United States
Environmental Protection
Agency
Office of Research and
Development
Washington DC 20460
EPA/625/R-95/007
October 1996
&EPA Seminar Publication
Managing Environmental
Problems at Inactive and
Abandoned Metals Mine
Sites
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EPA/625/R-95/007
October 1996
Seminar Publication
Managing Environmental Problems at
Inactive and Abandoned Metals Mine Sites
Center for Environmental Research Information
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio
Printed on Recycled Paper
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Notice
The information in this document has been funded wholly, or in part, by the U.S. Environ-
mental Protection Agency (EPA). This document has been subjected to EPA's peer and
administrative review and has been approved for publication as an EPA document. Mention
of trade names or commercial products does not constitute endorsement or recommenda-
tion for use.
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting
the Nation's land, air, and water resources. Under a mandate of national environmental
laws, the Agency strives to formulate and implement actions leading to a compatible bal-
ance between human activities and the ability of natural systems to support and nurture life.
To meet this mandate, EPA's research program is providing data and technical support for
solving environmental problems today as well as building the science knowledge base nec-
essary to manage our ecological resources wisely, understand how pollutants affect our
health, and prevent or reduce environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's center for
investigation of technologies and management approaches for reducing risks from threats
to human health and the environment. NRMRL's research program focuses on methods for
the prevention and control of pollution to air, land, water, and subsurface resources; protec-
tion of water quality in pubilc water systems; remediation of contaminated sites and ground-
water; and prevention and control of indoor air pollution. The goal of this research effort is to
catalyze development and implementation of innovative, cost-effective environmental tech-
nologies; develop scientific and engineering information needed by EPA to support regula-
tory and policy decisions; and provide technical support and information transfer to ensure
effective implementation of environmental regulations and strategies.
For many years, mine waste at inactive and abandoned metals mine has been an issue of
great interest to EPA. According to a 1985 Report to Congress, over 50 billion tons of mining
wastes is estimated to exist in the United States. The Agency, through NRMRL, has pro-
vided technical support for the management of wastes from inactive and abandoned metals
mines by conducting a series of seminars on the topic. The seminar series was developed
based on input from federal, state, and local government organizations; mining, engineer-
ing, and remediation companies; and other interested parties. The goal of the seminars was
to increase public awareness of environmental problems at inactive and abandoned metals
mine and provide information on practical approaches to more effectively manage these
problems.
This publication has been produced in support of NRMRL's strategic long-term research
plan. It is published and made available by EPA's Office of Research and Development to
assist the user community and to link researchers with their clients.
E. Timothy Oppelt
National Risk Management Research Laboratory
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Acknowledgments
This document was prepared (written and edited) under EPA Contract No. 68-C3-0315,
Work Assignments 7 and 52, by Eastern Research Group, Inc. (ERG) and consultants hired
by ERG, namely, the authors who contributed to this publication. The authors were pre-
senters at the seminars of the same name presented in the summer of 1994 under co-
sponsorship of the U.S. Environmental Protection Agency (EPA) and the U.S. Department
of Energy. The EPA project officer for the seminars was Jonathan G. Herrmann, with assis-
tance from Justice A. Manning, who was project officer for this document. Further technical
and financial support was provided by Jonathan G. Herrmann and Roger Wilmoth, respec-
tively, National Risk Management Research Laboratory. Eugene F. Harris, NRMRL, and
Kunsoo Kim, Ph.D., Columbia University, peer reviewed this document; appreciation is given
for their review. Appreciation is expressed to all who participated in the seminars to make
them a success, including three authors who were unable to contribute to this publication
because of extenuating circumstances.
IV
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Contents
Foreword "'
Acknowledgments iv
Chapter 1. Introduction: Focusing on the Problem of Mining Wastes
Thomas V. Durkin and Jonathan G. Herrman 1
Chapter 2. Understanding the Reasons for Environmental Problems
From Inactive Mine Sites
Dirk Van Zyl 4
Chapter 3. The Importance of Site Characterization for Remediation
of Abandoned Mine Lands
A. MacG Robertson 8
Chapter 4. U.S. Bureau of Mines Remediation Research: New Uses
for Proven Tools
William B. Schmidt 14
Chapter 5. The Technology and Operation of Passive Mine Drainage
Treatment Systems
Ronald R. Hewitt Cohen 18
Chapter 6. Cyanide Biotreatment and Metal Biomineralization in Spent
Ore and Process Solutions
Leslie C. Thompson 30
Chapter 7. Acid Mine Drainage: Reclamation at the Richmond Hill and
Gilt Edge Mines, South Dakota
Thomas V. Durkin 54
Chapter 8. The Mine Waste Technology Program and technologies to
Address Environmental Problems at Inactive Mine Sites
Martin Foote 62
Chapter 9. Innovative Approaches to Addressing Environmental Problems
for the Upper BlackfootMining Complex: Overview
Judy Reese 70
Chapter 10. Innovative Approaches to Addressing Environmental Problems
for the Upper Blackfoot Mining Complex: Voluntary Remedial Actions
J. Chris Pfahl 75
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Contents (continued)
Chapter 11. Innovative Approaches to Addressing Environmental Problems
for the Upper Blackfoot Mining Complex: Grouting as a
Hydrogeological Control for Acid Rock Drainage Reduction
A. Lynn McCloskey 81
Appendix A. Seminar Speaker List 85
Appendix B. Contributors 88
Note: Papers presented at the seminars but not included in this publication due to extenu-
ating circumstances include Case Study: Sharon Steel/Midvale Tailings Superfund Site,
presented by William Cornell, U.S. Bureau of Mines, Rolla, MT; Case Study: What We
Learned About Liability at Penn Mine, presented by Rick Humphreys, California State Wa-
ter Resources Board, Sacramento, CA; and History and Status of Congressional Initiatives
Pertinent to Mining and Mine Waste, presented by J. Curt Rich, Legislative Counsel, Sen-
ate Environment and Public Works Committee.
VI
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Chapter 1.
Introduction: Focusing on the Problem of Mining Wastes
Thomas V. Durkin and Jonathan G. Herrmann
Background
Mining waste, generated from active and inactive min-
ing sites and from beneficiation activities, and its impact
on human health and the environment are a continuing
problem for government entities, private industry, and
the general public. The nation's reported volume of min-
ing waste is immense. A scoping study conducted by
the Western Governors' Association Mine Waste Task
Force (1) collected the following statistics on inactive and
abandoned mines (lAMs) by state:
• Arizona—80,000 IAM sites covering 136,653 acres,
polluting 200 miles of surface waterways.
• California—2,484 IAM sites, 1,685 mine openings,
and 578 miles of polluted streams.
• Colorado—20,299 mine openings and 1,298 miles
of affected streams.
• Idaho—27,543 acres affected by lAMs.
• Missouri—7,655 IAM sites covering 48,175 acres,
with 109 miles of affected streams.
• Montana—20,000 IAM sites covering 153,800 acres,
with 1,118 miles of stream damage.
• New Mexico—25,320 acres and 69 miles of streams
affected by lAMs.
• Oklahoma—26,453 acres affected by lAMs.
• Utah—25,020 acres affected by lAMs, with 83 miles
of polluted streams.
Of this total volume, approximately 85 percent is attrib-
uted to copper, iron ore, uranium, and phosphate mining
and related activities. Approximately one-half of the waste
generated is mining waste and one-third is tailings, with
the balance consisting of dump/heap leaching wastes
and mine water.
Because of the extent of these problems, the U.S. Envi-
ronmental Protection Agency in conjunction with the U.S.
Department of Energy organized a series of seminars to
disseminate available information on approaches for
addressing mine waste. This document presents papers
written by the seminar presenters, for which this intro-
ductory paper provides a general context.
Definition and Chemistry of Acid Mine
Drainage (AMD)
The types of mine waste problems are numerous, but
the most difficult one to address is the acid mine drain-
age (AMD) that emanates from both surface and under-
ground mine workings, waste and development rock, and
tailings piles and ponds. AMD is defined as drainage that
occurs as a result of sulfide oxidation in rock exposed to
air and water. In the case of iron sulfide (pyrite/marca-
site), the chemical reaction in the acid-generating pro-
cess can be simplified to:
FeS2 + 1 5/4 O2
7/2 H2O
Fe(OH)3 + 2SO4 + 4H
In the presence of oxygen and water, pyrite oxidizes to
form iron hydroxide (commonly called "yellowboy"), sul-
fate, and hydrogen ions. The liberation of hydrogen ions
causes acidity in water passing over the rock. Every mole
of pyrite yields four moles of acidity.
AMD can be characterized by low pH and increased acid-
ity, elevated heavy metals, sulfate, and total dissolved
solids (JDS). The low pH water that results from acid
generation is capable of solubilizing heavy metals con-
tained within the waste rock. Most harmful to the envi-
ronment is the high metals loading in the water emanat-
ing from the waste material. As AMD flows away from
the acid-generating source and moves into the receiv-
ing environment where the pH is buffered, discoloration
of the stream bed or the material over which the AMD is
passing often is caused due to precipitation of solid metal
hydroxides.
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Stages in the Development of AMD
The development of AMD involves a complex combina-
tion of organic and sometimes inorganic processes and
reactions. To produce severe acid drainage, where the
pH of the system drops below 3, sulfide minerals must
create an optimum microenvironment for rapid oxidation
and must continue to oxidize for a sufficiently long time
to exhaust all of the neutralization potential of the rock
(2). The potential of sulfide rock to generate acid is
strongly related to the amount of alkaline, often calcare-
ous, material in the rock. For example, a rock containing
5 percent sulfide minerals may not generate acid due to
an overabundance of calcite in the rock that is available
for acid neutralization. Another rock, containing less than
2 percent sulfide minerals, might generate a consider-
able amount of acid if no neutralizing minerals are present
within it.
When reactive sulfide rock initially is exposed to flowing
water and oxygen, sulfide oxidation and acid generation
begins. Any calcium-based carbonate in the rock imme-
diately neutralizes this small amount of acidity and main-
tains neutral to alkaline conditions in water passing over
the rock (3). As acid generation continues and the neu-
tralizing agent is consumed or is rendered ineffective in
further neutralization, the pH of the water decreases,
which in turn enhances the conditions for further acid
generation. As the rate of acid generation accelerates,
the pH progressively decreases in a step-like manner.
Each plateau of relatively steady pH represents the dis-
solution of a neutralizing mineral that becomes soluble
at that pH (3). If the rate of acid generation remains high
enough to remove all of the neutralization potential in
the rock, the pH values will drop below 3 and AMD will
become severe. These various stages can last for weeks,
months, or centuries until the sulfide minerals completely
oxidize and the rock becomes inert, or until special waste
management and AMD control actions are taken.
Prediction of AMD
The prediction of AMD in particular is a rapidly evolving
science. Predictive tests specifically designed for sulfitic
coal mine wastes have been around for decades. Sig-
nificant advances in the predictive techniques applied to
hard rock metal mine waste samples have been made
in the past 5 to 10 years. Recent studies have been con-
ducted comparing various predictive tests for hard rock
samples (4,5). Accurate predictive testing, proper waste
rock characterization, and proper interpretation of the
resulting data are all of paramount importance in devel-
oping successful sulfide waste rock management tech-
niques. Conducting proper predictive tests prior to de-
veloping waste management plans is the preferred
choice from an environmental as well as economic stand-
point. Millions of dollars can be saved as a result of fo-
cusing on preventing AMD rather than reacting to prob-
lems it can cause.
Predictive analyses can range from simple comparisons
to complex laboratory testing and computer modeling. A
simple, but very useful, assessment might include com-
paring a proposed mining operation with geologically
similar and/or nearby mines where acid generation is
known to be a problem or not. Rock samples may un-
dergo relatively inexpensive, short-term "static" predic-
tive testing (e.g., acid/base accounting) in which the
amount of acid-generating potential of the rock is weighed
against the acid-neutralizing potential of the rock. Static
tests are qualitative tests only. Rock types that undergo
static tests that result in an indication for potential acid
generation may undergo more expensive, long-term "ki-
netic" tests (e.g., humidity cells or column leach tests) in
which actual weathering reactions are simulated in the
laboratory. Kinetic tests are qualitative indicators of the
rate and amount of acid that a given sample may gener-
ate.
Control of AMD
Much of the effort to control AMD in the past has been
directed at treating the symptoms rather than controlling
the problem at the source. In the early 1990s, significant
research was undertaken to develop improved sulfide
waste management techniques for hard rock mines.
Control of acid generation can be achieved by removing
one or more of the three essential components in the
acid-generating process (i.e., sulfide, air, or water). Steps
that can be taken to control AMD include:
• Waste segregation and blending. This would include
thoroughly blending the acid-generating rock with
enough rock of a net neutralizing potential that neu-
tral pH levels within the waste system are maintained.
• Base additives. Alkaline materials such as limestone,
lime, and soda ash can be added to the sulfide rock
upon disposal to buffer acid-generating reactions.
• Covers and caps. Soil, clay, and synthetic covers
can be placed over the acid-generating rock to mini-
mize the infiltration of water and air into the system.
Water covers at acid-generating tailing impound-
ments have been effective in controlling the prob-
lem.
• Bactericides. The introduction of certain chemicals
that reduce the bacteria (Thiobacillus ferrooxidans)
that catalyze the acid-generating reactions have
been effective in controlling AMD.
• Collection and treatment of contaminants. In this
case, AMD is collected and treated using active or
passive treatment systems. Active treatment might
include base additives to precipitate metals out of
solution, remove the resulting sludge, and discharge
the treated water. Passive treatment might include
passing contaminated water through a constructed
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wetland designed to remove contaminants. These
control options are less attractive in the long term
because they treat the symptoms of AMD ratherthan
controlling the problem at the source.
Conclusion
AMD and the sources of its production are the legacy of
over 100 years of mining in the western United States.
AMD has been a problem in the eastern United States
and throughout the world even longer. The presentations
in this publication describe only a small fraction of the
current thinking and ongoing research to address the
issue of mining wastes in general, and AMD in particu-
lar, using comprehensive and cost-effective approaches.
The problem of mining wastes is daunting. An all inclu-
sive description of the types of environmental issues
posed by mining wastes is beyond the scope of this docu-
ment. Nonetheless, the case histories presented reflect
common mine waste problems and provide insight to
state-of-the-art management techniques. Although these
techniques have been used to successfully address as-
pects of mine waste, they warrant further research and
site application. For the country's best scientists and en-
gineers, the challenge presented by mine wastes in-
volves developing solutions to problems created in the
past, while seeking ways to avoid these problems in the
future.
References
1. Interstate Mining Compact Commission (IMCC).
1992. Inactive and abandoned non-coal mines: A
scoping study. Prepared for IMCC of Herndon, VA,
by Resource Management Associates, Clancy, MT.
Cooperative Agreement X-817900-01-0 (July).
2. Steffen, Robertson, and Kirsten (BC) Inc., in asso-
ciation with Norcol Environmental Consultants and
Gormley Process Engineering. 1989. Draft acid rock
drainage technical guide, vols. 1 and 2. ISBN 0-7718-
8893-7. Prepared for the British Columbia Acid Mine
Drainage Task Force. BiTech Publishers, Richmond,
British Columbia, Canada.
3. Broughton, L.M., R.W. Chambers, and A. MacG.
Robertson. 1992. Mine rock guidelines: Design and
control of drainage water quality. Report No. 93301.
Prepared by Steffen, Robertson, and Kirsten (BC),
Inc. for Saskatchewan Environment and Public
Safety, Mines Pollution Control Branch. Vancouver,
British Columbia, Canada.
4. Coastech Research Inc. 1989. Investigation of pre-
diction techniques for acid mine drainage. DSS File
No. 30SQ.23440-7-9178. Report to Canada Center
for Mineral and Energy Technology for Mine Envi-
ronment Neutral Drainage program. Mine Environ-
ment Neutral Drainage (MEND) Secretariat, Ottawa,
Ontario, Canada.
5. Lapakko, K. n.d. Evaluation of tests for predicting
mine waste drainage pH. Draft report to the West-
ern Governors' Association by Minnesota Depart-
ment of Natural Resources, St. Paul, MN.
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Chapter 2.
Understanding the Reasons for Environmental Problems
From Inactive Mine Sites
Dirk Van Zyl
Background
Mining not only produced wealth, power, and fame
for the United States it also attracted worldwide at-
tention and investment to this underdeveloped nation,
one that was sorely in need of a financial transfusion.
Without mining—from coal to iron to gold—the United
States could not have emerged as a world power by
the turn of the century, nor could it have successfully
launched its international career of the twentieth cen-
tury. All this development did not take place without
disturbance—environmental, personal, economic,
political and social. Mining left behind gutted moun-
tains, dredged-out streams, despoiled vegetation,
open pits, polluted creeks, barren hillsides and mead-
ows, a littered landscape, abandoned camps and
burned-out miners and the entrepreneurs who came
to mine the miners [1].
As pointed out by historian Duane Smith, mining played
an important role in establishing America on its path to
becoming a superpower. Unfortunately, along with the
success of the mining industry came negative environ-
mental impacts such as acid drainage from mine adits
and waste rock piles. Indeed, old mining districts are
dotted with eroded tailings and waste rock piles.
In the nineteenth century, mining was quite widespread
in the United States, but was most concentrated around
the Rocky Mountains in Colorado, the western parts of
Montana, and California and Nevada. Mining operations
in Missouri and Kansas were mostly related to lead and
zinc. The major locations of hard rock mining activity
during the nineteenth century are shown in Figure 1.
Ore Mineralization and Metal Extraction
The following broad comments can be made about the
mineralization associated with hard rock mines:
• Gold and silver are found in oxidized zones near
the ground surface, although they often are associ-
ated with sulfides at greater depths.
• Lead, zinc, and copper often are found in sulfide
mineralization.
• Other metals can be associated with mineralization
(e.g., arsenic, iron, mercury, cadmium).
Often natural mineralizations contain metals that can be
economically exploited. These deposits also contain
lower concentrations of metals, however, that are typi-
cally discarded as waste or exposed to water and oxy-
gen following mining operations.
Historically, mine development occurred through pros-
pecting for surface outcrops. Thus, initially miners ex-
ploited the ore bodies close to the surface or practiced
vein-type mining. Lead zinc in Kansas and Missouri was
mined through shallow shafts to a depth of up to 150
feet, and eventually dewatering became a problem. In
mountainous terrain, dewatering was conducted through
a series of adits and tunnels to allow gravity drainage of
whole mining districts (e.g., the Yak Tunnel at Leadville,
Colorado). The mining activities significantly increased
the surface area of mineralized rock exposed to water
and oxygen.
Miners performed metal extraction by various means.
Physical processes such as grinding further increased
the surface area of the minerals exposed to water and
oxygen. Mercury was introduced for extraction of pre-
cious metals through amalgamation. Smelting also was
conducted to extract metals such as copper from open
stacks at mining camps (e.g., at Butte, Montana). This
led to air pollution and extensive firewood consumption.
Cyanidation as a process was introduced in the 1890s
in the United States and quickly gained popularity (2).
Flotation processes for the extraction of metal associ-
ated with sulfide minerals gained acceptance in the early
twentieth century.
The overall effect of metal extraction processes was the
increased exposure of minerals in the mine waste mate-
rials to water and oxygen. Geochemical interactions with
the waste resulted in acid generation and the leaching
of heavy metals to the surrounding environment. Smelt-
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Granby
Rich
Murphy's uamp
Tornl
Figure 1. Sites of major hard rock mining activity in the United States during the nineteenth century.
ing resulted in the atmospheric dispersion of contami-
nants such as arsenic and lead.
The presence of mineralization made mining possible.
Unfortunately, however, natural geochemical processes
in undisturbed mineralized areas as well as in areas ex-
ploited for metal production can cause degradation of
water quality. Although the major environmental conse-
quence of mining is the increased surface area of min-
erals exposed to water and oxygen, the release of sedi-
ments is also of concern. Chemicals used in metal ex-
traction, however, seldom have long-term impacts.
Water Quality
Effects on water quality associated with inactive mine
sites are of particular concern. Selected constituents for
three different catchment areas in Colorado are pre-
sented in Table 1. Alum Creek is a small catchment that
drains into the Alamosa River downstream of Wightman
Fork, which drains the Summitville area. Because min-
ing has never been conducted in the Alum Creek drain-
age, the water quality shown is exclusively a result of
leaching and runoff from natural mineralization.
Wightman Fork below Cropsy Creek is the exit point from
the Summitville mine site. The 1981 data are a useful
measure of the water quality as affected by past mining
activity in the area. The 1991 data indicate some of the
effects of continued mining at the site; to a significant
degree, the higher concentrations of copper, iron, and
zinc are due to discharge from the Reynolds Tunnel. The
section of Silver Creek at the highway bridge is a catch-
ment near Rico, Colorado. Typical ranges as well as
mean values of constituents for this catchment appear
in Table 1.
More extensive information on the geochemical behav-
ior and water quality at certain basins in the Upper
Alamosa River in the vicinity of Summitville is provided
in two recent publications (3,4). The geochemical char-
acteristics of the Alum Creek drainage appear to be dif-
ferent from those in the Cropsy Creek drainage because
of exposure to a different alteration assembly (3). Re-
searchers developed a conservative estimate of the
maximum possible contributions of mining to the degra-
dation of water quality in the Alamosa River above the
confluence with Wightman Fork (4). According to the
study, abandoned mines could be the source of about
11 percent of the iron, 18 percent of the aluminum, and
1 percent of the copper, manganese, and zinc; research-
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Table 1. Water Quality Data Comparison for Selected Mineralized Areas in Colorado
Parameter
(mean, max.,
min.)
PH
Arsenic
Cadmium
Copper
Iron
Lead
Alum Creek
at Mouth
(Aug. 1991)
NAa
5.7
9
3
7
10.2
4.9
259
261
258
126,500
171,500
103,000
4.2
6.8
2
Wightman
Fork Below
Cropsy Creek
(Oct. 1981)
3.44
2
5.4
3,560
6,300
18.5
Wightman
Fork Below
Cropsy Creek
(Oct. 1991)
NA
NA
62
26,000
82,000
NA
Silver Creek at
Bridge Hwy 145
(Mar. 1966 to
Dec. 1968)
7.9
8.4
7.4
NA
NA
NA
NA
NA
NA
111
1,100
0
5,407
125,000
0
655
6,350
0
Silver
Zinc
<0.5
652
843
543
1.02
770
<0.2
6,300
NA
855
2,000
100
1 NA - not available.
ers attributed the remainder of these constituents to natu-
ral mineralization.
Considerations
The discussion and data presented above demonstrate
that environmental problems from inactive mines are
related to natural mineralization as well as mining activi-
ties that result in increased exposure of minerals to wa-
ter and oxygen. Before the 1930s, for example, environ-
mental effects of mining were poorly understood. Eco-
nomic incentives were the driving force and not environ-
mental protection. Our appreciation of the effects of min-
ing on the environment has improved considerably since
that time, and more significantly during the last 10 years.
For instance, we now know that chemicals used for hy-
drometallurgical and flotation extraction typically do not
present a long-term concern at inactive mining sites.
Rather, natural mineralization and its exploitation are the
source of concern.
Problems experienced at inactive mine sites have re-
ceived increased attention because of changes in the
environmental awareness and regulatory environment.
Also, we now know more about environmental processes
from a multimedia perspective; that is, the interactions
involving land, air, and water are better understood. An-
other development that has contributed significantly to
the real or perceived problems at mining sites is our im-
proved analytical capability. Because instruments are
available to analyze to much lower concentrations, re-
searchers can identify the presence of some constitu-
ents previously not detected.
Another factor has the potential to contribute to certain
perceived or real concerns at mining sites: applying drink-
ing water or aquatic standards to streams in mineralized
areas without due regard for the likely baseline water
quality of the stream prior to mining operations. Water
quality can be restored only to what Nature gave us and
not better. Thus, site-specific risk issues should be rec-
ognized, and evaluation of the level of risk should go
beyond the broad application of conservative assump-
tions.
Conclusions
Natural mineralization is the greatest contributor to en-
vironmental problems at inactive mine sites. Man-made
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materials such as cyanide and flotation chemicals have
not played a significant role in contamination from these
mine sites. Rather, mining increased the exposure of
sulfides and other minerals to oxygen and water, which
leads to acid rock drainage associated with mining at
active and inactive sites. Thus, designing for closure is
our only option from an environmental and economic view
point.
References
1. Smith, D.A. 1987. Mining America. Lawrence, KA:
University of Kansas Press.
2. Von Michaelis, H. 1985. Role of cyanide in gold and
silver recovery. In: Van Zyl, ed. Cyanide and the en-
vironment, Vol. I. Geotechnical Engineering Program,
Colorado State University, Fort Collins, CO. pp. 51-
64.
3. Bove, D.J., J. Barry, J. Kurtz, K. Hon, A.B. Wilson,
R.E. Van Loenen, and R.M. Kirkham. 1995. Geol-
ogy of hydrothermally altered areas within the
Alamosa River Basin, Colorado, and probable ef-
fects on water quality. In: Posey, H.H., J.A.
Pendleton, and D. Van Zyl, eds. Proceedings of the
Summitville Forum '95, Denver, CO. Colorado Geo-
logical Survey, Special Publication 38. pp. 35-41.
4. Kirkham, R.M., J.R. Lovekin, and M.A. Sares. 1995.
Sources of acidity and heavy metals in the Alamosa
River Basin outside of the Summitville mining area,
Colorado. In: Posey, H.H., J.A. Pendleton, and D.
Van Zyl, eds. Proceedings of the Summitville Forum
'95, Denver, CO. Colorado Geological Survey, Spe-
cial Publication 38. pp. 42-57.
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Chapter 3.
The Importance of Site Characterization for
Remediation of Abandoned Mine Lands
A. MacG. Robertson
Requirements for Site Characterization
Mining is a disruptive activity involving physical distur-
bance of the earth's surface to gain access to the ore,
removal and processing of the ore, and deposition of
wastes generated by ore processing. Typically, mining
operations leave behind large man-made structures (e.g.,
roads, mine and mill buildings, and processing facilities),
the underground or open pit mine, and large deposits of
mine rock excavated to expose the ore as well as tail-
ings (i.e., the residue generated by ore processed to re-
cover valuable minerals). These man-made structures
and waste materials are often unstable or hazardous, or
they become so over time as they weather and deterio-
rate when subjected to the elements. Indeed, they may
disintegrate with time and may be vulnerable to vandal-
ism and fire.
Mining also removes minerals from the deep anoxic en-
vironment, where they are chemically stable, and ex-
poses them to the high oxygen atmosphere of the earth's
surface and the leaching action of rainwater. Many of
the newly exposed minerals can react with the gaseous
and liquid components in their new environment to yield
contaminants. These seep and flow—via ground- and
surface-water pathways—into the adjacent environment,
where they might be toxic to aquatic and terrestrial biota.
Remediation efforts at abandoned mine sites involve
identifying sites and aspects of particular mining opera-
tions that have caused, or could result in, damage to the
environment and loss of land-use values. Thus, the first
step in the remediation process is to characterize the
site in terms of:
• Premining conditions
• The nature of mine development and its present or
potential environmental effect
• Contaminant control or reclamation measures that
could be considered.
Many of the effects of mine development are time de-
pendent. For example, the processes of erosion and the
development of unstable ditch and dam conditions, as
well as the chemical evolution that develops into acid
mine drainage conditions, can take many years or tens
of years to develop. At initiation of mining operations,
anticipating the potential for such long-term degradation
or predicting its course often is difficult. Such assess-
ments depend on short-term laboratory tests using col-
lected material and on the modeling of long-term effects
using uncertain predictive models. Given the time that
has elapsed since mining operations were undertaken
at many abandoned sites, conditions of degradation and
instability or chemical change and contaminant plume
extension are often well developed. Thus, at abandoned
mines, long-term site characterization usually can be
determined directly from observation and characteriza-
tion of current conditions. In such situations, extensive
investigations and laboratory testing programs are not
required to make a preliminary assessment.
Remediation objectives can be divided into three broad
categories:
• Physical stabilization. Mine components must be
safe and stable.
• Chemical stabilization. Materials must not decom-
pose and yield soluble contaminants.
• Land use and aesthetics. The site must be useful
and look good.
Technical Guides for Site Characterization
Because comprehensive guidance on the characteriza-
tion of abandoned mine sites cannot reasonably be pro-
vided in this paper, the reader is referred to the following
technical guidelines:
• Rehabilitation of Mines: Guidelines for Proponents.
This document, issued by the Ontario Ministry of
-------
Northern Development and Mines, provides an ex-
cellent framework for the characterization of aban-
doned or closed mines (1).
• Draft Acid Rock Drainage Technical Guide. This
document, prepared for the British Columbia Acid
Mine Drainage Task Force, provides a sound de-
scription of acid generation investigations, including
testing and site characterization techniques for new
mines (2).
• Mine Rock Guidelines: Design and Control of Drain-
age Water Quality. This document, issued by the
Mines Pollution Control Branch of Saskatchewan
Environment and Public Safety, describes site char-
acterization techniques suitable for field reconnais-
sance and detailed investigation and characteriza-
tion of mine rock wastes. Such wastes represent one
of the most significant sources of environmental ef-
fects associated with abandoned mine sites (3).
The next section of this paper concentrates on a char-
acterization methodology well suited to sites where acid
drainage from mine rock waste is a particular concern.
The final text section contains techniques of particular
value for performing an initial investigation at sites with
acid rock drainage (ARD).
Steps in the Characterization of Aban-
doned Mine Sites With Acid Rock Drain-
age
Mine site characterization can be divided into two stages:
• Initial, or reconnaissance-level, investigation and
characterization
• Detailed investigation and characterization
For both of these phases, the activities required for in-
vestigation and characterization can be further divided
into three steps as illustrated in Figure 1 and described
in the list below.
1. The Planning Step:
• Define potential concerns for the site: What
problems to consider?
• Select a methodology for site characterization:
How to look at the site?
• Define the initial information requirements:
Where to start?
2. The Investigation Step:
• Establish a set of techniques for initial recon-
naissance: What can be seen from the site?
r
Planning
t
Investigation
t
Evaluation
All Steps must be
considered for
appropriate and
adequate site
charactterization
Figure 1. Site characterization steps.
• Evaluate existing information: Are data suffi-
cient to define concerns?
• Define additional data requirements: Where do we
go from here?
3. The Evaluation Step:
• "Quantify" potential issues of environmental li-
ability: What are the real problems?
• Evaluate alternative control measures: How
can these problems be solved?
• Conduct a cost/benefit evaluation: What is the
best control/remediation measure for the cost?
All three steps must be considered early in the site char-
acterization process. Only if the investigator has a sense
of the potential environmental impacts associated with
the site can a characterization plan be developed that
adequately addresses concerns. Moreover, early identi-
fication of the "real problems" and potential remediation
options ensures that site characterization provides suffi-
cient information for designing the most advantageous
remediation measures. Thus, the investigation and evalu-
ation steps are performed iteratively, preferably by the
investigator as site reconnaissance is in progress. The
investigator must:
• Anticipate the concerns that may be associated with
a site.
• Plan the investigation to explore for these concerns.
• Recognize new concerns as reconnaissance is in
progress.
• Evaluate significance of concerns as they are iden-
tified.
• Consider the reclamation options that might be ap-
plicable to these concerns.
• Assess the requirements of such remediation.
• Perform any additional characterization necessary
to provide the information for assessing the effec-
tiveness of the remediation measures.
-------
During the initial investigation and characterization, the
investigator performs all the planning, investigation, and
evaluation steps using low-cost techniques that can be
applied in the field. A description of some of these tech-
niques is the focus of this paper. The detailed level of
site characterization that follows the reconnaissance
phase can be planned to address subsequently the re-
maining data deficiencies. The effectiveness of the de-
tailed-level investigation can be improved considerably
by a complete initial site assessment. Moreover, addi-
tional characterization phases can be avoided.
Initial Investigations at Abandoned Mine
Sites With Acid Rock Drainage
The objective of such reconnaissance is to assess:
• Signs of ARD
• Factors that control ARD
• Control/remediation measures
• Environmental effects (with and without control/re-
mediation measures)
• Characterization requirements for the detailed-level
investigation
The investigator should take the following to the site:
• Equipment for collecting water samples for subse-
quent laboratory analysis.
• pH paper or, preferably, a field pH meter as well as
a conductivity meter for taking measurements of wa-
ter pH and conductivity as an indicator of acidity and
dissolved salt content.
• Demineralized water and a beaker in which paste
pH and conductivity tests can be performed on tail-
ings and rock waste samples.
• A10% hydrogen chloride solution for testing for car-
bonates in rocks.
• A hand lens, rock hammer, and mineral identifica-
tion book for examining mine rock and identifying
minerals.
• Sample bags
• A camera for recording observations of color, tex-
ture, and physical conditions.
To assess the ARD conditions on a site, the investigator
must have a basic understanding of the kinetics of acid
generation and contaminant leaching. Acid generation
occurs when sulfide containing rock is mined and brought
to the surface where it is exposed to air and water. The
sulfides react with the air and water to produce sulfuric
acid. If the resulting acidity is not neutralized by neutral-
izing minerals in the rock, then acidic conditions develop
that leach metals from the rock. This results in the con-
taminated drainage referred to as ARD.
Figure 2 is a plot of the normalized rate of oxidation of
sulfides for various pH values. In the absence of biologi-
cally catalyzed oxidation, oxidation rates are relatively
slow for all pH conditions. Biological oxidation by
Thiobacillus ferrooxidans occurs when the pH has
dropped to below 4.5 and is at a maximum at a pH of
about 3.5. Biological oxidation results in a dramatic (50
to 1,000 times) increase in the oxidation rate. Rocks ex-
posed in the field typically are at neutral pH, which is
controlled by the presence of alkali minerals such as
calcite in the rock. The paste pH for such fresh rock is
usually neutral with a low conductivity. Immediately after
exposure, oxidation starts but at the slow chemical oxi-
dation rate. Initially any acidity generated is neutralized
by the alkali minerals in the rock, maintaining the neutral
pH and controlling the rate of oxidation. During this phase,
the pH of the rock remains neutral but sulfates are pro-
duced; thus, a paste of the rock will produce a neutral
pH but a relatively high conductivity. If the quantity of
sulfides is sufficient over time to generate enough acid-
ity to consume all the available alkalinity, then acidic con-
ditions begin to develop. The paste pH of the waste rock
decreases and the conductivity becomes extremely high
as the concentration of dissolved salts increases.
The decrease in pH that can occur over time is illus-
trated in Figure 3. Each step in the downward curve rep-
resents the pH value at which a particular mineral in the
waste rock buffers the paste pH. As each buffering min-
eral type is consumed, the pH drops and the oxidation
rate might increase. The time required for acidic condi-
tions to develop depends on the amount and nature of
the sulfides and the alkali minerals present in the waste
rock. This process may take from months to many tens
of years. Because large variations in mineral assem-
blages occur in the waste rock, the rates and time of
onset for acid generation can vary considerably. Thus,
acid generation initiates in spots where conditions are
particularly favorable. At these locations color changes,
which occur as the minerals oxidize and are neutralized,
are often readily apparent. The selective sampling of such
'.trigger" spots results in paste pH and conductivity val-
ues indicative of the oxidation and acid-generation pro-
cesses. Thus, by performing field paste pH and conduc-
tivity tests an investigator can make an early assess-
ment of potential acid-generating conditions long before
the contaminants generated in the process have had a
chance to migrate to the seeps issuing from the waste
dumps or adjacent streams.
Once acidic conditions have developed locally, then the
acidic solutions can be leached by infiltrating waters and
carried along a seepage pathway. As the acidic solu-
tions migrate along this pathway, they encounter neu-
10
-------
.2
x
o
3
CO
IT
E
_N
"to
O
0.2 -
Biological
Figure 2. Kinetics of acid generation.
PH
Q.
8.0 -
6.0 -
4.0 -
2.0 -
pH Plateaus Resulting from Minerals
Buffering at Various pH Values
Time
Figure 3. pH control during acid generation.
11
-------
tralizing minerals and the acid solution is neutralized with
the resultant deposition of salts and metal hydroxides.
These deposits have many characteristic colors; they
range from red ferric hydroxide to white aluminum hy-
droxide and blue and green copper carbonates. As acid-
ity continues to migrate down a seepage pathway, the
available alkalinity in the pathway is consumed and the
acid front migrates farther from the source. At a particu-
lar point along a seepage pathway, a progressive change
occurs over time as the pH of the passing seepage wa-
ter decreases. This pH decrease is accompanied by in-
creases in metals and other contaminant concentrations.
The change in metals concentrations that can occur at a
point in a seepage pathway downstream of the acid-gen-
erating source is illustrated in Figure 4. The time needed
for increased metal concentrations to be apparent in
downstream wells and monitoring points can be ex-
tremely long (tens and hundreds of years). Thus, the
monitoring of downstream effects often is not a reliable
early indicator of potential acid-generation conditions.
For this reason, the site investigator must assess care-
fully the acid-generating conditions of the potential source
materials, rather than concentrate on trying to measure
the downstream environmental impacts.
Where the investigator should look:
• As close as possible to the potential acid-generat-
ing sources; perform paste pH and conductivity tests
on the materials themselves.
• Surface pools on the wastes
• Seeps at the toe of the wastes
• Decants and surface runoff
• Ground water and monitoring wells.
When the investigator should look:
• Spring and fall when the flushing by infiltration is
normally greatest
• In mid-summer when staining may be most appar-
ent.
• At first snowfall when hot spots can be readily ob-
served.
What the investigator should watch for:
• Field observations
- Visible sulfides
- Red, orange, yellow, white, blue stainings or pre-
cipitates
- Dead vegetation
- Melting snow or steaming vents on wastes
- Dead fish and other biota
• Water quality
- Low pH in seeps, ground water, decants
- Elevated or rising conductivity, sulfate and/or met-
als
- Increasing acidity or decreasing alkalinity
• Geochemistry
- Low paste pH of mine wastes
- High conductivity in field extractions
References
1. Ontario Ministry of Northern Development and Mines.
1992. Rehabilitation of mines: Guidelines for propo-
nents. Ontario Ministry of Northern Development and
Mines, Sudbury, Ontario, Canada. Version 1.2 (July).
2. Steffen, Robertson and Kirsten (BC) Inc. in associa-
tion with Norcol Environmental Consultants and
Gormley Process Engineering. 1989. Draft acid rock
drainage technical guide, vols. 1 and 2. Prepared
for British Columbia Acid Mine Drainage Task Force.
BiTech Publishers, Richmond, British Columbia,
Canada. ISBN 0-7718-8893-7.
3. Steffen, Robertson and Kirsten (BC) Inc. 1992. Mine
rock guidelines: Design and control of drainage wa-
ter quality. Prepared for Saskatchewan Environment
and Public Safety, Mines Pollution Control Branch,
Prince Albert, Saskatchewan, Canada. Report No.
93301.
12
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0)
Acidic
Drainage
Neutralized
Acidic Drainage
Process Water
• Original Groundwater
Time
Figure 4. Kinetics of contaminant front migration.
13
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Chapter 4.
U.S. Bureau of Mines Remediation Research*:
New Uses for Proven Tools
William B. Schmidt
Introduction
The U.S. Bureau of Mines (USBM) has been actively
involved in mine waste research for 3 decades, with par-
ticular emphasis for the past 8 years in the hard rock
area. Historically, USBM's research in the environmen-
tal area has focused on coal-related issues. From 1965
to 1982 this emphasis was consistent with USBM's in-
volvement in coal-related health and safety issues and
later with the implementation of the Surface Mining Con-
trol and Reclamation Act of 1977. The emphasis shifted
to hard rock issues as a result of the increasing public
and industry concern about associated environmental
issues, as well as consolidation of USBM's metallurgy
and mining research efforts and USBM's general rethink-
ing of its mission.
Consolidation of USBM's metallurgical and mining ar-
eas was beneficial, particularly in regard to hard rock
environmental issues. As a result of changes, extractive
metallurgists and process engineering specialists were
brought together with hydrologists, geologists, geophysi-
cists, and other mining related practitioners to address
the multidimensional problems typical of mine wastes.
Current remediation research at USBM focuses on the
following areas:
• Mine drainage technology
- Acid drainage from coal mines
- Acid drainage from metal and nonmetal mines
• Solid mine waste and subsidence
• Hazardous waste treatment technologies
- Characterization
- Treatment
• Abandoned mine land (AMI) remediation
• NOTE: Since these seminars, the U.S. Bureau of Mines has been abolished.
Two programs are related to the most critical problems
at present in the mine waste area—liquid and solid
wastes. One program is related to the extension of the
USBM's mining skills to the larger world of contaminated
wastes, and the other is related to the problems of re-
claiming abandoned coal mine lands, a subset of the
mine waste problem. This latter program is specifically
mandated by Congress and subject to legislative require-
ments.
The allocation of USBM funds between the four princi-
pal research areas in fiscal year 1995 is shown in Figure
1. Funding for these programs in fiscal year 1996 is ex-
pected to increase by about 50 percent.
Mine Drainage Research
USBM's research program for liquid mine waste (i.e.,
mine drainage) focuses on the following areas:
• Prediction
- Fundamental sulfide reactions
- Geochemical models (correlated with static and
kinetic testing and field test results)
- Host rock and waste rock dumps
• Mitigation/control
- Seals, grouts, and caps
- Passivation
• Treatment (contaminant removal)
- Chemical
- Biological
USBM mine drainage research is carried out in partner-
ship with the U.S. Forest Service (FS). Several years
14
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Mine Drainage 39.3%
Solid/Subsidence 31.1%
Abandoned Mine Land 9.4%
Hazardous Waste 20.2%
FY 95 = $19.4 Million
Figure 1. USBM funding distribution for remediation research in fiscal year 1995.
ago FS officials proposed this cooperative effort to USBM
to solve a most intractable environmental problem—acid
rock drainage (ARD).
Research concerning prediction of mine drainage prob-
lems concentrates on the host rock and waste dumps.
Field work draws heavily on the efforts of researchers in
Canada's Mine Environment Neutralization Drainage
(MEND) program and other activities in the ARD area
worldwide, including groups working on a major contribu-
tor to ARD—mine tailings. Although the research effort
focuses on the development and testing of better tools
for predicting ARD problems, considerable emphasis also
is placed on determining the generation, migration, and
ultimate fate of mining-reteted contaminants in nature.
Mitigation/control is important for situations where po-
tential ARD problems could not have been identified be-
forehand. If ARD cannot be predicted, the best approach
is to apply tools and techniques that interrupt the ARD
process or stop the flow of contaminants. The types of
tools being developed or investigated range from passi-
vation of reactive mineral surfaces to the use of grouts
and seals.
The development of treatment technology represents the
"holy grail" of much of the current research on mine
waste. In this area, a dichotomy exists between regula-
tors and mine operators. Regulators are faced with the
problem of contaminated discharges from an adit or other
mine opening and are looking for a black box that can
be attached to the end of a pipe to produce gold-book
quality water. Mine operators, as well as land manag-
ers, envision perpetual treatment, liability, and expendi-
ture of scarce resources as the inevitable consequence
of this approach. Short of these broad goals is the ob-
jective of developing low cost/low maintenance treatment
systems for remote sites.
The need for treatment is inevitable as is the need for
techniques that are both cheaper and pose less of a com-
promise than those offered by the current options. In
some cases, perpetual treatment will be the least costly
and most effective option. Nonetheless, many opportu-
nities for useful research exist. For example, "lime" treat-
ment (i.e., pH adjustment accompanied by precipitation
of acid mobilized metals) is the technology of choice for
many applications. Even this technology offers opportu-
nities for further improvement, such as development of
denser floes and approaches for removing metals that
would change a nonregulated sludge into a regulated
waste. In addition, researchers should address the many
"niche" needs for technologies to deal with special situa-
tions and problem contaminants. Also, biotreatment ap-
pears to offer great potential for improved treatment sys-
tems if researchers can engineer ways to use the bio-
logic phenomena that they are beginning to understand.
Recent changes in clean water compliance requirements
likely will shift attention to an area that has thus far re-
ceived little attention from the technology community—
nonpoint source controls. Instead of the black box at the
end of the pipe (the visible discharge flowing from the
picturesque old mine) the nonvisible flows through dis-
turbed host rock, old tailings, and waste piles that are
contaminating streams and rivers will need to be ad-
15
-------
dressed. USBM's research approach should prove ben-
eficial in this area, but a lot of new lessons will be learned.
Solid Waste Research
The solid waste area of USBM's program deals with a
fairly broad range of issues, as listed below:
• Reprocessing/process modification
- Pyrite removal
- Heavy metal removal
• Pyrometallurgical treatment (high temp)
- Vitrification
- Metal extraction
• Waste disposal
- Fly ash (i.e., only fly ash from coal covered by
this program)
- Dump stability
• Subsidence effects
- Prediction
- Prevention
A more accurate description of this topic might be
nonliquid, nongaseous environmental problems. Much
of this work (e.g., on fly ash disposal, dump stability, sub-
sidence-related research, and blasting vibration studies)
is intended to provide regulatory agencies, the mining
industry, and other interested parties with unbiased in-
formation upon which to base sound decisions. A com-
ponent of this work, however, relates to the issue of hard
rock mining wastes.
One of the subjects that has been of interest to many in
the field has to do with the practicality of separation of
the more reactive components of mine waste. This would
allow for the trouble-free disposal of the 90 percent of
waste that will not present an environmental problem
and the special treatment of the much smaller, problem
components. USBM's work using state-of-the-art min-
eral beneficiation technology would suggest that this ap-
proach to waste remediation has different applicability
to freshly processed wastes than it does to aged wastes
on abandoned sites.
Use of the Technology
In many ways the technology of the mining/mineral pro-
cessing industry, the focus of USBM, is well developed
for the remediation of various contaminated wastes. The
technology is "proven"—a strong technical underpinning
exists for these technologies. In addition, the equipment
used is robust and relatively simple. The industry is given
to building plants around the replication of a series of
"unit operations," each of which is well understood.
On the other hand, as USBM researchers discovered,
applying these technologies to nonmineral production
problems requires some rethinking of very basic consid-
erations in regard to the minerals industry. As a general
statement, mineral production operations are very sen-
sitive to the cost of reagents and supplies. Because the
plants are designed to run for a long time (e.g., 30 years),
capital costs diminish in importance. The situation with
regard to a 3-year Superfund cleanup is almost exactly
the opposite: Reagent costs are almost trivial and the
cost of a plant is significant. This presented two lines of
thought to USBM researchers. The first is that reagents
that they tended not to consider in regard to the screen-
ing process because of their cost (e.g., organic acids
instead of mineral acids) needed to be assessed in light
of changed circumstances. The second is that the cur-
rent process of treating each site as a unique problem
also needed to be rethought by those in charge of
cleanup. If the same plant could be reused 3, 4, or 5
times on similar wastes, the cost per yard of treated
material would fall dramatically as the capital costs were
spread over a larger base. Treatment (i.e., permanent
removal of the contaminants) became much more com-
petitive with, or cheaper than, other approaches, such
as stabilization or removal and disposal. Unfortunately,
implementation of this strategy is beyond the control of
USBM.
Recovery of Valuable Metals
Another issue is the potential for making money from
the treatment of wastes, particularly mine wastes, by
recovering valuable metal. In some instances, part of
the cost of remediation of mine wastes might be returned
from the metal recovered. Those instances will be few,
but far more numerous than instances of covering the
cost of the remediation as well as making a profit.
Most of the mineral sites are mine sites from which the
ore, the valuable metal concentrations, have been re-
moved. The cost of extracting additional value from pro-
cessed material generally exceeds the value of the prod-
uct. In addition, the material left at processing sites has
been altered by natural processes (e.g., oxidation) and
would require additional treatment to restore it to a spe-
cies that has value in the marketplace. Similar limita-
tions apply to liquid wastes. Any contaminated stream
might contain some valuable metals, but the concentra-
tions would be such that the kinetics of the reactions
needed to recover them would be generally unfavorable.
For example, a tremendous quantity of gold is in the
16
-------
oceans in aggregate; however, the concentration of gold
in any given cubic meter of seawater is minuscule.
Abandoned Mine Land
Another element of USBM's environmental research pro-
gram is the Abandoned Mine Land program. This work
primarily concerns areas east of the Mississippi River.
The program was established specifically to help reduce
the cost of reclaiming lands that were mined and aban-
doned before the passage of the Surface Mining Control
and Reclamation Act in 1977. The focus includes the
control of coal-mine acid drainage, coal subsidence, and
the extinguishing of fires in abandoned mines and coal
dumps. Some of the relevant technology (e.g., sealing
for mine shafts) can be applied to the remediation of
physical hazards from metal mine openings. Most of the
research enhances the USBM's technical base for ad-
dressing hard rock issues rather than being directly ap-
plicable.
USBM has been very active in seeking partnerships with
the users of mine technology. USBM encourages addi-
tional opportunities to work with others to advance the
cause of hard rock environmental remediation.
17
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Chapter 5.
The Technology and Operation of Passive Mine
Drainage Treatment Systems
Ronald R. Hewitt Cohen
Introduction1
Mining activity has increased since the late 1800s as a
result of technological improvements and economic ad-
vantages in blasting, materials handling, and an increase
in the size of equipment, combined with the constantly
increasing demand for minerals. The mining industry's
efforts to meet demand and minimize U.S. dependence
on foreign mineral supplies has meant an increase in
disturbed lands and adverse environmental effects. Min-
ing conducted prior to 1900 has also left us with a legacy
of waste rock, mine tailings, and drainage tunnels from
which metal-laden waters contaminate receiving waters.
Treatment of mine effluent using a passive mine drain-
age treatment system (PMDTS) is addressed in this pa-
per. Please note that the Colorado School of Mines
PMDTS can be used to treat wastewaters from galva-
nizing and cadmium, chromium, and nickel plating as
well as from lead-acid battery recycling industries.
Production of acid water is common to mining situations
where pyrite and other metal sulfides become exposed
to atmospheric conditions. Upon exposure to the atmo-
sphere, sufficient oxygen and water are present to ini-
tiate the oxidation of pyrite. The overall reaction is:
FeS2(s) + 4 °2 + 3 H2° -* Fe(°H)3 ^ + 2 SO4 + 3 H+ <1)
Notice the necessity for air and water (although the pro-
cess can occur in a dry environment). Few other natural
weathering reactions produce this amount of acidity.
At pH 3.5 or less, bacteria such as Thiobacillus
ferrooxidans accelerate the rate of conversion of Fe++ to
Much of this paper is based on information from research and development
studies performed in the laboratory, from the Big Tunnel Pilot system, and
from the Eagle Mine in Minturn, CO (research supported by Paramount Re-
sources, through Dames and Moore, Inc.) by Colorado School of Mines per-
sonnel. The documentation can be located primarily in Masters and Doctor-
ate thesis of graduate students at the Colorado School of Mines. In particular,
the paper makes significant use of results from studies by Toshisuke Ozawa,
Mark Willow, Mary Lanphear, Julia Reynolds, Margaret Staub, JoAnn Euler,
Peter Lemke, Steven Machemer, and Judy Bolis
Fe3+. Such bacteria may accelerate reactions by orders
of magnitude (2). Numerous studies have documented
the damage acid water causes for surface and ground-
water systems. Sources of acid coal mine drainage pol-
lution in Appalachian active and inactive mines number
66,500 (3). This mine drainage results in approximately
10,500 miles of streams with water quality below desir-
able levels.
Metals mining can result in a diffuse source of pollution
from multiple piles of waste rock and tailings. Each mine
portal, or opening, has mounds of rocks from the mine
workings. Some of the material is waste rock from the
mine and some is the result of crushing and sorting rock
to obtain the ore. In the Rocky Mountain region, it is not
unusual to see hundreds of small mines in an area of a
few square miles, each with mine tailings piles. Once in
piles, the waste material is exposed to the atmosphere
and water such that the remaining sulfide ores can be
oxidized. In addition, the broken and crushed rock offers
a large surface area for the chemical and biological re-
actions. Emerick (personal comm.)2 estimates that thou-
sands of kilometers of waterways are contaminated by
residuals of metal mining in Colorado alone.
Water contaminated with acid mine drainage may not
be suitable for drinking, livestock watering, support of
wildlife, irrigation, or industrial use. Effects can be asso-
ciated with cadmium, copper, lead, arsenic, and zinc as
well as antimony, arsenic, beryllium, chromium, nickel,
silver, thallium, uranium, radium (from uranium mine tail-
ings and phosphate mines), and selenium.
Metal Wastes Pollution Control
Pollution control in the U.S. mining and metals industry
is a major factor in any mining operation. This was not
always the case. Public demand for action resulted in
mining legislation to prevent damage to mined lands.
2 Personal communication with John C. Emerick, Colorado School of Mines,
Division of Environmental Science and Engineering, Golden, CO (1989).
18
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Today federal legislation is in place, and nearly every
state has enacted statutes and regulations concerning
mining and mined land reclamation. To conform to these
regulations, the mining industry has developed and con-
tinues to develop pollution control measures and treat-
ments. Nearly $1 million is spent each day on acid mine
drainage prevention and abatement by mining compa-
nies throughout the United States (4).
Removal of metals can be facilitated by neutralization
using a hydroxide precipitate-caustic soda treatment.
Often, chemical neutralization is accomplished with
slaked lime or calcium carbonate added directly to the
water (5). Also, an in-line aeration and neutralization sys-
tem (ILS) has been developed that incorporates the
chemical treatment processes into a functionally closed
system in which the treatment reactions can be more
closely monitored and accelerated. This system makes
possible the reduction of the chemical reagent costs and
reaction processing times (6). Electroprecipitation pro-
cesses accomplish similar results by the precipitation of
metal hydroxides or by metal ion adsorption (7). All of
these processes, both chemical and physical, are se-
verely limited, however, in that they cannot be used to
treat the sometimes excessive sulfate concentrations
associated with most acid-mine drainage; also, these
processes impart a high degree of hardness to the wa-
ter and produce waste sludge that requires additional
treatment and/or disposal (8). These methods also can
require large capital operations and maintenance costs.
Precipitation operations must be perpetual, and the re-
sulting high volumes of sludge must be disposed of in
increasingly space-limited hazardous waste repositories.
Passive Mine Drainage Treatment Systems
Treatment of acid mine drainage using artificial and natu-
ral wetlands is a promising new approach. The focus of
these PMDTSs (9) is to apply biogeochemical water treat-
ment mechanisms at or near the source of the mine drain-
age to concentrate and immobilize metals and raise pH.
Prototype PMDTSs have been constructed in Colorado,
Pennsylvania, and West Virginia. Egerand Lapakko(10)
estimated that PMDTSs required less than one-half the
capital costs and one-twentieth the maintenance costs
of conventional plants.
Past PMDTS technologies were based on constructing
shallow ponds or cells that resembled natural wetlands.
These systems were filled with peat or another organic
substrate. Cattails, sedges, and rushes were then trans-
planted from natural wetlands. Approximately 400 con-
structed wetland treatment systems have been built in
the United States (11).
PMDTS Evolution and Limitations
Klusman and Machemer (12) listed the major metals
removal processes in a PMDTS system as follows:
• Adsorption and complexation of metals by organic
substrates
• Microbial sulfate reduction followed by precipitation
of metals as sulfides
• Precipitation of ferric and manganese oxides
• Adsorption of metals by ferric hydroxides
• Metal uptake by plants
• Filtration of suspended and colloidal materials
The following discussion focuses on the evidence for
metal removal and a pH increase in the PMDTS by the
mechanisms listed above. The evidence is used in com-
bination with data from hydraulic studies to suggest de-
sign configurations and parameters.
Reynolds and coworkers (13) and Machemer (14) ex-
amined the chemical and biological processes in wet-
land treatment systems (PMDTSs) receiving acid mine
drainage and found that the rate of sulfate reduction to
sulfide was the most crucial parameter involved. This
conclusion has been corroborated by additional research
on the utilization of natural and artificial wetlands for acid
mine drainage treatment (15,16,17,18,19). The activity
of the sulfate-reducing bacteria in these systems con-
trols the efficiency of metal decontamination (15,12).
During respiratory processes, the sulfate-reducing bac-
teria oxidize simple organic compounds (represented by
the chemical formula CH?O), resulting in the formation
of hydrogen sulfide and bicarbonate ions at the circum-
neutral pHs of "optimal" sulfate reduction (19):
SOf + 2 CH2O
H2S + 2 HCO3-
The electron donors for this reaction can include mo-
lecular hydrogen (H2) and organic compounds such as
acetate and lactate. The formation of bicarbonate indi-
cates the ability of the sulfate-reducing bacteria to con-
trol the pH of their particular microenvironment (16,17).
The form of the sulfide from the bacterially mediated
sulfate reduction is dependent on the pH of the reaction
and is represented by the equilibrium:
HS <-> HS~
+ 2 H+
Both HS~ which occurs at neutral pH, and S2~, which
occurs at high pH, are soluble in water, while H2S, the
predominant form at low pH, is not soluble and tends to
evolve from solution, even at neutral pH where it is at
equilibrium with HS~.
The bicarbonate ion formed during sulfate reduction will
equilibrate between C02, HC03~, and CO 2~. The pre-
dominant form at the "optimal" pH range for dissimilar
sulfate reduction, however, will be the bicarbonate ion.
This rise in pH will facilitate the hydrolysis and precipita-
19
-------
tion of some contaminant metals from acidic waters as
insoluble hydroxides and oxides (1,21):
AI3+ + 3 H2O«-» AI(OH),(s) + 3 H*
The hydrogen sulfide created during the reduction reac-
tion also will react with many metal species, forming in-
soluble metal sulfide precipitates:
H2S + Fe2+<->FeS(s) + 2H+
These processes all contribute to the removal of con-
taminant metals from wastewaters through the action of
sulfate-reducing bacteria.
Other processes that may contribute to metal removal
within these systems include the precipitation of ferric
hydroxides and manganese carbonates, the subsequent
adsorption of metals by the ferric hydroxide, adsorption
to the organic substrate, and the physical removal of
colloidal particles through filtration by the substrate ma-
trix.
To thrive, sulfate-reducing bacteria require a strict anaero-
bic environment (they are obligate anaerobes) with a pH
in the range of 5 to 8 (21). When pH and/or redox condi-
tions are not optimum, the rate of microbial sulfate re-
duction declines. This in turn reduces metal removal
capacity. The rapid influx of acidic, aerobic waters ap-
pears to drive the pH of the treatment system down and
redox up, thus inhibiting bacterial sulfate-reducing pro-
cesses. The metal removal efficiency and loading ca-
pacity of the treatment system then becomes a function
of not only size and hydraulic conductivity, but of the
acidity and oxygen content of the influent water (15).
Results, Evidence, and Implications
The Role of Vascular Plants in the PMDTS
Many studies in the late 1980s either focused on plants
or assumed plant uptake of metals was an important
process in metal removal (22,23,24). Girts and
Kleinmann (11) suggested that metal removal was me-
diated by plants and bacteria. Such was the emphasis
on plant removal processes that Guntenspergen and
associates (23) evaluated 1,000 plant species. Consid-
erable emphasis was placed on cattail species, a plant
found in most wetlands that is particularly resistant to
poisoning by heavy metals and low pH (24,25,26). At
the Big Five Tunnel Pilot system in Idaho Springs, Colo-
rado, cattails not only dominated the PMDTS, but almost
completely outcompeted the other plants and formed very
high biomass densities. Evidence indicates, however,
that plants account for as little as 1 to 5 percent of metal
accumulation. Evidence for uptake of metals into the root,
stem, and leaves of plants suggests no net uptake of met-
als over the period of the experiments (25,27,28,29). A
possible, but not statistically supportable, increase in
plant tissue metals occurs for some metals, but that is
probably within the range of analytical and sampling er-
ror. As much evidence exists indicating decreasing metal
concentrations in the plants. In addition, one 3 by 3 by 1
meter unit at the Idaho Springs site was covered with
hay and a black, opaque liner. It proved to be the most
successful design for removing metals.
Although plants may not accumulate metals, they may
promote metal removal by generating microzones of oxi-
dizing or reducing conditions in the organic substrate.
Microzones around the root mass may be more aerobic
due to oxygen excretion (25), inducing precipitation of
manganese iron as Fe(lll). The process of manganese
and iron oxide formation may be a removal mechanism
for the metals, but it occurs in only 2 percent of the vol-
ume of the system. The remaining 98 percent of the sys-
tem is anaerobic. Thus, plants are not the dominant re-
moval mechanism for metals.
Adsorption and Complexation Processes
in Metal Removal
Adsorption is a process in which a cation like Fe2* is
bound to the solid phase that contains a residual nega-
tive charge on its surface (usually in the form of a hy-
droxide ion). Complexation is the result of humic materi-
als terminating in phenolic and carboxylic groups that
dissociate under particular pH conditions. Kerndorf and
Schnitzer (30) found that the strength of sorption to hu-
mic materials varied with metal species as follows:
Fe = Cu » Zn » Mn
The adsorption process also varies with pH.
For natural and constructed wetland systems, metal re-
moval due to adsorption takes place until sorption sites
are saturated. Thus, the system will have a fixed life-
cycle, perhaps as short as a month (14,15). When sul-
fate-reducing bacteria activity was terminated by poisons
specific to their systems, Willow (15) reported that all
metals were removed by the organic substrate for ap-
proximately 20 days, then manganese, zinc, copper, and
iron started breaking through to the effluent (Figure 1).
Cadmium, manganese, and zinc containing inflow was
fed to organic substrate that had no sulfate-reducing
bacteria activity. All metals were adsorbed to the sub-
strate for the equivalent of 20 days. The most weakly
sorbed metal, manganese, was displaced from the sorp-
tion sites first and demonstrates breakthrough starting
at 55 volumes. The next most weakly sorbed metal, zinc,
begins breakthrough at 75 volumes (15).
The interpretation of the data is that competition occurs
for the sorption sites, particularly after the sites are satu-
rated. Iron and copper, which bind to the particles more
strongly than zinc and manganese, cause desorption of
the zinc and manganese. Therefore, in 20 to 30 days,
20
-------
1.0 -I
0.9-
0.8-
0.7-
0.6-
§0.5-
0.4-
0.3-
0.2-
0.1 -
0.0-
2
jP
.cr--'Cr
;
1
1
1
p
/
»
Q j^.^^^
. ...... ^•.^jji LJ Lffjm.mAifmtjt | ^ • " H»- PE — ..-p 1
5 35 45 55 65 75 85 95 105
Volume of Influent Passed (L)
- Cadium
h" Manganese
• Zinc
Figure 1. Breakthrough of manganese, followed by zinc, from wetland system to the effluent after saturation ofsorption sites (15).
the sorption sites were saturated. Thus, sorption pro-
cesses are not the removal mechanism of choice if the
PMDTS is to have a multiyear life-cycle.
Sulfate-Reducing Bacteria
Sulfate-reducing bacteria (SRB) are obligate anaerobes
that decompose simple organic compounds using sul-
fate as the terminal electron acceptor. The result is the
production of sulfide that may be given off as H2S gas or
react with metals to form metal sulfides. Much of the
following comes from a review by Staub (17). As dis-
cussed in the Introduction, SRB reduce sulfate to sul-
fide, followed by precipitation of metals as metal sulfides.
FeS is one of a family of compounds called acid volatile
sulfides (AVS). These compounds will generate H2S with
the addition of acid. Reynolds and investigators (13) re-
ported that the dominant forms of sulfur resulting from
SRB activity in the PMDTS are H2S, dissolved S~ and
solid AVS. Reynolds and coworkers also noted that H2S
is present in small quantities when influent metal load-
ings are high, resulting in AVS being the major form (over
90 percent). Herlihy and Mills (31) also reported that most
of the sulfide readily reacts with metal ions to precipitate
them as metal sulfides.
Hedin and associates (32) have suggested that a good
estimate for rates of sulfate reduction is 300 nmole S-
produced per cubic centimeter per day. Reynolds and
investigators (13) reported typical levels to be 600 to 1200
nmole/cm3/day using both radiolabeled tracers and mea-
surements of rates of production of AVS (Table 1).
These numbers permit the calculation of theoretical treat-
ment capacities of the PMDTS if one assumes that most
removal of metals can be accounted for by sulfate re-
duction and the metals are removed on a one-to-one
molar basis as AVS. Reynolds and coworkers (13) re-
ported that sulfate-reducing activity could account for all
of the removal of metals in the Big Five Tunnel PMDTS.
In addition, work at the U.S. Bureau of Mines and Colo-
rado School of Mines demonstrated that as metals were
removed, pH increased and alkalinity increased (33,34).
This is not unexpected because bicarbonate is produced
and the loss of H2S gas represents a loss of hydrogen
ions.
Updegraf (personal comm.)3 and Reynolds and cowork-
ers (13) reported experiments examining the effects of
substrates and other variables of SRB activity. They used
many different substrates, including spent mushroom
compost, peat, corn wastes, rice waste, decomposed
wood chips, and composted cow manure. Results from
the Big Five Tunnel PMDTS showed that peat-based
systems were ineffective, even when limestone was
added (35). The wood chips and cow manure gave the
highest activity rates, with other materials often yielding
3 Personal communication with David Updegraf, Colorado School of Mines,
Chemistry and Geochemistry Department (in transitional retirement) (1992).
21
-------
Table 1. Results of Isotopic and Acid Volatile Sulfide Analyses of
the Rate of Sulfate Reduction in Samples Taken From a
Pilot-Scale System(13)
Rates of Sulfate Reduction (nanomoles of S2~ per cm3 of substrate
per day)
Isotopic Method 35S
Location Sample
Taken in Reactor
Surface
Bottom
Surface
Control
Date Rate
10/90 600
11/90 440
11/90 750
11/90 12.2
AVS Method
% Standard
Deviation
(number of
samples)
10.9(4)
10.4(3)
8.6 (6)
29 (3)
Surface
11/90
670
35 (6)
near-zero activity. Decomposed wood chips and
composted cow manure also had the highest buffering
capacity and pHs of the tested substrates. When pH-
raising additives and alkalinity were included in the poor
substrates, activities of SRB increased substantially.
Reynolds and coworkers (13) also found that water ex-
tracts of hay could increase sulfate reduction 2.5 to 7
times. SRB cannot utilize complex organics, however;
they require simple organics such as acetate and lac-
tate. Indeed, additions of these nutrients enhanced SRB
activity (13). A consortium of heterotrophic bacteria prob-
ably exists in the substrate that decomposes complex
organics into forms available to the SRB. That possibil-
ity is being studied in the laboratory at the Colorado
School of Mines.
Lemke (36) found that biofilms clog the pores of sub-
strates used in horizontal flow units, regardless of the
size or amount of amendments. Cohen and Staub (16)
used composted cow manure and hay in a 4:1 by vol-
ume ratio. The substrate used by Cohen and Staub was
able to efficiently (98 to 100 percent metal removal) treat
between 4 and 8 times the mine drainage flow rates of
previous systems used in the Rocky Mountain region.
The advantages of using cow manure and hay can be
seen in the section on sulfate reduction. The manure pH
was 8 to 9 and it had high buffering capacity. The hay
has been demonstrated to enhance SRB activity by 250
to 700 percent. The composted manure can neutralize
the pH of the mine drainage. The organic matter in the
manure encourages decomposition and generation of
low redox potentials and serves as an SRB nutrient
source. Thus, ideal conditions are presented to the SRB
until they can modify their own microenvironments.
Structural and Hydraulic Considerations
The Big Five Tunnel system in Idaho Springs was con-
structed in a horizontal flow pattern similar to natural
wetlands and other constructed wetland-like systems.
Lemke showed that hydraulic conductivity of the sub-
strate decreased two to three orders of magnitude in a
few weeks (36). As a result, very small quantities of
wastewater passed through in contact with the substrate
and most of the water flowed untreated over the surface
of the system. The system was reconfigured to force the
water through the substrate (35). Lemke (36) showed
that upflow systems retained their hydraulic conductivity
and guaranteed wastewater contact with substrate. A cell
of the Big Five Tunnel PMDTS was divided into an upflow
cell and a downflow cell. The upflow cell substrate re-
mained saturated throughout the experiments and
treated mine water efficiently. The downflow cell worked
well, but flows that were too low followed channels
through the substrate and a large percentage of the sub-
strate remained dry and unutilized. The upflow configu-
ration seems to fulfill the requirement of steady hydrau-
lic conductivity and water substrate contact. A schematic
of an upflow reactor is shown in Figure 2.
Five-hundred-gallon upflow reactors were constructed
in one area of the Eagle Mine at Minturn, Colorado, and
filled with composted livestock manure. The influent dis-
tribution pipe, made of perforated irrigation tubing, was
protected against clogging by the particulates in the sub-
strate. In the 500-gallon pilot system, the influent pipe
was covered with pea gravel and landscape fabric, which
in turn was covered with a water-permeable geomembrane
(Figure 3). The gravel disperses the inflow and the
geomembrane separates the influent chamber from the
substrate. Larger systems may require the construction of
an influent plenum that is covered with a geomembrane.
Results of the Pilot-Scale Experiments
Research at the Colorado School of Mines has demon-
strated that SRB activity is approximately 600 nanomoles
of sulfide produced per cubic centimeter of substrate per
day. Calculations based on the metal-loading rates at
the Eagle Mine and the 37 cubic feet of substrate of the
PMDT indicate that the system should theoretically reach
its limit of metal removal at a flow of between 200 and
400 ml_/min. Maximum removal rates of 97 to 100 per-
cent have occurred for all metals except for manganese
at the 200 mL/min and 400 mL/min flow rate (Figure 4).
A dramatic decrease in metal removal efficiency seem-
ingly occurred for iron, zinc, lead, copper, and cadmium
on two dates noted on the graphs. On or before August
27, an inflow valve to the system inadvertently was turned
up to very high flows, flooding the system at levels sig-
nificantly beyond its treatment design limits. Prior to Oc-
tober 28, a backup of untreated water into the system
22
-------
Sample
Ports
Influent Port
Over-Flow Drain
Sand Layer
Fiberglass Layer
Substrate Layer
Composed Livestock Manure
Ceramic Granule Composite
Gravel Layer
Figure 2. Construction of 1.5 meter, 15 centimeter diameter experimental reactor. Gravel layer separates substrate from distribution tubing. All
sampling ports extend the entire diameter of the unit with perforated tubing covered with permeable geomembrane.
Influent
Wells
B
f
o. .>:.?
T
HOPE Top
Hay
TJ\-
Effluent
• Substrate
Landscape Fabric
Gravel
Figure 3. Construction of pilot-scale reactor (total reactor volume is 500 gallons).
23
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pH in Single Stage Wells
9.00 •
8.00 •
7.00 •
6.00
5.00 H
4.00
3.00
2.00
10" from bottom
... 20" from bottom
— On top surface
30- 15- 27- 11- 23- 07- 28- 11- 25-
Jul Aug Aug Sep Sep Oct Oct Nov Nov
Date
Removal Efficiency for Cadium
Starting Concentration = 1 mg/L
30- 15- 27-11- 23- 07- 28- 12- 26-
Jul Aug Aug Sep Sep Oct Oct Nov Nov
Date
Removal Efficiency for Copper
Starting Concentration = 15 mg/L
30- 15- 27- 11- 23- 07- 28- 12- 26-
Jul Aug Aug Sep Sep Oct Oct Nov Nov
Date
Removal Efficiency for Lead
Starting Concentration = 0.5-0.9 mg/L
Removal Efficiency for Zinc
Starting Concentration = 200 mg/L
o
a 100
I 90
I I 80
70
60
N
30- 15- 27-11- 23- 07- 28- 12- 26-
Jul Aug Aug Sep Sep Oct Oct Nov Nov
Date
0)
Q.
30- 15- 27- 11- 23- 07- 28- 12- 26-
Jul Aug Aug Sep Sep Oct Oct Nov Nov
Date
Figure 4. Removal efficiency for iron, zinc, lead, copper, cadmium, and manganese in the Eagle Mine Pilot PMDTS. Arrows show where flow
was doubled. Regions of low treatment efficiency were due to backup of untreated water into the treated water area or sudden,
inadvertent surges of flow caused by mine personnel.
24
-------
occurred. The drain to which overflowing, untreated wa-
ter is discharged was clogged with metal hydroxides.
This water backed up and mixed with the treated water
near the sampling point. Evidence that this backup was
not a failure of the system's treatment capability was dem-
onstrated in that by the following week treatment effi-
ciencies for all metals except manganese were again
near 100 percent. Flows were doubled from 50 to 100
mL/min on September 3 and from 100 to 200 mL/min on
October 15. Near the end of the study, flows were doubled
to 400 mL/min. The times of flow adjustment are shown
as arrows in Figure 4.
Further Improvements
Until PMDTS optimization research and development
reduced hydraulic detention times required for 99 per-
cent or better metal removal rates to 40 hours or less
(16), PMDTSs were constrained in their volume/dis-
charge handling capacity. Older PMDTSs could treat
metal waste streams effectively (99 percent or greater
removal) for hydraulic detention times of 250 to 300
hours, or remove 40 to 70 percent of metals at shorter
hydraulic detention times.
To have high sulfate-reducing activity, and therefore a
system with high metal removal capacity, the sulfate-re-
ducing bacteria require a strict anaerobic environment
(they are obligate anaerobes) with a pH in the range of 5
to 8 (22). When pH and/or redox conditions are not opti-
mum, the rate of microbial sulfate reduction declines.
The rapid influx of acidic, aerobic waters appears to re-
duce the pH of the treatment system and increase re-
dox, thus inhibiting bacterial sulfate reduction. The metal
removal efficiency and loading capacity of the treatment
system then becomes a function not only of size and
hydraulic conductivity, but of the acidity and oxygen con-
tent of the influent water. One of the limiting factors ap-
pears to be the pH of the influent water (15).
A second possible limiting factor in the PMDTS at higher
inflow rates is the introduction of dissolved oxygen to
the system by the acid mine drainage (AMD). An in-
creased loading rate of oxygen would reduce the capac-
ity of sulfate-reducing bacteria, which require anaerobic
conditions, to produce hydrogen sulfide. With a greater
influx of dissolved oxygen, one may assume that redox
would increase, sulfate reduction would decrease, and
metals treatment capacity would decrease. If the dis-
solved oxygen content of the influent mine drainage could
be reduced prior to entering the treatment system, the
anaerobic conditions could be maintained for a greater
volume of the treatment substrate, thus allowing for an
increased influent treatment capacity.
Experiments at the Colorado School of Mines have
shown that pH is more critical to reactor efficiency than
dissolved oxygen. The metal-loading rate capacity of a
wet-substrate bioreactor can be enhanced and hydrau-
lic detention times reduced to as low as 16 hours by
modifying the pH of the influent to near neutral (15). The
neutral pH permits enhanced activity of SRBs, the pro-
duction of sulfide, and the removal of metals as metal
sulfide precipitates. The dissolved oxygen was com-
pletely removed in the first few centimeters upon enter-
ing the reactors, while the pH required a greater propor-
tion of the substrate to reach suitable levels for SRB ac-
tivity. As the pH of the influent increased, the rate of sul-
fate reduction increased, raising the metal removal ca-
pacity of the system.
Treatment of Oxyanions such as Arsenate
and Chromate
Not all metals appear as positively charged cations.
Some appear as negatively charged oxyanions with
metals such as arsenic, selenium, and chromium bound
to oxygen to yield arsenate, selenate, selenite, chromate,
and chromite. Can an anaerobic bioreactor dominated
by SRBs remove metal oxyanions? A pilot-scale, anaero-
bic PMDTS dominated by sulfate-reducing bacteria was
utilized to investigate the removal rates as well as re-
moval processes of arsenic and chromium in a waste-
water and/or acid mine drainage. A computer modeling
code, MINTEQAK (37), modified from MINTEQA2, was
utilized for the inverse modeling of the bioreactor. Ninety
to over 99 percent of the arsenic and 86 to 94 percent of
the chromium were removed (20). Cadmium, copper,
iron, lead, and zinc also were removed from the
feedwater. Several mechanisms could account for ar-
senic and chromium removal. We believe that the pri-
mary mechanism is microbial sulfate reduction, result-
ing in production of high concentrations of hydrogen sul-
fide and bicarbonate ion. Experimental evidence and
inverse modeling with MINTEQAK confirmed that most
(90 to 95 percent) of the removal of arsenic and chro-
mium occurred in the first quarter volume of the
bioreactor. Additional removal of target metals could still
occur in the remaining volume of the bioreactor. The in-
vestigation also supported the contention that removal
was the result of the reduction of Cr(VI) to Cr(lll) by hy-
drogen sulfide, followed by precipitation of chromium hy-
droxide [Cr(OH)3(s)], and reduction of As(V) to As(lll), fol-
lowed by precipitation of arsenic sulfides (As2S3 or AsS).
The use of a PMDTS was effective for wastewater and
acid mine drainage with elevated concentrations of ar-
senic and chromium.
Summary, Conclusions, and Design and
Construction Recommendations
The final design and construction decisions will be based
on the flow rate to be treated, the loading rates of met-
als, and the space available for the bioreactor. The deci-
sion whether to use vegetation should be based solely
on aesthetic and erosion considerations, not on a belief
25
-------
that vegetation is a major contributor to metal removal
or system longevity. Once operating, one can expect an
effective life of 4 to 6 years from a single load of sub-
strate, based on experience at the Big Five Tunnel. At
the end of the system's life, the concentrated AVS must
be disposed of as a Resource Conservation and Recov-
ery Act (RCRA) waste or recovered from the organic
substrate. Future work is required to determine if recov-
ery can be sufficiently efficient to justify recycling the
metal values from the laden sludge.
Mass Loading Rates of Metals
Metal concentrations must be converted from mass/vol-
ume (mg/L) to moles/L Then:
moles/d = Q x c ,
where
Q = discharge in volume/time (L/d), and
c = concentration, mass/volume (mg/L).
For example, at the Eagle Mine, the mass loadings for
the major metals was 1.49 moles metals/d for 100 ml/
min and 2.97 moles metals/d for 200 mL/min. Once
metal-loading rates are known, the total volume of sub-
strate required must be determined using estimated SRB
activity. At the Eagle Mine, the substrate volume was
2.46 x 106 cm3. The estimated sulfide production rate
based on our own study results and literature values
range from 300 to 1,200 Nm S~/cm3/d. Therefore moles
of S~ produced/d = V (volume of substrate) x SRB activ-
ity rate (mass/volume/d), and for this system the sulfide
produced should be 0.74 to 2.95 moles S~/d. Waters
with lower metals concentrations than the Eagle Mine
water, such as the effluent at the Big Five Tunnel (i.e.,
an order of magnitude lower concentrations), could ei-
ther be treated with a smaller system or with higher flow
rates.
Alternatively, and perhaps even better, assume an empty
bed hydraulic residence time of 20 to 40 hours. Forty
hours would be used if the feedwaters were below pH 5
and 20 hours if the feedwaters were near neutral pH.
Configuration to Minimize Hydraulic Prob-
lems and Maximize SRB Activity
The upflow configuration has been shown to pose the
least hydraulic problems of systems studied. Construc-
tion is more complicated than for horizontal flow sys-
tems, but hydraulic conductivity or surface flow problems
are fewer. The water is forced into contact with the sub-
strate. Downflow units are possible but require careful
control of flow rates. If flow is too high, water pools on
the surface. If flow is too low, water moves through chan-
nels, leaving most of the substrate dry and unused.
Distribution pipes in the upflow configuration require pro-
tection against contact with the substrate. Two possible
solutions are:
• Distribution pipes can be buried in pea gravel (or
similar material), then covered with a geomembrane
or landscape fabric.
• A plenum can be built to house the distribution sys-
tem. The plenum is covered with landscape fabric
or a geomembrane. The substrate then is placed
upon the geomembrane.
If a system is to be passive, the driving force for the
mine water is hydraulic head. Recent work suggests that
3 meters of head will drive water through the system for
the long term, although less head may suffice. Systems
have been built with valve control of flow rates. Globe
and ball valves rapidly clog with hydroxide precipitates
and need frequent maintenance. Butterfly and gate
valves seem to clog less frequently but need periodic
(weekly) adjustments and cleaning. The higher the flow
maintained through the system, the less frequent are
the requirements to remedy clogging and flow rate ad-
justment. The Eagle Mine system uses a constant head
tank to control flow to the reactors.
The reactor tanks can be made of high-density polyeth-
ylene (HOPE) or similar plastic, or the reactor can be
made of a wood or concrete support structure covered
by an HOPE liner. The Big Five Tunnel system uses a
concrete base and a Hypalon liner. If tailings ponds or
tailings dams are available, they can be lined and fitted
as a PMDTS. The Eagle Mine research also suggests
that units can be run in series and will act as a single
larger unit. The possibility exists of constructing units to
run in parallel. The result would be a group of smaller,
easier-to-access units.
Because maintenance is a consideration, one should
configure plumbing to be as accessible as possible. Ports
could be designed to access distribution pipes for clean-
ing and unclogging. Pipes should be oversized to re-
duce clogging by sediments of frozen water. All delivery
and effluent systems should be buried or insulated to
minimize frozen pipes.
Substrates
The preceding sections suggest that composted cow
manure, mixed with hay, is a good substrate. This sub-
strate supplies acid neutralizing capacity to bring pH into
the ideal range for SRB and organic nutrients for growth
of the complex microbiological consortium that devel-
ops in PMDTS.
26
-------
The hay also can act as a bulking agent, helping to main-
tain hydraulic conductivity. We have found that porous
ceramics used as a bulking agent for enhanced drain-
age on golf courses and athletic fields, when mixed in a
ratio of 9 units of substrate to 1 unit of bulking agent
(7.5:2.5 is even better for hydraulic conductivity), is con-
siderably better than hay for long-term permeability. In
the Colorado School of Mines studies, we used Turface
and Profile. This is not to say that it is the best or only
substrate for this purpose. Decomposed wood chips act
in a similar fashion. Additions of simple organic com-
pounds, such as lactate, are known to enhance SRB
activity. They can be added to the solid organic substrate
by a feed mechanism. In fact, the future may bring ac-
tive, batch units filled with liquid nutrient media to which
mine drainage is added for the requisite contact period
and AVS precipitated in a clarifier. Other substrates, such
as peat and "mushroom compost," have been shown in
both the laboratory and field to be inferior to composted
cow manure. They lack the buffering capacity or nutrient
composition to efficiently enhance SRB activity. Substrate
amendments, such as potting soil, dilute the nutrient and
buffering capacity of the manure and do not appreciably
enhance hydraulic conductivity.
Problems are associated with any organic substrate, be
it manure or wood chips, because a dissolved organic
carbon (DOC) component is leached from the system.
Also, nitrogenous materials such as nitrate or ammonia
might occur in the effluent. A plant-based polishing treat-
ment step might be required to bring the effluent to stan-
dards.
Ultimately, an efficient, long-lasting, low-sludge-genera-
tion, inexpensive, low-maintenance system can be con-
structed to treat metal-laden and acidic (or neutral) waste-
waters.
References
1. Stumm, W., and R.R. Morgan. 1981. Aquatic chem-
istry, 2nd ed. New York, NY. John Wiley and Son.
2. Taylor, B.E., M.C. Wheeler, and O.K. Nordstrom.
1984. Stable isotope geochemistry of acid mine
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et Cosmochim. Acta 48: 2,669-2,678.
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practice of water pollution biology. U.S. Department
of Interior, Federal Water Pollution Control Adminis-
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4. Kleinmann, R.L.P., and R.S. Hedin. 1993. Treat
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5. Wakao, N., T. Takahashi, Y. Saurai, and H. Shiota.
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6. Kleinmann, R.L.P. 1989. Acid mine drainage: U.S.
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7. Jenke, D.R., and F.E. Diebold. 1984.
Electroprecipitation treatment of acid mine waste-
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8. Grim, E.G., and R.D. Hill. 1974. Environmental pro-
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9. Holm, J.D., and T. Elmore. 1986. Passive mine drain-
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Proceedings of the High Altitude Revegetation Work-
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10. Eger, P., and K. Lapakko. 1988. Nickel and copper
removal from mine drainage by a natural wetland.
U.S. Bureau of Mines Circular 9183. pp. 301-309.
11. Girts, M.A., and R.LP. Kleinmann. 1986. Constructed
wetlands for treatment of mine water. American In-
stitute of Mining Engineers Fall Meeting. St. Louis,
MO.
12. Klusman, R.W., and S.D. Machemer. 1991. Natural
processes of acidity reduction and metal removal
from acid mine drainage. In: Peters, D.C., ed. Geol-
ogy in the coal resource utilization. Fairfax, VA: Tech
Books, pp. 513-540.
13. Reynolds, J., S. Machemer, T. Wildeman, D.
Updegraff, and R. Cohen. 1991. Determination of
the rate of sulfide production in a constructed wet-
land receiving acid mine drainage. Presented at the
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Surface Mining and Reclamation, Durango, CO (May
14-17).
14. Machemer, S.D. 1992. Measurements and model-
ing of the chemical processes in a constructed wet-
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School of Mines Thesis T-4074, Golden , Co.
15. Willow, M.A. 1995. pH and dissolved oxygen as fac-
tors controlling treatment efficiencies in wet substrate
bioreactors dominated by sulfate reducing bacteria.
Colorado School of Mines Thesis T-4747, Golden,
CO.
16. Cohen, R.R.H., and S.W. Staub. 1992. Technical
manual for the design and operation of a passive
mine drainage treatment system. U.S. Bureau of
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tion, Denver, CO.
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17. Staub, M.W. 1992. Passive mine drainage treatment
in a bioreactor: The significance of flow, area, and
residence time. Colorado School of Mines Thesis T-
4090, Golden, CO.
18. Tuttle, J.H., P.P. Dugan, and C.I. Randalls, 1969.
Microbial sulfate reduction and its potential utility as
an acid mine water pollution abatement procedure.
Appl. Microbiol. 17(2)297-302.
19. Dvorak, H.D., R.S. Hedin, H.M. Edenborn, and P.E.
Mclntire. 1992. Treatment of metal contaminated
water using bacterial sulfate reduction: Results from
pilot scale reactors. Biotechnol. Bioeng. 40:609-616.
20. Ozawa, T., R.R. Cohen, and R.W. Klusman, 1995.
Biogeochemistry and behavior of arsenic and chro-
mium in an anaerobic bioreactor. Presented at the
Symposium of the American Society for Surface
Mining and Reclamation, Gillette, WY (June).
21. Brown, D.E., G.R. Groves and J.D.A. Miller, 1993.
pH and Eh control of cultures of sulfate reducing
bacteria. J. Appl. Chem. Biotechnol. 23:141-149.
22. Brodie, G.A., D.A. Hammer, and D.A. Tomjanovich.
1989. Treatment of acid drainage with a constructed
wetland at the Tennessee Valley Authority coal mine.
In: Hammer, D.A., ed. Constructed wetlands for
wastewater treatment. Chelsea, Ml: Lewis Publish-
ers, pp. 201 -209.
23. Guntenspergen, G.R., F. Stearns, and J.A. Kadlec.
1989. Wetland vegetation. In: Hammer, D.A., ed.
Constructed wetlands for wastewater treatment.
Chelsea, Ml: Lewis Publishers, pp. 73-88.
24. Samuel, E., J.C. Sencindiver, and H.W. Rauch. 1988.
Water and soil parameters affecting growth of cat-
tails; pilot studies in West Virginia mines. Annual
Meeting of the American Society for Surface Mining
and Reclamation, Pittsburgh, PA. U.S. Department
of Interior, Washington, DC.
25. Sencindiver, J.C., and O.K. Bhumbla. 1988. Effects
of cattails on metal removal from mine drainage U.S.
Bureau of Mines Circular 9183. Kent, OH: Kent State
University Press, pp. 359-366.
26. Wenerick, W.R., and S.E. Stevens et al. 1989. Tol-
erance of three wetland plant species to acid mine
drainage: A greenhouse study. In: Hammer, D.A., ed.
Constructed wetlands for wastewater treatment.
Chelsea, Ml: Lewis Publishers.
27. Emerick, J.C., R.R.H. Cohen, T.R. Wildeman, and
R.W. Klusman. 1990. Results of an experiment us-
ing a pilot scale constructed wetland for remediation
of acid mine discharge at Idaho Springs, CO. Pre-
sented at the Thorne Wildlife Association Sympo-
sium, Snowmass, CO.
28. Heil, M.T., and F.J. Kerins. 1988. Tracy wetlands: A
case study of two passive mine drainage treatment
systems in Montana. Presented at the Annual Meet-
ing of the American Society for Surface Mining and
Reclamation, Pittsburgh, PA.
29. Emerick, J.C., and R.R.H. Cohen. 1991. Results of
an experiment using a pilot scale constructed wet-
land for remediation of acid mine drainage at Idaho
Springs, CO. In: Guidebook for surface water con-
tamination and its remediation near Idaho Springs,
CO. U.S. Geological Survey, Open File Report 91-
426.
30. Kerndorf, H., and M. Schnitzer. 1980. Sorption of met-
als onto humic acid. Geochimica et Cosmochimica
Acta 44:1,701-1,708.
31. Herlihy, AT., and A.L Mills. 1985. Sulfate reduction
in freshwater sediments receiving acid mine drain-
age. Appl. Environ. Microbiol. 49(1 ):179-186.
32. Hedin, R.S., R. Hammack, and D. Hyman. 1989.
Potential importance of sulfate reduction processes
in wetlands constructed to treat mine drainage. In:
Hammer, D.A., ed. Constructed wetlands for waste-
water treatment. Chelsea, Ml: Lewis Publishers, pp.
508-514.
33. Mclntire, P.E., H.M. Edenborn, and R.W. Hammack.
1990. Incorporation of bacterial sulfate reduction into
constructed wetlands for the treatment of acid and
metal mine drainage. National Symposium on Min-
ing: A New Beginning, Knoxville, TN. Report No. 284.
Lexington, KY: University of Kentucky, OES Publi-
cations.
34. Bolis, J., T. Wildeman, and R. Cohen. 1991. The use
of bench scale permeameters for preliminary analy-
sis of metal removal from acid mine drainage by
wetlands. Paper presented at the 1991 National
Meeting of the American Society for Surface Mining
and Reclamation, Durango, CO (May 14-17).
35. Cohen, R., P. Lemke, W. Batal, S. Machemer, and
D. Updegraff. 1989. October 1988 through May 1989:
Year end report for the Big Five Tunnel constructed
wetland treatment system. Contract No. CR 815325.
Site Emergency Technology Project, Colorado
School of Mines.
36. Lemke, P.R. 1989. Analysis and optimization of physi-
cal and hydraulic properties of constructed wetlands
substrates for passive treatment of acid mine drain-
age. Colorado School of Mines Thesis No. 3823,
Golden, CO.
28
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37. Klusman, R.W., D.H. Dvorak, and S.L. Borek. 1993.
Modeling of wetlands and reactor systems used for
mine drainage treatment. In: Proceedings (vol. II),
The challenge of integrating diverse perspectives in
reclamation, of the 10th National Meeting, Spokane,
WA (May 16-19). pp. 685-704.
29
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Chapter 6.
Cyanide Biotreatment and Metal Biomineralization in
Spent Ore and Process Solutions
Leslie C. Thompson
Introduction
Cyanide and heavy metals are by-products of gold and
silver production and are the focus of regulatory, legisla-
tive, and public scrutiny concerned with reforming min-
ing laws and operations. Thus, the development of eco-
nomical and effective treatment processes for mine waste
remediation is a critical issue facing the mining industry.
Bio remediation processes for cyanide detoxification and
metal immobilization or remineralization are emerging
as both cost-effective and efficient treatment technolo-
gies.
Metals in leachate solutions originating from mining op-
erations or acid mine drainage are one of the major en-
vironmental problems facing the mining industry today.
Sulfide and oxidized ores exposed during mining opera-
tions have the potential to produce leachate solutions
that contain high concentrations of dissolved metals.
Metal leachate solutions can affect the quality of plant
and animal health in surface water used for agriculture,
recreation, and human consumption. The problem posed
by these leachate solutions arises in historical and inac-
tive mining districts as well as current mining operations
where containment of metal solutions in leach heaps or
waste rock can require perpetual monitoring and per-
manent containment.
Pintail Systems has developed biological detoxification
processes for the decomposition of cyanide in spent ore
and process solutions and applied them at several gold
mines. This paper includes summaries of case studies
for three of these mines. In each case, the primary goal
was to biologically detoxify cyanide to meet closure re-
quirements at the end of the mine's operation. Second-
ary treatment goals included enhancing precious metal
production during detoxification and removing or
remineralizing soluble heavy metals.
Technology Description
Cyanide Biotreatment
Cyanide compounds are formed and transformed in na-
ture in a global mineral cycle. Cyanide is naturally present
in the biosphere in simple and complexed forms, and
numerous industrial processes use or produce cyanides.
In recent years, a variety of simple bacteria have been
identified that can use cyanide as a nutrient for cell-build-
ing reactions (1). Although cyanide is extremely toxic,
even in small doses, to many terrestrial life forms, these
primitive bacteria are able to take cyanide compounds
into the cell and use the carbon and nitrogen from the
cyanide as the basic building blocks for production of
amino acids and proteins in the cell. Using bacteria for
biodegradation of cyanide wastes from electroplating
operations was proposed as early as 1956 (2). Mining
industries in both the Soviet Union (3,4) and the United
States (5) have developed microbial treatment schemes
for cyanidation wastewaters.
Cyanide and cyanide compounds were important com-
ponents in the chemical evolution that occurred in the
earth's oceans and atmosphere before life formed (6).
This chemical evolution in the prebiotic earth likely was
necessary for the appearance of the first protolife and
primitive life forms. The development of early life forms
suggests that these organisms would have been able to
live and flourish in the presence of cyanide. Primitive
bacteria could have used cyanide compounds as a
source of carbon or nitrogen for cell-building reactions
(7). Recent research has demonstrated that various
amino acids, purines, and pyrimidines can be formed
from hydrogen cyanide precursors (8). Additional tracer
studies using radiolabeled cyanide have confirmed that
the purines adenine and guanine and the pyrimidines
30
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cytosine and thymine can be synthesized in bacteria cells
from cyanide raw materials (9).
Prokaryotic bacteria are defined as the simplest single
units of life. They do not have a membranebound
nucleus, contain only one chromosome, and do not have
any cell organelles. These simple bacteria exhibit a great
metabolic diversity and are ubiquitous in both normal
and extreme environments.
The reaction sequence in bacteria for cyanide oxidation
is summarized in the following equations:
2Fe(CN)6 + 29H2O + 6.502 -
12NH3 +2Fe(OH)3(s) + 16H+
• 12CO
2. MxCNy +2H2O + 0.502 -»M/bacteria + HCO3 +NH3
3. NH,
. NH2OH -» HNO?
. NO -» NO
N2O -» N2
4. NO3 -» NO2 -> NO
Biological remediation of cyanide mine waste is accom-
plished by introducing cyanide-metabolizing bacteria to
a waste source or stimulating indigenous bacteria by
adding nutrients. The bacteria chosen for field cyanide
treatment of spent ore at various mines are isolated from
the spent ore heap and process solutions. Some of the
species that are known to oxidize cyanide include spe-
cies of the genera Actinomyces, Alcaligenes,
Arthrobacter, Bacillus, Micrococcus, Neisseria,
Paracoccus, Pseudomonas, and Thiobacillus (10).
The biological cyanide detoxification process consists
of isolating native cyanide-oxidizing species from cya-
nide-leached spent ore. For successful cyanide
biodetoxification in spent ore solids and process solu-
tions, the natural detoxification ability of the microorgan-
isms must be augmented and the augmented bacteria
and nutrients must be applied to spent ore in process
solutions. Each mine has site specific and waste-spe-
cific chemistry that requires that biotreatment processes
be individually engineered for the particular waste treat-
ment. Every field biotreatment design consists of labo-
ratory, pilot, and field test programs. For each field de-
sign, process development includes the following ele-
ments:
• Isolate native bacteria from mine site waste envi-
ronments.
• Test native bacteria for natural waste treatment ca-
pacity.
• Augment natural detoxification processes by:
Eliminating nonworking portions of the back
ground population.
Putting the detoxification population under stress
in waste infusion and chemically defined media.
Preserving the detoxification population.
• Define nutrient requirements for lab, pilot, and field
bacteria production.
• Test the detoxification potential of augmented bac-
teria in column, batch, or continuous treatments.
• Design field treatment process:
Field bacteria production nutrient requirements
Staged bacteria culture production design
Bacteria application to process solution design
Environmental safety review
Operator training program design
• Mobilize for field treatment operation.
• Grow treatment bacteria at site in staged culture
system.
• Apply bacteria to spent ore and process solutions.
• Monitor treatment.
Biological processes for cyanide detoxification in mine
waste have many advantages over conventional chemi-
cal treatment options for spent ore detoxification. These
include:
• Low comparative treatment cost
• Shorter treatment time
• In situ treatment
• Complete detoxification
- Ends long-term liability
- Eliminates perpetual monitoring
- Allows for natural revegetation
• Natural and nontoxic nutrients, by-products, and pro-
cess end products
Metal Biomineralization
In addition to detoxification of cyanide and thiocyanate
compounds, biological processes can be adapted to
catalyze natural biomineralization reactions that immo-
bilize soluble and leachable metals in the heap.
Biomineralization is described as a surface process as-
sociated with microorganism cell walls where the
31
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remineralization occurs. The biogeochemical activities
initiated by microorganisms in ores, soils, surface, and
ground-water environments can dominate the formation
and transformation of those mineral environments.
Soluble metals leaching from spent ore heaps and waste
rock dumps presents a long-term environmental prob-
lem. Biological processes are the only technology that
has demonstrated in situ remineralization and immobili-
zation of leachable metals. Reactive minerals are trans-
formed naturally to new mineral species that may dis-
solve to produce acidic leachate solutions containing
soluble metals. Geochemical cycles forming metal
leachate solutions can be accelerated as a result of min-
ing activities.
Numerous species of bacteria, fungi, and yeasts are
capable of accumulating many times their weight in
soluble metals. Both living and dead biomass are effec-
tive in removing soluble metals from waste streams con-
taining gold, silver, chromium, cadmium, copper, lead,
zinc, cobalt, and others. Soluble metals also can be im-
mobilized in soils by natural or engineered
biomineralization reactions. Several commercial pro-
cesses using biological reactions are being applied on
an industrial scale for metal remediation. Bacteria found
in natural and extreme environments have developed a
wide variety of metabolic functions to adapt to these
environments. These natural microbial functions contrib-
ute to global mineral cycling that continuously forms,
transforms, and degrades minerals and metals in the
environment.
Two basic mechanisms are involved in metal uptake by
bacteria:
• Accumulation by surface binding to the bacterial cell
wall or extracellular materials.
• Uptake into the cell for use in metabolic processes
as necessary nutrients.
Surface reactions are accepted as the processes respon-
sible for the majority of the remineralization reactions
removing metals from solutions. Intracellular uptake of
metals to meet the nutritional needs of the cell has a
minor role in overall metal removal. Several cell surface
reactions contribute to biomineralization:
• Complexation with organic compounds produced by
the cell.
• Precipitation and ion exchange.
• Chelation by cell membrane components (e.g., pig-
ments, polymers, cellulosic ligands, chitin).
• Remineralization from complex interaction with ex-
tracellular by-products of cell metabolism.
In addition to direct biological metal accumulation and
remineralization reactions, microorganisms may catalyze
other chemical and physical processes on micro- and
macro-environmental scales that contribute to
remineralization reactions. Examples of these reactions
include:
• Production of hydrogen sulfide by sulfate-reducing
bacteria that precipitates insoluble metal sulfides
from solution.
• Reduction of available oxygen in the environment,
thereby limiting biooxidation and acid rock genera-
tion reactions.
The reactions for sulfate reduction and metal sulfide pre-
cipitation are:
2H+ + S04
-2
2CH2O -» H2S
2HCO
During biomineralization, a complex series of reactions
are initiated by microorganisms. In the mine case stud-
ies, microorganisms were added to heap-leached ore
and solutions. The metal remineralization process is cata-
lyzed by biological processes alone and by biological
processes initiating physical and chemical processes that
cause an alteration of the microenvironment. During the
course of the column and field treatment tests, a series
of observations were made on the changing surfaces of
spent ore. These observations are the basis of the fol-
lowing hypothesis for formation of biominerals:
• Bacteria added to the ore columns attach to the ore
surfaces forming a "bioslime" layer.
• Soluble metals bind to cell walls and extracellular
products excreted by the microorganisms (e.g., exo-
polymers, pigments, waste organics).
• Metal hydroxides, oxides, and carbonates are formed
in the primary bioslime layer as amorphous mineral
precursors. Curing, or maturation, of the amorphous
slimes suggests that a molecular rearrangement of
the hydroxy-metals to more stable forms occurs.
• Stabilization of the amorphous precipitates forms a
remineralization nucleation crystal template for fur-
ther mineralization to occur. The microenvironment
alteration and bacteria metabolism continue to cata-
lyze the remineralization by ongoing formation of or-
ganometallic compounds and precipitates as well as
by transformation of metal oxidation states. The
biomineralization appears to follow a sequential and
"layered" development on many of the surfaces.
Some of the possible minerals formed include cal-
cite, gypsum, bornite, pyrite, and covellite.
32
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Mine Site Biotreatment Case Studies
Hecla Yellow Pine Mine
The Yellow Pine Mine near Yellow Pine, Idaho, was the
first full-scale demonstration of in situ biotreatment pro-
cesses for cyanide detoxification in a spent ore heap.
Located east of McCall, Idaho, the site elevation is ap-
proximately 6,500 feet (Figure ^.Approximately 1.3 mil-
lion tons of agglomerated oxide ore were processed in a
single-use leach pad stacked in lifts to a total depth of
about 114 feet. The biotreatment process was begun at
the end of March 1992 and was completed in Septem-
ber 1992.
The goals of the heap detoxification process were to:
• Reduce weak acid dissociable (WAD) cyanide from
47 to 0.2 mg/L in heap leachate solutions.
• Treat spent ore and process solutions to remove the
cyanide point source.
• Complete ore and process solution treatment in one
operating season.
• Enhance gold production during detoxification op-
erations (secondary goal).
The site was a challenge for biotreatment processes due
to low solution temperatures and extreme cold weather
conditions throughout the operating season. Laboratory
and pilot tests were designed to produce an augmented
biotreatment engineered for site-specific conditions. A
final test program was designed using native, augmented
bacteria grown in a three-stage culturing system at the
mine site. Bacteria and nutrients were transferred to the
barren pond and applied to the spent ore heap in a drip
irrigation system. The decrease in WAD cyanide was
measured in preg pond solutions.
Yellow Pine Unit Location
Valley County, Idaho
Coeur
d'Alene
Figure 1. Site location map for Yellow Pine Mine.
33
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The treatment results demonstrated complete cyanide
detoxification in spent ore and process solutions after a
5-month treatment program. Less than 0.4 tons of treat-
ment solution per ton of ore were applied during the 180-
day process. Treatment time estimates for conventional
chemical treatments (peroxide and sulfur dioxide/air)
suggested two to four operating seasons for complete
detoxification.
A secondary benefit of the biotreatment process was an
enhanced gold production above predicted recoveries
for water rinse operations. Biological solutions catalyze
several biooxidation and biomineralization reactions that
contribute to enhanced gold recovery. Biologically cata-
lyzed processes include:
• Partial biooxidation of trace sulfides
• Biooxidation of gangue minerals, making gold more
available for recovery
• Surfactant processes improving wetability of ore
Hecla Mining Company received the 1992 Industrial
Pollution Award for the state of Idaho awarded by the
Northwest Pollution Control Association for application
of innovative and effective biotreatment processes. Ad-
ditional awards include recognition from the U.S. Forest
Service and the state of Idaho's Governor's Award.
A comparison of laboratory and field data is provided in
Figure 2.
1000-
100-
c
ro
>.
O
0.2 mg/l WAD
compliance
0.01
0.1
0.2 0.3 0.4
Tons solution per ton ore
0.5
Figure 2. Comparison of laboratory and field data for Yellow Pine Mine cyanide biodetoxification.
34
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Cyprus Copperstone Mine
The Cyprus Copperstone Mine is located near Parker,
Arizona (Figure 3). At this mine, 1.2 million tons of ore in
a single leach pad were biologically treated between July
and October 1993. The goal was to reduce WAD and
total cyanide (TCN) from 30 to less than 0.2 mg/L in heap
leachate solutions. A secondary treatment goal was to
monitor soluble copper in process solutions. The
biotreatment process was designed to be completed in
less than 5 months. The treatment processes were pro-
jected to be faster at Copperstone due to high solution
temperatures.
Development of a biotreatment process was similar to
Yellow Pine's, including a laboratory and pilot testing
phase to isolate and augment treatment bacteria. The
treatment process was designed from pilot test data.
Treatment bacteria and nutrients were transported to the
mine site and were grown in a three-stage culturing sys-
tem. The decrease in WAD cyanide was measured in
preg pond solutions.
The treatment was complete after 70 days or applica-
tion of less than 0.3 tons of solution per ton of ore. The
rapid treatment was due to the high temperatures (80 to
90 degrees Fahrenheit) in all process solutions during
the course of treatment. Both WAD and total cyanides
were reduced to less than 0.2 mg/L.
Data from cyanide detoxification and solution copper are
shown in Figures 4, 5, and 6.
Summitville Mine Focused Feasibility
Studies
Introduction
Results of laboratory and pilot demonstrations of cya-
nide detoxification and metal biomineralization of the
Summitville heap leach pad (HLP) spent ore and heap
leach solution (HLS) are presented in this portion of the
paper. The tests were run with support from EPA Region
8 and the Superfund Innovative Technology Evaluation
(SITE) program and provided data for the Report of In-
vestigation/Focused Feasibility Study. The HLP Focused
Feasibility Study Report for the Summitville Mine Site
was issued August 1994 by Morrison Knudsen Corpora-
tion to the EPA Region 8 office (under ARCS Contract
number 68-W9-0025).
The Summitville Mine was the site of mining operations
that began in 1873 with the discovery and development
of gold placer and lode deposits in the mine district. Lo-
cated about 25 miles south of Del Norte, Colorado, in
the San Juan Mountains, the mine site is at an altitude
of approximately 11,500 feet (Figure 7). The site was
actively mined for gold, silver, and copper between 1873
and 1947. The mine was inactive from 1947 to 1986,
when the Summitville Consolidated Mining Corporation,
Inc. (SCMCI), a wholly-owned subsidiary of Galactic
Resources, Ltd., started an open pit mine and heap leach
operation at the site.
SCMCI ran a large-tonnage open-pit and cyanide-heap-
leach operation from 1986 to 1992. Gold ore (approxi-
mately 10 million tons) was mined, crushed, and stack-
ed on a lined leach pad. This leach pad was unique be-
cause it was a lined bowl with containment dikes that
ponded leach solutions in the ore heap, as compared
with more standard, well-drained percolation-type leach.
Heap leach operators experienced problems with water
balance and unplanned solution discharges from the start
of the mine life. Solution containment complications and
ineffective water treatment contributed to environmental
problems. Despite the production of 249,000 troy ounces
of gold during the mine operation, SCMCI was unable to
meet remedial requirements and notified the state of
Colorado of its intention to file a Chapter VII bankruptcy
in December 1992. The EPA Region 8 Emergency Re-
sponse Branch took over site operations on December
16, 1992, to prevent a catastrophic release of hazard-
ous substances to the environment. The Summitville
Mine site was added to the National Priority List in June
1994.
Multiple sources of contamination at the site exist due to
past and recent SCMCI mining operations. Emergency
response operations at the site have prevented releases
of severely contaminated solution. Studies are under way
to define a permanent solution to detoxification or neu-
tralization of the various mine waste units. Demonstra-
tion activities of an innovative bioremediation technol-
ogy for treatment of cyanide and soluble teachable met-
als in the heap and heap solutions are addressed in this
paper.
Heap Leach Remediation Evaluation
The heap leach pad is a bowl-shaped structure located
within the Cropsy Creek drainage. A French drain struc-
ture underneath the heap comprises a network of gravel
trenches and perforated pipe designed to intercept
ground water and leakage from the heap. The heap con-
sists of approximately 10 million tons of cyanide-leached
ore and 90 to 150 million gallons of process solution.
EPA Region 8 commissioned a focused feasibility study
(FFS) and report of investigation (Rl) to evaluate reme-
dial options for the heap leach pad (HLP). The RI/FFS
was completed by Morrison Knudsen Corporation and
submitted to EPA Region 8 on August 19,1994. A cross
section of the heap is portrayed in Figure 8.
A request for proposal (RFP) was issued by Environ-
mental Chemical Corporation (ECC) in October 1993 at
the request of EPA Region 8, the U.S. Department of the
Interior, and the U.S. Bureau of Reclamation. The RFP
requested interested companies to provide information
35
-------
Figure 3. Site location map for Copperstone Mine.
1000
0.01
0.1
0.2 0.3
Tons solution per ton ore
Figure 4. Comparison of laboratory and field data for Copperstone Mine biodetoxification.
0.4
0.2 mg/l WAD
compliance
0.5
36
-------
1000 -g
0.01
0.2 0.3 0.4 0.5
Tons solution per ton ore
0.6 0.7
Figure 5. Comparison of column test data for copper in leachate solution at Copperstone Mine.
1000 ^
100 -
o
O
0.01
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Tons solution per tons ore
Figure 6. Comparison of laboratory and field data for copper in leachate solution at Copperstone Mine.
37
-------
Summitville
r
to Pagosa Springs
to Walsenburg
Figure 7. Site location map for Summitville Mine.
38
-------
Summitville Focused Feasibility Study
Cropsy Waste and Heap Leach Pile
Mine waste
4.0 MM Cu. Yds.
Heap leach
6.7 MM Cu. Yds.
Cropsy waste -|
topsoil stockpile
1968 surface -
Compacted waste
Severed fr. drain under Cropsy —
Liner removed, subliner inplace-| ""'''
Dike 2
Approx. location of break in french drain -J
Probable area of leak
3.1 MM
Cu. Yds. Ore
Cyanide saturation
3.6 MM Cu.
Yds. Ore
Dikel
11,775'
11,700'
11,550'
Fr. drain inplace and operationalJ
Fr. drain sump discharge-
Figure 8. Cross section of the heap leach pile at Summitville Mine.
on their ability to implement innovative treatment tech-
nologies to improve treatment efficiency and reduce the
cost of treatment of the heap-leach-pad spent ore and
leachate solutions. Dames & Moore and Pintail Systems,
Inc. (PSI) jointly submitted a proposal suggesting appli-
cation of biotreatment processes for the spent ore and
process solutions in the HLP. The proposal was accepted
for feasibility demonstration under the SITE program with
additional funding from EPA Region 8.
The primary objectives of the Dames & Moore/PSI pro-
posal were to:
• Demonstrate the feasibility of spent ore and process
solution cyanide biodetoxification.
• Develop site-specific biotreatment processes for
spent ore and process solution cyanide detoxifica-
tion.
• Provide treatment data for use in the RI/FFS and
record of decision (ROD) for the spent ore and en-
trained solutions operable units at the Summitville
Mine.
• Immobilize potentially leachable metals including
zinc, copper, manganese, iron, and arsenic within
the heap to improve water quality.
• Define the potential for enhancing precious metal
recovery (gold and silver) as a result of spent ore
cyanide biotreatment.
• Compare innovative biological treatment to conven-
tional peroxide treatment for cyanide detoxification.
Develop data to evaluate potential replacement of
peroxide treatment.
Tests and demonstrations outlined in the proposal were
conducted in PSI's Aurora, Colorado, lab and pilot plant
and at the mine site. Spent ore treatability testing in-
cluded waste characterization, bacteria isolation and
bioaugmentation, parallel column treatment tests, data
evaluation, and reporting.
Demonstration of copper remineralization as insoluble
mineral species was a primary goal of this focused fea-
sibility study.
Laboratory Work Plan
1. Samples of spent ore were collected from the
Summitville HLP in July 1994 by SAIC under con-
tract to the EPA Risk Reduction and Engineering
Laboratory and the SITE program. The sample col-
lection program provided HLP spent ore material
for the column test program and for isolation of in-
digenous microorganisms from the HLP.
2. Samples of the Summitville HLS were collected
concurrently with the HLP sampling program. Ap-
proximately 60 gallons of HLS were provided for
use in the column demonstration program.
39
-------
3. Spent ore from the HLP sampling program was
graded in the laboratory and was loaded into a to-
tal of six 6-inch x 10-foot polyvinyl chloride (PVC)
test columns. The column tests were designed to
evaluate biological detoxification of spent ore and
biomineralization of soluble metals in spent ore
leachate solutions. Each column represented dif-
ferent zones or ore types within the HLP. The col-
umn setup included:
Column #1: Sulfide zone ore, percolation leach
biotreatment.
Column #2: Oxidized ore, 25 to 90 ft depth, per-
colation leach biotreatment.
Column #3: Oxidized ore, 90 to 130 ft depth
(saturated zone), saturated with HLP
solution, percolation biotreatment.
Column #4: Oxidized ore, 0 to 90 foot depth, rinsed
zone (1993 peroxide rinse program),
percolation leach biotreatment.
Column #5: Oxidized ore, 0 to 25 foot depth, per-
colation leach biotreatment.
Column #6: Control column, oxidized ore, 90 to
130 ft depth (saturated zone), satu-
rated with HLP solution, percolation
leach with peroxide-treated HLP so-
lution.
4. Test columns #1 to 5 were treated with bacteria
solutions developed in a laboratory test program
for cyanide detoxification and metal biomineralization.
Column #6 served as a control column and was
treated with HLP solution in which WAD cyanide
had been detoxified with hydrogen peroxide.
5. Test results from the column treatment program
demonstrated that:
• Biological treatment of spent ore resulted in oxi-
dation of WAD cyanide in ore and leachate solu-
tions to less than 0.2 mg/L with application of
less than 0.6 tons of treatment solution per ton of
ore. The control column treatment WAD cyanide
did not reach the 0.2 mg/L compliance level with
application of more than 1.6 tons of solution per
ton of ore.
• Biological treatment of spent ore demonstrated
that total cyanide in column leachate solutions
was reduced to less than 1 mg/L with applica-
tion of between 0.3 and 0.65 tons of solution
per ton of ore. Total cyanide in the control test
column was only reduced to 40 to 50 mg/L in
column leachate solutions with application of 1.5
tons of solution per ton of ore.
• Soluble and leachable copper and cobalt were
reduced in column leachate solutions to 0.1 to 0.2
mg/L in the biotreatment test columns in the same
test period. Soluble copper in the control test
column was reduced to 1 to 2 mg/L with applica-
tion of 1.5 tons of solution per ton of ore.
• Metallic biofilms were evaluated using scanning
electron microscopy (SEM), which confirmed
that biological processes were responsible for
remineralization of soluble copper and iron into
crystalline mineral species.
6. The FFS program demonstrated that biological
treatment is an effective process for:
• Biomineralization of soluble and leachable met-
als in spent ore and heap leachate solutions.
• Biodetoxification of cyanide in spent ore
and heap leachate solutions.
The data collected from the pilot column ore treatment
program are presented in Figures 9 and 10 and summa-
rized in Table 1. Treatment compliance for successful
cyanide detoxification was 0.2 mg/L WAD cyanide mea-
sured in column leachate solutions. The control perox-
ide rinse column of saturated zone ore did not achieve
compliance with a WAD cyanide standard. All other col-
umn treatments reached compliance levels. Total and
WAD cyanide were plotted against the tons of solution
applied per ton of ore.
Amounts of treatment solution applied per ton of ore for
each column to reach compliance are listed in Table 1.
The amount of biotreatment solution required for com-
plete cyanide detoxification is projected to be 25 to 30
percent of the amount of solution required by conven-
tional chemical rinse detoxification treatments.
Biomineralization Observations—SEM
Investigation of Biomineralized Metallic
Films
During application of spent ore cyanide biodetoxification
processes at other mines, PSI has observed a substan-
tial reduction in many of the leachable metals in
biotreatment solutions. These field observations of
soluble metal reduction led PSI to propose that metal
biomineralization should be a possible secondary treat-
ment concurrent with spent ore detoxification in the FFS
for the Summitville Mine.
Thus, a secondary treatment goal in the FFS was to re-
duce the amount of leachable or soluble metals in the
spent ore and entrained heap leachate solution. This test
was designed to quantify reduction of metals in column
leachate solution and to identify any remineralized prod-
ucts in the column tests. Copper in column leachate so-
40
-------
100 ^
-------
0.1
0.6 0.8 1
Tons solution per ton ore
1.2
1.4
1.6
C1: Sulfide
C2: Oxide
C3: Ox, sat biotreat
------- C4: Oxide
illinium "in C5: Oxide ore
— —— C6: Sat detox barren
Figure 10. Leachate TCN versus tons of solution per ton of ore resulting from treatment program at Summitville Mine.
Table 1. Ore Effluent Solution Quality
Column #
1
2
3
4
5
6
Weak Acid Dissociable
Cyanide (mg/L)
0.2
0.1
0.1
0.1
0.1
0.4
Treatment Solution
per
Ton of Ore
0.32
0.56
0.28
0.53
0.60
1.49
42
-------
lutions is shown in Figure 11 for Columns #3 and #6.
Column #3 was the biotreatment test column run as a
saturation zone sample. Column #6 was a control rinse
using a barren solution detoxified with hydrogen perox-
ide in a saturation rinse.
In the FFS for Summitville Mine, spent ore from the HLP
was loaded into PVC test columns (6 in. x 10 ft) and was
leached with bacteria/nutrient solutions. Two treatment
designs were studied: a standard percolation leach (aero-
bic), and a saturated leach design in which the ore was
saturated with the heap leach solution to which bacteria
and nutrients were applied in a continuous biotreatment
leach.
The bacteria for all column treatment tests were isolated
from the spent ore at depth through the HLP in the satu-
rated and unsaturated zones. Bacteria isolated from the
heap material were tested for cyanide oxidation capac-
ity and were submitted to a bioaugmentation program to
improve reaction kinetics and metals tolerance. The fi-
nal treatment population consisted of several distinct spe-
cies, including aerobic heterotrophs, facultative anaer-
obes, and sulfate-reducing bacteria.
The remineralrzation of soluble metals was observed
through a decrease in copper and cobalt in column
leachate solutions and the formation of observable min-
eral products on ore surfaces in the columns. Several of
the tests were run in clear PVC columns to facilitate ob-
servation of mineral formation. The column ore contents
were photographed before, during, and after the
biotreatment process, which ranged from 10 to 20 days
for each test column. Ores were collected from each
column after the treatment was complete and were sub-
mitted for scanning electron microscopy (SEM) and trans-
mission electron microscopy (TEM) study at two labora-
tories—the U.S. Geological Survey (USGS) SEM Labo-
ratory in Denver, Colorado, and the City College of New
York (CCNY) SEM laboratory.
100 -=
-------
The first SEM work suggested that calcite spherules,
bladed gypsum, and layered bornite mineralization oc-
curred as shown in Figures 12a, 12b, 13a, 13b, 14a,
14b, and 14c with companion energy dispersive x-ray
spectroscopy scans for remineralized products from test
Columns #2 and #5. Column #5 was biotreatment of oxi-
dized ore collected from an unrinsed, unsaturated zone
in the HLP between 0 to 25 foot depths. Column #2,
spent oxide ore, was collected from an unrinsed, unsat-
urated zone of the HLP collected between 25 and 90
foot depths.
The stabilization of microorganisms in soils has been
linked to local microenvironmental factors such as clay
speciation and the availability of appropriate colloidal
surfaces (11,12,13). Microorganisms in macroscale sys-
tems establish population profiles in the near-surface
environment dependent on mineralogical/organic varia-
tions and the availability of oxygen in the environment.
In the case of the column treatment tests, the microenvi-
ronment was forced by the addition of bacteria and dis-
solved nutrients.
The microorganisms injected during the column experi-
ments may be indifferent to such environmental controls,
given the relatively short life of the experiments, and one
might expect that microbial populations are uniformly
distributed in the test column. In these column tests,
however, SEM investigation revealed that the metallic-
appearing coatings on run products are not uniform in
composition. Rather, they vary in a complex fashion from
point to point within a test column and also from one
column to the next. This variability may indicate that the
microorganisms are in fact not identically distributed in
columns or react differently at different times and places
over the course of an experiment. Thus, surface films of
remineralized product may provide important informa-
tion concerning the interplay between biological popula-
tions and the ambient fluids in bioremediation tests.
To illustrate the variability of the surface film formation of
biominerals, observations of material in test Column #5
and test Column #2 are compared. In both test columns
the metal-bearing biomineral sheets coat an aggregate
of kaolinite + halloysite + jarosite + alunite. A preliminary
TEM study indicates that the individual substrate miner-
als are compositionally similar and exist in about the
same proportions in both test columns. The sheets ex-
amined to date tend not to develop on quartz particles
as frequently as clay aggregates.
Biomineralization Test Observations—
Column #5
The generally three-part metal-enriched sheets of
biominerals tend to be amorphous at the base (TEM work
in progress) and grade upward into breccia-like admix-
tures of both variably crystallized and fully crystallized
minerals ending in outermost layers that are predomi-
nantly monomineralic and thin. Outer layers tend to be
either Cu, Cu-Fe, or Fe-enriched over lower horizons
and are markedly thinner, down to 20 Angstroms for cop-
per.
The middle layer(s) is punctuated by seemingly chaotic
populations of crystals (primarily sulfides and metals),
with metal fragments easily recognized by their high
reflectivity in backscatter images. The Cu-Fe-S sequence
of the upper layers tends to be stratified upward in a sort
of reverse "supergene enrichment" series, reflecting an
apparent evolution of increasingly neutral pH and reduc-
ing conditions as the tests proceed. The progression
appears to be made more cryptic by the entrapment of
both falling and tumbling particles, in addition to those
produced by in situ nucleation and growth.
While many embedded crystals of the middle layer(s)
follow the inverted supergene sequence (typically pre-
cursors to possible chalcopyrite overlain by more
covellitic phases), exceptions are numerous. A flake of
tin is shown in Figure 15a. The SEM image (right sec-
tion of Figure 15a) shows that the tin flake is embedded
with the copper sulfide materials and is not an artifact.
The backscatter image (right portion Figure 15a) casts
the tin flake as a bright object against a background of
copper sulfides, demonstrating that the tin (see Figure
15b) has a.greater atomic number than the average for
the copper sulfide substrate. This suggests tin over cas-
siterite (SnO). An energy dispersive spectrum (EDS)
trace (Figure 16a) also is given for a middle-layer Fe-Cu
particle located in the vicinity of the tin particle.
Whereas the stratigraphic relationship between height
and copper and sulfur speciation is still unclear, copper
and copper sulfide apparently are the probable domi-
nant final crystallization products in microcavities. The
intricate patterns formed by copper ribbons (Figure 16b)
and copper sulfide ribbons (not illustrated) indicate rela-
tively high structural integrity and high atomic number.
Note that much of the background film of Figure 16b is
also copper and that the background Cu-films are ex-
ceptionally thin, comprising a layer of less than approxi-
mately 20 Angstroms. Given that the underlying mate-
rial is Cu-Fe-S-Si-AI-bearing and the final stage is
monomineralic and strongly reduced, evidence is abun-
dant for precipitation mechanisms that either shift with
ambient experimental factors overtime or are themselves
variable, causing different metal populations to precipi-
tate at different times.
The geochemical observations are consistent with sev-
eral models for fluid-crystal evolution:
• Oxidation-state variability. A constant process (su-
persaturation response) whereby fluids in the mi-
croenvironment become more reducive over time.
44
-------
Figure 12a. Summitville Mine: Possible calcite spherule.
Calcite Spherules
Figure 12b. Summitville Mine: EDS spectrum lor calcite spherule.
45
-------
Figure 13a. Summitville Mine: Calcium-rich blades.
Ca-Rich Blades
Figure 13b. Summitville Mine: EDS spectrum of calcium-rich blades
46
-------
Figure 14a. Summitv/lle Mine: Biofi/m layering over ground mass.
Figure 14b. Summitville Mine: Possible two-layer bornite mineralization
47
-------
"Bornite" Coating - Top Layer
Figure 14c. Summitville Mine: "Bornite" coating (top layer).
Figure 15a. Summitville Mine: Tin flake imbedded with copper sulfide materials.
48
-------
Figure 15b. Summitville Mine: EDS spectrum for tin flake imbedded with copper sulfide materials.
Figure 16a. Summitville Mine: EDS spectrum of iron-copper particle.
49
-------
Figure 1Sb. Summitville Mine: Iron-copper particle.
• Ligand depletion. A constant process whereby sul-
fur and other agents are progressively removed by
bacterial action.
• Bacterial catalysis. A variable process accounting for
the plating out of a variable metal film dependent on
evolutionary changes taking place in the bacterial
colony.
Thus, numerous models for film production are possible,
several of which may be simultaneously active during
the nucleation and growth of films.
Biomineralization Test Observations—
Column #2
Although the bulk material composition of matter recov-
ered from Columns #2 and #5 are similar, if not identi-
cal, bacterial treatment has resulted in the production of
radically different films, at least locally in the column ex-
periments. In Column #2, films have evolved that differ
substantially in bulk composition and mineralogy from
those in test Column #5. Although the textures are com-
parable, the deposits tend to be thicker and more hum-
mocky, and the uppermost stratum is thicker and more
frosting-like, as shown in Figures 17a and 17b. The bulk
compositional shift, as before, is in the direction of re-
duced-chemistry phases and mineralogic simplicity. This
is apparent in the greater brightness of the surface of
the film and the correlative energy-dispersive determina-
tions (as shown in Figures 17a and 17b). Here, both the
innermost and outermost layers are iron enriched and
copper depleted.
This constitutes a marked departure from the overall Cu-
Fe-S films forming in samples from the near surface (Col-
umn #5). Therefore, to assign the control to depth of
sampling is tempting; however, because no major differ-
ences in substrate character are discernible (based on
TEM work to be reported elsewhere), the fundamental
local cause probably rests with the microbiological spe-
cies rather than mineralogy.
Conclusions—Cyanide Bioremediation
Cyanide detoxification in spent ore is a function of solu-
tion application efficiency and bacterial use of cyanide.
The ore biotreatment in this test gave similar results and
required a detoxification time comparable to prior PSI
experiments. The treatment bacteria adapted well to the
spent ore environment and effected a rapid detoxifica-
tion of cyanide in spent ore and ore solutions. The
Summitville ore is a suitable candidate for a field
biotreatment.
The biological treatment column achieved a greater than
99 percent removal of WAD cyanide with application less
than an average of 0.5 tons of solution per ton of ore.
50
-------
Figure 17a. Summitville Mine EDS trace #7.
Figure 17b. Summitville Mine EDS trace #2.
51
-------
Total cyanide in column leachate solutions at the end of
the test was less than 0.5 mg/L, indicating that bacterial
action in the treatment solution will metabolize strong
metal-cyanide compounds. A field treatment of a leach
pad cell or other division of spent ore could be planned
for a treatment program using less than 0.5 tons of solu-
tion per ton of ore.
Biotreatment in this study achieved a greater reduction
in total cyanide in a shorter application than competitive
treatments can achieve. In situ biotreatment is the most
efficient heap cyanide detoxification method as compared
with peroxide rinse treatments. The data generated in
this study indicate that the biotreatment processes have
the potential to operate as an effective field treatment.
Biological treatments are projected to be cost and time
competitive with chemical rinse treatments.
The objectives of the pilot column tests were met in this
biotreatment demonstration:
• Existing strains of cyanide-oxidizing bacteria were
adapted to grow in the ore environment and to use
cyanide as a carbon and/or nitrogen source.
• The adapted bacteria grew best in a chemically de-
fined nutrient media of food-grade reagents.
• Flask and column tests of the adapted, augmented
treatment population verified that bacteria would
grow and metabolize soluble cyanide in the
Summitville spent ore.
• Cyanide was detoxified in biotreatment tests in spent
ore and column leachate solutions with application
of less than an average of 0.5 tons of solutions per
ton of ore. Cyanide levels did not reach a 0.2 mg/L
discharge criteria with the peroxide kill, saturated,
barren rinse test column with application of more than
1.5 tons of treatment solution per ton of ore.
• Total cyanide and thiocyanate also were treated to
low levels in the column treatability studies. Con-
ventional chemical remediation methods for cyanide
detoxification do not treat the strongly complexed
metal cyanides, including ferrocyanide, ferricyanide,
gold cyanide, cobalt cyanide, or thiocyanates.
Biomineralization Test Conclusions
The microscale studies conducted by Professor Jeff
Steiner at CCNY and Dr. Gene Whitney at the USGS
clearly define several distinct microscale films that evolve
on generally the same substrate (agglomerations of ka-
olinite, halloysite, jarosite, and alunite) within the con-
fines of highly similar experimental systems. The rela-
tive proportions of copper- versus iron-enriched film ar-
eas have yet to be determined accurately. In studies at
CCNY, however, the suggestion clearly arises that the
microbial populations have acted locally to produce dif-
ferent film chemistry and endpoints in metal film deposi-
tion. The controlling factors are as yet unrecognized, but
the suggested possible controls include local production
of reducing atmospheres; changing ligand concentration
due to bacterial consumption; and varying tendencies to
catalyze precipitation reactions linked to changes occur-
ring in bacterial populations. These various localized
phenomena appear not to affect the overall release
(macroscale release) of dissolved chemicals in the re-
covered leachate in any pronounced fashion. The vari-
ability brought out by this study, however, encourages
the general concept that a wide range of metal-fixing
films is produced by bioremediation that can be engi-
neered to isolate and seal metals in ore waste.
This treatment concept should have application for both
in situ treatment of ore and waste rock heaps and for
surface passivation of exposed minerals in pit walls. Al-
though biominerals would be subject to natural weath-
ering cycles, the end effect on the environment would
be gradual and of relatively low impact.
References
1. Knowles, C.J. 1976. Microorganisms and cyanide.
Bacteriol. Rev. 40(3):652-680.
2. Pettet, A.E.J., and E.V. Mills. 1956. Biological treat-
ment of cyanides, with and without sewage. J. Appl.
Chem. 4:434-444.
3. Grableva, T.I. n.d. Production of Bacillus
cyanooxidans mutants with improved resistance to
cyanide compounds. Tr. Biol. Inst. Akad Nauk SSSR.
Sib. Otd. (in Russian) 39:63-70.
4. llyaletdinov, A.M., Z.G. Vlasova, and P.G. Enker.
1971. Decomposition of thiocyanates and cyanides
by microorganisms isolated from wastewaters from
the Zyryanovsk Beneficiation Plant. Tr. Nauch.-
Issled. Proekt. Inst. Obogashch. Rud Tsvet. Metal.
(in Russian) 6:97-102.
5. Mudder, T.I., and J.L Whitlock. 1984. Biological treat-
ment of cyanidation wastewater. Presented at the
Annual American Institute of Mining Engineers Con-
ference, Los Angeles, CA (February).
6. Oparin, A.I. 1938. The origin of life. New York, NY:
Macmillan Press.
7. Urey, H.C. 1952. On the early chemical history of
the earth and the origin of life. Proc. Nat. Acad. Sci.
38:349.
8. Miller, S.L, and H.C. Urey. 1959. Organic compound
synthesis on the primitive earth. Science 130:245.
52
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9. Orp, J. 1960. The mechanism of synthesis of ad-
enine from hydrogen cyanide under possible primi-
tive earth conditions. Nature 191:1,193.
10. Buchanan, R.E., and N.E. Gibbons. 1974. Sergey's
manual of determinative bacteriology, 8th ed. Balti-
more, MD: The Williams and Wilkins Company.
11. Burns, R. 1990. Microorganisms, enzymes, and soil
colloid surfaces. In: De Boodt, M.F. et al., eds. Soil
colloids and their association in aggregates. New
York, NY: Plenum Press, pp. 337-362.
12. Sorenssen, LH. 1975. The influence of clay on the
rate of decay of ami no acid metabolites synthesized
in soils. Soil Biol. Biochem. 7:171-177.
13. Stotzky, G. 1980. Surface interactions between clay
minerals, microbes, and viruses. In: Berkeley, R. et
al., eds. Microbial adhesion to surfaces. Chichester,
England: Ellis Norwood Chester, pp. 231-247.
53
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Chapter 7.
Acid Mine Drainage: Reclamation at the Richmond Hill and
Gilt Edge Mines, South Dakota
Thomas V. Durkin
Introduction
Acid mine drainage (AMD) is defined as contaminated
mine drainage that occurs as a result of weathering re-
actions between sulfide-bearing rocks, air, and water that
can lead to problems in the receiving environment. AMD
is characterized by low pH, increased acidity, elevated
heavy metals, sulfate, and dissolved solids in the drain-
age emanating from the sulfide rock source. Various
physical, chemical, and biological controls can be used
to prevent, minimize, and treat AMD. The best environ-
mental controls, and the least expensive in the long run,
are waste management practices that focus on "preven-
tion" rather than "treatment." Two cases are illustrative.
In 1992, the South Dakota Department of Environment
and Natural Resources (DENR) identified environmen-
tal problems associated with reactive sulfide rocks at a
valley-fill waste depository at LAC Minerals' Richmond
Hill gold mine in the northern Black Hills. This led to a
shutdown of the mine, a significant increase in the recla-
mation surety bond from $1.2 million to $10.7 million, a
settlement of $489,000 for permit and water quality stan-
dard violations, and the development of an AMD recla-
mation plan. This plan is in the process of being final-
ized, and preliminary results are impressive.
Numerous abandoned mine reclamation projects have
been conducted by active mine operators in the Black
Hills on a voluntary basis. These efforts have resulted in
a net improvement to the environment while lowering
the environmental liability posed by the abandoned mine
sites. One of the more notable reclamation projects was
conducted by Brohm Mining Corporation, which oper-
ates an active heap leach mine.
Case histories for these two mine waste remediation sites
are presented in this paper.
Richmond Hill Mine
Physical Setting and Ownership
LAC Minerals operates the approximately 400-acre Rich-
mond Hill Mine located in the northern Black Hills, four
miles northwest of Lead, South Dakota. This surface gold
mine, which is operated using conventional heap leach
technology, was permitted by the state of South Dakota
in 1988. At that time, the mine was owned and operated
by St. Joe American, Inc. Successors included St. Joe
Gold Corporation, St. Joe Richmond Hill, Inc., Bond Gold
Richmond Hill, Inc., Bond Gold Corporation, and Rich-
mond Hill, Inc., a subsidiary of LAC Minerals (USA), Inc.
The mine facilities are located at an elevation between
5,500 and 6,000 feet above sea level in an area of rela-
tively rugged terrain. Annual and daily temperature varia-
tions can be extreme. Annual precipitation averages
about 28 inches per year. The pit/waste facility is drained
by Spruce Gulch, an intermittent tributary to perennial
Squaw Creek, which flows into perennial Spearfish
Creek. The process facility is drained by Rubicon Gulch,
an intermittent tributary of Spearfish Creek. Ground wa-
ter is confined to two systems: In the shallow, alluvium
system, flow is predominantly controlled by topography;
in the deep, bedrock system, hydraulics are more com-
plicated and flow is structurally controlled (1).
The mine pit and valley-fill waste rock depository are
connected to the processing facility (e.g., crusher, leach
pads) by a 1.5-mile haul road. The nearest area to the
ore body that was sufficiently flat to construct the leach
pads was 1.5 miles away. South Dakota requires a double
liner system for leach pads and ponds, complete with
leak detection, collection, and recovery systems (2).
54
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Geology
The ore body is associated with a Tertiary breccia pipe
that intruded into Precambrian amphibolites, forming a
near vertical contact. Sulfide and oxide components of
the breccia exist. Oxidation of the Richmond Hill ore de-
posit resulted in a well-developed hematitic-jarositic cap
up to 260 feet thick. The oxidized cap closely follows the
extent of the breccia pipe. Primary sulfide mineraliza-
tion occurs below the oxide cap and consists of 70 to 80
percent feldspars, showing variable argillic alteration, and
10 to 20 percent pyrite and marcasite. Minor quartz, mi-
cas, carbonates, barite, rutile, apatite, zircon, and mona-
zite account for the rest of the rocks. Traces of chal-
copyrite, bornite, sphalerite, galena, and arsenopyrite are
found in the major sulfide species. The protolith of this
rock was determined to be the Precambrian amphibo-
lites, with the sulfide mineralization replacing the origi-
nal mafic minerals. Unaltered amphibolites contain little
to no sulfides (3).
Discovery and Description of the AMD
Problem
From the time operations began in 1988 until 1992, the
mine was operated without any significant environmen-
tal problems. In 1988, several general conditions were
written into the state mine permit that addressed AMD
prevention as follow-up to preliminary indications that a
small amount of sulfide rock might be encountered dur-
ing mining. The mine operators encountered a signifi-
cantly larger amount of sulfide rock, however, than they
originally anticipated.
During a routine inspection in January 1992, the Depart-
ment of Environment and Natural Resources (DENR)
identified a 200,000-ton stockpile of sulfide ore on top of
the Spruce Gulch waste rock depository as well as sul-
fide waste in the dump. Uncrushed sulfide ore had been
stockpiled on the waste dump to allow it to oxidize and
become more amenable to leaching, with the intent to
later crush and leach it. This prompted a series of addi-
tional inspections and communications with mine per-
sonnel to field-document the potential for AMD from the
sulfide ore and waste rock.
Richmond Hill's Spruce Gulch, valley-fill waste dump is
located in the upper reaches of an intermittent drainage
to perennial Squaw Creek, which is classified as a fish-
ery. The Spruce Gulch dump contained about 3.5 mil-
lion tons of waste rock. During the 1992 mid-winter in-
spections, no flow was exhibited at the toe of the dump,
but pH measurements of melting snow taken at the base
of the sulfide ore stockpile on top of the dump were be-
tween 4.5 and 5. A very apparent odor of oxidizing sul-
fides was noted. As a result of spring runoff in April 1992,
flow appeared at the toe of the dump; pH was 3.1 and
heavy metals, sulfate, and total dissolved solids (TDS)
were elevated. Preliminary field observations indicated
that AMD was a potential long-term problem, and an in-
tensive environmental and economic assessment was
undertaken.
Contamination of surface runoff at the toe of the dump
(located above the treatment system described below
under Short-Term Mitigation Actions) continued from the
discovery of the AMD problem in 1992 until this writing
in mid-1995. Field pH levels on the order of 2.6 to 3.6
are typical; sulfate levels commonly range between about
700 and 3,400 mg/L, and TDS between about 800 and
5,700 mg/L. Isolated spikes above these levels have oc-
curred on occasion. Elevated heavy metals include alu-
minum, copper, iron, manganese, and others. The short-
term treatment systems described below are effective in
removing most of the contamination from the water.
The chemical reactions involved with acid generation are
exothermic. The predominant problematic sulfide min-
eral is marcasite. Marcasite in the Richmond Hill rock is
extremely fine grained, exhibits a high surface area, and
oxidizes rapidly. During the late summer and early fall of
1992, fumaroles (areas of escaping steam) were noted
along the crest of the waste dump and in areas on top of
the dump where backhoes had disturbed the crust that
formed from compaction due to heavy equipment traffic.
The rate of acid generation was manifested in the tem-
peratures recorded at the fumaroles. A temperature probe
inserted just below the surface of one of the fumaroles
recorded a temperature of 180 degrees Fahrenheit (4).
Temperatures of AMD water flowing from the toe of the
dump were about 35 degrees Fahrenheit in the summer
of 1992, when temperatures of water flowing from the
base of non-acid-generating waste dumps in the Black
Hills that had been subjected to similar waste disposal
techniques were over 50 degrees Fahrenheit. An ice
block had formed within the rocks at the base of the waste
dump due to barometric pumping that pulled in cold air
during the winter. Another reason for the lower tempera-
tures of discharge water may be explained, in part, by
endothermic reactions that occur as metals precipitate
from solution as AMD enters the more neutral receiving
environment.
En vironmental/Economic Assessment
From 1992 through 1994 the company conducted an in-
tensive environmental and economic assessment. Ex-
pert company consultants were brought in to conduct
the assessments and to develop mitigative plans. The
DENR brought in its own consultants to review the re-
ports and plans as well as to give advice that could be
used in regulatory decisions. The Richmond Hill AMD
mitigation plan has been subjected to the scrutiny of
some of the world's leading experts in the field of AMD
reclamation.
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The environmental assessment included AMD predic-
tive testing and geochemical analyses. Static testing in-
cluded acid/base accounting (ABA) tests, net acid gen-
erating (NAG) pH tests, paste pH tests, and whole rock
analyses. Kinetic testing included humidity cells, column
leach tests, and mineralogical analyses. Samples were
taken from drill core and cuttings, crusher composites,
waste dump trenches, and pit walls.
Experts estimated that approximately 2.7 million tons of
rock in the waste depository was acid-generating, rep-
resenting all waste rock deposited in the dump since the
end of 1989. Much of the exposed material in the pit
was found to be acid-generating, contributing to contami-
nation of shallow ground water below the pit floor. Some
of the spent ore on the leach pads and rock within cer-
tain ancillary facilities also was found to be reactive. Rec-
lamation costs were estimated for the various compo-
nents of the site.
Other environmental assessments included hydrologic
impact studies, metals-loading evaluations and mass
balance assessments, aquatic impact studies, and iden-
tification of contaminant migration pathways and asso-
ciated environmental receptors. After considering sev-
eral short-term and long-term mitigative options, the com-
pany chose a course of action to address the immediate
problems and made plans to implement long-term clo-
sure requirements (1).
All water quality data and results from the various envi-
ronmental assessments are on file at the South Dakota
DENR Minerals and Mining Program in Pierre, South
Dakota.
DENR Enforcement Action and Bond
Increase
In December of 1992, the DENR issued two Notices of
Violation (NOV) to Richmond Hill for violating the state
mine permit and state water quality standards. Enforce-
ment negotiations continued until March of 1992 when a
Stipulation and Stipulated Order was signed. This in-
cluded a settlement of $489,000 for alleged violations
and specific requirements for short-term and long-term
mitigation, water quality and biological monitoring, and
provisions for postclosure maintenance and financial
assurance. The order required that a long-term AMD
mitigation/closure plan be submitted in the form of a for-
mal amendment to the state mine permit. Applications
to amend mine permits are subjected to a public review
process by the state Board of Minerals and Environment.
Richmond Hill's original reclamation bond before the acid
problem developed was $1.1 million. In response to the
economic assessment conducted after the acid problem
developed, the bond was incrementally raised to $10.7
million. The tenfold increase in bonding is testimony to
the financial liabilities of AMD and improper sulfide waste
management.
Short-Term Mitigation Actions
To counter the immediate problem of contaminated sur-
face discharge down Spruce Gulch into perennial Squaw
Creek in the early spring of 1992, a series of treatment
ponds were constructed at the toe of the waste dump to
chemically treat the dump effluent. Contaminated dis-
charge was treated first with an anoxic limestone drain
that proved ineffective. The limestone became armored
with iron hydroxide, which rendered it ineffective in neu-
tralization. Below the treatment ponds, a retention pond
designed to accommodate the 10-year, 24-hour storm
event was constructed. Treatment was accomplished first
by the addition of soda ash, and later the additive was
changed to caustic soda. The resulting metal hydroxide
sludges can be removed periodically .
Partially treated water in the retention pond then is
pumped to Richmond Hill's large, lined stormwater pond
at the process facility that has a capacity to accommo-
date about 80 million gallons. The partially treated water
undergoes significant dilution in the stormwater pond and
is contained and made available for further treatment in
a water treatment plant before discharge. Discharge to
ground water can be effected via land application, which
is regulated through a state ground-water discharge per-
mit or to surface water through a National Pollutant Dis-
charge Elimination System (NPDES) permit.
Other short-term mitigation actions included the follow-
ing. The sulfide ore stockpile was removed from the waste
dump and placed on the leach pads where resulting con-
tamination could be contained. Diversion ditches were
constructed around the Spruce Gulch waste dump to
direct clean surface runoff from above the dump, around
it. Certain amounts of lime, limestone, and alkaline fly
ash were added to the waste dump at key locations for
further neutralization. A semisealant material called Entac
was sprayed on the waste dump in 1992 in an attempt
to minimize infiltration of precipitation.
Migration of contaminated ground water was addressed
by constructing a cutoff trench in the shallow alluvium
across the valley below the waste dump. The resulting
water is collected and directed to the treatment ponds.
Although all of the water in the retention pond is pumped
to the lined stormwater pond, a certain amount of sur-
face flow remains in Spruce Gulch below the retention
pond. This water probably represents a combination of
retention pond water seeping through the embankment
and shallow ground water that is not cutoff at the trench
and that surfaces at springs just below the pond em-
bankment where alluvium pinches out to bedrock.
56
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These treatment processes effectively remove metals
and buffer pH. Sulfate and IDS are not removed effec-
tively by base addition to the Spruce Gulch treatment
ponds. Comparisons can be made of water quality data
representing samples taken from the toe of the waste
dump above the treatment ponds and samples taken
from Spruce Gulch below the treatment system to deter-
mine the effectiveness of the control measures. The water
quality data indicates that the combination of short-term
control methods have proven quite successful at improv-
ing surface water quality below the waste dump.
Long-Term Mitigation Actions
After considering several remedial options, a long-term
closure plan was chosen based on the tonnage calcula-
tions and identification of the locations of acid-generat-
ing rock obtained in the environmental assessment. Sys-
tem hydraulics, water balance, and other site-specific
logistics also were considered before deciding on a plan.
The state Board of Minerals and Environment reviewed
and conditionally approved the mitigation/closure plan
in February 1994.
The objective of the closure plan is to reduce the poten-
tial for long-term environmental risk to surface and ground
water, promote long-term hydrologic and geotechnical
stability, and maintain acceptable postclosure land uses.
The reactive waste rock from the dump (2.7 million tons)
will be removed from Spruce Gulch and backfilled in 3-
foot, compacted lifts in the pit impoundment. In addition
to removing the reactive wastes, LAC Minerals decided
to remove all 3.5 million tons of rock from the dump. A
portion of the nonreactive waste rock will be used in the
construction of the pit impoundment cap described be-
low. Some of the acid-generating sulfide-spent ore will
be removed from the leach pads in the same manner.
As of this writing in June 1995, over 90 percent of the
material from Spruce Gulch had been backfilled in the
pit.
The determination as to what constitutes material to be
removed to the pit impoundment is based on the follow-
ing criteria: waste rock having a NAG pH of less than 3,
which is indicative of an ABA of less than minus 5 tons/
kiloton calcium carbonate, and a paste pH of less than
4.5.
After backfilling is complete, the waste rock and corre-
sponding acid-generating pit surfaces will be graded to
slopes between 3:1 and 6:1 and capped with a multime-
dia cover shown in Figure 1. The cap system overlying
the compacted waste rock consists (from bottom to top)
of the following: 6 inches of onsite crushed limestone,
18 inches of compacted low permeability manufactured
soil, 4.5 feet of nonreactive crushed waste material for
thermal/frost/root protection of the manufactured soil
layer, and 4 to 6 inches of topsoil. The cap will be reveg-
6 Inches Topsoil
54 Inch Drain Layer
18 Inch Low Permeable
Manufactured Soil Layer
6 Inch Limestone Layer
Compacted Waste Rock Backfill
Figure 1. Cross section of Richmond Hill cap.
elated with a mixture of aggressive grass species to limit
the establishment of deeply rooting woody species and
trees that could damage the integrity of the soil liner.
The cap will include a riprap-lined channel to manage
runoff and control erosion.
The 18-inch low permeability layer (compacted, manu-
factured soil) is constructed in two 9-inch lifts and con-
sists of nonreactive waste rock crushed to minus 112 inch
and blended with about 13 percent bentonite to meet a
field permeability criteria of 1 x 1Q-7 cm/sec. Natural onsite
clay was considered, but was found to be of insufficient
quantities and of too heterogenous a nature to consis-
tently meet the permeability criteria. The bentonite-
amended material is blended in a pugmill and provides
material consistency that allows better quality assurance
and quality control during construction.
At the time of the Board of Minerals and Environment
hearing, a specific closure plan for the leach pads had
not been developed. Preliminary AMD predictive tests
indicated that a certain amount of acid-generating spent
ore is present within the material that will remain on the
pads. Limestone will be thoroughly mixed with reactive
spent ore that remains on the leach pad. A condition of
the permit amendment requires that an updated closure
and postclosure plan for the leach pads be submitted to
the DENR for approval prior to mine closure.
The details of the approved plans and specifications
(P&S) and the construction quality assurance (CQA) plan
for all components of the reclaimed facility required to
have such plans (i.e., cap systems and waste rock place-
ment in impoundment) are on file at the DENR Minerals
and Mining Program.
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This approach to long-term mitigation offers the best
chance of a walkaway situation, or as close to it as is
technically and economically feasible. The backfill op-
tion allows for control of the site's water balance and
avoids the need for perpetual water treatment of acid
mine drainage. Extensive environmental data will be col-
lected during the closure and postclosure period. Per-
formance monitoring criteria are being developed to as-
sess the success of reclamation and act as a trigger for
initiating additional reclamation and/or maintenance work
to ensure compliance with long-term reclamation goals.
Postclosure
The postclosure period begins at the time of reclama-
tion surety release (i.e., mine closure) and lasts for a
period not to exceed 30 years, unless the state Board of
Minerals and Environment determines that a longer or
shorter period of time is necessary for compliance with
performance standards or design and operating criteria.
The company will submit postclosure maintenance and
monitoring plans to the DENR for approval prior to the
start of the postclosure period. This includes contingency
measures that could be taken to mitigate recurring AMD
from any completed component of the reclaimed site.
Such measures might include:
• Addition of base material to waste rock.
• Capping or the improvement of capping systems.
• Recovery and treatment of contaminated ground
water.
• Mitigation of acid-generating material at ancillary
facilities.
• Removal of additional waste rock to the pit impound-
ment or other suitable location.
• Long-term water treatment of effluent from the pit
impoundment or waste dump.
Cost estimates for implementing contingency measures
will be included in the postclosure plan.
Prior to the start of the postclosure period, the company
will submit a postclosure financial assurance in the
amount of $1.7 million to cover estimated postclosure
care (this amount will be recalculated at the time of mine
closure). Unless the postclosure period is altered, the
financial assurance will be held for 30 years after recla-
mation surety release to ensure that the reclaimed site
is stable and free of hazards; has self-generating veg-
etation, minimal hydrologic impacts, and minimal re-
leases of substances that adversely effect natural re-
sources; and is maintenance free to the extent practi-
cable.
Performance Monitoring
During and after reclamation, the success of reclama-
tion efforts will be assessed through certain performance
monitoring indicators. Monitoring efforts will indicate
whether each component of the reclaimed facility is func-
tioning properly and whether additional touchup work is
needed to meet closure objectives.
Performance monitoring will be based on the results of
surface and ground-water sampling, biologic testing, and
outputs of various monitoring devices designed to as-
sess the integrity of the capping systems and AMD re-
duction in the reclaimed waste material. Such monitor-
ing devices include: lysimeters installed at key locations
within the pit impoundment designed to measure AMD
reduction and infiltration rates, temperature and oxygen
probes in the backfill designed to monitor sulfide oxida-
tion rates, and thermistors installed within the low per-
meability soil layer designed to indicate whether "heat of
reaction" from acid generation within the backfilled waste
or frost penetration below the thermal protection barrier
are compromising the integrity of the low permeability
layer.
Each year LAC Minerals, the DENR, and other appro-
priate regulatory agencies will meet to review the perfor-
mance monitoring data acquired during the previous year
and collectively assess the success of reclamation. Au-
thorities recognize that closure and postclosure objec-
tives, as determined through environmental monitoring
results, will take some time to be reached. Reclamation
efforts should not be expected to reach these objectives
immediately . Regulatory flexibility must be maintained
to allow for this and to ensure that reclamation objec-
tives are being approached over a reasonable amount
of time. The annual performance meeting will allow for
the identification of justifiable follow-up work to keep rec-
lamation goals on track (4).
The Importance of the Link between Com-
pany Operations and Corporate Environ-
mental Policy
Often local mine operations are owned by larger corpo-
rations. In many cases, the larger corporations have ex-
cellent environmental policies and advocate proper waste
management practices and financial provisions for clo-
sure plans. LAC Minerals is such a corporation. In fact,
LAC has a history of being actively involved with
Canada's Mine Environment Neutralization Drainage
(MEND) program, an international leader in the field of
AMD prediction, prevention, and abatement.
As is true in many arenas—government included—policy
and practice might not always run in parallel. In a mining
scenario, company-level operations might not be in
proper communication with corporate environmental
58
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policy makers. This lack of communication can be par-
ticularly damaging when it occurs with regard to the man-
agement of sulfide wastes because of the magnitude of
the financial and environmental liabilities posed by AMD
problems. Regulatory agencies can become keenly
aware of such shortcomings and can be drawn in when
problems develop. The issue is raised here in a general
sense, and is respectfully offered for industry consider-
ation.
Gilt Edge Mine
Numerous abandoned mine reclamation projects have
been conducted by active mine operators in the Black
Hills of South Dakota on a voluntary basis. These efforts
have resulted in a net improvement to the environment
while lowering the environmental liability posed by the
abandoned mine sites.
One of the more notable reclamation projects was con-
ducted by Brohm Mining Corporation, which operates
an active heap leach mine in the northern Black Hills.
Tailings from mining operations at Gilt Edge in the early
1900s were placed by the "old-timers" in the drainage of
Strawberry Creek, a perennial stream in its middle and
lower reaches. The Gilt Edge tailings were situated on
property controlled by Brohm Mining, adjacent to one of
the open pits associated with the active, permitted mine
operation.
The relic tailings originally contained relatively high con-
centrations of sulfide minerals. As the tailings continued
to erode, they produced severe acid mine drainage for
many decades along Strawberry Creek. Bear Butte
Creek, a perennial stream classified as a marginal fish-
ery into which Strawberry Creek flows, was impacted by
acid runoff for varying distances below the confluence,
depending on the season and contaminant load. In the
late 1980s a pH of 1.9 was recorded in Strawberry Creek
immediately below the tailings pile (5). Static tests con-
ducted on the relic tailings in 1993 showed that much of
the sulfides had oxidized, leaving behind a significant
amount of stored oxidation products (acidity and heavy
metals) as a result of previous oxidation reactions (6).
In the fall of 1993, Brohm Mining removed approximately
150,000 tons of reactive tailings from the upper reaches
of Strawberry Creek. The tailings were mixed thoroughly
with alkaline fly ash from a local coal-fired power plant
at a rate that provides sufficient neutralizing potential for
contained sulfides. The amended tailings were placed
in a "high and dry" disposal area in compacted, 12-inch
lifts, graded to a maximum slope of 3H:1 V, and capped
with a low permeability cover. The fly ash was applied to
the tailings in haul trucks and mixed again with bulldoz-
ers prior to compaction as it was spread out in the dis-
posal area.
Water was added to the fly ash/tailings mixture, which
allowed hydration reactions to occur. This mixing resulted
in achieving a pozzolanic (i.e., cementitious) behavior in
the mixture, effectively isolating the reactive tailings from
air and water. This type of AMD abatement procedure
can be much more cost effective than using portland
cement grout to achieve the desired reduction in perme-
ability (7).
The tailings were amended with fly ash at a rate suffi-
cient to ensure that the acid-neutralizing potential to acid-
generating potential (ANP:AGP) ratio is greater than or
equal to 3:1. The fly ash exhibited an average neutraliz-
ing potential of 467 tons/kiloton and was added to the
tailings at an approximate rate of 25 tons/kiloton of tail-
ings. This proportion was found to be sufficient to neu-
tralize available acidity in the tailings and produce a net
neutralization potential of 20 tons/kiloton in the amended
tailings (6).
The amended tailings were capped with a low perme-
ability clay liner in 1994. The requirements for the clay
liner included a stipulation that it be compacted in 6-inch
lifts to at least 90% modified proctor density or 95% stan-
dard proctor density. No rocks, sticks, or other debris
larger than 2 inches in size were allowed in the liner
materials. The permeability of the clay liner had to be
equivalent to a 12-inch layer with a maximum perme-
ability of 1 x 10'7 cm/sec. Approved CQA personnel were
required to be present on site at all times during the place-
ment of amended tailings and clay liner.
A gravity fed, leachate collection system consisting of
geosynthetic material was placed at the bottom of the
tailings depository to detect seepage through the cap
and amended tailings. Seepage has never been detected
since the cap was installed. Considering the added ben-
efit of the pozzolanic nature of the amended tailings,
seepage is not likely to be detected in the leachate col-
lection system.
In addition to removing the approximately 150,000 tons
of eroding streamside tailings in upper Strawberry Creek,
additional historical tailings that had accumulated behind
several abandoned beaver dams farther downstream
were removed with a dozer and excavator. Removal with
a vacuum truck was attempted but proved less efficient
than the dozer and excavator.
In 1995, the DENR made use of funds available through
the Western Governors' Association and the federal ini-
tiative to develop on-site innovative technologies (DOIT)
to have the effectiveness of abandoned mine reclama-
tion efforts evaluated on a "watershed basis." As part of
this watershed study, conducted by the South Dakota
School of Mines and Technology, Strawberry and Bear
Butte Creeks were monitored for water quality during
and after tailings excavation activities. This monitoring
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was conducted to assess the effectiveness of the recla-
mation project. The results were related to preexisting
water quality information. It was found that by employ-
ing a combination of best management practices (BMPs)
during excavation work, increased sediment load down-
stream and exacerbation of AMD were kept to a mini-
mum. BMPs included conducting the reclamation efforts
in the autumn low flow season, diverting Strawberry
Creek flow around work sites during excavation, ceas-
ing excavation activities during precipitation events, and
using adequate sedimentation and erosion control de-
vices. Although a slight increase in total dissolved and
suspended solids during remediation was noted, the in-
crease was judged to be insignificant and showed little
additional release of tailings downstream (8).
The tailings cleanup activities resulted in a significant
improvement in water quality and aquatic habitat in
Strawberry Creek. Total cost for the project was slightly
over $450,000. Reclamation was entirely funded by
Brohm Mining. Discharges below Brohm's active mine
operation, which had been of poor quality as a result of
the historical tailings, are now in compliance with state
Surface Water Discharge (i.e., NPDES) permit limitations.
Conclusions
Most aspects of modern mining in South Dakota have a
history of proper regulation and pollution prevention. The
only notable exception to this general rule concerns prob-
lems associated with acid-generating sulfide wastes.
AMD poses a significant threat to the environment and
to the liability for sulfide mine operations, if not properly
managed. Attention must be focused on preventing AMD
at the source rather than mitigating impacts after the fact.
With the implementation of effective, and notably expen-
sive, AMD reclamation practices such as those imple-
mented at the Richmond Hill facility, adequate environ-
mental protection can be achieved. Nonetheless, suit-
able mine waste management methods at active mine
operations in the Black Hills, demonstrating that acid-
generating sulfide wastes can be handled properly from
the start of operations, are yet to be incorporated into
South Dakota's regulatory history. In some cases, sul-
fide rock is mined in South Dakota and AMD problems
do not occur. In some situations, mined sulfide rocks
contain sufficient natural buffering capacity to prevent
acid generation; in others, reactive sulfides are identi-
fied early and kept to a subcritical volume in the mine
plan. Before the permitting of additional operations that
include sulfide rock of the problematic nature can be re-
alistically expected in South Dakota, however, "preven-
tative" waste management practices must be developed.
These practices must be put in place during all phases
of the mining operation, from start-up to closure.
The Richmond Hill AMD problem, with its regulation,
enforcement, and subsequent reclamation work, is the
most complex heap leach mining-related environmental
issue that has arisen in the Black Hills. The reclamation
work at the mine represents the culmination of exhaus-
tive environmental planning. This work is progressing in
excellent fashion and with very promising results.
Backfilling, compacting, and capping the reactive waste
in the Richmond Hill pit impoundment allows for control
of the site's water balance and avoids the need for per-
petual water treatment of AMD. With the exception of a
limited amount of performance monitoring, this approach
toward long-term reclamation offers the best chance of
a walkaway situation, or as close to it as technically and
economically feasible.
The cleanup of the acid-generating Gilt Edge tailings
along Strawberry Creek represents one of the most sig-
nificant abandoned mine cleanup efforts conducted in
the Black Hills. This project is one of several such efforts
undertaken by active mine operators in South Dakota to
manage environmental problems caused by abandoned
mines located on properties they control. Although South
Dakota does not have an abandoned mine reclamation
program, opportunities for cleanup of abandoned mine
sites are pursued cooperatively as they arise. An intent
to overcome regulatory barriers that might otherwise tend
to stifle cleanup efforts has proven successful at keep-
ing these reclamation projects out of the legal realm. This
allows resources to be expended for on-the-ground site
improvements, which is where they should be focused.
References
1. Richmond Hill Inc. 1993. Mined Land Reclamation Per-
mit No. 445 Amendment. Report prepared for the
South Dakota Department of Environment and Natu-
ral Resources, Pierre, SD.
2. South Dakota Department of Environment and Natu-
ral Resources, Office of Minerals and Mining, n.d.
Mine Permit No. 445 Files, Richmond Hill Mine.
3. Duex, T.A. 1994. Acid rock drainage at the Richmond
Hill Mine, Lawrence County, South Dakota. Proceed-
ings of the Fifth Western Regional Conference on
Precious Metals, Coal and the Environment, Soci-
ety for Mining Metallurgy and Exploration Inc., Lead,
SD (October), pp. 124-134.
4. Durkin, T.V. 1994. Acid mine drainage, an old prob-
lem with new solutions—Reclamation at the Rich-
mond Hill Mine, South Dakota. Proceedings of the
Fifth Western Regional Conference on Precious
Metals, Coal and the Environment, Society for Min-
ing Metallurgy and Exploration Inc., Lead, SD (Oc-
tober), pp. 16-24.
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5. South Dakota Department of Environment and Natu-
ral Resources, Office of Minerals and Mining, n.d.
Mine Permit No. 439 Files, Brohm Mining Corp.—
Gilt Edge Mine.
6. Steffen, Robertson, and Kirsten (US), Inc. 1993. Gilt
Edge project technical specifications for relocation
and capping of relic tailings. Lakewood, CO. SRK
Project No. 26705. Prepared for Brohm Mining Corp.
7. Scheetz, B.E., M.R. Silsbee, C. Fontana, X. Zhao,
and J. Schueck. 1993. Properties and potential ap-
plications of large volume use of fly ash-based grouts
for acid mine drainage abatement. Proceedings of
the Association of Abandoned Mine Land Programs'
15th Annual Conference, Jackson, WY. September
12-16.
8. Davis, A., and K. Webb. 1995. A pilot-scale water-
shed evaluation for assessment of impacts of inac-
tive and abandoned mines in the Strawberry Creek/
Bear Butte Creek Basin of the Black Hills. Report by
South Dakota School of Mines and Technology to
South Dakota Department of Environment and Natu-
ral Resources.
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Chapter 8.
The Mine Waste Technology Program and Technologies To Address
Environmental Problems at Inactive Mine Sites
Martin Foote
Introduction
Two separate topics are covered in this paper. The Mine
Waste Technology Program and a number of technolo-
gies that can be used to address mine waste. These
technologies are categorized into treatment technologies,
pathway interrupt technologies, and source control tech-
nologies.
In 1991 Congress established a pilot program for treat-
ing mine wastes in Butte, Montana. Under an Interagency
Agreement (IAG), the U.S. Environmental Protection
Agency (EPA) is collaborating with the U.S. Department
of Energy (DOE) to implement this congressional direc-
tive. MSE, Inc., is the performing contractor for the Mine
Waste Technology Program (MWTP).
The Mine Waste Technology Program
The MWTP covers the following activity areas:
• Activity A—Montana Tech identifies and prioritizes
technical issues, waste forms, and waste sites as
well as promising innovative treatment technologies.
After further evaluation of these topics, Montana Tech
recommends candidate sites and technologies for
demonstration or research projects.
• Activity //—Montana Tech develops a Generic Qual-
ity Assurance Project Plan.
• Activity ///—MSE proposes and then conducts large
pilot- and field-scale demonstration projects for sev-
eral innovative technologies that show promise for
cost-effectively remediating local, regional, and na-
tional mining waste problems.
• Activity IV— Montana Tech develops and then imple-
ments a plan to conduct bench- and small pilot-scale
research on several innovative technologies that
show promise for cost-effectively remediating local,
regional, and national mining waste problems.
• Activity V— MSE prepares and distributes program
reports and develops and conducts a series of sym-
posia/workshops to present the interim and final re-
sults of the demonstration projects to user commu-
nities.
• Activity I/A—Montana Tech develops and then imple-
ments a plan to establish training and educational
programs on mine waste treatment technologies.
MWTP Organization
The MWTP is directed by the IAG Management Com-
mittee, whose roles, responsibilities, and authorities are
described below.
Environmental Protection Agency
Program and technical oversight of the MWTP is the
responsibility of the Sustainable Technology Division of
the National Risk Management Research Laboratory
(NRMRL) in Cincinnati, Ohio. The NRMRL provides a
project officer, who also is a member of the IAG Man-
agement Committee, a quality assurance officer, and
support staff to the program. Additional technical over-
sight is provided by the EPA Region 8 office in Denver,
Colorado, and the EPA Montana operations office, both
of which provide a representative member to the IAG
Management Committee.
Department of Energy
Program oversight is the responsibility of the Western
Environmental Technology Office (WETO) of the DOE,
Environmental Management (EM), Office of Technology
Development. Under WETO, the Pittsburgh Energy Tech-
nology Center provides administrative support on envi-
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ronmental as well as safety and health issues and on
matters concerning regulatory compliance and opera-
tional conduct.
MSE, Inc.
MSE, the DOE contractor in Butte, Montana, is the prin-
cipal performing contractor for the MWTP. MSE provides
a Mine Waste Programs Manager, who is the point of
contact for all mine waste activities, including program
management and coordination, program status report-
ing, funds distribution, and communications.
Montana Tech
As a subcontractor to MSE, Montana Tech is respon-
sible to the Mine Waste Programs Manager for all work
performed under Activities I, II, IV, and VI.
Technical Integration Committee
The nine-member Technical Integration Committee (TIC),
made up of representatives of the public and private sec-
tors, reviews progress toward meeting program goals
and advises the IAG Management Committee on perti-
nent concerns.
Industrial Integration Committee
An Industrial Integration Committee (IIC) provides a link
between industry and the MWTP demonstration projects.
The IIC solicits information on industry's remediation
needs and requirements, provides evaluations of tech-
nology demonstrations, and assists in technology trans-
fer as required under Activity V.
Activity III Project Descriptions
A brief description and status of each of the projects being
conducted under Activity III and an overview of relevant
Montana Tech activities are provided below.
Project 1—Remote Mine Site Demonstration
EPA requested that MSE develop a facility at a remote
site for treatment of acidic metal-laden water. Given the
nature of such sites, the facility would be required to
operate on water power alone and without operator as-
sistance for extended periods. The Crystal Mine, located
7 miles north of Basin, Montana, was chosen as the site
for this technology demonstration because it is a good
example of a remote mine site with a point-source aque-
ous discharge. The Crystal Mine demonstration facility
treats a flow of water ranging from 10 to 25 gallons per
minute, approximately one-half of the total discharge.
The process consists of several unit operations: initial
oxidation, alkaline reagent addition, final oxidation, ini-
tial solid-liquid separation, pH adjustment, and final solid-
liquid separation.
Project 2—Clay-Based Grouting Demonstration
Inflow of surface and ground water into underground mine
workings is a significant problem worldwide. The tech-
nology selected for this demonstration project, clay grout-
ing, inhibits or eliminates this flow by injecting a fine-
grained clay slurry into the flow pathways. By virtue of
its chemical and physical characteristics, the grout sets
up within these spaces to block ground-water flow. The
distinguishing feature of clay-based grouts is that
throughout the stabilization period they retain their plas-
ticity and do not crystallize, unlike cement-based grouts.
Clay-based grouting is being demonstrated at the Mike
Horse Mine, located 15 miles east of Lincoln, Montana.
This project consists of three phases: site characteriza-
tion, grout formulation, and grout placement. The EPA
Superfund Innovative Technology Evaluation (SITE) pro-
gram provided sampling, characterization, and analyti-
cal data for the project.
Project 3—Sulfate-Reducing Bacteria Demonstra-
tion
The goal of this project is to demonstrate that the sul-
fate-reducing bacteria (SRB) technology can be used to
slow or reverse the acid-generation process and improve
water quality at affected sites. The Lilly/Orphan Boy Mine,
near Elliston, Montana, was chosen for this demonstra-
tion. This technology can reduce the contamination of
aqueous waste in three ways: 1) sulfate is reduced to
hydrogen sulfide through the metabolic activity of the
SRB, 2) the hydrogen sulfide reacts with dissolved met-
als, resulting in the formation of insoluble metal sulfides,
and 3) bicarbonate produced by the sulfate reduction
process increases the pH of the solution. Because SRB
need a source of carbon in the form of a simple organic
nutrient, an organic substrate composed of cow manure,
decomposed wood chips, and alfalfa was added to the
system. Application of the technology involves using the
subsurface mine workings of the Lilly/Orphan Boy Mine
as an in situ biological reactor. Pilot-scale testing of the
technology was conducted at the WETO in Butte, Mon-
tana.
Project 4—Nitrate Removal Demonstration
The presence of nitrates in water can have detrimental
effects on human health and the environment. Improv-
ing the economics of nitrate removal and reducing or
eliminating the waste generated during nitrate removal
are the goals of this project. To that end, the MWTP un-
dertook an extensive search to evaluate innovative tech-
nologies that could be applied to the nitrate problem. Of
the 19 technologies that were screened against selec-
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tion criteria, three showed the most promise for making
nitrate removal more cost effective and environmentally
sound: ion exchange with a nitrate-selective resin, bio-
logical denitrification, and electrochemical ion exchange.
This project involves the testing of combinations of these
three technologies. The Mineral Hill Mine, near Jardine,
Montana, was chosen for this demonstration. The pro-
cess train for this project will allow technical evaluation
of each technology combination as well as confirmation
of preliminary economic studies. Because the nitrate
problem is not exclusive to mining, data generated from
the proposed test process train also could be relevant
for other industries (e.g., for application to chemical pro-
cessing plants, agricultural runoff, municipal water treat-
ment).
Project 5—Biocyanide Demonstration
Cyanide is used in the mining industry to extract pre-
cious metals from ores and to improve the efficiency of
metals separation in beneficiation. Cyanide, however,
can be an acute poison and also has the ability to form
strong complexes with several metals, resulting in the
increased mobility of those metals. As such, cyanide can
contribute to environmental problems in several ways.
The McCoy/Cove Mine, near Battle Mountain, Nevada,
was selected as the preferred site for this demonstra-
tion. The first goal of this project is to develop a reactor
that will use the cyanide degrading effects of gelatinous
bead-contained bacteria to degrade cyanide from min-
ing wastewater. The bacteria within the beads and the
method of placing the bacteria into the beads were de-
veloped by researchers at the Idaho National Engineer-
ing Laboratory (INEL) and the Center for Biofilm Engi-
neering (CBE) at Montana State University, along with
Selma University (SU). This gelatinous bead reactor will
be tested in a side-by-side manner with another reactor
design developed by Pintail Systems, Inc., of Aurora,
Colorado. The second goal is to develop a method for
using the bacteria for in situ remediation of cyanide-con-
taminated solid mining wastes. In this phase of the
project, researchers will study the manner in which cya-
nide is held within heap leach and tailings piles and de-
termine the forms of cyanide within these forms of solid
wastes. Tests also will be conducted to determine the
best way to use the bacteria to degrade these forms of
cyanide within the solid waste pile itself.
In the remainder of this paper, technologies that can be
used to treat mine waste are described.
Treatment Technologies
Adsorption
Adsorption is a process by which dissolved materials in
a solution will adhere to the surface of other materials,
usually solids, introduced into that solution. Several ad-
sorption mediums have been developed for this purpose,
including activated carbon and charcoal, BIO-FIX beads,
filamentous fungi biomass, humic and fulvic acids, low
rank coals, and metal hydroxides.
Anoxic Limestone Drain
This device is used most often as a portion of a passive
system. It is composed of a long (lengths greater than
50 meters have been used) trench lined with an imper-
meable liner and filled with pieces of limestone. The
trench is covered by the same type of impermeable liner
and then buried beneath a layer of clay and a vegetated
crown. Acidic mine discharges are directed into the up-
per end of the covered trench and allowed to percolate
down through the contained limestone. The limestone is
dissolved slowly by the solution, which raises the alka-
linity and pH of the solution. The effluent from the drain
is directed into a settling pond to allow hydroxide pre-
cipitates to form and settle out of solution. These drains
are functional only on acidic mine drainages that are low
in ferric iron concentration and oxidation potential. If size-
able quantities of ferric iron exist in the inflow solution,
ferric hydroxides will form within the drain and armor the
limestone, rendering the drain ineffective.
Bioadsorption
Bioadsorption is a subform of the broader topic of ad-
sorption by which biological materials such as BIO-FIX
beads, humic and fulvic acids, and filamentous fungi bio-
mass are used as the adsorption medium.
Biological Reduction
This process is defined as the chemical reduction of dis-
solved species by the action of biological processes.
When dealing with the treatment of aqueous waste
streams, this process is generally limited to the reduc-
tion of dissolved sulfate to hydrogen sulfide and the con-
comitant oxidation of organic nutrient compounds to bi-
carbonate within the aqueous solution. Several species
of the Desulfovibrio family of bacteria will catalyze this
type of reaction. These bacteria are hardy and can toler-
ate wide temperature swings (-5 to 50 degrees Celsius)
and variation in solution pH (5 to 9). A pH below 5.0,
however, will severely reduce the activity of these bac-
teria. The bacteria also can be inhibited by high concen-
trations of certain aqueous metal species such as cop-
per and zinc. The bacteria do require reducing condi-
tions within the solution and will not tolerate aerobic con-
ditions for extended periods.
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Chelation Chromatography
Chelation is a well-known chemical process. Chelating
agents, complex organic chemicals that have more than
one reactive site, are materials that are capable of form-
ing more than one ionic bond with a substance dissolved
in a solution. If the chelating agent can be attached to a
surface, the dissolved material can then be removed from
the solution by removal of the attached medium.
Chemical Oxidation
This process involves the addition of an oxidizing reagent
to a waste stream. Some of the more common reagents
used in this process are hydrogen peroxide, potassium
permanganate, and sodium hypochlorate. The addition
of one of these chemicals to the waste stream will oxi-
dize the reduced forms of several of the dissolved me-
tallic ions to the oxidized forms. In most situations, the
oxidized ions hydrolyze to form insoluble hydroxide com-
pounds at lower pHs than the reduced forms of the ions.
Chemical Precipitation
Chemical precipitation is probably the oldest method
used to treat acidic, metal-bearing mine drainages. The
method involves adding a chemical reagent to the mine
effluent solution to facilitate a solid-forming reaction be-
tween the dissolved constituents of the mine effluent and
the reagent within the waste stream. The solid materials
formed are then removed from the water. Direct effects
on the pH of the waste solution might or might not occur,
depending on the reagent used. Chemical precipitation
is a very large field comprising hundreds of potentially
applicable processes.
Coagulation, Sedimentation, and Floccula-
tion
These three generic processes have all been used, both
naturally and in man-made methodologies, to remove
suspended and/or finely divided particulate matter from
aqueous streams. At least one of these generic pro-
cesses will have to be used in conjunction with all of the
previously described technologies, which produce a pre-
cipitate within the waste stream. These processes also
will have to be used in conjunction with several other
processes (i.e., ion-exchange, Chelation, solvent extrac-
tion, and some adsorption processes) that require a clear
liquid inflow to function efficiently.
Column Flotation
Column flotation functions on the same principle as
simple flotation, except the structure of the flotation de-
vice is in the form of a vertical tube rather than a short,
wide cell. The length of the column and the use of froth
wash water produce a very clean, highly concentrated
solid product. Column flotation units also have been
shown to be efficient in floating, and thus removing, very
small particles from the slurry. This function would be
most useful in the remediation of acidic mine discharges.
The removal of these fine particulates from the waste
stream in an efficient, cost-effective manner is essential
for the efficient use of several of the other remediation
methods.
Copper Cementation
This is an old and much used process for removing cop-
per from acidic mine waters. The process involves1 add-
ing metallic iron to the copper-bearing solution to cause
the reduction of the more nobel copper and the oxida-
tion of the iron. Thus, the copper precipitates out of the
solution as copper metal and the iron is dissolved. This
process is very effective at removing copper from solu-
tion, but it does not decrease the quantity of dissolved
solids in the solution as the amount of iron in solution is
increased. Also, the pH of the solution is not effected by
the process. The major reason for using this process is
to produce a valuable product for resale. Using this pro-
cess would be justifiable as a first step in a process
stream as a means of mitigating the total remediation
costs of a water.
Dilution
Dilution can be a major process in the reduction of dis-
solved constituents in acidic mine drainages in most
natural settings. The process also could be used in con-
junction with another process that produces an effluent
stream that more than meets discharge specifications.
A portion of untreated water could then be mixed with
the highly treated water to produce a greater quantity of
effluent that would still meet discharge specifications.
Such secondary processes have been proposed for use
with chelation, distillation, and freeze crystallization tech-
nologies to reduce the amount of water that would ulti-
mately have to be treated.
Distillation
Distillation has been used for many years as a method
of purifying water and other solvents. The process has
been hypothesized as a means of cleaning acidic mine
discharges and would be effective. The inefficiency and
subsequent high energy cost of using this basic tech-
nique, however, is prohibitive. Another problem with us-
ing simple distillation as a means of cleaning mine waste
streams arises from the quantity of dissolved solids in
the inflow stream. A functional maximum for the dissolved
solids contained in an inflow to a conventional distilla-
tion system is approximately 3,000 mg/L. This specific
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value depends on the saturation level of the specific salts
produced from the distillation process. High values of
most dissolved solids in the inflow, however, usually re-
sult in-numerous problems of scale buildup and precipi-
tate formation.
Electrochemical Precipitation
In this process two carbon steel electrodes are placed
into a waste stream. A continuous direct current is ap-
plied to the electrodes, causing the formation of ferrous
hydroxide at the anode. This solid hydroxide adsorbs
other metals from the waste solution and induces
coprecipitation of other hydroxides, thereby generating
a sludge containing the previously dissolved metals that
can be removed from the solution. The carbon steel elec-
trodes are continuously consumed and need to be re-
placed periodically.
Electrocoagulation
This process involves passing an electric current through
the mine waste stream by means of metal surfaces to
induce the precipitation of dissolved metal ions onto the
metal surfaces. The electric current used in the process
can be either direct or alternating. The electric potential
is reversed periodically to prevent the deposition of ex-
cessive quantities of precipitate on the positive or nega-
tively charged surfaces. The electrocoagulated waste
solution is passed into a thickener or clarifier to remove
the suspended particles.
Electrodialysis
In this process an electric potential is used to cause the
movement of dissolved, positively and negatively
charged, ionic materials through a semipermeable, hy-
brid membrane. As a result, the dissolved charged par-
ticles are concentrated into a brine that is separated from
the treated water by the semipermeable membrane. The
brine may comprise 15 to 25 percent of the original vol-
ume of the waste stream. This technology has been
proven viable in the-metals plating industry; however, it
has not been demonstrated as functional in acidic mine
drainages.
Electrokinetic Osmosis
This process is used to cause the movement of water
through a porous material that inhibits the movement of
particles along with the water. When particle movement
is restricted by the presence of a porous medium and a
direct electrical current is applied to the medium, cat-
ions will be attracted toward the cathode and anions to-
ward the anode. If a porous medium is chosen, such as
a clay that has a negative surface charge, the number of
mobile cations will be larger than the number of mobile
anions and a net movement of cations toward the cath-
ode will result. Thus, this movement of cations tends to
drag water toward the cathode.
Electrophoresis
This process uses an electrical potential introduced into
the waste stream to cause the movement of particles
and colloidal particulates toward the electrode, which is
of the opposite charge to that of the particle. The move-
ment of the colloidal particulates is caused by the inter-
action of the charged surfaces of the particles and the
electrical potential introduced to the waste stream. The
colloidal particles, one example of which is represented
by the previously described metal hydroxides, lose their
charge upon reaching the electrode toward which mi-
gration occurred and then coagulate as a precipitated
sludge.
Electrowinning
This process is a form of electrophoresis combined with
electrochemistry. One of the commercial applications of
this process is called electroplating, in which thin cover-
ings of a noble metal are deposited on metallic objects.
The process uses a direct electric current applied to elec-
trodes within the aqueous solution to attract the posi-
tively charged dissolved ionic material in the solution to
the negatively charged electrode, where the metal ion is
reduced and adheres to the electrode. The process re-
sults in adding a thin film of the metal to the electrode
surface.
Evaporation
Evaporation has been used commercially to reduce the
volume of aqueous brines that have been produced from
the application of several technologies. Evaporation is
distinguished from distillation in that the vapor phase is
recondensed in distillation to produce a clean fluid; in
evaporation the vapor is not recondensed but is allowed
to escape. Some of the problems encountered with
evaporation are the lack of a cleaned effluent stream,
which can be a concern in some situations, and the pre-
cipitation of saturated solids from the evaporating fluid
that have to be dealt with. The natural evaporation pro-
cess, which makes use of solar energy, has been ap-
plied to the problem of wastewater disposal in many ar-
eas with dry, warm climates, but has not been shown to
be effective in other climates.
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Filtration and Ultrafiltration
Filtration is the process of separating suspended solids
from their suspending liquids by passing the mixture
through a porous medium that retains the solid material.
Filtration as a means of removing solids from waste
streams has been in use for centuries. Many modern
practices and applications of filtration can be used as a
step in the remediation of acidic mine drainages.
Ultrafiltration is a membrane technology that uses pres-
sure applied on the liquid phase to separate macromo-
lecular/colloidal solutes from that liquid phase of the so-
lution. In essence, the liquid is driven through the mem-
brane by the pressure and the large, dissolved solutes
are retained. The technology has been applied in bench-
and pilot-scale tests to the separation of oil-water emul-
sions. The technology also has been tested on the re-
moval of very finely dispersed colloidal suspensions of
metal hydroxides from wastewaters.
Freeze Crystallization
The application of freezing to the problem of solvent
purification has been in use for quite some time; how-
ever, the use of this technology in the field of treating
water-based mine discharges has been attempted only
recently. The generic principle applied by this process is
the natural rejection of dissolved contaminants from the
crystal structures of a freezing solvent. Contaminants
that are included in the solid fraction of the freezing liq-
uid usually are included as engulfed particulates in larger
crystals and not as chemical components of the crystal
structure. Therefore, by partially freezing contaminated
water into a slurry of very small crystals and a concen-
trated brine, a separation of contaminants and clean
water, as ice, can be made. The clean ice crystals are
separated from the brine, washed of any brine residuum,
and melted to produce a cleaned effluent.
Froth Flotation
Froth flotation has been used for many years to sepa-
rate specific paniculate matter from water-based slur-
ries. The method uses chemical reagents to produce a
nonwetting surface on certain particles and then bubbles
a gas, usually air, through the slurry. The particles with
the nonwetting surfaces adhere to the gas bubbles and
are carried to the top of the flotation vessel where the
froth and slurry are separated.
Gas Hydrate Formation
Gas hydrates are solid materials formed when a gas,
usually a low molecular weight hydrocarbon or carbon
dioxide under high pressure, is introduced into water
within a closed vessel. Contaminants found in the water
are rejected from the crystal structure of the solid hy-
drate. Large amounts of heat are given off from the hy-
drate-producing reactions because the reactions are
exothermic. Several water molecules react with each of
the gas molecules to form a specific gas hydrate. The
small crystals of gas hydrate are removed from the waste
stream and the original water-borne contaminants are
concentrated in the remaining volume of brine. The solid
gas hydrate is then decomposed, by warming or by low-
ering the pressure, into water and the original gas.
Ion-Exchange Processes
Ion-exchange processes have been used for many years
to remove contaminants from many types of wastewater
streams. The process removes metal ions and some
anions from the waste streams by exchanging these ions
for other ions that originally are held on the surface of
the ion-exchange medium. The most common ions that
are added to the waste stream are sodium, potassium,
calcium, and chloride.
Physical Oxidation
This process involves agitation of the aqueous waste
stream to increase the reaction between the waste
stream and the oxygen in the air. The results of the pro-
cess are the same as the chemical oxidation process,
that is, precipitation of insoluble hydroxide compounds
due to hydrolysis.
Reverse Osmosis
This membrane technology uses high pressures applied
to the contaminated fluid to force the solvent phase of
the fluid through a semipermeable membrane, concen-
trating the contaminants in a remnant brine. The pro-
cess has been applied commercially to the desaliniza-
tion of brackish water and pilot plant-scale operations
have been used on several different types of wastewa-
ter. The process usually will recover up to 75 percent of
the inflow water efficiently, but difficulties have been en-
countered in attempting to increase this value, depen-
dent on the concentration and chemistry of the dissolved
contaminants.
Solvent Extraction
This technique is used commercially to remove dissolved
metal ions from acidic solutions. The largest use for this
process is in the copper mining industry, but the process
also has been used at zinc-producing facilities and sev-
eral other types of metal-producing plants. The process
brings an organic liquid into contact with the acidic mine
discharge. Ions dissolved in the aqueous waste solution
become concentrated within the organic liquid. The mix-
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ture of organic and aqueous liquids then is directed into
a tank where the organic liquid separates from the aque-
ous material due to immiscibility. The loaded organic liq-
uid is stripped of dissolved metals by sulfuric acid and
recycled. The metals then can be removed from the acidic
stripping solution by electrowinning or crystallization.
Pathway Interrupt Technologies
Chemical Stabilization
This process involves the addition of chemical additives
to mine waste piles and abandoned and active mine
workings to isolate the acid-generating minerals and thus
prevent the formation of acidic components by the reac-
tion of these minerals with oxygen and water. The pro-
cess is similar or identical to alkaline reagent addition
discussed above.
Alkaline Reagent Addition
The addition of alkaline reagents, both solids and liq-
uids, to acid-generating waste piles and to underground
mine workings has been used as a means of mitigating
the production of acidic mine drainages for some time.
This process is based on the neutralization process,
which also uses this type of reagent. The liquid reagents
have been used on waste piles and on surface recharge
areas for waters within underground mine workings. The
solid materials have been used with solid waste piles,
contaminated soils, and underground mine openings.
The use of the liquid reagents has proven to be disap-
pointing due to the rapid depletion of the reagent by pre-
cipitation and the channeling of the reagent solution within
the waste piles. Capping waste piles with solid alkaline
reagents, by simply layering the reagent, tends to form
a hardened crust of iron-rich solids within and immedi-
ately below the reagent layer. Although these crusts tend
to form a barrier to movement of water, they are pen-
etrated easily by plant roots and erosion and thus are
not considered to be good long-term remediation solu-
tions. Mixing the reagent with the waste material over a
depth of several feet has been shown to be a more vi-
able methodology.
Capping and Revegetation
This process is used as a method of decreasing the pro-
duction of acidic components emanating from mine waste
piles. The quantity of acid being generated from waste
dumps and tailings piles can be decreased and possibly
eliminated by stopping the flow of water and oxygen into
the pile. Attempts have been made to prevent this flow
by recontouring the piles and then capping them with an
impervious layer of material, usually a clay underlain by
a layer of solid alkaline reagent such as limestone. Some
of the clays used have been supplemented with salt so-
lutions. The capping clay layer then is buried with a layer
of gravels and one of soil and later revegetated. A sec-
ondary beneficial aspect of this process is the establish-
ment of conditions in the deeper portions of the capped
piles to reduce or eliminate the effects of oxidizing bac-
teria.
Phosphate Addition
Phosphate anions will react with iron to produce iron
phosphate, a highly insoluble solid. This reaction is the
basis for this technology. Phosphatic solutions have been
sprayed on test piles to assess the process in the same
way that alkaline reagents have been tested. Phosphatic
solutions, like alkaline solutions, have been added to the
recharge areas for water in abandoned underground
mine workings in an effort to mitigate the acid being gen-
erated in the wall rocks of these workings. Solid phos-
phate-bearing ores also have been mixed with test piles
to determine the functionality of the process.
Sulfide Extraction
A large number of mineral processing technologies could
be used to remove the acid-generating minerals from
solid mine wastes and therefore render the majority of
the waste mass harmless. The process of froth flotation,
described above, can be used for this purpose. Other
mineral processing techniques, such as gravity separa-
tion and magnetic separation, also could be used for this
purpose. To date, however, the majority of these meth-
ods have not been tested as to their ability to remove
pyrite and other acid-producing minerals from mining
wastes.
Source Control Technologies
Bactericide Addition
This process involves the addition of a material to the
solid mine waste that will inhibit or destroy the
ferrooxidans bacteria that aid in the oxidation of the sul-
fide minerals and thus facilitate production of acidic drain-
ages. The most common of these materials is sodium
laurel sulfate, which is an ingredient in detergent. This
material inhibits the ability of the bacteria to survive in
acidic mediums by damaging the protective slime coat-
ing that covers the bacteria. In general, these processes
have been effective only for limited periods of time due
to the effective life span of the reagents. Newer, timed
release versions of these materials have been devel-
oped.
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Grouting
Numerous methods have been considered, developed,
and tested to prevent the movement of water in the sub-
surface. Grouting is one of these technologies. Grout is
a material that is used in many sealing-type operations
in the geotechnical industry. In the proper situation, grout-
ing can be used as a method of preventing acid genera-
tion. The theory behind the method is quite simple: An
impermeable barrier is developed in the form of a grout
curtain or other assemblage to prevent ground water from
coming in contact with minerals having acid generating
capabilities. A grout curtain is established by injecting
grout into a series of boreholes, while the material is
under pressure, and allowing it to solidify. The
cementitious material permeates the various openings
and structures in the rock and seals them.
In Situ Vitrification
This process involves the use of electricity or another
external energy source to melt the waste material and
thus produce an impermeable glass that has very low
teachability and acid-production capabilities. The process
has been used to remediate contaminated sediments
and soils. The process could be functional for fine-grained
tailings but would not be of much use on waste dumps
with large masses and void spaces. The melting pro-
cess reduces the overall volume of the waste; therefore,
the area has to be backfilled to reduce the surface sub-
sidence.
Inundation and Saturation
This process is simply the storage of tailings and other
solid mine wastes underwater. This technology is based
on an attempt to reduce or terminate the production of
acid and the subsequent leaching of metals from solid
mine wastes by inhibiting the contact of oxygen with the
wastes. Evidence suggests that the chemical reactivity
of sulfide-based tailings is reduced by such methods of
storage. The amount of oxygen that is soluble in water
at saturation is approximately 8 parts per million, which
is much less than the amount of oxygen found in air (+/
- 20 percent). Thus, the oxidation potential of water is
much less than that of air or moist air.
Reducing Atmosphere
As stated, the source of acid generation in the vast ma-
jority of mine wastes is the oxidation of sulfide bearing
minerals. This oxidation process, often accelerated by
biological processes, requires the presence of oxygen
to initiate and continue the reaction. By creating an at-
mosphere in the vicinity of the acid production sites that
is devoid of or very low in oxygen, the acid-producing
reactions will be hindered. This process functions natu-
rally in several underground mines where carbon mon-
oxide/dioxide-rich atmospheres can be found in poorly
ventilated areas. The introduction of these or other gases
to sealed, secure mine workings in the form of smoke or
another gaseous mixture might constitute a low cost,
effective source-control type of mechanism, but this ap-
proach would be difficult to implement.
Sulfide Extraction
See description in Pathway Interrupt section.
Temperature Reduction
The rate of acid production is slowed if the temperature
of the reaction is reduced. This slowing is also true for
reactions catalyzed by biological processes. Therefore,
researchers have envisioned that reducing the tempera-
ture at the site of the acid production by an artificial
method could be used as a source-control type of tech-
nology for reducing acid production. This process might
not be feasible for mine waste piles or for large, com-
plex mine systems. The methodology might be viable,
however, for use in small-scale, underground, abandoned
operations that do not exhibit large amounts of geother-
mal heat production. Such processes may prove most
effective for mining operations based in northern latitudes
and high altitudes.
69
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Chapter 9.
Innovative Approaches to Addressing Environmental Problems for the
Upper Blackfoot Mining Complex: Overview
Judy Reese
Project Location
The Upper Blackfoot Mining Complex (UBMC), also
known as the Heddleston Mining District, is located ap-
proximately 16 miles east of Lincoln, Montana, in Lewis
and Clark County (Figure 1). It consists of numerous his-
toric mine sites, including but not limited to, the Mike
Horse, Anaconda, Mary P., Edith, Paymaster, and Car-
bonate (Figure 1). The distance from the Carbonate Mine
to the Mike Horse Mine is approximately 3 miles. The
Heddleston District is situated within the headwaters area
of the Big Blackfoot River, which originates at the
confluence of Anaconda and Beartrap Creeks.
Regional Setting
The UBMC lies within a high, forested basin bounded by
the continental divide to the north, northeast, east, and
southeast. Elevations along the divide range from 5,600
to 7,200 feet above mean sea level (msl). The elevation
of the Lower Carbonate Mine site is 5,200 feet above
msl and the Mike Horse Mine is approximately 5,600
feet above msl. Average annual precipitation in this area
is approximately 21 inches per year (1), with roughly two-
thirds of the precipitation as snowfall (2). A weather sta-
tion located 2 miles north of the UBMC recorded the low-
est temperature on record prior to 1970 in the contigu-
Carbonate ;
Mine.. / ^
Project Location
•Great Falls
Helena MONTANA
Bozeman Billings
Figure 1. Upper Blackfoot Mining Complex.
70
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ous United States (minus 70 degrees Fahrenheit on
January 20,1954) (1).
Geology and Mineralization
The rocks within the UBMC area range in age from Pre-
cambrian Spokane Formation to Tertiary intrusives and
include recent alluvial deposits. Late Proterozoic age
diorite sills and Tertiary age stocks, sills, and dikes of
quartz porphyry and monzonite porphyry intrude the
Spokane quartzite and argillite rocks. Two types of min-
eralization, silver-lead-zinc veins and copper-molybde-
num porphyry are present within this area. The silver-
lead-zinc mineralization occurs along northwest trend-
ing fractures and to a lesser degree along northeast ori-
ented fractures. Historically, mining was concentrated
along this fracture-controlled mineralization (3).
Historical Mining Activity
Silver-lead-zinc ore was first discovered at the UBMC in
1898 by Joseph Heitmiller. Minerals exploration activi-
ties continued through the early 1980s. Silver, lead, zinc,
and copper were mined from this area from 1898 through
1955 with minor gold extracted prior to 1900 (4). Mining
was conducted by several individuals and small compa-
nies from 1898 through 1945. ASARCO purchased most
of the private landholdings in 1945 and owned and op-
erated the Mike Horse Mine and Mill, as well as the town
of Mike Horse, from 1945 through 1955. The Mike Horse
Mine was the largest in the district. It consisted of 10
underground working levels, which were driven along
mineralized veins up to 2,000 feet long. Total production
from the Heddleston District was minor, in part due to its
remote location. The district produced 450,000 tons of
ore, of which 385,000 tons were produced from the Mike
Horse Mine, during 1945 to 1952 (4).
The Anaconda Company leased the ASARCO holdings
from 1964 through 1981. From 1962 through 1973, Ana-
conda conducted an extensive exploration program that
resulted in the delineation of a 93-million-ton near-sur-
face copper-molybdenum porphyry ore body (about one-
half percent copper) located east of Paymaster Creek.
In addition to its private holdings, ASARCO continues to
hold unpatented claims within the UBMC. The unpat-
ented land within and surrounding the UBMC area is
owned by the U.S. Forest Service.
Environmental Degradation
Historical mining practices resulted in contamination of
surface water, ground water, soils, and stream sediments.
The sources of contamination include mine wastes and
tailings (Table 1) as well as acid mine drainage from sev-
eral adits located throughout the complex. The primary
contaminants of concern from these sources include zinc,
cadmium, iron, manganese, aluminum, copper, and lead.
Acid mine drainage from the Mike Horse Mine 300-level
adit (Table 2) is the primary source of surface water and
stream sediment degradation within (5,6) and down-
stream of the UBMC (5,6,7). Flows from this adit vary
from 10 to 140 gallons per minute (gpm) (8). The pH
typically ranges from 5.4 to 6.3 (9) with an occasional
low in the range of 4 to 4.6 (10). Relative to the Mike
Horse adit discharge, acid mine drainage from adits lo-
cated at the Anaconda, Paymaster, and other mine sites
are minor sources of contamination, with flows of be-
tween less than 1.0 to 7.5 gpm.
Tailings from the Mike Horse Mill were used to construct
a tailings impoundment within the Beartrap Creek drain-
age. Mill tailings were conveyed via wooden flumes to
the impoundment site from 1916 through 1953 (4). In
1975 the Beartrap Creek tailings impoundment failed,
releasing approximately 200,000 cubic yards of tailings
into Beartrap Creek and the Upper Blackfoot River (11).
Table 1. Upper Blackfoot Mining Complex Mine Wastes and Tailings
Contaminants Ranges (mg/kg)
Aluminum
Arsenic
Cadmium
Copper
Lead
Manganese
Mercury
Zinc
3,278-18,240
42-3,555
1-134
59-7,405
112-21,803
11-8,540
50-3,400
23-4,333
Table 2. Mike Horse Mine Adit Water Quality (Totals)
Contaminants
Aluminum
Cadmium
Copper
Iron
Lead
Manganese
Sulfate
Zinc
Ranges
(mg/L)
0.14-1.3
0.02 - 0.2
0.15-1.8
4.2 - 74.0
0.005 - 0.48
8.7-53.0
346.0 - 2,927.0
26.0 - 90.0
sMCL"
0.2
0.005 (MCL)
1.0
0.3
0.01 5 (MCL)
0.05
250.0
5.0
• sMCL « secondary maximum contaminant level.
71
-------
The dam was reconstructed later in 1975 by the Ana-
conda Company.
A study conducted prior to the 1975 dam breach showed
bed sediment enrichment of cadmium, copper, and zinc
as well as coatings of iron-manganese oxyhydroxides
within the upper reaches of the Blackfoot River (5). Prior
to the dam breach, an extensive natural wetland system
mitigated transport of contaminants downstream. The
dam breach channelized the marshes, facilitating unim-
peded transport of contaminants downstream.
Concentrations of copper and cadmium in surface wa-
ter exceeding acute and chronic toxicity threshold val-
ues were found to be highest near the sources and ex-
tended the farthest downstream during spring flows (6,7).
The observed rapid decrease of solute contaminants
below the source is probably related to the precipitation
of iron oxyhydroxides (12) and high concentration of
sulfate (13). Elevated concentrations of sulfate and
bioavailable cadmium and zinc extended the farthest
downstream (6). The general downstream order of mo-
bilization of bioavailable metals is cadmium, zino cop-
per arsenic, nickel (12). Elevated levels of zinc, cop-
per, and cadmium were periodically detected as far as
10 miles downstream of the UBMC (7).
Levels of arsenic and nickel are not reported in Tables 2
and 3 because these metals are not significant contami-
nants of concern at this time. Elevated levels of nickel
(0.12 to 0.15 mg/L) above the maximum contaminant
level (MCL) have been reported only four times since
1972 and all have been associated with the Mike Horse
adit discharge. Geochemical analyses for arsenic from
the Anaconda and Mike Horse adit discharges have
found intermittently elevated levels (1973, 1989, 1990;
0.04, 0.058, 0.042 mg/L, respectively). Arsenic is being
monitored as a chemical of concern, however, because
the arsenic anion form that determines the extent of ad-
sorption, coprecipitation, and surface complexation is
greatly affected by pH; and the alkaline drains (i.e., lime-
stone used to raise pH) at the Mike Horse and Anaconda
sites will certainly alter the pH of both systems.
Table 3. Upper Blackfoot Mining Complex Ground-Water Quality
(totals)
Contaminants
Aluminum
Cadmium
Iron
Manganese
PH
Ranges (mg/L)
0.7
0.2
2.2
0.1
2.7
-10.3
-164.2
-105
-7.3
SMCL
0.2
0.005 (MCL)
0.3
0.05
6.5 -8.5
Downgradient ground-water samples from three wells
and four piezometers located in proximity to potential
contaminant sources at the Anaconda, Mary P., Edith,
Paymaster, and Carbonate mine sites were collected in
November 1992 and in February and May 1993. The
results of these sampling episodes are presented in Table
3 with only metal and pH values that exceeded MCLs or
secondary MCLs listed. Ground-water contamination
extending over 1,000 feet downgradient of the UBMC is
evidenced by samples collected from a well located in a
wetland area approximately 1,200 feet west of the Car-
bonate Mine site. This well had elevated levels of cad-
mium, lead, manganese, and iron during the same three
sampling events (14).
Reclamation History
The UBMC was a Montana Department of State Lands
Abandoned Mine Bureau reclamation project from 1987
through 1990. Very little remediation work was conducted
during this time. In 1991, the Montana Legislature trans-
ferred jurisdiction of the site from the Department of State
Lands to the Montana Department of Health and Envi-
ronmental Sciences' State Superfund Program. In June
of 1991, the state noticed ASARCO and the Atlantic
Richfield Company (ARCO) (ARCO purchased the Ana-
conda Company in 1977) as the potentially liable parties
under the Montana Comprehensive Environmental
Cleanup and Responsibility Act for the remediation of
the UBMC. During the fall of 1993 ASARCO and ARCO
completed the phase I remedial investigation/feasibility
study sampling and analysis for the UBMC. In April of
1993, ASARCO and ARCO began a 5-year voluntary
interim remedial action program at the UBMC. The state
is reviewing all remediation plans and conducting over-
sight of the voluntary remediation field activities. The
state, ASARCO, and ARCO have not entered into an
agreement regarding the voluntary action; consequently,
ASARCO and ARCO are conducting all remediation ac-
tivities at their own risk.
Voluntary Interim Remedial Actions
The schedule for completed, in-progress, and proposed
UBMC construction activities is delineated in Table 4.
ASARCO and ARCO began voluntary interim remedial
actions at the Carbonate and Mike Horse mine sites in
September 1993. Mine wastes and tailings in the Lower
Carbonate were removed, limed, and placed in a reposi-
tory located at the Upper Carbonate Mine area. A stream
diversion was built along an upper reach of Mike Horse
Creek and construction of the Mike Horse Mine treat-
ability pond began. Also, a reach of Mike Horse Creek
adjacent to the treatability pond was reclaimed.
72
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Table 4. Upper Blackfoot Mining Complex Voluntary Interim
Remedial Actions (5-year schedule)
Mine Site
1993 1994 1995 1996 1997
Carbonate
Removal/reclamation
Repository
Mike Horse
Pond
Water Treatment
Repository
Anaconda
Removal/reclamation
Water treatment
Paymaster
Water treatment
Reclamation
Edith and Mary P.
Removal
Tailings Pond
Revegetation
In 1994, the Upper Carbonate repository was completed
and reclamation of the Lower Carbonate area was nearly
completed. Construction of the Mike Horse treatability
pond continued with the installation of the pond liner and
the building of the pond spillway. Other activities in 1994
included relocation of a 318-foot section of Mike Horse
Creek, excavation and removal of hydrocarbon contami-
nated soils at the Mike Horse Mine site, and preparation
of the Mike Horse Mine repository site. Approximately
7,300 cubic yards of waste material was removed from
the Lower Anaconda mine area and relocated to the Mike
Horse Mine repository site. New monitoring wells were
installed at the Anaconda, Carbonate, and Mike Horse
mine sites.
Proposed remediation activities for 1995 include the fol-
lowing:
• Removal of the remaining Lower Anaconda mine
wastes and tailings.
• Removal of the Edith and Mary P. waste piles to the
Mike Horse repository.
• Completion of the Mike Horse Mine repository.
• Completion of the Mike Horse Mine treatability pond.
• Installation of an alkaline drain and hydraulic seal in
the Mike Horse adit.
• Installation of an alkaline drain at the Anaconda Mine
adit.
Construction of the phase I wetland treatment cells
at the Anaconda Mine site.
Construction of a pipeline from the treatability pond
to the phase I wetland cells.
Connection of the pond discharge to the pipeline.
Reclamation of the Upper Anaconda Mine and
Middle Mike Horse Mine waste piles.
Miscellaneous revegetation work at the Lower Car-
bonate wetland area.
References
1. Coffin, D.L, and K.R. Wilke. 1971. Water resources
of the Upper Blackfoot River Valley west-central Mon-
tana. U.S. Geological Survey in cooperation with
(and available from) the Montana Department of
Natural Resources and Conservation, Water Re-
sources Division, Helena, MT. Technical Report Se-
ries No. 1. 82 pp.
2. U.S. Department of Agriculture. 1990. Hydrology of
the Blackfoot River drainage. Soil Conservation Ser-
vice, Bozeman, MT. 25 pp.
3. Pardee, J.T., and F.C. Schrader. 1933. Metalliferous
deposits of the greater Helena mining region. U.S.
Department of Interior, Geological Survey Bulletin
842:87-108.
4. PTI Environmental Services. 1993. Upper Blackfoot
Mining Complex protected resources/facility history
report. Butte, MT. 86 pp.
5. Spence, L.E. 1975. Upper Blackfoot River—A pre-
liminary inventory of aquatic and wildlife resources.
Montana Department of Fish and Game, Missoula,
Montana. 236 pp.
6. Moore, J.N. 1990. Mine effluent effects on non-point
source contaminants in the Blackfoot River, Mon-
tana. A report to the Lewis and Clark City-County
Health Department and the Montana Department of
Health and Environmental Sciences, Water Quality
Bureau. 36 pp.
7. Ingman, G.L, M.A. Kerr, and D.L McGuire. 1990.
Water quality investigations in the Blackfoot River
Drainage, Montana. A report to the Big Blackfoot
River Oakbrook, Illinois Chapters of Trout Unlimited.
123pp.
8. McCulley, Frick & Oilman, Inc. 1995. Upper Blackfoot
Mining Complex draft 1995 remedial design report.
Boulder, CO. 70 pp.
73
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9. Hydrometrics. 1995. 1994 data summary report.
Upper Blackfoot Mining Complex, Lewis and Clark
County, Montana. Helena, MT. 37 pp.
10. PTI Environmental Services. 1993. Upper Blackfoot
Mining Complex historical data report. Butte, MT. 687
PP-
11. Helena National Forest. 1975. Mike Horse Dam re-
construction environmental analysis report. F.
Burnell, Team Leader. Helena, MT. 11 pp.
12. Moore, J.N., S.N. Luoma, and D. Peters. 1991.
Downstream effects of mine effluents on an inter-
montane riparian system. Can. J. Fish. Aq. Sci.
48(2):222-232.
13. Nordstrom, O.K. 1982. Aqueous pyrite oxidation and
the consequent formation of secondary iron miner-
als. Soil Sci. Soc. Am. Spec. Publ. 10:37-56.
14. PTI Environmental Services. 1994. Upper Blackfoot
Mining Complex phase I data report. Butte, MT. 106
PP-
74
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Chapter 10.
Innovative Approaches to Addressing Environmental Problems for the
Upper Blackfoot Mining Complex: Voluntary Remedial Actions
J. Chris Pfahl
Background
After ASARCO and Atlantic Richfield Company (ARCO)
(the Companies) received notices in February 1992 from
the state of Montana that they were liable parties for the
cleanup of the Upper Blackfoot Mining Complex (UBMC)
site, they quickly entered into an internal cost-sharing
agreement and developed a strategy for addressing is-
sues raised by the state and cost-effectively cleaning up
the historic mining site. As required by the February 1992
notice letter, the Companies submitted a draft final re-
medial investigation/feasibility study (RI/FS) work plan
for the UBMC in July 1992 and began the sampling and
data collection necessary for the RI/FS. Collected data
indicated that more than 90 percent of the metal load-
ings to the Blackfoot River was coming from the Mike
Horse adit. Thus, the Companies prepared work plans
for addressing the Mike Horse adit discharge and two
other sources of water quality degradation.
In April 1993, the Companies met with the Montana De-
partment of Health and Environmental Sciences and pre-
sented work plans for the preliminary remedial actions
at the UBMC. The meeting resulted in a verbal agree-
ment (subsequently documented in a letter to the Com-
panies, dated May 26,1993) to allow voluntary remedial
actions at the UBMC, subject to various provisions, in
lieu of performing the RI/FS, which typically is required
at state Superfund sites. In August 1993, the Compa-
nies hired a contractor and cleanup activities began at
the UBMC.
Cleanup Approach
The Companies developed an approach for addressing
the sources of mining-related metals loadings in the sur-
face waters at the UBMC. The approach consists of:
• Performing all voluntary cleanup activities under the
existing State and Federal permit systems. (A list of
permits obtained by the Companies is included in
Table 1.)
Table 1. Permits Required for Voluntary Cleanup of the Upper
Blackfoot Mining Complex
Permit
Description
Agency
404 Permit
Montana Pollutant
Discharge Elimina-
tion System (MPDES)-
Point source
Addresses locating a U.S. Army
structure, excavating, or Corps of
discharging dredged or fill Engineers
material in U.S. waters
Addresses point-source
discharges of pollutants
into state surface waters
3A Permit
MPDES-General
Stormwater Permit
Addresses short-term
exemption from surface-
water quality standards
for construction sites to
State waters
Addresses discharge of
storm water from con-
struction sites to State
waters
Montana
Department
of Health and
Environmen-
tal Sciences,
Water Quality
Bureau
(MDHES-
WQB)
MDHES-WQB
MDHES-WQB
MPDES-Construction Addresses discharge of MDHES-WQB
Dewatering-General
Discharge Permit
310 Permit
waste water resulting
from dewatering of
ground water and/or sur-
face water from construc-
tion sites, well pump tests,
and/or well development
to state waters
Addresses work in or
on stream channels or
banks and water use or
diversion, per Montana's
Natural Streambed and
Land Preservation Act
Lewis and
Clark County
Conservation
District
Consolidating numerous waste rock piles and accu-
mulated tailing into engineered repositories located
75
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in disturbed areas that are high and dry (i.e., away
from direct contact with surface water).
• Obtaining Montana Pollutant Discharge Elimination
System (MPDES) permits for the adit discharges and
constructing passive water treatment systems to treat
water sufficiently to achieve applicable discharge
standards.
• Constructing run-on and infiltration controls to pro-
vide adequate hydrologic isolation of mine wastes.
• Recontouring and revegetating areas disturbed by
mining activity, including construction of the mine
waste repositories.
• Constructing run-on/infiltration controls and/or adit
bulkheads to restrict the migration of water through
acid-generating mineralized zones, limiting the pro-
duction of acid and metal enriched mine drainage.
• Continuing to monitor surface- and ground-water
quality to assess the effectiveness of the completed
cleanup activities.
The Companies developed a comprehensive, site-wide
cleanup plan based on these standard mine reclama-
tion measures. The specific actions to be taken at each
subarea of the UBMC are outlined in the following sec-
tions of this paper.
Carbonate Mine
The Carbonate Mine is located adjacent to Montana
Highway 200 at the base of Rodgers Pass. Although
sampling indicated the mine was not a significant source
of metals for the Blackfoot River, it was considered a
high priority for reclamation due to its visibility from High-
way 200, the main highway between Missoula and
Greatfalls, Montana.
The Carbonate site consists of a one-half acre tailing
pond and mine waste rock dump situated in a wetlands
adjacent to the highway and a hillside mine waste rock
dump located approximately 500 feet north of the high-
way. Cleanup of the site consisted of excavating and
moving approximately 20,000 cubic yards of mine waste
and tailings from the wetlands to an engineered reposi-
tory constructed on top of the hillside mine waste rock
dump. Because of excessive moisture in the excavated
tailings, quicklime was incorporated into the material at
a rate of 8 percent by weight to achieve adequate com-
paction when the materials were placed in the reposi-
tory. In addition to drawing out moisture, the quicklime
provided the additional benefit of neutralizing the acid-
generating potential of the tailings and mine waste rock.
After all mine waste rock and tailings were removed from
the lower Carbonate, topsoil was applied and the area
was reclaimed as a wetland. Surface-water run-on con-
trols were constructed around the repository, the reposi-
tory was capped with a claymax geotextile liner, 12 inches
of topsoil were spread over the repository, and the area
was reseeded.
Mike Horse Adit Discharge
The Mike Horse adit is located on Mike Horse Creek,
approximately 1 mile upstream of the headwater of the
Blackfoot River (the confluence of Beartrap and Ana-
conda creeks) (Figure 1). The Mike Horse adit (at the
300 level of Mike Horse Mine) is the lowest surface open-
ing of the Mike Horse Mine, which produced approxi-
mately 450,000 tons of lead zinc ore between 1878 and
1955.
Water flow measurements taken by the Companies up-
stream of the Mike Horse adit indicated a significant re-
duction in the surface-water flow rate in the area where
Mike Horse Creek crossed the outcrop of the Mike Horse
vein structure. The Companies assumed that this water
was "leaking" into the mine and exiting via the Mike Horse
adit. To reduce this obvious surface-water inflow, in 1993
a dam was constructed upstream of the vein outcrop to
direct the surface-water flow to a pipeline. The pipeline
discharges the water into the natural stream channel
down from the outcrop. Effects of the surface-water di-
version can be seen in Figure 2, which is a graph of adit
discharge over time.
The Mike Horse Mine adit has a moderate discharge
rate (approximately 40 gpm during late summer through
winter, with a typical maximum flow of approximately 100
gpm during spring run-off). The adit drainage is slightly
acidic (a pH ranging from 5.2 to 6.4, with median pH at
about 6), has moderate to high dissolved metals con-
centrations (maximum concentrations of iron at 72 mg/L
and zinc at 89 mg/L), and has high sulfate concentra-
tions (typically greater than 1000 mg/L). More generally,
the mine adit discharge can be characterized as lightly
to moderately acidic, of moderate to high ionic strength,
and as a calcium-magnesium-iron sulfate solution.
The basic treatment train concept for this mine adit dis-
charge is to increase the pH of the water by utilizing an
adit anoxic limestone drain; oxidize and precipitate iron
in a pretreatment basin; provide additional intermediate
treatment for dissolved and suspended iron compounds
in a modified surface-flow wetland; polish residual met-
als in a series of subsurface-flow wetland cells; and, fi-
nally, provide finishing of the discharge in surface-flow
cells to reaerate effluent (e.g, reintroduce dissolved oxy-
gen, release residual hydrogen sulfide) immediately prior
to release to the Upper Blackfoot River. Figure 3 is a
schematic of the treatment train.
Initial passage of the anoxic, acidic mine drainage over
coarse, high-calcium limestone (at grades greater than
90 percent calcium carbonate) will add alkalinity to the
76
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Wetlands Treatment
Cells
Mike Horse
Creek
Diversion
Treatability
Pond
Mike Horse
Mine
Figure 1. Location of the Mike Horse Mine.
Surface Water
Diversion Installed
November 1993
20
May-90
Oct-95
Figure 2. Mike Horse adit discharge from May 1990 to October 1995.
77
-------
Anaconda
Adit Discharge
Mike Horse
Adit Discharge
Anoxic Limestone
Drain (ALP)
Anoxic Limestone
Drain (ALD)
In-Line Oxidation
System (ILS)
Mike Horse
Oxidation Pond
Subcell A1
Oxidation Pond
Subcell A2
Compost Filtration
Subcell A3
Subsurface Flow
Metals Polishing
Cell 4
Subsurface Flow
Metals Polishing
CellS
Subsurface Flow
Metals Polishing
Cell 6
Surface Flow
Aeration
Discharge to
Blackfoot River
Figure 3. Schematic ol the treatment process for discharge from the Mike Horse Mine adit.
78
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system and encourage rapid oxidation of ferrous iron
downgradient as the drainage enters the oxidation pond.
If the anoxic condition of the adit discharge can be main-
tained by appropriate plugging of the adit and if iron is
predominantly in the ferrous state, calcite in an anoxic
limestone drain (ALD) should not armor (i.e., become
coated with gypsum) when in contact with these waters.
Armoring of the calcite by calcium sulfate formation has
not been reported to be a problem in ALDs, although
stability calculations (i.e., Eh and pH curves) suggest
that some gypsum formation may occur above pH 4. For
the proposed UBMC treatment scheme, this ALD will be
placed within the Mike Horse adit behind a 6-foot thick
concrete plug.
The objective of the Mike Horse adit plug is to control
mine water drainage from the tunnel, to ensure that the
ALD remains submerged, and to develop static water
pressure. Once the plug is installed, sufficient pressure
will develop to provide for enhanced aeration by forcing
the water under pressure through the jet pumps. The
maximum expected head behind the Mike Horse adit
plug is approximately 80 feet, although the jet pumps
normally will operate at lower heads. The 80-foot maxi-
mum head was chosen to allow for a margin of safety
that would prevent flooding of the Mike Horse 200 level
and the possibility of a discharge from caved access tun-
nels at the 200 level. The plug will be installed in an area
of competent rock approximately 200 to 400 feet from
the portal.
Discharge from the adit will be conveyed via pipeline to
an in-line oxidation system (ILS) consisting of jet pumps,
which inject air into the water, and static mixers, which
mix the air with the water, to promote rapid oxidation of
the dissolved iron. Discharge from the ILS is directed to
a lined oxidation pond constructed just in from the Mike
Horse adit portal. The pond has a capacity of 600,000
gallons, giving it an estimated 3 to 6 day retention time.
While detained in the pond, the majority of the iron should
precipitate as iron hydroxide and form a sludge on the
pond bottom. The Companies anticipate that the sludge
will need to be pumped from the pond and disposed on
an annual basis. Discharge from the pond will be con-
veyed via pipeline approximately 1 mile to the constructed
wetland treatment system at the Anaconda Mine site.
Anaconda Adit Discharge
The Anaconda Mine is located in the hillside to the north
of the confluence of Mike Horse Creek and Beartrap
Creek (see Figure 1). The mine, which was developed
from 1919 to 1923, during 1933, and again in 1939 to
1940, consists of two original shafts and two adits with
workings on several levels extending to a depth of about
325 feet. The lower level adit is referred to in this paper
as the Anaconda adit. The ore mined at the Anaconda
Mine until 1939 was processed offsite with some ore
reportedly processed in the mill at the Mike Horse Mine.
An ore processing mill was installed at the Anaconda
site in 1940 that produced approximately 50 tons of tail-
ings.
The Anaconda adit discharge is smaller than that from
the Mike Horse adit, with rates on the order of about 1 to
2 gpm and a maximum flow of about 3 gpm during spring
run-off. The discharge typically is acidic (pH ranging from
about 3.0 to 6.4) and contains moderate dissolved met-
als concentrations (21 to 76 mg/L iron and 1 to 8 mg/L
zinc). At the Mike Horse adit, an ALD will be placed in
the Anaconda adit behind a 2-foot thick flow-through
concrete plug designed to keep the ALD submerged.
Drainage will be directed to a secondary oxidation pond
(subcell A1 of the constructed wetland treatment sys-
tem), where the discharge will be commingled with drain-
age from the Mike Horse adit.
Constructed Wetland Treatment System
The locations of the constructed wetland treatment cells
are shown in Figure 1. These locations comprise most
of the relatively flat area available at the UBMC. The
rectangular wetland cells located below the confluence
of Anaconda and Beartrap creeks comprise the Phase I
system, built in 1995, and the additional cell shown be-
tween Anaconda and Beartrap creeks is located on the
site of a contemplated Phase II wetland system. The need
for the Phase II system will be based on the performance
of the Phase I system. Also, construction of the Phase II
system is uncertain due to difficulties in obtaining per-
mission to use the relatively flat public lands on which
the system would be built.
The Phase I wetland treatment system comprises four
cells: Cell A (comprised of subcells A1, A2, and A3), Cell
4, Cell 5, and Cell 6. The schematic arrangement of these
cells is shown on Figure 3. The Phase II wetland system
would be hydraulically upgradient of the Phase I system
and would be comprised of Cells 1,2, and 3. The Phase
I system is described below.
As previously discussed, discharge from the Mike Horse
adit will undergo primary treatment in the in-adit ALD,
the ILS system, and the primary oxidation pond located
near the Mike Horse Mine. Discharge from the Anaconda
adit will undergo initial treatment within the ALD installed
in the Anaconda adit. These pretreated discharges will
be commingled in the initial portion of Cell A (subcell
A1). Subcell A1 consists of a small, lined oxidation pond
where ferrous iron in the Anaconda adit discharge and
remaining ferrous iron in the Mike Horse adit discharge
should become oxidized to ferric iron and settle out. Such
settling is important from an operational standpoint due
to the tendency of iron oxy-hydroxides to plug the front
end of constructed wetland treatment cells, diminishing
the quantity of flow that can be treated. The free water
surface of subcell A1 will inundate subcell A2, which con-
stitutes a two-layer system. The upper layer consists of
79
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a mixture of compost and gravel; the lower layer con-
sists of gravel only, again underlain by a liner. Flow from
the free water surface should move vertically downward
through the compost unit to the gravel unit, allowing ad-
ditional filtration of any remaining iron oxy-hydroxides.
Periodic replacement of the compost unit, if required,
would constitute an operations and maintenance item.
Wood fiber and sewage sludge are used in the compost
unit.
Flow from the lower layer of subcell A2 will move hori-
zontally into subcell A3, and then into Cells 4 and 5. Each
of these cells are 1) lined, 2) comprised of gravel through
which all flow generally is at subsurface, and 3) veg-
etated with local wetland plant species. Anaerobic con-
ditions in the gravel should invoke a variety of polishing
processes to remove divalent metal cations that are
present in the adit discharges. Such processes include
adsorption to biofilms, precipitation as immobile metal
sulfides, and physical filtration. Flow controls at the
downgradient ends of subcell A3, Cell 4, and Cell 5 will
allow manipulation of hydraulic gradients and thus will
control residence/treatment times within the wetlands.
The final treatment cell, Cell 6, comprises a lined sur-
face-flow finishing cell with baffles to increase residence
time. This cell should reaerate wetland effluent, releas-
ing hydrogen sulfide and adding oxygen prior to dis-
charge of the effluent to the Upper Blackfoot River. This
cell also should allow final polishing of the adit discharges
to be performed by contact with surface biofilms.
Miscellaneous Mine Dumps and Future
Activities
Several mine waste rock dumps ranging in size from
several hundred cubic yards to 25,000 cubic yards are
scattered throughout the UBMC. These dumps contain
heavy metals and are believed to affect the surface-wa-
ter quality. All of the accessible mine waste rock dumps
will be moved and consolidated into two onsite reposito-
ries constructed similarly to the Carbonate repository
described above. The main repository is located imme-
diately downstream of the Mike Horse oxidation pond at
the historic location of the Mike Horse mill. A smaller
repository will be constructed adjacent to the Paymas-
ter Mine to contain the wastes from that mine.
Other reclamation activities to be performed in the fu-
ture will consist of direct revegetation of the Mike Horse
tailing impoundment and surface disturbances at the
upper Mike Horse Mine workings and riparian area en-
hancements to the upper Blackfoot River in areas his-
torically affected by heavy metals.
Expectations are that when all reclamation activities are
completed, the water quality in the Upper Blackfoot River
will be improved significantly and, when coupled with
riparian enhancements, will result in an improved fish-
ery in the river and tributary streams.
80
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Chapter 11.
Innovative Approaches to Addressing Environmental Problems for the
Upper Blackfoot Mining Complex: Grouting as a Hydrogeologicai
Control for Acid Rock Drainage Reduction
A. Lynn McCloskey
Introduction
The U.S. Environmental Protection Agency (EPA) has directed
MSE, Inc., through the Mine Waste Technology Program
(MWTP), to evaluate and develop the subsurface application
of a clay-based grout. Spetstamponazhgeologia (STG)
Enterprises, a Ukrainian company, has developed the
grouting technology selected for demonstration at the
Mike Horse Mine site (1). This point-source control tech-
nology involves injecting clay-based grout into an un-
derground mine workings. Reduction of water inflow to
underground mine workings will decrease the volume of
impacted water discharging from the 300-level portal and
has the potential to improve the quality of the water sys-
tem downstream from the mine. The water quality im-
provements would result from a reduction of contami-
nant transport, acid generation, and discharge from the
mine portal.
MWTP Activity III, Project 2, Clay-Based Grouting Dem-
onstration Project, is funded by EPA and jointly adminis-
tered by the Agency and the U.S. Department of Energy
(DOE) through an Interagency Agreement. Program
oversight is provided by the Western Environmental Tech-
nology Office (WETO) of the DOE, Environmental
Management (EM), Office of Technology Development.
WETO administrative support is provided by the Pitts-
burgh Energy Technology Center for matters concern-
ing the environment, safety and health, as well as regu-
latory compliance and operational conduct.
The Mike Horse Mine site was selected for demonstra-
tion of the clay-based grouting project. As noted in pre-
sentations about the Upper Blackfoot Mining Complex
(see papers by Judy Reese and Chris Pfahl in this docu-
ment), slightly acidic waters containing elevated levels
of heavy metals discharge from the 300-level portal of
the Mike Horse Mine directly into Mike Horse Creek. The
mine discharge has been recognized by the state of
Montana as one of the major contributors of metal load-
ing into the Upper Blackfoot River (2).
The project consists of four major phases: 1) site char-
acterization, 2) grout formulation, 3) grout production and
placement, and 4) evaluation and monitoring. The project
is designed to test and evaluate the grouting technology
but not to achieve site remediation.
Site Characterization
Development and application of clay-based grout re-
quires acquiring information using an integrated ap-
proach. Thus, the source of water infiltrating the under-
ground mine workings and the hydrogeological system
must be defined in terms of the local and regional geol-
ogy, hydrogeology, geochemistry, geophysics, and past
mining history, all of which are considerations relevant
to the grout formulation. Critical data required for devel-
opment of the grout formulation and placement of the
grout include, but are not limited to:
• Hydrogeology (i.e., hydraulic conductivity).
• Physical and structural geology (i.e., fracture den-
sity and aperture).
• Physical and mechanical rock properties (i.e.,
strength).
• Geochemical/mineralogical properties (i.e., rock
types and compositions along with the chemical
makeup of the ground water).
Grout Formulation
Clay-based grouts are visco-plastic systems that com-
prise structure-forming cement and clay-mineral mortar.
The STG clay-based grout selected for application at
ASARCO's Mike Horse Mine is a system made up of
environmentally benign elements, of which kaolinitic/il-
litic clay is a major constituent. The distinguishing fea-
ture of clay-based grout is that throughout the entire sta-
81
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bilization period the grout retains its plasticity and does
not crystallize, as do cementitious grouts. Moreover, clay-
based grout does not shear or deteriorate during minor
rock movement and therefore can be used at mining sites
where blasting is conducted. Because of good rheologi-
cal characteristics, the clay grouts are not easily eroded
during injection to high-flow conditions. Also, due to the
finely dispersed clay particles, a greater fracture pen-
etration is realized than with cementitious grouts. The
overall properties of clay-based grouts depend on the
physical-mechanical properties of the initial clay mineral
as well as the properties of the cement and the chemical
reagents added.
Additional reasons for demonstrating and applying the
clay-based grouting technology exist also. These include
past successes with clay grouting in the Ukraine, other
unified countries, and the former Eastern Block nations;
the ability of the grout to eliminate flows of up to 4,000
gallons per minute; the low maintenance and longevity
of the grout; and the Theological properties of the grout.
Grout Production and Placement
The Clay-Based Grouting Demonstration Project site is
located approximately 1,000 feet due south of the Mike
Horse Mine's 300-level portal (Figure 1). The grout in-
jection holes are located directly north of ASARCO's dam,
by drillhole DH3. Each hole was drilled at an angle (35,
45, and 60 degrees from horizontal) and perpendicular
to the Mike Horse Fault/Vein system (to the extent pos-
sible) (Figure 2). As illustrated in Figure 2, even though
the dam reduces surface water in the area, the shallow
ground water in the drainage is able to infiltrate through
the subsurface alluvial material and into the fault/frac-
ture system. As indicated, the grout is placed within the
grout injection boreholes. Packers then are placed in the
holes so the grout can be directionally placed in the se-
lected interval.
STG Enterprises has found in studies that three distinct
stages are encountered in the injection and setup of clay
grouts (1). The first stage is a timeframe in which the
rate of structural strength development is slow. This pe-
riod must correspond with the time it takes to mix and
pump the grout. If the setup of the grout is premature,
fouling of the pumping equipment may occur. If the de-
velopment of structural strength takes much longer than
the mixing and pumping, then the material may be ex-
posed to hydraulic properties of the unit that result in
failure or at least weakening of the grout.
The second stage in the placement and setup of clay
grouts is a period when the structural strength of the
material develops much more rapidly. The required time
is controlled by addition of the appropriate amount of
structure-forming reagents.
The third stage in the placement and setup of clay grouts
produces the final strength of the grout, during addition
of the final reagent. The grout's final strength is a prede-
termined, calculated value that establishes the material's
design for the injection event. Each of the above-de-
scribed stages can be controlled by proper grout formu-
lation design.
Once the proper grout is formulated at the project site,
the material can be injected, using a positive displace-
ment slurry pump, through the grout lines and packer
system at a maximum header pressure of 600 pounds-
force per square inch.
Grout Evaluation and Monitoring
The technology evaluation will be performed by MSE,
Inc., under the MWTP, and by SAIC, under the Superfund
Innovative Technology Evaluation (SITE) program. Pa-
rameters used for the evaluation will include:
• Potentiometric surface fluctuations. Six monitoring
wells have been placed within the project site area.
Three monitoring wells are in a defined shallow aqui-
fer and three are in the deep aquifer system. From
these wells, the direction of flow trends toward the
mine workings (SW). Fluctuations in the static water
levels after grouting (indicating a flow direction trend-
ing to the north [downstream]) could be determined
to be a direct indication of grout influence.
• Surface water fluctuations. Flumes and weirs have
been placed in all surface water flows south of the
Mike Horse Mine's 300-level portal. These will be
used to define the water balance of the Mike Horse
Creek's flow regime and to determine if any trends
and immediate responses can be recognized dur-
ing grout injection.
• Water flow fluctuations at the 300-level portal. Two
continuous monitoring systems have been placed
at the 300-level portal of the Mike Horse Mine. These
monitoring stations will show any immediate re-
sponses to the grouting and will indicate any appar-
ent trends.
• Hydraulic conductivity changes. Slug, pump, and
packer tests were performed on the system during
pre- and post-grouting.
• Core drilling to determine dispersivity of the grout.
SAIC will redrill the areas where grout has been
placed. From these drill holes, SAIC will determine
the dispersivity and physical properties of the grout
and will evaluate the ability of the grout to reduce
the permeability of the fracture system.
82
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Mike Horse Mine
MSE73
Copper Wreath '
MS 7357 /
300 Level
•--*MSE70
0 50'100' 200
y Contour Interval: 100
Sterling
MS 10371
Little Nell
MS 10371
Mike Horse Mine
Corner
Hog All
MS 10371
Legend
200 Mine Workings
300 Mine Workings
DH1 • Drill Holes
Roads
Creek
Rev:E Date 6/21/94
Plot Scale: 1=2400
Well locations are approximate:
The wells will be surveyed in
Spring 1994.
Figure 1. Mike Horse Mine site map with project area.
83
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300 Level
Mine Workings
Figure 2. Conceptual cross section of the project area (looking west).
These parameters then will be evaluated to assess the References
changes that have occurred as a result of the injection
of the clay-based grout. 1.
Project Status
Site characterization for the Clay-Based Grouting Dem-
onstration Project was completed during August 1994.
Grout formulation was performed in the Ukraine and was 2.
finalized in May 1994. Grout placement was initiated
during September 1994 and completed during Novem-
ber 1994. At the time of writing (July 1995), the Clay-
Based Grouting Technology evaluation is in progress.
Kipko, E.Y., Y.U.A. Polpzov, O.Yu. Lushinkova, V.A.
Lagunov, Y.u.l. Svirskiy. 1991. Integrated grouting
and hydrogeology of fractured rocks in the USSR.
Spetstamponazhgeologia Enterprises, Antratsit, the
Ukraine. (Roy Williams, trans.) University of Idaho,
Moscow, I D.August.
Montana Department of State Lands, Abandoned
Mine Reclamation Bureau. 1991. Environmental as-
sessment. Upper Blackfoot River Abandoned Mine
Reclamation Project, Phase I. February. Helena, MT.
84
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Appendix A
Seminar Speaker List
Ronald Cohen
Professor
Department of Environmental Science & Engineering
Colorado School of Mines
14th & Illinois - Chauvenet Hall
Golden, CO 80401
303-273-3613
Fax:303-273-3413
Martin Foote
Technical Project Manager
Mine Waste Technology Pilot Program
MSE, Inc.
P.O. Box 3767 - Butte Industrial Park
Butte, MT 59702
406-494-7431
Fax: 406-494-7230
William Cornell
Rolla Research Center
Bureau of Mines
U.S. Department of the Interior
1300 Bishop Street - P.O. Box 280
Rolla, MO 65401
314-364-3169
Fax:341-364-7350
Robert Fox
Clark Fork Superfund Coordinator
U.S. Environmental Protection Agency
301 South Park - Drawer 10096
Federal Office Building
Helena, MT 59626
406-449-5720
Fax: 406-449-5436
Max Dodson
Director, Water Management Division
Region 8
U.S. Environmental Protection Agency
999 18th Street - Suite 500 (8WM)
Denver, CO 80202-2466
303-294-7594
Fax:303-294-1386
Thomas Durkin
Hydrologist
Office of Minerals & Mining
South Dakota Department of Environmental &
Natural Resources
523 East Capitol - Joe Foss Building
Pierre, SD 57501-3181
605-773-4201
Fax: 605-773-4068
Jonathan Herrmann
Assistant to the Director
Water & Hazardous Treatment Research Division
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
26 West Martin Luther King Drive (MS-497)
Cincinnati, OH 45268
513-569-7839
Fax:513-569-7787
Richard Humphreys
Abandoned Mines Coordinator
California State Water Resources Control Board
901 P Street-P.O. Box 100
Paul R. Bonderson Building
Sacramento, CA 95812-0100
916-657-0759
Fax:916-657-2388
85
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Fred Leif
Judy Reese
Senior Policy Advisor to the
Deputy Regional Administrator
Region 9
U.S. Environmental Protection Agency
75 Hawthorne Street
San Francisco, CA 94105
415-744-1017
Fax:415-744-2499
Environmental Scientist
Montana Department of Health and
Environmental Science
P.O. Box 200901
Cogswell Building
Helena, MT 59620
406-444-1420
Fax:406-444-1901
Justice Manning
Environmental Engineer
Center for Environmental Research Information
U.S. Environmental Protection Agency
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7349
Fax:513-569-7585
Lynn McCloskey
Project Engineer
Mine Waste Technology Pilot Program
MSE, Inc.
P.O. Box 4078 - Butte Industrial Park
Butte, MT 59702
406-723-8225
Fax: 406-723-8328
Thomas Mclntyre
ASARCO
100SnelterRoad
E. Helena, MT 59635
406-227-7195
J. Chris Pfahl
Site Manager
ASARCO, Inc.
516 Bank Street - P.O. Box 440
Wallace, ID 83873
208-752-1116
Fax:208-752-6151
J. Curt Rich
Legislative Counsel
Office of Senator Max Baucus, Chairman,
Senate Environment and Public
Works Committee
SH-511 Hart Senate Office Building
Washington, DC 20510-2602
202-224-2655
Fax: 202-228-3867
Andy Robertson
Principal
Steffen, Robertson & Kirsten (Canada), Inc.
580 Hornby Street - Suite 800
Vancouver, British Columbia V6C 3B6
Canada
William Schmidt
Chief, Division of Environmental Technology
Bureau of Mines
U.S. Department of the Interior
810 Seventh Street, NW
Washington, DC 20241
202-501-9271
Fax:202-501-9957
Leslie Thompson
Vice President, Research and Development
Pintail Systems, Inc.
11801 East 33rd Avenue - Suite C
Aurora, CO 80010
303-367-8443
Fax:303-364-2120
86
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Dirk Van Zyl
Director, Mining
Golder Associates, Inc.
200 Union Boulevard - Suite 500
Lakewood, CO 80228
303-980-0540
Fax: 303-985-2080
Organized by:
Ed Barth
Environmental Engineer
Center for Environmental
Research Information
U.S. Environmental Protection Agency
26 West Martin Luther King Drive (G-75)
Cincinnati, OH 45268
513-569-7669
Fax:513-569-7585
Jonathan Herrmann
Assistant to the Director
Water & Hazardous Treatment
Research Division
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
26 West Martin Luther King Drive (MS-497)
Cincinnati, OH 45268
513-569-7839
Fax:513-569-7787
Justice Manning
Environmental Engineer
Center for Environmental
Research Information
U.S. Environmental Protection Agency
26 West Martin Luther King Drive (G-75)
Cincinnati, OH 45268
513-569-7349
Fax:513-569-7585
Heather Fava
Series Coordinator
Eastern Research Group, Inc.
110 Hartwell Avenue
Lexington, MA 02173-3198
617-674-7316
Fax:617-674-2906
Kate Schalk
Vice President and Series Manager
Eastern Research Group, Inc.
110 Hartwell Avenue
Lexington, MA 02173-3198
617-674-7324
Fax:617-674-2906
87
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Appendix B
Contributors
Ronald R. Hewitt Cohen
Colorado School of Mines
Golden, CO
Dr. Cohen received a B.A. in biophysics from Temple University in Philadelphia. He also received a Ph.D. in environ-
mental sciences and engineering from the University of Virginia, where he combined the disciplines of water quality
engineering, water chemistry, hydrology, and applied math. He has worked as a project chief in the National Re-
search Program at the U.S. Geological Survey and currently is associate professor of environmental science and
engineering at the Colorado School of Mines. Dr. Cohen has been working on treatment, geochemistry, and trans-
port of mine drainage materials for 5 years. In addition, he has studied the distributions of 239'240plutonium and
137cesium in regions of the Rocky Mountains' front range both affected and unaffected by the Rocky Flats Plutonium
Weapons Plant. Also, he has participated in studies of surface runoff, storm runoff, graphic information systems, and
stream transport modeling. He has reviewed the U.S. Department of Energy's Treatment Plans and Treatment
Reports and made suggestions for additional remediation technologies.
Dr. Cohen has received the First Prize for Environmental Projects from the American Consulting Engineers' Council
for development of treatment systems for acid mine drainage. He is the recipient of a Certificate of Special Recogni-
tion from the U.S. Congress for environmental work associated with U.S. Department of Energy nuclear weapons
plants. He was selected to review the National Five Year Plan for Environmental Remediation of the Weapons
Plants. He has published numerous papers in journals such as the Journal of the American Society of Civil Engi-
neers, Limnology and Oceanography, and others. He has worked on contaminant problems in Charlotte Harbor
(FL), Chesapeake Bay, San Francisco Bay, the Potomac River, and Clear Creek and the Eagle River (CO). Cur-
rently, Dr. Cohen teaches courses on contaminant transport, water quality, water quality modeling, and hydrology at
the Colorado School of Mines. He has designed curriculum and coordinated the Hazardous Materials Management
Program for professionals dislocated from the energy and minerals industry.
Thomas V. Ourkin
South Dakota Department of Environment and Natural Resources
Office of Minerals and Mining
Pierre, SD
Mr. Durkin has an A.S. in biology from Nassau Community College, a B.S. in earth science from Adelphi University,
and an M.S. in geology from the South Dakota School of Mines and Technology. He is a certified professional
geologist. He has worked as a commissioned officer in the U.S. National Oceanic and Atmospheric Administration
Corps and as a mine regulator for the state of South Dakota for the past 8 years.
Mr. Durkin is employed by the South Dakota Department of Environment and Natural Resources as a hydrologist in
the Office of Minerals and Mining. His duties have involved him with the geochemical aspects of mine wastes and
mine waste management issues relating to large-scale surface gold mines in the Black Hills. He is concerned
particularly with regulating problems associated with acid mine drainage and developing effective prevention, con-
trol, and reclamation requirements. He is a member of the Western Governors'Association Mine Waste Task Force
-------
and the Abandoned Mine Waste Working Group of the Committee to Develop Onsite Innovative Technologies. He is
a member of the American Institute of Professional Geologists, the Society of Mining, Metallurgy and Exploration,
Inc., and the South Dakota Academy of Science.
Martin Foote
Mine Waste Technology Pilot Program
MSE, Inc.
Butte, MT
Dr. Foote has a B.S. in chemistry and an M.S. in geochemistry from Montana College of Mineral Science and
Technology, and a Ph.D. in geology from the University of Wyoming. He has worked as a geologist, geochemist, and
consultant to the mining industry for 11 years. He also has worked with both federal and state regulatory organiza-
tions in environmental remediation, permitting, and development.
Dr. Foote is employed by MSE as a technical project manager for the Mine Waste Technology Pilot Program. This
program is funded by U.S. Environmental Protection Agency (EPA) and jointly administered by EPA and U.S. De-
partment of Energy (DOE) to conduct research and field demonstrations on new and innovative technologies for
treating or remediating mine wastes. He has served on the Technology Screening Group for the In Situ Remediation
Integrated Program and reviewed grant applications for the Small Business Innovation Research Program for DOE.
Jonathan G. Herrmann
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH
Mr. Herrmann holds a B.E. in civil engineering from Youngstown State University and an MBA in marketing from
Xavier University. He is a licensed professional engineer in the state of Ohio and a diplomate in the American
Academy of Environmental Engineers. Mr. Herrmann has worked in the area of environmental protection since
1975 and began his career in the Region VIII Office of EPA, located in Denver, Colorado. Mr. Herrmann has worked
in the private sector, for a hazardous waste disposal firm, CECOS/CER, in the early-1890s, and has been with EPA's
Office of Research and Development for almost 16 years.
For the past 4 years, Mr. Herrmann has assisted one of the Division Directors for the National Risk Management
Research Laboratory located in Cincinnati, Ohio, being responsible for both administrative activities and special
projects in support of the Laboratory's overall mission and goals. Mr. Herrmann has recently been involved in rolling
out EPA's Environmental Technology Verification Program, which will evaluate and verify the performance of various
types of environmental technologies so as to speed their commercialization both domestically and abroad.
A. Lynn McCloskey
Mine Waste Technology Pilot Program
MSE, Inc.
Butte, MT
Ms. McCloskey has an M.S. in mining engineering, with a hydrogeology option, and a B.S. in geological engineering
from the Montana College of Mineral Science and Technology in Butte, MT.
She has worked for MSE Inc. for several years. Some of the projects she has been responsible for in her tenure at
MSE include designing remedial technology applications for mining and miningassociated wastes for bench- and
pilot-scale demonstrations, providing geotechnical services for building new water treatment facilities, conducting
environmental audits for commercial and private property, and designing leak detection systems for waste ponds,
under ground storage tanks, and heavy metals soil.
At present she is manager of an innovative project involving a clay-based grouting technology, under the Mine
Waste Technology Pilot Program. This program is funded by EPA and jointly administered by EPA and DOE under
an Interagency Agreement. The project involves using integrated processes to evaluate an entire hydrogeological
and geological system.
89
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J. Chris Pfahl
ASARCO, Inc.
Wallace, ID
Mr. Pfahl has a B.S. in mining engineering from the Montana College of Mineral Science and Technology. He is a
licensed professional engineer in the states of Idaho and Colorado and a licensed professional land surveyor in
Idaho. He has been employed by ASARCO in various engineering, supervisory, and management positions for the
past 17 years.
Mr. Pfahl is a site manager with ASARCO. He is responsible for all of ASARCO's activities at the Bunker Hill Superfund
site at Kellogg, ID; the Triumph Proposed Superfund site at Sun Valley, ID; the Upper Blackfoot Mining Complex
State Superfund site at Lincoln, MT; and several inactive mine site reclamation projects in Colorado, Idaho, and
Montana.
Judy Reese
Montana Department of Environmental Quality
Helena, MT
Judy Reese has a B.S. in geology from Wayne State University and an M.S. in environmental studies from the
University of Montana. She also has grades 7-12 teaching certification in earth science and chemistry. Ms. Reese
worked in minerals exploration for 8 years for Utah International, BHP-Utah International, Placer Dome, and Merid-
ian Gold Company.
Ms. Reese has worked for the Montana Department of Health and Environmental Sciences Solid and Hazardous
Waste Bureau's state Comprehensive Environmental Cleanup and Responsibility Act (CECRA) and federal (CERCLA)
Superfund programs since 1991. She is the project manager of the Upper Blackfoot Mining Complex site, and she is
responsible for all CECRA-related aspects of the site. She also manages a few other CECRA sites and participates
on the Clark Fork River Site-Specific Water Quality Criteria Committee.
A. MacG. Robertson
Robertson GeoConsultants Inc.
Vancouver, British Columbia, Canada
Dr. Robertson has a B.Sc. in civil engineering and a Ph.D. in rock mechanics from the University of Witwatersrand,
South Africa. After a few years spent working for a mining company as a rock mechanics engineer and for an
engineering company doing specialized site investigation and foundation designs and contract supervision, Dr.
Robertson became a cofounder of the firm Steffen, Robertson and Kirsten (SRK), Inc., Consulting Geotechnical and
Mining Engineers. He now heads the firm Robertson GeoConsultants. He has 28 years of experience in mining
geotechnics, of which the last 10 years have been devoted extensively to geoenvironmental engineering for mine
sites.
Dr. Robertson was responsible for developing the engineering capabilities of the North American practice of SRK
over 17 years and has specialized personally in technology for the safe and environmentally protective disposal of
mine tailings and waste rock, acid mine drainage prediction and modeling, mine closure plan development, and
financial assurance and remediation of abandoned mines. He has been extensively involved in the preparation and
writing of a number of manuals on these subjects, which are now widely used in the mining industry. In addition, he
gives regular short courses and consults internationally to mining companies and regulatory authorities on these
topics. He serves on a number of advisory boards, including the University of British Columbia Board of Studies for
the Geological Engineering Program and the Mine Waste Technology Pilot Program (Butte, MT), as well as on a
number of mining project-specific review boards.
90
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William B. Schmidt
Division of Environmental Research
U.S. Bureau of Mines
Washington, DC
Mr. Schmidt has worked for the federal government for 22 years in areas related to mining and minerals processing.
After graduating from the Colorado School of Mines and before joining the government in 1971, he worked for 8
years in the private sector, mostly on assignments related to tunneling and construction engineering.
Mr. Schmidt has managed various government programs related to regulation of coal mining, mining research, and
metallurgical research. For the U.S. Department of Energy, he served as director of the Office of Coal Technology,
where he was responsible for a $70 million per year coal mining and preparation research program. At the U.S.
Department of Interior's Office of Surface Mining (OSM), he was assistant director for Program Operations and
Inspection, responsible for OSM's enforcement, oversight, and Abandoned Mined Lands (AMI) programs. Mr. Schmidt
has visited Europe and Asia a number of times as a government technical expert. He works for the Bureau of Mines
in Washington, where he is chief of the Division of Environmental Technology. In this position, in addition to his
research program management responsibilities, he oversees the Bureau's technical assistance to the U.S. Forest
Service, EPA, and other agencies in the environmental cleanup arena.
Leslie C. Thompson
Pintail Systems, Inc., Aurora, Colorado
Ms. Thompson received a B.S. in biology from Purdue University and has continuing education and graduate course
work in geochemistry, environmental engineering, and environmental microbiology. She has worked as a chemist,
microbiologist, and chief of research and development of bioremediation processes in mining and engineering com-
panies. She has over 20 years of experience in chemical manufacturing, mining, and waste remediation.
Ms. Thompson is employed at Pintail Systems as vice president of research and development. Her responsibilities
include management of the environmental research program, oversight of field engineering, and development of
innovative biotreatment processes for industrial waste remediation. Under her leadership, new bacterial treatment
processes have been developed for control of acid mine drainage, heavy metal wastes, complexed metal cyanides,
nitrates, phenolic wastes, and aromatic hydrocarbons from petroleum and coal gasification production operations.
Ms. Thompson is a member of the American Chemical Society, the Society of Mining Engineers, the Metallurgical
Society, the American Society of Microbiologists, and the Mining and Metallurgical Society of America.
Dirk Van Zyl
Colder Associates Inc.
Denver, Colorado
Dr. Van Zyl has a B.S. (honors) in civil engineering from the University of Pretoria, South Africa, and an M.S. and
Ph.D. in civil engineering from Purdue University. As a researcher, consulting engineer, and university professor, he
has over 20 years of civil/geotechnical engineering experience and is a registered professional engineer in 11 states.
Dr. Van Zyl is director of mining in the Denver office of Colder Associates Inc. He is responsible for technical and
marketing efforts for mine waste disposal, mine closure, and heap leach projects. He also provides engineering
design and regulatory support in negotiations for permits. He has supported regulatory development in the United
States and internationally. He is a member of the Society of Mining, Metallurgy, and Exploration, Inc., the American
Society of Civil Engineers, and the South African Institute of Mining and Metallurgy. He has published over 50
technical papers, research reports, and books, and served as editor of conference proceedings. He has coordinated
and presented numerous short courses for the Society of Mining, Metallurgy, and Exploration, Inc., and the U.S.
Forest Service.
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