EPA/530//R-95/043

NTIS/PB96/109/103

BACKGROUND FOR NEPA REVIEWERS:

NON-COAL MINING OPERATIONS

December 1994

U.S. Environmental Protection Agency

Office of Solid Waste

Special Waste Branch

401 M Street, SW

Washington, DC 20460

Disclaimer and Acknowledgements

This document was prepared by the U.S. Environmental Protection Agency (EPA). The mention of company or product names is not to be considered an endorsement by the U.S. Government or by the EPA.

This Technical Document consists of nine sections. The first is EPA's overview of mining and the statutory and regulatory background. That is followed by a description of mining activities and their potential environmental impacts. The remaining sections cover specific environmental concerns, environmental monitoring, and pollution prevention. Also provided are a list of contacts, glossary, and references. This report was distributed for review to the U.S. Department of the Interior's Bureau of Mines, Bureau of Land Management, and National Park Service; the U.S. Department of Agriculture's Forest Service; Western Governors Association; and other industry and public interest groups.

The use of the terms "extraction," "beneficiation," and "mineral processing" is not intended to classify any waste stream for the purposes of regulatory interpretation or application. Rather, these terms are used in the context of common industry terminology.

TABLE OF CONTENTS

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LIST OF EXHIBITS

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LIST OF TABLES

CHAPTER I

INTRODUCTION

The primary purpose of this document is to assist Federal and state officials in providing scoping comments on National Environmental Policy Act (NEPA) documents for non-coal mining activities proposed on Federal lands. Pursuant to NEPA and Section 309 of the Clean Air Act, EPA reviews and comments on environmental impact statements (EISs) prepared for proposed major Federal agency actions significantly affecting the quality of the human environment. This document is constructed to assist the Federal or State reviewer in considering those issues most appropriate to a specific type of mining operation in the development of NEPA/Section 309 comments.

This document is not intended to be all-inclusive. Rather, it focusses on EPA's major concerns with surface water and groundwater, air, and sensitive receptors. This document does not restate traditional NEPA concerns about impacts on floodplains, endangered species, and wetlands since they may occur at any development. Further, the document does not discuss human health risks associated with mining practices, since such risks are site-specific. The document is intended to address all major non-coal mining sectors, including gold and silver, phosphate, and base metals (lead, zinc, copper, tin, and mercury). In addition, key terms are defined in both a technical and regulatory context. For example, the term "beneficiation" has a codified regulatory definition which differs from the definition used in the industry.

The document is organized to provide a general description of site operations, potential environmental impacts, possible prevention/mitigation measures, and the types of questions that should be asked in reviewing a proposed mining operation. Mines and mining operations are designed and operated to account for very site-specific conditions. Therefore, site-specific environmental consequences may result. Thus, the reviewer may have to conduct additional analyses to understand projected impacts more completely.

Mining operations consist of excavation (extraction in pits, underground mine workings) to remove ore; beneficiation units, such as mills, for upgrading or concentrating ore; and processing facilities for further purification of the metal from the concentrate. Not all of these activities are necessarily conducted at every mine site.

Generally, mines have extraction units that are pits or underground workings, and beneficiation units that are used to crush and size ore and concentrate or separate the valuable minerals from the less valuable material. Mining operations may also maintain processing units on-site, such as smelters and/or refineries that are used to refine or process the mineral into the desired mineral product. In addition, mining sites maintain units to manage wastes generated during their operations. Mining operations generate extremely large quantities of wastes. Overburden and waste rock are the non-liquid wastes generated in largest volumes by extraction activities; tailings and spent ore are generated by beneficiation; and slag is generated through processing.

Surface and underground mining are the two most common types of mining conducted; however, there are two other types of mining, placer and in situ. Surface mining methods most commonly employed for the extraction of metals are known as "open-pit" and "open-cut." Placer mining (including dredging) is used to mine and concentrate surficial sands and gravels. Underground mining techniques use adits and shafts for access and a variety of mining methods. Although surface and underground mines usually operate independently, underground techniques may be used before or after surface methods are employed. In situ mining involves the use of solvents (lixiviants) such as water, acids, or alkalies that are injected into an undisturbed ore body to leach and remove the valuable minerals. Major wastes generated by extraction include waste rock and mine water (if it is discharged).

Beneficiation procedures are used to increase the percentage of the desired mineral in the concentrate by separating the metal-bearing minerals from the non-valuable gangue (tailings). The separation is based on one or more differences between the mineral and the rest of the mined material, such as density or chemical nature. Wastes generated from beneficiation operations include tailings, spent lixiviant, excess process water, and spent ore (a form of tailings produced by leaching). Tailings ponds or piles are created as disposal sites for tailings. Spent ore is often left in piles and spent lixiviant may be recycled or neutralized and land-applied on-site.

Mineral processing of ores may also be conducted at the mine site (or at off-site locations). Processing operations often follow beneficiation operations and include techniques that change the chemical makeup of the ore or mineral, such as chemical digestion, electrolytic refining, and pyrometallurgical/thermal processes (roasting or smelting) in order to produce actual metal. Unlike extraction and beneficiation, ore processing generally produces wastes that bear little or no resemblance to the materials that enter the operation.

Mining operations are subject to a wide range of Federal, state, and local requirements. Many of these require permits before the mining operations commence, while some require approvals or consultations, mandate the submission of various reports, and/or establish specific prohibitions or performance-based standards. The following sections describe the purposes and broad goals of major Federal statutes. The discussion for each statute also provides an overview of the requirements and programs that are implemented by the respective implementing agencies.

The objective of the Clean Water Act (CWA)(33 U.S.C. §§ 1251-1376) is to "restore and maintain the chemical, physical, and biological integrity of the Nation's waters" (§101(a)). This is to be accomplished through the control of both point and nonpoint sources of pollution (§101(a)(7)). A number of interrelated provisions of the Act establish the structure by which the goals of the Act are to be achieved. Within this overall structure, a variety of Federal and State programs are implemented to meet the Act's requirements.

Under §303, states are responsible for establishing water quality standards for waters under their jurisdictions: these are the beneficial uses that various waters are to support and the numeric (and narrative) criteria that must be achieved to allow these uses to be met. Water quality standards serve as a basis both for identifying waters that do not meet their designated uses and for developing effluent limits in permitted discharges. EPA also establishes nonbinding numeric water quality criteria as guidance; when states fail to adopt sufficient water quality standards, EPA may do so.

Under §402 of the Act, all point source discharges of pollutants to navigable waters of the United States must be permitted under the National Pollutant Discharge Elimination System (NPDES). The term "point source" means "any discernible, confined, and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged" (CWA §502(14)). Effluent limits in NPDES permits may be either technology- or water quality-based. For various categories of industries, EPA establishes National technology-based effluent limitation guidelines pursuant to §§301, 306, and 307. More stringent water quality-based permit limits may be established when technology-based limits do not result in achievement of water quality standards. Additionally, states may establish effluent limits based on a "non-degradation" principle which does not allow for the receiving stream to be degraded from previously existing conditions.

EPA's NPDES regulations (40 CFR 122.21(l)) require prospective dischargers (in states without an approved NPDES program) to submit information to the EPA Region, prior to beginning on-site construction. Review of this information allows EPA to make a determination as to whether the facility is a new source. The Region must then issue a public notice of the determination. If the facility is determined to be a new source, the issuance of the NPDES permit by EPA is subject to NEPA and the applicant and EPA must comply with the environmental review requirements of 40 CFR Part 6 Subpart F.

EPA has established National technology-based effluent limitation guidelines for ore mining and dressing operations (40 CFR Part 440). These include new source performance standards based on the Best Available Demonstrated Technology (BADT), since new plants can install the best and most efficient production processes and wastewater treatment technologies. In general, the effluent limitations address mine drainage and mill discharges. Exhibit 1-1 provides examples of point source discharges that are subject to mine drainage and mill discharge limits (and examples of those that are subject to storm water permitting).

§402(p)(2)(B) (added by the Water Quality Act of 1987) required that point source discharges of storm water associated with industrial activity be permitted by October 1, 1992. Pursuant to this requirement, EPA's storm water program requires that all point source discharges of storm water associated with industrial activity, including storm water discharges from mining activity, be permitted under the NPDES program. "Storm water" is defined at 40 CFR 122.26(b)(13) as "storm water runoff, snow melt runoff, and surface runoff and drainage." "Storm water associated with industrial activity" is defined at §122.26(b)(14) as "the discharge from any conveyance which is used for collecting and conveying storm water and which is directly related to manufacturing, processing, or raw materials storage areas at an industrial plant . . . ." It also includes discharges from "areas where industrial activity has taken place in the past and significant materials remain and are exposed to storm water." There are no New Source Performance Standards for storm water discharges, so the issuance of an NPDES permit for storm water discharges (or the coverage by an existing permit of a new or previously unpermitted discharge) may not trigger NEPA.

§404 of the Clean Water Act addresses the placement of dredged or fill material into waters of the U.S. and has become the principal tool in the preservation of wetland ecosystems. "Jurisdictional wetlands" are those subject to regulation under §404. Jurisdictional wetlands are those that meet the criteria defined in the 1987 Corps of Engineers Wetlands Delineation Manual (USACE, 1987). Regulatory authority for §404 is divided between the Army Corps of Engineers (Corps) and EPA. §404(a) establishes the requirement for the Corps to issue permits for discharges of dredged or fill materials into waters of the United States at specific disposal sites. Disposal sites are to be specified for each permit using the §404(b)(1) guidelines; the guidelines were established by EPA in conjunction with the Corps. Further, §404(c) gives EPA the authority to veto any of the permits issued by the Corps under §404. In practice, EPA rarely exercises its veto power as it typically reviews and provides comments on §404 permits prior to their issuance, and any disputes are resolved at that time.

The Clean Air Act (CAA) (42 U.S.C. §§7401-7626) requires EPA to develop ambient air quality standards as well as standards for hazardous air pollutants. The Act also imposes strict performance standards applicable to new or modified sources of air pollution, a stringent approval process for new sources of pollution in both attainment and non-attainment areas, and emission controls on motor vehicles.

Under §109, EPA has established national primary and secondary ambient air quality standards for six "criteria" pollutants. These are known as the National Ambient Air Quality Standards (NAAQSs). The NAAQSs set maximum concentrations in ambient air for lead, nitrogen oxides, sulfur dioxide, carbon monoxide, suspended particulate matter of less than 10 microns in diameter, and ozone. States and local authorities have the responsibility for bringing their regions into compliance with NAAQSs or more stringent standards they may adopt. This is accomplished through the development and implementation of State Implementation Plans (SIPs), which are EPA-approved plans that set forth the pollution control requirements applicable to the various sources addressed by each SIP.

Under §111, EPA has promulgated New Source Performance Standards (NSPSs) applicable to metallic mineral-processing plants (40 CFR Part 60, Subpart LL). A processing plant is defined as "any combination of equipment that produces metallic mineral concentrates from ore; metallic mineral processing commences with the mining of the ore." However, all underground processing facilities are exempt from the NSPSs. Also, NSPS particulate emission concentration standards apply only to stack emissions.

In addition to the NSPSs, Prevention of Significant Deterioration (PSD) provisions are intended to ensure that NAAQS are not exceeded in those areas that are in attainment for NAAQSs. Under this program, new sources are subject to extensive study requirements if they will emit (after controls are applied) specified quantities of certain pollutants.

State programs to meet or exceed Federal NAAQSs are generally maintained through permit programs that limit the release of airborne pollutants from industrial and land-disturbing activities. Fugitive dust emissions from mining activities may be regulated through these permit programs (usually by requiring dust suppression management activities).

As indicated above, only six criteria pollutants are currently regulated by NAAQSs. Several other pollutants are regulated under National Emission Standards for Hazardous Air Pollutants (NESHAPs). NESHAPs address health concerns that are considered too localized to be included under the scope of NAAQSs. Prior to the passage of the Clean Air Act Amendments of 1990, EPA had promulgated NESHAPs for seven pollutants: arsenic, asbestos, benzene, beryllium, mercury, vinyl chloride, and radionuclides (40 CFR Part 61).

The CAA Amendments of 1990 substantially revised the existing statutory provisions of the CAA. The Amendments require that states develop air emission permit programs for major sources (these will supplement SIPs) and dramatically expand the air toxics (i.e., NESHAPs) program to address 189 specific compounds. Under the Amendments, Congress required EPA to establish stringent, technology-based standards for a variety of hazardous air pollutants, including cyanide compounds. In November 1993, EPA published a list of source categories and a schedule for setting standards for the selected sources. Among the mining-related industry groups that have been identified as sources of hazardous air pollutants are the ferrous and non-ferrous metals processing industries, and the minerals products processing industry (58 FR 63952; 12/3/93). Under the amended air toxics program, if a source emits more than 10 tons per year of a single hazardous air pollutant or more than 25 tons per year of a combination of hazardous air pollutants, the source is considered a "major source." Major sources are required to use the Maximum Available Control Technology (MACT) to control the release of the pollutants (CAA §112). The CAA Amendments also intensify the requirements applicable to nonattainment areas.

The Solid Waste Disposal Act was amended in 1976 with the passage of the Resource Conservation and Recovery Act (RCRA)(42 U.S.C. §§6901-6992k). Under Subtitle C of RCRA, EPA has established requirements for managing hazardous wastes from their generation through storage, transportation, treatment, and ultimate disposal. Hazardous wastes include specific wastes that are listed as such under 40 CFR §261 Subpart D as well as other wastes that exhibit one or more EPA-defined "characteristics," i.e., reactivity, corrosivity, ignitability, and toxicity. Other solid wastes (which can be solid, liquid, or gaseous) that are not hazardous wastes are subject to Subtitle D, under which EPA establishes criteria for State management programs, approves State programs, and can provide funding for State implementation. EPA has promulgated specific criteria for municipal solid wastes and more general criteria for all nonhazardous solid wastes.

The scope of RCRA as it applies to mining waste was amended in 1980 when Congress passed the Bevill Amendment, RCRA §3001(b)(3)(A). The Bevill Amendment states that "solid waste from the extraction, beneficiation, and processing of ores and minerals" is excluded from the definition of hazardous waste under Subtitle C of RCRA (40 CFR §261.4(b)(7)). The exemption was conditional upon EPA's completion of studies required by RCRA §8002(f) and (p) on the environmental and health consequences of the disposal and use of these wastes. EPA then conducted separate studies of extraction and beneficiation wastes and mineral processing wastes (including smelting and refining wastes). EPA submitted the results of the first study in the 1985 Report to Congress: Wastes from the Extraction and Beneficiation of Metallic Ores, Phosphate Rock, Asbestos, Overburden From Uranium Mining, and Oil Shale (EPA, 1985b). In July 1986, EPA made a regulatory determination that regulation of extraction and beneficiation wastes as hazardous wastes under Subtitle C was not warranted (51 FR 24496; July 3, 1986).

EPA reported its findings on mineral processing wastes from the studies required by the Bevill Amendment in the 1990 Report to Congress: Special Wastes From Mineral Processing (EPA, 1990). This report covered 20 specific mineral processing wastes. In June 1991, EPA issued a regulatory determination (56 FR 27300; June 13, 1990) stating that regulation of these 20 mineral processing wastes as hazardous wastes under RCRA Subtitle C is inappropriate or infeasible. Eighteen of the wastes are subject to applicable State requirements. The remaining two wastes (phosphogypsum and phosphoric acid process waste water) are currently being evaluated by EPA. Five additional types of wastes are listed as hazardous wastes and must be managed as such; other than these and the 20 wastes exempted in 1991, mineral processing wastes are subject to regulation as hazardous waste if they exhibit one or more hazardous waste characteristics.

EPA interprets the exclusion from hazardous waste regulation to encompass only those wastes that are uniquely associated with the extraction and beneficiation of ores and minerals. Thus, the exclusion does not apply to wastes that may be generated at a mine site but that are not uniquely associated with mining. For example, waste solvents are listed as a hazardous waste under 40 CFR §261.31 (Hazardous Wastes from Nonspecific Sources); they are generated at mining sites as a result of cleaning metals parts. Because this activity (and this waste) is not uniquely associated with extraction and beneficiation operations, such solvents must be managed as any other hazardous wastes, subject to the Federal requirements in 40 CFR Parts 260 through 271, or State requirements if the State is authorized to implement the RCRA Subtitle C program. In practice, most mine sites generate relatively modest quantities of hazardous wastes.

The Endangered Species Act (ESA) (16 U.S.C. §§1531-1544) provides a means whereby ecosystems supporting threatened or endangered species may be conserved as well as a program for the conservation of such species. Section 7 of the ESA requires Federal agencies to ensure that all Federally associated activities within the United States do not have adverse impacts on the continued existence of threatened or endangered species or on critical habitat that are important in conserving those species. Agencies undertaking a Federal action must consult with the U.S. Fish and Wildlife Service (USFWS), which maintains current lists of species that have been designated as threatened or endangered, to determine the potential impacts a project may have on protected species. The National Marine Fisheries Service undertakes the consultation function for marine and anadromous fish species while the USFWS is responsible for terrestrial (and avian), wetland and fresh-water species.

The USFWS has established a system of informal and formal consultation procedures; these must be undertaken as appropriate in preparing an EA or EIS. Many states also have programs to identify and protect threatened or endangered species other than Federally listed species. An EIS must be prepared if "any major part of a new source will have significant adverse effect on the habitat" of a Federally or state-listed threatened or endangered species (40 CFR 6.605(3)). If a Federally listed threatened or endangered species may be located within the project area and/or may be affected by the project, a detailed endangered species assessment (Biological Assessment) may be prepared independently or concurrently with the EIS and included as an appendix. States may have similar requirements for detailed biological assessments as well.

Where mining activities involve a proposed Federal action or Federally assisted undertaking, or require a license from a Federal or independent agency, and such activities affect any district, site, building, structure, or object that is included in or eligible for inclusion in the National Register of Historic Places, the agency or licensee must afford the Advisory Council on Historic Preservation a reasonable opportunity to comment with regard to the undertaking. Such agencies or licensees are also obligated to consult with state and Native American Historic Preservation Officers responsible for implementing approved state programs.

As provided for in 40 CFR 6.605(b)(4), issuance of a new source NPDES permit that will have "significant direct and adverse effect on a property listed in or eligible for listing in the National Register of Historic Places" triggers the preparation of an EIS. Many proposed mining operations are located in areas where mining has occurred in the past. Particularly in the west, states and localities are viewing the artifacts of past mining (e.g., headframes, mill buildings, even waste rock piles) as valuable evidence of their heritage. Since modern mining operations can damage remnants of historic operations, care must be taken to identify valuable cultural resources and mitigate unavoidable impacts.

The Mining Law of 1872 (30 U.S.C. §§22-54) establishes the conditions under which citizens of the United States can explore and purchase mineral deposits and occupy and purchase the lands on which such claims are located. The basic provision of the law provides that:

The Mining Law establishes the basic standards for the location, recording, and patenting of mining claims. In general, persons are authorized to enter Federal lands and establish or locate a claim to a valuable mineral deposit (originally, nearly all minerals but now a much more restricted number, as described below). Once a claim has been properly located (and, since 1976, recorded with BLM), the claimant gains a possessory right to the land for purposes of mineral development and thereafter retains the claim if small amounts of development work are done or small fees are paid. Upon proving that a valuable mineral deposit has been discovered, claim holders may patent the claim and purchase the land for nominal sums. Except as specifically authorized by law (e.g., certain inholdings), land management agencies have no further jurisdiction over patented lands. Mining claims, whether patented or not, are fully recognized private interests that may be traded or sold. The possessory interest is considered private property subject to Fifth Amendment protection against takings by the United States without just compensation. The standards set in the Mining Law may be supplemented by local law not in conflict with the Mining Law or State law.

Over time, various laws have restricted the minerals that are subject to location under the Mining Law; restrictions were generally not retroactive but were subject to valid existing rights. "Locatable" minerals subject to location of claims under the Mining Law now include most metallic minerals (except uranium) and some nonmetallic minerals. In addition, certain Federal lands have been or may be closed to mineral development, subject to valid existing rights (these include the National Parks and National Monuments, among other lands). In addition, only "public domain" lands are generally open to mineral location under the Mining Law.

The Federal Land Policy Management Act (FLPMA) (43 U.S.C. §§1701-1782) provides the Bureau of Land Management (BLM) with authority for public land planning and management, and governs such disparate land use activities as range management, rights-of-way and other easements, withdrawals, exchanges, acquisitions, trespass, and many others. FLPMA declares it to be the policy of the United States to retain lands in public ownership (i.e., rather than "disposing" of the lands by transferring ownership to private parties) and to manage them for purposes of multiple use and sustained yield. Under §202, BLM must develop and maintain plans for the use of tracts or areas of the public lands. To the extent feasible, BLM must coordinate its land use planning with other Federal, State, and local agencies. BLM also must provide for compliance with "applicable" pollution control laws (including Federal and State air, water, and noise standards and implementation plans) in the development and revision of land use plans. The overall protective standard is provided in §302(b), under which BLM is to take any necessary action, including regulation, to prevent "unnecessary or undue degradation" of public lands. Subject to this and several more limited exceptions, nothing in FLPMA "shall in any way amend the Mining Law of 1872 or impair the rights of any locators of claims under that Act, including, but not limited to, rights of ingress and egress" (§302(b)).

BLM regulations (43 CFR Group 3800) impose a number of broad requirements upon operations on BLM-managed lands, but contain few specific technical standards. The basic compliance standard is that operations must be conducted so as to prevent unnecessary or undue degradation of the lands or their resources, including environmental resources and the mineral resources themselves. According to 43 CFR §3809.0-5(k), "unnecessary or undue degradation" means surface disturbance greater than what would normally result when an activity is being accomplished by a prudent operator in usual, customary, and proficient operations of similar character and taking into consideration the effects of operations on other resources and land uses, including those resources and uses outside the area of operations. Failure to initiate and complete reasonable mitigation measures, including reclamation of disturbed areas, may constitute unnecessary or undue degradation. Finally, failure to comply with applicable environmental protection statutes and regulations constitutes unnecessary and undue degradation.

BLM's implementing regulations pertaining to development of mining claims include three levels of review:

A plan of operations must describe in detail the site and the proposed operation, including measures that will be taken to prevent undue and unnecessary degradation and to reclaim the site to regulatory standards. Reclamation must include salvaging topsoil for later use, erosion and runoff control, toxic materials isolation and control, reshaping the area, reapplication of topsoil, and revegetation (where reasonably practical). BLM may require operators to furnish bonds (site-specific or blanket) or cash deposits, with the amount left to the responsible official (policy now calls for full reclamation bonding for cyanide and other chemical leaching operations, and a similar policy is anticipated to be issued for potentially acid-generating mines). Following approval of a plan of operation, BLM may monitor the operation to ensure that the approved plan is being followed. Failure to follow approved plans of operations, or to reclaim lands, may result in a notice of noncompliance, which in turn can lead to injunctive relief.

Plans of operations may be modified at BLM's request or at the operator's behest. Significant modifications follow the same review and approval procedures as original plans. Proposed plans of operations (and modifications) are reviewed by BLM "in the context of the requirement to prevent unnecessary and undue degradation and provide for reasonable reclamation" (§3809.1-6(a)).

Upon receipt of a proposed plan of operations (or modification), BLM must conduct an environmental assessment (or supplement). This EA is used to assess the adequacy of proposed mitigation measures and reclamation procedures to prevent unnecessary and undue degradation. The EA then leads to a Finding of No Significant Impact (with or without stipulations) or to the preparation of an EIS and Record of Decision. If the proposed operation is to be issued a new source NPDES permit and is in a State where EPA is the permitting authority, or in other cases where EPA has significant environmental concerns, EPA typically becomes a cooperating agency in the NEPA process. In any event, EPA has the opportunity to review all EISs pursuant to §309 of the Clean Air Act.

The National Park System Mining Regulation Act (also known as the Mining in the Parks Act, or MPA) (16 U.S.C. §§1901-1912) reconciles the recreational purpose of the National Park System with mining activities affecting park lands. The Act subjects mining activities within the National Park System to such regulations as deemed necessary by the Secretary of the Interior. It also required that all mining claims within the park system be recorded by September 1977, or become void.

The National Park Service has extensive regulations governing exercise of valid existing mineral rights (36 CFR Part 9 Subpart A). The regulations restrict water use, limit access, and require complete reclamation. They also require that operators obtain an access permit and approval of a plan of operations prior to beginning any activity. A plan of operations requires specific site and operations information, and may require the operator to submit a detailed environmental report. Operators must comply with any applicable Federal, State, and local laws or regulations.

The Organic Act of 1897 (16 U.S.C. §§473-482, 551) has governed the Forest Service's activities since the earliest days of National Forest management. The Act delegates broad authority over virtually all forms of use in the National Forest System. It also provides for continued State jurisdiction over National Forest lands. Finally, it declares that forests shall remain open to prospecting, location, and development under applicable laws, and that waters within the boundaries of the National Forests may be used for domestic mining and milling, among other uses.

The Multiple Use and Sustained Yield Act of 1960 (MUSYA) (16 U.S.C. §§528-531) established that the National Forest System is to be managed for outdoor recreation, range, timber, watershed, and fish and wildlife purposes, and that these purposes are supplemental to the purposes for which the National Forests were established as set forth in the Forest Service Organic Legislation (16 U.S.C. §§475, 477, 478, 481, 551). MUSYA provides that the renewable surface resources of the National Forests are to be administered for multiple use and sustained yield of products and services. Nothing in MUSYA is intended to affect the use or administration of the mineral resources of the National Forest lands (16 U.S.C. §528). Section 530 of the MUSYA authorizes the Forest Service to cooperate with State and local governments in managing the National Forests. The National Forest Management Act of 1976 provides the Forest Service with authorities and responsibilities similar to those provided to BLM by FLPMA. It establishes a planning process for National Forests that in many ways parallels the process established under FLPMA for BLM lands.

Forest Service regulations (36 CFR Part 228) are broad and similar to BLM's in that they impose few specific technical standards. In all cases where the land's surface is to be disturbed, operators must file a notice of intent. For significant disturbances (i.e., where mechanized equipment or explosives are to be used), operators must submit a proposed plan of operations. Forest Service regulations concerning plans of operations and their review and approval, reclamation standards, and environmental review are similar to those described for BLM above. Like BLM's regulations, they require compliance with the Clean Water Act and other environmental statutes and regulations.

The Mineral Leasing Act of 1920 (MLA) (30 U.S.C. §§181-287) and the Mineral Leasing Act for Acquired Lands (1947) (30 U.S.C. §§351-359) create a leasing system for coal, oil, gas, phosphate, and certain other fuel and chemical minerals ("leasable" minerals) on Federal lands. In addition, §402 of Reorganization Plan No. 3 of 1946 (and other authorities) authorizes leases for locatable minerals on certain lands (e.g., some acquired lands, as opposed to public domain lands). Under the leasing system, the government determines which acquired lands will be available for mineral development. The Department of the Interior has promulgated extensive regulations governing various aspects of leases. BLM may issue competitive, noncompetitive, and preference right leases that set the terms, including environmental terms, under which mineral development can take place. Prior to lease issuance, BLM must consult with the appropriate surface managing agency (e.g., the Forest Service), and for acquired lands must have the written consent of the other agency. Regulations require compliance with Federal and State water and air quality standards, and failure to comply with lease terms can result in lease suspension or forfeiture.

CHAPTER II

This chapter presents a brief technical description of the processes and activities associated with metal and phosphate ore mining as currently practiced in the United States. The chapter has been divided into five sections: (1) ore extraction; (2) beneficiation; (3) mineral processing; (4) ancillary operations; and (5) waste management practices. Since many of the practices for mining various metal ores are similar, this chapter describes general concepts of ore mining and ore beneficiation which apply to one or more of the commodity sectors. Exhibit 2-1 summarizes the principal mining type, beneficiation process, and associated wastes for each major hardrock mining sector.

A wide variety of techniques are used to extract minerals from the earth. In general, mining consists of removing ore and associated rock or matrix in bulk form from a deposit and transporting it away from the mined site. In the interests of economic efficiency, the extraction process is designed to remove ore of a predetermined grade or higher, leaving behind lower-grade material and barren rock, if at all practicable. In practice, an ideal separation is not often possible, so that some lower-grade rock is mined and some higher-grade ore is left behind. Although mining processes may be classified according to the numerous techniques that are employed in removing ore, they can be broken down into two broad categories associated with the general setting of a mining operation: (1) surface mining or open-pit processes; and (2) underground mining processes.

Surface mining techniques are used for most of the major metallic ores in the United States. This is the method of choice when the ore deposit is near the surface, or is of sufficient size to justify removing overburden. At present, this is the most economical way of mining highly disseminated (lower-grade) ores. Surface mining methods typically used for ore extraction are described below.

Open pit mining involves ground excavation and ore removal from the resulting pit. Depending on the thickness of the ore body, it may be removed as a single vertical interval or in successive intervals, or "benches." In resistant materials, the procedure usually employed involves mining each bench by drilling vertical shot holes from the top of the bench, and then blasting the ore onto the adjacent lower level. The broken ore and waste rock then is loaded into trucks or rail cars for transport to a mill or waste rock dumps. In less resistant materials, the ore may be excavated by scrapers or digging machinery without the use of explosives.

The depth to which an ore body is mined depends on the ore grade, nature of the overburden, and the "stripping ratio." The stripping ratio is the amount of overburden and waste rock that must be removed for each unit of crude ore mined and varies with the mine site and the ore being mined. Note that, the cut-off grades at a given mine may change with the price of the ore, thus leading to more or less waste rock being disposed as the stripping ratio changes. Waste rock with ore concentrations just below the "cut-off" grade (i.e., the grade at which ore can be recovered economically) may be stockpiled separately from other waste rock. The primary wastes associated with open pit mining include mine water, waste rock, and overburden.

Placer deposits associated with watercourses or beaches (either current or ancient) can be mined by surface open pit methods, but in some cases can be better accessed by dredging. Although there were no known commercial dredges operating in the United States as of the 1990s, the practice, which for hard materials uses a mechanical digging system to break up and excavate the deposit, may be in use elsewhere. The primary wastes associated with placer mining include mine water and tailings (which closely resemble waste rock generated in other sectors).

Historically, underground mining was the major method used for the extraction of many metal ores, however, it is now much less commonly used in hardrock mining in the United States. There are numerous variations and combinations of underground mining techniques which have been developed in response to specific or unusual characteristics of the ore body. In general, underground mining involves sinking a shaft or "driving a drift" near the ore body to be mined and extending horizontal passages ("levels") from the main shaft at various depths to the ore. Mine development rock is removed, while sinking shafts, adits, drifts, and cross-cuts, to access and exploit the ore body. From deep mines, broken ore (or "muck") is removed from the mine either through shaft conveyances or chutes and hoisted in skips (elevators). From shallow mines, ore may be removed by train or conveyor belt. Wastes associated with underground mining include mine water and mine development rock (waste rock).

In situ mining is a method of underground mining that is applicable to certain ores under certain geohydrologic conditions. In situ mining involves mining a deposit in place using a lixiviant to leach the desired material from the deposit. When the deposit is not sufficiently permeable, blasting may be used to fracture the ore body. In buried ore bodies, leaching solution is injected through a well into the ore zone. At surface ore bodies, the solution can simply be sprayed over the deposit. Recovery wells (or old underground workings) are used to collect the pregnant solution after it percolates through the ore.

In situ leaching is currently used in the uranium and copper industries. In situ techniques have also been used experimentally in the gold industry. Use of in situ methods has obvious geochemical restrictions based upon the amenability of the ore minerals to being solubilized and the cost and practicality of solvents, and based on concerns related to groundwater quality. Hydrologic requisites include: (1) the host rock must be permeable to circulating fluids; and (2) the host rock must be overlain and underlain by impermeable formations or rock units that restrict the vertical flow of fluids. Wastes associated with in situ mining include spent leaching solutions.

Most ores contain valuable metals disseminated in a matrix of less valuable rock called "gangue" (pronounced gang). The purpose of ore beneficiation is to separate valuable minerals from the gangue yielding a product much higher in content of the valued material. To accomplish this, ore generally must be crushed and/or ground small enough so that each particle is composed predominantly of the mineral to be recovered or of gangue. This separation of the particles on the basis of some difference in physical or chemical properties between the ore mineral and the gangue yields a concentrate high in values, as well as waste (tailings) containing very low concentrations of values.

Many properties are used as the basis for separating valuable minerals from gangue, including: specific gravity, conductivity, magnetic permeability, affinity for certain chemicals, surface tension, solubility, and the tendency to form chemical complexes. Because of their widespread usage throughout the mining industry, descriptions of flotation (i.e., conventional milling) and leaching processes are provided below.

Prior to flotation, run-of-mine ores are reduced in particle size by crushing and/or grinding techniques. Crushing is commonly performed sequentially: first with jaw type crushers and, then, with cone crushers and screens which reduce the particles to approximately 3/4 inch. Grinding may then occur in ball or rod mills or in autogenous mills. Grinding is usually performed with the addition of water and the resulting slurry is then pumped to the flotation circuit. Froth flotation is a process in which the addition of chemicals to an ore slurry causes particles of one mineral or group of minerals to adhere preferentially to air bubbles. When air is forced through a slurry of mixed minerals, the rising bubbles carry with them the particles of the mineral(s) to be separated from the matrix. If a foaming agent is added to prevent the bubbles from bursting when they reach the surface, a layer of mineral-laden foam is built up at the surface of the flotation cell which may be removed to recover the mineral (or, in some cases, the gangue). Requirements for success of the operation are small particle size (typically flour-sized or less), use of reagents compatible with the mineral to be recovered, and water conditions in the cell which do not interfere with the attachment of reagents to minerals or to air bubbles.

Although the exact specifications for adequate flotation are highly variable, a complex system of reagents is generally used, including five basic types of compounds: pH conditioners (regulators, modifiers), collectors, frothers, activators, and depressants. Collectors serve to attach ore particles to air bubbles formed in the flotation cell. Frothers stabilize the bubbles to create a foam which may be effectively recovered from the water surface. Activators enhance the attachment of the collectors to specific kinds of particles, while depressants prevent such attachment. Activators are frequently used to allow flotation of particular minerals that have been depressed at an earlier stage of the milling process. In almost all cases, use of each reagent in the mill is generally less than 0.5 kg (approximately 1 lb.) per ton of ore processed; however, at large-capacity mills, the total reagent usage can be high, since thousands of tons of ore per day may be beneficiated.

Sulfide minerals are all readily amenable to flotation using similar reagents in small doses, although reagent requirements and ease of flotation vary throughout the mining industry class. Sulfide minerals of copper, lead, zinc, molybdenum, silver, nickel, and cobalt are commonly recovered by flotation. In addition to sulfides, other types of minerals may be recovered by flotation (e.g., oxidized ores of iron, copper, manganese, the rare earths, tungsten, titanium, phosphate, columbium, and tantalum). The primary wastestream associated with flotation/conventional milling is tailings.

Leaching is the process of extracting a soluble metallic compound from an ore by selectively dissolving it in a suitable solvent such as water, sulfuric or hydrochloric acid, or cyanide solution. The desired metal is then removed from the "pregnant" leach solution by chemical precipitation or another chemical or electrochemical process. Leaching methods include "heap," "dump," and "tank" operations. Heap leaching is widely used in the gold industry, and dump leaching in the copper industry; leaching operations in these two sectors are discussed in detail below.

The predominant methods used in the U.S. to beneficiate gold ore involve cyanidation. This technique uses solutions of sodium cyanide or potassium cyanide to recover precious metals (gold and silver) from the ore. Cyanide heap leaching is generally used to recover gold from low-grade ore while "tank" leaching is used for higher grade ore.

Heap Leaching. Since the late 1970s, heap leaching has developed into a cost-effective procedure to beneficiate a variety of low-grade, oxidized gold ores. Compared to conventional cyanidation (i.e., tank leaching), heap leaching has several advantages, including simplicity of design, lower capital and operating costs, and shorter startup times. Depending on the local topography, a heap or a valley fill method is typically employed. The sizes of heaps and valley fills can range from a few acres up to several hundred acres. The design of these leaching facilities and their method of operation are quite site-specific and may vary over time at the same site.

Heap leaching activities may involve any or all of the following steps (Bureau of Mines, 1978 and 1984; van Zyl, 1988; many others):

Leaching usually continues until the gold concentration in pregnant solution falls below about 0.005 ounces per ton of solution (Lopes and Johnston, 1988). When leaching ends, the spent ore may then be left in place (over which new lifts may be added) or detoxified and removed from the pad for disposal in a spent ore pile. The leaching cycle can range from weeks to several months, depending on the permeability, size of the pile, and ore characteristics. The "average/normal" leach cycle is approximately three months (Lopes and Johnston, 1988).

Recovery of gold from the pregnant solution is accomplished using carbon adsorption or, less commonly, by direct precipitation with zinc dust (known as the Merrill-Crowe process). These techniques may be used separately or in a series with carbon adsorption followed by zinc precipitation. Both carbon adsorption and zinc precipitation separate the gold-cyanide complex from the noncomplexed cyanide and other remaining wastes. Other less common techniques used to recover gold values include solvent extraction, direct electrowinning, and, more recently, ion exchange.

Carbon adsorption uses the Carbon-in-Column (CIC) technique in which the pregnant solution is pumped into a series of cascading columns containing activated carbon. The activated carbon collects gold from the cyanide leachate until it contains between 100 and 400 ounces of gold per ton of carbon, depending on the individual operation. The precious metals are then stripped from the carbon by elution with the use of a boiling caustic cyanide stripping solution (1.0 percent NaOH and 0.1 percent NaCN) or other similar solutions. Gold in the pregnant eluate solution may be electrowon or zinc precipitated.

Electrowinning (or electrodeposition) uses stainless or mild steel wool, or copper, as a cathode to collect the gold product. After two or more cycles of electrodeposition, the steel wool must be removed. The steel wool or electrowinning sludge, laden with gold value, is fluxed with sodium nitrate, fluorspar, silica, and/or sodium carbonate and melted in a crucible furnace for casting into bullion.

Although carbon adsorption/electrowinning is the most common method of gold recovery in the United States, zinc precipitation is the most widely used method for gold ore containing large amounts of silver. Because of its simple and efficient operation, the Merrill-Crowe process is used at the 10 largest gold producing mines in the world, all of which are in South Africa. In zinc precipitation operations, pregnant solution (or the pregnant eluate stripped from the activated carbon) is filtered and combined with metallic zinc dust resulting in a chemical reaction which generates a gold precipitate (Bureau of Mines, 1984). The solution is forced through a filter that removes the gold metal product along with any other precipitates. The gold precipitate recovered by filtration is often of sufficiently high quality (45 to 85 percent gold) that it can be dried and smelted in a furnace to make doré (unrefined metals).

Wastes associated with gold heap leaching activities include spent ore, spent leaching solutions, electrowinning sludges, and detoxification rinse water.

Tank Leaching. Tank leaching techniques for gold recovery are preferred over heap leaching for higher-grade ores, typically those with gold values averaging over 0.04 troy ounces per ton of ore. In tank leaching operations, primary leaching takes place in a series of tanks, often in the mill building, rather than in heaps. Finely ground gold ore is slurried with the leaching solution in tanks. The resulting gold-cyanide complex is then adsorbed on activated carbon. In the Carbon-in-Pulp (CIP) method, leaching and adsorption occur in two separate series of tanks; in the Carbon-in-Leaching (CIL) method they occur in a single series. In either, the pregnant carbon then undergoes elution, followed either by electrowinning or zinc precipitation, as described previously. The recovery efficiencies attained by tank leaching are significantly higher than for heap leaching.

Both the CIP and CIL methods produce fine tailings, which are generally pumped to an impoundment. The composition of the tailings reflects the characteristics of the ore body, along with small (but sometimes significant) amounts of residual cyanide. In some cases, the tailings may be treated to neutralize cyanide prior to disposal. Other wastes generated by facilities that use tank leaching include: spent leaching solutions, electrowinning sludges, and detoxification rinse water.

Solution mining techniques are being used increasingly for the recovery of copper and currently account for approximately 30 percent of domestic copper production. Two-thirds of all United States copper mines employ various types of solution operations (Weiss, 1985). Sulfuric and hydrochloric acid leaching at atmospheric pressure are the most common types of copper leaching.

Dump leaching refers to the leaching of oxide and low-grade sulfide ore in (typically) unlined piles. Copper dump leaches are frequently massive, with piles ranging in size from 20 to hundreds of feet in height and often covering hundreds of acres and containing millions of tons of ore. These operations involve the addition of leaching solution, collection of pregnant leach solution (PLS), and the extraction of copper by SX/EW or cementation. Natural precipitation/mine water are generally used to leach low grade sulfide ore, while dilute sulfuric acid is commonly used to leach oxide ores. Since widespread application of the leaching process is a relatively new process, copper mines have frequently applied leaching techniques to recover values from historic waste rock dumps. Thus, collection of PLS may not be maximized (i.e., some PLS may escape to the environment). New dump leach units are typically located and designed to prevent or minimize the loss of leach solution. Once collected, copper is commonly recovered from PLS in one of two ways; SX/EW or cementation.

The solvent extraction (SX) process is a two-stage method; in the first stage, low-grade, impure leach solutions containing copper, iron, and other base-metal ions are fed to the extraction stage mixer-settler. In the mixer, the aqueous solution is contacted with an active organic extractant (chelating agent) in an organic diluent (usually kerosene), forming a copper-organic complex. The organic phase extractant is formulated to extract only the desired metal ion (i.e., copper), while impurities such as iron or molybdenum are left behind in the aqueous phase. The barren aqueous solution, called raffinate, is typically recirculated back to the leaching units while the loaded organic solution is transferred from the extraction section to the stripping section. In the second stage, the loaded organic solution is stripped with concentrated sulfuric acid solution (spent electrolyte) to produce a clean, high-grade solution of copper for electrowinning.

Electrowinning (EW) is the method used to recover copper from the electrolyte solution produced by solvent extraction. Copper is plated on cathodes of stainless steel or on thin-copper starting sheets and the cathode copper is then shipped to a rod mill for fabrication. The spent acid is recycled and pumped back to the leaching operation, while some of the electrolyte is pumped to the solvent extraction process (Office of Technology Assessment, 1988; Engineering and Mining Journal, 1990).

In the past, copper produced from leach solutions was typically recovered by cementation techniques. In the cementation process, PLS flows to a precipitator pond filled with scrap iron or steel. The copper chemically reacts with, and precipitates onto the steel surfaces. The iron is dissolved into solution, and the copper precipitates out (i.e., replaces) the iron. While cementation has been a source of relatively inexpensive copper, the cement copper produced is relatively impure compared to electrowon copper and must be smelted and refined along with flotation concentrates (Beard, 1990). As a result, it has largely been replaced by SX/EW technology. Wastes associated with copper dump leaching operations include spent ore, spent leaching solutions, and SX/EW sludges.

The following paragraphs provide brief descriptions of some of the most common mineral processing practices currently employed in the United States in the alumina, copper, elemental phosphorus, ferrous metals (iron), lead, and phosphoric acid industry sectors. Mineral processing operations for minerals which are mined and processed predominantly as by-products (e.g., silver) are not discussed separately. Additionally, minerals such as gold, which may be completely or partially refined as part of the beneficiation process, are not discussed. Much of the information presented in this section was obtained from EPA's Office of Air Quality Planning and Standards document (EPA, 1985a) and the Report to Congress on Special Wastes from Mineral Processing (EPA, 1990).

Bauxite ore is purified to produce alumina (Al₂O₃) by the Bayer process and then is reduced to elemental aluminum. The production of alumina and the reduction of alumina to aluminum is seldom performed at the same facility. The production of alumina from bauxite ore using the Bayer process generally follows five steps. First the bauxite ore is dried, crushed, and screened and then mixed with a caustic alkaline solution (NaOH). The second step is the routing of slurried ore to digesters, where the aluminum is heated and solubilized as sodium aluminate (Na₂Al₂O₃). In the third step, the solution is cooled and purified. Purification is performed by separation and washing to remove sodium hydroxide and other impurities (known collectively as red mud). The fourth step is the precipitation of the cooled and purified aluminum hydroxide using sodium hydroxide seed crystals. The aluminum hydroxide precipitate is filtered, then concentrated by evaporation, resulting in a filter cake. The fifth and final step is the calcination of the hydroxide filter cake to produce a crystalline form of alumina, advantageous for electrolysis.

Electrolytic reduction of alumina occurs in shallow rectangular cells, or "pots," which are steel shells lined with carbon. Carbon electrodes extending into the pots serve as the anodes and the carbon lined steel shell is the cathode. Molten cryolite functions as both the electrolyte and the solvent for the alumina. Electrical resistance to the current passing between the electrodes generates heat and the resulting molten aluminum is deposited onto the cathode. The aluminum product is periodically tapped below the cryolite bath and fluxed to remove trace impurities.

Wastes associated with alumina processing and aluminum production include red mud (including residual water) and particulates from ore grinding and calcining during alumina processing; and gaseous and particulate hydrogen fluoride, alumina, carbon monoxide, volatile organics, and sulfur dioxide from the aluminum reduction operations.

Primary copper processing operations include, in general, roasting, smelting, converting, fire refining in an anode furnace, and electrolytic refining. The products from each operation, respectively, are calcine, copper matte, blister copper, copper anodes, and refined copper. Smelting involves the application of heat to a charge of copper ore concentrate, scrap, and flux, to fuse the ore and allow the separation of copper from iron and other impurities. Although several types of smelting furnaces are used in the United States, all furnaces produce two separate molten streams: copper-iron-sulfide matte and slag. Slag from some smelting operations may have copper concentrations higher than the original ore and therefore may be sent to a concentrator and the concentrate returned to the smelter. The copper matte from the smelter is typically routed hot to the converter furnace where high-silica flux and compressed air or oxygen are introduced. Most of the remaining iron combines with the silica to produce converter slag and additional air or oxygen is blown in to oxidize the sulfur and convert copper sulfide to blister copper, which can be 99 percent pure. The sulfur dioxide gas stream reports to an acid plant for sulfuric acid production.

To purify blister copper further, fire refining and electrolytic refining are used. In fire refining, blister copper is placed in an anode furnace, flux is usually added, and air is blown through the molten mixture to oxidize remaining impurities, which are removed as slag. The fire refined copper is cast into anodes; further electrolytic refining separates copper from impurities by electrolysis in a solution containing copper sulfate and sulfuric acid. The copper is dissolved from the anode and deposited at the cathode which can later be remelted to produce bars, ingots, or slabs which are 99.95 to 99.97 percent pure.

Wastes associated with copper processing include smelter slag; particulate and sulfur dioxide emissions; and process water from cooling, general wash-down activities, and air pollution control devices (scrubber blowdown).

Elemental phosphorus is used as a process input to produce a wide array of phosphorus chemicals. As a chemical manufacturing feedstock, it may be used directly, or oxidized and condensed to produce a high-purity "furnace-grade" phosphoric acid (see phosphoric acid production discussed below). In elemental phosphorus processing, sized phosphate rock or sintered/agglomerated phosphate rock fines are introduced into an electric arc furnace together with coke (a reducing agent) and silica (a flux) . The phosphorus within the rock is both liberated from the matrix and chemically reduced by the operation. The process generates calcium silicate slag and ferrophosphorus, which are tapped from the bottom of the furnace in molten form, and carbon monoxide (CO) off-gases, which contain volatilized phosphorus. The gas is treated using a precipitator to remove impurities and the cleaned gas, still containing the gaseous phosphorus, is condensed using water to produce liquid elemental phosphorus.

Wastes associated with elemental phosphorus processing include furnace slag; phosphoric acid mist; phosphoric acid scrubber water; and process wastewaters.

There are two processes for producing phosphoric acid: (1) the wet process, and (2) the thermal (furnace) process. The wet process is employed when the acid is to be used for fertilizer production, while the thermal process is employed when a higher purity acid is required for high grade chemicals and food products. The wet process consists of three operations: digestion, filtration, and concentration. Beneficiated phosphate rock is fed to a reactor with 93 to 98 percent sulfuric acid, which decomposes the phosphate rock. The product of this operation is a slurry that consists of the phosphoric acid (32 percent) and a suspended solid, calcium sulfate, commonly known as phosphogypsum. The slurry is routed to a filtration operation where the suspended phosphogypsum is separated from the acid solution. The acid isolated during filtration is concentrated through evaporation to produce "merchant-grade" (54 percent) phosphoric acid. The phosphogypsum is directed to settling ponds.

In the thermal process, elemental phosphorus is burned (oxidized) in a combustion chamber to form phosphorus pentoxide. The phosphorus pentoxide is hydrated with dilute acid or water to produce phosphoric liquid acid and mist. The final step is to remove the phosphoric acid mist from the gas stream by precipitation. The thermal process usually yields a product of 75 to 85 percent phosphoric acid.

Wastes generated during the wet process include phosphogypsum; process wastewater; gaseous fluorides (silicon tetrafluoride and hydrogen fluoride); and a small amount of particulate matter from process equipment and filters. The primary wastes generated during the thermal process are phosphoric acid mist and process waters from cooling and air pollution control devices.

Ferrous metals processing consists of smelting and iron and steel production. Iron ore, limestone, flux, coke, and recycled flue dust and sinter are usually fed to an updraft sintering machine which prepares the ore for smelting. The resulting charge is fed to a blast furnace (95% of which are submerged electric arc furnaces) which consists of a refractory-lined steel shaft in which a charge is continuously added to the top through a gas seal. Iron and steel scrap may also be added in small amounts. Preheated air is blown into an area near the bottom of the furnace. The coke is combusted to produce carbon monoxide, the iron ore is reduced to iron by the carbon monoxide, and the silica and alumina in the ore and coke ash are fluxed with limestone to form a slag that absorbs much of the sulfur from the charge. Molten iron and slag are intermittently tapped from the bottom of the hearth. The slag is drawn off and the product, pig iron, is removed, cooled, and crushed and transported to a steel mill operation. Steelmaking processes convert pig iron, scrap, or direct-reduced iron, or mixtures of these, into steel in a basic oxygen furnace that lowers the carbon and silica content and removes impurities.

Wastes associated with ferrous metals and ferroalloy processing include blast and basic oxygen furnace slag; particulate, sulfur dioxide, carbon monoxide, and organic emissions; and process waters from cooling, general wash-down activities, and air pollution control devices (scrubber blowdown).

Primary lead processing consists of smelting (blast furnace and dross furnace operations) and refining operations. Ore, limestone, flux, coke, recycled flue dust, and sinter are usually fed to an updraft sintering machine which prepares the ore for smelting by lowering the sulfur content by nearly 85 percent. Sintering also provides sulfur dioxide gas for sulfuric acid production. In the smelting process, sintered ore concentrate is introduced into a blast furnace along with coke, limestone, and other fluxing materials; the lead is reduced, and the resulting molten material separates into four layers: speiss and matte, two distinct layers of materials which contain recoverable concentrations of copper, zinc, and minor metals; blast furnace slag; and lead bullion (98 percent lead). The speiss and matte are either processed at the smelter for their metal content or sold to copper smelters for recovery of copper and precious metals. The lead bullion is then drossed to remove lead and other metal oxides, which solidify and float on the lead bullion. The solidified material (referred to as dross), is treated in a reverberatory furnace to concentrate the copper and other metal impurities before being routed to copper smelters for their eventual recovery. The lead bullion is further refined by operations which continue the process of removing various saleable metals and impurities. The refined lead is then cast into ingots for distribution.

Wastes associated with lead processing include blast and dross furnace slag; process wastewaters generated from cooling and general wash-down activities, and air pollution control devices (scrubber blowdown); and particulate, sulfur dioxide, lead, and organic emissions.

This section provides an overview of the waste and materials management practices typically used in the mining industry. Selection of individual approaches is highly dependent on site-specific conditions. Further, wastes and meterials are commonly co-managed in on-site units.

Mine Water

Water removed from a mine to gain or facilitate access to an ore body is known as "mine water." Mine water can originate from precipitation, flows into pits or underground workings, and/or groundwater aquifers that are intercepted by the mine. Mine water is only a waste if it is discharged to the environment via a point source. Mine water can be a significant problem at many mines, and enormous quantities may have to be pumped continuously during operations. When a mine closes, removal of mine water generally ends. However, underground mines can then fill (or partially fill) and mine water may be released through adits, or through fractures and fissures that reach the surface. Surface mines that extend below the water table fill to that level when pumping ceases, either forming a "lake" in the pit or inundating and saturating fill material. Pumped mine water is typically managed in on-site impoundments (often within the mine workings or tailings impoundments). Collected water may be allowed to infiltrate/evaporate, used as process make-up water or for other on-site applications such as dust control, and/or discharged to surface water subject to NPDES requirements.

Mine water can have environmentally significant concentrations of heavy metals and TDS, elevated temperatures, and altered pH, depending on the nature of the ore body and local geochemical conditions. In addition, mine water can acidify over time as sulfide minerals are exposed to water and air, resulting in acid mine drainage (AMD); the potential for acid drainage can cause significant threats to surface and groundwater quality/resources during active mining and for decades after operations cease.

Both underground and surface mining operations generate "waste rock." Waste rock consists of non-mineralized and low-grade mineralized rock removed from above or within the ore body during extraction activities. Waste rock is typically disposed in large piles or dumps in close proximity and down-slope of the point of extraction. Waste rock dumps may be loosely categorized as valley fills, cross valley fills, side-hill fills, or heaped fills (or piles) (British Columbia Mine Dump Committee, 1991). Each of these names derives from the particular topographical feature exploited for waste containment. Regardless of the layout of the unit, waste rock dumps are generally constructed on unlined terrain, with underlying soils stripped, graded, or compacted depending on engineering considerations. Such conditions may include steep foundations of unconsolidated material or partially saturated terrain that may not support the weight of fill material. Rock is generally hauled to the face of the unit in trucks or by conveyor systems and then dumped. Surface grading of fill material is typically performed to provide haulage trucks access to the working face. Most commonly, waste rock is deposited at the angle-of-repose.

Depending on site hydrology and regulatory constraints, drainage systems may be incorporated into dump foundations. In areas of groundwater intrusion or where catchment areas channel substantial surface water flows into the dump, drainage systems help to prevent instability due to foundation failures from saturation (BCMDC, 1991). Drainage systems may be constructed of gravel-filled trenches or gravel blankets, with capacity and configuration determined according to site-specific conditions. Dump toe drains may be particularly favored to reduce pore pressure near the face of the structure to prevent toe spreading or local slumping.

Most of the ore extracted at hardrock mines ultimately becomes mill tailings requiring disposal. Because tailings produced by mills are usually in slurry form, disposal of slurry tailings in impoundments made of local materials is the most common and economical method of disposal. There are four main types of slurry impoundment layouts: valley impoundments, ring dikes, in-pit impoundments, and specially-dug pits (Ritcey, 1989). The impoundment design choice is primarily dependent upon natural topography, site conditions, and economic factors. Other things being equal, it is economically advantageous to use natural depressions to contain tailings. Among other advantages are reduced dam size, since the sides of the valley or other depression serve to contain tailings.

There are two general classes of impounding structures: water-retention dams and raised embankments. The choice of impounding structure is influenced by economics and site-specific factors including the characteristics of the mill tailings and effluent. In general, impoundments are designed to control the movement of fluids both vertically and horizontally. Regardless of the layout of the impoundment, at most facilities ponded water is decanted from tailings ponds and recirculated to the mill for reuse in beneficiation processes. In general, two methods are available for decanting pond water: decant towers and pumping (usually from floating barges). In some cases, tailings are dewatered or dried and disposed of in piles. However, except under special circumstances, dry disposal methods can be prohibitively expensive due to additional equipment and energy costs. The advantages of dry disposal include minimizing seepage volumes, the land needed for an impoundment or pile, and the ability to conduct simultaneous tailings deposition and reclamation.

In addition to disposal in impoundments and piles, slurried tailings are sometimes disposed of in underground mines as backfill to provide ground or wall support. This decreases the above-ground surface disturbance and can stabilize mined-out areas. To increase structural stability, cement may be mixed with the sand fraction before backfilling. Subaqueous tailings disposal, which has been practiced primarily in Canada, is the placement of tailings below a permanent water surface such as a lake or ocean. Subaqueous disposal is practiced primarily to minimize the acid generating potential of tailings by not allowing sulfide ore to oxidize.

When leaching operations cease, the spent ore in the heap or dump is usually managed in place. Where on-off pads are used, however, spent ore is removed from heap leach pads for disposal in on-site piles or dumps (similar to waste rock dumps). Prior to final reclamation (or prior to ore removal from on-off pads), spent ore generally must be detoxified. This is typically accomplished by repeated rinsing with water, usually mine water or mill wastewater. At gold leaching operations, hydrogen peroxide or other oxidants may be added to rinse waters to oxidize residual cyanide. The time necessary for rinsing heaps is highly variable, ranging from a few days for some on-off heaps to months or years for other heaps and dumps.

Following detoxification, heaps and dumps may be regraded to more stable long-term configurations. If present, liners may be punctured and the heap/dump covered with topsoil and reclaimed. In some cases, heaps/dumps may require capping to reduce leaching of heavy metals. Because of the large volumes of materials typically placed in heap/dump units, any potential long-term environmental problems (associated with waste management) should be investigated and addressed during initial unit design rather than after leaching ceases and materials become wastes.

Solution ponds are potential sources of acid/metal releases to ground and surface water. Ponds associated with precious metal leaching operations and newer copper facilities are generally lined with synthetic materials (although liners are often susceptible to failure). At older copper sites, solution ponds may be unlined or lined only with natural materials. At closure, ponds are frequently backfilled. Pond liners may be removed, folded over and sealed to encapsulate sludges or other wastes, punctured, or otherwise handled, depending on applicable regulatory requirements.

When leaching operations cease, non-cyanide bearing leach solutions may either receive simple neutralization or pH adjustment and metals precipitation treatment. Cyanide-bearing solutions typically receive some form of cyanide destruction and neutralization treatment. These treated wastestreams may then be allowed to infiltrate/evaporate or may be re-applied to disturbed mine areas.

Slags from thermal mineral processing operations (copper and lead smelting and refining, blast furnaces, and elemental phosphorus production) are generally managed in unlined, on-site piles. Depending on the industry sector and the specific waste characteristics, significant quantities may be available for re-use in construction applications. For example, all of the slag produced by several elemental phosphorus operations is sold for off-site re-use.

Phosphogypsum and phosphoric acid production wastewater are co-managed in "phosphogypstacks." These massive units have historically been unlined to allow drainage through the stacks. The pH of stack water is typically less than one (reflecting residual phosphoric and sulfuric acid). Recycle/re-use alternatives for phosphogypsum have generally proven to be unfeasible and/or uneconomical.

Red muds from alumina production are disposed of in impoundments. Existing waste management units typically have runon/runoff controls and some have leachate collection systems (to address seepage). While research suggests that red muds could potentially be reused (as a blast furnace feed, in construction applications, etc.), little or no red mud waste has been re-used to date.

In addition to the wastes described above, extraction, beneficiation, and processing of minerals generate other wastes that are not uniquely related to mining, such as spent solvents and used oil. Large mining operations may operate hundreds of vehicles ranging in size from light trucks to immense earth moving vehicles. Vehicle and equipment maintenance activities generate large quantities of used oils and lubricants, solvents, antifreeze, tires, and wash waters. Raw material storage for maintenance activities also requires that large inventories must be maintained, including above and underground fuel tanks. If the facility is regulated by a storm water permit, a Spill Prevention Countermeasure and Control (SPCC) plan as well as a Storm Water Pollution Prevention Plan (SWPPP) are required.

In addition to the wastes already mentioned, wastes not uniquely related to mining include but are not limited to: PCBs (transformers, capacitors, and/or hydraulic fluid); vessel cleanouts; tank bottoms; empty or crushed drums; filters; pigging wastes; sewage/sanitary wastewaters; fossil fuel boiler wastes ( boiler blowdown, refractory brick ash, etc.); water pollution control sludges, blowdown, etc.; air pollution control dusts, sludges, filters, etc.; drilling fluids/muds; solid wastes (i.e., garbage); construction and demolition wastes; filter washing wastes; and laboratory wastes.

These wastes, as well as hazardous mineral processing wastes, may be commingled with Bevill wastes such as tailings, in tailings ponds or other units. Aside from possible RCRA compliance issues, managing these wastes in mining units may cause potential impacts to the environment. Where applicable, management of these wastes should be specifically addressed in the NEPA documentation for each mining operation. In addition, proper monitoring of storage and disposal units for these wastes should be described.

This chapter describes the potential environmental impacts associated with extraction, beneficiation, and mineral processing operations. The mining industry and its potential environmental impacts are unusual in a number of ways; of these, three may be the most important. First, many of the potential impacts are unique to the industry (acid rock drainage, releases from cyanide leaching units, structural failure, etc.). Second, many of the impacts may be manifested years or decades after mining ends and can intensify over time. Finally, the nature and extent of impacts from mining operations are based on factors that are specific to the location (including geology, hydrogeology, climate, human and wildlife populations, etc.). Impacts from similar types of operations can range from minimal to extensive, depending on local conditions. These factors emphasize the need for a full understanding of baseline conditions and careful planning to avoid/mitigate potential impacts.

As in all major industrial operations, careful design and planning play a critical role in reducing or mitigating potential impacts. In the case of the mining industry, the three characteristics that distinguish it from other industries make initial design and planning even more crucial. Design and operation plans, including measures to mitigate potential environmental impacts, are often only conceptual at the time of permitting. This makes it extremely difficult to delineate the types of information and analyses that are necessary to assess potential impacts.

The following sections describe potential impacts to surface and ground water, air, and ecosystems associated with mining operations, along with possible mitigation measures. The final section of this chapter identifies (by type of operation) questions that reviewers can ask to determine whether the potential impacts to all media have been fully considered in the NEPA process.

POTENTIAL IMPACTS ON SURFACE WATER

Suspended solids and toxic pollutants (primarily metals, sulfates, and nitrates) can be released to surface water from mining operations. Because of the large area of land that is disturbed by mining operations and the large quantities of earthen materials exposed at sites, erosion frequently is a primary concern at hardrock mining sites. Erosion control must be considered from the beginning of operations through completion of reclamation. Erosion may cause significant loadings of sediments (and any entrained chemical pollutants) to nearby streams, especially during severe storm events, as well as high snow melt periods. While acid rock drainage (ARD) can enhance contaminant mobility by promoting leaching from exposed wastes and mine structures (see Chapter IV), releases can also occur under neutral pH conditions. Primary sources of pollutants from hardrock mining operations include underground and surface mine workings; overburden and waste rock piles; tailings piles and impoundments; direct discharges from conventional milling/beneficiation operations; leach piles and processing facilities; blowdown from smelting and refining operations, phosphogypsum piles, and chemical storage areas (due to runoff and spills). The following sections describe the discharges associated with each of these operational areas as well as potential mitigation measures. A more detailed discussion of runoff and erosion is provided in Chapter IV.

Table 3-1 provides an overview of the types of pollutants potentially found in surface water discharges (process water, mine water, seepage, and runoff) from specific industry sectors. Any evaluation of the potential impacts of a new mining operation in a watershed requires an understanding of baseline (pre-construction) conditions. Baseline studies should describe flow conditions (including seasonal variability), substrate and sediment pollutant levels, and aquatic life. A brief discussion of monitoring approaches is presented in Chapter V.

TABLE 3-1

OVERVIEW OF TYPES OF POLLUTANTS FOUND IN SURFACE WATER

Potential Impact: During active operations where mining occurs below the water table, mine water is typically pumped from underground and surface operations and often discharged to surface water through NPDES-permitted outfalls. After operations cease, mine workings may overflow and uncontrolled mine water/runoff may be discharged. The characteristics of the ore body will affect the composition of mine water discharges. Specifically, the occurrence of ARD may cause acidic conditions and enhance pollutant mobility; however, toxic loadings can also occur under neutral conditions. Finally, residues from blasting or from fertilizer used during reclamation can cause elevated nitrate concentrations.

Development of appropriate mitigation measures for surface water discharges from mine workings requires a complete understanding of the baseline hydrogeology of the site, including bedrock and alluvial aquifers as well as the influence of fracturing. This information can be used to predict the volumes of mine water requiring management. At surface mines, proposed operators must also consider runoff contributions in planning water management. Data on the likely characteristics of mine water/runoff are necessary to evaluate the potential for re-use and/or the need for treatment prior to discharge. Where sulfide mineralization is encountered, testing for acid generation potential should be performed; see Chapter IV.

Mitigation Measures:

Potential Impacts: Waste rock and overburden are typically managed in piles adjacent to the mine workings. Materials are frequently end-dumped into angle-of-repose units that are often located on the slopes of natural drainages. These units are generally unlined. Potential pollutant loadings in runoff and seepage from waste rock piles are dependent on the site-specific mineralogy; they can include sediment as well as metals, sulfates, and radionuclides. Where sulfur mineralization is present, ARD can occur.

To determine the surface water impacts associated with a proposed waste rock dump and identify potential mitigation measures, baseline environmental data and waste rock characteristics are needed. The geology of the site will establish likely waste characteristics. ARD potential should be determined where sulfide minerals are found. A complete water balance should be provided to describe the projected flows in and out of the dump (as well as an evaluation of stability and the potential for slope failure).

Mitigation Measures:

Potential Impacts: Tailings impoundments are typically constructed in natural drainages (to facilitate water management). Most mines attempt to maximize re-use of tailings water in milling operations. However, impoundment designs frequently include underdrains and controlled discharges (especially in high precipitation/snow melt areas). Further, even where units are intended not to discharge, tailings impoundments are nearly always accompanied by unavoidable seepage through or beneath the dam structure. Similar to waste rock, the composition of surface water discharges from tailings is dependent on the local geology. However, fine tailings can be more susceptible to leaching/entrainment of particulates than coarser waste rock materials. Contaminants associated with the host rock often include heavy metals, arsenic, and radionuclides. ARD can occur if sulfide mineralization is encountered and may enhance metals mobility. Residual mill reagents may also be present in the tailings, however, they typically do not contribute significant pollutant loadings. Finally, where the outside slopes of dams or other units are constructed of tailings or other mining wastes, discharges and runoff from these areas can affect water quality and may require treatment.

Tailings are typically transported to impoundments by pipeline. Reclaimed water is collected from impoundments and returned to the mill by pipeline. Pipe failures may lead to surface water impacts if pipelines are located in drainages or residues contact runoff.

Development of appropriate mitigation measures for tailings impoundments necessitates an understanding of the overall water balance (including reuse, groundwater infiltration, evaporation, seepage, snow melt, and runoff). The composition of the tailings should be determined by evaluating the local geology and representative waste testing (including leachability testing). If sulfide mineralization is encountered, ARD potential should be determined.

Mitigation Measures:

Potential Impacts: Copper leaching operations are generally intended to have no surface water discharges during active leaching operations. Dumps are typically sited in natural drainages with downstream collection sumps. Pregnant solution and raffinate ponds are lined and SX/EW plant operations normally have secondary containment. However, a full understanding of the water balance and adherence to sound design standards are necessary to ensure that all drainage is collected. This is especially applicable to sites with significant variations in precipitation and snow melt. Further, any closed loop system will inevitably have spill events that can cause surface water impacts. Finally, surface water discharges are likely after leaching becomes no longer economical (to date, closure plans generally have not been developed during initial planning). Surface water discharges from copper dump leaches are likely to be acidic and contain metals, sulfates, and other pollutants associated with the geology of the host rock. Reagents such as kerosene are used in the SX/EW process; however, the small quantities suggest that they would be generally undetected in any discharges.

Mitigation Measures:

Potential Impacts: Cyanide heap leaches and associated processing operations can cause acute impacts to surface water through leaks or failures of containment systems. In addition, unless effective detoxification procedures are used, spent ore piles can cause releases of residual cyanide. Further, other pollutants (including heavy metals) can be mobilized in the leaching process and may be released to surface water through spills or leaks (during operations) and through seepage/runoff from spent ore (after closure). The characteristics of spent ore pile seepage/runoff will depend on the local geology and any residual effects of application of the leaching solution. Where sulfide mineralization is encountered, the potential for ARD should be investigated. Finally, cyanide degradation can also lead to nitrate contamination.

Mitigation Measures:

Potential Impacts: Phosphogypsum from phosphoric acid production is typically slurried to "phosphogypstacks." Except for facilities located in Louisiana, no direct surface water discharges are allowed from phosphogypstacks, except during heavy precipitation events (40 CFR Part 418.10). However, discharges of overflows during precipitation events may be highly acidic with elevated concentrations of metals, sulfate, phosphorous, and radionuclides. In addition, phosphogypstacks located near surface waters may be subject to failures that can cause uncontrolled pollutant releases. Surface water impacts from infiltration/seepage can also occur through groundwater recharge.

Mitigation Measures:

Mineral Processing - Slag Piles and Other Wastes From Furnace Operations

Potential Impacts: Mineral processing operations generate significant quantities of slag which is typically disposed of in lined or, more often, unlined piles. Although contaminant mobility may be reduced due to the nature of the slag matrix, surface water releases may be caused by precipitation that comes into contact with the slag.

In addition, at many smelting/furnace operations, ore, coke, flux, and other materials used in mineral processing operations are stored outside. Fugitive emissions from these materials, as well as stack emissions, can contribute to on-site soils deposition. Storm water which comes into contact with stored materials or affected soils can provide a transport mechanism for releases to surface waters through entrainment or leaching. Pollutants will reflect the characteristics of the ore.

Mitigation Measures:

Releases from mining operations can have significant impacts on groundwater quantity and quality. Drawdown associated with mine dewatering can reduce the availability of water for domestic water supplies and other uses, and can also affect wetland habitats. Releases of heavy metals, sulfates, nitrates, and radionuclides from mining materials can contaminate aquifers. Spills and leaks of cyanide solutions from leaching operations have also impacted groundwater quality.

To determine the potential for groundwater impacts, it is essential that the EA/EIS include a detailed description of the site hydrogeology, including both alluvial and bedrock aquifers as well as the influences of fracturing. NEPA documentation should also describe the likely characteristics of waste materials (including ARD potential) and how reagent use/handling may contribute to subsurface releases. This information will serve to predict potential groundwater impacts and guide design and implementation of appropriate mitigation measure during both active operations and closure/post-closure.

Potential Impact: Contact with exposed mine workings can lead to contamination of mine water. Pollutants can include heavy metals, sulfate, arsenic, and radionuclides. Metals releases can be enhanced by acid mine drainage (AMD) (where there is sulfide mineralization); although leaching can occur both under acidic and neutral conditions. Mine water can also be contaminated by blasting residuals (i.e., causing elevated nitrate concentrations). Infiltration of mine water from underground and surface workings/management units can lead to contamination of aquifers (some mining operations use infiltration ponds as a primary mine water management practice). Further, infiltration of groundwater into mine workings and subsequent use in processes, evaporation, and/or discharge can cause aquifer drawdown (currently being observed in the Carlin Trend area in northeastern Nevada). These effects can lead to diminished drinking water supplies as well as loss of riparian zones and wetlands associated with lowered groundwater levels.

Potential Impacts: Waste rock and overburden are typically managed in piles adjacent to mine workings. Precipitation that infiltrates waste rock piles can directly impact the underlying groundwater. In addition, seepage and runoff that flow from the pile can infiltrate soils and also affect groundwater quality. Potential pollutant loadings to groundwater from waste rock piles are dependent on the site-specific mineralogy, however, they can include metals, sulfates, and radionuclides. Where sulfur mineralization is present, ARD can occur. To determine the potential for groundwater impacts, it is necessary to collect data on the baseline hydrogeology (including aquifer depth and quality). The characteristics of the waste rock and the expected water balance (inflows and outflows from the pile) should also be determined.

Mitigation Measures:

Potential Impacts: Tailings impoundments are typically constructed in natural drainages (to facilitate water management). Newer tailings impoundments may be lined (with synthetic or natural materials) or keyed into bedrock. However, some tailings water often infiltrates into groundwater. Further, outside of the impoundment, releases to groundwater can occur from infiltration of seepage and/or runoff from the outside slopes. The composition of tailings water/infiltration can reflect residual mill reagents. However, contributions from these chemicals are generally small. Instead, pollutants in tailings are typically representative of the geology of the ore body and may include metals, sulfates, and radionucl