Acid Mine Drainage and Effects on 

Fish Health and Ecology: A Review 

  

For: 

 U.S. Fish and Wildlife Service, Anchorage Fish and Wildlife Field Office, 

Anchorage, Alaska, 99501 

Prepared by: 

Reclamation Research Group, LLC, Bozeman, Montana 

June 2008 

Suggested Citation: Jennings, S.R., Neuman, D.R. and Blicker, P.S. (2008). “Acid Mine Drainage and Effects on Fish 

Health and Ecology: A Review”. Reclamation Research Group Publication, Bozeman, MT. 
ii 
iii 

Table of Contents

Purpose ................................................................................................................................ 1

Acid Mine Drainage Overview ........................................................................................... 1

Chemistry of Acid Rock Drainage .................................................................................. 1

Acid Mine Drainage ........................................................................................................ 3

Effect of Acid Mine Drainage on Aquatic Resources ........................................................ 5

Major Environmental Incidents Caused by Acid Mine Drainage ....................................... 7

Prediction of Acid Mine Drainage ...................................................................................... 7

Assessment of Acid Rock Drainage and Metals Release ................................................. 11

Water Quality and Acid Mine Drainage: Pre-mine Predictions and Post-mine 

Comparisons ..................................................................................................................... 13

Factors Leading to Failures in Predicting Post-Mine Water Quality and Acid Mine 

Drainage ............................................................................................................................ 14

Treatment of Acid Mine Drainage .................................................................................... 16

Recommendations for Acidic Drainage Minimization ..................................................... 16

Summary ........................................................................................................................... 19

References and Literature Cited ........................................................................................ 20
1 

Purpose

In Alaska, several large mine projects are currently proposed, ranging from open-pit, hard 

rock mines to strip mines for extracting coal. These large-scale projects have the potential 

to impact fish and wildlife resources through alteration or removal of vast areas of 

habitat. The U.S. Fish and Wildlife Service (Service) is responsible for managing fish and 

wildlife resources for the American public and in carrying out its mission, participates in 

pre-development activities for industrial projects. This report was commissioned to 

provide information to the Conservation Planning Assistance branch of the Anchorage 

Fish and Wildlife Field Office to aid in review of documents required as part of the 

permit process with the U.S. Environmental Protection Agency (EPA), U.S. Army Corps 

of Engineers and the State of Alaska. 

Acid Mine Drainage Overview

Acid rock drainage (ARD) is produced by the oxidation of sulfide minerals, chiefly iron 

pyrite or iron disulfide (FeS2). This is a natural chemical reaction which can proceed 

when minerals are exposed to air and water. Acidic drainage is found around the world 

both as a result of naturally occurring processes and activities associated with land 

disturbances, such as highway construction and mining where acid-forming minerals are 

exposed at the surface of the earth. These acidic conditions can cause metals in geologic 

materials to dissolve, which can lead to impairment of water quality when acidic and 

metal laden discharges enter waters used by terrestrial or aquatic organisms. 

Chemistry of Acid Rock Drainage

The reaction of pyrite with oxygen and water produces a solution of ferrous sulfate and 

sulfuric acid. Ferrous iron can further be oxidized producing additional acidity. Iron and 

sulfur oxidizing bacteria are known to catalyze these reactions at low pH thereby 

increasing the rate of reaction by several orders of magnitude (Nordstrom and Southam 

1997). In undisturbed natural systems, this oxidation process occurs at slow rates over 

geologic time periods. When pyrite is exposed to oxygen and water it is oxidized, 

resulting in hydrogen ion release - acidity, sulfate ions, and soluble metal ions as shown 

in equation 1. The acidity of water is typically expressed as pH or the logarithmic 

concentration of hydrogen ion concentration in water such that a pH of 6 has ten times 

the hydrogen ion content of neutral pH 7 water. 
2 

2FeS2 (s) + 7O2

 + 2H2O –> 2Fe

+2 

+ 4SO4

-2 

+ 4H+ (1) 

Further oxidation of Fe

+2 

(ferrous iron) to Fe

+3 

(ferric iron) occurs when sufficient oxygen 

is dissolved in the water or when the water is exposed to sufficient atmospheric oxygen 

(equation 2). 

2Fe

+2 

+ 1⁄2 O2 + 2H+ –> 2Fe

+3 

+ H2O (2) 

Ferric iron can either precipitate as Fe(OH)3 , a red-orange precipitate seen in waters 

affected by acid rock drainage, or it can react directly with pyrite to produce more ferrous 

iron and acidity as shown in equations 3 and 4. 

2Fe

+3 

+ 6H2O <–> 2Fe(OH)3 (s) + 6H+ (3) 

14Fe+3 + FeS2 (s) + 8H2O –> 2SO4

-2 + 15Fe+2 + 16H+

 (4) 

When ferrous iron is produced (equation 4) and sufficient dissolved oxygen is present the 

cycle of reactions 2 and 3 is perpetuated (Younger, et al., 2002). Without dissolved 

oxygen equation 4 will continue to completion and water will show elevated levels of 

ferrous iron (Younger, et al., 2002). The rates of chemical reactions (equations 2, 3, and 

4) can be significantly accelerated by bacteria, specifically Thiobacillus ferrooxidans. 

Another microbe, Ferroplasma Acidarmanus, has been identified in the production of 

acidity in mine waters (McGuire et al. 2001) 

Hydrolysis reactions of many common metals also form precipitates and in doing so 

generate H+

. These reactions commonly occur where mixing of acidic waters with 
3 

substantial dissolved metals blend with cleaner waters resulting in precipitation of metal 

hydroxides on stream channel substrates (Equations 5 through 8). 

Al+3 + 3H2O <–> Al(OH)3(s) + 3H+ (5) 

Fe

+3 

+ 3H2O <–> Fe(OH)3(s) + 3H+  (6) 

Fe

+2 

+ 0.25 O2 + 2.5 H2O <–> Fe(OH)3(s) + 2H+  (7) 

Mn

+2 

+ 0.25 O2 + 2.5 H2O <–> Mn(OH)3(s) + 2H+ (8) 

Metal sulfide minerals in addition to pyrite may be associated with economic mineral 

deposits and some of these minerals may also produce acidity and SO4

-2. Oxidation and 

hydrolysis of metal sulfide minerals pyrrhotite (Fe1-xS), chalcopyrite (CuFeS2), sphalerite 

((Zn, Fe)S) and others release metals such as zinc, lead, nickel, and copper into solution 

n addition to acidity and SO4

-2 i (Jennings et al., 2000; Younger et al., 2002). 

Acid Mine Drainage

Acid rock drainage occurs when sulfide ores are exposed to the atmosphere, which can be 

enhanced through mining and milling processes where oxidation reactions are initiated. 

Mining increases the exposed surface area of sulfur-bearing rocks allowing for excess 

acid generation beyond natural buffering capabilities found in host rock and water 

resources. Collectively the generation of acidity from sulfide weathering is termed Acid 

Mine Drainage (AMD).1

 Mine tailings and waste rock, having much greater surface area 

than in-place geologic material due to their smaller grain size, are more prone to 

 

1

 As this literature review is focused on mining, the term AMD will be used in the text, yet rocks found in 

undisturbed environments are similarly able to generate acidity (or ARD) without the anthropogenic 

influence of mining. The term Mine Influence Water is also synonymous. 
4 

 

generating AMD. Since large masses of sulfide minerals are exposed quickly during the 

mining and milling processes, the surrounding environment can often not attenuate the 

resulting low pH conditions. Metals that were once part of the host rock are solubilized 

and exacerbate the deleterious effect of low pH on terrestrial and aquatic receptors. 

Concentrations of common elements such as Cu, Zn, Al, Fe and Mn all dramatically 

increase in waters with low pH. Logarithmic increases in metal levels in waters from 

sulfide-rich mining environments are common where surface or groundwater pH is 

depressed by acid generation from sulfide minerals.2

 These environmental, human health, 

and fiscal consequences, if not mitigated, can have long-lasting effects. Acid mine 

drainage continues to emanate from mines in Europe established during the Roman 

Empire prior to 467 AD (CSS, 2002). Georgius Agricola’s De Re Metallica (1556), the 

first and seminal treatise on mining exhibits detailed woodcut illustrations not only of the 

known mechanics of 16th Century mining, but also depictions of the devastation of 

streams. The cost of mitigation of environmental damage from acid mine drainage is 

great. The U.S. Forest Service (USFS) estimates that between 20,000 to 50,000 mines are 

currently generating acid on lands managed by that agency; with negative impacts from 

these mines affecting some 8,000 to 16,000 km of streams (USDA, Forest Service 1993). 

Many of these mines are small abandoned facilities located in remote areas of the western 

United States and originating prior to modern environmental controls. However, several 

large scale mines developed in the latter half of the twentieth century have declared 

bankruptcy and left tax payers with the responsibility of treating acid waters in 

perpetuity. Examples include the Zortman Landusky Mine in Montana, the Summitville 

Mine in Colorado, and the Brohm Mine in South Dakota. The largest and most expensive 

sites that EPA has listed under the Comprehensive Environmental Resource 

Compensation and Liability ACT (CERCLA; aka Superfund) are mining sites in the 

West, including Iron Mountain Mine in California, Bunker Hill in Idaho, and the ButteClark Fork River complex in Southwestern Montana. Human health risks and ecological 

injury, chiefly from elevated metals, have been identified by EPA and natural resource 

trustees at many of these mega-mining Superfund sites. 

Acidic drainage has been identified as the largest environmental liability facing the 

Canadian mining industry and is estimated at $2 to $5 billion dollars (MEND 2001). In 

response to the challenge presented by mitigation of AMD, 200 technology-based reports 

were generated to evaluate sampling, prediction, prevention, treatment and monitoring of 

potentially acid-generating materials and locations. A 1986 estimate for Canada suggests 

2

 Note: The authors recognize that AMD and elevated metal levels in water are inextricably linked, 

however the purpose of this report is to assess the effect of acidity on fisheries independent from elevated 

metals. 
5 

that acid-generating tailings cover 12,000 hectares plus an additional 350 million tons of 

mine waste rock were noted (MEND 2001). 

Effect of Acid Mine Drainage on Aquatic Resources

Once acid drainage is created, metals are released into the surrounding environment, and 

become readily available to biological organisms. In water, for example, when fish are 

exposed directly to metals and H+

 ions through their gills, impaired respiration may result 

from chronic and acute toxicity. Fish are also exposed indirectly to metals through 

ingestion of contaminated sediments and food items. A common weathering product of 

sulfide oxidation is the formation of iron hydroxide (Fe(OH)3), a red/orange colored 

precipitate found in thousands of miles of streams affected by AMD. Iron hydroxides 

and oxyhydroxides may physically coat the surface of stream sediments and streambeds 

destroying habitat, diminishing availability of clean gravels used for spawning, and 

reducing fish food items such as benthic macroinvertebrates. Acid mine drainage, 

characterized by acidic metalliferous conditions in water, is responsible for physical, 

chemical, and biological degradation of stream habitat. 

Water contaminated by AMD, often containing elevated concentrations of metals, can be 

toxic to aquatic organisms, leaving receiving streams devoid of most living creatures 

(Kimmel 1983). Receiving waters may have pH as low as 2.0 to 4.5, levels toxic to most 

forms of aquatic life (Hill 1974). Data relating to specific effects of low pH on growth 

and reproduction (Fromm 1980) may be related to calcium metabolism and protein 

synthesis. Fromm (1980) suggested that a “no effects” level of pH for successful 

reproduction is near 6.5, while most fish species are not affected when the pH is in a 

range from 5.5 to 10.5. Howells et al. (1983) reported interactions of pH, calcium, and 

aluminum may be important to understanding the overall effects on fish survival and 

productivity. Several reports indicate low pH conditions alter gill membranes or change 

gill mucus resulting in death due to hypoxia. Hatchery raised salmonids can tolerate pH 

5.0, but below this level hemeostatic electrolyte and osmotic mechanisms become 

impaired (Fromm 1980). 

A study of the distribution of fish in Pennsylvania streams affected by acid mine drainage 

(Cooper and Wagner 1973) found fish severely impacted at pH 4.5 to 5.5. Ten species 

revealed some tolerance to the acid conditions of pH 5.5 and below; 38 species were 

found living in waters with pH values ranging from 5.6 to 6.4; while 68 species were 

found only at pH levels greater than 6.4. Further, these investigators reported complete 

loss of fish in 90% of streams with waters of pH 4.5 and total acidity of 15 mg/L. 

Healthy, unpolluted streams generally support several species and moderate abundance of 
6 

individuals; whereas impacted streams are dominated by fewer species and often low to 

moderate numbers of only a few organisms. Streams affected by acid mine drainage are 

poor in taxa richness and abundance. In older studies (Warner 1971), more species of 

insects and algae were found in unpolluted West Virginia streams (pH > 4.5) compared to 

those streams polluted by acid (pH 2.8 to 3.8). Reductions of benthic fauna in a West 

Virginia stream severely affected by acid mine water were reported by Menendez (1978). 

In more recent studies (Farag et al. 2003), some streams in the Boulder River watershed 

in Montana impacted by nearly 300 abandoned metal mines are devoid of all fish near 

mine sources. Populations of brook trout (Salvelinus fontinalis), rainbow trout 

(Oncorhynchus mykiss), and cutthroat trout (O. clarki) were found further downstream 

and away from sources of acid mine drainage. In a 2003 study evaluating the effect of 

localized habitat degradation from a gold mine near the Yukon River (in AK?) on 

population structure of salmon, it was suggested that coho salmon (O. kisutch) may be at 

risk of losing genetic diversity due to localized habitat degradation (Olsen et al. 2004). 

The abandoned Britannia copper mine in British Columbia has been releasing acid mine 

drainage into local waters for many years. Investigators compared fish abundance, 

distribution and survival at contaminated and non-contaminated areas (Barry et al. 2000). 

Chum salmon (O. keta) fry abundance was significantly lower near the impacted waters 

(pH < 6 and dissolved copper > 1 mg/L) than the reference area. The investigators also 

reported that laboratory bioassays confirmed acid mine drainage from the Britannia Mine 

was toxic to juvenile chinook (O. tshawytscha) and chum salmon. Chinook salmon smolt 

transplanted to surface cages near Britannia Creek experienced 100% mortality within 2 

days (Barry 2000). 

The scientific literature is replete with studies designed to quantify the adverse 

environmental effects of acid mine drainage on aquatic resources. Most recent 

investigations focus on multiple bioassessments of large watersheds. These assessments 

include water and sediment chemistry, benthic macroinvertebrate sampling for taxa 

richness and abundance, laboratory acute water column evaluations, laboratory chronic 

sediment testing, caged fish within impacted streams, and development of models to 

explain and predict impacts of acid mine drainage on various aquatic species (Soucek et 

al. 2000, Woodward et al. 1997, Maret and MacCoy 2002, Hansen et al. 2002, Kaeser 

and Sharpe 2001, Baldigo and Lawrence 2000, Johnson et al. 1987, Griffith et al. 2004, 

Schmidt et al. 2002, Martin and Goldblatt 2007, Beltman et al. 1999, Hansen et al. 1999, 

Boudou et al. 2005). 
7 

Major Environmental Incidents Caused by Acid Mine Drainage

Releases of acid mine waters containing elevated metal and cyanide concentrations with 

resulting impacts to landscapes and waterways have been documented by several 

organizations (UNEP 2002). Fish kills resulting from the uncontrolled release of acid and 

metals from mine wastes into receiving streams have been reported from world wide 

areas in which hard rock mining, milling, and smelting activities have occurred. In 1998, 

a mine flood incident in Spain deposited some 6 million m3

 of acid water over the banks 

of the Guadiamar River with metal and sulfide rich sediments. The U.S. EPA described 

66 incidents in which environmental injuries from mining activities are detailed (EPA 

1995). Nordstrom and Alpers (1999) reported that millions, perhaps billions, of fish have 

been killed from mining activities in the U.S. during the past century. 

In 1989, a large fish kill (> 5000 salmonids) in Montana’s Clark Fork River resulted 

when acid, metalliferous tailings and efflorescent metal salts were flushed into the river 

during a thunderstorm event. Within 20 minutes, the acidity of the river water was 

reduced by several orders of magnitude, and copper concentrations rose dramatically. 

Fish gill tissue copper levels indicated acute toxicity (Munshower et al. 1997). The 

Sacramento River in California has experienced several fish kills due to sudden releases 

of acid water from upstream mine areas; more than 20 fish kills were reported since 

1963, and in 1967, at least 47,000 fish died (Nordstrom et al. 1977). 

Prediction of Acid Mine Drainage

Accurate prediction of acidic drainage from proposed mines is recognized by both 

industry and government as a critical requirement of mine permitting and long-term 

operation. Substantial emphasis has been placed on prediction of acid drainage 

associated with coal development in the Eastern U.S. (Pennsylvania DEP 1998; Skousen 

and Ziemkiewicz, 1996), and metal mining in the Western U.S. and in Canada (MEND 

2001). The standard protocols for evaluating geologic materials for their ability to 

produce AMD are generally agreed upon within the scientific community, yet much 

uncertainty remains in the ability of scientists and engineers to predict the ultimate 

drainage quality years in the future, as many complex variables influence acid generation 

and neutralization. 

The backbone of predicting acid generating potential from any geologic formation is the 

ability to characterize the presence and quantity of both acid-forming minerals and 
8 

neutralizing minerals in the geologic materials to be unearthed during mining operations. 

Typically samples are collected by drilling during exploration, analyzed and interpreted 

with respect to their risk of acid formation. Methods for characterizing acid-forming 

minerals were developed during the 1970’s in areas of the eastern U.S. mined for coal 

(Smith et al., 1974). Ultimately, these techniques lead to a standardized EPA protocol for 

characterization of mine soil and overburden (Sobek et al., 1978). In these analytical 

approaches, the amount of sulfur present in geologic materials is measured and attributed 

to being either an acid-forming mineral such as pyrite (FeS2) or non-acid-forming mineral 

such as gypsum (CaSO4▪2H2O). The relative amount of acid-forming minerals is then 

contrasted to the amount of neutralizing minerals such as calcite (CaCO3) to develop a 

prediction of the probability of acid generation. The ratio of neutralization potential (NP) 

to acid potential (AP) is commonly presented in graphical interpretations with the 

inference that geologic materials with an abundance of NP are unlikely to generate acidic 

drainage. In Eastern coal mines NP:AP ratios <1 commonly produce acidic drainage, 

NP:AP ratios between 1 and 2 may produce either acidic or neutral drainage and NP:AP 

ratios >2 should produce alkaline water (Skousen et al., 2002). However, this index does 

not always accurately predict the resultant acid generation from a mine. Of 56 mines 

evaluated by Skousen and others (2002) 11% did not conform to the expected results 

based on NP:AP ratios, including four sites with ratios > 2: these sites eventually 

produced acidic drainage. Furthermore, the applicability of the experimental findings 

from West Virginia coal deposits hosted in sedimentary rock to metal mines developed in 

igneous parent material is unknown. Sedimentary sulfide mineralization is caused by 

diagenetic interaction between microbes, Fe and S in a low temperature saturated 

environment resulting in formation of poorly crystallized pyrite while igneous pyrite is 

formed by high temperature magmatic fluids or molten rock cooling slowly to form well 

developed crystalline structure. Mineralogical variation between each geologic domain 

causes dissimilar reactivity to weathering conditions and leads to laboratory variability in 

assessment. Recurrence of inaccurate interpretations between laboratory and field data 

has caused investigators to reexamine the adequacy of the analytical methods. Because 

of the challenges inherent in interpreting laboratory data and predictive models, 

forecasting future water quality impacts from AMD should not be considered routine and 

robust, rather they should be considered an area of uncertainty and on-going research. 

If the rates of weathering and availability of acid-forming and neutralizing minerals are 

dissimilar the potential exists that acid-generation may overwhelm the pool of resident 

NP. Slowly reacting neutralizing minerals may lead to generation of acidic water. 

Sherlock and others (1995) evaluated the rates of weathering of sulfides, carbonates and 

silicates and determined that sulfide minerals reacted fastest and cautioned that 

conventional methods of prediction do not consider the specific mineralogy and reaction 

kinetics are at risk of erroneous interpretations and predictions. 
9 

 

Research has also focused on the presence of minerals which are detected by the NP 

analytical method, yet do not contribute to production of alkalinity. Siderite (FeCO3) has 

been found in mining environments and while contributing to the measured NP, no actual 

neutralization has been observed in the field (Frisbee and Hossner, 1989). In an 

evaluation of 31 overburden3

 samples containing siderite, pyrite, calcite and quartz using 

4 dissimilar methods for NP determination, siderite-containing samples showed wide 

variation in NP between three laboratories (Skousen et al., 1997). Using the standard 

Sobek (1978) test for NP, Weber and others (2004) showed that up to 432 hours may be 

required for complete hydrolysis of siderite-containing samples in laboratory testing, 

implying that inaccurate interpretations of NP are common for rock containing this 

siderite since routine laboratory tests would not be run for such a great length of time. 

The limitations of laboratory testing for NP without supporting mineralogical 

characterization can often lead to overestimation of NP (Lawrence and Scheske, 1997; 

Paktunc, 1999). Conventional laboratory methods for determination of NP employ wet 

chemical methods where the presence of carbonates in soil is made based on titration of a 

sample with acid followed by back titration with a base. No determination of the 

mineralogical source of carbonate is made by the NP test. Similarly, quantification of 

acid-forming minerals is challenging in a laboratory setting. Analysis of total sulfur 

levels is routinely accomplished using standardized laboratory equipment, however the 

typical Sobek method employs subsequent acid extractions to distinguish between acidforming minerals containing sulfur and non-acid sulfur minerals. In research using pure 

mineral samples, Jennings and Dollhopf (1995) showed that conventional analytical 

methods failed to accurately characterize acid-forming minerals. Incomplete recovery of 

sulfur-bearing minerals has been observed using the Sobek method since a residual sulfur 

fraction is commonly observed in laboratory testing implying the standard method of 

dissolution failed to solubilize or dissolve the sulfide found in the sample. Regional 

variation is observed in the interpretation of residual sulfur leading to non-standardized 

findings. The residual sulfur component is commonly characterized as non-acid forming 

organic sulfur in sedimentary rock and as acid-forming sulfide in metal mining samples. 

Collectively, the static tests described have significant limitations in accurately predicting 

whether acidic drainage will form. 

Kinetic4

 tests are commonly run as a companion to static5 testing to measure the 

weathering behavior of geologic material when exposed to field conditions. Kinetic tests 

3

 Overburden is defined as geologic material overlying a resource of interest. In surface mining overburden 

is typically removed as waste material. 

4

 Kinetic tests of mine waste are typically accomplished by monitoring the chemical constituents in water 

resulting from simulated laboratory weathering or actual field site weathering of mine waste materials over 

a period of months to years. Water is leached through the geologic material and recovered as drainage. 
10 

 

may be run in a laboratory column or in the field in large containers. The quality and 

quantity of leachate is subsequently evaluated to offer a supporting interpretation to static 

testing. Six large columns each containing 1.6 tons of waste rock were evaluated over a 

period of 3 years showing two pH controls: 1) sulfide oxidation with calcite dissolution 

sustaining a neutral pH, and 2) simultaneous silicate and sulfide weathering occurring at 

an equilibrium pH of 3-4 (Stromberg and Banwart, 1999). During the period of 

investigation the columns either remained at near-neutral pH or became acidic after 0.5 to 

3 years lag time. The lag time in appearance of low pH was caused by mineralogical 

reactions occurring in the waste rock that either neutralized the acidity formed until 

exhausted or rendered non-reactive, or the acid reactions required a period of time to 

initiate. In a companion study Stromberg and Banwart (1999) showed there was a large 

difference in weathering rates based on particle size. In the columns particles smaller 

than 0.25 mm were responsible for approximately 80% of both the sulfide oxidation and 

silicate dissolution. Calcite particles larger than 5-10 mm were found to react too slowly 

to neutralize acid produced by sulfide oxidation. Similar unique reaction kinetics has 

been observed at the Bingham Canyon Mine in Utah where fresh waste rock exhibits a 

paste pH6

 of 7.0. Within 6 years the pH of the waste rock dumps declines to 4.7 further 

decreasing to pH 3.7 after 50 years of weathering (Borden 2001). Scharer and others 

(2000) observed that NP was strongly related to particle size and particles greater than 1⁄4 

inch (6.4 mm) were only 20% consumed at the onset of acid conditions. Kinetic data on 

the depletion rate of NP supplemented by geochemical modeling suggests that waste rock 

with NP/AP ratios as high as 5 may turn acidic in the long term: this is much different 

than the results mentioned above by Skousen (2002) who identified 2 as the ratio below 

which NP/AP ratios would generally not become acidic. If neutralizing minerals are 

depleted or non-reactive long-term generation of acidic drainage may be initiated with 

potentially dire ecological consequences if untreated. 

Notable uncertainty exists in the long-term predictions of acid generation from geologic 

materials found in mining environments. Evaluation of Environmental Impact 

Statements from 25 mines performed by Kuipers and others (2006) showed 15 of 25 

mines (60%) exceeded surface water quality standards for metals and pH after permitting. 

5

 Static testing is the laboratory analysis of geologic materials for chemical characteristics such as total 

metal levels, pH or total S. Static testing is the analysis of the bulk concentrations in rock or soil material. 

6

 Paste pH or saturated paste pH is the measurement of pH in a slurry of soil or rock with deionized water 

after allowing time for reaction of the slurry. Paste pH is a measure of the soil solution indicative of the 

acidity of soil water in the context of plant growth or leaching to groundwater. 
11 

Similarly, kinetic tests performed using humidity cells7

 over a 3 to 7 year period showed 

that rates of acid generation have a 50% chance of stabilizing within one year while the 

remainder of the humidity cells fluctuated significantly throughout the test periods 

(Morin and Hutt, 2000). 

Assessment of Acid Rock Drainage and Metals Release

Canada’s Mine Environment Neutral Drainage (MEND) Program was implemented to 

develop and apply new technologies to prevent and control acid drainage. Recognizing 

acid drainage as the greatest environmental problem facing the mining industry and the 

regulatory agencies’ responsibility to protect the environment and safeguard human 

health, the MEND Program was funded jointly by Natural Resources Canada and The 

Mining Association of Canada. In 2005, MEND released a report titled List of Potential 

Information Requirements in Metal Leaching/Acid Rock Drainage Assessment (ML/ARD) 

and Mitigation Work (Price 2005). The purpose of this document is to improve the 

assessment and mitigation of metal leaching/acid rock drainage. It achieves this goal by 

providing a comprehensive list of information and data necessary to assess the potential 

for ML/ARD, and multiple strategies for mitigation. The document is intended to be used 

as a general guide for the mining industry, regulators, environmental advocacy groups, 

and other stakeholders. The MEND program uses the term ‘Acid Rock Drainage’ to 

describe the acidic water drainage from mines. 

The MEND report (Price 2005) recommends a set of informational variables and data 

that should be generated and developed so that informed decisions can be made with 

respect to the potential for acid drainage and toxic metal release. These 

recommendations were intended to mitigate the consequences of sulfide mineral 

oxidation caused by mining, milling, and other process involved in metal resource 

development. These information requirements are summarized in the following 

statements: 

General site characteristics: location, access, climate, ecology, history of previous 

mining, waste materials, geology, hydrology, mineralogy, descriptions of all materials 

that will be excavated or exposed, soils, reclamation objectives, end land uses, data 

tables, relevant figures, and other pertinent information. This is not exhaustive and sitespecific information and data will be required. 

 

7

 Humidity cells are laboratory equipment to simulate weathering of rock in a small benchtop enclosure 

where soil or rock is repeatedly wetted and dried over a period of months to years to monitor changes in 

drainage water quality. A humidity cell is a specialized type of kinetic testing. 
12 

Specific material characterization and predictions of ML/ARD: The ability to accurately 

predict the potential for ML/ARD requires a careful and complete characterization of all 

materials and waste types under the probable weathering (oxygen, bacteria, moisture, 

volumes of materials, etc.) conditions. Representativeness and adequacy of samples 

collected, measures of variability and uncertainty, and analytical procedures selected 

need to be appropriate. Industry-regulatory quality assurance and quality control 

procedures need to be followed. To be complete, predictions and assessments are to be 

made pre-mining (baseline data), during the operational phase, post-mining, and longterm. The document defines specific tests to define the geological and mineralogical 

properties of materials. 

Static and kinetic tests: Static tests require appropriate sampling intensity, sample 

preparation, determinations of elemental concentrations (total and water soluble), and full 

acid-base accounting. Kinetic tests are recommended to evaluate reaction rates and to 

predict and measure drainage chemistry. Humidity cell, column test and actual field 

verification tests should be conducted. Monitoring of site drainage (seeps, mine drainage, 

pit lakes, etc.) should include parameters to be evaluated and the frequency of monitoring 

during and post-mining. 

Assessments of waste materials: Waste materials may include waste rock, tailings, 

treatment wastes, low grade ore and overburden materials. All media require assessments 

and predictions for acid drainage and releases of metals. Post-disposal weathering of 

waste piles, including changes in pH, carbonate content, soluble weathering products 

(acid water and metals). Thermal properties, pore gas composition, and oxygen 

concentrations may be significant parameters in the assessments of long-term water 

quality degradation. 

The MEND document (Price 2005), also provides an approach to interpretation and 

display of the above characterization data. Identification of ARD generating materials is 

important, but toxicity from metals with neutral pH can be significant factors and are not 

to be overlooked. Predicting drainage chemistry is based on data and information 

gathered and their proper interpretation. Factors include the weathering environment and 

climate, data predicting ARD/ML potential, anticipated rates of leaching from mine 

wastes and mine workings, metal releases based on kinetic tests and geochemical 

modeling. Additional issues are in stream alkalinity, dilution, and natural attenuation. 

Estimating environmental and ecological impacts should be based on identifying 

potential receptors, endangered species, sensitivity and distributions of selected species 

and forms of exposure. A conceptual site model can be useful in determining mechanisms 

of contaminant release, contaminant pathways and receptors of concern. Acute and 
13 

chronic toxicity testing of identified aquatic and terrestrial receptors and pre- and postmining monitoring programs are recommended. 

In the United States, the National Research Council (1999) took up the issue of metal 

mining recognizing the controversy associated with permitting and compliance of 

hardrock mining. The committee was well versed on the potential deleterious impacts of 

mining and spent most of their deliberations contemplating the weaknesses of the existing 

regulatory framework. Recommendations were put forward for the Federal agencies 

consideration suggesting greater coordination and use of the best available scientific 

practices. This report did not explore technical topics such as AMD in detail, rather the 

recommendations were policy oriented. 

Water Quality and Acid Mine Drainage: Pre­mine Predictions and

Post­mine Comparisons

A major and unique study (Kuipers et al. 2006) was conducted comparing predicted and 

actual water quality at several mines in the United States. The overall purpose of this 

study was to examine the reliability of pre-mining water quality predictions at hard rock 

mining operations. The approach included reviews of the history and accuracy of water 

quality predictions in Environmental Impact Statements (EISs) for major hard rock mines 

and then examined and compared actual water quality to the predictions postulated in the 

EISs. A total of 183 mines were identified, with 71 having reviewed EISs. The 

investigation focused on 25 mines for in-depth analysis. Nearly all of the EISs reviewed 

reported that they expected acceptable water quality (concentrations lower than relevant 

standards) after mitigation was taken into account. Data analyses in this report, in 

general, refuted these EIS predictions. The following are major findings of the 

investigation: 

Surface water: Sixty percent of the case study mines (15/25) exceeded surface water 

quality standards due to mining-related activities. Of these, four (17%) noted a low 

potential to exceed standards, seven (47%) a moderate potential, two a high potential, and 

three had no information in their EISs for surface water quality impacts in the absence of 

mitigation measures. The specific water quality parameters exceeding standards varied 

between sites and were not specifically identified in the report. 

Ground water: The majority (64% or 16/25) of the case study mines also exceeded 

drinking water standards in groundwater. At three of the mines, all in Nevada, the 

elevated concentrations of metals that did not meet the standards may be related to 

baseline conditions. However, due to mining activities, 52% of the case study mines 
14 

clearly exceeded standards in surface water. In terms of post-mitigation groundwater 

quality impacts, 77% (10/13) of the mines that predicted low groundwater quality 

impacts in their EISs were above the water quality standards. Most mines predicted no 

impacts to groundwater quality after mitigation were in place, but in the majority of case 

study mines, impacts have occurred. 

Metals of Concern: Elements that most often exceeded standards or that had increasing 

concentrations in groundwater or surface water included toxic heavy metals such as 

copper, cadmium, lead, mercury, nickel, or zinc (12/19 or 63% of mines), arsenic and 

sulfate (11/19 or 58% of mines for each) and cyanide (10/19 or 53% of mines).

Acid mine drainage: The majority of the case study mines (18/25 or 72%) predicted low 

potential for acid drainage in one or more EISs. Of the 25 case study mines, 36% have 

developed acid drainage on site to date. Of these 9 mines, 8 (89%) predicted low acid 

drainage potential initially or had no information on acid drainage potential. The Greens 

Creek Mine in Alaska initially predicted moderate acid drainage potential but later 

predicted low potential for acid drainage for an additional waste rock disposal facility. 

Therefore, nearly all the mines that developed acid drainage either underestimated or 

ignored the potential for acid drainage in their EISs.

Factors Leading to Failures in Predicting Post­Mine Water Quality

and Acid Mine Drainage

In the report comparing predicted and actual water quality at hard rock mines (Kuipers et 

al. 2006), the authors identified two types of characterization failures that led to 

differences between predicted water quality as speculated in EIS documents and the 

actual water quality either during or after mining began. The two characterization failure 

types were: 1) insufficient or inaccurate characterization of the hydrology, and 2) 

insufficient or inaccurate geochemical characterization of the proposed mine. Inaccurate 

pre-mining characterization and interpretation can, therefore, result in a failure to 

recognize or predict water quality impacts. The authors reported primary causes of 

hydrologic characterization failures as follows: overestimations of dilution, lack of 

hydrological characterization, overestimations of discharge volumes, and 

underestimations of storm size. The primary causes of geochemical characterization 

failures were identified as: lack of adequate geochemical characterization, in terms of 

sample representativeness and sample adequacy. 

In the 25 case study mines, the authors identified mitigation failures with the following 

primary causes: mitigation measures were not identified or they were inadequate, or not 
15 

implemented; waste rock mixing and segregation was not effective, liners leaked, tailings 

were spilled, or embankments failed, and land application discharge was not effective. 

The authors provided a table summarizing these failures (Table 1) for the 25 case study 

mines. 

Table 1. Water Quality Predictions Failure Modes, Root Causes and Examples from Case 

Study Mines (Kuipers et.al, 2006).

Failure Mode Root Cause Examples

Hydrologic 

Characterization 

Lack of hydrologic 

characterization 

 Royal Mountain King, CA; Black Pine, MT 

Dilution overestimated Greens Creek, AK; Jerritt Canyon, NV 

Amount of discharge 

underestimated 

Mineral Hill, MT 

Size of storms underestimated Zortman and Landusky, MT 

Geochemical 

Characterization 

Lack of adequate geochemical 

characterization 

Jamestown, CA; Royal Mountain King, CA; 

Grouse Creek, ID; Black Pine, MT 

Sample size and/or 

representation 

Greens Creek, AK; McLaughlin, CA; 

Thompson Creek, ID; Golden Sunlight, MT; 

Mineral Hill, MT; Zortman and Landusky, 

MT; Jerritt Canyon, NV 

Mitigation 

Mitigation not identified, 

inadequate, or not installed 

Bagdad, AZ; Royal Mountain King, CA; 

Grouse Creek, ID 

Waste rock mixing and 

segregation not effective 

Greens Creek, AK; McLaughlin, CA; 

Thompson Creek, ID; Jerritt Canyon, NV 

Liner leak, embankment failure 

or tailings spill 

Jamestown, CA; Golden Sunlight, MT; 

Mineral Hill, MT; Stillwater, MT; Florida 

Canyon, NV; Jerritt Canyon, NV; Lone Tree, 

NV; Rochester, NV 

Land application ineffective Beal Mountain, MT 
16 

Treatment of Acid Mine Drainage

Water treatment for elevated metal levels and acidity is a common outcome of acid mine 

drainage. The effectiveness and feasibility of water treatment is highly variable 

depending on the treatments employed and unique site characteristics. Water treatment 

installations may include both passive and active systems. Passive water treatment 

systems, typically wetlands, operate without chemical amendments and without 

motorized or mechanized assistance. In contrast active water treatment systems are 

highly engineered water treatment facilities commonly employing chemical amendment 

of acid mine water to achieve a water quality standard specified in a discharge permit. 

In-depth evaluation of AMD treatment options was not performed as part of this literature 

review; rather emphasis was placed on prevention of AMD formation. Active treatment 

systems are operational at the Berkeley Pit, Butte, Montana; Britannia Beach, British 

Columbia; Iron Mountain Mine, Shasta County, California; and, Idaho Springs/Clear 

Creek, Colorado. Passive treatment systems are most frequently employed in 

Appalachian coal mining regions for control of acidic drainage. Semi-passive treatment 

systems are also in use where alkaline amendments are added to surface water at remote 

sites such as the Summitville Superfund site, Colorado. 

Recommendations for Acidic Drainage Minimization

Acidic drainage from mines is observed at many mine sites and the undesirable 

consequences of acidification are well known. Every effort should be employed to 

minimize the causes of acid generation. Because mineralogy and other factors (particle 

size, reactivity of NP and presence of oxidizers) that influence AMD formation are highly 

variable from one mine to another, and among different geologic materials within a 

proposed mine site, accurate prediction of future acid generation is difficult at best. 

Predicting the potential for AMD formation is costly, and of questionable reliability 

(Kuipers et al. 2006). In addition, concern has arisen over the lag time between waste 

emplacement and observation of an acid drainage problem. With acid generation, there is 

no general method to predict its long-term duration or to predict when acidic drainage 

will commence. There are historical, and now modern mining examples of long-term 

AMD generation requiring active treatment in perpetuity. There are two primary 

approaches to addressing AMD: circumvent mining sulfide rich ore deposits with high 

AMD potential, and implementing mitigation measures to limit potential AMD impacts. 

It is noted that avoiding mining of sulfide ores with the potential to form AMD may be 

difficult because they are most often associated with the mineral resource of interest. 
17 

Selective handling and avoidance of sulfide ore and overburden is a strategy for 

minimizing the risk of future acid generation (Skousen et al., 1998). In a review of 

selective handling of acid-forming materials in coal mining in the Eastern U.S., Perry and 

others (1997) found that selective handling had not eliminated acid formation due in part 

to the inherent difficulty in segregating benign overburden from acid-forming waste. In 

some mining operations acid-forming minerals can be avoided through the mine planning 

process or through using underground mining rather than surface mining. 

Mine waste isolation and avoidance of oxidizing conditions can be performed using 

several methods that keep sulfides isolated from oxygen. Subaqeous disposal of tailings 

and waste rock below the water table is commonly practiced in Canada as a protocol for 

mine reclamation (Samad and Yanful, 2004). Paste backfill is a mining methodology for 

minimization of acid formation by backfilling mine workings using a mixture of mine 

tailings, Portland cement and other binders to create a waste disposal option that is both 

geotechnically stable and geochemically non-reactive since sufficient NP can be added to 

neutralize any future acidity (Benzaazoua, T.B. and B. Bussiere, 2002). Depyritization of 

tailings can be accomplished to remove sulfide minerals from waste products to create a 

benign sand fraction suitable to use as a general backfill and a companion low-volume 

sulfide concentrate requiring careful disposal. Most mine tailings contain small amounts 

of sulfide minerals that can be readily separated from non-acid forming silicate minerals 

using conventional mineral processing equipment to create a cleaned material with 

sufficient NP to ameliorate any future acidity (Benzaazoua, B. et al., 2000). 

In many cases, the measures described above are most effective when used in 

combination and adapted to the situation at a specific site. For the most part, only limited 

data are available to document the long-term effectiveness of any of these controls. The 

Kuipers Report (2006) provides a unique view of the failure to predict the formation of 

AMD at many hardrock mines. There are many research investigations being conducted 

by university, government, and industrial entities to develop new treatment strategies for 

AMD. The transfer of laboratory data to site-specific conditions (climate, geology, 

physical properties of ores, etc.) can be problematic and significantly impact their 

feasibility and performance in the field. 

Thorough baselines studies of the biological, hydrologic, and geochemical conditions 

characteristic of the unique site are required to provide a basis for long-term monitoring 

and provide an insight into mechanistic processes involved in AMD evolution (Edwards 

et al., 2000). Associated financial assurances for resource mitigation in the event of 

default of a mine property are also required (NRC, 1999) to ensure both short-term and 

long-term mitigation of AMD and the associated impacts to water quality and fisheries. 
18 

Based on review of the acid mine drainage literature it is clear that severe world-wide 

ecological consequences, especially for aquatic resources, have resulted from mining ore 

deposits with acid-forming minerals. Accurate prediction of the onset and aggressiveness 

of low-quality acidic water discharge is perilously difficult using the best available 

science. Multiple complex geochemical, biological and hydrologic factors create a 

daunting task for mining engineers to profitably recover mineral resources while 

preventing discharges of metals and acidity to surface and ground water. The deleterious 

effects of elevated metals levels and acidity to salmonids are clearly reported in the 

scientific literature. The inevitability of impacts to fisheries from AMD caused by 

mining is an open question and dependent on the outcome of complex geochemical 

reactions and human attempts to understand and mitigate their consequences. The track 

record of industry is replete with problems, thus little comfort is afforded by extensive 

pre-mine studies. 
19 

Summary

Acid mine drainage commonly forms as a result of natural geochemical processes that 

oxidize metal sulfides exposed at the earth’s surface by mining. Oxidation of sulfur and 

hydrolysis of iron result in acid-sulfate waters which have been observed at thousands of 

historic mine sites and at operational mines where mitigation measures have failed to 

prevent the release of acid mine drainage to down-gradient surface waters. Resultant low 

pH conditions mobilize metals from waste materials resulting in degradation of water 

quality and impairment of aquatic health. Acid mine drainage and associated weathering 

products commonly result in physical, chemical and biological impairment of surface 

water. Pre-mine characterization of the risk of AMD formation is often inaccurate 

leading to notable post-mine risk to fisheries. Fisheries have been impaired world-wide 

by releases of AMD from mining areas. The mining industry has spent large amounts of 

money to prevent, mitigate, control and otherwise stop the release of AMD using the best 

available technologies, yet AMD remains as one the greatest environmental liabilities 

associated with mining, especially in pristine environments with economically and 

ecologically valuable natural resources. Problematic to the long-term operation of large 

scale metal mines is recognition that no hard rock surface mines exist today that can 

demonstrate that AMD can be stopped once it occurs on a large scale. Evidence from 

literature and field observations suggests that permitting large scale surface mining in 

sulfide-hosted rock with the expectation that no degradation of surface water will result 

due to acid generation imparts a substantial and unquantifiable risk to water quality and 

fisheries. 
20 

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