MEND/NEDEM

This report provides a critical literature review on the validity, strengths and weaknesses of studies conducted on acid-generating waste rock dumps. Various topics are covered, including:

• waste rock pile construction;
• migration of solids, water and gas in and around waste rock piles;
• internal reactions in waste rock piles;
• control technologies; and
• waste rock pile decommissioning.

The review demonstrates that groundwater movement through and beneath waste rock piles is the primary pathway for contaminant migration. As the process of acid generation is highly complex, detailed hydrogeological studies are required to understand and predict the migration of acid drainage.

The Database for Acid Rock Drainage (DBARD) for Paradox was developed as a repository for acid rock drainage prediction test data. This user guide describes the design, organization and use of the version of DBARD that was designed to run within Paradox Version 5.0 (for Windows). In this version, reporting capabilities were enhanced to permit the generation of a large number of report formats with many data combinations.

Iron oxidizing bacteria are microorganisms difficult to enumerate using conventional bacteriological methods. A modification of the most probable number (MPN) procedure was developed to improve their enumeration. Assays were conducted with Thiobacillus ferrooxidans strains which all showed comparable results.

Acid drainage from the south waste rock dump at Mine Doyon (Quebec) was first noted in 1985, and levels of contaminants continued to increase through 1988. Although the South Dump does not have high sulphide content (3-5%) it is estimated that 50% of the waste rock dump is composed of highly reactive sericitic schists. An exhaustive monitoring program was initiated in the summer of 1990 which included analysis of leachate coming from below and around the dump. This report provides a compilation of all chemical and mineralogical data from the south waste rock dump at Mine Doyon that was gathered and analyzed between 1990 and 1995.

This report presents an analysis of the thermal data gathered on a weekly basis over two years at the south waste rock dump at Mine Doyon (Quebec). As pyrite oxidation generates heat, the program included six wells drilled through the waste and equipped with thermistor strings reaching the underlying soil and bedrock. Measured temperatures reached up to 65oC halfway through the 30 metre thick waste rock dump. Since air convection seems to be the main mechanism responsible for the high acidic drainage production rate in these waste rocks, a conceptual model of air convection patterns within the dump is proposed based on the available monitoring data.

This report presents hydrologic data from various characterization programs at Mine Doyon (Quebec). A preliminary analysis of the hydrologic processes at the south waste rock dump is also provided. Classical and innovative methodologies for monitoring hydrological processes at Mine Doyon are presented, along with a comprehensive water budget of the south waste rock dump.

French report: This report presents the results of a two-year investigation of the impact of acidophilic iron-oxidizing bacteria in the south waste rock dump at Mine Doyon (Quebec). An innovative bacteria trap device was developed and used in this study. The traps, which included particles of pyrite, sphalerite, chalcopyrite or sulphur, were used to attract and collect microorganisms in the sampling wells.

Iron oxidizing activity was shown to be particularly important in sections of the dump where bacterial growth temperature is optimal, pH lies between 2 and 3.5 and porosity permits aeration. The results also show that the fairly high temperature inside the dump does not prevent bacterial colonization and activity. Notably, T-ferrooxidans, along with some other unidentified strains, are able to oxidize sulfur and sulfides to sulfuric acid in an anoxic environment under 30 m of rocks.

This report presents a summary of monitoring and modeling of acid rock drainage from the south waste rock dump at Mine Doyon (Quebec), which was conducted between September 1991 and December 1993. The main purpose of the study was to measure physical and chemical properties of an actual waste dump and to identify the key processes contributing to the generation of acid rock drainage – namely: hydrology, geochemistry, microbiology, and physical processes such as oxygen, mass, and heat transfer. New information on numerical modeling of acid mine drainage production in waste dumps is provided in the report.

The south waste rock dump at Mine Doyon (Quebec) has been generating acidic drainage since 1985 (two years after the dump was started). Between 1991 and 1994 the south dump has been the subject of extensive investigations and studies. One of the more important objectives of these studies was to measure physical and chemical properties of an actual waste dump and to identify key processes contributing to the generation of acidic drainage.

This report presents peer review commentary on the Mine Doyon studies conducted between 1991 and 1994. The peer review assessed five separate technical components:
i. hydrology;
ii. geotechnical and hydrogeology;
iii. geochemistry and mineralogy;
iv. microbiology; and
v. predictive modeling.

The overall conclusion of the peer review is that the Mine Doyon study has provided a new understanding of some specific technical issues and represents a thorough and exceptionally well-documented case study. The peer review also identified a number of inconsistencies and occasional technical errors in the reports which should be corrected. Finally, the review indicated that electrical conductance can be monitored continuously and used to detect changes in water quality.

La halde de stériles sud de la Mine Doyon, Cadillac, Québec est génératrice de drainage minier acide depuis 1985, soit deux ans après le début de son utilisation. La génération d’acide a progressivement augmentée de 1985 à 1988 et depuis 1988, la halde sud génère un drainage très acide qui est présentement capté et traité […]

This User’s Guide is for MINEWALL 2.0 – a program designed to assist users in predicting water chemistry during operation and closure at simulated open-pit mines and underground workings. The fundamental objective of MINEWALL 2.0 is to provide a flexible tool for forecasting geochemical conditions in a mine. This User’s Guide provides installation instructions and detailed instructions for using MINEWALL 2.0.

MINEWALL 2.0 is a computer program for predicting water chemistry in mines and to assist with predictions for complex scenarios. This report presents the results of a literature review of relevant theory, test-work, and case studies that were considered in designing MINEWALL 2.0. This information is combined into generalized conceptual models that define and summarize each important factor in the simulation of open-pit and underground mines.

This report presents water chemistry results at three BC mines as simulated using the computer program MINEWALL 2.0. Input data was largely drawn from company reports; other input values were estimated or obtained by fitting monitoring data to simulations of current conditions. This report illustrates the importance of various input data and the strengths and weaknesses of the MINEWALL 2.0 computer program. Challenges with the program largely relate to sampling for the purposes of obtaining representative data.

This report presents the results of a laboratory test program conducted on tailing and waste rock samples from Canadian mines. The goals of the program were to:
• evaluate and compare prediction methods of the formation of acidic drainage in mine wastes;
• evaluate the reliability of prediction methods to actual field behaviour at mine sites; and
• recommend prediction methods most suitable for laboratory and field use.

The study concluded that confident prediction of acid mine drainage is not likely to be achieved in a single test. Static tests are recommended for initial screening of samples, followed by some form of kinetic weathering test to confirm the initial prediction and to provide drainage quality and kinetic data. The static test procedures showed the importance of determining sulphate sulphur content. Choice of method can be made by comparing simplicity, time and equipment requirements, cost, ease of interpretation and correlation with the field data. The mode of waste deposition in the field can also affect the choice of test used.

This Manual provides background information on the generation and prediction of acidic drainage. It offers a guide to the components necessary for carrying out and implementing a prediction program. Detailed descriptions of field and laboratory static and kinetic prediction tests are provided, including their objectives, test principles, equipment and reagent requirements, test procedure implementation and reporting of results, and associated advantages and disadvantages.

Deficiencies of ABA procedures were investigated. These included the quantity of acid from pyrrhotite sulphur compared to pyrite sulphur, overestimation of potential acidity due to oxidized sulphur, and overestimation of neutralization by calcium carbonate, siderite (FeCO3) and silicate minerals. Methods were tested to eliminate or reduce these deficiencies.

This report presents the results of an evaluation of static test methods used for determining the neutralization potential (NP) of mining waste in acidic drainage prediction. The methods evaluated include: Sobek method, Modified Lawrence method, methods based on inorganic carbon content, and the Lapakko method. Special attention was given to the Sobek “fizz” test, and to the effect of mineralogical composition for interpreting NP results. The study showed that if the fizz test was erroneously interpreted, and more acid added than required, the NP values were much higher than if the correct amount of acid was used. The authors also propose a supplemental method for determining NP based on calculated mineralogical composition and mineral reactivity.

This report presents the results of a study evaluating the accuracy of acidic drainage prediction data against on-site water quality. The study involved extensive testing of tailings samples using standard and modified acid-base accounting methods; differences in neutralization potential results for different procedures were documented. The Neutralization Potential (NP) method described in MEND 1.16.1a is recommended due to over-estimation of NP using the Sobek method.

This study was based on the Database for Acid Rock Drainage (DBARD) and a detailed analysis of the tailings impoundment at the Gibraltar-McLeese Operations in BC. The evaluation of the database showed that ABA (Acid-Base-Accounting) results do not correlate with mineral deposit types and thus sites with similar geologic or geographic settings cannot be directly compared. This finding may, however, partly reflect a limitation of the database since it was not possible to screen out results caused by severe sampling biases. Nevertheless, experience from other sites can aid new sites in developing waste characterization programs. Based on the study results, recommendations are provided for analyses, data manipulation, interpretation criteria, and reporting of acidic drainage prediction data for the different stages of waste characterization – namely: mineralogical characterization, static testing, and kinetic testing.

This report is the final report of a four-year study of the Waite Amulet tailings site, in Quebec. The influence of various factors (gaseous oxygen and carbon dioxide concentrations, temperature, bacteria, sulphide content and pH) on acid generation are discussed, along with unsaturated and saturated zone pore water geochemistry, tailings hydrogeology, and surface hydrology. The study verified that the most important control on the pyrite oxidation process is the availability of oxygen.

The report also provides results of simulations of pore water flow by a two-dimensional steady state finite element model and discusses the evolution of acidic pore waters at the tailings site. Finally, the authors provide recommendations for future tailings impoundments, such as the promotion of high water tables by selective placement of fine-grained tailings across the site. Coarse-grained material, such as rock fill, should generally be avoided in tailings dam construction. Horizontal flow should be promoted by selective placement of horizontal fine-grained layers across the area of the tailings deposits.

This report presents the results of tests conducted at the Cinola Gold Project on the Queen Charlotte Islands in BC. These tests, which evaluated the long-term weathering of waste rock, were carried out on three different scales: humidity cells, leach columns and on-site waste rock pads. The trends in the waste rock pad tests were less apparent than in the other tests due to annual flushing events related to late summer and fall rainfall. Weathering rates were comparable when corrected for the differences in particle size.

The study showed that although limestone addition delayed full acid generation and release of copper and iron, significant zinc loads may be released in pH-neutral drainage several years before acid drainage is produced. The study also showed that small and large-scale tests produced similar results for quantitative long-term trends, sulphide oxidation reaction kinetics and average sulphate release rates. Tests results were dissimilar, however, for metal release rates. The authors note that these conclusions apply to the Cinola deposit, where sulphide mineralogy is relatively simple.

This report describes the results of a research project aimed at providing a quantitative analysis of the interrelated elementary chemical and physical processes responsible for pyrite oxidation and acid rock drainage in waste rock piles. The main objective was to determine the simple scaling laws that govern the geochemical and thermodynamic behaviour of pyritic rock in waste rock piles. The report presents a scaling parameter that combines information on pile porosity, pile size, effective reactive surface area, temperature dependence of the rate of pyrite oxidation, oxygen diffusion in the gas phase, heat of the pyrite oxidation reaction, thermal conductivity of waste rock, and ambient temperature. The strong decrease of dissolved oxygen concentration with temperature is also included in the model. The scaling analysis may, after further modifications and calibration, help to properly design and manage waste rock piles and dumps. An important conclusion of the work was the finding that the shrinking core model was predicted to underestimate oxidation rates.

This Manual provides a comprehensive overview and technical explanations on the methods, properties and processes involved in the prediction of drainage chemistry. The objective is to provide the necessary information required by experts and non-experts alike. A recommended flow-chart is provided for the prediction of mine site drainage chemistry, with references to relevant chapters of the Manual.

This Manual seeks to improve the practice of metal leaching and acidic drainage prediction. It provides a tool-box of procedures for laboratory analysis and data interpretation, along with a proposed framework for acid rock drainage testing. Final decisions on required tests and analyses are site-dependent; however, some generic tests are almost always required to provide the necessary information. This Manual provides detailed methodologies for analyses that may not be standard laboratory procedures. Critical guidance is provided on the methods, the manner in which they are used and reported, and their limitations.

The Reactive Acid Tailings Assessment Program for Base Metal Tailings (RATAP.BMT) was developed as a predictive modelling tool to:
• investigate the factors and processes that control the oxidation of sulfide minerals;
• simulate acid generation in mine tailings;
• estimate the long-term potential for acid generation in tailings; and
• evaluate the effects on acid generation of alternative closeout concepts.

This report describes the extension of the model validation by way of:
• quality assurance procedures followed during each stage of code development;
• documentation of recent code modifications;
• a critical review of the concepts behind the program; and
• a comparative evaluation of computer simulations with a more complete database for the Waite-Amulet zinc/copper mine tailings.

The authors note that although RATAP.BMT addresses more numerous and complex questions than other models, the tool also requires a more knowledgeable user.

This report presents the notes from a workshop on the modelling of reactive tailings held in Haliburton, Ontario between May 23 and 24, 1990. The discussion centered on the simulation program Reactive Acid Tailings Assessment Program (RATAP.BMT1) – a modelling program developed by CANMET to assess acid flux from base metal tailings. Presentations included perspectives on the use of models from consulting engineers, industry and regulatory agencies. Representatives of the US, Sweden and Australia also presented their thoughts. The report includes a summary of each presentation and the associated question and answer period.

Pyrite and pyrrhotite are the most abundant sulphides in mine wastes worldwide. However, unlike pyrite, there is a significant deficiency of information on the weathering reactions and the controls on pyrrhotite reaction rates. This report seeks to fill this gap by presenting results of a study into the kinetic controls on pyrrhotite oxidation. The effects of crystal structure, metal impurities, surface area, and bacterial catalysis on oxidation reaction rates are studied. In addition, the dynamics and effects on water quality of pyrrhotite oxidation in tailings column studies are assessed. The results are used to develop a modelling approach consistent with the mechanisms and controls on pyrrhotite oxidation reactions. Part of the work was conducted on pyrrhotite concentrate obtained from Inco’s Clarabelle Mill (Sudbury).

The results indicate that characteristics of pyrrhotite, such as metal impurities and crystallographic form, do not significantly affect oxidation rates. The surface area of the pyrrhotite particles is by far the most significant parameter required to assess oxidation rates for pyrrhotite in tailings. Small uncertainties in reaction kinetics will not significantly affect long-term predictions for tailings oxidation when both kinetics and oxygen mass transport are considered in geochemical modelling.

Oxidation of pyritic waste rock and the subsequent generation of acid mine drainage is controlled, to a large extent, by the availability and transport of oxygen to the reaction sites. An understanding of the interaction of the gas transfer mechanisms within a waste rock pile is thus key to developing cost effective management strategies to control acidic drainage.

This report describes the various techniques and procedures proven to be effective for measuring the principal parameters required to define gas transfer within a waste rock pile: thermal conductivity; gas diffusion; and gas permeability. Techniques and procedures are provided for monitoring temperature and oxygen concentrations within the pile; these measurements can provide insight into the oxidation process and the pollution potential from waste rock material. Finally, details are provided on field installations and procedural guidelines for the measurement and monitoring of these gas transfer mechanisms in waste rock.

This report presents the results of a study aimed at developing an understanding of the processes governing the pyrite oxidation rates in acid waste rock piles at the Heath Steele Mine in New Brunswick. Field monitoring and the numerical model FIDHELM were used to quantify these processes and to evaluate the effectiveness of the composite soil cover for acid waste rock management. A user’s manual for FIDHELM is included as an appendix. FIDHELM was shown to be a useful tool to assess the various gas transfer mechanisms in pyritic waste rock piles.

This study investigated a method for predicting water quality from old mines to assist with closure planning. In particular, it evaluated an empirical approach for predicting concentrations of metals in waste rock dump leachate using pH. The major problems encountered with the empirical models were outliers and excessive positive skewness, variable detection limits, non-normality of residuals, departures from linearity and sub-populations. The study investigated refinements to the approach by considering the application of other (multivariate) statistical methods. Five waste rock piles were selected in an effort to expand the application of the proposed empirical approach to other types of mines and mineral deposits. These five piles were from: Doyon (Quebec); Eskay Creek (BC); Cinola (BC); Sullivan (BC); and Vangorda (Yukon).

This report provides a simple characterization scheme for mineral deposits based on their mineral composition. A method is also provided for calculating Neutralization Potential (NP) based on mineralogical composition. Several common types of metallic mineral deposits occurring in western Canada are ranked according to their acidic drainage potential. As the mineral assemblages around an orebody generally reflect its acidic drainage potential, a formula is suggested for assessing acidic drainage potential based on field estimates of mineral abundance. The results of an experiment conducted to determine the relative weatherability of common sulphide minerals are also presented. Finally, a practical checklist for field assessment of acidic drainage potential during mineral exploration is suggested, and the tasks of a geologist in acidic drainage assessment at different stages of mine pre-development are described.

This study investigated a 5 million tonne waste rock pile at the Whistle Mine site near Sudbury, Ontario. The intent was to develop and illustrate technology for evaluating waste rock piles and to provide a database of information for characterizing waste rock. The study entailed data collection and compilation of the acid mine drainage characteristics of the Whistle Mine waste rock pile. Although the database is quite extensive and should be useful for supporting other investigations, there are several difference between the Whistle Mine waste rock pile and waste rock at other mines.

The differences between leachate produced from the column test and from the waste rock pile illustrate that caution should be taken in applying the results of short-term kinetic tests to longer term behaviour of waste rock. In addition, the absolute rate from columns can be much greater than that observed in the field due to high proportion of finer, more reactive material in the column, and accelerated rainfall cycles. The following data is of critical importance for an assessment of waste rock dumps:

• structural parameters of the dump;
• acid generation potential of the waste rock; and
• a detailed site water balance.

This report is a critical review of geochemical processes and models adaptable for the prediction of acidic drainage from waste rock. It describes the geochemical processes that occur in acid-generating waste rock piles and evaluates the ability of geochemical computer models to simulate geochemical processes in order to predict acidic drainage quality. The geochemical processes that most control acidic drainage quality are: precipitation and dissolution, chemical diffusion, and surface reactions. Drying and wetting are the most important physical processes that affect water chemistry. These processes affect water chemistry by concentrating aqueous solutions such that solids precipitate, and subsequently dissolving and removing these solids from solution contact. Field data required to describe geochemical processes in waste rock include:

• detailed water analyses;
• rock mineralogy and trace element chemistry;
• exposed surface area;
• temperature;
• oxygen availability;
• water infiltration rates; and
• thermodynamic data.

Existing geochemical models are divided into five classes: equilibrium thermodynamic models, mass transfer models, coupled mass transport-mass transfer models, supporting models, and empirical and engineering models. Each class addresses a different type of ARD prediction objective.

This report provides quantitative and qualitative information on mass transport and water infiltration within a waste rock pile. It documents the geochemical and physical characteristics of the 100,000 tonne valley-fill waste rock dump at the Eskay Creek Mine (BC), from its origin in underground workings in the early 1990’s to its disassembly and placement underwater in a nearby lake in 1995. The dump is confined along its axis by valley walls that direct runoff into it. A creek often flowed into and through the dump, enhancing the flushing and removal of acidity and metals from the dump. The dump was also found to contain fine grained material that limited infiltration; isolated pebbles, however, were found to have a significant role in enhancing infiltration.

Despite a significant amount of reactive neutralization potential within the dump, acidic drainage appeared within two years after the first rock was dumped. Mass-balance calculations indicated that only roughly 10-20% of total neutralization potential (NP) was consumed before acidic drainage began. This may have been caused by physical factors such as channelling or stratification within the dump. The study also demonstrated that geochemical processes are dependent on physical factors such as channeling or stratification within a dump.

This study provides a quantitative analysis of the interrelated elementary chemical and biological processes responsible for pyrite oxidation and acidic drainage. The study sought to determine whether the chemical reactions involved in multistage oxidation of pyrite lead to irregular or chaotic in-time changes of products from the chemical and microbial reactions responsible for acidic drainage. The model analysis shows an absence of such an irregular temporal behaviour. Further, the nonlinear nature of the elementary non-equilibrium processes was found to be responsible for the presence of the quasi-equilibrium values of the concentrations of ferrous and ferric iron – a property that is a key to understanding the complexity of acidic drainage and should be helpful in designing efficient ways of minimizing acidic drainage.

The report also provides a kinetic model, in the form of coupled nonlinear ordinary differential equations, that was constructed for the coupled chemical reactions responsible for acidic drainage. The equations describe the time dependence of the concentrations of the hydronium ions, ferrous and ferric iron, sulphate and oxygen dissolved in water. Quantitative results presented in this study should be confronted with field data and, after calibration, the kinetic model can be used as a part of a comprehensive physical waste rock model and an underwater disposal model.

This report presents the results of an in-depth study into the basic acidic drainage reactions. Models of the nonlinear kinetics of chemical reactions present in neutralization and acid production are provided for both homogenous and porous media. Finally, conclusions are drawn on the predictability of these nonlinear processes.

In this report, the applications of the following two acidic drainage control technologies at mines in northern Canada are considered:
• role of ice and snow cover on water covers used for disposing reactive tailings; and
• role of permafrost for the long-term management of acid generating tailings.

The impacts of cold temperature conditions on the water cover scenario were modelled. Impacts of reduced temperatures, ice formation and breakup, and snow cover were considered. The effectiveness of saturating tailings to limit the oxygen influx was calculated to decrease as the temperature lowered. It is suggested that ice scouring, and the resultant disturbance or re-suspension of deposited tails, is the most negative impact related to the application of water covers in the north.

Permafrost offers another option for management of acidic drainage in northern Canada. The characteristics of permafrost related to the active freeze-thaw layer, material transport, freeze-thaw cycles, potential for frost heave, and its use in tailings management are discussed in the report. Permafrost, while a promising factor in the management of sulphide oxidation and migration of acidic drainage, will not provide an absolute control to production of acidic drainage.

This report provides perspectives on issues, strategies, and research requirements for disposing potentially acid generating mine tailings and waste rock in a permafrost environment. The report briefly discusses mines in northern Canada for insight into acidic drainage production in mine tailings. It also describes the processes related to acidic drainage in cold climates and control strategies for acidic drainage in permafrost. Freeze control of tailings would appear to be a viable strategy; however, there is a need for more cost effective insulating cover designs and a more thorough understanding of frozen tailings thermal properties. Finally, a program for researching freeze control of mine tailings is scoped out in the report.

This study investigated leaching of tailings at low temperatures to simulate the effect of placement of a waste rock cover on the tailings and expected seasonal freeze-thawing of the tailings. Cold temperature column leaching tests at 2°C and 10°C were conducted for Cullaton Lake tailings to evaluate their oxidation and leaching characteristics at low ambient temperatures. The low temperature leaching studies were designed to simulate conditions similar to those expected within the Cullaton Lake tailings after the implementation of a decommissioning plan which entails covering the tailings with approximately 1.5 m of waste rock and overburden. This cover is intended to promote freezing and permafrost conditions within the tailings. This report is the second in a series of reports that recommends methods of safely decommissioning tailings and waste management facilities at the site.

Encapsulation in permafrost is more appropriate than a water cover in the Canadian North due to high evaporation rates in most of Canada’s permafrost region and higher construction, inspection and maintenance costs related to remote site locations. To successfully encapsulate tailings and waste rock in permafrost, a cover must be placed over them to prevent thawing of materials near the surface.

This report presents case studies of cover tests pads constructed over reactive tailings in continuous permafrost at four separate sites. The studies suggest that the dominant factors governing the thickness of the active (thaw) layer are: air temperature, water content, surface vegetation, slope orientation and colour. The author suggests that for permafrost encapsulation, the ground temperature at a depth of zero annual amplitude should be at least -2oC. Under present conditions, encapsulation of tailings is generally feasible northwest of the MacKenzie River, across all of Nunavut and in the northern region of Quebec. With global warming trends, however, permafrost encapsulation in some of the northern regions of the Northwest Territories and Quebec may not be sustainable in 100 to 200 years.

This report examines phenomena that could affect the performance of soil covers on mine wastes located in cold regions. Although soil covers are widely used in mine applications, soil cover design and construction practices are largely based on experiences in temperate regions that do not take into account many potentially important features and processes common in cold regions. These include: ground freezing, ground ice formation, ground thawing, freeze-thaw cycling and cold region hydrologic phenomena. Although the rates of these processes can be slow, they can still be fast enough to have significant effects over a cover design’s life. This report discusses industry experiences with cold region covers, offers guidance on cover selection, design and construction considerations, and examines frozen ground, hydrologic and other effects on cover performance.

This report presents the results on a series of tasks completed to study covers in cold regions – specifically:

• cold regions identified in MEND report 1.61.5a are characterized with regards to their ability to affect the performance of various types of soil covers;
• the role of vegetation on cold region covers is reviewed;
• literature on cold region evapotranspiration and rooting depth are surveyed;
• available computer models are discussed;
• possible applications of convective cooling is considered;
• the potential for insulating layers to limit freeze-thaw effects on low-permeability barrier layers is examined; and
• ongoing soil cover trials or research programs are identified and information from them compiled in table format.

Finally, the authors provide recommendations for additional studies into mine waste covers in cold regions.

Aboriginal Affairs and Northern Development Canada (AANDC) is responsible for the remediation of a number of abandoned mines in northern Canada. Several of these mines require soil covers to be constructed over reactive tailings and waste rock. This Guidance Document outlines:

• the current state-of-knowledge on soil cover system design in cold regions;
• AANDC’s expectations on how a cover system design should be conducted; and
• a summary of information that AANDC expects to receive during the design process so that it can make an informed decision.

Case studies are also included to illustrate practical application of cover systems in cold regions. The information presented in this report is relevant to both abandoned mines and to mines operating in cold regions that are developing their closure plans. Other groups, such as Aboriginal peoples and non-governmental organizations (NGOs), may also find this document of assistance to their review of proposed cover designs.

This report presents a compilation of data collected over ten years on low temperature effects at several sites. This data was collected as part of a larger project intended to increase the understanding of mine waste behaviour under cold conditions and to evaluate opportunities to exploit low temperatures for control of acid rock drainage. Research is compiled on eight specific mechanisms that are expected to occur differently at low temperature, or are unique to low temperature conditions:

• oxidation rates of iron sulphide minerals;
• oxidation rates of other sulphide minerals;
• activity of different types of bacteria;
• solubility and reactivity of acid buffering minerals including carbonates and silicates;
• formation and solubility of secondary minerals (weathering products);
• freeze concentration effects;
• physical exposure of minerals due to freeze-thaw processes; and
• solubility of oxygen in waters used to flood reactive wastes.

Data on the reactivity of iron sulphides at low temperatures indicated rate reductions at low temperatures. Other data clearly indicated that bacteria adapt to low temperature conditions and can be active at sub-zero temperatures. Blending of waste rock was identified a possible way to limit ARD because carbonates are more soluble at lower temperatures. It was also noted that the solubility of carbonates at lower temperatures causes greater solubility of heavy metals (e.g. zinc and cadmium). As the data demonstrating the effects of low temperatures are sparse and indicate site-specific effects, it is recommended that mine-site characterization test work and larger scale experiments be completed.

This report provides a high-level risk analysis of the impacts of climate change on ARD at Canadian mines. This assessment builds on previous work by looking more closely at the impacts for specific infrastructure elements and determining which of these impacts are most likely and significant for mining operations and for society. Specific risks contemplated include extreme weather events, changes in precipitation patterns, permafrost degradation, and drought conditions. The impact of these are then considered on water management and waste impoundment structures, and on the hydrologic / hydrogeologic / geochemical conditions affecting the flow of water and contaminants at mine sites. The authors highlight the importance of early planning and design of infrastructure and climate change adaptation measures to withstand long-term climate change conditions.

This report presents lab results on research into the thermal properties of mine waste materials (waste rock and tailings), with a focus on the thermal conductivity and unfrozen water content of saturated mine tailings samples. Tests were conducted on samples collected from the Wellgreen mine in the Yukon (discontinuous permafrost zone) and the Lupin mine in the Northwest Territories (continuous permafrost zone). The unfrozen hydraulic conductivity and the amount of unfrozen water provide an indication of the order of magnitude decrease in hydraulic conductivity that is realized after freezing. Estimates of frozen hydraulic conductivity are also reviewed in this report.

This report compares pre-approval acidic mine drainage modeling predictions, actual monitoring data and post-development modeling predictions at the Vangorda and Grum mines. These two open pit mines operated in the Yukon between 1990 and 1998. Monitoring programs during mine operation and after closure tracked water quality throughout the site.

Pre-development and post-operational models assessed receiving water quality by utilizing water and contaminant load balances that incorporated contaminant loads from key sources. The modeling approaches relied on empirical data for predicting the long-term geochemical performance of source materials, and considered the results of humidity cell tests for confirmation purposes. In both cases, the humidity cells predicted worse conditions than the empirical-based models. The empirical approach for predicting waste rock contaminant loads appeared to substantially underestimate loading in conditions where the empirical data was not reflective of well-developed acidic mine drainage conditions.

The study indicated that modeling results are most sensitive to the predictions of contaminant concentrations from key load sources, though flow rates through waste rock materials are also important. Caution should be taken in relying on seepage data from existing facilities as an empirical input for modeling. Changes in mine plans and failure to effectively implement key mitigation measures can lead to significant increases in contaminant loading above those predicted in modeling exercises. As mine development progresses and mine design evolves, water quality predictions need to be verified and updated based on monitoring data.

Although the focus of environmental management over the past two decades has been on acidic drainage, acid or low pH conditions are not necessary to cause impaired water quality, and many chemicals that are not necessarily related to acid generation can represent environmental risks when leached from mine waste. To begin to address this gap in knowledge, this report provides a background discussion on neutral drainage associated with mine wastes, identifies key issues and chemical elements of interests, and discusses treatment considerations for neutral drainage. A special focus is placed on neutral drainage issues associated with arsenic, molybdenum, nickel, selenium and sulphate.

Selenium and molybdenum are naturally occurring trace elements that are often released to the environment at relatively low concentrations as a result of mining discharges. The regulatory limits for selenium and molybdenum follow a risk-based approach involving numerous assumptions that are multiplicative in their conservatism. While these limits will ensure environmental protection, they are likely overly restrictive for most sites. A more site-specific approach to resolve effluent limits, based on ecological risk assessment, is advisable in most cases.

This report provides a review and summary of the general characteristics of selenium and molybdenum, including typical source characteristics, environmental fate and transport, and potential health effects. This information is integrated with mine-related release scenarios for locations with differing geology, which highlights the need to frame the complete assessments of selenium and molybdenum releases within a site-specific risk assessment (SSRA) framework. For selenium, the SSRA needs to consider virtually all environmental transport processes and pathways that may ultimately be linked to the environment and food web. Conversely, for molybdenum, the SSRA process is not likely to require the same level of detail and pathway delineation. This is primarily because molybdenum exhibits a much lower propensity to bioaccumulate than selenium, and exposure via the food web is typically low relative to toxicity thresholds. The SSRA framework should be part of an overall management plan that includes appropriate site characterization, release planning, and targeted and effective environmental monitoring programs.

This report provides a summary on current practices in the geochemical characterization of paste backfill, and on methods used to predict environmental impacts to surface and groundwater quality associated with the application of paste backfill in underground mine workings. To date, research has focused on the structural characteristics of paste to meet the required backfill strength using the most economic amount and mix of binder materials. In light of the belief that the chemical reactivity of tailings and the volume of leachate generated are reduced by thickening, and by the addition of alkaline additives such as cement, little information on the influence of paste backfill on mine water quality has been developed.

The general theories associated with paste backfill characteristics and geochemical reactivity appear sound, but there does not appear to be much field validation on the actual influence of key parameters. Further research is needed on the specific components of paste theory, examination of scale-up issues, collection of detailed case studies, and additional monitoring of mine waters to assess the influence of paste backfill on mine water quality over time. The lack of detailed information currently available is of concern, and highlights the need to compile detailed site data and monitoring data for future assessment and validation of predictions currently being initiated.

Selenium (Se) and nitrogen compounds represent constituents of environmental concern at coal mine operations in the cordillera of western Canada. There are data to indicate that, in some environments, nitrate (NO3) can affect both the oxidation and attenuation of Se. In order to provide more insight into the links between NO3 and Se in coal mine settings, a two-phased assessment was conducted: 1) literature review of information relevant to the interactions of NO3 with Se; and 2) compilation and assessment of drainage chemistry data for eight mines in British Columbia.

The analysis was used to examine three biogeochemical mechanisms by which NO3 may be linked to Se leaching, mobility, and attenuation. These included: 1) concurrent microbially-mediated reduction of NO3 and Se; 2) inhibition of Se reduction by NO3; and 3) Se mobilization via the direct oxidation of Se-bearing minerals by NO3. With regards to concurrent NO3 and Se attenuation, waste facilities characterized by anaerobic environments facilitate the removal of both Se and NO3 from solution through microbially-mediated reduction reactions, producing water compositions with relatively low NO3 concentrations and low Se:SO4 ratios. In terms of NO3 as a potential inhibitor of Se reduction and as an oxidant of reduced Se, the analysis suggests these processes may have relevance in coal mine environments, although the scale and magnitude of such influences are uncertain.

This report presents the results of a literature review on subaqueous disposal of reactive mine wastes. This study was completed based on a comprehensive review of all aspects of subaqueous disposal of reactive mine wastes in a freshwater environment, both theoretical and applied. Various literature sources were reviewed, along with relevant case study data where available. While emphasis was placed on the BC experience with underwater disposal practices, attention was also given to other parts of Canada and the United States. In addition, although the scope of this study is confined to freshwater (i.e. lake disposal), the literature review includes documentation on land-based tailings and leach dumps or heaps insofar as they contained data relevant to subaqueous disposal. Similarly, results from marine disposal operations are only included where such work illustrates principles which are applicable universally to aquatic systems.

Of all the conclusions drawn from this study, perhaps the most salient is that acidic drainage poses serious disadvantages for land-based disposal of reactive mine wastes whereas the underwater disposal of such wastes holds considerable promise for suppressing acid generation. Nevertheless, the potential long-term impacts associated with subaqueous disposal remain poorly understood. In addition, the complex processes of bioavailability of metals in lake-bottom sediments and bioaccumulation in the freshwater food chain are not well understood, particularly with regard to reactive mine waste disposal. Based on their review, the authors offer several recommendations for evaluating the suitability of future underwater waste disposal strategies.

The Benson Lake Coast Copper Mine operated from 1962 to 1973. During mine operation, tailings were discharged into Benson Lake. Tailing deposition occurred into progressively deeper waters to combat a continuing problem with lake turbidity caused by colloidal suspension of tailing fines. Field studies by the Environmental Protection Service in 1967 and 1973 found that the entire lake bottom was covered by tailings and devoid of benthic life.

This study constitutes the initial stage of a field assessment of the lake’s recovery from subaqueous disposal of reactive tailings. The 1989-90 work, presented in this repot, included mapping of the lake’s bathymetry and establishing staff and crest gauges as well as discharge sites on inlet and outlet streams.

This report presents the results of a preliminary field assessment of the effects of subaqueous disposal of tailings in Anderson Lake, Manitoba. The lake, a small and shallow Precambrian Shield waterbody with high biological productivity, has received approximately 7.5 million tonnes of tailings since 1979 from the Snow Lake mill. The lake is characterized by higher conductivity, dissolved solids and sulphate concentrations, as well as increased hardness since tailings discharges began. The pH has also generally decreased, and dissolved metal concentrations and turbidity have increased in the area near the discharge. Stations where tailings have been deposited in the past are developing an organic layer that is biologically active. Detailed analyses were performed to characterize the sediment and tailings. Tissue- concentrations in the stickleback suggest bioaccumulation of copper, lead and zinc. Metal levels in the fish were also significantly higher in populations from the tailings deposition area.

This report presents the results of a preliminary field assessment of long-term subaqueous disposal of reactive mine wastes in Mandy Lake, Manitoba. Mandy Lake, a shallow lake in the Precambrian Shield, received approximately 73,000 metric tonnes of high-sulphur-base metal tailings discharged from a single launder into the lake in 1943-1944.

In this study, lake water quality, sediments, aquatic vegetation and fish in the lake were mapped and samples collected for metals analyses. Elevated metal concentrations were found in the lake sediments, particularly for arsenic, copper, lead, mercury and zinc. However, decomposition of the thick organic layer overlying the sediments appears to maintain anoxic conditions, thereby reducing the potential for sulphide oxidation and subsequent release of acid-soluble metals. Since 1975, vegetation in the tailings area has become more diverse and comparable to other areas in the lake, In addition, fish sampling has revealed a healthy population.

This report examines the waters and sediments of the south basin of Buttle Lake, BC (the site of an inactive submerged tailing deposit) to assess the long-term environmental feasibility of subaqueous disposal of mine tailings. The Cu, Zn and Pb-rich mine tailings were deposited in the lake via a submerged outfall from 1966 to 1984. At present, the tailings are widespread across the basin and are being covered by a thin veneer of natural sediments.

This report presents a detailed study of the distributions of metals in both the solid phases and interstitial waters of the sediments, as well as in the overlying surface waters. Water quality sampling and reviews of past data indicate a considerable decrease in metal concentrations. This corresponds with a reduction in metal loadings from Myra Creek caused by the implementation of a water collection and treatment system in 1983. However, although metal concentrations of zinc, copper and cadmium have decreased, they occasionally exceed provincial objectives proposed for the lake, particularly at depth. Metal concentrations vary seasonally and the highest levels are found during the winter months when observed concentrations were also higher at depth.

This study examines underwater storage of tailings as a long-term disposal option. To assess the viability of this option, the chemistry of interstitial waters and the associated solid phases in tailings and natural sediments in Anderson Lake, Manitoba, was studied. Anderson Lake has been used as a receiving basin for tailings since 1979 and tailings are areally widespread across the lake.

Cores were collected in June 1990 and processed to extract interstitial waters. High dissolved Zn, Cu and Pb concentrations in supernatant water confirmed prior measurements indicating elevated concentrations of these metals in the lake water. The concentrations of all three elements decrease abruptly with depth. This indicates that both the tailings and natural sediments are acting as sinks for metals, rather than as sources. Thus, at present, the deposited tailings are not releasing metals to the overlying lake water. In the post-discharge future, the tailings will likely be progressively covered by a blanket of organic-rich natural sediments which will preserve the anoxic conditions. The authors conclude that it is thus unlikely that the tailings on the lake floor will support a benthic efflux of metals to Anderson Lake water.

This study examined the chemistry of interstitial waters and the associated solid phases in tailings and natural sediments in Mandy Lake, Manitoba. Mandy Lake was used as a receiving basin for tailings in 1943 and 1944. Tailings are widespread in the small lake and still occur in significant concentrations in surface sediments (top 5 mm). Two cores were collected in June 1990 and processed under nitrogen to extract interstitial waters. Based on the sample analyses, the authors conclude that the tailings on the floor of Mandy Lake show very little or now evidence of chemical reaction 46 years after discharge.

Pyrite-rich mine tailings from the Coast Copper mine were discharged into Benson Lake from 1962 to 1973. The tailings in the central basin of the lake are now covered with 30 cm of natural organic-rich sediments containing about 7 wt. % organic carbon. Nearby Keogh Lake is in a different watershed and never received input of any mining-related discharges. One sediment core from each lake was collected and processed under nitrogen to extract interstitial waters. High-resolution profiles of dissolved Zn, Pb and Cd in the pore waters of both lakes show that concentrations of these metals decrease across the sediment-water interface, and are invariably lower than the levels measured in core-top (bottom) water. The results show no evidence of a benthic efflux of dissolved copper from the sediments to bottom waters in Benson lake despite the fact that the “natural” sediments accumulating at present, and progressively burying the tailings, still contain higher concentrations of solid-phase copper than would be expected in a pristine basin.

This report examines whether the chemical and biological reactivity of mine tailings is inhibited by underwater storage. The water quality, geochemical conditions of sediments and biotic communities in Benson Lake, BC were studied. Benson Lake, a small, deep, oligotrophic coastal mountain lake, was used as a tailings repository for approximately eleven years before operations ended in 1973. The tailings deposition eradicated all benthic invertebrate life. Tailings deposition also resulted in elevated levels of zinc in the water and in the flesh of fish taken from the lake.

In September 1990, more than 17 years after cessation of tailings disposal, physical and chemical water quality sampling conducted at three stations in the lake indicated that lake water was similar to the waters of a nearby control lake. Differences noted were attributed to inherent characteristics of Benson Lake’s drainage basin and to the presence of a fish farm in the control lake.

Metal and petrographic analyses of lake samples indicated that tailings are areally widespread and a surficial organic layer is accumulating over them. Sampling revealed that underwater samples did not release any significant quantities of metals from the water-soluble or exchangeable cation phases. It was also found that the benthic invertebrate community in the lake had re-established itself. Aquatic vegetation was well established in the littoral zone of the lake. Compared to the control lake, aquatic vegetation in Benson Lake was found to contain elevated levels of arsenic and copper. Fish sampling confirmed the presence of rainbow trout and a species of char in Benson Lake. The concentrations of metals in the flesh of fish from Benson Lake were lower than body metal burden in fish from the control lake, but the concentrations of metals in the livers were higher. The concentrations of all metals in the fish were, however, within the range of concentrations for the same metals in fish tissues and livers from unpolluted Canadian waters.

This report provides a critical review of MEND studies conducted up to 1991 on subaqueous tailings disposal. The results of the technical and scientific assessment indicate that although the process of tailings disposal is potentially highly disruptive of lake ecosystems, remedial measures may be applied to reduce the extent of impact and accelerate recovery.

The MEND literature review of geochemical processes controlling metals release was considered to be excellent. However, the reviewers considered the background limnologies of the MEND case-study lakes to only be suitable for gross comparisons – they do not support clear interpretation of cause and effect associated with tailings disposal. Field studies were deemed sufficient to assess the reactivity of tailings disposed of underwater; however, the data were neither useful to address effects that occur during the process of disposal, nor long-term ecosystem adjustments to the introductions of tailings. Based on the review, the authors suggest that more detailed field studies be conducted of: metals fluxes in the case-study lakes; rates of accumulation; and measurements of whole lake ecological response.

This report presents the results of studies on the geochemical effects associated with subaqueous tailings disposal conducted since 1992. The literature study on biological effects demonstrated that sorption reactions on Fe, Mn oxyhydroxides and organic matter, and reactions with acid volatile sulphides allow reasonable prediction of geochemical behaviours under oxic and anoxic conditions. Attempts to combine field data and historical records (water quality/quantity and effluent loadings) provided valuable background information but were not sufficient to detail the effects of sulphide-rich tailings on lakes.

Test results indicated that there can be a small loss of metals (mostly Zn) from sediment to the overlying water, and some recycling (including metals) is probably related to the natural degradation of organic matter. In addition, tailings exposed to subaqueous oxidation react very slowly but actual rates in the lake environment are uncertain. The authors conclude that man-made containments and lakes with naturally anoxic bottom water are likely most suitable for subaqueous tailings disposal. Further studies are needed, including a comprehensive assessment of the advantages and disadvantages of subaqueous and subaerial disposal, as well as a better understanding of the “cradle to grave” effects of tailings.

This review identifies geochemical and ecotoxicological approaches that might be used to monitor the biological effects of sub-aqueous disposal of reactive mine tailings. Routes of metal exposure that are both direct (i.e., in macrofauna, by ingestion of the tailings and assimilation of the metals from the gut) and indirect (i.e., by leaching of the metals into the ambient water, followed by their assimilation from the aqueous phase) are discussed. The following topics are considered as they relate to the monitoring of biological effects of sub-aqueous disposal of reactive mine tailings:

• geochemical considerations;
• interactions between dissolved trace metals and aquatic organisms;
• interactions between particulate trace metals and aquatic organisms;
• biochemical indicators of metal-induced stress; and
• effects of metals at the population and community levels.

The authors highlight that certain community indices are more useful than others in detecting the impacts of contaminants such as metals or acids. For example, changes in the algal community are often observed. However, changes in dominance may also be due to other factors, such as the availability of nutrients, reduced grazing pressure, or the development metal tolerance by normally sensitive taxa. The most useful measures of the algal community appear to be species composition and richness. Observations are also provided on the usefulness of indices in crustacean zooplankton, benthic communities, and fish populations for detecting the impacts of contaminants.

This report provides an update of the literature review conducted in 1993 (MEND Report 2.11.2a) on the development and application of tools to predict the effects of transition metals in sediment, water and aquatic food. Several of these tools have now been validated, and can be used for mine effluent receiving waters to: assess the potential for metal toxicity in sediment; derive site specific water quality guidelines; and assess the risk for secondary exposure. The report reviewed the following tools in detail:

• acid volatile sulphide – simultaneous extracted metals (AVS – SEM) used to predict the absence of toxicity in anoxic sediments;
• biotic ligand model (BLM) used to predict waterborne metal toxicity; and
• dynamic multi-pathway bioaccumulation model (DYMBAM) used to predict metal bioaccumulation in aquatic organisms.

Based on the literature review, further research is recommended on chronic toxicity and particulate metal, especially for fish and plants. In addition, the ability to predict the effects of metal in sediment and metal in suspended particulate matter remains limited. Research should thus focus on improved assessment of the metal speciation in the exposure media, and a better understanding of the physiological effects and adaptation to trace metals.

Sulphide-rich zinc, copper, and lead bearing tailings have been deposited via floating pipeline into shallow (< 8 m) Anderson Lake in north-central Manitoba since 1979. This report presents the results of a summer and a winter geochemical survey performed of the water column and sediments in Anderson Lake in 1993. Two sites were sampled: one proximal to the tailings discharge, and the other about 2 km away. The results from these sampling programs are presented in this report.

This report presents the results of a geochemical survey performed at Buttle Lake, BC, in October 1993. The survey involved sampling of the water column as well as sampling of the sediments and associated porewater. The latter was accomplished utilizing two techniques: core extrusion and centrifugation, and membrane dialysis arrays (peepers) to address diffusive trace metal fluxes across the sediment-water interface with reasonably high resolution. This report also provides a background summary on the geochemical systems relevant to subaqueous disposal, including the distribution of dissolved metals in porewater.

This program was undertaken as part of a multi-disciplinary study to evaluate the effectiveness of using shallow water covers to control acid generation from mine tailings. A specific objective of the study was to collect data from the tailings pond at the Equity Silver Mine, in BC, which could then be used to evaluate calculations used to determine the depth of water cover required for bed stability (i.e., no movement of tailings at specified wind speeds) in a man-made tailings pond.

Baseline physical data was collected in September 1995. The field program included: a bathymetric survey of the pond; the collection of surficial sediment samples and sediment cores; and observations of bed forms at different locations within the pond. The data was consistent with the transport of sediment away from the tailings outfall during discharge into the pond. In addition, the decrease of in situ submerged weight density with increasing depth was consistent with the dewatering of tailings around the pond periphery following discharge. The presence of bed forms on the bottom of the pond indicated that wave-induced mobilization of sediments on the bed has occurred to a water depth of 1.3 to 1.4 m since tailings were deposited. The procedure outlined by Hay & Company Consultants Inc. (1995) indicated that the depth of water cover required for no movement of Equity tailings during a wind speed of 18.6 m/s (i.e., the maximum open-water wind speed recorded at the site since cessation of tailings deposition) was 1.4 m. At present, the percentage of the Equity pond with water depths shallower than 1.4 m was 7%.

This report presents the results of a geochemical survey performed on the tailings pond at Equity Silver mine, BC, in the fall of 1995. Highly reactive sulphide-rich mill tailings were deposited in this pond throughout the life of the operation. To carry out the survey, replicate peepers were used to collect pore waters from each of a shallow (~1 m) and deep site (~5 m) within the tailings pond. Ancillary solid-phase and water column data were also collected. The distributions of most elements were indicative of small-scale, lateral inhomogeneity. Dissolved Cu was neither released nor consumed by the tailings; however, Sb and As displayed opposing fluxes. The tailings oxidation rate was found to be within the range of values seen for other subaqueous tailings deposits.

This Manual is a design and operations guide for the subaqueous disposal of sulphide-rich tailings in constructed, permanently-flooded, tailings impoundments. It reviews the risk assessment process as it applies to subaqueous (underwater) disposal of tailings in engineered and man-made impoundments. The Manual is divided into 6 parts:

• Part 1 summarizes background chemistry of metal sulphide geochemical reactions that occur in tailings;
• Part 2 emphasizes the importance of data collection and management;
• Part 3 describes chemical considerations for tailings pond designs;
• Part 4 describes physical considerations for tailings pond design;
• Part 5 defines operational monitoring requirements; and
• Part 6 outlines closure monitoring requirements.

To increase accessibility to a wide range of audiences, broad general coverage is included on topics associated with geotechnical aspects, hydraulic design and risk assessment. Logic flow charts are also provided and intended as a guide in preliminary evaluations into the applicability of subaqueous disposal systems for particular projects. References are listed to other sources of information on detailed design procedures and standards (including risk assessments and geotechnical and hydraulic designs) that are only described in general terms in this report. Finally, a number of case histories are included in the appendix.

The Louvicourt project was multifaceted with contributions from industry, university, consulting and government organizations. These groups completed a broad range of studies and investigations. This provided the rare opportunity to assess and compare the effectiveness of different test procedures, equipment and predictive techniques. Previous investigations funded through the MEND (Mine Environment Neutral Drainage) Program had determined that subaqueous disposal […]

This report describes a study that integrated laboratory and field studies to understand the behaviour of tailings placed under a shallow water cover as a means of reducing oxidation and acid generation. The study entailed the construction of two test cells to simulate the conditions that might exist following the closure of Louvicourt basin. To represent post closure conditions, the facility had to be isolated from mill process water and replenished with natural water. The cells, which were constructed adjacent to the Mine Louvicourt tailings pond, were filled with 2 to 3 m of tailings and covered with a 0.3 m deep water cover. Testing included column testing in the laboratory, pilot-scale testing on site as well as laboratory work in humidity test cells and in column test cells.

This report presents the results of a study whose objective was to assess the effectiveness of an engineered shallow water cover in reducing the oxidation of sulfidic mine tailings, thereby preventing the development of acid rock drainage. Fresh tailings from the Louvicourt Mine (Quebec) were submerged under a 0.3-m water cover in experimental field cells. Between 1996 and 1998, the chemistry of the interstitial water near the tailings-overlying water interface was monitored using in situ dialysis. Dissolved oxygen (DO) and pH profiles across the tailing-water interface were also determined using micro-electrodes. Penetration of DO into the tailings was limited to < 7 mm; however, there was clear evidence of surface oxidation of the mine tailings at the mm scale. Unlike previous reports, which suggested that submerged tailings were effectively inert, these results show some alteration of the superficial layer over time. Results also show, however, that the Cd and Zn fluxes from the tailings to the overlying water would have only minor impacts on the overlying water quality.

This report presents the results of experiments designed to evaluate the effectiveness of shallow water covers in the prevention of acid drainage from reactive sulphidic tailings. The study was conducted on tailings samples from the Louvicourt mine (Quebec), and included tailings characterization, flow-through cell leach tests and humidity cells tested for eighty weeks to determine the rates of sulphide oxidation and acid neutralization. Data generated from the laboratory tests were used to predict field acid generation for a hypothetical field exposure. A new technique was employed to calculate the dissolution rates of individual neutralizing minerals and sulphide minerals from weekly leachate volume and chemical data. Mathematical modelling was used to evaluate the effects of oxygen transport mechanisms on the degree of subaqueous sulphide oxidation. Four cases were considered in the modelling: stagnant water cover, fully oxygenated and mixed water cover, fully oxygenated and mixed water cover with downward infiltration, and tailings re-suspension.

The tailings were found to contain sufficient buffering capacity to maintain the pore water pH nearly neutral. Mechanisms controlling metal releases included solubility control and dissolution rate control. Overall metal releases were low throughout the experiments, except during the initial flush-out of accumulated soluble constituents. The range of oxygen fluxes seen in the modelling results suggest that for most sites, a simple, well-maintained water cover alone, without additional measures, is sufficient to suppress oxidation of sulphides in reactive tailings while maintaining the discharge from the water cover during wet seasons in compliance. For exceptional circumstances where this is not achievable, supplemental measures, such as physical, chemical, and biological barriers/oxygen interceptors, are available to further reduce the oxygen flux and enhance the effectiveness of the water cover.

This report presents the results of an investigation into four subaqueous tailings disposal scenarios that might be applicable to mine closure of the Louvicourt mine, Quebec. The column experiments were designed to evaluate the effectiveness of two water depths (0.3 m and 1.0 m) and two intermediate barriers (peat and sand) to prevent weathering of submerged tailings. The column studies consisted of two major phases:

• Phase I, which lasted for 200 days, focused on oxygen diffusion and ionic fluxes under conditions of a circulated water cover.
• Phase II, which lasted for 13 months, incorporated precipitation, runoff and drawdown events at rates comparable to those observed in the field.

The results showed that after the initial flushing of stored weathering products, peat and sand provided an effective diffusion barrier to suppress chemical weathering of the underlying tailings. However, since the column studies were conducted under laboratory conditions that differed significantly from those occurring in the field, caution must be exercised in extending conclusions drawn from the column studies directly to the Louvicourt site.

The impact of periphyton layers on the performance of shallow-water covers was studied at Louvicourt Mine, Quebec. The study was initiated nine years after tailings at the mine were submerged under a shallow water cover to prevent oxidation of reactive tailings. It integrated geochemical, mineralogical and biological data to provide an overall assessment of the long-term performance of this cover.

Geochemical changes were monitored by in situ measurements of porewater chemistry. Samples of the biofilm, the oxic surface layer of tailings and the deeper tailings were analyzed for total metals content, solid-phase speciation and mineralogy. Molecular biological techniques were also used to characterize the microbial community associated with the biofilm. The mineralogical and chemical data confirmed that mobilisation of trace metals occurred in surface tailings, but also indicated that the overlying biofilm effectively trapped the released metals. There was a 10 fold decrease in Cd and Zn fluxes to the overlying water over the last seven years, whereas tailings switched from a sink to a source of Cu for the water cover. The results highlighted that the disposal system had not reached equilibrium after nine years of operation; the tailings were still acting as a net source of dissolved solids to the overlying water and chemical changes were still observed in the deeper part of the porewater profiles. The study concluded that biofilm development was beneficial since it: likely protected tailings from re-suspension; contributed to the maintenance of anoxic conditions in the underlying sediments; trapped mobilized dissolved metals; and decreased fluxes out of the tailings into the overlying water column.

This study was conducted on biofilm formation on submerged mine tailings. The objectives of the study were to:

• determine if photosynthetic biofilms are generally present on submerged mine tailings;
• identify the physicochemical conditions favourable for biofim formation; and
• clarify the effects of biofilm on metal mobilization.

Five mine sites located across northern Ontario and Quebec with submerged tailings of different compositions were selected for examination. Microbial mats were not found in any of the study sites. A comparison of the environmental settings between the former Louvicourt field cells, where a biofilm layer up to 5 cm thickness colonized the entire tailings/water interface, and the five sites visited for this study suggests that the requirements for the formation of continuous algal biofilm may include the following:

1. A shallow, oxygenated water cover with sufficient light and heat penetration;
2. A relatively quiescent environment, i.e., no active tailings movement; and
3. A suitable substrate for the microbial population to propagate.

Given that microbial mats were not found in any of the study sites, the authors concluded that microbial mat formation over submerged tailings does not appear to be a common phenomenon.

This report describes the results of laboratory column leaching studies that were conducted as a part of a broad research program titled “Development of Wet Barriers on Pyritic Uranium Tailings for Controlling Acid Generation”. Column leaching studies were conducted between 1989 and 1993 at the CANMET, Elliot Lake Laboratory to evaluate the oxidation and leaching characteristics of pyritic uranium tailings and crushed waste rock, under unsaturated and submerged conditions. Tailings were tested both with and without limestone amendments. The samples analyzed were collected from Quirke Mine, Ontario.

The unsaturated coarse tailings without limestone amendment oxidized readily and produced highly acidic drainage. The coarse tailings amended with coarse limestone also produced highly acidic drainage, but its onset was delayed by approximately one year in comparison to coarse tailings without limestone. The coarse tailings amended with pulverized wet ground limestone did not produce any acidic drainage during the four year study period. In comparison to unsaturated coarse tailings, submersion of tailings underwater decreased cumulative porewater acidity, sulphate and iron loadings. The submersion of coarse tailings also resulted in increased mobility and release of Ra-226 in the porewater when tailings developed acidic conditions at the surface after they were depleted of available alkalinity and gypsum. The increased drainage of Ra-226 in the porewater was accompanied by increased iron. The surface water above submerged tailings contained low concentrations of dissolved metals, when the water cover above the tailings was continuously maintained in a well oxygenated condition by fresh water inflow and where both surface and porewater flows were present in equal proportions.

The study concluded that a shallow water cover on pyritic uranium tailings is very effective in controlling/limiting their oxidation and acid generation to very low rates, but lacked in complete prevention. The tests also showed that radium mobility increases, in the absence of gypsum, when acidic conditions develop at the surface of underwater deposited tailings. Limestone amendments to tailings, in some cases, provided short-term controls on acidic drainage.

This report describes the results of laboratory diffusion lysimeter studies that were conducted as a part of a broad research program titled “Development of Wet Barriers on Pyritic Uranium Tailings for Controlling Acid Generation”. These studies were undertaken to determine the surface oxidation, leaching and mass release characteristics of underwater deposited pyritic uranium tailings for two different scenarios:

1) un-oxidized tailings that have been kept underwater for more than 12 years; and
2) weathered (partially oxidized) tailings.

The studies were conducted using lysimeters for: un-oxidized tailings, obtained from the Quirke mill and kept underwater in the laboratory since 1982; and weathered tailings, obtained from the Quirke waste management area and deposited underwater in the laboratory in 1990. The un-oxidized tailings oxidized very slowly and a narrow oxidized and iron hydroxide precipitate zone, 2-3 cm in thickness, was formed at the surface of the tailings at the water-tailings interface. Mobilization and release of iron to the surface water, under oxidizing conditions, resulted in its precipitation and covering of tailings with a layer of ferric hydroxide. Similar to the un-oxidized tailings, further oxidation of the weathered and partially oxidized tailings underwater was very slow and limited to near surface zone of the tailings.

The studies determined the mass transfer and diffusion related transfer parameters (transfer flux and coefficients) for metals and radionuclides from underwater deposited tailings to the upper lying water column. These results would provide suitable inputs for modeling the long-term surface water chemistry of water covered tailings. Based on the results, the authors concluded that the oxidation of pyritic uranium tailings underwater enhances Ra-226 release to the surface water and that Ra-226 mobility is greatly enhanced when acidic conditions develop.

French report: This report presents the results of Part 4 of an experimental research project intended to determine the effect of flooding the Solbec-Cupra tailings site in Quebec, and specifically the influence of flooding on water quality and porewater quality in oxidized and non-oxidized tailings. The focus of Part 4 was on the effect of neutralization of the oxidized layer of tailings prior to flooding, and involved a two-year monitoring period. The flooding experimentation consisted of simulating different “in situ” scenarios using instrumented basins. Five inert plastic cylinders were driven down to different depths in the tailings, each cylinder being long enough to allow a minimum water depth of one meter above tailings surface. Piezometers were also installed to assess tailings and sub-soil conditions prior to flooding.

The results indicated that flooding of tailings under a shallow water cover inhibits oxidation of acidic tailings, and prevents the continuation of the process in non-oxidized tailings. The inhibitive effect is progressive, and porewater in oxidized tailings remains acid for a certain period of time before reaching a neutral level. Neutralization of the oxidized layer of tailings by adding and mixing finely crushed limestone prior to flooding had the effect of rapidly stopping the oxidation process and raising and maintaining porewater pH to a neutral level. The monitoring results indicate that flooding of tailings under 1 m of water will eventually result in the pond having the same water quality as the incoming surface water.

This study evaluated the optimum height of water required to prevent the re-suspension of solid particles, thereby reducing the environmental impact. The focus was on tailings from the Solbec Cupra site. The research project consisted of three stages:

1) determination of wind conditions;
2) water wave investigation; and
3) behaviour of suspended solids as a function of the input energy.

Based on the experimental results, it was determined that the minimum height of water above the reactive tailings should be 1.341 m. However, with a layer of sand on top of the tailings, the required level may be reduced to 0.741 m. It was also calculated that a layer of sand could reduce the total sediment load from 331.1 to 41.8 m3/m/day.

French report: This study was undertaken to evaluate the impact on the production of acidic drainage of flooding of the Solbec-Cupra oxidized mine tailings. The specific objectives of the study were to:

• verify the efficiency of flooding on the viability and oxidative activity of microorganisms producing acidic drainage; and
• obtain data on the efficiency of the incorporation of lime into the tailings.

Representative oxidized and un-oxidized mine tailings samples were collected on the site and used in experimental columns and large lysimeters to simulate artificial flooding during a period of nine months.

Results showed that flooding of unoxidized tailings prevented their colonization by known iron-oxidizers such as Tlaiobacillus ferrooxiduns and Leptospirillum ferrooxiduns. Artificial flooding of un-oxidized tailings mixed with neutralizing lime material caused the inhibition of inoculated bacteria without eliminating them. The results also indicated that existing methods to assess lime dosage in soils are not adequate to predict neutralizing material needed in mine tailings.

This study sought to address uncertainties in the design of water covers for decommissioning oxidized tailings. Laboratory column experiments and field cell tests were carried out with tailings from the Mattabi Mine, Ontario. Experiments involved placement of attenuation layers made of sand or peat at the tailings-water interface. Tailings were not amended with alkaline material, either prior or after flooding.

Flooding oxidized tailings without prior installation of an attenuation layer resulted in the release of metals and sulphate from the porewater solution and soluble mineral phases to the water cover. Because the porewater of Mattabi tailings was rich in ferrous iron, the establishment of a water cover was accompanied by the precipitation of a thin layer of hydrous ferric oxide precipitate on the surface of the tailings. Over time, contaminant concentrations in the water cover decreased as a result of:

1) dilution of the water cover by addition of deionised water (laboratory columns) or rain and snowmelt (field test cell);
2) flushing of solutes by water infiltration from the cover to the tailings; and
3) removal of some metals by precipitation and sorption on a hydrous ferric oxide precipitate layer that formed at the water/tailings interface.

Results indicated that the geochemical characteristics of the oxidized tailings (pore water composition, soluble minerals) have a large influence on the time required to achieve discharge limits in the water cover. In the laboratory columns, fluxes of metals from the tailings to the water cover were greatly reduced by placing an attenuation layer (sand or peat) at the tailings-water interface. When a sand layer was used, the water cover met discharge limits during the entire duration of the tests. Conversely, peat obtained around the vicinity of mine sites did not appear to be a good candidate for building attenuation layers, as it was often a source of iron and other metals. Finally, economic considerations suggest that at sites with high seepage rates, a water cover may be suitable only if it can be supplemented with gravity-fed fresh water from a nearby source to the cover, thereby compensating for seepage losses.

The use of shallow water covers to flood reactive sulphide mine tailings is a popular method to prevent acidic drainage. In flooded tailings, wind-induced turbulence can increase the oxygen flux from air into water, thereby promoting mechanical mixing and maintaining dissolved oxygen concentrations at saturation levels. Turbulence can also re-suspend tailings particles in the oxygen-saturated water cover, thereby exposing tailings to greater contact with oxygen. This may increase oxidation and metal release.

This report presents the results of a laboratory study investigating the contribution to oxidation and acid generation created by re-suspension of tailings from wind-induced turbulence. The study involved a series of column experiments using unoxidized pyrrhotite tailings that were flooded with 45, 60 and 80 cm deep water covers. The tailings were obtained directly from the mill discharge pipelines at the Falconbridge Strathcona Mines, near Sudbury, Ontario.

The results indicate that re-suspension increases sulphide tailings oxidation, acid generation and metal release. Oxidation products include iron oxyhydroxides (possibly goethite) and gypsum. The results of the study suggest that when tailings are re-suspended, whether by mechanical stirring or by intense wind and wave activity, sulphide oxidation is accelerated with consequential precipitation of secondary iron oxyhydroxide minerals. Further research is recommended to assess the long-term stability of the oxyhydroxides, especially as conditions in the water become reducing, under which iron hydroxides tend to dissolve and are likely to release scavenged metals.

This report describes the application of an elevated water table as a method for saturating tailings while eliminating the need to maintain a water cover, thereby controlling and reducing acidic drainage from the tailings. A background discussion is first provided on required characterizations for applying elevated water table methodologies. Three basic approaches are then considered that can be applied to raise the elevation of the water table and the associated capillary zone within tailings:

1) Modifying the water balance of the tailings;
2) Enhancing the water retention ability of the tailings; and
3) Constructing groundwater flow barriers within the tailings.

Modification of the water balance involves increasing water input into, or decreasing water losses from, the tailings. Water retention can be improved by enhancing the physical characteristics of the tailings prior to placement – thickened tailings, which provide a very high level of saturation and considerable capillary zone height, represent one means of achieving this objective. The groundwater flow barrier involves the installation of a barrier within tailings to reduce the horizontal and often preferential downgradient flow of pore water within the tailings. The suitability of these approaches is dependent on site specific conditions. To illustrate this, experiences at nine mines sites were considered in the report.

Preliminary and conceptual cost comparisons were also carried out based on the closure of three types of tailings impoundments: a tailings stack; a valley impoundment underlain by a pervious zone; and a valley impoundment underlain by an impervious zone. Closure options included the perpetual collection and treatment of acidic drainage, the use of an engineered cover, and applications of elevated water table concepts. First order closure cost estimates indicate that elevated water table concepts, when suitable, can provide significant closure cost saving in comparison to collection and treatment, and the use of an engineered cap.

This report documents the design and performance of water covers used to prevent acid generation in sulphide-bearing mine waste in Canada, Norway and Sweden. The survey of water cover sites showed that the selection of the minimum depth of water is based on maintaining saturation of tailings in the event of a drought and preventing tailings resuspension. Predictions of resuspension are based on empirical correlations with bed shear stress, bed water velocity, or the wave height to water depth ratio. The authors noted that methods presently used to predict the quality of pond and effluent waters do not consider many biological, geochemical and physical phenomena that may significantly affect water cover performance. In addition, there is generally insufficient long-term field data available to verify water quality predictions.

Due to the dissimilarity of the sites examined, no correlation between water depth and design performance could be made. Observations common to many sites, however, included:

• a dramatic increase in pH during the summer, possibly due to microfauna activity, CO2 degassing and increase in alkalinity from surface runoff; and
• the formation of a thin coating of orange iron oxyhydroxides and organic matter at the tailings-water interface.

The use of a sand or a peat protective cover at the tailings-water interface reduces metal fluxes into the water cover to negligible levels. However, metal flux into the water cover may resume when the absorptive capacity of the protective cover is reached. The use of a peat layer creates highly anoxic and reducing conditions in the tailings. Peat also produces acidity that can significantly increase the mobility of some metals in the tailings pore water. The addition of lime to previously unoxidized tailings prior to flooding inhibited the activity of iron-oxidizing bacteria by keeping pH high. Mixing the top portion of tailings with lime was more effective than simply adding the lime to the surface. Laboratory test results showed that coarser tailings under a water cover initially generate higher amounts of acid drainage than finer tailings.

It is apparent from laboratory and field studies that flooding tailings is the most successful method presently known for preventing and controlling acidic drainage. However, in many cases the water cover discharge will require treatment to meet regulatory standards, and it is not currently possible to accurately predict the required amount and length of treatment. Although water covers are a promising technology, fundamental understanding of many phenomena influencing their performance is unknown, and the minimum depth of water required cannot presently be confidently determined.

The present report provides an update on previous literature reviews conducted in 1993 (MEND Report 2.11.2a) and 2009 (MEND Report 2.11.2b) that considered the biological aspects of the subaqueous disposal of mine tailings. The disposal of mine tailings under water can be used to limit their exposure to oxygen and to minimize their oxidation and prevent generation of acidic, metal-rich leachates.

The report deals with the biogeochemistry of selected metals and oxyanions in freshwater sediments and in submerged mine tailings. As a starting point, the behaviour of metals and oxyanions in the overlying water column and in the underlying solid phase (sediments/tailings) is considered, followed by an analysis of their interactions with the biota that colonize these metal‐rich sites. This information was derived largely from laboratory studies, from work done on lakes/ponds with elevated metal concentrations, and from post‐closure studies of subaqueous disposal facilities at mines in Canada and elsewhere. Based on these data, underwater disposal of sulphide-rich mine tailings has been successful in suppressing sulphide oxidation, preventing the development of ARD and greatly reducing the release of metals.

Sites used for the subaqueous disposal of tailings are expected to and some have become colonized by a variety of aquatic plants and animals, but little is known about the progression of this colonization and the health of biological communities that are established. For example, elevated concentrations of metals and trace elements present in the tailings could have an effect on the resident aquatic organisms. Alternatively, the physical properties of the tailings (for example, their grain-size distribution or their cohesiveness) or a scarcity of certain key components, such as inorganic nutrients or natural organic matter, may impede colonization and limit the development of the aquatic community.

Information is provided in the report about the sensitivity of aquatic organisms to the metals of concern and guidance is provided regarding recommended tools and methodologies to be used to predict and/or monitor the biological and ecological effects of submerged tailings. The report recommends that monitoring be conducted to determine the spatial variability of the submerged tailings and their changes over time. Field trials should be carried out on monitoring techniques that have been recommended but haven’t yet been tested on submerged tailings.

This study reviews dry cover theory and evaluates potential dry cover materials currently being lab or field tested, including geomembranes, as well as alternate materials from various other sources. Potential barrier materials are identified through a technical literature search; a literature review focussed on forest product industry wastes; and a search for potential materials that may be obtained from municipal and industrial waste streams. A short list of potential materials is developed by applying a two-stage screening process that takes technical aspects, cost, and practical application into consideration. Potential barrier materials considered to provide broadly based (Canada-wide) benefit and a good likelihood for success are listed. Potential materials given a high priority for future research include natural soils, modified soils, desulphurized tailings, tailings slimes, wood waste, and paper mill sludge. Materials given a lower priority for future research include peat, waxes, ashes, and the PHITO layer. Available barrier materials not requiring additional research are limestone (mixed into the tailings mass), and synthetic liners.

This study was conducted to develop laboratory and computer methodologies for evaluating the effectiveness of engineered soil covers for reactive sulphide tailings. Three laboratory columns were designed and constructed to provide reliable methodologies for soil cover evaluation. The transport of oxygen through tailings covers was shown to be mainly by molecular diffusion resulting from concentration gradients established between the atmosphere and soil void spaces. The rate of diffusion is controlled by the diffusion coefficient which is, in turn, dependent on the grain size, moisture content, porosity and other physical properties such as tortuosity or the flow path length.

Practical concepts were proposed for designing high performance soil covers. Critical material properties required for design and prediction of performance were identified, and included the diffusion coefficient, moisture drainage characteristics and long-term critical moisture contents under dry conditions. It was concluded, from limited laboratory testing, that freezing and thawing cycles could play an important role in soil cover performance.

This project evaluated the effectiveness of soil covers and a geomembrane cover in reducing acid generation in reactive mine tailings. The scope of work presented in this report covered:

• performance monitoring of field test plots at the decommissioned Waite Amulet tailings site; and
• laboratory column experiments to simulate soil-covered and uncovered tailings.

The soil cover consisted of a 60 cm thick compacted silty clay layer placed between two sand layers, each 30 cm thick. A 10 cm gravel crust blanketed the cover system to minimize erosion. The geomembrane cover consisted of an 80 mil (2 mm thick) high density polyethylene (HDPE) placed between the upper fine sand and the bottom coarse sand. Four test plots, consisting of two composite soil covers, one geomembrane cover and a control (tailings without cover) were constructed at the Waite Amulet site. A collection basin lysimeter, initially filled with unoxidized tailings, was installed below each cover to measure the quantity and quality of percolated water.

Results of the laboratory, field and modelling studies indicated that the oxygen flux is reduced by 91 to 99% by the soil cover. Acid fluxes, obtained from covered and uncovered tailings, indicated the same degree of cover effectiveness. Monitoring of acid fluxes over time suggested that the rate of acid production decreases with time. Investigations on the effects of freeze-thaw on the integrity of the compacted clay layer indicated that most of the negative effects occur during the first two freeze-thaw cycles. Tests on the stability of the geomembrane cover showed that the long-term stability of the HDPE cover is not a major concern, except for the possible effects of equipment, burrow animals and sunlight.

This project evaluated the effectiveness of soil covers and a geomembrane cover in reducing acid generation in reactive mine tailings. The results presented in this report pertain to the following specific technical scopes of work:

• measurement of geotechnical properties of the tailings (including grain size, compaction and drainage parameters, and resistance of the cover to freeze-thaw);
• measurement of the hydraulic properties of the tailings and flow modelling to verify the hydraulic conditions in covered and uncovered tailings;
• assessment of the effects of freeze-thaw on hydraulic conductivity and moisture retention characteristics;
• assessment of effect of acid leaching on the stability of cover materials;
• assessment of long term stability of high density polyethelene (HDPE) used as a cover; and
• investigation of the possible effects of sulphide oxidation on the concentration of sulphide gases such as COS, CS2, and SO2.

EXECUTIVE SUMMARY Prototype in situ covers were constructed at two mine sites, Heath Steele and Waite Amulet, as a part of the Mine Environmental Neutral Drainage (MEND) program. An independent study was undertaken by the Unsaturated Soils Group at the University of Saskatchewan to critically review the sites with respect to selection of soil materials, […]

A review of non-traditional materials used in environmental cover applications was conducted to determine which have potential use in acid rock/acid mine drainage cover systems. The following non-traditional materials were reviewed:

• asphalt covers;
• cementitious covers (polypropylene fibre reinforced shotcrete);
• cement-stabilized coal fly ash grout (Cefill, fly ash mixtures, and geopolymers);
• synthetic liners and covers (geomembranes, spray-on membranes barriers, and geosynthetic clay liners);
• bentonite modified soil barriers (soil-bentonite mixtures, polymer modified soil, and polymer surfactants);
• mine waste (tailings and waste rock); and
• wax barriers.

For acidic drainage applications, covers should have low hydraulic conductivity, prevent the transfer (ingress) of oxygen to the underlying waste, and provide a medium for the development of sustainable vegetation. Most of the non-traditional cover materials reviewed have the potential to be used as hydraulic barriers. Some of the non-traditional cover materials may also be effective oxygen barriers. These materials include bentonite modified sands, asphalt, spray-on membranes and wax. Other materials such as Cefill, geosynthetic clay liners and soil modified barriers can also be effective oxygen barriers if they are maintained in a saturated state.

The most attractive non-traditional cover materials for acidic drainage applications are mining wastes (tailings and waste rocks) since these are present on site. These materials may need to be modified with bentonite or fly ash to make the tailings and waste rock suitable as cover materials.

This report is the first volume of a five-volume manual on best available technologies for the design and construction of cover systems on mine wastes. This volume presents a background discussion on cover system design and factors that influence design objectives, followed by a summary on the following topics:

• basic theory of unsaturated zone hydrology;
• site characterization, including laboratory and field methods to evaluate potential cover materials;
• elements of conceptual cover system design and approaches to numerical modelling;
• field performance monitoring of test-scale and full-scale recovery systems;
• construction issues related to cover placement;
• vegetation on covers;
• issues related to erosion, surface water management and landform evolution;
• sustainable performance of cover systems; and
• case studies.

These topics are discussed in greater detail in Volumes 2-5 of the manual.

This report is the second volume of a five-volume manual on best available technologies for the design and construction of cover systems on mine wastes. This volume focuses on unsaturated zone hydrology as it relates to the design of cover systems. Background theory and fundamental concepts are presented in accordance with the following topics:

• moisture storage;
• moisture flow;
• evaporation and transpiration; and
• oxygen transport.

Capillary barriers are also discussed, along with issues of capillary barriers on sloping surfaces and an example of a diversion length calculation.

This report is the third volume of a five-volume manual on best available technologies for the design and construction of cover systems on mine wastes. This volume discusses:

• site characterization;
• field characterization and sampling methods; and
• laboratory methods including geotechnical and geochemical tests to characterize mine wastes and cover materials.

Numerical modelling methods for cover design are also presented and discussed in detail.

This report is the fourth volume of a five-volume manual on best available technologies for the design and construction of cover systems on mine wastes. This volume is divided into two sections. First, field performance monitoring is discussed, which includes descriptions of methods for measuring precipitation, evaporation, soil moisture content, soil suction, net percolation, runoff and erosion. Automated monitoring systems and data management and interpretation are also included in this section. Second, sustainable performance of cover systems is considered. This discussion includes a description of key physical, chemical and biological processes affecting long-term performance, surface water management and landform evolution, as well as a brief discussion on long-term cover performance.

This report is the fifth volume of a five-volume manual on best available technologies for the design and construction of cover systems on mine wastes. This volume presents a compilation of case studies previously presented in other reports, including in the MEND Manual. Successes and lessons learned in these case studies are highlighted in this report. The authors note the importance of transferring the design methodology, rather than the design itself, from one site to another as material properties, slope angles, slope lengths and climate conditions differ amongst sites. In addition, methodologies should be continuously updated as new information is collected and developed.

This Manual presents design and monitoring guidelines for mine waste soil cover systems on a macro-scale (i.e. on a watershed and landform-scale). Assessments at this scale are important for evaluating the success of reclamation of an entire area. Macro-scale design is not generally different from small-scale cover design; thus guidelines for choosing appropriate soil layers to support vegetation and restrict infiltration are not discussed in great detail here. The main difference is observed when the cover design is evaluated in the field. As time passes, soil horizons develop, vegetation matures and local hydrology establishes; thus, the true challenge in macro-scale cover design is to incorporate the evolution of the cover system into the design.

To help overcome this challenge, this Manual presents information on:

• macro-scale cover design (landform design);
• physical, chemical and biological processes that affect cover system evolution over time; and
• macro-scale (watershed-scale) monitoring methods.

Case studies are provided from Whistle Mine, Ontario, and from Syncrude, Alberta.

A productive vegetation community is critical to ensure the long term success of a cover system. A plant community will enhance cover system performance by increasing resistance to soil erosion, increasing organic matter content and structure, transpiring stored water, providing habitat for wildlife, and improving aesthetics. Numerical modelling investigations are often conducted to understand the effects that vegetation will have on cover system performance. However, many current modelling codes used in the cover system industry over-simplify the contribution of vegetation to cover system performance. Numerical modelling approaches that ignore the effect of a plant canopy and root dynamics do not fully capture the processes and mechanisms contributing to the performance of a cover system. Numerical model codes that do not account for plant physical and physiological processes and mechanisms are not appropriate for understanding how a cover system will behave.

The objective of this report is to determine the preferred approach for numerical simulation of vegetation in cover system design. This objective was met by summarizing physical, physiological, and ecological properties of vegetation that are relevant to cover system design. A summary of current modelling codes and their deficiencies is then compiled, followed by examples of how models that accurately capture plant processes are formulated. Finally, a set of recommendations and conclusions is provided.

French report: This study explores the use of tailings (free of acid generating materials) as part of a multi-layer cover over existing tailing ponds. The multi-layer cover considered here has the following layers (starting with the uppermost layer):

• Layer A – humid layer to support vegetation;
• Layer B – coarse material layer containing a large portion of cobbles to prevent biological intrusions from roots and animals;
• Layer C – sandy material acting as a drainage layer;
• Layer D – fine grain material acting as a moisture retention zone;
• Layer E – non-capillary layer to stop capillary rise from the underlying layer; and
• Layer F – reactive tailings.

The tailings fine fraction (slimes), obtained by natural segregation or by hydro-cyclones, could be used to build the capillary layer (i.e., Layer D), which is the most critical component of this cover system. The coarse tailings fractions (sands) could be used in Layers C and E, depending on their availability and hydrogeological properties. Layer B could include cobbles found in the overburden or waste rock from the mine. Finally, humid layer A could be made with the excavated overburden soil, with the original topsoil (stacked and protected) used as the final vegetative layer. The study concluded that 1 m layer of fine material saturated to greater than 90% sandwhiched between two sand layers can reduce the oxygen flux by a factor of 1000 or more.

This report also summarizes other interim reports and academic studies. In so doing, it presents a state-of-the-art view on cover technology, discusses capillary barrier effects created in layer covers, considers relevant material properties and presents model results.

French report: This report presents the preliminary results of a detailed study on the behaviour of a Cover with Capillary Barrier Effects (CCBE) used as an oxygen barrier to reduce the production of acidic drainage. A key feature of this cover system was that one of the layers consisted of “clean tailings” (tailings with very low sulphide content). This report presents the preliminary results of six experimental cells constructed on the Norebec-Manitou site (near Val d’Or, Québec) to study the behaviour of engineered cover systems in the field.

French report: This report presents the results of a detailed study on the behaviour of a Cover with Capillary Barrier Effects (CCBE) used as an oxygen barrier to reduce the production of acidic drainage. A key feature of this cover system was that one of the moisture retaining layers consisted of “clean tailings” (tailings with very low sulphide content). This report presents the final results of six experimental cells constructed on the Norebec-Manitou site (near Val d’Or, Québec) to study the behaviour of engineered cover systems in field conditions. The financial aspects of implementing the CCBE technology are also considered through the simple Evaluation of the Cost for Reclamation model. This model allows a relative comparison of the costs incurred by the application of various techniques, including:

• chemical treatment (lime) of acidic drainage;
• use of a water cover with impervious dams;
• construction of a CCBE made of soils and/or clean tailings; and
• inclusion of a desulphurization process to produce “non-acid generating tailings” that could be used as the fine material layer in a cover system.

This model shows that CCBE made of clean tailings can be a very competitive closure technique to control acidic drainage.

This report presents the results of a practical field application of a composite cover. The study assessed the performance of a composite cover placed on the acid generating tailings impoundment at Barrick Gold Corporation’s Les Terrains Auriferes (LTA) tailings site. The full scale composite cover was built in the winter of 1996 on the 60 hectare site. Alkaline tailings were used for the fine material layer. The various phases of the LTA project are described in this report – from the initial conceptual design of the cover to the final construction and monitoring.

Since January 1997, the site The Land Aurifères (LTA) is the subject of a detailed study in the MEND program (Project 2.22.4) in order to study the performance of the built-up roofing on the park potentially acid generating tailings. It is a collection multilayer built a large scale (60 hectares) in winter 1996. The thin […]

This report presents study results associated with the decommissioning of Les Terrains Aurifères (LTA-Barrick-Bousquet) site at Malartic. This study evaluated the performance of a composite cover constructed on the acid-generating tailings impoundment. A hydraulic barrier test cell was also constructed to study the performance of the hydraulic barrier. Monitoring results collected between 1996 and 1998 are presented in the report. The main finding was that, by capillary action, the cover remained practically saturated over a period of three years. The average tailings oxidation flux was also reduced by 95 % over the three year observation period. Although some areas showed local water contents that were lower than the design objective, the performance observed with the hydraulic barrier test cells indicate that this type of structure would be effective in these dryer areas.

Lors des travaux relatifs à la fermeture du site Les Terrains Aurifères (Barrick-Bousquet) à Malartic, l’option retenue pour la réhabilitation du parc à résidus potentiellement générateur d’acide a consisté en la construction d’une couverture multicouche. Celle-ci a été mise en place durant l’hiver 1995-1996 et complétée à l’automne 1996. Le site fait maintenant l’objet d’un […]

The Kidd Creek Division of Falconbridge Ltd. has been using the Thickened Tailings Disposal (TTD) method at its metallurgical site near Timmins, Ontario. This report presents the results of a two-year study that measured the hydraulic properties of the tailings site to analyze the long-term impacts to the environment.

The TTD method consists of thickening the tailings slurry and discharging it into an elevated central spigot line producing a cone-shaped depositing. At present, the tailings deposit at Kidd covers a surface area of 1215 ha and resembles a broad, gently sloping (+ 1%) cone. The tailings contain approximately 5% sulphur, and are considered strong net acid producers. In this study, principal components of the site hydrology were evaluated to obtain a verification of the high moisture retention of the TTD deposit. Hydraulic gradients suggest that pore water in the saturated zone tends to move downward near the centre of the cone, and upward along the slope of the tailings. Near-surface hydraulic gradients on the upper part of the cone indicate that upward flow dominates during summer water table drawdown, while downward flow dominates during the subsequent recharge period.

The porewater analysis indicates that sulphide oxidation is occurring in the tailings mass. De-watering during a drought year is expected to have little impact on long-term saturation of the tailings. However, during these periods, oxidation is promoted deeper in the tailings. Tailings saturation and water table position are expected to resemble that presently observed in areas of the cone where deposition is not active. Release of contaminants from the tailings to the environment should remain at present rates due to slow porewater velocities and sustained near-surface saturated conditions.

The Kidd Metallurgical Division of Falconbridge Ltd. undertook a study involving the injection of two tracer compounds into thickened tailings in 1992, followed by downstream pore water sampling and analyses in 1993 and 1996. Unlike in conventional tailings placement, thickened tailings do not segregate but remain homogenous when placed.

The key objective of this study was to verify the predicted movement of the pore water within the thickened tailings. Observed porewater was predominantly down-gradient and followed the tailings slope as previously modelled. The greatest velocities were in the horizontal direction, with the average downward velocity ranging from 8 to 16% of the average horizontal velocity.

This report presents the results of a geochemical, hydrogeological and hydrological study of the Kidd Creek thickened tailings impoundment. This is part of a larger investigation intended to aid in the development of a comprehensive, long-term environmental management program for the Kidd Creek tailings.

The current practice of co-disposing natrojarosite minerals with sulfide-rich tailings at Kidd Creek introduces natrojarosite to a neutral-pH and low-EH environment in which it is thermodynamically unstable. Results indicate that natrojarosite is dissolving, releasing Na, K, Mg, Mn, Fe, Zn, Pb, As, HCO3 and SO4 to the pore water. Mineralogical studies also indicate that a significant mass of natrojarosite remains in the tailings representing a long term source of contamination.

The effects of natrojarosite dissolution on the pore-water composition are distinguishable from the effects of sulfide oxidation. Sulfide oxidation generates low-pH conditions in the pore water near the surface and causes the dissolution of carbonate minerals, thereby initially increasing the pore-water concentration of HCO3. Continued oxidation, however, will consume the carbonate-mineral acid-neutralization capacity of the tailings and subsequently deplete the pore-water alkalinity. As sulfide oxidation has been limited by continuous tailings deposition on most of the main tailings cone, there is no discernable depletion of sulfur at the surface. Assuming there are no changes to the present tailings surface due to erosion or reclamation operations, sulfide oxidation modelling suggests that the most intense sulfide oxidation will occur in the first 20 years that the tailings are exposed to the atmosphere; the residence time for reaction products in the pore prior to discharge may, however, exceed 1000 years.

Hydrological studies were also conducted to determine the amount of low quality tailings pore water that contributed to the surface run off from the impoundment during storm events. The maximum measured pore-water contribution to the run off was 23.5% during a moderate intensity, long duration rainfall event. The long duration rainfall events that cause the water table to rise through the tailings impoundment represent the greatest potential for contributing low-quality pore water to the surface-water effluent.

This report presents the results of a hydrogeological investigation of the Fault Lake tailings site. The tailings were deposited in a kettle lake depression formed within glacial outwash sand and gravel. The specific objectives of the investigation were to analyze the chemical and physical hydrogeology of the site to delineate areas affected by acidic drainage from the tailings, and to verify the presence of the porous envelope effect. This unique effect occurs where flow through the tailings mass is low enough, relative to the surrounding and more permeable till, such that impacts to the groundwater from tailings oxidation is insignificant at a regional scale.

The results indicate that although sulphide oxidation has been at its highest rate since deposition discontinued in 1978, little impact of sulphide oxidation has occurred in the groundwater of the surrounding till. Sulphide oxidation products leaching from the tailings appear to be alleviated by the porous envelope effect. Several favourable factors contribute to the creation of this effect and limit metal concentrations downgradient of the tailings – including the:

• hydraulic conductivity contrast between the tailings and the surrounding sediments;
• limited infiltration through the surface of the tailings;
• dilution of metals flushed from the tailings by water flowing around and below the tailings; and
• chemical attenuation of metals, which likely plays a large role both inside the tailings mass and in the surrounding sediments.

This manual presents comprehensive methodologies for re-vegetation of reactive sulphide tailings disposal areas in Canada. This includes procedures for preparation, neutralization, fertilizing, seeding and follow-up maintenance, if required. The following basic building blocks are described in detail:

• macro and micro-climate and their effects;
• physical and chemical properties of soil;
• types of materials (overburden, waste rock and tailings) encountered at a mine; and
• general effects of lime, fertilizer and other amendments on soils and tailings.

A tailings re-vegetation program is outlined that covers a two to three year time frame with at least two growing seasons. This program is divided into seven segments: evaluation; program planning; site preparation; lime and fertilizer; vegetation selection; mulches, chemical stabilizers and other amendments; and establishing vegetation. Some of the more common agricultural equipment and implements required to prepare, seed and maintain mine waste areas are illustrated. Finally, a brief discussion of problems associated with establishing re-vegetation programs north of 60 degrees latitude is presented along with specific case studies on re-vegetation efforts undertaken at mines.

The report examines use of municipal solid waste (MSW) as an oxygen barrier on tailings to prevent oxidation and production of acidic drainage. MSW disposal is an increasing problem for municipalities. This approach may be a “win-win” situation, provided it is technically feasible, environmentally safe and socially acceptable.

Objectives were to :
1. Review current status of remediation of acidic mine tailings,
2. Determine the characteristics of MSW compost and other organic matter, and their use in tailings reclamation,
3. Examine regulations and socioeconomic concerns on use of MSW and other sources of organic matter,
4. Examine the availability and cost of MSW compost, and
5. Recommend studies to address unresolved questions.

The review showed that a compost layer on tailings offered several benefits. However, there is a risk of contaminants in the compost, which depends on the quality of feedstocks and the composting process. Transportation cost and regulations may prohibit this application. Laboratory studies and field work are needed to verify this application and determine environmental risk. Discussions need to be held among provincial and municipal governments and communities if applied for tailings reclamation.

This report presents the results of a study examining three compost cover layer models that might be beneficial in the suppression of tailings oxidation and acidic drainage. Laboratory studies were conducted to assess the potential compost cover layer benefits, and to facilitate the design of field tests. Two grades of municipal solid waste (MSW) compost were compared: immature (4 week old) and mature (14 week old). Analyses of the leachate quality from compost cover layers and tailings were conducted in light of the potential for MSW compost to release trace metals, organic chemicals and pathogens into the watershed outside the tailings area. A laboratory simulation experiment to compare the three cover layer models and two grades of compost was conducted in plexiglass columns over 290 days. From this preliminary study it is concluded that the compost model, using immature MSW compost, appears to be the simplest and most cost-effective tailings cover layer solution.

This study evaluated the effectiveness of organic covers in reducing acid generation from sulphidic tailings. The materials evaluated were:

• lime-stabilized sewage sludge (LSSS);
• municipal solid waste (MSW) compost; and
• peat.

Desulphurized tailings (DST), an inorganic material, was evaluated for comparative purposes. The study consisted of three components: physical and chemical characterization of the tailings and cover materials; salt migration column tests; and pilot-scale cells.

Material characterization indicated that the tailings were more finely grained and had a lower hydraulic conductivity than the LSSS, compost and peat. The compost and peat tended to decompose and compact with time. The LSSS, compost and peat were more readily drained than the tailings.

Pilot cell testing indicated a reduction in acid generation in tailings beneath the LSSS cover. The pH of the pore water and leachate increased, while the level of dissolved metals and sulphate decreased. The LSSS demonstrated a high oxygen consuming ability and maintained over 90% water saturation throughout the cover depth. The DST cover maintained high moisture levels, inhibiting the movement of oxygen and water into the underlying tailings. The high air entry value and low hydraulic conductivity resulted in reduced volumes of leachate. High evaporation rates and desiccation cracking were observed, however, indicating that DST would be unsuitable as a single cover material.

The results indicate that LSSS and DST offer the greatest potential for reducing metal and sulphate loading from oxidized tailings. The benefits of utilizing LSSS are based on chemical changes within the tailings pore water, while the benefits of DST are physical and include low hydraulic conductivity and a high degree of saturation.

A project was initiated to develop and test strategies for the long-term management of acid generating waste rock at the Heath Steele Mine, in New Brunswick. This report describes the results of the first three phases of that project. Phase I involved the selection of four acid generating waste rock piles that would be most amenable to monitoring and evaluation of remedial measures. Phase II involved the installation of monitoring equipment to collect detailed characteristics and background data on these four piles. In Phase III, the natural soils in the vicinity of the Heath Steele (within 15 km) were evaluated for potential use as engineered covers for the waste rock piles.

Finally, a composite soil cover was designed using natural soil materials. A 3-layer composite cover, consisting of a fine-grained saturated till, sandwiched between two coarse-grained layers, was proposed as an effective oxygen barrier. Computer modelling indicated that much lower oxygen fluxes could be expected from this composite system compared to a single till layer.

This report presents the results of the fourth phase of a project initiated to develop and test strategies for the long-term management of acid generating waste rock at the Heath Steele Mine, in New Brunswick. It describes the engineering design and construction of a 130 cm thick composite soil cover constructed on an experimental waste-rock pile at the Heath Steele Mine, in New Brunswick. The cover consists of a 30 cm thick sand base, a 60 cm thick compacted glacial till, a 30 cm thick granular layer, and a final 10 cm thick gravel layer for erosion protection. Results indicate a reduction in gaseous oxygen concentrations in the pile from 20% (pre-cover) to about 1% (post-cover placement). The decreased oxygen penetration implies reduced oxygen flux and acid production.

Temperatures in the pile decreased following cover installation but appear to be more influenced by climatic variability than by a decrease in heat production and sulphide mineral oxidation. Observed discharge from two lysimeters installed below the cover indicates infiltration of 2% precipitation during a 55-day period when rainfall was heavy. The volume of the seepage has reduced but the quality from the pile has not changed since cover installation. Further monitoring is required to confirm the reduction in acid production. Results indicated that it will take 30 years to flush 1 pore volume from the pile.

This report summarizes the results from a four-phase project initiated to develop and test strategies for the long-term management of acid generating waste rock at the Heath Steele Mine, in New Brunswick. All monitoring data collected since project implementation is included. The data collected over 72-months confirmed that uncovered acid waste rock piles provide a favorable environment for oxidation of the sulphide material and thus the generation of acidic leachates. Conversely, the composite cover on the waste rock pile depleted oxygen, reduced pile temperature and reduced leachate volume. In addition, the glacial till layer within the cover maintained its moisture content over the 36-month evaluation period. These results indicate that the composite soil cover was effective in reducing the oxidation reaction in the pile, and therefore, reducing the production rate of acidic leachate. The results from the analytical leachate testing indicate a decrease or no improvement in water quality immediately after construction of the cover. However, there was a well-defined and steady improvement of water quality after 1994, which suggests that the leachate quality is still improving.

The piles at Heath Steele are small compared to waste rock piles at many other sites, and different gas transfer mechanisms might apply elsewhere. Despite the promising performance to date, additional monitoring of the cover is still required before its long-term stability can be properly assessed as a full-scale final closure measure. In addition, performance of the cover depends on maintaining its integrity with respect to preventing damage by roots, burrowing animals and physical impacts. The glacial till layer must also remain saturated. Thus, low level of maintenance of a soil-covered pile would be required.

This report presents follow-up monitoring results to a project initiated to test strategies for the long-term management of acid generating waste rock at the Heath Steele Mine, in New Brunswick. The project entailed the construction of an experimental waste rock pile with a composite soil cover to limit the rate of sulphide mineral oxidation. After construction of the cover, monitoring continued for five years to assess its effectiveness.

Results showed reductions in gaseous oxygen concentrations in the waste rock pile after the cover was built, indicating reduced oxidation rates. Similarly, temperatures in the pile decreased and appeared to be controlled primarily by climatic conditions. Since cover placement, metal and sulphate concentrations in leachate have shown a gradual decline, but have also shown seasonal fluctuations. Gradual improvement in porewater quality is expected since the flushing rate is low.

Effluent loadings decreased immediately following construction of the cover due to reduced infiltration, and since then, declining porewater concentrations have reduced effluent loadings. Based on improved loadings, a savings in the cost of lime was calculated as $196/yr per 1000 tonnes of waste rock; 94% of the savings was observed shortly after construction of the cover due to reduced flushing flows through the cover. Other benefits for treatment include a low flow volume to be treated and effluent water quality consistency. The results of five years of monitoring indicate that composite soil covers on waste rock piles are effective in limiting the rate of sulphide oxidation. For a specific application, the cost and savings, as well as long term stability, need to be evaluated.

This study investigated the potential for acidic drainage at the proposed Kutcho Creek mine (BC), and the viability of blending waste rock to mitigate acidic drainage. Preliminary acidic drainage studies suggested that blending potentially acid generating waste rock with potentially acid consuming waste rock in a carefully designed dump would mitigate acid generation.

Research included static tests (acid base accounting) and kinetic experiments (laboratory humidity cells and on-site pilot scale weathering tests). Acid base accounting test results confirmed that footwall rocks are potentially acid generating and hanging wall rocks have the potential to neutralize acid. Laboratory humidity cell tests, composed of blended ratios of waste rock material, demonstrated significant reductions in the rate of acid generation. Results from the blended field test pads were not as conclusive: leachate quality was dependent on flushing rates as opposed to the actual acid generation rate.

Based on long-term extrapolations, blending of Kutcho waste rock, even at 1:1 ratio, does not appear to be a viable mitigation strategy for acidic drainage. A separate analysis has also determined that the costs associated with blending large amounts of waste material in a full scale waste dump would be excessive. Thus, the disposal of reactive waste material in a flooded impoundment is generally accepted as the most feasible method for long term disposal of reactive mine wastes for Kutcho Creek.

This report describes the implementation of ARD remediation techniques at four Norwegian mines. These techniques include:
• a composite geosynthetic cover on waste rock;
• a till cover on waste rock;
• seepage collection and treatment;
• flooding of underground mine workings;
• in-lake disposal of waste rock, with associated dam construction; and
• evaporation.

The report describes the implementation techniques applied at the respective sites, and where possible provides a performance evaluation based on the site water quality monitoring data. Summaries of the cost incurred for the implementation of the various measures are also provided.

The geosynthetic cover was effective in: preventing water infiltration, thereby reducing the overall metal load from the waste rock; reducing the entry of oxygen into the rock pile; and reducing the oxidation process. The effectiveness of the till cover could not be evaluated from available data.

The waste rock was not treated with lime before being placed in the lake; thus, the water in the submerged pile has a pH of about 2.5. Monitoring suggests that long-term pH values of 4.5 will be achieved in the lake.

A study was initiated to assess the performance of a cementitous cover for acid generating waste rock at Myra Falls mine, in BC. This report presents the results of phase 3 of this study, which entailed a large-scale field application of a shotcrete cover on a waste rock dump. A wet-mix shotcrete application was applied in August 1992. Mixes utilizing imported aggregate and mine tailings were tested. Laboratory and field monitoring were conducted through 1995 to determine the mechanical properties of the shotcrete and to evaluate the long term performance of the cover.

Visual inspections of the shotcrete cap over a three-year period indicated good overall durability. No frost damage was evident and no movement of the cap was detected. Lab results indicated that the compressive strength of the mixtures exceeded the design objective. Some reduction in compressive strength was observed in the tailings mix after 400 days. It is believed this is a result of oxidation of the sulfide minerals in the tailings material. An assessment of the cost of the shotcrete application indicated that the transport of the aggregate to the mine site is the largest cost component.

Recommendations for future study include evaluating the effects on the shotcrete cover from placement of overburden and vegetation and the effectiveness of the shotcrete cover in restricting acid generation in waste rock. In addition, as the long-term success of dry covers depends on the stability of the waste rock dump, geotechnical studies are required to estimate any movement of the final design slope.

This study evaluated the relative effectiveness of four techniques for controlling acidic drainage in waste rock:
• water cover;
• soil cover;
• wood bark cover; and
• addition of limestone and phosphate rock (apatite).

Test samples were collected from the Heath Steele mine (New Brunswick) and Les Mines Selbaie (Québec). The investigation involved outdoor lysimeter tests and laboratory column experiments.

The Heath Steele mine rock generated acid at a higher rate than the Selbaie rock, although the latter had higher pyrite content. This was due to the gangue composition of the Heath Steele mine rock, which had a major influence on its acid generation ability. The most effective control techniques were, in decreasing order: water cover, limestone, soil cover and phosphate addition. All the techniques, with the exception of the water cover, were found to be slightly more effective in the laboratory than outside. The effectiveness of the water cover may be enhanced by increasing the depth of the water or applying an organic layer on top of the waste. 10-15% increase in effectiveness was observed when the amount of limestone added to the rock was increased from 1 to 3%. A similar increase in the amount of phosphate yielded higher effectiveness, from 10 to 70%. The relative effectiveness of the different techniques is likely to change with time, due to depletion of alkalinity or phosphate materials.

Due to bacterial activity, the wood bark accelerated acid production by about 60% in the laboratory and 500% outside. A wood bark cover is thus not considered a good technique for reducing acid generation in sulphide-bearing waste mine rock.

This report investigated the backfilling of open pits and identified a range of approaches for the in-pit disposal of mine wastes. Four basic concepts in the placement of mine wastes in pits are discussed:
• underwater disposal;
• elevated water tables;
• dry disposal; and
• perched water tables.

Key aspects that need to be taken into consideration when evaluating the in-pit disposal of wastes are also considered. This includes technical factors such as geotechnical characteristics, predicted pore water, pit water, and groundwater quality, and the hydrology of the open pit. Mine related constraints must also be taken into consideration. These include wall stability, safety concerns and proximity of underground workings to the open pit. Consideration must be given to both the short term and long term implications of the in-pit disposal concept. Finally, the potential costs for future in-pit disposal of wastes should be considered in the preliminary economic evaluations used to establish final pit limits.

Select examples of research and field applications are provided from the published literature. Twelve case studies of actual and planned in-pit disposal of mine wastes are also described. This study determined that not all pits are suitable for in-pit disposal.

The options for disposal of mine waste that represent low long-term liabilities are limited at a large proportion of mine sites.  Although not new, the disposal of mine wastes into mined-out pits has, in recent years, received increased acceptance particularly for acid generating, metal leaching, radioactive and perceptively hazardous tailings, waste rock and water treatment […]

This report presents the results of the first phase of a research project undertaken to understand the geochemical and hydrological interactions between water and partially oxidised waste rock from the Stratmat pile at the Heath Steele mine. This study investigated the effect of flooding oxidized waste rock using laboratory leach columns.

The bulk density of the waste rock was measured in the field and samples were physically and geochemically characterised in the laboratory. The results were used to predict water quality for a hypothetical scenario in which waste rock was backfilled into the Stratmat pit. The column dissolution experiments indicated that dumping the waste rock into the flooded Stratmat pit would release stored metals and sulphate. Sequential release of various metals in response to pH change and depletion of sulphate was observed.

Geochemical modelling suggested different concentration control mechanisms for different metals. In the presence of uncontaminated groundwater movement, the water quality would gradually improve as the initial pore water was displaced or diluted. It would take nine pore volumes of flushing to reduce the concentrations of most metals to below 0.1 mg/L. Reduction of lead concentrations would, however, need more pore volumes of flushing. The results indicate that it would take a long time for pore water in the backfilled waste rock to become acceptable for discharge to the receiving groundwater.

This report presents the results of the second phase of a research project undertaken to understand the geochemical and hydrological interactions between water and partially oxidised waste rock from the Stratmat pile at the Heath Steele mine. The main objective of this phase was to understand the hydrology and solute transport within waste rock piles during infiltration and drainage events associated with precipitation. Large column tests were conducted to achieve this objective.

Geochemically, the experimental results suggest that the concentrations of Ca, Pb, and Al in the drainage are solubility-controlled while the concentrations of Zn, Fe, and sulphate are not. Hydrologically, the experiments have demonstrated that channelling is a ubiquitous phenomenon in the waste rock studied. Channelling is more pronounced in earlier stages of drainage events and tends to attenuate as the draining process continues. Channel stability is influenced by variables related to the rock bed properties and simulated rain characteristics.

The main challenges in flow and solute transport modelling are channelling and interactions between flows and geochemical processes. Factors influencing water flows and flow effects contributing to flow heterogeneity are discussed and a mathematical representation of channelling phenomena is developed. The kinematic wave model was applied to the experimental data but did not appear to adequately predict the channelling flow characteristics of the waste rock; this model may be more appropriate to coarser waste rocks.

This study evaluated processes occurring in subaqueous disposed waste rock. The objective of this project was to design a laboratory test protocol that could be used to quantify the chemical stability of waste rock oxidation products in a range of subaqueous environments. The report:

• examines the mechanisms that control the formation and stability of secondary minerals in waste rock dumps;
• identifies the minerals that may be present in the dumps (including weathered waste rock reaction products);
• evaluates the subsequent stability of the minerals in a subaqueous setting; and
• examines available laboratory methods and their applicability to assessing metal release from oxidized waste rock.

A number of test methods were examined to evaluate the subaqueous stability of oxidized waste rock, including: shake flask, column and tank tests; partial extractions and sequential extractions. Shake flask, column and tank tests have been used to determine the subaqueous stability of oxidation products. They do not, however, discriminate between the geochemical processes or mineral phases responsible for the release of metals to solution. Partial extraction tests are limited to simulating one environmental condition. Sequential extraction tests are best suited for use as an initial screening tool for evaluating metal release from subaqueous waste rock and can be used to evaluate metal release for a range of extreme environmental conditions.

A four-step sequential extraction scheme is proposed to examine metal partitioning in oxidized waste rock. This can be an effective tool to assess metal-phase associations in waste rock when more direct methods (e.g., SEM, XRD, etc.) become too expensive and time consuming due to the fine grained/amorphous nature of many secondary minerals. When combined with kinetic or in-situ testing, this method is an effective tool to assess environmental risk associated with the subaqueous disposal of oxidized waste rock.

This report presents the general theory behind blending and layering of waste rock for prevention and control of acidic drainage. Select case studies on both coal and metal mines are described.

The studies on coal wastes tended to examine the addition of alkaline materials rather than the deliberate blending of acid generating and acid consuming waste rock types. These studies indicated that fine alkaline material distributed uniformly throughout a waste pile was effective in delaying the onset of acidic effluent. Lime kiln dust was more effective than limestone in reducing the net acidity and in preventing the onset of acidic effluent. The order in which overburden was placed in relation to acid drainage generating strata had a significant effect on leachate quality. Placement of overburden as soon as possible after excavation proved beneficial in reducing acidic drainage.

Few metal mine sites were identified that had deliberately examined or applied blending and/or layering. The available results indicated that blending did not reduce sulphide oxidation rates in the potentially acid generating material unless highly reactive neutralizing material (limestone) was applied and the blending was near ideal. Perfect mixing was generally only possible in column or humidity cell tests. Blending and layering was effective in delaying the onset of acidic effluent, and reducing the metal and acidity loadings. Prevention of acidic effluent from the blended or layered materials did not, however, necessarily prevent dissolved metal levels from being problematic.

The review indicated that blending and layering of acid generating and acid consuming waste rock may be a legitimate method for neutralizing acidic drainage. However, there remains considerable uncertainty and further investigation into the application and practice of this method is required.

This study evaluated various methods to delay the onset of acidic drainage including:
• bactericide application;
• deposition in permafrost;
• phosphate application;
• irrigation with alkali;
• simple soil covers;
• oxygen-consuming organic covers;
• blending; and
• lime application.

Information about each of these methods was collected from literature and from interviews with mine operators and researchers. A brief overview of each method is presented in the report along with specific case studies. The extent to which the case studies prove the effectiveness of each method is also reviewed. This review indicated that there is a lack of well-designed and documented studies of methods to delay the onset of acidic drainage. However, several of the reviewed methods are promising enough to warrant further research, and recommendations are provided for study requirements for each method.

The Samatosum mine in BC implemented full-scale layering of acid-generating and acid-neutralizing rock in its waste rock dump. In this study, existing information was reviewed, old data reinterpreted, and new data obtained for the layered waste-rock dump and the column tests that simulated it.

Predictions and monitoring data were reconciled based on (1) the observations in the columns that layering does not suppress reaction rates in the potentially acid generating rock and (2) coarser rock can preferentially channel water through a layer. Consequently, the appearance of net acidity in some dump drainage was simply the result of physical conditions rather than a failure of geochemical principles. This highlights the importance of physical design and physical hydrogeology in any future design and construction of a layered dump. If drainage does not pass through all available neutralizing layers, acidic drainage may appear even in the presence of excess neutralizing potential.

Although acidic pH may be prevented with carefully designed and implemented layering, leaching of metals is not so easily controlled. Because reaction rates in even small layers of net-acid-generating Samatosum rock, on the order of 0.2 m, could proceed unattenuated by adjacent net-acid-neutralizing rock, metal leaching can probably occur at accelerated rates in layered dumps. If site-specific solubilities of secondary minerals are relatively high, metal concentrations may exceed water-quality requirements even in near-neutral drainage. Therefore, layering is not necessarily a control technique for metal leaching.

This study examined whether a microbial cap on uranium tailings could reduce the penetration of oxygen and water. It was predicted that ultramicrobacteria could consume oxygen and the biomass cap that was produced would block the pore spaces. This would prevent the growth of Thiobacillus ferrooxidans bacteria which oxidizes metal sulphides to sulphuric acid and soluble metals, creating acidic drainage.

Coarse oxidized uranium mill tailings from Denison Mines, Ontario were tested. Columns tests were set up to examine the best conditions for microbial cap formation. Of the two major criteria for successful cap formation (i.e., decreased permeability and oxygen scavenging by the bacteria) only the latter was attained with some degree of success. In addition, the use of the ultramicrobacteria was shown to not be essential since the column tested with liquid nutrient had equivalent results to the column tested with liquid nutrients and ultramicrobacteria. It is likely that the nutrients increased the metabolic activity of the indigenous bacteria already present in the tailings.

This report presents a review of mineral processing technologies and their application to the removal of sulphides from mill tailings. The study included a descriptive review as well as bench scale testing. Samples from mines in Quebec and Ontario were processed by gravity and flotation separation processes to split them into sulphide and non-sulphide fractions. The separation processes tested included:

• Falcon Concentrator;
• Knelson Concentrator;
• Reichert Tray;
• 1/8 Wilfley shaking table;
• Carpco LC3000 spiral concentrator; and
• direct flotation with a variety of pre-processing steps and collectors.

The samples were characterized initially, processed with the above techniques and reanalyzed to determine the effectiveness of the sulphide separation. The characterizations included humidity cell tests and acid base accounting, ICP analysis and a mineralogical evaluation. The results of the study proved that the gravity techniques tested were incapable of separating the sulphides sufficiently to remove the acid generating capability of the tailings. Direct flotation, however, proved successful in removing the acid generating potential of the tailings samples.

This report presents the results of a third year of study into the separation of sulphide minerals as a strategy for preventing acidic drainage. Results were reported from low, medium and high sulphide tailings tested in field lysimeters and in laboratory columns under saturated flow conditions. After more than three years of field study, the porewater pH in the low sulphur tailings lysimeter remained at near neutral. Conversely, the porewater in the medium and high sulphur tailings lysimeters showed high acidity and metal concentrations. Column experiments were still underway to evaluate acid neutralization capacity. The authors concluded that low sulphur tailings may be useful as a filling material in waste rock dams or as a cap to cover more reactive tailings; more research is needed, however, to confirm this.

This study assessed the benefits of encapsulating acid generating tailings with acid-consuming tailings to neutralize acid. Laboratory column tests were used to evaluate the effects of different source materials and of different thicknesses of the underlying tailings layer. Models were employed to evaluate arsenic attenuation and to guide the determination of the thickness of the overlying layer required to prevent oxidation of acidic high-sulphur tailings.

The column tests were designed to simulate the placement of low pH acidic tailings sandwiched between layers of neutral tailings with excess neutralizing potential. Water was added to the top of tailings and allowed to migrate through the tailings. Samples were collected from the drainage outlet and from lysimeters placed within the individual tailings layers to sample in-situ porewater.

The results confirmed that the neutral layers could consume the existing acidity in the low pH tailings and prevent acidic and metal-laden drainage. Better efficiency was observed with a greater thickness of and longer residence time for pore water in the underlying neutral layer. Modelling of arsenic attenuation showed that the effective removal of arsenic was very sensitive to the amount of ferric oxyhydroxide material in the bottom neutral tailings layer.

The results of pyrite oxidation modelling suggest that the residual sulphide content of the tailings will act as an oxygen scavenger while the neutralization potential prevents acid generation in that layer. The modelling results suggest that a 3 m thick layer of the neutral tailings with a low sulphide content would be sufficient to prevent ongoing acid generation in the high sulphur layer.

Executive Summary Facilities built to store mine tailings pose both physical and geochemical risks that must be managed throughout the life of the facility, from design and construction, through to the closure of the mine and beyond. In Canada, most mines manage their tailings as a slurry deposited behind containment dams (designated in this report […]

This report presents the results of a four-year investigation into the potential use of wetland ecology and microbiology to treat acidic drainage from metal mines. The study focused on ecological microbial processes that occur naturally in wetlands, lake and ocean sediments. Test cells were constructed at the perimeter of a tailings dam and a floating cattail cover was established. Organic amendments were added to two of the cells. In the third year of the study, the process was tested under defined flow conditions. Copper and nickel reductions were observed.

This report presents a summary of the components of the microbial ecosystem that played major roles in the process. Data results are used to define operating parameters, such as nutrient supply and chemical conditions. Limitations of the microbial approach and economic considerations are also presented. The results of this project provide a technical basis to define the conditions required to use microbial amelioration of acidic drainage in decommissioning seepage collection ponds, open pits and polishing ponds.

This study examined natural wetlands near six base metal mines in eastern Canada for evidence of biological mitigation of acidic drainage. The field program, conducted in the early fall, sought to describe and compare the sites with respect to water and sediment chemistry, hydrology, and vegetation.

There were large differences in the wetlands with respect to metal loadings, groundwater inputs, water retention times, sediment metal concentrations, and vegetation communities. None of the sites, however, appeared to significantly reduce downstream loadings of metals or acidity levels during the fall sampling period. This was most likely a consequence of low temperatures, channelized flow patterns within the wetlands, and limited contact of acidic drainage with anoxic sediments. Inputs of other seeps and groundwater to the wetlands were significant complicating factors. High metal concentrations in wetland sediments, however, indicate that the wetlands had removed metals in the recent past.

This study investigated the mechanisms that mitigate the effects of acidic drainage in a natural wetland ecosystem containing submerged uranium tailings at a waste management area near Elliott Lake, Ontario. It sought to establish whether the existing natural wetlands and water cover on acid generating tailings were providing any treatment of acidic drainage. It also sought to characterize wetlands tailings/sediment substrate for metals, sulphide and sulphate sulphur speciation, and its oxidizing/reducing microbe populations, and to determine their roles in geochemical and biological interactions.

The tailings were deposited in the basin by an upstream tailings spill in the late 1950s. The average thickness of the tailings in the basin was 0.92 m. Underneath the tailings, the basin contained a layer of peat 0.3 to 4 m thick, underlain by sand and gravel deposits. A beaver dam at the east end of the basin regulated the water level and its discharge flow. In the central and eastern parts of the basin where a permanent water body existed, the surface water was near neutral to moderately alkaline with low concentrations of dissolved solids, iron, calcium and sulphate.

The existing wetland system, because of its various physical, chemical and biological controls, retained or recycled approximately 96% of the total iron produced by pyrite oxidation. In all vegetation, the observed metal concentrations were below plant toxicity levels with little or no significant accumulation. The authors concluded that the wetland/water system in the Panel wetlands basin was effectively controlling the acidic drainage from partially submerged pyritic uranium tailings. Its performance could, however, be further improved if all the tailings were completely submerged.

This study investigated passive treatment technologies, and presents a summary of design parameters, operating requirements, performance data and cost information. Although passive systems have been proven at many locations around the world, the Canadian climate and aquatic environments present considerable challenges to large-scale use in Canada.

Four types of passive technologies for treating acidic drainage were examined:

• anoxic limestone drains;
• constructed wetlands;
• microbial reactor systems; and,
• biosorption systems.

Maintenance and monitoring requirements, long term implications, cost estimates, ability to meet regulatory standards, and case studies were discussed for each of these technologies. The study indicated that passive treatment of acidic drainage has a future in Canada, but is limited to applications where flows are relatively constant, water temperature is greater than 7oC, and water chemistry has low to medium acidity and low metal concentrations.

Further research and field experience is needed to ensure that metal mining effluent regulations are consistently met. No “passive treatment” system is truly passive. All systems require monitoring and replacement of consumed alkalinity or organic-based nutrients for bacteria. Metal precipitates must also be removed, and in some jurisdictions sludge falls under “hazardous waste” regulations and disposal may be a significant challenge.

This study assesses membrane separation technologies for the treatment of acidic drainage. Commercially available hybrid membrane systems that apply combinations of Microfiltration or Ultrafiltration (UF) with Reverse Osmosis or Nanofiltration are reviewed along with other innovative approaches. Case studies on the application of membrane separation in mining operations are also presented.

The review shows that membrane separation is an efficient and cost-effective technology for mine water and wastewater treatment and mitigation applications. A comparison with conventional treatment technologies shows that membrane separation, if properly designed and operated, can provide superior treatment results with lower capital and operating costs. Membranes cannot completely replace conventional treatment technologies and be a stand-alone treatment option. They can, however, be a powerful tool for volume reduction and waste minimization, allowing for the recovery and recycling of water and other potentially valuable by-products.

This study evaluated various conventional and alternative approaches for removing and recycling metals and other by-products from acidic drainage. Treatment alternatives considered include chemical treatment, solvent extraction, ion exchange, bioadsorption and electrowinning. The technical and economic feasibility of the techniques are evaluated in search of a process that produces a high quality effluent, secures satisfactory revenue and minimizes or eliminates production of hazardous sludge.

This study evaluated the extraction of specific metals (Sb, Cd, Cu, Ni and Zn) from acidic drainage using ion exchangers. Laboratory batch and column tests were run at low, neutral and mildly acidic pH. The results indicated that most commercial ion exchangers do not exhibit a marked selectivity for the metals of interest. Consequently, the co-extraction of iron is a major obstacle for the application of ion exchange to the treatment of acidic drainage. The co-extraction of calcium becomes a problem at higher pH when lime is used to neutralize the solution. The most promising results were obtained with copper and antimony, which were even amenable to extraction at low pH. Interestingly, while the selective extraction of Cd, Ni or Zn was not feasible under most conditions, the simultaneous extraction of all three metals could be accomplished at neutral pH using either a chelating resin or a synthetic zeolite.

This study investigated the prospect of recovering metals from acidic drainage while maintaining effluent quality and reducing the generation of sludge. Several chemical methods were evaluated to selectively precipitate and recover metal ions, leading to the development of a conceptual flowsheet for a three-step precipitation process. Several concerns were raised, however, when this process was investigated at the laboratory scale. Alternative processes were thus sought. Unfortunately, the processes investigated suffer from high costs relative to conventional lime treatment. In particular, the costs of chemical sulphide reagents and H2O2 are not economical. As a result, further research aimed at optimising the existing flowsheet is not recommended unless new concepts are involved that radically reduce costs or the separation steps. Nevertheless, suggestions for some alternative options for developing a process flowsheet are provided to guide future research.

This report presents a compilation of characteristics of 72 untreated acidic drainage streams in Canada. These characteristics include stream sources, flowrates, heavy metal concentrations, acidity, oxidizing conditions and suspended solids content. The data was presented in tabular format to allow seasonal comparisons, which revealed the following trends:

• copper and zinc concentrations tend to be highest in the spring;
• lead, iron and cobalt concentrations tend to be highest in the winter;
• zinc concentrations tend to be lowest for in the summer and fall;
• copper and cobalt concentrations tend to be lowest in the fall; and
• sulphate concentrations and acidity tend to be highest in winter and lowest in spring.

Confounding factors, such as adsorption phenomena, interactions along the drainage pathway or other site specific features that are not seasonal, have an overriding impact on many acidic drainage stream characteristic. Very little data was provided on oxidizing conditions in acidic drainage streams, probably because measurements of these parameters are difficult and the results are often suspect. This information is however necessary for the consideration of many treatment options.

This Manual describes chemical treatment of acidic drainage and sludge management practices at operating and decommissioned mine and mineral processing sites in Canada. It is a useful reference for chemical treatment processes including the batch treatment of ponded acidic water, conventional lime treatment and the high density sludge type lime-based treatment process. This Manual shows that a treatment system has to be compatible with site-specific conditions, including the acidic drainage collection and storm water management system, and allowable limits on the timing and quality of treated drainage.

Part 1 discusses current and alternate chemical treatment practices. These include conventional treatment methods, such as precipitation and neutralization with lime, as well as non-conventional processes, such as copper cementation, ion exchange and solvent extraction. Lime treatment is then characterized and a discussion is provided on sludge stability, dewatering of sludge, and sludge disposal. Finally, key post closure treatment issues are considered.

Part 2 delves into long-term post-closure treatment of acidic drainage and related costs. This includes capital and operating costs for conventional, high density and enhanced high density sludge treatment facilities. Finally, case studies are provided to illustrate chemical treatment processes and associated costs.

This study was undertaken to characterize acidic drainage treatment sludge and to investigate factors affecting sludge stability. The scope of work for this study consisted of the following:

• a site survey and sampling program of acidic drainage treatment sludge at 11 Canadian mine sites (seven base metal sites, two uranium sites, one gold site, and one coal site);
• a detailed characterization of the sampled sludge, including physical, chemical, mineralogical and thermal analyses; and
• leaching of the sludge samples using two distinct tests.

Fresh (i.e., end of pipe) and aged (i.e., sludge pond cores) sludge samples were also collected to study the effect of natural sludge aging. Based on the sampling program undertaken, a general sludge sampling protocol was recommended. Freeze-drying was selected as most suitable for maintaining sludge sample integrity. Finally, in most provinces and territories, the testing of treatment sludge and its storage/disposal is controlled by site-specific licences or permits based on appropriate legislation. A review of Canadian and American hazardous waste regulations, and other pertinent regulations and guidelines as they apply to the leachability testing of acidic drainage treatment sludges, was therefore also provided.

This study assessed the effects of sludge aging and of process parameters used in the treatment of acidic drainage on metal leachability and sludge density. A modular lime neutralization pilot plant facility was used for this investigation. During the continuous pilot plant testing, various process parameters were examined, including: recycle rate, agitation rate, flocculant usage and ferric-ferrous iron ratio. The produced sludge was characterized through physical, chemical, mineralogical and metal leaching analyses to ascertain optimal conditions for producing dense and stable treatment sludge. Batch tests were also carried out to study the effect of sulphate concentration in the acidic drainage.

The study results showed that recycling can affect several treatment related factors and can impact sludge density and long term sludge stability. Increased recycling, while beneficial for plant efficiency and reagent costs, increased the heavy metal content of the sludge and led to greater metal leachability.

Slow, controlled neutralization increased settling rates. Lime consumption could be reduced by selecting a controlled or staged method of neutralization, thereby reducing reagents costs by 10-15%. The addition of excess lime to HDS-type treatment sludges resulted in lower metal leachability; however, the physical properties of the sludge were adversely affected by this potential remediation technique. Finally, results indicated that when the aging time was increased, the degree of metal mobility from sludge samples declined and the proportion of calcite and gypsum increased.

This report reviews technologies for the management of acidic drainage treatment sludges – including:

• conventional disposal technologies, such as pond disposal, codisposal with tailings, use of sludge as a cover on tailings, and disposal in mine workings;
• reprocessing options for metal recovery;
• sludge stabilization and solidification; and
• sludge reuse options, such as in construction materials and as agricultural land applications.

Reclamation considerations are also discussed in some detail. Finally, knowledge gaps are identified and recommendations are made for further work.

Natural Resources Canada conducted a survey of mine drainage treatment and sludge management practices. A detailed survey was prepared which requested information such as site background and history, mine drainage characteristics, type of treatment and reagents used, treatment issues, sludge composition, sludge management practices and issues. Data on treatment practices and sludge management were collected on over 100 sites. Most sites in the database are located in Canada, but other sites that populate the database are in the USA, UK, Australia, Mexico, Peru, China, South Africa, Germany, Brazil, New Zealand and Hungary.

The majority of sites surveyed reported that they expect to treat in perpetuity and as such, their choice of treatment is critical not only for economic but also for environmental reasons. The majority of the sites surveyed also utilized sludge ponds for dewatering and permanent sludge disposal. Generally, sites reported having sufficient sludge storage capacity for an average of 25 years.

Lime sludge solids are very fine-grained and often non-crystalline, making them difficult to characterize by traditional microscopy methods. In this report, high density sludge from seven Canadian mine sites were examined by high-resolution microscopy techniques in combination with influent and effluent characterization. The objectives were to understand the metal phase associations in sludge materials and to determine links between ARD influent/effluent chemistry, treatment process and sludge composition.

Treatment sludges show variable elemental compositions, but in all cases, the elemental abundances and dominant metal-hosting phases can be linked to ARD influent chemistry. Crystalline materials identified by XRD include calcite or Mg-calcite and gypsum. However, none of these phases were shown to be significant repositories for precipitated trace metals.

The results of the assessment highlight the potential for the development of a sludge management framework, which may permit prediction of “sludge type” from the ARD composition.

Hatch was commissioned by the MEND Program to complete a study to identify best available technologies economically achievable (BATEA) to manage and control effluent from metal, diamond, and coal mines in Canada. The objective of the study was to provide reference information for potential forthcoming changes within the Metal Mining Effluent Regulations (MMER) to the types of regulated mining facilities, the list of Schedule 4 parameters, and the authorized limits of Schedule 4 concentrations in effluent discharged to the environment.

The study describes the effluent management and treatment technologies and techniques currently employed at metal (base metal, precious metal, uranium, iron ore), diamond and coal mine operations in Canada. The study provides an overview of each (sub)sector’s water management and effluent treatment practices and establishes a model effluent treatment process and treated effluent quality to carry forward for use in BATEA selection.

The study identifies effluent treatment technologies that could be considered best available technologies (BAT) for the Canadian mining sector. The technologies were screened against a set of criteria, and those that satisfied the criteria were considered BAT and carried forward for consideration as BATEA. A technical characterisation is presented for each BAT, which describes contaminant removal mechanisms, removal efficiencies and/or achievable concentrations, major equipment, synergies with other technologies, operational challenges, current application at Canadian operations, and capital and operating costs.

For each (sub)sector, BAT technologies were further screened to identify BAT that could be applied to augment the model effluent treatment system. Cost estimates were prepared based on capital and operating cost data from vendors and operations, in-house information, and literature. BATEA for the augmentation of the model effluent treatment system for each (sub)sector were selected based on a comparative assessment of the costs and benefits of the applicable BAT technologies.

Ultimately, BATEA for any given mining operation is site-specific, as a result of the multitude of geographic and operational factors that influence effluent quality, impact the technical feasibility of treatment technologies, and dictate financial constraints on capital and operating expenditures that can be borne by operations while still maintaining economic viability.

EXECUTIVE SUMMARY The mining industry has long recognized the potential value of open pits as a means to manage environmental liabilities with a focus on site closure.  Typically, open pits have been used as a repository for mine wastes, specifically as a strategy to manage potentially reactive wastes.  The use of open pits specifically within […]

This study assessed concerns related to the solubility of metal hydroxides in the hydrated lime neutralization solids in acidic leach conditions. The focus of the investigation was on aggressive leach of fresh and aged samples of wastewater treatment plant solids collected from NB Coal Ltd‘s Fireroad hydrated lime neutralization facility. The test results indicated that precipitated wastewater treatment plant solids can be reintroduced into the acidic mine water without re-dissolving significant metals or having a detrimental effect on either lime consumption in the treatment plant or the quality of effluent treated.

This study explored the use of lime neutralization sludge to cap acid generating rock at the abandoned Fire Road mine. The study included chemical, morphological and geotechnical evaluations of the sludge, on-site barrel reactors and weathering cells that monitored leachate quality, and a field test to evaluate the geotechnical laboratory results on applications of different ages of sludge on the waste rock.

Relocation practices involving dredging of the aged sludge onto the surface of the waste rock provided several benefits, including alkalinity to reduce the mine water acidity and a low cost final disposal area for the sludge. The lime neutralization sludge therefore proved to be an effective amendment for the acid generating waste rock.

This manual describes field sampling methods for tailings. It provides guidance and recommendations on the selection of appropriate sampling methodologies for tailing solids, liquids and poregas, while recognizing the importance of site-specific conditions and the value of on-site decision making. Emphasis is placed on maximizing sample quality by minimizing sample disturbance and artificial contamination during sampling. Individual chapters discuss the collection of solid, liquid and pore-gas samples, along with the different equipment requirements for each. Finally, quality control recommendations are outlined to ensure the collection of high quality solid, liquid and pore-phase samples.

This report provides an overview of Canadian and United Stated regulatory frameworks (existing in September 1993) relevant to the decommissioning of mine sites with acidic drainage. Criteria used by different regulatory agencies to assess the performance of a decommissioning site are also summarized. This review revealed that Canada is actively involved in research on the prediction and control of acidic drainage, particularly with respect to metal mining operations. Research on acidic drainage from coal mines is likely further advanced in the United States.

In general, regulatory strategies specifically geared towards decommissioning sites with acidic drainage are still in the development stage in both Canada and the United States. Overall, environmental legislation is more prescriptive in the United States than in Canada. Some of the criteria that would typically be used in assessing the success of decommissioning of acidic drainage are effluent quality leaving the mine site and groundwater and surface water quality downgradient from the mine site. In the United States, effluent limitations, drinking water standards and surface water quality criteria have been developed at the federal level and are enforceable at either the federal or state level, depending on whether a particular state has a federally approved regulatory program in place.

In Canada, on the other hand, non-enforceable water quality guidelines or objectives are the norm. Site-specific enforceable parameters, based on water quality guidelines or objectives, may however be incorporated in mine operation permits or licences. In addition, several provinces have enacted their own criteria for surface water and/or groundwater quality.

This report provides a comprehensive description of sampling techniques and a guide to waste rock sampling design for the exploration, operation and closure phases of a mining project. Part A presents a literature review, followed by a discussion of various waste rock sampling techniques. These techniques include, amongst others: chemical characterization, physical stability, porosity testing and water content. Part B provides guidance on sampling techniques and suggested methodologies to apply during the exploration and operational phases of mine development. The objective here is to ensure that adequate data is collected to build a sufficient database that can be used to evaluate the acid generating potential of the waste rock. Finally, to demonstrate the application of these techniques, Part C presents an actual example of how data was collected and utilized to assess the acidic drainage potential at La Mine Doyon, in Quebec.

This Handbook reviews the monitoring of surface water flows around waste rock piles and provides a concise summary of waste rock sampling techniques. This summary is based on a detailed survey of waste rock sampling practices applied at sites across North America, Australia and Europe, as well as the proceedings from a workshop held with experts on this topic. At the outset, representative sampling, sampling program design, data management and quality assurance and control is discussed. This is followed by a thorough description of different sampling techniques, including chemical characterization, static and dynamic tests, water monitoring, gas sampling and temperature measurements. Finally, a summary is provided of recommended techniques for obtaining information on: cost estimates for decision making on management, maintenance, monitoring and closure of sites with acidic drainage; prediction (modelling) of potential acidic drainage; and additional sample locations/sample types and associated analyses to supplement decision making. The report indicates that instantaneous flow measurements in a stream/channel should be conducted at a location that has the best cross-section for measurement.

This report reviews quality assurance / quality control (QA/QC) protocols for field studies. It focuses on programs for predicting or detecting acidic drainage and its environmental effects. A QA/QC program begins with setting a data quality objective, which defines the level of uncertainty that a decision maker is willing to accept in decisions made with environmental data. The quality assurance (QA) component of the program is the set of operating principles that, if strictly followed, should produce results that meet this data quality objective. The quality control (QC) component of the program is the assessment of whether the data quality objective has been achieved.

Common elements of QA/QC programs for field studies include: selection of the sampling locations; replicate samples; choice of the sampling device; maintenance of field notes; technician training and evaluation; and standardization of sample collection, preservation and storage protocols.

This document reviews the elements of field QA/QC programs for sampling surface and groundwater, effluents, sediments, soils, tailings and waste rock for chemical parameters related to acidic drainage. It also reviews QA/QC programs for stream flow measurements and biological effects monitoring, including sampling populations of fish, benthic invertebrates, periphyton, zooplankton, and phytoplankton; metals in fish tissues; and the presence of Thiobacillus bacteria.

This Manual is a single source introductory guide to acidic drainage monitoring, and provides information on literature sources for site-specific concerns and emerging monitoring techniques. Its main focus is on the pre-operational phase of new mines; however, additional information is provided for operating or decommissioned mines that face acidic drainage problems. Surface water sampling methods are reviewed and monitoring requirements are discussed for both source (i.e., the freshwater pathway between the acid generating source and the designated point of release) and receiving freshwater environments. Measurements of groundwater flows and of groundwater contaminant seepage to surface water are also addressed. In addition, comprehensive information is provided on sediment sampling, including chemical characterization studies, investigations of in situ benthic communities and sediment toxicity assays. Plankton and fish sampling methods are also discussed.

Basic concepts and principles are first described in the Manual. This includes a general description of geochemical and biological processes associated with the generation of acidic drainage, followed by the basic framework for the development of monitoring programs. Separate chapters are then dedicated to routine source monitoring and receiving environment monitoring. This latter chapter covers both abiotic monitoring components (i.e., hydrology, water quality and sediments) and biotic monitoring components (limited here to benthic macroinvertebrate communities and fish indices). A basic introduction is also provided on the role of toxicity testing in a mine’s environmental monitoring plan. Finally, technical summary notes with detailed information on specific sampling techniques are included in an accompanying appendix (see MEND 4.5.4 Appendix). The report notes that analysis of composite samples should be carefully reconsidered in light of the loss of information relating to variable water chemistry due to water column stratification.

This appendix accompanies MEND report 4.5.4 and presents technical summary notes. These notes are designed to provide basic information on specific sampling tools or protocols, including the advantages and disadvantages of each and, where possible, and assessment of the associated cost efficiencies.

This report demonstrates the application of geophysical methods for monitoring acidic drainage. This application is possible because increases in total dissolved solids in groundwater result in an increase in electrical conductivity. Lateral and vertical variation of conductivity can then be mapped using geophysical methods. Other geophysical methods can also be used to map the distribution of disseminated sulphides and zones of active oxidation or reduction reactions. Under suitable conditions, a combination of geophysical methods can be used to map: sulphides (i.e., the source of acidic drainage); zones of active oxidation; and the distribution of acidic drainage.

In this study, high-quality airborne, ground and borehole geophysical data were acquired over areas with well-documented problems of acidic drainage. The geophysical data were correlated with hydrological and groundwater chemical data to establish the utility of the methods. The results confirmed that electromagnetic methods that remotely measure the conductivity of the subsurface are very useful for detailed three-dimensional mapping of acidic drainage in groundwater. Airborne surveys can provide rapid reconnaissance scale surveys, while ground surveys and borehole surveys provide more detail. All these methods, however, require measurement of the electrical properties of the subsurface and are adversely affected by electrical noise from power lines, and from surface and buried metal. The response of acidic drainage may also be masked by naturally conductive groundwater, bedrock lithologies, and clay soils.

This report provides a compendium of information on methods in use at present, and tabular lists to assist readers in assessing the applicability of available techniques to detect and monitor acidic drainage.

This handbook outlines and describes various monitoring technologies used to determine the presence and progress of acidic drainage. A summary of state-of-the-art methods is presented, along with a compendium of information on methods currently in use, organizations active in the field, suppliers of equipment and services, and available products and equipment. Tabular form guides assist users to assess the applicability and effectiveness of techniques to detect and monitor acidic drainage.

Part 1 of this handbook covers remote sensing. This includes instruments based on film, video, radar and multi-spectral imaging. Specific instruments considered include satellite technology, airborne imagers, aerial photography and radar. Application of these instruments is considered with respect to three criteria: vegetation, moisture and soil/rock. Part 2 of this handbook covers geophysics. The geophysics instrumentation considered includes electromagnetic, airborne systems, DC resistivity and ground penetrating radar.

This study entailed the collection of data at tailings impoundments with different conditions, including:
• sulphide mineralogy (pyrite or pyrrhotite);
• sulphide content;
• acidic versus neutral conditions;
• age since deposition; and
• sites with oxygen barrier covers over existing tailings.

An oxygen consumption method was employed to provide a quantitative assessment of in-situ oxidation rates in tailings at six field sites. Results were examined to evaluate the rate of in situ oxidation at each site and to examine possible trends in oxygen consumption rates with other physical site characteristics.

A strong trend of increasing oxygen consumption rate with increasing sulphide content was observed. Lower oxygen consumption rates were also observed for cooler, wetter climatic conditions than for dryer, warm conditions. A trend of decreasing oxygen consumption rates with tailings exposure time was also observed. Oxygen consumption rates measured on highly saturated tailings were notably lower than for similar tailings where a developed vadose zone existed. Oxygen consumption rates measured on freshly deposited, fully saturated tailings and on tailings that were highly saturated indicate potentially significant loadings to receiving waters. Measurements of oxygen consumption rates to evaluate the effectiveness of various cover scenarios indicated that the addition of a layer of non-reactive material can substantially reduce the flux of oxygen to the tailings. This study clearly showed that the oxygen consumption method provides a rapid and cost effective assessment technique that can provide useful and critical data for a wide variety of sulphide tailings sites.

The oxygen consumption method, initially developed as a tool to assess reactive tailings in the laboratory and field, was adapted to measure reaction rates on waste rock samples in short-term experiments. This method involves placing a moist waste rock sample in a gas-tight reaction vessel and then monitoring the gas-phase oxygen concentration for 2 to 3 days at constant temperature and moisture content concentrations. The technique provides reaction rate data that can complement data from humidity cells. Many samples can be processed simultaneously and, therefore, a larger body of kinetic data can be developed for cost-effective statistical assessment and interpretation. This study represents the development of the technique, demonstration of the interpretation and a comparison of several waste rock types.

The oxygen consumption rate was expected to increase with decreasing particle size, increasing temperature, higher sulphur content and inoculation with T. ferrooxidans bacteria. The experimental results generally agreed with the expected trends. The oxygen consumption rate consistently over-estimated the rate of sulphate release for samples containing pyrrhotite. Conversely, samples containing pyrite as the dominant sulphide mineral exhibited oxygen consumption rates that correlated well with the amount of sulphate released.

This study showed that oxygen consumption measurements provide waste rock reaction rates that can be used to interpret potential acid generation and metal leaching rates. The method is simple, rapid and inexpensive with the capability of performing multiple tests simultaneously. The data can be used to assess depletion rates for sulphide minerals and neutralization potential. Although the method does not provide water chemistry, the oxygen consumption values can be used to infer drainage chemistry and provide complementary data for other kinetic testing such as humidity cells. The results of the oxygen consumption tests can also be used as input values for sophisticated waste rock models.

This report presents a monitoring design for sites with acidic drainage, with a focus on optimum water quality sampling frequencies and the most representative, measurable parameters for acidic drainage. First, the monitoring methods used in Waste Management permits at BC mines with acid drainage potential are examined. The un-replicated fixed-frequency samples are shown to be inaccurate in estimating mean concentrations. These are also inadequate for determining peak values and short-term fluctuations. Alternate monitoring methods are thus reviewed from the monitoring and statistical literature.

Different monitoring goals are discussed with reference to the different monitoring methods available. Basic sampling statistics are then reviewed as they apply to water quality data. Methods for performing preliminary sampling studies are also described. These studies determine the variances in different components of a site, thereby permitting the determination of sample sizes and strata to optimize sampling efficiency. Seasonal variations are considered and daily data are compared with the monthly official monitoring record to illustrate the short-comings of monthly sampling in a rapidly fluctuating system. Finally, general guidelines for the monitoring of untreated mine water and receiving environments are provided, followed by a brief discussion of biological monitoring as an alternative to water quality monitoring.

This report presents the results of a thorough literature review on biological monitoring techniques related to heavy metals in aquatic environments. Details are provided on the wide range of available indicators and the most promising and proven biological monitoring techniques are identified. Use of a suite of biological assessment tests that assess responses at the levels of individual, population and community is strongly recommended; no one method or level of examination will provide all the required information. Biological indicators require, for maximum utility, supporting data from analyses of tissue and environmental levels of contaminants, information about the history of exposure of the organisms to contaminated habitats, and some understanding of the vulnerability of the species to the particular contaminants.

Ecosystem health can be assessed by monitoring in two ways: a “bottom-up” or a “top-down” (reductionist) approach. Advantages and disadvantages of both are discussed. As a general rule, physicochemical criteria have probably been used with the least success in the long-term management and conservation of natural ecosystems. Therefore, it is not advisable to regulate solely based on physiological changes in algae, invertebrates or fish.

The best understanding of the effects of acid mine drainage will be reached through a progression of studies from the community level through to the level of biochemical responses within individuals. It is also essential to relate changes in the fish and benthos to changes in the water quality parameters. Suitable parameters include temperature, turbidity, chlorophyll a, dissolved oxygen, nutrient concentrations, pH, sulphates, conductivity, hardness and metal concentrations.

Environment Canada is undertaking a 10-year review of the Federal Metal Mining Effluent Regulations (MMER) that regulate what compounds the 105 metal mines in Canada can deposit in waterways. Part of these regulations are guidelines for Environmental Effects Monitoring (EEM), which are field biological studies that mines must perform. In these studies, mines test endpoints such as fish age, weight, condition, and gonad and liver size downstream of mines to assess whether their activities are having an effect on the receiving environment. Most of these 105 mines have undertaken three phases of monitoring; we obtained most of these data from Environment Canada, however, the data set is incomplete. With the data we had, we assessed whether fish downstream of metal mines in Canada are affected by metal mines. We found that fish downstream of base metal (Phase 1, 2 and 3/4) and precious metal (Phase 2 and 3/4) mines tended to have reduced condition, and that fish downstream of base metal mines (Phase 1 and 2) and precious metal mines (Phase 2) had enlarged livers. The effects on gonad size were variable between phases. There weren’t enough data to assess iron ore, uranium, and other metal mines in Phases 1 and 2, though results from Phase 3/4 show no effects across endpoints these mines, but do show reduced liver size and increased condition in iron ore mines. However, because our source data were incomplete, our results have to be interpreted with caution.

Experience from 10 years of EEM studies has shown that there are a large number of false positive tests, meaning that the EEM studies are showing an effect on downstream fish due when there may not be a problem. Therefore, Environment Canada and the Mining Association of Canada have suggested two major changes to the methodology: implementing Critical Effects Sizes (meaning that the difference between upstream and downstream fish has to be sufficiently large to trigger a “failure”) and a Bonferroni Correction (which would require that the level of certainty depend on the number of tests performed). We looked at how these changes would impact the findings. We found that using Critical Effects Sizes would reduce the number of mines that “fail” EEM tests by more than half. Because there were many false positives in the original program, we suggest that this will reduce the rate of false positives without reducing protection for the environment. However, we don’t find that the rate of false positives require a Bonferroni correction and in fact using this may be too conservative, and result in a number of mines not “failing” an EEM test when they should.

We conclude that there are measurable biological effects downstream of metal mines across Canada, particularly for base and precious metal mines, but note that our data set is incomplete and some caution must be afforded to these conclusions. We also conclude that implementing Critical Effects Sizes will do a great deal to address the rate of false positives in EEM studies, but that there is no need to use a Bonferroni correction, which is overly conservative and would result in the reduction of protection for the environment.

This study used a stream “mesocosm” to examine the effect of adding treated acidic drainage on the composition and abundance of periphytic algae and aquatic invertebrates downstream of the discharge from the Equity mine, in BC. An apparatus consisting of 10 flow-through troughs, suitable for invertebrate and periphytic algal colonization and growth was installed and tested at the site. After three weeks of running stream water through the troughs to permit colonization by stream invertebrates, treated acidic drainage was added to 5 randomly allocated troughs for a duration of three weeks. Water, algal, and insect (drift, adult emergence, and benthos) samples were collected for analysis. Results showed that at 10% dilution, the addition of treated acidic drainage did not impact aquatic insect composition and abundance.

The study showed that the application of the mesocosm approach, within a rigid and well-structured experimental design, can be a powerful tool to accurately determine ecosystem response curves for effluent discharges during mine operations or at closure. An important advantage of the method over more common single-species bioassays is the power of predicting changes in ecosystem functioning, which is fundamental to establishing site-specific water quality criteria.

This study was a continuation on previous research conducted at the Equity mine in BC to test the effects of the addition of acidic drainage to a stream mesocosm. Six troughs were added to the previous 10-trough layout to quantitatively describe the relationship between raw acidic drainage dilution and indices of abundance and composition of macrobenthos and periphyton communities.

At dilutions less than 1:1000, there was clear evidence that acid neutralizing capacity of the stream was exceeded. Metal levels increased by several orders of magnitude with declining dilution of acidic drainage. Metals that changed most from the additions of acidic drainage were those known to be most toxic to aquatic organisms. A separate group of processes that potentially contributed to toxicity included the ingestion of metals bound to a series of low and high energy binding sites on food particles. The abundance of the diatom dominated periphyton community and mayfly/chironomid dominated benthos declined with increasing doses of acidic drainage. Of the taxon that dominated the benthic community, only the abundance of the Orthocladiinae did not change as a function of the additions of acidic drainage. Insect drift analyses indicated an immediate avoidance response to the onset of the acidic drainage additions.

This study suggests that models based on community level responses to experimental dilutions of chemical mixtures are appropriate predictors to be used after an initial screening. The results also indicated that the concentration of a metal in solution that causes change in community structure can be lower when that metal is part of a complex acidic mixture with other metals compared to when the same metal acts individually on single organisms or simple populations.

This literature review focuses on the assessment of sediment quality through sediment chemistry, bioassay testing and benthic macroinvertebrate community structure. Analytical methods for sediment chemistry are reviewed and summarized. Sampling devices, design, handling and preparation are evaluated with respect to sediment toxicity testing. Freshwater sediment bioassays with bacteria, alga, invertebrates and fish are then reviewed. Application of several bioassays in a multitrophic or battery approach is recommended. The utility of benthic macroinvertebrate community structure and function as measures of sediment quality is also discussed. Sampling methods and design are reviewed, and natural substrate sampling is recommended over artificial substrates. Recommendations are also made for sorting, taxonomic identification and statistical analysis of benthic infauna datasets. Finally, guidelines for sediment chemistry, bioassay testing (test battery) and benthic macroinvertebrate community assessment are provided.

This report presents a model for the prediction of trace metal speciation in the environment. In this model, specific ionic species are evaluated and the interactions of catonic species with anionic species are considered. Data from the Tsolum River in BC is then applied to the model. Based on the results, recommendations are made to improve the basis of regulatory decision-making in evaluating the effect of increased metal loading to the environment.

Large scale studies in North America and Europe have successfully used paleolimnological indicators to show that acid precipitation has affected lakes. This study was thus carried out to investigate the potential for using paleolimnological techniques to provide “baseline” data to assess the impacts of acidic drainage from mines. To apply the paleolimnological techniques developed for acid rain studies to monitoring of acidic drainage in BC lakes, it is first necessary to develop a calibration data set that relates species assemblages of the chosen indicator taxon to levels of acidic drainage-related parameters (pH, iron, aluminum, copper, zinc, and/or other metals) in BC lakes.

This report recommends a methodology for carrying out the required calibration study. Suggestions include statistical tests for data analysis, coring techniques to obtain an undisturbed sediment record, laboratory analytical techniques, and quality assurance/quality control procedures.

Note: Paleolimnological research, in its broadest sense, is directed at reconstructing lake history.

In many geologic settings, seepage enters surface water invisibly through submerged fractures and bottom sediments. This study was designed to evaluate an innovative use of an electrical-conductance, bottom-contacting probe (sediment probe) that can be used to identify locations of groundwater discharge on the bottom of lakes and rivers. In this study, this method was applied at mine operations near Sudbury and Timmins, Ontario. A sediment probe was towed behind a slowly moving boat over more than 21 line-kilometres of lake and river bottom. This method effectively identified discharge of acidic drainage into surface waters. By quantifying the groundwater and solute-transport, it also provided estimates of impacts at specific points of discharge.

This report provides a comprehensive list of information requirements and factors to consider in assessing, and mitigating, acidic drainage. Specific requirements are listed under the two categories:

1. Material Characterization & Acidic Drainage Prediction:
• geology and mineralogy;
• static tests to measure material composition;
• kinetic tests to measure reaction rates and drainage chemistry;
• assessment of waste materials and site components; and
• interpretation of geochemical results.

2. Mitigation:
• flooding of mine wastes and workings;
• measures to reduce infiltration of drainage and/or oxygen entry;
• drainage treatment;
• addition of neutral materials; and
• desulphurization of tailings.

When developing or reviewing mining plans, this list can be used to identify what factors to consider and any outstanding information requirements. While this list will help ensure all relevant issues are addressed, it is only intended as a starting point. For any particular site, many of the listed factors or information requirements may not be relevant. Similarly, there will be instances where additional information requirements and factors must be considered. Users are encouraged to adapt the generic suggestions presented here to their own site and requirements, incorporating appropriate site-specific performance measures.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – essentially, a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.
The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:

• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 1, is intended as a stand-alone detailed summary of the Manual. It introduces the MEND program and provides a detailed summary of the five other volumes of the Manual. Readers are encouraged to read Volume 1 to get a good sense of the content of the entire Manual. People who want to learn about research developments in acidic drainage, including techniques available to prevent and control acid generation or treat drainage may find this volume sufficient for their needs. Background information on acidic drainage, including estimated associated liability in Canada, is also provided in Appendix A.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.

The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:
• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 2 reviews sample collection and analyses methods that have been assessed and used by MEND and others as part of their studies into the prediction, prevention, control and treatment of acidic drainage. It is a general reference on the methods used to collect samples (surface water, groundwater, solids, waste rock, mine surfaces, sludge, sediments, biological and geophysical) for acidic drainage-related purposes and associated chemical analyses. Given the complexities inherent in collecting samples for scientific analyses under diverse conditions, this volume cannot specifically indicate all the aspects that need to be considered in collecting a sample. However, general guidance is provided by identifying sampling methods and discussing relevant sampling issues. To further assist readers, Volume 6 (monitoring) addresses the development of acidic drainage and environmental monitoring strategies.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.

The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:
• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 3, is intended to give the reader an overview of available prediction techniques. It describes laboratory and field methods, and models used to predict the geochemical behaviour of mine wastes. This includes the acid generating potential, quality of drainage over time and effects of closure strategies.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.

The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:
• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 4, discusses prevention and control technologies for acidic drainage, including: water covers, saturation, dry covers, co-disposal of tailings and waste rock, blending and layering, separation and segregation, permafrost, and backfilling. The results from MEND studies indicate that prevention and control applications are not necessarily universally applicable, and site-specific conditions need to be taken account. Good quality, long-term data is also important. The process of selecting the most appropriate acid prevention or control technology should in most cases include an assessment of available technologies. At some sites, it may be possible to develop a cost-effective strategy that involves more than one acid prevention and control technology.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.

The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:

• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 5, discusses active and passive treatment methods for acidic drainage. The principal objectives in treating acidic drainage are to neutralize free acidity and reduce the concentrations of contaminants of concern to very low levels so that effluent quality is acceptable for recycle or release. Active treatment methods considered include chemical treatment, metal recovery / recycling, and treatment by-products. Active treatment is typically accomplished using lime-based processes that vary in application from batch treatment of ponded acidic water to continuous treatment using a high-density sludge type treatment plant. This results in the formation of a gypsum / metal hydroxide / carbonate sludge that requires disposal.

Passive treatment methods considered include limestone drains, aerobic wetlands, passive anaerobic treatment, biosorption treatment and in situ treatment. Associated costs are also discussed. The principal goal of a passive treatment system is the long-term, sustainable neutralization of acid and immobilization of metals at low cost and with relatively minor labour, raw materials, or energy inputs. The challenge facing the mining industry is to design a passive treatment system capable of consistently reducing contaminant concentrations in a time frame measured in hours or days, rather than centuries. To date, Canadian experience indicates passive systems, alone, cannot be relied on to consistently meet acidic drainage standards. As a result of MEND research, however, it is now possible to base feasibility evaluations of passive treatment on a far superior understanding of design principles and an ever broadening experience base.

The MEND Manual is a single source reference to acidic drainage research undertaken by the MEND program between 1989 and 2000, and of select complementary work completed outside MEND. It describes MEND-developed technologies and their applicability in term of costs, site suitability and environmental implications – a toolbox of techniques and options. Information is provided on chemistry, engineering, economics, case studies and scientific data relevant to mine and milling operations.

The MEND Manual includes a summary volume (Volume 1) and five technical volumes that address:

• Volume 2: Sampling & Analyses (MEND report 5.4.2b);
• Volume 3: Prediction (MEND report 5.4.2c);
• Volume 4: Prevention & Control (MEND report 5.4.2d);
• Volume 5: Treatment (MEND report 5.4.2e); and
• Volume 6: Monitoring (MEND report 5.4.2f).

This report, Volume 6, describes monitoring with respect to strategic collection and assessment of data relevant to the prediction, prevention, control and treatment of acidic drainage. Key objectives common to acidic drainage monitoring programs include: assessment of the potential for acidic drainage; detection of the onset of acidic drainage to allow for mitigation actions; assessment of the performance of acidic drainage prevention, control and treatment measures; establishment and regular updating of site-specific monitoring databases; and provision of data for management decision-making. Information is presented on acidic drainage monitoring and sampling techniques and more generally on environmental monitoring programs.

This study evaluated the costs of applying various technologies to reactive mine wastes to prevent, control or treat acidic drainage. The technologies evaluated included a composite soil cover, self-sustained and maintained water covers, a combination of these covers, a plastic liner cover, waste removal and the long term collect and treat option with or without a simple soil (or vegetation) cover.

The study results indicate that the self-sustained water cover and the collect and treat technologies may represent the best options from the perspective of the implementation costs. Unit costs of acidic drainage treatment are, however, site specific and can vary widely. This is particularly true for self-sustained water covers for tailings and for the collect and treat technologies for waste rock. In general, the composite soil cover and plastic liner technologies were confirmed to be the most expensive. The study results also indicate that it is unlikely that a walk-away option would be selected for a major waste rock dump that generates net acidity at the time of closure.

This report summarizes the result of a two-day workshop on mine reclamation and associated financial liability. The workshop was held between representatives from the mining industry and provincial and federal mining ministries. Questions concerning forms of financial assurance, marginal operators, consistent closure standards, funding for orphaned sites, post closure security and exit tickets were discussed. Estimates of acid-consuming and acid-producing mine wastes in Canada are also provided, along with an estimate of liabilities.

French version of MEND 5.8e: This report summarizes the result of a two-day workshop on mine reclamation and associated financial liability. The workshop was held between representatives from the mining industry and provincial and federal mining ministries. Questions concerning forms of financial assurance, marginal operators, consistent closure standards, funding for orphaned sites, post closure security and exit tickets were discussed. Estimates of acid-consuming and acid-producing mine wastes in Canada are also provided, along with an estimate of liabilities.

The MEND Program is a cooperative research program that is sponsored, financed, and administered by a voluntary consortium consisting of the mining industry, the Government of Canada, and eight provincial governments. The program develops technology to prevent and control acid mine drainage which is considered to be the largest environmental liability facing the mining industry.

This report presents the results of a performance assessment intended to establish whether MEND reached the key targeted users and stakeholders and whether it achieved the direct and intermediate outcomes established at its inception and logically connected to its long-term goals. The assessment considered: how MEND spent resources, carried on activities, and produced outputs; who the program has worked with in terms of users and stakeholders; what the program was intended to achieve; and, direct, intermediate, and longer-term outcomes and impacts. The results of this assessment showed that MEND has developed an exemplary model of public-private cooperation that has fostered increased cooperation and confidence in the Canadian mining sector and marketplace with respect to acid mine drainage prevention and treatment. This has led to some significant early benefits in mining operation cost reductions and improved environmental protection practices. A longer time frame for evaluation will be required to judge the full economic and environmental impacts of the program.

This report presents an overview on acidic drainage in permafrost. It begins with a discussion of the northern environment, including the occurrence and distribution of permafrost in different regions. The effect of temperature on acid generation is then explained. Case histories of thermal regimes at existing mines are reviewed to provide an understanding and baseline information on ground temperatures, temperature profile changes over the year, and the factors that influence the development of permafrost. This is followed with a brief outline of design considerations that can be used in the design of mines or in the development of closure plans in permafrost areas. Concepts for the prevention of acidic drainage through the disposal of tailings in permafrost conditions are considered. In addition, options to freeze and maintain mine tailings frozen in continuous and discontinuous permafrost regions are discussed. Finally, the report provides conceptual cover options, designs, and cost estimates for tailings impoundments in continuous and discontinuous permafrost.

This study tested the use of a super absorbent polymer (SAP) to create an impermeable cover on tailings. SAP is made of polyacrylamide-modified clay. When fully hydrated, one gram of SAP can absorb more than 650 grams of fresh water, thereby increasing its volume significantly. Preliminary tests with SAP/sand mixture showed a significant potential for SAP application in the abatement of acidic drainage from tailings. The hydraulic conductivity in the sand was lowered significantly, while the moisture retention capability increased. The use of SAP in a bottom liner of a tailings pond is not a viable option due to the poisoning effect of multi-valent cations on the SAP. Conversely, a SAP-bearing cover should be an effective hydraulic barrier. The cost for this material may be offset by the savings on the transportation of another barrier material and construction of the cover.

This report was written following on a two-week reconnaissance visit to Japan in 1993. Visits were made to government, industrial and university laboratories and research institutions engaged in studies on acidic drainage. A high degree of collaboration and unanimity of purpose was found between the various sectors involved in the research; one could almost consider it an integrated national effort. There appeared to be a consensus that the development of new treatment technologies will form the basis of a lucrative new industry both nationally and internationally. In addition, it is accepted that to protect its mineral supplies in developing countries, Japan must assist these countries in all aspects of mineral exploitation, including environmental protection measures.

Some new technologies have been fully developed and successfully introduced, notably those based on the bacterial oxidation of ferrous iron. The Ferrite and Iron Powder processes are also now widely used for the treatment of metalliferous industrial effluents. The sludge-densification process based on recycling precipitated sludge particles from the settling tank back to the neutralizing tank is also being successfully operated in several plants. Other new technologies have been extensively developed, but are not yet introduced. These include systems for the recovery of ferrite and hematite from iron-rich mine drainage waters and a flotation process for the recovery of metals from mine drainage.

At present, a whole range of new technological approaches are being examined, but are in the early or middle stages of development. The most important of these are processes involving ion-exchange technology, membrane technology, sulphate-reducing bacteria, sulphur-oxidizing bacteria and metal-absorbing organisms. Also, plans to use the stopes in abandoned mines for the disposal of sludges and solid wastes are being investigated.

Contains 47 reports on Prevention and Control.

Contains 51 MEND reports and workshop notes.

Following the completion of the MEND and MEND 2000 programs, a new multi-stakeholder program called “MEND3″ was initiated in 2001. The objective of MEND3 is to conduct carefully focused Canadian national and/or regional research that will improve environmental performance and stewardship and reduce financial liability associated with acidic drainage and metal leaching. To launch MEND3, this project was commissioned to determine, through workshops and consultations, where research activities should be focused. The results indicated that the widest technology gaps lay in the:

• prediction of the behaviour of underground mines, open pit mines and waste rock piles;
• application of blending of waste rock and/or tailings as a control measure;
• suitability of alternatives to conventional dry soil covers;
• application of low temperatures to prevention and control of acidic drainage;
• use of passive water treatment systems; and
• understanding of the chemistry of elements mobile under non-acidic conditions.

The benefits of research in these areas would be partly regional and specific to the phase of mine operation. Research on underground mines would have a national benefit, whereas open pit mines and large waste rock piles are primarily located in western Canada. Blending is applicable to proposed and operating mines where new facilities are being designed. The development of alternative cover materials would be primarily beneficial to the remediation of historic mine sites in eastern Canada with large tailings deposits. Finally, research on the application of low temperatures will primarily benefit the diamond mines in Northwest Territories and Nunavut, but will also be applicable to the closure of historic mines in permafrost regions.

This report presents the result of a workshop held to identify potential research in acidic drainage and related issues, and develop a list of research priorities to present to potential funders. A shift was identified from early work related to control and limitation of liabilities, to a broader recognition of environmental and sustainable development issues. Participants agreed that MEND should demonstrate adherence to the principles of sustainable development. This includes a discussion of the environmental, social and economic impacts of mining activities, as well as identification of key issues facing society through the life of a mine.

Workshop participants also recognized the value of completing a set of case studies that would both build on existing studies and provide information about new sites. Verification of MEND developed technologies through long-term monitoring will also expand the knowledge base and possibly extend application. Finally, an overriding recommendation was that the MEND initiative should continue operating with an expanded mandate beyond acidic drainage issues.

This report presents a thorough description of acidic drainage assessment and mitigation at the closed Johnny Mountain gold mine in BC. Mine components considered include the tailings, waste rock, and underground mine workings. The tailings have the highest potential to generate acidic drainage. This was recognized prior to mining, and the tailings were therefore placed in a flooded impoundment. Monitoring of the drainage indicates that flooding of the tailings has been successful in limiting sulphide oxidation. Remaining work items, such as increasing the geotechnical stability of the dams and leveling the tailings, will occur after placing waste rock in the impoundment.

Most of the focus of acidic drainage work since the mine closed has been on the waste rock. Early visual assessment of mineralization and acid base accounting results from four samples indicated that the waste rock had little or no potential for acidic drainage. Waste rock was thus placed in aerial dumps or used for construction. Analysis conducted after the mine closed indicated that most of the waste rock is potentially acid generating, and preventing acidic drainage will require costly re-handling. This experience illustrates the danger of relying on geological suppositions or visual observations of the extent of mineralization.

The proposed acidic drainage mitigation plan for the underground workings is to limit oxygen entry by placing bulkheads in the adits and covers over the ventilation raises. Questions include the effectiveness of bulkheads and covers in limiting air entry and the impact of progressive rock fall on the acid generation potential, especially in ore zones with high metals and pyrite. The experience at Johnny Mountain illustrates some of the gaps in our understanding and limitations in our ability to collect the information required for accurate acidic drainage assessment and cost effective remediation. This includes our limited understanding of the rate of air entry, oxygen concentrations and sulphide oxidation rates in closed, plugged underground mines in mountainous terrain.

This report presents a thorough description of acidic drainage assessment and mitigation at the closed underground Snip Mine in BC. It discusses: acidic drainage issues over the life of the mine and after mine closure; waste management approaches including flooding; and the diverse challenges associated with acidic drainage assessment and mitigation. From the perspective of metal leaching and acidic drainage, the main site components are the tailings impoundment and the underground workings. Waste rock was: used as underground backfill, either directly or crushed and cycloned to produce backfill sand; placed in dumps at the mouths of various portals; and used to construct the tailings impoundment. The majority of the tailings were cycloned to produce backfill sand for use underground. The slimes, the fine-grained reject of the cycloned tailings, and whole tailings when cycloning did not occur were placed in the impoundment on site.

A key lesson learned was the importance of early recognition of acidic drainage risks and information deficiencies. Early recognition of the geochemical risks associated with the underground workings would likely have resulted in modifications to the mine plan, with the mine either reducing the sulphide content of the backfill (e.g., desulphurization prior to cycloning) or not using tailings sand as backfill. Recognition of acidic drainage during exploration would also have permitted more complete grouting of exploration drill holes. Earlier recognition of the uncertainty regarding future water quality would have enabled the mine to use its operating facilities and site personnel to run long-term studies underground. Recognition of acidic drainage information deficiencies earlier in the mine life is especially important for underground mines where access is limited once mining ceases.

This report presents a thorough description of acidic drainage assessment and mitigation at the advanced Sulphurets exploration project in BC. The main focus was on assessment and remediation of acidic drainage associated with waste rock at the site. Reclamation and mitigation options are discussed for the waste rock, along with the conditions of the final permit for waste rock disposal in an adjacent lake.

This study revealed that despite their relatively small size, the costs and potential impacts make the mitigation of metal leaching and acidic drainage at historic mine sites and exploration projects, like Sulphurets, quite challenging. In common with many historic mine sites and exploration projects, challenges at Sulphurets included limited information on the site and materials, access difficulties and an adverse climate. The high access costs, lack of site personnel and small budget made it difficult to collect additional information. Access difficulties and climate constraints were also a major consideration in the review of potential mitigation measures. Mitigation constraints included a probable lack of suitable soil materials for the construction of covers and dams, a deep snow cover much of the year and the resulting large runoff, and the difficulty operating facilities and conducting monitoring and maintenance in such a harsh climate and remote site.

The experience at Sulphurets illustrates the need to consider hydrogeology when selecting a disposal site and the importance of characterizing soil hydrology prior to waste rock disposal. Even if it is just an exploration project, due care and attention is required in selecting a disposal site for sulphidic waste rock. Factors that may need to be considered include groundwater inputs, upslope drainage diversion, down slope drainage collection and ease of removal. A soil and vegetation survey should be conducted to collect the required information on the height of water table throughout the year.

This report presents the site rehabilitation work completed on tailings at the closed underground Dona Lake gold mine in Ontario. This case study provides an example application of the elevated water table concept for decommissioning a tailings management facility. The tailings impoundment is situated in a low lying area and is surrounded by natural topographic highs to the east and west. The elevated water table, maintained by the site topography, minimizes the ingress of oxygen in the saturated tailings and ultimately reduces their oxidation. In addition, a rockfill cover was installed over the exposed tailings to reduce the area of tailings potentially exposed to oxidation.

The neutral pH and low metal concentration in the tailings supernatant and the final effluent contaminant levels well below discharge criteria are indicators of successful rehabilitation at the Dona Lake mine. The rockfill cover efficiency, however, has not yet been conclusively demonstrated in the field.

This study assessed the effect of subaqueous disposal of high-sulphur base metal tailings into Mandy Lake, Manitoba in 1943-44. This site provides valuable information on long-term performance of underwater-deposited reactive tailings in natural waters. Two monitoring programs have been conducted at the mine since it ceased activities in 1944. Findings from these investigations are presented in this report and indicate that the physical and biological settings of the lake have recovered from the deposition of tailings. Water quality is good, and aquatic life is diverse, abundant and relatively healthy. An organic layer covers the shallower tailings and appears to be acting as an oxygen sink thereby reducing oxygen concentrations at the water-sediment interface, despite high metal content in the tailings.

The report authors emphasize the importance of determining the recovery rate of a lacustrine ecosystem following subaqueous disposal. At minimum, one long-term pilot project on a selected lake, where appropriate baseline information has previously been collected, should be envisaged to provide insight into the processes that govern recovery and the rate of that recovery.

This report presents a case study on the management of tailings at the Heath Steele Mine in New Brunswick. The mine and milling operations ended in 1999. During operations, tailings in the North Cell were deposited underwater, while in the Upper Cell, the deposition of tailings was sub-aerial. Providing a water cover as an oxygen barrier to prevent and reduce acid generation and metal leaching was the preferable option for the tailings basin. Tailings in the Upper and North Cell were dredged to lower elevations and a large volume of potentially oxidized tailings in the Upper Cell was moved to the North Cell. The water level in the Old Tailings Area was allowed to equilibrate with the water level in the Upper Cell by hydraulic connection created through a permeable sludge pond dam built on top of the old tailings dam.

Heath Steele Mine monitors the performance of the water cover in terms of surface water quality. It has observed a pH variation between the North and Upper Cells. The addition of lime at the internal dam has been necessary to raise the pH to meet the final effluent requirement. Two years after the completion of the water cover, a reduction of the metal loadings to the environment was observed.

This report describes the use of flooding for remediation of acidic drainage from tailings at the Solbe mine. The Solbec tailings pond was active from 1962 to 1977. Over 2.5 million m3 of sulfide waste were deposited at the site, and sporadic sampling performed between 1972 and 1980 confirmed the presence of acidic drainage. A 1987 characterization report of the tailings pond tabled flooding of the tailings as the most appropriate solution to the problem. This led to a series of studies between 1989 and 1993 to test the efficiency and viability of flooding, followed by flooding in 1994. Since then, the quality of the water cover and groundwater associated with the tailings pond has been monitored extensively. This monitoring program includes an evaluation of the viability and activity level of the oxidizing microorganisms and of the hydrology and wave impact on site.

The pH is now near neutral and the anomalous concentrations of iron, zinc and copper are resorbing. In addition, the basin retains enough water to keep the tailings submerged and thus prevent harmful wave action. The effectiveness of the solution is supported by a decrease in the oxidizing microbial population, the cessation of its oxidizing activity and the appearance of sulfate-reducing bacteria. These bacteria contribute to the inverse oxidation process by reducing sulfate ions to sulfide ions, which re-precipitate metals in the more stable form of metal sulfides.

EXECUTIVE SUMMARY A general concern for timely results of toxicity tests by industrial dischargers, including members of the metal mining sector and government regulators, has resulted in the investigation of several micro/screening toxicity test procedures emerging into the market place as alternatives to methods currently in place. The purpose of this evaluation is to determine […]

EXECUTIVE SUMMARY From a literature review, eight sublethal tests were recommended for further laboratory evaluation, and possibly for subsequent field validation: Microtox™ chronic test, Selenastrum microplate, multi-species algal microplate; duckweed, Ceriodaphnia; nematode; fathead minnow, larval growth; trout early life-stages. Ceriodaphnia was scored highest. The nematode test might prove to be a simple assay to represent […]

EXECUTIVE SUMMARY  The objective of the laboratory screening study was to evaluate nine sublethal toxicity tests through the testing of eight representative mining effluents. The evaluation considered the sensitivity, cost, and applicability of the tests. The toxicity tests included the Microtox chronic test, the Ceriodaphnia survival and reproduction test, the larval fathead minnow survival and growth test, the […]

EXECUTIVE SUMMARY Mines exist in geologically anomalous areas where elevated metals are a common feature of the surrounding area. Surfïcial mineralized zones cause elevated metal concentrations in the terrestrial and aquatic environments, and the natural biota, via acclimatization, tend to reflect these highly mineralized environments. The study is to provide realistic information on the environmental effects of mining activities […]

EXECUTIVE SUMMARY The Aquatic Effects Technology Evaluation (AETE) Program commissioned a study to evaluate and summarize the experience of the Canadian mining industry with Toxicity Identification/Reduction Evaluations (TI/REs). The objectives were: i) to complete a critical evaluation of the quality of TI/RE data, its benefits and limitations and, ii) to conduct a survey to evaluate […]

EXECUTIVE SUMMARY Under the auspices of the Aquatic Effects Technology Evaluation (AETE) program, a critical review was undertaken on the use of artificial substrates for collection of benthic invertebrate samples, and on the utility and limitations of this method as a cost-effective environmental monitoring tool for the Canadian mining industry. The review included a survey of colonization dynamics as […]

EXECUTIVE SUMMARY The Aquatic Effects Technology Evaluation (AETE) program commissioned a technical evaluation of field and laboratory methods for collection and enumeration of benthic invertebrates for biological monitoring at mine sites. The objective of the technical evaluation was to critically review the recent literature on field and laboratory methods for sampling benthic invertebrates, compare various methods and approaches, […]

EXECUTIVE SUMMARY Scope The Aquatic Effects Technology Evaluation (AETE) program commissioned a technical evaluation of methods in benthic invertebrate data analysis and interpretation for biological monitoring at mine sites. The objective of the technical evaluation was to review the recent literature and recommend analytical approaches that are valid, objective, effective, and ecologically relevant for monitoring Canadian metals mines. The […]

EXECUTIVE SUMMARY This review is intended to be supplementary and complementary to AETE report 2.1.3  Technical Evaluation on Methods for Benthic Invertebrate Data Analysis and Interpretation (Taylor & Bailey (1997)) which covered basic design and statistical analysis principles but was limited in the literature which was reviewed, and did not consider multivariate approaches to benthic invertebrate data analysis and interpretation […]

EXECUTIVE SUMMARY Benthic invertebrates are commonly used to monitor spatial and temporal impacts on aquatic systems. Similar to other aquatic monitoring tools, the methods have to be applied by adequately trained and experienced individuals to help ensure that the data generated are not of questionable quality. Unfortunately, even though benthic invertebrate community assessments have been a cornerstone of aquatic […]

EXECUTIVE SUMMARY Under the auspices of the Aquatic Effects Technology Evaluation (AETE) Program, a literature review was undertaken to assess eight population level, benthic macroinvertebrate fitness parameters as potential biomonitors for the Canadian mining industry. The parameters were reviewed primarily from the perspectives of ecological significance, technical ease/constraints of execution, and business considerations such as labour requirements and general costs […]

EXECUTIVE SUMMARY  Introduction The Aquatic Effects Technology Evaluation Program, AETE, has been established to assist the Canadian mining industry in meeting its environmental effects monitoring and related requirements, in as cost-effective a manner as possible. The program is coordinated by the Canadian Center for Mineral and Energy Technology (CANMET). The present report is a technical […]

EXECUTIVE SUMMARY This paper provides a technical evaluation of histopathology as a monitoring tool for the mining industry in Canada, and addresses its role in the determination and monitoring of fish health impacted by those activities. Initially, the paper gives the reader some background concerning diagnostic methodology, the importance of judgment in the process of making a diagnosis, […]

EXECUTIVE SUMMARY INTRODUCTION As part of the Aquatic Effects Technology Evaluation (AETE) program, currently available methods for monitoring effects of metal mining activities on fish in Canada were reviewed. Potentially applicable monitoring tools for all levels of biological organization (chemical to community level) were initially selected by the AETE Technical Committee based on their (a) successful use in the […]

EXECUTIVE SUMMARY Introduction The Aquatic Effects Technology Evaluation Program AETE has been established to assist the Canadian mining industry in meeting its environmental effects monitoring and related requirements, in as cost-effective a manner as possible. The program is coordinated by the Canadian Center for Mineral and Energy Technology (CANMET). The present report is a technical evaluation of molluscs as […]

EXECUTIVE SUMMARY The Aquatic Effects Technology Evaluation Program, AETE, has been established to assist the Canadian mining industry in meeting its environmental effects monitoring and related requirements, in a cost-effective a manner as possible. The program is coordinated by the Canadian Center for Mineral and Energy Technology (CANMET). The present report is a technical evaluation of monitoring methods using […]

EXECUTIVE SUMMARY  Recently, improvements in analytical chemistry technology have given scientists the ability to measure lower and lower concentrations of metals and other contaminants in water. Similarly, as the understanding of the environmental effects of contaminants has increased, the acceptable concentrations in water of many of these contaminants have decreased. When monitoring water quality, it […]

EXECUTIVE SUMMARY This evaluation reviewed the relationship between water quality and biological effects in freshwater ecosystems. The current definition of dissolved metals as the metals component of a water sample that passes through a 0.45 µm filter is inadequate. Specifically, recent research has shown that substantial amounts of metal bound to colloids can pass through this pore size, […]

Phase I:  Evaluation of Bottle Type, Bottle Cleaning, Filter and Preservation Technique EXECUTIVE SUMMARY  Background Guidelines and criteria levels for metals and metalloids in surface waters (CCME, BC, Ontario, EPA) are the subject of much discussion currently and there is a movement to (a) lower many of them from ppb to ppt levels and (b) define element […]

EXECUTIVE SUMMARY – AETE A literature review on the techniques of sonar profiling and grid sampling, using a grab sampler was undertaken as an evaluation step for environmental lake sediment monitoring. The sonar systems to be evaluated include the sub-bottom acoustic profiling system, with or without side-scan, and the echo sounding system. The sub-bottom acoustic profiling […]

EXECUTIVE SUMMARY Pore (or interstitial) water toxicity and sediment chemistry are important components of assessments which determine the bioavailability of contaminants in waterways receiving mining discharges. The methods and approaches used in pore water toxicity and sediment chemistry evaluations vary widely in their scope, application, sensitivity, accuracy and precision, resource requirements, scientific credibility, and effectiveness for […]

EXECUTIVE SUMMARY This study forms part of the Aquatic Effects Technology Evaluation Program (AETE), which is a cooperative government-industry program to review and evaluate environmental monitoring technologies for the assessment of mining-related impacts on the aquatic environment. The intention is to apply sound scientific principles to environmental effects monitoring in a cost-effective manner. The program […]

EXECUTIVE SUMMARY – AETE B.A.R. Environmental Inc. conducted toxicity tests involving effluents and receiving waters from Myra Falls, (Westmin Resources, B.C.), Sullivan Mine (Cominco Ltd., B.C.), Levack Mine, (Inco Ltd., ON), Onaping site (Falconbridge Ltd., ON), Dome Mine, (Placer Dome Canada, ON), Gaspé Division, (Noranda Mining and Exploration Inc., QC) and Heath Steele Division, (Noranda Mining and Exploration Inc., […]

EXECUTIVE SUMMARY The Aquatic Effects Technology Evaluation (AETE) Program was established to conduct field and laboratory evaluation and comparison of selected environmental effects monitoring technologies for assessing impacts of mine effluents on the aquatic environment. Field evaluations were conducted at seven mine sites in 1996 to determine which sites were suitable for further evaluation in […]

EXECUTIVE SUMMARY The Aquatic Effects Technology Evaluation (AETE) Program was established to conduct field and laboratory evaluation and comparison of selected environmental effects monitoring technologies for assessing impacts of mine effluents on the aquatic environment. Field evaluations were conducted at seven mine sites in 1996 to determine which sites were suitable for further evaluation in […]

EXECUTIVE SUMMARY As part of the Aquatic Effects Technology Evaluation (AETE) Program, a field survey was conducted of the Lupin Mine in the Northwest Territories. This site has been suggested as a candidate for detailed testing of monitoring tools in 1997 studies sponsored by the AETE Program. The purpose of this survey was to provide […]

EXECUTIVE SUMMARY As part of the Aquatic Effects Technology Evaluation (AETE) Program, a field survey was conducted of the Myra Falls Mine Site in British Columbia. This site has been suggested as a candidate for detailed testing of monitoring tools in 1997 studies sponsored by the AETE Program. The purpose of this survey was to […]

AETE

EXECUTIVE SUMMARY The Dome Mine (Ontario) study is one of four field evaluations carried out in 1997 under the Aquatic Effects Technology Evaluation (AETE) Program, a joint government-industry program to evaluate the cost-effectiveness of technologies for the assessment of mining related impacts in the aquatic environment. The other three mines studied were Myra Falls (British […]

EXECUTIVE SUMMARY The Heath Steele (New Brunswick) mine study is one of four field evaluations carried out in 1997 under the Aquatic Effects Technology Evaluation (AETE) Program, a joint government-industry program to evaluate the cost-effectiveness of technologies for the assessment of mining-related impacts in the aquatic environment. The other three mines studied were Dome (Ontario), […]

EXECUTIVE SUMMARY The Mattabi Mine (Ontario) study is one of four field evaluations carried out in 1997 under the Aquatic Effects Technology Evaluation (AETE) Program, a joint government-industry program to evaluate the cost-effectiveness of technologies for the assessment of mining-related impacts in the aquatic environment. The other three mines studied were Dome (Ontario), Myra Falls […]

EXECUTIVE SUMMARY  The Myra Falls (British Columbia) mine site study is one of four field evaluations carried out in 1997 under the Aquatic Effects Technology Evaluation (AETE) Program, a joint government-industry program to evaluate the cost-effectiveness of technologies for the assessment of mining-related impacts in the aquatic environment. The other three mines studied were Dome (Ontario), Mattabi (Ontario) […]

EXECUTIVE SUMMARY The Canadian Government committed to review the Metal Mining Liquid Effluent Regulations (MMLERs) in the early 1990’s. Discussions established the need to identify tools that could be used to monitor the effects of effluents from mining operations on the aquatic environment. This provided the impetus for the Aquatic Effects Technology Evaluation (AETE) program. The mandate for the […]

The draft Metal Mining Effluent Regulation (MMER) requires that all Canadian metal mines produce effluent that is non-acutely lethal to rainbow trout when tested in accordance with Environment Canada test methods. Mine operations will also be required to monitor the acute lethality of effluent to Daphnia magna. If a rainbow trout test produces mortality of […]

The draft Metal Mining Effluent Regulation (MMER) requires that all Canadian metal mines produce effluent that is non-acutely lethal to rainbow trout when tested in accordance with Environment Canada test methods. Mine operations will also be required to monitor the acute lethality of effluent to Daphnia magna. If a rainbow trout test produces mortality of […]

This study was conducted to gain a more detailed understanding of acidic drainage from mine walls. The report first describes the results of a detailed literature review that identified relevant information on the generation of acid and its migration in various modes of water movement.

Information related to acid generation, acid neutralization, metal leaching, and water movement at the Equity Silver Mine in BC was then evaluated, with a focus on the Main Zone Pit. This evaluation highlighted the locations in the pit that are generating or that will eventually generate net acidity, as well as the locations that are not expected to generate net acidity at any time.

The pit data was then applied to the predictive model MINEWALL to determine if acidic conditions might develop during decommissioning. For reliable predictions, MINEWALL requires detailed input on water movement, pit design, fracture characteristics, acid generation/neutralization, and metal leaching. The best-fit simulation of the Main Zone Pit to current data indicated the water in the pit will always remain near neutral values, except during an initial flush of acidity as flooding begins.

This comprehensive report presents the results of the first phase of a study on acidic drainage issues at the historic Britannia Mine, in BC. The major environmental concern at Britannia Mine is acid mine drainage and associated high copper and zinc levels emanating from old adits and waste dumps. While dissolved copper concentrations are an order of magnitude less than they were during mine operation, they still have an impact on the invertebrate and fish in Howe Sound.

The objectives of this study were to review all available information, critique the present system of control of acidic drainage, and to recommend possible long-term solutions to reduce or eliminate acid mine drainage. Remediation options considered include water management through diversion, drainage collection systems, and treatment through various processes including lime neutralization, sea water dilution and ion exchange. Capital and operating cost estimates are also provided, along with a discussion on permit conditions and monitoring requirements.

This report describes the studies conducted during a three year program to assess the generation and control of acidic drainage at the Myra Falls waste rock dump. The waste dump characterization indicated that the most active areas of oxidation occur within a 10 meter depth of exposed surfaces of the waste rock dump and in deeper zones where relatively high contents of sulfide minerals are encountered. Calculations suggest that a significant portion of the annual production of acidity is retained in the dump and remains available for flushing. Remediation and decommissioning planning must therefore address the neutralization of this acidity or the control of infiltration and water table variation.

Two methods to control acidic drainage were evaluated: the use of alternative bactericides to reduce the activity of Thiobacillus ferrooxidans, and the use of solidified mine waste materials to seal the waste rock to minimize moisture and air transfer. The laboratory studies and the results of the dump characterization study suggest that the bactericidal approach would not be effective for controlling acidic drainage from the waste dump. Limitations include application techniques and the need to control acid formation at depth.

The study program then focused on the possible formation of a durable solidified material using mine waste materials such as wastewater sludge and mine tailings. On the basis of laboratory and limited field scale studies, the approach of using solidified mine waste materials as a cover and grouting medium appears promising and further investigation of field application techniques should be pursued.

This report presents workshop notes on chemical prediction techniques for acidic drainage. A preliminary introduction is first provided on the prediction of acidic drainage. This is followed by a discussion on the theory of acidic drainage prediction, including pyrite oxidation reactions and pH buffering. Prediction methods are then described in detail, including field inspections, sampling methods, and static and kinetic tests. Finally, case studies are provided on two mines in the Yukon and one mine in BC.

The workshop notes from this short course describe modelling principles to predict acidic drainage from waste rock and tailings. Discussions are provided on key processes and characteristics that control oxidation reactions, acid generation and metal loadings to the environment. Specific computer models are presented, along with a discussion on their applicability to different cases.

These short-course slides present design principles, material characterization, analyses methods and construction/performance monitoring for dry covers placed on mine tailings and waste rock. Case studies are discussed to illustrate the use of dry covers in mining applications. A number of technical studies are also appended to these slides.

This short course explores treatment of acidic drainage through passive treatment. The discussion covers relevant chemical and design principles, laboratory studies, and bench-, pilot-, and full-scale investigations.

This short course discusses reclamation securities/bonds. Regulatory requirements under reclamation security legislation are described, including when security is required and acceptable forms of security. A case study is provided on the Equity Silver mine in BC to illustrate the application of reclamation security. Background information papers are also provided on government policy for reclamation securities in BC.

Predictions of whether and when a waste rock pile may start to generate acidic drainage, and how long a pile may release elevated concentrations of metals to the environment, are related to fluid flow within a waste rock pile. In this report, the hydrogeological properties of waste rock are analyzed based on a synthesis of data from four mine sites; Myra Falls, BC, Island Copper, BC, Elkview Mine, BC, and Golden Sunlight Mine, Montana. The emphasis in this study is on:

• pile hydrostratigraphy and the textural properties of the rock mass;
• spatial and temporal variations in water content within a waste rock pile;
• temperature profiles within a waste rock pile and their response to the infiltration of water following a rainfall event; and
• the large-scale hydrogeologic characterization of a waste rock pile inferred from outflow hydrographs recorded in toe drains.

The following four hydrostratigraphic models are proposed to characterize waste rock piles:

1. Non-segregated coarse-grained rock piles that transmit water rapidly to the base of the pile;
2. Non-segregated fine-grained rock piles that are likely to contain a basal saturated zone;
3. Segregated rock piles that contain a fine-grained crest zone that may not permit the passage of significant quantities of water; and
4. Layered, segregated dumps that contain a finer-grained crest and sandy gravel layers parallel to the face of the rock pile.

To better understand the hydrogeology of a waste rock pile, the authors recommend that the following measurements be given priority: water content and temperature profiles through the unsaturated zone, water table elevation, volumetric discharge at toe drains, rainfall and air temperature. Finally, work-plans are presented for three types of monitoring studies: a pile assembly study, a pile monitoring study, and a pile disassembly study.

This report describes MINTOX, a new simulation model that was developed to predict the behaviour of kinetic sulphide mineral oxidation within mine tailings impoundments. MINTOX can simulate: the diffusion of oxygen into a tailings impoundment; the subsequent kinetic oxidation of sulphide minerals; the speciation and reactions of the oxidation products; and their transport within the impoundment and into downstream aquifers.

MINTOX was tested against observed field data from the tailings impoundment near Elliot Lake, Ontario and to simulate the geochemical processes occurring at the Nickel Rim tailings impoundment. Simulated depth profiles of selected species, including oxygen and pyrite content, agreed well with observed data. Discrepancies in other phases were primarily due to the assumption of local geochemical equilibrium.

MINTOX was also applied to simulate the effects of reducing the rate of oxygen diffusion into the tailings by using a moisture-retaining surface cover, and adding limestone to increase the buffer capacity. These simulations suggest a need to determine the influence of spatial variation of physical and chemical properties on acidic drainage evolution, and to incorporate uncertainty into the interpretation of results.

This study assessed the feasibility of depositing pyrrhotite and sulphide tailings into the Strathcona tailings treatment system to control acid generation. The Strathcona tailings treatment system near Sudbury o covers an area of approximately 200 hectares, with a maximum depth of approximately 55 meters.

The research program entailed the characterization of the tailings, the Strathcona tailings treatment system and the Strathcona and Fecunis tailings area. Chemical, physical and mineralogical testing was conducted on high sulphide tailings (pyrrhotite concentrate) and low sulphide tailings (end of pipe slime tailings). In addition, pilot columns were constructed to observe physical and chemical changes in the water cover and pore water of the subaqueously deposited tailings. Based on the available data, it was concluded that the deposition of pyrrhotite tailings under a shallow cover layer of sediment substrate would be the most effective method for reducing acid generation compared to other deposition scenarios studied.

This workshop was held to present and discuss available knowledge on managing mine wastes in permafrost zones and to identify knowledge gaps. The workshop indicated that although engineered structures incorporating permafrost have been used successfully for mine waste control, there remains a lack of fundamental knowledge on the geochemical aspects of the behaviour of mine wastes in northern environments. A number of competing factors need to be studied to fully understand the fundamentals of mine waste oxidation at low temperatures. Technical issues yet to be resolved include: oxidation kinetics at low temperatures; unfrozen water in tailings; freezing point depression by process chemicals; thermal effects of oxidation at low temperatures; and effective covers in permafrost zones.