EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

January 2003

APPENDIX F

SOLID WASTE MANAGEMENT
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-i January 2003

TABLE OF CONTENTS

1.0 GOALS AND PURPOSE OF THE APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-1

2.0 TYPES OF SOLID WASTES AND MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-1

2.1 Overburden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-1

2.2 Waste Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-2

2.3 Tailings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-2

2.4 Spent Ore, Heap and Dump Leach Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-2

3.0 WASTE ROCK AND OVERBURDEN MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . F-3

3.1 Piles and Dumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-3

3.2 Mine Backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-6

3.3 Use in Facility Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-9

3.4 Use as Cover Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-9

4.0 TAILINGS MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-10

4.1 Tailings Impoundments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-10

4.1.1 Site Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-11

4.1.2 Impoundment and Embankments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-11

4.1.3 Liners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-13

4.1.4 Tailings Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-18

4.1.5 Operational Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-19

4.2 Dry Tailings Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-20

4.3 Subaqueous Tailings Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-22

4.3.1 Water Covers over Constructed Impoundments . . . . . . . . . . . . . . . . . . . . . F-22

4.3.2 Disposal into Flooded Mine Workings . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-23

4.4 Mine Backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-24

5.0 SPENT ORE/HEAP AND DUMP LEACH MANAGEMENT . . . . . . . . . . . . . . . . . . . F-25

6.0 ISSUES RELATED TO CLOSURE AND RECLAMATION . . . . . . . . . . . . . . . . . . . . F-28

6.1 Soils Placement and Revegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-28

6.2 Runoff and Erosion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-29

6.3 Infiltration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-30

6.4 Seepage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-31

6.5 Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-31

6.6 Spent Ore Treatment and Neutralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-33

6.7 Post-Closure Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-34

6.8 Information and Analytical Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-34
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-ii January 2003

TABLE OF CONTENTS

(continued)

7.0 ACID MINE DRAINAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-35

7.1 Controlling the Acid Generation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-36

7.2 Moderating the Effects of Acid Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-37

7.3 Controlling the Migration of Acid Mine Drainage . . . . . . . . . . . . . . . . . . . . . . . . F-38

7.4 Collecting and Treating Acid Mine Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-38

8.0 CITED REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-39

LIST OF TABLES

F-1. Data Needs for Waste Rock Disposal Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-5

F-2. Operational Monitoring of Waste Rock Dumps and Heap Leach Facilities . . . . . . . . . . . F-6

F-3. Example Siting Criteria for Tailings Impoundments and Dry Tailings Facilities . . . . . F-11

F-4. Operational Monitoring of Tailings Impoundments . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-19

F-5. Data Needs for Heap Leach Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-26

LIST OF FIGURES

F-1. Hydrologic Cycle for A Typical Waste Pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-8

F-2a. Water-Retention Type Dam for Tailings Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . F-14

F-2b. Sequential Raising, Upstream Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-15

F-2c. Sequential Raising, Centerline Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-16

F-2d. Sequential Raising, Downstream Embankment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-17

F-3. Layered Waste System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-32
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-1 January 2003

1.0 GOALS AND PURPOSE OF THE APPENDIX

Mining operations produce a variety of solid materials that require permanent

management. In order to prevent or minimize environmental impacts, applicants must pay

careful attention to the methods by which these materials will be disposed, the locations of the

disposal facilities, and the engineering designs of the disposal facilities. The largest mines may

generate over a billion tons of solid wastes that cover areas exceeding a thousand acres, and even

smaller operations must handle and dispose of formidable quantities of materials that can affect

large areas. The environmental behavior of these materials ranges from benign to deleterious,

with specific areas of concern arising from sediment loading, metals contamination, cyanide

release, and acidification. This appendix provides a brief overview of the issues related to the

disposal of solid wastes which applicants may be expected to address during the NEPA and

associated Clean Water Act permit application processes. It is not intended to provide a

comprehensive review of solid waste disposal practices. Related information is provided in

Appendix C, Characterization of Ore, Waste Rock, and Tailings and Appendix H, Erosion and

Sedimentation.

2.0 TYPES OF SOLID WASTES AND MATERIALS

This appendix is concerned with the disposal of the four types of mining wastes and

materials that are generated and managed in the highest volumes:

• Overburden

• Waste rock

• Tailings

• Heap and dump leach residues.

Other types of solid mining wastes that may require disposal include smelter slag, trash, 

construction debris, incinerator ash, wastewater treatment sludge, and sewage sludge. The

management of sludge from wastewater treatment is discussed in Appendix E. 

2.1 Overburden

Overburden consists of unconsolidated to poorly consolidated materials such as soils,

alluvium, colluvium, or glacial tills that must be removed to access the ore body that will be

mined and processed (Hutchinson and Ellison, 1991). In most cases, overburden materials will

not contain significant quantities of leachable metals or acid-generating minerals. However,

geochemical tests similar to those described in Appendix C, Characterization of Ore, Waste

Rock, and Tailings, may need to be conducted to ensure the benign character of these materials. 

Humus-rich forest soils may be slightly acidic and should be tested if they would be used as

cover materials or growth media atop metal-bearing wastes. Soils and unconsolidated deposits

may require proper handling and disposal to prevent erosion and sediment loading to streams and

other surface waters. Management of overburden is discussed in Section 3 below.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-2 January 2003

2.2 Waste Rock

Waste rock is removed from above or within the ore during mining activities. Waste

rock includes granular, broken rock and soils ranging in size from fine sand to large boulders,

with the fines content dependent upon the nature of the geologic formation and methods

employed during mining. Waste rock consists of non-mineralized and low-grade mineralized

rock. Materials may be designated as waste because they contain the target minerals in

concentrations that are too low to process, because they contain additional minerals that interfere

with processing and metals recovery, or because they contain the target metal in a form that

cannot be processed with the existing technology. Materials that are disposed as waste at one

point in a mine’s life may become ore at another stage, depending on commodity prices, changes

in and costs of technology, and other factors. 

Waste rock may be acid generating and may contain metals that can be mobilized and

transported into the environment. These materials generally will require extensive geochemical

testing (Appendix C, Characterization of Ore, Waste Rock, and Tailings) to determine if they

will impact the environment over the short or long term. Special engineering designs, waste

handling and disposal procedures, or closure and reclamation plans may be required for those

materials whose characteristics may pose significant risks. Waste rock management is discussed

in Section 3 of this Appendix. 

2.3 Tailings

Tailings are produced by beneficiation activities that separate the target minerals or

metals from the remaining host rock. Beneficiation begins when primary ore is crushed and

ground to particle sizes ranging from sand- to silt-sized. Target minerals are separated from the

ground ore using density or magnetic separation, froth flotation, or other concentration

techniques. The target metal is then separated from the mineral by leaching, electrowinning, or

other metallurgical techniques. Residues (tailings) from these processes may make up to ninety

percent of the original ore mined. Although lower in the target minerals, the tailings can have a

wide range of composition that depends on the mineralogy of the primary ore material, the type

of separation process employed, and the efficiency of the separation process. Based on the

original constituents, the tailings may contain acid-generating minerals and a variety of metals. 

The small grain size of most tailings makes them an important potential sedimentation source

that is susceptible to erosion and downstream transport. Characterization of tailings are

discussed in Appendix C. Section 4 below discusses tailings management. 

2.4 Spent Ore, Heap and Dump Leach Residues

Some primary ores, notably those of copper and gold, may be processed by heap or

dump leaching techniques. Dump leaching is the process of applying a leaching agent (usually

water, acid, or cyanide) to piles of ore directly on the ground, to extract the valuable metal(s) by

leaching over a period of months or years. Heap leaching is similar to dump leaching except the

ore is placed on lined pads or impoundments in engineered lifts or piles. Ores may be coarsely
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-3 January 2003

crushed prior to leaching or may be leached as run-of-mine materials. Spent materials contain

lower concentrations of the target mineral, and they may contain other metals, chemical

complexes of the target metal, acid-generating minerals, and small quantities of the leach

solution. After leaching, the spent ore may be treated by rinsing with fresh water or chemical

additives that dilute, neutralize, or chemically decompose leach solutions and metal complexes. 

Characterization of spent ore is discussed in Appendix C. Section 5 below discusses the

management of spent ore.

3.0 WASTE ROCK AND OVERBURDEN MANAGEMENT

Waste rock and overburden materials are managed according to specific site conditions,

regulatory requirements, and materials composition. Management practices that are suitable at

one site may be unsuitable at another due to factors as diverse as regulatory requirements,

material properties, climate, and cultural values. The disposition of these materials can vary

greatly depending on their mineralogical and chemical compositions and numerous economic

factors. Some materials may be suitable for beneficial uses such as road surfacing, aggregate,

structural rock, or decorative rock, whereas other materials possess characteristics that require

their permanent disposal in an engineered management facility. Recent contaminant releases

associated with waste rock materials or disposal practices at several mines emphasize the

importance of comprehensive geochemical testing programs and sound geotechnical studies and

engineering designs. This section briefly describes four widely used waste rock management

techniques, highlighting the issues and information needs that should be addressed for NEPA

and other analyses

3.1 Piles and Dumps

Waste rock and overburden that cannot be put to beneficial use or that contain

compounds that may be detrimental to the environment, generally are placed in a location where

they can be physically stabilized. Placement is accomplished using a variety of techniques that

may include end-, sidehill-, or random-dumping, and dozing. Dump design may vary markedly

depending on the nature of the mining operation and the terrain in which materials are being

placed. In steep, mountainous areas, dumps may have faces of a few hundred meters height. For

these dumps, the buildup of pore water pressures with time is an important variable that is

difficult to evaluate quantitatively, but that may lead eventually to partial slope failure (Kent,

1997). Dump designs of this type may require some level of risk analysis to determine potential

impacts should failure occur (Kent, 1997). Dumps placed as valley-fill deposits may require the

construction of rock underdrains to permit the flow of water through the drainage. The materials

used to construct these drains needs to be thoroughly tested to ensure that they will not

contribute metals, acid, or other constituents to surface (EPA, 1993a; 1993b). Dump underdrains

may need to be tied into the mine drainage or storm water drainage systems that convey seepage

to treatment facilities (see Appendix E, Wastewater Management).

Dumps that would contain waste rock capable of releasing significant quantities of

metals, acidity, or other constituents may require special design features or waste handling
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-4 January 2003

practices to minimize the potential for environmental impacts (SRK, 1992a; Environment

Australia, 1997). Dumps can be designed with features to control or reduce acid generation,

control the migration of poor-quality drainage, or collect and treat poor-quality drainage (SRK et

al., 1989). These features may include: 

• Waste segregation and encapsulation (i.e., cellular construction; SRK et al., 1989), 

• Blending and interlayering with materials that neutralize acidity and metals release

(i.e., base amendments; e.g., SRK et al., 1989; Mehling et al., 1997).

• Waste conditioning to remove acid generating minerals (SRK et al., 1989).

• Incorporating low permeability materials to slow the migration of poor-quality

drainage through a waste rock dump (SRK et al., 1989).

• Designing and preparing substrates that would minimize infiltration and route

seepage to collection and treatment points.

• Incorporating bactericides to slow the rate of pyrite oxidation (SRK et al., 1989;

Environment Australia, 1997). 

Mines that produce a mix of acid-generating and acid-neutralizing waste rock must be

careful to design and construct dumps in a manner that does not create local “hot spots” of acid

generation from which seepage could escape. Section 7 of this appendix discusses acid drainage

considerations in more detail. It is important that mine operators keep accurate and easily

interpretable records of the source, amount, and location of all waste placed in waste storage

facilities, and for ore material placed on heap leach pads. Reclamation design can then be

facilitated, especially if it is shown that the original geochemical characterization of the waste

(or the altered state of leached ore) is different than predicted. 

Table F-1 lists the type of data needed to select a suitable site for a waste rock dump and

some critical design factors of dump construction. Table F-2 identifies monitoring that may be

conducted during dump construction and operations. In order for regulatory agencies to perform

NEPA analyses and permitting, it is critical that mine applicants supply the following

information related to waste rock dump management:

• Describe the criteria that were used to determine whether proposed sites are

technically and economically feasible (e.g., Table F-1). Evaluate the importance of

critical factors such as foundation stability, substrate bearing capacity, ground water

conditions, and surface water hydrology. Compare to any applicable regulatory

requirements.

• Provide the rate and total volume of waste rock to be disposed. Characterize the

physical and chemical properties of the waste rock and how they relate to dump

stability and leachability. Characterization of waste rock is discussed in Appendix C.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-5 January 2003

• Develop a water balance (see Figure F-1) and predict the potential for seepage and

run-off from waste rock dumps during dump construction, operations, and closure in

order to design appropriate wastewater management (e.g., containment and/or

treatment, need for discharge permit, etc.). Various models are available to facilitate

this. For example, the HELP (Hydrologic Evaluation of Landfill Performance) model

may be used to predict leachate quantities. Where modeling is used, all model

assumptions, input parameters, and uncertainties should be disclosed and a sensitivity

analysis may be necessary (see Section 6 of Appendix A, Hydrology for general

considerations related to modeling). Methods for estimating a water balance for

waste piles, modeling of waste rock dumps, and techniques to estimate seepage

quality are provided in Hutchinson and Ellison (1991), MEND (1995), SRK (1992b),

MEND (1996), and Price (1997). Water balances are discussed in Appendix A. 

Wastewater management is discussed in Appendix E.

• Describe how the dump will be constructed and managed during operations and

closure in terms of maintaining dump stability and reducing impacts to the

environment. Develop performance standards and compare to any applicable

regulatory requirements (e.g., standards for containment, stability, etc.). 

• Develop and describe operational and environmental monitoring plans to ensure

dump stability, adherence to performance standards, and to identify impacts to

surface and ground water quality. Table F-2 identifies types of monitoring that may

be required. Monitoring plans should include action levels and contingency plans. 

Monitoring plans should incorporate quality assurance (QA) and quality control (QC)

(see Section 5 of Appendix B, Receiving Waters for a description of quality assurance

and quality control plans).

See Section 6 of this appendix for additional considerations related to waste rock dump closure

and Section 7 for considerations related to acid drainage.

Table F-1. Data Needs for Waste Rock Disposal Facilities

Critical Design Factor Data Needs Data Source/Methodologies

Facility Site Selection Topography Topographical maps, Aerial photos

Geology and Soils, including fault

mapping

Geological maps, Engineering tests of

site samples.

Seismicity (natural and blasting-induced) Geological maps, Seismic zone maps,

Uniform Building Code (U.S. ACE,

1995), Mine Plan of Operation,

Engineering tests of site samples.

Surface Water Hydrology See Appendix A

Ground Water Hydrogeology See Appendix A
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

Table F-1. Data Needs for Waste Rock Disposal Facilities

Critical Design Factor Data Needs Data Source/Methodologies

F-6 January 2003

Baseline Water Quality See Appendix B

Operational Considerations Mine Plan of Operation

Waste Rock

Characteristics

Physical Properties See Appendix C

Chemical Properties See Appendix C

Pile/Dump Construction Foundation Stability Geotechnical and engineering tests of

site soil samples.

Pile Stability Geotechnical and engineering tests of

waste rock materials.

Surface Water Diversion See Appendix H

Seepage/Run-off Collection and

Treatment

See Appendix D

Table F-2. Operational Monitoring of Waste Rock Dumps and Heap Leach Facilities

Type of Monitoring Methods Used Purpose

Geotechnical Visual inspection; Extensiometer;

Leveling surveys; Soil strength testing;

Soil borings.

Detect changes in slope stability,

compaction, and settling that may

identify structural weaknesses or signal 

potential failure of the facility.

Surface Water Flow/Runoff monitoring; Upstream and

downstream water quality analyses

Detect impacts to surface water quality.

Ground Water Water table monitoring; Upgradient and

downgradient water quality analyses

Detect impacts to ground water quality.

Hydraulic Precipitation/Infiltration measurements;

Piezometers; Water quality analyses.

Detect development of water table within

pile, identify fluid pathways, monitor

internal pore water pressures.

Thermal Temperature Probes Detect temperature increases within the

pile that may indicate sulfide oxidation.

Pore Water Water quality analyses Determine quality of leachate, Early

detection of acidification

3.2 Mine Backfill

Mine backfilling is the act of transporting and placing overburden, waste rock, or

tailings materials in surface or underground mines. Tailings are more often used as backfill than

waste rock or overburden. The technique is being used increasingly as a remediation measure
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-7 January 2003

(e.g., to minimize the potential for acid generation in mine walls and/or the backfilled material)

and to minimize the amount of surface disturbance required to store waste materials. Coarsegrained materials such as waste rock and overburden typically are hauled to backfill locations

using vehicles or conveyors. Due to the increase in rock volume that occurs through blasting

and excavation, mine voids can accommodate a maximum of approximately 70 percent of the

original material that was excavated and, in practice, the amount is likely to be significantly less. 

The remaining waste rock and overburden still must be put to beneficial use or disposed of in

surface facilities. Coarse backfill materials will have comparatively high porosity and

permeability. Their larger surface areas (compared to solid rock) increase the availability of

metals and make these materials more susceptible to leaching and acidification. Materials that

would be stored in locations above the water table may be subject to periodic flushing by

infiltrating meteoric waters which could remove accumulated soluble oxidation products and

transport them to surface or ground waters. 

Examples of the use of waste rock as mine backfill follow. The Goldbug Waste Rock

Repository at Landusky Mine in Montana is material that has been backfilled into the old

Goldbug Pit. The waste is placed atop 2-3 feet of crushed dolomite/ limestone which, in turn,

sits on a compacted clay liner that is engineered to drain to a collection area. Waste is

segregated within the dump to encapsulate acid-generating waste rock within non-acid

generating waste. Similarly, at the Castle Mountain Mine in California, waste rock has been

used to backfill the initial pit; there, no special handling was required or needed. 

If waste rock and overburden are to be used as backfill, mine applicants should provide

information of the following types to allow regulatory agencies to conduct full NEPA analyses

and make permitting decisions. 

• Describe backfill operations and closure, including: timing and amounts of material

proposed for backfilling; means of transporting the material to the backfill site; types

and timing of storage, if any; if material is to be stabilized or otherwise treated, full

description of additives and treatment processes.

• Describe physical characteristics (e.g., size distribution, including percent fines,

moisture content) and chemical characteristics of backfill materials and any additives

(see Appendix C) .

• Predict the structural stability and leachability of backfill material and enclosing mine

rock.

• Description of mine hydrology, including post-closure (see Appendix A). Prediction

of water quality in the mine, both with and without backfilling in order to determine

potential for impacts to groundwater and surface water and to design appropriate

controls. 

• Description of monitoring program to be used to verify predictions and allow

detection of the need for changes.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-8 January 2003

Figure F-1. Hydrologic Cycle for A Typical Waste Pile.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-9 January 2003

3.3 Use in Facility Construction

Waste rock and overburden materials can be beneficially used as construction materials

at many mine sites. Applicants proposing to use waste rock to construct roads, impoundments,

buttresses, underdrains, or other facilities or as rip-rap to line channels or stabilize embankments,

will need to conduct geochemical tests similar to those described in Appendix C,

Characterization of Ore, Waste Rock, and Tailings. Testing programs should be designed to

ensure that these materials will not themselves generate acid or otherwise cause negative

environmental impacts.

If waste rock and overburden are to be used in facility construction, mine applicants

should provide information of the following types to allow regulatory agencies to conduct full

NEPA analyses and make permitting decisions. 

• Describe how the waste rock or overburden will be used for facility construction,

including: timing and amounts of material proposed for use, and the purpose for

which they will be used; means of transporting the material from the mine to storage

and/or construction sites; types and timing of storage, if any. 

• Physical (e.g., size distribution, including percent fines, moisture content) and

chemical characteristics (e.g., acid generation potential, metals concentrations) and

how they relate to stability and leachability.

• Prediction of water quality in situations where the materials will be in contact with

wastewater/seepage (e.g,. when used as drains) and of any best management practices

(BMPs) or other controls necessary to meet standards.

• Description of alternate sources of construction materials, including the same types of

information provided for waste rock/overburden. 

• Description of monitoring program(s) to be used to verify predictions and allow

detection of the need for changes.

3.4 Use as Cover Materials

Waste rock may be used to cover and stabilize fine-grained tailings. The intent is to

reduce or prevent fluvial or aeolian erosion, transport, and redeposition of the fine-grained

materials (e.g., Woodward-Clyde, 1998). 

If applicants propose to use waste rock as cover material, they should provide the

following types of information to support the NEPA analyses and permitting decisions:

• Timing and amounts of material proposed for use, and the means of transporting the

material from the mine to the storage and/or tailings areas.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-10 January 2003

• Types and timing of storage, if any. This should include any storage site preparation

(e.g., run-on/run-off controls, temporary vegetation)

• Geotechnical evaluation of the stability of the underlying tailings materials, with and

without the waste rock cover.

• Geochemical evaluation of the waste rock/overburden that allows prediction of

changes in water quality of infiltrating run-on and precipitation, and of any run-off.

• Description of alternate sources of cover materials, if any, including the same types of

information provided for waste rock/overburden. 

• Description of the ability of the cover material to support vegetation or other longterm closure solution

• Demonstration that the cover will meet performance standards and regulatory

requirements during operations and following closure.

• Description of monitoring program(s) to be used to verify predictions and allow

detection of the need for changes.

4.0 TAILINGS MANAGEMENT

Tailings materials are typically disposed of in impoundments. Other management

practices that are becoming more common include disposal in dry tailing facilities, disposal

under water covers (subaqeous disposal), and disposal in mine voids (mine backfill). This

section briefly describes these tailings management techniques. More detailed descriptions are

provided in Vick (1990) and Johnson (1997); an overview of tailings disposal in impoundment

settings in given in EPA (1994a). As discussed in Section 2.3 and Appendix C, characterization

of the tailings materials is critical to predicting environmental impacts and designing appropriate

management. As this section will discuss, extensive studies are necessary to evaluate potential

tailings management sites and to design and operate the sites.

4.1 Tailings Impoundments

Most mines dispose of tailings in engineered impoundments that cover areas ranging

from a few acres to more than a thousand acres. Thickened tailings solids typically are sluiced to

the impoundment and deposited by spigotting or through single-point discharges or cyclones. As

solid particles settle out of suspension, clarified water from the top of the impoundment is

generally recycled to the milling process circuit for reuse. In some cases (e.g., in areas of net

precipitation or following mine closure), water may be discharged from the impoundment, in

which case an NPDES or land application permit is required. Tailings impoundments may also
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-11 January 2003

be used as emergency containment for excess storm water run-off from other areas of the mine

site and for disposal of sludges from on-site mine wastewater or sewage treatment plants.

Critical issues related to the design and management of tailings impoundments are

discussed in the following subsections. Issues related to closure and reclamation of tailings

impoundments are discussed in Section 6.

4.1.1 Site Characterization. 

The choice of a tailings impoundment site is based on the need to maximize desirable features

and minimize undesirable features. Criteria typically used to determine an appropriate tailings

impoundment site are presented in Table F-3. Site characterization studies need to include

comprehensive geological, geotechnical, and engineering evaluations to ensure the long-term

stability of the impoundment. As recently demonstrated at a Spanish zinc mine, failure to

conduct adequate site foundation studies can lead to tailings spills, leaks, and partial dam

collapse (Mining Engineering, 1998).

Table F-3. Example Siting Criteria for Tailings Impoundments 

and Dry Tailings Facilities

Criteria to Determine Initial Site Feasibility

Anticipated tailings volume

Tailings grain size and composition

Hydrological conditions

Proximity to milling/processing operations

Climate, including type and magnitude of storms

Topography

Geology and mineralization, including seismic 

activity

Hydrogeological conditions, including foundation

permeability

Criteria to Determine Final Site Suitability

Visual impact

Land use of site and surrounding area

Ecological resources

Site access

Run-on control feasibility

Seepage release potential

Surface water discharge potential

Airborne release potential

Development and operating costs

Wetland impacts

Source: Vick (1990); Johnson (1997)

4.1.2 Impoundment and Embankments

Vick (1990) and others discuss the different types of tailings impoundments and

embankments. The choice of impoundment type is determined primarily by site topography

(Vick, 1990). Cross-valley impoundments are used where drainages are incised into hilly

terrain. Sidehill impoundments are three-sided embankments arranged in stair-step fashion on

broad areas of sloping terrain. Valley bottom impoundments are constructed in stream valleys
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-12 January 2003

that are wide enough to route streams between the embankment and opposite valley wall. Fully

enclosed ring dike impoundments are used on flat terrain. 

Surface embankments can be classified into two general categories: water-retention type

dams and raised embankments (Vick, 1990). Water-retention type dams normally are placed in

valley bottoms, but occasionally are used on hillsides. They commonly are used for finely

ground materials such as flotation tails and to construct impoundments with high water storage

requirements. Water-retention type dams are constructed of earthen materials or concrete to

their full height prior to tailings placement. Because they are intended to prohibit horizontal

fluid flow, most are designed with impervious cores, filter material, drains, and rip-rap (Figure

F-2a) (Vick, 1990). 

Raised embankments begin with starter dikes that are designed to contain the amount of

tailings expected during the first few years of production. Starter dikes are constructed using a

wide variety of materials that range from natural borrow soils to waste rock to tailings (Vick,

1990). The embankment is raised periodically as dictated by mine operations. Embankment

height is increased using upstream, downstream, or centerline construction methods (Figure F2b, -2c, and -2d) (Vick, 1990). Upstream construction is generally the least costly because it

requires the least amount of dike fill material; however, it is susceptible to liquefaction and

requires careful control of tailings discharge (Vick, 1990). As a result, upstream construction is

rarely used now due to the risk of seismic failure. In contrast, downstream construction offers

good seismic resistance and can be used for water storage; this method is the most costly and

requires the largest amount of fill material (Vick, 1990). Centerline construction shares

advantages and disadvantages of the other methods. The raised embankment method is popular

because embankment designs are comparatively simple and it provides the economic benefit of

spreading construction costs over a longer period (Vick, 1990). 

Stream diversions may be incorporated into each category of impoundment if the

embankment is constructed in the bottom of a valley having significant drainage from storm

runoff or in a valley that produces substantial continual runoff. Especially in areas of high

stream flow or high precipitation, diverting water around impoundments can be necessary to

maintain proper water balances and to promote quiescent conditions in the impoundment for

settling. They can also be particularly useful for minimizing tailings erosion during storm events

(see Appendix H, Erosion and Sedimentation). Diversions can be constructed either as conduits

located below the impoundment or as ditches that skirt the perimeter of the impoundment. The

feasibility of diversions depends on the particular site conditions. 

Seepage control may be used to protect the structures associated with a tailings facility

and to provide barriers to contain fluids originating from the facility. It can be used to partly or

completely contain the lateral flow of tailings waters through the subsurface. Types of

commonly used seepage barriers, which restrict flow, include cutoff trenches, grout curtains, and

slurry walls (Vick, 1990). Seepage collection devices include collection wells, ditches, and

ponds. For so-called “zero discharge” impoundments where seepage is collected and returned to

the impoundment or otherwise used, long-term plans for seepage control/management have to be

considered during design, not just at the time of closure. 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-13 January 2003

For the NEPA process, applicants should provide at least the following information

related to tailings impoundment and embankment design and operation:

• Describe the criteria that was used to determine whether proposed tailings

impoundment sites and designs are technically and economically feasible (see Table

F-3). Evaluate the importance of critical factors such as foundation stability,

substrate bearing capacity, and ground water and surface water hydrology. Compare

predicted impoundment performance to applicable regulatory requirements.

• Specify the sources (and their acquisition), types and volumes of construction

materials required for the dam.

• Investigate naturally occurring hazards at the dam site or within the impoundment

area and assess the risks that these hazards pose.

• Perform stability and liquefaction analyses consistent with State and other regulatory

requirement.

• Provide the rate and volume of tailings to be disposed. Characterize the physical and

chemical properties of the tailings and how they relate to impoundment/embankment

stability and leachability. Characterization of tailings is discussed in Appendix C.

• Develop a water balance and predict effluent quantity and quality (including

seepage) under normal conditions and under storm scenarios, and describe how

seepage, if any, will be collected and managed. See Section 4.1.4. below.

• Describe impoundment construction and management, including construction

QA/QC, and performance standards necessary to meet applicable regulatory

requirements.

Information needs related to impoundment liners and monitoring is discussed below. 

Closure issues related to impoundments and embankments and discussed in Section 6 below. 

Issues related to acid drainage are discussed in Section 7. 

4.1.3 Liners

At sites where mill effluents containing toxic constituents (e.g., cyanide or radioactive

isotopes, or metals if there is a risk to ground water) will be discharged to a tailings

impoundment, tailings facilities may need to be fitted with a liner system. The decision to

choose a liner can be made after determining if the substances contained in the tailings are toxic,

if sufficient quantities of the substances exist, and if sufficient quantities of those substance can

reach ground water and degrade it. In addition, State regulations may require liners. Tailings

pond liners can be composed of compacted clay, synthetic materials, or tailings slimes. Each has

advantages and disadvantages. Compacted clay liners provide good containment for relatively

low material and placement costs. However, not 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-14 January 2003

Figure F-2a. Water-Retention Type Dam for Tailings Storage
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-15 January 2003

Figure F-2b. Sequential Raising, Upstream Embankment
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-16 January 2003

Figure F-2c. Sequential Raising, Centerline Embankment
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-17 January 2003

Figure F-2d. Sequential Raising, Downstream Embankment.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-18 January 2003

all sites contain sufficient suitable material. Synthetic liners have the advantages of low

permeability and consistent quality, but disadvantages that include high product cost, high

placement cost, and substantial foundation preparation requirements. Both clay and synthetic

liners can be subject to damage by settling. Mill slimes offer an inexpensive source of low

permeability material that is used in a similar manner to a clay liner. Careful placement of slimes

can provide good containment. A slime liner also can provide a superior seal in case of

foundation settling or geologic movement due to its plasticity. Disadvantages of slime liners

include the necessity of careful material placement, the requirement that the material not contain

toxic materials that could escape the containment area, and the difficulty in predicting long-term

effectiveness of containment. 

If a tailings impoundment is to be lined, or if a liner is to be used over part of an

embankment, mine applicants should provide information of the following types to allow

regulatory agencies to conduct full NEPA analyses and make permitting decisions. 

• Delineation of the initial area to be lined, anticipated expansions, and the maximum

area that might be lined, and the approximate schedule for expansions (including the

likely maximum amount of exposed liner at any one time under various scenarios–

this is crucial for estimating run-on/run-off).

• Description of liner site preparation activities (compaction, etc.).

• Description of the type and characteristics of liner proposed (type of synthetic

material, sources of clays, physical characteristics).

• Information on compatibility of tailings and liner materials, including long-term

compatibility.

• Description of leak detection, if any, and contingency plans for detected leakage.

• Analysis of liner effectiveness, such as a demonstration of how liner will meet

applicable performance standards for containment over the long term.

4.1.4 Tailings Water 

Tailings waters may contain elevated concentrations of metals, process chemicals,

acidity, and other constituents that have the potential to impact surface and ground water quality. 

Applicants must provide water balance information that describes the flow and composition of

waters into and out of the tailings impoundment. Modeling may be required. Water balances are

discussed in more detail in Appendix A (Hydrology) and Appendix E (Wastewater

Management). Applicants who request an NPDES permitted discharge from the tailings

impoundment should provide information on flow and composition and treatment of such

discharge. NPDES permitting needs are discussed in the main text of the source book and in

Appendix D (Effluent Characterization)
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-19 January 2003

4.1.5 Operational Monitoring. 

Monitoring of active tailings impoundments should focus on detecting changes in

embankment stability, surface and ground water quality, and ground water flow (Table F-4) (see

Sengupta, 1993). Embankment stability can be monitored using various geotechnical methods

and visual observation. Surface and ground water quality can be monitored by routinely

collecting and analyzing samples from upstream and downstream stations. Downstream surface

water stations should be located such that they would receive direct discharge from retention

ponds, seepage collection sumps, and diversion ditches and at selected downstream confluences. 

Ground water stations should be located around the perimeter of an impoundment in order to

detect changes to ground water flow that might occur as a result of a recharge mound that would

form beneath the impoundment (Vick, 1990). All water quality monitoring stations should be

sampled on a regular basis and analyzed for a suite of constituents as specified in an approved

Sampling and Analysis Plan (see Appendix B, Receiving Waters, and Appendix C,

Characterization of Ore, Waste Rock and Tailings). 

Table F-4. Operational Monitoring of Tailings Impoundments

Type of

Monitoring

Methods Used Purpose

Geotechnical Visual inspection; Soil strength testing;

Soil borings; Degree of saturation; Pore

water pressure.

Detect changes in slope stability, compaction,

and settling that may identify structural

weaknesses or signal potential failure of the

embankment.

Surface Water Flow monitoring; Upstream and

downstream water quality analyses.

Detect impacts to surface water quality.

Ground Water Water table monitoring; Upgradient and

downgradient water quality analyses

Detect impacts to ground water quality;

determine influence of recharge mound on

ground water flow.

Ambient air Visual (opacity), PM-10 monitoring Detect blowing dust, detect high particulate

(particularly important if high arsenic in tailings)

Tailings water and

seepage

Flow monitoring, Water quality analysis Early detection of water quantity and quality

changes, potential for acid drainage, detection

of process chemicals

Applicants should submit information of the following types to allow full NEPA

analyses and informed permitting decisions. 

• Description of all monitoring plans, both for operational components as well as

potentially affected environments, including frequency, the components to be

monitored, the parameters to be monitored, and quality assurance/quality control. 

Table F-4 identifies the types of monitoring.

• Description of strategy and schedule for updating and refining monitoring plans,

• Description of how monitoring data will be used during the active life of the facility,
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-20 January 2003

• Description of contingency plan for responding to various monitoring results,

including identification of action levels for each monitored component and parameter

(i.e., the level that will trigger further monitoring or some type of other action,

including corrective action).

4.2 Dry Tailings Facilities

Dry tailings disposal is a relatively new method of placing tailings that have been

dewatered to less than saturation using thickeners, belt filters, and filter presses (Johnson, 1997). 

Although best suited to dry climates and is most productive where water shortages exist, dry

tailings facilities also have been approved in wet climates (e.g., Greens Creek Mine and the

Kensington Project in Alaska). Dewatered tailings are transported to the disposal facility via

haul trucks, conveyors, or special pumps. The materials are then placed, compacted, and

covered. Dry tailings facilities typically are reclaimed concurrent with placement, resulting in

less disturbed area at any given time (Johnson, 1997). 

In addition, “paste” tailings, which are used extensively to backfill underground mines

(see Section 4.4), may be disposed on the surface. According to Norman and Raforth (1998),

paste materials have an initial moisture content of approximately 20 weight percent, most of

which is held by surface tension in the material matrix. This amount of water is sufficient to

permit the material to be pumped, but insufficient to create free-draining water or particle

segregation. A few percent of portland cement or fly ash can be added to increase material

strength and durability. 

A significant advantage to dry tailings management is that the technique reduces the

potential for surface and ground water contamination since it eliminates free process water from

the pile. Other advantages include the ability to reclaim more process water, the ability to place

dry material at locations where wet placement is difficult or impossible. Dry tailings

management also may result in less water to treat and discharge, which can be a significant

advantage in light of the zero discharge provisions of the NPDES New Source Performance

Standards. A disadvantage to this type of management is that the unsaturated and moist

condition of the tailings would permit any iron sulfide minerals that are present to oxidize and,

potentially, form acidic leachate. Other disadvantages include high unit costs and difficulty in

placing materials in wet climates. Saturation of a dry tailings pile by precipitation potentially

can lead to slope failures if a facility is not properly designed to accommodate storm events.

As with tailings impoundments, the choice of a dry tailings disposal site is important. 

General siting criteria are shown in Table F-3. Facilities are most easily located along valley

bottoms, on flat plains, or on gently sloping surfaces. Placing dry tailings on hillsides with steep

slopes requires larger facility footprints and higher pile heights, and it presents challenges for

access and foundation stability.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-21 January 2003

The decision to use dry tailings management depends partly on the volume of water

required by the process system and the site water balance. For some zero discharge facilities, the

use of dry tailings disposal may return too much water continuously to the process system. For

example, the water storage and/or evaporative loss components of a tailings impoundment may

be important elements of the facility water balance.

If applicants plan to use dry tailings management techniques, they should provide

information of the following types to support NEPA analyses and permitting. 

• Describe the criteria that was used to determine whether proposed tailings facility

sites are technically and economically feasible (see Table F-3). Evaluate the

importance of critical factors such as foundation stability, substrate bearing capacity,

and groundwater and surface water hydrology. Compare impoundment performance

to applicable regulatory requirements.

• Perform stability and liquefaction analyses consistent with State and other regulatory

requirements.

• Characterize the physical and chemical properties of the tailings and how they relate

to impoundment stability and leachability.

• Describe the rate and total volume of tailings to be dried and managed, means of

dewatering the tailings, and wastewater management.

• Description of dry tailings facility—location and topography, site preparation and

containment (compaction, berms, liners), long-term configuration, and means of

transporting dry tailings to the facility.

• Develop a water balance and predict effluent quantity and quality (including seepage)

under normal conditions and under storm scenarios. Describe how seepage, if any,

will be collected and managed. See Appendix E.

• Describe facility construction and management, including construction QA/QC, and

performance standards necessary to meet applicable regulatory requirements.

• Develop and describe operational and environmental monitoring plans, including

contingency plans and action levels. Monitoring similar to that described in Table F4.

Closure issues are discussed in Section 6, below. Issues related to acid drainage are

discussed in Section 7.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-22 January 2003

4.3 Subaqueous Tailings Disposal

The objective of subaqueous tailings disposal is to maintain a water cover over the

tailings to control oxidation of sulfides, bacterial action, and subsequent acid generation (see

Appendix C for discussion on the geochemistry of acid generation). This objective can be

accomplished by depositing mine tailings directly into a body of water such as a constructed

impoundment, a flooded mine, a freshwater lake, or a marine environment such as a fjord or

deep marine channel. Although practiced in other countries, disposal of tailings into lakes and

marine environments is not allowed in the United States. For most industry sectors, NPDES

effluent limitation guidelines prohibit process water discharges to waters of the U.S., including

both fresh and marine waters. Effluent limitation guidelines also limit the discharge of total

suspended solids. For these reasons, disposal of tailings into lakes or the marine environment is

not discussed in this Appendix. Instead, the Appendix focuses on the use of water covers in

engineered impoundments and disposal into flooded mine workings.

Subaqueous tailings disposal controls acid generation by limiting available oxygen for

the oxidation process, thereby controlling acid generation; eliminating surface erosion and dust

problems caused by wind and water action on tailings placed in a depositional basin, and;

creating a reducing environment, suitable for supporting sulphate and nitrate reducing microorganisms in sediments, in which soluble metals are precipitated as sulfides and ammonia is

generated by the reduction of nitrates. The physical and chemical stability of the tailings

materials are controlled by the oxidation, reduction, and diffusion kinetics in sediments;

interactions with the overlying water column; and tailings transport related to wave induced

turbulent motion.

4.3.1 Water Covers over Constructed Impoundments. 

Disposal of tailings into engineered impoundments where a permanent water cover is

maintained is a relatively new concept that presents a number of practical difficulties. These

facilities would require some sort of perpetual maintenance to ensure a permanent water cover

and continued structural integrity of embankments and dikes. In addition, these facilities would

require a permanent and regular water supply and a minimum water depth to maintain anaerobic

conditions at the bottom.

The advantages of using underwater disposal in a constructed impoundment include the

ability to mitigate the production and release of acid drainage and lower implementation costs

compared to the costs of a soil cover. Disadvantages include heightened potential for

embankment failure due to seismic events or erosion due to additional liquid in the impoundment

compared to conventional tailings impoundments; the displacement of resources (e.g., habitat,

vegetation, etc.) at the location of the tailings impoundment; the potential inability to keep

tailings flooded and maintain anaerobic conditions; and the potential release of metals present in

pore water solutions or in soluble mineral phases. Many of these disadvantages may be more

difficult to overcome in impoundments that are not designed for permanent water retention (i.e.,

whose design is modified after initial construction). 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-23 January 2003

Subaqueous tailings disposal in constructed impoundments has been evaluated at two

mines in Canada. At the Highland Copper Mine, British Columbia., a tailings impoundment was

flooded and monitored to evaluate the efficiency of the subaqueous disposal technique (Scott

and Lo, 1992). At the Fault Lake Mine, Falconbridge, Ontario, test plots of saturated tailings

were developed and evaluated to determine the effectiveness of various test scenarios.

Design and operational issues that should be analyzed for NEPA disclosure and

permitting relating to water covers include:

The issues discussed in Section 4.1 for the siting, design, operations, and monitoring of

tailings impoundments also apply to constructed underwater disposal impoundments (e.g.,

characterization of tailings, stability evaluation, water balance, monitoring plans, etc.). 

Additional issues specific to water covers include:

• Designs must demonstrate that the tailings will be maintained in an anaerobic state to

prevent sulfide oxidation and that the tailings will be placed below the level of wave

action to prevent redistribution.

• Impacts to the aquatic environment must be evaluated

• Operating and monitoring plan, including monitoring to ensure that tailings remain

saturated.

• Issues associated with the long-term maintenance need to continue saturation after

closure.

4.3.2 Disposal into Flooded Mine Workings. 

Tailings can be disposed of in the subaqueous environment provided by flooded

underground and surface mine workings. Placement is accomplished through sluicing to fill

mine stopes, adits, shafts, and pits. Tailings may be mixed with inert materials, such as cement

or sand or fly ash, to add structural integrity. 

The U.S. Bureau of Mines studied metal dissolution from mine tailings that were placed

underground as backfill in a flooded mine shaft (Levens and Boldt, 1993). Computer

simulations based on sample data collected during these studies indicated that metals release

from the backfill after flooding was expected to be low due to reduced rates of sulfide oxidation

and to buffering capacity provided by carbonate minerals.

The disposal of tailings in flooded mine workings offers advantages over standard

tailings impoundments that include placing mine wastes into a comparatively stable

environment; eliminating the potential for tailings dam failure and the need to maintain a facility

during post-closure; and reducing visual impacts and land surface disturbance. Disadvantages

include the potential for chemical transformations to create less stable minerals after placement

and the hydraulic conductivity of uncemented tailings which is likely to be higher than that of
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-24 January 2003

the surrounding rock. The latter may result in the formation of preferential ground water

pathways that enhance the potential for leaching of backfilled material (Levens and Boldt, 1993). 

It is also important to coordinate backfilling with mine planning. 

Issues associated with disposal in flooded pits or underground workings that should be

evaluated for NEPA analyses include:

• Describe the disposal operations and closure, including: timing and amounts of

tailings proposed for disposal; means of transporting the tailings to the backfill site; if

material is to be stabilized or otherwise treated, description of additives and treatment

process.

• Characterization of the backfill tailings and any additives.

• Demonstrating the structural integrity and physical consistency of the backfill

material.

• Characterizing geochemical effects of tailings solids and fluids on the quality of

ground water or pit lakes, including results from any necessary modeling.

• Characterizing any predicted discharges to ground water or surface water.

• Conducting rigorous hydrogeological and limnological studies to ensure that

workings will remain continuously flooded.

• Developing a monitoring plan for operational and post-closure periods to verify

predictions and allow detection of the need for changes or corrective actions. 

4.4 Mine Backfill

Tailings materials can be used to backfill underground mines. In this setting, they are

used to provide a working floor, provide wall and roof support and stability, maximize ore

recovery, minimize surface subsidence, and aid ventilation control (Vick, 1990; Johnson, 1997). 

Because most backfill applications require material with high permeability (to permit

dewatering) and low compressibility, generally only the sand fraction of tailings are used in

these operations and slimes still require an alternative disposal method (Vick, 1990). Tailings

are delivered underground using hydraulic systems or, if the tailings have been dewatered to

“paste,” using positive displacement pumps (Johnson, 1997). Slurried tailings (60 to 75 percent

solids) dewater underground and require drainage control to ensure that fluids are handled in a

manner that is environmentally acceptable. Paste backfills (80 percent solids) offer lower

permeability and can be used to restrict underground water flow (Johnson, 1997). Although

paste backfills introduce less water underground, water extracted during the filtering operation

requires environmentally acceptable disposal (Johnson, 1997). In some cases, tailings may be

augmented with cement or fly ash to provide additional stability and/or alkalinity. 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-25 January 2003

Issues associated with the disposal of tailings as backfill that should be analyzed for

NEPA disclosure include:

• Describe the backfill operations and closure, including: timing and amounts of

material proposed for backfilling; means of transporting the material to the backfill

site; if material is to be stabilized or otherwise treated, description of additives and

treatment process. 

• Characterization of the backfill tailings (e.g., particle size, chemical and physical

characteristics), including the effects of additives such as cement or fly ash.

• Predict the structural stability of backfill material and enclosing mine rock.

• Determine/predict the potential reactivity (particularly acid generation potential) of

backfill material (tailings and any additives) and enclosing mine rock. This would

involve laboratory testing, modeling, and other methods, as described in Appendix C. 

• Prediction of water quality in the mine and whether a discharge is needed in order to

determine potential impacts to ground water and surface water and to design

appropriate controls.

• Description of monitoring program to be used to verify predictions and allow

detection of the need for changes.

Issues associated with acid generation is discussed further in Section 7 of this Appendix

and in Appendix C. 

5.0 SPENT ORE/HEAP AND DUMP LEACH MANAGEMENT

Although the purpose of heap leach pads and dumps is to recover metals, these facilities

cross into the realm of waste management upon closure (Hutchinson and Ellison, 1991). Mines

presently use three types of heap leach facilities (Hutchinson and Ellison, 1991). Reusable pads

(also termed “on-off” pads) are designed for continual reuse, with spent ore materials removed

and transported to a separate disposal facility at the end of the leach cycle; fresh ore is replaced

on the pad for a new leach cycle. Dedicated or permanent expanding pads are engineered

facilities designed for a single use, with spent ore remaining in place at the end of the leach

cycle; fresh ore is placed on newly constructed portions of the pad. Valley leach facilities are

constructed in a natural stream valley, with ore contained on the downstream side by an

embankment; they are operated in a manner generally similar to dedicated pads. In part, the

choice of a facility type is dictated by site topography, geotechnical considerations, and the

mineralogy and metallurgical characteristics of the ore materials. In some cases, ore is leached

in vats or tanks rather than in open heaps; in such cases, the spent ore is generally disposed in a

manner similar to that used by on-off pads or in a manner similar to that used for conventional

tailings (see Section 4 above). 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-26 January 2003

Process solutions have the ability to degrade surface and ground waters should they

escape from leach pads and solution storage and conveyance systems. For most facilities,

solution containment is achieved through the use of impermeable liners beneath leach pads,

sumps, and pregnant and barren solution ponds, and dual-wall piping. Hutchinson and Ellison

(1991) describe the types of natural and synthetic liners that are commonly used for these

purposes. Regardless of the type of system that would be used, leach pads, solution storage

ponds, and solution conveyance systems will need to designed to accommodate the added

volume of water that occurs during low probability storm events. This makes performing a

rigorous analysis of the predicted water balance crucial to project design. Wastewater

management issues are discussed in more detail in Appendix E.

Many of the criteria for choosing the locations of waste rock dumps and tailings

impoundments also apply to the locations of heap leach facilities. Primary among these are

economic factors such as haulage distance and geotechnical concerns such as foundation stability

and liner integrity. The types of technical data that may be required for locating a suitable site

are summarized in Table F-5. 

Table F-5. Data Needs for Heap Leach Facilities

Critical Design Factor Data Needs Data Source/Methodologies

Facility Site Selection Topography Topographical maps, Aerial photos

Geology and Soils, including fault

mapping

Geological maps, Engineering tests of

site samples.

Seismicity (natural and blasting-induced) Geological maps, Seismic zone maps,

Uniform Building Code (U.S. ACE,

1995), Mine Plan of Operation,

Engineering tests of site samples.

Surface Water Hydrology See Appendix A

Ground Water Hydrogeology See Appendix A

Baseline Water Quality See Appendix B

Operational Considerations Mine Plan of Operation

Process Solution System Leaching and Processing Operations Mine Plan of Operation

Facility Water Balance See Appendix A

Pile/Dump Construction Foundation and Embankment Stability Geotechnical and engineering tests of

site soil samples.

Pile Stability Geotechnical and engineering tests of

ore materials.

Surface Water Diversion See Appendix H

Seepage/run-off Collection and/or Liner Model results, Meteorological data; See

Sections 4.1.4, 4.1.5, 6.5
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-27 January 2003

Spent ore that is removed from a reusable pad, or spent ore removed from vats or tanks,

will require disposal in a separate facility. The manner of disposal will be governed by the

likelihood that these materials could impact surface or ground water quality by releasing metals,

acidity, process chemicals, or other constituents. Consequently, the potential for water quality

impacts is expected to be a function primarily of the mineralogy of the spent materials and the

completeness of rinsing and process chemical neutralization actions (see Section 6.6). Spent

materials that are unlikely to have deleterious effects could be disposed of with other waste rock

materials; those expected to contribute to poor water quality may require special handling or

disposal (e.g., encapsulation).

Issues associated with heap management that should be analyzed for NEPA disclosure

and permitting include:

• Describe the criteria used to determine whether proposed heap sites and designs are

technically and economically feasible and how they fulfill regulatory requirements. 

Many of the criteria will be similar to that discussed for siting waste rock dumps and

tailings impoundments. Table F-5 lists some of the critical criteria.

• Characterize the physical and chemical properties of the heap material and how they

relate to heap stability and leachability (see Appendix C).

• Prepare a water balance and predict the potential for seepage and run-off from the

heap in order to design appropriate wastewater management. Various models are

available to facilitate this. Where modeling is used, all model assumptions, input

parameters, and uncertainties should be disclosed and a sensitivity analysis may be

necessary. Wastewater management is discussed in Appendix E.

• Describe how the heap will be constructed and managed during operations and

closure in terms of maintaining heap stability and reducing impacts to the

environment. Develop performance standards and compare to any applicable

regulatory requirements (e.g., predict liner performance). Additional closure

considerations are discussed in Section 6 of this appendix.

• Develop and describe operational and environmental monitoring plans to ensure heap

stability and predict impacts to surface and ground water quality. Table F-2

identifies types of monitoring that may be required. Monitoring plans should include

action levels and contingency plans. 

• For disposal units for spent ore from on-off pads and from vats and tanks, provide

similar information on unit design and performance, including performance following

closure and abandonment. 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-28 January 2003

6.0 ISSUES RELATED TO CLOSURE AND RECLAMATION

Closure and reclamation of permanent waste disposal facilities should be directed

toward preventing future impacts from these sites. Primary considerations center on creating

physically and chemically stable facilities that will not impact surface and ground water

resources through erosion, runoff, seepage, or windblown dust (Hutchinson and Ellison, 1991). 

Over the long-term, the stability of facilities such as waste rock dumps and spent leach piles

depends on factors such as the build-up of pore water pressure within the pile, erosion during

high intensity precipitation events, slope angle, and the presence of internal weaknesses (e.g.,

inclined layering) within the pile. In addition to those produced by sluicing practices, internal

weaknesses may be produced in tailings piles by sulfide oxidation, which creates hardpan layers

that restrict precipitation infiltration (Blowes et al., 1991). 

This section briefly describes aspects of closure and reclamation and associated analyses

that should be performed for permitting and NEPA analyses. The reader is referred to Section

7.0 for more detailed descriptions of techniques to control the formation and migration of acidic

drainage. Appendix H, Erosion and Sedimentation provides a more complete discussion of

runoff and sediment transport control.

6.1 Soils Placement and Revegetation

An understanding of soil resources can help applicants to establish realistic goals for

revegetation success and increase the likelihood of achieving those goals. Most mining activities

directly impact soils. The actions of stripping and replacing topsoil and overburden disrupt the

horizons that produce a soil’s physical and chemical characteristics and often inverts them in the

process of creating stockpiles. These actions also lead to soil compaction. However, even where

soils are not stripped, the operation of heavy equipment causes compaction that can significantly

reduce soil productivity (Ellis and Mellor, 1995). Compaction reduces pore space within a soil

which decreases the infiltration of water and air. Soil porosity is critical to maintaining the types

of biological activity that produce a healthy soil.

If there is a single key to reclamation success, it is the need to maintain or reestablish

biological activity within the soils or the growth material serving as soil. Soil structure, moisture

holding capacity, nutrients/pH, and stability are all critical to reclamation success.

The biological activities occurring within soils are key contributors to plant-soil interactions. 

Micro- and macroorganisms within the soil conduct all of the important soil-building processes,

such as the decomposition of organic material and nutrient cycling (Ellis and Mellor, 1995). 

Biological activity typically is lost when soils are stockpiled for a period of time. One handling

technique that maintains biological activity is to directly haul topsoil from an area to be stripped

to an area undergoing reclamation (Sengupta, 1993). This approach, also termed ‘live hauling’,

can enhance revegetation efforts by maintaining a viable seed bank of indigenous species. Live

hauling is only practical where concurrent reclamation is being employed; in settings where live

hauling is not possible, islands of native plant material and soil can be transplanted into newly

reclaimed areas to serve as propagule sources for important soil organisms. Windblown
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-29 January 2003

propagules can be collected using snow fences (Reeves and Redente, 1991). 

A number of reclamation options are available to operators, including directly seeding

waste piles or covering them with topsoil or growth media prior to seeding. Where soil

resources are limited, waste materials should be analyzed for their suitability as plant growth

media. Based on analytical results, amendments may be incorporated to improve fertility or

texture (e.g., Munshower, 1997). In such cases, amendments can be either chemical fertilizers

or organic mulches such as paper, wood chips, straw, hay, manure or compost which are tilled

into the upper portion of the soil. Many soils, particularly in the western U.S., have limited

phosphorus contents and require fertilization. However, the addition of a nitrogen-rich fertilizer

requires thorough consideration because the addition of nitrogen to native soils has been shown

to influence the species composition at reclamation sites and may predispose a site to invasion

by weedy species adapted to such a nutrient-rich regime. In some cases, successful nitrogen

additions have been made after plants have had two to three years to become established

(Peterson et al., 1991). Seed mixtures should be developed based on the type of soil being

placed on the site. While the long-term reclamation goals may reflect a later successional stage,

reclamation plans should acknowledge the limitations that ‘new’ soils may impose on the

establishment of new vegetation.

Reclaiming a large facility (e.g., a tailings impoundment) typically requires that a site

have significant soil resources so that a suitable growth medium can be placed. For mines that

are situated in arid or mountainous terrains with limited soil resources, this may be problematic. 

In these areas and in others where soils may need supplements, operators have used biosolids

(i.e., sanitary sewage sludge), wood chips, and other means of increasing organic matter in soil. 

Recent studies have shown that cattle grazing can provide an innovative, effective, and costcompetitive option for reclaiming fine-grained materials (i.e., tailings). In Miami, Arizona,

penned cattle helped to establish growth media on abandoned tailings by trampling hay mulch,

urine, and manure into the upper tailings layer (Norman and Raforth, 1998). In addition, cattle

helped to minimize erosion by creating sidehill terraces and pathways and to establish seed

germination areas in hoof depressions. 

6.2 Runoff and Erosion Control

The long-term control of sediment erosion and redeposition is an important aspect of

protecting water quality and aquatic resources. Runoff and erosion control typically is achieved

through grading, surface diversion, revegetation, and armoring in accordance with Best

Management Practices (BMPs) established by the operator. Predicting and controlling runoff

and erosion is discussed in detail in Appendix H, Erosion and Sedimentation. 

Grading and recontouring waste rock dumps and decommissioned heap leach piles

typically is intended to provide stable slopes that will not avalanche or erode. Grading and

recontouring techniques can be used to create benches or other features that reduce gully and rill

formation on sloping surfaces and to guide precipitation runoff to engineered swales or other

conveyance structures. In general, tailings are not regraded (although embankment faces may

be). More often, long-term diversions or conveyance structures are constructed around or even
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-30 January 2003

across tailings facilities to control erosion 

In most cases, runoff from a disposal facility (whether from dumps, piles, tailings

embankments, or flow around or over impoundments) is routed to a sediment control structure as

described in Appendix H, Erosion and Sedimentation. Surface water diversions are used to

direct up-gradient flows around or across a facility in order to prevent erosion of waste materials

and the embankments that contain them. Storm event planning is key in designing diversion

structures. Runoff control structures, including conveyance structures and detention basins, that

were initially sized and constructed to meet design life guidelines, may require reconstruction to

convey or detain flows that result from low probability precipitation events (e.g., 100 or 500 year

events). This may require measures to stabilize the beds and banks of ditches (e.g., with rip-rap),

increase the size of diversion structures and sediment detention ponds, or raise the height of

tailings embankments to prevent storm water overflow. Closure requirements will likely be sitespecific and intended to promote long-term drainage control. 

As described in Section 6.1, revegetation typically requires the addition of soil

amendments or the placement of topsoil or other growth media to provide a suitable substrate for

plant growth. Establishing vegetation on waste facilities lessens infiltration and decreases the

potential for erosion by diminishing rainwater impact and providing soil cohesion. Surface

armoring is intended to cover fine-grained, easily eroded materials such as tailings with more

resistant, coarse-grained rock.

6.3 Infiltration Control

Infiltration control is used to minimize the amount of meteoric water that enters a waste

disposal facility. These measures can help to stabilize facilities by maintaining low pore water

pressures and decreasing the potential for water quality impacts by reducing seepage quantities

and limiting oxygen diffusion. Requirements for infiltration control depend on climatic

conditions and the characteristics of the materials contained in a given disposal facility. 

Facilities situated in arid climates or that contain non-reactive materials may not require

infiltration controls at closure. 

Infiltration control typically is achieved through the use of impermeable caps, seals, and

capillary barriers, by establishing vegetation, and by recontouring facility surfaces. Caps and

seals may be composed of clay or other natural materials that are compacted to an acceptably

low permeability or a variety of synthetic materials such as PVC, HDPE, or asphalt and concrete

mixes. Compacted natural soils are effective at controlling water infiltration and are unlikely to

suffer long-term degradation. Similarly, clay caps can control water infiltration. Although

synthetic membrane covers may offer superior short-term performance, they can suffer long-term

degradation through the loss of plasticity, cracking, or tearing under differential settling

(Sengupta, 1993). Surface sealants such as shotcrete or asphalt provide more robust alternatives

to membrane covers. Capillary barriers can have a variety of designs (Hutchinson and Ellison,

1991). In general, they consist of a vegetated soil layer that overlies a coarse drainage layer that

is, in turn, underlain by a low permeability cover or low permeability wastes (Figure F-3)

(Hutchinson and Ellison, 1991). They are designed to intercept infiltration penetrating the soil
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-31 January 2003

layer and divert it from the surface of the waste disposal facility. Vegetation will take up

moisture that falls onto the surface of a disposal facility and minimize that which will infiltrate

(see Section 6.1). Infiltration also can be decreased by grading facility surfaces to eliminate

ponding and promote runoff (see Section 6.2). 

6.4 Seepage Control

Seepage control may be needed for certain facilities upon closure. Requirements for

seepage control are likely to differ significantly for waste management facilities in arid and

humid climates (Hutchinson and Ellison, 1991). In general, seepage can result from infiltrating

precipitation or snowmelt that percolates through a facility, the flow of surface or ground waters

through a facility, or from the release of pore waters upon dewatering and consolidation of 

tailings. 

Seepage control from waste disposal facilities can be achieved through the use of

impermeable liners and systems that are engineered to collect seepage and route it to treatment

facilities. Typically, these systems are designed to work in concert with runoff and infiltration

control systems. Types of seepage collection systems include sumps, ditches, drains, and ground

water interception wells (Hutchinson and Ellison, 1991). Seepage conveyance systems at

closure may need to be designed to accommodate increased seepage and runoff that could result

from low probability storm events. Poor quality seepage may need to be routed to a treatment

facility prior to its discharge to surface waters. These facilities can be in the form of active or

passive treatment systems (see Appendix E, Wastewater Treatment).

6.5 Other Considerations

The potential deleterious effects of highly reactive wastes (for example, materials with a

net acid generating potential) can be lessened by installing covers materials that limit oxygen

diffusion into waste facilities (e.g., Sengupta, 1993). Water covers are effective oxygen barriers,

but require maintenance to assure they remain intact. In addition, the use of water covers 

require that the original impoundment structure be designed to maintain such covers. Synthetic

membranes such as PVC and HDPE provide effective oxygen control but may suffer puncture or

long-term degradation. While compacted soil covers offer limited oxygen control, saturated

soils may preclude significant oxygen diffusion (Sengupta, 1993).

The control of windblown dust may be an issue for tailings and other fine-grained waste

materials. Dust can be suppressed by maintaining a water cover over tailings materials, placing

natural or synthetic covers, or promoting vegetative growth. The use of waste rock as a cover

for tailings should be thoroughly investigated to ensure that the tailings materials possess

sufficient strength to support the waste rock load (see Section 3.4).
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-32 January 2003

Figure F-3. Layered Waste System.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-33 January 2003

In some cases, facilities may be recontoured to blend with existing topography and

reduce visual impact. While coal mining regulations require that spoil piles and pits be regraded

to approximate original topography, there is no such requirement for non-coal mines. However,

permits may require that any facilities remaining upon closure be consistent with the surrounding

topography and support the approved post mining land use(s). 

6.6 Spent Ore Treatment and Neutralization

Spent ore materials may occur in the form of processed heap and leach facilities or

tailings materials. Pore waters and soluble metal compounds that remain in closed acid and

cyanide heap leach facilities or in tailings from cyanide leaching can be mobilized by infiltrating

rainwater. To prevent chemical releases to the environment, leached materials may require

rinsing and neutralization to remove potentially deleterious compounds prior to facility closure. 

In general, this can be accomplished by: 

• Applying a neutral rinse solution to remove constituents from the processed material,

then collecting and treating the solution; piles are rinsed until effluent concentrations

reach pre-determined acceptable levels. 

• Applying a rinse solution containing chemical or biological agents that neutralize or

chemically decompose constituents of concern in situ. 

In situ heap rinsing requires that piles have sufficient permeability to permit neutralizing

fluids to penetrate through and contact all materials within them. Piles with insufficient

permeability or with highly variable permeability or fluid flow pathways may need to be

dismantled and treated in smaller batches (EPA, 1994b). Climate can play a significant role in

determining the length of time required for complete neutralization. For example, cold weather

may slow or halt biological breakdown of cyanide. Experience has shown that initial treatment

may produce effluent that meets constituent guidelines, but that effluent quality may degrade

after treatment stops (EPA, 1994b). Thus, some facilities may require repeated treatment until

effluent quality remains at acceptable levels. 

Li et al. (1996) describe lab and pilot-scale experiments designed to determine the

appropriate methods to rinse and neutralize an acid leach pile. Their results demonstrated that

decommissioning tests should use large diameter columns or field-scale test piles to determine

rinsing times, solution application rates, and decommissioning costs. These experiments also

showed that precipitation and dissolution of secondary minerals controls the metals content of

the rinse effluent. Rinsing duration depends on the volume of the leached materials in the pile,

their mineralogical and chemical characteristics, and physical factors such as permeability,

porosity, and precipitation. Accelerated artificial rinsing, in which neutralizing solutions (e.g.,

calcium hydroxide) are applied using the leach solution system, can effectively remove acidity

and soluble metals from a large heap leach pile in a reasonable period of time.

There are a variety of techniques that can be used to chemically or biologically

breakdown residual cyanide and metal-cyanide complexes in heap leach and tailings facilities
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-34 January 2003

(EPA, 1994b summarizes these techniques; see also Appendix E, Wastewater Treatment). Some

of these methods produce by-product ammonia or nitrate that may require additional treatment in

effluent waters. In general, chemical or biological agents can be applied to leach piles using the

leach solution system. Rinsing continues until the cyanide content of seepage from the pile

reaches an acceptable level. Processed tailings from circuits using agitation leaching typically

are treated prior to discharge to a tailings impoundment. 

It should be noted that rinsing heaps, while effective in reducing cyanide, can mobilize

other metals (notably, selenium, mercury, and arsenic) to the point that rinsate or leachate will

not meet regulatory standards for discharge without treatment of the rinsate as well as future

leachate from infiltration. It also is important to note that other closure issues discussed in this

section (run-off and erosion control, infiltration and seepage control, soils placement and

vegetation, and post-closure monitoring, are important considerations following neutralization of

spent heaps. 

6.7 Post-Closure Monitoring

Post-closure monitoring is conducted to ensure long-term protection of the environment

and to identify any problems in the early stages of their development. Depending on the

facilities and methods of closure employed, post-closure monitoring may include visual

inspections of site conditions, evaluations of embankment integrity, surface and ground water

quality monitoring, determinations of available capacity in sediment retention structures,

assessments of the performance of stream diversions, seepage collection, and seepage treatment

systems, and the success and progress of reclamation activities. For each type of monitoring

conducted, there should be clear action levels that trigger specific responses (which could

include such things as heightened monitoring, notification of authorities, correction action). 

These responses should be clearly laid out in contingency plans that describe the actions that

have to take place when an action level is reached or exceeded. The types of monitoring that are

required, the schedule by which they are conducted, and the parties that are responsible for

conducting monitoring activities will depend on site-specific conditions and requirements. 

6.8 Information and Analytical Needs

Issues associated with closure and reclamation that should be analyzed for NEPA

disclosure and permitting include:

• Describe closure and reclamation techniques and timing. Develop performance

standards for reclamation measures. The performance standards should be consistent

with regulatory requirements and also provide for long-term stability (chemical and

physical).

• Describe any performance bonds or other financial assurance that may be provided to

authorities as potential mitigation for impacts, the means of calculating the amount

provided, and the conditions and timing of release. 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-35 January 2003

• Develop a long-term water balance, including prediction of run-off and seepage under

low probability conditions.

• Predict the short- and long-term effectiveness of infiltration controls, seepage

controls, revegetation, and other stability and water controls. Lab tests and field test

plots may be used to evaluate cover effectiveness and revegetation. Modeling may be

required to predict long-term impacts of weathering. 

• Describe any treatment and neutralization of wastewater, spent ore, or tailings prior to

site abandonment, including verification testing. 

• Describe all monitoring that is proposed at various stages of reclamation and closure

and afterward, including QA/QC, action levels and contingency plans. Section 6.7

describes the types of monitoring that may be needed.

7.0 ACID MINE DRAINAGE

Acid mine drainage (AMD) may often represent the greatest environmental concern at

mining sites. All of the mining solid wastes discussed in this appendix may be potential sources

of AMD. Measures to control and mitigate AMD production from solid mining wastes are

briefly discussed in this section. Management and treatment of AMD wastewaters is discussed

in Appendix E. The chemistry of AMD production is described briefly here and is described in

detail in many of the references provided in this section. 

AMD occurs when sulfide-bearing mine wastes and materials react with meteoric water

and atmospheric oxygen to produce sulfuric acid. The most reactive sulfide phases are the iron

sulfide minerals pyrite, marcasite, and pyrrhotite. Nordstrom et al. (1979) summarize the pyrite

oxidation process. In the initial stages of acid formation, pyrite reacts with water and oxygen to

form ferrous iron and sulfuric acid. Ferrous iron is slowly oxidized to ferric iron by oxygen. As

pH decreases below 4.5, ferric iron also begins to oxidize pyrite and it becomes the primary

oxidant at pH values below 3.0. Iron oxidizing bacteria (e.g., T. ferrooxidans) greatly accelerate

the oxidation of ferrous iron to ferric iron and serve to catalyze pyrite oxidation at low pH. 

When this occurs, the presence of oxygen has little effect on the rate at which pyrite oxidizes to

form acid. Acid generation at low pH is controlled by bacterially mediated ferric iron oxidation

(Singer and Stumm, 1970; Nordstrom et al., 1979). 

AMD can be initiated from any pyrite-bearing mine material that is exposed to air and

water. This includes ore piles, overburden and waste rock dumps, tailings impoundments, pit

walls, underground workings, and spent ore heaps. Appendix C describes tests that can be

performed on tailings, waste rock, etc. to determine their acid generating potential. To the

greatest extent possible, new facilities should seek to prevent acid drainage rather than treat or

abate AMD after it forms.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-36 January 2003

7.1 Controlling the Acid Generation Process

Acid generation can be controlled by regulating one or more of the primary reaction

components (pyrite, oxygen, water) or the catalyst (bacteria). Control can be achieved by

removing pyrite from materials and wastes or precluding interactions between the solid materials

and oxygen, water, or bacteria. The process can be slowed by using bactericides or eliminating

the environmental conditions that sustain bacterial populations.

Pyrite can be removed from mining wastes and materials by processing. The most

common procedure produces a sulfide-rich metal concentrate through flotation, which then can

be handled separately (SRK et al., 1989). Although flotation can be utilized at mines where it is

part of the beneficiation scheme, it is neither a practical nor cost-effective solution for treating

pyritic overburden or waste materials, subeconomic underground workings, or pit walls that

contain pyrite.

At any stage of the acid generation process, water (or moisture) and air are required for

acid production. Removing either or both of these reactants from the site of acid generation will

diminish acid production (SRK et al., 1989; Environment Australia, 1997). Low permeability

covers and seals are widely used to accomplish this task. Capillary soil barriers are engineered

covers that have a compacted, low permeability layer (generally clay) that is interlayered with

more permeable materials (typically sand) which serve as evaporation barriers. Erosion control

is achieved by covering the soil barrier with gravel. Capillary soil barriers have proven effective

in excluding oxygen and precipitation from mine wastes and materials (greater than 90 percent

exclusion) and are an effective AMD control agent (Groupe de Recherche, 1991; Robertson and

Barton-Bridges, 1992; Bell et al., 1994; Yanful et al., 1994; Ziemkiewicz and Skousen, 1996a). 

Synthetic barriers also are effective control agents, but are less widely used because of their high

cost. Synthetic barriers typically are PVC or HDPE liners placed over acid-generating materials

and protected with a cover of soil or rock (SRK et al., 1989; Ziemkiewicz and Skousen, 1996a). 

Oxygen can be excluded from mine materials and wastes by submerging them under

water (SRK et al., 1989). Although water contains a small amount of dissolved oxygen, it is

present in amounts insufficient to oxidize pyrite. Mine materials can be submerged by

depositing them in a constructed water body, depositing them in a flooded mine pit or

underground working, or depositing them on a specially prepared surface where they are

naturally saturated by perched water (Broughton and Robertson, 1992). Subaqueous tailings

disposal, which has been used successfully at several mine sites (Dave, 1993; Dave and

Vivyurka, 1994; Fraser and Robertson, 1994; ; Environment Australia, 1997), is discussed in

greater detail in Section 4.3.

At advanced stages of the acid-generation process, bacterial oxidation of ferrous iron

catalyzes acid generation. Consequently, controlling bacterial populations can provide

immediate control of acid generation. Anionic surfactants (e.g., sodium lauryl sulfate;

Kleinmann et al., 1981), which typically have liquid formulations, can be sprayed onto

potentially acid-generating materials prior to or during disposal (Parisi et al., 1994). Because

these compounds eventually decompose or leach from treated materials, they must be reapplied
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-37 January 2003

periodically and are not a permanent solution to the AMD problem (Ziemkiewicz and Skousen,

1996a). However, slow-release formulations (sorbates and benzoates; Erickson et al., 1985) are

available and have proven useful (Splittorf and Rastogi, 1995). Bactericides are most effective

when applied to fresh, unoxidized pyritic materials and can be a useful tool when used in

combination with other control methods (Ziemkiewicz and Skousen, 1996a).

7.2 Moderating the Effects of Acid Generation

The effects of acid generation can be moderated by neutralizing any acid that is

generated before it can migrate from a disposal site. Neutralization can occur as a result of

natural conditions, but commonly it is spurred by chemical amendments applied directly to the

wastes and materials prior to or during disposal or added to the cover materials that are placed

following disposal. When amendments are added to the waste materials, neutralization occurs

within the pile near the site of acid generation. In contrast, amendments added to cover materials

supply alkalinity to meteoric water that infiltrates the material pile and neutralizes acidity. 

Where mine materials include both acid-generating and net neutralizing solids, special handling

and construction practices can be used to mitigate acid generation. Acid migration from

underground workings can be reduced or prevented by backfilling and sealing mine portals.

Several types of alkaline amendments can be used at mine sites (SRK et al., 1989;

Ziemkiewicz and Skousen, 1996a, b; Environment Australia, 1997). Limestone (calcium

carbonate), which lacks cementing capability, is inexpensive, readily available, safe, effective,

and easy to handle. Fluidized bed combustion ash is a mix of coal ash, lime (calcium oxide), and

gypsum (hydrous calcium sulfate) that reacts quickly and hardens into a cement upon wetting. 

Kiln dust from cement and lime kilns is a mix of unreacted limestone, lime, and ash that is highly

reactive, absorbs moisture, and has cementing abilities. Steel slags also have high calcium oxide

contents but also may have high concentrations of trace metals which make them less suitable for

widespread use. Phosphate rock, which will react with ferrous iron to form insoluble coatings

on pyrite, is more expensive than the other amendments listed above. 

The amount of alkaline material that must be added to wastes and materials prior to their

disposal can be estimated from acid-base accounting tests of the disposed materials (see

Appendix C) and of the amendment. A cost-effective control strategy can be determined during

pre-mining planning when different disposal options can be tested. In theory, amendments

should be thoroughly admixed with mining materials prior to disposal to maximize their

chemical effectiveness. In practice, however, this may require repeated handling of the materials

which may not be cost effective. Consequently, it is common for amendments to be interlayered

with mine materials (termed layered base amendments). As described below, the construction of

piles that include heterogeneously distributed, layered base amendments is critical to their

success.

The construction of waste and material piles plays a significant role in determining

whether mixed acid-forming and acid-neutralizing materials will generate acid mine drainage. 

The formation, storage, and flushing of acid products in a rock or tailings pile depends on flow

paths within the pile, flushing rates through different parts of the pile, the distribution of acid-
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-38 January 2003

generating and acid-neutralizing materials, and localized physical and chemical conditions

(Robertson and Barton-Bridges, 1992). Consequently, it is possible for rock piles with net

neutralizing character to develop areas of acid generation. Regardless of the amount of

neutralizing material contained within a rock pile, acid generated within the pile will not be

neutralized if it percolates along a flow path that does not encounter alkaline materials

(Ziemkiewicz and Skousen, 1996b). Although hydrologic modeling of waste rock piles is still a

developing science (Robertson and Barton-Bridges, 1992), it is possible to design and construct

waste piles with internal drainage characteristics that route leachate to locations where it will be

neutralized.

Acid generation from underground mine workings can be moderated by several

methods. In cases where workings extend below the water table, sealing mine portals allow the

workings to flood, excluding oxygen and prohibiting acid generation (Kim et al., 1982). 

Alternatively, workings can be backfilled with alkaline materials (e.g., as slurries) that will

neutralize acid generated underground (Ziemkiewicz and Skousen, 1996a).

7.3 Controlling the Migration of Acid Mine Drainage

In cases where acid generation is not prevented, then AMD must be controlled by

preventing its migration to the environment. Because water is the dominant transport medium,

controlling water exit pays few dividends. Consequently, control technology focuses on

preventing water entry to the AMD source (SRK et al., 1989). Surface water entry can be

controlled using diversion ditches and berms and locating disposal facilities in areas with low

runoff. Ground water entry can be controlled using grout curtains or other seepage control

devices, avoiding areas of ground water discharge, and installing synthetic or compacted soil

liners. Infiltration can be controlled using surface covers and drainage control features. These

features are described in Sections 6.2 to 6.5. 

7.4 Collecting and Treating Acid Mine Drainage

Acid mine drainage that discharges to surface waters or infiltrates to ground waters from

waste piles, tailings impoundments, underground workings, or mine pits must be collected and

treated. Collection typically is accomplished using ditches, trenches, shallow wells, cut-off

walls, and pumps (SRK et al., 1989). Treatment is accomplished by several methods that fall

into the general categories of active and passive treatment. Treatment methods are described in

more detail in Appendix E, Wastewater Treatment.

7.5 Information Needs 

Issues associated with acid drainage that should be analyzed and presented for NEPA

disclosure and permitting include:

• Describe existing and proposed predictive testing that will be used to determine the

potential for and neutralization of AMD (see Appendix C). Testing proposed

throughout the mine’s life should be described. 
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-39 January 2003

• Describe and predict the effectiveness of AMD prevention, moderation, or control

measures. Present results of geochemical testing and treatability testing as well as

modeling results. 

• Describe QA/QC procedures during operations to ensure that acid-generating

material is handled according to mine plan.

• Describe monitoring programs to confirm that AMD preventive and control measures

are working and/or to provide early warning of any problems, including development

of action levels and contingency plans.

8.0 CITED REFERENCES

Bell, A.V., Riley, M.D., and Yanful, E.G., 1994. Evaluation of a Composite Soil Cover to

Control Acid Waste Rock Pile Drainage. In: Proceedings of the International Land

Reclamation and Mine Drainage Conference, U.S. Bureau of Mines Publication SP-06B94, p. 113-121.

Blowes, D.W., Reardon, E.J., Jambor, J.L., and Cherry, J.A., 1991. The Formation and Potential

Importance of Cemented Layers in Inactive Sulfide Mine Tailings, Geochimica

Cosmochimica et Acta, vol. 55, pp. 965-978.

Broughton, L.M. and Robertson, A.M., 1992. Acid Rock Drainage from Mines -- Where we are

Now. In: Science Applications International Corporation, Predicting Acid Generation

from Non-Coal Mining Wastes: Notes of a 1992 Workshop, Draft report prepared for the

Environmental Monitoring Systems Laboratory, Office of Research and Development,

U.S. Environmental Protection Agency, Las Vegas, NV, 19 pp.

Dave, N.K., 1993. Panel Wetlands -- A Case History of Partially Submerged Pyritic Uranium

Tailings under Water, MEND Project Report 3.12.2, Ontario, Canada.

Dave, N.K. and Vivyurka, A.J., 1994. Water Cover on Acid Generating Uranium Tailings —

Laboratory and Field Studies. In: Proceedings of the International Land Reclamation

and Mine Drainage Conference, U.S. Bureau of Mines Publication SP-06A-94, p. 297-

306.

Ellis, S. and Mellor, A., 1995. Soils and Environment, Routledge, New York, NY.

Environment Australia, 1997. Managing Sulphidic Mine Wastes and Acid Drainage, Best

Practice Environmental Management in Mining, Commonwealth of Australia, May 1997,

81 pp.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-40 January 2003

Erickson, P.M., Kleinmann, R.L.P., and Onysko, S.J., 1985. Control of Acid Mine Drainage by

Application of Bactericidal Materials, U.S. Bureau of Mines Information Circular, IC9027, p. 25-34.

Fraser, W.W. and Robertson, J.D., 1994. Subaqueous Disposal of Reactive Mine Waste: An

Overview and Update of Case Studies — MEND/Canada. In: Proceedings of the

International Land Reclamation and Mine Drainage Conference, U.S. Bureau of Mines

Publication SP-06A-94, p. 250-259.

Groupe De Recherche En Geologie de L’Ingenieur, 1991. Acid Mine Drainage Generation from

a Waste Rock Dump and Evaluation of Dry Covers Using Natural Materials: La Mine

Doyon Case Study, Quebec, Final report submitted to Service de la Technologie Miniere,

Center de Recherches Minerales, 22 pp.

Hutchinson, I.P.G. and Ellison, R.D., 1991. Mine Waste Management, California Mining

Association, Sacramento. 

Johnson, J.M., 1997. Tailings Disposal Design. In: Marcus, J.J., ed., Mining Environmental

Handbook, Effects of Mining on the Environment and American Environmental Controls

on Mining, Imperial College Press, London, pp. 428- 444.

Kent, A., 1997. Waste Rock Disposal Design. In: Marcus, J.J., ed., Mining Environmental

Handbook, Effects of Mining on the Environment and American Environmental Controls

on Mining, Imperial College Press, London, pp. 444-447. 

Kim, A.G., Heisey, B.S., Kleinmann, R.L.P., and Deul, M., 1982. Acid Mine Drainage: Control

and Abatement Research, U.S. Bureau of Mines Information Circular, IC-8905, 22 pp.

Kleinmann, R.L.P., Crerar, D.A., and Pacelli, R.R., 1981. Biogeochemistry of Acid Mine

Drainage and a Method to Control Acid Formation, Mining Engineering, vol. 33, p. 300-

305.

Levens, R.L., and Boldt, C.M.K., 1993. Environmental Impacts of Mine Waste Sandfill, U.S.

Department of the Interior, Bureau of Mines, RI 9493.

Li, M.G., Jacob, C., and Comeau, G., 1996. Decommissioning of Sulphuric Acid-Leached Heap

by Rinsing. In: Tailings and Mine Waste ‘96, Balkema, Rotterdam, pp. 295-304.

Mehling, P.E., Day, S.J., and Sexsmith, K.S., 1997. Blending and Layering Waste Rock to

Delay, Mitigate or Prevent Acid Generation: A Case Study Review, Proceedings of the

Fourth International Conference on Acid Rock Drainage, Vancouver, B.C., May 31 -

June 6, 1997, pp. 951-969.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-41 January 2003

MEND, 1995. Hydrology of Waste Rock Dumps, Mine Environment Neutral Drainage Program

Associate Project PA-1, Natural Resources Canada, Ottawa, ON, July 1995.

MEND, 1996. Guide for Predicting Water Chemistry from Waste Rock Piles, Mine

Environment Neutral Drainage Program Report 1.27.1a, Natural Resources Canada,

Ottawa, ON, July 1996.

Mining Engineering, 1998. Bedrock Shift Caused Spill in Spain, Industry Newswatch Column,

Mining Engineering, vol. 50, no. 11, p. 23.

Munshower, F.F., 1997. Seeding and Planting. In: Marcus, J.J., ed., Mining Environmental

Handbook, Effects of Mining on the Environment and American Environmental Controls

on Mining, Imperial College Press, London, pp. 205-217.

Nordstrom, D.K., Jenne, E.A., and Ball, J.W., 1979. Redox Equilibria of Iron in Acid Mine

Waters. In: Jenne, E.A., ed., Chemical Modeling in Aqueous Systems: Speciation,

Sorption, Solubility, and Kinetics, American Chemical Society Symposium Series, vol.

93, p. 51-79.

Norman, D.K. and Raforth, R.L., 1998. Innovations and Trends in Reclamation of Metal-Mine

Tailings in Washington, Washington Geology, vol. 26, no. 2/3, pp. 29-42.

Parisi, D., Horneman, J., and Rastogi, V., 1994. Use of Bactericides to Control Acid Mine

Drainage from Surface Operations. In: Proceedings of the International Land

Reclamation and Mine Drainage Conference, U.S. Bureau of Mines Publication SP-06B94, p. 319-325.

Peterson, G.A., Williams, S.E., and Moser, L.E., 1991. Inorganic Fertilizer Use and Its Effects

on Semiarid and Arid Region Soils. In: Skujins, J., ed., Semiarid Lands and Deserts, Soil

Resource and Reclamation, Marcel Dekker, Inc., New York, NY.

Price, W.A., 1997. DRAFT Guidelines and Recommended Methods for the Prediction of Metal

Leaching and Acid Rock Drainage at Minesites in British Columbia, British Columbia

Ministry of Employment and Investment, Energy and Minerals Division, Smithers, B.C.,

April, 1997, 143 pp.

Reeves, F.B. and Redente, E.F., 1991. The Importance of Mutualism in Succession. In:

Skujins, J., ed., Semiarid Lands and Deserts, Soil Resource and Reclamation, Marcel

Dekker, Inc., New York, NY.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-42 January 2003

Robertson, A.M. and Barton-Bridges, J., 1992. Cost Effective Methods of Long Term Acid

Mine Drainage Control from Waste Rock Piles. In: Science Applications International

Corporation, Predicting Acid Generation from Non-Coal Mining Wastes: Notes of a 1992

Workshop, Draft report prepared for the Environmental Monitoring Systems Laboratory,

Office of Research and Development, U.S. Environmental Protection Agency, Las

Vegas, NV, 22 pp.

Schroeder, P.R., Dozier, T.S., Zappi, P.A., McEnroe, B.M., Sjostrom, J.W., and Peyton, R.L.,

1994. The Hydrologic Evaluation of Landfill Performance (HELP) Model: Engineering

Documentation for Version 3, Office of Research and Development Report EPA/600/R94/168b, U.S. Environmental Protection Agency, Washington, D.C., September 1994.

Scott, M.D., and Lo, R.C., 1992. Optimal Tailings Management at Highland Valley Copper,

CIM Bulletin, July/August 1992, pp. 85-88.

Sengupta, M., 1993. Environmental Impacts of Mining: Monitoring, Restoration, and Control,

Lewis Publishers, Boca Raton, FL.

Singer, P.C. and Stumm, W., 1970. Acid Mine Drainage: The Rate Determining Step, Science,

vol. 167, p. 1121-1123.

Skousen, J.G. and Ziemkiewiscz, P.F., eds., 1996. Acid Mine Drainage: Control and

Treatment, 2nd edition, National Mine Land Reclamation Center, Morgantown, WV, 362

pp.

Splittorf, D. and Rastogi, V., 1995. Ten Year Results from Bactericide-Treated and Reclaimed

Mine Land, Proceedings of the American Society for Surface Mining and Reclamation

Annual Meeting, Gillette, WY, p. 471-478.

Steffen, Robertson and Kirsten (B.C.), Inc., Norelco Environmental Consultants, and Gormely

Process Engineering, (SRK et al.), 1989. Draft Acid Rock Drainage Technical Guide,

British Columbia Acid Mine Drainage Task Force Report, BiTech Publishers, Ltd.,

Vancouver, B.C.

Steffen Robertson and Kirsten (SRK), 1992a. Mine Rock Guidelines: Design and Control of

Drainage Quality, Saskatchewan Environment and Public Safety, Mines Pollution

Control Branch Report #93301.

Steffen Robertson and Kirsten (SRK), 1992b. Guidelines for Acid Mine Drainage Prediction in

the North, Indian and Northern Affairs Canada, Ottawa, ON.

U.S. Environmental Protection Agency (EPA), 1993a. EPA Region VIII - NPDES Inspection

Report, Landusky Mine, May 11, 1993.
EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska

Appendix F: Solid Waste Management

F-43 January 2003

U.S. Environmental Protection Agency (EPA), 1993b. EPA Region VIII - NPDES Inspection

Report, Zortman Mine, May 12, 1993.

U.S. Environmental Protection Agency (EPA), 1994a. Technical Report: Design and Evaluation

of Tailings Dams, Office of Solid Waste, Report EPA 530-R-94-038, August 1994, 59

pp.

U.S. Environmental Protection Agency (EPA), 1994b. Technical Report: Treatment of Cyanide

Heap Leaches and Tailings, Office of Solid Waste, Report EPA 530-R-94-037,

September 1994, 62 pp.

Vick, S.G., 1990. Planning, Design, and Analysis of Tailings Dams, BiTech Publishers,

Vancouver, B.C., 369 pp.

Woodward-Clyde International-Americas, 1998. Stibnite Area Site Characterization Report,

Report prepared for the Stibnite Area Site Characterization Voluntary Consent Order

Respondents, August 3, 1998.

Yanful, E.G., Abbe, B.A., Woyshner, M., and St-Arnaud, L.C., 1994. Field and Laboratory

Performance of Engineered Covers on the Waite Amulet Tailings. In: Proceedings of the

International Land Reclamation and Mine Drainage Conference, U.S. Bureau of Mines

Publication SP-06B-94, p. 138-147.

Ziemkiewiscz, P. and Skousen, J, 1996a. Overview of Acid Mine Drainage At-Source Control

Strategies. In: J.G. Skousen and P.F. Ziemkiewiscz, eds., Acid Mine Drainage: Control

and Treatment, 2nd edition, National Mine Land Reclamation Center, Morgantown, WV,

p. 69-78.

Ziemkiewiscz, P. and Skousen, J, 1996b. Prevention of Acid Mine Drainage by Alkaline

Addition. In: J.G. Skousen and P.F. Ziemkiewiscz, eds., Acid Mine Drainage: Control

and Treatment, 2nd edition, National Mine Land Reclamation Center, Morgantown, WV,

p. 79-90.