71.0 <90.0 Aluminum 0.1 1.0 45 0.2 2.2 Barium 0.09 0.76 1.24 7.3 39.8 Strontium 0.22 1.0 2 11.0 40.0 Boron 0.06 0.2 1.0 6.0 17.5 Bismuth Trace 0.002 Beryllium Trace 0.00001 Antimony Trace <1.0 Lead 0.007 0.02 0.41 1. 7 4.7 Lithium 0.004 0.1 2.0 0.2 4.7 Silver 0.0005 0.001 0.07 0.7 1.4 Tin 0.002 0.005 4.0 0.05 0.1 Titanium <0.003 0.0 0.3 0.1 3.2 Uranium 0.0003 0.004 1.4 0.02 0.3 Cadmium 0.005 0.04 0.07 7.1 38.1 asources: Schroeder (1973) and Berry and Wallace (1974). Comprehensive studies of radionuclides in coal mine drainage have not been undertaken, but some measurements have been reported (Caldwell et al., 1970). Gross alpha levels up to 180 pCi/liter were found in the Kiskiminetas River of Pennsylvania. Radioactivity was predominantly from 234U and z31u.
