The Industrial Green Game. 1997. Pp. 165–181.
Washington, DC: National Academy Press.
Environmental Strategies in the Mining Industry: One Company's Experience
PRESTON S. CHIARO
''Mining" probably conjures several images. One familiar scene is of the old West, where prospectors blast the sides of mountains, tunnel through the earth, or pan at a river's edge for gold. Another is of environmental impacts of acid mine drainage from older mines that did not benefit from modern technology and management practices. The common view of mining is of environmental degradation. Few individuals outside the industry are aware of modern mining practices and associated business, environmental, and public policy issues (highlighted in Appendix A) or of how mining companies are responding to today's environmental challenges.
The extraction of ore from underground or surface mines is but one stage in a complicated and time-consuming process of producing minerals. A mine is born through exploration and mine development. This is followed by mining and beneficiation, and ends with mine closure and rehabilitation. A mining company must undertake all mining activities to be viable and competitive. It must adhere to a comprehensive set of rules of regulations.
Most states have comprehensive environmental regulations for the mining industry. Federal regulations aimed directly at the mining industry have not yet been put into a place, but broad-based statutes such as the Clean Water Act, Clean Air Act, National Environmental Policy Act, and numerous others apply to mining activities. Further, the federal government has been addressing the cleanup of historic mine wastes through its Comprehensive Environmental Response, Compensation,
and Liability Act (CERCLA, otherwise known as Superfund). More recently, the U.S. Environmental Protection Agency (EPA) has used CERCLA to address active mining operations. There is no evidence that this attention from the general public or the regulators will diminish, and mining companies in the United States can expect an ever-increasing level of scrutiny and control over their operations.
Proper concern and regard for the environment is one of the fundamental elements of any successful business strategy. Given the increasing level of attention to environmental issues in the mining business, it is even more critical today, as illustrated by the experience of Kennecott Corporation. Kennecott Corporation—a wholly owned subsidiary of RTZ, PLC, the largest mining company in the world—manages mining operations and exploration activities across North America, including several low-sulfur coal mines in the Powder River Basin, precious metals mines in the Southeastern and Western United States, and copper mines in Wisconsin and Utah. Kennecott is best known for its Bingham Canyon copper mine near Salt Lake City, which generates one-sixth of the total U.S. copper production. Kennecott's environmental strategy is based on an environmental policy that builds from a foundation of compliance with the legal, regulatory, and consent requirements of the countries and localities in which it operates. The firm's environmental policy attempts to strike a balance between society's need for metals and an environmentally sound approach to operations.
In general, the company's environmental policy dictates that its operations go beyond simply meeting current regulatory standards. The operations must exemplify best contemporary practice for the minimization and, where feasible, elimination of adverse environmental effects. The company does so by
incorporating environmental matters as a basic part of short- and long-range planning for all projects and operations;
complying with all applicable environmental laws, regulations, and prescribed standards and criteria, and ensuring that its contractors do likewise;
participating in the development of environmental legislation;
promoting and, where feasible, implementing new or more effective practices for environmental protection, compliance, and emergency response;
taking reasonable measures to ensure that Kennecott operations are responsive to the environmental needs of the communities in which they operate; and
regularly reporting Kennecott's performance on environmental matters through the Board of Directors to RTZ, PLC, Kennecott's parent corporation based in London.
Kennecott's environmental policy is administered by the vice president of environmental affairs whose responsibilities, with the cooperation and support of the other departments within the company, are the following:
Review, approve, and monitor all environmental management and emergency response programs
Assess, coordinate, and monitor the environmental aspects of Kennecott's projects and operations for uniform and consistent compliance with current and anticipated laws, regulations, and standards
Direct environmental planning for and investigations of proposed projects and investments
Direct or review and approve, as appropriate, the preparation of all environmental studies and documentation for all operations, permits, and licenses
Evaluate applicable developments in environmental technology and waste-management practices, and provide technical assistance and guidance for management of environmental programs at each operation
Monitor and assess trends in environmental legislation and regulation and, where appropriate, actively represent Kennecott's interests
In conjunction with each operation or project, develop and implement community relations programs that provide open, timely, and responsive communication on environmental programs
Inform and advise Kennecott management on environmental compliance and performance and the technical and economic implications of environmental programs and developments
Develop and maintain a continuing education and training program in environmental matters for all staff
The managers of all operations, projects, or activities are responsible for carrying out this policy in accordance with the direction and guidance of the vice president of environmental affairs.
KENNECOTT UTAH COPPER
As the flagship of Kennecott's operations, Kennecott Utah Copper (KUC) provides as good example of this environmental strategy in action in a large mining operation. KUC occupies over 92,000 acres in the Oquirrh Mountains just west of Salt Lake City. Operations include the Bingham Canyon Mine, the Copperton and North Concentrators, the Magna Tailings Impoundment, the Garfield Smelter and Refinery, the Utah Power Plant, and miscellaneous support facilities (Figure 1 ). KUC produces over 300,000 tons of copper, 500,000 ounces
of gold, and 4 million ounces of silver annually with a gross market value exceeding $800 million. KUC is in the midst of a major modernization program representing an investment of nearly $2 billion. When complete, the program will ensure that KUC remains one of the world's cleanest and most efficient copper producers well into the next century. Environmental considerations are an integral part of the modernization program. In addition to designing modernized operating facilities to achieve very high levels of operating efficiency and environmental control, the modernization program includes the cleanup of historic waste sites.
Accompanying the modernization program are routine efforts to improve environmental performance in many areas, such as employee and community education, hazard elimination (e.g., elimination of underground storage tanks and polychlorinated biphenyl compounds), substitution of environmentally sound products (e.g., detergents for chlorinated solvent cleaning solutions), and extensive waste-minimization and recycling efforts. In all areas, Kennecott is attempting to stay ahead of the regulatory agencies in determining the pace and priorities of the cleanup program.
Bingham Canyon Mine and Concentrators
The first $400 million component of the modernization program, completed in 1988, included in-pit ore crushing and new grinding and flotation facilities north of Copperton near the mouth of Bingham Canyon. Transportation improvements included a 5-mile ore conveyor system and the installation of three pipelines to replace the outdated railroad ore and waste rock haulage system. The project incorporated some of the largest state-of-the-art crushing, conveying, grinding, flotation, and filtration equipment available in the industry. In 1992, the first stage of the modernization program was supplemented with the construction of the fourth grinding line at Copperton. Along with several other improvements, this program represented an additional investment of over $200 million.
The modernization of the Bingham Canyon Mine allows KUC to produce nearly 152,000 tons of ore per day. An equivalent amount of waste rock is removed from the mine each day. Ore and waste rock are transported within the pit to the adjacent waste rock disposal areas by haul trucks with capacities as large as 240 tons. About 80 percent of the ore is hauled to the in-pit crusher and then conveyed to the Copperton Concentration for grinding and flotation. The remaining ore is loaded on rail cars for transport to the older North Concentrator. Tailings (the sandy residue left after metals are stripped from ore) are delivered by gravity pipeline from the Copperton Concentrator to a 5,700-acre storage impoundment located 12 miles to the north along the shore of the Great Salt Lake. Concentrate slurry is piped nearly 18 miles from Copperton to the Garfield Smelter.
The modernization program at the mine and concentrators improves environmental performance primarily by making the operations among the most efficient in the world. In this regard, the modernization represents as win-win situation in which operating considerations are entirely compatible with environmental protection and improvement. Such energy-efficient operations achieve the highly desirable goal of both direct and indirect pollution prevention. Water conservation and recycling were designed as integral parts of the modernization effort. As plans move forward for developing additional tailings storage capacity, environmental considerations are playing a major role in site identification, selection, and design, and the acquisition of permits for the sites.
Garfield Smelter and Refinery
In March 1992, Kennecott announced plans to complete the modernization of its operating facilities with the construction of state-of-the-art smelting and refining facilities. This component of the modernization program represents an investment of $880 million, making it the largest private investment ever undertaken in Utah. The most dramatic environmental improvement will come with the reduction of sulfur dioxide emissions from the current level of about 3,700
pounds per hour to 200 pounds per hour. Of the sulfur contained in the concentrate feed, 99.9 percent will be captured, compared with the current, very respectable capture efficiency of about 93 percent. This translates to a sulfur dioxide emission rate of about 6 pounds per ton of copper produced, which is lower than the world's cleanest smelters now operating in Japan. These improvements will be achieved even though the smelting capacity will nearly double, enabling the modernized smelter to handle all of the concentrate produced from the Bingham Canyon Mine.
Water usage will be reduced fourfold through an extensive recycling program. Pollution prevention, workplace safety and hygiene, and waste minimization are being incorporated into all aspects of the design. The smelter will generate 85 percent of its own electrical energy through steam recovery from the furnace gases and emission-control equipment, eliminating the need to burn additional fossil fuel to provide power. The new facility will require only 25 percent of the electrical power and natural gas now used to produced copper.
The refinery modernization will improve plantwide efficiency, including energy efficiency. For example, the existing direct-current electrical system will be replaced by motor-generator sets with high-capacity solid state rectifiers. An ion exchange system will be added to control impurities, and the precious-metals refinery will be replaced with a simpler, faster hydrometallurgical process. The materials handling system will be updated to simplify and mechanize the flow of work.
Waste generated from the existing smelting and refining process consists of weak acid from smelter off-gas scrubbing, flue dust, and electrolyte bleed from the refinery. All of these materials will be processed in a new hydrometallurical plant to recover valuable products, thereby maximizing resource recovery while minimizing the amount of waste that will require off-site disposal. The existing wastewater treatment plant and sludge storage ponds will become obsolete and will be reclaimed. The smelter modernization program also includes plans to segregate storm water from process waters, reducing water management problems and once again allowing the natural storm flows drainages above the smelter to enter the Great Salt Lake.
HISTORIC WASTE SITE CLEANUP
The KUC property has a long history of mining activities dating to the 1860s, when the first lead, zinc, silver, and gold mining began in Bingham Canyon. Because the level of attention given to environmental matters in those early periods was not as great as today, there is a legacy of historic waste sites at and around KUC. The historic waste sites are primarily contaminated with waste rock, tailings, sludges, and other mining waste products.
Kennecott is proceeding expeditiously to clean up these sites as part of the overall modernization effort. Through 1994, over $140 million will have been
spent to remedy problems at historic sites, and several of the cleanup efforts are among the largest such projects ever undertaken. At the same time, Kennecott is working closely with the EPA and State of Utah Department of Environmental Quality to use nontraditional regulatory frameworks to oversee these voluntary cleanup efforts.
One of the first facilities to be addressed was the leach-water handling system. Acidic metals bearing leach waters are collected at the base of the waste-rock disposal areas and are processed to recover the dissolved copper. The barren leach water is then returned to the top of the waste rock disposal areas, where it is applied to leach additional metals from the rock. In the early days of mining, this acidic leach water was simply allowed to flow down Bingham Creek. Reservoirs and holding basins were constructed in the early 1900s to begin to recover metals, and flow down Bingham Creek was terminated in the 1930s. Additional leach collection system improvements were made through the years, culminating in the construction of the Large Bingham Creek Reservoir in 1965. The reservoir held storm waters as well as leach waters. Although the base of this reservoir was constructed of low-permeability soils, it nevertheless contributed contaminants to the local groundwater system.
When Kennecott realized the seriousness of the groundwater problem, it constructed the Small Bingham Creek Reservoir to serve as the leach-water surge basin. The Small Bingham Creek Reservoir is a double-lined impoundment equipped with leak detection and groundwater monitoring systems. It was completed and placed in service in 1990 at a cost of $13.5 million. Utah issued a groundwater discharge permit for the Small Bingham Creek Reservoir in 1992.
Once the Small Bingham Creek Reservoir was placed in service, Kennecott began the cleanup of the Large Bingham Creek Reservoir. This project consisted of removing over 3 million cubic yards of sludges, tailings, and contaminated soils; segmenting and reshaping the basin; installing a state-of-the-art lining system; and upgrading the water-handling systems. The excavation work has been completed, and the sludge and tailings have been relocated to the Bingham Canyon Mine waste-rock disposal areas. The acid-contaminated soils were treated with locally obtained soils with a high calcium carbonate content, and the neutralized soils are being reused for reclamation efforts. The relocation and reclamation activities have been married with a demonstration project examining approaches to final reclamation of waste-rock disposal areas.
The Large Bingham Creek Reservoir has been divided into two major segments—zone 1 and zone 2—by construction of an intermediate dike. Zone 1 has been lined with compacted clay, a lower 60-mil high density polyethylene (HOPE) liner, a leak detection and collection layer, and an upper 80-mil HDPE liner. The liner system incorporates never-before-used electrically conductive layers for liner integrity inspection and leak detection. The sludge removal and lining projects collectively will cost in excess of $40 million.
Other improvements to the leach-water collection system include the construction
of improved cutoff walls to intercept surface and subsurface leach-water flow. Each of the 22 drainages leading from the waste-rock disposal areas is being carefully studied to ensure that the geohydrologic system is well understood. Then alluvium is stripped from the drainage at the base of the waste rock. Cutoff walls keyed into competent, low-permeability bedrock are constructed to capture leach waters. These leach waters are then collected in a series of pipes and lined canals for conveyance to the copper precipitation plant. The barren waters from the precipitation plant are returned to the waste-rock disposal areas. Kennecott is beginning to experiment with wetland systems to create passive treatment mechanisms to handle excess acid-contaminated waters. The cost of the improvements to the leach-water collection system will exceed $28 million.
Major cleanup projects are also under way in the Bingham Creek drainage downstream from the mouth of Bingham Canyon. During the lead-zinc-silver mining era of the 1800s, tailings containing high concentrations of lead and arsenic were discharged into Bingham Creek. These tailings washed down stream to the end of Bingham Creek in the center of Salt Lake Valley. Many areas along the lower reaches of Bingham Creek have now been developed to accommodate the growing population of the region, and resident now may come in direct contact with these tailings.
Although Kennecott did not generate these mine wastes, it owns much of the land along Bingham Creek on which the tailings reside, and the companies that generated the wastes are almost all defunct. Kennecott has undertaken several voluntary efforts to assist with the cleanup of these lead tailings, including the construction of a waste repository on its property to hold the tailings. The cleanup of Bingham Creek is continuing this year with the participation of Atlantic Richfield Company (ARCO), the only other viable responsible party. ARCO inherited liability for these tailings through their purchase of Anaconda. Kennecott and ARCO are sponsoring a health study in the Bingham Creek area to demonstrate that cleanup of very low levels of contamination are not necessary, given the low bioavailability of the lead in the tailings. The Bingham Creek lead tailings removal efforts will cost nearly $40 million.
Kennecott received an Earth Day award for the cleanup of waste-rock containing lead and arsenic from the Butterfield Creek drainage at the south end of KUC. This waste rock was generated during the construction by a now-defunct mining company of a drainage tunnel. Nearly 900,000 cubic yards of waste rock were placed along Butterfield Creek in unprotected areas and were actively eroding into the stream. Butterfield Creek is used for irrigation, and Butterfield Canyon is a popular recreational area for the public, so there was some cause for concern. Kennecott excavated the waste rock and relocated it to an engineered repository at the base of the Bingham Canyon Mine waste rock disposal area. The project also included the relocation of a roadway, the stream, and a natural-gas pipeline. The cost of the project approached $5 million. The project was completed, and Butterfield Canyon was restored to its natural condition.
Another environmental cleanup of historic wastes was completed in the Lark area, immediately east of the Bingham Canyon Mine. This project consisted of the relocation of over 1.7 million cubic yards of potentially acid-generating waste rock and the reclamation of nearly 600 acres of tailings deposits. The waste-rock was transported to the Bingham Canyon Mine waste rock disposal areas (behind the leach-water collection system). Tailings were sampled and "hot spots" containing high concentrations of lead were excavated and placed in an engineered, state-approved waste repository. The remainder of the tailings contain relatively low concentrations of metals and were reclaimed by capping with soils and revegetation. The Lark project also included removal of asbestos from buildings in the area as well as the demolition of derelict structures. The cost of the Lark-area work was nearly $15 million.
These and many other major and minor environmental cleanup projects at KUC are being conducted on an expedited basis by Kennecott in advance of any formal agreements with EPA or the State of Utah. Although there is a risk that Kennecott's responses to these environmental problems will not be acceptable to the regulators, Kennecott is proceeding as rapidly as possible to implement the solutions it believes are appropriate. In all cases, Kennecott informs the regulators before work begins and provides for regular inspections of the work by the regulators and stakeholders from the local communities. Kennecott has incorporated reasonable agency and stakeholder suggestions into the cleanup programs. On a practical level, Kennecott is proceeding so quickly that the agencies are having a hard time keeping up. For example, for several of the cleanup projects described above, work was well under way before legally enforceable administrative agreements were signed with EPA to oversee the work. Fortunately, EPA technical representatives were able to conduct site inspection even without legal agreements.
As mentioned above, an aggressive community relations program has been an integral part of the cleanup program. Kennecott has encouraged local community leaders, citizen groups, labor unions, professional organizations, environmental groups, and the regulators themselves to tour the operations and the cleanup projects to see the remarkable progress being made. This tour program has been very successful, and press coverage of the cleanup projects has been very positive. As another example of the success of the community relations program, public meetings held to discuss possible solutions to a groundwater contamination problem generated essentially no adverse publicity, and comments from the public about Kennecott's environmental approach were favorable.
Kennecott had been negotiating a ground-breaking legal agreement with EPA that would have governed the comprehensive cleanup program at Utah Copper. The agreement would have deferred EPA's consideration of listing the Utah Copper facility on the National Priorities (Superfund) List in exchange for Kennecott agreeing to do at least all of the work that would have been required had Utah Copper been listed. EPA recently elected to discontinue negotiations on this agreement
because several key legal terms remained unacceptable to Kennecott. EPA has now begun actions to place Kennecott on the Superfund list. Kennecott will resist this action and will simultaneously continue its waste cleanup activities. Good working relationships that have been established between Kennecott and EPA's technical representatives are expected to continue, even if an adversarial position develops over legal terms. The cleanup will be virtually complete by 1996, which is when the modernized smelter is expected to reach full production.
Mining, the Environment, and Public Policy
Roderick G. Eggert
Mineral production takes place in stages. Both the principal effects of mining on the environment and the important issues for public policy in this area are perhaps best introduced within the context of this production stages.
MINERAL EXPLORATION AND MINE DEVELOPMENT
Before a mineral deposit can be mined, it must be discovered and its economic and technical viability demonstrated, this is the exploration stage. The environmental disruption caused by exploration tends to be localized and minor. Most damage that does occur can be remediated relatively easily. During initial assessment of a region's geologic potential, explorationists rely heavily on satellite images, airborne geophysical surveys, and large-scale geologic maps to study large areas of land—hundreds or even thousands of square kilometers. Environmental impacts are essentially nil.
Explorationists then narrow the focus of their search to smaller, more promising
areas, involving perhaps several hundred square kilometers. Typical activities include geologic mapping, geochemical sampling, and surface geophysical surveying, which are carried out on the ground without large-scale equipment. Although the environment is affected by these activities, the impacts are minor.
Only in the subsequent, subsurface examination of still smaller areas is there any appreciable environmental impacts—from drilling, trenching (bulldozing a trench to examine near-surface rocks), and the associated road building to provide access for drill rigs and bulldozers. Such impacts can be mitigated, albeit at a cost, by reclaiming drill sites and trenches and by revegetating roads. In some instances, the need for roads in remote areas has been eliminated by using helicopters to deliver drilling equipment.
For every one hundred or so mineral deposits that are discovered and evaluated in detail during exploration, fewer than ten on average will be prepared for production during the second stage of mineral production, mine development. During development, mining companies design and construct mining and beneficiation facilities, arrange for financing, provide for infrastructure, and develop marketing strategies, among other activities. The environmental impacts of these activities are more significant than those resulting from exploration but much less than those of mineral production itself.
Two types of public policy are critical during mineral exploration and mine development. The first type of public policy consists of land use rules governing whether land is available for exploration and development. The second type, applicable on those lands available for mineral activities, consists of environmental rules governing permits, environmental impact assessments, and other preproduction activities and approvals that are necessary to proceed from exploration to mine development and mining—in short, the process of environmental compliance prior to mining.
Land-use rules are important because, before mining companies can undertake mineral exploration and development, they need access to prospective mineralized lands. To be sure, in situations where mineral rights are privately held, land access is gained through negotiation between interested private parties. But for most lands worldwide, mineral rights are held by governments.1
Explorers or miners typically gain access to these lands in one of three ways: negotiation with a government agency, competitive bidding, and—in a few cases, such as in the United States—claim staking (that is, claiming the right to explore on a first-come, first-served basis when lands are considered open for exploration unless they are specifically declared off-limits, such as for national parks or wilderness areas). Existing land-use policies have placed large tracts of land off-limits to mineral exploration and development in a number of countries, including Australia, Canada, and the United States. The desire to avoid the environmental damages of mining is an important reason behind these withdrawals of land from mineral activities.
Public policies in the second category, rules governing the preproduction process of complying with environmental rules, take a number of forms. The most
common are environmental permits and environmental impact assessments. Mining companies typically are required to obtain environmental permits signifying government approval of various aspects of their mine plans, including those for reclamation, waste disposal, sewage treatment, drinking water, and construction of dams and other impoundments. Companies also often have to carry out detailed assessments of the environmental impacts of proposed mineral development, which in turn are used by governments in deciding whether to permit mine development at all.
Environmental permits and assessments are important to mining companies because they increase the time, costs, and risks associated with bringing a mine into production. Costs may rise because of expenditures on permitting and environmental assessment and on implementing changes in project design that the compliance process may require. Risks rise, from the perspective of the firm prior to mining, in the sense that governments may decide not to allow mine development after companies have spent significant sums of money on exploration.
MINING AND BENEFICIATION
Once a mineral deposit has been discovered and developed, it is ready for the next stages in the production process: mining and beneficiation. During mining, metal-bearing rock called ore is extracted from underground or surface mines. Metal concentrations in ore vary greatly, from less than 1 percent by weight for most gold deposits to over 60 percent for some iron ore deposits; most metallic mineral deposits have ore grades in the range of 1–5 percent by weight. Beneficiation, sometimes called milling, usually occurs at the mine site. During this stage, ore is processed (or upgraded) into concentrates, which will be processed still further, usually in a smelter or refinery.
Mining and beneficiation can have a variety of environmental effects.2 The most visible effect probably is the sight of land disturbed by mining and waste disposal. The environmental damage is largely aesthetic.
To put the problem of potentially unsightly land into perspective, consider the study by Johnson and Paone (1982). They estimated that over the fifty-year period 1930–1980, only 0.25 percent of the total land area of the United States was used for surface mining, disposal of wastes from surface and underground mines, and disposal of wastes from mineral beneficiation and further processing. Coal mining represented about half of this land, with mining of nonmetallic minerals accounting for about two-fifths and of metallic minerals about one-tenth. Some 47 percent of the land affected by mining and waste disposal had been reclaimed. The figures of course would vary considerably from country to country, but the essential point is that only a relatively small amount of land is involved in mining and associated waste disposal. Mining activities use much less land than agricultural production, urban development, logging and forestry, and national parks and wilderness areas.
Mining and beneficiation account for significant fractions of the total amount of solid waste generated each year. Very crude estimates compiled by the United Nations Environment Programme (1991) indicate that mining activities, apparently in this case including oil and gas production and coal mining, account for about three-quarters of the solid wastes generated annually in Canada, one-third in the United States, one-tenth in the European Community, and one-twentieth in Japan. The substantial differences reflect differences in the size of the extractive industries relative to the total economies in these countries. More detailed data for the United States suggest that non-coal mining accounts for about one-seventh of the solid waste generated annually that is considered nonhazardous, while coal mining accounts for less than a hundredth of such wastes. Manufacturing, on the other hand, generates more than half of nonhazardous solid wastes (Office of Technology Assessment, 1992).
These volumes of waste, however, are not good proxies for the amount of actual environmental damage caused by mining and beneficiation. For this point to be clear, it is necessary to know more about the three important types of solid waste generated by mining and beneficiation. Overburden is soil and rock removed to gain access to a mineral deposit prior to surface mining. Waste rock is separated from ore during mining. Overburden and waste rock typically are deposited adjacent to a mine (or in a mine, in the case of waste rock from underground mining). Tailings are the fine waste particles that are produced during the beneficiation of ore and typically suspended in water. Tailings from surface mines usually are deposited in a tailings (or settling) pond, while those from underground mines are deposited in the mine itself. (In a few countries, tailings can be deposited directly into the environment.)
The amount of solid waste generated during mining and beneficiation essentially is determined by, first, the type of mine and, second, the ore grade, or concentration of metal in the rock that will be beneficiated. The type of mine is important because underground mines generate no overburden, and mining techniques are selective enough to extract ore with only small amounts of waste rock. Surface mines, on the other hand, usually generate more than twice as much overburden and waste rock as ore.
As an example, for underground copper, gold, silver, and uranium mines in the United States, the ratio of overburden and waste rock to ore, is on the order of 0.1:1 to 0.3:1. For surface mines, the ratios range from 2:1 to 10:1 on average (EPA,) 1985; based on data from the U.S. Bureau of Mines).
Ore grade, the second determinant, governs the quantity of tailings generated by a beneficiation plant. An operation with ore grading 1 percent by weight, for example, will generate ninety-nine pounds of tailings for every pound of metal, assuming complete metal recovery. Actual recovery rates usually range between 90 and 100 percent, resulting in somewhat smaller volumes of tailings.
By themselves, the solid wastes of metal mining and beneficiation would cause little environmental damage, except aesthetically. But when surface and
ground waters interact with these wastes, acid mine drainage can be created, and this is probably the most serious environmental problem of metal mining and beneficiation. When water interacts in an oxidizing environment with the sulfide minerals typical of most metal mines, sulfuric acid is created. Metals then are dissolved in the resulting acidic water. Acid mine drainage can contaminate drinking water and affect aquatic and plant life if it gets into surface or ground waters.
The nature and extent of actual environmental damage caused by solid mine wastes and, in turn, acid mine drainage vary enormously from case to case, depending on several factors. The type of mineral deposit being mined is important: sulfide-poor deposits, for example, generate less of the sulfur needed to create sulfuric acid than sulfide-rich deposits, and high-grade deposits will have fewer tailing per unit recovered metal than low-grade deposits. Mining and beneficiation techniques are important: underground mining, a noted above, creates much smaller volumes of waste per unit of metal than does surface mining, and the higher the recovery rate during beneficiation, the smaller the amount of tailings created. Climate is important: in arid regions, there is little of the water necessary to create acid mine drainage. Location and population density are important: acid mine drainage that enters streams feeding into sources of human drinking water not only destroys fish and wildlife habitats, but also damages human health. Finally, the environmental management practices of mining companies are important: waste piles that are revegetated or in some other way sealed, for example, are much less likely to be accessible to the water necessary to create sulfuric acid.
Other environmental problems may be associated with mental mining and beneficiation. Another type of water contamination is waste-water from beneficiation plants, which may contain ore material. heavy metals, thiosalts, and chemical reagents used in beneficiation. Air pollution is limited largely to airborne dust. Underground mining may lead subsidence. (A major area not dealt with in this excerpts is the working environment, that is, worker health and safety; readers interested in this issue are referred to Section 11 of Hartman, 1992.)
The key issues for environmental policy affecting ongoing mining and beneficiation are for the most part the same as those affecting other economic activities: What should be the standards for environmental quality and how should they be determined? What policy tools—for example, direct regulation or economic incentives—are best suited for meeting these standards? How should rules be enforced?
Two aspects of mining and beneficiation noted above, however, bear on these more general questions. First, the extent to which the amount of solid waste generated from mining and beneficiation can be reduced has significant limits. Low-grade ores by their very nature are going to generate large volumes of tailings overlying soil and rock to get to the ore. This is not a call for complacency; rather, it suggests that efforts and policies should be aimed a those aspects
of environmental degradation over which miners have some control. Examples include efforts to recycle chemical reagents used in beneficiation, to place or seal waste piles so they are less exposed to the water necessary for acid formation, and to reduce the chances that tailings ponds will leak into surrounding soil and groundwater. Moreover improvements are encouraged, both in beneficiation techniques to increase rates of metal recovery and in mining techniques to the amount of overburden and waste rock extracted along with metallic ores.
Second, the amount of solid waste generated during mining and beneficiation is not good indicator of the actual amount of environment damage caused by these activities. The same mineral deposit or mine in different circumstances may generate the same amount of waste but cause substantially different amounts of environmental damage because of differences in climate, population density, or one of the other factors noted earlier. The implication for public policy is that rules need to be flexible to account for site differences among mines and beneficiation facilities.
MINE CLOSURE AND REHABILITATION
A mine eventually reaches the end of its useful life, either because it physically depletes its ore or because conditions become unfavorable (costs rise or mineral prices fall). When this happens, mine closure and rehabilitation (or reclamation) occur. Underground mines typically are sealed or plugged. Surface mines, as well as waste sites for both underground and surface mines, are rehabilitated. Pits and waste piles have slopes stabilized and may revegetated. In some cases, acid mine drainage continues even after mining stops, requiring some type of drainage control.
The precise nature of mine closure and rehabilitation varies from place to place because of different public policies and accepted industry practices. More fundamentally, closure and rehabilitation activities vary because potential damages from closed mines vary considerably for all the reasons cited earlier, such as type of mine, climate, and proximity to population centers.
Key issues for public policy in this area are: the rehabilitation requirements; the mechanism for ensuring that appropriate closure and rehabilitation procedures are followed; and the nature of postmining liability. The rehabilitation requirements often are only vaguely defined: for example, mined land must be returned to a ''usable condition," to a "stable condition," to the "greatest degree." or equal to the level of highest previous use" (Intarapravich and Clark, 1994). Moreover, economic considerations often seem to get short shrift when rehabilitation standards are being determined; the result can be standards levels for which the costs of rehabilitation exceed the associated benefits. Barnes and Cox (1992), for example, discuss the apparent "goldplating" of rehabilitation requirements in Australia.
The most common mechanism for ensuring that appropriate procedures are followed is reclamation bond or fund. With a reclamation bond, mining companies put money into escrow account or in some other way set aside money as a guarantee that they will perform the required reclamation work. The only way for a company to get the money back is to perform the required work. A critical issue for public is the size of the bond: high enough to ensure that mine operators actually perform the required work rather than simply forfeit the bonded money, but not so high as to discourage mining.
The nature of postmining liability is perhaps the most controversial issue affecting mine closure and rehabilitation. Subsidence and contaminated mine water are the most common sources of postmining damages for which companies may be required to pay fines or compensation. That companies should be liable for damages caused by nonprudent, negligent, and illegal activities is not controversial. But public policies sometimes define liabilities more broadly. In some cases, a company can held responsible for damages caused by subsidence and polluted mine water, even if it acted prudently and within existing laws and regulations or was only partially responsible for the damages. A company sometimes can be held responsible for damages retroactively, following changes in laws and regulations. These broader aspects of liability are designed to encourage companies to go beyond simple compliance with existing regulations. But such broad liability has been criticized for being unfair and for discouraging investment in mining activities.
Barnes, P., and A. Cox. 1992. Mine rehabilitation: An economic perspective on a technical activity. Pp. 149–158 in Rehabilitate Victoria: Advances in Mine Environmental Planning and Rehabilitation. Proceedings of the Australian Institute of Mining and Metallurgy Conference. Publication Series No. 11/92.
Hartman, H.L., ed. 1992. SME Mining Engineering Handbook. 2d ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration.
Intarapravich, D., and A. L. Clark. 1994. Performance guarantee schemes in the minerals industry:The case of Thailand. Resources Policy 20 (March):59–69.
Johnson, W., and J. Paone. 1982. Land Utilization and Reclamation in the Mining Industry, 1930–1980. Bureau of Mines Information Circular 9962. Washington, D.C.: U.S. Department of Interior, Bureau of Mines.
Office of Technology Assessment. 1992. Managing Industrial Solid Wastes from Manufacturing,Mining, Oil and Gas Production, and Utility Coat Combustion: Background Paper. OTA-BP-O-82. Washington, D.C.: U.S. Government Printing Office.
United Nations Environment Programme. 1991. Environmental Aspects of Selected Nonferrous Metals (Cu, Ni, Pb, Zn, Au) Ore Mining. A Technical Guide. UNEP/IEPAC technical report series no. 5. Paris: United Nations Environment Programme.
U.S. Environmental Protection Agency. 1985. Office of Solid Waste and Emergency Response. Report to Congress: Wastes from the Extraction and Beneficiation of Metallic Ores, Phosphate, Asbestos, Overburden from Uranium Mining, and Oil Shale. EPA/530-SW-85-033. Washington, D.C.: U.S. Government Printing Office.