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

January 2003

APPENDIX E

WASTEWATER MANAGEMENT
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TABLE OF CONTENTS

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

2.0 MINING WASTEWATERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-1

3.0 OVERVIEW OF MINING WASTEWATER MANAGEMENT . . . . . . . . . . . . . . . . . . . E-3

4.0 POLLUTION PREVENTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-3

5.0 ACTIVE TREATMENT OF MINING WASTEWATERS . . . . . . . . . . . . . . . . . . . . . . . E-4

5.1 Metals Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-4

5.1.1 Chemical Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-4

5.1.1.1 Hydroxide Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-5

5.1.1.2 Sulfide Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-6

5.1.1.3 Coprecipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-7

5.1.2 Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-7

5.1.3 Reverse Osmosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-8

5.1.4 Carbon Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-9

5.1.5 Biological Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-9

5.2 Cyanide Destruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-9

5.2.1 Alkaline Chlorination Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-10

5.2.2 Hydrogen Peroxide Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-11

5.2.3 Sulfur Dioxide/Air Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-11

5.2.4 Biological Treatment of Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-12

5.2.5 Natural Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-12

5.3 Solid-Liquid Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-13

5.4 Sludge Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-14

6.0 PASSIVE TREATMENT OF MINING WASTEWATERS . . . . . . . . . . . . . . . . . . . . . E-15

6.1 Commonly Used Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-15

6.2 Passive System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-16

6.3 Example Passive Systems at Metal Mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-17

7.0 TREATABILITY TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-18

7.1 Laboratory Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-19

7.2 Pilot-Scale Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-20

8.0 WASTEWATER DISPOSAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-21

8.1 Surface Water Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-21

8.2 Land Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-21

8.3 Evaporation/Infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-22

8.4 Underground Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-22
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TABLE OF CONTENTS

(continued)

9.0 STORM WATER MANAGEMENT AND BEST MANAGEMENT PRACTICES . . . E-23

10.0 WASTEWATER MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-24

11.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-24

LIST OF TABLES

E-1. Summary of Mining Wastewaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-2

E-2. Example Passive Treatment Facilities at Metal Mines . . . . . . . . . . . . . . . . . . . . . . . . . . E-18

E-3. Pilot-Scale Treatment Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-20

LIST OF FIGURES

E-1. Solubility of metal hydroxides and sulfides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-6
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1.0 GOALS AND PURPOSE OF THE APPENDIX

The goal of this appendix is to provide an overview of mining wastewater management and

identify information related to wastewater management that should be included in EISs and

NPDES permit applications for mines. The more specific goals for this appendix include:

• describing typical wastewater streams at mine sites, including process wastewaters,

mine drainage, and storm water

• describing approaches that can be used to manage waste streams;

• presenting EPA’s expectations for the level of detail required in a mine proposal, and 

• EPA’s expectations for the level of analysis needed to support NEPA disclosure,

permitting, and sound decision-making.

Appendix E is intended to be used in conjunction with other appendices in this source

book to which the reader is referred for more detailed information. Relevant appendices include

Appendix A, Hydrology, Appendix B, Receiving Waters, Appendix C, Characterization of Ore,

Waste Rock and Tailings, Appendix D, Effluent Quality, Appendix F, Solid Waste Management,

and Appendix H, Erosion and Sedimentation. 

Managing wastewater at a mine site encompasses physical handling and treatment 

methods, water and mass balance development, and recycling. Mine planners must evaluate the

natural waters and wastewaters at a site (Viessman and Hammer, 1993). Natural waters are

those waters that are not affected by the mining process. In contrast, wastewaters are waters that

have been affected by the mining process and must be managed because they have the potential

to release and/or transport contaminants. The types of wastewaters associated with mining

activities are described in the following section.

2.0 MINING WASTEWATERS 

 Understanding the generation of wastewaters associated with a mine site is an important

first step in developing a wastewater management scheme, especially in regards to maximizing

the opportunity for source control (Section 4.0). As discussed in the main text of the Source

Book, wastewaters associated with mining facilities are typically classified as mine drainage,

process water, or storm water. Table E-1 provides a description of the types of mining-related

waste waters that are associated with these classifications and some regulations that are

applicable to each. Section 2.0 of the Source Book provides more detail on the regulations

applicable to these terms and how they relate to NPDES permitting. 
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Table E-1. Summary of Mining Wastewaters

Type of

Wastewater

Description Applicable Regulations -1

Mine Drainage Any water drained, pumped, or

siphoned from an active mining

area, such as mine adit discharge

and open pit mine waters. 

Subject to effluent limitation guidelines at

40 CFR 440, which limit discharges of pH,

suspended solids and metals. Provides

for storm exemptions.

Process Water Mill effluent, tailings

impoundment/pile discharge or

seepage, leach pile runoff/seepage,

leach ponds.

Subject to effluent limitation guidelines at

40 CFR 440, includes combination of

effluent limits/no discharge requirements

for many facilities. Provides for storm

exemptions.

Storm Water

Associated with

Industrial Activity 

Storm water discharges directly

related to manufacturing,

processing, or raw materials

processing; includes storm water

runoff that contacts waste rock,

overburden, or tailings dams/dikes

not combined with mine drainage or

process water.

Storm water permit regulations, including

individual, baseline general permit and

multi-sector permit; see FR Volume 63,

No. 152, August 7, 1998, pp. 42533-

42548 for most recent listing of covered

discharges.

1- Wastewaters proposed for discharge to waters of the U.S. are subject to the NPDES regulations (40

CFR 122), including compliance with water quality standards.

It is important to characterize each type of wastewater to determine: (1) regulatory

constraints (for example, many process waters are subject to “no discharge” restrictions which

must be factored into plans for wastewater management), and (2) potential management options

(for example, in order to maximize the reuse of wastewaters, to determine if treatment is

necessary, etc.) It is particularly important to characterize the potential for production of acid

rock drainage (ARD). The oxidation of naturally occurring pyrite and other sulfide minerals in

mines, waste rock dumps, and tailings impoundments can produce acid water that contain

elevated levels of metals, sulfate, and total dissolved solids. The mechanism of ARD production

is described in Appendix F - Solid Waste Management. ARD testing is discussed in more detail

in Appendix C -Characterization of Ore Waste Rock and Tailings. Wastewaters should be

characterized in terms of both flow and chemistry. 

Wastewater proposed for discharge from the site (effluent) might also require whole

effluent toxicity testing . Characterization of effluent quality is discussed in detail in Appendix

D - Effluent Quality. Management of mining wastewaters is discussed in the following sections.
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3.0 OVERVIEW OF MINING WASTEWATER MANAGEMENT

As well as characterizing the chemistry of the wastewater, successful wastewater

management requires a thorough understanding of water flow and the site water and mass

balance. Decisions on water management practices and facility designs must be made based on

the water balance. Historically, mines have found it difficult to predict facility water balances. 

For example, there have been several cases in Region 10 where no discharge of process water

was predicted by the mine operator based on initial water balances that were later found to be

inadequate (and a discharge was required). Therefore, EPA recommends a conservative

approach to predicting flows taking into account all site development, operational, closure, and

post-closure/reclaimed conditions and considering seasonal climatic fluctuations. See Appendix

A - Hydrology for more information related to the development of a water balance.

Mine operators typically have a range of different options for wastewater management. 

These options are described in the following sections. Section 4.0 briefly discusses options for

source control and re-use. Section 5.0 provides a detailed discussion of active wastewater

treatment technologies and Section 6.0 describes passive treatment options. Section 7.0 presents

approaches to performing treatability studies. Section 8.0 discusses wastewater disposal

options. Section 9.0 discusses storm water management. 

4.0 POLLUTION PREVENTION

The volumes of mine wastewaters requiring treatment and disposal should be minimized

by pollution prevention practices. Pollution prevention includes source control, recycling, and

reuse. Source control involves minimizing the volume of potentially contaminated water

generated at a site. For example, contamination of surface runoff may be prevented by routing

surface flow around waste rock piles and tailings impoundments or capping these waste units to

prevent contact with pollution sources and/or infiltration and seepage (see Appendix F, Solid

Waste Management for discussion of pollution prevention practices for solid wastes.) Another

approach to minimizing the need for wastewater disposal is to maximize the potential for water

re-use/recycling.

Reducing the volume of wastewater produced by a mine clearly provides environmental

benefits through decreased loadings to surface and ground water. In addition, pollution

prevention can reduce overall operational costs. In wet climates, for example, the costs of

wastewater treatment and residuals disposal can be reduced because less treatment is required. 

(Less wastewater treatment is required in wet climates due to the sheer abundance of fresh water

and the dilution that is naturally available.) This results in lower capital expenditures for

treatment and, potentially, lower energy costs. In arid climates where water supply costs are

high, operational costs can be reduced by using recycled water. 

EPA encourages operators to use pollution prevention approaches to limit wastewater

generation and the need for disposal. EPA expects mine operators to demonstrate that they have
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considered and implemented all potential pollution prevention options for wastewater in

developing their plans of operations. 

5.0 ACTIVE TREATMENT OF MINING WASTEWATERS

Treatment of mining wastewaters may be necessary in order to reuse the water in

processing and/or to comply with NPDES permit effluent limitations. This section discusses

some treatment technologies that may be used for these purposes. Section 5.1 discusses

treatment for removal of metals, Section 5.2 discusses cyanide treatment, Section 5.3 discusses

solid-liquid separation, and Section 5.4 discusses sludge removal. The technologies discussed

may be used separately or in combination to meet treatment goals. Section 7 discusses

treatability testing and other considerations related to selecting a treatment technology or set of

technologies.

5.1 Metals Removal

This section describes technologies that may be used to remove metals from mining

wastewaters. The discussion is focused on the more commonly used physical and chemical

technologies. Biological techniques are also discussed, although they currently have more

limited application. Since metals cannot be destroyed, the treatment processes involve

separating the metals from the wastewater.

The selection of a treatment technology depends upon the characteristics of the

wastewater and treatment goals. Understanding the pH and oxidation state of various

wastewater streams is critical because these parameters largely determine the solubility and,

hence, mobility of metal species. Mine drainage typically is rich in metals; Smith et al. (1994)

illustrated a general negative correlation between metals concentrations and pH that extends over

5 orders of magnitude. Under oxidized, low pH conditions, metals usually occur as highly

soluble sulfate salts. Treatment technologies for mining wastewater often employ pH adjustment

to convert these soluble salts to less soluble hydroxide or sulfide salts, which then can be

removed by physical means (i.e., settling, precipitation/clarification or filtration). In

characterizing wastewater and selecting treatment technologies, it is always important to

understand both the soluble and total concentrations of metals present; pH conditions typically

determine this balance.

5.1.1 Chemical Precipitation

Chemical precipitation in wastewater treatment involves the addition of chemicals to

alter the physical state of dissolved and suspended solids and to facilitate their removal by

sedimentation. Chemical precipitation typically is a two-step process in which soluble metals

are first converted to an insoluble form (i.e., dissolved heavy metal ions may be chemically

precipitated as insoluble hydroxides or sulfides), then agglomerated into large, heavy particles

and removed by physical means such as sedimentation/clarification, filtration, or centrifugation. 
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This technique provides a well-developed and effective treatment process for removing a wide

range of heavy metals from wastewater.

Successful precipitation of metals depends primarily on two factors:

• The addition of sufficient anions to drive the chemical reaction toward precipitation

of the solute

• Physical removal of the resulting solid phase from the wastewater.

The three most common methods of chemical precipitation (hydroxide precipitation,

sulfide precipitation, and coprecipitation) are discussed in the following subsections. Other

precipitation processes have been developed (e.g., insoluble starch xanthate process) but are not

in widespread use. All these processes require subsequent solids-liquid separation (Section 5.3)

and sludge removal (Section 5.4).

5.1.1.1 Hydroxide Precipitation

Hydroxide precipitation is the conventional method of removing heavy metals from

wastewater. Normally, this process involves the addition of caustic soda or lime to adjust the

solution pH to the point of minimum solubility. The total residual metal concentration is a

complex function of pH, with the lowest residual metal concentration occurring at some

optimum pH value (Figure E-1). The residual concentration will increase when the pH is either

lowered or raised from this optimum value. 

Hydroxide precipitation is simple, effective, and widely practiced, but has limitations due

to the high solubilities and amphoteric properties of certain metal hydroxides (Kim, 1981).

(Amphoteric metals act as both acids and bases and will redissolve in excessively acid or

alkaline solutions.) In addition, the minimum solubilities for different metals occur at different

pH values and the precipitation of individual hydroxides occurs only in a narrow pH range

(Figure E-1). For these reasons, the maximum removal efficiency of mixed metals cannot be

achieved at a single precipitation pH (Bhattacharyya et al., 1981). Therefore, depending upon

treatment goals, multiple stages of precipitation at different pH levels may be required. 

Treatment by hydroxide precipitation alone may not be adequate to achieve some treatment goals

(e.g., NPDES permit effluent discharge limits based on aquatic life water quality criteria may be

very low for some metals). Therefore, additional treatment via some of the other technologies

discussed in the next sections or use of more effective, but less widely practiced, treatment

technologies may be necessary.

Theoretical metal concentrations based on hydroxide precipitation can be predicted;

however, numerical estimations of metal removal by precipitation as metal hydroxides should

always be treated carefully because over-simplifying theoretical solubility data can lead to errors

of several orders of magnitude (AWWA, 1990). For this reason, and other reasons discussed in

Section 7.0, treatability testing is critical to predict wastewater-specific metals removal

efficiency. 
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Figure E-1. Solubility of metal hydroxides and sulfides

5.1.1.2 Sulfide Precipitation

Sulfide precipitation is an alternative precipitation method that offers advantages due

mainly to the high reactivity of sulfides with heavy metal ions and the very low solubilities of

metal sulfides over a broad pH range. Metals can be removed by sulfide precipitation to

extremely low concentrations at a single pH (Figure E-1). Consequently, sulfide precipitation

may be a viable treatment alternative when hydroxide precipitation is not possible, or effective in

removing metal ions to the low concentrations that may be required to meet water quality-based

effluent limits . The extent to which metal sulfides precipitate is a function of pH, type of metal,

sulfide dosage, and the presence of other interfering ions (Bhattacharyya et al., 1981).
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The current methods of sulfide precipitation - the soluble sulfide method and the

insoluble sulfide method - differ in the technique of delivering sulfide ions. The soluble sulfide

method involves adding Na2S or NaHS solutions to the wastewater. The insoluble sulfide

method uses a sparingly soluble metal sulfide, such as FeS used by the proprietary Sulfex

method (Scott, 1979). Some sulfide precipitation occurs naturally in conventional hydroxide

precipitation systems because low levels of sulfides are often found in the untreated wastewater.

The current sulfide precipitation methods have several drawbacks. The addition of NaS

usually produces colloidal or very fine particles, which settle poorly and should be treated with

coagulants and flocculants before final clarification. The use of FeS requires an excessive

amount of reagent and produces a large amount of sludge because of the addition of iron (Kim,

1981). To minimize these problems, calcium sulfide can be used as the sulfide source. The

addition of CaS (as a slurry) produces precipitates that settle easily; the increase in the sludge

volume is minimal because calcium is mostly dissolved in the wastewater after reaction (Kim,

1981).

One example of the use of sulfide precipitation is the Red Dog Mine, operated by

Cominco, in Alaska. The Red Dog Mine implemented sulfide precipitation to meet effluent

limits for cadmium that could not be consistently achieved with their existing hydroxide

precipitation system. The currently approved plan of operations for the proposed Kensington

Project includes use of sulfide precipitation for mine drainage treatment. 

5.1.1.3 Coprecipitation

“Coprecipitation” generally describes a single-stage process that combines two

precipitants in a reaction vessel that serves to increase metal precipitation efficiency greater than

the use of either single precipitant. Chemical precipitants that have been used for mining

wastewaters include sulfides, hydroxide, and ferric iron. The advantages of coprecipitation, in

comparison with the lime and the sulfide precipitation processes, are that coprecipitation

consumes less of the expensive sulfide reagent, while also effectively removing metals that have

low sulfide solubilities. Thus, coprecipitation may allow for compliance with stringent discharge

limits at a cost less than that of sulfide precipitation alone. A conventional hydroxide

precipitation system can be modified easily to facilitate hydroxide-sulfide coprecipitation (Kim,

1981). The greatest disadvantage to coprecipitation is probably the need to maintain quantities

of more than one chemical precipitant onsite. At East Helena, Montana, ASARCO uses the term

“co-precipitation” to describe a different type of water treatment at its’ smelter site. ASARCO

adds iron sulfate along with hydroxide in a high density sludge (HDS) process to coprecipitate

iron and arsenic and meet the arsenic water quality criteria. 

5.1.2 Ion Exchange

The ion exchange process is essentially similar to the adsorption system in which the

wastewater is passed through a resin (solid porous particles with reactive surface “sites”). The

metal ions in the wastewater that have a stronger affinity for the reactive (adsorption) sites than
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the attached group, are exchanged with the attached group that results in removal of the metal

ions from the wastewater. The metal-loaded resins must periodically be regenerated by the

introduction of a solution of concentrated ions, such as sodium chloride, which displaces the

removed metals from the exchange sites. The regeneration stream, rich in displaced metals, must

then be treated or disposed.

The efficiency and performance of an ion exchange system generally depend on pH,

temperature, and pollutant concentrations. The highest removal efficiencies are most often

observed for polyvalent ions (EPA, 1979). Ion exchange systems usually require some degree of

pretreatment or preconditioning (e.g., coagulation and filtration) of wastewater to reduce

suspended solid concentrations, which tend to clog ion exchange resins.

Application of ion exchange technology has historically been limited, by economics and

resin exchange capacity, to the treatment of water containing 500 mg/L or less of total dissolved

solids (TDS) (EPA, 1979). The ion exchange process has relatively high operating and

maintenance costs. At higher TDS levels, calcium and magnesium removal predominates,

resulting in the need for frequent regeneration, and large volumes of regenerant to dispose. The

technology has been most commonly applied to water purification and selective removal of

heavy metals (i.e., only soluble, ionized metals) and metal-cyanide complexes from industrial

wastewater. For example, ion exchange is used by electroplaters discharging to publicly owned

treatment facilities to reduce high concentrations of arsenic, barium, cadmium, chromium,

copper, cyanide, lead, iron, manganese, mercury, selenium, silver, and zinc. EPA knows of no

active mines in Region 10 where ion exchange is currently being used to treat wastewater.

5.1.3 Reverse Osmosis

Osmosis is defined as the spontaneous passage of a solvent from a dilute solution to a

more concentrated one through a semi-permeable membrane (Ramalho, 1983). The process

utilizes semi-permeable membrane materials and pressure to selectively slow or stop the passage

of ions (including metals). In reverse osmosis, pressure is applied to the wastewater, forcing the

permeate (i.e., clean water) to diffuse through the membrane. Reverse osmosis divides the

wastewater into two components: the permeate, which is suitable for reuse/recycle or discharge ,

and a concentrated residue (i.e., brine stream) containing nearly all of the original pollutants. 

The reverse osmosis unit produces a brine stream equal to about 10 to 50 percent of the treated

in-flow volume that must be treated and disposed. In part, the volume of the brine stream will

depend on the initial TDS of the feed stream (brine volume increases with TDS concentrations). 

Reverse osmosis is a sensitive process that cannot withstand varying input conditions. 

For example, the presence of scale-forming ions (e.g., calcium, manganese, iron) may cause

fouling of the membranes. As a result, pretreatment (e.g., filtration and carbon adsorption) is

generally necessary. Generally the pH, temperature, and suspended solids levels of the

wastewater must be modified prior to reverse osmosis treatment in the interest of efficiency and

membrane life (EPA, 1979).
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Reverse osmosis is highly effective in removing metals to very low levels and it is one of

the few processes that will also reduce TDS in the waste stream. TDS concentrations of 100

mg/l can usually be achieved with single-pass systems. Two or more units operated in series can

achieve even lower TDS concentrations (10 to 25 mg/L). Historically, metals removal by

reverse osmosis has been limited by high capital costs, intensive maintenance requirements, and

high energy costs. EPA is not aware of any active mines in Region 10 which currently use

reverse osmosis to treat wastewater.

5.1.4 Carbon Adsorption

In carbon adsorption, wastewater is typically pumped through one or more vessels

containing activated carbon. Organics and some metals are adsorbed onto the carbon. As with

ion exchange, the carbon must be periodically reactivated or disposed and replaced with fresh

carbon. Carbon adsorption is most commonly used to remove organic materials in tertiary

wastewater treatment. It has been observed that some incidental metals removal also occurs in

such systems. Most probably, this removal is the result of organic material adsorbed on the

carbon degrading under anaerobic conditions and producing sulfide ions. These ions then form

insoluble sulfide salts with metals in the wastewater. The resulting insoluble particles are then

trapped in the carbon structure and essentially removed by filtration. The Grouse Creek Mine

(Hecla) in Idaho currently uses carbon adsorption following hydroxide precipitation for mercury

removal. 

5.1.5 Biological Treatment

Certain biological processes have been documented as effective technologies for the

removal of metals from mining process effluents. Biological treatment systems are based on the

addition of bacteria which promote biosorption of toxic heavy metals and suspended solids from

process effluents and biodegradation of cyanides. Other mechanisms, such as precipitation,

oxidation/reduction, filtration, and bioaccumulation, may be involved in the various types of

biological treatment, which range from constructed wetlands to contained reactor systems.

Biological treatment processes offer some advantages over chemical treatment methods,

including cost effectiveness, low sludge production, flexible design characteristics, compatibility

with effluent-receiving streams, and treatment performance. However, additional treatment may

be required to meet effluent discharge limits, and pretreatment may be required since biological

processes are sensitive to temperature and other seasonal fluctuations. As discussed in Section

5.2.4, the Homestake Mine uses biological treatment to destroy cyanide as well as removing

metals from the effluent . Several mines in Canada are evaluating the use of sulfide-reducing

bacteria for wastewater treatment (similar mechanism to chemical sulfide precipitation, except

the microbes act as the precipitants). 

5.2 Cyanide Destruction

Cyanide is used at some mines during ore processing operations. Cyanide has the ability

to create highly soluble metal complexes. For example, the most common process for the
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recovery of gold is that of cyanidation, in which gold is leached from the ore by a weak cyanide

solution (usually NaCN). Cyanide is also used as a flotation reagent to suppress iron during 

flotation processes. 

With the use of cyanide in ore processing comes the need for additional measures to

provide for chemical destruction of cyanide and cyanide-metal complexes in process waters. 

Cyanide exists in several forms in mine process wastewater, including free cyanide, cyanidesulfur compounds (thiocyanate) and metal-cyanide complexes. Metal cyanide complexes occur

as stable iron and cobalt cyanide complexes and the weak acid dissociable (WAD) metal

complexes of cadmium, nickel, zinc, and copper. Cyanide breakdown products such as

ammonia, nitrites, and nitrates may also be present. As with metals removal, it is important to

determine the form of cyanide and cyanide-metal complexes present in the wastewater. The

selection of a cyanide destruction technology will depend upon the characteristics of the

wastewater and treatment goals. 

The mining industry uses a number of treatment processes to destroy cyanide. This

section describes the more prevalent technologies, including alkaline chlorination, hydrogen

peroxide treatment, and sulfur dioxide/air treatment. Detailed information on the chemistry of

cyanide, technologies discussed in the following subsections, and other methods for cyanide

treatment can be found in Smith and Mudder (1991). The cyanide destruction processes

discussed accomplish two objectives: breakdown of the metal-cyanide bonds and destruction of

cyanide. Depending upon treatment goals, cyanide destruction may be followed by precipitation

or other metals removal processes (Section 5.1) and/or solid-liquid separation (Section 5.3) to

remove metals. 

5.2.1 Alkaline Chlorination Process

 The destruction of free and WAD cyanide is commonly accomplished through the

chemical process known as alkaline chlorination. The alkaline chlorination process destroys

cyanide through oxidation by chlorine under alkaline conditions. The chlorine can be supplied

in either a liquid form or a solid form as sodium or calcium hypochlorite.

Under ambient conditions, alkaline chlorination will remove all forms of cyanide,

excluding the extremely stable iron and cobalt cyanide complexes. Under ideal conditions,

cyanide can be reduced to below 1 ppm. Additional measures, such as increasing temperatures

or introducing ultraviolet light, must be implemented in the alkaline chlorination process to

reduce the concentrations of iron cyanide complexes. These measures are not often used because

of the associated increase in cost. As a result, alkaline chlorination is limited to wastewater

containing low concentrations of complexed iron cyanides.

When evaluating the feasibility of the alkaline chlorination process, additional

consideration must be given to the residual chlorine and chloramines found in the effluent. The

residual chlorine and chloramines (formed through the reaction of chlorine with ammonia in the

solution) are significant concerns because they are extremely toxic to aquatic life. 
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Advantages of alkaline chlorination are that it is a well established and widely used

technology that effectively destroys free and WAD cyanide, using chlorine, which is readily

available worldwide. Disadvantages of alkaline chlorination include high reagent costs, the

addition of TDS to the wastewater (due to the addition of alkaline salts to raise the pH), the need

for careful pH control, and the problem that iron cyanide complexes are not removed. Also, the

end products of alkaline chlorination, including residual chlorine and chloramines are extremely

toxic to aquatic life and must be removed.

5.2.2 Hydrogen Peroxide Process 

Hydrogen peroxide (H2O2) is a strong oxidizing agent that is capable of reducing free and

WAD cyanide to concentrations well below 1 ppm (Roeber et al., 1995). The hydrogen

peroxide process operates under alkaline conditions to rapidly oxidize free and complexed

cyanide to cyanate while in the presence of a metal catalyst such as copper, iron, aluminum or

nickel. Subsequently, the cyanate is hydrolyzed to form carbonate and ammonia (Knorre and

Griffiths, 1985). During the destruction of metal cyanide complexes by hydrogen peroxide,

liberated metals are precipitated as metal hydroxides. The required hydrogen peroxide dosage

depends on the WAD cyanide concentration in the wastewater, the strength of the hydrogen

peroxide solution, and the rate of mass transfer of hydrogen peroxide to the wastewater (Roeber

et al., 1995).

Although more costly than chlorination, hydrogen peroxide treatment, does not

contribute TDS to the wastewater since it reduces to water. Additional advantages of hydrogen

peroxide treatment is that iron complexed cyanides are destroyed and metals are removed

through precipitation (although additional metals removal may still be required). 

5.2.3 Sulfur Dioxide/Air Process

Two patented versions of the sulphur dioxide/air cyanide destruction process include one

marketed by Inco and another by Noranda, Inc. (Smith and Mudder, 1991). The Inco process

uses a mixture of sulphur dioxide (SO2), sodium sulfite (Na2SO3) or sodium meta-bisulphite

(Na2S2O5) and air within a controlled pH range to destroy cyanide (Roeber et al., 1995). The

Noranda process differs in that pure sulphur dioxide is utilized and air is not required. 

In the Inco process, both free and complexed cyanide are oxidized to produce cyanate. 

Hydrolysis of the cyanate results in the formation of carbon dioxide and ammonia. Iron cyanide

complexes are reduced to the ferrous state and continuously precipitated as insoluble metal

ferrocyanide salts of copper, nickel, or zinc . The Inco process also removes thiocyanate, but

only after cyanide has been eliminated. Normal operations will result in approximately 10 to 20

percent of influent thiocyanate levels (Smith and Mudder, 1991).

In the Noranda process, pure sulphur dioxide or industrial grade liquid sulphur dioxide is

fed into a solution or slurry to lower the pH levels to 7.0 to 9.0 (Smith and Mudder, 1991). 

Subsequently, a copper sulphate solution is added at a rate which yields desired cyanide

concentrations.
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Advantages of the sulfur dioxide/air cyanide destruction processes are that all forms of

cyanide are removed and metals are removed through precipitation (although additional metals

removal may be required, depending upon treatment goals). Disadvantages include high reagent

costs, the potential for production of high levels of TDS in the effluent, and strict process control

is required.

5.2.4 Biological Treatment of Cyanide

Biological destruction of cyanide occurs by oxidative breakdown of cyanide and cyanide

complexes and subsequent chemical complexation (adsorption/precipitation) of free metals

within the biomass. The Homestake Mine in Lead, South Dakota, has successfully operated a

biological wastewater treatment plant since 1984. This plant removes cyanide as well as heavy

metals by maintaining an oxygenated wastewater environment for a short retention time to

adsorb the metals in the biomass or biofilm. Bioadsorption of the metals is similar to the use of

activated carbon; however, the number and complexity of binding sites are much larger on the

biological cell walls (Whitlock, 1989). Five-year averages from 1984 through 1988 for effluent

from the Homestake wastewater treatment plant yielded removal rates of 94 to 97% for copper,

99 to 100% for thiocyanate, 96 to 98% for total cyanide, 98 to 100% for WAD cyanide, and 98

to 100% for ammonia conversion to nitrate. 

Advantages of biological treatment include low reagent costs compared to other cyanide

destruction methods, all forms of cyanide, cyanide complexes, and ammonia are treated, and

metals may be removed. Disadvantages include limited application, and process performance is 

effected by temperature. In addition, although the process can result in the removal of cyanide

to the ppb level, influent cyanide levels may need to be reduced, due to toxic effects of cyanide

on biological systems.

5.2.5 Natural Degradation

Cyanide in mine wastewaters will naturally degrade through volatilization, oxidation, 

photodecomposition, precipitation, hydrolysis, and adsorption to solids. Factors that affect

degradation include cyanide speciation and concentration, temperature, pH, sunlight, bacteria,

aeration, and pond conditions (Scott, 1985). Simovic et al. (1995) found that volatilization and

metallo-cyanide decay were the most important degradation mechanisms and that temperature,

UV light, and aeration were the key factors in the degradation process. Volatilization typically

occurs more rapidly than metal complex degradation. 

Historically, natural degradation in tailings ponds was the most common method for

cyanide removal. Currently, natural degradation may be used where tailings pond water is

recycled, but it is likely not suitable for tailings ponds that discharge. A major difficulty of

natural degradation is that operators cannot control the time required for cyanide destruction. 

Furthermore, natural degradation may not achieve the detoxification levels now required by

regulatory agencies (often 0.2 ppm WAD cyanide). Results of studies completed to date have

shown widely varied cyanide reductions. Simovic et al. (1985) developed a model to determine

natural cyanide degradation in gold mill effluents and indicated that total cyanide levels could be
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reduced to 1-10 ppm (WAD cyanide removals were not provided). Scott (1985), generally found

that natural degradation could reduce WAD cyanide levels to 0.42 - 42 ppm (depending on

influent concentration). Several Canadian mines have designed tailings ponds to enhance the

natural degradation processes. For example, at the Lupin Mine in Canada, Echo Bay Mines uses

natural degradation as the only treatment method. In 1991, average total cyanide concentrations

in untreated tailings at this site were reduced from 166 mg/l to 0.019 mg/l in the effluent. 

However, the retention time in the tailings impoundments is two years (EPA, 1994).

5.3 Solid-Liquid Separation

Solid-liquid separation is required after most of the metals treatment and cyanide

destruction processes. For example, after metals in the wastewater have been precipitated (e.g.,

as metal hydroxides or metal sulfides), they must be removed from the wastewater prior to

discharge or recycle/reuse. The separation of these solids occurs through a combination of

flocculation, settling, and, if necessary, filtration. Flocculation, settling, and filtration are widely

used technologies in wastewater treatment. A thorough discussion of these technologies can be

found in Metcalf and Eddy, Inc. (1979). The following briefly summarizes these three steps: 

(1) coagulation (the reduction of electrically repulsive forces on a particle’s surface) and

flocculation (the agglomeration of particles through adsorption);

(2) gravity separation (settling); and

(3) filtration.

In the first step, chemical coagulants are added to the wastewater under controlled

conditions of concentration, pH, mixing time, and temperature. Precipitated metal compounds

adsorb onto the coagulant and agglomerate to form flocs. Agglomeration increases the effective

diameter of the metal particles, which increases their settling rate. Since particle agglomeration

is induced by particle contact, flocculation generally occurs through mechanical mixing. After

agglomeration, the flocs are pumped to a clarifier, where an appropriate time is permitted for

settling (step 2). The particles settling within the clarifier produce an underflow sludge that must

be removed for additional treatment or disposal (see Section 5.4). Alternately settling may occur

in a pond or series of ponds.

 A common approach currently being applied at mine sites is the high-density sludge

(HDS) process. The HDS process is similar to conventional lime neutralization and settling

process, however, a portion of the settled solids in the clarifier is recycled back to the

precipitation cell where the sludge is again mixed with lime. Mixing of recycled sludge and lime

yields a high density sludge consisting of relatively large particles that settle quickly. The HDS

process has two advantages over conventional lime treatment and settling. First, recycling

sludge increases the sludge density which, in turn, results in a significant reduction in the volume

of sludge requiring dewatering and disposal. Second, the recirculated sludge results in

additional precipitation and adsorption reactions which increase metals removal efficiency. 

To further enhance the removal of metals from wastewater, a third step, filtration, is

applied if necessary to meet effluent discharge limits. Filtration removes fine particles that lack
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sufficient size to settle effectively. Over time, solids will build up on the filter necessitating the

removal of accumulated solids. The removal process, termed backwashing, may be done on a

batch or continuous basis, depending on the design of the filter.

Early filters used sand as a filter medium and operated in a down-flow mode. That is,

water flowed down through a sand bed to an underdrain system which collected the filtered

water. Backwashing was accomplished on a batch basis by forcing water upwards from the

bottom of the filter, with the filter off-line, with the accumulated material allowed to overflow

the filter surface. Newer filters may operate in the upflow mode, with accumulated material

removed on a continuous or semi-continuous basis. Newer filters also may contain two or more

filtration materials (e.g., anthracite coal and garnet sand) which, through density differences,

classify into distinct layers. Each of these media layers provides a different level of porosity,

allowing filtration to occur throughout the filter rather than just on the surface. This provides a

greater storage capacity for removed materials, allowing longer runs between backwashing. 

Sand filters are less expensive to construct, but media filters are capable of removing smaller

size particles. Determination of which filtration type, if any, is needed at a particular mining site

will be based on the characteristics of the wastewater and the effluent discharge limits that apply. 

Filtration has not been widely applied to date at mining facilities but may need to be considered

in the future to meet low effluent limits based on water quality criteria. The Red Dog Mine

(AK), for example currently uses sand filtration prior to discharge from one of its’ two treatment

plants. In Leadville, Colorado, sand filtration is used in a high density sludge process to treat

effluent from historic workings.

5.4 Sludge Removal

Chemical coagulation/precipitation systems produce a sludge that requires management. 

Waste sludge removed from clarifiers is a liquid typically ranging from 10 to 20 percent solids in

suspension. Disposal will usually require some degree of dewatering. The most common

methods of dewatering are belt filter presses or plate and frame filter presses. Mechanical sludge

dewatering is not generally practiced in the mining industry since sludges are generally disposed

of in tailings ponds. Other options for sludge disposal include backfill into mine voids and

disposal in an appropriate landfill.

Selection of sludge management techniques depends upon the volume and composition

of the sludge and regulatory requirements. Sludge composition is dominated by the coagulant

added to the system (e.g., lime), but will also reflect the metals and other insoluble constituents

removed from the wastewater. The stability of metals in the sludge depends on the pH of the

sludge remaining high. Disposal into a tailings impoundment may not be advisable since the

more neutral pH conditions of the impoundment may cause metals to redissolve into supernatant

waters.

Unlike many other wastes from extraction and beneficiation operations, sludges

generated from wastewater treatment at mines are not exempt from regulation under Subtitle C

of the Resource Conservation and Recovery Act (RCRA). Mine operators that generate sludges

that exhibit hazardous waste criteria should exercise care in co-management with exempt wastes
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including tailings; such co-management could cause entire units to become hazardous waste

management facilities. These issues can also arise from the use of sludge as a source of

hydroxide in processing operations. States may further regulate treatment sludges differently

from other mining wastes. Treatment sludge may need to be managed at a permitted hazardous

waste disposal facility. 

Mine operators need to provide data on the expected volumes and chemical and physical

characteristics of wastewater treatment sludges, including whether they will exhibit hazardous

waste characteristics. Appendix C, Characterization of Ore, Waste Rock and Tailings, provides

information on approaches to waste characterization. Operators should also describe proposed

management practices, including potential impacts associated with co-management scenarios.

6.0 PASSIVE TREATMENT OF MINING WASTEWATERS

Passive water quality treatment is being viewed increasingly as a viable option for the

post-closure environment at metal mining sites (Miller, 1996) and has recently been put into

operation at an active lead-zinc mine (Gusek et al., 1998). Passive systems achieve improved

water quality through a variety of physical, chemical, and biological processes that include

acidity reduction and concomitant alkalinity increase (either by bicarbonate addition, sulfate

reduction, ferric iron reduction, or a combination), metals removal (by hydroxide or oxide

precipitation , plant uptake, sorption onto organic materials, or sulfide precipitation), and sulfate

reduction (by microbial action or gypsum precipitation). Studies of natural wetlands systems

receiving neutral to acidic metal mine drainage with high metals values have been useful for

understanding how passive systems function. Studies of natural wetlands in Colorado and

Minnesota found that they removed iron, chromium, cobalt, copper, nickel, and zinc with

varying efficiency that depended on influent water quality, residence time, water temperature,

the distribution of flow within the wetland cells, sorptive capacity of the peat, and depth of

removal (Eger et al.,1993; Balistrieri, 1995; Walton-Day, 1996). 

 Passive treatment systems do not require routine maintenance, energy supply, or backup systems

and are more cost-effective to operate over long time periods. However, they are sensitive to

seasonal fluctuations (e.g., cold temperatures, increased loadings caused by increased

precipitation) and may be unable to consistently achieve low effluent limits. The next section

briefly describes three of the technologies most commonly used at metal mines: aerobic

wetlands, anaerobic wetlands/bioreactors, and anoxic limestone drains. 

6.1 Commonly Used Technologies

Constructed wetlands were initially designed as simple, rather empirical structures that

outwardly mimicked natural systems (Skousen et al., 1994). Recently constructed wetlands have

complex designs intended to produce specific chemical effects at each step of the treatment

process (e.g., Brodie, 1993; Cambridge, 1995; Wildeman and Updegraff, 1997). Flow rates,

residence times, redox conditions, cation-exchange capacities, alkalinity production, and metal

uptake in the wetlands are controlled by wetland size, flow path, substrate composition, and
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vegetation type (Wildeman et al., 1993). Substrate compositions vary widely among constructed

wetlands; several authors (e.g., Brodie et al., 1988; Howard et al., 1989; Gross et al., 1993) have

evaluated substrate performance. Limestone is commonly used as a substrate below the organic

matter to add alkalinity. Commonly used plants include cattails (Typha spp.; the most widely

used wetland plant), Sphagnum, bulrushes (Scirpus spp.), sedge (Carex spp.), and algae

(Cladophora). Most plants are relatively tolerant of high metal concentrations and acidity but

they vary in their ability to accumulate or take up metals from wetland waters and sediments

(e.g., Duggan et al., 1992; Sengupta, 1993; Garbutt et al., 1994; Erickson et al., 1996). An

important effect of wetland plants is their ability to stimulate microbial processes, add oxygen,

raise pH, and supply organic nutrients (Kleinmann, 1991; Wildeman and Updegraff, 1997).

Aerobic wetlands systems utilize oxidizing reactions to precipitate manganese and iron

oxyhydroxides that sorb selenium and arsenic from influent waters (Gusek, 1995; Wildeman and

Updegraff, 1997). These systems, which also can be used to remove WAD cyanide, operate

most effectively when influent pH exceeds about 5.5. 

Anaerobic wetlands and bioreactors (facilities that have a cap precluding oxygen

infiltration) use bacterially mediated sulfate reduction to precipitate iron, copper, lead, zinc,

cadmium, and nickel as sulfide minerals and to reduce uranium and radium to insoluble forms

(Gusek, 1995; Wildeman and Updegraff, 1997). Bacterial action has the added benefit of raising

pH by producing bicarbonate alkalinity. Anaerobic systems can function with influent pH levels

of less than 2.5.

Anoxic limestone drains (ALD) are used to intercept ground water and direct it through a

buried bed of limestone. In recent years, ALDs have been widely used to pre-treat AMD prior to

anaerobic wetlands treatment in order to add alkalinity in the form of bicarbonate (HCO3

-

) that

improves effluent quality and extends the effective life of wetlands treatment. Their intent is to

add sufficient alkalinity so that effluent waters do not re-acidify upon aeration and ferric iron

hydrolysis. In theory, the anoxic conditions maintained in an ALD permit dissolution of

limestone without concomitant armoring by sulfates or metal hydroxides (Skousen, 1991). In

practice, however, aluminum hydroxide and gypsum (calcium sulfate) may precipitate and

eventually clog the drain (Skousen, 1991; Ziemkiewicz et al., 1994), forcing influent water to

flow over the drain and escape treatment. Consequently, flow rates need to be high enough to

flush precipitating minerals through the drain. The effectiveness of an ALD as a passive

treatment option depends on influent water quality (Skousen, 1991; Brodie et al., 1993). ALDs

function most efficiently when influent waters have moderate to low dissolved oxygen contents

(<2 mg/L), low ferric/ferrous iron ratios, dissolved aluminum concentrations less than 25 mg/L,

and sulfate concentrations less than 2,000 mg/L (Hedin and Watzlaf, 1994; Ziemkiewicz et al.,

1994). 

6.2 Passive System Design

Important design factors for passive treatment systems include hydraulics (flow rate, flow

path, and residence time), longevity of the carbon source, rate of supply of carbon, temperature,

and metals load. Wetland size and treatment components are determined from the influent flow,
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water chemistry, and calculated loadings (Hedin and Nairn, 1992). Sizing criteria for wetlands

constructed at eastern coal mines were developed by Hedin et al. (1994) and Hellier et al. (1994). 

Their values should be used as a minimum guideline for passive treatment systems that would be

constructed at higher elevations (such as at many metal mines in the western U.S.) where

biological and chemical processes are likely to operate at slower rates (Sengupta, 1993). Mean

annual temperature and seasonal temperature variations are other factors that affect the

efficiency of a passive treatment system by influencing bacterial activity and wetland plant

growth.

The carbon source and its replenishment are particularly important since carbon is a vital

nutrient required to maintain bacterial populations in anaerobic systems. In general, anaerobic

cells have a projected life of 20 to 100 years, after which the organic substrate will need to be

replaced. Anoxic limestone drains have a projected life of 30 years before limestone

replacement. At present, it is unclear how long aerobic cells will function properly; however,

depending on metal loads, mineral precipitation may require replacement of substrate materials. 

Consequently, passive treatment is not a “walk away” technology that will work as designed in

perpetuity. Despite their high front-end costs, the low maintenance costs (primarily periodic

sampling and substrate replacement) makes them an attractive post-closure option. Passive

wetlands systems also have the potential to provide habitat, however, the environmental impact

of such habitat must be evaluated (e.g., to demonstrate that terrestrial and aquatic animals

inhabiting the wetlands will not bioaccumlate metals).

6.3 Example Passive Systems at Metal Mines

 Passive systems can be designed to treat runoff and seepage from waste rock dumps,

tailings piles, and spent ore heaps, and drainage from adits and historic mine facilities. The

technology was developed to treat acidic waters generated from abandoned coal mines in the

eastern U.S. and has gained widespread acceptance for this application (more than 600 passive

systems were constructed and operating in 1996; Gusek, 1998b). Metals levels in the low parts

per million or high parts per billion range are typically achieved. At coal mines, acidic waters

contain high concentrations of sulfate, aluminum, iron, and manganese, but few other metals. 

Only recently has passive treatment technology been used to treat acidic to neutral waters

draining from metal mining sites. These technological applications are still under development. 

In addition to high concentrations of TDS and sulfate, metal mine waters may contain a variety

of metals in moderate to high concentrations. The presence of numerous trace metals

complicates the geochemical system design.

Several examples of the use of passive systems at mine sites is shown in Table E-2. In

addition to the facilities shown in Table E-2, passive treatment is being employed at several

other inactive or historic sites described in the references of the previous two sections. The

mines in Table E-2 and referenced in the previous sections represent historic sites and ongoing

remediation projects. The only active mine that EPA is aware of that is using passive treatment

to meet NPDES permit effluent limits is the West Fork Mine in Missouri. Overall, a major

challenge to using passive systems is maintaining system performance, at all times, and under all

operating conditions. At present, passive systems appear to be a viable alternative only under
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limited conditions or when used in combination with other treatment approaches.

Table E-2. Example Passive Treatment Facilities at Metal Mines

Mine Influent Characteristics Passive

Technologies Used

Effluent

Characteristics

Wheal Jane, UK

Underground Sn-Cu

Inactive

3,500 gpm, pH = 3.8; Cd =

0.006 mg/L; Cu = 1.05

mg/L; Zn = 3.1 mg/L

Anaerobic cell ! ALD

! Aerobic Cell !

Anaerobic Cell !

Rock Filter

Not available.

West Fork, MO

Underground Pb- Zn

Active

1,200 gpm, pH = 7.9; Pb =

0.4 mg/L; Zn = 0.36 mg/L;

Cu = 0.037 mg/L

Settling Pond !

Anaerobic Cell !

Rock Filter !

Aeration Pond

pH = 7.2; Pb =

0.04 mg/L; Zn =

0.07 mg/L; Cu =

<0.008 mg/L. 

Ferris-Haggarty, WY

Underground Cu

Abandoned

20 to 480 gpm; pH = 4 to

7; Cu =2.0 to 6.5 mg/L;

Significant seasonal

variations.

Pilot Anaerobic Test

Cell

pH = neutral; Cu =

0.05 mg/L.

Sources: Wheal Jane: Cambridge, 1995; West Fork: Gusek et al., 1998a; Ferris Haggarty: Reisinger

and Gusek, 1998.

7.0 TREATABILITY TESTING

Each individual mining wastewater is a unique blend of metals, hardness, pH, TDS, and

trace components. Under actual production conditions, the composition will continually vary to

at least some degree. The complexity of the wastewater matrix limits the extent to which 

experience (e.g., treatment effectiveness) gained at one facility can be directly applied to

another. 

Although theoretical chemistry may indicate how a specific waste can be treated, the

complex matrix that exists at a specific site may limit the applicability of theoretical data to

actual conditions. Consequently, a treatability study is required prior to treatment system

design. Prior to treatment system selection and design it is essential to characterize the

wastewater and identify desired effluent quality (treatment goals). It is critical that wastewater

characterization and wastewater samples utilized in treatability studies are representative of the

range of operating conditions that will occur during the life of the mine and/or after closure. 

Also, a site-specific analysis showing that the treatment system is capable of consistently

meeting regulatory or permit limits under the range of operating conditions is needed for NEPA

analysis and permitting. Appendix C, Characterization of Ore, Waste Rock and Tailings and

Appendix D, Effluent Quality provided additional details on waste/ wastewater characterization.

The use of laboratory and pilot-scale treatability testing is necessary to select a

process(es) that will consistently meet treatment goals. Treatability testing provides valuable
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design data that can reduce capital investment, ensure greater reliability, and minimize operating

costs. It has the further benefit of expediting the regulatory permitting process by providing

assurance to the regulators that the proposed treatment system will meet environmental quality

objectives.

Treatability studies may range from laboratory bench-scale tests, involving the batch tests

of samples less than a liter in size, to field-scale pilot tests conducted at flow rates of a million

gallons per day. As a rule of thumb, design data from a test system can only be scaled up by a

factor of 10 to 20. Thus, the use of several test systems of progressively larger size may be

required to ensure the validity of a full-scale design.

In certain situations, more extensive testing would be required beyond that typical of

either laboratory or pilot-scale testing. Those situations can include:

C where innovative treatment technologies are proposed (e.g., biological treatment,

passive treatment)

C where site conditions are extreme (e.g., extreme variations in wastewater flow due to

precipitation, cold temperatures)

C where treatment goals are different than is normally practiced for the technology

(e.g., effluent limits are very low).

7.1 Laboratory Testing

Treatability testing is necessary for all stages of a treatment train (e.g., the

chemical/biological treatment stage, the clarification and settling stage, filtration, and sludge

characteristics). Laboratory-scale testing is most useful for screening different treatment

processes. Laboratory testing is usually done on samples shipped directly to the laboratory. 

Samples may be obtained from the mine site, in the case of mine drainage or site runoff, or from

mining process design studies conducted to evaluate milling or extraction processes. Laboratory

testing can be done through bench-scale batch tests, or by continuous flow-through tests. 

Selection of a test type depends on the goals of the test. Batch tests are less expensive and

quicker to conduct, but may provide less realistic results than flow-through tests.

Bench-scale tests typically are conducted using sample volumes of 1 liter or less. These

studies can be performed quickly and relatively inexpensively. Such tests are often used to

screen different treatment methods over a range of wastewater compositions and test conditions

(e.g., varying pH, reagent dosages, etc.). Use of different materials in the tests versus at the

mine may cause discrepancies. For instance, because filtration through membrane or paper

filters is typically used to represent the effects of full-scale clarification, bench-scale tests may

overestimate the efficiency of full-scale clarification.

Continuous flow-through tests typically are done at flow rates measured in milliliters per

minute. Cyanide destruction chemistry can be effectively evaluated in studies of this type. 

Testing time may range from hours to days. Continuous flow-through tests are useful to

estimate reaction times that are more representative of full-scale performance than batch tests.
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7.2 Pilot-Scale Testing

Pilot-scale tests are useful for optimizing the most promising treatment processes that are

identified in laboratory-scale testing. Pilot-scale tests may or may not be conducted on-site,

depending on the objectives of the test. The best place for conducting initial optimization pilotscale tests might be concurrent with the pilot-scale metallurgical testing 

Pilot-scale tests require large volumes of wastewater—flow rates may range from 5 gpm

to 100 gpm or more. Studies are typically conducted for periods of a month to as long as a year

depending upon the treatment process being tested. The capital cost for test equipment is

significantly greater than lab-scale testing, although in some cases test units may be leased from

equipment suppliers. Conducting tests outdoors will allow for the influence of ambient

temperature variations to be evaluated, although it should be noted that above grade, steel units

may be more susceptible to freezing than permanent, in-ground tankage.

At the pilot-scale, clarifiers and filters will perform more like full-scale units. Wind

effects on exposed pilot-scale clarifiers will be more representative of full-scale units, although

they may be magnified by the smaller scale. Reaction kinetics will approximate full-scale

performance. Considerations for designing a pilot plant testing program are shown in Table E-3.

Table E-3. Pilot-Scale Treatment Design

Setting Up A Pilot Testing Program

1. Clearly identify the objectives of the study. If there are multiple

objectives, separate the program into phases of study.

2. Identify the parameters to be analyzed for the experiment. For

parameters such as metals that may be present in both soluble and

colloidal forms, always run both total and dissolved forms. Collect

all samples needed for system evaluation. If the workload or

analytical costs are excessive, do all tests, but less frequently.

3. Replicate feed conditions (i.e., temperature, pH, variations in

composition, etc.) as closely as possible. Evaluate the test until

under the range of flow loadings that are expected under full-scale

operation.

4. Understand the dependence of the prime study unit on ancillary

equipment performance. Failure to destroy cyanide will impair the

performance of coagulation systems. Incomplete pretreatment of

ion exchange or reverse osmosis feed water my impact

performance due to clogging of the test unit.

5. Operate the pilot facility for a sufficient period to determine the

variability of the parameters studied.
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Appendix E: Wastewater Management

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8.0 WASTEWATER DISPOSAL

The following subsections describe several alternatives for disposal of wastewaters. 

Depending upon environmental and regulatory concerns, wastewater may require some level of 

treatment in conjunction using these practices.

8.1 Surface Water Discharge

Depending upon the site water balance and regulatory constraints, a mine may propose to

discharge wastewater to a nearby water body. Discharge of wastewater to waters of the U.S. is

regulated under the NPDES program. The main text of the Source Book, Appendix B -

Receiving Waters, and Appendix D - Effluent Quality describe the NPDES program and

information related to their proposed surface water discharges that mine proponents must collect

to fulfill NPDES permitting requirements. In general the following information related to

surface water discharges should be provided to the regulatory agencies for NEPA analyses and

permitting decisions:

• Characterization of effluent discharge flow and quality over range of proposed

operating conditions and closure (see Appendix D). 

• Description of water balance over range of operating conditions and closure (see

Appendix A).

• Description of any wastewater treatment and ability of the treatment to achieve

treatment goals (effluent limits) over the range of effluent variability (see Section 7).

• Description of outfall location and wastewater discharge system (e.g., pipeline,

diffuser, etc.)

• Characterization of receiving water flow and quality, including seasonal variations

(see Appendix B).

• Projected impacts on surface water resources (see Appendix B and Appendix G).

• Monitoring plans for the receiving water and effluent.

8.2 Land Application

An alternative to wastewater treatment and direct discharge to surface water is land

application. Land application of mining wastewaters is not generally subject to Federal

regulation. However, States may have specific permitting requirements for these activities,

including protecting ground water resources. The appropriate State agency should be contacted

to determine data needs for land application permitting. 

In the mining industry, land application is most commonly used for spent cyanide leach

solutions. Such solutions are typically neutralized prior to application. If land application is not

properly accomplished, it can pose threats to surrounding ground and surface water resources. In

general, land application will be governed by the agronomic uptake, and this information should

be available through agricultural support agencies. 

If a mine operator proposes to use land application as a water management method, the
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Appendix E: Wastewater Management

E-22 January 2003

following information should be provided for NEPA analyses and permitting:

• Expected composition data for the wastewater proposed for land application 

• Proposed schedule for land application (e.g., seasonal, climate, or soil moisture

limits)

• Land application procedures and rates (relative to agronomic uptake rates)

• Climatic data (precipitation and evapotranspiration rates)

• Area and topography of the land application site

• Chemical and physical soil characteristics, particularly infiltration rates and cation

exchange capacity

• Proximity to surface water

• Depth to and characteristics of underlying ground water resources,

• Specific BMPs to avoid ponding and overland flow

• Projected impacts on ground water quality (and any potential indirect effects on

surface water),

• Wastewater and ground water monitoring plan (e.g., using lysimeters) that will

demonstrate compliance with regulations and enable early detection of any adverse

impacts and corrective actions.

It is essential to have an accurate water balance for the site (see Appendix A, Hydrology),

including understanding precipitation versus evaporation versus infiltration rates. Mine

operators should project the potential effects on ground water quality and surface water

resources, taking into account any assumptions related to soil adsorption or other attenuation, for

the full range of operating conditions anticipated.

8.3 Evaporation/Infiltration

Infiltration and/or evaporation basins can be used to avoid or minimize direct surface

water discharges. Successful use of such basins depends on wastewater volume, facility design

and determining an accurate water balance. Any measures used to promote infiltration (bottom

materials) or evaporation (spraying/misting) should be specifically described along with

predications as to evaporation and infiltration rates. Operators must demonstrate the ability to

maintain sufficient freeboard in basins under all operating and climatic conditions. Facilities

proposing to use these basins need to predict potential direct impacts on underlying ground water

and any possible indirect effects on surface water through recharge. Operational and

environmental monitoring plans should allow for early detection of effects and corrective

actions.

8.4 Underground Injection

Another alternative for wastewater disposal is underground injection. Underground

injection can eliminate the need for direct discharge to surface water. However, this practice

poses potential risks to underlying ground water quality. At the Federal level, injection of

wastewater from mining operations is regulated under the Underground Injection Control (UIC)

Program of the Safe Drinking Water Act. As Class V wells, injection operations do not require
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Appendix E: Wastewater Management

E-23 January 2003

individual permits. However, operators typically must demonstrate compliance with drinking

water standards for wells that could be used as drinking water sources. This may require water

treatment prior to injection. In addition, states generally have regulations and permitting

requirements that address ground water protection. Mine operators proposing to use underground

injection should provide the following information:

• Expected composition and volume of wastewater to be injected,

• Ground water characterization (aquifer delineation, composition of aquifer material,

flow rate, direction, porosity, conductivity, water quality, and uses),

• Storage capacity and transmisitivity of the aquifer,

• Well construction (depth, construction materials, and QA/QC),

• Injection methods (volumes and timing), and

• Projected impacts on ground water quality (and any potential indirect effects on

surface water).

• Wastewater and ground water monitoring plan that will demonstrate compliance with

regulations and enable early detection of any adverse impacts and corrective actions.

It is essential that the aquifer have sufficient capacity to receive the injected water (to

avoid upwellings). In addition, operators must demonstrate proper construction methods and

quality assurance. A particular concern associated with recently permitted underground

injection at the Pogo Mine in Alaska was potential effects on permafrost. Operators should also

ensure that injected waters are compatible with aquifer materials. For example, it would not

generally be appropriate to inject acidic waste into a limestone formation.

9.0 STORM WATER MANAGEMENT AND BEST MANAGEMENT PRACTICES

Storm water control and best management practices (BMPs) provide alternatives that can

reduce or eliminate the need for wastewater treatment and discharge. A primary goal of BMPs is

to prevent or minimize the generation and the potential for release of pollutants from industrial

facilities to waters of the U.S. This may be accomplished by minimizing the contact between

water and potential pollutant sources. For example, Section 6 of Appendix H, Erosion and

Sedimentation, describes some BMPs for erosion control. While these are primarily related to

sedimentation, many also apply to preventing contamination from other pollutants. Other BMPs

should be utilized for spill prevention, proper management of chemicals, proper management of

solid wastes, etc. EPA has published several guidance manuals on storm water management,

development of pollution prevention plans, and BMPs, including:

• Storm Water Management for Industrial Activities - Developing Pollution Prevention

Plans and Best Management Practices. 1992. EPA No. 833-R-92-002.

• Storm Water Management for Construction Activities - Developing Pollution

Prevention Plans and Best Management Practices. 1992. EPA No. 833-R2-92-001

• Guidance Manual for Developing Best Management Practices (BMP). 1993. EPA
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Appendix E: Wastewater Management

E-24 January 2003

No. 833-B-93-004.8

Some states have also developed BMP guidance documents. For example, the Idaho

Department of State Lands published Manual for Best Management Practices for the Mining

Industry in Idaho, November 1992.

Mine operators should describe the types of BMPs to be used for wastewater and storm

water management, their design and predicted effectiveness, how they will be maintained

throughout the life of the project, and measures to monitor their actual performance. As

discussed in Section 2 of the Source Book, general and individual NPDES permits for storm

water discharges typically require development and implementation of BMP plans and/or storm

water pollution prevention plans. In addition, process water NPDES permits may include

specific BMP requirements and/or require preparation of BMP plans.

10.0 WASTEWATER MANAGEMENT KEY ISSUES

This Appendix has summarized alternatives for wastewater management and disposal,

including treatment and other options. Key issues emphasized related to wastewater

management include:

• Every attempt should be made to minimize wastewater generation and the need for

discharge. Mine proponents will need to demonstrate that proposed wastewater

management practices will limit environmental impacts and meet all applicable

regulatory requirements. 

• Estimated wastewater volumes must be based on an accurate site water balance (see

Appendix A, Hydrology). Wastewater volume and composition needs to be projected

under all operational and climatic conditions (see Appendix C, Characterization of

Ore, Waste Rock and Tailings and Appendix D, Effluent Quality). 

• All assumptions related to pollutant removal through treatment need to be supported

through proven performance at other mines and industrial facilities and treatability

studies. Operators must specifically demonstrate that any proposed wastewater

discharges will not cause exceedances of applicable surface water quality standards,

see Section 2.0 of the Source Book and Appendix B, Receiving Waters. 

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