EIA Guidelines for Mining
Environmental Impact Assessment Guidelines
for New Source NPDES Permits
ORE Mining and Dressing
and
Coal Mining and Preparation Plants
Point Source Categories
September 1994
U.S. Environmental Protection Agency
Office of Federal Activities
401 M Street, S.W.
Washington, D.C. 20460
Prinled on Recycled Paper
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DISCLAIMER
This document was prepared for the. U.S. Environmental
Protection Agency by Science Applications International
Corporation in partial fulfillment of EPA Contract No. 68-W2-
0026, Work Assignment 27-I. The mention of company or
product names is not to be considered an endorsement by the
U.S. Government or by the Environmental. Protection Agency.
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EIA Guidelines for Mining Table of Contents
TABLE OF CONTENTS
1. INTRODUCTION 1-1
1.1 ‘PURPOSE OF ENVIRONMENTAL IMPACT ASSESSMENT GUIDELINES.
1.2 SCOPE OF THE MINING INDUSTRY
1.3 ORGANIZATION OF GUIDELINES
2. NEPA REQUIREMENTS AND PROVISIONS 2-1
2.1 OVERVIEW .. .•
2.1.1 EPA REQUIREMENTS FOR ENVIRONMENTAL REviEw UNDER NEPA
2.1.2 ENVIRONMENTAL REVIEW PROCESS FOR NEW SOURCE NPDES PERMITS
2.2 TRIGGERS FOR NEPA REVIEW ACTIVITIES - .
2.2.1 PRIMARY CoNDITIoNs THAT TRIGGER NEPA REviEw
2.2.1.1 New Source Determination
2.2.1.2 EPA is the Permitting Authority 2-7
2.2.2 WHEN IS AN ElS REQUIRED 9
2.2.2.1 Impacts to Already-degraded Environments an 1 Cumulative Impacts
2.2.2.2 Uncertain Impacts
2.2.2.3 Delayed Impacts
2.2.2.4 Duration of Impacts
2.2.2.5 Transfer of Responsibility for Facility
2.2.2.6 Cbntroversial Actions and Impacts
2.2.3 THE RELATIONSHIP BEVWEEN NEPA REVIEW AND NPDES PERMrrrxNo ACTIVITIES
2.3 LEVELS OF REVIEW
2.3.1. ENVIRONMENTAL INFORMATION DOCUMENT (EID)
2.3.2 ENVIRONMENTAL ASSESSMENT DOCUMENTS (EA)
2.3.3 ENVIRONMENTAL IMPACT STATEMENTS (EISs)
2.4 INFORMATION REQUIRED FROM PERMIT APPLICANTS
2.5 TIME INVOLVED IN PREPARING AND PROCESSING NEPA DOCUMENTS
2.6 LIMITATIONS ON PERMIT APPLICANT ACTIONS DURING THE REVIEW PROCESS
3. OVERVIEW OF MINING AND BENEFICIATION ,. 3-1
3.1 ORE MINING
3.1.1 EXPLORATION .
3.1.2 SrrE DEVELOPMENT
3.1.2.1 Construction of Access Roads, Rail Lines, or ShipIBarge Terminals
3.1.2.2 Construction of Mining Facilities
3.1.2.3 Construction of Mill Facilities .
3.1.2.4 Other Pre-Mining Activities
3.1.3 MINING
3.1.3.1 SurfaceMining
3.1.3.2 OpenPitMining
.3.1.3.3 Dredging
3.L3.4 Underground Mining
3.1.3.5 In Situ Solution Mining
.3.1.4 MINING WASTES’AND WASTE MANAGEMENT
3.1.4.1 Mine Water
3.1.4.2 Waste Rock
1-2
1-3
1-4
2-1
2-2
2-4
2-7
2-7
2-7
2-8
2-9
2-11
.2-12
2-13
2-13
2-13
2-14
2-15
2-15
2-15
2-15
2-17
2-17
2-17
3-1
3-2
3-3
3-3
3-3
.3-4
.3-4
3-4
3-5
3-5
35,
3-6
3-8
3-9
3-9
3-10
September 1994
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Table of Contents EIA Guidelines for Mining
3.1.5 RESTORATION AND RECLAMATION 3-11
3.2 ORE DRESSING (BENEFICIATION) 3-13
3.2.1 GRAvn’Y CONCENTRATION 3-13
3.2.1.1 Sizing 3-14
3.2.1.2 Coarse Concentration 3-15
3.2.1.3 Fine Concentration 3-16
3.2.1.4 Sink/Float Separation 3-18
3.2.2 MAGNETIC SEPARATION .. 3-18
3.2.3 ELECTROSTATIC SEPARATION 3-19
3.2.4 FLOTATION 3-19
3.2.5 LEACHING 3-20
3.2.6 BENEFICIATION WAsms i u WASTE MANAGEMENT 3-22
3.2.6.1 Mine Backfihling 3-23
3.2.6.2 Subaqueous Disposal 3-24
3:2.6 3 Tailings Impoundments 3-24
3.2.6.4 Dry Tailings Disposal 3-28
3.3 COMMODITY-SPECIFIC MINING AND BENEFICIATION PROCESSES 3-29
3.3.1 GOLD AND SILVER 3-29
3.3.1.1 Geology of Gold Ores 3-30
3.3 1.2 Mining 3-34
3.3.1.3 Beneficiation 3-37
3.3.2 GOLD PLAcER MiN iNG 3-56
3.3.2.1 Mining 3-58
3.3.2.2 Beneficiation 3-59
3.3.2.3 Wastes and Management Practices 3-60
3.3.2.4 Environmental Effects 3-62
3.3.3 L -Zm c 3-63
3.3.3.1 Mining 3-64
3.3.3.2 Beneficiation 3-64
3.3.3.3 Wastes 3-66
3.3.3.4 Waste Management 3-67
3.3.4 COPPER 3-69
3.3.4.1 Geology of Copper Ores 3-69
3.3.4.2 Mining 3-71
3.3.4.3 Beneficiation 3-71
3.3.4.4 Wastes and Waste Management 3-80
3.3.5 IRON 3-82
- 3.3.5.1 Geology of Iron Ores 3-83
3.3.5.2 Mmmg 3-83
• 3.3.5.3 Beñeficiation 3-84
3.3.5.4 Wastes and Waste Management 3-87
3.3.6 URANIUM .. . . 3-88
3.3.6.1 Geology of Uranium Ores 3-88
3.3.6.2 Mining 3-89
3.3.6.3 Beneficiation 3-89
3.3.6.4 Wastes and Waste Management 3-96
3.3.7 OTHER M rAi..s 3-97
3.3.7.1 Aluminum 3-97
3.3.7.2 Tungsten 3-98
3.3.7.3 Molybdenum 3-99
3.3.7.4 Vanadium ,. 3-100
• 3.3.7.5 Titanium 3-100
3.3.7.6 Platinum 3-101
3.4 COAL MINING 3-102
3.4.1 CoAL FORMATION AND GEOGRAPHICAL DISTRIBUTION 3-102
3.4.1.1 Types and Composition ofCoaI 3-102
jj • • September 1994
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EIA Guidelines for Mining
Table of Contents
3.4.1.2 Coal Provinces 3-103
3.4.1.3 Trends 3-108
3.4.2 SURFACE MINING SYSTEMS 3-109
3.4.2.1 Area Mining 3-109
3.4.2.2 Contour Mining 3-112
3.4.2.3 OpenPitMining 3415
3.4.2.4 Special Handling 3-116
3.4.2.5 Equipment 3-116
3.4.3 UNDERGROUND MINING SYSTEMS 3-116
3.4.3.1 Development 3-117
.3.4.3.2 Extractióñ 3-118
• 3.4.3.3 Abandonment 3-123
3.4.3.4 Pollution Control 3-124
3.4.3.5 Environmental Effects . . 3-125
PROCESSING 3-125
BASIC PRINCIPLES 3-125
COAL CLEANING TECHNOLOGY .. 3-132
3.5.2.1 Stage Descriptions 3-137
3.5.2.2 Process Flow Sheet for Typical Operations 3-150
4. ENVIRONMENTAL ISSUES . 4-1
4.1 ACID ROCK’DRAINAGE
4.1.1 NATURE OF ACID ROCK DRAINAGE
4.1.1.1 Acid Rock Drainage/Oxidation of Metal Sulfldes
4.1.1.2 Source of Acid and Contributing Factors
4.1.2 ACID GENERATION PREDICTION
4.1.2.1 Sampling
4.1.2.2 Static Tests
4.1.2.3 Kinetic Tests
4.1.2.4 Application of Test Results in Prediction Analysis
4.1.2.5 Experience With Static and Kinetic Tests
4.1.2.6 Mathematical Modeling of Acid Generation Potential
4.1.3 ARD DETECTION/ENVIRONMENTAL MONITORING .•
4.1.4 MITIGATION OF ARD
4.1.4.1 Subaqueous Disposal
4.1.4.2 Covers
4.1.4.3 Waste Blending .
4.1.4.4 Hydrologic Controls
4.1.4.5 Bacteria Control
• 4.1.4.6 Treatment
4.1.5 SUMMARY OF FACTORS TO BE CONSIDERED IN EVALUATING PoTEwrI.kI. ARD
GENERATIONIRELEASE
4.2 CYANIDE HEAP LEACHING
4.2.1 UNCERTAINTIES IN CYANIDE BEHAVIOR IN ThE.ENVIRONMENT
4.2.1.1• Cyanide in the Environment
4.2:1.2 Analytical Issues
4.2.2 POTENTIAL IMPACTS AND APPROACHES TO MITIGATION DURING ACTIVELIFE
4.2.2.1 Acute Hazaxds
4.2.2.2 Spills and Overflows
4.2.2.3 Liner and Containment Leakage
4.2.3 CLOSURE/RECLAMATION AND LONG-TERM IMPACTS
4.2.3.1 Closure and Reclamation
4.2.3.2 Long-term Environmental Concerns and Issues
4.2.3.3 Assessments of Long-term Impacts
3.5 COAL
3.5.1
3.5.2
4-2
4-3
• 4-3
• 4-4
• 4-7
4-9
4-11
4-12
4-14
4-16
4-17
4-21
4-22
4-23
4-24
4-24
4-24
4-25
4-25
4-27
4-28
4-29
4-29
4-30
4-31
4-32
4-32
4 .34
4-35
4-35
4-36
4-38
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Table of Contents ETA Guidelines for Mining
4.5.1 BASIC EROSION PRINCIPLES
4.5.2 IMPACTS ASS0cLVrED wtht EROSION/RUNOFF FROM DISTURBED AREAs.
4.5.3 ESTABLISHING BAcKGROUND CONDITIONS
4.5.4 PREDICTING SEDIMENT LOADINGS FROM NEW SouRcEs
4.5.4.1 Available Techniques/Models
4.5.4.2 Modeling Considerations
4.5.5 SEDIMENT AND EROSION MITIGATION MEASURES .
4.5.5.1 Diversion Techniques
4.5.5.2 Stabilization Practices
4 5.5.3 Structural Practices
4.5.5.4 Contact Prevention Measures /Reclamation Process
4.5.5.5 Treatment Techniques
4.6 METALS AND DISSOLVED POLLUTANTS
4.7 AIR QUALITY
4.8 SUBSIDENCE ..
4.9 METhANE EMISSIONS FROM COAL MINING AND PREPARATION
5. IMPACT ANALYSIS . s -i
5 -1
5-2
5-3
5-3
5-4
5-4
5-5
5-5
5-6
5 -7
5-8
5-8
5-8
5 -9
5 -9
5-9
5-10
5-10
5-10
541
5-11
4.3 STRUCTURAL STABILITY OF TAILINGS IMPOUNDMENTS 4-39
4.3.1 SEEPAGE AND Smniutv 440
4.3.2 SEEPAGE/RELEASES AND ENVIRONMENTAL PERFORMANCE 4-42
4.4 NATURAL RESOURCES AND LAND USES 4-43
4.4.1 GROUNDWATER 4-43
4.4.2 AQUATIC LIFE 4-44
4.4.3 WILDLIFE 4-47
4.4.4 VEGETATION/WETLANDS 4-50
4.4.5 L D USE 4-52
4.4.5.1 Farmland 4-52
4,4.5.2 Timber 4-53
4.4.5.3 Grazing 4-53
4.4.5.4 Recreation 4-54
4.4.6 CULTURAL RESOURCES 4-54
4.4.7. AESTIiET 1CS . . . . 4-54
4.5 SEDIMENTATION/EROSION . 4-55
4-56
4-58
4-58
4-61
4-62
4-63
4-64
4-65
4-65
4-66
4-66
- 4-69
4-69
. 473
4 -74
4-75
5.1 DETERMINE ThE SCOPE OF ANALYSIS
5.2 IDENTIFY ALTERNATIVES
5.2.1 ALTERNATIVES AVAILABLE to EPA
5.2.2 ALTERNATIVES CONSIDERED B Y T I m APPLICANT
5.2.3 ALTERNATIVES AVAILABLE TO OTHER AGENCIES
5.3 DESCRIBE THE AFFECTED ENVIRONMENT
5.3.1 ThE PHYSICAL-CHEMICAL ENVIRONMENT
5.3.1 ,1 Air Resources
5.3.1.2 Water Resources
5.3.1.3 Soils and Geology
5.3.2 BIOLOGICAL CONDrrIONS
5.3.2.1 Vegetation
5.3.2.2 Wildlife
5.3.2.3 Ecological Interrelationships
5.3;3 SOCIOECONOMIC ENVIRONMENT
5.3.3.1 Community Services
5.3.3.2 Transportation
5.3.3.3 ’ Population
5.3.3.4 Employment
5.3.3.5 Health and SMety
5.3.3.6 Economic Activity
September 1994
iv
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EIA Guidelines for Mining
Table of Contents
5.3.4 LAND USE
5.3.5 AESTHETICS
5.3. ( CULTURAL RESOURCES .
5.4: ANALYZE POTENTIAL IMPACTS . . ...
5.4.1 METhODS OF ANALYSIS
.5.4.2 DETERMINATION OF SIGNIFICANCE
5.4.3 COMPARISONS OF IMPACTS UNDER DIFFERING ALTERNATIVES
5.4.4 SUMMARY DISCUSSIONS
5.5 DETERMINE MITIGATING MEASURES
5.6 CONSULTATION AND COORDINATION . .
6. STATUTQRY FRAMEWORK •0
6-1
6.13 NATIONAL PARK SYSTEM MINING REGULATION ACT 6-29
6.14 ORGANIC ACT; MULTIPLE USE AND SUSTAINED YIELD ACT; NATIONAL FOREST
MANAGEMENT ACT 6-30
6.15 MINERAL LEASING ACT; MINERAL LEASING ACT FOR ACQUIRED LANDS .. .. 6-30
6.16 COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION, AND LIABILITY
ACT 6-31
6.17 EMERGENCY PLANNING AND COMMUNITY RIGHT-TO-KNOW ACT 6-32
6.18 WILD AND SCENIC RIVERS AcT 6-32
6.19 FISH AND WILDLIFE COORDINATION ACT 6-33
6.20 FISH AND WILDLIFE CONSERVATION ACT 6-33
6.21 MIGRATORY BIRD PROTECTION TREATY ACT 6-33
7. REFERENCES . 7-1
5-11
5-11
5-12
5-12
5-13
5-14
5-16
5-16
5-17
5-18
6-1
6-15
.6-17
6-19
.
6-21
6-21
6-22
.. . . 6-22
. 6-23
6-23
6-25
6-26
6-27
6.1 CLEAN WATER ACT
6.2 CLEAN AIR ACT
6.3 RESOURCE CONSERVATION AND RECOVERY ACT
6.4 ENDANGERED SPECIES ACT
6.5 NATIONAL HISTORIC PRESERVATION ACT
6.6 COASTAL ZONE MANAGEMENT ACT
6.7 EXECUTIVE ORDERS 11988 AND 11990
6.8 FARMLAND PROTECTION POLICY ACT .
6.9 RIVERS AND HARBORS ACT OF 1899
6.10 SURFACE MINING CONTROL AND RECLAMATION ACT
6.10.1 PERMITrING PROGRAM FOR ACTIVE COAL MINING OPERATIONS
6.10.2 ABANDONED MINE LANDS PROGRAM
6.11 MINING LAW OF 1872
6.12 FEDERAL LAND POLICY MANAGEMENT ACT
V
September 1994
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Table of Contents EIA Guidelines for Mining
LIST OF EXHIBITS
Exhibit Page
Exhibit 1-1. Standard Industrial Classification Codes for the Metal Mining Industry 1-4
Exhibit 2-1. NEPA Environmental Review Process for Proposed Issuance of New Source
NPDES Permits 2-5
Exhibit 2-2. Model Schedules for EAs and EISs for Proposed Issuance of New Source
NPDES Permits 2-18
Exhibit 3-1. Twenty-Five Leading Gold-Producing Mines in the United States, 1991 3-31
Exhibit 3-2. Twenty-Five Leading Silver-Producing Mines in the United States, 1991 3-32
Exhibit 3-3. Materials Handled at Surface and Underground Gold Mines, 1988 3-34
Exhibit 3-4. Chemicals Stored and Used at Gold Mines 3-36
Exhibit 3-5. Gold Mining and Beneficiation Overview 3-38
Exhibit 3-6. Gold Ore Treated and Gold Produced, By Beneficiation Method, 1991 3-39
Exhibit 3-7. Steps for Gold Recovery Using Carbon Adsol:ption 3-42
Exhibit 3-8. Chemicals Used at Lead-Zinc Mines 3-68
Exhibit 3-9. Leading Copper Producing Facilities in the United States 3-70
Exhibit 3-10. Copper Flotation Reagents 3-72
Exhibit 3-11. Characteristics of Copper Leaching Methods 3-74
Exhibit 3-12. Typical Solvent ExtractionlElectrowinning (SX/EW) Plant 3-78
Exhibit 3-13; Types of Coal and Relative Percentages of Constituents 3-103
Exhibit 3-14. Coal Provinces of the United States 3-104
Exhibit 3-15. Summary of Environmental Considerations by Province 3-105
Exhibit 3-16. Area Mining With Stripping Shovel 3-110
Exhibit 3-17. Mountaintop Removal With Head-of-Hollow Fill 3-111
Exhibit 3-18. Box-Cut Mining Operations 3-113
Exhibit 3-19. Block-Cut Mining Operation 3-114
Exhibit 3-20. Operations in Conventional Room and Pillar Mining 3-120
Exhibit 3-21. Lengwall Mining System 3-122
Exhibit 3-22. Ash and Sulfur Reduction Potential of U.S. Coals, Vol. I p. 395, Eastern
Regions U.S. Department of Energy 3-129
Exhibit 3-23. Washability Partition Curve 3-131
Exhibit 3-24. Coal Preparation Plant Processes 3-133
Exhibit 3-25. Typical Coal Cleaning Facility 3-134
Exhibit 3-26. Typical Circuit for Coal Sizing Stage . 3-135
Exhibit 3-27. Metric and English Equivalents of U.S. Standard Sieve Sizes and Tyler Mesh
Sizes . 3-136
Exhibit 3-28. Typical Process Qtiantities for a 910 MT (1,000 ‘I ’) per Hour Coal Cleaning
Facility 3-137
Exhibit 3-29. Typical Three-Stage Crusher System for Raw Coal Crushing 3-138
Exhibit 3-30. Single-Roll (a) and Double-Roll (b) Crushers for Sizing of Raw Coal 3-139
Exhibit 3-3 1. Feed Characteristics of Unit Cleaning Operations for Sizing and Separation of
Crushed Coal 3-141
Exhibit 3-32. Typical Circuit for Dense Media Coal Cleaning 3-142
Exhibit 3-33. Typical Circuit for Jig Table Coal Cleaning 3-144
Exhibit 3-34. Typical Air Table for Pneumatic Coal Cleaning 3-145
Exhibit 3-35. Typical Circuit for Pneumatic Coal Cleaning 3-146
Exhibit 3-36. Desirable Chemical Characteristics of Make-Up Water for Coal Cleaning
Processes . 3-147
Exhibit 3-37. Typical Product Dewatering Circuit for Coal Cleaning 3-148
vi September 1994
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ELA Guidelines for Mining
Table of Contents
Exhibit 3-38.
Exhibit 3-39.
Exhibit 3-40.
Exhibit 3-41.
Exhibit 3-42.
Exhibit 3-43.
Exhibit 3-44.
Exhibit 3-45.
Exhibit 3-46.
Exhibit 4-I.
Exhibit 4-2.
Exhibit 4-3.
Exhibit 4-4.
Exhibit 4-5.
• 3-149
• 3-150
3-151
3-152
3-153
• 3-154
3-156
3-157
3-158
4-13
4-15
4-30
4-71
4-72
6-2
6-9
6-10
6-’.:
Typical Moisture Contents of Dried Product from Selected Drying Operations
in Coal Cleaning Facilities
Thickener Vessel for Dewatering of Coal Cleaning Products
Schematic Profile, of a Sieve Bend Used for Coal Sizing and Dewaterin
Profile View of a Coal Vacuum Filter
Thermal Dryer and Exhaust Scrubber
Typical Flash Dryer
Coal Cleaning Plant Flow Sheet for Coarse Stage Separation and Dewatering .
Coal Cleaning Plant Flow Sheet for Fine Stage Separation and Dewatering
Coal Cleaning Plant Flow Sheet for Sludge (Slime) Separation and Dewatering.
Summary of Static Test Methods, Costs, Advantages, and Disadvantages
Summary of Some Kinetic Test Methods, Costs, Advantages, and Disadvantages
Stability.of Cyanide and Cyanide Compounds in Cyanidation Solutions
Typical Pollutants Associated With Hardrock Mining Operations
Typical Pollutants Associated With Coal Mining Operations
Exhibit 6-1. Major Federal Statutes Generally Applicable to Mining Operations .‘. . . • .
Exhibit 6-2. New Source Performance- Standards for Coal Mining Category
(40 CFR Part 434) . ‘
Exhibit 6-3. New Source Performance Standards for Mine Drainage, Ore Mining and
Dressing Category (40 CFR Part 440, Subparts A-K and M)
Exhibit 6-4. New Source Performance Standards for Mills and Beneficiation Processes, Ore
Mining and Dressing Category (40. CFR Part 440, Subparts A-K and M)
Exhibit 6-5 Examples of Discharges From’ Ore Mining and Dressing Facilities
That Are Subject to 40 CFR Part ‘440 or to Storm Water Permitting
v i i
September 1994
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EIA Guidelines for Mining Introduction
1. INTRODUCTION
The National Environmental Policy Act of 1969 (NEPA, 42 U.s.c §4321 er seq.) was the first of
what has come to be an array of statutes whose individual and collective goals are the protection of
the human and natural environment from a variety of impacts that human activity can have. NEPA
introduced the requirement that Federal agencies consider the environmental consequences of their
actions and decisions as they carry out their mandated functions. For “major Federal actions
significantly affecting the quality of the human environment,” the Federal agency must prepare a
detailed environmental impact statement that assesses not only the proposed action but. also reasonable
alternatives.
The Federal Water Pollution Control Act (33 U.S.C. § 1251-1387), better known as the Clean Water
Act, seeks to restore and maintain the chemical, physical, and biological integrity of the Nation’s
waters. One of the major mechanisms by which the Clean Water Act is to attain that goal is the
requirement that all point source discharges of pollutants to waters of the United States be controlled
through permits issued under the National Pollutant Discharge Elimination System (NPDES).
The Clean Water Act [ 5 1 1(c)(1)] also requires that the issuance of a NPDES permit by the
Environmental Protection Agency (EPA) or authorized States for a discharge from a new source be
subject to NEPA. In 1979, EPA established the regulations by which it applies NEPA in such cases:
“Environmental Review Procedures for the New Source NPDES Program,” 40 CFR 6 Subpart F.
These procedures require EPA to prepare a written environmental assessment based on information
provided by the new source NPDES permit applicant and other available documentation. If the
environmental assessment concludes that no significant impacts will result from issuance of the new
source NPDES permit, EPA issues a Finding of No Significant Impact (FNSI). If the assessment
concludes that there may be significant environmental impacts that cannot be eliminated by changes in
the proposed project, EPA must prepare (or participate in the preparation of) an environmental impact
statement that contains the information and analyses described in 40 CFR Part 6 Subpart B and
conforms with Council on Environmental Quality regulations (40 CFR Part 1502) governing NEPA
compliance.
In preparing the environmental assessment, EPA relies on information and analyses provided by the
applicant for the new source NPDES permit in an “environmental information document,” or EID.
The scope and content of an EID is determined by EPA in consultation with the applicant, with the
regulatory caution that EPA “...keep requests for data to the minimum consistent with his
responsibilities under NEPA” [ 40 CFR 6.604(b)].
1-1 September 1994
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Introduction EIA Guidelines for Mining
1.1 PURPOSE OF ENVIRONMENTAL IMPACT ASSESSMENT GUIDELINES
Following the promulgation of New Source Performance Standards for new source discharges in the
late 1970s and early 1980s, EPA prepared a series of “Environmental Impact Assessment Guidelines”
for use in determining the scope and contents of EIDs for new source NPDES permits for facilities in
specific industries. The guidelines also were intended to assist EPA staff in reviewing and
commenting on applicants’ EID information and in preparing, overseeing the preparation of, or
commenting on environmental assessments and environmental impact statements.
Three of the environmental impact assessment ‘guidelines prepared by EPA addressed the mining
industry; one’ addressed facilities that mine and beneficiate ores and minerals to recover metals,
another 2 addressed underground coal mines and coal cleaning facilities, and a third 3 addressed
surface coal mines. EPA’s Office of Federal Activities, in cooperation with other EPA offices and
Regions, is now revising and Updating these guidelines to incorporate new information and to make
them more widely useful in identifying and evaluating the potential environmental impacts that
proposed mining projects may have. Because many of the potential impacts, and the information and
analyses needed to assess impacts, are common to metal and coal mining, the topics covered by the
three previous guidelines documents have been combined into this single document.
These guidelines are expressly intended to provide background information for EPA staff to assist
them in consulting with and directing new source NPDES permit applicants in the scope and contents
,of EIDs and as a reference to assist them in identifying and evaluating the potential impacts of
proposed mining projects. EPA anticipates several other audiences for these guidelines: EPA staff
who review and comment on other Federal agencies’ environmental impact statements and regulations
pursuant to §309 of the Clean Air Act; other EPA staff who deal with the mining industry and its
environmental impacts; new source NPDES permit applicants who must prepare EIDs for EPA; other
Federal agencies responsible for regulating or overseeing the mining industry; and State, local, and
foreign government environmental officials. Officials in States that have.been authorized to
implement the NPDES program may also find these guidelines useful in their reviews of permit
applications. All audiences should be aware that this document provides background information and
general guidance, but does not constitute an official EPA position on laws or regulations, or represent
Agency policy.
‘U.S. Environmental Protection Agency, Office of Environmental Review. 1981 (December 16). Environmental
Impact Assessment Guidelines for New Source Ore Mining and Dressing Facilities. Prepared for EPA by Wapora Inc. under
contract 68-01-4157.
2 U.S. Environmental Protection Agency, Office of Federal Activities. 1981 (October). Environmental Impact
Assessment Guidelines for New Source Underground Coal Mines and Coal Cleaning Facilities. EPA-I 30/6.81-002.
U.s. Environmental Protection Agency, Office of Environmental Review. 1979 (December). Environmental lnzpact
Assessment Guidelines for New Source Sumface Coal Mines. EPA-130/6-79-005.
1-2 September 1994
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EIA Guidelines for Mining Introduction
These guidelines supplement the more general document, Environmental Impact Assessment
Guidelines for Selected New Source Industries, which provides general guidance for preparing
environmental impact assessments (EIAs) and presents impact assessment considerations that are
common to most industries, including mining.
1.2 SCOPE OF THE MINING INDUSTRY
The ore mining and dressing (or beneficiation) industry is composed of mining facilities that remove
raw mineral ores’ from the earth, and of mill facilities that separate the mineral ores from overburden
and waste rock removed during mining activities. The industry also includes mill facilities that
further concentrate and purify metals in the ore to a condition specified for further processing
(smelting and/or refining) or for incorporation as a raw material by another industry. The mining and
beneficiation of various mneral ores occurs nationwide, and is viewed as critically important to the
Nation’s economy since it provides the raw materials on which many other industries rely.
The metal mining industry is identified as Standard Industrial Classification (SIC) Major Group 10.
This industrial group includes facilities engaged in mining ores for the production of metals and also
includes all ore dressing (or beneficiation) operations, whether performed at mills operating in
conjunction with mines or at mills operated separately. These include mills that crush, grind, wash,
dry, sinter, or leach ore, or that perform gravity separation or flotation operations.
EPA has promulgated effluent limitation guidelines for discharges of pollutants from existing and new
sources in the Ore Mining and Dressing Point Source Category (40 CFR Part 440). These effluent
limitation guidelines provide numeric limitations for discharges from mines and mills in various
industry subcategories (see also Chapter 5). Exhibit 1-1 shows the SIC categories covered by this
industrial group and the subcategories for which EPA has promulgated effluent limitation guidelines.
The coal mining industry is composed of facilities that mine coal of any rank from the earth, and of
preparation plants that clean or otherwise prepare the coal for combustion and other uses. The coal
mining industry is identified as Standard Industrial Classification (SIC) Major Groups’ 11 (anthracite)
and 12 (bituminous and lignite). These industrial groups include facilities that are engaged in mining
coal and preparation plants that operate in conjunction with mines or separately.
EPA has promulgated effluent limitation guidelines for discharges of pollutants from existing and new
sources in the Coal Mining and Preparation Plant Point. Source Category (40 CFR Part 434). These
effluent limitation guidelines provide numeric limitations .on discharges from mines (with separate
standards for acid and for alkaline discharges), preparation plants, and areas of mines that are being
reclaimed.
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Introduction EIA Guidelines for Mining
Exhibit 1-I. Standard Industrial Classification Codes for the Metal Mining Industry
SIC
Type of Ore
Subpart Within 40 CFR Part 440
1011
Iron Ores
Subpart A
1021
Copper Ores
Subpart J
1031
Lead and Zinc Ores
Subpart J
1041
Gold Ores
Subpart I (lode)
Subpart M (placer)
1044
Silver Ores
Subpart I
1051
Bauxite and Other Aluminum Ores
Subpart B
1061
Ferroalloy Ores, except Vanadium
•
Tungsten: Subpart F
Nickel: Subpart 0
Molybdenum: Subpart J
1092
Mercury Ores
Subpart D
1094
Uranium, Radium, and Vanadium Ores
Subpart C
Subpart H (vanadium when mined
alone—reserved)
1099
Other Metal Ores
.
Antimony: Subpart I
Platinum: Subpart K (reserved)
Titanium: Subpart E
1.3 ORGANIZATION OF GUIDELINES
The remainder of this document is organized as follows. Chapter 2 describes NEPA requirements
and provisions as they apply to issuance of new source NPDES permits. Chapter 3 presents
information on the mining industry. This chapter is intended to give the reader background
information on the operations that take place on mine sites. The apparent simplicity of mining—
removing ores from the earth and then concentrating the valuable product from the ores—disguises
what is in reality a formidable complexity. As a result, some understanding of the nature of mining
operations is necessary in any assessment of the potential environmental impacts and in identifying the
information and analyses that are necessary to conduct such an assessment. Metal mining and
beneficiation are described in the first three subsections of Chapter 3. The first two describe,
respectively, mining and beneficiation operations that are common to the industry; the third describes
each of the major industry sectors, with particular regard to the mining and beneficiation operations
that are unique to the individual sector. This third subsection focusses on the industry Sectors which
are most important to the U.S. mining industry, including gold, copper, iron, lead-zinc, and uranium.
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ELA Guidelines for Mining Introduction
Sectors for which EPA. has promulgated effluent limitation guidelines but in which there are currently
very few active mines (e.g., aluminum, molybdenum, platinum, tungsten) or no active or anticipated
mines (e.g., antimony, mercury) are also described, but in less detail. Following the subsections on
metal mining are two subsections that describe coal mining and coal preparation, respectively. All of
the subsections in this chapter describe the major operations that take place and identify the major
environmental concerns of these operations.
Chapter 4 then describes in some detail several of the major environmental issues and impacts that are
of most concern when evaluating the potential major impacts of proposed mining operations.
Separate subsections in this chapter describe each of a number of major potential impacts and the’
circumstances that can lead to their occurrence. These sections also describe the types of information
and analyses that are necessary to identify whether these impacts are of concern for a particular
operation, to evaluate these potential impacts and their significance, and to identify and evaluate
possible mitigation measures.
•The process of analyzing impacts within the context of NEPA and new source NPDES permits is
described in Chapter 5. Separate subsections describe each of the major steps in, the impact analysis.
Chapter 6 then provides information on the major Federal environmental and natural resource
management, statutes that directly affect or that regulate. mining operations. The purposes and broad
goals of each of these statutes are described, along with a brief indication of the requirements
imposed by the statute and the implementing agency’s regulatory or consultation programs.
Finally, references cited in the document are listed in Chapter 6,. as are a number of other valuable
references. Appendix A presents in outline, in the form of a “checklist,” of the types of information
and analyses that should go into an environmental information document. Appendix B presents a
glossary of terms.
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EtA Guideli nes for Mining NEPA Requirements and Provisions
L NEPA REQUIREMENTS AND PROVISIONS
2.1 OVsSVIEW
NEPA serves as the basic national charter for environmental protection. Section 102 of NEPA
establishes environmental review requirements for Federal actions. These reviews or impact
assessmçnts are required to be broad in scope, addressing the full range of potential effects of a
proposed action on the human and natural environment. A general framework for implementing these
requirements is presented in regulations issued by the Council on Environmental Quality (CEQ).
Federal agencies, in turn, have developed their own rules for NEPA compliance that are consistent
with the CEQ regulations but address their specific missions and program activities. Over the past 25
years, the NEPA framework for environmental review of proposed Federal actions has been
substantially refined, based on further congressional directives, action by CEQ, and an extensive body
of case law.
Congress has determined that most EPA activities are exempt from impact assessment requirements
under NEPA. In the case of EPA’s water quality programs, Section 5 11(c) of the Clean Water Act
(CWA) clearly specifies that actions taken by EPA under the Act shall not “be deemed a major
Federal Action significantly affecting the quality of the human environment within the meaning of the
National Enviromnentaf Policy Act of 1969.0 However, Congress did make two important exceptions
to this exemption:
(1) the provision of financial assistance for the construction of publiCly owned treatment works.
(2) the issuance of NPDES permits for new sources as defined in Section 306 of the CWA.
The specific riference to NPDES new source permits makes clear EPA ’s responsibility to review
proposed permit issuance actions from the broader per pective of the NEPA environmental assessment
framework.
Since EPA does have responsil ility for conducting euvironmental reviews for some types of proposed
activities, the Agency has developed and codified its own set of NEPA procedures. These
procedures, which are found at 40 CFR Part 6, have been revised a number of times. Some of the
relevant steps in the course of the development of EPA ’s current regulations are as follows:
• Initial EPA proposed rulemaking setting forth procedures for the preparation of E ISs (37FR
879; January 20, 1972)
• Interim EPA regulations for Part—Preparation of Environmental Impact statements (38 FR
1696; January 17, 1973)
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• Notice of proposed rulemaking—Preparation of EISs (39 FR 26254; July 17, 1974). This
proposed rulemaking reflects substantial public comment on the interim regulations as well
as additional CEQ requirements. The rulemaking addresses EPA’s nonregulatory programs
only.
• Final EPA regulations on the preparation of Environmental Impact statements (40 FR
16814, April 14, 1975). Although procedures for ‘new source NPDES permits are not
included in this rulemaking, EPA notes in the preamble that such regulations will be
subsequently issued in 40 CFR Part 6.
• Preparation of Environmental Impact Statements, New source NPDES permits (42 FR 2450,
January 11, 1977).- Presents an outline for the preparation of EISs for proposed new source
permitting action.
• Proposed rule—Implementation of Procedures on the National Environmental Policy Act (44
FR 35158; June 18, 1979). In response to major revision of CEQ’s regulations in 1978,
EPA revises its procedures accordingly. The revised procedures include streamlining and
clarification of procedures in general. In addition, requirements for NPDES new source
permitting actions were substantially revised and presented as Subpart F of the proposed
rule.
• Final rule—Irnplemçntation of Procedures on NEPA (44 FR 64174, November 6, 1979).
Issues raised during promulgation include limitation of construction activities during
permitting process and environmental review and the conditioning or denying or permits
based on factors identified during the NEPA review process.
• Minor changes to Subpart F,. involving the changing of citations, were made on September
12, 1986 (51 FR 32606).
2.1.1 EPA REQUIREMENTS FOR ENVIRONMENTAL REVIEW UNDER NEPA
EPA’s current National Environmental Policy Act Procedures (40 CFR 6) outline the Agency’s
policies and processes for meeting environmental review requirements under NEPA. Subpart A of
the Procedures provides an overview of the Agency’s purpose and policy, institutional responsibilities,
and general procedures for conducting reviews. Subpart A outlines EPA’s basic hierarchy of NEPA
compliance documentation as follows:
• Environmental Information Document (EID), which is a document prepared by
applicants, grantees, or permittees and submitted to EPA. This document must be sufficient
in scope to enable EPA to prepare an environmental assessment.
• Environmental Assessment (EA), which is a concise document prepared ‘by EPA that
provides sufficient data and analysis to determine whether an EIS or finding of no
significant impact is required.
• Notice of intent (NOD, which announces the Agency’s intent to prepare an ELS. The NOI,
which is published in the Federal Register, reflects the Agency’s finding that the proposed
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action may result in “significant” adverse environmental impacts and that these impacts can
not be eliminated by making changes in the project.
Environmental Impact Statement (EIS), which is a formal and detailed analysis of
alternatives including the proposed action, is undertaken according to CEQ requirements
and EPA procedures.
• Finding of No Significant Impact (FNSI), which announces EPA’s finding that the action
analyzed in an EA (either as proposed or with alterations or mitigating measures) will not
result in significant impacts. The FNSI is made available for public review, and is typically
attached to the EA and included in the administrative record fOr the proposed action.
• Record of Decision (ROD), which is a statement published in the Federal Register that
describes the course of action to be tak fi by an Agency following the completion of an
EJS. The ROD typically includes a description of those mitigating measures that will be
taken to make the selected alternative environmentally, acceptable.
• Monitoring, which’refers to EPA’s responsibility to ensure that decisions on any action
where a final EIS is prepared are properly implemented.
Subpart B of EPA’s Procedures provides a detailed discussion of the contents of EISs. This subpart
of the text specifies format and the contents of an executive summary, the body of the EIS, material
incorporated by reference and a list of preparers.
Subpart C of the Procedures describes requirements related to coordination and other environmental
review and consultation requirements. NEPA compliance involves addressing a number of particular
issues, including (1) landmarks, historical, and archaeological sites; (2) wetlands, floodplains,.
important farmlands, coastal zones, wild and scenic rivers, fish and wildlife, and endangered species;
and (3) air quality. Formal consultation with other agencies may be required, particularly in the case
of potential impacts on threatened and endangered species and potential impacts on historic or
archaeological resources.
Subpart D of the Procedures presents requirements related to public and other Federal agency
involvement. NEPA includes a strong emphasis on public involvement in the review process.
Requirements are very specific with regard to public notification, convening of public meetings and
hearings, and filing of key documents prepared as part of the review process.
Subpart F presents environmental review procedures for the New Source NPDES Program. This
Subpart specifies that the requirements summarized abàve (Subparts A through D) apply when two
basic conditions are met: (1) the proposed permittee is determined to be a new source under NPDES
permit regulations; and (2) the permit would be issued within a State where EPA is the permitting
authority (i.e., that State does not have an approved NPDES prog ani in accordance with section
402(b) of the CWA). This Subpart also states that the processing and review of an applicant’s
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NEPA Requirements and Provisions EIA Guidelines for Mining
NPDES permit application must proceed concurrently with environmental review under NEPA..
Procedures for the environmental review process are outlined. Subpart F also provides criteria for
determining when EISs must be prepared, as well as rules relating to the preparation of RODs and
monitoring of compliance with provisions incorporated within the NPDES permit. (A more detailed
discussion of the environmental review process and triggers for certain specific environmental
assessment ‘requirements are presented later in this chapter.)
The remaining Subparts of the EPA Procedures (i.e., Subparts E, 0, H, I, and J) address aspects of
EPA’s environmental review procedures that are not relevant to these guidelines for the proposed
issuance of new source NPDES permits.
2.1.2 ENVIRONMENTAL REVIEW PROCESS FOR NEW SOURCE NPDES PERMITS
As illustrated by Exhibit 2-1, the NEPA review of proposed new source permitting actions and the
process of NPDES permit issuance are to occur concurrently. However, completion of the
environmental review—either through the issuance of a FNSI or the issuance of a ROD—is to precede
actual permit issuance or denial.
As discussed in detail in a following section, EPA first must ensure that the two primary conditions
that trigger NEPA environmental review have been met. EPA Regional office staff then would
consult with the permit applicant to determine the scope of the information document; and upon
request by the permit applicant, to set time limits on the completion of the review process consistent
with 40 CFR 1501.8. (Information required from permit applicants is addressed in more detail later
in this chapter.)
Once the permft applicant has submitted the EID, EPA Regional office staff must review the
information provided by the applicant along with any other available information that is relevant.
EPA Regional staff then must prepare a written EA which ‘identifies alternatives, including the
proposed action, presents a concise analysis of the potential impacts of these alternatives, and
identifies any mitigation measures that could be (or will be) undertaken to address potential significant
impacts. ‘
The EA will result in one of two possible outcomes. If the review indicates that the proposed
issuance of the new source permit is likely to result in “significant” adverse impacts that cannot be
avoided through changes in the proposal, then EPA must initiate the more formal process of EIS
preparation. Should the EA review indicate that the proposed action would be unlikely to result in
significant adverse impacts or that those impacts could be avoided by modifying the proposal, EPA
would issue a FNSI.
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EIA Guidelines for Mining
NEPA Requirements and Provisions
Exhibit 2-i. NEPA Environmental Review Process for Proposed Issuance of New Source
NPDES Permits
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A FNSI, which identifies any mitigation measures necessary to make a project environmentally
acceptable, must be made available for public review (typically through publication in the Federal
Register) and comment before issuing the permit.
The process of preparing an EIS is a more complex and formal process that begins with EPA’s
consultation with any other Federal agencies that may be involved in the project. Should EPA be
designated as “lead” agency for the EIS, EPA would then begin the process through the publication
through EPA’s Office of Environmeni al Review of an NO! in the Federal Register. EPA also may
consult with the permit applicant at this point to discuss the option of preparing the EIS through a
“third-party method.” If the applicant and EPA agree on this method (and this agreement must be
expressed in writing), the applicant would then engage and pay for the services of a third-party
contractor to prepare the EIS. Such an agreement will eliminate the need for further independent
preparation of EIDs by the applicant. EPA, in consultation with the applicant, would choose the
contractor, which must provide appropriate disclosure statements attesting to a lack of fmancial or
other conflicting interest in the outcome of the EIS. EPA would manage the contractor and would
have sole authority for approval and modification of EIS conclusions.
At this early stage of the process, a preliminary set of alternatives would be identified, based on
several perspectives:
• Alternatives considered by the applicant
• Alternatives available to EPA
• Alternatives available to other agencies with jurisdiction over the facility.
Next is the scoping process, which involves identi1 ’ing key issues, refining the list and description of
alternatives, and setting general parameters for the data and analyses that will be required to complete
the assessment. Public involvement and interagency coordination are important parts of the scoping
process, which typically involves the convening of a scoping meeting attended by interested parties.
If a third-party contractor is to prepare the EIS, the contractor is not to begin work until after the
scoping meeting is held.
Following the scoping process, the potential impacts of alternatives, including the proposed action,
are analyzed and a Draft EIS (DEIS) is prepared in accordance with strict format and content
requirements. In the course of DEIS preparation, a number of specific coordination and consultation
requirements must be met. These include formal consultation with the U.S. Fish and Wildlife Service
(and/or the National Marine Fisheries Service) regarding threatened and endangered species issues as
well as formal consultation with the State Historic Preservation Offices (SHPO) on any relevant
cultural and historic resource issues.
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EIA Guidelines for Mining NEPA Requirements and Provisions
After the DEIS is reviewed internally by EPA, the public and interested parties are notified of its
availability through a FederaiRegister notice, notices in local newspapers, and letters to participants
in the scoping process. EPA also would conduct one or more public hearings to further solicit
comments on the DEIS.
Following the comment period for the. DEIS, EPA (or the third-party preparers as directed by EPA)
would respond to all comments and would prepare the final EIS (FEIS). After internal EPA. review
of the FEIS, n tification again is made through the Federal Register, notices, and letters to interested
parties. A final review period allows for any additi6nal comments by the public and interested
government agencies.
The lastS step in the EIS process is the preparation. of the ROD; which summarizes the permitting
action that will be taken, as well as any mitigation measures that will be implemented to make the
selected alternative environmentally acceptable. (A discussion of the relationship, between the NEPA
review and the permitting procedures. is presented later in this chapter.)
2.2 TRIGGERS FOR NEPA REVIEW ACTIVITIES
2.2.1 PRIMARY CoNDmoNs THAT TRIGGER NEPA REvIEw
As noted earlier in this chapter, the following two major conditions must be met before NEPA review
requirerñents apply.
2.2.1.1 New Source Determination
A proposed’ NPDES permittee must be determined to be a “new source” before NEPA review
requirement apply. The determination is made by the EPA Region in accordance with NPDES permit I
regulations under 40 .CFR 122.21(1) and 122.29(a) and (b).
2.2.1.2 EPA is the Permitting Authority
The second major condition that must be met before NEPA review requirements apply is that EPA is
the permitting authority. Under NPDES, States and Native Anier can tribes with an approved
program may administer the permttmg program In such cases, the proposed issuance of a new
source permit would not be a Federal action (unless EPA issues a permit in an approved-program
State pursuant to 40 CFR .123.44(h)). Thus,’NEPA requirements would not apply. As of mid-1994,
the NPDES permit program is administered in 40 States. In addition to tribal lands, States and other.
jurisdictions where. EPA is the permitting authority and where NEPA review requirements would
apply are listed below:
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NEPA Requirements and Provisions EIA Guidelines for Mining
• Alaska • Louisiana • Oklahoma
• Arizona • Maine • Texas
• District of Columbia • Massachusetts • American Samoa
• Florida • New Hampshire • Guam
• Idaho • New Mexico • Puerto Rico
2.2.2 WHEN IS AN EIS REQUIRED?
NEPA requires that an EIS be prepared for “major” Federal actions “significantly affecting the
human environment.” Generally, the determination of the need for an EIS hinges on a finding that
the proposedaction would result in significant adverse impacts.
EPA’s procedures provide general guidelines and specific criteria for making this determination
(40 CFR 6.605). General guidelines are (40 CFR 6.605(a)):.
• EPA shall consider both short- and long-term effects, direct and indirect effects, and
beneficial and adverse environmental impacts as defined in 40 CFR 1508.8.
• If EPA is proposing to issue a number of new source NPDES permits within a limited time
span and in the same general geographic area, EPA must consider preparing a
programmatic EIS. In this case the broad cumulative impacts of the proposals would be
addressed in an initial comprehensive EIS, while other EISs or EM would be prepared to
address issues associated with site-specific proposed actions.
EPA’s specific criteria for preparing EISs for proposed new source NPDES permits are found in 40
CFR6.605(b):
• The new source will induce or accelerate significant changes in industrial, commercial,
agricultural, or residential land use concentrations or distributions, which have the potential
for significant effects. Factors that should influence this determination include the nature
and extent of vacant land subject to increased development pressure as a result of the new
source, increases in population that may be induced, the nature of land use controls in the
area, and changes in the availability or demand for energy.
• The new source will directly, or through induced development, have significant adverse
effects on local air quality, noise levels, floodplains, surface water or groundwater quality
or quantity, or fish and wildlife and their habitats.
• Any . part of the new source will have significant adverse effect on the habitat of threatened
and endangered species listed either Federally or by the State:
• The new source would have a significant direct adverse impact on a property listed or
eligible for listing in the National Register of Historic Places.
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EIA Guidelines for Mining NEPA Requirements and Provisions
• Any part of the new source will-have significant adverse efforts on parkiands, wetlands,
wild and scenic rivers, reservoirs or other important water bodies, navigation projects, or
agricultural lands.
The determination of significance can be challenging. CEQ provides some guidance in the form of a
two-step conceptual framework which involves considering the context for a proposed action and its
intensity (40 CFR 1508.27). Context can be considered at several levels, including the region,
affected interests, and the locality. Intensity “refers to the severity of the impact.” CEQ lists a
number of factors to be cdnsidered when judging severity, including:
• Effects on public health and safety
• Unique characteristics of the geographic area
The degree to which effects are likely to be controversial
• The degree to which effects are uncertain or involve unique or uncertain risks -
• Cumulative effect of the action.
• Whether the action would threaten a violation of Federal, State, or local law or regulation.
In his review of legal issues associated with NEPA, Mandelker (1992) summarizes judicial criteria for
significance. He cites the results of Hanly v. Kleindienst (II), where the court stated four criteria that
could be used to make a significance determination:
“First, did the agency take a ‘hard look’ at the problem, as opposed to bald conclusions,
unaided by preliminary investigation? Second, did the Agency identify the relevant areas
of environmental concern? Third, as to problems studied and identified, does the agency
make a convincing case that the impact is insignificant? ... If there is an impact of true -
‘significance,’ has the agency convincingly established that changes in the project have
sufficiently minmu zed it?” -
The nature of the mining industry can make it particularly difficult to assess significance. Potential
impacts are often uncertain, they often are delayed in time from the permitting action, they can be -
quite controversial. Several of the more commonly raised issues surrounding whether the impacts of
a given mining operation could be considered significant are described below.
2.2.2.1 Impacts to Already-degraded Environments and Cumulative Impacts -
Mining operations -are often proposed in areas where previous mining has -occurred, sometimes
directly on. sites that have been mined in the past. Many of these areas have been severely impacted
by past mining activity, and the impacts of a modern mine would occur within the context of pre-
existing conditions (it should be noted that “remining” previously degraded sites can lead to net
improvements in the long-term environmental conditions of a site). In these cases, there are three
fundamental approaches for using baseline conditions to evaluate the significance of impacts:
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NEPA Requirements and Provisions ELA Guidelines for Mining
• Define natural background conditions as the baseline in assessing significance: this
approach emphasizes that additional impacts to already-affected environments are even more
serious than to more resilient undisturbed environments.
• Defme existing conditions as the baseline in assessing significance, but adjust the definition
of significance according to the current quality of the resource that would be affected (i.e.,
environmental effects that would be considered “significant,” and thus would trigger an
EIS, in an undisturbed natural environment may not be considered “significant” in one
where the resource affected is already degraded, and the degree of degradation also
influences the determination).
• Define existing conditions as baseline but use a consistent definition of “significant.”
CEQ regulations require descriptions of the affected environment in EISs (40 CFR 1502.15) but do
not address the issue of how or what pre-existing conditions should be taken into account in assessing
significance. The courts have addressed the issue and come to various conclusions. In practice,
existing conditions have assumed a central place both in assessing significance and in considering
mitigation measures in EAs and EISs. Environthental effects that would be considered significant in
one environment may not be considered significant in another. This has allowed impacts to
particularly “valuable” environments to be assigned a significance differently than similar or more
serious impacts in degraded environments. This is by no means absolute, however, since the
assessment of significance is generally made on a case-by-case basis.
It should be noted that the Clean Water, Act provides less flexibility: discharges to waters of the
United States that do not meet their State-designated beneficial uses and water quality standards are
not allowed to further degrade these waters. This has proven to be a problem in some areas where
waters affected by prior mining activities already fail to attain the beneficial uses and water quality
standards that have been assigned to them by the State. A proposed operation in such areas could
“threaten a violation of Federal, State, or local law or requirements imposed for the protection of the
environment” (40 CFR 1508.27(b)(l0)) and this would be a ‘factor for consideration in determining
the significance of the proposed action. This also points out the need for sufficient technical
documentation of the basis for determination of how a project will ensure compliance with applicable
water quality standards.
In addition, CEQ regulations include “cumulative” impacts among the environmental impacts that
must be assessed under NEPA. CEQ defines (40 CFR 1508.7) cumulative impacts as “the
incremental impact [ s] of the action when added to other past, present, and reasonably foreseeable
future actions....” This is important for proposed mining operations for two reasons. First, new
mines are often located in areas—or directly on sites—where mining took place in the past, and where
there are residual impacts from that mining. As noted above, this can complicate the process of
establishing baseline conditions, and make it extremely expensive. Second, metal mining operations
in particular almost invariably evolve and expand during their active lives. The nature and extent of
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EIA Guidelines for Mining NEPA Requirements and Provisions
future operations depends on the experience gained with the initial operation and on information that
is not obtained until operations begin.
For example, the sizes of and gold concentrations in ore bodies are never fully understood until the
ore body is mined, so the ultimate success in recovering the gold, and the ultimate extent of mining,.
are simply not known at the time initial environmental evaluations must be conducted. Typically,
facility design and operations evolve as more and better information is gained during mining
operations, and the evolution is captured in proposals for major expansions. Such proposed major
expansions usually trigger new evaluations of potential and actual environmental impacts. These,
evaluations are limited by similar information gaps at the time the evaluations are made. However,
there is always much more detailed site-specific information (both environmental and operational) at
the time of a planned expansion, since these types of information are gained during operations. This
information could be used to assess the adequacy of the initial environmental evaluation, and thus to
guide the evaluation for the expansion, but this is not always the case. Indeed, it is not uncommon
for secondary environmental evaluations to be confined to incremental effects of the expansion, not to
• the total impacts of the evolving operation. Thus, assessments of potential environmental impacts of
expanding operations may sometimes be less comprehensive even than initial evaluations. In
assessing impacts under NEPA, however, CEQ regulations make it clear that an environmental
assessment or EIS consider the sum total of impacts (i.e., the cumulative impacts).
2.2.2.2 Uncertain Impacts
As noted above, CEQ regulations (40 CFR 1508.27) indicate that assessing significance requires
considerations of “context” and “intensity.” Intensity, in turn, “refers to the severity of impacts,”
and the regulations list a number of factors that should be considered in evaluating intensity. These
include consideration of “the degree to which the possible impacts . . . are highly uncertain or
involve unique or unknown risks” (*1508.27(b)(6)). Uncertainty.regarding both immediate and
ultimate impacts is a characteristic of most mining operations, particularly metal mining.
In some cases, there may be a relatively low (but to some extent quantifiable) probability that a
mining operation will cause a significant environmental effect, but the effect, were it to occur, could
be severe. Whether such risks “require an impact statement has received surprisingly little attention”
by the courts (Mandelker, 1992). Mandelker cited one case that addressed the issue, in which it was
found that effects which were “only a possibility” could indeed be considered in an impact statement,
and that the agency would have “some latitude” in making a determination that an EIS was or was not
necessary ((Conservation Law Foundation v. Air Force, 26 Env. Rep. Cas. 2146 (D. Mass. 1987)).
This can be an important issue in the case of mining. Acid generation potential, and the development
of acid drainage, for example, can be extremely difficult to predict. There are some mines where
acid generation can be predicted with some confidence, and others where there is only a remote or no
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chance of acid generation. For many (perhaps most) mines, however, there is substantial uncertainty
as to its ultimate occurrence, as described in Chapter 4. Often, acid generation is considered unlikely
but possible, or likely but not certain, based on information available at the time. Other active and
abandoned mines in a particular area may give some idea of the possibility or probability that acid
generation will occur, and any such information should always be assessed. Uncertainty regarding
future acid generation is very common at the time of mine permitting (or approval). As the geology
and geochemistry of the ore body and of waste materials are better understood during the life of the
mine, more accurate predictions can be made; periodic testing and prediction are sometimes required
throughout the life of a mine by States or Federal regulators. There are some cases, however, where
substantial uncertainty exists even at mine closure/reclamation.
When acid drainage develops, it can have catastrophic effects on water quality and aquatic resources
in particular environments. It is nearly always possible to assess the potential impacts on water
quality should acid drainage occur, using various reasonable (and/or worst case) assumptions as to
flow rates and frequency, pH, metals concentrations, etc. This information could be used together
with information on existing surface water or groundwater quality and on aquatic resources, to. assess
the significance of acid drainage should it develop. The assessment of acid generation potential (in
terms of its probability) could then provide guidance as to whether an EIS should be prepared for new
source permit issuance (or for other agencies’ actions that authorize development of a mine).
When potential impacts could have catastrophic consequences, even if the probability of occurrence is
low, they should be analyzed. This analysis should be undertaken even if information is incomplete
or unavailable, and CEQ regulations (40 CFR 1502.22) guide how an agency is to proceed in such
cases. These regulations apply to situations where an EIS is being prepared. In general, the
regulations require that incomplete or unavailable information be obtained and included in the EIS
unless the cost would be “exorbitant.” When costs would be “exorbitant,” the EIS must include a
statement that the information is incomplete or unavailable,, a statement describing the relevance of the
information to the evaluation, a summary of relevant credible evidence, and the agency’s evaluation
of potential impacts based on “theoretical approaches of research methods generally accepted in the
scientific community.” Any such analyses must be “supported by credible scientific evidence,” must
not be “based on pure conjecture,” and must be “within the rule of reason.”
2.2.2.3 Delayed Impacts
Indirect impacts, as defined by CEQ regulations ( 1508.8(b)), include those “caused by the action and
later in time or farther removed in distance, but still reasonably foreseeable.” Such impacts must be
considered in an EA, and significant delayed mpacts can trigger an EIS. An example of a delayed
impact in the context of mining would be acid drainage whose onset occurs years or decades after the
mine opens (or closes). However, there must be a causal relationship between the Federal action (in
this case, permit issuance or other approval) and the indirect effect: the action must be “proximately
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EIA Guidelines for Mining NEPAReqwrements and Pt ovisions
related to a change in the physical environment” (Metropolitan Edison v. People Against Nuclear
Energy, 460 U.S. 7866 (1983)). This would be the case in the case of a new source permit (or other
approval), since the changes in the earth’s surface in excavating a pit or an underground mine, or the
placement of materials ma location and in a configuration that can lead to acid drainage, would be
the direct result ofissuing the permit (or approving theplan) and thus allowing the operation to go
forward. For at least some mines, however, it is not clear if acid generation is “reasonably
foreseeable,” since there can be substantial uncertainty as to its ultimate development. Any prediction
of acid drainage would seem to have to be quantifiable (or otherwise supportable) to some extent,
since at least one court has determined that “unquantified speculation” (American Public Transit
Association v. Goldschmidt 485 F. Supp. 811 (D.D.C. 1980)) that subsequent events would occur is
not sufficient to qualify an action as significant.
2.2.2.4 Duration of Impacts
In general, temporary impacts are not considered significant, but generally the operations of all but
the most ephemeral placer or coal mines would not be considered temporary. Specific activities
associated with mine development, operation, and closure/reclamation are indeed temporary (e.g.,
construction activities associated with mine development), but would have to be considered in terms
of the cumulative impacts of all the effects that result from the Federal action.
2.2.2.5 Transfer of Responsibifity for Facility
The possession of (or responsibility for) a mining facility can change hands several times over the
active life of the facility. In some cases, EPA (or another agency) may have reason to believe that
the new responsible party (i.e.; the new permittee) will be less able or less willing to carry through
on commitments made by the previous party. For example, the site, and the responsibility for
implementing mitigation measures, can become the responsibility of an owner or operator with less
experience in dealing with issues faced by the mine, smaller in size and/or financial resources, with a
worse history of environmental performance, and/or with differences in other regards that give rise to
the concern. The transfer itself would not be a “major Federal action” (certainly, it would not
involve issuance of a new source permit unless site conditions/operations changed). It is not clear if a
transfer accompanied by material changes in stipulated mitigation measures (e.g., a change in the type
or amount of bonding required by a State or Federal agency) would allow for any intervention by
EPA, even though this could have major environmental implications.
2.2.2.6 Controversial Actions and Impacts
CEQ regulations (40 CFR Part 1508.27(b)(4)) provide that agencies are to consider whether
environmental effects are “likely to be highly controversial” in assessing their significance, and thus.
determining whether an EIS must be prepared. Mandelker cites the leading case that addresses this
issue, Hanly v. Kleindienst (II) (471 F.2d 823 (2d Cir. 1972)): “the term ‘controversial’ apparently
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NEPA Requirements and Provisions ELA Guidelines for Mining
refers to cases where a substantial dispute exists as to the size, nature or effect of the major federal
action,” nOt to “neighborhood opposition.” Many or most proposed mining operations are subject to
some opposition, which would not by itself then seem to be a trigger for an EIS. However, for many
proposed mines there can be substantial scientific and engineering uncertainty regarding the “size,
nature or effect” of the potential impacts, or all three. This uncertainty can be particularly acute as to
the ultimate extent of the operation (this occurs at many metal mines, since the full extent of the ore
body is seldom known at the time the mine, begins operation) and to the potential impacts of a given
operation (given the uncertain extent of the operation in the case of metal mines and the difficulty in
predicting the course of reclamation and ultimate performance of mitigation in the case of both metal
and coal mines).
2.2.3 THE RELA11ONSHIP BETWEEN NEPA REvIEw ANI) NPDES PERMITrING AcTiviTiEs
How the NEPA review process affects NPDES permitting activities is a complex issue. EPA
regulations clearly establish procedural and timing relationships between the two processes.
However, how the fmdings of a NEPA review can affect the substantive outcome of the permitting
process is less certain. In particular, there is a gray area as to how EPA should address NEPA
review fmdings that are not related to water quality. As summarized by Mandelker (1992), in a
recent court case it was held that NEPA does not confer on EPA the authority to impose conditions in
effluent discharge permits that are not related to water quality or to other areas within the purview of
the Clean Water Act. 1 However, the court held that NEPA authorized EPA to impose NEPA-
inspired water-related conditions on permits for effluent discharges and to rely on NEPA to deny a
discharge permit. Thus, for example, if a NEPA review indicated that construction associated with a
proposed new source discharge would adversely affect a significant historic resource, EPA would not
be authorized to include in the NPDES permit any conditions that related to that construction.
However, EPA would be authorized to deny issuance of the permit based on a fmding that was not
strictly related to water quality.
It should be noted that most States in which mining occurs have assumed responsibility for
administering the NPDES program. Consequently, EPA now issues very few NPDES permits to
mining operations (new sources or otherwise) and thus is not responsible for NEPA compliance for
such permit issuance very often (neither State issuance of new source NPDES permits, nor EPA’s
concurrence in such issuance, triggers NEPA). However, other Federal agencies are frequently
responsible for preparing EAs or EISs on new mines. Mining often occurs on Federal lands in the
west, thus requiring NEPA compliance by the Bureau of Land Management, Forest Service, or other
land management agency. Also, new mines often require issuance of a Clean Water Act §404 permit,
thus requiring NEPA compliance by the Army Corps of Engineers. When an EIS is prepared in such
cases, EPA often participates as a cooperating agency in the NEPA process pursuant to 40 CFR Part
‘Nawral Resources Defense Council, Inc. v. Environmental Protection Agency, 859 F.2d 156 (D.C. Cir. 1988).
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EIA Guidelines for Mining NEPA Requirements and Prc sions
1501.7. Even where EPA does issue a new source permit, another Federal agency may be the lead
agency in preparing the ETS, again with EPA participating as a cooperating agency.
2.3 LEVELS OF REVIEW
Environmental analysis under NEPA is a process that is attended by extensive internal, interagency,
and public review. In particular, NEPA involves a strong mandate to involve the public in the
environmental analysis process. As discussed below, document’ review is an element of all major
aspects of the analysis process. The formality and intensity of review increases with each escalation
in the hierarchy of NEPA documentation. So, EIDs are subject to the least formal and extensive
review; while EISs are subject to the greatest level of review.
2.3.1 ENvIRONMENTAL INFORMATION DOCUMENT (Eli))
The EID, which is prepared by the permit applicant, is reviewed by the EPA Region. Although no
formal public notice is involved at this stage, documents prepared as part of the NEPA review process
are intended to be readily available for public review. The applicant may request confidential
treatment of certain types of business information that is provided as part of the EID.
2.3.2 Ei 4VIRONMENThL ASSESSMENT DOCUMENTS (EA)
The EA, which is prepared by EPA Regional office staff (or by contractors or the permit applicant
under EPA’s auspices), is reviewed and approved by the EPA Regional Administrator or designee.
The Regional Administrator is formally the “responsible official” for EPA’s action.
The Regional Administrator is required to give notice and make EAs and FNSIs available for public
inspection. EM and FNSIs are reviewed by staff responsible for making permitting decisions prior to
those decisions. Copies of EM and FNSIs are included in the official administrative record for those
permitting actions.
2.3.3 . ENVIRONMENTAL IMPACT STATEMENTS (EISs)
Notices, determinations and other reports and documentation related to an E!S are reviewed internally
by EPA to the level of the Regional Administrator, who serves as the “responsible official,” or the
Regional Administrator’s designee. Through consultation processes with cooperating and other
interested agencies, EPA provides opportunities for joint decision making and review. These
consultation activities take place throughout the EIS preparation process, beginning with initial
discussions regarding the determination of the appropriateFederal lead agencies through review and
comment on the (EIS) ROD.
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The public, too, is provided many oppornmities for review and participation in the assessment
process. These opportunities include the following:
• Publication of the NOI in the Federal Register provides an opportunity for parties to express
their interest in an EIS action.
• A scoping meeting is held early in the process to solicit public and government agency
advice on the issues that should be addressed and any relevant information that should be
considered in the assessment process.
• Draft EISs are made available for review by the public and interested government agencies.
Cooperating and interested parties are provided review copies of Draft EISs. Other copies
are provided in easily accessible areas, such as public libraries in the local area of the
proposed action. EPA must respond formally to all comments made on the Draft EIS.
Comments and responses are represented in a special section of the final EIS.
• Simlar notice is provided of the availability of Final EISs and RODs and copies are sent to
interested.parties for their review.
• The Office of Federal Activities (OFA) also maintains copies of EISs for public review and
also provides a copy to CEQ for its review and consideration.
Draft fmal EISs and RODs are subject to internal review at the regional level, prior to release.
Coordination of the internal review is by the lead branch among the regional program branches.
Depending upon the nature of the specific issue, EPA’s Office of General Counsel (OGC), OFA, the
Office of the Administrator, or other EPA offices may also be included in the internal review cycle.
As is noted elsewhere, EPA’s authorization of most States to administer the NPDES system has
resulted in only occasional issuance by EPA of new source NPDES permits for mining operations.
Even then, EPA Regions more often act as a cooperating or oversight agency on EISs prepared by
other Federal agencies (e.g., Federal land managers or the Army Corps of Engineers). In these case,
EPA reviews preliminary drafts and other EIS-related documents. The jurisdictional and other
reasons for determining lead vs. cooperating agency roles are discussed in CEQ regulations at 40
CFR Part 1501. Under these circumstances, the EPA Region typically drafts a memorandum of
agreement (MOA) with the lead Federal agency, defining respective roles. EPA participates to
varying levels in the preparation of the EIS document (with the objective of adopting the EIS), and
issues an EPA ROD. As would be the case if EPA were the lead agency, the EIS is part of the
administrative record for the NPDES permit and should be complete with regard to documenting the
basis for the decision to issue the permit.
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ELA Guidelines for Mining NEPA Requirements and Provisions
2.4 INFORMATION REQUIRED’ FROM PERMIT APPLICANTS
h cordânce with EPA NEPA procedures, the nature and extent of information required from
applicants as part of the EID are bounded by two separate requirements:
• Ems must be of sufficient scope-to enable EPA to prepare its environmental assessment.
• In determining the scope of the Eli), EPA must consider the size of the new source and the
extent to which the Applicant is capable of providing the required information. EPA must
not require the Applicant to gather data or perform analyses which unnecessarily duplicate
either existing data or the results of existing analyses available to EPA. EPA must keep
requests for data to the minimum consistent with the Agency’s responsibilities under NEPA.
The EPA procedures call for EPA to consult with the applicant to determine the scope of the ELD at
the outset of the process. As discussed in more detail in Chapter 5 of these guidelines, elements of
the EID will be consistent with general requirements for the contents of NEPA documents.
An ong the types of information required for EIDs is a balanced description of each alternative
considered by the applicant. These discussions should include the size and location of facilities, land.
requirements, operation and maintenance facilities, waste management units, auxiliary structures such
as pipelines or transmission lines, and construction schedules.
2.5 TIME INVOLVED IN PREPARING AND PROCESSING NEPA DOCUMENTS
The time required to complete NEPA documentation requirements will vary considerably depending
upon the complexity of issues, public controversy, and other factors. As shown on Exhibit 2-2,
completion of the EA process generally requires at least 5 to 6 months; while completion of the EIS
process ideally requires between 12’ to 20 months but usually takes somewhat longer. As noted on
this exhibit, some elements of the schedule (e.g., public review periods) are established by regulation,
while others are more flexible.
Under EPA’s NEPA procedures, the Applicant may request that EPA establish time limits for the
environmental’ review process consistent with 40 CFR 1501.8.
2.6 LIMITATIONS ON PERMIT APPLICANT ACTIONS DURING THE REVIEW
PROCESS
EPA NEPA procedures state that actions undertaken by the applicant or EPA shall be “performed
consistent with the requirements” of 40 CFR 122.29(c) (see amendment in 51 FR 32609, September
12,1986). In his treatise on NEPA law and litigation, Mandelker (1992) cites a key case that bears
on this issue. In Natural Resources Defense Council, Inc. v. EPA the court held that, provided no
discharge occurred, EPA could not prohibit construction of a new source.
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NEPARequiréments and Provisions
E IA Guidelines for Mining.
Exhibit 2-2. ModeiScheduies for EM and EISs for Proposed issuance of New Source
NPDES Pennits
Determination of New —.
Source/EPA is ________________________________
permitting authority
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Environmental Assessment (EA)
Action determined to • Consultation wfth other Federal agende&
determination of appropriate }ead(1 month)
irrçacts and action Drafting of NOt; internal review, publication end
cannot be moditied to dissemination to interested patties (1 month)
be environmentally
a c oeptable
S I
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0
0 _________________________
N
a Dlaserrtiatfon of Draft E IS; Preparation for Public’
N Sarin - convo*. of Pttfc Hearing (2-3 rmnitia). Public review
‘ r oran bs sSiabJe z is , uWic tentX penS ef 45
- prforbbeer lng ‘ ‘
Response to comments, preparation of final £15;
internal review and issuance (2-4 months).
Public re v iew period of 30 days
, Issuance & ROD and dissemination to parties who
commented on draft or final ElSe (1-2 months).
Environmental Impact Statement (E IS)
Mo EPA p.nnttUng decision r be made unW the taste? the followini dates: (1) day. from Vie beginning of the Draft tis public
renew paLed’; (2)30 day. from the beginning of the Final EJS public review peilet
- The m w psa’iod ol scially s5fls en the FflSy tSiorg the Federal Regissr mpoSg week when OFA rscewss 5 bound copes ala Draft
erF e w lElt
ThISS eta mprnflbve stheO Iss. StheSMs f or spsdfcases may vary based on tie wnçlexlty at Uses, avallabdity of ths. and ether
Sdon. bams tho r in bald are mnan d ebry in eccottance with EPA NEPApiooed.imn
September 1994
.CänsultSnwfthappfcard(1 t EI
Applicant prepares and aibrnits LID (1 month)
EPA revlew repazation of LA (12 months)
.‘ EPA preparation of Draft FNSI; internal review,
public notice (1 month)
Preparation of draft £15; Internal reviews
1 (3 . 6 months)
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EIA Guidelines for Mining Overview of Mining and Beneficiation
3. OVERVIEW OF MINING AND BENEFICIATION
This chapter presents an overview of the processes and activities associated with metal ore and coal
mining and beneficiation as currently practiced in the United States. The activities and processes for
mining and beneficiating many metal ores aré quite similar in many regards, so the first sections (3.1
and 3.2) describe general concepts of ore mining and ore beneficiation which apply to one or more of
the commodity sectors. These general overviews are followed by commodity-specific profiles
(Section 3.3), which discuss in greater detail those aspects of mining and beneficiation that are
particularly important within each of the commodity sectors. These profiles emphasize the process
variations that are unique to that ore, the chemical reagents typically used in beneficiation of each
ore, and physical/chemical properties that result in the discharge of unique waste streams. Coal
mining and coal processing are then addressed in individual sections (3.4 and 3.5).
3.1 ORE MINING
Mining activities generally consist of exploration, site development, ore extraction (including drilling
and blasting, surface mining, and underground mining), and restoration/reclamation. Processes
typical of these activities are discussed below.
In developing effluent limitation guidelines for discharges from mines, a mine was defined by EPA
(1982) as an area of land upon or under which minerals or metal ores are extracted from natural
deposits in the earth by any means or ‘methods. The mne includes the total area upon which such
acti’vities occur or where such activities disturb the natural land surface. A mine also includes land
affected by ancillary operations that disturb the natural land surface, and can include any adjacent.
land the use of which is incidental to any such activities; all lands affected by the construction of new
roads or the improvement or use of existing roads to gain access to the site of such activities; all
lands associated with haulage and excavations, workings, impoundments, dams, ventilation shafts,
drainage tunnels, entryways, refuse banks, dumps, stockpiles, overburden piles, spoil banks, tailings,
holes or depressions; and all repair areas, storage areas, and other areas upon which are sited
structures, facilities, or other property or materials resulting from or incident to sUch activities.
Similarly, in developing effluent limits for discharges from mills, a mill was defined by EPA (1982)’
as a preparation facility within which the mineral or metal ore is beneficiated by being cleaned,
concentrated or otherwise processed prior to shipping to the consumer, refmer, smelter or
manufacturer who will extract or otherwise use the metal contained in the ore. This ore preparation
includes such operations as crushing, grinding, washing,. drying, sintering, briquetting, pelletizing,
nodulizing, leaching, and concentrating by gravity separation, magnetic separation, flotation or other
means. A mill includes all ancillary operations and structures necessary for the cleaning and
concentrating, of the mineral or metal ore, such as ore and gangue storage areas and loading facilities.,
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Overview of Mining and Beneficiation EIA Guidelines for Mining
3.1.1 ExPLoRATION
In the ore mining industry, exploration is defined as all activities and evaluations performed to locate
and define mineral deposits for the purpose of extraction now or in the future. Exploration activities
range from efforts of a one-man prospector to use of sophisticated ground and airborne sensing
equipment, and extensive sampling and testing programs. A typical exploration program consists of
four principal stages (Bureau of Mines, 1977):
• Regional appraisal
• Detailed reconnaissance of favorable areas
• Detailed surface appraisal of target areas
• Detailed sampling and analysis.
A regional appraisal (Stage 1) typically consists of a review of aerial photographs, geologic maps,
geophysical maps, published reports, and other available literature and may cover an area from 2,600
to more than 260,000 square kilometers (1cm) (1,000 to 100,000 square miles). The detailed
reconnaissance of favorable areas (Stage 2) typically covers 26 to 260 km (10 to 100 square miles),
and involves more extensive geologic and geophysical surveys using techniques such as geologic
mapping; stream, sediment, and rock sampling; and non-destructive ground and airborne magnetic,
electromagnetic, radiometric, and remote-sensing imagery studies (Bureau of Mines, 1977a). Stage 3,
the detailed appraisal of target areas, may involve all of the non-destructive evaluation methods used
in Stage 2, and often includes destructive sampling efforts such as drilling and the, excavation of test
pits and trenches. These target area examinations usually cover from 3 to 130 km (1 to 50 square
miles), and may identify the existence of mineral deposits that constitute potential ore bodies. If
further definition of the potential ore appears warranted, then a three-dimensional sampling and
preliminary evaluation program (Stage 4) will be conducted. A Stage 4 investigation typically covers
from 1 to 25 km (0.4 to 10 square miles). Its purpose is to identify the study boundaiy’or limits, as
well as the depth, size, shape, mineralization, and grade of the potential ore deposit. Testing
activities may involve extensive drilling; excavation of test pits, trenches, shafts, and adits;
groundwater pumping tests; blasting tests; and many other forms of destructive testing, as well as the
non-destructive techniques already described. The extent of these tests will depend greatly upon the
location, accessibility, geologic setting, and types of minerals under investigation. In addition,
support activities such as the construction of access roads and the building of temporary living
quarters may be undertaken.
The first two principal stages include very limited destructive testing, if any. The potential for
adverse environmental impact is thus limited to those.impacts associated with gaining access to the
areas. The last two stages, however, involve destructive testing activities which may be undertaken
before or after permit applications are filed. Therefore, construction activities and destructive
exploratory testing that may result in adverse environmental impacts can occur prior to the filing of
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ELA Guidelines for Mining Overview of Mining and Beneficiation
applications for NPDES, PSD. and other Federal, State, and local permits. The exploratory tasks
conducted by the permit applicant, and the known environmental impacts (adverse and beneficial)
resulting from the exploratory activities, should be well documented within the EID.
3.1.2 SITE DEVELOPMENT
Once a mineral deposit of commercial value has been defined by exploration activities, it is necessary
to construct facilities for extracting the ore, beneficiating it if necessary, and transporting it to market.
The site development process has many possible stages depending on the type of mine projected and
its relation to the surrounding transportation system. Site development activities may. include the
following.
3.1.2.1 Construction of Access Roads, Rail Lines, or Ship/Barge Terminals
ROad and rail lines will require clearing a right-of-way, filling or excavating to a desired grade, and
paving or laying rail. This may involve the use of earthmoving equipment such as graders, scrapers,
bulldozers, power shovels or backhoes. These operations may result in the destruction of vegetation
along the rig a-of-way, and possibly the production of excess earth from excavation or the
requirement that borrow pits be created for obtaining fill material. Overburden or waste rock from
the developing mine may be used in road or other construction. In a few cases, acid-generating waste
rock used for various purposes has caused significant problems. In previously undeveloped terrain,
the removal of vegetation and/or soil cover may cause an increase in the rate of local erosion, and,
•where terrain is steep, increase the potential for mass wasting processes such as slumps, landslides,
and mud flows. If excavation extends into hard materials, blasting may be employed. It can be
expected that these operations will produce brush and timber debris which must be removed, buried,
or burned if permitted. There will also be dust generated during earthmoving. Development of ship/
barge loading facilities may require dredging and construction activities that disturb bottom sediment.
3.1.2.2 Construction of Mining Facilities
Initial work at most mines involves obtaining access to the ore bodies. At surface mines, topsoil and
overlying rock must be removed; at underground mines, shafts or adits must be driven. These
operations involve the operation of earth moving and construction equipment, the erection of
structures, and, possibly, major excavation. Waste rock dumps must be provided and topsoil may be
stockpiled for future use in restoration activities.
Also, ancillary facilities such as maintenance and office buildings may be constructed during this
stage. At many larger mining operations, living facilities for mine personnel may involve the
construction of major housing, shopping, and recreational developments.
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Overview of Mining and Beneficiation ELA Guidelines for Mining
3.1.2.3 Construction of Mill Facilities
Unless the ore is of such a high grade that it can be economically shipped for offsite beneficiation, a
mill must be constructed in order to beneficiate the ore to a marketable grade. Usually the mill will
be located as close to the mine as is practicable in order to reduce the costs of transporting the raw
ore. However, in some cases, conditions dictate construction of a mill at a considerable distance
from the mine and Sites at lower elevation are always preferred. Roads, railway lines, and/or
conveyors must be constructed from the mine to the mill. The impacts of mill construction itself will
generally be similar to those incurred in the construction of any industrial/manufacturing facility.
Land must be cleared of vegetation and prepared by excavation and grading. Materials must be
transported to the site and assembled by a sizeable labor force: These operations may result in the
production of vegetation and construction debns, emission of fugitive dust, generation of noise from
construction machinery, and increased sediment loading to local streams, as well as secondary effects
caused by the influx of construction laborers.
3.1.2.4 Other Pre-Mining Activities
Other aspects of mine/mill development may include the need for installing utilities (i.e., electrical
transmission lines or water lines) to the site, or in remote areas constructing a power plant and/or
water supply system. In very remote regions, it may even be necessary to construct a settlement
(i.e., living quarters and support facilities) for the mill construction and operation personnel.
3.1.3 MINING
Minerals are extracted from the earth by a wide variety of techniques. In general, mining consists of
removing the ore from the host rock or matrix 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 ore and barren rock if this is practicable. In practice,
such an ideal separation is not always possible, so that some lower-grade rock is mined and some
higher-grade ore left behind. (As noted below, the distinction between waste rock, “subore,” and ore
is an economic one that varies from mine to mine and can vary in time at specific mines.) Most
extraction processes result in the removal of o .re and associated rock or matrix in bulk form from the
deposit, using various mechanical means to break the ore into pieces of manageable size or to separate
the ore minerals from unwanted material.
Mechanical techniques include the use of explosives or heavy machinery to break up or to excavate
the ore-bearing rock.or matrix; high-pressure streams or jets of water, to disaggregate beds of
sediment; sluices, riffles and other hydraulic devices to separate placer minerals from the bedload of
streams. Some (copper and uranium) ore deposits are suitable for extraction by in situ solution
techniques, in which the ore minerals are dissolved in the ore body by solvents and pumped to
processing areas in solution.
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EIA Guidelines for Mining Overview of Mining and Beneficiation
Although mining processes may be classified according to the numerous techniques that are employed
in removing ore, they can be brokendown Into two broad categories that are associated with the
general setting of the running operation. These are: (1) surface mining or open-pit processes; and
(2) underground mining processes. Specific techniques and applications within this framework are
discussed below.
3.1.3.1 Surface Mining
Surface mining is the major type of mining operation 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. Generally, ore deposits must be within 150 meters
(approximately 500 feet) of the surface for surface mining methods to be economically feasIble.
Surface mining methods typically used for ore extraction are discussed in the following paragraphs.
3.1.3.2 Open Pit Mining
This method involves excavation of an area of ground and removal of the ore exposed in the resulting
pit. Depending on the thickness of the ore body, it may be rerno.ved as a single vertical interval or in
• successive intervals or benches. If the ore is mined as a single vertical interval, it may be feasible to
• place waste rock from one area in the space (pit) left by previous inining of the adjacent area.
However, the ore body generally is mined in benches after the overburden has been completely
removed from the mine area. 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 rail cars or trucks for
transport to the mill or waste rock dumps, as the case may be. In less resistant materials, the ore
may be excavated by scrapers or digging machinery without. the use, of explosives. A variation of
open pit mining involves use of a central shaft (or glory hole) into which ore from an open pit is
dropped. The ore is allowed to move downward through the vertical or inclined shaft to an
underground level where it is loaded into cars for transport to the surface. This method is especially
favored if the ore body is relatively deep and narrow.
3.1.3.3 Dredging .. . . .
Placer deposits are concentrations of heavy’ metallic minerals which occur in sedimentary. deposits
associated with watercourses or beaches (either current or ancient). These deposits can be mined by
surface open pit methods, but in some cases can be better handled by dredging. For this method, the
mine area is flooded and the excavating/mining equipment mounted on a barge. In hard materials the
dredge uses a mechanical digging system to break up and excavate the deposit, while soft deposits can
be removed by hydraulic suction alone. Mechanical dredges can use individual digging buckets
(clamshells) to excavate the material; or, if conditions permit, will use a chain of buckets which dig
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as a continuous sequence and transport material steadily into the dredge for processing. Suction
dredges essentially operate as “vacuum cleaners” to mine out the alluvial material, although some
have a revolving cutter head to aid in breaking up the material’ prior to its removal by suction. Placer
deposits can also be worked with small portable ‘suction units and by traditional hand’ sluicin,g and
panning; however, these portable suction and panning methods can handle only limited volumes of
material. There are no commercial dredges operating in the United States -as of the 1990s, although
the technology may be in use elsewhere. Also, suction dredging in the United States is mainly
practiced by recreational miners or very small commercial miners.
‘3.1.3.4 Underground Mining
Underground mining has been the major method for production of several metals but is increasingly
less common in the United States. Underground mining activities typically have significantly less
impact on the surface environment than do surface methods. This is due both to the fact that less
waste rock is mined with ores that are mined underground, and the fact that waste material can be
used to backfill mined out spaces. However, large underground openings such as stopes can cause
subsidence or caving at the surface, resulting in significant disturbance to structures, roads, drainages 1
etc. Drainage from underground mines also may cause significant alteration to the quality of surface
water and can affect groundwater quantity ‘and quality.
Several underground mining procedures rely on the natural support of the ground, including:
Room and Pillar. This method is suitable for level deposits that are fairly uniform in
thickness. It consists of excavating drifts (horizontal passages) in a rectilinear pattern so
that evenly spaced pillars are left to support the overlying material. A fairly large portion
of the ore (40%-50%) must be left in place. Sometimes the remaining ore is recovered by
removing or shaving the pillars as the mine is vacated, allowing the overhead to collapse or
making future collapse more likely.
• Open. Stope. In competent rock, it is possible to remove all of a moderate sized ore body,
resulting in an opening of considerable size. Such large, irregularly-shaped openings are
called stopes. The mining of large inclined ore bodies often requires leaving horizontal
pillars across the stope at intervals in order to prevent collapse of the walls.
Some other degree of support is required in most underground mines. ‘The basic concepts of the
methods described above can be extended to permit working in less competent rock to allow
extraction of a, greater percentage of the ore, by using various methods of permanent or temporary
support in order to prevent or delay collapse.
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Underground mining methods that use these temporary or permanent methods of support include the
following:
• Longwali. In level, tabular ore bodies it is possible to recover virtually all of the ore by
using this method (in the United States, only coal is known to have been mined using
longwall methods). Initially, parallel drifts are driven to the farthest boundary of the mine
area. The ore between each pair of drifts is then mined along a continuous face (the
longwall) connecting the two drifts. Mining proceeds back toward the shaft or entry, and
only enough space for mining activities is held open by moveable steel supports. As the
longwall moves, the supports are moved with it and the mined out area is allowed to
collapse. Various methods can be used to break up and remove the ore. In many cases,
the rock stresses that are caused by the caving of the unsupported area aids in breaking the
material, in the longwall face.
• Shrinkage Stoping. In this method, mining is carried out from the bottom of an inclined
or vertical ore body upwards, as in open stoping. However, most of the broken ore is
allowed to remain in the stope in order both to support the stope walls and to provide a
working platform for the overhead mining operations. Ore is withdrawn from chutes in the
bottom of the stope in.order to maintain the correct amount of open space for working.
When mining is completed in a particular stope, the remaining ore is withdrawn, and the
walls are allowed to collapse.
• Cut and Fill Stoping. If it is undesirable to leave broken ore in the stope during mining
operations (as in shrinkage stoping), the lower portion of the stope can be filled with waste
rock and/or mill, tailings. In this case, ore is removed as soon as it has been broken from
overhead, and the stope filled with waste to within a few feet of the mining surface. This
method eliminates or reduces the waste disposal problem associated with mining as well as
preventing .collapse of the ground at the surface.
• Square-set Stoping. Ore bodies of irregular shape and/or that occur in weak rock can be
mined by providing almost continuous support as operations progress. A squareset is a
rectangular, three-dimensional frame usually of timber, which is generally filled with waste
rock after emplacement. In this method, a small square section of the ore body is removed,
and the space created is immediately filled by a square-set. The framework provides both
lateral and vertical support, especially after being filled with waste. Use of this method
may result in a major local consumption of timber and/or other materials utilized for
construction of the sets.
• Top Slicing. Unlike the previously described methods in which mining begins at the
bottom of an ore body and proceeds upward, this procedure involves mining the ore in a
series of slices from the top downward, first removing the topmost layer of the ore and
supporting the overhead with timber. Once the top layer of an area is completely removed,
the supports are removed and the overlying material allowed to settle onto the new top of
the ore body. The process is then repeated, so that as slices of ore are removed from the
ore body, the overburden repeatedly settles. Subsequent operations produce an ever-
thickening mat of timber and broken supports. This method consumes major quantities of
timber.
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Additional methods of underground mining involve procedures in which ore is broken by removing its
support, allowing the forces produced as the ore mass subsides to break the ore into manageable
pieces. Methods based on this principal include:
• Block Caving. Large massive ore bodies may be broken up and removed by this method
with a minimum of direct handling of the ore required. Generally, these deposits are of
such a size that they would be mined by open-pit methods if the. overburden were not so
thick. Application of thi method begins with the driving of horizontal crosscuts below the
bottom of the ore body, or below that portion which is to be mined at this stage. From
these passages, inclined raises are driven upward to the level of the bottom of the mass
which is to be broken. Then a layer is mined so as to undercut the ore mass and allow it to.
settle and break up. Broken ore descenth through the raises and can be dropped into mine
cars for transport to the surface. When waste material appears at the outlet of a raise it
sigrnfies exhaustion of the ore in that interval. If the ore extends to a greater depth, the
entire process can be continued by mining out the mass which contained the previous
working passage.
•. Sublevel Caving. In this method, relatively small blocks of ore within a vertical or steeply
sloping vein are undercut within a stope and allowed to settle and break up. The broken
ore is then scraped into raises and dropped into mine cars. This method can be considered
as an intermediate between block carving and top slicing.
Naturally there are many variations and combinations of the basic methods discussed above. For
example, a stope which is not quite capable of standing open without support may be maintained by a
series of single timbers (or stulls) placed from wall to wall in a system called stull stoping. Many of
the variations and combinations of underground mining utilized today have been developed in
response to specific or unusual characteristics of the ore being mined. Mining methods used in the
production of specific ores are presented by ore subcategory in subsequent sections of this chapter.
3.1.3.5 In Situ Solution Mining
This is a method of underground mining that is applicable to certain ores under certain geohydrologic
conditions. In principal, a series of wells are drilled into the ore body and a solvent is circulated
through the ore-bearing formation by injection through some of the wells and withdrawal through
others. Use of the method has àbvious geochemical restrictions based upon the amenability of the ore
minerals to solution 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. In situ solution mining is at present applied most
widely to uranium and copper deposits in suitable geohydrologic settings.
Although there is little disturbance of the bulk properties of the surface and underground materials at
an in situ solution mine, the effects of the operation on the quality of underground water can be
enormous. In order to solubilize the ore minerals, the chemistry of the groundwater must be
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drastically altered by the introduced solvents. In addition to the ore minerals, other materials are
dissolved by the solvent action and these, too, enter the groundwater, generally rendering it
unacceptable for human or animal consumption and often presenting a hazard of further contamination
if the altered groundwater moves out of the mine area and into surrounding areas. Provisions for
emergency cleanup and post-mining restoration of the groundwater often are required prior to
issuance of permits for this type of operation.
3.1.4 MINING WASTES AND WASTE MANAGEMENT
The wastes generated by mining operations (as opposed to mills) in the largest quantities, and that
present the most significant environmental impacts during and after mining, are mine water and waste
rock. These are described in the following two subsections. Other wastes are generated in much
smaller quantities, and they generally have much less environmental significance. Many of these -
wastes are described in the commodity-specific discussions in Section 3.3. (It should be noted that
the use of the terms “mining waste” and “waste management unit” in this document does not imply
that the materials m questions are “solid wastes” within the meaning of the Resource Conservation
and Recovery Act.)
3.1.4.1 Mine Water
Mine water is water that must be removed from the mine to gain or facilitate access to the ore body.
For surface mines, mine water can originate from precipitation, flows into the pit or underground
workings, and-from groundwater aquifers that are intercepted by the mine. Mine water can be a
significant problem at many mines, and enormous quantities may have to be pumped continuously
from the mine during operations. Dewatering can result in significant groundwater drawdowns, and
this in turn can result in the loss of streamflows as well as wetland and riparian habitat in some areas.
Uses of mine water can include:
• Dust control on the mine site (with or without prior treatment, depending on its quality and
regulatory requirements).
• Process water in the mill circuit (again, with or without prior treatment).
• Discharge to surface water pursuant to an NPDES permit, which would include effluent
limits on the discharge (limits would be either the 40 CFR Part 440 effluent limits on mine
drainage or more stringent limits if those were necessary to protect water quality).
When a mine closes, removal of mine water from the mine generally ends. 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.
Recovery of groundwater to or near pre-mining levels following the cessation of pumping can take -
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substantial amounts of time, however,> and effects that result from groundwater drawdown (e.g.,
reduction or elimination of suffac water recharge) may continue to be felt for decades or centuries.
Mine water can have enviTonmentally 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, and release of mine water during active operations and for decades afterward can present
enormous problems to surface and ëroundwater resources.
3.1.4.2 Waste Rock
The primary waste generated by both underground and surface mining is waste rock. Waste rock
consists of non-mineralized and low-grade mineralized rock removed from above or within the ore
body during extraction activities (Hutchison, 1991). Waste rock includes granular, broken rock and
soils ranging in size from fme sand to large boulders, with fmes content largely dependent on the
nature of the formation and the methods employed during mining.
Depending on the nature of and depth to the ore deposit, mine waste rock may constitute the largest
volume waste stream generated by a mining project. The quantity of waste rock generated relative to
ore extracted from a mine is typically larger for surface mines than underground mines, reflecting the
greater costs àf underground mining operations. The ratio of waste rock to ore, described as the
stripping ratio, may range as high as 10:1 for some areas, with typical values ranging from 1:1 to 3:1
for most mineral types.
Waste rock geochemistry varies widely from mine to mine, and may vary significantly at individual
mines over time as differing lithologic units are exposed. Generally, waste rock at metal mines will
always contain some concentration of the target mineral along with other metals. The mobility of any
particular constituent of waste rock is highly dependant on ite specific conditions such as climate,
hydrology, geochemistry of the disposal unit and its foundation, mineralogy, etc. Waste rock from
metal mines often contains sulfidic materials as components of the host rock. The concentration of
sulfide minerals, and of neutralizing minerals, are important factors in the potential for waste rock to
generate acid rock drainage (ARD), which is discussed in detail in Section 4.1.
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. As the
name implies, valley fills partially or completely fill the topographical depression formed by valley
walls, with the walls providing stability and containment. Cross-valley fills span the mouth of a
valley but do not completely fill the up-slope volume of the depression. Side-hill fills are formed by
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disposing of waste rock down slope from the crest of a ridge and represent the most common form of
waste rock dumps (BCMDC, 1991). Heaped fills or waste piles are constructed in areas of flat
terrain where available topography and other factors require.
Regardless of the layout of the unit, waste rock dumps are generally constructed on unlined terrain,
with underlying soils stripped, graded, or compacted as regulations and engineering consideration
require. Such conditions may include steep foundations of unconsolidated material or partially
saturated terrain that may not support the weight of fill material. Rock is hauled to the face of the
unit in trucks or by conveyor systems and dumped. Surface grading of fill material is typically
perfonned to provide haulage trucks access to the working face. Most commonly, waste rock is
deposited at the angle of repose. If multiple lifts are constructed, or if stability of the dump is a
concern, side slopes maybe graded. Additionally, final dump slopes may be graded during
reclamation activities.
Depending on site hydrology and regulatory constraints, drainage systems may be incorporated into
dump foundations. In areas of ground water 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.
Equally important are surface water and run-on controls. Such controls are often necessary to
maintain stability and prevent mobilizatiOn of fines as well as erosion of exposed slopes. Upstream
surface water diversion ditches and rock drains are options often incorporated into design for these
purposes.
3.1.5 RESTORATION AND RECLAMATION
Restoration activities often are conducted during surface mining activities in order to reduce
environmental impacts and enhance visual aesthetics in the mining area. Although these restoration
activities do prove valuable, they do not replace or lessen the necessity for full and comprehensive
land reclamation at the completion of various staged mining activities. Temporary restoration
activities may involve tasks such as landscaping in non-mining areas, soil stabilization by replacement
of native grasses on spoil bank slopes, and using temporary vegetation covers on topsoil and other
stockpiles.
Restoration activities conducted during underground mining operations are similar to those used in
conjunction with surface mines, but are more limited since the waste piles developed as a result of
underground mining are relatively smaller. Restoration activities conducted during underground
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mining activities include landscaping and erosion control measures around the mining site, and the
periodic sealing of drift entryways to prevent mine drainage.
Full-scale land reclamation activities begin upon completion of mining or of planned unit mining
stages. These stages can be three to five year plans for large mines, or one- to three-month events
for very small mining operations. Land reclamation activities are not temporary restoration measures
taken to redute impacts of daily mining activities, but represent permanent measures that are taken to
restore the earth’s surface to some level of productivity and to reduce to the greatest extent possible
the permanent effects of the mining operation.
Surface mining activities involve massive disturbance. Thus, any reclamation activity itself is a major
undertaking. Reclamation of some sort is required by Federal land managers and nearly all States.
The specific reclamation that is undertaken by a given mine depends on the anticipated future uses of
the land and regulatory agency requirements.
Closure and reclamation of waste rock piles and dumps have three major purposes: isolating toxic or
reactive materials from the environment, providing for long-term stability, and returning as much of
the pile or dump to some semblance of long-term beneficial use. The latter two objectives have
received the most attention in the past, and techniques to achieve them are better understood. The
first has begun to receive much more attention, but techniques are as yet generally unproven. The
following techniques can be used alone and in combination to reclaim waste rock dumps. The
specific techniques that are used to reclaim particular waste rock dumps are based on site-specific
factors and regulatory requirements.
Grading the top surface of sidehill dumps so that it slopes gently back toward the hillside,
away from the face of the dump. When combined with prepared ditches (e.g., rip-rap)
where the hillside meets the dump, this minimizes erosion and reduces flows down the steep
face of the dump. For valley dumps, grading of the top surface should result in gentle
slopes that direct and control flows so as to reduce uncontrolled runoff over the face of the
dump. For freestanding piles, grading is generally intended to direct precipitation flows to
prepared channels that convey flow over and down the sides of the dump in a controlled
fashion. If the waste rock has no acid generation potential, some infiltration may be
encouraged by creating shallow topographic lows in the top surface. Infiltration near an
angle-of-repose slope should be avoided, since it could lead to saturation of surface
materials and cause slumping and slope failure.
Compacting the top surface of the dump, covering with stockpiled topsoil (possibly
amended with organic matter such as sewage sludge and/or mulch), and seeding with native
• plant species. This minimizes both erosion and infiltration. Drought-resistant plant species
• may be appropriate since the substrate is generally unsaturated. Revegetation should be
monitored for at least several years following reclamation to ensure that plant communities
become well-established.
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Removing waste rock and using it as backfill in underground workings or the open pit.
This can be prohibitively expensive, and is generally not an economic option after the waste
rock has already been placed in dumps. In addition, nonreactive (i.e., not acid forming)
waste rock can be used as construction material during successive stages of mine
development (e.g., roads, tailings dams, water diversion berms, building foundations,
underdrains) and for off-site construction.
• Regrading steep slopes of the dump. to slopes less than the angle of repose, thus enhancing
long-term stability. Regrading can include incorporating flat benches at intervals of the
slope to reduce runoff velocity and provide another surface suitable for revegetation.
Depending on the size of the waste rock, it may be appropriate to cover slopes with topsoil
and revegetate.
• If the dump contains acid-generating waste rock, reducing infiltration becomes even more
important. This can be accomplished by lining the top surfaces of dumps with synthetic
materials or clay. Then, the cap or liner is covered with a protective layer of fine-grained
material, covered witli topsoil, and revegetated; alternatively, the surface can be covered
with large rocks and boulders. When revegetating, particular care must be taken in
selecting the plant species, since they must resist extreme cycles of drought and saturation.
In addition, species must be shallow-rooted to avoid penetrating clay caps.
3.2 ORE DRESSING (BENEFICIATION)
Most ores contain the valuable metals disseminated in a matrix of less valuable rock called gangue.
The purpose of ore beneficiation is the separation of valuable minerals from the gangue to yield a
product which is 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 little value. Overall recovery is optimized
according to the value (and marketability) of the concentrate produced.
Many properties are used as the basis for separating valuable minerals from gangue, including:
specific gravity, conductivity, magnetic permeability, affmity for certain chemicals, solubility, and the
tendency to form chemical complexes. Processes for effecting separation may be generally considered
as: gravity concentration, magnetic separation, electrostatic separation, flotation, and leaching.
Amalgamatior and cyanidation are variants of leaching which bear special mention. Solvent
extraction and ion exchange are widely applied techniques for concentrating metals from leaching
solutions, and for separating them from dissolved contaminants.
3.2.1 GRAvrrY CONCENTRATION
Gravity-concentration processes exploit differences in density to separate ore minerals from gangue.
Several techniques (e.g., jigging, tabling, spirals, sink/float separation) are used to achieve the
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separation. Each is effective over a somewhat limited range of particle sizes • the upper bourid of
which is set by the size of the apparatus and the need to transport ore within it, and the lower bound
by the point at which viscosity forces predominate over gravity and render the separation ineffective.
Selection of a particular gravity-based process for a given ore will be strongly influenced by the size
to which the ore must be crushed or ground to separate values from gangue,. as well as by the density
difference and other factors.
Gravity concentration typically involves three general steps, the first to remove grossly oversized
material from the smaller fraction that contains the valuable mineral (generally gold), the second to
concentrate the mineral, and the third to separate the fine values from other fine, heavy minerals.
The same type of equipment is often used in more than one step; for example, an array of jigs may be
employed to handle successively finer material (Flatt, 1990).
Classification (sizing) is the initial step in the beneficiation operation. Large, oversized material
(usually over 3/4 inch) is removed. A rough (large diameter) screen is usually used. This step may
be fed by a bulldozer, front-end loader, backhoe, dragline or conveyor belt. Within the gold placer
industry, this step is also referred to as roughing (EPA, 1 988a). Previous studies have indicated that
the practice improves the efficiency of gold recovery and reduces water consumption (Bainbridge,
1979).
After the initial removal of the larger material during sizing, ore is subject to a coarse concentration
stage. This step, also referred to as cleaning, may employ trommels or screens. Other equipment
used in the coarse concentration stage includes sluices, jigs, shaking tables, spiral concentrators and
cones. Depending on the size of the particles, cleaning may be the final step in beneficiation (Flatt,
1990; Silva 1986).
Fine concentration is the final operation used to remove very small values from the concentrate
generated in the. previous stages. Many of the previously identified pieces of equipment can be
calibrated for finer separation sensitivity. Final separation uses jigs, shaking tables, centrifugal
concentrators, spiral concentrators or pinched sluices.
The following is a summary of the equipment commonly used in beneficiation. One of the key
determinants in selecting equipment is the volume of material that will pass through each step within a
given time period. Rates for ore handling for the equipment discussed below are included where the
information was available.
3.2.1.1 Si7ing
Sizing is the physical separation of material based strictly on size. The sizing step removes large
rocks prior to additional beneficiation. The waste generated is usually solid and is much lower in
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volume compared to the ore that passes through. Discharge material may be used for other
applications including road aggregates. This step typically involves the ore being loaded into a
grizzly, trommel or scróen, or a combination thereof.
A typical grizzly consists of a large screen or row of bars or rails set a specific distance apart (2 to 6
inches) such that undersized (gold-bearing)• material can readily pass through while oversized material
is rejected. Typically, the grizzly would be inclined to ease the removal of the rejected material..
Water is usually used to move material through the grizzly and wash off any fmes that may be
attached to larger fragments before they are discarded. The undersized material drops onto a
trommel, screen, or sluice depending on the operation. Grizzlies may be stationary or vibrating
(EPA, 1988a).
Trommels are wet-washed, inclined, revolving screens. They usually consist of three chambers, the
first uses a tumbling action and water to break up aggregated material. Successive chambers are
formed of screens or punched metal plates (smaller holes first) that allow the selected sized material
to pass through. The screens are typically 3/8 inch in the second chamber and 3/4 inch in the final
chamber. Material passing tl ough the screens is directed for further concentration. Material passing
through the trommel may be returned for a second pass or discarded (Cope and Rice, 1992; EPA,
1 988a).
A fixed punchplate screen (also called a Ross Box) consists of an inclined plate with holes ranging
from 1/2 to 3/4 inches. Ore is placed Onto the plate where nozzles wash the material with a high-
pressure water stream. The undersized (desirable) material is washed to the outside of the plate
where it is fed into a sluice designed to handle 3/4 inch material. The oversized material is directed
down the plate which typically has riffles to collect coarser gold. Oversized material passing off the
plate is discarded.
Screens function to separate oversized, undesirable material from the ore. Screen size (usually 1/2 to
3/4 inch) is selected based on ore characteristics. Screens may be fixed or vibrating. The action of
both is similar although vibrating screens speed the rate of particle separation. The concentrate
continues for further concentration while the oversized material is removed via a chute or stacker
conveyor belt. Different sized screens may be used to sort material into different sizes for use as
road construction aggregate or other purposes.
3.2.1.2 Coarse Concentration
Separation in the cOarse. concentration step involves particle density rather than size. Sluices are the
pieces of equipment most commonly used by gold placer mines in the coarse concentration step
although jigs and screens may also be employed. The wastes are discharged to a tailings pond, also
called a recycle pond or settling pond. Most of the material that enters the sluice exits as waste. The•
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gold and other heavy minerals settle within the lining material while the lighter material is washed
through. Coarse concentration generates the largest volume of waste during beneficiation.
A sluice consists of a long, narrow, inclined trough lined with riffles, perforated screens, astroturf,
corduroy, burlap, or a combination thereof. The sluice mimics the conditions that caused the
formation of the placer deposit initially. Ore is placed at the high end of the trough and washed with
a stream of water. Gold and other dense minerals settle between the riffles or in the lining while the
lighter material is ç arried through the sluice. Longer sluices are used for preliminary concentration.
Shorter, wider sluices are used following preliminary separation to separate fme gold from black
sands. The length, grade, riffles and lining are adjusted to suit the nature of the ore. However,
slopes of one to two inches per foot are typical.
Riffles are bars, slats, screens or material that act to create turbulence and variation of water flow
within the sluice. This action increases the efficiency of gravity separation. Riffles have ranged in
size from 12 inches wide, 12 inches high and 12 inches apart to 1 inch high, 1 inch wide and 2 inches
apart.
Hungarian riffles are angle irons mounted perpendicular to the sluice box. The vertical angle of the
angle irons may be adjusted to affect the degree of turbulence generated and maximize gold
deposition. Astroturf, carpet or coconut husks are sometimes placed between and under the riffles to
maximize their efficiency. The units are usually constructed so that sections of the riffles may be
removed so the gold can be recovered from the turf. As mentioned above, the height, spacing and
construction of the riffles may be adjusted to maximize efficiency of separation depending on the
character of the ore.
Other material has also been tested and/or used as riffles and liners. Expanded metal riffles are
employed at some operations. Like the hungarian riffles, the height, size and spacing is detennined
by the ore and sections are removable for cleaning. Miscellaneous materials including longitudinal or
horizontal wooden poles, blocks, rocks, railroad ties, cocoa mats, rubber and plastic strips have also
been documented as being used as riffles by different placer operations (EPA, 1988a).
3.2.1.3 Fine Concentration
After the ore is concentrated, typically through a trommel and sluice, most waste material has been
removed leaving a fme concentrate. The concentrate may then be subjected to fine concentration
methods including jigs, shaking tables and pinched sluices. Depending on the nature of the
concentrate and the equipment, 80 to 95 percent of gold can be recovered from the concentrate at this
stage. The waste at this stage is a slurry (often called shines), and is low in volume compared to that
generated in the other stages.
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Jigs are settling devices that consist of a screen through which water is pulsed up and down via’ a
diaphragm or plunger numerous times per second. A layer of rock or steel shot referred to as
ragging may be placed on the screen to accentuate the up and down motion. Slurry is fed above the
screen. The agitation keeps the lighter material in suspension which is then drawn off. The heavier
material falls onto or through the screen and is collected as concentrate. Efficiency is increased by
varying the inflow rate, pulse cycles and intensity. Jigs may handle from 7 to 25 tons per hour, and
can handle particles ranging from 75 mm to 25 mm. At some operations, jigs are also employed in
the cleaning stage. (Macdonald, 1983; Silva, 1986).
Shaking tables consist of small riffles over which a slurry containing fme ore is passed. The gold
settles into the riffles and, through a vibrating action, is directed to one side of the table where it is
collected. The tails are passed across the middle of the table or remain in suspension. Middlings,
material that is partially settled, may be collected. Heads and middlings are commonly reprocessed
on multi-stage tables. Shaking tables can handle materials from 15 urn to 3.0 mm (EPA, 1988a;
Macdonald, 1983).
Spiral concentrator is a generic term referring to a method of separation rather ‘a specific piece of
equipment. Ore concentrated from previous steps is fed with water into the top of the spiral and spins
down through the spiral. The heaviest materials are concentrated toward the center of the spiral while
lighter material moves to the outside. Concentrates are collected from the center of the spiral while
the tails pass down the entire spiral. Large operations may employ multiple spiral concentrators in
series to handle a wide range of sizes. Humphreys concentrators, as one example, can be used to
separate particles between 100 urn and 2 mm in diameter. These machines can handle low feed’ rates
(1.5-2 tons per hour) and low feed density (EPA, 1988a).
Centrifugal concentrators or bowls were typically used in dredges but may also be used in other
operations. Slurry is fed into the top of the circular machine. Driven from the bottom, the interior
portion ipins on its vertical axis, driving the slurry against a series of concentric circular riffles or
baffles. The lighter material (tails) is driven up the side of the bowl while the heavy material
(concentrate) collects on the bottom or in the riffles (Cope and Rice, 1992).
Pinched sluices work on the concept that as a fme feed is exposed to an opening, the arc formed by
the heaviest particles dropping will be much narrower than the arc formed by the lighter materials. A
divider placed perpendicular to and below the pinched outfall lets heavy materials (concentrate) collect
on one side while lighter material (tails) can be collected and reprocessed separately or directed out of
the operation completely. Reichert cones, which are based on the pinched sluice principle, can handle
75 tons per hour and recover particles in the minus 10 to plus 400 mesh range (45 urn to 0.5 mm)
(Gomes and Martinez, 1983).
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Magnetic separation (see Section 3.22) is not commonly used in gold placer mining but may be
employed when magnetite is a component of the black sand. This technique is used to remove
electrostatically charged tails from the neutral gold. To be effective, the method should involve
multiple magnetic treatments followed by demagnetization steps so that the magnetite is removed
slowly, not in a ‘magnetically coagulated’ form that may bind gold particles within it. Magnetic.
separation, when used, is one of the final steps of beneficiation.
3.2.1.4 SinkIFloat Separation
Sink/float (heavy media separation) separators differ from most gravity methods in that buoyancy
forces are used to separate the various minerals on the basis of density. The separation is achieved by
feeding the ore to a tank containing a medium whose density is higher than that of the gangue and
less than that of the valuable ore minerals. As a result, the gangue floats and overflows the
separation chamber, and the denser values sink and are drawn off at the bottom, often by means of a
bucket elevator or similar contrivance. The size of material separated by this method varies, and is
dependent on the density and viscosity of the medium. Because the separation takes plaèe in a
relatively still basin and turbulence is minimized, effective separation may be achieved with a more
heterogeneous feed than for most gravity-Separation techniques. Viscosity does, however, place a
lower bound on particle size for practicable separation, since small particles settle very slowly,
limiting the rate at which ore may be fed. Further, very, fine particles must be excluded, since they
mix with the separation medium, altering its density and viscosity. Media commonly used for
sink/float separation in the ore milling industry are suspensions of very fine ferrosilicon or galena’
(PbS) particles. Ferrosilicon particles may be used to achieve medium specific gravities as high as
3.5, and are used in “heavy-medium separation.” Galena allows the achievement of somewhat higher
densities of ore concentrate.
3.2.2 MAGNETIC SEPARATION
Magnetic separation is widely applied in the ore milling industry, both for extraction of values from
ore and for separation of different valuable minerals recovered from complex ores. Magnetic
separation is used in beneficiating ores of iron, coluinbium and tantalum, and tungsten. Separation is
based on differences in magnetic permeability (which, although small, is measurable for almost all
materials) and is effective in handling materials not normally considered magnetic. The basic process
involves transport of ore through a region of high magnetic-field gradient. The most magnetically
permeable particles are attracted to a moving surface, behind which is the pole of a large
electromagnet, ‘and are carried by it out of the main stream of ore. As the surface leaves the
high-field region, particles are released into a hopper or onto a conveyor leading to further
processing.
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For large-scale applications, particularly in the iron-ore industry, large rotating drums surrounding the
magnet are used. Although dry separators are used for rough separations, these drum separators are
most often run wet on the slurry produced in grinding mills. Wet and crossed-belt separators are
frequently employed where smaller amounts of material are handled.
3 2.3 ELECTROSTATIC SEPARATION
Electrostatic separation is used to separate minerals on the basis of their conductivity. It is an
inherently dry process using very high voltages. In a typical application, ore is charged at 20,000 to
40,000 volts, and the charged particles are dropped onto a conductive rotating drum. The conductive
particles lose their attractive charge very rapidly and are thrown off and collected, while the
non-conductive particles keep their charge and adhere by electrostatic attraction. They may then be
removed from the drum separately.
3.2.4 FLOTATION
Basically, flotation is a process where 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 carr with them the particles of the mineral(s) to be
separated from the matrix. If a foaming agent is added which prevents 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. Requirements for success of the operation are
that particle size be small (typically flour-sized or less), that reagents compatible with the mineral to
be recovered be used, and that water conditions in the cell not interfere with the attachment of
reagents to minerals or to air bubbles.
Flotation concentration has become a mainstay of the ore milling industry because it is adaptable to
very fme particle sizes of less than 0.01 mm (.0004 in.). It also allows for high rates of recovery
from slinies, which are inevitably generated in crushing and grinding and which ar not generally
amenable to physical processing.. As a physico-chemical surface phenomenon, it can often be made
highly specific, allowing production of high-grade concentrates from very low-grade ore (e.g., over
95% MoS 2 concentrate from 0.3% ore). Its specificity also allows separation of different ore
minerals (e.g., CuS, PbS, and ZnS) where desired, and operation with minimum reagent consumption
since reagent interaction typically occurs only with the particular materials to be floated or depressed.
Details of the flotation process (e.g., exact type and dosage of reagents, fineness of grinds, number of
regrinds, cleaner-flotation steps) differ at each operation where it is practiced and may often vary with
time at a given mill. A complex system ? 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
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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 low, being generally less than 0.5 kg (approximately I lb) per ton of ore processed; at large-
capacity mills, the total. reagent usage can be high, since tens of thousand of tons of ore per day may
be beneficiated. The bulk of the reagent adheres to tailings or concentrates.
Sulfide minerals are all readily recovered by flotation using similar reagents in small doses, although
reagent requirements and ease of flotation do vary throughout the class. Sulfide flotation is most
often carried out at alkaline pH. Collectors are most often alkaline xanthates having two to five
carbon atoms—for example, sodium ethyl xanthate (NaS 2 COC 2 H). Frothers are generally organ Cs
with a soluble hydroxyl group and a “non-wettable” hydrocarbon. Sodium cyanide is widely used as
a pyrite depressant. Activators useful in sulfide-ore flotation may include cuprous sulfide and sodium
sulfide. Other pyrite depressants which are less damaging to the environment may be used to replace
the sodium cyanide. Sulfide minerals of copper, lead, zinc, molybdenum, silver, nickel, and cobalt
are commonly recovered by flotation.
Minerals in addition to sulfides may be recovered by flotation (e.g., oxidized ores of iron, copper,
manganese, the rare earths, tungsten, titanium, and columbium and tantalum). Generally, these
flotation processes are more sensitive to feed-water conditions than sulfide floats; consequently,
oxidized ores can less frequently run with recycled water. Flotation of these ores involves very
different reagents from sulfide flotation and may require substantially larger dosages. Reagents used
include fatty acids (such as oleic acid or soap skimmings), fuel oil, and various amines as collectors;
and compounds such as copper sulfate, acid dichromate, and sulfur dioxide as conditioners.
3.2.5 LEACHING
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 hydrochloric acid, or sodium cyanide
solution. The desired metal is then removed from the “pregnant” leach solution by chemical
precipitation or other chemical or electrochemical process. When ores are (or can be) so fractured or
shattered in texture that air and water can be made to percolate through them as they exist in the
ground, then the ores can be profitably leached in-situ (in place) without being mined. Ores that are
mined, but are too low in grade to justify the cost of milling, can be recovered by placing the ore
rock in large piles on an impermeable surface and treating them with the leach solution, which is
collected through a drain system at the bottom of the pile. This method is termed 4 ’heap” or “dump”
leaching. Heap leaching is widely used in the gold industry, dump leaching in the copper industry.
Vat or tank leaching is similar to heap leaching, with the exception that the ore rock is placed in a
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ELA Guidelines for Mining Overview of Mining and Beneficiation
container (vat) equipped for agitation, heating, aeration, pressurization, and/or other means of
facilitating the leaching of the target mineral.
Ores can be leached by dissolving away either the gangue or the value in aqueous acids or base,
liquid metals, or other special solutions. Typical leaching situations include:
• Water-soluble compounds of sodium, potassium, and boron which are found in arid climates
or under impervious strata can be mined, concentrated, and separated by leaching with
water and recrystallizing the resulting brines.
• Vanadium and some other metals form anionic species (e.g., vanadates) which occur as
insoluble ores., Roasting of such insoluble ores with sodium compounds converts the values
to soluble sodium salts (e.g., sodium vinadate). ‘After cooling, the water-soluble sodium
salts are removed from the gangue by leaching in water.
• Uranium ores are only mildly soluble in water, but they dissolve quickly in acid or alkaline
solutions.
•‘ Native gold which is found in a finely divided state is soluble in mercury and can be
extracted by amalgamation (i .e , leaching with a liquid, metal).
• Nickel can be concentrated by ‘reduction Of the nickel with ferrosilicon at a high
temperature and extraction of the nickel metal into molten iron. This process, called
skip-ladling, is related to liquid metal leaching. S.
‘ Certain solutions (e.g., sodium cyanide) dissolve’specific metals (e.g., gold) or their
compounds, and leaching with such solutions immediately concentrates the values.
Leaching solutions can be categorized as strong, general solvents (e.g., acids) and weaker, specific
solvents (e.g., cyanide). The acids dissOlve certain metals present, which often include gangue
constituents (e.g., calcium from limestone). They are convenient to use, since the ore does not have
to be, ground very fine, if at all (i.e., approximately 5 to,30 cm (2 to 12 inches) in diameter), and
then separation of the tailings from the value-bearing (pregnant) leach• solution is not difficult. In the
case of sulfuric acid, the leach is cheap ‘but gangue constituents in addition to the value are dissolved.
Specific solvents attack only one (or, at most, a few) ore constituent(s), including the one being
sought. Ore must often be crushed or finely ground to expose the values, although this is 5 not always
necessary.
Countercurrent leaching, preneutralization of lime in’ the. gangue, leaching in the grinding process,
and other combinations of processes that simplify or improve the’ effectiveness of the leaching
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procedure are often seen in the industry. The values contained in the pregnant leach solution are
recovered by one of several methods, such as:
• Precipitation. The process of separating mineral constituents (i.e., values) from a solution
by chemical means, by evaporation, or by changing the temperature and/or pH of the
solution.
• Electrowinning. The recovery of metal values from solutions by an electrochemical
process similar to electrolytic refming. Insoluble (long-life) anodes are used, with the
desired metal produced as or on a cathode.
• Carbon Adsorption. The target mineral is adsorbed onto activated carbon and further
concentrated.
• Cementation. The process by which a metal is precipitated or “cemented” out of solution
as a finely divided metallic product by replacement with less active metal. For example,
when a copper solution (CuSO4) is brought into contact with scrap iron plates, (Fe), the
copper replaces the iron on the scrap plates and the iron goes into solution (FeSO4). The
copper is then removed by washing the scrap plates.
Amalgamation represents a special application of leaching and/or the recovery of the leached mineral.
Amalgamation is a process by which mercury, in its natural liquid state, is alloyed with some other
metal to produce an “amalgam” (a solution containing mercury and another metal(s) in liquid form).
This process is applicable to free milling precious metal ores, which are those in which the ore is
free, relatively coarse, and has clean surfaces. The current practice of amalgamation in the United
States is limited to small-scale barrel amalgamation of a relatively small quantity of high-grade,
gravity-concentrated gold ore. The gravity concentrate is ground in an amalgam barrel with steel
balls or rods before mercury is added. This mixture is then gently ground to bring the mercury and
gold into intunate contact. The resulting amalgam is collected in a gravity trap. Although the
amalgamation process has, in the past, been used extensively for the extraction of gold and silver
from pulverized ores, in recent years it has largely been superseded by cyanidation processes, as
described in Section 3.3.1.
3.2.6 BENEFICL4TION WASTES AND WASTE MANAGEMENT
Tailings are the wastes generated in by far the largest quantities by beneficiation operations that use
flotation and gravity separation. This section describes the most common method of managing and
disposing of tailings from metal mines. Tailings from gravity separation are described in the
discussion of gold placer mining in Section 3.3.2. Leaching operations also generate enormous
quantities of spent ore and small quantities of process solutions: the management of wastes from heap
leaching is described in the discussion of gold mining (Section 3.3.1), the industry sector in which
heap leaching is most commonly practiced; the management of wastes from dump leaching is
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EIA Guidelines, for Mining Overview of Mining and Beneficiation
described in the discussion of copper mining (Section 3.3.4), the industry sector in which dump
leaching is most commonly practiced.
Tailings are the coarsely and finely ground waste portions of mined material that have been separated
from the valuable minerals during beneficiation (crushing, grinding and concentration). By far the
larger proportion of ore mined in most industry sectors ultimately becomes tailings that must be
disposed of. In the gold industry, for example, only a few hundredths of an ounce of gold may be
produced for every ton, of thy tailings generated. Similarly, the copper industry and others typically
mine relatively low-grade ores that contain less than a few percent of metal values; the residue
becomes tailings. Thus, tailings disposal is a significant part of the overall mining and milling
operation. The physical and chemical nature of tailings varies according to the ore being milled and
the milling operations used to beneficiate the ore. The method of tailings disposal is largely
controlled by the percent water content of the tailings. Generally, three types of tailings may be
identified based on their water content: wet, thickened and dry.
Most ore milling processes require the use of water to classify (grinding stage) and concentrate the
valuable minerals. Although dewatering of tailings is a common final step prior to the transport and
disposal of the tailings, an equal or greater weight of water remains with the solids in a slurry
mixture. These tailings are known as wet tailings. More recently, some mills have begun to
significantly dewater tailings to where only 40 percent of their total weight is water. These tailings
are known as thickened tailings.
A few beneficiation operations, such as magnetic separation, may require little or no water for
preparing the ore. Tailings beneficiated with these methods are normally known as dry tailings.
Magnetic separation extracts magnetic minerals, such as iron, from the nonmagnetic particles, which
remain as tailings. Although tailings from beneficiation operations may be considered dry tailings,
they may Contain a small weight percentage of water. In ’ addition to the specific beneficiation
operations that produce dry tailings, belt filtering (which removes liquids from tailings by transporting
the tailings on a cloth belt over a vacuum box) results in tailings with only 20 to 30 percent total
weight in water. These tailings are also considered to be dry tailings.
3.2.6.1 Mine Backfilling
Slurry tailings are sometimes disposed in underground mines as backfill to provide ground or wall
support. This decreases the above-ground surface disturbance and can stabilize mined-out areas. For
stability reasons, underground backfilling requires tailings that have a high permeability, low
compressibility, and the ability to rapidly dewater (i.e., a large sand fraction). As a result, only the
sand fraction of whole tailings is generally used as backfill. Whole tailings may be cycloned to
separate out the coarse sand fraction for backfilling, leaving only the slimes to be disposed in an
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impoundment. To increase structural competence, cement may be added to the sand fraction before
backfihling (Environment Canada, 1987).
3.2.6.2 Subaqueous Disposal
Subaqueous disposal ma permanent body of water such as a lake, the ocean, or an engineered
structure (e.g., a pit or impoundment) is also a possible disposal method. The potential advantage to
underwater disposal is that it may prevent the oxidation of sulfide minerals in tailings, thus
prohibiting acid generation. However, there is substantial uncertainty regarding other short- and
long-term effects on the water body into which the tailings may be disposed (Rawson Academy 1992;
U.S. Bureau of Mines 1992). Canada’s Mine Environment Neutral Drainage (MEND) program is.
currently studying subaqueous disposal.
In a bench-scale 16-year simulation of deep-lake disposal using Ottawa River water by CANMET
(Canadian Centre for Mineral and Energy Technology), Ritcey and Silver (1987) found that the
tailings had little effect on pH when using ores with a low sulfide content. Ripley, et a!. (1978),
found that the tailings can cover large areas on the ocean or lake floor and cause turbidity problems if
the disposal practice is not designed correctly. There are little data on the long-term efficacy and
environmental effects of subaqueous disposal (Environment Canada, 1987), although this issue is
being intensively studied in Canada.
Subaqueous disposal recently has been practiced by eight mines in Canada, where its use predated
current regulations. Three of these mines still were active and disposing of their tailing underwater
(two in lakes, one in the ocean) as of 1990 (Environment Canada, 1992), as were a number of mines
elsewhere in the world. In the United States, regulations under the Clean Water Act (e.g., the
effluent limitation guidelines for mills that beneficiate base and precious metal ores) effectively
prohibit subaqueous disposal of tailings in natural water bodies (i.e., any discharge to “waters of the
U.S.”). The use of subaqueous disposal in engineered structures has not been tried in the U.S.,
although it has been proposed in at least one case.
3.2.6.3 T iHngs Impoundments
Because mine tailings produced by the mill 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. Because costs are often
directly related to the amount of fill material used in the dam or embankment (i.e., its size), major
savmgs can be realized by minimizing the size of the dam and by maximizing the use of local
materials, particularly the tailings themselves. Leakage from tailings impoundments is a serious and
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EIA Guidelines for Mining Overview of Mining and Beneficiation
ongoing environmental problem at many operating mines. Any leakage can transport contaminants to
ground or surface water; uncontrolled leakage can threaten the integrity of the impoundment structure
itself. Increasing numbers of impoundments are lined, with or without leachate collection systems.
Although this reduces the risk of leakage, at least in the short term, the long-term integrity of liners is
as yet untested, particularly following mine closure when routine inspections and maintenance may be
reduced or eliminated.
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 move, or control the movement of, fluids both vertically and horizontally.
Water retention dams are constructed to their final height before the impoundment begins to receive
tailings. The design and construction of these impoundments is similar to conventional earth dam
technology. A typical design includes an impervious core, downstream filter and drainage zone and
upstream riprap. Upstream slopes are often steeper than those required for a water storage dam
because rapid drawdown is not experienced. This impoundment type is best suited for tailings
impoundments which must retain large water volumes. Ponds which may require this type of
impoundment construction include those that receive large volumes of storm water runoff or store mill
effluent not recirculated back to the mill process.
Raised embankments are constructed over the life of the impoundment and are initially begun as a
starter dike constructed of native soils or borrow materials including waste rock and tailings.
Embankment raises are constructed to keep pace with the rising elevation of the tailings and
floodwater storage allowance. The embankment raises may be constructed using a variety of
materials including tailings, overburden and native soil and may be positioned downstream, upstream
or directly on top of the starter dike.
The three most common methods used to construct tailings embankments are upstream, downstream
and centerline. Upstream construction begins with a starter dam constructed at the downstream toe of
the planned impoundment, with tailings discharged peripherally from the crest of the starter darn
using spigots or cyclones. This deposition develops a dike and wide beach area composed of coarse
material which in turn becomes the foundation of the next dike. Some type of mechanical compaction
of the dike is typically conducted before the next stage of the dam is constructed.
As in upstream construction, downstream construction also begins with a starter dam constructed of
compacted borrow materials; however, this starter dam may be constructed of pervious sands and
gravels or with predominantly silts and clays to minimize seepage through the dam. The downstream
method is so named because subsequent stages of dike construction are supported on top of the
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Overview of Mining and Beneficiation EL4 Guidelines for Mining
downstream slope of the previous section, shifting the centerline of the top of the dam downstream as
the dam stages are progressively raised. Peripheral spigotting and on-dam cycloning and spreading
are common depositional methods used for downstream embankments. Again, some type of
mechanical compaction is typically performed.
Centerline construction is similar to both the upstream and downstream construction methods in that
the embankment begins with a starter dam and tailings are spigotted off the crest of the dam to form a
beach. The centerline of the embankment is maintained as fill and progressive raises ar’e placed on
both the beach and downstream face. The tailings placed on the downstream slope are typically
compacted to prevent shear failure.
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. In addition, tailings in valleys or other natural depressions
present less relief for air dispersion of tailings material.
Valley irnpoundnients (and variations) are the most commonly used impoundments. There are several
variations of valley-type impoundments. The Cross-Valley design is frequently used because it can be
applied to almost any topographical depression in either single or multiple form. Laid out similarly to
a conventional water-storage dam, the darn is constructed connecting two valley walls, confming the
tailings in the natural valley topography. This configuration requires the least fill material and
consequently is favored for economc reasons. The impoundment is best located near the head of the
drainage basin to minimize flood inflows. Side hill diversion ditches may be used to reduce normal
runon if topography allows, but large flood runoff ma)’ be handled by dam storage capacity,
spillways, or separate water-control dams located upstream of the impoundment.
Other types of valley impoundments may be employed when there is an excessively large drainage
catchment area and/or there is a lack of necessary valley topography. Two variations are the side-hill
impoundment and the valley-bottom impoundment. The side-hill layout consists of a three-sided dam
constructed against a hillside. This design is optimal for slopes of less than 10% grade. Construction
on steeper slopes requires much more fill volume to achieve sufficient storage volume.
If the drainage catchment area is too large for a cross-valley darn and the slope of the terrain is too
steep for a side-hill layout, then a combination of these two designs, the valley-bottom impoundment,
may be considered. Valley-bottom impoundments are often laid out in multiple form as the valley
floor rises, in order to achieve greater storage volume. Because the upstream catchment area is
relatively large, it is often, or usually, necessary to convey upstream flows around (and/or under)
valley-bottom impoundments.
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Where natural topographic depressions are not available, the Ring-Dike configuration may be
appropriate. Instead of one large embankment (as in the valley design), embankments (or dikes) are
required on all sides to contain the tailings. Construction can be similar to valley dams, with tailings,
waste rock, and/or other native materials typically used in later phases of construction. Because of
the length of the dike/dam, more materials are necessary for this configuration, and material for the
initial surrounding dikes is typically excavated from the impoundment area.
Open-pit backfilling is also practiced, where tailings are deposited into abandoned pits or portions of
active pits. The Pinto Valley tailings reprocessing operation, located in Arizona, uses this method to
dispose of copper tailings. In active pits, embankments may be necessary to keep the tailings from
the active area. However, since seepage from the tailings can adversely affect the stability of the pit
walls or embankmènts, it is unusual to see disposal in active pits. Williams (1979), for example,
discusses a failure due to pore water pressure in the floor of a pit in Australia. Ritcey (1989) notes
that the hydrogeological parameters affecting the migration of seepage and contaminants are poorly
understood, so tailings with toxic contaminants or reactive tailings may be poor candidates for this
• type of impoundment. This method is much less common than the valley and ring-dike
impoundments. Since the tailings are protected by pit walls, wind dispersion is minimized. Good
drainage can be incorporated into the design. Many of the failure modes common to tailings
embankments (e.g., piping, liquefaction) do not apply to this design. The lack of dam walls reduces
the possibility of slope failure, but the stability of the pit slopes do have to be checked.
Specially dug pit impoundments are fairly unusual and involve the excavation of a pit specifically for
the purpose of tailings disposal. The impoundment consists of four or more cells with impermeable
liners surrounded by an abovegrade darn. Material removed from the pit is used in construction of
the dam. This dug pit/dam design has some of the same advantages as the ring-dike design, including
site independence and uniform shape. Site independence benefits the design, since less effort and cost
are needed to counteract topographic obstacles, soil conditions, climatic conditions, and construction
obstacles. The uniform layout, shape, and flat terrain prevents surface runoff from entering the
impoundment and decreases the requirements for flood control measures.
Irrespective of the layout of the impoundment, at most facilities, water may be decanted from tailings
ponds and recirculated to the mill forreuse in beneficiation processes. In general, two methods are
available for decanting pond water; decant towers and pumping (usually from floating barges).
Decant towers are.vertical concrete risers with intake ports that rise from the bottom of the
impoundment upward through the tailings. A concrete conduit extends from the bottom of the decant
tower to beyond the dam toe. Decant towers may not be a preferred method for decanting due to the
potential for conduit rupture and the resulting potential for internal erosion and collapse of the dam.
Floating barges offer flexibility for relocation to various parts of the pond. and may not present a
potential for dam failure.
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Tailings slurry (wet tailings and thickened tailings) is usually abrasive and highly viscous, which
presents complications for the design, construction, operation and maintenance of tailings transport
systems. Slurried tailings may be transported from the mill to the tailings pond by gravity flow
and!or pumping through open conduits or pipes. Pipe wear is a significant problem that may be
mitigated by the use of rubber lined steel pipes or high-density polyethylene pipe. The transport
system may become plugged with settling solids if the minimum flow velocity is not maintained or if
provisions are not made for pipe drainage during mill shutdowns. Tailings may be discharged from
the conveyance system to any location along the impoundment perimeter; however, as discussed
previously, tailings (particularly sand tailings) spigotted along raised embankments may provide
additional stability.
Siting of tailings impoundments may be influenced by a number of factors, including location and
elevation relative to the mill, topography, hydrogeology and catchment area, geology and
groundwater. Layout of impoundments may be virtually independent of the type of embankment used
to confine it. Essentially any of the embankment types or raising methods discussed previously may
be used, provided that the embankment type is compatible with site-specific conditions and the
characteristics of mill tailings and effluent.
3.2.6.4 Dry T i1ings Disposal
In some cases, as noted above, tailings are dewatered (thickened to 60 percent pulp density or more)
or dried (to a moisture content of 25 percent or below) prior to disposal. The efficiency and
applicability of using thickened or dry tailings depends on the ore grind and concentrations of gypsum
and clay as well as the availability of alternative methods. Except under special circumstances, these
methods may be prohibitively expensive due to additional equipment and energy costs. However, the
advantages include minimizing seepage volumes and land needed for an impoundment or pile, and
simultaneous tailings deposition and reclamation (Vick, 1990).
Tailings piles are non-impounding structures that are designed for the disposal of dry tailings or
thickened tailings. Dry tailings piles are considerably different from tailings piles created as a result
of thickened tailings disposal. Dry tailings may be disposed of in piles that may be constructed in a
variety of configurations. These include: a valley-fill, where tailings are simply dumped to in-fill a
valley; side hill disposal, where tailings are disposed on a side of a hill in a series of piles; and level
piles that may grow as lifts are added through out the life of the mine. The maximum slope of
tailings piles is determined by the physical and chemical characteristics of the tailings.
Thickened tailings are typically spigotted as a very viscous slurry from a permanent discharge line,
creating a conical pile. No embankments are needed with the exception of a small dam constructed
down stream from the piles to intercept and collect seepage. This method of disposal may be best
suited for areas close to the mill and with low relief topography.
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EIA Guidelines for Mining Overview of Mining and Beneficiation
3.3 COMMODITY-SPECIFIC MINING AND BENEFICIATION PROCESSES
The remainder of this section describes the mining and milling of specific metal ores, with individual
ores discussed in separate subsections. The ores and industry sectors discussed in the following
subsections include gold and silver (Section 3.3.1), gold placer (3.3.2), lead-zinc (3.3.3), copper
(3.3.4), iron (3.3.5), uranium (3.3.6), and other ores (3.3.7). The industry sectors discussed in more
detail (in Sections 3.3.1 through 3.3.6) are those representing the most mining activity in the United
States as of the early 1990s. Although EPA has developed effluent limitations guidelines for other
industry sectors, there are few (and in some cases, no) actives mines for the other sectors, including
molybdenum, tungsten, and mercury.
3.3.1 GOLD AND SILVER
Historically, gold has been the principal medium of international monetary exchange, although its role
has changed significantly in recent years. Between 1934 and 1972, the United States monetary
system was on a gold standard at a fixed rate of $35 per troy ounce (a troy ounce equals 1.09714
‘avoirdupois ounces, so there are 14.6 troy ounces per pound). After leaving the gold standard in
1975 and allowing private ownership of the metal, the U.S. gold market grew rapidly and the price of
gold peaked at $850 per ounce in January 1980. Prices are notoriously volatile and gold prices are
set on a number of world exchanges. ‘In the 1990s, gold has generally traded in the $300 to $400 per
troy ounce range.
In 1992, U.S. gold operations produced an estimated 10.3 million troy ounces of gold from ore,
valued at $3.6 billion. This represented an increase of 10 percent over 1991 production and nearly a
tenfold increase over production in the early 1980s, which averaged less than 1.5 million troy ounces
annually. An estimated 70 percent of 1992 gold production was used for jewelry and art (including
coinage), 23 percent for industrial purposes (primarily in the electronics industry), and 7 percent in
dentistry (Bureau of Minàs, 1986a and 1993).
Many new gold mines opened in the United States throughout the 1980s (24 in 1989), and mines
continue to expand their production capabilities. The United States is now the second largest gold
producer in the world. According to the Bureau of Mines, there, are about 200 lode gold mines in the
United States, primarily in the west, and a dozen or more large placer mines in Alaska (plus hundreds
of small commercial placer mines in Alaska). In addition, there are hundreds or thousands of
“recreational” lode and placer gold mines that may operate periodically (Bureau of Mines, 1993).
Gold has been mined in virtually every State but production has been concentrated in 15: Alaska,
Arizona, California, Colorado, Idaho, Michigan, Montana, Nevada, New Mexico, North Carolina,
Oregon, South Carolina, South Dakota, Utah, and Washington. According to the Bureau of Mines,
approximately 10 percent of gold production is produced as a’ by-product of other mining, with the
3-29 September 1994
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Overview of Mining and Beneficiation EIA Guidelines for Mining
remainder produced at gold mines. In 1991, about 61 percent of newly mined domestic gold from
gold mines (or 5.7 million troy. ounces) was mined in Nevada, 10 percent in California, 6 percent in
both Montana and South Dakota, and 1 percent in Colorado, Arizona, Alaska, and Idaho. The 25
leading domestic gold-producing mines in 1991 are identified in Exhibit 3-1. These mines accounted
for 68 percent of all domestically produced gold in that year. (Bureau of Mines, 1992 and 1993).
Like gold, silver has been a principal medium of international monetary exchange. Silver, however,
is also an importazfl metal in many other applications. Mine production in 1992 exceeded 57 million
troy ounces. Nevada mines produced over 34 percent of the total, followed by Idaho (16 percent),
Montana (11 percent), and Arizona (7 percent). About 50 percent of silver is used in manufacturing
photographic products, 21 percent in electrical and electronic products, and 20 percent for a variety
of other uses (Bureau of Mines, 1993). Exhibit 3-2 identifies the U.S. mines that produced the most
silver in 1991; several of these have since closed, either permanently or temporarily.
Prices for silver also peaked in the early 1980s, but have been severely depressed in recent years.
This depressed price (generally in the range of $4 to $5 per ounce) has resulted in a significant
reduction in silver mining: although silver is produced by over 150 U.s. mines (Bureau of Mines,
1993), it is mined now only in conjunction with other metals, notably gold and copper. At the
present time, there is essentially no mining in the U.S. whose primary target is silver. This section
focusses on gold since silver is now recovered by U.S. operations only with gold or with other metals
that are discussed in separate sections. (Although Exhibit 3-2 identifies several mines whose silver is
derived from “silver ore,” in every case only the other metals recovered make recovery of silver
economic. Beneficiation processes for silver include flotation similar to other metals and cyarndation
similar to gold (although with higher cyanide concentrations), and silver mining presents no unique
operational or environmental issues.)
3.3.1.1 Geology of Gold Ores
Estimates of average abundance of gold in the Earth’s crust are on the order of 0.003 to 0.004 parts
per million (ppm) (U.S. Geological Survey, 1973). Deposits considered to be economically
recoverable at current market prices may contain as little as 0.69 to 1.37 ppm (0.02 to 0.04 troy
ounces of gold per ton of rock [ ozftI), depending on the mining method, total reserves, and the
geologic setting of the deposit. (In absolute terms, 0.04 troy ounces of gold per ton translates to a
gold:ore ratio of 1:729,150.)
All gold deposits, except placer deposits, were formed by hydrothermal processes. Hydrothermal
systems form in numerous geologic environments, ranging from dynamic systeini associated with
magmatic intrusives to low-energy systems associated with deep fluid circulation heated by geothermal
heat flow. Deposits formed from hydrothermal systems flowing at or near the surface (1,000 to
2,500 feet deep) are called epithermal deposits, while those formed deeper are called mesothermal
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E A Guidelines f r Mining Overview f Mining and Beneficiation
Exhibit 3-1. Twenty-Five Leading Gold-Producing Mines in the United States, 1991
Rank
Mine -
.
County and State
Oper tor
Sourceof
Cold
1
Nevada Mines operations
Elko and Eureka NV
r raont Gold Co.
Gold Ore
2
Goldatrike
f NV
Barrick Mercury Gold Mines Inc.
Gold Ore
2
Biz h cn Caawm
Salt Lake VT
Kennecou-Utah Copper Corp.
Copper Ore
4
Jerriut C w (Enfield Bell)
Elko NV
Freeport-McMoran Gold Co.
Gold Ore
5
Smoky valley Cotunion etazàoo
Nyc NV
Round Mountain Gold Corp.
Gold Ore
6
Homestake
Lzi rence SD
Hotnestake Mining Co.
Gold Ore
7
McCoy and Cove
Lander NV
Echo Bay Mining Co.
Gold Ore
8
McLaughlin
Napa CA
Homestake Mining Co.
Gold Ore
9
Chimney Creek
Humboldt NV
Gold Fields Mining Co.
Gold Ore
10
Fortitude and Surprise
Lander NV
Battle Mountain Gold Co.
Gold Ore
11
Bulldog
Hyc NV
Bond Gold, Bullfrog, Inc.
Gold Ore
12
Mesquite
Imperial CA
Goldfields Mining Co.
Gold Ore
13
Getchell
Humboldt NV
FMG Inc.
Gold Ore
14
Sleeper
Humboldt NV
Aniax Gold Inc.
Gold Ore
15
Cannon
Chelan WA
Asajnera Minerals (U.S.) Inc.
Gold Ore
16
Ridgeway
Fairfield SC
Ridgeway Mining Co.
Gold Ore
17
Jamestown
Tuolumne CA
Sonora Mining Corp.
Gold Ore
18
Paradise Peak
Nyc NV
FMC Gold Co.
Gold Ore
19
Rabbit Creek
Humboldt NV
Rabbit Creek Mining Inc.
Gold Ore
20
Barney’s Canyon
Salt Lake City UT
Kennecon Corp.
Gold Ore
21
Continental
Silver Bow MT
Montana Resources
Copper Ore
22
Zortman-Landusky
Phillips MT
Pegasus Gold Inc.
Gold Ore
23
Golden Sunlight
Jefferson MT
Golden Sunlight Mines Inc.
Gold Ore
24
Wind Mountain
Washoe NV
Amax Gold Inc.
Gold Ore
25
Foley Ridge & Annie Creek
Lawrence SD
Wharf Resources
Gold Ore
Source: Bureau of Mines, 1992.
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Overview of Mining and Beneficiation EIA Guidelines for Mining
Exhibit 3-2. Twenty-Five Leading Silver-Producing Mines in the United States, 1991
Rank
Mine
County and State
Operator
Source of Silver
1
McCoy and Cove
Lander NV
Echo Bay Mining Co.
Gold Ore
2
Greens Creek
Admiralty Island AK
Greens Creek Mining Co.
Zinc Ore
3
Rochester
Pershing NV
Coeur Rochester Inc.
Silver Ore
4
Bingham Canyon
Salt Lake UT
Kennecott-Utah Copper Co.
Copper Ore
5
Iroy
Lincoln MT
ASARCO Inc.
Copper ore
6
Red Dog
NW Arctic AK
Cominco Alaska
Zinc Ore
7
Sunshine
Shoshone ID
Sunshine Mining Co.
Silver Ore
8
Lucky Friday
Shoshone ID
Hecla Mining Co.
Lead-Zinc Ore
9
DeLamar
Owybee II)
NE CO De-Lamar Co.
Gold Ore
10
Paradise Peak
Nye NV
FMC Gold Co.
Gold ore
11
Galena
Shoshone ID
ASARCO Inc.
Silver Ore
12
Montana Tunnels
Jefferson MT
Montana Tunnels Mining Inc.
Zinc Ore
13
Mission Complex
Pima AZ
ASARCO Inc.
Copper Ore
14
White Pine
Ontonogon MT
Copper Range Co.
Copper ore
15
Candelaria
Mineral NV
NERCO Metals Inc.
Silver Ore
16
Continental
Silver Bow MT
Montana Resources Inc.
Copper Ore
17
Ray Unit
Pinal AZ
ASARCO Inc.
Copper ore
18
Denton-Rawhide
Mineral AZ
Kennecott Rawhide Mining Co.
Gold Ore
19
Zortman.Landusky
Phillips MT
Pegasus Gold Inc.
Gold ore
20
Morenci
Greenlee AZ
Phelps Dodge Corp.
Copper Ore
21
Bagdad
Yavapai AZ
Cyprus Bagdad Copper Co.
Copper ore
22
San Manuel
Pinal AZ
Magma Copper Co.
Copper ore
23
Battle Mountain Complex
Lander NV
Battle Mountain Gold Co.
Gold Ore
24
Chino
Grand NM
Phelps Dodge Corp.
Copper Ore
25
Pinto Valley
Gila AZ
Magma Copper Co.
Copper ore
Source: Bureau of Mines, 1992.
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September 1994
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EIA Gwdelines for Mining Overview of Mining and Beneficiation
deposits. Combinations of the various types of hydrothermal systems in various host rocks create
variations in deposit morphology, grade ranges (variation in gold content), and wall rock alteration.
Deposit morphology ranges in a continuum from veins several feet thick and hundreds to thousands of
feet in vertical and lateral dimensions (formed by mineral precipitation in voids in the host rock) to
disseminated mineralization (essentially micro veinlets) pervading through the host rock in irregular
pods up to several hundred feet in dimension.
Gold deposits m y be categori d based on similarities in geologic environment and generic
hydrothermal factors. Recent data show that the 25 largest gold producing mines in the U.S. may be
grouped into four types: sediment-hosted disseminated gold (examples are the Goldstrike and Gold
Quarry mines), volcanic-hosted epithermal deposits (McLaughlm, Chimney Creek), porphyry copper-
related deposits (Bingham Canyon), and greenstoñe gold-quartz vein deposits (Homestake). (Bureau
of Mines, 1990c).
Grades range in all deposit types from subeconomic margins to high-grade ores. The term “high
• grade” varies with mining methods but usually refers to ores greater than 0.1 or 0.2 oz/t. Likewise,
average deposit grades are economic distinctions. Deposits requiring high-cost mining and milling
methods may require bulk averages of 0.25 oz/t or more, at 0.15 or higher cutoffs Those deposits
that are amenable to the lowest-cost mining and milling methods may average 0.03 to 0.04 oz/t or
• less with an ore-to-waste separation grade of about 0.01 oz/t.
The mineral content or assemblage of a deposit is the result of reactions between hydrothermal
solutions and the wall rock, influenced by wall rock chemistry, solution chemistry, temperature, and
pressure. Most gold ores contain some amount of sulfur-bearing minerals; carbonate deposits may
also contain carbonaceous material. The weathering environment affecting the ore body following
deposition is determined mainly by the location of the water table (either present or past) in relation
to the deposit. Ores above the water table, in the vadose or unsaturated zone, will tend to be
oxidized (referred to as “oxide ores”), while ores below the water table will usually be unoxidized
(referred to as “sulfide ores”).
Gold ores may contain varying amounts of arsenic, antimony, mercury, thallium, sulfur, base metal
sulfides, other precious metals, and sulfosalts. The amount of these constituents depends on the
nature of the deposit and the amount of weathering that has occurred. Subsequent alteration of the
ore by oxidation influences both gold recovery and the byproducts of extracting the ore. Sulfide
minerals oxidize to form either oxides or sulfosalt minerals. Leaching of sulfides or other minerals
may occur in association with oxidation. Sulfide ores retain their original composition. Zones of
secondary enrichment may form at the oxidized/unoxidized interface.
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Overview of Mining and Beneficiation EIA Guidelines for Mining
The minerals found in gold ores, and elements associated with them, vary with the type of ore.
Sulfide ores contain varying amounts of native gold and silica (Si0 2 ), as well as sulfur-bearing
minerals, including, but not limited to, sphalerite (ZnS), chalcopyrite (CuFeS 2 ), cinnabar (HgS),
galena (PbS), pyrite (Fe 2 S), sylvinate ( [ Au,Ag]Te 2 ), realgar (AsS), arsenopyrite (FeAsS), ellisite
(TI 3 AsS 3 ), and other thallium-arsenic antimony-mercury-bearing sulfides and sulfosalt minerals.
Oxide ores may contain varying amounts of these minerals, as well as silica (Si0 2 ), limonite
(FeO OHn}1 2 O), calcite (CaCO 3 ), clay minerals, and iron oxides (Huribut and Klein, 1977).
The mineral assemblage of the ore deposit is an important factor in the beneficiation method to be
used. In general, the percent recovery of gold from sulfide ores using various cyanidation techniques
is lower and more costly than from oxide ores. Recovery is ieduced because the cyanide solution
also reacts with constituents such as sulfides in addition to gold. Increasingly, sulfide ores may be
oxidized in roasters or autoclaves. This is the result both of the development of more cost-effective
oxidation techniques and of the fact that oxide ores are becoming increasingly scarce (Weiss, 1985).
3.3.1.2 Mining
Gold ore may be mined by either surface or underground techniques. Mining methods are selected
based on maximum ore recovery, efficiency, economy, and the character of the ore body (including
dip, size, shape, and strength) (Whiteway, 1990). With notable exceptions (e.g., the Homestake
mine), most gold ore in the United States is mined using surface mining techniques in open-pit mines.
This is primarily because of economic factors related to mining large-volume, low-grade ores and the
improvement of cyanide leaching techniques. In 1988, a total of 160 million short tons of crude ore
(97.8 percent of the total) was handled at surface lode mines. In contrast, underground mines mined
only 3.56 million short tons (2.2 percent) (Bureau of Mines, 1991a). Exhibit 3-3 summarizes the
amounts of crude ore, waste, and marketable product generated by surface, underground, and placer
operations in 1988.
Exhibit 3-3. Materials Handled at Surface and Underground Gold Mines, 1988
Lode
Material Surface Underground Total
Placer
Material handled (1.000 short tons):
Total
553,000
4,890
558,000
32,900
Crude Ore
160,000
3,560
163,560
15,000
Waste
394,000
1,340
395,000
17,900
Marketable Product
(1,000 Troy oz.)
5,250
241
5,490
153
Source: EPA, compiled from Bureau of Mines, 1990b.
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EIA Guidelines, for Mining Overview of Mining and Beneficiation
The quantity and composition of waste rock generated at mines vary greatly by. site. This material
can contain either oxides or sulfides (or, more likely, both), depending on the composition of the ore
body. Constituents include mercury, arsenic, bismuth, antimony, and thallium, and other heavy
metals. These may occur as oxides, carbonates, and sulfides with varying degrees of solubility.
Sulfur-bearing minerals, such as pyrite and pyrrhotite, can oxidize to form sulfuric acid (Bureau of
Mines, 1984): Factors that influence acid generation by sulfide wastes include the availability of
oxygen and water; the presence and availability of acid-generating and/or neutralizing minerals in the
rock; and the design of the disposal unit. Overburden and waste rock are generally disposed of in
unlined piles known as mine rock dumps or waste rock dumps (occasionally, they can be called “low-
grade ore” or “subore” stockpiles). Waste dumps are generally unsaturated. Waste rock also is used
in constructing tailings dams, roads, and for other onsite purposes. Waste rock with high sulfide
content and sufficient mOisture content, and without adequate neutralization potential or other controls
in the dump itself (e.g., encapsulation or segregation of sulfide material within the dump), has led to
significant problems associated with acid drainage, both from waste rock dumps and from roads and
other onsite construction made of sulfide waste rock.
Mine water consists of water that collects in mine workings, both surface and underground, as a
result of inflow from rain or surface water, and groundwater seepage. Mine water may be used and
recycled in the beneficiation circuit, pumped to tailings impoundments, or discharged to surface water
under an NPDES permit. During the life of the mine, if necessary, water is pumped to keep the mine
dry and allow access to the ore body. This water may be pumped from sumps within the mine or
from interceptor wells surrounding the mine. Interceptor wells are used to withdraw groundwater and
create a cone of depression in the water table around the mine; thus reducing groundwater inflow.
Surface water is most often controlled using engineering techniques to prevent water from flowing
into the mine.
The quantity and chemical composition of mine water generated at mines vary by site. The chemistry
of mine water is dependent on the geochemistry of the ore body and surrounding area. After the
mine is closed and pumping stóps,.the potential exists for mines to fill with water. Water exposed to
sulfur-bearing minerals in an oxidizing environment, such as open pits or underground workings, may
acidify and mobilize metals in the rock matrix. In contrast, flooding of some mine workings may, in
some unusual situations, serve to slow or stop acidification by reducing or eliminating the source of
oxygen. .
In addition to wastes generated as part of gold mining and beneficiation, facilities also store and use a
variety of chemicals required by the mine and mill operations. Exhibit 3-4 presents a list of
chemicals used at gold mines, compiled from data collected by the National Institute for Occupational
Safety and Health (NIOSH, 1990).
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Overview of Mining and Beneficiation EIA Guidelines for Mining
Exhibit 3-4. Chemicals Stored and Used at Gold Mines
Acetic Acid Diisobutyl Ketone Methyl Acetylene- Sucrose
Acetone Ethanol Propadiene Mixture Silica. Sand
Acetylene Fluoride Methyl Alcohol Silica. Crystalline
Ammonia Graphite Methyl Chloroform Silver
Argon Hexone Mineral Oil Silver Nitrate
Asbestos Hydrogen Bromide Molybdenum Sodium Cyanide
Butyl Acetate Hydrogen Chloride Nitric Acid Sodium Hydroxide
Calcium Carbonate Hydrogen Peroxide Nitrogen Stoddard Solvent
Calcium Oxide iron Oxide Fume Nitrous Oxide Sulfuric Acid
Carbon Dioxide Kerosene Oxalic Acid Tin
Chlorine Lead Phosphoric.Acid Vanadium Pentoxide
Coal Lead Nitrate Portland Cement Xylene
Copper Litharge Potassium Cyanide 2-Butanone
Diatomaceous Earth Mercuric Chloride Propane Diesel Fuel No. I
Dichiorodifluoromethane Mercury Pyridine ______________________
Source: National Institute for Occupational Safety and Health. 1990.
Surface Mining
Surface mining methods associated with the extraction of gold include open-pit and placer (including
dredging, -which is often considered separately).: Placer mining is used to mine and concentrate gold
from alluvial sand and gravels and is described in Section 3.3.2.
Surface mining of gold is generally more economical than underground methods, especially in cases
when the ore body being mined is large and the depth of overburden covering the deposit is limited.
The primary advantage of surface mining is the ability to move large amounts of material at a
relatively low cost, in comparison with underground operations.
The predominant surface mining method used to extract gold ore is open-pit. Surface mining
practices follow a basic mining cycle of drilling, blasting, and mucking. The depth to which an ore
body is mined depends on the ore grade (and the extent of oxidation), 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.
Stripping ratios can range up to 5 to 10 tons of overburden and waste rock per ton of ore or higher at
open-pit mines; it usually ranges around 1 to 3 tons per ton. These materials become wastes that
must be disposed of, primarily in waste rock dumps. Because ore grades in mined material are
continuous, waste rock with gold concentrations just below the “cut-off” grade (i.e., the grade at
which gold can be recovered economically) may be stockpiled separately from other waste rock—this
materials is often referred to as “subore” or “low-grade ore.” In addition, the cut-off grade at a
given mine may change with the price of gold, thus leading to more or less waste rock being disposed
as the stripping ratio changes.
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ELA Guidelines for Mining Overview of Mining and Beneficiation
Underground Mining
Underground mining operations use various mining methods, including caving, stoping, and room and
pillar. 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. Waste rock, mine development rock, or mill tailings may be
returned to the mine to be used as fill for mined-out areas (EPA, Office of Water, 1982). The ratio
of waste rock to ore is much lower at underground mines than.at surface mines, reflecting the higher
cost of underground mining. Because of the higher costs, underground mining is most suitable for
relatively higher-grade ores. This in turn reduces the amount of beneficiation wastes (i.e., tailings)
generated (and disposed) per troy ounce of gold produced.
In Situ Mining
In situ leaching, although increasingly common in the copper industry, is only an experimental
procedure in the gold industry and is not used in commercial operations. It involves blasting an
underground deposit in place to fracture the ore and make it permeable enough to leach.
Subsequently, 20 to 25 percent of the broken ore is removed from the mine to provide “swell” space
for leaching activities. In buried ore bodies, cyanide solution is then injected through a well into the
fractured ore zone. At surface ore bodies, the solution can simply be sprayed over the deposit.
Recovery wells are used to collect the gold-cyanide solution after it percolates through the ore.
Groundwater and surface water concerns are commonly raised in discussions of potential in situ
operations. In situ leaching has only been tested at the Ajax Mine near Victor, Colorado (Bureau of
Mines, 1984).
3.3.1.3 Beneficiation
Four main techniques are used to beneficiate gold ore: cyanidation, flotation, amalgamation, and
gravity concentration. Exhibit 3-5 illustrates the common methods used to beneficiate gold. The
method used at a given operation depends on the characteristics of the ore and economic
considerations (Bureau of Mines, 1984). Each of the four techniques is described below. Base-metal
flotation is described only briefly, since gold is produced only as a byproduct at these operations.
Amalgamation also is discussed only briefly, since this method is primarily of historic significance in
the United States. Gravity concentration methods are generally used only in placer-type operations
and are discussed in a separate section (Section 3.3.2). Cyanidation operations are by far the most
common, and are described in more detail below. The two basic types of cyarndation operations,
heap leaching and tank leaching, are described separately.
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
3-38
September 1994
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EIA Guidelines for Mining Overview of Mining and Beneficiation
Exhibit 3-6 presents a comparison of gold ore treated and gold product produced by the various
beneficiation methods in 1991. As can be seen, cyanidation and direct processing (smelting of
precious metals recovered as a by-product from base metal mining) were used to produce 89 percent
and 10 percent of all domestic recovered lode gold, respectively. Placer mining accounted for 1
percent of the total gold produced. Amalgamation was used to beneficiate much less than 1 percent
of all lode gold in 1986, the last year for which complete data were reported (Bureau of Mines,
1990a).
Exhibit 3-6. Gold Ore Treated and Gold Produced, By Beneficiation Method, 1991
Beneficiation Method
Gold Ore Treated
Gold Produced
Percent
Short Tons
(000s)
Percent
Troy oz.
Cyanidation (All)
51
227,271
89
8,235,820
Heap Leaching
36
159,985
33
3,037,084
Tank Leaching
14
67,285
56
5,198,736
Amalgamation’
0.5
0.9
0.3
33,694
Smelting (ore and concentrates)b
49
221,507
10
909,736
Total L.ode
100
449,920
99
9,227,187
Placer (gravity)
,
100
5,500,000
cubic meters
1
92,851
Source: Bureau of Mines, 1992.
Notes:
Due to rounding and unit conversions, totals may not match exactly.
a Values for amalgamation are for 1986 production, the last year for which complete information
was available.
b Smelting of base metal ores and concentrates, mainly copper and lead ores. Production
information is not available specifically for flotation, but Bureau of Mines personnel have
suggested that these production figures approximate byproduct gold production by the base metal
industry.
By-Product Gold (Flotation)
As described above, flotation is a technique in which particles of a single mineral or group of
minerals are made to adhere, by the addition of reagents, preferentially to air bubbles (EPA, Office of
Water, 1982). This technique is chiefly used on base metal ore that is finely disseminated and
generally contains extremely small quantities of gold in association with the base metals. Gold is
recovered as a byproduct of the base metal recovery (for example, recovered from electrowinning
sludges or slimes).
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Ore is milled and sorted by size in preparation for flotation. The ore is then slurried with chemical
reagents of four main groups: collectors (promoters), frothers, activators, and depressants. In a
typical operation, the ore slurry and reagents are mixed in a conditional cell so the reagents coat the
target mineral. The conditional slurry is pumped to a flotation cell, and air is injected. Air bubbles
adhere to the reagents and carry the target mineral to the surface, away from the remaining gangue,
for collection. In the flotation technique, the target mineral is not necessarily the precious metal or
other value. Depending on the specific gravity and the reagents used, the values may be recovered
from the top or bottom of the flotation cell.
In general, there would be little or no incremental environmental concerns as a result of byproduct
gold recovery. Any significant concerns would be related to the base metal. mine and mill.
Amal2amation
In amalgamation operations, metallic gold is wetted with mercury to form a solution of gold in
mercury, referred to as an amalgam. This method of beneficiation is most effective on loose or free
coarse gold particles with clean surfaces (EPA. 1982). Because of its high surface tension, mercury
does not penetrate into small crevices of ore particles, so the ore generally must be crushed finely
enough to expose the gold material. Use of this method of gold beneficiation has been greatly
restricted in the u.s. in the recent past because of its high costs, inefficiency in large-scale
operations, and the scarcity of ores amenable only to this technique. In addition, environmental
concerns related to mercury contamination have contributed to its limited use. It is still used in other
parts of the world, particularly remote areas such as the upper Amazon, where its suitability for
small-scale operations and limited environmental concerns have not restricted its use.
Ore preparation consists of grinding, washing, andlor floating the ore. The ore is then fed into a ball
mill along with mercury to form an amalgam. The amalgam is then passed over a series of copper
plates where it collects. When fully loaded with amalgam, the plate is removed and the amalgam is
scraped off. Upon heating the hardened amilgam in a retort furnace, the mercury is vaporized and
the gold material remains. The mercury driven off by heating is captured, condensed, and reused.
Alternatively, hot dilute nitric acid may be applied to the amalgam, dissolving the mercury and
leaving the gold material. Amalgamation has traditionally been used in conjunction with other
beneficiation methods such as cyanidation, flotation, and gravity concentration (Beard, 1987).
Wastes generated as a result of amalgamation activities consist of gangue in the form of coarse- and
fme-grained particles and a liquid mill water component in the form of a slurry. The constituents of
the waste are similar to those found in the ore body (or gravel) plus any mercury lost during
amalgamation. This material can then be directed to a tailings impoundment. In the past, some U.S.
operations (as well as current operations in other parts of the world) simply directed the tailings to
nearby streams or valleys. In some areas, the amount of mercury lost during historic mining has
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EIA Gwdelines for Mining Overview of Mining and Beneficiation
been significant, and has led to widespread mercury contamination. For example, modern placer
operations in California have recovered substantial amounts of mercury from stream sediments
contaminated by past amalgamation operations.
Cyanidation
As noted previously, the predominant methods used in the U.S. and the developed world to
beneficiate gold ore involve cyanidation. This technique uses solutions of sodium or potassium
cyanide as lixiviants (leaching agents) to recover precious metals (including gold. and silver) from the
ore. Cyanide heap leaching is a relatively inexpensive method of recovering gold from lower-grade
ores while tank leaching is used for higher grade ore. Although other lixiviants are currently being
tested, none are known to be used in commercial operations. Alternative lixiviants include
malononitrile, bromine, urea, and copper-catalyzed thiosülfate (Bureau of ‘Mines, 1985; Bureau of
Mines, undated(a))’.
•The cyanidation-carbon adsorption processes most commonly used involve four steps: leaching,
loading, elution, and recovery (van Zyl et al., 1988) (see Exhibit 3-7). In leaching, the cyanide
reacts with the ore to liberate gold material and form a cyanide-gold complex in an aqueous’ solution.
Precious metal values in this solution are then loaded onto activated carbon by adsorption. When the
loading is complete, the values are eluted, or desorbed from the carbon, and recovered by
electrowinning or zinc precipitation prior to smelting. An alternative to cyanidatiànlcarbon adsorption
is cyanidation/zinc precipitation. The cyanidation-zinc precipitation technique also involves four
steps: leaching, clarification, deaeration, and precipitation. The precipitate (a solid) is smelted
directly.
Cyanidation is best suited to fme-grain gold in disseminated deposits. Cyanidation techniques used in
the gold industry today include:
• Heap or valley fill leaching followed by carbon adsorption (carbon-in-column, or CIC,
adsorption)
• Carbon-in-pulp (CIP) operations, where the ore pulp is leached in an initial set of tanks
with carbon adsorption occurring in a second set of tanks
• Carbon-in-Leach (CIL) operations, where leaching and carbon recovery of the gold values
occur simultaneously in the same set of tanks
• Cyanide leaching in heaps or tanks (CIP) followed by zinI precipitation (the. Merrill-Crowe
process). . .
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Overview of Mining and Beneficiation
E IA Guidelines for Mining
Exhibit 3-7. Steps for Gold Recovery Using Carbon Adsorption
(Adapted from various sources)
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As noted previously, in situ cyanide leaching to recover gold directly from ore bodies is’ a subject of
research by the Bureau of Mines and others, but is not used commercially at this time. Other
methods to recover the precious metal from the cyanide solution following leaching include solvent
extraction and direct electrowinning; these methods are not common in the industry and are not
discussed here.
Heap or valley fill leaching is generally used to beneficiate ores containing an average of less than
0.04 troy ounces of gold per ton of ore. CIP and CIL techniques, commonly referred to as tank or
vat methods, are generally used to beneficiate ores averaging more than 0.04 oz/t. Gold beneficiation
cut-off values are dependent on many factors, including the price of gold and an operation’s ability to
recover the precious metal (van Zyl et aL, 1988). At many heap leach operations, the lower cut-off
grade is around 0.01 to 0.02 oz/t.
The sections below describe gold beneficiation using the various cyanidation techniques. The first
subsection describes ore preparation that may take place before cyanidation. This is followed by
sections that describe heap leaching and tank leaching, respectively, with carbon adsorption and zinc
precipitation discussed in the heap leaching section. In each section, the discussion focusses on the
operations, the waste generated, and the major environmental concerns during and after operations.
Ore Preparation
Depending on the type of ore (sulfide or oxide), the gold concentration in the ore, and other factors,
the mine operator may prepare the ore by crushing, grinding, and/or oxidation (roasting, autociaving,
or bio-oxidation) prior to cyanidation or flotation.. Crushing and grinding are described briefly
below, as is oxidation.
Crushing and Grinding . In most cases, ore is prepared for leaching or flotation by crushing and/or
grinding. These operations produce relatively uniformly sized particles by crushing, grinding, and
wet or dry classification. Factors that determine the degree of ore preparation include the gold
concentration and the mineralogy and hardness of the ore, the mill’s capacity, the next planned step in
beneficiation, and general facility economics. Run-of-mine ores with very low gold concentrations
may be sent directly for heap leaching with no prior crushing or classification.
Milling begins when ore material from the mine is reduced in particle size by crushing and/or
grinding. A primary crusher, such as a jaw type, is used to reduce ore into particles less than 150
millimeters ( 6 inches) in diameter. Generally, crushing continues using a cone crusher and an
internal sizing screen until the ore is less than 19 mm ( 314 inch). Crushing in jaw and cone
crushers is a dry process, with water spray applied only to control dust.
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From the cone crusher, ore to be leached in tanks is fed to the grinding circuit where milling
continues in the presence of water, often with cyanide added to begin the leaching process (ore to be
leached in heaps or valley fills is routed from the crusher directly to the heap/fill). Water is added to
form a slurry containing 35 to 50 percent solids. Grinding then occurs in ball or rod mills to further
reduce the ore particle size. In some cases, ore and water are fed directly into an autogenous mill
(where the hard ore itself serves the grinding medium) or a serniaütogenous mill (where the ore
supplemented by large steel balls are the grinding media). Between each grinding unit operation,
hydrocyclones are used to classify coarse and fine particles, with coarse particles returned to the
circuit for further size reduction and fine particles continuing through the process. Milled ore is in
the form of a slurry, which is pumped to the next unit operation (Weiss, 1985; Stanford, 1987).
Fugitive dust generated during crushing and grinding activities is usually controlled by water sprays,
although there may be other air pollution control devices whose blowdown streams may be
recirculated into the beneficiation circuit.
Oxidation of Sulfides (Roasting, Autoclaving. and Bio-Oxidatioji) . Beneficiation of sulfide ores may
include oxidation of sulfide minerals and carbonaceous material by roasting, autoclaving, bio-
oxidation, or chlorination (chlorination is not commonly used because of the high equipment
maintenance costs caused by the corrosive nature of the oxidizing agent). Roasting involves heating
sulfide ores in air to convert them to oxide ores amenable to cyanidation. In effect, roasting oxidizes
the sulfur in the ore, generating sulfur dioxide that can be captured and converted into sulfuric acid.
Roasting temperatures depend on the mineralogy of the ore, but range as high as several hundred
degrees Celsius. Roasting of ores that contain carbonaceous material oxidizes the carbon that
otherwise interferes with leaching and reduces gold recovery efficiency. Autoclaving (pressure
oxidation) is a relatively new technique that operates at lower temperatures than roasting.
Autoclaving uses pressurized steam to start the reaction and oxygen to oxidize sulfur-bearing
minerals. Heat released from the oxidation of sulfur then sustains the reaction. Roasting and
autoclaving are being used more frequently in the U.S. as the technologies become more cost-
effective and as oxide ores become increasingly difficult to find and/or mine economically.
Bio-oxidation of sulfide ores employs bacteria to oxidize the sulfur-bearing minerals. This technique
is currently used on an experimental basis at the Congress Gold Property in Canada and at the
Homestake Tonkin Springs property in Nevada. The bacteria used in this technique are naturally
occurring and typically include Thiobacillusferrooxidans, Thiobacillus thicoxidans, and
Leptospirillumferrooxidans. In this technique, the bacteria are placed in a vat with sulfide gold ore.
The bacteria feed on the sulfide minerals and ferrous iron components of the gold ore. Research is
currently being conducted onother bacteria that can grow at higher temperatures; high-temperature
bacteria are thought to treat the ore at a much faster rate (Bureau of Mines, 1990a). Although more
time is required for bio-oxidation, it is considered to be less expensive than roasting or autoclaving
(Hackel, 1990).
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Heap Leaching
S;nce the late 1970s, heap leaching has developed into an cost-effective way to beneficiate a vanity of
low-grade, oxidized gold ores. Compared to conventional cyanidation (i.e., tank agitation 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
may be employed. Where level ground exists, a heap is constructed; the heap consists simply of a
flat-topped pile of the ore to be leached. In rough terrain, a valley n ay be dammed and filled with
the ore. Sizes S heaps and valley fills can range from a few acres up to several hundred. The
design of these leaching facilities and their method of operation are quite site-specific and may vary
over time at the same site. Gold recovery rates for heap and valley fill leaching generally range from
60 to 80 percent, but may be higher in some ases.
Leachij g . Heap leaching activities may involve any or all of the following steps (Bureau of Mines,
1978 and 1984; van Zyl, 1988; many others):
• Preparation of a “pad” (or base under the heap) with an impervious liner on a 1° to 6°
slope or greater for drainage. No gold heap o valley fill leaches are known to operate
without a liner (Hackel, 1990). Some liners may simply be compacted èoils and clays,
while others may be of more sophisticated design, incorporating clay liners, - french drains,
and multiple synthetic liners.
• Placement of historic tailings or other relatively uniform and pervious material on the liner
to protect it from damage by heavy equipment or other circumstances.
• Mining ore (or, as has been practiced in Cripple Creek, Colorado, and elsewhere, taking
material containing gold values from old waste piles or coarse tailings).
• Crushing and/or agglomerating the ore (agglomeration is discussed below), typically to
between 1/2 and 1 inch in size if necessary and cost-effective; some operations may leach
• nm-of-mine ore.
• Placing the ore on the pad(s) using trucks, bulldozers, conveyors, or other equipment.
• Applying cyanide solution using drip, spray, or pond irrigation systems, with application
rates generally between 0.5 and 1.0 pounds of sodium cyanide per ton of solution. This is
known as the “barren” solution because it contains little or no gold.
• Collecting the solution intercepted by the impervious liner via piping laid on the liner,
ditches on the perimeter of the heap, or pipes/wells through the. heap into sumps at the liner -
surface. The recovered solution, now “pregnant” with gold (and silver), may be stored in
“pregnant” ponds or routed directly to tanks for gold recovery, or it may be re-applied to
the heap for additional leaching.
• Recovering the gold from the pregnant solution.
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Two common types of pads are used in gold
heap leaching: pennanent heap construction on
a pad where ore is placed, leached, and left in
place; and on-off pads, where ore is placed on
the pad, leached, and removed to a permanent
disposal site, after which more ore is placed on
the pad for a new cycle. Permanent heaps are
typically built in successive lifts, with each lift
composed of a 5- to 30-foot layer of ore. Each
lift is then leached, a new lift is added to the
top and leached, and so on, until the heap
reaches its final height, which can range up to
200 feet or more. On-off pads are much less
common in the industry (Lopes and Johnston,
1988).
Agglomeration. Ores with a high proportion of
small particle size (minus 200 mesh) require
additional preparation before leaching can be done
effectively. Because percolation of the lixiviant
through the heap may be retarded as a result of
blocked passages by fine-grained particles (thus
preventing the solution from contacting and
recovering the gold from sections of theheap),
these types of ores are often agglomerated to
increase particle size. Agglomeration aggregates
individual particles into a larger mass, thus
enhancing percolation of the lixiviant and
extractiop efficiency. This technique may
increase the flow of cyanide solution through the
heap by a factor of 6,000, decreasing the overall
leaching time needed. Agglomeration is currently
used in about half of all heap leaching operations.
The agglomeration technique typically involves
the following (Bureau of Mines, 1986):
• Adding Portland cemeni (a binding agent)
and/or lime (for alkalinity) to the crushed ore
as or before it is placed on the heap
• Wetting the ore with cyanide solution to start
leaching as or before the ore is placed on the
heap (e.g., spraying cyanide solution over
ore on the conveyor that transports ore from
the crusher to the heap)
Mechanically tumbling the ore mixture so
flue particles adhere to the larger particles.
This can occur, for example, when ore is
dumped from the end of a conveyor or truck
and then mechanically spread on the heap.
Pad and liner construction methods and
materials vary with the type of pad, site
conditions, and perhaps most importantly,
regulatory requirements. Construction materials
may include compacted soil or clay, asphaltic
concrete, and low-permeability synthetic
membranes such as plastic or geomembrane
(van Zyl et aL, 1988). As noted above, sand,
historic tailings, or crushed ore may be placed
on top of the synthetic liner to provide a
pervious medium for leachate collection as well
as to protect the pad. Older pads tend to be
made of compacted clay, with little or no other
site preparation. Newer pads are usually constructed of synthetic materials, typically installed over a
compacted layer of native soil or imported clay. Some mines now use synthetic liners composed of
high-density polyethylene (HDPE) or very low-density polyethylene (VLDPE) in combination with
compacted native materials. These liner systems are referred to as composite liners 1 depending
largely on regulatory requirements, there may be a leachate collection system between the liners to
detect and collect any leakage through the primary liner. On-off pads are generally constructed of
asphaltic concrete to protect the liner from potential damage by heavy machinery used during
unloading.
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ELA Guidelines for Mining Overview of Mining and Beneficiation
As noted above, a variation of heap leaching is valley fill leaching. This method is used at facilities
with little or no flat land and utilizes liner systems similar to those used in heap leaches for solution
containment. In valley fill leaching, the ore material is placed on top of a liner system located behind
a dam on the valley floor. As in heap leaching, the ore is treated with lixiviant but is contained and
collected internally at the lowest point in the ore on the liner system for further beneficiation, rather
than in an external solution collection pond. Montana, Utah, and other States have approved valley
fill operations.
In either of these two configurations, cyanide complexes with gold and other metals as the barren
solution percolates through the ore. Leaching typically takes from weeks to several months,
depending on the permeability and size of the pile. An “average/normal” leach cycle takes
approximately three months (Lopes and Johnston, 1988).
The reaction of the solution with the free gold is oxygen-dependent. Therefore, the solution is
oxygenated prior to application or during spraying. Barren solution may be kept in a barren pond
prior to application, or may be routed directly to the heap from tanks. Barren solution is made up by
adding fresh water, cyanide, and lime to recycled water from the carbon columns (see below).
After being applied to the surface of the ore by sprays or drip irrigation, the cyanide solution
percolates through the ore and is collected by pipes placed on the liner beneath the pile, drains
directly to ditches or ponds around the pile, or is recovered from sumps constructed at the liner
surface (Bureau of Mines, 1986; Lopes and Johnston, 1988). The solution is then collected in a pond
or tank. The pregnant solution pond may be used as a holding pond, a surge pond, or a settling basin
to remove solids contained in the cyanide solution. Some operations use a series of ponds, which
may include one for the barren solution, an intermediate solution pond (from which semi-pregnant
solution is directed back to the heap for further leaching before gold is recovered), a pregnant
solution pond, and one or more emergency overflow ponds.
These ponds may be single-lined but are now more often double-lined with plastic (HDPE),
butylrubber, and/or bentonite clay to prevent seepage. Composite liners, often with leachate
collection systems to detect leaks are becoming increasingly common in response to more stringent
States requirements. Particularly in the arid west, but also in the east (e.g., South Carolina) wildlife
and waterfowl may be attracted to the ponds, and the c ’anide solutions present.an acute hazard. To
control wildlife access to cyanide solution, at least one operation (Castle Mountain in California) has
elected to construct tanks to collect and store leachate solutions as an alternative to open ponds.
Many active operations now fence or cover solution ponds with screening or netting to prevent
wildlife or waterfowl access, respectively.
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Overview of Mining and Benefidation ELA Guidelines for Mining
Leaching occurs according to the following reactions, with most of the gold dissolving in the second
reaction (van Zyl et al., 1988):
4Au + 8NaCN + 02 + 2H 2 0 -‘ 4NaAu(CN) 2 + 4NaOH (Elsener’s Equation and
Adamson’s 1st Equation)
• 2Au + 4NaCN + 02 + 2H 2 0 -. 2NaAu(CN) 2 + H 2 0 2 + 2NaOH (Adamson’s 2nd
Equation).
Leaching is generally effective at a pH of 9.5 to 11, with the optimum being approximately 10.5.
More acidic conditions may result in the ‘loss of cyanide through hydrolysis, reaction with carbon
dioxide, or reaction with hydrogen to form hydrogen cyanide (HCN). Alternatively,, more basic
conditions tend to slow the reaction process (Bureau of Mines, 1984). Typically, the recovered
cyanide solution contains between 1 and 3 ppm of gold material (Bureau of Mines, 1986). Leaching
continues until the gold concentration in pregnant solution falls below about 0.005 ounces per ton of
solution (Lopes and Johnston, 1988); when that occurs at permanent heaps, another lift is added and
leached or the heap is prepared for closure.
Barren solution must be treated to reduce cyanide levels to regulatory levels—cyanide species
regulated can be weak-acid-dissociable, free, or total cyanide—when recycling is no longer necessary.
Treatment occurs when contaminants build up in the recycling cyanide solution, at the end of leaching
seasons, and/or at facility closure. Depending on regulatory requirements, the solution may then be
land applied, stored in ponds, or evaporated.
When leaching ends, the spent ore that makes up the heap usually remains in place. Where on-off
pads are used, however spent ore will have been successively removed from the pad for disposal in
onsite piles or dumps. Prior to-final reclamation (or prior to ore removal from on-off pads), the
spent ore generally must be de-toxified. This is typically accomplished by repeated rinsing with
water, usually mine water or mill wastewater. Hydrogen peroxide or other oxidants may be added to
rinse waters. Cyanide in rinse water may be treated using one or more of the methods described
below. Most States require reductions in residual cyanide concentrations in rinse water/leachate to
below 0.2 mg/I and a pH from 6 to 9 s.u. before the heap can be reclaimed and/or abandoned. The
time necessary for rinsing heaps is enormously variable, ranging from a few days for some on-off
heaps to months or years for some permanent heaps.
Depending on the method and completeness of detoxification, spent ore may continue to have a high
pH. Heaps with agglomerated ores may prove particularly difficult to detoxify, since this tends to
keep pH high. Reclaimed piles may have ‘passive controls to control run-on and runoff; the design
capacity of these controls may be based on the 10-, 25-, or 100-year 24-hour maximum storm event
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EIA Guidelines for Mining Overview of Mining and Beneficiation
or the probable maximum precipitation event, depending on the component and State regulatory
requirements.
If sulfide ores are present, they may generate acidic leachate over tine, which in turn may mobilize
heavy metals that are present in the ore. Although heap leach piles are generally lined, liners may be
damaged or may deteriorate, or may be intentionally punctured as part of reclamation.
Current technology and environmental concerns have led to the development of several methods for
complexing or decomposing cyanide. These include:
Lagooning or natural degradation through photodecomposition, acidification by CO 2 and
subsequent volatilization, oxidation by• oxygen, dilution, adsorption on solids, biological
action, precipitation with metals, and leakage into underlying porous sediments.
• Oxidation by various oxidants:
- Chlorine gas
- Sodium and calcium hypochiorites
- Eleátro-oxidation and electrochlorination
- Ozone
- Hydrogen peroxide
- Sulfur dioxide and’ air.
In all cases, cyanide is oxidized initially to the cyanate, CNO. In some cases the cyanate
ion is oxidized further to NH 4 + and ’HCO 3 -, and finally the ammonium ion may be
oxidized to nitrogen gas.
• Acidification, with volatilization and possibly subsequent adsorption of HCN for reuse.
• Adsorption of cyanide complexes on ion exchange resins or activated carbon.
• Ion and precipitation flotation through cyanide complexation with base metals and recovery
with ‘special collectors.
• Conversion of cyanide to less toxic thiocyanate (CNS) or ferrocyanide (Fe(CN) 6 ) .
• Removal of ferrocyanide by oxidation or precipitation with heavy metals.
• Biological oxidation.
Hydrogen peroxide, for example, can be used to detoxify cyanide in spent heaps, tailings, and,
solution ponds’ and tanks. The cyanide-bearing solution is sent to a series of hydrogen peroxide
reaction tanks (Ahsan etal., 1989). Hydrogen peroxide and lime are added to the solution forming
precipitate of metal hydroxides and oxidizing free and wealdy complexed cyanide into cyanate
(OCN-). Additional steps precipitate copper ferrocyanide, a reddish-brown solid that is stable at a pH
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Overview of Mining and Beneficiation EIA Guidelines for Mining
of less than 9. Precipitates are separated from the solution and discharged to the tailings
impoundment. The solution is then recycled until the desired cyanide concentration is attained in the
effluent.
INCO has also developed a technique for detoxification of mine waste streams containing cyanide—
such as CIP and CIL puips, barren solution, tailings pond waters, and heap leach rinse solutions—by
removing cyanide and base metal complexes. The INCO process uses SO 2 and air, which is
dispersed in the effluent using a well-agitated vessel. Acid produced in the oxidation reaction is
neutralized with lime at a controlled pH of between 8 and 10. The reaction requires soluble copper,
which can be provided in the form of copper sulfate (Devuyst et al., 1990).
Each treatment method may generate a different waste, with the chemical compounds used in cyanide
removal as constituents. Some of these (e.g., chlorine, ozone, hydrogen peroxide) are toxic to
bacteria and other life forms but are unlikely to persist or can be cleaned up easily. Others (e.g.,
chloramine or chlorinated organic compounds) may persist for long periods in the natural
environment. In general, the long-term persistence of cyanide residues in mining waste are not
completely understood (University of California at Berkeley, 1988).
Following detoxification, heaps may be regraded to more stable long-term configurations. Liners
may be punctured and the heap covered with topsoil and reclaimed/revegetated. In some cases, heaps
may require capping to reduce leaching of heavy metals. Reclamation requirements vary among the
States, and the types of reclamation that are suitable for a given heap generally depend on the nature
of the site and of the spent ore. Any ponds are usually backfilled. Pond liners may be removed,
folded over and sealed to encapsulate sludges or other wastes, punctured, or otherwise handled,
depending on State requirements. Because of the enormous amounts of spent ore in heaps/valleys and
in spent ore dumps, any long-term environmental problems must be anticipated during design, since it
is not practical to move the materials after operations end.
Carbon Loading . Recovery of gold from the pregnant solutiOn generated by heap leaching is
accomplished using carbon adsorption or 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, including water and
spent ore. Unconventional techniques used to recover gold values include solvent extraction, direct
electrowinning, and, more recently, ion exchange resin. Activated carbon recovery and zinc
precipitation are described below.
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Activated carbon techniques are better able to process solutions with low metal concentrations and are
thus most often used on solutions with a gold concentration below 0.05 oz/t of solution (Bureau of
Mines, 1978 and 1984). Carbon adsorption is used both for heap leach solution and for tank
leaching.
In heap leaching, carbon adsorption uses the Carbon-in-Column (CIC) technique. In the dC
technique, the pregnant solution collected from the leach pile is pumped from a collection pond or
tank into a series of cascading columns containing activated carbon. The solution mixes with the
carbon column in one of two methods: fixed-bed or fluid-bed.
The fluid-bed method involves pumping pregnant solution upward through the column at a rate
sufficient to maintain the carbon bed in a fluid state moving gradually down through the column
without allowing the carbon to be carried out of the system. Thus, loaded carbon can be removed
from the bottom of the tank and fresh carbon added at the top. The fluid-bed method is the more
common of the two methods used in operations adsorbing gold-cyanide values from unclarified leach
solutions containing minor amounts of slimes. Because the fluid-bed method uses a countercurrent
operating principal, it is often more efficient and economical than the fixed-bed method in adsorbing
the gold-cyanide complex from solution (Bureau of Mines, 1978 and 1984).
In the fixed-bed method, the gold-laden cyanide solution is pumped downward through a series of
columns. The columns genera lly have either flat or dished heads and contain a charcoal retention
screen as well as a support grid on the bottom. Normally, the height-to-diameter ratio of the tanks is
2:1, although, in some instances, a larger ‘ratio will increase the adsorption capacity of the system
(Weiss, 1985). In each vessel, the gold-cyanide complex is adsorbed onto activated carbon granules
that preferentially adsorb the gold-cyanide complex from the remaining solution as the material flows
from one column to the next. The advantage of the fixed-bed method over the fluid-bed method is
that it requires less carbon to process the same amount of solution (Bureau of Mines, 1978 and 1984).
Elution . Typically, the activated carbon collects gold from the cyanide leachaté until it contains
between 100 and 400 ounces of gold per ton of carbon depending on the individual operation.
Loading efficiency decreases with solutions containing less gold (Bureau of Mines, 1978). The
precious metals are then stripped from the carbon by elution. The values can be desorbed from the
carbon using a boiling caustic cyanide stripping solution (1.0 percent NaOH and 0.1 percent NaCN).
Modifications of this method include the addition of alcohol to the stripping solution and/or stripping
under elevated pressure or temperature (40°C to 150°C) (Bureau of Mines, 1986). At least one
mine, Bameys Canyon, uses a stripping solution of hot sodium hydroxide that has proven to be as
effective as caustic cyanide (LeHoux and Holden, 1990).
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Carbon used in adsorption/desorption can be reactivated numerous times. The regeneration technique
varies with mining operations, but generally involves an acid wash before or after elution of the gold-
cyanide complex, followed by reactivation in a kiln and re-introduction into the adsorption circuit
(Bureau of Mines, 1985). Generally, activated carbon is washed with a dilute acid solution (pH of 1
or 2) to dissolve carbonate impurities and metal-cyanide complexes that adhere to the carbon along
with the gold. This technique may be employed either immediately before or after the gold-cyanide
complex is removed. Acid washing before the gold is removed enhances gold recovery. Based on
impurities to be removed,from the carbon and metallurgical considerations, different acids and
concentrations of those acids may be used. Usually, a hydrochloric acid solution is circulated through
3.6 metric tons (4 short tons) of carbon for approximately 16 to 20 hours. Nitric acid is also used in
these types of operations, but is thought to be less efficient than hydrochloric acid (HCL) in removing
impurities. The resulting spent acid wash solutions may be neutralized with a high-pH tailings slurry,
dilute sodium hydroxide (NaOH) solution, or water rinse. When the wash solution reaches a stable
pH of 10, it is typically sent to a tailings impoundment. Metallic elements may also be precipitated
with sodium sulfide (Smolilc et al., 1984; Zaburunov, ‘1989).
The carbon is then screened to remove fmes and thermally reactivated in a rotary kiln at about 730°C
for 20 minutes (Smolik Ct al., 1984). The reactivated carbon is subsequently rescreened and
reintroduced into the recovery system. Recirculating the carbon material gradually decreases
performance in subsequent adsorption and reactivation series. Carbon adsorption efficiency is closely
monitored and fresh carbon is added to maintain efficiency at design levels (Bureau of Mines, 1984
and 1986).
Carbon particles not of optimum size are either lost to the tailings slurry or, to the greatest extent
practicable, captured after reactivation.. Carbon lost to the circuit is replaced with virgin, optimum-
size carbon. Wastes from the reactivation circuits may include carbon fines and the acid wash
solution. The carbon may contain small amounts of residual base metals and cyanide. The acid wash
residues may contain metals, cyanide, and the acid (typically hydrochloric or nitric); according to
Newmont Gold Company, the acid is usually neutralized in a totally enclosed system prior to release.
Up to 10 percent of the carbon may be lost in any given carbon recovery/reactivation circuit from
abrasion, ashing, or incidental losses. Most perations capture less-than-optimum-size carbon
particles and extract additional gold values (or send fines offsite for gold recovery). Onsite or offsite,
this may involve either incinerating the carbon/gold that could not be desorbed chemically during the
normal course of operations or subjecting the material to an extended period of concentrated cyanide
leach. Any liquids used to wash or transport carbon material are recirculated.
Gold Recovery . 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
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removed and replaced The depleted stripping solution may then be reheated and recycled to the
carbon stripping system. The steel wool or electrowirming 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. For gold ores containing mercury, a retort step is required before gold smelting
to recover metallic mercury (Bureau of Mines, 1986; Smolik et aL, 1984).
Although carbon adsorption 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. This technique is well suited to new
mines where the ore has a high silver to gold ratio (from 5:1 to 20:1) (van Zyl et al., 1988).
In zinc precipitation operations (the Merrill-Crowe process), pregnant sOlution (or the pregnant eluate
stripped from the activated carbon) is filtered using clarifying filters coated with diatomaceous earth
to aid in the removal of suspended particles (see Figure 8) (Weiss, 1985). Dissolved oxygen is then
removed from the solution using vacuum tanks and pumps. This is necessary because the presence of
oxygen in the solution inhibits recovery (Bureau of Mines, 1984).
Metallic zinc dust then is combined with the deoxygenated pregnant solution. At some operations, a
small amount of cyanide solution and lead nitrate or lead acetate is added. Lead increases galvanic
• activity and makes the reaction proceed at a faster rate. Zinc precipitation proceeds according to the
reaction described below; the result is a gold precipitate (Bureau of Mines, 1984).
NaAu(CN) 2 + 2NaCN +Zn +H 2 0 -, Na 2 Zn(CN) 4 + Au + H + NaOH.
The solution is forced through a filter that removes the gold metal product along with any other
precipitates. Several types of filters may be used, including submerged bag, radial vacuum leaf, or
plate-and-frame. 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). In
cases where further treatment is necessary, the precipitate may be muffle roasted or acid treated and
calcined with borax and silica before smelting (Weiss, 1985). Following filtration, the barren
solution can be chemically treated (neutralized) or regenerated and returned to the leach circuit
(Weiss, 1985).
The wastes from zinc precipitation include a filter cake generated from initial filtering of the pregnant
solution prior to the addition of zinc, and spent leaching solution, which is often returned to the
leaching process. The filter cake consists primarily of fine gangue material and may contain gold-
cyanide complex, zinc, free cyanide, and lime. The filter may be washed with water, which is
disposed of as part of the waste. The waste is typically sent to tailings impoundments or piles.
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Tank Leaching
As noted previously, 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
method, leaching and adsorption occur in two separate series of tanks; in the Carbon-in-Leaching
method, they occur in a single series. Both are described below. 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.
Tank methods typically recover from 92 to 98 percent of the gold contained in the ore.
Continuous countercurrent decantaiion (CCD) is a method of washing the solution containing metal
values from the leached ore slurry to produce a clear pregnant solution. This procedure is used for
ores with high silver values that preclude the use of activated carbon and that are very difficult to
filter, thus precluding the use of filters. The resulting pregnant solution is generally treated by the
zinc precipitation technique described above.
A new technology employed in South Africa uses ion exchange resin in place of carbon in the CIP
technique. This technology—Resin-in-Pulp (RIP)—is expected to have lower capital costs and energy
consumption than CIP operations if it is operated effectively (Australia’s Mining Monthly, 1991). If
the use of ion exchange resins is found to be compatible with a wide range of ores, the industry may
shift to these resins wherever activated carbon is now used.
Carbon-in-Pulp (C1P . In the CIP technique, a slurry of ore, process water, cyanide, and lime is
pumped through a series of tanks for agitation and leaching. Then, the slurry containing leached ore
and pregnant solution is pumped through a second series of tanks for adsorption (or subjected to
continuous countercurrent decantation).
In the second series of CIP tanks, the slurry is introduced into a countercurrent flow with activated
carbon. The slurry enters the first tank in the series, which contains carbon that is partially loaded
with the gold-cyanide complex. In the suspended slurry, the activated carbon adsorbs gold material
on the available exchange sites. As the carbon material becomes laden with precious metals, the
carbon is pumped forward in the circuit toward the incoming solids and pregnant solution. Thus, in
the last tank, the low-gold percentage solution is exposed to newly activated and relatively gold-free
carbon that is capable of removing almost all of the remaining precious metals in the solutiOn. Fully
loaded carbon is removed at the feed end of the tank train for elution, followed by electrowinning or
zinc precipitation as described previously. (Bureau of Mines, 1978 and 1986; Stanford, 1987).
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Carbon-in-Leach (CIL) . The CIL technique, differs from CIP in that activated carbon is mixed with
the ore pulp in a single series of agitated leach tanks. Leaching and adsorption of values occur in the
same series of tanks. A countercurrent flow is maintained between the ore and the leaching solution
and activated carbon. In the first tanks of the series, leaching of the fresh pulp is the primary
activity. In later tanks, adsorption is dominant as fresh carbon is added to the system countercurrent
to the pulp. Adsorption takes place as the gold-cyanide complex mixes with the carbon. As with
Carbon-in-Pulp and heap leach operations, the pregnant carbon undergoes elution to remove values.
The pregnant eluate then ‘undergoes electrowinning or zinc ‘precipitation to recover the gold.
The number and size of tanks used in domestic CIP and CIL facilities vary. For example, the
Ridgeway facility in South Carolina uses 10 tanks measuring 52 feet in diameter and 56 feet in
‘height; the Mercury Mine uses 14 tthiks, each of which are 30 feet in diameter and 32 feet in height;
the Golden Sunlight Mine uses 10 tanks, each of which are 40 feet in diameter and 45 feet in height.
Retention times vary as well, ranging from 18 to 48 hours, depending on the facility, equipment used,
and ore characteristics (Smolik et at., 1984; Fast, 1988; Zaburunov, 1989).
For either CIP or CIL, ore preparation (including grinding, lixiviant strength, and pulp density
adjustment) and the time required to leach precious metal values vary depending on the type of ore.
.Oxide ores are typically beneficiated by grinding to 65 mesh and leaching with 0.05 percent sodium
cyanide (for a pulp density of 50 percent solids) over a 4- to 24-hour period. Sulfide ores are
typically beneficiated by grinding to 325 mesh and leaching with 0.1 percent sodium cyanide ,for a 10-.
to 72-hour period (for a pulp density of 40 percent solids) (Weiss, 1985).
‘Both of these tank beneficiation methods produce a waste slurry of spent ore pulp, or tailings, which
is pumped as a slurry to a tailings impoundment (Bureau of Mines, 1986; Calgon Carbon
Corporation, undated; Stanford, 1987). The tailings slurry is composed primarily of spent ore and
water, along with small (but sometimes significant) amounts of residual cyanide, lost gold-cyanide
complex, gold in solution, and any constituents in the water, including those added to control scale.
The solid component of tailings consists of very fine materials, ranging from sand-sized to talc-sized.
The characteristics of tailings vary greatly, depending on the ore, cyanide concentration, and the
source of the water (fresh or recycled). In some cases, the tailings slurry may be treated to neutralize
cyanide prior to disposal.
Tailings are disposed of in large tailings impoundment (up to hundreds of acres). Disposal requires a
permanent site with adequate capacity for the life of the mine. The method of tailings disposal is
largely controlled by the water content of the tailings. Generally,, three types of tailings may be
identified based on their water content: wet (greater than 40 percent of the total weight is water),
thickened (approximately 40 percent water), and dry (less than 30 percent water). Where topography
allows, tailings impoundments are located near the mill, but pipelines can be used transport tailings to
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suitable locations a mile or more away (always downhill). The design of tailings dams depends
primarily on the topography and the configuration of the impoundment (see Section 3.2.6); the
preferred method is for the dam to span a valley, with tailings impounded in the valley. Dam
construction materials include native soils and clays, waste rock, and components of the tailings (e.g.,
coarser sands in certain areas of the darn and fmer TM slimes” on the upper face.. Dams must be
engineered to withstand seismic events, and to control the flow of liquids through or under the, darn to
prevent catastrophic failure. Darn design must also consider water flow in the drainage following the
active life of the mine, since free water is typically kept to a niinimwn during operation by recycling
it back to the mill.
In part because of the Clean Water Act requirement that there be no discharge from gold beneficiation
operations that use cyanidation methods, most of the liquid component of tailings is recycled back to
th mill. Newer tailings impoundments are on prepared surfaces of compacted soils and clays, with a
few impoundments using clay or synthetic liners. In addition to water in the tailings slurry, there can
be infiltration of groundwater into the impoundment (this volume of water may be discharged under
the Clean Water Act). In many or most cases, it has been necessary to construct one or more seepage
and overflow ponds immediately downgradient of the tailings darn. This has proven necessary for
several interrelated reasons: the zero discharge effluent limitation guidelines, which require
impoundment of all liquids, but that allow seepage to groundwater; State groundwater protection
requirements that require liners ci other rneax s to reduce the loss of fluids to the subsurface; the
presence of liquids in the tailings from the mill and from groundwater infiltration; and the need to
control the movement of fluids through or under the dam. During the active life of the mine,
solutions captured in such ponds are generally pumped back to the impoundment itself or directly to
the mill.
States usually require reseeding/revegetation of impoundments when the mine closes. Because
impoundments are often in drainages, reclamation may include permanent diversions around the
tailings or preparing channels over or through the tailings. Reactive tailings (e.g., acid-forming) may
have to be capped before reclamation, and root penetration or erosion of any such caps may have to
be considered in reclamation planning.
3.3.2 Cow PLACER MINING
Placer mines have historically produced approximately 35 percent of the total U.S. gold production.
However, while net gold production has increased annually in recent years, placer production has
decreased as the readily accessible placer deposits have been mined out and with the development of
more cost-effective technologies for mining and beneficiating lode deposits. Placer mines produced
only two to three percent of the total U.S. gold production during the period from 1984 through
1989; since that time, placer production has accounted for approximately one percent of U.S. annual
production.
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The size and nature of placer mines range from open cut operations disturbing tens of acres annually
to small sluices operated solely as a recreational activity. In 1987, the average number of employees
at placer mines in the contiguous 48 states was between three and four, and few mines employed
more than 10 people (EPA, 1988b).
Regardless of size, most placer mines operate on a seasonal basis (ADEC, 1986; EPA, 1988a). The
small size of most placer operations and the relative ease in establishing an operation make it difficult
to establish the number of mines operating at any one time (EPA, 1988a). A 1986 EPA survey
showed a total of 454 placer mines in operation in the U.S. Also in 1986, the Bureau of Mines
estimated there were just more than 207 operational placer mines. While the final totals are quite
different, both surveys revealed the overwhelming majority of the mines were in Alaska (190
according to EPA and 195 according to the Bureau). All the mines identified in both surveys were
west of the Mississippi, with most large operations in Alaska.
Placers exist in different types of sedimentary deposits (fluvial, marine, eolian, etc.), although they all
originate from lode deposits. Most of the gold placers mined in the U.S. are of fluvial origin. Placer
deposits are typically found in unconsolidated sedimentary deposits, although depending on the nature
of the associated materials, placers may be cemented to varying degrees. The terms pay streak, pay
dirt, and pay gravel refer to the zone where the economic concentration of gold is located. This layer
is often found adjacent to the bedrock. Finer gold particles are carried farther from their source and
have a .greater tendency to be distributed throughout the sediments in which they are found. The
value of the pay streak is usually assessed as troy ounces per. cubic yard, and varies throughout the
deposit (Boyle, 1979).
The density of gold, and its resistance to weathering, are the two principal factors for the
development of placer deposits. Gold is considerably more dense that the minerals typically
associated with it (19.13 grams per cubic centimeter (g/cc) versus 2.65 g/cc for quartz). Heavy
minerals typicaliy settle to the bottom of a stream or beach, displacing lighter material in the process.
Gold continues a downward migration in response to additional agitation in the streambed. Settling
action also occurs on land in colluvium although the downward migration is not as pronounced in the
absence of a fluid matrix. Placer deposits are formed as particles accumulate in this manner (Park
and MacDiamid, 1970).
At a typical placer mine, overburden is removed and ore is blasted to fluff-up the material and make
it easier to excavate. The ore is then hauled by trucks to a wash plant, which consists of a
combination of equipment used to size and concentrate the ore. A typical wash plant consists of a
grizzly and/or a trommel, where sizing takes place. The ore is then washed into a sluice, where the
gold (and other heavy minerals) settle below the riffles and onto matting. The gold remains in the
sluice, while the tailings and wash water flow out of the sluice and into a tailings or settling pond.
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Periodically (every 1-2 days), the wash plant is shut down and the gold is removed. The concentrate
may then be subjected to further, more refmed concentration, with gravity separation techniques such
as jigs, shaking tables and pinched sluices 1 , and possibly magnetic separation, if niagnetite is present,
to produce a high grade concentrate suitable for processing.
3.3.2.1 Mining
Extraction methods employed at gold placer operations differ substantially from hardrock extraction
methods. Large amounts of overburden, waste rock, and ore must be excavated and concentrated to
remove the trace constituent gold. The stripping ratio (i.e., the ratio of overburden/waste rock to
ore) at gold placer mines is high, sometimes as high as 10:1. In the coldest regions where gold
placer mining occurs, frozen overburden (consisting of vegetation, muck, and waste rock) and ore
deposits must be loosened by blasting and/or mechanical means prior to extracting the, ore. They may
also be thawed by a system or grid of water pipes circulating over the deposit.
Gold ore extraction at placer operations may be conducted using either surface or underground
techniques, but surface methods are most commonly used because they generally are the least
expensive (Whiteway, 1990). The principal surface extraction method is open cut mining. Other
extraction methods employed at gold placer mines include dredging, hydraulicking, and other
recreational and small-scale extraction techniques, such as panning and small suction dredging.
Currently, use of dredging and hydraulicking methods is limited in the United States. Underground
mining methods include bore-hole and drift mining. (Alaska Miner’s Assu., 1986; Argall, 1987)
Open cut mining involves stripping away vegetation, soil, overburden, and waste rock to reach the
ore buried below. The pay ore is blasted if necessary and can be excavated by bulldozers, loaders,
scrapers, and draglines; conveyors or trucks then transport the ore to a wash plant for beneficiation.
Usually the excavation site is located upstream or upsiope of the wash plant, and the direction of the
mining activity is away from the plant. Once a cut has been mined, it is generally either backfilled
with excavated overburden and waste rock or convened to a water recycle or sediment pond (ADEC,
1987).
Dredges are used in both surface mining and underwater mining of placer deposits, but are generally
associated with the mining and beneficiation of metal-bearing minerals (values) below water level.
Dredges are limited by the availability of a saturated placer gold deposit or the existence of a water
table near the surface to create the appropriate excavating environment (i.e., a pond). Four
commonly used dredging systems include bucketline (also referred to as bucket-ladder), backfioe,
dragline, and suction dredging.
In hydraulic mining, water under pressure is forced through an adjustable nozzle called a monitor or
giant and directed at a bank to excavate gold placer ore and to transport it to the recovery unit, which
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is generally a sluice box. The pressurized water jet can also be used to thaw frozen muck and to
break up and wash away overburden. This is generally not used today, having been outlawed in most
jurisdictions. However, hydraulic removal of overburden may still be practiced at a few mines
Small-scale extraction methods include panning and suction dredging. Panning is a low budget, labor
intensive method involving fairly rudimentary gravity separation equipment. Panning is also a
sampling method used by prospectors to evaluate a placer gold deposit to determine whether it can be
mined profitably. Small-scale gold placer miners also use a variety of other portable concentrators,
including long’ toms, rocker boxes, and dip boxes (EPA, 1988a). Small suction dredges are used by
recreational or small (part-time) gold placer ventures. A pump varying from one to four inches
usually floats immediately above the mined area. The mechanism that recovers the gold sits in a box
next to the suctiori pipe and is carried under water. Alternatively, the nozzle has two hoses, one that
transports water to the head and the other that transports material to the surface of a beneficiation
device (i.e., usually a small sluice box that deposits tails back into the stream).
Drift mining and bore-hole mining are terms applied to working alluvial placer deposits by
underground methods of mining. Drift mining is more expensive than open cut sluicing and
hydraulicking, so it is used only in rich ground. In drift mining, the paystreak is reached through a
shaft or an adit. Ore that has been separated from the vein either by blasting or with hand tools is
carried in wheelbarrows or trammed to small cars that transport the gravel to the surface for
beneficiation. If a deposit is large, then regular cuts or slices are taken across the paystreak, and
work is generally performed on the deposit in a retreating fashion from the inner limit of the gravel
(00!, 1968; Argall, 1987).
3.3.2.2 Beneficiation
Beneficiation of placer ores involves the separation of fine gold particles from large quantities of
alluvial sediments. Gravity separation is the most commonly used beneficiation method. Magnetic
separation is used in some operations to supplement the gravity separation methods. Water is used in
most, if not all steps to wash gold particles from oversized material and then to move ore concentrate
through the wash plant. For land-based operations, the plant may be stationary but is often mounted
on skids so that it can be moved along with the mining operation as it progresses. Dredge operations
frequently employ floating wash plants, where the beneficiation equipment is carried within the
dredge.
Beneficiation typically involves three general steps: the first is to remove grossly oversized material
from the smaller fraction that contains the recoverable gold; the second is to concentrate the gold; and
the third is to separate the fine gold from other fine, heavy minerals. The same type of equipment is
often used in more than one step. For example, an array of jigs may be employed to handle
successively finer material (Flatt, 1990).
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Classification (sizing) is the initial step in the beneficiation operation when the large, oversize material
(usually over 3/4 inch) is removed during beneficiation. A rough (large diameter) screen is usually
used. This step may be fed by a bulldozer 1 front-end loader. backhoe, dragline or conveyor belt.
Within the industry, this step is also referred to as roughing (EPA. 1988a). The ore is then subjected
to a coarse concentration stage. This step, referred to as cleaning, may employ trommels or screens.
Other equipment used in the coarse concentration stage includes sluices, jigs, shaking tables, spiral
concentrators and cones. Depending on the size of the gold particles, cleaning may be the final step
in beneficiation (Flatt, 1990; Silva, 1986).
Fine concentration is the fmal operation used to remove very small gold values from the concentrate
generated in the previous stages. Many of the previously identified pieces of equipment can be
calibrated for finer separation sensitivity. Final separation uses jigs, shaking tables, centrifugal
concentrators, spiral concentrators or pinched sluices.
3.3.2.3 Wastes and Management Practices
Mining and beneficiation wastes associated with gold placer mining include tailings and water used
for beneficiation. Most of these materials are either disposed of at the mine site (overburden and/or
tailings), recycled during the active life of the mine (water), or used for onsite construction material
or reclamation concurrently with mining or after operations end (overburden andlor tailings). Large
amounts of overburden or waste rock are associated with placer mining. Because the desired material
is such a small fraction of the material mined (< 0.1 troy 01/ton) there is a tremendous amount of
waste rock generated. Then, large amounts of water are used to process the material. The type,
volume, and characteristics of the wastes resulting from gold placer mining, as well as the waste
management units associated with these wastes are discussed below. (Again, the use of the term
“wastes” is not intended to identify materials that are “solid wastes” under RCRA.)
Waste rock is generally disposed of in waste rock dumps near the point of excavation. Eventually,
the stockpiled waste rock may be used to backfill the mine cut during reclamation. Surface mining
operations generate more waste per unit of crude ore extracted than underground operations, although
stripping ratios vary from one site to the next. Overburden removed from the mine cut is stored
nearby, sometimes piled along the edge of the pit until mining ceases, at which time it is used to
backfill the cut.
Wastes from gravity concentration operations consist of a slurry of gangue (non-gold material) and
process water that passes through the concentration operation. Tailings are classified by their size
into three classes: coarse or oversize tailings, intermediate tailings (middlings), and fine tailings
(slirnes). Of the three grades delineated, fine tailings can be further broken down into two categories.
Components of the slurried tailings can be classified as settleable solids, which are made up of sand
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and coarse silt, or assuspended solids, composed mostly of fine silt and some clay size particles.
(EPA, 1988a)
Large volumes of flowing water are used to carry the ore through the classification operation. The
velocity of the flowing water generates a large volume of intermediate and fine tailings in the form of
suspended sediment and lesser quantities of dissolved solids. Historically, the water and sediments
were released to streams and created problems downstream from the mining sites. Currently, release
of sediment is controlled by using impoundment structures where the water is held and the velocity is
consequently reduced. As flow is restricted, sediments are deposited. Exposure of waste rock and
ore during mining and beneficiation greatly increases the likelihood that soluble constituents will be
dissolved. Once in solution, dissolved solids are much more likely to pass through sedimentation
structures and reach surface waters.
Recycling or recirculating water at gold placer mines reduces the volume of effluent to be discharged
• after treatment. Produètion statistics from 1984 show that 21.3 percent of the Alaska gold placer
• mining industry achieved 90-100 percent recycle of the process wastewater (Harty and Terlecky,
1984a). Operations that separate oversize tailings prior to sluicing typically use less water than mines
that do not classify the excavated material (Harty and Terlecky, 1984b). Where classification
methods are used, approximately 1,467 gallons of water per cubic yard of ore are needed, whereas at
mines that do not classify material, average water usage is 2,365 gallons per cubic yard of ore (EPA,
1988a; ADEC, 1987). The Clean Water Act effluent limitations guidelines for placer mines (40 CFR
Part 440, Subpart M), promulgated in 1989, generally require recycling of process wastewater and
have reduced the total discharge of wastewater from placer mining operations.
Chemicals are not typically used during beneficiation at placer gold mines, so tailings contain the
same constituents found in the extracted ore. Potential natural constituents of gold placer wastes
include mercury, arsenic, bismuth, antimony, thallium, pyrite, and pyrrhotite. These are often found
in discharges from placer mines.
Waste and non-waste materials generated as a result of extraction and beneficiation of gold placer ore
are managed (treated, stored, or disposed) in discrete units. These units are divided into two groups:
(1) waste rock piles and (2) tailings impoundments.
In general, the goal of treating or managing waste streams of gold placer mines is to separate the silt
and fme-grained solids from the water, reusing the water or ensuring it meets NPDES discharge
requirements prior to discharging to a stream. Most waste management occurs after sluicing; the
stacking of overburden and waste rock in areas proximate to the mining operation, however,
constitutes an interim method of managing the materials prior to their ultimate return to the mine cut
(Alaska Miner’s Assn., 1986).
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There are two ways to maximize the quality of the effluent discharged from a gold placer operation.
They are used separately or, increasingly frequently, together. The effluent can be treated using a
variety of impoundments (tailraces, pre-settling ponds, and settling/recycle ponds), filtration, and, in
rare instances, flocculants. The mining operati6n also can be modified to reduce water use during
beneficiation, thereby reducing the volume of effluent discharged. Waste management methods used
to achieve this reduction include classification, recycling, use of a bypass, and control of water gain
(i.e., surface and subsurface seepage) (Alaska Miner’s Assn., 1986).
Tailings are typically disposed of in impoundments or used for construction. The method of tailings
disposal is largely determined by the water content of the tailings. Tailings impoundments associated
with gold placer mines are generally unlined containment areas for wet tailings. ‘At most gold placer
operations, the disposal of tailings requires a permanent site with adequate capacity for the life of the
mine. The size of tailings impoundments varies between operations, however, if the impoundment is
going to function effectively, the dimensions and characteristics are tailored to meet the specifications
for a particular operation.
Tailraces and pre-settling ponds are characteristic of open cut surface mining operations. Even at
open cut mines, however, there are variations of the typical tailrace and pre-settling pond. Two pre-
settling ponds are sometimes used simultaneously and in series to provide extra storage in case the
first pond fills prematurely or in the event that a scheduled cleaning is missed. Alternatively, two
parallel pre-settling ponds might be used at alternating times. (Alaska Miner’s Assn., 1986; ADEC,
1987) Settling ponds are similar in form and function to tailings impoundments and are used
primarily by large-scale placer operations. Settling ponds are usually created by constructing a dam
composed of tailings across the downstream end of th mined cut. When the next cut is mined, most
of the extracted sediment is captured in this new pond. Thus, as mining progresses, a series of ponds
emerge.
3.3.2.4 Environmental Effects
Most envronmental effects associated with placer mining activities concern water quality.
Historically, the most severe impacts have been physical disturbances to stream channels and the
addition of large quantities of sediment downstream.
Prior to the initiation of any regulatory controls, little or no effort was made to recontour waste rock
piles to resemble premining topography. Natural revegetation of historical placer grounds from
Alaska to California ranges from none to complete. Depending on the remaining substrate, natural
stream patterns in some areas may take a century to return to premining condition. These operations
were also responsible for generating large quantities of sediment and increasing concentrations of
heavy metals, including arsenic, copper, lead, and mercury, downstream from mining activities
(ADECI, 1986; Clark, 1970; Holmes, 1981).
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A 1985 Alaskan field study indicated that total suspended solids were elevated in a number of actively
mined streams. During this study, sediment ponds were employed at some operations and provided a
wide range of effectiveness. Downstream uses such as water supply, aquatic life, and recreation were
precluded as a result of the increased sediment loads in two of the three streams studied. Fine
sediments were readily carried downstream in response to increased stream flows (spring runoff),
therefore the severity of local zed impacts could change with time as sediments were picked up and
redeposited in different locatLons downstream (ADEC, 19S6).
The same study found that total dissolved solids were not categorically increased as a result of mining
activities although levels of iron, manganese, cadmium, mercury, copper and arsenic were elevated
below mining operations in some streams. (It is not clear from the study whether these concentrations
are expressed as total or dissolved). A study of water quality within the Circle District, Alaska,
conducted in 1983, showed elevated levels of total arsenic, copper, lead, and zinc, and elevated levels
of dissolved arsenic and zinc downstream from placer mining activity. Mercury and cadmium levels
were not elevated downstream from mining. Concentrations of dissolved constituents are typically of
more concern in terms of water quality as the dissolved fraction is available for uptake by living
organisms (ADEC, 1986; LaPierriere, et al., 1985).
The physical locations of placer mining activities and wetland ecosystems often overlap. Mining
activities, particularly those mining recent alluvial deposits potentially impact. wetlands directly during
the removal of vegetation and soils or indirectly by removing or rerouting the hydrologic regimes that
support wetland hydrology. Operators impacting wetlands are required to obtain a Clean Water Act
Section 404 permit, and comply with Section 404(b)(1) guidelines.
Wildlife may also be impacted by placer mining through the physical disturbance of stream channels,
the addition of sediments to streams, and the presence of human activities and heavy equipment in
what are typically remote areas. Mining presents a physical barrier to fish migration through the
disruption or diversion of active stream channels. Sediment concentrations in streams can result in
gill damage, reduced fertility, and changes in blood chemistry, and reproduction may be inhibited or
precluded when spawning grounds are lost to siltation and eggs are suffocated when covered by
excess sediment (ADEC, 1986; Reynolds, 1989).
33.3 LEAD-ZINc
In 1990, there were a total of 29 lead/zinc mines operating within the United States. Of these 29
mines, 16 produce both lead and zinc; two produce lead but not zinà; and 11 produce zinc but not
lead. In 1990 alone, these mines produced 495,000 metric tons of lead concentrate (making the U.S.
the world’s largest primary producer) and 515,000 metric tons of recoverable zinc. For the same
year, employment figures were estimated to be 4,500 workers at mines and mills and 3,300 at
secondary smelters and refineries. Twenty-one of the mines are located west of the Mississippi, in
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the States of Missouri (9 mines), Idaho (3), Alaska (2), Colorado (2), Washington (2), Montana (1),
New Mexico (1), and Oregon (1). The remaining eight mines are located in Tenx ssee (5 mines) and
New York (3).
Lead a used primarily by transportation industries (70 percent) m batteries, fuel tanks, solder, seals,
and bearings. Another 25 percent is used in electrical/electronic/communication (including batteries),
ammunition, and other industries. U.S. and world demand has declined in recent years, in large part
in response to environmental concerns. Zinc is used in galvanizing (53 percent), zinc-based alloys
(20 percent), brass and bronze (14 percent), and for other purposes.
3.3.3.1 Mining
Lead and zinc are mined almost exclusively in underground operations, although a few surface
operations do exist. The decision to use underground or surface mining techniques is dependent on
the proximity of the ore body to the surface. Room-and-pillar techniques are commonly used to
extract lead-zinc ore from large, flat-lying, tabular-shaped, strata-bound deposits. In contrast,
extraction of lead-zinc ore from vein-type deposits is best suited to more, selective stope mining
methods. The exact mining method used is determined by the individual characteristics of each ore
body.
Profitable recovery of lead-zinc ores ranges from as low as three percent metal in ore for large, easily
accessed mines, to six percent for small, difficult-to-access underground mines, to more than 10
percent for extremely high-cost, remote areas. Low grade léad and zinc ores can also be mined
profitably when produced as a byproduct of copper mining, or when appreciable quantities of precious
metals (such as silver) are present (Weiss, 1985). Few lead-zinc deposits contain more than 50
million tons of ore.
3.3.3.2 Beneficiation
Beneficiation of lead and zinc ores is a three-step process consisting of milling, flotation, and
sintering. Before the advent of flotation in the early 1900s, gravity concentration was the chief
method by which lead-zinc ores were concentrated. However, with more selective reagents and
advancements in grinding techniques, flotation has virtually replaced gravity concentration. Gravity
concentration techniques, however, may still be used for preconcentrating before fine grinding and
flotation (Bureau of Mines, 1984c and 1985).
Milling
Milling begins with a multistaged operation of crushing and grinding. Crushing is usually a dry
operation, using water sprays only to control dust. Frequently, a primary crusher (jaw crusher) is
located at the mine site to reduce the ore material into particles less than 150 millimeters (mm) (6
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inches) in diameter. The crushed ore is then transported to a mill site for additional crushing,
grinding, classification, and concentration.
Additional milling uses a cone crusher, usually followed by grinding in rod and ball mills. Grinding
is a wet operation in which water and initial flotation reagents are added to form a slurry.
Alternatively, the ore may be fed into an autogenous mill (where ore itself acts as a grinding medium)
or a semi-autogenous mill (where the ore is supplemented with large steel balls).
Between each grinding unit operation, hydrocyclones are used to classify coarse and fine particles.
Coarse particles are returned to the mill for further size reduction. The resulting size of the classified
ore is usually about 65-mesh (6.3 mm). Chemical i’eagents that will be used during flotation
separation activities may be added to the ore during milling activities (Bureau of Mines, 1985 and
1990a). Mill production capacities can be as high ‘as 7,000 to 9,000 tons per day.
Flotation
Flotation is the most commonly used technique to concentrate lead-zinc minerals. Several separate
flotation steps may be necessary to beneficiate these polymetallic ores. Most sulfide ores contain
varying ‘amounts of minerals such as lead, zinc, copper, and silver; thus, multiple floats are needed to
concentrate ‘individual metal values (Bureau of Mines, 1985a; Weiss, 1985). - The tailings (residual
material) from one mineral float are then used as feed for a subsequent float to concentrate another
mineral. A typical example includes the following steps (Fuerstenau, 1976):
• Bulk flotation of lead-copper minerals
• Depression of zinc and iron minerals using such chemicals as sodium sulfite and zinc sulfate
• Flotation of a ‘copper concentrate
• Rejection of a lead (sink) concentrate using sulfur dioxide and siarch
• Activation and flotation of the sphalerite (using copper solution) from iron and gangue
minerals
• Flotation of pyrite, if recovery is desired
• Flotation of barite concentrate.
The froth recovered in each’of the cleaning ‘cells is transferred to thickeners, where the concent ate is
then thickened by settling. The ‘thickener underfiow (the concentrate) is pumped, dewatered by
passage through a filter prcss, and then dried. The liquid overflow from the thickener contains
wastewater, flotation reagents, and dissolved and suspended mineral products. This solution may be
recycled or sent to a tailings pond (Fuerstenau, 1976).
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Wastes from the various ‘cells (typically rougher, scavenger, and cleaning cells) are collected and
directed to a tailings thickener. Overflow from this unit (wastewater containing high solids and some
wasted reagent) is often recycled back to the flotation cells. Thickener underfiow (tailings) contains
remaining gangue, unrecovered lead-zinc material, chemical rçagents, and wastewater. This
underfiow is pumped as a slurry to a tailings, pond. The solid content of the’slurry varies with each
operation, ranging from 30 to 60 percent.
Sintering
Concentrates of lead and zinc minerals that are to be processed by pyrometallurgical methods, such as
smelting and refining, may require sintering, depending on the processing methods used. Sintering
operations consist of several steps, including blending, sintering, cooling, and sizing. Raw materials,
such as ore concentrates, ore screening, fluxes, plant recycle dusts, filter cake, and coke breeze are
blended with small amounts of moisture in pug mills, balling drums, or balling pans. The concentrate
feed is then fired (sintered) and cooled. The’ sinter is crushed during coaling and is typically less than
stx inches in diameter. This product will be graded and further crushed in some operations to
produce a smaller sinter product (Weiss, 1985). Four of the five priniary lead’ processing facilities in
the United States sifter the concentrate prior to processing.
3.3.3.3 Wastes
Wastes generated by lead-zinc operations, include mine water, waste rock, tailings, and refuse. Many
of ‘these wastes may be disposed of onsite or offsite, while others may be used’ or recycled during the’
active life of the operation. Waste constituents may include base metals, sulfides, or other elements
found in the ore, and any additives or reagents used in beneficiation operations. The primary waste
generated by underground mines is mine development rock, which is typically used in onsite
construction for road or other purposes. Surface mines usually generate large volumes of overburden
and waste rock that are usually disposed of in waste rock dumps. (As before, “wastes” discussed
here are not confined to RCRA solid wastes.)
Overburden and Mine Development Rock
Waste generated as a result of lead-zinc mining include overburden and mine development rock
collectively referred to as waste rock. As noted previously, the materials ‘can be used onsite or placed
in waste rock dumps. ,The quantity and composition of waste rock generated at lead-zinc mines varies
greatly between sites. These wastes will contain minerals associated with the ore body and host rock.
Typical minerals associated with sulfide ores ‘are chalcopyrite, pyrite, calcite, and dolomite (Weiss,
1985).
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Mine Water
Mine water consists of all water that collects in mine workings, both surface and underground, as a
result of inflow from rain or surface water, and groundwater seepage. As necessary, water may be
pumped from the mine to keep it dry and allow continued access to the ore. The pumped water may
then be used in beneficiation, pumped to tailings ponds, or discharged to surface water. The quantity
and chemical composition of mine water varies from site to site, depending on the geochemistry of
the ore body and the surrounding area. Mine water may also contain small quantities of oil and
grease from extraction machinery and nitrates (NO 3 ) from blasting activities. Based on studies of lead
mines in the United States, the range of concentrations in mine water (mg/i) for lead was 0.1-1.9,
zinc 0.12-0.46, chromium 0.02-0.36, sulfate 295-1,825, and pH 7.9-8.8. After the mine is closed
• and pumping stops, the potential exists for water exposed to sulfur-bearing minerals in an oxidizing
environment, such as open pits or underground workings, to acidify. This may lead to the
mobilization of metals and other constituents in the remaining ore body exposed by mining and to the
contamination of sUrface and/or groundwater. Alternatively, flooding of underground workings can
• reduce exposure of sulfide minerals to oxygen and effectively eliminate acid generation.
Flotation Wastes
After the removal of values in the flotation process, the flotation system discharges tailings composed
of liquids and solids. Between 1/4 and 1/2 of the tailings generated are made up of solids, mostly
gangue material and small quantities of unrecovered lead-zinc minerals. The liquid component of the
flotation waste is usually water and dissolved solids, along with any . remaining reagents not consumed
in the flotation process. These reagents may include cyanide, which is used as a sphalerite depressant
during galena flotation. Most operations send tailings to impoundments where solids settle out of the
suspension. The characteristics of tailings from the flotation process vary greatly, depending on the
ore, reagents, and processes used.
Chemical Wastes
In addition to wastes generated as part of extraction and beneficiation, facilities also store and use a
variety of chemicals needed for mine and mill operations. A list of chemicals used at lead-zinc mines
is provided in Exhibit 3-8.
3.3.3.4 Waste Man2gement
Wastes generated as a result of mining and beneficiating lead and zinc minerals are managed (treated,
stored, and/or disposed) in discrete units—waste rock piles or dumps, mine pits and underground
structures, and tailings impoundments.
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Exhibit 3-8. Chemicals Used at Lead-Zinc Mines
Acetylene Sodium Cyanide Kerosene
Calcium Oxide Sulfur Dioxide Methane, Chiorodifuoro-
Hexone Sulfuric Acid Sodium Aerofloat
Hydrogen Chloride Diesel Fuel No. 1 Sulfuric Acid Copper (2+)
Methyl Chloroform Diesel Fuel No. 2 Salt (1:1)
Methyl Isobutyl Carbinol Chromic Acid, Disodium Salt Zinc Solution
Nitric Acid Copper Solution Zinc Sulfate
Propane
Source: National Institute for Occupational Safety and Health, 1990.
Waste Rock Piles
Waste rock (overburden and mine development rock) removed from the mine is stored and/or
disposed in unlined piles onsite. Constituents of concern in runoff and leachate from waste rock piles
includes heavy metals. These piles also can generate acid drainage if sulfide minerals and moisture
are present in sufficient concentrations without adequate neutralization potential or other controls.
Mine Pits and Underground Workings
In addition to wastes generated during active operations, when the mines close or stop operation, pits
and underground workings may be allowed to fill with water. This accumulating water, which may
become mine drainage, can acidify through aeration and contact with sulfide minerals and become
contaminated with heavy metals. At pits where quartz minerals are associated with lead-zinc deposits,
silica dust exposure may be a problem both during mine operations and following closure. Asbestos
minerals, which may be present in pits where limestone and dolomite ores are mined, may also be a
concern (U.S. Department of Health and Human Services, 1982).
Tailings Impoundments
The disposal of tailings requires a permanent .site with adequate capacity for the life of the mine.
Impoundments can range up to several hundred acres in size. The method of tailings disposal is
largely controlled by the water content of the tailings. Two general classes of impounding structures
may be used to construct a tailings pond: water-retention dams and raised embankments. Water
retention dams involve the construction of a dam, usually in a natural drainage area, and tailings are
impounded behind the dam. The water retention method relies on natural topography to assist in the
impoundment of tailings and tailings water. A raised embankment is a phased approach to
impoundment construction in which the earthen dam structure, composed of native soils, waste rock,
and tailings, is built up in successive lifts over the life of the project as need arises and materials are
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available. Water retention dams are more costly but typically allow greater storage of process water
and effluent in the impoundment.
3.3.4 CoPPER
The physical properties of copper, including malleability and workability, corrosion resistance and
durability, high electrical and thermal conductivity, and ability to ahoy with other metals, have made
it an important metal to anumber of diverse industries. Copper was an historically important
resource for the production of tools, utensils, vessels, weapons, and objects of art. According to the
Bureau of Mines, in 1992, copper production was used for building construction (41 percent),
electrical and electronic products (24 percent), industrial machinery and equipment (13 percent),
transportation (12 percent), and consumer products (10 percent) (Bureau of Mines, 1993a).
The United States is the second largest copper producer in the world. Next to Chile, the United
States had the second lart est reserves (45 million metric tons) and reserve base (90 million metric
tons) of contained copper in 1992. United States’ copper operations produced about 1.7 million
metric tons in 1992. In 1991, 1.63 million metric tons were produced. The total value of copper
produced in 1992 was $4.1 billion. Arizona led production in 1992, followed by New Mexico, Utah,
Michigan, and Montana. In the same year, copper was also recovered from mines in seven other
States (Bureau of Mines, 1.93a and 1993b).
The number of operating copper mines decreased from 68 mines in 1989 to 65 mines in 1992. Of the
65 mines actively producing copper in 1992, 33 listed copper as.the primary product. The remaining
32 mines produced copper either as a byproduct or co-product of gold, lead, zinc, or silver (Bureau
of Mines, 1993b). Thirteen of the 33 active mines that primarily produce copper are located in
Arizona; the remaining mines are located in New Mexico, Utah, Michigan, and Montana (Bureau of
Mines, undated).
In 1991, the top 25 copper producers in the United States accounted for more than 95 percent of the
United States’ domestic copper production. These producers are listed in Exhibit 3-9 (Bureau of
Mines, 1993b).
3.3.4.1 Geology of Copper Ores
Copper deposits are found in a variety of geologic environments, depending on the rock-forming
processes that occurred. In general, copper deposits are formed by, hydrothermal processes (i.e., the
minerals-are precipitated as sulfides from heated waters associated with igneous intrusions or areas of
otherwise abnormal lithospheric heating). These deposits can be grouped in the following broad
classes: porphyry and related copper deposits, sediment-hosted copper deposits, volcanic-hosted
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Exhibit 3-9. Leading Copper Producing Facilities in the United States
Rank
Mine.
County and State
.. Operator
1
Morenci/Metcaif
Greenlee, AZ
Phelps Dodge Corporation
2
Bingham Canyon
Salt Lake, UT
Kennecott, Utah Copper Corporation
3
San Manuel
Pinal, AZ
Magma Copper Company
4
China
Grant, NM
Phelps Dodge Corporation
5
Tyrone
Grant, NM
Phelps Dodge Corporation, Burro Chief Copper
Company
6
Siemta
Pirna, AZ
Cyprus Sierrita Corporation
7
Ray Complex
Pinal, AZ
ASARCO Incorporated
8
Bagdad
Yavapai, AZ
Cyprus Bagdad Copper Company
9
Pinto Valley
Gila, AZ
Pinto Valley Copper Corporation
10
Mission Complex
Pima, AZ
ASARCO Incorporated
11
Inspiration
Gila, AZ
Cyprus Miami Mining Corporation
12
White Pine
Ontonagon, Ml
Copper Range Company
13
Continental
Silver Bow, MT
Montana Resources, Inc.
14
Twin Buttes
Pima, AZ
Cyprus Sierrita Corporation
15
Tray
Lincoln, MT
ASARCO Incorporated
16
San Xavier
Pima, AZ
ASARCO Incorporated
17
Superior (Magma)
Pinal, AZ
Magma Copper Company
18
Miami
Gila, AZ
Pinto Valley Copper Corporation
19
Casteel
Iron, MO
The Doe Run Company
20
Silver Bell
Pima, AZ
ASARCO Incorporated
21
Lakeshore
Pinal, AZ
Cyprus Casa Grande Corporation
22
Johnson
Cochise, AZ
Arimetco Incorporated
23
Oracle Ridge
Pinal, AZ
South Atlantic Ventures Ltd.
24
Yerington
Lyon, NV
Arimetco Incorporated
_25
Mineral Park
Mohave, AZ
Cyprus Mineral Park
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massive sulfide deposits, veins and replacement bodies associated with metamorphic rocks, and
deposits associated with ultramafic, mafic, ültrabasic, and carbonatite rocks.
Copper occurs in about 250 minerals; howeve , only a few of these are commercially important The
most common sulfide minerals are chalcopyrite (CuFeS 2 ), covellite (CuS), chalcocite (Cu 2 S), bornite
(Cu 5 FeS 4 ), enargite (Cu 3 AsS 4 ), and tetrahedrite ((CuFe) 12 Sb 4 S 13 ). Predominant oxide minerals are
chrysocolla (CuSiO 3 ), malachite (Cu 2 CO 3 ), azurite (Cu 3 (C0 3 ) 2 (OH) 2 ), and cuprite (Cu 2 0).
Chalcopyrite is the most common mineral found in porphyry-type deposits. Chalcocite occurs
predominantly in hydrothermal veins (U.S Geological Survey, 1973).
3.3.4.2 Mining
Conventional open-pit mining techniques are the predominant methods used today by the copper
mining industry, representing 83 percent of domestic mining capacity. In open-pit mining,
overburden is initially stripped off to expose the ore. The waste rock and ore are excavated by
drilling rows of 6- to 12-inch (diameter) blast holes. Subsequently, large electric or diesel shovels or
front-end loaders transport the ore onto trucks, trains, or conveyor belts for removal to milling or
leaching. facilities, depending on the type of ore (sulfide or oxide) and grade.
The remaining 17 percent of the active copper mines use various types of high-tonnage underground
operations. The three main underground mining methods used to mine copper ore are stoping, room-
and-pillar, and block caving. Waste rock and mine waler are generated by underground mining
operations (as well as by surface mines). See Section 3.1 for a broad discussion of conventional
open-pit and underground mining techniques.
3.3.4.3 Beneficiation
Beneficiation of copper ores and minerals can occur either through conventional milling and flotation
of high-grade sulfide ore or by leaching and solvent extraction/electrowinning (SX/EW) lower grade
sulfide and oxide ore. The beneficiation method(s) selected varies with mining operations and
depends on ore characteristics and economic considerations.
Conventional Milling/Flotation
The first step in the beneficiation of high-grade sulfide ore is comminution. Typically, this is
accomplished by sequential size reduction operations—commonly referred to as crushing and grinding.
Crushing and grinding operations at copper mines are typical of those found throughout the mining
industry, including primary crushing in jaw or gyratory crusher (often in the mine workings),
secondary and tertiary crushing in cone crushers (typically in the mill), and grinding in rod and ball
or autogenousfsemiautogenous mills. After grinding, ore is pumped to a classifier designed to
separate fine-grained material: (less than 5 mm) from coarse-grained material requiring further
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grinding. The hydrocyclone is the standard technology for classification (Office of Technology
Assessment, 1988; Taggart, 1945; Wills, 1981).
The second step in the beneficiation of sulfide ore is concentration. Froth flotation is the standard
method of concentration used in the copper industry for higher-grade ores. About 70 percent of all
copper is produced by this method. The ore is conditioned with chemicals to make the copper
minerals water-repellent (i.e., hydrophobic) without affecting the other minerals. Air is then pumped
through the agitate 1 slurry to produce a bubbly froth. The hydrophobic copper minerals are
aerophilhic; that is, they are attracted to air bubbles, to which they attach themselves, and then float to
the top of the cell. As they reach the surface, the bubbles form a froth that overflows into a trough
for collection. The other noncopper minerals sink to the bottom of the cell. Following copper
recovery, molybdenum (as molybdenite [ M0SJ) and other metals may then be recovered by selective
flotation before the slurry is disposed of as tailings;
Conventional flotation is carried out in stages. The purpose of each stage depends on the types of
minerals in the ore. Selective flotation of chalcocite-bearing sulfide ores and the rejection of pyrite
utilizes three types of flotation cells: roughers, cleaners, and scavengers. Many copper mills now
also include column flotation to further enhance product recovery after scavenger flotation. Reagents
used in flotation concentrators at copper mines include collectors, depressants, activators, frothers,
flocculants, filtering aides, and pH regulators. A list of the reagents typically used in a copper
flotation circuit is presented in Exhibit 3-10 (Biswas and Davenport, 1976; Bureau of Mines, 1987).
Exhibit 3-10. Copper flotation Reagents
Collectors Activators
Ethytxanthate Sodium sulfide or hydrosulfide
Amyixanthate pH Regulators
lsopropylxanthaze Lime
Isobutylxanthate Sulfuric acid
Unspecified xanthates Caustic soda (NaOH)
Aikyl dithiophosphate Frothers
Unspecified dithiophosphate Aliphatic alcohol
Xanthogen forma e Pine oil
Thionocarbamate Phenol
Unspecified sulfide collector Polyglycol ether
Fuel oil Unspecified polyol
Kerosene Flocculants
Depressants Anionic polyacTylamide
Phosphorous pentasulfide Nonionic polyaciylamide
Cyanide salt Polyaczylate
Sulfide salt Unspecified polymer
Sodium silicate Dispersants
Sodium silicate
— Polyphosphate
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Copper concentrates exiting the flotation circuit contain 60 to 80 percent water. The concentrate is.
dewatered in a thickener, then sent to disc or drum filters for final dewatering. The dewatered copper
mineral concentrat’e is then sint to a smelter for processing. The collected water is usually recycled
to the milling circuit. A second product, waste material or tailings, is sent to a tailings pond for
disposal (possibly after additional flotation steps to recover other metal values). The settling of solids
in the thickeners is enhanced by chemical reigents known as flocculants and filter cake moisture is
regulated by reagents known as filtering agents, Typical flocculants and filtering agents used are
polymers, nonionic surfactants, polyacrylate, and anionic and nonionic polyacrylamides (ASARCO,
1991).
Leach Operations
Copper is increasingly recovered by solution, or hydrometallurgical, methods. These include dump,
heap, and vat leaching techniques, as well as underground (or in situ) leaching methods. Each of
these methods results in a pregnant leach solution (PLS). Copper is recovered from the PLS through
cementation or, more commonly, by solvent extractionlelectrow inning (SXIEW) (U.S. Congress,
Office of Technology Assessment, 1988). Currently, solution copper mining techniques account for
approximately 30 percent of domestic copper production. Two-thirds of all United States cop ér
mines employ various types of solution operations (Weiss, 1985).
Most ores occur as mineral compounds that are insoluble in water; leaching involves chemical
reactions that convert copper into a water-soluble form followed by dissolution. Acid leaching of
ores and concentrates is the most common method of hydrometallurgical extraction. Its use is
confined to acid-soluble, oxide-type ores that are not associated with acid-consuming rock types
containing high concentrations of calcite (such as limestone and dolomite). Typical acidic leaching
agents include hydrochloric acid (HCL), sulfuric acid (H 2 SOJ, and iron sulfate (Fe 2 (S0 4 )). Sulfuric
and hydrochloric acid leaching at atmospheric pressure is the most common type of copper leaching.
For certain minerals, alkaline (or basic) leaching and microbial (or bacterial) leaching are effective
means of extracting copper. The principal reagents used in alkaline leaching are the hydroxides and
carbonates of sodium and ammonia. The organism associated with bacterial leaching is Thiobacillus
ferrooxidans.
Leaching Methods (In Situ, Dump, Heap, arid Vat)
Exhibit 3-11 summarizes the major copper leaching methods. Each of these methods is discussed in
the following sections.
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Exhibit 3-11. Characteristics of Copper Leaching Methods
...
:1 vatLeaching
::. lieap Leaching:
Dump Leaching
Underground and
In situ Leaching
Ore grade
Moderate to high
Moderate to high
Low
Low to high
(dependent upon
mine conditions
and layout)
Types of ore
Oxides, silicates,
and some sulfides
Oxides, silicates,
and some sulfides
.
Sulfides, silicates,
and oxides
Oxides, silicates,
and some
sulftdes
Ore preparation
May be crushed to
optimize copper
recovery
May be crushed to
optimize copper
recovery
Blasting
None
Container or
pad
.
Large impervious
vat
.
•
:
Impervious barrier
of clay, synthetic
material, or both
.
None for existing
dumps; new dumps
intended to be
leached would be
graded, and
covered with an
impermeable
polyethylene
membrane, or
bedrock, protected
by a layer of select
fill
None
Solution
Sulfuric acid for
oxides; acid cure
and acid-ferric cure
provide oxidant
needed for mixed
oxide/sulfide ores
Sulfuric acid for
oxides; acid cure
and acid-ferric cure
provide oxidant
needed for mixed
oxide/sulfide ores
Acid ferric-sulfate
solutions with good
air circulation and
bacterial activity
for sulfides
.
.
Sulfuric acid,
acid cure, acid-
ferric cure, or
acid ferric-
sulfate,
depending on the
oretype
Length of leach
cycle
Days to months
Days to months
Months to years
‘
Months
Solution
application
method
Spraying, flooding,
and circulation
Spraying or
sprinkling
Ponding/flooding,
spraying,
sprinkling, and
trickle systems
Injection holes,
recovery holes,
or suxnps
Metal recovecy
method
•
SX/EW for oxides
and mixed
oxide/sulfide ores;
iron precipitation
for mixed ores
SXJEW for oxides
and mixed
oxide/sulfide ores;
iron precipitation
for mixed ores
SXIEW for oxides
and mixed
oxide/sulfide ores;
iron precipitation
for mixed ores
SX/EW for
oxides and mixed
oxide/sulfide
ores; iron
precipitation for
mixed ores
Source: Office of Technology Assessment, 1988.
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in Situ Leaching . The leaching of low-grade copper ore without its removal from the ground is
kiiown as in situ leaching. In situ leaching allows only limited control of the solution compared to
other types of leaching (see below). There are 18 in situ copper operations in the United States that
leach ore in existing underground mines.
In situ leaching extracts copper from subsurface ore deposits without excavation. Typically, the
interstitial porosity and permeability of the rock are important factors in the circulation system. The
solutions are injected in wells and recovered by a nearby pump/production-well system. In some
cases (where the ore body’s interstitial porosity is low), the ore may be prepared for leaching (i.e.,
broken up) by blasting or hydraulic fracturing. Production wells (andlor sumps in underground
mines) capture and pump pregnant lixiviant solution from the formation to the leach plant where
copper metal is reäovered by an SX/EW operation (Biswas and Davenport, 1976; EPA, 1984a; EPA,
1989).
DumD Leach Operations . Dump leaching refers to leaching of low-grade sulfide or mixed-grade
sulfide and oxide rock that takes place on (usually) an unlined surface. Copper dump leaches are
typically massive, with rock piles ranging in size from 20 to hundreds of feet in height. These may
cover hundreds of acres and contain millions of tons of waste rock and low-grade ore (Biswas and
Davenport, 1976). These operations entail the addition of low pH solution to the piles to accelerate
leaching, the collection of PLS, and the extraction of copper by SX/EW or cementation. Since
widespread application of leaching process is a relatively new process, copper mines have frequently
applied leaching techniques to recover values from historic waste rock dumps. Collection of PLS
may not be maximized (i.e., some PLS may escape to the environment). The sites for these historic
dump leaches were selected primarily to minimize haulage distances. New dump leach units are
typically located and designed to prevent or minimize the loss of leach solution (EPA, 1989).
The materials placed in dump leaches vary considerably in particle size, from large angular blocks of
hard rock to highly weathered fine-grained soils. The material is typically less than 0.6 meter in
diameter. In most dump leach operations, the material is hauled to the top of the dump by trucks.
The material is deposited by end-dumping in lifts on top of materials that have already been leached.
Large dumps are usually raised in lifts of 15 to 30 meters. After the lift is completed, the top layer is
scarified (by a bulldozer and a ripper) to facilitate infiltration of the leach solution (EPA, 1989e).
Natural precipitatinn, mine water, raffinate (from the SX/EW plant), makeup water, and/or dilute
sulfuric acid may be used as leach solution (i.e., lixiviant). As the lixiviant infiltrates the pile, copper
minerals are leached by oxidizing the pyrite to form sulfuric acid and ferrous iron solution (the
sulfuric acid solution reacts with the ore minerals to ionize the copper into solution). Several methods
are used to distribute leach solutions over the dumps, including natural precipitation, sprinkler
systems that spray the leach solution over the piles, flooding of infiltration ditches or construction of
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leach solution ponds on top of dumps, distribution of leach solutions through perforated pipes on top
of dumps (known as trickle systems), and the injection of leach solutions through drill holes into
dumps. The leach solution percolates through the dump and PLS is collected in ditches or sumps at
the toe of the dump where the slope of the native terrain provides the means for collection of
pregnant liquor. These 4itches and sumps are lined at some sites, and are unlined at others. PLS is
then treated by solvent extraction or cementation. Metals associated with the copper minerals that are
also found in PLS include arsenic, cadmium, chromium, and selenium (EPA, 1985; EPA, 1984a).
Heap Leaching . In contrast to dump leaching (described above), heap leaching refers to the leaching
of low-grade ore that has been deposited on a specially prepared, lined pad constructed using
synthetic material, asphalt, or compacted clay. In heap leaching, the ore is frequently beneficiated by
some type of size reduction (usually crushing) prior to placement on the pad (EPA, 1989).
Heap leach pads are constructed above one or more layers of impermeable liner material. Liners can
be constructed using synthetic membranes [ such as High-Density Polyethylene (HDPE)] andior
natural material (such as compacted native soils or clays or unfracturedlunfaulted bedrock). Most
leach sites are selected to take advantage of existing, less permeable surfaces and to utilize the natural
slope of ridges and valleys for the collection of PLS. Land with this type of geology and terrain,
however, is not always within a reasonable hauling distance of the mining operation.
The same basic principles arid procedures discussed above with regard to dump leaching operations
apply to heap leach operations. Heap leach operations, as opposed to dump leach operations, have
the following characteristics: (1) higher lixiviant concentrations generally are used; (2) leach piles
may be neutralized after leaching operations are completed; (3) the leach pad design is substantially
different (i.e ., the size is smaller, averaging between 100,000 and 500,000 metric tons of ore); (4) the
ore is finer grained (i.e., usually less than 10 cm); (5) the leaching is considerably faster; and (6) the
extraction of oxide copper is greater (EPA, 1989e).
Vat Leaching . The vat leaching process works on the same principles as the dump and heap leaching
operations described above, except that it is a high-production-rate method conducted in a system of
vats or tanks using concentrated lixiviant soluiions. Vat leaching is typically used to extract copper
from oxide ores by exposing crushed ore to concentrated sulfuric acid (lixiviant) in a series of large
tanks or vats. The vats are usually designed in a series configuration, which acts to concentrate the
copper content of the solutions as a function of ore-lixiviant contact time (EPA, 1989e). A typical
25-meter-long, 15-meter-wide, and 6-meter-deep vat unit is capable of leaching between 3,000 and
5,000 tons of ore per cycle.
Vat and agitation (tank) leaching are usually performed on relatively higher grade oxidized ores.
Tank methods tend to recover copper more rapidly using shorter leach cycle times than heap or dump
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leaching operations. Generally, copper recovery is higher, and solution losses are lower with tank
methods (EPA, 1984). The advantages of this method are high copper extraction rates and
recoveries, short leach cycles, and negligible solution losses (EPA, I 989e). The disadvantages are
the low tonnages beneficiated, high suspended solids concentrations in PLS that a cause problems in a
SXJEW plant, and high operating costs.
Copper Recovery from Leach Solutions—Cementation and SX/EW .
Cementation . In the past, copper produced from leach solutions was typically recovered by
cementation techniques. In the cementation process, pregnant leach solution (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. The cemented copper later detaches from the steel surfaces as flakes or powder
when it is washed with high-pressure streams of water. Although subsequent treatment by a normal
smelting/refining method is required, copper recovery from the pregnant solution is very high.
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.
However, several compact and dynamic cementation systems have been developed and are used
industrially. The most successful is the Kennecott Cone System Precipitator, by which the PLS is
forced upwards in a swirling motion through shredded steel scrap. In this system, fine, undissolved
solid particles (called pulp) are concentrated with the copper cemented particles. Consequently, the
cement concentrates containing the pulp must be further beneficiated by flotation. The cemented
copper is easily floated with xanthate or dixanthogen collectors (Biswas and Davenport, 1976).
Solvent Extraction . The first SXIEW plant was developed during the 1960s at the Bluebird property
near Miami, Arizona. Historically, solvent extraction was largely confined to copper oxides.
However, recent refinements in leaching methods have made it economical for recovery from low
grade sulfide ores. The major advantage of solvent extraction (over cementation) is that the electrolyte
solution it produces is almost free of impurities.
Exhibit 3-12 provides a flow diagram for a typical SX/EW plant. The solvent extraction operation 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. The loaded organic solution is transferred from the extraction section to the
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stripping section. The aqueous-organic dispersion is physically separated in a settler stage (Office of
Technology Assessment, 1988; EPA, 1984; Engineering and Mining Journal, 1990).
In the second stage, the loaded organic solution is stripped with concentrated sulfuric acid solution
(spent tankhouse electrolyte) to produce a clean, high-grade solution of copper for electrow inning.
The stripping section can have one or more mixer-settler stages. The loaded-organic phase is mixed
with the highly acidic electrolyte, which strips the copper ions from the organic phase. Then, the
mixture is allowed to separate in settling tanks, where the barren organic solution can be recycled to
the extraction stage. The copper-enriched, strong electrolyte flows from the stripping stages to the
strong-electrolyte tanks, where it is pumped to the electrolyte filters for removal of the entrained
organics or solids. The clarified, strong electrolyte flows to electrolyte circulation tanks, where it
becomes the influent to the electrowinning tankhouse (Office of Technology Assessment, 1988; EPA,
1984a; Engineering and Mining Journal, 1990).
Electrowinning . Electrowinning is the method used to recover copper from the electrolyte solution
produced by solvent extraction. To stabilize the tankhouse operating temperature and preheat the
incoming electrolyte solution, strong electrolyte (after filtration) is passed through heat exchangers
where heat is extracted from outgoing, warmer, spent electrolyte. After passing through starting-
sheet cells, the strong electrolyte is received in a circulation tank. In the circulation tank, the strong
electrolyte is mixed with spent electrolyte returning from the electrowinning cells. The’ feed
electrolyte is then pumped to the electrolytic cells continuously. The electrochemical reaction at the
lead-based anodes produces oxygen gas and sulfuric acid by electrolysis. Copper is plated on
cathodes of stainless steel or on thin-copper starting s ieets. 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 strip-mixer-settlers via the electrolyte heat
exchangers (Office of Technology Assessment, 1988; Engineering and Mining Journal, 1990).
Over time, electrolyte in the electrowinning cells becomes laden with soluble impurities and copper.
When this occurs, the solution is removed and replaced with pure electrolyte (to maintain the
efficiency of the solution and prevent coprecipitation of the impurities at the cathode). Purification is
done by electrowinning in liberator cells. Liberator cells are similar to normal electrolytic cells, but
they have lead anodes in place of copper anodes. The electrolyte is cascaded through the liberator
cells, and an electric current is applied. Copper in the solution is deposited on copper starting sheets.
As the copper in the solution is depleted, the quality of the copper deposit is degraded. Liberator
cathodes containing impurities (such as antimony) are often sent to the smelter to be melted and cast
into anodes. Purified electrolyte is recycled to the electrolytic cells.
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3.3.4.4 Wastes and Waste Management
Wastes generated by copper mining and beneficiation operations include materials such as waste rock,
mine water, spent ore, tailings, SX/EW sludges, and spent leaching solution. Many of these materials
may be disposed of onsite or offsite, and others may be re-used or recycled during the active life of a
mine. Waste constituents may include heavy metals, sulfides, or other, elements found in’the ore, acid
mine drainage (AMD), and any additives used in beneficiation operations. (It should be noted that
the use of the terms “mining waste” and “waste management unit” in this, document does not imply
that the materials in questions are “solid wastes” within the meaning of the Resource Conservation
and Recovery Act. As indicated previously, the term “wastes” includes both RCRA wastes as well as
other materials.)
Mine Water
Mine water consists of all water that collects in surface and underground mine workings as a result of
inflow frOm surface water, precipitation, and groundwater. During the life of the mine, water is
pumped out to keep the mine relatively dry and to allow access to the ore body. At surface copper
mines, mine water may be pumped or allowed to drain to centralized surnps. At underground mines,
the quantity of water entering the mine depends on local hydrogeologic conditions. At some
facilities, little or no water is encountered. At others, groundwater may continually drain into the
mine workings. Underground water inflows are often allowed to drain to low areas of the mine
where sumps and pumps collect and pump the water from the mine. At some facilities, however, the
inflow of water is so great that the capacities of the underground holding and pump mechanisms are
exceeded, which can lead to mine flooding (Cumming, 1973). in these cases, wells near the mine
may be used to pump groundwater, leading to a cone of depression around the mine and reducing
inflow.
The quantity of mine water generated at mines varies from site to site. The chemistry of mine water
is dependent on the geochemistry of the ore body and the surrounding area. Water exposed to sulfur-
bearing minerals in an oxidizing environment, such as an open pit or underground workings, may
become acidified. This potentia1 is greatly dependent on site-specific factors (see Section 4.1).
Pumped water from copper mines may be used in extraction and beneficiation activities (including
dust control), pumped to tailings ponds, or discharged. Because mine water at copper mines is often
rich in dissolved copper and other metal ions, some operations pump it to an SX/EW plant to recover
the copper values (Cumming, 1973).
Waste Rock
Waste rock is typically hauled from the mine to onsite waste dumps for disposal. At some surface
mines, these dumps are located within the pits. Waste rock piles may be highly permeable to both air
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and water. Sulfur-bearing minerals in waste rock, such as pyrite and pyrrhotite, can oxidize to form
sulfuric acid. Factors that influence acid generation by sulfide wastes include: (1) the amount and
frequency of precipitation, (2) the design of the disposal unit, and (3) the neutralization potential of
the rock. Even where acid-generating conditions are not present, metals found in the waste rock m y
dissolve in infiltration runoff or runon. This low pH solution can dissolve and mobilize metals in the
rock matrix and be transported to ground or surface water. Waste rock disposal units are generally
constructed without liners. Because even waste rock would contain low concentrations of copper,
some operations refer to waste rockas “low-grade ore” or “subore.”
Spent Ore
Spent ore from heap and dump leaching contains residual amounts of lixiviant and associated copper
and other metal complexes. The spcnt ore itself typically contains unleached metals and other
minerals characteristic of the ore body. Dump leach piles are reported to range in size from 20 feet
to hundreds of feet in height and may cover hundreds of acres and contain millions of tons of waste
rock and low-grade ore. Most copper leaching operations are not constructed with synthetic liners
(i.e., they are dump leach units, rather than heap leach units). However, newer units are frequently
sited where natural low permeability features allow for drainage to a centralized collection point (to
facilitate recovery of pregnant leach solution). After collection of leaching solution no longer
becomes economic lly viable, operators must address reclamation/closure of the leach units and
management of drainage.
T2ilings
In 1985, 195 million tons of copper and copper-molybdenum ores were treated by flotation
concentration, resulting in the production of 5.8 million tons of concentrate using 97 million gallons
of water and 0.32 million tons of reagents. More than 97 percent (189 million tons) of ore tonnage
processed in 1985 was typically disposed of as tailings (Bureau of Mines, 1987).
Tailings impoundments are surface disposal units for tailings generated during flotation. Slurried
tailings are transported from the mill to the tailings pond by gravity flow and/or pumping through
open conduits or pipes. In the arid southwest, where the majority of copper mines are located and
evaporation rates exceed precipitation, the mine-mill water balance usually requires recycling tailings
pond water for reuse in the mill. At copper mines in the central United States (such as the White
Pine in Michigan) the reverse situation exists; precipitation exceeds evaporation rates and tailings
pond water is typically discharged to surface water. Tailings impoundments may also be used to
disposed of other smaller-volume wastes generated at copper mines including, spent electrolyte
solution, SX/EW tank sludge, etc.
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Upstream tailings impoundments are most commonly used in the copper mining industry. In this
method (as described in Section 3.2), the embankment is erected by depositing successive layers of
course material on top of the previous dike along the inside of its embankments. Thus, the centerline
of the berm progresses upstream toward the center of the dam, while the outer slope remains stable
(Bureau of Mines, 1984j.
Solution Ponds (PLS and Raflinate Ponds)
Leaching operation ponds can be a source of acidlmetal releases by ground and surface water. These
include: pregnant solution ponds or tanks (where the copper-laden solution is collected), barren
solution ponds (where lixiviant solution is held before being applied), surge ponds (to manage
leachate during high precipitation events), make-up water holding ponds, and associated pipes or
trenches. These units may be lined, depending on the quality of the solution to be contained,
applicable regulatory requirements, the agi of the unit, and permeability of the underlying formation.
and raffmate ponds generally measure several hectares in size and, where the topography
permits, are built into natural drainage basins. At most older copper leaching operations, the
collection ponds and trenches through which the solutions flow are unlined. In addition, these areas
received little or no surface preparation before leaching operations were initiated (EPA, 1989): At
newer leaching operations, liners have been installed in the collection ponds to increase solution
rdcovery and minimize environmental releases. Generally, the trenches have been lined with
concrete, gunite, clay, or synthetics such as polyethylene (EPA, 1989).
3.3.5 IRON
The total quantity of usable iron ore product shipped from mines in 1991 was estimated to be 52.8
million long tons (It),’ valued at $1.7 billion. Of the total 1991 domestic production, 1.97 million It
of iron product (4 percent) were exported. The United States also imported 12.9 million lt of usable
iron ore in 1991 for beneficiation and processing. According to the Bureau of Mines, “usable” iron
ore implies that less than 5 percent of the material is made up of manganese (Bureau of Mines,
1991 a).
In 1991, there were 20 companies operating 22 iron ore mines (21 open pit; 1 underground
operation), 16 concentration plants, and 10 pelletizing plants. The primary iron ore producers are
located in Minnesota and Michigan, which account for about 99 percent of all domestic crude iron
ore. In 1991, 7 mines operated by 4 companies produced approximately 87 percent of the industry’s
total output (Bureau of Mines, 1992). The trend in the industry is toward larger mines and larger
‘Industry tends to measure iron ore production in long tons (It), while the Bureau of Mines used short tons (st) before
1989 and now uses metric tons (mØ. Production data are presented here in b ug tons (1 long ton is equivalent to 2,240 bbs).
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capacity mills Operation capacities tend to be in the range of 1 to 10 million long, tons of product
per year (ltpy). A few, mines, however, produce less than 100,000 ltpy (Weiss, 1985).
Nearly 98 percent of the demand for iron ore comes from the steel manufacturing industry. Iron is
also a component in the manufacture of cement and heavy-media materials. Among the 22 mines
producing iron ore, most larger operations produce material for the steel manufacturers. Mines
producing for cement plants tend to be smaller operations located outside Michigan and Minnesota’
(Bureau of Mines, 1988b, 1991a, and 1992).
3.3.5.1 Geology of Iron Ores
Iron is an abundant element in the earth’s crust averaging from 2 to 3 percent in sedimentary rocks to
8.5 percent in basalt and gabbro. Because iron is’ present in many areas, it is of relatively low value
and thus a deposit must have a high percentage of metal to be considered ore grade. Typically, a
deposit must contain at least 25 percent iron to be considered economically recoverable. This
percentage can be lower, however, if the ore exists in a large deposit and can be concentrated and,
transported inexpensively (Weiss, 1985). Over 300 minerals contain iron but five are the primary
sources of iron-ore minerals: magnetite (Fe 3 0 4 ), hematite (Fe 2 0 3 ), goethite (Fe 2 O 3 H 2 O), siderite
(FeCO 3 ), and pyrite (FeS 2 ). The first three are of major importance because of their occurrence in
large economically minable deposits (U.S. Geological Survey, 1973).
Iron ore mineral deposits are widely dispersed in the continental United States and form in a wide
varety of geologic environments, including sedimentary, metamorphic, and igneous rock formations.
Iron ore deposits in the United States are formed by three geologic processes:
• Direct sedimentation forming bedded sedimentary deposits
• Igneous activity forming segregation or replacement deposits
• Enrichment due to surface and near surface weathering (EPA, 1985).
Historically, most iron ore was simply crushed and shipped directly tO a blast furnace. Currently,
some ores are high enough in iron content (greater than 50 percent) to be sent directly to furnaces
without beneficiation activities other than crushing and washing. Most ores extracted today, however,
must undergo a number of beneficiation procedures to upgrade the iron content and prepare the
concentrate for the blast furnace. Technological advancements at blast furnace operations require ore
feed of a specific size, structure, and chemical make-up for optimum efficiency (Weiss, 1985).
3.3.5.2 Mining
Iron ore is mined almost exclusively ‘in surface operations. The most predominant surface mining
methods used to extract iron ore are conventional open-pit and open-cut methods. However, there is
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currently one operating underground iron mine, located in Missouri (five were in operation in
Missouri in 1985). The. mining of taconite, a tough and abrasive low-grade ore (ranging from 40 to
60 percent silica, and 17 to 30 percent iron) common to Minnesota and Michigan, is especially
difficult because of the extreme hardness of the ore but now dominates U.S. iron production.
In the iron industry, stripping ratios (overburden/ore) may be as high as 1:1 (for high-grade wash
ores) or as low as 0.5:1 (for low-grade taconite Ores) (United States Steel, 1973). Wastes generated
as a result of open-pit and underground iron mining include overburden, waste rock, and mine water
containing suspended solids and dissolved materials.
3.3.5.3 Beneficiation
Beneficiation at iron mines can include the following: milling (crushing and grinding); washing;
filtration; sorting; sizing; gravity concentration; magnetic separation; flotation; and agglomeration
(pelletizing, sintering, briquetting, or nodulizing).. The American Iron Ore Association indicates that
milling and magnetic separation are the most common methods used. Gravity concentration is seldom
used at existing U.S. facilities. Flotation is primarily used to upgrade concentrates from magnetic
separation by reducing the silica content of the concentrate (Ryan, 1991). Most beneficiation
operations will result in the production of three materials: concentrate; middling or very low-grade
concentrate, which ‘is either reprocessed (in modern plants) or stockpiled; and tailings.
Milling
Milling operations are designed to produce uniform size particles by crushing, grinding, and wet or
dry classification. Primary crushing is accomplished by using gyratory and cone crushers (Weiss,
1985). Primary crushing yields chunks of ore ranging in size from 6 to 10 inches. Secondary
milling (comminution) further reduces particle size, to usually less than 1 inch (1/2 to 3/4 inches).
Secondary crushing, if necessary and economical, is accomplished by using standard cone crushers
followed by short head cone crushers. Gyratory crushers may also be used.
Subsequent fine grinding further reduces the ore particles to the consistency of fine powder (325
mesh, 0.0017 inches, 0.44 microns). Although most tacomte operations employ rod and/or mill
grinding, a few facilities use autogenous or semi-autogenous grinding systems. Autogenous grinding
uses coarse pieces of the ore itself as the grinding media in the mill. Semi-autogenous operations use
metallic balls and/or rods tu supplement the grinding action of the ore pieces (Weiss, 1985). Between
each grinding unit, hydrocyclones are used to classif ’ coarse and fine particles. Coarse particles are
returned to the mill for further sze reduction.
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Magnetic Separation
Magnetic separation Is most commonly used to separate natural magnetic iron ore (magnetite) from a
variety of less-magnetic or nonmagnetic material. Today, magnetic separation techniques are used to
beneficiate over 90 percent of all domestic iron ore (Ryan, 1991). Magnetic separation may be
conducted in either a dry or wet environment, although wet systems are more common. Magnetic
separation operations can also be categorized as either low or high intensity. Low intensity wet
processes typically involve conveyors and rotary drum separators using permanent magnets and are
primarily used on ore particles 3/8 inch in diameter or less. Low intensity separators use magnetic
fields between 1,000 and 3,000 gauss. High intensity wet separators produce high magnetic field
gradients by using a matrix of shaped iron pieces that act as collection sites for paramagnetic
particles. High intensity separators employ fields as strong as 20,000 gauss. (Weiss, 1985; United
States Steel, 1973). Primary wastes from magnetic separation include: tailings made up of gangue in
the form of coarse- and fme-grained particles, and wastewater slurry in the case of wet separation.
Particulate wastes from dry separation may also be slurried.
flotation
Conventional flotation is primarily used to upgrade concentrates resulting from magnetic separation.
Over 50 percent of all domestic iron ore is upgraded using this technique. Flotation, when used alone
as a beneficiation method, accounts for approximately 6 percent of all ore treated (Ryan, 1991).
Typically, 10 to 14 flotation cells are arranged in a series from roughers to scavengers. Roughers are
used to make a coarse separation of iron-bearing metallic minerals (values) from the gangue. -
Scavengers recover smaller quantities of remaining values from the pulp. The pulp moves from the
rougher cells to the scavengers as values are removed. Concentrates recovered from the froth in the
-roughing and scavenging cells are sent to cleaning cells to produce the final iron-bearing metallic
mineral concentrate (Fuerstenau, 1970). Flotation reagents of three main groups may be used:
collectors/amities, frothers, and antifoams.
Iron-bearing metallic mineral flotation operations are of two main types: anionic and cationic -
(although anionic flotation is not commonly used in North American operations). The difference
between the two methods is related to which material (values or gangue) is floated and which sinks.
In anionic flotation, fine-sized crystalline iron oxides, such as hematite or siderite, are floated away
from siliceous gangue material such as quartz or chert. In cationic flotation, the silica material is
floated and the value-bearing minerals are removed as underfiow (Nummela and Iwasaki, 1986).
Wastes from the flotation cell are collected from the tailings overflow weir. Depending on the grade
of the froth, it is recycled for further recovery of iron units or discharged as tails. Tailings contain
remaining gangue, unrecovered iron minerals, chemical reagents, and process waste water.
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Generally, tailings proceed to a thickener. Thickened tailings may be pumped to an impoundment or
may be recycled for further beneficiation to collect remaining values. Clarified water is often reused
in the milling process.
Gravity Concentration
Although gravity concentration was once widely used in the beneficiation of iron ores, today less than
one percent of total domestic iron ore is beneficiated using this method. Gravity concentration is used
to suspend and transport lighter gangue (nonmetallic or nonvaluable rock) away from the heavier
valuable mineral. Three gravity separation methods have historically been used for iron ore:
washers, jigs, and heavy-media separators (Weiss, 1985). Wastes from gravity concentration are
tailings made up of gangue in the form of coarse- and fine-grained particles and process water. This
material is pumped as a slurry to a tailings pond.
Agglomeration
After concentration activities, agglomeration is used to combine the resulting fine concentrates into
durable clusters. The iron concentrate is balled in drums and heated to create a hardened
agglomerate. Agglomerates may be in the form of pellets, sinter, briquettes, or nodules. The
purpose of agglomerating iron ore is to improve the permeability of blast furnace feed leading to
faster gas-solid contact in the furnace (Weiss, 1985). Pellets currently account for more than 97
percent of all agglomeration products (therefore, only the pelletizing technique is discussed below,
although the other agglomerates are produced by similar high-temperature operations).
Pelletizing operations produce a “green” (moist and unfired) pellet or ball, which is then hardened
through heat treatment (Weiss, 1985). The first step in pelletizing iron concentrates is forming the
pellets. This is usually accomplished in a series of balling drums or discs. Additives such as
limestone or dolomite may also be added to the concentrate in a process known as “fluxing,” prior to
balling to improve blast furnace recovery. One of three different systems can then be used to produce
hardened pellets:
• Travelling-Grate. Used to produce pellets from magnetite concentrates obtained from
taconite ores. Green pellets are fed to a travelling grate, dried, and preheated. The pellets
then proceed to the ignition section of the grate where nearly all the magnetite is oxidized to
hematite. An updraft of air is then used to cool the pellets.
• Shaft-Furnace. Green pellets are distributed across the top of a furnace by a moving
conveyor belt and pass vertically down the length of the furnace. In the furnace, the pellets
are dried and heated to 2400°F. The bottom 2/3 of the furnace is used to cool the pellets
using an upward-rising air stream. The pellets are discharged from the bottom of the
system through a chunkbreaker.
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• Grate-Kiln. Combines the grate technique with a rotary kiln. No fuel material is
incorporated into or applied to the pellets in this process. The pellets are dried and
preheated on a travelling grate before being hardened by high-temperature heating in the
kiln. The heated gas discharge from the kiln is recycled for drying and preheating (United
States Steel, 1973).
Agglomeration generates byproducts in the form of particulates and gases, including compounds such
as carbon dioxide, sulfur compounds, chlorides, and fluorides that are driven off during the
production process. These wastes are usually treated using cyclones, electrostatic precipitators (wet
and dry), and/or scrubbing equipment. These treatment technologies generate either a wet or a dry
effluent, which contains valuable iron units and is commonly recycled back into the operation.
3.3.5.4 Wastes and Waste Management
Overburden, Mine Development Rock, and Ore Piles
Overburden and mine development rock removed from iron mines are stored or disposed of in
unlined piles onsite. These piles may also be referred to as “mine rock dumps” or “mine dumps.”
As appropriate, topsoil may be segregated from overburden and mine development rock, and stored
for later use in reclamation and revegetation. These dumps are generally unsaturated and provide a
prime environment for acid generation if sulfide minerals are present. However, in Minnesota and
Michigan, where most crude iron ore is produced, sulfide-bearing minerals are present in only one
unique geologic environment (Guilbert, 1986). As a result, acid generation has only been observed at
one site, L1V’s Dunka site at the eastern edge of the Mesabi Range (see. below).
Mine Pits and Underground Workingc
In addition to wastes generated during active operations, pits and underground workings may be
allowed to fill with water when the mine closes or stops operation, since the need for dewatering is
over. At one site in Minnesota, the Dunka Mine, accumulated water, or mine drainage, has acidified
through contact with sulfide minerals in an oxidizing environment and become contaminated with
heavy metals, as well as suspended solids. However, the conditions at the Dunka site (as well as two
other abandoned iron mines with similar acid rock drainage) are generally considered unique in the
iron industry (because of localized sources of sulfide ore). Overall, mine water associated with iron
operations is characterized by low pollutant levels, in fact, the mine water from at least one mine in
Michigan is used to supplement the local drinking water supply.
At abandoned underground mines, deficiencies in mine shaft protection and mine subsidence may be a
problem. Although there is only one underground iron mine currently operating in the United States,
abandoned underground iron mines have contributed to the creation of subsidence features. In West
Iron County, Michigan, subsidence features caused by abandoned iron mines have grown into large
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pits and caused interruptions in utility service, damage to roadways, and loss of life (Michigan State,
Geological Survey Division, 1983).
Tailings Impoundments
Impoundments, rather than piles, are used exclusively for tailings management in the iron ore
industry. As a typical example, the tailings impoundment at LTV Steel Mining Company’s facility at
Hoyt Lakes is approximately 3,000 acres and contains about 500 million tons of tailings (LW Steel
Mining Company, 199l) Two general classes of impounding structures may be used to construct
tailings pond at iron mines: water-retention dams and raised embankments. As solids settle out in
either of these type of impoundments, water is either recycled to the mill or discharged.
Trace amounts of several toxic metals are found in raw mill tailings effluents. These metals include
antimony, arsenic, beryllium, cadmium, chromium, copper, lead, nickel, selenium, silver, and zinc.
In some instances (Silver Bay, Minnesota and Groveland Miné,Michigan), amphibole minerals with
flbrous characteristics may be a constituent in the tailings. While amphibole minerals (cummington-
gnsnerite) are present in some Eastern Mesabi Range tacothte formations, asbestos has not been
identified as such (EPA, 1976). Most of these contaminants are effectively removed or reduced by
settling in tailings impoundments.
3.3.6 Ucw’iruM
Uranium is extracted using surface, underground and solution mining (in situ) techniques. Although
the industry is relatively young, developing in the I 940s, the volume of ore recovered by U.S. mines
has dropped significantly since peaking in the early 1980s. Low commodity prices, a reduced
demand from the military and commercial power generators, and abundant foreign supplies are
responsible for the depressed market.
3.3.6.1 Geology of Uranium Ores
Elemental uranium is generally found in naturally occurring minerals in one of two ionic states: 136+
(the uranyl TM oxidized” ion) and U 4 ’ (the urapous “reduced” ion). Common uranyl minerals include
tyuyamunite (Ca(U0 2 ) 2 V 2 0 8 8H 2 O), autunite (Ca(U0 2 ) 2 (P0 4 ) 2 8-12H 2 0), torbernite
(Cu(UO 1 ) 2 (P0 4 ) 2 8-12H 2 O) and uranophane (H 3 0) 2 Ca(UO 2 ) 2 (SiO 4 ) 2 3H 2 O) (Smith, 1984; Hutchinson
and Blackwell, 1984). Common uranous minerals include uraninite (U0 7 ), pitchblende (a crystalline
variant of uraninite) and coffinite (USiO,) (Smith, 1984; Hutchinson and Blackwell, 1984). Uranium
occurs in the minerals as one of three isotopes: U-234, 13-235 and the most abundant of the isotopes,
U-238 (Tatsch, 1976). In the uranium market, references to ore, intermediate, and some final
products, are in terma of percent of uranium oxide or uranium oxide equivalent. Uranium oxide is a
generic term for a number of common chemical forms of uranium, the most common being 0308.
Yellowcake is another generic term, used to describe the yellow powder generated as the end product
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of uranium beneficiation. The purity of yellowcake typically ranges from 60 to 75 percent U O 8
(Merritt, 1971).
3.3.6.2 Mining
Economically recoverable uranium deposits in the United States historically fit into one of four types
of deposits: stratabound, solution breccia pipes, vein, and phosphatic. The most economically
important deposits occur within stratabound deposits within the Wyoming Basin, south Texas, and the
Colorado Plateau. Stratabound deposits have been mined using surface and underground techniques
and are currently the target of solution mining operations. Grades of ore mined from these deposits
range from 0.15 to 0.30 percent U 3 0 8 . Solution breccia pipe uranium deposits are located in the
Northern Arizona Strip and average approximately 0.64 percent U-238; these deposits have been
mined using surface and underground methods (Fillmore, 1992). Vein deposits have been mined on
an infrequent basis using underground methods in Colorado and Utah. Phosphatic deposits are
associated with phosphate ores in Florida; uranium has been recovered to a limited extent as a
• byproduct of phosphoric acid production from these ores.
Proprietary information surrounding the small number of mines currently producing uranium limits
the level of detail available about the nature and size of recent operations. The primary extraction
(and beneficiation) method used to recover uranium from ore deposits is in situ leaching. According
to the U.S. Energy Information Administration, in situ mining operations generated two-thirds of the
uranium produced in the United States m l991. The remaining 33 percent of the uranium produced
in 1991 was by conventional milling operations (DOE/EIA, 1992). Prior to the drop in uranium
prices, ore was more commonly beneficiated using conventional milling techniques.
3.3.6.3 Beneficiation
In conventional uranium milling, the initial step involves crushing, grinding, and wet and/or dry
classification of the ore to produce uniformly sized particles. Ore initially feeds into a series of
crushers where it is reduced to fragments less than 19mm (3/4 inch). Ore from the crushers feeds
into the grinding circuit where ball and/or rod mills, and/or autogenous or semiautogenous grinding,
continue to reduce the size of the ore. Water or leach liquor is added to the system in the grinding
circuit to facilitate the movement of the solids, for dust control, and (if leach liquor is added) to
initiate leaching (DO!, 1980).
Classifiers, thickeners, cyclones, or screens are used to size the fmely ground ore, returning coarse
materials for additional grinding. The slurry generated in the grinding circuit contains 50 to 65
percent solids. Fugitive dust generated during crushing and grinding is usually controlled by water
sprays or, if collected by air pollution control devices, recirculated into the beneficiation circuit.
Water is typically recirculated through the milling circuit to reduce consumption (EPA, 1983a).
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After grinding, the slurry is pumped to a series of tanks for leaching. Two types of leaching have
been employed by uranium mills, acid and alkaline. Acid leaching has been the predominant leaching
process employed by conventional mills, although some mills have used an alkaline system and some
have included both (Merritt, 1971). In the discussions that follow, an overview of leaching is
provided followed by a more detailed description of both acid and alkaline leaches.
The first step in any uranium leaching operation is oxidation of the uranium constituents. Uranium is
found as uranium dioxide (U0 2 , U 4 oxidation state) in many deposits (pitchblende and uraninite).
Uranium dioxide is insoluble; to create a soluble form, U0 2 is oxidized from the U’ 4 to the U 6
oxidation state. Iron present within the ore, and oxygen, are usedto perform oxidation via the
following reactions (Twidwell et al., 1983):
(1) alkaline U0 2 + ½02 I U0 3
(2) acid U0 2 + 2Fe 3 # UO 2 2 + 2Fe 2
Iron can be readily reoxidized by the addition of 02, sodium chlorate (NaCIO 3 ), or manganese oxide
(Mn0 2 ) to the lixiviant.
The second step in leaching is the tabilization of the uraniferous ions in solution. The uraniferous
ions form stable, soluble complexes with sulfate (SO 4 2 ) or carbonate (CO 3 ). Sulfuric acid is added
as the source forsulfate ions; sodium bicarbonate, sodium carbonate, or carbon dioxide are added to
alkaline leach circuits to provide a carbonate source. Uràniferous complexes are ‘formed through the
following reactions (Twidwell et aL, 1983):
(1) alkaline U0 3 + C0 3 2 + 2HC0 3 U0 2 (C0 3 ) 3 4 + H 2 0
(2) acid UO 2 2 + 6S0 4 2 U0 2 (S0 4 ) 6 4 .
In a typical acid leaching operation, sulfuric acid is added to the crushed ore slurry to maintain the
pH between 0.5 and 2.0. Twenty to 60 kilograms of sulfuric acid per metric ton of ore are normally
required to reach the target pH. NaC1O 3 or Mn0 2 is added to maintain the oxidation by iron.
Because iron is normally found in uranium deposits, the ore body itself supplies the iron in the 1each
step (Twidwell et al., 1983; EPA, 1983a).
Alkaline leaching is not as effective is acid leaching for uranium recovery and is not used except in
cases of high lime-content ores. Typically, ore bodies containing greater than 12 percent carbonates
will be alkaline leached. Alkaline leaching is primarily employed in in situ mining operations,
although a few conventional mills have maintained alkaline leach circuits (Merritt, 1971): Alkaline
leaching requires the use of a strong oxidant and long retention times to oxidize the uraniferous
minerals (Twidwell Ct al., 1983). As stated previously, oxygen and -a carbonate source are added to
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water to make up the lixiviant. The carbonate (C0 3 2 ) and bicarbonate (HCO 3 ) concentrations are
typically 40-50 gIL and 10-20 g/L respectively (Merritt, 1971). For its leaching process, the
Highland in situ project injects 0 2(Z) and C0 2 (g) into the lixiviant prior to underground injection.
The dissolution of CO 2 in the lixiviant produces both C0 3 2 and HC0 3 ions (Hunter, 1991).
Leaching may be performed in tanks, heaps or in situ. In situ leaching is practiced on low-grade
ores; after crushing and grinding, higher grade ores are typically leached in tanks at conventional
mills. Low-grade ores may also be amenable to heap leaching; however, the available literature
indicates that the application of this technique to uranium ores has been and is limited and
consequently it is not be discussed in detail. Leach times vary depending on the grade of the ore,
grain size (amount of grinding), and the method used. Leaching in tanks may take from four to 24
hours while heap leaching may be measured in days or weeks (Twidwell et al., 1983).
Once the uraniferous compounds have been leached from the ore, the pregnant leach solution is
separated from the solids using classifiers, hydrocyclones, and thickeners. Sand-sized particles are
• removed first and washed with clean water or barren lixiviant/raffinate. Continued treatment
removes the slimes, which are also washed. Depending on the settling time allowed by beneficiation
operations, flocculants may be added to the process to encourage settling of suspended solids. After
final washing, the solids (sands and slimes) are pumped as a slurry to a tailings pond for further
settling. The pregnant leach solution then enters a solvent extraction or ion exchange circuit. Wash
solution is recycled to reduce consumption of leach chemicals, solute, and water (DOl, 1980; EPA,
1983a).
Solvent extraction is an operation that concentrates specific ions. Generally, solvent extraction uses
the immiscible properties of two solvents (the pregnant leach solution and a solvent extraction
solution) and the solubility properties of a solute (uraniferous ions) in the two olvents. Solvent
extraction is typically employed by conventional milling operations since solvent extraction can be
used in the presence of fine solids. The pregnant leach solution is mixed in tanks with the solvent
exchange solution. Selection of a solvent in which the target solute (uraniferous ions) is preferentially
soluble allows the solute to migrate to the solvent exchange solution from the pregnant leach solution
while other dissolved compounds remain in the leach solution. Normally, the solvents are organic
compounds that can combir with either solute cations or solute anions. A r ny.. rbonata
sulfates are commoiüy generated in the leaching step, anionic soivent extraction solutions are typically
np1oyed; cationic solve t extr ts m solutions may be ençIoyed depending en unique characteristics
of die ores or leaching o&utions.
Among the anionic SX solutions are secondary arnines with aliphatic side chains, high molecular
weight tri-alkyl tertiary amines, and quaternary ammonium compounds. Cationic SX solutions
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include monododecyl phosphoric acid (DDPA), di-2-ethylhexyl phosphoric acid (EHPA), heptadecyl
phosphoric acid (HDPA), and dialkyl pyrophosphoric acid (OPPA): (Twidwell et al., 1983)
Typically, the solvent extraction solution is diluted in a low cost carrier such as kerosene with a
tributyl phosphate modifier or a long chain alcohol (Twidwell et aL, 1983). The uraniferous ions
preferentially move from the aqueous pregnant leach solution into the organic solvent as the two are
mixed and agitated (DO!, 1980). After the uraniferous compounds are thus extracted from the
pregnant leach solution, the barren lixiviant (raffmate) is typically recycled to the leaching circuit.
After the solute exchange has taken place, the pregnant solvent extraction liquor must be stripped.
The uraniferous solute is typically in an anionic state, and accordingly many solvent extraction
solutions are anionic-based. Amine solvent extraction solutions can be stripped by many different
agents such as nitrates, chlorides, sulfates, carbonates, hydroxides, and acids. Chlorides are used
most frequently due to their cost-effectiveness (Twidwell et at., 1983).
The pregnant stripping liquor is then pumped to the precipitation step while the stripped organic
solvent is recycled to the beginning of the solvent extraction circuit. Solvent exchange can be done as
a batch or continuous process (Twidwell et al., 1983).
Like solvent exchange, ion exchange operations make use of organic compounds to perform solute
concentration. Generally, fixed organic resins contained within a column are used to remove
uraniferous compounds from the pregnant leach solution by adsorption. After adsorption, the
uraniferous compounds attached to the resins are released (eluded) by a stripping solution and sent to
precipitation. Ion exchange is used by most if not all in situ operations and was employed by some
conventional mills. It was not determined if the currently operational mills employ ion exchange
circuits within their operations.
Resins are constructed with anionic or cationic functional groups (typically anionic for uranium
compounds) that have an affinity for the target compound and specifically bind the compound to the
resin. Resins are synthetic polymers in which hydrocarbon groups make up a three-dimensional
network that hold stable, reactive functional groups (e.g., strong acid-SO 3 H; weak acid-COOH;
strong base-NR 3 CI; weak base-NH 2 RC1). Resins containing acid groups are called cation exchangers
while resins containing basic groups are termed anion exchangers (Twidwell et a!., 1983). Chloride
ions can exchange with the anionic component of all the functional groups, thus providing an
inexpensive stripping solution (i.e., any chloride salt solution) for any of the resins.
As the pregnant leach solution passes through the ion exchange resins, the uraniferous compounds
bind to the resins. The barren leach solution is recycled back to the leaching circuit. As the resins’
binding ports are filled by the uranyl ions, the, uranyl ion concentration at the outlet of the ion
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exchange column increases. Once the uranyl ions at the outlet reach a predetermined concentration,
the column is considered to be loaded and ready for elution. Typically, the pregnant leach stream is
then directed to a fresh vessel of solvent exchange resins. A concentrated chloride salt solution is
then directed through the loaded resins, eluting off the uraniferous complexes. The pregnant elute
liquor can then be directed to the precipitation circuit. The pregnant elute solution may be acidified
slightly to prevent the premature precipitation of uraniferous compounds (Twidwell et al., 1983).
Once the uraniferous ions have been concentrated by solvent extraction or ion exchange, they are
precipitated out of solution to produce yellowcake. The precipitate is then washed, filtered, dried and
drummed. The chloride stripping solution is recycled back to the stripping circuit. The type of ion
concentration solution (e.g., acid or alkaline solution) governs the precipitation method employed.
With acid pregnant stripping liquors or pregnant elute liquors; neutralization to a pH of 6.5 to 8 using
ammonia hydroxide, sodium hydroxide or lime results in the precipitation of ammonium or sodium
diuranate (Merritt, 1971). Hydrogen peroxide may also be added to an acid pregnant stripping liquor
or pregnant elute liquor to precipitate uranium peroxide (Yan, 1990). All forms of the uraniferous
• precipitate are known as yellowcake.
Alkaline pregnant stripping liquors or pregnant elute liquors typically contain uranyl carbonates.
Prior to precipitation of the uranyl ions, the carbonate ions must be destroyed. An acid (usually
hydrochloric acid) is added to the carbonate concentrate solution to break down the carbonates to
carbon dioxide; the carbon dioxide is vented off. Once the carbonates have been destroyed, the
acidified solution is neutralized with an alkali or treated with hydrogen peroxide to precipitate the
uraniferous compounds. Precipitation operations based on neutralization of acid solutions are favored
because of the higher purity of the yellowcake product; sodium, carbonate, and, in some cases,
vanadium, are impurities that may be present in yellowcake produced from alkaline neutralization
(Merritt, 1971).
The yellowcake is separated from the precipitation solution by filtration. Thickeners may be used in
conjunction with filtration units. The filtered yellowcake can then be dried and packaged for
shipping (Bureau of Mines, 1978). The supernatant generated from precipitation and dewatering
circuits can be recycled to the respective solvent extraction or ion exchange stripping solution.
Typically, yellowcake is shipped to a Federal facility for processing. In the processing step, uranium
fluoride (UF 6 ) is produced from yellowcake. The uranium fluoride is then enriched, an operation that
concentrates the TJ-235 from 0.7 percent to approximately two to three percent. The enriched
uranium fluoride is further refined to ultimately produce the fuel rods used in nuclear reactors.
In situ leaching is the most commonly employed solution technique and continues to be employed by
at least twé mines in Wyoming. Nebraska’s Department of Environmental Control permitted an in
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situ operation in 1990 although its operational status was not determined (NDEC, 1990). Deposits
amenable to in situ leaching are usually (if not always) within an aquifer. Water quality within a
mineral deposit may vary depending on the presence of and boundary between oxidizing and reducing
groundwaters. Ore body characteristics, including chemical constituents, grade, arid permeability, are
key considerations in the development of production methods (selection of lixiviants, arrangement of
well patterns, etc.). Ideally, the deposit should be confined by impermeable strata above and below
the deposit to prevent contamination of adjacent aquifers by excursions (solution leaks from the ore
zone). In situ production operations consist of three phases: removal of minerals from the deposit,
concentration of uraniferous minerals, and generation of yellowcake. In addition to the production
operations, water treatment and, in some cases, deep well injection facilities, are employed.
In the case of in situ operations, beneficiation serves as the first phase of the mining operation. In in
situ mining, barren solvent (lixiviant) is introduced to the deposit through injection wells to initiate
the operation. The lixiviant contains both an oxidizing agent to solublize the target minerals and a
complexing agent that binds to the target minerals and keeps them in solution. Wyoming in situ
operations recover uraniferous compounds using oxygen gas as the oxidizer and carbon dioxide, as
the complexing agent (WDEQ, 1991). The barren lixiviant is charged with carbon dioxide as the
solution leaves the ion exchange facility. Oxygen is injected into the solution in the weilfields,
immediately before the lixiviant flows into the injection wells. As the solution moves through the
deposit, uraniferous minerals are oxidized and uraniferous ions move into solution. Carbon dioxide
in the lixiviant reacts with water, forming carbonic acid, which in turn complexes with the solubilized
uraniferous ions, forming uranyl carbonates. The uranyl carbonates and gangue minerals solubilized
in the operation remain in solution as the pregnant solution is pumped to the surface through
production (recovery) wells.
Pregnant lixiviant is pumped from the production wellbeads through sand filters to remove any large
particulates; the hxiviant is then transferred to ion exchange units. Depending on the facility, the ion
exchange units may be placed in trailer-mounted tanks or moved via tanker truck from satellite plants
to a central processing facility. When the resins in the ion exchange units are loaded, the uraniferous
compounds are stripped from the resins and precipitated to form yellowcake. The lixiviant, after
passing through the ion exchange units is recharged with carbon dioxide and oxygen following the ion
exchange circuit and injected back into the ore body.
Numerous well patterns have been investigated since the early 1960s when in situ mining techniques
were first employed. Five spot well patterns, which consist of four injection wells forming the
corners of a square, and a production well in the center, are common in the industry. Alternating
injection and production wells are used in narrow deposits. The spacing between injection and
production wells can range from 20 to 200 feet and the number of well patterns in a well field may
also vary.
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Mining units are portions of the deposit to be mined during one operation, often following “pods” of
ore deposited along a roll front. Mining units may be mined in sequence or simultaneously.
Pumping rates at one in situ operation in Wyoming ranged from two gallons per minute (gpm) to 30
wm. for injection wells and five gpm to 40 gpm for production wells. Approximately one percent of
the fluid drawn from the well field is removed as a bleed to generate a cone of depression Within the
“production zone.” Pumping rates can be varied at each well individually in order to compensate for
differences in permeability of the deposit ‘and the gradient being generated by the production
0_on.
Uranium recovery rates at in sine operations are highest within the first ye ar of operation;
economically viable recovery within a wellfield usually lasts one to three years under recent (1990s)
market conditioni.
Restoration of S aquifer can be conducted using one (or more) of the following techniques:
groundwater sweep, forward recirculation, reverse recirculation, and directional groundwater
sweeping. in some cases a reducing agein nay be injected prior to any restoration to reverse the
oxidizing environment created by the mining process. A reducing agent may also be injected during
later stages of restoration if difficulties arise in stabilizing the, aquifer (Lucht, 1990).
A groundwater sweep involves the selective operation of production wells to induce the flow of
uncontaminated groundwater into the mined zone while the withdrawn water continues to be treated
through the ion exchange circuit. Contaminated water withdrawn from the aquifer can be disposed ct
in lined evaporation ponds or treated and discharged. Groundwater sweeps are most effective in
aquifers with “leaky” confining layers, since uncontaminated groundwater can be induced to flow irLc
the mined areas. Typically, two or more pore volumes are required to improve water quality
parameters. The disadvantage to groundwater sweeping is its consumptive use of groundwater
(Osiensky and Williams, 1990).
Forward recirculation involves the withdrawal and reinjection of groundwater through the same
injection and production wells that were Used during the mining operation. Groundwater withdrawn
from the mined aquifer is treated using ion exchange or reverse osmosis with the clean water being
reinjected and recirculated through the system. The water being reinjected is treated to the extent that
it meets ox exceeds the water quality required at the endpoint of restoration. The method does not
allow the removal of any lixiviant or mobilized ions that may have escaped from the mined aquifer.
For this reason, forward recirculation is most effective in restoring the portions of the aquifer
associated with the interior of the well field (Osiensky and Williams, 1990).
Reverse circulation techniques can also be employed in which the function of production and recovery
wells is reversed. Again, “clean” water is injected, this time through the recovery wells, while the
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injection wells are employed to withdraw groundwater from the aquifer. This method is also more
effective in restoring the aquifer in the interior of the well field than along the perimeter (Osiensky
and Williams, 1990).
Directional groundwater sweeping techniques involve the pumping of contaminated groundwater from
specific wells while treated water (at or surpassing baseline quality) is injected into the aquifer beyond
the mined sections of the aquifer. The clean water is then drawn into the contaminated portions of
the aquifer, removing the residual mobilized ions. Clean water injection can progress across a
weilfield as the contaminants are progressively withdrawn (Osiensky and Williams, 1990).
Uranium can be recovered during the early stages of the restoration process as the water from the
production wells passes through the ion exchange system. Eventually, uranium recovery is abandoned
while restoration continues. A rinse of multiple aquifer pore volumes is typically required to reach a
satisfactory level of restoration. The, number of pore volumes required depends on the ease with
which the aquifer returns to baseline conditions and the permit requirements established in State
permits (Osiensky and Williams, 1990; Bureau of Mines, 1979).
Demonstration of successful aquifer restoration is accomplished through extended monitoring. The
State of Wyoming, for example, requires that selected wells be monitored for stability for a period of
at least six months following the return of monitoring parameters to baseline levels (WDEQ, 1990).
3.3.6.4 Wastes and Waste M nageinènt
Wastes generated by uranium mines and mills would include those generated in other mining sectors
(e.g., waste rock, spent extraction/leaching solutions, tailings, and refuse). Mining method
(conventional versus solution) has a bearing on the types of wastes produced. Under the Uranium
Mill Tailings Remediation Control Act (UMTRCA), source handling licenses issued by the Nuclear
Regulatory Commission (NRC) place specific requirements on the disposal of radioactive wastes; the
design and construction of tailings impoundments thus have to address requirements for permanent
storage of these wastes. Radionuclide-containing wastes generated by in situ operations are typically
shipped to tailings impoundments at mill sites.
The greatest volume of waste generated by open pit and underground mines is waste rock, which is
typically disposed of in waste rock piles. Some waste rock may be used for onsite construction
(roads, foundations, etc.). The generation of acid mine drainage is one of the principal concerns
surrounding waste rock in other mineral sectors. The potential for generation of acid drainage irom
uranium waste rock has not been addressed in available reference materials. However, pyrite is
typically a constituent of uranium-containing ores, and may present the potential to create acid mine
drainage. Other materials generated by open pit and underground mining operations, including low-
grade ore and mine water, are typically managed on-site during the active life of the facility. Low-
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grade ores that are not beneficiated ultimately become waste rock. If a mill is co-located with a
mine, mine water can be used as makeup water in the beneficiation operation. If a mill is not nearby,
mine water may be treated and discharged as mine drainage or used far dust suppression.
The principal waste generated by conventional beneficiation operations is tailings. In situ operations,
and to a lesser extent conventional nulls, generate waste leaching solutions. Disposal of these wastes
is dependent on the type of operation; beneficiation wastes generated by in situ operations are
disposed of by one of four management methods: evaporation ponds, land application, deep well
disposal, or shipment to NRC-licensed waste. disposal facilities. Most beneficiation wastes generated
at conventional mills are disposed of in tailings impoundments.
Waste constituents of concern include: radionuclides (radium, radon, thorium, and to a lesser extent
lead), arsenic, copper, selenium, vanadium, molybdenum, other heavy metals, and dissolved solids.
Brines, spent ion exchange resins, and chemicals used in beneficiation operations are also constituents
of wastes generated during beneficiation. Airborne particulates from blasting, loading, and vehicular
traffic can also be of concern.
3.3.7 OTHER METALS
3.3.7•1 Ajuminum
Bauxite (a mixture of primarily three aluminum hydroxide minerals, diaspore, gibbsite and boehmite,
and impurities) is the ore of aluminum (Hurlbut and Klein, 1977). Deposits of bauxite in the United
States are located in Arkansas, Georgia and Alabama In 1992, bauxite was being mined from
surface excavations in Georgia and Alabama (Bureau of Mines, 1993). Virtually all of this domestic
bauxite ore is consumed in the production of nonmetallurgical products (primarily refractory grogs)
and not in producing aluminum (Bureau of Mines, 1993). Imported metallurgical-grade bauxite is
used in the production of aluminum in the United States.
Alumina production is shifting to the laEge-scale bauxite producing countries in response to increasing
energy costs in North America and Europe (Bureau of Mines, 1993). If this results in increased costs
for alumina for U.S. plants, nonbauxitic aluminum resources in the United States may become
economically more attractive. Current conditions indicate that the United States will continue to be a
major importer of metallurgical-grade bauxite and alumina, precluding the need for extensive
expansions of U.S. bauxite mines (Bureau of Mines, 1993).
The two active bauxite mines use the general surface mining operations discussed in Section 3.1.
Draglines, shovels and haulers remove ore from open pits and transport it to a storage area. Ore may
be loaded directly from storage to the processing plant, or it may undergo beneficiation at the mine.
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Beneficiation commonly requires crushing, washing and drying. Crushing is common to all bauxite
processing; however, the steps following crushing depend on the makeup of the ore. After crushing,
the ore may be washed to remove sand and clay sized impurities. Impurities such as iron, and
titanium may be removed using heavy media or magnetic separation, jigging, or spiral concentrators.
The washed ore is generally shipped without further processing; however, it may be dried or calcined
at the mine. Most bauxite ores are not dried at the mine site, because drying may create serious dust
problems during transportation and handling (EPA, 1979).
The wastes produced from the beneficiation of bauxite ores is the wastewater used in the washing
process. Generally this water is discharged to the pits and not to surface waters. Chromium, copper,
mercury, nickel and zinc have all been found in low concentrations in drainage from bauxite mines
(EPA, 1982). In addition, the drainage can be of low pH (EPA, 1982).
3.3.7.2 Tungsten
The principal ore minerals for tungsten are wulframite ((Fe, Mn) W0 4 ) and scheelite (CaWO 4 ).
Tungsten’s physical properties, a high melting point (3,410°C), high density, good corrosion
resistance and good thermal and electrical conductivity, make it an important material for use in
domestic and military industries. As of 1992, the only two U.S. mines producing tungsten
concentrate were in California. Tungsten ores have generally been mined using conventional
underground mining methods.
Tungsten ores are often beneficiated using gravity concentration or flotation methods. The specific
gravity of tungsten minerals is high and therefore gravity concentration methods primarily are used.
However, scheelite (the principal U.S. ore) is very friable and in the process of wet-grinding a
considerable amount of slimes are produced and this reduces recovery by gravity techniques. To
increase overall recovery, fmely divided scheelite particles in the shines are concentrated by flotation
techniques using fatty acids ascollectors. Several hydrometallurgical procedures are used for
upgrading tungsten concentrates. Scheehite concentrates from flotation tend to be lower grade than
gravity concentrates. Calcite and apatite are the principal contaminants in these low-grade
concentrates (scheelite concentrates seldom contain sulfides in large amounts). These impurities may
be leached out with acid, and the concentrates upgraded in the process. A first-stage leach with
hydrochloric acid (HC1) removes the calcite as calcium chloride (CaCI 2 ) solution, which is discarded,
while a second-stage leach is used to dissolve the apatite, which is not dissolved in the presence of
calcium chloride.
One of the many variations of tungsten ore beneficiation procedures is the hydrometallurgical
treatment of low-grade scheelite group concentrates to produce calcium tungstate. A water slurry of
scheelite concentrates from flotation machines is digested in a pressurized digester vessel with sodium
carbonate and steam to produce tungstate and molybdate in solution. To remove the molybdenum,
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the solution is filtered and heated to 91 °C (195 °F), and sodium sulfide is added to precipitate
molybdenum. The solution is adjusted to pH 3.0 with H 2 S0 4 to complete this separation. The hot
purified solution is neutralized with sodium hydroxide to a pH 9.2, then treated with calcium chloride
to precipitate calcium tungstate. Alternatively, the filtered solution after molybdenum separation may
be solvent-extracted by a proprietary process to produce ammonium paratungstate, which is
crystallized out of solution and dried (EPA, 1976).
The discharge from tungsten milling operations has been found to contain high concentrations of
copper, lead, and zinc (EPA, 1982).
3.3.7.3 Molybdenum
Molybdenum is an important metal for use as an alloying agent in steel, iron and superalloys (Bureau
of Mines, 1993). Molybdenite is the major ore mineral mined for molybdenum. In the United
States, the economically important deposits of molybdenite are generally low-grade porphyry or
disseminated deposits, but contact-metamorphic zones, quartz veins, pegmatites and aplite dikes, and
bedded deposits in sedimentary rocks have also been exploited for molybdenite. Most porphyry
copper deposits contain low concentrations of molybdenite (0.02 percent to 0.08 percent). Primary
molybdenite deposits typically grade 0.2 percent to 0.5 percent molybdenite. In 1992, 45,500 metric
tons of molybdenum was mined in the United States, two-thirds for export. Three mines (in
Colorado and Idaho) mined molybdenum ore and 11 (in Arizona, California, Montana, New Mexico,
and Utah) recovered molybdenum as a byproduct. Thà United States was the major producer of
molybdenum in 1992, and will continue as a top five world producer throughout the rest of the
century (Bureau of Mines, 1993).
Molybdenum ore is mined by both open pit and underground operations in the United States. In
1992, approximately 40 percent of U.S. production was from underground mines and 60 percent fr
open pits. Underground mines typically use caving methods, since these methods allow for the
economic removal of large tonnages of low grade ores at a low cost. Conventional open pit mining
methods are used. In underground mines, very little waste rock is removed. Significant tonnages of
waste rock can be removed in the development and mining of an open pit.
After the molybdenum ore is mined, it is transported to a mill for beneficiation. The ore is generally
crushed and ground at the mill before traditional flotation methods are used to concentrate the ore
minerals. A final concentrate of 90 percent to 95 percent molybdenite is produced by the
beneficiation operation. The major impurities in the concentrate are copper, iron and lead minerals.
Molybdenite recovery from copper ore is more complex due to the low percentage present in the ore.
As in the flotation of other ores, the major wastes produced are tailings, and these are generally
disposed of in tailings impoundments.
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3.3.7.4 Vanadium
Vanadium is generally not mined as the primary metal of an ore, but as a co-product, as in carnotite
ores (recovered for uranium and vanadium) mined in the western United States. Currently, one mine
in the United States recovers vanadium as the primary constituent of the ore. The primary use of
vanadium is as an iron and steel alloying agent. Mining of the uranium and vanadium ores in the
western United States has employed open pit and underground mining methods. The vanadium mine
in Arkansas uses open pit methods to extract the vanadium ore.
Mined vanadium ore is crushed, dried, ground, and screened to sizes less than 1.17 mm (-14 mesh).
It is then mixed with about 7 percent weight of salt, pelletized, and roasted at 850 °C (1,560 °F) to
convert the vanadium to soluble sodium vanadate, NaVO 3 . It is then quenched in water and acidified
with sulfuric acid to pH 2.5-3.5. The resulting sodium decavanadate (Na 6 V 10 O ) removes impurities
such as sodium, calcium, iron, phosphorous, and silica. Slightly soluble ammonium vanadate,
NH 4 VO 3 , is precipitated from the stripping solution with ammonia. The ammonium vanadate is then
calcined to yield vanadium pentoxide, V 2 0 5 (EPA, 1976).
3.3.7.5 Titanium
Aircraft and space applications account for 75 percent of titanium metal consumption, with the
remainder used in chemical processing, power generation, and other applications. The principal ore
minerals for titanium are ilmenite (FeTiO 3 ), and rutile (Ti0 2 ). These minerals are found concentrated
in hard-rock and sand deposits. In 1993, only sand deposits of ilmenite were being mined in the U.S
(Bureau of Mines, 1993).
The method of mining titanium minerals depends upon whether the ore to be mined is a sand or rock
deposit. Sand deposits occurring in florida, Georgia, and New Jersey contain 1 to 5 percent Ti0 2 in
the form of grains of ilmenite, ilmemte/magnetite, rutile, and leucoxene, and are mined with floating
suction or bucket-line dredges handling up to 1,100 metric tons (1,200 short tons) of material per
hour. No hard rock deposits are currently active.
The sand ore is treated by wet gravity methods using spirals, cones, sluices, or jigs to produce a
bulk, mixed, heavy-mineral concentrate. As many as five individual marketable minerals are then
separated from the bulk concentrate by a combination of dry separation techniques using high-tension
electrostatic and magnetic separators, occasionally in conjunction with dry and wet gravity
concentrating equipment. The high-tension electrostatic separators are employed to separate the
titanium minerals from the silicate minerals. The minerals are fed onto a high-speed spinning rotor,
and a heavy corona (glow given off by high voltage charge) discharge is aimed toward the minerals at
the point where they would normally leave, the rotor. The minerals of relatively poor electrical
conductance are pinned to the rotor by the high surface charge they receive on passing through the
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high-voltage corona. The minerals of relatively high conductivity do not hold this surface charge as
readily and so leave the rotor in their normal trajectory. Titanium minerals are the only ones present
of relatively high electrical conductivity and are, therefore, thrown off the rotor. The silicates are
pinned to the rotor and are removed by a fixed brush.
Titanium minerals undergo final separation in induced-roll magnetic separators to produce three
products: ilménite, leucoxine, and rutile. Separation of these minerals is based on their relative
magnetic properties which, in turn, are based on their relative iron content: ilmenite has 37 percent to
65 percent iron, leucoxine has 30 percent to 40 percent iron, and rutile has 4 percent to 10 percent
iron.
3.3.7.6 Platinum
Platinum is one of the six closely related platinum-group metals (platinum, palladium, rhodium,
ruthenium, iridium, and osmium). Platinum and palladium are the most commercially important
metals of the group; in 1992, an estimated 1,730 kilograms of platinum and 6,050 kilograms of
palladium were mined. The United States automobile industry is a major consumer of platinum for
use in catalytic converters. Platinum group metals also are used in electrical and electronic (29
percent), medical (9 percent), and other applications (24 percent). Demand for platinum is expected
to remain high as the use of catalytic converters increases around the world to control automobile
emissions (Bureau of Mines, 1993).
In the past, platinum mining in the Umted States was mostly from placer deposits. The only
currently active platinum mine in the United States is the Stillwater Mine in Montana; platinum-group
metals also were recovered as byproducts of copper refining in Texas and Utah. Platinum and
palladium (at a ratio of 1:3) occur in an igneous, str taform ultramafic rock at the Stiliwater mine
(Stillwater Mining Company, undated). The deposit is exploited through underground cut and fill
mining methods. The ore is transported to the mill for crushing and grinding prior to entering the
concentrate circuit. After grinding, the ore is added to the froth flotation units along with reagents..
The recovered concentrate is dried before transport to a refining facility for the recovery of the
palladium and platinum. The mine received an amended permit in 1992 to double the mine’s daily
production from 1,000 tons to 2,000 tons.
The tailings slurry at the Stillwater Mine is separated into coarse and fine fractions prior to disposal
(Stiliwater Mining Company, undated). The coarse fraction is pumped underground to be used as
sand-fill in the underground mine. The fine fraction is pumped to a lined tailings impoundment. The
facility recycles water from the tailings impoundment back into the mill. Very little waste rock is
removed during mining. Most of the waste rock is used to raise the dam of the tailings impoundment
when additional capacity for the tailings impoundment is required (Stillwater Mining Company,
undated).
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3.4 COAL MINING
This section focuses on surface and underground coal mining operations and environmental impacts
unque to the coal mining industry. Specifically, the subsections below addresses types of coal,
geographic location of coal,, and mining and reclamation methods as the primary ‘determinants of
environmental impact. This approach was taken to isolate those areas of concern that are unique to
coal mining activities and to establish a workable methodology to assess the magnitude and
significance of potential impacts.
There are both similarities and.differences between coal and other types of mining operations. Any
type of surface mining requires the rernoval3 of overlying soil and rock (collectively known as
overburden) prior to the removal of the resource. Coal ‘and non-coal operations use many of the same
techniques in the development and often in the production phase of mining. All mining activities
must control surface water runoff, minimize fugitive dust, and avoid impacts to the surrounding
environment.
In addition to other environmental ‘regulations, coal mining operations must also comply with the
Surface Mining Control and Reclamation Act of 1976 (SMCRA). SMCRA greatly expanded the
regulatory requirements placed on the operation and reclamation of coal mines (see Chapter 6). One
of the most significant aspects of this program is that of reclamation; areas disturbed by coal mining
activities must be returned to approximate Original contour and reclamation must be conducted
concurrently with mining.
3.4.1 CoAL FORMATION AND GEOGRAPHICAL DISFRIBm1ON
3.4.1.1 Types and Composition of Coal
Coal was formed through the accumulation and compaction of marine and freshwater plants and
animals living in ancient marshes. The accumulated organic material was buried by sediments and
altered from complex organic. compounds to carbon.
Coal is classified based on the percentages of fixed carbon, natural moisture, and volatile matter
present. Lignite, subbituminous coal, bituminous coal, and anthracite comprise the major classes of
coal. The percentage of fixed carbon increases, the percentage of volatile matter decreases, and the
heating value increases from lignite to anthracite (see Exhibit 343). Based solely on heating value,
the market value of coal can be expected to increase from lignite t O anthracite. Because sulfur,
content and, other end-use specifications and requirements can’ significantly influence the demand for
coal, the heating value is only one of several criteria that determine the actual market value of coal
deposits.
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Exhibit 3-13. Types of Coal and Relative Percentages of’ Constituents
Type :
. Fixed Carbon’
(Percent),..
. . .
BTUs/Pound
Volatiles
(Percent)
Moisture
(Percent)
Anthracite
> 86
12,000 - 15,000
< 14
3
Bituminous
47-86
11,000-15,000
14
3-12
Subbitumi.nous
42
9,700 .
34
23
Lignite ‘.
30
6,600
25
45
Sulfur is the most abundant trace element in coal, and reduces the value of those coals in which it is
found. Sulfur occurs both as an inorganic constituent, mineral (mostly in the form of pyrite) in coal
itself and as part of organic complexes associated with the deposit. When the coal is burned, sulfur
contributes to air pollution and reduces coking quality. When exposed to oxygen and water, the
inorganic forms produce acid mine drainage.
The sulfur content of coals found in the United States ranges from 0.2 percent to about 7.0 percent by
weight. The percentage of sulfur in coal generally is greatest in the bituminous coals of the Interior
and Eastern coal fields. The sulfur content of coal generally is less than 1 percent in the Northern
Great Plains and Rocky Mountain Provinces for subbituminous coal and lignite. More than 90,000
million tons (64 percent) of the total surface-minable reserves in the United States are low-sulfur and
occur in the west.
Coal contains traces of virtually all elements. Burning coal results in the concentration of most of
these elements in the ash, although a few may be volatilized and emitted to the atmosphere. Arsenic,
barium, beryllium, bismuth, boron, cobalt, copper, fluorine, gallium, germanium, lanthanum, lead,
lithium, mercury, molybdenum, nickel, scandium, selenium, silver, strontium, tin, vanadium,
uranium, yttrium, zinc, and zirconium occur in some coals in concentrations that are greater than
their average abundance in the crust of the earth.
3.4.1.2 Coal Provinces
Six coal provinces (Exhibits 3-14 and 3-15) are defined in the United States: the Pacific Coast,
Rocky Mountain, Northern Great Plains, Interior, Gulf Coast, and Eastern.
Coal deposits in the Pacific Coast province are found in scattered fields in California and Oregon, and
in one large field and scattered small fields in Washington. California coals are mostly of Eocene to
Miocene age, and range in rank from lignite to high volatile bituminous. Oregon coals range from
subbiruminous to bituminous. Washington coals range from subbituminous to anthracite, but most are
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a
0
a
0
E.
Source: University of Oklahoma. 1975. Energy alternatives; a comparative analysis.
Science and Public Policy Program, Norman OK, OY1—Oll-00025—Y, variously paged.
Wa
— - . _______
-------
E.
j
Exhibit 3-15. Summary of Environmental Considerations by Province
Coal Province
Mining Method
Regional Characteristics
Environmental Considerations
Eastern
•
.
Mountaintop removal; contour;
room and pillar; longwall
Climate humid.
.
.
High sulfur concentrations in coal and
surrounding material; abundant surlace.
and groundwater resources; numerous
small mines; subsidence
Interior
Strip; longwall (limited)
Climate humid to subhumid
.
Prime farmland; pàtential large-scale
disturbances; surface and groundwater;
subsidence (limited)
Gulf
Strip
.
Climate humid. Precipitation recharges
aquifers directly through soils. Water
quality good to excellent.
Groundwater; land use
.
Northern Great Plains
.
Strip (limited underground)
Water quality ranges from poor (saline)
to good.
.
Groundwater; large tracts of surface
disturbance from adjacent mining; land:
use (alluvial valley floors, prime
farmland, wildlife habitat)
Rocky Mountain
.
Strip; longwall (limited); room
and pillar (limited)
.
--
Climate arid (low elevations) to
subhumid (high elevations),
Groundwater occurs in alluvium and in
fractured sandstone, shale, and coal.
Discharges to springs, baseflow of
streams, and through deep-rooted
plants. Quality variable throughout the
region from poor (saline) to good.
Groundwater; land use (wildlife
habitat)
•
‘
.
Pacific Coast
.
T
.
Surface
-
Climate humid. Groundwater in
alluvium, recharged by precipitation
and snowmelt; discharges to springs
and streams. Water quality is aquifers
surrounding coal typically adequate for
domestic purposes.
Steep slopes; abundant surface and
groundwater resources
.
0
0
I;
0
1
i.
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Overview of Mining and Beneficiation EIA Guidelines for Mining
subbituminous to bituminous; some also are of coking quality. Coals in Alaska range from lignite to
high volatile bituminous grades. Coals are found in large fields along the Arctic Coastal Plain, and in
smaller fields located both inland and along or near southern shorelines.
The Rocky Mountain Coal Province is bordered on the east by the Great Plains, and on the west by a
series of high plateaus, including most of New Mexico, Colorado, Utah, Arizona, and parts of
Montana and Idaho. Scattered small fields are found in central arid southern New Mexico.
High volatility bituminous coal is found in rocks of Upper Cretaceous age in the western Montana
area. Coal beds are thin, impure, and usually greatly disturbed by folding and faulting. The Big
Horn Basin coals of Wyoming and coal found in extreme southwest Wyoming range in age from late
Cretaceous and Paleocene and is classified from lignite through high volatile subbituminous. These
deposits occur in lenticular beds which rarely persist at a minable thickness for more than 5 miles at
outcrop. Dips of locally folded strata can reach 500, resulting in an irregular distribution of coal
outcrops. The Paleqcene age coals of the Hams Fork region range in rank from subbituminous to
high volatile bituminous. Beds of higher grade coals may be as thick as 20 feet; thicknesses of lower
grade coal range to 100 feet. These coal beds are situated in a highly complex zone of thrust faults
and folded rocks, resulting in steeply dipping strata and thereby making mining difficult in most parts
of the region.
In central Wyoming (the Wind River Basin) coal beds are Late Cretaceous to Paleocene in age, and
are mostly subbituniinous. Although coal beds may approach thicknesses to 17 feet, surface mining is
made difficult by the steep dips of the strata. In southwestern Wyoming, coals range in rank from
subbituminous to high volatile bituminous, and higher rank coals locally may occur in areas of
igneous intrusion and intense structural deformation.
Coals of the North Park area of the Colorado Mountains are.subbituminous and occur in several
major beds up to 77 feet thick. Coals found in the Green River Region within the Colorado Plateau
of Arizona, New Mexico, Colorado, and Utah, are generally found in horizontal strata of sedimentary
origin. Erosion of these strata has resulted in formation of canyons, mesas, and buttes. The
landscape comprises wide plateaus, uplifts, and broad basin areas. The Late Cretaceous age coal beds
of the Uinta Coal Region range in rank from subbituminous to coking quality high volatile
bituminous; some semianthracite and anthracite deposits occur in the Crested Butte Field of the Uinta
Region. Coal bed thicknesses generally range from 5 feet to 15 feet, but locally may approach 40
feet. The LateCretaceous age coals of the Southwestern Utah Coal Region range in rank from
subbituminous to high volatile bituminous, with local occurrences of anthracite. These coals are
found in flat-lying to gently dipping beds from 2 feet to 30 feet thick. The Late Cretaceous and
Eocene age coals of the San Juan River Coal Region occur as lenticular, discontinuous deposits up to
5 feet thick in areas of complex geologic structure. Thicker, more continuous coal beds up to 38 feet
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thick with numerous shaly partings are found in structurally less complex parts of this region. San
Juan River region coals are generally subbituniinous, but high volatile bituminous coals also are
found.
The Northern Great Plains coal province the includes coal regions that occur in the Great Plains east
of and adjacent to the Rocky Mountains. The area is characterized by little surface relief, gently
rolling plains, some areas of badlands and dissected plateaus, and isolated mountains. Rocks of this
province occur in nearly horizontil sedimentary strata which curl up sharply along the flanks of the
Rocky Mountains. Coal found in central Montana is of Late Jurassic age and is high volatile
bituminous àontaining 1.7 to 4.0 percent sulfur. Coals from north-central Montana are of Late
Cretaceous age and range from subbituminous to high volatile bituminous. These coal beds generally
are discontinuous and too thin to be of commercial importance, other than as sources of local fuel.
Coal deposits found in extreme northeastern Montana and western North Dakota contains an estimated
438 billion tons of lignite, the largest single coal resource in the United States. Coals are Late
Cretaceous to Paleocene in age, and increase westward from lignite in North Dakota to subbituminous
in Montana. Coals found in southern Montana and northeastern Wyoming are Upper Cretaceous to
Eocene in age, and range from subbituminous to high volatile bituminous. An 8,000 square mile area
of gently rolling plains in northeast central Colorado are underlain by Late Cretaceous and Paleocene
age coal bearing rocks. Coals generally are subbiturninous and occur in lenticular, discontinuous beds
up to 17 feet thick. Extensive deposits of lignite also are found in this region. The coal found in
southern Colorado is of Late Cretaceous and Paleocene age and range from coking high volatile
bituminous to non-coking high volatile bituminous.
The Interior coal province is. an extensive area of low relief underlain by flat-lying Paleozoic age
sandstones, limestones, conglomerates, and shales which lie between the Appalachian Plateaus and the
Rocky Mountains. Coal beds of this province are of Pennsylvanian age, and generally comprise high
volatile bituminous grades which improve in quality in the western part of the coal region. In
Oklahoma and Arkansas, some coal deposits have been devolatilized to coking low volatile bituminous
and sernianthracite ranks.
The Gulf Coast coal province comprises extensive lowlands and coastal areas. The subsurface
generally is composed of unconsolidated beds in detrital sediments and limestones which dip gently
seaward. Outcrops of rock become successively older inland. The province has a good supply of
surface water and groundwater, .and droughts are uncommon except in southwest Texas. Coal
deposits consist of Upper Cretaceous age bituminous beds near the Mexican border, and extensive
deposits of lignite which extend from southern Texas to Alabama.
The Eastern coal province extends 800 miles from northern Pennsylvania to northern Alabama and
essentially is mountainous for its entire length. Coals of this province were deposited in the
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Pennsylvanian age Appalachian Basin, which consists of a series of sandstones, shales, limesrones,
conglomerates, and coals. Structural features such as faults and fold axes trend northeast-southwest,
parallel to the basin margins. The eastern part of the basin is extensively folded and faulted, and
contains the higher grade coals of the region. These coals range in rank from medium volatile
bituminous coals of the major eastern Appalachian coal fields to the high quality anthracite of
northeastern Pennsylvania. The western part of the Appalachian basin is marked by strata in broad,
open folds which dip gently westward. Coals of the western part of the basin generally are of the
high volatile bituminous grade. The ranks of coals in the Eastern Coal Province generally decrease
from east to west in bands which trend northeast-southwest, parallel to major structural features.
3.4.1.3 Trends
Trends in the coal industry are primarily driven by a change in the accessibility of eastern and
western deposits and trends in the use of coal as a fuel, particularly in light of the Clean Air Act.
These trends are manifest in the continued development of large, Western surface mines as major
suppliers of coal, while underground techniques are being more widely applied in the eastand
midwest. The demand for the low sulfur coals that are common throughout the west and the
desulfurization of high sulfur coals for use as boiler fuels is produced by increasingly stringent
limitations on stack emissions on sulfur dioxide and particulates.
The coal industry will likely continue to grow at moderate levels within the foreseeable future.
Whether the trend n increasing production from western operators continues may be based on the
demand for clean burning coals. Western coals typically have lower sulfur concentrations and hence
burn cleaner than eastern coals. However, the lignite and subbituminous coals of the west contain
fewer BTIJs and carry increased transportation costs (either for the coal or for electrical power).
Production trends in the surface coal mining industry include (1) shifts of mining activity to coal
regions which contain large reserves of economically recoverable and usable coal and (2) shifts of
mining activity within regions to situations which previously were avoided because adverse
topography, overburden thickness, or other factors precluded an economic return on investment in
mining operations.
Several factors in addition to the low sulfur content have contributed to the dramatic expansion of the
western surface coal mining industry ince 1977. Large tracts of relatively flat land underlain by
thick, horizontal seams are amenable to high production surface mining operations. The pit, spoil
piles, haul roads, and ancillary facilities can be designed to minimize the cycle times of unit mining
operations, thus maximizing productivity per shift.
Operators of eastern surface mines use such methods as mountaintop removal combined with head-of-
hollow fill to offset the disadvantages of surface mining in steeply sloping terrain. Although the
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EM Guidelines for Mining Overview of Mining and Beneficiation
extent and magnitude of their environmental impacts have been controversial, mountaintop removal
and head-of-hollow fill will continue. The east has also demonstrated an increase in the number of
underground mining operations to address the limitations established by topography and economics.
3.4.2 SURFACE MINING SYSTEMS
Surface mining systems are sequences of unit operations which have been designed to accommodate
the limitations, on mining imposed by geology, topography, and regulatory requirements. Three kinds
of surface mining systems are employed in the removal of overburden and coal extraction. Area
mining and contour mining are by far the most commonly used methods, the third surface mining
technique, open pit mining, is used to a limited extent in southwestern Wyoming.
3.4.2.1 Area Mining
• Two forms of area mining are conducted, conventional or strip mining, and mountaintop removal.
Strip mining is employed throughout the United States, primarily in the large mid-western and
western coal fields and to a more limited extent in the Eastern coal province. This type of mining is
applied in regions with flat to rolling terrain where the coal seams lie horizontal or nearly horizontal
to the surface. Overburden in these areas is relatively shallow and regrading to approximate original
contour is possible. Mountaintop removal is used in rugged terrain of the Appalachian Mountains,
where regrading to approximate original contour may. not be feasible or desirable. Both methods
essentially result in total recovery of the mined resource.
A typical strip mining operation proceeds in the following manner (see Exhibit 3-16). A trench (box-
cut) is excavated through the overburden to the coal seam. This trench usually is extended linearly to
the perimeter of the permitted area, to the edge of the coal deposit, or to a location that
accommodates future development of the mine. The minàd overburden (spoil) from the box cut is
stockpiled parallel to the trench on unmined ground, and coal is recovered from the exposed seam.
Successive cuts are made parallel to the initial trench, and spoil from each succeeding cut is placed in
the trench of the previous cut. Spoil from the initial cut is typically placed in the trench of the final
cut. The disturbed area is progressively regraded t. the approximate original contour and reclaimed
as mining progresses. As required by SMCRA, approximate original contour requires the elimination
of all highwalls and other mining-related escarpments and depressions not needed to facilitate
revegetation and reclamation of the disturbed area.
The mountaintop removal method (Exhibit 3-17) does not return the mined area to the approximate
âriginal contour as an entire mountaintop is typically mined through. This type of operation often
makes use of a head of hollow fill to handle the box cut spoil and any excess overburden. To initiate
a mountaintop removal operation, a box-cut is made through the overburden along a line more or less
parallel to the coal outcrop. This cut is made in a manner such that at least a 15-foot-wide barrier of
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
Exhibit 3 16. Area Mining With Stripping Shovel
3-110
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i
0
E.
I
0
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Overview of M in ing and Beneficiation E IA Guidelines for Mining
coal seam at the outcrop remains undisturbed. This “bloom” or “blossom” of undisturbed coal acts
as a buttress to help stabilize spoil slopes during mining operations and subsequent reclamation. Spoil
from the initial cut is transported to the head of hollow fill or other approved stockpile area.
Successive cuts are made parallel to the initial cut, and spoil from each successive cut is stockpiled in
the trench of the previous cut. Final stabilization and revegetation of the mined area can result in flat
to gently rolling terrain suitable for various uses.
3.4.2.2 Contour Mining
Contour mining methods generally are employed in the mountainous terrain of the Eastern coal
province. Currently, contour mining makes use of one of three methods of operating: box-cut,
block-cut, or haul-back.
Box-cut operations resemble area mines (Exhibit 3-18) but make use of a smaller number of cuts,
usually two or three , The initial cut aligned parallel with the coal outcrop; mining progresses across
the hill within each cut and uphill in successive cuts. Prior to the initial cut, a bulldozer clears
vegetation from the box cut area and the area immediately downhill. As the initial cut is developed,
overburden is pushed downhill forming an outslope. After coal is removed from the box cut,
overburden from the next cut is placed in the mined out area. Operation of a dragline to place
overburden into the mined out cut requires the development of a bench on the uphill (highwall) side
of the operation. Operations making use of shovels and front end loaders can move overburden to the
mined out cut without the development of a bench. A barrier of undisturbed overburden at least 15
feet wide is typically left at the downhill foot of the coal outcrop.
A haul road and parallel drainage ditch are constructed along the coal outcrop and the exposed coal is
removed. Often the unrecovered coal seam at the base of the fmal highwall is mined with augers.
Following maximum recovery by the augers, the auger holes generally are sealed with clay or some
other nondeleterious, impervious material. The cut then is backtilled with previously stockpiled
overburden so that (1) the backfiRed slope is stable, (2) all highwalls are eliminated, and (3) toxic and
acid-forming wastes and unmined coal seams will not contaminate ground and surface waters with
deleterious siltation or leachate. Backfill is regraded to the approximate original contour, where
possible. The regraded site is then revegetated with appropriate species of plants and monitored for a
specified length of time to insure success of the revegetation effort. Haul roads are either abandoned
in an acceptable manner or are stabilized for use during and after reclamation (Gentry and McCarter,
1992; Grim and Hill, 1974).
The development of a block-cut contour mine (Exhibit 3-19) is similar to box-cut mining, with major
differences in spoil handling techniques and the sequence of mining sections. Whereas the box cut
method generally proceeds up and around a mountain in one direction, block cut mining progresses in
both directions along the coal outcrop. An initial block of overburden is excavated near the center of
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0
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I
0
I
I
Source: Adapted from Chronis, Nicholas P.(ed). 1978. Coal age operating handbook of coal
surface mining and reclamation. McGraw-Hill, Inc., New York NY 1 442 p.
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
Exhibit 3-19. Block-Cut Mining Operation
(Skellyand Loy, 1975)
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3-114
Undisturbed Area —
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8
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EIA Guidelines for Mining Overview of Mining and Beneficiation
the permit area, and spoil temporarily is placed downslope of the coal outcrop, or in a head of hollow
fill. The initial cut is two to three times larger than successive cuts. After the coal has been loaded
out, spoil from the second cut is placed in the trench of the first cut. Because the second cut is only
one-third to one-half the width of the first cut, spoil from the third cut also can be placed in the first
cut. The third cut is stripped as coal is loaded, out of the second cut. In some cases, each successive
cut is smaller than the previous cut, minimizing the amount of spoil to be hauled to final the cut.
Block-cut mining can.also be.applied in area mining (Ramani and Grim, 1978; Gentry and McCarter,
1992).
Haulback mining can be used on smaller coal outcrops requiring greater flexibility than box-cut or
block-cut methods. In this method, rectangular pits are developed along the contour of the seam.
The width of the rectangle (pit) is established by topographic or economic recovery constraints.
Overburden from the initial cut is stoclcpiled in a suitable location. As successive pits are developed,
spoil is “hauled back” to the previous pit by truck, scraper or conveyor. The spoil fro_m the initial
box cut is deposited in the final pit. Reclamation occurs progressively with the backfilling and
“regrading of each successive pit (Gentry and McCarter, 1992).
3.4.2.3 Open Pit Mining ,
The only open pit coal operation currently in production includes a combination of area mining and
contour mining techniques to recover coal from steeply dipping seams in the mountainous terrain of
the western Wyoming. This operation is classified under the “Special Bituminous Coal Mines”
category by OSM and is subject to special performance standards which closely parallel existing.
Wyoming law. Open pit techniques typically defer reclamation until the resource is mined out
completely or to economic limits. This deferred reclamation for open pit methods contrasts with
SMCRA’s contemporaneous reclamation requirements.
Equipment selection, spoil placement, and the depth to which coal will be mined are dependent on the
ratio of overburden thickness to coal seam thickness (overburden ratio) and the number of seams to be
mined. Mining usually is initiated in the oldest (lowest) coal seam in the permit area. A dragline or
stripping shovel can be used to cast overburden on both sides of the pit, forming spoil piles on the
previously mined highwall and adjacent to the outcrop of the next coal seam to be mined. ‘Coal is
loaded out with shovels or bucket loaders, and bulldozers reclaim the mined area to a configuration
approved by regulatory authorities. Combinations of scraper loaders and stripping shovels also can be
used for overburden removal.
Coal seams thicker than 70 feet with overburden ratios of 1:1 or less are mined by multiple bench
open pit methods. Emphasis in the development of this mining method is placed more on proper
sequencing of coal loading, hauling, and storage techniques than on overburden handling.
Overburqen is removed from the initial cut by scraper loaders or a combination of shovels and
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haulers, and is stockpiled adjacent to the pit. Subsequent overburden cuts are backfilled into the pit
as stripping shovels load coal into haulers for transport to conveyors or unit trains. Both of these
transpori systems can feed preparation facilities or generating plants.
3.4.2.4 Special Handling
If segregation or selective placement of overburden horizons is necessary to achieve rehabilitation of
the site to a particular post-mining land use, a combination of excavators, including scraper, loaders,
draglines, bucket wheel excavators, and truck/shovel operations can be employed. Pit geometry may
be engineered so that excavators can pass one another during bidirectional mining. It also may be
necessary to place two or more excavators on separate benches to achieve proper location of spoil.
3.4.2.5 Equipment
The operational details of surface mines primarily depend upon the excavating, loading, and hauling
equipment employed at the mine-site. Equipment selection generally is based on the depth and texture
of overburden to be removed, the number of coal seams to be mined, the thickness of partings
between multiple seams, the friability of the coal seams and the planned geometry of the pit.
Equipment used to remove overburden is based on the above criteria and includes the following,
which may be used alone or in combination: draglines, shovels, bucket wheel excavators, front end
loaders, scrapers, and bulldozers. Draglines and stripping shovels can be used if the overburden to
be regraded in the mined-out trench or pit can be homogenized during stripping without adversely
affecting the reclamation process. Shovels and front end loaders loading trucks can effectively handle
wastes that need selective placement in the backfill. (Usually, a limited amount of special handling
can be done using a dragline.) Scrapers are effective for removing shallow, unconsolidated
overburden and bulldozers may be employed to prepare for benches or pads for draglines.
Coal is transported from the mine site to cleaning plants, transfer points, and consumption points via
trucks and conveyors. Trucks used for coal hauling range in capacity from 25 to 150 short tons, and
may off-load in a rear-dump, bQttom-dump, or side-dump mode, depending on the design of the
receiving station. Trucks in the lower load ranges can be operated on-road and off-road, subject to
State and local restrictions. Mobile conveyor belts are used in some larger mines to decrease the
truck haulage cycle time. Permanent conveyors can be employed to transport coal from truck dump
points to cleaning plants, railheads, barge points, and consumption points.
3.4.3 UNDERGROUND MINING SYSTEMS
Underground mining systems range in complexity from conventional drill-and-shoot operations to
fully automated longwall systems. Summary discussions of mining systems (DOE, 1978; EPA, 1978,
1976d, and 1975) and comprehensive texts (Britton and Lineberry, 1992; Hittman Associates, Inc.,
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1976) describe in detail the technical aspects of the development, operation, and abandonment of
underground coal mines. This section presents an overview of underground coal production methods,
including a brief discussion of each production method, and a general discussion of the environmental
impacts typically associated with underground coal mining.
As stated previously, underground mines account for approximately 40 percent of domestic coal
production. The majority of this production comes from operations using room and pillar methods.
Longwall mining operations account for approximately 25 percent underground production. Shortwall
mining techniques are employed but only to a limited extent (McElfish and Beier, 1990).
The following presents descriptions of underground mining systems using the minimum level of detail
necessary to identify the -sources of potential environmental impact associated with underground coal
mining.
Like new operations in other mining sectors, opening a modern underground coal mine represents
planning, development, and intensive capital investment for several years preceding the profitable
production of coal from the mine. Underground mines are significantly more expensive to develop
and operate than surface mines. Therefore they usually are planned for long-term operation in coal
seams that are not recoverable economically by surface mining -methods alone. -
The considerations necessary to put an underground coal mine into production, including
- development, ventilation, roof stability, and moving the coal from the site of extraction to a loadout
or clàaning plant, are similar to those of other underground operations as discussed above in Section
3.1. The buildup of methane gas within the mine workings isan additional concern unique to
underground coal mining; additionally, in some circumstances, subsidence tends to be a greater
problem than in other underground mining operations. This discussion will focus on those aspects
where undergrOund coal mining techniques differ from those employed at non-coal operations.
3.4.3.1 Development
The development or construction of an entire underground coal mine may take decades, and
extraction may commence in some parts of the mine years before development begins in others.
While mine development is underway, the some coal may bee produced, however, the extent of
production may be minuscule compared to. the annual tonnages produced during full scale operation.
Plans for mine development and extraction may change radically after mining commences, based on
the availability of capital, innovative technology, and markets. However, after a operating plan has
been approved and a permit issued, these types of changes must be approved by OSM or the State
regulatory authority as amendments or revisions to the current permit.
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Mine development generally includes a standard set of operations beginning with the establishment of
access to the coal seam.. Conventional drill-and-blast techniques may be used to drive entryways for
initial access. Once the seam is accessed (or if the seam is acceisible by an outcrop), coal cutting
machinery is used further develop entryways arid crosseuts, producing a honeycomb of unexcavated
coal and voids. The configuration of entryway’s and crosscuts depends on the strength and thickness
of the coal seam and overburden, the! amount of subsidence permissible, arid the method used for
recovering the coal (Britton and Lineberry, 1992; Hittman Associates 1 Inc., 1976). Roof control
systems are installed within the entryway’s and crosscuts. The specific method used for roof control is
a function of the geàmetry of coal left in place during mine development. Bolts. props. trusses.
shields, and other artificial roof support systems are used to. prevent roof falls.
Ventilation, haulage, and electrical systems are installed as development progresses. One function of
the layout of pillars and barriers is to minimize the cost of providing adequate ventilation to all
working areas of the mine. A minimum number of entryways a id crosscuts also is necessary for
rapid and efficient transport of coal from work areas.
The pattern of crosscuts and entryways ap ropriate for an individual mine is determined on the basis
of lithology of the overburden, safety requirements, conservation practices, and workspace needs
underground. In the ideal situation, entryways andcrosscuts are advanced through the coal seam to
the limits of the property to be mined. Coal then is extracted front pillars arid longwalls in retreat
(that is, in the direction opposite to the development advance).
To support the roof properly, a generally symmetric system of pillars, barriers, abutments, and ribs
remains unexcavated until the extraction phase commences. The dimensions and georhetry o
unexcavated features generally reflect their intended life spans and purposes, as well as the strengths
and structural properties of the coal seam and overburden.
An underground mine may be reached through shaft, drift, or slope entryways. Shafts and slope
entryways are driven through overburden to reach the coal seam where it is not exposed at an
outcrop. The choice of vertical shaft versus slope entryway usually depends on the proposed size of
the entryway and the proposed haulage systeni, as well as the ventilation system and other service
considerations. A drift entryway is driven into a coal seam from its outcrop.
3.4.3.2 Extraction
Coal is extracted during production either with conventional drill and shoot techniques or by
continuous mining systems. Extraction systems for mine development and coal production are chosen
based on the operator’s experience, available capital, and the following coal seam variables:
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EIA Guidelines for Mining Overview of Mining and Beneficiation
• Seam height, which determines one economic basis for choosing a mining system.
• Conventional’ mining systems become less efficient as seam height or thickness increases.
Longwall mining systems are impeded by variations in seam height.
• Bottom quality, which ranges from excellent (dry, firm, and even) to poor (wet, soft, and
pitted or rutted), and affects machine operations by limiting traction and restricting
maneuverability.
• Roof quality, which limits the amount of coal that may be extracted from the without
artificial protection against collapse of the mine roof.
• Methane liberation, which in some seams occurs at a rate proportional to the rate at which
coal is cut or sheared from the working face. Methane accumulates and sometimes ignites
in u iderground workings when it is not removed by the ventilation system. Methane
accumulation is monitored at le,ast once every 20 minutes at the seam face, causing
disruptidn of therwise continuous work cycles.
• Hardness of seam, which primarily affects the choice of coal cutting equipment.
• Depth of seam, which determines the response of the overburden to excavation of the coal
seam.
• Water, which may infiltrate the underground workings through channels, fractures, fissures,
or other water transmitting voids in mine walls, roof, and bottom.
çonventioEial (drill and shoot) mining systems utilize five categories of unit operations (Hittman
Associates, Inc., 1976) which can proceed simultaneously at separate working faces. The categories
include:
• Cutting a slit or kerf along the bottom of the working face across its full length
• Drilling a pattern of blast holes into the working face
• Blasting the coal with chemical agents or charges of compressed gas
• Loading and hauling the fractured coal from the face to a centralized crushing and loadout
facility for shipment to the cleaning plant
• Roof bolting with rods, trusses, props, and bolts to ensure the safety of underground
personnel and to minimize the deterioration of roof conditions before a mining section’ is
abandoned.
A typical sequence for mine development and extraction with conventional techniques is shown in
Exhibit 3-20. The flow of work depicted in the figure is from right to left. Each numbered panel
represents an approximate 3 m (10 ft) thickness of coal to be extracted.
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E!A Guidelines for Mining
Exhibit 3-20. Operations in Conventional Room and Pillar Mining
0
LI,__ _ _ _
________ k 7° •i ________ ________ ________ ________
3 LL
Equipment Deployment
L Loading machine
S Shuttle car
0 Mobd coal drill
C Cutting machine
B Bolting machine
6
7
3-120.
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EIA Guidelines for Mining Overview of Mining and Beneficiation
The cycle of unit operations in Exhibit 3-20 starts with coal loading and ends with roof bolting. After
the coal is loaded from Panel 1, the bolting crew moves up to the face of Panel 8 to secure the roof
over Panel 1. A coal cutting machine then is moved or trammed to Panel 8. A cut 3 m (10 ft) deep
is made in the coal seam with the machine-mounted blade, which is extended into the seam from the
stationary machine. The cutting blade is inserted into the base of the coal and is traversed across the
width of the panel (usually 6 m or 20 ft); the blade produces a narrow ken, or slot along the base of
the recoverable coal. 0
After the cutting machine is trammed to the next panel (panel 9), the drilling crew cuts a specified
pattern of blast holes into the face of Panel 8. The holes are loaded with a blasting agent and then
shot, exposing the working face of Panel 15. The cycle at Panel 8 then returns to loading, and the
coil is removed from the face area ahead of the bolting crew.
Continuous mining systems generally employ fewer workers per face and produce more tons per
worker and per shift than conventional systems. The efficiency of continuous mining systems remains
essentially unchanged with increasing seam height. Conventional systems reach a point of
diminishing return as seam height reaches 1.8 m (6 ft).
Continuous mining systems use machinery to extract coal during room-and-pillar, shortwall, and
lorigwill operations. Machinery and panel configurations are chosen within the constraints of the coal
seam variables described previously.
Continuous room-and-pillar operations are based on the capabilities of coal cutting machinery to
combine the unit operations of conventional mining techniques (cut, drill, shoot, and load) into one
continuous operation; roof bolting may also proceed in conjunction (and slightly behind) continuous
mining. The opeEation may be halted periodically for methane checks and the installation of
electrical, conveyance, and ventilation services. Coal is cut from the face with cutters, borers,
augers, and shearers that direct the cuttings to conveyor belts mounted inboard on the machine
assembly. These inboard conveyors feed the coal to the mobile conveyor belts, shuttlecars, or load-
haul-dump (LHD) vehicles that transport the coal to the permanent haulage system, which may be
another conveyor or a train of mine cars pulled by a locomotive.
Longwall mining systems employ one or more parallel entryways located approximately 90 to 180 m
(300 to 600 ft) apart and connected by a cross cut (Exhibit 3-21). The equipment necessary to
conduct the operation including the cutter, conveyor, shield, and roof supports are inserted through
the crosscut. Coal is sheared or planed from the face and then directed onio the conveyor, which
feeds the coal to a semi-Stationary haulage system located in an adjacent entryway. Roof supports
advance toward the cut face hydraulically, leaving the roof of the mined area (gob) to collapse as the
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EIA Guidelines for Mining
Exhibit 3-21. Longwall Mining System
Rib
3000’—2 miles
Collapsed Roof
Coal in Place
_______ Mining Machine (“shear” or “plow”)
_______ Hydraulic Roof Support
H
—U
Entry 1
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unsupported overburden subsides into the mined-out chamber. When longwall mining methods are
used, there is a clear potential for surface subsidence, as described in section 4.8.
Longwall systems are typically applied in situations where uniformity exists throughout the coal seam
in terms of height, bottom and roof conditions, hardness, and areal distribution. Longwall mining of
multiple seams is possible under some conditions. Shallow seams are mined first, followed by
progressively deeper seams. Overburden structures and lithologic characteristics influence the rate
and form of the resultant caving and should be considered in the design/development phase.
Longwall mining systems offer the following advantages over other mining systems (DOE, 1978):
• Lower cost per. ton of coal produced
• Higher productivity per worker hour
• Higher percentage of recovery of coal resource
• Predictable subsidence
• Adaptability to thick and multiple seams
o Capability to mine at great depths.
Shortwall mining systems are similar in principle to longwall systems. During shortwall mining, coal
is cut from a panel approximately 45 m (150 ft) long. Roof supports advance toward the panel as
mining progresses. The unsupported, undermined areas subside into the void behind the advancing
roof supports. The panel length is short enough to be worked economically with the conventional
mining machinery used in room-and-pillar systems, although automated shearers also are available for
shortwall systems.
Shortwall systems can be used to change existing mining operations from room-and-pillar techniques
to wall-type mining techniques without additional costs f r the replacement of machinery or revision
of plans for mine development. Advanceable roofsupportsmay be the only additional equipment
required to consummate the change-over. Shortwail operations also offer the advantage of flexibility
in selecting the locations of mining panels or walls to minimize the interruptions in production that
result from changes in seam height and the presence of want areas, unsuitable roof and bottom
conditions, and gas and oil wells.
3.4.3.3 Abandonment
The techniques that are appropriate for the abandonment of an underground mine generally reflect the
manner in which the mine was developed. Water infiltrates to the mine void through overlying and
adjacent strata.. Drift entryways that are advanced up the dip of the coal seam will allow this water to
drain freely from the mine, unless suitable seals are installed at the drift mouth. Entryways that are
advanced down the dip of the seam must be pumped during mine operation. After abandonment,
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water drains to the depths of the mine, forming a subterranean pool that may slowly drain to the
surface through channels, fractures, and other small voids. -
The following kinds of seals frequently are installed at mine openings during abandonment:
• Dry seals to prevent the entrance of air and water into mine portals where there is little or
no flow of water and. minimal potential to develop hydrostatic pressure against the. seal.
• Air seals to reduce the flow of air into the mine while allowing water to drain from the
mine. Even these mines can still “breathe” thràugh minute cracks and fissures because of
continued changes in atmospheric air pressure. Enough oxygen usually is available under
these conditions for formation of acid drainage if sufficient pyrite and water are present.
• Hydraulic seals which plug the discharge from flooded mine voids and- exclude air from the
mine, thus retarding the oxidation of sulfide minerals.
Hydraulic seals may be employed to. seal the drift mouths of entryways that were developed up the
dip of the coal seam. A hydraulic seal may include one or more bulkheads constructed wIth limbers,
walls of concrete block, backfilled material, and grout curtains injected through boreholes from the
surface. These abandonment techniques and others are thoroughly described in other EPA
publications (EPA, 1973 and 1975).
3.4.3.4 Pollution Control
Significant advances have been made in pollution control techniques used in the surface coal mining
industry. Evolving technologies include:
• Alternate mining methods, emphasizing controlled spoil placement and reclamation
concurrent with extraction
• Wastewater treatment systems, emphasizing innovative techniques to replace limestone.
treatment systems and rapid-filling sediment ponds, both of which suffer from reduced
treatment cost ratios asa result of recent regulations
• . Revegetation systems, emphasizing the replanting of reclaimed areas with plant species
which have been specially bred for replanting of local minespoils
• Soil stabilization systems, emphasizing (1) the use of soil mechanics’ in slope design, and
(2) soil covering agents such as stubble mulches, cover crops, artificial soil amendments
and chemical binders, and mulches to prevent wind and water erosion of recently backfilled
areas or temporarily stockpiled soils.
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3.4.3.5 Environmental Effects
The physical disturbance associated with surface coal mining and the surface aspects of underground
mining are the same as those of other mining sectors. Surface disturbance reduces the cover and
primary productivity of the land. The loss of vegetation cover results in an increase in erosion and
without adequate control, sediment concentrations are likely to increase in nearby streams. Ground
disturbance and constant movement by vehicles also increases fugitive dust carried in the wind.
Wildlife habitat is lost at least temporarily with surface disturbance while noise and human activity
create additional impacts in the immediate vicinity of mining ‘operations. Although these impacts are
to be expected with any mining or other surface-disturbing activity, they thay be particularly acute
when mining operations are being, conducted on adjacent parcels of land over an extended period of
time.
Other environmental effects resulting from coal mines depend on the nature of the operation (surface
versus underground) and to some extent, its location (east versus west). In addition to the surface
water impacts associated with most mining activities, surface coal mining operations may’ also impact
groundwater. In the east, particularly, acid mine drainage remains a problem despite developments in
the technology surrounding prediction and control. Acid mine drainage is discussed, in Section 4.1,
and will not be discussed further here. Subsidence is a response to underground mining activities.
Although concentrated in the east and midwest, impacts from subsidence have also occurred in
Wyoming and Colorado. A discussion of subsidence is presented in Section 4.8.
The extent of impacts to groundwater depends primarily on the premining hydrologic system and the
chemical constituents of the overburden. As with other forms of surface mining, the geologic strata
overlying the coal (or ore) are removed during extraction. Non-coal mining operations typically store
this material in waste rock piles outside the pit while coal mining operations are required to place
overburden back into the mined-out portions of the mine. As overburden is placed into the pit the
hydrologic setting is changed from consolidated, heterogeneous strata o a highly permeable,
homogeneous mass. The groundwater level and flow rate can be affected by the increased
permeability of the backfill in the pit. The potentiometric surface will eventually stabilize, however
the new surface may not reflect the premining water level.
3.5 COAL PROCESSING
3.5.1 BAsic PRINCIPLES ‘
Coal preparation is a critical technology supporting both the mining and end-use of coal. The output
of a coal mine consists not only of coal but also non-combustible mineral matter. This mineral matter
ranges in size from large rocks to extremely small grains dispersed throughout the coal seam. The
primary objective of coal beneficiation is the separation and removal of mineral matter from coal to
3-12 September 1994
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Overview of Mining and Beneficiation EIA Guidelines for Mining
reduce transportation costs, and improve product quality by reducing ash loading in the boiler.
Burning coal with less ash increases boiler efficiency, boiler capacity, plant availability, and net heat
rate. Reductions in auxiliary power consumption, forced outages, particulate emissions and capital
costs of new power plants all accompany the use of lower ash coals. Additionally, as-mined raw coal
often fluctuates in quality and this is detrimental to boiler operation. Coal beneficiation produces a
relatively uniform product and therefore assures stable boiler operation. -
Concerns over the environmental effects of coal burning expanded the objective of coal beneficiation
to include removal àf inorganic sulfur in coaL More recently, researchers are examining coal
preparation as a means of reducing air toxic precursors. As New Source Performance Standards
(NSPS) were developed for coal-fired utility boilers, advanced coal cleaning technologies were
simultaneously developed to remove 70 to 80 percent of the pyritic sulfur present in coal and recover
70 to 80 percent of the combustible matter. The Clean Air Act Amendments of 1990 (CAAA)
provided further impetus for coal preparation. Utilities could now choose between several compliance
options such as switching to premium low-sulfur coals, emission allowance trading, or post-
combustion clean up. Risk averse utilities could choose to pursue a mixed CAA compliance strategy
because of the volatility of stand-alone strategies. Coal preparation became another viable option to
meet compliance regulations by its ability to convert high and medium-sulfur/ash coals to low-sulfur/
ash coals.
The types of equipment used to remove mineral matter from raw coal are numerous and the
configurations in which they are used in cleaning plants can be complex. Despite the complexity of
actual operating plans, there are only two underlying principles upon which all physical cleaning
plants operate: (1) differences in specific gravity between the organic, combustible matter and the
inorganic mineral matter present in coal, and (2) differences in surface properties between organic and
inorganic matter. Conventional coal cleaning processes are based on the former principle, whereas
advanced cleaning processes are based on the later principle.
Conventional coal cleaning involves the immersion of raw coal in a medium that simulates a
predetermined specific gravity. The lighter material is removed as a clean “float” product, while the
heavier material or “sink” is rejected as refuse. The majority of coal mined in the United States is
cleaned using this principle. A small percentage of coal consisting of very fine particles in the raw
product cannot be cleaned using gravity methods. With fine particles in aqueous systems, surface
forces become comparable with gravity forces and hence, gravity-based separation becomes
ineffective. Consequently, these fine particles, being only a small portion of the raw coal, are usually
discarded. Alternatively, a technique known as froth flotation may be used to clean these fme
particles. Unlike specific gravity separation which exploits differences in the specific gravities of
particles, froth flotation is based on differences -in the surface properties of coal and mineral matter.
Coal surfaces are typically hydrophobic but the surfaces of the refuse material associated with coal are
3-126 September 1994
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EIA Guidelines for Mining Overview of Mining and Beneficiation
hydrophilic. By passing air bubbles through a coal-water suspension, coal and refuse particles can be
separated; the refuse material sinks while the air bubbles attach themselves to the coal particles and
buoy them to the surface where they are collected in a froth.
The actual process of separating raw coal from its associated impurities, using either the specific
gravity separation principle or froth flotation, is only one of the four processes that coal cleaning can
involve. The other three processes are crushing, screening, and dewatering. Crushing serves to
break down largt heterogeneous particles into smaller, purer particles prior to separation. The extent
to which crushing can liberate coal from impurities depends in large part on the depositional
characteristics of the coal seam. For example, if the impurities are finely disseminated throughout the
seam, liberation may be relatively difficult. If, on the other hand, the impurities exist as thick bands
of rock within the seam, with weak bonds to the coal, then the raw particles will tend to break along
the weak bonding planes during crushing, resulting in extensive liberation of the coal from the rock.
In any event, the success of the subsequent separation process depends in large part on the degree of
• liberation achieved through the crushing process. All particles must report to either a float or a sink
fraction during the separation process; thus, the existence of heterogeneous particles means that the
clean float particles will contain mineral impurities, and the rejected sink material will contain coal.
Coal cannot be completely liberated from its associated impurities through crushing—some
.heterogeneous particles will remain. Whether any given heterogeneous particle reports to the float or
sink depends on the overall specific gravity (or, in the case of froth flotation, the overall hydrophilic
tendencies) of the particle.
Following crushing, but prior to separation, the raw coal is typically screened. Screening is used to
divide the raw particles into pre-defmed size ranges. The various types of equipment used in the
separation process typically achieve maximum efficiency when processing feed of a relatively
uniform, narrowly-defined size range. For example, equipment based on the specific gravity
separation principle fails below a minimum particle size; for coal partiàles this is usually 25 mesh
(575 microns) or 100 mesh (149 microns). For finer particles froth flotation must be used. Thus, the
separation process typically consists of two or three separate circuits, each using a different equipment
type designed to handle a specific size range of particles. Screening is used to direct the raw coal
particles to the proper circuits.
Finally, after separation, the clean coal and refuse are generally dewatered. Moisture, like ash and
sulfur, is an undesirable impurity; through the dewatering process the moisture content of the clean
coal can be reduced.
A perfect separation of coal from its associated impurities is not possible using either the specific
gravity separation or froth flotation. This is because, in practice the separation process is
3-127 September J994
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Overview of Mining and Beneficiation EIA Guidelines for Mining
fundamentally stochastic in nature. As mentioned earlier, some composite particles consisting of
mineral matter and coal will remain even after crushing.
Sulfur occurs in coal in both pyritic and organic form. Pyrite is a mineral that is not an integral part
of coal, but is normally associated with it. Hence, it is possible to separate coal and pyrite using a
physical cleaning technique. Organic sulfur on the other hand, is an integral chemical component of
coal and cannot be separated through physical cleaning. 2 The theoretical limit to the amount of
sulfur that can be removed from a given coal through physical cleaning is equivalent to the amount of
sulfur occurring in pyritic form.
The degree to which the separation falls short of perfection is dependent on the raw coal qualities, the
cleaning equipment used, plant operating conditions, and the washability of the coal. Coal
washability can be roughly defined in terms of the degree to which a coal can be separated from its
associated impurities.
Raw coal feed consists of particles combining coal and impurities in various proportions; thus, the
particles cover a wide spectrum of specific gravities. The washability of a coal defines this spectrum
and consists of the percentage (or cumulative percentage),’ by weight, of the raw coal comprising
contiguous specific gravity intervals, along with the quality (Btu, sulfur, and ash contents) of each
specific gravity fraction. ‘Exhibit 3-22 is an example of washability data for a sample of a
bituminous, high volatile A coal from the Pittsburgh bed in Jefferson County, Ohio. 3 The data are
divided into three size ranges of coal. Within each size category, the percentages (by weight) of the
raw coal with specific gravities less than 1.3, 1.4, and 1.5 are given (e.g., 48.6 percent of the raw
coal in the 1½ inch x 100 mesh size range has a specific gravity less than 1.3). Also, the Btu
content, ash content, and sulfur content corresponding to each specific gravity fraction are given; in
the previous example, that portion of the raw coal with a specific gravity less than 1.3 has a Btu
content of 14,146 (per pound basis).
Washability data are developed experimentally. A sample of coal is collected, crushed to a given
topsize, and screened into separate particle size ranges. A sample from each size range is immersed
in organic liquids possessing definite, precise specific gravities. The material that floats at each
specific gravity is weighted and analyzed to determine its Btu, sulfur and ash content. Returning to
our previous example, 48.6 percent of the 1½ inch x 100 mesh sample floated when place in a liquid
2 Organic sulfur can be removed through chemical cleaning. However, chemical cleaning is not a commercially viable
option at present.
3 Sulñir and Ash Reduction Potential of United States Coals, Vol. 1, p. 395, Eastern Region. U.S. Dept. of Energy,
DOE/PETCITR-9 0s ’7.
3-128 ‘ September 1994
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Exhibit 3-22. Ash and Sulfur Reduction Potential of U.S. Coals, Vol. I p. 395, Eastern Regions U.S. Department of Energy
State Ohio BR!) Pittsburgh BR!) Code 35
County Jefferson Rank High Volatile A Sample No 135
Cumulative Wáshabil1t Data l ) .: :.: : .:.:: .: :::
Sample Crushed to Pass 1-1/2”
(Float-Sink Performed on 1 2,2 ”: K 100 M.Materlal) .. .. ., : •.‘.‘ : :::..
Recover v, Percent
ASH %
Sulfur,
Percent
Heating Value
‘:.. :8TJ/LB .*
S02 Emission
.:*z is ro
PyrltIc
Total
Weight:..
....:STU
Float 1.30
48.6
53.1
4.6
0.82
1.82
14,146
2.6
Float 1.40
83.8
49.8
6.2
1.34
2.34
13,670
3.4
Float 1.60
92.6
97.5
7.5
2.60
2.54
13,645
3.7
COM (1-112 x lOOM)
100.0
100.0
11.6
2.10
3.05 .
12,936 .
4.7
lOOM *0
1.3
1.2
17.7
5.13
5.58
12,086
9.3
Total (1-1/2 x 0)
100.0
100.0
11.7
2.22
3.08
12,925
4.8
S S •. . . . SAMPLE CRUSHED TO PASS 3/8: .. . . . : .:
: (FLOAT-SINK PERFORMED ON 3/8” x lOOM MA RIAL) ..: :. . . ..
Float 1.30
54.9
60.9
3.9
0.74
1.65
14,267
2.3
Float 1.40
82.3
89.9
3.4
1.13
2.04
14,000
2.9
Float 1.60
90.9
97.0
6.8
1.38
2.26
13,767
3.3
COM (3/8 x lOOM)
100.0
100.0
11.9
1.98
2.79
12,904
4.3
lOOM x 0
4.6
4.5
13.3
4.03
4.56
12,645 .
7.2
Total (3/8 *0)
100.0
100.0
11.9
2.07
2.87
12,092
. 4.5
SAMPLE CRUSHED TO PASS 1411. .. : . S .. H
(FLOAT-SINK PERFORMED ON 1411” *0 MATERIAL) . : __.__: .
:.
S.
Float 1.30
41.9
49.9
2.9
0.38
1.33
14,439
1.4
Float 1.40
78.7
85.6
4.7
0.73
1.35
14,129
2.2
Float 1.60
89.9
96.4
6.2
0.94
1.78
13,870
2.6
COM (14H *0)
100.0
100.0
11.3
2.05
2.82
12,990
4.3
RAM COAL SIZE AND MOISTURE ANALYSES
Size DistrIbution, Percent; Sample Crushed to Pass 1-1/2”
5 MoIsture, Percent
-
1-1/2 x 3/8
77.1
Total 5
5.1
3/4 x 14M
17.2
As Received
4.2
14M x lOOM
4.4
100MxO
1.3
0
0
I.
I
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Overview of Mining and Beneficiation LIA Guidelines for Mining
with a specific gravity of 1.3; this “float” had a Btu content of 14,146 (per pound basis). The
specific gravity of the bath (1.3 in the example) is referred to as the specific gravity of separation.
Commercial cleaning plants achieve gravity separations by employing various techniques (including,
e.g., suspensions of ground solids in water) to simulate the heavy liquid media used in the laboratory.
The behavior of a coal sample in a laboratory bath, as measured during washability tests, provides a
theoretical limit of how the coal will behave in a commercial cleaning plant. 4 Washability data, like
those presented in Exhibit 3-22, are used to estimate the yield and clean coal quality for a given coal
cleaned at a given specific gravity of separation. For example, if the 1½ inch X 100 mesh coal from
the earlier example is to be cleaned at a specific gravity of separation of 1.6, Exhibit 3-22 predicts
that the yield will be 92.4 percent. The clean product will have a Btu content of 13,646 (per pound
basis), an ash content of 7.5 percent, and a total sulfur content of 2.54 percent. Commercial cleaning
plants rarely reach these theoretical levels of product quality. Computer models for simulating coal
preparation can be used to estimate commercial plant performance. Such models use washability data
to predict the yields associated with cleaning various coals to meet predefined quality specifications.
An important characteristic of all washability data is the trade-off between coal quality and quantity.
From Exhibit 3-22, for all three particle size fractions, Btu content increases and ash and sulfur
contetit decrease as the yield decreases. Thus, improvements in coal quality can be obtained only at
the expense of reductions in yield; this is true of all coals including the sample represented in Exhibit
3-22. Not only are there technical limits to the percentage of ash and sulfur that can be removed
from coal through cleaning, there are economic limits as well. For example, referring to Exhibit
3-22, we can see that it is technically feasible to reduce the sulfur content of 1½ inch x 100 mesh
coal to 1.82 percent; however, the resulting yield would be 8.6 percent. From an economic
standpoint, it is unlikely that the benefits obtained by reducing the sulfur content to 1.82 percent
would outweigh the costs associated with the loss of 51.4 percent of the coal.
The common way of assessing or evaluating coal cleaning systems that use gravity separation
techniques is to determine the sharpness of separation achieved. This is done using partition curves.
The partition curve of any given equipment that separates coal and mineral matter is essentially a
histogram of the distribution of coal groups of different densities in the product. Typically the
histogram is represented in the form of a cumulative curve with the partition coefficient on abscissa
and relative density on the ordinate. Such a curve is shown in Exhibit 3-23. In an ideal separation
the curve is parallel to the abscissa at the density of separation. The partition curve is typically
characterized by two parameters d and e . d, is the relative density corresponding to partition
coefficient 50. This is the relative density at which an infinitesimal increment df raw feed is equally
4 Laboratory washability data represents separation at ideal (equilibrium) conditions, whereas separations in an actual
plant do not have sufficient tune to reach equilibrium and conditions for separation are non4deal.
3-130 September 1994
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ELA Guidelines for Mining
Overview of Mining and Beneficiation
Exhibit 3-23.. Washability Partition Curve
Sw b r 1904
100
I
1.6 1.
Relative Density
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Overview of Mining and Beneficiation EIA Guidelines for Mining
divided between clean coal and refuse. e , the probable error, gives an indication of the deviation
from ideal separation and is calculated as the slope of the curve around d . e is also a function of the
particle size and the density of separation. Each equipment in a coal preparation plant operates at a
particular d and e .
Although washability data provide an indication of how coal will respond when cleaned using gravity-
based equipment, they do not indicate how coal’ will respond to surface-based separation equipment,
such as froth floatation.
Coarse ore tailings or coal refuse can be used to construct an impounding dam, typically within a
drainageway or narrow valley. Then, a slurry of fmer tailings or refuse can be pumped into the
impoundment area for settling (similar to tailings impoundments described for metal mining above).
As with other tailings impoundments, these can be quite large, with impoundments reaching over 100
feet high and 1,000 feet long. Both NPDES and Clean Water Act §404 regulations can, in some
situations, prevent the construction of sUch impoundments. When they are allowed, the major
enviromnental concern is the destruction of the drainage that is being filled. States generally require
that existing instreain uses of surface waters be protected and maintained (generally known as “ non-
degradation” policies), and these often prevent such impoundments.
3.5.2 COAL CLEANING TECHNOLOGY
EPA has an ongoing research and applications program that may significantly affect the future form
and economics of current and developing coal cleaning technologies (Section 1.3.3.). Reports of this
program describe in detail the coal cleaning technologies currently used by the mining industry
(Nunenkamp, 1976; McCandless and Shaver, 1978). The engineering principles of mechanical coal
cleaning also are, described more thoroughly in other sources (Leonard and Mitchell, 1968; Cummins
and Given, 1973; Merritt, 1978). The following discussion of coal cleaning technology summarizes
the elements of mechanical coal preparation in the detail necessary to identif ’ the impacts and
pollution control strategies associated with proposed projects.
The mechanical cleaning of coal generally includes the five basic stages (Exhibit 3-24) described
beløw. The numb er of stages employed and the unit operations that comprise each stage may vary
among individual operations, although Stages 1, 2, and 3 are common to most of the Nation’s coal
cleaning facilities (Exhibit 25).
• Stage 1—Plant Feed Preparation. Material larger than 21 cm (6 in) is screened from the
ROM coal on a grizzly. The properly sized feed coal is ground to an initial size by one or
more crushers and fed to the preparation plant.
• Stage 2—Raw Coal Si7ing. Primary sizing on a screen or a scalping deck separates the
coal into coarse- and intermediate-sized fractions (Exhibit 3-26). The coarse fraction is
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EIA Guidelines for Mining
Overview of Mining and Beneficiation
Exhibit 3-24. Coal Preparation Plant Processes
4..
PRODUCT WATER
DEWATERI NGWATE
5.:
PRODUCT
STORAGE
AND SHIPPING
COARSE
REFUSE
•1.
PLANT FEED
PREPARATION
OAR$E
2.
RAW COAL
SIZING
cOARSE
REFUSE
- I -
3.
RAW COAL.
L Tb0N __
FINE SIZE
RERJSE
3-133
September 1994
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Source: Nunenkanip, David C., 197&
Exhibit 3-25. Typical Coal Cleaning Facility
CLEAN COAL
STORAGE
RAW COAL
STORAGE
ROTARY
BREAKER
BIN
TRUCK DUMP
0
I
a
g
PREPARATION
PLANT
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EIA Guidelines for Mining
Overview of Mining and Beneficiation
Source: EPA, 1977.
Exhibit 3-26. Typical Circuit for Coal Sizing Stage’
September 1994
TRUCK DUMP
CARDUMP A
REFUSE BIN
FUGITIVE
A EMISSION POINTS
A
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Overview of Mining and Beneficiation EIA Guidelines for Mining
crushed again if necessary and subsequently is re-sized for cycling to the raw coal
separation step. The intermediate fraction undergoes secondary sizing on wet or dry
vibrating screens to remove fines, which may undergo further processing. The intermediate
fraction then is ‘fed to the raw coal separator. Coal sizes generally are expressed in inches
or mesh sze (Exhibit 3-27). in Exhibit 3-26, the notation 4 x 0 indicates that all of the
coal is smaller than 10cm (4 in). A notation such as 4 x 2 indicates that the coal is sized
between 5 and 10 cm (2 and 4 in). The notation 4+ indicates that the coal is larger than
10 cm (4 in).
Exhibit 3-27. Metric and English Equivalents of U.S. Standard Sieve Sizes and
Tyler Mesh Sizes
U S
:.:: :
Standard Sieve
Mach Size
MeshNo.”
. ,: “.H “:inches ‘
Ty
ler
4
.475
.187
4
6
.
.335
.132
.
‘
•
6
8
.236
‘
‘‘
.0937
•
8
•
10
•
.200
.0787
9
12
.170
.0661
10
14
.140
.0555
12
16
.118
.0469
14
18
.100
.
.0394
16
‘
20
.085
•
.0331
20
30
.060
.0234
28
35
.050
•
.0197
•
32
40
.0425
.0165
35
45
.0355
‘
.0139
42
50
.030
.0117
.
48
60
.025
.0098
60
70
.0212
.0083
65
80
.0180
.0070
80
100
.015
‘
.0059
100
‘
120
.0125
.0049
‘
115
140
.0106
.0041
150
170
009
.0035
17C)
200
‘
•
0075
.0029
200
230
•
.0063
.0025
250
270
.0053
.0021
.
270
325
.0045
.0017
•
325
Stage 3—Raw Coal Separation. Approximately 97.5 percent of the U.S. coal subjected to
raw coal separation undergoes wet processes, including dense media separation, hydraulic
separation, and froth flotation. Pneumatic separation is applied to the remaining 2.5 percent
(DOE, 1978b). The coarse-, intermediate-, and fine-sized fractions are processed separately
by equipment uniquely suited for each size fraction. Refuse (generally., shale and
sandstone), middlings (carbonaceous- material denser than the desired product), and cleaned
coal are separated for the dewatering stage.
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EIA Guidelines for Mining Overview of Mining and Beneficiation
• Stage 4—Product Dewatering andlor Drying. Coarse- and intermediate-sized coal
generally are dewatered on screens. Fine coal may be dewatered in centrifuges and
thickening ponds and dried in thermal dryers.
• Stage 5—Product Storage and Shipping. Size fractions may be stored separately in silos,
bins, or open air stockpiles. The method of storage generally depends on the method of
loading for transport and the type of carrier chosen.
For a typical coal cleaning plant with 910 MT (1,000 T) per hour capacity, approximately 70 percent
of the crushed coal reports to the coarse cleaning circuit. Sizing and recrushing of the coarse coal
result in the cycling of 34 percent of the coarse coal charge to the fine and intermediate cleaning
circuits. Approximately 27 percent of the coarse charge is removed as refuse. The remaining 39
percent is removed as clean product. Process quantities for the fine and intermediate cleaning circuits
appear in Exhibit 3-28.
Exhibit 3-28. Typical Process Quantities for a 910 MT (1,000 1’) per Hour
Coal Cl ning Facility
Washing
Circuit
Dewatering
Circuit
Process -
Water’’
Refuse
Recovery
MT/hr
%
MT/hr
%
MTfhr
%
MT/hr
%‘
Coarse coal fraction
630
69
245
39
3,293
12
173
63
Intermediate coal fraction
190
21
330
52
‘ 7,040
26
82
30
Fine coal fraction
90
10
58
9
16,427
61
19
6
Thermal dryer dust
‘
3
1
Total
910
100
633
100
26,760
100
277
100
Source: Nunenkamp, David C. 1976. Coal Preparation Environmental Engineering Manual. EPA,
Office of Research and Development, EPA-60012-76-138, Washington. D.C., 727 p.
3.5.2.1 Stage Descriptions
The initial screening and crushing of ROM coal at Stage 1 (Exhibit 3-24) may be accomplished in one
or more substages (Exhibit 3-29). The grizzly can be a set of iron bars, welded on 21 cm (6 in)
centers to a rectangular frame. Oversized material that would otherwise inhibit the operation of the
primary crusher is scalped from the feed coal on the grizzly bars. In a multicrusher system, the
output from the primary crusher is screened. Over-sized coal is fed next to a series of crushers, and
finer material reports directly to sizing and separation stages.
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Overview of Mining and Befleficiation
EIA Guidelines for Mining
The types of mills that are available for Stage 1 crushing include rotary breakers, single and double
roll crushers, hammermills, and ring crushers. Each type of mill is available in various models which
crush the ROM coal at different rates to different sizes. The general characteristics of crushing mills
appear below (McClung, 1968).
• Rotary breaker. Often called the Bradford breaker after its inventor, this large, rotating
cylinder is driven at 12 to 18 revolutions per minute by an electric motor via a chain and
reducer drive. ROM coal is introduced through one end of the cylinder and’ is crushed
against the encircling steel plates. The crushed coal’ exits the breaker through the precut
holes in the plates and feeds to a conveyor. Slate, overburden, rock, and other gangue
materials that resist breakage are carried by a series of baffles to the far end of the cylinder,
where they are removed from the mill by a continuously rotating plow.
• Single- and Double-Roll Crushers. A roll crusher comprises one or two steel rollers
studded with two different lengths of heavy teeth. The long teeth slice the large pieces of
coal into fragments and feed the flow of coal into the smaller teeth, which make the proper
size reduction; In single-roll mills, the coal is crushed against a stationary breaker place
(Exhibit 3-30a). Double-roll crushers also fragment the coal with specially designed teeth.
Crushing action against the rollers (between the teeth) is minimal (Exhibit 3-30b). Both
mills are fed through the top. Product exits through the bottom.
Exhibit 3-29. Typical’Three-Stage Crusher System for Raw Coal Crushing
COASSE OU SIN
‘tED’S’
PtNE 051 115
3-138
September 1994
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EIA Guidelines for Mining
Overview of Mining and Beneficiation
Exhibit 3-30. Single-Roll (a) and Double-Roll (b) Crushers for Sizing of Raw Coal
Source: McClung, J.D., 1968. Breaking and crushing. Jii Joseph W. Leonard and David R.
Mitchell (eds.), 1968.
(A)
(B)
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Overview of Mining and Beneficiation EIA Guidelines for Mining
• Il nnmerniil1. This mill uses a set of hammers to strike the feed coal against a breaker
base plate. The rebounding fragments are swept against a perforated steel plate or crushing
grate and discharged to a bin or conveyor.
• Ring crusher. The principles of hainmermill and ring crusher operations are similar.
Instead of hammers, the ring crushers uses a set of smooth and toothed rings to drive the
feed coal against the breaker plate.
The unit operations that commonly are employed at Stage 3 of Exhibit 3-24 (separation) vary
considerably among. modem cleaning installations nationwide. The choice of unit operations for a
particular installation depends on a number of factors, including coal preparation objectives,
availability and costs of equipment, and operator experience. Nine of the typical unit operations that
currently are employed during the separation step are listed below (McCandless and Shaver, 1978).
With the exception of froth flotation, all of these operations utilize the specific gravity principle to
affect a coal/impurities separation. Water requirements, sizes and rates of feed, and dewatering
efficiencies of selected unit processes are described in Exhibit 3-31.
• Dense Media. Light, float coal is continuously skinuned from a suspension of solids in
water that separates from heavy liquid with a defined specific gravity (usually magnetite;
Exhibit 3-32). Finely-ground magnetite is usually used in the suspension, in part because it
can be easily recovered from the clean coal and refuse by magnets. Accuracy of separation
is sharp from 0.059 to 20 cm. Quality and sizes of feed can fluctuate widely.
• Froth Flotation. A slurry of coal and collector agents is blended to induce water-attracting
tendencies in selected fractions of the feed coal. After the addition of a frothing agent,
finely disseminated air bubbles are passed through the slurry. Selected coal particles adhere
to the air bubbles and float to the surface, to be skimmed off the top. The process can
separate fractions in a band of 0.045 to 1.18 mm (0.002 to 0.05 in). Froth flotation affects
a good separation between coal and ash, but does not successfully separate coal from pyrite,
because the latter mineral is, like coal, hydrophobic. Better sulfur reduction results can be
obtained using two-stage flotation. The first stagc proceeds as described above. In the
second stage, the float product is re-slurried and then treated with an organic colloid that
selectively prevents the coal particles from floating to the top with the pyrite.
• Humphrey Spiral. A slurry of coal and water is fed into the top of a spiral conduit. The
flowing particles are stratified by differences in density, with the denser fractions flowing
closer to the wall of the conduit. A splitter at the end of the stream separates the stratified
slurry into final product and middlings. These products are fed to separate dewatering
facilities.
• Hydrocydones. A slurry of coal and water is subjected to centrifugal forces in an
ascending vortex. The denser refuse material forms a layer at the bottom of the vessel.
Circulating water skims the clean coal from the top of the stratified slurry and directs the
product to a vortex fmder, which feeds the cyclone overflow into the product dewatering
stage (Nunenkamp, 1976). Feed coal sizes range between 0.044 and 64 mm (0.002 and
2.5 in).
3-140 September 1994
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EllA Guidelines for Mining Overview of Mining and Beneficiation
Exhibit 3-31. Feed Characteristics of Unit Cleaning Operations
for Si2ing and Separation of Crushed Coal
..
Cc)a) Cleaning UnIt ::
W t Required
per MT of Feed
(1pb) :
Maximum
Feed Rate
(MTph)• :.::
Range of
Feed Sizes
(cm) ’
Percent Solids
in Feed
aum jig
12 to 21
9.8 to48 per m
of jig area
0.3 to 20
85 to 90
Belknap washer
21
124
0.6 to 15
85 to 90
Chance cone
29 to 50
488 per m 2 of
cone area
0.2 to 20
•
85 to 90
Concentrating table
50 to 67
9.1 to 14
0 to 0.6
20 to 35
DSM heavy media cyclone
83to125
(heavy media
slurry)
4.5 to 32
.
0 to 0.6
‘
.
12 to 16
Flotation cell
54 to 67
1.8 to 3.6
0.030 to 0.0075
20 to 30
Humphrey spiral
125
0.9 to 1.4
0.6 to 0.0075
15 to 20
Hydroseparator’
.
58 to 75
1.4 per vertical
cm of vessel
1.3 to 13
85 to 90
Hydrotator
50 to 67
49 per m 2 of
surface
0 to 5.1
85 to 90
Menzies cone
58 to 75
273
1.3 to 13
85 to 90
Rheolaveur free discharge
12 to 17
1.1 to 1.8 per cm
of vessel
0 to 0.6
15 to 30
Rheolaveur sealed
discharge
to 50
2.9 to 3.6 per cm
of vessel
0.6 to 10
15 to 30
tRange of feed sizes is listed for bituminous coal only. Anthracite feeds for Menzies cones and
hydroseparators range between 0.08 and 13 cm. The DSM cyclone accepts anthracite feeds between 48
mesh and 0.75 in. The flotation cell accepts 200 to 28 mesh. The Belknap washer does not process
anthracite.
Source: Aplan, F. F: and R. Hogg. 1979. Characterization of Solid Constituents in Blackwater
Effluents From Coal Preparation Plants. Prepared for the EPA and U.S. DOE, EPA-600/7-79-006, FE-
9002-1, Washington, D.C., 203 P.
3-14 1 September 1994
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
Exhibit 3-32. Typical Circuit for Dense Media Coal Cleaning
114
TO
A
a
C
0
£
F
G
H
I
A1Th L}.
l R !1N6 PLPJ TlAL
1/2 z 0
CURSE NAG. SEP*R. COAl.
FIME NAG. 5EPAL A
CENTRIFUGE LOADING CR STORAGE
CENTRIFUGE
CENTRIFUGE
CRUSHER
CYCLONE
LIGHT MEDIA JNP
HEAVY MEDIA SLN4P
HEAVY MEDIA SW P
(J
MV COAl. SCREEN (K
•PRE WET SCREEN
REF. RINSE SCREEN (N)
COAl. RINSE SCREEN N
SLURRY SCREEN P
REFUSE RINSE SCREEN P
SIEVE 8E (S
HVY. MEDIA lATh (1
HYT. MEDIA CYCLONE CV)
A EMISSIO,N POiNTS
(1) TO RATER cLMIFICATION
Source: EPA. 1977.
3 142
September 1994
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EIA Guidelines for Mining Overview of Mining and Beneficiation
• Jiggings. A slurry of coal and water is stratified by pulsating fluid. Clean, low density
coal is skimmed from the top of the vessel. The accuracy of separation is low. Sizes of
feed coal range between 3.4 and 76 mm (0.1 and 3 in; Exhibit 3-33).
• Launders. Raw coal is fed with a steam of water into the high end of a trough. The coal-
water stream stratifies as it flows down the incline. The denser refuse material forms the
bed load of the trough while the less dense coal is suspended in the stream. The cleaned
product is split from the stream at the low end of the trough. Feed coal sizes range
between 4.76 and 76 mm (0.19 and 3 in).
• Pneumatic. Streams of pulsating air stratify the feed coal across a table equipped with
alternating decks and wells (Exhibit 3-34). Refuse is pushed into the wells and withdrawn
under the table. The cleaned product rides over the refuse and is withdrawn at the
discharge end of the table. Feed coal sizes range to a maximum of 9.5 mm (0.38 in;
Exhibit 3-35).
• Wet tables. A slurry of coal and water is floated over a table that pulsates with a
reciprocating motion. Denser refuse materials flow toward the sides of the table, while the
cleaned coal is skimmed from the center. Feed coal sizes range between 0.15 and 6.4 mm
(100 mesh and 0.25 in).
The process waters used during the coal separation stage generally are maintained between pH 6.0
and 7.5. Waters with lower pH inhibit the flotation of both coal and ash-forming substances. As pH
increases, the percentage of floating coal maximizes, but the percentage of floating refuse also
increases. The pH of process waters may be elevated with lime. Reagents may be added to control
the percentage of suspended fines (Zimmerman, 1968).
Make-up water fo cleaning plant operation ideally has a neutral pH, low conductivity, and low
bicarbonate content. The water preferably is free from contamination by sewage, organic material,
and acid mine drainage. Other dissolved constituents also should occur in low concentrations (Exhibit
3-36).
Product dewatering (Stage 4 of Exhibit 3-24) includes the use of mechanical devises, thermal dryers,
and agglomeration processes to reduce the moisture contents of processed coal and refuse
(McCandless and Shaver, 1978; Exhibit 3-37). The moisture contents of products dried by typical
processes appear in Exhibit 3-38. Mechanical processes are of two general types:
• In-stream process that do not produce a final product (hydrocyclones and static thickeners).
These processes remove approximately 30 to 60 percent of the moisture in feed material.
l’hickeners and cyclones usually are placed on line with other drying devices that reduce the
moisture contents further.
• End-of-stream processes that produce a final product (screens, centrifuges, spiral classifiers,
and filters).
3-143 September 1994
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Overview of Mining and Reneficiation
EIA Guidelines for Mining
Exhibit 3-33. Typical Circuit for Jig Table Coal Cleaning
fl) TO EATER CLARIFICATION
A POINTS OF ENISSION
3-144
September 1994
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EIA Guidelines for Mining
Overview of Mining and Beneficiation
Several of the process that are used for Stage 3 separation also are used for Stage 4 dewatering,
including hydrocyclones, centrifuges, and spiral classifiers. These processes are described above.
Static thickeners, screens, and filters may also have a separation function, but are more appropriately
described as dewatering processes.
Static thickeners generally are used in conjunction with flocculants to settle the fines from a
static pool of preparation plant refuse water (blackwater). A typical thickener feed contains
1 to 5 percent solids; thickened underfiow contains 20 to 35 percent solids. Common
flocculants include inorganic electrolytes such as lime and alum, and organic polymers such
as starches and polyacrylamide (Aplan and Hogg, 1977). Sludge from the thickener
underflow may be dewatered further by mechanical devices, thermal drying, or
agglomeration. A typical thickener vessel appears in Exhibit 3-39.
• Screens serve dual functions of dewatering and sizing. The mode of operation (fixed or
vibrating), mesh size, and bed depth of feed material are chosen on the basis of raw feed
characteristics (gradation and moisture content), feed rates, and the desired efficiency of
sizing and dewatering. The sieve bend, a typical dewatering and sizing screen, appears in
Exhibit 3-40 (Nunenkamp, 1976).
• Filters are of two types—pressure and vacuum. Both types generally accept a feed with 30
percent solids at 27 dry MT (30 T) per hour. Pressure filters produce a cake with 20 to 23
percent moisture. Product cake from vacuum filters may contain 34 to 40 percent moisture.
The moisture removal efficiency of the pressure filter is offset by its higher capital cost
relative to vacuum filter systems. A typical vacuum filter appears in Exhibit 3-41
(Nunenkamp, 1976).
Exhibit 3-34. Typical Air Table for Pneumatic Coal Cleaning
BIN
UNIT
REDUCER
DUCT
CLEAN COAL
iTcn
3-145
September 1994
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
PRDI*RY
A D4ISSI N POINTS
STACK OIISSIOIG
VENTTO
ATMOSPHERE
RUBBER
_________ SLURRY TO
b-
A
SCREEN
3-146
September 1994
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EIA Guidelines br Mining Overview of Mining and Beneficiation
Parameter
C oflCefltratlon
•
pH
7.8
Hardness as
CaCO 3
,
190
Ca
.
64
.
•Mg
•
7.5
Na
19
,K
‘
4.7
•
NI ! 4
0.4
ço 3
0
.
HCO 3
157
•
•
CI
S
35
SO 4
•
49
NO 3
15
NO 2
Trace
P0 4
0.5
Si0 2
•
7.2
Most thermal dryers. at coal cleaning fa’cilities use coal as the combustion feed stock. Thermal dryers
include two general types.
• Direct heat dryers use the produc& of combustion to dry the coal. The direct heat concept
is used in most U.S. thermal drying facilities (Nunenkamp, 1976).
• Indirect heat dryers circulate the products of combustion around the drying coal, avoiding
direct contact with the coal.’
Direct heat thermal dryers fall into six categories (McCandless and Shaver, 1978):
• Fluidized bed dryers use a constriction plate fitted to a housing that forces the drying air to
pass uniformly through the plate (Exhibit 3-42). Feed coal enters the plate while hot air is
lifted through the plate by a fan. The air currents thus produced cause the feed coal to float
above the plate and flow toward the discharge point. Fine material is scrubbed from the
exhaust gases, and the resultant residue reports to a thickening and dewatering step.
3-147 September 1994
ExhibIt 3-36. Desirable Chemical Characteristics of Make-Up Water for
Coal Cleaning Processes
‘pH expressed in standard units.
Source: Lucas, J. Richard, David R. Maneval, and W. E. Formean. 1968. Plant Waste Contaminants.
In: Leonard, Joseph W; and David R. Mitchell. 1968. Coal Preparation. Amer can Institute of
• Mining, Metallurgical, and Petroleum Engineers, Inc., New York, New York, 926 p.
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
3-148
September 1994
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EIA Guidelines for Mining Overview of Mining and Beneficiation
Type of
Equlp t or o ess : .
Moisture Content of
. D cha e oduct (%)
Dewatering screens
Centrifuges
Filters
Hydraulic cyclones
Static thickeners .
Thermal dryers
Oil agglomeration
8 to 20
10 to 20
20 to 50
40 to 60
60 to 70
6 to 7.5
8 to 12
• Multilouver dryers comprise two concentric, revolving cylindrical shells, each fitted with
louvers that support the bed of feed coal and direct it toward the discharge point.
Multilouver dryers can handle large volumes of wet material that require a relatively short
drying time to minimize the potential for in-dryer combustion of the feed product.
• Rotary dryers consist of a solid outer cylinder and an inner shell of overlapping louvers that
support and cascade the drying coal toward the discharge end. Drying action can be direct
(using the products of combustion), or indirect (using an intermediate fluid for heat transfer
between the shells).
• Screen dryers apply gas pressure from combustion to squeeze the moisture mechanically
from the feed coal through the supporting screens. A lower percentage of coal fines
(relative to other drying processes) thus may be lifted from the bed. Coal is exposed to
drying heat for approximately 50 seconds.
• Suspension or flash dryers continuously introduce feed coal into a column of high
temperature gases (Exhibit 3-43). Surface moisture is dried almost instantaneously (flash
dried). Coal is exposed to the drying gases for approximately 5 seconds.
• Turbo-dryers contain an inert nitrogen atmosphere (less than 3 percent oxygen) that
prevents the explosion or ignition of coal fines in the sealed drying compartment. Wet coal
enters a stack of rotating circular trays that successively feed the coal to lower trays using
stationary wiper blades.
Indirect heat dryers use heat transfer agents (including oil, water, or steam) that do not come into
contact with the feed coal. Drying coal is circulated through the heating chamber on covered
conveyors that may be equipped with helical (worm) screws, fines, paddles, or discs. The drying
fluid circulates around the conveyor and through the hollow screws.
3-149 September 1994
Exhibit 3-38. Typical Moisture Contents of Dried Product from Selected Drying
Operations in Coal Cle ining Facilities
Source: McCandless, Lee C., and Robert B. Shaver. 1978. Assessment of Coal Cleaning Technology:
First Annual Report. EPA, Office of Research and Development, Washington, D.C., EPA-60017-78-
150, 153 p.
-------
Uvervlew 0 Mining anci isenencianon
r1A uwaeunes br Mining
Coal storage and shipment operations (Stage 5 of Exhibit 3-24) are discussed more thoroughly in
subsequent sections of this document. The degree of sophistication in individual storage and loading
systems reflects in part the volume of coal being processed, stored, and shipped, as well as the kinds
of coal transportation services available. Some systems can load a moving train directly from
overhead storage. Other systems may be intermittent, using bucket loaders and dump trucks to feed
hoppers that load trains either directly or via conveyors.
3.5.2.2 Process Flow Sheet for Typical Operations
The complete coal cleaning plant utilizes a series of unit processes to prepare ROM coal for storage
and shipment. These processes must be mutually compatible for proper operation of the plant. Rates
and sizes of feed for one unit process should compliment the capabilities of other in-line processes.
Process water generally is recycled, especially in operations that use heavy media such as magnetite
3-150
September 1994
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EIA Guidelines for Mining
Overview of Mining and Beneficiation
Exhibit 3-40. Schematic Profile of a Sieve Bend Used for Coal Sizing and Dewatering
Source: Nunenkamp , David C., 1976.
FEED
S EEN SJRFA E
MOiSTURE $
DEWATERED
PROOUCT
3-15 1
September 1994
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Overview of Mining and Beneficiaton
EIA Guidelines for Mining
Exhibit 3-41. Proffle View of a Coal Vacuum Filter
Source: Nunenkamp, David C., 1976.
DISC$A GE
4
3LU Y
INDIVIDUAL.
TROUGH
I
3-152
September 1994
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Source: Nunenkamp, David C., 1976.
Exhibit 3-42. Thermal Dryer and Exhaust Scnibber
0
E.
I.
I
UtAH DIV. COOL PIODUCT
OISCHAIGI to
SLUOCt tAH 01 POND
0
I
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
Exhibit 3-43. Typical flash Dryer
C-E RAYMOND FLASH DRYING
ALTERNATE ARRANGEMENT
FOR VERY FINE WET COAL
DRY COAL DISCHARGE
FROM AIR LOCK
AUTOMATIC
DRY DIVIDER
DRY RETURN
WET FEED
MIXER
NG COLUMN
CONVEYOR
CONVEYOR
BIN
FEEDER
FLAP VALVE
AIR DAMPER
‘ ALTERNA VENT’..
I
—
$ I
• I
WET SCRUBBER I —*
(IF REQUIRED) • I
• I
I I
SYSTEM FOR COAL
RELIEF VENT
STARTING
3-154
September 1994
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EIA Guidelines for Mining Overview of Mining and Beneficiátion
slurries for the separation of product from refus ., Evaporation and consumptive water use may
require the introduction of make-up water to the process cycle.
A complete process flow sheet can be broken into three parts:
• Coarse stage (Exhibit 3-44)
• Fine stage (Exhibit .3-45)
• Sludge stage (Exhibit 346).
The coarse stage feed fme co J and refuse to the fme stage. Coal slime, which includes fine coal and
refuse, is fed to the sludge stage. Each stage produces characteristic blackwater and refuse. Process
waters from the fme coal and sludge processing stages generally contain higher proportions of fines,
especially clay-size particles, than coarse stage process waters. A series of thickeners, cyclones,
screens, filters, and dryers may be used to recover a maximum percentage of solids from the recycled
process waters. S
3455 5 5 September 1994
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Overview of Mining and Beneficiation
EIA Guidelines for Mining
Exhibit 3-44. Coal Cleaning Plant Flow Sheet for Coarse Stage Separation and
Dewatering
4I ó t I
RATION’
jw.• 35 )
PREPARATION
‘±! S..’_ )±.
‘I
c_ R jte of Fm. Coal
s -Routs of Coors. Cool
•... -Rout. of Rsfuu
- Pouts of P$sovy Media Slurry
F ’ #4 Optional Re-S ost’Muiii
—— -Routs of Sink-F!o I+MidIø
*ss.sus.+ -Rout. of Moç etit.
-Rouls of Dirty Process Water
uIuu.r_.Irl. .. of Cl.oA Process Water
- %ute of Frssh MoM- ç Waler
Source: EPA. 1976.
3-156
September 1994
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ELA Guidelines for Mining
Overview of Mining and Benêficiation
LEGEND
——-- uRa.I. of S *•FbooI+Msós
—..•R ut• c i Mo iistte Optionol Route of Fins Cool
-Rouls of Dirty Procu& a ..... +-R.uis c i
Raa$e i i Cissi ‘e_ i Wuix R JlS c i ‘!Y MS S tF’y
- R Is c i FrssI
Source: EPA, 1976.
Exhibit 3-45. Coal Cleaning Plant Flow Sheet for Fine Stage Separation and Dewatering
Cool Fu Frim D.s1w, nq Scn
— •• (SeeFi irs 34)
To Desliming Screen.
(Sis Fiquri 34 )
3-157
Septt’nber 199t
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Overview of Mining and Beneficiation
ELk Guidelines for Mining
Exhibit 3-46. Coal Cleaning Plant Flow Sheet for Sludge (Slime) Separation and
Dewatering
LEGEND
-Route of Dirty Procm Water — acS .Ppflóno) Route *1 Cool Slim.
nsaa. - RoUte of Clean Protsa WaS nnnnss- Route of C*S Clean Cool
t - Route of Coal Slime s ts s,-e-RoWe of Coked Refuse
•... . -Route of Refuse
To
Clean
Cool
Storage
To
Ref use
Disposal
3 -158
September 1994
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EIA Guidelines for Mining Environmental Issues
4. ENVIRONMENTAL ISSUES
This section describes the environmental impacts associated with new source mining operations. The
mining industry and its potential environmental impacts are unusual in a number of ways, of which
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 those manifested years.or decades after mining ends and can intensify over time.
Finally, the nature and extent of impacts from mining operations, perhaps more than any other
industrial category, 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 full understanding of baseline conditions and careful planning to avoidl
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 (unique impacts, often delayed, that depend on site-specific
factors) make initial design and planning even more crucial. This in turn makes any assessment of
potential iinpacts both immediate and long-term, reliant on detailed information on site-specific
conditions, and on the design and operation of the facility. Site-specific information is generally
incomplete at the time of permitting. Design and operation plans, including operations 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 subsections are organized according to the major environmental issues that are raised
by mining operations. These include:
• Acid rock drainage
,• Cyanide
• Structural stability of tailings impoundments
• Natural resources and land uses
• Sedimentationlerosion
• Metals and dissolved pollutants
• Airquality
• Subsidence
• Methane releases from coal mining and preparation.
I_i September 1994
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Environmental Issues EIA Guidelines for Mining
The. discussion of each of these subjects includes a description of the topic and of the types of
information that are necessary to determine potential impacts.
4.1 Acm ROCK DRAINAGE
The formation of acid drainage and the contaminants associated with it has been described as the
largest environmental problem facing the U.S. mining industry (U.S. Forest Service, 1993; Ferguson
and Erickson, 1988; Lapakko, 1993b). Commonly referred to as acid rock drainage (ARD) or acid
mine drainage (AMD), acid drainage from mine waste rock, tailings, and mine structures such as pits
and underground workings is primarily a function of the mineralogy of the rock material and the
availability of water and oxygen. While acid may be neutralized by the receiving water, dissolved
metals can remain in solution. Dissolved metals inacid drainage may include the full suite of heavy’
metals, including lead, copper, silver, manganese, cadmium, iron, and zinc. Elevated concentrations
of metals in surface water and groundwater can preclude their use as drinking water supplies.
Further, low pH levels and high metals concentrations can have acute and chronic effects on aquatic
life/biota. .
Acid drainage from coal and mineral mining operations is a difficult and costly problem. In the
eastern United States, more than 7,000 kilometers of streams are affected by acid drainage from coal
mines (Kim et al., 1982). Similar impacts are observed in coal mining areas of the Midwest. As one
of many examples of historic coal mining areas, 2,400 acres of abandoned surface mine land
northwest of Montrose, Missouri, are impacted by acid mine drainage. More than half of the 100
lakes in the areas have a pH less than 4 and there are 1,200 acres of “barren, acidic spoil.” Overland
runoff from mine spoil has pH values between 2.9 and 3.5 (Blevins, 1990). In the western United
States, the Forest Service estimates that between 20,000 and 50,000 mines are currently generating
acid on Forest Service lands, and that drainage from these mines is impacting between 8,000 and
16,000 kilometers of streams (US. Forest Service, 1993).
Acid generation prediction tests are increasingly relied upon to assess the long-term potential of a
material or waste to generate acid. Because mineralogy and other factors affecting the potential for
ARD formation are highly variable from site to site, predicting the potential for ARD is currently
difficult, costly, and of questionable reliability. Further, concern has developed because of the lag
time at existing mines between waste emplacement and observation of an acid drainage problem
(University of California, Berkeley, 1988). With acid generation, there is no general method to
predict its !ong-term duration (in some cases necessitating perpetual care). The issue of long-term or
perpetual care of acid drainage at historic mines and some active mines has focused attention on the
need for improving prediction methods and for early assessment of the potential during the
exploratory phase of mine development. The U.S. Forest Service sees the absence of acid prediction
technology, especially in the context of new mining ventures, as a major problem facing the future of
metal mining in the western United States (U.S. Forest Service, 1993).
4-2 September 1994
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EIA Guidelines for Mining Environmental Issues
The problems presented by acid drainage are encountered worldwide, and there is a growing body of
literature that documents examinations of all aspects of the phenomenon, from the genesis of acid
drainage to prediction of the timing of its occurrence to prevention. The most recent advances in the
field are compiled in the proceedings Of the International Land Reclamation and Mine Drainage
Conference and Third International Conference on the Abatement of Mine Drainage, which was held
in April 1994 (U.S. Bureau of Mines 1994).
The remainder of this section addresses the major topics related to understanding how acid rock
drainage is geneEated, how to predict it during mine planning, how to detect it during operations, and
approaches to mitigating its impacts.
4.1.1 NATURE OF AcID RocK DRAINAGE
4.1.1.1 Acid Rock Drainage/Oxidation of Metal Sulfides
Acid is generated at mine sites when metal sulfide minerals are oxidized. Metal sulfide minerals are
common constituents in the host rock associated with metal mining activity. Prior to mining,
oxidation of these minerals and the formation of sulfuric acid is a function of natural weathering
processes. The oxidation of undisturbed ore bodies followed by release of acid and mobilization of
metals is slow. Natural discharge from such deposits poses little threat to receiving aquatic
ecosystems except in rare instances. Mining and beneficiation operations greatly increase the rate of
these same chemical reactions by removing large volumes of sulfide rock material and exposing
increased surface area to air and water. Materials/wastes that have the potential to generate acid as a
result of metal mining activity include mined material such as spent ore from heap and dump leach
operations, tailings, and waste rock units, including overburden material. Equally or more important
at some mines are the pit walls in the case of surface mining operations, and the underground
workings associated with underground mines.
The oxidation of sulfide minerals consists of several reactions. Each sulfide mineral has a different
oxidation rate. For example, marcasite and framboidal pyrite will oxidize quickly while crystalline
•pyrite will oxidize slowly. For discussion purposes, the oxidation of pyrite (FeS 2 ) will be examined
(Manahan, 1991):
2FeS 2 (s) + 2H 2 0 + 702 —> 4H 4 + 4S0 4 2 + 2Fe 2
In this step, S is oxidized to form hydrogen ions and sulfate, the dissociation products of sulfuric
acid in solution. Soluble Fe 2 is also free to react further. Oxidation of the ferrous ion to ferric ion
occurs more slowly at lower pH values:
4Fe 24 + 02 + 4W —> 4Fe 3 + 2H 2 O
43 September 1994
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Environmental Issues EIA Guidelines for Mining
At pH levels between 3.5 and 4.5, iron oxidation is catalyzed by a variety of Metallogenium, a
naturally occurring filamentous bacterium. Below a pH of 3.5 the same reaction is catalyzed by the
naturally occurring iron bacterium Thiobacillusferrooxidans. If the ferric ion is formed in coiitact
with pyrite the following reaction can occur, dissolving the pyrite:
2FeS 2 (s) + 14Fe 3 + 8H 2 0 —> 15Fe 2 + 2S0 4 2 + 16 W 4
This reaction generates more acid. The dissolution of pyrite by ferric iron (Fe 3 ), in conjunction with
the oxidation of the ferrous ion constitutes a cycle of dissolution of pyrite. Ferric iron precipitates as
hydrated iron oxide as indicated in the following reaction:
Fe 34 + 3H 2 0 <-> Fe(OH) 3 (s) + 3W
Fe(OH) 3 precipitates and is identifiable as the deposit of amorphous, yellow, orange, or red deposit
on stream bottoms (“yellow boy”).
4.1.1.2 Source of Acid and Contributing Factors
The potential for a mine or its associated waste to generate acid and release contaminants is dependent
on many factors and is site-specific. Ferguson and Erickson (1988) identified primary, secondary,
and tertiary factors that control acid drainage. These factors provide a convenient structure for
organizing the discussion of acid formation in the mining environment. Primary factors involve
production of the acid, such as the oxidation reactions. Secondary factors act to control the products
of the oxidation reaction, such as reactions with other jninerals that consume acid. Secondary factors
may either neutralize acid or react with other minerals, thereby releasing contaminants. Tertiary
factors refer to the physical aspects of the structure or waste management unit (e.g., pit walls, waste
rock piles, or tailings impoundments) that influence the oxidation reaction, migration of the acid, and
consumption. Other downstream factors change the character of the drainage by chemical reaction or
dilution.
Primary factors of acid geneiation include sulfide minerals, water, oxygen, ferric iron, bacteria to
catalyze the oxidation reaction, and generated heat. Some sulfide minerals are more easily oxidized
(e.g., framboidal pyrite, marcasite, and pyrrhotite) and hence, may have a greater impact on timing
and magnitude during acid prediction analysis compared to other metal sulfides. Also important is the
physical occurrence of the sulfide mineral. Well crystallized (euhedral) minerals will have smaller
exposed surface areas than those that are disseminated.
Both water and oxygen are necessary to generate acid drainage. Water serves as both a reactant and a
medium for bacteria in the oxidation process. Water also transports the oxidation products. A ready
supply of atmospheric oxygen is required to drive the oxidation reaction. Oxygen is particularly
September 1994
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EIA Guidelines for Mining Enviromnental Issues
important to maintain the rapid bacterially catalyzed oxidation at pH values below 3.5. Oxidation of
sulfides is significantly reduced when the concentration of oxygen in the pore spaces of mining waste
units is less than 1 or 2 percent. Different bacteria are better suited to different pH levels and other
edaphic factors (edaphic factors pertain to the chemical and physical characteristics of the soil and
water environments). The type of bacteria andtheir population sizes change as their growth
conditions are optimized (Ferguson and Erickson, 1988).
The oxidation reaction is exothermic, with the potential to generate a large amount of heat, and
therefore thermal gradients form within the waste unit. Heat from the reaction is dissipated by
thermal conduction or convection. Research by Lu and Zhang (undated) on waste rock using stability
analysis indicates that convective flow can occur because of the high porosity of the material.
Convection cells formed in waste rock would draw in atmospheric air and continue to drive the
oxidation reaction. Convection gas flow due to oxidation of sulfide minerals depends on the
maximum temperature in the waste rock. The maximum temperature depends on ambient
atmospheric temperature, strength of the heat source, and the nature of the upper boundary. If the
sulfide waste is concentrated in one area, as is the case with encapsulation, the heat source may be
very strong. Lower ambient air temperatures improve conditions for convective gas flow. If the
upper boundary is covered, convection is less likely.
Secondary factors act to either neutralize the acid produced by oxidation of sulfides or to change the
effluent character by adding metals ions mobilized by residual acid. Neutralization of acid by the
alkalinity released when acid reacts with carbonate minerals is an important means of moderating acid
production. The most common neutralizing minerals are calcite and dolomite. Products from the
oxidation reaction (hydrogen ions, metal ions, etc.) may also react with other non-neutralizing
constituents. Possible reactions include ion exchange on clay particles, gypsum precipitation, and
dissolution of other minerals. Dissolution of other minerals contributes to the contaminant load in the
acid drainage. Examples of metals occurring in the dissolved form include aluminum, manganese,
copper, lead, zinc, and others (Ferguson and Erickson, 1988).
Some of the tertiary factors affecting acid drainage are the physical characteristics of the waste or
structure, how acid-generating and acid-neutralizing wastes are placed in the waste unit, and the
hydrologic regime in the vicinity. The physical nature of the waste, such as particle size,
permeability, and physical weathering characteristics, is important to the acid generation potential.
Particle size is a fundamental concern since it affects the surface area exposed to weathering and
oxidation. Surface area is inversely proportional to particle size. Very coarse grain material, as is
found in waste rock dumps, exposes less surface area but may allow air and water to penetrate deeper
into the unit, exposing more material to oxidation and ultimately producing more acid. Air
circulation in coarse material is aided by wind, changes in barometric pressure, and possibly
convective gas flow caused by heat generated by the oxidation reaction. In contrast, fine-grain
4.5 September 1994
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Environmental Issues EIA Guidelines for Mining
material (e.g., tailings) may retard air and very fme material may limit water flow; however, finer
grains expose more surface area to oxidation. The relationships between particle size, surface area,
and oxidation play a prominent rote in acid prediction methods and in mining waste management
units. As waste material weathers with time, particle size is reduced, exposing more surface area and
changing physical characteristics of the waste unit. Though difficult to weigh, each of these factors
influences the potential for acid generation and are therefore important considerations for long term
waste management (Ferguson and Erickson, 1988; Lu and Zhang, undated).
The hydrology of the area surrounding mine workings and waste units is important in the analysis of
acid generation potential. When acid generating material occurs below the water table, the slow
diffusion of oxygen in water retards acid production. This is reflected in the portion of pits or
underground workings located below the water table. Where mine walls and underground workings
extend above the water table, the flow of water and oxygen in joints may be a source of acid. A
similar relationship is evident with tailings, which are typically fine grained and disposed of
subaqueously; the slow diffusion of oxygen inhibits formation of acid. However, since tailings are
typically placed in either raised or valley impoundments, they are likely to remain saturated for only a
limited period of time during mine operation. Following mine closure, the free water surface in the
impoundment may be drawn down substantially, favoring ARD conditions. (Also, as tailings dry
over time, previously impermeable layers of fine material may develop cracks or fissures, providing a
conduit for air and water.)
The spatial distribution of mining wastes in units, or waste placement, affects acid generation
potential. For example, the distribution of acid generating wastes with neutralizing wastes may be
controlled by the stacking sequence. Calcareous material may be mixed with or placed above sulfidic
wastes to buffer acid production or provide alkalinity to infiltrating solution prior to contact with acid
generating wastes. An alternative to layering or mixing is encapsulation. This technique attempts to
isolate acid generating wastes from oxygen and water, thereby reducing its potential to produce acid.
Both these techniques are currently being used in waste rock dumps. It is unclear if they are effective
over the long-term, since highly acidic material may overwhelm the buffering capacity of calcareous
material or other alkaline sources.
Wetting and drying cycles in any of the mine workings or other waste management units will affect
the character of any acid drainage produced. Frequent wetting will tend to generate a more constant
volume of acid and other contaminants as water moves through and flushes oxidation products out of
the system. The build-up of contaminants in the system is proportional to the length of time between
wetting cycles (Ferguson and Erickson, 1988; Doepker, 1993). As the length of the dry cycle
increases, oxidation products will tend to accumulate in the system. A high magnitude wetting event
will then flush accumulated contaminants out of the system. This relationship is typical of the
September 1994
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EIA Guidelines for Mining Environmental Issues
increase in contaminant load observed following heavy precipitation for those areas having a wet
season.
4.1.2 AcID GENERATION PREDICTION
The objectives of predictive testing are to (1) determine if a discrete volume of mining waste will
generate acid, and (2) predict the quality of the drainage based on the rate of acid formation measured
(California Mining Association, 1991). There are two important points that must be considered when
evaluating the acid generation potential of a rock material. The first is how to collect samples from
the field for use in analytical testing. The second is which analytic test method should be used. Both
points have a profound impact on the reliability of analytical tests. Results from any analytical test
are only as reliable as the samples used for the test. Once the sampling strategy is selected, an
appropriate analytical method or methods can be selected. Methods used to predict the acid
generation potential are classified as either static or kinetic. Factors affecting the selection of
sampling regime and analytical method include an existing knowledge of the geology, costs, and
length of time available to conduct the test. This section will examine sample methodology and
analytic tests used to predict acid generation potential.
The following list of components describes the solid phase composition and reaction environment of
sulfide minerals. Potential contamnants are included to indicate their importance in the scope of acid
generation. These components should .be kept in mind while evaluating information on acid
generation potential.
Components affecting the total capacity to generate acid are characterized by:
• Amount of acid generating (sulfide) minerals present (assuming total reaction of
sulfide minerals),
• Amount of acid neutralizing minerals present
• Amount and type of potential contaminants present.
Components affecting the rate of acid generation include:
• Type of sulfide mineral ‘present (including crystal form)
• Type of carbonate mineral present (and other neutralizing minerals, as appropriate)
• Mineral surface area available for reaction
- Occurrence of the mineral grains in the waste (i.e., included, liberated)
- Particle size of the waste
4.7 , September 1994
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Environmental Issues EIA Guidelines for Mining
• Available water and oxygen
• Bacteria.
Analytical tests used to assess a material’s acid generation potential are either static or kinetic in
nature. A static test determines both the total acid-generating and total acid-neutralizing potential of a
sample. The capacity of the sample to generate acidic drainage is calculated as either the difference
of the values or as a ratio of the values. These tests are not intended to predict the rate of acid
generation, only the potential to produce acid. Static tests can be conducted quickly and are
inexpensive compared to kinetic tests. Kinetic tests are intended to mimic the processes found in the
waste unit environment, usually at an accelerated rate. These tests require more time and are
considerably more expensive than static tests. Data from the tests are used to classify wastes
according to their acid generating potential. This information can be collected and evaluated during
the economic analysis of mines in their exploratory phases. Based on this information, management
decisions can be made with respect to specific mitigation practices.
Efforts by both the mining industry and State regulatory agencies to develop the best protocols for
sampling and/or analytical methods to predict acid generation potential have demonstrated that site-
specific conditions (e.g., climate and geology) dictate a case-by-case approach when evaluating acid
potential. This is complicated by the fact that a variety of research efforts on different methods by
the Bureau of Mines, EPA, and the Canadian Mine Environment Neutral Drainage (MEND), as well
as those used by mining companies and their consultants, make comparison of data difficult. Several
researchers have conducted comparative evaluations of predictive tests (Lapakko. 1992; Bradham and
Caruccio, 1990; Coastech, 1989). Lapakko, of the Minnesota Department of Natural Resources, has
conducted comparative evaluations of static and kinetic test methods using a range of rock types.
Bradham and Caruccio conducted a comparative study on tailings.
When evaluating the acid generation potential of a waste, a phased testing plan selects samples
appropriate for the detail needed (California Mining Association, 1991). This approach allows
investment in acid prediction testing to be commensurate with a deposit’s economic potential and
saves time and expense associated with unnecessary tests. Sampling and testing should be an iterative
process, collecting, testing, and evaluating a small amount of information to establish the acid
generation potential. Based on the preliminary findings, subsequent sampling and testing can be
selected to refme the information as needed.
The typical steps in predicting the acid-forming potential of a waste, as compiled from summary
documents on the subject, are listed below (California Mining Association, 1991; British Columbia
AMD Task Force, 1989):
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EIA Guidelines for Mining Environmental Issues
1. Define the geologic (or lithologic) units that will be. encountered during mining. Describe
the geology and mineralogy of these units in detail.
2. Develop a sampling plan based on understanding of geology (rock mass, etc.). Collect
samples to represent ranges of compositional variation within a rock unit (see Lapakko,
1988, 1990a).
3. Select static or kinetic tests and evaluate potential for acid formation.
4. Evaluate sampling criteria and conduct additional kinetic tests as req iired.
5. Develop a model as appropriate.
6. Based on fmdings, classify geologic (lithologic) units as acid, non-acid forming, or
uncertain. (Note: the potential to produce acid may vary within a given geologic unit.)
4.1.2.1 Sampling
Selection of samples has important implications for subsequent acid prediction. The purpose of
testing rock material is to allow classification and planning for waste disposal. based on the predicted
drainage quality from that material. Samples must be selected to characterize both the type and
volume of rock materials and also account for the variability of materials that will be exposed during
mining. When to collect samples for testing is an equally important consideration.
Researchers agree that sampling and testing should be concurrent with resource evaluation and mine
planning (Lapakko, 1990a; British Columbia AMD Task Force, 1989). Sampling techniques used to
evaluate recoverablemineral resources (assay samples) are similar to those required for prediction of
acid generation potential. Active mining operations for which predictive tests were not conducted in
advance of mining lack the advantage of front end planning, but can still use sampling and other site-
specific information (e.g., geology and mineralogy) to establish the acid generating potential.
The pressure is increasing for new operations or those in the exploratory phase to accurately predict
future drainage water quality. By compar son, the acid drainage potential at old mines may be well
established. Examples of information needed from existing operations are the quantity of existing
acid products, the potential and stage of acid generation in each of the waste units, and the acid
forming potential of future wastes to be generated. Broughton and Robertson recommend that the
first two stages of an acid prediction analysis for either new or existing mines are (1) to review the
geology and mineralogy and (2) classify the rock and collect samples (Robertson and Broughton,
undated; Broughton and Robertson, 1992).
Sample collection for prediction tests for both old and new mines should consider both geologic and
environmental factors. Geologic factors for sample selection are primarily a good understanding of
the local geology. If available, this may include information from mines, core logs, or other sources
September 1994
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Environmental Issues EIA Guidelines for Mining
in the immediate area. This information is important to both the sampling program and application of
test results. Environmental factors include consideration of the potential environmental contaminants
in the rock and climatic variables. A quality assurance/quality control program should be developed
and coordinated with the mine plan for sample collection and acid generation testing.
There are many opinions concerning the number of samples to be collected in a fixed-frequency
sampling program. One mining consulting firm recommends about 8 - 12 samples of each significant
rock type or a minimum of one sample for each one million tons (Schafer, 1993). In this case a
significant rock type represents one or two percent of the total mine rock volume. A representative
of the U.S. Forest Service suggests that one sample (about 1,500 grams) be collected per 20,000 tons
of waste rock, or about 50 samples for each one million tons (U.S. Forest Service, 1992). These
samples would be collected by compositing cuttings from individual drill holes made prior to blasting.
The British Columbia AMD Task Force recommends a minimum number of samples based on the
mass of the geologic unit. Their recommended minimum sample number is 25 for a one million ton
geologic unit, or one sample for every 40,000 tons. Using the British Columbia method, as waste
volume increases, the proportional number of samples decreases. For example, for a unit of 10
million tons, the minimum sample number is 80, or one sample for every 125,000 tons (British
Columbia AMD Task Force, 1989).
There are reservations to prescribing a number of samples for collection per volume of material.
This is particularly true for existing mines when collecting samples from waste rock dumps for acid
generation potential tests. Waste rock dumps are usually constructed by end-dumping rock from
trucks, creating heterogeneous deposits that are very difficult to sample with confidence. Tailings are
comparatively more uniform due to milling and depositional methods used, and it is easier to charac-
terize their variability. Fixed-frequency sampling does not rely on the use of best judgment on the
part of the sample collector (typically a mining company). It also does not provide the statistical basis
to account for variability among samples. Therefore, the actual numbers of samples to be collected
should be determined on a site-specific basis.
Factors to consider in a sampling program for existing or planned mines include the method of
sample collection, length of time samples are to be (or have been) stored, and the sample storage
environment. Each of these can affect the physical and chemical characteristics of a sample. Samples
collected from cores exposed to the environment may be physically and/or chemically altered. If
samples are collected from a drill core, contamination may be a problem if a lubricant was used. At
existing mines, tailings samples should be taken over a variety of depths to determine, if oxidation of
sulfide minerals is occurring. The influence of lime addition during milling may maintain alkaline
conditions. Collecting samples of waste rock is difficult because of the variability inherent in these
waste units. Drilling is considered to be the preferred method for collecting samples from waste rock
dumps (Ferguson and Morn, 1991).
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EIA Guidelines for Mining Environmental Issues
Since individual samples will be used to test and classify larger volumes of waste, it is important to
consider how represe.ntitive samples are to be collected. Compositing is a common practice used to
sample large volumes of material. Typically, composite samples are collected from drill hole cuttings
on benches prior to blasting. Holever, compositing merges information about the variation of
sample that would be identified if more sampleè were collected and analyzed. Therefore, information
about sample variability is lost (British Columbia AMD Task Force, 1990; Robertson and Broughton,
indited). Composite sampliij of tailings may be useful as a “firsf look” for characterizing tailings;
compositing with stratification by lithology and alteration can help to avoid the problems of simple
composite samples (Schafer, 1993).
To be most effective, sampling programs for acid generation prediction should not be confined to
initial prediction during mine permitting. The uncertainties associated with sampling, analytical
techniques, and prediction methods all serve to make continued sampling and prediction appropriate
throughout the life of a mine This can allow early identification of changed conditions that can lead
to problems, and thus allow early intervention to prevent major impacts.
4.1.2.2 Static Tests
Static tests predict acid drainage by comparing the waste sample’s maximum acid production potential
(AP) with its maximum neutraliza tion potential (NP): The AP is determined by multiplying the
percent of total sulfur or sulfide sulfur (dependinj on the test) in. the sample by a conversion factor
(AP = 31.25 x % S). NP ii a measure of the carbonate material available to neutralize acid. The
value for NP is determined either by adding acid to a sample and back-titrating to determine the
amount of acid consumed or by direct acid titration of the sample (the endpoint pH is dependent on
the test method). The net neutralization potential (NNP), or acid/base account (ABA) is determined
by subtracting the AP from the NP (NNP = NP - AP). A ratio of NP to AP is also used. An 1 1NP
of 0 is equivalent to an NP/AP ratio of 1 (Ferguson and Morn, 1991). Units for static test results
(AP, NP, and NNP) are typically expressed in metric tons of calcium carbonate (CaCO 3 ) per 1,000
metric tons of rock.
If the difference between NP and AP (i.e., the NNP) is negative then the potential exists for the waste
to form acid. if it is positive then there mAy be lower risk. Prediction of the acid potential when the
NNP is near zero (between -20 and 20) ii especially difficult (Brodie et al., 1991). Similar to”Brodie,
Smith and Barton-Bridges also suggest an NNP criteria of greater than 20 where the risk of acid
generation is low (Smith and Barton-Bridges, 1991). Other studies conducted by the State of
Pennsylvania on surface coal mine drainage suggest that sites with an NNP of greater than 10 exhibit
alkaline drainage, with a gray zone ranging from I to 10 (Brady et al., 1994). Finally, the State of
Tennessee has encountered acid generation (along with elevated iron and manganese levels) in
backfilled portions of six area coal mines, where positive NNPs were initially observed (some
samples had ,NPPs between 5 and 20, but averages were generally greater than 20). The
4- 11 September 1994
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Environmental Issues E IA Guidelines for Mining
inconsistency between test results and actual conditions has been attributed to carbonate materials with
slow dissolution rates, heterogeneity between carbonate and sulfidic materials, and the availability of
large volumes of well-oxygenated water (that ultimately recharges surface water).
If ratios are used, Brodié indicated that when the ratio of a sample’s neutralization potential to acid
production potential is greater than 3:1, experience indicates that there is lower risk for acid drainage
to develop. Those samples with a ratio of 1:1 or less are more likely to generate acid. Brodie refers
to ratios -between 3:1 and 1:1 as the zone of uncertainty, where additional kinetic testing is usually
recommended and acid mitigation measures may be required (Brodie et al., 1991). Data from coal
mines in the eastern United State,s indicate that an NP/AP of greater than 2.4 is required to ensure
acid will not be released (Cravotta et al., 1990). Finally, data from a single Canadian mine show that
an NP/AP of up to 4.0 must be maintained to provide for near neutral drainage. Morin and Hutt
suggest that the criteria for determining ABA should be established based on site-specific conditions
(Morin and Hun, 1994).
The uncertainty in establishing “cutoff’ levels for acid generation is due to several factors, including
the heterogeneous distribution of sulfide and carbonate minerals, the slow dissolution of carbonate in
non-acidic conditions (the early phases of ARD are often under pH neutral conditions), coating of
carbonate grains by precipitated hydroxides, and climatic factors that lead to faster weathering of
carbonaceous materials than sulfide materials (Day, .1994). When reviewing data on static tests, an
important consideration is the particle size of the sample materjal and how it ii different from the
waste or material being characterized.
There are several different methods for conducting static testing. Five types of static tests are
summarized in Exhibit 4-1. Comparative testing was performed by Lapakko (Lapakko, I 994a) on a -
wide range of samples using the ABA, the modified ABA, the BC method, and the modified BC test
methods (proposed by Lapakko). Lapakko’s results suggest that the ABA and modified ABA methods
tend to overestimate actual neutralization potential (and potentially underestimate acid generation).
The BC and modified BC methods results most closely conelat e to the actual mineralogic NP. As
shown in Exhibit 4-1, the modified BC process determines NP by titrating to pH = 6.0 rather than
pH = 3.5 (the endpoint using the standard BC method). Lapakko noted that a pH of 6 (the typical
water quality standard) better approximates the neutralization that would be required to meet
applicable water quality standards (Lapakko, 1994a). -
4.1.2.3 Kinetic Tests
Kinetic tests are distinguished from static tests in that they attempt to mimic the natural oxidation
reactions of the field setting. The tests typically use a larger sample volume and require a much
longer time for completion than do static tests. These tests provide information on the rate of sulfide
mineral oxidation and therefore acid production, as well as an indication of drainage water quality.
4-12 September 1994
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(Source: Lapakko. 1993b)
Exhibit 4-1. Summary of Static Test Methods, Costs, Advantages, and Disadvantages
1 = Coastech 1989. as referenced in Lapakko 1993
2 = Bradham and Caruccio 1990, as referenced in Lapakko 1993
3 = Ferguson 1984, as referenced in Lapakko 1993
4 = Lawrence 1991, as referenced in Lapakko 1993
Acid Base Accounting
(Sobek et al , 1918)
MODIFIED Acid Base BC Research Initial
Accounting (Duncan and
(Coastech. 1989) Bruynesteynb 1979)
MODIFIED BC
Research Initial
(Lapakko 1994a)
Alkaline Production
Potential Sulfur
(Caruccto et al 1981)
.
Net Acid Production
(Coastech, 1989)
ACID PRODUCTION DETERMINATION
.
Acid Producing Potential =
31.25
Total S
Acid Producing Potential = Total Acid Production
31.25 31.25
• Total S • Total S
Total Acid Production
= 31.25
* Total S
Total S used as
indicator
•
300 ml. H 2 0 2 added to 5 g
rock to directly oxidize
sulfides present
NEUTRALIZATION POTENTIAL DETERMINATION
-60 mesh (0.24 mm)
sample
add HCI as indicated by
fizz test, boil one minute
then cool
titration endpt pH 7.0
cost: 34-110
-60 mesh (0.24 mm)
sample
add HCI as indicated by
fizz test, agitate for 23
hours at room temperature
pH 1.4 - 2.0 required after
6 hours agitation
titration endpt pH 8.3
cost: 34-110
-300 mesh (0.038 mm)
sample
titrate sample to pH 3.5
with 1.0 N H 2 SO ,
.
titration endpt not
applicable
cost: 65-170 -
-300 mesh (0.038 mm)
sample
titrate sample to pH 6.0
with 1.0 N H 2 SO ,
titration endpt not
applicable
cost: unknown
-0.023 mm sample
20 mL 0.1 N HCI to
0 4g solid for 2 hours
at room temperature
titration endpt pH 4.0
cost: 34-110
particle size not presented
acid produced by iron
sulfide oxidization
dissolves buffering
minerals
titration endpt pH 7.0
cost: 25-68
ADVANTAGES AND DISADVANTAGES
simple and short time,’ 3
no special equipment, and
easy iflterpretatjon; many
samples can be tested’
does not relate to kinetic;’
assumes parallel
acid/alkaline release;’ 3 if
APP and NP are close,
hard to interpret and
different particle size not
reflected 3
simple, short time, no
special equipment, and easy
interpretation’
does not relate to kinetic;’
assumes parallel
acid/alkaline release; 23 if
AP and NP are close, hard
to interpret and different
particle size not reflected 3
simple and fairly short
time,’ 3 no special
equipment, and easy
interpretation;’ many
samples can be tested 3
assumes parallel
acid/alkaline release,
different particle size not
reflected, and if APP
and NP are close, hard
to interpret’
simple and fairly short
time,’’ no special
equipment and easy
interpretation,’ many
samples can be tested’
assumes parallel
acid/alkaline release,
different particle size not
reflected, and if APP
and NP are close, hard
to interpret 3
simple, short time, and
no special equipment’
moderate
interpretation’
simple, short time, no
special equipment, and
easy interpretation’
limited reproducibility 4
uncertain if extent of
sulfide oxidation simulates
that in field
tTl
0
E.
.1
I
r i
-t
I
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Environmental Issues EIA Guidelines for Mining
Of the different kinetic tests used, there is no one test that is preferred. The preference for tests
changes with time as experience and understanding increase. In a 1988 summary article by Ferguson
and Erickson, the B.C. Research Confirmation Test was considered to be the most widely used. A
similar 1991 article by Ferguson and Morin stated that the use of modified humidity cells was
becoming more common, and there seems to be a trend toward the preference for modified humidity
cell and column type tests. Six types of kinetic tests are summarized in Exhibit 4-2.
Kinetic tests can be used to assess the impact of different variables on the potential to generate acid.
For example, samples may be inoculated with bacteria (a requirement for some tests). The
temperature of the sample environment may also be controlled during the test. Most tests require the
sample particle size to be less than a specified sieve size (e.g., minus 200 mesh). Larger sample
volumes and test equipment may examine acid potential from coarse particles. Acid drainage control
mechanisms, such as increasing alkalinity by adding lime, may also be examined using kinetic tests.
It is helpful to supplement kinetic tests with an understanding of empirical data characterizing the
sample. Examples include analysis of specific surface area, mineralogy, and metals. Such
information may affect the interpretation of ‘test data and are important when making spatial and
temporal comparisons between samples based on the test data. As with static tests, it is important to
consider the particle size of the test sample, particularly when comparing test results with field scale
applications.
4.1.2.4 Application of Test Results in Prediction Analysis
Results from static and kinetic tests are used to classify mine wastes on the basis of their potential to
generate acid. Static tests yield information about a sample’s ability to neutralize acid and generate
acid. The difference or ratio of these values becomes the basis of the classification. As discussed
above, for samples with NNP values greater than 20 tons CaCO 3 /1,000 tons of waste and/or NP/AP
ratios of greater than 3.25:1, the potential to generate acid is low (Smith and Barton-Bridges, 1991).
For NNP values between -20 and 20 (ratios between 1:1 and 3.25:1), the potential for acid generation
remains, and uncertainty will exist. (It is important to note that each of these values are generalities
and can be affected by a wide range of site-specific conditions that can either promote or retard ARD
generation; the relative availability of surface areas of iron sulfides and calcium-magnesium
carbonates, reaction rates, drying/wetting conditions, etc.)’
The determination of AP based on estimated or reactive sulfur content in the sample has some
inherent limitations. When total sulfur is used as the basis to estimate sulfide content, this uncertainty
may be attributable to possible errors in (1) assessment of true acidity and neutralization in the
sample; (2) calculated acidity based on total sulfur conversion value; and (3) analytical error. Similar
errors exist for static tests that determine reactive sulfide mineral concentrations. Estimating long-
4-14 September 1994
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EIA Guidelines for Mining Environmental Issues
Exhibit 4-2. Summary of Some Kinetic Test Methods, Costs, Advantages, and
Disadvantages
SoxhdetE rt ctlon:iS .
Humidity Cells (Singleton and Lavkulicb 1978 Sullivan
(Sobek at al., 1978)’ ‘ .‘ and Sobek, 1982)
‘: COh T s tS
(Bruyncstcyn and Hackl 1982 Hood
and Oeitel, 1984)
SUMMARY OF TEST METHOD
‘
-2.38 mm particle size
particle size not presented
variable particle size
200g of rock exposed to three days diy
T=70 ’C (Singleton and Lavkulich,
columns containing mine waste are
air. 3 days humidified air, and rinsed
1978); T=25°C (Sullivan and Sobek,
leached with discrete volumes or
with 200 mL on day 7 ‘
1982); water passed through sample is
recirculating solutions
distilled and recycled through sample
cost: 425-850
cost: 212-425
cost: dependent upon scale
ADVANTAGES AND DISADVANTAGES
models AP and NP well and models
simple, results in short time, and
models AP and NP, models effect of
wet/diy, ’ approximates field conditions
and rate of acidity per unit of sample
assessment of interaction between AP
and NP’
different rock types, models wet/dry,
and models different grain sizes’
moderate to use, results take long time,
moderate to use and need special
difficult interpretation, not practical for
and some special equipment’
equipment’
large number of samples’
moderate case of interpretation;”' large
moderate interpretation”' in
large volume of sample’ lots of data
data set generated 2
developmental stage and relationship to
generated, long time, and potential
natural processes not clear’
problems: uneven leachate application,
channelizauon ” 3
(Source: Lapakko, 1993b)
BC Research Confirmation •,..,. .“ , .,‘ Batch Reactor. , Field Tests
(Duncan and Walden, 1975) : (Halbert etaL, (983) ‘ “S; (Eger and Lapakko. 1985)’
METHOD
-400 mesh particle size
-200 mesh parncte size’
field scale particles
15-30g added to bacterially active
sample/water slurry is agitated
800 to 1300 methc ton test piles
solution at pH 2.2 to 2.5, T=3YC; if
200g1500 m l .’ ‘
constucted on liners flow and water
pH increases, sample is non acid
quality data collected; tests began in
pmducer if pH decreases, 1/2 original
1977 and are ongoing
sample mass is added in each of two
increments
cost 170-340
cost: 425-850
cost: initial constnlction is expensive,
subsequent costs arc comparable
ADVANTAGES AND DISADVANTAGES
simple to use, low cost, assesses
able to examine many samples
uses actual mine waste under
potential for biological leaching 3
simultaneously and relatively simple
environmental conditions; can be used to
equipment’
determine drainage volume; mitigation
methods can be tested
moderate to use, longer time needed,
subject to large sampling errors and lack
expensive initial consmiction long tune
and some special equipment needed;’
of precision’
difficult interpretation if pH change is
‘
small, does not model initial AP step,
and long time for pH to stabilize’
(Source: Lapakko, 1993)
I Coastech 1989, as referenced in Lapakko 1993
2 Bradhani and Casuccio 1990, as referenced in Lapakko 1993
3 Ferguson 1985, as referenced in Lapakko 1993
4 Bab j ci al. 1980, as referenced in Lapakko 1993
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term reactive sulfide based on short-term tests may result in uncertainty due to difficulties in making
oxidation rate predictions (British Columbia AMD Task Force, 1989).
Acid base accounting tests conducted on an iterative basis, where the initial sample Set is small, are
helpful when establishing boundaries between lithologic units. As data from static tests is collected
and evaluated, the sampling selection can be refined. The goal of sampling is to collect representative
samples that define the variability of the lithologies present. If significant variability in the acid
generation or neutralization potential is identified in the initial sample test results, additional sampling
to refine lithologic boundaries is necessaiy (California Mining Association, 1991).
Kinetic tests are often conducted to confirm results of static tests, to test the potential for ARD in the
uncertainty zones of static testing, and to estimate when and how fast acid generation will occur.
These tests provide insight on the rate of acid production and the water quality potentially produced
and are used to evaluate treatment and control measures. Unlike static tests, there is no standardized
method for evaluating test results. Data are examined for changes through time and water quality
characteristics. Kinetic tests tend to accelerate the natural oxidation rate over those observed in the
field. This may have the advantage of condensing time, and providing earlier insight into the
potential for acid generation.
Generally, kinetic tests are evaluated for changes in pH, sulfate, acidity and a host of potential metals.
According to the British Columbia AIt4D Task Force (1989), samples with pH values less than 3 are
considered strongly acid; between 3 and 5 the sample is acid-generating and there may be some
neutralization occurring; at pH values >5, the sample is not significantly acid or an alkaline source is
neutralizing the acid. Sulfate is a by-product of sulfid oxidation and can be used as a measure of the
rate of oxidation and acid production. When evaluating test data it is important to examine the
cumulative sulfate production curve as an indicator of sulfide oxidation, in addition to other
parameters. An analysis of metals in the sample solution serves as an indicator of contaminant load
but is not usually a good indicator of acid generation.
4.1.2.5 Experience With Static and Kinetic Tests
Ferguson estimated that for about 50 percent of mines it. is easy to determine the likelihood for acid
generation to be a problem. For some, acid generation would be expected; for others, it would
definitely not be expected. Predicting the potential for the other 50 percent is more difficult (U.S.
EPA, 1992). When data collected from static and kinetic tests is inconclusive, it may be necessary to
extrapolate from existing data using oxidation rates and other factors and project how a sample may
react. The soundness of the extrapolation is dependent on the representativeness of the sample,
accuracy of the tests data, and the interpretation of the data.
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EIA Guidelines for Mining Environmental Issues
Ferguson and Morin (1991) found that samples with an NP/AP ratio of less than 0.1 tended to
produce acid during typical laboratory timeframes. They expected that if laboratory tests were
conducted for longer time periods the NPIAP ratio would shift closer to 1 and did not speculate on
what the values for NNP and NP/AP would be in the future. Extrapolating a sample’s ability to
generate acid was divided into short (less than one year), medium (a few years), and long term (many
years) time frames. Short-term projections are based on laboratory data. Medium-term projections
require knowledge of the neutralization process, primarily consumption of carbonate. Long-term
extrapolations of acid generation poiential will require an understanding of weathering rinds and
diffusion of oxygen into and reaction products out of that rind. Long-term projections were identified
as being extremely difficult.
Researchers in British Cálumbia have examined results of static and kinetic tests conducted on tailings
and waste rock (Ferguson and Morin, 1991). The results are based on a study of 20 active or
abandoned mines in British Columbia. Their fmdings indicate that for tailings, only those samples
having a negative NNP produced acid. The test method was not identified and the limitations are
therefore not discussed here. According to this report, waste rock data from static tests is very
limited and demonstrates the variability expected with these waste units. They observed that samples
of waste rock that had weathered for one month (prior to sample collection) needed to be flushed
initially to remove existing oxidation products.
Lapakko (1990b) used solid phase characterization of the sample in conjunction with acid base
accounting data and the rates of acid production and consumption to extrapolate information beyond
the timeframe of kinetic tests. The rates of acid production and consumption were based on kinetic
test results over a 20-week period. The time required to deplete sulfide and carbonate minerals was
determined using rates established from kinetic tests. Based on these observations the time required
to deplete the iron sulfide content was 950 weeks and the time to deplete the carbonate content was 40
weeks. This prediction agreed with an observed drop in pH between week 36 and week 56 from 8.7
to 6; after another 20 weeks the pH dropped below 5.
4.1.2.6 Mathematical Modeling of Acid Generation Potential
As the preceding discussion indicates, static and kinetic testing provide an incomplete picture of the
potential for mine wastes to produce ARD. Static testing estimates the ultimate AP and NP of waste
material but is generally silent with regard to the rates of generation of acidic and alkaline flows in
actual waste matrices. Kinetic testing is more helpful with regard to estimating the rates of oxidation
and neutralization within waste units. However, as discussed above, actual waste units can be very
non-homogenous and anisotropic with respect to the distributions of mineral types, particle size,
hydrologic conditions and so forth. Thus, while a given kinetic test may well approximate the
potential for ARD in a portion of a waste unit, the result may not be representative of the “global”
potential for ARD. Equally important is the practical limitation on the duration of kinetic tests:
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Environmental Issues ELA Guidelines for Mining
because kinetic tests are generally short-livàd with respect to the potential period of persistence of
ARD, they inadequately mimic the evolutionary nature of the process of acid generation.
To overcome the uncertainties inherent in short-term testing, as well as avoid the prohibitive costs of
very long term testing, some researchers have developed mathematical models to aid in predicting the
long-term effects on mine waste water quality of acid generating wastes. Predictive modeling offers
the hope of providing tools for estimating the potential extent of acid generation prior to its
occurrence. Ideally, such information may be compared for scenarios entailing alternative
management options to identify the design, operating, and closure methods that best meet economic
and environmental objectives. As a practical matter, existing ARD models fall short of the ideal.
Nevertheless, these models may provide valuable information for planning purposes, and may have an
important role in understanding and predicting ARD.
Overview of Existing Models
A. number of distinct approaches to modeling ARD have emerged to date. In general, all the models
attempt to describe the time-dependant behavior of one or more variables of a mine waste
geochemical system in terms of observed behavior trends (empirical models) or chemical and/or
physical processes that are believed to control ARD (deterministic models). Empirical models
extrapolate values for the desired output variables (e.g., acid generation) from laboratory or field data
(British Columbia AMD Task Force, 1989). Deterministic models simulate the changes in system
values according to the causal mechanisms relating each element .of the system to the others.
It is important to remember that all ARD models are siznplifications of reality. Simplification is
required by incomplete understanding of all factors influencing AMD. Further, simplification can
substantially reduce the cost and time required to model the system under study. However,
simplifying assumptions can lead to erroneous conclusions if they result in the omission of important
causal mechanisms. For instance, failure to consider the presence of neutra!izir g m aterials in a waste
pile could result in an overestimation of the rate of acid generation. Similarly, fai’ure to consider
hydrogeochemical conditions within a waste pile may preciude umsiderarion of adsorption!
precipitation reactions invoLving me als, thereby miscalculating the potential for metals loading in
cffl nt strtams. Because the importance of my giva conirollmg factor may vary from site to site
(and fi au tine to tinr), the significance of a simplifying assumption for any particular modeling
effort must be weighed carefully.
Empirical Models
As stated above, empirical models extrapolate values of sulfide oxidation from existing laboratory and
field test data. The method of extrapolation typically involves determination of the “best-fit lines”
through test data points (British Columbia AMD Task Force, 1989). The equations so derived may
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EIA Guidelines for Mining Environmental Issues
then be solved to provide, for instance, the acid generation rate of a particular waste unit at some
time in the future. Using the projected acid generation rate as an input to a separate
hydrogeochemical model that accounts for attenuation of seepage constituents in soils and dilution in
receiving waters, the estimated constituent loading rates and consequent receiving water quality at
time T may be estimated (Broughton and Robertson, 1991).
Empirical models generally do not explicitly consider the causal mechanisms driving oxidation of
sulfides and neutralization of seepage. Rather, such models assume that the operation of such
controls is accurately represented in the test data. Therefore, the accuracy of empirical models in
predicting ARD depends heavily on the quality of the test data used in the models. Principal sources
of uncertainty may be expected to include variations in the spatial and particle size distribution of
sulfide and alkaline minerals not captured by the data due to insufficient spacial distribution of
samples; changes in the distribution of particle sizes throughout the waste unit (due to weathering) not
captured by the data; and failure to accurately calibrate the model to reflect the actual quantity and
type of materials (British Columbia AMD Task Force, 1989).
It is important to note that empirical models, by their nature, are site-specific. Because the models
rely on actual trends observed at a specific site, rather than generic causal mechanisms, the best fit
lines for one site cannot be assumed to be representative for another site. Further, significant changes
in waste unit composition, geometry, or controls over time may invalidate previous representativeness
of empirical models. Nevertheless, empirical models may provide cost-effective and reasonably
reliable estimations of short-term future ARD conditions for sites with sufficient spatial and temporal
data.
Deterministic Models
Deterministic models simulate ARD by solving systems of equations that represent the various
controlling factors in the waste reaction process (Broughton and Robertson, 1991). The simulation
approach allows the users to examine the potential sulfide oxidation rate and resulting seepage quality
over periods of tens to hundreds of years in the future. The greatest promise of deterministic models
is that they may allow the user to predict ARD as it evolves over time under the changing influence
of rate-controlling factors. Existing models have built upon earlier work on acid releases from coal
mine spoils as well as work on leachate quality in metals heap leach operations (Nicholson, 1992).
The models may rely solely on the causal relationships described in the equations, or may include
empirical data as exogenous drivers (outside the model structure) to solve for certain aspects of the
system (Nicholson, 1992; Broughton and Robertson, 1991). The most important differences between
the models lie in the particular causal mechanisms (e.g., oxygen diffusion, changing particle size,
temperature variations due to exothermic reactions) addressed within each model structure.
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Environmental Issues EIA Guidelines for Mining
Nicholson presents a review of ARD models. En that review, Shumaten (1971), as cited in Nicholson
(1992), is credited with. first recognizing that diffusion of oxygen within mine rock limits the overall
rate of oxidation of sulfides (Nicholson, 1992). The first working models to incorporate this process
(Morth, 1972; Rica and Chow 1974; both cited in Nicholson, 1992) used the acid generation rate to
calculate resulting drainage water quality. Rittchie (1977), as cited in Nicholson (1992) added to this
concept by explicitly accounting for the removal of oxidized sulfur from the store of available
unreacted sulfide. Jaynes et al., working with a model of pyritic shale in coal mine spoils, assumed
pyritic particles to oxidize as shrinking cores of unreacted material surrounded by an outer layer
depleted of pyrite (Nicholson, 1992). The outer layer results in decreased diffusion rates of oxygen,
while the shrinking core provides a smaller reactive surface area. Other models have included
convection as a means of oxygen transport within waste piles (Lu and Zhang, undated). Convection
may be influenced by changes in barometric pressure or by the release of heat from the exothermic
oxidation of sulfides. Some researchers have modeled the feedback mechanisms operating between
temperature and biological and chemical oxidation rates, noting that the mechanism is only significant
where waste permeabilities are high enough to allow convective oxygen transport to occur (Nicholson,
1992).
More recent models have addressed the hydrologic and geochemical conditions in waste unit matrices,
as well as reaction product transport, to more realistically represent changes in seepage quality
(Nicholson, 1992). Bennett (1990) and others found that water flow through the waste pile strongly
influences sulfide oxidation rates by acting as a heat sink and removing heat produced by oxidation.
Jaynes et a!. and Schafer (as cited in Nicholson, 1992) have incorporated chemical equilibrium
relationships of varying complexity to model the mobilization and attenuation of oxidation and
dissolution products within the waste pile. These relationships drive the residence times of various
constituents within “mixing cells” of the waste matrix, and, along with allowing for consumption of
acid by alkaline materials, result in changes in effluent chemistry as conditions within the matrix
evolve (Nicholson, 1992). The Bureau of Mines is currently developing a deterministic model where
initial results have successfully matched humidity cell data (White, 1994).
Model developments such as those listed above have significantly contributed to understanding of the
processes controlling ARD. For instance, explicit consideration of oxygen diffusion reveals that, in
instances where diffusion is restricted, fast processes such as biologically catalyzed oxidation can be
unimportant to the overall rate of oxidation. Similarly, consideration of hydrologic flow within the
waste matrix shows that the rate of release of oxidation products from waste piles depends strongly on
the flow characteristics within the wastes (Nicholson, 1992). More recent models have corroborated
the proposition that waste dump geometry can be important to oxidation rates by influencing the
surface area exposure and air infiltration rates (Nicholson, 1992).
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ELA Guidelines for Mining Environmental Issues
Notwithstanding the understanding that existing models have provided, ARD models to date have not
found extensive applications in predicting oxidation rates and effluent quality at operating or proposed
sites (Ferguson and Erickson, 1988). As stated above, models are simplifications of reality, and
consequently are subject to a high degree of uncertainty. Among the sources of uncertainty are
incomplete or invalid model structure; natural variability of certain parameters; and lack of parameter
calibration and model verification (British Columbia AMD Task Force, 1989).
Incomplete model structure leads to uncertainty in predictions by ignoring potentially important rate
controlling factors. In general, incomplete model structure results from an incomplete understanding
of the system being modeled, or the overuse of simplifying assumptions (British Columbia AMD Task
Force, 1989). For example, failure to accurately account for water flow within the waste matrix
prevents consideration of the thermal gradient within the pile, the transport of oxidation and
dissolution products, and the conduction of oxygen via water. It is worth noting that modeling water
flow in waste rock piles presents greater difficulties than in tailings piles, and has received little
attention to date (Nicholson, 1992). For this reason (among others), waste rock pile models are
subject to a higher level of uncertainty.
Natural variability of some parameters of a system can lead to uncertainty in model predictions. For
example, changes in rainfall patterns, which directly effect the hydrologic conditions in the waste pile,
are difficult to predict with certainty. Likewise, particle size distribution and mineral type distribution
throughout the waste pile can be highly variable and difficult to predict.
Among the greatest concerns facing the reliability of predictive deterministic models are model
calibration and validation. Model parameters must be adjusted to match the conditions prevailing at
an actual site. Therefore, reliable waste characteristics, hydrologic and geochemical data must be
collected and incorporated into the model structure. Validation requires comparison of model
predictions with actual field sampling results. To date, the availability of field data for validation is
very limited.
4.1.3 ARD DETECTION/ENVIRONMENTAL M0Nrr0RING
Where there is the potential for encounterng sulfide mineralization, an assessment of potential
impacts should include appropriate testing for ARD potential (using one or more of the methods
described in the previous section). Where testing results demonstrate potential for ARD generation or
where such test results are inconclusive (particularly in sensitive environments), an applicant’s
environmental monitoring program should include specific testing directed at early identification of
ARD. This should involve sampling of effluent streams as well as surface water and groundwater.
Existing data on ARD generation indicate that tt is highly variable. (Mine discharge sampling data
compiled by the British Columbia Acid Mine Drainage Task Force at sites with known ARD
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Environmental Issues EIA Guidelines for Mining
generation show significant day-to-day variability in pH and concentrations of dissolved metals.) As a
result, regular monthly or quarterly sampling (commonly used to monitor effluents/impacts from
industrial operations) may not be adequate to detect ARD generation. Where ARD is a potential
concern, baseline studies should be designed to establish conditions where ARD is likely to occur.
Monitoring programs during and after operations should be tailored to address the factors that affect
ARD generation. These factors include:
Seasonal Variability. Most mines where ARD is observed exhibit seasonal variability in
ARD generation (except undergroUnd adit discharges which are relatively unimpacted by
changing seasonal conditions). Generally, either the first rain after a dry season or high
snowmelt periods are most likely to produce ARD. (ARD generation can be specifically
increased by the buildup of salts on rock surfaces during dry conditions.)
Treated Effluent Variability. At mine sites, the treatment system effluent quality may be
variable due to different influent volumes and characteristics—for example, where natural
conditions affect the influent flow and composition. For example, potentially acidic mine
water and runoff may be significant influents to the system under certain conditions.
Impacts on Aquatic Life. The actual effects of ARD on a receiving water may be
dependent on the behavior/occurrence of specific aquatic life within the watershed. For
example, the presence of migratory species may suggest the need for monitoring during
specific time periods. Similarly, seasonal releases of ARD may occur during critical life
stages of individual species.
• Stream and River Effects. Streams and rivers may be heavilyimpacted due to sudden
high releases of ARD (especially where there is limited dilution). In snowmelt areas,
impacts can be particularly significant when a melting at the mine site occurs during a
different time period than other areas within the watershed (thereby reducing dilution).
Sampling plans should consider when “maximum” flows/discharges can be expected.
• Lake Effects. In lakes, the effects of ARD may be impacted by physical and biological
conditions in the lake. In designing a monitoring plan, factors such as thermal
stratification, turnover events, flushing rates, and seasonal cycles of aquatic life growth
should be considered.
As stated above, baseline and operational monitoring programs should be designed to address each of
the above factors. A reasonable, cost-saving pption is to provide for frequent pH or other ARD
indicator (sulfate, alkalinity, etc.) monitoring of effluent discharges and ground and surface water
quality. When indicator parameters exceed thresholds, increased monitoring could be required for
other parameters (including metals and toxicity) to detennine the extent of ARD releases/impacts
(British Columbia AM1) Task Force, 1990).
4.1.4 MITIGATION OF ARD
There are two primary approaches to addressing ARD: avoiding mining deposits with high ARD
potential; and isolating or otherwise special-handling wastes with ARD potential. In practice,
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EIA Guidelines for Mining Environmental Issues
completely avoiding mining in areas with the potential to form ARD may be difficult due to the
widespread distribution of sulfide minerals. The individual applicant’s pre-project testing (using the
methods described in the previous section) should be representative of each rock type, provide good
spatial coverage, and be proportional to waste quantities. As discussed above, this may frequently
require collection and analysis of an extensive number of samples. The results of truly representative
sampling should allow the applicant to develop a mine plan to avoid, wherever possible, sulfide-
bearing/acid-generating rock.
Effective isolation of wastes (backfill, waste rock, or tailings) with the potential to develop ARD is a
key element to conducting mining activities while minimizing perpetual effects to surface water and
groundwater. In isolating these wastes, the acid generation process is brought under control. The
requirements for the formation of ARD, as discussed in previous sections, include the presence of
sulfides, oxygen, and water. Control of materials with a potential for acid generation can therefore
be implemented by preventing oxygen from contacting the material (or minimizing oxygen contact),
preventing water from contacting the material, and/or ensuring that an adequate amount of natural or
• introduced material is available to neutralize any acid produced.
The following sections generally describe specific types of mitigation measures for ARD control. For
the most part, only limited data are currently available to document their effectiveness. Further,
individual site conditions significantly impact their feasibility and performance in the field. In many
cases, the measures discussed below are most effective when used in combination and adapted to the
situation existing at a specific site.
4.1.4.1 Subaqueous Disposal
Where fluctuations in water levels are not expected, placement of acid forming materials below the
final potentiometric surface may be an effective means to exclude oxygen. Similarly, some dry waste
management units can be closed by flooding/subaqueous disposal of potentially acid generating
material. The water must be of a sufficient depth to ensure that it is not well oxygenated (since
sulfide can oxidize in subaqueous environments) and it should not pass rapidly through the system.
Wetting conditions must be permanent and physical mechanisms must not be present to allow
entrainment of wastes in the water. Further, it should be noted that metals found in waste materials
can dissolve into neutral waters. Both Lapakko 1994b) and St.-Arnaud (1994) have suggested
placing protective layers over acid generating tailings disposed of in a subaqueous manner. Similarly,
mine operations in upland conditions and in drier portions of the west may not be able to consider
submersion as an effective mitigation tool for acid formation. (See also Section 3.2 above.)
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Environmental Issues EIA Guidelines for Mining
4.1.4.2 Covers
Another common technique used to isolate water (and oxygen) from acid forming materials is the use
of a low penneability cover. Covers may consist of compacted soils or synthetic materials. Proper
function of covers requires that their integrity remain intact; those subject to erosion, weathering,
cracking, settling, or penetration by plant roots may not provide adequate protection for an indefinite
period of time. Most (if not all) cover materials are more effective at controlling infiltration of water
than excluding oxygen. By reducing the amount of water infiltrating a covered system, the potential
for migration of any acid drainage formed beneath the cover also is reduced. Similar to covers,
subsurface seepagefgrout walls can be installed near the highwall to isolate disturbed areas from
inflows. Finally, during actual waste disposal, mines can segregate materials to minimize acid
generation potential. For example, carbonate materials can be placed on the surface of piles, while
potentially acid generating materials are placed below the surface.
The limitations imposed by covers are availability and costs of cover materials. If only limited
volumes of material must be covered over the life of an operation, those wastes which require special
handling must be precisely identified in the field. In coal mining operations, the complexity of the
situation is compounded by the requirement that reclamation be contemporaneous. In these cases, a
special waste disposal area is generally not permitted for extended periods of time.
4.1.4.3 Waste Blending
Blending activities during the mining operation may be used to mix alkaline materials with acid
forming materials within the waste disposal unit. The effectiveness of blending wastes is directly
related to the weathering properties of the alkaline materials; if a CaCO 3 equivalent is available at a
rate equal to or exceeding the oxidation of sulfides, acid formation could be adequately controlled.
Alkaline and phosphate materials such as lime and alkaline fly ash can also be added to selected
wastes to provide the same function (as well as placement in. surface and underground mines at
closure). It should be noted, however, that the neutralization of acid may also lead to the
precipitation of metals from solution. These metal precipitates may form crusts on the alkaline solids,
reducing the surface area of the alkaline material available for further neutralization of the acid. In
addition, it is difficult to accomplish heterogeneous mixing of sulfide and carbonate materials. This
has led some government entities to require a 3:1 ratio of neutralizing material to acid generating
material. In some cases, “neutralizing materials” that are used in blending consist of any waste rock
that is not acid-forming (e.g., it is above the NP/AP ratio set by the regulatory agency). This
material may or may not actually have adequate neutralizing capacity.
4.1.4.4 Hydrologic Controls
Hydrologic controls may be employed to some extent to reduce the amount of water percolating
through acid forming wastes. Often, diversions are installed that direct surface flows around waste
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EIA Guidelines for Mining Environmental Issues
disposal facilities. French drains may also be installed to promote ground and surface water flow
underneath a disposal unt. However, french drains constructed under disposal units (waste rock
dumps, head of hollow fills), that eventually generate acid can function as a conduit for acid rock
drainage into surface waters.
At some metal mines, acid-forming waste rock is being “encapsulated” within larger waste rock
dumps. Relatively low-permeability neutralizing material (often waste rock from other lithologic units
that is compacted) is placed under and/or over sulfide rock. The intent is both to reduce water flow
to and through the sulfide rock and to neutralize any acid that may form.
4.1.4.5 Bacteria Control
ThiobacillusferrooxidaM is the principal organism responsible for the bacterial oxidation of sulfides
that may dramatically (up to a fivefold) increase the rate of acid formation. Studies using bactericides
to control ARD have been conducted with some degree of success. A summary of the effectiveness
‘of bactericides presented by the British Columbia Acid Mine Drainage Task Force indicates that these
compounds can effectively reduce acidity by 50 to 90 percent (British Columbia AMD Task Force,
1989). However, bactericides are degraded and leached with time, ultimately having a limited life
span. Additionally, if acid generation is occurring in an absence of bacteria, bactericides will only
control the rate and not the presence of ARD.
4.1.4.6 Treatment
Mines currently in operation experiencing acid mine drainage may face a costly and long-term battle.
If acid drainage develops (as it often has) unexpectedly, well after waste disposal units have been
constructed, mitigation may require extensive earth moving activity, if sources are small enough to be
pinpointed. Alkaline material (e.g., lime) may be added in solid form to flows moving into or out of
the acid-forming area (the use of “sorbent” polymers and microorganisms is also being studied). The
effectiveness of raising the pH of the water before or after contact with acid-forming material is
limited by the chemistry of the constituents involved, and the volume of acid being produced.
Demonstration projects have made use of injecting alkaline solutions into acid producing material;
however, the long-term effectiveness of this treatment has not been documented (Bureau of Mines,
1985).
Anoxic limestone drains (ALDs) are currently being studied as passive treatment technologies. The
Tennessee Valley Authority has successfully used ALDs to enhance the performance of constructed
wetlands (Brodie, 1991). Combined ALD and wetland treatment systems have also been successfully
tested in Pennsylvania (Hedin and Watzlaf, 1993; Rowley et al., 1994). However, limited data are
currently available to assess the long-term effectiveness (including potential limiting factors, such as
coating of limestone surfaces with iron and aluminum oxides) and widespread applicability of ALDs
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Environmental Issues EIA Guidelines for Mining
in mitigating ARD, especially where they are used alone. In addition, design of ALDs or any other
alkaline/precipitation treatment system must include a settling area. Hedin and Watzlaf (1993)
provide additional information on the design and performance of ALDs.
In cases where mine drainage is only slightly acidic and metal loadings are low to moderate, natural
and constructed wetlands show some ability to improve water quality (Brooks et al., 1990). In
wetlands, “treatment” of ARD (and associated metals) occurs through physical (settling and
adsorption), chemical (hydrolysis and oxidation), and biological (bacterial desulfurization) processes.
Cohen and Staub (1992) provides technical guidance on the design and operation of wetlands
treatment systems. Based on data from an operating wetlands treatment system at the Big Five
Tunnel in Idaho Springs, Colorado, an effective life of approximately 4-6 years is projected for a
single loading of substrate material (Cohen and Staub, 1992). At some sites, operators may need to
provide separate areas for anaerobic (chemical/physical) and aerobic (biological) processes. Based on
a study of six artificial wetlands constructed by the Commonwealth of Pennsylvania, a surface flow
criteria of 6 grams/day/square per meter was recommended (Dietz et al., 1994).
Testing conducted by the Commonwealth of Pennsylvania has shown that passive wetlands treatment
can be effective in mitigating ARD for coal mines, especially for mildly acidic drainage (performance
of more than 73 wetlands was evaluated). However, it should be noted that study results generally
showed that treatment levels for metals were lower than predicted (Hellier et aL, 1994). Further,
studies such as those performed by the State of Minnesota, have shown that the capacity of wetlands
for metals removal is often limited. The Minnesota study found that metals removal was limited to
the upper 20 centimeters of a constructed wetland and that limited flows/periodic maintenance would
be necessary to provide long-term mitigation (Eger et al., 1994).
While combined ALD and wetland systems show some promise for passive treatment of highly acidic
streams (Rowley et al., 1994), current data to support their widespread effectiveness and feasibility
are limited. Therefore, where flows contain low pH values and high metals concentrations, active
long-term treatment may be necessary to achieve acceptable water quality in the mine’s discharge. A
potential alternative to conventional active treatment practices (neutralization/precipitation with lime,
etc.) involves the use of Sulfate Reducing Bacteria (SRB) to treat acid drainage. SRB decompose
organic compounds and produce sulfide (which is either given off as hydrogen sulfide gas or reacts
with metals to form metal suffides). At a February 1994 EPA workshop on SRB treatment, several
participants noted success in reducing metals levels. However, SRB performance data are still limited
and results vary from site-to-site. Issues related to optimum design parameters, temperature and p14
impacts, toxicity to organisms, and hydrogen sulfide control need to be address (U.S. EPA, 1994).
Finally, Cohen and Staub note research indicating SRB are found in wetlands and are important for
metals removal in wetlands treatment systems (Cohen and Staub, 1992).
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ELA Guidelines for Mining . Environmental Issues
4.1.5 SUMMARY OF FACTORS TO BE CONSIDERED IN EVALUATING POTENTIAL ARD
GENERATIONIRELEASE
ARD from coal and hardrock mining operations has been shown to have significantly affected aquatic.
life in thousand of miles of stream segments throughout the country. These effects can be long-term
and the costs of remediation are prohibitive where it is even feasible. While there is extensive
ongoing research on ARD, there is substantial uncertainty associated with virtually every methodology
used to predict, detect, and mitigate ARD. Further, the extent of’ARD generation and the potential
risks are generafly dependent on a wide range of site-specific factors. No assessment of potential
environmental impacts of a proposed mine should dismiss acid generation potential based on limited
test data, especially where sulfide ore will be mined. In addition, care must be taken not to be
overconfident in the efficacy of specific mitigation measures that may be used if ARD is encountered.
ARD-related factors to be considered in evaluating potential impacts include:
• Comprehensive baseline acid generation potential testing of the ore and waste materials.
Where there is any historic basis for believing that ARD could occur and/or where new
sources are proposed in particularly sensitive environment areas, the applicant should
conduct testing of each geological unit as well as analysis of representative waste samples.
Further, the applicant must be cognizant of the areas/ranges of uncertainty associated with
static testing. Where there is evidence ARD can occur or where static test methods indicate
uncertainty, kinetic testing should be performed to determine the drainage characteristics
(and facilitate mine planning).
• An ongoing environmental monitoring program to detect ARD when it occurs. Sampling of
wastes, discharges, and surface water/groundwater should be tailored to site-specific
conditions that favor ARD generation (e.g., monitoring during or immediately after a major
precipitation event after a long-term dry period). An effective monitoring program should
emphasize the need for a full understanding of site conditions, including hydrology,
geology, and climate. Typical one-time quarterly or bi-annual sampling events may not be
adequate to detect ARD.
• Where ARD could be encountered, detailed information on the design and operation of
proposed mitigation measures (including a quantitative engineering assessment of their likely
effectiveness based on their historic use under similar cOnditions). If any uncertainties
arise, operators should provide for contingencies if proposed measures are ineffective.
• An approach to reclamation bonding that accounts for the long-term impacts of ARD must
be cognizant of the potential for a significant lag-time/delay in ARD observance (thus
necessitating care in bond release). Also, the need for perpetual treatment measures (and/or
perpetual maintenance of passive treatment techniques) should be considered.
While the potential for ARD generation is highly variable, extensive documentation is available on a
wide range of site conditions. Further information is available from the references cited in this
section and from many other sources. In addition, Canada’s Laurentian University Library has
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established the on-line Mining Database, which contains citations and abstracts reLated to ARD and
reclamation. Finally, while there is no consistent National policy related to ARD, several regulatory
entities have developed specific requirements to address ARD generation at new mining operations.
For example, BLM has recently promulgated an ARD policy t&guide approval of proposed
operations (Williams, 1994). OSM requires acid-base accounting to assess acid generation potential.
Similarly, the British Columbia government has specific requirements for ARD prediction,
environmental monitoring, mitigation, and bonding (Price and Errington, 1994). Some States and
National Forests also have policies related to prediction, monitoring, mitigation, and bonding.
4.2 CYANIDE HEAP LEACHING
Cyanide has long been used in the mining industry. For decades, it has been used as a pyrite
depressant in base metal flotation. It also has been used for over a century in gold extraction. In the
1950s, technologies that allowed large-scale beneficiation of gold ores using cyanide (first
demonstrated in Cripple Creek, Colorado) set the stage for the enormous increase in cyanide usage
when gold prices skyrocketed in the late 1970s and 1980s. Continued improvements in cyanidation
technology have allowed increasingly lower-grade gold ores to be mined economically. Together with
continued high gold prices, this has resulted in increasing amounts of cyanide being used in mining.
A substantial proportion of sodium cyanide produced in the U.S. is now used by the mining industry,
with over 100 million pounds used by goldlsilver leaching operations (both tank and heap leaching) in
1g90, less than S million pounds for copper/molybdenum flotation, and much less than 5 million
pounds in lead/zinc flotation.
The acute toxicity of cyanide, and a number of major incidents, has focussed attention on the use of
cyanide in the mining industry. When exposure occurs (e.g., via inhalation or ingestion), cyanide
interferes with many organisms’ oxygen metabolism and can be lethal in a short period of time.
Through the 1980s, as cyanidation operations and cyanide usage proliferated, there were a number of
incidents where waterfowl were killed when they attempted to use tailings ponds or other cyanide-
containing solution ponds (e.g., pregnant or barren ponds). For example, operators in Nevada,
California, and Arizona reported to regulatory authorities on over 9,000 wildlife deaths, mostly
waterfowl, that had occurred on Federal lands in those States from 1984 through 1989 (GAO, 1991).
in addition, a number of major spills have occurred, including one in South Carolina in 1990, when a
dam failure resulted in the release of over lOmillion gallons of cyanide solution, causing fish kills for
nearly 50 miles downstream of the operation.
In many cases, regulatory authorities—Federal land managers and States—have responded by
developing increasingly stringent regulations or, in many or most cases, nonmandatory guidelines.
These regulations and/or guidelines can address the design of facilities that use cyanide (e.g.,
requiring/recommending liners and site preparation for heap leach piles or tailings impoundments),
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operational concerns (e.g., monitoring of solutions in processes and in ponds, and in some cases
treatr nt requirements for cyanide-containing wastes), and closure/reclamation requirements (e.g.,
rinsii . ,- to a set cyanide concentration in rinsate before reclamation can begin).
There are a number of major issues associated with evaluating the potential impacts of cyanide
operations on the, environment. These include the complexity of cyanide’s chemistry, uncertainties
about its behavior in the environment, and inadequate laboratory analytical methods. These issues are
discussed briefly below.
4.2.1 ‘ UNCERTAINTIES IT CYANIDE BEHAVIOR IN THE ENVIRONMENT
4.2.1.1 Cyanide in the Environment
Cyanide concentrations are generally measured as one of three forms: free, weak acid dissociable
(WAD), and total. Free cyanide refers to the cyanide that is present in solution as CN or HCN, and
includes cyanide-bonded sodium, potassium, calcium or magnesium.’ Free cyanide is very difficult to
‘measure and its results are often unreliable, difficult to ‘duplicate, or inaccurate. WAD cyanide is the
fraction of cyanide that will volatilize to HCN in a weak acid solution at a pH of 4.5. WAD cyanide
includes free cyanide, simple cyanide, and weak cyanide complexes of zinc, cadmium, silver, copper,
and nickel. Total cyanide measures all of the cyanide present in any form, including iron, cobalt, and
gold complexes. Exhibit 4-.3 shows one means of classifying various forms of cyanide. Free cyanide
would include the “readily soluble” simple compounds, and WAD cyanide would generally include all
of the forms in the exhibit except the “strongly complexed cyanides.”
Aqueous cyanide (CN) has a negative valence and reacts readily to form more stable compounds.
Aqueous cyanide complexes readily with metals in the ore, ranging from readily soluble complexes
such as sodium and calcium cyanide through the complexes measured by WAD analytical methods to
strong complexes such as iron-cyanide. At a pH below about 9 s.u., weaker cyanide compounds can
dissociate and form hydrogen cyanide (HCN), a volatile gas,that rapidly evaporates at atmospheric
pressure. The stronger complexes are generally very stable in natural aqueous conditions.
Unsaturated soils provide significant attenuation capacity for cyanide. Within a short time and
distance, for example, free cyanide can volatilize to HCN if solutions are buffered by the soil to a pH
below about 8 s.u. Adsorption, precipitation, oxidation to cyanate, and biodegradation can also
attenuate free (and dissociated complexed) cyanide in soils under appropriate conditions. WAD
cyanide behavior is similar to that of free, although WAD cyanide also can react with other metals in
soils to form insoluble salts. (Hutchison and Ellison, 1991)
Free cyanide is extremely toxic to most organisms, and this, form has been most frequently regulated.
Under the Safe Drinking Water Act, EPA has established a maximum contaminant level (MCL) of
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Exhibit 4-3. Stability of Cyanide and Cyanide Compounds in Cyanidation Solutions
Classification’
:. “: , : Compounds: ‘‘
Solution chemistry
Free cyanide
CN, HCN
Extremely toxic. In natural waters below
pH about 8.3, HCN form is predominant.
Simple compounds
a. Readily soluble
b. Neutral insoluble
salts
a. NaCn, KCN, Ca(CN), Hg(CN) 2
b. Zn(CN) 2 , Cd(CN) 2 , CuCN,
N’(CN) 2 . AgCN
Water soluble. Dissociate or ionize readily
and completely to yield free cyanide and
Weak complexes
Zn(CN) 4 2 , Cd(CN) , Cd(CN) 4 2
.
Rates of dissociation and release of free
cyanide affected by light, water
temperature, pH, total dissolved solids, and
complex concentration. pH and
concentration most affect stability and
extent of dissociation (breakdown increases
with decreases in pH, concentration).
Moderately strong
complexes
Cu(CN) . Cu(CN) 3 2 . Ni(CN) 2 ,
Ag(CN) ,
Strong complexes
Fe(CN)j’, Co(CN) 6 , Au(CN)j’,
Fe(CN) 6 3 ,
Iron is most common! important: Very
stable in absence of light. Long-term
stability uncertain.
Source: Column 3, Mudder and Smith 1989; columns 1 and 2 cited in Mudder and Smith.
0.2 mg/I free cyanide in drinking water. The Clean Water Act ambient water quality criterion
recommended for protection of freshwater aquatic life from chronic effects is 0.0052 mg/I free
cyanide; the acute criterion is 0.022 mg/I free cyanide. More recently developed mining-related
staiidards and guidelines often specify weak acid dissociable (WAD) cyanide, largely because of the
difficulty in measuring free cyanide at the low concentrations of regulatory concern (Mudder and
Smith, 1992). Longer-term environmental concerns with cyanide, those not related to acute hazards
from spills, revolve around the dissociation into toxic free cyanide of complexed cyanides in waste
units and in the environment.
4.2.1.2 Analytical Issues
In developing the effluent limitation guidelines for the Ore Mining and Dressing Point Source
Category (at 40 CFR Part 440), EPA established a technology-based standard for all discharges from
mills that use the “cyanidation” process to recover gold and silver, and mills that use cyanide in froth
flotation of copper, lead, zinc, and molybdenum ores. In this process, the Agency considered several
treatment methods for reducing cyanide levels in mill wastewaters. However, EPA found that the
cyanide levels in both treated and untreated mill wastewaters were below the 0.4 mg/I quantification
limit for EPA-approved test methods (i.e., treatment performance could not be evaluated). Because
of this, and because complete recycling of mill waters was practiced at many facilities, the Agency
established a zero discharge requirement. EPA was aware of specific sites where laboratory methods
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were effectively being used to quantify cyanide removal and suggested that these methods could be
used by permit writers to establish cyanide limits in individual NPDES permits on a site-by-site basis.
Analytical methods used to determine cyanide concentrations in tailings and tailings solutions,
effluents, and heap pore water are still being debated. At low concentrations, testing is inaccurate
and measurements of cyanide may not be good pred)ctors of actual cyanide concentrations in the field.
(Durkin, 1990; Colorado, 1992a; U.S. EPA ORD, 1993) Many complex axd cumbersome analytical
methods have been developed as a result of the need for measuring cyanide in a variety of matrices.
Many “random” modifications of procedures also have made it very difficult to interpret many
analytical results (California Regional Water Quality Control Board, 1987).
EPA’s Office of Research and Development (ORD) is currently evaluating cyanide test procedures
and methods, and is investigating a proprietary, privately developed, distillation method that appears
to be successful for cyanide analysis. One of ORD’s activities includes revising the current methods
for measuring and detecting cyanide fractions and eliminating interferrents. ORD is also reviewing
performance data and problems of 17 currently used methods. Future efforts will involve continued
evaluation of cyanide species (ORD, 1993).
Because of the uncertainty involving cyanide forms and analytical methods, regulatory standards and
guidelines may not be clear on the form of cyanide being addressed. Nor, in many cases, do
environmental monitoring data make clear which form or which analytical method has been used.
This can make it difficult or impossible to evaluate the short- or long-term potential environmental
impacts of aproposed (or an existing) operation. Thus, it is important that environmental
documentation be clear as to the form of cyanide that is described and addressed, and that appropriate
analytical methods be specified. Similarly, the types of cyanide complexes that are expected to occur
in heap leach piles and tailings should be assessed, along with the rate and extent to which the
complexes may break down to toxic forms upon their release (even in low concentrations) to
receiving waters.
4.2.2 POTENTIAL IMPACTS AND APPROACHES TO MITIGATION DURING ACTIvE LIFE
In general, cyanide can cause three major types of potential environmental impacts: first, cyanide-
containing ponds and ditches can present an acute hazard to wildlife and birds. Less frequently
(because of lower cyanide concentrations), tailings ponds present similar hazards. Second, spills can
result in cyanide reaching surface water or groundwater and cause short-term (e.g., fish kills) or long-
term (e.g., contamination of drinking water) impacts. Finally, cyanide in active heaps and ponds and
in mining wastes—primarily heaps and dumps of spent ore and tailings impoundments—may be
released and present hazards to surface water or groundwater, and there may be geochemical changes
that affect the mobility of heavy metals. These impacts and the major issues and uncertainties
associated with each are described briefly below.
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4.2.2.1 Acute Hflz rdS
The heightened awareness of the threat to wildlife and birds presented by cyanide-containing ponds
and wastes have led regulatory authorities (generally, Federal land managers and States) to require
operators to take steps either to reduce/eliminate access to cyanide solutions or to reduce cyanide
concentrations in exposed materials to below lethal levels. Regulatory requirements and guidelines as
to the allowable concentration of cyanide in exposed process solutions are widely variable (when
numeric limitations are established, they generally range around 50 mg/i), as are the means by which
operators comply. Operators reduce access in several ways, including covering solution ponds with
netting or covers, using cannons and other hazing devices (e.g., decoy owls) to scare off waterfowl
and other wildlife, and/or installing fencing to preclude access by large wildlife. At least one mine
uses tanks to contain all solutions. In addition, operators may be required or may elect to treat
tailings slurries to reduce cyanide concentrations, they may maintain higher fluid levels in
impoundments so as to dilute concentrations, or they may reduce the amount of free liquids in
impoundments to minimize pond surface area. Some facilities also provide “micro-nets” over ditches
to keep out rodents and smaller wildlife not excluded by large fences. In evaluating the threat that
cyanide usage at a proposed facility may pose to wildlife and birds, and the effectiveness of control
and mitigation measures, environmental documentation should describe the standards that must be
met, the types of organisms of most concern (e.g., waterfowl at an operation in a migratory flyway or
near nesting or staging areas), -and the specific measures that will be used to reduce exposures and
mortality. The program by which the measures will be evaluated for effectiveness should also be
described; it will generally involve monitoring and reporting deaths and supplementing existing
methods as necessary.
4.2.2.2 Spills and Overflows
Most actual environmental impacts resulting from cyanide releases have been associated with spills
and major failures of containment structures (e.g., dam failure, failure of heap slopes). Minor spills
of cyanide are not uncommon at gold facilities. These occur typically when portions of a heap leach
pile slumps into a drainage ditch or solution pond and cause an overflow of cyanide-containing
solution or when a pipe carrying pregnant or barren solution, or tailings slurry, fails or is
puncturedisevered by mining equipment or vehicles. In all but a few major cases, cyanide spills have
been contained on-site, and soils provide significant attenuation in most cases. Facilities routinely
store hypochiorite or other oxidants for use in detoxifying such spills. In addition, some operators
have increased the distance or placed barriers between pipelines and equipment routes. Others have
reinforced pipelines in high-risk areas.
The proximity of sensitive environments—generally including any water bodies—may be the most
important factor in assessing the potential impacts of spills. In all cases, environmental
documentation should describe the practices or methods that will be used to reduce the risk of
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ruptures and spills, and in responding to minor and major releases. More details would be necessary
for operations in sensitive environments, including details on spill-prevention practices and on spill
response procedures. Particularly when cyanide facilities and structures (e.g., pipelines, heaps,
impoundments) are near streams or wetlands, extra precautions are appropriate, including double-
walled pipelines, additional setbacks of heaped ore or intervening barriers between heaps and solution
ponds, automatic pump shutoffs in the event of pressure loss, etc.
During facility operations, great attention is paid to the waier balance and the efficient movement of
solution through the sysiem. Facilities are generally required to be able to contain at least the normal
24-hour process solution flow and the maximum volume from the 10-year/24-hour precipitation event.
Many States require additional capacity, sufficient to contain the flows from the 100-year/24-hour
event. Because of the size of mining operations and the large areas that can contribute flows, this can
be an enormous volume, well beyond feasibility for many operations. Thus, most States allow an
operation’s required storage capacity to include the volume of precipitation and solution that can be
held in heaps as wçll as in solution ponds and overflow ponds. As a result, continued circulation of
solution is necessary to ensure that heaps do not dewater and overwhelm the capacity of ponds. Most
States require onsite generators to ensure continued supply of electricity to pumps in the event of
power failures. All details of storage capacity and solution management may not be available at the
time environmental documentation is prepared. However, conceptual plans that identi1 ’ most
components of storage capacity and the means by which capacity will be ensured usually are.
Because miscalculations involving solution management can be catastrophic (for example, this was a
major problem at the Summitville mine, now proposed for the National Priorities List), reviewing
water balance plans, even conceptual plans, is cruciaf in assessing potential environmental impacts.
This is particularly true when operations are in or near sensitive environments. Every aspect of water
balance calculations should be assessed: the amount of precipitation and runon/runoff assumed to
occur in the designated storm event, the area of the operation that will contribute flows and the
amount, the amount that can be held in each component of the water management system (e.g., the
saturation status of a heap under normal operating conditions), even the pumping capacities of
solution recirculation pumps. In addition, some assessment should be made of water balances under
conditions other than the designated storm event. For example, spring snowmelt can provide flows
over several days that are more significant than long return-interval precipitation events. Similarly, a
series of less significant storms (e.g., several 5- or 10-year events) can collectively be more
significant than one extremely large storm. Meteorological data are often provided in environmental
documentation (or in proposed operating plans submitted to States and/or Federal land managers), and
these should be evaluated carefully to determine whether reasonable assumptions have been made
regarding hypothetical worst-case events. Also of importance is how both operators and regulators
may respond to unexpected water balance problems. In most cases, such problems are addressed as
they arise, with never a reconsideration of the entire system and whether the original planning and
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design were sound, and thus no re-evaluation of potential environmental impacts. It may be
appropriate in some cases to require more formal contingency planning at the outset, with a
reassessment of potential environmental impacts required when critical components of the water
management system are modified.
4.2.2.3 Liner and Cont2inment Leakage
As described in Chapter 3, heap leach operations use liner systems of various sorts under heaps and
solution ponds., In general, liner systems consist of a prepared foundation (compacted subsurface,
with large rocks and objects removed), a bedding layer (if used), synthetic or clay liner,’ seepage
collection/detection layer (if used), and a cover layer of material to protect the liner. Perhaps the
single most important factor in preserving the integrity of liner systems is their proper installation,
including comprehensive construction QA/QC. The type of liner system that is used generally is
based On site conditions, operator preference, and regulatory requirements (Van Zyl, 1991). Liners
are usually of polyvinyl chloride (PVC) or high density pàlyethylene (HDPE); recently, very low
density polyethylene (VLDPE) liners have emerged. Although there now is ultraviolet-resistant PVC,
there have been some problems with older PVC liners degrading when pond or ditch liners are
exposed to ultraviolet light. In most cases where there have’been significant liner failures, they have
been due to improper installation or accidents combined with inadequate construction QA/QC.
There is a clear economic incentive to minimize pregnant solution loss during operations; this is often
cited as a reason why operators’ design plans should be accepted as proposed. In practice, operators
assess the optimum balance of economic and environmental considerations in design planning. Thus,
the costs of actual containment technologies and practices are balanced with the et onomic losses
associated with a certain amount of solution loss as well as regulatory and env wninental
considerations. As noted in Chapter 3, regulatoiy authorities (Federal land managers and States) are
increasingly requiring solution ponds to be d ub&e-.ined, often with a composite liner system that
includes leak detection/collection. Requiremeris 11w heaps more often specify single liners, which
may be synthetic or clay. In southern California, for example, the great depth to groundwater and
the attenuation capacity of soils led the Regional W .ex Qnalily Contro’ Board to specify single liners
for heaps.
In many locations, however, heaps are located entirely or partially in drajnageways ( cnvidlly
ephemeral) over shallow alluvial or shallow bedrock aquifers. This is usually the case for tailings
impoundments, but these are infrequently lined; seepage throughand under dams is generally
cOllected in toe ponds, but some seepage may bypass such ponds. Should leaks occur through heap
liners or should seepage bypass collection ponds, cyanide can reach the alluvium and/or shallow
groundwater. This can then affect downgradient surface waters or springs or can reach bedrock•
aquifers. Whether subsurface materials can attenuat any such leaks and reduce cyanide levels
depends on the nature of the materials and the location and extent of water present in the subsurface.
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Evaluating the likelihood and the potential consequences of cyanide leaks is particularly dependent on
detailed information on the subsurface and on proposed liner systems, and on construction QA/QC.
Subsurface information of concern includes the nature and characteristics of the material (depth,
mineral composition, compressibility, shear strength, seasonal saturation levels, presence of springs,
etc.) Liner systems should be fully described, along with a clear justification for their selection (e.g.,
why PVC over VLDPE, why flexibility was or was not important, why and how their resistance to
sunlight/punctures was considered, etc.). Detailed design and QA information is often not provided
in great detail, bi t in some cases may be necessary. Information on the minimum standards that are
imposed by applicable regulatory authorities can assist in determining if more detailed information is
needed—if standards are very general, then more information may be appropriate, for example.
Should a proposed operatiOn be located in an envIronment where leakage could be especially
damaging, specific information on the subsurface, on site preparation, and on the liner system and
installation and construction QA/QC are always necessary for an evaluation of potential impacts.
Finally, the presence or absence of comprehensive monitoring programs (for example, monitoring of
seepage detection/collection systems, if any; of bedrock and alluvial groundwater, of materials and
pore water in heaps or impoundments themselves; of solution and slurries; of dam/heap stability; of
the integrity of containment devices, etc.) and commitments torespond to unexpected events can be a
significant determinant in the level of information needed. A sustained monitoring program,
combined with financial commiunents and/or regulatory guarantees that environmentally appropriate
responses will be taken if necessary, can provide significant assurances that long-term impacts will be
minimized, even in the absence of detailed information and analyses.
4.2.3. CLOSURE/RECLAMATIoN AND LONG-TERM IMPACrS
4.2.3.1 Closure and Reclamation
Until the recent past, reclamation (if required) commenced immediately upon cessation of operations.
With increasing concern over environmental quality in general and toxic pollutants specifically in
recent decades, however, the concept of pre-reclamation closure has received more attention by States
and Federal land managers. However, relatively few cyanide operations have been completely
reclaimed to date, since large-scale cyanidation operations are a phenomenon of recent vintage.
Consequently, closure and reclamation measures are not yet well established.
Closure entails those activities conducted after a cyanide unit ceases operating in order to prepare the
site for reclamation. Closure essentially consists of those activities that are required to remove a
hazard or undesirable component, whether it be chemical or physical, to the extent required by States
or Federal land managers. It can entail detoxification/neutralization of wastes, treatment and/or
evaporation of rinse liquids and pond water, dismantling associated equipment and piping, removal or
treatment of waste, reconstruction, grading or stabilizing, and/or chemical testing.
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Reclamation consists of those activities that are undertaken to return the site to a condition suitable for
the future uses specified by the State or land manager. Reclamation may involve regrading;
backfih ling ponds; removal of wastes; site drainage control such as diversions, channels, riprap, and
collection basins; perforating liners to allow drainage through heaps; capping to reduce infiltration
and/or to provide a substrate for revegetation; and revegetation to establish ground cover and protect
against erosion.
4.2.3.2 Long-tenn Environmental Concerns and Issues
The principal concerns with closure of spent ore and tailings impoundments are long-term structural
stability and potential to leach contaminants. Structural stability is dependent on the physical
characteristics of the waste material (e.g., percent slimes vs. sands in impoundments), the physical
configuration of the waste unit, and site conditions (e.g., timing and nature of precipitation, ups treaml
uphill area that will provide inflows). The potential to leach contaminants is largely dependent on site
conditions, including reclamation and mineral(s) geochemistry.
Cyanide is not the only contaminant that is present in tailings effluents or heaps; numerous other
constituents may be present in the waste material and present potential problems following closure and
reclamation. Nitrate (from cyanide degradation) and heavy metal (from trace heavy metal sulfides in
the ore) migration are examples of other significant problems that can be faced at closure of cyanide
operations. As noted above, testing and analysis of cyanide is a major issue because it is difficult to
obtain consistent and reliable test results. Another significant concern is the generation of acid
drainage, typically caused by the presence of iron sulfides that break down to form sulfuric acid.
Because of the great variability among cyanide operations, including ore characteristics and climatic
conditions, adequate ôharacterization of wastes and materials is an important consideration for site
closure and reclamation. In part because few have been closed/reclaimed, there is limited information
available on the mobility of cyanide and cyanide complexes in closed and/or reclaimed heaps and
tailings impoundments. However, at several South Dakota sites, nitrate, one of the degradation
products of cyanide, has been detected in areas beyond the heap. Operators were able to meet the
0.2 mg/i cyanide detoxification criteria, but elevated levels of nitrate have prevented the attainment of
other criteria developed by the State for the site. The nitrate levels in surface runoff from the mine
sites have exceeded treatment criteria and low levels of nitrate have been detected in downgradient
wells. (Durkin, 1990)
In addition, the chemistry of a spent heap or tailings impoundment may change over time. Although
effluent samples at closure/reclamation may meet State requirements, the effluent characteristics may
be dependent on the pH. The question of what happens to the heap or impoundment when the pH or
moisture content changes is one that is now being addressed by many operators and authorities.
Modeling can be performed to assess the long-term geochemical conditions at the site taking into
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consideration the chemistry of a spent heap over time, and be used to design closure and reclamation
plans. Factors affecting chemical changes in a heap or tailings impoundment include pH, moisture,
mobility, and geochemical stability of the material.
In addition to high cyanide concentrations, the post-leach solution (pre-cyanide treatment) at heap
leach operations is likely to have the following characteristics (Mudder and Smith (1992):
• High p 1 (9.5 to. 11 s.u.)
• Moderate to high dissolved species, mainly sodium, calcium (from added lime), and sulfate.
• Potentially elevated metals of ionic-forming complexes such as arsenic, molybdenum, and
selenium
• Potentially elevated metal which form soluble metallo-cyanide complexes such as iron,
copper, mercury, cadmium, and zinc.
Rinsing spent ore for detoxification typically takes from several weeks to several months; however, in
some cases a site may require several rounds of rinsing in order to meet State or Federal standards.
One problem that frequently has been encountered is that rinsing/treatment is conducted and effluent
standards may be met, but subsequent rinsing or testing reveals increased cyanide and other
constituent concentrations. (Nevada, 1993b) Spring snowmelt also has caused effluent concentrations
to rise. Several States, as well as the Bureau of Land Management, now request follow-up effluent
sampling after periods of rest or after rainy season/spring snowmelt prior to approving completion of
detoxification. (BLM, 1992; Idaho, 1993, South Dakota, 1993) Although the reasons for incomplete
or variable rinsing have not been confirmed, Durkin (1990) suggests that non-uniform neutralization
or dilution may be factors. A number of facilities have had to switch treatment methods after a
chosen method failed to reach the desired concentrations. Thus, in practice, rinsing may take many
seasons, or years, to complete.
Agglomerated heaps are more difficult to rinse because aggregating the material prior to leaching
(with lime or cement or other materials) keeps the pH elevated, which in turn makes reduction of pH
and detoxification of cyanide more difficult. One Nevada mine (Trinity), for example, operated an
agglomerated heap; when leaching ended, initial WAD cyanide concentrations were 400 - 500 mgI!
and the facility proposed using natural degradation to reduce the cyanide concentrations but continued
high pH has prevented this from being effective (Nevada, 1993c). As a result of this and many other
site-specific circumstances that affect detoxification success, State-granted variances from rinsing
criteria are not uncommon in many States.
One mine in Nevada encountered a major problem during rinsing of a spent heap. While
recirculating the solution during leaching, gold was removed from the pregnant solution but other
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metals and constituents continued to accumulate and were not removed from the solution. As a
result, during rinsing, the mercury levels in the rinse water rose to 4.0 mg/I, three orders of
magnitude higher than the primary drinking water standard of 0.002 mg/i. The tremendous amount
of water required for consecutive rinses in order to reach the 0.2 mg/i cyanide standards has also
been an issue in Nevada. (Nevada, 1993b)
Several mines in five western states have experienced elevated selenium levels (Altringer, 1991). The
Bureau of Mines is investigating the use of biological and chemical reduction of selenium in cyanide
tailings pond water. Although high costs may make the treatment prohibitive, the research study was
successful in reducing selenium concentrations in the laboratory from up to 30 ppm selenium to 0.02
ppm.
Water balance is a major concern at some sites. In arid regions, with limited water resources, the
amount of water that is necessary to rinse heaps to a required standard may be a significant concern.
Conversely, in wet climates like South Carolina, excess water from heavy precipitation and/or
snowmelt can place a strain on system operations and may make draining or revegetating a heap or
impoundment very difficult (ELI, 1992).
Another potential problem may be caused by “blind-offs,” less permeable lenses or isolated areas of a
heap that affect percolation and flow through the heap, leading to preferential paths for fluid
migration. Available research data suggest that preferential flow paths and blind-offs increase with
time and volume of liquid. These preferential flow paths can limit the effectiveness of
treatment/neutralization and may leave pockets of contaminants behind in a heap during closure,
which then have the potential to leach out after reclamation.
Acid generation also may be a major problem facing many mines. At one time, acid generation at
cyanide sites was not considered to be a potential problem as many mining facilities used only oxide
ores (not sulfide ores). However, cyanide leaching facilities that mined predominantly oxide ores
have reported cases of acid generation. Even tailings that were originally alkaline have subsequently
experienced acid generation. Although lime may be added during cyanide leaching, with residuals
existing in tailings or agglomerated heaps, the lime component may eventually wash away through
weathering, leaving sulfide compounds to form acid drainage. (Ritcey, 1989; California, 1993b) As
noted above, the reverse situation may also occur, when residual lime/cement can keep pH too high to
allow cyanide to dissociate and degrade. This only emphasizes the extreme site-specific nature of
operations and of potential and actual environmental impacts that may be expected to occur.
4.2.3.3 Assessments of Long-term Impacts
In general, cyanide is not believed to present a significant problem over the long term, particularly if
the obstacles to detoxification and reclamation are overcome. As noted above, however, there are
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many complexities with detoxification and reclamation and which if any difficulties will be
encountered are seldom known at the time that the potential environmental impacts of a proposed
mining operation are evaluated. As a result, environmental documentation should describe
contingency plans for overcoming possible difficulties and potential impacts under these conditions.
If detoxification is successful, most residual cyanide in closed heaps and impoundments will be
strongly complexed with iron. Although the stability of such complexes over long periods is not well
understood, cyaipde is generally considered to be much less of a long-term problem than acid
generation, metals mobility, and stability (which are discussed elsewhere). Thus, evaluating the
potential post-operational environmental impacts associated with cyanide in heaps, spent ore dumps,
and tailings would involve assessing the means by which operators will ensure that cyanide and its
breakdown products and metallic complexes are contained and reduced to environmentally benign
levels prior to site abandonment. It also may’ involve an assessment of the ability and authority of
applicable regulatory authorities to guarantee this. Conceptilal plans for operators who will detoxify
and reclaim heaps• and tailings are generally available at the time environmental impact assessments
are performed, but not the details. This may be sufficient, given that cyanide may not be an
important environmental issue over the long term. What is important is that the plans describe not
only what is anticipated to occur at closure and reclamation (e.g., continued recycling of rinse water
until WAD cyanide levels reach regulatory standards) but also the implications for long-term
environmental performance that potential difficulties and changes in plans could have.
4.3 STRUCTURAL STABILITY OF TAILINGS IMPOUNDMENTS
The most common method of tailings disposal is placement of tailings slurry in impoundments formed
behind raised embankments. Modern tailings impoundments are engineered structures which serve
the dual functions of permanent disposal of the tailings and conservation of water for use,in the mine
and mill. Impoundments are often favored over other tailings disposal methods (e.g., tailings piles,
mine backfihling) because, among other things, they are “economically attractive and relatively easy to
operate” (Environment Canada, 1987). Such economy derives in part from the fact that tailings and
waste rock may accowit for a major part of the embankment construction materials. Additionally, the
phased nature of embankment construction spreads the capital expense of disposal unit construction
over the life of the project, reducing initial capital outlays. Section 3.2.6.2 discusses the types of
tailings impoundments used and their construction methods.
The disposal of tailings behind earthen dams and embankments raises a number of concerns related to
the stability and environmental performance of the units. in particular, tailings impoundments are
nearly always accompanied by unavoidable and often necessary seepage of mill effluent through or
beneath the dam structure. Such seepage results from the uncontrolled percolation of stored water
downward through foundation materials or through the embankment as well as the controlled release
of water in order to maintain embanknient stability. Impoundment seepage raises the ‘prospect of
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surface water and groundwater contamination and, coupled with the potential for acid rock drainage
(see ab?ve), may necessitate long-term water treatment well after the active life of the facility has
passed. Moreover, failure to maintain hydrostatic pressure within and behind the embankment below
critical levels may result in partial or complete failure of the structure, causing releases of tailings and
contained mill effluent to surrounding areas.
Therefore, the challenge posed by raised embankment tailings impoundments is achieving a balance
between cost, stability, and environmental performance objectives. Because raised embankments
evolve over the life of the project they present the need and the opportunity to reevaluate design
parameters to address changing conditions and project objectives over time. The evolving nature of
raised embankments also means that finished impoundments often differ substantially from their initial
plans. Accordingly, it can be very difficult to determine in advance the potential for environmental
difficulties or the need for environmental controls.
4.3.1 SEEPAGE AND STABILiTY
In general, tailings impoundments and the embankmnents that confine them are designed using
information on tailings characteristics, available construction materials, site specific factors (such as
topography, geology, hydrology and seisniicity) and costs, with dynamic interplay between these
factors influencing the location (or siting) and actual design of the impoundment.
The three methods of embankment construction (upstream, downstream, and centerline) differ with
respect to the quantity of materials required for construction and the types of operational and designed
controls that may be incorporated into the structures for stability and environmental performance.
For instance, upstream embankments are the most economical but present difficulties in installation
and operation of in-dam drainage systems. Downstream embanknients require substantially more fill
material than either of the other methods, but can readily be designed to include filters and drains,
and hence are more appropriate when large water storage capacity in th impoundment is desired.
Tailings present several disadvantages as dam-building,material, including: high susceptibility to
internal piping, highly erodible surfaces, and high susceptibility of the fine tailings to frost action. To
overcome some of these disadvantages, the coarse fraction of tailings streams, the tailings sands, may
be separated from the remaining fmes and slimes by spigotting or cycloning of the tailings slurry.
Additionally, compaction will substantially increase resistance to sliding and liquefaction.
A primary concern in the design of tailings impoundments is the control of pore water pressure within
and beneath the embankment. Excessive pore pressure within the embankment may lead to
exceedence of the sheer strength of the fill material, resulting in local or general slope failure.
Additionally, high pore pressures within or beneath the embankment face may result in uncontrolled
seepage at the dam face leading to piping failure (discussed below). Similarly, seepage through weak
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permeable layers of the foundation may result in piping or exceedence of soil shear strength, causing
foundation subsidence and compromising the stability of the overlying embankment.
The phreatic surface is the level of saturation in the impoundment and embankment (the surface along
which pressure in the fluid equals atmospheric pressure (CANMET, 1977)); in natural systems it is
often called the water table. Factors that affect the phreatic surface in the embankment include the
depositional characteristics of ihe tailings (permeability, compressibility, grading, pulp density, etc.)
and site-specific features such as foundation characteristics and the hydrology and hydrogeology of the
impoundment area and its upstream catchment area. Changes to the phreatic surface can be caused
by: malfunction of drainage systems, freezing of surface layers on the downstream slope of the dam,
changes in construction method (including the characteristics of the placed material), and changes in
the elevation of the pond. The level of the water table also may be altered by changes in the
permeability of the underlying foundation material; sometimes these are caused by strains and
subsidence induced by the weight of the impounded tailings (Vick, 1990).
impoundment design must provide for a cost-effective and reliable containment system. Choices
regarding materials, slope angles, drainage control, raising rates, etc., all affect the cost as well as
the stability of the structure. Therefore, stability analysis is peiformed to optimize the structure with
respect to cost and other objectives while maintaining reliability.
Slope stability analysis begins with an estimation of the reliability of the trial embankment.
Typically, the embankment designer proposes the internal and external geometry of the trial
embankment and then calculates the safety factor of the design. Using detailed information on the
physical properties of the fill material and estimates of the volume of tailings and water to be
contained in the impoundment, the phreatic surface is predicted. The designer then examines a wide
range of failure modes to calculate the estimated stresses expressed at hypothetical failure surfaces.
The safety factor for each failure mode is then calculated by dividing the estimated resistance of the
embankment to stress along the failure surface by the stress load expressed at the failure surface.
With this process the designer can look at changes in design parameters and the resulting influence of
the safety factor to arrive at the least-cost option consistent with safety objectives (Inyang, 1993).
The major design precept is that the phreatic surface should not emerge from the embankment and
should be as low as possible near the embankment face (Vick, 1990). The primary method of
maintaining a low phreatic surface near the embankment face is to increase the relative permeability
(or hydraulic conductivity) of the embankment in the direction of flow. This is accomplished by
using progressively coarser material from upstream (i.e., the tailings side) to downstream and/or by
incorporating drainage features (e.g., chimneys drains, blanket drains) in the dam itself to keep fluids
away from the downstream face. Tailings slimes, clays, and/or synthetic liners (rarely) may be used
to reduce permeability of the upstream face.
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Other means that, in various combinations, are used to maintain a low phreatic surface near the dam
include:
• Reducing the water content of tailings by dewatering prior to disposal.
• Reducing groundwater infiltration into the tailings. This can be a serious problem, at least
seasonally, when tailings impoundments are placed over alluvial materials. Infiltration can
be reduced by preparing the ground surface in the impoundment area: “lining” with
compacted native soils and clays, imported clays, or even synthetic liners, and possibly
including drains under these liners to convey the groundwater underneath the tailings.
• Incorporating drains underneath and through the dam to ensure that any seepage/drainage is
controlled. This can include incorporating filters or filter zones upstream of drains to help
prevent clogging and hence maintain differences in permeability across zones. Filter zones
may be constructed of graded sands or synthetic filter fabrics (Vick, 1990).
• Maintaining as little free water in the impoundment as possible by recycling water to the
mill or by. decanting water and pumping it to an alternative fines settling and water storage
impoundment.
• Maintaining free water as far behind the crest of the dam (i.e., as high in the catchment) as
possible by sloping the surface of the tailings upstream away from the dam.
• Allowing fluids to escape into the subsurface. This is generally not an option since States
generally impose strict groundwater protection standards..
• Diverting runon away from and around the impoundment and dam. This is accomplished
with berms and other water diversion techniques.
4.3.2 SEEPAGE/RELEASES AND ENVIRONMENTAL PERFORMANCE
The selection of any of these approaches to embankment design has implications for the operational
and long-term environmental performance of the impoundment system. For example, incorporation
of drains within and beneath the dam structure to reduce pore pressure within the dam provides a
conduit for release of contaminated fluids. Under existing NPDES effluent guidelines, such releases
typically will require collection and return to the impoundment since discharges are prohibited from
many tailings. The toe pond collection system may also require a liner to prevent downward
migration of pollutants to shallow groundwater. Embankment drainage systems also create a post-
closure environmental concern: because the impoundment is by design not impermeable,
contaminated effluent, possibly including acid rock drainage, may be released from the impoundment
after the active life of the project. If the active pump-back system for the toe pond is no longer in
operation, such effluent may be released to area surface water. Accordingly, treatment-in-perpetuity
or some alternative passive treatment or containment method may be necessary to prevent surface
water releases.
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Another trade-off between stability and environmental performance is the incorporation of liners. In
areas of shallow alluvial groundwater, liners may be necessary to prevent intrusion of water into the
impoundment. However, such liners will simultaneously increase the retention of impounded water
behind the dam and reduce dam stability, all else being equal. On the other hand, the absence of a
liner may increase the downward migration of impoundment constituents to shallow groundwater.
Surface water controls may be of particular importance in post-closure stability considerations.
Surface water rulloff diversions are generally employed to limit the intrusion of excessive amounts of
water into the impoundment, which reduces dam stability and prevents drying of tailings. Failure of
surface water controls after impoundment closure could result in an increase in pore water pressure
within the impoundment, threatening the stability of the embankment. In general, active measures to
control surface water runon and runoff during the operative life of the project may require alternative
methods or long-term management after closure.
4.4 NATURAL RESOURCES AND LAND USES
The act of mining can result in major changes to all natural resources on and in the vicinity of the
mine. This section describes several major natural resource systems that may potentially be impacted
and the types of impacts that may occur.
4.4.1 GROUNDWATER
The potential mpacts to the groundwater resources in the area of a mine are similar to those that can
impact surface water quality. Acidic water from mine drainage, metals, cyanides, or other toxics
from the mining operation may enter groundwater in the vicinity of the mine. Elevated pollutant
levels can contaminate drinking water supply wells. Disturbance in groundwater flow regime may
also affect the quantities of water available for other local uses. Further, the groundwater may
recharge surface water downgradient of the mine, through contributions to base flow in a stream
channel or springs. Conversely, surface water affected by mining operations can recharge
groundwater, particularly alluvial aquifers.
An assessment of potential groundwater impacts requires that the baseline groundwater resources in
the area of the mine be completely characterized, including descriptions of the aquifers (bedrock and
alluvial systems), aquifer characteristics, flow regime (an understanding of the potentiometric surface
for each aquifer), springs, and background groundwater quality. At least two years of groundwater
quality data are generally needed (or an alternative interval that is sufficiently representative of likely
variabilities in groundwater quality). The collection of baseline groundwater data should be described
in study plans that ensure that useable data is being collected. The collection of these data usually
requires the installation of a groundwater monitoring network of wells. Where wells are installed,
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documentation should describe the location, depth, construction/completion data, and sampling and
analytical methods.
In addition to the baseline characterization of the groundwater in the project area, the following
information is generally needed to allow an assessment of potential impacts on groundwater resources:
• Location and construction design plans for toxic materials storage areas (cyanide, oil, etc.),
waste management units (focusing on impoundments), leach units, solution transport
ditches, process ponds, and surface and underground workings. These should be reviewed
in conjunction with. hydrogeologic data (particularly the potentiometric surface for each
aquifer in the area of the proposed units). Any practices to be used to protect groundwater
resources (liners, grouting, etc.) should be examined closely.
• Acid generation potential for the waste rock, tailings, and the mine workings.
• Whole rock geochemistry of the waste rock and ore to determine what metals and other
pollutants may be present and available for leaching (under neutral conditions and acidic
conditions, where applicable).
• If the rock has a net acid generation potential, mitigation measures should be outlined.
• Locations of and information on any local residential wells or well fields and an evaluation
of how they may be impacted by the new source (both in terms of quantity and quality)
liners, grout.
• Where there is a hydraulic connection between ground and surface water, an analysis of
how potentially affected groundwater could affect surface water flow and quality (and vice
versa). When dewatering can create a significant cone of depression and affect the
availability of ground water for surface water recharge (see section 3.1.4.1), information on
both short- and long-term effects would be necessary.
4.4.2 AQUATIC LIFE
The nature of mining is such that it causes massive land disturbances. These disturbances in turn can
have two major types of impacts on aquatic resources, including aquatic life. The first type of impact
would result from the contribution of eroded soil and material to streams and water bodies (see
section 4.5) and from the release of pollutants from ore or waste rock (sections 4.1 and 4.6). The
second would be the direct disruption of ephemeral, intermittent, or perennial streams; wetlands; or
other water bodies. Temporary disruptions would occur from road construction and similar activities.
Permanent impacts would be caused by actual mining of the area or by placement of refuse, tailings,
or waste rock directly in the drainageway—more often than not, this is in the upper headwaters of
intermittent or ephemeral streams. (Both types of activities are subject to §404 of the Clean Water
Act—see section 6.1.)
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Means to prevent future impacts from.the release of pollutants to surface waters from waste materials
or from mine workings should be addressed in a reclamation plan, and effective reclamation can
provide substantial mitigation. As is. noted elsewhere, however, reclamation plans for metal mines
are often only conceptual at the time of mine permitting. Thus, preparers and reviewers of EAs and
EISs often must rely on applicable reclamation requirements and on the processes that are in place to
ensure that reclamation planning proceeds according to those requirements.
For impact assessmànt purposes,. aquatic life is generally defmed asfish and benthic
macroinvertebrates; however, phytoplankton and other life forms may also be considered, depending
on the type of aquatic habitat and the nature of impacts being assessed.
Impacts to relative abundance or biological diversity may occur as a result of chemical and physical
changes or from direct removal or introduction of species.
A detailed discussion of the many approaches and methodologies that may be used to defme and
monitor aquatic resources is beyond the scope of this document. However, there are numerous
reference documents that can be used in assessing the environmental impacts to aquatic life associated
with a proposed action. Several examples include:
• Harrelson, C.C., C.L. Rawlins, and J.P. Potyondy. 1994. Stream Channel Reference Sites:
An Illustrated Guide to Field Technique. U.S. Department of Agriculture, U.S. Forest Service,
Fort Collins, Colorado.
Plaits, W.S., W.F. Megahan, and G.W. Minshall. 1983. Methods for Evaluating Stream,
Riparian, and Biotic Conditions. General Technical. Report INT-138. U.S. Department of
Agriculture, U.S. Forest Service, Ogden, Utah.
U.S. Environmental Protection Agency. 1989. Ecological Assessment of Hazardous Waste
Sites: A Field and Laboratory Reference. EPA/600/3-89/013.
U.S. Environmental Protection Agency. 1989. Rapid Bioassessment Protocols for Use in
Streams and Rivers: Benthic Macroinvertebrates and Fish. EPA/440/4-89/OO 1.
U.S. Environmental Protection Agency. 1993. Habitat Evaluation: Guidance for the Review
of Environmental Impact Assessment Documents.
The impacts of a proposed action on aquatic resources can be either beneficial or adverse. It also
may vary significantly, depending on the species; For example, increases in stream flow may
preclude habitation of certain species of macroinvertebrates and/or fish but, at the same time, may
also provide new habitat for other species of aquatic life. Too often, impact assessment is based on
single species management. A more productive approach is to consider the entire ecosystem.
Whether the analysis considers the entire ecosystem or an individual species, endpoints/criteria must
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be established by which the impacts of the project will be evaluated. Assessmeát endpoints are
environmental characteristics which, if they were found to be significantly affected, would indicate a
need for potential mitigation/modification of proposed activities. For example, an endpoint/criteria
for an ecosystem analysis might be: “The proposed project decreases the diversity of aquatic life in
the stream proposed for discharge.” Likewise, an endpoint for a single species analysis might be:
“The proposed project decreases the number of individuals of a certain species of fiSh.”
In many cases, impact assessments for proposed actions are based on what species are determined to
be valuable to society (in the affected area). Value can be indicated by legal (e.g.. listing as
threatened or endangered), commercial, recreational, ecological, or scientific importance of the
resource. Regardless of the approach taken, the interrelationships between species (in addition to
their connection to their environment) should be considered. For example, an individual non-
regulated species of macroinvertebrate may not be directly considered a valuable species but it could
be an important component of the food chain and local ecosystem which contains other valuable
species.
The impacts of a proposed action on aquatic life can most effectively be determined if sufficient
baseline data are available. In general, baseline aquatic life studies of one or more years reflecting
data from multiple seasons (e.g., spring, summer, fall) are needed to adequately describe reference
conditions. Annual and seasonal variation in aquatic life populations (especially macroinvertebrates)
are normal. Without adequate baseline data, it is not possible to measure if changes in abundance
and/or diversity are due to natural conditions or impacts from anthropogenic activities (e.g., mining).
Wherever possible, baseline data should be obtained directly from the drainage to be affected by the
proposed action. If this is not feasible, background data should be collected from an unimpacted
aquatic ecosystem (e.g., reference site) with similar characteristics to the proposed impact area. (In
many areas, aquatic resources have been degraded by historic mining (or other) activity. There, it
may be very difficult to determine the “natural” background status of water quality and aquatic life in
the watershed of concern. Other nearby watersheds may not provide an adequate surrogate because
even “natural” water chemistry in mineralized areas may be substantially different from that in other
watersheds.)
To determine which techniques and tools should be used to sample aquatic life, the consideration must
be given to the targeted organisms (e.g., fish, benthic macroinvertebrates, phytoplankton); the
objective of the sampling program (qualitative versus quantitative); and numerous parameters such as
substrate, water depth, flow, and type of water body. Benthic macroinvertebrates may be sampled
using a variety of methods such as Surber sampler, Hester-Dendy sampler, activity traps, invertebrate
box samplers, drift nets, ki k nets, or any of a number of dredges. Fish sampling methods include
electrofishing, seining, rotenoning, or using gill nets. Each method has advantages and disadvantages
and selection is dependent upon site-specific conditions and the goals/requirements of the study. If
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the primary purpose of a study is to determine the presence of a threatened or endangered fish
species, for example, it would be inappropriate to use rótenone, which has a 100 percent mortality
rate. The references cited above provide guidance on method selection and use (both for baseline and
long-term monitoring). In addition, the potential presence and effect of metals such as mercury or
selenium that are bioaccumulated should be addressed.
An important variable that the operator and the reviewer should consider in aquatic resource
assessments is the duration and extent of the proposed impacts. For example, if the proposed action
(or potential alternatives) will temporarily decrease stream flow during one season, the impacts on
aquatic resources would be expected to be different than if the activity will lead to long-term effects
(including post-mining conditions). The related indirect impacts of the activity should also be
evaluated. For example, if development of a proposed mining operation provides access to an
otherwise inaccessible landldrainage area, the potential affects of non-mining related human activity
(e.g., recreation) should be considered. Another important consideration in an historically mined area
would be the cumulatIve impacts of the proposed operation. Thus, the fact that the area to be mined
• was degraded from past mining activity would not eliminate the need for a full-scale assessment of the
cumulative impacts of mining (and other) activities on the aquatic resources and of the incremental
impacts of the proposed operation.
4.4.3 WILDLIFE
Similar to aquatic resource evaluations, numerous references are available to assist in evaluating
potential impacts on wildlife or in evaluating data and studies that are submitted by applicants.
Several examples include: -
U.S. Environmental Protection Agency. 1993. Habitat Evaluation: Guidance for the Review
of Environmental Impact Assessment Documents.
U.S. Environmental Protection Agency. 1989. Ecological Assessment of Hazardous Waste
Sites: A Field and Laboratory Reference. EPA/600/3-89/013.
Wildlife Society, The. 1980. Wildltfe Management Techniques Manual. Fourth Edition:
Revised. Sanford D. Schemnitz (editor). Washington, D.C.
In general, many of the same concepts described above (section 4.4.2) for aquatic life apply to
assessing impacts to terrestrial wildlife. The assessor/reviewer must still determine the endpoints for
the assessment, including whether to consider impacts on individual species, populations,
communities, and/or entire ecosystems In determining which species or communities are of concern
in the affected area, there should be consultations with experts from State and Federal agencies.
Species’ importance/value may be defmed by legal (e.g., threatened and endangered listing),
commercial, recreational, ecological, or scientific value. In some instances, it may be desirable to
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focus on certain species; however, it is usually preferable, to assess impacts on the overall
ecosystem.
Biological diversity is often viewed as a way to measure the health of an ecosystem. For example, a
decline in the species diversity of an area could indicate a deterioration in’ the quality, and possibly a
decrease in the stability, of that ecosystem. Direct loss of individuals (mortality) or a decrease in
fecundity may affect species diversity. The above references describe available methodologies for
measuring biodiver ity.
Similar to aquatic resources, the duration and extent of the impact is an important consideration for
wildlife. Noise during the construction phase or during operations, for example, may displace local
wildlife populations from otherwise undisturbed areas surrounding the site. Some individuals or
species may rapidly acclimate to such disturbances and return while others may return during less
disruptive operational activities. Still other individuals may be permanently displaced for the life of
the project. Other key components of wildlife impact assessment include habitat loss, degradation, or
alteration. The U.S. Fish and Wildlife Service (USFWS) Habitat Evaluation Procedure (HEP)
measures the quality of habitat as it relates to certain species. Wildlife may be displaced into poorer
quality habitat and therefore may experience a decrease in productivity, or other adverse impact.
Habitat loss may be temporary (e.g., construction-related impacts), long-term (e.g., over the life of a
mine), or essentially permanent (e.g., the replacement of forested areas with’ waste rock piles).
Assessment/prediction of potential wildlife impacts requires an accurate description of baseline
conditions (as well as a long-term monitoring program to identify any changes from the pre-
disturbance environment). Wherever possible, quantititive assessments of wildlife populations and
their habitat are always preferred. Quantitative assessment of impacts often includes comparison of
pre- and post-impact species populations. This typically’ requires field surveys of local populations
(and, as necessary, extrapolations to determine overall area populations).
In selecting techniques and tools to be used to survey or sample wildlife, the operator must consider
the targeted animals (e.g., raptors, songbirds, big game, and small mammals); the objective of the
program (qualitative versus quantitative); and numerous parameters such as the size of the project
area, home range of the animal, and habitat andlor plant communities found in the project area.
There are many methods that can be used to determine presence and relative abundance of wildlife.
Small mammals may be surveyed using Sherman live traps, pit traps, and’ snap traps. Raptors may be
surveyed from aircraft or on foot. Auditory surveys are often used to survey for wildlife which is
difficult to observe (e.g., songbirds and frogs). Surveyors may count animals observed and/or rely
on animal signs (tracks, scat, etc.). Use of signs is particularly helpfi l when surveying for animals
which are rare or elusive.
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The indirect impacts of a proposed action on wildlife near the project area should also be considered.
For example, a mining operation may be located to avoid impacting an elk migration corridor.
However, elk could be adversely affected by associated increases in housing construction which may
result from an improved local economy.
NEPA documentation for proposed mining activities should include mitigation measures which may. or
will be used to minimize or avoid impacts to wildlife. Potential mitigation measures for use at mine
sites include:
• Avoid construction or new disturbance during criticil life stages. For example, delay
construction activities’ until after sage grouse strutting occurs at nearby leks.
• Reduce the chance of cyanide poisoning of waterfowl and other wildlife, particularly in arid
environments, by neutralizing cyanide in tailings ponds or by installing fences and netting to
keep wildlife out of ponds. Explosive devices, radios, and other scare tactics have
generally not been proven effective.
•. Minimize use of fences or other such obstacles in big game migration corridors. If fences
are necessary, use tunnels, gates, or ramps to allow passage of these animals.
• Utilize “raptor proof” techniques on power poles to prevent electrocution of raptors. For
example, use anti-perching devices to discourage birds from perching or nesting on poles,
or place conductors far enough apart to ensure both wings don’t contact them at the same
time.
• To minimize the number of animals killed on mine-related roadways, use buses to transport
employees to and from the mine from an outer parking area..
• To limit impacts from habitat fragmentation, minimize the number of access roads and close
and restore roads no longer in use.
• Prohibit use of firearms on site to minimize poaching.
As noted above, mining operations can have substantial impacts on terrestrial wildlife, ranging from
temporary noise disturbances to destructioz of’ food resources and breeding habitat. Unless closure
and reclamation return the land essentially to its pre-mining state, at least some impacts to some
individuals or species will be permanent. Coal mines, as discussed in chapter 6, must return the land
.to its “approximate original cOntour” and revegetate as part Of reclamation. When successful, this
can often minimize any long-term impacts. Metal mining, on the other hand, only rarely goes this far
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in reclamation; although most disturbed areas are often returned to productive states following metal
mining, there are usually significant differences in topography and in vegetation. These in turn result
in long-term impacts to wildlife, in that they affect available food, water and cover. One of the major
purposes of reclamation is to minimize permanent impacts, so reclamation plans are crucial to
mitigation. Because reclamation plans are often (or usually) only conceptual at the time of metal
mine permitting, preparers and reviewers of EM and EISs must often rely on applicable reclamation
requirements and on the processes that are in place to ensure that reclamation planning proceeds
according to those requirements.
4.4.4 VEGETATION/WErLANDS
Vegetation consists of natural and managed plant communities. Native uplands consist of forests,
shrublands and grasslands; managed uplands include agricultural lands, primarily croplands and
pastures. Lowland vegetation occurring within drainages’ forms riparian communities, including
wetlands. The discussion below focuses on upland and lowland plant communities; the impact of
mning on agricultural lands is discussed below in the Land Use section.
Native plant communities perform a number of functions in the landscape. As discussed previously,
vegetation supports wildlife, with the diversity of vegetation strongly related to the diversity of
wildlife within the area. Vegetation stabilizes the soil surface, holding soil in place and trapping
sediment that may otherwise become mobilized; it also functions to modify microclimatic conditions,
retaining soil moisture and lowering surface temperatures. A diverse landscape also provides some
degree of aesthetic value, in the case of rangeland, native communities provide the primary
production used to feed livestock. Riparian communities and wetlands provide additional functions as
defined in Wetland Evaluation Technique (WET) Volume II: Methodology (Adamus et aL, 1987):
(1) groundwater recharge; (2) floodflow attenuation; (3) sediment stabilization; (4) sediment/toxicant
retention; (5) nutrient removal/transformation; (6) primary production export; (7) wildlife diversity!
abundance; (8) recreation; and (9) uniqueness and heritage.
All vegetation within the active mining area is removed prior to and during mine development and
operation. Vegetation immediately adjacent may be impacted by the roads, water diversions or other
development. Vegetation further removed from activities may be impacted by sediment carried by
overland flow and by fugitive dust.
Assessment of the extent of disturbance to vegetation typically involves a study describing the major
plant communities or associations within the affected area. The description of each community should
include the percent of vegetation cover, a measure of productivity (biomass production), a measure of
plant species diversity, and a qualitative description of the dominant species. The extent of
disturbance within each community should also be identified. Mitigation measures surrounding
vegetation typically consist of reseeding the reclaimed area after mining is completed.. In the case of
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non-coal mines, the change in surface configuration may result in completely different plant
communities being established. Coal mines, under the SMCRA requirement to restore the
approximate original contour and premining land use, often attempt to establish plant communities
that resemble those that existed prior to mining.
The requirements for defining and mitigating impacts to wetlands is more rigorous than other
vegetation community types because of their protection under §404 of the Clean Water Act (see
Section 6.1). The placement of dredged or fill materials into wetlands or other waters of the U.S.
requires that a Section 404 permit be obtained from the U.S. Army Corps of Engineers (Corps).
Permit applications must include a jurisdictional wetland delineation for each of the wetlands that may
be impacted. Delineations are conducted as described in the Corps of Engineers Wetlands Delineation
Manual (USACE, 1987), and are based on an assessment of vegetative, hydrologic and soils criteria.
If “jurisdictional wetlands” are identified, the project must comply with the §404(b)(1) guidelines (40
CFR Part 230).
Compliance with the §404(b)(1) guidelines requires mitigation for any impacts to jurisdictional
wetlands. The guidelines require that avoidance of impacts be considered as a first mitigation option.
If avoidance is not possible, the guidelines further require the selection of an alternative that results in
the least amount of impact to wetlands and that some measure of compensation be implemented for
impacted areas. Under the guidelines, the Corps may not issue a permit if the discharge will
substantially damage the aquatic ecosystem if practicable alternatives exist.
Development of a mitigation plan should include an evaluation of the functions and values provided
by the wetland areas under analysis, the extent of proposed disturbance (acreage), and an assessment
of potential cumulative impacts to surrounding wetlands. Based on these site-specific factors,
mitigation requirements are usually established on a case-by-case basis. Mitigation may involve
restoration, creation, enhancement, exchange, or in some cases, preservation of wetlands located
either onsite or offsite.
The assessment of wetland functions and values, in the context of a mitigation plan, tend to be
inherently subjective. While functions are tied to properties of the wetland itself, value tends to
reflect societal influence and are necessarily subjective. However, the proximity of one wetland to
others, the uniqueness of a particular wetland, and the number of functions it performs all influence a
wetlands value. Mitigation considerations include whether the target is to be an “in-kind” or “out-of-
kind” wetland in terms of functions or community types compared to the original. Location (onsite
or offsite), timing (before, concurrent, or after), and mitigation type (restoration, creation,
enhancement, exchange, or preservation) are other variables that must be considered in developing a
mitigation plan. Depending on the variables involved, the ratio of the areal extent of compensation to
disturbance can range from 1:1 to more than 3:1. Barring avoidance, the preferred approach would
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be the restoration of a former wetland, in-kind and onsite, completed before development activities
began. In such a case, the restored:impacted ratio may be close to 1:1. The ratios increase in
situations where success can only be achieved through a greater degree of difficulty or when the
mitigation cannot be completed before initiation of the project (Kruczynski, 1990).
Wetland restoration and creation tends to be as much art as science under the current state of
knowledge. Therefore, success should be evaluated using a set of clearly defined goals to be achieved
within a specific june frame. Goals should be established in the planning stages. A monitoring pian
should be developed and implemented to ensure that newly restoredlcreated wetlands progress toward
the previously defined target in a timely manner. The establishment of clear goals and an effective
monitoring plan are of key importance to project success but are often overlooked in the planning
stages.
4.4.5 LAND USE
Metal mining nearly always results in significant changes to beneficial uses of land after mining. A
description of land use should identify the current use of land needed specifically for the mine and
land use patterns in the nearby area that will be indirectly affected by the project. Particular emphasis
should be placed on land uses that pose potential conflicts with mining operations—farming, timber,
grazing, recreation—and on the local or regional zoning laws that may limit the development of
mining operations.
4.4.5.1 Farmland
The U.S. Soil Conservation Service (SCS) is charged vith identifying and locating Prime and Unique
fanñland under Public Law 95-87. The SCS works with State and local agencies, to identify
farmland of statewide or local importance. Farmlands in the vicinity of the mining project under
evaluation should be identified.by SCS categories.
The SCS generally maintains lists of all soil series that fall into the categories of prime, unique, and
State/locally important. Depending on location, lists may be generated and maintained on a county,
district, or statewide basis. Where appropriate, the reviewer (or the applicant) should contact SCS (or
the applicable State/local agencies) to verify the existence of designated farmland in the vicinity of a
proposed mining action.
Prime farmland is defined as having the best combination of physical and chemical characteristics for
producing food, feed, forage, fiber, and oilseed crops that is available for those uses. Prime farmland
demonstrates particular physical characteristics and exists within favorable climatic conditions.
Physical characteristics include a lack of rock fragments, a pH range of 4.5 to 8.4, water holding
capacity to a depth of 40 inches and adequate to produce crops, and an average annual soil
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temperature of greater that 32°F at a depth of 20 inches. The prime designation also relates to the
availability of irrigation or a sufficient precipitation regime to sustain crop production.
Unique farmland demonstrates similar characteristics to prime soils and produce high value food or
fiber crops. However, these soils lack a particular characteristic that separates them from prime -
precipitation for example, may limit crop production to eight out of ten years. Soils of statewide or
local importance are identified based on unique characteristics identified on a local basis. Ldcal
conditions or characteristics restrict: production on these soils to a greater extent. than soils classified
as prime and unique.
in addition to prime, unique, and State/locally important farmland, EPA’s September 1987 policy
identifies three other types of environmentally significant agricultural lands for protection. These
include: farmlands in or contiguous to environmentally sensitive areas, farmlands important for waste
utilization, and farmlands with significant capital investments in best management practices. Such
determinations are made on a site-by-site basis.
Potential impacts from proposed mining actions to farmlands can range from complete elimination of
the land for farming use to temporal cessation in farmland production. Analysis under NEPA should
specifically consider the effects of an activity on the important soil/farmland categories described
above (as well as the feasibility and likely effectiveness of proposed mitigation measures). Wherever
possible, mitigation measures should allow for returning the land to its previous productivity. For
example, the operator could strip a particular soil series by horizon and stockpile each separately,
with the intent of restoring the soil profile upon completion of mining. Under SMCRA, coal mines
are required to restore prime farmland to its previous state (no such uniform requirements exists for
noncoal’ mines).
4.4.5.2 Timber
Timber lands should be identified in the project area and the board feet of lumber represented by that
timber should be estimated. Impacts to timber are typically the loss of the resource in the areas to be
cleared for the mine. Mitigation of the• loss of timber lands includes the economic harvest of the
existing timber prior to clearing and construction of the mine. Reclamation of the mined areas may
require the replanting of trees but the land may be rendered unusable for timber growth at the close
of mining as a result of poor growing media, or the presence of large excavations. Any mitigation
measure that calls for tree planting (or, indeed, any revegetation) should include monitoring for
several years to verify its success.
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4.4.5.3 Gr ing
The extent of lands used foi grazing should be identified within the vegetation survey conducted for
the site. The areal extent of each plant community in which grazing. occurs and the extent of
disturbance within those communities should be reported. The animal unit months (AUMs) each
community is able to support and vegetation biomass data should be included. Where slopes of pits,
benches and highwalls do not prohibit it, reclamation in most cases will readily support grazing in the
post-mining landscape.
4.4.5.4 Recreation
Lands in the area of proposed mining projects may be used for public recreation. The types of
recreation provided by the lands in the vicinity of the project should be identified. Potential impacts
should be described with respect to the current level of recreational use as well as opportunities for
additional uses. The extent to which recreational uses will be restored after reclamation should also be
discussed.
4.4.6 CULTURAL RESOURCES
Cultural resources encompass several areas relating to man’s knowledge and appreciation of
prehistoric and historic events. The location of a mine or beneficiation facility, at or near significant
historical and cultural sites can degrade the resource value or emotional impact of the historic or
cultural site. The location of the following kinds of sites should be described in relation to the project
site:
• Archeological sites (where man-made artifacts or other remains dating from prehistoric
times are found). These are not uncommon, particularly in the west.
• Paleontological sites (where significant events happened or where well-known people lived
or worked). Again, these frequently occur on proposed sites in the west.
• Sites of particular educational, religious, scientific, or cultural value. Once again, these are
commonly encountered, particularly .in the west. Native American values (including
religious and cultural values associated with certain areas) are of particular concern. As
noted in Chapter 5, artifacts and remnants of historic mining are also increasingly being
protected as cultural resources.
• Properties on or eligible for listing on the National Register for protection under Section
106 of the National Historic Preservation Aci.
In addition to identifying the location of each site in relation to the project, a discussion of mitigation
measures should be presented if any of the sites will be directly impacted by the mining and
beneficiation activities.
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4.4.7 A s’nIE11cs
Aesthetics involve the general visual, aura], and tactile environment. A, description of the aesthetic
characteristic of the existing environment should include things that are seen, heard and smelled in
and around the site and their emotional or psychological effect on people. Descriptions (or pictures)
of views of the site, of unique features or features deemed of special value, and public use and
appreciation of the site provide information that must be available for the assessment of impacts.
Potential aesthetic impacts include the loss of visually pleasing areas as ground is disturbed and
previous surface expressions are eliminated or damaged. Mines typically create signifiàant noise
above the baseline conditions (from blasting, heavy equipment operation, materials/waste transport
and disposal, etc.). •Mitigation measures to address aesthetic impacts involve siting of mine features,
as well as facility design and mining practices.
4.5: SEDIMENTATIONIEROSION
• Because of the large area of land that is disturbed by mining operations and the large quantities of
earthen materials exposed at sites, erosion is frequently of primary concern at coal and 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
chémi al pollutants) to nearby streams, especially during s vere storm events, as well as high
snowmelt periods.
Major sources of erosion/sediment loadings at mining sites can include:
• Open pit areas
• Heap and dump leaches
• Waste rock and overburden piles
• Tailings piles
• Haul roads and access roads
• Ore stockpiles
• Vehicle and equipment maintenance areas
• Exploration areas
• Reclamation areas.
The, variability in natural site conditions (e.g., geology, vegetation, topography, climate, and
proximity to and characteristics of surface waters) combined with significant differences in the
quantities and characteristics of exposed materials at mines preclude any generalization of the
quantities and characteristics of sediment loadings. Further, new sources are frequently located in
areas with other active operations as well as historic mines (left in an unreclaimed state): There may
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also be many other non-mining sources of erosions in the watershed (other types of industrial
operations, naturally unstable areas, soil conditions, etc.). Therefore, in considering the erosion
effects from a new mining source, the cumulative impacts of sediment loadings from all sources
within a watershed need to be considered. An important element of this analysis is the potential for
the new source to alter downstream flow conditions and thereby alter contributions from downstream
sediment sources.
The following subsections describe: (1) the basic principles of erosion, (2) the impacts associated
with erosion/runoff (i.e.. the physical/chemical effects on the watershed), (3) approaches to
establishing baseline conditions, (4) methodologies to determine the sediment contributions from a
new source, and (5) measures to reduce/mitigate sediment loadings (i.e., best management practices
and treatment technologies).
4.5.1 BAsic EROSION PRINCIPLES
Water erosion may be described as the process by which soil particles are detached, suspended, and
transported from their source of origin. Sedimentation may be described as the by-product of
erosion, whereby eroded particles are deposited at a different location than the source of origin. Soil
detachment results from the energy of raindrops striking the soil surface or it results from suspension
of soil particles from overland flow. Runoff may be the result of rainfall or snowmelt. Erosion
occurs from the movement of water in sheet flow, in rills or gullies of ephemeral waterways, or
through channel erosion in ditches and streams. Wind erosion occurs when wind energy exceeds the
ability of soil to remain cohesive and the particles become detached. Typically, wind erosion is a
problem in arid climates.
The factors influencing erosion and sedimentation are interrelated and all relate to either the impact of
precipitation or runoff velocity and volume. Sedimentation is considered the final stage in the erosion
process, thus the mechanisms affecting erosion also affect sedimentation. . The main factors
influencing erosion include:
• RainfalllSnowmelt Runoff. The volume and velocity of runoff from storm events are
determined by the rainfall intensity and the duration of the rainfall event. A more intense
storm applies greater forces which results in greater displacement of soils; storms of longer
duration naturally produce more runoff, and thus greater erosion. Runoff also occurs
during snowmelt periods (with volume and velocity depending on melting conditions),
including rainfall-induced melting.
• Infiltration. Infiltration is the rate by which water moves downward through the soil.
Water that infiltrates does not become runoff, thus greater infiltration results in less erosion.
Infiltration is a function of the soil type, with porous soils tending to have greater
infiltration rates. Saturated and frozen ground impedes infiltration, resulting in greater
runoff.
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• Soil Texture and Structure. Soil texture describes the percentage composition sand, silt,
and clay particles in a soil. Soil structure generally refers to the aggregation 9 f soil
particles. Sand particles are heavier, and disregarding aggregation are generally less
susceptible to transport than are silt particles. Soils with high clay content are also less
susceptible to erosion because the particles tend to stick together. Soils high in silt content,
on the other hand, unless well aggregated, are the most erodible soils. The structure will
influence the erodability of each type of soil. Well aggregated soils are less likely to
detach. Runoff or airflow over these soils however may be increased, due to
impermeability and thus reduced infiltration. The relationships between soils type and
structure and potential water erosion are well known, yet complex. (Similar principles
apply to water erosion of waste/materials management units.)
• Vegetative Cover. Vegetative cover influences erosion by:
- Reducing the rainfall or wind energy striking the soil’s surface
- Lowering the velocity of overland and channel flow which:
— Reduces peak runoff rates and resultant impacts of channel erosion, and
— Decreases the velocity of overland flow, enabling sediment deposition to occur
closer to the original site
— Providing roots to hOld the soil in place.
Because vegetation acts in multiple facets, the relationship between vegetation and erosion ii
dramatic. This is perhaps best illustrated through curve numbers. Curve numbers are used
in the U.S. Geological Survey soil-cover complex method for estimating rainfall runoff arid
are an estimate of the percentage of rainfall runoff that will occur. The curve numbers for
forested land of varying soil conditions range from 25 to 83, meaning that forested lands
will produce from 25 to 83 percent runoff. In comparison, the curve numbers for a
denuded construction site of varyng soil conditions, range from 77 to 94.
• Slope length. The term “slope length” is defined as the distance from the point of origin
of overland flow to the defined point of interest, which may be a channel, or the point
where deposition begins. Longer sloped surfaces result in higher runoff velocities for the
particular segment.
• Erosion Control Practices in Place. Various practices and structures can be employed to
reduce the effects of land disturbances and developments. Erosion control practices work
by one or more of the following mechanisms:
- Reducing the impact of raindrops
- Reducing the runoff volume and velocity
- Increasing the soils resistance to erosion.
Specific erosion control BMPs applicable to mining site& are described in Section 4.5.5
bet ow.
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4.5.2 IMPACTS ASSoOATED wim ERosION/RuNOFF FROM DISrURBED AREAS
Particulate matter is toxic to fish. Decreased densities of macroinvertebrate and benthic invertebrate
populations have been associated with increased suspended solids. Enhanced sedimentation within
aquatic environments also has the effect of inhibiting spawning and the development of fish eggs and
larvae, as well as smothering benthic fauna. In addition, high turbidity may impair the passage of
light, which is necessary for photosynthetic activity of aquatic plants.
Further, exposed materials from mining operations (mine workings, wastes, contaminated soils, etc.)
may contribute sediments with chemical pollutants, including heavy metals. Contaminated sediments
in surface water may pose risks to human heaLth and the environment as a persistent source of
chemicals to human and aquatic life. Human exposure occurs through direct contact, eating fishi
shellfish that have bioaccumulated toxic chemicals, or drinking water exposed to contaminated
sediments. Continued bioaccumulation of toxic pollutants in aquatic species may limit their use for
human consumption. Accumulation in aquatic organisms, particularly benthic specifies, can also
cause acute and chronic toxicity to aquatic life. Finally, organic-laden solids have the effect of
reducing dissolved oxygen concentration, thus creating toxic conditions. There are no National
sediment criteria for the toxic pollutants likely to be released from mining sites, although criteria for
metals are currently under development and some States have established sediment standards.
Beyond the potential for pollutant impacts on human and aquatic life, there are physical impacts
associated with the increased runoff velocities and volumes from new land disturbance activities.
Increased velocities and volumes lead to downstream flooding, scouring of stream channels, and
structural damage to bridge footings and culvert entries.
4.5.3 ESTABLISmNG BACKGROUND CoNDmoNs
A characterization of background conditio s within a stream is necessary to assess the potential
impacts of new erosion/sedimentation sources. An important element in assessing baseline stream
habitat quality is an evaluation of the physical parameters of the stream. EPA (1989b) has suggested
that the following physical stream parameters be characterized at each stream sampling st’ation in the
assessment of a stream habitat.
• Predominant surrounding land use. A description of the predominant types of land use is
needed. In addition, secondary land uses may also potentially affect water quality.
• Local watershed erosion. A visual estimate of erosion can be made by observing the
watershed land surface and the stream characteristics (both channel characteristics and
sediment loads).
• Estimated stream width. A representative transect should be measured from shore to
shore to provide an estimate of stream width.
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• Estimated stream depth. Stream depth should be determined for three habitat types: riffle,
run and pooi. Measure the vertical distance from the water surface to stre ,bottom.
.‘ High water mark. Measure the vertical distance from the bank to the peak overflow level.
The peak, overflow level may be indicated by debris hanging in bank or floodplain
vegetation or deposition of silt or clay.
• Velocity. Stream vclocity should be estimated in a representative stretch of the stream.
• DamIobstades to flow present. The presence of a dam upstream or downstream of the
stream segment under study should be noted. Also, any other impediments to flow or
sediment transport should be noted. How the dam or obstacles affect flow should be noted.
Ch2nnelization. Describe whether the stream is channelized at any point along the stretch
of stream under study.
• Canopy cover. A description of the percentage of shaded area at each sampling station
along the stream should be provided.
• Sediment odors. Any odors emanating from the disturbed sediment should be noted.
•, ‘ Sediment oils. A visual estimate of the proportion of any oils in the sediment should be
noted.
• Sediment deposits. A description of the type of deposits present in the stream (sand,
sludge, organic material, etc) and any blackened undersides of rOcks (indicates low
dissolved oxygen or anaerobic conditions).
• Inorganic substrate components. A visual estimation should be made of the percentage of
• inorganic substrate components present.
• Organic substrate components. A visual estimation should be,made of the percentage of
organic substrate components present.
This method for evaluating the physical condition of a stream can be made more rigorous by
including quantitative evaluations of sediment transport. A quantitative evaluation of sediment
transport may be more suited for areas where significant disturbances already exist and more rigorous
documentation and understanding of the baseline conditions is necessary. Quantitative measurements
may be made of suspended and bedload sediment in the stream, as well is measurements of sediment
deposits (sediment, bars, substrate; eic.) and turbidity (turbidity measures the ability of a fluid to
transmit light). These data provide a rough estimate of the concentration of suspended sediments in
water. A quantitative baseline measurement may also be made of the stream channel throughout the
area of impact.
The sampling of suspended sediment can provide information on the physical and chemical
characteristics of the sediment in suspension. Depth-integrated sampling, as opposed to point
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sampling, is preferred to characterize both the concentration of suspended sediment carried by the
stream, as well as providing a representative sediment sample for chemical characterization of the
sediment and adsorbed constituents (USGS, 1977). Depth-integrated sampling involves the use of a
depth-integrated sampler that is lowered/raised throughout the depth of the stream at a constant speed.
If the depth-integrated sampler is also used to sample across a stream transect, the concentration of
suspended sediment obtained can be multiplied by the water discharge through the sample zone and a
total suspended sediment discharge can be obtained (USGS, 1977). Consequently, to provide an
accurate measurement of suspended sediment loads in a stream, samples should be collected near
stream gauging stations.
Sample site selection should take into account the following preferences: located near a stream
gauging station, located away from any flow distorting obstacles, and far enough either upstream or
downstream of confluences to prevent the hydraulic variances that exist in those zones (USGS, 1977).
Frequency of sampling should be determined by the known historical streamfiow or precipitation
records, at a minimum, the stream should be sampled at periods of annual low and high flow.
Sampling of the deposited sediment in the streambed can provide a wide range of information
including the type of sediment available for transport, mineralogy of the sediments, stratigraphy, and
amounts and distribution of contaminants (USGS, 1977). Sampling methods are available for
collecting disturbed or undisturbed samples. For the purposes of baseline sampling for a mining
project, an undisturbed sample may not be necessary.
In addition to a physical characterization of the stream, a habitat assessment should be conducted to
determine the baseline conditions of the stream’s ability to support aquatic life. The parameters to be
assessed represent measurements/observations of substrate and instream cover, channel morphology
and riparian and bank structure. EPA (1989b) has identified the following parameters for evaluating
the baseline conditions of stream habitat.
• Bottom substrate/available cover. A visual observation of the ability of the bottom
substrate to provide niches for aquatic life should be made.
• Embeddedness. Embeddedness refers to the percentage of fines surrounding large size
(boulders, rubble or gravel) particles.
• Stream flow/stream velocity. The volume and velocity of stream flow should be evaluated
with respect to optimal conditions for aquatic life.
• Ch2nnel alteration. An observation of growth or establishment of sediment bars or other
deposition can indicate changes in upstream erosion. The development of channelization
should also be noted.
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Bottom scouring and deposition. An observation should be made of the degree to which
the substrate is scoured and the amount of siltation in riffles and, pools. This observation is
typically reported as a percentage of the observed stretch that is scoured or silted. Bottom
scouring and deposition result from sediment transport and may provide an indication of
watershed erosion.
• Pool/riffle or run/bend ratio. This ratio is calculated by dividing the average distance
between riffles or bends by the average stream width. This parameter assumes that the
higher proportion of riffles and bends provides more diverse habitat than a straight or
uniform depth stream.
• Bank stability. Bank stability is typically determined by the steepness of the bank and any
observed erosion into the stream. Steeper banks generally indicate poor quality instream
• habitat due to there susceptibility to erosion, however, stream banks of clay may not be as
susceptible to erosion as stream banks composed of other sediment.
• Bank vegetative/rock stability. Bank stability may also be estimated by the type and
amount of vegetation and rock cover present. Proportions of shrub, trees, grasses and
rocks providing bank cover should be estimated.
• Streamside cover. An estimate of the primary type of vegetation that is providing
streamside cover should be made. It should also be noted if no cover is provided.
The above information on the sediment and habitat quality should be considered in conjunction with
baseline studies of aquatic ‘organisms within the watershed (including fish count, macroinvertebrates,
etc.). The combined data will allow the reviewer to correlate background aquatic life conditions to
sediment quality.
4.5.4 . PREDICTING SEDIMENT LOADINGS FROM NEW SOURCES
There are currently several approaches/models available to. assist in the prediction of sediment losses
and flow responses of basins both before and after landscape alterations due to mining and other
human activities. As with any models, they are highly sensitive to the input data supplied and caution
must be used in identifying and quantifying the important factors for a specific project.
The primary factors affecting basin sediment yields are:
• Precipitation. Volume, intensity, and duration are all important
• Vegetation. Vegetation increases the ability of hilislopes to retain overland flow, increase
infiltration, and reduce the velocity of overland flow
• Basin size. Basin size controls the lagtime between the beginning of the storm event and
the time of peak flow .
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• Elevation and relief. Basins with steeper overall slopes will have higheT overland flow
velocities and quicker response times to storm events
• Soil/rock type. Different soil types have varying degrees of erodability, infiltration
capacities
• Human activity.
4.5.4.1 Available TechniquesfModels
Modeling basin hydiology can take forms varying in complexity from “back of the envelope”
calculations to computer-based, inultivariate modeling based on data from comprehensive field
investigations. Most modeling, of any level of complexity, is based on several basic equations
developed Specifically to predict soil losses from known basin characteristics. These equations
include: the Universal Soil Loss Equation (USLE), the Modified USLE (MUSLE), and the Revised
USLE (RUSLE). These equations are described below.
The Universal Soil Loss Equation (USLE)
The liSLE has been developed utilizing data gathered at a large number of experinental sites. The
equation utilizes six hydrologic variables to generate predictions of annual total soil loss in tons per
acre for a given drainage basin. Values of the equation variables are determined by comparing site
specific observations. of basin characteristics to published graphs and tables to determine the
appropriate value. The U.S. Soil Conservation S vice publishes many of the appropriate standard
tables which have been developed from numerous studies of basin dharacteristics in a numbçr of
climates.
The liSLE is written:
A=RK(LS)CP
Where A is the total soil loss in tons per acre per year, R is the rainfall erosivity index, K is the soil
erodability index, LS is the length-slope steepness factor, C is the cropping management factor, and P
is the erosion control practice fact’or. An increase of any of these factors will result in increases in
the total predicted soil losses for an area.
The Modified Universal Soil Loss Equation (MUSLE)
The MUSLE equation is written in final form identically to the USLE. It varies from its predecessor
in the introduction of an exponential flmction lot the determinaiion of the length-slope factor (LS).
The modified LS-factor has been shown to work well on slopes up to 15 to 20 percent but on steeper
slopes predictions of erosion become much greater than those actually observed. The R-factor is also
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changed and is now a product of the total per-acre runoff volume and the maximum rainfall intensity
for a given storm.
MUSLE also improved its predecessor by allowing predictions of soil losses for single storm events.
This is important because allows for the examination of losses during peak conditions which may
account for a large percentage of total annual losses.
The Revised Universal Soil Loss Equation (RUSLE)
RUSLE takes the same basic form as both the USLE and MUSLE. However, the RUSLE improves
upon both previous incarnations by using several LS functions to model slopes of different steepness.
Of the three approaches, RUSLE works best for steep basins (slopes greater than 20 percent).
Other Soil Loss Equations
Several other soil loss prediction models have been developed that are based less on standardized
tables of factors and equations but are instead theoretically based. These models are important in that
they. allow for the testing of hypotheses on the physics of hillslope hydrology. However, to date, they
have not yet been shown to be accurate predictors of total sediment losses and so remain more
theoretical than practical.
Computer Models
A number of computer models are available which utilize variations of the USLE and other soil loss
equations to perform automated analysis of soil losses from basins. These models are available from
commercial, governmental, and academic sources. The most sophisticated. of these allow for theY
subdividing of larger basins into smaller sub-basins and, utilize routing functions to predict the
response to the same storm of sub-basin areas which may have very different soil, vegetative and
land-use conditions. -
4.5.4.2 Modeling Considerations
In the -use of any of the above modeling schemes, the accurate determination of current and potential
site conditions is viti to generating, accurate results. In some cases, what seem to be fairly small
variations in site conditions can make great differences in predicted sOil losses. For example, the
cropping management factor, C, can vary by a factor of 3 with a change in yegetative cover of 20
percent (U.S. Soil Conservation Service, 1975). Under- or over-estimating’ canopy cover by 20
percent will produce a 300 percent variation in the predicted soil loss.
Great importance should be placed on the accurate determination of the conditions within the basin.
It is possible, and not too uncommon, to approximate values for some factors without actually visiting
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a site. The Soil Conservation Service has made available tables and maps which provide probable
ranges of values for various site conditions. However, since the strength of a model depends on the
strength of input data, final determination of the factors to be used in a model should be based upon
observations made on site. Some important factors affecting soil erodability, such as the presence of
thick leaf litter on a forest floor, are not determinable from aerial photos or maps. Any modeling
performed without actual site observation should be considered a first approximation.
The final step in any modeling is verification. A model should not be considered to have predictive
power for hypothetical conditions until its ability to accurately model known conditions has been
shown. This means comparing actual measurements of soil losses with those predicted by the model.
A great disparity between these two values indicates the need to examine either assumptions of the
model or the field measurement techniques.
The selection of storm events for use in modeling predictions should also be carefully considered.
Since both intensity and duration affect the generation of overland flow, both short duration/high
intensity storms and long duration/moderate intensity storms should be considered. Also, antecedent
conditions at a site may be important. High intensity storms will produce higher peak flows and
greater erosion rates if they fall on already saturated, frozen, andJor snow covered soils.
Overall, modeling results should allow the operator to quantify the impacts of the proposed land
disturbance on the affected watershed (in terms of losses of soil per unit area and total solids
loadings). However, available methodologies do not address deposition of generated sediments in
downstream reaches. There. are no specific criteria to determine what level of increase in TSS
concentrations, turbidity, or total sediment loadings coi stitutes a significant impact. To a large
extent, this is subject to best professional judgment (in consideration of the baseline watershed
conditions as discussed above). Similarly, BPJ is necessary to assess how any toxic pollutants
associated with solids loadings could affect sediment quality, and this should always be considered.
Factors to consider include: potential sources of toxic pollutants, existing sediment quality, any
available data on the affects of similar operations/land disturbance within the watershed (where
applicable), and the nature/designated uses of the receiving water.
4.5.5 SEDIMENT AND EROSION MITIGATION MEASURES
Sediment and erosion mitigation measures are used to reduce the amount of materials carried off site
and deposited in a receiving stream. To meet this objective, mine operators should consider methods
to limit runon, minimize the areas of disturbed soil (exposed to precipitation), reduce runoff velocity,
and remove sediment from on-site runoff before it leaves the site. In many cases, a range of different
BMPs/sediment and erosion controls are used concurrently at mine sites. The three main categories
of sediment and erosion controls are: diversion techniques, stabilization practices, and structural
controls. The following subsections briefly describe each of these categories.
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4.5.5.1 Diversion Techniques
Diversion techniques are measures that prevent run-on, precipitation, and other flows from crossing
areas where there is a risk of significant erosion. Diversion practices often use on-site materials, and
take advantage of on-site topographic, vegetative, and hydrologic factors to divert flows away from
disturbed areas/soils. Typical diversion practices used at mine sites includà: interceptor dikes and
swales; diversion dikes, curbs and berms; pipe slope drains; subsurface drains; and drainage/storm
water conveyance systems (ch.annels or gutters; open top bOx culverts, and waterbars; rolling dips and
road sloping; roadway surface water deflectors; culverts).
4.5.5.2 Stabilization Practices.
Stabilization, as c iscussed here, refers to covering or maintaining an existing cover over soils. The
cover may be vegetation, such as grass, trees, vines, or shrubs. Stabilization measures can also
include nonvegetative controls such as geotextiles (matting, netting or blankets), mulches, riprap,
gabions (wire mesh boxes filled with rock), and retaining walls. These stabilization practices act to
prevent or minimize erosion by holding soil in place, shielding it from the impact of
precipitationlsnowrnelt, and increase surface contours to slow runoff velocity.
The establishment and maintenance of vegetation is one of the most important factors in preventing
erosion. Veletative controls are often the most important measures taken to prevent Off-site sediment
movement, and can provide a six-fold reduction in the discharge of suspended sediment levels. In
addition, these practices can enhance habitat values and the appearance of a site. Examples of
vegetative practices include temporary or permanent seeding, vegetative buffer strips and protection of
trees. Nonvegetative stabilization practices can be used as a temporary or permanent erosion
prevention measure. These controls can be used in order to aid in establishing vegetation or as stand
alone practices.
Vegetative controls are low cost and require low or no maintenance once a ground cover has been
established. However, prior to the establishment of a vegetative cover, considerable site preparation
may be necessary such as contouring of disturbed areas, placement of topsoil on barren areas, soil
conditioning (e.g., with municipal sewage sludge), or spraying areas with fertilizers.
Contouring refers to a number of practices including recontouring, regrading, reshaping, and surface
roughening. Contouring of waste piles will provide a number of benefits, including aiding in the
reduction of storm water and run-on velocities, assisting in the establishment of a permanent
vegetative cover, and improving site aesthetics. Specifically, reducing the height and steepness of a•
slope can greatly reduce erosion and sedimentation at a site.
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Where recontouring wastes is not practical due to geographic or resource considerations, reshaping of
wastes may be a viable option. Reshaping BMPs refer to the rearranging of waste piles and exposed
areas in such a way as to reduce the steepness of slopes (terracing/benching), moving waste piles out
of streanibeds or other highly erodible areas, and other methods to reduce run-on and storm water
velocities over and around areas susceptible to erosion.
After an irea has been recontoured or reshaped, surface roughening may be employed to further
reduce runoff velocjty and promote infiltration, as well as supporting revegetation. A rough soil
surface is amenable to revégetation, through creation of horizontal grooves, depressions, and/or
terraces that parallel the contour of the land.
4.5.5.3 Structural Practices
Structural controls involve the installation of devices to store flow or limit runoff velocity. Structural
practices can be used to remove sediment from runoff before the runoff leaves the site. Approaches
to removing sediment from site runoff include diverting flows to a trapping or storage device or
filtering diffuse flow through silt fences before it reaches the receiving water. These methods are
designed to slow the flow of water discharged from a site; resulting in the settling of solids and the
limiting of downstream erosion. Structural controls also promote infiltration.
Structural sediment and erosion control practices are typically low in cost. However, structural
practices require periodic maintenance (including sediment removal) to reman functional. As such,
they serve as more active-type practices which may not be appropriate for permanent use at inactive
mines. However, these practices may be effectively used as temporary measures during active
operation and/or prior to the implementation of permanent measures. -
Some examples of structural practices include: settling ponds/detention basins, check dams, rock
outlet protection, level spreaders, gradient terraces, straw bale barriers, silt fences, gravel or stone
filter berms, brush barriers sediment traps, grass swales, pipe slope drains, earth dikes, and other
controls such as entrance stabilization, waterway crossings or wind breaks.
In some cases, the elimination of a pollution source through capping sources of erosion may be the
most cost effective control measure for sediment discharges and.other pollutants. Depending on the
type of management practices chosen, the cost to eliminate the pollutant source may be very high.
Once completed, however, maintenance costs will range from low to nonexistent.
4.5.5.4 Contact Prevention Measures!Reclaination Practices
Permanent reclamation, as discussed here, refers to covering or maintaining an existing cover over
disturbed areas. The cover may consist of grass, trees, vines, shrubs, bark, mulch and/or straw.
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Ultimately, revegetation involvesestablishing a sustainable ground cover aCa site through permanent
seeding, mulching, sodding, and other such practices.
The establishment and maintenance of vegetation is one of the most important factors in minimizing
erosion. A vegetative cover reduces the potential for erosion of a site by: absorbing the kinetic
energy of raindrops which would otherwise impact soil; intercepting water so it can infiltrate into the
ground instead of running off; and by slowing the velocity of rurioff to promote qnsite deposition of
sediment: Vegetative controls are often the most important measures taken tq prevent offsite sediment
movement, and can provide a six-fold reduction in the discharge of suspended sediment levels. In
addition, these practices can enhance the habitat and aesthetic values of a site.
Typically, the costs of vegetative controls are low relative to other discharge mitigation practices.
Given the limited capacity to accept large volumes of runoff, and potential erosion problems
associated with large concentrated flows, vegetative controls should typically be used in combination
with other management practices. These rnea ures are universally considered to, be nearly always
appropriate for mining sites, as evidenced by their being required by all States that require
reclamation of closing coal and non-coal sites.
As noted above, vegetative controls are low cost and require low or no maintenance once a ground
cover has been established. However, prior to the establishment of a vegetative cover, considerable
sue preparation may be necessary such as contouring of disturbed areas, placement of topsoil on
barren areas and the spraying of areas with fertilizers. Further, predicting the likely success of•
reclamation practices at mine sites has often proven difficult. Where reclamation/revegetation is a
key element of lon -éerm erosion control, the operator should consider establishing representative test
plots to increase the , likelihood of success.
Contouring
Prior to the establishment of vegetation, surface contouring is often required. Coniouring refers to a.
number of practices including recontouring, reshaping, and surface roughening.
Recontouring waste piles/disturbed areas at a site will provide a number of benefits. Recontouring
wastes or disturbed areas to match the original land contours ‘of a site will aid in the reduction of
storm water and run-on velocities, assist in .the establishment of a permanent vegetative cover, and
improve site aesthetics. Reducing the height and steepness of a slope, combined with other diversion
BMPs discussed above, can greatly reduce etosion and sedimentation at site. This practice is also
often times necessary to establish a vegetative cover over exposed materials.
Where recontouring wastes is not practical due to geographic or resource consIderations, reshaping of -
wastes may be a viable option. Reshaping refers to the rearranging of waste piles and exposed areas
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in such a way as to reduce the steepness of slopes (terracing/benching) and other methods to reduce
run-on and storm water velocities over and around areas susceptible to erosion.
After an area has been recontoured or reshaped, surface roughening may be employed to aid in the
establishment of vegetation. A rough soil surface is amenable to revegetation, through creating
horizontal grooves, depressions, or steps that run with the contour of the land. Slopes may also be
- left in a roughened condition to reduce dischaEge flow and promote infiltration.
Surface roughening• aids in the establishment of vegetative• cover by reducing runoff velocity and
giving seed an opportunity to take hold and grow. Increased vegetative cover, in turn, provides
increased filtration and sediment trappiI g, further decreasing runoff velocity and erosion.
These techniques are appropriate for all slopes steeper than 3:1 in order to facilitate stabilization of
the slope and promote the growth of a vegetative cover. Once areas have been contoured, they
should be seeded as quickly as possible;
Topsoiling
Topsoiling may be necessary to improve, provide, or preserve the area on which -a permanent
vegetative cover will be established. These practices are not used alone to provide erosion control,
but are an integral part of establishing vegetative controls. Conditioning may be required where soil
is of poor quality. More resource intensive topsoiling measures may be needed where soils are
without nutrient properties, where the need to quickly establish vegetation is paramount, where the
existing soils contain materials toxic to plant growth (i.e., acidic soil such as that found at some
mines), or where the soil rooting zone is not deep enough to support plants.
Soil conditioning may include the use of fertilizers, or less expensive measures such as the land
application of municipal sewage sludge. Using topsoil may require the importing of soils from an
alternate location or the use of soil from a nearby site.
Whçn applying soil conditioners -or topsoil’; measures must be put in place to prevent washouts prior
to the establishment of vegetation. The timing of this practice shOuld be coordinated with seeding and
planting practices so that they can be performed immediately after soil conditioning or topsoiling is
completed. Additionally , it is necessary to provide measures, such as mulching or. diversion which
prevent erosion of the topsoil or conditioned soil. These practices should be coordinated with seeding
and planting practices so’ that they can be performed immediately after conditioning or topsoiling.
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Seeding
The establishment of plant life stabilizes soils and helps to reduce sediment in runoff from a site. In
addition, vegetation filters sediments, maintains the soil’s capacity to absorb water, improves wildlife
habitats, and enhances site aesthetics.
Seeding and planting are appropriate for any disturbed area that is subject to erosion. This practice is
particularly effective in areas where soils are unstable due to texture, structure, high water table,
and/or high slope such as those commonly found at inactive mining, landfill, and oil and gas sites.
Selection of appropriate vegetation, good seed bed preparation, timing, and maintenance are needed to
ensure the success of this practice. Selection of native species will increase the chances for success
and may lessen future maintenance requirements..
Capping of WastesIMaterials
Capping/sealing of wastes/materials (includingsurface mine workings, tailings and waste rock) is
designed to limit or eliminate contact between runoff and potential sources of sediment/toxic pollutant
loadings. The use of this practice depends on the level of control desired, the materials available, and
cost considerations. Many common types of caps may be effective including soil, clay, and/or
synthetic materials. Generally, soil caps will provide appreciable control for the lowest cost. Any
type of cap may be covered with up to several feet of rock and soil and revegetated.
4.5.5.5 Treatment Techniques
Discharge detention structures can achieve a high removal rate of sediment and metals, such as those
which may be expected to be discharged from inactive mining operations. Complemented by ease in
construction and simple operations and maintenance, the use of detention structures desirable as a
treatment mechanism for discharges from inactive mines and landfills. Site characteristics must be
such that discharges can practically be channeled to a centralized area for treatment.
Detention basins are most cost-effective at larger sites. In addition to their pollutant treatment
capacity, detention ponds can also create wildlife habitat, recreational, and landscaping benefits.
Even at larger sites, however, hydrologic and topographic factors, as well as inaccessibility and cost,
may limit their utility.
4.6 METALS AND DISSOLVED POLLUTANTS
Dissolved pollutants (primarily metals, sulfates, and nitrates) can migrate from mining operations to
local ground and surface water. While ARD can enhance contaminant mobility by promoting
leaching from exposed wastes and mine structures (see Section 4.1), releases can also occur under
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Environmental Issues EIA Guidelines for Mining
neutral pH conditions. Primary sources of dissolved pollutants from coal and metal mining operations
include: underground and surface mine workings; overburden and waste rock piles; tailings piles and
impoundments; direct discharges from conventional millingfbeneficiation operations; leach piles and
processing facilities; coal processing units; chemical storage areas (runoff and spills); and reclamation
activities. Discharges of process water, mine water, runoff, and seepage are the primary transport
mechanisms to surface water and groundwater.
One potential source of dissolved pollutants is chemicals used in mining and beneficiation. Common
types of reagents include copper, zinc, chromium, cyanide, nitrate and phenolic compounds, along
with sulfuric acid at copper leaching operations. With the exception of leaching operations and
possibly the extensive use of nitrate compounds in blasting and reclamation, the quantities of reagents
used are very small compared to the volumes of water generated. As a’ result, the risks from releases
of toxic, pollutant from non-leaching-related reagents are generally limited (see Sections 4.1 and 4.2
for discussions of the potential impacts associated with acid and cyanide releases).
A. major source of pollutants is naturally occurring substances in the ore. Mined ore not only
contains the mineral being extracted but varying concentrations of a wide range of other minerals
(frequently other minerals may be present at much higher concentrations and can be significantly
more mobile than the target mineral). Depending on the local geology, the ore (and the surrounding
waste rock and overburden) can include trace levels of aluminum, arsenic, asbestos, cadmium,
chromium, copper, iron, lead, manganese, mercury, nickel, silver, selenium, and zinc.
The occurrence of specific pollutants, their release potential, and the associated risks are highly
dependent on facility-specific conditions, includinE: de ign and operation of extraction and
beneficiation operations, waste and materials management practices, extent of treatment/mitigation
measures, the environmental setting (including climate, geology, hydrogeology, waste and ore
mineralogy and geochemistry, etc.) and nature of and proximity to human and environmental
receptors. In the development of the National effluent guidelines for the Ore Mining and Dressing’
and Coal Mining Point Source categories (40 CFR Parts 434 and Part 440), EPA conducted sampling
and analysis at mine sites to identif r pollutants of concern at mining operations (focusing primarily on
mine water and process water, not runoff). E,thibit 4-4 provides a summary of the metal pollutants
commonly associated with discharges from specific types of hardrock/non-coal mining operations
(along with typical treatment practices). Exhibit 4-5 describes dissolved pollutants often found in
discharges from coal mining, operations.
As stated above, the data presented in the tables were primarily obtained from sampling of mine
drainage and beneficiation process wastewater. With the exception of coal and refuse pile runoff at
coal mining operations, runoff (as well as infiltrationJseepage) have not been well characterized.
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Exhibit 4-4. Typical Pollutants Associated With Hardrock Mining Operations
Potential Pollutants of Concern in
Discharges to Surface and
Mining ‘. ‘. “• Groundwater “ ‘ “
•
•
Typical Treatment
Asbestos, arsenic, and copper, iron
Settling ponds and flocculation.
Zinc, Gold, Aluminum, antimony, arsenic,
Molybdenum cadmium, chromium, copper, lead,
de leaching manganese, nickel, ‘thallium, and zinc
Recycling/reuse and
settling/precipitation ponds
None found at high concentrations
Not Applicable
Copper, lead, and zinc.
.
Recycle (mines have generally been
located in arid regions)
‘ Most toxic metals
Evaporation ponds and/or
recycle/reuse
Radium 226
Evaporation; ion exchange;
flocculation; settling; and
recycle/reuse
Antimony, arsenic, and asbestos
Recycle/reuse
Most toxic metals
Settling and precipitation
(lime/caustic addition)
Mercury, arsenic, cadmium,
chromium, copper, mercury, lead
and zinc
Neutralization, settling and
precipitation
Source: EPA, 1982; ore mining and dressing development document.
Further, they have historically not been subject to the same level of control/treatment as mine and
process wastewater.
In assessing the nature and extent of potential dissolved pollutant releases from new source mining
operation, reviewers can often supplement general information (such as the above tables) with site-
specific data. This will include information on local geology (focussing on the chemistry of each
geological unit and the likely composition of wastes/exposed materials). In addition, mining
operations are often located in historic mining districts. Where this is the case, significant existing
data may be aviilable (or collected under baseline monitoring) to describe past releases to surface
water and groundwater, how they have affected the environment, and the effectiveness of current
treatment/control measures. It is not uncommon to find naturally occurring levels of metals and
sulfates (particularly iron and manganese) in highly mineralized ground and surface water. However,
mining and land disturbance activities have the potential to increase the loadings and mobility of
specific pollutants.
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Exhibit 4-5. Typical Pollutants Associated With Coal Mining Operations
Wastewater pe..:.:
Potential Pollutants of Concern in..
Discharges to Surface and
‘ ..: ..:. :: . Gro dwater. :
pical eatment
Coal preparation plant
wastewater
Arsenic, cadmium, copper, lead,
silver, and zinc,
Settling and precipitation,
recycle/reuse
Coal pile runoff
.
.
Manganese, iron, arsenic, chromium,
copper, lead, mercury, nickel,
selenium, and zinc
Neutralization and precipitation
Refuse pile runoff
Copper, cadmium, silver, and zinc
Neutralization and precipitation
Alkaline mine drainage (see
Section 4.1 for discussion
of acid mine drainage)
Iron and manganese .
Neutralization and precipitation
..
EPA’s Quality Criteria for Water provides information on the acute and chronic impacts of dissolved
pollutants in surface water (including suggested water quality standards). Each State has promulgated
water quality criteria for surface waters based on the designated uses of the waters as well as
establishing guidelines on how to apply the standards. Reviewers should be cognizant that, unlike
many other types of industrial operations and discharges, there can be extreme variability in toxic
constituent loadings from mining operations, both from day to day and over months and years.
Further, the receiving water may be particularly sensitive to loadings of toxic pollutants during
specific periods (e.g., under certain flow conditions). In conducting baseline analysis, the operator
should ensure that such conditions are identified. A long-term sampling plan should then be
developed to include sampling and analyses during these critical periods. As discussed in Sections
4.1 and 4.5, traditional quarterly or biannual monitoring programs may not provide for sampling
when dissolved pollutant loadings could have the most adverse impacts on surface water quality.
Dissolved pollutants discharged to surface waters can partition to sediments. Specifically, some toxic
constituents (e.g., lead and mercury) associated with discharges from mining operations are often
found at elevated levels in sediments, while nbt being detected in the water column. Sediment
contamination may impact human health through consumption of fish that bioaccumulate toxic
pollutants. Further, elevated levels of toxic pollutants in sediments can have direct acute and chronic
impacts on macroinvertebrates and other aquatic life. Finally, sediment contamination provides a
long-term source of pollutants through potential redissolution in the water column. As noted in
Section 4.5, there are currently no national sediment standards/criteria for toxic pollutants associated
with mining operation (although EPA is in the process of establishing criteria and partitioning
techniques for toxic metals). Reviewers must typically rely on BPJ to determine the sediment impacts
from new sources.
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Finally, the ability of pollutants to dissolve and migrate from exposed materials/waste management
units to groundwater varies significantly depending on the constituent of concern, the nature of the
material/waste, the design of the management unit, soil characteristics, and local hydrogeology
(including depth, flows, and geochemistry of the underlying aquifers). Potential risks to human
health and the environment from contaminated groundwater usage are a functionof the types of and
distance to local users. In addition, impacts on groundwater can also indirectly affect surface water
quality (through recharge and/or seepage). At some sites, the potential for groundwater
contamination may be limited, to alluvial aquifers which have limited beneficial uses but are significant
source of recharge. Section 4.5.1 describes elements to consider in performing baseline and long-
term groundwater monitoring.
4.7 AIR QUALITY
The primary air pollutant of concern at mining sites is particulate matter. As noted in Chapter 5,
particulates with a diameter of less than 10 microns is one of the air pollutants for which’ EPA
‘established National Ambient Air Quality Standards. State Imp!ementation’ plans must ensure that
particulate emissions from whatever source are controlled sufficiently to allow attainment of the
ambient air standard and to meet opacity requirements.
Particulates are emitted from a variety of mining o erations, usually as fugitive dust (as opposed to
emissions from stacks), and re’atively simple controls are typically sufficient:
• Ore crushing and conveyors can be ‘a substantial ,source of fugitive dust, and control
generally involves water sprays or mists in the immediate area of the crusher and
along conveyor routes.
• ‘ Loading bins for ore, limestone, and other materials also generate dust. Again, water
sprays are, typically used.
• Blasting generates’ dust that can be, and sometimes is, controlled with water sprays.
• Equipment and vehicle travel on access (and haul roads is a major source of fine and
coarse dust. Most mines use water trucks to dampen the surface periodically
• Waste rock dumping can generate dust; but this ‘generally consists of coarse particles
that settle out rapidly with no other controls. ‘
• Wind also entrains dust from dumps and spoil piles, roads, tailings (either dry as
disposed or the dry portions of impoundments), and Other disturbed areas. Spray
from water trucks are often used when the mine is operating. During temporary
closures and particularly after the active life, stabilization and reclamation are aimed’
in part at reducing fugitive dust emissions. Tailings in particular can be a potent
source of fine particulates. Rock and/or topsoil covers, possibly with vegetative
covers, can be effective controls.
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As discussed in various sections above, tailings and waste rOck at metal mines usually contain trace
concentrations of heavy metals. Fugitive dust would also contain such metals, and areas immediately
downwind could accumulate troubling amounts of dust as coarse particles settle out ,of suspension in
the air.
In addition, on a few occasions, wind has caused cyanide sprays on heap leach piles to blow short
distances and caused very localiied damage. For this reason, more opetators are turning to drip
applicationof cyanide solutions.
• 4.8 SUBSIDENCE
Mining subsidence can be defined as the ‘surface results that occur as a result of the collapse of
overlying strata into, mine voids.’ The potential for subsidence exists for all forms of underground
mining. Subsidence may manifest itself in the form of sinkholes or troughs. Sinkholes are usually
associated with the collapse of a portion of a mine void (such as a room in room and pillar mining);
the extent of the surface disturbance is usually limited in size. Troughs are formed from ‘the
subsidence of large portions of the underground void and would be typical over areas where most of
the resource had been removed (Singh and Bieniawski, 1992).
The threat and extent of subsidence is related to the method of mining employed. . In many instances,
traditional, room and pillar methods leave enough material in place to avoid subsidence effects.
However, high volume extraction techniques including pillar retreat and longwall mining result in a
strong likelihood that subsidence will occur (McElfish and Beier, 1990; Britton, 1992).
Modern mining operations typically consider subsidence-in the planning process. Two approaches
may be taken to addressing the problem: planned subsidence or planned subsidence prevention
(Britton, 1992). The approach can be governed by the type of mining activity planned or by the
degree of severity of subsidence impacts.
Planned subsidence iiivolves predicting the maximum areal extent and depth of ground lowering
induced by the proposed mning activities. This prediction can be used to develop surface mitigation
measures or appropriate modification of surface land uses in response to the subsidence. Typically,
subsidence will occur within a few weeks after the mining face passes under an area although it may
take up to ten years for the, area to completely settle.
Subsidence prevention involves leaving supports (pillars) in place following mining activities to
prevent subsidence from occurring. In this approach, factors governing subsidence are also analyzed
so that a maximum amount of the resource may be removed while leaving enough material (either the
resàurce or backfill) in place to prevent subsidence. A combination of the planned subsidence and
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planned subsidence prevention approaches could be used in cases where some surface features require
protection while most of the overlying area do not.
The subsidence that occurs in areas overlying abandoned mines is referred to as unplanned
subsidence. These mines, in many cases, lacked any overlying development and were operated
without concern for subsidence. Unplanned subsidence can also occur in association with more
modern mining operations, arising when subsidence is not considered in the development of the mine
plan, or in the event of an unpredicted occurrence (i.e., roof or pillar failures, groundwater inflow).
In these cases, the depth and extent of surface disturbance cannot be (or is not) determined. Likewise
the tune frame for the occurrence of subsidence cannot be predicted.
The extent of subsidence depends on the thickness of the seam (or deposit) mined, the amount of coal
(or ore) left in place or the amount of backfill placed in the void, the nature and thickness of the
overlying strata, the depth to the void, the permeability of the overburden to water, and the presence
or absence of groundwater. The area potentially affected by subsidence extends beyond the area
• directly above the mining void; these effects to the adjacent lands extend into what is termed the angle
of draw.. The angle of draw extends 15° to 30° from the edge of the mining void outward (McElfish
and Beiàr, 1990, Singh, 1992).
Effects of subsidence may or may not be visible from the ground surface. Sinkholes or depressions
in the landscape interrupt surface water drainage patterns; ponds and streams may be drained or
channels may be redirected. Farmland can be impacted to the point that equipment cannot conduct
surface preparation activities, irrigation systems and drainage tiles may be disrupted. In developed
areas, subsidence has the potential to affect building foundations and walls, highways, and pipelines.
Groundwater flow may be interrupted as impermeable strata break down, and could result in flooding
o. the mine voids. Impacts to groundwater include changes in water quality and flow patterns
(including surface water recharge). . .
The Bureau of Mines has estimated that of the seven million acres of land underlain by underground
mining, two million have been affected by subsidence (McElfish and Beier, 1990). SMCRA requires
that underground coal mining operations prevent subsidence from causing material damage to the
extent technologically and economically feasible or, to. employ a mining method which provides for
“planned subsidence in a predictable and controlled manner.” Regulations governing subsidence from
non-coal mines is dependant on the individual regulatory authority responsible for those operations.
4.9 METHANE EMISSIONS FROM COAL MINING AND PREPARATION
The biogeochemical processes known as coalification give rise to the formation of methane (natural
gas) and other gases which remain closely associated with coal in virtually all coal-bearing
formations. Adsorbed to surface sites within the highly fractured coal matrix, methane typically
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constitutes only a small fraction of the total energy content of the in-place coal. Within the
formation, methane remains bound to surface sites in a monomolecular layer under the influence
formation pressure. However, under reduced pressure conditions resulting from mining, water draw
down, or erosion, methane desorbs from coal and becomes free to migrate within and beyond the coal
matrix.
Miners have long known of the release of methane from mined coal; methane is responsible for some
of the worst mine explosions to have occurred in this country and elsewhere. Accordingly, coal
mining operations always include substantial ventilation equipment to maintain airborne methane
concentrations below one or two percent.. Typically the vented ar is released directly to the
• atmosphere, though in some instances an effort has been made to collect and compress the methane
for onsite energy use or pipeline sales.
The necessity of venting methane from coal mines in advance of and during extraction operations
raises a number of environmental issues, both local and global. In particular, current political and
scientific concern over the prospect of global warming associated with the release of greenhouse gases
to the atmosphere has focused an increasing amount of attention on the role of methane in radiative
forcing. Methane is a potent greenhouse gas with a radiative forcing potential of 30 to 55 times that
of carbon dioxide. Because methane’s estimated contribution to the total atmospheric radiative
forcing associated with industrial emissions is significant, and because at least some of those
emissions may be relatively easily and profitably reduced, such emissions from coal mine
degassification may warrant consideration as incremental or cumulative impacts associated with coal
mining.
One recent study by EPA (EPA, September 1990) estimated the total methane emissions associated
with U.S. coal mining activity in 1987 to be roughly 7 million metric tons of methane, amounting to
approximately 7-12 percent of annual methane emissions from all U.S. sources. Methane is released
during degassification of operating mines (78 percent of releases), during pre-mining coal seam
degássification (18 percent), and during coal preparation (4 percent). Further, due to increasing
methane concentrations in coal with depth (due to temperature and pressure), an estimated 88 percent
of all methane releases from coal mining and use results from underground coal, with the remaining
12 percent attributable to surface-mined coal.
As a practical matter, few or no individual mines could be expected to release sufficient methane to
constitute a significant impact on the global atmospheric methane budget. However, the importance
of the overall potential impacts of greenhouse gas emissions make it appropriate to examine methane
emissions from coal mines in the context of cumulative and incremental impacts.
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More locally, some of the technologies associated with pre-mining degassification may have direct
surface impacts similar to those associated with oil and gas exploration and production activities.
Specifically, wells closely resembling conventional gas pr duction wells may be completed into the
area directly above long wall mining panels several years in advance of mining for the purpose of
removing (and recovering) methane from the coal seam. The wells are designed to draw down
formation water pressure allowing methane to enter the gas phase and flow to the well. Under
favorable conditions, methane may be recovered in sufficient quantities and under sufficient pressure
to allow onsite use or pipeline sale. In fact, co’albed methane development projects have grown
dramatically in,number since the early 1980s, particularly in areas where coal is too deep to mine
economically.
Coalbed gas development wells typi ally produce substantial quantities of fOrmation water along with
the gas. Such water may be high in chlorides and other dissolved solids, and presents a surface
management challenge. Additionally, drilling muds, workover and completion wastes, and other oil
and gas associated wastes may be generated at the degassification site. Any impacts caused by
‘coalbed degassification prior to or during mining could be considered as indirect effects of issuance of
a new source permit. Accordingly, the effects should be assessed along with other cumulative
impacts..
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5. . IMPACT ANALYSIS
This chapter describes specific NEPA documentation requirements and needs. Where appropriate, the
following sections distinguish among requirements that apply to EIDs; EAs, and EISs.
In many ways, this chapter builds on information presented in previPus sections. Chapter 2 provided
an overview of requirements for NEPA reviews of new source NPDES permitting actions. Chapter 4
identified the key.environmental issues and impacts associated with mining industry operations.
5.1 DETERMINE THE SCOPE OF ANALYSIS
‘Scoping” refers to the process of determining the nature and extent of significant issues associated
with a proposed action. Scoping is a key preliminary step for all types of assessments, allowing the
analyst to focus on what is most important.
In the case of EIDs, scoping is an informal process. As part of an initial consultation between EPA
and the permit applicant, the applicant should be prepared to explain why a permit for a new source
discharge is being requested. The applicant should be prepared to discuss the context for the permit
application and to address such questions as:
• How is the action related to your firm’s business or other objectives?
• How would the proposed new activities relate to any existing operations?
• - What issues are thought to be important with regard to the new source permit (e.g., any
additional employment opportunities or effects on the local economy, pollution, nearby
historic or cultural sites)?
• What existing environmental or other studies or data would be helpful in this review?
• is the pEoposed new source discharge anticipated to raise any concerns within your
community?
• Are any groups or individuals likely to be particularly interested in or concerned about the
new wastewater discharge?
in preparing an EA.. on the proposed issuance of a new source permit, EPA will review information
provided: by the applicant to help identify any potentially significant issues. EPA. also will contact
representatives of any Federal, State, or local government agencies that may have a particular interest
in the proposed action. Among those agencies likely to offer information that may be helpful in the
early identification of key issues are State mine land regulatory agencies and Federal land managers,
local land use planning agencies, the State environmental protection and natural resource management
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agencies, and the State Historic Preservation Officer (SHPO). Contact with Regional representatives
of the U.S. Fish and Wildlife Service and the National Marine Fisheries Service can be helpful in
early identification of .any potential issues relating to federally listed threatened and endangered
species.
Where an EIS is required scoping becomes a formal process that involves public participation and
interagency coordination.
Generally, a Notice of Intent for EIS preparation will contain an initial identification of potentially
important issues associated with a proposed action. The NOl also will describe the proposed method
for conducting the scoping process and will identiI ’ the office or person responsible for matters
related to scoping.
E IS preparation also involves holding one or more scoping meetings, .where affected Federal, State,
and local agencies, affected Tribes, and other interested persons are invited to participate in the
identification of key issues. Participants help draw attention to any other actions or previous
assessrnenà that may bear On the proposed action.! In addition, the scoping process may involve
addressing procedural issues. For example, the review and consultation procedures for the process
may be identified, a planning s hedule may be developed, and page and time limits for the assessment
may be set. -
5.2 IDENTIFY ALTERNATIVES.
In accordance with NEPA, impact analysis requires a description of the proposed action as well as a
description of all reasonable alternatives. The identification of alternatives is an essential step in the
preparation of EDs, EM, and EISs. For EISs, alternatives should be described in great detail.
The description of alternatives should include an identification of any alternatives that were considered
aztd rejected during the planning process. Any reasonable alternative should be considered by the
Applicant in order tO provide EPA with mote latitude in considering whether to issue the permit or
not. The rationale for the elimination of any alternatives from further consideration should be
provided. Alternatives generally are rejected based on techthcal, economic, envirOnmental, or
institutional considerations. In the case of an EIS, the decision to 4ismiss an alternative must be,
supported by data sufficient to respond to a challenging question or comment.
EPA ’s NEPA procedures recognize three general categories of alternatives: alternatives available to
EPA; alternatives considered by the applicant; and alternatives available to other agencies with
jurisdiction.
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5.2.1 ALTERNATIVES AVAILABLE TO EPA
Three types of alternatives are available to EPA in assessing the potentia] impacts of a proposed new
source NPDES permitting action:
• Issue the NPDES permit
• Issue the NPDES pernut with modifications to the proposal (including modifications that
may not have, been considered by the Applicant)
• Deny the NPDES permit.
The third option is generally referred to as the “rio action alternative.” This alternative provides a
baseline for comparing the impacts of other-options.
5.2.2 ALTERNATIVES CONSIDERED BY THE APPLICANT
When new industrial facilities are planned, operators typically undertake feasibility and planning
studies. Companies typically investigate processing options, markets, siting alternatives, and a host of
other technical, financial, and legal issues. These planning studies can be h tpful in the early
identification of critical issues, including potential land use conflicts, proximity to protected. natural
resources or historic sites, or any indication of hazard potential (e.g., location of facilities in
floodp lains).
The Applicant should explain the planning process to provide insight into the breadth and depth of
alternatives considered and rejected or pursued for further study. A well-documented explanation of
the Applicant’s analysis of alternatives is critically important to the impact assessment process.
In prirticular, it is important for the Applicant to explore and document a broad scope of alternatives
that look, at pollution prevention opportunities.
As part of an Em, the Applicant should provide a detailed description of the proposed action(s) as
well as a description of any alternatives that were considered, but rejected. The Applicant should also
consider the “no action alternative,” which would be not to apply for the NPDES permit.
EPA’s NEPA procedures require that the Applicant provide: (1) “balanced” descriptions of each
alternative and (2) a discussion covering size and location of facilities, land requirements, operations
and management requirements, auxiliaxy structures such as pipelines or transmission lines, and
construction ‘schedules.
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The Applicant should explain the implications of each option with regard to the firm’s goals and
objectives. The Applicant should consider the full range of options for meeting these goals and
objectives, including options that do not involve a discharge subject to permit requirements.
5.2.3 ALTERNATIVES AvAILABLE TO OrilER AGENCIES
A third category of alternatives are those available when EPA is preparing an EIS or other
environmental document in conjunction with another Federal or State agency. These additional
alternatives would be based on other relevant regulatory authorities. For example, in addition to a
new source NPDES discharge, a proposed project might involve dredging or filling of a wetland. In
this case, the U.S. Army Corps of Engineers would be responsible for issuing a permit under Section
• 404 of the CWA. Accordingly, the environmental analysis should account for the various alternalives
available to the Corps of Engineers, which.would include: granting the permit; granting the permit
with modifications or conditions; or denying the permit. The information to support issuance of a
permit under Section 404 should be included in the EIS, including how impacts to aquatic resources
wçre avoided, minimized, or compensated for.
5.3 DESCRIBE THE AFFECTED ENVIRONMENT
The affected environment section of any NEPA document should be no longer or, more detailed than
needed to understand potential environmental impacts. Background information on topics not directly
related to expected effects should be summarized, consolidated, or referenced to focus attention on
important issues.
The scope and content of this section of an EID will be determined during an initial consultation
between EPA and the Applicant. Generally, the Applicant will be required to provide any relevant
information that is readily available. In establishing the scope of this section of an EID, EPA will
consider the size of the new source ‘and the extent to which the Applicant, is capable of providing’
information. Requests for data should be kept to a minimum consistent, ‘with requirements under
NEPA.
For an EA, the description of the affected envIronment should focus on key issue areas, including the
following:
• Current and projected land use within the project area and within the region
• Current and projected population and population density
• Relevant land use regulations
• Local and regional patterns of energy demand and supply
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• Local ambient air quality conditions
• Local ambient noise levels
• Location of designated floodplains within the vicinity of the project
• Surface water and groundwater quality and quantity
• Local biological coi munities and fish and wildlife, habitats
• Critical habitats of any Federal- or State-listed threatened or endangered species
• Location of any properties listed in or eligible for listing in the National Register of
Historic Places
• Location of specially protected areas, including parkiands, wetlands, wild and scenic rivers,
• navigational areas, or prime agricultural lands.
‘In the case of an EIS, the description of the affected environment is more extensive and detailed. The
breadth of topics typically addressed within an EIS is. discussed below.
5.3.1 THE PHYSICAL-CHEMICAL ENVIRONMENT
The physical-chemical environment comprises the air, water, and geological characteristics of sites,
•where the environmental impacts of alternatives will be evaluated. This section of an EIS should
provide sufficient information to determine whether impacts are likely to be significant.
5.3.1.1 Air Resources
Air resources are described by the physical dynamic behavior of the lower atmosphere and by
variations in the concentrations of various gases and suspended matter. Physical dynamic behavior is
described by parameters such as the seasonal distribution of wind velocity and the frequency and
height of inversions. Wind velocity and the frequency of occurrence of inversions are often
determined by specific local topographic features, particularly surrounding hills or mountains. AIr
quality is described by the variations in the concentrations of pollutant gases in the lower atmosphere.
Both are needed to determine the environmental impacts of facility stack emissions, the effects of
mobile sources on local air quality, and the likelihood that dust will be of importance during
construction, operation,, and after abandonment. -
The description of meteorological regime(s) should include a generalized discussion of regional and
‘site-specific climate including:
• Diurnal and seasonal ground-level temperature
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• Wind characteristics at different heights and times (wind roses are particularly helpful and
provide wind speed, direction, frequency, and stability characteristics of the atmosphere)
• Total monthly, seasonal, and annual precipitation, frequency of storms and their intensity,
including both average and extreme events
a Height, frequency, and persistence of inversions and atmospheric mixing characteristics
• Description of pattern(s) evident for days of significantpollution episodes; evaporation.
Information on ambient air quality is often required to predict the impacts during construction and the
operation of a facility. Using existing air quality as the background, incremental increases in air
pollution concentrations can be predicted for comparison with various Federal, State, and local
standards. Depending on the, scale of the analysis, data should be presented for the relevant airshed,
for the site itself, or both. Also, the site’s location relative to any Class I areas (e.g., National Parks)
and any areas that are in nonattainment with any National Ambient Air Quality Standard should be
provided.
Emission inventories and ambient air quality as reported by State and local air pollution control
districts are the data sources for an air basin or regional airshed level analysis. At a minimum, major
stationary •sources and their emissions should be characterized, with diurnal variations in emissions by
month, year, and peak season for pollutants of concern. Projections of increases in emissions and
long-term pollutant concentrations are also important at this level. ‘The comparison of expected trends
with existing Federal, State, and local standards (including identification of Class I areas and the
attainment status of the area) becomes a major design parameter fOr gaseous emission controls.
Site-level analyses are more detailed in their geographic scope, but require similar information. One
of the major concerns at the site level is the transport of odors, dust, and emissions towards
potentially sensitive environments. Thus local variations in wind velocities, frequency of inversions,
and ambient pollutant concentrations may become important in determining local impacts. Air quality
models are often used to determine the directions and ground level concentrations of pollutants of
concern, and these models require most of the information described in the previous paragraph along
with specific stack characteristics such as stack height, emission temperature, emission velocity, and
the chemical composition of the stack gases.
5.3.1.2 Water Resources
Information on water resources to be included in the affected environment chapter should cover:
whether these waterbodies are jurisdictional waters of the United States, any special aquatic sites,
descriptions of waterbody types (i.e., local streams, lakes, rivers, and estuaries), and descriptions of’
groundwater aquifers. Descriptions of water body types, flows and dilutions, pollutant
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EIA Gwdelines for Mining Impact Analysis
concentrations, special aquatic sites, and habitat types near potential discharges are necessary to
determine the changes in the water environment that will occur with facility construction and.
operation. Descriptions of alluvial and bedrock, aquifers are necessary to determine the potential for
contamination of groundwaters from site activities. Of key importance here is the depth to the water
table, and the nature of overlying soils and geologic features. Descriptions of groundwaters should
include the location of recharge areas, and, in areas’ of water shortage, their present uses.
Descriptions of surface waters should include seasonal and historical ‘maximum, minimum, and mean
flows for rivers and streams, and water levels or stages and seasonal patterns of thermal stratification
for lakes and impoundments. The use of surface waters (diversions, returns, and reclamation) may
also be important in certain locations where water resources are scarce. Information on ambient
concentrations of pollutants, and other local sources, are also necessary to determine resulting
concentrations of pollutants with new discharges.
If imported water is to be used at the site for process water or other purposes, the source, quantity,
‘and quality of the water should be described. Any existing NPDES permtts should be identified along
with a description of wastewater flows and quality.
If the site might be subject to. flooding (is within the 100-year. floodplain), the dates, levels, and peak’
discharges of previous floods should be reported along with the meteorological conditions that created
them. Projections, of future flood levels should also be included for typical planning levels of 50- and
100-year floods,. These projections should include anticipated flood control projects such as levees’
and dams that will be built.
5.3.1.3 Soils and Geology
The physical structure of soils and ‘their underlying geologic elements determine the extent to which
soils will be affected by facility construction and operation. Useful parameters include permeability,
erodability, water table depth, and depths to impervious layers. The engineering properties and a
detailed description of surface and subsurface soil materials and their distribution over a site provide
most of the information’ necessary. . ‘
Local and regional topographic features such as ridges, hills, mountains, and valleys provide,.
information on watershed boundaries, and site topography (slope and elevation, characteristics)
provides information that is neede in determining the potential for ,erosion. ‘
Geological features are ‘important when paleontological sites and other areas of scientific or
educational value’may be disturbed or overlain by facility strUctures.
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In regions of the country that are seismically active, the description of the affected environment.
should information necessary to assess potential risks; Relevant informatiOn can include proximity to
faults, the history of earthquakes in the area, locations of epicenters, magnitudes, and frequency of
occurrence.
5.3.2 BIOLOGICAL CONDrI -JONS
Key elements of a description f biological conditions include the distribution of dominant species,
identification and description of rare threatened, or endangered species, and a characterization of
ecological interrelationships.
5.3.2.1 Vegetation
To understand the significance of vegetation changes associated with construction and operation of a
facility, it is necessary to know the types -of plant communities in the general area and the specific
distribution of vegetation types within the project area. The presence in the area of rare, threatened,
Or endangered species and unique plani assemblages are particularly important, especially if any are
likely to occur at the site. There are a variety of ways to describe vegetation, but the most useful is
to divide the site flora into four or five “typical” assemblages and map their distribution and that of
recognized scientific and educational areas. For threatened, endangered, or rare species, however, it
is necessary to map their occurrence separate from the assemblages.
In areas subject to forest fires, fire hazard should be described by describing the history of fires in the
area, projecting the severity of fire hazard in the future, and describing existing fire control and
management actions.
Aquatic and marine vegetation, particularly in the vicinity and downstream of proposed discharges,
also should be characterized. General community characteristIcs, including dominant species and
diversity, should be identified.
5.3.2.2 Wildlife
The presence of wildlife at a site is largely dependent on the nature and distribution of vegetation.
Particular emphasis should be placed on the presence of rare, threatened, or endangered sp cies in the
general vicinity of the site, and site-specific discussions are mandatory when the site provides habitat
that is used by rare, threatened, or endangered species. Under these circumstances, the relative
abundance of all rare, threatened or endangered species and the dominant wildlife fauna should be
surveyed on site and presented in the EIS. Otherwise, a general description of the wildlife species
within the area is sufficient.
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5.3.2.3 Ecological Interrelationships
A characterization of the key interrelations and dynamics within an ecosystem provides a foundation
for impact assessment.
Although it is difficult to determine the extent to which plants and animals are interdependent at a
given site, specific attention should be given to identifying the food sources of dominant or rare
animal species, the factors that limit these food sources (including factors such as soil structure and
moisture content, soil surface temperature ranges, and specific soil micronutrients), and the ability of
animal species to substitute food sources should current food sources be reduced in abundance,
Ecological interdependencies in aquatic systems are also important, and aquatic communities change
dramatically with large increases in nutrient or sediment discharges. While prediction of changes in
plant and animal populations is difficult under the best of circumstances, significant changes (either
positive or negative) cause conconutant changes in both terrestrial and aquatic fauna.
5.3.3 Soc ioEcoNoMic ENVIRONMENT
The socioeconomic environment encompasses the interrelated areas of community services,
transportation, employment, health and safety, and economic activity. The activities associated with
the construction and operation of new source facilities must impact human resources (employment,
population, and housing), institutional resources (services or facilities), and economic activity. The
information required to assess impacts are described below.
5.3.3.1 Community Services
Community services such as water supply, sewerage and storm drainage, power supply, and
education, medical, and fire and police services are almost always affected by major new projects. It
is important in an EA or EIS to describe the nature of existing public facilities and services within the
general vicinity, the quality of the service provided, and the ability of the existing public facilities and
services to accommodate additional users. The most critical consideration is the level of services that
would be provided in the anticipated peak year assuming no project were to be undertaken.
Permanent and temporary household relocations create demands on the housing market. The number
of nearby housing units, their cost, vacancy rates, and owner-occupancy rate are all significant factors
in determining the suitability of the existing housing stock for occupancy by a temporary or
permanent workforce. In addition, the present rate of growth within the housing sector can be
compared with the anticipated growth in housing supply and demand and the amount of land available
for new housing to determine whether existing policies and attitudes toward growth are adequate to
accommodate the additional residents.
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5.3.3.2 Transportation
Transportation systems provide access to a facility for the import of raw materials, export of final
products, and the movement of staff and service personnel. All relevant forms of transport for the
facility should be described. For all facilities, road-based transport is of potential significance, but
railways, airways, pipelines, and navigable waterways may also be important for some facilities.
Current traffic volumes, current traffic capacity, and an assessment of the adequacy of the systems for
meeting peak demands during construction and operation should be presented.
5.3.3.3 Population
Total population, rate of growth, general socioeconomic composition, transient population, and the
urban or rural nature of the local population are parameters needed to assess the importance of the
impacts of project-induced changes on the local community. Information on average household size,
average age, age/sex distributions, ethnic composition, average household income, percent of
households below poverty level, and median educational level allow a more refined analysis of
project-induced changes. Projections of demographic trends for the region and project area without
the project are also necessary to determine the relative impacts of the project in future years.
5.3.3.4 Employment
Employment is generated by the construction and operation of any new facility. Construction is
normally carried out by a temporary workforce of construction workers, not by the permanent
workforce in the area near the site. On the other hand, facility operation usually relies on a
permanent workforce, and the source of personnel for this workforce may be local or from other
parts of the country. In any case, increases in the number of personnel required to build or operate a
facility, direct employment, is accompanied by increases in employment in enterprises required to
support the facility, indirect (secondary, non-basic) employment, as demands for goods and serviàes
are increased. The direct and indirect employment generated by a project, in turn, generates
movements of households, resulting in population shifts and changes in the demographic
characteristics of communities.
To determine impacts of additional employment on the local environment ,, it is necessary to present
information about the local labor base—where people work, what they do, their skills and education
level, their rates of pay, and the unemployment rate. The characteristics of the unemployed
population are especially important if there is an expectation that a new facility will generate
employment for them. Projections should also be included on anticipated trends in employment and
unemployment without the project so that project-induced changes in these parameters can be
compared against a baseline.
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5.3.3.5 Health and Safety
Description of the present health and safety environment should include statistics on industrial
accidents in the local area; a discussion of air, water, and radioactive emissions from existing and
prior facilities and their effects on human health and the environment; and an analysis of present
levels of noise and their impacts on people and wildlife. The identification of applicable regulatory
standards provides a benchmark against which the present and future health and safety environment,
with and without the project, can be judged..
5.3.3.6 Economic Activity
Economic activity will lways be affected by new facilities. Current economic activity should be
described by characteristics of local businesses (number and types of businesses, annual revenues, and
ownership patterns) and the availability of capital for future growth. To predict changes in the kinds
of economic activity that would occur with the project, it is, necessary to describe the kinds of goods
and services, that would be required by the project or associated workforce and determine whether
they. are provided locally or imported. Unique features of the business community such as high
seasonality, high outflow of profit, declining trade, or downtown revitalization should also be.
included.
5.3.4 LAND USE
A description of land use should identify the current use of land needed specifically for the facility, its
system components, its safe area, and its residuals, and land use patterns’ in the nearby area. that will
be indirectly affected by the project. Particular emphasis should be placed on land uses that pose,
potential conflicts for large-scale industrial activity—residential areas, agricultural lands, woodlands,
wetlands—.and on the local or regional zoning laws that may limit the development of industry or
commercial activities on,which it relies. Also of crucial importance is the anticipated (andlor
• required) use of the land once mining operations end.
5.3.5 AESTHETIcs
Aesthetics involve the general visual; audio, and tactile environment (imagine the sensory differences
among urban, industrial, agricultural, and forest environments). A description of the aesthetic . , -
characteristics of the existing environment should include things that are seen, heard, and smelled in
and around the site and their emotional or psychological effect on people. Descriptions (or pictures)
of views of the site, of unique features or features deemed ‘of special value, and public use and
appreciation of the site provide information that must be available for. the assessment of impacts.
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5.3 .6 CuLTURAL RESOURCES
Cultural resources is a broad category that encompass resqurces of current, prehistoric and historic
significance. The location of a. facility nearS significant historical and cultural sites can degrade their
resource value or emotional impact. The location of the following kinds of sites should be described
in relation to the project site:
• Archeological sites (where man-made artifacts or other remains dating from prehistoric
times ar found)
• Paleontotogical sites (where bones, shells, and fossils of ancient plants or animals are found
in soil or imbedded in rock formations)
• Historic sites (where significant events happened or wher! well-known people lived or
worked)
• Sites of particular educational, religious, scientific, or cultural value.
Of particular concern would be complying with §106 of the National Historic Preservation Act for
sites listed on, Or eligible for listing on, the National Register.
5.4 ANALYZE POTENTIAL IMPACTS
The major envirolunental issues associated with th mining industries were discussed in the previous
chapter. Although Chapter 4 presents guidance for the analysis of impacts that tend to be common to
these industrial categories, it is important to recognize.that other-types of impacts are bound to be
associated with specific proposed actions. Thus, reviewers must ensure that all key issues identified
during the scoping process are fully analyzed. The section below provides more specific guidance on
the preparation of the “Environmental Consequences” section of an ELS. It also serves as the focus
of any administrative ippeal or legal challenge of the permit.
The “Environmental Consequences” section of an EIS forms the scientific and analytical basis for the.
comparison of alternatives. Accordingly, it should contain discussions of beneficial and adverse
impacts of each reasonable alternative and mitigation measure (40 CFR 1502.16 and 1508.8)
including clear, technical demonstrations of:
• Direct effects and their significan e—direct effects are caused by the proposed action and
occur at the same time and place.
• Indirect effects and their significance—indirect effects are those caused by the action but are
later in time or farther removed in distance, but are reasonably foreseeable. This also.
includes growth effects related to induced changes in the pattern of land use, population
density, or growth rate and related effects on air, water, and ecosystems.
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• Possible conflicts between proposed actions and the objectives of Federal, regional, State,
local and tribal land use plans, policies, and controls for the area concerned.
• Energy requirements and conservation potential.
• Natural or depletable resource requirements and conservation potential.
• Urban quality, historical and cultural resources, including reuse and conservation potential..
• Means to mitigate adverse environmental impacts not fully covered by the alternatives.
• Project compliance with water quality standards and the significance of the anticipated
impact of the discharge (this is particularly important for new source permits).
• Project compliance with National Ambient Air Quality Standards and, if applicable,
Prevention, of Significant Deterioration increments.
The potential impacts of each alternative are identified by a systematic disciplinary and
interdisciplinary examination of the consequences of implementing each• alternative.
5.4.1 METHODS OF ANALYSIS
While information may be gathered from new source NPDES applications, LIDs, and other sources,
EPA is responsible for the scientific and professional integrity of any information used in EISs for
which it is responsible. The applicant’s EU) and other sources of data, therefore, must clearly
explain all sources, references, methodologies, and models used to analyze or predict results:
Applicants should consider the uses and audiences fortheir data and EPA’s affirmative responsibility
in using them. EPA has the same responsibility in the use of data submitted by other agencies,
private individuals, or groups.
Each impact has its own means of identification, qualification, and quantification. For example, air
quality impacts are modeled using standard State or Federally approved programs. These numerical
models depend on standardized parameters and site-specific data. Stationary source emissions from
plant operation as well as mobile emissions related to traffié circulation from induced employment or
growth all contribute to air quality impact quantification. The goal is to quantify impacts on air
quality, water quality, employment, land use, and community services—categories that lend
themselves to numerical calculations,. modeling, and projections. Some environmental elements like
aesthetics lend themselves to more qualitative or graphic analyses.’
Biological impacts frequently are not readily quantifiable becaus: absolute abundance of individual
species are difficult to determine. Impacts may be described as acres of habitat lost or modified or to
qualitative impact descriptions of population changes in major species or species groups. The key in
the Environmental Consequences section is to clearly and succinctly lead a reader through each impact
5-13 . September 1994
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Impact Analysis ETA Guidelines for Mining
identification, qualificatidn and/or quantification. Detailed methodologies or extensive data can be
incOrporated by reference if the source is readily obtainable. Wildlife agencies can be sources of data
for this section. Materials’ from applicants must carefully follow this pattern to facilitate validation
and incorporation in the E IS.
5.4.2 DETERMINATION OF SIGNIFICANCE
As discussed in Chapter 2 of these guidelines, Thc term “significant effect” is pivotal under NEPA,
for an EIS must be prepared when a new source facility is likely to cause a significant impact. What
is signif icant can be set by law, regi.ilation, policy, or practice of an agency; the collective wisdom àf
a recognized group (e.g., industry or trade association standards); or the professional judgment of an
expert or group of experts. CEQ (4OCFR 1508.27) expLains significance in terms of contextand
intensity of an action. Context relates to scale—local, regional, State, national, or global; intensity
refers to the severity of the impact. Primary impact areas include affects on public health and safety,
and unique characteristics of the area (e.g., historical or cultural resources, parks, prime farm lands,
wetlands, wild and scenic rivers, or ecologically critical areas). Other important factors include:
• Degree of controversy
Degree of uncertain or unknown risks
• Likelihood a precedent will be set
• Occurrence of cUmulative impacts (especially if individually not significant)
• Degree to which sites listed, or eligible for listing, in the National Register of Historic
Places may be affected
• Degree to which significant scientiflc, cultural, or historical resources are lost
• Degree to which threitened or endangered species or their critical habitat is affected
• The likelihood of violations of Federals State; regional or local environmental law or
requirements or alternatively, likelihood that applicable standards applicable to the’ operation
and various environmental media can be achieved.
EPA ’s NEPA pràcedures require that the Agency consider short-term and long-term effects, direct
and indirect effects, and beneficial and adverse effects. Of particular concern are the following types
of impacts:
• The new source wi lL induce or accelerate significant changes in industrial, comMercial,
agricultural, or residential land use concentrations or distributions which haveS the potential
.5-ti September 1994
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EIA Guidelines for Mining Impact Analysis
for significant environmental effects. Factors that should, be considered in determining
whether these changes are environmentally significant include but are not limited to:
- The nature and ‘extent of the yacant land subject to increased development pressure as a
result of the new source
-. The increases in population or population density which may be induced and the
ramifications of. such changes
- ‘The nature of the land use Eegulation in the affected areas and their potential effects on
development and the environment
- The changes in the availability or demand for energy and the resulting environmental
consequences.
• The new source will directly, or through induced development, have significant adverse
effects upon local ambient noise levels, floodplain, surface or groundwater quality or
quantity, fish, wildlife, and their natural habitats.
• Any major part of the new, source will have significant adverse effect on the habitat of
threatened or endangered species on the,. Department of the Interior’s, or a State’s. list of
threatened and endangered species.
• The environmental impacts of the issue of a new source NPDES permit will have significant
direct and adverseeffect on property listed in the National Register of Historic Places.
• Any major part of the source will have significant adxerse effects on park lands, wetlands,
wild and scenic rivers, reservoirs, or other important bo,dies of water, navigation projecti,
or agricultural lands.
With the regulations in mind, it is ultimately up to the EA and/or EIS preparer(s) to make judgments
on what constitutes a significant impact. The threshold of significance is different for.each impact,
and those maldng thejudgments’need to explain the rationale for the thresholds chosen. Clear
descriptions of the choice of the threshold of significance provides a reviewer with a basis for
agreeing or disagreeing with the determination of significance on based on specific assumptions,
criteria, or data. Sometimes the thresholds are numerical standards set by regulation. In other cases,
the thresholds may •be set by’ agency practice (e.g., the U.S. Fish,and Wildlife Service may consider
the potential loss of a single individual of an endangered species as a significant impact), or the EPA
preparer’s professional judgment that determines the rationale for the threshold. The NPDES permit
applicant may suggest a threshold for each impact identified in the EID, but it is critical to carefully
defme how and why each particular threshold was chosen and applied.
5-15 ‘ September 1994
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Impact Analysis E IA Guidelines for Mining
5.4.3 COMPAB1SONS OF IMPACrS UNDER DIFFERiNG ALTERNATIVES
Alternatives can be compared in several different ways. All of the impacts associated with a single
alternative may be examined together and summarized in a final list of significant unavoidable
impacts, or the like impacts of all the alternatives can be determined and compared within a final
summarized list of significant unavoidable impacts. The choice of approach should be determined by
the E IS preparers based on the approach that would provide the most clear, concise evaluation for
decision makers and reviewers. The summary information on possible impacts and mitigation
measures is usually prepared in tabular form and included in the executive summary. Examples of
formats that can be used are found in standard environmental assessment technology texts, agency
manuals, EM, EISs, and similar documents.
5.4.4 SUMMARY DISCusSIONS
CEQ and EPA NEPA guidelines describe the expected general contents of the section called
“Environmental Consequences.” In addition to identifying, quantifying, and comparing the impacts
of each alternative, 40 CFR 1502.16 specifies that discussions will include “...any adverse
environmental impacts which cannot be avoided should the proposal be implemented, the relationship
between short-term uses of man’s environment and the maintenance and enhancement of long-term
productivity, and any irreversible or irretrievable commitments of resources which would be involved
in ,the proposal should it be implemented.”
Over the last 20 years, these three topics have been included as a separate chapter(s) in draft EISs
along with chapters called cumulative impacts, adverse effects which cannot be avoided, or residual
impacts and mitigation. No mater what format is used with these topics, they often receive only
cursory treatment. Such a practice is unfortunate because these long-term, larger scale issues are
those that affect overall environmental quality and amenities. The important point is not the location
of these topics in the document, but the need to present data, and analytical procedures used to qualify
and quantify these concerns.
A section called cumulative impacts can be addressed in several ways. Some ELSs consider
cumulative impact sections to be summaries of all residual impacts for each alternative. They may
also include any synergistic effects among impacts. A second, and more helpful, approach to
cumulative impacts reflects a broad view of environmental quality and suggests how impacts of the
proposed project or alternatives contribute to the overall environmental quality of the locale, in the
immediate future and over a longer time. In this approach, the impacts of the new source project are
considered in relation to the impacts associated with projects approved, but not constructed; projects
being considered for approval; or planned projects. This “accumulating” impacts approach to
cumulative impacts is particularly instructive when no single project is a major cause of a problem,
but contributes incrementally to a growing problem.
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EtA Guidelines for Mining Impact Analysis
All of these summary topics focus on broad views and long time lines in a attempt to put project
impacts in perspective.. The data requests from EPA to applicants must specify the environmental
setting and consequences data needed to qualify and quantify the potential impacts and put each
potential impact in perspective in terms. of local, regional and perhaps State or national environmental
quality.
5.5 DETERMINE MITIGATING MEASURES
Initial efforts to meet requirements under NEPA emphasized the identification of mitigation measures
for all potential impacts conceivably associated with a project or its alternatives. Current practices
emphasize avoiding and minimizing potential impacts before a NEPA document is prepared. This is
accomplished by refining the proposed project and alternatives during siting, feasibility, and design
processes. The goal is to propose project alternatives with as few significant impacts as possible.
CEQ NEPA regulations defme mitigation (40’CFR 1,508.20) to include:,
• Avoiding the mpact ‘altogether by not taking a certain action or parts of an action
Minimizing impacts by limiting the degree or magnitude of the action and its
implementation
• Rectifying the impact by repairing, rehabilitating, or restoring the affected environment
.. Reducing or eliminating the impact over time by preservation and maintenance operations
during the life of the action’ ,
• Compensating for the impact by replacing or.providing substitute resources or
environments.
This listing of mitigation measures has been interpreted as a hierarchy with “avoiding impacts” as the
best mitigation and “compensating” for a loss as the least desirable (but preferable to loss without
compensation). This hierarchy reinforces the present approach of trying to ‘avoid or minimize
potential impacts during project siting and design. The goal is to have the most environmentally
sound project and alternatives to carry into the impact assessment process of NEPA.
Even with the best project siting and design, there will be environmental impacts associated with each
of the alternatives. For the impacts, especially for the impacts judged to be significant impacts,
mitigation measures need to be suggested.
The first source of possible mitigation measures should be those offered in an applicant’s EID. Each
mitigation measure, should be described in enough detail so that its environmental consequences can
be evaluated and any residual impacts clearly identified.
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Impact Analysis EIA Guidelines for Mining
The preferred alternative typically reflects choices among tradeoffs. The tradeoffs can include
different processes, pollution control technologies, costs, or other features. Typically the tradeoffs
are complex for new source facilities with dissimilar beneficial and detrimental impacts among the
alternatives. The EIS always should’describe the process that led to, and the rationale for, the
selection of the preferred alternative. The analysis should be deemed complete if:
• The alternatives brought forward for analysis are all reasonable
• All possible refinements and modifications for environmental protection have been
incorporated in the alternatives
• Any residual impacts and consequences of mitigating those impacts have been evaluated.
5.6 CONSULTATION AND CO0RDrNATI0N
Each of the many laws, regulations, executive orders, and policies identified in Chapter 6 should be
addressed in the Consultation and Coordination section of an EIS. The’ applicant shoUld provide a
record of their activities and actions under each of the initiatives. The applicant-provided
environmental setting and environmental consequences’ materials should include sufficient data on the
environment issues raised by these laws, regulations, and orders to identify and analyze the potential
impacts.
5-18 September 1994
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EIA Guidelines for Mining Statutory Framework
6. STATUTORY FRAMEWORK’
Mining operations are subject to a complex web of Federal, State, and local requirements. Many of
these require permits before the mining operations commence, while many simply require
consultations, mandate the submission of various rts, andlor establish specific prohibitions or
performance-based standards. Among the Federal statutes that are potentially applicable are those
shown in Exhibit 6-1. Also shown are the agency with primary responsibility for implementing or
administering the statute and the types of requirements that are imposed on those subject to various
statutory provisions.
The ‘following sections describe the purposes and broad goals of these statutçs. The discussion for
each statute also provides an overview of the requirements and programs that are implemented by the
respective implementing agencies.
.6.1 CLEAN WATER ACT
The objective of the Clean Water Act is to “restore and maintain the chemical, physical, and
biological integrity of the Nation’s waters” ( 1Ol(a)). This is to be accomplished through the control
of both point and nonpo nt sources of pollution ( 1O1(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 Fàderal and State programs are implemented to meet the Act’s requirements.
Under §303, States are responsible for establishing water quality’ standards and criteria 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 and criteria 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 (see beiow) of pollutants to navigable waters of the
United States must be permitted under the National Pollutant Disch rge Elimination System (NPDES).
Effluent lirrüts in NPDES permts may be technology- or water quality-based. For various categories
of industries, EPA establishes National technology-based effluent limitation guidelines pursuant to
301, 306, and 307.
The term “navigable waters” or “waters of the U.S.” includes all waters within the territorial’seas
(i.e., within the three-mile contiguous zone around the United States). Waters of the United States
need not be navigable in fact (see U.S. v. Ashland Oil, 504 F2d 1317 (6th Cir. 1974)), and may be
6-1 September 1994
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0
Exhibit 6 -1. Major Federal Statutes Generally Applicable to Mining Operations
.t’J
Statute/Section ——
hnplementing/Responsible Agency
Procedural
Requirements
Overview
Federal Water Pollution Control
Act (Clean Water Act)
(33 U.S.C. § l25l-1387)
EPA, Authorized States and Tribes;
Army Corps of Engineers,
Authorized States ( 404)
Permit;
Standards;
Reporting;
Prohibitions
•
.
Permit required (or all point source discharges to waters of
the U.S.
.
Technology-based effluent limits established for ore mining
and dressing, coal mining and preparation.
Water quality-based in lieu of technology-based limits must be
developed on site-specific basis for discharges that contribute
to non-attainment of State-established beneficial uses and
water quality standards
Permit required for dredging/filling in waters of U.S..
including wetlands.
EPA-issued NPDES permits issued to new sources trigger
NEPA reviews.
Clean Air Act
(42 U.S.C., § 740l-7626)
EPA. States .
.
Standards;
Approvals;
Permits
.
Establishes ambient air Concentrations for criteria pollutants,
including particulates from dust. 1990 amendments call for
studies and, if necessary, regulation of hazardous air
pollutants from specified industries, including mining.
Resource Conservation and
Recovery Act (42 U.S.C. § 6901-
6992k)
EPA, Authorized States
.
.
Permits
(hazardous waste);
Standards
(hazardous and
nonhazardous)
Under Subtitle C, EPA regulates hazardous waste
management from generation to disposal. Wastes that are
uniquely associated with mining (including tailings, waste
rock) are exempt from hazardous waste regulation. Under
Subtitle D, EPA establishes non-mandatory criteria for State
programs regulating nonhazardous solid wastes. Existing
criteria are generally not suitable for mining wastes.
National Environmental Policy Act
(42 U.S.C., §*4321-4370a)
EPA, Federal land managers
Studies;
Approvals;
Consultations
Triggers examination of all of applicable statutes.
I
tTI
E.
t
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cl
I
0
I
Exhibit 6-1. Major Federal Statutes Generally Applicable to Mining Operations (Continued)
E.
t
: : •
lmplementlnglftesponsible Agency
Procedural
Requirements
A.::.:: .:::. ::
Overview
Act (16 Fish and Wildlife Service
.
Prohibitions;
Consultations
Requires federal agencies to ensure that all federally
associated activities within the U.S. do not have adverse
impacts on the continued existence of threatened or
endangered species or on critical, habitat.
Agencies undertaking a federal action must consult with the
U.S. Fish and Wildlife Service (USFWS) or the National
Marine Fisheries Service (NMFS) to determine the potential
impacts a project may have on protected species.
Preservation Act Advisory Council on Historic
et seq.) Preservation
Consultation
•
Federally licensed mining activities that affect any district,
site, building, structure, or object that is included in or
eligible for inclusion in the National Register, must afford the
Advisory Council on Historic Preservation a reasonable
opportunity to comment.
Management Act (16 EPA, States
Notification
..
Applicants for federal licenses or permits must submit
consistency certifications indicating that their activities comply
with CMP requirements.
In addition, activities of federal agencies that directly affect
the coastal zone must be consistent with approved state CMPs
to the maximum extent practicable.
Policy Act U.S. Soil Conservation Service
Consultation
U.S. Soil Conservation Service (SCS) must be asked to
identify whether a proposed facility will affect any lands
classified as prime and unique farmlands.
Act (33 U.S.C. U.S. Corps of Engineers
,
Permits
The RHA regulates obstructions to navigation and prohibits
the unpermitted dumping or discharging of refuse into a
navigable water of the U.S. The Act also provides authority
to regulate the disposal of dredgings in navigable waters.
Also see §402 and §404 of the CWA.
-------
E.
I..
Exhibit 6-1. Major Federal Statutes Generally Applicable to Mining Operations (Continued)
0
I
:
ImplementIng/Responsible Agency
Procedural
Requirements*
:
Overview
Control and Office of Surface Mining,
(30 U.S.C. Authorized States
.
Permits;
Standards,
Reporting;
Royalties
Regulates surface effects of surface and underground coal
mining that occurred after 1977. -Permit required for all
mines over two acres. Provides for reclamation of coal mines
abandoned before 1977.
1872 (30 U.S.C. Bureau of Land Management,
Federal land managers
.
Notification
Provides rights of free access to unrestricted public lands for
purposes of claiming and recovering most metallic minerals.
Provides mechanism for claimants to obtain full title to
claimed public lands.
Management Bureau of Land Management
§ 1701-1782)
‘
.
Notification;
Studies;
Approvals
Requires BLM to prevent unnecessary and undue degradation
of public lands. Implementing regulations specify
noncompliance with Clean Water Act and other statutes as
“unnecessary and undue” degradation.
Establishes land planning process, including compliance with
NEPA.
Regulations impose procedural requirements on mining
operations on BLM lands (e.g., approval of plans of
operations), with most technical requirements determined by
managers of BLM units or BLM State offices.
System Mining National Park Service
(Mining in the
(16 U.S.C.
.
Standards;
Notification;
Approvals
Regulates mining activities within the National Park System.
.
All mining claims in NPS system made prior to September,
1977 has to be recorded by that time. No claims are allowed
after that time.
Protects natural or historic landmarks within the park system
by requiring that persons conducting mining operations that
threaten such landmarks notify NPS and the Council on
Historic Preservation.
‘0
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9’
Exhibit 6 -1. Major Federal Statutes Generally Applicable to Mining Operations (Continued)
Statute/Section
ImplementIng/Responsible Agency
Procedural
Requ irements*
Overview
Multiple Use and Sustained Yield
Act (16 U.S.C. § 528-531),
National ForestManagement Act
.
Forest Service
Notification;
Studies;
Approvals
Establishes that the National Forest System is to be
managed for outdoor recreation, range, timber, watershed,
and fish and wildlife purposes.
Provides that the renewable surface resources of the
national forests are to be administered for multiple use and
sustained yield of products and services.
Establishes land planning process, including compliance
with NEPA.
Regulations impose procedural requirements on mining
operations on FS lands (e.g., approval of plans of
operations), with most technical requirements determined by
managers of FS units or FS State offices.
Mineral Leasing Act (30 U.S.C.
§ 181-287)
.
Bureau of Land Management
Lease (permit);
Reporting;
Studies
Requires leases and royalty payments for mining fuel
minerals (including coal and uranium) on Federal lands, and
for mining hardrock minerals on acquired lands.
Comprehensive Environmental
Response, Compensation, and
Liability Act (42 U.S.C. § 9601
9675)
EPA
.
‘
Reporting
(releases);
Studies
.
Requires reporting of spills of reportable quantities of
specified hazardous substances.
,
Requires remediation of contaminated sites that meet
specified criteria.
Emergency Planning and
Community Right-to-Know Act (42
U.S.C. § 11001-11050)
States, local agencies, EPA
-
Reporting
.
Requires submission to State and local emergency response
agencies of data on specified toxic chemicals that are
produced/used/stored.
Mining operations not subject to National Toxic Release
Inventory reporting requirements, which are currently
applicable only to SIC codes 20-39.
r’i
C ’)
E.
C
I
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Exhibit 6-1. Major Federal Statutes Generally Applicable to Mining Oper:tions (Continued)
‘NOTE:
Permits: License” to undertake an action subject to enforceable standards, reporting requirements, prohibitions. etc.
Approvals: Formal approvals by responsible official/agency of specified actions.
Standards: Numeric performance- or technology-based standards to limit emissions/discharges/releases, or numeric standards foç protection of environmental
medium.
Prohibitions: General restrictions or prohibitions on specified actions or on causing a particular effect by any action.
Studies: Requires studies of site-specific environmental conditions, proposed or existing operation, and/or potential environmental effects of operation.
Consultation: Requires consultations with specified officials/agencies prior to undertaking an action.
Reporting: Periodic reporting to regulatory agency on compliance.
tTl
E.
eD
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ELk Guidelines for Mining Statutory Framework
Point Sources Under the Clean Water Act
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)1 For purposes of the [ CWAJ, the term
“point source” includes a landfill leachate collection system 1987 Water Quality Act, PL 100-
4, §507 The definition has been codified at 40 CFR 122 2
In the preamble for a storm water rulemaking (55 FR 47997, November 19, 1990), EPA cited
court decisions that bear on the definition (Sierra Club v Abston Construction Company, 620
F 2d (5th Cir 1980)) “ Nothing in the [ Clean Waterj Act relieves [ dischargersj from
liability simply because operators did not construct those conveyances, so long as they are
reasonably likely to be the means by which pollutants are ultimately deposited into a navigable
body of water Conveyance of pollution formed either as a result of natural erosion or by
material means, and which constitute a component of a. drainage sys tem, may fit the
statutory definition and thereby subject the operators to liability under the Act” Overall, EPA
concluded that a intended to” embrace the broadest possible definition of point source
consistent with the legislative intent of the CWA and court interpretations to include any
identifiable conveyance from which pollutants might enter the waters of the United States”
Further, EPA noted that facilities themselves had the burden of determming whether an
application should be subnutted for a point source (and, by implication, of determining whether
a discharge was from a point source) and advised facilities to submit an application or consult
with permitting authorities in cases of uncertainty It should be noted that Federal courts have
spoken to the issue of point sources at mine sites for example, in Kennecott Copper Corp v
EPA, 612 F 2d 1232 (10 Cir 1979), the court was asked to rule on whether certain discharges
were subject to 40 CFR Part 440 One of the court’s conclusions was that whether certain of
Kennecott’s facilities were point sources was a determination “to be made in the first instance in
the context of a permit proceeding”
intermittent or seasonal. In at least one case, a discharge which was traced into and through
groundwater was considered a discharge to waters of the United States (see Quivera Mining Co. v.
U.S. EPA, 15 ELR 20530 (10th Cir. 1985)).
EPA’s NPDES regulations [ 40 CFR 122.21(1)] require prospective dischargers (in States without an
approved NPDES program) to submit information to the EPA Region, prior to beginning on-site
construction, that will allow a determination by EPA of whether the facility is a new source. The
criteria for this determination are in 40 CFR 122.29. The Region must then issue a public notice of
the deteñnination. If the facility is determined to be a new source, the applicant must,comply with
the environmental review requirementi of 40 CFR Part 6 Subpart F. In preparing a draft new source
NPDES permit, the administrative record on which’the draft permit is based must include the
environmental information document prepared by the applicant, the environmental assessment (and, if
applicable, the FNSI) prepared by EPA, and the environmental impact statement (EIS) or supplement;
6-7 September 1994
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Statutory Framework EIA Guidelines for Mining
if applicable 140 CFR Part 124.9(b)(6)]. In addition, public notice for a draft new source NPDES
permit for which an EIS must be prepared cannot take place until the draft EIS is issued [ 40 CFR
Part 124.10(b)].
EPA has established National technology-based effluent limitation guidelines for coal mining and
preparation plants (40 CFR Part 434) and ore mining and dressing (40 CFR Part 440). National
effluent limits are based on three levels of technologies. First, Best Practicable Control Technology
Currently Available (BPT) limits are based on the best existing performance (in the mid-i 970s) at
plants of various sizes, ages, and unit processes in the industry. Limits based on the Best Available
Technology Economically Achievable (BAT) control toxic pollutants (i.e., 126 chemical substances
identified by Congress) and nonconventional pollutants (any pollutant other than toxic and
conventional [ BOD, TSS, oil and grease, fecal coliforms, and pH] pollutants). BAT limits generally
represent the best existing performance in the• industry. Finally, new source performance standards
are based on the Best Available Demonstrated Technology (BADT), since new plants can install the
best and most efficient production processes and wastewater treatment technologies. Exhibits 6-2
through 6-4 present the new source performance standards for coal mining and preparation plants and
ore mining and dressing facilities.
In general, standards have been established for “mine drainage” and mill/preparation plant discharges.
For coal mining, there also are standards for post-mining areas (i.e., reclamation areas prior to bond
release). For coal mining, mine drainage generally includes all point source discharges other than
those from haul and access roads, rail lines, conveyor areas, equipment storage and maintenance
yards, and coal handling buildings and structures (discharges/runoff from these areas are subject to
storm water permitting, as described below). For metal mining, the discharges to which mine
drainage limitations apply have proven somewhat more difficult to delineate; Exhibit 6-5 provides
examples of point source discharges that are subject to mine drainage limits (and examples of those
that are subject to storm water permitting).
The National effluent limitations consist of maximum concentrations of individual pollutants that may
be present in specific discharges as well as various conditions and exemptions; in some cases, the
effluent limitation allows no disâharge. Typically, only a limited number of the pollutants that are
likely or known to be present are limited in the NatiOnal standards, since the technologies on which
the limits are based prove effective in treating/removing other pollutants as well. Permit writers must
use Best Professional Judgment to develop technology-based limits for any other pollutants of
concern, and discharges, for which there are no National effluent limitations. In addition; when
technology-based effluent limits will not ensure compliance with applicable water quality standards for
the receiving waters, permit writers must develop water quality-based limits that are more stringent
than the technology-based limits.
6-8 September 1994
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Exhibit 6-2. New Source Performance Standards for Coal Mining Category (40 CFR Part 434)
Preparation plants aud
associated areas
(Subpart B)
1-day 30-day
Characteristic maximum average
Acid or ferruginous
mine drainage
(Subpart C)
Alkaline mine drainage
(Subpart D)
Post-mining areas (Subpart E)
Reclamation
areas prior
to bond
release :
Underground mine
drainage
1-day
maxunurn
30-day
average
1-day
maximum
30-day
average
1-day I 30-day
maximum average
6.0-
9.0
6.0-
9.0
6.0-
9.0
6.0-9.0
6.0-9.0
70
35
70.0
35.0
70.0
35.0
N/A
70.0 I 35,0
2 6.0
3.0
6.0
3.0
6.0
3.0
N/A
6.0 I 3.0
(mg/i) 2 4.0
2.01
4.0
2.0
N/A
N/A
4•Q 5 2.0
(mI/i) 2 N/A
N/A
N/A
0.5
N/A
NOTES:
N/A Not applicable (standard not promulgated)
1 pH limit may be slightly > 9.0 s.u. if neutralization and sedimentation technology does not result in compliance with applicable manganese limits (Subpart F,
§434.62).
S. D 2 Alternative standards may be applied to discharges during precipitation (Subpart F, §434,63):
Some discharges may be subject to pH limit and to limit of 0.5 mI/I for settleable solids rather than otherwise applicable TSS, iron, and manganese limits if caused
by 24-hour precipitation 10-year/24-hour event [ Subpart F, §434.63(a), (b), and (c)j:
• Discharges of alkaline mine drainage (with exceptions), discharges from steep slope areas and mountaintop removal (as defined in SMCRA), and discharges from
preparation plants (except from acid coal refuse piles) caused by 24-hour precipitation I0-year/24-hour event.
• Discharge from acid coal refuse piles caused by 24-hour precipitation > 1-year/24 ’hour event and l0-year/24-hour event.
• Discharges of acid mine drainage (except from steep slope areas and mountaintop removal, underground mines, and controlled surface mine, discharges) caused
by 24-hour precipitation > 2-year/24-hour event and 10-year/24 hour event. Discharges from 24-hour precipitation 2-year/24-hour event also subject to
daily maximum limits of 7.0 mg/I of total iron.
Some discharges may be subject only to pH limit if caused by 24-hour precipitation > 1O-year/24-hour event [ Subpart F, §434.63(d)I:
• All discharges subject to alternative limits above.
• Discharges of acid mine drainage from underground mine workings which are commingled with other discharges eligible for this alternative limit.
• Controlled acid surface mine drainage and discharges from reclamation areas.
3 Acid or ferruginous mine drainage is drainage which, before any treatment, either has pH < 6.0 or total iron concentration 10.0 mg/I. Alkaline mine drainage is
drainage which, before any treatment, either has pH 6.0 or total iron < 10.0 mg/I.
4 These manganese standards are applicable only to preparation plants where the pH is normally < 6.0 prior to treatment.
5 These manganese standards are applicable only to acid mine drainage from underground mines.
Co nmingIed wastestreams: discharge concentrations of pollutants in combined wastestreams may not exceed the most stringent limitation applicable to any component
wastestream.
0
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I
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I
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0
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I
Exhibit 6-3. New Source Performance Standards for Mine Drainage, Ore Mining and Dressing Category
(40 CFR Part 440, Subparts A-K and M)
(units in milligrams per titer except as noted)
.
Iron ore
(Subpart A)
I-day 30-day
maximum - average
Aiwninuin ore
(Subpart B)
Uranium, Radium,
Vanadium ores I
(Subpart C)
..
Mercury ore•
D)
-
Titanium ore
(Subpart E)
1-day I 30-day II
maximum average,
1-day 30-day.
maximum average:
1-day 30-day
maximum average
1-day
maximum 30-day average
6.0 - 9.0 .
6 0 - 9.0
- - 6.0 - 9.0
6.0 - 9.0
6.0 - 9.0
30.0 20.0
30.0 20.0
30.0
20.0
30.0 20.0
- 30.0 20.0
N/A
. N/A
200
i OO
N/A
N/A
N/A
- 2.0 1.0
N/A
N/A
N/A
N/A .
N/A
N/A
N/A
N/A
N/A .
N/A
N/A
N/A
N/A
2.0’ 1.0’
1.02 . 0.52
N/A
N/A
2.0 10
. N/A
N/A
N/A
-0002 1 0.001
- N/A
N/A
N/A .
N/A
N/A
N/A
N/A
N/A
4.0
2.0
N/A
N/A
N/A
N/A
1.0
0.5
N/A.
N/A
(pCi/I)’ N/A
N/A
10.0
3.0
N/A . :
N/A
(pCi/I) 2 N/A
N/A
. 30.0
10.0
N/A
N/A
lx i
0
E.
•1
I
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‘1
Exhibit 6-3. New Source Performance Standards for Mine Drainage, Ore Mining and Dressing Category
(40 CFR Pan 440, Subparts A-K and M) (Continued)
0
I
(units in milligrams per liter except as.notèd)
tTj
C)
E.
I
Tungsten ore
(Subpart F)
.
Characteristic 1-day maximum . 30-day average
Copper, Lead, Zinc, Gold, Silver, Molybdenum ores
(Subpart J).
1-day
max imum
.
30-day average
. 6.0 - 9.0
6.0 - 9.0
30.0 20.0
30.0 20.0
N/A
. - N/A
‘ , 0.10
0.05
0.1
. ‘0.05
0.3
0.15
0.3
‘ 0.15
. . N/A .
N/A
, N/A - .
. 0.002
- 0.001
. . N/A .
0.6
0.3
. . N/A -
N/A.
- , 1.0 - 0.5
‘ , 1.5 ‘ 0.75
NOTES:
N/A Not applicable (standard not promulgated)
• New Source Performance Standards for mine drainage from facilities mining Nickel (Subpart G), Vanadium (H), Antimony (I), and Platinum (K) ores are reserved.
Discharges are thus subject to limits based on’Best Professional Judgment.
1 .Dissolved
2 Total
Storm exemption (Subpart L, §440.131(b): overflow resulting from rainfall/snowmelt may be exempt from standards at facilities designed/constructed/maintained to contain
or treat the normal 24-hour wastewater flow and the maximum volume from the 10-year/24-hour precipitation event, including runon/runoff. The exemption is available
only if provided for in the facility’s permit and if thepermittee takes all reasonable steps to treat the flow and minimize overflow and meets notification requirements.
-------
Exhibit 6-4. New Source Performance Standards for Mills and Beneficiation Processes, Ore Mining and Dressing Category
(40 CFR Part 440, Subparts A-K and M)
(units in milligrams per liter except as noted)
Emuent
ChrnacterLstlc
S
iron ore’
(Subpart A)
Ur Ium,
Vanadiwn
ores ‘
(Subpart C)
S
Mercury ore
(Subpart I))
:.
Titanium ore
(Subpart E)
Tungsten ore
(Subpart F)
Copper, Lead,
ZInc, Gold,
Silver,
Molybdenum
ores ‘
(Subpart J)
•
Gold placer
(Subpart M)’
1-day 30-day
maximum average
1-day
maximum
30-day
average
I-day 30-day,
maximum average
pH (s.u.)
6.0 - 9.0
Zero discharge
Zero dischaTge
.
.
6.0 - 9.0
6.0 -
9.0
Zero discharge
N/A
30.0 20.0
30.0
20.0
N/A
TSS
30.0 20.0
Settleabic solids
(mi/I)
N/A
N/A
N/A
0.2
N/A
0.1
0.05
N/A
Cd
N/A
N/A
0.3
0.15
Cu
N/A
N/A
Fe (dissolved)
2.0 1.0
N/A
‘ N/A
N/A
1.0 0.5
1.0 f 0.5
N/A
Zn
N/A
NOTES:
N/A Not applicable (standard not promulgated)
NSPS for Nickel (Subpart 0), Vanadium (H), Antimony (1), and Platinum (K) subcategories are reserved. Discharges are thus subject to limits based on BPJ.
1 These standards are applicable to iron ore mills other than in the Mesabi Range. NSPS for iron ore mills in Mesabi Range is zero discharge
2 Standards for gold placer mints (Subpart M) are for process wastewater” (beneficiation water).
3 Mills subject to Subpart i NSPS where contaminants build up in recycle water and interfere with ore recovery may be allowed to discharge the necessary amount to
correct the interference problem following treatment, subject to mine drainage standards.
Net precipitation areas: Facilities subject to zero discharge standards thai are located in net precipilation zones (i.e., precipitation exceeds evaporation) may be allowed to
discharge an amount equal to the excess precipitation, subject to the mine drainage standards for the applicable subcategory.
Storm exemption ISubpan L, § 440.131(b) and 440.131(c) ): overflow resulting from rainfall/snowmelt may be exempted from siandards, including zero discharge
standards, at facilities designed/constructed/maintained to contain or treat the normal 24-hour wastewater flow (or normal operating volumes, for zero discharge facilities)
and the maximum volume from the l0-year/24-hour precipitation event (5-year/6-hour event for gold placer mines). The exemption is avaitable only if provided for in the
facility’s permit and if the permittee takes all reasonable steps to treat the flow and minimize overflow, and meets notification requirenients (and, for gold placer, if BMPs
are implemented).
Groundwater infiltration: If facilities subject to zero discharge standards demonstrate that groundwater infiltrates the tailings impoundment or wastewater holding facility,
they may be allowed to discharge an equivalent volume subject to mine drainage standards.
C ,,
0
I
til
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t
C,,
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ETA Guidelihes for Mining Statutory Framework
Exhibit 6-5. Examples of Discharges From Ore Mining and Dressing Facilities
That Are Subject to 40 CFR Part 440 or to Storm Water Permitting
Runoff/drainage discharges subject to
40CFR Part440. effluent 1 tión guideIine& ’. .”
Subject to storm water permitting
“.: : subject to 40 CFR Part 440)
Mine drainage limits S
Topsoil piles
Haul roads not on active mining area
Onsite haul roads ‘not constructed of waste ‘rock or
spent ore (unless wastewater subject to mine
drainage limits is used for dust control)
Tailings dams/dikes when not constructed of waste
rock/tailizigs
Concentrationlmil building/site (if discharge is storm
water only, with no contact with piles)
Reclaimed areas released from reclamation bonds prior
to 12/17/90
Partially/inadequately reclaimed areas or areas not
released from reclamation bond
Most ancillary areas (e.g., chemical and explosives
storage, power plant, equipment/truck maintenance
and wash areas, etc.)
‘
‘
Land application area
Crusher area ,
Spent ore piles surge piles, ore stockpiles, waste
rockioverburden piles
Pumped and unpumped drainage and mine water from’
pits/underground mines
Seeps/French drains ,
Onsite haul roads, if constructed of waste rock or
spent ore or if wastewater subject to mine drainage
limits is used for dust control
Tailings dams/dikes when constructed of waste
rock/tailings
Unreclaimed disturbed areas
Mill discharges limits (including zero ,
discharge limits)
L.and application area
Crusher area
Spent ore piles , surge piles, waste rock/overburden
piles
Seeps/French drains
Tailings impoundment/pile
Heap leach runoff/seepage
.
Pregnant, barren, overflow, and polishing ponds
Product storage areas (e.g., concentrate pile)
‘
NOTE: ,
1 Point source discharges from these areas are subject to 40 CFR Part 440 effluent limitation guidelines for (a)
mills if process fluids are present or (b) mine drainage if process fluids are not.
Section §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 defmed 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
‘6-13 , 5 September 1994
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Statutory Framework EIA Guidelines for Mining
where industrial activity has taken place in the past and significant materials remain and are exposed
to storm water.”
Certain storm water discharges from mine sites, whether active or inactive, are not subject to NPDES
permitting: storm water that is not contaminated by contact with or that has not come into contact
with any overburden, raw material, intermediate products, finished products, byproducts, or waste
products located on the site of the operation is not subject to permitting by virtue of §402(l)(2) of the
Act. Also, inactive sites where there is no identifiable owner/operator are not subject to permitting
under the storm water rule (however, it is not clear that any sites are actually excluded by virtue of
this, since there is presumably an owner of all lands on which sites may be located). Finally, sites on
Federal lands where claims have been established under the Mining Law of 1872 and where only
nominal claim-holding activities are being undertaken are not subject to permitting. However, it is
not clear how the program will address claims where this is the case but where there is a discharge of
contaminated storm water from mines abandoned by a previous claimant. Finally, NPDES permits
are not required for discharges of contaminated storm water from coal mines that have been released
from SMCRA reclamation bonds or from noncoal mines that have been released from applicable
StatefFederal reclamation requirements on or after DeceInber 17, 1990.
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) would not trigger NEPA.
Section 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 pres rvation of wetland ecosystems. “Jurisdictional
wetlands” are those subject to regulation under Section 404. Jurisdictional wetlands are those that
meet the criteria defined in the 1987 Corps of Wetlands Delineation Manual (USACE, 1987).
Regulatory authority for Section 404 is divided between the Army Corps of Engineers (Corps) and
EPA. Section 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)(l) 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 then.
Section 404(e) establishes that the Corps may issue general permits on a State, regional, or National
basis for categories of activities that the Secretary deems similar in nature, cause only minimal
adverse environmental effects, and have only a minimal cumulative adverse effect on the
environment. General permits may be issued following public notice and a period for public
6-14 September 1994
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EIA Guidelines for Mining Statutory Framework
comment; the permits must be based on the §404(b)(1) guidelines and establish conditions that apply
to the authorized activity. Exceptions to §404 requirements are established in §404(f) and
conditionally include the construction of temporary roads for moving mining equipment.
The process of issuing a §404 permit begins.with a permit application. The application typically
contans information describing the project and the project area; wetlands to be disturbed and the
extent; and, mitigation plans. : Upon receipt of the application, the Corps issues a public notice
describing the proposed activity and establishing a deadline for public comment. Although a public
hearing is not normally held, one may be scheduled at the request of concerned citizens. Following
the comment period (typically 30 days), the Corps evaluates the application based on requirements of
the Clean Water Act. In the final stages, the Corps prepares an environmental assessment and issues
a statement of finding. A permit is then issued or denied based on the finding. It is at this tme that
EPA may exercise its veto authority.
Enforcement authority is divided between the two agencies; the Corps provides enforcement action for
operations discharging in violation of an approved permit while EPA has authority over any operation
discharging dredged or fill materials without a permit. Within EPA, the Office of Wetlands
Protection addresses wetland issues through two divisions. The Regulatory Activities Division
develops policy and regulations, and administers the statutory requirements including appeals and
determinations. The Wetlands Strategies and State Programs Division works to expand protection
and further scientific knowledge of these ecosystem types through coordination efforts with other
Federal and State agencies (Want 1990).
6.2 CLEAN AIR ACT
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. ambi nt 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 stri t 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.
6-15 September 1994
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Statutory Framework EIA Guidelines for Mining
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 only apply to
stack emissions. NSPSs require operations to contain stack-emitted particulate matter in excess of
0.05 grains per dry standard cubic meter (dscm). In addition, -stack emissions must not exhibit
greater than 7 percent opacity, unless the stack emissions are discharged from an affected facility
using a wet scrubbing emission control device. However, on or after 60 days following the
achievement of the maximum production rate (but no later than i 80 days after initial startup),
operations must limit all process fugitive emissions (meaning fugitive dust created during operation
though not released through a stack) to 10 percent opacity.
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 managemeru 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 Amendments of 1990, the EPA had promulgated
NESHAPs for seven pollutants: arsenic, asbestos, benzene, beryllium, mercury, vinyl chloride, and
radionuclides (40 CFR Part 61).
The Clear Air Act 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 of 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
6-16 September 1994
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EIA Guidelines for Mining Statutory Framework
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 Max mum Available Control
Technology (MACT) to control the release of the pollutants (CAA § 112). The CAA Amendments
also intensif ’ the requirements applicable to nonattainment areas.
6.3 RESOURCE CONSERVATION AND RECOVERY ACT
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 their 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-
defmed “characteristics,” ‘including reactivity, corrosivity, 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 Section 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 (roughly, mining and milling wastes) and processing wastes
(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, 1985). 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 found that a wide variety of
existing Federal and State programs already addressed many of the risks posed by extraction and
beneficiation wastes. To address gaps in existing programs, EPA indicated that these wastes should
be controlled under a Subtitle D program specific to mining wastes.
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
6-17 September 1994
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Statutory Framework EIA Guidelines for Mining
wastes are subject to applicable State requirements. The remaining two wastes (phosphogypsum and
phosphoric acid process waste water) are currently being evaluated under the authority of the Toxic
Substances Control Act (TSCA) to investigate pollution prevention alternatives. Five specific 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 related to the extraction and beheficiation 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 are 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 small quantities of hazardous wastes. There are a few large coal and noncoal mines,
however, that generate large quantities and thus may be regulated as hazardous waste treatment,
storage, or disposal facilities. In these cases, the units in which exempt wastes are managed may be
subject to. the requirements of 40 CFR §264.101, which require corrective action at certain solid
waste management units at regulated facilities.
Since the 1986 Regulatory Determination, EPA’s Office of Solid Waste (OSW) has undertaken a
number of activities to bolster State programs and to e thance EPA’s understanding of the mining
industry and its associated environmental impacts. To identify and focus discussion on the key
technical and programmatic issues of concern, EPA developed staff-level approaches to regulating
mining wastes under RCRA Subtitle D that were widely reviewed and discussed. EPA also
established a Policy Dialogue Committee under the Federal Advisory Committees Act to facilitate
discussions with other Federal agencies, States, industry, and public interest groups. Grant funding
was provided to the Western Governors’ Association to support a Mine Waste Task Force, which has
fostered the refinement of State programs that regulate mining operations, allowed coordinated
discussions among States of mining-related issues, and commissioned a number of technical studies.
Grant funding also has been provided to several States for developing and enhancing mining-related
programs and to educational institutions for technical investigations.
OSW also has continued its investigation of the mining industry. EPA is currently preparing detailed
profiles of a number of mining industry sectors. These profiles are intended to represent current
extraction and beneficiation operations and environmental management practices, and applicable
Federal and State regulatory programs.
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EIA Guidelines for Mining Statutory Framework
In addition, OSW visited a number of mine sites and prepared comprehensive reports on the
operational, environmental, and regulatory characteristics of the sites. Together with the profiles,
reports on visits to mines in specific industry sectors are being compiled into Technical Resource
Documents. OSW also has compiled data from State regulatory agencies on waste characteristics,
releases, and environmental effects; prepared detailed summaries of over 50 mining-related sites on
the Superfund National Priorities List (NPL); and examined a number of specific waste management
practices and technologies, including several currently available pollution prevention practices
technologies. EPA has also conducted studies of State mining-related regulatory programs and their
implementation. Finally, EPA has undertaken a number of technical studies, including investigations
of prediction techniques for acid generation potential, tailings dam design, closure and reclamation of
cyanide heap leach facilities, and other topics. (Profiles and technical studies, currently in draft form,
were used extensively in preparing these guidelines).
6.4 ENDANGERED SPECIES ACT
The Endangered Species Act (ESA) (16 U.S.C. § 1531-1544) provides a means whereby ecosysten
supporting threatened or endangered species may be conserved and provides a program for the
conservation of such species. Under the ESA, the Secretary of the Interior or the Secretary of
Commerce, depending on their program responsibilities pursuant to the provisions of Reorganization
Plan No. 4 of 1970, must determine whether any species is endangered or threatened due to habitat
destruction, overutilization, disease or predation, the inadequacy of existing regulatory mechanisms,
or other natural or manmade factors. When the Secretary determines that a species is endangered or
threatened, the Secretary must issue regulations deemed necessary and advisable for the conservation
of the, species. In addition, to the extent prudent ancf determinable, she or he must designate the
critical habitat of the 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, and 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. As noted in Chapter
2, 40 CFR 6.605(3) requires that an EIS 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
6-19 September 1994
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Statutory Framework EIA Guidelines for Mining
species. If a Federally listed threatened or endangered species may be located within the project area
andlor may be affected by the project, a detailed endangered species assessment (Biological
Assessmtnt) 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.
6.5 NATIONAL HISTORIC PRESERVATION ACT
The National Historic Preservation Act (NHPA) (16 U.S.C. § 470 et seq.) establishes Federal
programs to further the efforts of private agencies and individuals in preserving the historical and
cultural foundations• of the Nation. The NHPA authorizes the establishment of the National Register
of Historic Places. It establishes an Advisory Council on Historic Preservation authorized to review
and comment upon activities licensed by the Federal government that have an effect upon sites listed
on the National Register of Historic Places or that are eligible to be listed. The NHPA establishes a
National Trust Fund to administer grants for historic preservation. It authorizes the development of
regulations to require Federal agencies to consider the effects of Federal-assisted activities on
properties included in, or eligible for, the National Register of Historic Places. It also authorizes
regulations addressing State historical preservation programs. State preservation programs can be
approved where they meet minimum specified criteria. Additionally, Native American tribes may
assume the functions of State Historical Preservation Officers over tribal lands where the tribes meet
minimum requirements. Under the Act, Federal agencies assume the responsibility for preserving
historical properties owned or controlled by the agencies.
A series of amendments to the NHPA in 1980 codify portions of Executive Order 11593 (Protection
and Enhancement of the Cultural Environment—16 U.S.C. §470). These amendments require an
inventory of Federal resources and Federal agency programs that protect historic resources, and
authorize Federal agencies to charge Federal permittees and licensees reasonable costs for protection
activities.
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, 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 noted in Chapter 2, 40 CFR 6.605(b)(4) provides that issuance of a new source NPDES permit,
that will have 4 ’signiflcant direct and adverse effect on a property listed m 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 and
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Alaska, 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
obliterate any renmants of historic operations, care must be taken to identify any valuable cultural
resources and mitigate any unavoidable impacts. Innovative approaches are often called for and
implemented. In Cripple Creek, ColOrado, for, example, a mining operation wished to recover gold
from turn-of-the-century waste rock piles. As mitigation for removing this evidence of the area’s past
mining, the operator replaced the piles with waste rock from their modern pit. In addition, they will
provide interpretative signs in the area for the public.
6.6 COASTAL ZONE MANAGEMENT ACT
The Coastal Zone Management Act’s (CZMA) (16 U.S.C. § i451-1464) seeks to “preserve, protect,
develop, and where possible, restore or enhance the resources of the Nation’s coastal zone for this
and future generations.” To achieve these goals, the Act provides for financial and technical
assistance and Federal guidance to States and territories for the conservation and management of
coastal resources.
Under the CZMA, Federal grants are used to encourage coasta1 States to develop a coastal zone
management program (CMP). The CMPs specify permissible land and water uses and require
participating States to specify how they will implement their management programs. In developing
CMPs, States must consider such criteria as ecological, cultural, historic and aesthetic values as well
as economic development needs. Applicants for Federal licenses or permits must submit consistency
certifications indicating that their activities comply with CMP requirements. In addition, activities of
Federal agencies that directly affect the coastal zone must be consistent with approved State CMPs to
the maximum extent practicable. The CZMA also establishes the National Estuarine Reserve System,
which fosters the proper management and continued research of areas designated as national estuarine
reserves.
To the extent that mining activities are federally licensed or permitted, applicants must certify that
such activities are consistent with applicable CMPs.
6.7 EXECUTIVE ORDERS 11988 AND 11990
Executive Orders 11988 (Floodplain Management) and 11990 (Protection of Wetlands) apply to
executive agencies that acquire, manage or dispose of Federal lands or facilities; construct or finance
construction on such lands; or conduct Federal activities or programs affecting land use. Under E.O.
11988, such agencies are required to”. . . avoid to the extent possible the long- and short-term
adverse impacts associated with the occupancy and modification of floodplain and to avoid direct and
indirect support of floodplain development wherever there is a practicable alternative. . .“ within the
100-year flood elevation. This requires that alternatives to avoid development in a floodplain be
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considered and that environmental impacts be assessed. If development requires siting in a
floodplain, action must be taken to modify or design the facility in a way to avoid damage by floods.
E.O. 11990 is similar to E.O. 11988 in that it requires such agencies to”. . avoid to the extent
possible the long-and short-term adverse impacts associated with the destruction or modification of
wetlands and to avoid direct or indirect support of new construction in wetlands wherever there is a
practicable alternative . .“ When constructing a new facility, actions that minimize the destruction,
loss, or degradation of wetlands, and actions to preserve and enhance the natural and beneficial value
of wetlands are required. If there is no practicable alternative to wetland construction projects,
proposed actions must include measures to minimize harm. Construction in wetlands also falls under
§404 of the Clean Water Act, administered by the U.S. Corps of Engineers.
6.8 FARMLAND PROTECTION POLICY ACT
The Farmland Protection Policy Act (FPPA) (P.L: 97-98) seeks to minimize the conversion of
farmland to non-agricultural uses. It requires that, to the extent practicable, Federal programs be
compatible with agricultural land uses. The Act requires that in conducting agency actions Federal
agencies follow established criteria for considering and taking into account any adverse effects such
actions may have on farmland. Where adverse effects are anticipated, Federal agencies must consider
alternatives that will mitigate any harmful impacts. Under the Act, the U.S. Soil Conservation
Service (SCS) is required to be contacted and asked to identify whether a proposed facility will affect
any lands classified as prime and unique farmlands. However, beyond considering potential adverse
effects and alternatives to agency action, the Act doesnot provide the basis for actions challenging
Federal programs affecting farmlands.
6.9 RIVERS AND HARBORS ACT OF 1899
The Rivers and Harbors Act (RHA) (33 U.S.C. § 40l-413). was originally enacted to regulate
obstructions to navigation and to prohibit the unpermitted dumping or discharging of any refuse into a
navigable water of the United States. The Act also provides authority to regulate the disposal of
dredgings in navigable waters. The provisions of §407 forbid any discharge of any refuse matter of
any kind or description whatever other than that flowing from streets and sewers in a liquid state.
Under §403, a permit is required from the U.S. Army Corps of Engineers for the construction of any
structure in or over navigable waters of the United States. Section 403 is usually combined with §404
of the Clean Water Act, which addresses the discharg es of fill to all waters of the United States.
Since the passage of the Clean Water Act, the waste discharge-permitting function of the RHA has
been superseded by NPDES program under §402 of the CWA. Nevertheless, some provisions of the
RHA, primarily Sections 403, 404, and 407, could still be used to enforce single-instance waste
discharges that affect navigation and anchorage.
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6.10 SURFACE MINING CONTROL AND RECLAMATION ACT
The Surface Mining Control and Reclamation Act (SMCRA) addresses all elements of surface coal
operations and the surface effects of underground coal mining. The major component of SMCRA
relevant to new• mining operations is Title V, which establishes a regulatory and permit program for
coal mines operating after 1977. SMCRA Title IV primarily addresses the Abandoned Mined Lands
(AML) Program, under which coal mine sites that were abandoned prior to 1977 are reclaimed.
SMCRA provides, for delegation of program implementation authority to States, with State programs
overseen by the Office of Surface Mining Reclamation and Enforcement (OSM) and direct OSM
implementation in nondelegated States. To date, OSM has delegated primacy to 23 States. In
addition, three Native American tribes administer their own AML programs. OSM administers
SMCRA requirements in 13 States (most of which have no current coal production) and on all other
Native Ameri n lands.
6.10.1 PERMrFrING PROGRAM FOR AcrivE COAL M1N NG OPERATIONS
SMCRA requires permits to be issued for all active mining operations. In 30 CFR Parts 816 and
817, OSM has promulgated specific design, operating, and performance standards to ensure that
statutory performance standards are met. ‘Special performance standards were established for: auger
mining;, anthracite mines in Pennsylvania; operations in alluvial valley floors; operations in prime
farmlands; mountaintop removal;, special bituminous mines in Wyoming; coal preparation plants not
locat ed within the permit area of amine; and in situ processing. Some of the significant standards
covering surface and underground operations include:
• Surface Resources
- Disturbed areas must be returned in a timely manner to conditions that support the land
use(s) of the site prior to mining or to a “higher and better use” Land uses include
industrial, agricultural, fish and wildlife habitat, or combinations of land uses.
- Backfilling and grading to achieve approximate original contour (AOC); AOC includes’
elimination of highwalls, spoil piles, and depressions. Exceptions to AOC requirements
are permitted for mountaintop removal’operations and mines that are considered to
operate in thick or thin overburden conditions.
- Exposed’ coal seams and combustible, toxic, or acid-forming materials must be covered
with a minimum of four feet of suitable material.
- Reclamation/revegetation requirements include that a permanent, diverse and effective
vegetation cover of native plants be established that will support the postmining ‘land
uses.
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.. Water Resources
- Mining should be conducted to minimize disturbance to the prevailing hydrologic
balance to prevent long-term adverse impacts. Changes in quality and quantity of
ground and surface water must be minimized. Protection of the hydrologic system
requires that runoff from all disturbed areas (including those that have been regraded
and seeded) pass through a sedimentation pond prior to discharge. Sediment ponds
must be designed to retain at least the 10-year 24-hour precipitation event. Effluent
limitations have been established under the Clean. Water Act, as discussed in Section
6.1 above.
- The groundwater recharge capacity of reclaimed lands must be restored and backtilled
materials must be placed to minimize impacts to flow and quality of the aquifer.
- Alluvial valley floors west of the 100th meridian must be restored to their full
hydrologic function, including gradient, shape, capillary and perched water zones, and
moisture-holding capacity.
Permits can be issued only if a mine can be successfully reclaimed. Along with permit applications,
applicants must submit reclamation plans that include approaches to addressing all environment risks
identified in t.he:application. Permit applicalions must be denied if the operator (or corporate
affiliates) has, at any other site in the country, unabated violations of SMCRA or other environmental
laws. In addition, permits can be denied or revoked if applicants or permittees have shown a
consistent pattern of violations, again at any site. The Comprehensive National Energy Policy Act of
1992 provided for an exemption from the permit prohibition process at SMCRA §510(c). This
exemption specifically applies to authorized remining sites where violations of permit conditions occur
due to “unanticipated events.” The exemption does not preclude the permitting authority from taking
other enforcement actions, however.
SMCRA specifically requires that discharges to surface waters be in compliance with applicable State
and Federal water quality regulations and the coal mining effluent guidelines at 40 CFR Part 434.
Several of the design requirements under 30 CFR Part 816 ‘also pertain to controlling discharges from
active mining areas. Permittees are specifically required to design and install sediment/siltation
control measures that represent the “Best Technology Currently Available (BTCA).” For sediment
áontrol, BTCA originally consisted of controlling discharges from disturbed areas through
sedimentation ponds. This uniform approach was challenged and BTCA determinations are now made
on a case-by-case basis. ‘
SMCRA requires reclamation bonds for all sites. The basic requirement is a bond for the full cost of
site reclamation, although OSM can approve alternative bonding approaches if they are deemed
adequate. Alternative approaches such as fixed amounts per acre disturbed have been adopted by
some States.
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In practice, reclamation plans and bonding requirements have emphasized land restoration’(i.e.,
recontouring and revegetation) rather than water quality issues (except for impacts from erosion).
Following reclamation and full bond release, any point source discharges of pollutants remain subject
to NPDES permitting. However, NPDES permits have not generally been required following
reclamation and bond release (i.e., after discharges are’ not subject to effluent guidelines). ‘The
NPDES storm water program has followed this lead: sites that have been reclaimed after SMCRA’s
enactment are’ not subject to the program. In some cases, operators have forfeited bonds that were
inadequate to reclaim sites (and to address water quality). The responsible party for any remaining
discharges is a maüer of some contention at the present time; under the storm water program, the
owner of the site would be responsible for obtaining a permit for point source discharges of
contaminated storm water.
A limited exception to EPA’s 40 CFR Part 434 effluent guidelines was provided in the Water Quality
Act of 1987, which allows modifications to the National technology-based limits in cases where
rernining abandoned sites will result in the potential for improvement of water quality. Where such
exemptions are granted, technology-based limits are based on the permit writer’s best professional
judgment. Limits on pH, iron, and manganese cannot exceed the levels discharged prior to remining;
discharges also cannot violate”applicable water quality standards and criteria under §303 of the Clean
Water Act. Pennsylvania is notable for having used this provision to encourage remining of problem
sItes, and other States are increasingly using or considering the provision.,
It should be noted that certain provisions of SMCRA and the Clean Water Act may provide
disincentives to ‘remining abandoned coal sites. For example, neither SMCRA stanuards nor the
effluent limitation guidelines established under the Clean Water Act distinguish between remining
previously abandoned sites and mining undisturbed land (except as noted above). To the extent that
there is a greater potential for noncompliance at remining sites (e.g., because of greater complexity or
unpredictability of the hydrogeologic regime), the “permit. block” provisions of SMCRA ( 5 10(c))
could be a disincentive to remining: failure to comply with an NPDES permit can prevent the
operator from obtaining future SMCRA permits. The relative stringency of water quality standards,
particularly for pH, also may prevent operators from remining sites, since permits must provide for
attainment of water quality standards and criteria,,notwithstanding any prior nonattainment. (To the
extent that water quality standards and criteria act as a disincentive to remining, this may increase as
numeric criteria are established for an increased number of toxic pollutants in response to the 1987
amendments to §303.)
6.10.2 ABANDONED MINE LANDs PROGRAM
Title IV of SMCRA established the Abandoned Mine Lands (AML) Program to provide for
reclamation of mine sites abandoned prior to 1977 (the date of enactment). The program was
subsequently amended to allow the expenditure of funding to reclaim post-1977 operations where an’
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abandonment occurred between 1977 and the date of State program approval and the
reclamation/abatement bond was not sufficient; or where a surety provider became insolvent and
available funds were not sufficient to reclaim the site. The AML program is supported by the
Abandoned Mine Reclamation Fund. The fund receives reclamation fees paid by active mining
operations: for lignite coal, the contributionto the fund is LOC per ton; for other coal, the fee is 15C
per ton of coal from underground mines and 35C per ton of surface-mine coal. The fund is currently
authorized to collect fees through the year 2004.
6.11 MININGLAWOF1872
The Mining Law of 1872 (30 US.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:
Except as otherwise provided, all valuable mineral deposits in lands belonging to the
U.S. . . . shall be free and open to exploration and purchase, and the lands in which they
are found to occupation and purchase, by citizens of the U.S. . . . under regulations
prescribed by law, and according to the local customs or rules of miners in the several
mining districts, so far as the same are applicable and not inconsistent with the laws of the
U.S.
The Mining Law establishes the basic standards for the location, recordation, 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 1oc ted (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 is done or small fees are paid. Upon proving
that a valuable mineral deposit has been discovered (this proof must meet regulatory standards), claim
holders may patent the claim and purchase the land for nominal sums. Except as specifically
authorized by law (e.g., certan 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
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and National Monuments, among other lands). Inaddition, only “public domain” lands are generally
open to mineral location under the Mining Law.
Only since 1976 have claimants been required to record claims with BLM. Through the end of fiscal
year 1991, more than 2,700,000 claims had been accepted for recording by BLM. Of these, more
than 1,500,000 had been abandoned, relinquished, or rejected, leaving more than 1,100,000
unpatented claims on Federal lands. The number of claims on which significant prospecting or
mining occurred prior to 1976 is simply unknown, since there were no reporting (and few other)
requirements at the time.
6.12 FEDERAL LAND POLICY MANAGEMENT ACT
The Federal Land Policy Management Act (FLPMA) (43 U.S.C. § 170i-1782) provides the Bureau
of Land Management 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
mining claims 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.
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BLM’s implementing regulations pertaining ‘to development of mining claims include three levels of
review:
• Casual use—for which no notification. or approval is necessary
• Notice-level—for cumulativeannual disturbances total less than five acres. Operators must
notify BLM officials (and commit to reclamation), but no approval is required..
Consultation may be required if access routes are to be constructed.
• Approval-level—for disturbances exceeding 5 acres in a calendar year or in certain
specified areas (wilderness areas, wild and scenic rivers, critical habitat, areas of the
California Desert Conservation Area). Operators must obtain ELM approval (within
specified timeframes) of a Plan of Operations for such operations.
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 in
1994 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)). Within
30 days, BLM must notify the operator that: the plan is approved; changes or additions to the plan
are necessary; that up to 60 more days are required for review; that the plan cannot be approved until
after an EIS is prepared and filed with EPA; Or that the plan cannot be approved until BLM complies
with the Endangered Species Act or National Historic Preservation Act or consults with other surface
managing agencies. (Should cultural resources be discovered uring an inventory, BLM is
responsible for any costs of salvage that may be necessary.)
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
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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 if in other cases where EPA has significant
environmental concerns, EPA typically becomes a cooperating agency in the NEPA process.
There are a number of issues related to plans of operations and BLM regulatory oversight that bear
noting. For example, plans of operations themselves beàome the “permit” to which operators must
adhere. These are often enormous multi-volume documents that reflect the uncertainties of mining:
they often note multiple contingencies in the event that specific conditions are found or develop.
Detailed descriptiOns of planned operations under each contingency are not generally feasible (and are
certainly not economic). As a result, plans provide appropriate, caveats that additional plans,
consultations, studies, or modifications will be made if necessary. It is not practical to modify plans
of operations with every such change, and even when plans are formally modified, they often address
only the modification, not the entire operation. Thus, a mine that evolves over time, as most do,
comes to resemble the original plan less and less, and determining exactly which modification
addresses a particular mine component can be extremely difficult. In addition, BLM administration of
its regulations is very decentralized, with State offices and local resource area offices generally
responsible. This recognizes the site- and region-specific nature of the mining industry, and its
environmental impacts, but has led to inconsistency in several areas, including the level of
“significance” that triggers preparation of an environmental impact statement. Environmental impact
assessments (whether in EAs or EISs) follow the same pattern as plans of operations: they often
address the plan or modification at hand, not necessarily the entire mining operation as it has grown
and evolved over time. Finally, BLM considers itself extremely constrained by the Mining Law;
thereis no provision for BLM disapproval of proposed plans of operations, only the prevention of’
unnecessary and undue degradation of public lands.
6.13 NATIONAL PARK SYSTEM MINING REGULATION ACT
The National Park System Mining Regulation Act (also known as the Mining in the Parks Act, or
MPA) (16 U.S.C. § 19O1-1912) 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.
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6.14 ORGANIC ACT; MULTIPLE USE AND SUSTAINED YIELD ACT; NATIONAL
FOREST MANAGEMENT ACT
The Organic Act of 1897 (16 IL S.C. § 473-482, 551) has governed the Forest Service’s activities
since the earliest days of National Forest management. The Act delegated 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) establishes 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. MUSYA is
implemented by the Secretary of Agriculture. The National Forest Management Act of 1976 provides
the Forest Service with authonties 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.
6.15 MINERAL LEASING ACT; MINERAL LEASING ACT FOR ACQUIRED LANDS
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) created a leasing system for coal, oil, gas, phosphate,
and certain other fuel and chemical minerals (“leasable” minerals) on Federal lands. In addition,
Section 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
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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 wicn lease terms can result in lease suspension or forfeiture. At the end of fiscal year 1991, a
total of 69 nonenergy mineral leases (more than 49,000 acres) were in effect; in addition, there were
475 coal leases n effect, covering nearly 700,000 acres of public domain and acquired land
6.16 COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION, AND
LIABILITY ACT
The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (42
U.S.C. § 9601-9675) established the Superfund program to deal with releases and threatened releases
•of hazardous substances to the environment. CERCLA provides funding and enforcement authority
for Federal and State clean-up programs at thousands of sites throughout the United States that are
contaminated due to the release of specified hazardous substances. The statute establishes notification
requirements for releases of hazardous substances in reportable quantities (RQs), provides abatement
and response authorities for situations where a substance or pollutant may present an imminent and
substantial danger to the public health or welfare, requires the development of a National Contingency
Plan (NCP) designed to provide for consistent and coordinated responses (both removal and remedial)
to hazardous substance discharges, and creates a Hazardous Substance Response Trust Fund
(Superfund) to pay for emergency removal actions and long-term remediations at abandoned sites
where liable parties cannot be identified. CERCLA establishes that owners and operators of
contaminated sites, as well as waste generators and others who were responsible for waste disposal
and waste transportation are subject to strict, joint, and several liability for response costs and natural
resources damages. The Statute also establishes site cleanup standards.
Over 52 mining- and mineral processing-related sites are currently on the NPL, including some of the
largest and most complex of all NPL sites. The cleanup standards applied to specific NPL sites are
determined on a site-specific basis, following detailed studies of the site, the potential and actual risks,
and possible remedial actions. Because the United States is the land owner at several of the mining-
related NPL sites, Federal agencies are responsible persons in some cases.
It should also be noted that several Federal courts have addressed the issue of whether mining wastes
are “hazardous substances” under CERCLA, and thus whether mining sites where releases of mining
wastes occur are subject to CERCLA removal or remedial actions. The basic question is whether the
exemption of mining wastes from regulation as hazardous wastes under RCRA excludes them from
the definition of “hazardous substance” in §104(14). In Eagle Picher Industries v. EPA (245 U.S.
6-31 September 1994
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Statutory Framework EIA Guidelines for Mining
App. D.C. 196, 759 F.2d 922 (D.C. Cir. 1985), it was determined that mining wastes exempt from
hazardous waste regulation were within the CERCLA definition of hazardous substances. There has
been additional judicial consideration of this issue, with the decisions generally consistent with the
Eagle Picher decision.
Issuance of an NPDES permit for a discharge(s) from a new source mining operation can exclude the
operator from potential CERCLA liability. New operations are often located in historic mining
districts, where CERCLA action may be ongoing or could occur in the future. In such cases, the
reviewer should be especIally cautious that the project will not further degrade water quality
(including sediment) and that water quality-based limits/requirements are included in the NPDES
permit. Further, prior to operation of the new source, adequate baseline data should be available to
characterize existing water column arid sediments conditions. This will minimize any uncertainty
related to the sources of pollutant levels (PRPs versus the non-liable new operator).
6.17 EMERGENCY PLANNING AND COMMUNITY RIGHT-TO-KNOW ACT
The Emergency Planning and Community Right-to-Know Act (EPCRA) (42 U.S.C. § 1 1001-11050)
requires States to establish emergency response commissions and emergency planning districts as well
as local emergency planning committees. These planning groups must prepare and review emergency
plans. The Act also requires that owners and operators of facilities who must submit materials safety
data sheets under the Occupational Safety and Health Act (OSHA) must report information about
these ha7 Lrdous substances to the local emergency planning committee, the State emergency. response
commission, and the local fire department. Mining operations must report on chemical storage and
use, and on spills or releases, to these entities.
EPCRA also requires facilities that use, manufacture, or process certain listed toxic chemicals to
report the amount of each chemical released to the environment on an annual basis. These data
comprise the Toxics Release Inventory, or TRI. TRI reporting requirements apply to manufacturing
facilities in Standard Industrial Classifications (SIC) Codes 20 through 39. Mining operations are not
within these SIC codes and thus are not subject to 1’RI reporting. However, it should be noted that
the TRI list of chemicals and the types of facilities required to report releases are currently being
expanded or considered for expansion by EPA.
6.18 WILD AND SCENIC RIVERS ACT
The Wild and Scenic Rivers Act of 1968 (16 U.S.C. 1273 et seq.) provides that “ [ c]ertain selected
rivers. . . shall be preserved in a free flowing condition, and that they and their immediate
environments shall be protected for the benefit and enjoyment of present and future generations.”
Section 7 of the Act prohibits the issuance of a license for construction of any water resources project
that would have a direct adverse effect on rivers (or reaches of rivers) that have been selected on the
6-32 September 1994
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EIA Guidelines for Mining Statutory Framework
basis of their remarkable scenic, recreational, geologic, fish and wildlife, historic, cultural, or other.
similar values for the National Wild and Scenic Rivers System.
The System includes rivers and streams placed in the System by acts of Congress and rivers that have
been studied and deemed to be suitable foi inclusion. Any potential impacts on rivers and streams in
the System must be considered, and direct adverse effects on the values for which the river was
selected for the System must be prevented.
States also have their own systems for protecting rivers and streams or portions thereof. While EPA
has no legal requirement to consider State-protected wild and scenic rivers and streams, any potential
impacts to such areas should nevertheless be considered and addressed.
6.19 FISH AND WILDLIFE COORDINATION ACT
The Fish and Wildlife Coordination Act of 1934 (16 U.S C. 661 et seq., P.L. 85-624) authorizes the
Secretary of the Interior to provide assistance to, and cooperate with, Federal, State, and public or
private agencies and organizations in. the. development, protection, rearing, and stocking of all species
of wildlife, resources thereof, and their habitat. The majority of the Act is associated with the -
coordination of wildlife conservation and other features of water-resource development programs.
6.20 FISH AND WILDLIFE CONSERVATION ACT
The Fish and Wildlife Coordination Act of 1980 (16 U.S.C. 2901 er seq.) encourages Federal
agencies to conserve and promote conservation of nongame fish and wildlife and their habitats to the
maximum extent possible within each agency’s statutory responsibilities. The Act places no
affirmative requirements on Federal agencies.
6.21 MIGRATORY BIRD PROTECTION TREATY ACT
The Migratory Bird Protection Treaty Act (16 U.S.C. 703-711) prohibits the killing, capturing, or
transporting of protected migratory birds, their nests, and eggs. Consultations with the Fish and
Wildlife Service are encouraged if project activities could directly or indirectly harm migratory birds.
September 1994
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EIA Guidelines for Mining References
7. REFERENCES
Adamus, P.R., E.J. Clairain, Jr., R.D. Smith, and R.E. Young. 1987. Wetlands Evaluation
Technique (WEI); Volume I!. Methodology. Operational Draft Technical Report Y-87-_, U.S.
Army Corps of Engineer Waterways Experiment Station, Vicksburg, MS.
Ahsan, M.Q., et a!: 1989. “Detoxification of Cyanide in Heap Leach Piles Using Hydrogen
Peroxide.” In World Gold, proceedings of the First Joint SME/Australian Institute of Mining
and Metallurgy Meeting. R. Bhappu and R. Ibardin (editors).
Alaska Department of Environmental Conservation. 1986. A Water Use Assessment of Selected
Alaska Stream Basins Affected by Gold Placer Mining. Prepared by Dames & Moore, Arctic
Hydrologic Consultants, Stephen R. Braund and Associates, L.A. Peterson and Associates, and
Hellenthal and Associates.
Alaska Department of Environmental Conservation. 1987 (March). Placer Mining Demonstration
Grant Project Design Handbook (prepared by L.A. Peterson & Associates, Inc.). Fairbanks,
AK
Alaska Miners Association. 1986. Placer Mining — A Systems Approach. Short Course, Alaska
Miners Association Eleventh Annual Convention, October 29-30, 1986. Anchorage, Alaska.
Altringer, P. B., R.H. Lien, and K.R. Gardner. 1991. Biological and Chemical Selenium Removal
From Precious Metals Solutions. Proceedings of the Symposium on Environmental
Management for the 1990s, Denver, Colorado, February 25-28.
Argafl, G.O., Jr. 1987 (December). “The New California Gold Rush.” Engineering & Mining
Journal: 30-37.
Arizona BADCT Guidance Document for the Mining Category, Draft Guidance Document. 1990.
Arizona Revised Statute 49-243 B. 1., For Permitted Facilities Utilizing BADCT.
ASARCO. 1991 (February 4). Ray Unit Tailing Impoundment Alternative Analysis. Appendix
11.19. Submitted to EPA Water Management Division Region LX Wetlands Program.
Beard, R.R. 1987 (March). “Treating Ores by Amalgamation.” Circular No. 27. Phoenix, AZ:
Department of Mines and Mineral Resources.
Beard, R.R. 1990 (October). The Primary Copper Industry of Arizona in 1989. State of Arizona
Department of Mines and Mineral Resources, Special Report No. 16.
Biswas, A.K., and W.G. Davenport. 1976. Ertractive Metallurgy of Copper. Pergamon
International Library, International Series on Materials Science and Technology, Vol. 20,
Chapter 2.
Boyle, R.W. 1979. The Geochemistry of Gold and Its Deposits. Canada Geological Survey Bulletin
280. Canadian Publishing Centre. Hull, Quebec, Canada. 584 pp.
7-1 September 1994
-------
References ELA Guidelines for Mining
Bradham, W. S., and F T. Caruccio. 1990. A Comparative Study of Tailings Analysis using Acid!
Base Accounting, Cells, Columns and Soxhelets. Proceeding of the 1990 Mining and
Reclamation Conference and Exhibition, Charleston, WV.
Brady et al. 1994. Evaluation of Acid-base Accounting to Predict the Quality of Drainage at Surface
Coal Mines in Pennsylvania, U.S.A. In the Proceedings of the International Land Reclamation
and Mine Drainage Conference and Third International Conference on the Abatement of Acidic
Drainage, April 24-29.
British Columbia AMD Task Force. 1989. Acid Rock Drainage Draft Technical Guide, Volumes I
and 11. Report 66002/2. Prepared for the British Columbia AMD Task Force by SRK, Inc.
British Columbia AMD Task Force. 1990 (August). Monitoring Acid Mine Drainage. Prepared by
E. Robertson in association with Steffen Robertson and Kirsten (B.C.) Inc. Bitech Publishing,
Richmond, British Columbia.
Britton, S.G. 1992a. Mine Exploitation, in SME Mining Engineering Handbook, 2nd Edition (HL.
Hartrnan, ed.). Society for Mining, Metallurgy and Exploration, Inc. Liuleton, CO.
Britton, S.G. and G.T. Lineberry. 1992b. “Underground Mine Development, “in SME Mining
Engineering Handbook, 2nd Edition (H.L. Hartman. ed.). Society for Mining, Metallurgy and
Exploration, Inc. Littleton, CO.
Brodie, M. J., L. M. Broughton, and Dr. A. MacG. Robertson. 1991. A Conceptual Rock
Classification System for Waste Management and aL.aboratory Method for ARD Prediction
From Rock Piles. In Second International Conference on the Abatement of Acidic Drainage.
Conference Proceedings, Volumes I - 4, September 16, 17, and 18, 1991, Montreal, Quebec.
Broughton, L. M. and Dr. A. MacG. Robertson. 1991. Modeling of Leachate Quality From Acid
Generation Waste Dumps. Second International Conference on the Abatement of Acidic
Drainage. Conference Proceedings, Volumes 1 - 4, September 16, 17, and 18, 1991, Montreal,
Quebec.
Broughton, L. M. and Dr. A. MacG. Robertson. 1992. Acid Rock Drainage From Mines - Where
Are We Now. Steffen, Robertson and Kirsten, Vancouver, British Columbia. Internal Draft
Paper.
Bruynesteyn, A. and R. Hackl. 1982. “Evaluation of Acid Production Potential of Mining Waste
Materials.” Minerals and the Environment 4(1).
California Mining Association. 1991. Mine Waste Management. Edited and Authored by Ian
HutchisQn and Richard D. Ellison. Sponsored by the California Mining Association,
Sacramento, California.
California Regional Water Control Board. 1987 (April 22). “Cyanide Requirements for Cyaiudation
Process Wastes.” Internal Memorandum from Dr. R.S. Gill to O.R. Butterfield.
7-2 September 1994
-------
EIA Guidelines for Mining References
California Regional Water Quality Control Board. 1993 (January 19). Personal communication
bet-ween Richard Humphreys and Joe Rissing, Science Applications International Corporation.
Falls Church, VA.
‘Clark, W.B. 1970. Gold Districts of Ca4fornia. California Division of Mines and Geology,
Bulletin 193. San ,Francisco, CA.
Coastech Research Inc. 1989. Investigation of Prediction Techniques for Acid Mine Drainage.
MEND Project’ 1.16.la. Canada Center for Mineral and Energy Technology, Energy, Mines,
and Resources Canada.
Cohen, Ronald R.H. and Staub, Margaret W. 1992 (December). Technical Manual for the Design
and Operation of a Passive Mine Drainage Treatment System, prepared for the U.S. Bureau of
Reclamation. Golden, CO.
Colorado Department of Natural Resources. 1992 (March). Guidelines for Cyanide Leaching
Projects. Mined Land Reclamation Division.
Cravotta, F. T. et al. 1990. Effectiveness of the Addition of Alkaline Materials at Swface Mines in
Preventing or Abating Acid Mine Drainage: Part 1. Theoretical Considerations. In
Pràceedings of the 1990 Mioning and Reclamation Conference and Exhibition, April 23-26.
Cumming, A.B. (Chairman of Editorial ‘Board). 1973. SME Mining Engineering Handbook. , Society
of Mining Engineers, AIME. New York, New York. S
Dadgar, A. ‘1989. “Extraction of Gold from Refractory Concentrates: Cyanide Leach vs. Bromide
Process.” Presented at the Metallurgical Society Annual Meeting. Las Vegas, NV. February
27-March 2, 1989.
Day. 1994. Evaluation of Acid Generating Rock and Acid Consuming Rock Mixing to Prevent Acid
Rock Drainage. In the Proceedings of the International Land Reclamation and Mine Drainage
Conference and Third International Conference on the Abatement of Acidic Drainage, April 24-
29 .
‘Devuyst, E.A., et al. 1990 (September). ‘Inco’s Cyanide Destruction Technology. Preprint No. 90-
406. Littleton, CO: Society For Mining, Metallurgy, and Exploration, Inc.
Dietz et al. 1994. Evaluation of Acidic Mine Drainage Treatment in Constructed Wetland Systems.
‘In the Proceedings Of the International Land Reclamation and Mine Drainage Conference and
Third International Conference on the Abatement of Acidic Drainage, April 24-29.
Doe Run Company. 1990 (February). Fletcher Project: Application for Metallic Minerals Waste
Management Area Permit.
Doyle, F.M. (editor.). 1990. Mining and Mineral Processing Wastes, proceedings of the Western
Regional Symposium on Mining and Mineral Processing Wastes. Berkeley, CA. May 30-June
1, 1990. Littleton, ‘CO: Society for Mining, Metallurgy and Exploration, Inc.
7-3 September 1994
-------
• References EIA Guidelines for Mining
Duncan, D. and C. Walden. 1975. Prediction of Acid Generation Potential. Report to Water
Pollution Control Directorate 1 Environmental Protection Service, Environment Canada.
Durkin, T.V. 1990. Neutralization of Spent Ore from Cyanide Heap Leach Gold Mine Facilities in
the Black Hills of South Dakota - Current Practices and Requirements. AIME’s Proceedings of
the 4th Western Regional Conference an Precious Metals and the Environment, Lead. South
Dakota.
• Eger, A., and K. Lapakko. 1985. Heavy Metal Study Progress Report on the Field Leaching and
Reclamation Program: 1977-1983. MN Dept. Nat. Res., Division of Minerals, St. Paul, M l.
Eger et al. 1994. Metal Removal in Wetland Treatment Systems. In the Proceedings of the
International Land Reclamation and Mine Drainage Conference and Third International
Conference on the Abatement of Acidic Drainage, April 24-29.
Engineering and Mining Journal. 1990 (January). “Technology Turns Southwest Waste into Ore.”
Vol. 191, pp. 41-44.
Environmental Law Institute. 1992 (November). State Regulation of Mining Waste. Current State of
the Art.
Fast, John L. 1988 (June). “Carbons-rn-Pulp Pioneering at the Canton Mill.” Engineering &
Mining Journal. 56-57.
Ferguson, K. D. and P. M. Erickson. 1988. Pre-Mine Prediction of Acid Mine Drainage. :
Dredged Material and Mine Tailings. Edited by Dr. Willern Salomons and Professor Dr.
Ulrich Forstner. Copyright by Springer-Verlag. Berlin, Heidelberg.
Ferguson, K. D., and K. A. Mann. 1991. The PredicJion of Acid Rock Drainage - Lessons From
the Database. In Second International Conference on the Abatement of Acidic Drainage.
Conference Proceedings, Volumes 1 - 4, September 16, 17, and 18, Montreal, Quebec.
Flatt, P. 1990 (March). “Fine Placer Gold Recovery Methods.” California Mining Journal: 5-8.
Fuerstenau, M. C., (editor). 1976. tlotation, Volume 2. New York: Societyof Mining Engineers.
Gentry, D.W. and M.K. McCarter. 1992. “Surface Mining: Mechanical Extraction Methods, “ in
SME Mining Engineering Hai2dbook, 2nd Edttion (H.L. Hartmän, ed.). Society for Mining,
• Metallurgy and Exploration, Inc. Littleton, CO.
Guilbert, John M., and Charles F. Park, Jr. 1986. The Geology of Ore Deposits, W.H. Freeman
• and Company, New York, New York.
Hackel, R.P. 1990 (December). “Operating A Commercial-Scale Bioleach Reactor at the Congress
Gold Prèperty.” Mining Engineering.
Halbert, B., J. Scharer, R. Knapp, and D. Gorber. 1983. Determination of Acid Generation Rates in
• Pyritic Mine Tailings. Presented at the 56th Annual Conference of Water Pollution Control
Federation, October 2-7.
74 September 1994
-------
EIA Gwdelines for Mining References
Harrelson, C.C., C.L Rawlins, and .I.P. Potyondy. 1994. Stream Channel Reference Sires: An
Illustrated Guide to Field Technique. U.S. Department of Agriculture, U.S. Forest Service,
Fort Collins, Colorado:
Harty, D.M. and P.M. Terlecky. 1984a (February). “Existing Wastewater Recycle Practices at
Alaskan Placer Gold Mines”, Frontier Technical Associates, Memo randum to B.. M. Jarrett,
U.S. EPA, Effluent. Guidelines Division.
Harty, D.M. and P.M. Terlecky. 1984b (February). “Water Use Rates at Alaskan Placer Gold
Mines Using Classification Methods”, Frontier Technical Associates, Memorandum to B.M.
.Jarrett, U.S. EPA, Effluent Guidelines Division.
Hedin, Robert S. and Watzlaf. 1994. The Effects of Anoxic Limestone Drains on Mine Water
Chemistry. In the Proceedings of the International Land Reclamation and Mine Drainage
Conference and Third International Conference on the Abatement of Acidic Drainage, April 24-
29.
Hellier, William W. 1994. Best Professional Judgement Analysis for Constructed Wetlands as a Best
Available Technology for the Treatment of Post-Mining Ground-water Seeps. in, the Proceedings
of the International Land Reclamation and Mine Drainage Conference and Third International
Conference on the Abatement of Acidic Drai age, April 24-29.
Hittman Associates, Inc. 1976. Underground Coal Mining: An Assessment of Technology. Prepared
for Electric Power Research Institute, Palo Alto, CA, EPRI-AF-219, variously paged;
Holmes, K.W. 1981 (January). Natural Revegetation of Dredge Tailings at Fox, Alaska. In
Agroborealis: 26-29.
Hood, W. and A. Oertèl. 1984. A eaching Column Method for Predicting Effluent Quality From
Surface Mines. Jil Proc. Symp. on Surface Mining Hydrology, Sedimentology and
Reclamation. University of Kentucky.
Hürlbut, C.S., and C. Klein. 1977. Manual of Mineralogy. New York: John Wiley & Sons.
Hutchinson, R.W. and J.D. Blackwell. 1984. Time, crustal evolution and generation of uranium
deposits. In: Uranium Geochemistry, Mineralogy, Geology, Exploration and resources. The
Institution of Mining and Metallui gy, London, England.
Idaho, Division of Environmental Quality, Water Quality Bureau. 1993 (May ii). Personal
conmumicationbetween Jerry Yoder and Michelle Stowers, Science Applications International
Corporation. Falls Church, VA.
Jarrett, A.R. (1983). Water Management, 5th Edition.
Kim, A. G., B. Heisey, R.. Kleinmann, and M. Duel. 1982. Add Mine Drainage: Control and
Abatement Research. U.S. DOl, Bureau of Mines IC 8905.
7. .5 September 1994
-------
References EIA Guidelines for Mining
Kruczynski, Wi. 1990. Options to be considered in preparation and evaluation of mitigation plans.
: Wetland Creation and Restoration: the Status of the Science, J.A. Kusler and M.E. Kentula
(eds.). Island Press, Washington, D.C. pp. 555-569.
Lapakko, K. 1988. Prediction of Acid Mine Drainage From Duluth Complex Mining Wastes In
Northeastern Minnesota. : Mine Drainage and Surface Mine Reclamation. Volume I: Mine
Water and Mine Waste. U.S. Department of Interior, Bureau of Mines Information Circular
9183.
Lapakko, K. 1990a. Regulatory Mine Waste Characterization: A Parallel to Economic Resource
Evaluation. k: Mining and Mineral Processing Wastes. Proceedings of the Western Regional
Symposium on Mining and Mineral Processing Wastes, May 30 - June 1, 1990, Berkeley,
California p.31-39. Edited by Fiona Doyle, Published by the Society for Mining, Metallurgy,
and Exploration, Inc., Littleton, CO.
Lapakko, K. 1990b. Solid Phase Characterization in Conjunction with Dissolurián Experiments for
Prediction of Drainage Quality. : Mining and Mineral Processing Wastes. Proceedings of
the Western Regional Symposium on Mining and Mineral Processing Wastes, May 30 - June 1,
1990, Berkeley, California p.31-39. Edited by Fiona Doyle, Published by the Society for
Mining, Metallurgy, and Exploration, Inc., Littleton, CO.
Lapakko, K.. 1992. Evaluation of Tests for Predicting Mine Waste Drainage pH. Draft Report to
the Western Governors’. Association, May 1992.
Lapakko, K. 1993a. Predictive Testing for Mine Waste Drainage Quality. j . j Mine Operation and
Closure Short Course. Sponsored by EPA and others April 27 - 29. Helena, Montana.
Lapakko, K. 1993b. Mine Waste Drainage Quality Prediction: A Literature Review. Draft Paper.
Minnesota Department of Natural Resources, Division of Minerals, St. Paul, Minnesota.
Lapakko, K. 1994a. Evaluation of Neutralization Potential Determinations for Metal Mine Waste
and a Proposed Alternative. In the Proceedings of the International Land Reclamation and-
Mine Drainage Conference and Thud International Conference on the Abatement of Acidic
Drainage, April 24-29.
Lapakko, K. 1994b. Subaqueous Disposal of Mine Waste: Laboratory Investigation. In the
Proceedings of the International Land Reclamation and Mine Drainage Conference and Third
International Conference on the Abatemçnt of Acidic Drainage, April 24-29.
LaPierriere, J.D., SM. Wagener and D.M. Bjerklie. 1985 (April). Gold-Mining Effects on Heavy
Metals in Streams, Circle Quadrangle, Alaska. Water Resources Bulletin: 245-252.
Lefloux, P.L., and Holden, L. T. 1990 (December). “Atmospheric Carbon Elution Without the Use
of Cyanide at Barneys Canyon Mine.” Mining Engineering: 1323.
Lopes, R.F., and R.J. Johnston. 1988 (August). “A Technical Review of Heap Leaching.” In
Environmental Management for the 1990s, proceedings of the Symposium on Environmental
Management for the 1990s. Denver, CO. February 25-28, 1991. D.J. Lootens, W.M.
7-6 September 1994
-------
EIA Guidelines for Mining References
.Greenslade, andJ.M. Barker (editors). Littleton, CO: Society for Mining, Metallurgy, and
Exploration, Inc.
LTV Steel Mining Company. 1991 (June). LIV Steel Hoyt Lakes, Minnesota 2-B Tailing Basin Site
• Investigation and Stability Analysis. Prepared by EBASCO. 19 PP.
Lu, Ning, and Yiqiang Zhang, undated. Thermally Induced Gas Convection in Mine Wastes.
Disposal Safety Inc., Washington, D.C.
Lucht, R. 1990 (September 12). Personal communication between Mr. Robert Lucht, Underground
Injection Control Coordinator, Wyoming Department of Environmental Quality, and Ms. Laurie
Lamb, Science Applications International Corporation. Denver, CO.
Manahan, Stanley E. 1991. Environmental Chemistry. Fifth edition. Lewis Publishers, Inc.,
Chelsa, Michigan:
Mandelker, D.R. 1992. NEPA Law and Litigation. Second edition. Clark Boardman Callaghan,
New York.
McElfish, J.M., Jr. and A.E. Beier. 1990. Environmental Regulation of Coal Mining SMCR4 ‘s
Second Decade. Environmental Law Institute. Washington, DC.
Merritt, R.c. 1971. The Extractive Metallurgy of Uranium. Colorado School of Mines, Golden,
Co.
Michigan State, Geological Survey Division. 1983 (December). Assessment of Inactive Iron Mines in
East Iron County, Michigan. Lansing, Michigan.
Mine Safety and Health Administration. 1988. Closed Metal/Nonmetal Mine Employment and
Address Data Tape. Washington, DC.
Morin, Kevin A. and Hutt, Nora M. 1994. Observed Preferential Depletion of Neutralization
- Potential Over Sulfide Minerals in Kinetic Tests: Site-specific Criteria for Safe NP/AP Ratio.
In the Proceedings of the International Land Reclamation and Mine Drainage Conference and
Third International Conference on the Abatement of Acidic Drainage, April 24 29.
Mudder T.I. and A. Smith. 1992. Solution Management During Decommissioning of Heap Leach
Operations. Paper presented at Society for Mining, Metallurgy, and Exploration’s Annual
Meeting, Phoenix, Arizona, February 24-27.
National Institute of Occupational Safety and Health. 1990 (August 17). National Occupational
Health Survey of Mining: Gold Report. Morgantown, WV.
National Institute for Occupational Safety and Health. 1990 (August 27). National Occupaiional
Health Survey of Mining: Lead-Zinc Report. Unpublished. Morgantown, WV.
Nevada, Bureau of Water Quality Planning. 1993 (January 21). Personal communication between
Kathy Sertic and Joe Rissing, Science Applications international Corporation. Falls Church,
VA.
7..7 September 1994
-------
• References EIA Guidelines for Mining
Nicholson, Ronald V. 1992. A Review of Models to Predict Acid Generation Rates in Suiphide
Waste Rock at Mine Sites. Presented to the International Workshop on Waste Rock Modelling,
sponsored by the Mine Environment Neutral Drainage Program. September 29 - October 1,
1992 in Toronto, Ontario.
Nummela, W., and I. Iwasaki. 1986. “Iron Ore Flotation.” SME Advances in Mineral
Processing. Society of Mining Engineers of the American Institute of Mining, Metallurgical,
and Petroleum Engineers. Inc. New York, New York.
Osiensky, J.L. and R.E. Williams. 1990. “Factors affecting efficient aquifer restoration at in situ
uranium mine sites.” Groundwater Monitoring Review, p. 107-112.
Park, C.F. and R.A. MacDiarmid. 1975. Ore Deposits, published by W.H. Freeman and Company,
San Francisco.
Piimore, D.M. 1992. “Arizona Strip Uranium Mining District Northern Arizona.” The
Professional Geologist 29(4):8.
Platts, W.S., W.F. Megahan, and G.W. Minshall. 1983. Methods for Evaluating Stream, Riparian,
and Biotic Conditions. General Technical Report INT-138. U.S. Department of Agriculture,
U.S. Forest Service, Ogden, Utah.
Price, William A. and Errington, John’ C. 1994. ARD Policy for Mine Sites in British Columbia. In
the Proceedings of the International Land Reclamation and Mine Drainage Conference and
Third International Conference on the Abatement of Acidic Drainage, April 24-29, 1994.
Ramani, R.V. and E.C. Grim. 1978. “Surface mining - a review of practices and progress in land
disturbance control.” In: Reclamation of Drastically Disturbed Lands, F. W. Shaller and P.
Sutton (eds.). American Society of Agronomy, Crop Science Society of America, Soil Science
of America. Madison WI.
Rawson Academy of Aquatic Science. 1992 (July 21). A Critical Review of MEND Studies
Conducted to 1991 on Subaqueous Disposal of Tailings. Canada Centre for Mineral and
Energy Technology (CANMET); Energy, Mines and Resources Canada.
Reynolds, J.B., R.C. Simmons and A.R. Burkholder. 1989 (June). Effects of Placer Mining
Discharge on Health and Food of Arctic Grayling. Water Resources Bulletin: 625-635.
Ritcey, G.M. 1989. “Tailings Management, Problems and Solutions in the Mining Industry.”
Process Metallurgy 6.
“RIP Move in South Africa.” 1991 (March). Australia’s Mining Monthly.
Robertson, Dr. A. MacG. and L. M. Broughton. 1992 (April). Reliability of Acid Rock Drainage
‘Testing. Steffen, Robertson and Kirsten, Vancouver, British Columbia.
Rowley, Michael V et al. 1994. The Biosulfide Process: Integrated Biological/Chemical Acid Mine
Drainage Treatment - Results of Laboratory Piloting, In the Proceedings of the International
7-8 September 1994
-------
EIA Guidelines for Mining References
Land Reclamation and Mine Drainage Conference and Third International Conference on the
Abatement of Ack ic Drainage, April 24-29.
Ryan, 0. 1991. Personal Com,nunication between G. Ryan, the American Iron Ore Association,
and Jonathan Passe of Science Applications International Corporation. McLean, Virginia.
Schafer, Dr. William M. 1993. Design of Geochemical Sampling Progrwns. Iii Mine Operation and
Closure Short Course. Sponsored by EPA and others April 27 - 29. Helena, Montana.
Singleton, G. A. and L.. M. Lavkulich.. 1978. “Adaption of the Soxhelet Extractor for Pedologic
Studies.” Soil Science Society of America Journal, Vol. 42, p. 984-986.
Schwandt, A.J.W.’ 1970. “The Magmont Operation.” In AIME World Symposium on Mining and
Metallurgy of Lead and ZinC; Volume 1: Mining and Concentrating of Lead and Zinc. New
York: American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
Silva, M. 1986. Placer Gold Recovery Methods. California Division of Mines and Geology.
Special Publication 87. Sacramento, CA.
‘Silva, M.A. .1988 (July). “Cyanide Heap Leaching in California.” California Geology: 147-56.
Singh, M.M, and Z.T. Bieniawski., 1992. Geomechanics, in SME Mining Engineering Handbook,
2nd Edition (H.L. Hartthan, ed.). Society for Mining, Metallurgy and Exploration, Inc.
Littleton, CO.
Smith, A. and J. B. Barton Bridges. 1991. Some Considerations in the Prediction and Control of
Acid Mine Drainage Impact on Groundwater From Mining in North America. : Proceeding of
the EPPIC Water Symposium, Johannesburg, South Africa,’ May 16-17.
Smith, D K, Jr. 1984. Uranium mineralogy. In: Uranium, geochemistry, mineralogy, geology,
exploration and resources. The Institution of Mining and Metallurgy, London, England.
Sobek, A. A., Schuller, W. A., Freeman, J.R. Smith, R.M. 1978. Field and Laboratory Methods
Applicable to Overburden and Minesoils. EPA 600/2-78-054.
Society of Mining Engineers. 1973. SME Mining Engineering Handbook. Volume 1 and2
Published by the Society of Mining Engineers, Littleton, CO.
Society of Mining Engineers, Mineral Processing Handbook 1985. Edited by N.L. Weiss,. Volume 2.
Published by the Society of Mining Engineers, Littleton, CO.
South Dakota, Office of Minerals and Mining. 1993 (January 19). Personal communication between
Tom Durkin and Joe Rissing, Science Applicztions International Corporation. Falls Church,
VA’.
St. Arnaud, Luc. 1994. Water Covers for the Decommissioning of Sulfidic Mine Tailings
Impoundments. In the Proceedings of the International Land Reclamation and Mine Drainage
Conference and Third International Conference on the Abatement of Acidic Drainage, April 24-
29, 1994.
7. .9 September 1994
-------
References EIA Guidelines for Mining
Stanford, W.D. 1987 (April). “Amx Sleeper Mine Exceeds Expectations On All Counts As Low-
Cost Gold Producers.” Mining Engineering (1987): 241-46.
Stiliwater Mining Company. Undated. Stiliwater Mining Company (company produced brochure).
Sullivan, P.. J. and A. Sobek. 1982. “Laboratory Weathering Studies of Coal Refuse.” Minerals
and the Environment 4(1).
• Tatsch, J..H. 1976. Uranium deposits. Tatsch Associates, Sudbuiy Massachusetts.
• Tenut, Carl. 1994. Memorandum from Carl Tenut, State of Tennessee to Cheryl Espy, EPA Region
4.
U.S. Congress, Office of Technology Assessment. 1988 (Septethber). Copper. Technology and
Competitiveness. OTA-E-367. .U.S. Government Printing Office. Washington DC.
U.S. Department of Agriculture, Forest Service. 1992. A Conceptual Waste Rock Sampling Program•
for Mines Operating in Metallic Sulfide Ores With a Potential for Acid Rock Drainage. Written
by Gene Farmer with the Department of Agriculture, Forest Service, Ogden, Utah.
U.S. Department of Agriculture, Forest Service. 1993. Acid Mine Drainage From Mines on the
National Forests, A Management Challenge. Program Aid 1505, p.12.
U.S. Department of the Army, Corps of Engineers. 1987. Corps of Engineers Wetlands Delineation
Manual. Final Technical Report Y 87-1. U.S. Army Corps of Engineers, Envirot mental
Laboratory, Waterways Experiment Station, Vicksburg; MS.
U.S. Department of Energy (USDOE). 1978b. International Coal Technology Summary Document.
Office of Technical Programs Evaluation, Washington DC, JHCP/P-3885, 178 p.
U.S. Department of Energy, Energy Information Administration. 1992. Uranium Industry Annual
1991. DOEIEIA-0478(91), Distribution Category UC-98, Washington, DC.
U.S. Departmeiit of Health and Human Services. 1982 (April). Technological Feasibility of Control
• ‘of Asbestos at Mines and Mills, Task I Progress Report, Exposure Profiles. Washington, DC.
U.S. Department of the Inter or, Bureau of Land Management. 1992. Solid Minerals Reclamation
• Handbook. BLM Manual Handbook H- 042-1.
U.S. Department of the Interior, Bureau of Mines. 1968. A Dictionary of Mining, Minerals, and
Related Terms. Washington, D.C.
‘U.S. Department of the Interior, Bureau of Mines. 1977. Capital and Operating Cost Estimating
System Handbook for Mining and Beneficiarion of Metallic and Non-metallic Minerals Except
Fossil Fuels in the U.S. and Canada. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1978. Processing Gold Ores Using Heap
Leach-Carbon Adsorption Methods. Information Circular No. 8770. Washington, DC.
7-10 September 1994
-------
EIA Guidelines for Mining References
U.S. Department of the Interior, Bureau of Mines. 1979. Environmental Assessment of In Situ LeUch
Mining, Final Report. Prepared by PRC Toups and Mountain States Research and
Development. 292 p.
U.S. Department of the Interior, Bureau of Mines. 1983a. Development Guidelines for Closing
Underground Mines: Michigan Case Histories. Washington, DC.
U.S. Depamnent of the Interior, Bureau of Mines. 1984a. Gold and Silver Leaching Practices in the
United States. Information Circular No. 8969. Washington, DC.
U.S. Department of the Interior, Bureau of Mines, Division of Minerals Availability. 1984b
(November). Waste Disposal Activities and Practices: Copper, Lead, Zinc, Gold, and Silver
Waste Disposal Activities and Practices in the United States. Division of Minerals Availability
Open File Report. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1984c (November). Waste Disposal Activities
and Practices in the United States: Copper, Lead, Zinc, Gold, and Silver. Division of
Minerals Availability Open File Report, by L.V. Coppa. Washington, DC.
U.S. Department ofthe Interior, Bureau of Mines. 1985. “Gold” (by J.M. Lucas). In Mineral
Facts and Problems, 1985. Washington, DC GPO.
U.S. Department of the Interior, Bureau of Mines. 1985. “Lead” (by W.D. Woodbury). In Mineral
Facts and Problems, 1985. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1985. “Mineral Facts and Problems 1985
Edition” (by Jolly, J.L.). Bulletin 675. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1986. Precious Metals Recovery for Low-Grade
Eesources, proceedings of the Bureau of Mines Open Industry Briefing Session at the National
Western Mining Conference. Denver, CO. February 12, 1986. Information Circular No.
9059. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1987. “Froth Flotation in the United States,
1985” (by Edelstein, D.). Information Circular. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1990a. “Gold” (by J.M. Lucas). In 1988
Minerals Yearbook, Volume 1: Metals and Minerals. Washington, DC: GPO.
U.S. Department of the Interior, Bureau of Mines. 1990a. “Lead” (by W.D. Woodbury). In
Minerals Yearbook, Volume 1: Metals and Minerals, 1988. Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1990b. “Mining and Quarrying Trends in the
Metals and Industrial Minerals Industries” (by A.O. Tanner). In 1988 Minerals Yearbook,
Volume 1: Metals and Minerals. Washington, DC
U.S. Department of the Interior, Bureau of Mines. 1990c. “Gold” (by J.M. Lucas). In 1989
Minerals Yearbook. Washington, DC: GPO.
7-11 September 1994
-------
References EIA Guidelines for Mining
U.S. Department of the Interior, Bureau of Mines. 1992a. “Gold 1991 Annual Report” (by J.M.
Lucas). Published in Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1992b. “Iron Ore.” Mineral Commodity
Summaries, 1992 (by P.H. Kuck). Washington, D.C.
U.S. Department of the Interior, Bureau of Mines. 1991a (May). “Mining and Quarrying Trends in
the Metals and Industrial Minerals Industries” (by A.Q. Tanner). In 1989 Minerals Yearbook.
Washington, DC: GPO.
U.S. Department of the Interior, Bureau of Mines. 1992. Submarine Disposal of Mill Tailings from
On-Land Sources - An Overview and Bibliography. An Overview and bibliographic
Compilation of References on the Biological, Chemical, Environmental, and Technical Aspects.
By R.L. Baer, G.E. Sherman, and P.D. Plumb. OFR 89-92.
U.S. Department of the Interior, Bureau of Mines. 1993a. Mineral Commodities Summaries, 1993.
Published in Washington, DC.
U.S. Department of the Interior; Bureau of Mines. 1993b. 1991 Copper Annual Repo,rt (by Janice
Jolly). Washington, DC.
U.S. Department of the Interior, Bureau of Mines. 1993c. Platinum-Group Metals 1992 Annual
Report.
U.S. Department of the Interior, Bureau of Mines. 1993d. Tungsten 1992 Annual Report.
U.S. Department of the Interior, Bureau of Mines. ‘1993e. Molybdenum 1992 Annual Report.
U.S. Department of the Interior, Bureau of Mines. 1993f. Thanium 1992 Annual Report.
U.S. Department of the Interior, Bureau of Mines. 1993g. Vanadium 1992 Annual Report.
U.S. Department of the Interior, Bureau of Mines. 1993h. Aluminum, Bauxite and Alumina 1992
Annual Report.
U.S. Department of the Int rior, Bureau of Mines. 1994. International Land Reclamation and Mine
Drainage Conference and Third International Conference on the Abatement of Acidic Drainage.
Proceedings of a conference held in Pittsburgh, Pennsylvania, April 24-29, 1994. Bureau of
Mines Special Publications SP 06A-94 through SP 06D-94. 4 volumes.
U.S. Department of the Interior, Bureau of Mines. Undated(a). Gold Environmental Research
Highlights (by S.L. McGill and T.G. Carnahan). Reno, NV.
U.S. Department of the Interior, Bureau of Mines. Unpublished. Copper Mine Address and Current
Status All Mines Operating 1984-1987 and Status of Domestic Copper Mines, Leaching, and SX
Operations. Washington, DC.
7-12 September 1994
-------
EIA Guidelines for Mining References
U.S. Department of the Interior, Geological Survey. 1973. “Copper”. In United States Mineral
Resources. Geological Survey Professional Paper 820, by F.S. Simons and W.C. Prinz.
Reston, VA;
U.S. Department of the Interior, Geological Survey. 1973. “Gold.” United States Mineral
Resources. Professional Paper No. 820. Reston, VA.
U.S. Department of the Interior, Geological Survey. 1973a. “Iron.” Ii. United States Mineral
Resources; Geological Survey Paper 820 (by H. Kiernic, H.L. James, and G.D. Eberléin).
Reston, VA.
U.S. Department of Interior, U.S. Geological Survey. 1977. National Handbook of Recommended
Methods for Water-data Acquisition/Prepared Under the Sponsorship of the Office of Water Data
Coordination. Reston, VA.
U.S. Department of Interior, U.S. Geological Survey. 1990. Water Resources Investigations Report.
Blevins. No.90-4047. Reston VA.
U.S. Environmental Protection Agency. 1973. Processes, Procedures, and Methods to Control
Pollution from Mining AcrivirieE. Washington DC, DOE/EPA-430/9-73-01 1, 390 p.
U.S. Environmental Protection Agency. 1975. Coal Mining Point Source Category. Washington
DC. Federal Register 40 202 48830-8.
U.S. Environmental Protection Agency, Office of Water and Hazardous Material. I 976a.
Development document for interim final effluent limitations guidelines and new source
pe?for nance standards for the coal mining point source category. Washington, DC. EPA
440/1-761057-a, 288 p.
U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory. 1976b
(June):. Metals Mining and Milling Process Profiles with Environmental Aspects. Prepared by
Battelle Columbus Laboratories for U.S. Environmental Protection Agency. NTIS Publication
No. 256394. Washington, DC.
U.S. Environmental Protection Agency. 1.978a. Acid Mine Drainage and Subsidence: Effects of
Increased Coal Utilization. Washington DC, EPA-600/2-78-068, 141 p.
U.S. Environmental Protection Agency. 1978b. Site Selection and Design for Minimizing Pollution
from Underground Coal Mining Operations. Washington DC, EPA-600/7-78-006, 98p.
U.S. Environmental Protection Agency. 1979. Assessment of Environmental Impact of the Mineral
Mining Industry. Prepared by PEDCo Environmental, inc. •EPA-600/2-79-107. Washington
DC.
U.S. Environmental Protection Agency, Office of Water, Effluent Guidelines Division. 1982 (May).
Development Document for Effluent Limitations Guidelines and Standards for the Ore Mining
and Dressing Point Source Category. EPA 440/1-82/061. Washington, DC..
7-13 Stemb r 1994
-------
References EIA Guidelines for Mining
U.S. Environmental Protection Agency. 1q84 (December). Overview of Solid Waste Generation.
Management, and Chemical Characteristics. Prepared for U.S. EPA under Contract Nos. 68-
03-3 197, PN 3617-3 by PEI Associates, Inc.
U.S. Environmental Protection Agency, Office of Solid Waste. 1985 (December). Report to
Congress -Wastes from the Extraction and Beneficiation of Metallic Ores, Phosphate Rock,
Asbestos, Overburden from Uranium Mining, and Oil Shale. EPA 530-S W-85-033.
Washington, DC.
U.S. Environmental Protection Agency. 1986. Quality Criteria for Water. REPA 440/5-86-001.
Washington, DC.
U.S. Environmental Protection Agency, Office of Water. 1988a (May). Development Document for
Effluent Limitations Guidelines and New Source Performance Standards for the Ore Mining and
Dressing Point Source Category: Gold Placer Mine Subcategoiy (Final Draft). Washington,
DC.
U.S. Environmental Protection Agency: 1988b. Economic Impact Analysis of Final Effluent
Guidelines and Standards for the Gold Placer Mining Industrj. Office of Water Regulations
and Standards. Washington, DC.
U.S. Environmental Protection Agency. 1989a. Final Report: Copper Dump Leaching and
Management Practices that Minimize the Potential for Environmental Releases. Prepared by
PEI Associates, Inc. (Hearn, R. and Hoye, R.) under U.S. EPA Contract No. 68-02-3995.
Washington, DC.
U.S. Environmental Protection Agency. 1989b. Rapid Bioassessment Protocols for Use in Streams
and Rivers. EPAI44O/4-89/OOL Washington, DC.
U.S. Environmental Protection Agency. 1989c. Ecological Assessment of Hazardous Waste Sites: A
Field and Laboratory Reference. EPAI600/3-89/013.
U.S. Environmental Protection Agency. 1990 (January). Performance of Current Sediment Control
Measures at Maryland Construction Sites. Metropolitan Washington Council of Governments.
U.S. Environmental Protection Agency. 1990 (April). Draft - Sediment and Erosion Control, An
Invenory of Current Practices. Washington, DC.
U.S. Environmental Protection Agency, Office of Research and Development. 1992. Draft.
Predicting Acid Generation From Non-Coal Mining Waste: Notes of July 1992 Workshop.
Prepared for the Environmental Monitoring Systems Laboratory, Las Vegas, Nevada 89193-
3478 by SAIC, Falls Church, Virginia.
U.S. Environmental Protection Agency, Office of Research and Development. 1993 (May 20).
Personal communication between Ed Heithmar, U.S. EPA Office of Research and Development.
and Michelle Stowers, Science Applications International Corporation. Falls Church, VA.
U.S. Environmental Protection Agency: 1993a. Habitat Evaluation: Guidance for the Review of
Environmental Impact Assessment Documents.
7-14 September 1994
-------
E IA Guidelines for Mining References
U.S. Environmental Protection Agency. 1994. Workshop on the Use of Sulfate Reducing Bacteria.
for Treating Mine Drainage from Metals Mines. Cincinnati, OH, February 23-24, 1994.
U.S. General Accounting Office. 1991(June). Mineral Resources: Increased Attention Being Given to
Cyanide Operations. Report to the Chairman, Subcommittee on Mining and Natural Resources,
Committee on Interior and insular Affairs, House of Representatives. GAO/RCED-91- 145.
U .S. Soil Conservation Service. 1975. hocedure for Computing Sheet and Rill Erosion on Project
Area. Technical Release No. 51.
United States Steel. 1973. The Making, Shaping, and Treating of Steel (HE. McGannon, editor).
Herbick and Held, Pittsburgh; PA.
University of California at Berkeley. 1988 (July). Mining Waste Study, Final Report. Prepared for
the California State Legislature. Berkeley, CA.
University of Nevada - Reno. 1993 (January 13). Personal communication between Glen Miller and
Joseph Rissing, Science Applications International Corporation. Falls Church, VA.
van Zyl, D.’J.A., 1.P.G. Hutchison, and J.E. Kiel (editors): 1988. Introduction to EvaluatiOn,
Design and Operation of Precious Metal Heap Leaching Projects. Society for Mining,
Metallurgy, and Exploration, Inc. Littleton, CO.
Want, W.L. 1990. Laws of Wetlands Rekulations. Clark Boardman Company, Ltd. New York,
NY.
Weiss, N.L. (editor). 1985: SME Mineral Processing Handbook. Volume 2; New York: Society
of Mining Engineers.
White, William W. et al. 1994.: Chemical Predicative Modeling of Acid Mine Drainage From Waste
Rock: Model Development and Comparison of Modeled Output.to Experimental Data. in the
Proceedings of the International Land Reclamation arid Mine Drainage Conference and Third
International Conference on the Abatement of Acidic Drainage, April 24-29.
Whiteway, P. (editor). 1990. “Mining Explained: A Guide To Prospecting and Mining.” The
Northern Miner.
I The Wildlife Society, 1980: Wildlife Management Techniques Manual. Fourth Edition: Revised.
Sanford D. Schemnitz (editor). Washington, D.C.
Williams, R. David. 1994. The Bureau of j.and Management Acid Rock Drainage Policy An
Evolution in Environmental Protection. In the Proceedings of the. International Land
Reclamation and Mine Drainage Conference and Third International Conference on the
Abatement of Acidic Drainage, April 24-29.
Wyoming Department of Environmental Quality, Land Quality Division. 1991. In Situ Mining State
Decision Document for Everest Minerals Highland Uranium, WDEQILQD Permit No. 603-A2.
7-is September 1994
-------
References .. EIA Guidelines for Mining
Wyoming Department of Environmental Quality, Land Quality Division. 1990. Guideline No. 4, In
Situ Mining.
Zabumnov, S.A. 1989 (August);,'•-• "Ridgeway: Gold Deposit Producing Big Returns Through Good
Design." Engineering & Mining Journal: 52-55.
7.16 September 1994
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