&EPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/600/R-93/041
March 1993
Predicting Acid
Generation from
Non-Coal Mining Wastes
Notes of
July 1992 Workshop
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EPA/600/R-93/041
March 1993
PREDICTING ACID GENERATION
FROM NON-COAL MINING WASTES:
Notes of the July 1992 Workshop
by
Thomas A. Hinners
Quality Assurance and Methods Development Division
U.S. Environmental Protection Agency
Las Vegas, Nevada 89193-3478
and
Science Applications International Corporation
Falls Church, Virginia 22043
Contract Number 68-C2-0101
Work Assignment Number 5
Work Assignment Manager
Thomas A. Hinners
Quality Assurance and Methods Development Division
U.S. Environmental Protection Agency
Las Vegas, Nevada 89193-3478
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89193-3478
Printed on Recycled Paper
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NOTICE .- ,
;
The information in this document has been funded wholly or in part by the United States Environmental
Protection Agency under contract number 68-C2-0101 to Sierra Technical Services. It has been subjected to
the Agency's peer and administrative review, and lit has been approved for publication^as an EPA document.
Mention of trade names, commercial products, or terminology (such as acid rock drainage) does not constitute
endorsement or recommendation for use. j
This document is not intended to and does not constitute any rulemaking, policy, or guidance by the Agency. It
is not intended to and cannot be relied upon to create a substantive or procedural right enforceable by any party.
Neither the United States Government nor any of [its employees, contractors, subcontractors or their employees
makes any warranty, expressed or implied, or asstunes any legal liability or responsibility for any third party's
use of or the results of such use of any information or procedure disclosed in this report, or represents that its
use by such third party would not infringe on privately owned rights.
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CONTENTS
INTRODUCTION 1
WORKSHOP SUMMARY 2
REPRESENTATIVE SAMPLING 3
STATIC TESTING 7
KINETIC TESTING 10
COMMENTS AND QUESTIONS FROM THE AUDIENCE 17
ACID PREDICTION AND MINE PLANNING 18
IDENTIFICATION OF RESEARCH NEEDS .21
CONCLUSION 23
REFERENCES 24
APPENDICES
A. PANELISTS AND ATTENDEES AT WORKSHOP ON ACID GENERATION FROM
NON-COAL MINING WASTES 26
B. BIOGRAPHIES FOR TECHNICAL EXPERTS ON THE PANEL 30
C. APPROACH TO EVALUATING POTENTIAL FOR ACID GENERATION AND
METAL LEACHING 37
D. INFORMATION AND SAMPLE SOURCES 39
111
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INTRODUCTION
Acid generation is a major environmental problem at many mining sites where certain sulfides,
primarily iron pyrite (FeSj), react with water and oxygen by natural processes to form sulfuric acid. This acid
can increase the concentrations of toxic components (such as metals) in drainage from the mining wastes or
from soil exposed to the drainage. Reliable procedures are needed to predict acid generation from future
mining operations to prevent or mitigate this environmental impact.
The U.S. Environmental Protection Agency's Office of Research and Development (EMSL-LV,
Methods Research Branch) sponsored a Workshop on Predicting Acid Generation from Non-Coal Mining
Wastes. The Workshop was held in Las Vegas, Nevada on July 30 and 31, 1992. The purpose of the
Workshop was to identify reliable analytical-testing procedures that may be useful in the prediction of acid
generation from mining wastes. EPA assembled a panel of experts in the area of acid generation measurement
techniques from the regulated community, the private sector, and Federal and state regulatory agencies. EPA
also invited interested parties to attend and share their observations on the selected topics and on the panel's
discussion. Panel members and workshop attendees are listed in Appendix A. Appendix B contains brief
biographies of the technical experts on the workshop panel.
The objective of the workshop was to assist EPA's Office of Solid Waste in the development of a
program, under Subtitle D of the Resource Conservation and Recovery Act, that addresses wastes generated by
the extraction and beneficiation of ores and minerals. In preliminary stages of development, this program
clearly will have to address acid-generation potential, because acid drainage has proved to be one of the more
significant long-term environmental problems at sulfide mines.
While predicting the actual amount of acid generation from mining wastes is certainly desirable, it
could be premature in 1992 to identify specific kinetic tests for long-term regulatory use. In the 1991
Proceedings of the Second International Conference on the Abatement of Acidic Drainage.1 Keith Ferguson (as
Head of the Mining and Metallurgy Program at Environment Canada) stated that "little is understood about the
factors that control ARD [acid rock drainage] in the long term, especially for waste rock." If kinetic testing of
a waste material produced a false-negative prediction for the long term, the unanticipated acidic drainage could
cause significant environmental degradation and costly remediation. A false-positive prediction could cause
needless expenses in management and monitoring of the waste material as potentially hazardous.
Published reviews'with guidance on acid prediction are available. A study funded by EPA's Risk
Reduction Engineering Laboratory contains an assessment of testing procedures.2 Detailed method descriptions
with comments on interpretations, advantages, and limitations are provided in a 1991 technical manual.3 A
chapter on the "Prediction of Acid Generation Potential" is included in a recent publication4 by the California
Mining Association. Government scientists with relevant experience have reviewed and provided guidance5-6 on
predictive methods for acid mine drainage. Fundamental references on this subject include reports by Caruccio
et al.7 and Sobek et al.8
The Workshop opened with a welcome from Christian Daughton, Chief of the Methods Research
Branch of EPA's Environmental Monitoring Systems Laboratory in Las Vegas. The Workshop organizer, Tom
Hinners of the Methods Research Branch, gave a brief introduction concerning the purpose of the Workshop,
discussion topics and format, followed by the introduction of the Panel Members. He emphasized that the
workshop was intended to foster a discussion of ideas, not to reach specific conclusions.
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WORKSHOP SUMMARY
Topics addressed during the workshop (with post-meeting summaries) include Ithe following:
Representative Sampling
The actual acquisition of mining waste samples that are representative of the acid drainage
potential has critical importance. Some failures to predict acid drainage have been traced to
inappropriate or insufficient sampling. Average or composite values! may not reflect die acid
generation potential of sulfide-rich veins or pockets. During a mining operation, the sulfide-
content of the ore or overburden may change. Sampling plans for evaluating the potential for
acid generation should consider the approach used in mapping the ore body, with the focus
changed to mapping the reactive sulfide body. Using a blocking design for material of
different geological types can reduce the number of samples that need to be analyzed to
characterize the mining wastes in contrast with random geographic sampling.
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Static and Kinetic Testing
Static testing is sufficient to identify wastes that have strong or negligible potential to generate
acid. When the neutralization potential (NP) of a mining waste is 2 or 3 times the acid
potential (AP), the material is considered to have a negligible potential to yield acidic drainage.
When the neutralization potential is less than the acid potential, the waste is considered to have
a strong potential to produce acidic drainage. Depending upon the geological region, this may
account for about 50 percent of the mining wastes. When the neutralization potential exceeds
the acid potential by less than 2 or 3 fold, kinetic testing is recommended to assess the
probable acid generation by the waste. Testing recommendations are available in the
literature1"8 and in Appendices C and D. !
'
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Acid Prediction and Mine Planning I
Prediction of acid generation and drainage for mining wastes under field conditions involves
many factors. These include sampling, geology, mineralogy, static testing, kinetic testing,
climate, disposal arrangements for the mine wastes, and accuracy of decision values or rates in
long-term models. The mine plan needs to address acid generation not only before and during
mine operation but also after mining ceases. :
Identification of Research Needs
Research needs identified at the workshop include (1) more data from field studies (using old
and new waste piles with control measures) to evaluate factors and to allow correlations with
predictions, (2) an assessment of reactive sulfide and neutralization potential that are
"available" under field conditions including factors affecting depletion rates for each, (3) the
relationships between mineralogy and reactivity, (4) cheaper methods to predict acid generation
(such as the peroxide test described by Miller's group in Australia), |(5) the effects of climate,
(6) the determination of a minimum sulfur value, (7) an assessment of acid generation from
underground mine walls, (8) a better understanding of the bacterial role in acid generation, and
(9) as the factors above are better understood, develop both simple and complex models for
acid drainage from tailings, waste rock, and mine walls.
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Each of these major topics was discussed in a separate session during the workshop, although there was
some overlap among sessions. This document describes the discussions among panel members and audience
participants on each of the topics. It does not represent a verbatim transcription of the proceedings; rather, it is
a condensation of the discussions by the various participants. In a few cases, comments or discussions that
occurred in one session have been moved when they were more relevant to another session. Otherwise, the
comments are presented in chronological order.
REPRESENTATIVE SAMPLING
Steve Hoffman (U.S. EPA) opened the sampling discussion by describing EPA's interest in selecting
methods of analysis for predicting acid generation from mining wastes. He wondered whether a lengthy debate
on representative sampling of wastes for analysis was necessary.
Richard Humphreys (California Water Resources Control Board) suggested that sampling
requirements should be based on consistency, yet allow for flexibility to account for the extreme variability
between mines, their rock type, and sulfur concentration. He also noted that mines have to have a sampling
plan.
Keith Ferguson (Placer Dome, Inc.) stated that the sampling representativeness is critical and must be
dealt with. Some mines are easy to characterize, while others require thousands of samples to determine a
mine's acid generation potential. It is important to understand the mine's geology and to describe it in detail
and link this to the sampling program and test results.
Linda Broughton [Steffen, Robertson and Kirsten, Inc. (SRK)] wanted clarification on whether the
concern is for predicting acid generation potential or predicting drainage quality, as the testing procedures and
interpretation are very different. She observed that sampling should not focus on the total mass of the rock, but
concentrate on the samples or rock types that are a potential problem. Steve Hoffman asked about variability
and suggested step-wise sampling with continuous evaluation based on input from existing sample data.
Richard Humphreys stated that from a regulatory perspective, if staff members feel existing sampling is
insufficient, they ask for additional samples to be taken. Steve Hoffman asked if it was possible to establish a
set of criteria (7 or 8) to guide sampling requirements and identified geology and waste units as examples.
Andrew Robertson [Steffen, Robertson and Kirsten, Inc. (SRK)] made several suggestions to help
organize the sampling discussion:
He asked if the group was addressing only wastes and wondered how rock walls, mine
disturbed rock, and collapse zones would be dealt with.
He noted mat EPA had not emphasized contaminated drainage but rather acid generation (he
felt that not enough attention was given to contaminant generation and oxidation).
He noted that if acid or contaminant sampling is to be for the purpose of comparison with
some regulatory standard value, then a high-quality test would be required.
He suggested that mining wastes could be subdivided by mineralogy and particle size, and that
the geology could be characterized by lithology and mineralogy.
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Steve Hoffman asked if such a system could differentiate between waste types. Andrew Robertson
responded that it could not, stating that it looks at rock type independent of waste; the' waste type would be
accounted for by knowing the mineralogy and particle size.
Keith Ferguson stated that in determining the risk of acid generation, it is important to consider
climate (e.g., a sampling program in an arid climate may not be as detailed) and sensitivity of the environment
(e.g., salmon). Climate has a critical effect, for example, on the migration of acid and the ultimate impact. In
addition to climate, he raised some additional factors including: \
Composite versus discrete sampling. Although composites may underestimate acid potential
(by disguising variation), compositing over the heights of benches may be effective.
Quality assurance/quality control I
Using all relevant data is important: core logs, visual categorization, metal scans, etc.
Must account for planned pit limits (depths, bench heights) and/or rock type in a sampling
program to assess variability. For example, the first level of testing could involve a few
hundred samples to assess the variability and determine the need for! additional sampling.
Steve Hoffman asked how mines could be directed to sample and by which method. Keith Ferguson
stated that from his experience roughly 50 percent of mines will yield a good indication of the acid generation
potential from the initial sampling; the remainder will require more sampling. ,.
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Patricia Erickson (U.S. EPA) suggested that initial sampling could be used [to establish the variability
of acid potential and/or contaminants in rock and the variability would be a factor driving the resultant sampling
regime. f
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Andrew Robertson offered the following papers prepared by SRK on aspects of the workshop topics:
Robertson, A. MacG., and L. M. Broughton, Undated. Reliability of Acid Rock Drainage Testing.
Unpublished report available from the authors at the address in Appendix A.!
Broughton, L. M., and A. MacG. Robertson, Undated. Acid Rock Drainage From Mines - Where We
Are Now. Unpublished report available from the authors at the address in Appendix A.
Broughton, L. M., Chambers, R. W., and A. MacG. Robertson, April 1992. Mine Rock Guidelines,
Design and Control of Drainage Water Quality. (See Reference 9.)
Tom Hinners (U.S. EPA, ORD, EMSL-Las Vegas) then asked the panel to'summarize the sampling
discussion and recommended the classification of waste material. Steve Hoffman suggested that a series of
issues covering sampling be identified, and mentioned a multi-tiered approach.
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Linda Broughton offered the following issues for consideration in the design of a sampling program:
Level of concern for potential impact
State of operation
- new site
- control of an old operation
Scope of problem
Accessibility
Composition/variability
Spatial Coverage
Quality Assurance/Quality Control
Ms. Broughton asked Keith Ferguson if his sampling programs reflect the different sizes of operations.
Mr. Ferguson noted that from his experience, there is a great deal of variability among sites. Placer Dome
does not sample based on tons of waste generated; he stated that this issue was a primary concern on his
research list at Placer Dome and that at this time he did not have a critical sample number to characterize the
contaminant or acid-generation potential. Steve Hoffman asked if a range could be developed and used widely,
and then be further refined with experience.
Richard Humphreys offered California's experience with the Penn Mine. They selected a 3:1 ratio of
neutralization potential to acid potential (NP:AP) to provide for a margin of safety at that site, but felt that a
single number was not plausible for all situations. Keith Ferguson agreed, stating that it is difficult to
accurately characterize hundreds of millions of tons of waste rock. Therefore, it is important to set a sample
size, monitor, test the assumptions, and then to revise the sampling regime as necessary. Keith Ferguson noted
that the Canadian Province of British Columbia requires large bonds, prediction plans, prevention plans, and
contingency plans. Steve Hoffman asked if the development of a contingency plan depended on the sampling
network. Keith Ferguson said it could be, in that initial sampling may be used to locate potential problems and
to develop a detailed mine plan. Steve Hoffman asked about the operating plan. Keith Ferguson said the
mine plan was described in the Environmental Impact Plan. Steve Hoffman expressed interest in the steps of
the process, and noted that the sampling issue must be raised during the development of the operating plan or
pre-operating plan.
Following the panel discussion, several of the observers offered comments.
Gene Farmer [U.S. Forest Service (USFS), Ogden, Utah] made the following observations:
Representative sampling [as an assumption behind static testing] is a fantasy since certainty in
the area of representative sampling does not exist. It is more important to give a qualitative
answer to the question of whether material will be acid-generating. However, most mines will
fall in a gray area. One answer to that uncertainty is a continuing sampling program during
the active life of die mine: USFS takes that approach. He suggests one sample per 20,000
tons of waste (which can include samples of the ore body, because most of the ore body
becomes waste).
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He suggested that active mines be separated from inactive mines and from re-mining situations.
He agrees that sampling programs are the most important, with specific reference to sampling
procedures and numbers, including sample size and location.
I, .'.!-, ' ''
He noted a strong tendency to composite samples, particularly for in-pit sampling of reverse
circulation cores. He noted a neetl to avoid compositing samples because it reduces
variability, and the population mean is not of concern. ;
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He agrees with the use of block models to describe sulfide distribution in a given ore body, not
static or kinetic testing.
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He observed that real neutralization potential (NP) does not exist. It only exists in the
laboratory, in that none of the static tests has been shown to correlate ^th those hi the field.
This has led to a 3:1 (NP:AP) as jthe rule-of-thumb for some investigators. Accurate tests of
percent sulfur and NP may be incapable of predicting acid drainage. Sulfur content, ratios,
etc. are all used because of this lack of correlation. ;
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He also noted two phases of acid generation: the oxygen cycle and the iron cycle.
Tom Card (Nevada Division of Environmental Protection) offered the following comments:
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Sampling is a major concern for regulation of mining operations. ;
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Incremental sampling based on tonnage is not always necessary if tests are consistent.
He emphasized the nature and importance of the risk. In Nevada, he indicated that the low
atmospheric precipitation minimizes the environmental risk, and Hh^ the concern is different
from, for example, Vancouver Island. .
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There is no simple recipe for sampling, but it may be possible to develop a matrix based on
risk. i
Glenn Miller (University of Nevada) stated that predicting land uses over cenjuries is problematic,
therefore current risk may not be the proper driving force behind sampling and regulatory
decisions/requirements. He asked whether any retrospective prediction studies have been conducted (e.g., by
going to old mine sites that exhibit acid drainage, by sampling and predicting acid potential, and then correlating
field and laboratory data). .
Richard Humphreys stated that there are different definitions of risk depending on perspective. In
California, for example, there is a policy of non-degradation of surface water quality. j In addition, the concepts
of ecological risks versus human health risks are changing (in revising the Hazard Ranking System used in the
Superfund program, for example). Steve Hoffman said water quality standards are based on "risk" to aquatic
organisms; there are no analogous standards for terrestrial organisms. ,
Pat Rogers (Independence Mining Company) stated that mines are fairly adequate in developing
sampling programs to address risk. He recommended that the real focus should be on
real-world reliability of laboratory tests.
testing methods and the
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Michael Smith (Barrick Goldstrike Mine) described a general approach to sampling: an unbiased
geostatistical estimator approach is a systematic method of sampling exploration hole data. He indicated mat
mis can be used for reserves estimation and that the resolution is high. It allows an estimation of the
3-dimensional distribution of NP:AP values. He raised the issue of sampling at the exploration stage because
most sites never go to the production stage.
STATIC TESTING
Tom Hinners began the discussion by asking if false negatives (i.e., cases where laboratory testing
indicates no significant acid-generation potential when, in reality, there is) were a major issue of concern.
Richard Humphreys stated that testing was not the issue, but whether the material is acid generating
or not. Measuring acid generation potential as a prediction tool in the disposal environment [e.g., standard
excess (acid)] may be useful for materials with low sulfur content. He recommended that a conservative NP:AP
ratio of 3:1 may provide a margin of error. A net NP of 50 tons CaCO3/1000 tons was not always predictive of
acceptable water quality.
Frank Caruccio (University of South Carolina) added that through his work with mines in the northern
Appalachian coal field he was able to empirically determine that a 2:1 NP:AP ratio can be used as a reasonable
guide toward identifying potential acid problems. And certainly the 3:1 proposed provides a wide margin of
error.
Kim Lapakko (Minnesota Department of Natural Resources) stated that inherent in static testing is the
assumption that all acid-producing and acid neutralizing components are accurately measured. It is tacitly
assumed that the neutralizing components will react to maintain a neutral drainage pH. Acid-producing
components can be quantified to a reasonable degree. However, neutralization potential (NP) measurements
tend to overestimate the ability of a mine waste to neutralize acid in the field.
The methods for NP measurements specify the addition of acid to the mine waste sample to produce a
sample/solution pH which is often 3.5 or lower. For discussion purposes, this value will be denoted pHA The
amount of acid neutralized is then measured either directly or by back-titrating the solution to pH 7.0 or 8.3.
This measures the acid that would be neutralized when drainage pH reaches pHA. This value will be greater,
than the acid neutralization available to maintain a drainage pH of 6.0 or above, which he believes is a common
water-quality standard. The concept of overestimation of NP, as well as data confirming this concept, is
presented in the Draft Report to the Western Governors' Association (WGA), "Evaluation of Tests for
Predicting Mine Waste Drainage pH," Lapakko, K.A., 1992., pp. 22-30. Other factors contributing to NP
overestimation are also discussed in this report. ''-.-
This problem can be partially addressed by using an endpoint greater than or equal to the desired
drainage pH for the "downward" titration (that is, the addition of acid to the mine waste sample as opposed to
the back titration.) Information on the mine waste composition (e.g., mineralogy, petrology, particle size, etc.)
will help compensate for the weakness in static testing. Quantification of the NP available above pH 6.0 is
presently being examined in cooperative research between the U.S. Bureau of Mines and the Minnesota
Department of Natural Resources.
Fiona Doyle (University of California at Berkeley) asked if current sulfide analysis is enforceable - and
noted that total sulfur content is not a measure of acid production potential (i.e., non-pyritic sulfur does not
contribute acid). She noted10 that the Sobek H2O2 method8 is a better technique for pyrite testing, if careful
testing procedures are followed (control of sample temperature during testing is critical). Temperature rises
from the exothermic reaction as pyritic sulfur is oxidized. She suggested that the test may be more reliable if
excess peroxide is used.
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- Patricia Erickson stated that the accuracy of the standard sulfur analysis or speciation was an
important factor, noting QA/QC problems from several projects. Pyritic-sulfur analysis using peroxide is not
common; sulfur analysis is the standard. She cited a round-robin study in which a single material was found to
contain 0.3 to 1.3 percent sulfur, NP of 0.1 to 2.5 tons CaCO3/1000 tons, and a net NP of -30 to +14 tons
CaCO,/1000 tons. This has to be considered in methods development.
3 i
Frank Caruccio suggested that the analysis of pyritic sulfur could also be performed through the
digestion of a pulverized sample in a 2N nitric acid solution, bringing the solution to a constant volume, and
determining the iron concentration of the solution that is stoichiometrically related to the iron disulfide
concentration. Prior to digestion, the sample is stripped of non-pyritic iron with dilute hydrochloric acid. This
technique circumvents the necessity of partitioning of sulfur species and makes pyritic sulfur determinations
more direct. . [
William White [U.S. Bureau of Mines (BOM)] noted that their analysis of the Sobek NP test method3
yielded "crazy" numbers. Samples were screened! to <60 mesh, HC1 digested, titrated with base, and boiled;
the analysis had a standard deviation of 12 to 13 units. A modified method with agitation for 24 hours instead
of boiling gave lower standard deviation numbers. They got different NPs depending ion endpoint pH (e.g., 14
for pH 6, >95 for pH 3.5). BOM assessed the neutralization potential of four different sizes of the same
sample, using both a modified and regular Sobek inethod8, and a modified version of the BC Research Initial
Test. All lines crossed at about pH 6, with a NP of about 15. His conclusion was that NP was a function of
particle size. When asked what test should be used, White answered that the Bureau uses all three. The BOM
is currently assessing particle size in tests and will report on their findings. ;
1 i . .
Keith Ferguson noted that static tests are not precise for determining the amount of acid production,
and that the NP is not a precise measure of consumption. These should be considered, as indicator tests. The
key is to understand how static tests compare with kinetic tests, and more importantly; how they compare with
field tests. In the absence of something better, Sobek? is the method of choice. If nothing else, it is used
extensively and, therefore, has a large database which allows for comparisons. William White cautioned
against boiling because it may be a source of variability. Kim Lapakko observed that the pH required for
drainage must be considered when determining NP. If a drainage pH of 6.0 is desired, the NP available to
maintain this pH must be quantified. Quantifying the NP available to maintain a pH of 3.5 may yield an upper
bound for the NP available to maintain a drainage pH of 6.0, but this upper bound may be considerably higher
than the value of concern. Consequently, it is more useful to quantify the NP available to maintain a drainage
pH of 6.0 directly. j .
Frank Caruccio stated that temperature plays a critical role in the dissolution of CaCO3. Thus, whole
rock analyses that include boiling or heating the samples may selectively dissolve the Carbonates, isolating the
acid component (pyrite) from further interactions, and modifying the chemical weathering attributes of the
sample. One common problem in analyzing samples containing siderite (FeCO3) is a |masking affect that flu's
mineral has on the true NP value of the sample. Through the acid digestion of the sample, in preparation for
the NP analysis, siderite is consumed by the acid and registers as an NP component, when in fact under natural
conditions it is a neutral reactor. A modified NP analysis that includes hydrogen peroxide addition to complete
the ferrous oxidation has been proposed. In addition, within the coal mining sector, it has been proposed that
the 31.25 conversion factor for the CaCO3 equivalent to the acid derived from the pyritic suliEur content be
changed to 62.5 to accommodate, in part, the siderite masking and to adjust alkalinity equivalents from
limestone dissolution. (The 31.25 conversion factor is based on the assumption that each molecule of carbonate
can neutralize two H+ ions, and the 62.5 conversion factor is based on neutralization of one W- ion per
carbonate.) Under natural conditions, the coal-associated strata with NP values in excess of 20 tons CaCO3
equivalents/1000 tons are generally non-acid generating. The pH of drainage from these strata commonly is
around 6 to 6.5, which effectively precludes bacterial intervention and retards the acid producing reactions.
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Linda Broughton believes static and kinetic tests should be tied together - a definition of static test is
needed. Kim Lapakko agreed with Linda that static and kinetic test results can be more useful if considered
jointly. Both the availability and die dissolution kinetics of NP can influence die accuracy of static tests. Static
tests assume all NP is available for reaction and will react fast enough to neutralize acid present in drainage that
contacts the neutralizing minerals. Thus there are assumptions on both the availability of NP and the rate of its
neutralization. Fine grained calcium carbonate and magnesium carbonate minerals dissolve rapidly, and
therefore determining the availability of these minerals would be of greater benefit than the rate of reaction
(which is known). Larger particles are less effective, although they will neutralize to some degree. Quantifying
this degree will similarly be beneficial in assessing the true NP of a waste.
In contrast, calcium feldspar minerals dissolve more slowly, and the rate at which they neutralize acid
within the mine waste disposal unit may be more important than knowing their availability. For example,
Duluth Complex rock contains over 50% calcium feldspar, which is highly available. However, the calcium
feldspar dissolution rate is very slow, and this slow rate of dissolution (as opposed to calcium feldspar
availability) limits its neutralization.
Frank Caruccio stated that acid-base-accounting analysis (ABA) is applicable to soils, but was
developed for assessing suitability of coal-mine sites for revegetation, not for estimation of water quality.
Richard Humphreys stated that regulators were concerned with the confidence interval boundary, and
did not deal with changes in particle size. Tom Hinners asked Richard Humphreys if static tests were most
appropriately used for tailings. Richard Humphreys said he thinks static testing is useful for tailings but not
for waste rock. Keith Ferguson responded that NP is inherently variable. He recommended that initial
sampling tests be used to establish potential to generate acid. If there is no potential acid generation, mere
should be no concern. He also noted that, from his experience, siderite was rarely a problem in metal mines.
With respect to the ratio of neutralization potential to acid generation potential, he thought 3:1 was high and
recommended 2:1 (based on theoretical considerations) be used as an initial screening of ABA data for waste
rock. If a conversion factor (percent sulfur to CaC03 equivalent) of 62.5 tons per 1000 tons of waste (at 1
percent sulfur content) were selected, the ratio would be 2:1. He noted that these ratios apply to samples, not
to waste units.
Steve Hoffman reviewed the factors affecting the variability of static tests, and identified temperature
control during testing (boiling versus agitation); particle size; and petrology.
William White added that variability can occur as a result of:
Reproducibility of the test method (e.g., whether samples are boiled or agitated)
Particle size
pH (values of 6, 5, and 3.5, for example, can give different results)
The amounts of total sulfur, sulfide sulfur, and sulfatฎ sulfur. If barite (BaSOJ and gypsum
(CaSO4 2HjO), which do not generate acid, are present in the sample and total sulfur
analysis is used, the acid generating potential will be over-estimated because the sulfur in these
minerals is non-reactive.
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Frank Caruccio added that cations should be added to this list noting that calcium and magnesium, in
particular, affect the leachate quality. He also suggested that pyritic-sulfur analyses using the nitric acid
digestion be considered as an alternative to the conventional methods to resolve the sulfur speciation problem.
Instead of using the furnace method for sulfur, he measures iron in HNO3 digests of material pulverized to a
particle size ฃ63 /nm. Linda Broughton stated that sulfur speciation is not warranted at total sulfur values
below 1 percent. , .
KINETIC TESTING |
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Tom Hinners introduced the topic of kinetic testing and asked the panel for recommendations on
methods. He noted that Kim Lapakko was revie\*fing kinetic methods for the Westernj Governors' Association.
Frank Caruccio commented that since 1978 there have been several breakthroughs concerning the Sobek kinetic
method.8 These updates should be incorporated, and a modified method should be issued. A manual3 of
procedures and recommendations prepared by Rick Lawrence could serve this purpose.;
j .:.. ,
Linda Broughton asked Mr. Lapakko the following questions: \
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Was the purpose to predict field water quality or acid generation potential?
What are the flushing rates for the samples?
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What was the particle size used?
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Km Lapakko stated that the WGA study examined the capability of such tests to predict whether a
mine waste would produce acid. The ability of a test to describe field drainage quality in greater detail was not
addressed. The influence of flushing rates in predictive testing was not specifically addressed, although flushing
rates did vary in the tests examined. Other design!parameters also varied among the tests; consequently, a
rigorous analysis of the effect of flushing rate was not conducted. Particle size varied as a function of the
protocol prescribed in the predictive tests examined. .
Richard Humphreys stated that kinetic testing was the "black art" of geochemistry, and that
interpreting long-term data is a difficult task. Froin a regulatory perspective, this is compounded by the fact
that permit writers may not be geologists. Also, for mitigation, one can manage acid-generating waste or
change the characteristics of .the waste so that it does not require management. ;
Andrew Robertson stated that SRK had examined the issue of kinetic testing. He felt that a humidity
cell had no relevance for waste rock; however, it does have yes/no potential if run long enough. It is not
reasonable for water quality measures. Humidity cell tests also tend to flush everything out. By contrast, in the
real world (waste rock pile) what comes out may be only a small portion of what is actually generated. Both
tho fine and coarse fraction are important; SRK uses four-inch diameter material to represent the large fraction,
with sample sizes ranging from 25 to 50 kilograms. Column sizes are greater than or equal to 15 inches in
diameter, greater than or equal to 18 inches high, and may be stacked. \
He noted that time and how the sample is treated are important to consider. For example, crushing
may release alkalinity and inhibit Thiobacillus. Other procedures such as the initial flush are important; trickle
vs. flush vs. field conditions must simulate field conditions as closely as possible. The low levels of flow in die
field are difficult to mimic in the lab. In laboratories, more water may be added, which reduces storage
time/retention. The time required for reactions to occur in lab settings is often too slop so samples may be
inoculated or spiked with bacteria to accelerate; it is necessary to compare spiked and imspiked samples. He
explained the value of field tests (e.g., piles) to predict field behavior. He emphasized that tests must simulate
field disposal conditions.
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Frank Caruccio offered two reasons for using crushed samples; first, if the sample is a composite of
heterogeneous strata, mechanically riffling splits for analysis will be more representative of the whole the finer
the samples are crushed. At his laboratory it has been found that crushing samples to pass 4-mm pores provides
both adequate drainage from weathering cells as well as suitability for riffling. Second, within a waste-rock
backfill the rapid, acid-forming reactions are produced by the smaller material (generally the relationship is
asymptotic peaking rapidly for the material at around 4 to 6 inches in diameter). Thus, die smaller-size fraction
enhances chemical weathering processes, yet, at the same time, more closely simulates field conditions.
Keith Ferguson reviewed quantitative vs. qualitative prediction of drainage, stating that qualitative
prediction is easier but still difficult. Factors include sample selection, the numbers of samples, analytical
procedures, and time. However, he questioned whether the quality of the drainage could be predicted in the
laboratory at the present time. Quantitative factors include temperature, particle size, and flushing rates.
Steve Hoffman asked if there was some reasonable way to deal with water balance issues. Andrew
Robertson said there was and referred to landfill work to determine infiltration rates (HELP model). This
gives a first estimate of infiltration rates, budgets through dumps (including measuring). But, in the laboratory,
to mimic low precipitation (< 30 inches), flushing is necessary. Keith Ferguson identified some factors to
consider: flush in terms of volumes and loadings, acid production during dry periods followed by flush during
snow melt (e.g., Equity Mine) or storm events, and.length of dry period.
Steve Hoffman asked how a regulatory agency could deal with the unpredictable nature of acid
generation given these observations. Keith Ferguson correlates results from the static and kinetic tests, and
examines mineralogy. This requires a good database of kinetic tests.
Kim Lapakko summarized a test plot study started by the Amax Mining Company and carried on by
the State of Minnesota. .
In 1977 the company set up a series of six test piles composed of waste rock of Duluth
Complex material (1,000 tons each) with varying sulfide content. There has been long-term
monitoring by the State to assess the quality and quantity of drainage, as well as other
questions. The data increased the State's confidence in prediction. To date, IS years of data
have been collected.
They have obtained "fairly good" information on what the critical sulfur content is in the
Duluth Complex material. He emphasized that the numbers themselves cannot be extrapolated
to other situations; however, the State has good information on the Complex in the event that
another firm begins operation.
They are able to correlate laboratory test results with field results fairly well. Lab data that
agree with field data makes the State more comfortable with laboratory efforts.
The laboratory took into account the usage of reduced particle sizes when making predictions.
They also took one pile apart to characterize particle size; this allowed for a comparison of
sulfide surface area between laboratory and field material.
Gene Farmer observed that many mines will be permitted even though the mine's acid generation
potential is unknown. When there is doubt, "we want these kinds of long-term ( > 3 years) testing programs."
Regulators and miners finally agree that long-term testing programs are necessary, so that the State knows when
it releases the bond whether there will be acid generation.
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I .
Steve Hofftnan stated that the EPA must consider what materials will be exposed, not necessarily all
materials (some of which may be capped, etc.). It must be recognized, however, that over time, these caps can
faU While monitoring is important, reliance on ground and surface water monitoring can only identify already-
existing problems. Thus, field validation of kinetic tests is important. He observed that there is much variation
in results using humidity cells among laboratories; what is needed is a preferred method for comparing field
tests and laboratory results. |
William White stated that the Bureau of Mines and the American Society for Testing and Materials
(ASTM) are looking at a standard method for accelerated weathering (kinetic testing). An ASTM committee
will put forth a draft recommendation at the October 1992 ASTM meeting in Miami, Florida, for distribution to
ASTM members using humidity cells. So, there is some movement toward standardization.
' I '
Andrew Robertson explained that there are two reasons for kinetic tests beyond the "yes/no" question
of acid generation. Kinetic tests examine material properties but if the concern is prediction in field, system
properties are of increasing concern. Examining how "system" tests vary from "materials" tests is of value.
i '
Richard Hammack (U.S. Bureau of Mines) discussed an evolved gas analysis^ (EGA) technique that
may incorporate aspects of both static and kinetic test methods. It gives an idea of the reactivity of pyrite
(kinetic aspect) and gives carbonate and sulfur (sulfate and sulfide sulfur) content (static aspect). This technique
involves crushing the material, heating it gradually in a furnace while passing 10 percent oxygen and 90 percent
nitrogen gas over the sample, and determining at what temperatures CO2 and SO2 are lost (similar to LEGO
Corporation method for sulfur). This technique allows for discrimination between sulfide and sulfate sulfur,
which helps in acid-base accounting. It can also discriminate between how much calcite and dolomite are in the
sample (carbonates that contribute to NP). If both marcasite and pyrite are in the material, however, this can
confound the results. Their laboratory abandoned the EGA approach because of instrumental problems (using a
mass spectrometer with a capillary tube presented problems with low ranges of sulfur values). Now, there are
commercially available instruments that do not have this original problem. i
Steve Hoffman asked if this method was currently in use by anyone present. Richard Hammack
noted that Penn State was going to take over the BOM's work in this area. Mr. Hoffman asked if it needed to
be examined as a possible technique, and Mr. Hammack noted that the instrument cost! was about $20,000
(compared to $30,000 for a LECO Sulfur Analyzer). A new system, considered top-of-the-line, runs about
$80,000 (Bomem Inc., Maarssen, The Netherlands). It is not based on mass spectrometry, but uses Fourier
transform infrared spectroscopy. BOM work was on coal mines; tests on metal mine waste samples in
conjunction with a study by Richard Lawrence have not been completed.
Tom Hinners raised the question: if kinetic testing does not predict acid generation, how are results to
be interpreted and extrapolated? He noted that one approach is to determine how fast neutralizing material is
being consumed. Keith Ferguson summarized a paper presented in 1991 by Kevin Moran and himself in
Montreal.1 They looked at 200 kinetic data sets from 25 to 30 mine sites; relatively few have produced acid
drainage from the initial neutral condition,(roughly 75 percent have remained alkaline during the 10 to 20
weeks, or longer, of testing). Twenty percent were acidic from the beginning, 15 tests went from neutral to
acidic (pH 1). They plotted NP: AP ratios vs. time to acid production and roughly fitted a curve to the plot.
The equation provided a rough idea before testing whether there was any expectation of a sample generating
acid The curve showed that the NP:AP values hkd to be less than 0.3 or 0.5 for there to be a chance for acid
generation within 20 weeks. He noted this was strictly for standard kinetic laboratory tests (7 days: 3 days dry
air, 3 days wet air, and on the 7th day rinse the test material with water). |
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Steve Hoffman asked what the policy implications of these results were. Keith Ferguson stated that if
the criteria to decide if a sample is going to go acid is based on a kinetic test that generated acid, the NP:AP
should be less than 0.3; if it is 0.3 or higher, extrapolation may be required. There is a problem in
extrapolation: available sulfur and carbonate versus the total amounts. A test is needed to show how much
carbonate and sulfide is available on the surface of particles. One promising test12 is the Net Acid Generation
(NAG) method using hydrogen peroxide to oxidize the reactive sulfides before titration to pH 7. If a reliable
test of net acidity were available and a line could be drawn from the kinetic tests of the rates, then it should be
possible to predict the time the waste drainage is likely to go acid. There is a proposal from Australia (Stuart
Miller) for a research program ($200,000) that should begin in the next 2-3 months; the results would allow
quantitative assessment of this method. This is also part of the Canadian Mine Environment Neutral Drainage
(MEND) program. With a low NP:AP ratio (high sulfur and low carbonate), then it is worthwhile to conduct a
kinetic test as it should give a fairly definitive answer (i.e., pH drops from 7 to 3.5), and then one can measure
the metals in the extract. With samples having an NP of about 50, there is a long lag period, and this makes
interpretation difficult.
Frank Caruccio noted that the chemistry of the ore processing fluid in copper mines in Arizona had a
dominating affect on the leachate quality and on the chemical behavior of the tailings samples. Although the
whole rock analyses showed samples to have high concentrations of pyrite and low NP (projected to be high
acid producers), the leaching tests consistently produced alkaline leachates. Several samples that were leached
for over one-and-a-half years did not produce acidity. Samples "as received" when bathed in dilute HC1 were
rendered acidic. It is therefore important to factor in the effects of the carrier fluid of tailings when making
determinations of leachate qualities.
Andrew Robertson stated that non-acid kinetic testing should remain part of the water quality testing
procedure; these tests offer other results that are helpful in understanding impacts. As an example, he cited a
mine in British Columbia with a drainage pH of 8.4 where there is molybdenum dissolution as a result of the
sulfides oxidizing (alkali leaching). Also, he indicated that examining ("cutting into") existing dumps may show
they are not currently acid-generating, but it can provide an idea of conditions and possibly identify a "trigger"
point. He suggested adding the trigger point to kinetic tests, but expressed concern for biasing the test.
Keith Ferguson felt that we are approaching the stage where for many samples it is possible to predict .
whether they will go acid on the basis of static, kinetic, petrography, EGA, and other data. The next stage,
mixing samples of different acid generating character, will be much more difficult to evaluate. Predicting
behavior of different (or mixed) rock types is even more complex than for single types (e.g., mixing samples:
acid-generating and acid-consuming layers). The complex reactions of flushing, coating formation, relative
reactivities, and the biological factors expressed by Andrew Robertson are critical. Determining how to blend
and establishing the stacking sequence are goals that are difficult to achieve. Laboratory tests are being set up
with stacked column designs. A math-ematical model will help, but for now an empirical approach will do.
Using a 1976 coal mine data set of 20 mines (they are reluctantly using weighted acid-base accounts), they
found that if the weighted NP:AP ratio is S2.5, it appears that these mines have not generated acid. These
results are tenuous, but are the best available at this time.
Richard Humphreys noted that in California waste segregation is being tried at one site. Pre-mine
testing concluded that the waste was not acid-generating, but there was an acid-generation problem. The pile
has been re-engineered to allow encapsulation. Test plot work on an encapsulation technique would have
increased the state's confidence in the practice.
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Keith Ferguson observed that notwithstanding all the uncertainty, there are many sites (about 50
percent) that can be predicted accurately. The other 50 percent are the concern. One must conservatively
assume such units will.generate acid. For such wasjtes Canada uses aqueous disposal in tailings impoundments,
other water bodies, or saturated covers. If segregation or blending is to be used, some $ort of blending test may
be the only recourse. Even in clear-cut "benign" cases, there has to be continued awareness (e.g., watch for
increasing sulftdes in the rock wastes if there is low carbonate content).
Linda Broughton said they were trying to characterize the drainage water quality at the toe of waste
dumps and to compare it with laboratory data. They found that fresh samples from the dumps were not
available, and information on the material was not available. She asked for data on old dumps.
Richard Humphreys indicated that establishing test plots before a mine is developed is problematic.
At an existing mine, the mine serves as the plot. They are trying to encapsulate to mitigate acid drainage
problems. Kirn Lapakko's experience with the Duluth Complex was unique, but offered^ a valuable tool to study
the waste problem. The issue is who will be interested in the study over the long term, i Andrew Robertson
observed that there is much moire to be learned from existing waste piles rather than from small test piles.
These are full-size piles with all the reactions occurring under the actual field conditions. It is fairly easy to
sample waste piles, to conduct paste pH tests, and to analyze the pore water. This allows one to characterize
where in the waste pile acid generation is taking place before there is any sign of acid drainage in the toe
discharge from the waste pile. Sampling with the Becker Hammer Drill (air is the flushing medium) works
well. It does cause some crushing and does liberate a certain amount of the alkali. But it is cheaper than
column tests. i
Gene Fanner asked how deep sampling was conducted in the waste dump, and if it was below the
point of oxidation. Andrew Robertson noted that pxidation penetrates very deeply. Coarse material below
creates a chimney effect and pulls oxygen in. As an example, in low-grade stockpiles, oxidation is seen
throughout. , i
i
Michael Smith asked about humidity cell tests and what variables should be considered in assessing
why or whether it went acid (e.g., sulfate production, alkalinity, acidity, pH, and iron). Keith Ferguson
reviewed kinetic tests and indicated that he uses them to validate static test results. For, each kinetic test, the
sample is studied for petrography, the sulfide mix, morphology, grain size, and the spatial position of the
sulfides and carbonates. Sulfate production rates are compared with values in a database to determine what
percentile it is. | i
I , i i - :
Linda Broughton agreed on the importance of sulfate production versus alkalinity consumption
(mineralogy is important). Extrapolating to the long term requires discriminating amonjg carbonates/acid
neutralizers and buffering due to silicates. The two relative rates and the near-neutral drainage water quality are
critical to determining if there is or will be a problem. Zinc was found to be good indicator, and aluminum was
also useful as a "clue" in prediction. Keith Ferguson gave an example where static testing showed the sample
was an acid producer, and kinetic tests said it was not. They simply had to make conservative decisions, which
included monitoring.
Frank Caruccio stated that humidity cell leachate data could be normalized to i adjust the variations in
weight and pyrite contents to a common base. The adjusted data can then be plotted on a cumulative acid (or
sulfate, metals, etc.) versus time graph, the slopes of which reflect the kinetics of the sample's reactivity and
allows comparison between samples. In so doing, samples can be ranked as strongly acid producing, moderate,
and weakly acidic. In his work, involving hundreds of samples leached in humidity cells, he was able to divide
the samples into four groups based on cumulative acid production versus time for a given time frame and
percentage pyrite by weight; 2 mg/L, 20 mg/L, 200 mg/L, and 2000 mg/L acid produced as calcium carbonate
equivalents.
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This is significant because samples in the first two groups can be treated in situ with limestone additions, which
normally generate 65 mg/L alkalinity (as calcium carbonate) and provides for adequate neutralization and
buffering capacity.
Keith Ferguson noted that it is very important to check with the geologist who has a good'idea of the
variability, because only minute portions of the waste can be tested. There should be an initial geological
model, initial acid-base accounting, and possibly block modeling, check benches, etc. The degree of rigor of
testing depends on the variability. Steve Hoffman asked if prescriptive standards were possible. Keith
Ferguson recommended that even in "benign" cases (about 50 percent of mines are easy calls) there should be
some continuation of testing.
Tom Hinners asked about contaminants that may be released, even if the drainage is not acidic. He
identified work conducted by Richard Doepker (BOM) with leaching tests, and pointed out that Andrew
Robertson expressed the opinion that humidity cell tests were not suitable for determining drainage-water
quality. Richard Doepker (Bureau of Mines, Spokane, WA) stated that he is currently conducting column
leaching. He has looked at 30 to 40 different tailings to determine acid generation and metal release, and the
parameters that affect this process. He cautioned that a major concern was equating acid formation and metals
release. He has analyzed many samples that show high metals release but no acid. Thus, water quality and
metals must be addressed as well as acid generation.
He noted that columns do allow metal mobilities to be studied and, if designed and constructed well,
acid formation. However, he emphasized the limitations of columns; they are slow, particularly if they are
correlated to field conditions; if the column is shallow, it can have strong wet-dry cycles and cause changes in
pH or metal loads as a result of oxidation of sulfides. Field variability is reflected in columns: COj pockets,
flow changes, etc. They are not predictive per se, but long-term studies can provide a lot of information. In
their studies, mineralogy information is often not available and tailings are hard to characterize, but they can
infer from chemical analysis of leachates.
They made no attempt to simulate field conditions; instead, they are looking at how different
parameters affect rates of dissolution (how temperature changes oxidation, how pH changes leachates, ionic
strength effects, etc.). Most of this work is nearing completion, and they know most of what they can know
from simple columns. They are now looking at specific mineral dissolution (besides the obvious pyrite). How
different sulfide minerals behave and how removal of these sulfides from the waste stream before reaching
tailings can affect later behavior (i.e. what are the problem sulfides, and whether they can be removed). With
this work they do some blending (pyrite, galena, sphalerite, etc.) to determine the effect on total dissolution for
comparative, not predictive, purposes.
George Watzlaf (U.S. Bureau of Mines) is looking at coal pyrite and the factors influencing pyrite
oxidation. He noted that there has to be a distinction between leaching tests as "yes/no" statements of acid
generation potential and column leaching tests used to characterize field conditions. He was skeptical that any
column test could do that and referenced Keith Ferguson's comment that a factor of two was described as
"good."
Linda Broughton presented a discussion of the SRK papers (cited above by Andrew Robertson).
These reports consider the stages in acid generation. These reports include results from spiked and inoculated
humidity cells using phyllite composite. At the start of a test, there is often a peak from the flushing of stored
products or of oxidation products. A second peak may occur following a flush if conditions of acid generation
and contaminant leaching recur.
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Frank Caruccio agreed that this dual peak for acid production is common to samples that have
undergone some weathering and have stored acid salts. Based on the results of numeroi>s cell tests, the dual
peak was never found with fresh samples collected directly from the cores. !
George Watzlaf added that pore-volume replacements take more time. In trying to predict water
quality, it may be necessary to flood the sample to determine total production. In this type of column test,
however, it is best to try not to flood, but to allow flow patterns to be established. Generally, higher
concentrations are seen during higher flow events. Columns were examined following the tests to look at flow
paths, Fe(OH)3 stains, and coating on sulfide minerals. The coal column cells held 15 kilograms and were 12
inches in diameter. There were differences between flow paths (in precipitation, coating, etc.) within the
column (smaller-size columns may be more uniform even if they are trickled rather than flooded). In some
cases, it may be appropriate to flood to get total release and oxidation rates. Also, comparing flood and non-
flood tests can be useful. \
i
Steve Hoffman asked about the effect of freeze/thaw cycles. George Watzlaf; noted there are
differential temperatures in and out of a pile, and indicated there is no right answer on how to deal with that.
Some research on the effects of temperature seems to affect timing but not the end result. With freeze-thaw, it
is more complex. Some parallel tests (one at 4 ฐC.) have shown effects on bacteria. >
Steve Hoffman asked if anyone was looking at movement of oxygen through tight rock (and referenced
Bea Ross' Yucca Mountain work for the Department of Energy). Keith Ferguson has Iconsidered it. He
indicated that this work deals only with convective flow and does not link oxidation with gas transport and
identified more advanced Australian work on gas transport in rock. Diffusive and convective gas transport are
linked, but geochemistry of the drainages are not available. The MEND program is examining this. It may be
possible to use this in a comprehensive waste rock model (by linking this gas transport with hydrological and
geochemical components). They are trying to begin a 3- to 4- year, $1,500,000 project.
George Watzlaf said there were restrictions on tailings in kinetic cells [e.g., the amount of water
retention (which leads to saturation), cracking and ฃdge effects for the test sample, and the fact that (if there is
much sulfur present) gypsum, saturation can occur]. Richard Doepker agreed, saying columns have an
advantage (for tailings) even though there are some problems with shrinkage and channeling. Generally, this is
overcome during cycles. For one pore-volume, 5 percent is lost within the sample if near-saturation conditions
are maintained; for dry cycles, add excess water to obtain one pore-volume to give good flush-out. Waste rock
presents major problems. The question is the objective of the test sequence. The WGA article by Kim
Lapakko addresses a lot of the shortcomings. Ove|raU, Mr. Doepker did not feel humidity cells worked with
tailings. I
Frank Caruccio reported on a recent study2 conducted with tailings samples provided by the MEND
program. la this study, samples of a common si4 (hence the surface area variations were minimized) were
tested using whole rock analysis, column tests, humidity cell tests, and Soxhlet extractors to determine which
testing procedure best approached the drainage quality of the areas from which the saniples were collected. The
sample mass was about 360 g, and the samples were flushed on a weekly basis with about one pore volume of
deionized water. Of all the methods used, only the humidity cell tests produced a leachate quality similar to that
observed in the field. Examination of the columns showed that the fine texture of the failings inhibited free
drainage and some of the samples became air locked, thereby inhibiting the oxidation process and production of
acid. In these columns, the sulfate contents were well below the gypsum saturation, and the low sulfate
contents can only be ascribed to lack of pyrite oxidation. The Soxhlet extractor tests, because of the high
temperature of the leaching solution, selectively dissolved the carbonates, and converted all samples to high
pyrite/low NP qualities, destroying the integrity of the samples. In this study it was concluded that of all the
testing methods used, the humidity cell test was the most accurate. ,
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Richard Doepker reported that 9- to 11-inch columns for waste tailings are the maximum if you want
a good wet/dry cycle. He suggested common particle size and chemistry were critical. In their study, acid-base
accounting predicted acid generation correctly for 7 of 11 materials. In dry cycles, there was oxidation on side
surfaces, but when wet it sealed nicely. Steve Hoffman asked if compaction rates were simulated when
columns were packed. Richard Doepker indicated that the columns are packed dry, and four columns are
prepared to evaluate repeatability. Generally, good agreement is achieved among the replicate columns. He
noted that things get confusing when secondary oxidation begins. They tried slurry packing, and he emphasized
that they do not try to simulate field conditions, except for in-situ samples.
COMMENTS AND QUESTIONS FROM THE AUDIENCE
Gene Farmer asked about closing a tailings pond: what is the relationship between vertical and
horizontal transmissivity through the tailings? Andrew Robertson stated that transmissivity varies depending on
placement of material, but that vertical transmissivity is typically 0.1 of horizontal transmissivity. He indicated
that horizontal permeability is seldom less than 5 times the vertical permeability. Richard Humphreys noted
that tailings impoundments begin to behave like waste rock piles when dewatering; the surface starts to crack.
If there are lenses, the unit may need to be treated like waste rock. Keith Ferguson described some work with
silt and sand layers that had been done at the Westmin minesite. They sampled sand under the silt layer and
found that where there was a continuous silt layer, there were high pH values near 7. Because silt holds water,
it prevents oxygen migration. Conversely, sand does not hold water, and oxygen penetrates easily. Near
cracks in the silt layer, there were low pH values near 3. The cracks served as conduits for oxygen when the
silt barrier was broken.
Glenn Miller asked if it is a common practice to inoculate humidity cells with Tbiobacillus bacteria.
Keith Ferguson indicated that it is generally not necessary but it depends on what is being investigated. If the
interest is in low pH, inoculation is necessary. For neutral pH and higher, the role of bacteria is unclear. If
the cell is expected to be alkaline, inoculation is unnecessary. Also, how to add bacteria to alkaline cell adds
procedural complexity. Still, bacteria may be present in site micro-environments. Frank Caruccio noted that
regulatory agencies require inoculation, but he has found that samples contain abundant bacteria naturally.
Generally, the introduction of the iron bacteria is through the addition of 1 mL of culture medium (the medium
serves as the host vehicle). In so doing, the leachate chemistry is impacted by the addition of 8 mg of acidity,
20 mg of sulfate, and a difference in specific conductance of about 250 /tS, in a solution with a pH of 1.7.
These affects should be factored out from the quality of the leachate collected following inoculation. Richard
Humphreys offered that there is no control on the strain of bacteria used in inoculation tests. Andrew
Robertson stated that as pH changes, strain changes, but some bacteria are always present in samples. Some
strains operate more effectively in different pH ranges.
John Woodward (Nerco Minerals Company) gave the following scenario for Nerco's new operations:
(1) exploration drilling; (2) if drilling yields promising information for mining, start doing geological inspections
on cuttings to determine whether oxide or sulfide type mineral; (3) also examine previously mined material.
Based on these tests, the alternatives are:
If oxide mineral, they consider the material not to be acid-forming.
If sulfide mineral, conduct static tests, with three alternatives depending upon NP:AP ratio
(< 1:1, consider acid-generating material; > 1:1 but <3:1, conduct kinetic testing; >3:1
consider non-acid generating material).
Look at previously mined material. If it is acid producing, no more testing necessary. If it is
non-acid generating, conduct kinetic testing.
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Gene Farmer gave a regulator's perspective. He noted that kinetic tests cost from $1,500 and up per
sample, and there may be thousands of samples required. Thus, an option is to do realftime sampling during
operation and set triggers with regulators. For exajmple, a mine could sample initially at about one sample per
20,000 tons until variability can be assessed. Then, the results can be correlated to determine the need for more
tests. Over the life of a mine, its acid generation problem can be assessed, and this can give an operator
alternatives. Although there is a need to know before operations begin, often it is not realistic to expect to
know before permitting. As a result, real-time sampling/testing is necessary so that problems can be identified.
ACID PREDICTION AND MINE PLANNING \
i
;
Linda Broughton summarized a report' prepared for the office of Saskatchewan Environment and
Public Safety on evaluating the potential for acid generation and metal leaching. The figure in Appendix C
outlines an approach to evaluating the potential for acid generation and metal leaching. The approach is
presented in 3 stages: |
Stage 1: Geology and mineralogy: discussions with geologist, rock classification, representative
sampling in consultation with geologists, preliminary static testing an4 geochemical analyses.
All this serves to define the level of concern. ;
Stage 2: Static testing, preliminary design and controls: Integrate geological and geographical
information; define geological units from an environmental (as well as from an ore and
operational) perspective; develop preliminary mine rock management plan (e.g., identifying
when in the mine's life acid generating rock will be mined); sample each defined unit; perform
range of static testing; evaluate results and classify rocks; determine if potentially acid
generating or leaching. This step allows the development of a preliminary control plan.
Stage 3: Kinetic testing, detailed rock/waste management plans: Select samples for kinetic testing to
define rates of acid generation and leaching; conduct kinetic testing; use results to guide the
design of controls for drainage water quality; conduct more tests if necessary; perform
environmental impact assessment (extrapolation modeling); and develop the final rock
management plan. Stage 3 may be more flexible. Objectives must be defined at the beginning
of the stageit may be necessary to take steps to better understand variability (block modeling,
mineralogy studies, field or laboratory kinetic programs, etc.) rather than simply progressing
through the steps. Block modeling may be added at the water quality modeling stage. As for
the accuracy of the final stage, more and more certainty and more quantitative data on water
quality loadings are being required by regulatory agencies, but it must be recognized that
uncertainty remains. Regardless of uncertainty, however, there must be prediction of at least a
reasonable range of "hard numbers" to meet specific standards. t
i
Ms. Broughton noted that following these stages, an operation would proceed with approval,
operation, and monitoring. It should be noted that this may not necessarily be a linear process. There can, and
should, be various loops, especially as one step identifies the need for more information. In British Columbia,
operations must have a closure plan before commencing operation, which makes these steps necessary. Also,
from a company's point of view, the long-term environmental liabilities have led to the recognition that these
stages are necessary.
She presented the table in Appendix D on identifying sources of information and samples.
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Keith Ferguson commented that there was a need to study mineral controls before deciding on field or
laboratory tests and on a detailed acid-base-accounting program. He noted the need to make the model more
holistic to account for more factors.
Andrew Robertson stated that the three-stage process was demonstrated "technology." He clarified
that static tests conducted in Stage n could include more than ABA testing. He also noted that where there is a
receiving-water standard, the standard must be modeled. Wherever there is a risk of environmental problems,
they must be mitigatible by existing technology. Requirements are making their way down to the level of the
Canadian provinces. By mine closure, operations are required to have 100 percent bonding to cover closure
(reclamation) and long-term maintenance; bonding is incremental and by the mine's life or 10 years, whichever
is lesser, it should be fully bonded.
Kim Lapakko mentioned that it is possible to determine the maximum potential of a mine waste to
produce acid (by analysis for acid-producing sulfur species) and the maximum potential for the waste to
neutralize acid (by analysis for calcium carbonate and magnesium carbonate and/or direct titration of a sample,
although the second technique requires verification). If a mining company designs a mitigation scheme that
assumes "worst case" water quality for its mine waste, these detailed analyses become academic as does the
frequency of sampling for representative wastes. In such a case the resources expended on a detailed mine
waste characterization procedure would be better spent on mitigation.
Gene Fanner expressed a concern with the numbers of samples and statistical reliability. He
emphasized the danger that one can produce data that are not reliable unless guidelines provide for statistical
uncertainty. He noted that a sampling program over a mine's life is the only remedy for uncertainty. It can be
simplified if, instead of a long list of activities, a block model were used with thousands of core samples. If the
mine operators began thinking about sulfides and acid generation early, they could prevent problems.
Patricia Erickson noted that Miller and Murray in Australia conducted a comparison of net NP for 30 base-
and precious-metal mines using four classifications. They could divide these mines into barren, acid,
potentially acid, and not acid. The level that would not produce acid was set at 10 tons excess NP/1000 tons.
The data were not convertible to ratios. She referred to Keith Ferguson's paper on tailings (NP:AP break point
about 1.0) and Kim Lapakko's paper for tailings (break in pH at about 0.8 percent sulfur, specific to that
particular rock).
Keith Ferguson described ABA data for waste rock from six dumps at three base-metal mines. Mean
NNP and NP/AP were calculated for drill-hole samples from each of the six waste rock dumps. The break
between acid and non-acid generation was at a mean NNP of 0 or at a mean NP/AP between 2:1 and 3.4:1.
These values agree generally with data from the coal mining sector. He noted a case where some sections were
acid generating and some were not, with problems occurring where acid-generating rocks were concentrated in
one area.
Richard Humphreys asked Keith Ferguson about what sort of variance is found in the population
AB As for waste rock. Keith Ferguson noted that there was a fair amount of variance from site to site. For
drilling of existing waste rock dumps, they divide the data into categories of NP:AP of < 1, 1 to 2, and > 2.
For the base-metal dumps (cited above) that generated AMD, the vast majority of samples had an NP:AP < 1.
One dump [Island Copper (sic)] that is producing acid had about 50 percent of the samples with acid-predictive
NP:AP <1.
Richard Humphreys said that in California, mere are a couple of gold heap leach piles ready to be
closed (about one million tons). The company did a drilling study to demonstrate that they would not generate
acid. Statistics on sulfur content of 80 samples gave average of 2.5 percent with much variance. The NP: AP
19
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ratios were all high. Steve Hoffman noted that various cyanide species may affect the geochemistry driving
acidification. Thus, the application of knowledge to hj-ap leaches may be risky. ;
Michael Smith discussed the use of standard jcutoff (decision) values. He suspected that they were
applicable to wet climate areas, but they may not be applicable to arid conditions. He woujd hesitate to use wet
climate ratios in arid areas. He emphasized the need to look at old dumps in the west; some may have 20-30
percent sulfides but no acid generation. Thus, any sort of cutoff values should accommodate climatic conditions
in the area; also, site-specific factors must be considered (e.g., a dump above a spring).
i i !'
Keith Ferguson agreed that site-specific conditions are critical. In wet climates, they see a preferential
stripping of carbonates, so in general they would want! a higher NP:AP ratio as a safety faptor. Thus, all the
data are an initial screen before looking at the specific site and assessing site-specific data.,
Kim Lapakko indicated that the waste rock type can also influence cutoff. The use of different
analytic procedures also affects Acid Production Potential data results. i
Linda Broughton, referring to the three-stage process, indicated that mine rock classification should be
beyond the geologist's description of the drill core, to include factors important from the ARD view (e.g., do
sulfides and carbonates occur in veins or disseminated). This information should be used in the sampling plan.
i
Richard Humphreys noted that permits may'be based on faulty predictions; though based on science,
this does not address problems when they develop. I
:
Steve Hoffman noted that EPA is confronted with operational mines with existing piles. The mine
operators may have had good intentions and may have conducted acid prediction tests, but^t simply did not
work out. A regulatory agency then is faced with a noncompliance situation; the ability to alter management
practices is limited due to the volume of materials. The concern is that regulators cannot take action until there
are violations, and by then it is too late. Richard Humphreys responded that, if he were a permit writer (and
he is not), he would like to know about the uncertainty beforehand, during the permitting phase. One problem
is that permit writers may not have expertise, and repbrts may not explain uncertainty well Budgets and time
are another issuo. Gene Farmer responded that mines should not be permitted forever. If a Plan of Operations
is approved, it should have trigger points and action limits built in. For example, the plan could provide for re-
examination if sulfide or ABA hit certain limits. As an example, oxide heap-leach operations are finding it
difficult to avoid sulfide zones (because there is gold fhere), thus making continuous examination necessary. In
addition, the sulfide and oxide "zones" are actually a continuum, with transition zones. Sp, if a regulator pays
attention and sets trigger points, the problem Steve Hoffman described may be avoided, i
Patricia Erickson cautioned that using the terminology "acid mine drainage" or "acid rock drainage"
tends to make us forget about sulfate and the metals that are dissolved by the acid. Part of the monitoring
program on the flow chart should look at a range of indicator parameters (sulfate, calcium, etc.) in seeps as a
forecast of future regulated-contaminant migration. ;
i.
Keith Ferguson offered some advice concerning Steve Hoffman's points: !
The mining company (industry) is liable, so they must do the lion's share of work and
planning. The government also has a responsibility.
!
Both parties must be involved during planning, operation, and closure; and these steps should
not be separated.
20
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Regulators must be involved in the process from beginning to end or not at all (cannot
effectively enter midway in the process).
There must be flexibility (by both parties) to address unpredicted or unpredictable conditions.
Andrew Robertson noted that this type of approach is being increasingly followed by Canadian provinces. For
reference, see the Ontario legislation/guidelines for closure (Rehabilitation of Mines, Guidelines for Proponents,
Ontario Ministry of Northern Development and Mines).
IDENTIFICATION OF RESEARCH NEEDS
Tom Hinners and Steve Hoffman requested panelists and audience participants to identify the research
needs considered to be the most critical. They also asked about the appropriate role of EPA in conducting or
assisting research.
Keith Ferguson noted that some research is currently underway in which there is long-term testing to
characterize waste rock and the factors affecting acid generation. Key needs include:
Waste rock model: Both a simple and a complex model are needed. The purpose of a MEND
meeting in September 1992 in Toronto is to coordinate research on a complex model
conducted on an international basis. A model should address climatic conditions, variability of
samples, stacking, blending (i.e., factors that physical testing can not address).
Available sulfur and NP: We can determine total sulfur and total NP, but we do not really
know what is available under field conditions. If we knew that and the rates of acid and
alkalinity release, we could extrapolate the tuning of net acid production.
Factors that control sulfur and NP depletion in the long term: Coating, slaking potential,
preferential leaching. This, unfortunately, requires long-term tests, but would address some
important complex relationships, particularly under neutral pH conditions.
Cheaper methods to characterize samples for acid generation potential: Acid-base accounting is
currently about $50 per sample.
Geostatistical and modeling approaches: Gold-reserves modeling is now common, and mere are
some models being started for acid drainage as well.
Relation between mineralogy and reactivity: Factors include grain size, morphology, sulfide
mix, the position of carbonates and sulfides. There are many tests, but the linkages are not
known. Some projects under the MEND program are considering this issue.
ซ Climate: The effect of dry climate is a key in terms of acid production and migration in arid
regions.
Low-sulfur cutoff (decision) value: Is a value of 0.6 percent sulfur a reasonable minimum for
concern about potential acid generation?
Prediction techniques and sampling for underground mine walls: This is very poorly
understood.
21
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Linkage of prediction to field conditions: Field data are critical, and there is a need for much
more. A case study book based on more field plots and old dumps would be valuable.
Richard Humphreys indicated he would like to see some research directed at biological activity. The
general assumption is that bacteria become important at pH 3.5 or below, but there is a need to understand the
mechanism much better because it may be related to surface activity and the microenvironments.
Steve Hoffman summarized two major areas: EPA will soon request the WGA Mine Waste Task
Force to identify possible research topics and laboratory research. Both areas need more industry involvement,
and the Office of Solid Waste needs suggestions early in 1993. There are limited funds fbr mine waste research
available through OSW, but OSW will continue to participate (along with the Bureau of Mines) in international
conferences. Mr. Hoffman asked about the cost of a study for dumps.
' i
Richard Humphreys indicated it can be fairly expensive, especially at abandoned mines (e.g., about
$500,000 for thฉ Perm Mine). Where there are numerous dumps, it is complex and costly to characterize
materials. Andrew Robertson-gave a cost of around $100,000 for an existing 3-million ton dump for outside
trenching, drilling, lab testing, etc., for detailed ARB and water-quality predictions. Keith Ferguson indicated
that for existing mine operations a comparison of field data with predictions from laboratory methods would
cost about $25,000 per site (using previously collected cores and existing geological and operating records).
;
Andrew Robertson: A site reconnaissance costs about $10,000 for a 3.5-millioDJ ton dump (looking at
geologic information, sampling the dump surface, and measuring paste pHs). Add on a small amount of ABA
testing, and it will cost about $15,000. Andrew Robertson added that we have discussed mainly prediction
testing ahead of mining and the prediction of water quality associated using essentially uncontrolled testing.
When we observe a problem, our thinking actually changes. We need to do the predictions under the controlled
conditions to be installed (e.g., if covers are added, there are very low leach rates, so limited work on water
quality may be necessary). i
i
Also, we need research into various levels of pH control (blending, or adding finely crushed limestone)
and testing at a controlled level of continued acid generation. As to Keith Ferguson's concern for test costs,
there is a lot to do with kinetic testing. To control costs, one can cut out the dry cycle and put samples through
a crude device. It should be possible to develop a standard, crude kinetic test. :
i !
In response to a question from Tom Hinners, Patricia Erickson described the use of the Finkelman
peroxide test" where the rate of pH change (10-minute test) is monitored. They were not able to get correlation
between sulfur content, NP, and peroxide results for coal samples. There may have been problems with the
laboratory procedures because they did not precisely! follow Finkelman's procedure. Testing on coal may be
more complicated than hard rock due to the organic content. It may be possible to determine whether it should
be pursued with metal mines. j
Fiona Doyle described the use of peroxide ^with coal. They found excess acid production because
peroxide was oxidizing coal and surface organic acids. It would not be reliable for coal,! but might be for hard
rock. Keith Ferguson indicated that there is currently Australian work12 on the Net Acid Generation (NAG)
test involving peroxide use. Placer Dome is rinding good correlation between the NAG .test and ABA at some
mines and poor correlation at others.
Frank Caruccio described his work with peroxide oxidation coupled with leaching chambers, where he
found that organic matter content interfered with the solution in contact with the peroxide. Michael Smith
observed that mining material in Nevada's Carlin Ttend may have 2-3 percent organic carbon, so peroxide may
not be useful in tests of Nevada mining wastes.
22
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Tom Card commented that statistics may be useful in determining the number of samples to establish
confidence limits to satisfy regulators. A research project to gather useful statistics to increase sampling
confidence may help. He would like to see some guidance provided on statistical treatment of test data. Keith
Ferguson expressed his opinion that standard sampling programs are not appropriate for mining wastes.
Sampling must be site-specific. Standard methods for presenting data, however, are appropriate. Placer Dome,
for example, is developing systems of presentation. They are trying various nonparamelric statistics to compare
data sets. Statistics are a very critical part of the entire assessment package.
Richard Humphreys indicated that in the area of water quality, there is movement toward having large
data sets submitted to regulators on diskettes so data can be statistically manipulated.
Patricia Erickson noted problems with accuracy and precision, particularly in the way tests are used.
For at least static tests and some of the kinetic tests, there need to be standard methods in place. Tom Hinners
noted that the National Institute of Standards and Technology (NIST) released in 1991 a pyrite ore reference
material (RM 8455) that could be used in method evaluations.
Ben Haynes (Bureau of Mines, Washington, DC, deceased 12/25/92) noted that BOM has been
involved in acid generation research for some time. BOM is able to direct attention to specific short- and long-
term projects. He noted BOM's work with EPA, the Forest Service, and the MEND program. As for
abandoned sites, he noted that there can be improvements in water quality even if strict standards cannot be
met. Finally, he noted that BOM is co-sponsoring (with EPA and other Federal and State agencies) the Third
International Conference on Abatement of Acidic Drainage in April 1994 in Pittsburgh.
Michael Smith recommended a study of existing dumps. He suggested they be broken up by
geographical areas within the west (different domains, climate zones), then survey dumps at abandoned sites,
and design the sampling plans - overall, a thorough documentation of a range of dumps similar to the
Saskatchewan process described earlier. He emphasized thatlt is critical to get good representation of different
climatic zones. He also added that when site-specific expertise is needed, it is more appropriate to use experts
who are there whether or not they are registered geologists (as specified in proposed California regulations).
CONCLUSION
Tom Hinners then closed the meeting by thanking the panel members and the audience participants.
He reiterated that the workshop was intended to foster a discussion of ideas, not to reach specific conclusions.
Official notes of the workshop (i.e., this document: Predicting Acid Generation from Non-Coal Mining Wastes -
Notes of July 1992 Workshop) will be provided to the attendees after a draft document provided by Science
Applications International Corporation is reviewed by the panel members and EPA personnel, the document is
revised as appropriate, and it has been formally cleared by EPA. EPA will consider the recommendations
provided during the workshop in planning research efforts.
23
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REEERENCES ! '
1. Ferguson, K. D., and K. A. Morin. The Prediction of Acid Rock Drainage - Lessons from the
Database. In: Proceedings of the Second International Conference on the Abatement of Acidic
Drainage, Montreal, QufSbec, Canada Centre for Mineral and Energy Technology (CANMET), Ottawa,
Ontario, K1A OG1, CANADA, 1991. Vol. 3, pp. 83-106. - i
2. Bradham, S. W., and F. T. Caruccio. A Comparative Study of Tailings Analysis Using Acid/Base
Accounting, Cells, Columns and Soxhlets, In: Proceedings of the Second International Conference on
the Abatement of Acidic Drainage, Montreal, Quebec, Canada Centre for Mineral and Energy
Technology (CANMET), Ottawa, Ontario, K1A OG1, CANADA, 1991. Vol. 1, pp. 157-173.
3. Coastech Research Inc. Acid Rock Drainagp Prediction Manual. MEND Project No. 1.16. l(b).
Canada Centre for Mineral and Energy Technology (CANMET), Ottawa, Ontario, K1A OG1,
CANADA, 1991. 117 pp.
4. The California Mining Association. Mine Waste Management. Lewis Publishers, Inc., Chelsea,
Michigan, 1992. 654 pp.
5. Ferguson, K. D., and P. M. Erickson. Approaching the AMD Problem - From Prediction and Early
Detection. In: Proceedings of the International Conference on Control of Environmental Problems
from Metal Mines, Roros, Norway, June 19|88, Federation of Norwegian Industries and State Pollution
Control Authority, Qda, NORWAY, 1988, pgs 101-143.
6. Ferguson, K. D., and P. M. Erickson. Pre-Mine Prediction of Acid Mine Drainage. In: W.
Salomons and U. Forsmer (eds.), Environmental Management of Solid Wastes, Dredged Materials and
Mine Tailings. Springer-Verlag, Heidelberg, Baden-Wurttemberg, GERMANY; 1988. pp. 24-43.
7. Caruccio, F. T., Geidel, G., and M. Pelletier. Occurrence and Prediction of Acid Drainages. J.
Energy Div. Amer. Soc. Civil Engineers, 107(EY1): 167-178, 1981.
| i
8. Sobek, A. A., Schuller, W. A., Freeman, J. R., and R. M. Smith. Field and Laboratory Methods
Applicable to Overburdens and Minesoils. EPA-600/2-78-054, microfiche PB-280 495, U.S.
Environmental Protection Agency, Cincinnati, Ohio, 1978. 219 pp.
9. Broughton, L. M., Chambers, R. W., and A. MacG. Robertson. April 1992. Mine Rock Guidelines,
Design and Control of Drainage Water Quality. Report No. 93301. Saskatchewan Environment and
Public Safety, Mines Pollution Control Branch, 12th Floor, 800 Central Avenue, Box 3003, Prince
Albert, Saskatchewan, S6V 6G1, CANADA, 1992. 159pp. ;
10. Mirza, A. H., Herrera, M. N., and F. M. Doyle. Characterization of Pyrite-Bearing Materials by
Chemical Oxidation. In: Proceedings of the Symposium on Emerging Process Technologies for a
Cleaner Environment, February 1992, Phoenix, Arizona, Society for Mining, Metallurgy, and
Exploration, Inc., Littleton, Colorado, 1992. pp. 121-129. ;
11. Finkelman, R.B., and D. E. Giffin. Hydrogen Peroxide Oxidation: An Improved Method for Rapidly
Assessing Acid-Generating Potential of Sediments and Sedimentary Rocks. Reclamation and
Revegetation Research, 5:521-534, 1986. ! '
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12. Miller, S. D., Jeffery, J. J., Wong J. W. G., and A. J. Goldstone. In-Pit Identification and
Management of Acid Forming Waste Rock at the Golden Cross Gold Mine, New Zealand. In:
Proceedings of the Second International Conference on the Abatement of Acidic Drainage, Montreal,
QueTjec, Canada Centre for Mineral and Energy Technology (CANMET), Ottawa, Ontario, K1A OG1,
CANADA, 1991. Vol. 1, pp. 137-151.
25
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APPENDIX A
PANELISTS AND ATTENDEES AT WORKSHOP ON
ACID GENERATION FROM NON-COAL MINING WASTES
JULY 30-31, 1992
PANELISTS
Linda Broughton
Steffen, Robertson
find Kirsten, Inc.
Suite 800
580 Hornby St
Vancouver, BC V6C 3B6
CANADA
(604)681-24196 -
Frank Caruccio
Department of Geological
Sciences
University of South. Carolina
Columbia, SC 29208
803-777-4512
Richard Doepker
U.S. Bureau of Mines
Spokane Research Center
315 East Montgomery Avenue
Spokane, WA 99207
509-484-1610
Fiona M. Doyle
Department of Materials Science
and Mineral Engineering
University of California
at Berkeley
Berkeley, CA 94720
510-642-2846
Patricia Erickson
U.S.EPA
Risk Reduction
Engineering Laboratory
5995 Center Hill Avenue
Cincinnati, OH 45324
513-569-7884
Keith Ferguson
Placer Dome, Inc.
Bentall Center
Vancouver, BC V7X 1P1
CANADA
(604) 661-1916
Richard Hammack
U.S. Bureau of Mines
P.O. Box 18070
Pittsburgh, PA 15236
412-892-6585 !
Thomas Hinners
U.S. EPA, EMSL'
P.O. Box 93478 ;
Las Vegas, NV 89193
702-798-2140
Stephen D. Hoffman
U.S. EPA/OSW \
401 M Street, SW
Washington, DC 20460
703-308-8413
Richard Humphreys
California Water '
Resources Control Board
P.O. Box 944212 I
Sacramento, CA 94244
916-739-4254 ;
Kim Lapakko ;
Minnesota Department of
Natural Resources
P.O. Box 45
500 Lafayette Road
St. Paul, MN 55155
612-296-1358
26
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Andrew Robertson
Steffen, Robertson
and Kirsten, Inc.
#800-580 Hornby St.
Vancouver, BC V6C 3B6
CANADA
604-681-4196
Kenneth Sala
U.S. EPA
401 M Street, SW
RD-680
Washington, DC 20460
202-260-9711
George Watzlaf
U.S. Bureau of Mines
Cochrans Mill Road
P.O. Box 18070
Pittsburgh, PA 15236
412-892-6754
William White
U.S. Bureau of Mines/SLRC
729 Arapeen Drive
Salt Lake City, Utah 84103
801-524-6114
ATTENDEES
Steven Barringer
Holland & Hart
1001 Penn. Ave.
2Washington, DC 20004
202-737-8930
Julia Benham
Barrick Goldstrike
P.O. Box 29
Elko, NV 89801
702-738-8043
Charles Bucknam
Newmont Gold Company
417 Wakora Way
Suite 210
Salt Lake City, UT 84115
805-583-8974
Thomas Card
Nevada Department of
Environmental Protection
333 W. Nye Lane
Carson City, NV 89710
702-687-4675
ป
Robert Carlson
Nevada Department of
Environmental Protection
Bureau of Mining
Regulations and Reclamation
333 W. Nye Lane
Carson City, NV 89710
702-687-4675
Terrence Chatwin
Huntingdon Northern
350 W. 2700 S.
Salt Lake City, UT 84115
801-487-3661
Christian Daughton
U.S. EPA, EMSL
P.O. Box 93478
Las Vegas, NV 89193
702-798-2207
Jane Denne
U.S. EPA, EMSL
P.O. Box 93478
Las Vegas, NV 89193
702-798-2655
David Deisley
Parsons Behoe
P.O. Box 11898
Salt Lake City, UT 84117
801-532-1234
Eugene Farmer
U.S. Forest Service
324 25th St.
Ogden, UT 84401
801-625-5271
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Emil Fattu
SVL Analytical
P.O. Box 929
Kellogg, ID 83837
208-784-1258
Thomas Foertsch
Barrick Goldstrike Mine
P.O. Box 29
Elko, NV 89801
702-738-8043
Walter Galloway
U.S. EPA, EMSL
P.O. Box 93478
IMS Vegas, NV 89193
702-798-2568
Gwen Geidel
CARGEID
3823 Edinburgh Road
Columbia, SC 29204
803-787-1920
Benjamin Haynes (died 12/25/92)
U.S. Bureau of Mines
810 7th St., NW
Washington, DC 20241
202-501-9223
Edward Heithmar
U.S. EPA, EMSL
P.O. Box 93478
Las Vegas, NV 89193
702-798-2626
Lary Jack
U.S. EPA, EMSL
P.O. Box 93478
Las Vegas, NV 89193
702-798-2373
Sandra McGill
U.S. Bureau of Mines
1605 Evans Ave.
Reno, NV 89512
702-334-6665
Glenn Miller
University of Nevada-Reno
Dept. of Biochemistry
M/S 330
Reno, NV 89557
702-784-4108
Timothy Miller :
Gold Fields - Mesquite
6502E. Hwy78
Brawley, CA 92227
619-352-6514 !
Delbert Parr
AMAX Gold
600 Sod House Road
Winnemucca, NV!89445
702-623-1112
Daniel Pool '.
U.S. Bureau of Mines/RERC
1605 Evans Ave. '
Reno, NV 89512
702-334-6673 j
Patrick Rogers :
Independent Mining Company
HC31 Box 78 I
Elko, NV 89801 ;
702-758-9221
Valerie Sawyer
Barrick Goldstrike Mine
P.O. Box 29
Elko, NV 89801
702-738-8043 i
Michael R. Smith
Barrick Goldstrike Mine
P.O. Box 29
Elko, NV 89801
702-738-8043 |
Susan Sorini
Western Research Institute
P.O. Box 3395
University Station
Laramie, WY 82071
307-721-2232
28
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William Stelz
USEPA/ORD
RD-680
401 M St., SW
Washington, DC 20460
202-260-5798
Meade Striland
Echo Bay Mines
5401 Longley Lane
Reno, NV 89511
702-829-1000
Daniel Tecca
Nevada Department of
Environmental Protection/Mining
333 W. Nye Lane
Carson City, NV 89710
702-687-4675
Ronald Thoreson
Newman Exploration
P.O. Box 669
Carlin, NV 89822
702-778-4635
David White
Newmont Gold Co.
P.O. Box 669
Carlin, NV 89822
702-778-4471
William Wilson
Kappes, Cassiday & Assoc.
1845 Glendale Ave
Sparks, NV 89431
702-356-5609
John Woodward
NERCO Minerals Company
500 NE Multinonah
Suite 1200
Portland, OR 97232
503-731-8058
Ronald Zuck
Magma Nevada Mining Co.
P.O. Box 382
Rum, NV 89319
702-289-4470
29
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APPENDIX B
BIOGRAPHIES FOR TECHNICAL EXPERTS ON THE PANEL
..
LINDA M. BROTJGHTON
Steffen, Robertson and Kirsten, Inc.
Vancouver, BC, CANADA
i
Linda M. Broughton, P. Eng. is a mining engineer specializing in acid rock drainage (ARD) and
environmental impact assessment from mining projects. Ms. Broughton has developed expertise in the
prediction and control of acid rock drainage. As head of Steffen, Robertson and Kirstem's Acid Rock
Drainage Division in Vancouver, she is responsible for the development and design of ARD prediction and
control technology on SRK projects. !
i
Ms. Broughton is involved in projects both for prediction of ARD for new operations, assessment of
ARD and design of control technologies for existing mines, and closure and remediation [for old mines. Over
the past year she was the principal author of the "Mine Rock Guidelines for Design and Control of Drainage
Water Quality" prepared for the Saskatchewan Mines Pollution Control Branch and of the "ARD Prediction in
the North" for Department of Indian Affairs and Northern Development. She is currently involved in a number
of projects related to ARD prediction for the B.C. Acid Mine Drainage Task Force and ihe National MEND
committee including "Compilation of ARD Prediction Rules" and a model to predict drainage water quality from
waste dumps. She has extensive experience in the evaluation of acid drainage conditions from mine sites and
recently participated in a study tour of ARD remediation sites in Sweden.
Ms. Broughton is the co-presenter of ARD and mine closure short courses with Dr. Andy Robertson
which have been presented in Canada, the U.S., Sweden, the U.K. and South Africa, j
FRANK T. CARUCCIO
Department of Geological Sciences
University of South Carolina
Columbia, SC 29208
Ph.D. in Geology, 1967 Pennsylvania State University
M.S. in Geology, 1963 Pennsylvania State University
B.S. in Geology, 1958 City College of New York j
(Professor of Geology, May 1983 to present)
Over the past 20 years most of my research has been concerned with the identification of the hydro-
geologic variables responsible for the occurrence of acid mine drainage in the bituminous coal fields of
Appalachia and abandoned gold mines in South Carplina. With funding (exceeding $2 million since 1972) from
the Environmental Protection Agency, the National Science Foundation, the Bureau of Mines and the Office of
Surface Mining, we have investigated the acid problem in West Virginia, Pennsylvania, eastern Kentucky, Ohio,
Tennessee, and South Carolina. The results of these studies have led to the formulation of a predictive model,
through which, mine drainage quality can be predicted from cores of exploratory drill holes. The results of my
studies dealing with rock - water interactions are currently used in mine plans to minimize acid production. My
research in this field has expanded to the point whereby laboratory results have been translated to field trails
through the use of active, large-scale coal and gold mines. Publications include over 35 papers and chapters in
refereed journals and books dealing with the problems of occurrence, prediction and abatement of acid mine
drainage. Field ground water monitoring networks established in several mines in central West Virginia
30
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provided the basis for the formulation of a unique model and the characterization of groundwater flow and
occurrence in reclaimed mine backfills. Numerous presentations and papers have been presented and appear in
the proceedings of symposia dealing with the environmental impacts of acid drainage on surface and
groundwater regimes.
Appointed to numerous national (including NATIONAL RESEARCH COUNCIL/NATIONAL
ACADEMY OF SCIENCES) and international committees (including BEDER INSTITUTE, ROYAL
SWEDISH ACADEMY OF SCIENCES) dealing with the acid mine water-related problems throughout the
United States, southern Africa, northern South America, and Canada. Five separate gubernatorial appointments
to the South Carolina Mining Council, representing non-governmental conservation interests continuously
serving since 1974; served as the Council's first chairman.
Research specialty relates rock-water interactions to leachate quality and the potential impact on the
quality of surface water and the groundwater regime and flow systems. Research efforts are toward the :
development of an in-situ technique for the abatement of acid mine drainage.
RICHARD D. DOEFKER
U.S. Bureau of Mines
Spokane, WA 99207
Richard Doepker was bom hi Findlay, Ohio, educated at Xavier University (BS and MS chemistry)
and Carnegie Institute of Technology, (now Carnegie Mellon University), Ph.D. in physical chemistry. After
.two years military duty at the Army Chemical Center, MD, (research in the anti-material program) and two
years National Academy of Science, National Research Council post doctoral research fellowship at the National
Bureau of Standards, Washington, D.C., with 7 publications in the area of radiation and photochemistry, Dr.
Doepker joined the chemistry faculty at the University of Miami. During the eighteen years of tenure at U of
M, Prof. Doepker headed a graduate research program in gas phase kinetics, and vacuum UV photochemistry
which lead to 17 jured publications, four granted Ph.D.'s and five Masters. Funding for the most of this
graduate research program was furnished by the National Science Foundation. In addition to his physical
chemistry research Prof. Doepker took over as Head of Analytical Chemistry and conducted research in the
chemical characterization of the exhaust from methanol powered engines for the Dept. of Energy.
Dr. Doepker and family moved west in 1983. After two years of university teaching in Washington,
he joined the research staff at the Spokane Research Center, U.S. Bureau of Mines as a research chemist and
principle investigator in the dissolution mechanism of metals from mine waste. This research has led to 10
publications mainly related to the parameters affecting metal dissolution from metal-mine tailings. Studies have
also been carried out on metal dissolution and the oxidation mechanisms of waste rock (manuscript in
preparation). Current research interests still include long-term metal dissolution characteristics of aged tailings
and the apparent inhibited oxidation of fresh tailings. Methods for the determination of the rate of oxidation of
waste rock is under investigation as well as studies of the metal release, oxidation mechanism and rates of
dissolution from individual mineral of mining interest. Through this latter project it is hoped that particular
minerals or combinations of minerals can be identified that are instrumental in the formation of mobilized metal
from mine wastes.
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EEONAM. DOYLE
Associate Professor
University of California at Berkeley
EDUCATION
B.A. Metallurgy and Materials Science, University of Cambridge, England, 1978
M.A. Natural Sciences, University of Cambridge^ England, 1982
M.Sc.(Eng.) Extractive Metallurgy (awarded with Distinction), Imperial College of Science and
Technology, University of London, England, 1979
Ph.D. Hydrometallurgy, Imperial College of Science and Technology, University of London,
England, 1983. Thesis titter "Hydrolytic Stripping of Mixed Metal Carboxylates"
Diploma of Membership of Imperial College (D.LC) 1979 and 1983
PROFESSIONAL EXPERIENCE
1979-1982: Teaching Assistant, Imperial College of Science and Technology
1983: Graduate Trainee, David McKee, Metals and Minerals Division, Stockton-on-Tees,
England ' ,
1983-1988: Assistant Professor, Department of Materials Science and Mineral Engineering,
University of California at Berkeley
1990: Acting Associate Dean, Special Programs, College of Engineering, University of California at
Berkeley j
PROEESSIONAL AFFILIATIONS
i
TMS, American Institute of Mining, Metallurgical and Petroleum Engineers, Institution of Mining and
Metallurgy, The Electrochemical Society, American Chemical Society, Materials Research Society, Chartered
Engineer, Great Britain |
PROFESSIONAL ACTIVITIES ;
' f
Intramural: 1990-91, Chair, Committee on courses of Instruction, Academic Senate, University of California at
Berkeley \
'
Editorial: Co-editor, Mineral Processing and Extractive Metallurgy Review (1990-present), Board of Review,
Metall. Transactions B (1985-1990), Editorial Board, Hydrometallurgy (1986-present)
!
Professional Society Activities: TMS/SME Hydrometallurgy/Chem. Processing Committee (1986-1989) (1988-
89 Chair), TMS Aqueous Processing Committee, (1988-present) (1989-90 Chair), TMS/EPD Programming
Committee (1989-90, 1992-95 Chair), TMS/EPD Executive Committee (1989-present), TMS Copper, Nickel,
Cobalt Committee (1989-present), TMS Education and Professional Affairs Committee ,(1989ipresent), TMS
International Activities Committee (1991-92), TMS Reactive Metals Committee (1989-present), TMS Student
Affairs Committee (1989-92)
i
AWARDS
Institution of Mining and Metallurgy; Bosworth Scaith Trust Fund Award, 1981 Rio Tinto Zinc Corporation,
Research Award, 1981/82
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RESEARCH INTERESTS
Aqueous chemistry in the processing and behavior of minerals and materials. Equilibrium, kinetics, mass
transfer and mechanisms in aqueous, organic and solid systems. Leaching and transformation of minerals.
Hydrolysis, precipitation and coprecipitation. Solvent extraction and organic phase reactions. Electrochemistry.
Chemical thermodynamics. Applications in hydrometallurgy, materials science, environmental engineering and
waste management, and earth sciences.
47 Publications in Journals, Conference Proceedings, etc, 22 Abstracts, Preprints, Invited Talks
PATRICIA M. ERICKSON
U.S. Environmental Protection Agency
Cincinnati, OH 45324
Patricia (Trish) Erickson is a chemist with the EPA's Office of Research & Development, Risk
Reduction Engineering Lab. For the past 2 years she has managed research on characterization and remediation
of RCRA and Superfund wastes. From 1980 to 1990 she was with Jhe Bureau of Mines' Environmental
Technology Group, conducting and managing research on acid mine drainage. The research program
encompassed characterization of mine waste, mitigation of existing or predicted acid discharges, and water
treatment. Ms. Erickson has contributed to more than 30 publications on mine waste and mine water.
B.A., SUNY College at Buffalo, Chemistry.
M.S., Pennsylvania State University, Analytical & Inorganic Chemistry.
KEITH D. FERGUSON
Placer Dome, Inc.
Vancouver, BC, CANADA
EDUCATION
1977: Masters of Applied Science (Environmental Engineering) University of British Columbia
1975: Bachelor of Applied Science (Geological Engineering) University of British Columbia
EXPERIENCE
1992-present: Senior Environmental Engineer, Placer Dome Inc. Responsible for studies and assessments of
Acid Rock Drainage for large international mining corporation.
1982-1992: Manager/Head Mining and Metallurgy Program, Environment Canada. Responsible for
managing the mining program in the Pacific and Yukon Region. Conducted reviews and
assessments of new mine proposals in the region, inspected existing mining operations and
negotiated environmental controls. Chaired the Prediction Committee of die Mine
Environment Neutral Drainage Program, and Prediction and Prevention Committee of
B.C. Acid Mine Drainage Task Force. Member of U.S. EPA Science Advisory Board
reviewing amendments to RCRA and CERCLA legislation regarding mining wastes.
1979-1982: Project Engineer, Mining and Metallurgy Program, Environment Canada. Conducted reviews
and assessments of environmental controls for new and existing mine projects.
33
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1977-1979: Project Engineer, Municipal Program, Environment Canada. Conducted assessments of
contamination of shellfish growing waters, sewage treatment plant operations, and of
stormwater discharges to the Fraser River.
1976-1977: Research Assistant, Environmental Engineering Group, University of British Columbia.
Conducted bench scale experiments to minimize the environmental impact of area used for
airport runway de-icing.
PUBLICATIONS
j
More than 25 publications in the environmental engineering field, including more than 15 oa acid rock drainage
prediction and abatement.
RICHARD W. HAMMACK '
U.S. Bureau of Mines [
Pittsburgh Research Center \
I
Richard (Rick) Hammack received a B.S. in geology and a M.S. in geochemistry from West Virginia
University. For the past 13 years, he has worked for the U.S. Bureau of Mines as an exploration geologist and
as a research geochemist. Rick has spent 8 years evaluating the intrinsic reactivity of sedimentary and
hydrothermal pyrite using evolved gas analysis, x-ray photoelectron spectroscopy, electron beam induced current
microscopy, MSssbauer spectroscopy, and corrosion voltammetry. Much of this effort was directed towards the
development of quick and simple methods for determining pyrite reactivity. Rick has also examined, on a
microscopic scale, the effect of oxygen, humidity, chemolithotropic bacteria, and passivating,agents on the
oxidation of pyrite surfaces. I
RICHARD D. HUMPHREYS
California Water Resources Control Board
Sacramento, CA 94244
Richard (Rick) D. Humphreys, P.O. (California Water Resources Control Bodrd) is a geologist with
more than ten years experience in hazardous waste management, water quality issues, and mine waste
management. He has been with the Water Resources Control Board for six years as a technical consultant to
the California Regional Water Quality Control Boards and as a developer of ground water monitoring
regulations. Currently, he is developing mine waste management regulations that emphasize the proper
management of acid-generating mine waste.
Prior to working for the State, Mr. Humphreys worked for several consulting firms that specialized in
hazardous waste management and ground water cleanup. He also worked for the United States Geological
Survey on sulfide geochemistry. ',
34
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KJM A. LAPAKKO
Minnesota Department of Natural Resources
St. Paul, MN 55155-4045
Kim Lapakko is a Senior Engineer for the Division of Minerals at the Minnesota Department of Natural
Resources. His work in non-coal mine waste management began at the University of Minnesota, the results of
which are compiled in the Master's thesis "The Kinetics and Mechanisms of the Oxidative Dissolution of Metal
Sulfide and Silicate Minerals Present in the Duluth Gabbro" (1980). Subsequent projects have encompassed five
major areas of non-coal mine waste drainage impact assessment and mitigation: determination of background
water quality; quantification of chemical release from mine waste and description of the subsequent chemical
transport; mitigation of undesirable chemical release; prediction of mine waste drainage quality; and
development of nonferrous mine waste regulations. His recent projects include:
1. evaluation of procedures for predicting acid mine drainage;
2. predictive testing on acid and trace metal release from wastes generated by gold mining;
3. predictive testing for sulfide-bearing waste management at a Minnesota mine;
4. developing an approach for integrating mine waste characterization and mine waste drainage
quality prediction into a regulatory program for mine waste reclamation;
5. conducting laboratory column experiments and a pilot scale alkaline treatment system to
neutralize acidic stockpile drainage;
6. laboratory experiments on the mitigation of waste rock acid generation by incorporation of
alkaline solids;
7. compiling and analyzing laboratory and field drainage quality data for a cooperative project
with the US Bureau of Mines, directed at developing a mathematical model for mine waste
drainage quality prediction.
ANDREW MacG. ROBERTSON
Steffen, Robertson and Kirsten, Inc.
Vancouver, BC CANADA
Dr. Andrew (Andy) Robertson, P. Eng., a Principal of Steffen, Robertson and Kirsten (B.C.) Inc. is
a civil engineer specializing in mine geotechnics and mine waste management. He has over 25 years of
experience in the design or mine waste facilities, and has developed a particular interest and expertise in the
field of acid rock drainage (ARD). Dr. Robertson has written and published twelve technical papers
specifically on ARD.
Now an acknowledged expert in this field, Dr. Robertson has been involved in a large number of key
ARD projects in Canada, the USA, Norway, Sweden, France, Germany, South Africa and other countries
internationally. Dr. Robertson was the principal author for the development of the "Draft Acid Rock Drainage
Technical Guide" for the British Columbia Task Force on ARD, and has lectured extensively in Canada, the
USA, Sweden, the UK and South Africa on appropriate prediction, control and reclamation measures. He has
provided specialist ARD review and mine decommissioning consulting services to a number of national
authorities including the provincial governments of B.C., Saskatchewan and Ontario, and to Norway, Sweden,
35
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South Africa, and the US Bureau of Mines. His consulting to the mining industry includes participation in ARD
prediction and control studies and closure plan development for more than 30 base and precious metal and
uranium mines internationally.
GEORGE R. WATZLAF
U.S. Bureau of Mines
Pittsburgh Research Center
Mr. Watdaf received B.S. degrees in Secondary Physics Education and Mining Engineering, and a
M.S. degree in Environmental Engineering from the University of Pittsburgh. He has worked for the
Environmental Technology group as an Environmental Engineer at the United States Bureau of Mines'
Pittsburgh Research Center for the past twelve years. Mr. Watdaf has been involved in a variety of acid mine
drainage (AMD) research projects. Much of his research has focused on factors that affect the rate of pyrite
oxidation; particularly, pore gas oxygen concentration, iron-oxidizing bacteria, water saturation, and leaching
frequency. He'has also researched AMD treatment alternatives to remove manganese and the chemical stability
of metals in AMD treatment sludges. He has recently become involved in researching the utility of limestone
for treatment of mine drainage under anoxic conditions.
WILLIAM, W. WHITE, m
U.S. Bureau of Mines/SLRC
Salt Lake City, UT 84108
EDUCATION
B.S. in Geology, 1967 University of Utah
M.S. in Geology, 1973 University of Utah
CAREER EXPERIENCE
1979-1988:
1988-1991:
Field Geologist/Project Leader - Mineral Resource Potential Evaluation of Federal Wilderness
Study Areas, U.S. Bureau of Mines, Western Field Operations Center.
Co-Researcher - Investigation of Enhanced Recovery Methods for Refractory Gold Ores, U.S.
Bureau of Mines, Salt Lake Research Center.
1991-Present: Principal Investigator - Geochemical Predictive Modelling of Acid Mine Drainage from Waste
Rock Produced by Metals Mines, U.S. Bureau of Mines, Salt Lake Research Center.
Member of AIME/SME
Registered Professional Geologist, State of Idaho
36
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APPENDIX C
APPROACH TO EVALUATING POTENTIAL FOR ACID GENERATION
AND METAL LEACHING9
Initial discussions with project geologists
Mine rock classification
r
Representative mine rock samples selected in consultation with project geologist
4
Preliminary static testing and geochemical analysis
I
Definition of level of concern for various rock classes
I
Geographical, geological comparisons if information available
Detailed discussions with project geologists to define units from an "environmental
concern" perspective based on lithology, mineralogy, and continuity of zones
I
Develop conceptual mine rock management plan for rock units
~* Take samples from each defined unit using minimum number guidelines
I
Static testing
I
Evaluate static test results and rock classification: Were samples representative?
I
Are units potentially acid generating or leaching?
37
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_ , -> preliminary control measures in mine rock management plan
i ซi*
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Select samples for kinetic testing to define rates of acid generation and leaching
i 4,
I
Kinetic tests to represent conditions with and without control measures
Carry out further tests if required
|
Environmental impact assessment
Ir
Finalize mine rock management plan
I
Approval and operation
Monitoring
38
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